The history of implant arthroplasty has shown that every new innovation is not necessarily an improvement over the past. Historical data, current knowledge and personal observation has shown that durability of cemented total hip arthroplasty in the age group 60 -80 years has been 85 -90% at 15 -20 years follow-up. In younger patients (< 50 years) the results have been in favor of non-cemented fixation up to 10 years. However increased wear has emerged as a cause of failure requiring revision. The pathophysiology of wear and osteolysis comprises the wear particles themselves; mechanical factors such as fluid pressure and joint alignment and biological factors such as the host chemomediators and bone quality. Therefore the main issue in improving longevity of total hip arthroplasty with or without cement fixation requires improved bearing surfaces.

The metal on metal bearing surfaces no doubt produce a lower volume of smaller particles. The concern however is that the particles generated are heavy metal ions such as chromium, that are able to overcome the local barriers and hence expose patients to the possible long-term biological consequences and risk of lymphoma and other malignancies. In addition, the head-neck impingement of titanium femoral components against the chromium-cobalt acetabular components will further increase the load of the metal ions to the system.

Bearing surfaces involving ceramics have problems of brittleness and fracture due to the sensitivity to mal alignment and trunion tolerances. In addition, ceramic-ceramic bearing surfaces await FDA clearance before they can be more widely used. The additional disadvantages of ceramics are cost and quality control during manufacture.

The reduction of polyethylene wear has been achieved through direct compression molded polyethylene, sterilization in an inert environment and more recently cross-linking. Hip simulator data on highly cross-linked polyethylene has shown 80 -100% reductions in wear over conventional polyethylene. If this data holds true in humans, the wear of the polyethylene and consequent osteolysis and aseptic loosening with or without cement fixation will be significantly reduced and possibly eliminated.

Therefore it appears that in the near future the predominant bearing surface in practice will be metal on polyethylene utilizing highly cross-linked polyethylene. Long-term controlled studies with the three bearing surfaces may someday provide the answers to the debate on the best bearing surfaces in total hip arthroplasty.

Twelve reports in the literature have provided data on infected hips treated with direct-exchange arthroplasty and the status of the infection at the last clinical follow-up. The average duration of follow-up was 4.8 years, but the range was broad (0.1-17.1 years). Of the 1,299 infected hips treated with direct exchange, 1,077 (83%) were thought to be free of infection at the last follow-up.

Antibiotic-impregnated bone cement was utilized in 1,282 of the cases (99%). There was wide variability in the duration of parenteral antibiotic therapy, ranging from 24 hours to eight weeks. In some cases, no oral antibiotics were ever given, while in others, oral antibiotics were given for up to eight months following parenteral antibiotic therapy. Factors associated with a successful direct-exchange included: 1) absence of wound complications following the initial total hip replacement, 2) good general health of the patient, 3) antibiotic (methicillin) sensitive Staphylococcus epidermidis, Staphylococcus aureus, and Streptococcus species, and 4) an infecting organism that was sensitive to the antibiotic mixed into the bone cement. Factors associated with failure of the direct-exchange included: 1) polymicrobial infection, 2) gram-negative organisms, especially Pseudomonas species, and 3) certain gram-positive organisms: methicillin resistant Staphylococcus epidermidis and Group D Streptococcus.

There is little data on direct-exchange without antibiotic-impregnated bone cement. Many current revision surgical techniques utilize cementless implants. In addition to the prognostic factors identified, fixation without cement (no depot antibiotics) may be a contra-indication to direct-exchange. Further, there is essentially no data on the use of bone graft in association with direct-exchange. For these reasons, the indications for direct-exchange are limited.

In a group of thirty-seven infected hip arthroplasties treated consecutively between January 1997 and October 1999, the feasibility of a published set of patient selection criteria for direct exchange was tested. These criteria include the requirement of a healthy patient with good soft tissues, minimal femoral bone loss, and an organism identified preoperatively as a gram-positive organism which is antibiotic sensitive. Fifteen (40.5 %) of the hips had gram-negative or methicillin-resistant gram-positive organisms obtained from preoperative joint aspirations. Among the remaining 22 hips, 9 hips had moderate or severe femoral bone loss and 4 hips required a proximal femoral osteotomy for component removal which also excluded these hips from direct exchange. Two patients (2 hips) with poor health status and two hips with poor soft tissues were also excluded.

After assignment of the selection criteria, only four hips (11%) were potential candidates for a direct exchange procedure. In one of these direct exchange candidates, a culture result obtained from intraoperative tissue revealed the presence of an antibiotic-resistant organism that was not discovered with the preoperative joint aspiration. In the overall patient group, eleven (30%) of the hips had growth on culture media from tissue samples obtained at debridement which grew organisms not identified by the preoperative aspiration cultures.

Due to the increasing emergence of antibiotic-resistant bacteria and an increased prevalence of revision arthroplasties with associated bone loss, the feasibility of these selection criteria for direct exchange are limited. A philosophy of delayed reconstruction for management of the infected hip arthroplasty seems most appropriate in the current era of patient management.

The strategy for retention or removal of the acetabular component to address osteolytic activity is becoming an increasingly debated issue amongst joint replacement surgeons. It is paramount to the success of the revision surgery to eliminate the particulate debris source and thoroughly debride and graft the peri-acetabular regions. Visualization and complete access to all peri-acetabular regions require acetabular component removal. We present an opinion on acetabular component removal and introduce an impaction grafting method for addressing peri-acetabular osteolysis. The intermediate results at an average of 56 months are excellent (97% survival, average Harris Hip Score 72) with no adverse radiographic events that would warrant revision acetabuloplasty. One well-fixed acetabular component was revised due to a failed locking mechanism. The outcome of revision total hip arthroplasty is shown to be inferior to primary total hip arthroplasty, with each following revision having less probability for success ualing the preceding procedure. However, it is the authors’ opinion that removing the entire acetabular component is the only choice to eliminate and avoid the introduction of adverse variables that may contribute to the continuation of the osteolytic process.

While the presence of peri-articular osteolysis may require component removal or revision, it does not demand that this always be done. The appropriate treatment of implant related osteolysis requires the evaluation of multiple factors relative to the individual patient, including: the extent, location, and rate of progression of the lesion; stability of the underlying component, and the amount of bone stock which will be lost in component removal; features intrinsic to the component: the known presence of an accelerated wear mechanism (design flaws such as poor poly locking, back-surface wear, or specific material property abnormalities or defects); and patient related features such as stability, positioning or alignment abnormalities, as well as underlying health status, age, activity level and symptoms.

In cases where the patient is asymptomatic, there is no known or obvious wear generator and the patient is reliable, regular follow-up to determine the rate of progression may be the only indicated treatment. Certainly the removal of a well fixed component may result in substantial additional bone loss and in these cases the benefit of component removal must be balanced against the risk of further bone loss. In cases where the components are well fixed, poly wear is the only apparent source of lysis, the implant has an adequate locking mechanism for the poly (or can be cemented into place), and removal of the well fixed component would result in a massive defect, then approaching the lesion through a trap door or other more direct approach may be preferable. Evidence indicates that these lesions can heal radiographically without grafting when the particulate burden is reduced. While many components will not meet the criteria for remaining in-situ, each case should be individualized, as many components will still be capable of providing useful service.

All cemented acetabular components done between 1970 and 1998 were evaluated utilizing most recent follow-up and initial post-operative radiographs. Failure was defined as radiographic loosening and/or revision of the component. Radiolucencies in zone 1 on initial post-operative radiographs were tabulated. There were a total of 1,841 cemented acetabular components implanted, which were separated into 5 groups based on cementing techniques. The percentage of radiolucent lines in zone 1 was calculated for each of the five groups. The percentage of loose or revised cups were calculated for six groups based on type of prosthesis utilized.

There were 185 Charnley cups implanted between 1970-1974 with 12 being loose or revised (6.4%). There were 440 T-28/TR-28 cups implanted between 1974-1980 with 66 cups loose or revised (15%). There were 100 MOSC all polyethylene cups implanted between 1980-1982 with 15 cups loose or revised (15%). There were 138 MOSC metal-backed polyethylene cups implanted between 1982-1983 with 31 cups loose or revised (22%). There were 512 metal-backed polyethylene cups implanted between 1984-1989 with 174 cups loose or revised (34%). There were 404 all polyethylene cups implanted between 1989-1994 with 6 cups loose or revised (1%). There were 458 all polyethylene cups implanted between 1995-1998 with 1 cup loose or revised (0.2%). With only finger packing cement technique 40 of 245 cups (22%) had zone 1 radiolucencies. With gouging the acetabulum, use of water pick lavage, and finger packing, 114 of 380 cups (30%) had zone 1 radiolucencies. With gouging, water pick, and localized pressurization with a cement gun, 76 of 238 cups (32%) bad zone 1 radiolucencies. With vacuum or centrifuge mixing, gouging, water pick, and localized pressurization 202 of 916 (22%) cups had zone 1 radiolucencies. With reaming through subchondral bone, hypotensive anesthesia, complete cup coverage, multiple -mall drill holes, drying of the acetabulum, complete pressurization, and without vacuum or centrifuge mixing but bowl mixing only, 52 of 458 all poly cups (11%) had zone 1 radiolucencies.

We conclude that the preparation of the bone and cement insertion with pressurization are the most important factors in the success of cemented acetabular components through elimination of bone-cement radiolucency. For the acetabular side of a total hip replacement, the biology of the bone and the techniques of cement insertion which include a dry cancellous bone bed, perforation and removal of peripheral sclerotic areas, pressurization of the entire cement mantle at one time, and complete burying of the acetabular component within the boundary of the bony acetabulum are the essential factors for long-term success of the component, not so called third generation techniques which reduce the porosity in the cement

The starting point of this article is the legacy of successful designs from the past. The limitations of those designs will be examined, which will help to identify the opportunities for improvement. The process of the introduction of new designs which were intended to have one or more advantages will be studied. From this study useful lessons will be deduced. The rationale of the present Regulatory Systems will be examined comparing the USA and European approaches. Finally, a number of suggestions are made which point to a more holistic approach to encourage innovative designs, with a particular emphasis on a more effective use of the sophisticated designs and evaluation tools which are available. More extensive funding and collaboration is proposed as an important part of this process.

The most influential total hip from the past was developed in several versions by Sir John Charnley. Another innovator of the 1960s was Mr. George McKee from Norwich in the UK, whose metal-on-metal bearing in the McKee-Farrar design has been recently revisited due to the exceptionally low wear rate. Professor Maurice Muller produced his own metal-on-plastic hip designs, innovated techniques and popularized hip replacement throughout Europe. These hip designs, together with numerous other approaches to treating the arthritic hip, have provided the foundation for the hundreds of designs which have been produced since.

In writing about innovation, Huiskes stated that for a new Design, an Explicit Statement of Purpose is required. In other words, Which problem is it trying to solve? That theme will now be used in a number of examples, although the space does not allow a detailed review of each subject.

The Charnley can be regarded as the reference hip design due to the vast experience and number of published studies. However, it must be emphasized that the results vary depending on the hospital center, the surgeon group, the patient population and which version of the Charnley was used. In a 5-year study of over 1,000 Charnleys performed across a U.K. Health Region, Fender et al. found 7.5% either revised or grossly loose, as well as 5% dislocation. The authors suggested that in general orthopaedic practice, the failure rate is higher than in the specialist centers and may be more representative of the norm. While the surgeon experience is likely to be an important factor, a further point is that the surgical technique may not sufficiently dictate the ideal component placement and cement technique

In the early years of hip replacement, fracture of the stem was a problem. That was solved by the use of improved processing, forged alloys and titanium alloys for uncemented use. However, in the 1990's, fatigue failures occurred of a well-designed hip stem made from forged cobalt-chrome alloy. The fracture occurred through the laser-etched lettering which produced a local stress concentration. Exacerbating factors were age (average 61 years), weight (average 96 kg), a poor cement mantle and undersized stems. Even if the final product with etching had been subject to the ISO fatigue test, if right hips had been tested, the hips would have passed. The laser-etching only intruded on the antero-lateral corner of left stems, where the failures initiated. Whether the testing was sufficiently thorough can be asked, but there was certainly an element of impredictability here.

Total joints provide major benefits to large numbers of patients at relatively little cost. Further substantial improvements can still be made in outcome and performance by modest improvements, or by more innovative approaches even including the combination of artificial and tissue engineered materials. To achieve these advances, an appropriate proportion of federal funding is needed for studies in this area, on subjects including design methods, biomechanical testing, biomaterials and surgical technique. In the past, such research has often been regarded as the responsibility of industry. However, the benefits are more general and can involve complex scientific methodologies implying that a broader spectrum of funding source should be available. There is an ever-increasing volume of lectures, articles and new products on the subject of hip replacement, such that a clear and informed view is often difficult to formulate. Conferences are often not sufficiently informative due to the increasing pressure for more presentations which leads to less discussion. On the other hand, meetings which bring together a group of experts from various disciplines, to discuss a particular subject in depth, are invaluable. An example is the NIH Consensus meeting on Total Hip Replacement held in 1994. As noted earlier, there are no simple answers, but there are signs that improvements by innovation are steadily being made and that such innovations are being introduced more carefully than in the past.

The ideal bone implant bond should be easy to achieve, reproducible, should provide good pain relief and function, be durable, and without local or systemic ill effect. Thus far, no method of fixation meets all these requirements.

The reported clinical failure rate of socket fixation is < 5% at 10-15 years follow-up from < 10% to 23% at 17-20 years follow-up. The radiographic failure rate using global radiolucency and migration of 3 mm as criteria is around 25%. The primary reason for early aseptic loosening, i.e. within 10 years, is failure to achieve good micro and macro interlock at the time of surgery. Later failure involves both mechanical and biological factors as a consequence of an histiocytic response to the wear debris.

Meticulous cement technique is necessary to achieve a rigid fixation of the implant to the bone and consequently improved clinical and radiographic results¹. They include the use of hypotensive epidural anesthesia², adequate exposure via the posterior approach, preparation of the acetabular bed, mixing and pressurization of the cement and proper insertion/orientation of the acetabular component. With modern cement technique and a mean follow-up of 9.5 years, the clinical and radiographic failure of the bone cement interface was 7.2%³. This includes 0.8% clinical failure rate, 3% radiographic migration and 3.4% of progressive global radiolucency. Recent review has confirmed clinical and radiographic survivorship (both components) of 90% at 15 years and 80% at 20 years (best case scenario). Since 1991, our experience in 200 cemented THA's with the direct compression molded all polyethylene socket has demonstrated clinical survivorship of 99% at a mean follow-up of 8 years. We believe that the state of the bone cement interface, as seen on the early postoperative radiograph, is a predictor of the longevity of the cemented socket to a high degree of probability.

We recommend the use of the cemented all polyethylene socket in total hip arthroplasty as the implant/technique of choice for patients who are 60 years old or older. A cemented all polyethylene socket is not advocated in the presence extensive cyst formation, excessive bleeding, in dysplastic or rheumatoid patients and where the reamed socket diameter is 48 mm or less.

In summary, fixation of the all-polyethylene cemented socket is reproducible and provides excellent hip function for 15 -20 years.

The two authors (PMP, RP) independently began using an identical enhanced posterior soft tissue repair after total hip replacement through a posterior approach. In the first author's experience, a dislocation rate of 4% in 395 patients before using the enhanced closure was reduced to 0% in 395 patients in whom the enhanced closure was performed. In the second author's experience, 160 total hip replacements had a dislocation rate of 6.2% before the enhanced closure whereas 124 total hip replacements had a dislocation rate of 0.8 % after the enhanced closure. These results are highly statistically significant.

This video demonstrates a technique used at Anderson Orthopaedic Institute that employs an antiprotrusio acetabular support ring with particulate allograft. Considered a salvage procedure, the approach provides an option when a hemispheric acetabular component cannot be adequately placed or properly positioned on host bone. It is recommended for low-demand, elderly patients or those with multiple failures in which no other reconstruction alternative is viable.

The partial-pelvic reconstruction ring used in this case has a caudal flange. It comes in multiple sizes and also has flexible flanges that can be contoured to the ilium. The caudal flange secures fixation to the ischium. The acetabular cage enables re-creation of a normal hip center and thus, improved hip joint stability. Disadvantages are the extensive exposure required and lack of opportunity to trial reduce components.

As shown in the video, unique aspects of the surgical exposure are sciatic nerve exposure to prevent injury during surgery; a trochanteric osteotomy to mobilize abductors and allow exposure and fixation of the cage to the ilium; extensive mobilization of the femur to visualize acetabular defects and exposure of the ischium for inferior fixation of the cage.

Revision arthroplasty is being performed with increasing frequency and the cases are becoming increasingly complex. A key component to successful revision surgery is the surgical exposure. This is influenced by the surgeon's experience, the reason for revision, the type of components to be revised, the type of bone defects and the previous exposures used. In simple revisions one of the standard hip approaches that the arthroplasty surgeon is familiar with will often suffice. However with more complex cases an extensile or specialized approach maybe necessary. No one approach is suitable for all cases and the revision surgeon needs to be familiar with several such approaches, their relative indications and possible complications.

This approach to the hip is direct lateral in nature. It takes down the anterior one third of the abductors in continuity with the anterior one half of the vastus lateralis joined by a small medallion or wafer of trochanteric bone.

The major advantage to this approach is that it has an extremely low dislocation rate, reported less at 1%, because of the retention of the posterior capsule and the external rotators. The advantage of the trochanteric medallion is that the gluteus medius, minemus and anterior capsule is reattached bone to bone rather than soft tissue to bone as is done with other direct lateral approaches, thus minimizing an abductor lurch.

This approach can be used in most cases where routine expose to the hip is needed. Care must be taken to avoid the superior gluteal nerve which is at risk if the gluteus medius is split greater than four to six centimeters above its insertion on the trochanter.

With bone to bone reattachment of the abductors excellent function and outstanding stability can be maintained with this approach.

It can be used in almost any primary total hip situation with a few exceptions and it should be very much considered for any primary hip replacement where the patient may be at substantially increased risk for dislocation.

The video demonstrates an anterior approach with partial osteotomy of the anterior superior iliac spine to facilitate medial reflection of the tendon of origin of the sartorius in continuity with the iliacus. The rectus is elevated anteriorly from the hip capsule and the indirect head cut with a knife and the direct head released from the anterior inferior spine.

The pubic osteotomy is then performed with a Gigli saw while the obturator neurovascular structures are protected with subperiosteal retractors.

Sharp dissection of the medial capsular attachment of the iliacus permits access to the ischium, which is cut with the 40-degree angled AO (Synthes) Ganz osteotome under fluoroscopic control. Normally this instrument is placed lateral to the iliopsoas tendon, except in cases of shortened femoral neck (Perthes).

The principal proximal osteotomy is then made with a power saw from ASIS to within 15mm of the pelvic brim, on a trajectory just inferior to the sciatic notch. A curved osteotome is used to cut the pelvic brim. The angled osteotome is then used to cut the lamina quadrilatera parallel to the edge of the posterior column.

After completing all of the cuts, the fragment is mobilized. At this point an arthrotomy is performed to confirm clear joint fluid and to permit inspection of the labrum.

The fragment is mobilized until fluoroscopic view in AP and oblique projections confirm good coverage enhancement. Three or four 4.5mm cortical screws from the pelvic crest provide good fixation.

With precision fit hemi-resurfacing of the hip consistent results can be obtained in the treatment of large Ficat Stage II, Ficat Stage III and early Ficat Stage IV lesions in the young patient. The Conserve system enables one to replicate the head and neck length with sizing in 1 mm increments. We recommend the posterior approach and resect the entire capsule and synovium, mobilize the femoral head sufficiently to accurately view the acetabulum. Sizing is performed by using ring gauges and a plastic see-through gauge pressed into the acetabulum for precision fitting to the best remaining articular cartilage. Instrumentation facilitates accurate pin placement down the central neck axis to guide cylindrical and chamfer reaming. All of the yellow, necrotic bone is removed. Drill holes are placed into the reactive underlying, sclerotic bone. Cement fixation is used. The procedure has had minimal morbidity with patients returning to the work force after a few weeks. Conversion and subsequent survivorship of the total hip is not compromised. If hemi-surface is an option we recommend that the patient be placed on non-weight bearing to minimize articular cartilage damage of the acetabulum caused by the irregular collapsed femoral head. However, despite femoral head large lesions and poor acetabular grading, most patients get reliable pain relief and some have surprising durability. Survivorship has been 80% at five years, 60% at ten years and 45% at fifteen years even with titanium alloy compounds used in the 1981-85 era. Hemi-resurfacing is a time-buying bone conserving procedure with a predictable outcome.

The increasing demand for bone allografts to reconstruct deficient bone for revision hip replacement requires an understanding of bone graft biology and function. Bone grafts may be autogenous or allogeneic, cancellous or cortical. The main functions of grafts are: osteogenesis either graft derived or by osteoinduction, osteoconduction and mechanical support. All bone grafts are initially resorbed; cancellous grafts are ultimately replaced by the ingress of host bone, while cortical bone may remain a mixture of donor and host bone for a prolonged period of time. Autologous cancellous bone provides excellent osteogenesis and osteoconduction without structural support. Nonvascularized cortical autografts provide structural support and are somewhat osteogenic. Allogeneic demineralization bone matrix is highly osteoinductive. Cancellous allogeneic bone is osteoconductive while cortical allografts provide structural support, if not freeze-dried and are minimally osteoconductive. The demand for allograft bone depends upon the type of revision. Type I; no graft is required, while Type III requires bone graft for the stability of the component and should be avoided if possible. The selection of the appropriate bone graft depends upon the classification of the bone deficiency. Cavitary (contained) defects can be reconstructed with cancellous morselized autograft, frozen or freeze-dried allograft or allogeneic demineralized bone matrix. Segmental defects require bulk corticocancellous and cortical autografts or allografts. Freeze-drying does significantly reduce the material properties of the bone in torsion and bending. The ultimate incorporation of the bone graft depends upon the interaction of the graft and host soft tissue, and host-bone graft contact and stability.

The enduring success of the low friction arthroplasty advanced by Sir John Charnley as a solution for hip arthritis is appreciated by the 456,000 primary and revision hip and knee procedures performed in 1997 in the United States. Despite this obvious success, polyethylene debris is increasingly identified as the principle causative factor of bone loss and failure of TJA procedures. The conditions of occurrence, severity and clinical consequences suggest limitations on the in vivo integrity of contemporary arthroplasty designs. Material remedies inclusive of carbon reinforced polyethylene, heat pressing and Hylamer with its variants have been advanced as alternatives with negative clinical results. Contemporary attempts to improve longevity (i.e., post-processing heat stabilization, peroxide additives and increased radiation with remelting) focus on the benefit of increased cross-linking while minimizing free radical creation. With increasing patient longevity and activity levels a search for the ultimate polymer is important. Variations on an already successful theme hope to lead to its optimization in this century. However, these "new age polys" offer no direct clinical evidence to demonstrate their efficacy. It is known that reprocessing techniques will alter mechanical characteristics. Contemporary improvements in laboratory evaluative capabilities suggest significant reduction in component wear, but past experiences, in these regards, have not always predicted clinical viability.

The authors defend the debate title, "Food Additives (Glucosamine, Chondroitin Sulfate, Etc. For Osteoarthritis of The Hip) Are Useful". Many of our most important pharmaceuticals have their origin in plants, such as digoxin, penicillin, and coumadin. However, many physicians are deeply skeptical about the use of natural remedies. This skepticism is based on the concerns about patient self-diagnosis and treatment as well as the lack of scientific testing of claims. Nonetheless, a new class has emerged called nutraceuticals - nutritional supplements with pharmaceutical properties. Because these substances are relatively unregulated there is no requirement for rigorous scientific testing prior to marketing. This lack of regulation also poses problems with purity and quality control. Even so, patients are being bombarded with, and responding to, claims of the results of the use of herbs, nutraceuticals, and nutritional supplements. Glucosamine and chondroitin sulfate sales alone in the U.S. are estimated at $600 million in retail sales of all nutraceuticals and vitamin supplements in the U.S. exceeding 12 billion dollars in 1999.

Many physicians took offense at the title of the book by Theodosakis et al., The Arthritis Cure, because they know no cure exists. That offense translated into discounting the very reasonable recommendations in the book. Patients, on the other hand, pushed sales of the book to the best seller list. Moreover, glucosamine and chondroitin sulfate have been widely studied in tissue culture, animal models of arthritis, veterinary clinical trials, and human comparative or placebo controlled trials. No published study has failed to show a positive effect and no trial has shown significant side effects. These nutraceuticals have become our first line of treatment for osteoarthritis.

Since these supplements, glucosamine and chondroitin sulfate, are neutraceuticals they require no regulation by the Food and Drug Administration in the United States. The consumer, even if the optimal concentration of either compound was well understood, cannot be assured of the purity of the product they are choosing at their local grocery store, not alone whether the more expensive products are more efficacious. In addition at least 40% of people in most studies obtain no relief and these patients should not be encouraged to continue with this treatment. Finally the claims of these substances "chondroprotective" capabilities as well as their abilities to widen the joint space shadow on radiographs will require more thorough scientific investigation.

The number and complexity of revision total hip arthroplasty cases continues to increase. Among the challenges of complex hip arthroplasty include bone loss in the proximal femur as well as dealing with deformity, perforation, or periprosthetic fracture. The use of bone graft has become so common as to be routine in such cases. Because of the added time and morbidity of harvesting autograft, this is infrequently done at present and the use of various types of allograft is elected the vast majority of the time. Contained defects are effectively managed with cancellous allograft. When there is a need for immediate structural support, however, cortical grafts are often utilized. Cortical grafts have the notable disadvantage of slower graft incorporation and a higher rate of nonunion and resorption compared to cancellous allograft. Nonetheless cortical strut graft has been widely utilized in conjunction with hip arthroplasty with a relatively high degree of success. Head et al and Emerson et al have reported on strut grafts applied to the proximal femur in revision hip arthroplasty with a union rate of over 95%. The average time to union, however, was approximately eight months. Pak et al reported on ninety-five strut grafts with a slightly lower union rate of approximately ninety per cent.

While the use of strut grafts wired or cabled to the proximal femur has been generally successful, the time course to healing is slow. In addition, delayed union or nonunion occasionally does occur. Strut grafts are being utilized in increasing numbers and for a wider variety of applications. As this technique is applied to more patients with multiple revisions, severe bone loss, stress shielding, and advanced age, the biology of strut graft healing may well be put to a stringent test. Under such circumstances there would be a substantial advantage to enhancing the healing potential of cortical strut grafts so that more extensive bone formation and mechanical strength could be attained more reliably and more quickly. This would lower the risk of graft nonunion and periprosthetic fracture as well as speeding rehabilitation and shortening the time of protected weight-bearing and attendant functional disability for the patient.

A study was undertaken to determine whether cortical strut graft healing to the femur could be significantly enhanced in a canine model utilizing recombinant human osteogenic bone protein-1 (rhOP-1).

Six animals underwent bilateral onlay allograft strut procedures to the mid-femur. A subperiosteal onlay graft was secured to the lateral femur with two stainless steel cables. Strut graft was centered over the osteotomy site and fixed with two cables above and below. In each animal one femur received 400 milligrams of rhOP-1 device interposed between graft and host bone. Animals were sacrificed at six weeks post-operative. Histologic sections from the proximal, middle, and distal portions and weekly radiographs were graded for new bone formation and graft-host bone incorporation.

Despite recognition that the amount of wear is a function of use and not simply time, clinical wear rates have been reported in millimeters per year because of convenience; it is much easier to quantify the length of time that a prosthesis has been in situ than it is to quantify the amount of use. In contrast to the myriad of uncontrolled variables that affect wear in vivo, the conditions under which wear occurs in a laboratory hip joint simulator are highly controlled. In contrast to clinical methodology, all laboratories report wear as a function of the number of cycles. However, there is lack of agreement on what should be the baseline wear rate of a "standard" polyethylene (ultra-high molecular weight; neither extensively oxidized nor extensively crosslinked) in a hip simulator. The lack of agreement is, at least in part, because there has been no clinical study that has reported wear as a function of use, i.e. the polyethylene wear rate, per million cycles, adjusted for a 70kg patients weight.

In the present study, patient activity, the use of the prosthesis, was measured in several ways. For the most thorough evaluation of the ambulatory activity of patients with total hip replacements, we introduced the SAM (step activity monitor), which is a microprocessor worn on the ankle that records steps in real time. Linear and volumetric wear in 37 hips was measured from digital images using a validated two-dimensional, edge detection-based computer algorithm. Regression analyses were performed to evaluate the relationship between polyethylene wear and 1) patient-related variables such as gender, height, weight and activity, 2) the biomechanics of the surgical reconstructive technique, 3) the implanted components and 4) the length of follow-up.

Univariate regression analysis indicated that the strongest factor influencing wear in this cohort was male gender (p=0.001), followed by height (p=0.007) and weight (p=0.04) (which were both highly correlated to male gender; p=0.001 and p=0.003), liner thickness (p=0.03), and hip center of rotation (p=0.015). The data suggests higher walking speed (steps per minute) was positively correlated to wear (p=0.07). Multivariate regression analysis indicated that male gender (p<0.001), femoral off-set (p=0.034) and Hylamer® (p=0.043) were closely related to wear. For the subset of hips with Enduron®, femoral off-set (p=0.02) was also closely related to wear. In addition to being taller and heavier, data from the SAM indicated the males had a higher average walking speed (p=0.035) and spent more time walking fast (0.060) than the females. Intensity may be an important variable affecting wear in vivo.

Time in situ had no relationship to wear (p=0.99). A measure of joint use [total sliding distance x (patient weight in kg/70kg)] was related to wear at the 90% confidence level. Case analysis indicated that two hips had substantially less wear relative to use than expected, and one hip had substantially more wear relative to use than expected. Absent these outliers, wear was highly correlated to use (p<0.0001). Exclusion of these three hips, or any other three hips, could not establish any relationship between wear and time. Using another measure of activity, a visual-analog scale activity rating of the patient by the investigator, wear was significantly related to activity (p=0.04) for standard polyethylene. Wear is a function of use, not time.

Hips with standard polyethylene were used to determine a target wear rate for hip wear simulators. Using these data, the volumetric wear per year was divided by the number of cycles per year (expressed in millions, as extrapolated from the average steps per day measured by the SAM, multiplied by 365). This gives a volumetric wear rate of 34mm³ per million cycles. The average patient weight in this study was 79kg, and an adjustment was made to standardize for a 70kg patient weight. This decreased the average volumetric wear to 30mm 3 per million cycles for a 70kg patient load. There were three outliers with volumetric wear rates in excess of 50mm 3 per million cycles. Absent these three outliers, the average volumetric wear rate was 23mm 3 per million cycles.

Recent modifications of polyethylene, such as crosslinking, have shown promise in hip wear simulator tests. The enthusiasm generated by the potential of these materials will almost certainly result in the extension of total hip replacement technology to very young and very active patients. There is clearly a need for close, detailed monitoring of such cases, especially in the early experience with a new bearing material. In this setting, it is more important than ever to assess the activity of the patient and compare the in vivo experience to the in vitro experience -based on a measure of joint use, rather than time in situ. Such analyses will not only provide a more thorough assessment of the clinical outcome, but also provide information on the future direction of wear simulator studies. The methods used in this study are a major "step" in that direction.

The optimal surface finish for polymethylmethacrylate (PMMA) cemented femoral components remains controversial. Concerns about early debonding of the prosthesis cement interface have led surgeons to use femoral components with roughened surfaces to enhance the cement prosthesis bond. However, the clinical results of roughened stems have been variable. Recently, the use of polished stems has increased because of concerns that roughened stems will generate excessive wear debris and cause osteolysis if and when they become loose. It is generally agreed that cement technique will influence the longevity of a cemented stem. The question is should the time to cementation vary according to the surface finish of the femoral component?

The purpose of this study was to determine if the time to cementation influenced the cement prosthesis bond of 4 roughened Cobalt Chrome surfaces (60 Grit blast, 10 grit blast, 10 grit blast with PMMA precoating, glass bead blast) and 1 polished Cobalt Chrome surface. Fixation strength was assessed using mechanical pushout and tensile testing. The results of the mechanical testing revealed a significant interaction between degree of surface roughness and the time to cementation. Roughened and PMMA precoated surfaces demonstrated significantly greater tensile and shear strengths at early cementation times compared to polished surfaces, as well as significant decreases as time to cementation increased from 2 to 6 minutes. In contrast, tensile and shear strengths for polished surfaces were significantly lower than the roughened groups and did not change with longer cementation times. In summary, for polished stems, with low interface bond strengths at all cementation times, there is no disadvantage in cementingat 4 or 6 minutes when the cement is more doughy which facilitates maintaining the proper orientation of the component. When cementing roughened or precoated stems, the surgeon should consider cementing earlier with "wetter" cement, in order to maximize the cement prosthesis bond. The time to cementation should be varied according to the surface finish of the femoral component used.

Thc ROBODOC®-System contains a REVISION SOFTWARE which enables you to plan and execute total hip revision surgery with ROBODOC®. The program uses a special technique to enhance the CT images so that all existing bone cement in the cavity and around the old prosthesis is clearly visible and can be distinguished from bone structures. Besides, metal artifacts caused by the existing prosthesis are minimized. A cutting path can be planned to remove all the existing bone cement The next step is the planning of the new prosthesis. The prosthesis can be adjusted in any direction until a satisfactory position is reached. Intraoperatively, after the pin finding procedure, the robot mills out the existing bone cement and mates a new cavity for the planned implant. The advantages of using ROBODOC® for revision THR are obvious. Optimized preoperative planning of the procedure is possible, the anteversion can be corrected, the fibrous membrane and sclerosis in the cavity are being removed by the cutter. The duration of the operation greatly reduced compared to the traditional method of removing the bone cement manually. There is no risk of intraoperative fractures. A loose uncemented prosthesis can be replaced as well as a loose cemented implant . Out of 2,500 robot-assisted THR's that have been performed at BGU Frankfurt since 1994 there are 56 revision cases. 27 patients were male, 29 female. In 35 patients the primary implant was cementless, in 21 patients cemented. The average age of patients with a cemented implant at time of revision was 65.5 years, with a cementless implant 53.9 years. The average time between primary THR and revision THR was 9.5 years for the cemented group and 7.5 years for the cementless group. Intra-/ postoperative complications were dislocation in 1 case, thrombosis/embolism, in 1 case, fracture of the greater trochanter in 1 case and infection in 2 cases.

In an attempt to establish patterns of practice for prophylaxis of deep vein thrombosis a survey was performed of the Hip and Knee Societies. There was universal use of routine prophylaxis in hip replacement and 93% utilization in total knee replacement. The agents used after hip replacement were warfarin by 62%, aspirin by 21% and low molecular weight heparin by 15%. Seventy-six per cent used some type of mechanical device after hip replacement and this was evenly divided between plantar pumps and sequential compression devices. Only 22% routinely screened for DVT and this was by doppler ultrasound in 86%. Regional anesthesia was used by 76% of surgeons in some form and intraoperative heparin was utilized by 10%.

In a second survey of polyethylene utilization only 15% were using cross-linked polyethylene at this time. Ceramic/ceramic and metal/metal bearings were used infrequently. Management of periprosthetic infection was by two stage reimplantation in most cases with one stage exchanges being reserved for selective cases of early infection with sensitive organisms. Debridement procedures and antibiotic suppression were used uncommonly primarily in debilitated patients.

Developmental dysplasia of the hip (DDH) is a spectrum of anatomic hip abnormality which represents the etiology of osteoarthrosis of the hip in as many as 40 percent of cases. In many of these cases of dysplasia-arthrosis, the initial diagnosis was made well after the "golden period" of early infancy during which simple treatment with a Pavlik harness or a brace usually results in permanently normal hips. True primary prevention of DDH is not currently possible. Prevention of dysplasia-arthrosis, however, may be achievable with treatment methods now available if very early detection of all cases of dysplasia were possible. Appropriate powerful screening methods, representing "secondary prevention", could allow appropriate prophylactic treatment.

In North America, universal neonatal hip screening is carried out clinically with the Ortolani and Barlow tests. In Europe, particularly in Germany and Austria, neonatal ultrasound is employed much more widely as a screening tool and has been shown to be very cost effective in Austria in eliminating late-diagnosed dislocations and greatly reducing the need for surgery in DDH. In North America and the United Kingdom, hip ultrasonography in DDH has been employed more selectively, generally being used to screen subgroups at particular risk, and to follow the anatomic development of the dysplastic infant hips under treatment.

The effectiveness of current methods of detection and treatment of infant DDH in America must wait decades of follow-up before meaningful long-term results are known. It seems likely, though, that the incidence of both late-diagnosed congenital dislocations and associated surgery is somewhat higher in North America than in Austria and Germany where ultrasonographic screening is universal. Controversy over both the specificity of early US hip abnormalities and its cost has prevented its use as a universal screening tool in North America.

The rate of success of treatment of DDH in infancy depends directly on both the age at which treatment is instituted and the severity of the lesion being treated. Ortolani-positive hips treated with Pavlik harness or splint yield 80+ percent normal hips. Pavlik harness and closed reduction/cast for Ortolani-negative, irreducible hips seem to yield approximately 50 percent normal hips in the long-term. Results of primary open reductions done prior to walking age may prove statistically better than closed reduction in long-term follow-ups, but many more years of follow-up are necessary before this is known.

The ultimate risk of dysplasia-arthrosis in infant hip dysplasia undergoing primary treatment today is of course unknown. Historically, the rates of osteoarthrosis have risen regularly with the passage of every decade in each series, from 11 percent in the second decade of life to as high as 80 percent in the fourth decade, depending to a great degree on the following anatomic factors at maturity: femoral head deformity or incongruity, subluxation and degree of residual acetabular dysplasia. We now know that any incongruity, subluxation, or lateral center-edge angle less than 20 degrees at maturity will lead to osteoarthrosis in virtually every hip by age 60, and, in many hips, long before that.

In summary, optimizing neonatal detection allows the earliest possible treatment. Very early treatment of hip dysplasia encourages normal growth and development, but universal radiographic follow-up at least until skeletal maturity is needed to detect recurrent dysplasia. The role for more widespread radiographic screening in adolescence of subgroups at risk is uncertain but may merit additional consideration.

Optimal surgical correction of hips with acetabular dysplasia requires careful clinical assessment and preoperative planning. The ideal patient for surgical correction by acetabular redirection osteotomy has high grade acetabular dysplasia with minimal or no arthritis and a round, concentric joint. Patients with some degree of arthritis or an aspherical joint surface present an even greater challenge in determining both the appropriateness for surgery and the optimal surgical plan to stabilize the hip and improve function.

Preoperative imaging can include plain radiographic, fluoroscopic, MR, and CT studies. Plain radiographs and fluoroscopic views in various functional positions can predict the appearance of the joint after surgery. Specifically, an AP pelvis in abduction can show reduction of the hip in the coronal plane and can demonstrate the presence or absence of hinging. A false profile (65 degree standing lateral view) with the hip in slight flexion can show concentric reduction of anterior subluxation in the sagittal plane. MR studies are most useful to identify the degree and location of cartilage loss in patients where the appropriateness of joint-preserving surgery may be in doubt. Finally, CT studies can be used to form the basis for three-dimensional prediction of hip joint contact pressures both before and after simulated surgery.

Prediction of joint contact pressures in the hip joint can be calculated by first creating a three-dimensional reconstruction of the acetabular joint surface and then distributing joint reaction forces (derived from in-vivo studies and scaled for patient weight) across the joint surface. Joint contact pressure distributions can be predicted both before and after simulated surgery to determine the optimal position of the acetabulum at surgery.

Careful preoperative clinical assessment and planning can serve to better identify which patients are appropriate candidates for joint preserving surgery and to identify the optimal surgical plan that would maximize the function and longevity of the dysplastic hip joint.

Developmental dysplasia of the hip results in abnormal anatomy on both the femoral and acetabular side.

Femoral abnormalities often require specialized prostheses to cope with the differences in version and shape of the proximal femoral metaphysis and diaphysis. Derotation osteotomy is sometimes indicated for severe rotational deformities in order to bring the greater trochanter into a lateral position to optimize abductor function.

In all cases of DDH, acetabular deficiency is the rule. In Crowe, groups I and II medialization at the level of the true acetabulum with or without "eyebrow" grafts have been shown to be highly effective.

When the hips are in the group III and IV category, the acetabulum is deficient and will generally require some bone grafting. The surgical approach to high riding hips is often difficult. Trochanteric osteotomy approaches lead to attempts to create union between trochanter and cortical bone after metaphyseal removal unpredictable.

We describe a technique that has evolved over the past 15 years where the author has used a transfemoral approach to acetabular reconstruction with subsequent femoral shortening in the subtrochanteric region preserving the abductors. This approach mandates the use of noncemented prostheses in order to obtain union of the osteotomy. Follow up ranges from two years to sixteen years. The potential complications will be discussed.

The subtrochanteric approach to high riding DDH preserves the abductors while shortening the limb in the subtrochanteric area does not threaten the sciatic nerve. Over the past 16 years we have found this to be a very successful method of restoring the anatomical center of rotation while minimizing compromise to the abductor musculature.

The problem of total hip replacement in cases of total dislocation of the hip was of such magnitude that Sir John Charnley concluded that the operation should not he attempted. Many solutions were subsequently developed including augmenting the deficiency of acetabular bone stock with bulk allografts. The history of the subsequent studies of the outcomes of these grafts has taught us the following lessons:

1. Union of the allograft to the host is almost always successful.
0. This major augmentation of bone stock is immediately effective and, in general, permitted successful cemented acetabular reconstruction.
1. The success of these operations is excellent over the first five to eight years but showed an increasing failure rate thereafter.
2. The major adverse reactions are biologic. They include "creeping substitution", resorption of the lateral portion of the graft, periprosthetic osteolysis and fatigue fracture of the trabeculae under load.
3. The late incidence of failure is high. By 16 years, two thirds of the acetabular components have required revision.
4. If a revision becomes necessary, there is often a secondary gain from the graft. Frequently one can use a cementless acetabular component of larger diameter than the cemented socket, fixed to a combination of the host bone and to revascularized, structurally intact residual allograft.
5. The final lesson is that there are now a large number of alternatives to this grafting, which make the use of this type of graft quite uncommon.

Acetabular dysplasia is the most common cause of premature, secondary arthritis of the hip in adults. In fact, advanced arthritis of the hip is often incorrectly described as "primary osteoarthritis" even though it has arisen as a consequence of developmental dysplasia. Rotational osteotomies of the pelvis are effective in treating symptomatic, skeletally mature patients, as long as advanced radiographic arthritis has not yet become established.

The 'periacetabular osteotomy', as introduced by Ganz, Mast and coworkers in the late 1980's, and as subsequently modified by Millis, Murphy and others, has proven to be a safe and effective, though technically demanding, surgical treatment. The Tonnis juxta-articular rotational osteotomy, the triple innominate osteotomy, the dial osteotomy and others are also effective. Given the magnitude of the surgery involved, and the potential for complications, prophylactic surgery on asymptomatic individuals is not recommended. Additional contraindications include moderate and advanced arthritis, morphology in which the radius of curvature of the acetabulum is less than that of the femoral head and fixed subluxation. Indications include dysplasia and Legg-Calve-Perthes.

Femoral osteotomies have been performed much less frequently in recent years. Some patients with high valgus neck-shaft angles benefit from combined periacetabular and intertrochanteric varus osteotomies. These can be performed under a single anesthetic.

An anterior approach for the periacetabular osteotomy, between the sartorius and tensor muscles below, and medial to the iliac crest above, permits all cuts and repositioning to be accomplished without stripping or any dissection of the lateral iliac wing muscles (tensor and glutei). This virtually eliminates the risk of surgically produced limp and enhances the rapidity of recovery from surgery. Most patients resume walking without support by two and one half to three months after surgery. Bilateral procedures can be accomplished six months apart.

Revision total hip arthroplasty in the dysplastic hip begins with careful preoperative assessment of leg lengths, neurovascular status, soft tissue contractures, bone stock deficiencies, prior incisions and implant evaluation. Extensile exposures including trochanteric, subtrochanteric or extended trochanteric osteotomy may be required to provide adequate exposure, soft tissue releases, leg length equalization and safe implant removal and reinsertion. While the majority of acetabular revisions can be managed with a porous, hemispherical implant, segmental deficiencies are more common in the dysplastic hip. A high hip center position, oblong sockets, antiprotrusio cages, and structural and/or particulate bone grafting may be required to manage these deficiencies and provide adequate biomechanical reconstruction. A near anatomic positioning of the new hip center of rotation is preferred to reduce wear, loosening and dislocation rates while improving abductor strength and gait. Increased anteversion, loss of primal bone and small femoral canals make femoral revisions difficult in the dysplastic hip. Modular stems, long or calcar replacement necks, custom or microcomponents may be required to manage these difficult revisions.

Twenty-two athletes (25 hips) were referred with intractable hip pain preventing sports had mechanical symptoms and gradual atraumatic onset occurring for an average of 17.8 mos. prior to referral. Extraarticular and referred lumbar pathology were ruled out prior to arthroscopy.

Anterior labral tears were revealed in 92% of cases with associated anterior acetabular chondral defects in 80%. Femoral head chondromalacia was noted in 6 cases (24%), three with additional chondral defects and associated loose bodies. Pre-operative symptoms lasting greater than 3 years had larger chondral defects and more diffuse degenerative changes, suggesting these lesions may predispose to early degenerative changes if left untreated. Labral tears and chondral defects were debrided to stable healthy bases. Acetabular defects necessitating debridement to bone were drilled. All patients had improvement in pain and alleviation of mechanical symptoms. Those with greater than six-month follow-up returned to their sports.

Intraarticular pathology may be a potential result of repetitive axial loading in high torque positions associated with particular sports. The anterior location of the labral tear/chondral defect complex may account for subtle instability symptoms.

This symposium will be one in which the moderator (Lawrence D. Dorr, M.D.) will present to the panel: Dr. Charles Eng, Dr. Hugh Cameron and Dr. Miguel Cabanela x-ray and video examples of hip cases and ask for the opinion of the panel members in regard to the best treatment choice for that situation. The examples which will be discussed will cover both primary and revision situations. Primary situations will include bilateral total hip replacements and the treatment of congenital disease of the hip. The treatment options for avascular necrosis will be discussed; for revision problems will be the acetabular reconstruction and the use of bone graft or cages; for the femur the use of distal fixation and the choice of proximal femoral allograft for significant proximal femoral bone loss. The treatment of dislocation both prevention and treatment after occurrence will also be shown in case forms. This symposium will not include case presentations by the audience nor does this symposium have audience participation, but will be directed by the moderator to the panelists with cases selected by the moderator.