Richard Rothman, M.D., J.J. Purtill, M.D., W. Hozack, M.D., P. Sharkey, M.D.

The authors report 15-year experience with total hip arthroplasty using a collarless wedge-fit tapered circumferentially porous coated femoral stem (Trilock, Dupuy, Warsaw, In and Taperlock, Biomet, Warsaw IN).

Excellent clinical results (Charnley pain function and motion scores improved from 3, 2.7 an 3.2 to 5.7, 5.5 and 5.2 respectively and Harris hip score of 91 at 15 years), low rates of thigh pain (1.4% and 4% for the Trilock and Taperlock respectively) combined with low rate of mechanical failure ( 5% for the Trilock and 0% for the Taperlock) were achieved with these implants Successful THA was performed in subsets of the population traditionally thought to have poor bone stock (over 80 years old and rheumatoid arthritis).

Initial stability of these implants was confirmed with an Instron machine and fresh frozen cadaveric femora. Excellent stability was noted with similar plastic deformation and micromotion to cemented femoral implants. Clinically, immediate postoperative weight bearing is well tolerated with minimal subsidence (mean 0.86 mm) and no directly attributable failures.

Hydroxyapatite coating appears to provide no clinical or radiological advantage at 2-year mean follow-up with Charnley pain, range of motion and function scores of 5.6, 5.6 and 5.6 with hydroxyapatite and 5.6, 5.6, 5.6 without, respectively. Visual analog pain scores however showed less thigh pain at 3 and 6-month evaluations in the hydroxyapatite augmented stems.

Design features (collarless tapered wedge-fit circumferentially porous coated) are thought to be responsible for the excellent results.

11:00 a.m.

The rationale and evolution of proximal porous coating and porous coating in general have to be understood in the context of total hip arthroplasty circa 1978-80. The claims of 98% or even 90%, 10 to 15+ year survival of cemented implants were not being made, both because there was a paucity of results over that time period, and at least USA surgeons felt they were seeing enough short to intermediate term failure, especially in younger people, that an alternative fixation mechanism was warranted.

Animal laboratory work extending from an initial observation about screw stability in bone suggested that bone ingrowth into either porous beaded surfaces or fiber metal mesh surfaces may provide a very predictable, sturdy fixation methodology. Choice of metal, porous structure, and extent of porous coating were all considered by a variety of scientists and manufacturers.

From the outset there was concern about observations of very strong bony attachment to pegs and rods that were porous coated, feeling that distal coating in the proximal femur could lead to proximal stress shielding. There were then laboratory studies raising this concern, and it is the opinion of many of us that today there are abundant clinical examples corroborating this concern.

As a result, some, actually most, of the first “modern” attempts at porous femoral fixation (PCA’s and proximally coated AML’s) restricted the porous coatings to the proximal 25 to 40% of the femoral component surface. In addition to the concern about proximal stress shielding secondary to rigid distal fixation, some saw the broader, obviously vascular, proximal cancellous bone as an attractive bed from which ingrowth would sprout.

It is safe to say that the initial experience from 1982-3 out to 1985-7 revealed satisfactory but less than optimal 3 to 5 year results with a slightly higher failure rate for component revision in many surgeon’s hands and the development of a situation, disputed by some surgeons but not by their patients, affectionately referred to then and now as thigh pain. Beyond that early experience we also began to recognize more consistently osteolysis and look for explanations and solutions to it also.

The AML group led by Charles Engh pursued the course of increasing the extent of porous coating, while others addressed stem geometry, changes to more flexible metals and stem designs, also HA coatings---still with adherence to the goal of avoiding proximal stress shielding.

There is more to the concern about extensively coated stems than proximal stress shielding, and that is the recognized difficulty of stem extraction or bail-out in the event of infection, fracture, recurrent instability associated with component malposition, etc. As a result many of us have held steadfast to the use of the proximally coated stems and today feel increasingly confident in their use.

As we review intermediate and now long-term results one can extract any conclusion that he/she desires, and we get down to a choice that is akin to issues of religion and politics. Our task today cannot be to convince someone, one way or the other but to explain the issues and allow therefore a choice which addresses those points an individual surgeon feels are most important for his/her patient.

11:10 a.m.

A novel total hip femoral component was designed to simultaneously achieve stable skeletal fixation, structural durability, and reduced femoral stress shielding. The prosthesis combines a thin, forged, cobalt chrome core, surrounded by a polyaryletherketone material that is molded between the core and an extensive porous bone ingrowth surface comprised of titanium metal fibers. The resultant construct allows for proximal and distal canal filling, yet is significantly less rigid than all-metallic femoral stems crafted of either cobalt chrome or titanium alloy. Canine studies revealed favorable biological fixation and stability. Clinical experience is now approaching six years of duration, with a cohort of 366 patients (386 hips) treated at 21 institutions under a structured, multicenter clinical evaluation protocol. To date, complications have been unremarkable, and no femoral implants have required revision. Clinically, patients have shown excellent return to function, and exhibit very high Harris hip scores at each annual evaluation beyond one year postoperatively. Low levels of hip and thigh pain characterize the clinical outcome. Radiographically, the implants appear well fixed and exhibit no progressive radiolucencies or osteolysis. Radiostereometric analysis (RSA) studies on one subset of patients showed strong initial fixation and minimal stem micromotion in direct comparison to other metallic porous and cemented control implants. Dual-energy x-ray absorptiometry (DEXA) analysis on another subset of patients revealed excellent periprosthetic bone mineral density retention, with significant reduction in stress shielding as compared to literature reports on other fully porous coated, all-metallic implants. Additional clinical and radiographic follow-up of this novel prosthesis is planned, in hopes that the long-term biological response to a low-stiffness hip implant may become better understood and appreciated.

11:20 a.m.

This review reports long-term outcomes of 223 consecutive nonselected cementless primary total hip arthroplasties using extensively (>50%) porous-coated nonmodular AML stems and Trispike acetabular components. The arthroplasties were performed from October of 1982 through December of 1984. Mean patient age was 55. Eleven patients (12 hips) did not have minimum 2-year follow-up, leaving 204 patients (211 hips) with a mean follow-up of 13.4 years and a radiographic follow-up of 12.1 years. Thirty-nine patients (39 hips) had primary component revisions. One complete revision was performed for infection. Three stems were revised for aseptic loosening. Eighteen acetabular shells were revised: 7 for loosening, 4 for osteolysis, 3 for wear, 3 for recurrent dislocation, and 1 for sepsis. Seventeen polyethylene liners were exchanged: 9 for wear, 6 for osteolysis, and 2 for recurrent dislocation. Five rerevisions were performed. Accounting for revisions for loosening and the stability of the remaining components, the loosening rate was 3.4% for femoral components and 4.9% for acetabular components. In summary, porous coated fixation with the AML stem and Trispike acetabular component is durable. The most common reasons for reoperation are polyethylene wear and osteolysis. Factors contributing to wear-related acetabular revisions included younger patient age, the use of nonmodular 32-mm femoral heads, and proactive polyethylene liner exchanges to avoid wear-through.

11:30 a.m.

This study was designed to test the hypothesis that press-fit femoral components with proximal press-fit and distal mechanical interlock can achieve fixation sufficient to allow bone ingrowth in osteoporotic as well as in normal bone. Addition of steps along the tapered distal stem improved fixation in osteoporotic bone enough to reduce micromotion to less than 20 microns in response to physiologic axial and torsional load. The clinical portion of the study included 226 consecutive hips (223 patients) with two-to-four year clinical results after total hip arthroplasty with a rectangular femoral component using proximal porous coating and distal mechanical interlock. Patient age ranged from 36 to 92 years. At two years postoperative, four percent of the femurs with type A (normal) bone, three percent with type B (intermediate) bone, and none with type C (osteoporotic) bone had thigh pain. No clinical cases of loosening have occurred either in normal or osteoporotic femurs.

1:00 p.m.

It is well recognized that the etiology of osteoarthritis of the hip is multifactorial, with significant contributions from genetic, structural, biochemical and morphologic factors. Moreover, previous attempts to classify degenerative hip disease as either idiopathic or secondary have failed to explain the underlying cause of many cases of hip pathology, despite sensitive and exacting measures of normal skeletal morphology and intraarticular pressures. These observations have led us to suspect that, in many cases of so-called “idiopathic” degeneration, predisposing factors may have been present that are not readily appreciated using conventional diagnostic and radiographic modalities. Previous authors have postulated that the high incidence or early arthritis observed in dysplastic hips is due to the instability of the articulation und the repetitive shearing of the articular surface with functional joint motion. This suggests that other disturbances of the soft-tissue structures stabilizing the hip may also precipitate degenerative changes due to compromised joint stability. Potentially, one such condition is mechanical disruption of the hip labrum.

Although lesions of the acetabular labrum were once considered a rarity, the prevalence of labral pathology has become more evident with the refinement and increased utilization of hip arthroscopy. However, the natural history of labral lesions has yet to be well­­­ defined and the functiona1 significance of the nom1allabrum remains a subject of debate. Moreover, though some authorities have suggested that acetabular labral pathology could conceivably contribute to the development of hip osteoarthritis, this hypothesis has yet to be adequately investigated.

This study was conducted in three stages to examine the hypothesis that labral lesions contribute to early degenerative hip disease and to determine the feasibility of measures to prevent joint pathology through treatment of labral injuries. The goal of the first stage was to define the relationship between articular degeneration and labral lesions in patients whose joint symptoms were suggestive of labral pathology. The second stage was to determine whether similar correlations exist in individuals without symptoms without a documented history of joint disease. The third stage was to determine whether the hip labrum has a vascular supply that might potentiate the repair and regeneration of labral lesions, thereby preventing articular degeneration.

1:15 p.m.

Quality of the cement mantle around the femoral stem is often quoted as a critical factor in the success of cemented total hip arthroplasty. Concern has been raised about the reliability of plain radiographs for its assessment. A new in vitro method of cement mantle measurement is described. Exact plastic replicas of six contemporary designs were implanted into cadaver femora using modern techniques and following the manufacturers' instructions. One-millimeter thick axial images were obtained every five millimeters with a high-speed helical CT scanner. Computer assisted analysis of mantle thickness was performed. A deficient mantle was defined as less than two millimeters. Comparisons were made between designs. A subset was compared to standard radiographs. Standard radiographs overestimated thickness (p<0.05) and underestimated the deficiencies. There is significant variability in the mantle produced by different designs (p<0.001). Commonly used designs have significant deficiencies in their mantles.

1:30 p.m.

Morphology of the hip joint, in particular those features germaine to the determination of acetabular and femoral anteversion angles and offset of the femoral head, was studied in 50 male and 50 female human skeletons with bilateral normal hip joints. Age distribution typified that of a total hip arthroplasty (THA) population. Four distinct configurations were identified relative to the anterior acetabular ridge. The majority (121,60.5%) were curved; 51 (25.5%) were angular; 19 (9.5%) were irregular; and 9 (4.5%) were straight. The anteversion angle (AA) of the acetabulum measured 19.9 ± 6.6º (range, 7 - 42º) and was significantly larger in females (21.3 ± 7.1º) versus males (18.5 ± 5.8º). The notch acetabular angle (NA), which can easily be identified intraoperatively, was defined as the angle created at the intersection of a line from the sciatic notch along the posterior acetabular ridge and a line from the posterior to the anterior acetabular wal1. The NA was measured as 89.0 ± 3.5º and, as a result of being nearly perpendicular, this angle may be useful for determining an accurate estimate of acetabular anteversion and component placement during THA. Knowledge of the anatomic differences found between sexes with regard to the acetabular anteversion angle, the anterolateral bowing of the femur, and the neck shaft angle may assist the surgeon in decreasing the relatively higher incidence of dislocation in females and may possibly lead to different implant designs for males and females.

1:50 p.m.

Dislocation following total hip arthroplasty is stressful to the patient and surgeon. Prevention rather than treatment of dislocation is preferable to the surgeon and patient. Issues related to prevention include patient education and compliance, soft tissue reconstruction considerations, and component positioning considerations. With the expanded indications for primary hip surgery and the increasing need for revision hip surgery the need for preoperative education and, especially in the early postoperative period, postoperative compliance is essential. In fact some patient compliance is probably necessary throughout life as 20% of dislocations occur after five years. Over the past decade, the use of modularity and higher offset stems have enabled the surgeon to adequately reconstruct the soft tissues of the hip without performing trochanteric osteotomy. However the surgeon must understand that some aspects of modularity including skirted modular heads and extended liners can also compromise stability. When the present authors switched to small modular heads the dislocation rate significantly increases.

In addition to soft tissue considerations the surgeon needs to be aware of bony impingement to include peripheral osteophytes. Accurate component positioning requires proper positioning of the patient at the time of surgery as well as identifying bony landmarks and using trial components intra-operatively to adequately position the acetabular component in the 30 to 50 degree “safe abduction zone” and to avoid retroversion of either component. Especially in the revision situation, in the lower demand patient, when adequate stability cannot be obtained consideration should be given to the use of constrained acetabular components. Postoperative bracing or casting can also be helpful. Dislocation, especially in the revision situation has been reduced with this approach (constrained components or early immobilization). These considerations will help minimize dislocation but will never eliminate the problem.

2:00 p.m.

The posterolateral surgical approach with complete posterior capsulectomy for total hip replacement is complicated by a significant incidence of early posterior dislocation. Formal repair of the posterior capsule and short external rotator tendons has been described as an approach modification to reduce the incidence of this early complication. The purpose of the study was to compare the incidence of early postoperative dislocation in the first six months following primary total hip replacement using the posterior capsulectomy technique and the posterior capsular repair technique. The identical posterolateral approach was used in all primary total hip replacement patients with the exception of management of the posterior capsule. The posterior capsulectomy technique (Group I) involved complete excision of the posterior capsule with no attempt at repair or reattachment of the short external rotators. Group I had 1,078 total hip replacements. The posterior capsular repair technique (Group II) involved reattachment of a broad flap of posterior capsule and short external rotators through drill holes in the posterior border of the greater trochanter. Group II had 437 total hip replacements. Only dislocations noted in the first six months were recorded because this is the high-risk period during which the posterior capsule is either reforming or re-adhering. In Group I (posterior capsulectomy), 52 of 1,078 total hip replacements (4.8%) had an early posterior dislocation. In Group II (posterior capsular repair), 3 of 437 total hip replacements (0.7%) had an early posterior dislocation. This difference was statistically significant. Internal rotation was reduced by approximately 50% by the reattachment process. No external rotation contracture was noted. A small avulsion fracture of the greater trochanter was noted in 4 of 437 total hip replacements (0.9%). The posterior capsular flap could not be reattached in 3 of 437 total hip replacements (0.7%). In posterolateral approach in primary total hip replacement, formal reattachment of the posterior capsule and short external rotators resulted in a statistically significant reduction of posterior dislocations when compared to patients who had complete posterior capsulectomy.

2:10 p.m.

Instability following a total hip arthroplasty is a serious complication. Dislocation rates up to 6.5% following posterior approaches have been reported within the last decade. For this reason, our institution favors the direct lateral approach for primary and revision total hip arthroplasty.

A review of our arthroplasty database yielded 1,515 primary total hip arthroplasties performed via a direct lateral approach in 1,333 patients. These arthroplasties were all performed within a 10-year period and patients with follow-up data of less than 12 months were excluded. At most recent examination, 11.7% of the patients had a moderate or severe limp and 2.6% had severe heterotopic ossification. Only 5 hips (0.33%) had a dislocation or episode of instability. Two patients had more that one dislocation and required revision surgery.

The results of this study demonstrate that dislocation after primary total hip arthroplasty can be nearly eliminated with the use of the direct lateral approach. The associated risks of heterotopic ossification or limp are felt to be acceptable.

2:20 p.m.

Proper component positioning is essential if post-operative dislocations are to be avoided. We undertook a computer analysis of ROM of a total hip prosthetic construct using impingement as an end point in order to determine the effect of component position on hip stability and ROM. The ideal position for maximal motion in all planes before impingement was 45 degrees of abduction and 25 degrees of flexion of the acetabular component with the femoral component in 15 degrees of anteversion. Increased abduction to 55 degrees allowed more motion than less abduction (35 degrees). Other factors that influence stability were femoral neck geometry, head diameter, and neck diameter. A cadaveric anatomic study was done to look at the relationship of the greater sciatic notch and acetabular anteversion. It was found to reflect anteversion accurately and is easily accessible at surgery. Finally two of the authors (WNC and JAD) routinely use the posterior approach in total hip arthroplasty and use only internal landmarks for acetabular orientation particularly the greater sciatic notch. Both contributed patients to a multi-centered prospective randomized controlled study investigating a ceramic on ceramic bearing used with a hydroxyapitite coated stem and either a HA coated socket or a porous coated socket, and into a continued access extension of the study. A total 717 hips were entered into this study nationwide. Nineteen dislocations have occurred for a rate of 2.6%. The two authors contributed 225 patients one of whom has dislocated for a rate of 0.4%. If one subtracts the authors patients from the 717 the dislocation rate increases to 3.6% (18/492) p<.05. We believe that dislocations with the posterior approach can be reduced if proper component positioning is understood and internal bony landmarks are used to orient the components.

2:30 p.m.

Treatment of recurrent hip dislocation in part is predicated upon understanding the etiology of the hip dislocation. Implant malposition usually is treated with component repositioning; soft tissue tension problems usually are treated with procedures designed to re-tension the soft tissues (using modular implants, component revision or greater trochanteric advancement) and problems with prosthetic or extra-articular impingement usually are treated with procedures designed to remove the source of impingement.

Not all patients with a dislocation problem have a clearly definable etiology and even for those with a clearly definable etiology not all problems can be solved with the methods outlined above. Fortunately, other methods of treating recurrent hip dislocation are available: these include conversion to a constrained socket, conversion to a bipolar hemiarthroplasty and conversion to a non-constrained socket with a very large bipolar or monopolar femoral head. Each of these methods have theoretical and practical advantages and disadvantages, which will be discussed in this paper.

Data from analysis of the various methods used to treat recurrent dislocation over the last three decades of total hip arthroplasty will be presented that demonstrate how operative methods of treating recurrent dislocation have evolved over time. The early and mid-term success rates associated with each of the available techniques to treat dislocation will be delineated.

3:05 p.m.

One of the first steps in revision hip arthroplasty surgery is the extraction of retained components prior to surgical reconstruction. In revision arthroplasty, the removal of well-fixed components and cement can be extremely demanding, time consuming, and damaging to the remaining host bone. Competent preoperative planning is imperative and assures that the appropriate equipment is accessible. Furthermore, preoperative planning aids in determining the proper extraction technique best suited for each particular implant. The preservation of host bone stock is of utmost importance, especially during the extraction of well-fixed cementless components. The revision of acetabular components may only require polyethylene exchange. In contrast, the removal of cemented acetabular components and well-fixed porous coated implants can be dangerous, especially in cases with mediallized acetabular components. One may elect to section the acetabular implant prior to removal in an attempt to preserve bone. During femoral implant removal, restricted access to the in-growth surface or cement may make component removal exceedingly difficult and increase the risk of iatrogenic damage to the remaining femoral bone. A preponderance of femoral components and the surrounding cement can be removed without the use of any trochanteric osteotomy. However, the use of an extended proximal femoral osteotomy may hasten implant removal, simplify cement removal, and protect the remaining bone stock These emerging implant removal techniques should allow the orthopaedic surgeon to extract both acetabular and femoral components skillfully and expeditiously, thus improving the efficacy of reconstruction. Our results in patients with noncemented porous coated acetabular component removal and noncemented femoral component removal are described.

3:20 p.m.

Experience is the best educator. Careful pre-operative planning minimizes complications and maximizes clinical results. Standardization of instrumentation with careful elimination of all superfluous tools makes the intra-operative experience more pleasant for both surgeon and surgical team. However, a full range of tools and equipment is crucial. A systematic approach to surgical exposure and component or cement removal is critical. On the other hand, the surgeon must have the flexibility and adaptability to change course in mid-operation should the situation dictate. Whatever surgical approach is chosen, the surgeon must have the ability intra-operatively to expand the exposure.

Keep things simple. If there are two ways to solve a situation that are equally appropriate, choose the way that is the simplest and easiest.

Preoperative planning

1. Evaluate all possible scenarios – don’t assume that plan A will work.
2. If a component does not need to be removed, make sure the previous operative report is available to identify special component or equipment needs.
3. Assess the need for special or extended approaches.