C. Anderson Engh

Long-Term Results of Use of the Anatomic Medullary Locking Prosthesis in Total Hip Arthroplasty*

A total hip arthroplasty was performed, with use of the anatomic medullary locking hip system, in 223 consecutive, non-selected hips in 215 patients. The mean age of the patients at the time of the operation was fifty-five years (range, sixteen to eighty-seven years). Twenty-one patients (twenty-two hips) were lost to follow-up and twenty-seven patients (twenty-seven hips) died less than ten years postoperatively. The remaining 167 patients (174 hips) were followed for a minimum of ten years (mean, eleven years; maximum, thirteen years). There were twenty reoperations involving a component. The rate of survival at twelve years was 0.97 ± 0.02 (mean and standard error) for the stem and 0.92 ± 0.03 for the cup. Patients who had osteolysis were younger than those who did not have osteolysis (mean age, forty-seven compared with fifty-six years; p < 0.01). Similarly, patients who had a reoperation were younger than those who did not have a reoperation (mean age, forty-six compared with fifty-four years; p < 0.01). The radiographic appearance of progressive wear that, in our opinion, was severe enough to cause the femoral head to completely penetrate the polyethylene liner was the most frequent reason for reoperation.

Long-Term Clinical Consequences of Stress-Shielding after Total Hip Arthroplasty without Cement*

Remodeling of the femur, or so-called stress-shielding, was observed on the two-year postoperative radiographs of forty-eight (23 per cent) of 207 hips that were part of a consecutive, non-selected series of 223 hips that had had a primary arthroplasty with use of the anatomic medullary locking hip system. Three patients (three hips) died within ten years after the arthroplasty, leaving forty-four patients (forty-five hips) who had a minimum of ten years of clinical follow-up. At the time of the latest follow-up, thirty-eight patients (86 per cent) reported that they had either no or mild pain related to the hip, forty-two (95 per cent) had less pain than they had had preoperatively, and forty-one (93 per cent) were satisfied with the results of the arthroplasty. Two patients had a reoperation, but neither procedure involved the femoral component; specifically, one patient had a revision of a loose acetabular component and one had an exchange of a polyethylene liner. No femoral component was associated with clinical or radiographic evidence of loosening. Femoral osteolysis, confined to zones 1 and 7 of Gruen et al., was observed on the ten-year radiographs of four of the thirty-three hips for which such radiographs were available. Stress-shielding (defined as evidence of pronounced femoral bone-remodeling on the two-year radiographs) had not adversely affected the outcome for these four hips by the time of the latest follow-up. The findings regarding postoperative pain, function, and over-all satisfaction for the forty-four patients (forty-five hips) who were included in the present study were similar to those reported for our larger (parent) series of patients who had been managed with the anatomic medullary locking hip system and to those reported for a similar series of patients who were followed for 9.5 years after the insertion of a porous-coated anatomic prosthesis. In addition, the prevalence of acetabular and femoral osteolysis (four [12 per cent] of thirty-three hips) and that of revision of the femoral component (zero [0 per cent] of forty-five hips) were lower than those for our larger (parent) series (fifty-four [39 per cent] of 137 hips and three [1 per cent] of 201 hips, respectively) as well as those for the series of patients who had been managed with the porous-coated anatomic prosthesis (thirty-five [45 per cent] and four [5 per cent] of seventy-eight hips, respectively).

Comparison of CT, MRI, and radiographs in assessing pelvic osteolysis: a cadaveric study.

In this study, we compared the accuracy of radiography, computed tomography, and magnetic resonance imaging in assessing periacetabular osteolytic lesions. Using a previously published cadaver model, we created 87 lesions in pelves implanted with total hip replacement components. The sensitivity for detecting lesions was 51.7% for radiography, 74.7% for computed tomography, and 95.4% for magnetic resonance imaging. For all three techniques, sensitivity increased as lesion size increased. Magnetic resonance imaging emerged as the most effective tool for detecting small periacetabular osteolytic lesions (≤ 3 cm3). For lesions larger than 3 cm3, which are of more concern clinically, computed tomography and magnetic resonance imaging were effective in identifying lesions with detection rates greater than 80%. For radiography and computed tomography, lesion detection was dependent on lesion location, whereas magnetic resonance imaging had consistently good sensitivity in all lesion locations. Although the mean volumetric errors for computed tomography and magnetic resonance imaging (0.3 cm3 and 0.8 cm3) were small compared with mean lesion volume (6.1 cm3), computed tomography was more accurate than magnetic resonance imaging at measuring lesion volume, with a lower mean absolute error. This study verifies the problems associated with radiographic detection of osteolysis while showing the effectiveness of computed tomography and magnetic resonance imaging in determining the presence of lesions and assessing their three-dimensional volume.

Factors associated with the loss of thickness of polyethylene tibial bearings after knee arthroplasty.

BACKGROUND Wear of the polyethylene tibial bearing is a leading cause of failure of knee replacements done prior to the current decade. The objective of this study was to determine how patient-related factors, implant-related factors, and limb or tibial component alignment influenced the amount of thickness loss in polyethylene tibial bearings that were retrieved at the time of revision surgery or after the death of the patient. METHODS We retrieved polyethylene tibial bearings from eighty-one unicondylar and eighty-nine total knee replacements that had been performed because of osteoarthritis with varus deformity from 1984 to 1998. All of the polyethylene bearings had been sterilized with gamma radiation in air. Polyethylene loss was quantified as the change in the minimum bearing thickness per years in vivo (the mean time in vivo [and standard deviation] was 8 +/- 4 years). Multiple linear regression was used to assess whether polyethylene loss was associated with age, weight, gender, varus angle of the tibial component, postoperative hip-knee-ankle angle, initial thickness of the polyethylene, shelf age of the polyethylene, and either the type of polyethylene (for total knee replacements, which were of one posterior cruciate ligament-retaining design) or the manufacturer (for unicondylar knee replacements), and to determine the magnitude by which polyethylene loss would change if any of the significant risk factors were changed. RESULTS The mean loss (and standard deviation) of polyethylene thickness in the medial compartment of total knee replacements (0.33 +/- 0.28 mm/yr) and that in medial unicompartmental knee replacements (0.49 +/- 0.40 mm/yr) were significantly (p < 0.05) associated with the same three variables: patient age, postoperative hip-knee-ankle angle, and shelf age of the polyethylene. A total knee bearing with a one-year increase in shelf age, a unicondylar knee bearing with a six-month increase in shelf age, a patient who was ten years younger at the time of operation, or a limb that was aligned in 5 degrees more varus (less valgus) had similar effects on the loss of polyethylene thickness in the medial compartment; the coefficients of the linear regression equations indicated that any one of these changes would increase polyethylene loss by 0.11 to 0.14 mm/yr. CONCLUSIONS The wear-related loss of thickness in gamma-irradiated-in-air polyethylene bearings from unicondylar and total knee replacements implanted in osteoarthritic knees with varus deformity is influenced mainly by the shelf age of the polyethylene, the age of the patient, and the postoperative angulation of the knee in the coronal plane. CLINICAL RELEVANCE Although polyethylene bearings have not been sterilized with gamma radiation in air since the end of the last decade, many arthroplasty patients have polyethylene bearings that were sterilized with use of this method. An understanding of the findings of this study may be of value as these patients return for follow-up care. Whether the study findings have relevance to bearings sterilized with other methods is unclear and will remain so for many years. LEVEL OF EVIDENCE Prognostic Level II.

Acetabular Revision with Use of a Bilobed Component Inserted without Cement in Patients Who Have Acetabular Bone-Stock Deficiency*

Background: Massive deficiency of acetabular bone stock is a challenging problem in the increasing number of patients who need a revision of a failed hip arthroplasty. The bilobed cup has been presented as one alternative reconstruction technique for hips with extensive acetabular bone loss. The purpose of this study was to assess the results with use of a bilobed acetabular component inserted without cement for revision reconstruction in hips with acetabular bone deficiency in order to clarify the indications for its use and to identify the factors that influence the clinical and radiographic outcome. Methods: Forty-one hips in thirty-eight patients had an acetabular revision with a bilobed acetabular component inserted without cement between December 1991 and December 1995. These hips were a subset of the 414 hips treated with an acetabular revision during the same period of time. One patient was lost to follow-up, and one died during the study period. Two patients who could not return for radiographic evaluation completed questionnaires. The remaining thirty-four patients (thirty-seven hips) were evaluated radiographically and clinically and were followed for an average of forty-one months (range, twenty-four to sixty-six months). Results: Radiographic analysis demonstrated an improvement in the average vertical displacement of the hip center. At the time of the latest follow-up examination, 76 percent (twenty-eight) of the thirty-seven cups were stable, 8 percent (three) were probably unstable with a change in the screw position but no definite migration of the cup, and 16 percent (six) were unstable. Eight of the nine loose or probably loose components were in patients who had more than two centimeters of superior migration of the component and disruption of Kohlers line on preoperative radiographs. Additionally, implants were more likely to become unstable (demonstrating more than 4 degrees of change in the abduction angle or more than four millimeters of radiographic migration) when the inferior aspect of the component did not extend to or distal to the interteardrop line, which indicated that the component was undersized. Conclusions: On the basis of our early rate of probable or definite loosening of 24 percent (nine of thirty-seven cups) and the technical difficulties involved, we do not recommend the routine use of this component. We believe that this device is indicated when a patient has an oblong-shaped acetabular defect and the surgeon wants to correct an elevated hip center. However, the medial wall of the acetabulum (Kohlers line) should be intact if the failed component has migrated more than two centimeters. An alternative reconstruction technique, such as use of a structural allograft with or without an acetabular cage, is also an option in this situation.

Long-term results using the anatomic medullary locking hip prosthesis.

Since the introduction of cementless total hip arthroplasty in the early 1980s, concern has shifted from component loosening toward polyethylene wear and osteolysis. The current review of 223 consecutive unselected Anatomic Medullary Locking femoral and acetabular components extends the followup on a series of patients previously reported on at 5 and 10 years. The purposes are to describe the reasons for revisions and to assess the onset and size of osteolytic lesions, with the hypothesis that osteolysis represents an important cause of loosening. The population included 204 patients (211 hips) with mean followup of 13.9 years (range, 2-18 years). Among them, 122 patients (129 hips) had a minimum 15-year followup. Minimum 2-year radiographs with a mean radiographic followup of 12.2 years (range, 2-18 years) were available for 204 hips (197 patients). Of the entire study group, 39 hips (38 patients) had 44 component revisions, increasing the number of revisions by 24 since this series was reported previously. Twenty-six patients (27 hips) had their first revision surgery more than 10 years after the primary surgery. The most common reason for revision of original components was wear or osteolysis occurring in 22 of the 39 hips (21 of 38 patients). The overall loosening rate was 3.4% (seven of 204) for femoral components and 5.4% (11 of 204) for acetabular components. Twenty-four percent of hips (48 of 204) had evidence of femoral or pelvic osteolytic lesions larger than 1.5 cm2. Femoral osteolysis was not associated with any case of femoral loosening, whereas seven of the 11 loose acetabular components were associated with pelvic lesions larger than 1.5 cm2.

Analysis of Temporal Wear Patterns of Porous-Coated Acetabular Components: Distinguishing Between True Wear and So-Called Bedding-in*

BACKGROUND Standard radiographic assessment of penetration by the femoral head into a polyethylene liner does not enable clinicians to distinguish between the two processes that cause movement of the head: true wear (the removal of polyethylene particles) and so-called bedding-in (other factors, such as creep and settling-in of the liner). By analyzing radiographs made over time, researchers can distinguish true wear from the bedding-in process. The purpose of the current study was to compare the wear performance of the initial modular acetabular cup design (so-called first-generation components) of three different manufacturers with that of a so-called second-generation component made by one of the manufacturers. METHODS A two-dimensional computerized radiographic method was used to analyze 1300 radiographs of 315 hips that were followed for 3.0 to 10.5 years. Temporal penetration by the head in the three groups of first-generation cups was compared with penetration in the group of second-generation cups. Multiple linear regression analysis was used to model penetration-versus-time data as a line for each group. The slope of each regression line indicated the true rate of wear, and the intercept of the regression line indicated the amount of bedding-in. RESULTS Modifications in the design of the second-generation components, including thicker polyethylene and an improved locking mechanism, led to a decrease in the mean penetration by the head; however, the second-generation component did not have a lower true rate of wear than two of the first-generation components. Rather, the decreased penetration by the head into the second-generation component resulted from decreased bedding-in of the liner. CONCLUSIONS These findings and this technique of analysis are clinically relevant to surgeons who evaluate polyethylene wear radiographically. First, penetration by the head in the early postoperative years might not be due entirely to abrasive wear of the polyethylene liner but, rather, to a change in the position of the head resulting from the bedding-in process. The inclusion of bedding-in in calculations of wear artificially inflates the rate of wear and may result in a misrepresentation of the potential risk of wear-related complications. This is especially true with regard to comparisons of different designs of modular cups, in which conformity and tolerances between the polyethylene liner and the metal shell can vary greatly. Second, analysis of penetration by the head at multiple time-intervals can be used to distinguish true polyethylene wear from the bedding-in process. Such an analysis allows more accurate determination of the true rates of wear of different designs of modular cups and, therefore, of potential wear-related complications.

Radiographic Evaluation of Penetration by the Femoral Head into the Polyethylene Liner over Time

We examined the pattern of temporal penetration by thirty-two-millimeter-diameter femoral heads into polyethylene liners in a group of 105 hips (103 patients) in which an Arthropor metal-backed cup had been implanted. Each patient was evaluated radiographically and clinically at a minimum of four different postoperative intervals. The initial evaluation was performed a mean of 2.9 weeks (range, one to fifteen weeks) postoperatively, and the latest evaluation was performed a mean of 7.9 years (range, five to ten years) postoperatively. Two-dimensional wear—that is, penetration by the femoral head into the ultra-high molecular weight polyethylene liner—was determined from anteroposterior radiographs of the pelvis with a computer analysis system that calculated the change in the position of the center of the head relative to the center of the cup. Three new findings are reported. First, there was a large difference (mean, 1.1 millimeters) between the center of the head and that of the cup as measured on the initial postoperative radiographs. This difference underscores the need for researchers to consider the initial displacement of the head when measuring and reporting polyethylene wear. Second, although there was wide variation in responses among individuals, temporal examination of the data revealed a trend toward a decreasing rate of penetration with time. Moreover, the rate of penetration appeared to reach a steady-state value after the sixth postoperative year and remained nearly constant until the ninth postoperative year. Third, by comparing the subsets of patients who had the greatest and the least initial penetration by the head, we found that penetration behavior, although remarkably different between the groups in the first three years postoperatively, became similar with time. CLINICAL RELEVANCE: When making decisions regarding individual patients or hip systems that demonstrate penetration by the femoral head into the polyethylene liner, clinicians should consider the patterns of penetration over time. Measurements of the amount and rate of penetration that are based solely on the most recent radiograph do not represent the full clinical picture. We advocate more frequent radiographic follow-up and, when available, analysis of serial radiographs for patients who have excessive penetration by the femoral head into the acetabular liner.

Osteonecrosis of the Femoral Head Treated with Cementless Total Hip Arthroplasty

Background: The treatment of young patients who have osteonecrosis of the femoral head associated with collapse or substantial secondary degeneration remains a therapeutic challenge, with total hip arthroplasty being a treatment of choice. However, concerns about the durability of the results of hip arthroplasty in this population necessitate long-term evaluation of this treatment option. To determine its advantages and limitations, we evaluated the results of cementless total hip arthroplasty in a consecutive series of young patients with advanced osteonecrosis. Methods: We reviewed the results of fifty-five consecutive primary total hip arthroplasties, after an average of 117 months of follow-up, in forty-five patients with a preoperative diagnosis of advanced osteonecrosis of the femoral head (Ficat and Arlet stage III or IV). The average age was thirty-one years (range, twenty-one to forty years) at the time of the operation. We collected data prospectively with the use of patient questionnaires and radiographs. Results: Five patients died and one patient was lost to follow-up before the time of the minimum five-year follow-up; this left forty-eight hips in thirty-nine patients for inclusion in the study. Ten (21 percent) of the forty-eight hips required revision. No revisions were due to aseptic failure of the femoral component. Of the remaining twenty-nine patients (thirty-eight hips), twenty-seven (93 percent) reported few or no functional limitations and twenty-three (79 percent) could walk an unlimited distance at the time of the latest follow-up. Pain was absent or mild in twenty-five patients (86 percent). Twenty-three patients (79 percent) were employed full-time. Radiographically, thirty-seven femoral components (97 percent) were bone-ingrown and the remaining component was judged to be fibrous stable. All thirty-eight acetabular components were bone-ingrown. Conclusions: Cementless total hip arthroplasty remains a reasonable treatment option for advanced osteonecrosis of the femoral head. Wear of the bearing surface continues to limit the long-term success rate, but we are encouraged by the predictable long-term stability of the bone-implant interface achieved with cementless fixation. These results compare favorably with those of published reports of total hip arthroplasty with cement in younger patients with osteonecrosis.

Wear of Polyethylene Cups in Total Hip Arthroplasty. A Study of Specimens Retrieved Post Mortem

The wear of polyethylene components of total hip replacements has previously been studied radiographically and by analysis of retrieved components. The extent of wear, however, has largely been determined from components retrieved at reoperation and has therefore been based on a subset of patients in whom the prosthesis is more likely to show excessive wear. The study of cups retrieved post mortem provides a better indication of the extent of wear of well functioning components. Twenty-six polyethylene liners were retrieved at autopsy from nineteen patients, after a mean of ninety-one months (range, thirty-three to 206 months) in situ. Each component had articulated with a thirty-two-millimeter-diameter femoral head. The components were evaluated visually for evidence of polyethylene wear such as pitting, scratching, and burnishing. Additionally, a shadowgraph technique was used to examine molds of the inner surface of the liner to determine the direction and extent of wear. The mean extent of linear wear of the retrieved liners was 0.45 millimeter (range, 0.17 to 1.07 millimeters), and the mean rate of wear was 0.07 millimeter (range, 0.02 to 0.18 millimeter) per year. The mean volumetric wear was 245.3 cubic millimeters (range, 13.0 to 779.1 cubic millimeters), and the mean rate of volumetric wear was 39.8 cubic millimeters (range, 1.0 to 131.3 cubic millimeters) per year. The mean rate of wear for the twenty-six liners was 45 to 69 per cent less than the rates reported in the literature for polyethylene liners retrieved at reoperation. Examination of the articulating surface did not reveal gross evidence of surface failure such as delamination or fatigue cracks. In general, the surfaces were merely burnished and scratched. The rates of wear of press-fit, metal-backed liners were significantly higher than those of all-polyethylene cemented components (p < 0.05). Additionally, statistical analysis revealed no correlation between wear and the patients age, weight, or gender; the duration of implantation; or the thickness of the polyethylene. These results indicate that wear of the polyethylene of well functioning hip replacements is not as excessive as reported previously.