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In this study, we compare the in vivo wear performance of electron beam-irradiated, postirradiation-melted, highly cross-linked polyethylene (HXLPE) and traditional UHMWPE via the Martell method. Seventy hips with HXLPE performed at the Massachusetts General Hospital had 138 radiograph pairs for wear analysis and a 31.2-month average follow-up (range, 24-44 months). An age-matched, sex-matched, and body mass index-matched subgroup of 111 hips with 214 acceptable radiograph pairs and a 4-year follow-up from our previously published study on traditional polyethylene performed at Rush-Presbyterian-St. Luke's Medical Center served as a control group. Martell wear analysis was performed for each group. Overall and steady-state wear rates were compared via a specialized t test. The steady-state wear in the HXLPE arm was observed after 2.0 years, was 0.007 mm/y, and was significantly less than the steady-state wear in the traditional arm (0.174 mm/y) (P = .003). Highly cross-linked polyethylene penetration rate was not affected by sex, age, activity, or body mass index by Mann-Whitney analysis.

The results of 57 revision total knee arthroplasties performed for aseptic failure between 1984 and 1992 with a cemented posterior-stabilized or constrained condylar prosthesis were reviewed at follow-up examinations at a minimum of 36 and an average of 62 months (range, 36-120 months). The reason for revision was aseptic loosening of 1 or both components in 32 knees (56%), instability in 16 knees (28%), polyethylene wear and osteolysis in 4 knees (7%), supracondylar femur fracture in 2 knees (4%), and a failed allograft, pain, and arthrofibrosis in 1 knee each (5% total). The average age of the patients at the time of the revision was 74 years (range, 38-90), and the original diagnosis for the majority of patients was osteoarthritis (74%). All of the revision prostheses were cemented posterior stabilized or constrained condylar-type implants. Bone deficiencies were grafted with cancellous allograft in contained defects and cortical allograft in noncontained defects. Five knees were reconstructed with allograft-prosthesis composites. The average modified Hospital for Special Surgery knee score improved from 49 to 82 (100 points possible) at final follow-up evaluation (P < 0.001). Seventy-nine percent of knees were graded as good or excellent. Kaplan-Meier survivorship analysis predicted 94%+/-6.2% survival at 40 months and 75%+/-25% at 99 months. There were 4 clinical failures, 3 of which were related to residual instability in patients with a posterior-stabilized prosthesis. Complications (3 knees) were exclusively related to the extensor mechanism. Radiographically, overall knee alignment improved from 0.3 degrees varus to 3.0 degrees valgus. Fifty-six percent of tibial components were placed in slight varus alignment. Radiolucent lines occurred in 33% of knees, but there were no complete or progressive radiolucencies. Radiolucent lines were more prevalent adjacent to press-fit intramedullary femoral stems compared with cemented stems (P < .02), but the difference did not correlate with clinical or radiographic failure. The median bone defect score, as proposed by the Knee Society Committee on Bone Defects, was significantly greater in knees that were revisions of a failed cemented total knee arthroplasty compared with revision of a failed cementless total knee arthroplasty (P = .02) but was not correlated with clinical or radiographic outcome (P > .05).

The functional influence of patellofemoral design was evaluated by testing two cohorts of patients with total knee arthroplasty while walking, climbing stairs, and rising from a chair. The two cohorts received one of two different designs of total knee arthroplasty. The designs differed primarily in the curvature of the femoral trochlea. These differences in curvature have been shown in in vitro studies to influence the tracking of the patella. One design had a smaller radius on the patellar flange, which caused the patella to articulate more anteriorly and distally than the second design, which had a larger radius in this region. The second design more closely replicated the curvature of the femoral trochlear anatomy. There was a significant functional difference during stairclimbing between the patient groups, whereas there was no difference during walking or chair rising. The group with the design that had nonanatomic tracking of the patella had a higher than normal moment tending to flex the knee (net quadriceps moment) during late stance phase. The increased net quadriceps moment during late stance was concurrent with an increased knee flexion. The abnormal function occurred when the patellar was tracking over the nonanatomic portion of the trochlea. Patients in the group with the anatomic trochlea did not have abnormal function. These results suggest a relationship between a nonanatomic trochlea and abnormal function during stair-climbing.

The initial migration and micromotion of the revision femoral stem stabilized with morselized impacted cancellous allograft and bone-cement and the influence of cement pressurization on fixation of the cement/allograft composite to the host were examined with human cadaver femurs. The stability of the allograft/cemented reconstruction was found to be intermediate between those of conventional cemented and cementless stems. In most cases, the stability of the reconstruction was closer to that of cemented than to that of cementless stems. This may account for histologic findings of graft incorporation in experimental and retrieved specimens reported by other authors. Although increased cement pressurization led to greater penetration of cement into the graft bed, greater cement penetration did not increase fixation strength of the cement/allograft composite to the host.

From a group of 643 total hip arthroplasties, 98 patients required trochanteric osteotomies, and in 68 the trochanteric osteotomies were repaired with the Dall-Miles cable grip system (Howmedica, Rutherford, NJ). Trochanteric nonunion occurred in 17 of these patients (25%), with fraying and fragmentation of the cable present in 15 (88%). Of the 51 patients with radiographic union, 18 (35%) also had signs of fraying and fragmentation. Bone destruction around the cable in the area of the lesser trochanter was seen in seven patients (10%). Large deposits of metal debris at the inferior border of the acetabulum were seen in eight hips (12%). Multifilament cable did not appear to offer significant advantages over standard monofilament wire, and the potential problems of fraying, fragmentation, and free-floating metallic debris must be considered.

A consecutive series of 62 Miller-Galante (Zimmer, Warsaw, IN) unicompartmental knee arthroplasties were evaluated. Patients had unicompartmental degenerative arthritis or osteonecrosis, a sagittal plane deformity of 15 degrees or less, and minimal patellofemoral involvement. The average age was 69, with osteoarthritis in 85% and osteonecrosis in 15%. Ninety-five percent were medial and 5% lateral compartment replacements. The Hospital for Special Surgery knee score averaged 56 +/- 11 before surgery and 96 +/- 5 at the final follow-up evaluation, with an average postoperative pain score of 48 +/- 2. Three patients suffered intra-operative or immediate postoperative tibial plateau fractures without apparent sequelae, one patient required a postoperative manipulation under anesthesia, and one patient required an arthroscopic debridement for retained cement in the posterior capsular space. Limb alignment was corrected to within 5 degrees of the neutral mechanical axis in 77%, with 19% undercorrected and 3% overcorrected. Seventy percent of knees showed at least a single radiolucent line. Complete radiolucent lines were noted about three tibial components (6%) and progressive partial radiolucency was noted about four additional components (8%).

The purpose of this study was to determine the incidence of positive intraoperative cultures, correlate the findings of the permanent histopathology with the results of culture, and determine the natural history and predictive value of the positive intraoperative culture in a consecutive series of 138 revision total hip arthroplasties. The incidence of positive cultures was 30% (42 hips). Of these 42 hips, only 1 ultimately developed sepsis, requiring a second surgical procedure. After a mean follow-up period of 48 months, the remaining 41 culture-positive hips show no evidence of sepsis and are considered clinical successes. The histologic appearance of the infected case was characterized by polymorphonuclear leukocyte infiltration suggestive of acute inflammation. The remaining hips demonstrated findings of chronic inflammation consistent with a diagnosis of aseptic loosening. With the development of sepsis as an endpoint, the positive predictive value of a positive intraoperative culture is 2.4%. The results demonstrate that intraoperative cultures are an unreliable predictor of sepsis and that permanent histologic sectioning is a more useful tool in determining sepsis at the time of revision surgery.

The interfacial membrane between implant and host-bone in aseptically loose total hip arthroplasties has a potential role in the etiology of local bone resorption and loosening of the prosthetic component. Inflammatory/potential "bone-resorbing" agents (cytokines/mediators) released by the cells of the interfacial membranes of loosened uncemented and cemented total hip arthroplasties were measured. Synovial tissues from patients with acute femoral neck fractures, patients with osteoarthritis, and cadavers without joint disorders were used as control subjects. Control synovial tissue from osteoarthritic patients secreted the highest levels of prostaglandin E2, interleukin-8, and tumor necrosis factor alpha. Interleukin-1 alpha was the only cytokine whose levels were elevated as much as 4-fold around uncemented implants compared with cemented implants, and up to 16-fold compared with control synovial tissue. An apparent inverse relation between interleukin-1 alpha and interleukin-6 interfacial membranes of total hip arthroplasties compared with control synovial tissues suggests a complex cellular mechanism through a cytokine/prostaglandin cascade; this may regulate the observed bone resorption in aseptic loosening.

Bone ingrowth and the distribution of wear debris within the porous coating of 13 primary cementless porous-coated tibial components removed for reasons unrelated to fixation or infection were quantitatively described. The average length of implantation was 15.3 months (range, 3-30 months). The implants were all of the same design, made for Ti6A14V with a commercially pure titanium fiber-metal porous coating, which covered the undersurface of the tray and the four fixation pegs. In all but one component, supplemental screw fixation was used. The average extent of bone ingrowth within the tray was 27.1 +/- 16.1%, and the average volume fraction was 9.5 +/- 7.5%. There was significantly more bone ingrowth within the fixation pegs than within the tray and also more bone ingrowth in the anterior half of the tray than posteriorly. There was no correlation between the amount of bone ingrowth and the length of implantation, age, or sex of the patient; however, the depth and orientation of the resection plane were found to correlate with the topographic distribution of bone ingrowth. Particulate debris appeared to gain access to the interface via soft tissue pathways both at the periphery and through the holes for adjuvant screw fixation.

Ninety consecutive total hip arthroplasties in 73 patients with osteonecrosis of the femoral head yielded 81 hips in 64 patients (37 men and 27 women) available for evaluation after a 4-8-year follow-up period. The average age at surgery was 39.9 years (range, 20-66 years). Osteonecrosis etiology was idiopathic in 13 hips, alcohol-induced in 15, femoral neck fracture in 12, and slipped capital femoral epiphysis in 2. The remaining 39 cases were related to steroids, which were administered for a variety of reasons. Two types of noncemented, porous-coated, straight-stem femoral components and three types of acetabular components were utilized. Good or excellent clinical results were recorded in 80.2% of the patients. Average Harris hip scores improved from 52.9 to 87.9 points. Nine patients required revision of at least one component and were significantly younger than those with unrevised components. A revision rate of 24.1% was recorded in patients under 35 years of age at the time of primary surgery. Good or excellent clinical results were seen in 92.3% of the idiopathic cases, 86.7% of the alcohol-induced cases, 77.8% of the renal transplant cases, and 62.5% of the systemic lupus erythematosus cases. The overall mortality rate at the follow-up evaluation was 14%; it was 50% in renal transplant patients. Analysis of the clinical results based on the implants showed no significant differences in Harris hip scores or pain and function scores. While total hip arthroplasty using noncemented porous-coated femoral stems appears to give better results than cemented procedures in patients with osteonecrosis of the femoral head, the results appear to be inferior to those reported in patients with other diagnoses.

The authors examined 11 cementless acetabular components of one design retrieved at autopsy and made observations concerning tissue ingrowth and local tissue reaction, radiographic-histologic correlation, and the distribution of particulate wear debris. The cups were hemispherical in design with a commercially pure titanium fiber-metal porous coating. All of the prostheses were implanted with screws. The implants were in place for an average of 41 months (range, 5 weeks to 75 months). Ten of the cups had bone ingrowth, with the average volume fraction being 12.1 +/- 8.2%. There were no differences in the amount of bone ingrowth when the component was partitioned into nine anatomic regions. However, there was more bone adjacent to screw holes through which screws were inserted compared with empty screw holes. As the number of radiolucent zones increased on the clinical radiographs less bone ingrowth was observed histologically. The amount of metal debris in holes with screws and holes without screws was similar. In the longest term cases, polyethylene debris was noted within empty screw holes, but no granulomatous reactions or osteolytic processes were observed.

A retrospective gait analysis of patients with cemented Charnley-Mueller total hip arthroplasties was conducted to determine if functional differences exist between patients with femoral stems placed in varus and valgus orientations. Twenty patients and ten normals were studied using gait analysis to quantify joint motion and moments during level walking. In addition, a radiographic analysis of stem placement and mechanics of the reconstructed hip was performed on the total hip patients. All patients selected for the study had excellent clinical results on the basis of a score of 95 or better on the Harris hip rating form. The patients were divided into two subgroupings on the basis of stem orientation. A valgus group was defined as having a valgus stem orientation relative to the femoral shaft, with the femoral head-shaft offset shortened by 5 mm or greater compared to the contralateral unoperated hip, while the varus group was defined on the basis of having a varus stem orientation relative to the femoral shaft, with the femoral head-shaft offset restored to normal or greater than normal. A difference in gait was found between the varus and valgus patient groupings. The varus group had abnormal gait characteristics in the range of hip motion, the flexion-extension moments at the hip, and stride length. The patients in the valgus group had statistically normal gait. The differences in the gait characteristics were interpreted as an attempt to alter forces on the hip joint for patients in the varus group. These alterations were possibly an early indication of a subtle adaptation in patients with varus-placed femoral stems since, historically, a greater percentage of the patients in this configuration, retrospectively, go on to mechanical failures.(ABSTRACT TRUNCATED AT 250 WORDS)

Twenty-one knees in 14 patients were studied during walking, in clinical follow-up, and radiographically. The purpose was to examine the relationship between dynamic loading at the knee joint during level walking in the early postoperative period (1-2 years) and longer-term (4 years) prosthetic performance. Joint kinematics and kinetics were measured while patients were walking in the laboratory. The results were compared with an age-matched control group of healthy normal subjects. Patients were analyzed when grouped according to original diagnoses of rheumatoid or osteoarthritis. After total knee arthroplasty, patients with rheumatoid arthritis walked with a significantly lower magnitude peak adduction moment (force tending to thrust the knee into varus) about the knee than patients with osteoarthritis. The osteoarthritic group had an increased varus axial alignment when compared to the rheumatoid group. There was a strong correlation between postoperative varus alignment and the magnitude of the adduction moment. These results suggest that dynamic loading at the knee is greatly affected by static alignment of the joints in patients with total knee arthroplasty. In spite of the lower adduction moment during level walking and its associated effects on lower compressive loads at the knee, the patients with rheumatoid arthritis had a significantly higher radiolucency index. Thus, it appears that quality of bone stock may be a more important factor in determining prosthetic loosening than dynamic loading at the knee joint following total knee arthroplasty.

Retention of the posterior cruciate ligament in total knee arthroplasty is discussed in biomechanical and clinical terms and the implications for design, kinematics, function, and prosthesis longevity considered. The specific roles of passive range of motion, femoral rollback, stresses on the implant-bone-prosthesis cement system, and wear are examined. The authors argue that the posterior cruciate ligament improves passive range of motion, the mechanical efficiency of the knee musculature and thus improved stairclimbing efficiency, reduces stress at the cement-bone-implant interfaces, and has little or no impact on the polyethylene wear problems.

The authors quantitatively evaluated the relationship between component placement, limb alignment, and function following unicompartmental knee replacement surgery. It was found that anatomic alignment, prosthetic positioning, and prosthetic design influence the patients' ability to walk and climb stairs. There was wide variation in the placement of the tibial and femoral component among patients. The placement of the femoral component corresponded directly to function during stairclimbing and level walking. Anterior malpositioning of the femoral component resulted in reduced ability to climb stairs. The tibial component position varied primarily in varus-valgus position. Varus-valgus alignment in the frontal plane correlated directly with the magnitude of the adduction moment during level walking. A varus alignment produced a twofold increase in the magnitude of the adduction moment at the knee during walking. Given the potential advantages of the unicompartmental knee, improved precision in component placement should improve the long-term results of hemiarthroplasty knee surgery.

The biomechanics of the knee joint provide an important basis for the rationale in the design and selection of appropriate total knee arthroplasty. This article examines knee biomechanics in terms of patient function, prosthesis design, cruciate ligament retention, alignment, and fixation of the tibial component. While design and surgical technique for total knee replacement progress, a better understanding of the characteristics of joint loading, stress distribution, and the biologic response of bone to stress will provide the potential to improve both function and implant longevity.