Harlan C. Amstutz

Modes of failure of cemented stem-type femoral components : a radiographic analysis of loosening

In view of the increasing incidence of stem-type femoral component loosening, a detailed retrospective radiographic zonal analysis of 389 total hip replacements indicated a 19.5% incidence (76 hips) of radiological evidences of mechanical looseness, i.e., fractured acrylic cement and/or a radiolucent gap at the stem-cement or cement-bone interfaces. Detailed serial radiographic examination demonstrated progressive loosening in 56 of the 76 hips and these were categorized into mechanical modes of failure. The 4 modes of failure characterizing stem-type component progressive loosening mechanisms consisted of stem pistoning within the acrylic (3.3%), cement-embedded stem pistoning with the femur (5.1%), medial midstem pivot (2.5%), calcar pivot (0.7%) and bending (fatigue) cantilever (3.3%).

Metal-on-Metal Hybrid Surface Arthroplasty: Two to Six-Year Follow-up Study

BACKGROUND Following the reintroduction of metal-on-metal articulating surfaces for total hip arthroplasty in Europe in 1988, we developed a surface arthroplasty prosthetic system using a metal-on-metal articulation. The present study describes the clinical and radiographic results of the first 400 hips treated with metal-on-metal hybrid surface arthroplasties at an average follow-up of three and a half years. METHODS Between November 1996 and November 2000, 400 metal-on-metal hybrid surface arthroplasties were performed in 355 patients. All femoral head components were cemented, but only fifty-nine of the short metaphyseal stems were cemented. The patients had an average age of forty-eight years, 73% were men, and 66% had a diagnosis of osteoarthritis. Clinical and radiographic follow-up were performed at three months postoperatively and yearly thereafter. RESULTS The majority of the patients returned to a high level of activity, including sports, and 54% had activity scores of >7 on the University of California at Los Angeles activity assessment system. Kaplan-Meier survivorship curves demonstrated that the rate of survival of the components at four years was 94.4%. For patients with a surface arthroplasty risk index score of >3, the rate of survival of the components at four years was 89% compared with a rate of 97% for those with a score of </=3. The patients with a higher risk index were 4.2 times more likely to undergo revision to a total hip replacement at four years. Twelve hips (3%) had a revision to a total hip replacement. Seven of the twelve hips were revised because of loosening of the femoral component, and three were revised because of a femoral neck fracture. Substantial radiolucencies were seen around sixteen uncemented metaphyseal femoral stems. No femoral radiolucencies were observed among the hips in which the metaphyseal stem was cemented. The most important risk factors for femoral component loosening and substantial stem radiolucencies were large femoral head cysts (p = 0.029), patient height (p = 0.032), female gender (p = 0.005), and smaller component size in male patients (p = 0.005). CONCLUSIONS The preliminary experience with this hybrid metal-on-metal bearing is encouraging. Optimal femoral bone preparation and component fixation are critical to improving durability. The metal-on-metal hybrid surface arthroplasty is easily revised to a standard femoral component if necessary. LEVEL OF EVIDENCE Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.

Assessing activity in joint replacement patients

Outcome evaluations of lower extremity joint reconstructions should include an assessment of patient activity. In vivo wear assessments of total joint prostheses should be based on a measure of use, not time in situ or a proxy such as age or gender; however, clinicians lack a simple method to reliably assess the activity of patients with joint replacement. The modern pedometer can be a satisfactory means of quantifying the use of lower extremity joints. The pedometer, however, requires special effort on the part of the physician or evaluator and the patient. Therefore, we compared the quantitative assessment of walking activity of 100 total joint replacement patients, as measured with a pedometer, to the UCLA activity score and a simple visual analog scale that can easily be employed during a routine office evaluation. Both the UCLA activity rating (P = .002) and the visual analog scale rating of the investigator (P = .00001) had a strong correlation with the average steps per day as recorded by the pedometer. There was, however, up to a 15-fold difference in the average steps per day for individual patients with the same UCLA score. The visual analog scale as rated by the patients of their own activity did not have as strong a correlation with the pedometer data (P = .08) as did patient age (P = .049). For practical reasons, the pedometer is probably best reserved for the evaluation of extreme cases of activity (or inactivity). This study indicates that both the UCLA activity rating and the investigator visual analog scale are valid for routine activity assessment in a clinical setting. Adjustments of the UCLA activity score for the frequency and intensity of activity, as can be done with the investigator visual analog scale, increase the accuracy of the activity rating.

Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty.

Of 285 total hip arthroplasties (260 patients) performed for primary osteoarthritis during a six-year period, 135 were resurfaced using a Tharies prosthesis (total hip articular replacement with internal eccentric shells) and 150 were treated with the Trapezoidal-28 total hip replacement. From each of these two groups 100 hips (ninety-one patients in the Tharies group and eighty-six in the Trapezoidal-28 group) that had been followed for two to seven years were evaluated at the time of follow-up in accordance with a predetermined protocol. The patients were younger in the Tharies than in the Trapezoidal-28 group (average ages, fifty-eight and sixty-six years), included more men (sixty compared with thirty-five), and were more active postoperatively. The average follow-up was forty-seven months for the total joint-replacement group and thirty-eight months for the surface replacement group. At follow-up the ratings for pain, walking, and function according to the University of California at Los Angeles 10-point scale and the clinical results were identical in the two groups. Heterotopic ossification (Brooker grade III or IV) developed after thirteen Trapezoidal-28 and twenty-two Tharies arthroplasties. Radiographs made at six and twelve months and at final follow-up showed that the incidence of radiolucencies about the acetabular component was higher in the resurfacing group: fifty-seven with complete radiolucent lines after an average follow-up of thirty-eight months compared with thirty-six with complete lines after an average follow-up of forty-seven months. There were three failures in the joint-replacement group: a hematogenous staphylococcal deep infection that required a Girdlestone procedure, a femoral stem fracture that required revision, and loosening of an acetabular component for which revision was performed. There was also one dislocation, successfully treated by closed reduction. Similarly, in the resurfacing group there were three failures: two loose acetabular components, revised successfully, and one loose femoral component that necessitated total joint arthroplasty. Multivariate stepwise regression analysis showed that the factors that affected the final extent and width of the acetabular radiolucencies adversely after resurfacing were: any radiolucent lines that were visible at six months, a high level of physical activity after arthroplasty, and a thin superior cement mantle.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism and clinical significance of wear debris-induced osteolysis.

Loosening of joint replacement components is often multifactorial. The quality of initial fixation is very important to the outcome of the arthroplasty and is often a factor in short-term and long-term failure. This paper discusses another important factor of implant loosening, namely wear debris induced osteolysis. Macrophages activated by the phagocytosis of particulate wear debris are the key cells in this process, which can potentially occur in any implant system regardless of implant design or fixation mode. This is because each implant system creates wear debris from the articulating surfaces and the interfaces. The clinical consequences of wear debris cover a broad spectrum from radiolucencies to massive osteolysis and implant failure. For this reason, the reduction of wear debris should be a primary goal of orthopedic research in the future.

Metal wear particle characterization from metal on metal total hip replacements: Transmission electron microscopy study of periprosthetic tissues and isolated particles

The less intense tissue reaction around metal on metal total hip replacements (THRs) compared to metal on polyethylene (PE) THRs may be explained by the differences in the characteristics of metal wear particles. In this study, transmission electron microscopy was used to study metal wear particles that were either in situ in cells or had been extracted from the cells by a new technique based on enzymatic tissue digestion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearing couples. Most of the CoCrMo wear particles were smaller than 50 nm (range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE particles. While even a small volume of metal wear will produce high numbers of particles, the apparently less severe local tissue reaction to metal particles may be due to the possibility that corrosion, dissolution, and dissemination of metal particles may result in fewer local biological effects than the long-term retention of PE particles in the periprosthetic tissues.

Histological Features of Pseudotumor-like Tissues From Metal-on-Metal Hips

BackgroundPseudotumor-like periprosthetic tissue reactions around metal-on-metal (M-M) hip replacements can cause pain and lead to revision surgery. The cause of these reactions is not well understood but could be due to excessive wear, or metal hypersensitivity or an as-yet unknown cause. The tissue features may help distinguish reactions to high wear from those with suspected metal hypersensitivity.Questions/purposesWe therefore examined the synovial lining integrity, inflammatory cell infiltrates, tissue organization, necrosis and metal wear particles of pseudotumor-like tissues from M-M hips revised for suspected high wear related and suspected metal hypersensitivity causes.MethodsTissue samples from 32 revised hip replacements with pseudotumor-like reactions were studied. A 10-point histological score was used to rank the degree of aseptic lymphocytic vasculitis-associated lesions (ALVAL) by examination of synovial lining integrity, inflammatory cell infiltrates, and tissue organization. Lymphocytes, macrophages, plasma cells, giant cells, necrosis and metal wear particles were semiquantitatively rated. Implant wear was measured with a coordinate measuring machine. The cases were divided into those suspected of having high wear and those suspected of having metal hypersensitivity based on clinical, radiographic and retrieval findings. The Mann-Whitney test was used to compare the histological features in these two groups.ResultsThe tissues from patients revised for suspected high wear had a lower ALVAL score, fewer lymphocytes, but more macrophages and metal particles than those tissues from hips revised for pain and suspected metal hypersensitivity. The highest ALVAL scores occurred in patients who were revised for pain and suspected metal hypersensitivity. Component wear was lower in that group.ConclusionsPseudotumor-like reactions can be caused by high wear, but may also occur around implants with low wear, likely because of a metal hypersensitivity reaction. Histologic features including synovial integrity, inflammatory cell infiltrates, tissue organization, and metal particles may help differentiate these causes.Clinical RelevancePainful hips with periprosthetic masses may be caused by high wear, but if this can be ruled out, metal hypersensitivity should be considered.

Wear is a function of use, not time

Polyethylene wear (linear penetration) in 37 hip replacements was assessed from digital images using a validated two-dimensional, edge detection-based computer algorithm. Patient activity was assessed with a pedometer, a step activity monitor and a simple visual analog scale. Joint use was related to wear at the 90% confidence level. Without three recognized outliers, wear was highly correlated to use. The visual analog scale activity rating was significantly related to wear for the 24 hip replacements with standard polyethylene. Univariate regression analysis indicated that male gender, height, weight (which were both highly correlated to male gender) and hip center of rotation were significantly correlated to wear. Multivariate regression analysis indicated that male gender, femoral off-set, and Hylamer® were significantly correlated to wear. Based on the wear and activity data from the 24 hip replacements with standard polyethylene, the average volumetric wear rate per million cycles with a 70 kg patient weight was 30 mm3. This unique in vivo result can be considered a target wear rate for standard polyethylene in hip simulator studies.

Quantitative assessment of walking activity after total hip or knee replacement

Accumulating data suggest that the amount of use, and not simply the duration in situ, influences the wear and survival of total joint replacements. An electronic, digital pedometer was used to record the number of steps taken by 111 non-randomized volunteers who had had at least one total hip or knee replacement. The patients averaged 4988 steps per day, which extrapolates to approximately 0.9 million cycles per year for each joint of the lower extremity. Average activity ranged widely from 395 to 17,718 steps per day, an approximately forty-five-fold difference. The most active patient walked more than 3.5 times the average number of steps per day. Age was significantly associated with activity (p = 0.048), but there was a high degree of variability (standard deviation, 3040 steps per day). Patients who were less than sixty years old walked 30 per cent more on average than those who were sixty years old or more (p = 0.023). Men walked 28 per cent more on average than women (p = 0.037), and men who were less than sixty years old walked 40 per cent more on average than the rest of the patients (p = 0.011). These data indicate that individual differences in the activity of the patient can be a substantial source of variability in rates of polyethylene wear in vivo. The pedometer is an inexpensive investigational tool with many potential applications, including standardizing wear measurements of joint replacements on the basis of gait cycles rather than time. This quantitative approach may provide prognostic information regarding the survival of joint prostheses. Pedometer data may also be useful for quantitative assessment of walking ability in outcome studies.

In vivo knee stability. A quantitative assessment using an instrumented clinical testing apparatus.

Twenty-eight male and twenty-one female subjects with no history of previous injury to their knees were examined using a newly developed clinical testing apparatus designed to record anterior-posterior tibial force versus displacement and varus-valgus moment versus angulation during manual manipulation of the knee. Joint stiffness and laxity were measured from test tracings made with the knee muscles relaxed and tensed. Agreement between these measurements and those made previously on thirty-five fresh cadaver knee specimens was very good. Anterior-posterior laxity averaged 3.7 millimeters in full extension, 5.5 in 20 degrees of flexion, and 4.8 millimeters in 90 degrees of flexion, while the mean varus-valgus laxity was 6.7 degrees in full extension. The common clinical assumption that normal right-left differences are negligible was found to be invalid. Individual right-left differences averaged 26 to 35 per cent for laxity and 19 to 24 per cent for stiffness. There was no discernible tendency for one knee to be more stable than the other; random interchanges of relative stability between the right and left knees were observed for each individual at different knee positions. When requested to tense the knee muscles, these subjects were able to increase their knee stiffness an average of two to four times while knee laxity was reduced to 25 to 50 per cent of the normal value.