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The stresses that occur between femoral head and cup in a total human hip joint prosthesis are especially calculated for the running-in phase when transition takes place between the Hertzian stress distribution and the stress distribution caused by wear. It turns out that the Hertzian stress distribution has already altered considerably after nearly 1 year of wear.
Total hip arthroplasty in the young patient remains a considerable challenge. Cemented arthroplasty has an unacceptably high failure rate. Porous ingrowth designs are one alternative, but bone ingrowth is unpredictable, thigh pain is a frequent clinical finding, stress shielding is often observed, revision is more complicated, and microporous components are mechanically weaker. A new anthropometric femoral component has been designed with a goal of long-term stability through osseointegration. The prosthesis is optimized for canal fill in the distal metaphysis and proximal diaphysis. The components are manufactured in 16 sizes, with cutting broaches precisely machined to the same dimensions to provide an exact fit to the femur. The high-strength TiAl6V4 alloy stem is combined with heads of either CoCr alloy or alumina (Al2O3) for reduced polyethylene wear. The 135 degrees neck-shaft angle and modular design allow for restoration of the abductor lever arm. Because the prosthesis is not porous coated, it is also suitable for use with cement. In cemented application, the prosthesis shape provides an optimal cement mantle. Seventy-one total hip arthroplasties have been performed using the Anthropometric Total Hip (ATH) prosthesis: 31 with exact-fit cementless fixation and 40 with cement. Of those using cementless fixation, 21 have been followed for more than one year (mean, 20 months; range, 12-48 months). The early clinical findings are as good as, or superior to, other cementless designs used at the authors' institution. Stress remodeling of the proximal femur occurs early and stabilizes by one year. The observed changes appear to improve the stability of the prosthesis. Clinical and roentgenographic findings suggest the osseointegration of the ATH femoral component.
Using a simplified model, tests were made to investigate the shear stress distribution at a hip joint prosthesis. A marked increase of stress at the tip of the prosthesis was found through photoelasticity. This peak stress resulted in a safety factor of 3 against exceeding the shear strength of bone cement. Since the calculation of the stress is based on unfavourable assumptions, the actual factor of safety should show a higher value still.
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With the help of survival curves we analysed in 111 aseptically loosened endoprostheses of the hip the function of the implants. We found a mediate rate of 6.04 years for the total survival time. We discussed two peaks after 2 years and between the 5. and 8. year after the implantation. There was a reduction of the survival time in the upper age and in the right side of the implantation. The second implantation had a worse prognosis compared with the first implantation (medial rate of 2.38 to 6.6 years). Important causes for the loosening were an enlarged angle of the hip socket and a varus position of the stem. But the survival curves showed in connection with these factors no statistical significance. We found a reduction of the survival time in the cases with no complete boundary of the bone cement in the proximal part of the stem.
The article makes a comparison between the results of total arthroprosthesis operation of the hip with traditional Mckee Arden prosthesis (50 cases operated in the two-year period 1976-77) and those with the new McKee Arden model with C.A.D. stem (52 cases operated in the two-year period 1977-78). All operations were performed at the "G. Pini" Orthopaedic Institute by the same team and with the same surgical technique. The results are based mainly on three parameters (according to McKee): pain, amplitude of movement, and need to use supports. THe Authors conclude by stressing the efficiency of the new model of prosthesis and noting a decrease in intra and post-operative complications.
In three patients pain in the groin and thigh which was initially attributed to either a malfunctioning hip prosthesis or osteoarthritic hip, was shown to arise in the spine. All patients had positive myelograms and one had electromyographic evidence of nerve root compression. Referred pain from the spine must always be considered in the differential diagnosis of pain thought to be arising from a hip replacement.
Several mathematical models to predict tissue adaptation have been derived since Julius Wolff proposed a function-form relationship for bone. These can be formulated as computational procedures (algorithms) to predict bone adaptation around implants. The objective of this paper was to further develop the damage-adaptive algorithm, to test its validity, and to determine the relationship between it and algorithms based on strain energy. This was achieved using finite element models of the proximal femur, one for the intact case and another for the case where a noncemented hip prosthesis is implanted. The finite models were generated using CT scan data. Initial bone resorption patterns around a femoral prosthesis following total hip arthroplasty were computed for both damage-adaptive and strain-adaptive adaptation rules. It is found that the damage-adaptive algorithm can successfully predict the bone's adaptive behaviour in response to altered mechanical loading provided that account is taken of the nonlinear nature of damage accumulation. Predictions are made using a strain energy stimulus for comparison with the damage stimulus, and a theoretical relationship between the two is proposed. It is shown that an advantage of the damage approach over the strain-based approach is that the nonlinearity required to replicate clinically observed resorption patterns can be derived theoretically, whereas for strain-adaptive remodelling, empirical relationships are assumed.
OBJECTIVE: To study early hip involvement in rheumatoid arthritis (RA) and to evaluate the usefulness of ultrasonography in the detection of hip joint synovitis in RA. METHODS: Study I: The number of hip joint replacements was recorded in a cohort of 113 patients with RA of at least five years disease duration followed from an early stage. Study II: Ultrasonography was evaluated as a method to identify hip joint synovitis in 76 patients with RA of shorter disease duration, by relating it to radiograms and clinical findings. RESULTS: Study I: Twenty one hip joint replacements were performed in 15 of the 113 patients. The median disease duration at the time of first arthroplasty was 48 (range 10-76) months; the annual incidence was approximately constant between two and six years. High disease activity at the start of the study was predictive of requirement for hip prosthesis. Study II: Hip ultrasonography was pathological in 13 of the 76 patients studied, bilaterally in nine. Hip joint synovitis could not be confirmed on clinical grounds only as seven of the patients with positive ultrasonographic findings were asymptomatic, and the remaining six patients had only mild symptoms of hip involvement. Also, six of the 63 patients with normal ultrasonography had mild symptoms. There was no difference regarding demographic, clinical, and laboratory findings in patients with and without hip synovitis. CONCLUSIONS: Early hip joint destruction giving symptoms mostly at a very late stage is frequent in RA. Ultrasonography rather than signs or symptoms could identify patients with hip joint involvement and provide a rationale for early treatment.
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Brucella canis was isolated from the cement or bone surrounding a hip prosthesis after total hip replacement was performed for treatment of hip dysplasia in 2 dogs. Lameness or signs of infection were not evident for 9 and 16 months after surgery. Osteomyelitis surrounding the prostheses was detected radiographically only after the lameness developed. The origin of the B canis infection in the 2 dogs was believed to be hematogenous because of the biologic behavior of this organism and because of the duration of excellent limb function after hip replacement. A slide agglutination test for B canis should be performed as a screening test on any canine total hip candidate when the anamnesis and physical examination indicate that the dog may have been exposed to or infected with B canis.
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This is a retrospective clinical evaluation of 1028 primary hip arthroplasties performed with the non-cemented Harris-Galante I acetabulaer cup. Hospital records regarding all hips operated from July 1985 through March 1992 were evaluated after a median of 48 (12-93) months. Furthermore, questionnaires were sent out to all patients still alive in order to establish the actual function of the hips. At time of evaluation, 43 of the 1028 primary acetabular cups (4.2%) had been or were due to be revised. (20 because of one or more episodes of dislocation or displacement of the cup, 10 due to deep infection, eight following aseptic loosening of the cup, two because of implant failure and three due to other reasons). Four hundred and twenty-six hips were without pain, 274 had only mild or slight pain, whereas 84 experienced moderate or worse pain. We conclude, that the results after non-cemented hemispheric acetabular arthroplasties in this study are satisfying with a low rate of aseptic loosening.