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Unicompartmental arthroplasty has proved to be a reliable option for monocompartmental arthritis in well selected patients. Unicompartmental knee arthroplasty (UKA) is not a temporary procedure and its ten year survival is comparable to TKA and better than High Tibial Osteotomy. The success of the procedure depends on strict patient selection, meticulous surgical technique and proper implant selection. The renewed interest in UKA is due to improved results, more conservative nature of the procedure, faster rehabilitation, decreased cost and the minimally invasive techniques. The sedentary patient with unicompartmental arthritis is currently the primary indication for UKA. The role of unicompartmental arthroplasty in younger patients needs more investigation. Revision of UKA has not found to be as complicated as reported in the early series. Minimally invasive UKA has shown short term promising results but more long term studies showing similar implant longevity compared with the standard approach are required to establish its role. Due to high level of patient satisfaction and low morbidity and complications compared with TKA, unicompartmental arthroplasty is an attractive option for patients with predominantly unicompartmental non inflammatory arthritis.

The distal migration of polyethylene wear debris appears to be a major cause of loosening and osteolysis of cementless total hip arthroplasties. The use of modern cementing techniques, circumferential porous or hydroxyapatite (HA) coating has been advocated as a means of preventing access of the particles to the bone-implant interface. The purpose of this study was to compare the ability of different methods of implant fixation to prevent wear debris migration. Three each of smooth, porous-coated, HA-coated, and cemented hemiarthroplasties were implanted in the right hip of 12 dogs. Polyethylene particles were injected into the hip once a month for 4 months and then the femurs were sectioned. The percentage bone ingrowth was 8% for the smooth, 38% for the porous, and 83% for the HA-coated sections. Infiltration of the interface membrane by histiocytes containing polyethylene particles, and endosteal scalloping or osteolysis were found on all sections of the smooth prostheses. No particles or osteolysis were found on any sections of the other three types of prostheses. Capsular and lymph node sections from all dogs revealed histiocytic infiltration with numerous polyethylene particles present. It is concluded that the use of cement, porous, or HA coating prevents or delays access of the polyethylene wear debris to the bone-implant interface. No one of these methods of fixation proved more advantageous in the 5-month limit of this study.

In 33 dogs we implanted femoral stems made either of carbon composite, some coated with hydroxyapatite, or of titanium alloy with a porous coating. Osseointegration was greater in the hydroxyapatite-coated than in the un-coated stems (p less than 0.001). Push-out tests, at an average of 7.2 months after implantation, showed a six-fold increase in interface shear strength and a twelve-fold increase in shear stiffness in the hydroxyapatite-coated group compared with noncoated implants. The highest shear-strength values were found in the porous-coated titanium alloy stems, around which there was also the most resorptive bone remodelling.

The purpose of this study was to determine the biological effects of the elastic modulus of the femoral stem in canine hip arthroplasty. Cementless total hip arthroplasty was performed in 12 dogs, six had a low elastic modulus polyacetal resin stem and six had a high modulus stainless steel stem. The components were otherwise similar. At six and 12 months after operation, radiographic and histomorphometric analysis showed that those with steel implants had more cortical porosity than did the other group (p less than 0.01). We suggest that the elastic modulus of the implant is an important factor in controlling cortical bone resorption. A low modulus femoral prosthesis can significantly decrease bone resorption which might otherwise eventually lead to implant failure.

Twelve total knee arthroplasties were performed on 12 patients who had osteoarthritis. The freshly resected tibial plateaus and femoral condyles were divided in 2, and each half was subjected to different methods of preparation. One half of the specimen was irrigated with saline with a standard bulb syringe, while the other half was irrigated with pulsed lavage. Cement then was pressurized into the cut surfaces. Sections were analyzed using the Image Analysis Software Morphometry System. A significant increase in cement penetration and decrease in bone debris were found in pulsed lavage specimens as compared with controls (p0.05). The penetration of cement in total knee components can be significantly increased by using pulsed lavage of the cancellous surfaces.

The study deals with the bone-prosthesis interface using an in vivo experimental animal model in relation to loading and walking on the prosthetized hip, studied by force plate analysis. The interface is studied from a histological and morphometric point of view by means of a LECO 2001 system. Results show that titanium favors osteointegration according to the criteria of Branemark even in conditions of physiological loading; bone ingrowth (that cannot be considered a true process of osteointegration) was 27.6%; furthermore, we quantified two models of periprosthetic bone growth in an osteointegrative sense: total bone bonding (27.4%) and core bone bonding (bone that grows in direct contact with the prosthesis) that was 16.1%. Finally, osteointegration tends to be greater where contact between the bone and the prosthetic is closer, regardless of the type of prosthetic coating.

That hydroxyapatite (HA) can form a strong chemical bond with bone has been confirmed by several precedent workers using unloaded implants. The relationship between the histomorphometric measurements of the interface of the cementless femoral stems with and without HA coating and their mechanical properties in a weight-bearing canine model was evaluated in this study. Seven HA-coated and seven uncoated titanium (Ti6Al4V) hemiarthroplasties were implanted in the right hip of 14 dogs for a 5-month period. The specimens were taken to conduct mechanical testing and morphometric measuring. The average interface shear strength of 2.13 MPa for the HA-coated specimens was significantly higher than 0.93 MPa for the uncoated specimens (P.05). There was greater bone apposition with the HA coating (72.39%) than without the coating (15.96%). Bone interfaces were divided into two types histomorphometrically: type A, simple bony shell without supporting trabeculae and type B, buttressed bony shell with supporting trabeculae. A positive correlation between the type B HA-bone interface and interface shear strength was found (r = .81).

We reviewed the results of 277 intertrochanteric valgus-extension osteotomies performed between 1973 and 1975 for primary or secondary osteoarthritis. The average age of the patients was 51 years and follow-up varied from 11 to 15 years. At the latest evaluation 67% of the hips were good or excellent on the Merle D'Aubigne scale. Better results were obtained in patients under 40 years of age with unilateral involvement and a mechanical (secondary) aetiology. An elliptical femoral head, minimal subluxation and an adequate pre-operative range of motion were also favourable. There was radiographic evidence of regression of the arthritic changes in 39% of the hips at final review. Valgus-extension osteotomy is effective for secondary osteoarthritis of the hip in selected younger patients, but not for those with primary hip disease or a poor range of movement.

Nine pairs of human cadaveric femora were used to study the biomechanical characteristics of the Gamma nail and a standard telescoping screw plate implant (Ambi) to determine whether there were any mechanical advantages of one system over the other. Parameters studied included structural stiffness, strain distribution, and failure modes for intertrochanteric and subtrochanteric fractures. There was no significant difference in structural stiffness for stable intertrochanteric and subtrochanteric fractures. The Gamma Nail composites, however, were stiffer than the Ambi for unstable subtrochanteric fractures. Both implants effectively unloaded the proximal medial cortex. In each instance, failure of the Gamma nail composite occurred through the distal locking screws. The Gamma nail does not appear to offer any distinct biomechanical advantage over the sliding hip screw system in the treatment of stable and unstable intertrochanteric fractures, but it may play a role in the treatment of unstable subtrochanteric fractures.

We have reviewed the results of 106 intertrochanteric osteotomies performed for osteonecrosis of the femoral head. The average age at operation was 47.5 years. At two years from operation 71% of the hips had a clinically satisfactory result and at final follow-up, an average of 8.2 years after operation, 58% continued to have excellent or good rating. Twenty-four hips had needed total replacement or arthrodesis because of pain. Patients aged less than 55 did better than those operated on after that age, and hips with an idiopathic or post-traumatic aetiology did considerably better than alcohol-induced or steroid-induced cases. In view of these findings we believe that in the younger adult, in the absence of metabolic bone disease or advanced joint destruction, intertrochanteric osteotomy should be considered for the treatment of osteonecrosis.

We evaluated the results of 85 patients having L4-L5 disc excision (52 having disc excision alone, and 33 having disc excision and fusion) using the Smiley-Webster scale at an average follow-up of 7.3 years. Both groups (fusion and nonfusion) were comparable except that the nonfusion group had a significantly higher percentage of patients with a history of chronic back pain and degenerative changes on their initial radiographs. The fusion group had significantly better results compared with the nonfusion group (85% satisfactory results versus 39% satisfactory results). The most common cause of unsatisfactory results in the fusion group was pseudarthrosis (two) while progressive degenerative disc disease (18) and recurrent disc prolapse (eight) were the most common cause of unsatisfactory results in the nonfusion group. The overall reoperation rate was 9.4% (13.5% in the nonfusion group, and 3% in the fusion group.

Virtually complete extramedullary insertion of an Austin Moore prosthesis is a rare complication. The prosthesis is seldom left in such a position once the complication has been recognized. To the authors' knowledge, this is the first reported long-term follow-up study of such a case in which the result could be considered reasonably well-tolerated. The prosthesis was revised to a total hip arthroplasty 15 years following implantation. That the reason for excision was acetabular wear indicates that the prosthesis was load bearing. This case raises the question of whether the concept of extramedullary fixation of hip prostheses could be valid.