Osseointegration of hydroxyapatite porous-coated femoral implants in a canine model.

This study evaluated the quality and quantity of osseointegration of two thicknesses of hydroxyapatite coating on press-fit, porous-coated titanium implants in a canine hip model. In 12 dogs, titanium press-fit porous-coated prostheses were implanted. The stems had a 50-microm thickness hydroxyapatite coating, 100-microm thickness hydroxyapatite coating, or no hydroxyapatite coating. The animals were randomized into one of three groups and received one of the three implants. The implants were retrieved and examined 4 months after implantation. Direct juxtaposition of bone to the surface of the hydroxyapatite-coated implants with no intervening fibrous tissue layer was observed. There was no histologic evidence that hydroxyapatite initiated any foreign body reaction, nor was there any irregularity or resorption of the hydroxyapatite coating. There was a statistically significant greater degree of total bone apposition and bone ingrowth in the implants coated with hydroxyapatite at the level of the isthmus and the calcar. No statistical difference was found between the two groups with hydroxyapatite coatings in the degree of bone ingrowth or bone apposition.

Cement penetration with pulsed lavage versus syringe irrigation in total knee arthroplasty.

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 (p < 0.05). The penetration of cement in total knee components can be significantly increased by using pulsed lavage of the cancellous surfaces.

Osteointegrated porous-coated titanium implants.

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.

Migration of polyethylene wear debris in hip arthroplasties: a canine model.

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.

Functional osseointegration of hydroxyapatite-coated implants in a weight-bearing canine model.

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).

Hydroxyapatite coating on carbon composite hip implants in dogs.

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.

Effect of stem modulus in a total hip arthroplasty model.

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.

Valgus-extension osteotomy for osteoarthritis of the hip. Indications and long-term results.

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'Aubigné 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.

Inadvertent extramedullary placement of Austin Moore prosthesis. A case report.

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.

Results of L4-L5 disc excision alone versus disc excision and fusion.

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.

Lumbar disc herniation in the elderly.

Thirty-two patients older than 60 years underwent surgical treatment for lumbar disc herniation over a 10-year period. Other causes of low-back pain and sciatica were investigated, and bony nerve root entrapment syndromes were not included. Sciatica was a predominant symptom and was present in all patients, with 81% showing positive nerve root tension signs. Motor deficit was found in more than half of the cases. A sequestrated disc was present in 50%. The follow-up ranged from 1 to 10 years with an average of 50 months. Eighty-seven percent of the patients had excellent or good results. There were no poor results and no one required reoperation. Lumbar disc herniation in the elderly is not a common problem, but surgery yields a high rate of satisfactory results if a proper investigation and correct diagnosis is obtained.

The Madreporic cementless total hip arthroplasty: short-term North American experience.

Forty-four Madreporic, cementless, total hip arthroplasties performed on 41 patients were reviewed, with special attention to overall clinical results and radiologic findings. Follow-up averaged 17 months (range from 6 to 27 months). Subjectively, 87% of patients rated the results of their operation as being excellent or good; objectively, 92.5% were in the excellent or good category, using the Harris hip scale rating system. Short-term radiologic findings were of major interest, with proximal medial calcar reabsorption (7 hips), thickening of the lateral cortex at the tip of the femoral stem (2 hips) and sclerosis at the tip of the femoral component (15 hips) all being present. Complications were associated with 11 operations, but adversely affected long-term results in only two hips. The authors conclude that short-term clinical results using Madreporic total hip replacement are satisfactory. However, long-term biomechanical effects of stress shielding and use of a large, rigid, femoral component in the uncemented total hip replacement are unknown. A long-term, follow-up study is necessary to demonstrate whether the early radiologic findings in this series are progressive and whether they will result in serious morbidity with time. The authors strongly believe that the Madreporic cementless total hip arthroplasty should be used only in centres dealing with a large volume of hip conditions where staff are committed to documenting and reporting the results of surgery regularly.

Treatment of unstable fractures of the distal radius by external fixation.

The Roger Anderson external fixator was used in the treatment of unstable fractures of the distal radius in 52 patients, and the results evaluated after a follow-up averaging 58 months. The indications for its use were failure to maintain adequate closed reduction using plaster, and instability of the fracture as determined by the initial radiographs. Our radiological criteria for instability included dorsal angulation of more than 20 degrees, fractures involving the joint, radial shortening of more than 10 mm, and severe dorsal comminution. Using the Lucas modification of the Sarmiento demerit point-rating system, we found that 46 patients (89%) had good or excellent results and six (11%) were classified as fair. There were no poor results. Seven patients (14%) developed complications. None of these affected the long-term results except in one elderly woman where the pins loosened and had to be removed.