A comparison of structural and mechanical properties in cancellous bone from the femoral head and acetabulum.

Mechanical interlock obtained by penetration of bone cement into cancellous bone is critical to the success of cemented total hip replacement (THR). Although acetabular component loosening is an important mode of THR failure, the properties of acetabular cancellous bone relevant to cement penetration are not well characterized. Bone biopsies (9 mm diameter, 10 mm long) were taken from the articular surfaces of the acetabulum and femoral head during total hip replacement. After mechanical and chemical defatting the two groups of bone specimens were characterized using flow measurement, mechanical testing and finally serial sectioning and three-dimensional computer reconstruction. The mean permeabilities of the acetabular group (1.064 x 10(-10) m2) and femoral group (1.155 x 10(-10) m2) were calculated from the flow measurements, which used saline solution and a static pressure of 9.8 kPa. The mean Young's modulus, measured non-destructively, was 47.4 MPa for the femoral group and 116.4 MPa for the acetabular group. Three-dimensional computer reconstruction of the specimens showed no significant differences in connectivity and porosity between the groups. Results obtained using femoral head cancellous bone to investigate bone cement penetration and fixation are directly relevant to fixation in the acetabulum.

Early femoral loosening in one design of cemented hip replacement.

We have studied aseptic loosening of the femoral component in 76 patients with primary total hip replacement using the Capital prosthesis. The mean follow-up was 26 months (10 to 37). Twelve femoral components (16%) were definitely and eight (10%) were possibly loose. They were characterised by a thin cement mantle (p < 0.001) and excessive residual cancellous bone in the proximomedial region (p < 0.01). We recommend that the cement mantle around the prosthesis should be 2 to 3 mm and that further long-term studies are needed to evaluate the wear properties of titanium-nitride-coated titanium femoral heads.

Effects of lamination on the strength of bone cement.

To improve cement penetration into the cancellous bone of the acetabulum in hip arthroplasty, sequential cementation of each anchoring hole may be feasible. Since this procedure creates laminations in the cement, we have determined the conditions under which such laminations affect the strength of the cement. Cement bars made at 2, 3 or 4 minutes after the start of cement mixing and with either dry laminations or laminations including blood or saline were tested for tensile strength. Solid unlaminated bars were used as references. Dry and saline laminations made up to 4 minutes after the start of cement mixing did not reduce the strength of the cement. However, there was a time-dependent decrease in cement strength if blood was entrapped in the interface. In such cases, there was a decrease in strength for laminations made at 4 minutes, at 3 minutes this was less pronounced and at 2 minutes no weakening at all was noted. Our findings indicate that a sequential cementation procedure is permissible as regards cement strength, provided it is performed with 2-3 minutes after the start of cement mixing. If the cement area is kept free from blood, the time may be prolonged up to 4 minutes, without the risk of weakening the cement strength.

Circulating blood diminishes cement penetration into cancellous bone. In vivo studies of 21 arthrotic femoral heads.

We compared the penetration depth into cancellous bone when pressurizing cement at predetermined pressure levels, and at different times after cement mixing, in 21 arthrotic femoral heads during total hip replacement. To determine the influence of circulating blood on cement penetration, cement was injected into holes drilled into the femoral head before and after osteotomy of the femoral neck. The penetration of cement increased on the average 100 percent in the absence of circulation.

Cementation pressure in arthroplasty. In vitro study of cement penetration into femoral heads.

We analyzed the pressure needed for adequate cement penetration into the human arthrotic hip. 85 holes in 39 arthrotic femoral heads were cemented under predetermined pressures and times after cement mixing. Cement penetration correlated well to both pressure and time after mixing. No correlation to the degree of sclerosis was found. At 0.2 MPa, the average penetration into bone was 2 mm. However, 3-5 mm is considered the minimum depth for good fixation of an implant. To achieve a consistent adequate interdigitation, a pressure of approximately 0.3 MPa is recommended.

A modified Hauser procedure for recurrent dislocation of the patella. A long-term follow-up study with special reference to osteoarthritis.

A modified Hauser operation was used for the treatment of recurrent dislocation of the patella. Thirty-seven patients (40 knees) were traced for the purpose of long-term follow-up with regard to subjective and objective results and the degree of osteoarthritis in the patellofemoral joint. The mean follow-up time was 18 years. Only 12% of the patients had objectively satisfactory results, but 48% were satisfied with their operation. There was no correlation between the opinion of the patients and the objective findings. Dislocation recurred in 20% of the knees. More than two-thirds of the patients had some degree of osteoarthritis, and a poor result was always combined with osteoarthritis. The incidence of osteoarthritis increased with the time of follow-up and the age of the patient, but it was also found in younger patients. It seems that distal realignment of the patella enhances the development of osteoarthritis.