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25 hemispherical acetabular components retrieved from patients who had a total hip arthroplasty (THA) were studied histologically. All of the components had titanium fiber metal porous coatings and were implanted with adjuvant screw fixation, 18 in primary THA and 7 in revision THA. None of the cups had been removed because of infection or failure of fixation. The components had been in place an average of 30 (1-140) weeks. 18 cups had bone ingrowth into the porous coating. Up to one third of the available void space within the porous coating was occupied by bone, while the maximal proportion of the area of the bone-implant interface with bone ingrowth was over 80 percent. Bone ingrowth was more often observed at the dome and in the vicinity of sites of screw fixation than elsewhere. Peripherally, bone ingrowth was less consistent, and in isolated areas fibrocartilage and mineralized fibrocartilage were occasionally observed. The longer-term cases had more bone ingrowth than the shorter-term cases. Apparent metallic debris was observed within histiocytes adjacent to screw holes, and the amount of this material increased with duration of implantation.

The influence of stem thickness, stem orientation, and insertion pressure on the strength of a prosthesis-cement-bone system was studied in vitro. Three types of prostheses were used with thick and thin stems, allowing for thick or thin cement envelopes. They were implanted with different stem orientations, and with and without a distal femoral cement plug. They were then loaded in a testing machine until a discontinuity of the load deflection curve occurred. The main factor determining the failure load was the presence of the distal plug. In specimens with plugs the main load at failure was 6.5 N, in specimens without a plug it was 4.8 N (P greater than 0.05). The most stable combination was the thick stem with a thin cement envelope placed in valgus or neutral orientation, and implanted with a distal cement plug. It was concluded that when no plug was present failure occurred at the bone-cement interface; when a plug was present it occurred at the prosthesis-cement interface.

A study was made of bone ingrowth into fiber metal composite prostheses used to replace large segments of the femur in baboons. Bone grafts of two different types were used to cover the segment: chips of bone with large particle size and ground bone with a smaller particle size. The prosthetic segment was bridged by bone at 3 and 6 months in all cases irrespective of the structure of the transplant. In animals sacrificed at 6 months bone ingrowth occurred, with a marked difference between specimens with the two different grafts. In the ground bone specimens ingrowth occurred over the total surface area, and bone penetrated deep into the composite. With the chip grafts ingrowth was more irregular occurring only in some areas and it was always superficial. The difference is believed to be due to the improved contact between the fiber metal surface and the transplant. The lesser bulk of the ground transplant is advantageous when the soft tissue cover of the bone is thin.

Twenty-six knee arthroplastics in 22 subjects were studied clinically and in a gait laboratory before and on one or more occasions after surgery. The purpose was to identify changes in gait characteristics and relate them to changes in the clinical situation of the patients. The gait patterns of the patients changed following surgery mainly with respect to their time-distance characteristics; stride length, cadence, time of swing, and time of support. Positive correlations were noted between these gait changes and the patient's pain, his limp, and his walking distance. It is concluded that the information obtained in sophisticated gait laboratory is of limited value to the surgeon in his clinical assessment.