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In five straight-stemmed, proximally porous-coated femoral components that were retrieved at revision arthroplasty from patients who had radiographic and clinical evidence of loosening, there was growth of bone into the porous coating. The components had been inserted during a primary arthroplasty in one woman and four men. The patients ranged in age from thirty-seven to sixty-seven years. Three patients were heavy, and all five were active. All patients had had an excellent early result from the initial arthroplasty; at the one-year follow-up, the mean Harris hip score had been 91 points. Pain in the hip developed in all of the patients, between one and three years after the index procedure. Initial radiographs had revealed excellent position and fixation of the prosthetic components, but the components then subsided between one and three and one-half years after the index procedure. All of the femoral components were found to be grossly loose at the revision operation. Nevertheless, all of the prosthetic components demonstrated growth of bone into 4 to 44 per cent (mean, 24 per cent) of the pore spaces available for ingrowth. Woven bone and fracture callus were found in the curettings from the proximal part of the femur. The findings in these five patients suggest that late failure of uncemented porous-surfaced femoral components can occur despite the presence of extensive ingrowth of bone. These failures may be the result of fatigue fractures of the trabeculae of the osseous ingrowth into the porous surfaces. Caution is warranted in the liberal use of these prosthetic components in heavy, active patients.

Uncemented straight-stemmed proximally porous-coated femoral components were press fitted into the femoral canals of seven dogs using a rasp 0.5 mm smaller than the components (press-fit group). In seven other dogs the components were fit precisely into the femoral canals using a rasp that was the same size as the components (control group). Using this technique, all of the dogs in the press-fit group developed longitudinal fractures in the femoral cortex, while none of the dogs in the control group developed fractures. None of the fractures were recognized at operation. Two of the dogs in the press-fit group displaced the fractures at 1 week and were sacrificed. The other five dogs were bearing weight on their limbs and completed the 3-week experimental period. Follow-up radiographs of these femurs showed marked periosteal new bone formation, but did not reveal any fractures. Serial sections of these femurs showed longitudinal healing fractures in the anterior cortex. The fractures had an adverse effect on the bone ingrowth into the porous surface of the press-fit group compared to the control group without fractures, and the porous surface adjacent to the fractures was ingrown with fibrous tissue. The amount of bone ingrowth expressed as a percentage of the porous coating area measured, on average, only 3.9% in the press-fit group at 3 weeks compared to 5.6% in the control group--a statistically significant difference at P < .025. This experience in the dog illustrates the inherent risk of driving a larger femoral component into a smaller cavity prepared in the femur.(ABSTRACT TRUNCATED AT 250 WORDS)

Six porous-coated, uncemented femoral components were revised at a mean of 34.5 months for persistent thigh pain. At operation the stems were rigidly stable, difficult to extract, and showed good bony ingrowth. The four men and two women, with an average age of 59 years, all had thigh pain starting within the first year, progressive over time and unresponsive to conservative measures. These cases show that rigid fixation with good bony ingrowth does not guarantee the clinical success of a porous-coated uncemented femoral stem.

In five straight-stemmed, proximally porous-coated femoral components that were retrieved at revision arthroplasty from patients who had radiographic and clinical evidence of loosening, there was growth of bone into the porous coating. The components had been inserted during a primary arthroplasty in one woman and four men. The patients ranged in age from thirty-seven to sixty-seven years. Three patients were heavy, and all five were active. All patients had had an excellent early result from the initial arthroplasty; at the one-year follow-up, the mean Harris hip score had been 91 points. Pain in the hip developed in all of the patients, between one and three years after the index procedure. Initial radiographs had revealed excellent position and fixation of the prosthetic components, but the components then subsided between one and three and one-half years after the index procedure. All of the femoral components were found to be grossly loose at the revision operation. Nevertheless, all of the prosthetic components demonstrated growth of bone into 4 to 44 per cent (mean, 24 per cent) of the pore spaces available for ingrowth. Woven bone and fracture callus were found in the curettings from the proximal part of the femur. The findings in these five patients suggest that late failure of uncemented porous-surfaced femoral components can occur despite the presence of extensive ingrowth of bone. These failures may be the result of fatigue fractures of the trabeculae of the osseous ingrowth into the porous surfaces. Caution is warranted in the liberal use of these prosthetic components in heavy, active patients.