Hip arthroplasty using the cementless CLS stem. A 2--4-year experience.

Fifty-one Cementless Spotorno (CLS, Protek A. G. Berne) stems were implanted in 43 patients with either a Harris Galante (Zimmer, Warsaw, IN) socket or bipolar head. Patients were evaluated at a mean of 31 months. Eighty percent of the hips were in patients who were less than 50 years of age or weighed more than 80 kg. The CLS stem achieved initial stability by wedging a proximally fluted, straight stem into a retained bed of femoral trabecular and cortical bone. Distal canal fill was avoided. The postoperative mean Harris hip score was 95. Eighty percent of the hips were rated excellent, 16% good, 2% fair, and 2% poor. No stem required revision. Six percent had slight, occasional thigh pain. No patient had mild, moderate, or severe thigh pain. Six percent had a limp related to the operated hip. Fifty-three percent of the hips developed a radiographic appearance of bone apposition at the stem tip. Fifty-five percent of the hips had some reduction in proximal bone density. These changes suggested that as bone remodeling occurred, the initial proximal load transfer situation expected from the CLS stem design changed to include some distal load transfer resulting in proximal stress shielding. Ninety-four percent of the hips had either no change in femoral bone density or only patchy loss of density isolated to zone 7. A high dislocation rate was attributed to an unfavorable head-to-neck diameter ratio, a valgus neck shaft angle, and a patient population capable of excellent hip motion.

Augmentation of spinal fusion with bone morphogenetic protein in dogs.

Bone morphogenetic protein (BMP) induces mesenchymal cells to differentiate into cartilage and bone. To investigate the action of BMP on the growth of host bed-derived bone in experimental spinal fusions, posterior intervertebral spinal fusions of the lower thoracic spine were performed in 13 mature mongrel dogs. Four different fusion methods were used at single intervertebral levels within each dog. Three levels in each dog were used as controls for the BMP level. The spinal columns were examined by radiohistomorphometric methods at three weeks, six weeks, and 12 weeks and showed the BMP level to have two to three times more new bone than control levels. At the BMP level, an increase in the amount of new bone was observed in the interval from three to 12 weeks, in contrast to a decrease seen at the control levels. Fusion was present in five of seven of the BMP levels compared with zero of seven, one of seven, and two of seven in the control levels. The BMP level exhibited an increased number and volume of areas of de novo cartilage and woven bone formation at all time intervals compared to all control levels. The polylactic acid polymer carrier was not resorbed and partially retained in the fusion site. The preliminary observations suggest that BMP may serve as a useful adjunct in spinal fusions, but research is required to find a rapidly degradable delivery system. The objective of BMP research is to augment the host bed capacity for bone generation and regeneration and to spare children and adults the pain and complications involved in removing excessive volumes of iliac crest bone grafts.

Early femoral component loosening in DF-80 total hip arthroplasty.

Forty-seven DF-80 total hip arthroplasties performed in 40 patients were evaluated to determine the incidence and causes of early femoral component loosening. With an average 37.1-month follow-up period, 48.9% of the femoral components developed bone cement-bone radiolucent lines worrisome for stem loosening. Twenty-three percent of the stems had subsided and 4.3% had been revised. Radiolucent lines were apparent very early (average, 8.8 months). Statistical analysis revealed positive correlations between the use of the larger (45-mm) offset stem and both the appearance of radiolucent lines and stem loosening. Being male and tall also were associated with stem loosening. The causes for early DF-80 femoral component loosening could not be defined with certainty. The results of this study and a review of the literature suggest that failure may be a result of early biologic weakening of the proximal cement-bone interface combined with a stem design that maintains proximal bone loading. Metal debris did not appear to be a factor in loosening of this titanium alloy stem.