The purpose of this study was to evaluate the long-term clinical and radiological results of patients with hip dysplasia who underwent spherical acetabular osteotomy. The surgical technique used was that described by Wagner.

The first 26 unilateral spherical osteotomies performed by one surgeon at one institution were reviewed at a minimum clinical follow-up of 20 years (median 23.9, maximum 29 years). One patient had died 5 years after the index operation unrelated to the procedure. Three patients (3 hips, 11 %) could not be traced. Preoperative and follow-up radiographic measurements included lateral and anterior centre-edge angle, acetabular index angle, and acetabulum-head index of Heyman and Herndon. Antero-posterior radiographs of the pelvis were evaluated for the presence of joint congruency, joint space narrowing, increased sclerosis of the subchondral bone, and bone cysts.

Osteotomy improved the mean lateral centre-edge angle from −20 to +130, and the acetabular head index from 52% to 72%. The mean postoperative anterior centre-edge angle of Lequesne and de Seze was 23 (range: −10 to 62). Seven of 22 hips (32%) needed conversion to total hip replacement. The average Harris hip score at latest follow-up of the remaining 15 hips was rated 86 points (range: 50 to 100 points). Overall, 11 of the 15 hips were clinically rated good or excellent. On latest follow-up severity of osteoarthritis was unchanged in 13 of 15 hips. Only 3 of 9 hips requiring conversion to total hip replacement or showing progressive osteoarthritis were rated congruent after the index operation. On the other hand, 10 of 13 hips not requiring conversion to total hip replacement or progressive osteoarthritis were congruent. The 20-year-follow-up Kaplan-Meier survival estimates based on conversion to total hip replacement as an end point was 86.4%. (95% confidence interval: 63.4% to 95.4%). The 25-year-follow-up survivorship was 65.1 % (95% confidence interval: 35.6% to 83.7%).

The long-term results of the spherical osteotomy are satisfactory from the standpoint of both improvement in clinical condition and the radiological appearance of the joint. The Wagner spherical osteotomy had prevented progression of degenerative changes in 13 out of 22 hips (59%) after a median 23.9 year follow-up. Congruency of the joint seems to be a major factor predicting long-term outcome.

This is a biomechanical study measuring the maximum pull-out strength of implants inserted into vertebral bodies of the calf spine. The objective is to investigate the influence of different anchoring systems.

The following implants were used: Zielke USIS (Ulrich, Ulm), Kaneda KASS (DePuy, Sulzbach). Universal Spine System (USS, Synthes, Umkirch) and Hollow Modular Anchorage (HMA) system (Aesculap, Tuttlingen). We selected nine groups with seven vertebrae equal in mean sizes and Bone Mineral Density (BMD) for each system. Vertebral body and implant were connected to both ends of a servohydraulic testing machine. Distraction was applied until failure and the maximum axial pullout force was recorded.

No significant correlation of BMD and pullout strength appeared. The student t-test showed significant higher stability for USS with pullout resistant nut (4.0 kN) and KASS (two-screws, 4.2 kN) compared to all other systems (p < 0.025). The mode of failure was a burst fracture in these vertebrae and shearing in all other systems. Bicortical screws of USS (3.2 kN) showed stronger hold than single bicortical KASS (2.5 kN) and HMA 12 mm (2.6 kN). Zielke (2.1 kN) was equal to monocortical KASS (one screw 2.1 kN) and superior to monocortical USS (1.6 kN). All those provided less stability than HMA 14 mm (2.4 kN).

For in-vitro testing with calf spines the influence of BMD seems to be less important than that of implant design. Maximum strength of Kaneda KASS depends on angulation of screws. Stability of USS implants can be increased by use of pullout resistant nuts. Of all monocortical implants only HMA presents pullout resistant strength comparable to bicortical screws. In-vivo use of monocortical anchorage bears the lowest risk of vascular injury, because the far cortex remains intact.