Purpose: To assess the performance of a constrained liner in an unstable hip prosthesis.

Materials and methods: This is a retrospective study of 66 hip prostheses implanted in 66 patients by means of the same constrained cup (Lefevre, Lepine Group, France). The cup was implanted into 15 primary prostheses and 51 revision ones in order to treat recurrent dislocations (10 cases) or to prevent dislocations (56 cases with a deficit of the periarticular musculature or mental or neuromuscular disorders). The mean age was 76.7 years, 75.7% were female, 53% were operated in the right side and the mean follow up was 30.2 months.

Results: By the time the last review was made, four patients died for reasons not related to their hip surgery. One patient showed a dissociation between the femoral head and the stem at the level of the Morse taper; the head was trapped in the retentive liner and an open reduction was needed to replace the existing prosthetic head by a new one with a long neck. Another patient had a prosthetic infection that was treated by means of a two-stage replacement. Radiolucent lines were observed in de DeLee’s zone 1 in 1.5% of patients, in 3% the lines were in zone II and in 3% they were in zone. However, according to Hodgkinson’s radiographic criteria, no cups were loose.

Conclusions: Although retentive cups do address hip instability, the various cases of failure that have occurred, the appearance of radiolucencies and the concerns about their long-term fixation suggest that their use should be carefully weighted.

Purpose: To assess the use of abdominal aorta cryopreserved allografts as guided regeneration membranes in long bone defects.

Materials and methods: This is a prospective randomized blind study of 10 White New Zealand rabbits. 10 mm-long diaphyseal defects were created in both radii: on one side the defect was separated from the surrounding tissue by means of a tube-shaped cryopreserved aortic allograft; the contralateral radius (control) was left to develop spontaneously with no membrane. The animals were put down after 6, 12, 24 and 30 months. A whole range of different studies were made: x-rays, CT, MRI, morphodensitometric techniques and optical and electronic microscopy.

Results: No complete bone regeneration was observed in any of the controls. In 9 out of the 10 defects for which an aortic allograft was used complete bone regeneration was achieved as well as a restoration of continuity with a corticomedullary pattern. A progressive increase in density and thickness was observed in the regenerated cortex, which reached values similar to those of normal bone. A gradual reduction of the medullary/cortical thickness index was also detected.

Discussion: The microscopic images taken suggest that cryopreserved arterial allografts used in guided regeneration behave like barrier membranes and as osteoinductive agents because of the osteoblastic differenciation of endothelial and/or muscular cells and/or ossification secondary to proteic changes in the extracellular matrix of the artery. This could be regarded as the application of artery calcification and ossification (usually associated with arteriosclerosis, ageing, diabetes and renal failure) to the regeneration of bone defects.

Conclusions: It is possible to use cryopreserved aortic allografts as osteostimulating membranes in the guided regeneration of bone defects.