[Are patellar tension band reconstructions with absorbable materials possible? An animal experiment]

Different biodegradable tension band reconstructions of transverse osteotomies of sheep patella were tested in an experimental pilot study. Without postoperative immobilization, 4 metallic fixations in the control group dislocated secondarily 3 +/- 2 days after the operation. After tenotomy of the gastrocnemius muscle tendon, 6 other metallic fixations showed good bone healing after 12 weeks. Therefore all other fixations were immobilized postoperatively. In 5 of 6 tension band fixations with pure polydioxanone cords (PDS) ventral callus distraction started after 18 +/- 7 days, but total consolidation had taken place after 14 weeks. One PDS fixation failed for technical reasons. The combination of two axial polyglycolide rods (BIOFIX) with two ventral PDS cords showed different results: when rods 4.5 mm in diameter were used 1 fixation dislocated because the fragments were burst by the oversized rods. With rods 3.2 mm in diameter 3 other fixations were followed by complete consolidation with no dislocation after 12 weeks. Other tested combined fixation systems made up of polyglycolide and polylactide composites (cords, screws) failed secondarily, either because the fragments were burst by the oversized implants or because of the fragility of the polylactide cords. It was impossible to use polylactide screws as lag screws, because the screw heads gave way to torque. In an additional study we observed a decrease in tissue pH after implantation of polyglycolide rods in the medullary space of the tibia. Compared with the control medullary space without implants, the pH decreased from 7.38 to 6.92 at the point of greatest implant mass.(ABSTRACT TRUNCATED AT 250 WORDS)