Interference fit fixation of soft-tissue grafts is in clinical focus to allow anatomic graft fixation which increases stability and graft isometry. Although clinical data show promising results with different screw materials, the issue of biodegradability, handling and stability in the first weeks remain under demand. The purpose of the present study was to investigate anterior cruciate ligament (ACL) reconstruction radiologically, biomechanically and histologically using direct tendon-to-bone interference fit fixation with a newly designed tap locking screw synthesized from a mixture of ceramic and hydroxyapatite in a sheep model.
Twenty-eight skeletally mature sheep underwent a bilaterally ACL reconstruction with an autologous Achilles tendon split graft. Grafts were directly fixed with poly-(D,L-lactide) interference screws (PLLA) in 14 control sheep and with HA-screw in another 14 sheep. Animals were operated on the right knee first and left to heal for 52-weeks, however the left knee was left to heal for 6 weeks.
All grafts by time of insertion were stable and did not pullout from bone tunnel in both experimental and control group. Post mortem at 6 and 52 weeks, knees were scanned using μCt. The HA-screw showed better stability in the bone tunnel at the 6-weeks time points when compared with the PLLA screws. Also cystic legions were noticed at this time point. After 52-weeks, the HA screw bone – implant interface exhibited good osteointigration in both femoral and tibial screws. Over the whole healing period the graft fixation was not weakened through the screw design. The direct interference fit fixation withstood loads without motion restriction in all sheep.
Currently, radiological quantification, histological assessment and biomechanical testing are under investigation. However, the HA-screw provides stability in the initial 6-week critical phase.
14 May 2016 - 17 May 2016