Comparison of polylactide screw and expansion bolt in bioabsorbable fixation with patellar tendon bone graft for anterior cruciate ligament rupture of the knee - A preliminary study

In a preliminary study, 24 patients with rupture of the anterior cruciate ligament (ACL) were operated an using implants made of self-reinforced poly-L-lactide (SR-PLLA). The operation method was outside-in bone-tendon-bone reconstruction. In 10 patients the fixation was made with an SR-PLLA screw with a diameter of 6.3 mm,in 12 with an SR-PLLA expansion plug with a diameter of 6.0 mm, and in two cases both implants were used, but these cases were excluded from comparison. The purpose of the study was to evaluate and compare the use and fixation results of these two implants. The follow-up time averaged 3.2 years. Twenty patients attended follow-up. On subjective evaluations, seven of the eight patients following SR-PLLA screw fixation and six of the ten after expansion plug fixation regarded their knee as normal or nearly normal. Arthrometric testing showed the side-to-side difference to average 2.9 mm following SR-PLLA screw fixation and 2.6 mm after expansion plug fixation (NS). Six of the patients had giving-way symptoms (two after screw fixation and four after plug fixation). The pivot shift test was slightly positive in two patients and positive in one patient after SR-PLLA screw fixation, and in three knees slightly positive and in another three knees positive following expansion plug fixation. Radiography showed variation in the location and orientation of the bone channels. Magnetic resonance imaging was performed in seven cases, and in two cases an edema was found in the tendon of the anterior cruciate ligament graft and in six cases the implants were visible. No statistical difference in results between the SR-PLLA screw and SR-PLLA expansion bolt was noted. Fixation with expansion plug seems technically more challenging, with a tendency to inferior results compared to screw fixation. In the absorbable fixation of a bone-tendon-bone graft there are no metallic artifacts on magnetic resonance imaging and no need to remove the fixation material regarding the revision surgery.