Tunnel widening in ACL reconstruction with hamstrings: the state of the art

Background The pathogenesis of bone tunnel enlargement following anterior cruciate ligament (ACL) reconstruction is not yet clearly understood. Mechanical and biological hypotheses have been proposed to describe this short-to-mid term phenomenon which takes place after ACL reconstructions. In this paper we describe clinical and radiological results of studies performed at our Orthopaedic Department, in which we examined the effects on bone tunnel diameters of accelerated post-operative rehabilitation protocols and use of different stiffness graft fixation devices (among mechanical factors) and the effects on bone tunnel diameters of the synovial bathing effect and the presence of high level of proinflammatory cytokines (among biological factors) in patients operated for ACL reconstruction. Methods Along series of patients operated on for ACL reconstruction was prospectively enrolled in these studies and followed-up right before the operation and at a mean time of 10 months post-op. All the patients were operated on using autologous hamstrings. All patients underwent an accurate physical examination, the mean knee evaluation scales (Tegner, Lysholm and IKDC), and the KT-1000 arthrometer. Radiological evaluation was done with a CT exam. We enrolled only patients in which a 9 mm bone tunnel was done. Mechanical factors were studied comparing a group of patients who underwent an accelerated post-op rehabilitation protocol (20 patients, group A), with no use of a post-op brace and who immediately recovered range of motion, with a group of patients (25 patients, group B), in which a standard rehabilitation protocol was performed. In a second study, the impact of mechanical factors was evaluated comparing a group of patients (22 patients, group C) in which very strong fixation devices (Swing-bridge and Evolgate, Citieffe, Bologna) were used, with a group of patients (23 patients, group D) in which less strong fixation devices were used (Endobutton- Smith and Nephew- and Bioabsorbable screws-BioRCI-HA). Finally, biological factors were studied comparing a group of patients (8 patients, group E) in which a post-operative septic arthritis was discovered after the ACL reconstruction (therefore in which a high concentration of proinflammatory cytokines and high synovial fluid pressure was present inside the joint for a long period of time) with a control group of patients in which no post-operative complications were registered (8 patients, group F). Results The mean femoral tunnel diameter increased significantly from 9.04±0.03 (post op) to 9.94±1.12 mm (follow-up) in group A and from 9.04±0.05 to 9.30±0.8 mm in group B. The mean tibial tunnel diameter increased significantly from 9.04±0.03 to 10.60±0.78 mm in group A and from 9.03±0.04 to 10.01±0.80 mm in group B. The increase in femoral and tunnel diameters observed in group A was significantly higher (p<0.05) than that observed in group B.