Introduction: After adopting a new low suspensory bio-absorbable femoral fixation technique for single bundle, four strand, hamstring Anterior Crutiate Ligament (ACL) in conjunction with a rapid rehabilitation program, we observed at routine follow up that there was no evidence of femoral tunnel widening, as often observed with conventional high suspensory fixation systems.
Method: We conducted a retrospective observational cohort study to test the hypothesis that the Rigid-Fix (Mitek) system of femoral fixation, a low suspensory technique, is less prone to tunnel widening than traditional suspensory techniques.
14 subjects were recruited at routine follow up, and assessed by interview, clinical examination and plain digital raiodgraphs.
All radiographs were taken under clinical supervision, with a scale reference, hence allowing digital rescaling.
Results: All subjects had regained knee stability, and all but one had returned to their pre-injury level of sport. Clinically all knees were ligamentaly stable, exhibiting negative Luchman and pivot shift tests.
Examination of the radiographs demonstrated only a 1.1mm (+/− 0.9mm) mean femoral tunnel widening, which represents a 12% increase in diameter (21% increase in area), and compares very favourably to the observed tunnel widening in high suspensory techniques, as cited in the literature.
Conclusions: We conclude that the Rigid-Fix femoral ACL fixation system does not exhibit any evidence of clinically significant tunnel widening, even when used in conjunction with a rapid rehabilitation program.
Systems of low suspension benefit from the advantage of not relying on interference fit which risks posterior cortical ‘Blow Out’. A shorter graft working length within the tunnel lessens graft micro-movement, making early low biological fixation within the femoral tunnel more likely, and reduces the amount of tunnel widening. These micro-movement have been described as the ‘Windscreen Wiper’ and ‘Bungee Cord’ effects, and are well documented in traditional high suspensory fixation.
