Knee rotational laxity in a randomized comparison of single- versus double-bundle anterior cruciate ligament reconstruction.

ABSTRACT

BACKGROUND: While single-bundle anterior cruciate ligament reconstruction reduces anterior-posterior laxity, studies have demonstrated residual rotational instability. Improved pivot-shift results have been shown with the double-bundle graft; however, no study has compared rotational laxity outcome of these surgical techniques in vivo under quantified, isolated torsional loading. HYPOTHESIS: The anterior cruciate ligament-deficient knee exhibits greater rotational laxity than the contralateral uninjured knee. The double-bundle reconstruction restores rotational joint stability to a greater extent than single-bundle surgery. STUDY DESIGN: Controlled laboratory study. METHODS: Rotational laxity of 32 patients with unilateral anterior cruciate ligament injury was assessed in both knees at full extension and 30° of flexion using a magnetic resonance imaging-compatible torsional loading device. Patients were randomly allocated either a single- or double-bundle reconstruction and reassessed 5 months after surgery. RESULTS: The anterior cruciate ligament-deficient knees demonstrated greater laxity to internal rotational torque in the extended position, but not in the 30° flexed position. No significant differences in rotational laxity were found between single- and double-bundle reconstructions. In extension, excessive internal rotational laxity of injured compared with contralateral knees was reduced by anterior cruciate ligament reconstruction. The single-bundle reconstruction did not affect internal rotation compared with contralateral or preoperative groups. In response to internal rotational torque in the flexed knee position, the double-bundle reconstruction reduced laxity to 10.8° from the pre-operative value of 15.3° (P = .058); postoperative rotation was also significantly less than the contralateral laxity of 16.4° (P = .022). CONCLUSION: The ruptured anterior cruciate ligament resulted in increased internal rotational laxity only in the extended position. The single-bundle reconstruction did not affect rotational restraint compared with contralateral or preoperative groups. The double-bundle procedure significantly reduced internal laxity in the flexed position when compared with normal. CLINICAL RELEVANCE As the anterior cruciate ligament is not the primary restraint to rotation, its contribution to joint stability is limited under isolated torsional load. While the double-bundle graft demonstrates superior rotational constraint, this may be excessive for isolated anterior cruciate ligament rupture.