Purpose: This prospective study documented patterns of scar formation after anterior cruciate ligament (ACL) rupture in order to test the hypothesis that ACL remnants can contribute to anterior knee passive motion limits tested with a ligament arthrometer.
Type of study: Prospective cohort study.
Methods: Forty-eight consecutive patients undergoing ACL reconstructions had intra-operative ligament arthrometry testing before and immediately after preparation of the notch and debridement of the ACL remnant. Patterns of scar formation were compared with changes in knee laxity after debridement of the ACL remnant.
Results: Eighteen patients (38%) had ligament scarring to the posterior cruciate ligament (group 1). Four patients (8%) had scar tissue that appeared to extend from the ACL fibers to the roof of the notch (group 2). Six ACL remnants (12%) appeared to have healed to the lateral wall of the notch or the medial aspect of the lateral femoral condyle in a position anterior and distal to the ACL anatomic footprint (group 3). In 20 patients (42%), there was no identifiable ligament tissue remaining (group 4). Changes in anterior laxity were associated with the specific pattern of scar formation within the notch. The greatest increase in anterior laxity after debridement was observed in knees in which the injured ACL had an aberrant reattachment to the femur: group 1 (mean, -1.3 mm; P < .01), group 2 (mean, -3.4 mm; P < .05), and group 3 (mean, -4.3 mm; P < .05). In group 4, the change in knee laxity was not significant (mean, 0.2 mm; 95% CI, -0.29 to 0.74 mm). Overall, 14 of 48 knees (29%) loosened more than 2 mm after ACL resection ( P < .01).
Conclusions: Resection of the ACL scar resulted in a measurable increase in passive anterior laxity in a subset of ACL-deficient knees. This increase in anterior laxity occurred in patients whose ligament healed to the femur, effectively crossing the joint. When performing arthroscopy without reconstruction in ACL-injured knees, we recommend caution in resecting the torn ACL or scar tissue because removal of this tissue contributed to increased anterior laxity in some ACL-deficient knees.
Level of evidence: Level II, diagnostic study of consecutive patients.