Abstract
Objectives:
Single-bundle, anatomic anterior cruciate ligament reconstruction (ACLR) may not fully restore rotatory knee stability, and the addition of a lateral extra-articular tenodesis (LET) has been proposed as means for reducing residual rotatory knee instability. However, the magnitude of the in vivo, time zero effects of these procedures on rotatory knee instability remain poorly defined. The pivot shift test is used to assess for rotatory knee instability; however, it is a subjective grading system with limited generalizability and ability to predict clinical outcomes. Consequently, a quantified pivot shift (QPS) test software application, PIVOT iPad, has been developed and validated to measure the magnitude of rotatory knee laxity. The objective of this study was use intraoperative QPS (iQPS) to assess for differences in residual rotatory knee instability after ACLR versus ACLR augmented with lateral extra-articular tenodesis (ACLR + LET.)
Methods:
During examination under anesthesia (EUA), QPS was performed on both the operative and non-operative knees prior to ACLR (Figure 1A) Three, yellow ¾ inch markers were attached to skin overlying bony landmarks: lateral epicondyle, Gerdy’s tubercle and 3 cm posterior to Gerdy’s tubercle. The PIVOT software application was used to measure lateral compartment translation (Figure 1B) ACLR were randomly augmented with a LET if the lateral compartment translation measured during QPS was greater than or equal to double the amount of lateral compartment translation measured for the unaffected knee. iQPS measurements were subsequently performed after either ACLR or ACLR + LET with sterile markers (Figure 1C) iQPS data were recorded and compared to both the preoperative QPS measurements of the affected and unaffected knees. Based upon normative QPS data established from a database of >150 previously performed ACLR at our institution, it was determined that 8 patients in each group would be required to achieve 80% power with an effect size of 1.2 mm and an alpha level of 0.05. Post-procedure iQPS data were compared to preoperative QPS measurements with paired samples t-tests.
Results:
iQPS measurements were performed in 20 ACLR (10 ACLR and 10 ACLR + LET). The mean age in the cohort was 17.3 years old (range: 17-24 years old.). Both ACLR and ACLR + LET resulted in significant decreases in rotatory knee instability when compared to preoperative QPS measurements (pre-ACLR: 4.7 ± 1.9 v. post-ACLR: 1.3 ± 0.70, P < 0.001; pre-ACLR +LET: 3.6 ± 1.8 v. post-ACLR + LET: 0.9 ± 0.5, P < 0.001.) When comparing isolated ACLR to ACLR + LET, no significant differences were observed in the magnitude of change in iQPS between the pre and post-intervention states (ACLR: - 3.5 ± 1.6 mm v. ACLR + LET: -1.5 ± 3.1 mm, P = N.S.) Furthermore, there were no significant differences in lateral compartment translation between the operative knees and non-operative knees (ACLR: -0.1 ± 0.9 mm v. ACLR + LET: -0.5 ± 1.0 mm, P = N.S.), suggesting that neither ACLR nor ACLR + LET led to over-constrained kinematics.
Conclusion:
In this randomized control study, both ACLR and ACLR + LET resulted in significant decreases in rotatory knee instability. However, there were no significant differences in time-zero, rotatory knee instability detected between isolated ACLR versus ACLR combined with LET in patients. The utility of combining a LET with ACLR remains unclear, and future research is necessary to refine the indications for LET in patients with high-grade rotatory knee instability.
