Summary

The cut-off point established to discriminate an ACL re-tear was 6.5 degrees of hyperextension.

Abstract

Background

The outcome of an ACL reconstruction surgery depends on many factors. The degree of knee hyperextension in isolation has not been studied in detail as a risk factor that may lead to graft failure after an ACL reconstruction. The aim of this study is to create a cut-off point for hyperextension that best discriminates re-tear and to verify whether this cut-off point can predict re-tear regardless of other characteristics after primary ACL reconstructions with hamstrings autografts.

Methods

A cohort of patients submitted to primary isolated ACL reconstruction with hamstrings autografts was retrospectively evaluated. Patients were stratified according to the degree of passive knee hyperextension measured in the normal contralateral knee at surgery time. The following data were collected: patient demographic data (age and gender), time from injury to surgery, passive knee hyperextension, KT-1000 and pivot-shift, associated meniscus injury and treatment, intra-articular graft size, follow-up time, occurrence of graft failure and postoperative Lysholm and IKDC subjective form. A ROC curve was constructed to identify the cut-off point of the hyperextension that best discriminates re-rupture. Unadjusted odds ratios (OR) were estimated with the respective 95% confidence intervals of each characteristic with re-rupture using bivariate logistic regressions to quantify the association of characteristics with re-rupture.

Results

Data from 457 patients were evaluated. Thirty-two presented a re-tear. There was a significant difference in hyperextension between patients with and without re-tear (p < 0.001), with the cut-off point established by the ROC curve from 6.5 degrees, with sensitivity of 78.1% and specificity of 76.7%. Patients with greater hyperextension had a statistically higher frequency of women, longer injury time, greater intra-articular graft size, greater post-op KT-1000 and higher frequency of re-tear, whereas the subjective IKDC and Lysholm were statistically lower in patients with greater hyperextension. When a meniscus injury was present, in patients with greater hyperextension, the frequency of medial meniscus injury was statistically higher than in patients with less hyperextension. Only hyperextension showed a statistically significant association with re-rupture when evaluated alone (p < 0.001). Regardless of the other characteristics evaluated, only hyperextension statistically influenced the re-tear of patients (p < 0.001), and the chance of re-tear in patients with hyperextension greater than 6.5 was 14.65 times the chance of patients with hyperextension less than 6.5.

Conclusion

The cut-off point established to discriminate an ACL re-tear was 6.5 degrees of hyperextension. Only hyperextension statistically influenced a re-tear and the chance of re-tear in patients with hyperextension more than 6.5 degrees was 14.65 times the chance of patients with hyperextension less than 6.5.