Introduction
Residual rotatory knee laxity (RKL) after anterior cruciate ligament reconstruction (ACLR) is a pathological factor that affects the clinical outcomes of patients who undergo ACLR. Therefore, controlling residual RKL of reconstructed knees is an important strategy in the treatment of ACL-deficient patients. In recent clinical papers, lateral meniscus tear (LMT) accompanied with ACL injuries has been reported to provoke rotatory instability of the affected knee joint. Moreover, LM repair (LMR) immediately improved the rotatory instability provoked by LMT. Unfortunately, these previous papers did not determine whether LMT-derived rotatory instability is residual because there exists only preoperative or time zero data. Therefore, this study is aimed to evaluate the longitudinal relationship between the signal intensity (SI) of LMR on MRI and residual RKL after ACLR.
Methods
Eighty-seven patients (mean age: 23.5 years, BMI: 23.7 kg/m2 56 Females/31 Males) have participated with provided informed written consent. All subjects underwent anatomical double-bundle ACLR with autologous hamstring tendon and concomitant LMR. Proton-density weighted (PDW) and T2-weighted (T2W) MRIs were performed 3 months, 6 months, and 12 months after surgery. SI ratio (SIR) was measured by [SI of repaired LM] / [SI of PCL]. At the 12-month follow-up after ACLR, several surgeons at our sports medicine clinic examined RKL by the pivot-shift test. According to the International Knee Documentation Committee grade, if the patients exhibited grade 1 or severe pivot-shift phenomenon, they were defined as having residual RKL.
Results
Out of 87 subjects, 12 subjects (13.8%) exhibited RKL. The SIR of PDW (SIR-PDW) in those with RKL (1.98±0.77) was significantly higher than those without RKL (1.49±0.52, p = 0.007, non-paired t-test) at 3 months after ACLR. On the other hand, the SIR of T2W exhibited no significant difference between those with and without RKL. SIR-PDW at 3 months after ACLR was negatively correlated with patient’s age (r = –0.304, p = 0.004, Pearson's correlation coefficient). If we stratified the subjects into those =22 years old (younger group, N = 53 and RKL = 7 [13.2%]) and <22 years old (older group, N = 34 and RKL = 5 [14.7%]), the ROC curves of SIR-PDW in younger group were statistically significant to predict the prevalence of RKL (range of AUC: 0.733 to 0.788); that of SIR-PDW in older group could not predict the prevalence of RKL. Based on the ROC curves of SIR-PDW in younger group, we can acquire the cut-off values of SIR-PDW in 3 months (SIR-PDW: 2.00), 6 months (SIR-PDW: 1.50), and 12 months (SIR-PDW: 1.50), respectively. Finally, multiple logistic regression analysis clarified that if the younger subjects consistently exhibited the higher SIR-PDW than the cut-off, they are more likely to have the risk of residual RKL (range of odds ratio: 10.24 to 23.57 times).
Discussion
Primary finding of this study is that the higher SI of repaired LM is associated with the higher odds ratio of residual RKL for the younger patients who underwent ACLR and LMR at the same time. Using the categorical classification, previous studies revealed that the most severe MRI grade (Stoller’s classification grade 3) indicated the higher risk of non-union after meniscus repair. In line with these data, the current data consistently revealed that the higher SI of repaired LM was associated with the non-union of LMR and indicated the risk of residual RKL derived from the deficiency of LM function.