Researchers found that Kaplan fiber injury was independently associated with greater anterior tibial subluxation in the lateral compartment, an imaging marker of knee instability, among patients with anterior cruciate ligament injury.
In this retrospective, single-center study, researchers evaluated 132 patients aged 14 to 55 years who underwent primary anterior cruciate ligament (ACL) reconstruction between January 2020 and December 2023. All patients underwent magnetic resonance imaging (MRI) within 12 weeks of injury and had arthroscopically confirmed ACL injury. Two trained readers independently assessed Kaplan fibers (KF), the anterolateral ligament, anterior tibial subluxation of the lateral compartment, and knee morphologic features using standardized MRI criteria. The primary outcome was the independent association between KF injury and anterior tibial subluxation. Secondary analyses examined structural and morphologic factors associated with KF injury and predictors of high-grade anterior tibial subluxation, defined as 4.5 mm or greater.
KF injury was present in 36% of patients. Compared with patients without KF injury, those with KF injury had a higher frequency of concomitant anterolateral ligament injury (81% vs 60%) and larger lateral femoral condyle depth, height, and width ratio measurements on MRI. Rates of posterior cruciate ligament, collateral ligament, and meniscal injuries did not differ significantly between the groups.
In multivariable analysis, KF injury remained independently associated with greater anterior tibial subluxation after adjustment for demographic, structural, and morphologic factors. Adding KF injury to the regression model increased the explained variability in anterior tibial subluxation by 15%, and KF injury was associated with an average increase of 3.4-mm in anterior tibial subluxation. After accounting for KF injury, anterolateral ligament injury was no longer independently associated with anterior tibial subluxation.
Among the 98 patients with combined ACL and anterolateral complex injuries, the lateral femoral condyle width ratio was the only independent predictor of high-grade anterior tibial subluxation. Each 1% increase in the width ratio was associated with approximately 1.3 times the odds of high-grade subluxation. A width ratio cutoff of 27.5% showed high sensitivity and negative predictive value but limited specificity, indicating that it should not be used as a standalone predictor.
The researchers noted several limitations, including the retrospective, single-center design, reliance on MRI without confirmation by additional imaging modalities or direct visualization of all anterolateral structures, potential measurement bias, incomplete assessment of meniscal root integrity, limited clinical data, and the lack of external validation of the proposed lateral femoral condyle width ratio threshold.
Overall, the findings suggest that KF injury may serve as an imaging marker of greater knee instability following ACL injury. The researchers noted that larger, multicenter studies are needed to validate these findings and determine their clinical applicability.
"Based on single-center data, the incidence of KFs injury within 12 weeks of ACL injury was 35.6%, and it was closely associated with ALL injury and LFC morphology. KFs injury was independently associated with increased ATSLC, a marker of knee instability," wrote lead study author Bailin Pan, of Fujian Medical University, and colleagues.
Disclosures: The authors did not report any conflicts of interest.