New combined knee index linked to ACL rupture risk in retrospective study

A narrower combined measure of two bony landmarks in the knee—the femoral intercondylar notch and the tibial spine—is associated with anterior cruciate ligament (ACL) rupture, according to a retrospective case–control study published in BMC Musculoskeletal Disorders. The new metric, called the Combined Notch–Spine Width Index (CNSWI), merges normalized width measurements from both regions into a single value, and in this cohort a lower index was independently associated with ligament tearing alongside a steeper lateral posterior tibial slope.

Knee osseous morphology has long been studied as a possible contributor to ACL injury. Femoral intercondylar notch dimensions and tibial spine features have each been examined separately in previous work, but the study’s authors proposed that combining normalized measures from both regions could offer a broader description of the osseous anatomy related to ACL rupture.

The research team screened 903 patients with knee injuries treated between December 2024 and December 2025. After applying predefined criteria, 369 patients were included in the analysis: 154 with ACL rupture confirmed by both MRI and arthroscopic visualization, and 215 with an intact ACL serving as controls.

From MRI and radiographs acquired using standardized sequences and planes, the investigators derived ten knee osseous morphometric parameters. Between-group comparisons were used to describe morphometric differences between patients with and without ACL rupture, and multivariable logistic regression was used to evaluate associations with ACL rupture after adjustment for demographic and anthropometric covariates.

Compared with controls, the ACL rupture group showed a greater lateral posterior tibial slope (LPTS) and a lower CNSWI, both with P values below 0.001. Differences were also observed in the medial femoral condyle length–to–medial tibial plateau length ratio (MFCL/MTPL) and in the adjusted lateral femoral condyle width index (ad-LFCWI).

On multivariable analysis, two parameters emerged as independently associated with ACL rupture. Higher LPTS carried an odds ratio of 1.116 per 1-degree increase (P = 0.002), while lower CNSWI carried an odds ratio of 0.475 per 1-unit increase (P < 0.001). In other words, within this cohort, a steeper tibial slope and a narrower combined notch–spine measure each contributed independently to the odds of having a ruptured ACL.

In exploratory receiver operating characteristic (ROC) analyses, CNSWI achieved an area under the curve of 0.718 (95% CI, 0.666–0.771), and pairwise comparisons showed higher AUCs than its individual components, the adjusted notch width index (ad-NWI) and the adjusted tibial spine width index (ad-TSWI). The authors characterized these ROC analyses as exploratory, intended to describe ROC-derived estimates rather than to establish diagnostic performance.

The study’s conclusion frames CNSWI as a composite morphometric parameter combining normalized femoral notch and tibial spine width measures, and notes that a lower CNSWI together with a steeper LPTS was independently associated with ACL rupture in this retrospective cohort. The authors state that these findings support further validation of CNSWI as an adjunctive morphologic parameter in ACL-related imaging assessment.

As a retrospective, single-cohort case–control design, the study describes associations between measured anatomy and confirmed ACL rupture rather than demonstrating that these features predict future injury in the general population. The authors position CNSWI as a candidate adjunctive measure whose value in ACL-related imaging assessment would require further validation before broader clinical use.

Subject of Research: A combined knee morphometric index and its association with anterior cruciate ligament rupture

Article Title: Combined notch–spine width index and its association with anterior cruciate ligament rupture: a retrospective case–control study

Article References: Zhang, M., Zhou, T., Jia, D., Wang, K., Yu, Y., Shi, Z., Yuan, P., Li, K., & Li, Y. (2026). Combined notch–spine width index and its association with anterior cruciate ligament rupture: a retrospective case–control study. BMC Musculoskeletal Disorders. https://doi.org/10.1186/s12891-026-10682-7

Image Credits: AI Generated

DOI: 10.1186/s12891-026-10682-7

Keywords: ACL rupture, CNSWI, knee morphology, intercondylar notch, tibial spine, posterior tibial slope, MRI, case-control study, orthopedics, BMC Musculoskeletal Disorders, Combined, notch