Association of Geometric Characteristics of Knee Anatomy (Alpha Angle and Intercondylar Notch Type) With Noncontact ACL Injury

Abstract

Background: The femoral intercondylar notch type and the alpha angle (the angle between the femoral notch roof and the long axis of the femur) are easily measured in clinical settings; however, their associations with anterior cruciate ligament (ACL) injury remain unclear. Hypothesis/Purpose: The purpose was to determine if the alpha angle and the femoral notch type are associated with noncontact ACL injury univariately and in combination with previously identified knee geometric risk factors. We hypothesized that the alpha angle and the femoral notch type are associated with noncontact ACL injury and that the association differs between men and women. Study Design: Case control study; Level of evidence, 3. Methods: The alpha angle and the femoral notch type were measured via 3T magnetic resonance imaging (MRI) acquired from 61 women and 25 men with a first-time noncontact ACL injury. Each injured patient was matched with a control participant based on age, sex, and participation on the same sports team. A conditional logistic regression was used to assess univariate associations with ACL injury as well as multivariate associations using MRI-based risk factors of knee geometry identified in previous analyses: femoral intercondylar notch width at the anterior outlet, femoral intercondylar notch anteromedial ridge thickness, volume of the ACL, tibial plateau lateral compartment subchondral bone slope, lateral compartment middle articular cartilage slope, lateral compartment meniscus-cartilage height, lateral compartment meniscus-bone angle, and medial tibial spine volume. Results: For female athletes, the alpha angle (odds ratio, [OR], 1.82 per 1-degree increase; P = .001), the tibial lateral compartment articular cartilage slope (OR, 1.25 per 1-degree increase in the posterior-inferior directed slope; P = .022), and the femoral notch anteromedial ridge thickness (OR, 3.36 per 1-mm increase; P = .027) were independently associated with ACL disruption. For men, no other variables entered the models after the alpha angle was inputted as the first step (OR, 2.19 per 1-degree increase; P = .010). Conclusion: For women, ACL injury was most strongly associated with increased alpha angle, increased tibial plateau slope, and increased femoral notch ridge thickness. For men, increased alpha angle was the most significant factor associated with ACL injury. The mechanism of injury might be associated with a combination of impingement of the ACL against the bone and increased ligament loading.

Endurance running during late murine adolescence results in a stronger anterior cruciate ligament and flatter posterior tibial slopes compared to controls

“…The lack of a significant difference in ACL size between treatment groups may potentially be related to the size limiting effects of the intercondylar notch, which is more stenotic (A-shaped) in runners and nonrunners. Recently, Barnum et al [ 2 ] and Bouras et al [ 10 ] found an association between a stenotic intercondylar notch and ACL injury risk in female patients, which potentially reflects a greater risk for ACL impingement while transitioning from knee flexion into extension. Interestingly, in earlier running studies using pubescent inbred strains of mice (i.e., B6 and A/J), the ACL of B6 runners was found to be 13.5% larger than that of nonrunners, while A/J runners showed a 7% smaller ACL than their respective controls.…”

Increased lateral and medial femoral posterior radius ratios are risk factors for anterior cruciate ligament injury

“…Although the mechanism leading to ACL injury has not been established, identifying risk factors help prevent noncontact ACL injury and achieve optimal outcomes in ACL reconstruction. Many studies have investigated distal femoral osseous morphological characteristics as risk factors for noncontact ACL injury [ 6 ], including an A-shaped notch [ 7 ], decreased notch width index [ 8 , 9 ], smaller femoral notch volume [ 10 ], and increased thickness of the medial intercondylar ridge [ 8 ]. These osseous morphological characteristics have been shown to have a significant association with noncontact ACL injury.…”

A wear model to predict damage of reconstructed ACL

“…It is now established that the risk of graft impingement can be greatly reduced by a correct tunnel placement adjusted to the individual patient anatomy (Barnum et al, 2021;Iriuchishima et al, 2010). This can be assessed by a preoperative planning procedure consisting in imaging the knee of the patient prior to the surgery, to select a patient specific placement of the graft (Connors et al, 2019).…”