In Vivo Anterior Cruciate Ligament Deformation During a Single-Legged Jump Measured by Magnetic Resonance Imaging and High-Speed Biplanar Radiography

Abstract

Background: The in vivo mechanics of the anterior cruciate ligament (ACL) and its bundles during dynamic activities are not completely understood. An improved understanding of how the ACL stabilizes the knee is likely to aid in the identification and prevention of injurious maneuvers. Purpose/Hypothesis: The purpose was to measure in vivo ACL strain during a single-legged jump through use of magnetic resonance imaging (MRI) and high-speed biplanar radiography. We hypothesized that ACL strain would increase with the knee near extension, and a peak in ACL strain would occur just before landing from the jump, potentially due to quadriceps contraction in anticipation of landing. Study Design: Descriptive laboratory study. Methods: Models of the femur, tibia, and ACL attachment sites of 8 male participants were generated from MRI scans through use of solid modeling. High-speed biplanar radiographs were obtained from these participants as they performed a single-legged jump. The bone models were registered to the biplanar radiographs, thereby reproducing the in vivo positions of the joint throughout the jump. ACL and bundle elongations were defined as the centroid to centroid distances between attachment sites for each knee position. ACL strain was defined as ACL length normalized to its length measured in the position of the knee at the time of MRI. Results: Peaks in ACL strain were observed before toe-off and 55 ± 35 milliseconds before initial ground contact. These peaks were associated with the knee positioned at low flexion angles. Mean ACL strain was inversely related to mean flexion angle (rho = −0.73, P < .001), such that ACL strain generally increased with knee extension throughout the jumping motion. ACL bundle lengths were significantly (rho > 0.85, P < .001) correlated with overall ACL length. Conclusion: These findings provide insight into how landing in extension can increase the risk of ACL injury. Specifically, this study shows that peak ACL strain can occur just before landing from a single-legged jump. Thus, when an individual lands on an extended knee, the ACL is relatively taut, which may make it particularly vulnerable to injury, especially in the presence of a movement perturbation or unanticipated change in landing strategy. Clinical Relevance: This study provides a novel measurement of dynamic ACL strain during an athletic maneuver and lends insight into how landing in extension can increase the likelihood of ACL failure.

Reconsidering Reciprocal Length Patterns of the Anteromedial and Posterolateral Bundles of the Anterior Cruciate Ligament During In Vivo Gait

“…11 Each in vivo experiment used a radiographic protocol not exceeding 110 kVp/200 mA. 10,11 To assess radiation risk to participants, the radiation effective dose was calculated by our institution’s radiation safety department from the total skin entrance exposure and energy absorption by the tissues and was found to be <0.14 mSv per participant.…”

“…After the in vivo positions of the bones during the full gait cycle were reproduced, the knee flexion angle and the length of the ACL-defined as the distances between attachment site centroids-were determined for each knee position. 10,32 We then measured the lengths of 1000 virtual ACL bundles for each participant by randomly sampling 1000 locations each on the femoral and tibial attachment site surfaces and measuring the distances between pairs of these locations. Spearman rho rank coefficients were used to determine the relationships between each of the 1000 virtual bundle lengths and ACL length throughout gait for each participant.…”

“…6 Furthermore, the findings of several in vivo imaging studies are in contrast to the findings of previous work with regard to the length patterns of the AM and PL bundles during flexion. Specifically, in vivo imaging studies that measured the length patterns of AM and PL bundles reported that both bundles are elongated with knee extension and less elongated in flexion during weightbearing 17,22,32 and nonweightbearing knee flexion, 36 single-leg hopping, 10 and gait. 11,12,33 Thus, to better elucidate the functional anatomy of the ACL, we aimed to comprehensively investigate the length patterns of numerous subdivisions of the ACL during gait using high-speed biplanar radiography integrated with models of the knee joint derived from magnetic resonance (MR) images.…”

“…The methodology used here allows for precise measurement of in vivo length changes of the native ACL during common dynamic activities. 4,10,12 We hypothesized that the virtual bundles would elongate in parallel as the knee extends during gait. Furthermore, we hypothesized that the lengths of the bundles that originated and terminated in the anterior and medial aspects of the ACL would be positively correlated with the lengths of the bundles that originated and terminated in the posterior and lateral aspects of the ACL.…”

Mechanism of anterior cruciate ligament loading during dynamic motor tasks

“…There are few studies reporting direct measurement of ACL loading during dynamic tasks such as jumping and landing [7,8] and similarly few using indirect image-based assessments [9].…”