Abstract
BackgroundAnterior cruciate ligament (ACL) injury rates continue to rise among youth involved in recreational and competitive athletics, requiring a better understanding of how the knee structurally and mechanically responds to activity during musculoskeletal growth. Little is understood about how anatomical risk factors for ACL injury (e.g., small ACL size, narrow intercondylar notch, and steep posterior tibial slope) develop and respond to increased physical activity throughout growth. We hypothesized that the ACL-complex of mice engaged in moderate to strenuous physical activity (i.e., endurance running) throughout late adolescence and young adulthood would positively functionally adapt to repetitive load perturbations.MethodsFemale C57BL6/J mice (8 weeks of age) were either provided free access to a standard cage wheel with added resistance (n = 18) or normal cage activity (n = 18), for a duration of 4 weeks. Daily distance ran, weekly body and food weights, and pre- and post-study body composition measures were recorded. At study completion, muscle weights, three-dimensional knee morphology, ACL cross-sectional area, and ACL mechanical properties of runners and nonrunners were quantified. Statistical comparisons between runners and nonrunners were assessed using a two-way analysis of variance and a Tukey multiple comparisons test, with body weight included as a covariate.ResultsRunners had larger quadriceps (p = 0.02) and gastrocnemius (p = 0.05) muscles, but smaller hamstring (p = 0.05) muscles, compared to nonrunners. Though there was no significant difference in ACL size (p = 0.24), it was 13% stronger in runners (p = 0.03). Additionally, both the posterior medial and lateral tibial slopes were 1.2 to 2.2 degrees flatter than those of nonrunners (p < 0.01).ConclusionsPositive functional adaptations of the knee joint to moderate to strenuous exercise in inbred mice offers hope that that some anatomical risk factors for ACL injury may be reduced through habitual physical activity. However, confirmation that a similar response to loading occurs in humans is needed.
Highlights
As anterior cruciate ligament (ACL) injury rates continue to rise among youth involved in recreational and competitive athletics, a better understanding of how the knee structurally and mechanically responds to activity during musculoskeletal growth is needed
We hypothesized that if work-to-run was increased in mice that ran throughout late adolescence into young adulthood, their ACLcomplexes would show greater functional adaptation to endurance running than that which we previously reported in younger mice [30]
Following block randomization of all mice to treatment groups based on body weight (BW), weight distributions between runners and nonrunners were not significantly different (p = 0.81) at the beginning of the study
Summary
Anterior cruciate ligament (ACL) injury rates continue to rise among youth involved in recreational and competitive athletics, requiring a better understanding of how the knee structurally and mechanically responds to activity during musculoskeletal growth. Little is understood about how anatomical risk factors for ACL injury (e.g., small ACL size, narrow intercondylar notch, and steep posterior tibial slope) develop and respond to increased physical activity throughout growth. As anterior cruciate ligament (ACL) injury rates continue to rise among youth involved in recreational and competitive athletics, a better understanding of how the knee structurally and mechanically responds to activity during musculoskeletal growth is needed. Some of the primary clinical risk factors for ACL injury are Ochocki et al Journal of Experimental Orthopaedics (2022) 9:3 anatomical in nature These risk factors include a smaller ACL cross-sectional area [15, 26], a narrower intercondylar notch width/shape [24, 33], and a steeper posterior tibial plateau slope [6, 9]. These biomechanically induced differences in pubescent knee development were in accordance with an earlier mouse study [29] that reported significant differences in femoral diaphysis shape and strength following pre-pubescent exercise
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