Association between lower extremity movement patterns and ACL loading in CAI patients across varied ankle sprain frequencies within a year.

Purpose: To investigate the relationship between the biomechanical characteristics of lower extremity and anterior cruciate ligament (ACL) loading during single-leg landing in patients with chronic ankle instability (CAI) who have different ankle sprain frequencies within a year.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: The incidence of ankle sprains among 74 male participants was meticulously documented over a one-year period. The participants had an average age of 21.78 years, a height of 176.37 cm, and a weight of 72.61 kg. Subsequently, a one-year monitoring period was implemented to assess the incidence of ankle sprains among the participants. The participants were classified into five groups according to their documented frequency of ankle sprains. The categories were as follows: The 2, 3, 4, 5, and 6 or more ankle sprain groups. Kinematic, kinetic, and electromyographic data were collected while participants performed a single-leg landing task. Lower extremity muscle force and ACL loading were modeled using OpenSim software.

Results: CAI patients with more than four ankle sprains had higher peak ACL loading during single-leg landing than those with only two or three ankle sprains (P < 0.05). Additionally, CAI patients with more than four ankle sprains exhibited a limited range of ankle dorsiflexion and biceps femoris muscle force, which was significantly correlated with ACL loading (P < 0.05). CAI patients with more than 5 ankle sprains had greater ankle inversion angle, inversion angular velocity, vertical ground reaction force (GRF), rectus femoris muscle strength, and lower gastrocnemius, soleus muscle force during single-leg landing, and these biomechanical indices were significantly correlated with ACL strain (P < 0.05).

Conclusion: Based on these findings, it appears that experiencing four ankle sprains within a year might be a threshold for the development of knee compensation in CAI patients. This compensation could result in a significant increase in ACL loading. The study also found that CAI patients with more than four ankle sprains commonly exhibited altered motor characteristics such as limited ankle dorsiflexion angle, increased ankle inversion angle, excessive vertical GRF, and insufficient gastrocnemius and soleus muscle force during the landing phase. These characteristics might be responsible for the observed increase in ACL loading. In the future, clinical practice and scientific research may benefit from targeted interventions to prevent ACL injuries in CAI patients with different sprain histories, in accordance with the findings of this study.