Correlation between lower limb biomechanics during single-leg landing and hip joint muscle strength in patients with anterior cruciate ligament reconstruction

Abstract

BACKGROUND: Recovery of knee joint function and muscle strength is a key focus of rehabilitation after anterior cruciate ligament reconstruction. However, abnormal inter-joint mechanical patterns of the lower limbs may alter lower limb biomechanics during movement and increase the risk of anterior cruciate ligament injury. OBJECTIVE: To explore the lower limb biomechanical characteristics of anterior cruciate ligament reconstruction patients during single-leg landing 2 years after surgery, and their correlation with hip joint muscle strength. METHODS: Totally 23 subjects who underwent anterior cruciate ligament reconstruction were randomly recruited. The Qualisys three-dimensional motion capture system and AMTI three-dimensional force platforms were used to capture kinematic and kinetic data of both lower limbs during single-leg landing. The Biodex isokinetic muscle testing system was used to measure muscle strength of both hip and knee joints at an angular velocity of 60°/s. Paired sample t-tests were used to compare bilateral lower limb joint biomechanical characteristics and isokinetic muscle strength of hip and knee joints. Pearson correlation analysis was used to explore the correlation between kinetic data during single-leg landing and isokinetic muscle strength of hip and knee joints. RESULTS AND CONCLUSION: (1) During single-leg landing, the surgical side showed smaller knee extension angle at initial contact, knee flexion/extension range of motion, vertical ground reaction force, hip extension, hip abduction, and knee extension peak moments, and larger hip flexion angle at initial contact and hip flexion/extension range of motion. (2) At 60°/s, the surgical side showed significantly reduced hip abduction, hip extension, knee flexion, and knee extension muscle torques. (3) The peak vertical ground reaction force and hip extension moment on the surgical side were significantly correlated with hip abduction muscle strength, while the peak knee extension moment on the surgical side was significantly correlated with hip abduction, flexion, and extension muscle strength. (4) These results indicate that 2 years after surgery, muscle strength on the surgical side had not recovered to the level of the healthy side, possibly related to neural inhibition caused by surgery. Patients adopted a buffering strategy recruiting hip joint muscle strength to actively reduce vertical ground reaction force during single-leg landing, but the smaller hip abduction moment peak on the surgical side also reduced knee joint stability in the coronal plane. Therefore, it is recommended that hip and knee muscle strength training, especially hip abduction, extension, and knee flexion, extension muscle strength, be continued for 2 years after anterior cruciate ligament reconstruction, along with targeted neuromuscular training and motor technique guidance to improve neuromuscular control during movement and avoid negative effects of maladaptive strategies.

1. Introduction

Anterior cruciate ligament injury is one of the most common knee injuries, often occurring in sports involving sudden stops, side cuts, and jump landings [1]. Anterior cruciate ligament injury can lead to knee pain, limited range of motion, instability, and accelerate the occurrence of degenerative diseases such as knee osteoarthritis [2]. Therefore, the focus of rehabilitation after anterior cruciate ligament injury is to restore knee function and sports performance.

Anterior cruciate ligament reconstruction is a common treatment for anterior cruciate ligament injury, with good results in restoring knee function and sports performance. Despite undergoing anterior cruciate ligament reconstruction, many patients still cannot return to their pre-injury sports level. Surveys show that less than 45% of patients return to their pre-injury sports level after anterior cruciate ligament reconstruction [3], and within 2 years after injury, the incidence of secondary anterior cruciate ligament injury is more than 6 times that of the initial injury [4]. However, 2 years after surgery, the risk of complications or sequelae gradually decreases [5]. Therefore, 2 years is a critical period for rehabilitation after anterior cruciate ligament reconstruction. Lower limb biomechanical characteristics and neuromuscular adaptations similar to the initial injury are major risk factors for secondary anterior cruciate ligament injury [6]. Patients after anterior cruciate ligament reconstruction typically undergo physical and sports rehabilitation to enhance lower limb muscle strength, improve neuromuscular control, and prognosis [7]. Previous studies have found that movements such as running, single-leg hopping, triple hopping, and cross-over hopping increase the incidence of secondary anterior cruciate ligament injury by more than 4 times [8], especially single-leg landing, which has a sensitivity of up to 78% in predicting anterior cruciate ligament injury [9]. Therefore, exploring the differences in bilateral lower limb biomechanical characteristics during single-leg landing 2 years after anterior cruciate ligament reconstruction is particularly important for understanding the mechanisms of secondary anterior cruciate ligament injury. During landing, the load on the anterior cruciate ligament may depend on the impact force on the lower limbs and the buffering mode adopted [10]. Thus, previous studies have explored the relationship between biomechanical characteristics of single-leg landing, vertical jumps, and anterior cruciate ligament injury from aspects such as vertical ground reaction force, neuromuscular control, and knee joint load. However, with deeper research, more attention has been paid to the role of hip joint muscle strength in knee stability and injury risk.