Impact of subject’s physical properties on joint biomechanics: Hypermobility alters lower extremity biomechanics during knee-bearing activity

Hypermobility is a physical specificity of the subject that refers to an increased range of motion in one or more joints beyond what is considered normal or expected for an individual's age, gender, and body type. The previous studies on hypermobility stated that generalized joint hypermobility (GJH) may cause joint instability and muscle weakness [1]. The knee joint structural integrity and function maintained essentially by the cruciate ligaments. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) work together to provide stability to the knee joint by preventing excessive movement of the tibia (shin bone) in relation to the femur (thigh bone). The more common ligament injury is ACL injury and non-contact ACL injuries remain a serious problem among athletes [2]. Activities demanding mechanical bearing on the knee joint recommended for classifying an athlete's anterior cruciate ligament injury risk [3]. Some biomechanical factors determined in these tests are associated with future injuries [4]. In order to protect the athlete from injury, it is necessary to determine the causes of biomechanical factors determined by functional tests. The aim of this study is to examine the effects of GJH on Pelvis and lower body joint biomechanics with Single Leg Landing (SLL) test. Does hypermobility alter lower extremity biomechanics? Eight healthy volunteers with no history of musculoskeletal injury or pain participated in this study (mean age: 16.6±4.2). Casual sports participants were divided into two equal groups (control ≤4, hypermobile ≥6) according to the Beighton score which measures GJH [5]. SLL tests were acquired for each subject using 3D motion analysis (6 Vantage 5 Camera, 2 Force Platforms, Vicon Motion Systems Ltd UK). Plug-in-gait model for lower extremity is utilized as marker set that described in the previous studies [4]. Three repetitive tests were evaluated for each leg side. An Independent t-test was used for statistical analysis. Participants with hypermobility exhibited higher peak angles of pelvic external rotation (p=0.01), hip adduction (p=0.03), and knee valgus (p=0.02) during the stance phase of knee-bearing activity (see Table 1). In contrast, peak values of pelvic posterior tilt angle (p=0.03), foot internal progression (p=0.05), and knee flexion moment (p=0.01) were found to be decreased in participants with hypermobility.Download : Download high-res image (113KB)Download : Download full-size image It has been determined that joint hypermobility can lead to alterations in lower extremity biomechanics during SLL test. Increase in peak hip adduction and knee valgus angles lead to both acute (ACL rupture factor) and overuse sport injuries [6]. Further studies are needed to investigate the effects of joint hypermobility using detailed marker set for better quantification of specifically knee joint movement.