Evidence suggests that anterior cruciate ligament (ACL) injured individuals do not use the same movement strategies as healthy individuals. It is unknown how this may affect them in more challenging activities of daily living and sport. The aim of this study is to evaluate how ACL injured patients perform a single leg squat (SLS) compared to healthy controls. SLS was evaluated as it is more challenging than gait and therefore more relevant to clinical decision making about progressing to sporting maneuvers.

To date, 6 ACL deficient (ACLD) (5 males, 1 female; mass=88±22 kg; height=1.78±0.11 m; age=35±11 years), 5 ACL reconstructed (ACLR) (5 males; mass= 83±12 kg; height=1.74±0.07 m; age=29±10 years) and 5 controls (3 males, 2 females; mass= 72±13 kg; height=1.70±0.09 m; age=30±3 years) performed a SLS on the injured leg for the ACL injured participants and the dominant leg for the control group. Motion analysis was performed using a Vicon Nexus system and a Kistler force platform. Knee extension moments and angles were calculated using Vicon Nexus software.

The ACLD group had reduced peak flexion angles compared to ACLR and control groups (65±5, 77±7 and 82±9 degrees respectively). Peak extension moments were similar across all groups (ACLD= 0.94±0.26 Nm/kg, ACLR=1.06±0.37 Nm/kg, control=1.04±0.36 Nm/kg). Peak knee moments occurred just after peak flexion and therefore at a smaller flexion angle for the ACLD group compared to the ACLR and control group (59±13, 75±7 and 80±6 degrees). Extension moments were similar when evaluated at a consistent angle of 50 degrees (ACLD=0.70±0.30Nm/kg, ACLR=0.63±0.34Nm/kg control=0.61±0.32Nm/kg).

In this sample, the controls squatted deepest followed by the ACLR group, with the ACLD group squatting least deep. This did not translate to an identical pattern for the knee extensor moments. Performance of ACL injured individuals needs to be evaluated on more challenging tasks to fully assess recovery. Further research, with more subjects, will clarify if ACLD individuals are using a strategy to protect their knee or if others factors are preventing them from squatting deeper. This would suggest that these individuals may not have fully recovered and will not be able to perform more challenging activities

ACL injured patients show variability in the ability to perform functional activities (Button et al., 2006). It is unknown whether this is due to differences in physical capability or whether fear of re-injury plays a role. Fear of re-injury is not commonly addressed in rehabilitation. This study aimed to investigate whether fear of re-injury impacts rehabilitation of ACL injured patients.

An initial group of five ACL reconstructed participants (ACLR, age: 30±11 years, weight: 815±115 N, height: 1.74±0.07 m, all male), five ACL deficient participants (ACLD, age: 31±12 years, weight: 833±227 N, height: 1.80±0.11 m, four male and one female), and five healthy controls (age: 30±3 years, weight: 704±126 N, height: 1.70±0.09 m, three male and two female) were compared. Fear of re-injury was assessed using the Tampa Scale for Kinesiophobia (Kvist, 2004). Quadriceps strength was measured on a Biodex dynamometer. Functional activity was assessed by a single legged maximum distance hop (on the injured leg for ACL patients). Motion analysis was performed with a VICON system, and a Kistler force plate. Hop distance was calculated using the ankle position. The peak knee extension moment during landing, and the knee angle at this peak moment were calculated in VICON Nexus.

The ACLD group scored worse on the Tampa scale for Kinesiophobia than the ACLR group (32±4 and 26±4). The ACLD patients did not hop as far as the ACLR and control groups (1.0±0.3, 1.3±0.1 and 1.4±0.3 m). The peak knee extension moments during landing were lowest in the ACLD group (263±159 Nm), slightly higher in the control group (354±122 Nm) and highest in the ACLR group (490±222 Nm), while knee flexion angles at these moments were similar (ACLD: 28±11, ACLR: 33±7 and control: 36±13 degrees). The ACLD group had weaker quadriceps than the control group, while the ACLR group was stronger (143±44 Nm, 152±42, and 167±50 Nm respectively).

Fear of re-injury and decreased quadriceps strength potentially both impact on the functional performance of ACL injured patients. Rehabilitation of ACL injured patients could therefore be improved by addressing strength and fear of re-injury. Future research with more participants will further clarify this.