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Stensdotter A-K1, Tengman E2, Häger C2
1Norwegian University of Science and Technology, NTNU, Neuromedicine and Movement Science, Trondheim, Norway, 2Umeå University, Community Medicine and Rehabilitation, Section for Physiotherapy, Umeå, Sweden
Background: A knee injury is seldom a problem isolated to the knee but may have consequences for the whole body. Movement strategies obviously differ depending on the task and there may be several reasons for altered strategies. Injury to the anterior cruciate ligament (ACL) often affects joint position sense, mechanic joint stability, motor control, and muscle strength. In earlier studies we have found that, >20 years after ACL injury, strength and balance are reduced, the latter even bilaterally, and that forward lean is increased in hop-landings with decreased knee and hip flexion. The injured leg is generally more affected. In the present study, we addressed movement strategies in squats standing on both legs.
Purpose: To determine if detailed motion analysis of bilateral squats discriminates between ACL injured persons in the long term post-injury and controls without knee injury.
Methods: 70 individuals who had unilateral ACL injury >20 years ago (33 with ACL reconstruction =ACLR and 37 without =ACLPT) and 33 matched healthy controls (mean age 46 ±5.3) were instructed to perform 10 consecutive squats to minimum 80o. Whole body 3D kinematics were captured with 8 high-speed cameras (240 Hz, Oqus, Qualisys®). At 80o knee-flexion angle, upper body forward lean was determined relative to space and knee-joint moment estimated using inverted dynamics. Weight distribution was calculated from the projection of center of mass relative (%) to the midpoint between the ankles at 0o and 80o knee-angle. Squat depth was calculated as the minimum height of the sacrum marker from the floor relative to position in standing (%).
Results: Forward lean of the upper body was similar across groups at 80o knee-flexion angle, Knee-joint moment at this angle was also comparable across groups. Compared to controls, squat depth was less in ACLPT (p=.022), whereas no difference was found for ACLR. For weight distribution, 65% in ACLPT and 75% in ACLR favored the uninjured leg at 0o by mean 9 and 5%, respectively. At 80o knee flexion, some switched sides, but in general the same percentages were true at this angle. In the control-group, 73% favored the right and dominant side by mean 5%.
Conclusion(s): Bilateral squats may only partly discriminate between ACL injured persons in the long term post-injury and controls. Nonetheless, ACLPT displayed inferior performance with regard to squat depth. Increased forward lean to reduce torque across the knee-joint and compensate for quadriceps weakness was not found in anyone of the ACL-groups as an expected compensation for muscle weakness. Favoring of the uninjured side was similar between ACL-groups and similar to favoring of the dominant side in the control-group, i.e., all groups favored the “safer” side.
Implications: Inferior performance in ACLPT many years post-injury needs further attention. Notably, allocation to surgery was not randomized. Lower performance in ACLPT may thus be due to several factors such as mechanic knee instability, reduced strength, motor control, and joint position sense, or movement fear. Bilateral squats may not discriminate ACL-injured form non-injured persons, but rather reveal functional level.
Keywords: Compensation, knee, ACL
Funding acknowledgements: Swedish Scientific Research Council; Västerbotten county council; Swedish National Centre for Research in Sports, Ingabritt & Arne Lundbergs research foundation
Purpose: To determine if detailed motion analysis of bilateral squats discriminates between ACL injured persons in the long term post-injury and controls without knee injury.
Methods: 70 individuals who had unilateral ACL injury >20 years ago (33 with ACL reconstruction =ACLR and 37 without =ACLPT) and 33 matched healthy controls (mean age 46 ±5.3) were instructed to perform 10 consecutive squats to minimum 80o. Whole body 3D kinematics were captured with 8 high-speed cameras (240 Hz, Oqus, Qualisys®). At 80o knee-flexion angle, upper body forward lean was determined relative to space and knee-joint moment estimated using inverted dynamics. Weight distribution was calculated from the projection of center of mass relative (%) to the midpoint between the ankles at 0o and 80o knee-angle. Squat depth was calculated as the minimum height of the sacrum marker from the floor relative to position in standing (%).
Results: Forward lean of the upper body was similar across groups at 80o knee-flexion angle, Knee-joint moment at this angle was also comparable across groups. Compared to controls, squat depth was less in ACLPT (p=.022), whereas no difference was found for ACLR. For weight distribution, 65% in ACLPT and 75% in ACLR favored the uninjured leg at 0o by mean 9 and 5%, respectively. At 80o knee flexion, some switched sides, but in general the same percentages were true at this angle. In the control-group, 73% favored the right and dominant side by mean 5%.
Conclusion(s): Bilateral squats may only partly discriminate between ACL injured persons in the long term post-injury and controls. Nonetheless, ACLPT displayed inferior performance with regard to squat depth. Increased forward lean to reduce torque across the knee-joint and compensate for quadriceps weakness was not found in anyone of the ACL-groups as an expected compensation for muscle weakness. Favoring of the uninjured side was similar between ACL-groups and similar to favoring of the dominant side in the control-group, i.e., all groups favored the “safer” side.
Implications: Inferior performance in ACLPT many years post-injury needs further attention. Notably, allocation to surgery was not randomized. Lower performance in ACLPT may thus be due to several factors such as mechanic knee instability, reduced strength, motor control, and joint position sense, or movement fear. Bilateral squats may not discriminate ACL-injured form non-injured persons, but rather reveal functional level.
Keywords: Compensation, knee, ACL
Funding acknowledgements: Swedish Scientific Research Council; Västerbotten county council; Swedish National Centre for Research in Sports, Ingabritt & Arne Lundbergs research foundation
Topic: Musculoskeletal: lower limb; Musculoskeletal
Ethics approval required: Yes
Institution: Umeå University
Ethics committee: Regional Ethical Review Board
Ethics number: dnr 08-211M
All authors, affiliations and abstracts have been published as submitted.
