Injuries to the passive stabilizers of a joint (ligaments, meniscus, joint capsule, etc) can lead to mechanical instability. Surgery can be utilized to restore deficits in mechanical stability, but does not necessarily correct impairments of the sensory system, including proprioception. Failure to address such changes may increase one’s risk of suffering a future injury.
In the knee, for instance, injury of the anterior cruciate ligament (ACL) can be treated via surgical reconstruction. While this operation restores mechanical stability, disturbances in proprioception and postural control have been shown to persist without appropriate rehabilitation.
Postural control is commonly measured while an individual stands on one leg. While this test is useful, it does not simulate more complex tasks that are encountered throughout the day. For this reason, the authors of the first study below used a single-leg squat to assess dynamic postural control and performance.
Interestingly, postural control deficits were observed in the injured and uninjured limbs (a good reason to make sure to train both sides during the rehabilitation process). Furthermore, the second study showed that the total number of repetitions that could be completed predicted who would develop knee osteoarthritis.
Whether you are recovering from a knee injury or looking to reduce your risk of suffering one, consider adding a simple single-leg squat exercise to your program. Being able to perform >22 repetitions may help reduce your risk of suffering an injury or developing arthritis later in life.
It should also be noted that they only squatted to 60 degrees of knee flexion in these studies. To perform this on your own, find a chair or other surface that contacts the back of your leg just above the fold of your knee. From here, squat slowly on one leg until your butt contacts the surface and then return to the start position (see image below). See how many you can do!
Culvenor AG, et al. Dynamic Single-Leg Postural Control Is Impaired Bilaterally Following Anterior Cruciate Ligament Reconstruction: Implications for Reinjury Risk. J Orthop Sports Phys Ther. 2016.
Thorstensson CA, et al. Reduced functional performance in the lower extremity predicted radiographic knee osteoarthritis five years later. Ann Rheum Dis. 2004.