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  • Writer's pictureKristen Huber

It's All in the Knees

Updated: Apr 1, 2022

As a practitioner who has worked with everyone from college level athletes to volunteer firefighters to hikers, when it comes to the knee it seems that the most feared injury is a full thickness ACL sprain.

The ACL, or anterior cruciate ligament functions to prevent the tibia (lower leg bone) from sliding forwards beneath the femur (thigh bone). This ligament also assists in preventing anteromedial translation of the bone, meaning it aids in some rotational stability at the inside portion of the knee joint. Something we commonly see with full thickness ACL sprains, is a sensation of giving out or the knee actually giving out when exposed to a twisting force. Being that I live in Canada and experience a balmy 8 months of winter each year, another common occurrence for clients is "tweaking" the knee joint, and twisting it when they step on ice. Getting into the car on an icy surface seems to pose an issue as well.

Although we can classify the knee as a hinge joint that can flex and extend, we do see rotation at the knee as well. If the knee is in a position of 30-90 degrees of flexion, we can expect to see about 45 degrees of external tibial rotation, and 25 degrees of internal tibial rotation in a healthy joint. For every plane of movement at a joint, we have structures that function to oppose such movement. So if the ACL is there to prevent anterior movement, why are there so many issues with rotational stability following an ACL injury? The easy answer, is that the mechanism of injury responsible for an ACL sprain, typically a "plant and rotate", also damages smaller, lesser discussed ligaments responsible for the opposition of rotation at the knee.

A 2013 study surrounding the prevalence of rotational stability issues following acute ACL ruptures also noted that many surgeons struggle with correcting these issues even after surgery. And the reason for this is simple. A corrective ACL surgery, whether it is cadaver tissue, hamstring graft or patellar tendon graft, if it is single or double bundle, corrects only the lack of ACL. It does not repair damage to the other intracapsular soft tissue structures impacted at the time of injury. Researchers in this study utilized cadaver knee joints to test rotational instability, as it is impossible to know whether the ACL was the only tissue damaged within the knee in a living subject. For their purposes, researchers took intact cadaver knees, and cut only the ACL tissue. They then utilized the pivot shift test for assessing anterior tibial glide and rotation to assess perceived instability.

When I learned to perform a pivot shift test in school, we were always told that a positive test would show a subluxation of the tibia on the femur as we moved an internally rotated limb from full extension into flexion. In layman's terms, we were looking to see the tibia pop forward as we moved the leg. We also learned that after the Lachmann's test for anterior translation, the pivot shift was the next gold standard for determining damage to the ACL. I have in fact observed several positive pivot shifts that displayed a clunking anterior subluxation of the tibia. And until recently, all I ever thought was "ACL rupture". In the aforementioned study, researchers observed that in performing a pivot shift on 10 knees where only the ACL was cut, three joints showed a glide, seven showed a "jerk" and none displayed a subluxation of the tibia. This implies that rotational stability deficits may be more closely related to other structures such as the coronary meniscal ligaments or the anterolateral femoral tibial ligament which may be stretched or torn during an acute traumatic event.

So if ACL surgery won't correct rotational instability at the knee, what do we do next? If we look at the many research articles online, we will be told to strengthen the quadriceps, hamstrings and calf muscles. We will also be told to apply perturbations (random external force) to the client in a weight bearing position to improve awareness of safe joint positioning. To my surprise, no studies that I read indicated that it is important to strengthen rotation specifically. Yes, the different segments of the hamstrings contract in specific ways to initiate rotation, and yes many of the rehab programs I read specified hamstring strengthening with the leg in a rotated position. But if we don't specifically train rotation, how are we to expect our client's knee to magically improve in terms of rotational stability? Not to mention that rotation occurs from the hip when the knee is in full extension, so really what are we training by doing a hamstring curl? Probably not the action of tibial rotation.

Of course, isolating tibial rotation can be difficult. The compensation that I typically see, is inversion and eversion of the ankle in an open chain, because tibial rotation is so minute that people often do not understand what it feels like to isolate this movement. When I am giving clients an exercise for tibial rotation strengthening (and when I say strengthening I really mean controlling the joint through a range of movement), we start with a flat foot on top of a towel, a stabilized thigh, and small isolated rotations. Once we establish the appropriate neuromuscular connections and proprioceptive abilities, we can move to an open chain movement utilizing resistance bands. From here, what we really want to move towards are agility type movements such as clock hops, progressing from double to single leg. Although this motion does not directly isolate rotation, the knee, hip and ankle are required to respond to rotational forces and surrounding muscles must compensate accordingly.

When it all comes down to it, if you have an ACL injury you may have very slight rotational instability, or it may be major. In the case of notable instability, you likely will not see great amounts of improvement immediately after surgery. This being said, with a solid rehab plan and focus on the basics, as well as introduction of exercises specific to tibial rotation, we can always improve stability. It is important to keep in mind that following a traumatic injury, we always have a lot of work to do to train muscles to compensate for ligamentous laxity, to regain joint awareness and to rebuild neuromuscular information pathways. It may take time, but by putting in the work with your physical therapy journey there is endless possibility for improvement.

Kristen Huber BaKin, CAT(C)

Owner, The Gentle Athletic Therapist


A. Ferretti., E. Monaco., & A. Vadala. (2013). Rotatory instability of the knee after ACL tear and reconstruction. Journal of Orthopaedics and Traumatology, 15(2): 75–79. doi: 10.1007/s10195-013-0254-y

J.B. Lunden, et al. (2010). Current concepts in the recognition and treatment of posterolateral corner injuries of the knee. Journal of Orthopaedic & Sports Physical Therapy, 40(8): 502-516.

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