Sports Medicine Research: In the Lab & In the Field: Improving Ankle Range of Motion may be a Key Factor in Reducing ACL Injuries (Sports Med Res)
Monday, February 14, 2011

Improving Ankle Range of Motion may be a Key Factor in Reducing ACL Injuries

Ankle-Dorsiflexion Range of Motion and Landing Biomechanics

Chun-Man Fong, LAT, ATC; J. Troy Blackburn, PhD, ATC; Marc F. Norcross, MA, ATC; Melanie McGrath, PhD, ATC; Darin A. Padua, PhD, ATC

Anterior Cruciate Ligament (ACL) injuries account for a large portion of athletic knee injuries. Although the ACL can be repaired arthroscopically and some patients can resume sporting activities without surgery, this injury has been reported to lead to symptomatic osteoarthritis within a few years of the injury. Therefore, preventative strategies to reduce the incidence of ACL injury are exceptionally important at preserving the integrity of the knee joint. ACL ruptures often occur during landing or jump-landing motions when the athlete assumes a dynamic valgus position of the knee joint. Inability to absorb the shock during landing (by flexing the knee) can increase this abnormal valgus motion and also increase the rate and magnitude of the ground reaction force. One limiting factor in knee flexion and shock absorption during landing is ankle dorsiflexion range of motion. It has been suggested that reduced ankle dorsiflexion is related to reduced knee flexion during landing, although no study has evaluated the relationship between goniometric measures of ankle motion and landing biomechanics. In other words, we don’t know if patients with less passive dorsiflexion will land with a greater loading rate and less knee flexion which was the objective of the study. Thirty-five healthy and physically active volunteers were tested in the descriptive laboratory study. Passive dorsiflexion was measured with the knee in an extended and semi-flexed position and this value was compared to knee flexion, knee valgus, vertical ground reaction force and posterior ground reaction force upon landing from a 30 cm height using correlational analysis. The authors found that reduced dorsiflexion range of motion was associated with reduced knee flexion displacement during landing and greater ground reaction forces, potentially setting the stage for an ACL injury.

This is an important finding and these authors were the first to report a direct correlation between passive ankle motion and landing mechanics that are linked to ACL injury. Ankle dorsiflexion can be improved by a variety of stretching techniques, so this may be an easy way to reduce the chance of ACL injury in patients with reduced ankle motion. This paper sets the stage for future research. It would be ideal if future researchers evaluated if ACL injuries are more prevalent in athletes with reduced dorsiflexion or if simple stretching programs can reduce the incidence of ACL injury in high risk athletes. Although more research is required to answer these important clinical questions, the fact that “the foot bone is connected to knee bone” lets us know that we may need to look beyond just the knee when we are trying to reduce the chance of ACL injuries.

Written by Joseph Zeni, Jr PT PhD
Reviewed by Stephen Thomas, PhD ATC


Andrew Lynch, PT said...

Nice post (much more interesting than the shoulder).

A limitation in ankle dorsiflexion also theoretically makes sense in the non-contact, plant/pivot mechanism of injury. As the athlete attempts to change direction, the foot is planted and the cutting limb must absorb all of the weight of the body and create propulsion in the opposite limb. In an ankle with normal range of motion, more absorption can occur in the gastroc/soleus, whereas, in a stiff ankle, forces are translated more rapidly to the knee joint, potentially contributing to the injury mechanism.

It would be very interesting to see how limited dorsiflexion can change the mechanics of a run/cut task at the knee joint.

Christian Marks, MS, ATC, CSCS said...

I, also, have to admit this was a much easier read than the recent post about shoulder ROM and special tests; however, I enjoyed that one too. When I imagine all these subjects performing their landing tasks and seeing knee flexion increase with dorsiflexion I'm not terribly surprised. If a foot remains flat on the ground, and the ankle bends forward, surely the knee must flex more to keep the body's center of mass over its base of support. It seems that, once a foot is flat on the ground, that you're left with a spectrum of sagittal plane force absorption styles characterized by its poles: a stiff-legged landing in which both the ankle and knee have minimal flexion displacements, and a "soft" landing in which both the ankle and knee have large flexion displacements.

A (very) quick search on patellofemoral pain and ankle dorsiflexion returns some intersting abstracts that report greater ankle dorsiflexion in subjects with PFPS than in those without it ( ... If we bring this back to imagining our subjects in this landing task. We might begin to suspect that as one progresses further toward the "soft" landing strategy his risk for PFPS may increase. If this is so, it may be due to a strong activation of the quadriceps while the patella is in a more inferior position due the increased knee flexion.

The end take-away from this reasoning is that you may be able to help identify two "at risk" populations with dorsiflexion as one of your measurements. The first would be a population that would be at risk for an ACL tear in an uncontrolled landing that is characterized by a "stiff" (reduced flexion force absorption) landing strategy in which forces in the knee act strongly on the ACL. The second would be a population that may be at risk for PFPS from repeated uncontrolled landings characterd by a "soft" (increased flexion force absoption) landing strategy in which forces in the knee cause an increased or abnormal compression of the patellofemoral space.

Jeffrey B. Driban, PhD, ATC, CSCS said...

It's great to see that this article is fostering some discussion. There are some really good points that were brought up in the post and the comments and I just wanted to throw in my two cents. I think that we need to keep in mind when the studies are measuring dorsiflexion, what activities the participants were asked to perform (walking, running, jumping, etc), or what their sport/physical activity is (running versus landing intensive sports). I think when a person has limited passive dorsiflexion (as assessed via goniometry) then the participant will adapt two potential landing strategies 1) increased knee flexion (to compensate for the ankle), or 2) decreased knee flexion (because their landing strategy is a stiff landing). We should be a bit cautious with this study though because we don't know for sure how much dorsiflexion was used during the landing (I could have a lot of passive dorsiflexion but use very little of that range of motion when I land). Therefore, in the current study it would have been interesting to see the amount of plantar/dorsiflexion that occurred during the landing.

In contrast to this study, when the ankle is measured during an active closed chain task (for example, landing) increased ankle dorsiflexion is probably indicating that the knee is translating forward relative to the foot and therefore increasing the contact pressure on the patella.

The other thing that I think we also sometimes need to keep in mind is that when we start talking about changing a person's biomechanics we could possibly be changing a movement pattern that they have adapted over 1000s of repetitions and maybe optimal for that person even though it's not normal.

Thanks for the great discussion thus far. I'm curious to hear more responses to the posts and comments.

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