For those who know me well, it is safe to say I am an “ACL geek” of sorts.  I love studying, reading and searching for the best way to rehab and prevent these injuries.  As I have grown in the profession, I have become increasingly concerned with articular cartilage damage and the long term effects it has on our young athletes.

Perhaps I am getting more concerned as my knees aren’t getting any younger either (lol).  Anyway, I truly believe we often underestimate how deleterious cartilage injuries can be long term.  In addition, I feel we, as rehab and conditioning professionals, need to better understand how our training impacts the cartilage regardless of whether patients had a concomitant bone bruise with their ACL injury or not.

One of my favorite prehab exercises is a single leg hop and stick (see below)


I typically begin with an alternate leg approach (push off right and land on left) prior to initiating takeoff and landing on the same leg to teach proper landing mechanics.  By now, we know increasing hip and knee flexion, as well as shifting center of mass forward reduces ACL strain and injury risk through a diminished extension moment.

However, what we may not know as much about is how an ACL reconstruction alters tibiofemoral joint mechanics at such a landing.   I want to share some interesting information from a recent article in the September edition of The American Journal of Sports Medicine.  The article by Deneweth et al. looked at tibiofemoral joint kinematics of the ACL reconstructed knee during a single-legged hop landing.

In the study, the authors used high speed biplane radiography to quantify 3D tibiofemoral joint kinematics in 9 subjects who underwent ACL reconstruction.  Graft choices included single bundle (2) and double bundle (5)  hamstring autografts as well as double bundle allografts (2).  All subjects completed a standard rehab protocol and then were tested between 4 and 5 months post-op.

The single leg hop testing consisted of three trials (on each leg) in which the subject was required to hop over a 4 cm barrier and land at a distance 30 cm forward of the takeoff point.  Upon landing, the subjects were coached to hold the position as long as possible.  And now for the results:

  • The reconstructed limb was significantly less flexed at initial contact
  • Maximum knee flexion was significantly less on the reconstructed side
  • The reconstructed leg was significantly more adducted throughout the landing phase, but not significant at initial contact or at maximum angles
  • The surgical side was more externally rotated both at initial contact and and at maximum internal-external rotation
  • There was no significant differences between the single and double bundle approach (some argue that a double bundle approach more closely approximates the native ACL and improves rotational stability – keep in mind though that this is a very small sample size here)
  • The reconstructed knee experienced  a larger anterior tibial translation by an average of 1.52 plus/minus 1.55 mm

So, what does it all mean?  Well, in a nutshell the study indicates that significant kinematic differences exist for athletes who have been cleared to return to play by their physicians.  Athletes will perform activities in sport like the single-legged hop to decelerate and change direction.  It is known that landing in a more extended position at impact will subject the articular cartilage to much higher compressive loads than would normally be felt in the more flexed uninjured knee.

In medical circles, it has been suggested that ACL tears need to be fixed to prevent early arthritis in the knee.  However, a recent study in the November American Journal of Sports Medicine suggests in a 10 and 15 year follow-up after ACL reconstruction for isolated and combined injuries that both groups still develop arthritis radiographically (combined injuries more so than isolated tears).  So, perhaps not all ACL tears need fixed?

So, I think we still have much to learn about how best to treat those with these injuries and how to carefully manage the rehab, return to play and surgical strategies to best preserve articular cartilage and sustain a high quality of life well beyond athletics.  In addition, this article highlights the importance of repetitve neuromuscular training in prehab and rehab with emphasis on increasing knee and hip flexion angles with deceleration, as well as perhaps giving us pause at sending our athletes back to high impact loading too quickly.

As with all research, we must also be careful not to extrapolate the results of one study to all cases, but I myself think we need to keep learning and critically evaluating our loading progressions with respect to the cartilage/joint and strive to avoid creating harm too soon in the rehab process.  I hope you will join me in seeking out the very best rehab and conditioning techniques for our athletes in this light moving forward.