Using the DXA to Determine Return to Play Following ACL Surgery

A doctoral student in my laboratory is completing a study in females that have undergone anterior cruciate ligament (ACL) surgery. As part of the study, we have been examining the changes in regional composition that occur in the surgically repaired leg as well as the contra-lateral non-surgical leg following 4 and 6 months of post-surgical rehabilitation

This study has piqued my interest in the changes that occur with ACL surgery and the effect of the rehabilitation process on the composition of both legs. Recently, we scanned an athlete about 6 months before they tore their ACL and had to undergo ACL repair surgery. We just scanned this same athlete about 4 months after ACL surgery.  At the time of the second dual X-ray absorptiometry (DXA) scan, the athlete was still undergoing rehabilitation and had not returned to any type of sports training.  In the table below, I have presented the DXA data pre- and 4-months post ACL surgery.

DXA Scans
Below you see the pre-surgical and 4-month post-surgical DXA scans of our individual. If you look at the 4-month post-surgical DXA scan, you can see the metal screws on the left leg (red box) that were inserted to hold the graft in place.

Changes in regional composition before and 4 months following ACL surgery
Now let us look at the data from these two scans. The table below provides the regional composition data for both the non-surgical (right) and surgically repaired (left) leg before surgery and 4 months post-surgery. What is interesting is the change in total mass between the two legs. Both legs have undergone changes - the non-surgical (right) leg gained 762 grams (1.68 lbs.) of total mass while the surgical (left) leg lost 331 grams (0.73 lbs.) of total mass. What is interesting is that as expected the surgical leg lost lean muscle mass (637 grams or 1.40 lbs.), while the non-surgical leg gained lean muscle mass (414 grams or 0.91 lbs.).  The gain in lean muscle mass in the non-surgical leg is probably due to the extra weight bearing required of the leg following surgery. Also interesting is the fact that both legs also lost bone mineral content (surgically repaired leg 25 grams [0.06 lbs.]; non-surgical leg 15 grams [0.03 lbs.]). That corresponds to a loss in bone mineral density (BMD) of 0.032 g/cm2 in the surgical (left) leg and 0.054 g/cm2 in the non-surgical leg. Another interesting point is that both legs gained similar amounts of fat mass (@350 grams [0.77 lbs.]). The result of this change in fat mass is the surgically repaired (left) leg has a 4.3% change in fat composition while the non-surgical leg (right) had a gain of 1.1% percent fat. This table clearly illustrates the changes that have occurred in leg composition in this athlete.

Take Home Message
There are a couple of things to take away from these two DXA scans.  The first is that the changes in leg composition that have occurred in this individual are easily evident with the DXA scan.  Not only do we see changes in the surgically repaired leg, which would be expected, but we also see changes in the contralateral non-surgical leg that did not undergo surgery.  The second is the potential to use the DXA in helping to monitor recovery from surgery and, possibly, in determining when it would be safe for this individual to return to training and competition. If an individual has a scan prior to injury, it may be effective to use as a baseline scan to monitor recovery. DXA makes it easy to track the loss of muscle and, hopefully, the return of muscle mass as the athlete works through rehabilitation.  Even if there was not a recent pre-injury scan, it is worth considering whether scanning the individual prior to surgery would be useful to monitor recovery and influence a decision to return to competition. It is an interesting idea and one that I think deserves further discussion. I hope this blog has given you some things to think about regarding the use of DXA in the monitoring of athletes’ recovery from surgery. 

About the Author: Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.

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