Patellofemoral joint contact force peak and impulse are lower after ACL reconstruction
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Patients who underwent ACL reconstruction exhibited lower peak patellofemoral joint contact force in the reconstructed limb, according to published results.
Researchers compared patellofemoral joint (PFJ) contact force at 12 to 24 months after unilateral ACL reconstruction (ACLR) in ACLR limbs and uninjured limbs.
According to the study abstract, researchers analyzed kinematics and ground-reaction forces in 55 patients who underwent ACLR (mean age of 27 years) to determine joint moments and muscle forces. The values were then input into a PFL model to calculate force peak and impulse.
“The PFJ contact force peak and impulse during running at 12 to 24 months postoperatively were about 10% and 11% lower, respectively, in ACLR knees than uninjured knees,” the researchers wrote. “The magnitude of the knee extension moment at the time instant of the peak PFJ contact force was also lower in ACLR limbs,” the researchers wrote.
This could be explained “by a small anterior shift in the foot-ground center of pressure during stance that offloaded the torque demand away from the ACLR knee,” they added.
“Lower net PFJ loading during running in the ACLR limb more than 12 months after ACLR suggests that underloading might play a role in the onset of PFJ osteoarthritis after ACLR,” the researchers concluded.
Perspective
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William R. Post, MD
Biomechanical differences 12 to 24 months after hamstring tendon ACL reconstruction were small but significant resulting in less patellofemoral joint reaction force in the reconstructed knee. Reconstructed knees during running were not normal. This could be a result of the altered biomechanics of the ACL stability itself, hamstring harvest or sequelae of incomplete rehabilitation.
It would be interesting to see the same cohort studied in the future. Further time after surgery may improve joint homeostasis and function. They importantly note that they did not assess quadricep strength or level of fear during running in these patients, both of which might affect the results.
I agree with their experimental conclusion that the lower knee extension moment essentially shifted workload away from the reconstructed knee and distributed toward the hip and ankle joints. Their clinical conclusion that the lower patellofemoral loading during running noted at this intermediate timeframe plays a role in the onset of patellofemoral arthritis seems a bit of a reach but does not diminish the overall value of their study.
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