Development of Dynamic Knee Stability after Acute ACL Injury
Development of Dynamic Knee Stability after Acute ACL Injury
Abstract & Commentary
Synopsis: By using a pertubation training regimen, Chmielewski and colleagues were able to alter muscle contraction patterns in a way beneficial to coping with an ACL-deficient knee.
Source: Chmielewski TL, et al. Development of dynamic knee stability after acute ACL injury. J Electromyogr Kinesiol. 2002;12(4):267-274.
Acl-injured subjects who function at high levels are termed "copers."1 "Non-copers," who do not function well during high-level sports, demonstrate decreased knee motion and extensor moment, increased soleus activity, altered gastrocnemius and hamstring timing, and use significantly more co-contraction.
Chmielewski and colleagues state that no single muscle activation strategy has been determined to be optimal to produce dynamic knee stability (DNS) in all patients. Therefore, rehabilitation should involve activities that challenge knee stability. Chmielewski et al reference the force feed-back hypothesis: When perturbing force is applied to a joint, muscles that resist the perturbation are stretched and activated to resist that force. By using a perturbation training regimen, Fitzgerald et al2 were able to get a 93% return to high level with perturbation, strength, and agility training, compared to only 50% return to high level with strength and agility alone. The purpose of this present study was to determine if perturbation training predictably alters muscle activation patterns.
Chmielewski et al screened for those patients with "good potential for nonoperative management." They used a very small sample of 9 subjects (7 males, 2 females). Though they were all injured during athletics, it was not clear that they were currently involved in the same level of sport. The screening testing included objective quadriceps index (isometric quadriceps strength on the involved relative to the noninvolved side), timed 1-legged hop tests, subjective knee outcome survey-ADL scale (KOS-ADL), and global rating self-report of function questionnaire. Objective gait analysis with EMG, kinetic, and kinematic measures was also used.
Perturbations incorporated 3 basic exercises: rollerboard, rockerboard, and rollerboard with stationary platform. These exercises require that the subject either resists the force or regains balance. The protocol progressed from a focus on sagittal plane and predictable perturbations with verbal cues to random challenges in all planes of greater intensity. During the last 5 treatments, the perturbations were presented while subjects performed sport-specific tasks.
The quadriceps index and the mean timed hop were the same pre- vs post-training. KOS-ADL (92-97%) and global rating (84-94%) scores both significantly increased. Gait assessment demonstrated that the vastus lateralis (VL) integral EMG significantly increased after perturbation training, and the time to peak VL activity correlated to both soleus onset and the integrated EMG activity of the lateral hamstrings. These correlations didn’t exist before training or on the uninvolved side.
Comment by Timothy E. Hewett, PhD
This is a good study of the effects of conservative treatment on high-functioning patients with ACL deficiency. Chmielewski et al report that perturbation training in these high-functioning "copers" alters muscle activity in the affected limb. They recommend perturbation training in athletes who pass a screening examination that includes objective and subjective assessments. The study results are limited only to this high-functioning population. In addition, Chmielewski et al may have over-interpreted their findings in the discussion.
They carefully selected their study population, which might have led to a selection bias in their results. This fact and the small sample size make it difficult to generalize the applicability of the findings of this study. Five of the 9 patients went on to ACL reconstruction. It is a bit concerning that the objective scores didn’t change post-training but the subjective did (perhaps subjects were told the perturbation training was good for them). There was no control group to study this effect.
The integral of the quadriceps activity increased after training, though the quadriceps can destabilize the knee. Chmielewski et al explain this by pointing out that hamstrings and soleus activation predicted quadriceps activity. However, the data showing differences in the timing of muscle activity pre- and post-training are not very convincing. The amount of soleus and gastrocnemius activity did not increase, the changes in onset appear small, and they don’t appear to be altered much relative to quadriceps activity. Other questions include: Why did Chmielewski et al test EMG during gait? They didn’t train gait? Why not test while doing a more training-specific activity?
Non-copers may account for approximately two-thirds of the ACL-injured population and Chmielewski et al categorized them as similar to "quadriceps avoiders." Berchuck et al3 speculated that quadriceps avoidance was a positive adaptation. This paper says they are non-copers. This discrepancy is interesting and more research needs to be performed to determine if non-copers and quadriceps avoiders are truly one and the same.
I would recommend this study for those physicians who desire to keep their high-level athletes who suffer an ACL injury functioning through the remainder of their sports season in order that reconstruction can be deferred to the off-season.
Dr. Hewett is Director and Assistant Professor, The Sports Medicine Biodynamics Center, University of Cincinnati College of Medicine, Cincinnati, OH.
References
1. Snyder-Mackler L, et al. The relationship between passive joint laxity and functional outcome after anterior cruciate ligament injury. Am J Sports Med. 1997; 25(2):191-195.
2. Fitzgerald GK, et al. The efficacy of perturbation training in nonoperative anterior cruciate ligament rehabilitation programs for physical active individuals. Phys Ther. 2000;80(2):128-140.
3. Berchuck M, et al. Gait adaptations by patients who have a deficient anterior cruciate ligament. J Bone Joint Surg (Am). 1990;72(6):871-877.
Synopsis: By using a pertubation training regimen, Chmielewski and colleagues were able to alter muscle contraction patterns in a way beneficial to coping with an ACL-deficient knee.Subscribe Now for Access
You have reached your article limit for the month. We hope you found our articles both enjoyable and insightful. For information on new subscriptions, product trials, alternative billing arrangements or group and site discounts please call 800-688-2421. We look forward to having you as a long-term member of the Relias Media community.