Commentaries to Accompany
Patients who undergo total knee arthroplasty (TKA) experience what is arguably the most quadriceps strength loss of any cohort of people who have had a knee injury or surgery. Much of the research surrounding TKA has focused on topics such as pain relief, knee range of motion, and prosthesis longevity. Investigating quadriceps central activation deficits (CAD) and quantifying patients’ functional performance after surgery is a relatively new, but burgeoning, field of study. Given the important relationship between muscle strength and function in patients who have TKA, the comprehensive and directed review by Drs. Thomas and Stevens-Lapsley (11) in this issue of Exercise and Sport Sciences Reviews is a timely and useful summary of the sparse existing literature.
Their plea for further research related to the etiology of quadriceps CAD after TKA is an appropriate point of emphasis in their review. For instance, the usual suspects of pain and knee effusion appear to play an unexpectedly limited role in influencing quadriceps CAD after TKA. At 1 month after TKA, when quadriceps CAD are substantial, the relationship between knee pain and activation failure is small (6,7,10). There does appear to be some relationship between knee pain during contraction and the degree of CAD, but nearly half of the patients with TKA did not report experiencing knee pain during strength assessments (7). Thus, the absence of knee pain with quadriceps contraction does not equate to an absence of activation failure.
As the review aptly states, acute and pain-free knee effusions consistently induce quadriceps CAD in healthy volunteers, but the influence of chronic effusion and CAD is not as clearly established (4). The potential impact the iatrogenic damage to the joint capsule during surgery could have on intraarticular fluid pressure is unknown. The few reports that attempt to quantify knee swelling use volumetric or circumferential girth measures. These clinical measures do not discern the change of intracapsular versus extracapsular fluid. Currently, there is one published report that found a moderate relationship with acute increases in knee girth and quadriceps strength loss as patients were discharged from the hospital (3).
Although causal data for quadriceps CAD are limited, the study of how interventions can influence CAD is especially rare (8). In fact, the findings from a 2003 National Institutes of Health consensus conference on TKA stated that “there is no evidence supporting the generalized use of any specific preoperative or postoperative rehabilitation intervention” (8). Drs. Thomas and Stevens-Lapsley (11) present excellent cases for the utilization of high-intensity neuromuscular electrical stimulation (NMES) and early progressive strengthening exercise as both appear to positively impact muscle strength and CAD in a way that enhances patients’ functional mobility. I believe that their work will help shape the standard of practice for postoperative care.
As TKA surgery can have a considerable negative impact on quadriceps muscle strength, it is appropriate to discuss the potential impact of less invasive surgical approaches. The review provides a high-quality summary of some of the risks versus gains of a minimally invasive TKA surgery technique. Another important consideration when discussing the potential impact of surgery on the soft tissues around the knee is the timing of when to use TKA for people with advanced knee osteoarthritis. There is evidence to suggest that patients often wait too late in the disease process to maximize the gains made with knee replacement (2). The best solution against difficulties in quadriceps muscle function and limited patient mobility may be to undergo surgical intervention before the precipitous declines observed in the late phases of osteoarthritis.
It is worth noting that even with the considerable gains made with progressive strengthening and high-intensity NMES cited in the review by Thomas and Stevens-Lapsley (11), quadriceps CAD were not completely resolved back to normal levels (i.e., central activation close to ≥95%). Patients also exhibit a relatively small quadriceps cross-sectional area in long-term testing. Other options to consider when mitigating CAD are the use of biofeedback tools to increase muscle force output or enhancing volitional recruitment during exercise (1). Cryotherapy is another potential adjunct that has had some success in addressing experimentally induced quadriceps CAD (9). Also, the use of eccentric exercises that produce a high muscle tension with relatively low muscle recruitment could be another path to accelerated strength gains (5). Continued efforts to study ways to enhance quadriceps strength gains while considering the presence of large CAD will have important implications in helping patients achieve results with TKA that go beyond the typical benchmark of achieving good pain relief.
Ryan L. Mizner
School of Physical Therapy and Rehabilitation Science
University of Montana
The author reports no conflicts of interest.
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