Physical Therapy and EMS: Restores Activation, Strength 1 Year Post TKA

”The use of neuromuscular electrical stimulation to improve activation deficits in a patient with chronic quadriceps strength impairments following total knee arthroplasty. Journal of Orthopaedic & Sports Physical Therapy. 2006 Sep;36(9):678-85.”

This was a single-patient case study of a patient who had high level function but persistent quadriceps weakness and activation deficits 13.5 months post op.

Treatment consisted of reasonably aggressive unilateral leg strengthening with an emphasis on quadriceps for 6 weeks. On the weaker of his quadriceps they also did electric muscle stimulation with 2 electrodes, 2500 Hz, sinusoidal alternating waveform current at a burst rate of 75 bursts with intensity to the patients maximum tolerance, 10 seconds on and 80 seconds off, 3 times per week prior to doing his resistance training.

The addition of the electric stimulation was pretty effective, as the authors put it:

“The patient was a 62-year-old male cyclist 12 months following simultaneous, bilateral TKA with impairments in left quadriceps strength and volitional muscle activation. His left quadriceps strength was 26% weaker than his right and central activation ratio (CAR) of his left quadriceps was 13% lower than his right quadriceps CAR. NMES to the left quadriceps was implemented for 6 weeks, in addition to an intense volitional weight-training program with emphasis on unilateral lower extremity exercises.”

“The patient demonstrated a 25% improvement in left quadriceps femoris maximal volitional force output following 16 treatments of combined NMES and volitional strength training over a 6-week period. The patient’s volitional muscle activation improved from a CAR of 0.83 before treatment to 0.97 after treatment. At discharge from physical therapy and at his 18-month postoperative follow-up, the patient’s left quadriceps strength was only 4% lower than his right quadriceps strength. At the 24-month follow-up, the patient’s left quadriceps strength was 6% stronger than his right quadriceps strength.”

“The patient was able to achieve symmetrical quadriceps strength and complete muscle activation following 6 weeks of NMES and volitional strength training. An intense strengthening program may have the potential to reverse persistent strength-related impairments following TKA.”

“Aggressive strength training at 75% of 1-repetition maximum can increase force-generating capacity and induce muscle hypertrophy. However weakness combined with activation deficits presents even greater challenges. If a muscle can not be activated to its full potential it can be argued that strengthening solely through volitional exercise will not be sufficient to overload the muscle and enhance strength”

Chad’s comments:

The latter paragraph says a lot. In addition to the primary findings of the report, the introduction discussed other studies that noted failure to restore lower extremity strength may lead to an emergence or progression of symptomatic osteoarthritis in other joints. The next most likely joint replacement being the other knee, the other hip, and finally the same hip as the original knee replacement. One might conclude that such progression on the contralateral (other) leg was because it was taking on an increased burden during activities of daily living, picking up the slack from the replaced knee that remained weak. Only after the contralateral leg was weakened from its joint replacement would the ipsilateral (same side) hip require replacement. All of this may be prevented by fully restoring strength to the originally replaced side from the start.

While it would have been ideal to get the patient started with more aggressive strengthening and EMS as early as possible, this study was able to show substantial progress over a year post op which has not been researched in any of the other EMS/TKA studies.

The researches used only one channel/2 electrodes on the subjects quadriceps.   They used large electrodes making the electric stimulation more comfortable. However, in my experience they would have had even greater recovery if they had placed 4 electrodes on the quadricep to recruit a greater number of nerves and subsequent muscle fibers. The additional channel on the same quadriceps doubles the muscle fiber recruitment without the increase in discomfort you would get from further increases in current intensity. Also, if the EMS machine has additional channels you might as well put 4 electrodes on the hamstrings as well, or any other muscle that tests as relatively weak.  On most good EMS units those additional channels are there, so it seems a shame not to use them.

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Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.

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