The following is another article written for the online, video-based physical therapy continuing education company MedBridge Education…
Following any type of surgery, significant weakness of the primary and secondary musculature is common. For example, quadriceps weakness has been documented during the immediate post-operative phase following surgery (Snyder-Mackler et al), as well as years following rehabilitation (Rosenberg et al). Additionally, patients who undergo Total Knee Arthroplasty (TKA) exhibit similar findings. According to Mizner et al and Stevens et al, quadriceps strength drops 50-60% of pre-operative levels one month following TKA, despite the initiation of rehabilitation within 48 hours of surgery. Following this trend, Rokito et al found external rotation deficits following rotator cuff repair of 79% and 90% at six months and one year, respectively. Considering the severity and chronicity of these strength deficits, more effective interventions are warranted to restore strength and improve long-term outcomes. One particular modality that has been shown to improve these deficits is neuromuscular electrical stimulation (NMES).
Kim et al recently published a systematic review investigating the utility of NMES following ACL reconstruction to improve quadriceps function and strength. In this review, which involved 8 randomized controlled trials (RCTs), it was demonstrated that NMES in conjunction with exercise, compared to exercise alone or in combination with electromyographic bio-feedback, results in greater quadriceps strength recovery. As discussed in a previous article, return to sport is the ultimate goal for most patients and quadriceps femoris strength is of the utmost importance. Schmitt et al conducted a cross-sectional study to determine the impact of quadriceps weakness on return to sport functional testing. Those patients who presented with a quadriceps index (quadriceps strength involved/uninvolved) of < 85% performed inferiorly when compared to those with a quadriceps index of > 90%. Additionally, quadriceps weakness predicted performance on single-leg hop testing regardless of graft type, presence of meniscus injury, knee pain, and knee symptoms. Similarly, Fitzgerald et al not only measured increased quadriceps strength, but also length of time until progression to agility/plyometric training. This randomized controlled trial found that those in the NMES group met the criteria for progression in a greater proportion than those in the control group. At 16 weeks, 85.7% (18/21) of patients receiving NMES achieved progression to agility training, whereas only 68% (15/22) of those in the control group achieved similar results.
In addition to ACL rehabilitation, those undergoing total knee arthroplasty enjoyed similar benefits. Stevens-Lapsley et al conducted a prospective, longitudinal, randomized controlled trial investigating the effects of NMES on patients following TKA. Patients were randomized into a group receiving standardized rehabilitation or to a group receiving the same rehabilitation in addition to NMES, which was initiated 48 hours following surgery. In both the short-term (3.5 weeks) and long-term (52 weeks), patients in the NMES group demonstrated superior quadriceps strength, hamstring strength, and functional performance (Timed “Up & Go” Test, the Stair-Climbing Test, and the Six-Minute Walk Test). Additionally, Walls et al investigated the pre-operative utility of this modality. Those individuals who received NMES achieved significant increases in quadriceps strength from weeks 6-12, whereas the control group did not achieve the same feat. Lastly, in a case report published by Petterson et al, a cyclist presenting 12 months following bilateral TKA displayed significant impairments with regards to quadriceps strength and volitional muscular contraction. Following six weeks of NMES and volitional therapeutic exercise, this patient achieved a 25% improvement in left quadriceps femoris maximal volitional force output and his central activation ratio (CAR) also improved from 0.83 to 0.97 as quantified by the burst superimposition technique. Furthermore, strength gains continued after the end of treatment as his quadriceps strength index was 94% of his right leg at 12 months following treatment.
While the majority of research pertaining to the efficacy of NMES has been done in the lower extremity, this is not the only region where its benefits can be found. As previously stated, muscular deficits frequently accompany patients following rotator cuff repair. To this end, Reinold et al investigated the ability of NMES to affect maximum voluntary contraction of the infraspinatus muscle. In comparison to trials without NMES, peak force production was significantly greater with an average force of 3.75 kg in comparison to just 3.08 kg. This increase was present regardless of patient age, size of the tear, intensity of the current, or the number of days following surgery. While this preliminary study does not give credence to the effect during a full course of rehabilitation, it does speak to the ability of NMES to increase the ability of this musculature to contract safely and more efficiently following surgery. Further research will define the effectiveness of this intervention following rotator cuff pathology, however this study lends hopeful possibilities.
Neuromuscular electrical stimulation should play an integral role in your practice regardless of setting. Patients presenting with strength deficits and impairments will benefit from NMES when combined with volitional exercise. Meryl Gersh, PT, PhD goes into great detail with regards to electrode placement, optimal dosage, and indication criteria in her course “Applying Electrical Stimulation in Your Physical Therapy Practice”. Increasing your patients’ volitional muscular contraction is of the utmost importance when it comes to fostering improved long term outcomes and NMES in conjunction with their current program should yield enhanced results.