The influence of orthopaedic implants on patient tolerance of neuromuscular electrical stimulation (NMES)

Neuromuscular electrical stimulation (NMES) is a potential deep vein thrombosis (DVT) preventative measure that is often over-looked. NMES could be used postoperatively in conjunction with pharmacological prophylaxis to further reduce the incidence rate of DVT following orthopaedic surgery. However, the use of NMES in the recovery period following orthopaedic surgery on patients with metallic hip/knee implants has not been tested to date. The presence of a metallic implant may interfere with the NMES generated electric field causing hypersensitivity at the implant site. This may essentially limit the use of NMES postoperatively. Consequently, patient tolerance of NMES must be assessed before any treatment can be administered. Five hip replacement patients and 5 knee replacement patients participated in this study that were at least 3 weeks post-op. NMES was applied to the calf muscles of each patient using skin surface electrodes and the stimulation intensity was slowly increased. Comfort was assessed by asking the patient to indicate the stimulation intensity corresponding to 4 thresholds: when they first felt the stimulus sensation (sensory threshold), when a muscle contraction was observed (motor threshold), when stimulation became uncomfortable (pain threshold) and when the stimulation became unbearable (pain tolerance). Patients also indicated their overall comfort level on a visual analogue scale and completed a short verbal interview detailing their experience of the NMES treatment. Results indicated that the presence of a metallic implant did not give rise to hypersensitivity to NMES. Patients found the application of calf muscle NMES comfortable and acceptable as a treatment. We conclude that use of NMES on postoperative orthopaedic patients can be safely considered as a DVT prevention method.