Patient tolerance of neuromuscular electrical stimulation (NMES) in the presence of orthopaedic implants.

Neuromuscular electrical stimulation (NMES) may help reduce the incidence of deep vein thrombosis (DVT) in the postoperative total hip and knee arthroplasty patient. However, discomfort associated with stimulus may reduce patient acceptance of NMES as therapy. The aim of this study was to determine if patient comfort and tolerance of NMES was affected by applying stimulation in proximity to an orthopaedic implant. There was a concern that this may cause a concentration of current around the metal which could result in hypersensitivity of NMES and reduce its effectiveness. Twenty patients took part in this study, 10 total hip and 10 total knee arthroplasty patients. Each patient was at least 3 weeks post surgery. NMES was applied to the calf muscles of each leg using skin surface electrodes. Four excitatory levels were recorded, which were: sensory threshold, motor threshold, pain threshold and pain tolerance. Following this, patients underwent a 5 min stimulation session and indicated their overall comfort level on a visual analogue scale. Measurements of peak venous velocity, mean velocity and volume flow were recorded by duplex scanning from the popliteal vein at rest and in response to NMES elicited contractions during this session. Finally, patients completed a short verbal interview detailing their experience with the NMES treatment. The blood flow results showed increases in peak venous velocities, mean velocities and volume flow produced by NMES of 200%, 60% and 60% respectively when compared to resting blood flow. Comfort assessment indicated that the presence of a metallic implant did not give rise to hypersensitivity due to NMES. Patients found the application of calf muscle NMES comfortable and acceptable as a treatment. We conclude that the use of NMES on postoperative orthopaedic patients can be safely administered as a DVT prevention method.