The Effect of Lower Limb Cast Immobilization on Calf Muscle Pump Function

Abstract

We have investigated the role of the calf muscle pump in casted patients. An audit of venous thromboembolism (VTE) in casted patients showed that the thrombosis occurred in the casted leg; this has not been previously assessed. We postulated that local factors play a major role, and we set out to assess the calf muscle pump in casted patients and to determine whether this can be optimized despite below-knee cast immobilization. We measured the flow in the popliteal vein using a validated method of Doppler ultrasound measurement of peak velocity with and without a below-knee plaster cast. We demonstrated that a simple strategy of toe and ankle exercises can maintain venous return despite below-knee cast immobilization. This is the first study to examine the effect of the calf muscle pump in the presence of a plaster cast. Major muscle groups such as the flexor hallucis longus and gastrocsoleus extend beyond the field of control of the cast and can still be recruited. We recommend that all patients treated with a below-knee cast be given a program of exercises that can be comfortably performed with the cast; this could provide a useful, inexpensive, and safe thromboprophylaxis strategy acting at the site of greatest risk and targeting a major cause of VTE.