Profound Calf Muscle Dysfunction following Hip Dislocation Monitored by Air Plethysmography

Introduction

Muscular atrophy regularly occurs as a consequence of immobilization or disuse after sport injuries. ¹ Muscular strength has been noted to decrease most significantly within the first week of immobilization. Muscle atrophy is characterized by a catabolic metabolism, with impaired protein synthesis and possible alterations in local oxygen supply. Air plethysmography (APG) provides an easily reproducible, noninvasive, diagnostic test that enables the ejection fraction (EF) of the calf to be measured. The EF is useful in quantifying calf muscle pump function. APG may be a useful tool in measuring the restoration of calf muscle function in patients with injuries requiring extended immobilization.

Case Study

A 25-year-old female patient presented to the emergency department a month after sustaining a hip disarticulation injury in a waterskiing accident. Her chief complaints included lower-extremity cyanosis and coolness, paresthesias, fluctuating pulse exam, and swelling. An ankle brachial index was performed in the vascular laboratory, which revealed normal ankle brachial pressure index with triphasic waveforms. The emergency department physician then ordered an arterial duplex to exclude arterial injury. The results of the arterial duplex examination were normal. However, the consulting vascular surgeon performed an arteriogram to exclude an arterial injury in the more proximal iliac artery, or a potential transiently symptomatic injury, such as an intimal flap. A venous duplex was also obtained to exclude venous valvular insufficiency and deep venous thrombosis. With a completely negative work-up thus far, APG was ordered as a physiological evaluation to rule out venous disease. APG venous filling index (VFI), residual volume fraction (RVF), and outflow fraction were within normal limits, testing negative for venous insufficiency. The APG revealed a profoundly abnormal EF of 36%. The patient had been immobile for a month at the time of her baseline study. Physical therapy was then recommended, with special attention towards calf muscle strengthening.

Methods

APG (APG 1000; ACI Medical, San Marcos, CA) is performed with the patient in supine position, elevating the leg at 45 degrees with the hip externally rotated and resting on a 20–cm support cushion. A pneumatic cuff measuring (cuff size) is placed around the patient's leg from knee to ankle. The cuff fills with air until it makes contact with the skin. A known amount of air equaling 10 mmHg is injected into the cuff and serves as the calibration for the volume changes of the limb. APG measures reflux as VFI (venous volume in milliliters per second of refill time). Increasing values of VFI have been associated with chronic venous insufficiency. An outflow fraction less than 38% may represent venous obstruction. ² Calf muscle function is expressed through the EF and is reflected by volume changes with muscular activity. EF is the percent of ejected volume in one toe raise. Normal values of EF are expressed at greater than 60%, ³ and profoundly abnormal values are less than 40%. ⁴ RVF is the amount of volume that remains in the calf after 10 tiptoe maneuvers with normal values less than 35%. RVF correlates most closely to ambulatory venous pressure. ³

Results

After 3 months of physical therapy, the patient's APG EF increased to a normal value of 74%. In addition to normalization of the APG, all symptoms of cyanosis, paresthesias, and swelling were resolved.

Discussion

The possible etiologies resulting in decreased calf muscle function are: 1) failure of pumping muscles relating to activity, paralysis, or disease; 2) proximal obstruction that prevents blood from exiting the calf veins; and 3) calf varicosities that retain venous volume and remains located in the calf during contraction. ⁵ Venous insufficiency, reflux, and obstruction were unlikely causes for the patients symptoms with normal venous duplex ultrasound imaging and other than EF, normal APG values. The profoundly diminished calf muscle pump function resulting from extended immobilization thus became the most likely cause of this patient’ signs and symptoms. Complete improvement after a dedicated physical therapy program that emphasized calf muscle pump strengthening exercises confirmed this diagnosis. As in this case, calf muscle strengthening as evidenced by EF can be monitored and evaluated with the use of APG before and after physical therapy to evaluate and monitor the effectiveness of the treatment.

Our group has put together a protocol for calf muscle pump strengthening in patients with chronic venous insufficiency. ⁶ This protocol includes 45 to 60 minutes of weight-bearing (i.e., treadmill on a grade, stair-stepper, recumbent stepper) cardiovascular exercise two to three times per week. It also includes lower-body strength training, targeted towards strengthening the calf muscles. Examples of recommended exercises are calf raises, leg lunges, and wall squats. Although the specifics of this protocol need to be validated more widely, we have found that patients experience a measurable improvement in their calf muscle pump function after completing this protocol. We reserve such protocol for patients who do not respond to the more typical exercise protocols like walking, bicycling, and swimming.

Conclusion

Extended immobilization may cause profound muscle atrophy and a decrease in calf muscle pump function. Objective assessments of atrophy, such as measuring leg circumference, may not correlate well with function, whereas subjective evaluations of symptom improvement are difficult to quantify and highly variable. APG provides an easily reproducible and noninvasive assessment of calf muscle pump function by measuring EF. As demonstrated in this case, physical therapy with an emphasis on calf muscle exercises is beneficial in restoring diminished muscle function caused by immobility and atrophy, and APG provides an excellent objective measure of improvement.