BACKGROUND:
Piriformis muscle is originated from anterior-lateral surface of sacrum and inserted on greater trochanter, acting as a hip external rotator. It is not a common source of hip pain, but this case suggests that muscle pain from piriformis could be occurred in patient with excessive femoral anteversion. Considering anatomy of piriformis muscle, excessive anteversion of femur can cause additional stretching stress on piriformis muscle, which may induce muscle pain syndrome of piriformis muscle. Moreover, in patient with hemiparesis whose muscle around hip joint are not able to protect piriformis muscle from excessive stress, symptoms could be worsened.
CASE REPORT:
A 62-year-old female diagnosed acute right anterior cerebral artery infarction was transferred to the department of rehabilitation medicine in May 2020. Motor power of the patient’s left hip flexor was poor grade, hip extensor was fair, and hip abductor and adductor were poor grade by manual muscle test (MMT). The patient showed gait patterns with circumduction with hip elevation, and toe-in. After starting gait training, the patient had severe left hip pain with tenderness on gluteal region, midline between sacrum lateral boarder and greater trochanter. Pain was exacerbated with walking and position with hip flexion, internal rotation, and adduction (FLAIR). Interestingly, with solid ankle foot orthosis (AFO), patient’s hip pain and toe-in were decreased. Patient reported that she had toe-in gait pattern before stroke event, so tibial torsion or femoral anteversion was considered to cause toe-in gait pattern. In CT pelvis(Figure 1), anteversion angle of femur neck was 25.7° on right and 20.3° on left side. The patient’s femoral anteversion angle was around upper normal limit range. Previous study reported that plastic AFO can force hip to external rotation, although its mechanism was unclear. In this patient, reduced hip internal rotation by AFO could reduce strain on piriformis muscle. After ultrasound-guided trigger point injection on the left piriformis muscle and repetitive self-stretching of piriformis muscle, symptom was resolved. This therapeutic effect also supported the diagnosis of piriformis muscle pain syndrome.
CONCLUSION:
Weakness of muscles around hip joint could exacerbated stress on themselves, and with excessive femoral anteversion which force hip joint to internal rotate, external rotator muscle such as piriformis muscle received excessive stress. AFO was used for preventing foot drop while gait and joint contracture, in this case AFO could be used for other purpose, reducing piriformis muscle stress. Piriformis muscle pain was relieved by AFO, trigger point injection and self-stretching. This case suggests possible mechanism and treatment strategy of piriformis muscle pain syndrome.
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