35-Year-Old Female Triathlete With Right Hip Pain.

Abstract

CASE DESCRIPTION A 35-yr-old female professional triathlete with history of anorexia, relative energy deficiency syndrome, and multiple previous stress fractures presented for a second opinion regarding anterior right hip pain that had largely resolved. She was evaluated at an outside institution 3 mos prior and diagnosed with a right femoral neck bone stress injury, characterized as grade 1, compression-sided, on magnetic resonance imaging (MRI). After 3 mos of appropriate activity modification, she had 98% pain resolution. She resumed swimming and cycling pain-free but had mild anterior hip pain with running. Follow-up MRI at the outside institution revealed a grade 4 stress injury with new tension-sided fracture line (Fig. 1). This was discordant with her overall symptom improvement, which prompted her to seek a second opinion in our clinic where she presented without pain with walking, swimming, or biking. Physical examination revealed full right hip range of motion with 1/10 pain with hip flexion and internal rotation. Strength and sensation were intact. Hip scour, Stinchfield, and FABER were negative.FIGURE 1: Coronal T1 (A) and coronal T2 images (B) of right hip MRI without contrast demonstrating a right femoral neck bone stress injury, characterized as grade 4, compression-sided (solid arrow), with a new tension-sided (dashed arrow) fracture line.Because the findings on MRI were discordant with her clinical presentation, a right hip computed tomography scan was performed to better evaluate the femoral neck stress fracture and provide additional information on interval healing. The right hip computed tomography confirmed a femoral neck stress fracture involving the compression and tension sides (Fig. 2).FIGURE 2: Coronal (A) and axial (B) images of right hip computed tomography scan, which revealed an anterior-posterior dimension cortical marrow fracture of the medial compression side (solid arrow) of the femoral neck with a small fracture line involving the tension side (dashed arrow) similar to the previous MRI.Femoral neck pinning to prevent stress fracture completion was recommended. Given her minimal pain, she elected nonoperative management with continued activity modification and 6 mos of teriparatide, used off-label to promote stress fracture healing.1,2 Six weeks after presentation to our clinic, a repeat MRI revealed stress fracture healing. She participated in a 4-mo gradual return to running program while on teriparatide. At 8-mo follow-up, she was running 30–35 miles per week pain-free and had recently run a personal best in a 5-km race. LEARNING POINTS Femoral neck stress fractures typically present with poorly localized, gradual onset hip or groin pain that worsens with weight-bearing activity.3 They are commonly seen in distance runners because of repetitive submaximal loading, often in the setting of low energy availability.3 The differential diagnosis for a runner with hip or groin pain includes femoral neck stress fracture, femoral head avascular necrosis, hip labral tear, femoral acetabular impingement, hip osteoarthritis, iliopsoas tendinopathy, rectus femoris tendinopathy, and adductor tendinopathy.4 Plain radiographs are the initial imaging modality of choice. However, MRI, which is nearly 100% sensitive and specific, is often required for diagnosis.3 Magnetic resonance may demonstrate periosteal edema or a fracture line on imaging depending on the grade of injury.5–7 Based on the MRI classification by Arendt and Griffiths,6 grade 1 femoral neck stress fractures show signal change on STIR sequencing exclusively; grade 2 show change on STIR and T2; grade 3 show change on STIR, T1, and T2 with no fracture line present; and grade 4 show change on STIR, T1, and T2 with a fracture line present. Computed tomography is highly specific for stress fractures and may have a role in cases where MRI results are equivocal or discordant from the patient’s clinical presentation.8 Femoral neck stress fractures are characterized as compression or tension-sided based on location and the forces involved causing the injury.3 Compression-sided stress fractures occur on the inferior-medial femoral neck and are typically treated conservatively with activity restriction.3 Tension-sided stress fractures occur on the superior-lateral femoral neck and often require surgical intervention with pinning to prevent completion of the fracture and development of avascular necrosis.3