Case Study: A fourteen-month-old boy had abruptly stopped bearing weight on his left lower extremity. Parents reported no history of trauma to the limb, but the boy’s medical history included undescended testes. On presentation, the patient had a fever of 100.4°F, which rose to 101.5°F He held his left leg externally rotated and flexed at the hip and refused to extend or bear weight on the limb or crawl. The left hip was tender, but without any palpable masses. He showed minimal signs of discomfort with passive rotation and axial loading. The passive range of motion of the hip showed limitations in extension and adduction.
Radiographs revealed symmetric hip joints with no evidence of acute bony injury. Laboratory studies showed a leukocyte count of 16,700 cells/mL, an erythrocyte sedimentation rate (ESR) of 103 mm/hr, and a C-reactive protein (CRP) level of 4.7 mg/dL. Despite these suggestions of inflammation, ultrasound of the left hip showed no evidence of joint effusion or capsular thickening. Given the disparity between laboratory results, physical examination, and ultrasound findings, an MRI was obtained (shown here), which revealed a large heterogeneous mass (arrow) in the left inguinal region.What is the diagnosis?
1252% Inguinal canal abscess
263% Transient synovitis of left hip
1901% Testicular torsion
809% Septic arthritis of left hip with localized iliopsoas abscess
1132% Teratoma in inguinal region
The patient underwent a testicular ultrasound and was taken urgently to the OR, where he was found to have a gangrenous, torsioned, undescended left testis with edema and inflammatory changes in the left inguinal canal. Surgeons removed the left testis and reconstructed the inguinal canal. Six months after a benign postoperative course, he had a normal gait and full hip range of motion and strength.
Torsion of an undescended testis (UDT) is a relatively rare phenomenon that requires prompt diagnosis and treatment. Children with a history of UDT are at an increased risk of testicular torsion and resulting necrosis. When a child presents as this toddler did, clinicians should also consider septic arthritis of the hip. Kocher’s algorithm—fever, a history of non-weight-bearing, an ESR of >40 mm/hr, and a white blood-cell count (WBC) of >12,000 cells/mL—is often used to differentiate septic arthritis from more benign conditions.
This patient exhibited all four criteria in Kocher’s algorithm, plus elevated CRP, but he had characteristics incompatible with septic arthritis, including minimally painful range of hip motion and no evidence of effusion on ultrasound. Because the sensitivity of ultrasound in diagnosing septic arthritis is relatively low, an MRI was obtained, which revealed the inguinal mass.
This case emphasizes that abdominal or genitourinary pathology can mimic hip pathology and therefore must be considered in the differential diagnosis. Clinical algorithms can be extremely valuable, but clinicians should not use them as “cookbooks.”