What signs and symptoms can be used to differentiate low back pain of a musculoskeletal origin from a potentially more serious non-musculoskeletal condition in a 12-year-old girl?

A12-year-old girl with no previous history of back pain was referred to our outpatient physical therapy department after developing an insidious onset of back pain, bilateral thigh pain, and difficulty walking. Her symptoms began approximately 3 months prior to her referral to therapy. The initial symptoms were pain and tightness in the right posterior thigh, which progressed to pain in the lumbar region and the left posterior thigh and buttock. She had radiographs of the right hip that were reported by the radiologist to be negative for a fracture or any developmental abnormality. She reported her pain to be mild (2/10 on a pain rating scale) and mostly unaffected by activity. Her chief complaint was the inability to play soccer due to changes in her walking and running. She had received physical therapy 6 months before. At that time, she reported only pain and tightness in the right posterior thigh, and her primary care physician referred her to our department with a diagnosis of “hamstring strain.” These symptoms resolved with 2 weeks of therapy that focused on stretching exercises. She returned to the same physician for the current episode, and the physician again made the diagnosis of “hamstring strain.” She had not received any further imaging studies since the initial episode. The initial examination of the patient revealed an abnormal gait pattern with reduced stride length bilaterally, which was worse on the right side than on the left. Observation showed a scoliotic curve in the lumbar region with the convexity on the right and what appeared to be visible muscle spasm in the lumbar paraspinal musculature. Active range of motion in the lumbar spine revealed 10 degrees of lumbar extension, 85 degrees of flexion, 5 degrees of right side bending, and 20 degrees of left side bending. Extension caused a …