P3A357: Not Cheering for Hip Pain: A Case of Unicameral Bone Cyst with Associated Pathologic Femoral Neck Fracture

Introduction: A 13-year-old female cheerleader presented with three days of acute-onset right hip pain after landing on her extended right leg while tumbling. She denied hearing a pop or crack. She was unable to bear weight on her right lower extremity due to pain. The pain was aggravated by weightbearing and improved with rest. She reported vague right anterior hip pain in the same location three weeks prior to injury. She presented to a pediatric sports medicine clinic for evaluation.

Case Description: Physical Exam:
Right lower extremity: There was no erythema, edema, or deformity. Tenderness to palpation was present along the proximal hip flexors. She had full active and passive range of motion of the hip. She had 4/5 strength with right hip flexion and abduction. Additional testing displayed negative log roll, FABERs, FADIRs, and Scour tests. Gait was antalgic.
Left lower extremity: Contralateral exam was normal.

X-ray and MRI of the pelvis showed a unicameral bone cyst with associated pathologic femoral neck fracture,

The patient underwent curettage and bone grafting of the right proximal femoral bone cyst through a trans-trochanteric approach with fixation of the fracture with a fixed-angle femoral neck fracture system. Intra-operative specimen pathology displayed a benign fibro-osseous lesion consistent with a unicameral bone cyst. The patient was 25% touchdown weightbearing for 4 weeks post-operatively but was non-compliant with weightbearing restrictions and walked into clinic at week 4 without pain. Physical therapy was ordered with the goal of full return to play at 3 months post-operatively.

Discussion: Unicameral bone cysts (UBCs) are benign lytic bone lesions commonly found in children, with their origin still not completely understood. Theories suggest they result from local disturbances in bone growth or due to blockage of venous drainage at the growth plate. UBCs typically occur in the metaphysis of long bones, commonly the proximal humerus and femur. Although often asymptomatic and discovered incidentally, UBCs can cause mild localized pain and lead to pathologic fractures.

Treatment approach for UBCs depends on size, location, and presence of pathologic fractures. When the cyst is small and asymptomatic, observation may suffice. However, in the presence of a pathologic fracture or risk of fracture, surgical intervention is warranted. Surgical options include curettage and bone grafting, with or without internal fixation.

Conclusion: In summary, UBCs are common benign lytic bone lesions in children, and their treatment depends on the specific circumstances of each case. In this unique case of a UBC in the hip with an associated pathologic femoral neck fracture, the surgical team chose a trans-trochanteric approach for its muscle-sparing properties and improved visualization of the lesion. This approach led to a successful treatment outcome, with the patient expected to make a full recovery and return to her previous activities.