Pathognomonic acetabular cysts in camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome

An eight year old boy presented to the Orthopaedic outpatient department of Osmania General Hospital, Hyderabad, India, in January 2014 with a complaint of pain, bilateral swellings of the knee and ankle joints and difficulty squatting and sitting cross-legged (Fig. 1a, b, c). On examination, there was synovial thickening of knee joints. There was no clinical evidence of pericarditis. Echocardiogram was normal. Laboratory results for inflammatory markers were in the normal range. Synovial fluid analysis revealed a straw coloured turbid liquid.

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Fig. 1 (a, b). Picture showing bilateral knee swellings (black arrows). (c) The child, unable to squat because of inability to achieve full knee flexion (red arrow) of both knees, only 120 degrees of knee flexion was possible.

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Radiographs of the pelvis showed an immature skeleton with large acetabular cysts, considered diagnostic of camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome. Increased joint space, flattened femoral heads, broadening of femoral neck and coxa vara (Fig. 2a, b) were observed. MRI clearly demonstrated the multiple acetabular cysts (Fig. 3a, b, c, d). Aggressive physiotherapy with a global range of motion exercises for hips and knees was initiated along with paracetamol for pain relief. Eight months after the first visit, there was slight improvement in the range of motion of knees and hips.

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Fig. 2 (a, b). Anteroposterior (AP) and frog leg lateral views of pelvis radiographs showing large acetabular cysts (black arrows), which are pathognomonic, flattening of the femoral heads, coxa vara of the femoral necks.

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Fig. 3 (a, b, c, d). Coronal short tan inversion recovery (STIR) (a) and coronal, axial and sagittal T2 weighted (b, c, d) MRI images of the both hip joints showing multiple large cysts (white arrows) in the acetabulum.

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The occurrence of multiple joint swellings (arthropathy) without inflammatory signs and deformities in hands and feet (camptodactyly) with or without pericarditis are characteristics of this syndrome. The chief differential is juvenile idiopathic arthritis, for which it is commonly mistaken.