Extracortical bridging callus after limb salvage surgery about the knee

The increasing survival of children treated for osteosarcoma has led to an increase in limb sparing surgery. Little published information is available about the postoperative imaging appearance of this technique. Thus, information gleaned from medical records and imaging reviews was correlated with clinical outcome of 19 consecutive children (median age at diagnosis, 12.3 years) treated for distal femoral osteosarcoma with a cemented rotating hinged knee endoprosthesis with porous coated collar. An extracortical bridging bony callus was identified in 16 patients who were followed up after surgery for a median of 2.8 years (range, 1.4-6 years). Extracortical bridging bony callus formation was circumferential in eight and preferentially posterior in nine, and ranged from 0.5 to 0.7 cm in thickness; 14 patients had lucent lines subjacent to the bridging bone. Thirteen patients had good functional use of the surgically treated leg. Five patients had progressive metastatic disease develop. One patient had local disease recurrence 8 months after surgery. Extracortical bridging bone was not identified in three patients, two of whom had infection develop 7 months and 17 months after surgery; both infections required amputation. Extracortical bridging bone preferentially develops posteriorly, along the compression side of the femur, often is associated with subjacent lucency, and seems to reflect increased prosthetic stability.