Authors: Darryl Auston, MD/PhD; Timothy A Damron, MD
Author Affiliations: DA: OrthoOne, Thornton, CO; TAD: Upstate Orthopedics, Syracuse, NY

Introduction: Benign osseous lesions are amenable to curettage of the lesion with grafting of the osseous defect for definitive management. Grafting materials include autogenous bone graft, allograft, or commercially available bone graft substitutes. Commonly used synthetic fillers are comprised of either an ultraporous beta-tricalcium phosphate (TCP) paste, or a calcium sulfate/calcium phosphate (CSCP) composite paste. These materials are intended to form an osteoconductive structure through which normal osseous ingrowth can occur. Recently we reported that a commonly used TCP can persist up to a year on radiographs. CSCP composites should mitigate this effect by dissolution of the calcium sulfate, allowing osseous ingrowth into the remaining calcium phosphate scaffold. Currently we are prospectively comparing the results of these two synthetic bone graft substitutes in benign lesions. This report is intended to describe an unexpected outcome related to a subset of patients treated with the CSCP composite.

Methods / Materials: Plain radiographs of all 110 patients treated with curettage and CSCP composite paste during a five year period from 12/2007 to 12/2012 were retrospectively reviewed. The typical pattern of integration was one of concentric centripetal incorporation. Patients were identified with radiographic failure of the graft as defined by non concentric resorption of the CSCP cement on plain film. The patient charts of subjects exhibiting this radiographic failure pattern were then reviewed for age, type, location, and size of lesion, prophylactic plate fixation, time to radiographic failure by plain film imaging, reoperations, and fracture. Computed tomography of the lesion after failure was also reviewed if available to confirm graft failure.

Results: Twelve patients with average age of 24 (6-64) were identified with early failure of CSCP cement. Lesions treated were identified by the university pathologists as aneurysmal bone cyst (3), unicameral bone cyst (2), fibrous dysplasia (2), and one each of intraosseous ganglion, non-ossifying fibroma, chondromyxoid fibroma, chondroblastoma, fibrosis and chronic inflammation. Four lesions were located in the tibia, two in metatarsal, and one each in the femur, fibula, talus, humerus, ulna, and clavicle. Average size of the lesions preoperatively was 12.3 cubic centimeters (1.2 – 37.5). Prophylactic plate fixation was placed in one femur and one ulna. Average time to radiographic failure of the graft was 23 weeks (6-41). One reoperation is currently planned for graft failure in a metatarsal. Currently no perilesional fractures have been detected.

Discussion / Conclusion: The vast majority (89%) of patients treated with CSCP cementing after curettage of benign bone lesions go on to uneventful healing in our series. There does exist, however, a minority of patients in whom the calcium phosphate scaffolding collapses prior to osseous ingrowth and filling of the lesion. These lesions tend to be larger with an average size of 12 cubic centimeters. The failure also tends to be later, with one as late as 41 weeks. CSCP is not intended for structural support in weight bearing bones, and it is our policy to prophylactically stabilize at risk regions with plate fixation. It is likely due to this practice that no perilesional fractures have occurred. Given our results, we recommend close follow up of lesions treated with CSCP for signs of graft failure.

Description: Lateral projection of knee showing typical pattern of resorption at (A) Index, (B) 3 months, (C) 6 months, and (D) 1 year.

Description: Lateral views of foot showing collapse of graft between 16 and 32 weeks