(P 500) IMPROVING OUTCOMES OF INTERCALARY EWING SARCOMA RESECTIONS AND ALLOGRAFT RECONSTRUCTIONS WITH PATIENT-SPECIFIC CUTTING GUIDES AND VIRTUAL SURGICAL PLANNING

Objective: We report our early experience with 3D-printed patient- and allograft-specific instrumentation for the resection and allograft reconstruction through a series of patients treated with intercalary resections of Ewing Sarcoma. With intercalary resection of bone sarcomas in pediatric patients, maintaining the integrity of the physes and not spanning the physis with the reconstruction are critical to the biologically growing limb salvage. Matching the allograft to the native bone at the junctions in selection and at the time of osteotomy aids in healing and eventual incorporation. We aim to evaluate improvements in union, margin status and reduction in revision reconstruction with the use of 3D printed cutting guides for the resection osteotomies and preparation of the allograft. We describe preoperative virtual planning and intraoperative techniques to best leverage this emerging technology and solve classic limitations with short fixation segments around the physis.

Methods: A case series of 21 patients who underwent intercalary resection and allograft reconstruction for Ewing sarcoma, including 13 patients treated with the use of custom 3D-printed cutting guides for the resection with matching cutting guides for the allograft, and 8 patients for which the guides were not used. Over a mean follow-up of 2.8 years, complications including non-union and revision reconstruction were collected in both groups.

Results: Reconstructions using this innovative instrumentation more likely to create better junction fit (OR 1.62, 95% CI 1.18, 2.06] and a lower rate of revision reconstruction (14% vs 75%). Bone marrow margins were negative in all cutting guide cases, but positive in 2 of the free-handed osteotomy resections. We describe techniques to maximize allograft fit and plan physeal-sparing fixation by simulating and pre-selecting hardware as well as pre-contouring implants.

Conclusion: Our early experience with 3D-printed cutting guides for intercalary resection and reconstruction in primary bone sarcomas demonstrates the potential to improve resection and bone-allograft fit. Osteotomies made in multiple planes with the 3D-printed cutting guides also provided more surface area for contact at the junctions. Using our method we have also been able to pre-select and pre-contour fixation implants preoperatively, reducing operative time and additional manipulation of the final allograft. There are additional opportunities to improve virtual surgical planning, implant selection and preparation for complex intercalary resections and reconstructions.