Primary malignant bone tumor often requires a surgical treatment to remove the tumor and sometimes restore the anatomy using a frozen allograft. During the removal, there is a need for a highest possible accuracy to obtain a wide safe margin from the bone tumour. In case of reconstruction using a bone allograft, an intimate and precise contact at each host-graft junction must be obtained (Enneking 2001). The conventional freehand technique does not guarantee a wide safe margin nor a satisfying reconstruction (Cartiaux 2008). The emergence of navigation systems has procured a significant improvement in accuracy (Cartiaux 2010). However, their use implies some constraints that overcome their benefits, specifically for long bones. Patient-specific cutting guides become now available for a clinical use and drastically simplify the intra-operative set-up. We present the use of pre-operative assistances to produce patient-specific cutting guides for tumor resection and allograft adjustment. We also report their use in the operative room.

We have developed technical tools to assist the surgeon during both pre-operative planning and surgery. First, the tumor extension is delineated on MRI images. These MRI images are then merged with Computed Tomography scans of the patient. The tumor and the CTscan are loaded in custom software that enables the surgeon to define target (desired) cutting planes around the tumor (Paul 2009) including a user-defined safe margin. Finally, cutting guides are designed on the virtual model of the patient as a mould of the bone surface surrounding the tumor, materialising the desired cutting planes. When required, a massive bone allograft is selected by comparing shapes of the considered patient's bone and available allografts. The resection planes are transferred onto the selected allograft and a second guide is designed for the allograft cutting. The virtually-designed cutting guides are then manufactured by a rapid prototyping machine using biocompatible material. This procedure has been used to excise a local recurrence of a tibial sarcoma and reconstruct the anatomy using a frozen tibial allograft.

The pre-operative planning using virtual models of the patient's bone, tumor and the available allografts enabled the surgeon to localise the tumor, define the desired cutting planes and select the optimal allograft. Patient- and allograft-specific guides have been designed and manufactured. A stable and accurate positioning of guide onto the patient's tibia was made easier thanks to the plate formerly put in place during the previous surgery. An accurate positioning of the allograft cutting guide has been obtained thanks to its design. The obtained reconstruction was optimal with a adjusted allograft that was perfectly fitting the bone defect. The leg alignment was also optimally restored.

Computer assistances for tumor surgery are progressively appearing. We have presented at CAOS 2010 an optical navigation system for tumor resection in the pelvis that was promising. However, such a tool is not well adapted for long bones. We have used patient-specific guides on a clinical case to assess the feasibility of the technique and check its accuracy in the resection and reconstruction. The surgeon has benefited from the 3D planning to define his strategy. He had the opportunity to select the optimal transplant for his patient and plan the same cuttings for the allograft and the patient. During the surgery, guide positioning was straightforward and accurate. The bone cuttings were very easy to perform. The use of custom guides decreases the operating time when compared to the conventional procedure since there is no need for measurements between cutting trajectories and anatomical landmarks. Furthermore, the same cutting planes were performed around the tumor and onto the allograft to obtain a transplant that optimally fills the defect. We recommend the use of such an intra-operative assistance for tumor surgery.

Purpose of the study: Resection of sarcomas from the pelvis is particularly difficult because of the risk of injury to the vascular and neurological structures and the complex helicoidal anatomy of the iliac bone. Salvage of the lower limb is preferable but raises the risk of an insufficient resection margin. Imaging procedures (CT scan, magnetic resonance) allow preoperative planning but intraoperative landmarks are not always easy to recognise. Navigation might be highly useful for this type of surgery.

Material and methods: Two patients with a sarcoma of the pelvis (chondrosarcoma and synovial sarcoma) underwent tumour resection using a navigation system. For the second patient, the cut for the bone graft was also navigated enabling reconstruction with a perfectly adjusted graft. The tumour was delimited on each magnetic resonance slice to produce a 3D reconstruction image. This volume was co-recorded on the scanner. The scan with the tumour limits was fed into the navigation machine. Resection planes were chosen taking into account the surgical approach, the type of reconstruction desired, and the healthy margin accepted. These planes were then transposed onto the allograft scan to enable an exactly adapted cut. Plaster prototypes were modelled from the scan of the patient’s pelvis and the allograft scan. The tumour resection and the allograft procedures were repeated on the prototypes using the navigation system.

Results: The navigation system was used successfully as planned preoperatively. The planes of the cuts were as planned. The healthy margin was sufficient in all cases and confirmed at the pathology exam.

Discussion: Navigation enables exact localisation in relation to the tumour throughout the operation. A healthy margin of one centimetre or more can be achieved safely. The allograft cut can be made by another surgeon simultaneously with the tumour resection, saving time. The allograft-host contact surface is improved giving a good congruency with the graft.

Conclusion: Navigation is a very useful tool for resection of pelvic tumours and their reconstruction.

Purpose: Only very partial integration of massive allografts is generally achieved, affecting bone-graft junctions and the peripheral cortical. In clinical practice, this is not a major problem for massive reconstructions with a sleeve prosthesis but can be a handicap for junctional grafts or osteoarticular grafts where weak recolonisation can be a source of complications.

Material and methods: Extraperiosteal resection measuring 5 cm in length was made in the mid shaft region and bridged by a cyropreserved non-irradiated allograft before stabilisation with a static locked nail. Three groups of ten sheep were studied. The first group received a simple allograft without perforation; the allograft was perforated in the second group (1.1 mm drill bit); and the perforations in the allograft in the third group were lined with decalcified bone powder with assumed potential for inducing bone growth. The implantation was studied after a delay of six months. There were three infections so the analysis was made on 27 grafts. Plain x-rays (consolidation of the graft-bone junctions), histomorphometrics (porosity, new peripheral and endomedullary bone deposit, cortical thickness), and bone density were studied.

Results: Rate of bone-graft consolidation was not significantly different in the three groups. The callus was more endosteal in groups 2 and 3 (p< 0.02) and endomedullary bone deposit was greater (p=0.0001) than in group 1 without perforation. There was approximately three times more bone deposit in the perforated allografts than in the non-perforated allografts; Adjunction of demineralised bone around the perforated grafts did not lead to any significant difference compared with the perforated allografts (group 2).

Discussion: Significantly more bone deposit observed with perforated allografts should lead to better biomechanical behaviour. This is being tested in further work.

Conclusion: Perforations induce a significant increase in new bone deposit in massive cortical allografts, remodelling is much more active and extensive than with non-perforated allografts. It would be logical to propose perforated allografts for junctional or osteochondral massive cortical grafts.