Resecting bone tumours within the pelvis is highly challenging and requires good cutting accuracy to achieve sufficient margins. Computer-assisted technologies such as intraoperative navigation have been developed for pelvic bone tumour resection. Patient-specific instruments have been transposed to tumour surgery. The present study reports a series of 11 clinical cases of PSI-assisted bone tumour surgery within the pelvis, and assesses how accurately a preoperative resection strategy can be replicated intraoperatively with the PSI. The patient series consisted in 11 patients eligible for curative surgical resection of primary bone tumor of the pelvis. Eight patients had a bone sarcoma of iliac bone involving the acetabulum, two patients had a sacral tumor, and one patient had a chondrosarcoma of proximal femur with intra-articular hip extension. Resection planning was preoperatively defined including a safe margin defined by the surgeon from 3 up to 15 mm. PSI were designed using a computer-aided design software according to the desired resection strategy and produced by additive manufacturing technology. Intraoperatively, PSI were positioned freehand by the surgeon and fixed on the bone surface using K-wires. The standard surgical approach has been used for each patient. Dissection was in accordance with the routine technique. There was no additional bone exposure to position the PSI. Histopathological analysis of the resected tumor specimens was performed to evaluate the achieved resection margins. Postoperative CT were acquired and matched to the preoperative CT to assess the local control of the tumor. Two parameters were measured: achieved resection margin (minimum distance to the tumor) and location accuracy (maximum distance between achieved and planned cuttings; ISO1101 standard). PSI were quick and easy to use with a positioning onto the bone surface in less than 5 minutes for all cases. The positioning of the PSI was considered unambiguous for all patients. Histopathological analysis classified all achieved resection margins as R0 (tumor-free), except for two patients : R2 because of a morcelised tumour and R1 in soft tissues. The errors in safe margin averaged −0.8 mm (95% CI: −1.8 mm to 0.1 mm). The location accuracy of the achieved cut planes with respect to the desired cut planes averaged 2.5 mm (95% CI: 1.8 to 3.2 mm). Results in terms of safe margin or the location accuracy demonstrated how PSI enabled the surgeon to intraoperatively replicate the resection strategies with a very good cutting accuracy. These findings are consistent with the levels of bone-cutting accuracy published in the literature. PSI technology described in this study achieved clear bone margins for all patients. Longer follow-up period is required but it appears that PSI has the potential to provide clinically acceptable margins

Objective. To evaluate functional and oncological outcomes following sacral resection. Methods. A retrospective review was conducted of 97 sacral tumours referred to tertiary referral spinal or oncology unit between 2004 and 2009. Results. The study included Chordoma 26; Metastases 17; Chondrosarcoma 9; Osteosarcoma 8; Lymphoma 7; Ewing's Sarcoma 6; Giant Cell Tumours 5; Other Sarcomas 5; Aneurysmal Bone Cyst 4; Myeloma 4; Others 7. There were 61 males, 37 females with an average age of 47 (range 3-82). The average duration of pre-diagnosis symptoms was 13 months. In 17 cases the diagnosis was metastatic disease and these were excluded from further discussion. Of the remainder 36/81(44%) underwent surgery: 21 excision, 9 excision and instrumented stabilisation, and 6 curettage. Thirteen (16%) patients were inoperable: 8 advanced disease, 3 unable to establish local control and 2 cases of recurrence. Colostomy was performed in 11/21 (52%) patients who underwent excision. Deep wound infections in 6/21 (29%). No difference in infection rates between definitive surgery with or without colostomy – 3/11 (27%) vs 3/10 (30%). In the instrumented group, no colostomies were performed due to concerns about deep infection and none resulted (0/9). Radiological failure of stabilisation was noted in 7/9(78%). However, functionally, 3/9 (33%) were mobilising independently, 3/9 (33%) with crutches, 2/9 (22%) able to transfer and 1/9 (11%) undocumented. Mean follow-up was 25 months (range 0-70). Local recurrence in 9/36 (25%) of operated patients. Metastasis occurred in 4/36 (11%) and mortality 8/36 (22%) although follow-up period was noted to be short. Conclusions. Results are comparable with current literature. Mechanical stabilisation for extensive sacral lesions is challenging. Despite radiological failure in 7/9 instrumented stabilisations, patients were relatively asymptomatic and only 1/9 required revision stabilisation surgery. By design none had colostomies and there were no deep infections

CT and MRI scans are complementary preoperative imaging investigations for planning complex musculoskeletal bone tumours resection and reconstruction. Conventionally, tumour surgeons analyse two-dimensional (2-D) imaging information, mentally integrate and formulate a three-dimensional (3-D) surgical plan. Difficulties are anticipated with increase in case complexity and distorted surgical anatomy. Incorporating computer technology to aid in this surgical planning and executing the intended resection may improve precision. Although computer-assisted surgery has been widely used in cranial biopsies and tumour resection, only small case series using CT-based navigation are recently reported in the field of musculoskeletal tumor surgery. We investigated the results of CT/MRI image fusion for Computer Assisted Tumor Surgery (CATS) with the help of a navigation system. We studied 21 patients with 22 musculoskeletal tumours who underwent CATS from March 2006 to July 2009. A commercially available CT-based spine navigation system (Stryker Navigation; CT spine) was used. Of the 22 patients, 10 were males, 11 were females, and the mean age was 32 years at the time of surgery (range, 6–80 years). Five tumours were located in the pelvis, seven sacrum, eight femurs, and two tibia. The primary diagnosis was primary bone tumours in 16 (3 benign, 13 sarcoma) and metastatic carcinoma in four. The minimum follow-up was 17 months (average, 35.5 months; range, 17–52 months). Preoperative CT and MRI scan of each patient were performed. Axial CT slices of 0.0625mm or 1.25mm thickness and various sequences of MR images in Digital Imaging and Communications in Medicine (DICOM) format were obtained. CT and MR images for 22 cases were fused using the navigation software. All the reconstructed 2-D and 3-D images were used for preoperative surgical planning. The plane of tumour resection was defined and marked using multiple virtual screws sited along the margin of the planned resection. We also integrated the computer-aided design (CAD) data of custom-made prostheses in the final navigation resection planning for eight cases. All tumour resections could be carried out as planned under navigation guidance. Navigation software enabled surgeons to examine all fused image datasets (CT/MRI scans) together in two spatial and three spatial dimensions. It allowed easier understanding of the exact anatomical tumor location and relationship with surrounding structures. Intraoperatively, image guidance with the help of fusion images, provided precise visual orientation, easy identification of tumor extent, neural structures and intended resection planes in all cases. The mean time for preoperative navigation planning was 1.85 hours (1 to 3.8). The mean time for intraoperative navigation procedures was 29.6 minutes (13 to 60). The time increased with case complexity but lessened with practice. The mean registration error was 0.47mm (0.31 to 0.8). The virtual preoperative images matched well with the patients' operative anatomy. A postoperative superficial wound infection developed in one patient with sacral chordoma that resolved with antibiotic whereas a wound infection in another with sacral osteosarcoma required surgical debridement and antibiotic. After a mean follow-up of 35.5 months (17–52 months), five patients died of distant metastases. Three out of four patients with local recurrence had tumors at sacral region. Three of them were soft tissue tumour recurrence. The mean functional MSTS score in patients with limb salvage surgery was 28.3 (23 to 30). All patients (except one) with limb sparing surgery and prosthetic reconstruction could walk without aids. Multimodal image fusion yields hybrid images that combine the key characteristics of each image technique. Back conversion of custom prosthesis in CAD to DICOM format allowed fusion with navigation resection planning and prosthesis reconstruction in musculoskeletal tumours. CATS with image fusion offers advanced preoperative 3-D surgical planning and supports surgeons with precise intraoperative visualisation and identification of intended resection for pelvic, sacral tumors. It enables surgeons to reliably perform joint sparing intercalated tumor resection and accurately fit CAD custom-made prostheses for the resulting skeletal defect