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.

Introduction: Spinal fusions have been shown to be useful in correcting spinal deformities resulting from degenerative disc disease. We sought to produce a prospective analysis of functional outcomes following lumbar spinal fusion surgery for degenerative spondylolisthesis or degenerative scoliosis secondary to degenerative disc disease. We present the interim results from our case cohort of 74 patients.

Methods: Over a period of 3 years (2005–2007), all patients who presented to this private practice with symptoms of canal stenosis or radicular pain secondary to degenerative spondylolisthesis or degenerative scoliosis were offered decompressive laminectomy and posterior lumbar interbody fusion (PLIF) surgery with interbody cages, pedicle screw instrumentation, bone morphogenic protein (BMP) and bicalcium phosphate (BCP). Patients who presented only with low back pain and did not have radicular pain or neurogenic claudication were excluded from this study. All patients who were offered spinal fusion surgery were consecutively offered the opportunity to enrol in this functional cohort analysis. Those patients who consented were prospectively entered into this functional analysis and were asked to complete Oswestry and SF-36 function questionnaires preoperatively and post-operatively. Post-operative data has been collected in some cases up to 16 months postoperatively. Patients were also assessed post-operatively by the surgeon and given an Odom clinical assessment score. Complications were also collated.

Results: 102 patients were offered surgery with 18 patients not consenting to participate in this study. Of the 84 patients who consented to participate in this study, 10 patients failed to submit both pre-operative and postoperative questionnaires, leaving 74 patients who were followed for a median 7 months (range of 1.5–16 months). There were 30 males and 44 females in the study with a median age of 73 (range 46–89). Of these 74 patients, 63 had degenerative spondylolisthesis and 11 had degenerative scoliosis. 52 patients had sufficient follow-up to assess bony fusion, of which 1 patient failed to fuse. 32 of the patients who fused reported to have improved, but 16 did not and the remainder did not submit both pre-operative and post-operative questionnaires. For the SF-36 questionnaire, the median pre-operative SF-36 score was 30 (96.6% CI 26–35) and the median post-operative SF-36 score was 48 (95.3% CI 42–56). The mean difference between the preoperative and post-operative SF-36 scores was 14 (95% CI 11–18) (p< 0.0001. The median preoperative Oswestry score was 46 (96.6% CI 42–50) and the median post-operative Oswestry score was 30 (96.6% CI 24–40) and the median post-operative Oswestry score was 30 (96.6% CI 24–40). The mean difference between the preoperative and post-operative Oswestry scores was 14 (95% CI 10–19) (p= 0.0001). 45 patients (61%) reported improvements of greater than 20 between their pre-operative and post-operative scores in either their SF-36 or Oswestry questionnaires. Of these 45 patients, 40 (89%) were also given moderate or good Odom (clinical) scores. 29 patients (39%) reported that they had not experienced improvement in their symptoms based on either their SF-36 or Oswestry questionnaires, with 12 (41%) of those 29 patients scoring poorly on their Odom scores. In all, there were 18 complications ranging from wound collections (4) and breakdowns (2) to repositioning of screws (6) and nerve root injury (2), to DVT (1) and transfusion (3).

Discussion: Interim results suggest that most patients undergoing PLIF and pedicle screw surgery with decompressive laminectomy for treatment of degenerative spondylolisthesis and degenerative scoliosis report significant improvements in function which correlate fairly well with clinical assessments performed by the surgeon at pre-operative and post-operative reviews. IInterestingly, patients generally reported either significant improvements (rather than borderline improvements) or that they had not improved at all, and that those who did report significant improvements also generally scored well on their Odom assessments. These reported improvements currently seem to be independent of whether bony fusion is achieved or not, as 16 of the 29 patients who did not report improvement actually achieved fusion. This is not unexpected as the initial PLIF procedure provides initial pre-fusion in situ rigid internal fixation.