(a–b) Axial T2 and coronal STIR magnetic resonance images of a large pelvic chondrosarcoma, displaying its difficult anatomic location that poses challenge to resection. Note the proximity to the rectum, vas deferens, prostate, and bladder
In the case of metastatic disease, it is rare than an acetabular or pelvic lesion would require resection. However, in light of recent evidence that resection of certain solitary metastatic bone tumors may increase survival, it is possible that these types of resection may be increasingly performed.
Minimally Invasive Treatment of Tumors Not Requiring Resection
In addition to pelvic and sacral tumor resection, navigation is also useful in management of subchondral, periarticular, or periacetabular lesions that do not require wide resection. This may include certain metastatic lesions of bone. Wu et al. described computer-assisted curettage and radiofrequency ablation of a chondroblastoma located in the proximal humeral epiphysis of a child, with preservation of the articular surface and full return to painless shoulder range of motion within 1 month . This group also described the application of navigation in cases of radiofrequency ablation of acetabular osteoid osteoma, curettage of ischial pheochromocytoma metastases, and curettage and cementation of supracetabular lytic lesions secondary to multiple myeloma. Cheng et al. also described the advantages of navigated radiofrequency ablation of osteoid osteomas . By guiding precise approaches to these lesions, outcomes can be optimized with minimally invasive exposures and less perioperative morbidity (Fig. 30.2). In the case of metastatic disease, bone lesions that need to be treated without the need for mechanical stabilization may be good targets in which to consider the use of navigation technology.
Coronal STIR magnetic resonance imaging of a juxtacortical chondroma in a 19-year-old field hockey player with back pain. Note the nearby L5 nerve root. Navigation facilitated precise localization and a minimally invasive approach to the mass for resection through an incision of less than 5 cm in length, allowing for rapid return to sport
Alternative Resection Capabilities
Navigation also offers the ability to perform tumor resection via surgical approaches that are not possible or less safe with traditional techniques, due to visualization challenges or soft tissue concerns. In the author’s experience, one case involving a large ischial mass requiring type III internal hemipelvectomy was approached surgically through an all-posterior buttock incision. The large posterior-based flap on the inferior gluteal pedicle that was created allowed excellent ability to maintain a margin on the most posterior and inferior portions of the mass, which would have been particularly challenging through a standard ilioinguinal hemipelvectomy incision. With navigation assistance, accurate osteotomies within the ischium and pubis were created through the posteriorly based incision. Without navigation, this surgical approach would have been less safe and likely less effective at achieving satisfactory tumor resection. The described surgical plan afforded a direct approach to the tumor, relatively short operative time, excellent visualization of the mass, negative surgical margins, and a rapid return to function following soft-tissue healing that may not have been achievable had a traditional approach been utilized. Likewise, for metastatic bone disease resections (when performed) it would be beneficial to minimize the scale and scope of surgery while still obtaining the desired resection. It is possible, in fact, to argue that patients with metastatic disease who require resection of bony metastases benefit even more than patients with primary disease from resections that heal faster and with less dissection, as the need for return to systemic therapy may be more pressing in these patients. For this reason, it is possible to speculate an important upcoming role for navigation in the treatment of these types of metastases.
Seong et al. described the application of navigation to periarticular mass resection . In the past, high-grade sarcomas involving the metaphyseal or epiphyseal area of long bones often required sacrifice of the entire adjacent joint in order to achieve a negative margin . In skeletally immature patients, the preservation of the adjacent epiphysis could sometimes be achieved thanks to the physis acting as an intraoperative landmark [30, 31]; however in skeletally mature patients lacking this physeal landmark, navigation now allows for precise localization and subsequent joint preservation. The authors showed that on pathological examination, the actual distances from the tumor to the resection margin were in accordance with their preoperative plan, and at their most recent postoperative follow-up their patients demonstrated healing at all periarticular osteotomy sites, with no evidence of recurrence, and satisfactory MSTS scores in all patients. It has been the author’s experience that navigation provides considerable assistance with periarticular resections, where precisely defined margins of resection are critical and an allograft can be fashioned based of a pre-generated template. This has allowed for allograft–host junctions that can be more precisely mated, allowing for improved healing and future function  (Fig. 30.3). In the case of metastatic disease, periarticular lesions are seen more frequently with certain subtypes of primary cancers. For instance, lung metastases have a higher predilection for periarticular locations. In the event of this type of metastasis, resection and reconstruction is often necessary to limit pain, preserve function, and maintain ambulation. The ability to perform improved periarticular resections and reconstructions using navigation is an important benefit of this type of technology.
(a–f) Preoperative X-ray and saggital STIR MRI images (a–c, respectively) of an 18-year-old male patient with clear cell chondrosarcoma of the proximal medial tibia. To preserve the joint, a navigation-assisted hemi-condylar resection and allograft reconstruction is performed. The system is used to replicate the bone cuts on both the host tibia and allograft, optimizing the allograft fit into the defect. (d–f) Display postoperative X-ray and CT images after reconstruction, demonstrating the level of precision that can be achieved with this technique. No visible gap can be appreciated between the host bone and allograft, which is difficult to achieve with freehand methods and maximizes the healing potential at the allograft–host junction
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Navigation technology also has application in reconstruction after tumor resection, as it allows for precise planning of an implant or prosthesis after guided resection. Computer-aided design and computer-aided modeling (CAD/CAM) surgical jigs are patient-specific instruments that facilitate customized, preplanned bone resection, followed by reconstruction with a precisely designed prosthesis that has been created to match accurately to the skeletal defect . One study testing customized CAD/CAM cutting jigs in a cadaver trial found the dimensional difference between the achieved and planned bone resection to be <1 mm, with the bone resections performed via the slots in the jig. After reporting their cadaveric results, they also described successful application of this technique to a patient with low-grade osteosarcoma of the femur. This system offers improved guidance and some extent of limitation to aberrant surgeon motion during bone cuts. CAD custom prostheses were also shown to achieve positions comparable to their planned positions based on postoperative CT scans, suggestive that this technique may facilitate not only planned resection with negative margins, but also planned reconstruction with custom implants .
Docquier et al. developed a novel reconstruction technique utilizing navigation to create a precisely replicated allograft specimen to fit within the pre-planned resection planes (illustrated in Fig. 30.3, above) . In their report, they describe how the allograft was fashioned by a separate surgeon using navigation technology on the back table, simultaneously during resection of the pelvic sarcoma. They describe the surgical efficiency of this strategy, along with achievement of a highly precise reconstruction in a complex anatomical location, where fit of the allograft or implant is a challenge with traditional techniques. An additional advantage of this technique, the shortened surgical time has implications both clinically and financially.
The orthopedic spine literature supports the use of navigation as a means to improve accuracy and precision of hardware placement. In areas of the pelvis that are difficult to visualize, this can be an advantage during reconstruction. When anatomic landmarks are resected en bloc with the tumor, which are commonly used as touchstones for implant placement (for example, the transverse acetabular ligament for establishing the version of an acetabular cup), navigation allows for accurate estimation of component position. In cases where a megaprosthesis is utilized, navigation has served particularly useful in the author’s experience at maximizing safety when placing lag screws between neural foramina during endoprosthetic hemipelvis reconstruction (Figs. 30.4 and 30.5).
(a–h) Example of a grade II chondrosarcoma of the right acetabulum. Preoperative X-ray and both axial and coronal STIR magnetic resonance images illustrate the periarticular location of this tumor (a–c). Preoperative planning of osteotomy planes on coronal T1 MRI images is shown in (d, e), with computer simulation of the planned resection illustrated in (f). The implant is designed by the surgeon and engineer, and the system generates a model of the prosthesis fitting into the planned resection defect, (g, h) display the postoperative X-ray, demonstrating the implant. This patient began walking with an assistive device 8 weeks from surgery
(a, b) Sequential axial CT images illustrating an example of difficult screw placement. Insertion of these trans-sacral screws was facilitated by navigation guidance. Two screws were needed at both the S1 and S2 levels to provide secure fixation for a hemipelvis implant; this would be nearly impossible to perform safely without navigation guidance, even by the most experienced pelvic surgeon