Sarcoma resections are done with pre-operatively planned margins based on imaging the extent of the tumor. These margins are “sacred” and cannot be compromised. In the limbs, where the tumor is resected through the joint, the proximal extent is measured based on MRI scans and it is simple to make a cut through the cylindrical femur perpendicular to the long axis freehand. An imprecise cut with angulation in either the frontal or the saggital plane will not greatly affect the margin or the alignment of the implant and is easy to correct if very oblique. But if the cut requires being precise within millimetres, as is the case when joint preserving surgery is done, an imprecise cut can compromise the margin and result in tumor recurrence which can be limb as well as life threatening. The accuracy is even more difficult in the pelvis where the shapes are not geometrical and eyeballing can cause errors which are disastrous. Cartiaux et al1 in an experimental study demonstrated that even experienced surgeons had a greater than 33% error rate in making a cut in the pelvis despite ideal conditions like lack of soft tissues and blood on the saw bone model. This is well in line with studies which have shown higher than normal rates of positive margin and local recurrence for pelvic tumours.2,3 Just as modern aeroplanes are guided by sophisticated computerised navigation systems, a surgeon’s saw also requires precise guidance to ensure safety of margins as well as preventing damage to vital structures. A bad cut in arthroplasty can cause early implant failure which can be revised but a bad cut resulting in sarcoma recurrence cannot be corrected. Therefore we may argue about necessity of navigation in routine arthroplasties, but in tumour surgery where the risks are greater, navigation is necessary to improve precision. Technology has been useful to augment the skills of a surgeon, especially in tasks that require mathematical precision. We have steadily improved our precision by using intra-operative x-rays in trauma as well as cutting blocks and guides in arthroplasty. It is now safe to have a slightly longer operating times if it improves technical accuracy. In orthopaedic oncology, the gains are double in terms of better disease control as well as in the accuracy of reconstruction. Both these benefits far outweigh the drawback of increased operating time.
As with any other technology, it improves with time and experience. The current navigation systems are far superior to those available a decade ago and will again be much easier and more accurate in a few years time. We must thus today adopt a seemingly difficult practice to improve our accuracy and thus outcomes. The authors themselves have first used CT based planning, then done CT-MR fusion to use for planning and now currently use MR directly for planning navigation. The authors have used MRI compatible fiducial markers for more accurate registration and to further reduce the errors from CT-MRI fusion pictures. This is probably the correct way to go as the extent of a tumour is best judged on MRI. The planning, setup and registration times have also changed from a few hours in the past4,5 to 30 minutes currently as reported by the authors of this paper.
With their technique, the authors have shown an accuracy of within 2mm from the preoperatively defined plan. Logically this would translate into a reduced local recurrence rate. The authors have therefore presented a strong case for use of computer aided navigation in operations where precision would directly effect the results, particularly in the pelvis and sacrum. It is also likely to be useful in limbs where reliable landmarks are hard to get as in joint sparing operations with close margins of resection.
Thus, the availability of navigation opens up the possibility of using methods of reconstruction, not possible without it, for example, unorthodox pelvic or limb cuts and custom-made implants to precisely fit those cuts. We can now have much closer resections and better function from the preservation of normal tissue, particularly in the pelvis and joint sparing resections.
Dr Manish Agarwal, Consultant Orthopaedic Oncologist, firstname.lastname@example.org
Dr Prakash Nayak, Clinical associate, email@example.com
P.D Hinduja National Hospital & Medical Research Centre, Veer Savarkar Marg, Mahim, Mumbai 400007, India
1. Cartiaux O, Docquier PL, Paul L, et al. Surgical inaccuracy of tumor resection and reconstruction within the pelvis: an experimental study. Acta Orthop 2008;79:695-702.
2. Delloye C, Banse X, Brichard B, Docquier P L, Cornu O. Pelvic reconstruction with a structural pelvic allograft after resection of a malignant bone tumor. J Bone Joint Surg [Am] 2007;89-A: 579-87.
3. Ozaki T, Flege S, Kevric M, et al. Osteosarcoma of the pelvis: experience of the Cooperative Osteosarcoma Study Group. J Clin Oncol 2003;21:334-41.
4. Wong KC, Kumta SM, Chiu KH, Antonio GE, Unwin P, Leung KS. Precision tumour resection and reconstruction using imageguided computer navigation. J Bone Joint Surg [Br] 2007;89-B:943–47.
5. Reijnders K, Coppes MH, van Hulzen AL, et al. Image guided surgery: new technology for surgery of soft tissue and bone sarcomas. Eur J Surg Oncol 2007;33:390–8.