This paper by Pagenstert evaluates SPECT-CT imaging and its role in the localisation of disease in the foot and ankle. As the authors state “precise localisation of osteoarthritis is crucial for selective surgical treatment.” We must remember that in the foot and ankle, as elsewhere, osteoarthritis is a clinical disease. Radiological change is often asymptomatic, and in these cases will not usually require treatment. We also know that fusing one joint, can lead to the development of degenerative change in the adjacent joints over time.
The foot and ankle surgeon has various ways of determining the source of symptoms. The first, as always, is clinical. I ask the patient to point, with a single finger, to the area of his or her most severe pain. If this fails to resolve the issue various options are available:
1) Selective injection of the joints with local anaesthetic can be useful, although it has been shown that there are frequent intercommunications between joints in the foot.1
2) MRI scanning is also useful, and has been shown to increase the confidence in diagnosis, as well as reducing the number of differential diagnoses.2 Of course MRI and ultrasound scanning give information on the soft tissues, as well as bony structures. Nevertheless, there are concerns about the lack of specificity with MRI scanning.
3) 99mTechnetium bone scanning can be used. Unfortunately in anatomically complex areas the bony definition of the scan can make the precise localisation of disease difficult.
With this latter concern in mind we described a technique for co-registering radiographs and technetium bone scans.3 This technique superimposes areas of increased metabolic activity shown by bone scanning onto radiographs taken with the limb in the same position. It was shown that co-registering bone scans and radiographs overcame the very poor spatial definition and resolution of the technetium scan, and significantly increased the certainty of the localisation of disease. However the technique was never widely adopted as it was not made commercially available and was time consuming to undertake.
SPECT imaging was strongly driven by cardiology, primarily nuclear perfusion studies. SPECT CT was then introduced to try and reduce the number of equivocal SPECT studies by determining the extent and location of radiopharmaceutical uptake. SPECT-CT technology can be applied in musculoskeletal imaging. A Technetium isotope scan is superimposed upon a three dimensional CT scan. With the advances in technology and the production of a single image showing accurately localised and superimposed biological activity and radiological detail, maybe this is the usable form of co-registration.
Pagenstert has shown that this technique gives good intraobserver and interobserver reliability in the hands of a radiologist, nuclear medicine physician, board certified and non-board certified orthopaedic surgeons. As such SPECT-CT allows accurate interpretation of the bone scan. Areas of isotope uptake can be mapped and localised to an affected joint. This is of obvious benefit in areas where there are numerous small bones, and this technique should be of interest to foot, hand and spinal surgeons. It is stated that the spatial resolution of CT scanning is less than 1 mm and that of bone scanning is 7 mm.
Obviously neither this study, nor, for that matter, our own on co-registration with plain radiographs, are the final answer on this subject. Neither study looks at the clinical outcome of the treated patients. It needs to be proved, or disproved, that fusion of those joints with high biological activity cures the patient’s symptoms. Obviously the more limited the fusion that can be undertaken the better for the patient in the short-term and also in the longer term to prevent the development of secondary degeneration. However, if all that happens is that the adjacent joints, with radiologically positive change but an absence of metabolic activity, become symptomatic, one would have to consider fusion of the radiologically abnormal joint, and not simply those with positive bone scans. Anecdotally I have observed that fusion of those joints which are active on the bone scan has given satisfactory and durable clinical results.
As such I suspect SPECT-CT may become a useful, all be it selectively used, part of the armamentarium of the orthopaedic surgeon where the correlation of disease activity and radiological change is felt to be desirable. The principle and initial uses of this technology were by the cardiologists, however others may find the technology of use in their specialities, especially as cardiological demand is not as great as was anticipated.
Finally in appraising this paper we have to acknowledge that not all the advances in surgery are surgical, or even made by surgeons. Indeed over the years our colleagues in anaesthesia, radiology and from extra-medical disciplines such as engineers and biologists have contributed hugely to orthopaedic progress.
1. Carmont MR, Tomlinson JE, Blundell C, Davies MB, Moore DJ. Variability of joint communications in the foot and ankle demonstrated by contrast-enhanced diagnostic injections. Foot Ankle Int. 2009;30:439-42.
2. Bearcroft PW, Guy S, Bradley M, Robinson F. MRI of the ankle: effect on diagnostic confidence and patient management. Am J Roentgenol. 2006;187:1327-31.
3. Robinson AH, Bird N, Screaton N, Wraight EP, Meggitt BF. Coregistration imaging of the foot: A new localisation technique. J Bone Joint Surg [Br] 1998;80:777-80.
Robinson A, BSc, MBBS, FRCS
Cambridge, United Kingdom