SPECT-CT Compared with Conventional Imaging Modalities for the Assessment of the Varus and Valgus Malaligned Hindfoot Markus Knupp, 1 Geert I. Pagenstert, 1 Alexej Barg, 1 Lilianna Bolliger, 1 Mark E. Easley, 2 Beat Hintermann 1 1 Department of Orthopedic Surgery, Kantonsspital Liestal, Liestal, Switzerland, 2 Division of Orthopedic Surgery, Duke University Medical Center, Durham, North Carolina Received 13 February 2009; accepted 20 April 2009 Published online 26 May 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jor.20922 ABSTRACT: The combined single-photon emission computed tomography and conventional computed tomography (SPECT/CT) technique has increased the sensitivity and specificity of bone scans. We examined the value of using SPECT/CT for the assessment of coronal plane hindfoot deformities. Twenty-seven patients with varus (11 patients) or valgus (16 patients) malalignment of the hindfoot were assessed using radiography, conventional CT, bone scintigraphy, and SPECT/CT. The amount of deformity, stage of osteoarthritis, and level of activation on bone scans and SPECT/CT were measured. Activation was assessed in 12 regions of interest. The stage of osteoarthritis seen on plain radiographs correlated significantly with the level of activation detected on bone scans (p < 0.05). No correlation was observed between the amount of deformation and activity, and between bone scan activation and signs of osteoarthritis on CT scans. The varus malaligned ankles showed higher radioisotope uptake in the medial areas, while the valgus malaligned ankles showed increased uptake in the lateral areas (p < 0.05). SPECT/CT may be a valuable tool for the assessment and staging of osteoarthritis. Our findings underline the adverse effects of coronal plane deformity of the hindfoot. In addition, results from this study provide useful information for future basic research on coronal plane deformity of the hindfoot and for determining appropriate surgical approaches. ß 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1461–1466, 2009 Keywords: hindfoot; alignment; SPECT; ankle; osteoarthritis The ankle joint is rarely affected by osteoarthritis. 1 Rather, it is trauma and/or abnormal ankle mechanics that are mainly responsible for the majority of degenerative changes in the malaligned ankle joint. 2,3 Several authors have reported the deleterious effects of coronal malalignment on the hindfoot and ankle joint as well as on neighboring structures. 4–7 Nevertheless, the natural history, particularly the early development, of degenerative disease in the malaligned ankle joint remains poorly defined. Current imaging strategies, particularly those that evaluate disorders of the foot and ankle, provide only limited information on early degenerative changes in articular cartilage. Plain radiography is commonly used to define malalignment 8–11 and moderate to advanced degenerative changes. 12 Computed tomography (CT) and magnetic resonance imaging (MRI) are sensitive techniques for detecting osteochondral cysts and defects or concomitant lesions, such as alterations of the ligaments or the tendons. 13–15 However, these modal- ities give little information about cartilage pathology. 16 Hybrid imaging with single-photon emission com- puted tomography (SPECT) and conventional CT was recently introduced. Combined SPECT/CT imaging permits direct fusion of morphological (CT) and func- tional (SPECT) data sets. In our opinion, applying this technology to the assessment of hindfoot and ankle deformity provides a reproducible method to diagnose and evaluate the progression of degenerative articular disease. An important advantage of SPECT/CT com- pared with conventional modalities is the simultaneous high-resolution imaging of bone morphology and high- sensitivity imaging of bone metabolism. This approach enables the clinician to assess even early stages of disease that are poorly detected by other imaging modalities. The purpose of this study was to evaluate the combination of SPECT and conventional CT for the detection of early and progressive degenerative articular disease in the overloaded areas of malaligned hindfoot and ankle joints. METHODS Patients A total of 27 consecutive patients with symptomatic ankle varus (11 patients; eight men and three women) or valgus (16 patients; nine men and seven women) malalignment were referred by their local physician/orthopedic surgeon to our clinic for operative treatment after having failed conservative treatment. The 27 patients were informed of the potential risks of the study and gave an informed consent to participate in the study. All patients (mean age 49 years, range 19 to75 years) were evaluated clinically and by radiography according to standard protocol and then examined by SPECT/CT. The study was approved by the Research Ethics Committee at our institution. Plain Radiographs Weight-bearing anteroposterior and lateral ankle radiographs were performed. All radiographs were evaluated with a high- resolution monitor using the DICOM/PACS review application E-Film. The radiographs were evaluated by an investigator who was a board-certified orthopedic surgeon working in the foot and ankle unit but not directly involved in the clinical aspects of our study. The dimensions assessed included the angle of distal tibial joint surface (TAS, a) and the tibiotalar angle (TTA, g). 11,12,17 The TAS angle was defined by the midlongitudinal axis and the plafond of the tibia. The weight-bearing axis of the tibia was defined by bisecting the tibia 8 and 15 cm above the medial tibial JOURNAL OF ORTHOPAEDIC RESEARCH NOVEMBER 2009 1461 Correspondence to: Markus Knupp (T: þ41-61-925-22-20; F: þ41- 61-925-28-08; E-mail: markus.knupp@ksli.ch) ß 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.