Seminars in Nuclear Medicine
Volume 40, Issue 1 , Pages 41-51, January 2010

SPECT/CT in Imaging Foot and Ankle Pathology—The Demise of Other Coregistration Techniques

  • Hosahalli K. Mohan, MBBS, MRCP, MSc

      Affiliations

    • Department of Nuclear Medicine, Guy's and St. Thomas' Hospitals, NHS Trust, London, United Kingdom
    • Corresponding Author InformationAddress reprint requests to Hosahalli. K. Mohan, MBBS, MRCP, MSc, Department of Nuclear Medicine, Ground Floor, New Guy's House, Guy's Hospital, St. Thomas' St, London SE1 9RT, United Kingdom
    • ,
  • Gopinath Gnanasegaran, MBBS, MD, MSc

      Affiliations

    • Department of Nuclear Medicine, Guy's and St. Thomas' Hospitals, NHS Trust, London, United Kingdom
    • ,
  • Sanjay Vijayanathan, MBBS, MRCP, FRCR

      Affiliations

    • Department of Radiology, Guy's and St. Thomas' Hospitals, NHS Trust, London, United Kingdom
    • ,
  • Ignac Fogelman, MBBS, FRCP, MD

      Affiliations

    • Department of Nuclear Medicine, Guy's and St. Thomas' Hospitals, NHS Trust, London, United Kingdom

Article Outline

Disorders of the ankle and foot are common and given the complex anatomy and function of the foot, they present a significant clinical challenge. Imaging plays a crucial role in the management of these patients, with multiple imaging options available to the clinician. The American College of radiology has set the appropriateness criteria for the use of the available investigating modalities in the management of foot and ankle pathologies. These are broadly classified into anatomical and functional imaging modalities. Recently, single-photon emission computed tomography and/or computed tomography scanners, which can elegantly combine functional and anatomical images have been introduced, promising an exciting and important development. This review describes our clinical experience with single-photon emission computed tomography and/or computed tomography and discusses potential applications of these techniques.

 

Disorders of the ankle and foot are common and are a significant clinical challenge. The complex anatomy and function of the foot make it difficult to localize origin of the pain by routine clinical examination. This has resulted in the evolution of an orthopedic sub-speciality focused on the foot and ankle. In keeping with this trend, there needs to be an evolution of imaging techniques, which would assist the clinician in optimal management of these complex problems. Anatomical (x-ray, magnetic resonance imaging [MRI], ultrasound, and computed tomography [CT]) and functional imaging (bone scan, MRI, and ultrasound) techniques have been used in the management of patients with chronic foot pain.

Coregistration of anatomical and functional imaging (hybrid imaging) combines the advantages of individual studies in a synergistic manner aiding the clinician in the efficient management of complex problems. The value of hybrid imaging is well established with positron emission tomography (PET/CT) in the management of various oncological and nononcological conditions. Coregistration of routine nuclear medicine studies with radiological imaging is well described1, 2, 3 and the value of coregistered images in the management of patients with wrist pain is well recognized. Similar techniques have been described in the coregistration of images of the feet by Robinson et al.4 More recently, Groves et al. have described the technique of coregistering bone single-photon emission computed tomography (SPECT) images of the wrist with multislice CT images using a software,5 and the clinical value of this technique.6 CT images provide exquisite details of the bone anatomy while the bone scan provides the functional information. More recently hybrid scanners with the ability of acquiring SPECT and multislice CT data simultaneously have been introduced. Combined single-photon emission computed tomography and/or computed tomography (SPECT/CT) study may prove to be an excellent technique for the evaluation of complex bony pathology in the feet, although at present MRI remains the most widely used technique for the evaluation of chronic foot pain.

In this article, we describe the current techniques available for imaging pathology in the feet, describe our clinical experience with the new SPECT/CT technique, and discuss its potential applications.

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Conventional Radiography (X-Ray) 

This remains the most widely used, accessible, and cost-effective imaging modality for evaluation and management of acute and chronic foot pain. This has a particularly important role in the management of acute trauma, while its role in chronic injuries remains limited and at best complementary to the other techniques.

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CT 

CT is an established technique that has been widely available for 2 decades and the advent of multidetector computed tomography (MDCT) has expanded its utility. MDCT helically acquires data that may be reconstructed in any plane, and advances in technology allows submillimeter resolution which aid the clinician to better evaluate the bones, image hardware and related complications, articular cartilage lesions, and even limited assessment of tendon disease.7 The complex anatomy of the hind- and midfoot can be evaluated in multiple planes using reformatted images. This enhances the ability to detect fractures, osteochondral lesions, and disease not appreciable on plain radiographs.7, 8, 9 MDCT also provides high-resolution images essential for presurgical planning and can also be used to generate a realistic full-sized 3-dimensional model that allows the surgeon to practice corrective osteotomies in complex cases on a life-size model before operating on a patient. It has also been suggested that CT arthrography may prove to be superior to MR for the postoperative assessment of chondral repair where MRI images may be degraded because of postoperative changes and micrometallic artefacts.9 However, the role of MDCT in the assessment of soft-tissue disease, including tendinous and ligamentous pathologies in the feet, has not been proven and remains the main limitation when compared with MRI or ultrasound.10

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MRI 

MRI has rapidly become the preferred modality for evaluating a variety of musculoskeletal disorders, including diseases of the foot and ankle. Advances in MRI [ultrahigh field strength magnets (>1.5 T)] and in the imaging protocols offer the potential of better signal-to-noise ratio, improved resolution, and faster scan times.11 Improved resolution permits more accurate depiction of small structures, such as the articular cartilage in small joints. MRI is routinely used in the evaluation of soft-tissue pathology of the feet, including tendinosis, bursitis, fasciitis, and for the diabetic foot. MR angiography allows examination of the vasculature as well. It has been successfully used in the management of diabetes-related osteomyelitis. Optimal evaluation of tendinous pathology, however, remains elusive and in a recent study, maximum of 27% of patients who presented with clinical evidence of posterior tibial tendon disease had a normal MR examination result.12 Even patients with severe Achilles tendon symptoms were frequently observed to have a normal examination, and ultrasonography remains the investigation of choice in this population. Some of the potential disadvantages that one must be aware of with MRI are metallic artifacts associated with hardware or micrometallic material in an operative bed, which are more pronounced in high-field systems and worse with increasing field strength. Postoperative follow-up imaging in the presence of micrometallic artifacts may not be carried out using a high-field system. Additionally, coil design has not yet been optimized for high-field imaging of the extremities. Imaging parameters are not transferable from 1.5-3.0 T systems and must be modified to take advantage of the potential benefits of high-field strength imaging.11, 13 Also, due to claustrophobia the use of general anesthesia has been seen in a maximum o 10% of patients imaged in a closed high-field MR system, and obese patients frequently cannot be imaged in the constrained geometry of closed systems. The larger apertures afforded by open systems may be the only option for these patients but comes with the price of loss of resolution compared with the high-field systems.

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Ultrasonography 

Ultrasound is used in patients with foot pain, to examine the soft tissue, and is often the preferred imaging modality when Morton's neuroma or Achilles tendinosis is suspected.12 Sonographic evaluation of the ankle has distinct advantages and disadvantages. Advantages include direct correlation of sonographic findings with the patient's symptoms in comparison with the asymptomatic ankle, dynamic imaging of the foot in multiple planes and positions, wide availability of sonographic equipment, lower cost when compared with MRI, and speed of the examination. Also, the equipment is portable and can be moved to the bedside of an unwell patient, and it also has the advantage of not using ionizing radiation. Disadvantages of ultrasound include unfamiliarity with the scanning technique and appearance of ultrasound pathology, operator dependence, and limitation of imaging structures superficial to the bony cortex.14

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Nuclear Medicine 

A bone scan is a highly sensitive technique that has been used in the diagnosis and management of skeletal pathology for nearly 3 decades.15 Groshar et al16 in their review article have described the role of bone scintigraphy in specific conditions resulting in foot pain. Although the sensitivity of the bone scan in the diagnosis of bony pathology in the foot remains high, specificity remains suboptimal. This coupled with relatively poor resolution compared with MRI and CT remains the main drawback of the bone scan. SPECT studies routinely performed in patients with equivocal findings noted on planar bone scans have demonstrated improved sensitivity and specificity, although it has shown only limited benefit17 in the evaluation of foot pathology.

Coregistration of bone scan images with x-ray4 and CT have been performed using software6, 18 and low-dose CT systems.19, 20 Recently, hybrid systems capable of acquiring high-resolution multislice CT image sets that directly match SPECT findings in the same sitting have been developed. This is expected to further increase the diagnostic accuracy of this already highly sensitive but generally nonspecific study. Potential applications include the ability to detect and/or exclude osteomyelitis, to map out sites of degeneration and/or inflammation, and confirm the precise anatomical localization of focal findings in both benign and malignant disease,20, 21 to name a few. To date, however, there has been an extremely limited experience of using SPECT/CT in the evaluation of patients with foot pain.

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Method 

Standard 2 phase bone scintigraphy after intravenous injection of 800 MBq 99mTc-methylene diphosphonate (as specified in the “Notes for Guidance on Clinical Administration of Radiopharmaceuticals and Use of Sealed Radioactive Sources −2006”) is carried out in accordance with the department bone scintigraphy protocol. This includes early blood pool imaging at 5 minutes postinjection of tracer followed by the standard delayed planar images at 3 hours postinjection. Anterior, posterior, lateral, and plantar views are acquired.

SPECT/CT imaging of the feet is performed using a dual head gamma camera SPECT/CT system (Philips Precedence 16; Philips, Milpitas, CA). Data are acquired with low-energy high-resolution collimators in 128 projections of 20 seconds each over 360° on a 128 × 128 pixel matrix. Helical CT data are acquired with an exposure of 100 mA per slice, 120 kV, a pitch of 1.188 with rotation time of 0.75 seconds, collimation of 16 × 0.75 mm, and reconstructed to images of 0.683 mm transverse pixel size and 1.5 mm slice thickness.

SPECT data were reconstructed with Orderly Subsets Expectation Maximum (5 iterations over 8 subsets), by incorporating depth-dependent resolution compensation (Philips Astonish) implemented in the manufacturer's software (AutoSPECT+ v3.5). Images were fused using the manufacturer's software (Syntegra v2.2).

The effective dose from 800 MBq 99mTc-methylene diphosphonate is 5 mSv, while the effective dose per 10 cm from the CT scan is ∼0.33 mSv (DLP 469.1 mGy.cm, CTDIvol 18.1 mGy).

SPECT/CT studies are reported jointly by a nuclear medicine physician and a musculoskeletal radiologist.

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Potential Applications 

Postoperative Evaluation of Joint Fusion 

Joint arthrodesis has long been used for the treatment of painful malalignment or arthritis of the hindfoot.22, 23, 24 Successful osseous union after joint arthrodesis is usually expected to occur within 6 months of the procedure25, 26, 27 and is confirmed if no joint motion is detected on clinical examination and there is evidence of trabeculation across the arthrodesis site as observed on plain film radiographs. Delayed union is defined as a successful fusion 6-9 months after surgery.

In patients who continue to suffer from pain after arthrodesis, nonunion is suspected. Other complications that result in persistent pain after arthrodesis include overload of the adjacent joints, with development of arthritis in about 30% in the medium term.28 This is more common in patients with triple arthrodesis leading to substantial reduction of movement in the triple joint complex, which leads to an increased incidence of selective joint fusions. Postoperative assessment of the success of fusion has been routinely evaluated using x-ray and CT techniques. MRI would be unsuitable in this situation because of in situ metal hardware or the presence of micrometallic artifacts. When fusion attempts have been made on multiple joints, selective injections may aid in determining the location of pain. Selective intra-articular rear- and midfoot injections have been shown to improve pain localization as plain radiographs and CT scanning may underestimate or poorly localize the most symptomatic joints.29 However, this remains an invasive procedure with associated risks. Computed tomography scanning has gained use in identifying nonunion sites associated with pain, but may provide limited information if metal implants are retained because of scatter effects. Retained metal implants may be removed before CT scanning to improve diagnostic accuracy that may be beneficial anyway as the hardware can be the source of discomfort, with removal providing relief. SPECT/CT may provide a valuable technique (Fig. 1) for the evaluation of continuing pain in the context of arthodeses with in situ hardware as sites of altered metabolic activity on the bone scan would allow a more focused examination of the area on the CT study. This may improve the accuracy of identifying nonunion or malunion or subjacent arthritis as the cause for continuing pain.

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  • Figure 1. 

    Nonunion: A 59-year-old patient with previous talonavicular fusion complaining of continuing pain. Clinically the is joint immobile. X-rays are not conclusive. On the delayed images there is focal increased tracer uptake (arrow) in the right midfoot, and on the blood pool images there is increased vascularity noted to this site (arrow). On the SPECT/CT study, this area of uptake corresponds to nonunion of talonavicular joint (CT image) causing continued pain postsurgery in the patient.

Assessment of Infection Postarthrodesis 

Despite strict aseptic measures and prophylactic antibiotic usage, superficial wound infections have been reported in as many as 3% of patients undergoing midfoot30 and rearfoot fusions.31 Elderly patients have been seen to experience a significantly higher infection rate with rearfoot fusions reported at 11%,32 but advanced age is not necessarily a contraindication for performing a midfoot or rearfoot fusion. Deep infections place the extremity at risk, and in such instances appropriate and aggressive surgical debridements are undertaken by the surgeon. Revision triple arthrodesis has a deep infection rate of 3.5%.33 Deep cultures are carried out before and after irrigation and debridement. Postsurgical osteomyelitis presents a dilemma, in that surgeons often are hesitant to debride infected bone aggressively in the hope that union will proceed and the bone infection can be resolved with appropriate antibiotics. Retained implants may also act as a nidus for persistent infection. Debridement of all infected and devitalized bone, removal of implants, and placement of antibiotic-impregnated polymethylmethacrylate beads for large fusion areas may salvage an otherwise difficult infection. Revision fusion efforts are usually attempted after a satisfactory response to a 4-6-week course of culture-directed antibiotics, adequate debridement, and negative operative cultures.

SPECT/CT bone scan may provide an excellent tool in assessing the presence and extent of infection, with the SPECT study delineating the extent of bony involvement and the CT study demonstrating the associated soft-tissue changes. This would be preferred to MRI given the problems posed by postsurgical scarring and micrometallic artifacts and also for diabetic patients in whom there is the additional risk of nephrogenic fibrosis associated with gadolinium contrast. A SPECT/CT white cell study (Fig. 2) would be useful in confirming bone- and soft-tissue infection and also in monitoring response to treatment.

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  • Figure 2. 

    Chronic osteomyelitis: A 42-year-old man with a history of right fibular fracture and internal fixation, complaining of continuing pain and swelling around the right ankle after removal of fixation screws and plates. He underwent a white cell scan to assess for infection. The planar images showed focal accumulation of white cells in the medial aspect of the right ankle (arrow). SPECT/CT study confirms uptake in the soft tissue of the medial aspect of right ankle with further focal increased uptake involving the right lower fibula where there are areas of lysis and/or sclerosis noted on the CT study and associated soft-tissue swelling in keeping with chronic osteomyelitis (arrow).

Talar Osteochondral Defect 

An osteochondral lesion of the talar dome is often subtle and missed on plain films. Acute and subacute injuries of the articular cartilage and underlying subchondral bone are believed to be the principal cause of the aseptic necrosis observed by histopathology. Bilateral lesions may occur in approximately 10% of cases, although medial lesions are more common. Although uncommon, it remains one of the treatable causes of unexplained chronic ankle pain.34

Bone scan is a sensitive screening test used in the diagnosis of talar osteochondral defect (OCD).35, 36, 37, 38 Increased blood flow and blood pool at the talar region associated with focally increased activity at the talar dome is suggestive of an osteochondral lesion. Abnormal focal activity at the talar dome was found to have 94% sensitivity and 76% specificity for osteochondral lesions.37 CT scan provides high quality anatomical images for accurately assessing the location and size of the OCD lesions. In a prospective study, Verhagen et al39 observed no statistically significant difference between the diagnostic value of helical CT in comparison with MRI. In addition, CT provides information about the loose fragments within the lesion that makes surgical intervention a necessity.40 The combination of highly sensitive bone SPECT images with a highly specific CT study provides the clinician with an excellent tool for the diagnosis and management of talar OCD (Fig. 3). It would also be beneficial in the postoperative assessment, particularly where MR images may be difficult to interpret.

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  • Figure 3. 

    Osteochondral defect: A 27-year-old man with pain in left hindfoot—There was a history of fall. Delayed images show increased focal uptake of tracer in left ankle medially with increased vascularity on the early images (arrows pointing). SPECT/CT study confirms focal uptake in the talar dome, and on the CT images (arrow) there are cystic changes noted in keeping with an osteochondral defect in the talus.

Achilles Tendonitis, Bursitis, and Plantar Fasciitis 

Plantar fasciitis is a common enthesopathy causing heel pain. It may occur at any age but is common in patients aged 40-60 years.41 Typically, plain radiography is not helpful, but is always done to rule out other conditions. Radiography may reveal a plantar calcaneal spur, but as this type of spur is commonly observed in asymptomatic adults, it is not specific.

Bone scanning and MRI have been shown to be helpful in determining a diagnosis.42 However, MRI is rated 9 on the American College of Radiology (ACR) appropriateness criteria scale, whereas bone scanning is rated 2 because MR images can demonstrate more detail, including the thickening of the proximal plantar fascia, inflammation in the plantar aponeurosis, adjacent soft-tissue edema, reactive calcaneal marrow edema, and any evidence of rupture of the fascia.43 One study showed that ultrasonography is effective in differentiating normal plantar fascia from plantar fasciitis.44

SPECT/CT can provide information about local alterations of metabolic activity in addition to providing excellent anatomical resolution of the plantar fascia (Fig. 4).

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  • Figure 4. 

    Plantar fasciitis and retrocalcaneal bursitis and/or Achilles tendonitis: A 21-year-old man presented with a 3-year history of right heel pain. There was no history of trauma. Clinically, Achilles tendonitis was suspected. There is increased vascularity seen on the early blood pool images along the plantar fascia with more focal uptake at the plantar aspect of the calcaneum on the delayed images (arrow). On the SPECT/CT images, the uptake corresponds to the insertion of the plantar fascia, with associated plantar fascia thickening also identified on the CT study (arrow). Also, there is marked increase in the vascularity on the early blood pool and increased uptake on the delayed images in the superior aspect of the right calcaneus noted (arrow). On the SPECT/CT images the increased area of uptake superiorly localizes to the superior aspect of the calcaneus at the site of insertion of the Achilles tendon (enthesopathy). There is associated opacification of the Kager fat pad noted on the CT images which is seen in patients with Achilles tendonitis (arrow).

Achilles tendon is the strongest tendon in the human body. Achilles tendonitis causes much morbidity in the athletic and nonathletic population and is essentially an overuse, degenerative condition.45 MRI and ultrasonography remain the main modalities for the evaluation of the Achilles tendon.

In patients with Achilles tendonitis, associated edema may be noted within the Kager fat pad, which lies at the superior aspect of the posterior calcaneum and anterior to the Achilles tendon seen on MRI studies. In addition, inflammation of the retrocalcaneal (subtendinous) bursal sac where the Achilles tendon attaches to the calcaneum may be associated, which is also well demonstrated on MRI.

Although the role of bone scintigraphy remains limited in patients with Achilles tendonitis, SPECT/CT may provide useful coincidental imaging information for the clinician. The SPECT study would demonstrate the metabolic abnormalities associated with the calcaneus (edema/enthesophyte trauma, etc.) while CT would be useful in demonstrating the associated soft-tissue abnormalities with the Kager's fat pad and/or retrocalcaneal bursa (Fig. 4).

Stress Fracture 

Plain radiography is not listed in the original ACR Appropriateness Criteria Scale for stress fracture, because of its poor sensitivity. However, it still remains the first investigation that is ordered in patients with suspected stress fracture.

Bone scan46 and recently MRI have demonstrated high sensitivity in identifying early stress injury.47 Bone scanning demonstrates the abnormal increased bone metabolism and osteoblastic activity associated with osseous remodeling as a response to continued stress, whereas MRI detects the bone marrow edema associated with osseous stress reactions, and these changes may often be present days to weeks before radiographic changes (a fracture line) are visualized. Interestingly, Gaeta et al48 in their recent article suggest that the earliest finding of abnormal repetitive stress may be osteopenia that can only be demonstrated by dedicated high-resolution CT studies. In view of their findings, although this needs to be confirmed by further studies, one would anticipate that SPECT/CT may find a more prominent role to play in the early diagnosis and management of patients with suspected stress fractures (Fig. 5). Ultrasonography has also been used to evaluate superficial bone cortices, such as feet and distal tibia. It can also depict periosteal and muscle edema, cortical fracture lines, and callus.

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  • Figure 5. 

    Stress fracture: A 36-year-old patient who had had left leg amputation in a road traffic accident underwent bone scintigraphy to evaluate the cause of severe pain in the right midfoot. Delayed planar images show focal increased uptake in the right ankle midfoot with increased vascularity (arrow) on the early blood pool images. SPECT images confirm uptake in the midfoot which on the SPECT/CT images correspond to a stress fracture involving medial aspect of talus resulting in the patient's symptoms (arrow).

Painful Accessory Bones 

Potentially, painful normal bony variants, such as accessory tarsal navicular and os trigonum, have been described with chronic foot pain.49, 50 The accessory tarsal navicular is situated adjacent to the medial and posterior margins of the tarsal navicular and has a prevalence of 4%-14%.49 Os trigonum is located adjacent to the posterior margin of the talus and has a prevalence of 14-25%.49 The mechanism of pain in the presence of an accessory tarsal bone has been attributed to traumatic or degenerative changes at the synchondrosis or to soft-tissue inflammation. Symptomatic accessory tarsal navicular bones have been studied with bone scanning and MRI. Symptomatic lesions are reported to show increased radiotracer uptake or marrow edema across the synchondrosis. For a painful os trigonum, fluoroscopy-guided contrast injection of the synchondrosis followed by local anesthetic injection localizes the source of pain.50 A SPECT/CT study provides an excellent technique for the evaluation of the cause of chronic pain in this situation, with the SPECT study elegantly demonstrating any altered metabolic activity in the joint while CT demonstrates the associated anatomical abnormalities (Fig. 6).

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  • Figure 6. 

    Painful accessory bone, os trigonum: A 47-year-old woman with pain in right ankle and known to have bilateral os trigonum. There is increased uptake in the delayed images and increased vascularity on the early blood pool images noted within the posterior aspect of right ankle (arrow). On the SPECT/CT study, the increased tracer uptake is seen corresponding to the syndesmosis between the os trigonum and the talus (arrow). Although the CT study shows only minor asymmetrical sclerosis and irregularity along the joint margin, the increased uptake on the SPECT study helps confirms the site of symptoms allowing appropriate surgical management.

Tarsal Coalition 

Tarsal coalition is a deformity that results from abnormal bridging across 2 or more tarsal bones, resulting in painful deformity of the hindfoot with restricted motion. Three types of coalition exist: fibrous (syndesmosis), cartilaginous (synchondrosis), and osseous (synostosis) fusion. The true incidence of tarsal coalition in the general population is unknown, but is <1%.51 The coalition is bilateral in about one-half of patients. Calcaneonavicular and talocalcaneal (middle facet at the level of the sustentaculum tali) coalition are the most common sites. Oblique anteroposterior radiography of the foot may at times identify calcaneonavicular coalition, whereas talocalcaneal coalition is often overlooked on plain radiographs because of overlapping structures, and such a diagnosis on x-ray may be deduced by the presence secondary signs suggestive of talocalcaneal coalition. These signs include talar breaking,52 flattening and broadening of the lateral talar process, positive C sign,53, 54, 55 absent middle facet sign,56 and narrowing of the posterior talocalcaneal joint. Although CT and MRI are not the imaging studies of choice for tarsal coalition, CT of the subtalar joint is often diagnostic.57 SPECT/CT may be an improved alternative to CT alone with addition of supplementary functional information from the bone scan (Fig. 7). The area of uptake on the SPECT study may also help guide intra-articular injections. MRI has also been shown to be reasonably effective in depicting most types of coalition. Inversion-recovery MRI may reveal bone marrow edema along the margin of the abnormal articulation, which is an important clue to the diagnosis.

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  • Figure 7. 

    Tarsal coalition: A 33-year-old woman with right ankle pain. The delayed images of the ankles show increased tracer uptake within the right ankle (arrow) which on the SPECT/CT images correspond to the lateral aspect of the subtalar joint. The cortical irregularity and sclerosis along the margins in the medial aspect are consistent with the clinical suspicion of a fibrous coalition (arrow). The increased uptake in the lateral aspect of the joint (arrow) was thought to be due to associated alteration in biomechanical load. This area was injected with steroids and has resulted in improvement of pain.

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Our Experience 

We have assessed the additional value of SPECT/CT in 16 patients referred from a specialist orthopedic clinic, and it was observed that SPECT/CT provided additional information in 13 of 16 (81%) patients and was unhelpful in 3 (19%) cases. A specific diagnosis was made in 6 of 13 (46%) patients, which included malunion, OCD, osteomyelitis, and inflammatory arthritis. More accurate localization of degenerative or postsurgical changes was observed in the remaining 7 patients. When compared with conventional bone scintigraphy, SPECT/CT provides more specific information (malunion, nonunion, stress fractures, impingement, etc.) as well as allowing more accurate localization of the abnormalities detected.58, 59 The assessment of its role in directing the management of bony foot and ankle pathology59 suggested that in 75% of patients there was benefit with regard to accurate localization and additional pathology was identified in 40% of patients. It was found that in >50% of patients, management was changed after the findings of the SPECT/CT study and many patients did not undergo any further investigation. We have also demonstrated the value of SPECT/CT in the investigation of heel pain60 in a patient with retrocalcaneal bursitis and plantar fasciitis.

The limitations of SPECT/CT imaging are the additional radiation exposure and the increased cost compared with planar bone scintigraphy.

The ACR has previously made recommendations regarding the appropriateness of each investigation in evaluating pathology of the foot and ankle. However, the role of a bone scan remains limited, with the best use seen in identifying patients with reflex sympathetic dystrophy syndrome. However, with the combination of functional and structural information in a single study, SPECT/CT may prove to be a very useful technique for the evaluation of foot pain, especially in patients with previous surgery or in situ metal work. This would also reduce the inconvenience of extra hospital visits for patients who previously may have had a stand-alone bone scan and/or a CT study performed. This would also result in a more efficient use of resources and likely to be cost-effective for the health provider. We believe that the ACR recommendations will need to be revisited to incorporate the role of SPECT/CT as more evidence becomes available with regard to its benefits. We have developed a diagnostic algorithm (Fig. 8) in our institution in conjunction with the orthopedic department for the investigation of patients with chronic foot pain aimed at ensuring quick and convenient service for the patients and making the best use of imaging modalities.

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Conclusion 

Imaging of chronic foot pain remains complex and challenging. Currently MR remains the favored modality although with gradually increasing evidence, SPECT/CT shows promise as a valuable addition to the imaging armamentarium available to the clinician, particularly in the evaluation of pathology after surgery or in patients not suitable for MR, and may also play a role in guiding intra-articular injections.

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PII: S0001-2998(09)00070-1

doi:10.1053/j.semnuclmed.2009.08.004

Seminars in Nuclear Medicine
Volume 40, Issue 1 , Pages 41-51, January 2010

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