Evaluation of the diagnostic accuracy of skeletal scintigraphy for the causes of front foot pain determined by magnetic resonance imaging

Abstract

There is good correlation between increased radiopharmaceutical uptake anywhere in the feet of sports or leisure horses and the presence of foot pain. However, low sensitivity of scintigraphy for identifying lesions contributing to foot pain as determined by magnetic resonance imaging (MRI) has been reported. The aim of this retrospective, cross-sectional, analytical study was to assess the accuracy of scintigraphy for identifying the cause(s) of foot pain, using MRI as the reference standard. Sports and leisure horses that underwent both skeletal scintigraphy and MRI of the front feet between March 2008 and December 2014 and for which a definitive diagnosis of the cause(s) of front foot pain was reached were included (121 feet of 70 horses). Imaging studies were evaluated retrospectively, blindly. Agreements between scintigraphic localization of increased radiopharmaceutical uptake and subjective categorization of lesions with MRI diagnosis were assessed using Kappa statistics (κ). Measures of diagnostic accuracy were calculated. Sensitivity of increased radiopharmaceutical uptake varied among regions (31.8-76.2%) but specificity was at least high for all (84.6-100%). Agreements between both scintigraphy measures and MRI diagnosis were substantial for the distal phalanx (palmar processes and body) (κ = 0.77 and κ = 0.74, respectively), and ungular cartilages and chondral ligaments (κ = 0.62, for both). When all regions were combined, agreements of increased radiopharmaceutical uptake (κ = 0.49) and relevance categorization (κ = 0.45) with MRI diagnosis were moderate. In conclusion, skeletal scintigraphy does not meet the minimum reliability level for a diagnostic test, but is reliable for identification of osseous trauma to the distal phalanx and ungular cartilages.

Attenuation From Shoes and Pads in Equine Nuclear Scintigraphy, With Relevance to Solar Views

“…The agreement between IRU and lesion identification on MRI was significant for the palmar process and body of the distal phalanx (7). The region of insertion of the deep digital flexor tendon (DDFT) onto the coffin bone and collateral ligaments of the distal interphalangeal joint can also be evaluated on the solar view (2,3,7). Current advances in Positron Emission Tomography (PET) with 18 F-NaF in equine diagnostic imaging shows promise in providing additional and valuable information in evaluation of structures in the equine distal limb (19,20).…”

“…The aforementioned studies revealed an excellent agreement between radiographic and scintigraphic grades of ossification of the collateral cartilages and all fractured cartilages had a greater IRU. The agreement between IRU and lesion identification on MRI was significant for the palmar process and body of the distal phalanx (7). The region of insertion of the deep digital flexor tendon (DDFT) onto the coffin bone and collateral ligaments of the distal interphalangeal joint can also be evaluated on the solar view (2,3,7).…”

“…Nuclear scintigraphy of the equine foot is an established imaging modality in the investigation of equine lameness and poor performance (1). Increased radiopharmaceutical uptake (IRU) has been described by researchers and clinicians in association with abnormalities of the navicular bone (1-5) collateral ligaments of the distal interphalangeal joint (2,3,6), deep digital flexor tendon (1,2), distal phalanx (2,7,8) and ungular cartilages (9)(10)(11) and used to evaluate laminar perfusion (12). Nuclear scintigraphy of the equine musculoskeletal system has been considered to be very sensitive, but not specific for injuries in lame or poorly performing horses (1,2).…”

“…The value of nuclear scintigraphy has been documented for several anatomic sites within the foot (1,3). The agreement between both increased radiopharmaceutical uptake and relevance categorization with the presence of foot pain is substantial (13), and a lack of radiopharmaceutical uptake does not preclude injury and can still provide potentially important information in the foot (7).…”

Clinical insights: Advances in imaging of the equine distal limb

“…MRI has not met major technological changes in the recent years but has surely continued to grow with large clinical studies further refining the available knowledge 11–17 . Although, not surprisingly, the advanced cross‐sectional imaging techniques represent the majority of the novelties in the last few years, a few studies relating to the more traditional imaging techniques still provided significant advances in their field: non‐weight‐bearing ultrasound, 18 creative new radiographic projections 19 and assessment on bone scans value with comparative imaging 20 have been very pertinent recent contributions to the literature.…”