Improved diagnostic criteria for digital flexor tendon sheath pathology using contrast tenography.

Abstract

Pathology of the digital flexor tendon sheath is a significant cause of lameness in the horse. Imaging is important to identify lesions and inform on prognosis prior to tenoscopic surgery. To use a large population to evaluate 1) the sensitivity and specificity of digital flexor tendon sheath (DFTS) contrast radiographs in diagnosing manica flexoria (MF) tears, deep digital flexor tendon (DDFT) tears and constriction of the palmar/plantar annular ligament (PAL) using novel criteria; 2) predisposition to pathology in signalment and limb affected. Multicentre retrospective cohort study. The medical records of 206 horses with lameness localised to the DFTS, contrast radiographs and subsequent tenoscopic surgery were reviewed. Breed and limb predispositions were evaluated for pathology of the DDFT, MF and PAL constriction. Contrast radiographs of the DFTS were reviewed by four masked operators and for each pathology the sensitivity, specificity and interobserver variability were calculated. Contrast tenography was a sensitive test for MF tears (92% confidence interval [CI] 88.4-94.4%; specificity 56%, CI 51.1-61.1%) and specific for diagnosing DDFT tears (73%, CI 68.6-76.8%; sensitivity 54%, CI 47.8-60.2%) but had a lower sensitivity (71%, CI 65.1-75.9% ) and specificity (45%, CI 39.1-52.0%) for PAL constriction. It had good to substantial interobserver agreement for MF and DDFT tears (Krippendorff's alpha 0.68 and 0.46 respectively). Ponies (57%) and cobs (58%) were significantly more likely to be affected with MF tears (other breeds 20-39%, P=0.003) and Thoroughbreds (50%), warmbloods (45%) and draught breeds (48%) were more likely to have DDFT tears (other breeds 22-34%, P=0.01). MF tears and PAL constriction were overrepresented in the hindlimbs compared to DDFT tears in forelimbs. No standardisation of contrast radiographs was possible. The subjectivity of diagnosis of PAL constriction may also have led to bias. Radiographs were read as JPEGS reducing ability to manipulate images. Contrast radiography of the DFTS is accurate in the pre-operative diagnosis of DFTS pathologies. Different pathologies are overrepresented in certain breeds and limbs.