Oblique sesamoidean ligaments: what is normal?

Equine Vet J. 2019 Nov 30.
Magnetic Resonance Imaging and histopathological evaluation of equine oblique sesamoidean ligaments.
Ellis KL1,2, Barrett MF1,3, Selberg KT1,3, Frisbie DD 1,2.

Author information:
1. Gail Holmes Equine Orthopedic Research Center, Colorado State University, Fort Collins, CO, USA.
2. Colorado State University, College of Veterinary Medicine and Biomedical Sciences, Department of Clinical Sciences, Fort Collins, CO, USA.
3. Colorado State University, College of Veterinary Medicine and Biomedical Sciences, Department of Environmental and Radiological Health Sciences, Fort Collins, CO, USA.
Abstract
BACKGROUND:

Pathology involving the oblique sesamoidean ligaments (OSLs) is commonly diagnosed during magnetic resonance imaging (MRI) of the equine distal limb. Presence of striations within the ligament and magic angle artifact can result in an incorrect diagnosis of pathological change. No studies have been performed using histopathology, the gold standard, to corroborate their imaging diagnosis.
OBJECTIVES:

1) To determine which MRI characteristics are associated with normal versus abnormal OSLs and 2) to evaluate the ability of MRI to correctly identify abnormal versus normal oblique sesamoidean ligaments using histopathology as the gold standard.
STUDY DESIGN:

Observational, cross-sectional study.
METHODS:

Cadaver limbs (n = 77) were obtained from horses (n = 21) euthanised at the hospital. MRI and histopathology was performed on each of the limbs. MRI scoring was performed for multiple MRI characteristics, and each limb was deemed normal or abnormal. Histopathology scoring was performed to give an overall score of normal or abnormal. Mixed model logistic regression was performed to evaluate which MRI characteristics were associated with normal versus abnormal OSLs using backwards elimination and a significance level of <0.1. Sensitivity and specificity were also calculated.
RESULTS:

The sensitivity and specificity of MRI to correctly identify abnormal OSLs was 81% (95% CI 54-96%) and 90% (95% CI 79-96%), respectively. Based on logistic regression, increased cross-sectional area at the origin (OR: 26.77, 95% CI 1.1-4640, p = 0.07), increased ligament hyperintensity (OR: 9.59, 95% CI 1.23 - 155; p = 0.04), and reduction in striations (increased hypointensity score) (OR: 7.8. 95% CI 0.72-218, p = 0.07) were associated with abnormal OSL.
MAIN LIMITATIONS:

Lameness exam was not performed on any of the horses prior to euthanasia. Findings can only be applied to chronic, degenerative changes, rather than an acute injury.
CONCLUSIONS:

Increased cross-sectional area and changes in the signal intensity are associated with pathology within the OSLs. Medial to lateral size asymmetry and striation pattern variation can occur in histologically normal OSLs and should be interpreted with caution if other signs of pathology are absent.