Three Views, Big Payoff: LM+Obliques Match Full Fetlock Series in PPE (EVJ 2025)

Lateromedial and oblique radiographs detect most fetlock pathologies as effectively as a full series in horses

A. Northwood; D. Berner

Background

Radiographic protocols for the equine fetlock during pre-purchase examinations (PPE) vary internationally, and the effect of reducing the number of views on pathology detection and observer agreement is uncertain. This study assessed whether fewer projections could balance diagnostic performance with efficiency and radiation exposure.

Methods

Retrospective observational study of fetlock radiographic series from a single referral archive (May 2013–August 2023). Two observers (ECVDI diplomate and resident) independently reviewed anonymized series in staged combinations: LM alone; LM+DP; LM+obliques (DLPMO & DMPLO); and the full four-view series. Diagnostic quality scoring, predefined lesion grading, McNemar’s tests, and Cohen’s kappa (including weighted kappa for severity) were used; reduced combinations were compared against the full series. A total of 673 fetlock series met inclusion criteria after exclusions.

Results

Across 673 series, the LM+oblique (LM/OB) combination showed no significant difference from the full series for detecting most pathologies. LM alone reliably detected fragmentation, sesamoid fractures, and osseous cyst-like lesions; obliques were superior for sesamoid bone changes. Observer agreement was generally highest with the full series; intra-observer agreement tended to be highest with LM/OB, except that subchondral bone changes in P1 favored LM/DP but still had poor agreement overall.

Diagnostic metrics (experienced observer) favored LM/OB: sensitivity was highest for most conditions, including osteoarthritis (88.79%) and osteochondrosis (70.53%); sesamoid fracture sensitivity, specificity, and NPV reached 100% with LM/OB. Enthesopathy sensitivity was low with LM or LM/DP (~9–10%) but improved markedly with LM/OB (80.34%).

Limitations

There was no gold-standard verification (advanced imaging or histopathology) to validate radiographic findings. The case mix was predominantly lame horses rather than true PPE populations, which may bias lesion prevalence and visibility; some specific pathologies (e.g., osseous cyst-like lesions) were too infrequent for robust analysis. Only two imaging observers were used.

Conclusions

LM/OB provides a practical alternative to a full four-view fetlock series for many PPE contexts, balancing diagnostic reliability with reduced time and radiation, while remaining cautious about subchondral bone changes that may require additional views or advanced imaging. A tailored approach by age, discipline, and clinical risk is recommended; reducing four to three projections can lower per-fetlock radiation by ~25% and supports ALARA, with DP retained when risk for subchondral disease is higher.

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