Comparison of the measurement of the calcaneal X/Y ratio on plain radiograph and CT scan.

BACKGROUND

Tourne et al. introduced the calcaneal X/Y ratio measured on standing radiographs to describe the "overlong" calcaneal morphology in the assessment of Haglund's syndrome, concluding that a ratio less than 2.5 can predispose to heel pain. Our study aimed to evaluate the reliability of X/Y ratio measurement on the plain radiographs reflecting the morphology of the calcaneum. This was achieved by comparing the X/Y ratio on X-rays and CT scans.

METHODS

A cross-sectional observational study was conducted on 50 patients. Two assessors (one foot and ankle fellow and one registrar) were trained by a specialist Musculoskeletal Radiologist and fellowship-trained Orthopaedic Foot & Ankle Surgeon to measure the X/Y ratio on both plain radiographs and CT scans. The CT images on the sagittal cuts were adjusted to run parallel to the calcaneum's long axis at its centre to reflect the true morphological length of the calcaneum. For each assessor, the intra-observer agreement between X-ray and CT measurements of the X/Y ratio was assessed. The inter-observer agreement between the two assessors was evaluated for each modality (X-ray and CT).

RESULTS

The mean X/Y ratio measured by both assessors was lower on X-ray (2.71 ± 0.43, 2.69 ± 0.41) than on CT (3.14 ± 0.44, 3.10 ± 0.44). The intra-observer agreement between X-ray and CT scan measurements of the X/Y ratio was poor for both assessors (ICC =.487,.476). Inter-observer reliability was good on X-ray and excellent on CT (ICC =.808,.956).

CONCLUSIONS

The X/Y ratio assessment on plain radiograph remains the only clinically correlated method of measuring the ratio however, it doesn't necessarily reflect the true calcaneal morphology. The published association between Haglund's Syndrome and an X/Y ratio of 2.5 requires further research using advanced cross-sectional imaging techniques with clinical correlation. This is a Level III diagnostic study.