2.1

This study was designed as a retrospective, observational, and comparative radiological analysis. Between April 2022 and March 2024, all ankle MRI examinations performed at our institution were retrospectively reviewed. A total of 1052 patients who had undergone ankle MRI for various reasons were identified. This cohort represented a heterogeneous population, including acute trauma and emergency department cases, as well as outpatient referrals in a multi-specialty hospital setting.

From this population, patients older than 18 years with osteochondral lesions of the talus (OLT) and adequate image quality for morphometric analysis in axial, coronal, and sagittal planes were selected and evaluated for inclusion. Prior to inclusion, not only the MRI reports but also the MR images were reviewed by radiologists to confirm the diagnosis.

Exclusion criteria were as follows: previous history of ankle or foot surgery (to avoid postoperative morphological changes), severe trauma associated with ankle fracture or deformity, systemic rheumatologic or inflammatory diseases affecting the ankle joint, congenital ankle or foot deformities, inadequate image quality due to motion artifacts or incomplete sequences, and additional anatomical abnormalities such as tarsal coalition, severe ligamentous injuries, or space-occupying lesions. Another exclusion criterion was severe degeneration with prominent bone contour deformity and large osteophytes, corresponding to Kellgren–Lawrence grade IV osteoarthritis on plain radiographs.

Between April 2022 and March 2024, all patients who underwent ankle MRI and met the inclusion criteria were consecutively enrolled in the OCD group. To minimize selection bias, no selective inclusion was performed. The control group consisted of 70 age- and sex-matched individuals without OCD, randomly selected from the same MRI database during the same period. Identical inclusion and exclusion criteria were applied to both groups to ensure methodological consistency. The study protocol received ethical approval from the Institutional Review Board of the Medical Research and Ethics Committee (Approval No: TABED 1–25–1313) and was conducted in accordance with the principles of the Declaration of Helsinki.

2.2

Prior to data collection, an a priori power analysis was conducted using G*Power 3.1 (Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany). Based on previous similar studies (e.g., Sonnow et al., 2022), an expected moderate to large effect size (Cohen’s d = 0.7) was assumed for the primary parameters. With α = 0.05, β = 0.20 (i.e. 80 % power), and allocation ratio 1:1 between OCD and control groups, the analysis indicated that a sample size of 60 participants per group (total N = 120) would be sufficient to detect significant between-group differences. To account for potential data exclusion due to inadequate image quality or measurement error, the sample size was increased to 70 per group.

2.3

All examinations were performed using a 1.5-Tesla MRI scanner (Achieva DS Advance, Philips Healthcare, Eindhoven, The Netherlands) equipped with an 8-channel ankle coil. The ankle joint was imaged in a neutral position. The protocol included proton density–weighted (PDw) spectral presaturation inversion recovery (SPIR) sequences, T1-weighted turbo spin-echo (TSE), and T2-weighted SPIR sequences, following standard clinical ankle imaging routines. Images were transferred to the PACS workstation (Sectra IDS7, Sectra AB) for analysis. All measurements were performed on proton density–weighted sagittal and coronal MRI sequences at the level of maximal talar dome visualization to ensure consistency across cases.

2.4

Nine morphometric parameters of the ankle joint were evaluated:

1-Tibial axis–medial malleolus (TMM) angle : Measured on coronal images as the angle between the tibial shaft and the articular surface of the medial malleolus( Fig. 1 ).

Measurement of the Tibial Axis–Medial Malleolus (TMM) Angle.

2-Talus position (TalPos) : Measured on the coronal plane as the perpendicular distance between the tibial shaft axis and the center of the talus. Positive values indicated lateral deviation and negative values medial deviation( Fig. 2 ).

Measurement of Talus Position (TalPos).

3-Anterior opening angle of the talus (AOT): Measured on axial images as the angle between the medial and lateral articular surfaces of the talar trochlea( Fig. 3 ).

Measurement of the anterior opening angle of the talus (AOT).

4-Plafond malleolar angle: Defined on coronal images between the tibial plafond and the line through both malleoli ( Fig 4 ).

Measurement of the plafond malleolar angle.

5-Lateral distal tibial angle (LDTA): Measured on coronal images as the angle between the tibial shaft axis and the tibial plafond( Fig 5 ).

Measurement of the lateral distal tibial angle (LDTA).

6-Anterior distal tibial angle (ADTA): Measured on sagittal images as the angle between the tibial shaft axis and the distal tibial articular surface( Fig. 6 ).

Measurement of the anterior distal tibial angle (ADTA).

7-Trochlear tali arc length (TaL): Measured on sagittal images as the maximum anteroposterior length of the talar trochlea( Fig. 7 ).

Measurement of the trochlear tali arc length (TaL).Measurement of the trochlear tali arc height (TaH). Measurement of the trochlear tali arc surface (TaS).

8-Trochlear tali arc height (TaH): Measured on sagittal images as the perpendicular distance from the highest point of the trochlea to the line connecting its anterior and posterior margins ( Fig. 7 ).

9-Trochlear tali arc surface (TaS): Measured on sagittal images as the articular arc surface area of the talar dome ( Fig. 7 ).

All measurements were independently performed by two orthopedic surgeons using the PACS system. Each observer repeated all measurements after an interval of 2 weeks, in random order, and blinded to their previous results and those of the other observer. Intra- and interobserver reliability were assessed using intraclass correlation coefficients (ICC) with 95 % confidence intervals. Representative screenshots were obtained during the measurement process and included as figures to illustrate the methodology.

2.5

The morphometric parameters were selected based on prior studies linking them to ankle biomechanics, stability, and susceptibility to talar osteochondral lesions. Changes in TMM angle and TalPos have been associated with abnormal alignment and increased joint contact pressures ^, . The AOT reflects trochlear morphology relevant to load distribution, while TAL and TAS describe articular surface geometry affecting contact stress ^, . Yet, most studies have examined only a few of these measures. Our study sought to address this gap by simultaneously evaluating nine parameters to provide a more comprehensive understanding of morphological variations in relation to OCD.

2.6

Statistical analyses were performed using IBM SPSS Statistics version 26.0 (IBM Corp., Armonk, NY, USA). Normality was assessed with the Shapiro–Wilk test. Group comparisons used independent-sample t -tests or Mann–Whitney U tests for continuous variables and chi-square tests for categorical data. ROC curve analysis determined optimal cut-off values for significant parameters, and logistic regression identified independent predictors. Intra- and interobserver reliability was assessed with ICC (95 % CI). A p-value < 0.05 was considered significant, with Bonferroni correction applied for multiple testing.