Summary

Retromalleolar fibular groove morphology differs according to the level of the assessed axial computed tomography scan

Abstract

Background

The association between the retromalleolar fibular groove morphology and the development of peroneal tendon dislocation has been well reported. Most previous studies evaluated the type of retromalleolar groove using an axial magnetic resonance imaging (MRI) slice at the level of 10 mm above the tip of the lateral malleolus. However, there is no evidence to support that this single slice can appropriately evaluate the retromalleolar groove morphology, and there is a lack of studies that investigated the method for evaluating the retromalleolar fibular groove morphology. The purpose of this study is to evaluate the influence of the level of axial computed tomography (CT) scans on the assessment of the type of retromalleolar fibular groove.

Methods

The study population included 122 subjects (mean age, 27.9 ± 11.8 years; male/female, 69/53) who underwent CT scans to evaluate foot or ankle pathologies at a single institute from 2020 to 2023. The shape of the retromalleolar groove was classified into four types according to the previous studies: concave, flat, convex and irregular. The retromalleolar groove shape was assessed on axial CT scans obtained at three different levels (8 mm, 10 mm and 12 mm above from the tip of the lateral malleolus) independently by two senior orthopaedic surgeons. All statistical analyses were performed using the SAS software (JMP Pro, ver. 15.2.0). Descriptive statistics were reported as percentage or mean ± standard deviation. The significance of threshold was set at p<0.05. The chi-squared test was conducted for categorical variables. The Cohen’s Kappa coefficient was calculated to assess the intra-rater and inter-rater reliability of the CT findings. The Cohen's Kappa coefficient was presented with 95% confidence interval (CI) and graded by Landis’s classifications (slight, 0.0-0.20; fair, 0.21-0.40; moderate, 0.41-0.60; substantial, 0.61-0.80; almost perfect, 0.81-1.00).

Results

The intra- and inter-rater reliabilities of the CT findings at each CT scan level were classified as almost perfect and substantial, respectively. The proportion of the types of the retromalleolar groove was significantly different according to the level of the CT scans (8 mm vs 10 mm, p<0.0001; 10 mm vs 12 mm, p<0.0001; 8 mm vs 12 mm, p=0.001). The type of retromalleolar groove was the same in all three levels in only 31.1% (38/122). There was no significant difference in the proportion of the groove types by gender.

Conclusions

The shape of the retromalleolar fibular groove was affected by the levels at which CT scans were obtained. Approximately 70% of the patients showed different types of retromalleolar grooves among the three CT scan levels. The study findings suggest that the retromalleolar fibular groove shape should be evaluated using multiple slices rather than a single slice.