Abstract
Submission Type:
Ankle Instability
Research Type:
Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies
Introduction/Purpose:
Measurement of lateral talar subluxation (LTS) is proposed in the literature as an adjunct and perhaps superior metric to medial clear space (MCS) for distinguishing intact versus disrupted medial restraints in SER-variant ankle fractures. Arbitrary cutoff values have been explored for dichotomizing increased compared to normal LTS. The present study sought to elucidate normative data for LTS which can assist with treatment decision-making for SER fractures. The objectives of this investigation were as follows: (1) define the mean LTS value in a population with normal ankle anatomy; (2) define the mean LTS value with subanalyses according to biological sex and ankle side; (3) compare mean LTS to mean values for existing radiographic measurement tools of MCS and superior clear space (SCS).
Methods:
Adult patients (aged 19 and over) seen in consultation at a foot and ankle orthopaedic outpatient office over a 2.5 year period without a primary pathology of the ankle joint were considered eligible. Patients were included provided x-rays had been obtained of separate bilateral weight-bearing films with a mortise view. Exclusion criteria consisted of evidence of prior trauma, prior operative intervention or concurrent degenerative changes to the ankle joint, as well as inadequate imaging technique. Radiographic measurements of LTS, MCS and SCS were retrospectively performed by two independent observers with overall mean values calculated. Subanalyses offering comparisons based on biological sex and ankle side were performed using a two-sample unpaired t-test and descriptive statistics, respectively. Assessment of intrarater and interrater reliability was facilitated by producing intraclass correlation coefficients (ICC).
Results:
Data from 120 patients were included (88 with adequate bilateral ankle views; 106 with left and 102 with right ankle radiographs). The population mean age was 55.23 [±13.28 SD] years, with 78.3% being female. Mean measurements were: LTS 1.09 [±0.76 SD; range 0-3.70] mm, MCS 2.36 [±0.50 SD; range 1.42-4.23] mm, and SCS 3.23 [±0.47 SD; range 2.08-4.48] mm. Ankle side subanalysis showed mean LTS of 0.97 [±0.91 SD] mm for the right and 1.21 [±0.93 SD] mm for the left, with no significant difference evident. There was no significant difference in mean LTS for female (1.07 [±0.78 SD]) versus male (1.16 [±0.74 SD]) patients. Mean ICC for LTS was 0.64 for intrarater and 0.56 for interrater reliability representing moderate agreement.
Conclusion:
Our investigation generated a mean normative LTS value of 1.09 mm, expanding upon limited literature on this measurement tool in uninjured ankles by using a sample of sufficient size. Only 1.2% of initial LTS measurements by the two observers were > 4.0 mm, suggesting this previously proposed cutoff should provide an effective threshold for detecting increased LTS. The current study newly demonstrated that a single LTS cutoff may be generalizable regardless of biological sex or ankle side. However, our work found achieving reliable LTS values presented a greater challenge compared to other commonly applied measurement tools, namely MCS.