Glenoid bony anatomy in patients with epilepsy is influenced by their tonic-clonic seizure burden

Patients with epilepsy often sustain uncommon shoulder injuries, including bilateral lesions and posterior dislocations. Increased glenoid retroversion is associated with posterior instability, although it remains unclear whether this is a cause or an adaptation. During tonic-clonic seizures, the humeral head is driven cranially and posteriorly against the glenoid by muscle contractions, potentially leading to acute dislocation or plastic deformation, which can be particularly relevant during skeletal development, even without instability episodes. This cross-sectional study aimed to evaluate whether the cumulative frequency of tonic-clonic seizures affects glenoid anatomy in patients with epilepsy who have not experienced shoulder instability. Patients with epilepsy referred to a tertiary epilepsy center were enrolled sequentially. The duration of epilepsy and the frequency of tonic-clonic seizures were recorded and the glenoid version, the glenoid vault angle and the scapulohumeral subluxation index were measured on axial magnetic resonance imaging scans. The cumulative Burden of Recurrent Seizures over Time (BuRST) was calculated multiplying the duration of epilepsy by the number of yearly tonic-clonic seizures to compare patients with no BuRST, with those with a low BuRST (<40) and with a high BuRST (&#x2265;40). Statistical tests, including one-way analysis of variance with post hoc Tukey's test for multiple comparisons, were used to assess variable differences, correlations, and measurement reliability. Data were collected for 91 epileptic patients, 34 of which with a low and 28 with a high BuRST. A significant difference between the 3 BuRST groups emerged for all investigated parameters, with higher BuRST correlated with more pronounced changes (glenoid version angle: -1.93 &#xb1; 4.02&#xb0;; -3.80 &#xb1; 4.34&#xb0;; -6.67 &#xb1; 4.73&#xb0;; glenoid vault angle: -12.78 &#xb1; 3.81&#xb0;; -16.58 &#xb1; 4.02&#xb0;; -20.66 &#xb1; 4.35&#xb0;; subluxation index: 51.2% &#xb1; 4.7%; 54.6% &#xb1; 5.2%; 55.9% &#xb1; 5.1%). Intra- and interrater reliability was good to excellent for angular measurements and moderate to good for subluxation measurements. Patients with epilepsy who experience frequent tonic-clonic seizures, but have not yet had a shoulder instability episode, show increased glenoid retroversion, a more retroverted vault, and a higher scapulohumeral subluxation index compared to those with none or rare tonic-clonic seizures. These findings may suggest a possible link between recurrent tonic-clonic seizures and plastic deformation of the glenoid during growth, potentially influenced by repeated, powerful posteriorly directed muscular contractions. Although causality cannot be established, these results may pave the way for prospective studies aimed at better understanding the increased incidence of posterior shoulder instability observed in patients with epilepsy and recurrent tonic-clonic seizures.