Permanent functional lengthening of the anterior capsule leads to instability.
Types of capsular attachment:
Type 1: anterior capsule (MGHL) inserts into labrum
Type 2: anterior capsule inserts within 1 cm of labrum
Type 3: anterior capsule inserts more than 1 cm from labrum
Type of capsular attachment has no role in prediction of shoulder instability
Anterior capsule:
Neutral/ internal rotation position: capsule is lax
ABER: Capsule tightens
Best measured on oblique sagittal sequences from the glenoid centre.
No significant difference in two positions, i.e, loss of capsular tightening, indicates lax capsule
Reference:
1. Ng AWH et al. Assessment of capsular laxity in patients with recurrent anterior shoulder dislocation using MRI. AJR 2009: 192: 1690-1695
2. Palmer WE et al. Anterior shoulder instability: diagnostic criteria determined from prospective analysis of 121 MR arthrograms.December 1995 Radiology, 197, 819-825.
