Clinical History
Recurrent right shoulder instability in a 20-year-old man with a history of previous shoulder dislocation.
Imaging Findings
The anterior glenoid rim is bare, with the detached and medially displaced anterior labrum seen as a low-signal mass attached to the scapular neck by the periosteal sleeve. The labrum also rotates inferiorly, which makes it appear large on axial images and inferior to the scapular neck on the coronal images. A small contrast-filled crease is visible on the axial images where the lateral margin of the detached synovium-covered labrum meets the glenoid rim, which can be identified on arthroscopy.
Note that the anterior band of the inferior glenohumeral ligament attaches onto the ALPSA lesion (Figure 1), in part accounting for the instability. A subtle Hill-Sachs lesion is also observed at the posterior superior humeral head (Figure 1).
Findings are consistent with chronic anterior labrum periosteal sleeve avulsion (ALSPA).
Discussion
Anterior labrum periosteal sleeve avulsion (ALPSA) lesion is common in chronic instability of the shoulder, especially in those with repeated dislocations. It is considered a variant of anteroinferior labral tear and consists of a tear of the anteroinferior labrum with associated capsuloperiosteal stripping [1]. It can originate from a Perthes lesion, when continued traction transmitted along the anterior band of the inferior glenohumeral ligament strips the periosteum which remains attached to the labrum medially along the glenoid neck. The anteroinferior labrum retracts further medially with each episode of dislocation or subluxation and becomes adherent to the glenoid neck through scarred tissue [2].
ALPSA is one of the manifestations of chronic glenohumeral instability which affects the inferior labral-ligametous complex, the primary passive stabilizer of the joint. Affected individuals may develop shoulder pain and recurrent dislocations following initial traumatic dislocation. MRI allows lesion characterisation for the purpose of treatment planning, with the primary goal of stabilisation.
In chronic ALPSA lesions, the torn and medially displaced anteroinferior labrum is seen along the glenoid neck as a low signal mass, representing the scarred down labrum held by the periosteal sleeve. It is often rotated inferiorly and appears larger on axial images, with abnormal thickening and flattening resulting from healing with synovial fibrous tissue between the labrum and glenoid margin. A small cleft or separation can be observed between the glenoid margin and the labrum. The anteriorinferior glenoid rim is bare or deficient [1-2].
Differential Diagnosis List
Chronic anterior labrum periosteal sleeve avulsion (ALPSA)
Bankarts lesion
Perthes lesion
Final Diagnosis
Chronic anterior labrum periosteal sleeve avulsion (ALPSA)
