Anatomy of the acromial arch: correlation of anatomy and magnetic resonance imaging

Abstract

Based on a retrospective study of 179 MRI records covering four populations (patients presenting with impingement without known injury (n = 90), post-traumatic shoulder pain (n = 28), instability or dislocation (n = 36) and controls (n = 25)), morphologic criteria are suggested to define presumedly normal arches and arches compatible with subacromial impingement. The subacromial arch is presumed normal or without impingement if the sagittal and frontal views show it to be parallel to the humeral head, and/or if there is a fatty layer interposed between the arch and the supraspinatus m. The arch is presumed "aggressive" or actually capable of giving rise to impingement if, in either the sagittal or frontal view, there is a zone of narrowing of the subacromial passage with an impression of the arch on the supraspinatus tendon or tendinous thinning at this level or just lateral to this narrowed zone. Based on these criteria, study of the 179 MRI records demonstrated a significant difference of distribution of the arches in the four populations. "Aggressive" arches were found in 45.5% of patients with impingement, 25% of patients with posttraumatic pain, 8.9% of patients with an acute or recurrent dislocation and 12% of controls. Conversely, a presumedly normal arch was found in 56% of the controls, 55% of patients with dislocation, 25% of posttraumatic painful shoulders and only 5.5% of patients with clinical impingement. Subacromial impingement may be due to the type 3 acromial dysplasia described by Bigliani or to a thickening of the coracoacromial ligament at its acromial attachment. This study was supplemented by 15 anatomic dissections which confirmed the regularity of attachment of the coracoacromial ligament at the inferior aspect of the acromion along its lateral border.

Correlation between the four types of acromion and the existence of enthesophytes: A study on 423 dried scapulas and review of the literature

“…Concerning the relationship of the fourth (convex) acromial type with RCTs and shoulder impingement, Gagey et al (1993) noted that this acromial type seemed to have no association with RCTs. Farley et al (1994) confirmed this, but considered it important in acromioplasty.…”

“…Four types of acromion were found: the three classical ones as described by Bigliani et al ([1986] Orthop Trans 10:216) and a fourth one, where the middle third of the undersurface of acromion was convex (Gagey et al [1993] Surg Radiol Anat 15:63-70). The correlation between the four types of acromion and the presence of enthesophytes at its anterior undersurface was also recorded.…”

Tests for diagnosing subacromial impingement syndrome and rotator cuff disease

“…Thus, any dysfunction of the tendon complex is likely to lead to an upward movement of the head as the arm is actively raised, which will inevitably cause an increase contact pressure of both the upper surface of the tendon and the interposed subacromial bursa upon the undersurface of the acromion and the coraco-acromial ligament 1 . Although this cause for pain is intrinsic to the tendon itself, regardless of whether it is caused by inflammation (with or without calcification) or partial and full-thickness tears, there may also be extrinsic causes, such as an alteration in the dimensions of the subacromial space (as is found with the differing morphological types of acromial development) 2 , hypertrophy of the coraco-acromial ligament 3 or bursal anomalies such as a plica 4 or thickening 5 from repeated episodes of inflammation, or regional thickening of the tendons themselves, as found in chronic calcinosis after episodes of acute calcific tendinitis 6 . Finally, the complex dynamic coordination of scapular movements as the arm is elevated can give rise to pain from the subacromial structures 7 .…”

Acromial Morphology and Subacromial Architecture in a South African Population

“…Type I acromia presented with a flat inferior surface (17.2%), Type II acromia were characterized by a curved inferior surface (42.9%) and Type III acromia portrayed a hooked inferior surface (39.3%) (Bigliani et al, 1986;Rockwood et al, 2004). Despite the proposal of a fourth acromial type (convex inferior surface) by Gagey et al (1993) and Natsis et al (2007), it has not been related to rotator cuff tendinopathy.…”