1.1 The morphology of the acromion according to Bigliani [1, 9, 11]*
One hundred and forty shoulders in 71 cadavers (52% male, 48% fe- male) were studied to determine the shape of the acromion and its rela- tionship to full-thickness tears in the rotator cuff. The average age of the cadavers was 74.4 years (range, 51±97 years).
The overall incidence of full-thickness rotator cuff tears in this el- derly population was 34%. In this series 24% of rotator cuffs had full- thickness rotator cuff tears.
Lateral radiographs were performed in the longitudinal axis so that the anterior slope of the acromion could be measured.
Three distinct types of acromions were identified (Fig. 1a±c):
n Type I: flat (17.1%)
Angle of anterior slope: 13.18 Full-thickness rotator cuff tears: 3.0%
n Type II: curved (42.9%) Angle of anterior slope: 29.98
Full-thickness rotator cuff tears: 24.2%
n Type III: hooked (39.3%) Angle of anterior slope: 26.98
Full-thickness rotator cuff tears: 69.8%
In addition, anterior acromial spur formations were noted in 14.2% of the series overall, but 70% were present in patients with rotator cuff tears. It is important to distinguish between spurs, which are probably acquired, and variations in the native architecture of the acromion.
Acromion/spina scapulae 1
1.2 Classification of the acromial morphology
on sagittal oblique MRI according to Epstein [36]*
Acromion shape was classified as (Fig. 2):
n Type 1: flat
n Type 2: smoothly curved
n Type 3: hooked
Sagittal oblique T2-weigthed or fast spin-echo images were obtained at a 908 angle to the long axis of the supraspinatus tendon as determined with an axial localizing image.
The acromions were classified according to their appearance on the image obtained just lateral to the acromioclavicular joint. This image consistently demonstrated the greatest longitudinal length of the acro- mion, and was at or just beyond the tip of the coracoid. Occasionally, it was difficult to differentiate between type 2 and type 3 acromions. If the apex of the curve or hook was within the middle one-third of the acromion, it was considered a type 2 acromion. If the apex of the curve 2 1 Acromion/spina scapulae
Fig. 1. A Type-I acromion: flat.
B Type-II acromion: curved.
C Type-III acromion: hooked A
B
C
A A
A
Fig. 2. a Classification of acromial shape in MRI. Illustration depicts the three acro- mial shapes: flat (type 1); smoothly curved (type 2); and hooked (type 3). b Sagittal oblique MRI demonstrates a flat (type-1) acromion. c Sagittal oblique MRI demon- strates a smoothly curved (type-2) acromion. d Sagittal oblique MRI demonstrates a hooked (type-3) acromion. A anterior, P posterior. (From [36])
a
b c
d
or hook was in the anterior one-third of the acromion, it was classified as a type 3 acromion.
1.3 Types of os acromiale according to Liberson [77, 90]*
Liberson [77] reviewed the roentgenograms of 1800 shoulder girdles, chosen at random, and found 21 typical and 4 atypical cases of os acro- miale, for an incidence of os acromiale of 1.4%. The lesion is bilateral in 62% of patients.
Definition of os acromiale: when there is a failure of union of any one of the ossifications centres to its neighbour, the resulting separate bone is an os acromiale.
Four different types of unfused acromia were described (Fig. 3):
n The most common nonunion is between the meso-acromion and the meta-acromion (typical os acromiale)
n Nonunion between the pre-acromion and meso-acromion (atypical)
n Nonunion between pre-acromion and meso-acromion as well as meso-acromion and meta-acromion (atypical)
n Nonunion between pre-acromion and meso-acromion, and pre-acro- mion and meso-acromion as well as meta-acromion and basi-acro- mion (atypical)
4 1 Acromion/spina scapulae
Fig. 3. Types of os acromiale according to Liberson [77, 90]
1.4 Types of scapular notch according to Rengachary et al. [110]*
Rengachary et al. [110] observed six basic types of supracapular notch in 211 cadaveric adult scapulae (Fig. 4):
n Type I (no notch): The entire superior border of the scapula showed a wide depression from the medial superior angle of the scapula to the base of the coracoid process.
Relative frequency 8%.
n Type II: This type showed a wide, blunted ªvº-shaped notch occupy- ing nearly a third of the superior border of the scapula. The widest point in the notch was along the superior border of the scapula.
Relative frequency 31%.
n Type III: The notch was symmetrical and ªUº-shaped with nearly parallel lateral margins.
Relative frequency 48%.
Fig. 4. Types of scapular notch
n Type IV: The notch was very small and ªvº-shaped. Frequently a shallow groove representing the bony impression by the suprascapu- lar nerve was visible adjacent to the notch.
Relative frequency 3%.
n Type V: This type was very similar to Type III (U-shaped), with par- tial ossification of the medial part of the ligament resulting in a notch with the minimal diameter along the superior border of the scapula.
Relative frequency 6%.
n Type VI: The ligament was completely ossified, resulting in a bony foramen of variable size located just inferomedial to the base of the coracoid process.
Relative frequency 4%.
Although the majority of the scapulae were easily classified into the six types defined above, occasional transitional types did occur. In addi- tion, there were many minor variations within a given type.
Transitions tended to occur more frequently between Types II, III and IV.
6 1 Acromion/spina scapulae
