Acromion Type Research Articles

Relationship between os acromiale and acromioclavicular joint anatomic position

Most of the orthopaedic literature on os acromiale is focused on the clinical implications, such as impingement and rotator cuff tears; although os acromiale is present in 8% of subjects, scarce information is reported on the causes that may predispose patients to it. Our aim is to investigate whether the origin of os acromiale is related to the position of the acromioclavicular (AC) joint. The acromions of 211 volunteers (control group) and 33 subjects without or with os acromiale were radiographically (axillary view) classified by the Edelson and Taitz method. The method distinguishes the acromion into three types on the basis of the distance between the anterior aspect of the acromion and the AC joint. Of 33 subjects with os acromiale, 11 were without pain. We have compared the frequency of the three types of acromion observed in the two investigated cohorts. Half of the acromions of the control group (52.1%) had the articular facet of the AC joint on the acromion tip, whereas in 45.4% the facet tip was located distally. On the other hand, of 33 subjects with os acromiale, 18.1% and 81.1%, respectively, had the AC joint lying on or distal to the acromion tip. Our data suggest that the greater the distance of the AC joint from the anterior edge of the acromion, the higher the likelihood of an os acromiale. (J Shoulder Elbow Surg 2003;12:6-8)

Shape of the acromion: Congenital or acquired—A macroscopic, radiographic, and microscopic study of acromion

Debate continues as to whether the differing shapes of the acromion are congenital or acquired. This has been investigated by neonatal cadaver study, adult cadaver study, radiographic study, magnetic resonance imaging study, or various other means. No one, to our knowledge, has investigated this by histologic study. A macroscopic and histologic study of 22 cadaveric shoulder joints was carried out to establish what, if any, developmental changes occur in the differing patterns of acromion. The cadaveric shoulders were dissected and examined macroscopically. All of the acromion processes were transected and photographed, and the histology of the anterior and inferior surfaces was studied. In all of the curved and hooked types of acromion, a common pattern of degeneration of collagen, fibrocartilage, and bone was observed, consistent with a traction phenomenon. None of the flat acromions exhibited these changes. Extensive histologic changes were noted on the anterior surface of acromion as compared to the inferior surface in curved or hooked acromion. We conclude that the different shapes of acromion are, therefore, acquired as a response to traction forces applied via the coracoacromial ligament and are not congenital in origin. (J Shoulder Elbow Surg 2001;10:309-16.)

肩峰の形態および傾斜と骨きょく発生との関係 骨標本計測値による検討

This study investigated the relation ship between the slope and shape of the acromion and the spur at the antero-inferior surface of the acromion no clarify the cause of subacromial impingement. This investigation was performed with 205 scapular dry bone specimens. The specimens of 107 males were used. Their ages ranged from 20 to 83 years with an average age of 56.5 years. The presence of acromial spurs was identified. All acromions were classified visually as type I (flat), type II (curved) or type II (hooked) as described by Bigliani et al. And the slope of the acromion was measured in all specimens.A spur at the antero-inferior surface was seen in 96 acromions (46.8%). And almost all spurs were located in the anterior one third of the acromion. In all specimens, fifty-six acromions (27.3%) were type I, one hundred and eight (52.7%) were type II and forty-one (20.0%) were type III. The type of acromion was not related to the presence or absence of a spur. The average slope of all acromions was 46±8°, that of acromions with spur was 44±7° and that of acromions without spur was 49±8°. There was a significant difference between the slope of the acromion with spur and acromions without spur. From this study it can be concluded that the type of acromion had no relation ship to subacromial impingement and the flattened slope of the acromion might be one cause of subacromial impingement.

Release and reattachment of the coracoacromial ligament: A cadaveric study

The purpose of this study was to examine the anatomy and ability to reattach the coracoacromial ligament (CAL) after acromioplasty. Twenty-eight fresh cadaveric shoulder specimens were dissected, and the CAL dimensions and pattern of attachment were examined. The ability to reattach the CAL to the anterior acromion after acromioplasty was investigated, comparing release along the anterior acromion (traditional anterior acromioplasty) versus subperiosteal elevation from the acromial undersurface. The influence of CAL length, acromial “type”, and amount of acromioplasty on reattachment were examined. In 96% of the specimens (27 of 28) confluent medial and lateral bands of the CAL insertion along the acromion precluded “selective” release. The ability to anatomically reattach the CAL was directly related to the method of ligament release (anterior release versus subperiosteal elevation) (p < 0.0001). When directly released from along the anterior acromion, the CAL could not be anatomically reattached in any specimen. Nonanatomic reattachment to a more medial anterior acromial insertion site, however, was possible in 22 (79%) of 28 specimens. Reattachment required an average medial positioning of 60% (range 16% to 88%) along the anterior acromion from the anterolateral tip. Six (21%) specimens could not be reattached despite attempted medial positioning. In contrast, when subperiosteally elevated from the anterior inferior acromion, the CAL was reattachable in all specimens, anatomically in 26 (93%) of 28. The two nonanatomic reattachments required medially reattaching the ligament's normal acromial insertion by an average of 30%. There was no relationship between specimen sex, age, presence of rotator cuff tear, type of acromion, and CAL reattachment. The confluent anatomy of the CAL does not permit “selective” release of discretely identifiable portions of the CAL (i.e., the lateral band). In cases in which CAL restoration is important, careful subperiosteal elevation from the acromial undersurface will facilitate anatomic reattachment. Standard release of the CAL from the anterior acromion precludes anatomic, and in some cases any, reattachment of the CAL.

肩峰の形態および傾斜と肩インピンジメントとの関係 骨標本計測値による検討

This study investigated the relation ship between the slope and shape of the acromion and the spur at the antero-inferior surface of the acromion no clarify the cause of subacromial impingement. This investigation was performed with 205 scapular dry bone specimens. The specimens of 107 males were used. Their ages ranged from 20 to 83 years with an average age of 56.5 years. The presence of acromial spurs was identified. All acromions were classified visually as type I (flat), type II (curved) or type II (hooked) as described by Bigliani et al. And the slope of the acromion was measured in all specimens.A spur at the antero-inferior surface was seen in 96 acromions (46.8%). And almost all spurs were located in the anterior one third of the acromion. In all specimens, fifty-six acromions (27.3%) were type I, one hundred and eight (52.7%) were type II and forty-one (20.0%) were type III. The type of acromion was not related to the presence or absence of a spur. The average slope of all acromions was 46±8°, that of acromions with spur was 44±7° and that of acromions without spur was 49±8°. There was a significant difference between the slope of the acromion with spur and acromions without spur. From this study it can be concluded that the type of acromion had no relation ship to subacromial impingement and the flattened slope of the acromion might be one cause of subacromial impingement.

Changes in acromial morphology with age

It has not been determined whether acromial morphology is an innate anatomic characteristic or whether it represents a degenerative process with type I acromions changing to type III acromions over time. The purpose of this study was to determine the incidence of the three types of acromial morphology with respect to age. The acromial morphology of 272 patients (176 patients with no signs of mechanical impingement or rotator cuff disease and 96 patients with mechanical impingement) was determined by supraspinatus outlet radiographs. In the entire group of 272 patients there was a significant increase in the incidence of type III acromions and a decrease in the incidence of type I acromions in patients older than 50 years of age (p = 0.046). In 176 patients with no symptoms there was a very significant increase in the number of type III acromions in those patients older than 50 years of age (p = 0.004) with a corresponding decrease in the incidence of type I acromions. The incidence of the three acromial types also varied between patients with and without symptoms of mechanical impingement. The incidence of the three acromial types varies with respect to the age of the patient and whether he or she has symptoms of mechanical impingement. This raises the possibility that type I acromions may progress to type II acromions and then further change into type III acromions over time.

Acromial morphology: relation to sex, age, symmetry, and subacromial enthesophytes.

To evaluate acromial shape in relation to age, sex, symmetry, and presence of subacromial enthesophytes. Three hundred ninety-four cadaveric scapulas were reviewed. Specimens were categorized by sex and age (age range, 20-89 years). Acromial morphology was typed according to the Bigliani classification: type I, flat; type II, curved; and type III, hooked. The presence and degree of subacromial enthesopathy was recorded. Selective radiographic correlation was obtained. The relative percentages of acromial types I, II, and III were 22.8% (90 acromions), 68.5% (270 acromions), and 8.6% (34 acromions), respectively. There was a greater percentage of type III in men (10.2% [21 of 205] vs 6.9% [13 of 189] and type I in women (27.5% [52 of 189] vs 18.5% [38 of 205]). There was no relationship between acromial type and age (P = .667). Enthesophytes were most common in type III (20 [59%] of 34 acromions) versus type II (115 [42.6%] of 270 acromions) and type I (22 [24%] of 90 acromions). Acromial morphology was symmetric in 135 (70.7%) of 191 pairs of acromions and asymmetric in 56 pairs (29.3%). Acromial shape does not vary significantly with age. It does, however, differ between sexes. The relative percentages of the types differ from previously reported values. Acromial shape tends to be symmetric. A trend between acromial type and the presence of enthesophytes is observed.

Morphologic variants of acromion in neonatal cadavers

In this study, the morphology of the acromion in neonatal cadavers was investigated. The hooked-type acromions (Bigliani and Morrison type III), which are said to be responsible for rotator cuff lesions in adults, were found to have a very low incidence in this age group (5%). This finding challenges the validity of the assumption that some individuals have a congenital tendency for rotator cuff lesions, depending on their acromion types.

Reliability of radiographic assessment of acromial morphology

The most widely used radiographic classification system for acromial morphology identifies three distinct acromial shapes: type I (flat), type II (curved), and type III (hooked). The purpose of this study was to measure the interobserver and intraobserver reliability of determinations of acromial morphology as defined by this system. Between 1990 and 1992, one hundred twenty-six supraspinatus outlet radiographs were obtained from 126 patients by technicians from Triangle Orthopaedic Associates in Durham, N.C. Six fellowship-trained shoulder surgeons independently reviewed each radiograph and classified it as type I, II, or III on the basis of established guidelines. Two surgeons classified each film a second time in random order. Analysis of variance was performed to obtain coefficients for interobserver and intraobserver reliability. Consensus ratings were then used to classify the 126 radiographs into consensus type I, consensus type II, or consensus type III groups. Percentages of type I, II, and III individual ratings within each consensus group were determined. The intraobserver reliability coefficient was 0.888, interpreted as good to excellent reliability. The interobserver reliability coefficient was 0.516, interpreted as poor to fair reliability. Of the 126 radiographs, 26 (20.6%) were rated as consensus type I, 76 (60.3%) were rated as consensus type II, and 24 (19.1%) were rated as consensus type III. The reliability of observer ratings was lowest when delineation between acromial types II and III was required. The low interobserver reliability makes comparisons of studies by different authors difficult to interpret and obscures the true incidence of acromial morphologic types. It also questions reported correlations between acromial type and shoulder pathologic conditions. It is concluded that a system that incorporates more objective classification criteria and acknowledges the continuous nature of acromial morphologic types may improve interobserver reliability and validate the system's use in making clinical and surgical judgments.

Relationship between the lateral acromion angle and rotator cuff disease

One hundred consecutive magnetic resonance imaging (MRI) studies of the shoulder obtained for the purpose of evaluating rotator cuff symptoms were retrospectively reviewed to assess the relationship between acromion morphologic appearance and rotator cuff disease. The studies were reviewed simultaneously by two authors. Each cuff was assigned a tendon grade and an overall cuff score with MRI criteria previously described in the literature. A newly described "lateral acromion angle" was measured from a specified oblique coronal cut on each MRI study and was correlated with the corresponding MRI-determined rotator cuff score and supraspinatus tendon grade. Observed correlations were analyzed by using statistical methods. The average measured lateral acromion angle was 78 degrees, with a range from 64 degrees to 99 degrees. Eight shoulders had angles less than or equal to 70 degrees, and all eight of these patients were found to have full-thickness rotator cuff tears. As the lateral acromion angle decreased, a statistically significant increase in rotator cuff disease was noted (p < 0.0001). A significant correlation between increasing age and rotator cuff disease was also observed (p < 0.0001). Multiple regression analysis confirmed that both the lateral acromion angle and the age of the patient were independent predictors of rotator cuff score. Finally, although a trend was noted suggesting a correlation between acromion type (I--flat, II--curved, and III--hooked) and MRI-determined rotator cuff disease, this trend did not reach statistical significance (p = 0.12). Surgical correlation with MRI rotator cuff findings in 35 patients showed an MRI sensitivity of 100% and specificity of 83%. A statistically significant correlation between the lateral acromion angle and MRI-determined rotator cuff disease has been noted. The described angle may be a useful adjuvant in the evaluation and management of rotator cuff disease.

Acromial structure and tears of the rotator cuff.

Rotator cuff lesions have been related to the structure of the acromion. We report a clinical review of 56 shoulders and the analysis of their acromial structure as seen on the radiographic arch (outlet) view and magnetic resonance imaging. The shoulders were classified as acromial type I (flat), type II (curved), or type III (hooked). On plain radiographs 89% of type III acromions had tearing of the rotator cuff (p < 0.001). The association between acromial type as determined on magnetic resonance imaging and the presence of rotator cuff tearing was less significant. Magnetic resonance imaging offered no additional benefit over plain radiographs for determining acromial type. In addition, a method of quantitating acromial structure (the "acromial angle") was devised. This angle showed a significant association with acromial types (p < 0.0001) seen on plain radiographs and had good interobserver reproducibility (coefficient of variation, 0.1). With this measurement system a type I acromion had an acromial angle of 0 degrees to 12 degrees; a type II acromion, 13 degrees to 27 degrees; and a type III acromion, greater than 27 degrees.

Morphologic variants of acromion in neonatal cadavers.

In this study, the morphology of the acromion in neonatal cadavers was investigated. The hooked-type acromions (Bigliani and Morrison type III), which are said to be responsible for rotator cuff lesions in adults, were found to have a very low incidence in this age group (5%). This finding challenges the validity of the assumption that some individuals have a congenital tendency for rotator cuff lesions, depending on their acromion types.

Isolated subacromial bursal fluid on MRI of the shoulder in symptomatic patients: correlation with arthroscopic findings

Fluid in the subacromial bursa (SAB) is a common finding on magnetic resonance (MR) images of the shoulder, and the implications of this finding have not been clarified. We retrospectively reviewed and correlated the MR features with arthroscopic findings in 21 symptomatic patients who had fluid in the SAB on MR imaging without demonstrable rotator cuff tear. Rotator cuff impingement was the most frequent surgical finding (42.9%). Other frequent surgical observations were glenoid labrum abnormality (28.6%), bursitis (19%), and supraspinatus tendinitis (14.3%). Distribution of acromial types was similar to that reported by Bigliani et al., and impingement was evenly distributed among acromial types in our study population. We conclude that in our patient population group the MR finding of isolated SAB fluid in symptomatic patients is highly likely to be associated with the finding of other abnormalities in the shoulder joint at surgery.

Hooked acromion: prevalence on MR images of painful shoulders.

An association between the morphology of the acromion and the occurrence of rotator cuff tear (RCT) has been suggested by findings at both pathologic examination and routine radiography. As a tomographic technique, magnetic resonance (MR) assessment of acromial shape may be more accurate than routine radiography. The authors studied acromial morphology on sagittal oblique MR images of a control population (47 shoulders), of patients with isolated impingement (30 shoulders), and of patients with full-thickness RCTs (34 shoulders) to assess the association of acromial shape with disorders of the rotator cuff. Acromions were classified as flat (type 1), smoothly curved (type 2), or hooked (type 3). Data were collected by two observers, blinded to clinical and surgical information, who acted in consensus. Patients with RCT had a significantly increased prevalence of type 3 acromions compared with control patients (62% vs 13%, P < .001). Type 3 acromions tended to be more prevalent in the group with impingement (30%, P = .17). There was no significant difference in the distribution of acromion types among control patients with respect to age or gender.