1. SONOGRAPHIC EVALUATION OF SUBACROMIAL SPACE
Azzoni Roberto, Cabitza Paolo, Parrini Matteo
Orthopaedic Dept., State University of Milan – San Donato Milanese (Milan) 30, via Morandi, Italy. (
Aim of the study: The size of the subacromial space varies in relation to anatomy (Fig.1) and gender. Some pathologies of rotator cuff can be due to a reduction in subacromial space, which is usually measured by means of radiography using the antero-posterior and supraspinatus outlet views. The aim of this study was to verify the value of sonographic measurements of subacromial space, and their variations in relation to anatomy, age, gender and rotator cuff pathologies.
Materials and Methods: Between 1 January and 31 July 2001, we prospectively examined 200 consecutive painful shoulders using the sonography, and measured the subacromial space in all cases using our own method (see below).
The measurements of subacromial space were made using coronal axis views of the shoulder. The patient was in a sitting position with the upper limb hanging in backward flexion and internal rotation (Fig. 2). The measurement reference points were the acromion itself and the head of the humerus at the level of the greater tuberosity, which allows optimal visualisation of the long axis of the supraspinatus. The sonographic measurement calipers were positioned on the lowest echo from the external and inferior margin of the acromion, and the nearest point of the surface of the humeral head, thus giving the smallest distance. The 200 shoulders were divided into four groups on the basis of rotator cuff conditions: sonographically normal shoulders (group 1), shoulders with tendinopathy but without cuff tears (group 2), shoulders with partial tears limited to the supraspinatus (group 3), and shoulders with complete tears of the rotator cuff (supraspinatus and subscapular) (group 4).
Before or after sonography, all of the subjects underwent an X-ray examination of the affected shoulder using anteroposterior, transaxiallary and supraspinatus outlet views in order to study the morphology of the acromion and any osteoarthritic alterations in the acromioclavicular joint, and to measure the subacromial space.
A comparison was made of the results of radiographic and sonographic measurements of subacromial space.
Fig. 1: Types of acromion by Wuh and Snyder (Orthop. Trans ; 16: )
Groups
Numbers of cases
Sonographic
Measurement
Radiographic 1 70
10,5
11,0 2 54
14,4
13,9 3 20
10,0
10,1 4 26
08,6
09,0
Groups
Acromion type B
Acromion type C 1
Sonographic measurement
09,4
08,5
Radiographic measurement
10,0
07,7 2
10,5
11,0
09,3 3
07,2
10,3
06,5 4
07,8
09,8
07,0
groups
median males
median females
median in group 1
11,3
9,8
10,5 2
10,7
11,5 3
13,3
12,4 4
8,6
Tab. I: US Vs X-Ray measurement of subacromial space (value in mm.)
Tab. II: Comparison to US and X-Ray measurement in relation to the types of acromion (value in mm.)
Tab.III: US subacromial space in relation to sex (value in mm.)
Results: Group 1 consisted of 38 females and 32 males aged years (median 47.5 years) whose painful shoulder showed a normal sonographic rotator cuff image, and a subacromial space of between 6.9 and 16.6 mm (median: mm). The median X-ray measured subacromial space was mm. (Fig. 3)
Group 2 consisted of 22 females and 32 males aged years (median 55 years) whose painful shoulder showed a sonographic picture of rotator cuff tendinopathy without any sure signs of tears, and a subacromial space of between 9.6 and 17.4 mm (median: 14.4 mm). The median X-ray measured subacromial space was 13.9 mm. (Fig. 4)
Group 3 consisted of 14 females and 6 males aged years (median 64 years) whose painful shoulder showed an echographic image of a partial supraspinatus tendon tear and a subacromial space of between 6.5 and 13.1 mm (median: 10.8 mm). The median X-ray measured subacromial space was 10.1 mm. (Fig. 5)
Finally, group 4 consisted of 10 females and 16 males aged years (median 63.2 years) whose painful shoulder showed a sonographic image of a complete (supraspinatus and subscapular) tear of the rotator cuff, and a subacromial space of between 6.1 and 12.9 mm (median: 8.6 mm). The median X-ray measured subacromial space was 9.0 mm.. (Fig. 6)
Fig. 2: Patient’s position during sonography
The radiographic pictures in group 1 indicated type B acromonial morphological abnormalities in 24 shoulders (with sonographic and radiographic subacromial spaces of respectively 9.45 and 10.0 mm) and type C abnormalities in 12 (sonographic and radiographic subacromial spaces of respectively 8.55 and 7.79 mm); none of the radiographic images suggested the presence of acromioclavicular osteoarthritis.
Group 2 included 18 cases with a radiographic type B acromion (with sonographic and radiographic subacromial spaces of respectively and mm) and 14 with type C (sonographic and radiographic subacromial spaces of respectively 9.48 and 9.30 mm); there were radiographic signs of acromioclavicular osteoarthritis in three cases.
The variations in subacromial space in relation to age were not significant: the median measurement was 9.55 mm between the ages of 40 and 50 years (lowest within-group value) and mm between the ages of 30 and 40 years (highest within-group value); the median value between the age groups was mm.
The variations in subacromial space in relation to gender were more significant: in all of the rotator cuff pathology groups, the median subacromial space was smaller among the females.
Fourteen patients in group 3 and 11 in group 4 underwent surgical acromioplasty according to Neer with cuff reconstruction; six patients in group 3 underwent arthroscopic disimpacting acromioplasty.
Group 3 included two radiographic type B acromions (with sonographic and radiographic subacromial spaces of respectively 10 and mm) and six type C (sonographic and radiographic subacromial spaces of respectively 7.26 and 6.56 mm); there were radiographic signs of acromioclavicular osteoarthritis in one case.
Finally, group 4 included four radiographic type B acromions (with sonographic and radiographic subacromial spaces of respectively and 9.81 mm) and 20 type C (sonographic and radiographic subacromial spaces of respectively 7.82 and 7.09 mm); there were radiographic signs of acromioclavicular osteoarthritis in one case.
There was a highly significant correlation between the sonographic and radiographic measurements of the subacromial space (p = 0.8, Student’s t test), as well as between these and the X-ray typed acromion itself.
Fig. 3: Normal supraspinatus tendon and subacromial space (mm. 12,2).
Fig. 4: Tendinopathy od supraspinatus, without tears, subacromial space normal (mm. 11,3)
Discussion and Conclusions: Sonography measurements are sure and precise, and sonographic examinations of the shoulder can be usefully completed by measuring subacromial space. When  
beginning the diagnosis of painful shoulder, subacromial space measurement can avoid the need for a radiographic examination, thus reducing costs and patient radiation exposure. It is inexpensive, non-invasive and already widely used for the diagnosis of rotator cuff pathologies, and our technically simple and rapid method of using it to measure subacromial space during the course of a routine sonographic examination of the shoulder is reliable. Method is reproducible since we have execute 24 measures of 25 healthy subjects by two different operators, gaining median values of measure with per cent difference of 1,5% and statistical meaning with p=0,5 (t Student test).
Keywords: Shoulder, Subacromial space, sonography, impingement syndrome.
Fig. 5: Partial tear of supraspinatus, subacromial space reduced (mm. 10)
Fig. 6: Complete tear of supraspinatus, climb of humeral head, subacromial space indeed reduced (mm. 5,3)