Fig. 1
X-ray of a left shoulder in true AP view. Oblique glenohumeral radiogram in indifferent position of the limb – zero starting position (ZSP). Normal position of the acromion. District radiopacity of the great tubercle of the humerus
In fact, we all know that a reduction of the joint space between acromion and humeral head and between acromioclavicular joint and humerus causes an impingement of the soft tissues creating a mechanical insult, most of the time responsible of the tendinous tear.
Traditional radiology allows us to evaluate the tissue characteristics of soft tissues, including the presence of possible calcifications and the characteristics of the skeletal district we are examining, and especially the aspect of the acromion, the bone tuberosity of the humeral head, the sclerosis of the greater tuberosity of the humerus and its following curvature (supraspinatus weakness that allows the head to go back up), the identification of vacuolar degenerating cists, the return of the humerus head, and concurrent acromioclavicular arthritic deformation [4].
The evaluation of morphology and skeletal characteristics is given by an adequate radiological exam.
There are many different projections able to define the bone characteristics of the shoulder, but the most valuable and substantial for the assessment of the rotators cuff pathology, included in the radiological protocol of the shoulder, are mainly 4:three anteroposteriors and one outlet view.
In the anteroposterior projection, it is very important to abide by the position of the patient and the upper limb.
In fact, in the starting anteroposterior projection, defined as real anteroposterior or else “zero starting position” (ZSP), the upper limb of the patient lays along the side [5].
This is how we acquire the real AP (anteroposterior) projection, valuable in the detection of all the angles.
The anteroposterior radiogram acquisition technique in orthostatic ZSP provides for:
The incidence ray that must fall about 2 cm away from the coracoid process with a craniocaudal tilting angle of 20–30° (depending from the anatomy of the patient), by the glenohumeral joint line spacing.
The patient is then turned by a 45° angle with the scapula leaning against the radiographic coil (Fig. 1).
This radiogram must include the proximal third humerus, the glenohumeral joint, the coracoid, the clavicle, and the acromial-clavicle joint.
In this position, without any changes in the patient as well, we also carry out the following intra- (Fig. 2a) and extra-rotation projections (Fig. 2b) of the upper limb, with the movement of the upper limb alone, in abduction as well as in adduction.
Fig. 2
X-rays of a right shoulder: (a) AP in intra-rotation of the limb with the beam etching on the glenoid surface. (b) AP view obtained with the arm in external rotation position. (c) Outlet view. The X-ray shows the reduction of space between acromion, humeral surface, and the acromioclavicular joint
Such projections better define the characteristics of the radiologic semeiotic of the humeral tuberosity of both tubercles and the glenoid and acromion outline and allow the assessment of possible calcifications that lie on the bone surface of the humeral head.
The fourth projection used in the assessment of a suspect rotators cuff lesion is the outlet view projection, which is able to better show the tendinous sliding space of the cuff itself and the morphological characteristics of the acromion [6].
The outlet view projection helps also to better assess the skeletal characteristics of the joints in the acromioclavicular glenohumeral space (Fig. 2c).
We obtain it in orthostatic position with the patient standing by the radiologic table in a slanting anterior position with the involved limb laying against the radiological table in a 45° angle and a craniocaudal incidence of about 15–20° of the incidence beam. The central incidental beam must point on the passing area of the supraspinatus tendon “defilè”, under the acromion process.
The arm of the patient lies along the side of the body, in neutral position.
This way, we create a “y” with the bone base made of the glenohumeral joint, the roof made of the acromioclavicular joint and medially by the coracoid (Fig. 3).
Fig. 3
Outlet view: the X-ray of a right shoulder shows a good profile of acromion surface and Y shape
The radiological assessment highlights the bone characteristics of the district under examination, and especially the humeral bone tuberosity, the acromion surface, and the real extent of the sliding space of the rotators cuff, normally ranging between 12 and 14 mm [7].
In fact, the causes of impingement are often associated with a skeletal deformation and the morphology of joints.
Traditional radiology cannot define the extent of a total or partial lesion of the rotators cuff, nor can it give information on the extent of degeneration, but it certainly is fundamental in defining the tendon’s sliding space, the presence of calcifications or osseous calcified metaplasia and the extent of any bone deformation, often associated with phenomena of bone degeneration. In international literature, they speak of a high incidence of total lesions in the elderly caused by the high degree of arthritic bone deformation [4].
A minor bone damage is associated, instead, with partial lesions of the rotators cuff.
Among the crucial skeletal factors able to help the assessment of a tendinous degeneration that could induce partial or total lesion for the rotators cuff, three are considered responsible: the acromion, the humerus head and its tuberosity, the deformation of acromion clavicle joint on its humeral plane.
Important role have also the characteristics of the acromion, such as shape, slope, anomalies of the joint surface on the glenohumeral side (rough undersurface of the acromion).
Up to now, international literature acknowledges Bigliani classification as fundamental in the evaluation of acromial morphology [7, 8]:
- 1.
Flat
- 2.
- 3.
Hooked
Most anterior portion of the acromion has a hooked shape. This form is considered associated with increased incidence of shoulder impingement.
According to the acromion slope against the glenoid, different authors give different possible measurements that could predict a partial or total lesion of the rotators cuff, according to the value obtained [6, 9].
Among them all, we will take into consideration, according to the most recent international literature, the acromial index (AI) and the critical angle [10–12].
Such measurements have been taken radiologically either in the real AP projection or in the ZSP.
Some authors have suggested using the same measures taken with the magnetic resonance imaging (MRI) on the coronal plane and with the CT scan, on the reconstruction coronal plane [13, 14].
Parallel studies have confirmed that these offer a major radiological accuracy, compared with the other two radiological techniques.
The AI measurement represents a radiological index that evaluated the lateral extension of the maximum acromial profile, responsible for the impingement and following lesion of the rotators cuff.
Authors such as Nyffeler et al. agree that if Ai value is greater than 0.7 a cuff tear is present. Higher the index is, more complex the rupture will be (Fig. 4).
Fig. 4
True AP, zero starting position (ZSP) X-ray of a left shoulder. Evaluation of the acromion index (AI) by perpendicular lines of the shoulder, through the distance from the joint surface of the glenoid and the lateral edge of the acromion (GA) divided by the distance between the glenoid and the maximum lateral edge of the greater tubercle of the humerus (GH). In this case, the value >0.7 suggests a tear
AI absolute value is obtained calculating the difference between glenoid and acromial lateral tip, obtained drawing one perpendicular line on the glenoid and one parallel to the first and perpendicular to the acromial tip, defined as GA [11].
The value obtained is then divided by another absolute value calculated in the distance between the line perpendicular to the glenoid and an equal parallel line, perpendicular to the lateral border of the greater tuberosity of the humerus, defined GH.
The difference between GA/GH gives the value AI which, if >0.7, preannounces a higher risk of lesion of the rotators cuff (Fig. 4 and 5).
Fig. 5
True AP, zero starting position (ZSP) X-ray of a left shoulder. The value of the acromial index (AI) is <0.7 meaning negative condition for a cuff tear
Lately, however, we started to prefer another measurement, which certainly means the rapture of the rotators cuff.
And this, also, is calculated on the real AP or ZSP radiograms.
We are talking of the critical shoulder angle CSA, acknowledged as a valuable evaluation of a possible tendency to a tendinous lesion of the rotators cuff, against a more external position of the acromion and the slope of the glenoid.
The measurement is taken drawing a line perpendicular to the glenoid and a second one starting from the lower edge of the glenoid and ending to the farthest sideline of the acromion, creating an angle defined CSA, where the values higher than 35° suggest a greater incidence of rotators cuff rapture (Fig. 6). Instead, values lower than 30° (Fig. 7) are more common in presence of osteoarthritis of the glenohumeral joint [12, 14].
Fig. 6
X-ray in zero starting position (ZSP) of a left shoulder. The critical shoulder angle (CSA) is a valuable indicator of the degenerative rotator cuff disease. The measurement is obtained drawing a line parallel to the glenoid surface and another one starting from the lower edge of the glenoid bone and going to the maximum lateral extension of the acromion. The value >30–35° is indicative of rotator cuff degeneration/tear
Fig. 7
X-ray in true AP view of a right shoulder. The critical shoulder angle (CSA) in a young athlete with pain on his right shoulder is <30°
Such value is always associated to greater AI values.
Bouaicha et al. suggested comparing CT scans and X-rays to define such values and have demonstrated that there is a strong correlation between the values obtained with the CT scan and those calculated through a real AP of the CSA [12].
A third measurement is the lateral tilt of the acromion (LTA) or the lateral acromial angle (LAA).
Banas et al. believe that the most external position of the acromion is connected to the insertion of the deltoid, which can tend to give a more cranial position of the humeral head, with a greater incidence of reduction in the acromial humeral distance and an increase of impingement in the abduction movements of the arm. The same author has also suggested measuring the lateral tilt on the slanting coronal plane in an MRI [12].
As the majority of authors, we prefer the LTA measures taken on the ZSP radiogram [14] as well.
Such value is calculated drawing a line perpendicular to the glenoid and another one parallel to the humeral surface of the acromion, creating a lateral tilt angle, where values lower than 75° mean higher tendency to the rapture of the rotators cuff (Fig. 8a, b).
Fig. 8
(a, b) X-rays in true AP view of a left shoulder for lateral tilt angle. Lines are drawn on the inferior acromial surface and on the joint surface of the glenoid bone
Such value is also always associated to a higher AI value.
A LAA lower than 70°, a more lateral extension of the acromion, and a CA higher than 30–35°, a high AI value, connected to a more external position of the acromion, are associated to a higher possibility of impingement and lesion of the rotator cuff.
MRI
Magnetic resonance imaging (MRI) is an assessing technique on the matter based on the processing of the spin of protons of other nuclei presenting a magnetic moment, when they undergo a magnetic field. It was discovered independently in 1946 by the physicists Felix Bloch and Edward Purcell who received the Nobel Prize in 1952 for it. Studies were carried on by Paul Lauterbur and Peter Mansfield to develop the technique, and for this reason, they also received the Nobel Prize in 2003. The fields of application of the magnetic resonance are many: medicine, chemistry, petrophysics, etc. In the medical field, it is mainly used for diagnostics. The density signal is given by the atomic nucleus of the element under examination.
The multi-parametric effect of the MRI allows the direct characterization of tissue, while the multiple plane effect allows the direct visualization of an anatomic segment on different planes.
The main application of MRI in traumas of the shoulder and upper limbs is the assessment of lesions to the soft tissues and of joint and intraspongious damages. There are many causes to shoulder pain, and most of them start from pathology of the rotators cuff or instability [15–17].
The most common indication of MRI in the painful scapulohumeral pathology is the study of patients with a suspect tear of the rotators cuff or presenting an impingement [18–23].
The rotators cuff gives 33–50 % of the muscle strength needed for the abduction, and 80–90 % of the one needed for the external rotation [24, 25]. Zlatkin [20] classified the etiology of rotators cuff tears as extrinsic (impingement, impingement with instability, subcoracoid impingement) and as primary degeneration of the cuff, which can also have an ischemic nature. Bone anomalies or anatomic variations of the coracoacromial arch, ligaments or soft tissue anomalies inside the arch can determine impingement. Even traumas can be associated to the tear of the rotators cuff.
The majority of tears of the rotators cuff starts from the anterior portion of the supraspinous by the insertion of the great tuberosity of the tendon of the long head of biceps [26]. In the more wide or extensive tears, other components of the rotators cuff can have a major role. The tears of the rotators cuff increase with aging [27].
The rotators cuff tears can be classified as partial or total. The criterion that specifies a partial lesion from a complete one is the presence or absence of communication between the subacromial-subdeltoid bursa and the glenohumeral joint. The majority of tears of the rotators cuff interest the supraspinatus muscle tendon: more than 89 % of the partial tears and 47 % of the full thickness ones [28].
Many studies showed that fast spin-echo sequences (or turbo spin-echo) [FSE (or TSE)] are equivalent to conventional spin-echo. Sonin et al. demonstrated a 100 % correlation between the sequences T2-weighted and T2-weighted TSEs in the evaluation of rotator cuff integrity, as well as an increase in the signal to noise ratio in TSE sequences. They also showed sensitivity higher than 89 %, a specificity of 94 %, and an accuracy of 92 % in diagnosing rotator cuff full thickness lesions [28]. It is possible to obtain TSE sequences images with thinner layers in order to obtain less motion artifact and finally reduce acquisition time compared to conventional IF sequences [29]. Fat suppression or saturation signal (FAT-SAT) improves the contrast of soft tissues because it eliminates the artifacts from chemical shift taking place at fat–water interface and reduces artifacts from breathing. Singson et al. [32] have shown in the diagnosis of full-thickness rotator cuff injuries that the use of FSE T2-weighted sequences has optimal results both with and without fat suppression signal, while partial tears are better demonstrated using fat suppression sequences. Some authors have proposed a sequence of short Tau inversion recovery (STIR) with an inversion time reduced from 110 to 150 ms, which allows a more homogeneous (non-selective) fat suppression signal and improved signal/noise ratio [30, 31]. Kijowski et al. [33] showed equivalence between STIR and FAT-SAT FSE T2-weighted sequences in assessing rotator cuff integrity.
Studying suspect tears of the rotators cuff, we need to evaluate cuff’s damage and the surrounding structures; MRI should analyze the extent of the tear, the degree of damage of the tendon, the tendon’s edges, the muscle withering and the bone’s alterations (the kind of acromion, the presence or absence of the acromial bone, the degeneration of the acromial-clavicle joint).
Partial Thickness Tears
The partial tears of the rotators cuff have been classified with the MRI [15] according to the depth or vertical thickness of the affected tendon as: (a) I degree (<3 mm in depth), II degree (between 3 and 6 mm in depth), and III degree (>6 mm in depth). It is important noticing that the thickness (craniocaudal diameter) of the supraspinous tendon is about 12 mm. Furthermore, the partial lesions can be divided according to the site of interest in: (a) superficial lesions (28 %) (which interest only the bursal plane) (Fig. 9) intralaminar (or intratendinous) (Fig. 10a, b) (more than 50 % of the partial lesions) characterized by the complete absence of communication with the joint or bursal plane (33 %) (Fig. 11) (c) when they interest the joint surface (Fig. 12) and (d) when they interest both joint and bursal surfaces (39 %) [31].
