Shoulder:Radiographic Evaluation of Shoulder Problems

Introduction

The shoulder is a complex joint involving a variety of pathologies, whether traumatic or related to a natural aging process. With a population becoming increasingly aging and active, surgery of this joint has grown significantly. Considering this, knowledge of anatomy and its radiological representation is essential in the management of patients with a shoulder problem. Thus, MRI and CT scans play an important role in the lesion evaluation. In a recent study, Small et al. showed that up to 40% of patients who had MRI for shoulder pain prescribed by a non-specialist did not have a prior conventional radiograph. These MRI scans seem to have no significant influence on the treatment meaning that a non-specialized physician could over prescribe an MRI as a screening test. However, in clinical practice, the standard procedure in the assessment of a shoulder pathology is to start with a conventional radiography which, together with the symptomatology, will be the decision-making procedure for further investigations or the treatment. Neer in 1970 described the fractures of the proximal humerus with the surgical indications based on the conventional radiography. In the nineties, we see an emergence of hypotheses concerning the involvement of the scapular anatomy in the tendinopathies of the cuff. Bigliani describes the implication of acromial morphology as a risk factor in rotator cuff injury while Hamada describes the arthropathy related to the cuff and its radiological implications. More recently, other authors have described these anatomical implications in rotator cuff disorders and radiological diagnosis. Furthermore, understanding the anatomy of the shoulder also involves making surgical decisions according to standard radiography and implant designs.

Traumatology

Greater Tuberosity Displacement

The isolated fracture of the trochiter has been described for many years with the most important decision criterion being the displacement measured on the x-ray. In the past, many authors have placed the surgical indication from 1 cm and a conservative treatment below 5 mm. Although Neer in 1970 describes good functional results in conservative treatments for fractures of less than 1 cm with early rehabilitation, there is still a shadow area for fractures with displacement ranging from 5 mm to 1 cm. Understanding the effects of a displacement for this 5-10 mm range becomes clearer. Park et al. describes better functional results when trochiter fixation is performed from a 5 mm displacement or even 3 mm in patients with jobs involving the use of the upper limbs above the head. These results are confirmed by the study by Platzer et al, which shows significantly better functional results with fractures whose displacement is less than 5 mm and which are conservatively treated. He adds, however, that there is a non-significant difference from 3 mm, which could motivate surgery in a particular case. These results can be explained by a defect in abduction due to alteration of the rotator cuff. Bono et al. shows in an in vitro study that the increase in force required for abduction, when the displacement is more than 5 mm, is statistically significant. This study also reveals a functional deficit when the displacement is posterior. The classification according to Neer does not allow us to judge this displacement. In this context, Mutch et al. describes a classification based on the morphology of fractures that may influence the management of great tuberosities fractures by classifying them according to whether there is an avulsion, depression or split. They also describe a method of measurement based on radiology to guide the therapeutic decision (Figure). It is therefore essential to measure and analyze the displacement of isolated fractures of the great tuberosity and to include the patient's characteristics in the decision-making strategy in order to avoid functional disorders related to the healing process.

Neck-Shaft angle (NSA)

The anatomy of the proximal humerus is an essential point in shoulder surgery. In addition to fragments displacement during fractures, the neck-shaft angle is an essential point. Indeed, displacement in valgus or varus during fracture of the proximal humerus can negatively influence the long-term function of the shoulder particularly in a varus positioning being more unstable and of worse prognosis. Restoring the native neck-shaft angulation thus plays an important role in the therapeutic strategy and represents a key factor in the development of surgical techniques for the planning of osteosynthesis or of corrective osteotomy. Moreover, the understanding of this angle has made it possible to better adapt prosthetic surgery to the shoulder, particularly in the improvement of implants. Thus the normal average value described is 135 ° (Figure 3). In the majority of cases, this angle is evaluated on 2D imagery. However, the position of the patient and his shoulder during these examinations may vary from one center to another or even within the same center. Thus, Malatova et al. Analyzed angle variations on standard anteroposterior radiography according to the rotation of the shoulder. He shows that the angle varies little if the shoulder is in neutral, external or internal rotation with a good correlation between the different observers. On the opposite, other more recent studies contradict this affirmation. Hengg et al. demonstrates that the external and internal rotation of the arm can result in an incorrectly diagnosed valgus. For his part, Adikrishna et al. analyzed the relationships between rotation and NSA with significant differences as early as 10 ° from RI and 18 ° from external rotation. It is difficult to judge the rotation by looking at an x-ray, without knowing the positioning of the patient. Tan et al. in a cadaveric study analyzes an anatomical reference that can be used to judge the rotation on an x-ray. It shows that the proportional distance of the crest of the small tuberosity from the diameter of the humeral head is about one-third. This proportion decreases with the external rotation and increases with the internal rotation. This would make it possible to judge the rotation on an X-ray or even on intra-operative fluoroscopy. It would therefore appear that standardizing the taking of neutral rotating shots is essential for good practice.

Degenerative

Acromial Morphology (AM)

The anatomical characteristics of the scapula also have an important implication in the pathologies of the shoulder. The shape of the acromion and its involvement in the lesions of the rotator cuff has been studied by numerous authors [5], [6], [32], [33]. Thus, a link has been demonstrated between the radiological morphology and the risk of degenerative lesion of the rotator cuff, especially the supraspinatus with Bigliani describing 3 types of acromion, namely flat, curved or hooked [5]. It shows an increase in prevalence with progression of type of acromion. However, there is a low inter-observer reliability, especially for types 2 and 3. Other studies confirm this analysis with the absence of objective criteria making the delimitation between type 2 and 3 more complicated [34]. It was in 2001 that Park et al. did a study to give standardized and objective criteria to distinguish the different types based on Neer’s radiological incidence images (Figure 4) [35]. Thus they demonstrate a better inter-class correlation (0.94) with their measurement systems which is more objective and reliable, especially when it is necessary to distinguish type 2 and 3.

Acromial Slope (AS)

Another radiological sign based on the morphology of the acromion is described in 1986 by Aoki et al [36]. It describes the influence of the acromial slope on the lesions of the rotator cuff. Thus, a weak acromial slope measured on the Neer’s incidence is an important factor in the subacromial impingement(Figure 5). Other studies also confirm this trend [37], [38], [39].

Lateral Acromion Angle (LAA)

In 1995, Banas et al. introduce the notion of the lateral acromion angle (Figure 6) [40]. In this study, measurements are performed on MRI coronal sections. It is demonstrated that a low LAA is significantly associated with a lesion of the cuff at MRI with in particular a limit below 70 ° which would be an indicator for an antero-lateral decompression of the acromion. These results are confirmed by a more recent study based this time on standard radiographs of the face [39]. It is also shown that below the threshold of 70 °, the lesion of the cuff is constant. Thus this measure could help to guide the therapeutic attitude without complementary exams and help the surgeon in the decisional process.

Acromial Index (AI)

Recently, Nyffeler et al. was interested in the implication of the extension of the acromion in the tears of the rotator cuff [8]. His hypothesis is that a broad acromion implies higher deltoid ascending forces which favors impingement and degenerative changes. He therefore describes the radiological measurement of the acromial index (AI) which represents the ratio between the glenoid-acromion distance and that between the glenoid-trochiter (Figure 7). There is therefore an association between a high AI and a degenerative lesion of the rotator cuff, thus allowing it to be predicted radiologically. Conversely, he describes an increase in compressive forces on the glenoid when the acromion is short and thus the AI low. This increase in compressive force would therefore favor the appearance of omarthrosis. These findings are confirmed by other studies that also demonstrate an association between elevated AI and a tear in the rotator cuff [41], [42], including one also demonstrating higher AI in patients with recurrences of postoperative rotator cuff tears [43]. The involvement of the AI in the pathologies of the rotator cuff is not however unanimous [44], [45], [46]. Hamid et al. does not demonstrate any significant association between elevated AI and rotator cuff disease [46], while Kircher et al. does not show an association between a low AI and omarthrose, which refutes the theoretical concept of a low AI resulting in increased contact pressure [44]. Furthermore, Melean et al. does not find correlation between AI and the rate of recurrence of rupture of the rotator cuff after surgery. The importance of the AI in assessing a shoulder radiograph remains controversial.

Critical Shoulder Angle (CSA)

In addition to the morphology or size of the acromion, the variation of the inclination of the glenoid is a radiographic marker that may indicate rotator cuff lesions. Thus, several studies show a relationship between a high glenoid tilt and the upper migration of the humeral head [47], [48]. This migration favors subacromial compression of the supraspinatus and therefore tendon tears. In 2013, Moor et al. describes a new radiological marker, the critical shoulder angle (CSA) [9]. The interest is to include in one measure the concept of the AI and the glenoid inclination. It is represented by the angle between a line connecting the upper and lower pole of the glenoid and another connecting the lower pole of the glenoid with the lateral edge of the acromion (Figure 8). It demonstrates an association between a tear of the cuff and a CSA greater than 35 ° and inversely an association between an osteoarthritis and a CSA of less than 30 °. Gerber et al. confirms this relationship in a biomechanical study [49]. He shows that the increase in CSA is associated with an increase in shear forces, especially in degrees of mobility associated with a large number of activities of daily life. The result is a greater antero-superior instability involving more necessary activity on the part of the supraspinatus to stabilize the shoulder and leading more easily to tears. These theories and the association between CSA, osteoarthritis and tear of the cuff are also demonstrated significantly in more recent studies [50], [51], [52], [53], [54], [55]. Engelhardt et al. Even independently analyzed the three different parameters (AI, IG, CSA) demonstrating that CSA is the best parameter for estimating the risk of rotator cuff injury [42]. This can be explained by the fact that it combines the influence of a GI and a high AI on the upper migration of the humeral head. However, he does not find this precision when it comes to correlating the CSA with osteoarthritis. More recently, Chalmers et al. achieves less satisfactory results [56]. He obtains differences up to 2 °, but too low to have a significant association on the presence of a tendinopathy of the cuff. Since the CSA is a radiological measure, it is important to have a good correlation of the measurement. Bouaicha et al. demonstrated in their study that the correlation between anteroposterior standard radiography and scanner is very satisfactory and that the differences that can occur between these two modalities are quite negligible [57]. Spiegl et al. and Cherchi et al. demonstrate a good intra- and inter-observer correlation in the radiological analysis of the CSA [54], [55]. However, Suter et al. describes the measurement of the CSA as a function of the spatial relationship of the scapula as a function of the radiological monitor [58]. He thus notes that the CSA is sensitive to the ante or retro-version of the scapula relative to the radiological monitor, with a change from 5 to 8 ° which can change the CSA measurement by 2 ° and thus influence the clinical interpretation.

Acromiohumeral Distance (AHD)

Tendinopathies of the rotator cuff are frequent pathologies which may have as their origin intrinsic and/or extrinsic factors. An MRI or scanner imaging allows these lesions to be visualized with good precision. However, a standard X-ray marker was described long ago. This is the subacromial space (Figure 9). In the 1960s, Golding was one of the first to describe a link between the decrease in subacromial space and rotator cuff disease [59]. Later in 1970, Weiner et al. also describes an association between the reduction of the subacromial space and the tear of the rotator cuff [60]. n 1984, Petersson describes the average distance of 9 to 10 mm for a normal acromio-humeral space, with a pathological threshold suspecting a lesion of the supraspinatus at 6 mm [61]. Thus, in the years that followed, many authors came to the same conclusion with a widely described association between a subacromial space less than 7 mm and a massive rupture of the rotator cuff [62], [63],[64], [65], [66] with a massive rupture of the rotator cuff described as a tear of at least two tendons, often the supraspinatus and infraspinatus [67]. Thus, Saupe et al. shows in the study a strong association of the decrease of the subacromial space to less than 7 mm and a tear of the supraspinatus and infraspinatus [62]. Nové-Josserand et al. explains that a decrease of the subacromial space to less than 7 mm indicates a rupture of the infraspinatus. The reduction of the space is due to the loss of the infra-spinatus lowering function with a migration of the humeral head in the space deserted by the supraspinatus. Furthermore, there is a higher rate of recurrence of rupture after surgery in a patient with a massive rupture of the cap and therefore a decreased subacromial space. Moreover, the radiological measurement showed a very good correlation whether it is compared to the scanner [68] or when comparing inter-observers [69], [70], [71]. All these elements therefore make it possible to use the measurement of the subacromial space in the evaluation and the therapeutic decision-making of a patient with shoulder pain. However, this remains a good indicator in the evaluation of the posterior superior cuff without giving information on the anterior cuff [72]. In connection with the reduction of subacromial space, Hamada et al. introduced in 1990 the notion of arthropathy linked to a massive rupture of the rotator cuff [7]. It declines in 5 grades progressive, each associated with radiological changes. In 2005, Walch et al. modified this classification somewhat by creating two subtypes of grade 4. However, the same year, Nové-Josserand et al. show that there is no linear progression of the Hamada classification [73]. However it confirms that the tendinopathy of the rotator cuff is more involved in the aging of the shoulder than the osteoarthritis. A new study proposed in 2011 by Hamada et al. examines in more detail the different implications in terms of grades [74]. The greater role of a lesion involving the subscapularis from Grade 3 and a rate of recurrence of rupture after intervention more frequent from Grade 2. Thus, surgery should be considered before the subacromial space is reduced.

Conclusion

The management of a patient in the field of shoulder surgery requires a good knowledge of the anatomical and lesional representations of the standard radiography. This investigation should guide the surgeon for surgical indication or direct him towards further investigations. Although some radiological markers have demonstrated their evidence (great tuberosity displacement, subacromial space, acromial morphology and Hamada classification), others still require extensive studies and protocol standardization (AI, CSA, LAA and Neck-shaft angle).

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