| ROTATOR CUFF | |
|---|---|
| Muscles on the dorsum of the scapula, and the Triceps brachii. | |
| The scapular and circumflex arteries. | |
| Gray's | subject #123 |
In anatomy, the rotator cuff is the group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff, along with the teres major muscle, the coracobrachialis muscle and the deltoid, make up the seven scapulohumeral (those that connect to the humerus and scapula and act on the glenohumeral joint) muscles of the human body.
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The rotator cuff muscles are important in shoulder movements and in maintaining glenohumeral joint (shoulder joint) stability.[1] These muscles arise from the scapula and connect to the head of the humerus, forming a cuff at the shoulder joint. They hold the head of the humerus in the small and shallow glenoid fossa of the scapula. The glenohumeral joint has been analogously described as a golf ball (head of the humerus) sitting on a golf tee (glenoid fossa). [2]
During abduction of the arm, the rotator cuff compresses the glenohumeral joint, a term known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle. The anterior and posterior directions of the glenoid fossa are more susceptible to shear force perturbations as the glenoid fossa is not as deep relative to the superior and inferior directions. The rotator cuff's contributions to concavity compression and stability vary according to their stiffness and the direction of the force they apply upon the joint.
| Muscle | Origin on scapula | Attachment on humerus | Function | Innervation |
| Supraspinatus muscle | supraspinous fossa | superior and middle facet of the greater tuberosity | abducts the arm | Suprascapular nerve (C5) |
| Infraspinatus muscle | infraspinous fossa | posterior facet of the greater tuberosity | externally rotates the arm | Suprascapular nerve (C5-C6) |
| Teres minor muscle | middle half of lateral border | inferior facet of the greater tuberosity | externally rotates the arm | Axillary nerve (C5) |
| Subscapularis muscle | subscapular fossa | lesser tuberosity (60%) or humeral neck (40%) | internally rotates the humerus | Upper and Lower subscapular nerve (C5-C6) |
The supraspinatus muscle fans out horizontally band to insert on the superior and middle facets of the greater tuberosity. The greater tubercle projects as the lateral most structure on anterior to posterior radiographs of the shoulder with the bicipital groove just medial to it at the humeral head. Medial to this, in turn, is the lesser tuberosity of the humeral head. The subscapularis muscle origin is divided from the remainder of the rotator cuff origins as it is deep to the scapula.
The tendons at the ends of the rotator cuff muscles can become torn, leading to pain and restricted movement of the arm. A torn rotator cuff can occur following a trauma to the shoulder or it can occur through the "wear and tear" of tendons, most commonly that of the supraspinatus under the acromion. It is an injury frequently sustained by athletes whose duties involve making repetitive throws, such as cheerleaders, baseball pitchers, American football quarterbacks, volleyball players (due to their swinging motions), water polo players, team ropers, shotput throwers (due to using poor technique), swimmers, boxers, kayakers, western martial artists, fast bowlers in cricket, tennis players (due to their service motion) and tenpin bowlers due to the repetitive swinging motion of the arm with the weight of a bowling ball. This type of injury also commonly affects orchestral conductors, choral conductors, and drummers due to the swinging motions and other movements used to lead their ensemble. It is commonly associated with motions that require repeated overhead motions or forceful pulling motions.
A systematic review of relevant research found that the accuracy of the physical examination is low.[3] The Hawkins-Kennedy test[4][5] has a sensitivity of approximately 80% to 90% for detecting impingement. The infraspinatus and supraspinatus[6] tests have a specificity of 80% to 90%.[3]
As with all muscle injuries, R.I.C.E. is an initial response to injury recommended by health providers:
Cold Compression Therapy shoulder wraps facilitate the icing and compression of an otherwise difficult body area to ice and compress.
Depending on severity of symptoms, further imaging with radiograph, or MRI may be warranted to see if surgery or an underlying bone injury exists.
Postures and sleeping positions may be modified to provide relief.[7]
The rotator cuff can be strengthened to rehabilitate shoulder injuries, and prevent future ones. There are different exercises to target the individual rotator cuff muscles.
| Description | Beginning | End |
| The most effective is the side-lying external rotation, which activates the supraspinatus, subscapularis, infraspinatus and teres minor.
Lie on a bench sideways, with the arm next to the side and flexed about 90 degrees at the elbow. Rotate the upper arm, raising the dumbbell towards the ceiling to a 45 degree angle. Keep the elbow flexed, and the upper arm close to the body. Pace at two seconds up and four seconds down. This is an excellent all-around shoulder exercise. |
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| The propped external rotator targets the infraspinatus and teres minor.
Sit perpendicular to the barbell with arm flexed at 90 degrees at the elbow, and the forearm resting parallel on the barbell. Raise the dumbbell up until the forearm points up. Slowly lower the dumbbell and repeat, exercising both arms. The posterior deltoid also aids in external rotation. Like the posterior deltoid, both the infraspinatus and teres minor also contribute to transverse extension of the shoulder, such as during a bent over row to the chest. They can be trained in this way besides isolating the external rotation action. |
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| The lateral raise with internal rotation (LRIR) primarily targets the supraspinatus.
Grasping a dumbbell in each hand, internally rotate the arms so that the thumbs point towards the floor when extended (as if emptying a drink into a bin). Raise the arms sideways, keeping the thumbs pointing downwards, until the dumbbells are just below the shoulders. This exercise is sometimes called a lateral raise. |
Strengthening the rotator cuff allows for increased loads in a variety of exercises. When weightlifters are unable to increase the weight they can lift on a pushing exercise (such as the bench press or military press) for an extended period of time, strengthening the rotator cuff can often allow them to begin making gains again. It also prevents future injuries to the glenohumeral joint, balancing the often-dominant internal rotators with stronger external rotators. Finally, exercising the rotator cuff can lead to improved posture, as without exercise to the external rotator, the internal rotators can see a shortening, leading to tightness. This often manifests itself as rounded shoulders.
Even for full thickness rotator cuff tears, conservative care (i.e., non-surgical treatment) outcomes are usually reasonably good.[8] However, many patients still suffer disability and pain despite non-surgical therapies. For massive tears of the rotator cuff, surgery has shown durable outcomes on 10 year follow-up.[9] However, the same study demonstrated ongoing and progressive fatty atrophy and re-tears of the rotator cuff. Shen has shown that MRI evidence of fatty atrophy in the rotator cuff prior to surgery is predicative of a poor surgical outcome.[10] If the rotator cuff is completely torn, surgery is usually required to reattach the tendon to the bone.[11]
There are several ways to depict the structures of the shoulder, which consist of muscles, tendons, bones, cartilage and soft tissue. When deciding which medical imaging technique should be used, there are a couple of factors that need to be taken into account. Firstly, one has to consider the suspected clinical diagnosis. Together with the knowledge of the advantages and limitations of the various medical imaging techniques ( i.e. conventional radiography, ultrasound, computer tomography and magnetic resonance), one has to make an informed decision which technique would best suit the specific situation.
Hodler et al. recommend to start scanning with conventional x-rays taken from at least two planes, since this method gives a wide first impression and even has the chance of exposing any frequent shoulder pathologies, i.e. decompensated rotator cuff tears, tendinitis calcarea, dislocations, fractures, usures and/or osteophytes. Furthermore are x-rays required for the planning of an optimal CT or MR image.[12]
Conventional x-rays and ultrasonography are the primary tools used to confirm a diagnosis of injuries sustained to the rotator cuff. For extended clinical questions, imaging through Magnetic Resonance with or without intraarticular contrast agent is indicated.
The conventional invasive arthrography is now-a-days being replaced by the non-invasive MRI and US and is used as an imaging reserve for patients who are contraindicated for MRI, for example pacemaker-carriers with an unclear and unsure ultrasonography.[13]
The scapula should be positioned perpendicularly to the x-ray film. The body has to be rotated about 30 to 45 degrees towards the to be imaged shoulder, and the standing or sitting patient lets the arm hang.
This method allows to judge:[14]
The humerus head should be aligned in the neutral position and external rotation in a way towards the socket, that a fictive continuous line can be seen. This line is called Bandi line, otherwise known as the Ménard-Shenton line. A discontinuous line alludes to a cranial decentralization of the humerus head.[15]
The arm should be abduced 80 to 100 degrees at a precise defined scapular or frontal plane.
This method allows to judge:[16]
The lateral contour of the shoulder should be positioned in front of the film in a way that the longitudinal axis of the scapula continues parallel to the path of the rays.
This method allows to judge:[17]
This Y-projection can be traced back to Wijnblath’s 1933 published cavitas-en-face projection.[18]
It must be pointed out that this projection has a low tolerance for errors and correspondingly needs proper execution.[19]
There are several solid advantages of ultrasound. It is relatively advantageously priced, does not emit any radiation, it is accessible, it is capable to visualize in real time any tissue function and it allows to perform provocative maneuvers in order to replicate the patient’s pain. Those apparent benefits surely helped ultrasound to be today’s first choice for assessing tendons and soft tissues on the quick. Limitations include for example: The high degree of operator dependence, the inability to define pathologies in bones. One also has to have an extensive anatomical knowledge of the examined region and keep an open mind to normal variations and artifacts created during the scan.[20]
Although musculo-skeletal US training, like medical training in general, is a lifelong process, Kissin et al. suggest that, rheumatologists who taught themselves how to manipulate US, can use US just as good as international musculo-skeletal US experts to diagnose common rheumatic conditions.[21]
After the introduction of the high-frequency transducers in the mid-eighties, US has become a widely conventional tool for taking accurate and precise images of the shoulder to support the diagnosis.[22][23][24][25][26]
Adequate for the examination are high-resolution, high-frequency transducers with a transmission frequency of 5, 7.5 and 10 MHz. To improve the focus on structures close to the skin an additional „water start-up length“ is advisable. During the examination the patient is asked to be seated, the affected arm is then adducted and the elbow is bent to 90 degrees. Slow and cautious passive lateral and/or medial rotations have the effect of being able to visualize different sections of the shoulder. In order to also demonstrate those parts which are hidden under the acromion in the neutral position, a maximum medial rotation with hyperextension behind the back is required.[27]
To avoid the different tendon echogenicities caused by different instrument settings, Middleton compared the tendon’s echogenicity with that of the deltoid muscle, which is still lege artis.[28][29]
Usually the echogenicity compared to the deltoid muscle is homogeneous intensified without dorsal echo extinction. Variability with reduced or intensified[30] echo has also been found in healthy tendons. Bilateral comparison is very helpful when distinguishing and setting boundaries between physiological variants and a possible pathological finding. Degenerative changes at the rotator cuff often are found on both sides of the body. Consequently unilateral differences rather point to a pathological source and bilateral changes rather to a physiological variation.[31]
In addition, a dynamic examination can help to differentiate between an ultrasound artifact and a real pathology.[32]
To accurately evaluate the echogenicity of a US, one has to take into account the physical laws of reflection, absorption and dispersion. It is at all times important to acknowledge that the structures in the joint of the shoulder are not aligned in the transversal, coronal or sagittal plane, and that therefore during imaging of the shoulder the transducer head has to be hold perpendicularly or parallel to the structures of interest. Otherwise the appearing echogenicity may not be evaluated.[33]
Orientation-aid for the longitudinal plane:
As an aid to orientation, it is advisable to begin the examination with the delineation of the acromion, as it is easy to palpate and it has an identifiable echo extinction. To adjust the longitudinal plane image the way it is known in the x-rays and the physical examination, the acromion has to be visible at the image border.[34]
Orientation-aid for the transversal plane:
Again it is advantageous to start above the acromion and then move the transducer to the humerus. The acromion echo extinction disappears and the wheel-like figure with almost concentric projection of the deltoid muscle, supraspinatus muscle tendon and humeral head-outline turns up as soon as the transducer is directed perpendicularly and parallel to the acromion edge. Using the anterior transversal plane one can depict the intraarticular part of the long head of the biceps brachii muscle. Additionally one can use the posterior transversal plane to depict the intersection of the infraspinatus muscle tendon and the posterior edge of the fossa.[35]
| usual longitudinal front vision | usual longitudinal back vision | usual transversal side vision | |
|---|---|---|---|
| supraspinatus tendon | acromion of the left shoulder in the left half of the image and vice versa. (In order to explore the entire tendon the examiner must move the transducer from ventral to dorsal perpendicular at the acromion axis. Either trough a maximal medial rotation or an according position of the transducer it is possible to see the supra- infraspinatus tendon intersection.) | ventral right shoulder in the right half of the image and vice versa. | |
| infraspinatus tendon | scapula spine of the right shoulder in the left half of the image and vice versa. |
Orthopedics established early the MRI as the tool of choice for joint- and soft tissue-imaging, because its non-invasiveness, the lack of radiation exposure, multi planar slicing possibilities and the high soft tissue contrast.[36]
The MR Imaging should provide joint details to the treating orthopedist, to help him diagnose and decide the next appropriate therapeutic step. To examine the shoulder, the patient is lying and the concerned arm is in lateral rotation. For signal detection it is recommended to use a surface-coil. To find pathologies of the rotator cuff in the basic diagnostic investigation, T2-weighted sequences with fat-suppression or STIR sequences have proven value. In general, the examination should occur in the following three main planes: axial, oblique coronal and sagittal.[37]
Most morphological changes and injuries are sustained to the supraspinatus tendon. Traumatic rotator cuff changes are often located antero-superior, meanwhile degenerative changes more likely are supero-posterior.[38]
Tendons are predominantly composed of dense collagen fiber bundles. Because of their extreme short T2-relaxation time they appear typically signal-weak, respectively, dark. Degenerative changes, inflammations and also partial and complete tears cause loss of the original tendon structure. Fatty deposits, mucous degeneration and hemorrhages lead to an increased intratendinal T1-image. Edema formations, inflammatory changes and ruptures increase the signals in a T2-weighted image.[39]
Erickson et al. noticed and described a typical artifact and gave the phenomenon the name „magic angle“. The „magic angle“ describes a changed T2-relaxation time depending on the spatial orientation of the tissue to the main magnetic field. If parts of the tendon are located at the area of the magic angle at 55 degrees to the main magnetic field, their T2-relaxation time gets influenced and the signal heavily intensified. Unluckily these artifacts occupy similar areas where clinical relevant pathologies are found. To avoid a wrong diagnosis it is recommended to exclude this phenomenon in a case of doubt through a heavy T2-weighted sequence or an additional fat-suppression at a proton weighted sequence.[40]
While using MRI, true lesions at the rotator interval region between the parts of the supraspinatus and subscapularis are all but impossible to distinguish from normal synovium and capsule.[41]
In 1999, Weishaupt D. et al. reached through two readers a significant better visibility of pully lesions at the rotator interval and the expected location of the reflection pulley of the long biceps and subscapularis tendon on parasagittal (reader1/reader2 sensitivity: 86%/100%; specificity: 90%/70%) and axial (reader1/reader2 sensitivity: 86%/93%; specificity: 90%/80%) MRA images. [42]
When examining the rotator cuff, the MRA has a couple of advantages compared to the native MRI. Through a fat suppressed T2-weighted spin echo, MRA can reproduce an extreme high fat-water-contrast, which helps to detect water-deposits with better damage diagnosis in structurally changed collagen fiber bundles.[43]
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