The human shoulder has adapted to enhance the use of another unique and specialized structure — a hand with an opposable thumb. However, our species has sacrificed a great deal of shoulder stability to produce what is arguably the most mobile articulation in the human body. To allow multiplanar movement, shoulder biomechanics have evolved via the development of at least three finely tuned force couples that must occur at the scapula and at the shoulder in both transverse and coronal motions.

Four muscles of the rotator cuff interact with the three heads of the deltoid to produce one of these force couples. Collectively, the four muscles — supraspinatus, infraspinatus, teres minor, and subscapularis — form the rotator cuff. The serratus anterior, rhomboids, levator scapula and the trapezius group provide motion at the scapula, and the pectoralis major, teres major, and latissimus dorsi provide large gross movements.¹

Because of the complexity and instability of the shoulder anatomy, the shoulder is at risk for the development of numerous pathologies, many of which are amenable to evidence-based physical therapy interventions. Moreover, because the rotator cuff acts in concert with larger, more powerful muscles of the shoulder girdle to create a total shoulder complex motion known as scapulohumeral rhythm, the rotator cuff itself is often incriminated in shoulder pathologies.

Joints of the Shoulder Complex

Three synovial joints and one “muscle joint” make up the articulations of the shoulder and shoulder girdle. The synovial joints include the sternoclavicular, acromioclavicular (AC), and the glenohumeral joints. The muscle joint is the scapulothoracic joint. For normal scapulohumeral rhythm to occur, normal motion must take place in all four of these joints. Particularly important is the motion that occurs at the scapulothoracic joint; that is, the movement of the scapula on the chest wall, and the glenohumeral joint, a freely moveable synovial joint of a convex humeral head moving in the shallow concave surface of the glenoid fossa. The shallow glenoid cavity is deepened by the glenoid labrum, a fibrocartilage ring surrounding the glenoid rim.

Muscles of the Shoulder Complex

One method particularly useful to physical therapists and biokinesiologists for classifying muscles that attach to and move the shoulder girdle and shoulder is according to their kinetic functions:^1,2

Pivoters include both scapulovertebral muscles (trapezius, levator scapula, and rhomboids) and scapulothoracic muscles (serratus anterior and pectoralis minor).

Positioners are muscles that position the humerus during or following action of the pivoters and include the anterior, middle, and posterior heads of the deltoid muscle.

Propellers are muscles that offer a wide array of strong, gross humeral movements, depending on concomitant or prior scapular and humeral positioning by the pivoters and positioners. Propellers include latissimus dorsi, pectoralis major, and teres major. The first two of these muscles originate at the vertebral column and anterior chest wall respectively, while the teres major originates on the dorsal aspect of the inferior angle of the scapula. The three muscles insert respectively on the floor, lateral lip, and medial lip of the bicipital groove of the humerus. In this latter structure, the long head of the biceps brachii tendon courses its way to insertion on the supraglenoid tubercle; the biceps muscle acts as an important humeral decelerator.

Protectors act as a force couple with the positioners (deltoid group) to keep structures, in what has been referred to as the critical zone (between the coracromial arch and the humeral head), out of harm’s way.³ The protectors also act as decelerators to prevent subluxation and/or dislocation of the humerus during powerful, explosive, or repetitive movements, such as throwing or swimming. These muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis. The first three of these muscles originate on the scapula and insert in close proximity to the others on the greater tubercle of the humerus. The subscapularis originates anteriorly on the scapula and inserts on the anteriorly positioned lesser tubercle of the humerus. The supraspinatus is a shoulder abductor (although it cannot be isolated from the middle deltoid except as a joint compressor), the infraspinatus and teres minor are external rotators, and the subscapularis is an internal rotator.

Specific Biomechanics of the Rotator Cuff

The three significant force couples that occur in normal overhead shoulder movement are the scapular force couple (acting on the scapula), the transverse force couple, and the coronal force couple.^4,5,6 The latter two force couples act at the glenohumeral joint.

The scapular force couple consists of cocontraction of the serratus anterior and the lower trapezius, resulting in elevation of the acromion, thereby increasing the relative distance between the coracoacromial arch and the humeral head.⁷

The transverse plane force couple occurs between the anteriorly oriented subscapularis muscle and the posteriorly positioned infraspinatus and teres minor. A cocontraction of all three of these muscles downwardly translates and compresses the humeral head during overhead movements. The muscles offer protection of the structures inferior to the coracoacromial arch and also act as dynamic stabilizers.

The coronal plane force couple occurs between the deltoid muscle and the inferiorly placed rotator cuff muscles during overhead elevation of the shoulder as follows: Contraction of the deltoid and supraspinatus begin to pull the humeral head superiorly, while cocontraction of the transverse force couple muscles (subscapularis, infraspinatus, and teres minor) exert a caudal force on the humeral head, simultaneously compressing the humeral head into the glenoid fossa in conjunction with the supraspinatus. The resultant motion is smooth overhead motion of the humerus.

Scapulohumeral rhythm occurs as the transverse and coronal force couples perform their work during the movement of overhead elevation. The scapula begins to abduct and upwardly rotate a moment later via the scapular force couple. The sequence of events in normal scapulohumeral rhythm in regard to overhead elevation is:⁴

• 0–30 degrees: Scapula creates a stable platform, all significant motion occurs at the glenohumeral joint
• 30–90 degrees: Scapula abducts and upwardly rotates 1 degree of motion for every 2 degrees of humeral elevation
• 90 degrees to full abduction: Scapula abducts and upwardly rotates 1 degree for each 1 degree of humeral elevation.

The smaller (and weaker) muscles of the rotator cuff work with larger glenohumeral muscles to protect the critical zone from trauma. The scapular force couple aids the glenohumeral force couples by promoting scapulohumeral rhythm. The cuff tendons lying in the critical area of the shoulder in the adult are relatively avascular. The glenohumeral joint itself is weak by bony and ligamentous arrangement with stability being sacrificed for mobility. The articular surfaces of the glenoid fossa and humeral head are lined with hyaline cartilage and joint congruency is increased by the fibrocartilage rim around the glenoid, known as the glenoid labrum. Thus the shoulder articular surfaces are subject to degenerative changes, as are the tendons, most notably those of the rotator cuff.

Common Rotator Cuff Pathologies

Problems with the rotator cuff involve impingement and tears. Impingement, which may be primary or secondary, demonstrates a possible progression of a degenerative process.^6,8

In primary impingement, repetitive overhead motions may cause shoulder pain by impingement of the rotator cuff tendons underneath the coracoacromial arch. The impingement thus is mechanically caused by subacromial crowding.

In secondary impingement, the relative narrowing of the subacromial space may be caused by instability of the glenohumeral joint due to weakness or fatigue of the rotator cuff muscles or the long head of the biceps brachii.

Such weakness leads to an overload of passive restraints during repetitive overhead activities, which results in glenohumeral joint laxity. The joint laxity increases the workload of the rotator cuff and biceps and the fatigue in these muscles results in decreased humeral head depression and hence mechanical impingement of the rotator cuff by the coracoacromial arch. Additional causative factors of secondary impingement include weakness of the scapulothoracic
muscles, which produces scapular instability; abnormal positioning of the scapula; and a loss of scapulohumeral rhythm. Impingement occurs due to insufficient elevation of the acromion.

A continuum beginning with primary or secondary impingement could lead to abnormal biomechanics (secondary to structural conditions, including congenital or acquired capsular laxity) which, in turn, could lead to excessive wear and tear on the rotator cuff muscles, biceps tendon, and/or subacromial bursa as well as the articular surfaces of the glenohumeral joint itself. The ultimate result could be severe degenerative arthritis of the shoulder and failure of the rotator cuff, either through a slow recession of the tendons from their humeral insertions or a sudden failure of these structures from a fall on an outstretched arm or other seemingly benign overload, such as lifting an object overhead.

Examination of the Shoulder

The general clinical examination scheme consists of a history and physical examination. The three basic steps involved in taking a history are a review of the physical therapy referral slip (if any), a review of the patient’s medical history, and a patient interview.

From the patient history, the examiner should glean pertinent medical and surgical information concerning the patient as well as information concerning:

• Recent shoulder-related surgery
• Presence of “red flags,” such as constant unremitting pain and vascular disease (especially a past history of angina)
• Inflammatory disease
• Neck pain, past or present
• Location of shoulder pain, including its origin and spread
• Sudden or slow onset of pain and/or weakness
• Constant pain and whether it is better with rest or with movement
• Ability to lie on the shoulder or the presence of night pain
• An estimate of the pain on a numeric pain scale of 0 (lowest) to 10 (highest), evaluating the current pain, the mildest pain and when it occurs, and the worst pain and when it occurs
• Any other information the patient wishes to share

The physical examination begins with inspection with the patient standing with the shoulder, cervical, and thoracic spine appropriately exposed.

The clinician should observe:

• Head, neck, and thoracic posture
• Evidence of recent or past trauma, surgical scars, or swelling
• Scapular position noting any winging scapulae, or depressed or elevated acromion
• Deformity at shoulder, clavicle, sternoclavicular joint, acromioclavicular joint, or biceps areas
• Muscular atrophy, especially of deltoid and posterior cuff muscles
• Any asymmetry noted when comparing involved to noninvolved shoulder.

Movement assessment takes place in the following order:

• Active movements (tests willingness to perform given movement)
• Passive movements (tests range of motion and status of inert structures)
• Resisted movements (tests status of contractile elements)
• Joint play/accessory motions (tests status of joint)
• Special tests, such as Apley’s scratch test (patient touches superior and inferior aspects of opposite scapula); impingement sign (arm in full flexion with internal rotation); and apprehension tests (abduction and external rotation with anterior pressure on the posterior humeral head).

Palpation is performed to both the involved and noninvolved shoulder to detect tenderness and deformity. Areas likely tender to palpation with rotator cuff pathology may include the long head of biceps brachii tendon, lesser humeral tubercle, greater humeral tubercle, and the lateral/inferior aspect of acromion process. Additionally, the examiner should comparatively palpate the right and left posterior cuff muscles and deltoid for atrophy and hypertrophy.

Primary impingement findings: Look for a history of insidious or sudden onset of shoulder pain, particularly with repeated activities of daily living involving abduction and/or internal rotation. The inspection may be unremarkable, although atrophy of deltoid and posterior cuff musculature may be present in chronic states.

During palpation an overly prominent greater tuberosity may be present and tender; pain along the anterolateral underside of the acromion process may also be present. Imaging may reveal a hooked acromion, spurring, and/or calcific deposits.

Secondary impingement findings: History nearly always includes an insidious and progressive onset of pain, usually secondary to overhead athletic activities such as throwing and swimming. Inspection may reveal a low or depressed acromion compared with the noninvolved shoulder, particularly in throwers and racquet sport athletes.

The movement assessment may be similar to those found in primary impingement with the possible additional findings of general overall hypermobility, especially with Apley’s scratch test, and positive apprehensive/relocation tests.

Palpation may find tenderness of bicipital groove structures, lesser and greater humeral tubercle structures, and particularly the anterior capsular area. Imaging may reveal capsular laxity and labral abnormalities.

Partial rotator cuff tear (slow-onset) findings: Past history will include injury and/or overuse with progressive shoulder pain and weakness. The patient may be older and/or have a history of overhead athletics.

Common findings with inspection, particularly in older individuals, include deltoid and posterior cuff muscle atrophy. Other observations may be similar to those found in impingement syndromes. Once again, movements may be similar to those found in impingement syndromes with the possible additional findings of weak and/or painful resisted abduction and resisted external or internal rotation.

Palpation also has findings similar to those in impingement signs. Imaging will likely show the presence of rotator cuff tear.

Partial rotator cuff tear (sudden-onset) findings: Indications will be similar to the slow-onset rotator cuff tear with the possible exceptions of a report of trauma or injury, greater tenderness to palpation, and more difficulty in achieving active overhead elevation.

Complete rotator cuff tears (slow- and sudden-onset) findings: Slow-onset complete rotator cuff tears are characterized by a progressive history of pain and weakness. Sudden-onset tears are associated with a single event and extreme difficulty (but often not impossibility) in achieving and maintaining active overhead elevation.

Sudden-onset complete rotator cuff tears typically also present with extreme pain in the acute stage, inability to actively elevate one arm to horizontal and beyond, and extremely weak resisted abduction and external and internal rotation.

Selected Shoulder Rehabilitation Treatment

The following treatment techniques are based on current evidence for best practices. Keep in mind the degenerative continuum described above where a primary or secondary impingement wears on the critical zone structures, glenoid labrum, and potentially on articular joint surfaces to ultimately lead to a partial or complete rotator cuff tear.

Physical therapy techniques are based on the findings of the evaluation and current evidence. Techniques may be classified into four categories: pain-relieving modalities, manual therapy, neuromuscular re-education exercises, and strengthening, endurance, and stretching exercises.

Pain-relieving techniques and modalities typically include:

1. Limb placement in a position of comfort (usually with the patient supine and the arm supported at approximately 20 to 30 degrees of flexion and 20 degrees or so of external rotation)
2. Heat/ultrasound
3. Cryotherapy/ice
4. Electrical stimulation.

However, these modalities and other passive interventions have not been shown to significantly reduce shoulder symptoms and disability^12,13 with the notable exception in the use of ultrasound over 24 visits with each visit consisting of 15 minutes of ultrasound treatment.¹⁴

Manual therapy has the support of multiple studies as an effective technique, especially when combined with exercise.^15,16,17 Some researchers have found that mobilization to the shoulder and surrounding joints combined with exercise is more effective for reducing pain and improving outcomes in patients with rotator cuff disease when compared with competing treatment interventions. Manual therapy techniques were directed at relevant movement limitations in the upper quarter. While the movements were directed primarily to the shoulder, the cervicothoracic region as well as the costotransverse articulations also received manual therapy in the form of passive accessory or passive physiological joint mobilization.¹⁵

Neuromuscular re-education exercises techniques generally target control and endurance of the anterior and posterior musculature (pec major, latissimus dorsi, serratus anterior, and rhomboids) as well as the deep neck flexors due to the intimate relationship between the shoulder and the cervical spine.^15,18  Most of the exercises are performed three times weekly for three sets of 10 repetitions using elastic band-resistant techniques where external resistance is indicated, and include specific movements, such as rowing and shoulder flexion. Exercises using a stationary bench, such as seated press-ups and push-ups with a plus, can be performed to fatigue or for a maximum of 25 repetitions.¹⁵

Strengthening, endurance, and stretching exercises have gained current support. Recent evidence in the realm of muscle recruitment has demonstrated that when working with the rotator cuff musculature, both eccentrically and concentrically, increased resistance to internal and external rotation is typically dealt with by a corresponding increase in activity in all shoulder-rotating musculature, including the rotator cuff.¹⁹ Studies looking at the efficacy of therapeutic exercise demonstrate that scaption (shoulder elevation in the plane of the scapula) and horizontal extension/external rotation, in combination with anterior shoulder musculature and posterior shoulder capsule stretching (three times for 30 seconds each with 10 seconds rest between sets) along with the neuromuscular re-educating movements described above elicited a significant reduction in pain with a commensurate increase in function.¹⁵

Functional movement techniques are a large variety of movements that closely approximate or are actually instrumental activities of daily living. Keeping in mind the rule of specific adaptations to imposed demands, treatment can be customized based upon the patient. For an athletic population such exercises might involve intense proproiceptive neuromuscular facilitation patterns for a tennis player or pitcher. For older, more sedentary individuals, exercises, such as placing objects on an overhead shelf or reaching behind the back to approximate toileting or bra-fastening activities, may be more appropriate.

The human shoulder is one of the most complex structures of the body, relying upon an elaborate interaction of static and dynamic structures to provide stable mobility. Although one of the most frequently injured structures in the body, the rotator cuff is also one of the most amenable to physical therapy treatment. Up-to-date knowledge of shoulder anatomy, biomechanics, pathology, examination, and selected treatment techniques can help physical therapists to aid patients in coping with this pervasive condition.

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