Editor: Eugene Sherry, MD MPH FRACS
- Anatomy and Biomechanics
- Instability – Indirectional (dislocation, subluxation)
- Tendinitis and impingement
- Rotator cuff tears
- Internal derangements within the glenohumeral joint
- SLAP lesions
- Labral tears
- Loose bodies
- Acromioclavicular joint dislocation/fractures
- Clavicle fractures
- Outer clavicular osteolysis/Medial Clavicular Sclerosis
- Sternoclavicular dislocation
- Muscle ruptures
- Biceps tendon injuries
- Nerve injuries – Suprascapula
- Prevention of injury to the shoulder
With its extreme mobility and structural insecurity, the shoulder is probably the most vulnerable joint in the body.
The shoulder joint and the muscular supports around it are required to circumscribe large arcs of motion, with high speed and force, to enable the athlete to achieve peak performance.
It is not surprising then that the joint is prone to such a variety of injuries with significant stresses being placed on the bones, chondral surfaces and the soft tissues. Between 8 – 13% of injuries sustained by athletes involve the shoulder (Fig. 1).
Anatomy and Biomechanics
The shoulder function is a compilation of coordinated motion between four separate joints. The glenohumeral joint is the main one. The others are the acromial-clavicular, sternoclavicular joints and Scapulo-thoracic. Disorders in any of these may be reflected as dysfunction of the glenohumeral joint.
The glenohumeral joint (GHJ) is a ball and socket joint.
The humeral head constitutes about one third of a sphere, and the articular surface has a medial angulation of 45 degrees to the shaft and retroversion of about 30 degrees to the transverse axis of the elbow. The glenoid fossa is pear shaped. Its radius of curvature is half that of the humeral head and so the area of bony contact is minimal. The addition of the glenoid labrum increases the depth of the fossa and improves the surface area of contact between the humeral head and the total glenoid cavity. Ligamentous stability is conferred by the superior, middle, and inferior glenohumeral ligaments and the capsule. Further stability comes from negative intraarticular joint pressures, the rotator cuff muscles and the coracohumeral ligament (Fig.2).
The acromioclavicular joint (ACJ) is a diarthrodial joint linking the arm to the axial skeleton. Its bony configuration confers minimal stability to the joint. Within the joint there is a variable fibrocartilaginous disc/meniscus. The capsule with the superior acromioclavicular ligaments stabilise the joint at physiological loads. Further stability is from the coracoclavicular ligaments, the conoid and trapezoid (Fig.3).
The sternoclavicular joint (SCJ) comprises tow incongruent articular surfaces with an intervening fibrocartilaginous disc separating it into two independent joints. It is stabilised by the interclavicular, anterior and posterior sternoclavicular ligaments as well as the costoclavicular ligament (rhomboid ligaments). The joint allows for three planes of motion. The fulcrum of movement is the rhomboid ligament, not the SCJ articulation.
Despite the low weight of the arm, (5% of body weight, i.e. 3.5kg in a 70kg man) high torque forces are generated by the long lever of the arm. The rotator cuff and other shoulder muscles are used to generate movement as well as glenohumeral control. While the shoulder is susceptible to injury from direct forces on to the joint, it is in throwing that all the muscles of the trunk and upper limb work in a synchronized balanced manner to propel an object forward. Throwing can be divided into: cocking (or wind-up), acceleration and follow-through phases. Imbalance, fatigue, or damage to any structures or muscles may result in pain, tendinitis and/or instability (Fig. 4).
Should instability occurs commonly in many sports.
Whereas in the past only complete dislocation was recognized, these days a wide spectrum of symptoms occur with a varying degree of slipping of the shoulder. It is common to refer to partial dislocation of the shoulder as subluxation. Many may feel that this is a lesser injury to the glenohumeral joint, however, significant and severe injuries can occur with patients who may have only subluxed their joints. It is better to simply refer to the injuries as “instability events” and regard all as potentially damaging to the joint. In the majority of cases (95%) shoulder instability is in the anterior or antero-inferior direction. Other, less common, directions include posterior and multidirectional.
Anterior instability is most likely to occur when the arm is positioned in abduction/external rotation and an anterior load placed on the shoulder joint, as might occur in a fall on the outstretched hand or tackling a player with the arm out from the side, (rugby). In other situations, the instability may occur without an obvious traumatic event. In upper limb, overhead sports, (baseball or tennis), gradual stretch of the anterior capsule may occur and give symptoms of the shoulder slipping. There is a hierarchy of support mechanisms controlling glenohumeral stability which, depending on the severity of the force, determine the nature of the damage which might occur (Fig. 5).
Hierarchy of Shoulder
Finite Joint Volume
The symptoms of instability include: frank dislocation; slipping; pain with the arm in abduction/external rotation; apprehension using the arm overhead or a “dead arm” feeling with a tackle or overhead action. The clinical examination shoulder include looking at range of motion, strength, increased antero-posterior translation of the humeral head (Fig. 6), apprehension and relocation signs (Fig.7), coincident tendinitis or labral tears and also signs of ligament laxity.
The natural history of the acute first time anterior should instability is now more clearly described. The chance of a younger patient (less than 22 years of age) having a further instability event within two years is 62%. Many feel that if these patients participate in contact sports the likelihood of repeat instability is over 90%. Older patients have a lesser chance of further instability (in 30 – 40 years old patients the risk is 25%). Over a ten year period there is a 12% chance of instability occurring in the opposite shoulder. Most significantly, however, over ten years there is a 20% incidence of arthritic change on radiograph occurring in the shoulder (9% moderate or severe). This arthropathy is not influenced by the number of dislocations or whether surgery as been performed.
It is easy to remember:
TUBS ( Traumatic, Uni directional,Bankart lesion, Surgery) and
AMBRI( atraumatic, multi directional, bilateral, rehabilitation, inferior capsular shift) as a guide to type of dislocation and whether surgery is required.
All patients should be assessed for any associated nerve or vascular injury (Fig. 8). Appropriate x-rays of the shoulder are essential (Fig. 9). Closed reduction can be achieved in the emergency room using either Pethidine/Diazepam/Nitrous oxide or with an intra-articular injection of lignocaine 1%. General anaesthesia may be required where the patient is having excessive muscle spasm. (See Fig.10 – Techniques for Closed Reduction of the Dislocated Shoulder). The arm should be placed in a sling and physiotherapy organised after a 1 – 3 week period of rest. In younger patients where there is a high risk of recurrence and/or special sporting requirements, an acute arthroscopic assessment and repair may be offered.
Where recurrent instability becomes a problem, the options of treatment include modification or avoidance of the precipitating event, a physiotherapy rehabilitation programme to strengthen the shoulder; or surgical reconstruction of the shoulder. A variety of surgical techniques can be used and are divided into those which correct the pathology and those which tighten or use bone blocks to prevent dislocation. Correction of the pathology of instability inclues repairing the avulsed inferior glenohumeral ligament (Bankhart Lesion) and correcting any associated capsular redundancy (capsular shift). This is the preferred option in surgical management of the unstable shoulder. The success rate for surgery is approximately 95%. Those procedures which correct the pathology (i.e. anatomical reconstructions) are most likely to restore almost full range of motion. This is important for those athletes involved in upper limb sports requiring a throwing action, e.g. baseball.
Many of the non-anatomical reconstructions restrict external rotation and prevent these athletes from being able to perform their sports (see Fig. 13 – Types of Surgical Shoulder Reconstructions).
All shoulders demonstrate a variable degree of laxity which is normal. In some patients marked laxity may contribute to symptoms. These may be insidious in onset or be related to a traumatic event. It is important to differentiate laxity from instability.
Laxity is simply a physical finding, whereas instability is the combination of symptoms and signs. To make the diagnosis of MDI, there is usually instability in at least two directions, inferior plus either/or both anterior and posterior. Patients often have pain and weakness associated with a shoulder that subluxes inferiorly as well as anterior and posterior.
Care is needed in the evaluation of these patients. A small subgroup of MDI patients demonstrate a habitual/voluntary aspect to their problem. This group of patients should be evaluated by appropriate counselors for associated psychological problems and potential secondary gains. Surgical procedures are likely to fail in this group.
Treatment for these patients focuses around rehabilitation.
This includes strengthening of the rotator cuff and scapular stabilisers, proprioceptive/biofeedback techniques and modification of activities. The majority of patients will respond to physiotherapy. If necessary surgery may be needed and should include an inferior capsular shift with closure of the rotator capsular interval and tightening of the superior glenohumeral ligament. The results of surgery are not as good as in unidirectional anterior reconstructions, however it is still of the order of 80 – 90%.
Techniques for Closed Reduction
Of the Dislocated Shoulder
Patient lies prone on table with injured arm hanging off the edge of the table. The scapula is manipulated to open the front aspect of the joint allowing congruence of the humeral head and glenoid to be restored (inferior tip scapula pushed towards the spine). Elegant and effective (Fig. 11).
Patient lies supine and the affected arm is slightly abducted. Traction is applied to the arm with the foot (minus shoe) in the axilla or sheet around chest applying counter traction. Simple and effective (Fig.12).
The patient lies prone. Weight is applied to the arm with the affected shoulder hanging off the edge of a table.
Kocher Manoeuvre( may cause Fx., :DON’T USE)
The patient is supine. A sheet is applied around the patient’s chest. Traction is placed on the arm in slight abduction while the arm is externally rotated, adducted and then internally rotated. Old technique. Painful. May fracture or displace the neck of the humerus.
The patient lies supine. The arm is gently elevated in the plane of the scapula up to about 160 degrees. Traction is applied in elevation with outward pressure on the humeral head.
Types of Shoulder
The anterior detached capsule and labrum are repaired back to the glenoid neck
Stretched or redundant capsule is tightened by placation
Inferior Capsular Shift
Similar to a capsulorrhaphy but mobilisation of the capsule extends inferiorly to take up redundant inferior pouch. Done in patients with very lax shoulders.
The anterior capsule and subscapularis muscles are divided, overlapped and tightened. Similar to converting a single-breasted coat to a double-breasted coat. This decreases external rotation of the arm.
The coracoid process is detached from the scapula and screwed on to the anteroinferior glenoid neck to give extra support to the shoulder.
The subscapularis, capsule and a portion of the lesser tuberosity is detached fixed more laterally on the humeral head. This tightens the anterior shoulder structures decreasing external rotation.
Posterior dislocation is uncommon and constitutes about 4% of dislocations. It may occur with a fall, but is more commonly associated with violent muscle contractions such as might occur in an electrocution or grand mal convulsion.
The diagnosis is often delayed or missed.
The patients may have pain and cannot externally rotate the arm past neutral (Fig. 14). The anteroposterior x-ray may look normal (Fig. 15) however the axillary view is diagnostic (Fig. 16). If there is any doubt then a CT scan should be performed (Fig.17).
Posterior subluxation can occur in athletes involved in sports such as baseball and should be suspected where the patient experiences symptoms with the arm in front of the trunk. In these situations it can often be associated with multidirectional instability of the shoulder. Clinical examination my show increased posterior glide, and reproduction of symptoms on posterior load of the shoulder in 90 degrees forward flexion (Fig. 18). The x-rays are often normal.
Where the shoulder is a “locked posterior dislocation”, early recognition and reduction is essential. If the dislocation is longer standing or a large portion of the humeral head is damaged then open reduction with surgical reconstruction of the humeral head defect by autograft, allograft or tuberosity transfer is preferred. Where chondral damage has occurred, total shoulder replacement may be necessary.
In patient with posterior subluxations and associated multidirectional laxity, and intensive physiotherapy rehabilitation programme is recommended. Most patients will respond to conservative treatment. If instability continues then surgical reconstruction should be considered. This may be performed from an anterior or posterior approach. The anterior surgery consists of an inferior capsular shift and tightening of the superior glenohumeral ligament. The posterior reconstruction undertakes an inferior capsular shift only. In both situations the patient is immoblised in a neutral rotation brace for 6 – 8 weeks then placed on a graded rehabilitation programme extending over twelve months. Return to sports is not encouraged for at least twelve months.
Tendinitis and Impingement
The supraspinatus is the most likely tendon to become inflamed as it passes under the coraco-acromial arch (Fig. 19). Tendinitis of the rotator cuff can occur because of overload/fatigue of the cuff tendons, trauma, and age related degenerative changes. Occasionally, the acromion may have a shape which increases the crowding of the cuff tendons in the subacromial space that leads to impingement (Fig. 20). Tendinitis may also occur in patients with very lax shoulders as a consequence of the muscles overworking to stabilise the humeral head. It is important to beware of tendinitis in patients younger than 25 year as this may often be secondary to subtle instability.
Patients present with pain occurring in the anterior aspect of the shoulder with radiation into the deltoid. The pain is minimal at rest and rarely radiates down the arm or into the neck. The pain is aggravated with overhead and rotation activities. Night pain with waking is a feature of more severe cases. On examination, tenderness is located over the grater tuberosity and impingement signs are present (Fig. 21). Biceps provocation test may be positive as tendinitis of the biceps can occur coincidentally (Fig. 22). The acromioclavicular joint may also be tender if it is pathological. Range of motion and strength are usually normal, wasting may occur early (Fig. 23). There may be pain on loading the rotator cuff muscles and any weakness is due to inhibition from pain. As cervical conditions may refer pain into the shoulder, it is important to exclude any such causes for patients complaint. Patients with associated cervical irritation may hold the shoulder posture in a depressed or elevated position.
In most cases the diagnosis of tendinitis is made on clinical grounds. Ancillary tests however my assist in, or confirm the diagnosis. A plain x-ray is essential (also include a supraspinatus outlet view) (Figs. 24 and 25). The next investigation is the impingement test. Here, 5 – 10 mls of lignocaine is injected into the subacromial bursa and after waiting five minutes, there is a significant decrease in pain on forward elevation of the arm to perform the impingement sign.
Further tests are indicated to demonstrate the present of impingement and possible associated rotator cuff tears, either partial or full thickness. Ultrasound in experienced hands is reasonably accurate in predicting the presence of full-thickness tears and impingement. It is important to note that al shoulders which are stiff, e.g. adhesive capsulitis, will demonstrate impingement on ultrasound due to tightness of the posterior capsule limiting the inferior glide of the humeral head. Hence, investigations should be considered in the clinical context in which they are performed. Arthrography will show any cuff tears. MRI may show tendinitis changes in the supraspinatus as well as any rotator cuff tears.
Treatment includes activity modification, non-steroidal anti-inflammatory medications, and physiotherapy (consisting of stretching and strengthening of the rotator and scapular muscles). In most cases this should help the pain. If pain persists an injection of corticosteroid and local anaesthetic into the subacromial space is often diagnostic, and therapeutic. If conservative treatment doe not help after six months, then acromioplasty (open or arthroscopic) is successful in 90% (Fig. 26).
Rotator Cuff Tears
Normal tendons rarely tear. Younger patients require a violent injury (instability or direct trauma to tear the cuff. In the older patient there is often underlying degenerative changes within the rotator cuff tendons so less significant trauma is required to disrupt the cuff. With repetitive overhead use of the arm, e.g. tennis or baseball, micro damage to the rotator cuff can progress to full-thickness tears.
The symptoms are very similar to tendinitis. Pain is aggravated with overload use of the arm, and at night. Weakness is almost always present, however in the majority of patients with full thickness tears there is a normal active range of motion. Only massive rotator cuff tears lose active range of motion. The long head of biceps may be torn.
Investigations include x-rays which may show an acromial spur. Narrowing of the acromiohumeral gap occurs where the tear is large. Other investigations should include either an arthrogram, ultrasound or MRI to confirm the diagnosis, extent of damage, atrophy of muscles and associated joint disease (Fig. 27). MRI is becoming a lot more available as an imaging modality.
In the young patient (less than 50 years) surgery with acromioplasty and rotator cuff repair is recommended as there is risk of increase in tear size and deterioration of shoulder function. In the older patient a short trial of activity modification, non-steroidal anti-inflammatory medications, physiotherapy and corticosteroid injection is reasonable. If pain persists then surgery with acromioplasty and rotator cuff repair is indicated (Figs. 28 and 29).
Internal Derangements Within the Glenohumeral Joint –
Labral tears, SLAP (Superior Labral Anterior Posterior) Lesions, Loose Bodies.
These are often caused by trauma, either direct or in association with instability. The labrum is most developed in the upper portion of the shoulder point and tears in this area may extend into the biceps attachment (anchor). Superior labral tears are referred to as SLAP (Superior Labral Anterior Posterior) lesions and there are four types (see – Classification of SLAP Lesions, Figs. 30, 31 and 32). Loose bodies may arise from trauma or synovial disease (as in synovial chondrometaplasia).
The patient experiences pain with sudden motion, clicking or catching with rotation of the shoulder. Pain is experienced with resisted elevation of the arm while it is forward flexed 90 degrees and slightly adducted across the body with the hand in internal rotation. When the hand is externally rotated in the same position then the pain decreases. There may be associated features of instability.
Diagnosis is difficult and often requires further investigation. The best test is an MRI scan with gadolinium arthrography. The treatment is usually arthroscopic with either resection or repair of the torn labrum and removal of loose bodies. It is also important to treat the underlying cause, e.g. instability.
Acromioclavicular Joint Injuries
The acromioclavicular joint (ACJ) is usually injured from a fall on to the point of the shoulder. The resulting injury may cause chondral or meniscal damage. More severe injuries may result in subluxation or dislocation of the joint. (see – classification of Acromioclavicular Joint Dislocation, Fig. 33).
On examination, localised tenderness and swelling if often seen. In dislocation of the joint the outer clavicle appears superiorly displaced, though, in most cases, it is the shoulder that sags below the clavicle. Forced cross body adduction may provoke discomfort.
X-rays of the joint should include standing weighted views of the ACJ with the weight tied to the writs of the patient (Fig. 34).
For undisplaced or type I and II dislocations ice, rest and then gradual return to activity over a 2 – 6 week period is usually adequate. It is important to remember that seemingly minor ACJ injuries may give rise to grumbling discomfort for up to six months. Major dislocations may require surgical stabilisation in athletes if their dominant arm is involved, especially if they intend to participate in upper limb sports or are workers who use their arms overhead (Fig. 35).
Fractures can occur with a fall on to the outstretched hand. Most of these fractures occur in the mid-shaft, though medial or lateral injujires also occur. Clinically there is pain with swelling and deformity over the site of the fracture. Neurological lesions are rare but may include brachial plexus injury. Vascular injuries are very rare.
The majority of fractures will go on to union with little morbidity, even with moderate shortening or angulation. Some patients however may develop symptoms with cross body actions if the clavicle is too shortened. Where the fractures are lateral and involve the coracoclavicular ligaments or AC joint, treatment may include stabilisation of the outer end of the clavicle. Most fractures are treated non-operatively with a sling for elbow support. Clavicle rings to pull shoulders back may decrease discomfort and help stabilise the fracture ends. Care is necessary to avoid skin pressure problems and axillary neurovascular compression. With marked displacement or shortening, early open reduction and internal fixation may be considered.
Outer Clavicular Osteolysis
This occurs from a direct blow or fall, but often develops in individuals who work out in the gymnasium on overhead machines or are involved in overhead sports. The probable pathology is a chondral or minor osteochondral fracture which initiates an inflammatory response and leads to resortpion of the outer clavicle.
Patients complain of pain over the AC joint which may radiate to the deltoid or base of neck. On examination there is localized tenderness and swelling over the AC joint. In more advanced cases a palpable gap is evident at the site of the AC joint. X-rays show irregularity of the outer clavicle with osteolysis (Fig 36). A bone scan, which is not always necessary, will be hot in the region of the outer clavicle.
Treatment includes rest, activity modification and non-steroidal anti-inflammatory medications. If the pain persists then surgical excision of the outer clavicle is indicated.
Medial Clavicular Sclerosis (Osteitis Condensans)
This is a rare disorder characterized by osteoclerosis of the medial end of the clavicle. The aetiology is unknown, though low grade osteonecrosis or Osteomyelitis have been proposed, though never proven. Most commonly it occurs in middle aged females who present with a long history of insidious onset of pain and discomfort with elevating the arm.
X-rays show mil enlargement and sclerosis of the medial end of the clavicle without any bone destruction or periosteal reaction. Confirmation of the diagnosis is with CT scan though MRI can also be used.
Treatment is non-operative with analgesics and non-steroidal anti-inflammatory medications. Patients may be symptomatic for many years. Surgical excision has been describes though the condition is rarely painful enough to warrant this.
Despite the limited ligamentous support of the inner end of the clavicle, dislocations are rare. It may be anterior or posterior. The dislocation usually occurs with a fall on to the side and compression of the shoulder from another player falling on top of the patient.
Anterior dislocation has a painful prominence of the medial end of the clavicle. In the acute situation it may be reduced closed, though many surgeons prefer to leave the dislocation and treat the patient symptomatically (Fig. 37). The diagnosis is best confirmed with a CT scan as x-rays of this region are difficult to interpret.
Posterior dislocation may cause pressure on structures in the neck with dysphagia, dyspnoea or great vessel compression. This can be a surgical emergency. Posterior dislocations should be reduced urgently if there is compromise of the thoracic outlet or mediastinal structures. A bolster is placed between the shoulder blades and posterior directed pressure is applied to the shoulders. If the clavicle does not reduce closed, then under sterile conditions a surgical towel clip may be hooked around the clavicle and pulled forward to reduce the clavicle.
Apart from the rotator cuff a number of muscles may rupture bout the shoulder. These commonly include: pectoralis major; long head of biceps (Fig. 38); and subscapularis. The muscle tears when there is contraction of the muscle against an unexpected resistance. Weight lifters, trying to bench press large weights, are a common source of patients. If the arm is in 90 degrees of abduction and is forced into extension subscapularis may tear.
The patients complain of severe pain and tearing sensation at the time of rupture, and this is followed by swelling and bruising. The damaged pectoralis major bunches on contraction. Long head of biceps rupture may be associated to rotator cuff disease. Subscapularis rupture is difficult to pick, with weakness on the posterior lift-off test being the only sign (Fig. 39).
For the ruptured pectoralis muscle surgical repair is recommended, as the patients will notice a deformity and weakness in the future (Gig. 40). For patients with a subscapularis tear there may be long term changes in rotator cuff balance and function, and so repair is recommended.
Biceps Tendon Injuries
The biceps may be injured with anterior instability or be associated with impingement and rotator cuff tears. Only 5% of biceps tendinitis is primary, whereas, 95% is secondary to other causes.
The patients complain of pain over the anterior aspect of the shoulder. Examination shows tenderness in the biceps groove. Sometimes a click from subluxation of the tendon may occur with rotation of the arm.
Treatment includes rest, non-steroidal anti-inflammatory medications and steroid injections in the biceps groove. If pain persists or there is dislocation of the biceps then surgical tenodesis is recommended. If the long head of biceps ruptures after a period of tenodesis then the pain often subsides. The rupture is treated symptomatically and surgery is rarely recommended.
Nerve injuries about the shoulder can occur as a result of direct trauma, traction, compression or secondary to instability. The nerves may sustain a neuropraxia or division depending on the type of injury. Nerves which can be involved often include the axillary, suprascapular, musculocutaneous, long thoracic (Fig. 41) and radial nerve. A brachial plexus palsy (partial or complete) occur with high energy trauma (Fig. 42).
The patient complains of pain related to the injury and this may be associated with weakness. Winging of the scapula occurs with long thoracic nerve injury. To localize the nerve damage careful neurological examination is important.
In most cases the injury is a neuropraxia and will recover with time. EMG studies are recommended to help ascertain whether the lesion is complete and/or recovering. Exploration and repair of the nerves may be indicated if the lesion does not recover within six months. If suprascapular nerve compression is evident then an MRI scan may reveal a spino-glenoid notch ganglion cyst pressing the nerve. This requires surgical excision.
Presentation of Injury to the Shoulder
The most important step to prevent injury during sports participation is the implementation of a general conditioning programme. In those sports where upper limb activity is essential the programme needs to encompass appropriate muscle strengthening and stretching about the shoulder and scapula. Appropriate strength and muscle length allows for optimal muscle function.
Prior to exercising or sports participation warm-up is the first step. Stretching of the rotator cuff and posterior capsule and then gentle strengthening exercises with attention to the rotator cuff and scapular stabilisers is necessary.
Technique of throwing or other sports activity should be carefully developed under skilled supervision to optimise performance without causing undue strain on the shoulder capsule or muscles. At the first sign of fatigue or discomfort the athlete should cease the sport to prevent any injury progressing to a more serious level. After coming from the field the athlete should cool down the affected area and then reinstate a gentle stretching programme before rest.
It is important that all athletes recognize that high level performance at sport places an extreme demand on the bodies tissues and the off season plays an important role in allowing micro damage to heal itself. Aside from the in season conditioning appropriate complementary exercises are important in the off season. These should not place the same strains on the tissues but should be directed at maintain aerobic fitness in preparation or the next season.
With these thoughts in mind all athletes should be able to enjoy their sports for many seasons with minimal risk of injury.
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