Shoulder instability represents a spectrum of disorders resulting in shoulder dysfunction, including subluxation, dislocation, and symptomatic laxity.1 Instability is classified as either unidirectional or multidirectional.
Scapular dyskinesis is the term used to describe loss of normal scapular physiology, biomechanics, and kinetics. This may be secondary to a painful condition of the shoulder; however, it does not necessarily mean a pathological condition2, but, rather, a previously asymptomatic condition in the shoulder girdle.3
Unidirectional instability (UDI) typically results from shoulder subluxation/dislocation. Multidirectional instability (MDI) results from atraumatic laxity of the anterior capsule and glenohumeral (GH) ligaments.4 MDI effectively increases the ratio of elastin in capsular tissues5, indirectly increasing glenohumeral joint volume.7
There are six categories of causative factors contributing to scapular dyskinesis.6,8 Surgical intervention may be considered for the bone and joint factors prior to beginning rehabilitation treatment.8
- Nerve damage: long thoracic or spinal accessory nerve palsy
- Inflexibility factors: glenohumeral internal rotation deficit (GIRD), total range of motion deficit or tightness of pectoralis minor
- Muscular damage: weakness of lower trapezius or serratus anterior, hyperactivity of upper trapezius, and detachment of peri-scapular muscles
- Kinetic chain problems: weakness of hip/leg and core muscles
- Bone factors: thoracic kyphosis, clavicular fracture and scapular fracture
- Joint factors: acromioclavicular separation, GH instability, biceps tendinitis and labral damage
Epidemiology including risk factors and primary prevention
More than 90% of unidirectional instability results from anterior dislocations. Males aged 18-25 are the most susceptible and injury is often associated with sports participation.9,10 MDI reportedly occurs more often in gymnasts and swimmers, but is also seen in other overhead athletes such as throwers and volleyball players. Scapular dyskinesis occurs in overhead athletes and is associated with posterior capsular tightness, GIRD, and serratus anterior/lower trapezius weakness.6 The majority of volleyball players are considered as tall athletes. In this population, the prevalence of Marfan’s syndrome may be higher than a general population (1:5000).11 The connective tissue disorder related to Marfan’s syndrome might be a risk factor of shoulder instability in tall athlete’s population.
The GH joint has little inherent bony stability. During shoulder abduction, the humeral head rolls superiorly, simultaneously sliding inferiorly to prevent impingement.12 GH joint stability depends on both static and dynamic restraints. Static restraints include the interface of the humeral head, glenoid fossa, GH ligaments, and glenoid labrum.12,13 Dynamic stability is achieved primarily through the eccentric action of the rotator cuff, keeping the humeral head “seated” within the glenoid fossa during motion.12,13
Scapulohumeral rhythm is the coordinated movement of the scapulothoracic and GH joints. Below 30 degrees of abduction, the majority of motion occurs at the GH joint. Beyond 30 degrees of abduction, the ratio of glenohumeral to scapulothoracic movement generally occurs at a ratio of 5:4.14 Scapular movement includes upward/downward rotation, anterior/posterior tilt, and internal/external rotation. Scapular retraction is the coupling of external rotation, posterior tilt, upward rotation, and medial translation.
The normal kinematic pattern of the scapula during arm elevation is upward rotation, posterior tilt, and external rotation. This allows the humeral head to clear the acromion during upward rotation. The scapula has an important function in the proximal-to-distal sequencing of shoulder movements. The body segments and muscles are coordinated to transfer forces to the terminal link (ie, hand) through the shoulder, which is known as kinetic chain.15
Specific secondary or associated conditions and complications
Traumatic UDI is often associated with a soft tissue or bony Bankart lesion, Hill-Sachs lesion, rotator cuff tears, and proximal humerus fractures. MDI and scapular dyskinesis are often associated with external/internal impingement, rotator cuff tendinopathy, subacromial bursitis, biceps tendinopathy, acromioclavicular joint arthropathy, scapulothoracic bursitis and rarely, scapular tumors.
2. ESSENTIALS OF ASSESSMENT
UDI is often associated with trauma. The clinician must determine the mechanism of injury, associated neurologic symptoms, and if reduction occurred, whether it occurred manually or spontaneously. MDI generally presents atraumatically, bilaterally and with reports of weakness and/or poor athletic performance. Identify inciting activities, prior history, pain, paresthesia, and history of hypermobility.
- Look for atrophy, resting scapular position, side to side symmetry, and prominence of the inferior and medial scapular border.2,6
- The presence of a rounded shoulder posture suggests anterior chest wall tightness.2
- Dynamic observation of scapular motion during flexion and abduction may display prominence of the medial scapular border and dyskinetic patterns, part of a dynamic scapular dyskinesis test.2,6
- Examine the entire shoulder girdle for areas of tenderness. Tenderness over the coracoid process suggests pectoralis minor tightness associated with scapular dyskinesis.2,6
- Assess both active and passive ROM in multiple planes.
- Test for posterior capsular tightness.2,6
- Load and Shift: Laxity observed by increased anterior or posterior motion of humeral head upon glenoid.16
- Drawer test: Suggests humeral head subluxation.5
- Sulcus Sign: Inferior instability may be indicative of multidirectional instability/congenital laxity.13,16
- Relocation Test: Suggests anterior instability.1,2
- Scapular Assistance Test: With active arm elevation apply gentle pressure on the inferior medial scapular border in the direction of upward rotation and posterior tilt. A positive test results in an increased arc of motion and relief of impingement reduced symptoms. 6,13,17
- Scapular Retraction Test: Stabilize the scapula in a retracted position. A positive test results in relief of impingement symptoms.6,13,17
- Gagey hyper-abduction test: Above 105 degrees of passive abduction is associated with laxity of glenohumeral ligament.5
- Radiography (orthogonal view): Identify traumatic lesions at pre- and post-reduction stage. (i.e. bony Bankart lesions, Hill-Sachs defects, or other fractures).18 Assess underlying atraumatic diseases. (i.e. bony pathology and humeral head position).
- MRI or CT: Assess lesions if there is high possibility of fracture but negative radiographs or if patients are older than 40 years old to identify possible rotator cuff tears.18
- Ultrasound: Evaluate instabilities and lesions in soft tissue cost-effectively.
- Nerve conduction test: Identify traumatic long thoracic nerve, dorsal scapular nerve or spinal accessory nerve damage.15
- Electromyography: Assess degree of periscapular muscle damages.15
3. REHABILITATION MANAGEMENT AND TREATMENTS
Available or current treatment guidelines
In MDI, current treatment guidelines recommend an initial course of non-operative management with a structured rehabilitation program. A surgical referral may be considered for an identified anatomic lesion and failure of the rehabilitation program. According to a recent review article, the surgical intervention revealed 14% of unsatisfactory result due to persistent instability or pain.19
In order to decrease the failure rate, a well-designed and structured rehabilitation program should be provided to the patients. Focus should be on kinetic chain deficits, scapular stabilizer strengthening, appropriate shoulder girdle flexibility, and scapulothoracic mechanics. Maximal rotator cuff strengthening requires a stabilized, retracted scapula and should occur only after scapular control is achieved.2,6,8
For traumatic first-time dislocations, non-operative treatment is often recommended. Operative treatment is indicated for recurrent dislocations, Bankart lesions involving greater than 20% of the glenoid fossa, and significantly displaced proximal humerus fractures.
Prior to return to sport or occupation, the patient should be symptom-free, functionally prepared for return, and without persistent biomechanical abnormalities.
At different disease stages
Phase I-Soft Tissue Flexibility
- Increase the length of pectoralis minor and stretch short head of the biceps (i.e. “unilateral stretch,” “sitting manual stretch,” and “supine manual stretch).8,20
- Address posterior capsular tightness and glenohumeral internal rotation deficit (i.e., “sleeper stretch,” and “cross body stretch”).8,20
Phase II-Muscle Performance
- Stage 1-Kinetic Chain
- Focus on hip extensor deficits, core stability, and pelvic control. Initial strengthening should involve static exercise with progression to dynamic multiplanar exercises involving trunk rotation.8
- Stage 2-Scapular Orientation
- Achieve a neutral position of lumbopelvic, scapulothoracic, and cervical posture (i.e. “occipital lift maneuver”).20
- Stage 3-Muscle Control
- Open chain exercise
- Improve the stability of scapular control.8,20 Focus on rehabilitation of the lower trapezius and serratus anterior (i.e. “low row,” “inferior girdle,” “lawnmower,” and “robbery” exercise).20
- Closed chain exercise
- Improve the dynamic stability of glenohumeral joint after achieving joint mobility and scapular stability.8,20
- Enhance fixation of scapula on thoracic wall by activating rotator cuff muscles (i.e. “wall sliding exercise,” and “push-ups”).20
- Open chain exercise
- Stage 4- Sports-specific Exercise
- Power and endurance training for the upper extremities.
- Perform multiplanar exercise for neuromuscular control.
- Also include sport- and job-specific exercise.
Scapular Dyskinesis Treatment
|Phase I – Soft Tissue Flexibility||Phase II Muscle Performance|
|Stretch pectoralis minor and short head of the biceps||Stage 1: Kinetic Chain Exercise||Stage 3: Muscle Control|
|Focus on flexibility of the posterior capsule and internal rotation of the glenohumerus||Stage 2: Scapular Orientation||Stage 4: Sports Specific Exercise|
Coordination of care
The physiatrist’s role is to coordinate care and ensure a patient-centered approach. Members of the team may include the physiatrist, patient, surgeon, primary care physician, physical therapist, athletic trainer, and coach. If symptoms do not resolve with a rehabilitation program, the patient should be reevaluated to ensure accurate diagnosis, consider further imaging, and/or consider surgical intervention.
Patient & family education
Patient and family understanding of the injury, risk factors, future prevention, and the treatment plan are key to patient “buy in” and subsequent recovery. The patient and family must play an active role in the rehabilitation process. In athletes, it is important to involve coaches and athletic trainers as early as possible.
Multiple standardized metrics are used to measure shoulder dysfunction. No one test has been identified as the gold standard. Condition-specific measures such as the Melbourne Instability Shoulder Score (MISS) and Western Ontario Shoulder Instability Index (WOSI) have been utilized. A recent review of more than ten standardized metrics was completed and recommended the use of these tests because they have been shown to be reliable, valid, and responsive in patients with shoulder instability.21 Other outcome measures provide general assessments such as: Oxford Shoulder Instability Questionnaires, Disability of the Arm, Shoulder and Hand (DASH), and Constant Shoulder Outcome Score.
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
Patients with MDI are more likely to experience subluxations than dislocations (84.6% vs. 15.4).7,22 Majority of them are recurrent compared to primary subluxations (54.5% vs. 45.5%).22 Asymptomatic shoulder laxity must be distinguished from laxity associated with symptomatic instability.7
No single diagnostic test can confirm the presence of multidirectional instability or scapular dyskinesis.7 All six categories of causative factors mentioned above should be tested to properly evaluate scapular dyskinesia.
Always consider scapular dyskinesis when evaluating a patient with symptoms of shoulder impingement.
4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE
Cutting edge concepts and practice
In the last two decades, scapular stabilization has become a key component of shoulder rehabilitation. Inclusion of scapular exercises as part of a rehabilitation program achieves better results and higher patient-rated outcomes.23 The systemic review of MDI indicates arthroscopic capsular plication and open capsular shift as the best surgical procedures after rehabilitative treatment failure.24
5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE
Gaps in the evidence-based knowledge
The effects of scapular-focused programs have not been studied across all relevant shoulder diagnosesand, thus, more information is needed.23 In addition, there is a lack of studies focusing on chronic neck problems followed by shoulder dyskinesis. The validity and reliability of the aforementioned physical examinations are yet unanswered. 25 The role of biologic treatments such as PRP has not yet been identified in treatment of shoulder instability.
There remains controversy regarding the role of immediate surgical intervention for early dislocation. Labral injury, internal impingement, rotator cuff injury, clavicle fractures and AC separations can cause muscle inhibition, which eventually results scapular dyskinesis. In these cases, the surgical intervention such as arthroscopic plication should be considered primarily.15 The recurrent shoulder instability event increases after primary traumatic instability event. According to the traumatic shoulder instability study, 54.5% of subluxation and 33.3% of dislocation cases were secondary instability events.22
- Mahaffey BL, Smith PA. Shoulder instability in young athletes. Am Fam Physician. 1999;59(10):2773-2782.
- Kibler WB, Sciascia A. Current concepts: Scapular dyskinesis. Br J Sports Med. 2010;44:300-305.
- Postacchini R, Carbone S. Scapular dyskinesis: Diagnosis and treatment. OA Musculoskeletal Medicine. 2013;1(2):20.
- Debarardino TM, Arciero RA. Shoulder instability. In: O’Connor FG, Casa DJ, Davis BA, et al, eds. ACSM’s Sports Medicine: A Comprehensive Review. 1st ed. Philadelphia, PA:Lippincott Williams and Wilkins; 2013:312-322.
- Merolla G, Cerciello S, Chillemi C, Paladini P, Santis ED, Porcellini G. Multidirectional instability of the shoulder: biomechanics, clinical presentation, and treatment strategies. European Journal of Orthopaedic Surgery & Traumatology. 2015;25:975-985.
- Kibler WB, Sciascia A. Scapular Dyskinesis and Its Relation to Shoulder Injury. J Am Acad Orthop Surg. 2012;20:365-372.
- Johnson SM, Robinson MC. Shoulder instability in patients with joint hyperlaxity. J Bone Joint Surg Am. 2010;92:1545-1557.
- Kibler WB, Sciascia A. Rehabilitation of the athlete’s shoulder. Clin Sports Med. 2008;27:821-831.
- Simonet WT, Melton LJ, Cofield RH, Ilstrup DM. Incidence of anterior shoulder dislocation in Olmstead County, Minnesota. Clin Orthop Relat Res. 1984;186:186-191.
- Owens BD, Dawson L, Burks R, Cameron KL. Incidence of shoulder dislocation in the United States military: demographic considerations from a high-risk population. J Bone Joint Surg Am. 2009;91(4):791-796.
- Yim ES. Aortic Root Disease in Athletes: Aortic Root Dilation, Anomalous Cardiac Artery, Bicuspid Aortic Valve, and Marfan’s Syndrome. Sports Medicine. 2013;43:721-732.
- Neuman DA. Shoulder complex. In: Neuman DA. Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. 1st ed. Philadelphia, PA: Elsevier; 2002: 91-130.
- Gaskill TR, Taylor DC, Millett PJ. Management of multidirectional instability of the shoulder. J Am Acad Orthop Surg. 2011;19:758-767.
- Poppen, NK, Walker, PS. Normal and abnormal motion of the shoulder. J Bone Joint Surg. 1976;58A:195-201.
- Roche SJ, Funk L, Sciascia A, Kibler WB. Scapular dyskinesis: the surgeon’s perspective. Shoulder & Elbow. 2015;7(4):289-297.
- Bowen JE, Malanga GA, Tutankhamen P, McFarland E. Physical examination of the shoulder. In: Malanga GA, Nadler SF. Musculoskeletal Physical Examination: An Evidence-Based Approach. 1st ed. Philadelphia, PA: Elsevier Mosby; 2006:59-118.
- Boselli KJ, Ahmad CS, Levine WN. Treatment of glenohumeral arthrosis. Am J Sports Med. 2010;38:2558.
- Blaine TB, ed. Glenohumeral instability. In: Johnson TR, Steinbach LS, eds. Essentials of Musculoskeletal Imaging. 1st ed. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2004: 196-201.
- Warby SA, Pizzari T, Ford JJ, Hahne AJ, Watson L. Exercised-based management versus surgery for multidirectional instability of the glenohumeral joint: a systemic review. Br J Sports Med.2017;50:1115-1123.
- Cools AMJ, Struyf F, Mey KD, Maenhout A, Castelein B, Cagnie B. Rehabilitation of scapular dyskinesis: from the office worker to the elite overhead athlete. Br J Sports Med.2014;48:692-697.
- Plancher KD, Lipnick SL. Analysis of evidence-based medicine for shoulder instability. Arthroscopy. 2009; 25:897-908.
- Owen BD, Duffey ML, Nelson BJ, DeBerardino TM, Taylor DC, Mountcastle SB. The Incidence and Characteristics of Shoulder Instability at the United States Military Academy. The American Journal of Sports Medicine. 2007;35(7):1168-1173.
- Kibler WB, Ludewig PM, McClure PW, et al. Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the “scapular summit.” Br J Sports Med. 2013;00:1-12.
- Longo UG, Rizzello G, Loppini M, Locher J, Buchmann S, Maffulli N, Denaro V. Multidirectional instability of the Shoulder: A systemic review. The Journal of Arthroscopic and Related Surgery. 2015;31(12):2431-2443.
- Lange T, Struf F, Schmitt J, Lutzner J, Kopkow C. The reliability of physical examination tests for the clinical assessment of scapular dyskinesis in subjects with shoulder complaints: A systemic review. Physical Therapy in Sport. 2017:1-26.
Original Version of the Topic
A. Michael Henrie, DO, Robert Engelen, DO. Shoulder instability, dysfunction and scapular dyskinesis. 09/20/2013.
Soo Yeon Kim, MD
Nothing to Disclose
Keonhee Kim, BS
Nothing to Disclose