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Anteroposterior radiograph of a 68-year-old woman shows no fracture after a left shoulder dislocation and a closed reduction.
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Outlet radiograph of the patient’s left shoulder.
A 68-year-old woman presents 3 weeks after sustaining a left shoulder dislocation after a fall at her home. At that time, a closed reduction was performed in the emergency department, and the arm was placed in a sling immobilizer. Postreduction radiographs show a reduced glenohumeral joint with no evidence of fracture. The patient denies any history of shoulder instability, pain, or weakness prior to the fall. On examination, there is significant weakness with arm abduction and with the belly press test.
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The patient sustained a first-time anterior shoulder dislocation. In those aged >40 years, shoulder dislocation is associated with a high incidence of rotator cuff tear—approximately 30% in those aged >40 years and as high as 80% in those aged >60 years. The rotator cuff weakens with age and is therefore more susceptible to injury.
Rotator cuff tear after shoulder dislocation is rare in those aged <40 years. In these patients, the rotator cuff remains intact during dislocation, and as a result, the anterior shoulder stabilizers (labrum and capsule) are frequently injured. Injury to the anterior stabilizers causes a higher incidence of recurrent instability in younger patients. The rate of recurrent dislocation is up to 90% for those in their 20s and 30s; comparably, patients aged >40 years have less recurrent instability (recurrence rate <10%) because the anterior stabilizers remain intact.1,2
Rotator cuff tear is likely if there is persistent abduction weakness of the involved arm without fracture. Axillary nerve palsy may also cause abduction weakness after an anterior shoulder dislocation. However, unlike a rotator cuff tear, axillary nerve palsy causes loss of sensation to the proximal lateral arm and nonpainful abduction weakness.
Weakness on the belly press test may indicate a tear of the subscapularis tendon. If radiographs are negative for fracture and a rotator cuff tear is suspected, magnetic resonance imaging (MRI) should be ordered. MRI is the study of choice to diagnose rotator cuff tear and rule out other associated injuries. MRI can also determine whether the rotator cuff tear is acute or chronic, based on the presence of fatty infiltration in the rotator cuff muscle.2,3
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
References
- Abbasi D. Traumatic Anterior Shoulder Instability (TUBS). Orthobullets website. http://www.orthobullets.com/sports/3050/traumatic-anterior-shoulder-instability-tubs. Updated April 13, 2016. Accessed June 13, 2016.
- Murthi AM, Ramirez MA. Shoulder dislocation in the older patient. J Am Acad Orthop Surg. 2012;20(10):615-622.
- Neviaser RJ, Neviaser TJ, Neviaser JS. Concurrent rupture of the rotator cuff and anterior dislocation of the shoulder in the older patient. J Bone Joint Surg Am. 1988;70(9):1
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