Posterior Shoulder Instability

Understanding Posterior Shoulder Instability

Most shoulder instability is anterior, with the ball slipping forward. In posterior instability the ball of the humerus slides toward the back of the socket. It is less common, and rather than full dislocations, patients more often notice pain, weakness or a sense of the shoulder slipping during activities that push the arm backward, such as blocking, bench pressing or push-ups ^{[1, 2]}.

Posterior instability is common in football linemen, weightlifters, rowers and swimmers, where repeated force on the front of the arm drives the ball backward and stretches or tears the back of the labrum and capsule (a reverse Bankart lesion) ^{[2, 3]}. A single traumatic event, such as a fall, a seizure or an electric shock, can also dislocate the shoulder backward; these dislocations are easily missed on routine X-rays ^[1].

Treatment starts with physical therapy to strengthen the rotator cuff and shoulder blade muscles. When pain and instability continue, arthroscopic posterior stabilization repairs the labrum and tightens the capsule. In a systematic review, about 91% of patients were satisfied after arthroscopic posterior stabilization, recurrent instability occurred in about 7%, and about 86% returned to sport ^[4].

Causes & Risk Factors

• Repeated force pushing the arm backward (football linemen, weightlifting, push-ups)
• Swimming and other repetitive overhead sports
• A fall on an outstretched arm
• Seizures or electric shock, which can dislocate the shoulder backward
• Generalized ligament laxity

Symptoms

Common signs and symptoms of Posterior Instability include:

• Deep, aching pain in the back of the shoulder
• Pain or weakness when pushing, blocking or bench pressing
• A feeling of the shoulder slipping toward the back
• Clicking or catching
• Fatigue or loss of strength with overhead or pushing activity

Treatment Options

Treatment for Posterior Instability depends on the severity of your condition and may include:

• Activity modification
• Physical therapy focused on rotator cuff and scapular strength
• Arthroscopic posterior labral repair and capsular shift
• Bone or soft-tissue procedures for rare cases with bone loss or failed prior surgery

References

1. Hawkins RJ, Koppert G, Johnston G. Recurrent posterior instability (subluxation) of the shoulder. J Bone Joint Surg Am. 1984;66(2):169-74. pubmed.ncbi.nlm.nih.gov/6693442/
2. Bradley JP, Baker CL 3rd, Kline AJ, et al. Arthroscopic capsulolabral reconstruction for posterior instability of the shoulder: a prospective study of 100 shoulders. Am J Sports Med. 2006;34(7):1061-71. doi.org/10.1177/0363546505285585
3. Kim SH, Ha KI, Park JH, et al. Arthroscopic posterior labral repair and capsular shift for traumatic unidirectional recurrent posterior subluxation of the shoulder. J Bone Joint Surg Am. 2003;85(8):1479-87. doi.org/10.2106/00004623-200308000-00008
4. Ralph JE, Hurley ET, Lunn K, et al. Outcomes of arthroscopic stabilization for posterior shoulder instability: a systematic review. J Shoulder Elbow Surg. 2024;33(11):2530-2538. doi.org/10.1016/j.jse.2024.04.006