A COMMON MISSED DIAGNOSIS: POSTERIOR SHOULDER INSTABILITY

Holly Lipson

November 1, 2021

Introduction

We see a large amount of shoulder injuries at our clinic having backgrounds in both tennis and sports physiotherapy and a common presentation we see in the clinic is posterior shoulder instability, which is frequently missed as a diagnosis. Non-traumatic posterior shoulder instability is defined as the painful excessive backwards movement of the humeral head on the glenoid (ball on the socket) and usually comes about due to excessive load or exercise. Classically, athletes who participate in sports such as tennis, swimming, volleyball and weight lifting are at greatest risk of developing this issue as these sports repeatedly stress the posterior capsule or shoulder in positions of elevated forward flexion, abduction (arm out to the side), horizontal flexion (across body) and/or internal rotation (McIntyre et al., 2016). This injury is much more common in the young sporting population or tradesperson and may represent up to 24% of all painful shoulder instability cases (Song et al., 2015).

How can injury occur and who gets it?

  • People who participate in sports that stress the back of the shoulder (eg. Tennis, swimming, weight-lifting)
  • Hypermobility or too much mobility
  • Congenital anatomical variations of the shoulder
  • Structural lesions to the back portion of the shoulder (posterior labral tears, glenoid bone loss)
  • Posterior instability can be present in shoulders with structural lesions yet can also be present in those without. In those cases who do not have structural lesions, symptoms are often due to alterations in muscle control and strength of the rotator cuff and scapular (shoulder blade) stabilisers. It is unclear however if this is the cause or is a result of, posterior instability.

Assessment:

Patients commonly present with;

  • Pain in the front and/or back of the shoulder.
  • Aggravation with positions of forward flexion, horizontal flexion (across body), Internal rotation (reaching behind back) or a combination of both. This may present in tasks such as bench press, taking off a T-Shirt or sports Bra, a backhand or follow through of serve in tennis, pull through phase of swimming or overhead weights.
  • Inability to lie on the sore shoulder.

Often these patients will be misdiagnosed as rotator cuff tendinopathy, Impingement syndrome, AC joint pain or a stiff shoulder. However, these are simply by products of an overly unstable shoulder which in turn is causing secondary rotator cuff tendon pain or AC joint irritation.

Treatment:

The best evidence supports trialling an exercise program that targets strengthening and motor control of the posterior deltoid, shoulder blade stabilisers and rotator cuff muscle groups; particularly the external rotators (Watson et al., 2017). In general, if a patient has a structural lesion or bony abnormality surgery may be indicated. However, for most patients with non-traumatic posterior shoulder instability, there will be no structural lesion and they may have excessive ligamentous laxity or joint movement. In these cases, intensive and targeted physiotherapy rehabilitation for 3-6 months is recommended as a first line treatment to improve muscle strength and control around the shoulder and get you back swimming, working over head or playing tennis (Frank, Romeo & Provencher, 2017).

About the Author:

Holly Lipson is a titled Sports & Exercise Physiotherapist with special interests in the shoulder, knee and concussion. Holly works from our Torquay clinic. Holly also works with the Australian Olympic Winter Institute and Snow Australia. She will be heading away with the Para Alpine team for their Winter Paralympic campaign in early 2022 as physiotherapist. To book an appointment with Holly call 52772151 or book online.

References:

Frank RM, Romeo AA, Provencher MT. Posterior Glenohumeral Instability: Evidence-based Treatment. J Am Acad Orthop Surg. 2017 Sep;25(9):610-623. doi: 10.5435/JAAOS-D-15-00631. PMID: 28837454.

McIntyre, K., Bélanger, A., Dhir, J., Somerville, L., Watson, L., Willis, M., & Sadi, J. (2016). Evidence-based conservative
rehabilitation for posterior glenohumeral instability: A systematic review. Physical Therapy in Sport, 22, 94–100.
https://doi.org/10.1016/j.ptsp.2016.06.002

Song DJ, Cook JB, Krul KP, et al. High frequency of posterior and combined shoulder instability in young active
patients. J Shoulder Elbow Surg. 2015;24(2):186-190. doi:10.1016/j.jse.2014.06.053

Watson, Lyn, B AppSci , GradDip of Manipulative Physio, DProf, Balster, Simon, B Sci, B Physio, Warby, Sarah Ann,
PhD, B Physio, Sadi, Jackie, MSc, Hoy, Greg, MBBS, FRACS, & Pizzari, Tania, PhD, B Physio. (2017). A comprehensive
rehabilitation program for posterior instability of the shoulder. Journal of Hand Therapy, 30(2), 182–192.
https://doi.org/10.1016/j.jht.2017.05.007