Diagnosis and Therapeutic options for posterior shoulder dislocation

Arnaud Godenèche; Steven Roulet

doi:10.71165/3msf-l88p

Summary

Background: Posterior shoulder instability is a rare clinical entity, representing 2% to 5% of all shoulder instability cases. Management is complicated by diverse clinical presentations, varying anatomical lesions, and the presence of predisposing factors such as glenoid retroversion or hypoplasia.

Objective: This study evaluates the outcomes of a multicenter symposium involving 188 patients to identify prognostic factors and refine management algorithms for involuntary, voluntary, and painful posterior instability.

Key Points: Involuntary instability associated with anatomical lesions demonstrated superior outcomes with surgical intervention compared to functional rehabilitation. Arthroscopic capsulolabral repair, particularly when combining labral reattachment with capsular shift, yielded high satisfaction rates (80%) and successful return to competitive sports. While posterior bone blocks are indicated for significant glenoid deficiency, they showed no statistical superiority over soft tissue repair in cases without major bone loss. Conversely, purely voluntary instability remains a contraindication for surgery, requiring neuromuscular reprogramming. In "voluntary-to-involuntary" cases triggered by trauma, surgery is justified, though outcomes are less predictable than in purely involuntary forms. The "unstable painful shoulder" (UPS) variant presents diagnostic challenges; preoperative glenoid cartilage damage in these patients is a significant negative prognostic factor for pain relief.

Conclusion: Surgical success in posterior instability is highly correlated with the presence of discrete anatomical lesions and the absence of chondral damage or generalized hyperlaxity. Arthroscopic labral repair is the preferred treatment for young athletes with involuntary instability, while bone blocks should be reserved for substantial glenoid rim defects.

Pierre Mansat, P. Clavert, G. Nourrissat, J. Garret, M-B. Hardy, P. Métais, J. Barth, P. Abadie,
F. Sirveaux, Blandine Marion, Yves Bouju, Kevin Andrieu, French-Speaking Arthroscopy Society (SFA)

Introduction

Posterior shoulder instability is rare, with an incidence ranging from 2–5%.[1,2]

The difficulties in managing the condition comes from the patient profile, recognising the different clinical forms, and interpreting the different anatomical forms.

In 2016, the French-Speaking Arthroscopy Society held a symposium on posterior shoulder instability. A multi-centre study across mainland France was presented comprising two cohorts (one prospective and one retrospective). One hundred and eighty-eight patients were recruited and 167 were operated.

After a brief review of the different clinical presentations, imaging studies and treatments, we report the results of this multi-centre study and the prognostic factors for treating this pathology. The aim is to identify how our attitude towards, and management of this rare condition could change.

Clinical presentations

1. Involuntary instability

This form is most similar to anterior instability in terms of clinical presentation, physiopathology and management.

Four in every five cases affect men in their thirties. Only 40% are involved in competitive sports, yet another 40% do no sport at all. The shoulder has no predisposing factors including joint capsule distension, hyperlaxity or excessive glenoid retroversion. There is always a history of trauma, with or without true dislocation, resulting in an anatomical lesion evidenced by imaging studies. The patients subsequently experience recurring and painful dislocation or subluxation, contrary to what Neer has described. The instability is the primary presenting complaint, more so than the pain. The patient is unable to reproduce the instability.

2. Voluntary instability

On average (but not necessarily) patients experience greater hyperlaxity than with the other forms and have a higher predisposition. They find it hard to pinpoint when the problem began.

There are two clearly defined sub-types:

patients who remain voluntary and can dislocate the joint at will (reproducible), maintaining control over their shoulder; painless, with or without any associated psychological or psychiatric disorder.

Voluntary patients who later become involuntary (voluntary-to-involuntary), usually following a decompensating trauma that causes them to lose control over their joint, worsens the instability and makes it painful. This instability is often still reproducible but is no longer voluntary (unintentional).

3. Unstable painful shoulder

Patients with an unstable painful shoulder (UPS) do not necessarily present with hyperlaxity. The pain is the primary symptom.

Imaging studies

1. Standard x-rays

The basic examination should include frontal views in three rotations and a Bernageau view. Look for a glenoid fracture (reverse Bankart), posterior glenoid rim flattening or anterior notching on the head of humerus (McLaughlin notches or reverse Hill-Sachs lesion).

2. Arthrography

A CT scan is the best way to both analyse bone lesions and search for glenoid hypoplasia, dysplasia or retroversion as predisposing factors (Fig 1). Posterior labral damage on contrast-enhanced images may also indicate a labral fissure (Fig. 2). However, any such capsulolabral detachment is only pathological if located at the inferior, subequatorial portion of the bone.

Figure 1: CT scan revealing anterior notching on the head of humerus (McLaughlin notches or reverse Hill-Sachs lesion).

Figure 2: CT scan revealing posterior labral damage (reverse Bankart lesion).

Likewise, take time to check for any associated cartilage damage since this is a very important prognostic factor, as discussed below. For detecting soft tissue lesions and cartilage defects MR imaging is superior to CT and can also be done as Arthro-MRI.

Functional medical treatment

Treatment can start with functional management based on neuromuscular reprogramming and physiotherapy to improve stability and proprioception. This education can involve strategies aimed at addressing pain, including advice on sleeping position and regaining motor control.[3] This is in fact the only form of treatment offered to patients with voluntary instability Reproducible voluntary instability may benefit from psychological therapy, or even wider family support if the patient is an adolescent.

Surgical treatment

1. Arthroscopic capsulolabral repair (arthroscopic posterior Bankart)

This technique is indicated when the only damage is posterior labral detachment (Fig. 3) with no significant bone lesions. The posterior labrum can be reinserted by using anchors (Fig. 4), but posterior capsule tensioning [4] is crucial in order to recreate the glenoid concavity and restore the constraints from the capsuloligamentous structures.

Figure 3: Arthroscopic view of a labral lesion: the posterior labrum is detached

Figure 4: Arthroscopic view of the posterior labral reattached with anchors

2. Arthroscopic capsulolabral repair + anterior notch filling

If there is a posterior labral lesion together with a large humeral defect (McLaughlin notch or reverse Hill-Sachs), the subscapularis tendon can be detached and transferred to fill the the bony defect. This technique described by McLaughlin can now be performed arthroscopically, allowing for simultaneous capsulolabral reinsertion.

3. Posterior bone block procedure

This technique can be performed as an open procedure [5] or by arthroscopy,[6,7] with or without simultaneous posterior labral repair. The main indication is a posterior glenoid rim defect, such as a fracture (reverse bony Bankart) or flattening. The graft is harvested from the iliac crest or acromion and transferred to the posterior glenoid rim. It is the equivalent of an anterior block, technically more accessible via arthroscopy.

4. Glenoid osteotomy

This is relatively complex surgical procedure. A posterior opening-wedge glenoid osteotomy is reserved for the treatment of excessive retroversion. Complications are common, and the procedure is no longer widely used.