A 47-year-old male amateur cyclist presented at the emergency department after a fall from a bike. He complained of pain in his left shoulder and restricted mobility. Clinical examination was limited because of antalgic posture of his right arm.
The setting and clinical presentation were very suggestive for a fracture or dislocation. Plain radiograph (basic AP view in endo- and exorotation) showed no fracture, but was strongly suggestive for posterior shoulder dislocation. Additional scapular Y view confirmed the diagnosis. CT (with reconstructions) was performed to exclude associated subtle fractures. A reversed Hill-Sachs lesion and bony Bankart lesion were both present on CT.
Subsequent a closed reduction under general anesthetics was performed.
Posterior shoulder dislocation (PSD) is very uncommon, accounting for merely 2-4% of all shoulder dislocations. PSD is caused by a forceful blow on the anterior humeral head in internal rotation. The most frequent causes are direct trauma and convulsive seizures. A less frequent cause is spontaneous PSD in patients with predisposing lax joints.
Clinical examination is limited due to pain, swelling and antalgic posture. If external rotation of the humeral head is still possible, PSD is unlikely.
Patients presenting in the typical setting of trauma or convulsive seizures, should raise the suspicion of PSD. Y-view or axillary projections are diagnostic in most cases. Additional CT can exclude associated lesions. A study of Rouleau showed a percentage of 65% of associated injuries, most frequently a fracture, reverse Hill-Sachs lesion or cuff tear.
Cisternino et al. described five typical radiographic signs of PSD: (1) A fixed internal rotated humeral head on frontal X-rays, giving the humeral head a "light bulb” appearance. (2) The “rim sign” is an increased distance between medial border of the humeral head and the anterior glenoid rim, caused by a lateral displacement of the humeral head with respect to the posterior glenoid rim. This sign is not specific and can also occur in haemarthrosis. (3) The same applies to an absent “half moon” overlap of the humeral head and glenoid. (4) When PSD is associated with a reverse Hill-Sachs lesion, the humeral head is displaced medially, showing an abnormal overlap on tangential view of the glenoid. (5) The “through line” on frontal X-ray is made up by two parallel lines of cortical bone on the superomedial aspect of the humeral head. The medial line is the articular cortex of the humeral head and the lateral is the border of the impaction fracture.
Treatment depends on time interval between dislocation and diagnosis. If a humeral head defect is present, the size of the defect also influences treatment strategy. Closed reduction under general anesthesia is the treatment of choice for acute dislocations(< 3 weeks) with small humeral head defects (<20% of articular surface). If closed reduction is unsuccessful (or if there is a large humeral head defect), the following step is open or arthroscopic reduction. For intermediate/large size defects, one can opt for implantation of bone grafts or allografts, whether or not combined with a standard or modified McLaughlin procedure. Without surgery, recurrent posterior instability can occur, which can be fixed with a labrum repair or posterior stabilization procedure.
Posterior shoulder dislocation
Based on the provided left shoulder X-ray and CT images, the following characteristics can be observed:
1. On the anteroposterior (AP) X-ray, the humeral head is clearly in an internally rotated position, showing the “light bulb sign,” indicating a reduction or disappearance of the normal overlap between the humeral head and the glenoid.
2. An increased distance between the humeral head and the posterior rim of the glenoid (“rim sign”) can be seen, along with the disappearance of the “half moon” overlap, all of which suggest a posterior dislocation of the humeral head.
3. CT cross-sectional images show the humeral head displaced posteriorly relative to the glenoid, deviating distinctly backward compared to normal anatomy. Some images reveal possible compression or a bony defect in the anteromedial portion of the humeral head, raising concern for a reverse Hill-Sachs lesion (i.e., localized compression fracture at the anteromedial aspect).
4. Compared to the surrounding soft tissues, there is no obvious large-scale abnormal density or shape, but clinical correlation is needed to rule out rotator cuff tears or other soft tissue pathologies.
Combining the patient's history of trauma (fall), imaging features of a fixed internal rotation with posterior displacement of the humeral head, and classic signs of posterior dislocation, the most likely diagnosis is: Posterior Dislocation of the Left Shoulder (Posterior Shoulder Dislocation). As the imaging suggests a localized defect in the anteromedial portion of the humeral head, a reverse Hill-Sachs lesion or other fractures should be considered as concurrent injuries.
Treatment Strategy:
1. Closed Reduction: For acute cases (usually <3 weeks) with a small humeral head defect (<20% of the joint surface), attempt a closed reduction under general anesthesia or adequate analgesia.
2. Surgical Treatment:
- Open or Arthroscopic Reduction: If closed reduction fails, if the dislocation has lasted for a prolonged period, or if there is a large humeral head defect (≥20% of the joint surface), consider surgical reduction with bone grafting, defect patch repair, or a modified McLaughlin procedure.
- Concurrent Rotator Cuff Injury or Instability: In cases with rotator cuff tears or recurrent dislocation, repair of the rotator cuff as well as capsulolabral reconstruction may be needed either simultaneously or at a later stage.
3. Postoperative or Conservative Rehabilitation: If reduction is successful and there is no significant fracture instability, conservative rehabilitation with regular imaging follow-up is indicated. If the joint remains unstable or the humeral head defect is large, further surgery and complete repair should be evaluated.
Rehabilitation/Exercise Prescription (FITT-VP Principle Example):
1. Frequency (F):
- Early Phase (0–2 weeks): Primarily shoulder immobilization or protective activities, 1–2 sessions of gentle passive movement per day, avoiding excessive pain.
- Intermediate Phase (2–6 weeks): Gradually increase active movement within the tolerance of pain, 3–5 sessions per week focusing on basic muscle strength and joint flexibility.
- Late Phase (6 weeks and beyond): Progressively strengthen the muscles around the shoulder, 3–4 sessions per week targeting strength, coordination, and proprioceptive recovery.
2. Intensity (I):
- Begin with low resistance and low load in the early phase, avoiding any traction or high-impact actions.
- As joint stability and muscle strength improve, gradually increase resistance (e.g., using resistance bands or light dumbbells).
3. Time (T):
- Each session can start at 10–15 minutes, then gradually increase to 20–30 minutes based on recovery status.
4. Type (T):
- Passive Movements: Utilizing manual assistance or mechanical devices to maintain joint mobility.
- Active Movements: Include wall slides, pendulum exercises, and resistance band training.
- Proprioception Training: Use of balance balls or posture-corrective exercises.
5. Progression (P):
- Increase strength and endurance of the biceps, triceps, and rotator cuff muscles incrementally, provided pain and swelling are controlled and the joint alignment is stable.
- For recreational or professional athletes, return to sport-specific training only after thorough assessment of shoulder stability.
6. Warnings and Safety:
- If significant pain, swelling, or instability recurs, reduce activity levels and consult a physician promptly.
- For those with weaker bones or comorbidities (e.g., cardiac or pulmonary issues), adjust load appropriately, prioritizing safety and proper form.
Disclaimer: This report is a reference-based analysis derived from the available imaging data and clinical information, and cannot replace an in-person consultation or individualized professional medical advice. Specific treatment and course of action should be determined by the patient’s actual condition and the attending physician’s judgment.
Posterior shoulder dislocation
