Quick facts
- Rare compression of the axillary nerve+ posterior humeral circumflex artery
- Typical in 20- to 40-year-old swimmers, tennis & volleyball players
- Key sign: point tenderness just below the rear corner of the deltoid
- Best imaging clue: teres minor or deltoid atrophy on MRI
- Most cases settle with targeted physiotherapy; surgery is a last resort
What is quadrilateral space syndrome?
Quadrilateral space syndrome (QSS) occurs when the axillary nerve and its companion artery are squeezed in a tight gap bordered by teres minor, teres major, the long head of triceps, and the surgical neck of the humerus. Compression produces pain, altered feeling, or weakness in the outer shoulder and may reduce blood flow to the arm during overhead activity.
Who gets it and why?
- Young male athletes are most affected, especially throwers and servers who repeat abduction-external rotation(AER) at speed.
- Risk factors
- Muscle hypertrophy around the space (dynamic QSS)
- Fibrous bands, cysts or bone spurs narrowing the space (static QSS)
- Previous shoulder dislocation or trauma
Main symptoms
Symptom | Typical pattern |
Dull ache | Low behind the shoulder; worse at night or with overhead play |
Paresthesia | ‘Pins and needles’ along the outer arm (non-dermatomal) |
Weakness | Difficulty with external rotation or overhead reach |
Visible changes | Isolated wasting of the deltoid or teres minor |
Vascular cases (“Pitcher syndrome”) may show hand coldness, colour change or early fatigue due to artery spasm or clot
How is it diagnosed?
- Careful examination – check posture, scapular control and feel for tenderness over the quadrilateral space.
- Reproduction test – holding the arm in 90° abduction + external rotation for one minute often recreates symptoms.
- Imaging
- MRI: focal atrophy or oedema of teres minor/deltoid; may reveal cysts or tumours.
- Plain X-ray: screens for fractures or bone spikes.
- Electromyography can show axillary nerve delay but may be normal at rest.
- Ultrasound-guided lidocaine block – pain relief after local anaesthetic confirms the diagnosis and guides treatment.
Treatment pathway
- Conservative care (first-line)
- Activity change: reduce overhead loading for 6–12 weeks.
- NSAIDs or simple analgesia for comfort.
- Physiotherapy focus:
- scapular stabilisers and posterior deltoid strength
- posterior-capsule stretches
- proprioceptive drills for throwing mechanics
- Progress is reviewed at three and six months; most athletes improve without surgery.
- Surgical decompression (only if…)
- Persistent pain or weakness despite a full rehab course
- Clear compressive lesion on MRI
- Acute vascular compromise
Open posterior decompression releases fibrous bands and removes any mass; associated labral tears can be repaired arthroscopically in the same sitting. Early movement prevents re-scarring, and sport-specific drills start around week 6.
Recovery & outlook
- Conservative: 70 – 80 % return to play within six months.
- Post-op: most regain full strength by nine months; recurrence is uncommon when rehab is completed.
Clinical pearls / Key points
- Always palpate the quadrilateral space in athletes with vague posterior pain.
- Teres minor atrophy on MRI is highly suggestive but not pathognomonic.
- A normal EMG does not rule out a dynamic QSS test during provocative arm positions.
- Early rehab that corrects scapular dyskinesis may prevent surgery.
Patient FAQs
Is QSS the same as shoulder impingement?
No. Impingement pinches tendons under the acromion at the front; QSS involves a nerve and artery at the back of the shoulder.
Will the nerve recover fully?
Most nerves recover once pressure is relieved, either by therapy or surgery, but long-standing cases may leave mild weakness.
Can I still train?
Yes, but swap overhead drills for core, legs and below-shoulder conditioning until symptoms ease.
What happens during the lidocaine test?
A small amount of local anaesthetic is injected under ultrasound guidance into the quadrilateral space. Immediate pain relief suggests the nerve is the pain source.
Could this cause blood-flow problems?
Rarely, the companion artery can narrow or clot. If your hand becomes cold or discoloured seek urgent review.
Call to Action
If you have pain, book an appointment to be reviewed by Prof Imam or another member of our specialist team at The Arm Clinic. Early specialist care helps prevent long-term issues. Visit www.TheArmDoc.co.uk or book your consultation today. Phone: 020 3384 5588 | Email: Info@TheArmDoc.co.uk
Disclaimer
This information is for general education and not a substitute for personal medical advice. Always consult a qualified clinician for diagnosis and treatment.
Content reflects UK practice and evidence current to July 2025.