Extensor Carpi Ulnaris Subluxation

Background

• ECU subluxation is a recognized cause of ulnar-sided wrist pain.
• The ECU tendon runs in the ulnar groove and is stabilized by a fibro-osseous tunnel.
• A subsheath acts as labrum on the ulnar border to prevent subluxation; can tear during activities like forearm supination, wrist flexion, and ulnar deviation.
• Common in athletes (racquet/stick sports) and rheumatoid patients due to synovitis.

Anatomy

• ECU originates at the lateral epicondyle of the humerus and inserts at the base of the fifth metacarpal.
• Runs within the sixth dorsal compartment, stabilized by a subsheath.
• The subsheath lacks elastic fibers, is reinforced by linea jugata and prevents subluxation.

Figure 1

• Illustrates the 6th dorsal compartment and stabilization methods.

Pathophysiology

• ECU tendinopathies: constrained (tight subsheath) & unconstrained (torn subsheath).
• Maximal stress on ECU occurs when wrist is supinated, flexed, and ulnarly deviated.
• Subsheath tear types:
  • Type A: Ulnar side tear, tendon returns under torn edge.
  • Type B: Radial side tear, tendon lies outside, less likely to heal.
  • Type C: Detachment from periosteum, tendon remains in a false sheath.

Figure 2

• Shows classification of subsheath tears.

Physical Exam

• Symptoms: swelling, tenderness, pain (acute), tendon snapping, wrist instability (chronic).
• Diagnostic maneuvers:
  • ECU Synergy Test: Detects constrained tendinopathy, involves resistance at the radial side.
  • ECU Subluxation Test: Resistance on ulnar aspect, compares wrists.

Figure 3

• Demonstrates the ECU synergy test.

Imaging

• Wrist radiographs rule out bony pathology.
• Ultrasonography assesses ECU tendon.
• MRI for tendon and groove anatomy, not routine pre-op.

Treatment

• Initial: Immobilization in a long-arm cast for six weeks.
• Surgery indicated for persistent pain/instability.

Surgical Options

• Acute: Primary subsheath repair possible.
• Chronic: Subsheath reconstruction often needed using extensor retinaculum.

Surgical Technique

• Incision over dorsal ulnar wrist, avoiding the ulnar nerve.
• Flap of extensor retinaculum passed under, around ECU tendon, sutured.
• Potential additional surgeries for other wrist pathologies.

Figures 4-7

• Illustrate surgical techniques, flap positioning, and completed reconstruction.

Post-operative

• Long arm splint in neutral position for 4-6 weeks.
• Avoid strenuous activities for three months.
• Recurrence of symptoms is rare; careful sizing of sheath is crucial.

Discussion

• Subsheath reconstruction has high patient satisfaction.
• MRI can confirm diagnosis and compare post-op results.
• Complex relationship between subluxation and pain; further research necessary.

Summary

• ECU subsheath stabilizes wrist; damage leads to pain.
• Conservative management effective only in some cases.
• Surgical repair recommended for return to activity.

Key Points

• Subsheath tears from movements combining supination, flexion, ulnar deviation.
• Surgical repair with extensor retinaculum flap recommended.

Clinics Care Points

• Challenging diagnosis; surgery for non-responsive cases.
• Tension-free subsheath repair preferred.

Synopsis

• Diagnosis through examination, ultrasonography; surgery for stabilization.

Funding and Disclosures

• Supported by NIH grant; no financial disclosures.