Thumb MP Joint

Modern Study Review (AI-Generated)

High-Yield Summary

The thumb metacarpophalangeal (MP) joint is critical for hand dexterity, allowing a wide range of motion including flexion, extension, abduction, and adduction. Injuries to the ulnar collateral ligament (UCL), commonly known as Gamekeeper’s or Skier’s thumb, are frequent and can lead to chronic instability if untreated. Accurate diagnosis, including identification of a Stener lesion, guides management between conservative immobilization and surgical repair. Modern treatment prioritizes restoring joint stability to preserve pain-free function and pinch strength.

Key Diagnostic Findings

Aspect	Details
Anatomy	Thumb MP joint allows ~115° flexion, ~10° abduction/adduction; UCL supported dynamically by adductor aponeurosis.
Clinical Presentation	UCL injury: pain, swelling at ulnar MP joint, instability with valgus stress; Stener lesion suspected if complete tear.
Imaging	Stress radiographs show valgus laxity; avulsion fractures at proximal phalanx base; MRI can confirm Stener lesion.
Classification Systems	No formal classification for UCL tears; Stener lesion presence is critical for treatment decisions.

Current Gold Standard Treatment

Injury Type	Treatment
Partial UCL Tear	Thumb spica cast with MP joint slight flexion (15°-20°) for 3-4 weeks; early mobilization after.
Complete UCL Tear without Stener Lesion	Surgical repair indicated if instability present; direct repair with suture anchors or pull-out sutures.
Complete UCL Tear with Stener Lesion	Surgical repair mandatory due to interposed adductor aponeurosis preventing healing.
Chronic UCL Tears	Modified Neviaser reconstruction if joint stable; arthrodesis if arthritic changes present.
Radial Collateral Ligament Injury	Usually immobilization in thumb spica for 3-4 weeks; surgical reconstruction if instability persists.
Thumb MP Dislocations	Closed reduction with wrist flexion and axial load; open reduction if irreducible (volar plate or sesamoid interposition). Early motion post-reduction.
Volar Plate Injuries	Immobilization in thumb spica with slight flexion for 3-4 weeks; rare surgical capsulodesis for chronic cases.
Sesamoid Fractures	Immobilization for 3-5 weeks; excision if symptomatic and persistent pain.

Modern Complications & Outcomes

Missed Stener lesion leads to chronic instability and weakness of pinch grip.
Inadequate immobilization risks persistent laxity and arthritis.
Surgical complications include stiffness, infection, and hardware irritation.
Early mobilization after stable repair improves functional outcomes.
Chronic untreated injuries may require reconstructive surgery or arthrodesis, with variable functional results.
Thumb MP joint dislocations have excellent prognosis if promptly reduced; irreducible dislocations require open surgery to prevent chronic dysfunction.

Classic Clinical Notes

THUMB MP JOINT

Anatomy

The thumb MP joint allows flexion, extension, abduction, adduction, and a limited range of rotation.
Flexion is to 115°, abduction/adduction of about 10°.
The ulnar aspect has particular significance, with the adductor aponeurosis, an ulnar expansion of the dorsal aponeurosis, supporting the ulnar collateral ligament dynamically.

Ulnar Collateral Ligament Injury (Gamekeeper’s/Skier’s Thumb)

Mechanism: sudden abduction/extension, injuring the ulnar collateral ligament and volar plate.
Stener lesion: completely torn ligament folds back on itself, held by adductor aponeurosis, preventing healing; occurs in ~50%.
Clinical diagnosis of complete tear by stress testing under regional anesthesia (median and radial nerve block). Positive test criteria controversial (10° or 35° more than contralateral side).
Radiographic diagnosis by stress testing; risk of creating Stener lesion debated. Look for chip or avulsion fractures at proximal phalanx base.

Treatment

Acute Partial Tears: Thumb spica cast with MP slightly flexed for 3-4 weeks.
Acute Complete Tears:
Most tears at proximal phalanx insertion.
Operative repair with pull-out suture over button or bone anchor.
Midsubstance tears: direct repair.
Operate if displaced intra-articular fracture >25% or avulsion fracture displaced >5 mm.
Chronic Partial Tears: Cast or splint immobilization for 3 weeks, then intense physiotherapy.
Chronic Complete Tears:
If joint intact: modified Neviaser reconstruction.
If arthritic: fusion.

Radial Collateral Ligament Injuries

Less common than UCL injuries; fewer anatomic obstacles to healing.
Treatment: immobilization in thumb spica for 3-4 weeks; Neviaser-like reconstruction described.

Dislocations of the Thumb MP Joint

Dorsal dislocations more common than volar; may be irreducible due to volar plate or FDP.
Irreducibility diagnosed clinically by parallel alignment of proximal phalanx and dimple in thenar eminence; sesamoid interposition on x-ray is pathognomonic.
Treatment:
Closed reduction with wrist flexed, hyperextension with axial load, then flexion.
Check lateral stability; if stable, mobilize immediately.
Open reduction if irreducible; early postoperative motion.

Volar Plate Injuries

Caused by hyperextension; diagnosed by increased hyperextension or volar pain.
Treatment: thumb spica immobilization for 3-4 weeks with MP in 15°-20° flexion.
Chronic injuries: volar plate capsulodesis described but rarely done.

Sesamoid Fractures

Rare. Most people have 5 sesamoids: one at thumb IP joint, two at thumb MP joint, one each at index and little finger MP joints.
Thumb MP sesamoids are universally present in volar plate.
Adductor pollicis inserts into ulnar sesamoid; flexor pollicis brevis into radial sesamoid.
Treatment: thumb spica immobilization for 3-5 weeks; excision if symptomatic.

Last Updated on January 24, 2026 by orthonet