Thumb Oa

Question 1

Eaton and litter classification of thumb CMCJ, pathoanatomy and beak ligament

Answer 1

Eaton and litter classifcation
1. widened joint space - synovitis
2. slight narrowing, sclerosis, subluxation and osteophytes
3. marked narrowing, sclerosis, subluxation and osteophytes
4. pantrapezial arthritis (STT involvement)

Pathoanatomy
attenation of the beak ligament leading to:
- instability
- subluxation - squaring
- CMCJ OA

Beak ligament
- anterior oblique
- volar trapezium to ulnar metacarpal base
- primary stabiliser of CMCJ
- lateral and dorsal ligaments seconday stabilisers

Question 2

Assessment of CMCJ OA
- clinical features
- imaging
- differential diagnosis

Answer 2

Clinical features
- squaring of base of thumb metacarpal
- z-deformity of thumb
- grind test - axial pressure and circumduction
- thenar wasting - 30% carpal tunnel syndrome
- pain - night and screwing jars
- check for MCPJ and STT OA

pain with dart throwers motion - STT OA

Imaging
- roberts view - AP of CMCJ
- AP/ Lateral
- important to identify a DISI deformity

Differential diagnosis
- dequervian’s disorder
- STT arthrirtis
- SLAC/ SNAC wrist
- radioscaphoid OA

Question 3

Why do you get a z deformity of the thumb in base of thumb OA?

Answer 3

Thumb Z-deformity
due to adduction contracture of CMCJ
-CMCJ adduction/ flexion
- MCPJ - hyperextension
- IPJ - flexion

compensatory MCPJ hyperextension to allow grip

Question 4

Management of CMCJ OA

Answer 4

Non-op
- thumb spica splint
- hand therapy - thenar muscles
- steroid injection

Goals of surgery
- allow pain free function of the thumb

Operative
- neurectomy
- trapeziectomy gold standard
- fuse
- replace

Decisions:
WHO?
- low demand elderly - trapezectomy vs replacement
- high demand young - fuse

APPROACH?
- wagner approach
- dorsal approach

CMCJ fusion
- Fused in clenched fist position - 20 deg palmar abduction, 30 deg radial abduction and 15 deg prontation
- better grip strength
- risk of non-union
- can’t be used for pantrapezial OA
- Fixation - T-plate with 2.4mm screws
- CONTRAINDICATED - STT arthritis

Trapezectomy
- loss of grip strength
- proximal migration
- CONTRAINDICATED - SNAC/ SLAC wrist - leads to carpal instability

Trapezectomy - LRTI?
ligament reconstruction and tendon interposition
- FCR or APL tendon
- dorsal approach use APL
- Tim Davis RCT 2011 - no functional difference at 6yrs

Complications of trapezectomy
- early - superficial dorsal radial nerve, infection, haematoma
- late - proximal migration with pain, instability, tender scar and CRPS

Residual deformity management
- adduction of CMCJ - trapezectomy causes shortening so shouldn’t be a problem
- MCPJ hyperextension > 30 degrees - risk of swan neck deformity - MCPJ fusion or volar capsulodesis

Question 5

What is the approach for a trapezectomy?

Answer 5

Dorsal approach

skin incision
- draw base of metacarpal and trapezium
- longitudinal incision centred over dorsal CMCJ

approach
- APL and EPB
- mobilise radial artery dorsally
- confirm position
- longitudinal capsule incision
- subperiosteal dissection of trapezium
- remove piecemeal

dangers
- dorsal branches of the superficial radial nerve - in fat layer
- radial artery - cross superficial to capsule at STT level from proximal palmar to distal dorsal - branches ligated and retracted dorsally