MEM camp = bent tent
Definition
Greek for bent finger in sagittal plane
Usually little finger
Typical deformity is FFD of PIPJ & extension of MCPJ
Epidemiology
<1% of population
Strong familial predisposition
- 60% bilateral
- bimodal pattern
- present in infancy or adolescence
- 1 in 1000 live births
Aetiology
Unknown
- not related to trauma, infection, NMD
- ? due to incomplete extensor mechanism
Usually due to imbalance of pull between flexor & extensor mechanisms
- contracture of collaterals
- secondary abnormality PIPJ common
- usually base of P2 is subluxed volar to head P1
Most commonly accepted theory
- an anomalous insertion of the lumbrical muscle into the flexor sheath causes the abnormality
Multiple causes reported
- aberrant lumbrical insertion
- flexor sheath contracture
- phalangeal head deformity
- FDS contracture
- abnormal extensor tendon mechanism
Classification
1. Infantile
2. Adolescent
3. Severe form affecting all triphalangeal digits
DDx
Traumatic boutonnière deformity
Juvenile aponeurotic fibromatosis
- involves palmar fascia & skin
- increased flexion deformity
NHx
80% progress
- progress during growth spurts
Doesn't progress after maturity
Clinical Features
85% present at birth
15% present in adolescence
Volar skin may bowstring
- can be mild to severe FFD
- functional compromise when FFD ->90o
Fixed v flexible
Xray
Head of P1 has bullet shape
PIPJ is subluxed
Management
Non-operative
Usual treatment
- watch to see if deformity progresses especially at growth spurts
- some studies show that splinting does work if 24 hours per day
- other studies without 24 hours splinting show not much difference
- passive stretching & static & dynamic splinting
No series has shown surgical release does better than well motivated and controlled regimen of flexion and extension splinting
Operative
Indications
Progressive deformity
Failure of non-operative management
> 60° & functional disability
Poor outcomes especially loss of flexion
- some series report only 35% success rate
Technique
Fixed
- release all tight volar structures
- skin / FDS / volar plate / capsule
- +/- FDS transfer to the extensor hood
Skeletally mature
- extension osteotomy / dorsal closing wedge
- must avoid excess straightening -> stretch nv bundle
Do not perform release and simultaneous transfers as need to mobilise immediately post-operatively