Ulna Nerve Compression

Sites of Compression

 

Proximal

 

Arcade of Struthers 

- thick myofascial band, 1.5-2cm wide

- present in 70%

- 8cm proximal to medial epicondyle

- from medial head of triceps to medial intermuscular septum, superficial to nerve

 

Medial intermuscular septum

- with subluxation, nerve may impinge on it 

 

Medial head of triceps

- hypertrophied (body builders)

 

Medial epicondyle

 

Tardy ulna nerve palsy / cubitus valgus

- compression due to valgus deformity of the bone

- previous supracondylar / lateral condyle fracture

 

Cubital tunnel / Osbourne's ligament

 

Anatomy

- walls are humeral & ulna heads of FCU

- floor is MCL

- roof is Osbourne's fascia (continuation of fibro-aponurotic covering of epicondylar groove)

 

Nerve compression 

- occurs in flexion as Osbourne's fascia tightens

- MCL bulges out and tunnel becomes flattened ellipse

 

FCU

 

Nerve passes intramuscular for ~5cm

- penetrates fascial layer to lie on FDP

- proximal and distal compression possible

 

Other

 

A. Lesions in the groove

- medial epicondyle fracture / arthritic spurs / HO

- lipomas / ganglia / osteochondromas / synovitis / rheumatoid nodule

- infection (TB, leprosy) /bleeding (haemophilia)

 

B. Conditions outside the groove

- external compression

- anomalous anconeus muscle

 

C. Subluxation / Dislocation from the groove

- laxity / traumatic tear of fibro-aponurotic roof