Background

Trochlea and ulna highly conformed

- trochlea covered by cartilage in arc 300^o

- trochlea separated from the capitellum by groove 

- trochlea 6^o valgus which creates carrying angle

Concave radial head

- articulates with capitellum

- posteromedial 2/3 articulates with sigmoid notch ulna

- anterolateral 1/3 has no cartilage /  safe zone

Tilted anteriorly 30^o in lateral plane

- 5^o internally in transverse plane

- 6^o of valgus in front plane

Radial head important secondary stabiliser, especially when MCL deficient

Centre of rotation

- trochlea

- centre of rotation anterior to humeral shaft

Provide valgus stability in flexion

Radiocapitellar joint provides valgus stability in extension

Annular Ligament - anterior edge supinator crest to posterior edge

Radial Collateral Ligament - common extensor origin to annular ligament

Lateral Ulna Collateral Ligament 

- most important restraint to posterolateral instability

- common extensor origin to supinator crest

- in line with edge of anconeus, deep to it

- must protect in surgical approach between anconeus and ECU / Kocher

Accessory Collateral Ligament - from crest to annular ligament

Anterior band

- common flexor origin to sublime tubercle

- most important

Transverse band

- olecranon to sublime tubercle

- groove for ulna nerve

Posterior band - common flexor origin to olecranon

Stage 3A - anterior band MCL intact

- posterolateral dislocation

- elbow stable with hand pronated

Posterolateral instability

Spontaneous reduction

Coranoid perches on trochlea

Spontaneous reduction

Stage 3B - entire MCL torn

- elbow needs to be flexed to > 30 - 40^o to be stable

Stage 3C - MCL torn and CFO /CEO torn

- elbow needs to be flexed > 90^o to be stable