Abstract
The stability of the elbow is based on a combination of primary (static) and secondary
stabilizers (dynamic). In varus stress, the bony structures and the lateral ulnar
collateral ligament (LUCL) are the primary stabilizers, and in valgus stress, the
ulnar collateral ligament (UCL) is the primary stabilizer. The flexor and extensor
tendons crossing the elbow joint act as secondary stabilizers. Elbow instability is
commonly divided into acute traumatic and chronic instability. Instability of the
elbow is a continuum, with complete dislocation as its most severe form.
Posterolateral rotatory instability is the most common elbow instability and can be
detected at imaging both in the acute as well as the chronic phase. Imaging of suspected
elbow instability starts with radiographs. Depending on the type of injury suspected,
it is followed by magnetic resonance imaging (MRI) or computed tomography evaluation
for depiction of a range of soft tissue and osseous injures. The most common soft
tissue injuries are tears of the LUCL and the radial collateral ligament; the most
common osseous injuries are an osseous LUCL avulsion, a fracture of the coronoid process,
and a radial head fracture.
Valgus instability is the second most common instability and mostly detected in the
chronic phase, with valgus extension overload the dominant pattern of injury. The
anterior part of the UCL is insufficient in valgus extension overload due to repetitive
medial tension seen in many overhead throwing sports, with UCL damage readily seen
at MRI.
Keywords
posterolateral instability - valgus extension overload
