Gamekeeper's thumb--a treatment-oriented magnetic resonance imaging classification.

PURPOSE: To investigate by magnetic resonance imaging the degree of ulnar collateral ligament (UCL) displacement in order to create a simple classification to aid in determining which UCL injuries require surgery.

METHODS: We evaluated 43 cases of UCL injury with a dedicated extremity magnetic resonance imaging and measured the degree of ligament displacement. This was correlated to clinical outcome with planned surgical intervention reserved for patients with a Stener lesion. By collating results we could generate 4 types of injury based on the appearances of the UCL.

RESULTS: Partial and minimally displaced UCL tears (type 1) and tears displaced less than 3 mm (type 2) typically healed by immobilization alone, whereas 90% of tears displaced more than 3 mm (type 3) failed immobilization and required surgery as did all of those with a Stener lesion (type 4).

CONCLUSIONS: Our 4-stage, treatment-oriented classification of thumb UCL injury is based on the degree of UCL displacement in, with correlation with the likelihood of success with either immobilization or operative intervention. Tears of the UCL with more than 3 mm of displacement are likely to require operative repair even in the absence of a true Stener lesion.