Binary Soong grading as a predictor for flexor pollicis longus tendon rupture after distal radial fracture fixation: a retrospective study

This retrospective cohort study evaluates the concordance between Soong grades classified from radiographs and computed tomography (CT) scans and whether a Soong grade >= 1 is associated with flexor pollicis longus (FPL) injury and reoperation incidence. We included 181 patients with 185 dorsally displaced distal radial fractures treated with anterior locking plates. For the analysis of binary Soong grades, grade 0 was compared with grades 1 and 2. A moderate correlation was found between Soong grades on radiographs and CT scans (MCC 0.66). FPL injury occurred in 3% (6/185) and reoperation in 15% (28/185) of cases. There was no statistically significant difference between Soong grades when correlated with the incidence of FPL injury or reoperation, but no patients with a Soong grade 0 had an FPL injury. Binary Soong grading is non-inferior in predictive value and has a better correlation between radiographs and CT scans. Using the Soong classification as a binary system may be easier than a ternary system in clinical practice.Level of evidence: IV