Impact of Corticosteroid Injection Site on the Treatment Success Rate of Trigger Finger: A Prospective Study Comparing Ultrasound-Guided True Intra-Sheath and True Extra-Sheath Injections

The aim of this study was to investigate whether differences in corticosteroid injection site influence the therapeutic effect on trigger finger and thickness of local structures such as the A1 pulley and flexor tendons. Previously untreated trigger fingers were randomly assigned to receive either a true intra-sheath (group I) or an extra-sheath (group E) injection under ultrasonographic guidance. Symptom remission and recurrence rates and recurrence timing did not significantly differ between the groups. Ultrasonography revealed mean (standard deviation) pre-injection A1 pulley thicknesses of 1.1 (0.3) and 1.1 (0.2) mm in groups I and E, respectively. One month after injection, these decreased to 0.7 (0.2) and 0.8 (0.2) mm, respectively (p < 0.05). Furthermore, mean (standard) pre-injection flexor digitorum tendon thickness was 4.1 (0.4) and 4.0 (0.5) mm in groups I and E, respectively, and, 1 mo after injection, decreased to 3.9 (0.3) and 3.8 (0.5) mm, respectively (p < 0.05). However, the difference at each time point between the two groups was not statistically significant. True intra-sheath injection offers no apparent advantage over extra-sheath injection for treating trigger fingers because both have the same effect on local structures.