gms | German Medical Science

Objectives/Interrogation: Percutaneous extension block pinning (pinning) for mallet fracture is simple and less invasive method. However, we occasionally encounter poor outcomes. We reviewed our cases in order to find out the factors causing poor outcomes.

Patients: From 2012 to 2017, fifty mallet fingers of 50 patients were consecutively operated on by pinning. There were 32 men and 18 women with an average age of 43. The patients followed more than 6 months were involved in this review. The affected fingers were 2 index, 10 middle, 22 ring, and 16 little fingers. The average interval between injuries to surgery was 7.6 days. The surgery was done according to Ishiguro method with some modification. The K-wire was removed at 5 to 6 weeks, then followed by night splint in extension.

The patients were evaluated by DIP joint motion, then divided into good or poor group. Either more than 10 degrees of extension lag or less than 30 degrees of active flexion was rated as poor. Fracture type was divided as avulsion type or axial compression type. The length of the dorsal cortex and the joint surface ratio of the bony fragment were measured on the lateral X-ray.

Results: Thirty-three fingers were resulted into good, and 17 fingers were poor. The average patients' age was 40.1 years in good group and 50.6 years in poor group, which was statistically significant (P<0.05). The involved fingers and the interval to surgery were not significantly difference between two groups. Regarding fracture type, 67% of fingers showed avulsion type in good group, on the other hand 65% showed axial compression type in poor group. Joint surface ratio of the bony fragment was not significantly different between two groups, but the average length of dorsal cortex was 2.4 mm in poor group and 1.8mm in good group, which was significantly different (P<0.05).

Discussion: The average age was significantly high in poor group. Bone quality might be not rigid enough to secure K-wire, or pre-existing osteoarthritic changes caused restriction of DIP joint motion. Regarding fracture type, compression type and long bone fragment caused poor outcomes. The extension block pin aims to decrease traction force by terminal tendon, but it does not effectively prevent rotation deformity of bone fragment. We have to use an additional pin to directly fix bone fragment to the distal phalanx, or small screw would be effective. We should know the limitations of percutaneous pinning.