Beware of ulnar nerve entrapment in flexion-type supracondylar humerus fractures

A recent study reported a higher incidence of pre-operative ulnar nerve symptoms in patients with flexion-type supracondylar fractures than in those with the more common extension supracondylar fractures and a greater need for open reduction (Kocher in POSNA paper #49 2006). We have encountered a specific pattern of flexion supracondylar fractures that often require open reduction with internal fixation (ORIF) due to entrapment of the ulnar nerve within the fracture.

Medical records and X-rays from 1997 to 2005 at our children's hospital were examined to identify flexion supracondylar fractures that required open reduction. The operative reports were reviewed to identify cases that had the ulnar nerve blocking the reduction.

During the 8 years examined, 1,650 supracondylar fractures had been treated by means of closed reduction and percutaneous pinning. Of these, only 1.8% or 30 cases could not be reduced closed and required open reduction internal fixation, excluding 11 open fractures. Of the 30 fractures requiring open reduction internal fixation, 24 were of the extension type needing ORIF because of interposed periosteum/muscle. The other 6 patients had flexion-type supracondylar fractures that failed closed reduction. All had a persistent medial gap at the fracture site. All 6 fractures had interposed periosteum or muscle, while in 3 cases the ulnar nerve was also entrapped within the fracture site (Figs. 1, 2)

Flexion-type supracondylar fractures remain a relatively uncommon variant (2-3%) of supracondylar fractures. Recent reports have noted that open treatment of these fractures is required more frequently than for extension fractures. In our series, 20% of the open cases were flexion-type fractures and in half of these the ulnar nerve was found to be entrapped in the fracture, preventing reduction.