Biomechanical Analysis of Supracondylar Humerus Fracture Pinning for Slightly Malreduced Fractures

Author(s): Bloom T, Robertson C, Mahar AT and Newton P

Source: J Pediatr Orthop 28:766-772, 2008.

Summary:

There have been a number of recent articles on the treatment and outcome of supracondylar humerus fractures in children.  These articles have shown that pin configuration is an important determinant of outcome.  Adequate pin fixation has reduced the incidence of angular deformities compared with cast only or skeletal traction.  Lateral only configuration or crossed medial and lateral pin fixation have been effective.  Lateral only pin configurations reduces the risk of iatrogenic ulnar nerve injury, and has been shown to be successful in the clinical setting.  This study looked at the effect of internal rotation of the distal fragment on fixation strength via a biomechanical study.  In other words, does the reduction play a part in fracture rigidity after fixation?

The authors utilized a synthetic humerus model.  Osteotomies were created and reduction varied.  The fracture was then reduced in either anatomic position or with an internal rotation configuration.  Clinically, this configuration leads to cubitus varus, which is the most common problem following supracondylar fractures.  A variety of different pin configurations were used ranging from 2 to 3 pins and in different orientation.  Testing was performed with an MTS machine with a variety of forces. 

The authors clearly show that internally rotated fractures were significantly less stable than the anatomic group for parameters of external rotation, internal rotation, and varus loading regardless of pin configuration.  Within the mal-reduced group, 3 pin configurations were more stable than 2 pin configurations.  These results clearly indicate that fracture reduction plays an important role in maintaining reduction.  Persistent internal rotation of the distal fragment will lead to decrease construct strength regardless of the number of pins utilized.  This information needs to be applied in a clinical setting, such that anatomic reduction is a necessary prerequisite to internal fixation, which will optimize the outcome following supracondylar fractures and minimize the complication of cubitus varus.