BACKGROUND:
The purpose of this study was to identify whether surgical approach affected the incidence of iatrogenic nerve injuries when surgically treating extra-articular humeral shaft fractures (EAHSFs) with meta-diaphyseal extension. Our hypotheses were that the lateral paratricipital approach would lower iatrogenic ulnar and radial nerve palsy, and that lateral intermuscular (IM) septum release would further lower the iatrogenic radial nerve palsy rate. 

METHODS:
A review of all surgically managed humerus fractures from 2010-2018 at a single level 1 trauma center was completed to identify all extra-articular humeral shaft fractures (AO/OTA 12 & 13A2/A3). Two cohorts were compared. 

Group A comprised 37 patients treated by 6 different surgeons from 2010-2018 with various surgical approaches (anterior, posterior, or intramedullary nailing) but without release of the lateral IM septum. 

Group B was a prospectively collected cohort of 34 patients treated from 2015-2018 by a single surgeon employing a lateral intermuscular septum release for every case. Only two surgical approaches were employed in this cohort: lateral paratricipital (LPT) approach for all distal EAHSFs and modified anterolateral approach for all proximal EAHSFs with diaphyseal extension. 

RESULTS:
Pre-operative nerve palsy rate (total, radial, and ulnar) was similar between Group A (4/37, 10.8%; 4/37; 10.8%; 1/37, 2.7%)  and Group B (3/31, 8,8%; 3/31, 8.8%; 0/30, 0%). 

There were no post-operative nerve palsies in group B.

Group A had  statistically higher post-operative nerve palsy rates compared to group B: total nerve palsy (11/33, 33.3% versus 0/31, 0%;  p=0.0004); radial nerve palsy (7/33, 21.1% versus 0/31, 0%; p=0.011); and ulnar nerve palsy (6/36, 16.7% versus 0/34, 0%; p=0.0251)

Subgroup analysis by approach demonstrated that the total post-operative nerve palsy rate was higher in the group A anterior approach when compared to the group B modified anterolateral approach with lateral IM septum release, but only trended toward statistical significance (2/6, 33.3% versus 0/14, 0%; p=0.079). Group A posterior approaches had a statistically higher total post-operative nerve palsy rate  than group B LPT with lateral IM septum release (10/23, 43% versus 0/17, 0%; p=0.002).

Group A posterior approaches were subdivided into the following groups: triceps split, olecranon osteotomy, medial and lateral paratricipital, and LPT. When compared to the group B LPT with lateral IM septum release, group A triceps split had higher post-operative nerve palsy rates: total nerve palsy (4/6, 66.7% versus 0/17, 0%; p=0.0017); radial nerve palsy (3/6, 50% versus 0/17, 0%; p=0.0113) and ulnar nerve palsy (2/7, 28.6% versus 0/20, 0%; p=0.0598).  The group A medial and lateral paratricipital approach had a higher ulnar nerve palsy rate (3/7, 42.9% versus 0/20, 0%; p=0.012). 

CONCLUSION:
For distal EAHSFs, the LPT decreases both radial and ulnar iatrogenic nerve injuries when compared to other posterior surgical approaches. Furthermore, release of the lateral IM septum during surgical fixation of EAHSFs can decrease the incidence of iatrogenic radial nerve injury.

Optimal Surgical Approach for the Surgical Fixation of Extra-Articular Humeral Shaft Fractures to Minimize Iatrogenic Nerve Injury