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Elevated Body Mass Index Negatively Impacts Recovery of Shoulder Abduction Strength in Triceps to Axillary Motor Nerve Transfers
Aneesh Karir, MD1, Linden K Head, MD, HBA, BSc, BPHE2, Maria C Médor, MD1, Gerald Wolff, BSc, MD, FRCSC3 and Kirsty Usher Boyd, MD, FRCSC4, (1)University of Ottawa, Ottawa, ON, Canada, (2)Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada, (3)Division of Physical Medicine and Rehabilitation, University of Ottawa, Ottawa, ON, Canada, (4)Department of Surgery, Division of Plastic Surgery, University of Ottawa, Ottawa, ON, Canada

INTRODUCTION: Axillary nerve injury resulting in deltoid paralysis yields marked disability to shoulder function. Triceps to axillary motor nerve transfer is one option for shoulder reanimation in patients with axillary nerve injuries. A growing body of research has explored the outcomes of this nerve transfer, with patients reliably achieving at least Medical Research Council (MRC) grade 3 deltoid strength and greater than ninety degrees of shoulder abduction. Despite this, there remains a scarcity of information regarding patient selection and factors influencing outcomes of these nerve transfers. The purpose of this work was to evaluate the clinical outcomes of triceps to axillary nerve transfers and to identify prognostic factors which may influence these outcomes.

METHODS: A retrospective cohort of prospectively collected data included all patients who underwent a triceps to axillary nerve transfer (2010-2019) who had a minimum of 12-months follow-up. Data was collected regarding demographics, comorbidities, injury etiology, as well as preoperative and postoperative clinical assessments. The primary outcome measure was shoulder abduction strength assessed with MRC. Statistical analysis was performed using parametric and non-parametric statistics.

RESULTS: Ten patients (90% male, mean age 45.8 ± 16.9 years) were included with a mean follow-up of 19.1 ± 5.9 months. Patients had either an isolated axillary nerve injury (40%) or brachial plexus injury (60%). The most common etiology was secondary to trauma (90%). Mean time from injury to surgery was 5.4 ± 1.7 months. The difference in mean preoperative (0.2 ± 0.4) and postoperative MRC (2.8 ± 1.6) for shoulder abduction was statistically significant (p=0.005). Increased body mass index (BMI) was significantly associated with worse postoperative MRC (p=0.014). Patients with a 'Normal' (18.5 - 24.9) BMI had a mean postoperative MRC of 4.3 ± 0.5 (n=4), whereas patients who were 'Overweight' (25 - 29.9) or 'Obese' (>30) had a mean postoperative MRC of 2.5 ± 2.1 (n=2) and 1.5 ± 1.0 (n=4), respectively. There were no significant differences in outcomes based on age, time to surgery, or the presence of comorbidities.

CONCLUSIONS: This retrospective study adds to the growing body of literature demonstrating that triceps to axillary motor nerve transfer can be used for shoulder reanimation in axillary nerve injuries. Notably, patients with elevated BMI may not have as robust strength recovery following triceps to axillary motor nerve transfer - this should be an important consideration in patient selection and be appropriately integrated into patient counselling regarding prognosis.
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