Abstract
BACKGROUND: Diagnosis and assessment of functional deltoid recovery following axillary nerve injury is challenging due to numerous other muscular contributions to shoulder movement - particularly supraspinatus, rhomboids and long head of triceps. We present the deltoid abduction lag test (DALT) which offers four clear benefits: 1) it successfully isolates deltoid in the presence of a functioning supraspinatus with intact tendon and attachment; 2) it is safe to perform early following anterior shoulder dislocation (the most common cause of axillary nerve injury); 3) it allows assessment of early functional reinnervation of posterior deltoid to aid decision-making with respect to surgical intervention; 4) it is an objective measure which does not rely on patient compliance with initiation of active movement. METHODS: A retrospective review of consecutive patients referred with axillary nerve injury to a national centre for Peripheral Nerve Injury between 2014 and 2024 was conducted. Inclusion criteria was isolated persistent axillary nerve injury confirmed on neurophysiological testing with intact rotator cuff, rhomboid and triceps function. Patients who had undergone prior nerve transfer to address axillary nerve injury were excluded. Patients were independently assessed by two orthopaedic surgeons and a Cohen's kappa (κ) value was calculated to assess inter-rater reliability. The DALT was performed with a goniometer used to measure degree of lag comparative to the coronal plane. Passive range of shoulder movement, rotator cuff / triceps / rhomboid power, upper lateral cutaneous nerve sensation, swallow-tail test, deltoid extension lag test, 'akimbo' test and Bertelli test were documented for both shoulders. RESULTS: Six patients with a mean age of 36 (15-68) were included. The DALT was positive in all cases of ongoing axillary nerve palsy. There was no discrepancy between both surgeons' independent clinical interpretation of the DALT. CONCLUSION: The DALT successfully and reproducibly isolates deltoid function and identifies axillary nerve palsy. We specifically advocate using this test immediately following injury to confirm the presence of an axillary nerve lesion, at 3 months post-injury to identify patients who have experienced a neurapraxic injury and at 6 months to identify axonal lesions which may benefit from surgical intervention.