MRI Volumetric Assessment of Reinnervated Elbow Flexor Muscles Following Nerve Transfer

Purpose: Nerve injury is common following blunt or penetrating trauma. Quantitative magnetic resonance imaging (MRI) parameters have been applied to monitor outcome in pathologies associated with muscle denervation. However, application in muscle reinnervation is awaited. Animal models of nerve injury have shown that data from monitoring muscle mass can be used to predict the likely functional recovery. Therefore, this study aimed to quantify the recovery of muscle volume following a standardized surgical model of elbow flexor muscle reinnervation (Oberlin’s nerve transfer) using quantitative MRI at a range of acute and chronic time points postoperatively. Furthermore, the relationship of muscle volume as assessed with MRI with objective and subjective measures of muscular function was investigated.

Methods and Materials: Patients who underwent Oberlin’s nerve transfer were identified during a retrospective review of the institution’s database at the Peripheral Nerve Injury Unit, Royal National Orthopaedic Hospital. A total of 18 patients (17 male) with a mean age of 34.2 years (range: 23–59 years) were included. Sixteen patients had right-sided and two had left-sided C5–C6 avulsions. All injuries were sustained following road traffic accidents. Patients were followed up with a mean of two MRI scans of their injured arms for a median duration of 224 days (range: 0–1,626 days) postoperatively using multiplanar T1-weighted, proton-density (PD)-weighted, and short tau inversion recovery sequences. Objective (Medical Research Council [MRC]) grading of peak volitional force and subjective measurements (Stanmore Percentage of Normal Elbow Assessment [SPONEA]) of muscular function were recorded at the time of the imaging. Scans of uninjured elbow flexor muscles were acquired from six healthy volunteers and used for comparison. Volumetric analysis of elbow flexor muscles was evaluated by manual segmentation on all the scans (33 injured arms and 6 uninjured arms) using axial PD-weighted images in the NiftyView software package.

Results: Volumetric changes on MRI in elbow flexor muscles preceded the clinical onset of muscle reinnervation (palpable volitional activity) and spontaneous activity on electromyelogram (EMG). The recovery of elbow flexor muscle volume demonstrated a strong and statistically significant correlation (r² = 0.74; p < 0.001) with time following surgery. These changes also demonstrated strong and statistically significant correlations with SPONEA (r² = 0.80; p < 0.01) and MRC grading (r² = 0.78; p < 0.05). Muscle volume that recovered to 42% (ranging between 29% and 72%) of uninjured values was predictive of MRC grade 3 elbow flexion.

Conclusion: Volumetric changes in muscle, as assessed on quantitative MRI, precede changes evident on current clinical assessments of reinnervated muscle (palpable volitional activity and EMG). It is suggested that quantitative MRI volumetric analysis is a responsive assessment measure that relates to objective and subjective measures of muscular function. With further data, this technology can drive the clinical translation of new treatments and assess the likely functional recovery following nerve injury.

Publication History

Article published online:
17 December 2020