Abstract
With great eagerness, we have read the article by Gunasagaran et al. titled ‘Video-Assisted Thoracoscopic Surgery (VATS) Aided Full-Length Phrenic Nerve Transfer for Restoration of Elbow Flexion.’ This research article’s results and comparisons between full-length phrenic nerve transfer dissected via VATS and conventional phrenic nerve transfer via sural nerve graft to the musculocutaneous nerve or the motor branch of the biceps were deemed significant among this letter’s authors. As a result, we intend to provide commentary on this study and offer suggestions for future research on this topic.
Gunasagaran et al. compared the functional results of full-length phrenic nerve transfer and conventional phrenic nerve neurotization for restoration of elbow flexion in complete brachial plexus injuries. 1 Recently, full-length nerve transfers have been increasingly used to restore critical upper extremity function. In alignment with this pattern, Gunasagaran et al. found that both groups had improvement in the muscular power of elbow flexion at 3 years post-surgery. The power of elbow flexion was determined by the Medical Research Council (MRC) Muscle Power Scale (MPS), which is widely accepted, frequently used, and is a reliable and valid test of muscle strength. 2 The full-length phrenic nerve transfer group had three patients with a grade of 3 on the MRC Muscle Power Scale and two patients with a score of 4. In the conventional phrenic nerve transfer group, five patients achieved a grade of 3. In each group, two patients did not achieve recovery of the biceps. While this shows the treatment’s significance for return to function in a complete brachial plexus injury, further research and consideration should be given to strengthen the authors’ conclusions. This letter will comment on the consideration of sensory alterations and the use of further examination modalities to consider for the validation of clinical findings.
To begin, the assessment of muscle strength restoration through the MPS is essential for the analysis of return-to-function results for the patients in this study. Ensuring upper extremity dexterity is an important factor of consideration for patients undergoing this classification of nerve transfer and we commend the authors for their detailed discussion of the patients’ recovery of elbow flexion. Nonetheless, we believe that a broader range of evaluation methodologies could have been implemented to capture more detailed aspects of the recovery process. The authors did not make reference to the sensory functional outcomes before or after neurotization and we would suggest providing insight on these aspects, which are relevant to patient function and satisfaction. While less imperative to the overall performance of the patient’s daily maneuverability, restoration of sensation is reported to improve quality of life. 3
Regarding sensation, the researchers could have evaluated this nervous process through the two-point discrimination test, vibration test, and temperature perception tests, as well as evaluating levels of pain and discomfort. By considering the results of these tests, a comparison of these measures could have been made between different patient groups, providing valuable insight into the effectiveness and difference between outcomes among the neurotization surgeries used. It is worth noting that these tests are frequently used for nerve damage assessment and evaluation of sensory outcomes after nerve repair. Therefore, we believe these examinations would provide valuable insight for readers of this manuscript and should be utilized in this study to identify and report patient outcomes and guide future studies.
Lastly, the MRC Muscle Power Scale, utilized in this study is a valid and effective test for gauging the return to function for the patients. Many of the patients achieved a 3 out of 5 or a 4 out of 5 on this scale, which provided them with a re-establishment of their ability to obtain active movement against gravity (score of 3) and against gravity and resistance (score of 4). However, the researchers did not provide information from electromyography (EMG) or nerve conduction studies, which would provide more information on the activity of the muscles and nerves in question. EMG and nerve conduction studies would be useful in this scenario to elucidate how the muscles are responding to nerve impulses pre- and post-operatively. A study by Son et al. found that the compound muscle action potential (CMAP) improved and correlated with the MRC grade as the patients recovered from a brachial plexus injury and underwent nerve transfer operations. 4 Providing this information would bolster this study’s data integrity and the authors’ conclusions regarding the physiological benefits achieved by the techniques employed.
The authors displayed an exceptional aptitude for addressing the implications regarding the phrenic nerve (PN), its innervations, and the implications upon its transfer. Issues that may arise include ipsilateral diaphragm paralysis and respiratory symptoms, yet these issues have been shown to subside in the literature and in this case, they were not seen. 1 Furthermore, the phrenic nerve neurotization performed by the authors provides comparatively magnified value for the patient over these potential detriments, including the ability to maneuver their upper extremities in space. In future research, it would be valuable to consider the analysis of sensory diagnostic measures and the evaluation of nervous electric signaling between pre- and post-operative phrenic nerve transfers. This would provide further insight into the sensory outcomes and the effectiveness of the nerve transfer procedure.
