“Median nerve hand”: Replacing “T1 hand” in brachial plexus injuries

This editorial letter propose a shift in how we conceptualize a specific pattern of brachial plexus injury, currently known as “T1 hand.” While acknowledging the historical usage of this term, I posit that “median nerve hand” offers a more precise and surgically relevant designation, leading to a clearer understanding of the injury's characteristics and the optimal treatment strategies.

1. Challenging the “T1 hand” paradigm

The term “T1 hand,” introduced by Bertelli and Ghizoni in 2022,¹ describes a C5-C8 brachial plexus root injury with the supposed preservation of the T1 root. This terminology likely stemmed from early observations focused on preserved intrinsic hand muscle function, which was often attributed to T1. However, this label is misleading. It fails to highlight the crucial role of the intact and functional median nerve—formed by contributions from C6-T1—and its branches. Furthermore, it obscures the essential role of C8 in radial nerve-mediated functions, such as wrist and finger extension. While a traditional C5-C7 classification was used for patients with deficits in shoulder abduction, external rotation, elbow flexion/extension, and wrist and finger extension, it is now understood that C8 involvement is a prerequisite for compromising these radial nerve functions. This evolving understanding is supported by clinical evidence highlighting the importance of C8-T1 in upper limb function, especially following these injuries.

This clinical evidence includes: (1) intraoperative electrostimulation findings demonstrating C8-T1 contributions to elbow, thumb, and finger extension; (2) the resultant weakness of thumb and finger extension following inadvertent injury to the posterior division of the lower trunk (C8-T1); and (3) the restoration of elbow, thumb, and finger extension, linked to respiratory effort, after phrenic nerve transfer to the posterior division of the lower trunk.1, 2, 3, 4 The clinical presentation of C5-C8 root injuries varies, particularly regarding the radial nerve territory, with elbow, wrist, and finger extension potentially exhibiting partial preservation or complete paralysis.

Although Bertelli et al.'s¹ work on “T1 hand” reconstruction is valuable, it further reveals the limitations of the current terminology. In their series, intact C5 roots were found in 35 % and combined C5-C6 roots in 3 % of cases, suggesting that the injury pattern is not solely defined by T1 preservation. While they propose a role for T1 in triceps reinnervation in some patients, this is not the primary defining characteristic of this injury pattern.

2. Advocating for “median nerve hand”: A paradigm shift

Shifting to the term “median nerve hand” offers several key advantages:

• 1.Reflecting Preserved Function: This terminology accurately reflects the consistent preservation of median nerve-innervated muscles in this injury pattern. Specifically, the flexor carpi radialis (FCR, C6-C7), pronator teres (PT, C6-C7), and the anterior interosseous nerve (AIN, C8-T1) innervated muscles, flexor pollicis longus (FPL), flexor digitorum profundus (FDP) to the index and middle fingers, and pronator quadratus (PQ) remain functional. These muscles and their corresponding nerve branches are invaluable donor sources for nerve reconstruction.
• 2.Emphasizing Donor Nerve Reliability: The median nerve and its branches are consistently reliable donor nerves in these cases. For example, the FCR branch can restore elbow flexion via transfer to the biceps branch of the musculocutaneous nerve. Similarly, the FDS (C8, T1) or AIN branch can reinnervate the ECRB branch to restore wrist extension. If the posterior interosseous nerve (PIN) shows weak function, the FCR branch can augment wrist and finger extension through side-to-end coaptation. In my experience with over 20 such cases, along with observations from Bertelli et al.,¹ the ulnar nerve is often weak and unreliable as a donor, frequently exhibiting minimal or no contraction during intraoperative stimulation.
• 3.Guiding Surgical Strategy: “Median nerve hand” immediately informs surgeons of reliable median nerve donor availability, facilitating more precise surgical planning and targeted nerve transfers. This ultimately optimizes patient outcomes and minimizes donor site morbidity.
• 4.Highlighting Practicality: This designation offers a pragmatic perspective that directly informs surgical decision-making, unequivocally pointing to the median nerve as the key to restoring function.
• 5.Accurate Neuroanatomical Representation: The term accurately reflects the neuroanatomy of the injury, acknowledging that functional muscles receive innervation from C6, C7, C8, and T1 nerve roots, all integral components of the median nerve. It avoids the misleading focus on T1 alone, as in the previous “T1 hand” designation.

3. Supporting evidence from myotomal studies: The Chiba et al.⁵ findings

Recent research by Chiba et al.⁵ provides compelling support for the “median nerve hand” designation. Their study on myotomal innervation patterns revealed a crucial finding: median-innervated forearm flexor muscles, specifically the FDS, FDP (index finger), and FPL (excluding pronator teres and FCR), receive dominant T1 innervation. This is particularly relevant to the “median nerve hand” pattern, as it demonstrates that in C5-C8 root injuries with preserved median nerve function, these T1-dominant muscles are likely to remain functional and available for use as donors. This challenges the traditional view that T1 primarily innervates intrinsic hand muscles and underscores the median nerve's pivotal role in this injury pattern. Furthermore, Chiba et al. found C8-dominant innervation of ulnar-innervated forearm flexor muscles (FCU and FDP-ring finger), supporting the clinical observation of a frequently weaker ulnar nerve in “median nerve hand” cases, where the C8 root is typically compromised. These findings refine our understanding of myotomal innervation and improve localization in clinical neurology. For instance, the dissociated weakness between the FDP-index finger (median nerve, T1-dominant) and FDP-ring finger (ulnar nerve, C8-dominant) muscles, a characteristic also seen in our case series, can now be interpreted not only as a potential sign of a peripheral nerve lesion but also as an indicator of a segmental lesion involving the C8 root, as observed in the “median nerve hand” pattern.

4. Anatomical considerations in “median nerve hand"

The anatomical configuration of the infraclavicular brachial plexus further supports the “median nerve hand” concept. The lateral cord (C5, C6, C7) and medial cord (C8, T1) converge to form the median nerve. The lateral root crosses the axillary artery to join the medial root, creating a robust median nerve. In this injury pattern the median nerve typically demonstrates significantly greater strength upon electrical stimulation than the ulnar nerve derived from medial cord. Therefore, the use of the median nerve as a donor is consistently reliable, while the ulnar nerve's utility is less certain. Additionally, patients with this injury pattern often exhibit minimal or weak thumb and finger extension upon stimulation of the posterior cord, the radial nerve in the arm, or the PIN in the forearm. This diminished extensor function likely results from the compromised contribution of the posterior division of the lower trunk (C8-T1), which is typically involved in this type of brachial plexus injury and provides innervation to these extensor muscles. This often presents a challenge for surgeons, making it difficult to determine the optimal strategy between immediate nerve transfers versus delayed tendon transfers to restore hand function. The term “median nerve hand” offers a clearer direction.

5. Acknowledging the nuances: Anatomical variations and the ‘median nerve hand

While the “median nerve hand” concept offers a valuable framework for understanding and treating this specific brachial plexus injury pattern, it is crucial to acknowledge its nuances. Anatomical variations, particularly in the median nerve's communication with other nerves, can significantly influence the clinical presentation and intraoperative findings. The presence of neural interconnections such as the Martin–Gruber anastomosis (MGA) between the median and ulnar nerves in the forearm, the Marinacci anastomosis (MA) (a reverse MGA), the Riche–Cannieu anastomosis (RCA) between the deep branch of the ulnar nerve and the recurrent thenar branch of the median nerve in the hand, and the Berrettini anastomosis (BA) between the digital sensory branches of the median and ulnar nerves can alter the expected pattern of muscle weakness and the availability of donor nerves. These variations may manifest as atypical presentations or unexpected responses during intraoperative nerve stimulation, necessitating surgical adaptability. A thorough understanding of these anatomical variations, including their prevalence and potential impact, is therefore essential for accurate diagnosis and optimal surgical management. Thus, while “median nerve hand” provides a useful conceptual model, careful clinical and electrophysiological assessment, coupled with meticulous intraoperative evaluation, remains paramount in each individual case. Future research should investigate the prevalence and clinical significance of these anastomoses in patients presenting with the “median nerve hand” injury pattern.

6. Conclusion

The term “T1 hand” is an inadequate descriptor that fails to capture the pivotal role of the median nerve in both the clinical presentation and surgical management of this specific brachial plexus injury pattern. “Median Nerve Hand” provides a more precise, clinically relevant, and surgically informative designation. It emphasizes the preserved function, highlights the donor potential, and clarifies the surgical implications associated with the median nerve. This ultimately leads to a more profound understanding and improved treatment of these challenging injuries. The supporting evidence from Chiba et al.'s¹ myotomal studies further validates the importance of the median nerve and its T1-innervated forearm muscles in this context. While acknowledging the potential influence of anatomical variations, I strongly encourage the field to consider embracing this terminology to enhance communication and advance patient care.

Disclosure of interest

The authors declare that they have no known competing financial or personal relationships that could be viewed as influencing the work reported in this paper.

Author contributions

All authors attest that they meet the current International Committee of Medical Journal Editors (ICMJE) criteria for Authorship. Individual author contributions are as follows:

J. Terrence Jose Jerome, effectively contribute in collecting datas, review and writing.

Funding

Nil funding.