From the Guidelines
The three most common median nerve variations within the carpal tunnel are bifid median nerve, persistent median artery, and variations in the course of the median nerve, which can be identified using ultrasound (US) due to its high sensitivity and specificity for diagnosing carpal tunnel syndrome (CTS) 1. When evaluating the median nerve within the carpal tunnel, it is essential to consider these variations, as they can impact the diagnosis and treatment of CTS.
- The bifid median nerve is a common variation, where the median nerve splits into two distinct branches, often with a persistent median artery running between them.
- The presence of a persistent median artery can also be a significant variation, which can increase the risk of nerve injury during surgical procedures.
- Variations in the course of the median nerve, such as a more radial or ulnar position, can also be present and may require careful dissection and identification during surgery. The use of US as a diagnostic tool can help identify these variations and guide surgical decisions, reducing the risk of iatrogenic nerve injury 1. In clinical practice, recognizing these median nerve variations is crucial for accurate diagnosis and effective treatment of CTS, and US has emerged as a valuable tool in this context 1.
From the Research
Median Nerve Variations
The median nerve variations within the carpal canal can be classified into different groups based on their anatomical characteristics. According to the Lanz classification, these variations can be categorized as follows:
- Group 0: extraligamentous thenar branch (standard anatomy)
- Group 1: variations of the course of the thenar branch
- Group 2: accessory branches at the distal portion of the carpal tunnel
- Group 3: divided or duplicated median nerve inside the carpal tunnel
- Group 4: accessory branches proximal to the carpal tunnel 2
Common Median Nerve Variations
The three most common median nerve variations within the carpal canal are:
- Bifid median nerve (high division of the median nerve proximal to the carpal tunnel), which has an incidence rate of 2.8% 3 to 2.3% 2
- Variations of the course of the thenar branch (Group 1)
- Divided or duplicated median nerve inside the carpal tunnel (Group 3), which includes the bifid median nerve 2
Clinical Significance
These anatomical variations are important to recognize in order to avoid complications during carpal tunnel release surgery 3, 4, 2. The bifid median nerve, in particular, can facilitate compression of the median nerve in the carpal tunnel due to its increased cross-sectional area 2. Preoperative imaging studies can help identify these variations and guide surgical planning 3.