Cutaneous innervation of the distal forearm and hand — Minimizing complication rate by defining danger zones for surgical approaches

Systematic review of nerves at risk at the wrist in common surgical approaches to the forearm: Anatomical variations and surgical implications

Three commonly used approaches to the forearm in orthopedic surgery are Henry's, Thompson's, and the ulnar approach, each of which has the potential to cause injury to nerves around the wrist. Preserving these nerves is important to prevent complications such as neuroma formation and motor and sensory changes to the hand. We conducted a review of the literature to assess the nerves at risk and whether 'safe zones' exist to avoid these nerves. An independent reviewer conducted searches in Embase and MEDLINE of the literature from 2010 to 2020. A total of 68 papers were identified, with 18 articles being included in the review. Multiple nerves were identified as being at risk for each of the approaches described. In the anterior approach, the palmar cutaneous branch of the median nerve (PCBMN) is most at risk of injury. An incision immediately radial to the flexor carpi radialis (FCR) or directly over the FCR is most likely to avoid injury to both superficial branch of the radial nerve (SBRN) and PCBMN. With Thompson's approach, the safest zone for an incision is directly over or slightly radial to Lister's tubercle to avoid injury to SBRN and lateral cutaneous nerve of the forearm. For the ulnar approach, a safe zone was shown to be on the ulnar side of the wrist around the ulnar styloid (US) when the forearm was in supination or a neutral position to avoid injury to the dorsal branch of the ulna nerve (DBUN). Care must be taken around the US due to the density of nerves and the proximity of the last motor branch of the posterior interosseous nerve to the ulnar head. This review highlighted the proximity of nerves to the three most common surgical incisions used to access the forearm. In addition, anatomical variations may exist, and each of the nerves identified as being at risk has multiple branches. Both factors increase the potential of intraoperative damage if the anatomy is not properly understood. The surgeon must adhere carefully to the established approaches to the wrist and distal forearm to minimize damage to nerves and optimize surgical outcomes for the patient.

Clinical anatomy of the lateral antebrachial cutaneous nerve: Is there any safe zone for interventional approach?

INTRODUCTION

The lateral antebrachial cutaneous nerve (LACN) is a somatosensory nerve coursing in the lateral portion of the forearm. The nerve is located in a close proximity to the cephalic vein (CV) all along its course with a danger of being injured during venipuncture. The LACN also overlaps and communicates with the superficial branch of the radial nerve (SBRN) in the distal forearm and hand, making the awareness of their relationship of great importance in the treatment of neuroma. The aim of the study was to observe the relationship of the LACN to surrounding structures as well as its branching pattern and distribution.

MATERIALS AND METHODS

Ninety-three cadaveric forearms embalmed in formaldehyde were dissected. The relationship of the LACN to surrounding structures was noted and photographed, and distances between the structures were measured with a digital caliper. The cross-sectional relationships of the LACN and SBRN to the CV were described using heatmaps.

RESULTS

The emerging point of the LACN was found distally, proximally or at the level of the interepicondylar line (IEL). The LACN branched in 76 cases (81.7 %) into an anterior and posterior branch at mean distance of 47.8 ± 34.2 mm distal to the IEL. The sensory distribution was described according to the relationship of the LACN branches to the medial border of the brachioradialis muscle. The LACN supplying the dorsum of the hand was observed in 39.8 % of cases. The LACN and the SBRN intersected in 86 % of upper limbs with communications noticed in 71 % of forearms. The LACN was stated as the most frequent donor of the communicating branch resulting in neuroma located distal to the communication and being fed from the LACN. The relationship of the LACN and the CV showed that the IEL is the most appropriate place for the venipuncture due to maximal calibers of the CV and deep position of the LACN. The LACN was adjacent to the cubital perforating vein and the radial artery in all cases. The medial border of the brachioradialis muscle was observed less than 1.8 mm from the LACN.

CONCLUSION

The study provides morphological data on the LACN distribution, branching pattern and relationship to surrounding structures in a context of clinical use in different spheres of medicine. The branching pattern of the LACN appears to be more constant compared to data provided by previous authors. We emphasized the meaning of cross-sectional relationship of the LACN to the CV to avoid venipuncture outside the cubital fossa if possible. The posterior branch of the LACN was predicted as appropriate donor of the graft for a digital nerve. The LACN appeared to be in a close proximity within the whole length of the brachioradialis muscle what the orthopedic surgeons must be concerned of. The meaning of the donor-nerve of the communicating branch in neuroma treatment was also introduced.

Evaluation of the effectiveness of artificial intelligence for ultrasound guided peripheral nerve and plane blocks in recognizing anatomical structures

BACKGROUND

We aimed to assess the accuracy of artificial intelligence (AI) based real-time anatomy identification for ultrasound-guided peripheral nerve and plane block in eight regions in this prospective observational study.

METHODS

After obtaining ethics committee approval and written informed consent from 40 healthy volunteers (20 men and 20 women, between 18 and 72 years old), an ultrasound device installed with AI software (Nerveblox, SmartAlfa, Turkey) were used to scan regions of the cervical plexus, brachial plexus, pectoralis (PECS), rectus sheet, femoralis, canalis adductorius, popliteal, and ESP by three anesthesiology trainees. During scanning by a trainee, once software indicates 100 % scan success of associated anatomic landmarks, both raw and labeled ultrasound images were saved, assessed, and validated using a 6-point scale between 0 and 5 by two expert validators. Evaluation scores of the validators for each block were compared according to demographics (gender, age, and BMI) and block type exists.

RESULTS

The scores were not different except ESP, femoralis, and cervical plexus regions between the experts. The mean scores of the experts for the PECS, popliteal and rectus sheath were significant between males and females (p < 0.05). In terms of BMI, significant differences in the scores were observed only in the canalis adductorius, brachial plexus, and ESP regions (p < 0.05).

CONCLUSIONS

Ultrasound guided AI-based anatomy identification was performed in commonly used eight block regions by the trainees where AI technology can successfully interpret the anatomical structures in real-time sonography which would be valuable in assisting anesthesiologists.

The communication patterns between the lateral antebrachial cutaneous nerve and the superficial branch of the radial nerve

INTRODUCTION

The superficial branch of the radial nerve (SBRN) and the lateral antebrachial cutaneous nerve (LACN) are sensory nerves coursing within the forearm in a close relationship. This high degree of overlap and eventual communication between the nerves is of great surgical importance. The aim of our study is to identify the communication pattern and overlap of the nerves, to localize the position of this communication in relation to a bony landmark, and to specify the most common communication patterns.

MATERIALS

and methods: One hundred and two adult formalin-fixed cadaveric forearms from 51 cadavers of Central European origin were meticulously dissected. The SBRN, as well as the LACN, were identified. The morphometric parameters concerning these nerves, as well as their branches and connections, were measured with a digital caliper.

RESULTS

We have described the primary (PCB) and secondary communications (SCB) between the SBRN and the LACN and their overlap patterns. One hundred and nine PCBs were found in 75 (73.53%) forearms of 44 (86.27%) cadavers and fourteen SCBs in eleven hands (10.78%) of eight cadavers (15.69%). Anatomical and surgical classifications were created. Anatomically, the PCBs were classified in three different ways concerning: (1) the role of the branch of the SBRN within the connection; (2) the position of the communicating branch to the SBRN; and (3) the position of the LACN branch involved in the communication to the cephalic vein (CV). The mean length and width of the PCBs were 17.12mm (ranged from 2.33-82.96mm) and 0.73mm (ranged from 0.14-2.01mm), respectively. The PCB was located proximally to the styloid process of the radius at an average distance of 29.91mm (ranged from 4.15-97.61mm). Surgical classification is based on the localization of the PCBs to a triangular zone of the SBRN branching. The most frequent branch of the SBRN involved in the communication was the third (66.97%). Due to the frequency and position of the PCB with the third branch of the SBRN, the danger zone was predicted. According to the overlap between the SBRN and the LACN, we have divided 102 forearms into four types: (1) no overlap; (2) present overlap; (3) pseudo-overlap; and (4) both present and pseudo-overlap. Type 4 was the most common.

CONCLUSION

The patterns of communicating branch arrangements appeared to be not just a rare phenomenon or variation, but rather a common situation highlighting clinical importance. Due to the close relationship and connection of these nerves, there is a high probability of simultaneous lesion.

Density mapping of nerve endings in the skin of the palm and flexor retinaculum of the hand. Application to open carpal tunnel release

In order to re-evaluate the safest area to incise skin and the flexor retinaculum (FR) when performing a carpal tunnel release (CTR), we carried out a mapping study of the nerve endings in the skin and FR on cadaver specimens, which, unlike previous studies for the first time, includes histomorphometry and image digital analysis. After dividing the skin and FR into 20 and 12 sections, respectively, we carried out a histomorphological analysis of nerve endings. The analysis was performed by two neutral observers on 4-μm histological sections stained with hematoxylin-eosin (H-E), and Klüver-Barrera with picrosirius red (KB + PR) methods. A semi-automatic image digital analysis was also used to estimate the percentage of area occupied per nerve. We observed a lower quantity of nerve endings in the skin of the palm of the hand in line with the ulnar aspect of the 4th finger. The ulnar aspect of the FR was the most densely innervated. However, there are no statistically significant differences between sections in the percentage of area occupied per nerve both in the skin and in the FR. We concluded that there is not a safe area to incise when performing carpal tunnel surgery, but taking into account the quantity of nerve endings present in skin and FR, we recommend an incision on the axis of the ulnar aspect of 4th finger when incising skin and on the middle third of the FR for CTR.

The radiological approach to the carpal tunnel release - An anatomical pilot study

Different techniques are available for carpal tunnel release such as classical surgical operations or minimally invasive procedures. A minimally invasive approach and the relevant regional anatomy are reported in this pilot study which was conducted with bodies from a body donation program. The method described here uses a hook knife to cut through the transverse carpal ligament or flexor retinaculum under ultrasound guidance. The results are documented by means of magnetic resonance and ultrasound imaging as well as by anatomical dissection.

A ratio to approximate the proximodistal extent of the flexor retinaculum in relation to the hand length

The flexor retinaculum of the hand is a fibrous structure forming the carpal tunnel in conjunction with the carpal bones. To prevent incomplete release of the carpal tunnel it is of benefit to know about the expected longitudinal expansion of the flexor retinaculum. The objective of the present study was to identify a possible correlation between the proximodistal expansion of the flexor retinaculum and the length of the hand. We conducted an anatomical study on 124 hands of 62 body donors. The hand length and the length of the flexor retinaculum were measured in millimeters. By dividing the length of the flexor retinaculum by the hand length an individual ratio was calculated. The mean length of the observed hands was 187.8 mm. The mean proximodistal length of the flexor retinaculum was 27.2 mm (range, 14-39 mm). A positive correlation was noted between the proximodistal length of the flexor retinaculum and length of the hand (p = 0.01). On average, the length of the flexor retinaculum corresponded to 14% (range, 8-20%) of the hand length in right hands versus 15% (range, 11-20%) in left hands. A greater proximodistal length of the flexor retinaculum in longer hands compared to shorter hands can be expected. The length of the flexor retinaculum corresponds to 14-15% of the length of the hand. However, one should be aware that the length of the flexor retinaculum extends as far as 20 % of the length of the hand.

Anatomical analysis of antebrachial cutaneous nerve distribution pattern and its clinical implications for sensory reconstruction

This study aimed to reveal the distribution pattern of antebrachial cutaneous nerves and provide a morphological basis for sensory reconstruction during flap transplantation. Forearm specimens containing skin and subcutaneous fat were obtained from 24 upper extremities of 12 adult cadavers. Cutaneous nerves were visualized using modified Sihler's staining. Then the data was used to show the distribution pattern and innervation area of the forearm cutaneous nerve. The anterior branch of lateral antebrachial cutaneous nerve innervates 26% of the medial anterior forearm; the posterior branch innervates 38.21% of the lateral anterior forearm and 24.46% of the lateral posterior forearm. The anterior branch of medial antebrachial cutaneous nerve innervates the medial aspect of the forearm covering 27.67% of the anterior region; the posterior branch the lateral part of the forearm covering 7.67% and 34.75% of the anterior and posterior regions, respectively. The posterior antebrachial cutaneous nerve covers 41.04% of the posterior forearm. Coaptations were found between the branches of these cutaneous nerves. The relatively dense secondary nerve branches were found in the middle 1/3 of the lateral anterior forearm and the middle 1/3 of the medial posterior forearm. The relatively dense tertiary nerve branches were the middle 1/3 and lower 1/3 of the medial anterior forearm. The intradermal nerve branches were the relatively dense in the middle 1/3 of the medial anterior and lateral posterior forearm. The middle 1/3 of the medial and lateral forearm had the relatively dense total nerve branches. These results can be used sensory matching while designing forearm flaps for reconstruction surgeries to obtain improved recovery of sensory.