Fifty intact upper limbs were dissected for evaluation in this cadaveric cross-sectional study which were obtained from the Department of Anatomy, Sri Ramachandra Medical College during August 2020 to December 2020. Ethical clearance was obtained from the Institutional Ethics Committee. (REF:IEC-N1/20/JAN/73/01 dated 24.8.2020).

Inclusion criteria: The upper limbs of normal surface anatomy and bony landmarks of both genders and sides were included in the study.

Exclusion criteria: The upper limbs with trauma, deformity and contractures were excluded from the study.

Radial nerve was exposed by routine dissection in all the upper limbs and its entire course was studied and observed for any variation [9]. For dissection, the limbs were placed in an extended position. An incision was made from the tip of the acromion process to the superior aspect of the olecranon process [10]. The skin and subcutaneous tissues were removed from the back of arm to view the triceps brachi muscle. The long and lateral heads of the triceps were separated. Radial nerve was exposed by incising through the lateral head of triceps, then in the spiral groove between lateral and medial heads of the triceps. The radial nerve was traced upto the elbow as it passes into the anterior compartment of the arm by piercing the LIS.

The distance from the biceps tendon to the radial nerve at the elbow, distance of the radial nerve from its entry point in LIS to the medial epicondyle, distance of the radial nerve from its entry point in LIS to the lateral epicondyle at the elbow were measured. Radial nerve localisation was done in elbow, at LIS using USG techniques [11].

The data was recorded and analysed using SPSS version 16.0. The incidence of each variation was expressed in frequency (N) and percentage. The distance variable was expressed as Mean±Standard deviation.

In present study, the mean distance from the biceps tendon to the radial nerve at the elbow was 1.75±0.22 cm [Table/Fig-1], the mean distance of the radial nerve in the LIS to the medial epicondyle was 12.4±0.31 cm [Table/Fig-2] and to the lateral epicondyle was 12.18±0.28 cm [Table/Fig-3]. The results were compared with those of previous researchers [Table/Fig-4] [1,12,13].

The radial nerve is best exposed by dissection above the lateral aspect of the elbow, where it lies between the brachioradialis and the brachialis muscles [Table/Fig-5]. The nerve divides into the superficial (sensory) and deep (motor) branches in the forearm [Table/Fig-6]. The nerve can be visualised by Ultrasonography 3-4 cm above the elbow crease. [Table/Fig-7a,b]. A single injection at this point blocks both the branches of the nerve. The nerve travels closer to the posterior surface of the humerus in the spiral groove [Table/Fig-8]. There was no variation observed in the course of the radial nerve in the upper limbs.

[Table/Fig-5]:

Radial nerve lying between brachialis and brachioradialis at the elbow.

[Table/Fig-6]:

Radial nerve dividing into superficial and deep branches in proximal forearm.

[Table/Fig-7a]:

USG localisation of Radial nerve at the elbow.

[Table/Fig-7b]:

USG localisation of Radial nerve where it pierces the Lateral Intermuscular Septum (LIS).

[Table/Fig-8]:

Radial nerve in the spiral groove.

Radial nerve lies between the brachialis and brachioradialis muscles, 1 to 2 cm lateral to the biceps tendon at the elbow [1]. In the present study, the mean distance from the biceps tendon to the radial nerve at the elbow was 1.75±0.22 cm. The mean distances between the entry point of the nerve in the LIS and the medial and lateral epicondyles were 133±14 and 110±23 mm, respectively [12]. The radial nerve is prone to injury where it is in relation to the lateral aspect of the humerus in its distal third from 10.9 cm±1.5 proximal to the lateral epicondyle [13].

In the present study, the mean distance of the radial nerve from its entry in the LIS to the medial epicondyle was 12.4±0.31 cm [Table/Fig-2] and to the lateral epicondyle was 12.1±0.28 cm [Table/Fig-3], respectively

The results were compared with those of previous researchers [Table/Fig-4]. Most researchers have only measured the distance of the radial nerve in LIS to the lateral epicondyle [13]. But in the present study, distances from both epicondyles were measured. Researchers have measured the distance of the radial nerve to the triceps aponeurosis [14,15], but in index study, the distance from the biceps tendon was measured.

During surgical fixation of humeral fractures, identification and conservation of the radial nerve may avoid secondary nerve palsy. Improper plate fixation can result in transaction of the radial nerve by screws [16]. Distal-third diaphyseal fractures of the humerus are treated by modified posterior approach [17]. It is possible that the more extensive radial nerve exploration in this approach leads to a higher risk of radial nerve injury [18].

The nerve can be visualised by the Ultrasonography 3-4 cm above the elbow crease. A single injection at this point blocks both the branches of the nerve [11]. This is an important landmark to perform radial nerve block to achieve sensory anaesthesia in its terminal distribution. Such a peripheral nerve block of the radial nerve will be useful in minor surgical procedures in the areas supplied by the nerve. Ultrasound-guided radial nerve block will improve the proper localisation and also ensures safety and decreased duration of the procedure [11].

Landmark based techniques of peripheral nerve block in the upper limb have been restricted to sites at the elbow and wrist where surface landmarks are readily identified [8]. Injection at these levels carries the risk of neurovascular injury. Using ultrasound guidance, the local anaesthetic can be safely injected in other sites also without the risk of neurovascular injury. Variations in upper limb anatomy are commonly identified by ultrasonography. It also helps faster sensory onset of anaestheia, avoiding motor loss and greater block success compared with Landmark based techniques [19].

Hence, the present study will be useful to the Orthopaedic Surgeons to identify the radial nerve during surgical fixation of humeral shaft fractures and prevent it from being injured during surgeries. This study will be of use to the Anaesthesiologists to localise the radial nerve using surface landmarks like lateral and medial epicondyes, biceps tendon and also using ultrasound guidance during peripheral nerve blocks.

The present research study is limited by a small number of specimens and also the measurements were made from disarticulated limbs and hence, gender variation if any could not be found.

A single terminal nerve occasionally needs block in addition to the brachial plexus block with local anaesthetic to have an adequate block for minor surgical procedures of the hand. From present study it can be inferred that effective peripheral blockade of the radial nerve can be achieved by blocking the nerve 1.75 cm lateral to the biceps tendon at the elbow 3 cm above the elbow crease.

Present study helps to understand the surgical anatomy of the radial nerve which would be of use to surgeons in order to avoid iatrogenic injuries to the adjacent neurovascular structures.