Journal of the Anatomical Society of India

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 70  |  Issue : 2  |  Page : 69--74

Anatomical considerations regarding the posterior interosseous nerve for surgical approaches in the proximal forearm: A cadaveric study


Jenny Jacob, Bina Isaac 
 Department of Anatomy, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
Dr. Bina Isaac
Department of Anatomy, Christian Medical College, Vellore - 632 002, Tamil Nadu
India

Abstract

Introduction: The posterior interosseous nerve (PIN) is at risk of injury when surgical procedures are undertaken in the proximal forearm. The aim of the present study was to determine the relationship of the PIN to adjacent anatomical landmarks, which can be used to prevent iatrogenic injury to the nerve. Material and Methods: Forty upper extremities were used for this study. The landmarks used to measure the required parameters were intercondylar reference point, styloid process of ulna, proximal and distal borders of superficial layer of supinator muscle, and head of radius. The number of trunks of PIN and the innervation pattern of supinator muscle were studied. Results: The mean values and standard deviations of the measurements obtained were determined. There was no statistical difference of data between right and left sides. Discussion and Conclusion: The data obtained in the study will be of use to surgeons and orthopedicians during interventional procedures on the proximal part of radius and in decompression procedures of the PIN.



How to cite this article:
Jacob J, Isaac B. Anatomical considerations regarding the posterior interosseous nerve for surgical approaches in the proximal forearm: A cadaveric study.J Anat Soc India 2021;70:69-74


How to cite this URL:
Jacob J, Isaac B. Anatomical considerations regarding the posterior interosseous nerve for surgical approaches in the proximal forearm: A cadaveric study. J Anat Soc India [serial online] 2021 [cited 2021 Oct 25 ];70:69-74
Available from: https://www.jasi.org.in/text.asp?2021/70/2/69/320250


Full Text



 Introduction



The posterior interosseous nerve (PIN) is vulnerable to injury during surgical exposures of the radial head and neck, due to the closeness of the nerve to the proximal radius and the absence of clear intermuscular planes.[1],[2],[3] Moreover, the use of retractors to allow adequate exposure of the radial head and neck could lead to compression or traction injuries of the PIN.[4]

Extensive exposure of the proximal radius is required in cases of fractures of the proximal radius, trauma, and in certain conditions of the elbow.[5] Incisions in radial head fractures are placed over the radial head and knowledge of the relationship of the PIN to the radial head is important in such cases. In addition, decompression procedures undertaken for PIN in cases of its entrapment require the exact localization of PIN.[6],[7]

The radial nerve passes from the posterior to the anterior compartment, after piercing the lateral intermuscular septum in the lateral part of the distal arm. Here, it divides into its two terminal divisions-the superficial branch and the deep branch or the PIN. The PIN descends, passing over the anterior aspect of the elbow joint, and travels deep to the proximal border of the superficial layer of supinator muscle (arcade of Frohse). It passes between the superficial and deep layers of the supinator and after exiting from the supinator muscle gives branches to the muscles of the extensor compartment of the forearm. It travels posterior to the interosseous membrane and anterior to the extensor pollicis longus muscle onto the dorsum of the carpus, where it sends filaments to the ligaments and articulations of the dorsal carpus.[8]

The aim of the present study was to determine the distances of the PIN to certain adjacent landmarks that can be used intraoperatively to locate the nerve and prevent iatrogenic injury during the proximal dissection of the radius. The pattern of innervation of supinator was studied, as it is essential for effective regional anesthetic block and for harvesting the motor branches for nerve transfer procedures.

 Material and Methods



The study was an observational type of study, and the duration of the study was 2 years. Forty embalmed upper limbs belonging to 28 male and 12 female adult cadavers were dissected. The age at death ranged from 40 to 90 years (mean 74.5 years). All the upper limbs were scar free and had no signs of trauma or deformities. Limbs were maintained in a midprone position during dissection. The study was conducted after the approval from the Institutional Review Board.

A vertical incision was made extending 5 cm proximal to the interepicondylar line to the wrist. A fasciocutaneous flap was removed from the lower third of the arm to the middle of the forearm. The radial nerve and its main branches were dissected from the lateral intermuscular septum of arm to the distal arcade of the supinator muscle. The lateral epicondylar muscles were identified. The proximal and distal borders of the superficial layer of supinator were defined, and the PIN was dissected out carefully. All measurements were made with a measuring tape. Measurements included distances from the interepicondylar reference point and styloid process of ulna to exit of PIN from supinator, and distance from the origin of PIN to proximal border of the superficial layer of supinator (arcade of Frohse). The length of the forearm and the distance from the lateral epicondyle to the entry of PIN at the arcade of Frohse were determined.

Other measurements included the distances from the radial head to the entry and exit of PIN from supinator and the distances from the radial head to the proximal and distal borders of superficial layer of supinator. In addition, the number of trunks of PIN, length of PIN within supinator, and the branches to supinator were delineated.

Data were expressed as mean ąnd standard deviation. The data were analyzed by using paired t-test. SPSS, version 16.0 software was used IBM Corp. Newyork, USA.

 Results



The PIN was consistently identified in all 40 embalmed cadaveric forearms. The distances of the PIN from important adjacent anatomic landmarks like midpoint of interepicondylar line (interepicondylar reference point), ulnar styloid process, radial head, and proximal border of superficial layer of supinator (arcade of Frohse) are shown in [Table 1].{Table 1}

The radial head can be easily identified, as it moves during pronation and supination of the forearm. Distances from the radial head to the proximal and distal borders of the superficial layer of supinator offers surgeons a consistent method of predicting the borders preoperatively before making incisions to relieve compression in cases of PIN entrapment [Table 1] and [Figure 1]. There was no statistically significant difference between the sides.{Figure 1}

The distance between the tip of lateral epicondyle and proximal border of superficial layer of supinator muscle (distance AF) and the mean forearm length are shown in [Table 2].{Table 2}

The “ratio AF” was found by dividing the distance AF by the forearm length (ratio AF = distance AF/forearm length). Then, the mean value of the ratio AF was calculated. The mean ratio AF may be used to predict the distance AF of any upper extremity with a known forearm length. Thus, the predicted distance AF of any upper extremity may be found by multiplying its forearm length by the mean ratio AF (predicted distance AF = measured forearm length x mean ratio AF).

The PIN entered most commonly as a double trunk [Figure 2]. Nine of the PIN dissected entered the supinator muscle as a single trunk (22.5%) and 31 entered as a double trunk (77.5%) [Table 2]. The course of the PIN and whether the nerve supplied branches to supinator before entering the muscle or after it entered the muscle interstice were observed and shown in [Table 3].{Figure 2}{Table 3}

The length of PIN within supinator was found to be 48.35 ± 9.37 mm. The average number of total branches supplying supinator was found to be 6.65 ± 1.03, the number of radial branches being 3.30 ± 1.34 and the number of ulnar branches being 3.35 ± 1.46. The type of exit of PIN – whether proximal to the distal border [Figure 3] or at the distal border of supinator are shown in [Table 4].{Figure 3}{Table 4}

 Discussion



There are many studies describing the course and branches of the PIN to the muscles of the forearm.[9],[10],[11] Palsies of the PIN can develop after an unreduced radial head dislocation, associated with proximal ulnar fractures, and with anterolateral dislocations of the radial head.[12] Injury to the PIN is a major potential complication of surgery involving the proximal radius.[1],[5] The posterolateral or Kocher approach, (Kocher, 1911), and the Thompson approach, are two approaches used by surgeons for the proximal radius but these interventions seem to place the PIN at risk of injury.[5],[13] In addition, repair undertaken for the rupture of the distal biceps tendon can jeopardise the safety of the PIN.[14],[15] Injury to the PIN is a known complication in elbow arthroscopy.[16],[17],[18] Hence, it is imperative to visualize and protect the PIN while performing surgical interventions on the proximal radius.[1]

Other causes of paralysis of PIN include neuromas,[19] schwannomas,[20] traumatic aneurysms of the posterior interosseous artery,[21] neurofibromas,[22] and ganglion cysts.[23] Understanding the anatomical relationship between the supinator muscle and the PIN is important to limit the surgical morbidity when interventions are undertaken in that area.[2]

Comparison between studies to locate the PIN intraoperatively using certain anatomic landmarks is shown in [Table 5].{Table 5}

Calfee et al.[1] found the PIN crossed the radius at a mean of 4.2 cm (range, 2.5 to 6.2 cm) distal to the radiocapitellar joint in neutral rotation. During pronation, the distance increased to 5.6 cm (range, 3.1–7.4 cm) (P < 0.01) and in supination, the distance decreased to 3.2 cm (range, 1.7–4.5 cm) (P < 0.01).

In another study, Hohenberger et al.[26] studied the distance between the tip of the radial head and the PIN's exit point from the supinator during maximum supination and pronation. It was found that the distance was significantly shorter during supination in comparison to pronation. With the lateral approach to the proximal radius, the distance was found to be 60.3 mm during supination and 62.7 mm in pronation (P < 0.001). In the dorsal approach, the distance was 60.2 mm during supination and 62.9 mm in pronation (P < 0.001). In the present study, the distance between the tip of the radial head and the PIN's exit point from the supinator in the midprone position of the forearm was found to be 69.45 ± 8.86 mm. Hence, supination should be avoided during the lateral and dorsal approaches to the proximal radius to protect the PIN.

High-resolution ultrasound can help in the rapid assessment of the nerve in cases of posttraumatic radial nerve or PIN palsy. The affected segment of the nerve is identified by decreased echogenicity, change in caliber, or loss of continuity of the nerve. Magnetic resonance imaging helps in identifying soft-tissue details and in characterizing the lesion.[27]

Knowledge of the trunks of PIN and branches of PIN as it passes through the supinator muscle may be useful to neurosurgeons during decompressive or neurotisation procedures. Seradge et al.[28] have reported a case in which the PIN split, with half of the fibers exiting at the distal border of the supinator and the other half exiting proximal to the distal border. If the PIN entered the supinator as two trunks, or branched and exited as two, both have to be decompressed for complete relief of symptoms.

Tubbs et al.[29] conducted a study on the branching pattern of PIN to supinator in 52 cadaveric upper extremities and their findings are compared with those of the present study [Table 6].{Table 6}

Abrams et al.[30] found a mean of 3.9 ± 1.4 branches to the supinator in a study of 20 cadavers, which is similar to the present findings.

The number of trunks of PIN, its length within the supinator, branches to that muscle and exit of PIN is important to the anesthetist, while performing a regional block of PIN for doing surgical exploration in the region of the supinator muscle.[30]

The function of the hand is impaired in lesions of the lower brachial plexus. In C7 – T1 injuries, there is the absence of finger flexion and intrinsic muscle control, as well as thumb and finger extension.[31] Since the supinator is innervated by the upper roots of the brachial plexus, it is unaffected in lower brachial plexus palsy.[30],[31],[32] The motor branches supplying supinator muscle could be transferred directly to the PIN, without using a nerve graft, resulting in a fair return of finger and thumb extension.[31]

 Conclusion



The findings in the present study have documented many potentially useful anatomic landmarks for locating the PIN that can be used intraoperatively during the surgical management of fractures of the proximal radius to avoid iatrogenic injuries. Decompressive procedures undertaken for entrapment neuropathies require intimate knowledge of PIN anatomy. In addition, the findings on the branching pattern of PIN to supinator muscle may be useful when considering transfer of these branches to PIN for restoration of hand function.

Financial support and sponsorship

Fluid research grant

Conflicts of interest

There are no conflicts of interest.

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