Anatomic study of posterior interosseous nerve in the arcade of Frohse

Danger zone for screw placement in minimally invasive plate osteosynthesis (MIPO) of diaphyseal fractures of forearm: a cadaveric study

PURPOSES

To identify the anatomical relationship between neurovascular structures and screws and to evaluate the danger zone of screw placement during minimally invasive plate osteosynthesis (MIPO) technique following the volar approach for the radius and the subcutaneous approach for the ulna in diaphyseal forearm fractures.

METHODS

Sixteen cadaveric forearms were fixed with a 3.5-mm, 14-hole, locking compression plate (LCP) using the MIPO technique with a volar approach of the radius. Two locking screws were fixed at each end via two separated incisions, and the remaining ten  screws were inserted percutaneously. The same MIPO technique was performed at the ulna with the subcutaneous approach. The forearms were then dissected to identify any damage to or direct contact between the screws and the radial artery (RA), the superficial branch of the radial nerve (SBRN), the posterior interosseous nerve (PIN), and the dorsal cutaneous branch of the ulnar nerve (DCBUN). The distances from the screws to the structures at risk, as well as the radial and ulnar length, were measured.

RESULTS

The average lengths of the radius and ulna were 24.74 cm and 25.93 cm, respectively. On the volar aspect of the radius, the danger zones of RA and SRN were between 15.26 and 81.24% of the length of the radius from the radial styloid. The zone of PIN injury at the posterior aspect of the radius was between 41.45 and 81.24% of the length of the radius from the radial styloid. Meanwhile, the danger zone of DCBUN was between 12.21 and 27.23% of the ulnar length from the ulnar styloid.

CONCLUSION

Based on our study, the percutaneous screw fixation in MIPO for the treatment of diaphyseal fractures of the forearm is a dangerous procedure, especially for the volar approach of the entire radius and the subcutaneous approach of the distal ulna.

The arcade of Frohse: a systematic review and meta-analysis

PURPOSE

The structure of the proximal margin of the superficial layer of the supinator muscle is of high interest to many researches. Its tendinous appearance, called the arcade of Frohse, may be clinically important because of its close relationship to the deep branch of the radial nerve passing beneath it and is considered to be the cause of several syndromes. Given the importance of this structure, we aimed to provide a comprehensive and evidence-based review with meta-analytic techniques.

MATERIALS AND METHODS

The meta-analysis was performed in adherence to the PRISMA guidelines. Three medical databases were searched in order to identify all potentially eligible articles. Included studies were assessed for quality and the extracted morphological and morphometric data from the relevant articles was analyzed with the use of random effects meta-analysis.

RESULTS

A total of 20 studies were included into this meta-analysis. The pooled prevalence of the arcade of Frohse was calculated to be 66% within the adult population and 0% in the fetuses. Other variations regarding the arcade of Frohse were identified as very rare. Analysis of the morphometric parameters revealed the average proportions to be 23.22 mm for the length, 11.05 mm for the width and the mean thickness is 0.67 mm.

CONCLUSIONS

The arcade of Frohse is a commonly found structure in adults and thoughtful knowledge of its texture and morphology is especially useful in neurology, neurosurgery, orthopedics, trauma surgery and hand surgery, because it is considered to be the most common source of compression for the deep branch of the radial nerve.

Evaluation of the supinator muscle and deep branch of the radial nerve: impact on nerve compression

PURPOSE

The aim of this study was to investigate the superficial head of supinator muscle (SM) and deep branch of the radial nerve (DBRN) course in SM to see whether the texture characteristics of the superficial head of SM might have a potential compressive effect on the nerve.

MATERIALS AND METHODS

Elbow and proximal forearm region of 20 preserved cadavers (n 40, 12 M, 8 F) were dissected in order to measure total and part of DBRN lengths between some reference points. The texture characteristics of both the proximal (where DBRN enters SM) and distal arcade (where DBRN exits SM) of the superficial head of SM were evaluated based on its structure's being muscular, musculotendinous, tendinous, or membranous.

RESULTS

The total length of DBRN between sexes without taking side (L/R) into consideration (P = 0.030) and left radiocapitellar joint (RCJ)-arcade of Frohse (AF) length between sexes (P = 0.050) were statistically significant. There was a gradual increase in caliber getting more flattened in every consecutive level which was statistically significant when every two consecutive levels were compared. When compared according to the texture type, there were also significant differences.

CONCLUSIONS

Flattening of DBRN in the supinator canal suggests a chronic compression on the nerve. Differences in the texture of the superficial head of the supinator might facilitate this compression. An understanding of the anatomy and nerve topography is of utmost importance in the accurate diagnosis and effective management of peripheral nerve compression.

The posterior interosseous nerve crosses the radial head midline and increases its distance from bony structures with supination of the forearm

BACKGROUND

This study investigated whether forearm movements change the relative position of the posterior interosseous nerve (PIN) with respect to the midline of the radial head (Rh) under direct arthroscopic observation.

METHODS

The PIN was identified in 10 fresh frozen cadaveric specimens dissected under arthroscopy. The forearm was moved first in full pronation and then in full supination, and the displacement of the PIN from medial to lateral with respect to the midline of the Rh was recorded. The shortest linear distance between the nerve and the most anterior part of the Rh was measured with a graduated calliper inserted via the midlateral portal with the forearm in neutral position, full pronation, and full supination.

RESULTS

The PIN was identifiable in all specimens. In all cases the PIN crossed the Rh midline with forearm movements, moving from medial in full pronation to lateral in full supination. The distance between the PIN and Rh is significantly greater in supination than in the neutral position and pronation (P = .0001).

CONCLUSIONS

This study confirms that the PIN movement described in open surgery (medialization with pronation) also occurs during arthroscopy. The role of pronation in protecting the PIN in extra-articularprocedures is therefore confirmed. Supination, however, increases the linear distance between the PIN and Rh and should therefore be considered to increase the safe working volume whenever intra-articular procedures are performed on the anterolateral aspect of the elbow.

Ultrasonographic reference values for the deep branch of the radial nerve at the arcade of Frohse

PURPOSE

The deep branch of the radial nerve (DBRN) enters the forearm as it passes under the arcade of Frohse. This is the most common entrapment site of the DBRN in the forearm. In this study, we investigated the ultrasonographic reference values for the diameters and cross-sectional area (CSA) of the DBRN at the level of the arcade of Frohse in a healthy sample of the population.

METHODS

Sixty-five healthy Caucasian volunteers (130 nerves) were recruited for this study. The reference range [mean ± 2 standard deviations (SD); 2.5th-97.5th quintiles] and the upper limit of the side-to-side difference were determined. The effects of age, gender, handedness, height, and body mass index were examined.

RESULTS

The mean age was 41.8 ± 11.2 years (range 18-75 years). The mean ± 2SD of the CSA was 0.50-1.42 mm². The upper limit of the normal side-to-side difference was 0.35 mm². The differences between males and females and between the dominant and non-dominant arms were not significant. The mean anteroposterior and transverse diameters were 0.83 ± 0.13 and 1.23 ± 0.29 mm, respectively. A significant correlation between the dominant-side CSA and age (r = 0.41; p < 0.001) was observed. The correlations between CSA and height (r = 0.19; p = 0.12) and body mass index (r = 0.22; p = 0.07) were not significant.

CONCLUSION

The measurements obtained in this study are valuable for examining DBRN pathologies using high-frequency ultrasound. The findings showed that age was associated with the DBRN CSA, while gender, height, and body mass index were not.

Avoiding radial nerve palsy in proximal radius shaft plating - a cadaver study

BACKGROUND

Opinions vary concerning the position of forearm rotation during detachment of the supinator in radial nerve palsy Henry's and Thompson's approaches.

PURPOSE

To define the optimal forearm position for a safe detachment of the supinator during these approaches and to clarify their close relationship to the posterior interosseous nerve (PIN).

METHODS

The study sample comprised 90 upper extremities of 45 human adult cadavers, embalmed using Thiel's method. After detection of the radial nerve in the interval between the brachialis and brachioradialis, its pathway was traced to the Arcade of Frohse (AF). Measurements involved the distance between the AFand the radial border of the distal biceps tendon (DBT) in pronation and supination, the interval between the AF and the radiocapitellar joint space (RCJS) in supination and the radial length (RL).

RESULTS

Distances between the DBT and the AF were significantly shorter during pronation (right side: 14.1 ± 3.4mm; left side: 13.5 ± 3.2mm) compared with supination (right side: 20.5 ± 3.6mm; left side: 19.8 ± 3.5mm) for both right and left extremities. The mean interval between the AF and the centre of the RCJS was 25.2 ± 5.9mm for the right side and 24.7 ± 5.6mm for the left side, which correlated positively with the RL.

CONCLUSION

These results indicate a safe detachment of the supinator from the radius with the forearm placed in supination during both Henry's and Thompson's approaches.

Distance of the Posterior Interosseous Nerve from the Radial Head during Elbow Arthroscopy: An Anatomical Study

Purpose  The aims of this study were to measure the distance of the posterior interosseous nerve (PIN) from the radial head (RH) and its variations with forearm movements.

Methods  Five fresh frozen cadaver specimens were dissected under arthroscopy. An anterior capsulectomy extended to the entire lateral compartment was performed. The need of soft tissue dissection to isolate the nerve in the extracapsular space was recorded. The distance between the nerve and the anterior part of the RH was then measured with a graduated caliper inserted via the midlateral portal with the forearm in neutral position, full pronation, and full supination.

Results  The PIN was identifiable in all the specimens. In four cases, it was surrounded by a thick layer of adipose tissue, and further dissection was necessary to isolate it. Damage of the PIN during dissection occurred in one case, in which the proximal part of the nerve was accidentally cut. In three of the remaining cases, an increased distance was measured with the forearm in supination, as compared with neutral and full pronation position.

Conclusion  This anatomical study suggests that in most of the cases, the PIN does not lay just extracapular at the level of the radiocapitellar joint, but is surrounded by a thick layer of adipose tissue. Furthermore, its distance from the RH appears to increase with forearm supination. This position could increase the safe working space between RH and PIN.

Clinical Relevance  Knowledge of PIN position in relation to the anterior elbow capsule and its changes with forearm movements can help reduce the iatrogenic injuries during elbow arthroscopy.

Anatomic cadaveric study of the extensile extensor digitorum communis splitting approach for exposing the ulnar coronoid process

BACKGROUND

The extensile extensor digitorum communis (EDC) splitting approach can access the ulnar coronoid process (UCP), which can be used to treat terrible triad injuries. The present study anatomically examined the extensile EDC splitting approach for exposing the UCP.

METHODS

Twenty fresh frozen cadaveric upper limbs were dissected. The splitting length of the EDC and detachment length of the extensor carpi radialis brevis (ECRB)-extensor carpi radialis longus (ECRL)-brachioradialis (BR) origin were measured to expose the UCP. The distance between the most distal site of the EDC splitting and the point at which the posterior interosseous nerve (PIN) crosses the anterior aspect of the radial shaft, and the distance between the most proximal site of the ECRB-ECRL-BR origin detachment and the point at which the radial nerve crosses the anterior aspect of the humeral shaft were measured.

RESULTS

The splitting length of the EDC was 45.4 ± 4.8 mm, the detachment length of the ECRB-ECRL-BR origin was 30.2 ± 4.7 mm, the distance between the distal site of the EDC splitting and PIN was 10.6 ± 6.1 mm (minimum distance, 1.1 mm), and the distance between the proximal site of the ECRB-ECRL-BR origin detachment and the radial nerve was 49.5 ± 9.7 mm (minimum distance, 31.7 mm).

CONCLUSIONS

The extensile EDC splitting approach can sufficiently expose the UCP. However, splitting must be performed carefully because the most distal site of the EDC splitting is close to the point at which the PIN crosses the anterior aspect of the radial shaft (average distance, 10 mm; minimum distance, 1 mm).

Effect of elbow flexion on the proximity of the PIN during 2-incision distal biceps repair

The posterior interosseous nerve (PIN) is at risk for injury during surgical dissection for distal biceps repair, yet the optimal position of elbow flexion to avoid a PIN injury has never been established for the 2-incision approach. The purpose of this study was to determine the proximity of the PIN to the radial tuberosity during surgical dissection in different degrees of elbow flexion. Ten cadaveric specimens with an intact elbow and forearm were dissected in full pronation using a modified Boyd-Anderson approach. Half of the dissections were completed in 90° of flexion and the other half were completed in maximal flexion. To simulate the location of the PIN during a single-incision biceps repair, the distance of the PIN to the radial tuberosity was recorded in full extension and supination. Results from these measurements were assessed for differences using paired t tests, with differences deemed significant for P values less than .05. The PIN was not identified in any of the 2-incision surgical dissections. Based on these findings, the proximity of the PIN to the radial tuberosity is not significantly affected by the degree of elbow flexion in the muscle-splitting 2-incision approach. In addition, a safe zone exists for avoiding PIN injury in a single-incision technique for distal biceps repair because a drill bit exiting the radial tuberosity greater than 1 cm in a distal-radial direction would place the PIN at risk.

Posterior interosseous nerve palsy in a child associated with recurrent dislocation of the head of the radius

Injuries to the posterior interosseous nerve (PIN) appear to be very uncommon in children. In this paper, the authors describe a 9-year-old boy with a radial malunion and radial head instability that resulted in PIN compression. Surgical decompression via transection of the overlying supinator muscle with correction of the radial deformity and instability resulted in complete return of PIN function. The clinician should be aware of anterior dislocation of the radial head as a cause of PIN injury. Based on the authors' experience, nerve decompression and correction of the bone deformity result in return of normal PIN function.

The supinator muscle: anatomical bases for deep branch of the radial nerve entrapment

PURPOSE

Our goals were to carry out an anatomical description of the internal architecture of the supinator muscle in order to describe potentially compressive structures for the deep branch of the radial nerve (DBRN) and to establish reference landmarks for the surgical treatment of radial tunnel syndrome.

METHODS

Thirty upper limbs were dissected. The pennation angle of proximal and distal arcades of the supinator to the radial shaft axis was measured. Possible compressive structures of both superficial and deep heads of supinator were recorded. Proximal and distal arcades of the superficial layer of the supinator were classified according to their fiber content as tendinous, musculo-tendinous, muscular or membranous. The distances of superficial layer of the supinator muscle to the humeroradial joint line and lateral epicondyle were measured.

RESULTS

Pennation angle was 33.6° (±4.2°) for the superficial layer and 50.2° (±6.6°) for the deep layer. The difference was statistically significant (p < 0.0001). The proximal arcade was purely tendinous in 20 cases (66.7 %). The distal arcade was mainly tendinous or musculo-tendinous (70 %). The average distance between the lateral epicondyle and the proximal arcade was 41.6 mm. We did not find any other potentially compressive structure within DBRN course between both layers.

CONCLUSION

Our anatomical results about pennation angle could be used as a basis for a thorough functional study about the supinator. Both proximal and distal arcades appeared as the two zones ables to compress the DBRN. Their localization should help the surgeon for the DBRN neurolysis.

Physical examination of upper extremity compressive neuropathies

A thorough history and physical examination are vital to the assessment of upper extremity compressive neuropathies. This article summarizes relevant anatomy and physical examination findings associated with upper extremity compressive neuropathies.

Variations in the anatomic relations of the posterior interosseous nerve associated with proximal forearm trauma

BACKGROUND

The posterior interosseous nerve is at risk for iatrogenic injury during surgery involving the proximal aspect of the radius. Anatomic relationships of this nerve in skeletally intact cadavers have been defined, but variations associated with osseous and soft-tissue trauma have not been examined. This study quantifies the effect of a simulated diaphyseal fracture of the proximal aspect of the radius and of a radial neck fracture with an Essex-Lopresti injury on the posterior interosseous nerve.

METHODS

In twenty unembalmed cadaveric upper extremities, the distance from the radiocapitellar joint to the point where the posterior interosseous nerve crosses the midpoint of the axis of the radius (Thompson approach) was recorded in three forearm positions (supination, neutral, and pronation). Specimens were then treated with either proximal diaphyseal osteotomy (n = 10) or radial head excision with simulated Essex-Lopresti injury (n = 10), and the position of the nerve in each forearm position was remeasured. We evaluated the effect of the simulated trauma on nerve position and correlated baseline measurements with radial length.

RESULTS

In neutral rotation, the posterior interosseous nerve crossed the radius at a mean of 4.2 cm (range, 2.5 to 6.2 cm) distal to the radiocapitellar joint. In pronation, the distance increased to 5.6 cm (range, 3.1 to 7.4 cm) (p < 0.01). Supination decreased that distance to 3.2 cm (range, 1.7 to 4.5 cm) (p < 0.01). Radial length correlated with each of these measurements (r > 0.50, p = 0.01). Diaphyseal osteotomy of the radius markedly decreased the effect of forearm rotation, as the change in nerve position from supination to pronation decreased from 2.13 ± 0.8 cm to 0.24 ± 0.2 cm (p = 0.001). Proximal migration of the radius following radial head excision was accompanied by similar magnitudes of proximal nerve migration in all forearm positions.

CONCLUSIONS

Forearm pronation has minimal effect on posterior interosseous nerve position within the surgical window following a displaced diaphyseal osteotomy of the proximal aspect of the radius. The nerve migrates proximally toward the capitellum with proximal migration of the radius in all forearm positions following a simulated Essex-Lopresti lesion. Visualization and protection of the posterior interosseous nerve is recommended when operatively exposing the traumatized proximal aspect of the radius.

Innervation of the supinator muscle and its relationship to two-incision distal biceps tendon repair: an anatomic study

Reinsertion of the ruptured distal biceps tendon has been performed using either a single-anterior incision or a two-incision approach. A systematic review of these two repair methods has identified a higher incidence of supination weakness following the two-incision approach. The objective of this study was to describe the innervation of the supinator muscle and its implications regarding a two-incision distal biceps repair. Twelve fresh upper extremity specimens from 12 males were dissected with the forearm in full pronation. The number of branches of the posterior interosseous nerve (PIN) to the supinator, their site of exit from the PIN trunk, and their distance from a variety of known anatomic landmarks were recorded. Specimens were characterized as high (<5 mm), moderate (6-10 mm), or low (>10 mm) risk of nerve branch injury depending on the proximity of nerve branches to the bicipital tuberosity. In general, we found the innervation of the supinator to be highly variable. There were from two to nine branches of the PIN which supplied the supinator, with 0-3 arising from the ulnar side of the nerve. Four specimens were at low, five at moderate, and three at high risk of nerve branch injury during dorsal exposure of the bicipital tuberosity. We conclude that there is a substantial amount of variability in the innervation of the supinator, with certain patterns being at higher risk of nerve branch injury if dissection of the supinator is carried out over the bicipital tuberosity.

Frohse's arcade is not the exclusive compression site of the radial nerve in its tunnel

INTRODUCTION

The radial tunnel is a musculo-aponeurotic furrow which extends from the lateral epicondyle of humerus to the distal edge of the supinator muscle. The superficial head of the supinator muscle forms a fibrous arch, the arcade of Frohse (AF), which is the most common site of compression of the radial nerve motor branch. The latter is less commonly compressed by the adjacent muscular structures. This tunnel syndrome might be worsened with repeated pronation and supination of the forearm. The double object of that work was: (1) to define the radial nerve anatomic landmarks, (2) to determine the anatomical relationship of the radial nerve main trunk and branches to the peripheral osseous and muscular structures in the anterior aspect of the elbow joint in order to identify which of these conflicting elements are likely to cause a compressive neuropathy.

MATERIAL AND METHODS

The study design involved the dissection of 30 embalmed cadaveric upper limbs. Anatomic and morphometric investigations of the radial nerve, its terminal and motor branches were carried out. The presence of adhesions between radial nerve and joint capsule, tendons and aponeurotic expansions of epicondylar muscles and supinator arch was investigated. All measurements were taken in both pronation and supination of the forearm.

RESULTS

Neither macroscopic radial compressive neuropathy at the level of the supinator arch nor adhesions between the radial nerve and the joint capsule were found. In four cases (13%), dense fibrous tissue surrounded the radial nerve supply to extensor carpi radialis brevis (ECRB). The fibrous arch of the supinator muscle arose in a semi-circular manner and was noted to be tendinous in 87% of the extremities and of membranous consistency in the remaining 13%. The length of the AF averaged 25.9 mm. The angle formed by the radial shaft and the supinator arch was 23 degrees. Neither fibrous structures nor adhesions of the deep branch of the radial nerve (DBRN) along its course through the supinator muscle were observed.

DISCUSSION

Anatomic studies have revealed a variable rate of occurrence of a tendinous AF, which range from 30 to 80% (87% in our study) according to authors. It is reported to be a predisposing factor to the development of chronic entrapment neuropathy of the DBRN, especially if it is thick and provides a narrow opening for passage of the DBRN. The tendinous consistency of the supinator arch is believed to develop in adults, in response to repeated rotary movements of the forearm. Repetitive pronation and supination of the forearm induces compression of the radial nerve and its branches between two inextensible structures. The fibrous AF and the proximal end of the radius (radial head and radial tubercle). This condition is aggravated by the supinator muscle repeated activity. Repetitive compression might then promote histological changes in radial tunnel content and progressive development of a local fibrous zone. We also observed that the radial nerve supply to ECRB could be entrapped between the superolateral aspect of the ECRB and the superior edge of the supinator muscle.

The course and branching pattern of the deep branch of the radial nerve in relation to the supinator muscle in fetus elbow

We aimed to make first demonstration of the course and branching pattern of deep branch of the radial nerve (DBRN) in relation to the supinator muscle in the forearms of fetuses and make morphological measurements in both fetuses and adults. We carried out dissection on 80 radial nerves from 20 adult cadavers (16 males and 4 females), ranging from 30 to 56 years old and 20 formalin-fixed, spontaneously aborted fetuses (10 males and 10 females) without detectable malformations, ranging from 20 to 37 weeks of gestation. There were three different branching patterns of the DBRN in fetuses. It divided its terminal branches at entrance of the supinator in 2 (5%), after entry of the supinator in 4 (10%) and after the supinator in 34 (85%) forearms. The course was bilaterally same in fetuses. Dividing pattern at the entrance of the supinator was not seen in adults. Only 4 (10%) were seen at after entering to the supinator and 36 (90%) were seen at after the supinator. We saw in fetuses neither fibrous band deep from the extensor carpi radialis longus nor upper border of the supinator. We assume that these fibrous structures appear after birth, perhaps favored by physical exercise, such as repeated pronation-supination movements. We think that it is one of the reasons why DBRN compression has never been reported in children. This is the first fetal study about the course and branching pattern of the DBRN and there is a constant ratio (mean 4.3) between the measurements of the fetuses and adults.

Surgical anatomy of the radial nerve at the elbow

An anatomical study of the brachial portion of the radial nerve with surgical implications is proposed. Thirty specimens of arm from 20 fresh cadavers (11 male, 9 female) were used to examine the topographical relations of the radial nerve with reference to the following anatomical landmarks: acromion angle, medial and lateral epicondyles, point of division between the lateral and long heads of the triceps brachii, lateral intermuscular septum, site of division of the radial nerve into its superficial and posterior interosseous branches and entry and exit point of the posterior interosseous branch into the supinator muscle. The mean distances between the acromion angle and the medial and lateral levels of crossing the posterior aspect of the humerus were 109 (+/-11) and 157 (+/-11) mm, respectively. The mean length and calibre of the nerve in the groove were 59 (+/-4) and 6 (+/-1) mm, respectively. The division of the lateral and long heads of the triceps was found at a mean distance of 126 (+/-13) mm from the acromion angle. The mean distances between the lateral point of crossing the posterior aspect of the humerus and the medial and lateral epicondyles were 125 (+/-13) and 121 (+/-13) mm, respectively. The mean distance between the lateral point of crossing the posterior aspect of the humerus and the entry point in the lateral intermuscular septum (LIS) was 29 (+/-6) mm. 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. Our study provides reliable and objective data of surgical anatomy of the radial nerve which should be always kept in mind by surgeons approaching to the surgery of the arm, in order to avoid iatrogenic injuries.

MR imaging findings of anterior interosseous nerve lesions

OBJECTIVE

To study and characterise the MR imaging findings of lesions of the anterior interosseous nerve (AIN).

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) findings of the forearm of ten patients referred to our institution with suspected AIN lesions were retrospectively studied. Five healthy volunteers with normal forearm MRI findings formed a control group. Two musculoskeletal radiologists assessed the forearm musculature for oedema in the distribution of the AIN, median, posterior interosseous and radial nerves on T2-weighted (T2W) fat-saturated sequences. T1-weighted (T1W) images were assessed and graded for the presence of muscle atrophy and fatty involution.

RESULTS

Six patients had undergone surgical exploration; five of these had surgically confirmed AIN compression. Four patients had diagnoses other than AIN compression made on imaging features. Of the cases of proven AIN compression, oedema within the pronator quadratus (PQ) muscle was identified in all cases. PQ atrophy and fatty involution were seen in three (43%) surgically confirmed cases. Cases 2 and 3 also demonstrated oedema in the flexor digitorum profundus (FDP)1 and FDP2 muscles. These cases also showed oedema in the flexor-carpi radialis (FCR) and FDP3/FDP4 muscles, respectively. The four cases of non-AIN compression demonstrated muscle oedema patterns that were atypical for the AIN distribution. They included a rupture of the flexor pollicis longus (FPL) tendon, brachial neuritis, amyotrophic lateral sclerosis and compression of the proximal median nerve.

CONCLUSIONS

MRI is a useful investigation in the diagnostic workup of AIN syndrome. AIN syndrome is likely when there is diffuse oedema of AIN innervated muscles on T2W fat-saturated images. The most reliable sign of an AIN lesion is oedema within the PQ. Oedema in the flexor carpi radialis, FDP3 and FDP4, although not in the classical distribution of the AIN, does not preclude the diagnosis of AIN syndrome.

Superficial surgical landmarks for identifying the posterior interosseous nerve

OBJECT

There is a paucity of information in the neurosurgical literature regarding the surgical anatomy surrounding the posterior interosseous nerve (PIN). The goal of the current study was to provide easily recognizable superficial bone landmarks for identification of the PIN.

METHODS

Thirty-four cadaveric upper extremities obtained from adults were subjected to dissection of the PINs, and measurements were made between this nerve and surrounding superficial bone landmarks. In all specimens the main radial trunk was found to branch into its superficial branch and PIN at the level of the lateral epicondyle of the humerus. Proximally, the PIN was best identified following dissection between the brachioradialis and extensor carpi radialis longus and brevis muscles. At its exit site from the supinator muscle, the PIN was best identified after retraction between the extensor carpi radialis longus and brevis and extensor digitorum communis muscles. This site was a mean distance of 6 cm distal to the lateral epicondyle of the humerus. No compression of the PIN by the tendon of origin of the extensor carpi radialis brevis muscle was seen. One specimen was found to have a proximally split PIN that provided a previously undefined articular branch to the elbow joint. The mean diameter of the PIN proximal to the supinator muscle was 4.5 mm. The leash of Henry crossed the PIN in all but one specimen and was found at a mean distance of 5 cm inferior to the lateral epicondyle. The PIN exited the distal edge of the supinator muscle at a mean distance of 12 cm distal to the lateral epicondyle of the humerus. Here the mean diameter of the PIN was 4 mm. The exit site from the distal edge of the supinator was found to be at a mean distance of 18 cm proximal to the styloid process of the ulna. This exit site for the PIN was best identified following dissection between the extensor carpi radialis longus and brevis and extensor digitorum communis muscles. The distal articular branch of the PIN was found to have a mean length of 13 cm and the proximal portion of this terminal segment was located at a mean distance of 7.5 cm proximal to the Lister tubercle.

CONCLUSIONS

The addition of more anatomical landmarks can help the neurosurgeon to be more precise in identifying the PIN and in avoiding complications during surgery in this region.

Anatomic and morphometric study of the arcade of Frohse in cadavers

The most superior part of the superficial layer of the supinator muscle is named as the arcade of Frohse (AF). The deep branch of the radial nerve runs under this arch. The AF is reported to be the most common structure causing entrapment neuropathy of the deep branch of the radial nerve. The aim of our study was to reveal the anatomical properties and especially morphometric measurements of the AF in cadavers. This study was performed on 55 cadaver upper extremities. The AF was classified macroscopically as either tendinous or membranous. The width, length and thickness of the AF were measured as the dimensions of the AF. The "distance AF" between the lateral epicondyle of the humerus and the AF was measured. The "forearm length" between the lateral epicondyle of the humerus and the styloid process of the radius was measured. The distance AF was divided by the forearm length to find the "ratio AF". In 87% of the extremities the AF was tendinous, and in 13% it was membranous. The mean width, length and thickness of the AF were 10.13, 8.60 and 0.77 mm, respectively. The mean distance AF and forearm length were 46.23 and 233.17 mm, respectively. The mean ratio AF was 0.199 (approximately 1/5). These measurements of the dimensions of the AF may contribute to the anatomy of the AF. The surgeon may find the predicted distance AF of any upper extremity by dividing its forearm length by 5.

Nerve injuries in the throwing elbow

The unique anatomy of the elbow combined with the angular velocity and stresses placed across this hinge joint while throwing can cause a large number of pathologic changes associated with nerves. Although the ulnar nerve is the most commonly injured, neuropathies are also seen with the branches of the median and radial nerves. These neuropathies are typically responsive to rest, activity modification, ice, splinting, and anti-inflammatories. A graduated return to throwing is then needed before returning to play. When conservative measures fail, surgical decompression is warranted, but results have been less than perfect.

Investigation of two possible compression sites of the deep branch of the radial nerve and nerve supply of the extensor carpi radialis brevis muscle

The posterior interosseous nerve arises from the deep branch of the radial nerve, and compression by adjacent structures results in posterior interosseous nerve syndrome. Sixty upper limbs from 30 Turkish subjects (18 males and 12 females) were dissected to reveal the course of the posterior interosseous nerve and to examine possible compression sites at the proximal and distal edges of the supinator muscle, and the exit of the nerve from the extensor carpi radialis brevis muscle. Posterior interosseous nerve syndrome is most probably caused by the tendinous part of the supinator muscle at the proximal edge.