Distal locking technique affects the rate of iatrogenic radial nerve palsy in intramedullary nailing of humeral shaft fractures

BACKGROUND

Intramedullary humeral nailing is a common and reliable procedure for the treatment of humeral shaft fractures. Radial nerve palsy is a common complication encountered in the treatment of this pathology. The radial nerve runs from posterior to anterior at the lateral aspect of the distal humerus. Hence, there is reason to believe that due to the anatomic vicinity of the radial nerve in this area, lateral-medial distal locking in intramedullary nailing of the humerus may be associated with a greater risk for iatrogenic radial nerve injury compared to anterior-posterior locking.

QUESTIONS/PURPOSE

To assess whether the choice of distal locking (lateral-medial versus anterior-posterior distal locking) in intramedullary humeral nailing of humeral shaft fractures affects the risk for iatrogenic radial nerve injury.

PATIENTS AND METHODS

Overall, 203 patients (116 females, mean age 64.3 ± 18.6 years), who underwent intramedullary nailing of the humerus between 2000 and 2020 at a single level-one trauma center, met the inclusion criteria and were analyzed in this retrospective case-control study. Patients were subdivided into two groups according to the distal locking technique.

RESULTS

Anterior-posterior locking was performed in 176 patients versus lateral-medial locking in 27 patients. We observed four patients with iatrogenic radial nerve palsy in both groups. Risk for iatrogenic radial nerve palsy was almost 7.5 times higher for lateral-medial locking (OR 7.48, p = 0.006). There was no statistically significant difference regarding intraoperative complications, union rates or revision surgeries between both groups.

CONCLUSIONS

Lateral-medial distal locking in intramedullary nailing of the humerus may be associated with a greater risk for iatrogenic radial nerve palsy than anterior-posterior locking. Hence, we advocate for anterior-posterior locking.

LEVEL OF EVIDENCE

Level III retrospective comparative study.

Two fingerbreadths, one finger's width: on the proximity of the radial nerve to the deltoid tuberosity

INTRODUCTION

The aim of this study was to find a convenient technique to evaluate the location of the radial nerve (RN) with reference to the deltoid tuberosity (DT).

MATERIALS AND METHODS

Sixty-eight upper extremities, embalmed using a modified version of Thiel's method, were included in the study. The interval between the tip of the greater tubercle of the humerus and the distal tip of the lateral humeral epicondyle (LE) was defined as humeral length (HL). The most prominent point of the DT was used as the point of reference. Through this point, a horizontal reference line which met the humeral axis at the dorsal side of the humeral shaft was simulated. The longitudinal distance between the crossing point of the horizontal line and the humeral axis and the RN was measured (distance 1). The interval between the intersection point and the reference point at the DT was measured (distance 2). Data were evaluated in centimeters.

RESULTS

For the whole sample, the HL averaged 31.0 cm (SD: 2.3; range 26.2-36.9). Distance 1 averaged 2.2 cm (SD: 0.3; range 1.6-3.1), and distance 2 averaged 1.2 cm (SD: 1.0; range 0-2.8). The HL was larger in the male group when compared to females (p < 0.001; males mean: 32.2 cm; females mean 29.5 cm). There was no difference regarding distance 2 (p = 0.59; males mean: 1.2 cm; females mean: 1.3 cm) between the sexes. Distance 1 was significantly (p = 0.02) larger in the male group (mean: 2.3 cm) when compared to females (mean: 2.1 cm). Concerning sides, there were no differences regarding all evaluated parameters (HL: p = 0.6; Distance 1: p = 0.6; distance 2: p = 0.8).

CONCLUSIONS

This study provides an easily applicable technique to localize the RN with reference to the DT.

Apex of Triceps Aponeurosis: A Reliable Landmark to Localize the Radial Nerve

The posterior approach to the humerus is an extensile approach, which provides excellent access to the distal aspect of the humerus. The approach is traditionally utilized for internal fixation of fractures of the distal third of the humerus, to perform sequestrectomy, and for radial nerve exploration. The radial nerve is susceptible to damage when utilizing this approach^1-3. Hence, accurate localization of the radial nerve is required to aid in identification during dissection and to minimize the risk of palsy. Various anatomical landmarks have been described in the literature that can help locate the radial nerve intraoperatively.

Description

The patient is anesthetized and placed in the lateral decubitus position with the elbow of the operative limb hanging freely over a bolster. A posterior midline incision centered over the fracture is made on the posterior aspect of the arm. The superficial and deep fascia are incised. The triceps aponeurosis is formed by the convergence and fusion of the lateral and long heads of the triceps. The most proximal confluence can be termed the "apex of the triceps aponeurosis." The radial nerve can be isolated approximately 2.5 cm proximal to the apex by developing an intramuscular plane. The remainder of the intramuscular dissection for plate fixation can then be performed safely without risking injury to the radial nerve.

Alternatives

Numerous studies have established the relationship of the radial nerve to a fixed osseous point such as the medial epicondyle, lateral epicondyle, and angle of the acromion^4-9. Additionally, the wide range of measurements of these anatomic relationships, as reported in various studies, makes it difficult for the operating surgeon to locate the radial nerve, especially in the setting of a fractured humeral shaft. For example, the reported distance of the radial nerve from the lateral epicondyle ranges from 6 to 16 cm and the distance from the angle of the acromion ranges from 10 to 19 cm. Even identification of the superficial branch of the radial nerve has been shown to help intraoperative localization of the radial nerve¹⁰. However, these studies have been conducted on cadavers with intact humeri, and their accuracy has not been demonstrated on the patients in the clinical milieu of trauma.

Rationale

The described soft-tissue landmark, which lies approximately 2.5 cm proximal to the apex of the triceps aponeurosis, reliably locates the radial nerve intraoperatively¹¹. It is based on the anatomical fact that the origins of the lateral head (oblique ridge corresponding to the lateral lip of the spiral groove) and long head (infraglenoid tubercle of the scapula) are well above fractures of the middle and distal thirds of the humerus. Hence, the relationship of the radial nerve to the soft point represented by the apex of the aponeurosis is not likely to be disturbed in the setting of fractures distal to it, in sharp contrast with previously described osseous landmarks.

Expected Outcomes

Employing this anatomical understanding resulted in early localization of the radial nerve (within 6 ± 1.5 minutes of skin incision) and less blood loss (188 ± 13 mL)¹¹. Patients are likely to retain their ability to perform active dorsiflexion of the wrist and fingers and have sensory preservation in the distribution of autonomous zone of the radial nerve after the procedure.

Important Tips

The relationship of the radial nerve to the soft point represented by the apex of the aponeurosis is not likely to be disturbed in the setting of typical fractures distal to it; however, this may differ in cases of severely displaced or comminuted fractures, and the surgeon should be aware of this fact.The surgeon should remain careful to protect the vena comitans.

Surgical Anatomy of the Radial Nerve at the Dorsal Region of the Humerus: A Cadaveric Study

BACKGROUND

Surgery for humeral shaft fractures is associated with a high risk of iatrogenic radial nerve palsy (RNP). Plausible causes are difficult anatomical conditions and variants.

METHODS

We performed a cadaveric study with 23 specimens (13 female and 10 male Caucasian donors) to assess the course and anatomy of the radial nerve (RN) with its branches alongside the humeral shaft. The accuracy of identification of the RN in the surgical field was analyzed by measuring the location, course, diameter, and form of each nerve and vessel of interest.

RESULTS

The RN is not a single structure running alongside the humeral shaft; at least 4 parallel structures crossed the dorsal humerus in all subjects. The RN was accompanied by 2 vessels and at least 1 other nerve, which we named the musculocutaneous branch (MCB). With an oval profile and an average diameter of 3.1 mm (range, 2.6 to 3.8 mm), the MCB was thinner but, in some cases, close to the average diameter of 4.7 mm (range, 4.0 to 5.2 mm) of the RN, which had a round profile. Both accompanying vessels had similar diameters: 3.5 mm (range, 2.6 to 4.2 mm) for the radial collateral artery and 4.0 mm (range, 2.9 to 4.4 mm) for the medial collateral artery. In 20 (87%) of the cases, the RN ran proximal to and in 3 (13%) of the cases, distal to the MCB. Furthermore, a distal safe zone of at least 110 mm (range, 110 to 160 mm) was found, measured from the radial (lateral) epicondyle proximally.

CONCLUSIONS

The RN does not cross the dorsal humerus alone, as often stated in anatomical textbooks, but runs parallel to vessels and at least 1 nerve branch with a similar appearance. Thus, for reliable preservation of the RN, we recommend identification and protection of all crossing structures in posterior humeral surgeries 110 mm proximal to the radial epicondyle.

The radial nerve at revision/redo surgery - using the lower lateral cutaneous nerve to prevent a postoperative radial nerve deficit

Background

The posterior approach to the humeral shaft is commonly used for surgical procedures on the humeral shaft. We present our experiences using the modification of the surgical exposure described by Gerwin M. which we have found useful at the time of revision surgery.

Methods

Between 2014 and 2019, six patients who underwent a revision surgical procedure for a nonunion of the humeral shaft where a prior surgical procedure was performed through a posterior incision were included. The approach used a modification of the posterior approach described by Gerwin M. where the lower lateral cutaneous nerve branch of the radial nerve is used to identify trace, mobilize, retract, and protect the radial nerve to achieve adequate exposure of the humeral shaft.

Results and Discussion

None of the patients had a postoperative nerve deficit.Adequate exposure to aid hardware removal, osteosynthesis, and bone grafting was achieved in all patients.

Conclusion

The modification of the posterior approach described by Gerwin M. is useful at the time of revision or redo surgery on the humeral shaft where other bony and soft tissue landmarks are altered to prevent an iatrogenic injury to the radial nerve while providing adequate exposure to treat a nonunion.

Surgical anatomy of the radial nerve in the arm: a cadaver study

PURPOSE

The purpose of this study was to analyse the anatomic course of the radial nerve (RN) in the arm, in order to minimize the potential risk of surgical injury.

METHODS

The study was performed in 19 embalmed upper extremities of 11 adult human cadavers. We measured: distance from deltoid insertion (DI) into the humerus to lateral epicondyle (LE); distance from RN piercing point into the lateral intermuscular septum (LIS) to three other points-DI, LE and RN division into superficial and deep terminal branches; distance between the LE and the RN division. To assess variability, we correlated the distances between the landmarks to the overall length of the arm.

RESULTS

The RN was found to pierce the LIS within 31.6 mm of the most distal DI into the humerus. The mean distance between the entry point of RN in the LIS and the LE was 107.2 mm. The mean distance between RN perforating point in the LIS and RN division in its terminal branches was 86.4 mm. The DI-LE and the LIS-LE showed a moderate positive correlation with the length of the arm.

CONCLUSION

We describe the DI relationship to the RN course and also report its proportion within overall arm length which has not been previously described. Using the arm length as reference, our results show that RN can be found to perforate on the LIS at a point distal to the DI by 11% and proximal to the LE by 38%.

Reliable Method of Radial and Ulnar Nerve Identification During the Posterior Approach to the Humerus: A Clinical and Cadaveric Correlation Study

OBJECTIVE

To determine the reliability of using "fingerbreadths" and anatomic landmarks as reference points for predictable identification of the radial and ulnar nerves when using the posterior approach to the humerus.

METHODS

A systematic approach using "fingerbreadths" to mark and measure the skin before incision. Two markings were made: the first 4 fingerbreadths proximal to the lateral epicondyle (radial nerve location) and the second 2 fingerbreadths proximal to the medial epicondyle (ulnar nerve location). Once the posterior approach was made, the same fingerbreadths were used on the radial and ulnar sides to identify the radial and ulnar nerves within the deep interval. Measurements were taken at each stage in cadaveric specimens. Clinical correlations followed. Statistical analysis was performed comparing measurements (outer vs. inner) in both cadaveric and clinical specimens.

RESULTS

Thirty-two elbows evaluated in this study, 20 patients and 12 cadaveric specimens. In the cadaveric specimens, the mean distance of the radial nerve was 7.59 cm from the lateral epicondyle, SD ± 0.17 cm (P = 0.55), and the ulnar 3.68 cm from medial epicondyle, SD ± 0.63 cm (P = 0.302). In the clinical measurements, the radial nerve was 7.46 cm, SD ± 0.48 cm, never within 7.0 cm (P = 0.425), and the ulnar nerve was 3.14 cm, SD ± 0.31 cm (P = 0.051). Statistical analysis yielded no difference between skin marking and actual location in the deep interval, between cadaveric and clinical specimens, observer fingerbreadth widths, or between left or right arms.

CONCLUSIONS

Use of "fingerbreadths" is a reliable, efficient, and reproducible method of identifying both the radial and ulnar nerves during the posterior approach to the humerus.

Identification of most consistent and reliable anatomical landmark to locate and protect radial nerve during posterior approach to humerus: a cadaveric study

The location of the radial nerve (RN) is described with various bony landmarks, but such may be disturbed in the setting of fracture and dislocation of bone. Alternative soft tissue landmarks would be helpful to locate the nerve in such setting. To recognize certain anatomic landmarks to identify, locate and protect RN from any iatrogenic injury during surgical intervention such as open reduction and internal fixation. Forty arms belonging to 20 adult cadavers were used for this study. We measured the distance of RN from the point of confluence of triceps aponeurosis (TA), tip of the acromion and tip of the lateral epicondyle along the long axis of the humerus. These distances were correlated with the upper arm length (UAL). The average UAL was 32.64±0.64 cm. The distance of the RN from the point of confluence of TA (tricepso-radial distance, TRD), tip of acromion (acromion-radial distance) and tip of lateral epicondyle of humerus (condylo-radial distance, CRD) was 3.59±0.16 cm, 14.27±0.59 cm, and 17.14±1.29 cm respectively. No correlation was found with UAL. Statistically, TRD showed the least variability and CRD showed maximum variability. The minimum TRD was found to be 3.00 cm. So this should be considered as the maximum permissible length of the triceps split. The point of confluence of the TA appears to be the most stable and reliable anatomic landmark for localization of the RN during the posterior approach to the humerus.

Safe zone for lateral pin placement for external fixation of the distal humerus

External fixation is a common, efficient technique used for humeral shaft stabilization and elbow fractures. There are reports of radial nerve injuries associated with this procedure. In this study, we investigated the course and variability of the radial nerve along the lateral humerus in relation to the elbow joint to determine a relatively safe zone for lateral pin placement in external fixation. Twenty upper extremities from 10 cadavers were studied. The nerve branches and course of the radial nerve along the lateral humerus were carefully dissected. Straight lines (a, b, and c) were made connecting three landmarks (the acromion, coracoid process, and anterior wall of the axilla) in the proximal upper extremity to the lateral condyle (LC) of the humerus; their intersections with the radial nerve (A, B, and C) were marked. We analyzed whether the intersection positions were correlated with the connecting line lengths. The mean lengths of the connecting lines were (a) 27.24 ± 2.57, (b) 26.18 ± 2.79, and (c) 20.95 ± 1.44 cm; the distance between the intersection points and the LC of the humerus were (Aa) 7.56 ± 1.31, (Bb) 6.90 ± 2.27, and (Cc) 5.01 ± 0.83 cm; and the measured intersection points of the radial nerve in the lateral aspect of the humerus were (A) 18.48%-34.82%, (B) 13.48%-40.00%, and (C) 19.27%-28.05% of the lengths of lines a, b, and c, respectively. Our data provide a more reliable reference to predict the course of the radial nerve on the lateral humerus and define a safe zone for pin placement. Clin. Anat., 33:637-642, 2020. © 2019 Wiley Periodicals, Inc.

Fingerbreadths Rule in Determining the Safe Zone of the Radial Nerve and Posterior Interosseous Nerve for a Lateral Elbow Approach: An Anatomic Study

Introduction

The purpose of this study was to investigate whether a safe zone rule could be applied to prevent iatrogenic injuries to the radial nerve (RN); and determine whether there is a relationship between the diameter of the radial head and capitellum and the distance of the posterior interosseous nerve (PIN) to the radiocapitellar joint.

Methods

Ten fresh-frozen cadaveric specimens were used to measure the distances between the RN and the lateral epicondyle; the PIN and the radiocapitellar joint; the lateral epicondyle and the PIN as it crossed the ulnohumeral joint; the diameter of the radial head; the width of the capitellum; and the fingerbreadths of the specimens.

Results

Four fingerbreadths determined a safe zone between the lateral epicondyle and the RN proximally at the point at which it pierced the intermuscular septum and the mid-lateral portion of the humeral shaft. Two fingerbreadths provided a safe zone for the PIN from the radiocapitellar joint to the midpoint of the axis of the radius only with the forearm in pronation.

Conclusion

A four-finger rule, two-finger rule, and radial head diameter or capitellum size may predict a safe zone for the RN and PIN except for the segment of the nerve where it crosses the anterior cortex of either the humerus or radius.

Level of Evidence

Preclinical cadaveric study.

Safe Zones for Cerclage Wiring of the Humeral Diaphysis

Cerclage wiring of the humeral diaphysis entails particular danger to the radial nerve and the deep brachial artery. We sought to delineate safe zones for minimally invasive cerclage wiring of the humeral diaphysis, specifically in relation to the radial nerve and accompanying vasculature. Cerclage wires were percutaneously inserted into three groups of fresh-frozen cadaveric humeri. Group 1-proximal midshaft humerus at 30% of humeral height (n = 4); Group 2-midshaft spiral groove at 45% of humeral height (n = 4); and Group 3-distal midshaft humerus at 60% of humeral height (n = 4). Subsequently, an extensive surgical exploration of the arteries and nerves around the humerus was performed, noting any disturbance to the vessels or nerves and measuring the distance from the cerclage wire to the radial nerve. Neurovascular structures were injured in 75% of specimens when the cerclage wire was inserted at the level of the spiral groove. Both posterior structures, e.g. the radial nerve and the deep brachial artery, and medial structures, e.g., the median nerve and brachial artery, were incarcerated. Application of the cerclage at 30% or 60% of humeral height did not cause neurovascular injury. Minimally invasive application of the cerclage wire at the spiral groove, which is at 45% of humeral height, is likely to cause injury to neurovascular structures. Application of the cerclage at the proximal or distal midshaft humeral areas is associated with less risk of such injury. Clin. Anat. 33:552-557, 2020. © 2019 Wiley Periodicals, Inc.

Effects of the Elbow Flexion Angle on the Radial Nerve Location around the Humerus: A Cadaver Study for Safe Installation of a Hinged External Fixator

Background: This study aimed to investigate whether the distance between the radial nerve and rotational center of the elbow joint when observing from the lateral surface of the humerus changes according to passive elbow joint flexion for safe external fixation with a hinged fixator of the elbow joint.

Methods: Twenty fresh-frozen cadaveric arms were dissected. The points where the radial nerve crosses over the posterior aspect of the humerus, crosses through the lateral center, and crosses over the anterior aspect of the humerus were defined in the lateral view of the elbow joint, using fluoroscopy, as R1, R2, and R3, respectively. The distances between the rotational center and each point on the radial nerve were measured when the flexion angle of the elbow joint was 10°, 50°, 90°, and 130°.

Results: The distances between the rotational center and R1, R2, and R3 were 118 mm, 94 mm, and 65 mm, respectively, when the flexion angle was 10°; 112 mm, 93 mm, and 74 mm, respectively, for 50°; 108 mm, 93 mm, and 77 mm, respectively, for 90°; and 103 mm, 94 mm, and 83 mm, respectively, for 130°. The distance between the rotational center and R2 was constant regardless of the flexion angle. With elbow joint extension, the distances between R1 and R3 increased; the safe zone, a region where the radial nerve would not be located on the humerus, was the smallest in extension. When the elbow joint was flexed, the distances between R1 and R3 decreased; the safe zone was the largest in flexion.

Conclusions: This study showed that the radial nerve location on the humerus varied based on the flexion angle of the elbow joint; the safe zone may change. A half-pin can be likely inserted safely, avoiding the elbow joint extension position.

Localisation of the radial nerve at the spiral groove: A new technique

Background

Localisation of the radial nerve (RN) in the spiral groove by previously reported methods has a wide range and is generalised. The objective of this study was to establish a method unique to a patient to accurately localise the nerve.

Methods

The distance between RN at the midpoint of the spiral groove (D) and the tip of the olecranon (O) was compared with the most distal wrist flexion crease and fingertips on 100 healthy volunteers. The RN was found by ultrasound examination.

Results

The mean distance from O to D was 16.22 cm (12.5–20.5 ± 1.55), and mean distances from wrist crease (WC) to second, third, fourth and fifth fingertips were 17.79 (14–20 ± 1.28), 18.66 (15–21 ± 1.32), 17.71 (14.5–20.5 ± 1.32) and 15.62 (12.5–20.5 ± 1.34) cm, respectively. With regards to O–D distance, the strongest relationship was obtained for the distance between the fifth fingertip to the WC (r = 0.708, p < 0.001). This relationship was stronger among females than males (p < 0.001).

Conclusion

The course of the RN can be easily found at the upper arm by this method, which is unique to a patient.

The translational potential of this article

This study presents a new and individualised approach to accurately predict the location of the RN in the spiral groove. This method is clinically relevant and can be used to guide the surgical explorations or expedite interventional methods.

The course of the radial nerve in the distal humerus: A novel, anatomy based, radiographic assessment

Iatrogenic nerve injury during fracture surgery of the upper arm is a well-known complication. Prevention of this type of injuries would be of great value. The literature describes several methods to reduce this type of injury, but no perfect solution is at hand. In this study we introduce a new radiographic evaluation of the course and variation of the radial nerve in the distal part of the humerus in relation to bony landmarks as observed on a plain (trauma) radiographs. Aim of this new approach is to reduce the chance of iatrogenic nerve injury by defining of a danger zone in the distal upper arm regarding the radial nerve and hence give an advise for future implant fabrication.

Vascular anatomy relevant to distal biceps tendon repair

BACKGROUND

Avoiding bleeding and vascular complications in open repair of distal biceps tendon rupture requires knowledge of the local vascular anatomy. This study examined the vascular anatomy relevant to distal biceps tendon repair.

METHODS

The antecubital regions of 17 cadaveric upper extremities were dissected using ×2.5 loupe magnification to identify the brachial artery, the radial artery and its recurrent branches, and venous branches crossing the distal biceps tendon. With the elbow in full extension and supination, the position of each vascular structure was measured relative to the most proximal aspect of the bicipital tuberosity.

RESULTS

The most common pattern (13 of 17 specimens) was a single radial recurrent artery (RRA) crossing volar to the tendon at a mean of 4 mm proximal to the tuberosity and positioned 15.4 mm volar to the tuberosity. The RRA bifurcated 2 to 9 mm from its origin in 6 arms and demonstrated a single bifurcation. In 8 of 17 specimens, an additional recurrent branch off the brachial artery traveled dorsal to the intact biceps tendon 16 mm proximal to the RRA. Two arms demonstrated a high brachial artery bifurcation. The crossing veins were venae comitantes of the RRAs and radial and ulnar arteries. They connected to the superficial veins by way of a perforating branch. Most often, 3 transverse veins positioned on average 0.2 mm proximal and 16 mm volar to the tuberosity were seen.

CONCLUSIONS

The vascular anatomy encountered during distal biceps repair is variable, and RRAs occasionally travel dorsal to the biceps tendon. Most often, a single RRA on average 4 mm proximal to the tuberosity will branch once.

Minimally invasive approach to the radial nerve--A new technique

PURPOSE

To describe a minimally invasive approach to find the radial nerve (RN) simply and safely by tracing the posterior antebrachial cutaneous nerve (PACN) without damaging muscles, using only the surgeon's hand to define a window for the skin incision.

BACKGROUND

Although it is absolutely necessary to locate the radial nerve during osteosynthesis of the humerus, the literature lacks guidelines on how to do so.

METHODS

We have dissected the upper extremities of 54 adult human cadavers, embalmed using Thiel's method. After the PACN was identified in a defined space, its course was traced proximally by incising the lateral intermuscular septum (LIS) of the upper arm and thereby reaching the radial nerve (RN). Subsequently, using the lateral epicondyle (LE) of the humerus as a reference point, the distances to the points where the PACN perforated the LIS, and where the RN was identified, were measured. These individual data were related to the total length of the humerus.

RESULTS

The results indicate that with this approach and without harming musculature, the RN can be reached by tracing the PACN at a height of 11.1-13.0 cm (females) and 11.9-14.0 cm (males) starting from the LE.

CONCLUSION

Our examination shows the PACN to be a convenient guide to the RN.

Radial nerve location at the posterior aspect of the humerus: an anatomic study of 100 specimens

PURPOSE

Radial neuropathy represents a devastating complication in a posterior approach to the distal humerus. This study aimed to propose "safe zones" regarding the radial nerve (RN) location at the posterior aspect of the humerus to minimize the risk of iatrogenic injury.

METHODS

In 100 embalmed specimens, the distances of the proximal edge of the olecranon fossa (OF) to the radial nerve at the medial edge (R1), at the center (R2) and at the lateral edge (R3) of the posterior aspect of humeral shaft were measured. Humeral length (HL) and transcondylar width (TW) were evaluated and correlated to R1, R2 and R3.

RESULTS

R1 was 15.0 (±2.1; 10.6-19.5) cm, R2 averaged 12.7 (±1.6; 8.9-15.7) cm, R3 was 10.6 (±1.3; 7.6-13.7) cm. HL was 30.8 (±1.9) cm. TW averaged 6.3 (±0.6) cm. TW and HL correlate with R1, R2, R3 (r = 0.451-0.565 [95% CI 0.279-0.685]). The mean ratio was 2.3 (±0.18) for HL/R1, 2.6 (±0.23) for HL/R2 and 3.1 (±0.31) for HL/R3. The ratio averaged 2.2 (±0.20) for R1/TW, 1.9 (±0.18) for R2/TW and 1.6 (±0.15) for R3/TW.

CONCLUSIONS

We present the OF as an osseous landmark to reduce the risk of iatrogenic radial neuropathy. HL and TW can be reliably used to estimate the RN location. The consistent "safe zones" of the RN in relation to the OF are 10.5 cm at the medial edge, 9 cm at the center and 7.5 cm at the lateral edge of the posterior aspect of the humeral shaft.

Safe zone for superolateral entry pin into the distal humerus in children: an MRI analysis

BACKGROUND

The radial nerve is at risk for iatrogenic injury during placement of pins, screws, or wires around the distal humerus. Unlike adults, detailed anatomic information about the relationship of the nerve to the distal humerus is lacking in children.

QUESTION/PURPOSES

This study evaluates the relationship of the radial nerve to the distal humerus in a pediatric population on conventional MRI and proposes an anatomic safe zone using easily identifiable bony landmarks on an AP elbow radiograph.

METHODS

To determine the course of the radial nerve at the lateral distal humerus, we reviewed 23 elbow radiographs and MRIs of 22 children (mean age, 9 ± 4 years; range, 3-12 years) obtained as part of their workup for various elbow conditions. We described a technique using distance ratios calculated as a percentage of the patient's own transepicondylar distance, defined as the distance measured between the apices of the medial and lateral epicondyles, on the AP elbow radiograph and the midcoronal MR image. The cross-reference tool on a Picture Archiving and Communication System was then used to identify axial MR image at the level where the transepicondylar distance was measured. On this axial image, a line was drawn connecting the medial and lateral epicondyles (the transepicondylar axis) and its midpoint was determined. The radial nerve angle was measured by a line from the radial nerve to the midpoint of the transepicondylar axis and a line along the lateral half of the transepicondylar axis. On this axial slice, the closest distance from the nerve to the underlying cortex of the distal humerus was measured. To further localize the nerve along the distal humerus, predetermined percentages of the transepicondylar distance were projected proximally from the level of the transepicondylar axis along the longitudinal axis of the humerus on the midcoronal MR image. At these designated heights, the corresponding axial MR image was identified using the cross-reference tool and the nerve was mapped in a similar fashion. We then proposed a simpler method using a best-fit line drawn along the lateral supracondylar ridge on the AP radiograph to define the safe zone for lateral pin entry.

RESULTS

On axial MR images, the radial nerve was located in the anterolateral quadrant with a mean radial nerve angle of 54° (range, 35°-87) at 0% transepicondylar distance (23 MRIs), 41° (range, 24°-63°) at 50% transepicondylar distance (23 MRIs), and ≥ 10° at 75% transepicondylar distance (on the 13 MRIs that extended this far cephalad). The mean closest distance between the radial nerve and the underlying humeral cortex was 10 mm (range, 3-26 mm) at 0% transepicondylar distance and 7 mm (3-16 mm) at 50% transepicondylar distance. On the AP elbow radiograph, the height of the lateral supracondylar ridge, determined by a best-fit line drawn along the lateral cortex of the ridge, diverged from the most proximal extent of the ridge at a point located at 60% transepicondylar distance (range, 51%-76%). At the corresponding location on the axial MR image, the nerve was located anterolaterally with a mean radial nerve angle of 39° (range, 15°-61°) and a mean distance of 6 mm (range, 2-10 mm) from the underlying humerus.

CONCLUSIONS

Our data suggest that percutaneous direct lateral entry Kirschner wires and half-pins can be safely inserted in the distal humerus in children along the transepicondylar axis, either at or slightly posterior to the lateral supracondylar ridge, when placed caudal to the point located where the lateral supracondylar ridge line diverges from the proximal extent of the supracondylar ridge on AP elbow radiograph.

Course of the radial nerve in relation to the center of rotation of the elbow--the need for a rational safe zone for lateral pin placement

PURPOSE

To investigate the course and variability of the radial nerve along the lateral humerus in relation to the center of rotation of the elbow joint in the context of lateral pin placement for hinged external fixation.

METHODS

A total of 95 formalin-fixed upper extremities were dissected. The course of the radial nerve along the lateral aspect of the humerus was measured at 3 landmarks with respect to the center of rotation of the elbow. We analyzed the data and the landmark positions correlated with the length of the humerus.

RESULTS

The measured positions of 3 landmarks of the radial nerve in the lateral aspect of the humerus ranged from 19% to 43% of the length of the humerus and were located, on average, 6.0, 9.7, and 13.5 cm from the lateral center of rotation.

CONCLUSIONS

These data help predict the humeral course of the radial nerve and define a safe zone for pin implantation. However, because of variability in the course of the radial nerve, a safe zone cannot fully ensure prevention of iatrogenic injury to the nerve. The safest method of pin application remains mini-open dissection and visual implantation.

CLINICAL RELEVANCE

Based on this cadaveric study, it is not possible to define a rational safe zone. The safest method of pin application for dynamic external fixation of the elbow is to perform a mini-open dissection with direct visualization.

Subpectoral biceps tenodesis: an anatomic study and evaluation of at-risk structures

BACKGROUND

The neurovascular structures of the proximal arm may be at risk for iatrogenic injury during open subpectoral biceps tenodesis (OSPBT).

PURPOSE

To define the anatomic relationships and at-risk structures during OSPBT and to quantify the effect of arm rotation on the position of the musculocutaneous nerve.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The OSPBT approach was performed in 17 unembalmed cadaveric upper extremities. The tenodesis site was inferior to the bicipital groove and positioned so the musculotendinous portion of the long head of the biceps rested at the inferior border of the pectoralis major. A meticulous dissection identified the brachial artery, deep brachial artery, cephalic vein, brachial vein, medial brachial cutaneous nerve, medial antebrachial cutaneous nerve, intercostal brachial cutaneous nerve, musculocutaneous nerve, axillary nerve, median nerve, and radial nerve. Superficial structures were measured from the superior and inferior aspects of the incision, and deep structures were measured from the tenodesis site and nearest retractor. The musculocutaneous nerve was measured with the arm in neutral, internal, and external rotation.

RESULTS

The musculocutaneous nerve was 10.1 mm (range, 6-18 mm) medial to the tenodesis location and 2.9 mm (range, 1-6 mm) medial to the medially placed retractor in neutral arm position. The radial nerve and deep brachial artery were 7.4 mm (range, 2-12 mm) and 5.7 mm (range, 1-10 mm) deep to the medially placed retractor, respectively. With the arm internally rotated to 45°, the musculocutaneous nerve was 8.1 mm from the tenodesis site, compared with 19.4 mm with the arm 45° externally rotated (P = .009). The median nerve, brachial artery, and brachial vein were >2.5 cm from the tenodesis site and nearest retractor during deep dissection.

CONCLUSION

The musculocutaneous nerve, radial nerve, and deep brachial artery are within 1 cm of the standard medial retractor. External rotation of the arm moves the musculocutaneous nerve 11.3 mm further away from the tenodesis site compared with the internally rotated position.

CLINICAL RELEVANCE

The musculocutaneous nerve, radial nerve, and deep brachial artery course in close proximity to the operative field and are therefore at risk during OSPBT. Limiting the use of medial retraction and placement of the arm in an externally rotated position will minimize neurovascular injury.

A method to localize the radial nerve using the 'apex of triceps aponeurosis' as a landmark

BACKGROUND

The relationship of the radial nerve is described with various osseous landmarks, but such relationships may be disturbed in the setting of humerus shaft fractures. Alternative landmarks would be helpful to more consistently and reliably allow the surgeon to locate the radial nerve during the posterior approach to the arm.

QUESTIONS/PURPOSES

We investigated the relationship of the radial nerve with the apex of triceps aponeurosis, and describe a technique to locate the nerve.

MATERIALS AND METHODS

We performed dissections of 10 cadavers and gathered surgical details of 60 patients (30 patients and 30 control patients) during the posterior approach of the humerus. We measured the distance of the radial nerve from the apex of the triceps aponeurosis along the long axis of the humerus in cadaveric dissections and patients. This distance was correlated with the height and arm length. For all patients, we recorded time until first observation of the radial nerve, blood loss, and postoperative radial nerve function.

RESULTS

The mean distance of the radial nerve from the apex of the triceps aponeurosis was 2.5 cm, which correlated with the patients' height and arm length. The mean time until the first observation of the radial nerve from beginning the skin incision was 6 minutes, as compared with 16 minutes in the control group. Mean blood loss was 188 mL and 237 mL, respectively. With the numbers available, we observed no difference in the incidence of patients with postoperative nerve palsy: none in the study group and three in the control group.

CONCLUSION

The apex of the triceps aponeurosis appears to be a useful anatomic landmark for localization of the radial nerve during the posterior approach to the humerus.