An Initial Anatomic Study With Ultrasound For Predicting Radial Nerve Location

Background&ObjectiveThe radial nerve(RN)has intimate relationship with the humerus when it runs around the posterior aspect of the humerus,resulting in its easy damage in surgical exploration of this region.Thus,an anatomic understanding of the radial nerve location at the posterior aspect of the humerus is essential to minimize the risk of iatrogenic damage.Owing to the clinical relevance,the cadaveric studies have been used for anatomic understanding of the course of the radial nerve and its relationship to surrounding landmarks.However,there are some common limitations in the cadaveric studies,which may lead to inaccurate conclusions.Therefore,noninvasive methods that allow localization of the nerve dynamically and in-situ would be of value.Recently,ultrasound has been widely used to study the peripheral nerve,with its resolution and imaging capabilities greatly improved.Previous studies reported that High-resolution ultrasound(HRUS)can offer an accurate and noninvasive assessment of the morphology,course and excursion of the RN in real-time and in vivo.However,ultrasound-guided approach to establish normative data for predicting radial nerve location in healthy populations has yet to be described.Therefore,this study aimed to provide an initial measurement of radial nerve location at the posterior humerus in healthy volunteers under the guidance of HRUS.We hypothesized that HRUS-guided approach would allow more accurate prediction of RN location at posterior humerus than previous cadaveric studies and,thus,reduce the risk of iatrogenic injuries.Methods1.Fifty-six volunteers were recruited from the students of Southern Medical University.The participants included in the study were healthy individuals aged more than 18 years.Participants with a history of immobility,injury,deformity or surgery of the upper extremity were excluded.2.Equipment and procedures(1)Equipment:A high-resolution ultrasound system(LOGIQ E9;GE Healthcare,Milwaukee,WI,USA)with a 6-15 MHz linear array transducer was used.(2)Procedures:HRUS was used to localize the segment of RN that was in direct contact with posterior humerus in 56 healthy volunteers.Three reference points were defined in this segment:the proximal margin(R1),the center(R2)and the distal margin(R3).The posterolateral tip of the acromion,the anterolateral of the acromion,the medial epicondyle,the lateral epicondyle as well as deltoid insertion were used as the anatomy landmarks.After marking all landmarks and reference points,distances?between the reference points of the RN and the corresponding landmarks were measured.Furthermore,humeral length(HL),transcondylar width(TW),height and weight were correlated to other obtained distances.In the second part,the factors associated with the anatomic relationships between RN and landmarks,such as elbow position,side and gender were investigated in this study.Results1.The first part:The segment of RN studied in this study was clearly visible in all volunteers.The segment of radial nerve was found to be in direct contact with the posterior Humerus from 16.0±1.5cm proximal to medial epicondyle,from 13.6±1.5cm proximal to the central of transcondylar line,from 11.4±1.3cm proximal to lateral epicondyle.Besides,this study found HL,TW,height and weight were associated with all other measured distances in the first part,especially HL showed intimately associated with all other measured distances(r = 0.65-0.79,p<0.0001).2.The second part:the proximal margin of this segment investigated in this study was located approximately at the middle level of the humerus.In the second part,we found that the location of RN in relation to the landmarks except deltoid insertion was altered when changing the elbow position.There was no significant difference between left and right sides for all the measured distances.All obtained values but the distance from deltoid insertion to the proximal margin of RN are significantly larger in male volunteers when compared to female volunteers(p<0.0001).Conclusion1.HRUS,as a simple and noninvasive method to locate the segment of RN in the posterior humerus,make it possible to explore anatomic distribution of the radial nerve in the upper arms among the normal people;2.This study propose "safe zones" regarding the RN location at the posterior aspect of the humerus and provide some practical methods for RN localization to minimize the risk of iatrogenic injury;3.HL can be reliably used to estimate the RN location.4.Importantly,the deltoid insertion is a consistent and practical anatomic landmark that can be used to determine the level of the radial nerve along the posterior aspect of the humerus during surgery.