Investigation of Two Possible Compression Sites of the Deep Branch of the Radial Nerve and Nerve Supply of the Extensor Carpi Radialis Brevis Muscle

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1 Neurol Med Chir (Tokyo) 44, 14 19, 2004 Investigation of Two Possible Compression Sites of the Deep Branch of the Radial Nerve and Nerve Supply of the Extensor Carpi Radialis Brevis Muscle Yalcin KIRICI and M. Kemal IRMAK* Departments of Anatomy and *Histology-Embryology, Faculty of Medicine, Gulhane Military Medical Academy, Ankara, Turkey Abstract 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. Key words: posterior interosseous nerve syndrome, compression, course Introduction The posterior interosseous nerve is a deep branch of radial nerve which innervates the extensor carpi radialis brevis and the supinator muscles. 20) Posterior interosseous nerve syndrome is an entrapment neuropathy of the posterior interosseous nerve within the forearm extensor muscles. 7,10,17,20) Nerve branches to the extensor carpi radialis brevis muscle and the supinator muscle may arise from the main trunk of the radial nerve or from the proximal part of the posterior interosseous nerve, but almost invariably originate above the arcade of Frohse. The posterior interosseous nerve is vulnerable to both traumatic 1,18) and nontraumatic mechanical damage. 8) ThearcadeofFrohseisthemostcommon structure that causes compression of the posterior interosseous nerve, especially if the arcade is fibrous. Iatrogenic compression may also develop after surgical procedures involving the proximal radial region. 6) Patients with posterior interosseous nerve syndrome present with weakness in finger extension and thumb extension and abduction. 4,7,20) Posterior interosseous nerve syndrome has been described in several populations, 2 4,14,15,17) but only one anatomic study has considered the posterior Received February 26, 2003; Accepted July 29, 2003 interosseous nerve syndrome in the Turkish population, in which the texture of the arcade of Frohse was fibrous in 80% and was membranous in 20% of cadavers. 13) In addition, the innervation of the extensor carpi radialis brevis muscle is unclear. The present study measured the anatomical characteristics of the posterior interosseous nerve and examined two possible compression sites at the proximal and distal borders of the supinator muscle, as well as the innervation of the extensor carpi radialis brevis muscle. Materials and Methods Sixtyupperlimbsfrom30cadavers(18malesand12 females) were examined during routine dissections between at the School of Medicine, Gulhane Military Medical Academy. All subjects were Turkish citizens and the mean age at death was 32 years. The dissection was started where the radial nerve pierced the lateral intermuscular septum in the distal arm and followed this nerve to the distal border of the supinator muscle in the proximal forearm. The radial nerve and its two branches were reached by dissecting between the extensor carpi radialis longus and extensor carpi radialis brevis muscles. The radial nerve and its divisions in the elbow area were studied in detail. Figure 1 shows 14

2 Posterior Interosseous Nerve Syndrome 15 the anatomical distances and their measurement points as described previously. 14) The proximal arcade of the superficial layer of the supinator muscle (arcade of Frohse) and the distal border of the supinator muscle were studied as structures that may cause compression of the posterior interosseous nerve. The arcade of Frohse was observed under a stereomicroscope (Stemi 2000; Carl Zeiss, Jena, Germany) and classified as tendinous if the medial and lateral halves of the arch were fibrous in texture and white in color, or membranous if the medial half of the arcade was muscular or translucent. The distal edge of the supinator muscle at the exit of the posterior interosseous nerve was similarly classified. In addition, the exit of the nerve which supplies the extensor carpi radialis brevis muscle was also studied. All statistical analyses were performed with the SPSS 10.0 package (SPSS for Windows; SPSS Inc., Chicago, Ill., U.S.A.). All values are given as mean ± standard deviation. Differences between the left and rightarmswereexaminedwiththepairedsamplet test, and continuous variables with the chi-square or Fisher exact tests. Since the data were distributed normally, the Pearson coefficients of correlation were calculated to investigate the relationships between two variables. P values less than or equal to 0.05 were evaluated as statistically significant. Fig. 1 Schematic illustration of the anatomical measurements. A line: horizontal line through the humeroradial joint, L 1 :lengthof the radial nerve from the point piercing the lateral intermuscular septum to the A line, L 2 : length of the posterior interosseous nerve from the point of branching from the radial nerve to the A line, L 3 :lengthofthe posterior interosseous nerve from the A line to the proximal edge of the superficial head of the supinator muscle, L 4 : length of the posterior interosseous nerve from the A line to the distal edge of the supinator muscle, L 5 : entire length of the radius from the A line to the radial styloid process. Results Measurements of the five distances are given in Table 1. Only the L 1 distance was significantly different between the right and left arms (p º 0.05). The other measurements showed no significant differences. There was a positive correlation between the distances L 1 and L 5 in the left arm (r = 0.642, p = 0.001), and a positive correlation between L 1 and L 2 and negative correlation between L 1 and L 3 in the right arm. There was no significant correlation between proximal and distal structure types on either side. The posterior interosseous nerve passed through the radial tunnel anterior to the humeroradial joint and then coursed beneath the arcade of Frohse, which is the proximal edge of the superficial layer of the supinator muscle. The proximal edge of the supinator muscle had a well-developed tendinous arch in 40 of the specimens (67%) and was membranous in the remaining 20 specimens (33%). The distal edge of the supinator muscle had a thick Table 1 Measurements of the anatomical distances L 1 L 2 L 3 L 4 L 5 Right side 8.48±1.05* 3.48± ± ± ±1.52 Left side 9.20±1.70* 3.23± ± ± ±1.78 Values are mean±standard deviation. *p= Neurol Med Chir (Tokyo) 44, January, 2004

3 16 Y. Kirici et al. Table 2 Number of tendinous or membranous edge of the supinator muscle Rightside Leftside Proximal edge Distal edge Proximal edge Distal edge Male Female Male Female Male Female Male Female Tendinous * 5 0 Membranous * *pº Fig. 2 Photograph showing the muscles and nerves of the lateral aspect of the arm. a: posterior antebrachial cutaneous nerve, d: brachioradialis muscle, M: biceps brachii muscle,n:brachialismuscle,p:posterior brachial cutaneous nerve, R: radial nerve, T: lateral head of the triceps brachii muscle. Fig. 3 Photograph showing the muscles and nerves of the lateral aspect of the anterior cubital region. e: superficial branch of the radial nerve, G: extensor carpi radialis brevis muscle, H: brachioradialis muscle, mt: biceps brachii muscle tendo, pi: posterior interosseous nerve, Q: bicipital aponeurosis, rs: nerve supply extensor carpi radialis brevis muscle, S: supinator muscle. tendinous edge in 10 (17%), and a membranous texture in 50 (83%) of the extremities. We did not observe any significant difference in tendinous or membranous edges between males and females in the right arm (Table 2). However, 11 of the female cadavers (91.7%) had tendinous edges in the left arm whereas only one (8.3%) had a membranous edge. This sex difference at the proximal edgeofthemusclewassignificant(pº 0.018). The other parameters showed no significant differences. Fourteen extensor carpi radialis brevis muscles (47%) were supplied by the posterior interosseous nerve, and 16 (53%) by the radial nerve in the right arm. Eighteen extensor carpi radialis brevis muscles (60%) were supplied by the posterior interosseous nerve, and 12 (40%) by the radial nerve in the left arm. Photographs of the posterior interosseous nerve and radial nerve, and related muscles are shown in Figs. 2 and 3. Discussion A previous study found the extensor carpi radialis brevis muscle is innervated by the superficial radial nerve in 43% of arms, the radial nerve in 55%, and the posterior interosseous nerve in 2%. 14) Classical anatomy textbooks report that this muscle is innervated mostly by the posterior interosseous nerve. Our study suggests that the posterior interosseous nerve is responsible in 47% of arms and the radial nerve in 53%. The L 2,L 3,L 4,andL 5 distances measured at the both sides were nearly equal in all 30 cadavers. The L 1 distance was significantly different, possibly because the extensor carpi radialis brevis muscle can be innervated by various nerves. We thought that if the nerve which supplies the extensor carpi radialis brevis muscle is derived from Neurol Med Chir (Tokyo) 44,January,2004

4 Posterior Interosseous Nerve Syndrome 17 the posterior interosseous nerve, and compression occurs, this nerve will also be entrapped together with the posterior interosseous nerve. However, we could not observe any relationship between the fibrous texture of the arcade of Frohse, and the innervation type of the extensor carpi radialis brevis muscle. Four structures may compress the posterior interosseous nerve. 11) The nerve is commonly compressed at its entrance into the supinator muscle, but also at its exit from the supinator muscle. 16) The most common site of compression in the forearm is the arcade of Frohse. 6) Fibrous texture of the arcade of Frohse may cause posterior interosseous nerve syndrome if the supinator muscle shows hypertrophy with intensive usage of the muscle. However, the present study could not show a causative relationship between the nature of the arcade of Frohse and posterior interosseous nerve syndrome. Thearcadewastendinousin57%ofcasesand membranous in 43%. The distal edge of the supinator muscle was tendinous in 65% of cases and membranous in 35%. 14) Both the proximal and distal edges of the supinator muscle are potential sites of compression of the posterior interosseous nerve. Both radial tunnel syndrome and posterior interosseous nerve compression syndrome are caused by compression of the posterior interosseous nerve. Posterior interosseous nerve syndrome occurs in less than 10% of cases. 10) Entrapment of the posterior interosseous nerve is caused by the tendinous margin of the extensor carpi radialis brevis muscle, 21) or by a fibrous band at the distal edge of the body of the supinator muscle. 5,15) There are numerous reports suggesting that the fibrous texture of the arcade of Frohse is an etiologic factor leading to posterior interosseous nerve syndrome. Hypertrophic muscles of this kind may cause entrapment of the nerve. 3,4,6,7,12 14) Fibrous change in the arcade of Frohse of the supinator muscle may cause posterior interosseous nervesyndromeifotherfactorssuchasenlargement of the muscle are also present. Another explanation of the lower ratio of posterior interosseous nerve syndrome in population groups, despite the higher ratio of fibrous arcade of Frohse, is that symptoms related to posterior interosseous nerve syndrome may be attributed to underlying factors other than posterior interosseous nerve syndrome. Tendinous arcade of Frohse is an important factor in the development of the posterior interosseous nerve syndrome. 4) Four cases were the result of paralysis of the posterior interosseous nerve, caused by compression of the nerve between the arcade of Frohse and the two heads of the supinator muscle. 3,12) Posterior interosseous nerve syndrome is an etiologic factor in tennis elbow. 9,19) Based on our findings, we conclude that the tendinous arcade of Frohse is an important factor in the development of the posterior interosseous nerve syndrome. Our results in the Turkish population show no differences from the results of other studies on the Turkish population and other population groups. 13) Similar results were obtained in a number of studies, so we cannot say that there is a racial difference between populations. 3,13,14,17,19) Acknowledgments We want to thank Yavuz Sanisoglu (Ph.D., statistics) forhelpwiththestatisticalanalyses. References 1) Benini A, Di Martino E: [Lesion of the ramus profundus of the radial nerve (supinator syndrome). Dissociated radial paralysis of the proximal under arm type]. Schweiz Med Wochenschr 106: , 1976 (Ger, with Eng abstract) 2) Carr D, Davis P: Distal posterior interosseous nerve syndrome. JHandSurg[Am] 10: , ) Chen DS, Gu YD, Zhang GM, Yan JG, Chen XM, Zhang LY, Cai PQ, Xu JG: Entrapment of posterior interosseous nerve of forearm. Report of 25 cases. Chin Med J (Engl) 107: , ) Cravens G, Kline DG: Posterior interosseous nerve palsies. Neurosurgery 27: , ) Derkash RS, Niebauer JJ: Entrapment of the posterior interosseous nerve by a fibrous band in the dorsal edge of the supinator muscle and erosion of a groove intheproximalradius.jhandsurg[am] 6: , ) Eaton CJ, Lister GD: Radial nerve compression. Hand Clin 8: , ) Fuss FK, Wurzl GH: Radial nerve entrapment at the elbow: surgical anatomy. 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5 18 Y. Kirici et al. muscle. A report of four cases. Acta Orthop Scand 47: , ) Ozkan M, Bacakoglu AK, Gul O, Ekin A, Magden O: Anatomic study of posterior interosseous nerve in the arcade of Frohse. J Shoulder Elbow Surg 8: , ) Prasartritha T, Liupolvanish P, Rojanakit A: A study of the posterior interosseous nerve (PIN) and the radial tunnel in 30 Thai cadavers. JHandSurg[Am] 18: , ) Serra G, Aiello I, Rosati G, Tugnoli V, Traina GC, Cristofori MC: Posterior interosseous nerve palsy. Report of three unusual cases. Ital J Neurol Sci 5: 85 87, ) Sponseller PD, Engber WD: Double-entrapment radial tunnel syndrome. JHandSurg[Am] 8: , ) Suematsu N, Hirayama T: Posterior interosseous nerve palsy. JHandSurg[Br] 23: , ) Theodorou SD, Ierodiaconou MN, Roussis N: Fracture of the upper end of the ulna associated with dislocation of the head of the radius in children. Clin Orthop 228: , ) Wilhelm A: [Treatment of therapy refractory epicondylitis lateralis humeri by denervation. On the pathogenesis]. Handchir Mikrochir Plast Chir 31: , 1999 (Ger, with Eng abstract) 20) Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dessek JE, Ferguson MWJ: Gray's Anatomy, ed 38. New York, Churchill-Livingstone, 1995, pp ) Witthaut J, Steffens K: [Paralysis of the interosseous nerve by a tendinous margin of the extensor carpi radialis brevis]. Handchir Mikrochir Plast Chir 27: , 1995 (Ger, with Eng abstract) Address reprint requests to: Y. Kirici, M.D., GATA Anatomi AD, Etlik, Ankara, Turkey. ykirici@gata.edu.tr Commentary on this paper appears on the next page. Neurol Med Chir (Tokyo) 44,January,2004

6 Posterior Interosseous Nerve Syndrome 19 Commentary This manuscript has all of us carefully reevaluate the distal aspects of the radial nerve as it traverses into the forearm. When the nerve goes past the sensor carpi radialis brevis, the classic anatomy books say that muscle is enervated by the posterior inner osseous nerve. But in the review in 30 cadaver dissections that muscle is enervated by the radial nerve more than half to the time. The extensor carpi radialis brevis can actually be enervated by both aspects of the nerve. When there is compression in this area, while the fibrous texture of the arcade of Frohse may be important. It appears that the nerve's entrance into the supinator muscle may indeed be more important. However, if there are fibrous changes in the arcade of Frohse the spinator muscle, especially associated with enlargementofthatmuscle,thenthesymptomsare related to the interosseous nerve compression will be apparent. In the article, there is some discussion on the etiology of ``tennis elbow.'' The interosseous nerve could be part of this. More commonly, this is extensor tendinitis, coming further up the arm away from the radial nerve. These people are to be congratulated on their extensive section. Thomas B. DUCKER, M.D., F.A.C.S. Department of Neurosurgery Johns Hopkins University Annapolis, Maryland, U.S.A. Neurol Med Chir (Tokyo) 44, January, 2004