Surg Radiol Anat (2005) 27: 171–175 DOI 10.1007/s00276-005-0321-z ANATOMIC BASES OF MEDICAL, RADIOLOGICAL AND SURGICAL TECHNIQUES Adnan Ozturk Æ Cigdem Kutlu Æ Nurcan Taskara Aysin Cetiner Kale Æ Bulent Bayraktar Æ Aycicek Cecen Anatomic and morphometric study of the arcade of Frohse in cadavers Received: 4 July 2004 / Accepted: 20 January 2005 / Published online: 9 July 2005 Springer-Verlag 2005 Abstract 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. Keywords Arcade of Frohse Æ Supinator muscle Æ Radial nerve Æ Anatomy Æ Morphometry Introduction N. Taskara Tuccarbasi Istasyon Caddesi, No 54/20, Erenkoy, 34738 Istanbul, Turkey The deep branch of the radial nerve (DBRN) runs between the superficial and deep parts of the supinator muscle to enter the posterior compartment of the forearm. Then, it continues as the posterior interosseous nerve [12, 27]. The most superior part of the superficial layer of the supinator muscle may form a fibrous arch [22]. This arch (arcade of Frohse, AF) was first described by Frohse and Fränkel [6] in 1908. The DBRN runs under the AF, and enters the plane between the two parts of the supinator muscle [22]. Kopell and Thompson [9] initially reported the entrapment of the DBRN by the AF in 1963. Capener [2] recorded the vulnerability of the DBRN at the AF in 1966. Spinner [22] stated the compression of the DBRN at the AF in 1968. The AF is reported to be the most common structure causing entrapment neuropathy of the DBRN [1, 3, 4, 5, 7, 8, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26]. The aim of our study was to reveal the anatomical properties and especially the morphometric measurements of the AF in cadavers. A. C. Kale Department of Anatomy, Medical Faculty, Ondokuz Mayis University, 55139 Samsun, Turkey Materials and methods A. Cecen Neurosurgical Clinic of Kartal Research and Teaching Hospital, Kartal, 34865 Istanbul, Turkey This study was performed on 55 upper extremities of the formalin-fixed human cadavers used for the routine A. Ozturk (&) Æ B. Bayraktar Department of Anatomy, Istanbul Medical Faculty, Istanbul University, Capa, 34390 Istanbul, Turkey E-mail: [email protected] Tel.: +90-212-4142176 Fax: +90-212-6358522 C. Kutlu Department of Internal Medicine, Haseki Education and Research Hospital, Aksaray, 34200 Istanbul, Turkey 172 dissection courses in the Anatomy Department of the Istanbul Medical Faculty, Istanbul University, Turkey during 2000 and 2003. All the cadavers were Caucasian men, and the causes of their death were the diseases of the respiratory and cardiovascular systems. The mean age of the cadavers was 51.54 years (range 32—76 years). There were no pathological findings in the dissection region of the upper extremities. From the available records it was not possible to obtain any information about the dominant hand, occupation, habits and sporting activities of the specimens. All the upper extremities were carefully dissected. The radial nerve and its two terminal branches, the supinator muscle and the AF were identified in the anatomical position. The tip of the lateral epicondyle of the humerus and the tip of the styloid process of the radius were marked. In this study, acupuncture needles (size 0.25 · 25 mm) were used to mark the measuring points for each measurement. All the measurements were made manually and macroscopically on the upper extremities in the anatomical position by two experienced anatomists (A.O., B.B.), with digital calipers (measuring range 300 mm, resolution 0.01 mm, maximum error 0.02 mm). The anatomical structures of the supinator muscle, radial nerve and its two terminal branches were observed and recorded. The anatomical structure of the AF was examined macroscopically. First, the shape of the AF was recorded (Fig. 1a, b). Then, according to the classification of Prasartritha et al. [15], the AF was classified: as tendinous if the medial and lateral halves of the AF were fibrous in texture (Fig. 1a), or as membranous if the medial half of the AF was muscular (Fig. 1b). These two types of the AF were photographed. The width, length and thickness of the AF were measured as the dimensions of the AF. The superolatFig. 1. a Photograph of a cadaver which has a tendinous AF (right upper extremity). b Photograph of a cadaver which has a membranous AF (left upper extremity). rn, radial nerve; bp, bifurcation point (where the radial nerve divides into its terminal branches); sb, superficial branch of the radial nerve; db, deep branch of the radial nerve; AF, Arcade of Frohse; sm, supinator muscle; long arrow, proximal tip of the AF; short arrow, distal tip of the AF eral tip of the AF was named as the proximal tip. The inferomedial tip of the AF was named as the distal tip. The proximal and distal tips were marked. First, four imaginary lines were drawn to measure the width, length and thickness of the AF (Fig. 2): (1) the first passed horizontally from the proximal tip (the imaginary horizontal line), (2) the second passed vertically from the distal tip (the imaginary vertical line), (3) the third extended from the proximal tip to the distal tip (the imaginary line connecting the two tips of the AF), and (4) the fourth was perpendicular to the midpoint of the third imaginary line. Then, the point where the first imaginary line met the second imaginary line was marked. This point was named as the meeting point. The horizontal distance between the proximal tip and the meeting point was measured as the width of the AF on the coronal plane, and the vertical distance between the distal tip and the meeting point was measured as the length of the AF on the coronal plane (Fig. 2). Next, the point where the fourth imaginary line intersected the AF was marked. This point was named as the thickness point, because we measured the thickness of the AF from this point (Fig. 2). This measurement of thickness was performed when the long axes of the jaws of the digital calipers were parallel to the fourth imaginary line. The vertical distance between the tip of the lateral epicondyle of the humerus and the thickness point of the AF was measured on the coronal plane and this distance was named as the ‘‘distance AF’’ (Fig. 3). The vertical distance between the tip of the lateral epicondyle of the humerus and the tip of the styloid process of the radius was measured as the ‘‘length of the forearm’’ on the coronal plane (Fig. 3) to allow readers to understand the size of the specimens and also to find the mean ‘‘ratio AF’’. The ‘‘ratio AF’’ was found by dividing the distance AF by the forearm length (ratio AF = distance AF/ 173 Fig. 2 Diagram of the width, length and thickness of the AF on the photograph of a cadaver which has a tendinous AF (right upper extremity). db, deep branch of the radial nerve; AF, Arcade of Frohse; sm, supinator muscle; pt, proximal tip of the AF; dt, distal tip of the AF; mp, meeting point (where the imaginary horizontal line meets the imaginary vertical line); W, width of the AF (the horizontal distance between the pt and the mp); L, length of the AF (the vertical distance between the dt and the mp); tp, thickness point (where the imaginary line perpendicular to the midpoint of the imaginary line connecting the two tips of the AF intersects the AF). The thickness of the AF was measured from the tp forearm length) for each upper extremity. Then, the mean value of the ratio AF was calculated. This value may be used to predict the distance AF of any upper extremity with a known forearm length. Thus, the predicted distance AF of any upper extremity may be found by multiplying its forearm length by the mean ratio AF (predicted distance AF = measured forearm length · mean ratio AF). All the findings about the supinator muscle, the radial nerve and its two terminal branches, and also the shape and type of the AF, the appropriate measuring points for each measurement and the accuracy of the measurements were determined by the consensus of six researchers. Fig. 3 Diagram of the ‘‘distance AF’’ and the ‘‘forearm length’’ (left upper extremity). rn, radial nerve; db, deep branch of the radial nerve; sb, superficial branch of the radial nerve; sm, supinator muscle; AF, Arcade of Frohse; le, lateral epicondyle of the humerus; sp, styloid process of the radius; D, ‘‘distance AF’’ (between the lateral epicondyle and the AF); L, ‘‘forearm length’’ (between the lateral epicondyle and the styloid process) Statistical analysis of all the measurements was performed using the SPSS 7.5 statistical program (SPSS Inc., Chicago, USA) for Windows, and the mean, standard deviation and range of values were calculated for each measurement. The results of our study were compared with the findings of previous studies. Results The supinator muscle, the radial nerve and its two terminal branches showed no variations. In all the extremities it was observed that the shape of the AF was semicircular (Fig. 1a, b). In 87% of the extremities (48/ 55) the AF was tendinous (Fig. 1a) and in 13% (7/55) it was membranous (Fig. 1b). All our measurement results are given as the mean±SD (minimum–maximum). The width of the AF was 10.13±2.10 mm (5.65–13.61), the length of the AF was 8.60±3.51 mm (2.77–20.20) and the thickness of the AF was 0.77±0.34 mm (0.25–1.78). The distance AF was 46.23±9.84 mm (24.97–84.04) and the forearm length was 233.17±19.11 mm (196.23– 174 274.39). We found the ratio AF to be 0.199±0.047 (0.101–0.418). The mean ratio AF (=0.199) is approximately 1/5. extremity by dividing its forearm length by 5 (predicted distance AF = forearm length of the patient/5). Conclusions Discussion The AF is most often reported as the site of the compression of the DBRN in anatomical and clinical studies [17]. The cause of compression of the DBRN at the AF has been reported as only a tendinous AF [9, 26], or any pathological condition in addition to tendinous AF [2, 4] such as the space-occupying lesions (ganglion, lipoma, etc.), edema, spasm, repeated rotary movement, etc. In 1908, Frohse and Fränkel [6] first described this arch (AF) as a normal anatomical tendinous structure. In his anatomical study of 25 adults and 10 full-term fetuses, which was performed in 1968, Spinner [22] reported that none of the newborn full-term fetuses had a sharp tendinous AF, and that the most superior part of the superficial layer of the supinator muscle was always muscular. He suggested that the semicircular fibrous AF probably formed in adults due to repeated rotary movement of the forearm. The percentage of tendinous AFs has varied from 30% to 80% in previous anatomical studies [4, 5, 13, 14, 15, 17, 22, 24, 26]. The high percentages of tendinous AFs were reported by Werner [26] (89%, 80/90 patients) and by Lister et al. [10] (100%, 20/20 patients) in clinical studies. In our study, the percentage of the tendinous AFs was found to be 87%. Debouck and Rooze [4] reported that the difference between Spinner’s percentage of tendinous AFs (30%) [22] and their own (64.1%) could be explained by a difference in the classification criteria of the appearance of the AF structure, or the fact that the two populations were not comparable. They declared that the tendinous AF was a normal anatomical structure. According to Spinner [22], entrapment of the DBRN becomes a distinct possibility when a tendinous AF is present, particularly if it is thick, and the hiatus for the passage of the nerve is narrow. In the light of Spinner’s suggestion [22], we measured the width, length and thickness of the AF. In the literature, the width, length and thickness of the AF were measured only by Ebraheim et al. [5]. They found the width of the AF to be 2.8 mm, the length to be 18.6 mm and the thickness to be 0.8 mm in male cadavers, and the width of the AF to be 2.5 mm, the length to be 18.5 mm and the thickness to be 0.7 mm in females. The distance AF was reported as 3.8 cm by Low et al. [11], 4.7 cm by Werner [26] and 4.91 cm by Papadopoulos et al. [14]. However, they did not give any information about forearm length. In our study, the distance AF was found to be 46.23 mm. The surgeon may calculate the predicted distance AF of any upper extremity using our mean ratio AF, or may easily find the predicted distance AF of any upper The semicircular tendinous AF is anatomically a normal condition in adult cadavers, but clinically it is a potential anatomical factor causing compression of the DBRN. Our measurements of the dimensions of the AF may contribute to the anatomy of the AF. The mean ratio AF may be used to localize the AF in this region during forearm surgery. 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