The Distal Biceps Tendon: Footprint and Relevant Clinical Anatomy. George S. Athwal, MD, Scott P. Steinmann, MD, Damian M.

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1 The Distal Biceps Tendon: Footprint and Relevant Clinical Anatomy George S. Athwal, MD, Scott P. Steinmann, MD, Damian M. Rispoli, MD From the Hand and Upper Limb Centre, St. Joseph s Health Care London, University of Western Ontario, London, Ontario, Canada; the Department of Orthopaedics, Mayo Clinic, Rochester, MN; and the Department of Orthopaedics, Wilford Hall Medical Center, Lackland Air Force Base, TX. Purpose: There is little information in the literature describing the anatomy of the biceps tendon insertion. The purpose of this study was to map the footprint of the biceps tendon insertion on the bicipital tuberosity and to report on the relevant anatomy to assist surgeons with correct tendon orientation during surgical repair. Methods: Fifteen fresh-frozen adult upper extremities were used in this study. The relationships between the long head of the biceps tendon, the short head of the biceps tendon, the muscle bellies, and the distal tendon orientation were examined. The length, width, and area of the biceps tendon insertion were measured. Results: In all specimens examined, the biceps musculotendinous unit rotated 90 externally from origin to insertion. The long head of the distal tendon was inserted onto the proximal aspect of the bicipital tuberosity, while the short head of the distal tendon was inserted onto the distal aspect of the tuberosity. The lacertus fibrosus, in all specimens, originated from the distal short head of the biceps tendon. On average, the biceps tendon insertion started 23 mm distal to the articular margin of the radial head. The average length of the biceps tendon insertion on the tuberosity was 21 mm, and the average width was 7 mm. The average total area of the biceps tendon insertion (footprint) was 108 mm 2. The average area of the long head of the biceps tendon insertion was 48 mm 2, and the average area of the short head of the biceps tendon insertion was 60 mm 2. Conclusions: Landmarks have been identified that will allow anatomic orientation of the distal biceps tendon during operative repair. The distal short head of the biceps tendon has a consistent relationship with the lacertus fibrosus and a distinct insertion on the bicipital tuberosity. The dimensions of the distal biceps tendon footprint have been determined to assist with bone tunnel or suture anchor placement during surgical repair. (J Hand Surg 2007; 32A: Copyright 2007 by the American Society for Surgery of the Hand.) Key words: Anatomy, biceps, footprint, tendon. The biceps musculotendinous unit consists of two parts, the short head and the long head. The long head of the biceps arises from the superior aspect of the glenoid and the short head from the corocoid process. Both heads of the bicep muscle are innervated by the musculocutaneous nerve and are thought to coalesce into a single distal tendon inserting on the ulnar aspect of the bicipital tuberosity of the radius. Ruptures of the distal bicep tendon are common and are thought to be due to intrinsic tendon degeneration and hypovascularity. 1 3 Surgical repair of acute distal biceps tendon avulsions has become commonplace, and several techniques exist with good reported outcomes. 3 8 There is little information in the literature describing the anatomy of the biceps tendon insertion. Mazzocca et al 9 recently described the bony anatomy of the bicipital tuberosity. The authors examined 178 dried cadaveric radii and dissected 18 fresh frozen cadaver elbows. They reported the bony dimension of the bicipital tuberosity in detail The Journal of Hand Surgery 1225

2 1226 The Journal of Hand Surgery / Vol. 32A No. 8 October 2007 and classified the morphology of the bicipital tuberosity ridge as smooth (absent), small, medium, large, or bifid. The purpose of our study was to map the footprint of the biceps tendon insertion on the bicipital tuberosity of the radius and to report on the local relevant anatomy to assist surgeons with correct tendon orientation for anatomic repair. Materials and Methods Fifteen fresh frozen adult upper extremities were used in this study. The specimens had no signs of prior trauma or surgery and individuals were a mean age of 78 years at the time of death (range, y). Specimens were from 7 men and 8 women. This study was approved by our institutional research committee. The specimens were stripped of all skin and subcutaneous tissue to identify the long head of the biceps, the short head of the biceps, the lacertus fibrosus, and the distal biceps tendon. The long and short heads of the biceps muscle were then detached from their origins along with the lacertus fibrosus from its insertion. The proximal radius was then removed en bloc with the biceps muscle. Dissection was performed, using 2.5 loupe magnification, from the proximal tendons (long and short) toward the muscle bellies to separate the short head of the biceps muscle belly from the long head of the biceps muscle belly. The relationships between the long head of the biceps tendon, the short head of the biceps tendon, the muscle bellies, and the distal tendon orientation were examined. The length and width of the biceps tendon insertion and the distance between the articular margin of the radial head and the start of the biceps tendon insertion was measured with calipers (General Tools, New York, NY). The tendon footprint area was measured by sharply incising the tendon and marking the insertion with a permanent ultrafine-tipped marker. The marked area was measured by laying an acetate grid sheet over the bicipital tuberosity and counting the number of 1 1 mm squares occupied by the marked area. The measurements were repeated 3 times by the same investigator. Results Gross Anatomy In all specimens examined, the biceps musculotendinous unit rotated 90 externally from origin to insertion (Fig. 1). In 2 specimens, the long head of the biceps and the short head of the biceps remained as Figure 1. The biceps musculotendinous unit is illustrated from origin to insertion. The lacertus fibrosus is found to originate from the proximal aspect of the short head of the distal tendon. The short head of the distal tendon was inserted at the distal ulnar aspect on the bicipital tuberosity while the long head of the distal tendon was inserted at the proximal ulnar aspect. independent muscle bellies and as independent distal tendons to their uniquely separate insertions on the bicipital tuberosity. In these 2 specimens, the long head of the distal tendon was inserted onto the proximal aspect of the tuberosity while the short head of the distal tendon was inserted onto the distal aspect of the tuberosity. In 8 specimens, the long head and short heads of the muscle bellies and their corresponding distal tendons could be easily separated and followed to their unique insertion areas on the bicipital tuberosity. As in the 2 specimens with completely separate muscle bellies, the long head of the distal tendon in these 8 specimens was inserted proximally on the tuberosity, and the short head of the distal tendon was inserted distally on the tuberosity (Fig. 2). In 5 specimens, the short and long heads of the muscle bellies coalesced distally, and their corresponding distal tendons were connected together. In these specimens, the muscle bellies could be separated with a minimal amount of dissection. Their distal tendons were more adherent to each other and could be grossly divided; however, their fibers coa-

3 Athwal, Steinmann, and Rispoli / Distal Biceps Tendon Anatomy 1227 Figure 2. The long- and short-head biceps tendon insertions are illustrated (A). The mean footprint area of the long head of the tendon was 48 mm 2 and of the short head of the tendon was 60 mm 2. A cadaveric specimen (B) demonstrates the separation between the short and long heads of the distal tendons (white arrow) with near complete rupture of the short head of the distal tendon (black arrow). lesced enough that precise calculation of the individual footprints was difficult and therefore thought to be imprecise and was abandoned. The lacertus fibrosus was examined and found to originate from the proximal aspect of the short head of the distal tendon (Fig. 1) in all 15 specimens. Tendon Insertion In all specimens, the biceps tendon insertion was located along the extreme ulnar margin of the bicipital tuberosity (Fig. 3). The tendon is ribbon-shaped just proximal to its insertion; however, as it approaches the tuberosity the tendon thickens in width and length creating a true footprint on the tuberosity. The average distance from the articular margin of the radial head to the start of the biceps tendon insertion in all specimens was 23 mm (range, mm); the average distance in the male specimens was 25 mm (range, 22 to 27 mm) and in the female specimens was 22 mm (range, mm). The average length of the biceps tendon insertion on the tuberosity was 21 mm (range, mm) and the average width was 7 mm (range, 6 10 mm). The average length and width of the biceps insertion in the male specimens were 22 mm and 8 mm, respectively, and in the female specimens were 20 mm and 7 mm, respectively. The average area of the biceps tendon insertion (footprint) in all specimens was 108 mm 2 (range, mm 2 ). The average area in the male and female specimens was 112 mm 2 and 104 mm 2,respectively. In 10 specimens the exact dimensions and area of the short- and long-head tendon insertions could be calculated. The short-head tendon insertion on the bicipital tuberosity averaged 12 mm in length, 7 mm in width and 60 mm 2 in area. The long-head tendon insertion on the bicipital tuberosity averaged 9 mm in length, 7 mm in width and 48 mm 2 in area. Discussion The purpose of this anatomic project was to provide quantitative data on the dimensions and area of the biceps tendon insertion on the radius and to identify local landmarks to assist with correct tendon orientation. The clinical importance of re-creating normal distal biceps tendon orientation is unknown; how-

4 1228 The Journal of Hand Surgery / Vol. 32A No. 8 October 2007 Figure 3. A left cadaveric proximal radius demonstrating the far ulnar insertion of the biceps tendon complex on the bicipital tuberosity. ever, it is reasonable that restoration of normal anatomy would increase the probability of a more normal clinical outcome. The concept that the distal biceps tendon is a simple cylindrical tendon was challenged. The qualitative findings of this study demonstrate that the distal biceps tendon has a consistent orientation and that the long and short heads of the muscles have distinct distal tendons that insert at unique locations on the bicipital tuberosity. It was observed that the long head of the biceps muscle gave rise to the long head of the distal tendon, which inserted on the proximal ulnar aspect of the bicipital tuberosity. The short head of the muscle gave rise to the short head of the distal tendon, which inserted on the distal ulnar aspect of the bicipital tuberosity. The novel finding that the short head of the distal tendon was also the origin of the lacertus fibrosus was key, as it identified the lacertus fibrosus as an important landmark that allows identification of the short head of the tendon and, therefore, correct orientation of the entire distal biceps tendon during surgical repair (Table 1). The biceps tendon insertion started a mean of 23 mm distal to the articular margin of the radial head. The dimensions of the biceps footprint average 21 mm in length and 7 mm in width. The average area was 108 mm 2. Knowledge of the size and location of the normal footprint can assist surgeons during surgical repair of distal biceps tendon ruptures. Repairs are done via a one-incision technique, commonly using suture anchors or a two-incision technique using a bone trough and tunnels. 3,4,7,8 Familiarity with the normal footprint dimensions can assist with correct suture anchor and bone trough placement. Understanding of the normal distal biceps tendon orientation and insertion can also assist surgeons in determining the size of partial thickness tears and the associated muscle involved. Mazzocca et al recently defined the internal and external osteology of the bicipital tuberosity by examining 118 dried cadaveric radii. 9 The authors further examined 48 specimens with computed tomography to determine the cortex-to-cortex diameter of the proximal radius at the level of the tuberosity. The main purpose of Mazzocca et al s study was to define the bony anatomy and dimensions of the bicipital tuberosity. The authors also examined the distal biceps tendon insertion in 18 fresh-frozen cadaver elbows and reported a mean length of 14 mm and width of 2 mm. The authors reported mean distal biceps tendon dimensions are less than those reported in our study. We theorize the discrepancies may be due to variability in specimen sizes or gender-related differences, as our study had specimens from 7 men and 8 women, while Mazzocca et al had 12 male and 6 female specimens. Due to the differences between studies, we believe further investigations are required. Table 1. Key Points of Distal Biceps Tendon Anatomy Gross Anatomy - biceps musculotendinous unit rotates 90 externally from origin to insertion - lacertus fibrosus originates from the distal short head of the biceps tendon - short head inserts distally on the bicipital tuberosity - long head inserts proximally on the bicipital tubersity - short and long heads of the distal tendons insert along the ulnar margin of the bicipital tuberosity *Combined short head and long heads. Footprint Dimensions - average length:* 21 mm - average width:* 7mm - average area:* 108 mm 2 - average length short head: 12 mm - average length long head: 9 mm - average area short head: 60 mm 2 - average area long head: 48 mm 2

5 Athwal, Steinmann, and Rispoli / Distal Biceps Tendon Anatomy 1229 Several new anatomic features identified in our study include that the lacertus fibrosus originates from the proximal aspect of the short head of the distal tendon and that it can be used as a landmark to correctly orientate the tendon during repair, as the short head of the tendon inserts distally and the biceps complex rotates 90 externally. The biceps tendon insertion footprint area, not previously reported, was also determined and may have implications for surgical tendon repair. The weaknesses of this study include the low sample size, the use of fresh-frozen cadavers versus fresh specimens and not correlating the dimensions of the cadaver distal biceps tendons to whole specimen sizes (length of the cadaver arm, total length radius/ ulna/humerus and cadaver height). A thorough knowledge of the anatomy of the distal biceps tendon may enhance our understanding of its disorders. This information may assist surgeons in correctly orientating the distal biceps tendon during anatomic repair, which may help restore more normal muscle kinematics. Received for publication January 23, 2007; accepted in revised form May 24, No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Corresponding author: George S. Athwal, MD, Hand and Upper Limb Centre, St Joseph s Health Care, University of Western Ontario, 268 Grosvenor St., London, Ontario, Canada, N6A 4L6; gathwal@uwo.ca. Copyright 2007 by the American Society for Surgery of the Hand /07/32A $32.00/0 doi: /j.jhsa References 1. Seiler JG 3rd, Parker LM, Chamberland PD, Sherbourne GM, Carpenter WA. The distal biceps tendon. Two potential mechanisms involved in its rupture: arterial supply and mechanical impingement. J Shoulder Elbow Surg 1995;4: Koch S, Tillmann B. The distal tendon of the biceps brachii. Structure and clinical correlations. Ann Anat 1995;177: El-Hawary R, Macdermid JC, Faber KJ, Patterson SD, King GJ. Distal biceps tendon repair: comparison of surgical techniques. J Hand Surg 2003;28A: McKee MD, Hirji R, Schemitsch EH, Wild LM, Waddell JP. Patient-oriented functional outcome after repair of distal biceps tendon ruptures using a single-incision technique. J Shoulder Elbow Surg 2005;14: Bain GI, Prem H, Heptinstall RJ, Verhellen R, Paix D. Repair of distal biceps tendon rupture: a new technique using the Endobutton. J Shoulder Elbow Surg 2000;9: Greenberg JA, Fernandez JJ, Wang T, Turner C. EndoButtonassisted repair of distal biceps tendon ruptures. J Shoulder Elbow Surg 2003;12: Ramsey ML. Distal biceps tendon injuries: diagnosis and management. J Am Acad Orthop Surg 1999;7: Kelly EW, Morrey BF, O Driscoll SW. Complications of repair of the distal biceps tendon with the modified twoincision technique. J Bone Joint Surg 2000;82AA: Mazzocca AD, Cohen M, Berkson E, Nicholson G, Carofino BC, Arciero R, et al. The anatomy of the bicipital tuberosity and distal biceps tendon. J Shoulder Elbow Surg 2007;16: