Clinical History: A 56 year-old male presents with swelling and ecchymosis in the antecubital fossa following a “pop” and acute onset of pain while lifting a heavy weight one week earlier. What are the findings? What is your diagnosis?
Complete tear and retraction of the short head component of a bifurcated distal biceps tendon.
Ruptures of the distal biceps tendon are seen most commonly in the dominant arm of males greater than 40 years of age and account for 3-10% of biceps injuries. The injury also affects athletes involved in strength training or who have sustained athletic related trauma. With increased understanding of the anatomy and biomechanics of the distal biceps tendon, surgeons are more likely to recreate the normal anatomy and restore supination and flexion at the elbow in patients who have sustained a distal biceps rupture. MRI is useful to delineate the extent of distal biceps tendon tears and retraction. In addition MRI provides information that helps differentiate other entities that may simulate distal biceps injury.
Anatomy and Function
The long head of the biceps arises from the supraglenoid tubercle and the short head of the biceps arises from the coracoid process. Cadaveric studies have shown that the long and short head muscles of the biceps have few muscular and distal tendinous connections1,2,3. The long and short head muscles interdigitate distally over a variable segment at the level of the distal musculotendinous junction, termed the “goose quill” because of its gross appearance to a goose’s feather3. Instead of a single cylindrical distal biceps tendon, in the majority of cases the distal biceps tendon is composed of two macroscopically distinct tendons with varying degrees of decussating tendon fibers1,2,3. The result is a distal biceps tendon that commonly consists of two independent units representing continuations of the proximal long and short head musculotendinous units of the biceps4.
The distal tendon arising from the long head of the biceps muscle inserts onto the proximal bicipital tuberosity and the distal tendon of the short head inserts onto the distal portion of the bicipital tuberosity2. The insertional footprint of the short head is larger than the more proximal long head1,2. The short head footprint inserts over the apex of the bicipital tuberosity while the long head footprint lies more posterior with the result being a slightly oblique orientation of the entire footprint relative to the long axis of the radius5. Biomechanically, this footprint orientation results in the short head providing the greatest amount of flexion and supination force when the forearm is in pronation and neutral position5. When the forearm supinates past 60 degrees, the long head provides stronger supination torque based on the incompletely unwound slightly posterior position of the footprint5.
The lacertus fibrosus (bicipital aponeurosis) arises at the level of the distal biceps myotendinous junction. Dissection studies are contradictory as to the exact origin. Athwal et al. found that the lacertus fibrosus originated from the short head tendon alone and felt that this was a consistent landmark to help the surgeon properly orient the torn distal biceps tendon at the time of repair2. Other studies indicate a shared origin from the short and long heads1,3. The lacertus fibrosus extends over the proximal flexor muscles and is tethered by several strong fascial adhesions before inserting at the ulnar aspect of the proximal ulna2. Fibers of the lacertus fibrosis also extend radial to the flexor muscles, the median nerve, and the brachial artery before inserting into the radial aspect of the proximal ulna1. The lacertus fibrosus functions to help protect the neurovascular structures, to aid in transmitting the biceps flexion force to the ulna, and with forearm muscle flexion may redirect the orientation of the biceps1.
The bicipitoradial bursa is a synovial lined bursa consistently found between the distal biceps and bicipital tuberosity, and is normally collapsed and not visualized. The distended bursa can extend proximally and surround the distal biceps tendon1. The distal biceps tendon does not have a synovial lined tendon sheath.
Normal MRI appearance
Axial images (Figure 7) are most helpful in evaluating the distal biceps with additional information supplied by orthogonal views. The FABS (flexed elbow, abducted shoulder, forearm supinated) view (Figure 8) has been advocated to improve imaging of the distal biceps insertion6. The normal tendon is low signal on all sequences. The normal distal biceps tendon may appear as a single tendon with an ovoid cross-section on axial images, as a partially bifurcated tendon with bridging fibers, or as two separate tendons. The bifurcated appearance is most easily identified in the proximal portion of the distal biceps tendon (Figure 9) and may persist to the insertion at the bicipital tuberosity, but more frequently the tendon fibers become inseparable by MRI more distally (Figure 10).
Mechanism of Injury
Distal biceps rupture most commonly affects the dominant arm of men from age 40 to 60. The mechanism of distal biceps tendon rupture is forced extension of the elbow held in 90 degrees flexion with the forearm supinated. Distal biceps tendon ruptures most commonly present after a single traumatic event. However, evidence suggests that tendon hypovascularity and mechanical impingement during forearm rotation are contributory factors, increasing tendon susceptibility to rupture7. Consequently, tendinosis and partial tears of the distal biceps tendon may precede complete ruptures. Smoking and anabolic steroid use may also increase the risk of distal biceps rupture8,9.
Distal biceps tears in women are extremely rare and typically occur over the age of 60. The injury is most often a partial tear unrelated to a single traumatic event but with a more insidious onset10.
Injuries of the distal musculotendinous junction with an intact distal tendon are exceedingly rare and most commonly occur with the elbow extended, the forearm supinated, and the glenohumeral joint in active or passive elevation11.
Clinical Presentation and Physical Examination Findings
In the classic clinical presentation of an acute complete biceps tendon rupture the patient relates a painful “pop” followed by swelling and ecchymosis in the antecubital region, asymmetry in biceps muscle contour, absence of a palpable distal tendon, and weakness and/or pain primarily in flexion and supination. The retracted distal biceps tendon leads to a palpable “mass” in the antecubital fossa.
Frequently, the diagnosis of a complete distal biceps tear is not straightforward. In a study by Devereaux and ElMaraghy only 33% of patients described an audible or palpable “pop” and only 38% had a visible deformity with surgically proven complete distal biceps tears12. Swelling and hematoma can mask distal biceps muscle asymmetry despite a retracted tendon12. Retraction of the ruptured distal biceps tendon is prevented if the bicipital aponeurosis (lacertus fibrosus) remains intact, and in such cases the typical “mass” of retracted tendon in the antecubital fossa is absent. In addition, an intact lacertus fibrosus may limit ecchymosis formation by confining the hematoma13. With more chronic injuries (older than 4 weeks) edema and ecchymosis are often absent.
Partial tears of the distal biceps tendon typically present with a more insidious onset with the patient complaining of chronic pain, often without significant loss of strength.
Physical examination tests that can assist in diagnosing a complete distal biceps rupture include the hook test, the passive forearm pronation (PFP) test, and the biceps crease interval (BCI) test12. The hook test is performed by the examiner attempting to hook a finger posterior to the distal cord-like biceps tendon from the lateral side with the elbow held in 90 degrees of flexion and forearm supination. This can be accomplished with an intact distal biceps, but with a complete distal rupture there is no cord-like structure under which the examiner’s finger may be hooked14. An intact tendon but with a painful response to the hook test is indicative of a partial tear14. The PFP test evaluates the functional continuity of the distal muscle-tendon-bone complex15. With complete avulsion of the distal biceps tendon there is loss of visible and palpable proximal to distal movement of the distal biceps muscle belly with passive pronation of the forearm starting from a supinated position15. The BCI test evaluates the extent of tendon retraction associated with distal biceps rupture by measuring the distance between the antecubital crease of the elbow and the cusp of distal descent of the biceps muscle16. An abnormal BCI indicates a rupture of the distal biceps and lacertus fibrosus16.
MRI allows characterization of distal biceps injuries that range from tendinosis to distal biceps tendon tear by demonstrating abnormalities of tendon diameter, tendon signal intensity, and tendon retraction. Tendinosis, partial tear, and complete rupture may affect a single distal biceps tendon and individual or both components of a bifurcated distal tendon.
MRI findings of an acute complete distal biceps tendon rupture are best seen on fluid sensitive series and include discontinuity of the tendon at the insertion site with a fluid-signal filled gap, increased intratendinous signal intensity, and increased signal intensity in the biceps muscle belly and surrounding soft tissues (Figure 11). Ill-defined peritendinous fluid signal resulting from hemorrhage and edema is typically present with acute ruptures. An intact lacertus fibrosus may prevent significant retraction of the torn tendon and may make the differentiation of a complete rupture from a partial tear more difficult (Figure 12).
Partial tears of the biceps tendon are diagnosed by abnormal intra-tendinous fluid signal and alterations in tendon caliber (Figure 13). Avulsive marrow edema in the bicipital tuberosity and bicipitoradial bursitis are frequent accompanying findings17. With an improved understanding of the commonly bifurcated distal biceps tendon architecture, partial tears may be further described by the status of the distal short and long heads (Figure 13). What were once diagnosed as partial tears of the distal biceps tendon with longitudinal delamination or splitting were, in many instances, likely complete tears of an isolated component of a bifurcated distal biceps tendon as in the test case19. Using minimally invasive single incision repair techniques, such an injury may be missed because of the intact, taut remaining tendon19. The short head component is most commonly torn19 with variable involvement of the more proximally inserting component by tendinosis, partial tear, or complete tear3. Isolated tears of the long head component are less commonly seen.
The MRI appearance of tendinosis is made on the basis of abnormal tendon diameter or increased tendon signal intensity that does not parallel fluid (Figure 14)3. The features of severe tendinosis may overlap with the appearance of low-grade partial tears18.
Bicipitoradial bursitis can present as a painful antecubital mass39. Bicipitoradial bursitis commonly accompanies partial tears of the distal biceps tendon. In the absence of underlying biceps tendon pathology, bicipitoradial bursitis is most commonly associated with overuse and repetitive mechanical trauma39. Bursal involvement by inflammatory processes such as rheumatoid arthritis and infection and by synovial metaplastic processes such as synovial osteochondromatosis may also be seen. Distension of the bursa by simple or complex fluid, synovial proliferation, and synovial osteochondromatosis are readily demonstrated by MRI (Figure 15). Surrounding edema and synovial proliferation are more suggestive of an underlying inflammatory or infectious etiology.
Brachialis muscle strain
Brachialis muscle strains, like distal biceps tendon tears, often present following a similar mechanism of injury and may accompany distal biceps tendon rupture. Alternatively, brachialis muscle strains may be an isolated finding with an intact distal biceps (Figure 16). With the increasing popularity of climbing sports, including more specialized training, certain previously rare injuries are more commonly seen. Brachialis tendinitis results from prolonged elbow flexion and pronation typical of climbers and has been coined “climber’s elbow”. This mechanism may lead to brachialis tendinosis, muscle strains or even ruptures.
Surgical repair of distal biceps rupture results in superior supination and flexion strength and pain relief compared to conservative management21. Early surgical repair is most desirable. Repairs done after 4 weeks from the time of injury may require use of a tendon graft because of muscle atrophy, loss of tendon length, and obliteration of the biceps tunnel22,23,24. Treatment of partial tears often begins conservatively with splinting, non-steroidal therapy, and physical therapy25. However, many of these patients will eventually require surgical repair for pain relief and to regain strength25.
Repairing the distal biceps as closely as possible to its native footprint is important for optimal function. Biomechanical studies have shown that a repair that is too anterior to the footprint results in loss of supination torque between neutral and full supination of the forearm26. Failure to recognize the presence of separate bundles at the time of repair may result in incorrect placement of the short or long head, hindering the restoration of biceps function5. Several studies have shown that repair of the distal biceps tendon to its native footprint is much easier to accomplish by a posterior surgical approach27,28. However, a more recent technique utilizes a single anterior incision with transosseous sutures to reattach the distal biceps tendon to its normal footprint in order to maximize supination29.
Initial attempts at reattachment of the torn distal biceps tendon to the bicipital tuberosity were performed through an anterior incision and resulted in a significant number of neurovascular complications30. Subsequent techniques attempted to more accurately restore the anatomic footprint by utilizing an anterior incision to retrieve the tendon and a posterior incision to reattach the tendon to the biceps tuberosity. These type repairs were met with an increased incidence of heterotopic bone (Figure 17) and proximal radioulnar synostosis resulting from partial stripping of the interosseous membrane and ulnar periosteum with dissection of the muscles off of the lateral aspect of the olecranon to gain exposure. Subsequent muscle-splitting techniques of the supinator and the common extensor muscle mass have significantly reduced the incidence of radioulnar synostosis when using a two incision approach30. Both single and double incision approaches are currently used. A recent randomized clinical trial demonstrated no significant differences in outcomes between single and double incision approaches with the exception being an approximate 10% greater flexion strength in the double incision group31. In addition, there was a significantly greater incidence of minor, transient complications such as transient neuropraxia of the lateral cutaneous nerve with the single incision approach31. A variety of fixation techniques are used for distal biceps tendon repair including transosseous sutures, suture anchors, cortical buttons, interference screws, and combinations of cortical button and interference screws32,33,34,35,36.
Repair of the lacertus fibrosus has been shown to strengthen the distal biceps tendon repair, but at present there is no proof of improved clinical results following lacertus fibrosus repair38. The underlying brachial vessels and median nerve may be subjected to direct injury, such as laceration, and compression of the median nerve may occur with a tight repair38.
Complications of surgical repair of the biceps tendon continue to include heterotopic ossification (Figure 18). Mechanical failure of the repair may occur with recurrent rupture or breakage or displacement of the fixation method. Poly-L-Lactide and other bioabsorbable interference screws commonly result in significant osteolysis and bone tunnel enlargement (Figure 19) but without significant correlation between the amount of osteolysis and functional and clinical outcomes37. Additional complications of bioabsorbable screws include foreign body reactions, which range from mild, self-limited reactions to severe, inflammatory responses including masses, collections, and the development of draining sinuses, which may mimic infection (Figure 20).
The diagnosis of distal biceps tendon rupture may be difficult if tendon retraction is absent or if a partial rupture is present. The presence of a bifurcated distal biceps tendon may further complicate the clinical presentation when only one component is torn. MRI allows evaluation of the bifurcated distal biceps tendon and is able to assist in the differentiation of a complete from partial tendon ruptures. Following surgery, MRI allows assessment of tendon repair and identification of post-operative complications that may occur.
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- Potapov, A., Laflamme, Y. G., Gagnon, S., Canet, F. & Rouleau, D. M. Progressive osteolysis of the radius after distal biceps tendon repair with the bioabsorbable screw. J. Shoulder Elbow Surg. 20, 819–26 (2011).