Typically, the biceps brachii originates proximally with two heads from the
scapula that unite to form a common tendon that inserts into the radial
tuberosity, with the bicipital aponeurosis inserting onto the ulna. Multiple
anatomic anomalies of the biceps brachii muscle have been
identified1-4.
These variations are far more common at the muscular origin than at the
insertion, with the muscle occasionally having accessory heads at its
origin1,2,4.
Much less commonly, anomalous insertions of the biceps have been described;
these variations have included slips extending to the medial intermuscular
septum, the medial epicondyle, the pronator teres, or the extensor carpi
radialis
brevis3,5.
We are aware of only a single case report that has described the clinical
relevance of these
anomalies6, and
their importance is unclear.
Distal biceps rupture is a relatively rare injury that is much less
frequent than proximal tendon rupture. The etiology of distal biceps rupture
is unclear. However, it may involve some degeneration of the tendon at its
insertion on the radial tuberosity. Partial ruptures of the distal biceps
tendon are quite rare relative to complete tears and may be difficult to
diagnose7-9.
A recent report documented excellent outcomes for eight patients in whom a
partial tear had been repaired through a single posterior
incision10.
We report the case of a patient who had a rupture of a bifurcated distal
biceps tendon with separate musculotendinous junctions, findings that were
consistent with an unfused biceps brachii muscle. The patient was informed
that information concerning this case would be submitted for publication. We
are aware of no previous reports of this anomaly.
Athirty-nine-year-old, right-hand-dominant man who worked as a
law-enforcement officer injured the right arm while lifting weights. He was
performing an isolated biceps-strengthening exercise when the injury occurred.
At the time of the injury, the patient reported hearing and feeling a pop in
the vicinity of the elbow. He denied any premorbid symptoms in this area. The
patient was in otherwise good health. He did not take any medications and
denied anabolic steroid use.
At the time of the initial examination, substantial ecchymosis was present
over the proximal aspect of the forearm and the medial aspect of the elbow.
Both the active and passive ranges of motion of the elbow were full and were
symmetrical with those on the contralateral side. Palpation of the distal
biceps tendon in the antecubital fossa elicited substantial tenderness.
However, loss of continuity of the distal biceps tendon was not readily
palpable. Manual motor testing revealed pain with resisted supination and
elbow flexion. There was no clear weakness, although this was difficult to
assess given the patient's complaints of pain. There was no tenderness over
the long head of the biceps. The distal neurovascular examination and initial
radiographs revealed normal findings. Given that the clinical history was
consistent with a distal biceps tendon rupture but a palpable tendon appeared
to be present on examination, a magnetic resonance imaging study was
performed. This examination was thought to reveal a complete avulsion of the
distal biceps tendon from the radial tuberosity, with 2 cm of retraction
(Fig. 1-A). Despite this
finding, a provisional diagnosis of a partial distal biceps tendon rupture was
made given the continuity of the distal biceps tendon as noted at the time of
the physical examination. Treatment options, including operative and
nonoperative repair of the ruptured portion, were discussed. Given his
occupation and activity level, the patient elected to proceed with operative
repair.
The patient underwent surgery twelve days after the injury. The procedure
was performed with use of a two-incision technique, as described by Boyd and
Anderson11. A 10-cm
curvilinear incision was made over the anterior aspect of the elbow, and a
5-cm incision was made laterally over the proximal part of the forearm. Upon
anterior exposure of the biceps tendon, it was immediately noted that the
distal biceps tendon was duplicated, with two distinct tendons and
musculotendinous junctions. Each tendon could be followed proximally for 8 to
10 cm, with no evidence of fusion of the biceps brachii muscle bellies
(Fig. 2). The lateral tendon
unit was intact, had a normal appearance, and was attached to the radial
tuberosity. The medial tendon unit was avulsed, with degenerative tissue at
the tendon stump (Fig. 3).
After exposure of the radial tuberosity, the area from which the tendon had
been avulsed was easily identified. The medial tendon unit was subsequently
repaired back to the tuberosity, adjacent to the intact lateral tendon. A
single 1-mm cottony Dacron Krackow suture was placed, with both limbs being
passed through a bone trough and out through drill-holes and then tied over a
cortical bridge.
Postoperatively, the elbow was splinted at 90° of flexion for twelve
days. The patient then began active range of motion with the elbow in a
dynamic flexion brace that blocked the terminal 30° of extension. At four
and one-half weeks postoperatively, the block was removed. The patient had
full range of motion of the elbow by seven weeks and began resisted biceps
activities at twelve weeks. At the time of the six-month follow-up, the
patient had a full range of motion of the elbow with no objective weakness in
flexion or supination. At that point, the patient noted slight subjective
weakness in the right arm and was permitted to begin weight-lifting.
Multiple anatomic anomalies of the biceps brachii have been reported. The
most commonly reported anomaly has been an accessory head at the origin of the
muscle1,2,4,5.
Fewer variants of the distal insertion have been
reported3,5.
Most authors have recommended operative anatomic repair of complete distal
biceps tendon ruptures in order to restore optimal function in active
individuals7,8.
Studies comparing operative and nonoperative treatment have consistently
demonstrated deficits in supination and elbow flexion when this injury is
treated
nonoperatively12,13.
The appropriate treatment of partial ruptures remains unclear, with both
operative and nonoperative treatment having been
recommended9,10.
Surgical débridement or repair of recalcitrant partial ruptures that
initially were treated nonoperatively has provided good
results14,15.
To the best of our knowledge, we are the first to report on a completely
unfused and bifurcated distal biceps muscle-tendon unit that was noted either
during an anatomic study or in the clinical setting. The clinical diagnosis
was consistent with a partial tendon rupture, whereas the findings on magnetic
resonance imaging were consistent with a complete rupture. This discrepancy
resulted in difficulty in determining the appropriate treatment option. Given
the patient's functional demands and concerns about the apparent retraction of
the tendon as seen on magnetic resonance imaging, surgical repair was elected.
In retrospect, careful review of the magnetic resonance imaging scans showed
the unaffected lateral portion of the biceps muscle and tendon along with
evidence of injury of only the medial portion (Figs.
1-B,
1-C, and 1-D).
The case of our patient likely demonstrates an embryologic failure of
fusion of the biceps brachii along its entire length. This allowed for rupture
and retraction of the medial portion of the bifurcated distal tendon while the
lateral portion remained uninjured, creating difficulty in diagnosis and
subsequent uncertainty as to whether surgery was indicated. Given that the
medial portion of this tendon contributes a substantial proportion
(approximately 50%) of biceps function, it is our belief that surgical repair
of this structure probably resulted in improved function for the patient. In a
patient in whom the clinical history seems to be consistent with complete
distal biceps rupture but the tendon appears to be palpable across the elbow,
rupture of one tendon of a bifurcated muscle should be considered. If this
diagnosis is contemplated, magnetic resonance imaging can help to determine
whether such a rupture is present. It is possible that other patients who have
been diagnosed with a partial tendon rupture actually represented cases of a
similar anatomic variation. In the case of our patient, repair of the tear
involving one head of the biceps resulted in an excellent functional
recovery.