Background: Transfer of the tendon of the brachioradialis muscle to
the tendon of the flexor pollicis longus restores lateral pinch function after
cervical spinal cord injury. However, the outcomes of the procedure are
unpredictable, and the reasons for this are not understood. The purpose of
this study was to document the degree of variability observed in the
performance of this tendon transfer.
Methods: The surgical technique used for the brachioradialis tendon
transfer was assessed in two ways. First, the surgical attachment length of
the brachioradialis was quantified, after transfer to the flexor pollicis
longus, with use of intraoperative laser diffraction to measure muscle
sarcomere length in eleven individuals (twelve limbs) with tetraplegia.
Second, ten surgeons who regularly performed this procedure were surveyed
regarding their tensioning preferences. Using a biomechanical model of the
upper extremity, we investigated theoretically the effect of different
surgical approaches on the active muscle-force-generating capacity of the
transferred brachioradialis in functionally relevant elbow, wrist, and hand
Results: The average sarcomere length (and standard deviation) of
the transferred brachioradialis was 3.5 ± 0.3 µm. That length was
significantly correlated to the in situ sarcomere length (r2 =
0.53, p < 0.05). Surgical tensioning preferences varied considerably;
however, six of the ten surgeons positioned the patient's elbow between full
extension (0° of elbow flexion) and 50° of flexion when selecting the
attachment length, and six of the ten stated that their goal was to tension
the transfer slightly tighter than its resting tension. The computer
simulations suggested that a "tighter" brachioradialis transfer
would produce its peak active force in an elbow position that is more flexed
than the elbow position in which a "looser" transfer would produce
its peak active force.
Conclusions: This study provides evidence that experienced surgeons
perform this tendon transfer differently from one another. Biomechanical
simulations suggested that these differences could result in substantial
variability in the active force that the transferred brachioradialis can
produce in functionally relevant postures.
Clinical Relevance: The surgical attachment length and the position
of the patient's limb at the time of tendon transfer are both controllable and
measurable parameters. Understanding the relationship between surgical
technique and postoperative muscle function may provide surgeons with more
control of clinical outcomes.