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 postures.
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.