Sarcomere length changes after flexor carpi ulnaris to extensor digitorum communis tendon transfer

Area of Science:

• Orthopedic Surgery
• Muscle Physiology
• Biomedical Engineering

Background:

• Radial nerve palsy often necessitates tendon transfer procedures to restore hand function.
• The flexor carpi ulnaris (FCU) is a common donor muscle for transfers to the extensor digitorum communis (EDC).
• Optimizing the transferred muscle's sarcomere length is crucial for maximizing force generation.

Purpose of the Study:

• To quantify sarcomere length changes in the FCU muscle after transfer to the EDC.
• To evaluate the relationship between intraoperative passive tension, sarcomere length, and predicted muscle force.
• To assess the feasibility of using intraoperative laser diffraction to guide optimal tendon transfer placement.

Main Methods:

• Intraoperative measurement of sarcomere length using laser diffraction in five patients undergoing FCU to EDC tendon transfer.
• Comparison of pre- and post-transfer sarcomere lengths at various wrist and finger positions.
• Prediction of muscle force generation based on sarcomere lengths and joint angles.

Main Results:

• FCU sarcomere length and operating range significantly increased post-transfer (p < .001).
• Post-transfer, sarcomere lengths were longer in both lengthened (4.96 ± 0.43 microns) and shortened (3.50 ± 0.06 microns) positions.
• Optimal force generation was predicted in specific ranges of wrist and finger movement, with potential for improvement if transferred at longer initial sarcomere lengths (approx. 5 microns).

Conclusions:

• Tendon transfer of the FCU to the EDC can significantly improve sarcomere length and operating range.
• Intraoperative laser diffraction is a feasible tool to guide tendon transfer for optimal sarcomere length and predicted muscle force.
• Transferring the FCU at a longer initial sarcomere length may enhance functional outcomes in radial nerve palsy reconstruction.