The Effect of Forearm Shortening on Finger Flexion: A Biomechanical Study

Timothy Daugherty; Justin Sawyer; Thomas Gillin; Pooyan Abbasi; Gabriel Yohe; James P Higgins; Kenneth R Means Jr

doi:10.1016/j.jhsa.2024.09.005

The Effect of Forearm Shortening on Finger Flexion: A Biomechanical Study

J Hand Surg Am. 2024 Oct 11:S0363-5023(24)00429-5. doi: 10.1016/j.jhsa.2024.09.005. Online ahead of print.

Authors

Timothy Daugherty¹, Justin Sawyer², Thomas Gillin¹, Pooyan Abbasi¹, Gabriel Yohe¹, James P Higgins¹, Kenneth R Means Jr³

Affiliations

¹ Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD.
² SIU Institute for Plastic Surgery, Southern Illinois University School of Medicine, Springfield, IL.
³ Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD. Electronic address: editor@curtishand.com.

PMID: 39396359
DOI: 10.1016/j.jhsa.2024.09.005

Abstract

Purpose: Surgeons may shorten the forearm for many indications. We quantified the impact of shortening on finger flexion with a cadaver model.

Methods: Ten fresh cadaver proximal forearms were pinned to a static block. We pinned each distal forearm/hand to a block that could unlock, slide, and relock on a mounting track. This block allowed wrist-neutral or 30-degree extension. With the sliding block locked, we removed the central 10 cm of the radius/ulna. We placed sutures in the proximal end of each flexor digitorum profundus (FDP). After pretensioning, we simulated near-maximum baseline FDP muscle-generating force by applying 100 N via a load cell at the proximal sutures. We then anchored the load cell system proximally to set the initial length-tension relationship for simulating near-maximum baseline muscle-generating force. We called subsequent load cell readings the simulated muscle force (SMF) and pressure sensor readings between fingertips and the palm the tip-to-palm force (TPF). We shortened the forearm in 1 cm increments with the distal sliding-locking block. At each increment, we recorded SMF and TPF in the wrist-neutral position. Once a specimen lost measurable TPF, we applied 30 degrees wrist extension until again losing TPF.

Results: Incremental forearm shortening was associated with exponential decreases in each FDP's SMF and TPF. In wrist-neutral, 3 cm mean shortening had a loss of 99% and 98% SMF and TPF, respectively. Wrist extension marginally improved SMF and TPF up to 4 cm mean shortening, where both lost 99%. Loss of any fingertip touchdown occurred after a mean shortening of 4.9 cm in wrist-neutral and 5.3 cm in 30 degrees wrist extension.

Conclusions: Mean forearm shortening of 3 or 4 cm had a near-complete loss of FDP SMF and TPF in wrist-neutral/wrist extension, respectively. With ∼5 cm shortening, there was a complete loss of fingertip touchdown.

Clinical relevance: Surgeons should consider the influence of forearm shortening on the FDPs and contemplate flexor tendon shortening or alternative reconstructions as indicated.

Keywords: Biomechanics; finger flexion; flexor digitorum profundus; forearm shortening; simulated muscle forces.