Use of Thermoplastic Rings Following Venting of Flexor Tendon Pulleys: A Biomechanical Analysis

Assaf Kadar; Mohammad M Haddara; Stacy Fan; Shrikant Chinchalkar; Louis M Ferreira; Nina Suh

doi:10.1016/j.jhsa.2020.11.003

Use of Thermoplastic Rings Following Venting of Flexor Tendon Pulleys: A Biomechanical Analysis

J Hand Surg Am. 2021 Jun;46(6):485-492. doi: 10.1016/j.jhsa.2020.11.003. Epub 2020 Dec 25.

Authors

Assaf Kadar¹, Mohammad M Haddara², Stacy Fan³, Shrikant Chinchalkar⁴, Louis M Ferreira², Nina Suh⁵

Affiliations

¹ Division of Orthopedic Surgery, University of Western Ontario, Roth-McFarlane Hand and Upper Limb Center, St Joseph's Health Care, London, Ontario, Canada; Department of Orthopedics, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
² Division of Plastic and Reconstructive Surgery, University of Western Ontario, Roth-McFarlane Hand and Upper Limb Center, St Joseph's Health Care, London, Ontario, Canada.
³ Department of Biomedical Engineering, University of Western Ontario, Roth-McFarlane Hand and Upper Limb Center, St Joseph's Health Care, London, Ontario, Canada.
⁴ Division of Orthopedic Surgery, University of Western Ontario, Roth-McFarlane Hand and Upper Limb Center, St Joseph's Health Care, London, Ontario, Canada.
⁵ Division of Orthopedic Surgery, University of Western Ontario, Roth-McFarlane Hand and Upper Limb Center, St Joseph's Health Care, London, Ontario, Canada. Electronic address: nina.suh@sjhc.london.on.ca.

PMID: 33357985
DOI: 10.1016/j.jhsa.2020.11.003

Abstract

Purpose: Normal digital flexion relies on flexor tendon pulleys to convert linear muscular force to angular digital motion. However, there is a growing trend to vent them partially during flexor tendon repair. The objective of this study was to examine the effects of a thermoplastic ring, acting as an external pulley, on flexor tendon biomechanics and finger range of motion (ROM) after pulley venting.

Methods: We tested 15 cadaveric digits using an in vitro active finger motion simulator. We measured loads induced by flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) as well as joint ROM with sequential sectioning of the A2, A3, and A4 pulleys compared with an intact pulley condition. At each stage, external thermoplastic pulley rings were applied snugly over the proximal and middle phalanges to recreate A2 and A4 function, respectively.

Results: After complete venting of the A2, A3, and A4 pulleys, proximal interphalangeal joint ROM significantly decreased by 13.4° ± 2.7° and distal interphalangeal joint ROM decreased by 15.8° ± 2.1°. Application of external rings over the proximal and middle phalanx resulted in a residual ROM decrease of 8.3° ± 1.9° at the proximal interphalangeal joint and 7.9° ± 2.1° at the distal interphalangeal joint, nearly restoring ROM. Similarly, complete pulley venting resulted in reduced FDS load by 37% and FDP load by 50% compared with intact pulleys. After application of external rings, loads were restored almost to normal, with a 9% reduction for FDS load and 9% reduction for FDP load compared with intact pulleys.

Conclusions: The application of thermoplastic rings acting as external pulleys is an effective, noninvasive, and reproducible approach to restore flexor tendon biomechanics and digit ROM after pulley venting.

Clinical relevance: Thermoplastic rings may be a useful therapeutic adjunct in restoring joint ROM and flexor tendon loads after surgical venting of the pulleys.

Keywords: Flexor tendon; pulley reconstruction; thermoplastic rings; venting.

MeSH terms

Biomechanical Phenomena
Finger Joint / surgery
Fingers
Hand*
Humans
Range of Motion, Articular
Tendons* / surgery