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Biomechanical Properties of Donor Tendons in the Forearm snd Hand
Timothy F. Tirrell1; Siddharth Bhola, MD1; John J. Finneran, MD2; Reid A. Abrams, MD1; Jan Fridén, MD, PhD3; Richard L. Lieber, PhD1
1Department of Orthopaedics, University of California, San Diego, San Diego, CA; 2Department of Anesthesia, University of California, San Diego, San Diego, CA; 3Department of Hand Surgery, Sahlgrenska University Hospital, Goteborg, Sweden

There are many autologous tendon graft and tendon transfer donor choices, each of which has different morphological and mechanical properties. Depending on the intended use, tendons with certain properties may be more advantageous than others. Relevant morphological characteristics (length, cross-sectional area, volume) and mechanical properties (ultimate load, ultimate stress, elastic modulus) were tested in eight tendons of the upper extremity. Tendons exhibited wide variability in all properties studied, demonstrating that hand and forearm tendons are morphologically diverse (Fig. 1) and respond to load differently (Fig. 2). Flexor digitorum profundus to the index finger was the longest tendon (236±20 mm), but flexor digitorum superficialis to the middle finger (FDS-M) had the greatest volume (2.2±0.4 cm3) and flexor carpi radialis (FCR) had the greatest cross-sectional area (15.3±1.3 mm2). FDS-M withstood the greatest maximum load before failure (504±87 N). FCR bore the least stress at max loading (22.3±3.0 MPa) and was the most compliant tendon, as demonstrated by its low modulus (377±39 MPa). The three stiffest tendons (and their modulus values) were palmaris longus (PL) (823±95 MPa), followed by extensor indicis (776±86 MPa) and extensor digitorum minimi. Certain tendons may be more suited donors for specific procedures because of desired mechanical properties. Our anatomic and mechanical data may assist surgeons choosing between potential tendon donors based on mechanical needs. For example, BR has an ultimate load that matches the scapholunate ligament (SLL) closer than the PL, which has ~2/3 the ultimate load of the SLL[1]. While these mechanical properties are helpful, tendon dimensions, also reported here, also play a role in reconstructions requiring tendon donors.

Figure 1: Tendon (A) length, (B) volume, (C) and cross-sectional area. Note that all tendons provide at least 8 cm of potential graft material and that tendon volumes and cross-sectional areas are quite variable across muscle types; these considerations may be important when using the tendon as a space-filling object or grafting into a volume-restricted space.

Figure 2: Tendon (A) maximum load, (B) maximum stress, and (C) modulus. General trends are similar between cross-sectional area measurements (Fig. 1C) and maximum load, but variability in maximum stress suggests that there may be some difference in the intrinsic composition of collagen or other load bearing structures in tendons from each muscle.

[1] Johnston JD et al. J Orthop Res. 2004 Jul;22(4):867-71

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