Morphologic and biomechanical comparison of tendons used as free grafts

The palmaris longus (n = 10), plantaris (n = 11), and extensor digitorum longus (n = 10) tendons were harvested from cadaver limbs for morphologic and biomechanical comparisons. Eleven flexor digitorum profundus tendons from the index finger were also harvested for comparison of biomechanical properties of the free graft tendons with those of a typical digital flexor. Maximal tendon length, cross-sectional area, volume, stiffness, and modulus of elasticity were determined by measurement, laser micrometry, and tensile testing. The plantaris and extensor digitorum longus yielded the longest grafts, 334 and 325 mm, respectively, compared with the palmaris longus, which yielded only 161 mm of length. Cross-sectional areas were as follows: palmaris longus, 3.1 mm2; plantaris, 1.4 mm2; extensor digitorum longus, 3.3 mm2; and flexor digitorum profundus, 10.6 mm2. Mean volumes were as follows: palmaris longus, 529 mm3; plantaris, 557 mm3; and extensor digitorum longus, 1006 mm3. The palmaris longus and the extensor digitorum longus showed greater stiffness, 42.0 and 47.8 N/mm, respectively, than the plantaris, which had a stiffness of 25.5 N/mm. However, the flexor digitorum profundus showed significantly greater stiffness than all of the graft tendons. The modulus of elasticity ranged from 1161.6 to 1673.0 MPa, with no significant difference between tendons tested. The findings in this study provide data that may be useful in the selection of a specific donor for free tendon grafting.