Flexor tendon healing in four different animal species was explored in a tissue culture system. Ninety percent transverse lacerations were made in 88 tendon segments obtained from rabbits, chickens, dogs, and monkeys. The tendons were removed from culture and studied by light and electron microscopy at intervals of 3, 6, 9, and 12 weeks. A characteristic sequence of repair including epitenon thickening, cellular differentiation, cell migration, and phagocytosis was seen in each of the repaired tendons. The endotenon cells of several animal tendons appeared to be synthesizing collagen. There was a consistent difference in the rate of healing between the four species. The rabbit tendons demonstrated nearly complete closure of the repair site by 12 weeks. A lesser response was seen in the chicken, followed by the dog and monkey. The differences in healing rate appeared to be due to the non-species-specific in vitro culture media. The in vitro flexor tendon culture system is particularly useful in studying the tendon repair responses of various species with the contributions of vascularity and synovial cells excluded.

Flexor tendon function following excision of various portions of the fibro-osseous pulley system was measured biomechanically using a tensile testing machine. The biomechanical parameters measured were tendon excursion (the excursion of the tendon required to fully flex the digit) and work of flexion (the area under the force-excursion curve, representing all the forces that resist tendon flexion). In this experiment, work of flexion included the forces necessary to accomplish full digital flexion against a 15-g counter-weight, as well as the frictional forces that resist tendon gliding. The results indicate that the work of flexion was affected to a greater degree by pulley loss than was tendon excursion, suggesting that it is a more sensitive measurement of tendon function. A2 was found to be the single most important pulley for flexor tendon function, followed by A4. However, both A2 and A4 had to be present if near-normal hand function was to be achieved; sacrificing the A1 pulley was not associated with a significant loss of flexion. The "pulley effect" of the skin and soft tissue as a supplement to the fibro-osseous pulleys in reducing tendon bow-stringing was also noted. Although the parameters of tendon excursion and work of flexion were used in this study to determine the effect of pulley loss on tendon function, they can also be used to evaluate other flexor tendon studies, such as pulley reconstruction.

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