Healing characteristics of deep digital flexor tenorrhaphy within the digital sheath of horses.
Authors: Jann Henry, Blaik Margaret, Emerson Robert, Tomioka Michiko, Stein Larry, Moll David
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: Deep Digital Flexor Tendon Repair Within the Digital Sheath Surgical repair of deep digital flexor (DDF) tendon lacerations within the digital sheath presents a significant clinical challenge, prompting Henry and colleagues to investigate healing outcomes following intrathecal tenorrhaphy in five horses managed with 6 weeks of cast immobilisation in partial flexion followed by 14 weeks in extended heel shoes. Sequential ultrasonographic evaluation revealed progressive gap formation at the repair site—averaging 0.93 cm at 3 weeks, increasing substantially by 6 weeks, and reaching 5 cm by the 26-week endpoint—indicating that unloaded healing did not produce primary tendon union. Rather than direct fibre-to-fibre healing, the transected DDF ends adhered to the dorsal surface of the superficial flexor tendon (SDF) whilst fibrous tissue progressively reduced the intrathecal space; mechanical testing showed repair tissue failed consistently at this DDF–SDF adhesion interface with a mean load to failure of 4,616 N (stress 12.99 MPa), substantially lower than intact tendon. Although horses achieved functional soundness at pasture by 26 weeks, the structural compromise evident histologically and mechanically—combined with the consistent failure pattern—suggests that current immobilisation protocols are insufficient to promote first-intention healing and alternative fixation methods warrant investigation to prevent adhesion formation and intrathecal fibrosis in clinical cases.
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Practical Takeaways
- •Current intrathecal DDFT repair techniques with 6-week casting in partial flexion do not achieve primary tendon healing; gap healing with adhesion formation occurs instead
- •Horses may become pasture-sound clinically despite mechanically weak repair tissue with reduced load-bearing capacity compared to intact tendon
- •Better immobilization or surgical techniques are needed to prevent gap formation and abnormal adhesion between deep and superficial flexor tendons in sheath repairs
Key Findings
- •Gap formation at repair site increased from 0.93 cm at 3 weeks to 5 cm by 26 weeks in immobilized limbs
- •Transected tendon ends adhered to superficial flexor tendon dorsal surface rather than healing end-to-end
- •Mean maximum load to failure of repair tissue was 4,616 ± 3,556 N (12.99 ± 2.78 MPa stress)
- •Repair consistently failed at the adhesion site between deep and superficial flexor tendons despite achieving pasture-soundness at 26 weeks