Lag screw compression effectively treats proximal subchondral bone cysts and fissures in the first phalanx of mature performance horses.

Objective: To determine the outcome of skeletally mature performance horses with subchondral bone cysts and fissures in the proximal aspect of the first phalanx treated by lag screw compression.

Methods: Case records of horses that underwent lag screw compression to treat subchondral bone lesions in the proximal aspect of the first phalanx were reviewed. Performance horses > 5 years old with lameness referrable to the fetlock region; radiographic or other advanced imaging evidence of subchondral bone lesions, with no other concurrent cause for lameness; and at least 6 months of follow-up data were included. Follow-up information was obtained from referring veterinarians and telephone questionnaires with owners.

Results: 41 horses met the inclusion criteria: 29 horses with subchondral bone cysts and 12 horses with subchondral bone fissures. Warmblood was the predominant breed type, and show jumping was the predominant athletic discipline. At 6 months postoperatively, 85% (35 of 41) of horses were sound (95% CI, 74.6% to 96.2%), with a return to previous athletic level in 73% (30 of 41; 95% CI, 59.7% to 86.7%). Horses treated for subchondral bone cysts had higher rates of soundness (90% vs 75%; risk difference, 14.7%; Cohen's h = 0.36) and return to intended use (76% vs 67%; risk difference, 9.2%; Cohen's h = 0.28) compared with those treated for subchondral bone fissures. However, these differences were not statistically significant.

Conclusions: Lag screw compression may be beneficial in the treatment of subchondral bone lesions in the proximal aspect of P1.

Clinical relevance: This surgical technique may provide an effective treatment for subchondral lesions of the first phalanx where conservative therapies have failed, and may have mitigated the risk of progression to macrofracture.