Surgery

Lag screw fix for first phalanx lameness

By Adam Marcus

Injury to the subchondral bone of the first phalanx is a common cause of lameness in performance horses, and one for which optimal treatment can sometimes be unclear. Conservative treatments, such as stall rest, controlled rehab, steroids and other approaches, often fail. While minimally invasive arthroscopic debridement can be effective, the location of the lesions can limit the applicability of the technique.

A new study suggested lag screw compression may be a better approach, either as a front-line strategy or for cases where conservative treatments have failed.

The proposed mechanism of healing is related to Wolff’s law: Changing the direction of the forces applied to an injured bone stimulates tissue remodeling and leads to repair of the subchondral lesion, according to Michelle Maguire, DVM, of the Palm Beach Equine Clinic in Wellington, Fla.

“Lag screw compression has been used to treat subchondral lesions in other anatomic locations with success for return to performance,” Dr. Maguire said. “Lag screw compression appears to be an appropriate treatment for the condition, with promising preliminary results from this retrospective study.”

For the study, Dr. Maguire and Robert Brusie, DVM, DACVS, also of Palm Beach Equine Clinic, analyzed case records from 41 performance horses older than 5 years that had undergone lag screw compression for subchondral bone lesions near the first phalanx. Of those, 29 had subchondral bone cysts while 12 had bone fissures.

Follow-up information was obtained from referring veterinarians and from telephone questionnaires with the veterinarians and owners. According to the records and follow-up interviews, 35 of the 41 animals (85%) were physically sound, and 30 (73%) had returned to their previous level of athletic performance—mainly show jumping, the researchers reported. Those treated for cysts were somewhat more likely to be sound at follow-up (90% vs 75%) and to have returned to their intended use (76% vs 67%) than were those with fissures, the study found, but the differences did not reach statistical significance.

“We are comfortable recommending the surgical technique based on the outcomes presented in our study, as well as our clinical experience with the procedure,” Dr. Maguire told Modern Equine Vet. “While a prospective, randomized controlled trial would serve as the gold standard to validate these findings, such studies can be challenging to conduct in equine medicine due to relatively low case numbers compared with human or small animal populations. Nonetheless, our current data provide encouraging support for the use of this technique in appropriately selected cases.”

However, Dr. Maguire said the surgery requires advanced training and experience. Misalignment of the implant in proximal P1, for example, can lead to inflammation of the extensor branch of the suspensory ligament or inadvertent penetration of the fetlock joint—neither of which was reported in the study but can occur if the procedure is not performed correctly, according to Dr. Maguire. “For this reason, the procedure should be performed by a board-certified surgeon with advanced knowledge of regional anatomy,” she said.

Although placement of lag screws is not inherently risky, it carries the potential for adverse events, as does any orthopedic surgery involving implants in horses. Postoperative pain and inflammation, delayed wound healing and infections—both of the surgical site and the implant—can occur, she said. So, too, can inadvertent injury to adjacent tissues.

“If performed under general anesthesia, the inherent anesthetic risks in equine patients must be considered,” Dr. Maguire added. “While no intraoperative complications were reported in our study, delayed complications can remain a concern. Serial clinical evaluations and imaging can help detect any implant-related changes or diagnose reasons for persistent lameness postoperatively.” MeV

FOR MORE INFORMATION
Maguire M, Brusie R. Lag screw compression effectively treats proximal subchondral bone cysts and fissures in the first phalanx of mature performance horses. J Am Vet Med Assoc. 2025;263(9):1127-1135.
https://avmajournals.avma.org/view/journals/javma/263/9/javma.25.03.0134.xml