34th Annual Scientific Meeting proceedings

Introduction
Coxofemoral luxation is uncommon in equids due to joint anatomy, including a deep acetabulum, strong ligaments, and soft tissue support. It most often affects small equids like ponies, Miniature Horses, and foals. The initiating cause is typically blunt trauma, but conditions like upward patellar fixation or hindlimb casting can predispose to coxofemoral luxation. Luxation is usually craniodorsal and presents with severe lameness, external limb rotation and shortening. Conventional imaging confirms the diagnosis.

Treatment is difficult in animals over 250 kg, and reluxation is common following closed reduction and immobilization. Options for surgical management include open reduction with dorsal (and/or internal) stabilization, or femoral head ostectomy. Total hip arthroplasty is rarely used in equids. In a proof-of-concept cadaveric study, we recently demonstrated the possibility of toggle-pin stabilization via a minimally invasive approach, using computer-assisted surgery (CAS) guidance. Here, we report on the clinical application and outcomes of this technique in a small cohort of small equids.

Materials & Methods
Medical records and imaging data from 10 small equids treated for coxofemoral luxation at the ISME Equine Clinic Bern (Sept 2021–Dec 2024) were reviewed. Collected data included signalment, injury duration, imaging findings, procedure details, complications, rehabilitation, and outcomes. All procedures were performed under general anesthesia in lateral recumbency, with a calf jack used for closed reduction and stabilization.

Cone beam computed tomography (CBCT; O-arm, Medtronic) and optical navigation (StealthStation, Medtronic) were used for planning and intraoperative guidance. A minimally invasive lateral approach to the proximal femur allowed drilling of a 5.5 mm canal through the femoral neck, fovea capitis, and acetabular fossa. A toggle construct was secured with a tensioned suture-button system. Recovery was hand-assisted, with or without a rescue sling for additional support. When possible, patients were suspended for a variable duration postoperatively in a rescue sling, with gradual reintroduction of exercise and, in later cases, physical therapy.

Results
Ten equids (seven Shetland ponies, one Miniature Horse, one warmblood foal, one donkey) underwent attempted stabilization. Median age was 14 years (range: 3 weeks–24 years); median weight 115 kg (range: 80–180 kg). Luxation was unilateral in all cases. Closed reduction was successful in 9/10. In one case, femoral neck fracture was induced during closed reduction due to unrecognized femoral head entrapment within the obturator foramen. This pony was not subjected to toggle-pin stabilization and was euthanized.

CAS-guided toggle-pin placement succeeded in nine cases. Median anesthesia time was 135 minutes; surgery time ranged from 29 to 58 minutes. Sling immobilization ranged between 12 and 45 days for all subjects, except for the foal. Eight subjects underwent desmotomy of the medial patellar ligament (five bilateral, three unilateral) under the same general anesthesia or under standing sedation in the days following the toggle-pinning procedure. One subject was castrated under the same general anesthesia.

In the 3-week-old foal, which was not immobilized, the suture of the toggle-construct sawed through the soft bone within hours postoperatively. This led to reluxation and subsequent euthanasia of the foal. Of the eight remaining, six returned to intended use; five were sound, one (with pre-existing osteoarthritis of the affected coxofemoral joint) remained mildly lame. In one pony, the closed reduction and CAS-guided toggle-pinning procedure was repeated 24 hours after the toggle rod had dislodged into the coxofemoral joint when the pony reared up and spread its hind limbs wide, refusing to load onto the trailer 6 weeks after the first surgery. This pony made a full recovery and had an excellent outcome. Two subjects were later euthanized: one after early exercise and reduced sling time led to subluxation; another due to intraarticular fragmentation and suboptimal closed reduction and implant positioning.

Discussion
Closed reduction using a calf jack is readily feasible, even with delayed presentation, but pre-/intraoperative imaging should guide manipulations for closed reduction to avoid complications like femoral neck fractures and to identify intraarticular fragments. CAS enables minimally invasive and accurate toggle placement and targeted fragment removal. Prognosis is reduced when articular surfaces are damaged. Young foals with soft bones are not suitable candidates for the described technique.

Early physical therapy during sling suspension was well tolerated and may enhance recovery. Future improvements could include modifications of the toggle constructs that accommodate for translational joint motion and reduce the risks of implant or bone failure. Additional research should define optimal construct placement, tensioning forces, and rehabilitation strategies, including the role of prophylactic desmotomy.

In conclusion, CAS-guided toggle pinning is a viable treatment for coxofemoral luxation in small equids under 200 kg. When performed promptly and without significant articular damage, outcomes are favorable. Based on our experiences, postoperative sling support for six weeks is advised to minimize reluxation risk.

References

1. Claeys I, Van der Vekens E, Kümmerle J, et al.: Computer-assisted surgery for placing toggle constructs across the coxofemoral joints of small equids using a minimally invasive approach-A proof-of-concept cadaveric study. Veterinary surgery VS 2023; 52:994–1008.
2. García‐López JM: Coxofemoral luxations in the horse: Surgical options and challenges. Equine Veterinary Education 2010; 22:554–6.
3. Richardson DW, Ortved KF: Femur and Pelvis, in Auer J, Stick JA, Kümmerle JM, et al (eds): Equine surgery. St. Louis, Missouri, Elsevier, 2018, pp 1777–1789