34th Annual Scientific Meeting proceedings

Introduction
The goal of repair for articular fractures is perfect anatomic reduction and stabilization of the articular surface in order to prevent the development of post-traumatic osteoarthritis (PTOA). Arthroscopic-guidance allows debridement of fracture lines, removal of intra-articular debris, and monitoring of fracture reduction via a minimally invasive approach. Arthroscopy can also be useful for prognostication with accurate assessment of articular surfaces. Arthroscopic-guided repair facilitates minimally invasive osteosynthesis, while minimizing soft tissue trauma and improving incisional healing. Fortunately, many articular fractures in the horse are amenable to arthroscopically-guided repair.

Specific Fractures amenable to Arthroscopically-guided repair
Fractures of the Metacarpal and Metatarsal Condyles
Condylar fractures occur commonly in racehorses with the articular component stabilized by screws placed in lag fashion. Arthroscopy can assist in the repair of both non-displaced and displaced condylar fractures. In horses with non-displaced condylar fractures, palmar/plantar comminution is not uncommon¹ and arthroscopic debridement can be useful to improve congruity of the articular surface if needed. Displaced condylar fractures are particularly amenable to arthroscopically-guided repair as the arthroscope can facilitate debridement of fracture fragments when necessary and can be used to monitor reduction.

Fracture reduction can be performed with the horse positioned in lateral recumbency and the arthroscope in the dorsal pouch, or less commonly palmar/plantar pouch, of the joint looking down the fracture line.  Reduction can usually be accomplished by extension of the fetlock joint with internal rotation of the foot. Some surgeons prefer to drill the first glide hole in the epicondylar fossa to facilitate manipulation of the fracture fragment with the centering sleeve. Once reduction is achieved, 1-2 bone reduction forceps are placed, and the screw is inserted using routine lag fashion with arthroscopic monitoring of reduction and compression. Both the dorsal and palmar/plantar joints should be evaluated for reduction, comminution and free debris. As mentioned, palmar/plantar and/or dorsal comminution occur commonly in both displaced and non-displaced condylar fractures. Arthroscopic removal of small fragments is recommended, while preservation of large wedge fragments through fracture reduction and compression is ideal.² Palmar/plantar comminution is usually located at the distal extent of the condyle that can be accessed arthroscopically, therefore, a distal instrument portal through the collateral sesamoidean ligament, small and angled arthroscopic instruments, and fetlock flexion can facilitate debridement.

Arthroscopy can also be used to examine the articular surfaces and provide a more accurate prognosis. The proximal sesamoid bones often sustain significant trauma and cartilage erosions, especially in horses with displaced condylar fractures. Concurrent fractures of the sesamoid bone can also occur with axial fractures being noted most commonly. Extensive articular damage and fractures of the proximal sesamoid bones significantly decreases prognosis for racing post-operatively.¹

Fractures of the Proximal Sesamoid Bone
Mid-body sesamoid fractures can be successfully treated with arthroscopic-guidance. With the horse in lateral recumbency and affected sesamoid positioned up, the glide hole can be created under radiographic or fluoroscopic control. The drill bit is placed at the base of the sesamoid aimed in a proximal direction. Care must be taken to avoid aiming too dorsally as the palmar/plantar surface is the tension surface of the bone. Some fracture configurations e.g., oblique fractures and fractures with small proximal fracture fragments, are better suited to proximal to distal screw insertion. Once the glide hole is prepared, a centering sleeve and/or pin is kept in place to facilitate fracture reduction. The arthroscope is then inserted into the mid-proximal palmar or plantar fetlock joint. An instrument portal is created distal to the arthroscope portal at the level of the mid-sesamoid bone to facilitate direct debridement of the fracture line. Fracture reduction can be aided with flexion of the fetlock, manipulation of the centering sleeve and pin, and/or with an instrument applying pressure to the fracture fragments. Bone reduction forceps are then placed, and reduction is assessed arthroscopically once again. If reduction is satisfactory, the screw is placed routinely with additional screws placed as needed. Few reports of outcome following arthroscopically-guided repair of sesamoid fractures exist. A study by Busschers et al. (2009) found that 44% of horses raced after mid-body sesamoid fracture repair using this technique.³ The prognosis was decreased in horses with fractures of the front medial sesamoid affected and with increased displacement and decreased reduction.

Fractures of the Proximal Phalanx
Fractures of the proximal phalanx also occur commonly in racehorses but can occur in sport horses as well. While most fractures can be repaired under radiographic or fluoroscopic guidance, many surgeons prefer to incorporate arthroscopy into the repair. For dorsal plane fractures, the medial and lateral extent of the fracture plane can be defined with placement of needles into the joint parallel to the articular surface of P1. The planned trajectory of the screw can then be highlighted by a needle placed to transect the fracture line. Placement of the needles is guided by arthroscopy. For displaced sagittal/oblique fractures, alignment and reduction of the articular surface in the dorsal aspect of the joint can be assessed arthroscopically. Collateral ligament avulsion fractures and palmar/plantar eminence fractures can also benefit from arthroscopic-guidance with the arthroscope placed in the palmar/plantar aspect of the joint to monitor reduction. However, many collateral ligament avulsion fractures will require an open approach as significant displacement is often present.

Carpal Fractures
Arthroscopically-guided repair of carpal slab fractures is the treatment of choice.⁴ The 3^rd carpal bone is the most commonly affected bone with both dorsal and sagittal plane fractures occurring. Slab fractures of the radial and intermediate carpal bone occur but much less frequently, while slab fractures of the 2^nd, 4^th and ulnar carpal bones occur rarely. For 3^rd carpal bone fractures, the horse can be positioned in dorsal (preferred) or lateral recumbency. The arthroscope is placed into the joint routinely through either a dorsolateral portal (slab fractures of the radial facet) or dorsomedial portal (slab fractures of the intermediate facet) to facilitate debridement and assessment of the fracture line. An instrument portal is created, and the fracture line is gently debrided, removing any fragments that may hinder reduction. Fracture reduction is achieved with flexion of the carpus. A glide hole can also be drilled to allow manipulation of the fracture fragment with the centering sleeve +/- pin. Fracture repair is guided by placement of needles and radiography or fluoroscopy to guide screw trajectory. For dorsal plane fractures, an 18g needle is placed along the medial and lateral extents of the fracture line with 1-2 spinal needles placed along the articular surface of the 3^rd carpal bone in the direction of intended screw placement. It is helpful to stabilize the spinal needles by placing them within in the soft tissues in the palmar aspect of the joint. A 21g needle is then placed into the carpometacarpal joint to define the distal extent of the 3^rd carpal bone. Once fracture reduction is satisfactory on both arthroscopic and radiographic assessment, cortex screws are placed in lag fashion. Following fracture repair, further arthroscopic debridement of the fracture line can be performed. Slab fractures commonly have concurrent articular lesions that benefit from arthroscopic debridement; therefore, complete examination of the joint is necessary. For sagittal fractures of the 3^rd carpal bone, needles can also be placed under arthroscopic-guidance to guide screw placement, with a spinal needle placed from medial to lateral across the fracture line. A similar needle-guided technique can be used to repair slab fractures of the radial and intermediate carpal bones, however, in these cases both the middle carpal joint and radiocarpal joint should be examined arthroscopically.

Tarsal Fractures
Few tarsal fractures are amenable to arthroscopically-guided repair but include fractures of the malleoli of the tibia and sagittal and parasagittal fractures of the talus. Occasionally, medial and lateral malleolar fractures are large enough that they are suitable for lag screw fixation. Arthroscopy can be useful to guide debridement of the fracture line, remove intra-articular debris and monitor reduction. This can also be useful in sagittal and parasagittal fractures of the talus that are being repaired using lag screw technique.

Conclusions
Arthroscopically-guided fracture repair can guide anatomic reconstruction of the articular surface while using a minimally invasive approach. It can also facilitate debridement of fracture lines, removal of intra-articular debris, and prognostication. Arthroscopically-guided fracture repair should be considered the standard of care in many equine fractures.

References

1. Cianci JM, Wulster KB, Richardson DW, Stefanovski D, Ortved KF. Computed tomographic assessment of fracture characteristics and subchondral bone injury in Thoroughbred racehorses with lateral condylar fractures and their relationship to outcome. Vet Surg. 2022;51(3):426-437. doi:10.1111/VSU.13770
2. Wright I, Nixon A. Fractures of the Condyles of the Third Metacarpal and Metatarsal Bones. In: Nixon A, ed. Equine Fracture Repair. 2nd ed. Wiley Blackwell; 2020:378-424.
3. Busschers E, Richardson DW, Hogan PM, Leitch M. Surgical repair of mid-body proximal sesamoid bone fractures in 25 horses. Vet Surg  VS  Off J Am Coll Vet Surg. 2008;37(8):771-780.
4. McIlwraith C. Fractures of the Carpus. In: Nixon A, ed. Equine Fracture Repair. 2nd ed. Wiley Blackwell; 2020:480-514.