Implant Removal in Horses: Why, When and How

Indications for implant removal

Removal of surgical implants (screws, plates, wires) are generally for one the following reasons:

• The function of the implants is complete (fracture healing, correction of deformity).
• The presence of the implant may potentially cause lameness.
• The presence of the implant is not cosmetic.
• The presence of the implant prevents resolution of sepsis.

Risk of implant removal

A decision on implant removal should be balanced with the risk/ benefits of the procedure. The risk of implant removal varies with the location and function of the implant and the original injury and time from fracture repair to removal of the implant(s). Removal of single or multiple screws for correction of angular limb deformity or fracture repair generally carries little to no risk. Infection of the soft tissues is possible during implant removal and can occasionally become serious. A second fracture of a long bone is possible after implant removal even after staged removal of plates.

Timing of implant removal

Implant removal is required after resolution of angular deformities to prevent overcorrection of a deformity. Timing of removal is based on rate of growth, degree of deformity, and age at the time of removal. Recommendations for removal of single or multiple screws for fracture management vary by the location of the fracture and surgeon’s preference. Unicortical screws placed for the treatment of dorsal cortical metacarpal stress fracture are typically removed 8 weeks post-operatively and after fracture healing. Removal of plates after long bone fracture repair is generally required if the horse is to be used for athletic purposes. An exception to this is plates used for olecranon fracture repair, since in most circumstances no morbidity associated with the presence of the implant is recognised. Typically plate removal is 12 to 16 weeks after fracture fixation and at least 30 days after the beginning of pasture turnout. In foals plate removal can occasionally occur earlier and as quickly as 4 to 6 weeks in some circumstances. If two plates are present, removal of the plates is typically staged. I tend to remove the plate which is theoretically under more loading first, followed by removal of the second plate if required after at least 30 days of pasture activity. Occasionally secondary neutralisation plates remain if their presence is not a considered a risk for future lameness. Engagement of cortices which are placed in bending when loading may lead to lameness, either by union of the cortices or potential differences between the modulus of elasticity of the bone and the implants.

If implants are to be removed secondary to sepsis, then a decision needs to be made about balancing the effectiveness of leaving an infected implant in for stability and/or fracture healing, and the effect of the local sepsis on fracture healing, extension of infection to adjacent structures and cosmetic outcome.

Preoperative preparation

Implant removal is often performed in the conscious, sedated horse using local anaesthesia. General anaesthesia can be used if the location of the plate removal precludes effective local anaesthesia, such as the proximal limb, or the nature of the patient prevents safe removal of the implants in the conscious patient.

Technique for implant removal

For removal of single screws or screws/wire transphyseal bridge the surgical technique consists of localising the head of the screw with a small gauge hypodermic needle followed by a small stab incision with a number 15 scalpel blade over the screwhead. Typically, some soft tissue is present in the screwhead and this can be removed by placing the tip of a pair of mosquito haemostatic forceps in the screwhead to identify the location to seat the screwdriver and confirm the angle of placement of the implant. The surgeon should be confident that the screwhead has been identified with the hypodermic needle prior to making the stab incision.

If a plate is to be removed a 3 to 4 cm incision is typically made over the proximal or distal end of the plate through which the plate is to be removed. On occasion it may be necessary to use an osteotome to remove bone that has overgrown on to the plate. Once the screwheads are identified, stab incisions with a number 15 blade are made and the screws removed. Bone and soft tissue can grow into the screw heads and removal is aided with hypodermic needle or Kirschner wires. After removal of the screws the plate typically needs to be loosened using an osteotome and mallet. After loosening of the plate, a hole in the plate can be hooked with a haemostat or thyroid retractor and removed through the initial incision. On occasion, the depth of the plate is such or bone overgrowth so excessive that multiple 3 to 4 cm incisions or one large incision is necessary for plate removal. The stab incisions for screw removal are typically left unsutured but can be sutured if elected or if excessive in length. The incision for plate removal is closed in two or three layers. Penrose drains are occasionally placed to prevent seroma formation if a large dead space or excessive haemorrhage has occurred. The use of drains and absorbable antimicrobial beads are recommended after removal of infected implants.

Post implant removal management

Post-operative management differs with the individual cases. After removal of implants for correction of angular limb deformities, no special restrictions aside from wound management are necessary. After removal of plates for fracture repair, the author generally radiographs the affected area after recovery from anaesthesia to check for any injury or re-fracture post plate removal. After discharge a period of 10 to 14 days of stall rest followed by small paddock turnout for 4 weeks is recommended. If a second plate is present the author prefers staged removal which occurs 4 to 6 weeks after removal of the primary plate.

[...]