Refracture of the Toy Breed Radius

Kenneth A. Johnson, MVSc, PhD, FACVSc, DACVS, DECVS

Fractures of the radius and ulna in toy breed dogs are often transverse or short oblique in configuration and located close to the distal metaphyseal region. These fractures are known to be at increased risk for development of non-union. The causes of such non-unions probably involve both biomechanical and biological factors. One explanation for the poor biology has been the purported meagre vascularity. Also, the lack of appropriately sized plates and screws has made open reduction and internal fixation challenging. Excessively stiff plate fixation is associated with implant-induced osteoporosis of the radial bone under the bone plate.[1] More recently small bone plates applied using 1.5-mm cortical screws or locking screws have become more readily available. A clinical and radiographic study reported that radiographic union of 29/30 radial–ulnar fractures in toy breed dogs repaired with 1.5-mm locking plates was achieved at a median of 8 weeks.[2]

Implant-induced osteoporosis is potentially reversible by implant removal, especially in growing dogs.[1] However, the benefits of the implant removal are unclear and carry the risk of refracture of the radius at the original fracture site or through an empty screw hole in the bone.[3]

An interesting finding from two recent studies was that peri-implant refracture of the radius occurred in some dogs months or years after the original radial fracture had been repaired and healed.[2] [3] The original distal radial fractures were in young growing dogs, and the most distal screw was inserted into the distal metaphyseal bone immediately adjacent to the physis. At the time of repair, the screw–bone ratio was considered to be appropriate. However, with continued bone growth and distal elongation of the radial diaphysis, the distal screw in the plate was subsequently located relatively more proximally in the radial diaphysis – the refracture in the bone surrounding the distal plate screw had a screw–bone ratio of 35% in one case.[2] In another case, the escalation in screw–bone ratio that resulted in a peri-implant refracture was even more pronounced with a tee-shaped locking condylar plate with two side-by-side screws distally.[3] These complications highlight the need to modify the planning of implant selection in young growing dogs. It was suggested that the screw diameter in the distal plate hole should be “downsized” from 1.5 to 1.0 mm for implants intended for stabilization of distal radial fractures in young growing small breed dogs.[3]

Conflict of Interest

None declared.

• References

• 1 Muroi N, Shimada M, Murakami S. et al. A retrospective study of postoperative development of implant-induced osteoporosis in radial-ulnar fractures in toy breed dogs treated with plate fixation. Vet Comp Orthop Traumatol 2021; 34 (06) 375-385
• 2 Swepson R, Crowley J, Glyde M. et al. Clinical and radiographic outcomes of 1.5-mm locking plate fixation for 30 radial and ulnar fractures in dogs. Vet Comp Orthop Traumatol 2025; (Epub ahead of print ).
• 3 Muroi N, Kanno N, Harada Y, Hara Y. A retrospective study of risk factors associated with refracture after repair of radial-ulnar fractures in small-breed dogs. Vet Comp Orthop Traumatol 2025; 38 (02) 77-86

Publication History

Article published online:
13 March 2025