34th Annual Scientific Meeting proceedings

Fractures occur in all breeds of foals and are typically the result of trauma from collisions or kicks or during strenuous activity especially after periods of confinement. Unlike in horses in training repetitive stress injury is not a component of fractures in the foal.  Due to the presence of physis at the ends of long bones fractures in foals present unique challenges due to limited amounts of bone stock at the ends of the bones and issues with limb growth or angular deformity after fractures and /or repair of these fracturs.  Conversely because of foal’s lighter bodyweight and the tendency for fractures in foals to be closed there are opportunities for fracture repair in the foal that do not exist in adult horses.  

Stability and immediate weight bearing should the surgeon’s foremost goal in dealing with foal orthopedic injury.  The longer a period of time a foal is not comfortable the more likely they are to develop angular deformity and / or flexor laxity on the weight bearing limb or flexural contracture on the injured limb. As in adult equine fracture repair stability equals comfort and comfort equals success. Surgical planning and execution should be aimed at restoring the boney column with proper alignment and length in a way to allow full weight bearing with minimal pot-operative coaptation.

Principles of fracture repair in the foal

• Reestablish axial alignment of the limb for growth and weight bearing
• Determine the tension side of the fracture in order to place implants correctly for optimal strength
• Use implants of the appropriate strength for the type of injury and size of animal
• Apply the implants systems in the correct manner
• Understand effect of implants on future growth and angular deformity
• Determine the optimal time for removal of implants if appropriate
• Determine and apply appropriate coaptation

Critically evaluate the result.  Did you achieve your goals? Is modification required

PHYSEAL FRACTURES
All types of physeal fractures occur in foals. The most common type is Salter Harris Type II fractures, which is like other species.  Since these fractures occur at the end of the bones and lead to instability, rigid coaptation or fixation is essential to restore axial alignment. In most fractures interna fixation is elected unless anatomic alignment and stability can be obtained with coaptation alone. Internal fixation is elected adequate purchase must be gained in the fracture fragments to allow weight bearing and comfort. In many cases the physis must be bridged by implants to accomplish this.  Doing so will cause physeal retardation or cessation of growth. An advantage of fixed angle screw implant system is to prevent growth on both sides of the physis if the cis and trans cortices are engaged with at least two screws in the plate.  It is likely in many cases that the injury itself had disrupted potential growth enough to alter limb length. It seems more often than not compensatory growth from other growth plates in the limbs has allowed adequate limb length in such cases.  In determining a management strategy of physeal fractures maintaining axial alignment and removing implant to allow potential growth need to be considered.

Common physeal fracture location in the foal
Type I fractures - proximal femur, distal radius, proximal P1

Type II fractures - proximal tibia, distal femur, proximal and distal radius, distal MC/ MTIII, proximal P1

Type III fractures – distal radius, distal MC/ MTIII

Type IV – distal radius, distal MC/MTIII, proximal P1

Management of physeal fractures in the foal
Due to the limited purchase in the epiphysis and proximity to articular surfaces make repair of physeal fractures challenging.  Careful reduction of the fracture is paramount for future limb alignment. Accurate placement of implants on the tension side of the bone (where the fracture is distracting while weight bearing) is essential.  In my opinion only fractures that are inherently stable and non-displaced fractures or those that can be made stable with coaptation can be treated non surgically. Displaced unstable fracture generally have poor outcomes without internal fixation due to discomfort compensatory overlengthening and malalignment.  Repair of the SH II fracture of the proximal tibia is a good example of applying internal fixation techniques to obtain limb alignment and comfort. In the proximal tibia the metaphyseal spike is characteristically lateral and the tension side of the fracture is the medial aspect of the physis.  After proper reduction of the fracture apply a bone plate to the medial aspect of the bone provides the rigid stability and resistance to the distracting tension force on the bone. This principle is applied to other physeal fractures in the foal.

Management of diaphyseal fractures in the foal
Bone plates are used for the repair of most diaphyseal fractures in the foal. Plates have advantages over other methods of repair by their ability to counteract axial compression, bending and torsion loads that are applied to the bone.  The bending stiffness of a bone plate is related to the third power of its thickness and directly proportional to its modulus of elasticity.  It is easier to increase the stiffness of the implant-bone construct is by choosing thicker or multiple plates. Anatomic reconstruction of the fractured bone is a requirement for successful repair.  Failure to properly reconstruct the bone prevents load sharing between the implants and the bone and quickly leads to failure of the construct.  Double plate fixation is the method of choice for management of many diaphyseal fractures in the in the foal.  In general, the larger plate is used on the tension surface of the bone and the narrow plate placed ninety degrees to the broad plate.  Placement of a plate on the tension surface is biomechanically advantageous since the plate-bone construct has its greatest stiffness when placed in tension compared to compression.  Placing a plate at ninety degrees to the first plate optimizes resistance to axial compression, bending and torsional loads.  and techniques for placement of bone plates are made to optimize load sharing, diminish compression forces and reduce cyclic fatigue.  The use of fixed angle plate systems has a decided advantage in fracture repair in the foal and will often maintain stability despite in the face of sepsis if that were to occur.