tibial shin bone fracture repair on dogs and cats
Tibial fracture repair for your dog and cat: Options for management
- Fractures of the tibia are relatively common in dogs and cats, comprising 21% of long-bone fractures. The entire spectrum of internal and external fixation devices is applicable to these fractures.
- Tibial fractures are common and may present in a variety of form, because there is little soft tissue covering over the cranio-medial aspect of the tibia(shin bone), open fractures are common.
- Tibial fractures have the highest rate of non-union after those of the radius (25% and 60% of all non-unions, respectively).
- The majority of fracture complications come as a result of poor decision-making by, rather than poor technical expertise of, the attending veterinary surgeon.
- Pre-operative assessment of the fracture and planning the repair helps to limit complication rates of tibial fractures.
The location and anatomy of the tibia provides several advantages to the surgeon:
- As it is superficial, it is easy to approach medially, with only one neurovascular bundle present, also, minimal muscle elevation is necessary
- It is a relatively ‘familiar’ surgical site
- The proximal tibia is a relatively ‘powerful biological’ site, with good muscle attachment on the proximal lateral aspect and a low cortical:cancellous bone ratio which leads to relatively rapid bone healing.
Fractures of the tibia also create several potential difficulties for the surgeon:
- As the tibia is superficial, open fractures are common
- The tibia is an irregular shape. In the proximal third it is triangular in cross-section. It is much wider proximally than distally and tapers to an isthmus in the distal diaphysis. The tibia also has a sigmoid shape in both a cranio-caudal and medi-olateral plane and has approximately 10-15o of torsion (twist) along its length. The distal half of the bone is torsed medially relative to the proximal half
- Unlike the femur, the tibia has articular surfaces proximal and distal to the line of the shaft, making intra-medullary pin placement difficult
- The insertion of the patella tendon on the tibial crest can produce high tensile and bending loads on repairs to fractures of the proximal tibia
- The limited muscle attachments to the distal tibia and the high cortical:cancellous bone ratio of the distal third of the tibia result in a relatively slow rate of bone healing compared to the proximal tibia. Blood supply to a healing fracture comes initially from the surrounding muscle attachments through the periosteal blood vessels, the so-called extra-osseous blood supply of healing bone
- Concurrent fissure fractures are common in tibial fractures, particularly of the distal third.
All of the fracture repair modalities (bone plates, external skeletal fixators, intra-medullary pins, external coaptation) may be used on the tibia. It is essential to consider the strengths and weaknesses of each fracture repair method when making an assessment of any fracture and planning which method of repair to use.
Intramedullary (IM) pins are only suitable for relatively simple tibial fractures. Normograde pin placement is the only suitable method in the tibia. Tibial fractures should never have an IM pin placed by a retrograde method because the pin will pass into the articular part of the stifle joint. In these instances the pin commonly damages the cruciate ligaments, menisci and articular cartilage resulting in pain,
lameness and, ultimately, degenerative joint disease. For normograde IM pin placement, make a 1-2cm skin incision over the medial tibial condyle at the junction of the cranial and middle thirds. The pin should be driven distally entering the medial ridge of the tibial plateau at that location. The fracture is held in reduction while the pin is driven into the distal fragment. Judge the correct depth of insertion by measuring with a second pin ofidentical length. It is essential to remember that the medial malleolus extends distally past the location of the talocrural joint. As the IM pin is being driven distally, it is important to remember this, it will help to prevent the pin from penetrating the talocrural joint. The base of the medial malleolus, rather than the tip, is the distal extent of maximum pin insertion. Flex and extend the hock joint to ensure that the pin has not been driven too far distally and penetrated the joint. Tibial pins should not be too large (they are usually 50 to 60% of the medullary diameter at its narrowest point); they need to curve slightly as they pass down the shaft of the tibia. Once seated, the pin must be cut short enough so that it will not touch the femoral condyles at full extension of the stifle joint. The reduced pin size means a consequent reduction in stability. Therefore, IM pins should only be used for tibial fractures where significant compressive and rotational forces are not present.
The use of external coaptation is only suitable in relatively simple tibial fractures. Full casts are reasonably good at preventing bending and rotational forces of low magnitude, which occur in simple transverse fractures in small or medium sized animals. External coaptation is unsuitable for use in fractures where bending and rotational forces of high magnitude (such as in large breed or very active dogs) are expected. External coaptation is also unsuitable in comminuted fractures or in long oblique fractures as it cannot prevent collapse and overriding of the fracture fragments.
Bone plates are very useful for the repair of tibial fractures. They can be used for grade 1 open fractures although for more severe open fractures such as grade 2 or 3 fractures, external fixators are preferable. Bone plates are applied to the medial aspect of the tibia. The use of the plate-rod technique is possible for the tibia although this procedure is technically more difficult than when applied to the femur (the narrowest part of the tibia is in the distal half and the limited widening in the distal tibial metaphysis makes distal screw placement more difficult).
Make a skin incision on the cranial aspect of the crus for the medial approach to the tibia. This approach will simplify closure and prevent the skin being closed directly over the plate. Wound breakdown over the distal tibia is a problem if this is not done. Intra-operative contouring of the bone plate, prior to application to the bone, is necessary due to the sigmoid shape of the tibia in a medi-olateral and craniocaudal plane.
The use of aluminum bending templates greatly simplifies contouring and they are a useful (and inexpensive) investment:
- When viewed from a medial aspect, the plate is applied to the line of ‘best fit’ and typically requires placement along the caudal edge of the proximal third
- Bending of the plate can be done with either a bending press, bending pliers or bending irons
- Slight twisting of the plate is usually necessary if the plate is applied to the full length of the tibia, to account for the 10-15o of tibial torsion. Whether twisting of the plate is necessary will be apparent from using a plate template and needs to be done with bending irons.
- Remember when applying bone plates to the distal tibia that the talocrural joint lies proximal to the medial malleolus by 0.5 to1cm. The distal tibial widens or flares at about a 20 degree angle to the long (sagital) axis of the tibia. If the most distal screw is placed perpendicular to thebone surface, rather than perpendicular to the long axis of the tibia, penetration of the talocrural joint may result.
External fixators (ESF) are the gold standard in the repair and management of open tibial fractures. The tibia is the easiest bone to which to apply an ESF. It is recommended that surgeons developing their ESF technique should work first on the tibia before repairing fractures of the radius and other long bones using this method. All types of ESF can be applied to the tibia. The most useful ESF for the repair of tibial fractures are the type II and modified type II ESF.