For any fracture patient, the decision as to which stabilization system to apply is made by assessing the mechanical, biologic, and clinical factors that influence outcome. There are two mechanisms by which a fracture can be stabilized: (1) internal or external fixation and (2) formation of a biobuttress (biological buttress, callus).
For any fracture patient, the decision as to which stabilization system to apply is made by assessing the mechanical, biologic, and clinical factors that influence outcome. There are two mechanisms by which a fracture can be stabilized: (1) internal or external fixation and (2) formation of a biobuttress (biological buttress, callus). By assessing the three influential aspects of treatment (mechanical, biological, clinical), the attending surgeon is able to choose a fixation method that will balance the stability gained through application of a fixation device with the stability gained by the formation of a callus (biobuttress). Exposure technique is one essential method to preserve the biologic response. Exposure technique may be closed, open, or minimally invasive via strategically placed portals.
Minimally invasive fracture repair has gained popularity in recent years. Initially the technique seems difficult but as with other techniques, with practice and adherence to principle, the technique is readily mastered. Following assessment and stabilization of the animal, the attending surgeon must decide upon the appropriate management of the case. Assessment includes factors important relative to the biologic potential (potential for callus formation), technique of reduction, and clinical factors. Biologic factors evaluate the potential for callus (biobuttress) formation. Other biologic factors to consider are bone involved, location of the fracture (cortical vs cancellous), injury to the surrounding soft tissue envelope and surgical technique. Once the biologic assessment has determined the potential time for callus deposition, the attending surgeon must decide upon the method of exposure and reduction technique. Exposure choices are closed exposure, minimally invasive exposure or open exposure; reduction technique choices are direct reduction or indirect reduction.
Closed exposure methods cause the least damage to the surrounding soft tissue. This technique is most commonly used with application of external skeletal fixation for fractures of the radius or the tibia. Occasionally closed intramedullary pinning is applied when the biologic assessment indicates very rapid biobuttress formation and a single IM pin can be used for stabilization. As a rule this is only true in very young animals (3-4 months of age).
Minimally invasive exposure technique is an open technique whereby direct or indirect fracture reduction is achieved with small exposure portals. Each portal is strategically located to allow proper reduction and application of an implant. Implants commonly used fro minimally invasive technique are bone plate, clamp/rod internal fixation, and interlocking nails. With direct reduction, two or three portals are commonly used depending on the type of fracture (transverse, oblique) and location of the fracture plane relative to the proximal and distal metaphyseal region of the bone. An incision (1-2cm) is made overlying the metaphyseal-epiphyseal area of the proximal and distal parent bone. Soft tissue is reflected to expose the bone surface where the implant will be applied. An additional small portal may be necessary to expose the transverse (short oblique) fracture site. A periosteal elevator is used to create an avenue on the surface of the bone for positioning the implant. The fracture is visually aligned and the implant applied. With bone plates and screws or CRIF, the implant is slid beneath the soft tissue into the previously created avenue on the surface of the bone. One proximal and distal screw is applied to hold fixation while alignment is examined. The remainder of screws is then inserted. As a generally rule, 2-3 screws are inserted into each fragment.
Minimally invasive technique using indirect reduction also uses two or three portals depending on the location of the zone of comminution relative to the proximal and distal eiphysis. In general, a proximal and distal portal are all that is needed. An alignment pin is inserted first to achieve axial alignment and maintain reduction of the proximal and distal parent bones. The pin is normograged in the femur and tibia but may be retrograded in the humerus. With radius and ulna fractures, the alignment pin is first placed in the ulna through a small posterior portal. This maintains alignment as the portals are made for insertion of the plate onto the radius. When applying to the femur or humerus, an army/navy hand retractor is used to lift the incision and soft tissue of the distal portal. This allows observation of the pin as it exits the marrow cavity at the fracture site and allows observation of the pin as it enters the distal parent bone. Once in place, the pin maintains alignment as the plate is readied for insertion. The plate is contoured to the shape of the bone and slid into position via a tunnel made with a periosteal elevator. Plate screws are then inserted proximally and distally through the soft tissue portals. The pin can remain in place to make a plate/rod construct. In general with a plate/rod construct, two screws proximal and two screws distal are all that is needed.
Minimally invasive technique in a comminuted radius and ulna fracture. Note portal sited for application of implants. The radiograph shows consolidation of the fracture 4 weeks following surgery.
Mechanical factors influencing case outcome are those affecting the degree of implant loading and those affecting interfragmentary strain (motion). Implant loading is determined by the intended function of the implant. Will the implant function to share weight bearing loads with the bone column following treatment or will the implant function to carry all the weight bearing loads until a fracture gap is bridged with callus (biobuttress). If the fractured column of bone is anatomically reduced and the interfragmentary fracture lines are stabilized with compression, the bone shares post operative weight bearing loads with the implant(s). Examples would be a compression plate, neutralization plate, interlocking nail/cerclage wire combination, or an intramedullary pin/ cerclage wire combination.
When a surgeon chooses this method of fracture management (anatomic reduction), he/she is said to have applied the technique of direct reduction in the management of the fracture. If the fractured column of bone is not anatomically reduced and the fracture area bridged with an implant, the implant must carry all weight bearing until biobuttress is formed. When a surgeon chooses this method of fracture management, he/she is said to have applied the technique of indirect reduction in the management of the fracture.
The advantage of direct reduction (load sharing between the implant and bone) is lower stress on the implant system and therefore, fewer complications. However, to apply the technique of direct reduction, a number of criterions must be fulfilled. First, the fracture configuration must be such that anatomic reduction and interfragmentary stabilization are possible. Second, the surgeon must be able to achieve anatomic reduction and stabilization without significant injury to the surrounding soft tissue. If the soft tissues are excessively damaged, the biologic response needed for bone union will be delayed. This prolongs bone healing and increases the likelyhood of complications. Fracture configurations amendable to anatomic reduction are those with single fracture lines (transverse, obligue) or comminuted fractures having one or two large fragments. These fracture configurations also allow relatively easy interfragmentary stabilization of all fracture planes without significant disruption of the surrounding soft tissue envelope.
Interfragmentary stabilization is an important criterion with the application of direct or indirect reduction. This is because reduction technique and bone healing relate directly to interfragmentary strain (motion). High interfragmentary strain levels slow or impede bone formation, whereas lower interfragmentary strain levels favor bone formation. The level of interfragmentary strain will vary depending on the length of the original fracture gap. Small fracture gaps (single fracture lines) concentrate strain, but longer fracture gaps (multiple fracture lines) lower interfragmentary strain by distributing the motion over a larger area. As is quickly evident, the method of reduction influences interfragmentary strain.
Direct reduction creates fracture planes with small gaps between fragments (anatomic reduction). For example, transverse fractures have small gap lengths (when reduced) and, therefore, inherently concentrate motion. Since high interfragmentary strain (motion) impedes bone formation, small gap lengths created with the use of direct reduction must be rigidly stabilized to eliminate strain.
If the fracture configuration is such that anatomic reconstruction and stabilization of fracture planes of the bone column are not possible, the surgeon should then use the technique of indirect reduction. Fracture configurations where this method of treatment is commonly employed are highly comminuted diaphyseal fractures. The use of the implant in this situation is referred to as a bridging or buttress implant since it is crossing an area of bone fragmentation. The implant must therefore be strong enough and stiff enough to withstand all weight bearing loads until sufficient callus is formed. Implant systems useful for bridging osteosynthesis are plates, plate/IM pin combination, interlocking nails, external skeletal fixators. Since the goal is to achieve rapid callus (biobutress) formation to unload the implant, the surgeon must create an environment where this will occur. There are a number of advantages of indirect reduction that help create an environment conducive to rapid callus formation. First, indirect reduction preserves the biology (soft tissue) because there is no attempt to reduce small fragments of bone in the area of comminution. Preserving the injured site conserves remaining vasculature, hematoma, and various peptides needed for induction of bone healing. Second, interfragmentary strain is low within the area of comminution. Recall that the level of interfragmentary strain will vary depending on the length of the original fracture gap. Small fracture gaps (single fracture lines) concentrate strain, but longer fracture gaps (comminuted fractures) lower interfragmentary strain by distributing motion over a larger area. Spatial realignment of the column of bone (rotation, length, varus-valgus) instead of anatomic reduction does not create small fracture gaps that concentrate motion. Rather, a fracture zone with multiple bone fragments is maintained which distributes strain (motion) over a larger area. This therefore, lowers strain within the fragmented zone favoring rapid bone formation.
In summary, choose direct reduction when the fracture configuration allows for anatomic reduction and interfragmentary stabilization. The load sharing between the implant-bone construct is a powerful method to avoid implant failures and accelerate return to function. Choose indirect reduction if the fracture configuration is such that anatomic reduction is not possible or if reduction cannot be accomplished without significant injury to the soft tissue. The implant must be strong and stiff so as to bridge the fracture area until callus is formed. Do all possible to preserve the soft tissue environment and maintain an environment of low interfragmentary strain to enhance callus formation.
Bone plates have been used effectively for treatment of fractures in dogs and cats for over 30 years. Over the years, different designs of plates have become available, including DCP (dynamic compression plates), LC-DCP (limited contact dynamic compression plates) and special situation plates (veterinary cuttable plate, acetabular plates). The most recent plate design to become available is the locking compression plate (LCP). The unique feature of the locking plate is the presence of a combi plate hole. The combi hole is a plate hole through which the surgeon can apply compression using a standard cortical screw or a locking screw. Using a locking screw threads in the head of the screw engage threads in the plate hole, locking the screw to the plate. The ability to lock the screw to the plate increases the stiffness of the construct and the pull out strength of the bone plate and screws. Standard plates do not have threaded holes; stability is achieved through compression applied between the plate and bone surface when tightening the screws. The friction between the plate and the bone provides the stability to the bone-implant construct. In contrast, the locking plate achieves stability through the concept of a fixed-angle construct. The locking plate is not pressed firmly against the bone as the screws are tightened. The locking screws and plate function more like an external fixator. The plate functions as a connecting bar and the screw functions as a threaded fixator pin. The threads in the head of the locking screw engage the hole of the plate, similar to the clamp of an external fixator.
Locking plates are particularly useful when screw pull-out is at a greater risk. Screws may be susceptible to pull-out failure in the metaphyseal region of bones where the bone cortex is thin, in osteoporotic bone, older patients, patients having slow bone healing conditions and patients that have poor compliance to restricted activity during the postoperative period. A locking plate is also useful with the presence of a limited proximal or distal target (epiphyseal or metaphyseal fracture). Minimally invasive plate osteosynthesis (MIPO) is best accomplished with the application of a sliding plate technique. MIPO is usually accomplished with small proximal and distal portals where one applies two – three screws in each fracture segement. The locking plate is also useful when revising fractures that did not heal when using traditional plates when disuse has resulted in fracture disease (osteoporotic bone).
Many of the same instruments used for application of traditional plates are used for locking plates. The 3.5 mm locking plate and screws are most commonly used in small animals. The 3.5 mm locking plate will accommodate 3.5 mm cortical screw, 4.0 mm cancellous screws or 3.5 mm locking screws. A 2.8 mm drill bit is used when applying 3.5 mm locking screws. A guide is screwed into the intended hole to center the hole when drilling. The locking screw is self-tapping and is placed with a hand or power driver.
Series of images showing application of a LCP/rod used for MIPO in a comminuted radius & ulnar fracture. Healed at 6 weeks. An LCP is beneficial when applying the technique of MIPO since minimal number of screws are applied proximally and distally. The locking screw exhibits superior pullout resistance relative to standard screws. In this case, a combination of locking and standard screws are used to maintain stability.
Series of images showing application of an LCP/rod in a commniuted distal humeral fracture. The plate and rod have been applied using a strategically placed portals, ie, minimally invasive plate osteosynthesis (MIPO). The LCP is particularly useful in this case due to the small target distally (humeral epiphysis). A locking screw in this position has superior pullout resistance compared to a standard cortical or cancellous screw
The Clamp Rod Internal Fixation (CRIF) system is a novel fixation system developed by the AO VET. The system is an internal fixation device comprised of stainless steel rods (diameter of 2mm, 3mm, 5mm) and clamps which accept 2.0, 2.7, and 3.5 mm screws. There are two types of clamps: standard clamps and end clamps; end clamps are positioned at the ends of the bar and provide axial support. Instrumentation has been developed to assist the surgeon in sliding and positioning clamps from on the bar.
Trauma Vet locking system; versatile, simple application, effective