Surgical repair of comminuted long bone fractures in animals is shifting from the traditional, mechanical emphasis of anatomic reconstruction to a more functional, biological approach.
As with many other veterinary protocols, this trend in orthopedic surgery has been adapted from human studies performed in the late 1980s and early 1990s.
Successful clinical results using this method of biological fracture fixation (also termed bridging osteosynthesis of indirect reduction) are now routinely appearing in the veterinary clinical journals and have become standard textbook inclusions. In both injured people and animals, faster healing and fewer complications were reported with biological fixation methods compared to anatomic reconstruction.
Clinicians who perform orthopedic surgery should consider the biological approach for fracture fixation in lieu of attempts to anatomically reconstruct comminuted bone segments.
Surgeons have several options including bone plates , interlocking nails , and external fixators in treating these complex fractures. Preservation of hard and soft tissue integrity along with utilization of stable implants are the keys for reduction of patient morbidity and a return to function.
With the older, standard approach of anatomic reconstruction, a fragmented bone's integrity was restored by meticulous (and often tiresome) dissection and reuniting of numerous cortical bone segments; a 5 or 7 piece puzzle was initially stabilized with small pins, wires or screws until the final two main pieces of bone could be solidly fixed with a plate or, to a lesser extent, by an intramedullary pin.
The radiographic result of this seemingly 'picture perfect' reconstructed bone column would often be offset by the reality of prolonged operative time, infection, sequestra, and iatrogenically traumatized periosseous soft tissues.
Furthermore, little if any mechanical advantage is gained by this reconstruction and high strain rates between closely apposed, but unstable, bone fragments would often lead to fracture collapse and implant failure.
Success of anatomic reconstruction is based on three critical factors: rigid fixation, cortical contact of fragments, and preservation of soft tissue viability. Infection, although detrimental to fracture healing, is not an absolute impediment to bone union.
For surgeons, post-operative complications such as delayed, mal-, and nonunion are associated with technical errors directly related to the aforementioned factors.
Clinical mistakes include:
small size, improperly placed, or inadequate number of wires;
open screw holes in plates overlying bone defects;
too small bone plates, not enough bone screws in bone fragments;
weak external fixator constructs.
The mechanical approach for fracture repair is predicated upon load sharing by a reconstructed bone column. There is little margin for error, hence fractures with greater than 2 or 3 fragments are at high risk for failure in healing.
The biological approach for fracture healing or osteosynthesis is characterized by:
Stabilization of the main proximal and distal bone segments with a bone plate or screws (bridge or biological plating), interlocking nail (with screw), or external skeletal fixation. In general, between 6-8 cortical (near and far cortices) surfaces in each of the main fragments should be engaged by screws or fixator pins for adequate stability.
Minimum periosseous dissection around the fractures to preserve vascularity and reduce the risks of infection and bone sequestration. Limited dissection is most easily accomplished when fractures are stabilized with linear or circular external fixators compared to bone plates or nails. Multiple fragments are left alone and serve as an in situcorticocancellous graft to aid in fracture healing. Small, displaced bone pieces can be encircled by absorbable suture to realign and become incorporated into the main callus along the central bone axis.
In the femur and humerus, alignment of main bone fragments with an intramedullary pin is used initially prior to plate application, or, in the humerus, connected (tied-in) externally to a linear fixator. The intramedullary (IM) pin diameter is approximately 1/3 of the medullary canal at its narrowest diameter. This size permits perpendicular placement of screws or percutaneous pins through the medullary canal. The pin protects, by neutralizing bending forces, a buttress plate or fixator spanning large defects. Alternatively, lengthening plates, which lack central holes, can be used to provide greater rigidity to the overall construct than open hole dynamic compression plates. In general, external skeletal fixation is a poor choice for stabilization of femoral fractures because of the transfixation of the large lateral muscle mass by fixation pins. Plates or interlocking nails are the preferred choice for femoral fractures. Interlocking nails can be difficult to use in humeral fractures because the area of communition is often just proximal to the distal segment where little medullary cavity exists for placement of an appropriately sized interlocking nail.
Comminuted fractures of the radius are best managed by plate fixation or external fixation; concurrent placement of an IM pin is ill-advised because it is impossible to place an appropriately sized IM pin without damaging the adjacent carpal joint. Even if the pin enters the distal fragment cranial and proximal to the joint surface, the pin will impact the carpus with normal carpal extension.
Comminuted fractures of the tibia are best managed by plate-rod fixation, external fixation, or interlocking nail.
A new alternative to plate-rod fixation is the use of locking plate fixation. With this device, the screw heads are threaded and lock into corresponding threads in the plate. The effect is essentially an "internal" external fixators. Not all screws must or should be locked to achieve adequate stability. These plates are expensive and their exact place in the realm of veterinary orthopedics remains to be seen.
Staged disassembly of the implants (removal of IM pins or fixation pins or connecting bars in the case of external fixators) can be done to transfer to the bone some of the mechanical load associated with weight bearing. This increase in force transmitted through the bone stimulates the callus present at the fracture site to mineralize and remodel and hastens fracture healing. While there are many factors that govern the optimum time to destabilize a fracture repair to enhance fracture healing, destabilization should generally occur at about 4-6 weeks after surgery.
Variable (6-14 weeks) healing rates based on primarily endosteal callus formation and not primary bone union nor exuberant perisosteal reactions. Immature patients will heal faster than mature ones and should therefore be evaluated radiographically and clinically every 3-4 weeks while older animals are examined at 4-6 week intervals.
The biological approach is extremely useful for comminuted humeral, radial, femoral, and tibial fractures, although nuances of each fixation (plate, nail or fixator) should be noted.
Proximal limb musculature and the body wall limit external fixation devices to the lateral aspect of the humerus.
A plate/rod combination or interlocking nail is advantageous for repair of the humerus or femur because either of these fixations provides enhanced stability along the neutral axis of the bone and avoids muscle penetrations by percutaneous pins.
Pinning or nailing are not technically feasible for radial fractures and the curved, saucer-shaped nature of the bone.
Plating, especially lengthening plates lacking central holes, is useful for radial injuries.
Tibial fractures can be treated by any of the fixations; IM pin placement should avoid trauma to the stifle joint. In fractures involving the paired bone systems (radius/ulna, tibia/fibula), only the major weight-bearing bones are treated. The secondary bone fractures will often self reduce during surgical manipulations and heal in an uncomplicated manner by indirect bone union.
Several protocols have proved to be useful in promoting the biological surgical approach:
Robert Jones bandages applied to fractures below the elbow or stifle joint, or spica splints used for proximal limb injuries help control traumatic soft tissue swelling and prevent further displacement of bone fragments pending definitive surgical repair.
Pre- and intra-operatively, a hanging limb preparation for radial or tibial fractures is useful in realigning the limb axis, reducing muscular contractions, and permitting circumferential approaches for external fixation. In this instance, the paw is secured via tape to a ceiling hook or IV stand and the surgery table dropped several centimeters so the patient's weight creates linear limb traction. Utilization of fresh autogenous cancellous graft material harvested from the greater tubercle or wing of the ilium and placed at the fracture site(s) in mature patients, will promote healing via osteosynthesis, osteoinduction, and osteoconduction.
Rigid fixation allows post-operative physical therapy to be pursued with limited concern for fixation failure and nonunion.
Post-operative physical therapy and rehabilitation are actively promoted to reduce soft tissue swelling, regain joint and limb functions, prevent soiling, and stimulate healing of all tissues, including bone.
This is achieved by encouraging leash walks on flat or inclined surfaces, swimming therapy, and passive flexion/extension of joints.
Horstman C L, Beale B S, Conzemius M G & Evans R R (2004) Biological osteosynthesis versus traditional anatomic reconstruction of 20 long-bone fractures using an interlocking nail: 1994-2001. Vet Surg 33 (3), 232-237 PubMed.
Reems M R, Beale B S & Hulse D A (2003) Use of a plate-rod construct and principles of biological osteosynthesis for repair of diaphyseal fractures in dogs and cats: 47 cases (1994-2001).JAVMA223 (3), 330-335 PubMed.
Johnson A L, Smith C W & Schaeffer D J (1998) Fragment reconstruction and bone plate fixation versus bridging plate fixation for treating highly comminuted femoral fractures in dogs. JAVMA 213, 1157-1161 PubMed.
Hulse D, Human W & Nori M (1997) Reduction in plate strain by addition of an intramedullary pin.Vet Surg 26, 451-459 PubMed.
Aron D N, Johnson & Palmer R H (1995) Biologic strategies and a balanced concept for repair of highly comminuted long bone fractures. Comp Cont Educ Pract Vet 17 , 35-49.
Other sources of information
Palmer R H (1999) Biological osteosynthesis. Vet Clin North Am Sm Anim Pract 29, 1171-1185 PubMed.
Vetstream contributor(s)
Mark C Rochat DVM MS, Professor and Chief, Small Animal Surgery, Department of Veterinary Clinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, 01 Farm Road, Stillwater, OK 74078, USA.
Dr Joseph Harari DVM MS DipACVS , Veterinary Referral Services, 21 East Mission Avenue, Spokane, WA 99202, USA.
In both injured people and animals, faster healing and fewer complications were reported with biological fixation methods compared to anatomic reconstruction.
There is little margin for error, hence fractures with greater than 2 or 3 fragments are at high risk for failure in healing.