Equine Fracture Repair, the Principles of Closed Fractures Fracture Compression and Rigid Stabilization Remain
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127 9 Principles of Fracture Fixation Alan J. Nixon1,2, Joerg A. Auer 3, and Jeffrey P. Watkins4 1 Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA 2 Cornell Ruffian Equine Specialists, Elmont, NY, USA 3 Vetsuisse Faculty, University of Zurich, Zurich, Switzerland 4 Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, USA INTRODUCTION MANAGEMENT OF SOFT TISSUE INJURY Fracture management in horses follows many of the same Many fractures in horses involve considerable impact basic techniques used for fracture repair in humans and energy, which is transformed to both comminuted small animals. Techniques and equipment used in osseous fragmentation and extensive soft tissue injury. humans, particularly those developed by the Association The additive effect of motion on an unstable limb can for Osteosynthesis (AO; DePuy Synthes, West Chester, compound the soft tissue trauma of the initial fracture, PA, USA), are used in equine fracture reconstructions, reducing the prognosis for repair and increasing the cost. sometimes with modification and sometimes with- The possibility of disruption to the skin by the fracture out.16,42 Specific recent improvements are described in ends depends on the energy of the fracture, the ana- this chapter, including the 5.5 mm cortical screw, the tomic location of the break, particularly the amount of limited‐contact dynamic compression plate (LC‐DCP), surrounding musculature, and the care of the limb in the the locking compression plate (LCP), the dynamic con- postfracture phase. The classification of open fractures is dylar screw (DCS) plate and dynamic hip screw (DHS) described in Chapter 4. Injury can involve small skin plate, the equine intramedullary interlocking nail (IIN), wounds and increase to extensive skin wounds, muscle and the equine external fixator. These implants and loss, and finally damage to the vasculature and peripheral devices expand on prototypes developed to fill a need for nerves. Casting and splinting techniques are designed immediate weight bearing of large animals, using implants to prevent exacerbation of soft tissue injury following a able to withstand extraordinary stress, and yet capable of fracture and are described in Chapters 5 and 6. being applied expeditiously. Given the new implants entering use in equine fracture repair, the principles of Closed Fractures fracture compression and rigid stabilization remain. Further, the care of adjacent soft tissues is critically Intact skin generally prevents skin‐borne organisms important in the optimization of fracture healing. The from invading the fracture site. However, intact skin increased application of the LCP has done more to pre- that has been extensively bruised or stretched or covers serve the soft tissues than most previous plating systems, extremely swollen structures becomes pervious to bacte- and minimally invasive approaches to plate insertion are rial invasion. Vascular compromise can often result from possible due to the reduced need for precise plate con- the stretching of vessels, such as with fetlock breakdown touring and bone to plate surface contact. Detailed infor- injuries, in which compromise of the digit is rapid unless mation on LCP application is provided in Chapter 10. hyperextension of the fetlock is corrected. Equine Fracture Repair, Second Edition. Edited by Alan J. Nixon. © 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc. 128 Part I Introduction to assist in fracture reduction are important factors in minimizing the soft tissue damage. Plate luting for improved plate–bone contact is a spe- cial compromise between more secure fixation and dis- turbed vascular supply. Use of bone cement as an interpositional material to improve plate–bone congruity has been shown to reduce screw loosening and implant failure by increasing the number of cycles to failure for plate application in horses.47 Several studies in small ruminants demonstrate that cortical density is main- tained beneath luted plates, although several other studies showed reduced vascularity and increased bone loss beneath the plates.47,53,56 Regardless, carefully applied bone cement enhances frictional contact between implants and Figure 9.1 High‐energy fracture of the radius in a weanling showing massive muscle bruising and stripping of the periosteal bone, and, provided that the bone cement is not allowed sleeve for 10 cm. to penetrate the fracture line, improves the chance of bone union before implant failure. More detailed information on plate luting is available later in this chapter. The repair principles for closed fractures include: Intraoperative care of exposed muscle, fascia, and neurovascular structures should include careful padded 1) Immediate preoperative stabilization to reduce retraction of tissues, use of soft Penrose drains to swelling, to support the fracture, to prevent bone ends retract vessels and nerves, and frequent moistening penetrating the skin or entrapping nerves and lacerat- of tissues with saline or lactated Ringer’s solution. ing vessels, and to alleviate stretching of vessels that Addition of antibiotics to the saline or lactated Ringer’s may promote vascular spasm or thrombosis. solution is also recommended. Air‐borne organisms 2) Carefully planned surgical approaches to minimize settle on exposed tissues in most surgical suites, despite the additional soft tissue damage. This becomes vital in precautions, and local lavage reduces bacterial num- high‐energy fractures in which muscles are frequently bers. Neomycin (4 mg ml−1) and potassium penicillin macerated and the periosteum is stripped from the (5 × 103 IU ml−1) are commonly added to the lavage. bone (Figure 9.1). Application through a spray bottle efficiently wets the 3) Stabilization techniques that minimally interrupt the surfaces and minimizes solution waste. soft tissue attachments and blood supply to the bones. In many complex and comminuted fractures, such as Open Fractures unstable fractures of the proximal phalanx, avoiding surgical dissection and internal fixation by the use of High‐energy fractures frequently result in comminuted external fixators has been recommended. In other configurations that have an increased tendency to pene- circumstances, comminuted long bone fractures such as trate the skin. Limited muscle coverage of the third met- those of the third metacarpus in foals may be better man- acarpus and metatarsus, and the medial aspects of the aged by casts with transfixation pins. For fractures of the tibia and radius, makes fractures of these bones more femur, tibia, and humerus, interlocking nails have been prone to become open. Open fractures are classified into developed that can be inserted without extensive expo- three types, as described in Chapter 4. sure of the entire bone. Similarly, LCP application requires Repair of all open fractures commences with appropri- less plate–bone contact, and thereby less plate contouring ate first aid and initiation of broad‐spectrum antimicro- and soft tissue removal for an exact plate–bone fit. Where bial therapy. The skin wound is cleaned of hair and debris plating or screw insertion is required, the preservation of and packed with antimicrobial gels. Small skin punctures soft tissue attachments is critical in the maintenance of may represent external wounds rather than penetrations blood supply. Muscle attachments should be minimally from the fracture ends. Gentle probing after the initial disturbed, and plates should be applied to the surface of cleansing may define a shallow subcutaneous wound the bone after the periosteum has been dissected laterally rather than a path to the fracture. It should be assumed only enough to allow full plate contact. Complete strip- that deep wounds are made by fracture ends until proven ping of the periosteum should be avoided. Reduction of otherwise at surgery. equine fractures can often be difficult and some associ- Most equine open fractures are type 1 (skin laceration ated trauma to adjacent structures is inevitable. The <1 cm) or type II (large skin laceration but little actual tis- surgeon’s experience and the methods or devices used sue loss). If repair is being considered, most horses will 9 Principles of Fracture Fixation 129 already have been commenced on a course of penicillin for exact plate–bone contact and makes luting obsolete. or a cephalosporin, and gentamicin or amikacin. For standard luting, the plates are loosened sequentially Supplementation with metronidazole for increased and polymethylmethacrylate (PMMA) applied beneath anaerobe coverage may also be warranted. Following each prior to retightening. Some benefit is derived if only induction of anesthesia, all hair is clipped for a wide mar- the heads of the screws are luted in the dynamic compres- gin, the wound edges and proposed incision site are sion plate (DCP) slots.71 Adding antibiotics to the PMMA shaved, and the skin is sterilely scrubbed. After the initial used for plate luting in the repair of open fractures is skin preparation, the skin opening and deeper wounds always indicated. All excess methacrylate is removed are draped and further explored using a separate set of before it polymerizes, and all fracture gaps must be care- instruments. All debris is removed by tissue debridement fully cleaned of residual bone cement. and rigorous pulsatile lavage of lactated Ringer’s solution Drain placement is