Canine-composite Fixation For Ace Tabular Fractures In Dogs

Vol. 22, No. 9 September 2000

CE

Refereed Peer Review

FOCAL POINT ★Screw/wire/polymethylmethacrylate (PMMA) composite fixation has proven to be a successful technique for stabilizing acetabular fractures in dogs.

KEY FACTS ■ Screw/wire/PMMA composite fixation provides comparable stability and yields superior anatomic reduction compared with veterinary acetabular plates. ■ Strict asepsis must be maintained when using composite fixation. ■ Clinical use of screw/wire/ PMMA composite fixation has been associated with few complications and has enabled acetabular fractures to heal by what appears to be primary bone union. ■ Interfragmentary Kirschner wires can help maintain anatomic reduction of fracture segments and enhance the stability of repair. ■ PMMA can improve the biomechanic stability of the fixation in part by neutralizing rotational forces.

Composite Fixation for Acetabular Fractures in Dogs University of Florida

Krista B. Halling, DVM Alan R. Cross, DVM Otto I. Lanz, DVM

Daniel D. Lewis, DVM Daniel P. Beaver, DVM W. Preston Stubbs, DVM

ABSTRACT: The optimal clinical outcome of acetabular fractures depends on precise anatomic reduction and rigid internal fixation. Although bone plating has traditionally been the most commonly used method of stabilizing acetabular fractures in dogs, difficulty contouring the plate and maintaining adequate fracture reduction has prompted the development of alternative techniques. A composite fixation technique that uses screws, Kirschner wires, stainlesssteel orthopedic wire, and polymethylmethacrylate (PMMA) has been used to stabilize acetabular fractures. By achieving accurate anatomic reduction and sufficient biomechanic stability, screw/wire/PMMA composite fixation has proven successful in repairing acetabular fractures in dogs. This paper describes the application of and clinical results associated with this technique. The results of our experimental evaluation of bone plates versus composite fixation, composite fixation with and without PMMA, and composite fixation with and without ancillary Kirschner wires are also discussed.

A

cetabular fractures are common in dogs.1–10 For optimal clinical results, most veterinary surgeons advocate open reduction and internal fixation of acetabular fractures unless the complexity of the fracture precludes anatomic reconstruction of the acetabulum.1–10 Anatomic reduction and rigid internal fixation must be obtained when stabilizing acetabular fractures to promote primary bone healing and mitigate the development of degenerative joint disease (DJD).1,2,4,7,10–17 Although numerous methods of internal fixation have been described for stabilizing acetabular fractures in dogs, bone plating is most commonly used.1–9,11 Several types of plates, including small fragment plates, standard and mini dynamic compression plates, reconstruction plates, and veterinary acetabular plates, have been used to stabilize acetabular fractures.1,2,12–14,18–24 Veterinary acetabular plates are curvilinear, stainless-steel plates designed specifically for stabilizing acetabular fractures in dogs.1,2 Although its curvilinear shape facilitates molding the implant to conform to the dorsal surface of the acetabulum, precise contouring of these plates can be challenging.20,25–27 Plate ap-

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coxofemoral joint (the gemelli and internal obturator muscles) can also be incised and reflected caudodorsally to expose fractures involving the caudal portion of the acetabulum. The sciatic nerve should be identified and protected throughout the procedure. The coxofemoral joint capsule should be incised to allow assessment of the reFigure 1A Figure 1B duction. The fracture surfaces should be debrided. A separate approach can then be made to the tuber ischii6 and bone reduction forceps can be applied to the ischium to manipulate the caudal acetabular segment and facilitate reduction27 (Figure 2A). When anatomic reduction is achieved, a Kirschner wire (1.0-mm diameter for small dogs, 1.6-mm diameter for Figure 1C Figure 1D large dogs) should be placed Figure 1—(A) Ventrodorsal radiograph of a central acetabular fracture in a 3-year-old Afghan hound. Ventrodorsal (B) and lateral (C) radiographs immediately following fracture stabiliza- across the fracture. If the tion with composite fixation. (D) Ventrodorsal radiograph obtained 3 months after surgical re- fracture involves the cranial or central aspect of the acpair; note that the fracture has nearly achieved radiographic union. etabulum, the Kirschner wire can be inserted at or near the plication is particularly difficult when fractures involve bony protuberance of the origin of the rectus femoris the caudal aspect of the acetabulum where the adjoinmuscle in a craniolateral-to-caudomedial direction. The ing ischial surface has an irregular conformation and Kirschner wire generally must be inserted through the surgical exposure is limited6,20,24,27; anatomic reduction regional musculature in order to be placed at the appromay not be achieved or can be lost as the screws are priate angle to traverse the fracture and avoid penetratightened. tion of the articular cartilage of the coxofemoral joint. An alternative method for stabilizing acetabular fracA second Kirschner wire of equal length should be used tures is screw/wire/polymethylmethacrylate (PMMA) to judge penetration of the fracture segments and to composite fixation. In 1977, Renegar and Griffiths28 reavoid having the wire protrude into the pelvic canal. In ported the use of screws, an encircling 20- or 22-gauge some fractures, multiple wires may be required to instainless-steel orthopedic wire, and PMMA bone cecrease stability and maintain anatomic reduction.30 Large reduction forceps can be placed cranial and caument to stabilize acetabular fractures. In 1992, we bedal to the acetabulum in some fractures to maintain regan using a modification of this technique (Figure 1). duction before, during, and after Kirschner wire placeThis paper describes the screw/wire/PMMA composite ment.30 fixation and reviews our clinical experiences and experiA bone screw is placed in both the cranial and caudal mental investigations using this technique to repair acacetabular segments, midway between the dorsolateral etabular fractures. margin of the acetabular rim and the dorsomedial asPROCEDURE pect of the pelvis. The screws should be positioned apA dorsal approach to the acetabulum is done via an osproximately 5 to 7 mm cranial and caudal to the fracteotomy of the greater trochanter of the femur.29 The tenture, respectively. A line drawn between the two screws dons of insertion of the external rotator muscles of the should intersect the fracture at a right angle. Screw diACETABULUM ■ SCIATIC NERVE ■ ARTICULAR CARTILAGE ■ BONE SCREW

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of the drill hole by approximately 4 mm. The screws should then be placed such that the screw heads do not contact the cis-cortex, thereby leaving the screw shank and possibly one or two of the threads exposed (Figure 2B). Stainless-steel orthopedic wire (20 gauge for small dogs, 18 gauge for larger dogs) should then be placed Figure 2A Figure 2B around the screws in a figure-of-eight pattern. The two free ends of the wire can be grasped with a wire twister. While applying tension to the instrument, the wire can be tightened by twisting the two strands into a braid, thereby compressing the fracture (Figure 2C). In fractures that are difficult to anatomically reduce, tightening of the figure-of-eight wire can be used Figure 2C Figure 2D to facilitate fracture reduction.30 The braided strands of wire should be cut, leaving at least three twists. The exposed implants should then be covered with medical-grade PMMA. We routinely add 1 g of sodium cefazolin to 20 g of PMMA powder and mix the PMMA under vacuum (Figure 2D). Strict asepsis must be maintained throughout the proceFigure 2E Figure 2F Figure 2—(A) Acetabular osteotomy model in a canine cadaver hemipelvis, simulating a midac- dure to prevent contamina26 etabular fracture. (B) A bone screw was placed in each of the cranial and caudal segments, leav- tion of the PMMA. Rather ing one or two threads exposed to facilitate placement of the wire and polymethylmethacrylate than applying the entire (PMMA). (C) Orthopedic wire was applied in a figure-of-eight fashion. Interfragmentary com- mass of bone cement at pression of the fracture fragments should occur as the wire is twisted. The wire was cut, leaving once, the PMMA should be three twists. (D) A fume-evacuating bone cement mixer (center) and two brands of PMMA packed in small aliquots unbone cement (left and right). (E) Care should be taken to thoroughly pack the PMMA around der and around the implants, the screws and wire to ensure adequate incorporation of the implants in the cement. (F) The thereby increasing the interrepaired osteotomy model, showing anatomic reduction and good coverage of the screw heads digitation of the PMMA by the PMMA. with the implants (Figures 2E and 2F). The PMMA ameter can vary from 2.0 mm in very small toy breeds should completely cover the implants while avoiding an to 4.5 mm in giant breeds, but typically 2.7-mm screws excessive amount that could interfere with the coxare used in smaller dogs and 3.5-mm screws in larger ofemoral joint or impinge on the sciatic nerve. Dependdogs. Screw length should exceed the measured depth ing on the dog’s size, we have found that a total PMMA ORTHOPEDIC WIRE ■ FIGURE-OF-EIGHT PATTERN ■ BONE CEMENT

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volume of 2 to 4 ml is generally sufficient. Because polymerization of PMMA is an exothermic reaction, the adjacent soft tissues—especially the sciatic nerve—should not be in direct contact with the PMMA when this reaction occurs. When the PMMA has polymerized, the joint capsule should be closed and the greater trochanter can be Figure 3A Figure 3B reattached using a pin-and- Figure 3—Ventrodorsal (A) and lateral (B) radiographs of a 4-year-old mixed breed dog 18 tension band technique, lag months after surgery to stabilize a left acetabular fracture. Note the mild degenerative joint disscrews, or multiple divergent ease and resorption of the femoral neck caused by the fracture and its repair. Kirschner wires.29 Following surgery, the dog the protruding wires because of their proximity to the should be confined for 4 to 8 weeks with exercise rerectum and urethra. All fractures obtained union by 3 stricted to short leash walks for the purpose of urinamonths and appeared to heal by primary bone union. tion and defecation. Serial radiographs should be obProspective long-term clinical and radiographic evaltained monthly after surgery to assess healing and uations (mean ± SD, 347 ± 261 days; median, 380 manage postoperative care. Normal activity level may days) were satisfactory in 13 of the 14 dogs.30 Ten dogs be resumed gradually after the fracture has achieved rahad no apparent lameness and three had subtle weightdiographic union. bearing lameness of the affected limb. The remaining CLINICAL RESULTS dog had a persistent non–weight-bearing lameness for The results of acetabular fractures repaired using comseveral weeks after surgery. This animal had an ipsilatposite fixation were evaluated in 14 dogs.30 Ages of the eral sacral fracture that was not repaired, resulting in dogs ranged from 4 to 95 months (mean ± standard demarked dorsomedial rotation of the repaired hemipelvis viation [SD], 34 ± 25 months; median, 25 months) and luxation of the affected coxofemoral joint eventualand body weights ranged from 8 to 39 kg (mean ± SD, ly requiring femoral head and neck excision. 25 ± 6 kg; median, 27 kg). Medical records and radioFollow-up radiographs (mean ± SD, 347 ± 260 days; graphs were retrospectively evaluated to determine fracmedian, 380 days) revealed no DJD in the affected coxoture location, presence of preexisting DJD, accuracy of femoral joint in 3 dogs, mild disease in 10 dogs, and fracture reduction, and surgical complications. Prospecmoderate development of disease in 1 dog30 (Figure 3). The dog with moderate DJD also had a concurrent untive evaluation of long-term results included subjective treated sacral fracture and resultant mild dorsomedial assessment of lameness, elicitation of pain or crepitus on rotation of the hemipelvis. Dorsomedial rotation of the manipulation of the coxofemoral joint, measurements of acetabulum has been used experimentally as a means of pelvic limb circumference, goniometric measurements producing coxofemoral DJD.31 Reduction and stabiof coxofemoral joint range of motion, radiographic evallization of the concurrent ipsilateral sacral fractures may uation of fracture healing, implant complications, and have resulted in a more favorable clinical outcome in the development of DJD. this dog as well as in the dog that developed a coxoCongruency of the lunate articular surface of the acfemoral joint luxation after surgery. etabulum was reestablished in all of the fractures; fracAlthough decreased limb circumference has been ture reduction was considered anatomic in 13 dogs.30 Craniolateral displacement of the caudal acetabular segnoted after open reduction and internal fixation of acment attributed to over-zealous tightening of the reducetabular fractures,1 limb circumference in dogs stabilized with composite fixation did not differ significanttion forceps and prohibited the reduction of one fracly during final evaluation. A pain response could be ture from being considered anatomic.30 There were few complications following the surelicited during coxofemoral joint manipulation in half geries.30 In four dogs, interfragmentary Kirschner wires of the dogs that had acetabular fractures repaired with protruded into the pelvic canal. Two of these dogs uncomposite fixation; this finding is consistent with other derwent a second surgery to replace or retract and cut reports of dogs undergoing acetabular fracture stabilizaEXOTHERMIC REACTION ■ RADIOGRAPHS ■ BONE UNION

HEMIPELVES ■ ILIUM ■ ISCHIUM ■ THERMAL INJURY

376.5± 99.2 336.2 ± 85.3 significant differences between stabilization techniques. significant differences between intact hemipelves and stabilization techniques. PMMA = polymethylmethacrylate; NR = not reported bDenotes

aDenotes

1100.5 ± 331.6b Maximum load sustained (Newton)

2796 ± 152.9b

1192 ± 202.7b

200.8 ± 32.2 209.7 ± 28.2 NR NR Yield point (Newton)

NR

443.8 ± 180.3 457.8 ± 178.0 NR NR NR Distraction stiffness (Newton/mm)

77.2 ± 17.8 110 ± 51.3b Bending stiffness (Newton/mm)

267.5 ± 61.9b

136.3 ± 76.5b

1.06 ± 0.45a 0.21 ± 0.25a 0.48 ± 0.29a NR Reduction (mm)

Parameter Evaluated

Intact Hemipelves

Stubbs and colleagues32 Veterinary Screw/Wire/PMMA Acetabular Plates Composite Fixation

COMPOSITE FIXATION WITH AND WITHOUT POLYMETHYLMETHACRYLATE Polymethylmethacrylate, if contaminated intraoperatively, can serve as a nidus of infection,26 and we have experienced this complication in one dog. Thus, omitting PMMA as a component of composite fixation would reduce the risk of implant infection. Additionally, the possibility of thermal injury to the sciatic nerve would be eliminated and abduction of the coxofemoral joint may be improved. Stabilization of acetabular fractures using screws and a figure-of-eight wire without PMMA augmentation has been described4,18,25; however, we have experienced failure of fixation and loss of reduction when PMMA was omitted (Figure 4). These experiences prompted us to compare the biomechanic characteristics of interfragmentary Kirschner wire, screw, and figure-of-eight wire fixation with and without PMMA augmentation for stabilization of acetabular osteotomies in canine cadaver pelves.34 Stiffness, yield point, and maximum load sustained were significantly greater for hemipelves stabilized with composite fixation. Failure of hemipelves stabilized with composite fixation occurred primarily

TABLE I Results of Composite Fixation Studies

COMPOSITE FIXATION VERSUS BONE PLATING Two studies32,33 using pelves obtained from canine cadavers compared veterinary acetabular plates and composite fixation for the stabilization of uniform central acetabular osteotomies. In one study,32 hemipelves were placed in an inverted position and tested in cantilever bending. The wing of the ilium was embedded in PMMA while the ischium rested unconstrained on an aluminum block. In the other study,33 the hemipelves were placed in an inverted position unconstrained on aluminum rollers and loaded in a three-point bending fashion. Both studies concluded that the osteotomy reductions, as evaluated subjectively by visual assessment and objectively from measurements made from casts of the acetabulum, were superior in the hemipelves stabilized with composite fixation. Although neither repair technique approached the strength or stiffness of intact hemipelves, strength and stiffness did not differ significantly between hemipelves stabilized with composite fixation and the acetabular plate (Table I).32,33

Lanz and colleagues33 Veterinary Screw/Wire/PMMA Acetabular Plates Composite Fixation

tion using other methods of fixation.1 Pain response was usually mild and only elicited on full abduction or extension. Decreased abduction of the coxofemoral joint was noted in dogs that had acetabular fractures repaired with composite fixation. This observation, which has not been previously reported, was ascribed to the intertrochanteric ridge of the femoral neck contacting the mass of PMMA.30

74.6 ± 9.1

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0.23 ± 0.05a

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by ventrolateral bending of the cranial and caudal pelvic segments at the osteotomy site. Failure of hemipelves stabilized without PMMA occurred by ventrolateral bending of the cranial and caudal pelvic segments at the osteotomy site with pronounced concurrent ventrolateral rotation of the cranial pelvic segment. PMMA improved the mechanical characteristics of the acetabular fracture fixation, partly by neutralizing rotational forces. The results of this study 34 support the use of PMMA as a component of composite fixation when repairing acetabular fractures.

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Figure 4A

Figure 4B

Figure 4—(A) Lateral pelvic radiograph taken immediately after surgery to stabilize an acetabular

fracture. Polymethylmethacrylate was not used in this 5-year-old Yorkshire terrier because of a concurrent rectal perforation and concern for enteric bacterial contamination of the bone cement. (B) Lateral radiograph 3 weeks after surgery. Note the loss of reduction and failure of fixation.

CONTRIBUTION OF INTERFRAGMENTARY KIRSCHNER WIRES Although successful healing has been reported in dogs with acetabular fractures stabilized using composite fixation without an interfragmentary Kirschner wire,28,30 we believe that the interfragmentary Kirschner wire is also an integral component of composite fixation, facilitating initial and long-term anatomic reduction. In our experience, the number of interfragmentary Figure 5—Ventrodorsal radiographs of the four different interfragmentary Kirschner-wire configurations (clockwise from top left: no wires, one wire, multiple divergent wires, two crossing wires used ranged from zero wires) used in composite fixation of acetabular fractures in dogs. to three, with highly variable wire orientation30 (Figunaffected by Kirschner-wire placement. Before applying ure 5). However, the correct placement of one, and parthe PMMA, the stability of the hemipelves was subjecticularly multiple, interfragmentary Kirschner wires can tively assessed by manual manipulation. This simulated be technically challenging. maintaining fracture reduction before application and Another study35 using our central acetabular osteotomy model evaluated the contribution of interfragmentary polymerization of the PMMA. All hemipelves were stable Kirschner wire(s) on anatomic reduction and mechanical when stressed in a dorsal-to-ventral direction because in properties of composite fixation. Acetabular osteotomies this orientation of loading, the screws and figure-of-eight were repaired using the screw/wire/PMMA composite fixwire function as a tension band. When manually stressed ation with or without one of three Kirschner-wire configin rotation and ventral-to-dorsal, medial-to-lateral, laterurations in 32 canine hemipelves (Figure 6). Anatomic real-to-medial bending plane, hemipelves secured with one duction, assessed both subjectively and objectively, was or two Kirschner wires were significantly more stable than ROTATIONAL FORCES ■ WIRE ORIENTATION ■ ANATOMIC REDUCTION

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tained with the addition of one and then two Kirschner wires were observed. These differences, however, were not significant, with the exception that hemipelves repaired with two Kirschner wires had significantly greater yield loads than did hemipelves repaired without Kirschner wires (Figure 7). The results of this study support the use of at least one interfragmentary Kirschner wire; however, fracture configuration and location may dictate the number and pattern of interfragmentary Kirschner wires used in stabilizing a particular fracture.35

CONCLUSION Acetabular fractures reFigure 6—Photographs and respective radiographs (insets) of osteotomized hemipelves repaired using screw/wire/polymethylmethacrylate composite fixation with four different interfragmen- main a challenge for veteritary Kirschner wire configurations: (A) no wire, (B) one wire, (C) two parallel wires, (D) two nary surgeons. To achieve crossing wires.35 (From Beaver DP, Lewis DD, Lanz OI, et al: Subjective and objective evalua- primary bone healing and tion of four interfragmentary Kirschner wire configurations as a component of screw/wire/poly- mitigate the development of methylmethacrylate composite fixation for the stabilization of acetabular fractures in dogs. DJD, treatment objectives JAAHA 36:456–462, 2000; reprinted with permission) include accurate anatomic reduction and rigid internal fixation. This requires fixation devices that can be applied with minimal difficulty, facilitate and maintain fracture reduction, and impart sufficient strength and mechanical stability to the repair. Studies have demonstrated that screw/wire/ PMMA composite fixation is a successful repair technique for acetabular fractures and is associated with few complications. ACKNOWLEDGMENT

Figure 7—The relative biomechanic differences among four interfragmentary Kirschner-wire configurations for augmentation of screw/wire/polymethylmethacrylate composite fixation of hemipelvic acetabular osteotomies: gray bar, no Kirschner wires; orange bar, one Kirschner wire; white bar, multiple divergent wires; blue bar, two crossing Kirschner wires.35

were those without a Kirschner wire. Biomechanic testing was performed after PMMA application. Incremental increases in stiffness, yield load, and maximum load sus-

The authors thank Debby Sundstrom, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, for her technical assistance with this manuscript.

REFERENCES 1. Anson LW, DeYoung DJ, Richardson DC, et al: Clinical evaluation of canine acetabular fractures stabilized with an acetabular plate. Vet Surg 17:200–225, 1988. 2. Braden TD, Prieutt WD: New plate for acetabular fractures: Technique of application and long-term follow-up evaluation. JAVMA 188:1183–1186, 1986. 3. Brinker WO, Piermattei DL, Flo GL: Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadel-

WIRE CONFIGURATION ■ GREATER YIELD LOAD ■ PRIMARY BONE HEALING

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phia, WB Saunders Co, 1990, pp 83–95. 4. Hulton JEF, Dyce J: Management of pelvic fractures in the dog and cat. Waltham Focus 4:17–25, 1994. 5. Brinker WO, Hohn RB, Prieur WD (eds): Manual of Internal Fixation in Small Animals. New York, Springer-Verlag, 1984, pp 32–62. 6. Olmstead ML: Pelvic fractures, in Olmstead ML (ed): Small Animal Orthopedics. St. Louis, Mosby, 1994, pp 219–228. 7. DeCamp CE: Principles of pelvic fracture management. Semin Vet Med Surg 7:63–70, 1992. 8. Betts CW: Pelvic fractures, in Slattter DH (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1769–1786. 9. Newton CD: Fractures of the pelvis, in Newton CD, Nunamaker DM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, Lippincott, 1985, pp 393–402. 10. Wendelberg KL: Disorders of the hip joint in the canine athlete, in Bloomberg MS, Dee JF, Taylor RA (eds): Canine Sports Medicine and Surgery. Philadelphia, WB Saunders, 1998, pp 174–195. 11. Henry WB: A method of bone plating for repairing iliac and acetabular fractures. Compend Contin Educ Pract Vet 7(11): 924–939, 1985. 12. Hulse DA, Root CR: Management of acetabular fractures: Long term evaluation. Compend Contin Educ Pract Vet 11(3):189–199, 1980. 13. Braden TD, Prieur WD: New plate for acetabular fractures: Technique of application and long-term follow-up evaluation. JAVMA 188:1183–1186, 1986. 14. Dyce J, Houlton JEF: Use of reconstruction plates for repair of acetabular fractures in 16 dogs. J Small Anim Pract 34: 547–553, 1993. 15. Hulse DA: Pelvic fractures: Conservative and surgical management. Vet Med 2:267–278, 1990. 16. Boudrieau RS, Kleine LJ: Nonsurgically managed caudal acetabular fractures in dogs: 15 cases (1979–1984). JAVMA 193:701–705, 1988. 17. Pennal GF, Davidson J, Garside H, et al: Results of treatment of acetabular fractures. Clin Orthop Rel Res 151:115– 123, 1980. 18. Wheaton LG, Hohn RB, Harrison JW: Surgical treatment of acetabular fractures in the dog. JAVMA 162:385–392, 1973. 19. Robins GM, Dingwall JS, Sumner-Smith G: The plating of pelvic fractures in the dog. Vet Rec 93:550–554, 1973. 20. Ost PC, Kaderly RE: Use of reconstruction plates for the repair of segmental ilial fractures involving acetabular comminution in four dogs. Vet Surg 15:259–264, 1986. 21. Denny HR: Pelvic fractures in the dog: A review of 123 cases. J Small Anim Pract 19:151–166, 1979. 22. Roush JK, Manley PA: Mini plate failure after repair of ilial and acetabular fractures in nine small dogs and one cat. JAAHA 28:112–118, 1992. 23. Hinko PJ: The use of a precontoured pelvic bone plate in the treatment of comminuted pelvic fractures: A preliminary report. JAAHA 14:229–232, 1978. 24. Chalman JA, Layton CE: Osteotomy of the ischial tuberosity to provide surgical access to the ischium and caudal acetabulum in the dog. JAAHA 26:505–514, 1990. 25. Herron MR: Screw-wire fixation of acetabular fractures. Canine Pract 2:43–50, 1977. 26. Anderson GI: Polymethylmethacrylate: A review of the implications and complications of its use in orthopedic surgery. Vet Comp Orthop Traumatol 2:74–79, 1988.

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27. Eaton-Wells RD, Matis U, Robins GM, et al: Pelvic fractures, in Whittick WG (ed): Canine, ed 2. Philadelphia, Lea & Febiger, 1990, pp 387–417. 28. Renegar WR, Griffiths RC: The use of methyl methacrylate bone cement in the repair of acetabular fractures. JAAHA 13:582–588, 1977. 29. Piermattei DL: An Atlas of Surgical Approaches to the Bones and Joints of the Dog and Cat, ed 3. Philadelphia, WB Saunders Co, 1993, pp 240–244. 30. Lewis DD, Stubbs WP, Neuwirth L, et al: Results of screw/ wire/polymethylmethacrylate composite fixation for acetabular fracture repair in 14 dogs. Vet Surg 26(3):223–234, 1997. 31. Inerot S, Heinegaard D, Olsson SE, et al: Proteoglycan alterations during developing experimental osteoarthritis in a novel hip joint model. J Orthop Res 9:658–673, 1991. 32. Stubbs WP, Lewis DD, Miller GJ, et al: A biomechanical evaluation and assessment of reduction for two methods of acetabular osteotomy fixation in dogs. Vet Surg 27:429–437, 1998. 33. Lanz OI, Lewis DD, Madison JB, Blaeser LL: A biomechanical comparison of composite fixation and veterinary acetabular plates for stabilization of acetabular osteotomies in dogs loaded in three-point bending fashion. Vet Comp Orthop Traumatol 11:152–157, 1998. 34. Lanz OI, Lewis DD, Madison JB, et al: A biomechanical comparison of screw and wire fixation with and without

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polymethylmethacrylate re-enforcement for acetabular osteotomy stabilization in dogs. Vet Surg 28:161–170, 1999. 35. Beaver DP, Lewis DD, Lanz OI, et al: Subjective and objective evaluation of four interfragmentary Kirschner wire configurations as a component of screw/wire/polymethylmethacrylate composite fixation for the stabilization of acetabular fractures in dogs. JAAHA, accepted for publication, 2000.

About the Authors Drs. Halling, Lewis, and Cross are affiliated with the Department of Small Animal Clinical Sciences and the Center for Veterinary Sports Medicine, College of Veterinary Medicine, University of Florida, Gainesville. Dr. Lanz is affiliated with the Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Technical Institute, Blacksburg. Dr. Beaver is associated with Affiliated Veterinary Specialists, Orange Park, Florida. Dr. Stubbs is affiliated with the Alameda East Veterinary Hospital, Denver, Colorado. Drs. Lewis, Cross, Lanz, and Stubbs are Diplomates of the American College of Veterinary Surgeons.