Composite Fixation of Comminuted Ilial Wing Fractures in Cats: Three Cases

Abstract

Clinical summary The surgical repair of comminuted ilial wing fractures (comprising a long oblique fracture with ventral multiple fragmentation) in three cats using composite internal fixation is reported. The technique comprised the use of pins, screws, wire and polymethylmethacrylate. All cases had an excellent outcome with uneventful bone healing. One case had a very mild reduction in pelvic canal diameter postoperatively. There was no evidence of implant loosening or migration in any cat on follow-up radiographs.

Practical relevance This technique provided a quick and highly adaptable means of stabilising this fracture configuration, as well as restoring pelvic symmetry, when limited buttressing support and bone stock were available cranial and ventral to the acetabulum. This method of fixation may have biomechanical advantages over lateral or dorsal plating techniques for this particular type of fracture configuration.

Introduction

Pelvic fractures are common injuries in cats, accounting for 22% of all feline fractures according to one study.¹ Of the pelvic fracture configurations described, a retrospective study of 103 cats documented 48% of cases to have ilial body fractures,² with transverse, long oblique, comminuted and short oblique configurations occurring in decreasing order of frequency.

The ilium functions as part of the ‘weight-bearing axis’ of the pelvis which comprises the sacroiliac (SI) joints, ilial bodies and acetabulae.³ Loss of structural integrity of this axis, secondary to fracture, may result in collapse of the pelvic canal as the caudal fragment of the ilial wing is most commonly displaced both medially and cranially.⁴ Instability of fracture fragments causes discomfort with the potential for rectal perforation,⁵ impingement on the lumbrosacral nerve trunk with resultant sciatic neuropraxia,⁶ and, as sequela, malunion, obstipation and megacolon.⁷ Thus, internal fixation of ilial body fractures is desirable to restore pelvic symmetry, acetabulofemoral alignment and congruity, and patient comfort.⁸

Multiple fixation techniques are described in the literature for the internal fixation of ilial body fractures, including bone plating,^9,10 lag screw fixation,^11,12 external skeletal fixation¹³ and pin fixation.¹⁴ Segmental ilial body fractures with concurrent acetabular fractures have also been stabilised with the use of precontoured reconstruction plates.¹⁵

Complications following internal fixation of ilial body fractures in cats have been described. A recent study reviewing lateral ilial body plating in a small series of cases highlighted complications such as postoperative loss of reduction of the fracture with medial divergence of the hemipelvis and resultant loss of pelvic canal diameter (100% of cases), and screw loosening (62% cases).¹⁶ Topographically the feline ilial body is thinner in its lateromedial plane compared with its canine counterpart,¹⁷ and there is thus reduced opportunity for screw purchase compared with dogs.¹⁶ However, even with the additional bone purchase in the dog, screw loosening with lateral plating of the ilial body has been reported at a rate of 26% for fractures and up to 57% for plating for triple pelvic osteotomy.¹⁸ With such a high incidence of screw loosening, locking screw implant systems may be advantageous in the lateral fixation of ilial body fractures. As yet, the effectiveness of such systems in reducing the incidence of ilial body screw loosening remains theoretical.

Composite fixation allows great versatility in both the size and orientation of constituent implants.

Composite fixation, comprising pins, screws, orthopaedic wire and polymethylmethacrylate (PMMA), has been described for the treatment of canine acetabular fractures.^19–21 This technique has been shown to provide comparable rigidity and more accurate articular reconstruction than conventional acetabular plating. Composite fixation for acetabular fractures allows great versatility in both the size and orientation of constituent implants. Conversely, the orientation of screws through either a conventional dynamic compression plate or acetabular plate is limited by both the position and distance apart of consecutive screw holes in the plate, which dictate the position of, and constrain, the angle of the screw. In addition, it is not possible to have screws of varying diameter within the same plate system in order to take advantage of varying bone stock around the fracture site.

Here, the author reports the surgical management, and clinical and radiographic outcomes, of three cats with a similar comminuted ilial body fracture configuration stabilised with a composite technique.

Materials and methods

Case records for three cats presenting to the University of Bristol Small Animal Hospital between February and March 2010 with similar comminuted ilial wing fracture configurations were reviewed. The fracture configuration in each case consisted of a cranioventral to caudodorsal long oblique ilial wing fracture extending above the acetabulum, with a variably comminuted cranioventral juxta-acetabular segment (Fig 1).

Information obtained from each case record included signalment, cause of pelvic fracture, preoperative clinical assessment, implants used, pre- and postoperative radiological assessment, postoperative lameness and function, and any complications that occurred. In all cases, cats were assessed at the referral hospital 6 weeks postoperatively and telephone follow-up was performed 8–9 months post-operatively. Pre- and postoperative radiographs were assessed for fracture configuration, pre- and postoperative pelvic canal diameter, and any evidence of implant loosening.

FIG 1

The fracture configuration in each case comprised a cranioventral to caudodorsal long oblique ilial wing fracture extending above the acetabulum, with a variably comminuted cranioventral juxta-acetabular segment

TABLE 1

Details for the three cats treated with composite internal fixation

Case	Signalment	Cause of trauma	Fracture(s)	Implants	Follow-up	Clinical outcome^∗	Sacral index postop	Sacral index 6 weeks postop	Radiographic outcome
1	DLH MN 2.5 years 4.25 kg	Found in owner's garden — presumed RTA	L SI luxation Fr R pubis Fr ischium Fr R ilial wing	2.4 mm SI screw 3 × 1.5 mm screws 6 × 2.0 mm screws 3 × 0.9 mm TBW PMMA	9 months	Excellent^○	1.053	1.016	No implant loosening or migration
2	DLH FN 3.5 years 4.46 kg	Found in owner's garden — presumed RTA	R SI luxation Fr L pubis Fr L ischium Fr L ilial wing (comm)	2.4 mm SI screw 3 × 0.9 mm K wires 4 × 1.5 mm screws 2 × 2.0 mm screws 1 × 0.9 mm TBW 2 × 0.6 mm TBW PMMA	8 months	Excellent. No residual lameness	0.85	0.896	No implant loosening or migration
3	DSH FN 7 years, 8 months 3.2 kg	Found under owner's car — presumed RTA	Fr L pubis Fr L ischium Fr L ilial wing (comm)	2 × 2.0 mm screws 6 × 1.5 mm screws 3 × 0.9 mm TBW PMMA	8 months	Excellent. No residual lameness	1.0769	1.021	No implant loosening or migration

DLH = domestic longhair, DSH = domestic shorthair, MN = male neuter, FN = female neuter, K = Kirschner, RTA = road traffic accident, L = left, R = right, Fr = fracture, SI = sacroiliac, comm = comminuted, TBW = tension band wire, PMMA = polymethylmethacrylate

^∗ Clinical outcome was assessed at 6-week follow-up consultation by the veterinary surgeon and via telephone follow-up with the owner at a minimum of 8 months postoperatively. An excellent outcome was characterised by a complete return to normal activity (eg, running, jumping and climbing with no perceived problems)

^○ Mild residual sensory sciatic deficits on the side of the SI luxation at 6-week revisit. Sciatic deficits resolved by 3 months postoperatively

Results

Clinical details for the three cats reported are presented in Table 1. All cases were referred following initial radiological assessment, provision of treatment for shock and the administration of analgesia by their referring veterinary surgeon. All cats were referred at a time they were deemed medically stable to travel. All cases had been in presumed road traffic accidents and presented to the referral hospital between 4 and 36 h following their initial presentation to the referring veterinary surgeon.

On clinical examination all cats were able to stand voluntarily. Cats 1 and 2 had concurrent contralateral SI luxation. In addition, cat 1 had sensory deficits in the right pelvic limb (ipsilateral to the SI luxation), consistent with sciatic neuropraxia, as assessed by loss of sensation to the dorsolateral pes skin dermatome and knuckling of the foot when attempting to ambulate. Orthogonal radiographs of the pelvis were obtained in all cats if they had not been performed prior to referral. All cats subsequently underwent internal fixation of their fractures, with surgery being performed in all cases within 6–36 h of referral to the hospital.

All cats were premedicated with a combination of either acepromazine (ACP, 2 mg/ml; Novartis Animal Health UK) and methadone (Physeptone 10 mg/ml; Martindale Pharmaceuticals), or midazolam (Hypnovel 5 mg/ml; Roche UK) and ketamine (Narketan 100 mg/ml; Vétoquinol UK). Meloxicam (Metacam injection 5 mg/ml; Boehringer Ingelheim) was administered perioperatively. Anaesthesia was induced with alfaxalone (Alfaxan 10 mg/ml; Vétoquinol UK) and maintained with isoflurane (Isoflurane Vet; Merial Animal Health), nitrous oxide and oxygen.

All cats were positioned in lateral recumbency for surgery. For cats 1 and 2, stabilisation of the concurrent SI luxation was performed before internal fixation of the contralateral ilial wing fracture. SI luxations were stabilised with a single 2.4 mm cortical screw applied in lag fashion via a gluteal roll down approach, as previously described.^22–24 Stabilisation of the ilial wing fracture was performed as described in the box on page 378.

Surgical stabilisation of the ileal wing fracture

The affected pelvic limb was clipped from dorsal midline and caudally to include the ipsilateral ischial tuberosity, to below the hock. The limb was quarter draped, the foot being isolated in a sterile foot bandage.

The surgical approach used to expose the ilial wing in all three cats was a ‘gluteal roll up’ procedure,²² which was subsequently, in all cases, combined with tenotomy of the insertion of the middle and deep gluteal tendons in order to facilitate exposure of the dorsal acetabulum for screw placement. Fracture haematoma was removed and Hohmann retractors and pointed reduction forceps used to lateralise the caudal ilial fragment(s). In all cases, Kern bone holding forces were applied to the ischial tuberosity to aid alignment of the caudal portion of the ilial wing.

Following alignment of the oblique ilial wing component of the fracture, 0.6 mm or 0.9 mm Kirschner (K) wires were variably placed from the ventral aspect of the ilial wing (caudal ilial fragment into the dorsal aspect of the cranial ilial segment). Additional K wires were used as appropriate to stablise any ventral comminuted fragments of sufficient size. Bone fragments too small to hold implants were left in situ and not removed.

Then 1.5 mm and 2.0 mm cortical screws were placed in the ilial wing either side of the fracture, including in bone immediately craniodorsal to the acetabulum. Additional screws were placed in ventral comminuted fragments of bone if the fragments were of sufficient size. Screws were applied with traditional AO/ASIF techniques, except that an additional 2 mm of screw length was added and screws were left 2 mm proud of the ilial wing cis cortex. Next 0.6 mm (with 1.5 mm screws) or 0.9 mm (with 2.0 mm screws) orthopaedic wire was placed in a ‘figure-of-eight’ configuration around adjacent screws and tightened by twisting to compress adjacent fracture fragments. Details of the implants applied in each case are listed in Table 1.

Following vacuum mixing, bone cement (Refobacin Bone Cement 40 g; Biomet Orthopaedics, Switzerland) was applied over the construct to a depth just sufficient to bury the head of each screw (Fig 2). Care was taken when applying cement caudo-dorsally above the acetabulum to protect the sciatic nerve. Cement was lavaged with chilled sterile saline while curing.

Tenotomies were repaired with continuous cruciate mattress sutures of 2 metric polydioxanone (PDSII; Ethicon UK). The incision between middle gluteal and tensor fasciae latae was closed with a simple continuous suture of 2 metric polydioxanone. Subcutaneous closure was performed with 2 metric poligle-caprone (Monocryl; Ethicon UK) and skin staples (Autosuture; Tyco Healthcare, Norwalk, Connecticut, USA).

FIG 2

Fracture fragments were stabilised with a combination of K wires, 1.5 mm and 2.0 mm cortical screws, and 0.6 mm and/or 0.9 mm orthopaedic wire placed in a figure-of-eight configuration around adjacent screws. Screws were left 2 mm proud of the cis cortical bone to facilitate placement of orthopaedic wire and to allow keying in of PMMA, which was then placed over the construct

Postoperatively, lateral and ventrodorsal radiographs were obtained for each case. Analgesia was instigated, comprising morphine or methadone for the first 12–24 h followed by buprenorphine every 8 h as required. A 5-day course of amoxicillin-clavulanic acid (Clavaseptin; Vétoquinol UK) and a 5-day course of meloxicam (Metacam oral suspension for cats; Boehringer Ingelheim) were prescribed. All cases were discharged 24–48 h postoperatively, at which time all animals were ambulatory.

Radiography was repeated after 6 weeks of cage rest (Figs 3–5). In all cases there was no evidence of implant breakage, loosening or migration. Following the repeat radiographs the cats underwent a progressive return to full activity.

The immediate postoperative and 6-week postoperative radiographs were assessed using a recently described technique to determine ‘sacral index'¹⁶ — defined as the ratio of the width of the sacrum at the cranial border to the width of the pelvic canal at the narrowest point, measured between the medial cortices of the acetabular bones. This was assessed to quantify any postoperative loss of reduction of the fracture with resultant pelvic canal narrowing. The normal value for cats has previously been defined as 0.97 ± 0.025.¹⁶

FIG 3

(a,b) Ventrodorsal and mediolateral radiographs of case 1 showing a right ilial wing comminuted fracture with concurrent ipsilateral pubic and ischial fracture and contralateral sacroiliac luxation. (c,d) Immediate postoperative radiographs demonstrate good realignment of the ilial wing and re-establishment of pelvic canal diameter and pelvic symmetry. (e,f) Radiographs taken 6 weeks postoperatively show maintenance of fracture reduction and pelvic canal diameter with no evidence of implant loosening or migration

FIG 4

(a,b) Ventrodorsal and mediolateral radiographs of case 2 showing a left ilial wing comminuted fracture with contralateral sacroiliac luxation and concurrent pubic and ischial fractures. (c,d) Immediate postoperative radiographs demonstrate adequate realignment of the ilial wing. (e,f) Radiographs taken 6 weeks postoperatively show maintenance of fracture reduction and pelvic canal diameter with no evidence of implant loosening or migration

Sacral indices for each case are presented in Table 1. A paired t-test performed on this data revealed no significant difference between immediate postoperative and 6-week postoperative sacral index (P = 0.67).

‘Sacral index’ was assessed on radiographs to quantify any postoperative loss of reduction of the fracture with resultant pelvic canal narrowing.

Discussion

This small case series describes the successful use of composite fixation in the management of comminuted feline ilial wing fractures. The technique was found to be highly adaptable to variations in individual fracture configuration and was quick and easy to perform in all three cases. This form of internal fixation is likely to be applicable to a wide range of ilial wing fracture configurations. However, it was deemed especially desirable for this particular configuration in that the long oblique ilial wing fracture with concurrent ventral juxta-acetabular comminution was not ideally suited to either lateral or dorsal plating.

FIG 5

(a,b) Ventrodorsal and mediolateral radiographs of case 3 showing a left ilial wing comminuted fracture and concurrent pubic and ischial fractures. (c,d) Immediate postoperative radiographs demonstrate adequate realignment of the ilial wing. (e,f) Radiographs taken 6 weeks postoperatively show maintenance of fracture reduction and pelvic canal diameter with no evidence of implant loosening or migration

Lateral plating was considered inferior due to the difficulty in contouring a single plate to engage the dorsocranial and ventrocaudal ilial wing and dorsal acetabular bone. In addition, conventional lateral plating of feline ilial wing fractures has been associated with a high rate (62%)¹⁶ of screw loosening, due to a thin feline ilial body limiting screw purchase. The risk of screw loosening appears to be negated with the composite technique described here. The use of PMMA as an adjunctive fixative in canine acetabular fractures has been shown to impart improved construct stiffness and yield load by the neutralisation of rotational force.²¹ PMMA used in this way, moulded to the ilial wing, acts as a ‘connecting bar’ attached to the bone via the screws, limiting bending and torsion of both bone and implants. In addition, the overlying PMMA functions as a locking mechanism, preventing the screws from backing out of the ilial bone. This is evidenced by assessment of the radiographs in each of the three cases which revealed no screw loosening or implant migration.

Dorsal plating was considered undesirable as plating the compression surface of the ilium with a concurrent ventral cortical deficit inherent with comminution would not provide optimum stability to the ventral portion of the ilial wing. In addition, screws placed through a dorsally applied plate have limited ability to competently engage comminuted ventral ilial fragments in an optimum position and orientation. Likewise, placement of a ventral plate and/or ventral screws in isolation¹¹ was not possible due to comminution in this area and, thus, insufficient bone stock in which to place the implants.

This is a quick, highly adaptable and apparently biomechanically rigid means of restoring pelvic symmetry and functional stability to the feline ilial wing.

Extreme care was required during placement and curing of the PMMA used in these cases to protect the sciatic nerve from thermal damage. This was achievied by careful retraction of the nerve dorsocaudally with Langenbeck retractors and application of the PMMA in its ‘dough’ phase, allowing precise control over its spread. Cement was also lavaged with saline during curing to dissipate heat.

Neither implant loosening nor sepsis were evident in this case series during the 8–9 month period of evaluation. However, should such complications be observed in the long term, removal of the fixation would be indicated. The author would predict this to be unlikely as these complications have not been cited when composite techniques were employed in the stabilisation of acetabular fractures in both the dog and cat.^19,25

Specific conclusions cannot be drawn due to limited case numbers. Comminuted feline ilial wing fractures are comparatively rare, with a 10-year study recording only a 2.7% incidence.² However, in cases where comminution is present, the technique described is quick, highly adaptable and appears to be a biomechanically rigid fixation by which to restore both pelvic symmetry and functional stability to the feline ilial wing.

References

Hill

FWG

. A survey of bone fractures in the cat. J Small Anim Pract 1997; 18: 457–63

Bookbinder

Flanders

. Characteristics of pelvic fracture in the cat. Vet Comp Orthop Traumatol 1992; 5: 122–27

Denny

Butterworth

, (eds). The hip. In: A guide to canine and feline orthopaedic surgery. 4th edn. Oxford: Blackwell Science, 2001: 455–94.

DeCamp

. Fractures of the ilium. In: Johnson

Houlton

JEF

Vannini

(eds). AO principles of fracture management in the dog and cat. Stuttgart, Germany: Thieme AO publishing, 2005: 171.

Lewis

Beale

Pechman

Ellison

. Rectal perforations associated with pelvic fractures and sacroiliac fracture-separations in four dogs. J Am Anim Hosp Assoc 1992; 28: 175–82

DeCamp

. Principles of pelvic fracture management. Semin Vet Med Surg 1992; 7: 63–70

Colopy-Poulsen

Danova

Hardie

Muir

. Managing feline obstipation secondary to pelvic fracture. Compend Contin Educ Pract Vet 2005; 27: 662–68

Lanz

. Lumbrosacral and pelvic injuries. Vet Clin North Am Small Anim Pract 2002; 32: 949–62

Henry

. A method of bone plating for repairing ilial and acetabular fractures. Compend Contin Educ Pract Vet 1985; 7: 924–38

10.

Brinker

Piermattei

Flo

. Fractures of the pelvis. In: Handbook of small animal orthopaedics and fracture repair. 4th edn. Philadelphia: WB Saunders, 2006: 443–60.

11.

Vangundy

Hulse

Nelson

Boothe

. Mechanical evaluation of two canine iliac fracture fixation systems. Vet Surgery 1988; 17: 321–27

12.

Hulse

Vangundy

Johnson

Waldron

. Compression screw stabilisation of oblique ilial fractures in the dog. Vet Comp Orthop Traumatol 1989; 4: 162–67

13.

Fitzpatrick

Lewis

Cross

. A biomechanical comparison of external skeletal fixation and plating for the stabilization of ilial osteotomies in dogs. Vet Comp Orthop Traumatol 2008; 21: 349–57

14.

Bowlt

Shales

. Repair of a transverse ilial fracture in a cat using an intramedullary pin. Vet Comp Orthop Traumatol 2010; 23: 186–89

15.

Ost

Kaderly

. Use of reconstruction plates for the repair of segmental ilial fractures involving acetabular comminution in four dogs. Vet Surgery 1986; 15: 259–64

16.

Hamilton

Evans

Langley-Hobbs

. Feline ilial fractures: assessment of screw loosening and pelvic canal narrowing after lateral plating. Vet Surgery 2009; 38: 326–33

17.

Dyce

Sack

Wensing

CJC

. The locomotor apparatus. In: Textbook of veterinary anatomy. 2nd edn. Philadelphia: Saunders, 1996: 44.

18.

Bogoni

Rovesti

. Early detection and treatment of screw loosening in triple pelvic osteotomy. Vet Surgery 2005; 34: 190–95

19.

Lewis

Strubbs

Neuwirth

. Results of screw/wire/polymethylmethacrylate composite fixation for acetabular fracture repair in 14 dogs. Vet Surgery 1977; 26: 223–34

20.

Stubbs

Lewis

Miller

. A biomechanical evaluation and assessment of the accuracy of reduction of two methods of acetabular osteotomy fixation in dogs. Vet Surgery 1998; 27: 429–37

21.

Lanz

Lewis

Madison

Miller

Martin

. A bio-mechanical comparison of screw and wire fixation with and without polymethylmethacrylate re-enforcement for acetabular osteotomy stabilization in dogs. Vet Surgery 1999; 28: 161–70

22.

Piermattei

. Approach to the ilium through a lateral incision. In: An atlas of surgical approaches to the bones and joints of the dog and cat. 3rd edn. Philadelphia: WB Saunders, 1993: 224–29.

23.

Burger

Forterre

Brunnberg

. Surgical anatomy of the feline sacroiliac joint for lag screw fixation of sacroiliac fracture-luxation. Vet Comp Orthop Traumatol 2004; 17: 146–51

24.

Shales

Moores

Kulendra

White

Toscano

Langley-Hobbs

. Stabilization of sacroiliac luxation in 40 cats using screws inserted in lag fashion. Vet Surgery 2010; 39: 696–700

25.

Langley-Hobbs

Sissener

Shales

. Tension band stabilisation of acetabular physeal fractures in four kittens. J Feline Med Surg 2007; 9: 117–87