Reluxation Rates Following Different Techniques for Open Stabilisation of Feline Coxofemoral Dislocations

a Knowledge Summary by

Elly Russell MA, VetMB, Cert AVP, MRCVS ^1*

¹The Minster Veterinary Ptactice, Salisbury Road, York, YO26 4YN
^*Corresponding Author (ellythevet@hotmail.com)

Clinical scenario

A 4 kg 3-year-old male neutered domestic short-haired cat has been presented to you following a road traffic accident. After initial stabilisation, radiographs have identified a craniodorsal luxation of the right coxofemoral joint. Closed reduction was performed but the joint could not be maintained in reduction. No concurrent orthopaedic or other body system injuries have been identified. You advise the owners that surgical stabilisation would be the best course of action, particularly for a young active cat, and whilst the patient is not insured the owners are happy to make funds available for surgery at your practice. You have previously performed stabilisation of coxofemoral luxations in three feline patients using the transarticular pinning technique and whilst two patients recovered uneventfully, the third experienced reluxation. A colleague has recently attended a CPD course on treatment of common feline orthopaedic conditions and advises you that stabilisation using a toggle rod technique results in lower reluxation rates. You wonder which procedure should be performed in this case.

The evidence

Three studies were identified which addressed the PICO question and fitted the inclusion and exclusion criteria applied. All the studies identified were noncomparative case series. The number of cases included in the studies was low: 4, 14 and 20 (median 14). Some other case series reporting outcomes for both feline and canine patients were excluded due to the low number of feline patients (three or less), along with a number of case reports.

All three studies described a surgical technique used for the open reduction and stabilisation of craniodorsal coxofemoral luxations in feline patients from a referral population. Two of the studies (Sissener et al., (2009) and Pratesi et al., (2012)) presented only feline patients, whilst Ash et al., (2012) presented findings for four feline patients and five small dogs. Only the results as they applied to the feline patients were considered.

Sissener et al., (2009) described the use of transarticular pins (1.6 mm diameter in the majority of cases with 1.2 mm and 2.0 mm pins also used) left in-situ for between 2 to 6 weeks in 20 cases. Radiographic follow up was performed at pin removal and, for 12 of the cases, at a time point > 6 months postsurgery. No reluxations were identified at short-term follow up, but two patients radiographed > 6 months later demonstrated reluxation. In addition to reluxation, complications included a bent 1.2 mm pin identified 6 weeks postoperatively in one patient and spontaneous resorption of the femoral head and neck identified 6 months postoperatively in another.

Pratesi et al., (2012) described a toggle rod technique used in 14 cases. A 3.2 mm IMEX toggle rod with two strands of 4 metric polydioxanone was used for the majority of cases. In two cases three strands of 4 metric polydioxanone were used and in one case the polydioxanone size was increased to 5 metric. A single case also had a smaller 2.7 mm toggle used. Short-term radiographic follow up was performed at 3.5–8 weeks postoperatively, revealing two patients had suffered reluxations. No other complications were reported.

Ash et al., (2012) applied an identical technique to all four feline cases, using an Arthrex Mini TightRope toggle and Arthrex FiberWire suture. No reluxation was noted at 6 week postoperative radiographs and none of the feline patients experienced any other complications.

Reluxation rates including time of assessment for all three studies are summarised in the following table (Table 1):

Table 1: Reluxation rates and assessment times for the 3 studies

Summary of the evidence

Appraisal, application and reflection

There is a lack of high quality evidence available to address the clinical question as all of the relevant studies identified and appraised here are retrospective case series. These sit low on the hierarchy of evidence and, particularly as they are not comparative studies, are not appropriate for assessing the impact of a specific surgical technique on outcome. Randomised, controlled, blinded studies that compare the two surgical techniques are needed to generate high quality evidence on which to base clinical decisions.

A large number of surgical stabilisation procedures are described for the management of coxofemoral luxation, but there is little evidence to guide technique choice (Moore, 2006). Reluxation is reported to be the most common complication following open reduction and surgical stabilisation of coxofemoral luxations. Rochereau et al., (2012) reports rates of around 28% for a variety of open reduction techniques including extra-articular stabilisation and ventral approach for the placement of stainless steel rope cases. It should be noted that many of the studies quoted examine reluxation rates for studies in dogs only. The reluxation rates quoted in all the studies (Table 1) appear to compare favourably with this, providing some evidence to support the use of these techniques. However, alongside the low case numbers, the variability in follow up time reduces the quality of information generated. In addition to this, none of the three studies described standardise the observer for short-term follow up radiographic assessments and whilst presence of coxofemoral luxation on a radiograph is relatively objective, observer bias is possible.

Longer-term radiographic follow up is only performed in the transarticular pinning study (Sissener et al., 2009). It is interesting that reluxation was first identified at least 6 months after surgery, at least 5 months after pin removal, in two cases. Ash et al., (2012) argues that 6 week follow up is adequate for assessing reluxation rates since long term periarticular fibrosis is responsible for stability after this stage and reluxation rates beyond this time frame are very low. However, the findings of the Sissener et al., (2009) study suggest that longer-term follow up is important in establishing reluxation rates. The evidence generated by these studies would be more valuable if follow up was standardised and long term, greater than 12 months, follow up was available for all the surgical techniques.

All of the studies identified describe management of cases at referral centres. This means the cases reported are unlikely to directly reflect those managed in the primary care setting. Specifically, cases are likely to have a higher incidence of concurrent injuries and for more time to have elapsed between luxation and treatment. Both of these factors might be expected to increase reluxation rates. Pre-surgical management is also variable and variably reported. Duration of luxation is not reported by Sissener et al., (2009) whilst pre-referral management is not described by Ash et al., (2012). Postoperative care is also affected by management of concurrent injuries and therefore the patients in these studies are not always subject to the same postoperative management, which would be expected to impact on reluxation rates.

Differences in inclusion and exclusion critera, or the lack of these criteria, across the studies compromises the ability to compare reluxation rates for the different surgical procedures. Ash et al., (2012) excludes patients with radiographic evidence of periarticular fracture, hip dysplasia or osteoarthritis whilst Pratesi et al., (2012) includes two patients with suspected pre-existing hip dysplasia (HD) and three with periarticular bone fragments. Sissener et al., (2009) details inclusion criteria including concurrent injuries and failure of previous surgical stabilisation but does not mention HD or periarticular fractures. It is interesting to note that one of the 2/14 cases experiencing reluxation in the Pratesi et al., (2012) study had hip dysplasia since pre-existing pathology such as this might be expected to impact upon the success of open reduction and stabilisation of traumatic luxations. For this reason, inclusion of these cases in the Pratesi et al., (2012) and possibly in the Sissener et al., (2009) study limits the conclusions we can draw on reluxation rates from these studies.

For the transarticular pinning technique, accurate placement of the transarticular pin is crucial for correct seating of the femoral head in the acetabulum, which is very likely to correlate with reluxation rates. Sissener et al., (2009) reports three separate methods for pin placement were used, it would be useful to assess if any of these methods resulted in a better outcome. Similarly, pin size selection is poorly described and weight, which we would expect to guide size selection, is omitted from signalment. Evidence to guide pin size selection and placement technique would be useful but is lacking.

For the toggle techniques, Pratesi et al., (2012) uses different toggle sizes, suture sizes and thread numbers. Reasons for these variations are not always stated (although one patient received three strands of suture due to suspected pre-existing HD) and there is no obvious trend, for example increasing suture size or number with increasing patient weight. Again, the variation in surgical technique limits the conclusions we are able to draw about reluxation rates, and the study fails to generate guidelines for selection of toggle size or suture.

The surgical technique described by Ash et al., (2012) is consistently applied across all cases, which allows better assessment of the procedure’s impact on reluxation rates. The toggle system reported by Pratesi et al., (2012) used both different toggle (Arthrex Mini- TightRope) and suture (Arthrex FiberWire) than the Ash et al., (2012) study. Suture type/strength and toggle construct are likely to impact upon reluxation rates. This limits the potential to combine data about ‘toggle procedures’ from these two studies (Ash et al., 2012 and Pratesi et al., 2012). Further, this difference in suture material highlights again the need for longer-term follow up, since polydioxanone utilised in the Pratesi et al., (2012) study will lose tensile strength at around 3–4 weeks, whilst the Arthrex FiberWire is more durable. The discovery of reluxation > 6 months postoperatively (Sissener et al., 2009) might suggest that maintaining reduction requires more persistent implants and that periarticular fibrosis alone may be insufficient.

It should be noted that Sissener et al., (2009) reports owner outcomes for the patients with reluxations > 6 months postoperatively to be very good and Pratesi et al., (2012) describes limb use as good despite reluxation within 6 weeks of surgery in two cases, one of which received no further treatment. It is important to consider if reluxation is the most clinically useful outcome measure. All the studies include other outcome measures, all subjective, including veterinary lameness assessments without observer standardisation and owner questionnaires completed at very wide ranging time points. Long-term degenerative joint disease may be a more important clinical comparator between surgical techniques and more objective outcome measures such as measuring ground reaction force on pressure sensitive walkways (Schnabl et al., 2015) could be considered.

In general, the studies fail to generate any descriptive rationale for the selection of one surgical procedure over another. All the cases in the Ash et al., (2012) study seem to have been managed using the toggle technique, and similarly in the Sissener et al., (2009) study for the pinning technique, whilst Pratesi et al., (2012) implies not all presenting cases were managed with the toggle technique but does not explain the choice of this technique for these cases.

Further studies using randomised, controlled, blinded trials comparing two standardised surgical techniques, ideally in a primary care setting, with objective outcome measures are needed.

Methodology Section

Search Strategy
Databases searched and dates covered:	CAB Abstracts on CABI direct platform 1973 to week 8 2018 MEDLINE on OVID platform 1946 to week 8 2018 Scopus 1973 to week 8 2018 Web of Science 1973 to week 8 2018
Search terms:	(cat OR cats OR feline OR felines) AND (hip dislocation OR hip luxation OR coxofemoral dislocation OR coxofemoral luxation) AND (transartic* OR transtroch* OR pin* OR togg* OR rod)
Dates searches performed:	Feb 25th 2018

Exclusion / Inclusion Criteria
Exclusion:	wrong species luxation not craniodorsal surgical technique not recognisable as transarticular pinning or toggle rod reluxation not given as outcome measure not English language conference proceedings review articles case reports or case series with < 3 feline cases
Inclusion:	Correct species, craniodorsal luxation managed surgically with technique recognisable as transarticular pinning or toggle rod with outcome measures including reluxation.

Search Outcome
Database	Number of results	Excluded – non-English language publication	Excluded – Case reports, Reviews, Conference proceedings	Excluded – Does not address PICO question	Excluded – Full text not available	Total relevant papers
CAB Abstracts	21	6	5	7	1	2
MEDLINE	14	1	1	9	1	2
Scopus	8	2	1	3	0	2
Web of Science	38	7	3	25	0	3
Total relevant papers when duplicates removed						3

The author declares no conflict of interest.

1. Ash, K., Rosselli, D., Danielski, A., Farrel, M., Hamilton, M. & Fitzpatrick, N. (2012) Correction of craniodorsal coxofemoral luxation in cats and small breed dogs using a modified Knowles technique with the braided polyblend TightRope systems. Vet Comp Ortho Traumatol, 25 (1), pp. 54-60. http://dx.doi.org/10.3415/VCOT-11-02-0019 
2. Nunamaker, D. M. (1973) Repair of femoral head and neck fractures by interfragmentary compression. JAVMA,162, 569-572
3. Moore, A. (2006) Decision making in the management of hip luxations in dogs and cats. In Practice, 28 (10), pp. 570-576. http://dx.doi.org/10.1136/inpract.28.10.570
4. Pratesi, A., Grierson, J. & Moores, A. (2012) Toggle rod stabilisation of coxofemoral luxation in 14 cats. JSAP, 53 (5), pp. 260-266. https://doi.org/10.1111/j.1748-5827.2012.01199.x
5. Rochereau, P. & Bernardé, A. (2012) Stabilization of coxofemoral luxation using tenodesis of the deep gluteal muscle. Technique description and reluxation rate in 65 dogs and cats (1995-2008). Vet Comp Ortho Traumatol, 25 (1), pp. 49-53.
6. Schnabl, E. & Bockstahler, B. (2015) Systematic review of ground reaction force measurements in cats. The Veterinary Journal, 206 (1), pp. 83-90. http://dx.doi.org/10.1016/j.tvjl.2015.05.017
7. Sissener, T.R., Whitelock, R.G. & Langley-Hobbs, S, (2009) Long-term results of transarticular pinning for surgical stabilisation of coxofemoral luxation in 20 cats. JSAP, 50 (3), pp. 112-7. http://dx.doi.org/10.1111/j.1748-5827.2008.00625.x