1st February 2013: Plain XR for Paediatric Patellar Subluxation


Where can I find this paper?


What is this paper about (what is the research question)?

Do plain post-reduction XRs provide clinically useful and ED management-altering information in paediatric patients with patellar subluxation?

Summary of the Paper

Design: retrospective chart review

Objective:  to estimate the incidence of fractures detected on post-reduction XRs for patients with lateral patellar subluxation and to identify whether (and how) the presence or absence of a fracture alters ED management

Outcome: primary – presence or absence of fracture on post-reduction XRs for patients with lateral patellar subluxation. Secondary – differences in ED management between patients with and without fractures on plain post-reduction films.

Population:  patients <21 years presenting to the ED of a tertiary children’s hospital between January 1st 2000 and 31st December 2010

  • Inclusion: ICD coding related to patellar dislocation with reduction in the ED
  • Exclusion: patients with medial or intra-articular dislocations, patients with spontaneous reduction

Results: 80 patients identified of whom 79 (98.8%) underwent reduction of their dislocation/subluxation in the ED.

11 (13.7%) of patients had a pre-reduction XR – none of these had a fracture identified by radiologist report.

74 (92.5%) of patients had a post-reduction XR – fractures were idenfied in 8 cases (10%: 95% CI 3-17)

Patients with both pre- and post-reduction XR had a longer length of ED stay (median 3.4h, range 1.5-5.2h) compared with those receiving a single XR set only (median 1.9h, range 0.6-6.0h).

All patients, regardless of presence or absence of fracture, had uneventful reduction and were discharged with knee immobilisation and outpatient follow-up.

Authors’ Conclusions:

Pediatric patients with lateral patellar dislocations may be candidates for discharge from the ED after reduction without plain radiography. The modality by which to best determine the presence of a complicating osteochondral fracture (i.e., plain radiography, computed tomography, MRI, or arthroscopy) may be left to the discretion of the orthopedic surgeon accepting the child in follow-up.

On the study design

A nice short paper this week – and a relevant question – do we need to XR knees post-reduction of patellar subluxation/dislocation?

A couple of methodological issues with this one though. Retrospective studies are always open to bias – in this case, relying on ICD-9 classification introduces a potential for selection bias as we are reliant upon the accuracy of coded data to identify our patient cohort. However, with such small numbers (only 80 patients in an 11-year period) a prospective study is unlikely to generate enough subjects to maintain momentum and as such retrospective data collection is far more pragmatic.

The wide timeframe, while providing a reasonable sample size (albeit difficult to guage in terms of its epidemiological accuracy) does open the study up to the confounding effect of changes in practice. Arguably the introduction of alternative imaging modalities (ultrasound) and the relative availability of MRI scan might impact clinician decisions regarding whether to perform post-reduction XRs. The study can give us no account of this.

The other major issue is the lack of blinding in the data collection stage; this paragraph of the methods section is particularly interesting as it sounds as though the research assistant was specfically trained to identify qualities and points of interest among the identified case notes – this would almost certainly introduced an element of observation bias, exacerbated by the use of a single unblinded data collector.

Still, formal radiology reporting was used to determine the presence or absence of fractures – a reasonable standard. Given that the article talks about the use of other imaging modalities, it’s hard not to wonder how the radiology report might have been influenced; they were almost certainly not blinded to the clinical data, were CT/MR reports also available which might have “added” to the interpretation of plain films? When were reports made relative to the injury and availability of other imaging?

What were the results and what does this mean?

First, let’s look at pre-reduction films. These were taken in 11 patients. We know from the paper that in 79/80 patients the clinician had documented that there was clinically visible displacement of the patella laterally. So why the XRs? Habit perhaps? In fact, of those without pre-reduction XRs, 68/69 had specific documentation about the clinically visible displacement (so that’s where the 1/80 was) – simple maths tells us that all 11 patients having pre-reduction films had dislocation/subluxation apparent on examination alone.

And for the post-reduction films; these were performed in 74/80 patients (92.5%). 8 patients had fractures (10%), of whom none had pre-reduction films taken. None of the patients required intervention beyond ED reduction apart from a multiply injured patient whose patella was reduced in theatre while other injuries were being treated.

So, for all the methodological problems, it doesn’t look as though plain films – with or without fractures – change our ED management.

What can we take from this paper into clinical practice?

Well, from this small and moderately flawed study, it doesn’t look as though plain XRs add anything to ED management of patellar subluxation/dislocation. I certainly can’t think of a time in my clinical practice when a post-reduction film has led to admission (assuming reduction was successful, of course). So why do we do them?

What we don’t know is how these patients are subsequently managed at outpatient clinic. While CT/MR scans are more sensitive (see discussion section of paper for references) for identifying osteochondral fractures, does the presence of a fracture on plain film have important prognostic significance? Does it lead to earlier operative intervention or increased likelihood of operative management?

So not quite enough to throw plain films out altogether, but certainly worth exploring with a longer study period to include follow-up, together with some good quality orthopaedic opinion (other than, “get an x-ray because that’s what we do”).

More questions to ask

  •  Can this data be extrapolated to patients with spontaneous reduction and are these patients routinely x-rayed in any case?
  • Would a period of follow-up including outpatient review change the outcomes of this paper? Would we discover that the patients with fractures who were discharged should have had emergency treatment?
  • How does this sit with our orthopaedic colleagues?

Follow us on twitter: @PEMLit

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s