Ferkel RD, Tyorkin M, Applegate GR, Heinen GT.  MRI Evaluation of anteriorlateral soft tissue impingement of the ankle.  Foot and Ankle Int.  2009 Sep-Oct; 48(5): 525-7.   (PubMed ID: 20727312)

WHY did the authors undertake this study?
There are numerous soft tissue pathologies that can result in lateral ankle pain and symptoms, including anterolateral soft tissue impingement.  The objective of this study was to quantify the effectiveness and reliability of MR imaging for the diagnosis of anterolateral soft tissue impingement.

HOW did they attempt to answer this question?
The primary outcome measure of the study was a positive MRI result for anterolateral soft tissue lesion.  Lesions were graded based on the sagittal T1 and STIR images, and verified with axial images.  All MRs were performed with the same 1.5 Tesla imager with a “chimney” coil forefoot stabilizer, and read by the same experienced musculoskeletal radiologist. 

MRI results were then compared to intraoperative arthroscopic findings.  24 patients met inclusion criteria of appropriate pre-operative MR images and surgical arthroscopic examination.

WHAT were the specific results?
MR imaging was found to be 78.9% accurate (defined as the percent of times the MRI was correct, both positively and negatively), 83.3% sensitive (defined as the percent of times the MRI correctly diagnosed lateral soft tissue impingement), and 78.6% specific (defined as the percent of times the MRI correctly reported no soft tissue impingement in the control group) with their described specific technique. 

HOW did the authors interpret these results?
From these results, the authors concluded  that MR imaging may be beneficial in the diagnosis of anterolateral ankle impingement in complicated clinical presentations. 

Jones SR, Carpin KM, Woodward SM, Khiabani KT, Stephenson LL, Wang WZ, Zamboni WA.  Hyperbaric oxygen inhibits ischemia-reperfusion-induced neutrophil CD18 polarization by a nitric oxide mechanism.  Plast Recon Surg.  2010 Aug; 126(2): 403-411. (Pubmed ID#: 20679826)

WHY did the authors undertake this study?
Ischemia-reperfusion injury describes the process whereby previously ischemic tissue is injured via inflammatory mechanisms following a restoration of blood flow.  This is a common finding in the clinical situations of myocardial infarction, stroke, transplantation, replantation and free tissue transfer.  Previous studies have indicated that this may be triggered when neutrophils adhere to the endothelium of postcapillary venules and release free radicals.  Further, it is known that hyperbaric oxygen decreases this adhesion and inflammatory damage.  The objective of this study was to determine if this hyperbaric oxygen protective effect is regulated by nitric oxide and nitric oxide synthase.

HOW did they attempt to answer this question?
The primary outcome measure of this study was the percentage of adhered and polarized neutrophils in a clinical model.  A gracilis muscle flap was raised in a several groups of rats, and ischemic injury induced by clamping the pedicle vessels for 4 hours.  Groups were treated with hyperbaric oxygen, and then with various nitric oxide synthase inhibitors and scavengers. 

WHAT were the specific results?
Statistically significant differences were found in the percentages of adhered and polarized neutrophils with the application of nitric oxide synthase inhibitors and scavengers. 

HOW did the authors interpret these results?
From these results, the authors conclude that the protective effect of hyperbaric oxygen with respect to ischemia-reperfusion injury appears to be regulated through a nitric oxide mechanism.

Let’s take a closer look at the topic of standard reference markers, particularly as it applies to the Ferkel et al article.  The Ferkel et al study provides another common study design within the foot and ankle literature, namely looking at some measure of reliability of a diagnostic test.  The authors of this study essentially hypothesized that their specific MRI technique would be valuable for clinicians in the diagnosis of anterolateral ankle impingement.  But in order to determine if MRI is useful in making this diagnosis, we need some other means to confirm the diagnosis in the first place!  The standard way that we make a diagnosis is known as the standard reference marker, and the new technique that is being investigated is then directly compared back to this. 

Another way to think about standard reference markers is in terms of the “gold standard”, and a good example of a “gold standard” for foot and ankle surgeons is bone biopsy.  Any podiatric medical student can tell you that the “gold standard” for diagnosis of osteomyelitis is bone biopsy (or so we think…).  So if we wanted to investigate a new, non-invasive diagnostic test for osteomyelitis (say some new advanced imaging modality, for example), then we would perform the new imaging analysis on a patient and then compare the results to bone biopsy of the same patient. 

The standard reference marker is the way that we would typically confirm a diagnosis, and any measure of reliability of a new diagnostic test is simply a comparison to an old diagnostic test.  So from a critical analysis standpoint, the measure of reliability is only as good as the standard reference maker.  If you don’t have confidence in the standard reference marker for making a diagnosis, then it doesn’t really matter what the reliability shows for the new diagnostic test.

Let’s apply this to the Ferkel et al article.  They found certain measures of reliability for their MRI technique (78.9% accurate, 83.3% sensitive, and 78.6% specific), but what was their standard reference marker?   In this case it was direct arthroscopic examination.  Although it may not be considered the “gold standard”, most people would agree that the best way to diagnosis someone with having an intra-articular soft tissue lesion would be to directly visualize it.  So in this case we have confidence in the standard reference marker, and can have confidence in the reliability results of the new diagnostic test.
 
We’ll take a specific look as some measures of reliability in the next PJC, but I also wanted to point out that this topic also relates back to our last PJC dealing with clinical levels of evidence.  The fourth column of the table (click here for table) we worked with last time deals with the level of evidence for studies investigating a diagnostic test.