Kim PJ, Richey JM, Wissman LR, Steinberg JS.  The variability of the Achilles tendon insertion:  a cadaveric examination. J Foot Ankle Surg.  2010 Sep-Oct; 49(5): 417-20.   (PubMed ID: 20579910)

WHY did the authors undertake this study?
There are multiple pathologies affecting the Achilles tendon that can result in patient complaint and a podiatric office visit.  In addition, it is imperative that foot and ankle surgeons have a detailed appreciation for the anatomy of the Achilles insertion prior to surgical intervention.  The primary aim of this study was to examine the specific insertion of the Achilles tendon onto the posterior aspect of the calcaneus.

HOW did they attempt to answer this question?
The primary outcome measure of the study was the most distal insertion site of the Achilles tendon on the posterior aspect of the calcaneus.   The posterior aspect of the calcaneus was subjectively divided into 1/3s, and three investigators came to a consensus as to the most distal insertion site.  A secondary outcome measure was contiguity of the Achilles tendon with the plantar fascia, again decided by gross appearance and a consensus agreement between three evaluators. 

Inclusion criteria of the population cohort were 60 limbs from 40 cadaveric specimens obtained from the Department of Anatomy of a medical school. 

WHAT were the specific results?
Ninety-five percent (95%) of Achilles tendons inserted onto the superior or middle 1/3 of the posterior aspect of the calcaneus.  Fifty-five percent (55%) of samples inserted onto the superior 1/3, while 40% of samples inserted onto the middle 1/3 of the calcaneus. 

Further, a contiguous relationship between the Achilles tendon and plantar fascia was found in only 8% of limbs, more commonly in younger cadaveric specimens.  

HOW did the authors interpret these results?
From these results, the authors hoped to provide unique anatomic evidence with respect to the insertion of the Achilles tendon onto the posterior aspect of the calcaneus.

Moon JS, Shim JC, Suh JS, Lee WC.  Radiographic predictability of cartilage damage in medial ankle osteoarthritis.  Clin Orthop Rel Res.  2010 Aug; 468(8): .

WHY did the authors undertake this study?
There are various plain film radiographic staging systems available for the evaluation of osteoarthritis affecting the ankle joint.  However, we have very little evidence with respect to how these radiographic staging systems correlate to actual surgical findings and visualization of the joint.  This is obviously important to determine whether a joint-sparing or joint-destructive procedure is better indicated for a given patient.  The objective of this study was to evaluate the reliability of radiographic findings to predict visualized cartilage damage of the ankle joint. 

HOW did they attempt to answer this question?
With a relatively sound study design, the authors compared pre-operative radiographic imaging to intra-operative findings of 83 patients with primary medial ankle osteoarthritis who underwent (at least) ankle arthroscopy within one month of the radiographic examination. 

WHAT were the specific results?
The authors packed reliability assessment into their results section, and we will only highlight a small portion of these results here.  However, the sensitivity, specificity and odds ratio analysis for the radiographic parameters as predictors for ankle osteoarthritis were as follows respectively:  osteophytic spurs (94.2, 29.2, 5.7), any medial joint space narrowing (96.0, 12.5, 3.4), medial joint space narrowing without talar tilting (20.3, 16.7, 0.1), and medial joint space narrowing with talar tilting (75.7, 95.8, 71.6). 

HOW did the authors interpret these results?
Based on these results, the authors concluded that the incorporation of talar tilt into the radiographic evaluation of ankle arthritis improved the overall assessment of actual cartilage damage.

Let’s piggy back on our last discussion (PJC#23) and continue to take a closer look at measures of reliability as they apply to these articles, particularly sensitivity and specificity within the Moon et al article.  The study design of the Moon et al article is roughly similar to our last article review (the Ferkel et al article from PJC#23) in that it is comparing some radiographic measurement to intra-operative findings.  In both articles, intra-operative arthroscopic findings are utilized as the standard reference marker, and in the Moon et al article we are attempting to determine the ability of plain film radiographs to tell us about the changes we can see with the standard reference marker. 

In other words, we feel confident in our ability to diagnosis “ankle joint arthritis” based on intra-operative arthroscopic findings (defined in the Moon et al article as an Outerbridge classification grade of 2, 3 or 4).  We also feel confident in our ability to see osteophytic spurs, medial joint space narrowing and talar tilting on plain film radiographs.  What we don’t know however, is if seeing osteophytic spurs, medial joint space narrowing and talar tilting on plain film radiographs gives us any information about “ankle joint arthritis”.  The Moon et al authors attempted to correlate what was seen on plain film radiographs with what was seen with an arthroscope, and used several reliability measures to do so, the simplest of which is sensitivity and specificity. 

If you have the article, refer to Table 5 on page 2194 to follow along with this discussion.  The respective sensitivity and specificity of each of these measures is osteophytic spurs (94.2, 29.2), any medial joint space narrowing (96.0, 12.5), medial joint space narrowing without talar tilting (20.3, 16.7) and medial joint space narrowing with talar tilting (75.7, 95.8).  Something to appreciate right off the bat is that sensitivity and specificity should be expressed as percentages, and we assume that the standard reference marker has a sensitivity of 100% and a specificity of 100%.  In other words, the identification of osteophytic spurs on a plain film radiograph has a sensitivity of 94.2% compared to reaching the diagnosis with the standard reference marker arthroscope.  In the same way, the identification of osteophytic spurs on a plain film radiograph has a specificity of 29.2% compared to reaching the diagnosis with the standard reference marker.  We can plainly appreciate that the identification of osteophytic spurs is much more sensitive than specific, but what does this mean? 

Sensitivity measures the percentage of those studied who actually have the diagnosis who are correctly identified with the new test.  To use our example here, approximately 94% of patients who have actually have “ankle joint arthritis” (as defined by our arthroscopic examination) will have osteophytic spurs on a plain film radiographic examination.    That’s pretty good.

Specificity measures the percentage of those without the disease who are correctly identified as not having the disease with the new test.  To again use our example, approximately 29% of patients who don’t have “ankle joint arthritis” (as defined by our arthroscopic examination) will not have osteophytic spurs on a plain film radiographic examination.  That’s not as good, and tells us that the presence/absence of osteophytic spurs on a plain film radiograph gives us more information about people that have “ankle joint arthritis” compared to people that don’t.  In other words, you can be pretty confident that someone with osteophytic spurs has ankle joint arthritis, but just because you don’t see osteophytic spurs doesn’t necessary mean that they don’t have arthritis.

As a general rule of thumb, a good diagnostic test should have about a sensitivity of 80% and a specificity of 90% compared to the standard reference marker or gold standard.  We can tell from our above measures that only the presence of medial joint space narrowing with talar tilting on a plain film radiograph (with a sensitivity and specificity of 75.7% and 95.8% respectively) comes close to this rule of thumb.  Sensitivity and specificity are not the only measures that we use of course, but they are ones that you will commonly see.