:Lamm BM, Gottlieb HD, Paley D.  A two-stage percutaneous approach to Charcot diabetic foot reconstruction.  J Foot Ankle Surg.  2010 Nov-Dec; 49(6): 517-22.   (PubMed ID: 20864361)

WHY did the authors undertake this study?
Surgical intervention and reconstruction in the treatment of diabetic Charcot neuroarthropathy represents a significant clinical challenge without a clear most-effective treatment protocol.  The authors of this study describe their preferred minimally invasive reconstructive technique utilizing a combination of internal and external fixation with gradual deformity correction. 

HOW did they attempt to answer this question?
A series of 11 feet in 8 patients were retrospectively identified with a mean follow-up of 22 months (range 6-36 months).  The authors’ preferred surgical technique was discussed in detail and includes a first stage of Achilles tendon lengthening with application of a Taylor spatial frame (TSF) to achieve gradual deformity correction via ligamentotaxis.  After realignment of pedal anatomy had been achieved with the external fixation (described in 1-2 months; report mean of 12 weeks with a range of 5-30 weeks), a minimally invasive (percutaneous) arthrodesis of the midfoot is performed with large-diameter, cannulated intramedullary screws through the medial and lateral columns.  External fixation is removed at the time of arthrodesis, and the patients remain non-weight bearing for an additional 2-3 months.

Inclusion criteria of the population cohort were neuropathic diabetic patients with midfoot and/or subtalar Charcot neuroarthropathy.  Patients with Lisfranc or ankle Charcot were not included as the authors do not feel as though this specific treatment protocol is amendable to these deformities. 

The primary outcome measures of this investigation were descriptive surgical outcomes of the patient cohort.  Pre- and post-operative radiographic parameters were also performed.

WHAT were the specific results?
Statistically significant differences were found  between pre- and post-operative radiographic measurements with respect to the transverse plane talar-first metatarsal angle (p=0.02), as well as the calcaneal inclination angle (p=0.001) and Meary’s angle (p=.008).

All patients went on to radiographic union with a mean return to normal shoe gear in 22 weeks (range 8-37 weeks).  No recurrent ulcerations were noted at time of last follow-up.

HOW did the authors interpret these results?
From these results, the authors concluded  that their described protocol represents an effective treatment for Charcot reconstruction.

Karunakar MA, Staples KS.  Does stress-induced hyperglycemia increase the risk of perioperative infectious complications in orthopaedic trauma patients?  J Orthop Trauma.  2010 Dec; 24(12): 752-6. (Pubmed ID#: 21076247)

WHY did the authors undertake this study?
Hyperglycemia is a known risk factor for the development of post-operative infection, even in patients without a history or diagnosis of diabetes mellitus.  The aim of this study was to determine if stress-induced hyperglycemia was associated with post-operative infection in orthopedic trauma patients. 

HOW did they attempt to answer this question?
The primary outcome measure of this investigation was the development of a post-operative infection originating from wound infections, pneumonia, urinary tract infections, sepsis and/or bacteremia.  Patients were classified as having either positive stress-induced hyperglycemia (serum glucose level > 220 mg/dl) or not (all serum glucose levels < 220 mg/dl), as well as other patient factors including age, co-morbidities, transfusions, tobacco use, open fracture, sex, body mass index, Injury Severity Score and the initial presence of infection. 

One hundred twenty five consecutive patients who sustained operative orthopedic injuries from car accidents were analyzed from a crash injury database.

WHAT were the specific results?
64% (7/11) of patients with stress-induced hyperglycemia developed a post-operative infection compared to 21% (21/99) without stress-induced hyperglycemia (p=0.0056).

Neither age, associated co-morbidities, transfusions, tobacco use, open fracture, sex, body mass index, nor Injury Severity Score were associated with the development of post-operative infection.

HOW did the authors interpret these results?
From these results, the authors concluded that transient hyperglycemia associated with stress from orthopedic trauma may be a risk factor for the development of post-operative infection.

Let’s take a closer look at the topic of case reports and case series’, specifically as it applies to the Lamm, Gottlieb and Paley Charcot reconstruction study.  Most everyone has a conceptual idea about what a “case report” is.  They generally present an interesting patient with an unusual pathology, disease process, post-operative course, etc.  In fact, each edition of the Journal of Foot and Ankle Surgery (and most other journals) has a special section just for case reports.  The Nov-Dec JFAS edition we are reviewing in this PJC published 4 of them for example.  There’s even an entire peer-reviewed journal dedicated to case reports entitled “Journal of Medical Case Reports”.

Case reports are typically very descriptive in nature, as opposed to comparative.  There are several reasons for this, but one reason is that it is nearly impossible to generate statistical significance or power with so few patients.  For this reason, case reports are usually ranked pretty low from an evidence-based standpoint.  Utilizing the “level of clinical evidence” that JFAS uses and that we’ve talked about in previous PJCs, case reports are categorized as Level 4 evidence.

So why is the Lamm et al study also categorized as Level 4 evidence by JFAS?  It’s more than a case report, isn’t it?  In fact, the study examines 11 feet in 8 patients.  Shouldn’t it be more powerful than Level 4 evidence?  Interestingly, from an evidence-based standpoint, this article carries the same rank as a case report.  However, because there is more than 1 patient examined, it is better titled a case series than a case report. 

Think about the design of this study.  We have only one group of patients (diabetics with midfoot/rearfoot Charcot disease), all undergoing the same intervention (the specific surgical protocol developed by the authors).  Further, the outcome measures are almost entirely descriptive (prevalence of post-operative complications, time to radiographic fusion, recurrence rates, etc).  There is no comparison between different groups of patients, or between different surgical techniques, or between different post-operative protocols for example. 

In fact, the only comparison that takes place in this study is between pre- and post-operative radiographic angles, and this study clearly demonstrates the problem of generating statistical significance and power with so few patients.  The authors noted that 3 radiographic measurements “significantly” improved with their intervention:  transverse plane talar-first metatarsal angle, calcaneal inclination angle, and sagittal plane talar-first metatarsal angle (Meary’s angle).  The difference between pre- and post-operative measurements for each of these angles was 18±22°, 15±12°, and 21±21° respectively. 

Take a second look at the amount of variation in each of those differences.  If the data was actually coming from a normally distributed population, than we could say that 95% of the difference in Meary’s angle pre- versus post-operatively would fall within a range of -21° and 63°.  I would think so!

Smaller patient populations generate higher degrees of variation when attempting to compare data.  This is one of the reasons that comparative studies are considered stronger “evidence” than descriptive studies, and that case reports and case series’ are not considered very strong “evidence”.  Usually you need somewhere in the ballpark of >20-30 patients to fall out of this problem. This in no way implies that this study or its results are flawed, or takes away anything from the surgical technique, it simply explains where and how this study ranks on the level of clinical evidence.