The outcome after open reduction and internal fixation of displaced intra-articular calcaneal fractures varies considerably. Serious and deep infection rates after open reduction and internal fixation have ranged from 0% to 20%1,2. Although a recent randomized trial indicated that the number of patients needing subtalar arthrodesis for the treatment of posttraumatic arthritis is reduced after open reduction and internal fixation3, the risk of infection discourages some from advocating open reduction and internal fixation.
It has been assumed that the outcome after open reduction and internal fixation may be reflected by the presence of institutional trauma care and fracture load. Evidence of advantages related to specialist care for calcaneal fractures is, however, generally absent. Several studies have indicated that the infection rate may be influenced by the time between trauma and the surgical procedure4; patient-related risk factors, such as diabetes and smoking habits5; and fracture-related risk factors, such as the presence of open or highly comminuted fractures6. Another study indicated that the operative fixation of calcaneal fractures is technically challenging and has a substantial learning curve7, although until now no studies have demonstrated a correlation between the numbers of operatively treated calcaneal fractures and actual outcome measures.
Therefore, a systematic review of the literature was performed to study the effect of institutional fracture load on the outcome after open reduction and internal fixation of closed displaced intra-articular fractures of the calcaneus. The aim of the study was to investigate the relationship between institutional fracture load and the rates of serious infection and subsequent subtalar arthrodesis. We hypothesized that a low fracture load increases the rates of deep infection and subtalar arthritis.
Materials and Methods
Three methods were used to retrieve information for this review8,9. First, MEDLINE and EMBASE databases for the years 2000 to 2006 were searched. This time frame was chosen to limit the influence of advancements in fracture care on outcome measurements. The literature was searched with the following MeSH headings: “calcaneus” and “fracture” and “surgery” or “operation.” The second method was to search personal files and communications to find additional citations and to search Current Contents (Ovid Technologies) for recently published studies. The third method was to search the reference lists of the articles found with use of the above-mentioned methods for additional articles.
With use of this retrieval method, all English-language abstracted studies describing adult patients (defined as those with an age of at least eighteen years) who were managed with open reduction and internal fixation through a lateral approach for the treatment of a unilateral or bilateral fracture were included. Both prospective and retrospective studies were included in the meta-analysis. Patients with open fractures and patients who were managed with percutaneous and/or external fixation procedures were excluded. We also excluded studies that included a subgroup of patients from other studies, those in which >30% of the patients had been lost to follow-up, and those in which primary parameters (inclusion time and the rates of deep infection and arthrodesis) were not recorded.
From the studies that were included, the fracture load was calculated by dividing the number of calcaneal fractures that were treated operatively by the inclusion time of the reported studies in months. A serious infection was defined as the presence of a clinically proven soft-tissue infection requiring antibiotic therapy, surgical débridement, and hardware removal; the presence of osteomyelitis; and/or reconstruction with a flap. Traumatic subtalar arthritis was considered severe when a subtalar arthrodesis was required.
Several factors that could confound the relationship between fracture load and the outcome parameters were analyzed. Data regarding the study design (retrospective or prospective) and whether the patients who were included in the study were a selection of the total population of patients who were managed operatively were recorded. The number of surgeons performing the procedures, the timing of surgery, the duration of the surgical procedure, the use of antibiotics, and the presence of multiple trauma were recorded. The Sanders classification was recorded when provided7,10.
Other data that were recorded (when available) included the percentage of joint depression-type fractures as compared with tongue-type fractures as shown on radiographs, the preoperative and postoperative Bohler angles, the duration of follow-up postoperatively, and the percentages of patients who had a bilateral fracture, who smoked, who had diabetes, and who received Workers' Compensation.
Methodological Quality Analysis
Selected analyses were subjected to a blinded validity assessment with use of clinical epidemiological criteria adapted from previously published criteria11 assessed independently by two of the authors (M.P., J.P.A.M.V.). This analysis provides insight into the strength of evidence referring to the extent to which potential sources of bias may affect the validity of the results. This method has been used and validated previously in studies including patients with upper extremity trauma12. In previous studies, important validity issues that were identified included study design hierarchy, the use of adequate case definition, application of the intention-to-treat principle, blinded outcome assessment, the adequacy of follow-up, control for confounding prognostic factors, and appropriate statistical analysis (Table I). The maximum score of the quality assessment was 17.
Data are shown as percentages, as the median and the range, or as the mean and the standard deviation. The primary outcome parameters were the rate of deep infection and the rate of subtalar arthrodesis. The relationship between the primary outcome variables and fracture load was assessed with the Spearman correlation coefficient for nonparametric correlations. The relationship between the methodological score and the infection rate, arthrodesis rate, and institutional fracture load was also assessed with the Spearman correlation coefficient. Studies with and without the primary outcome parameter were compared with regard to the presence of confounding factors. Group parameters were compared with use of one-way analysis of variance for parametric data, with use of the Mann-Whitney U analysis for ordinal nonparametric values, and with use of the Kruskal-Wallis test for continuous nonparametric data.
Receiver-operating characteristic curves were made by calculating the sensitivity and 1 − specificity values for the prediction of the rate of serious infection for every possible value for the institutional fracture load. The optimal cut-off value for fracture load was calculated as the point with the greatest combined sensitivity and specificity for the development of a serious infection as derived from receiver-operating characteristic curves with the institutional fracture load as the dependent factor. The validity of this cut-off point was evaluated by means of a method for comparing areas under the receiver-operating characteristic curves as previously described in detail13,14. Subsequently, the rate of deep infection as defined by this cut-off point for the fracture load was used to make a dichotomous division of the studies, with which we could calculate the estimated odds ratios.
A multivariate procedure was performed after logarithmic transformation of the nonlinear parameters to provide a linear regression analysis and an analysis of variance for the multiple dependent factors with the rate of deep infection as the dependent factor and with the fracture load, the time to surgery, the time of surgery, the Sanders classification, the percentage of patients with a bilateral fracture, the percentage of patients with diabetes, the percentage of patients who smoked, and the postoperative Bohler angle as independent covariates. In order to determine in the logistic regression analysis which regression curve best summarized the change in the dependent measure (the infection rate) relative to a unit change in one or more of the above-mentioned independent measures, two models were used. The goodness-of-fit for the regression curve (represented by R square) of the first model, which included the regression constant and the fracture load, was compared with the R square of the second model, which additionally included all of the above-mentioned independent measures. Data are presented as unstandardized regression coefficients (B) (with standard error). Missing data were replaced for regression analysis with use of the “series mean” principle. Several analyses were performed to test the accuracy of the model. Standardized residuals during casewise diagnostics indicate the absence of outliers when 95% of the standardized residuals lie between ±2. In addition, multicollinearity analysis indicates whether predictors of the model are not correlated to each other. The tolerance in this analysis should be >2, and the variance inflation factor should be <1015.
A p value of <0.05 was considered to be significant with use of a two-tailed test of significance.
With use of the MeSH headings, we identified 236 studies that were published between 2000 and 2006. After the initial screening, fifty-four candidate studies were identified. A total of twenty-one studies were included in the final analysis (see Appendix)1-5,16-31. The other studies were excluded from the analysis because of the inclusion of only open calcaneal fractures32-36 or pediatric patients37, because of incomplete data presentation or the inability to calculate the end points38-41, because of the use of only external or minimally invasive surgical procedures42-55, or because the studies represented a subanalysis of another published patient dataset56-61 or only presented experimental data62-64.
The total number of fractures included in the studies was 1656. The median number of fractures that were treated in the individual studies was forty (range, twelve to 341), with a median institutional fracture load of 0.8 fracture per month (range, 0.2 to 4.6 fractures per month). The median fracture load per surgeon was 0.4 fracture per month (95% confidence interval, 0.09 to 4.7 fractures per month, based on fourteen studies). The median percentage of patients who had a bilateral fracture in the included studies was 8.5% (range, 0% to 100%). The mean institutional fracture load was not different between the sixteen studies that included all operatively managed patients and the five studies that included a selection of the total number of operatively managed patients (1.3 ± 1.2 compared with 1.0 ± 0.8; p = 0.5). In addition, the five prospective studies did not have an increased fracture load compared with the sixteen retrospective studies (mean 1.4 ± 0.6 compared with 1.2 ± 1.2; p = 0.7). The median methodological quality score for all studies was 9 (range, 7 to 15). No correlation could be found between the methodological quality score and the institutional fracture load (r2 = 0.2, p = 0.5), the rate of serious infection (r2 = 0.21, p = 0.4), or the rate of subtalar arthrodesis (r2 = −0.06, p = 0.8).
The median infection rate in the studies combined was 5.0% (95% confidence interval, 0.0% to 20.0%). The infection rate increased with a decreasing institutional fracture load (Spearman correlation coefficient, −0.5; p = 0.03) (Fig. 1). A cut-off point for the institutional fracture load could be identified at the cut-off point of one operation per month, below which the rate of deep infection increased exponentially. The median rate of deep infection was 1.8% (95% confidence interval, 0.04% to 6.19%) for studies with a fracture load of more than one open reduction and internal fixation operation per month, compared with 8.9% (95% confidence interval, 6.24% to 14.00%) for studies with a fracture load less than one operation per month (p = 0.005). With use of these cut-off points to divide the studies (a fracture load of more or less than one operation per month and a serious infection rate of above or below 6.2%), the odds ratio for the development of a deep infection was 24 (95% confidence interval, 2.1 to 279).
The median rate of arthrodesis for the treatment of subtalar arthritis in the studies combined was 2.5% (95% confidence interval, 0.0% to 15.4%). There was a significant inverse correlation between the institutional fracture volume and the rate of subtalar arthrodesis (Spearman correlation coefficient, −0.7; p = 0.008) (Fig. 2). Studies with a fracture load below the cut-off point of 0.75 operation per month had a significantly higher arthrodesis rate as compared with studies with a fracture load above this cut-off point (mean, 6.4 [95% confidence interval, 2.4 to 10.5] compared with 1.9 [95% confidence interval, 0.2 to 3.5]; p = 0.03).
There was a significant correlation between the median infection rate and the individual fracture load (Spearman correlation coefficient, −0.5; p = 0.04), and there was a tendency toward a significant correlation between the median rate of arthrodesis for the treatment of subtalar arthritis and the individual fracture load (Spearman correlation coefficient, −0.5; p = 0.07).
Studies with a deep infection rate above 6.2% had a significantly higher subtalar arthrodesis rate (p = 0.02) and a significantly lower institutional fracture load (p = 0.005) (Table II). No significant differences existed between studies in which the deep infection rate was above or below the cut-off value of 6.2% with respect to the percentage of patients with joint depression-type fractures as compared with tongue-type fractures, the percentage of patients with a Sanders type-IV fracture, the percentage of patients with a bilateral fracture, the percentage of patients with diabetes or who smoked, the number of surgeons performing the procedures, the mean time to surgery, the mean duration of surgery, the mean postoperative Bohler angle, or the mean duration of follow-up (Table II). No differences were found either with respect to the design of the study (prospective or retrospective) or whether a selected population was studied. There was no correlation between the infection rate and the above-mentioned confounding factors (data not shown). These factors also were not distributed significantly differently between studies with a high (>3.5%) or low rate of subtalar arthrodesis (data not shown).
Multiple regression analysis showed that institutional fracture load is a significant independent predictor of the development of serious infection after surgery (Table III) compared with the above-mentioned confounding factors. The complete model explained 51% of the observed variance, whereas the fracture load accounted for 23% of this variance (p = 0.04). There was no collinearity between either of the independent variables (tolerance range, 0.73 to 0.92; variance inflation factor range, 1.08 to 1.37). Standardized residuals during casewise diagnostics were not higher than 2 (maximum, −1.6).
The outcome of open reduction and internal fixation of displaced intra-articular calcaneal fractures is known to be determined by factors related to the patient and the fracture. To our knowledge, this is the first study that has investigated the outcome of open reduction and internal fixation in relation to the fracture load of displaced intra-articular calcaneal fractures. This systematic review showed that the number of fractures that are operatively treated is an important determinant of two important complications after open reduction and internal fixation. Using a systematic strategy, we were able to retrieve twenty-one articles describing epidemiological studies on the outcome of the surgical treatment of these fractures. These primary studies can be considered as the best available evidence. In the present meta-analysis, the number of prospective studies was relatively small. However, no differences in institutional fracture load could be found between the studies with a retrospective or prospective design. In addition, other methodological quality issues, as potential sources of bias, were not related to the reported institutional fracture load. We did not include studies with insufficient information to estimate the fracture load or deep infection ratio. We did include studies that evaluated a selection of the total population of patients who were managed for calcaneal fractures as we did not find a difference in fracture load or infection rate between the studies with and without a selected population. Although, in general, selection bias may have occurred because of an underreporting of less favorable results, the infection and arthrodesis rates ranged from very low to high. The presence of a serious infection was defined as an infection that did not respond to antibiotics alone but that required additional surgical intervention, including removal of the osteosynthesis material, or a surgical procedure to treat proven osteomyelitis. The limitation of this definition may be that it provides an underrepresentation of the actual infection rate. This definition excludes the less severe cases of wound infection, but the definition of the most serious wound infection was very consistent over the different studies.
To our knowledge, this is the first meta-analysis that has evaluated the impact of the number of treated fractures on the occurrence of postoperative complications. Other orthopaedic studies have focused on the morbidity and mortality rates after total hip replacement65, total knee arthroplasty66, and shoulder replacement surgery67. All studies concluded that increased hospital and surgeon volume significantly reduced the number of postoperative complications. Comparable data are available on outcomes from other surgical fields, such as esophageal cancer surgery68, breast cancer surgery69, and coronary bypass surgery70.
Our findings offer more support for recommendations to concentrate trauma surgery that can be performed electively in high-volume referral centers71. The odds ratio of 24 indicates a strong association between volume and outcome. Moreover, the exponential dose-effect relationship adds to this association.
We found a comparable relationship between fracture load and outcome on the institutional and individual surgeon levels, although not all studies included the number of surgeons performing the procedure. It seems logical that the skills of the individual surgeon in part determine the quality level in the institution. Whether a fellowship-trained foot and ankle surgeon contributes to this individual skill level and reduces the rates of serious infection and arthrodesis cannot be inferred from these data. The study by Sanders et al., which demonstrated a learning curve of thirty-five to fifty calcaneal fractures, may provide evidence for this7. It may be deduced from the present study that an individual surgeon should perform approximately five procedures per year to maintain an adequate skill level. Of course, other institutional factors that are not necessarily related to the individual surgeon, such as the use of protocolized antibiotics or a multidisciplinary approach to these patients, are also likely contributors to the final outcome.
In conclusion, the rate of serious deep infection after open reduction and internal fixation of displaced intra-articular calcaneal fractures is significantly related to the number of fractures that are operatively treated in a specific hospital. Moreover, the number of patients with symptomatic post-traumatic subtalar arthritis is also significantly related to the fracture load. We conclude that an institutional fracture load of less than one fracture per month per center jeopardizes the outcome of the operative treatment of displaced intra-articular calcaneal fractures.
A table describing all twenty-one included studies is available with the electronic versions of this article, on our web site at jbjs.org (go to the article citation and click on “Supplementary Material”) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).
Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Section of Traumatology, Department of Surgery, University Hospital Maastricht, Maastricht, The Netherlands
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