Short-term outcome of isolated lateral malleolar fracture treatment is independent of hospital trauma volume or teaching status: a nationwide retrospective cohort study

The national database of the Swiss Working Group for Quality Assurance in Surgery (Arbeitsgemeinschaft für Qualitätssicherung in der Chirurgie, AQC) was used for data collection. The AQC is an association for prospective data collection and scientific data analyses regarding surgical interventions and diseases. Membership and data entry is voluntary for surgical departments, however the Swiss Surgical Association gives a recommendation to use it. Since the AQC was established in 1995, more than 80 Swiss surgical departments have entered over 1.5 million cases into the database, this accounts for 85% of all Swiss surgical departments [13, 14]. The AQC database provides useful, prospective in-hospital data for scientific studies [15‐17]. Using this database, a retrospective analysis of patients who suffered isolated lateral malleolar fractures between 1998 and 2018 was performed.

We included only patients with an isolated malleolar fracture who were treated operatively between 1998 and 2018. To identify these patients, we used the corresponding World Health Organization (WHO) International Classification of Disease Code (ICD-10) [18] S82.6 and the corresponding Schweizerische Operationsklassifikation procedure code (CHOP Code) [19] 79.36 with its subcategories. Additionally, a complete AQC form must have been available. These criteria were met by 6760 data sets after excluding 1813 patients due to incomplete AQC forms. In this study we used only anonymised data, therefore no additional ethical approval was required according to the local cantonal ethical review board (KEK, Zurich, Switzerland) [20]. Patients must however be informed and give general consent to enter their data prospectively into the AQC database.

During the study period, 69 surgical units provided data for patients with lateral malleolar fractures via the AQC system. The AQC data contain information on patient age and gender, specifications about the type of admission (registered/planned or emergency), insurance status (private or statutory), length of hospital stay, time in the intensive care unit (ICU), concomitant injuries, American Society of Anesthesiologists (ASA) score (physical status classification system), comorbidities, need for reintubation and information about the discharge status (death, home, nursing home, senior residence, rehabilitation clinic and others). Moreover, the following procedural characteristics were available: fracture site (classified according to ICD-10 [18]); education level of the surgeon (divided into three groups—senior attending, junior attending (fellow) and residents); teaching status of the operation; procedure code (coded according to the CHOP code [19]) and duration of the surgery; other interventions; presence and severity of any perioperative complications (no complications, complications with conservative therapy, complications with surgical therapy, complications with long-term damage with conservative therapy and mortality); and the use of thromboembolism prophylaxis and antibiotics [12].

The hospitals providing data for this study were divided into two groups solely based on the number of ankle fracture cases treated surgically during the study period. By dividing the total cases arbitrarily in half, 12 HVCs (n = 3327, 49%; HVC) and 56 LVCs (n = 3433, 51%; LVC) were identified. Mortality, complication rates, and LOS were evaluated as outcome parameters. Independent variables were, among others, HVCs vs. LVCs and teaching status of the procedures. The definition of HVC/LVC is arbitrary—to minimize the grey zone for quantitative differences, we added a subanalysis: the highest 10% (2 centres with 704 patients) and lowest 10% (29 centres with 667 patients) were examined separately.

We extracted our data online from the AQC database using the evaluation tool AdjumedAnalyze (Adjumed Services AG, Zurich, Switzerland) and used the Statistical Package for Social Sciences (SPSS, version 24; IBM Corp., Armonk, NY, USA) for our statistical analysis. Chi-square, Mann–Whitney U and Fisher tests were used where applicable for bivariate analysis. We found no normal distribution in our data based on a Kolmogorov–Smirnov test. Significant (p < 0.05) or nearly significant factors (p < 0.1) in bivariate analysis were chosen as potential risk factors for complications. These risk factors were evaluated as confounders in a stepwise backward likelihood logistic regression analysis. We performed only bivariate analysis with predictors for mortality due to the low number of deaths (n = 15). A p value of < 0.05 was considered statistically significant.

On average, 277 patients (209–382) were treated at HVCs, while 61 patients (1–176) were treated at LVCs. Patients at HVCs were younger (48 vs. 50 years old), predominantly male (52% vs. 48%), had a higher ASA category on average (ASA I 54% vs. 57%, ASA II 41% vs. 37%) and had more comorbidities (26% at HVCs and 19% at LVCs). However, patients categorised as ASA III–V were more often treated at LVCs (5.2%, 0.58%, 0.55% at LVCs vs. 4.1%, 0.06%, 0% at HVCs). The rate of emergency and planned admissions were similar between HVCs and LVCs. The rate of privately insured patients was higher at HVCs (29% vs. 24%). A higher number of open fractures (oFx) were treated at HVCs (n = 16, 0.48% at HVCs vs. n = 5, 0.15% at LVCs) (Table 1).

The most common surgical treatment was open reduction and internal fixation (ORIF) (96%), followed by external fixation (1.5%). ORIF was less frequently used at HVCs compared to LVCs (95% vs. 98%), while external fixation was more frequently used at HVCs (2.5% vs. 0.55%). In the subgroup of oFx treatment, external fixation was more common (33% in the oFx subgroup vs. 1.4% in the closed fracture (cFx) subgroup; p < 0.001). Duration of surgery was slightly longer at HVCs (65 ± 32 min at HVCs vs. 61 ± 28 min at LVCs). Antibiotics were administered in most cases (89%). The usage of prophylactic antibiotics was more common at HVCs (94% at HVCs vs. 83% at LVCs). All patients with an oFx received antibiotics (Table 2).

Overall, the complication rate was 2.5% (3.2% at HVCs vs. 1.9% at LVCs) (Table 1). We found an almost quadruple rate of complications in oFx compared to cFx (9.5% vs. 2.5%; p = 0.041). The most common complications were disturbance of wound healing, secondary dislocation, malpositioning of the implants, lesion to the nerve and hematoma. Predictors for complications were age, ASA III–IV, junior attending vs. senior attending, duration of surgery and hospital volume (Table 3). Preoperative LOS had no influence. On average, the LOS was 6.7 ± 4.9 days (7.2 ± 5 days at HVCs and 6.3 ± 4.8 days at LVCs). A significantly longer pre- and postoperative stay was observed at HVCs. ICU stays were very rare, lasting 0.15 ± 3.6 h when they did occur (even shorter duration at HVCs), and had no statistical significance (Table 1). A significantly longer hospital stay was noticed for the oFx subgroup (15 ± 6.9 for the oFx subgroup vs. 6.7 ± 4.9 for the cFx subgroup, p < 0.001). Most patients were discharged home (92%), followed by discharge to a rehabilitation clinic (2.7%), nursing home (0.75%) or senior residence (0.72%); this was similar for HVCs and LVCs. Fifteen patients died in hospital (0.22%; 0.15% at HVCs and 0.29% at LVCs) (Table 1).

A total of 28% of the operations were performed as teaching procedures. The rate was significantly higher at HVCs (HVCs 30% vs. LVCs 26%) (Table 2). Teaching was not associated with a higher mortality rate (0.16% in teaching yes vs. 0.047% in teaching no) or a higher complication rate (2.8% in teaching yes vs. 2.9% in teaching no). However, a significantly longer operation time (68 ± 29 in teaching yes vs. 59 ± 30 in teaching no) and a prolonged LOS (6.9 ± 5 in teaching yes vs. 6.2 ± 4.7 in teaching no) were observed (Table 4).

Patients in the 10% highest volume centres were slightly older (50 vs. 48 years), sicker (33% vs. 26% comorbidities), more often admitted as planned surgery (24% vs. 17%), more often operated by junior attendings (45% vs 40%) as a teaching procedure (43% vs. 30%) within longer time of surgery (76 vs 65 min) than in the other HVC. ORIF was the primary treatment in 90% (vs. 95%). The length of stay and outcome were similar.

Patients in the 10% lowest volume centres were quite similar with the other LVC cohort.

The subgroup analysis of the top-10% and low-10% centres confirmed the results of the HVC vs. LVC evaluation—except for age (Tables 5 and 6).