Significant results and other interesting aspects of the results will be discussed in this section. The results show correlation between the length of the operation for THA and the necessity for reoperation as the result of PJI. That is, long operative time constitutes a significant risk as each 10-min interval of surgery considerably increased the risk for reoperation. Other studies also confirm the risk of prolonged operative times related to complications [19, 20]. Overall, in various surgical procedures, the mean operative time was 30 min longer in operations followed by a SSI compared to those without SSI [20]. Time of exposure to air is a risk factor due to possible microbiological contamination of the wound [21] and therefore it should be short. “Chasing minutes” during a surgical procedure is multifaceted and must be carried out without comprising quality of care. For example, careful closure of the tissue layers reduces wound leakage [22]. However, operative time should never be longer than necessary. Experienced surgeons and surgical teams (i.e., high annual surgeon volume) is associated with less adverse events such as reoperation [23]. Typically, well-functioning surgical teams have clear strategies and skilled communication, characteristics associated with effective and safe care [24]. The cause of prolonged operative times need to be identified at each clinic performing THA.
In our studied population, the lateral surgical approach was associated with more reoperations as the result of PJI than the posterior surgical approach. A previous study [25] found that elective primary THA using the posterior surgical approach had a significantly lower rate of the most common complications (PJI, fracture, and prolonged wound drainage), although pain and functional outcomes were not considered. Both the lateral and posterior approach are commonly used worldwide when performing THA, and they both have their advantages and disadvantages. Choice of approach is closely related to the surgeon’s experience and comfort with one approach over another. The importance of the surgeon’s experience in a specific approach should not be underestimated [26].
The association between being overweight and PJI is difficult to determine. The linear association between BMI and PJI may not apply to THA. Both sex and age affect how being overweight can be used as a predictor for PJI. Surgeons need to consider each patient’s individual conditions to decide a reasonable limit for BMI [27]. The results in our study show that obesity classes 1–3 (BMI > 30) represent significant risk for reoperation as the result of PJI after THA. Therefore, patients should receive fact-based and transparent information about the risks associated with obesity. As individual consultation with a dietitian makes a small but significant difference in weight control [28], there could be value in studying the role of dietitians in weight management for this group of patients (i.e., patients with BMI > 30 who need THA). Moreover, weight loss needs to be controlled to avoid performing surgery on patients with poor nutrition status.
Clinical association between unidirectional airflow and decreased rates of PJI is still unclear and controversial. Overreliance on ventilation systems may weaken strict OR discipline, ultimately increasing rather than decreasing the risk [29]. However, a study based on data from the Norwegian Arthroplasty Registry showed lower risk for reoperation when surgery was performed in ORs with unidirectional airflow compared to conventional ventilation, which is the same as mixed turbulent airflow [30].
The increased risk for reoperation caused by PJI regarding age and ASA class were expected. ASA class defines morbidity well and with increased age more physical limitations come into play. It is clear that men are at higher risk than women for reoperation, but it is not clear why this is so. However, compared to women, men tend to have worse overall physical health, a fact that might explain why men have a higher risk for reoperation [31].
Strengths and limitations
The main strength of registry studies in general is that data already exist and the research includes complete study populations [32]. The 35,056 cases in this study represent a total population even though the sample was reduced because the SPOR was incomplete during first and second year of data collection. Cases not registered in SPOR more often had their surgery at private clinics, were younger, were less morbid, and required fewer reoperations due to PJI. Variables with low coverage registered in SPOR were not used in this study.
This is the first study to link the data in SHAR and SPOR and therefore adds new valuable data to orthopaedic registry-based research.
All patients who met inclusion criteria and included in both registries between 2015 and 2019 were included. This study excluded patients with trauma and fracture due to THA, another strength of the study as it reduced heterogeneity. Higher rates of PJI within that group of patients could be a confounder due to different preoperative circumstances.
Ventilation type is reported annually to SHAR. This information was manually controlled to specifically control each operating room to a specific type of ventilation. Although this was time consuming, it ensured data were correct.
This registry study has some limitations. Change of practice and differences in registration may have varied over time, possibly affecting the outcome. In addition, as SPOR is relatively new, some variables had insufficient data. For example, we could not analyse number of people present inside OR during surgery, time interval between preoperative antibiotics and start of surgery, body temperature at the end of surgery, interesting aspects that need to be investigated when data are more complete. Follow-up of 1-year may be seen as a limitation. Longer follow-up may have strengthened data and the conclusions derived from its analysis.
