Abstract
Introduction
Carbon emissions are one of the greatest contributors to the acceleration of climate change. (Rajak, 2021) With the direct and indirect impacts on human health expected as the atmosphere warms, it is essential that the medical sector reduces its carbon emissions to slow the progression of climate change. (Bartholy & Pongrácz, 2018; Rossati, 2017) Within the medical sector, orthopaedic surgery produces the most waste of any speciality, with the sub- speciality of arthroplasty creating the most waste of all of the orthopaedic sub-specialities. (Kooner et al., 2020) This thesis investigates the carbon emissions of the two most common fixation techniques for total knee and hip arthroplasty to identify a method for reducing the carbon emissions of these procedures. It is expected to be found uncemented fixation for TKA and THA will emit less CO2e than cemented fixation. This is because intraoperatively procedures using uncemented fixation are expected to take less time and create less waste as the cementation process requires extra time for the bone cement to set and extra waste from the mixing apparatus.
Literature Review
3 fields of literature were investigated and analysed to provide the basis of knowledge required to complete the subsequent study.
The first field was the examination of carbon emissions, their impacts, and proven ways to reduce them. In this section, the extent that global warming will have on the earth's environment was investigated. Warming of the earth's atmosphere leads to multiple downstream impacts that can further increase the speed at which global warming occurs.
(Rajak, 2021; Rossati, 2017) The impacts on human health can be indirect or direct ranging from an increased risk of infectious diseases and increased allergens and pollutants in the air, which increase the risk of respiratory diseases, to increased hospitalisation due to cardiovascular problems with increased temperature and increased radiation exposure with the depletion of the ozone layer increasing the risk of skin cancers. (Bartholy & Pongrácz, 2018; Rossati, 2017)
The second field investigated is how carbon emissions and carbon footprints are calculated for a specific process or procedure. It was found that a total carbon footprint is calculated using life cycle assessments (LCAs). LCAs can be conducted in two different ways, the top- down or bottom-up approach. (Pandey et al., 2011; Rizan et al., 2020) The bottom-up approach was decided as the most appropriate to be used in the subsequent study. However, it was not applicable to the timeframe of the study. Instead, the investigation of individual variables that are most likely to contribute to a difference in carbon emissions for the two investigated fixation techniques for TKA and THA. 5 variables were found from similar studies that investigate the carbon emissions of different surgical procedures. These variables are waste, energy consumption of the operating theatre, anaesthetic consumption, acquisition of bone cement and acquisition of prostheses.
The final field investigated is the clinical differences of fixation techniques for TKA and THA. This includes differences in the methodology, prostheses, indications for either fixation technique, revision rates, patient-reported outcome measures and other unfavourable outcomes. In this section, it was found that the difference in the methodology across fixation techniques is only the use of bone cement in cemented TKA and hybrid THA, with no other differences in the way the procedure is performed. (Maggs & Wilson, 2017) The prostheses
differ only in the way the bone-prostheses or cement-prostheses interface is manufactured. For prostheses fixated using uncemented osseointegration, the bone-prostheses interface is grit or plasma spraying with hydroxyapatite to create the pores that allow for optimal bone growth onto the prostheses. (Maggs & Wilson, 2017) Prostheses fixated using cementation, the cement-prostheses interface can be polished smooth or be rough as the PMMA doesn’t stick to the prostheses but rather acts as a grout wedging between the prostheses and the bone to fixate it in place. (Maggs & Wilson, 2017) Using cemented fixation is indicated for in two types of patients for both TKA and THA, patients that have severe osteoporosis and patients who have had bone irradiation for the treatment of bone cancers are both indicated for cemented fixation. Both conditions reduce the ability of the bone to grow and undergo osseointegration with the prostheses if uncemented fixation is used. (Anderson et al., 2020; Krishnan et al., 2012) Cemented fixation is also indicated in patients that have a Dorr type C femur which is an abnormally wide femoral canal. The bone cement provides an adequate connection between the bone and the prostheses required for successful fixation that cannot be obtained using uncemented fixation in patients with this type of femoral canal. (Johanson et al., 2011) There were no differences found in the revision rates for different types of fixation techniques used across both TKA and THA procedures. (Corbett et al., 2010; Kim et al., 2014; Miller et al., 2018; Nugent et al., 2019; Prasad et al., 2020; Swarup et al., 2018; Toci et al., 2022; Wechter et al., 2013)Within the research investigated most commonly, it was shown there was no difference within all investigated outcomes regardless of fixation technique. However, in some of the studies investigated showed reduced revision rates in cemented fixation for both TKA and THA and some studies investigated showed reduced revision rates in uncemented fixation for both TKA and THA.
Method
All data used in the study was collected at Burwood Hospital in Christchurch, with data collected from 5 cases from each study group. In each case, five variables that were identified in the literature review that were most likely to cause a difference in the carbon emissions between fixation techniques for TKA and THA were investigated. Three of these variables are impacted by intraoperative factors and therefore considered intraoperative, these variables are waste, energy, and anaesthetic usage. Each of these variables was measured by its determining factor during the procedure; waste was weighed, energy usage was calculated by the time the patient spent in theatre, and anaesthetic usage was calculated by the time the patient spent under anaesthetic. From this raw data, calculations then allowed for the conversion into CO2e emitted from each variable. The final two variables are impacted by extra-operative factors and therefore considered extra-operative, these variables are the acquisition cost of bone cement and prostheses. Using acquisition data, the CO2e emitted by these two variables from manufacturing and shipping to Burwood Hospital is accounted for.
Results
The study showed that when comparing the overall CO2e emitted from TKA and THA procedures, the use of cemented fixation resulted in less CO2e being emitted than procedures using uncemented fixation. This difference is due to the prostheses used for cemented fixation costing less to manufacture and therefore having a lower calculated CO2e emitted from acquisition than prostheses used for uncemented fixation. This result is the opposite of what was predicted in the hypothesis.
Conversely when only comparing the CO2e emitted from the three intraoperative variables TKA and THA procedures using uncemented fixation emit less CO2e than TKA and THA
procedures using cemented fixation. This is because uncemented fixation requires less time to complete and creates less waste without the need for additional single-use equipment such as cement mixing apparatus. This is the expected result as predicted in the hypothesis.
The amount of CO2e emitted from the acquisition of prostheses required by both procedures was so large it drowned out the results from the other four variables. It resulted in the overall results showing that cemented fixation emits less CO2e than uncemented fixation. However, uncemented fixation emitted less CO2e than cemented fixation for all other variables.
Conclusion
When analysing the study multiple limitations were found that resulted in a lack of both internal and external validity. These limitations showed that the quantification for the difference in CO2e emitted from uncemented and cemented fixation used in TKA and THA was inaccurate. However, there is confidence in saying that intraoperatively uncemented fixation emits less CO2e than cemented fixation for TKA and THA but this difference cannot be quantified at this time.
From this thesis including the literature review and clinical study, it has been found that much more research will need to occur within this field before similar studies can be conducted in a more efficient and effective while creating accurate quantifications for the CO2e emitted from medical procedures. It is recommended that the first step is creating an easy-to-use but accurate LCA process for medical procedures. This process will allow for quick and simple calculations of the CO2e emitted from medical procedures accurately and allow for larger study groups and sample sizes increasing the external validity for studies of similar natures.