The effect of obesity on the outcome of total knee replacement (TKR)

Editorial note

Editorial Note (29^th June 2023): Since publication, concerns have been raised to the Editorial Team regarding the ethical approval and the dataset used in this research. The Editorial Team requested the raw underlying data and ethical approval details from the authors on 22^nd March 2023. The authors have not provided the raw underlying data despite repeated requests and issues with the ethical approval remain. The Editorial Team contacted the authors' institution on 22^nd June 2023 in order to seek further information on this matter. The Editorial Team will update this Editorial Note as the situation progresses. Peer review activity has been suspended for this article until an explanation has been provided by the authors or their institution.

Introduction

Osteoarthritis of the Knee (OAK) is common and debilitating degenerative disease, which pins the patients down to the wheelchairs in the later part and requires a Total Knee Replacement (TKR) for relief of pain and to increase mobility. It has been suggested that age, sex and body weight influence the severity of the disease. The prevalence of OA of the knee is unknown but recently it was an estimated that 12.5% of the general population aged ≥45 years suffers from OA of the knee.¹ Among the ethnic Saudi Arabian population OA of the knee was reported to be between 1.19 to 3.5%,^2,3 but in a decade and half the prevalence of clinical OA of the knee jumped to 13%⁴ and radiological OA of knee to 53% in males and 60.9% in females.⁵ Total knee replacement now is an important and successful procedure which can relieve the patients of pain and suffering and limit the complications of immobility in the advanced age. It has been reported that over a million TKRs are performed in the world and the numbers are increasing in many countries.⁶

Complications after TKR can occur are not uncommon and there is a long list which can occur after routine surgery but obesity is known to be an important risk factor in increasing the complications.^7–9 There is enough evidence that complications post TKR in obese patients are higher than those with the normal weight patients, to the extent that in United Kingdom obese patients are being denied surgery before they loose weight prior to TKR.^10,11 In spite of this number of morbidly obese patients with OAK are getting their joints replaced.¹² Studies have also shown that there is no additional risk of complications in obese and morbid obese patients.^13,14

An extensive review of literature did not reveal any reported studies on this aspect in Saudi Arabia nor the Arab world, even though WHO reports 30% of the population in the region is obese and overweight. Hence we decided to retrospectively study the effect of obesity of the outcome of Total Knee Replacement performed at the King Fahd Hospital of the University at AlKhobar.

Methods

The study was carried out after receiving the approval by the Institutional Review Board of Imam AbdulRahman Bin Faisal University, Dammam and informed written consent was taken from all the patients prior to surgery and with approval of publishing the data without revealing their names. STROBE guidelines were followed in reporting of the observational studies. The data of all patients who had undergone primary TKR between 2005 and 2015 were collected from the QuadruMed Patient Care System and crosschecked with the operating room. The biometric data of age, gender, weight, and postoperative follow up, any complications will be collected from the medical charts. Patients were classified as per the BMI (Body Mass Index). BMI is classified as per the WHO classification of 2000¹⁵ (Table 1). Patients were classified as per the WHO classification and grouped accordingly based on the BMI. Only patients who came for final follow up were included for analysis. Gender differences were not taken into consideration for the design of the study nor for analysis of results as only BMI was considered as a factor for complications. At the final follow up Knee society score (KSS) will be filled up. The patients’ the SF-36 questionnaire (version 1) and knee stability, ROM, pain, and functional ability will be assessed and the WOMAC grading were calculated. Only those patients who came for the final follow up and had at least of five years of follow up were included for the analysis. Post hoc power analysis for comparing the four groups was done to and found the sample size was adequate for the comparison. Patients who completed the follow-up period and came for the final examination were compared the t-test. For the statistical analysis, the SPSS Inc. ver 25 was used. All p-values < 0.05 were considered statistically significant.

Results

Two hundred and four patients fulfilled the criteria for inclusion. The demographic data is given in Table 2. The average age 59.8±9.3 years. Right side was operated in 103 and left in 101 patients. The average BMI was 35.88±7.47 (Range 21.95-54.78); mean duration of surgery was 163.37±29.9 (Range 88-250) minutes. The range of follow up was 5-14 years with the average of 7.49±2.56 years. There were 18 (8.8%) complications. Table 3 shows the comparison of outcome based on BMI. One hundred and three (50.5%) of the patients belonged to Class II Obesity (BMI ≥36 kg/m²). Complications related to the surgery are given in Table 4. Between class II obesity and Class III obesity (BMI ≥41 kg/m², the later had 94.4% of the complications. The level of satisfaction was similar in all the groups at 80%. High BMI and longer duration of surgery were important and statistically significant risk factors (p<0.0001 and <0.009) for complications during TKA (Table 5). Table 6 gives the post-operative data on VAS, Modified Knee Scoring Score and WOMAC grading, showing low scores of all the assessment in the patients with higher BMI.

Discussion

Our study shows that patients with higher BMI have higher risk to develop complications after TKR. The second important risk factor we have observed was the duration of surgery. The longer the duration of surgery higher was the risk. There has been a conflicting opinion with regard to the influence of obesity on the outcome of the TKR. DeMik et al (2021)¹⁶ concluded that patients with BMI ≥ 40 kg/m² suffer from higher risk of superficial and deep infections when compared to patients who are non-morbidly obese. Earlier McElroy et al (2013)¹⁷ reported that incidence of complications in obese and morbidly obese patients the observed complications were 15, and 22%. In our study the complications were 18.8% in the two groups. Contrary to this belief, reports also indicates that obese patients undergoing joint arthroplasty do as good as normal weight patients.^18,19 Recent studies concluded that weight of the patients did not effect the outcome in clinical and functional improvement.^20–22 Our study has convincingly showed otherwise. Nearly all patients with Class II and III obesity had complication. This study further supports the policy of United Kingdom, which made mandatory to reduce weight before joint replacement surgery.^10,11 In our study we did not find and difference of complications between male and female patients, but the high BMI was the driving force for increased complications. We concur with the other studies on negative impact of gender on complications.^23,24

Duration of surgery influences complications in any surgery and joint arthroplasty should be an exception. Yasunaga et al (2009)²⁵ suggested that with the average operating time was 127 ± 47 min; they had postoperative complications of 9.8%. A decade down the line Ravi et al (2019)²⁶ reported in their review that the safe cut off point of 100 minutes to be ideal duration and anytime longer than that will carry a risk of deep infection. In our study the average time of the surgery was 163 minutes but in obese patients the average time was ≥20 minutes which could have added to the increased complications.

The prevalence of obesity is increasing in the World and Saudi Arabia is not behind.

Al-Raddadi et al (2019)²⁷ reported that the pervasiveness of obesity in the Saudi Arabian population persists high and preventing measures are not working. This makes the incidence of OAK to become higher as overweight women carry four times and men five times the risk of developing OAK and the association of obesity and OAK is well established.²⁸ More and more obese and morbidly obese patients are being offered TKR and many of these patients ending up with complications, revisions and extortionate levels of morbidity.

Conclusions

Our study indicates that obese and morbidly obese patients undergoing TKR carry a high risk of complications post TKR and these patients should be counseled to reduce weight before they envisage joint replacement to avoid unnecessary complications.