Reoperation and Complication Rates after Hip and Knee Replacement Surgery in 1 046 145 Obese Patients

The worldwide prevalence of obesity has nearly tripled since 1975. Between 1999 and 2017 it rose from 30.5 to 42.4% in the USA and from 11.5 to 16.3% in Germany (1). Obesity is a risk factor for osteoarthritis of the hip and even more so of the knee, which is why obese patients often present for joint replacement. However, they have a greater risk of complications in comparison with the non-obese. So far, studies dealing with this issue have only examined smaller cohorts, while data from Germany are lacking altogether. The aim of our study was to examine the association between obesity and complication rates, revision rates, and mortality after primary and revision replacement surgery of the hip and knee (HRS, R-HRS, KRS, R-KRS), respectively.

Methods

The data for this study were taken from pseudonymized inpatient billing data and insured persons’ master data of the AOK (General Local Health Insurance Funds). The analyses included primary hip and knee replacement surgery (HRS, KRS) and revision replacements (R-HRS, R-KRS) performed during the period 1/2008–12/2017. Obesity was classified into the following categories: Grade 1: body mass index (BMI) 30–34 kg/m² (ICD-10 code: E66.X0); Grade 2: BMI 35–39 kg/m² (ICD-10 code: E66.X1); Grade 3: BMI ≥40 kg/m² (E66.X2); reference category: BMI less than 30 kg/m². The association between BMI categories and the endpoints 90-day mortality, one-year revision surgery, 90-day post-operative complications, and severe general complications during hospital stay was analyzed using multiple logistic regression models, and adjusted odds ratios (OR) were calculated with 95% confidence intervals (CI) and robust sandwich variance estimators. Adjustments were made for age, sex, implant type, previous joint replacement of the same joint (number of exchange procedures within ten years prior to the index operation; only R-HRS, R-KRS), antithrombotic medication in the previous year, actual operation year, and comorbidities. Comorbidities were defined by the Elixhauser classification system (2) without the variable “obesity”.

Results

A total of 1 046 145 inpatient cases from the years 2008 to 2017 were included in the analysis: 448 424 HRS, 63 581 R-HRS, 485 835 KRS, and 48 305 R-KRS. The median age was 71 years each for HRS, KRS, R-KRS. Patients with R-HRS were a median of three years older at 74 years. Sixty-one percent of the HRS and R-HRS cases and 67% of the KRS and R-KRS cases were females. During the study period, the proportion of patients with obesity increased, especially the share with a BMI equal to, or more than, 40 kg/m². Overall, obesity was more common amongst the knee cohorts and was documented in 24.2% of the KRS cases, 24.7% of R-KRS, 16.1% of HRS, and 14.5% of R-HRS.

Obesity was associated with a greater risk of revision surgery and of surgical and general complications in all the groups (Table 1). A BMI of more than 40 kg/m², in particular, increased the risk of complications (for example, one-year revision surgery for BMI equal to, or more than, 40 kg/m²: HRS: odds ratio: 2.6 (95% confidence interval [2.4; 2.8]), R-HRS: 1.7 [1.5; 1.9], KRS: 1.4 [1.3; 1.5], R-KRS: 1.3 [1.1; 1.5]). The risk of revision surgery due to dislocations increased with a higher BMI in the primary hip replacement cohort, whereas it fell for revision hip replacement (Table 2). The risk of mortality was only increased with a BMI equal to, or more than, 40 kg/m² in the HRS and KRS cohorts (BMI ≥40: HRS: 1.5 [1.2; 1.9], KRS: 1.4 [1.1; 1.8]).

Table 1

Risk-adjusted association between BMI and complications up to one year after primary and revision hip and knee replacements

Table 2

Risk-adjusted association between BMI and revision surgery up to one year after primary and revision hip and knee replacements

Discussion

In our study, obesity was associated with an increased risk of revision surgery within one year. Moreover, in the HRS cohort, the risk of revision surgery rose with each BMI category. More recent studies have shown that obesity is connected with an increased risk of aseptic loosening and subsequent implant exchange (3, 4). There are also reports of an increased infection rate in obese patients with subsequent implant removal or exchange following HRS (3, 4), KRS, R-HRS (5) and R-KRS. Revision procedures for dislocation rose in the HRS cohort with increasing BMI category, whereas they decreased in the R-HRS cohort with increasing BMI. The latter finding contradicts other studies which report of an increased rate (5).

The increase in the risk of a surgical complication after HRS and KRS with each increasing BMI category which we discovered in our study concurs with the majority of earlier studies (2, 3). In all cohorts, obese patients also continued to show higher rates of adverse events in hospital, which was particularly evident in those with a BMI equal to, or more than, 40 kg/m². Mortality within 90 days was only increased in individuals with an obesity grade 3 in the HRS and KRS cohorts.

The present study examined patients exclusively from the General Local Health Insurance Funds. They could differ from other insured individuals with respect to their patient characteristics. For this reason, our analysis was risk-adjusted with regard to age, sex, and comorbidities. Furthermore, routine data were used which had been collected for billing purposes and were regularly checked for accuracy.

Elke Jeschke, Thorsten Gehrke, Christian Günster, Karl-Dieter Heller, Hanna Leicht, Jürgen Malzahn, Fritz Uwe Niethard, Peter Schräder, Josef Zacher, Andreas M. Halder

Conflict of interest statement

KDH is Past President of the German Endoprosthetics Society. The other authors declare that no conflict of interests exists.

Manuscript received on 23 November 2022, revised version accepted on 06 March 2023.

Translated from the original German by Dr. Grahame Larkin MD.

Cite this as:
Jeschke E, Gehrke T, Günster C, Heller KD, Leicht H, Malzahn J, Niethard FU, Schräder P, Zacher J, Halder AM: Reoperation and complication rates after hip and knee replacement surgery in 1 046 145 obese patients. Dtsch Arztebl Int 2023; 120: 501–2. DOI: 10.3238/arztebl.m2023.0067

References

1. [Body-Mass-Index der Bevölkerung, unter anderem nach Alter]. In.: [Statistisches Bundesamt] 2020.

2. Elixhauser A, Steiner C, Harris DR, Coffey RM: Comorbidity measures for use with administrative data. Med Care 1998; 36: 8–27

3. Onggo JR, Onggo JD, de Steiger R, Hau R: Greater risks of complications, infections, and revisions in the obese versus non-obese total hip arthroplasty population of 2,190,824 patients: a meta-analysis and systematic review. Osteoarthritis Cartilage 2020; 28: 31–44

4. Liu W, Wahafu T, Cheng M, Cheng T, Zhang Y, Zhang X: The influence of obesity on primary total hip arthroplasty outcomes: a meta-analysis of prospective cohort studies. Orthop Traumatol Surg Res 2015; 101: 289–96

5. Kenney C, Dick S, Lea J, Liu J, Ebraheim NA: A systematic review of the causes of failure of revision total hip arthroplasty. J Orthop 2019; 16: 393–5