The impact of elective total hip and knee arthroplasty on physical performance in orthogeriatric patients: a prospective intervention study

This study is part of the ongoing Special Orthopaedic Geriatrics (SOG) trial (German Clinical Trials Register, 19/01/2021, DRKS00024102). The SOG study is a monocentric, prospective, randomised controlled trial funded by the German Federal Joint Committee (GBA). The original study aimed to investigate a specially developed multimodal care model (SOG care model) for orthogeriatric patients with total hip and total knee arthroplasty compared to usual orthopaedic care without orthogeriatric co-management. Physical performance as measured by the SPPB was the primary outcome measure. A detailed description of the study can be found elsewhere [13]. The current study enrolled 145 patients from the SOG trial between 01April 2021 and 15 April 2023. This additional analysis was not planned when the original study was designed.

In the Orthopaedics Department of our University Centre, about 18,000 patients are treated annually in the university outpatient clinic and > 1,500 endoprosthetic procedures on hip and knee joints are performed each year. Participants were recruited at the university outpatient clinic if they were diagnosed with primary hip or knee osteoarthritis and had an indication for THA or TKA. The study data were collected preoperatively (t1), 3 and 7 days postoperatively (t2 and t3), 4–6 weeks (t4) and 3 months (t5) after surgery.

Eligibility criteria included: primary hip or knee osteoarthritis, age ≥ 70 years and multimorbidity or age ≥ 80 years and indication for elective unilateral hip or knee replacement. Exclusion criteria were age < 70 years, previous bony surgery or tumour in the area of the joint to be treated, acute infection and increased need for care (care level ≥ 4; severe impairment of independence, need for help with basic care 24 h a day).

Out of a total of 145 subjects in the SOG study, there were 10 drop-outs. The reasons were cancellation of surgery or refusal to participate in the study. As a result, the number of people included in the analysis was 135. In 5 participants, SPPB could not be performed on postoperative days 3 and 7. The number of patients lost to follow-up was 8 at 4–6 weeks (follow-up 1) and 8 at 3 months (follow-up 2).

All operations were performed in a single Department of Orthopaedic Surgery of a University Medical Centre. The lateral decubitus position was used for the THA. A minimally invasive anterolateral approach was chosen [14]. Press-fit acetabular components and stems from a single manufacturer (Pinnacle cup, Corail stem; DePuy, Warsaw, IN) were used in all THAs. Cementless stems were preferred. Knee arthroplasty was performed via a medial parapatellar approach. Cemented components from a single manufacturer (PFC Sigma; DePuy) were used in all TKAs. Patella resurfacing was not performed. All patients were mobilised under full weight bearing immediately after surgery. Postoperatively, patients with THA and TKA remained in hospital for 7 days unless complications occurred. They received daily physiotherapy and were then discharged to inpatient rehabilitation. With a few exceptions, outpatient rehabilitation was performed at the patient’s request. Most patients were transferred to the rehabilitation clinic belonging to the hospital. The duration of inpatient and outpatient rehabilitation was three weeks.

Physical performance was measured using the Short Physical Performance Battery (SPPB), a commonly used and validated assessment in geriatrics that includes three objective tests of lower body function [8]. SPPB evaluates balance, mobility and muscle strength by examining an individual’s ability to stand in different positions, time to walk 4 m, and time to rise up from and sit down on a chair 5 times. The individual tests are scored between 0 and 4, with a maximum total score of 12 (range 0–12). Higher total scores indicate better lower body function [10, 15]. Small meaningful changes in the SPPB are present at 0.5 points, substantial changes are assumed from a 1-point improvement [16].

Descriptive statistics including demographic and morbidity-related characteristics were calculated for the whole sample. As a core statistical method, the non-parametric Friedman test was employed, as an alternative to the one-way repeated measures ANOVA. The Friedman test was preferred due to the scale and distribution of the outcome variable. It was tested whether there were significant differences between the five times of measurement, with the SPPB score being the dependent variable of interest. Medians and interquartile ranges were reported for each time of measurement alongside the respective p-values yielded by the Friedman test. Post-hoc tests were then performed for significant differences comparing all of the time points against each other using Wilcoxon signed-rank tests. In this procedure Bonferroni-correction was applied to reduce the risk of a type I error. Effect sizes and p-values will be reported for each comparison. Further analyses included Friedman tests as well as post-hoc tests for hip replacement surgery patients and knee replacement surgery patients separately as well as for each of the three subscores (standing balance, 4 m gait speed test, and the timed five-repetition sit-to-stand test) of the SPPB. Taking into account the drop-outs and patients lost to follow-up described under study population, the following number of patients were available for the analyses: t1: n = 135, t2: n = 130, t3: n = 130, t4: n = 127, t5: n = 127. All analyses were conducted in R version 4.2.1. using the package using the R-package “rstatix”. p-values p < 0.05 were considered statistically significant.