DOI: https://doi.org/10.21203/rs.3.rs-2372579/v1
Background: No consensus has been reached on which is better in terms of functional outcomes between simultaneous bilateral and unilateral total knee arthroplasty (TKA). As patient characteristics, such as age, sex, and body mass index, have significant effects on functional outcomes after TKA, we should match these factors before making comparisons. This study aimed to compare time courses in functional outcomes between simultaneous bilateral TKA and unilateral TKA after matching the patient characteristics.
Methods: In this retrospective study, we reviewed the clinical records of patients admitted to our hospital. After excluding the patients who did not meet the criteria, 43 underwent simultaneous bilateral TKA and 382 underwent unilateral TKA were included in this study. We performed propensity score matching for age, sex, and body mass index between simultaneous bilateral and unilateral TKA patients. We measured pain intensity, knee extensor strength, and knee-specific functional outcomes using the new knee society score, including total score, symptoms, patient satisfaction, patient expectations, and functional activities preoperatively and at 3 and 12 months postoperatively. Two-way repeated analysis of variance was performed to compare the time courses in functional outcomes between simultaneous bilateral and unilateral TKA.
Results: After propensity score matching, 40 patients each for underwent bilateral TKA and unilateral TKA were selected. Knee extensor strength in simultaneous bilateral TKA patients was significantly lower than that in unilateral TKA patients at 3 months postoperatively (p = 0.04). A significant interaction was observed between the effects of time and group on knee extensor strength (F [1, 78] = 3.338; interaction: p = 0.042; η2 = 0.052). No significant interactions were found among the other variables measured.
Conclusions: Patients who underwent simultaneous bilateral TKA showed delayed recovery in knee extensor strength at 3 months postoperatively, but recovered to the same level at 12 months postoperatively. Patients who underwent simultaneous bilateral TKA should undergo postoperative rehabilitation focused on alleviating delayed recovery in knee extensor strength during the acute phase.
Total knee arthroplasty (TKA) has been proven as a safe surgical procedure for patients with end-stage knee osteoarthritis [1] and a cost-effective intervention for improving knee pain and physical function [2]. Some patients with knee osteoarthritis have bilateral symptoms [3] and require simultaneous bilateral TKA, which is defined as the surgery of both knees in a single surgery. While simultaneous bilateral TKA is superior in terms of cost, length of rehabilitation [4], perioperative blood transfusion parameters, and complications rates, mortality rates are higher for patients with simultaneous bilateral TKA than those with unilateral TKA [5, 6].
Many studies have compared the functional outcomes between simultaneous bilateral and unilateral TKA [7–10] and no consensus has been reached on which is better in terms of functional outcomes. Huang et al. [7] reported no differences in the recovery of pain, stiffness, and knee function between simultaneous bilateral and unilateral TKA, whereas March et al. [8] reported that the recovery of physical function in patients with simultaneous bilateral TKA was better than that in those with unilateral TKA. Several reasons for the lack of consensus have been identified. First, in these studies, patient characteristics, such as age, sex, and body mass index (BMI), were not adjusted between simultaneous bilateral and unilateral TKA cases. As patient characteristics have significant effects on functional outcomes after TKA [11–13], we should match these factors before making comparisons to clarify the differences in functional outcomes between simultaneous bilateral and unilateral TKA. Second, previous studies have only compared functional outcomes at a single point [7–10]. Few studies have compared the time course of functional outcomes. Patients with unilateral TKA may show better pain control and early functional recovery than the patients with simultaneous bilateral TKA in the short term because unilateral TKA has a shorter operation time and lower blood loss than simultaneous bilateral TKA.
Thus, this study sought to compare the time courses in functional recovery between simultaneous bilateral TKA and unilateral TKA after matching the patient characteristics. We hypothesized that the patients with unilateral TKA have greater improvement in functional outcomes in the short term than those with simultaneous bilateral TKA, but no differences between the two in the long term. The results of this study could provide new evidence for improving functional outcomes after TKA.
In this retrospective study, we reviewed the clinical records of patients admitted to our hospital between January 2018 and June 2020. A total of 538 patients who underwent TKA were assessed both clinically and radiographically at 1 month preoperatively and 3 and 12 months postoperatively. All surgical procedures were performed by five trained surgeons using the medial para-patellar approach. The inclusion criteria were as follows: (i) undergoing TKA for knee osteoarthritis assessed as grade 3 or 4 on the Kellgren–Lawrence radiographic grading system (KL grade) and (ii) walking independently with the use of a cane or other gait-assisting tools. The exclusion criteria were as follows: (i) could not be followed up for up to 1 year postoperatively and (ii) neurological conditions, such as Parkinson’s disease or stroke. A total of 526 patients met the inclusion criteria. After the exclusion of patients who could not be followed up for up to 1 year after surgery (n = 98) or who had neurological conditions (n = 3), 425 patients were ultimately selected for the study. This research was approved by the Institutional Review Board of the authors’ affiliated institutions. All participants provided written informed consent in accordance with the Declaration of Helsinki.
During their postoperative stay in the hospital, the patients with unilateral TKA were treated twice daily for 40 min by physiotherapists and received standard inpatient rehabilitation for 5–7 days, whereas the patients with simultaneous bilateral TKA underwent the same rehabilitation program as those with unilateral TKA twice daily for 60 min for 12–14 days. All patients received weekly outpatient rehabilitation for 6 months. Inpatient rehabilitation consisted of passive knee range-of-motion exercises, patellofemoral joint mobilization as needed, lower extremity flexibility exercises for the quadriceps and calves, icing, gait training, and functional training for stair climbing and descending. Non-weight resistance training, such as isometric quadriceps setting, was administered. Range-of-motion and resistance exercises were each performed 20 times during the treatment session and were carried out at an intensity level that enabled patients to manage their pain. After discharge from the hospital, patients received outpatient physiotherapy once per week. Outpatient rehabilitation consisted of passive and active knee range-of-motion exercises, quadriceps strengthening, gait training, and activities of daily living training (i.e., climbing and descending stairs). Additionally, all patients were prescribed a standard home exercise program that was performed twice daily. The home exercise program included active knee range-of-motion exercises and strengthening exercises for the quadriceps, hip abductors, and hip extensors in both weight-bearing and non-weight-bearing conditions [14].
The new knee society score (new KSS) questionnaire was used to assess knee-specific functional outcomes [15, 16]. The new KSS consists of four categories: symptoms (3 items, 25 points), patient satisfaction (5 items, 40 points), patient expectations (3 items, 15 points), and functional activities (19 items, 100 points), which is further divided into walking and standing (5 items, 30 points), standard activities (6 items, 30 points), advanced activities (5 items, 25 points), and discretionary activities (3 items, 15 points). Higher scores represent lower pain and greater patient satisfaction, expectations, and physical functioning. The new KSS is a validated and reliable instrument for use before and after TKA [17].
Pain intensity was evaluated using the numerical rating scale (NRS). The NRS is a valid and reliable instrument used in clinical practice due to its high degree of sensitivity [18]. In this study, the NRS was used to quantify knee pain during walking. Patients were asked to verbally rate walking pain on a scale from 0 to 10 immediately after walking, with 0 representing no pain and 10 representing the worst pain imaginable.
Knee extensor strength was measured as the maximal isometric strength using a hand-held dynamometer (µTas F1; ANIMA, Chofu, Japan). This method uses a belt to measure the strength of knee extension, and has been shown to be highly reliable [19] and produce results consistent with those of the isokinetic dynamometer method [20]. Participants were seated with their hips flexed to 90° and the knees flexed to 75°. They were instructed to extend the knee maximally for 3 s under verbal encouragement to facilitate the maximal volitional force production. Peak torque was estimated as the product of the force being exerted and the distance between the attachment of the dynamometer and the center of rotation of the knee joint. The maximal contraction was attempted twice, and the trial that produced the higher volitional force was normalized to body weight and used for analysis.
We collected demographic data, such as age, sex, weight, height, BMI, and bilateral KL grade, from medical records. Knee range of motion was measured using a standard 2-arm plastic goniometer, with the axis of the goniometer placed over the lateral epicondyle of the femur, the proximal arm aligned with the greater trochanter of the femur, and the distal arm aligned with the lateral malleolus of the ankle. Gait speed was measured twice for each participant at 1 month preoperatively. All participants were instructed to walk at their preferred speed along a 16-m smooth, horizontal walkway. A 10-m section of the walkway was marked off by two lines positioned 3 m from each end to allow space and time for acceleration and deceleration. The time taken to complete the middle 10-m distance was recorded to the nearest hundredth of a second using a stopwatch [14].
Participant characteristics represented by continuous variables were expressed as mean ± standard deviation after confirming normal distributions of their data using the Shapiro–Wilk test. Categorical variables were expressed as frequencies and percentages. In simultaneous bilateral TKA cases, the mean of the bilateral values were used.
First, we performed propensity score matching to match patient characteristics between simultaneous bilateral TKA and unilateral TKA cases. Second, we compared baseline characteristics and preoperative knee function in both sets of patients after propensity score matching. The differences between the patient groups were analyzed using Student’s t-test for continuous variables and the Mann–Whitney U test for non–normally-distributed variables. Finally, we performed a two-way repeated analysis of variance (ANOVA) to examine the differences in the `time courses between simultaneous bilateral and unilateral TKA. If two-way repeated ANOVA showed significant interactions, a Bonferroni post hoc test was used to identify the mean difference. The statistical significance level was set at p < 0.05. All analyses were performed using SPSS for Windows 28.0 version (IBM, Tokyo, Japan).
Of the 425 patients, 43 underwent simultaneous bilateral TKA, whereas 382 underwent unilateral TKA. We performed a propensity score matching to match patient characteristics for age, sex, and BMI. After propensity score matching, 40 patients were selected for each simultaneous bilateral TKA and unilateral TKA (Fig. 1).
Table 1 summarizes the baseline characteristics and knee function of simultaneous bilateral and unilateral TKA cases after propensity score matching. The baseline characteristics, such as age, sex, and BMI, between simultaneous bilateral TKA and unilateral TKA were well matched (simultaneous bilateral vs. unilateral: age, 67.3 ± 7.5 vs. 67.7 ± 7.0; sex (female), 27 vs. 27; and BMI, 27.1 ± 4.6 vs. 27.0 ± 4.4). Additionally, there were no significant difference in the new KSS score, pain intensity, knee extensor strength, knee range of motion, and gait speed at preoperatively.
| Variable | Simultaneous bilateral TKA patients (n = 40) | Unilateral TKA patients (n = 40) | p-value |
|---|---|---|---|
| Age, years | 67.3 ± 7.5 | 67.7 ± 7.0 | 0.74 |
| Female, n (%) | 27 (67.5%) | 27 (67.5%) | 1.00 |
| Height, cm | 157.8 ± 8.5 | 158.6 ± 8.6 | 0.67 |
| Weight, kg | 67.5 ± 12.1 | 68.3 ± 13.6 | 0.78 |
| BMI, kg/m2 | 27.1 ± 4.6 | 27.0 ± 4.4 | 0.95 |
| KL grade in the surgical limb | |||
| 3/4, R, L | 10/30, 8/32 | 8/32 | 0.79, 1.00 |
| KL grade in the nonsurgical limb | |||
| 1/2/3/4/TKA, n | - | 6/10/7/12/5 | - |
| Preoperative knee function | |||
| New KSS, score | |||
| Total | 82.4 ± 19.7 | 84.7 ± 18.2 | 0.60 |
| Symptom | 7.8 ± 4.9 | 8.4 ± 4.2 | 0.76 |
| Patient satisfaction | 12.3 ± 4.0 | 12.4 ± 4.5 | 0.78 |
| Patient expectation | 13.4 ± 2.2 | 13.2 ± 3.0 | 0.68 |
| Functional activities | 49.1 ± 17.1 | 50.9 ± 16.8 | 0.59 |
| Pain intensity, NRS | 6.2 ± 2.6 | 5.8 ± 1.8 | 0.56 |
| Knee extensor strength, N⋅m/kg | 0.91 ± 0.41 | 0.94 ± 0.37 | 0.81 |
| Knee flexion ROM in the surgical limb, degree, R, L | 120.1 ± 17.2, 121.3 ± 13.4 | 124.3 ± 10.7 | 0.053, 0.06 |
| Knee extension range of motion in the surgical limb, degree, R, L | −9.2 ± 6.3, − 9.6 ± 6.5 | −8.5 ± 6.6 | 0.84, 0.62 |
| Gait speed, m/s | 0.99 ± 0.26 | 1.06 ± 0.27 | 0.37 |
| Data are expressed as mean ± standard deviation. BMI, body mass index; KL grade, Kellgren–Lawrence grade; New KSS, new knee society score; NRS, numerical rating scale | |||
Table 2 summarizes the results of two-way repeated ANOVA performed at 1 month preoperatively and at 3 and 12 months postoperatively after TKA. In both patients with simultaneous bilateral and unilateral TKA, new KSS total, symptoms, patient satisfaction, functional activities, and pain intensity were significantly improved at 3 and 12 months postoperatively compared with the preoperative values, whereas knee extensor strength was significantly improved at 12 months compared with the preoperative values. New KSS total, patient satisfaction, functional activities, and knee extensor strength were significantly improved at 12 months compared with those at 3 months. In patients with simultaneous bilateral TKA, knee extensor strength was significantly lower than that in patients with unilateral TKA at 3 months postoperatively (simultaneous bilateral TKA: 0.85 ± 0.34; unilateral TKA: 1.00 ± 0.24, p = 0.04). A significant interaction was observed between the effects of time and group on knee extensor strength (F [1, 78] = 3.338; interaction: p = 0.042; η2 = 0.052). No significant interactions were observed among the other variables measured.
| Preoperatively | 3 months preoperatively | 12 months postoperatively | Group × Time | Effect size | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| F-value | η2 | |||||||||
| New knee society score | ||||||||||
| Total | S-Bilateral | 82.4 ± 19.7 | 122.3 ± 25.5 | † | 135.8 ± 22.4 | †, ‡ | 0.100 | 0.002 | ||
| Unilateral | 84.7 ± 18.2 | 123.1 ± 26.9 | † | 139.6 ± 22.9 | †, ‡ | |||||
| Symptoms | S-Bilateral | 7.8 ± 4.9 | 19.6 ± 3.8 | † | 20.4 ± 4.9 | † | 0.609 | 0.011 | ||
| Unilateral | 8.4 ± 4.2 | 18.5 ± 4.5 | † | 20.4 ± 4.4 | † | |||||
| Patient satisfaction | S-Bilateral | 12.3 ± 4.0 | 24.1 ± 5.9 | † | 28.6 ± 6.1 | †, ‡ | 0.225 | 0.004 | ||
| Unilateral | 12.4 ± 4.5 | 25.4 ± 6.6 | † | 29.5 ± 6.7 | †, ‡ | |||||
| Patient expectations | S-Bilateral | 13.4 ± 2.2 | 12.5 ± 2.8 | 12.2 ± 3.1 | 0.107 | 0.002 | ||||
| Unilateral | 13.2 ± 3.0 | 11.8 ± 2.9 | 12.5 ± 2.9 | |||||||
| Functional activities | S-Bilateral | 49.1 ± 17.1 | 69.5 ± 14.9 | † | 74.4 ± 12.8 | †, ‡ | 0.262 | 0.005 | ||
| Unilateral | 50.9 ± 16.8 | 70.3 ± 19.2 | † | 76.9 ± 11.4 | †, ‡ | |||||
| Pain intensity | S-Bilateral | 6.2 ± 2.6 | 0.9 ± 1.2 | † | 1.0 ± 1.8 | † | 0.859 | 0.016 | ||
| Unilateral | 5.8 ± 1.8 | 1.6 ± 1.8 | † | 1.3 ± 2.1 | † | |||||
| Knee extensor strength (Nm/kg) | S-Bilateral | 0.91 ± 0.41 | 0.85 ± 0.34 | § | 1.19 ± 0.51 | †, ‡ | 3.338 | * | 0.052 | |
| Unilateral | 0.94 ± 0.37 | 1.00 ± 0.24 | 1.20 ± 0.40 | †, ‡ | ||||||
| Values are expressed as mean ± standard deviation. | ||||||||||
| * Significant interaction (group × time) (p < 0.05). | ||||||||||
| † Significant different from the values at preoperatively (p < 0.05). | ||||||||||
| ‡ Significant different from the values at 3 months (p < 0.05). | ||||||||||
| § Significant different from the value of Unilateral at 3 months postoperatively (p < 0.05). | ||||||||||
We aimed to compare the time courses in functional outcomes between simultaneous bilateral and unilateral TKA after matching patient characteristics, such as age, sex, and BMI. The most important finding of this study was the delayed recovery in knee extensor strength in patients who underwent simultaneous bilateral TKA compared with those who underwent unilateral TKA at 3 months postoperatively. Conversely, no differences were observed in other measurements at 3 and 12 months postoperatively between the patient groups. This is the first study to compare time courses in functional recovery between simultaneous bilateral and unilateral TKA after matching for patient characteristics.
This study showed that the new KSS total, symptoms, patient satisfaction, functional activities, and pain intensity were significantly improved at 3 and 12 months postoperatively compared with the preoperative values in both simultaneous bilateral and unilateral TKA groups. Additionally, the patients who underwent simultaneous bilateral TKA showed delayed recovery of knee extensor strength at 3 months postoperatively compared with the patients who underwent unilateral TKA, which remained the same at 12 months postoperatively. These results support our hypothesis. Decreasing gait ability may have led to a delay in the recovery of knee extensor strength. Gait ability after TKA was associated with knee extensor strength on both the involved and uninvolved limbs [21–24]. Knee extensor strength in the uninvolved limb was maintained in patients who underwent unilateral TKA, whereas that in patients who underwent simultaneous bilateral TKA decreased due to surgery. Therefore, the gait ability in simultaneous bilateral TKA was possibly lower than that in unilateral TKA due to bilateral muscle weakness and pain during the acute phase. For these reasons, because the improvement of gait ability was delayed in the patients who underwent simultaneous bilateral TKA, the recovery of knee extensor strength in the involved limb might be delayed in the patients who underwent simultaneous bilateral TKA. Further studies should be conducted, including the assessment of gait ability.
Conversely, no differences were observed in the recovery of new KSS (including total score), symptoms, patient satisfaction, patient expectations, functional activities, and pain intensity between simultaneous bilateral and unilateral TKA patients at 3 and 12 months postoperatively. This study suggests that the patients who underwent simultaneous bilateral TKA could recover to the same level as the patients in these outcomes compared with those who underwent unilateral TKA. Previous studies have reported that simultaneous bilateral TKA has advantages over unilateral TKA in terms of a shorter rehabilitation period and lower medical costs [4]. We believe that the results of this study confirmed the advantages of simultaneous bilateral TKA, and this study will assist attending clinicians in considering simultaneous bilateral TKA for patients at low risk of mortality and who would benefit from bilateral TKA.
This study has several limitations. First, this study is limited by its retrospective design and convenience sampling method. Thus, we could not measure other potential confounders, such as psychological factors and physical activity [25, 26], and could not increase the sample size. Further studies should be conducted with a larger sample size and consider the potential influences of these factors. Second, we did not confirm whether home exercise was performed after 3 months postoperatively. This might have affected the results of this study. Given these limitations, care should be taken when extrapolating the results of this study to all patients who undergo TKA.
This study thus showed that while functional recovery was similar between simultaneous bilateral and unilateral TKA at 12 months postoperatively, the patients who underwent simultaneous bilateral TKA showed delayed recovery in knee extensor strength at 3 months postoperatively. Patients with simultaneous bilateral TKA are recommended to undergo postoperative rehabilitation focusing on the delayed recovery of knee extensor strength during the acute phase.
ANOVA , analysis of variance
BMI, body mass index
NRS, numerical rating scale
Ethics approval and consent to participate
This research was approved by the Institutional Review Board of the Anshin Hospital (approval protocol number: No. 60; date of approval:December 20, 2020). All methods were carried out in accordance with the Declaration of Helsinki. All participants provided written informed consent in accordance with the Declaration of Helsinki.
Consent for publication
Not applicable.
Availability of data and materials
The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.
Competing interests
The authors declare that they have no competing interests.
Funding
Not applicable.
Authors’ contributions
TO and OW helped in the research idea and study design; TO and KM acquired data; TO, OW, and KM were involved in data analysis and interpretation; TO was involved in statistical analysis; OW and KM were involved in supervision or mentorship. Each author contributed important intellectual content during article drafting or revision and accepts accountability for the overall work by ensuring that questions pertaining to the accuracy or integrity of any portion of the work are appropriately investigated and resolved.
Acknowledgements
We acknowledge all subjects who participated in this study.