A comparison of clinical and patient-reported outcome measures of TKR: Comparison of Asian to North American patients

Abstract

Background:

Cultural differences between continents may also affect the outcome on interventions. This study compared an Asian and North American cohort of total knee replacement (TKR) patients.

Questions/purposes:

This study aims to compare the patient-reported outcome measures as well as a functional outcome after TKR between these two different patient populations with a different cultural societal background in two different countries.

Patients and Methods:

A retrospective study on two cohorts of 76 Asian TKR patients and 64 North American TKR patients were compared. Demographics, patient-reported outcome measures (Knee Society Score (KSS), Patient-Administered Questionnaire (PAQ), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)), knee range of motion (RoM), and radiographic component position were compared.

Results:

The Asian cohort had more females compared to the North American and significantly worse preoperative RoM, and worse KSS function score and PAQ pain scores. The preoperative KSS knee score and WOMAC scores were comparable between the two groups. Postoperatively, the differences in WOMAC and KSS knee scores were significant, while KSS function and PAQ were comparable between groups.

Conclusions:

Even though Asian TKR patients had significantly worse preoperative scores, their postoperative outcomes were comparable to North Americans. The higher preoperative functional deficit and the higher pain levels in the Asian population might be due to cultural differences and/or socioeconomic reasons, which made Asian patients present with more severe conditions in the preoperative consultation for a possible surgical treatment compared to North Americans. More research is needed to investigate the difference between these cultural impacts on TKR outcomes.

Level of Evidence:

Level III/Retrospective cohort study.

Keywords

Asian cultural differences North American patient-reported outcome measures rotating platform knee replacement total knee replacement

Introduction

Osteoarthritis (OA) is a common cause of debilitating knee pain. Total knee replacement (TKR) has emerged as an effective treatment for OA of the knee. Clinical outcomes have been positive and TKRs are now performed worldwide.^1
–3 Previous studies have examined the outcomes and compared the results across different Western countries, such as Sweden, The Netherlands, United States, United Kingdom, and Australia.^4

–7 The variation of patients preoperatively has been thought to be a result of different health care systems and access. However, these populations are largely Caucasian, living in comparable societies with presumably similar stresses on their knees during daily living. There has not been a comparison of total knee clinical outcomes between a Western population and an Asian population who live in their continent with their specific societal surroundings, which will also have an impact on the lower extremity and more specifically, knee use.

Asian populations have different cultural practices than Western populations and have been found to have a higher prevalence of tibiofemoral OA when compared to Caucasian subjects.^8,9 Studies suggest that the cause is due to squatting, which is common among Asian populations. Squatting requires a high degree of knee flexion and five to six times more tibiofemoral contact forces than bodyweight. It has been found that the tibiofemoral reaction forces from posterior direction to anterior happens rapidly when squatting and those have significant long-term effects on the joint cartilage.¹⁰ These effects could result in variations between Western and Asian populations both at the preoperative and at the postoperative state.

There is also an average size difference between Asian and Caucasian populations. Morphometric analyses have found that typically an Asian knee is smaller than a Caucasian knee.^11
–13 These factors could contribute to different clinical outcomes between an Asian and a Caucasian population in its relations with implant design^14,15 and warrants more research.

In addition to the morphological differences, there are large socioeconomic differences between certain Asian and North American populations. For example, the World Bank classifies the United States as a “high income” country and Indonesia as “lower middle income”.¹⁶ Socioeconomic factors have been found to contribute to different preoperative status in various ethnic groups.¹⁷

We aim to compare the clinical and patient-reported outcome measures (PROM) and postoperative radiographic measurements between the two patient cohorts. Our first objective was to assess the variation in clinical and PROM of TKR between these two populations. The second objective was to identify what factors influence the variation in clinical and PROM between the two populations.

Materials and methods

A retrospective analysis of two institutional review board approved registries of patients with TKRs at two institutions between 2007 and 2014. One institution was located in Indonesia and has a patient base that is primarily of Chinese, Malay, or Indian ethnic backgrounds, whereas the other location was located in the United States with a patient base majority of Caucasian. To prevent confounding data due to knee implant design, the same implant was studied between the Asian and Caucasian cohorts. The inclusion criteria were patients with OA who underwent primary TKR using the PFC Sigma rotating platform with high flexion posterior stabilized design (DePuy Synthes, Warsaw, Indiana, USA). The exclusion criteria were patients with revision TKR and patients with periprosthetic joint infection. Thus, 76 TKRs from the Indonesia Institution and 64 from the United States Institution could be included. None of the patients were lost to follow-up. The follow-up averaged between 4.27 years and 4.40 years for the Asian and North American cohorts, respectively.

Two fellowship trained, high-volume, arthroplasty specialists performed all TKRs, using similar gap-balancing techniques. Both surgeons used similar pain protocols, which included an intra-articular injection, and both cohorts of patients went home with the same rehabilitation protocols after surgery. All patients were matched for age and body mass index (BMI).

All patients had clinical findings recorded preoperatively and at their latest annual follow-up. Clinical findings included range of motion (RoM) as measured by a goniometer by one of the two senior authors. Flexion values, as well as the presence of flexion contractures, were measured at each follow-up appointment. Full RoM was defined as flexion values minus the degree of the flexion contracture. Pain and function were assessed preoperatively and at the last follow-up using both the knee society pain and function scores (KSS, a higher score indicates better function), as well as the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC, a lower score indicates better function). Additionally, a patient-administered questionnaire (PAQ) was utilized to assess patient satisfaction, pain, and difficulty performing flexion-based activities, including kneeling, negotiating stairs, squatting, and sitting on heels.¹⁸ The pain domain portion of the PAQ was reported separately (a higher score indicates more pain).

Anteroposterior (AP) and lateral knee radiographs were collected at the last follow-up at both institutions. AP femoral flexion, AP tibial angles, lateral femoral flexion, and lateral tibial angles were calculated with the same technique to assess component positioning and alignment in the coronal and sagittal planes. This technique was previously described in Gromov et al.¹⁹

Statistics were primarily descriptive with means and standard deviations calculated for continuous variables; frequencies and percentages were calculated for discrete variables. Comparison between cases and controls was made using independent t-test. Significance was set at a p-value <0.05. Analyses were performed using SPSS version 25.

Results

Preoperative patient demographics are found in Table 1. No significant difference in demographic data between Asian and North American patients was seen. The mean age for Asian and North American was 68.85 ± 3.90 years and 70.02 ± 5.29 years, respectively, with no significant difference (p = 0.107). The mean BMI for Asian and North American was 27.46 ± 3.58 and 28.40 ± 4.41, respectively, with no significant difference (p = 0.276).

Table 1.

Preoperative patient characteristics.

	Asian		North American		p Value
	Mean	SD	Mean	SD
Age (years)	68.85	3.90	70.02	5.29	0.107
BMI	27.46	3.58	28.40	4.41	0.2763
Follow-up	4.27	1.29	4.40	0.63	0.763

SD: standard deviation; BMI: body mass index.

Preoperative clinical scores showed that the Asian cohort had significantly lower scores than North American patients for both KSS function score (54.34 ± 12.00 vs. 61.79 ± 18.63; p = 0.006) and knee RoM (103.88 ± 19.41 vs. 111.17 ± 13.11; p = 0.016). Compared to the American cohort, the Asian patients also had significantly higher (i.e. more pain) preoperative PAQ pain scores (18.4 ± 4.3 vs. 16.1 ± 2.0; p = 0.001) but better for total PAQ score (65.15 ± 10.58 vs. 74.01 ± 16.90; p = 0.0001). No significant difference between Asian and North American for KSS knee score (53.40 ± 14.55 and 55.67 ± 14.10, respectively; p = 0.266) and WOMAC score (70.25 ± 7.55 and 68.56 ± 11.53, respectively; p = 0.173).

Postoperatively, the Asian cohort had a slightly lower KSS knee score (93.18 points ± 4.72 vs. 96.50 points ± 4.64; p = 0.0001) but better WOMAC scores (33.36 ± 10.11 vs. 37.90 ± 12.71; p = 0.021) compared to North American TKR patients. The postoperative RoM of the knee (p = 0.661), KSS function score (p = 0.441), and total PAQ score (p = 0.335) was comparable between the two cohorts (Table 2).

Table 2.

Clinical and patient-recorded outcome scores comparing Asian with North American patients.

	Preoperative					Postoperative
	Asian		North American			Asian		North American
	Mean	SD	Mean	SD	p Value	Mean	SD	Mean	SD	p Value
Range of motion (°)	103.88	19.41	111.17	13.11	0.016	123.94	11.35	124.42	10.55	0.661
Knee society knee score^a	53.40	14.55	55.67	14.10	0.266	93.18	4.72	96.50	4.64	0.000
Knee society function score^a	54.34	12.00	61.79	18.63	0.006	97.23	3.50	93.75	11.81	0.441
WOMAC^b	70.25	7.55	68.56	11.53	0.173	33.36	10.11	37.90	12.71	0.021
PAQ^b	65.15	10.58	74.01	16.90	0.000	20.05	14.04	26.89	22.95	0.335
PAQ pain score^b	18.4	4.3	16.1	4.3	0.0009	11.3	2.0	11.7	2.7	0.2936

SD: standard deviation; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index; PAQ: Patient-Administered Questionnaire.

^aHigher scores are better.

^bLower scores are better.

The postoperative mean femorotibial angle was 184.9 ± 1.09° for the Asian TKR patients and 184.2 ± 2.82° for the North American TKR (p = 0.133). The position of the TKR as measured at radiographs showed that the mean AP femoral component angle of the TKR in the Asian cohort was 95.6 ± 1.19° and the North American 94.4 ± 2.28° (p < 0.0001). The mean AP tibial angle in Asian knees was 89.3 ± 1.1° and the North American TKR 89.8 ± 2.1° (p = 0.051). On the lateral radiographs, TKR positions were different as well, the Asian cohort had less lateral femoral flexion position than the North American TKRs (8.3 ± 3.02° vs. 14.9 ± 3.74°; p < 0.0001); the lateral tibial slope angle was slightly higher in the Asian TKRs compared to the North American TKRs (86.0 ± 2.12° vs. 90.8 ± 3.2°; p < 0.0001) (Table 3).

Table 3.

Comparison of postoperative TKR position at AP and lateral radiographs in the two cohorts.

Degree	Asian TKR position	North American TKR	p Value
AP femoral component angle^a	95.6 ± 1.2°	94.4 ± 2.3°	<0.0001
AP tibial component angle^a	89.3 ± 1.1°	89.8 ± 2.1°	0.06
AP femorotibial angle^b	184.9 ± 1.2°	184.1 ± 3.4°	0.04
Lateral radiograph femoral component position^c	8.3 ± 3.0°	14.9 ± 3.7°	<0.0001
Lateral radiograph tibial slope^d	86.0 ± 2.1°	90.8 ± 3.2°	<0.0001

TKR: total knee replacement; AP: anteroposterior.

^a>90° is in valgus, <90° is in varus.

^b>180° is valgus.

^cLarger value indicates more component flexion versus extension.

^d<90° more posterior slope.

Discussion

Both the Asian and North American cohorts had an improvement in postoperative RoM, function, and pain scores. Interestingly, despite a lower preoperative RoM of the knees in the Asian patients, postoperatively, there was no significant difference between the two patient populations. This is interesting because preoperative RoM is found in multiple studies to be an important determinant of postoperative RoM, which is again associated with overall patient satisfaction and functional level.^20

–25 Asian patients with the same TKR design as the North American population had a larger improvement of postoperative RoM of knees despite a worse ROM preoperatively. This is caused by implant position and/or postoperative rehabilitation. The femoral component was in 7° more flexion position in North American knees, while the tibial component was in about 4° more posterior tilt; thus, these component positions seemed not to be a major cause for better postoperative RoM improvement in Asian TKR. With respect to rehabilitation, both hospitals started with a protocol of immediate postoperative RoM exercises and ambulation. A possible difference in the Asian and the Caucasian patients is that the former needs hyperflexion for daily life, either for squatting or for praying position (i.e. Muslim). These cultural differences in knee use are most probably related to the better functional recovery of the knees in Asian patients. The significant improvement in postoperative KSS pain score, KSS functional score, and WOMAC score was found in Asian cohort especially in WOMAC pain night in bed, pain sitting, pain standing, AM and PM stiffness, rising from sitting, standing, bending WOMAC, and on/off WOMAC. The most important is KSS functional and WOMAC pain sitting and standing, and AM and PM stiffness, since we know that Asian people have many cultural and religious activities that require improvement of those functions. Although other factors such as obesity also influence postoperative RoM, the BMI was comparable between both cohorts.

Our results are in contrast with another study using the same mobile-bearing high flexion design Rotating Platform Flexion (Sigma RPF), which concluded that preoperative flexion and the design of the knee prosthesis were the predominant factors of postoperative flexion.²⁶ But that study was most likely done in Caucasians. Another previous study also found that preoperative flexion played a significant role in the postoperative gain in flexion and not the type of prosthesis.²⁷ These results have been found for more than two decades by others.^17,25

–28 Furthermore, our results also indicate that for North American and Asian patients, despite the various differences in knee morphology, preoperative deformity, and postoperative use in daily life, the implant provides comparable postoperative outcomes in both patient cohorts.

In our study, we found a slightly worse, preoperative WOMAC score for Asian compared to North American and a higher PAQ pain scores (i.e. more pain). The latter might reflect cultural and social differences between these countries. In the Asian cohort, it is possible that socioeconomic status is associated with delayed health care, with a subsequent worse OA stage at presentation for treatment. Although this research was done in a private hospital in Indonesia, the insurance coverage, from both National health care and private do not fully cover the surgery expenses. This economic shortcoming causes patients to delay getting their surgeries. Despite this, the postoperative patient-reported scores were comparable between these two groups and even slightly better (i.e. KSS knee score, WOMAC, and overall PAQ) for the Asian patients. The overall PAQ (i.e. patient satisfaction, flexion-based activities including kneeling, negotiating stairs, squatting, and sitting on heels) was 30% better in Asians (20 vs. 27 points in North Americans) but did not reach significance.

A study from Singapore among different ethnicities did also found no statistical difference in outcome measures for TKR of different ethnic groups.²⁴ The difference between that study and ours is most likely the result of the different patient ethnicities within different social settings (Indonesia and USA) in contrast to different patient ethnicities (Malay, Chinese, and Indian) within the same social setting (Singapore).

Preoperative PAQ pain score in the Asian cohort was significantly higher than in North American cohort. Based on a previous study by Mangelson et al,²⁹ pain is a major determinant for the outcome of TKA among women, and different perceptions of pain are noted in various ethnic groups, thus ethnicity should be considered as a covariate in evaluating TKA outcomes. Nevertheless, Asian patients had higher postoperative KSS knee score and WOMAC outcome scores.

Preoperative clinical score comparison between these two cohorts showed slightly but significantly worse scores (i.e. in ROM, KSS function score and PAQ pain score) in Asian cohort compared to the North American. These results supported a previous study conducted across Europe, Canada, the United States, United Kingdom, and Australia for the outcome of TKR, which showed a wide range of preoperative scores across these countries.^4,5 The authors attributed the worse WOMAC scores and knee function to the long waiting times in the United Kingdom compared to other countries as well as to cultural differences. Gossec et al., comparing almost 2000 patients, found high preoperative pain levels mainly in Canada, with lower pain levels in most European countries.⁵ For that matter, the severity of the preoperative pain level is considered by most surgeons to be the major determinant to indicate a TKR in the presence of at least moderate radiological OA and old age.⁷

It has been reported that ethnic minorities in the United States are less likely to consider TKR, due to limited health care access, cultural and socioeconomic factors, such as familiarity and cost.¹⁷ Such social differences are seldom mentioned in articles but are a major driver when indicating and performing elective arthroplasty surgery. For that matter, comparing results between countries can be severely biased, health care access differences are present in the Netherlands, which has a solidarity system of private health insurance.⁶ Reliance on natural remedies, religious beliefs, and fear of surgery are also additional factors, which have been found to influence the decision to engage in TKR. We presume that a variety of these reasons cause a delay in presentation in Asian patients, which explained why Asian patients had lower function score, worse RoM, and higher patient pain scores preoperatively.

Postoperative outcome scores were clinically comparable even after controlling for confounding variables. Our results mirror other studies in finding that geographic location alone does not dictate outcome scores,¹ despite differences in socioeconomic environment.⁶ However, in a study examining outcomes in the United States, United Kingdom, and Australia, patients in the United Kingdom had lower postoperative functional scores even after controlling for confounding variables.⁴ They were not able to determine an exact cause but noted that WOMAC pain scores were similar for all countries. While there are few data comparing an Asian country versus a North American one, we believe that our results agree with other studies and show that location is not a factor in TKR outcomes, despite perceived differences with respect to daily use of the lower extremity in Asian and Caucasian patients.

As for component position, AP femoral and tibial component measurements were statistically different between the two groups. On the lateral view, the Asian patients had less femoral flexion and more posterior tibial slope in comparison with the North American patients, despite the use of similar intraoperative guiding systems. These differences in sagittal plane alignment between countries are interesting and potentially indicative of the previously described morphological differences between Asian and non-Asian patients. However, postoperative and change in RoM values were not significant between the two cohorts. More research is needed to explain these differences.

This study has certain limitations. First, all surgeries were performed by two specialized knee surgeons in specialized arthroplasty centers. Therefore, the postoperative outcome scores can be partially overestimated when extrapolated to the general TKR population. Further studies are needed to evaluate the effect of their differences. Second, only patients with the Sigma RPF knee were used to eliminate prosthesis difference on the outcome between these two cohorts. Third, the North American population had a wide variety of ethnic groups and both cohorts did not have detailed ethnic and socioeconomic demographic data. We assume both cohorts are similar demographically to the city and country they reside in, the North American cohort was based in a major American metropolitan city and the Asian came from a major Indonesian metropolitan city. The North American demographic data show the majority to be Caucasian. In addition, patients’ socioeconomic condition might influence the outcomes of TKR. We have not studied the differences of socioeconomic between the two populations. Finally, although preoperative outcome score data and RoM data were collected prospectively, this is a retrospective study and as such unknown confounders could not be corrected for.

Conclusions

Asian patients had significantly worse preoperative outcome scores, on the pain score, function score, and knee RoM but postoperative outcome results were slightly better for the Asian patients compared to the North American counterpart. Cultural and societal differences (i.e. health care access) may be drivers in both the preoperative presentation and the postoperative perception of outcome (i.e. patient-reported outcome) as well as function (i.e. the need for a knee to high flex during social activities). Both aspects, cultural and social, should be taken into account when comparing the outcome of elective arthroplasties between different countries.

Footnotes

Acknowledgments

We thank Lily Lee, MS, from the Biostatistics Department from Hospital for Special Surgery for assisting in the statistical analysis; we also thank Kiki Novito, MD, and Imelda Lumban Gaol, MD, from Orthopaedic Surgery Department from Medistra Hospital for assisting in the data collection and data analysis.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was approved by the Hospital for Special Surgery Institutional Review Board.

ORCID iD

Michael A Gaudiani

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