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The Patterns of Limb Length, Height, Weight and Body Mass Index Changes after Total Knee Arthroplasty
The Journal of Arthroplasty 28 (2013) 1856–1861
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
The Patterns of Limb Length, Height, Weight and Body Mass Index Changes after Total Knee Arthroplasty Moon Jong Chang, MD a, Yeon Gwi Kang, MS a, Chong Bum Chang, MD, PhD a, b, Sang Cheol Seong, MD, PhD b, Tae Kyun Kim, MD, PhD a, b a b
Joint Reconstruction Center, Seoul National University Bundang Hospital, Seongnam, Korea Department of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul, Korea
a r t i c l e
i n f o
Article history: Received 20 November 2012 Accepted 24 March 2013 Keywords: limb length leg length discrepancy height weight body mass index total knee arthroplasty
a b s t r a c t The objective of this retrospective review of 466 patients was to document changes in limb length, leg length discrepancy (LLD), height, weight, and body mass index (BMI) 1 year after TKA and the patterns of height, weight, and BMI during 5 years. To determine change patterns over 5 years, the data of 291 patients were analyzed and compared with those of age and gender-matched normal subjects. Limb length, height, and weight increased, BMI remained unchanged, and LLD decreased 1 year after TKA. The bilateral group had a greater height increase and lower rate of LLD. Preoperative mechanical tibiofemoral angle was related to limb length increase, and patients with a smaller preoperative BMI showed more weight gain. During the 5 years, weight and BMI at 1 year were maintained, but height diminished, while the healthy population showed a decreasing trend in weight. © 2013 Elsevier Inc. All rights reserved.
Patients undergoing total knee arthroplasty (TKA) may experience changes in body statistics, such as, limb length, leg length discrepancy, height, weight, or body mass index (BMI) [1–7]. Patients awaiting TKA often wonder how their body shapes will change after surgery and often expect that TKA will increase mobility and allow weight loss, as changes in weight are certainly linked to the general health [8]. In addition, perceivable leg length discrepancy could be a source of patient dissatisfaction [9], but cannot be accurately controlled by preoperative planning [4]. Furthermore, in contrast to total hip arthroplasty (THA), information is limited regarding the frequency and magnitude of limb length changes after TKA. Although TKA can improve knee function and mobility, published results disagree as to whether weight reduces after TKA [1–3,5–7]. In addition, TKA may have substantial effects on BMI because of potential changes in height and weight. Therefore, information of these changes after TKA is valuable for counseling patients and planning postoperative care. Changes in body statistics may depend on patient factors, the duration of follow-up, and whether TKA is unilateral or bilateral. In theory, greater amounts of soft tissue release to assure symmetrical
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.03.024. Reprint requests: Tae Kyun Kim, MD, PhD, 166 Gumi-ro, Bundang-gu, Seongnam-si, Gyeonggi-do (463-707), Republic of Korea. 0883-5403/2810-0033$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.03.024
gaps cause larger gaps, and thus, more severe deformities may increase limb length changes, as could relief of flexion contracture. On the other hand, preoperative obesity and postoperative functional outcomes affect level of mobility, and thus, are likely to influence weight change. In the long term, change patterns may be different from those in the short term, because functional outcomes after TKA can change with time, and the patients also experience senile change. However, previous studies provide only limited relevant information [1,3,5–7]. Some studies included only small numbers of patients [3], whereas, others involved TKA and THA [3,6]. Furthermore, the majority included only unilateral TKA even though TKA is frequently performed as bilaterally [6,7]. In addition, many involved a follow-up period of 1 or 2 years [1,3,5–7]. Therefore, we considered that a largescale study was required that included unilateral and bilateral TKA and a longer-term follow-up. The first aim of this study was to document normative interval changes in limb length, leg length discrepancy, height, weight, and BMI 1 year after TKA. We were particularly interested in determining whether unilateral and bilateral TKA differ in terms of the amount of postoperative leg length discrepancy and changes in limb length, height, weight, and BMI. The second aim was to determine whether degrees of preoperative deformities (deviations of mechanical tibiofemoral angle from neutral and flexion contracture) are related to limb length change and whether preoperative BMI and postoperative functional outcomes are related to weight change at 1 year after surgery. Finally, we attempted to determine whether the height, weight, and BMI at 1 year are maintained until 5 years after TKA and
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whether patterns of change differ from those shown by the healthy population. We hypothesized as follows: (1) limb length and height would increase whereas leg length discrepancy, weight, and BMI would decrease after TKA, and that patients after bilateral TKA would exhibit smaller postoperative leg length discrepancies and greater changes in limb length, height, weight, and BMI than after unilateral TKA; (2) limb length changes are dependent on degree of deformity, and that weight changes depend on preoperative BMI and postoperative functional outcomes; and (3) changes in height, weight, and BMI at 1 year after TKA are maintained until 5 years after surgery, and that patterns of change are similar to those shown by healthy individuals. Patients and Methods Study Design and Subjects This retrospective review was conducted using the prospectively collected data of 466 patients for 1-year follow-up analysis. Primary TKA for osteoarthritis was performed at our institution on 969 patients from November 2003 to December 2008. Of these 969 patients, 302 were excluded for previous surgery on the ipsilateral lower extremity (28), spine surgery (18), a diagnosis other than primary osteoarthritis (54), Parkinson disease (17), a previous cerebrovascular accident (25), cancer (27), death due to diseases unrelated to TKA (11), a periprosthetic infection (13), or another condition capable of affecting the result of this study, such as depression, dementia, or problems of the contralateral knee (109). After these exclusions, 667 patients were left eligible for inclusion. Of these 667 patients, 201 (30%) did not have standing full-limb anteroposterior (AP) radiographs or complete information of height, weight, and BMI and was excluded. Consequently, 466 patients (761 knees) (70% of the eligible 667 patients) were included in the final analysis. There were 440 females (95%) and 26 males (5%) with a mean age 67.9 years (SD, 5.9 years; range, 49–84 years). One hundred seventy-one patients (34%) underwent unilateral TKA and 295 (66%) underwent bilateral TKAs. Of the 440 patients eligible for 5year follow-up analysis, 291 patients (66%) with follow-up data during the 5 years were included to allow the analysis of temporal height, weight, and BMI patterns. These 291 patients comprised 278 females (96%) and 13 males (4%) with a mean age of 68.3 years (SD, 6.1 years; range, 53–84 years). This study was approved by the institutional review board of our hospital. Surgery and Rehabilitation All surgeries were performed by a single surgeon (one of the authors) using the medial parapatellar approach with a tourniquet, and all patients underwent the same postoperative rehabilitation protocol [10]. Patellar resurfacing was performed in all cases. Implant fixation was carried out using cement. A compressive dressing was applied without immobilization for 24 h after surgery, and then, a continuous passive motion machine was applied. On the second postoperative day, all patients began walking with crutches or a walker and started active and passive range of motion exercises. Clinical Evaluation Clinical information including demographics, preoperative degree of flexion contracture, functional outcomes, height, weight, and BMI, was prospectively collected by one independent investigator (one of the authors). Preoperative flexion contractures were measured using a goniometer with the patients supine. Functional statuses were measured using American Knee Society (AKS) function scores [11], Western Ontario McMaster University Score (WOMAC) [12], and Short-Form 36 (SF-36) [13] questionnaire scores preoperatively, and at 6 and 12 months post-TKA and then annually. The height, weight
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and BMI were measured preoperatively, and at 1, 2, 3, and 5 years postoperatively. The height was measured in centimeters and weight in kilograms using an electronic device (DS-102, JENIX, Seoul, Korea). Body mass index (BMI) was calculated by dividing weight in kilograms by height in meters squared. Radiographic Evaluation Radiographic measurements, including preoperative mechanical tibiofemoral angle and limb length were taken by one observer (one of the authors), who was not the primary surgeon, using standing fulllimb AP radiographs on a 14 × 51-inch grid cassette preoperative, 6 weeks and at 3, 6, and 12 months postoperatively, and then annually. When radiographs were checked, a reference template on the platform was used to control limb rotation [14]. Preoperative mechanical tibiofemoral angles were used as an absolute value in both varus and valgus knees. Limb length was defined as the distance from the top of the femoral head to the center of the tibial plafond, as previously described [4]. All radiographic measurements were performed using a picture archiving and communication system (PACS) (Infinite, Seoul, Korea). Minimum detectable changes were 0.1 mm for length measurements and 0.1° for angular measurements. To determine the intra- and interobserver reliabilities of measurements, 20 subjects were chosen and measured twice (a week apart) by two observers (two of the authors). The reliabilities of measurements were confirmed using intraclass correlation coefficients (ICC). The ICCs for the intra- and interobserver reliabilities of limb length measurements were almost perfect (N 0.9). Statistical Analysis Statistical analysis was performed throughout using SPSS for Windows (version 17.0; SPSS Inc, Chicago, IL). To document the proportions of patients who experienced a clinically meaningful change, meaningful change was set at our discretions. A minimum of 1-cm change from preoperative values was set for limb length, leg length discrepancy, and height. The amount of meaningful change for weight and BMI was set at a minimum of 5% [15,16]. All statistical analyses had more than a power of 80% to detect the aforementioned meaningful changes at the different time points with less than a 5% probability of a type I error. For the 5-year follow-up analysis, age and gender-matched individuals were selected from the database of the Korean National Health and Nutritional Examination Survey (KNHANES). Unfortunately, KNHANES data were cross sectional, and thus, we did not have longitudinal data of healthy controls spanning the same period. Therefore, corresponding numbers of subjects were randomly and repeatedly selected from KNHANES according to age and gender at each time point (preoperative, and 1, 2, 3, and 5 years after TKA) of the analysis to form control groups. Changes in body statistics and rate of leg length discrepancy at 1 year post-TKA were calculated versus preoperative levels. Mean differences and ranges were used to describe overall changes in limb length, leg length discrepancy, height, weight, and BMI at 1 year postoperatively. The paired t-test was used to determine statistical significances. The magnitudes of changes in limb length, leg length discrepancy, height, weight, and BMI were categorized, and frequencies were noted. Magnitude and frequency of leg length discrepancy preoperatively and at 1 year after surgery were also compared, and chi-square test was used to determine statistical significance. The Student's t-test was used to determine the significances of the differences in the interval changes of limb length, height, weight, and BMI and residual leg length discrepancy between the unilateral and bilateral groups. Multivariate regression analysis was used to evaluate the relationship between degrees of deformity (preoperative mechanical
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tibiofemoral angles and preoperative flexion contractures) and amounts of leg length change, and the relationships between preoperative BMI and functional outcomes at 1 year postoperatively and weight changes. Temporal changes in height, weight, and BMI over the 5-year follow-up period assessed and compared with those of controls. The Student's t-test was used to compare the heights, weights, and BMIs of TKA patients and controls at each time point, and the mixedeffects model repeated measures (MMRM) was used to analyze changes in the heights, weights, and BMIs of patients over the 5-year follow-up period. In addition, the one-way analysis of variances (ANOVA) with Tukey method as the post hoc analysis was used to analyze changes in the heights, weights, and BMIs of control groups during the same period.
Table 2 Frequency of Subjects for Selected Intervals of the Changes of Limb Length, Leg Length Discrepancy, Height, Weight and Body Mass Index 1 Year after TKAa. Parameters
Interval
Frequencies (N = 466)
Limb length change (cm)b
≤−1 −1b, b1 1≤, b2 ≥2 ≤−1.0 −1 b, b−0.5 −0.5≤, b0.5 0.5≤, b1.0 ≥1.0 ≤−1 −1b, b1 1≤, b2 ≥2 ≤−5 −5b, b5 ≥5 ≤−5 −5b, b5 ≥5
3.4 (26) 52.7 (401) 28.0 (213) 15.9 (121) 6.0 (28) 12.3 (57) 68.0 (317) 11.8 (55) 1.9 (9) 4.3 (20) 31.3 (146) 40.4 (188) 24.0 (112) 21.7 (101) 69.1 (322) 9.2 (43) 12.6 (59) 70.2 (327) 17.2 (80)
LLD change (cm)
Height change (cm)
Weight change (%)
Results Average limb length, height, and weight increased, BMI remained unchanged, and mean leg length discrepancy decreased 1 year after surgery (Tables 1 and 2). Limb lengths increased by an average of 0.9 cm (range, − 2.3 to 4.9 cm) (p b 0.001). Of the 761 operative limbs, 334 (43.9%) experienced limb lengthening by ≥1 cm but 26 (3.4%) experienced limb length shortening of ≥ 1 cm. Mean leg length discrepancy was 0.1 cm (range, − 2.6 to 1.9 cm) smaller at 1 year after TKA. The proportion of patients with a leg length discrepancy of ≥ 1 cm reduced from 17.2% (80) to 10.3% (48) at 1 year after surgery (p = 0.007). Mean increase in height over the same period was 0.9 cm (range, − 3 to 4 cm) (p b 0.001). Of the 466 patients, 300 (64.4%) showed an increase in height of ≥ 1 cm (average 1.5 cm). In contrast, 4.3% (20) decreased in height by 1 cm or greater (average 1.2 cm). Mean weight increased by 0.9 kg (range, − 10 to 13 kg) after TKA (p b 0.001). One hundred one patients (21.7%) had a weight increase of ≥ 5%. In contrast, only 43 patients (9.2%) lost ≥ 5%. No change in mean BMI was observed (preoperative 27.1 kg/m 2 vs. postoperative 27.1 kg/m 2, p = 0.413). BMI increased in 80 patients (17.2%), decreased in 59 patients (12.6%) but remained unchanged in the majority (70.2%, 327 patients). The bilateral group showed different amounts or patterns of changes in the parameters investigated (Table 3). The bilateral group achieved a greater increase in limb length (0.9 vs. 0.7 cm, p = 0.050) and had smaller mean residual leg length discrepancy (0.5 vs. 0.6 cm, p = 0.006) than the unilateral group. Furthermore, the bilateral group had a lower proportion of patients with residual leg length discrepancy (≥0.5 cm; 41.4% vs. 53.8% and ≥1 cm; 7.8% vs. 14.6%, p = 0.011). The bilateral group also showed a greater increase in height (1.1 vs. 0.7 cm, p = 0.001) than the unilateral group. However, mean weight gain tended to be greater in the unilateral group (1.3 vs. 0.7 kg, p = 0.064). Although no mean difference in BMI was found overall in TKA patients, BMI increased by 0.3 kg/m 2 in the unilateral group but decreased by 0.1 kg/m 2 in the bilateral group (p = 0.008). Regression analyses identified preoperative mechanical tibiofemoral angle and BMI as patient factors for limb length change and
BMI change (%)
Abbreviations: N = number, LLD = leg length discrepancy, BMI = body mass index. a Data are presented as percents with numbers in parenthesis. b For patients with bilateral TKAs, both knees were measured separately, and the number of knees measured was 590.
weight change, respectively. Greater preoperative deformity in the coronal plane, as determined by mechanical tibiofemoral angle, was related to a greater increase in limb length (β = 0.833, p b 0.001). Linear regression analysis showed that limb length increased 7.6 mm per 10° of preoperative mechanical tibiofemoral angle. However, no association was found between degree of preoperative flexion contracture and limb length change (p = 0.486). Mean mechanical tibiofemoral angle was varus 11.9º (SD, 5.5º; range, varus 37 to valgus 9º) preoperatively and varus 1.5º (SD, 2.7º; range, varus 11 to valgus 6º) 1 year after TKA. Preoperatively, mean flexion contracture was 13.6º (SD, 7.4º; range, 0 to 50º) and 0.2º (SD, 1.3º; range, 0 to 15º) 1 year after TKA. Postoperative mechanical tibiofemoral angle and flexion contracture were not associated with limb length change (p = 0.447 and 0.322, respectively). On the other hand, patients with a smaller preoperative BMI showed a greater increase in weight at 1 year postoperatively (β = − 0.262, p b 0.001). In contrast, no association was found between weight change and any functional outcome measure at 1 year postoperatively (p N 0.05). Patients after TKA showed different patterns of changes in height, weight, and BMI from the normal healthy population over the 5-year period (Figs 1, 2, and 3). In the patients after TKA, mean height decreased at every follow-up from 1 year post-TKA (p b 0.05 for all). A similar decreasing pattern was observed in controls. However, patient mean height at 5 years after TKA was still greater than that of controls (151.8 cm vs. 150.3 cm; p b 0.001), which was probably due to the height increase by TKA (Fig. 1). Temporal patterns of weight
Table 1 Interval Changes in Limb Length, Leg Length Discrepancy, Height, Weight and Body Mass Index of 466 Patients at 1 Year after TKAa. Preoperative Parameters Limb length (cm) LLD (cm) Height (cm) Weight (kg) BMI (kg/m2)
Mean 76.0 0.6 152.6 63.1 27.1
(3.8) (0.5) (6.1) (9.2) (3.4)
1 year after TKA
Differences
Range
Mean
Range
Mean
Range
64.9–91.1 0–3.9 136–178 36–99 18–38
76.9 (3.8) 0.5 (0.4) 153.5 (6.0) 64.0 (9.1) 27.1 (3.3)
67.3–92.1 0–3.8 136–179 36–100 16.9–38.8
0.9 (1.1) −0.1 (0.6) 0.9 (1.0) 0.9 (3.3) 0.05 (1.5)
−2.3–4.9 −2.6–1.9 −3.0–4.0 −10–13 −6.6–5.7
Abbreviations: LLD = leg length discrepancy, BMI = body mass index. a Data are presented as means with standard deviations in parenthesis. b Values b 0.05 are displayed in bold font.
p-Valuesb b0.001 b0.001 b0.001 b0.001 0.413
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Table 3 Comparisons of the Amount of Changes in Limb Length, Leg Length Discrepancy, Height, Weight and BMI 1 Year after Surgery between the Unilateral and the Bilateral Groupsa. Parameters Limb length change (cm) Residual LLD (cm) Height change (cm) Weight change (kg) BMI change (kg/m2)
Unilateral (N = 171) Bilateral (N = 295) p-Valuesb 0.7 (1.1) 0.6 (0.4) 0.7 (1.0) 1.3 (3.2) 0.3 (1.4)
0.9 (0.9) 0.5 (0.4) 1.1 (1.0) 0.7 (3.4) −0.1 (1.5)
0.050 0.006 0.001 0.064 0.008
Abbreviations: LLD = leg length discrepancy, BMI = body mass index. a Data are presented as means with standard deviations in parenthesis. b Values less than 0.05 are displayed in bold style.
and BMI changes in patients differed from those of controls. Patient mean weight and BMI were greater than those of controls (p b 0.05 at all time points). Furthermore, in patients, mean weight at 1 year after TKA was maintained throughout the 5-year follow-up. On the other hand, control mean weight showed a decreasing trend during the same 5 years (Fig. 2). Mean patient BMI showed an increasing tendency because mean height decreased and mean weight was maintained over the 5-year period (Fig. 3). On the other hand, mean BMI in controls did not change because both mean height and weight decreased. Discussion Information on postoperative changes in body statistics after TKA is valuable for preoperative education purposes and for planning postoperative rehabilitation. However, no detailed information has been reported on such changes. In the present study, we sought to evaluate changes in body statistics and to determine whether the unilateral and bilateral TKAs differentially affect changes at 1 year after surgery. In addition, we attempted to identify patient factors that influence limb length and weight changes, and to determine whether
Fig. 1. The increased height observed at 1 year after TKA decreased during subsequent follow-up. The height of the healthy population showed a similar decreasing temporal pattern. However, the effect of TKA on height was maintained at 5 years postoperatively. *p b 0.05; #p b 0.05 between patients and controls; KNHANES = Korean National Health and Nutritional Examination Survey; Y = year.
Fig. 2. Mean patient weight was greater than mean weight in the healthy population. In addition, the increased weight observed at 1 year post-TKA did not change over 5 years of follow-up, and at 5 years mean weight was greater than preoperative weight. In contrast, a decreasing trend was observed in controls. *p b 0.05; #p b 0.05 between patients and controls; KNHANES = Korean National Health and Nutritional Examination Survey; Y = year.
height, weight, and BMI at 1 year are maintained over 5 years of follow-up period and whether the patterns shown by patients and normal healthy controls differ. The present study has several limitations that warrant consideration. First, most of the study subjects were female. However, female predominance is common in most TKA series, and this is true especially in studies of Asian patients [17–21]. Furthermore, female predominance is more obvious with Koreans and it is supported by recent studies [18,22]. A recent population-based cohort study in Korea reported that women had more than 10 times the prevalence of TKA candidates than men [22]. In addition, there was no difference in change patterns between female and male patients in this study (data not presented). Thus, it suggests that there was no selection bias in the present study regarding gender. Furthermore, despite the female gender dominance in our study population, our study may provide valuable information to clinicians, particularly who care for patient
Fig. 3. The mean BMIs of patients showed an increasing tendency because height decreased but weight increased with time. No change in BMI was observed in controls because both height and weight both decreased. *p b 0.05; #p b 0.05 between patients and controls; KNHANES = Korean National Health and Nutritional Examination Survey; Y = year.
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populations with similar gender compositions. Second, a considerable number of patients were excluded from the final analysis, and this could have introduced selection bias, although a relatively large number of patients were included without any intended selection. Third, medical conditions, such as, diabetes mellitus or other metabolic diseases, which might have affected our results, were not considered. Fourth, amounts of bone and tissue resected and implant weights were not considered in the weight change calculations. On the other hand, mean weight gain tended to be greater in the unilateral group than in the bilateral TKA group (1.3 vs. 0.7 kg, p = 0.064), and therefore, we believe that weights of implants or of bone and tissue resected did not substantially affect body weight changes. Finally, clinically meaningful differences were set arbitrarily at our discretions, and thus, we do not know whether the patients have functional and psychological problems according to the amount of meaningful differences of this study. Our findings support the hypotheses that limb length increases but leg length discrepancy decreases after TKA and that the bilateral group has a smaller postoperative leg length discrepancy than the unilateral group. Our findings of increasing limb length and decreasing leg length discrepancy after TKA are in line with a previous study of 98 patients with TKA reporting that limb length increased and residual leg length discrepancy decreased [4]. In our study, however, despite the decrease of leg length discrepancy in mean values, considerable proportions of patients (14.6% in the unilateral group and 7.8% in the bilateral group) still had a residual leg length discrepancy of ≥ 1 cm. Our findings indicate that patients considering TKA can be informed of the likelihood of an increase in limb length and cautioned regarding the possibility of residual leg length discrepancy. Patients awaiting TKA often argue that knee pain limits mobility increases weight, and they expect prior to TKA increased mobility will reduce weight. Our findings indicate that the wishful scenario typically is not the case. On the contrary, more than half patients (21.7%) of this study gained weight greater than 5%. This striking finding, which is typically contradictory to patients' expectation, was also observed in several previous studies [1,3,5–7,16]. Therefore, patients undergoing TKA, who typically require weight loss for the sake of knees and other health issues should be advised to take measures to achieve weight loss. In this study, despite substantial postoperative changes in weight, BMI changes did not parallel weight changes because of changes in height. Accordingly, BMI did not increase 1 year after TKA despite a mean weight increase. Actually, BMI decreased in bilateral TKA group because of the greater height increase. In addition, similar effects of height changes on BMI were found during the 5-year follow-up. Although weight at 1 year after TKA remained at similar levels over the 5-year period, BMI tended to increase due to the decreasing pattern of height. It is uncertain whether these BMI changes are of clinical relevance, but caution is needed when interpreting the BMIs of TKA patients, especially bilateral TKA patients as a parameter of health status. Regression analyses affirmed our hypothesis that limb length change would be influenced by the severity of preoperative deformity but did not support the hypothesis that weight change would be influenced by preoperative BMI and postoperative functional outcomes. It is intuitive that knees with severe preoperative deformity in coronal plane, which was represented by mechanical tibiofemoral angle in this study, achieved greater limb length increase with the surgical procedures of TKA. A previous study reported the same finding that limb length change was associated with the severity of coronal deformity [4]. On the contrary, we found no association between the degree of preoperative flexion contracture and limb length change. This negative finding might be explained by the fact that we often took additional bone resections from distal femur to address a smaller extension gap resulting from flexion contracture. On
the other hand, to our interest, patients with a smaller BMI had greater weight gain at 1 year postoperatively. We are unaware how to explain this finding. Originally we had assumed that obese patients would perform less physical activity and continue to do so even after surgery, which would contribute to weight gain after surgery. Likewise, we had assumed that better functional outcomes are associated with greater physical activities which would contribute to weight loss after surgery. Our findings of no associations between preoperative BMI or postoperative functional outcomes and weight changes indicate that weight changes after TKA are a complex phenomenon which involves multiple unidentified factors. The question, whether the long-term change patterns of height, weight, and BMI after TKA are similar to those of the healthy population is important during patient counseling and planning general health care policy. However, we could not obtain long-term longitudinal data on height, weight, and BMI in the healthy population. Instead we extracted cross-sectional data on an age- and gendermatched healthy population from KNHANES. Therefore, it was not possible to direct compare our findings in TKA patients with those in the control subjects. However, it appears to be certain that in TKA patients, weight change patterns over the 5-year period after TKA differ from those of the healthy population. Whereas weight decreased gradually in the control, increased weight at 1 year after surgery in TKA patients remained at similar levels. Considering that weight management is essential for general health care, this pattern of weight changes should be considered in providing patients after TKA with long-term health care. In conclusion, this study documents that TKA increases limb length and reduces leg length discrepancy, but that patients tend to gain weight after surgery. These patterns of change after TKA and the factors found to be associated with limb length and weight changes should be considered during preoperative patient counseling and when planning postoperative rehabilitation. References 1. Abu-Rajab RB, Findlay H, Young D, et al. Weight changes following lower limb arthroplasty: a prospective observational study. Scott Med J 2009;54:26. 2. Aderinto J, Brenkel IJ, Chan P. Weight change following total hip replacement: a comparison of obese and non-obese patients. Surgeon 2005;3:269. 3. Donovan J, Dingwall I, McChesney S. Weight change 1 year following total knee or hip arthroplasty. ANZ J Surg 2006;76:222. 4. Lang JE, Scott RD, Lonner JH, et al. Magnitude of limb lengthening after primary total knee arthroplasty. J Arthroplasty 2011;27:341. 5. Stets K, Koehler SM, Bronson W, et al. Weight and body mass index change after total joint arthroplasty. Orthopedics 2010;33:386. 6. Woodruff MJ, Stone MH. Comparison of weight changes after total hip or knee arthroplasty. J Arthroplasty 2001;16:22. 7. Zeni Jr JA, Snyder-Mackler L. Most patients gain weight in the 2 years after total knee arthroplasty: comparison to a healthy control group. Osteoarthritis Cartilage 2010;18:510. 8. Bombelli M, Facchetti R, Sega R, et al. Impact of body mass index and waist circumference on the long-term risk of diabetes mellitus, hypertension, and cardiac organ damage. Hypertension 2011;58:1029. 9. Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplasty 2004;19:108. 10. Kim TK, Park KK, Yoon SW, et al. Clinical value of regular passive ROM exercise by a physical therapist after total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2009;17:1152. 11. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989:13. 12. Bellamy N, Buchanan WW, Goldsmith CH, et al. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988;15:1833. 13. Ware Jr JE, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30:473. 14. Chang CB, Choi JY, Koh IJ, et al. What should be considered in using standard knee radiographs to estimate mechanical alignment of the knee? Osteoarthritis Cartilage 2010;18:530. 15. Paans N, Stevens M, Wagenmakers R, et al. Changes in body weight after total hip arthroplasty: short- and long-term effects. Phys Ther 2012;92:680. 16. Riddle DL, Singh JA, Harmsen WS, et al. Clinically important body weight gain following knee arthroplasty: a five-year comparative cohort study. Arthritis Care Res (Hoboken) 2013;65:669.
M.J. Chang et al. / The Journal of Arthroplasty 28 (2013) 1856–1861 17. Kim HA, Kim S, Seo YI, et al. The epidemiology of total knee replacement in South Korea: national registry data. Rheumatology (Oxford) 2008;47:88. 18. Koh IJ, Kim TK, Chang CB, et al. Trends in use of total knee arthroplasty in Korea from 2001 to 2010. Clin Orthop Relat Res 2013;471:1441. 19. Memtsoudis SG, Della Valle AG, Besculides MC, et al. Trends in demographics, comorbidity profiles, in-hospital complications and mortality associated with primary knee arthroplasty. J Arthroplasty 2009;24:518.
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20. Mitsuyasu S, Hagihara A, Horiguchi H, et al. Relationship between total arthroplasty case volume and patient outcome in an acute care payment system in Japan. J Arthroplasty 2006;21:656. 21. Yan CH, Chiu KY, Ng FY. Total knee arthroplasty for primary knee osteoarthritis: changing pattern over the past 10 years. Hong Kong Med J 2011;17:20. 22. Cho HJ, Chang CB, Kim KW, et al. Gender and prevalence of knee osteoarthritis types in elderly Koreans. J Arthroplasty 2011;26:994.
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The Patterns of Limb Length, Height, Weight and Body Mass Index Changes after Total Knee Arthroplasty Moon Jong Chang, MD a, Yeon Gwi Kang, MS a, Chong Bum Chang, MD, PhD a, b, Sang Cheol Seong, MD, PhD b, Tae Kyun Kim, MD, PhD a, b a b
Joint Reconstruction Center, Seoul National University Bundang Hospital, Seongnam, Korea Department of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul, Korea
a r t i c l e
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Article history: Received 20 November 2012 Accepted 24 March 2013 Keywords: limb length leg length discrepancy height weight body mass index total knee arthroplasty
a b s t r a c t The objective of this retrospective review of 466 patients was to document changes in limb length, leg length discrepancy (LLD), height, weight, and body mass index (BMI) 1 year after TKA and the patterns of height, weight, and BMI during 5 years. To determine change patterns over 5 years, the data of 291 patients were analyzed and compared with those of age and gender-matched normal subjects. Limb length, height, and weight increased, BMI remained unchanged, and LLD decreased 1 year after TKA. The bilateral group had a greater height increase and lower rate of LLD. Preoperative mechanical tibiofemoral angle was related to limb length increase, and patients with a smaller preoperative BMI showed more weight gain. During the 5 years, weight and BMI at 1 year were maintained, but height diminished, while the healthy population showed a decreasing trend in weight. © 2013 Elsevier Inc. All rights reserved.
Patients undergoing total knee arthroplasty (TKA) may experience changes in body statistics, such as, limb length, leg length discrepancy, height, weight, or body mass index (BMI) [1–7]. Patients awaiting TKA often wonder how their body shapes will change after surgery and often expect that TKA will increase mobility and allow weight loss, as changes in weight are certainly linked to the general health [8]. In addition, perceivable leg length discrepancy could be a source of patient dissatisfaction [9], but cannot be accurately controlled by preoperative planning [4]. Furthermore, in contrast to total hip arthroplasty (THA), information is limited regarding the frequency and magnitude of limb length changes after TKA. Although TKA can improve knee function and mobility, published results disagree as to whether weight reduces after TKA [1–3,5–7]. In addition, TKA may have substantial effects on BMI because of potential changes in height and weight. Therefore, information of these changes after TKA is valuable for counseling patients and planning postoperative care. Changes in body statistics may depend on patient factors, the duration of follow-up, and whether TKA is unilateral or bilateral. In theory, greater amounts of soft tissue release to assure symmetrical
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.03.024. Reprint requests: Tae Kyun Kim, MD, PhD, 166 Gumi-ro, Bundang-gu, Seongnam-si, Gyeonggi-do (463-707), Republic of Korea. 0883-5403/2810-0033$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.03.024
gaps cause larger gaps, and thus, more severe deformities may increase limb length changes, as could relief of flexion contracture. On the other hand, preoperative obesity and postoperative functional outcomes affect level of mobility, and thus, are likely to influence weight change. In the long term, change patterns may be different from those in the short term, because functional outcomes after TKA can change with time, and the patients also experience senile change. However, previous studies provide only limited relevant information [1,3,5–7]. Some studies included only small numbers of patients [3], whereas, others involved TKA and THA [3,6]. Furthermore, the majority included only unilateral TKA even though TKA is frequently performed as bilaterally [6,7]. In addition, many involved a follow-up period of 1 or 2 years [1,3,5–7]. Therefore, we considered that a largescale study was required that included unilateral and bilateral TKA and a longer-term follow-up. The first aim of this study was to document normative interval changes in limb length, leg length discrepancy, height, weight, and BMI 1 year after TKA. We were particularly interested in determining whether unilateral and bilateral TKA differ in terms of the amount of postoperative leg length discrepancy and changes in limb length, height, weight, and BMI. The second aim was to determine whether degrees of preoperative deformities (deviations of mechanical tibiofemoral angle from neutral and flexion contracture) are related to limb length change and whether preoperative BMI and postoperative functional outcomes are related to weight change at 1 year after surgery. Finally, we attempted to determine whether the height, weight, and BMI at 1 year are maintained until 5 years after TKA and
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whether patterns of change differ from those shown by the healthy population. We hypothesized as follows: (1) limb length and height would increase whereas leg length discrepancy, weight, and BMI would decrease after TKA, and that patients after bilateral TKA would exhibit smaller postoperative leg length discrepancies and greater changes in limb length, height, weight, and BMI than after unilateral TKA; (2) limb length changes are dependent on degree of deformity, and that weight changes depend on preoperative BMI and postoperative functional outcomes; and (3) changes in height, weight, and BMI at 1 year after TKA are maintained until 5 years after surgery, and that patterns of change are similar to those shown by healthy individuals. Patients and Methods Study Design and Subjects This retrospective review was conducted using the prospectively collected data of 466 patients for 1-year follow-up analysis. Primary TKA for osteoarthritis was performed at our institution on 969 patients from November 2003 to December 2008. Of these 969 patients, 302 were excluded for previous surgery on the ipsilateral lower extremity (28), spine surgery (18), a diagnosis other than primary osteoarthritis (54), Parkinson disease (17), a previous cerebrovascular accident (25), cancer (27), death due to diseases unrelated to TKA (11), a periprosthetic infection (13), or another condition capable of affecting the result of this study, such as depression, dementia, or problems of the contralateral knee (109). After these exclusions, 667 patients were left eligible for inclusion. Of these 667 patients, 201 (30%) did not have standing full-limb anteroposterior (AP) radiographs or complete information of height, weight, and BMI and was excluded. Consequently, 466 patients (761 knees) (70% of the eligible 667 patients) were included in the final analysis. There were 440 females (95%) and 26 males (5%) with a mean age 67.9 years (SD, 5.9 years; range, 49–84 years). One hundred seventy-one patients (34%) underwent unilateral TKA and 295 (66%) underwent bilateral TKAs. Of the 440 patients eligible for 5year follow-up analysis, 291 patients (66%) with follow-up data during the 5 years were included to allow the analysis of temporal height, weight, and BMI patterns. These 291 patients comprised 278 females (96%) and 13 males (4%) with a mean age of 68.3 years (SD, 6.1 years; range, 53–84 years). This study was approved by the institutional review board of our hospital. Surgery and Rehabilitation All surgeries were performed by a single surgeon (one of the authors) using the medial parapatellar approach with a tourniquet, and all patients underwent the same postoperative rehabilitation protocol [10]. Patellar resurfacing was performed in all cases. Implant fixation was carried out using cement. A compressive dressing was applied without immobilization for 24 h after surgery, and then, a continuous passive motion machine was applied. On the second postoperative day, all patients began walking with crutches or a walker and started active and passive range of motion exercises. Clinical Evaluation Clinical information including demographics, preoperative degree of flexion contracture, functional outcomes, height, weight, and BMI, was prospectively collected by one independent investigator (one of the authors). Preoperative flexion contractures were measured using a goniometer with the patients supine. Functional statuses were measured using American Knee Society (AKS) function scores [11], Western Ontario McMaster University Score (WOMAC) [12], and Short-Form 36 (SF-36) [13] questionnaire scores preoperatively, and at 6 and 12 months post-TKA and then annually. The height, weight
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and BMI were measured preoperatively, and at 1, 2, 3, and 5 years postoperatively. The height was measured in centimeters and weight in kilograms using an electronic device (DS-102, JENIX, Seoul, Korea). Body mass index (BMI) was calculated by dividing weight in kilograms by height in meters squared. Radiographic Evaluation Radiographic measurements, including preoperative mechanical tibiofemoral angle and limb length were taken by one observer (one of the authors), who was not the primary surgeon, using standing fulllimb AP radiographs on a 14 × 51-inch grid cassette preoperative, 6 weeks and at 3, 6, and 12 months postoperatively, and then annually. When radiographs were checked, a reference template on the platform was used to control limb rotation [14]. Preoperative mechanical tibiofemoral angles were used as an absolute value in both varus and valgus knees. Limb length was defined as the distance from the top of the femoral head to the center of the tibial plafond, as previously described [4]. All radiographic measurements were performed using a picture archiving and communication system (PACS) (Infinite, Seoul, Korea). Minimum detectable changes were 0.1 mm for length measurements and 0.1° for angular measurements. To determine the intra- and interobserver reliabilities of measurements, 20 subjects were chosen and measured twice (a week apart) by two observers (two of the authors). The reliabilities of measurements were confirmed using intraclass correlation coefficients (ICC). The ICCs for the intra- and interobserver reliabilities of limb length measurements were almost perfect (N 0.9). Statistical Analysis Statistical analysis was performed throughout using SPSS for Windows (version 17.0; SPSS Inc, Chicago, IL). To document the proportions of patients who experienced a clinically meaningful change, meaningful change was set at our discretions. A minimum of 1-cm change from preoperative values was set for limb length, leg length discrepancy, and height. The amount of meaningful change for weight and BMI was set at a minimum of 5% [15,16]. All statistical analyses had more than a power of 80% to detect the aforementioned meaningful changes at the different time points with less than a 5% probability of a type I error. For the 5-year follow-up analysis, age and gender-matched individuals were selected from the database of the Korean National Health and Nutritional Examination Survey (KNHANES). Unfortunately, KNHANES data were cross sectional, and thus, we did not have longitudinal data of healthy controls spanning the same period. Therefore, corresponding numbers of subjects were randomly and repeatedly selected from KNHANES according to age and gender at each time point (preoperative, and 1, 2, 3, and 5 years after TKA) of the analysis to form control groups. Changes in body statistics and rate of leg length discrepancy at 1 year post-TKA were calculated versus preoperative levels. Mean differences and ranges were used to describe overall changes in limb length, leg length discrepancy, height, weight, and BMI at 1 year postoperatively. The paired t-test was used to determine statistical significances. The magnitudes of changes in limb length, leg length discrepancy, height, weight, and BMI were categorized, and frequencies were noted. Magnitude and frequency of leg length discrepancy preoperatively and at 1 year after surgery were also compared, and chi-square test was used to determine statistical significance. The Student's t-test was used to determine the significances of the differences in the interval changes of limb length, height, weight, and BMI and residual leg length discrepancy between the unilateral and bilateral groups. Multivariate regression analysis was used to evaluate the relationship between degrees of deformity (preoperative mechanical
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tibiofemoral angles and preoperative flexion contractures) and amounts of leg length change, and the relationships between preoperative BMI and functional outcomes at 1 year postoperatively and weight changes. Temporal changes in height, weight, and BMI over the 5-year follow-up period assessed and compared with those of controls. The Student's t-test was used to compare the heights, weights, and BMIs of TKA patients and controls at each time point, and the mixedeffects model repeated measures (MMRM) was used to analyze changes in the heights, weights, and BMIs of patients over the 5-year follow-up period. In addition, the one-way analysis of variances (ANOVA) with Tukey method as the post hoc analysis was used to analyze changes in the heights, weights, and BMIs of control groups during the same period.
Table 2 Frequency of Subjects for Selected Intervals of the Changes of Limb Length, Leg Length Discrepancy, Height, Weight and Body Mass Index 1 Year after TKAa. Parameters
Interval
Frequencies (N = 466)
Limb length change (cm)b
≤−1 −1b, b1 1≤, b2 ≥2 ≤−1.0 −1 b, b−0.5 −0.5≤, b0.5 0.5≤, b1.0 ≥1.0 ≤−1 −1b, b1 1≤, b2 ≥2 ≤−5 −5b, b5 ≥5 ≤−5 −5b, b5 ≥5
3.4 (26) 52.7 (401) 28.0 (213) 15.9 (121) 6.0 (28) 12.3 (57) 68.0 (317) 11.8 (55) 1.9 (9) 4.3 (20) 31.3 (146) 40.4 (188) 24.0 (112) 21.7 (101) 69.1 (322) 9.2 (43) 12.6 (59) 70.2 (327) 17.2 (80)
LLD change (cm)
Height change (cm)
Weight change (%)
Results Average limb length, height, and weight increased, BMI remained unchanged, and mean leg length discrepancy decreased 1 year after surgery (Tables 1 and 2). Limb lengths increased by an average of 0.9 cm (range, − 2.3 to 4.9 cm) (p b 0.001). Of the 761 operative limbs, 334 (43.9%) experienced limb lengthening by ≥1 cm but 26 (3.4%) experienced limb length shortening of ≥ 1 cm. Mean leg length discrepancy was 0.1 cm (range, − 2.6 to 1.9 cm) smaller at 1 year after TKA. The proportion of patients with a leg length discrepancy of ≥ 1 cm reduced from 17.2% (80) to 10.3% (48) at 1 year after surgery (p = 0.007). Mean increase in height over the same period was 0.9 cm (range, − 3 to 4 cm) (p b 0.001). Of the 466 patients, 300 (64.4%) showed an increase in height of ≥ 1 cm (average 1.5 cm). In contrast, 4.3% (20) decreased in height by 1 cm or greater (average 1.2 cm). Mean weight increased by 0.9 kg (range, − 10 to 13 kg) after TKA (p b 0.001). One hundred one patients (21.7%) had a weight increase of ≥ 5%. In contrast, only 43 patients (9.2%) lost ≥ 5%. No change in mean BMI was observed (preoperative 27.1 kg/m 2 vs. postoperative 27.1 kg/m 2, p = 0.413). BMI increased in 80 patients (17.2%), decreased in 59 patients (12.6%) but remained unchanged in the majority (70.2%, 327 patients). The bilateral group showed different amounts or patterns of changes in the parameters investigated (Table 3). The bilateral group achieved a greater increase in limb length (0.9 vs. 0.7 cm, p = 0.050) and had smaller mean residual leg length discrepancy (0.5 vs. 0.6 cm, p = 0.006) than the unilateral group. Furthermore, the bilateral group had a lower proportion of patients with residual leg length discrepancy (≥0.5 cm; 41.4% vs. 53.8% and ≥1 cm; 7.8% vs. 14.6%, p = 0.011). The bilateral group also showed a greater increase in height (1.1 vs. 0.7 cm, p = 0.001) than the unilateral group. However, mean weight gain tended to be greater in the unilateral group (1.3 vs. 0.7 kg, p = 0.064). Although no mean difference in BMI was found overall in TKA patients, BMI increased by 0.3 kg/m 2 in the unilateral group but decreased by 0.1 kg/m 2 in the bilateral group (p = 0.008). Regression analyses identified preoperative mechanical tibiofemoral angle and BMI as patient factors for limb length change and
BMI change (%)
Abbreviations: N = number, LLD = leg length discrepancy, BMI = body mass index. a Data are presented as percents with numbers in parenthesis. b For patients with bilateral TKAs, both knees were measured separately, and the number of knees measured was 590.
weight change, respectively. Greater preoperative deformity in the coronal plane, as determined by mechanical tibiofemoral angle, was related to a greater increase in limb length (β = 0.833, p b 0.001). Linear regression analysis showed that limb length increased 7.6 mm per 10° of preoperative mechanical tibiofemoral angle. However, no association was found between degree of preoperative flexion contracture and limb length change (p = 0.486). Mean mechanical tibiofemoral angle was varus 11.9º (SD, 5.5º; range, varus 37 to valgus 9º) preoperatively and varus 1.5º (SD, 2.7º; range, varus 11 to valgus 6º) 1 year after TKA. Preoperatively, mean flexion contracture was 13.6º (SD, 7.4º; range, 0 to 50º) and 0.2º (SD, 1.3º; range, 0 to 15º) 1 year after TKA. Postoperative mechanical tibiofemoral angle and flexion contracture were not associated with limb length change (p = 0.447 and 0.322, respectively). On the other hand, patients with a smaller preoperative BMI showed a greater increase in weight at 1 year postoperatively (β = − 0.262, p b 0.001). In contrast, no association was found between weight change and any functional outcome measure at 1 year postoperatively (p N 0.05). Patients after TKA showed different patterns of changes in height, weight, and BMI from the normal healthy population over the 5-year period (Figs 1, 2, and 3). In the patients after TKA, mean height decreased at every follow-up from 1 year post-TKA (p b 0.05 for all). A similar decreasing pattern was observed in controls. However, patient mean height at 5 years after TKA was still greater than that of controls (151.8 cm vs. 150.3 cm; p b 0.001), which was probably due to the height increase by TKA (Fig. 1). Temporal patterns of weight
Table 1 Interval Changes in Limb Length, Leg Length Discrepancy, Height, Weight and Body Mass Index of 466 Patients at 1 Year after TKAa. Preoperative Parameters Limb length (cm) LLD (cm) Height (cm) Weight (kg) BMI (kg/m2)
Mean 76.0 0.6 152.6 63.1 27.1
(3.8) (0.5) (6.1) (9.2) (3.4)
1 year after TKA
Differences
Range
Mean
Range
Mean
Range
64.9–91.1 0–3.9 136–178 36–99 18–38
76.9 (3.8) 0.5 (0.4) 153.5 (6.0) 64.0 (9.1) 27.1 (3.3)
67.3–92.1 0–3.8 136–179 36–100 16.9–38.8
0.9 (1.1) −0.1 (0.6) 0.9 (1.0) 0.9 (3.3) 0.05 (1.5)
−2.3–4.9 −2.6–1.9 −3.0–4.0 −10–13 −6.6–5.7
Abbreviations: LLD = leg length discrepancy, BMI = body mass index. a Data are presented as means with standard deviations in parenthesis. b Values b 0.05 are displayed in bold font.
p-Valuesb b0.001 b0.001 b0.001 b0.001 0.413
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Table 3 Comparisons of the Amount of Changes in Limb Length, Leg Length Discrepancy, Height, Weight and BMI 1 Year after Surgery between the Unilateral and the Bilateral Groupsa. Parameters Limb length change (cm) Residual LLD (cm) Height change (cm) Weight change (kg) BMI change (kg/m2)
Unilateral (N = 171) Bilateral (N = 295) p-Valuesb 0.7 (1.1) 0.6 (0.4) 0.7 (1.0) 1.3 (3.2) 0.3 (1.4)
0.9 (0.9) 0.5 (0.4) 1.1 (1.0) 0.7 (3.4) −0.1 (1.5)
0.050 0.006 0.001 0.064 0.008
Abbreviations: LLD = leg length discrepancy, BMI = body mass index. a Data are presented as means with standard deviations in parenthesis. b Values less than 0.05 are displayed in bold style.
and BMI changes in patients differed from those of controls. Patient mean weight and BMI were greater than those of controls (p b 0.05 at all time points). Furthermore, in patients, mean weight at 1 year after TKA was maintained throughout the 5-year follow-up. On the other hand, control mean weight showed a decreasing trend during the same 5 years (Fig. 2). Mean patient BMI showed an increasing tendency because mean height decreased and mean weight was maintained over the 5-year period (Fig. 3). On the other hand, mean BMI in controls did not change because both mean height and weight decreased. Discussion Information on postoperative changes in body statistics after TKA is valuable for preoperative education purposes and for planning postoperative rehabilitation. However, no detailed information has been reported on such changes. In the present study, we sought to evaluate changes in body statistics and to determine whether the unilateral and bilateral TKAs differentially affect changes at 1 year after surgery. In addition, we attempted to identify patient factors that influence limb length and weight changes, and to determine whether
Fig. 1. The increased height observed at 1 year after TKA decreased during subsequent follow-up. The height of the healthy population showed a similar decreasing temporal pattern. However, the effect of TKA on height was maintained at 5 years postoperatively. *p b 0.05; #p b 0.05 between patients and controls; KNHANES = Korean National Health and Nutritional Examination Survey; Y = year.
Fig. 2. Mean patient weight was greater than mean weight in the healthy population. In addition, the increased weight observed at 1 year post-TKA did not change over 5 years of follow-up, and at 5 years mean weight was greater than preoperative weight. In contrast, a decreasing trend was observed in controls. *p b 0.05; #p b 0.05 between patients and controls; KNHANES = Korean National Health and Nutritional Examination Survey; Y = year.
height, weight, and BMI at 1 year are maintained over 5 years of follow-up period and whether the patterns shown by patients and normal healthy controls differ. The present study has several limitations that warrant consideration. First, most of the study subjects were female. However, female predominance is common in most TKA series, and this is true especially in studies of Asian patients [17–21]. Furthermore, female predominance is more obvious with Koreans and it is supported by recent studies [18,22]. A recent population-based cohort study in Korea reported that women had more than 10 times the prevalence of TKA candidates than men [22]. In addition, there was no difference in change patterns between female and male patients in this study (data not presented). Thus, it suggests that there was no selection bias in the present study regarding gender. Furthermore, despite the female gender dominance in our study population, our study may provide valuable information to clinicians, particularly who care for patient
Fig. 3. The mean BMIs of patients showed an increasing tendency because height decreased but weight increased with time. No change in BMI was observed in controls because both height and weight both decreased. *p b 0.05; #p b 0.05 between patients and controls; KNHANES = Korean National Health and Nutritional Examination Survey; Y = year.
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populations with similar gender compositions. Second, a considerable number of patients were excluded from the final analysis, and this could have introduced selection bias, although a relatively large number of patients were included without any intended selection. Third, medical conditions, such as, diabetes mellitus or other metabolic diseases, which might have affected our results, were not considered. Fourth, amounts of bone and tissue resected and implant weights were not considered in the weight change calculations. On the other hand, mean weight gain tended to be greater in the unilateral group than in the bilateral TKA group (1.3 vs. 0.7 kg, p = 0.064), and therefore, we believe that weights of implants or of bone and tissue resected did not substantially affect body weight changes. Finally, clinically meaningful differences were set arbitrarily at our discretions, and thus, we do not know whether the patients have functional and psychological problems according to the amount of meaningful differences of this study. Our findings support the hypotheses that limb length increases but leg length discrepancy decreases after TKA and that the bilateral group has a smaller postoperative leg length discrepancy than the unilateral group. Our findings of increasing limb length and decreasing leg length discrepancy after TKA are in line with a previous study of 98 patients with TKA reporting that limb length increased and residual leg length discrepancy decreased [4]. In our study, however, despite the decrease of leg length discrepancy in mean values, considerable proportions of patients (14.6% in the unilateral group and 7.8% in the bilateral group) still had a residual leg length discrepancy of ≥ 1 cm. Our findings indicate that patients considering TKA can be informed of the likelihood of an increase in limb length and cautioned regarding the possibility of residual leg length discrepancy. Patients awaiting TKA often argue that knee pain limits mobility increases weight, and they expect prior to TKA increased mobility will reduce weight. Our findings indicate that the wishful scenario typically is not the case. On the contrary, more than half patients (21.7%) of this study gained weight greater than 5%. This striking finding, which is typically contradictory to patients' expectation, was also observed in several previous studies [1,3,5–7,16]. Therefore, patients undergoing TKA, who typically require weight loss for the sake of knees and other health issues should be advised to take measures to achieve weight loss. In this study, despite substantial postoperative changes in weight, BMI changes did not parallel weight changes because of changes in height. Accordingly, BMI did not increase 1 year after TKA despite a mean weight increase. Actually, BMI decreased in bilateral TKA group because of the greater height increase. In addition, similar effects of height changes on BMI were found during the 5-year follow-up. Although weight at 1 year after TKA remained at similar levels over the 5-year period, BMI tended to increase due to the decreasing pattern of height. It is uncertain whether these BMI changes are of clinical relevance, but caution is needed when interpreting the BMIs of TKA patients, especially bilateral TKA patients as a parameter of health status. Regression analyses affirmed our hypothesis that limb length change would be influenced by the severity of preoperative deformity but did not support the hypothesis that weight change would be influenced by preoperative BMI and postoperative functional outcomes. It is intuitive that knees with severe preoperative deformity in coronal plane, which was represented by mechanical tibiofemoral angle in this study, achieved greater limb length increase with the surgical procedures of TKA. A previous study reported the same finding that limb length change was associated with the severity of coronal deformity [4]. On the contrary, we found no association between the degree of preoperative flexion contracture and limb length change. This negative finding might be explained by the fact that we often took additional bone resections from distal femur to address a smaller extension gap resulting from flexion contracture. On
the other hand, to our interest, patients with a smaller BMI had greater weight gain at 1 year postoperatively. We are unaware how to explain this finding. Originally we had assumed that obese patients would perform less physical activity and continue to do so even after surgery, which would contribute to weight gain after surgery. Likewise, we had assumed that better functional outcomes are associated with greater physical activities which would contribute to weight loss after surgery. Our findings of no associations between preoperative BMI or postoperative functional outcomes and weight changes indicate that weight changes after TKA are a complex phenomenon which involves multiple unidentified factors. The question, whether the long-term change patterns of height, weight, and BMI after TKA are similar to those of the healthy population is important during patient counseling and planning general health care policy. However, we could not obtain long-term longitudinal data on height, weight, and BMI in the healthy population. Instead we extracted cross-sectional data on an age- and gendermatched healthy population from KNHANES. Therefore, it was not possible to direct compare our findings in TKA patients with those in the control subjects. However, it appears to be certain that in TKA patients, weight change patterns over the 5-year period after TKA differ from those of the healthy population. Whereas weight decreased gradually in the control, increased weight at 1 year after surgery in TKA patients remained at similar levels. Considering that weight management is essential for general health care, this pattern of weight changes should be considered in providing patients after TKA with long-term health care. In conclusion, this study documents that TKA increases limb length and reduces leg length discrepancy, but that patients tend to gain weight after surgery. These patterns of change after TKA and the factors found to be associated with limb length and weight changes should be considered during preoperative patient counseling and when planning postoperative rehabilitation. References 1. Abu-Rajab RB, Findlay H, Young D, et al. Weight changes following lower limb arthroplasty: a prospective observational study. Scott Med J 2009;54:26. 2. Aderinto J, Brenkel IJ, Chan P. Weight change following total hip replacement: a comparison of obese and non-obese patients. Surgeon 2005;3:269. 3. Donovan J, Dingwall I, McChesney S. Weight change 1 year following total knee or hip arthroplasty. ANZ J Surg 2006;76:222. 4. Lang JE, Scott RD, Lonner JH, et al. Magnitude of limb lengthening after primary total knee arthroplasty. J Arthroplasty 2011;27:341. 5. Stets K, Koehler SM, Bronson W, et al. Weight and body mass index change after total joint arthroplasty. Orthopedics 2010;33:386. 6. Woodruff MJ, Stone MH. Comparison of weight changes after total hip or knee arthroplasty. J Arthroplasty 2001;16:22. 7. Zeni Jr JA, Snyder-Mackler L. Most patients gain weight in the 2 years after total knee arthroplasty: comparison to a healthy control group. Osteoarthritis Cartilage 2010;18:510. 8. Bombelli M, Facchetti R, Sega R, et al. Impact of body mass index and waist circumference on the long-term risk of diabetes mellitus, hypertension, and cardiac organ damage. Hypertension 2011;58:1029. 9. Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplasty 2004;19:108. 10. Kim TK, Park KK, Yoon SW, et al. Clinical value of regular passive ROM exercise by a physical therapist after total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2009;17:1152. 11. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989:13. 12. Bellamy N, Buchanan WW, Goldsmith CH, et al. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988;15:1833. 13. Ware Jr JE, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30:473. 14. Chang CB, Choi JY, Koh IJ, et al. What should be considered in using standard knee radiographs to estimate mechanical alignment of the knee? Osteoarthritis Cartilage 2010;18:530. 15. Paans N, Stevens M, Wagenmakers R, et al. Changes in body weight after total hip arthroplasty: short- and long-term effects. Phys Ther 2012;92:680. 16. Riddle DL, Singh JA, Harmsen WS, et al. Clinically important body weight gain following knee arthroplasty: a five-year comparative cohort study. Arthritis Care Res (Hoboken) 2013;65:669.
M.J. Chang et al. / The Journal of Arthroplasty 28 (2013) 1856–1861 17. Kim HA, Kim S, Seo YI, et al. The epidemiology of total knee replacement in South Korea: national registry data. Rheumatology (Oxford) 2008;47:88. 18. Koh IJ, Kim TK, Chang CB, et al. Trends in use of total knee arthroplasty in Korea from 2001 to 2010. Clin Orthop Relat Res 2013;471:1441. 19. Memtsoudis SG, Della Valle AG, Besculides MC, et al. Trends in demographics, comorbidity profiles, in-hospital complications and mortality associated with primary knee arthroplasty. J Arthroplasty 2009;24:518.
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20. Mitsuyasu S, Hagihara A, Horiguchi H, et al. Relationship between total arthroplasty case volume and patient outcome in an acute care payment system in Japan. J Arthroplasty 2006;21:656. 21. Yan CH, Chiu KY, Ng FY. Total knee arthroplasty for primary knee osteoarthritis: changing pattern over the past 10 years. Hong Kong Med J 2011;17:20. 22. Cho HJ, Chang CB, Kim KW, et al. Gender and prevalence of knee osteoarthritis types in elderly Koreans. J Arthroplasty 2011;26:994.