| | Activity Level in Young Patients With Primary Total Hip Arthroplasty: A 5-Year Minimum Follow-upReceived 6 July 2005; accepted 8 February 2006. Abstract Increased activity level after total hip arthroplasty (THA) is considered a risk factor for early prosthetic failure in young patients. Forty-one primary total hip arthroplasties in 34 patients were evaluated. Walking activity was measured using a pedometer to record gait cycles. Patients completed a University of California, Los Angeles (UCLA) activity questionnaire. Linear wear rates were measured. Mean ages at surgery and final follow-up were 42 and 50.3 years, respectively (mean gait cycles per year, 1.2 million; mean UCLA score, 6; mean linear wear, 0.16 mm/y). Increased body mass index and age correlated with decreased gait cycles per year. Patients with systemic disease were less active than patients with localized hip conditions. Femoral head diameter was a predictor of linear wear. The average gait cycles per year and wear rate for this population do not appear accelerated relative to average values reported in older populations. Increased activity level after total hip arthroplasty (THA) is considered by most orthopedic surgeons as a major risk factor for early prosthetic failure in the young patient [1]. Patients younger than 50 years with advanced hip disease are perceived to be at risk for early postoperative prosthetic failure due, in large part, to a more active lifestyle accelerating polyethylene wear and osteolysis 2, 3. However, no study of young patients after THA has ever objectively examined activity level, and few studies have quantified polyethylene wear rates in such a population 4, 5, 6, 7. The purpose of our study was twofold: (1) to quantify the postoperative activity level in young patients after THA and (2) to measure linear polyethylene wear rates. We hypothesized that a population of patients younger than 50 years would demonstrate increased walking activity after THA relative to that which has been documented in older populations (approximately 1 million gait cycle per year) 8, 9. In addition, we hypothesized that linear polyethylene wear rates would be increased relative to the average rate reported for older populations (approximately 0.1 mm/y) 10, 11, 12. Materials and Methods  Study Design This study was retrospective in design with all data collected prospectively. Thirty-four consecutive patients with 41 primary THAs were identified. All patients were 50 years or younger at the time of the index procedure. Patient preoperative demographics including age, sex, diagnosis, and body mass index (BMI; weight in kilograms divided by the square of height in meters) were recorded. In addition, preoperative Harris hip score (HHS), the presence of other artificial joints, and history of contralateral hip surgery were recorded. All procedures were performed at one institution by 2 senior surgeons between 1993 and 1997. All patients received the same brand of porous-coated acetabular component (Reflection, Smith & Nephew, Memphis, Tenn) with the requisite modular Reflection Microstable polyethylene liners, which had been sterilized in ethylene oxide. All femoral stem components were cementless and both designs (Anatomic and Anatomic Bias Revision) were from the same manufacturer (Zimmer, Warsaw, Ind). The femoral head components were either cobalt chrome or an alumina ceramic material and were either 22 or 28 mm in diameter. All 34 patients were contacted and consented by phone or at the time of their routine follow-up visit. At the time of consent, each patient was interviewed by one of the authors. During these interviews, medical histories were updated. Current height and weight were recorded and used to calculate individual BMIs. Patients were asked to complete a Harris hip questionnaire. Patient activity level was measured by 2 methods: (1) University of California, Los Angeles (UCLA) Activity Score and (2) use of a digital pedometer to record gait cycles. Activity Measurement UCLA Activity Score The UCLA activity score subjectively rates activity on a scale from 1 (totally inactive) to 10 (regularly active in impact sports such as tennis, skiing, jogging, aerobics, etc). The parameters of this scoring system [13] and its application to an arthroplasty population have been described in the literature [14]. Patients were provided with a UCLA activity score survey and asked to rate themselves. Pedometer Patients were provided with a digital pedometer (Sportline, Campbell, Calif) and a pedometer-based activity log. We provided both verbal and written instructions on proper usage of the pedometer and proper documentation of activity. Patients were instructed to measure and record their average step length by taking 10 steps, measuring the distance traveled (in feet), and then dividing the distance by 10. Patients were asked to wear the pedometer during all walking hours of the day and night and to record daily mileage in the activity log over 1 week. During the year in which the pedometer data was collected, with only one exception, all patients were living in the Midwest. To correct for seasonal impact on walking activity 15, 16, we randomly divided patients into 4 groups corresponding to the 4 seasons. Each group completed the pedometer portion of the study during a different season of the year. Upon completion, activity logs were mailed to our office for analysis. Activity data consisted of a patient's average step length and a daily record of mileage walked over 1 week. Simple calculations were performed to standardize all distance measurements. The number of steps per day was determined by averaging the patient's daily mileage and dividing by his or her unique step length. The number of gait cycles per day was calculated by dividing the number of steps per day by 2. Finally, the number of gait cycles per year was estimated by multiplying gait cycles per day by 365 d/y. Polyethylene Wear For all patients studied, early postoperative hip radiographs (taken at 1 year after THA) were compared with current radiographs taken with comparable imaging technique, patient positioning, and weight-bearing status. All early postoperative radiographs and most follow-up radiographs were performed within our clinic with standardized imaging technique. Patients unable to return for on-site follow-up evaluation were directed to have comparable radiographs taken locally and forwarded to the senior author's office. The amount of linear polyethylene wear was determined using the technique described by Livermore et al [17], measuring the change in the shortest distance between the center of the prosthetic femoral head and the periphery of the acetabular component as seen in the early postoperative radiographs compared with that seen on radiographs obtained at the latest follow-up evaluation. Magnification was standardized against the known circumference of the femoral head. Measurements were performed using a portable electronic device (X-Caliper, Eisenlohr Technologies, Inc, Davis, Calif) that had accuracy to within 0.25 mm at 120% magnification. Wear measurements were recorded in millimeters by 2 independent observers experienced with this technique. Interobserver reliability was significant (r = 0.72, P < .001). We report the averaged measurements of the 2 independent observers. Individual patient linear wear rates were then estimated by dividing their total linear wear by time between radiographs and expressed as millimeters per year. Statistical Analysis Statistical analyses were performed with SPSS statistical software (version 11.0, Chicago, Ill). Pearson correlation coefficients were computed to assess the relationship between objective (gait cycles per year) and subjective measures of activity (UCLA score) and to assess the relationships between clinical, demographic, and radiographic variables. Interobserver reliability of linear wear measurements was assessed with Pearson correlation. Analysis of variance was used to compare diagnostic groups using clinical and radiographic variables. t Tests were used to compare specific preoperative and postoperative demographic variables, such as BMI, as well as to compare sexes in terms of outcome variables. The t tests were used to compare different femoral head sizes in relation to the amount of polyethylene wear. A multiple regression model was used to evaluate the effects of predictor variables on linear wear. Analysis of the data in exploratory studies (such as this one) often requires multiple separate comparisons. In this study, we recognized the increased possibility of type I error due to multiple comparisons. Therefore, a more rigorous criterion for statistical significance was selected. P values of .01 or less were considered significant. Results Thirty-four consecutive patients with 41 primary, uncemented THAs were studied at mean follow-up of 6.3 years (±1.2 SD; range, 5-9.9 years). There were 17 females and 17 males. The mean age at the time of index surgery was 42 years (±6.5 SD; range, 27-50 years). The mean preoperative BMI was 28.1 kg/m2 (±8.3 SD; range, 15.6-54.5 kg/m2). Preoperative diagnoses were as follows: rheumatoid arthritis (RA) in 6 hips (14.6%); avascular necrosis (AVN) in 8 hips (19.5%); degenerative joint disease related to osteoarthritis (OA) in 15 hips (36.6%); and 12 pediatric hip conditions including Perthes disease (n = 2), developmental dysplasia of the hip (DDH; n = 8), and epiphyseal dysplasia (n = 2). Eight patients (24%) had a history of previous surgery on the index hip (range, 0-2). The mean preoperative HHS for this population was 55 (range, 9-78). Surgical approaches to the hip included the posterior approach (n = 24), the anterolateral approach (n = 14), and the transtrochanteric approach (n = 3). All patients received Reflection porous-coated acetabular components with modular polyethylene liners. The average outer diameter of the acetabular component was 55 mm (range, 46-66 mm). Femoral head components were either cobalt chrome (n = 25) or alumina ceramic (n = 16). Use of one femoral head material or the other was based on an informed decision made by the patient preoperatively. Femoral head diameter was either 28 mm (n = 36) or 22 mm (n = 5). The decision to use 22-mm diameter heads was made by the surgeon intraoperatively and predicated upon allowing for adequate polyethylene thickness in younger patients (mean age, 38.2 years) with small acetabular cup diameters (mean diameter, 50 mm). Femoral stem components were all cementless. The mean age at time of follow-up was 50.3 years (±6.5 SD; range, 37-59 years). The mean postoperative BMI was 29.1 kg/m2 (±7.8 SD; range, 16.1-52.6 kg/m2), an insignificant increase relative to the preoperative BMI (matched-pair t test, P = .05). The mean postoperative HHS was 81 (range, 45-95), significantly increased relative to the preoperative score (P < .001). In addition, at final follow-up, 17 patients (50%) reported a history of surgery on the contralateral hip (range, 0-5 surgeries), and 17 patients (50%) reported presence of another artificial joint (hip or knee). Activity Measurement UCLA Activity Score For all patients, the self-reported mean UCLA activity score was 6.3 (range, 3-10). Patients with a history of contralateral hip surgery perceived themselves as less active and thus had significantly lower UCLA scores (r = −0.50, P = .001). Likewise, patients with more than 1 artificial joint rated themselves lower on the UCLA 10-point scale (r = −0.46, P = .003). The UCLA score positively correlated with postoperative HHS (r = 0.52, P = .001). In addition, male patients perceived themselves as significantly more active than female patients (P = .004) (see Gender Influence on Data section). The UCLA score did not correlate with the number of index hip surgeries (r = −0.13, P = .41), age (r = 0.29, P = .07), BMI (r = −0.07, P = .67), weight (r = 0.23, P = .16), or gait cycles per year (r = 0.02, P = .98). Pedometer For all patients, the mean number of gait cycles per year as measured by pedometer was 1.2 million (range, 03-2.7 million). Advanced age correlated negatively, but not significantly, with fewer gait cycles per year (r = −0.30, P = .05) (Fig. 1). Increased BMI negatively influenced number of gait cycles per year (r = −0.47, P = .002) (Fig. 2). The number of gait cycles per year did not correlate with presence of other artificial joints (r = 0.03, P = .86), the number of index or contralateral hip surgeries (r = −0.08, P = .63 and r = −0.03, P = .85, respectively), or UCLA score (r = 0.02, P = .98). Polyethylene Wear Linear Wear The mean linear polyethylene wear rate was 0.16 mm/y (range, 0.02-0.38 mm/y; ±0.10 SD). This value did not significantly correlate with the UCLA score measure of activity (r = 0.27, P = .09) or the number of gait cycles per year (r = 0.001, P = .99) (Fig. 3). We do not believe this is a type II error finding as a power analysis demonstrated that our sample size for correlating linear wear rates with gait cycles per year was sufficient to detect a correlation coefficient of 0.45 at the P = .05 level with 80% statistical power. When several theoretically important patient variables were used to predict linear wear in a multiple regression model (ie, age, sex, BMI, time in situ, presence of other artificial joints, number of index hip surgeries, number of contralateral hip surgeries, femoral head diameter, femoral head material, UCLA score, gait cycles per year), the only significant predictor was femoral head diameter (P = .001). A Student t test comparing wear rates of the 28- vs 22-mm-diameter femoral head demonstrated significant difference in linear wear rates (P = .01) (Fig. 4). When only femoral head diameter and gait cycles per year were included in a regression model, femoral head diameter remained significant (P = .01) whereas gait cycles per year remained nonsignificant (P = .762). In addition, many investigators have reported greater polyethylene wear measurements to be associated with thinner acetabular liners 18, 19, 20, 21. In our study, however, regression analysis of polyethylene liner thickness and linear wear rates, we did not find such a trend. Because of our small sample size, these relationships (significant or not significant) between linear wear rates and predictor variables should be considered preliminary as use of so many predictors can lead to unstable estimates of importance. Influence of Preoperative Diagnosis Between diagnostic groups, a significant difference in weight and BMI from preoperative to postoperative was observed. Except for patients with RA, each diagnostic group demonstrated a trend toward weight gain over time. Only patients with a history of pediatric hip disease demonstrated a statistically significant increase in BMI (P = .007) and weight gain (P = .004) from preoperative to postoperative. There were no significant differences in terms of presence of other artificial joints, number of index/opposite hip procedures, or change in HHS. UCLA Activity Score Mean UCLA scores according to preoperative diagnoses were as follows: AVN = 5.75 (±2.6 SD); pediatric hip disease = 5.2 (±2.2 SD); OA = 7.2 (±1.5 SD); RA = 4.8 (±0.75 SD). Analysis of variance showed no significant differences between diagnostic groups (F = 3.21, P = .03). Polyethylene Wear Mean linear wear rates according to preoperative diagnoses were as follows: AVN = 0.16 mm/y (±0.09 SD); pediatric hip disease = 0.17 mm/y (±0.14 SD); OA = 0.17 (±0.09 SD); RA = 0.13 (±0.04 SD). Analysis of variance showed no significant difference in linear wear rates between diagnostic groups (F = 0.256, P = .85) (Fig. 6). Because post hoc power analysis revealed an observed power of 9.4%, to find a significant effect would require a minimum sample size of approximately 100 hips per diagnostic group, or n = 400 hips. Based on this apparently small effect size, it seems unlikely that any significant relationship exists. Gender Influence on Data Preoperatively, there were no significant differences between male or female patients in terms of age, BMI, prior hip procedures, presence of other artificial joints, or HHS. Postoperatively, only 1 significant sex-based relationship was identified using a t test for equality of means. Male patients rated themselves significantly more active on the UCLA scale than our female patients (male mean, 7 ± 2; female mean, 5 ± 1) (P = .004). No significant difference was found between male and female HHSs (male mean, 85 ± 10; female mean, 77 ± 14) (P = .05). No significant difference was found between male and female mean gait cycles per year (male mean, 1.04 ± 491 794 million; female mean, 1.33 ± 785367 million) (P = .175). No significant difference was found between male and female linear wear rates (male mean, 0.18 ± 0.11; female mean, 0.14 ± 0.09) (P = .178). Discussion Young patients with primary THA may not be as active as thought. In our study of patients with a mean age of 42 years at the time of surgery and a mean age of 50 years at the time of follow-up, the average number of gait cycles per year was 1.2 million (range, 0.3-2.7 million). Interestingly, this value is consistent with what has been reported in studies of older patients after THA, which also used pedometers to estimate gait cycles per year. For example, Goldsmith et al [22] reported pedometer-based measure of activity level in 54 patients (mean age, 58 years) to be 1.4 million gait cycles per year. Schmalzried et al [4] studied 97 patients (>50 years of age) after THA and reported 0.9 million gait cycles per year (range, 72000-3.2 million). In another study, 31 patients (mean age, 72 years) after THA demonstrated 1.2 million gait cycles per year (range, 90000-3.1 million) [23]. More recently, Silva et al [24] studied 33 patients (mean age, 71.5 years) after THA and reported a mean of 1.3 million gait cycles per year (range, 87600-3.1 million). Thus, despite the considerable age differences between patients in our study compared with the more senior populations previously studied, the average number of gait cycles per year is comparable. There are numerous possible explanations for this finding. Foremost, many of our patients may have developed an inactive lifestyle preoperatively that remained unchanged postoperatively despite improved hip function. In addition, our younger patients requiring THA are routinely counseled to modify their postoperative activity level to prevent premature prosthetic failure. Compliance with such guidelines could account for the similar number of gait cycles per year measured between young and old. Another explanation is pedometer underrecording of activity 25, 26. Silva et al reported that digital pedometers similar to the one used in this study may under-record up to 34% of patient gait cycles. In that study, obesity was associated with decreased pedometer accuracy [24]. Finally, our study suggests certain patient factors may influence postoperative activity: age at index surgery, BMI, and preoperative diagnosis. Advanced age correlated negatively with the number of gait cycles per year. This finding is consistent with what has been reported in older populations after THA 14, 24. Thus, our patient population with preoperative ages ranging from 27 to 50 years not only demonstrated an activity level similar to older populations, but also demonstrated a similar trend of age-related decline in activity. Increased BMI significantly influenced the number of gait cycles per year of our patients after THA. It has been previously shown in older populations after arthroplasty that those with a higher BMI demonstrate a decreased level of walking activity 24, 27. Our study suggests this relationship remains valid for patients in their thirties, forties, and fifties as well. It should be noted of our study population that both the mean preoperative and postoperative BMIs (28.1 and 29.1, respectively) were consistent with grade I (moderate) obesity according to the World Health Organization international guidelines [28]. This finding may be, in part, due to a geographical influence as the Midwest has been shown to have a high prevalence of overweight and obese individuals [29]. As mentioned above, obesity has been associated with decreased pedometer accuracy and may have influenced quantification of gait cycles per year in this study. The influence of preoperative diagnosis on activity level in the young patient after THA is not widely described in the literature. According to our pedometer data, patients with systemic disease (ie, RA, OA) may remain relatively less active after THA when compared with patients who have localized conditions of the hip such as AVN, DDH, and Perthes disease. This finding is consistent with the observations of others who have studied young patients after THA 2, 30. Dorr et al studied patients younger than 45 years and observed that patients in Charnley functional class A seemed to be more active than those in class B or C. Chandler et al studied patients younger than 30 years and observed that those patients with either juvenile rheumatoid arthritis or dermatomyositis reported lower levels of activity than patients with other diagnoses (ie, AVN, slipped capital femoral epiphysis, trauma, sepsis). The marked variability in gait cycles per year (range, 0.3-2.7 million) recorded for this young population (range, 27-50 years) is interesting but not well understood. Our most active patient demonstrated approximately 8 times more gait cycles than the least active. As illustrated in Fig. 1, some patients younger than 30 years were relatively inactive compared with some patients older than 40 years. Furthermore, patients in their forties demonstrated an SD of ±0.6 million gait cycles per year. Major differences in level of activity may reflect major differences in lifestyle. For example, some differences may exist as a function of geographic location (urban vs rural community and/or cold vs warm climate) or occupation (accountant vs professional golfer). Certainly, these factors and others (ie, preoperative activity level) should be quantified in future studies. It is apparent from our data that, just because certain patient characteristics such as age may have a relationship to walking activity, caution must yet be exercised when applying these trends to individuals. Patient-reported level of activity (as measured by the 10-point UCLA activity score) is a perception that appears influenced by clinical and demographic variables. UCLA scores were significantly lower in patients with more than 1 artificial joint and/or with a history of contralateral hip surgery. UCLA scores were significantly higher when reported by a male patient rather than a female. Although patients' UCLA scores strongly correlated with their perceptions of pain and function as measured by the HHS, neither the UCLA score nor the HHS correlated with gait cycles per year as measured by pedometer. Linear polyethylene wear rates in this young population do not appear accelerated. The mean linear wear rate for this study group was 0.16 mm/y (range, 0.02-0.38). Other recent studies of patients younger than 50 years after THA have reported mean linear wear rates ranging from 0.09 to 0.29 mm/y 3, 4, 5, 6, 7, 31. Furthermore, contemporary studies of wear in older populations report comparable mean linear wear rates (ranging from 0.05 to 0.22 mm/y) 32, 33. We recognize the limited strength of comparisons made between our study and other clinical investigations of in vivo wear rates due to a number of potentially confounding variables 34, 35. These comparisons do, however, provide some perspective of the wide variation of wear rates across different age groups and suggest that wear rates in the young population may more closely approximate those of more senior patients with THA than originally thought. Walking activity as measured by a pedometer did not significantly correlate with in vivo wear rates. This finding is consistent with other pedometer-based studies of older patients that have analyzed the relationship between gait cycles and wear 22, 23. Although it has been reported that polyethylene wear is a function of use, “use” as defined by the authors is not synonymous with gait cycles per year [23]. Thus, neither our study nor any other has discovered a significant and/or positive relationship purely between gait cycles per year and in vivo polyethylene wear. Weaknesses of this study include the relatively small sample size (n = 41 hips), short-term follow-up (mean = 6.3 years), and a retrospective design. In addition, alternate methods of radiographic wear measurement 36, 37, 38] as well as activity measurement 39, 40, 41 have been described and might have been used. We selected the technique of Livermore as our method of wear analysis based on its relative simplicity, low cost, and demonstrated accuracy in assessing clinical radiographs compared with that of the more cumbersome and costly 3-dimensional computer-based methods [42]. Likewise, the digital pedometer was selected as our objective method of activity measurement based on its ease of operation, low cost, and commercial availability. In conclusion, young patients with primary THA may not be as active as originally thought. Advanced age and obesity negatively impact postoperative walking activity (gait cycles per year). Furthermore, patients with preoperative diagnoses of systemic disease (ie, RA, OA) may be relatively less active after THA when compared with patients who have localized conditions of the hip (ie, AVN, DDH, Perthes disease). Patient-reported level of activity is a perception that appears influenced by clinical and demographic variables and should be interpreted carefully. In this study, patients' perception of activity (UCLA activity score) strongly correlated with their perception of pain and function (HHS), but did not correlate with gait cycles per year. Linear polyethylene wear rates in this population do not appear accelerated when considered in the broad context of other in vivo wear studies of both young and old patients. Thus, our hypotheses that youth would predict a relatively high level of walking activity after THA as well as an accelerated rate of linear wear were not supported. Although walking activity as measured by pedometer was not significantly correlated with in vivo linear wear rates in this study, because of our small sample size, we can offer no strong conclusions as to the impact of activity on wear. The correlation between activity level and polyethylene wear has been studied by others, but results in the literature are conflicting, and the relationship remains uncertain 9, 23, 43, 44, 45. Further studies of patients with THA, perhaps using multiple different methods to assess activity level and in vivo wear, are needed to clarify this relationship. References 1. 1Wroblewski BM. Charnley low friction arthroplasty in patients under the age of forty years. In: Sevastik J, Goldie I editor. The young patient with degenerative hip disease. Stockholm: Almquvist and Wiksell; 1985;p. 197. 2. 2Chandler HP, Reineck FT, Wixson RL, et al. Total hip replacement in patients younger than thirty years old: a five-year follow-up study. J Bone Joint Surg Am. 1981;63:1426. MEDLINE 3. 3Callaghan JJ, Forest EE, Olejniczak JP, et al. Charnley total hip arthroplasty in patients less than fifty years old. J Bone Joint Surg Am. 1998;80:704. MEDLINE 4. 4Kim YH, Kook HK, Kim JS. Total hip replacement with a cementless acetabular component and a cemented femoral component in patients younger than fifty years of age. J Bone Joint Surg Am. 2002;84:770. 5. 5Kim YH, Oh SH, Kim JS. Primary total hip arthroplasty with second-generation cementless total hip prosthesis in patients younger than fifty years of age. J Bone Joint Surg Am. 2003;85:109. 6. 6Crowther JD, Lachiewicz EF. Survival and polyethylene wear of porous coated acetabular components in patients less than fifty years old: results at nine to fourteen years. J Bone Joint Surg Am. 2002;84:729. 7. 7Kim YH, Oh SH, Kim JS, et al. Contemporary total hip arthroplasty with and without cement in patients with osteonecrosis of the femoral head. J Bone Joint Surg Am. 2003;85:675. 8. 8Seedhom BB. Walking activities and wear of prostheses. Ann Rheum Dis. 1985;44:838. MEDLINE |
CrossRef
9. 9Schmalzried TP, Szuszczewicz ES, Northfield MR, et al. Quantitative assessment of walking activity after total hip or knee replacement. J Bone Joint Surg Am. 1998;80:54. MEDLINE 10. 10Dowd JE, Sychterz CJ, Young AM, et al. Characterization of long-term femoral-head-penetration rates. Association with and prediction of osteolysis. J Bone Joint Surg Am. 2000;82:1102. 11. 11Oparaugo PC, Clarke IC, Malchau H, et al. Correlation of wear debris-induced osteolysis and revision with volumetric wear-rates of polyethylene: a survey of 8 reports in the literature. Acta Orthop Scand. 2001;72:22. MEDLINE 12. 12Orishimo KF, Claus AM, Sychterz CJ, et al. Relationship between polyethylene wear and osteolysis in hips with a second-generation porous-coated cementless cup after seven years of follow-up. J Bone Joint Surg Am. 2003;85:1095. 13. 13Belcher GL, Radomisli TE, Abate JA, et al. Functional outcome analysis of operatively treated malleolar fractures. J Orthop Res. 1997;11:106. 14. 14Zahiri CA, Schmalzried TP, Szuszczewicz EX, et al. Assessing activity in joint replacement patients. J Arthroplasty. 1998;13:890. Abstract |
Full-Text PDF (497 KB)
|
CrossRef
15. 15Pivarnik JM, reeves MJ, Rafferty AP. Seasonal variation in adult leisure-time physical activity. Med Sci Sports Exerc. 2003;1004. 16. 16Levin S, Jacobs DR, Ainsworth BE, et al. Intra-individual variation and estimates of usual physical activity. Ann Epidemiol. 1999;9:481. Abstract | Full Text |
Full-Text PDF (157 KB)
|
CrossRef
17. 17Livermore J, Ilstrup D, Morrey B. Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg Am. 1990;72:518. MEDLINE 18. 18Bartel DL, Bicknell VL, Wright TM. The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement. J Bone Joint Surg Am. 1986;68:1041. MEDLINE 19. 19Collier JP, Maor MB, Surprenant VA, et al. The biomechanical problems of polyethylene as a bearing surface. Clin Orthop. 1990;261:107. 20. 20Maxian TA, Brown TD, Pedersen DR, et al. The Frank Stinchfield Award. 3-Dimensional sliding/contact computational simulation of total hip wear. Clin Orthop. 1996;333:41. 21. 21Oonishi H, Iwaki H, Kin N, et al. The effects of polyethylene cup thickness on wear of total hip prostheses. J Mater Sci Mater Med. 1998;9:475. MEDLINE |
CrossRef
22. 22Goldsmith AA, Dowson D, Wroblewski BM, et al. The effect of activity levels of total hip arthroplasty patients on socket penetration. J Arthroplasty. 2001;16:620. Abstract | Full Text |
Full-Text PDF (82 KB)
|
CrossRef
23. 23Schmalzried TP, Shepherd EF, Dorey FJ, et al. Wear is a function of use, not time. Clin Orthop. 2000;381:36.
CrossRef
24. 24Silva M, Shepherd EF, Jackson WO, et al. Average patient walking activity approaches 2 million cycles per year: pedometers under-record walking activity. J Arthroplasty. 2002;17:693. Abstract | Full Text |
Full-Text PDF (106 KB)
|
CrossRef
25. 25Washburn R, Chin MK, Montoye HJ. Accuracy of pedometer in walking and running. Res Q Exerc Sport. 1980;51:695. MEDLINE 26. 26Shepherd EF, Toloza E, McClung CD, et al. Step activity monitor: increased accuracy in quantifying ambulatory activity. J Orthop Res. 1999;17:703. MEDLINE |
CrossRef
27. 27McClung CD, Zahiri CA, Higa JK, et al. Relationship between body mass index and activity in hip or knee arthroplasty patients. J Orthop Res. 2000;18:35. MEDLINE |
CrossRef
28. 28World Health Organization . Obesity: preventing and managing the global epidemic. Report of a WHO consultation of obesity, Geneva, 3-5 June 1997. Geneva: World Health Organization; 1998;. 29. 29Kottke TE, Clark MM, Aase LA, et al. Self-reported weight, weight goals, and weight control strategies of a Midwestern population. Mayo Clin Proc. 2002;77:114. MEDLINE |
CrossRef
30. 30Dorr LD, Takei GK, Conaty JP. Total hip arthroplasties in patients less than forty-five years old. J Bone Joint Surg Am. 1983;65:474. MEDLINE 31. 31Kim YH, Oh SH, Kim JS. Total hip arthroplasty in adult patients who had childhood infection of the hip. J Bone Joint Surg Am. 2003;85:198. 32. 32Bankston AB, Keating EM, Ranawat C, et al. Comparison of polyethylene wear in machined versus molded polyethylene. Clin Orthop. 1995;317:37. 33. 33Hernandez JR, Keating EM, Faris PM, et al. Polyethylene wear in uncemented acetabular components. J Bone Joint Surg Br. 1994;76:263. 34. 34Berry DJ. Factors influencing polyethylene wear. Orthopaedics. 1996;19:729. 35. 35Schmalzried TP, Callaghan JJ. Current concepts review—wear in total hip and knee replacements. J Bone Joint Surg Am. 1999;81:115. MEDLINE 36. 36Devane PA, Bourne RB, Rorabeck CH, et al. Measurement of polyethylene wear in metal-backed acetabular cups. Three-dimensional technique. Clin Orthop. 1995;319:303. 37. 37Martell JM, Berdia S. Determination of polyethylene wear in total hip replacements with use of digital radiographs. J Bone Joint Surg Am. 1997;79:1635. MEDLINE 38]. 38]Shaver SM, Brown TD, Hillis SL, et al. Digital edge-detection measurement of polyethylene wear after total hip arthroplasty. J Bone Joint Surg Am. 1997;79:690. MEDLINE 39. 39Coleman KL, Smith DG, Boone DA, et al. Step activity monitor: long-term, continuous recording of ambulatory function. J Rehabil Res Dev. 1999;36:8. MEDLINE 40. 40Leenders NYJM, Sherman WM, Nagaraja HN. Comparisons of four methods of estimating physical activity in adult women. Med Sci Sports Exerc. 2000;32:1320. MEDLINE |
CrossRef
41. 41Resnick B, Nahm ES, Orwig D, et al. Measurement of activity in older adults: reliability and validity of the Step Activity Monitor. J Nurs Meas. 2001;9:275. MEDLINE 42. 42Ebramzadeh E, Sangiorgio SN, Lattuada F, et al. Accuracy of measurement of polyethylene wear with use of radiographs of total hip replacements. J Bone Joint Surg Am. 2003;85A:2378. 43. 43Charnley J, Halley DK. Rate of wear in total hip replacement. Clin Orthop. 1975;112:170. 44. 44Griffith MJ, Seidenstein MK, Williams D, et al. Socket wear in Charnley low-friction arthroplasty of the hip. Clin Orthop. 1978;137:37. 45. 45Feller JA, Kay PR, Hodjkinson JP, et al. Activity and socket wear in the Charnley low-friction arthroplasty. J Arthroplasty. 1994;9:341. Abstract |
Full-Text PDF (427 KB)
|
CrossRef
⁎ Department of Orthopaedic Surgery, The University of Minnesota, Minneapolis, Minnesota † Department of Orthopaedic Surgery, Hennepin County Medical Center, Minneapolis, Minnesota ‡ The Minneapolis Geriatric Research, Education and Clinical Center, Minneapolis Veterans Administration Medical Center, Minneapolis, Minnesota  Reprint requests: V. Franklin Sechriest II, LCDR, MC, US Navy, Department of Orthopaedic Surgery, Naval Medical Center San Diego, 34800 Bob Wilson Drive, San Diego, CA 92134-1401.
No benefits of funds were received in support of the study. PII: S0883-5403(06)00154-9 doi:10.1016/j.arth.2006.02.083 © 2007 Elsevier Inc. All rights reserved. | |
|
FULL TEXT00154-9/journalimage?img=PIIS0883540306001549.gr1.lrg.gif&fig=fig1&kwhquery=&issn=0883-5403&ishighres=false&allhighres=false&free=yes','journalimage');)
00154-9/journalimage?img=PIIS0883540306001549.gr2.lrg.gif&fig=fig2&kwhquery=&issn=0883-5403&ishighres=false&allhighres=false&free=yes','journalimage');)
00154-9/journalimage?img=PIIS0883540306001549.gr3.lrg.gif&fig=fig3&kwhquery=&issn=0883-5403&ishighres=false&allhighres=false&free=yes','journalimage');)
00154-9/journalimage?img=PIIS0883540306001549.gr4.lrg.gif&fig=fig4&kwhquery=&issn=0883-5403&ishighres=false&allhighres=false&free=yes','journalimage');)
00154-9/journalimage?img=PIIS0883540306001549.gr5.lrg.gif&fig=fig5&kwhquery=&issn=0883-5403&ishighres=false&allhighres=false&free=yes','journalimage');)
00154-9/journalimage?img=PIIS0883540306001549.gr6.lrg.gif&fig=fig6&kwhquery=&issn=0883-5403&ishighres=false&allhighres=false&free=yes','journalimage');)