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Clin Orthop Relat Res. 2011 October; 469(10): 2855–2865.
Published online 2011 June 23. doi:  10.1007/s11999-011-1921-z
PMCID: PMC3171538

Women Recover Faster Than Men after Standard Knee Arthroplasty

Abstract

Background

Specific anatomic differences are believed to account for gender-specific function and health-related quality of life after TKA. However, there are conflicting data in the literature regarding these gender-specific outcomes, especially as woman appear to have surgery later in the course of the disease compared with men.

Questions/purposes

We asked whether (1) women had worse knee function and health-related quality of life after TKA compared with men, (2) lower improvements in scores, and (3) slower recovery after surgery.

Methods

Using a cohort study design, we retrospectively analyzed prospectively collected data from three multicenter randomized controlled trials evaluating rehabilitation measures after standard unisex knee arthroplasty in 494 patients (141 men and 353 women). The primary outcome was self-reported physical function as measured by the WOMAC at 3, 6, 12, and 24 months after surgery. Secondary outcomes included the pain and stiffness scales of the WOMAC and the physical and mental component summaries of the SF-36. At the time of surgery, the women were on average older (70.8 versus 67.8 years), had lower mean physical function (55 versus 47), higher mean pain scores (54 versus 48), and greater stiffness (54 versus 46) as measured by the WOMAC.

Results

At the 3-, 6-, 12-, and 24-month followups, men and women had similar WOMAC scores. Improvements were greater for women compared with men for WOMAC function and pain subscale scores at the 3-month (function, 28 versus 23; pain, 32 versus 25) and 6-month followups (function, 32 versus 27; pain, 36 versus 31). At the 12- and 24-month followups we noted no differences in improvement between men and women.

Conclusion

Although women had greater functional limitations at the time of surgery than men, they recover faster early after standard TKA although function is similar at 12 and 24 months. Women also had greater improvement of WOMAC scores after standard TKA than men.

Level of Evidence

Level II, prognostic study. See the guidelines for authors for a complete description of levels of evidence.

Introduction

Gender-specific TKA implants are a current and debated issue [8, 10, 11, 14, 20], especially after a new TKA system has been introduced that is marketed specifically to women. The rationale for that gender-specific TKA design is based on the theory that there are specific anatomic differences and that function differs between men and women when the same type of design is used in both. Although a couple reports document morphologic differences in the distal femur, with the female knee tending to be slightly narrower than the male knee for any given AP dimension [6, 12], it is unclear whether function differs by gender after TKA. Some authors have reported that women score inferior in the Knee Society knee and function scores [8, 18, 20] after TKA, when compared with men. However, in several studies women also scored lower before surgery when looking at the Knee Society function score [4, 8, 18, 20]. Women tend to be older than men before they undergo surgery and they appear to delay surgery for osteoarthritis of their knees and wait until their symptoms are more severe than men [15, 16, 20]. To compensate for these different preoperative function scores, some authors have calculated change (improvement scores) after TKA but the findings are conflicting. There are reports of similar improvement between genders [8, 20] and greater improvement in men [4, 18], as measured by Knee Society function scores. However, improvement in WOMAC scores are reportedly similar for men and women [4] or show greater improvement for women [18]. The followup periods in these studies were variable, ranging from a mean of 1.56 years to 10.5 years. In the latter study [18], there was a difference of followup periods between men and women thereby possibly adding bias. Therefore it is unknown if the conflicting findings of these studies could be influenced by different followup intervals.

We therefore asked whether (1) women had worse knee function and health-related quality of life after TKA compared with men, (2) lower improvements in scores, and (3) slower recovery after surgery.

Patients and Methods

This is a closed cohort analysis, secondarily analyzing existing prospectively collected data of 1198 patients, who participated in three multicenter randomized controlled trials evaluating different rehabilitation measures. Data from 362 of those patients suggested ergometer cycling enhanced rehabilitation after THA, but not after TKA [17].

For these trials, eligible patients were identified by the admitting physicians and were approached to participate in the trial. Participating centers were two university hospitals, two rural, and one municipal hospital, all located in Germany. Patients providing written informed consent were enrolled in the trial. Information regarding the study was given to participants on the day of admission to the hospital. These patients were enrolled from January 1, 2003, to April 30, 2006. After exclusion of the patients who had a THA, and of 99 patients who were unwilling to participate or who had one of the following exclusion criteria: (1) history of septic arthritis; (2) hip or knee fracture; (3) intraoperative complications; (4) revision arthroplasty; (5) rheumatoid arthritis; (6) lower extremity amputations; (7) malignancy; and (8) inability to complete the questionnaires because of cognitive or language difficulties, 494 patients were left. Followups were performed after 3, 6, 12, and 24 months. Of the 494 patients, 443 (90%) completed the postal questionnaire at 3 months. The followup rate decreased to 88% at 6 months, 81% at 12 months, and 76% at 24 months. There was no association between patients who did not respond to the followup questionnaire and patient baseline characteristics. The study protocol was approved by the local ethics committee. A data and safety monitoring board monitored the study.

Of the 494 patients, 353 (71%) were women and 141 (29%) were men. At the time of surgery, their average age was 70.0 years. The mean body mass index (BMI) was similar in males and females as were the number of comorbidities, and additional limitations resulting from other joints of the lower or upper extremities, or the result of low back pain (Table 1).

Table 1
Baseline characteristics

All patients received a standard total or UKA (Table 2). As the cohort includes patients who had a UKA, we have provided an analysis for the whole cohort and one for TKA only.

Table 2
Surgical details

All patients participated in a standard postsurgery program of daily supervised physiotherapy during hospitalization, consisting of ROM activities, exercises for improvement of muscle tension, venous return, balance, coordination and gait, and instruction in activities of daily living, including transfers, walking, and negotiation of stairs and uneven surfaces. Patients were mobilized starting postoperative Day 1, initially using a walker and later using crutches. Continuous passive motion machines were used on a daily basis after removal of suction drains. All patients were given analgesics and mechanical and medical thrombosis prophylaxis according to a standard scheme.

The primary outcome was self-reported physical function 3, 6, 12, and 24 months postoperatively. We chose 3 and 6 months as the appropriate study intervals because the most improvement in postoperative physical health occurs during these times [9]. We added 12-month and 24-month study intervals to standardize our research with that of others who have analyzed health-related quality of life after TKA [9]. This was measured using the WOMAC osteoarthritis index [3] using a validated translated version [22]. Secondary outcomes consisted of leg-specific stiffness and pain measured with the WOMAC and the physical component summary (PCS) and mental component summary (MCS) of the 36-item SF-36 [5, 24]. For the WOMAC, responses were recorded on a visual analog scale with terminal descriptors. Scores were added for each category and standardized to a score of 0 to 100 with higher scores indicating more pain, more stiffness, or more dysfunction. All patients were asked to answer the questionnaire at the time of hospital admission. During the hospital stay, the study nurse visited the patients to ensure the questionnaire was filled in completely. The questionnaire included, among others, the list of comorbidities adapted from the “current health assessment” section of the Hip and Knee—Baseline Questionnaire of the musculoskeletal outcomes data evaluation and management system developed by the AAOS [13]. After 3, 6, 12, and 24 months, participants were mailed a questionnaire in a prepaid return envelope. Nonresponding participants were reminded by mail up to three times at intervals of 2 weeks. Participants still not responding were contacted by telephone to determine their reason for not responding. Data were entered in a database at the coordinating center.

At the time of surgery, the women were a mean of 3 years older compared with the men (Table 1), and they reported lower physical function, more pain, and more stiffness as measured by the WOMAC. In addition, women scored lower on the MCS of the SF-36 and the Knee Society function score (Table 1).

Absolute baseline and followup scores of the outcome scores were evaluated. Because the baseline scores were not comparable between genders, we calculated improvement (change) scores for the outcomes. Continuous data initially were tested for normal distribution with the Kolmogorov-Smirnov test. Apart from age, BMI, and the improvement (change) scores, these data were not normally distributed. Therefore, we used the nonparametric Mann-Whitney U test to determine differences between genders in the absolute WOMAC and SF-36 scores. To adjust for potential confounding variables, multivariable regression models were developed in which the improvement of the primary outcome (WOMAC physical function) served as the dependent variable and the dichotomous variable for gender served as an independent variable, along with BMI, age, and number of comorbidities as confounding variables. The type III sum-of-squares option was used to calculate the adjusted effect of gender on the improvement of WOMAC physical function for each of the four followup periods. All p values are two-tailed; no corrections were made for multiple comparisons. Effect sizes [1] as the standardized differences between two groups were calculated as described by Cohen [7]. We used SPSS (SPSS Inc, Chicago, IL, USA) for data analysis.

Results

At the 3-, 6-, 12-, and 24-month followups, men and women had similar scores for the absolute values of the primary outcome and for all other outcomes studied, with the exception of the MCS of the SF-36 at 3 months followup and the PCS of the SF-36 at 24 months followup, with women having inferior scores (Table 3). For WOMAC function as the primary outcome, the maximum difference between genders ranged from 0.6 to 3.7 WOMAC function units.

Table 3
Raw outcomes at 3-, 6-, 12-, and 24-month followups

Improvements were greater for women for WOMAC function and pain scores at the 3- and 6-month followups when compared with men (Table 4; Fig. 1), however at the 12- and 24-month followups we noted no differences in improvement between men and women. After adjusting the primary outcome for the covariates age, BMI, and number of comorbidities, the gender difference remained at the 3-month followup, although not by the 6-month followup (Table 5).

Table 4
Improvement in outcomes at 3-, 6-, 12-, and 24-month followups
Fig. 1
The graph shows the improvement of WOMAC physical function at 3-, 6-, 12-, and 24-month followups, with greater improvement for woman when compared with men at the 3- and 6-month followups. Scores ranged from 0 to 100, with lower scores representing lower ...
Table 5
Results of the multivariate analysis

When compared with men, woman had greater improvement for WOMAC function and pain scores at the earlier followups, but not at the later followups.

Discussion

Several studies [16, 18, 21] suggest women report more pain and less health-related quality of life after TKA than men, possibly owing to women undergoing knee arthroplasty at a later stage than men. Although some have concluded that TKA is less successful in restoring normal knee function in women than in men [20], others have reported that women in general overall had the greatest improvements in outcomes after TKA [18]. Therefore, the literature is contradictory regarding the gender-specific improvement of clinical outcome after standard TKA. For this reason we retrospectively analyzed prospectively collected data to determine whether (1) women had worse knee function and health-related quality of life after TKA compared with men, (2) lower improvements in scores, and (3) slower recovery after surgery.

This study has several limitations. First, although our analysis is based on the data of randomized controlled trials, we found differences between genders for baseline measures. This was expected because the randomization was not stratified by gender and therefore the baseline gender differences reported in the literature were likely to be reflected in our database as well. This study was not designed to answer the question if a gender-specific implant is necessary. To answer that question, a randomized controlled trial comparing the results with gender-specific implants versus nongender-specific implants would be necessary. However, we anticipate high external validity, as this trial was conducted in a multicenter setting, performed at two university hospitals, two rural, and one municipal hospital. Furthermore, this setting provided broader surgical experience levels and implants when compared with a monocenter study and is less likely to be biased by the results of one implant or surgical technique. In addition, our overall preoperative and postoperative results compare well with those of other authors [18]. Second, as with any uncontrolled analysis, some aspects of treatment (eg, postoperative care, surgical experience, selection of different prostheses) could have changed during the study period, thereby diluting a possible effect of gender. In addition, other patient characteristics, such as preoperative ROM or radiographic severity of disease were not analyzed. Therefore it is unclear if the gender effect observed in this study is attributable to the patients having gender-specific anatomic variances, or to other, possibly yet unknown factors, that may be associated with gender, such as psychologic factors, behavior, or social support. Third, although the followup rate was 90% at 3 months followup, 88% at 6 months followup, and 81% at 12 months followup, it decreased to 76% at 2 years followup. Because the results of the 2-year followup are similar to the results of the 1-year followup, we think it is unlikely a more complete 2-year followup would have altered the study results. Finally, we used the WOMAC and SF-36 scores as outcome measures. There is no ideal clinical outcome tool for evaluation of a patient with arthritis before and after TKA. We used the WOMAC as the primary outcome score, because the WOMAC is validated and is recommended in this setting [19]. Because this analysis using the WOMAC failed to identify different absolute outcomes between genders after knee arthroplasty, it could be argued that the WOMAC as an outcome measure is not sensitive enough to capture these apparently subtle differences in postoperative outcome. The question remains, however, if these subtle differences are of any clinical relevance and justify a change of treatment decisions.

Our data confirm the results of previous investigations (Table 6) that women tend to be older when undergoing TKA and have greater functional limitations at the time of surgery than men. We found that women were a mean of 3 years older when undergoing TKA, which compares well to the literature, as Parsley et al. also reported that women are 3 years older at the time of surgery [20], whereas Macdonald et al. reported women were only 6 months older than men [18]. Macdonald et al. also reported lower baseline scores for women as measured by the WOMAC [18]. It has been assumed that these lower baseline scores could be the result of women undergoing surgery for more advanced osteoarthritis than men [20]. In addition, in our study women scored lower on the MCS of the SF-36 and the Knee Society function score, which also has been observed by others [4, 8, 18, 20].

Table 6
Published gender-specific outcomes regarding health-related quality of life after knee arthroplasty

We found no postoperative differences between genders for the absolute values of the primary outcome and for all other outcomes studied with the exception of the MCS of the SF-36 at 3 months followup and the PCS of the SF-36 at 24 months followup. Although the latter is in concordance with the literature, where inferior preoperative MCS scores, as in our study, were associated with smaller improvements in health-related quality of life [2], our overall findings are in contrast to other reports [8, 18, 20] where women scored less than men after TKA in all outcomes studied. Although we observed the general trend that women scored less in all outcomes, that difference was not significant. It could be argued that statistical significance could be achieved if the number of patients studied was increased. However, that would not increase the clinical relevance, as the maximum difference between genders for the primary outcome, WOMAC function, ranged from 0.6 to 3.7 WOMAC function units, which is below the “minimal clinically important difference” [23]. As the women of our study scored inferior to men before surgery, but scored comparable to men after surgery, we could not confirm the view that TKA is less successful in restoring normal knee function in women than in men [20].

Our data show that early function after TKA improves to a greater degree in women than in men, because the WOMAC change scores were higher among women at the 3- and 6-month followups. These change scores appeared to compensate for the lower functional levels of women at baseline, because there were no differences between genders in absolute health-related quality of life scores after surgery. Greater postoperative change scores for women also were reported by MacDonald et al. [18], however, using predefined followups, we observed that women appear to recover faster, given the improvements at 3 and 6 months after knee arthroplasty.

Although we identified greater early improvement in women when the WOMAC was used, this improvement was not seen with the SF-36 score. This finding is in agreement with another study in which the SF-12 was used and no difference in improvement was seen with that outcome [18]. This observation gives rise to the impression that judgment of clinical success of knee arthroplasty depends on the outcome selected.

Our data confirm those of previous investigations that women tend to be older and have lower health-related quality of life before knee arthroplasty than men. However, our study failed to confirm previous reports stating that women have inferior health-related quality of life than men after knee arthroplasty. To a large extent, this appears related to women achieving higher change scores after surgery and that women had faster recovery at 3- and 6-month followups than men. Why women recover faster from surgery than men is not known. It could be attributable to the lower preoperative health-related quality of life in women, thereby women having more to gain from surgery, or other factors currently unknown and thereby speculative, such as different postoperative activity levels, psychologic factors, or different utilization of treatment. Additional studies are needed to elucidate these factors to identify an approach to further improve the clinical results of patients after knee arthroplasty.

Footnotes

The institution of the authors (TRL, JH) has received funding from the Society for Support of Research in and Fighting of Rheumatic Diseases Bad Bramstedt, registered society (Verein zur Förderung der Erforschung und Bekämpfung rheumatischer Erkrankungen, Bad Bramstedt e. V.); the Society for Support of Rehabilitation Research in Schleswig-Holstein, registered society (vffr, Verein zur Förderung der Rehabilitationsforschung in Schleswig Holstein, e. V.); the State Insurance Agency of the Free and Hanseatic City of Hamburg (LVA Freie und Hansestadt Hamburg); and the German Arthrosis Society, registered society (Deutsche Arthrose-Hilfe e. V.).

Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.

This work was performed at all academic affiliations mentioned plus the University of Schleswig-Holstein Medical Center, Lübeck Campus, Department of Orthopaedic Surgery, Lübeck, Germany; Ostseeklinik Damp, Department I of Orthopaedic Surgery, Damp, Germany; and Kliniken des Kreises Pinneberg, Krankenhaus Wedel, Wedel, Germany.

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