Abstract
Gender-specific total knee replacement design is a recent and debated topic. We determined the survivorship and clinical outcomes of a large primary total knee arthroplasty cohort, specifically assessing any differences between gender groups. A consecutive cohort of 3817 patients with 5279 primary total knee replacements (3100 female, 2179 male) with a minimum of 2 years followup were evaluated. Preoperative, latest, and change in clinical outcome scores (WOMAC, SF-12, KSCRS) were compared. While men had higher raw scores preoperatively, women had greater improvement in all WOMAC domains including pain (29.87 versus 27.3), joint stiffness (26.78 versus 24.26), function (27.21 versus 23.09), and total scores (28.35 versus 25.09). There were no gender differences in improvements of the SF-12 physical scores. Men had greater improvement in Knee Society function (22.1 versus 18.63) and total scores (70.01 versus 65.42), but not the Knee Society knee score (47.83 versus 46.64). Revision rates were 10.2% for men and 8% for women. Women demonstrated greater implant survivorship, greater improvement in WOMAC scores, equal improvements in SF-12 scores, and less improvement in only the Knee Society function and total scores. The data refute the hypothesis of inferior clinical outcome for women following total knee arthroplasty when using standard components.
Level of Evidence: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.
Introduction
Recently much debate and discussion has focused on the effect of gender and the results of total knee arthroplasty (TKA) [3–5, 8]. The release of a new knee system (Gender Solutions™, Zimmer Inc., Warsaw, IN) marketed specifically to women catalyzed this debate. The challenge has been the lack of evidence that any implant changes or modifications could result in a clinical improvement to patient outcomes and more specifically the lack of support that women have inferior outcomes following TKA using conventional knee replacement systems using available devices.
There are specific gender differences seen with respect to access to care and anatomic variability. Several reports demonstrate that, in general, women tend to delay surgery for their arthritic knees and may wait until their symptoms are more severe than men [12, 13]. There may also be a gender bias with physicians more likely to recommend total knee arthroplasty to a male patient than a female patient [6]. Several authors have demonstrated distal femoral morphological differences, with the female knee tending to be slightly narrower than the male knee for any given anteroposterior dimension [7, 10]. However, there is substantial variability in these patterns [7, 10], and there are more differences between races than between genders [11, 14, 17–20].
One of the outstanding questions is whether women derive less benefit, or perhaps less predictable benefit, from total knee replacement than do their male counterparts with conventional devices. While there is no ideal patient-specific or disease-specific clinical outcome tool, there are several validated scoring systems in current use for the evaluation of the arthritic patient.
We therefore reviewed prospectively collected clinical outcome scores (WOMAC, SF-12, KSCRS) used in our institution in a consecutive series of patients undergoing TKA to determine whether gender influenced preoperative, postoperative, and change scores.
Materials and Methods
We identified from our database a consecutive series of 3817 patients with 5279 primary total knee replacements between 1988 and 2004. Criteria for inclusion into the study consisted of a primary diagnosis of degenerative arthritis and a minimum followup of 2 years. There were 3100 women and 2179 men. Beginning in 1973 patients undergoing total joint arthroplasty surgery have had demographic data collected prospectively, which was then entered into an institutional clinical database. Beginning in 1988 this included surgical information, and preoperative and postoperative WOMAC, SF-12 (version 1), and Knee Society clinical ratings (KSCRS) scores. All surgeries were performed at a single institution by one of five surgeons (SJM, RBB, RWM, DDN, and CHR). Ethics approval was granted by the institution’s internal review board.
Multiple orthopaedic manufacturers and implant designs were used over this period of time including: 2419 Genesis® I and II (Smith and Nephew Inc., Memphis, TN), 1279 AMK® (DePuy Orthopaedics Inc., Johnson and Johnson, Warsaw, IN), 552 Miller-Galante I and II (Zimmer Inc., Warsaw, IN), 314 SAL® (Sulzer Orthopaedics Ltd, Switzerland), 170 Sigma® (DePuy Orthopaedics Inc., Johnson and Johnson, Warsaw, IN), 115 Natural-Knee® (Zimmer Inc., Warsaw, IN), and 430 were performed with a variety of other primary knee replacement systems.
Preoperative and latest clinical outcome scores were analyzed as well as the change in score between preoperative and latest score. Categorical variables (eg, gender, BMI group, survival status) were analyzed using crosstabs with chi-square test. Student’s t-test with Levene’s test for equality of variance was used to analyze continuous variables (eg, height, weight, outcome score totals). We used SPSS v.15 (SPSS Inc., Chicago, IL) for all analyses.
Results
The average ages of the women (69 ± 9 years) and the men (68.5 ± 8.8 years) at surgery were similar (p = 0.051) (Table 1). The average implantation time was greater (p = 0.013) for women than men (10.5 ± 6 years versus 10.1 ± 6 years, respectively). Men were taller (mean, 173.9 cm versus 159.5 cm) and heavier (mean, 92 kg versus 82.4 kg) than the women (p < 0.0001), but the female patients had a higher (p < 0.0001) BMI (mean, 32.4 versus 30.4). More (p < 0.0001) women were morbidly obese (BMI > 40) than men (13.4% versus 4%). Compared to the female patients, a higher (p < 0.0001) percentage of males had a preoperative varus alignment (64.5% versus 55.2%). More (p < 0.0001) women had a preoperative valgus alignment than men (18.6% versus 8.2%).
Table 1.
Patient demographics by gender
| Variable | Gender | p Value | |
|---|---|---|---|
| Female | Male | ||
| N (number of cases) | 3100 | 2179 | na |
| Followup (mean, years) | 10.5 ± 6 | 10.1 ± 6 | 0.013 |
| Age (mean) | 69.02 ± 9.11 | 68.53 ± 8.84 | 0.050 |
| Height, cm (mean) | 159.53 ± 7.36 | 173.93 ± 8.06 | < 0.0001 |
| Weight, kg (mean) | 82.43 ± 17.52 | 91.99 ± 16.68 | < 0.0001 |
| BMI (mean) | 32.43 ± 6.78 | 30.39 ± 5 | < 0.0001 |
| Morbidly obese (%) | 13.4% | 4% | < 0.0001 |
| Previous operation (%) | 60.2% | 68.8% | < 0.0001 |
| Varus alignment | 55.2% | 64.5% | < 0.0001 |
| Valgus alignment | 18.6% | 8.2% | < 0.0001 |
All preoperative outcome measure scores (WOMAC, SF-12, KSCRS) were different between the genders with men having higher (p < 0.0001) scores in all cases. All latest outcome measure scores also demonstrated male patients had higher (p < 0.013) scores. The change scores (preoperatively to latest postoperative) demonstrated gender-specific differences. The change in WOMAC scores for all domains (pain, joint stiffness, function, and total) demonstrated a greater change (p < 0.019) in women (Table 2). The change in SF-12 mental score was statistically significant (p < 0.001) between genders in favor of the female (females 0.6459 versus males −0.9614) (Table 3). The change in SF-12 pain score was similar between genders (females 8 versus males 7.92; p = 0.866). Men had greater (p < 0.0001) improvement in KSCRS total from preoperative to latest scores than females (70.01 versus 65.42, respectively) (Table 4). Preoperative, latest, and change in outcomes scores and significances were recorded (Tables 2–4).
Table 2.
Preoperative, latest, and change in WOMAC scores, number of cases, mean values, standard deviations, and significance grouped by gender
| WOMAC | Gender | N | Mean ± SD | p Value |
|---|---|---|---|---|
| Preoperative | ||||
| Pain | Female | 1537 | 44.08 ± 17.73 | < 0.0001 |
| Male | 1074 | 48.34 ± 17.51 | ||
| Joint stiffness | Female | 1543 | 38.75 ± 19.16 | < 0.0001 |
| Male | 1076 | 43.91 ± 20.21 | ||
| Function | Female | 1533 | 42.51 ± 17.32 | < 0.0001 |
| Male | 1073 | 47.71 ± 17.19 | ||
| Total | Female | 1532 | 42.38 ± 15.86 | < 0.0001 |
| Male | 1072 | 47.2 ± 16 | ||
| Latest | ||||
| Pain | Female | 2211 | 73.06 ± 23.56 | 0.008 |
| Male | 1535 | 75.08 ± 22.65 | ||
| Joint stiffness | Female | 2245 | 65.03 ± 23.79 | 0.001 |
| Male | 1541 | 67.71 ± 23.47 | ||
| Function | Female | 2193 | 67.9 ± 22.5 | 0.001 |
| Male | 1525 | 70.35 ± 22.26 | ||
| Total | Female | 2187 | 69.57 ± 21.51 | 0.001 |
| Male | 1522 | 71.85 ± 21.04 | ||
| Change | ||||
| Pain | Female | 1500 | 29.87 ± 24.69 | 0.008 |
| Male | 1064 | 27.3 ± 23.56 | ||
| Joint stiffness | Female | 1522 | 26.78 ± 26.79 | 0.019 |
| Male | 1069 | 24.26 ± 27.1 | ||
| Function | Female | 1488 | 27.21 ± 22.96 | < 0.0001 |
| Male | 1057 | 23.09 ± 22.66 | ||
| Total | Female | 1485 | 28.35 ± 22.26 | < 0.0001 |
| Male | 1055 | 25.09 ± 21.8 | ||
Table 3.
Preoperative, latest, and change in SF-12 scores, number of cases, mean values, standard deviations, and significance grouped by gender
| SF-12 | Gender | N | Mean ± SD | p Value |
|---|---|---|---|---|
| Preoperative | ||||
| MCS | Female | 1507 | 51.53 ± 11.15 | < 0.0001 |
| Male | 1040 | 54.38 ± 10.36 | ||
| PCS | Female | 1507 | 29.1 ± 7.31 | < 0.0001 |
| Male | 1040 | 31.64 ± 8.13 | ||
| Latest | ||||
| MCS | Female | 2246 | 51.79 ± 10.73 | < 0.0001 |
| Male | 1522 | 53.09 ± 9.97 | ||
| PCS | Female | 2246 | 36.48 ± 10.65 | < 0.0001 |
| Male | 1522 | 39.1 ± 11.13 | ||
| Change | ||||
| MCS | Female | 1491 | 0.65 ± 11.62 | < 0.0001 |
| Male | 1027 | −0.96 ± 10.24 | ||
| PCS | Female | 1491 | 8 ± 11.04 | 0.866 |
| Male | 1027 | 7.92 ± 11.79 | ||
Table 4.
Preoperative, latest, and change in KSCRS scores, number of cases, mean values, standard deviations, and significance grouped by gender
| KSCRS | Gender | N | Mean ± SD | p Value |
|---|---|---|---|---|
| Preoperative | ||||
| Function | Female | 2527 | 41.33 ± 16.25 | < 0.0001 |
| Male | 1781 | 48.67 ± 14.01 | ||
| Knee | Female | 2407 | 40.17 ± 15.29 | 0.419 |
| Male | 1694 | 40.55 ± 14.49 | ||
| Total | Female | 2407 | 81.58 ± 24.97 | < 0.0001 |
| Male | 1694 | 89.41 ± 22.29 | ||
| Latest | ||||
| Function | Female | 2954 | 59.98 ± 26.16 | < 0.0001 |
| Male | 2073 | 70.76 ± 23.78 | ||
| Knee | Female | 2871 | 86.66 ± 16.73 | 0.013 |
| Male | 2004 | 87.85 ± 16.36 | ||
| Total | Female | 2871 | 147.06 ± 35.7 | < 0.0001 |
| Male | 2004 | 158.84 ± 33.58 | ||
| Change | ||||
| Function | Female | 2483 | 18.63 ± 24.81 | < 0.0001 |
| Male | 1747 | 22.1 ± 23.46 | ||
| Knee | Female | 2307 | 46.64 ± 21.85 | 0.084 |
| Male | 1615 | 47.83 ± 20.84 | ||
| Total | Female | 2307 | 65.42 ± 37.7 | < 0.0001 |
| Male | 1615 | 70.01 ± 36.07 | ||
The revision rate was higher (p = 0.006) for men than for women (223 revisions or 10.2% versus 249 revisions or 8%). Men had more revisions for polyethylene wear than women (37.2% of male revisions, 26.5% of female revisions; p = 0.012) and more infections (two-stage procedure) (17% of male revisions, 8.8% of female revisions; p = 0.008) (Table 5). All other revision relationships were similar between the genders.
Table 5.
Revision rates and reason for revisions grouped by gender
| Reason | Revision rate | p Value | |
|---|---|---|---|
| Female | Male | ||
| Aseptic loosening | 18.9% | 17% | 0.604 |
| Polyethylene wear | 26.5% | 37.2% | 0.012 |
| Osteolysis | 9.2% | 7.6% | 0.53 |
| Instability | 17.3% | 16.1% | 0.744 |
| Implant fracture | 1.2% | 1.3% | 0.892 |
| Bone fracture | 3.2% | 2.2% | 0.52 |
| Patellar maltracking | 0% | 0% | na |
| Failed patellar component | 8% | 9.9% | 0.485 |
| Infection | 10.4% | 18.4% | 0.014 |
| Total | 8% | 10.2% | 0.006 |
Discussion
There are well-documented anatomic variations between the male and female lower extremity in terms of alignment and distal femoral anatomy. Women tend towards more valgus alignment and for any given anteroposterior dimension tend towards a narrower medial-lateral dimension [7, 10]. These findings have led some authors to conclude there is a need to develop specific knee implants designed to better fit these anatomic variations [4]. The fundamental premise of this approach assumes that outcomes for women are inferior following total knee replacements and at least some of these inferior outcomes must be due to the inherent differences in anatomy and thus need for gender specific designs.
This series reflects the results of various surgeons utilizing multiple implants and is much less likely to be biased by the results of one implant or design or technique. At the same time, subtleties in implant sizing between implant designs and their relative effects cannot be determined. It remains to be demonstrated if specific total knee designs do demonstrate gender differences in outcomes. It is possible the outcome measures that have been historically collected fail to capture the nuances of postoperative outcomes, such as anterior knee pain.
However, it has never been demonstrated in the literature that women indeed have poorer outcomes following total knee replacement surgery. In one of the few reports looking at patient satisfaction following total knee replacement, Robertsson et al. [16] reported on 27,372 patients having had a total knee replacement and reported 18% of women were unsatisfied or uncertain, compared with 16% of men. There were no preoperative evaluations in that series and it is critical that one considers the baseline differences in the population to begin with, as Paradowski et al. [15] demonstrated that in a general population survey women had more knee-related complaints than men.
In the current study a significant difference was seen in implant survivorship between genders with men having a higher revision rate than women (10.2% and 8% respectively). Other authors have demonstrated similar findings [2]. Perhaps the largest series demonstrating this trend is seen in the Australian Joint Registry [1], reporting on 134,799 primary total knee replacements. A statistically significant difference is seen in the cumulative 5 year revision rate of 4% for men and 3.3% for women. However, a report discussing the revision rates of 35,857 unicompartmental and total knee arthroplasties in the Swedish Arthroplasty Registry did not demonstrate any differences between genders in revision rates [9].
Historically authors have focused on preoperative and postoperative scores; however, it is the change scores that represent the effect of the intervention under investigation. Absolute preoperative and postoperative scores are affected by many factors including disease state, comorbidities, and test bias. Men, in general, demonstrate a greater functional capacity on these scoring systems, but this must be taken into account when reporting the results of total knee replacements and the effect that the surgery has on the improvement in patients’ outcomes. Without taking into account the change in scores from preoperative to postoperative, conclusions may be drawn that more accurately represent the bias in the test itself, rather than the effect of the surgery.
In this large series of patients we could not demonstrate a definitive gender bias in outcome scores. Women demonstrated the greatest improvement in all domains of the WOMAC scores including pain, joint stiffness, function, and total scores and each of these was statistically significant. While the raw postoperative scores for men were indeed better than for women, it was even more so preoperatively, and quite clearly the female patients derived equal if not greater benefit from receiving a total knee replacement than their male counterparts. The same findings are demonstrated in the SF-12 scoring system. Women begin and end with lower absolute physical scores than men, however, the change in scores, representing the effect of the total knee replacement, are not different between the groups. Additionally women demonstrated a statistically significantly greater improvement in the SF-12 mental scores than the men. It was only in the Knee Society clinical rating scores that men had greater improvement than the women.
Our data suggest no negative female gender bias in outcomes, but instead demonstrate women in general had overall the greatest improvements in outcomes scores with a lower revision rate than men.
Footnotes
Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.
Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.
References
- 1.Australian Orthopaedic Association Joint Replacement Registry – Publications page. 2007 Annual Report. Available at: http://www.aoa.org.au/jointregistry_pub.asp. Accessed January 15, 2008.
- 2.Baker PN, Khaw FM, Kirk LMG, Esler CAN, Gregg PJ. A randomised controlled trial of cemented versus cementless press-fit condylar total knee replacement: 15-year survival analysis. J Bone Joint Surg Br. 2007;89:1608–1614. [DOI] [PubMed]
- 3.Barrett WP. The need for gender-specific prostheses in TKA: does size make a difference? Orthopedics. 2006;29(9 Suppl):S53–55. [PubMed]
- 4.Booth RE Jr. Sex and the total knee: gender-sensitive designs. Orthopedics. 2006;29:836–838. [DOI] [PubMed]
- 5.Booth RE Jr. The gender-specific (female) knee. Orthopedics. 2006;29:768–769. [DOI] [PubMed]
- 6.Borkhoff CM, Hawker GA, Kreder HJ, Glazier RH, Mahomed NN, Wright JG. The effect of patients’ sex on physicians’ recommendations for total knee arthroplasty. CMAJ. 2008;178:681–687. [DOI] [PMC free article] [PubMed]
- 7.Chin KR, Dalury DF, Zurakowski D, Scott RD. Intraoperative measurements of male and female distal femurs during primary total knee arthroplasty. J Knee Surg. 2002;15:213–217. [PubMed]
- 8.Greene KA. Gender-specific design in total knee arthroplasty. J Arthroplasty. 2007;22: 27–31. [DOI] [PubMed]
- 9.Harrysson OLA, Robertsson O, Nayfeh JF. Higher cumulative revision rate of knee arthroplasties in younger patients with osteoarthritis. Clin Orthop Relat Res. 2004;421:162–168. [DOI] [PubMed]
- 10.Hitt K, Shurman JR 2nd, Greene K, McCarthy J, Moskal J, Hoeman T, Mont MA. Anthropometric measurements of the human knee: correlation to the sizing of current knee arthroplasty systems. J Bone Joint Surg Am. 2003;85:115–122. [DOI] [PubMed]
- 11.Ho WP, Cheng CK, Liau JJ. Morphometrical measurements of resected surface of femurs in Chinese knees: Correlation to the sizing of current femoral implants. Knee. 2006;13:12–14. [DOI] [PubMed]
- 12.Karlson EW, Daltroy LH, Liang MH, Eaton HE, Katz JN. Gender differences in patient preferences may underlie differential utilization of elective surgery. Am J Med. 1997;102:524–530. [DOI] [PubMed]
- 13.Katz JN, Wright EA, Guadagnoli E, Liang MH, Karlson EW, Cleary PD. Differences between men and women undergoing major orthopedic surgery for degenerative arthritis. Arthritis Rheum. 1994;37:687–694. [DOI] [PubMed]
- 14.Kwak DS, Surendran S, Pengatteeri YH, Park SE, Choi KN, Gopinathan P, Han SH, Han CW. Morphometry of the proximal tibia to design the tibial component of total knee arthroplasty for the Korean population. Knee. 2007;14:295–300. [DOI] [PubMed]
- 15.Paradowski PT, Bergman S, Sunden-Lundius A, Lohmander LS, Roos EM. Knee complaints vary with age and gender in the adult population. Population-based reference data for the Knee injury and Osteoarthritis Outcome Score (KOOS). BMC Musculoskelet Disord. 2006;7:38. [DOI] [PMC free article] [PubMed]
- 16.Robertsson O, Dunbar M, Pehrsson T, Knutson K, Lidgren L. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand. 2000;71:262–267. [DOI] [PubMed]
- 17.Shelbourne KD, Gray T, Benner RW. Intercondylar notch width measurement differences between African American and white men and women with intact anterior cruciate ligament knees. Am J Sports Med. 2007;35:1304–1307. [DOI] [PubMed]
- 18.Uehara K, Kadoya Y, Kobayashi A, Ohashi H, Yamano Y. Anthropometry of the proximal tibia to design a total knee prosthesis for the Japanese population. J Arthroplasty. 2002;17:1028–1032. [DOI] [PubMed]
- 19.Vaidya SV, Ranawat CS, Aroojis A, Laud NS. Anthropometric measurements to design total knee prostheses for the Indian population. J Arthroplasty. 2000;15:79–85. [DOI] [PubMed]
- 20.Yip DK, Zhu YH, Chiu KY, Ng TP. Distal rotational alignment of the Chinese femur and its relevance in total knee arthroplasty. J Arthroplasty. 2004;19:613–619. [DOI] [PubMed]