While it is generally recognized that anatomical differences exist between the male and female knee, the literature generally refutes the clinical need for gender-specific total knee prostheses. It has been found that standard, unisex knees perform as well, or better, in women than men. Recently, high-flex knees have become available that mechanically accommodate increased flexion yet no studies have directly compared the outcomes of these devices in men and women to see if gender-based differences exist. We retrospectively compared the performance of the high-flex Vanguard knee (Biomet, Warsaw, IN) in 716 male and 1,069 female knees. Kaplan-Meier survivorship was 98.5% at 5.6–5.7 years for both genders. After 2 years, mean improvements in Knee Society Knee and Function scores for men and women (50.9 versus 46.3; 26.5 versus 23.1) and corresponding SF-12 Mental and Physical scores (0.2 versus 2.2; 13.7 versus 12.2) were similar with differences not clinically relevant. Postoperative motion gains as a function of preoperative motion level were virtually identical in men and women. This further confirms the suitability of unisex total knee prostheses for both men and women.
Morphometric differences exist between the male and female knee populations. Such differences include smaller size [
Recently, there has been interest in high-flex knees [
The purpose of this study was to compare the mid-term functional outcomes and survivorship of large male and female cohorts receiving the same cruciate-retaining (CR) high-flex knee. Our hypothesis was that there would be no difference in these metrics between the genders with this prosthesis.
The Vanguard knee (Biomet, Warsaw, IN) is a high-flex design as it can mechanically accommodate up to 145° of flexion although that achieved clinically may be less due to the soft tissue restraint of the patient [
Kaplan-Meier survivorship analysis was performed for each gender (716 male knees and 1,069 female knees), including 95% confidence limits, with the endpoint defined as revision of any component for any reason. Final survivorship intervals were chosen to correspond to those at which 20 knees remained at risk to avoid the instability that can result when the remaining population becomes too small [
Functional analysis was performed on only those knees with a minimum of 2 years of complete clinical follow-up. Clinical assessment consisted of preop and final postop Knee Society Score (KSS) [
Preoperative and ≥2-year postoperative passive range of motion (ROM) and passive peak flexion (PF) data was available for 462 male and 671 female knees. Motion results were stratified by preoperative motion range, that is, <95°, 95–105°, and >105°.
Interval data means between the genders (patient age, body mass index, length-of-stay, length of follow-up, KSS, SF12, ROM, and PF) were compared using the pooled
Table
Patient demographics.
Parameter | Total | With ≥ 2-year complete follow-up | ||
---|---|---|---|---|
Female | Male | Female | Male | |
Number of patients | 802 | 526 | 463 | 313 |
Number of knees | 1069 | 716 | 574 | 397 |
Proportion right knees | 51.7% | 49.4% | 51.4% | 49.4% |
Patient age, mean (range) years | 71.9 (39–95) | 70.9 (44–96) | 73.3 (50–94) | 71.6 (48–95) |
Body mass index mean (range) kg/m2 | 33.2 (18–76) | 32.3 (8–79) | 32.6 (18–62) | 32.0 (8–57) |
Diagnosis | ||||
Osteoarthritis | 97.5% | 98.6% | 97.4% | 98.7% |
Rheumatoid arthritis | 1.6% | 0.8% | 1.9% | 1.0% |
Avascular necrosis | 0.6% | 0.3% | 0.4% | 0.3% |
Osteonecrosis | 0.1% | 0.0% | 0.2% | 0.0% |
Posttraumatic arthritis | 0.1% | 0.1% | 0.2% | 0.0% |
Others | 0.2% | 0.1% | 0.0% | 0.0% |
Length-of-stay, mean (range) days | 2.5 (1–18) | 2.2 (1–22) | 2.4 (1–10) | 2.1 (1–11) |
Follow-up, mean (range) years | 2.4 (0.7–7.2) | 2.4 (0.8–6.9) | 2.9 (2–7.2) | 2.9 (2–6.9) |
Table
Knee Society Score and SF-12 outcomes summaries after a minimum of 2 years.
Gender | Score | Component | Preop, mean (range) | Postop, mean (range) |
|
---|---|---|---|---|---|
Female | Knee Society Score | Knee | 43.5 (0–100) |
89.8 (25–100) |
<0.0001 |
Function | 51.4 (0–100) |
74.5 (0–100) |
<0.0001 | ||
SF-12 | Physical | 31.6 (12.5–56.7) |
43.8 (8.4–63.0) |
<0.0001 | |
Mental | 51.8 (13.6–77.8) |
54.0 (26.3–70.6) |
<0.0001 | ||
|
|||||
Male | Knee Society Score | Knee | 40.2 (0–93) |
91.0 (32–100) |
<0.0001 |
Function | 59.8 (5–100) |
86.3 (20–100) |
<0.0001 | ||
SF-12 | Physical | 32.4 (12.1–56.7) |
46.0 (14.3–65.0) |
<0.0001 | |
Mental | 55.5 (21.2–75.5) |
55.7 (31.4–72.5) |
0.729 |
Table
Comparison of preop to postop score changes (Δscores).
Score | Δscores (average ± SD) |
|
|
---|---|---|---|
Female ( |
Male ( |
||
KSS Knee | 46.3 ± 22.6 | 50.9 ± 21.8 | 0.002 |
KSS Function | 23.1 ± 25.2 | 26.5 ± 20.2 | 0.026 |
SF-12 Mental | 2.2 ± 10.3 | 0.2 ± 10.1 | 0.003 |
SF-12 Physical | 12.2 ± 10.7 | 13.7 ± 10.5 | 0.031 |
Tables
Range of motion (ROM) comparisons after a minimum of 2 years.
Preop ROM | Female | Male |
|
||
---|---|---|---|---|---|
Postop ROM (°) |
ΔROM (°) |
Postop ROM (°) |
ΔROM (°) |
||
<95° | 113.2 ± 10.0 ( |
34.1 ± 11.0 ( |
117.4 ± 8.4 ( |
32.3 ± 8.7 ( |
0.329 |
95°–105° | 118.9 ± 4.5 ( |
17.5 ± 5.8 ( |
119.3 ± 4.5 ( |
17.9 ± 6.0 ( |
0.542 |
>105° | 119.9 ± 5.4 ( |
3.6 ± 6.7 ( |
120.3 ± 5.8 ( |
4.2 ± 8.0 ( |
0.293 |
Note:
Peak flexion (PF) comparisons after a minimum of 2 years.
Preop flex | Female | Male |
|
||
---|---|---|---|---|---|
Postop PF (°) |
ΔPF (°) |
Postop PF (°) |
ΔPF (°) |
||
<95° | 111.4 ± 13.2 ( |
23.9 ± 12.1 ( |
110.9 ± 12.2 ( |
23.2 ± 10.3 ( |
0.867 |
95°–105° | 117.1 ± 5.6 ( |
15.2 ± 5.7 ( |
119.0 ± 4.5 ( |
17.4 ± 5.7 ( |
0.045 |
>105° | 119.9 ± 4.7 ( |
3.9 ± 6.2 ( |
120.2 ± 4.7 ( |
3.9 ± 6.6 ( |
1.000 |
Note:
A total of seven revisions were performed including four male knees at 0.65 years (aseptic loosening), 0.73 years (infection), 2.01 years (infection), and 2.13 years (aseptic loosening), and three female knees at 2.51 years (infection), 4.18 years (aseptic loosening), and 5.25 years (dislocation). All components were replaced in four revisions, only the tibial component and liner in two revisions, and the femoral component, tibial component, and liner in one revision. Kaplan-Meier survivorship was identical in both cohorts, that is, 98.5% (95% CI: 97.8–99.2%) at 5.6 years for males and 98.5% (95% CI: 96.5–100%) at 5.7 years for females.
There is little doubt that morphometric differences exist between female and male knees [
Four studies collectively examined 308 bilateral female patients, each having one knee replaced with a gender-specific high-flex knee and the other knee receiving a unisex knee (high-flex or non-high-flex) [
In our study, the total population of 1,785 high-flex cruciate-retaining knees resulted in only seven revisions. Stratifying survivorship by gender yielded Kaplan-Meier survivorship estimates of 98.5% for both men and women at 5.6 years and 5.7 years, respectively. Other investigators have found similar Kaplan-Meier survivorship for the same knee, that is, 97.8% at 7.0 years reported by Schroer et al. [
With the exception of the KS Knee score, the preoperative condition of the male knees was better than that of the female knees, which was significant (
As regards the KSS and SF-12 outcome comparisons between the men and women, it is best to compare the Δscores since the preop scores were different. The Δscores were significantly greater for males than females for KS Knee score (50.9 versus 46.3,
In general, the change in motion following TKA is inversely related to the preoperative value, that is, patients presenting with restricted motion tend to gain much motion after surgery while those with a high degree of motion initially tend to stay about the same, or perhaps lose a small amount of motion, after surgery [
Taken in aggregate, the survivorship, KSS, SF-12, ROM, and PF values suggest similar performance, overall, of this CR high-flex knee in both men and women. While there were some statistically significant differences in some outcomes between the genders, these differences were small and were of the magnitude obtained by others who did not ascribe clinical relevancy to them [
Gender considerations notwithstanding, current trends in high-flex knee design, include reducing the posterior radius of curvature which increases the contact area between the posterior femoral condyle and the tibial insert [
So what does this all mean? First, the literature has generally concluded that standard, unisex knee designs are equally suitable for both men and women. Second, our study helped fill a void in the literature by comparing the same unisex high-flex knee design in both men and women, thereby extending the results of others while reaching the same conclusions. Third, the complete compatibility of the entire range of femoral and tibial component sizes of the studied knee with each other may have allowed sufficient latitude to address patient needs regardless of gender. In other words, knee gender differences can be largely addressed through implant size rather than implant design considerations.
There were limitations in our study that should be considered. First, this was a retrospective study so there may be inherent biases that could have influenced the results. Despite this, the knee populations were large which may have partially mitigated this limitation. Second, only one type of high-flex knee was studied. As such, these results cannot be directly extended to other high-flex knee designs. Third, only mid-term survivorships were reported. Long-term survivorships of at least 10 years will be required to fully document gender-related outcomes differences that may exist with this knee design.
In summary, we found this knee to be highly effective in both men and women as evidenced by significant improvement in KSS and SF-12, similar ROM and PF outcomes, and high mid-term survivorship of 98.5%, confirming our study hypothesis.
It is important that surgeons have the necessary information available to make an informed decision about treatment options for their patients. This is particularly true in joint replacement where there are a plethora of implant types and design philosophies. The contention that women have inferior outcomes following standard TKA, which is the
Dr. Nassif is a consultant to Biomet Inc. Dr. Pietrzak has no competing interests to disclose.
Funding for this study was provided by Biomet Inc.