Question:
In women having total knee replacement, how do outcomes from a sex-specific posterior-stabilized prosthesis compare with those from a high-flexion posterior-stabilized prosthesis?
Design:
Randomized (allocation concealed), blinded (patients and outcome assessor), controlled trial with 1-year follow-up.
Setting:
University Hospital of Hvidovre, Hvidovre, Denmark.
Patients:
24 women (mean age, sixty-six years) with osteoarthritis who were having bilateral total knee replacement. Patients with cardiopulmonary disease were excluded. All patients were included in the one-year analysis. Radiographic evaluation was available for 83% and gait data for 75% of patients.
Intervention:
Patients’ bilateral knees were allocated to a cemented Gender Solutions high-flex prosthesis (Zimmer, Warsaw, Indiana) and a cemented NexGen LPS-Flex prosthesis (Zimmer), in random order. A medial parapatellar approach was used in both knees. Bone cuts were made with reference to the posterior condyles, the anteroposterior axis defined by the so-called Whiteside line, and the transepicondylar axis in combination to ensure external rotation of the femoral component. Thorough resection of osteophytes and posterior capsular release was completed to ensure that all knees had a range of movement (range of motion) from full extension until the calf met the posterior aspect of the thigh. Mobilization was started when the patient arrived on the ward, and physiotherapy was started on the first postoperative day and continued with up to 8 group outpatient sessions.
Main outcome measures:
Active and passive flexion and extension were measured with the use of a goniometer. A visual analog scale (VAS) was used to assess pain (0 = no pain; 10 = worst pain imaginable), satisfaction and feel of the knee (0 = not feeling natural or working normal at all; 10 = feeling natural and working normal). The study had 90% power to show a 2-point difference between groups in feel of the knee.
Main results:
There were no differences between the sex-specific and LPS-Flex knees with regard to range of motion. At one year, 22 sex-specific and 23 LPS-Flex knees were able to extend to 0° (p = 0.55) and the mean active flexion was 125° in both groups (p = 0.82). Twenty-three knees in both groups were able to extend to 0° in passive flexion (p = 1.00), and the mean passive flexion was 131° in the sex-specific group and 132° in the LPS-Flex group (p = 0.64). The sex-specific and LPS-Flex groups did not differ in VAS measurements of median knee pain (0 versus 0, p = 0.95), satisfaction (8 versus 9, respectively; p = 0.98), or feel of the knee (8 versus 9, respectively; p = 0.66). There were no differences in gait analyses between the two designs in terms of various temporospatial or kinematic parameters.
Conclusion:
In women having bilateral total knee replacement, a sex-specific posterior-stabilized prosthesis did not improve range of movement or affect pain, satisfaction, or feel of the knee as compared with the outcomes associated with a high-flexion posterior-stabilized prosthesis.
Source of funding: In part, Zimmer, Warsaw, Indiana.
For correspondence: Mr. M.G. Thomsen, University Hospital of Hvidovre, Department of Orthopedics, Kettegård Allé 30, 2650 Hvidovre, Denmark. E-mail address: morten@grovethomsen.dk
Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, one or more of the authors has had another relationship, or has engaged in another activity, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
Differences between male and female knee anatomy are well known: women have narrower medial-lateral to anterior-posterior ratios (aspect ratios) of the femur and tibia with smaller anterior condylar height and an increased Q-angle. The question is whether prostheses developed to deal with these differences improve outcomes.
Thomsen and colleagues detected no differences in knee range-of-motion, pain, “feel,” or any gait parameters between the two alternately implanted total knee prostheses of 24 women. Traditional designs frequently result in component overhang among women, which has been clinically associated with increased pain. While a more anatomically conforming prosthesis could improve outcomes, the method of femoral component-size selection in this study eliminated component overhang. As a result, we are left with a comparison of control versus treatment groups that have median 4.5-mm and 8.6-mm bone undercoverage, respectively. Furthermore, the analyses did not take into account their paired design, which may have compromised study power1.
Mahoney and Kinsey found that women have more lateral overhang when a standard prosthesis is used and that an overhang of >3 mm was correlated with postoperative pain2. Clarke and Hentz found reduced overhang (17% versus 5%) when a sex-specific prosthesis was used3. Therefore, while no clinical advantage was observed in the present study, surgeons may prefer these designs for their potential to benefit women, particularly if cost differences are modest.