Bicruciate-stabilized TKA Does Not Result in Improved Patient-reported Outcomes Compared With Posterior-stabilized...

Traditional posterior-stabilized implants use a cam-post mechanism as a substitute for the PCL, aiming to enhance stability and ROM. Bicruciate-stabilized TKA has been developed to mimic the function of both the ACL and PCL using a dual-cam mechanism. Despite these theoretical advantages, improvements in actual clinical and functional outcomes of bicruciate-stabilized implants compared with posterior-stabilized implants, if any, remain unproven.

(1) Does bicruciate-stabilized TKA result in improved posterior offset ratio and patellar tendon angle (AP position and translation of the femur in relation to sagittal plane parameters) compared with posterior-stabilized TKA? (2) Are postoperative patient-reported outcomes (PROs) superior in knees treated with bicruciate-stabilized TKA than those treated with posterior-stabilized TKA?

A prospective, single-center, patient-blinded, parallel-group randomized controlled trial was performed in 50 patients (100 knees) undergoing simultaneous bilateral TKA for primary osteoarthritis between November 2019 and April 2020. All patients underwent same-day bilateral TKAs using a bicruciate-stabilized implant (bicruciate-stabilized group) in one knee and a posterior-stabilized implant (posterior-stabilized group) in the other. Fifty patients were screened and enrolled, but two patients were lost to follow-up, so 48 patients (96 knees) were analyzed. The mean ± SD patient age was 75 ± 6 years, and 96% (46) of patients were women. Preoperatively, there were no between-group differences in terms of clinical parameters, including ROM, hip-knee-ankle angle, Knee Society Score (KSS), and WOMAC score. Radiographic measurements, including the posterior offset ratio, patellar tendon angle, joint line orientation angle, and static AP laxity, were obtained at 2 years postoperatively. Also at 2 years postoperatively, PROs were compared using the KSS, WOMAC score, and Forgotten Joint score (FJS); in addition, patients were asked which knee was their "preferred" knee. To address the challenge of evaluating PROs for a single patient with bilateral TKA, patients were instructed to independently evaluate each knee while performing daily activities, including distance walked and stair climbing, based on their subjective perception of comfort and functionality in each knee.

The radiographic results showed that at 2 years, knees treated with the bicruciate-stabilized device had greater patellar tendon angles than those treated with the posterior-stabilized device (patellar tendon angle: 15° ± 4° versus 9° ± 4°; mean difference -6° [95% confidence interval (CI) -7° to -5°]; p < 0.001). The knees treated with the bicruciate-stabilized device had a smaller posterior offset ratio than those treated with the posterior-stabilized device (5% ± 4% versus 18% ± 4%, mean difference 13% [95% CI 11% to 15%]; p < 0.001). The increase in posterior offset ratio was less in the bicruciate-stabilized group compared with the posterior-stabilized group (1% ± 12% versus 14% ± 12%, mean difference 13% [95% CI 11% to 15%]; p < 0.001). The decrease in patellar tendon angle was less in the bicruciate-stabilized group compared with the posterior-stabilized group (patellar tendon angle: 1° ± 6° versus 7° ± 5°, mean difference 6° [95% CI 4° to 7°]; p < 0.001). There were no differences in 2-year PROs, including the KSS and WOMAC, in the bicruciate-stabilized and posterior-stabilized groups (KSS: 145 ± 23 versus 144 ± 24, mean difference -1 [95% CI -5 to 3]; p = 0.57, WOMAC: 28 ± 13 versus 30 ± 17, mean difference 2 [95% CI -1 to 6]; p = 0.21). Likewise, the FJS did not differ between groups (51 ± 20 in the bicruciate-stabilized group versus 50 ± 22 in the posterior-stabilized group, mean difference -1 [95% CI -5 to 2]; p = 0.44), reflecting an absence of differences between implant designs in terms of patient awareness of the knee. Additionally, at 2 years, 35% (17) of patients preferred the knee treated with the bicruciate-stabilized device whereas 25% (12) of patients preferred the knee treated with the posterior-stabilized device (p = 0.54). Thus, the patients did not express a clear preference for either device.

Although the bicruciate-stabilized implant demonstrated better replication of static radiographic implant positions, these findings did not translate into superior PROs compared with the posterior-stabilized TKA. Until or unless further well-designed RCTs substantiate the superiority of bicruciate-stabilized TKA in terms of endpoints that patients can perceive (such as pain, function, or implant longevity), we recommend against the wide adoption of this device in clinical practice.

Level Ⅰ, therapeutic study.