Sex-related outcome differences after implantation of low-contact-stress mobile-bearing total knee arthroplasty.

PURPOSE: The aim of the study was to investigate outcome differences between female and male patients after implantation of low-contact-stress (LCS) mobile-bearing total knee prostheses at a minimum follow-up of five years with respect to clinical and radiological parameters. METHODS: We retrospectively analysed 128 prostheses in 126 patients (90 women and 34 men) using our hospital database. Data was extracted with respect to range of motion (ROM), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, the Knee Society Score (KSS) and radiolucent lines on conventional X-rays. RESULTS: At follow-up, we observed no significant differences between female and male patients after LCS total knee prostheses. Benefit after implantation of LCS total knee prostheses after five years of minimum follow-up was not significantly different between female and male patients in terms of clinical outcome or radiolucent lines. CONCLUSIONS: We found no factors in favour of gender-specific total knee prostheses.

The influence of an anterior-posterior gliding mobile bearing on range of motion after total knee arthroplasty. A prospective, randomized, double-blinded study.

BACKGROUND: Range of motion is a crucial measure of outcome after total knee arthroplasty. In order for maximum flexion to occur, the femur must progressively shift posteriorly on the tibia, a movement that is known as femoral rollback. Mobile bearings with free anterior-posterior translation could improve knee flexion by allowing such motion. The purpose of the present study was to determine the influence of an anterior-posterior gliding mobile bearing on the postoperative range of knee motion in patients with an intact posterior cruciate ligament. METHODS: We performed a prospective, randomized clinical trial of fifty consecutive total knee arthroplasties that were performed with use of the LCS-Universal prosthesis. Participants were randomized to receive either a deep-dish rotating platform or a mobile bearing that allowed additional anterior-posterior translation, the latter of which requires an intact posterior cruciate ligament. The ranges of motion of the knees were assessed to detect a 15 degrees difference in the active non-weight-bearing range of motion with a power (1 - beta) of 20% and with the level of significance (alpha) set at 0.05. The translation of the mobile bearing was measured with use of a standardized ultrasound technique and was correlated with maximum knee flexion. The participants and the assessor were blinded throughout the study. RESULTS: At the time of the one-year follow-up evaluation, forty-eight knees were available for an intention-to-treat analysis. The mean active non-weight-bearing range of motion at one year was 113 degrees (95% confidence interval, 108 degrees to 118 degrees ) in the twenty-six knees that had received a rotating platform and 111 degrees (95% confidence interval, 115 degrees to 125 degrees ) in the twenty-two knees that had received an anterior-posterior gliding bearing (p = 0.57). In the latter group, a continuous rollback occurred in two knees. There was no significant correlation between knee flexion and anterior-posterior translation (r(2) = 0.015). CONCLUSIONS: The use of a mobile bearing that allowed free anterior-posterior translation did not regularly restore femoral rollback and did not improve range of motion after total knee arthroplasty compared with the findings seen in association with the use of a rotating platform.

The accuracy of ultrasound for measurement of mobile- bearing motion.

After anterior cruciate ligament-sacrificing total knee replacement, mobile bearings sometimes have paradoxic movement but the implications of such movement on function, wear, and implant survival are not known. To study this potential problem accurate, reliable, and widely available inexpensive tools for in vivo mobile-bearing motion analyses are needed. We developed a method using an 8-MHz ultrasound to analyze mobile-bearing motion and ascertained accuracy, precision, and reliability compared with plain and standard digital radiographs. The anterior rim of the mobile bearing was the target for all methods. The radiographs were taken in a horizontal plane at neutral rotation and incremental external and internal rotations. Five investigators examined four positions of the mobile bearing with all three methods. The accuracy and precision were: ultrasound, 0.7 mm and 0.2 mm; digital radiograph, 0.4 mm and 0.2 mm; and plain radiographs, 0.7 mm and 0.3 mm. The interrater and intrarater reliability ranged between 0.3 to 0.4 mm and 0.1 to 0.2 mm, respectively. The difference between the methods was not significant for neutral rotation but ultrasound was significantly more accurate than any one degree of rotation or higher. Ultrasound of 8 MHz provides an accuracy and reliability that is suitable for evaluation of in vivo meniscal bearing motion. Whether this method or others are sufficiently accurate to detect motion leading to abnormal wear is not known.