O1201 FLEXION INSTABILITY IN TOTAL KNEE REPLACEMENT. A COMPARISON OF POSTERIOR-STABILISED AND DEEP-DISHED COMPONENTS

Abstract

Aim: To examine the flexion stability of posterior stabilised (PS) vs deep dished (DD) tibial inserts, in PCL sacrificing total knee arthroplasty using posterior stress radiography. Methods: A simple jig was designed to allow kneeling posterior stress radiographs (at 90 degrees flexion) to be taken. This method was used to take pre and post-operative radiographs in 36 knees undergoing primary arthroplasty with PCL resection (26 DD and 10 PS implants). Sagittal plane tibial translation was measured. Results: The DD inserts all showed posterior displacement (mean: −5.1 mm, range: −2 to −12mm). The PS implants were all displaced anteriorly (mean: +6.7mm, range: +3 to +12mm). The difference in translation was highly significant (P< 0.0001). There was a strong correlation between implant and position of the tibia (R=0.86). In 7 patients, comparison was possible between a DD component in one knee and a PS implant in the other. There was a mean post-operative side-to-side difference of 11mm (range: 5 to 21mm). Conclusions: This study validates a simple new method for flexion stress x-rays (by accurately discriminating between the two implant types). The posterior tibial displacement in the DD group suggests that this implant does not provide enough posterior flexion stability to compensate for the PCL resection. The anterior translation in the PS group has implications for the design and wear of the post, as well as advice to patients about possibly avoiding kneeling in this PS design.