Similar stability and range of motion between cruciate-retaining and cruciate-substituting ultracongruent insert total knee arthroplasty
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The use of an ultracongruent (UC) insert with a standard femoral component for substitution of the posterior cruciate ligament (PCL) is a bone-preserving and therefore interesting alternative to the established box and cam mechanism of posterior-stabilized total knee arthroplasty (TKA). Despite the regular use of these UC inserts, there is little evidence about stability and range of motion (ROM).
The aim of this study was to evaluate the stability and ROM in standard cruciate-retaining (CR) and cruciate-substituting UC inserts of the same TKA. In 39 patients, intraoperative measurements of stability and ROM were taken (1) before soft tissue release and bone cuts, (2) after implantation of a CR TKA and (3) after resection of the PCL and substitution with an UC insert. All measurements were taken using a navigation system.
Stability measurements demonstrated no differences between CR (PCL intact) and UC TKA (PCL resected), but significantly increased anteroposterior translation at 60° and 90° of knee flexion compared with the preoperative condition. ROM measurements demonstrated improvement of knee flexion from preoperatively mean 105° (SD 14.1°) to intraoperative 120.2° (SD 6.7°) with the CR and 121.0° (SD 7.5°) with the UC insert and 113.5° (SD 14.0°) at the 1-year follow-up.
This study demonstrates similar stability of an UC insert compared with a standard CR insert. UC inserts are therefore a bone-preserving solution if the PCL needs to be substituted. ROM was not improved after resection of the PCL and substitution with the UC insert.
Level of evidence
KeywordsTKA TKR Ultracongruent insert UC insert Stability Range of motion Results
The authors are grateful to Brit Brethfeld and Franziska Beyer for her valuable assistance during follow-up and data management.
Conflict of interest
This study was supported by a research grant from Aesculap AG (Tuttlingen, Germany).