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Assessment of isometricity before and after total knee arthroplasty: a cadaver study

Markus Kuster, Benjamin O Jeffcote, Andreas C Schirm, Hilaire Jacob & Rochelle L Nicholls

abstract Total knee arthroplasty (TKA) relies on soft tissue to regulate joint stability after surgery. In practice, the exact balance of the gaps can be difficult to measure, and various methods including intra-operative spreaders or distraction devices have been proposed. While individual ligament strain patterns have been measured, no data exist on the isometricity of the soft tissue envelope as a whole. In this study, a novel device was developed and validated to compare isometricity in the entire soft tissue envelope for both the intact and TKA knee. A spring-loaded rod was inserted in six cadaver knee joints between the tibial shaft and the tibial plateau or tibial tray after removing a 7 mm slice of bone. The displacement of the rod during passive flexion represented variation in tissue tension around the joint. The rod position in the intact knee remained within 1 mm of its initial position between 15 degrees and 135 degrees of flexion, and within 2 mm (+/-1.2 mm) throughout the entire range of motion (0-150 degrees). After insertion of a mobile-bearing TKA, the rod was displaced a mean of 6 mm at 150 degrees (p<0.001). The results were validated using a force transducer implanted in the tibial baseplate of the TKA, which showed increased tibiofemoral force in the parts of the flexion range where the rod was most displaced. The force measurements were highly correlated with the displacement pattern of the spring-loaded rod (r=-0.338; p=0.006). A simple device has been validated to measure isometricity in the soft tissue envelope around the knee joint. Isometricity measurements may be used in the future to improve implantation techniques during TKA surgery.
   
citation kuster m, Jeffcote B O, Schirm A C, Jacob H, Nicholls R L. Assessment of isometricity before and after total knee arthroplasty: a cadaver study. The Knee 2009; 16:352-7.
   
type journal paper/review (English)
date of publishing 10-2009
journal title The Knee (16/5)
ISSN electronic 1873-5800
pages 352-7
PubMed 19211251
DOI 10.1016/j.knee.2009.01.002