Knee joint instability, which is a primary reason for TKA revision surgeries, is typically caused by deficiency in the knee ligaments [1, 2]. Managing ligament deficiency and restoring joint stability continues to be one of the greatest challenges for revision surgeries [3]. To treat such patients, revision TKA implants frequently incorporate a constrained post and cam mechanism to provide enhanced varus-valgus constraint to supplement the function of the collateral ligaments. The aim of this study was to evaluate knee kinematics during a weight bearing deep knee bend for both a primary TKA system and its complimentary revision system. The hypothesis of the study was that the revision tibial insert would demonstrate improved knee stability, in the form of a reduced range of motion under out-of-plane loading, when compared to the primary system Eight cadaveric knees (age: 59±10 years, BMI 23.3±3.5) were implanted with an ATTUNE™ revision femoral component and a primary posterior stabilized tibial component. Each knee was mounted and aligned into the Kansas Knee Simulator (Fig. 1) [4]. A deep knee bend was performed between 10° and 110° flexion with no out-of-plane loading. Additional deep knee bends were performed with constant 6Nm external and 6Nm internal torques about the tibial long axis, and with 40N medial and 40N lateral loads applied at the ankle sled. The 40N medial and 40N lateral loads produce approximately 15Nm adduction and abduction moments at the knee, respectively. The primary tibial insets were then replaced with revision tibial inserts from the same TKA system and the deep knee bend cycles were repeated. The revision tibial inserts included a larger tibial post intended to constrain the varus-valgus rotation of the knee. The change in knee kinematics of the revision tibial insert compared to the primary insert was calculated and student t-tests were performed to identify significant differences between the two tibial insert types for each loading condition.Introduction
Methods
Tibiofemoral constraint in patients with total knee replacements (TKR) is dependent on both implant geometry and the surrounding soft tissue structures. Choosing more highly constrained geometries can reduce the contribution of soft tissue necessary to maintain joint stability [1]. Often when knee revision surgeries are required, the soft tissue and bone are compromised leading to the use of more constrained implants to ensure knee stability [2]. The current study quantifies the differences in varus-valgus (VV) and internal-external (IE) constraint between two types of total knee revision systems: SIGMA® TC3© and ATTUNE® REVISION. Nine cadaveric knees (7 male, age 64.0 ± 9.8 years, BMI 26.28 ± 4.92) were implanted with both fixed-bearing SIGMA TC3 and ATTUNE REVISION knee systems. Five knees received the TC3 implant first, while the remaining 4 received the ATTUNE implant first. The knees were mounted in an inverted position, and a six degree-of-freedom force-torque sensor (JR3, Woodland, CA) was rigidly secured to the distal tibia (Fig. 1). A series of manual manipulations applying IE and VV torques was performed through the flexion range [3]. Each specimen was then revised to the alternate revision system, and the manual manipulations were repeated. Joint loads were calculated, and tibiofemoral kinematics were described according to the Grood-Suntay definition [4]. VV and IE kinematics were calculated as a function of flexion angle, VV torque, and IE torque as has been described previously [3]. The knees were analysed at ±6 Nm VV and ±4 Nm IE, and the kinematics were normalized to the zero load path. A paired t-test (p < .05) was employed to identify significant differences between the kinematics of the two knee systems at 10º flexion increments.Introduction
Methods
