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INTRODUCTIONHideki Mizu-Uchi - Scripps - La Jolla, USACesar Flores-Hernandez - Scripps - La Jolla, USAClifford Colwell Jr. - Scripps - La Jolla, USANikolai Steklov - Scripps - La Jolla, USAShuichi Matsuda - - Fukuoka, JPNYukihide Iwamoto - Kyushu Universith - Kyushu, Japan*Darryl D'Lima - Scripps - La Jolla, USA*Email: ddlima@gmail.comKnee contact force during activities after total knee arthroplasty (TKA) is very important, sinceit directly affects component wear and implant loosening. While several computational modelshave predicted knee contact force, the reports vary widely based on the type of modelingapproach and the assumptions made in the model. The knee is a complex joint, with threecompartments of which stability is governed primarily by soft tissues. Multiple muscles controlknee motion with antagonistic co-contraction and redundant actions, which adds to thedifficulty of accurate dynamic modeling. For accurate clinically relevant predictions a subjectspecificapproach is necessary to account for inter-patient variability.METHODSData were collected from 3 patients who received custom TKA tibial prostheses instrumentedwith force transducers and a telemetry system. Knee contact forces were measured duringsquatting, which was performed up to a knee flexion angle that was possible without discomfort(range, 80–120°). Skin marker-based video motion analysis was used to record kneekinematics. Preoperative CT scans were reconstructed to extract tibiofemoral bone geometryusing MIMICS (Materialise, Belgium). Subject-specific musculoskeletal models of dynamicsquatting were generated in a commercial software program (LifeMOD, LifeModeler, USA).Contact was modeled between tibiofemoral and patellofemoral articular surfaces and betweenthe quadriceps and trochlear groove to simulate tendon wrapping. Knee ligaments weremodeled with nonlinear springs: the attachments of these ligaments were adjusted to subjectspecificanatomic landmarks and material properties were assigned from published reports.RESULTSTotal measured peak ground reaction force was 0.9–1.1 xBW (times of bodyweight) andmeasured peak knee contact force was 2.2 (±0.2) xBW during squatting. Model predicted peaktibiofemoral contact forces were within the cycle-to-cycle variations for each subject. Modelpredicted peak patellofemoral contact forces were 0.9–1.1 xBW and peak quadriceps forceswere 1.3–1.6 xBW. Mean peak ligament tensions were 55.5 ± 8.8 N for the MCL and 47.1 ±10.4 N for the LCL.DISCUSSIONSmall differences between predicted and measured forces were likely due to the complexity ofthe squatting activity, the inherent error in skin marker-based motion capture, and the fact thatmuscle force was computed from muscle shortening history. Trunk flexion significantlyaffected the contact force, especially at higher knee flexion angles. Trunk flexion reduced theexternal flexion moment at the knee leading to reduced quadriceps force and therefore reducedtibiofemoral contact force.Peak patellofemoral contact forces and quadriceps muscle forces were also lower thanpreviously reported. Although others have reported on hamstring muscle activity during thesquat, hamstring forces were low in our models in qualitative agreement with the EMG data thatwe recorded during squatting. The lack of significant hamstring activity may explain the lowernet tibiofemoral contact forces. This model would be very useful tool to predict the effect ofsurgical techniques on contact forces. Such a model could be used for implant designdevelopment to enhance knee function and to predict forces generated during other activities.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]