ESB clinical biomechanics award 2008: Complete data of total knee replacement loading for level walking and stair climbing measured in vivo with a follow-up of 6–10 months

BackgroundDetailed information about the loading of the knee joint is required for various investigations in total knee replacement. Up to now, gait analysis plus analytical musculo-skeletal models were used to calculate the forces and moments acting in the knee joint. Currently, all experimental and numerical pre-clinical tests rely on these indirect measurements which have limitations. The validation of these methods requires in vivo data; therefore, the purpose of this study was to provide in vivo loading data of the knee joint.MethodsA custom-made telemetric tibial tray was used to measure the three forces and three moments acting in the implant. This prosthesis was implanted into two subjects and measurements were obtained for a follow-up of 6 and 10 months, respectively.Subjects performed level walking and going up and down stairs using a self-selected comfortable speed. The subjects’ activities were captured simultaneously with the load data on a digital video tape. Customized software enabled the display of all information in one video sequence.FindingsThe highest mean values of the peak load components from the two subjects were as follows: during level walking the forces were 276 %BW (percent body weight) in axial direction, 21 %BW (medio-lateral), and 29 %BW (antero-posterior). The moments were 1.8 %BW*m in the sagittal plane, 4.3 %BW*m (frontal plane) and 1.0 %BW*m (transversal plane). During stair climbing the axial force increased to 306 %BW, while the shear forces changed only slightly. The sagittal plane moment increased to 2.4 %BW*m, while the frontal and transversal plane moments decreased slightly. Stair descending produced the highest forces of 352 %BW (axial), 35 %BW (medio-lateral), and 36 %BW (antero-posterior). The sagittal and frontal plane moments increased to 2.8 %BW*m and 4.6 %BW*m, respectively, while the transversal plane moment changed only slightly.InterpretationUsing the data obtained, mechanical simulators can be programmed according to realistic load profiles. Furthermore, musculo-skeletal models can be validated, which until now often lacked the ability to predict properly the non-sagittal load values, e.g. varus–valgus and internal–external moments.