Jean-Michel Sprauel

Influence of the optical system and anatomic points on computer-assisted total knee arthroplasty

BACKGROUND For over a decade, computer-assisted orthopaedic surgery for total knee arthroplasty has been accepted as ensuring accurate implant alignment in the coronal plane. HYPOTHESIS We hypothesised that lack of accuracy in skeletal landmark identification during the acquisition phase and/or measurement variability of the infrared optical system may limit the validity of the numerical information used to guide the surgical procedure. METHODS We built a geometric model of a navigation system, with no preoperative image acquisition, to simulate the stages of the acquisition process. Random positions of each optical reflector center and anatomic acquisition point were generated within a sphere of predefined diameter. Based on the virtual geometric model and navigation process, we obtained 30,000 simulations using the Monte Carlo statistical method then computed the variability of the anatomic reference frames used to guide the bone cuts. Rotational variability (α, β, γ) of the femoral and tibial landmarks reflected implant positioning errors in flexion-extension, valgus-varus, and rotation, respectively. RESULTS Taking into account the uncertainties pertaining to the 3D infrared optical measurement system and to anatomic point acquisition, the femoral and tibial landmarks exhibited maximal alpha (flexion-extension), beta (valgus-varus), and gamma (axial rotation) errors of 1.65° (0.9°); 1.51° (0,98°), and 2.37° (3.84°), respectively. Variability of the infrared optical measurement system had no significant influence on femoro-tibial alignment angles. CONCLUSION The results of a Monte Carlo simulation indicate a certain level of vulnerability of navigation systems for guiding position in rotation, contrasting with robustness for guiding sagittal and coronal alignments. LEVEL OF EVIDENCE Level IV.

Quality Measurement on CMM

In the first section we wile discuss the sources of errors and uncertainties of the Coordinate Measuring Machine (CMM) [1]. The mastery of this process depends on a good knowledge of the initialisation methodology of the CMM.

Inspection of Mechanical Tolerance by Using the Virtual Gauge on a Coordinate Measuring Machine

The function to obtain associated surfaces on coordinate measuring machines (CMM’s) is based on the minimization of the distance between measured points and the ideal surface. This function is non-linear for usual surfaces. In many works, to accelerate iterative calculations, the problem is linearized. The aim of this work is to reduce scraps using a transcription optimization of the fitting functionality of mechanical parts in maximum state of matter. An adaptive verification method is suggested. It takes account of the interface properties. A control by a virtual gauge and verification a process is developed to validate the tolerancing according to the previously suggested methodology.