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.


OBJECTIVE
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.


CONCLUSIONS
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.


METHODS
Level IV.
Aix-Marseille Université, CNRS, ISM UMR 7287, 13288 Marseille cedex 09, France; Institut Monégasque de Médecine et Chirurgie du Sport, 98000 Monaco, Monaco. Electronic address: schlattererb@im2s.mc.
B
B
Schlatterer
Aix-Marseille Université, CNRS, ISM UMR 7287, 13288 Marseille cedex 09, France.
J-M
JM
Linares
Aix-Marseille Université, CNRS, ISM UMR 7287, 13288 Marseille cedex 09, France.
P
P
Chabrand
Aix-Marseille Université, CNRS, ISM UMR 7287, 13288 Marseille cedex 09, France.
J-M
JM
Sprauel
Aix-Marseille Université, CNRS, ISM UMR 7287, 13288 Marseille cedex 09, France; Institut du Mouvement et de l'Appareil Locomoteur, Hôpital Sainte-Marguerite, CHU Marseille, 13274 Marseille, France.
J-N
JN
Argenson
D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D003198:Computer Simulation; D005269:Femur / Q000601:surgery; D006801:Humans; D009010:Monte Carlo Method; D055096:Optical Devices; D012399:Rotation; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013977:Tibia / Q000601:surgery
Anatomic landmarks; Computer-assisted surgery; Infrared optical system; Navigation; Total knee arthroplasty