Evaluation of formal methods in hip joint center assessment: an in vitro analysis.
BACKGROUND
The hip joint center is a fundamental landmark in the identification of lower limb mechanical axis; errors in its location lead to substantial inaccuracies both in joint reconstruction and in gait analysis. Actually in Computer Aided Surgery functional non-invasive procedures have been tested in identifying this landmark, but an anatomical validation is scarcely discussed.


METHODS
A navigation system was used to acquire data on eight cadaveric hips. Pivoting functional maneuver and hip joint anatomy were analyzed. Two functional methods - both with and without using the pelvic tracker - were evaluated: specifically a sphere fit method and a transformation techniques. The positions of the estimated centers with respect to the anatomical center of the femoral head, the influence of this deviation on the kinematic assessment and on the identification of femoral mechanical axis were analyzed.


RESULTS
We found that the implemented transformation technique was the most reliable estimation of hip joint center, introducing a - Mean (SD) - difference of 1.6 (2.7) mm from the anatomical center with the pelvic tracker, whereas sphere fit method without it demonstrated the lowest accuracy with 25.2 (18.9) mm of deviation. Otherwise both the methods reported similar accuracy (<3mm of deviation).


CONCLUSIONS
The functional estimations resulted in the best case to be in an average of less than 2mm from the anatomical center, which corresponds to angular deviations of the femoral mechanical axis smaller than 1.7 (1.3) degrees and negligible errors in kinematic assessment of angular displacements.
Lopomo
Nicola
N
Laboratorio di Biomeccanica, Istituto Ortopedico Rizzoli, Bologna, Italy. n.lopomo@biomec.ior.it <n.lopomo@biomec.ior.it>
Sun
Lei
L
Zaffagnini
Stefano
S
Giordano
Giovanni
G
Safran
Marc R
MR
D053587:Arthrometry, Articular / Q000295:instrumentation / Q000379:methods*; D002102:Cadaver; D003198:Computer Simulation; D006621:Hip Joint / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D008953:Models, Anatomic; D008954:Models, Biological; D016059:Range of Motion, Articular / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity