Biomechanics of the Patello-Femoral Joint. Part II: A Study of the Effect of Simulated Femoro-Tibial Varus Deformity on the Congruity of the Patello-Femoral Compartment and Movement of the Patella

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Abstract
This paper investigates the effect of different degrees of varus deformity on the pattern of contact, congruence of the patello-femoral joint, and movement of the patella. Varus deformity of 5, 10, and 15 degrees was imposed on the same cadaveric knee specimen used in the study reported in Part I (Fujikawa, Seedhom, Wright, 1983). This was done by high tibial osteotomy and the introduction of a wooden wedge of the appropriate thickness to effect the deformity. It was found that the contact gradually shifted to the medial side of the knee, and the congruence of the patello-femoral compartment was gradually destroyed as the degree of varus deformity increased to 15 degrees, although the effect of 5 degrees of varus deformity was minimal. Clinically, contact is shifted to the lateral side of the knee with varus deformity, but this is invariably associated with lateral tibial rotation. This rotation explains the difference between the results of the varus deformity imposed on cadaveric knees and those observed clinically. It is proposed that an adverse change in the congruence of the knee will occur after a sudden correction by high tibial osteotomy, just as that occurring in the normal cadaveric knee after imposing a sudden varus deformity, and therefore it may be useful to consider performing the correction at an early stage of the deformity. The effect of the varus deformity on the movement of the patella is also described.