Determination of the Mechanical Medial Proximal Tibial Angle Using a Tangential Radiographic Technique

Abstract

To assess whether there is a difference in the mechanical medial proximal tibial angle (mMPTA) measured on a tangential caudocranial (tCdCr) radiographic projection versus a straight caudocranial (sCdCr) projection before and after inducing a varus deformity in the proximal tibia. In vitro study. Cadaveric canine tibiae (n=4 pair). For each tibia, a mediolateral radiographic projection was performed and the tibial plateau angle was measured. sCdCr and tCdCr radiographic projections were obtained and the mMPTA measured. A varus deformity was created in the proximal aspect of the tibia and sCdCr and tCdCr projections were repeated and mMPTA measured. mMPTA for tCdCr was statistically different from mMPTA for the sCdCr projection for the varus tibiae (P<.05). There was no significant difference in the mMPTA measured on the sCdCr projections before and after creation of a varus deformity (P>.05). There was a significant difference in mMPTA measured on the tCdCr projection before and after creation of a varus deformity (P<.05). Varus deformity in the mMPTA was identified on tCdCr projections of the varus tibiae whereas it was not identified on sCdCr projections. Tangential radiographic projections of the tibial plateau may be useful for evaluating varus deformities involving the articular surface of the tibia and should be performed during preoperative evaluation of angular limb deformities involving the proximal aspect of the tibia and for tibial plateau leveling osteotomy (TPLO) planning.