Comparison of axial tibial-metatarsal alignment in dogs of varying size with and without medial patellar luxation.

Abstract

OBJECTIVES: To compare tibial torsion angle (TTA) and proximal tibial metatarsal angle (PTMTA) between dogs weighing < 10&#x202f;kg and dogs weighing &#x2265; 10&#x202f;kg with and without medial patellar luxation (MPL) to assess whether transverse plane tibial-metatarsal malalignment is size dependent. STUDY DESIGN: Retrospective computed tomographic analysis. SAMPLE POPULATION: One hundred and one limbs from 55 client-owned dogs. METHODS: Computed tomographic (CT) scans of pelvic limbs that met inclusion criteria were categorized by dog size (dogs weighing less or over 10&#x202f;kg) and presence and grade of medial patellar luxation (normal, Grade 2, Grade 3 and Grade 4). A single investigator measured both TTA and PTMTA in each limb. Both TTA and PTMTA were compared between dogs of varying degrees of MPL and between dogs weighing < 10&#x202f;kg and dogs weighing &#x2265; 10&#x202f;kg. RESULTS: A clear association between increasing TTA and higher grades of MPL was not discerned in dogs weighing < 10&#x202f;kg. However, dogs weighing < 10&#x202f;kg did exhibit a trend of worsening tibial-metatarsal malalignment as patellar luxation grade increased with grade 4 MPLs having a significantly larger PTMTA than all other groups. Among dogs weighing &#x2265; 10&#x202f;kg, those with grade 3 MPLs possessed a significantly larger TTA compared to all other groups, but dogs with grade 4 MPLs were not different from normal dogs. However, dogs weighing &#x2265; 10&#x202f;kg did exhibit a trend of increasing PTMTA values associated with worsening grades of patellar luxation with grade 2 and 4 MPL dogs showing more tibial-metatarsal malalignment than normal dogs. There were differences between dogs weighing < 10&#x202f;kg and dogs weighing &#x2265; 10&#x202f;kg with respect to TTA measurements with dogs < 10&#x202f;kg showing more tibial torsion in MPL Grades 2 and 4. However, no differences were detected in PTMTA between sizes with any grade of MPL. CONCLUSION: Tibial-metatarsal malalignment measurable through an increased PTMTA may be a more predictably associated transverse plane deformity with MPL than tibial torsion alone as measured by the TTA. Both dogs weighing less or over 10&#x202f;kg appear to exhibit tibial-metatarsal malalignment with increasing severity in cases of higher grades of MPL.