358 Limbs, 202 Patients, Valgus Cut Angle Resolved!?

What determines the valgus cut angle (VCA) for total knee arthroplasty (TKA)?

In the May 2017 edition of The Journal of Arthroplasty, an international team of researchers has published their work exploring this issue. The work, undertaken by researchers from Israel, Iran, Canada, and the U.S., was entitled, “Patient’s Height and Hip Medial Offset Are the Main Determinants of the Valgus Cut Angle During Total Knee Arthroplasty.”

David Backstein M.D., M.Ed., associate professor at the Granovsky Gluskin Division of Orthopaedics, Mt. Sinai Health System, University of Toronto, told OTW, “First of all, I would like to highlight the fact that this study was the brainchild and largely the product of the work of my co-author, Mansour Abolghasemian, M.D.”

“As for the study itself, the appropriate distal femoral cut angle has never been fully agreed upon. We recognized that measurement of the VCA for each individual limb is still a matter of significant debate. With the evolution of the kinematic alignment concept, factors affecting VCA require more attention than ever. Assuming a surgeon desired a neutral mechanical axis, we studied how to achieve this.”

The authors wrote, “Standard standing 3-joint views were used to measure a number of anatomical measurements in 358 limbs, 202 patients (116 women, 86 men). Neck-shaft angle, medial offset, femoral length (FL), distal femoral articular angle, and VCA were measured. Demographic data including gender and height were extracted from hospital charts. The correlation of VCA with each of the other factors was evaluated using linear regression and t-test and finally multivariate analysis.”

Dr. Backstein told OTW, “The high number of ethnically uniform patients and use of a comprehensive multivariate analysis (for the first time) add to the validity and interest of this study.”

Commenting on the results, he noted, “First, the diversity of VCA among the patients makes it necessary to assess this value for each individual in order to avoid significant malalignment. Second, patients’ height is the main determinant of the VCA. It was surprising to find a lack of correlation between gender and VCA that had been frequently reported before, and the strong effect of the patient’s height on the VCA which had been refuted once before.”

“This study was done on a large number of patients all with straight (non-bowed) knees. Even in these patients, VCA can be from 4 to 8 degrees (in order to achieve a neutral mechanical axis). Knowing the patient’s height and hip offset, one can have an idea about the magnitude of the VCA. However, obtaining a three joint view (standing view) remains the only reliable method for accurate measurement of this angle.”