Journal of experimental orthopaedics
The inwardly pointing knee angle: A novel computed tomography-based measurement technique and validation study
By Manilov RD, Maldonado AS, Bórbore A and 5 others.
Abstract
Purpose
Inwardly pointing knee (IPK) is a clinically recognized manifestation of torsional malalignment in patients with patellofemoral pain and instability. However, current imaging protocols primarily quantify isolated components of malalignment, such as femoral anteversion or tibial torsion, without also capturing the net orientation of the knee relative to the direction of gait. The purposes of this study were to describe a functional computed tomography (CT) protocol for patellofemoral assessment and to introduce and validate the measurement of the inwardly pointing knee angle (IPKA).
Methods
A total of 1230 bilateral CT examinations, performed between 2017 and 2025 in patients with anterior knee pain and/or patellofemoral instability, were retrospectively reviewed. Patients were positioned according to their individual foot progression angle (FPA), documented from plantar footprints obtained during walking before image acquisition. CT scans were obtained with the knees in full extension (0°) and at 30° of flexion while the feet remained fixed on the recorded FPA footprint. In addition to conventional torsional and patellofemoral parameters, IPKA, FPA and AVA were measured on these images. Reliability of IPKA was assessed in 60 randomly selected knees measured by three observers on three occasions, using intraclass correlation coefficients (ICCs), the standard error of measurement (SEM) and the smallest detectable change (SDC).