Standardisation of the description of patellofemoral motion and comparison between different techniques

Abstract

Patellofemoral motion is significant clinically, yet in the literature many different methods and terminologies are used, thus making comparison between papers difficult. The aim of this study was to review and explain the different methods used for the description of patellofemoral joint motion, compare these methods by experimentation, and propose a standardised method. We found three main methods for describing patellar motion: motion of the patella about femoral body fixed axes, about patellar body fixed axes, or a combination of these. Description about femoral body fixed axes does not make sense clinically. Description about patellar body fixed axes is straightforward, yet the definition of these axes is prone to error due to the lack of anatomical landmarks. The combination method makes most sense clinically and uses more easily found anatomical landmarks. Patellar flexion varied by up to 26% when describing the motion about different axes. Tilt and shift were highly sensitive to the choices of coordinate systems and the axes of motion. The pattern of rotation was consistent between all methods, however, differences between the methods increased with patellar flexion. We propose the description of patello-femoral motion in terms of shift (along a femoral medial-lateral axis), tilt (about the patellar long axis), rotation (about a floating patellar anterior-posterior axis) and flexion (about the femoral medial-lateral axis).

Three‐dimensional patellar motion at the natural knee during passive flexion/extension. An in vitro study

“…30 Calculations of PFJ flexion/extension, tilt, and rotation was based on these anatomical frames and occur respectively about Z f , Y p , and the floating axis perpendicular to these two, according to recent proposals. 10,11 PFJ flexion occurs when the distal apex of the patella moves Figure 1. Experimental setup: view from the infrared camera system of the KNS.…”

“…11 These navigation systems are based on standard stereophotogrammetric technology and allow anatomical-based tracking of human bony segments by trackers and the digitization of anatomical landmarks. Two recent proposals 10,11 concur with the use of a standard mechanical convention 30 and established bone-embedded reference frames 31 also for describing PFJ motion.…”

“…[7][8][9] An accurate quantitative reference for normal PFJ kinematics is therefore necessary to identify maltracking. [10][11][12] This is important also during computer-assisted arthroplasty in addition to standard TFJ kinematics, for more appropriate bone preparation and implant positioning. 11 This reference has not yet been established.…”

“…10,13 For this goal, patellar motion must be tracked in all six degrees of freedom, thus overcoming the traditional twodimensional X-ray based views. 14 A number of studies, both in vitro [9][10][11][12][15][16][17][18][19][20] and in vivo, [21][22][23][24][25][26][27][28] have dealt with patellar tracking by different methodological approaches and measuring devices. Among them, magnetic resonance and X-ray stereo-photogrammetry do not allow the acquisition of natural and continuous movements in a large range of knee positions.…”

“…In addition, no standard anatomical and kinematics conventions have been established, and this hinders the rational comparison of the results from the literature. 10,11,13 Finally, the majority of the studies on PFJ kinematics were conducted on very small population sizes. 13 Among possible measuring devices, current knee navigation systems (KNS), designed to assist the placement of prosthesis components in the operating room, 29 have shown good potential.…”