Understanding patellofemoral pain with maltracking in the presence of joint laxity: complete 3D in vivo patellofemoral and tibiofemoral kinematics

Abstract

Patellofemoral pain is widely accepted as one of the most common pathologies involving the knee, yet the etiology of this pain is still an open debate. Generalized joint laxity has been associated with patellofemoral pain, but is not often discussed as a potential source of patellar maltracking. Thus, the objective of this study was to compare the complete 6 degree of freedom patellofemoral and tibiofemoral kinematics from a group of patients diagnosed with patellofemoral pain syndrome and maltracking to those from an asymptomatic population. The following null hypotheses were tested: kinematic alterations in patellofemoral maltracking are limited to the axial plane; knee joint kinematics are the same in maltrackers with and without generalized joint laxity (defined by a clinical diagnosis of Ehlers Danlos Syndrome); and no correlations exist between tibiofemoral and patellofemoral kinematics or within patellofemoral kinematics. This study demonstrated that alterations in patellofemoral kinematics, associated with patellofemoral pain, are not limited to the axial plane, minimal correlations exist between patellofemoral and tibiofemoral kinematics, and distinct subgroups likely exist within the general population of maltrackers. Being able to identify subgroups correctly within the omnibus diagnosis of patellar maltracking is a crucial step in correctly defining the pathophysiology and the eventual treatment of these patients.

Figure 1. Coordinate Systems for non-EDS (S13) and EDS (S2) maltrackers

Medial, superior, and anterior directions were positive for the x, y and z-directions, respectively. All systems were derived from dynamic full extension images. The patellar image was at the level of the mid-patella (middle images), and the femoral image was at the level of the epicondyles (bottom images). At 10º extension, patellar tilt was 14.7º for the normative population. Thus, S13 and S2 had patellar tilt angles that were medial and lateral from normative, respectively. The knee angle at the time point shown was 1º and 7º for the S13 and S3, respectively. Qualitatively, the patella alta of S2 can be seen by viewing the patellar inferior pole (Pt, top images).

Figure 2. PF kinematics, comparing asymptomatic population to all maltrackers

Asymptomatic population average (n=34: black line, no symbol ±1SD is shown in grey shading). Maltracking group average (n=25: black line with circles placed at 5º increments and 1 SD shown with a bar). Data were averaged to single knee angle increments, but limited symbols provided clarity. Left column contains the 3 scaled translations; right column contains the 3 rotations, based on a body fixed XYZ rotation sequence. The dotted line represents 10º extension, where statistical comparisons were made.

Figure 3. Tibiofemoral kinematics, comparing asymptomatic population to all maltrackers

Asymptomatic population average (n=34: black line, no symbol ±1SD is shown in grey shading). Maltracking group average (n=25: black line with circles placed at 5º increments and 1 SD shown with a bar). Left column contains the 3 scaled translations; right column contains the 3 rotations, based on a body fixed XYZ rotation sequence. The dotted line represents 10º extension, where statistical comparisons were made.

Figure 4. Patellofemoral kinematics, comparing asymptomatic population to non-EDS and EDS subgroups

Asymptomatic population average (n=34: black line, no symbol ±1SD is shown in grey shading). Non-EDS (EDS) group has squares (circles) placed at 5º increments with 1 SD shown with a bar for both groups. Left column contains the 3 scaled translations; right column contains the 3 rotations, based on a body fixed XYZ rotation sequence. The dotted line represents 10º extension, where statistical comparisons were made.

Figure 5. Tibiofemoral kinematics, comparing asymptomatic population to non-EDS and EDS subgroups

Asymptomatic population average (n=34: black line, no symbol ±1SD is shown in grey shading). Non-EDS (EDS) group has squares (circles) placed at 5º increments with 1 SD shown with a bar for both groups. Left column contains the 3 scaled translations; right column contains the 3 rotations, based on a body fixed XYZ rotation sequence. The dotted line represents 10º extension, where statistical comparisons were made.