Patellar maltracking: an update on the diagnosis and treatment strategies

Abstract

Patellar maltracking occurs as a result of an imbalance in the dynamic relationship between the patella and trochlea. This is often secondary to an underlying structural abnormality. The clinical evaluation can provide useful clues for the presence of such entity; however, the diagnosis can often be challenging especially in the absence of a documented history of patellar dislocation. Imaging, particularly MRI, can detect subtle features that could lead to the diagnosis, probably even more importantly when there is no clear history of patellar dislocation or before its development. This can provide a road map for formulating a treatment strategy that would be primarily aimed at stabilizing the patellofemoral joint to halt or slow the progression of articular cartilage loss. The purpose of this article is to discuss the clinical and radiologic evaluation of patellar maltracking providing an update on the cross-sectional imaging assessment and also a synopsis of the management options.

Keywords: Anterior knee pain; Patellar instability; Patellar maltracking; Patellofemoral osteoarthritis.

Fig. 1

Trochlear depth assessment. Axial PDFS left knee MR image, demonstrating the method used for the measurement of trochlear depth. First, a line is drawn paralleling the posterior femoral condyles surfaces. Perpendicular to this baseline, trochlear depth is calculated by measuring the mean of the maximum AP distance of the medial (a) and lateral (b) femoral condyles minus the distance between the deepest point of the trochlear groove and the line paralleling the posterior condylar surfaces (c). Trochlear depth = [(a + b)/2] − c

Fig. 2

Lateral trochlear inclination measurement on axial MRI. It is the angle between a line tangential to the subchondral bone of the posterior aspect of the femoral condyles and a line along the lateral trochlear facet. a Normal trochlea. b Trochlear dysplasia (9° inclination)

Fig. 3

Facet asymmetry assessment for trochlear dysplasia on axial MRI. It is the percentage of the medial (a) to the lateral (b) trochlear facet length (a/b × 100%)

Fig. 4

Patella alta assessment. a Sagittal PD knee MRI showing the method of assessing the Insall–Salvati index, calculated as the ratio of the patellar tendon length at its inner aspect (white dashed line) to the greatest diagonal length of the patella (white line). b Patellar alta evaluation using the Caton–Deschamps index, which is the ratio between a line measured between the inferior margin of the patellar articular surface and the anterior aspect of the tibial plateau (black line) and the greatest length of the patellar articular surface (white line)

Fig. 5

Tibial tubercle–trochlear groove distance (TT-TG) assessment. a Axial PDFS right knee MR image at the level of the trochlear groove. b Axial MRI at the level of the tibial tuberosity. TTTG is the distance between the solid and the dashed lines in (b). Note the edema in the superolateral aspect of Hoffa’s fat pad (arrow)

Fig. 6

Patellar tilt assessment. a The posterior condylar line is drawn on the slice where the posterior femoral condyles are largest (dashed line). b The patella tilt angle is measured between the posterior condylar line (dashed line) and the maximal patella width (solid line).

Fig. 7

Transient lateral patellar dislocation. Axial PDFS MR image showing MPFL disruption (open arrow) and trochlear dysplasia (arrowheads). There is edema of the medial patella and of the lateral femoral condyle (arrow), consistent with bone contusion due to recent lateral patellar dislocation

Fig. 8

CT of both knees in 20° flexion demonstrating bilateral shallow trochlear groove (arrows) compatible with dysplasia and bilateral lateral patellar subluxation and lateral tilt. The two features are associated with patellar maltracking

Fig. 9

Knee CT images in the early post-operative period in a 19-year-old male with history of patellar maltracking. a Axial CT image demonstrating MPFL reconstruction (arrow heads). b Axial CT image showing tibial tuberosity transfer surgery with screw placement (arrow)