Patellar Tendon–Trochlear Groove Angle Measurement

Abstract

Background:The tibial tubercle–trochlear groove (TT-TG) is used as the gold standard for patellofemoral malalignment.Purpose:To assess 3 patellar tendon–trochlear groove (PT-TG) angle measurement techniques and the PT-TG distance measurement (tendinous cartilaginous TT-TG) as predictors of patellar instability.Study Design:Cohort study (diagnosis); Level of evidence, 3.Methods:Three PT-TG angle measurements and the PT-TG distance were measured in 82 participants with patellar instability and 100 controls using magnetic resonance imaging (MRI). Measurement landmarks were the line tangent to the posterior femoral condyles, the deepest point of the trochlea, the transepicondylar line, and the patellar tendon center. All measurements were recorded once by 1 examiner, and the measurements were recorded twice by 2 examiners in a random group of 100 knees. Mean values and standard deviations (SDs) were obtained. Normality cutoff values were defined as 2 and 3 SDs above the mean in the control group. The sensitivity, specificity, and positive likelihood ratio (LR+) were calculated. Inter- and intrarater reliability were assessed based on the intraclass correlation coefficient (ICC).Results:The measurements from the patellar instability and control groups, respectively, for angle 1 (16.4° and 8.4°), angle 2 (31° and 15.6°), angle 3 (30.8° and 15.7°), PT-TG distance (14.5 and 8.4 mm), and patellar tilt (21.1° and 7.5°) were significantly different (P < .05). The angle measurements showed greater sensitivity, specificity, and LR+ than the PT-TG distance. Inter- and intrarater ICC values were >0.95 for all measurements.Conclusion:The PT-TG angle and the PT-TG distance are reliable and are different between the patellar instability and control groups. PT-TG angles are more closely associated with patellar instability than PT-TG distance.Clinical Relevance:PT-TG angle measurements show high reliability and association with patellar instability and can aid in the assessment of extensor mechanism malalignment. A more sensitive and specific evaluation of extensor mechanism malalignment can improve patient care by preventing both redislocation and abnormal tracking of overlooked malalignment and complications of unnecessary tibial tuberosity medialization.

Increased external tibial torsion is an infratuberositary deformity and is not correlated with a lateralized position of the tibial tuberosity

“…The distal patellofemoral alignment is influenced by the localization of the tibial tuberosity. The TT-TG and TT-PCL distances have become the most frequently used parameters to assess the position of the tibial tuberosity as indicators for distal patellofemoral realignment procedures (i.e., tibial tuberosity osteotomy) [ 25 , 41 ]. It has been hypothesized that a lateralized tibial tuberosity may be caused by excessive external tibial torsion [ 13 ].…”

Effects of knee flexion and extension on the tibial tuberosity–trochlear groove (TT–TG) distance in adolescents

“…TT–TG distance measured on computed tomography images is considered the gold standard for assessing the increased lateral quadriceps vector (Hinckel et al 2015a ). However, it has been proposed that TT–TG can also be reliably determined by magnetic resonance imaging (MRI) using either cartilage or bony landmarks (Schoettle et al 2006 ), but data indicates that normal values of TT-TG obtained with CT scan and MRI are not the same (Hinckel et al 2015b ; Schoettle et al 2006 ).…”

Anatomical Risk Factors for Anterior Cruciate Ligament Injury Are Not Important As Patellar Instability Risk Factors in Patients with Acute Knee Injury

“…21 Tendon-cartilaginous measurement of PTTG is performed on axial images. 24 A primary line was drawn tangent to cartilage of the posterior medial and lateral condyles and two perpendicular lines were drawn: one at the midpoint of the patellar tendon insertion in the tibial tuberosity, and the other at the deepest point of the trochlear cartilage. The distance between these two lines is the PTTG distance measure.…”