Knee Surgery, Sports Traumatology, Arthroscopy
Tibial tubercle–trochlear groove distance and angle are higher
in children with patellar instability
Ilhan A. Bayhan
· Akay Kirat
· Yakup Alpay
· Baris Ozkul
· Deniz Kargin
Received: 29 December 2017 / Accepted: 30 May 2018
© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2018
Purpose The purpose of this study was to assess the variations in tibial tubercle–trochlear groove distance and angle as a
function of age and gender in a population of children without patellar instability (PI) compared with those with PI.
Methods A retrospective review of 869 children’s knee MRIs, ages 5 to 15 years, were evaluated using a control group (792
children) without evidence of PI and a group with PI (77 children). Tibial tubercle–trochlear groove distance (TT–TGd) and
angle (TT–TGa) were measured twice by two readers to assess intra- and inter-observer reliability and compared between
PI and control groups. In both groups, functions of age and gender on TT–TGd and TT–TGa values were evaluated.
Results Both TT–TGd and TT–TGa measurements showed excellent intra- and inter-observer reliability. The mean TT–
TGd for the PI group was 17.2 mm (SD 6.6) and signiﬁcantly higher than the mean TT–TGd for the control group (10.4
SD 3.8 mm, P = 0.001). The mean TT–TGa for the PI was 20.8° (SD 8.3°), which was also signiﬁcantly higher than the
mean TT–TGa for the control group (12.5° SD 4.6°, P < 0.001). Control group revealed a positive correlation between age
and TT–TGd measurements (r = 0.243, P < 0.001). The mean TT–TGa for girls (13.3° SD 4.7°) was higher than the mean
TT–TGa for boys (11.9° SD 4.4°) in the control group (P < 0.001).
Conclusion TT–TGa and TT–TGd are reliable and can be used for the evaluation of the extansor mechanism alignment in
children with and without PI. However, it must be considered that TT–TGd is increasing in growing patients. Soft-tissue
procedures may be prone to failure, since bony procedures for patellar alignment cannot be done until skeletal maturity.
Level of evidence III.
Keywords Patellar dislocation · Patellar instability · Risk factor · Tibial–trochlear groove · TT–TG · Patellofemoral · MRI
Patellar dislocation is one of the common disorders in chil-
dren and adolescents with an estimated incidence of 29–43
per 100,000 [7, 12, 16]. Risk factors related to patellar
instability can include bone structural changes (trochlear
dysplasia, patella alta, lateralization of tibial tubercle, and
rotational abnormalities around the knee) and soft tissue fac-
tors (weak medial patellofemoral ligament, atrophic vastus
medialis obliquus muscle, and conditions associated with
generalized ligamentous laxity) [4, 18].
One of the risk factors, lateralization of the tibial tuber-
cle, has been considered as an important element in the
assessment and treatment of the patellar instability (PI).
The lateralization distance, which was defined as tibial
tubercle–trochlear groove distance (TT–TGd), was initially
described by Goutallier on axial radiograph of the knees .
Later, Dejour et al. used axial computed tomographic (CT)
* Ilhan A. Bayhan
Department of Orthopedics, Health Science University
Baltalimani Bone Diseases Education and Research
Hospital, Rumeli Hisari Sok. No 62 34470, Baltalimani
Sariyer, Istanbul, Turkey