Reliability of the TT-TG Index Versus TT-TG Distance on MRI: Morphometric Analyses in Asian Children and Adolescents

Sin Hyung Park; Wonchul Choi; Siyeong Yoon; Jeongbae Rhie; Wooyeol Ahn; Jongbeom Oh; Dong Hun Han; Soonchul Lee

doi:10.1177/23259671221145228

Reliability of the TT-TG Index Versus TT-TG Distance on MRI: Morphometric Analyses in Asian Children and Adolescents

Orthop J Sports Med. 2023 Jun 22;11(6):23259671221145228. doi: 10.1177/23259671221145228. eCollection 2023 Jun.

Authors

Sin Hyung Park¹, Wonchul Choi², Siyeong Yoon², Jeongbae Rhie³, Wooyeol Ahn², Jongbeom Oh², Dong Hun Han², Soonchul Lee²

Affiliations

¹ Department of Orthopaedic Surgery, Bucheon Hospital, Soonchunhyang University School of Medicine, Bucheon-si, Gyeonggi-do, Republic of Korea.
² Department of Orthopaedic Surgery, CHA Bundang Medical Center, CHA University School of Medicine, Seongnam-si, Gyeonggi-do, Republic of Korea.
³ Department of Occupational and Environmental Medicine, Dankook University College of Medicine, Cheonan-si, Chungcheongnam-do, Republic of Korea.

Abstract

Background: The tibial tuberosity-trochlear groove (TT-TG) distance measured on magnetic resonance imaging (MRI) is commonly used to decide the treatment for patellar instability; however, the patient's joint size is not considered in this measurement. The TT-TG index has been proposed as a knee size-adjusted measurement for tibial tuberosity location.

Purpose: To evaluate the reliability of the TT-TG index compared with the TT-TG distance by analyzing variations in measurement according to age and sex in a pediatric Asian population.

Study design: Cohort study (diagnosis); Level of evidence, 3.

Methods: A total of 698 knee MRI scans were collected in patients between 4 and 18 years of age who did not have any patellofemoral problems. Patient age, sex, height, and weight were recorded. The scans were divided into 5 groups according to patient age (4-6 years, 46 scans; 7-9 years, 56 scans; 10-12 years, 122 scans; 13-15 years, 185 scans; and 16-18 years, 289 scans); MRI scans were also divided by sex (497 male, 201 female). Three independent observers measured the TT-TG distance and TT-TG index on each scan, and age- and sex-based differences in the measurements were evaluated after adjusting for body mass index (BMI). The reliability of the measurements was calculated with the intraclass correlation coefficient (ICC).

Results: Good to excellent inter- and intraobserver agreement was found for TT-TG distance (ICC, 0.74) and TT-TG index (ICC, 0.88). The TT-TG distance was significantly different among the groups and increased with age, while variations in the TT-TG index were minimal between age groups and sexes. This finding was also consistent after compensating for the effect of BMI.

Conclusion: The TT-TG distance changed with age, while the TT-TG index was relatively constant. Therefore, the TT-TG index may be more reliable and effective for diagnosing and planning treatment, especially in children and adolescents.

Keywords: distance; index; morphometry; tibial tuberosity; trochlear groove.