Normative Values of Tibial Tubercle–Trochlear Groove Distance and Tibial Tubercle–Posterior Cruciate Ligament Distance in Children

Park, Se Jin MD
Won, Seung Hyun PhD
Park, Moon Seok MD
Sung, Ki Hyuk MD

^*Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Gyeonggi, Republic of Korea
^†Division of Statistics, Medical Research Collaborating Center, Seoul National University Bundang Hospital, Gyeonggi, Republic of Korea
^‡Department of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Gyeonggi, Republic of Korea
Investigation performed at Seoul National University Bundang Hospital, Gyeonggi, Republic of Korea

Ki Hyuk Sung, MD, Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 82 Gumi-ro 173 Beon-gil, Bundang-Gu, Sungnam, Gyeonggi 13620, Republic of Korea (email: [email protected]).

Received September 20, 2022

Accepted February 13, 2023

American Journal of Sports Medicine 51(7):p 1785-1791, June 2023. | DOI: 10.1177/03635465231165521

Background:

Patellar instability is a common knee pathology in skeletally immature patients. In skeletally mature populations, a tibial tubercle–trochlear groove (TT-TG) distance of ≥20 mm is generally considered a pathological value. However, as pediatric patients grow and as the TT-TG distance varies with age, applying the same cutoff value as adult patients to them is unreasonable.

Purpose/Hypothesis:

This study aimed to analyze the normative values of the TT-TG and tibial tubercle–posterior cruciate ligament (TT-PCL) distances in children with no patellofemoral instability and to propose the cutoff value of the TT-TG and TT-PCL distances predictive of increased risk of patellofemoral instability in pediatric patients. We hypothesized that the TT-TG and TT-PCL distances increase with age in children and adolescents.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Magnetic resonance imaging scans of the knee were collected from the patellar instability group and the control group. The TT-TG and TT-PCL distances were measured. The normalized values of the TT-TG and TT-PCL distances were calculated by dividing them by the femoral width. Segmented analysis with 1 breakpoint was performed for both the TT-TG and the TT-PCL distances. The optimal cutoff values of the TT-TG and TT-PCL distances were calculated by maximizing the sum of the sensitivity and specificity.

Results:

A total of 87 patients had patellar instability, and 509 patients did not. The median values of TT-TG and TT-PCL distances in the control group (8.18 mm and 19.48 mm, respectively) were significantly smaller than those in the instability group (16.10 mm and 24.41 mm, respectively). For those aged <15 years, the TT-TG distance significantly increased by 0.39 mm as the age increased by 1 year. The TT-PCL distance increased by 1.14 mm/year until the age of 11 years. In our cohort, the cutoff value of the TT-TG distance of 14.90 mm yielded 66% sensitivity and 81.9% specificity for predicting an increased risk of patellar instability. The cutoff value of the TT-PCL distance of 23.68 mm yielded 63.9% sensitivity and 65.3% specificity for predicting an increased risk of patellar instability.

Conclusion:

In our cohort of 596 participants, we have documented the normative values of the TT-TG and TT-PCL distances in children aged <20 years. During the surgery for patellar instability in pediatric patients, orthopaedic surgeons should consider the normative values of the TT-TG and TT-PCL distances according to age to determine which patients need distal realignment surgery.