Correlation Between Changes in Tibial Tuberosity-Trochlear Groove Distance and Patellar Position During Active Knee Extension on Dynamic Kinematic Computed Tomographic Imaging.
OBJECTIVE
The purpose of this study was to evaluate changes in tibial tuberosity-trochlear groove (TTTG) distance with knee flexion in patients with patellar instability and correlate it with patellar position.


METHODS
Patients with symptomatic patellar instability underwent dynamic kinematic computed tomography (CT) during a cycle of knee extension from flexion. Knee flexion angles and corresponding TTTG distances, bisect offset, and patellar tilt were measured. Of the 51 knees, 37 had data available for interpolation between 5° and 30°. Results were interpolated to standardized intervals between 5° and 30° of knee flexion. Repeated-measures analysis (to identify differences between TTTG measurements at various knee flexion angles) and linear regression models (to assess for correlations between TTTG distance and bisect offset and between TTTG distance and patellar tilt) were used.


RESULTS
Fifty-one symptomatic knees in 38 patients were available for analysis. Bisect offset and patellar tilt correlated significantly (P < .001) with TTTG distance over all flexion angles. Interpolated results for comparison resulted in 37 knees in which the mean TTTG distance of 17.2 ± 5.8 mm at 5° decreased to 15.5 ± 5.7, 13.0 ± 5.5, and 11.5 ± 4.9 mm at 10°, 20°, and 30° of knee flexion, respectively. Mean TTTG at 5° was 1.5 times greater than that at 30° (P < .001). At 5°, 70.3% (26 of 37) of knees had a TTTG distance of more than 15 mm; at 30°, only 24.3% (9 of 37) exceeded this threshold.


CONCLUSIONS
Knee flexion angle during imaging is a critical factor when measuring TTTG distance to evaluate patellofemoral instability. We found that the mean TTTG distance varied by 5.7 mm between 5° and 30° of flexion in patients with symptomatic instability, although this relationship was not completely linear. Bisect offset and patellar tilt measurements mirrored this pattern, suggesting that TTTG distance influences patellar tracking in these patients.


METHODS
Level IV, prognostic case series.
Regeneration Orthopedics, St. Louis, Missouri, U.S.A.
Miho J
MJ
Tanaka
Department of Orthopaedic Surgery, Akron General Medical Center, Akron, Ohio, U.S.A.
John J
JJ
Elias
Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, Maryland, U.S.A.
Ariel A
AA
Williams
Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, Maryland, U.S.A.
John A
JA
Carrino
Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, Maryland, U.S.A.. Electronic address: editorialservices@jhmi.edu.
Andrew J
AJ
Cosgarea
D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging; D016014:Linear Models; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging*; D016059:Range of Motion, Articular; D012015:Reference Standards; D012189:Retrospective Studies; D013977:Tibia / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D055815:Young Adult