Radiographic and Anatomic Evaluation of Tibial Tubercle to Trochlear Groove Distance

BackgroundA lateralized tibial tubercle is an important anatomic predictor of patellar instability and can be used as an indication for a distal realignment procedure. Currently, tibial tubercle to trochlear groove (TT-TG) distance is measured on computed tomography (CT); however, radiographs could be a safer and more efficient modality. The aim of this study is to evaluate and compare TT-TG measurements obtained using CT, anatomical dissections, and a novel radiographic technique. Furthermore, we evaluated the effects of knee flexion and tibial rotation on these measurements. MethodsTT-TG distances were measured on 11 fresh cadaver specimens with CT and compared with anatomic measurements obtained from dissection in full knee extension and 90-degree flexion. Both imaging- and dissection-derived measurements were obtained in neutral, external, and internal tibial rotation. The TT-TG distance was also measured on a modified sunrise X-ray view (knee at 90 degrees). ResultsThe TT-TG distance obtained on CT was 13.001.05mm and was comparable to measurements derived from anatomic dissections in extension (14.881.10 mm) and 90 degrees (12.40 +/- 1.93 mm) (p0.05). The X-ray measurements of TT-TG distance (5.62 +/- 1.16 mm) were significantly different than those measured on CT (p0.05). TT-TG distances in neutral tibial position measured on CT and dissection were significantly different than distances measured in full external (19.79 +/- 1.33 and 20.92 +/- 1.15mm, respectively) and internal tibia rotation (6.45 +/- 1.00 and 10.33 +/- 1.19mm, respectively) (p0.05). ConclusionsTT-TG distance measured on CT is comparable to measurements from dissections in both full extension and 90-degree flexion. Tibial rotation has a significant effect on TT-TG measurements. Radiographic measurements did not correlate with CT and anatomic measurements. Clinical RelevanceCT-derived TT-TG measurements are accurate throughout knee range of motion; however, it is important to maintain neutral lower leg rotation to not generate a false-positive or false-negative measurement. Radiographic measurement of TT-TG ration is not currently recommended.