Three-Dimensional Tibial Tubercle Transfer Planning.

Background: Historically, decisions regarding tibial tubercle transfer have been made using 2-dimensional (2-D) criteria. This work is based on the belief that tibial tubercle transfer planning, aided by 3-D imaging, will be more accurate. Indications: Understanding how the patella enters the trochlea and the path it follows to a deepening trochlea upon knee flexion, using objective metrics, will help in planning tibial tubercle transfer surgery. Technique Description: Computerized tomography was used to create 3-D replications of patellar instability in patient knees at 0° and 20° of flexion. Studying these 3-D studies has yielded new metrics-the entry point-trochlear groove (EP-TG) angle and the entry point-transition point (EP-TP) angle-to objectify patellar tracking paths in patients with patellar instability. Tibial tubercle-trochlea groove (TT-TG) distance, Caton-Deschamps ratio (C-D ratio), and heat map contours were also determined using 3-D to maximize accuracy. Results: Understanding EP-TG and EP-TP angles, TT-TG in 3-D, and heat map contours provides further insight when combined with traditional TT-TG and C-D ratios in planning tibial tubercle transfer for the surgical treatment of patellar instability. This has led to a Discussion/Conclusion: A 3-D understanding of trochlea shape, orientation, and contours improves knowledge of the femoral trochlea, particularly proximally, where the patella is most vulnerable to dislocation in the majority of patients with patellar instability, adding further objectivity to surgical planning regarding tibial tubercle transfer, visualizing the 3-D path as a skier or bobsledder might view a downhill course, and can enable surgical adjustment of the patellar position through tibial tubercle transfer to maximize safe and stable patella tracking.