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Three-Dimensional Tibial Tubercle Transfer Planning
John Fulkerson1, Nancy Park1, Armita R Manafzadeh1
1Yale University Departments of Orthopedic Surgery and Mechanical Engineering, New Haven, Connecticut, USA.
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 winter sports approach, in which we plan tibial tubercle transfer to guide the patella safely along and past contours in its tracking path that might lead to displacement of the patella (also known as the skier or bobsled effect) out of its groove. Preoperative planning enables the precise determination of how to relocate the tibial tubercle optimally, and even the possibility of creating 3-D custom-printed surgical guides to achieve the desired osteotomy with precision.
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.
