The Effects of Tibial Tuberosity-Trochlear Groove Distance on Lateral Translation of the Patella: A Cadaveric...

The tibial tuberosity-trochlear groove (TT-TG) distance is a key measurement in guiding surgical management of patellofemoral instability. A TT-TG of 20 mm is often used as the threshold for supplementing soft tissue procedures with tuberosity medialization, although this remains an active area of investigation.

To identify the relationship between TT-TG distance and the force required to cause lateral translation of the patella in a cadaveric model at 30º of flexion.

Descriptive laboratory study.

Eight fresh-frozen human cadaveric knee specimens were acquired, and computed tomography scans were obtained to measure anatomic features of patellar instability. A flat tibial tuberosity osteotomy was performed. Specimens were mounted on an Instron ElectroPuls E10000 in 30° of flexion. The force (N) required to produce 10 mm of lateral patellar translation over a 1-second interval was measured under the following tibial tuberosity translation conditions: (1) native; (2) predetermined translation (+5, 10, and 15 mm from native); and (3) predetermined TT-TG values (10 to 25 mm by 5 mm increments).

For TT-TG values ≤20 mm, there was a significant negative linear relationship between the TT-TG distance and the force required for lateral patellar translation (-1.63 N/mm [95% CI, -1.637 to -1.629]; P < .001); 1 mm of TT-TG increase resulted in a 1.63 N decrease in the required force. With TT-TG testing conditions >20 mm, this linear relationship was no longer present (slope, -0.5 N/mm [95% CI, -1.36 to 0.36]; P = 0.25).

The force required to translate the patella laterally decreased linearly as the TT-TG distance increased up to 20 mm. However, for TT-TG distances >20 mm, our model showed variability in the relationship between force and TT-TG distance.

The linear relationship identified between translational force and anatomic alignment, with TT-TG distances <20 mm, suggests a predictable biomechanical response to tibial tuberosity translation. The disruption of this relationship >20 mm confirms a threshold at which patellofemoral biomechanics are altered.