Summary
Objectives: To calculate the difference between the desired tibial tuberosity advancement (TTA)
along the tibial plateau axis and the advancement truly achieved in that direction
when cage size has been determined using the method of Montavon and colleagues. To
measure the effect of this difference on the final patellar tendon-tibial plateau
angle (PTA) in relation to the ideal 90°.
Methods: Trigonometry was used to calculate the theoretical actual advancement of the tibial
tuberosity in a direction parallel to the tibial plateau that would be achieved by
the placement of a cage at the level of the tibial tuberosity in the osteotomy plane
of the tibial crest. The same principle was used to calculate the size of the cage
that would have been required to achieve the desired advancement. The effect of the
difference between the desired advancement and the actual advancement achieved on
the final PTA was calculated.
Results: For a given desired advancement, the greater the tibial plateau angle (TPA), the
greater the difference between the desired advancement and the actual advancement
achieved. The maximum discrepancy calculated was 5.8 mm for a 12 mm advancement in
a case of extreme TPA (59°). When the TPA was less than 31°, the PTA was in the range
of 90° to 95°.
Clinical significance: A discrepancy does exist between the desired tibial tuberosity advancement and the
actual advancement in a direction parallel to the TPA, when the tibial tuberosity
is not translated proximally. Although this has an influence on the final PTA, further
studies are warranted to evaluate whether this is clinically significant.
Keywords
Maquet - TTA - tibial tuberosity advancement - trigonometry
