Discrepancy between true distance of tibial tuberosity advancement and cage size: An ex vivo study.

Abstract

To determine the discrepancy between true distance of tibial tuberosity advancement (tTTA) and the most commonly used cages. The null hypothesis was that tTTA would be within 1.5 mm difference of the cage size. Ex vivo study. Eight foam cortical shell specimens modeled from canine tibias. Modified tibial tuberosity advancement (TTA) was performed to allow repeated measurement of the tTTA. The Pearson correlation test was used to evaluate the relationships of tTTA and cage sizes (P < .05). The difference between tTTA and cage size was calculated to establish the degree of underadvancement during the TTA. Two hundred forty tTTA measurements were recorded. The tTTA was less than each corresponding cage size (P < .001). Four cage sizes resulted in a difference greater than 1.5 mm (P < .001-.04). The 6-mm cage resulted in median tTTA of 4.3 mm, which did not differ significantly from 4.5 mm (range, 3.2-6.65). The median underadvancement ranged from 1.7 to 2.5 mm for the tested cage sizes. The percentage underadvancement ranged from 21% to 28% for the tested cage sizes. The tTTA was less than the corresponding cage sizes by at least 1.5 mm in all except the 6-mm cage. Selection of a larger cage size during the TTA may be advantageous to compensate for underadvancement and to minimize the risk of residual cranial tibial translation.