Biomechanical testing of a β-tricalcium phosphate wedge for advancement of the tibial tuberosity

to evaluate in vitro the strength of different compositions of beta-tricalcium phosphate (β-TCP) wedges in comparison with titanium foam and cages. To study the response to cyclic loading of the strongest β-TCP wedge, titanium foam and titanium cage.

Compression test: Twenty-five tibiae were prepared for tibial tuberosity advancement using the modified Maquet technique. Five groups were defined depending on the material used to maintain the tibial tuberosity: Group 1=titanium cage; Group 2=wedges of porous titanium foam with 50% porosity (OrthoFoam®); Group 3=blocks of biphasic synthetic bone (60% hydroxyapatite [HAP] and 40% β-TCP, porosity 80%); Group 4=blocks of biphasic synthetic bone (60% HAP and 40% β-TCP, porosity 70%) and Group 5=blocks of biphasic synthetic bone (65% HAP and 35% β-TCP, porosity 60%). Loads to failure were calculated for each implant. Cyclic study: Five additional tibiaes of group 1, 2 and 5 were fatigue tested from 100 to 500 N at a rate of 4 Hz for 200,000 cycles or until failure.

Compression test: For the five groups, the mean load at failure was 1895 N, 1917 N, 178 N, 562 N and 1370 N respectively. Cyclical study: All samples in the three groups tested withstood 200,000 cycles without failure.

The ideal implant to maintain tibial tuberosity advancement after the modified Maquet technique would be absorbable and allow osteoconduction and osteoinduction. As such, β-TCP wedges have many advantages and our study shows that they can withstand loads in the patellar tendon up to 500 N over 200,000 cycles in vitro and deserve more investigation.