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

Objectives: 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.

Methods: 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.

Results: 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.

Clinical Significance: 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.