Introduction: A tibial tubercle osteotomy can be used in the exposure of severe articular deformity and the tight knee in total knee arthroplasty, especially revision surgery. This osteotomy has been popularised by Dr. L. Whiteside [1] who described transosseous wiring to secure the osteotomy following joint reconstruction. Other fixation techniques including the use of cables and screws may provide options for this technique. The current study exmained 3 different fixation methods for tibial tubercle osteotomy using an in-vitro sheep model.

Materials and Methods: Tibial tubercle osteotomies (5 cm in length) were performed in ten adult sheep tibias. The osteotomies were fixed sequentially using circumferential Dall-Miles cables (Howmedica, Ritherford, NJ) (Fig. 1), transosseous wires and lastly 2 AO screws. Testing of each fixation configuration was performed using an MTS 858 Mini Bionix servo hydraulic testing machine (MTS Systems Corporation, USA). The loading regime used a cyclic 200 N load applied along the line of the patellar tendon with micromotion measured at the osteotomy and adjacent bone using optical sensors (MEL, Bahnhofstr, Germany). Data was analyzed using ANOVA. Micromotion at the end of the osteotomy fragment was recorded for 150 cycles for each tibia following reconstruction with cables, wires, and screws in succession.

Results: Cable fixation provided the most stable construct followed by screws and wires respectively. Wire fixation had the greatest variation in micromotion (370 microns). The ovine tibia model provides a reproducible bone bed to evaluate different fixation strategies for tibial tubercle osteotomy. Clinically, differences may even be marked considering anatomic and bone quality issues as well as magnitude of the load that have not been addressed in this in-vitro study.

Discussion: Fixation of the osteotmoy is an important surgical technique. Wolff et al. found that major complications related to the surgical technique occurred in 23% of the knees performed in 26 cases [2]. Reis et al. [3] observed fixation with 3 or 4 titanium screws was sufficient after a follow-up period of 18 months. Twenty-nine of the osteotomies healed primarily. One patient developed postoperative displacement of the tibial tubercle requiring additional screw and suture fixation. This study has shown that micromotion of a tibial tubercle osteotomy fixation in sheep is dependent upon fixation technique. Cables provided the most stable fixation compared to screws and wires in an ovine tibial model.