Jordy van Sambeeck

Chapter 3 52 Discussion In this study, we describe the risk on complications in a large cohort of patients with a tibial tubercle osteotomy (TTO). The major findings of this study are the low incidence of non-union and tibial fracture after a self-centering technique of tibial tubercle transposition in a large cohort. The rate of nonunion in this cohort (0.6%, 3/529 procedures) is slightly lower than the incidence Payne et al. 4 reported in their systematic review (0.8%, 6/787 procedures). Two patients (0.4%) sustained a postoperative fracture, one of the tibia and one of the tibial tuberosity. In Payne’s review article the rate of fracture was 1.0%. The rate of non-union and fracture together is slightly lower than 1%, which confirms our hypothesis. We believe the non-union rate is related to the technique. When only the lateral periosteum is transected in order to make the osteotomy and the medial and distal periosteum remains intact, the blood flow decreases 25%. If a complete detachment of the tibial tubercle is performed and the medial, lateral and distal periosteum is transected, this leads to a complete arrest of the blood flow 7 and a higher chance of non-union. Fractures seem to be caused by mechanical issues. With this technique tibial fracture is rare. In other series fractures did occur, both acute and delayed 5, 8-12 . In a previous article 5 two fractures occurred (one acute and one late in a cohort of 29 patients) when a step cut osteotomy (such as employed in total knee arthroplasty) was used, this produced a stress riser in the tibia and weakens the cortex. This can also lead to late fractures, usually a few months after surgery caused by bone fatigue induced by altered tibial biomechanics. In this series only one tibia fracture occurred at the site of a removed large AO fragment screw hole from a previous osteotomy in a revision case. Large fragment screw might have a higher change of fracture after removal then small fragment screws because of cortical weakening. In retrospect perhaps a staged approach would have been wiser, with removal of the screws first and a TTO only after complete bone healing. Another patient had a split fracture of the tibial tubercle after fall from the stairs. Despite the trauma as contributing factor, lessons that can be learned from this case is to avoid placing screws close to each other and to avoid placing them in one line. Post-operative infections were seen in seven patients (1.3%) with 2 deep infections and 5 superficial wound infections. This is comparable to the rate of infection in the systematic review of Payne et al. 4 . In most of the reviewed articles by Payne 4 only patients with primary surgery were included, while in our cohort infection was more often seen in patients who had previous surgery. None of the patients who had an isolated TTOhad decreased ROM, but a decreased ROM was observed in nine patients with additional procedures, such as a MPFL and/or trochlea osteotomy implicating that the cause of the decreased ROM is intra articular fibrosis (arthrofibrosis) induced by intra- or periarticular surgery.