Jordy van Sambeeck

Chapter 5 78 Discussion In this study, we showed that a VAS pain score increased with higher age after a lateral facet elevating trochlear osteotomy. Although the increase is relatively small for every year of age (0.95), it is a clinically relevant increase for every ten years of age (9.5). This study was not designed to investigate the underlying cause of increased pain, however, the following hypothesis could well be true. Older patients have a longer history of patellofemoral instability (peak incidence of first dislocation is in adolescence 11 ). They might have a history of patellar dislocations with a longer period of maltracking of the patella. As a consequence, increased cartilage damage and degenerative changes of the patellofemoral joint would be present at time of surgery. This might have an influence on the level of correction that is possible, the congruency of the new trochlea, the presence of microtears during surgery and the load bearing capacity of the cartilage. These factors could also be influenced by the pliability of the articular cartilage, which decreases with increasing age due to molecular changes. Despite the fact that increasing age is correlated with a higher VAS pain score at rest in our study, we don’t assume that this is caused by early PF OA. Although the present study didn’t evaluate the radiological presence of PF OA , a study by Tigchelaar et al. 32 showed no clear correlation between VAS pain and the grade of PF OA after trochlear osteotomy. They analyzed data from patients with 12 years of follow-up. Radiological PF OA after surgery was generally limited to lower grades on the Iwano scale 32 . In our study, two older patients (age at surgery 27 and 46 years) had radiologically confirmed PF OA during follow-up; this was radiologically examined because of the presence of persisting pain. Both patients scored high on VAS pain at rest and therefore contributed to an overall increased average in our study. Early symptomatic PF AO is not expected to be the main reason for an increase in mean VAS score at higher age. We hypothesize that decreased adaptation of the cartilage to the new situation results in increased subchondral pressure and higher pain scores at rest. Age at time of surgery did not have a significant effect on other outcome measurements. However, it should be noticed that a relatively high rate of redislocation after trochlear osteotomy (10%) was found. Age of these patients ranged between 12-22 years with an average of 16 years and is lower than the average age of patients in our cohort (19.8 years). Furthermore, results of the multivariate linear regression analysis revealed significantly higher VAS instability score in females vs. males. With the exception of gender, no other risk factors were significantly correlated with VAS instability. In our cohort, an additional MPFL-reconstruction was only performed in 5.6% of patients. Recently published literature and new surgical techniques for MPFL reconstruction have narrowed the indication for an isolated trochlear osteotomy without MPFL-reconstruction. An additional MPFL-reconstruction probably decreases the rate of redislocation. With