Osteochondral Fractures After Patellar Dislocation: Characteristics, Risk Factors and Treatment Outcomes

This dissertation examined trends in surgical techniques for patellar dislocation over the recent decades. The dissertation also focuses on the characteristics, risk factors and treatment outcomes of common concomitant injuries, osteochondral fractures, a potential area of development in the treatment of patellar dislocation.

Trends in patellar dislocation surgery were examined using a population-based register sample drawn from the Finnish National Hospital Discharge Register for the years 1997-2016 (Study I). Overall and annual incidences as well as the annual incidences of different types of procedure were calculated using population data from the Statistics Finland database. Trends in incidences were examined across the study period.

Osteochondral fractures were examined in a retrospective multicenter study sample drawn from the records of two large Finnish hospitals (Studies II, III and IV). The study sample consisted of all patients treated for patellar dislocation in the two hospitals during 2012–2018. In total, 135 patients with an intra-articular osteochondral fragment verified by magnetic resonance imaging (MRI) were included in the analysis. Demographic and clinical data were collected from electronic patient records and knee MRIs were examined to establish the characteristics of osteochondral fractures and the patellofemoral anatomy. Study II examined the characteristics of osteochondral fractures in different patient groups. Study III compared the anatomical measures of the patellofemoral joints of patients with an osteochondral fracture after patellar dislocation with those of propensity score-matched patients without osteochondral fracture. Study IV examined the outcomes of patellar dislocation patients with an osteochondral fracture treated according to the treatment protocol of the study hospitals. Patients were divided into groups according to the primary treatment approach and later surgery. Groups were compared on the characteristics of the injury, patellofemoral anatomy, and patient- reported outcomes.

The results showed that although the overall incidence of patellar dislocation surgery has remained stable over the past two decades, the surgical techniques used have shifted towards the reconstruction of damaged structures and modification of congenital anatomical risk factors for patellar dislocation (Study I).

Osteochondral fractures after patellar dislocation most commonly occurred in the medial facet of the patella (approximately two-thirds of cases) or in the lateral femoral condyle (one-third of cases (Study II). In women, patellar lesions were more common than in men. Osteochondral fractures sustained after primary patellar dislocation may be larger than those sustained after recurrent dislocation.

The prevalence of anatomical malformations related to patellar instability was very similar between the patellar dislocation patients with and those without an osteochondral fracture (Study III). However, the patterns of malformations differed between the groups, the non-osteochondral fracture patients showing more a severely high lying patella and deformed trochlea and the osteochondral fracture patients showing more severe patellar lateralization.

Lastly, although the primary treatment decision was definitive in the majority of the patellar dislocation patients with an osteochondral fracture, a relatively high proportion needed further surgery (Study IV). In the patients who underwent surgery in the primary phase, the osteochondral fragment was reimplanted in the majority of cases whereas in the patients who underwent surgery in the later phase, the fragment was removed. Additional stabilizing procedures were often performed in primary or later surgery. Patient-reported outcomes indicated generally acceptable results in all patient groups.

Our results show that the treatment of patellar dislocation, anatomical malformations, and concomitant injuries has evolved considerably during decent decades. However, patellofemoral problems in patients with osteochondral fractures after patellar dislocation include the risk of chronic patellar instability, cartilaginous injury, and degeneration of the patellofemoral articular cartilage in the long term. Hence, the treatment of these patients remains challenging. Further research is needed on individually tailored surgical procedures as well as standardized conservative treatment in patients with an osteochondral fracture after patellar dislocation. In addition, long-term outcomes pertaining to cartilage degeneration remain to be determined.