Mylène Jansen

Clinical evidence and molecular mechanisms of KJD 197 10 Complications other than pin tract skin infections occurred only sporadically (all less than 5% of the 172 patients included in the published studies of table 1). The two most occurring ones were osteomyelitis (6 patients, 3%), treated with pin tract wound cleaning and a combination of oral and intravenous antibiotics, as a result of too late or inappropriately treated skin infections, and deep venous thrombosis (4 patients, 2%), treated with additional anticoagulation (in addition to the preventive anticoagulation which is considered important and standard for distraction treatment). This percentage of more serious complications is similar to alternative treatments like HTO and TKA. 25 Possible mechanisms of joint repair Despite the fact that joint distraction is studied for over 20 years, the mechanisms involved in the observed benefit are largely speculative. Only recently literature touching this specific subject has emerged. 43–45 To date, several concomitant occurring underlying mechanisms have been postulated to be involved in the clinical and structural benefit observed after joint distraction (see also Figure 2). Firstly, joint distraction results in temporary relief of mechanical stress (strain and shear) on the cartilage, which prevents further wear and tear of the cartilage. Secondly, maintained nutrition of the cartilage during mechanical unloading is considered of importance. Joint fluid pressure oscillation remains present as a result of loading and unloading during distraction due to the resilience in/of the external device. A third mechanism is transient periarticular osteopenia developed during the distraction. Mechanical stresses on the bone within the distraction frame are taken over by the frame. This results in permanent diminished subchondral sclerosis and with that diminished mechanical impact on the cartilage. Significant changes in bone turnover during and after distraction may provide growth factors. Bone is a storage of growth factors that have been demonstrated to facilitate cartilage repair. Moreover, stem cells from the different joint tissues, including the synovial tissue and fluid, are facilitated by the distraction environment, mechanically and biochemically, to restore cartilage tissue. Lastly, the altered molecular milieu during mechanical unloading of the normally mechanically loaded tissue results in a reset of the balance between anabolism and catabolism in the joint. Mechanical unloading and maintenance of synovial fluid pressure oscillation OA is influenced in its early and late phases by joint mechanics (loading) and thereby its effect on joint metabolism.46 The mechanical properties of the joint at the macro andmicro environment are severely disturbed in OA. Especially in the more advanced disease stage, overloading of the cartilage and bone are a continuous stimulus for progressive joint degeneration. As such it is logical that creating a favorable mechanical environment is a prerequisite to enable repair activity. Unloading the joint might be a first rational to provide such a condition. There is a clear