Mylène Jansen

Clinical evidence and molecular mechanisms of KJD 199 10 It should be noted that with this variation in resilience in the devices, joint distraction creates a condition different from complete immobilization, like obtained by casting. As mentioned, during distraction, loading of the affected joint is encouraged. This will not only result in partial mechanical contact between the cartilage surfaces, but also in joint fluid pressure oscillations because of the stiffness of the joint capsule when the two bone ends are nearing each other during loading. The combination of loading and resilience of the distraction frame and the stiffness of the joint capsule provides fluctuation of the intra-articular fluid pressure as naturally occurring during normal loading and unloading of a joint. 7 Not only is this intermittent fluid pressure oscillation considered essential in nourishment of the cartilage, it also plays a role as mechanical stimulus of the chondrocytes in the anisotropic cartilage extracellular matrix. In vitro, it has been demonstrated that these fluid pressure changes are beneficial specifically to OA cartilage. 70 Normal healthy cartilage seems less sensitive. Moreover, these fluid pressure changes are able to diminish the inflammatory activity of OA synovial cells. 71 Production of catabolic cytokines such as interleukin (IL)-1 and tumor necrosis factor (TNF)-a were decreased. Other joint-saving techniques with partial unloading such as tibial osteotomy or unicompartmental load absorbing implants (Atlas system) show clinical 72 and even structural beneficial changes. 73–75 Both techniques significantly reduce (medial) compartment contact pressure and peak contact pressure 76,77 and maintain joint fluid pressure oscillations as well. Clearly, more research is needed which exact (hydro)mechanical condition during (and after) distraction treatment is the most favorable. Periarticular bone changes The significant bone changes during distraction, a process starting with inducing osteopenia followed post-treatment by normalization of bone characteristics, are considered another important promoter of cartilage repair. Moreover, bone changes may be a key factor relating to the observed pain relief. The mechanical stresses during distraction are taken over by the distraction frame connected to the bone pins and fixing both bone ends. This will result in osteopenia during distraction even during loading and unloading the joint during distraction because the bone within the outer bone pins will remain mechanically (partially) unloaded. 78 A study where advanced post-traumatic OA patients were treated with ankle distraction indicated an overall decrease of subchondral bone density, which persisted over at least two years. 32,79 Pre- treatment, the subchondral bone demonstrated regions of cystic (relatively low density) and sclerotic (relatively high density) areas. While overall density decreased, density in cystic lesions increased, representing an overall normalization of bone density. Similar results were reported for KJD, where a decrease and normalization in bone density was reported. 21 The mechanism for the disappearance of the cystic areas might relate to the changes in mechanical and biochemical environment induced by distraction. Cysts represent regions of bone necrosis 80 , and have the potential to not only increase but also diminish over time. 81 Decreased surrounding sclerosis and subsequently less stiff bone, may allow mechanical stimuli to reach the cystic area and