Muscular Atrophy, Axial Deformities & Risk of Prosthetic Instability
In hemophiliac patients, marked muscular atrophy (quadriceps) is often found, and this along with acute axial deviations of the knee (varus or valgus) causes joint instability. In patients who exhibit these characteristics, it must be taken into account that a standard primary TKR that is not constrained may not be sufficient to achieve prosthetic stability (Figures 2 & 3).
Total knee replacement in a young adult hemophilia patient with severe axial deformity of both knees: anteroposterior projection showing severe varus deformity of the left knee. (A) A rotating-hinge prosthesis was implanted to get good joint stability. Anteroposterior (B) and lateral (C) projections of the left knee after surgery.
The image shows the rotating-hinge prosthesis that was implanted at the patient of Figure 2 and also the other knee with signs of severe arthropathy (A). A year later, a standard unconstrained prosthesis was implanted in the other knee (the right knee, to the right of the image) (B). The result was satisfactory in both knees, achieving adequate bilateral joint stability.
The surgeon's 'arsenal' must therefore always include semiconstrained prostheses (CCK, constrained condylar knee) and even rotating hinged prostheses (rotating-hinge prosthesis). The objective will always be to achieve prosthetic stability, so that the pain is reduced and knee function is improved as much as is possible. The CCK prostheses are more constrained (more stable) than the standard primary prostheses, and the rotating-hinge prostheses are even more constrained than the other two. Biomechanically speaking, the standard primary prostheses mimick the three degrees of movement of the healthy knee (flexion–extension, varus–valgus, rotation) with an stable joint, whereas the more constrained prostheses loose a certain amount of normal movement of the knee in return of giving more joint stability.
Expert Rev Hematol. 2013;6(6):637-642. © 2013 Expert Reviews Ltd.