PubMed · 11083621
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E E Johnson. Tibial bracing.. https://doi.org/10.1097/00005131-200009000-00016
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Knee malpositions, for example valgus or varus deformations or flexion contractures, were often cited in the historical literature. In earlier times, clinical pictures such as rickets were often the reason for this kind of deformity. A causal therapy did not exist until the twentieth century. In most cases of rickets, genu valgum was reported as the typical knee deformation. The differential diagnosis for genu valgum caused by rickets was genu valgum traumaticum, paralyticum, and inflammatorium. The most important reports on the pathogenesis of valgus deformation can be found in publications by Hueter and von Mikulicz. The causal therapy of rickets was introduced at the beginning of the twentieth century.Vitamin therapy and UV phototherapy were developed during this period. Using these therapies, rickets decreased dramatically. Kurt Huldschinsky, a pediatrician from Berlin,was one of the main inventors of UV phototherapy in Germany. At the end of the nineteenth century, the operative correction of knee deformities increased while conservative treatment continued to be applied. Plaster casts,orthoses, and osteoclast therapy were the main noninvasive therapeutic possibilities. Positive aspects of the conservative techniques were mostly the good results and easy, timesaving technique compared with the operative treatment. The operative therapy increased with the knowledge of antisepsis and asepsis as well as advances in anesthetic procedures. Operative treatment modalities, for example tibial and femoral osteotomies, were more precise, but connected with multiple complications and greater time expenditure. Sufficient vitamin prophylaxis rendered knee deformations caused by rickets a rarity.
Total knee replacement requires exact implantation in order to avoid long-term failure. Longitudinal in vivo studies of malaligned prostheses are problematic for ethical reasons. To assess the critical angle of tibial (varus/valgus) malalignment of knee prostheses in vitro, a simulator investigation was performed. Mobile-bearing prostheses were implanted in a simulator with 1-3 degrees valgus and varus malalignment as well as in a neutral position. More extreme malalignment caused unacceptable forces in the simulator. After each 500,000 cycles (ca. 0.5 years of walking) the replicas of the polyethylene inlay were examined and the extent of the tribocontact areas was measured until 1,500,000 total cycles. Finally the original polyethylene was examined with a scanning electron microscope. The polyethylene showed only abrasive wear without any fatigue effect. Tribocontact areas of 900-1500 mm(2) were observed under malalignment of mobile-bearing prostheses according to the manufacturer's specifications. With 1-3 degrees of malalignment, tribocontact areas were located at atypical polyethylene zones, but still showed abrasive wear only. Increasing malalignment due to a lift off of the femoral part of the prostheses with a strong torsional strength of the polyethylene made more extreme simulation impossible. Malalignment of 3 degrees could be suggested as maximum in vivo tolerability; perfect alignment with ideal implantation should be the goal. Soft tissue was given less consideration in this simulator study.
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