Altough the preoperative planning of total knee arthroplasty in severe deformities of the lower extremities must take into consideration static factors, it must be evaluated one the basis of the complex dynamics of the knee as a whole. Indeed, when walking, articular reaction and axial compression forces move from the medial to the lateral compartment of the tibial plane, according to the change of the axis (varus-valgus angulation), the flex-estension and the walking pace. As knee joint stability is totally dependent on soft-tissues, if there is lateral laxity or insufficient muscle force, lateral opening may increase. Thus, a ''high'' adduction moment is created when walking, which is even higher in varus alignment of the knee. The relationship between the post-traumatic or degenerative malalignment and the onset of deformity after articular disease or prostheses failure, is also reported. Ten clinical cases are presented showing some principles on which the authors based their choice of arthroplasty and how their experience over time influenced these choices. The capsular-ligament structure is modified in severe deformities. The aim of arthroplasty is that of creating a new structural balance to obtain stability together with the maximum congruence and range of movement. The articular bone sections are performed according to the mechanical axis. Treatment of the most severe cases of post-traumatic deformity require a correction time. The reason why there has been a tendency to use a total knee prosthesis with mobile bearing, rather than a hinged prosthesis over the last few years, is also analysed. In order to preserve the implant from high lateral opening after total knee arthroplasty, during the adduction phase when walking, it is important to avoid varus angulation thus keeping a good capsular-ligament balance. On the based of the aforementioned criteria, the aim of be authors is to avoid the use of a prosthesis with high intrinsic stability whenever possible, also for severe deformities.
Le protesi di ginocchio nelle gravi deformità dell'arto inferiore.
CROVA, Maurizio
2003-01-01
Abstract
Altough the preoperative planning of total knee arthroplasty in severe deformities of the lower extremities must take into consideration static factors, it must be evaluated one the basis of the complex dynamics of the knee as a whole. Indeed, when walking, articular reaction and axial compression forces move from the medial to the lateral compartment of the tibial plane, according to the change of the axis (varus-valgus angulation), the flex-estension and the walking pace. As knee joint stability is totally dependent on soft-tissues, if there is lateral laxity or insufficient muscle force, lateral opening may increase. Thus, a ''high'' adduction moment is created when walking, which is even higher in varus alignment of the knee. The relationship between the post-traumatic or degenerative malalignment and the onset of deformity after articular disease or prostheses failure, is also reported. Ten clinical cases are presented showing some principles on which the authors based their choice of arthroplasty and how their experience over time influenced these choices. The capsular-ligament structure is modified in severe deformities. The aim of arthroplasty is that of creating a new structural balance to obtain stability together with the maximum congruence and range of movement. The articular bone sections are performed according to the mechanical axis. Treatment of the most severe cases of post-traumatic deformity require a correction time. The reason why there has been a tendency to use a total knee prosthesis with mobile bearing, rather than a hinged prosthesis over the last few years, is also analysed. In order to preserve the implant from high lateral opening after total knee arthroplasty, during the adduction phase when walking, it is important to avoid varus angulation thus keeping a good capsular-ligament balance. On the based of the aforementioned criteria, the aim of be authors is to avoid the use of a prosthesis with high intrinsic stability whenever possible, also for severe deformities.
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