Prótesis unicompartimental de rodilla / Unicompartmental knee prosthesis

Resumen: En un paciente con artrosis unicompartimental de rodilla grave, donde se agotaron los tratamientos conservadores que tiene clínica dolorosa localizada en el lado afectado y con alteración del eje reductible, la prótesis unicompartimenal de rodilla (PUR) es la primera opción para nuestro grupo de trabajo. Dentro del estudio para confirmar el diagnóstico y planificar la cirugía destacan las radiografías de rodillas con carga, radiografía de Rosenberg y telerradiografías de extremidades inferiores. El objetivo de la cirugía es reemplazar la zona afectada, restituyendo la anatomía con un adecuado balance de partes blandas. Respecto al alineamiento el desafío es no sobrecargar el lado contrario ni tampoco el de la prótesis. Existen de platillo móvil y fijo y aunque los resultados clínicos y de supervivencia son semejantes, en los últimos años con la incorporación de la cirugía robótica, la balanza se ha inclinado para el uso de los platillos fijos. En pacientes con artrosis unicompartimental los resultados clínicos y funcionales son mejores con PUR y tiene menos complicaciones que cuando se usan prótesis totales (PTR). La supervivencia estudiada en registros es menor que para PTR, pero cuando se usa en centros de alto flujo en que el porcentaje de PUR es cercano a un tercio del total con una estricta selección de pacientes, la duración es tan buena como en la PTR.

Abstract: In a patient with severe unicompartmental knee osteoarthritis where conservative treatments have been exhausted, with painful symptoms located on the affected side and with a reducible axis, the unicompartmental knee prosthesis (UKP) is the first option for our work group. Within the study to confirm the diagnosis and plan the surgery, weight-bearing knee x-rays, Rosenberg x-rays, and teleradiographs of the lower extremities stand out. The objective of surgery is to replace the affected area, restoring the anatomy with an adequate balance of soft tissues. Regarding alignment, the challenge is not to overload the opposite side or that of the prosthesis. There are mobile and fixed plates and although the clinical and survival results are similar, in recent years with the incorporation of robotic surgery, the balance has tipped towards the use of fixed plates. The clinical and functional results are better and there are fewer complications than when total knee prostheses (TKP) are used in the same type of patients. The survival studied in registries is lower than for TKP, but when used in high-flow centers where the percentage of UKP is close to a third of the total with strict patient selection, the duration is as good as in PTR.

Finite element simulation of contact stress on a novel total knee prosthesis during gait cycle / 医用生物力学

Objective To perform finite element analysis on a type of newly designed total knee prosthesis,and investigate the influence from changing twist angle of the lateral condyle surface on mechanical environment of the knee joint.Metheds Based on CT measurement data from a volunteer,3 artificial knee prostheses with the same medial condyle were established.In Model 1,the twist angle of lateral condyle surface was 0°,while 10° and 20° in Model 2 and Model 3,respectively.The prosthesis models were imported into finite element software and applied with gait cycle data to simulate the motion of knee prosthesis during the gait cycle.The simulated stress results in the knee joint were then compared with the calculated results,which were obtained from theoretical formula of contact mechanics.Results The maximum stress of 3 models appeared at 13％ of the gait cycle,when the axial force (2.6 kN) was also the maximum.The maximum stresses of medial and lateral condyle in Model 1,Model 2 and Model 3 were 35.5 and 30.6 MPa,38.4 and 32.6 MPa,38.3 and 43.1 MPa,respectively.The stress curves of Model 2 and Model 3 during the gait cycle were relatively smooth compared with those of Model 1.The simulated stress trend was basically similar to the theoretical calculation,except at a few moments in the gait cycle.Conclusions The mechanical environment of the total knee prosthesis can be improved by twist angle of the lateral condyle surface.This newly designed prosthesis can preserve implants from abrupt change of the stress during the gait cycle and prolong the service life of prostheses.

Finite element simulation of contact stress on a novel total knee prosthesis during gait cycle / 医用生物力学

Objective To perform finite element analysis on a type of newly designed total knee prosthesis, and investigate the influence from changing twist angle of the lateral condyle surface on mechanical environment of the knee joint. Methods Based on CT measurement data from a volunteer, 3 artificial knee prostheses with the same medial condyle were established. In Model 1, the twist angle of lateral condyle surface was 0°, while 10° and 20° in Model 2 and Model 3, respectively. The prosthesis models were imported into finite element software and applied with gait cycle data to simulate the motion of knee prosthesis during the gait cycle. The simulated stress results in the knee joint were then compared with the calculated results, which were obtained from theoretical formula of contact mechanics. Results The maximum stress of 3 models appeared at 13% of the gait cycle, when the axial force (2.6 kN) was also the maximum. The maximum stresses of medial and lateral condyle in Model 1, Model 2 and Model 3 were 35.5 and 30.6 MPa, 38.4 and 32.6 MPa, 38.3 and 43.1 MPa, respectively. The stress curves of Model 2 and Model 3 during the gait cycle were relatively smooth compared with those of Model 1. The simulated stress trend was basically similar to the theoretical calculation, except at a few moments in the gait cycle. Conclusions The mechanical environment of the total knee prosthesis can be improved by twist angle of the lateral condyle surface. This newly designed prosthesis can preserve implants from abrupt change of the stress during the gait cycle and prolong the service life of prostheses.

Hemiarthroplasty Using a Modular Hip Segment in a Patient with a Long Stem Total Knee Prosthesis

Femoral neck fractures frequently occur in elderly patients and the treatment strategies for this are well documented. Revision knee arthroplasty using a long intra-medullary stem has recently been increasingly used for treating complications such as infection, aseptic loosening or instability. The current case had a femoral neck fracture with a well-fixed, long stem knee prosthesis, which reached to near the lesser trochanter of the femur. The authors performed the surgery using impaction of the modular hip segment; its inner diameter was fit to the outer diameter of the femoral stem of the knee prosthesis. At two years postoperative follow-up, the result was excellent without loosening or osteolysis.

Fracture of Tibial Base Plate Following Total Knee Arthroplasty: Report of a Case / 대한정형외과학회잡지

Fracture of the metal base of tihial components of total knee arthroplasty has heen occasionally reportecl. The most common cause of the failure of the metal hase plate was known to be a fatigue fracture around the screw hole where the strength of the metal hase plate was the weakest. We experienced a case of the fracture of the metal hase plate secondary to the t'racture of the posteromedial corner of the metal tihial condyle which was weakened due to the shoil peg hole for the base plate of MG II implant. Since the proximal portion of the posterior tihial condyle was normally thin, cutting the hone for the base plate made it thinner and wcaker than normal. Therefore stress fracture of the bone occurred and the overlying metal plate was subsequently hroken. From this experience. we concluded that the posterior peg hole may cause unwanted failure of the posteromedial corner of the tibial base plate.

Experimental Study for Development of New Alloy for Domestic Total Knee Prosthesis / 대한정형외과학회잡지

The total knee replacement is an excellent method for the treatment of osteoarthritis, rheumatoid arthritis, etc. of the knee joint. The tendency of the use of total knee prosthesis is increasing now in Korea. But domestic production of the prosthesis is not avaliable and all are imported from abroad. Moreover, these prosthesis are not well adapted to Korean people, and in occation, the custom-made prosthesis should be needed. So, domestic production of the prosthesis is required. For production of new prosthesis, in cooperation with KAIST(Korea Advanced Institute of Science and Technology), we developed the new alloy 15-57 for total knee prosthesis. We conducted an animal experimental study to confirm the biocompatibility of the new alloy. In this experiment, the Zimmer® company vitallium was compared with this new alloy as control study. The results are as follows: 1. Biocompatibility of the new alloy 15-57 is similar than that of Zimmer® company vitallium in histological study of metal-bone interspace area. 2. Surface corrosion of both metal was nearly absent. 3. In summary, the new alloy 15-57 is suggested as an acceptable metal for the production of total knee prosthesis.