A mechanical comparison of high-flexion and conventional total knee arthroplasty

The question addressed in this study was whether high-flexion total knee arthroplasty (TKA) designs improve the mechanical behaviour of TKAs in high flexion and whether they maintain the mechanical performance of conventional TKAs at normal flexion angles.

A finite element study was performed in which the mechanical behaviour of the conventional Sigma RP and the new high-flexion Sigma RP-F were compared, during a dynamic simulation of a high-flexion squatting activity. Forces, stresses, and contact positions were calculated during different stages of the simulations.

In general, higher stresses were found with larger flexion angles for both designs. Mechanical parameters were similar in normal flexion. In high flexion, lower stress and deformation values were found for the high-flexion Sigma RP-F, except for the contact stress at the post of the insert.

This study confirms that a high-flexion design can improve mechanical behaviour at high-flexion without changing the performance in normal flexion. Hence, although a high-flexion TKA may show a similar or better performance in comparison with a conventional TKA, high-flexion activities still cause an increase in the implant stress levels. Therefore, the patient's demand for large flexion angles may reduce the longevity of TKA implants.

Augmentation in anterior cruciate ligament reconstruction-a histological and biomechanical study on goats

We studied reconstruction of the anterior cruciate ligament (ACL) in skeletally mature goats. In one group, the autogenous tissue was augmented with polydioxanone (PDS), the other group had no augmentation. Histological complete incorporation and remodeling of the transplant was found in both groups. The newly formed connective tissues gradually assumed the microscopic properties of the normal ligament. The augmented group showed a delay in remodeling and maturation of the fiber bundles. Mechanically, the PDS-augmented transplants were stronger than the nonaugmented transplants immediately after surgery. During the first 6 weeks, a rapid decrease in strength of the augmented transplants was found, whereas the strength of the nonaugmented group gradually increased. The results of our experiment do not favor augmentation of autografts in reconstruction of the ACL.

Symptomatic ring-shaped lateral meniscus

Abnormalities of the lateral meniscus in humans are a long-known fact. Three different types of discoid menisci are described in Watanabe's atlas, being considered as congenital malformations. For the second time in the literature, a fourth ring-shaped type of discoid lateral meniscus was described as an incidental finding in this Journal by Monllau et al. in 1998. The present case is the first description of a symptomatic, ring-shaped lateral meniscus with a concomitant, recurrent cyst at the lateral aspect of a child's knee.

Influence of soft structures on patellar three-dimensional tracking

During knee flexion, the human patella moves along a complex path resulting from the combined actions of articular contact and soft-tissue stabilization. The current study is an attempt to characterize the role of these soft structures on patellar kinematics. To this end, the three-dimensional patellar motion during full knee flexion was accurately measured before and after partial dissection of the joint. The guiding role of the femoral groove prevailed over soft-tissue action through most of the range of motion. At full extension, however, when the patella and the femur were not in contact, the influence of the retinaculi was most noticeable, highlighting the unstable behavior of the patella near extension. The differences between the intact and dissected knee kinematics suggested that control over patellar motion is ensured by the transverse soft-tissue structures near extension and by the patellofemoral joint geometry during further flexion.