Elsevier

The Journal of Arthroplasty

Volume 19, Issue 2, February 2004, Pages 217-223
The Journal of Arthroplasty

An in vivo biomechanical analysis of the soft-tissue envelope of osteoarthritic knees

https://doi.org/10.1016/j.arth.2003.09.008Get rights and content

Abstract

Soft-tissue balancing and the amount of tension applied to the ligaments in a well-functioning total knee arthroplasty (TKA) has, thus far, not been accurately quantified. A ligament-tensioning device was used to measure displacement between the tibia and femur versus load during 86 consecutive TKAs. Measurements were made in flexion and extension following bone cuts and final soft-tissue balancing to calculate mean effective stiffness (MES) of the soft-tissue envelope and mean resting force on the implanted polyethylene component. MES was not affected by age or gender and did not differ in flexion versus extension. MES was significantly higher in posterior cruciate-retaining knees compared with posterior cruciate-sacrificing knees. There was no statistical difference between mean resting force on the polyethylene in flexion versus extension, or in posterior cruciate-retaining versus -sacrificing knees. These biomechanical data will serve as a good starting point for which to compare the expected stiffness of the ligaments and resting load on the polyethylene in well-balanced knees.

Section snippets

Materials and methods

The surgical technique and soft-tissue balancing procedure for TKA utilizing the ligament tensioning device (Fig. 1) used in this study has been previously reported in detail [11]. Since that report [11], the torque meter handle has been added to the ligament-balancer device. The calibration of the device was performed by the manufacturer (Stryker Howmedica Osteonics, Allendale, NJ).

Following the distal femoral and proximal tibial bone cuts, the knee is balanced in extension. The tensioner

Results

The generalized load versus displacement curves for both posterior cruciate-retaining and posterior cruciate-substituting knees are indicated in Fig. 2. Mean effective stiffness (MES) was not affected by age in either posterior cruciate-substituting knees (r2=.09) or posterior cruciate-retaining knees (r2=.07). For posterior cruciate-substituting knees, no significant difference in the average effective stiffness could be demonstrated between men and women in either flexion (P=.42) or

Discussion

To the best of our knowledge, this is the first time in vivo measurements of the effective stiffness of the soft-tissue envelope of osteoarthritic knees have been measured using a balancer. Attfield et al. [12] used an electronic tensioning device during 8 TKAs; however, the goal of their study was to determine soft-tissue imbalance of the medial compartment compared with the lateral compartment. They found that the medial-lateral imbalance reached a maximum before decreasing to a lower level

Conclusions

The MES of the soft-tissue envelope around osteoarthritic knees has been approximated and the load versus displacement curve has been characterized. The only factor that appears to affect this biomechanical property is retention of the PCL, which increases the effective stiffness. In addition, the mean resting force on the polyethylene implant has been estimated in this series of TKAs. These data serve as a baseline in our attempt to establish quantifiable guidelines for how “tightly” or how

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No benefits or funds were received in support of this study.

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