2002 OITE Question 264

Question

While performing a revision arthroplasty with a trial component in place, the surgeon notes that the knee has full extension but is loose in flexion. What is the next step in managing this situation?

1) Resect more distal femur and use a thicker polyethylene insert

2) Use a smaller femoral component

3) Use a more constrained polyethelene insert

4) Cut more posterior slope on the tibia

5) Release the posterior capsule

Figures

Answer (click for answer)

The answer is 1.

First there is an excellent review of sagittal plane balancing in Millers Review Book on page 259. Basically the pt has an asymmetric gap. With the patient good in extension but loose in flexion you have several options. First you can increase the size of the femoral component. Secondly, you can use posterior augments or cement to fill up the gap. Lastly , you can take more distal femur, which will increase your extension gap. Now you have a symmetric gap – meaning you are loose in both flexion and extension. Once you have a symmetric problem you can adjust the tibial side of the system i.e. using thicker poly. If you have an asymmetric flexion/extension gap you must address the femur or change it into a symmetric gap as above. By using a smaller femoral component or cutting more posterior slope you will increase the flexion gap. Releasing the posterior capsule will only help if you are tight in extension.

Reference: Miller, M. Review of Orthopaedics. 2000, p259.