Orthopedic Teaching Cases 2023, Jan, 20 | 12:00 am

unicompartmental knee replacement

A 59-year-old male with BMI 32 presents with severe medial knee pain corresponding to focal osteoarthritis of the medial compartment. He has undergone physical therapy, cortisone injections, and takes nonsteroidal anti-inflammatory medications with incomplete relief of his pain.

Which of the following is FALSE with respect to medial unicompartmental knee replacement in this patient?

  1. UKA can be performed if he has a passively correctible varus deformity less than 10 degrees

  2. UKA should be avoided if he has a fixed flexion contracture more than 5 degrees

  3. An incompetent ACL is an absolute contraindication to UKA

  4. Recent reports suggest UKA can be performed in the setting of mild obesity

 

Discussion

The correct answer is (C). Although historically an intact ACL has been included in the list of requisites for UKA, the absence of an ACL is not an absolute contraindication. UKA can be performed successfully in the ACL deficient knee as long there is not excessive instability of the knee. Excessive tibial slope should be avoided in the ACL deficient knee that undergoes UKA.

Which of the following concerning mobile-bearing unicompartmental knee

replacement is TRUE?

  1. There is a similar rate of dislocation of the bearing surface in comparison to fixed-bearing devices

  2. Mobile-bearing UKA is recommended for both medial and lateral UKA procedures

  3. Soft tissue balancing is critical in order to reduce the rate of spinout of the mobile-bearing insert

  4. The results of mobile-bearing devices far exceed that of fixed bearing

 

Discussion

The correct answer is (C). One of the primary mechanisms of failure of a mobile-bearing UKA is spinout of the polyethylene insert. Meticulous soft tissue balancing is necessary to reduce the risk of this complication. Currently in the United States, mobile-bearing UKA is recommended for use only in the medial compartment. Data from the United Kingdom has shown a 10% rate of dislocation of the mobile-bearing insert when used in the lateral compartment.

 

Helpful Tip:

To accurately balance the mobile-bearing unicompartmental knee replacement, a leg holder that allows the leg to hang freely should be used to allow gravity to distract the knee in flexion so that the gap balancing can be appropriately assessed in order to select the appropriate bearing thickness.

 

Objectives: Did you learn...?

 

The indications for unicompartmental knee replacement?

 

The importance of soft tissue balancing and component position for the success of PF and unicompartmental knee