THE VARIABLES OF SUCCESSFUL LONG-TERM RERULTS OF TKA

Abstract

To know how to succeed and survive for his or her whole life after the primary TKA by studying the causes of aseptic failure of the cruciate retaining type primary TKA. One hundred and seventy nine cases of revision of the TKA were analyzed concerning the causes of failure. The longest follow-up period was 25 years. All cases of the immediate postoperative and pre-revision weight bearing x-rays were reviewed. The operative findings of the revision surgery were compared with the pre-revision x-rays and physical findings.

The results of this study were:

1. The incidence of wear of the tibial polyethylene insert was predominant.

2. The most severe disability before revision was instability and dislocation of the joint due to excessive eccentric wear of the posteromedial part of the tibial polyethylene insert.

3. All cases showed full ROM after primary TKA.

4. The causes of the failures could be classified as follows:

   1. Implant Design:

      1. Flat surfaced tibial polyethylene insert could be related with an eccentric wear and a resultant instability.

      2. Posterior pegs of the tibial base plate might be related with a stress fracture of the posteromedial part of tibial condyle, which ended up with an eventual fracture of the tibial base plate and dislocation of the tibial polyethylene insert.

      3. The metal backed patella could cause early wear of the patellar polyethylene insert.

   2. Bone Cutting: The most common cause of the failure related with the bone cutting was insufficient valgus of the femorotibial angle, which was related with a wear of the medial side of the tibial polyethylene insert. Less than 50 of valgus could be related with an early wear of the tibial polyethylene insert.

   3. Soft tissue balance: Most important factors were insufficient medial release and tight PCL, which caused early wear of the posteromedial portion of the tibial polyethylene especially in high flexion knees.

   4. Fixation: All cases of loosening occurred in cases of cementless TKA.

   5. The excessive body weight which is known to be one of the causes of early failure was not a significant factor in this series.

All aseptic failures occurred in high flexion knees. The causes of failures could be classified into four, the implant design, the bone cutting and the soft tissue balance and fixation. Long time survival could be achieved if those factors are perfect.