A comparison of joint line height after revision total knee replacement using a rotating hinge versus a condylar revision knee system

Purpose: This retrospective study aimed to assess the effects of two differing revision total knee implants designs (condylar and rotating hinge) on joint line height.

Method: The use of distal augmentation and pre and post revision radiographic joint line heights were compared in 19 condylar type knee replacements (Zimmer NexGen Legacy Constrained Condylar Knee - LCCK) and 40 LINK-Endo-rotating hinge knee replacements. Joint line and patellar heights were determined for each implant using four validated methods. For comparison within a group a two tailed paired Student's t-test was used, for comparison between the groups an unpaired, two tailed Student's t-test was used. A p value of less than 0.05 was deemed statistically significant.

Results: In 15 of 19 NexGen revision knee replacements distal augments were used. No distal augments were used in the LINK-Endo RHK group. In both systems there was no tendency to elevate the joint line relative to the tibia. The joint line was distalised relative to the femur in the NexGen group and proximalised in the rotating hinge knee group. Measurements using antero-posterior radiographs were found to be the most reliable method of assessing joint line height when compared to lateral radiographs.

Conclusion: Both revision knee implant systems adequately restored joint line height. In condylar type knee revision implants elevation of the joint line height may be avoided through the use of distal augmentation. We found AP radiographs to be the most reliable method of accurately assessing joint line height.