RESTITUTION OF THE JOINT LINE IN REVISION TOTAL KNEE ARTHROPLASTY OR “BONE BALANCE”

Abstract

Purpose: Revision total knee arthroplasty using gliding prostheses raises numerous technical difficulties. One of the main objectives is to restore the level of the joint line to correspond the space in flexion and extension and maintain patellar height. This is difficult in the event of bone loss which modifies usual landmarks. The basic problem is to find a correspondence between the preoperative planning and the intraoperative execution. We propose a simple method to achieve this objective.

Material and methods: The height of the joint line is determined indirectly from measurements of the lengths of each of the lower limb segments and the mechanical axes. Restoration of the respective lengths of the femur and tibia enables obtaining the original height of the joint line. This produces true bone balance for revision procedures where the ligament balance is limited. The surgical technique consists in drilling two holes with a 4.5 mm drill in the anterior cortical of the femur and tibia at a known distance from the joint line (8–10 cm) before removal of the implants. Once the trial pieces are in place, the distance to the joint line of each bone segment is check to adapt the prostheses. Measurement of the joint line is dependent on the tibia and the femur. It is evaluated by comparison of the lengths of the limb segments (femur and tibia) before and after operation. We measured a continuous series of 26 patients Pre and postoperative goniometry was used with the length of the contralateral fibula serving as a guide to avoid magnification effects.

Results: The mean difference in length before and after surgery was 1.15 mm for the tibia and 2.01 mm for the femur.

Discussion: It is always possible to restore femur length. The trend is globally to lengthening. This is usual and attributed to ligament balance before the operation. Restoration of the joint line is not always possible or desirable. The hole landmark method is useful and reliable to localise and restore the joint line desired by the surgeon. It is the key to restored space symmetry in flexion and extension while preserving the length of each of the bone segments to achieve bone balance.