LATE OUTCOMES IN TKR

Abstract

The outcomes of any procedure in our clinical practice have to be looked upon in several ways:

a.The benefit the individual obtains from the procedure, in respect to the quality of life or well being.

b.All these gains, if they are produced, must have a cost inferior to the ones that had occurred if the operation had not been done: (medical and social costs).

c.The changes observed in pain, mobility and stability of the joint before and after the operation.

d.The changes in the individual functional state: what the patient can do in his normal life activities (walk, stairs, fasten shoes, personal wash-up, etc) and any needed help for a normal daily living.

e.Length of time the procedure will be holding the results, and the necessity of revision (survivorship), depending on the clinical state and the radiographic studies (migration, inclination, subsidence, lucent lines in the surfaces, etc).

The aspects on well-being and cost-benefit after the total knee replacement have changed for better in a parallel way to the improvement on the function of the knee joint and the function of the body as a whole. We have recently studied the first two (a and b) outcome measures with positive results, that compare well to the published ones.

In considering others aspects or measures of the outcomes, we agree with M. A. R. Freeman that the year 1980 could be the milestone for looking back and forth in the history of total knee replacement. Before 1980 the number of early failures was high, mainly due to sinkage and inclination of the tibial component, wear of the components, instability of the joint, and patelo-femoral pain.

We did work on the design of a new method of fixation for the tibial plateau from 1980 to 1988, because of the many publications on bad results due to tibial loosening; our method of fixation was based in an intramedullary elastic, press-fit, stem, trying to avoid the fixation on the tibial surface, mainly because the trabecular bone was weak to stand the weight pressures, and because it was very difficult to cover all the surface of the tibia cut (the tibial not only differs in size but also in shape).

Following the introduction of the ligament tensor by Freeman and the use of the “gaps” technique by Insall, in order obtain hte proper ligament tension and equal flexion and extension spaces and proper joint alignment, the short-term results published made us think that the tibial plateau problems were due more to bad surgical technique, that to other causes; we, therefore left aside our work.

The functional results since then have shown little changes; we have not obtained more flexion or stability, and the patello femoral problems have not improved much. The different new designs have more to do with early wear of the polyethylene and consequent osteolysis and instability, than with function.

The challenges of the future, in order to get better outcomes are:

1. To obtain better flexion.

2. To obtain a better patelar tracking.

3. To reduce the lucent lines around the prosthetic components.

1 and 2 should be addressed with a better geometry of the components. Practically every design and every technique change the geometric arrangement, specially, of the distal femur.

We change the troncoconical (medial bigger than lateral) shape of the condyles into a cylindrical one; we change the oblique hinge into a normal one; we do not allow space for the lateral condyle to run backwards and forwards on the lateral tibial plateau in flexion and extension. This last problem is made even worse by the tension of the lateral ligament in flexion of the knee.

If we had all this into consideration we could get more flexion and better patellar tracking. Actually, we are working on this subject.

The issue 3 on the radiolucent lines: the coating of Hydroxiapatite might finally give a better fixation than cement. Hydroxiapatite resists the micromovements better and its interface membrane dissapears in favour of bone.