High Tibial Osteotomy – Fixation

HTO-fixation
Title: Fixation in High Tibial Osteotomy

Reference: Chandler R.W., Seltzer, D. In Knee Surgery, 1993, Chapter 56

Main Message

There are lots of methods of osteotomizing the tibia, and then lots of methods of fixing them. All have their advantages and disadvantages.

Points of Interest

Studies that have looked at HTO�s conclude that the success of the procedure correlates well with the 1. Correction achieved and maintained, and 2. The degree of arthritis to begin with. Good candidates typically are in MILD varus (5-10o) and are corrected to about 5-15 degrees of anatomic valgus (there is a range of �acceptable valgus�, looking at the literature) – ie. we really don�t know – this is an area of controversy.

Fujisawa – 1979 Orthop Clin North Am 10(3):586
– looked arthroscopically before and after HTO to assess the cartilage lesions. Found that the knees which demonstrated healing cartilage had the weight-bearing axis moved to a point 30-40% LATERAL to the transverse midpoint of the knee.
– but this is all STATIC – probably, this is better correlated to a dynamic (gait analysis) study. I wonder how he assessed the actual cartilage… And on top of that, to move the mechanical axis that far over laterally requires a BIGTIME osteotomy, which may be cosmetically very unacceptable to short people in particular.

Currently, probably the best idea is to bring them to an anatomic axis of about 10o of valgus.

Some people have looked at using the mechanical axis rather than the anatomic axis, and trying to restore the former rather than just the latter.

Be careful about medial sided laxity – in the varus knee, you may not notice the MCL laxity. Once the valgus osteotomy is performed, the load bearing conditions change, and the full weight-bearing radiograph will reflect the combined influence of the osteotomy and the MCL laxity. All of a sudden, you may find that the anatomic valgus is much more than expected!

Some people have done these with just a cast – the current argument is that loss of correction is too high with just casting alone. It should be noted though, that the superiority of internal fixation has not been demonstrated prospectively yet…

Techniques:

Staple fixation – Coventry
Buttress plates – Weber
(unfortunately, the lateral side needs to resist varus BENDING, not collapse – which would be the better indication for a �buttress� plate)
Medial opening wedge with tricortical iliac crest graft – Hernigou
Blade plate – Koshino
Tension band plates – Weber semitubular plate, Miniaci

There have been no comparative studies on the various internal fixation devices

Things to consider:
– Where should the fibular osteotomy be?
– Try not to cut through the medial osteo-periosteal sleeve. This destabilizes the whole thing…
– Where should the tibial osteotomy be made – how close to the joint surface, how close to the patellar tendon? It seems that most people cut the tibia as close as possible to the joint surface bearing in mind the risk of cutting into it. Most seem to make the inferior cut proximal to the tibial tubercle.

Why is patella infera created if the tibia is being shortened proximal to the insertion?

Thoughts….

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