OSTEOTOMY IN THE TREATMENT OF KNEE OSTEOARTHRITIS: PLANNING, TECHNIQUES

Abstract

Osteotomies around the knee are still utilized a lot in Europe and in Asia while in US unicompartmental and total arthroplasty for the same indications have more and more taken over, partially due to fear of complications. We think that with careful planning and technique the indications can be maintained. Furthermore with modern methods of cartilage repair it is of utmost importance to unload overloaded compartments. Also many young patients having suffered ligamentous tears of the knee and having been reconstructed are in need of OT’s later on.

Many of the poor results are due to absent or poor planning and to poor OT technique and fixation. Not every knee needs to be operated to an overcorrected position. While opening wedge OT has become trendy because of fewer neurological complications we think there are definite indications for closing wedge technique.

In this lecture we would like to summarize the principles and the steps which are very personal and that are based on 20 years of practice.

Indications for osteotomies around the knee

Varus Knee

Opening wedge osteotomy: Advantages: Rapid surgery, small incision, fast healing, precise correction. Indicated when:

• Degree of OA moderate and angular correction of not > 8°

• Useful in associated MCL Instability

• Useful when open surgery on medial femoral condyle needed (Mosaicplasty)

• In case of associated ACL instability when tibial slope is not > 10°

• Patella alta

• Has a tendency to increase the tibial slope.

• We use tricortical grafts from the iliac crest where the base of the wedges in mm corresponds to the degrees of correction. A cervical spine AO plate with for screws is used for fixation.

• Creates less deformity of the proximal tibia which is an advantage for a later total knee. Increases the intraarticular pressure even when the MCL is cut or detached distally, without us knowing the effect on the degree of OA, no long term studies being known to us.

Closing wedge osteotomy: Advantages: Allows higher degrees of correction

• Degree of OA advanced, need for higher corrections

• Useful when open surgery on lateral femoral condyle needed

• In ACL instability when tibial slope must be corrected, because of need to break the medial cortical hinge a heavier implant is needed may be enforced by a sagital Ex.Fix.

• Patella baja

Corrections over 5 degrees need an OT of the proximal or distal fibula. We perform the resecting OT in the fibular neck, the proximal cut is incomplete removing only the anterior and lateral cortex, the distal cut is complete. This allows to shift the distal fragment proximally and in front of the proximal cortical shelf allowing nerve protection.

For fixation of the tibial OT we use the 90° angled cannulated AO osteotomy plate, that is inserted over a 2,0 K wire using a specific “transporteur” in relation to the amount of correction. The OT is done using the precise AO osteotomy jig, cutting along 2,5 mm K wires inserted through the jig. The two cuts meet 5–10 mm short of the opposite cortex.

The closing wedge OT creates more deformity, carries a certain risk of peroneal nerve injury and of compartment syndrome. Surgery must therefore been done very skilfully and demands expertise.

All the studies about long term effect of HTO have been done one using closing wedge technique.

Double Osteotomy

Indications:

• For deformities of over 12° to avoid obliquity of the joint line otherwise created by tibial or femoral OT alone.

• When sagital deformity needs to be corrected together with frontal plane deformity, eg a flexum of 20° and a varus of 10°.

Valgus knee

Closing wedge Osteotomy of the distal femur: Advantages are the potent fixation using the same plate as on the tibia leading to rapid healing. Approach is rather extensive. Indicated:

• When deformity of valgus and sagital plane ( flexion contracture) need to be addressed.

• When valgus is marked ( in small deformities the OT can also be performed in the tibia).

Opening wedge Osteotomy of the distal femur. Indicated:

• When the deformity is small.

• When cartilage gestures need to be performed on the lateral femoral condyle.

Planning of Osteotomies:

We use one leg standing films in ap, pa 45° flexion, and lateral projection, varusvalgus stress films with 15 kp (Telos) and Orthoradiogramm (hip-ankle). A potential contralateral opening on the standing film is compensated on the drawing by a push orthoradiogram which virtually brings both compartments into contact.

For the varus knee the ideal crossing point of the mechanical xis sits at 30% in the lateral compartment, the centre between the tibial eminences being 0% the medial or lateral border of the tibia being 100%. This is the displacement corresponds to the classical 3° over-correction that is useful when the medial compartment is down to bone. This would be an overcorrection for the less damaged medial joint lines where however an OT may already be indicated.

We therefore have prospectively studied and validated a more balanced approach.

If the medial compartment in a varus knee has lost up to one third of his cartilage the axis is calculated to pass at 10% in the lateral compartment.

If is down by two thirds it is meant to pass at 20% laterally.

If it is totally worn it passes at 30%.

The drawing for the high tibial OT on the orthoradiogram is simple:

1. Connect the centre of the femoral head with the point at 10, rsp. 20, rsp. 30% in the lateral compartment and prolong this new axis of the leg distally to a point lateral of the ankle joint.

2. Now select the hinge joint for the opening or closing wedge OT 2–3 cm distal to the joint line and connect this point with the old and the new centre of the ankle. Measure the angle between the t line which corresponds to the amount of correction and the angle to open or resect.

The planning for the varus OT of the distal femur in valgus deformity is somewhat more complicated but should aim at a correction which leaves a femorotibial valgus of 1–2°.

Using these rules one is able to reach adequate correction.