IS THE 3–6° POSTOPERATIVE VALGUS RULE TO OBTAIN A GOOD 10–13 YEAR RESULT AFTER VALGUS TIBIAL OSTEOTOMY VALID? INFLUENCE OF THE TIBIO-FEMORAL INDEX

Abstract

Purpose: It was demonstrated in 1986 that to obtain a good radioclinical result at 10–13 years after valgus tibial osteotomy for the treatment of medial femorotibial osteoarthritis that the frontal valgus at this follow-up had to be 3–6°. In 1995, it was demonstrated that the side of deterioration in knees initially aligned between 2° varus and 2° valgus or with genu valgum (≥ 3° valgus) depended on the tibiofemoral axis: a positive index (tibial torsion greater than femoral torsion) favouring medial femorotibial deterioration and progressive varisation, and a negative index favouring lateral femorotibial deterioration and progressive valgisation. Can the post-osteotomy valgus be modified by the tibiofemoral index and prevent obtaining ideal correction at 10–13 years?

Material and methods: Forty-five knees with femortibial deterioration of the medial compartment were treated between 1987 and 1990 by tibial medial opening osteotomy for valgisation. Functional outcome in the 45 knees was assessed at a mean follow-up of 11 years (range 10–13 years). Postoperative frontal axis after healing and frontal axis at last follow-up was measured by goniometry in the standing position for all knees. A scan in the torsion position was obtained for 36 knees to measure the tibiofemoral index.

Results: At maximum follow-up, outcome was good in 58% of the knees, fair in 24%, and poor in 18%, differences which were not statistically different. Frontal axis changed with time. Among the 36 knees which had been realigned correctly (3–6° valgus) after healing, four exhibited an increase in valgus beyond 6° and five lost valgus passing below 3°. But ideal valgus was achieved at last follow-up for three of five knees which had been undercorrected, Among the 38 knees for which a torsion scan was available, 33 were correctly realigned postoperatively and 22 were well aligned at last follow-up. There was no statistical difference between knees with good, fair, or poor outcome among the 33 knees well corrected postoperatively (3–6° valgus). There was however a statistical difference between the good (64%), fair (27%), and poor (9%) functional results among knees with ideal valgus at last follow-up (p = 0.03).

The variation between the postoperative and last follow-up goniometry data exhibited a statistical correlation with the tibiofemoral index (p = 0.0005). If the index was less than 13°, most of the knees showed an increase in valgus (13 out of 19 knees); if valgus was greater than or equal to 13°, valgus was lost (for 12 of 19 knees).

Conclusion: To have the best chance of obtaining a good functional result 10 to 13 years after tibial osteotomy for valgisation, the valgus at this follow-up must be between 3° and 6°. But to achieve this valgus, the postoperative valgus must be modulated in relation to the tibiofemoral index. For an index ≥ 13°, the postoperative valgus should be pushed towards 6°; for an index < 13°, valgisation should aim at achieving a 3° postoperative valgus or less.