INTRODUCTION

Lateral closing wedge high tibial osteotomy has been a standard procedure for genu varum secondary to osteoarthritis of the knee.1-7 The correction angle is the most important factor attributing to the long-term revarisation and arthropathy,1,8 in addition to age, the extent of deformity of the knee and degeneration of articular cartilage.1,4-6,8-11 To avoid recurrent varus deformity, it has been advised that the femorotibial angle be overcorrected,9,10 and be maintained as such throughout the postoperative period.2,5,6,12,13 We compared the results of staple versus locking compression plate fixation after closing wedge high tibial osteotomy.

MATERIALS AND METHODS

A group of 11 men and 12 women (24 knees) aged 49 to 68 (mean, 56) years underwent box high tibial osteotomy14 and staple fixation between February 1999 and April 2002, and were followed up for 3 years. The operation involved removal of a 'base-lateral' bony wedge from the proximal tibia, leaving behind a bony ledge on the distal fragment anteriorly and another on the proximal fragment posteriorly. The distal fragment was abducted for valgisation and translated anteriorly to decompress the patellofemoral joint. Fragments were fixed with a stepped staple and the knee immobilised for 6 weeks in a cylindrical plaster cast.

Another group of 11 men and 8 women (20 knees) aged 48 to 60 (mean, 55) years underwent a similar procedure but with locking compression plate fixation between June 2002 and November 2004 and were followed up for 3 years. The incision was modified from a transverse to a midline vertical one, so as to accommodate the locking compression plate and when necessary enable switching to a total knee arthroplasty. Fragments were fixed with a locking compression plate using 3 screws instead of a stepped staple. The knee was kept in a removable long knee brace instead of a cylindrical plaster cast. The enhanced rigidity with the locking compression plate facilitated early mobilisation and exercises.

All other conditions remained the same for both groups. All the patients were clinically and radiologically examined preoperatively, and postoperatively every 6 weeks until 6 months, at one year, and yearly thereafter. Toe touch weight bearing was started at 6 weeks. Full weight bearing was allowed after bone union. The Hospital for Special Surgery (HSS) Knee Scores15 were determined based on pain, function, range of movement, muscle strength, flexion deformity, and instability (Table 1). Scores of 85 to 100 were considered excellent, 75 to 84 as good, 60 to 74 as fair, and <60 as poor. Bone union was defined as no tenderness along the osteotomy line and no pain during weight bearing,16 together with radiological evidence of callus formation in the form of crossover trabeculae.17 Delayed union was defined as non-union at 4.5 months, with distinct tenderness along the osteotomy line, pain during weight bearing, and scarcity of crossover trabeculae (Fig. 1). The femorotibial angle was measured. The stage of osteoarthritis were determined using anteroposterior radiographs of the legs in stance position, according to the Hokkaido University grading system10 (Table 2).

The normality of data was tested by the Shapiro Wilk procedure. Significance was tested using the Mann-Whitney U test, as the data distribution was not normal. Fisher's exact test and Chi squared test were used for qualitative analysis. A p value of <0.05 was considered significant.

RESULTS

Preoperatively, there was no significant difference between the 2 groups in terms of age, HSS score, femorotibial angle, and stage of osteoarthritis. Nonetheless, there were more stage-III osteoarthritic knees in the staple (n=11) than the locking compression plate fixation group (n=8). There were no significant differences between the 2 groups in terms of operating time and blood loss.

Postoperatively, at 6 months the median HSS scores and the proportion of patients with excellent or good scores were significantly higher in the locking compression plate than the staple fixation group (76 vs 62, p=0.003, Mann-Whitney U test; 75% vs 42%, p=0.0354, Fisher's exact test), but not at one and 3 years (Table 3). The range of movement was significantly greater in the locking compression plate than in the staple fixation group in the short term (6 weeks, 3 and 6 months), but not after one year (Table 3). The median time to full weight bearing was significantly shorter in the locking compression plate fixation group (86 vs 116 days, p<0.001, Mann- Whitney U test). There were fewer delayed unions in the locking compression plate fixation group but not significantly (1 vs 5, p=0.198, Fisher's exact test), possibly because of the small numbers involved. There was no difference, within the limits of measurement error, with respect to femorotibial angles or correction losses between the 2 groups (Table 3). Peroneal palsy or compartment syndrome was not observed. One knee in each group developed a superficial infection.

DISCUSSION

Locking compression plate fixation obviates the use of a plaster cast, enables early mobilisation and bone union, and reduces the number of delayed unions and the time to full weight bearing. These advantages are attributable to a combination of angular stability and dynamic inter-fragmentary compression. Closing wedge high tibial osteotomy should aim at maintaining close approximation between fragments, otherwise delayed union may occur.6 Adequate correction and maintenance of valgus alignment are important.1,5,7-9,11 To prevent recurrent varus deformity when osteoarthritis progresses, we aimed to achieve a femorotibial angle of 170°, with a correction not only for the varus deformity but also a provision of 5° for normal valgus and another 5° for overcorrection (Fig. 2).3,4,7,18 In all our patients, the stage of osteoarthritis remained the same throughout the study period. Nonetheless, a longer follow-up is needed to confirm that the corrected femorotibial angle can be maintained.

Our study was retrospective, the follow-up period was short, and the sample size was small. Longer follow-up studies are needed to confirm whether earlier rehabilitation and bone union translate into better maintenance of correction and hence help prevent worsening of arthropathy.

ACKNOWLEDGEMENT

We thank Dr Ranjit Mankeshwar of P.D. Hinduja National Hospital and Medical Research Centre, Mumbai, India for his statistical analysis.

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