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The effect of lateral opening wedge distal femoral osteotomy on leg length

Introduction

Varising distal femoral osteotomy is a well-described treatment for lateral compartment arthrosis in the young, active patient. Distal femoral varising osteotomy may be performed using a lateral opening wedge or medial closing wedge technique [1-2-3-4]. The most commonly described technique is the medial closing wedge [5-11]. In our center, the preferred method is the lateral opening wedge. Little literature exists regarding the results and complications of this technique [12-15]. This treatment may potentially alter the length of the lower limb. The objective of this study is to quantify the change in leg length following lateral opening wedge distal femoral osteotomy using a blade plate.

Material and method

Between January 1998 and December 2011, we treated twenty-seven patients (29 knees) with symptomatic genu valgum with signs of lateral compartment osteoarthritis, with or without associated lateral patello-femoral degenerative changes as seen on standard radiographs. All patients underwent lateral opening wedge distal femoral osteotomy. Two patients underwent bilateral procedures. We excluded patients who underwent combined high tibial osteotomy or femoral rotational correction.

The mean age was 44.4 years. We used the newly validated Knee Society Score (KSS), French version. This measure gives an objective score based on symptoms, range of movement and axis, and a subjective score based on knee function and patient satisfaction [16]. Patients were reviewed two, six and twelve months post-operatively. The mean follow-up was 80.2 months (23.1-198.7). The mean deformity in the twenty-nine knees, as measured by the femoro-tibial mechanical axis (mFTA) [17], was 187.8° (183.0°-197.0°).

The aim of the osteotomy was to correct the axis of the lower limb to a neutral alignment of between 0° and 3° of varus, with a preference for slight over-correction rather than under-correction. Careful pre-operative planning was used to determine the degree of correction and magnitude of opening of the osteotomy.

A lateral incision, 15 to 18cm in length, was used, and the bone approached in front of the iliotibial band but behind the vastus lateralis.

Two guide wires were introduced using artery forceps: one across the femoro-tibial joint and one across the patello-femoral joint. These were used to guide the orientation of the blade plate and reduce the need for fluoroscopic control.

A horizontal osteotomy was used, at the superior border of the lateral trochlea. The blade osteotome was introduced into the epiphysis for optimal fixation, with an entry point proximal and anterior to the origin of the lateral collateral ligament.

The optimal obliquity of the blade in relation to the joint line depends on the location of the deformity and the magnitude of the desired correction.

The osteotomy was performed using a saw, at least 25mm from the entry point for the blade plate to ensure an adequate cortical bridge. The blade plate was then introduced. The medial cortex was weakened by perforation with a guide wire, taking care to maintain cortical continuity.

The osteotomy was opened using two or more Lambotte osteotomes, whilst the blade plate was impacted. The opening and impaction was continued until the plate was in contact with the lateral cortex of the femur. Fixation was then completed in the diaphysis using bicortical 4.5mm screws above the level of the osteotomy. The osteotomy was grafted using cortico-cancellous autograft from the ipsilateral iliac crest.

Operative data were collected, and pre- and post-operative alignment and leg length were measured.

Results

The mean osteotomy opening was 8.3° (5°-13°). The femoro-tibial mechanical axis (mFTA) was improved significantly, from 187.8° (183.0°-197.0°) to 180.4° (176.0°-186.0°) post-operatively (p<0.001), without loss of correction over the follow-up period (fig. 1 et 2). The pre-operative leg length discrepancy was -0.7cm, compared to -0.6cm post-operatively, which was not significant.