Case Report Distal Femoral Varus Osteotomy for

Case Report

Distal Femoral Varus Osteotomy for Valgus Deformity of the Knee as a Surgical Alternative to Total Knee Arthroplasty: A Case Study Drew W. Taylor, M.Sc., Institute of Biomaterials and Biomedical Engineering, University of Toronto Kyle C. Bohm, B.Sc., University of Michigan Medical School

Abstract An Osteotomy is a surgical operation where a bone is cut to shorten, lengthen, or change its alignment. Osteotomies are a valuable alternative to total knee arthroplasties, where the entire joint is replaced by prosthetic surfaces. In active, relatively young patients who are experiencing knee pain, a total knee replacement may not be the most desirable option. If good range of motion and stability are displayed, an osteotomy can delay the need for a total replacement and prolong the length of an athletically involved lifestyle. In this case study we show the benefit of using a varus distal femoral osteotomy to treat valgus deformity that is primarily located in the femur. Being an active sportsman, osteoarthritis in the lateral compartment was limiting the patient’s recreational and daily activities. Anterior cruciate (ACL), posterior cruciate (PCL), medial collateral (MCL), and lateral collateral ligaments (LCL) all appeared to be intact and only minor effusion was present. Through radiographic analysis, including four-foot standing x-rays, valgus deformity was evident through the drawing of biomechanical axis. Supero-lateral tilt of the joint line in the coronal plane is also derived in this manner. In this type of patient who is young and active and whose stability of the joint is not in question, it is shown how painful unilateral osteoarthritis caused by genu valgus originating in the femur can be corrected through distal femoral varus osteotomy.

Introduction

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algus deformity of the knee (also known as outward angulation or knock-knees) is much less common than a varus deformity (also known as inward angulation or bow-leggedness), whether due to a developmental, degenerative, inflammatory, ischemic, or traumatic cause.1-2 The pathoanatomy of the genu valgum and genu varum differs greatly. While degenerative processes in medial compartment osteoarthritis predominantly causes loss of bone on the tibial side, the femoral condyle experiences greater bone loss in osteoarthritis of the lateral compartment.3 Major valgus deformity of the knee is characterized with a joint line that slopes superolaterally in the anterior-posterior

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plane, and the abnormal plane cannot be corrected unless the osteotomy is done proximal to the joint.4-5 Coventry reported in 1987 that in the valgus knee, osteotomy through the proximal tibia fails to correct this supero-lateral tilt of the joint line.6 Therefore, in patients where the deformation lies in the femur, biomechanics prefer a distal femoral site for osteotomy.7 Multiple studies have showed that the correction of valgus deformity through a high tibial osteotomy produced an obliquity of the knee joint axis in the coronal plane,8-9 leading to undesirable mechanics.3-5,10-14 A biomechanical axis is drawn as a line passing through the midpoint of the femoral head through the midpoint of the ankle mortice. In the normal knee this line passes directly through the middle of the knee joint with a tibiofemoral angle approximately 5º to 6º valgus. In valgus deformity this axis is shifted lateral to the midline of the knee joint, overloading the lateral compartment. This mechanical loading causes degeneration of articular cartilage, subsequent loss of subchondral bone, and eventually the supero-lateral tilting of the joint line in the coronal plane.5,15 In time, the medial collateral ligament stretches leading to joint instability which in turn confers shear stresses in the lateral compartment and possible subluxation.5,16 Because of the unsuitability of proximal tibial varus osteotomy to correct genu valgum with superolateral tilt, Coventry reported that distal femoral varus osteotomy should be performed when the angulation of the valgus deformity exceeds 12 degrees or the obliquity of the joint line exceeds 10 degrees.6 This methodology is supported by many subsequent studies.4-5,13-16

Case Report A 49 year old male patient presented with pain in his right knee. He had open lateral meniscectomy, 18 years prior, to repair a small tear of the posterior horn of the medial meniscus. He also underwent a further arthroscopic resection 8 years ago. Over the last two years his knee was becoming more symptomatic with increased pain and swelling. Being a very active sportsman, the pain was impeding both his recreational and daily activities. Upon physical examination the patient showed mild valgus in the right leg with minor effusion. A lateral scar was evident from the prior surgeries. Right knee flexion range of motion extended from 0 to 130 degrees, slightly less flexion than was seen on the left side. ACL, PCL, MCL, and LCL all appeared to be intact. X-Rays revealed osteoarthritis in his lateral compartment. The four foot standing x-ray showed that the right knee was in fact much more valgus than the left. Sagittal and UTMJ • Volume 85, Number 3, May 2008

Case Report Distal Femoral Varus Osteotomy for Valgus Deformity of the Knee as a Surgical Alternative to Total Knee Arthroplasty

coronal x-rays of the knee, as well as the four foot standing xray image are presented in Figure 1. The patient was at a relatively young age to receive a total knee arthroplasty. Additionally, he displayed good range of motion and stability. Since the deformity is primarily in the femur, the patient was a great candidate for a distal femoral varus osteotomy to correct the supero-lateral tilt to the joint line.

Figure 1. Pre-operative x-rays including sagittal (1A) and coronal (1B) images of the right knee as well as the sagittal four-foot standing image (1C). Osteoarthritis is evident in the lateral compartment of the right knee. Additionally, it is evident from the four foot standing x-ray that the right knee is more valgus than the left. A longitudinal biomechanical axis is drawn (shown as a dotted line) passing through the midpoint of the femoral head through the midpoint of the ankle mortice. In the normal knee, this line passes directly through the middle of the knee joint with a tibiofemoral angle of 5º to 6º valgus. This axis is shifted lateral to the midline of the knee joint due to valgus deformity. The superolateral tilting of the joint line in the coronal plane is evident from the axis drawn perpendicular.

UTMJ • Volume 85, Number 3, May 2008

Surgical Technique The operative technique was explained in detail by Gross et al. in 2000 and Backstein et al. in 2007 and briefly reiterated here.15-16 A tourniquet was used, but is optional. The preoperative application of antibiotics (Ancef 1 gm) was given prior to inflation. With the patient positioned supine on the operating table, a straight midline incision was made longitudinal along the femur of sufficient length to allow simultaneous access to the knee joint and the distal femur (beginning from slightly distal to the joint line and continuing proximally for about 15 cm). Medial incisions can be used as well if desired. The fascia over the vastus medialis was incised and the muscle was elevated from the medial inter-muscular septum and reflected forward and laterally to expose the medial portions of the femoral cortex and femoral condyle. The exposed femoral cortex can be visualized operatively in Figure 2. The superior medial and descending genicular arteries were encountered and ligated as necessary. The additional vessels in the adductor hiatus region were not at risk, and are not usually unless an extra-long plate is used. Guide wires were used, the first one passing from medial to lateral across the joint parallel to the articular surface and the second one passing parallel to the first, 1 cm proximal to the femoral articular surface. Radiography was used to confirm that the second guide wire was parallel to the articular surface as this ensures the blade of the condylar plate is inserted correctly. This is of utmost importance and can be visualized in Figure 3. An area was selected in the medial anterior half of the femoral condyle 2.0 cm to 2.5 cm proximal to the femoral articular surfaces. Here, three 4.5 mm drill holes were made along the line where the chisel is inserted. This helps to prevent comminution upon introduction of the chisel. The chisel was driven from medial to lateral to a depth of 50mm. This is usually dependent on the size of the distal part of the femur and the blade-plate chosen and can sometimes reach a depth of 70mm. After the chisel was inserted, anteroposterior and lateral radiographs were again taken to ensure correct positioning, shown in Figure 3. Visualization through the medial arthrotomy was used to confirm that the chisel had not penetrated the intercondylar notch or the anterior part of the femoral articular surface. A longitudinal line (parallel to the long axis of the femur) was drawn with methylene blue on the medial part of the femoral cortex acting as a guide for rotational alignment after completion of the osteotomy. The closing wedge femoral osteotomy was completed from the medial side, proximal to the adductor tubercle and the anterior part of the femoral articular surface. A medially-based wedge of bone was removed from the distal femur with an oscillating saw. The size of the wedge at its base should be between 5 to 10mm, as reflected in this case. This wedge can be seen prior to removal and after removal in Figure 2. It is not imperative to accurately measure the base of the wedge considering the blade plate. A 90 degree blade plate can be used and screwed to the medial cortex of the distal femur. The resulting correction will render the transcondylar axis perpendicular to the axis of the femoral shaft and the tibiofemoral axis netural or slightly valgus (due to the flare of the femoral metaphysis). The lateral 145


Figure 2. Intraoperative images depict the progression of the surgery beginning from the exposure of the femoral condyles (2A). The distal femoral closing wedge is shown removed, before closing (2B) and after (2C). Finally, the blade-plate is inserted and fixated holding the closing wedge osteotomy (2D).

Figure 3. Intraoperative radiographic images using portable Stenoscop x-ray confirm that the guide wire is in place and that the chisel is parallel to the articular surface (3A). The blade-plate is inserted and checked to ensure it has followed the path of the chisel and is parallel to the articular surface (3B). Finally, before closing the incision, images are again taken in the coronal (3D) and sagittal (4D) planes after the blade-plate is in place and fixated. 146



part of the cortex was perforated with multiple drill holes. The wedge was removed and the lateral part of the cortex fractured. Only a small wedge of bone was removed, so it is possible for the proximal fragment to impact the cancellous bone of the femoral metaphysis since the diameter of the proximal cortex was less than the diameter of the distal cortex. A 90 degree offset dynamic compression blade-plate was inserted into the femur. The osteotomy was closed and, as preferable, this union was made quickly. The blade-plate was then fixed to the femur with screws. The removed wedge was saved and utilized for autograft as required. The femoral transcondylar line was now perpendicular to the long axis of the femur as desired. The fixated blade-plate can be visualized operatively in Figure 2 and radiographically in Figure 3. The tibiofemoral anatomical axis should be neutral, while the biomechanical axis approximately 5 to 6 degrees varus. The vastus medialis was fastened back to the medial septum. Subcutaneous tissue and skin were then closed over suction drains and a compression dressing applied. It is important to remember that an outrigger AO compression device should not be used due to its proximity to the adductor canal (Hunter canal), endangering its contained femoral vessels.

when the dressing was changed and reduced. Ambulation on crutches without weight-bearing was allowed and active flexion of the knee began under the supervision of a physiotherapist after the removal of the cast. After union, indicated through radiography, progressive weight-bearing was implemented. X-rays were taken 2 months after the surgery to evaluate the union of the osteotomy. Good fusion was seen at the site of the osteotomy in addition to a corrected supero-lateral tilt. Sagittal and coronal x-rays of the blade-plate position and corrected supero-lateral tilt can be seen in Figure 4. The blade-plate (Zimmer 90o-15-50 Cat.239-7005) can be seen slightly anterior, but had excellent fixation by the use of 4 cortical screws (Zimmer 40mm, 46mm, and two 50mm). The patient may expect to return to full activity roughly 3 to 6 months after the operation.

Acknowledgments Drew Taylor and Kyle Bohm would like to thank Dr. Allan Gross, Orthopaedic Surgeon at Mount Sinai Hospital and Professor of Surgery at the University of Toronto, for his guidance throughout the case study. In addition, we would also like to thank the rest of the orthopaedic surgical staff and Dr. Nazish Ahmed for their help throughout the project.

Results and Discussion References 1. 2. 3. 4.

5.

6.

7. 8. 9.

10. 11.

Figure 4. Post-operative x-rays taken 2 months after surgery were used to evaluate the position of the blade-plate and fusion at the site of the osteotomy. Sagittal (4A) and coronal (4B) x-rays of the blade-plate position and corrected supero-lateral tilt are presented.

12. 13. 14.

The post-operative regimen included warfarin, as a prophylaxis against deep venous thrombosis, with the first dose administered the evening prior to the operation. The right leg was immobilized for two weeks in a cylinder cast, with the immediate encouragement of isometric quadriceps contractions. One drain was left, and removed on the second day


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