13 Supracondylar varization osteotomy of the femur with plate fixation
The aim of varization osteotomy of the distal femur is to relieve lateral single-compartment degeneration at the knee by shifting the mechanical axis medially. Degeneration of the lateral knee with valgus deformity is a frequent consequence of subtotal or total lateral meniscectomy. Valgus deformities that are posttraumatic or subsequent to growth disorders or partial epiphyseodesis also require surgical correction.
Varization osteotomy of the distal femur can be performed by a medial closed-wedge or lateral open-wedge technique. Less frequently used dome osteotomies can also be performed in the supracondylar region of the femur. Supracondylar varization osteotomy of the femur today is generally performed as a medial closed-wedge osteotomy. Stabilization of the osteotomy is achieved by application of conventional blade plates, angular-stable plates, or insertion of a distal femoral nail .
In recent years incomplete open-wedge osteotomy through a lateral approach has gained increasing acceptance due to the development of spacer plates . The authors have, however, observed that this technique may result in disturbed bone healing and symptoms at the lateral aspect of the femur due to friction as the iliotibial tract moves over the plate. In this chapter an improved technique for medial closed-wedge osteotomy is described that involves an incomplete osteotomy and application of a special internal plate fixator.
2 Principles of medial closed-wedge femoral osteotomy
Stable osteosynthesis is of great importance in a supracondylar osteotomy of the femur as it permits undisturbed bone healing and functional rehabilitation. In addition to the angled blade plate [3–11], the curved semitubular plate [12, 13] and a more recently developed plate fixator  can be considered for osteotomy stabilization. In biomechanical investigations substantial differences have been found in the primary stability of different fixation methods, and these differences must be respected when planning postoperative rehabilitation .
Apart from the fixation technique, the type of osteotomy, its orientation and localization also play an important role in primary stability. An incomplete, medial closed-wedge osteotomy with an intact lateral bone bridge is far more stable than a complete osteotomy that cuts through the lateral cortex. In terms of closed-wedge osteotomies of the distal femur, an oblique, proximal to distal, descending osteotomy will yield greater primary stability than a transverse osteotomy since the osteotomy surfaces are more congruent and the medial cortical support is more secure [12, 15]. Primary stability is also markedly increased by compression of the osteotomy surfaces, whereby optimal cortical contact is essential for effective compression to avoid risk of overcorrection due to subsidence of the distal fragment into the proximal fragment. Compression also accelerates bone healing and prevents delayed union and nonunion.
Type, direction, and localization of the osteotomy as well as the fixation technique are very important for the primary stability of the osteotomy. An incomplete medial closedwedge osteotomy with an intact lateral cortical bridge is far more stable than an osteotomy that cuts through the bone bridge. Oblique, proximal to distal descending osteotomies are more stable than transverse osteotomies.
3 Design of the fixed-angle plate fixator TomoFix MDF
The specific plate fixator TomoFix MDF was developed in collaboration with the Knee Expert Group (KNEG) of the AO. It is a special “spoon-shaped” locking compression plate (LCP) that has four threaded holes in the distal part and four combination holes in the proximal shaft ( Fig 13-1 ). Alignment and angulation of the distal threaded holes are designed to fit the anatomy of the supracondylar zone of the distal femur. Left and right versions facilitate correct positioning of the plate in the anteromedial segment of the distal femur and secure anchorage of the locking head screws in the condylar block. Utilization of an LCP guide sleeve to predrill the screw holes ensures correct alignment of the distal locking head screws. The screws are inserted with the torque screwdriver and locked at a fixed angle in the conical threaded hole. Self-tapping locking head screws are inserted in the distal part and self-tapping/selfdrilling locking head screws combined with self-tapping screws with predrilling in the proximal part. The proximal locking head screws can be anchored mono- or bicortically ( Fig 13-2 ). Secondary correction loss during screw tightening is avoided since the fixed-angle locking head screws do not develop a lag screw effect. This feature permits stable fixation of the TomoFix plate fixator even in osteoporotic bone. Temporary insertion of a 3 mm spacer in the most proximal plate hole preserves the periosteal blood flow.
4 Indications and contraindications
The indication for varization osteotomy of the distal femur and plate fixation is lateral single-compartment degeneration at the knee with valgus deformity of the lower extremity The patient should have a desire to be active and should not be older than 55 (female) to 60 (male) years of age. The procedure can be combined with other reconstructive measures in the lateral compartment, eg, osteochondral autogenous transplantation (OATS), autogenous chondrocyte transplantation (ACT), and matrix-induced autogenous chondrocyte implantation (MACI).
Relevant symptomatic valgus deformities due to growth disorders or as the result of trauma should likewise be corrected prior to the development of manifest arthrosis. Planning must always respect the need for the surface of the knee joint to be as horizontal as possible after correction. If there is a deformity at the proximal tibia in addition to the femoral deformity, a double osteotomy must be considered since isolated varization of the femur may lead to excessive deviation of the knee base-line from the horizontal, leading to long-term symptoms (see chapter 14 “Double osteotomies of the femur and the tibia”).
The preoperative range of motion at the knee should be at least extension/flexion 0-0-90°. Extension and flexion deficits can be corrected to some extent by the osteotomy involving additional wedge extraction in the sagittal plane. This requires a complete femoral osteotomy.
Contraindications include obesity loss of the inner meniscus, arthrosis, or third degree cartilage damage of the medial compartment as classified by Outerbridge , or restricted movement at the knee, especially an extension deficit greater than 15-20°. The operation should not be performed if the soft-tissue situation at the distal femur is inadequate or if there is acute or chronic infection. In addition there should be no nicotine abuse.
Indications: Single-compartment lateral joint degeneration with valgus deformity, patients aged 55-60 years.
Contraindications: Obesity, extension deficit of >20°, loss of the inner meniscus, third degree cartilage injury of the medial compartment, or manifest arthrosis, insufficient soft-tissue situation, and nicotine abuse.
5 Preoperative work-up
Correction of axial deformity by osteotomy of the distal femur requires thorough preoperative planning. Full explanation of the possible complications and risks must be given to the patient. This does not just include information on general risks such as vessel and nerve injuries, thrombosis, embolism, disturbed wound healing, early and late infections, but also the possibility of delayed bone healing. Hematoma at the distal thigh, protracted swelling, and lymph edema are often to be expected postoperatively. Despite the submuscular approach, recovery of full flexion may require a long rehabilitation period.
5.1 Preoperative diagnostics
Clinical examination includes assessment of the range of motion and the laxity of the knee ligaments. The skin and soft-tissue situation should be normal. Radiological diagnosis requires views of the knee in three planes and an x-ray of the whole leg under loading. Additional information about the extent of damage of the knee can be derived from a weight- bearing view in 45° flexion, known as the Rosenberg view, and MRI, but these procedures are not essential. Stress views may be valuable if there is also ligament laxity. It is essential to take soft-tissue and ligament laxity with asymmetrical opening of the joint into account during preoperative planning of the overall correction angle (see chapter 4 “Basic principles of osteotomies around the knee”).
Until the indication is certain, preoperative prescription of a varus brace (lateral unloader brace) may be helpful. Application of this brace should lead to a substantial decrease of symptoms. Prior to the correction or at the same operation, arthroscopy may be performed to assess the joint surfaces. The cartilage surfaces and inner meniscus should be more or less intact medially. Lateral cartilage damage is recorded in detail and frayed body or cartilaginous tissue is cut away. Sometimes microfracturing is useful for localized defects.
5.2 Radiology: preoperative planning
Currently, there is a lack of agreement on the desired realignment of the mechanical axis of the leg. One group recommends restoration of the mechanical axis to normal values (mechanical femorotibial axis 0°) , whereas other groups advocate a realignment of the mechanical axis more or less into the medial compartment. Mechanical femorotibial angles of between 1° and 3° are proposed [3, 5, 7, 8] or anatomical angles of 6-10° [4, 9–11]. The authors correct the mechanical axis to the normal position or beyond so that it lies slightly medially. In valgus deformities involving an intact lateral joint compartment, the mechanical axis of the contralateral side can be used as a reference. In patients with an oblique knee joint line, planning aims to achieve a horizontal knee baseline and normal mechanical axis after correction.
Radiological planning of a supracondylar closed-wedge femoral osteotomy is shown in Fig 13-3 . The same principles apply as for the preoperative planning of proximal tibial head osteotomy. The correction angle for the osteotomy is calculated on the basis of the preoperative x-rays and is reproduced intraoperatively with the help of an appropriate saw guide and a calibrated goniometer. In addition, the height of the osteotomy wedge base can be determined by radiological planning (taking into account the magnification factor); these measurements can be checked intraoperatively with a ruler or depth gauge.
5.3 Positioning, implants, and instruments
Closed-wedge medial femoral osteotomy is performed with the patient in the supine position and under general anesthesia, local anesthesia close to the spinal cord, or single-leg anesthesia. The patient is positioned so that hip, knee, and ankle joints can be assessed. Draping leaves the entire leg and iliac crest free so that the leg axis can be assessed intraoperatively. A sterile tourniquet is not generally necessary but, if required, it should be placed as far proximal as possible to leave sufficient room for the surgical approach. Systemic antibiotic prophylaxis is given preoperatively as a single-shot. The image intensifier for intraoperative screening is positioned on the side of the leg to be operated on, the surgeon stands on the contralateral side.
In addition to the standard instrument set for bone surgery, the following are required:
TomoFix MDF plate fixator with bicortical and monocortical locking head screws
Oscillating saw with 90 mm long, wide saw blade
Special saw guide or K-wires to mark the osteotomy
Sterile metal rod to evaluate leg axis
Sterile ruler or standard depth gauge to determine the height of the osteotomy wedge base