14 Double osteotomies of the femur and the tibia
1 Introduction and definition
In addition to single osteotomies of the femur or tibia, their combination in form of a double osteotomy around the knee allows for treatment of complex deformities of the lower extremity. Double osteotomies can generally be performed in the frontal, sagittal, or transverse plane. In this chapter, the authors discuss one-stage corrections of the distal femur and proximal tibia. The overall correction of the weight-bearing line in the frontal plane is made by two simultaneous osteotomies at different levels. Precise planning and the surgical technique are the premises for achieving the desired correction [1, 2]. The same principles that apply to single osteotomies of the femur or tibia must also be applied to double osteotomies; however, a double osteotomy is a more extensive procedure. This explains why it is only indicated in well-selected cases. Originally, double osteotomy of the femur and tibia was performed to relieve pressure on a knee compartment in cases of joint degeneration . However, in patients with rheumatoid arthritis, satisfactory outcomes were not achieved with this procedure [4, 5]. Due to more recent biomechanical findings the principles of double osteotomy have been redefined [1, 6].
2 Biomechanical principles
The biomechanical principles, on which planning and correction of deformities of the lower extremity are based, have already been presented in other chapters of this book. There are some additional biomechanical considerations that need to be taken into account when planning a double osteotomy. Five aspects should be considered to analyze bone deformities around the knee:
Frontal weight-bearing axis
Sagittal leg axis
Rotational deformity of the leg
The physiological axes of the lower extremity are discussed in chapter 1 “Physiological axes of the lower limb”. The pathology is most frequently localized in the frontal plane and in the sagittal plane.
In double osteotomies for axial correction of the knee, precise planning is mandatory. Imprecise planning may aggravate the existing deformity or even cause new symptomatic deformities. For example, a slight decrease of the tibial slope in a high-tibial osteotomy can lead to severe gait disturbance with hyperextension of the knee if a distal femoral osteotomy leads to simultaneous recurvatum deformity of the femur as well.
The relevance of the midjoint line as an important third plane has been given not enough consideration in the past [1, 7]. The midjoint line (MJL) is centered between the knee baseline of the femur and the baseline of the tibial plateau and forms femorolateral and mediotibial angles of 87 ± 3° with the mechanical axis (Mikulicz line) ( Fig 14-1 ). Slight varus inclination of this knee baseline is physiological and is explained by the greater distance between the centers of the hip joints in relation to the centers of the ankle joints. During stance and gait the planes of the knee joint and ankle joint shift into a horizontal position , thus ensuring optimal biomechanical load distribution. Any correction in the frontal plane should take these patterns into consideration and should result in parallelism of the knee-joint line and the ankle-joint line as well as achieving correct loading of the joints . Frontal plane correction can result in a pathological alteration of the joint line if the correction is not performed at the site of the bone deformity, therefore leading to subsequent loading on an incorrectly aligned plane ( Fig 14-2 ). It has been possible to prove that only 31 % of patients with varus deviation of the leg have osseous deformity at the tibia only. In 59 % the varus deformity is located at the femur and in 10 % both femur and tibia are affected. The situation for valgus deformity of the leg is similar. In these cases the deformity is situated in the femur in only 22 %. In 45 % the valgus deformity is located at the tibia and in 33 % it affects both femur and tibia . The frequently quoted tenet for correction of varus malalignment at the tibia and valgus malalignment at the femur is, consequently, incorrect for about 50 % of varus and valgus joint degeneration deformities.
Cartilage can distribute mechanical loading very effectively due to the “cushion principle”. This compensatory mechanism is, however, limited with regard to shear forces . Chronic shear forces lead to overload and damage of the cartilage surface. In addition, the development of a pathological joint line (see above) may lead to overload of the capsuloligamentous structures . After biomechanically correct adjustment of the axes in the frontal plane, alterations of the joint line and/or tibial slope that have been overlooked can cause persistent symptoms . Based on his 1965 study, Coventry postulated that an inclination of the joint line in the frontal plane of up to 10° is acceptable after a correction osteotomy . A more recent study from the Mayo Clinic, conducted with a computerassisted biomechanical analysis programs (OASIS), has shown that the maximal inclination of the joint line should not exceed 4° . As a result of precise observance of the joint line, the survival rate of 8 years after double osteotomy for this prospective study was 96 %, which is comparable to the results achieved after minimally invasive implantation of a unicompartmental prosthesis. The clinical outcomes are also remarkable with a total of 85 % very good and good scores for double osteotomy.
Several authors held the opinion that combined deformities of the femur and tibia had to be corrected at both levels, otherwise the pathology would partially remain or be aggravated [7–9, 11]. Correction at only one level (the femur alone or the tibia alone) may achieve correction of the overall leg axis in patients with combined tibial and femoral deformities, but may simultaneously result in an alteration of the joint line beyond the standard values. To achieve a biomechanically correct axial correction, on the one hand, and to maintain a correct joint line, on the other, requires combined femoral and tibial double osteotomy in about 10 % of patients with axial deformities around the knee [1, 2].
The fourth aspect of preoperative analysis in a correction osteotomy is the patellofemoral joint. The role of the patella in indication for axial correction is still subject of discussion. In the past, no great importance was attributed to the patella with regard to correction osteotomies. By contrast, Schoettle states “any preoperative disorder of the patella” is a contraindication for correction osteotomy . Biomechanically important parameters are the so-called Q-angle and patella contact pressure. Identification of the tibial tuberosity trochlear groove (TTTG) distance by easily reproducible CT scan diagnostics is, however, superior to measuring the Q-angle  (see chapter 15 “Rotational osteotomies of the femur and the tibia”). Correction of the leg axis, especially in rotational osteotomies can lead to a change in the TTTG distance. This must be taken into account during preoperative planning. An unphysiological gliding mechanism of the patella can be corrected by reorientation of the trochlea or by medial or lateral translation of the tibial tuberosity . Furthermore, the height of the patella is altered in both closed- and open-wedge osteotomies of the proximal tibia. In cases of a preexisting patella infera, an anterior osteotomy of the tuberosity extending distally should be combined with medial open-wedge tibial osteotomy  in order to prevent further reduction of the distance between the tip of the patella and the tibial tuberosity when the osteotomy gap is opened.
Rotational deformities of the lower extremity are the fifth aspect of preoperative analysis of correction osteotomies around the knee, and must be taken into account in the clinical and radiological examination. Preoperative clinical and radiological diagnosis of rotation deformities is discussed in detail in chapter 15 “Rotational osteotomies of the femur and the tibia”.
In a combined deformity of femur and tibia, both segments must be corrected; otherwise new bone deformities are created. Correction of only one segment (either tibia or femur) may result in a straight leg axis but may lead to a pathological alteration of the joint line.
The indication for a double osteotomy is a complex axial deformity of the leg such that correction at one level, femur or tibia, would lead to a significant deviation from the physiological orientation of the knee-joint line . A further indication for double osteotomy is the combination of an existent pathological joint-line obliquity with only slight or no axial deformity of the leg. Typical causes are hereditary cartilaginous exostosis adjacent to the growth plates, status after epiphysiodesis, or previous correction osteotomy that straightened the leg at the cost of a highly pathological joint line. These patients complain primarily of knee instability and joint pain. Persistent shear stress on the joint can rapidly lead to slackening of the collateral ligaments, which increases instability and induces knee-joint degeneration.
The indications and contraindications for double osteotomy correspond to those defined in previous chapters for single osteotomy (see chapter 9 “High-tibial open-wedge valgization osteotomy with plate fixator” and chapter 13 “Supracondylar varization osteotomy of the femur with plate fixator”). Nevertheless, in these cases, the authors are particularly meticulous in their analysis of both the deformity and the correction (see chapter 13 “Supracondylar varization osteotomy of the femur with plate fixator”). It can generally be stated that a double osteotomy should be considered if single correction would shift the midjoint line orientation beyond 90 ± 4°.
3.1 Double osteotomies for deformities around the knee
As already described, the Mikulicz line, the mechanical lateral distal femoral angle (mLDFA), and the mechanical medial proximal tibial angle (mMPTA) represent the essential characteristics of a bone deformity around the knee (see chapter 1 “Physiological axes of the lower limb”, Fig 1-5 ). The position of the midjoint line should always be measured in the weight-bearing views. The above-mentioned parameters allow correct classification of the deformity (Table 14-1).
3.2 Preoperative diagnostics
Clinical examination includes assessment of the range of motion and ligamentous laxity of the knee joint. Of special importance are the movement of the patella, the alignment of the extensor mechanism, and any instability of the patella. A rotation profile (examination protocol according to Staheli; see chapter 15 “Rotational osteotomies of the femur and the tibia”) is always included in order to exclude additional rotational deformity. Skin and soft tissue should be in good condition.
Radiological diagnosis requires x-rays of the knee in three planes and a weight-bearing view of the entire leg. A weight-bearing view in 45° knee flexion, a so-called Rosenberg view, and/or MRI may offer additional information on the extent of damage to the knee, but are not mandatory. MRI can nevertheless reveal zones of subchondral bone marrow edema (BME) as a sign of overloading, thus facilitating the decision to operate. It has been shown that for patients with varus degeneration where MRI shows BME in the medial joint compartment, there is a 4.5 times greater risk that degeneration will progress than for patients without edema. BME in knee degeneration is however a nonspecific sign and must be differentiated from other forms of BME (eg, transient bone marrow edema) [2, 18].
Stress views may be valuable if there is additional ligament instability. It is absolutely essential to take ligament laxity with asymmetrical opening of the joint gap into account during preoperative planning of the overall correction angle.
Computed tomography to evaluate the TTTG distance is required if pathological alignment of the patella is evident or suspected (see chapter 15 “Rotational osteotomies of the femur and the tibia”). Measurement of the TTTG distance allows preoperative planning of an osteotomy of the tibial tuberosity. Additional transverse CT scans at the level of the femoral neck, the distal femoral condyles, tibial head, and ankle should be obtained if an additional rotational deformity of the extremity is suspected.