Introduction

The main principle of correction osteotomies is to achieve a transfer of loading from diseased, arthritic areas of the joint to areas with relatively intact, healthy cartilage. The valgus opening-wedge high tibial osteotomy (HTO) is an option for the treatment of medial varus osteoarthritis of the knee that aims to change the loading of the tibiofemoral joint by a correction of the leg axis. The degenerated medial compartment cartilage is thus decompressed, resulting in a relief of pain and a delay of cartilage damage.

Good clinical short- and mid-term results have been reported.^1–8 However, favorable results seem to be strongly dependent on a precise correction of the loading axis.⁹ Under-correction with persisting varus usually leads to poor results; overcorrection into large valgus may result in medial joint opening and rapid development of lateral osteoarthritis.¹⁰ Various recommendations on the precise amount of the valgus alignment achieved postoperatively have been published. Some authors refer to the anatomical axes of the femur and tibia and recommend a postoperative alignment of 8 to 10 degrees valgus.^1–14 Others focus on the mechanical axes of the femur and tibia and suggest a postoperative alignment of 3 to 5 degrees valgus.^5,10,15,16 However, these suggestions are based on individual clinical experiences and a few retrospective studies.

Probably the most commonly applied concept in preoperative planning is based on the work of Fujisawa et al.¹⁴ In this retrospective clinical study, preoperative and postoperative arthroscopy with a follow-up for 4 months to 6 years was performed on 54 knee joints before closing-wedge HTO, and the tibiofemoral joint cartilage was evaluated. The postoperative weight-bearing axis was correlated with changes in cartilage findings. The correction achieved postoperatively was measured with reference to the intersection of the weight-bearing axis with the tibial plateau. The tibial plateau was divided into four sections and the point of intersection assigned to the corresponding section. Fujisawa et al.¹⁴ concluded from their findings that for ideal correction the postoperative axis should lie within the lateral 30% of the tibial plateau as measured from its midpoint. From this study derived the recommendation that the weight-bearing axis should postoperatively pass through the “Fujisawa point” (i.e., it should intersect with the knee joint line at 62% of the tibial plateau width measured from its medial cortex).^17–19

Effect of Different Load Axes on Tibiofemoral Cartilage

Experimental Study of the Authors

The authors conducted an experimental study to investigate the effect of different loading axes in the frontal plane on the tibiofemoral cartilage pressure.¹⁹ Seven knee joints were tested in full extension under axial loading according to a standardized loading protocol (peak load 1000 N) in a materials testing system (MTS 858 Mini Bionix II test system, Eden Prairie, Minn.). Different loading situations of the lower leg were simulated by varying the anatomical alignment angles of the distal femur and the proximal tibia as well as the offset created by the femoral head using a specially designed and constructed fixture. The fixture was allowed to compensate for different preexisting anatomical femoral and tibial angles, and a standardized and reproducible intersection between the mechanical loading axis the knee joint line was set up for each testing. The distal end of the tibia and the proximal end of the femur were potted in cylinders attached to universal joints, which allowed frontal- and sagittal-plane movement but constrained axial rotation.

The knee joint line was measured as the width of the tibial plateau and divided into percentages along its length beginning from the medial margin of the cortex (Fig. 12-1).

FIGURE 12-1 Axial loading of the cadaveric knee joint using a specially designed fixture in a mechanical testing machine (MTS).

Accurate positioning of the load line was determined by a vertical laser beam translating the frontal plane rotation axes of the proximal and distal universal joints (Fig. 12-2). Zero percent varus alignment was defined as an offset of 0% of the width of the tibia plateau from the medial margin. Other axial alignments then tested were at 25%, 50% (neutral axis), 62% (Fujisawa point), and 75%. Subsequently, an intraligamentous opening-wedge HTO was performed in standard technique with medial approach (discussed later). The opening was standardized at 9 mm, the medial collateral ligament initially left intact, and the load axis again adjusted to 62%. Finally, the distal superficial part of the medial collateral ligament bridging the osteotomy was dissected from anterior to posterior in two stages.

FIGURE 12-2 For simulation of the loading axis, a vertically projected laser beam was used, which allowed the precise visualization of the reproduced loading axis. Opening of the osteotomy was achieved by several flat chisels tapped into the osteotomy gap.

The pressure measurements were performed using pressure-sensitive films (K-Scan 4000) and contact force (N), contact area (mm²), and contact pressure (MPa), as well as the topographical pressure distribution between the medial and lateral tibiofemoral joint were continuously recorded during the load cycle in every testing (Figs. 12-3 through 12-6).

FIGURE 12-3 Pressure-sensitive film (K-scan 4000, Tekscan) comprising two separate measuring fields inserted into the medial and lateral tibiofemoral joint space.

FIGURE 12-4 Several loading axes were simulated: varus (0%), neutral (50%), valgus (62%), and valgus (75%).

FIGURE 12-5 The valgus osteotomy was performed in an opening wedge technique from medial in a biplanar fashion.

FIGURE 12-6 The fibers of the superficial medial collateral ligament, which run across the osteotomy, have to be released distally from the tibia.

The contact pressure distribution between the medial and lateral joint compartments was shown to be clearly dependent on the different load axes. For varus deformity, about 65% of the total pressure was measured in the medial compartment and 35% in the lateral compartment (Fig. 12-7). The more laterally the load axis was shifted, the lower were the percentages for contact pressure recorded medially and the higher the lateral percentages. Surprisingly, after medial, open-wedge osteotomy with intact medial collateral ligament under a loading of 1000 N the medial percentage of contact force was considerably higher than laterally (71.4% versus 28.6%), although the load axis was in a slightly valgus position at 62% of the width of the tibial plateau. Measurement with the same mechanical loading axis (62%) without osteotomy had produced a reverse and predicted pattern of contact pressure distribution (i.e., medial contact pressure was clearly lower than lateral contact pressure). Thus, the aim of decompressing the cartilage in the medial joint compartment was not achieved by osteotomy, but instead the contact pressure was even slightly increased despite a valgus instead of a varus malalignment (0%). Even without axial loading, a certain amount of contact pressure was measured in the medial compartment with an open HTO and intact medial collateral ligament. Only after step-by-step dissection of the superficial distal portion of the medial collateral ligament was medial contact pressure reduced and the lateral contact pressure increased, reaching values that were previously recorded in the 62% position without osteotomy (Fig. 12-8). Medial decompression compared to original simulated varus alignment was also achieved.

FIGURE 12-7 Topographical pressure distribution in the medial and lateral tibiofemoral joint space after valgus opening wedge osteotomy with intact medial collateral ligament (MCL) and after successive MCL release. Valgus opening wedge osteotomy resulted in a significant increase of the medial contact pressure, which was only decompressed after complete release of the medial collateral ligament (MCL).

FIGURE 12-8 Mechanical load on the cartilage after open-wedge osteotomy (left field: medial; right field: lateral): for opening-wedge osteotomy and intact medial collateral ligament despite valgus axis (62%) significant mechanical loading in the medial compartment with contact pressure peak in the middle of the tibial plateau. After complete release of the medial collateral ligament, there is a substantial reduction in contact pressure medially and contact pressure increases laterally.

Clinical Consequences of the Study

The results of the biomechanical experiments showed that a redistribution of contact pressure from the medial to the lateral tibiofemoral compartment as intended by a correction osteotomy is possible by shifting the mechanical axis laterally. In cases of medial (or lateral) tibiofemoral cartilage degeneration, an osteotomy is an effective tool to decrease the load in the diseased joint compartment. An efficient medial decompression requires a slight valgus over-correction, as with the use of the Fujisawa point. However, the mechanical axis should not be oriented purely on the basis of “geometric” considerations without taking into account ligament tension. In a valgus high tibial osteotomy the opening-wedge technique from the medial approach, (HTO) will eventually lead to an even greater mechanical loading medially than in the original varus deformity because of excessive over-tension of the medial collateral ligament. Therefore, in this type of osteotomy, a complete release of the distal superficial medial collateral ligament is mandatory to accomplish an effective decompression of the medial joint compartment.

Indication for High Tibial Osteotomy of the Knee

An osteotomy is a biological procedure that aims to shift the peak load areas from the diseased compartment to central or contralateral joint areas. Basically the indication is a moderate monocompartmental arthritis of the knee combined with a malalignment of the leg in the frontal plane in younger patients. Most often varus malalignment results from a constitutional deformity, which is mostly located in the proximal tibia (primary varus). Often in symptomatic patients this primary varus is aggravated by medial meniscus loss or medial cartilage wear (secondary varus).

The patient should not be older than 65 to 70 years although this is not a hard criterion. The patient should not be severely overweight, and the range-of-motion should be at least 0/0/120°. Flexion contracture may be accepted if a saggital correction of the tibial slope is included in the surgical plan. Open-wedge osteotomy should not be used if leg lengthening is contraindicated and if the medial soft tissue coverage is compromised. Patella pain is not a contraindication; however, in cases with patella baja, a special type of osteotomy described later should be used. An intact lateral compartment of the knee is an obligatory prerequisite for this technique. The patient should not have lateral joint line pain, and no radiographic signs of lateral osteoarthritis should be present.

Type of Deformity and Preoperative Planning

One of the most important factors for the success of an osteotomy is the preoperative analysis of the deformity and the planning of the correction. This means that the location and the amount of the malalignment have to be investigated in a bipodal standing long leg x-ray. According to the recommendations of Paley,¹⁷ the respective angles between the mechanical axes of the femur and tibia and the joint line (mechanical medial proximal tibial angle mMPTA and mechanical lateral distal femoral angle [mLDFA]) have to be measured. A varus deformity in the tibia means that the mMPTA is less than 87 degrees; a valgus in the distal femur by definition is a result of an mLDFA less than 87 degrees.

Ideally a correction osteotomy is carried out at or at least close to the area where the deformity is located (i.e. for a varus deformity the ideal location for the correction is located in the proximal tibia).

Operative Technique

The principles of deformity correction as formulated by Paley¹⁷ should be generally respected.

Most of the HTO techniques described in the literature are lateral based closing wedge osteotomies. Mostly they require either a fibula osteotomy or a release of the proximal tibia-fibular joint. Osteosynthesis is performed on the lateral side of the tibia. Large corrections cause shortening of the leg and often a large offset of the proximal tibia, which may compromise later placement of the tibial component of a total knee replacement. Furthermore, two saw cuts are needed and only frontal plane malalignment can be corrected. The required exposure on the lateral side, including release of the extensor musculature, has the risk of damage to the peroneal nerve.

Medial open wedge HTO techniques, on the other hand, avoid muscle detachment, peroneal nerve dissection, leg shortening, and fibula osteotomy. They only require one saw cut, and corrections in the frontal plane can be combined with corrections in the sagittal plane.

For this reason, the authors’ preferred method of valgus osteotomy of the proximal tibia is the medial opening wedge technique (Fig. 12-9, A-C).

FIGURE 12-9 Operative technique for medial opening wedge valgus high tibial osteotomy. A, A transverse skin incision is made at the medial side of the proximal tibia. B, The osteotomy is made in a biplanar fashion and, C, opened medially, maintaining direct bony contact in the anterior bone surfaces behind the tibial tuberosity.

An oblique osteotomy level related to the knee joint base line should be achieved. This means that the starting point medially should be slightly above the pes anserinus and run obliquely upward to the lateral side aiming for the upper third of the proximal tibiofibular joint.

This has the advantage of avoiding a medial cortical offset, which would necessarily occur in cases of an osteotomy parallel to the knee base line. However, only the posterior two thirds (in posterior-anterior [pa] direction) of the tibial head should be intersected transversely with the anterior third including the region of the tibial tuberosity initially left intact. This is because a second osteotomy in the coronal plane angled approximately 100° related to the first and directed upward underneath the tibial tuberosity should be performed, thus creating a biplanar osteotomy. Essentially this modification has two advantages: first, interference of the transverse osteotomy with the insertion of the patellar tendon at the tibial tuberosity, which in many cases would occur, is excluded; more important, this biplanar arrangement provides additional rotational stability and an anterior restraint against the extension force created by the quadriceps tendon. Moreover, instability in the sagittal plane created by the long lever arm of the distal tibia, which is probably only insufficiently excluded by any osteosynthesis, is minimized.

For quick and safe bone healing of the osteotomy, as much “bone biology” as possible needs to be maintained at the surface areas of the osteotomy. The bone cutting should be performed with an oscillating saw using K-wires placed under fluoroscopy as guides. Continuous cold irrigation and a careful and slow sawing technique should be applied to allow the bone to preserve as much of its potential healing factors as possible.

After completion of the biplanar osteotomy leaving about 10 mm of the lateral bone intact, which serve as a hinge for opening of the wedge, the tibia is gradually opened medially. The opening should be performed little by little over several minutes, and care should be applied not to overstress this elastic lateral deformation. In our experience, this can best be achieved by subsequently inserting several adjacent flat osteotomes into the tibial head. One chisel after the other is carefully tapped into the osteotomy gap under fluoroscopic control, thus slowly spreading the medial gap open. Even larger corrections can be accomplished without damage to the lateral bone bridge using this careful technique. Another advantage is that medially at the site of the opening the integrity of the cortical edges of the osteotomy is preserved, which is important because the implant for osteosynthesis is placed here.

Sagittal tibial anatomy, namely the posterior tibial slope, has been shown to be an important factor influencing the amount of knee extension and stability in the sagittal plane. If with the osteotomy the tibial slope is increased, hyperextension in patients with genu recurvatum can be corrected. Furthermore, a growth in posterior tibial slope has been shown as cause for increased anterior tibial translation, which is unfavorable in chronic (anterior) knee instability. The mentioned effect may be desired in cases of posterior knee instability because overextension bothering these patients is minimized and posterior tibial drawer is antagonized.

Sagittal tibial anatomy has to be carefully assessed in the opening-wedge technique. Preoperatively, the slope should be measured in the lateral x-ray and determined if with the osteotomy the present slope should be maintained or a correction (increase or decrease) should be performed.

The medial collateral ligament running across the osteotomy (discussed earlier) has to be released distally from the tibia to avoid ligament related overcompression in the medial compartment after opening of the wedge. An adjustable spreader is used in the posterior part of the osteotomy to keep the gap open. The spreader can be inserted as desired anteriorly or posteriorly in the osteotomy gap and the tibial slope thus directly be accustomed, which can additionally be monitored on the fluoroscope.

Stability of the osteosynthesis after high tibial osteotomy is crucial for the outcome. It is not only important for quick and functional postoperative rehabilitation with immediate postoperative partial weight bearing but for safe healing of the osteotomy without any loss of the performed correction. Spacer plates designed by Puddu can be used to keep the osteotomy open and serve as osteosynthesis. However, they offer only minimal stability in cases of larger corrections as they cannot adequately eliminate the tremendous lever arm forces created by the quadriceps and the distal tibia. Probably this is why the authors and others have seen implant failures and nonunions in some (especially tall or obese) patients where the spacer implants were used. Therefore, in cases of larger openings (>10 mm), in tall or obese patients or in patients with minor bone stock quality, another more stable implant should be used for osteosynthesis. TomoFix (Synthes, West Chester, Pa.) is a specially designed rigid plate that serves as an internal plate fixator (Figs. 12-10 through 12-12, A-E). Angle-stabilized locking bolts, which can be positioned percutaneously, completely eliminate wobbling of the bolts within the plate, thus largely enhancing the stability of the osteosynthesis. In the case of fractures of the lateral cortex, which frequently occur in openings of more than 12 mm, a lag screw can be applied. This screw is inserted in the first plate hole distal to the osteotomy, and after fixation of the plate it is proximally advanced in a posterolateral direction. By doing so, reapproximation of the lateral cortical edges of the osteotomy can be achieved. Altogether nine locking bolts are used with the TomoFix device, with three bolts proximal and four distal to the osteotomy.

FIGURE 12-10 Rigid plate fixator for medial opening wedge osteotomy of the tibia (TomoFix). The system is anatomically precontoured to the medial proximal tibia and equipped with 4.5-mm locking bolts.

FIGURE 12-11 Percutaneous application of the plate fixator to the tibia.

FIGURE 12-12 Preoperative (A and B), direct postoperative (C and D), and postoperative after 1 year (E and F) radiographs of a valgus opening wedge osteotomy of 9 mm showing the plate TomoFix fixator and the bony healing in the wedge.

Conclusion

Osteotomy around the knee is an established procedure, which has been proven to provide significant improvement of joint function and pain level for 10 to 20 years, especially in younger patients and those with moderate cartilage degeneration. Decompression of diseased cartilage areas in cases of frontal place malalignment allows the patients to safely load and use their legs and knees and even perform sports activities and strenuous labor.

In patients with cartilage replacement procedures and a frontal plane deformity, an osteotomy eliminates hyper compression of the regenerated cartilage areas, avoiding the risk of early failure of these procedures.

Acknowledgments

The biomechanical study presented in this chapter was performed in collaboration with the Laboratory for Biomechanics and Biomaterials, Orthopaedic Hospital of the Medical University Hannover (Director: PD Dr. Christof Hurschler [Ph.D.]).