Standard X-Ray Evaluation

A full-length, double-stance AP x-ray is mandatory to evaluate femorotibial alignment (Fig. 19-1), as described by Moreland and coworkers.¹⁰ An AP x-ray is taken from the hips to the ankles with the patient standing and the patellae looking forward using a suitable cassette to filter the x-ray beam gradually for proper visualization of both hips and ankles.

FIGURE 19-1 Standard radiographic assessment of the knee. A, Standing AP view and posteroanterior view in 30 degrees of knee flexion (left); bilateral standing long-leg anteroposterior view from hip to ankle (center); Merchant and lateral views (right). B, Standing AP view of both limbs to calculate correction required. See text for details.

Dugdale and colleagues⁸ have proposed two methods to quantify the amount of correction to perform if a malalignment is present. In both methods, a line along the tibial plateau and its intersection with the desired mechanical axis of the lower extremity is marked (in this chapter this point is called P for simplicity). A line is traced from the center of the femoral head to P and a line is traced from the center of the tibiotalar joint to P. In the first method, the angle formed at the intersection between these two lines represents the amount of correction required. In the second method, the radiographic film is cut along the osteotomy line and along a vertical line that converges with the first. Leaving a 2-mm hinge at the medial tibial margin, the distal part of the film is rotated until the femoral head, P, and the tibiotalar joint are along the same line. The overlapping wedge margin is the amount of correction to perform. It was also demonstrated that if lateral and/or posterolateral soft tissue structures are insufficient, for every increase of 1 mm in the lateral joint line width, there is 1 degree of added varus. Supine X-rays are important to eliminate the added varus because of the deficiency of the lateral and/or posterolateral structures and to evaluate the actual amount of correction to perform. It was also shown that after HTO, the mechanical axis of the lower extremity is translated laterally—3 to 4 mm for each degree of valgus correction—and this value depends on the height of the patient. We essentially use the same technique as described earlier to estimate the correction required.

The bilateral long-leg standing view is used (see Fig. 19-1B) to calculate the desired location of the new mechanical axis. If the two intersection lines are drawn from the center of the hip and from the center of the ankle, through the lateral tibial spine or 62% of the joint, bringing these two lines together will create the new mechanical axis. The osteotomy is drawn (line A) and measured and transposed to the two intersecting lines (line A′); the amount of opening measured at that point is the amount of correction required.

A lateral x-ray view is used to evaluate posterior tibial slope. A number of methods have been reported to quantify its value. Dejour and Bonnin⁴ have recommended tracing a line along the proximal tibial anatomic axis (PTAA) and a line along the tibial plateau; the angle between these two lines is tibial slope. Moore and Harvey,¹¹ in 1974, described the tibial plateau angle. They recommended tracing a line along the anterior tibial cortex (ATC) and a line along the medial tibial plateau; the angle between these two lines is tibial slope.

Brazier and associates⁵ have proposed three other methods:

They compared these three techniques and stated that the most reliable are the PTAA and PTC methods.

Cullù and coworkers¹² have compared the various methods and found higher values for the same patients using the method described by Moore and Harvey¹¹ and lower values with the PFAA method.⁵ We recommend using the line along the articular surface of the medial tibial plateau and the anatomic axis (PTAA) for assessing the posterior slope, because it is simple and reproducible.

Stress X-Ray

The lateral stress view, according to the Telos method, was first described by Jacobsen in 1976.¹³ The patient lies in the lateral decubitus position with the knee flexed at 90 degrees and is encouraged to relax. The heel is fixed to a stand and the arm of the Telos GA II device (Telos; Weterstadt, Germany) applies a posterior force to the tibia. In this position, a lateral x-ray is taken. The test is then performed with the knee at 25 degrees of flexion.¹³ This method is important in chronic PCL-deficient knees to evaluate anterior and posterior tibial translation with regard to the femur. It is also useful to detect a fixed posterior tibial subluxation, as described by Strobel and colleagues¹⁴ in 2002; they found it to be present in 44% of patients with a PCL lesion.

The lateral stress view using the kneeling method¹⁵ also measures posterior subluxation. The patient kneels on a bench with the knee in 90 degreesof flexion; the bench supports the lower legs only up to the tibial tubercle. A lateral x-ray is taken.

In addition, a lateral stress view with hamstring contraction was described by Chassaing and associates¹⁶ in 1995. The patient lies in the lateral decubitus or seated position, with the knee at 90 degrees of flexion and the heel fixed to a stand. A lateral x-ray is taken while the patient contracts the hamstring for at least 10 seconds.¹⁷

Finally, a lateral stress view is obtained according to the gravity method described by Stäubli and Jakob in 1990.¹⁸ The patient lies in the supine position with the hip and the knee at 90 degrees of flexion, supported by an assistant, with the leg in neutral rotation. In this position, a lateral x-ray is taken.

The axial stress view described by Puddu and coworkers¹⁹ in 2000. The patient lies in the supine position, with both knees at 70 degrees of flexion, the feet plantigrade in moderate plantar flexion, and the tibia in neutral rotation. The x-ray beam is directed parallel to the longitudinal patellar axis from distal to proximal and the distance between the anterior tibial profile and the center of the femoral groove is measured. The side to side difference is the amount of posterior instability.

Jung and colleagues, in 2006,¹⁷ compared these five methods, focusing on posterior translation, side to side difference, condylar rotation, time to perform the test, and pain during the test. Considering all these factors, they stated that the most effective methods are with the Telos device at 90 degrees of knee flexion and the kneeling method, even if they are painful and time-consuming procedures. The Telos procedure is the most expensive but the most reliable for detecting a posterior tibial subluxation.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is useful to evaluate the meniscal, articular cartilage, and soft tissue (ligamentous) status of the knee. In addition, with compartment overload, there may be subchondral edema, indicating the need for unloading that compartment. Traumatic subchondral bone lesions²⁰ can easily be detected.

Indications

Varus knee with mild to moderate medial compartment osteoarthritis

Varus knee with associated medial cartilage defects (i.e., osteochondritis dissecans, osteonecrosis)

Varus knee associated with a medial meniscal transplantation

Varus knee with associated instability (ACL, PCL, PLC) and evidence of medial compartment overload or lateral or posterolateral thrust

Mild valgus deformity (may be corrected on the tibial side)

Age, activity level, status of the patellofemoral joint, gender of patient, body mass index (BMI)—relevant factors

Contraindications

Extreme deformity associated with a fixed subluxation of the tibia

Severe lateral or tricompartmental OA

Fixed flexion contracture, more than 10 to 15 degrees

Inflammatory disease

Severe osteoporosis

Severe patellofemoral osteoarthritis,²⁰ age, high BMI—relative contraindications

Lateral Closing Wedge Osteotomy (Acute Correction)

Jackson²¹ in 1958 and Wardle²² in 1962 described the earliest techniques of proximal tibial valgus osteotomies with a lateral closing wedge, but it was popularized by Coventry²³ and Insall and coworkers.²⁴ The goal is correction of alignment, as noted, which is achieved by removing a laterally based wedge of bone and closing the resultant defect. The main cited advantages of this procedure over the opening wedge technique are avoidance of the need for a bone graft, a more stable construct postoperatively allowing earlier weight bearing, and ta heoretically decreased risk of nonunion. The disadvantages of this procedure include the following: (1) difficulty in predicting the amount of correction in the coronal and sagittal planes; (2) inability to adjust the correction intraoperatively; (3) the requirement for two bone cuts; (4) violation of proximal tibiofibular joint or fibular head; and (5) palsy of the external popliteal sciatic nerve. The proximal anteromedial tibial cortex, viewed in cross section, has an oblique or triangular shape and forms an angle of 45 ± 6 degrees with the posterior margin of the tibia; the lateral tibial cortex, however, is almost perpendicular to the posterior margin of the tibia. Because of the same anatomic features, a lateral closing wedge osteotomy causes small decreases in the posterior tibial slope. However, Amendola and colleagues²⁵ have demonstrated that a lateral closing wedge HTO causes a decrease in the posterior tibial slope (Fig. 19-2).

FIGURE 19-2 A, Cross section of the tibia seen from above. Note the different angles between the medial and posterior cortices and between the lateral and posterior cortices. B, A closing wedge HTO causes a decrease in posterior tibial slope; an opening wedge HTO causes an increase in posterior tibial slope.

The technique described here is used at our institution when a lateral closing wedge osteotomy is indicated. All patients should receive a prophylactic preoperative dose of intravenous antibiotics. The patient lies in a supine position on the radiolucent operating table; the leg is draped in a sterile fashion. Setup should allow radiographic visualization of the lower limb from hips to ankles, with the fluoroscope coming in from the contralateral side. A lateral support is placed to allow the knee to rest unsupported at 90 degreesof flexion, the position used during most of the procedure. A marking pen is used to outline the fibular head, lateral joint line, patellar tendon, and tibial tubercle. The leg is raised and a tourniquet is inflated. Arthroscopy is performed to treat mechanical symptoms, evaluate articular cartilage and menisci, and occasionally to confirm the indication for HTO.⁹ We use an L-shaped skin incision with the vertical limb along the lateral edge of the tibial tubercle and the horizontal limb parallel and 1cm distal to the lateral joint line, taken posteriorly to the anterior aspect of fibular head. Dissection is carried down to expose the fascia of the anterior compartment, which is incised along the anterolateral crest of the tibia, leaving a 5-mm cuff for later closure. A Cobb elevator is used to elevate the muscle from the anterolateral surface of the tibia and the iliotibial tract is elevated from Gerdy’s tubercle proximally. The common peroneal nerve is not routinely exposed but is palpated and protected throughout the procedure.

A number of methods for treatment of the proximal tibiofibular joint have been described, including joint excision or disruption, fibular osteotomy, and excision of the fibular head. We prefer to disrupt the joint but preserve the fibular head. The proximal tibiofibular joint is exposed, the anterior capsule incised, and a curved osteotome is directed posteromedially to disrupt this articulation and mobilize the fibula so as not to impede later correction. A Z-shaped retractor is placed through this joint along the posterior aspect of the tibia to protect posterior soft tissues. It is critical that this retractor be placed directly against bone along the posterior cortex to protect the neurovascular structures.

The lateral edge of the patellar tendon is identified and a second Z retractor is placed underneath it to protect it during the osteotomy. In this way, the proximal tibia is exposed from the tibial tubercle to the posterolateral cortex and is therefore prepared for the osteotomy. In removing a laterally based wedge, an angular cutting guide can be used or a specific-sized wedge can be removed. The angled cutting jig system (Guidant) was initially described by Hofmann and colleagues²⁷; it allows for easier use of preoperative calculations and should increase the accuracy of the resultant correction. With this system, the initial step involves making two 3.5-mm drill holes parallel to and approximately 1cm distal to the joint line, across to but not through the medial cortex. A line drawn between these two holes should match the posterior slope of the tibia and the position is checked in both planes with the fluoroscope. These holes are the site of the final proximal fixation and serve as the reference for the remainder of the cuts. Two temporary pins are placed in these holes and a third hole is then drilled distal to these through the medial cortex; this allows measurement of the tibial width to guide for depth of the saw cut. Using the jig, the proximal cut of the osteotomy is performed using a calibrated saw blade to a depth 10 mm less than the measured tibial width. The first jig is removed and a second jig is used, which has a blade that lies in the first saw cut to its full depth and has angled cutting slots at 2-degree increments. The second saw cut is made through the chosen angled slot, with the jig controlling the depth of the saw cut by its position.

In making these cuts, it is important to check the position of the anterior and posterior retractors to ensure soft tissue protection and to cut the anterior and posterior cortices fully, to within 1 cm of the medial cortex. The wedge can then be removed. If initial wedge removal is incomplete, it is important to ensure complete removal of the entire wedge using a combination of curettes, rongeurs, and osteotomes before closing the osteotomy; otherwise, there is a significant risk of intra-articular fracture. It is also important to ensure that the wedge is complete to 1 cm from the medial cortex or there is a chance of the hinge opening medially, making the osteotomy unstable and potentially leading to overcorrection.

A three-holed L-shaped plate is fixed to the proximal fragment using two 6.5-mm cancellous screws through the previously drilled holes. A unicortical drill hole is then made distal to the plate in the lateral cortex; this serves as an anchoring point for a compression clamp, which is applied to the distal hole of the plate. Using this clamp, the osteotomy is closed slowly, at approximately 1 mm/min, allowing for plastic deformation of the intact medial hinge and thus a stable construct. Under fluoroscopic control, the final result is checked before the plate is secured with three 4.5-mm cortical screws distally. A drain is placed against the bone and closure is completed in layers. Fascial closure is interrupted and should attempt to cover the plate as much as possible without undue tension.

Medial Opening Wedge Osteotomy (Acute Correction)

Open wedge osteotomy has not been used as long as the lateral closing wedge osteotomy. It was first described by Hernigou and coworkers²⁶ although this technique had been used since 1951 by Debeyre. At the beginning of the 1990s, Puddu²⁸ developed a plate (Puddu plate, Arthrex spacer plate; Arthrex; Naples, Fla), which supports osteotomy surfaces internally by metal spacers (wedges) to prevent further collapse and that has metal blocks (spacer teeth). In 2000, Fowler and colleagues²⁹ modified Puddu’s open wedge osteotomy technique. The most recent modification is lower profile and is a six-hole spacer plate (ContourLock HTO plate; Arthrex). The TomoFix plate (internal plate fixator, plate fixator, or rigid plate fixation; Synthes; West Chester, Pa) was developed by Lobenhoffer and colleagues.³⁰ In addition, a C plate or T plate can be used.

The theoretical advantages of opening wedge over closing wedge osteotomy include the restoration of anatomy with the addition of bone to the diseased medial side, the ability to achieve predictable correction in the coronal and sagittal planes, the ability to adjust correction intraoperatively, the requirement for only one bone cut, avoidance of proximal tibiofibular joint disruption and invasion of the lateral compartment, and the relative ease of combining it with other procedures, such as ACL reconstruction. The disadvantages of this procedure include the creation of a defect that requires bone graft with attendant harvest morbidity and a theoretic higher risk of nonunion, as well as the longer period of restricted weight bearing postoperatively.

Medial opening wedge osteotomy has been the preferred technique in our institution for the last 10 years for these reasons. All patients should receive a prophylactic preoperative dose of intravenous antibiotics; general endotracheal anesthesia is preferred because it allows the surgeon to get a bone block from the iliac crest, if needed. The patient lies in a supine position on the radiolucent operating table and the leg is draped in a sterile fashion; if a bone block is needed, the ipsilateral iliac crest is similarly draped. Setup should allow radiographic visualization of the lower limb from hips to ankles, different from the closing wedge osteotomy in which the fluoroscope is coming from the ipsilateral side. A lateral support is placed to allow the knee to rest unsupported at 90 degrees of flexion, the position used for much of the procedure. A marking pen is used to outline the fibular head, lateral joint line, patellar tendon, and tibial tubercle. The leg is raised and tourniquet is inflated.

Arthroscopy is performed as indicated, as with the closing wedge technique. A vertical incision is made just behind the pes anserine, between the medial border of the patellar tendon and the posterior border of the tibia. the sartorius fascia is cut to visualize the hamstring tendons. Under fluoroscopic control, a guide wire is positioned medially to laterally. The wire is placed at the level of the superior aspect of the tibial tubercle anteromedially, at about 1.5 cm below the lateral articular margin of the tibia. A cortical osteotomy is performed with an oscillating saw, inferiorly to the guide wire, and it is continued with an osteotome under fluoroscopic control (Fig. 19-3). When the osteotomy is completed, the medial tibia is opened with a wedge of a suitable width (Fig. 19-4). It is important to make the cut parallel to the joint surface in the sagittal plane, with the apex of the osteotomy at the proximal tibiofibular joint, to obviate the need for disrupting this articulation.

FIGURE 19-3 A, B, Under fluoroscopic control, a guide wire is positioned medially to laterally. The wire is placed at the level of the superior aspect of the tibial tubercle anteromedially. C, A cortical osteotomy is performed with an oscillating saw, inferior to the guide wire. D, E, F, It will be continued with an osteotome under fluoroscopic control.

FIGURE 19-4 A, B, When the osteotomy is completed, the medial tibia is opened with a wedge of a suitable width. The position of the wedge is important to correct the deformity in the sagittal plane; a wedge placed anteriorly causes an increase in the posterior tibial slope, whereas a posterior wedge tends to decrease the posterior tibial slope slightly.

Wedges have a graduated scale to quantify the angular correction achieved.⁹ The position of the wedge is important to correct the deformity on the sagittal plane; the proximal anteromedial tibial cortex, viewed in cross section, has an oblique or triangular shape and forms an angle of 45± 6 degrees with the posterior margin of the tibia. However, the lateral tibial cortex is almost perpendicular to the posterior margin of the tibia. Because of these anatomic features, a wedge placed anteriorly causes an increase in posterior tibial slope, whereas a posterior wedge tends to decrease the posterior tibial slope slightly.³¹

Anterior and posterior gaps of the osteotomy are then measured with a ruler, which is important to calculate the amount of increase in posterior tibial slope. If the anteromedial gap is half of the posteromedial gap, the slope will not change; for each millimeter of increase of the anterior gap, the posterior tibial slope will increase by 2 degrees. An image intensifier and alignment rod are used to control coronal and sagittal alignment during axial loading of the joint (Fig. 19-5). If the anterior gap is more than 1 cm, it is better to perform an osteotomy to lift up the tibial tubercle of the same amount to avoid patella infera (patella baja). When the correction in the two planes is achieved, the osteotomy is stabilized with a plate with four holes (Arthrex), with two 6.5-mm proximal cancellous screws and two 4.5-mm distal cortical screws (Fig. 19-6). Generally, to fill the osteotomy gap, a carefully shaped allograft bone block from a donor is used (Fig. 19-7). Under fluoroscopic contro,l the final result is checked before the tourniquet is deflated; hemostasis and skin suturing are then performed.⁹

FIGURE 19-5 A, B, An image intensifier and an alignment rod are used to control coronal and sagittal alignment during axial loading of the joint.

FIGURE 19-6 The osteotomy is stabilized with a plate with four holes (Arthex) with two 6.5-mm proximal cancellous screws and two 4.5-mm distal cortical screws.

FIGURE 19-7 A-D, Generally a carefully shaped bone block from a donor is used to fill the osteotomy gap.

External Fixation (Gradual Correction)

Use of an external fixator to achieve a gradual correction has been advocated by some for f large deformities, and good results have been reported with this technique.³² There are potential advantages with this technique. First, large corrections may be technically impossible with standard closing or opening wedge techniques because of excessive bone removal compromising fixation and creating deformity in the closed wedge technique, or excessive soft tissue tension in the opening wedge technique. External fixators also allow constant manipulation of the alignment during the healing process to optimize alignment.³² Circular external fixators also allow easy manipulation of angular and translational correction in all three planes, as required.

Cartilage Resurfacing Procedures

The ability of HTO to stimulate articular cartilage reparation with fibrocartilage has been reported by many authors.³³ The use of cartilage resurfacing techniques in association with HTO has the rationale of trying to achieve better cartilage regeneration and potentially better outcomes. Articular cartilage defects can be managed by marrow stimulation (e.g., subchondral drilling, abrasion arthroplasty, microfracture), autologous cultured chondrocyte implantation, osteochondral autograft transplantation (e.g., mosaicoplasty), or autogenous periosteal grafts.³⁴

The most commonly performed procedures reported in the literature are abrasion arthroplasty, microfractures, and the implantation of autologous chondrocytes. Some have demonstrated that autologous chondrocyte implantation is a management option for chondral defects, but this is contraindicated in the presence of tibiofemoral malalignment, which would impose mechanical overload to the repair tissue. For this reason, in patients with concurrent chondral defects and varus knee malalignment, we recommend correcting the malalignment with a proximal tibial osteotomy plus arthroscopic autologous chondrocyte implantation.³⁵ Some researchers have agreed that the degenerative knee can be treated by using a chondral resurfacing procedure, such as microfracture or abrasion arthroplasty, will improve results obtained with an osteotomy alone.³⁶ Akizuki and colleagues,³⁶ in a prospective study, compared the cartilage regeneration in osteoarthritic knees treated with HTO alone and HTO plus abrasion arthroplasty. At approximately 12 months after arthroscopy, they observed better regeneration in the abrasion arthroplasty group. They did not find any significant clinical difference between the two groups at 2 to 9 years of follow-up.

Matsunaga and associates³⁷ have compared patients with medial knee OA treated with proximal lateral closing wedge tibial osteotomy alone, osteotomy plus microfracture, and osteotomy plus abrasion arthroplasty. They observed that the repair of the cartilage was better in the abrasion arthroplasty group than in the other two groups at 1 year after surgery. No difference in the clinical outcome was found among the three groups at 5 years after surgery. In conclusion, all these techniques demonstrated the ability to stimulate cartilage regeneration better than osteotomy alone, but the clinical benefit has still to be demonstrated.

Meniscal Transplantation

Generally, meniscectomy results in joint overload and osteoarthritis in the long term. The use of meniscal transplantation has been popularized and described in many studies and reviews. The association of an osteotomy with meniscal transplantation proposes to relieve pain in a compromised medial compartment and protect the transplanted tissue from overload, improving its long-term viability.³⁸

The indications for unloading the compartment undergoing meniscal transplantation with an osteotomy remain author- and surgeon-dependent. Our indications and preferred techniques are as follows. We do not compare the alignment with the unaffected knee because we believe that is mandatory to protect the graft. Usually, the correction needed is small, unless a congenital deformity is present. Although overcorrection in osteoarthritic knees yields better result, it should be avoided in this case and the target should be a knee with an alignment as normal as possible.

Medial meniscus transplantation is indicated when the mechanical axis lies within that compartment on double-limb standing x-rays. The preferred technique is opening wedge HTO to correct the mechanical axis to the lateral tibial spine (do not overcorrect). Lateral meniscus transplantation is also indicated when the mechanical axis lies within that compartment on double-limb standing x-rays. The preferred technique is opening wedge distal lateral femoral osteotomy to correct the mechanical axis just to the medial tibial spine (do not overcorrect). Better results were reported when meniscal transplantation was associated with the osteotomy than with medial meniscal transplantation without osteotomy.³⁹

In conclusion, it seems logical that protecting the transplanted tissue from overloading, or at least changing the original loads that led to its failure, is a necessity. However, but the long-term clinical benefit has still to be demonstrated.

Ligament Instability

Traditionally, knee instability has been considered a contraindication. Currently however, the indications for HTO include patients with chronic ligament deficiencies and malalignment, because this procedure can change not only the coronal but also the sagittal plane of the knee. The sagittal plane modification has a significant impact on biomechanics and joint stability. Decreased posterior tibial slope causes posterior tibia translation and helps the ACL-deficient knee. Conversely, increased tibial slope causes anterior tibial translation and helps the PCL-deficient knee (Fig. 19-8). A medial opening wedge HTO increases posterior tibial slope if the plate is placed anteromedially but does not change the posterior tibial slope if the plate is placed posteromedially. A lateral closing wedge HTO that has equal anterior and posterior gaps along the lateral tibial cortex would have little effect on posterior tibial slope. Some have noted that soft tissue techniques alone, without correction of the alignment, often have poor results because a bone deformity overstresses them.⁴⁰ Furthermore, soft tissue destruction causes a decrease in neuromuscular joint control, which over time can worsen the malalignment.⁴¹ Some studies²⁶ have found satisfying results after HTO in monocompartmental knee OA and varus alignment, but there are few studies about the results of HTO in the unstable knee.^42,43 Rupture of the ACL, if untreated, leads to chronic anterior knee instability. Recurrent nonphysiologic translation-rotation movements of the unstable knee cause increased stress for menisci and cartilage, which often results in meniscal tears and medial cartilage degeneration. However, the problem of the combination of painful unicompartmental degeneration and symptomatic instability cannot be addressed by osteotomy or ACL reconstruction alone. There is no agreement in the literature about which patients require one and which require both procedures, and whether they are to be performed staged or simultaneously.^9,44

FIGURE 19-8 A, A decrease in posterior tibial slope causes posterior tibial translation and helps the ACL-deficient knee. B, An increase in tibial slope causes anterior tibial translation and helps the PCL-deficient knee.

Generally, the most common indication for simultaneous HTO and ACL replacement is anterior knee instability (chronic) in symptomatic varus malalignment. If malalignment is constitutional and no medial symptoms are present, osteotomy in addition to ACL replacement should only be performed if there is considerable meniscal loss and varus angulation is significant. The extent of unicompartmental joint degeneration should be mild. Usually, patients who are considered for the combined HTO and cruciate ligament reconstruction procedures is younger than 40 years. However, there is no absolute contraindication for the simultaneous procedure in older patients. Factors more important than age in the diagnostic assessment include the patients’ level of activity and extent of the medial degenerative changes. For example, if degeneration is advanced and the primary complaint is pain rather than instability, only HTO should be performed because in advanced osteoarthritis, tight joint play may even worsen the symptoms. In this case, a staged procedure, with HTO initially followed by ACL reconstruction if instability problems persist, may be considered.

In conclusion, chronic knee instability in varus malaligned knees with mild unicompartmental degeneration can effectively be treated by simultaneous HTO and cruciate ligament reconstruction, especially in younger patients. Patients with a varus of the knee and posterolateral instability often present the so-called hyperextension varus thrust gait; during the gait cycle, the knee with posterolateral instability tends to go in varus and hyperextend, with an increase in adduction and a decrease in abduction moments. For the treatment of a PCL- or PLC-deficient knee associated with varus malalignment to improve function and stability, recent studies on the biomechanics of the knee after HTO suggest performing this procedure before soft tissue reconstruction, because soft tissue procedures alone often give poor results. The patient should be evaluated 6 to 8 months later and, if the knee is still unstable, soft tissue reconstruction should be performed. We believe that evaluation of the deformity is essential for the treatment of complex knee instability. Before performing any type of soft tissue surgery, correct bone alignment should be determined in the coronal and sagittal planes.