Valgus Malalignment: Diagnosis, Osteotomy Techniques, and Clinical Outcomes

Introduction

The use of osteotomies has decreased, particularly in North America, caused by the advent of more reliable and predictable arthroplasty solutions for younger and middle-aged patients with knee arthrosis. However, interest in osteotomy has recently undergone resurgence with the advent of cartilage repair procedures, increased understanding of multiligament knee instability in the context of malalignment, and loss of meniscal tissue and function.

Fewer reports have been published regarding osteotomy for valgus knee arthrosis when compared with varus knee arthrosis. Opening-wedge osteotomy on the medial tibial side has been well established as the procedure of choice for varus deformity malalignment. The majority of studies on femoral osteotomy have focused on medial closing-wedge procedures, and survivorship rates have varied from 64% to 87%. Small case series have reported lateral opening-wedge distal femoral osteotomy survivorship rates of 82% at 7 years and 91% at 8 years. Overall, these studies had statistically significant improvements in the functional outcomes.

Osteotomy is a biologic treatment alternative for unicompartmental disease for patients in whom total knee replacement (TKR) is undesirable owing to age, life expectancy, or activity level, which would be considered inappropriate for prosthetic replacement. In this patient population, distal femoral osteotomy (DFO) can be an appropriate joint-preserving solution that relies on the redistribution of forces in the knee joint away from a mechanically overloaded, and thus symptomatic, lateral tibiofemoral compartment. In general, opening-wedge techniques allow a smaller approach and a reliable deformity correction and have gained popularity lately to adequately address cases of dysplastic lateral femoral condyles in valgus knees as well as medial tibial plateau defects in varus gonarthrosis.

Indications

Despite less predictable pain relief and relatively inferior long-term results compared with TKR, joint-preserving osteotomy is an appealing, yet reluctant, choice for high-demand patients with increased life expectancies and reservations about prosthetic replacement. The main indication for DFO is the correction of frontal plane deformities, especially in valgus knees with lateral compartment arthrosis, posttraumatic arthrosis, and in valgus knees eligible for lateral cartilage repairs and meniscal transplantation. A second indication is to correct malalignment associated with medial ligamentous insufficiency, such as in valgus knees with valgus thrust or to unload any ligament reconstruction. A less common and reliable indication is the correction of maltracking patella caused by excessive valgus deformity. This chapter focuses on the main indication of DFO.

The DFO procedure has gained significance as part of a joint-preserving treatment for less advanced cartilage or meniscal disease of the lateral compartment. At our institution, osteotomy has also been used increasingly to unload and optimize the biologic environment of a compartment undergoing osteochondral or meniscal transplantation. Therefore different groups of patients with valgus limb malalignment may benefit from the procedure.

Primary osteotomy to correct malalignment will alleviate symptoms by reducing stresses on the articular cartilage and the underlying subchondral bone. Secondary osteotomy, adjunct to resurfacing procedures addressing osteoarticular lesions resulting from a pathologic biomechanic environment, protects the resultant repair tissue by correcting the underlying condition that contributed to the original lesion.

According to the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS) guidelines on the management of osteoarthritis of the knee before TKR , the ideal patient for DFO has isolated lateral compartment symptoms, ages 40 to 60 years, body mass index (BMI) less than 30, nonsmoker, high-demand activity but no running or jumping, alignment of less than 15 degrees valgus deformity in the distal femur, range of motion (ROM) with less than 10 degrees of extension loss, more than 90 degrees of flexion, normal medial and patellofemoral compartments, normal ligament balance, and no notch osteophytes. Although some have considered men to be better candidates for osteotomy than women, we have not found a correlation between gender and outcome.

Because of the generally good clinical results and survivorship of TKR, the threshold for considering osteotomy over arthroplasty is typically patients ages 65 and younger. Older, physically active patients may be candidates for DFO if they are expected to return to an activity level that would be inappropriate for TKR. Young, active patients (<50 years) are better candidates for joint-preserving osteotomy owing to the absence of implant-related activity restrictions despite the relatively inferior long-term results compared with TKA. In these individuals, the osteotomy should be considered a temporizing procedure amenable to possible future conversion to TKR. The 50- to 65-year-old group presents a unique challenge in determining whether or not osteotomy is the most appropriate treatment choice. Finally, young patients (<40 years) with even small amounts of valgus limb malalignment should be carefully evaluated for osteotomy when there is symptomatic loss of lateral compartment chondral or meniscal tissue. In this setting, it may be reasonable to consider (though not proven) that the osteotomy may delay the progression to more advanced arthrosis. When cartilage or meniscal restoration is performed in the lateral compartment, the adjunctive use of DFO may help protect the reconstruction as well.

Contraindications

Absolute contraindications to DFO include the presence of symptomatic medial compartment arthrosis, inflammatory arthrosis including advanced crystal-induced arthropathy, and metabolic bone disorders that would significantly interfere with osseous healing of the osteotomy. Conversely, neuromuscular disorders are not a contraindication because the osteotomy may be a more reasonable and durable operation than TKR in this setting.

Relative contraindications include severe angular deformity (consideration in these cases should be given to a double osteotomy of the distal femur and proximal tibia), limited knee ROM (>15 degree flexion contracture or <90 degrees of flexion), poor motivation, or poor rehabilitation potential. Although excessive BMI has not been proven to be a contraindication, it may be assumed that the well-described orthopedic surgical risk factors associated with obesity also apply to osteotomy, and some surgeons consider a BMI greater than 30 a relative contraindication. Rehabilitation issues of concern include the inability to follow postoperative weight-bearing restrictions and the use of drugs or substances such as nicotine that may interfere with bone healing. The extent of lateral joint arthrosis (as defined by the amount of cartilage loss on the femoral and tibial surfaces) has not, to our knowledge, been shown to have a demonstrable effect on outcome, barring frank end-stage arthrosis. Therefore we do not use the amount of radiographic or clinical joint space loss as a criterion or contraindication. The presence of patellofemoral arthrosis as a relative contraindication is controversial. Some studies have shown that arthrosis of the patellofemoral joint has no bearing on the outcome, but others have even shown improvement in patellofemoral symptoms with DFO.

Clinical Biomechanics

The weight-bearing line (WBL) of the lower extremity is defined as the line drawn from the center of the femoral head through the center of the ankle mortise. Depending on where this line crosses the knee joint, overall limb alignment is considered varus (medial to the center of the knee), valgus (lateral to the center of the knee), or neutral relative to the center of the knee. Based on morphologic studies of normal subjects with neutral overall alignment, Hsu and coworkers determined that 75% of weight-bearing forces are transmitted through the medial compartment of the knee in a one-legged simulated weight-bearing stance. Other studies have determined that 60% of the load is passed through the medial compartment during weight bearing. Alterations in the overall alignment will change these forces and create an unfavorable mechanical environment, potentially leading to injury and degeneration of the overstressed compartment that may be stopped or slowed by timely correction of the malalignment.

With a valgus deformity, the mechanical axis passes through (or lateral to) the lateral compartment of the knee, thus overburdening that compartment and leading to pain and development of arthritis. Additional pathologic features of the valgus knee include progressive posterolateral soft tissue contractures including the iliotibial band, popliteus, lateral collateral ligament, posterolateral capsule, lateral head of the gastrocnemius, lateral intermuscular septum, and long head of the biceps. In addition, these contractures may lead to attenuation of the medial collateral ligament and medial capsular laxity.

Osseous deformities should be understood in the context of “normal” anatomy and “physiologic” valgus. Kapandji illustrated that the average distal femoral angle is 7 to 9 degrees of valgus, and the average proximal tibial angle is 0 to 3 degrees of varus, producing the overall tibiofemoral angle of 5 to 7 degrees of valgus, which, after accounting for hip offset, leads to a mechanical limb axis through the center of the knee. Osseous deformities in the valgus knee are usually limited to the lateral femoral condyle, which is typically hypoplastic, thus leading to excessive distal femoral valgus. Conversely, the lateral tibial plateau is usually well preserved, except in the case of fracture.

The important distinction is that for the majority of valgus knees, the deformity lies in the distal femur and not in the tibia. In some cases, this excessive distal femoral valgus may be minimal, but in other more severe cases, the distal femoral angle can be around 15 to 20 degrees of valgus. Although the exact prevalence of valgus deformity of the knee is unknown, it is generally considered less common than varus deformity about the knee. Cooke and associates examined full-length radiographs of 167 white patients with osteoarthritis. Valgus alignment was seen in 24% and varus in 76%. In addition, valgus deformity has been noted to be more common in females, patients with inflammatory arthritis, and posttraumatic arthritis, as well as those with metabolic abnormalities such as rickets or renal osteodystrophy.

The rationale of the DFO is to correct the excessive tibiofemoral valgus by shifting the mechanical axis line from the lateral compartment to a more median or even medial position. Historically, this correction has been performed both above and below the level of the joint line. Initial reports of correction of painful valgus deformity described a proximal tibial varus-producing osteotomy. However, Coventry recommended that deformity of greater than 12 degrees of tibiofemoral valgus should be corrected above the joint line to avoid excessive joint line obliquity, which leads to increased shear stresses across the joint, ligamentous and capsular attenuation, and subsequent joint subluxation. A general rule is that the osteotomy should be performed at the site of the primary deformity, which in most patients with valgus deformity lies in the distal femur.