INTRODUCTION

Originally described in the German literature in the 19th century, multiple reports on knee osteotomy have appeared in the English literature over the last 50 years, most of which have detailed the proximal tibial valgus osteotomy for varus arthrosis. The popularity of these procedures decreased in the latter part of the century as confidence in the durability and outcomes of total knee replacement (TKR) improved. However, interest in osteotomy has recently undergone resurgence with the advent of biologic treatments for cartilage deterioration and loss of meniscal tissue and function.

Fewer reports have been published regarding osteotomy for valgus knee arthrosis, probably owing to the lower incidence of valgus deformity of the knee. Valgus malalignment may be either a cause or a consequence of lateral unicompartmental gonarthritis in young, active adults. Osteotomy is a biologic treatment alternative for unicompartmental disease in patients in whom TKR is undesirable owing to age, life expectancy, or activity level that 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. Opening wedge techniques generally allow a more physiologic approach and precise 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 total knee arthrosis (TKA), joint-preserving osteotomy is an appealing, yet reluctant, choice for high-demand patients with increased life expectancy and reservations about prosthetic replacement. The traditional indication for DFO is the correction of valgus limb malalignment in a knee with symptomatic lateral compartment osteoarthritis or post-traumatic arthrosis. The procedure has also gained significance as part of a joint-preserving treatment for less advanced cartilage or meniscal disease of the lateral compartment. At the authors’ institution, osteotomy has also been used increasingly to unload and optimize the biologic environment of a compartment undergoing osteochondral or meniscal transplantation. Therefore, two distinct 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 biomechanical environment, putatively protects the resultant repair tissue by correcting the underlying condition that contributed to the original lesion.

The ideal patient for DFO has an extended life expectancy, isolated lateral compartment symptoms, knee flexion greater than 90°, less than 15° of flexion contracture, no ligamentous instability, normal body mass index, and reasonable expectations. Although some have considered men to be better candidates for osteotomy than women, the authors have not found a correlation with gender and outcome. Rather, other criteria such as age, motivation, and fitness have been found to be far more critical. Other considerations when indicating DFO include age, activity level, and magnitude of deformity.

Because of the generally good clinical results and survivorship of TKR, the threshold for considering osteotomy over arthroplasty is typically patients aged 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 yr of age) 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 TKA. The 50- to 65-year-old group presents a unique challenge in determining whether osteotomy is the most appropriate treatment choice. Finally, young patients (<40 yr of age) 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 TKA 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 range of motion (>15° flexion contracture or <90° of flexion), poor motivation, or poor rehabilitation potential. Rehabilitation issues would 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 amount of cartilage loss on femoral and tibial surfaces) has, to our knowledge, not been shown to have a demonstrable effect on outcome. 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, whereas others have even shown improvement in patellofemoral symptoms with DFO.¹⁴

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. Based 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 coworkers⁸ 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.^1,11 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.¹³

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. Kapandji⁹ illustrated that the average distal femoral angle is 7% to 9% of valgus, and the average proximal tibial angle is 0% to 3% of varus, producing the overall tibiofemoral angle of 5% to 7% 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 approach 15% to 20% of valgus. Whereas 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 associates³ 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, post-traumatic arthritis, and 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, Coventry⁴ recommended that deformity of greater than 12% of tibiofemoral valgus should be corrected above the joint line in order 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.

CLINICAL EVALUATION

Radiographic Evaluation

All patients who are candidates for DFO obtain full-length, standing anteroposterior (AP) radiographs of bilateral lower extremities. In addition, standing AP views of both knees, standing posteroanterior (PA) views in 45° of flexion (Rosenberg), lateral flexion views of the knee, and patellofemoral (Merchant) views are obtained. The long-alignment films help determine the overall mechanical axis of the limb and whether the lateral compartment is experiencing overload due to overall genu valgum. The standing AP and Rosenberg views of the knee allow determination of the amount of joint space narrowing in the anterior and posterior portions of the lateral compartment, respectively. The lateral and patellofemoral views are helpful for determining the condition of the patellofemoral joint. If there is any concern, stress radiographs may be obtained to test for ligamentous stability and joint subluxation.

Critical Points RADIOGRAPHIC EVALUATION

• Full-length, standing anteroposterior (AP) radiographs of bilateral lower extremities.

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