Anterior Cruciate Ligament Deficiency in the Varus-Angulated Knee: Diagnosis, Surgical Techniques, and Clinical Outcomes

Authors’ note: This chapter represents a condensed version of a previously published work: Noyes FR, Barber-Westin SD. Tibial and Femoral Osteotomy for Varus and Valgus Knee Syndromes: Diagnosis, Operative Techniques, and Clinical Outcomes. In: Noyes’s Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes . 2nd ed. Philadelphia: Elsevier; 2017;773–847.

Introduction

High tibial osteotomy (HTO) is a widely accepted operation for medial tibiofemoral osteoarthritis and varus deformity of the lower extremity. The predominant indication is lower limb osseous malalignment in younger patients who have medial tibiofemoral joint pain and wish to maintain an active lifestyle. The goal is to correct the mechanical abnormality of excessive loading of the medial tibiofemoral compartment by redistributing weight-bearing loads onto the lateral compartment. Because underlying arthritis is expected to progress, it is advisable to perform HTO before the development of advanced articular cartilage deterioration. In general, HTO is avoided in knees that have more than a 15- by 15-mm area of exposed bone on both the tibial and femoral surfaces, and in knees that demonstrate (on standing 45-degrees posteroanterior [PA] radiographs) no remaining articular cartilage space in the medial compartment. A relative contraindication to HTO is increased medial slope to the medial tibial plateau in the coronal plane from advanced medial plateau concavity because HTO will not unload the medial compartment. Marked patellofemoral symptoms also contraindicate an HTO.

There are varus-angulated knees with associated symptomatic ligament deficiencies that usually involve the anterior cruciate ligament (ACL) and, in some cases, the posterolateral structures (fibular collateral ligament [FCL], popliteus muscle-tendon-ligament unit [PMTL], and posterolateral capsule). In these knees, multiple abnormalities exist to the lower limb and knee joint that must be diagnosed to devise a rational treatment program. These include the anatomic tibiofemoral osseous coronal and sagittal alignment, abnormal knee motion limits, abnormal knee positions (subluxations of the medial and lateral tibiofemoral compartments), and the corresponding specific deficiencies of the ligament structures. The goal in these patients is to first correct the varus malalignment to a neutral alignment and then proceed, usually in a staged manner, with an ACL and/or posterolateral reconstruction. Uncorrected varus malalignment increases the risk of failure of knee ligament reconstructive procedures.

The terms primary varus , double varus , and triple varus classify varus-aligned knees with associated ligament deficiencies ( Table 103.1 ). This classification system is based on the underlying tibiofemoral osseous alignment and the additional effect of separation of the lateral tibiofemoral compartment (due to deficiency of the posterolateral structures) on the overall varus lower limb alignment. A bilateral physiologic varus tibiofemoral alignment is usually present; however, in some cases, a normal tibiofemoral alignment gradually converts to varus after medial meniscectomy.

The term primary varus refers to the physiologic tibiofemoral osseous angulation and any further increase in angulation due to altered geometry (narrowing) of the medial osteocartilaginous tibiofemoral joint ( Fig. 103.1 ). As the tibiofemoral weight-bearing line (WBL) shifts into the medial compartment, increased tensile forces occur in the posterolateral structures. A combination of active and passive restraints resist separation of the lateral tibiofemoral compartment under dynamic loading conditions. If muscle forces do not provide a functional restraint from excessive lateral tensile forces, separation of the lateral tibiofemoral joint occurs during standing, walking, and running activities (lateral condylar lift-off). The term double varus knee refers to lower limb varus malalignment, resulting from two factors: tibiofemoral osseous and geometric alignment and separation of the lateral tibiofemoral compartment from deficiency of the posterolateral structures.

The term triple varus knee indicates lower limb varus malalignment resulting from three causes: tibiofemoral varus osseous malalignment, increased lateral tibiofemoral compartment separation (due to marked insufficiency of the FCL and PMTL), and varus recurvatum in hyperextension. The varus recurvatum occurs because of abnormal external tibial rotation and knee hyperextension reflecting deficiency of the posterolateral structures and possibly the ACL.

Clinical Evaluation

The physical examination to detect all of the abnormalities in the varus-angulated knee ( Table 103.2 ) includes assessment of (1) the patellofemoral joint, especially possible extensor mechanism malalignment from increased external tibial rotation and posterolateral tibial subluxation; (2) medial tibiofemoral crepitus on varus loading, indicative of articular cartilage damage; (3) pain and inflammation of the lateral soft tissues from tensile overloading; (4) gait abnormalities (excessive hyperextension or varus thrust) during walking and jogging; and (5) abnormal knee motion limits and subluxations compared with the contralateral knee.

The tibiofemoral rotation test (dial test) was first described by the senior author and is used to estimate the amount of posterior tibial subluxation. If an increase in external tibial rotation is present, it represents either a posterior subluxation of the lateral tibial plateau (indicating injury to the FCL and PMTL) or anterior subluxation of the medial tibial plateau (indicating injury to the superficial medial collateral ligament [SMCL] and posteromedial structures). In some knees, both anteromedial and posterolateral subluxations are present.

The tibiofemoral rotation test involves close observation of the location of the internal and external tibial rotation axis and comparison of the location of this axis to that in the normal knee. With posterior subluxation of the lateral tibial plateau during external tibial rotation, the examiner may detect a shift in the axis of tibial rotation to the medial tibiofemoral compartment. Alternatively, with an anterior subluxation of the medial tibial plateau, the center of tibial rotation shifts to the lateral tibiofemoral compartment as the maximal external tibial rotation position is reached. The dial test is not recommended to be performed in the prone position, because the medial or lateral subluxation cannot be detected.

Double-stance, full-length AP radiographs showing both lower extremities from the femoral heads to the ankle joints are obtained. If separation of the lateral tibiofemoral joint is observed on radiographs, it is necessary to subtract the lateral compartment opening so that the true tibiofemoral osseous alignment is determined and a valgus overcorrection at surgery is avoided. Additional radiographs include lateral at 30 degrees knee flexion, weight-bearing PA at 45 degrees knee flexion, and patellofemoral axial views. Telos medial or lateral stress radiographs may be required in select knees. The height of both patellas is measured on lateral radiographs to determine whether an abnormal patella infera or alta position exists that may be a factor in selecting an opening or closing wedge osteotomy, which would further decrease or elevate the patella position. The clinical algorithm for the preoperative clinical and radiographic assessment to determine candidates for HTO is shown in Fig. 103.2 .

Preoperative Planning