INDICATIONS

High tibial osteotomy (HTO) has gained wide acceptance as a treatment option for patients with medial tibiofemoral osteoarthritis and varus deformity of the lower extremity. Most candidates are in their 3rd to 5th decade and wish to remain active and avoid unicompartmental or total knee replacement. The recommendations for this procedure are derived from a careful evaluation of subjective symptoms, findings on physical examination, radiographic evidence of malalignment and arthritis, and gait analysis when available.

The predominant indication for HTO is lower limb osseous malalignment (Fig. 31-1) 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. Varus malalignment is present when the weight-bearing line (WBL) crosses less than 50% of the mediolateral transverse width of the tibial plateau.

FIGURE 31-1 Bilateral varus malalignment in a 40-year-old man who presented with bilateral medial joint pain after 1 to 2 hours of ambulation.

Unfortunately, a prior medial meniscectomy is a major risk factor for progression of arthritis in these knees. Because any underlying arthritis is expected to progress, it is advisable to perform HTO while the joint damage is in the early stages before the development of severe articular cartilage deterioration and loss of tibiofemoral joint space.^52,113

One advantage of performing HTO in young patients who have early medial tibiofemoral arthritis after medial meniscectomy is the opportunity to also perform a meniscus transplant and a cartilage restoration procedure if indicated.

The appropriate level of physical activity that can be recommended after HTO remains questionable. Patient education is important so that activity limitations to be followed postoperatively are well understood. The goal of the osteotomy is to allow an active, pain-free lifestyle that includes low-impact recreational pursuits, but not high-loading activities such as twisting, turning, jumping, and pivoting.

The majority of patients who undergo HTO are 50 years of age or younger with varus malalignment and mild to moderate medial tibiofemoral joint arthritis. Many patients have had a prior medial meniscectomy. Patients older than 60 years are usually candidates for partial or total joint replacement. The difficult decision is the treatment recommendation for patients between 50 and 60 years of age. With the increasing longevity of unicompartmental knee replacements, patients who have advanced medial compartment damage with major areas of bone exposure will likely experience symptoms after HTO and are better candidates for partial replacement. Individuals who undergo a unicompartmental replacement may participate in recreational activities similar to those who undergo HTO. Osteotomy is performed in patients 55 years of age and younger who are athletically active, have remaining medial tibiofemoral cartilage (although thinned), and wish to maintain reasonable athletic pursuits such as tennis and skiing. These patients have early medial compartment symptoms; however, the joint damage is not advanced to a bone-on-bone state that would warrant unicompartmental replacement. Careful patient selection is the key issue, and the surgeon should not overstate or guarantee results of an HTO because the arthritis will eventually progress. In short, the goal of an HTO is to buy time in younger-aged patients (hopefully 10–15 yr) prior to joint replacement. If there is any question that the arthritis of the medial tibiofemoral compartment is advanced to where the HTO will not last 10 years, it is preferable in patients 50 years of age or older to perform a partial replacement. This is particularly true for sedentary patients in whom the goals of ambulating activities are achieved with partial joint replacement, avoiding the more prolonged postoperative recovery from an HTO.

Critical Points INDICATIONS

• Varus osseous malalignment: weight-bearing line < 50% of tibial width.

• Mild to moderate symptomatic arthrosis medial tibiofemoral compartment.

• Articular cartilage retained in medial tibiofemoral compartment.

• To achieve normal limb alignment before

Medial meniscus transplant.

Articular cartilage restorative procedures.

Cruciate ligament or posterolateral reconstruction in double and triple varus knees.

• Patients ≤ 50 yr of age, athletically active, wish to maintain reasonable athletic pursuits.

There exists a group of varus-angulated knees with associated symptomatic ligament deficiencies requiring reconstruction. These ligament deficiencies most commonly involve the anterior cruciate ligament (ACL) and posterolateral structures (fibular collateral ligament [FCL], popliteus muscle-tendon-ligament unit [PMTL], and posterolateral capsule). In these knees (double and triple varus), a normal axial alignment must be achieved before proceeding with ligament reconstructive procedures.

Lower limb varus malalignment in these knees is not overcorrected to valgus when there is no damage to the articular cartilage in the medial tibiofemoral compartment. The goal in these knees is to correct the varus to a neutral alignment and then proceed in a staged manner (if required) with a cruciate and posterolateral reconstruction as required. Correction of the varus alignment decreases the risks of failure of the ligament reconstructive procedures.^96,98,99,101

CONTRAINDICATIONS

One commonly debated issue regarding contraindications to osteotomy is the extent of damage to the medial tibiofemoral compartment. In general, HTO is avoided in knees in which there is more than a 15- × 15-mm area of exposed bone on both the tibial and the femoral surfaces. There are knees in younger patients in which the area of exposed bone may be greater and partial replacement is not an option. However, as a general rule, the remaining articular cartilage should be present over the majority of the medial joint surfaces.

Major concavity of the medial tibial plateau with loss of bone stock is a contraindication to HTO. On standing 45° posteroanterior (PA) radiographs,¹²¹ knees that demonstrate no remaining articular cartilage space to the medial compartment are not candidates. An arthroscopic procedure just before HTO helps to assess the amount of remaining articular cartilage and remove symptomatic meniscus fragments and other tissues.

Additional contraindications are a limitation of knee flexion (>10°), lateral tibial subluxation (>10 mm), prior lateral meniscectomy, or lateral tibiofemoral joint damage.

An absolute contraindication for a medial opening wedge osteotomy is the use of nicotine products in any form. The complication of a nonunion is not worth the risk, and a minimum of 8 to 12 weeks’ abstinence before surgery is required. The patient is warned that there may still be an increased risk of osteotomy healing.

A relative contraindication is a body weight over 200 pounds (91 kg) (Fig. 31-2). Although there may be some patients in whom HTO is indicated who weigh up to 225 pounds (102 kg), this operation is avoided in patients with a higher body weight because the beneficial effect of unloading the medial compartment will not be achieved.²⁸

FIGURE 31-2 Anteroposterior (AP) radiographs of the right (A) and the left (B) knees in a 45-year-old retired professional football player. The patient’s weight was 260 pounds. His chief complaint was bilateral medial joint pain with walking. The patient was advised to lose a significant amount of weight to decrease body size. In the authors’ opinion, high tibial osteotomy (HTO) is contraindicated in this case owing to the advanced medial compartment arthritis. Many athletes of large stature with varus malalignment undergo medial meniscectomy, continue athletic participation, and rather promptly lose the remaining cartilage in the medial tibiofemoral joint. An early HTO after weight loss could have been of benefit, but at this point, too much deterioration has occurred.

A relative contraindication is increased medial slope to the affected medial tibial plateau in the coronal plane due to advanced medial plateau concavity.²⁷ This finding indicates that it will not be possible to significantly unload the medial compartment with HTO, and the joint will remain with all of the weight-bearing confined to the medial compartment. This problem can be tested prior to surgery with varus-valgus stability tests at 30° knee flexion. In these knees with advanced medial arthritis, there is no neutral point in which there is simultaneous contact of the medial and lateral compartments. The tibia behaves like a teeter-totter, with contact alternating between the medial and the lateral compartment and obvious separation of the noncontacted compartment.

The issue of concurrent patellofemoral arthritis has been addressed by prior studies.^28,83,123 In general, the symptomatic state should be addressed and the patient warned preoperatively that patellofemoral symptoms might continue or progress. Marked patellofemoral symptoms would contraindicate an HTO.¹²³ The finding of asymptomatic articular cartilage changes to the patellofemoral joint is not a contraindication to HTO, because clinicians have noted that the end result in terms of longevity of the HTO depends on the symptomatic medial tibiofemoral compartment.^28,68,93

Medical contraindications to HTO include diabetes, rheumatoid arthritis, autoimmune diseases, and malnutrition states.

LOWER LIMB ALIGNMENT: PRIMARY, DOUBLE, AND TRIPLE VARUS KNEES

An added complexity in the varus-angulated knee with medial compartment arthritis is the presence of ACL deficiency. An associated deficiency of the posterolateral structures may add to the varus angulation and clinical symptoms. Patients who have these combined abnormalities often experience pain, swelling, giving-way, and functional limitations that may result in a disabling condition. In these complex knees, multiple abnormalities exist to the lower limb and knee joint that must be correctly diagnosed to outline 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 (single and combined).

The terms primary varus, double varus, and triple varus knee were devised to classify varus-aligned knees with associated ligament deficiencies (Table 31-1).⁹³ 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, as calculated from the WBL.

TABLE 31-1 Causes of Varus Angulation in the Anterior Cruciate Ligament–Deficient Knee

In patients with a varus-angulated knee, a bilateral physiologic varus tibiofemoral alignment is usually present. In others, a normal tibiofemoral alignment may convert to a varus malalignment after medial meniscectomy. With loss of the medial meniscus and resultant articular cartilage deterioration, narrowing of the medial tibiofemoral compartment occurs along with an increase in varus lower limb alignment. For example, a patient with a physiologic varus alignment of 3° (mechanical axis) with an additional loss of 3 mm of the medial articular cartilage would develop an overall 6° varus tibiofemoral alignment.

The term primary varus refers to the physiologic tibiofemoral osseous angulation and any further increase in angulation owing to altered geometry (narrowing) of the medial osteocartilagenous tibiofemoral joint (Fig. 31-3). The tibiofemoral WBL shifts into the medial tibiofemoral compartment as the narrowing progresses and the lateral compartment is unloaded. Three degrees of varus angulation approximately doubles medial compartment pressures.^36,46

FIGURE 31-3 Schematic illustration of primary, double, and triple varus knee angulation. WBL, weight-bearing line.

As the WBL shifts into the medial compartment, there are increased tensile forces in the posterolateral soft tissues, including the iliotibial tract and ligament structures. There is corresponding separation of the lateral tibiofemoral compartment during standing, walking, and running activities (lateral condylar lift-off).^75,125 This is called a double varus knee because the lower limb varus malalignment results from two factors: the tibiofemoral osseous and geometric alignment and separation of the lateral tibiofemoral compartment from deficiency of the posterolateral structures.

A combination of active and passive restraints resists separation of the lateral tibiofemoral compartment under dynamic loading conditions.^45,86 The quadriceps, biceps femoris, and gastrocnemius muscles and iliotibial band act in a dynamic manner to resist adduction moments at the knee joint during gait and, with weight-bearing loads, resist lateral tibiofemoral separation. If these muscle forces do not provide a functional restraint to excessive lateral tensile forces, separation of the lateral tibiofemoral joint occurs.

The FCL normally allows a few millimeters of separation of the tibiofemoral compartment, and pathologic stretching (interstitial injury) may occur to this ligament in chronic varus-angulated knees. Under these circumstances, a transfer of all of the weight-bearing loads to the medial compartment occurs, which can be especially deleterious if damaged articular cartilage or prior meniscectomy is present.

The patient symptoms commonly increase with pain in both the medial compartment and the lateral aspect of the knee joint owing to excessive medial compressive and lateral soft tissue tensile forces, respectively.

In the triple varus knee, injury to the FCL and posterolateral structures produces a varus recurvatum position of the limb.⁵⁴ The triple varus knee results 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 extension. The varus recurvatum occurs because of abnormal external tibial rotation and knee hyperextension reflecting deficiency of the posterolateral structures and possibly the ACL. Owing to the increase in lateral compartment opening, the WBL shifts farther medially, as shown in Figure 31-3.

HTO is indicated in patients with varus malalignment who demonstrate a varus thrust on walking. An ACL reconstruction in these knees would not address the instability and would be expected to fail if the varus osseous malalignment was not corrected owing to the abnormal lateral tibiofemoral joint opening. A varus recurvatum or back-knee instability indicates a triple varus knee in which the posterolateral structures require reconstruction along with the ACL.

Eckhoff and coworkers³⁶ reported important three-dimensional measurements in 90 individuals (180 limbs) and showed that there is considerable variation in coronal alignment between subjects and between right-left lower limbs (Fig. 31-4). One qualification to the data is that the hip-knee-ankle computed tomography (CT) measurements were obtained under non–weight-bearing conditions.

FIGURE 31-4 Histogram of the data illustrates the relative deviation of limb alignment from a straight line in the normal population of 180 limbs. Of the 90 individuals, 37 had bilateral valgus, 22 had bilateral varus, 31 had varus alignment of one limb and valgus of the other limb or varus or valgus alignment of one limb and neutral alignment of the other limb.

(Reprinted with permission from Eckhoff, D. G.; Bach, J. M.; Spitzer, V. M.; et al.: Three-dimensional mechanics, kinematics, and morphology of the knee viewed in virtual reality. J Bone Joint Surg Am 87:71–80, 2005.)

Given the variation in lower limb alignment in individuals, a frequent question is what is the effect of correcting one limb to neutral or a valgus overcorrection on overall gait and the (unoperated) opposite limb, particularly when a marked varus alignment is present bilaterally. In the authors’ experience, the opposite extremity does not require operative correction, except in a small percentage of patients who have marked bilateral varus alignment, usually medial tibiofemoral pain in the opposite extremity, and subsequently undergo HTO.

GAIT ANALYSIS

Although a high adduction moment may be anticipated as a result of varus malalignment, the moments and loads on the knee joint cannot be reliably predicted from the static measurement of lower limb alignment on radiographs.¹⁰⁹ Many factors in patients with ACL deficiency, varus malalignment, and posterolateral deficiency can be assessed by gait analysis. Abnormal limb alignment, either varus or valgus in the coronal plane or hyperextension in the sagittal plane, produces substantial alterations in the moments and forces about the knee joint (Fig. 31-5).¹⁰⁹ The analysis of external moments about the knee during gait allows the clinician to understand the effect of the altered gait dynamics on the knee joint. Abnormally high knee adduction moments increase the risk for progression of medial tibiofemoral arthritis owing to excessive loading.¹¹⁸ The success of HTO has been related to lowering these moments to below-normal values.^118,137 In addition, gait analysis allows calculation of abnormally high tensile forces in the lateral soft tissue restraints that increase the risk of elongating these tissues from lateral condylar lift-off with activity. Abnormal tensile loads on posterolateral soft tissues preclude successful FCL and PMTL reconstruction. Markholf and associates⁷⁶ reported that lateral tibiofemoral compartment loading lateral condylar lift-off had a marked effect on providing joint stability.

FIGURE 31-5 The knee adduction moment that produces medial tibiofemoral compartment loading and lateral joint tensile loads is dependent on both the mechanical axis (A) and patient gait characteristics such as the rotation of the lower limb and the foot angle at stance phase (B).

(A and B, Reprinted with permission from Andrews, M.; Noyes, F. R.; Hewett, T. E.; Andriacchi, T. P.: Lower limb alignment and foot angle are related to stance phase knee adduction in normal subjects: a critical analysis of the reliability of gait analysis data. J Orthop Res 14:289–295, 1996.)

Many studies have documented that the external moments about the knee joint and the corresponding tibiofemoral compartment loads are markedly influenced by individual gait characteristics and adaptations that occur after injury.^{5,8–11,16,23,62,85,118,137} ACL deficiency may produce marked abnormalities in moments about the knee joint in the sagittal plane, which is further affected by lower limb varus malalignment. Patients with ACL deficiency may show a decrease in the magnitude of the external flexion moment (quadriceps-reduced gait) or an increase in the external extension moment (hamstrings-protective muscle force).^6,7 These effects are discussed in Chapter 6, Human Movement and Anterior Cruciate Ligament Function: Anterior Cruciate Ligament Deficiency and Gait Mechanics. The alignment of the foot markedly influences the knee adduction moment. Patients with toe-in, or less than normal external axial rotation of the foot during stance phase, tend to have a higher knee adduction moment as the WBL passes farther medial to the knee joint.⁴

Gait analyses were conducted in a study at the authors’ institution¹⁰⁹ involving 32 patients with ACL deficiency and varus angulation. A force plate and an optoelectronic system were used to measure forces and moments of the lower limb and knee joint. Knee joint loads and ligament tensile forces were calculated using a previously described mathematical model.¹²⁵ Sixty-two percent of the patients had an abnormally high magnitude of the moment, tending to adduct the affected knee (Fig. 31-6). The calculated medial tibiofemoral loads were excessively high in 66% of the patients (P < .01). Forty-seven percent of the patients had predicted abnormally high lateral ligament tensile forces (P < .05). The adduction moment showed a statistically significant (P < .05) correlation to predicted high medial tibiofemoral compartment loads and high lateral ligament tensile forces (P < .01). A shift had occurred in the center of maximal joint pressure to the medial tibiofemoral compartment, with a corresponding increase in the lateral ligament tensile forces to achieve frontal plane stability (Figs. 31-7 and 31-8). If muscle forces are not sufficient to maintain lateral tibiofemoral compressive loads, tensile forces develop in the lateral ligament tissues. The data indicate that, in knees with high lateral ligament tensile forces, separation of the lateral tibiofemoral joint occurs with “condylar lift-off” during weight-bearing.

FIGURE 31-6 The distribution of the adduction moments during walking in the anterior cruciate ligament (ACL)–deficient knees. The cutoff value (3.30) (% body weight [BW] x height) represents the control mean minus 1 standard deviation.

(Reprinted with permission from Noyes, F. R.; Schipplein, O. D.; Andriacchi, T. P.; et al.: The anterior cruciate ligament–deficient knee with varus alignment. An analysis of gait adaptations and dynamic joint loadings. Am J Sports Med 20:707–716, 1992.)

FIGURE 31-7 A critical interaction between the dynamic muscle forces and the forces in the passive soft tissues is needed to stabilize the knee joint during walking. The knee joint remains closed laterally if either pretension in the lateral soft tissues or increased muscle force resulting from antagonistic muscle groups is present. Distances l and l₁ = 20 mm; l₂ = 60 mm. F_l, soft tissue force; F_m, F_m1, F_m2, muscle forces; M_A, adducting moment.

FIGURE 31-8 The external adducting moment is resisted by the minimum sagittal plane muscle force (F_m) and axial load acting over l. Pretension in the lateral soft tissues would maintain equilibrium if the muscle force were insufficient.

The magnitude of the flexion moment (which is related to quadriceps muscle force) was significantly lower in 47% of the patients (P < .05), and the extension moment (related to hamstring muscle force) was significantly higher in 50% (P < .05). These findings indicated that a gait adaptation occurred that diminished quadriceps muscle activity and enhanced hamstring muscle activity hypothesized to provide anteroposterior stability of the knee joint.¹⁶

Equally important in the results was the finding that approximately one third of the patients had normal or low adduction moments and corresponding normal to low medial tibiofemoral compartment loads. These patients had gait characteristics or adaptations that lowered medial tibiofemoral loads despite the varus lower limb alignment. Gait analysis allowed identification of patients with a potentially better overall prognosis; the adduction moment and medial tibiofemoral loads were not excessively high, and a HTO would result in a substantial lowering of the loads placed on the medial tibiofemoral joint.

The authors⁹⁹ studied patients with varus-angulated knees with insufficient posterolateral structures in whom prior posterolateral reconstructive procedures failed and an HTO was required before further soft tissue reconstructive procedures could be done. One explanation for these clinical findings is that these knees had a varus or hyperextension thrust during the stance phase of gait, which placed undue tensile forces on the deficient posterolateral structures (Fig. 31-9). Untreated varus malalignment has also been identified as a predisposing cause of failure of ACL reconstructions^98,101 and posterior cruciate ligament (PCL) reconstructions⁹⁶ as well.

FIGURE 31-9 An example of the increased adduction moment, medial compartment load, and lateral soft tissue force in an involved knee compared with a control knee.

(Reprinted with permission from Noyes, F. R.; Schipplein, O. D.; Andriacchi, T. P.; et al.: The anterior cruciate ligament–deficient knee with varus alignment. An analysis of gait adaptations and dynamic joint loadings. Am J Sports Med 20:707–716, 1992.)

CLINICAL EVALUATION

Diagnostic Clinical Tests

The medial posterior tibiofemoral step-off on the posterior drawer test is done at 90° of flexion (Fig. 31-10). This test is performed first to identify that the tibia is not posteriorly subluxated, indicating a partial or complete PCL tear. A KT-2000 arthrometer test may be done at 20° of flexion (134 N force) to quantify total anteroposterior (AP) displacement. The Lachman test is performed at 20° of knee flexion. The pivot shift test is done and the result recorded on a scale of 0 to 3, with a grade of 0 indicating no pivot shift; grade 1, a slip or glide; grade 2, a jerk with gross subluxation or clunk; and grade 3, gross subluxation with impingement of the posterior aspect of the lateral side of the tibial plateau against the femoral condyle.

FIGURE 31-10 Manual knee tests. A and B, Posterior drawer test at 90° knee flexion. C, Lachman test. D, Valgus manual test for medial joint opening. E, Varus manual test for lateral joint opening. Dial test at 90° of knee flexion in neutral tibial rotation (F) and maximum external tibial rotation (G). Varus recurvatum in the supine (H) and the standing (I) positions.

FCL insufficiency is determined by the varus stress test at 0° and 30° of knee flexion (see Fig. 31-10). The surgeon estimates the amount of joint opening (in millimeters) between the initial closed contact position of each tibiofemoral compartment, performed in a constrained manner avoiding internal or external tibial rotation, and the maximal opened position. The result is recorded according to the increase in the tibiofemoral compartment of the affected knee compared with that of the opposite normal knee. This comparison is crucial, and it is important to avoid measuring only the degrees of varus or valgus rotation in the involved knee.

An increase in medial joint opening may occur compared with the opposite knee that represents a pseudolaxity, because the increase is actually due to medial tibiofemoral joint narrowing. When the test is conducted under a varus stress, the medial joint opening returns the limb to a more normal alignment, and there is no true medial ligamentous damage. The true amount of medial and lateral tibiofemoral compartment opening is later confirmed during the arthroscopic examination with gap tests. The primary and secondary restraints that resist lateral joint opening have been described previously.⁴⁵ The abnormal medial joint opening depends on the knee flexion angle at which the test is conducted and the integrity of the secondary restraints.