Valgus Deformity Correction in Total Knee Replacement: An Overview

Abstract

The correction of deformities in valgus knee is a challenge to perform a total knee arthroplasty (TKA) for a surgeon. Approximately 10% of patients who sustain a TKA have a valgus deformity. The bone and soft tissue deformities complicate the restoration of proper alignment, positioning of components and achievement of joint stability. In the valgus knee are often present lateral femoral and tibial deficiencies, contracted lateral and elongated medial soft tissues and multiplanar deformities. Different classifications have been reported to guide surgical management and various surgical strategies have been described with variable clinical results. In relation to the severity of the deformity, different implant designs may be used. The important factors to obtain stability and longevity of TKA for good functional outcome are restoration of neutral mechanical axis and correct ligament balance.

1. Introduction

An estimated 10 to 15% of total knee arthroplasties (TKAs) are implanted for a diagnosis of valgus arthritis. Osteoarthritis is the first cause of valgus deformity, while other pathological conditions, such as posttraumatic deformities, rheumatoid disease, rickets and renal osteodystrophy, can lead to a valgus knee [1].

The valgus knee presents typical problems that must be corrected at the time of positioning of TKA. The restoration of anatomic alignment is obtained after correcting the preexisting deformities [2].

The valgus knee includes contracted lateral capsular and ligamentous structures, laxity of the medial structures and acquired or preexisting bony anatomic deficiencies [3].

The modern literature has showed the importance of ligament balancing and the procedures to obtain this balance with a range of motion (ROM) during the trial reduction of the total knee components [4].

The correct comprehension of the anatomic deformities and a meticulous clinical and radiological preoperative evaluation are fundamental for surgical management.

1.1 Alignment and bone deformities

In the valgus knee, complex deformities, such as hypoplastic lateral condyle, lateral tibial plateau bone loss, external rotation deformity of the tibia, femoral and tibial metaphyseal valgus remodeling, are present. The patellofemoral joint can be affected with lateral subluxation of the patella and trochlear blunting secondary to lateral femoral condylar wear [5].

The knee normal mechanical axis is obtained by a line that passes from the center of the hip to the center of the ankle. Normal alignment is characterized by the line that passes through the center of the knee. In the valgus knee, the center of the joint lies medial to the mechanical axis (Figure 1a–c).

Figure 1.

a) Normal mechanical and anatomic axis; b) the center of the knee is medial to the mechanical axis; and c) the knee angle is increased (source: [6]).

The anatomic axes of the femur and tibia are represented by lines down the center of their respective shafts. The anatomic femoral axis is generally 6° lateral from the femoral mechanical axis, while the mechanical and tibial shaft axes are coincident. A valgus knee is generally defined as a tibiofemoral angle >10° [7].

The TKAs mechanically aligned have a neutral coronal plane alignment and the tibial cut is orthogonal to the mechanical axis. In a valgus knee, it is important to obtain correct femoral and tibial bone cuts. The identification of the deformity based on radiographs does not provide complete information regarding the nature of the deformity, especially of the involvement of periarticular soft tissues [8].

In the valgus knee, more frequently one is interested in the lateral femoral condyle and/or the posterior aspect of the lateral tibial plateau. In the valgus misaligned knee, the posterior lateral femoral condyle is often deficient, and this determines an incorrect posterior condylar axis that can result in malrotation of the femoral component. The anteroposterior (AP) axis (Whiteside’s line) and the transepicondylar axis should be used as reference to achieve correct femoral component rotation (Figure 2a–c). Alternatively, the posterior condylar resection should be parallel to tibial cut and so orthogonal to the tibial mechanical axis [10].

Figure 2.

a) To form rectangular flexion space, after tibia has been cut perpendicular to its axis, plane of posterior femoral condylar cuts must be externally rotated approximately 3° from posterior condylar axis. b) Alignment axes in knee with normal condylar shape. Resection perpendicular to anteroposterior (AP) axis or parallel to epicondylar (epi) axis results in resection line (x) that is slightly externally rotated relative to posterior condylar (PC) axis by 3° on average. c) Hypoplastic lateral condyle causes relative internal rotation of the femoral component if the posterior condylar axis is utilized while the anteroposterior axis places it in the proper position (source: [9]).

1.2 Soft tissue deformities

The soft tissue structures interested in valgus knee are iliotibial band (ITB), lateral collateral ligament (LCL), posterolateral capsule (PLC), posterior cruciate ligament (PCL) and popliteus tendon (PT).

The alterations of these soft tissues determine lateral patellar subluxation, patellofemoral maltracking symptoms and represent the prevalent cause of postoperative knee instability (Figure 3).

Figure 3.

Lateral soft tissue involved in valgus knee.

The contraction of lateral soft tissue structures may be associated with weakening of medial collateral ligament (MCL) and sometimes MCL is incompetent when the deformity is severe [11].

1.3 Classifications

Different classifications are published for valgus knee, and they are based on the severity of the deformity and the extent of soft tissue involvement. Ranawat et al. (Figure 4) and Krackow et al. described a similar classification of valgus malalignment.

Figure 4.

Ranawat description [12].

Ranawat described three grades for valgus deformity [12]:

• Grade I (80% of all valgus knees), minimal coronal valgus deformity less than 10°, which is correctable by varus stress test and the MCL is functional and intact.

• Grade II (15% of valgus knees), the fixed coronal deformity ranges between 10° and 20° and MCL is functional but elongated.

• Grade III (remaining 5% of valgus knees), includes severe bony deformity with valgus higher than 20° with nonfunctional medial soft tissues (Figure 5a).

Figure 5.

a) Ranawat classification and b) Kracow classification.

Kracow described three types for valgus deformity [13]:

• Type I valgus deformity secondary to bone loss in the lateral compartment and soft tissue tightening with competent medial soft tissues.

• Type II mild attenuation of the medial soft tissue complex.

• Type III severe valgus deformity with alteration of the femoral and tibial joint line (Figure 5b).

2. Preoperative evaluation

Before all TKAs, the preoperative planning is mandatory, and the surgeon must inform the patients about potential peroneal palsy in cases of severe valgus deformity. Surgical management depends on the extension of deformity.

2.1 Clinical examination

Every candidate should be clinically evaluated for weight-bearing alignment, flexion contracture and ligamentous instability (Figure 6).

Figure 6.

Clinical finding (personal case).

2.2 Radiograph examination

The radiological studies include weight-bearing anteroposterior, lateral and sunrise radiographs associated to measurement of the axis deviation with long-standing views of the knee for overall coronal alignment (Figure 7a and b).

Figure 7.

a) Anteroposterior (AP) view and b) lateral view (personal case).

The radiographs need to evaluate osseous deformities, patellar abnormalities, alignment of the ipsilateral hip and soft tissue slackness.

With the lateral radiograph it is important to show posterior osteophytes that must be removed during surgery [14].

2.3 Implant types

In relation to deformity, it is important to choose the correct implant [15] such as:

• Posterior-stabilized [PS]

• Constrained condylar knee [CCK]

• Hinged

2.4 Thromboembolic prophylaxis

It is recommended to start at least 12 h before incision with enoxaparin 4000 IU (international units) and then continue the same for at least 6 weeks.

2.5 Antibiotic prophylaxis

It is recommended to start before anesthetic induction with Cefazolin 2 g ev or in case of allergies Clindamycin 600 mg ev and after 6 h second dose with Cefazolin 1 g ev or Clindamycin 600 mg ev.

3. Surgical management

It is important to arrange for a correct preparation of the operative room with sterile surgical field with skin disinfection with chlorhexidine, surgical instruments, radiology technician, anesthesiologist, room nurses (minimum 3), orthopedic surgeons (minimum 2) and a prosthetic specialist.

3.1 Medial parapatellar approach

Medial parapatellar approach is the standard approach to TKA and most surgeons prefer this technique (Figure 8).

Figure 8.

Medial parapatellar approach.

The use of this approach does not allow viewing of the posterolateral corner and releasing of tight lateral soft tissues in moderate and severe valgus knees.

In this approach, there is a difficult management of the patella disorders and if a concomitant lateral release is performed, it is possible to have an increased risk for over-release of medial soft tissues resulting in instability [16].

3.2 Lateral parapatellar approach

Lateral parapatellar approach has a better result compared to the medial approach while performing a TKA for a valgus knee (Figure 9).

Figure 9.

Lateral parapatellar approach.

There is a direct access for the release of tight lateral structures with preservation of the medial structures. This approach maximizes patellar tracking and maintains medial blood supply reducing the use of constrained implants.

In difficult cases, it is necessary to perform a tibial tubercle osteotomy to obtain a good exposition of knee articulation but then there is a possible difficulty in the soft tissue closure after alignment correction [17].

3.3 Alignment and bone resection

In a valgus knee, the femoral and tibial deformities should be corrected by bone cuts planned preoperatively. In TKA with mechanical alignment, the coronal plane alignment is neutral, and the bone cuts should be orthogonal to the mechanical axis [18].

A distal femoral bone cut is made with a moderate overcorrection to avoid repeat of medial soft tissue distending. It is important to have a correct entry point in the femoral canal, which is often more medial than varus knee.

The distal femoral resection is performed in 3° of valgus with respect to the anatomical axis compared to the typical 5°–7° of valgus used for a varus knee.

It is given to prevent undercorrection of the primary defect [19].

The tibial resection should be orthogonal to the tibial mechanical axis. The tibial resection should be confirmed with use of a guide of alignment if the planned cut is based on proximal tibial anatomy, because there can be an undercorrection of the deformity if there is unidentifiable extraarticular valgus. Conservative femoral and tibial cuts are made in cases of recurvatum or medial soft tissue swelling to allow balancing without elevating the joint line or creating a too large extension gap [20].

After the proximal tibial and distal femoral bone resections are performed, the knee is extended and distracted with a spreader demonstrating a trapezoidal extension gap [21].

For the rotational alignment of the distal femur, it is important to place an anteroposterior resection block parallel to the tibial cut surface at the same time a lamina spreader divides the posterior edge of the cutting block from the tibial cut surface. Prior to resection of the posterior femoral condylar parallel to the tibial surface, it is mandatory to verify that the tibial resection is made at 90° in relation to the long axis of the tibia and that the soft tissues are balanced in extension [22].

If a varus tibial cut or over-release of the medial soft tissue is performed, there is a risk of positioning in internal rotation the femoral component and a risk of patellar tracking problems. In case of suspected rotational malalignment, the correct alignment is checked by referencing the cutting block with respect to the anteroposterior axis of Whiteside or the transepicondylar axis (Figure 10a–c). After a correct tibial and femoral resection, a rectangular extension gap is showed (Figure 11a and b) [25].

Figure 10.

a) Normal knee distal rotation; b) valgus knee distal rotation; and c) valgus knee incorrect distal rotation (source: [23]).

Figure 11.

a) Trapezoidal space in extension prior to soft tissue release; b) rectangular extension gap after soft tissue release (source: [24]).

3.4 Soft tissue balancing

After correction of bony alignment with planned femoral and tibial cuts, it is necessary to regulate the tension of soft tissue to provide optimal balance. Soft tissue balancing is the most challenging aspect of TKA in a valgus deformity [26].

A capable lateral soft tissue release is mandatory to prevent residual valgus and patellofemoral alignment problems impeding large releases that may lead to residual instability. It is necessary to facilitate sequential releases of the ITB, popliteus (POP), LCL and lateral head of the gastrocnemius in relation to different intraoperative scenarios [27] such as:

• Tight laterally in extension: release the ITB (most common) at the joint line

• Tight in flexion and extension: release the LCL +/− popliteus from lateral epicondyle.

• Still tight in extension: release the ITB.

This works for almost all knees. In case of combined flexion contracture:

• PCL complete section

• Extra distal femur resection

• Release posterolateral capsule by multiple perforations.

• Section of lateral head of gastrocnemius

In 2004, Clarke et al. described the “pie crusting” technique to release posterolateral compartment (Figure 12a and b). Keeping the knee in extension and using a spreader to distract the femorotibial joint space, the tight structures are palpated. Using a small blade (No. 15) the capsule is incised at the level of the tibial cut of the posterior capsule, following the lateral corner anterior to the popliteal tendon. Be careful not to cut the popliteal tendon, because this resection leads to instability in flexion. The pie-crusting release is then made in a progressive step with multiple horizontal incisions involving the ITB at the tibial resection level and continuing proximally as needed reaching a rectangular gap. The LCL is occasionally involved in the pie-crusting (for the LCL, it is indicated adopt a puncturing technique using a 16-gauge needle). The transverse incision and multiple stab incisions through the lateral structures should be made with the tip of the knife blade (No. 15), and soft tissue penetration should be limited to 5 mm or less [29].

Figure 12.

a) Pie-crusting technique anatomic view; b) pie-crusting technique schematic view; c) inside-out technique anatomic view; and d) inside-out schematic view (F = femur, T = tibia, PT = popliteus tendon, PLC = posterolateral capsule, ITB = iliotibial band, and CPN = common peroneal nerve) [28]).

In 2005, Ranawat et al. developed a less extensive “inside-out” technique of soft tissues’ release (Figure 12c and d). In this procedure, the soft tissues’ balancing is obtained using an electrocautery in extension to perform a rectangular gap after bone resection. The first step is to remove peripheral osteophytes then keep the knee in extension and distraction and palpate the tight structures and then release any remnant of the posterior cruciate ligament, release the posterolateral capsule intra-articularly with electrocautery at the level of the tibial cut surface from the posterior cruciate ligament to the posterior border of the iliotibial band (electrocautery is used to prevent lesion of the peroneal nerve, which is normally located <1 cm from the articular side).

Preserve the popliteus, if possible, the iliotibial band is elongated, if necessary, from the inside to outside with multiple transverse stab incisions a few centimeters proximal to the joint line with use of the so-called pie-crusting technique, repeat these steps after manual stress testing if necessary [12].

3.5 Implant selection

There is no consensus on the degree of implant constraint that should be used in valgus knee arthroplasty. The selection of implant must be made based on the degree of joint instability and the presence of bone defects.

In Grade I of valgus knee, it is possible to use cruciate retaining (CR) implants, but it is mandatory to correct bony resections with adequate soft tissue release. When the coronal deformity is mild, but the MCL tension is inadequate, it is possible to use a PS implant [30].

In the presence of severe deformities, the mechanical stress distributed on the polyethylene can lead to premature failure of the implant. In these cases, it is recommended to use a CCK implant, which has a larger cam and stems that distribute and dissipate mechanical stress on the metaphysis and the diaphysis.

In elderly patients with severe soft tissues’ insufficiency and multiplanar instability, severe bone defects, valgus deformity greater than 20° or rheumatoid arthritis, it is mandatory to use a hinged implant [31].

• Mild valgus: CR or PS (Figure 13a–d)

• Moderate valgus: PS, may need augments (Figure 14a–d)

• Severe valgus with medial instability: constrained (TS or hinge)/stems, may need augments (Figure 15a–d)

Figure 13.

Mild valgus 10° – PS implant; a, b) preop view; c, d) post op view (personal case).

Figure 14.

Moderate valgus 19° – PS implant with tibial augment; a, b) preop view; c, d) post op view (personal case).

Figure 15.

Severe valgus 23° – CCK implant; a, b) preop view; c, d) post op view (personal case).

3.6 Closure

It is important to use an adequate suture of parapatellar tissue with the knee in 30° of flexion to avoid a patellar maltracking and accurate skin closure to avoid reduction of blood supplies (Figure 16a–e).

Figure 16.

a) Clinical finding; b) parapatellar lateral approach; c) exposure of articulation; d) trial component; and e) closure (personal case).

4. Postoperative care

The outcome of TKA is influenced by postoperative physical therapy and rehabilitation. The use of a compressive dressing decreases postoperative bleeding and the use of knee brace in extension is recommended until the recovery of quadriceps strength to ensure stability during walking.

The rehabilitation protocol includes range of motion exercises with or without the assistance of a continuous passive motion machine, lower extremity muscle strengthening concentrating on the quadriceps and gait training with weight bearing allowed in relation to specific knee reconstructions [32].

5. Complications

One of the most significant complications after TKA is the development of deep vein thrombosis (DVT). Low-molecular-weight heparin and fondaparinux have been shown to be effective in DVT prophylaxis after TKA. Infection is one of the most feared complications with reported incidence of 2 to 3% in several large series. In Medicare data, 1.5% of patients develop a periprosthetic infection in the first 2 years after TKA [33].

The other mentioned complications in patients with TKA in valgus knee are instability (2–70%), recurrent valgus (4–38%), stiffness necessitating manipulation (1–20%), wound disorders (4–13%), patellar bone problems (1–12%), patellar tracking problems (2–10%) and peroneal nerve lesions (3–4%). If peroneal nerve palsy is diagnosed, the knee should be flexed to reduce the tension compressing the nerve [34].

6. Unicompartment lateral knee replacement (UKA)

The use of lateral UKA is controversial. The patient with moderate valgus has a high mechanical load on the lateral compartment in the static phase, but this load moves to the medial compartment during the dynamic phase.

In relation to these mechanical considerations, in 2001 Ohdera et al. recommended more valgus alignment performing lateral UKA to prevent progession of medial osteoarthritis (OA).

The indications for a lateral UKA implant are symptomatic isolated lateral OA (Kellgren-Lawrence [KL] grade 2 or more), posttraumatic OA, lateral isolated osteonecrosis and absence of medial or patellar OA (KL grade lower than 2).

The contraindications for a lateral UKA implant are OA in any compartment, moderate to severe knee instability, a preoperative range of motion (ROM) <90°, flexion contracture >10° and inflammatory disease [35].

The 10% of all knees considered for a knee replacement are generally suitable for a lateral UKA. Most of the patients are female. Flexion deformity is less common compared to medial and hyperextension is sometimes seen. A lot of these patients had open or arthroscopic lateral meniscectomy in the past or avascular necrosis of the lateral femoral condyle (Figure 17a–d). Radiological diagnosis can sometimes be a challenge because standard AP views may look normal. Bone-on-bone contact is usually seen in 30°–40° of flexion in valgus stress. The Rosenberg view (posteroanterior (PA) standing X-ray in 40° of flexion) is very helpful to demonstrate this. Magnetic resonance imaging (MRI) can also confirm the diagnosis of lateral osteoarthritis; however, the status of the ACL can be misinterpreted due to osteophytes in the notch pretending that the ACL is defective [37].

Figure 17.

Unicompartment knee arthroplasty (UKA) in valgus arthritis; a, b) preop view; c, d) post op view (source: [36]).

Usually, a lateral parapatellar approach is performed. Lateral osteophytes of the patella need to be removed, however in case of a big and overhanging patella the lateral part of the patella is also resected. The tibial sagittal cut is performed through a vertical incision of the patella tendon to address internal rotation of the tibia in flexion. Special lateral tibia designs should be used to allow proper sizing of the tibial component, avoiding either undercoverage or overcoverage.

Posterior joint line is restored with the femoral component and the knee is balanced in extension. Overcorrection should be avoided as it may result in progression of medial compartment arthritis. Elevation of the joint line can lead to instability, particularly when mobile bearing implants are utilized.

A valgus alignment less than 4° after lateral UKA is correlated to poor clinical and functional results associated to higher revision rate than valgus alignment at least 4° at a mean follow-up of 8 years. In relation to these results, it is important to achieve a postoperative valgus alignment greater than 4° to obtain good results. It is mandatory to avoid an undercorrection in lateral UKA compared to medial UKA [38].

The literature has shown that patients who underwent UKA compared to TKA showed less blood loss, a decreased infection rate, a shorter length of stay, a reduced complication rate, a faster recovery, a shorter rehabilitation time and a lower morbidity rate in terms of thromboembolic events and major cardiac events as well as a lower mortality rate. Excellent clinical results and survival data of 92–98% or even 100% at a mean of 5 and 12 years are reported in the literature for fixed bearing implants [39].

7. Robotic-assisted surgery (RAS)

Total knee arthroplasty implanted for valgus knee presents many difficulties to obtain correct soft tissue balance and alignment. Robotic-assisted surgery (RAS) with navigation (NAV) represents a potential solution to help surgeons approaching these cases. Literature has showed that robotic-assisted surgery TKA (RAS-TKA) helps to improve alignment and soft tissue release compared to conventional TKA.

Previously, the RAS and NAV systems used a technology with pressure sensor to determine medial and lateral gaps at static points in full extension, 45° of flexion and 90° of flexion [40].

Recently, there are systems that measure the medial and lateral gaps dynamically through the entire range of motion of the knee. One of these systems is the BalanceBot device (Corin USA, Raynham, MA, USA).

The pins are placed in both the femur and tibia and the registration landmarks are taken through a range of motion from the full extension to approximately 110° of flexion and repeated with varus and valgus stress applied to the knee. The consequent tibial and femoral resection plan was processed by the OmniBot software.

After the cuts of femur and tibia are completed and the femur posterior osteophytes are removed, the trial components are positioned, and a new registration is taken from full extension to full flexion.

The acquired data are elaborated from OmniBot software that indicates the necessity and amount of soft tissue release made by pie crust or inside-out technique (Figure 18a–c). In the future, it is necessary to study the role of RAS to minimize the risk of peroneal nerve lesion in patients with severe bone alterations [41].

Figure 18.

a) the software indicates valgus deformity in full extension; b) the software elaborates the size of the tibial component after bone resection; and c) the software shows lateral tightness requiring a soft tissue release [41].

8. Conclusions

The TKA in valgus deformity is a challenge for the surgeon. It is important to know the femoral and tibial deformities and the mechanical axis to prevent instability and patellar disorder. It is mandatory to identify the soft tissue disorders to obtain a correction with a proper balancing. The lateral surgical approach is a better choice for TKA compared with a medial approach but it requires a long learning curve.

The most important aspect of primary total knee arthroplasty in a valgus knee is achieving soft tissue balance. Whiteside recommended sequential releases of the iliotibial band, popliteus, lateral collateral ligament and lateral head of the gastrocnemius associated with medial soft tissue advancement.

The constraint of implant must be based on the degree of joint instability and the presence of bone defects. When possible, therefore, it is advisable to use the lowest possible degree of constraint to achieve optimal stability.

In the lateral UKA, valgus alignment less than 4° is correlated to poor clinical and functional results and augmented revision rate compared to valgus alignment at least 4°. In relation to these data, the objective is to obtain a valgus alignment greater than 4° for best results. A more undercorrection is mandatory in lateral UKA compared to medial UKA.

The RAS with NAV is a new potential solution to obtain correct soft tissue releases in valgus deformity. The possibility to study in real time with RAS and NAV the soft tissue to obtain an accurate correction is an important help for the surgeon to perform a correct release and balancing.

Several complications have been reported more frequently in this subset of patients caused by lengthening the lateral aspect of the knee during lateral stabilizer release and subsequent traction. It is generally recommended that patients be evaluated carefully for symptoms postoperatively.

Postoperative physical therapy and rehabilitation greatly influence the outcome of TKA. The postoperative rehabilitation protocol includes continuous passive motion machine, quadriceps muscle strengthening and recovery of gait dynamics with weight bearing.

In conclusion, the TKA in valgus deformity necessitates the correction of bone and soft tissue deformities. The new instrumentations allow us to obtain correct bone cuts and easy alignment but do not permit an accurate ligament balance.

For the management of the soft tissue in valgus knee, there are many procedures that are not technically demanding in producing good clinical and functional results.

In the treatment of valgus knee, it is mandatory to adopt a stepwise approach to correct the bone and soft tissue deformities and it is important to decide the choice of implant in relation to preoperative instability and alignment to obtain good clinical results.

Conflict of interest

The author declares no conflict of interest.