Greater than half of the patients older than 65 years have radiographic changes in the knee consistent with osteoarthritis.² Knee deformities in the arthritic patient can be classified into intra-articular and extra-articular deformity and further divided into three types. Flexible deformities are those that can be passively corrected into a neutral leg alignment. Fixed deformities are those that cannot be passively corrected. Mixed deformities may be partially correctable but are still partially fixed. Extra-articular deformity can be metaphyseal or diaphyseal. The ability to correct extra-articular deformity will depend on the magnitude of the deformity and the distance from the joint. Full-leg standing radiographs with the use of various mechanical and anatomic angles can be measured to assist in planning for these extra-articular deformities.

Pain may preclude the examiner for making a proper evaluation during the physical examination as to the nature of the patient’s deformity. Final determination as to whether the deformity is fixed or flexible should be made with the patient under anesthesia. When a large series of patients undergoing knee replacement were evaluated, less than one-third of the varus deformities that appeared fixed preoperatively were indeed fixed when the patient was anesthetized. It was only the fixed deformities that required soft-tissue releases. If a surgeon were to erroneously perform a soft-tissue release for a varus deformity that was not truly fixed, the outcome could lead to knee instability postoperatively.

Many patients with fixed varus deformities have a concomitant inability to fully extend the knee passively. Laskin noted that over 75% of patients who underwent total knee arthroplasty with a fixed varus deformity also had a fixed flexion contracture in a 10-year period of patients studied.³ Su estimated that up to 60% of the total patients undergoing total knee arthroplasty had some degree of knee flexion contracture.⁴ There is no appreciated correlation between the exact magnitude of the varus deformity and the magnitude of the flexion deformity.

Some patients have a varus deformity of the leg secondary to angulation of the femoral or tibial shaft at some distance from the knee. This is considered to be an extra-articular malalignment. Causes of this may include a malunited fracture, Paget disease, or a congenital deformity such as Blount disease or fibrous dysplasia. Other more rare underlying metabolic processes may also contribute to these deformities. Although such deformities must be taken into account when assessing overall leg alignment and surgical planning, the majority of knee deformity exists because of a pathologic process that is intra-articular or immediately adjacent to the knee joint.

The basic intra-articular cause a varus deformity is an asymmetric loss of articular cartilage or bone that is greater from the medial side than from the lateral side of the knee. Loss of cartilage often occurs from medial mechanical overload and/or a knee with abnormal kinematics. The two most common conditions are insufficient anterior cruciate ligament or prior medial meniscus surgery, such as a partial or total meniscectomy. Meniscal tears are the most common knee injury, with approximately 700,000 partial meniscectomies performed in the United States yearly.⁵,⁶,⁷ Degenerative meniscal tears are more common in patients aged 42 to 65 years and can occur from gradual loss of inherent meniscal stability, chronic wear, athletic activities, activities of daily living, and traumatic twisting injuries.⁸ The injured meniscus has an impaired ability to distribute load and resisted tibial translation. Partial or complete loss of the meniscus and meniscus stability promotes early development of chondromalacia and osteoarthritis.⁹ Medial overload may also occur in the leg with a varus hip alignment, bowing of the femoral shaft, or varus collapse after a high tibial osteotomy.

Regardless of the mechanism, the physiological process of cartilage loss medially results in increased stress to the underlying bone of the tibial plateau resulting in subchondral sclerosis. The stiffness of the subchondral bone can result in elevated stresses in the articular cartilage, naturally evolving into wear/chondromalacia and further joint line collapse. With fraying and wear of the cartilage, the synovial fluid can be pressurized into the bone surface potentially causing cystic changes to occur. Periarticular osteophytes can form as the joint degenerates, increasing the surface area through which the joint distributes force. Unlike a valgus knee, which can be associated with hypoplasia or dysgenesis of the posterior lateral and distal aspects of the lateral femoral condyle, there does not appear to be a significant difference in the shape or extent of the posterior portion of the medial femoral condyle when varus knees are compared with knees in a neutral or valgus alignment.

In addition to bony changes, the medial soft tissue around the knee also endures changes. Initially, the medial soft tissues in a patient with a varus deformity will remain relatively normal. Thus the deformity remains flexible. Through the natural progression of the varus deformity, the soft tissues medially can become contracted or pseudo-contracted, which makes the joint no longer correctable and a fixed deformity. The contracture can be accentuated by peripheral osteophyte formation both medially and posteriorly. Fixed deformity requires surgical correction techniques for adequate soft tissue balance.

Careful preoperative evaluation and planning can lead to successful management of a degenerative varus knee. Surgeons should obtain a detailed history and perform a physical exam that includes evaluation of the hip, knee, ankle, and overall limb alignment. This should also include an assessment of the quality of the soft tissue envelope surrounding the knee including the presence and location of previous incisions, stability to varus and valgus stress throughout the range of motion, the presence of flexion contracture, and the ability to correct the coronal deformity at 30° of flexion. A complete set of knee radiographs including a weight-bearing anteroposterior view, a lateral view, and a sunrise/merchant view should also be evaluated. Particular attention should be given for the presence of subchondral sclerosis, cystic changes, and osteophytes. Medial and posterior osteophytes may give indication that there is impinging soft tissue that can confound a physical examination. Consideration should be given in the preoperative planning and intraoperative surgical technique to address these medial and posterior osteophytes. Additional discussion with the patient and planning should be undertaken with options to address previous retained hardware as well as options to treat defects found from previous ligament reconstruction, for example, bone tunnels from previous ACL reconstructions.

While full-length weight-bearing films are not necessary in preoperative planning, these can assist in determining the distal valgus resection angle and the level of bony resection at both the distal femur and proximal tibia. The authors find full-length films particularly useful in patients with previous posttraumatic deformity and in short- or tall-statured individuals. Special attention should be paid to lateral radiographs with regard to the patella and tibial tuberosity. With patella baja, patellar abnormality, or prominent tibial tuberosity, surgical exposure of the knee could be more challenging due to difficulty with the version or subluxation of the patella. Consideration should be given in preoperative planning and choice of surgical instrumentation with these types of patients. It is the recommendation of these authors that surgeons use an appropriate physical examination
and radiographic evaluation (Figs. 43-1 and 43-2) when determining implant type for the planned total knee arthroplasty and always have options available for a more constrained device if needed due to significant bony deformity, ligamentous laxity, or soft-tissue imbalance.

When performing a total knee arthroplasty on a varus knee, the medial soft tissues are typically tight. Balancing therefore relies on appropriate understanding and potential release of the medial soft-tissue structures. Static stabilizers include the superficial fibers of the medial collateral ligament, posterior oblique ligament, posterior cruciate ligament, and posterior capsule. Dynamic stabilizers include the pes anserine tendons and the semimembranosus tendon. Release of anterior structures primarily affects the flexion gap, while release of posterior structures affects the extension gap.

Insall and Ranawat described the traditional method for correction of a combined varus and flexion deformity of the knee in the 1970s.¹⁰,¹¹ The correction of a varus deformity during total knee arthroplasty should be gradual and progressive, as aggressive and immediate releases can lead to an imbalance of both the extension and flexion spaces. Soft-tissue releases do not always affect flexion and extension equally and symmetrically.¹²,¹³ Careless releases of the medial or lateral structures can lead to early, mid-, and late-term knee instability. The authors encourage appropriate templating prior to total knee arthroplasty, even for the most routine of cases. This typically involves utilizing an anteroposterior view radiograph with a
vertical line drawn down the center of the femoral and tibial shafts. On the tibial shaft, a perpendicular line is drawn to the first line at the level of the tibial plateau with consideration of the relative amount of the bony resection, which can be determined based on the deformity and the ratio of the lateral to medial resection. In general, approximately 2 mm is estimated to be removed from the most involved side on the tibial plateau. On the femoral side, a horizontal line is drawn that is approximately 5° of valgus from the vertical line that was drawn previously. The valgus angle is taken into consideration with the stature of the patient and overall length of the femur. This more horizontal line passes through the most proximal point of the intracondylar notch to give an idea of the bony resection needed from the medial and lateral femoral condyles. The lateral view should be inspected for any posterior osteophytes. Osteophytes are taken in consideration for removal during the exposure, particularly paying attention to how these might affect the extension stability as well as achieving full extension considering capsular tightness from the posterior capsule. The lateral view may also be used for sizing the femoral component as part of the templating process.