Tibial Osteotomy

Arthritis and Malalignment

The premise of knee osteotomy surgery is to correct malalignment at the site of the deformity and relieve pressure on the overloaded or arthritic compartment. In general, medial compartment osteoarthritis of the knee coexists with a varus knee secondary to deformity in the metaphysis of the tibia. The joint line is generally horizontal to the floor. Femoral varus is unusual but may occur secondary to metabolic bone disease such as rickets or trauma but are usually excluded with long alignment x-ray images. Hence tibial osteotomy is usually performed for varus leg alignment with medial compartment overload or osteoarthritis.

Similarly, valgus malalignment of the knee with lateral compartment osteoarthritis usually coexists with deformity in the distal femur, which consists of dysplasia or hypoplasia of the lateral column of the distal femur. There is usually a superior and lateral directed joint line. Osteotomy through the distal femur thereby corrects the deformity at its location and produces a horizontal joint line. If a varus proximal tibial osteotomy was performed in this situation, further superior lateral joint line obliquity would result with the risk of subluxation of the tibia on the femur. Although Coventry described the use of proximal tibial varus osteotomy for valgus osteoarthritis of the knee, he recommended that this be performed for a deformity of less than 10 degrees and noted the risk of subluxation.

Why Osteotomy?

In 1994, the Centers for Disease Control and Prevention reported that by the year 2020 osteoarthritis will have the largest increase in numbers of new patients of any disease in the United States. Approximately 60 million Americans referred to as Baby Boomers are at risk, which is 20% of the population of the United States. Total knee arthroplasty has become one of the most commonly performed procedures with reproducibly good results in the United States. This is in part largely a result of generically designed anatomic implants with universal knee instrumentation. Prior to its development, high tibial osteotomy was commonly performed. However, in 2008, 220,000 total knee replacements were performed in patients under the age of 55 and a total of 450,000 total knee replacements were performed overall. As good as total knee replacement surgery is, patient satisfaction only remains approximately 80%. Reasons for dissatisfaction include persistent pain, stiffness, and prosthetic arthroplasty failure. Failures typically result from polyethylene osteolysis, mechanical loosening, joint infection, or problematic revision surgery secondary to ligamentous laxity or bone deficiency. The re-evaluation of joint preservation techniques have led to a resurgence of osteotomy and cartilage repair surgeries as well as more bone-sparing partial prosthetic arthroplasties.

Tibial osteotomy had been a procedure routinely performed in patients with tibial varus malalignment and medial unicompartmental disease over the age of 50 years. The average age for tibial osteotomy in the Coventry series was 63 years. Today, it would be difficult for a surgeon to do a tibial osteotomy at this age because of the reproducible long-term results with total knee arthroplasty surgery in this age category.

However, unicompartmental arthrosis is becoming prevalent among patients in their 20s, 30s, and 40s. As Baby Boomers age and activity levels remain high because of interest in sports, injuries to the anterior cruciate ligament, meniscus, and articular cartilage predispose to unicompartmental disease in patients much younger than those treated in the past. The average age of high tibial osteotomy patients for bone-on-bone medial compartment disease in my practice was 44 years old when reviewed (Harvard hip and knee course, Korbyl, Minas, 2003.). Unicompartmental and total knee arthroplasty cannot offer these patients a long-term, high functional level of activity.

Sharma et al. have demonstrated that the risk of progression of unicompartmental osteoarthritis with malalignment is four times more common in a varus knee than a neutrally aligned knee and five times more common in a valgus than a neutrally aligned knee, over an 18-month period with evidence of progression on standing radiographs. Osteoarthritis in the malaligned limb with unicompartmental disease remains a problem in young athletes and adults. Tibial osteotomy remains the procedure of choice in limbs with unicompartmental osteoarthritis with malalignment.

A long-term Swedish study evaluating the natural course of arthrosis of the knee over 20 years noted that patients with Ahlbäck stage 1 osteoarthrosis (50% joint space narrowing) would have progression of disease in 61% of the cases with 39% remaining stable without further reduction in the joint space. In patients with Ahlbäck stage 0 arthrosis, defined by osteophytes or subchondral bone sclerosis with normal joint space, 57% would not progress over time. In more advanced cases with Ahlbäck stages 2, 3, 4, and 5, the condition would progress over time.

If we are to use tibial osteotomy in our treatment algorithm to help these young patients, it is important to avoid both technique-related problems and patient-related issues that have led to the disfavor of tibial osteotomy in the past.

Technique-Related Issues Against High Tibial Osteotomy

Arthroplasty surgeons have conceptual difficulty with osteotomies because of the potential to make the arthroplasty more challenging and to compromise the results of a primary arthroplasty. Issues that have led to these problems include placement of skin incisions, patella baja, infrapatellar tendon contracture, contracture of the lateral ligament and posterolateral corner with release of the proximal tibial fibular joint, obliquity of the joint line, and distortion of the upper anatomy of the tibia (see Fig. 10.1 ). Excessive valgus correction has also resulted in difficult arthroplasty balancing of the flexion/extension gap and obtaining adequate alignment and increases the risk of peroneal nerve palsy. The total joint literature is abundant with reports of inferior outcomes following tibial osteotomy to primary total joint replacement; others report that results are equivalent but that experienced surgeons with modified surgical techniques are needed to obtain results equal to total knee replacement as a primary procedure. If we are to pursue osteotomy surgery as a treatment for our young patients undergoing cartilage repair, treatment for instability or unicompartmental arthritis, we must not compromise or make more difficult the eventuality of total knee replacement.

Patient-Related Issues

Closing wedge osteotomy with staple fixation and postoperative casting in full extension often lead to patient dissatisfaction arising predominantly from overcorrection into valgus with cosmetic disfigurement (see Fig. 10.2 ). Release of the proximal tibiofibular joint leads to lateral laxity, which results in the sensation of a sloppy knee secondary to posterior-lateral ligament instability. Cast immobilization leads to various problems for the patient and the surgeon. Patients have difficulty ambulating and challenges returning to work. The treating surgeon is faced with managing patella infera, lateral contracture, and decreased joint motion, as previously discussed. These problems can be avoided or eliminated by appropriate procedural osteotomy technique selection, patient selection, and careful pre- and postoperative planning and care. Renewed interest in joint preservation and cartilage repair has led to innovative new osteotomy techniques that are more precise and improved technical ease with reproducible results.

Procedural Planning

In a multi-variate analysis of predictors of good outcome, Coventry’s findings were that the long-term outcome was determined by the mechanical correction to 8 degrees or more of tibiofemoral valgus, and ideal body weight of the patient was less than 1.32 times normal. Rinonapoli noted that the longevity was also proportional to the stage of disease at the time of osteotomy. Updated reports with experimental cadaveric loading have demonstrated similar findings. The authors found that when tibiofemoral alignment was shifted from varus to valgus alignment, a decrease in medial contact pressure and medial contact area occurred. For defect chondral sizes of 10 to 20 mm, all contact pressures within the medial compartment were shifted to the lateral compartment at between 6 and 10 degrees of tibiofemoral valgus. Contact pressures were found to concentrate around the defect rims for all defect sizes. It was recommended that 6 to 10 degrees of tibiofemoral valgus be the optimal axial alignment to favor cartilage repair.

My experience is similar; if the patient is relatively slim, i.e., ideal body weight less than 1.32 times normal, a nonsmoker, highly motivated, and has unicompartmental medial disease with varus deformity, they are a good candidate for osteotomy surgery. An arc of range of motion of 90 degrees or better is desired. Patellofemoral symptoms can be accepted if they can be dealt with by a concomitant tibial tubercle osteotomy. Attention to clinical varus thrust and baseline leg length discrepancy is also important.

Preoperative x-ray examinations (see Fig. 10.3 ) include long axial alignment x-rays on 54” cassettes to include the hip, knee, and talus as a standing film in extension. Rosenberg 45-degree bent PA films, standing AP, lateral, and skyline films, and radiograph measurement of leg length are important.

The mechanical axis is measured from the center of the femoral head to the center of the talus. If this falls through the medial joint compartment with evidence of peripheral osteophyte formation, flattening of the articulation, subchondral bone sclerosis, and/or joint space narrowing, the patient is a candidate for osteotomy surgery if they do not have subluxation of the tibiofemoral joint or lateral symptoms. Lateral symptoms must be assessed to disprove lateral compartment degenerative changes or meniscal tear. A high-resolution MRI scan is the most sensitive method of assessing the lateral and patellofemoral compartments if in doubt. I use MRI routinely to rule out pathology in the other two compartments prior to osteotomy.

Preoperative Planning for Angular Correction of Tibial Osteotomy

Consider the normal tibiofemoral alignment of the knee; a neutral mechanical access requires that a line passes from the center of the femoral head through the center of the knee into the center of the ankle (see Fig. 10.4 ). This assumes that the neck shaft angle at the hip joint is within normal limits, 130 to 135 degrees, and that the tibiofemoral axis at the knee is 5 to 7 degrees of valgus.

My desired angular correction for medial OA ( Fig. 10.5 ) is to place the mechanical axis through the center of the lateral intercondylar spine or just to the downslope of this. This is 2 degrees overcorrected from a neutral mechanical axis. This is different from the classic teaching that the mechanical axis is recommended to pass through the Kurosaka point at 62% across the width of the tibia. I feel that this is overcorrected to a level that is cosmetically unacceptable to patients and alters the kinematics of the patient's athletic endeavors so that they are difficult to perform. If the osteotomy is performed for a cartilage repair procedure with an intact joint space, the mechanical axis should pass through the center of the knee joint and not be overcorrected. In addition to the mechanical axis, consider the tibiofemoral axis. From previous basic science research, a 6- to 10-degree tibiofemoral valgus angle is sufficient to unload a medial compartment. If there is varus in the proximal femur, the knee alignment may be markedly overcorrected by looking only at the mechanical varus of the overall leg alignment.

Assuming that the proximal femur has a normal neck shaft angle, my preferred technique to calculate the angular correction is as follows ( Fig. 10.6 ). A simple angular correction as measured on the long axial standing films is performed as follows. Pass a line from the center of the femoral head to the desired axis at the knee joint, e.g., the lateral intercondylar spine. A second line from the center of the talus then intersects this same point. The acute angle between the two is the angular correction desired. Ligamentous instability of the medial complex and anterior cruciate ligament (ACL) should be assessed so that if there is laxity it can be accounted for at the time of osteotomy to ensure that marked overcorrection does not ensue.