Preoperative Planning for Total Knee Arthroplasty





Total knee arthroplasty (TKA) is performed for millions of patients on a global scale annually. In the United States, the projected increase in annual primary TKA in 2040 is 401%, based on the National Inpatient Sample database. The increasing numbers of primary TKA being performed have resulted in more revision procedures, causing an increase in clinical and economic burden on our health care system. Common reasons for revision surgery include instability, infection, polyethylene wear, aseptic loosening, fracture, and arthrofibrosis. Of these indications for revision surgery, several early modes of failure can be prevented with appropriate preoperative planning, intraoperative decision-making, and appropriate surgical technique.


Preoperative surgical planning allows the surgeon to anticipate difficulties during surgery, prepare the surgical team for specific challenges, confirm the availability of all instrumentation and implants, and prevent complications. In this chapter, we will discuss key elements of preoperative planning and their importance for a successful patient outcome.


History


Preoperative history should include standard demographic information, pertinent medical and social history, a detailed description of symptoms, previous treatments, involvement of other joints, and prior surgery. It is also important to ascertain the patient’s current activity level, use of ambulatory devices, and postoperative goals, as expectation-outcome mismatch has potential to result in surgical dissatisfaction. Past medical history—including diabetes, obesity, cardiac disease, end-stage renal disease, and chronic organ failure—are independent risk factors for postoperative complications. Patients with a history of prior periprosthetic joint infection (PJI) are at risk for PJI with primary arthroplasty of other joints. Diabetic patients with poorly controlled glucose (Hgb A1c > 8.0%) and elevated perioperative hyperglycemia have increased risks of in-hospital and 90-day postoperative complications. Morbidly obese patients pose a significantly higher risk of complications in nearly all categories. Furthermore, there is an inverse relationship between implant longevity and body mass index. An accurate preoperative history of bleeding disorder or thromboembolism should be obtained, as this can alter anticoagulation management. Patients with inflammatory arthritis may benefit from stopping certain immunomodulators and continuing others through the perioperative period. Additionally, smoking history, opioid use, intravenous drug use, and social support system are important social factors influencing postoperative outcomes.


Common indications for TKA include osteoarthritis, inflammatory arthritis, posttraumatic arthritis, osteonecrosis of the knee, fracture, and neuropathic arthropathy. Preoperative diagnosis heavily influences surgical planning. For example, the diagnosis of posttraumatic arthritis with prior surgery may indicate the need for specialized equipment/implants, modified soft-tissue management, or deviations from the standard operative workflow. Post-polio patients and patients with neuromuscular disorders may benefit from a higher level of constraint. Patients with a history of native septic arthritis may benefit from a preoperative infectious workup and/or primary two-stage arthroplasty. Further, elderly or low-demand patients with distal femoral or proximal tibial fractures may benefit from arthroplasty to allow immediate weight bearing. There are many pathologic disease processes that may benefit from TKA, but the goals of the operation are the same: pain relief, restoration of function, stability in all planes, and long-term implant durability. Absolute contraindication to performing a TKA are the presence of an active infection within the knee, intravenous drug abuse, and the presence of soft-tissue defects surrounding the knee that are not amenable to reconstruction. History of vascular bypass surgery or peripheral vascular disease can preclude subluxation of the tibia in performing a TKA. Further, withholding the use of a tourniquet has not been shown to reduce the risk of arterial thrombosis. Relative contraindications include active infection in other areas of the body, severe quadriceps paralysis or weakness, significant nonmodifiable medical comorbidities, and severe cognitive deficits.


Physical Exam


Physical examination begins with inspection. Patients often present with an antalgic gait; however, abnormal findings such as varus thrust, hip and knee flexion contractures, drop foot, and Trendelenburg gait may influence decision-making. Coronal and sagittal standing knee alignment should also be evaluated, as the presence of femoral or tibial deformity not appreciated in standard radiographs may result in unanticipated intraoperative challenges. When significant or abnormal deformity is present, long-limb radiographs may prove helpful. Previous surgical incisions should be assessed for their ability to be incorporated into a midline incision. If there are multiple incisions, it is recommended to maintain a skin bridge ranging between 2.5 and 8 cm and to use the lateral-most incision, as the predominant vascular supply to the knee originates from the medial side. , To optimize wound healing, incisions should be made at angles greater than 60 degrees to prior incisions. The presence of prior flaps and/or grafts may benefit from plastic surgery consultation or intraoperative involvement. Finally, the presence of a large soft-tissue envelope may indicate greater surgical complexity, increased risk for wound complications, or the need for specialized wound care, such as an incision wound vac.


Palpation of the knee allows physicians to assess for intra- and extraarticular areas of tenderness, soft-tissue mobility, the presence of large synovial cysts requiring decompression during surgery, and decreased muscle bulk. Palpation allows transition into assessment of knee stability, which lends valuable information regarding ligamentous integrity and degree of deformity correction. The medial and lateral collateral ligaments are assessed with a valgus and varus stress throughout the arc of motion, respectively, and significant laxity may indicate the need for increased constraint. Conversely, patients with noncorrectable deformities may benefit from more extensive soft-tissue releases or modified implant alignment. Additionally, the presence of a significant posterior draw may preclude the ability to utilize a cruciate-retaining design.


Active and passive range of motion allows for evaluation of extensor mechanism integrity (e.g., extension lag), flexion contracture, limited flexion, hyperextension, and total range of motion. Preoperative range of motion is correlated with postoperative range of motion; patients with significant range of motion deficits should be informed that their deficits are expected to improve but may not completely resolve. For patients with large flexion contractures, surgeons should anticipate performing a more extensive posterior capsular release with osteophyte removal. Following this, more distal femoral bone can be resected at the expense of raising the joint line, which has been associated with mid-flexion instability. In patients with hyperextension, decreased distal femoral resection may be planned. However, patients with significant hyperextension may require a hinged implant.


Assessment of preoperative patellar tracking, especially in valgus knees and in knees with predominantly patellofemoral pathology, is imperative for anticipating intraoperative patellar tracking issues. Common surgical adjustments to optimize tracking include femoral component external rotation and lateralization, tibial component external rotation, patellar component medialization, and lateral soft-tissue releases when necessary.


A proper neurovascular exam should be performed. Patients with a foot drop are encouraged to use an orthosis postoperatively to decrease fall risk. Distal pulses should be readily palpable, and a Doppler scan should be done to assess for flow when necessary. An ankle-brachial index (ABI) is a valuable tool for evaluating patients with tenuous vascular supply. An ABI <0.9 may benefit from evaluation by a vascular surgeon. Finally, a previous arterial bypass may preclude the use of a tourniquet.


The contralateral knee and ipsilateral hip should be examined on every patient. Asymptomatic knees may serve as a baseline for each patient; patients with pathology of bilateral knees may benefit from bilateral or staged knee reconstruction. Patients demonstrating mild degenerative changes on knee radiographs and complaining of significant dysfunction may suffer from hip pathology interpreted by the patient as knee pain. Limited hip range of motion and hip pain during the hip exam should result in a radiographic hip evaluation.


Radiographs


A thorough evaluation of radiographs is crucial to the preoperative planning process. The standard radiographs used to evaluate for degenerative joint disease of the knee include a weight-bearing anteroposterior (AP) view, lateral view, and sunrise view of the patellofemoral joint. Often, it is helpful to obtain a posteroanterior (PA) flexion view, also known as a Rosenberg view, for evaluation of the mid-flexion weight-bearing surface. When considering patients for unicompartmental knee arthroplasty, Rosenberg views have been shown to be an effective tool for simulating AP stress views. The weight-bearing AP view provides a snapshot of the functional coronal alignment, allowing surgeons to anticipate intraoperative releases on the concave side of the knee. In varus deformity, the AP view may also be used to identify lateral translation of the proximal tibia, indicating ligamentous laxity or deficiency, bony defects, and potential osteophytes requiring resection. In valgus deformity, the AP view can identify a hypoplastic lateral condyle, which can result in intraoperative internal rotation of the femoral component with resultant patellofemoral maltracking and flexion gap imbalance. The lateral view of the knee consists of complete medial and lateral femoral condylar overlap. The lateral view allows identification of sagittal plane deformity, large posterior osteophytes, intraarticular loose bodies, patellar height, AP translation of the tibia, and tibial slope. The axial sunrise view of the patellofemoral joint is obtained with the knee in 30 degrees of flexion and the x-ray beam tangential to the patella. It allows for assessment of patellofemoral degeneration, patellofemoral (mal)tracking, lateral patellar subluxation, and relative thickness of the patellar facets. Although not routinely performed at many institutions, a full-length preoperative scanogram can help assess mechanical limb alignment, extraarticular deformities, and leg-length discrepancies.


Prior to starting the radiographic templating process, it is important that the surgeon know the magnification of the radiographs or be able to calibrate the measurements from a radiographic marker. The first step in preoperative templating is to determine the mechanical axis. On the full-length scanogram, a line from the center of the femoral head to the center of the ankle can give an idea of varus or valgus malalignment ( Fig. 6.1 ). If a full-length scanogram is not obtained, a tibiofemoral angle can be drawn to quantify a coronal deformity on the AP view ( Fig. 6.2 ). The distal femoral cut is then planned, which recreates the joint line parallel to the floor. The distal femoral resection angle is the angle at which the distal femur is cut to make up the difference between the mechanical axis and the anatomic axis of the femur ( Fig. 6.3 ). Most commonly, surgeons use a resection angle between 5 and 7 degrees of valgus. Mullaji et al. advocate against using a standard fixed angle and recommend using an individualized resection angle for proper restoration of the mechanical axis. However, Andrews et al. found that using a fixed angle of 6 degrees restored a neutral mechanical axis in 86% of patients. Next, the tibial bone cut is generally templated perpendicular to the mechanical axis of the tibia. The amount of resection is often based on the composite thickness of the polyethylene insert plus the tibial implant, which amounts to approximately 10 mm in most systems. Finally, the distal femur and proximal tibia are templated for implant sizing ( Fig. 6.4 ). Generally, the femur and tibia are sized on a lateral radiograph and matched in the AP dimensions of the respective bones. This confirms availability of appropriate implant sizes and plans for implant location, such as preventing anterior notching. Recent studies have also shown that patient demographics can play a useful role in predicting intraoperative implant sizes for routine TKA.




Fig. 6.1


Full-length scanogram—a line from the center of the femoral head to the center of the ankle to give an idea of varus or valgus malalignment.



Fig. 6.2


Tibiofemoral angle to quantify a coronal deformity on the anteroposterior view.

Jun 18, 2022 | Posted by in ORTHOPEDIC | Comments Off on Preoperative Planning for Total Knee Arthroplasty

Full access? Get Clinical Tree

Get Clinical Tree app for offline access