Painful Total Knee Arthroplasty Workup

Introduction

Total knee arthroplasty (TKA) has seen vast improvement over the past several decades with respect to implant design, improved polyethylene wear properties and advances in surgical technique, all of which have led to excellent survivorship. Despite these improvements, patient satisfaction following TKA continues to be a concern, with approximately 19% of patients not satisfied with their TKA. Patient satisfaction following TKA is based on several factors, including alleviating pain, achieving appropriate limb alignment, providing flexion and extension gap soft-tissue balance for stability, restoring knee motion for functional activities, and meeting patient expectations while minimizing complications. An understanding of the most common failure mechanisms following primary TKA is essential for the evaluation and treatment of the painful TKA. The etiology of the painful TKA can be divided into two primary categories: intrinsic and extrinsic. Intrinsic causes include periprosthetic joint infection (PJI), aseptic loosening, instability, malalignment, osteolysis, extensor mechanism disruption, contracture, and fracture. Extrinsic causes that can refer pain to the knee include spine or hip pathology; vascular etiology, such as claudication; local soft-tissue inflammatory processes, such as popliteal tendinitis and knee bursitis; and neurogenic pain from a neuroma or genicular nerve trauma. This chapter will provide an overview of the most recent literature on evaluation and subsequent workup for the etiology of the painful TKA.

History, Physical Examination, and Imaging

The differential diagnosis of a painful TKA begins with a thorough history of the patient’s index TKA followed by a physical examination. The thought process to identify the etiology of the painful TKA has to take into account multiple factors, including the length of time from the index procedure to the onset of the painful TKA along with the nature or characteristics of the pain, such as localized versus diffuse, severity, any radicular component, or any startup pain with activities or pain that persists even at rest. The nature of the pain is helpful since pain with initiation of weight bearing, such as startup pain, may suggest implant loosening, whereas a more constant pain may imply other etiologies, such as an infectious or inflammatory process. Persistent wound drainage greater than 5 to 7 days or delayed wound healing at the time of the index procedure also supports a chronic infectious etiology. An associated recent illness, dental procedure, or other recent surgical procedures prior to the onset of symptoms may also indicate hematogenous infection. A history of recurrent knee effusions along with difficulty with inclines or stairs may suggest instability despite normal-appearing radiographs. It is also important to identify the specific implant and manufacturer used for the index TKA. Following the initial history, physical exam, and initial radiographs (to include weight-bearing anteroposterior [AP], lateral, Merchant and long-leg imaging studies), a well-thought-out differential diagnosis should be developed.

The physical examination should note the prior surgical incision and integrity of the soft-tissue envelope, including signs of instability or malalignment in the coronal, sagittal, and axial planes, along with the presence of an effusion. Examination should include evaluation for tenderness along the periarticular soft tissues to help localize the pain. The hip joint should also be examined since hip pathology can refer pain to the knee. A neurovascular exam is important to assess for potential neurogenic pain emanating from the spine or local surrounding genicular nerves due to the surgical trauma. Knee pain can also be due to vascular etiology presenting as claudication. Knee range of motion (ROM)—along with quadriceps strength, extensor mechanism integrity, stiffness, and patella component tracking—should be assessed. For activities of daily living, it is ideal to have 105 degrees of knee flexion or greater. It is also important to evaluate the patient’s gait for any limp, dynamic instability, neurogenic conditions, and hip and spine pathology.

Adequate radiographs are essential during the workup for a painful TKA. Images should include weight-bearing AP and lateral radiographs along with a Merchant view to assess patellofemoral alignment in addition to wear, loosening, osteolysis, malposition, fracture, and patella alta or baja. Long-leg radiographs to include the hip, knee, and ankle are helpful to identify any malalignment and offer a limited radiographic evaluation for hip pathology ( Fig. 15.1 ). Radiographic images of the knee prior to the index TKA should also be reviewed in order to evaluate the extent of the preoperative arthritic disease and/or deformity and extent of the degenerative disease prior to the primary TKA. Advanced imaging in evaluation of painful TKA includes fluoroscopic views to assess for radiolucent lines along with computed tomography (CT) scans and nuclear medicine studies. CT scans allow for assessment of component rotation in the axial, sagittal, and coronal planes. Nuclear medicine imaging can also be used to evaluate for component loosening in the painful TKA. However, this should be reserved for delayed pain greater than 2 years postoperatively given the high false-positive rate if obtained prior to that time.

Intrinsic Etiologies for Knee Pain Following Total Knee Arthroplasty

As the projected volume of TKA is expected to increase to over 3 million procedures per year in the United States, it is important that the common reasons for TKA failure are understood. The success rate of primary TKA is approximately between 80% to 85% with respect to patient satisfaction. However, there are 15% to 20% of patients who continue to have ongoing pain. Pain following TKA can result from several etiologies, some of which can be readily apparent—such as a culture-positive PJI or instability presenting with an effusion and gross laxity ( Boxes 15.1 and 15.2 ). The etiology of a painful TKA can also be elusive; in that case, it requires a thorough, algorithmic workup with a process of elimination to narrow the differential diagnosis ( Table 15.1 ). The most common etiologies for failed TKA requiring revision surgery include aseptic loosening, PJI, instability, periprosthetic fracture, and arthrofibrosis. ^, The incidence of polyethylene wear leading to failed TKA requiring revision has declined due to improvements in polyethylene wear characteristics. This chapter will explore the evaluation of a painful TKA and discuss some of the more common etiologies, such as PJI, loosening, malalignment, arthrofibrosis, instability, polyethylene wear, and osteolysis. Other more obvious etiologies for pain after a TKA include extensor mechanism disruption and periprosthetic fractures, which are covered in detail in Chapter 11, Chapter 14 , respectively.

Table 15.1

Algorithmic Approach to the Evaluation of a Painful Total Knee Arthroplasty

From Flierl MA, Sobh AH, Culp BM, Baker EA, Sporer SM. Evaluation of the painful total knee arthroplasty. J Am Acad Orthop Surg . 2019;27(20):743–751. https://doi.org/10.5435/JAAOS-D-18-00083