Classification of Bone Defects

Introduction

Revision total knee arthroplasty (TKA) is challenging in the presence of significant bone loss. In the revision setting, bone deficiencies can be secondary to removal of the implant, subsidence of a loose implant, periprosthetic osteolysis, osteonecrosis, stress shielding, or infection. Goals of revision TKA include preservation of host bone, restoration of flexion/extension balance, optimization of ligamentous stability, correction of sagittal and coronal alignment, and establishment of a stable bone–implant interface. There are numerous strategies for managing bone loss in the revision setting. A systematic assessment of bone defects can result in successful management. The reconstructive method selected is dependent on the location and quantity of the osseous deficit. This chapter evaluates the pros and cons of the various surgical approaches to manage bone loss in revision TKA.

Preoperative Assessment

Before any surgical intervention, the surgeon must determine whether the patient’s symptoms are consistent with a failed TKA. One must rule out conditions in which revision TKA may be contraindicated, such as infection, Charcot’s arthropathy, neuromuscular disease, or adverse medical conditions. Preoperative patient evaluation begins with a meticulous history and detailed clinical examination. Analysis of previous surgical procedures, including review of previous operative reports, is necessary to assess the surgical approach used, soft tissue releases performed, and size and type of prosthetic components implanted. To rule out an infection, blood studies such as a complete blood count (CBC) with differential, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) level should be obtained. We also favor routine knee aspiration for culture and cell count with differential. Synovial fluid aspirates with leukocyte counts of 2500 cells/mm ³ or greater in conjunction with a neutrophil percentage of 60% or greater are highly suggestive of infection.

Critical review of imaging studies directs the preoperative planning. Weight-bearing anteroposterior, lateral, and Merchant patellar views are required to evaluate femoral and tibial component size, to assess current bone stock and diaphyseal deformities, to review the position and fixation of present implants, and to critique patella height and coronal position. Full-length radiographs detail coronal alignment and the presence of diaphyseal deformities. Because preoperative radiographs often underestimate the true amount of bone loss, definitive evaluation and management of bone loss will take place intraoperatively. Computed tomography (CT) can aid in more accurately assessing bone loss and component rotation.

The goal at completion of the preoperative assessment is precise determination of the mechanism of failure so as to not repeat mistakes that led to the failure of the initial TKA. Results of revision TKA in cases of unexplained pain are often unsatisfactory. The surgeon needs to determine what is deficient and, subsequently, what is necessary to reconstruct both the bone and the soft tissue deficits.