summary TKA Revision is most commonly performed to address aseptic loosening, fracture, instability, or infection associated with a prior TKA. Diagnosis and etiology of TKA failure can be determined by a combination of physical examination, labs, and radiographs. Treatment depends on etiology of failure, prior surgery and patient activity demands. Etiology Most common causes of failure infection should always be ruled out prior to any revision considered the most common reason for revision TKA overall based on national database epidemiology studies when categorized further, infection is the most common cause of early (<2 years from primary) failure aseptic component loosening aseptic loosening is the second most common reason for revision TKA overall based on national database epidemiology studies when categorized further, aseptic loosening is the most common cause of late (>2 years from primary) failure tibial loosening more common than femoral femoral loosening more difficult to detect due to obscured view of posterior femoral condyles where lesions typically occur oblique radiographs may help identify detected on serial radiographs osteolytic wear most common in uncemented technique motion between modular tibial insert and metal tray (backside wear) ligament/flexion instability (~8%) MCL/LCL incompetence can to lead to laxity flexion instability PCL attenuation (in CR knees) unbalanced flexion gap excessive posterior slope undersized femoral component femoral component placed in excessive extension periprosthetic fracture (~5%) most commonly supracondylar femur region need for revision due to combination of excessive comminution/bone loss with loose component arthrofibrosis (~5%) patellofemoral maltracking most commonly caused by component malpositioning abnormal joint line problems patellar clunk fibrotic scar tissue that 'clunks' as the knee moves from flexion into extension and patella jumps the femoral notch arthroscopic treatment to remove fibrotic tissue metal hypersensitivity Presentation History original etiology and indications for TKA preoperative range of motion, ambulatory status history of infection, thrombophlebitis, recent falls history of THA comorbidities type of implant, review of prior records and imaging Symptoms temporal course is crucial: pain persistent since index procedure or new onset pain (may indicate potential acute vs. chronic infection) pain with weight bearing indicates likely mechanical etiology stiffness instability environment of instability (i.e. stairs, level ground, rising from chair) Physical Exam gait (stiff legged gait, inability to fully extend during stance phase) range of motion (passive or active) skin changes, presence of effusion, warmth (infection vs. complex regional pain syndrome (CRPS)) ligamentous exam for laxity patellar tracking Imaging Radiographs Serial AP and lateral radiographs to provide timeline of TKA Weight bearing radiographs can provide evaluation of any asymmetric wear Skyline view to assess patellar tracking Standing leg length views to assess overall alignment AP pelvis to rule out any hip pathology Computed tomography Femoral version study can aide in assessing component rotation when also compared to the femoral neck Can also aide in assessing severity and location of bony defects Bone scan Can be positive for up to 2 years after primary TKA Positive scan nonspecific can indicate loosening, infection, or stress fracture Negative scan rules out loosening Diffuse uptake can indicate CRPS Studies Serum labs CBC, ESR, CRP to rule out infection Knee aspiration to rule out infection via cell count and culture Technique - Prosthesis Selection Unconstrained Posterior Cruciate Retaining indicated if PCL is intact always have a PCL substituting implant available as it is difficult to evaluate the integrity of the PCL prior to surgery Unconstrained Posterior Cruciate Substituting indicated if there is a PCL deficiency Constrained Nonhinged large central post substitutes for MCL/LCL function indicated for varus/valgus instability LCL attenuation or deficiency MCL attenuation or deficiency (controversial because load may lead to breaking of central post) flexion gap laxity can be made stable with a tall post Constrained Hinged with rotating platform tibial component is allowed to do internal/external rotation within a yoke reduces rotational forces that would otherwise be on prosthesis-bone interface indicated for global ligament deficiency LCL attenuation or deficiency MCL attenuation or deficiency (deficiency of MCL is controversial because load may lead to breaking of central post) flexion gap laxity with component mismatch post-traumatic or multiply revised TKR hyperextension instability seen in polio resection of the knee for tumor or infection relatively indicated for charcot arthropathy Technique - General Steps Goals extraction of components with minimal bone loss and destruction restoration of bone deficiencies restoration of joint line balance knee ligaments stable revision implants adequate soft tissue coverage General Steps surgical exposure should be extensile when compared to the standard medial parapatellar approach for revision total knee arthroplasties, the oblique rectus snip approach shows no difference in outcomes tibial tubercle osteotomy allows for good exposure and is especially indicated if there is patella baja as it allows proximal translation of the tibial tubercle removal of implants proceed with tibial side first by establishing tibial joint line tibial joint line should be 1.5 to 2 cm above head of fibula (use xray of contralateral knee to determine exact distance) after tibia joint line established proceed with femoral side to match the tibia balance flexion-extension gaps balance medial and lateral gaps address patellofemoral tracking keep patellar thickness >12mm to avoid fracture Technique - Bone Defect Reconstruction Anderson Orthopaedic Research Institute (AORI) Classification Description Treatment Type 1 Minor bone defects with intact metaphyseal bone that do not compromise stability Cement fill or impaction allograft Type 2A Metaphyseal bone damage that involves 1 femoral condyle or tibial plateau Cement fill, augments, small bone graft Type 2B Metaphyseal bone damage that involves both femoral condyles or tibial plateaus Cement fill, augments, small bone graft Type 3 Massive bone loss comprising a large portion of condyle/plateau, and can involve the collateral ligaments/patellar tendon Bulk allografts, custom implants, megaprosthesis, porous tantalum, metaphyseal sleeves, rotating hinge Metaphyseal bone in TKR is often severely deficient due to mechanical abrasion osteolysis extraction technique infection/bone loss Classification Anderson Orthopaedic Research Institute (AORI) Classification classification systems not used as commonly as revision THA Reconstruction is addressed with: long stems to promote load sharing to the femoral and tibial diaphysis usually done with a long intramedullary stem press-fit: advantages good 'scratch' fit within diaphysis can help in obtaining correct alignment no need for cement removal in future disadvantages typically no in-growth increased risk of iatrogenic fracture cannot use in femur with excessive bow cemented: advantages can use in scenarios of excessive femoral bow ability to delivery antbiotics useful in severely osteopenic bone disadvantages increases complexity of any future revision cavity defect filling cavitary defect <1cm cement is adequate for small defects, structurally better than allograft cavitary defect >1cm metaphyseal sleeves advantages encouraging mid-to-long term data efficient, simple, can be used as cutting guides instrumented morse taper interface with implant disadvantages expensive difficult to remove specific to each implant manufacturer not useful for uncontained defects trabecular metal cones advantages short-to-mid term data encouraging variety of shapes/sizes with custom shaping/contouring is possible trials/specific instrumentation available compatible with several different implant companies can be used for uncontained defects disadvantages expensive difficult to remove cemented interface to implant can be irritant to soft tissues structural allograft advantages custom shaping available satsifactory survivorship in mid-to-long term potential biologic interface with host disadvantages time-consuming disease transmission risk long-term failure due to graft resorption infection risk technically demanding Complications Pain pain scores less favorable than primary TKR activity related pain can be expected for 6 months Stiffness Neurovascular problems peroneal nerve subject to injury with correction of valgus and flexion deformity Infection upwards of 4-7%, double the risk of primary TKA risk increases with MSIS grade C hosts Skin necrosis prior scars should be incorporated into skin incision whenever possible bloody supply to anterior knee is medially based, so lateral skin edge is more hypoxic if multiple previous incisions, use most lateral skin incision can use wound care, skin grafting, or muscle flap coverage (gastroc) for full thickness defects Extensor mechanism disruption can use extensor mechanism allograft using achilles tendon bone block residual lag due to attenuation is common extensor mechanism reconstruction with mesh may offer better mid-term results in function and survivorship