Causes / typical injury mechanism: Several complications may occur following total knee arthroplasty (TKA). Complications may be categorized as surgical complications, perioperative complications, or chronic complications. The evaluation of the painful TKA is complex and requires a detailed history and physical examination in combination with radiographs and possibly other tests to find the etiology. This summary is a general overview of the painful TKA and diagnostic steps. Complications include those listed below. See individual summaries for additional details.

• Vascular injury
• Intraoperative fracture
• Peroneal nerve injury
• Medial collateral ligament injury
• Patellar maltracking
• Wound complication, wound healing complications
• Periprosthetic joint infection
• Arthrofibrosis
• Heterotopic ossification
• Aseptic loosening, osteolysis
• Global or midflexion instability
• Dislocation
• Metal hypersensitivity
• Polyethylene wear

The most common cause of TKA failure is aseptic loosening, followed by prosthetic joint infection.

Classic history and presentation: TKA is overall a successful surgical procedure for symptomatic knee degenerative disease with significant improvements in patients' quality of life. However, several complications following TKA have been described that differ in underlying etiology and presentation, ranging from continued pain and swelling to stiffness and instability, loosening, or infection. Up to 20% of patients remain unsatisfied with the outcome of TKA and may present with a painful TKA. Evaluation of the painful TKA is challenging and requires a systematic approach.

Risk factors:

• Previous knee surgeries, possible revision surgeries
• Wound healing complications
• Increased body mass index (BMI)
• Female sex
• Middle-aged
• Diabetes mellitus
• Inflammatory arthritis (rheumatoid arthritis, psoriatic arthritis, gout, pseudogout)

Pathophysiology: Aseptic loosening of the TKA generally occurs either secondarily to a slow loss of fixation over time, or due to inadequate fixation of hardware at the time of the initial surgery. Instability following a TKA can be due to many different pathologies including iatrogenic soft tissue injuries, polyethylene wear, infection, periprosthetic fracture, etc. Infections can be acquired perioperatively or hematogenously from another area of the body.