Causes / typical injury mechanism: Stiffness after total knee arthroplasty (TKA) has varied definitions in the literature with regard to arc of motion. Generally, preoperative knee range of motion (ROM) is predictive of postoperative ROM. While immediate postoperative ROM can be decreased due to swelling and pain, improvement in ROM is expected. Stiffness can be defined as ROM < 90 degrees of flexion or a fixed flexion contracture of 10-15 degrees at around 6-8 weeks after surgery.

Prevalence: This may occur in 8%-12% of TKA patients.

Risk factors: The risk of stiffness after TKA is likely multifactorial. Preoperative range of motion is the most important factor influencing postoperative ROM. Other patient risk factors include medical comorbidities, low pain tolerance, patella baja, and history of prior knee surgery.

Technical factors during surgery can also influence ROM postoperatively: Malrotation of the components, insertion of larger components than necessary resulting in tight flexion gap, inadequate osteophyte resection, raising the joint line > 10 mm, inadequate posterior tibial slope, and over-tightening of the extensor mechanism during closure.

Postoperative complications such as prosthetic joint infection, arthrofibrosis with intraarticular scar tissue formation, heterotopic ossification, complex regional pain syndrome, and delayed rehabilitation can lead to inadequate range of motion and stiffness.

Pathophysiology: ROM after TKA relies on the interplay between the implanted components and the soft tissue envelope that crosses the joint space or interacts with the components intraarticularly. Any alteration of this balance can limit ROM.