Causes / typical injury mechanism: Patellar maltracking after total knee arthroplasty (TKA) is the improper tracking of the native or retained patella or patella component in the trochlear grove of the femoral component. Patellar maltracking can lead to the feeling of instability during range of motion, patellar subluxation or dislocation, peripatellar pain, and/or limited knee flexion. Patellar maltracking is a multifactorial issue and often requires revision surgery. Proper patellar tracking during TKA is achieved by correct femoral and tibial component alignment, restoration of the native Q-angle (angle between the quadriceps muscle and patella tendon), correct patellofemoral offset, and overall ligament balancing.

Classic history and presentation: Restoration of the native Q-angle during TKA is important to maintain the patella in the trochlea groove. The Q-angle is influenced by femoral component rotation and patella rotation. In patients with a preoperative valgus deformity and a hypoplastic lateral femoral condyle, a measure resection technique may lead to internal rotation of the femoral component, which increases the Q-angle and may result in lateral displacement of the patella and subluxation or dislocation. Raising the joint line during primary or revision TKA may cause decreased postoperative flexion. Inadequate or asymmetric patella resection when placing a patellar component may cause overstuffing of the patellofemoral joint or patella tilt. Ligament imbalance can be related to a tight lateral retinaculum or weak vastus medial obliquus.

Patients may present with peripatellar pain or pain with knee flexion. Patients report the feeling of patellar subluxation or rarely patellar dislocation with range of motion.

Prevalence: This is seen in older adults who are more likely to qualify for and receive a TKA. About 0.5% of all revisions of TKA are due to patellofemoral pain (it is unclear if all of these surgeries are due to patellar maltracking causes), although more recent patellar-conscious implant designs have decreased maltracking outcomes of TKA surgeries.

Risk factors: Risk factors for this condition include pre-existing patellar maltracking prior to TKA, preoperative valgus alignment and deformity with a high Q-angle and hypoplastic lateral femoral condyle increasing the risk of femoral component internal rotation, and revision TKA.