Review Question - QID 220133

This patient has persistent anterior knee pain following a total knee arthroplasty (TKA). Increased patellofemoral contact pressures have been reported following TKA at all flexion angles and are even more elevated in cruciate-retaining (CR) devices (answer choice 4).

This patient underwent a TKA for chronic right knee osteoarthritis. Residual anterior knee pain following a TKA can occur for a multitude of reasons, including patellar maltracking, loose components, infection, and malalignment. However, it has also been shown that patellofemoral contact pressures are increased following TKA in all flexion angles. This has been proposed as a potential reason for postoperative anterior knee pain. Contact pressures have been shown to increase with multiple TKA designs, the most significant being CR and condylar-stabilizing (CS) designs. Common postoperative complications following a TKA are associated with patellofemoral problems, including anterior knee pain, patella fractures and subluxation, patellar clunk syndrome, and patellar tendon rupture. This increase in patellofemoral contact pressure has been hypothesized to be secondary to a decrease in femoral rollback. All TKA designs have been shown to reduce femoral rollback when compared to a native knee. However, CS and CR TKA designs have been found to result in a larger reduction. This increased patellofemoral pressure found in CR and CS designs may suggest that a retained posterior cruciate ligament (PCL) is less stable when compared to a tibial post (found in PS designs) or to a native knee.

Tanikawa et al. conducted a cadaveric study analyzing the influence TKA has on patellar kinematics and patellofemoral pressure. They measured patellofemoral pressure, patellar offset, and patellar tilt on 5 cadavers. They compared these measurements in a normal knee (with patella replacement only), CR design, CS design, and posterior-stabilizing (PS) design. In their study, they reported that patellofemoral pressure increased significantly after the CR and CS TKA designs when compared to the normal knee. They concluded that the relatively high patellofemoral pressures and kinematic changes following a TKA may be associated with postoperative anterior knee pain.

Lee et al. compared the biomechanics of hyperflexion and kneeling before and after a TKA. Patellofemoral and tibiofemoral joint contact area, contact pressure, and kinematics were evaluated in cadaveric studies using a Tekscan pressure measuring system. Normal knees, CR-TKA design, and PS-TKA designs were included and compared at varying flexion angles from 90-135 degrees. Moving from double to single stance kneeling increased pressures in the CR group, but decreased pressures in the PS group. The CR group resulted in significantly larger contact areas compared to the PS group (p < 0.05). They conclude that if greater than 120 degrees of flexion can be achieved after a TKA, there is less risk to the patellofemoral joint than what has been previously described.

Figures A and B are preoperative weight-bearing AP and lateral radiographs, respectively, demonstrating medial compartment collapse in a varus knee with moderate to severe osteoarthritis.

Incorrect answer choices:
Answer choices 1 and 2: Similar increases in contact pressures are observed when resurfacing the patella or not. Both are less than the expected increase with CR-TKA designs.
Answer choice 3: Posterior stabilizing (PS) TKA designs have demonstrated an increase in patellofemoral contact pressure, however, CR-TKA designs have been shown to cause a greater increase in pressure.
Answer choice 5: Medializing the patellar component in TKA has demonstrated superior results and a reduction in the incidence of patellar maltracking. There is not a known increase in contact pressure related to medialization.