Increased patellofemoral contact pressure was described after total knee arthroplasty (TKA). Aim of this in vitro study was to compare the influence of a posterior stabilized (PS) design in comparison to a cruciate retaining (CR) design on patellofemoral contact pressure. Patellofemoral area contact pressure, peak contact pressure and the centre of pressure motion were determined in eight fresh frozen human cadaveric specimens using a Tekscan sensor (K-Scan 4000). A robotic knee simulator was used simulating an isokinetic knee extension cycle from 120 degrees of flexion to full extension. All knees were tested in a first test cycle after implantation of a CR design and in a second test cycle after replacement by a PS design, both using a 11 mm PE inlay (Genesis II, Smith & Nephew, Memphis, TN, USA). The patella remained unresurfaced. A paired sampled t test to compare mean values (significance, P < or = 0.05) was used for statistical analysis. After implantation of the PS design, average patellofemoral area contact pressure was significantly lower (P < or = 0.006) compared with the CR design (PS: 3.58 +/- 1.25 MPa; CR: 4.31 +/- 1.40 MPa). Accordingly, average patellofemoral peak contact pressure decreased significantly (P < or = 0.02) with the PS design (6.12 +/- 2.37 MPa) in comparison with the CR design (7.17 +/- 2.41 MPa). On average, the centre of pressure motion was more physiological with the PS design compared to the CR design over the complete extension cycle. However, this was not significant. In conclusion, the data suggest less patellofemoral contact pressure of a posterior stabilized TKA design in comparison to a cruciate retaining design.

The results of this study suggest that a posterior stabilized prosthesis design reduces the patellofemoral peak and mean pressure in comparison with a high conforming design. The better reproducible femoral rollback with a posterior stabilized model at a tibial ventral shift could serve as a possible explanation.

At intact PCL peak quad forces and mean forces beyond 70° of flexion could be shown to be significantly lower with a PS TKA design in comparison with cruciate preserving designs such as CR and DD. In the PCL deficient knee quad forces with a highly conforming implant (DD) and CR were significantly higher than with a PS TKA. The use of PS implants in all PCL deficient knees seems to be advisable

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