To quantify patellofemoral contact pressures and forces during infrapatellar (IP) and suprapatellar (SP) intramedullary tibial nail insertion.

Fresh-frozen hemicadavers with intact lower extremities and pelves were used for this study. A standard IP entry portal was used on nine tibiae, whereas an SP entry portal was used in eight tibiae. A digital electronic pressure sensor system was used to dynamically measure peak pressures within the patellofemoral joint during each procedure. Data were continuously recorded from the start to completion of each procedure. Mean pressure and force as well as peak contact pressures recorded were then compared between the two techniques.

Mean patellofemoral pressures and forces as well as peak contact pressures were higher in the SP group than the IP group. The mean peak contact pressure was 0.90 MPa (range, 0.48-1.26 MPa) during IP nailing. The mean peak contact pressure on the patella and femoral condyles was 1.84 MPa (range, 1.09-2.95 MPa) and 2.13 MPa (range, 1.10-2.86 MPa), respectively, during SP nailing.

It is known that structural integrity of articular cartilage is compromised at impact loads exceeding 25 MPa, and chondrocyte apoptosis can occur at sustained loads of as little as 4.5 MPa in immature bovine cartilage. The results of this study indicate that although the patellofemoral contact pressures are higher with SP nail insertion, they remain below the values reported to be detrimental to articular cartilage. Based on these data, we do not believe that the SP entry portal poses a significant risk to the viability or structural integrity of the articular cartilage of the patellofemoral joint. Clinical correlation is needed.