Effects of a contoured articular prosthetic device on tibiofemoral peak contact pressure: a biomechanical study

Abstract

Many middle-aged patients are affected by localized cartilage defects that are neither appropriate for primary, nor repeat biological repair methods, nor for conventional arthroplasty. This in vitro study aims to determine the peak contact pressure in the tibiofemoral joint with a partial femoral resurfacing device (HemiCAP, Arthrosurface Inc., Franklin, MA, USA). Peak contact pressure was determined in eight fresh-frozen cadaveric specimens using a Tekscan sensor placed in the medial compartment above the menisci. A closed loop robotic knee simulator was used to test each knee in static stance positions (5 degrees /15 degrees /30 degrees /45 degrees ) with body weight ground reaction force (GRF), 30 degrees flexion with twice the body weight (2tBW) GRF and dynamic knee-bending cycles with body weight GRF. The ground reaction force was adjusted to the living body weight of the cadaver donor and maintained throughout all cycles. Each specimen was tested under four different conditions: Untreated, flush HemiCAP implantation, 1-mm proud implantation and 20-mm defect. A paired sampled t test to compare means (significance, P < or = 0.05) was used for statistical analysis. On average, no statistically significant differences were found in any testing condition comparing the normal knee with flush device implantation. With the 1-mm proud implant, statistically significant increase of peak contact pressures of 217% (5 degrees stance), 99% (dynamic knee bending) and 90% (30 degrees stance with 2tBW) compared to the untreated condition was seen. No significant increase of peak contact pressure was evaluated with the 20-mm defect. The data suggests that resurfacing with the HemiCAP does not lead to increased peak contact pressure with flush implantation. However, elevated implantation results in increased peak contact pressure and might be biomechanically disadvantageous in an in vivo application.

Fig. 1

Schematic drawing of the knee simulator that was used for this study

Fig. 2

Different testing conditions (a Untreated; b Flush; c 1 mm; d Defect)

Fig. 3

Mean peak contact pressures with one standard deviation

Fig. 4

Peak contact pressure at 15° static knee stance position with single body weight of specimen No. 2. The color represents the spectrum of pressures (high pressure-red; low pressure-blue). From left to right the different testing conditions are displayed (a Untreated, b Flush, c 1 mm proud, d Defect). Marked increase of peak contact pressure at the edge of the implant to the adjacent cartilage is demonstrated (b)

Fig. 5

Picture of specimen No. 2 before testing with flush implantation of the device in front view (a) and top view (b). The arrow indicates the area of peak contact pressure displayed in Fig. 4b