Corroboration of in vivo cartilage pressures with implications for synovial joint tribology and osteoarthritis causation

Abstract

Pressures on normal human acetabular cartilage have been collected from two implanted instrumented femoral head hemiprostheses. Despite significant differences in subjects' gender, morphology, mobility, and coordination, in vivo pressure measurements from both subjects covered similar ranges, with maximums of 5-6 MPa in gait, and as high as 18 MPa in other movements. Normalized for subject weight and height (nMPa), for free-speed walking the maximum pressure values were 25.2 for the female subject and 24.5 for the male subject. The overall maximum nMPa values were 76.2 for the female subject during rising from a chair at 11 months postoperative and 82.3 for the male subject while descending steps at 9 months postoperative. These unique in vivo data are consistent with corresponding cadaver experiments and model analyses. The collective results, in vitro data, model studies, and now corroborating in vivo data support the self-pressurizing "weeping" theory of synovial joint lubrication and provide unique information to evaluate the influence of in vivo pressure regimes on osteoarthritis causation and the efficacy of augmentations to, and substitutions for, natural cartilage.

Fig. 1.

Locations of pressure transducers on pseudo femoral heads of hemipros-theses. (A and B) Views along the axis of the head through transducer 1. A is the implant in the first subject, and B is the implant in the second subject. (C) Location of central transducer 1.

Fig. 2.

Female subject showing garter around right thigh over hip-implanted instrumented-endoprosthesis for powering prosthesis and receiving PAM-FM signal from prosthesis. Light-emitting diode arrays for TRACK kinematic acquisition are attached to the foot, shank, thigh, and pelvis. The cane is also force-instrumented. (Reproduced from ref. .)

Fig. 3.

Pressure (MPa) measured at transducers in femoral head versus time for the male subject in free-speed gait at 12 months postoperative.

Fig. 4.

Maximum pressures in regions of acetabulum. (A and B) Data for free-speed gait. A shows data from the female subject at 11 months postoperative. B shows data from the male subject at 12 months postoperative. (C) Data for the female subject rising from a chair, 11 months postoperative. (D) Data for the male subject descending steps, 12 months postoperative. The views are into the right hip socket (the male's data are rotated to the right hip) with the subject's anterior toward the right side of each plot.