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.

Boundary lubrication of articular cartilage: Role of synovial fluid constituents

“…Early signs of articular cartilage wear have recently been associated with a loss of the boundary lubrication function of SF postinjury (32). Accordingly, boundary lubrication has been postulated to be critical to cartilage homeostasis by facilitating low friction and low wear (2). Future studies of the postulated role of boundary and other modes of lubrication in arthritic disease are needed.…”

“…Lubricant molecules within a surface layer or film at the articular surface also mediate load bearing, particularly the surface-to-surface contact in the boundary mode of lubrication. This mode of lubrication has been proposed to be important for the protection and maintenance of articular surfaces since the apposing cartilage layers within the joint make contact over ϳ10% of the total area, where much of the friction may occur (2). Synovial fluid (SF) contains the molecules hyaluronan (HA) (3), proteoglycan 4 (PRG4) (the name assigned by the Human Genome Organization Gene Nomenclature Committee for proteins also known as lubricin, superficial zone protein, and megakaryocyte-stimulating factor) (4,5), and surface-active phospholipids (SAPL) (6), each of which interacts with and adsorbs to the articular surface.…”

Extensional flow of hyaluronic acid solutions in an optimized microfluidic cross-slot device

“…24 We note that in a real joint the bounding surfaces (i.e., the cartilage) are in fact charged, porous and compressible 25,26 and several mechanisms of joint lubrication have been suggested based on these physical properties of cartilage and their interaction with the synovial fluid. These include squeeze-film lubrication, 25 weeping lubrication, [27][28][29] boundary lubrication mediated by surface adsorbed lubricin proteins, 30 and electrostatic binding of an HA network to the cartilage. 26 While our simple picture of the compressing joint (as illustrated in Fig.…”

Acetabular Loading in Rehabilitation

“…It should be noted, however, that these in vivo measurements were performed with angular velocities above 30 ∘ and therefore also include the dynamic component of loading. The limitations of the direct stress measurement method (Morrell et al, 2005) include the facts that the sensors measure the cartilage-on-metal surface and not the cartilage-on-cartilage surface, that the metal prosthesis in contact with natural acetabulum may differ from physiologic morphology of the hip, that sensors were located on the femoral head surface while the values of stress on the acetabular joint surface were estimated from the kinematic data. Further, hip pressure measurements of abduction exercises were performed in one patient only.…”