Physiological incongruity of the humero-ulnar joint: a functional principle of optimized stress distribution acting upon articulating surfaces?

Abstract

Abstract.Investigations into the distribution of subchondral bone density in the human elbow have suggested that the geometry of the trochlear notch deviates from a perfect fit with the trochlea, and that the load is transmitted ventrally and dorsally rather than through the centre of the humero-ulnar joint. We therefore decided to make a quantitative assessment of the degree of incongruity between the two components in 15 human specimens (age distribution 60 to 93 years) with different types of joint surface. Polyether casts of the joint cavity were prepared under loads of 10, 40, 160 and 640 N. The thickness of the casts was then measured at 50 predetermined points, and an area distribution of the width of the joint space represented in a two-dimensional template of the trochlear notch. The reproducibility of this procedure was tested by image analysis. At a load of 10 N, only a narrow space was present ventrally and dorsally in the joint, but in the depths of the trochlear notch a width of 0.5 to 1 mm was recorded in the centre, and up to 3 mm at its medial and lateral edges. Specimens with continuous articular cartilage showed a lower degree of incongruity than those with a divided articular surface. As the load was increased to 640 N, however, the original incongruity between the articular surfaces disappeared almost completely. The joint surfaces became more congruous, probably because of the viscoelastic properties of the articular cartilage and the subchondral bone, and the contact areas merged in the centre of the joint. It is suggested that this physiological incongruity brings about an optimal distribution of stress over the articular surface during the transmission of the load, and it may lead to better nourishment of the articular cartilage by providing intermittent mechanical stimulation and circulation of the synovial fluid.

Computer simulation of subchondral bone adaptation to mechanical loading in an incongruous joint

“…The current study shows that, if the natural incongruity of the humeroulnar joint (Bullough and Jagannath, 1983;Eckstein et al, 1993Eckstein et al, , 1995a is appropriately modeled, the formation of a subchondral bone plate can be predicted as can the typical bicentric distribution pattern of subchondral bone density reported for this joint (Tillmann, 1971(Tillmann, , 1978Eckstein et al, 1994aEckstein et al, , 1995c. This result extends earlier experimental (Eckstein et al, 1994a(Eckstein et al, , 1995bHillebrand et al, 1995) and computational (Eckstein et al, 1994b(Eckstein et al, , 1995c work in which the characteristic distribution pattern of subchondral bone density of the trochlear Fig.…”

“…The morphological and biomechanical data were adopted from the humeroulnar joint because it has been investigated intensively, but the general structure of the model is also typical of other concavely incongruous joints. The joint socket was modeled 10% deeper than the radius (half the diameter) of the trochlea, according to the magnitude of joint space width determined from casting studies (Eckstein et al, 1993(Eckstein et al, , 1995a. Figure 1B shows the normal incongruity of the humeroulnar joint as visualized by high-resolution magnetic resonance imaging (from Eckstein et al, 1996).…”

“…However, this model only accounts for the instantaneous response of the tissue to dynamic loading but not for its behavior during static loads, in which fluid flow plays a crucial role (Mow et al, 1984). Also, the possibility of pressurization of the joint space fluid was ignored because in the mediallateral direction the socket becomes wider, the fluid is not sealed (Eckstein et al, 1993(Eckstein et al, , 1995b, and the capsule of the elbow is rather lax. An infinitesimal, isotropic, and homogeneous cartilage model was adopted and, to determine the effect of cartilage material properties on subchondral bone remodeling, simulations were carried out with the cartilage modulus changed to 5 MPa and 25 MPa.…”

Morphomechanics of the humero‐ulnar joint: II. Concave incongruity determines the distribution of load and subchondral mineralization

“…In model 2 (4,297' of freedom), concave incongruity of the magnitude described by Eckstein et al (1993), was incorporated. The socket was formed as an ellipsoid, its depth exceeding the radius of its entrance by 10% (Fig.…”

Knee Posture Predicted from Subchondral Apparent Density in the Distal Femur: An Experimental Validation

“…Mü ller-Gerbl and colleagues introduced a procedure called computed tomography osteoabsorptiometry (CT-OAM), which has been widely used to characterize patterns in apparent density in the subchondral bone of several human joints, including the hip Eckstein et al, 1994;Von Eisenhart-Rothe et al, 1999), patella (Eckstein et al, 1992(Eckstein et al, , 1993Mü ller-Gerbl et al, 1992), tibial plateau (Mockenhaupt and Koebke, 1988;Ahluwalia, 2000), coraco-acromial arch (Oizumi et al, 2003), scapular glenoid fossa , wrist (Giunta et al, 1999(Giunta et al, , 2004Hoogenbergen et al, 2002), and metacarpophalangeal joints (Meirer et al, 2004). The majority of these studies have clinical applications, and their goals have primarily been to evaluate the patterns of normal and pathological load magnitudes.…”