Hydraulic Joint Function and Osteoarthritis

Abstract

» This review of bone perfusion work introduces a new field of subchondral physiology.» Intraosseous pressure (IOP) measured through an intraosseous needle reflects conditions only at the needle tip rather than being a constant for the whole bone.» Measurements of IOP in vitro and in vivo, with and without proximal vascular occlusion, show that at rest, bone is perfused at normal physiological pressures.» A subtraction perfusion range or bandwidth at the needle tip offers a better measure of bone health than a single IOP.» With ordinary loads, very great subchondral pressures are generated.» Subchondral tissues are relatively delicate but are microflexible with bone fat being essentially liquid at body temperature.» Collectively, the subchondral tissues transmit load mainly through hydraulic pressure to the trabeculae and cortical shaft.» White vascular marks on normal magnetic resonance imaging scans are present but are lost in early osteoarthritis.» Histological studies confirm the presence of those vascular marks and also choke valves capable of supporting hydraulic pressure load transmission.» Osteoarthritis seems to be at least partly a vasculomechanical disease.» Understanding subchondral physiology will be key to better classification, control, prognosis, and treatment of osteoarthritis.

Fig. 1

Needle clearance by saline injection reduces IOP with a slow recovery over about 10 minutes. Following clearance by aspiration IOP recovery takes less than half a minute.

Fig. 2

Cardiac and respiratory waves seen in an IOP recording lasting about two minutes.

Fig. 3

Simultaneous IOP recording from the femoral head (upper), femoral condyle (middle) and upper tibia (lower) traces with (a) basal state, (b) proximal arterial clamp applied, (c) load one body weight applied, (d) load removed, (e) arterial clamp removed, (f) proximal venous clamp applied, (g) load one body weight applied, (h) load removed, (i) venous clamp removed, (j) return to basal state. Pressure range 0–100 mmHg for each trace, total 10 minutes duration.

Fig. 4

Top row steroid treated, lower row controls. Barium angiography followed by excision and decalcification. Steroid treated bones whiter due to retaining more barium than controls. Example angiograms from each group on right side.

Fig. 5

IOP loading and perfusion. Example of IOP with loading during perfusion (left group), with proximal venous pressure tourniquet (central group) and perfusion alone (right group). Blue – serum perfusion pressure, Red – metacarpal epiphysis IOP, Green – metacarpal subchondral IOP. Each set shows the effect of a static load of 10 kg applied for 10 seconds with 10 second rest intervals, x 3. The tourniquet was applied at 6 minutes and removed at 12 minutes (arrows).

Fig. 6

Normal proximal tibial slice from a PD_SPAIR MRI scan showing the radiating water bright vascular marks.

Fig. 7

Number of vascular marks in the upper tibial slices with corresponding plain x-ray grade of osteoarthritis on Kellgren-Lawrence scale for lateral (red) and medial (blue) compartments.

Fig. 8

Upper pair: Cortex on the left, example of vessels seen on MRI in the subchondral plane about 1 cm below the tibial joint surface. Vascular distortion or possible choke valve as they reach the cortex. Goldner's trichrome x 20 and Masson's trichrome x 20. Lower pair: Left normal femoral head with plentiful subchondral vessels, right early osteoarthritic femoral head with none. H+E x 20.