Intraosseous pressure during loading and with vascular occlusion in an animal model

Abstract

Objectives: We studied subchondral intraosseous pressure (IOP) in an animal model during loading, and with vascular occlusion. We explored bone compartmentalization by saline injection.

Materials and methods: Needles were placed in the femoral condyle and proximal tibia of five anaesthetized rabbits and connected to pressure recorders. The limb was loaded with and without proximal vascular occlusion. An additional subject had simultaneous triple recordings at the femoral head, femoral condyle and proximal tibia. In a further subject, saline injections at three sites were carried out in turn.

Results: Loading alone caused a rise in subchondral IOP from 11.7 mmHg (sd 7.1) to 17.9 mmHg (sd 8.1; p < 0.0002). During arterial occlusion, IOP fell to 5.3 mmHg (sd 4.1), then with loading there was a small rise to 7.6 mmHg (sd 4.5; p < 0.002). During venous occlusion, IOP rose to 20.2 mmHg (sd 5.8), and with loading there was a further rise to 26.3 mmHg (sd 6.3; p < 0.003). The effects were present at three different sites along the limb simultaneously. Saline injections showed pressure transmitted throughout the length of the femur but not across the knee joint.

Conclusion: This is the first study to report changes in IOP in vivo during loading and with combinations of vascular occlusion and loading. Intraosseous pressure is not a constant. It is reduced during proximal arterial occlusion and increased with proximal venous occlusion. Whatever the perfusion state, in vivo load is transferred partly by hydraulic pressure. We propose that joints act as hydraulic pressure barriers. An understanding of subchondral physiology may be important in understanding osteoarthritis and other bone diseases.Cite this article: M. Beverly, S. Mellon, J. A. Kennedy, D. W. Murray. Intraosseous pressure during loading and with vascular occlusion in an animal model. Bone Joint Res 2018;7:511-516. DOI: 10.1302/2046-3758.78.BJR-2017-0343.R2.

Keywords: Intraosseous; Physiology; Pressure; Subchondral; Weight bearing.

Fig. 1

Diagram showing experimental set up. The spring-loaded pusher covers the foot and prevents flexion and extension while applying a longitudinal one body weight load (4520 g to 5400 g; IOP, intraosseous pressure).

Fig. 2

Graph showing the basal intraosseous pressure (IOP) during perfusion at rest (IOPb), an increase in IOP with loading by one body weight (IOPb+Ld) p < 0.0002; IOP during proximal arterial occlusion (IOPa) and with loading during arterial occlusion (IOPa+Ld) p < 0.002 and IOP during venous occlusion (IOPv) and loading during venous occlusion (IOPv+Ld) p < 0.003; (all p-values t-test). Error bars are standard error of the mean.

Fig. 3

Graph showing the effect of loading alone with one body weight. Upper trace - femoral head, middle trace - femoral condyle and lower trace - proximal tibia. All traces shows basal intraosseous pressure, loading by one body weight for two minutes, rest for six minutes and load for three minutes. Vertical scale 0 mmHg to 100 mmHg on all traces, trace speed 12.5 mm/min.

Fig. 4

Graphs showing the upper trace from the femoral head, middle trace femoral condyle and lower trace proximal tibia. From left to right, the traces show the effect of arterial occlusion, arterial occlusion with loading, load removal and arterial clamp removal. The second part shows changes at the same sites after venous occlusion, venous occlusion with loading, removal of load and removal of the occluding clamp. The intraosseous pressure changes are seen to be similar at all three sites and simultaneous. Vertical scale 0 mmHg to 100 mmHg on all traces, trace speed 12.5 mm/min.

Fig. 5

Graph showing the upper trace from the femoral head, middle trace femoral condyle and lower trace proximal tibia. Left: injection (between the arrows) at the femoral head caused a rise in intraosseous pressure (IOP) at the femoral condyle, but not the proximal tibia. Centre: injection at the femoral condyle caused a rise in IOP at the femoral head, but not the proximal tibia (some artefactual shake is seen on the femoral condyle trace during injection). Right: injection at the proximal tibia had no effect on femoral head or femoral condyle IOP. Vertical scale 0 mmHg to 100 mmHg on all traces, trace speed 12.5 mm/min.