Intraosseous Pressure as a Measure of Hemodynamic Changes in Bone Marrow

Intraosseous pressure measurement during iliac bone marrow biopsy: its feasibility and difference of IOP in diseased marrow and non-diseased marrow

OBJECTIVE

The purposes of this study were (1) to establish the feasibility and safety of an imaging-guided technique for intraosseous pressure (IOP) measurement in a large cohort of patients, and (2) to compare IOP values between normal and diseased bone marrow.

METHODS

Adult patients undergoing CT-guided marrow biopsy were prospectively and consecutively enrolled from November 2020 to February 2022. IOP measurements were obtained connecting the biopsy needle to a monitoring device using a standard arterial line setup. Clinical data including sex, age and pathology results were obtained. Student t test and Pearson correlation were used for continuous variables comparisons. Univariable analyses were performed using Fisher's exact test. A P value of .05 was considered statistically significant.

RESULTS

A total of 139 participants were initially enrolled, and four were excluded during technique optimization. There were no complications related to the measurement technique. Ninety participants (90/135, 67%) had histology confirming marrow pathology. The participants in the diseased marrow group were older than those in the normal marrow group (63 ± 14 vs. 55 ± 14 years; P < .01). There was no difference in mean IOP between both groups (66 ± 23 vs. 64 ± 28 mmHg; P = .69). There was no correlation between mean arterial blood pressure and mean IOP (P = .08).

CONCLUSION

There was no difference in IOP measurements between patients with normal and diseased marrow undergoing CT-guided biopsy. IOP does not appear to be influenced by systemic blood pressure. No complication occurred during the procedures.

Hydraulic Joint Function and Osteoarthritis

» 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.

Vascular deficits contributing to skeletal fragility in type 1 diabetes

Over 1 million Americans are currently living with T1D and improvements in diabetes management have increased the number of adults with T1D living into later decades of life. This growing population of older adults with diabetes is more susceptible to aging comorbidities, including both vascular disease and osteoporosis. Indeed, adults with T1D have a 2- to 3- fold higher risk of any fracture and up to 7-fold higher risk of hip fracture compared to those without diabetes. Recently, diabetes-related vascular deficits have emerged as potential risks factors for impaired bone blood flow and poor bone health and it has been hypothesized that there is a direct pathophysiologic link between vascular disease and skeletal outcomes in T1D. Indeed, microvascular disease (MVD), one of the most serious consequences of diabetes, has been linked to worse bone microarchitecture in older adults with T1D compared to their counterparts without MVD. The association between the presence of microvascular complications and compromised bone microarchitecture indicates the potential direct deleterious effect of vascular compromise, leading to abnormal skeletal blood flow, altered bone remodeling, and deficits in bone structure. In addition, vascular diabetic complications are characterized by increased vascular calcification, decreased arterial distensibility, and vascular remodeling with increased arterial stiffness and thickness of the vessel walls. These extensive alterations in vascular structure lead to impaired myogenic control and reduced nitric-oxide mediated vasodilation, compromising regulation of blood flow across almost all vascular beds and significantly restricting skeletal muscle blood flow seen in those with T1D. Vascular deficits in T1D may very well extend to bone, compromising skeletal blood flow control, and resulting in reduced blood flow to bone, thus negatively impacting bone health. Indeed, several animal and ex vivo human studies report that diabetes induces microvascular damage within bone are strongly correlated with diabetes disease severity and duration. In this review article, we will discuss the contribution of diabetes-induced vascular deficits to bone density, bone microarchitecture, and bone blood flow regulation, and review the potential contribution of vascular disease to skeletal fragility in T1D.

Mechanisms of bone blood flow regulation in humans

Bone is a highly vascularized tissue. However, despite the importance of appropriate circulation for bone health, regulation of bone blood flow remains poorly understood. Invasive animal studies suggest that sympathetic activity plays an important role in bone flow control. However, it remains unknown if bone vasculature evidences robust vasoconstriction in response to sympathoexcitatory stimuli. Here, we characterized bone blood flow in young healthy individuals [n = 13, (four females)] in response to isometric handgrip exercise (IHE) and cold pressor test (CPT). These provide a strong stimulus for active vasoconstriction in the inactive muscle, and perhaps also in the bone. During sustained IHE to fatigue and CPT, we measured blood pressure, whole leg blood flow, and tibial perfusion using near-infrared spectroscopy. Tibia perfusion was determined as oxy- and deoxyhemoglobin. For both stimuli, tibial metabolism remained constant (i.e., no change in deoxyhemoglobin) and thus tibial arterial perfusion was represented by oxyhemoglobin. During IHE, oxyhemoglobin declined (beginning -0.20 ± 1.04 μM; end -1.13 ± 3.71 μM, both P < 0.01) slower than whole leg blood flow (beginning -0.85 ± 1.02 cm/s; end -2.72 ± 1.64 cm/s, both P < 0.01). However, during CPT, both oxyhemoglobin (beginning -0.46 ± 1.43 μM; end -0.60 ± 1.59 μM, both P < 0.01) and whole leg blood flow (beginning -1.52 ± 1.63 cm/s; end -0.69 ± 1.51 cm/s, both P < 0.01) declined with a similar timecourse, even though the magnitudes of decline were smaller than during IHE. These responses are likely due to the different timecourses of sympathetically mediated vasoconstriction in bone and muscle. These results indicate that sympathetic innervation of the bone vasculature serves a functional role in the control of flow in young healthy individuals.NEW & NOTEWORTHY The current study is the first one to noninvasively investigate control of bone blood perfusion in vivo in humans, on a moment-by-moment basis. Our results indicate that tibial bone vasculature demonstrates active vasoconstriction in response to sympathoexcitatory stimuli in young healthy individuals. Compared with whole leg vasculature, bone vasoconstrictor response seems to be smaller, delayed, and more variable.

Subchondral pressures and perfusion during weight bearing

Background

Joints withstand huge forces, but little is known about subchondral pressures and perfusion during loading. We developed an in vitro calf foot model to explore intraosseous pressure (IOP) and subchondral perfusion during weight bearing.

Methods

Freshly culled calf forefeet were perfused with serum. IOP was measured at three sites in the foot using intraosseous needles, pressure transducers, and digital recorders. IOP was measured during perfusion, with and without a tourniquet and with differing weights, including static loading and dynamic loading to resemble walking.

Results

IOP varied with perfusion pressure. Static loading increased subchondral IOP whether the bone was non-perfused, perfused, or perfused with a proximal venous tourniquet (p < 0.0001). Under all perfusion states, IOP was proportional to the load (R² = 0.984). Subchondral IOP often exceeded perfusion pressure. On removal of a load, IOP fell to below the pre-load value. Repetitive loading led to a falling IOP whether the foot was perfused or not.

Conclusion

Superimposed on a variable background IOP, increased perfusion and physiological loading caused a significant increase in subchondral IOP. Force was thereby transmitted through subchondral bone partly by hydraulic pressure. A falling IOP with repeat loading suggests that there is an intraosseous one-way valve. This offers a new understanding of subchondral perfusion physiology.

An in vitro model to explore subchondral perfusion and intraosseous pressure

Background

Little is known about subchondral perfusion physiology. We developed a 3Rs (Replace, Reduce, Refine) compliant in vitro calf foot model to explore perfusion and intraosseous pressure (IOP).

Methods

Calf feet were catheterised and perfused with serum. IOP was measured at three sites, the metacarpal diaphysis (MCD), metacarpal subchondral epiphysis (MCS) and proximal phalanx diaphysis (PPD) using intraosseous needles with pressure transducers and digital recorders. Fresh (< 4 h post mortem) and old feet (> 4 h post mortem) were perfused at different pressures, with and without a proximal tourniquet.

Results

There was a wide range in basal IOP with a mean IOP of 30.0 mmHg, SD 14.4, range 7.6 mmHg to 52.7 mmHg (n = 40 records) in 15 subjects. There was no significant difference between the three sites tested (p = 0.54, 0.12 and 0.051). At each individual site IOP correlated with perfusion pressure (r = 0.993). With a proximal venous tourniquet, IOP increased from 15.1 mmHg (SD 11.3 mmHg) to 44.9 mmHg (SD 24 mmHg), p < 0.0001, n = 9. Filling and emptying curves during perfusion and with using a tourniquet were similar, indicating that the model behaves in an elastic hydrodynamic manner. In fresh feet IOP peaked after about 1 min irrespective of perfusion pressure, possibly due to auto regulation. Older feet showed a continuously rising IOP and became oedematous. There was no significant difference in IOP between fresh and old feet perfused with serum at 150 cms pressure for 1 min.

Conclusion

Though basal intraosseous pressure varies, IOP behaves predictably. IOP measurements reflect the perfusion microclimate at the individual needle tip. This 3Rs compliant model will be used for further exploration of subchondral perfusion physiology with loading.

Upper tibial MRI vascular marks lost in early knee osteoarthritis

Background

We describe upper tibial radiating vascular marks on MRI scans. They are lost in early osteoarthritis (OA).

Methods

A literature search revealed no previous description of upper tibial MRI radial vascular marks. Fifty-six consecutive patients with anteroposterior knee X-rays and an axial PD_SPAIR MRI scan of the same knee within 1 year were studied. Their mean age was 53.1 years (range 22–85) with 27 males and 29 females. The medial and lateral compartments of each knee were scored for osteoarthritis using the Kellgren-Lawrence (K-L) classification. Marks on the MRI scans were counted by layer and quadrant position.

Results

Radial vascular marks were present in the first axial upper tibial subchondral slice, peaked between 6 and 10 mm depth and were absent by 16 mm depth. There was no association with age, left or right knee, BMI, or weight. There was more K-L graded OA medially and more vascular marks laterally. There was an inverse correlation between the number of marks and early grades of osteoarthritis medially (p < 0.001) and laterally (p < 0.002).

Conclusion

We demonstrate previously undescribed subchondral vascular marks on axial MRI scans of the tibia and their inverse correlation with the presence and severity of early knee osteoarthritis. Our work offers a new insight into the possible vascular aetiology of osteoarthritis and potentially a means of earlier diagnosis and a therapeutic target.

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

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.

Factors affecting intraosseous pressure measurement

BACKGROUND

Although a raised intraosseous pressure (IOP) has been found in osteoarthritis and osteonecrosis, the normal physiology of subchondral circulation is poorly understood. We developed an animal model and explored the physiology of normal subchondral perfusion and IOP.

METHODS

In 21 anaesthetised rabbits, 44 intraosseous needles were placed in the subchondral bone of the femoral head (n = 6), femoral condyle (n = 7) or proximal tibia (n = 31). Needles were connected to pressure transducers and a chart recorder. In 14 subjects, the proximal femoral artery and vein were clamped alternately. In five subjects, arterial pressure was measured simultaneously in the opposite femoral artery.

RESULTS

The average IOP at all 44 sites was 24.5 mmHg with variability within SD 6.8 and between subjects SD 11.5. IOP was not significantly influenced by gender, weight, site or size of a needle. Needle clearance by flushing caused a prolonged drop in IOP whereas after clearance by aspiration, recovery was rapid. IOP recordings exhibited wave patterns synchronous with the arterial pulse, with respiration and with drug circulation time. There was a correlation between IOP and blood pressure (13 sites in 5 subjects, Pearson correlation 0.829, p < 0.0005). There was a correlation between IOP and the associated pulse pressure (PP) in 44 sites among 21 subjects (Pearson correlation 0.788, p < 0.001). In 14 subjects (31 sites), arterial occlusion caused a significant reduction in IOP and loss of PP (p < 0.0001). Venous occlusion significantly raised IOP with preservation of the PP (p < 0.012).

CONCLUSION

Our study shows that subchondral cancellous bone behaves as a perfused tissue and that IOP is mainly a reflection of arterial supply. A single measure of IOP is variable and reflects only perfusion at the needle tip rather than being a measure of venous back pressure. Alternate proximal vessel clamping offers a new means of exploring the physiology of subchondral perfusion. We describe a model that will allow further study of IOP such as during loading.

Long-term therapeutic effects of vertebroplasty for painful vertebral compression fracture: a retrospective comparative study

As a treatment for painful vertebral compression fractures (VCFs), vertebral perforation does not require bone cement infusion. Here, we retrospectively assessed the long-term therapeutic effects of vertebroplasty in a comparison with those of vertebral perforation. The subjects were 64 patients who underwent percutaneous vertebroplasty (PVP group) and 67 patients who underwent vertebral perforation (Perforation group) between 2006 and 2011 at Takeda general hospital. We compared the analgesic effects of the treatments and the incidences of new VCFs between the groups at 15 months postsurgery. The pain scores on a visual analog scale 15 months postsurgery were 2.3 ± 2.0 in the PVP group and 2.1 ± 1.4 in the Perforation group, a nonsignificant difference (p = .90). The presence of vertebral mobility did not influence the analgesic effect in either group. New VCFs developed at a significantly higher rate in the PVP group (n = 27, 52%) compared to the Perforation group (n = 11, 24%; p = .0017). This difference was even greater within 3 months of the surgery, in 19 PVP patients (38%) and two Perforation patients (3.0%; p < .0001). However, the incidence after 3 months was eight PVP patients and nine Perforation patients, a nonsignificant difference (p = .50). The Kaplan-Meier analysis suggested that the new fractures after surgery in both treatment groups may occur at the same frequency at around 31 months postoperatively. Vertebroplasty is more effective than vertebral perforation in relieving pain early in the course of treatment, but over the long term, no significant difference in pain was seen between the two treatments. The complication of new fractures seen with cement vertebroplasty is only seen after the procedure.

Blood and interstitial flow in the hierarchical pore space architecture of bone tissue

There are two main types of fluid in bone tissue, blood and interstitial fluid. The chemical composition of these fluids varies with time and location in bone. Blood arrives through the arterial system containing oxygen and other nutrients and the blood components depart via the venous system containing less oxygen and reduced nutrition. Within the bone, as within other tissues, substances pass from the blood through the arterial walls into the interstitial fluid. The movement of the interstitial fluid carries these substances to the cells within the bone and, at the same time, carries off the waste materials from the cells. Bone tissue would not live without these fluid movements. The development of a model for poroelastic materials with hierarchical pore space architecture for the description of blood flow and interstitial fluid flow in living bone tissue is reviewed. The model is applied to the problem of determining the exchange of pore fluid between the vascular porosity and the lacunar-canalicular porosity in bone tissue due to cyclic mechanical loading and blood pressure. These results are basic to the understanding of interstitial flow in bone tissue that, in turn, is basic to understanding of nutrient transport from the vasculature to the bone cells buried in the bone tissue and to the process of mechanotransduction by these cells.

Relationships of intraosseous and systemic pressure waveforms in a Swine model

BACKGROUND

Despite some focus on the use of intraosseous (IO) catheters to obtain laboratory samples, very little is known about the potential for obtaining other forms of clinical data. Largely unstudied is the relationship between IO pressures (IOPs) and systemic hemodynamic pressures such as mean arterial pressure (MAP) and central venous pressures (CVP).

OBJECTIVES

The objective was to explore the relationship between hemodynamic parameters (blood pressures) measured through an IO catheter and intravascular catheters placed in the arterial and central venous circulation.

METHODS

Eight pigs (Sus scrofa) weighing 30 to 45 kg were sedated with a short-acting agent, intubated with a cuffed endotracheal tube, and anesthetized with 2% to 3% isoflurane. Intravascular catheters were placed into the femoral or carotid artery and the femoral or jugular vein for MAP and CVP measurements. IO catheters, 15 mm for the sternum and 25 mm for the long bones, were placed percutaneously into the proximal tibia, proximal femur, proximal humerus, right proximal ulna, and/or sternum. Pressures were recorded during normotension, hypotension, and hypertension.

RESULTS

Averaged across all eight animals, the means (ranges) for baseline systemic pressures were as follows: MAP = 66.5 (55.6 to 76.7) mm Hg, tibia IOP = 17.4 (9.3 to 34.5) mm Hg, femur IOP =18.4 (3.3 to 33.1) mm Hg, humerus IOP = 15.7 (2.8 to 28.9) mm Hg, ulna IOP = 16.0 (7.9 to 25.6) mm Hg, sternum IOP = 5.7 (-0.5 to 47.9) mm Hg, and CVP = 2.7 mm Hg (-3.3 to 7.9) mm Hg. The best median correlation occurred between femur IOP and mean MAP (r = 0.65). The four highest correlations between IOP and MAP were associated with mean femur IOP. Only one IO site had a correlation coefficient over 0.50 for CVP. The long bones tended to correlate better with the MAP and the sternum tended to correlate better with the CVP. Nonlinearity was observed in the actively rising pressure phases, which can be explained by a hysteresis model.

CONCLUSIONS

The relationship between IOP and MAP or CVP is variable by site, with the MAP and CVP tending to be estimated by the femur and sternum, respectively. The relationship to actively rising pressures is nonlinear and a hysteresis model is proposed to explain the phase change. Further experimentation is needed to refine the IOP relationship to the MAP and CVP and assess the potential of these measurements to provide clinically relevant information.

Evaluation of intraosseous pressure in a hypovolemic animal model

BACKGROUND

In emergent situations, access to the vascular bed is frequently required for fluid and medication administration. Central venous catheter placement is associated with risk and may slow resuscitation in the unstable patient. The purpose of this study was to determine whether intraosseous pressure (IOP) could be consistently recorded and how similar this pressure was to central venous and arterial pressure in a porcine hemorrhagic shock model.

MATERIALS AND METHODS

After sedation, eight female swine had catheters placed in the femoral vein, aorta via femoral artery, and superior vena cava. IOP lines were placed in the proximal humerus, distal femur, and proximal tibia. Pressure readings were recorded continuously through the five stages of progressive hypovolemia. Pressure data were descriptively summarized, with the percent of change of IOP at each stage compared with arterial pressure using a multilevel mixed effects linear model with log transformation.

RESULTS

The IOP baseline values were between 16 and 18 mm Hg, approximately 22% of baseline arterial pressure. The intraosseous (IO) waveform mostly closely resembled the arterial pressure waveform, including the presence of a dichroitic notch. Pressure variations caused by ventilation (respiratory variability) were also identified in all the tracings. The rate of pressure change in the humeral IO most closely matched the change in arterial pressure rate. IO blood gas analysis showed gas composition to most closely match venous blood.

CONCLUSIONS

IOP was reliably obtained in this porcine model and suggests potential for clinical application in humans.

Use of an intraosseous device for invasive pressure monitoring in the ED

Venous access is essential to providing emergency care for critically ill or injured patients. Obtaining peripheral or central access can be problematic and time consuming. Intraosseous (IO) fluid administration provides similar flow rates and central circulation times compared to central lines, but use of these devices to monitor blood pressure has not been explored. We report a case of successful IO pressure (IOP) monitoring through an IO during the resuscitation of a 31-year-old male. This is the first report of monitoring IOP in a clinical setting and comparing it to traditional measures of central pressure.

Validity of intervertebral bone cement infusion for painful vertebral compression fractures based on the presence of vertebral mobility

BACKGROUND AND PURPOSE

It is uncertain whether analgesic effects of vertebroplasty in patients with painful VCF are actually attributable to intervertebral cement infusion. This study aims to assess the validity of cement infusion performed for pain relief based on the presence or absence of pseudoarthrosis.

MATERIALS AND METHODS

We compared therapeutic effects between PVP and vertebral perforation without bone cement infusion in patients with painful VCF. The subjects were 64 patients undergoing PVP (PVP group) and 67 undergoing vertebral perforation (perforation group). In all patients, preoperative dynamic radiography was performed to assess the presence of vertebral mobility. Patients were classified into 2 groups, those with and those without vertebral mobility, and changes in VAS and ADL scores before and after surgery were compared between the PVP and perforation groups.

RESULTS

Regarding patients with vertebral mobility, VAS improved during the 3 months immediately after surgery in the PVP group compared with the perforation group (P < .05). Although no significant difference in postoperative ADL scores was observed between the 2 treatment groups, the scores 3 months after surgery were better in the PVP group than in the perforation group. Meanwhile, in the subgroup of patients without vertebral mobility, both treatments produced marked pain relief, but the difference was not significant (P > .05). Moreover, there was no difference in ADL scores between the 2 treatment groups.

CONCLUSIONS

Intervertebral cement infusion exerts analgesic effects in patients with VCF with pseudoarthrosis. However, in those without vertebral mobility, the analgesic effects of vertebroplasty are the same regardless of bone cement infusion.

Intraosseous vascular access: A review

Intraosseous cannulation is an increasingly common means of achieving vascular access for the administration of fluids and medications during the emergent resuscitation of both paediatric and adult patients. Improved tools and techniques for intraosseous vascular access have recently been developed, enabling the healthcare provider to choose from a wide range of devices and insertion sites. Despite its increasing popularity within the adult population, and decades of use in the paediatric population, questions remain regarding the safety and efficacy of intraosseous infusion. Although various potential complications of intraosseous cannulation have been theorized, few serious complications have been reported. This article aims to provide a review of the current literature on intraosseous vascular access, including discussion on the various intraosseous devices currently available in the market, the advantages and disadvantages of intraosseous access compared to conventional vascular access methods, complications of intraosseous cannulation and current recommendations on the use of this approach.

Comparative study of percutaneous vertebral body perforation and vertebroplasty for the treatment of painful vertebral compression fractures

BACKGROUND AND PURPOSE

Percutaneous vertebral body perforation is a new technique for treating painful VCFs. Herein, we compare the therapeutic effect of vertebral perforation and conventional vertebroplasty for treating VCFs.

MATERIALS AND METHODS

One hundred eight patients with single painful VCFs were assigned to undergo vertebral perforation (perforation group) or vertebroplasty (PVP group). Clinical outcomes were assessed by using the VAS. The associations of analgesic effect and clinical factors were also analyzed by multivariate regression. Plain radiographs were used to quantify the progression of vertebral body compression after surgery and to evaluate cement leakage and new vertebral fractures. The median follow-up time was 10 months.

RESULTS

Baseline characteristics were similar in the 2 groups. No factors correlated with analgesic effects in the PVP group. The analgesic effect of vertebral perforation was, however, related to the preoperative severity of vertebral compression and was low in patients with severe deformity (P < .05). Among patients with preoperative vertebral percentage of compression below 30%, there were no significant differences between the 2 groups in analgesic effect at any postoperative intervals. Progression of vertebral compression after surgery occurred in 22.2% and 16.0% of treated vertebrae in the perforation and PVP groups, respectively (P = .38). Respectively, 3.7% and 20.0% of the perforation and PVP groups had new postoperative fractures during follow-up (P < .05). There were no other complications.

CONCLUSIONS

Vertebral perforation was safe and effective for painful VCFs with slight compression. However, vertebroplasty should be considered for patients with marked vertebral body compression.

The mechanical environment of bone marrow: a review

Bone marrow is a viscous tissue that resides in the confines of bones and houses the vitally important pluripotent stem cells. Due to its confinement by bones, the marrow has a unique mechanical environment which has been shown to be affected from external factors, such as physiological activity and disuse. The mechanical environment of bone marrow can be defined by determining hydrostatic pressure, fluid flow induced shear stress, and viscosity. The hydrostatic pressure values of bone marrow reported in the literature vary in the range of 10.7-120 mmHg for mammals, which is generally accepted to be around one fourth of the systemic blood pressure. Viscosity values of bone marrow have been reported to be between 37.5 and 400 cP for mammals, which is dependent on the marrow composition and temperature. Marrow's mechanical and compositional properties have been implicated to be changing during common bone diseases, aging or disuse. In vitro experiments have demonstrated that the resident mesenchymal stem and progenitor cells in adult marrow are responsive to hydrostatic pressure, fluid shear or to local compositional factors such as medium viscosity. Therefore, the changes in the mechanical and compositional microenvironment of marrow may affect the fate of resident stem cells in vivo as well, which in turn may alter the homeostasis of bone. The aim of this review is to highlight the marrow tissue within the context of its mechanical environment during normal physiology and underline perturbations during disease.

On bone adaptation due to venous stasis

This paper addresses the question of whether or not interstitial fluid flow due to the blood circulation accounts for the observed periosteal bone formation associated with comprised venous return (venous stasis). Increased interstitial fluid flow induced by increased intramedullary pressure has been proposed to account for the periosteal response in venous stasis. To investigate the shear stresses acting on bone cell processes due to the blood circulation-driven interstitial fluid flow, a poroelastic model is extended to the situation in which the interstitial fluid flow in an osteon is driven by the pulsatile extravascular pressure in the osteonal canal as well as by the applied cyclic mechanical loading. Our results show that under normal conditions, the pulsatile extravascular pressure in the osteonal canal due to cardiac contraction (10mm Hg at 2Hz) and skeletal muscle contraction (30mm Hg at 1Hz) induce peak shear stresses on the osteocyte cell processes that are two orders of magnitude lower than those induced by physiological mechanical loading (100 microstrain at 1Hz). In venous stasis the induced peak shear stress is reduced further compared to the normal conditions because, although the mean intramedullary pressure is increased, the amplitude of its pulsatile component is decreased. These results suggest that the interstitial fluid flow is unlikely to cause the periosteal bone formation in venous stasis. However, the mean interstitial fluid pressure is found to increase in venous stasis, which may pressurize the periosteum and thus play a role in periosteal bone formation.

Avascular necrosis of the femoral head after femoral neck fracture

Trauma-induced avascular necrosis of the femoral head represents the most common femoral head aseptic necrosis. An alteration in blood supply to the femoral head is the cause of the vascular necrosis. Another mechanism in the genesis of femoral head necrosis is the tamponade effect. Femoral head necrosis may be asymptomatic for a long time, even in patients in whom late segmental collapse already is present. Radiography does not allow diagnostic reliability until 6 months after fracture. The presence of a low signal intensity band away from the fracture line on magnetic resonance images clearly delimits the necrotic area. Once segmental collapse has developed, the diagnosis becomes simple using plain radiographs. The treatment of established femoral necrosis complicating fractures of the upper end of the femur is approached as a therapeutic problem lacking an optimal solution. The main therapeutic options are femoral head-preserving procedures and joint reconstruction. Among the procedures that preserve the femoral head are joint unloading, femoral head core decompression, electric stimulation, osteotomy, and bone grafting. Joint reconstruction procedures including cup arthroplasty, hemiresurfacing, total hip resurfacing, femoral head replacement, femoral head endoprosthesis, and total arthroplasty will be reviewed.

Endogenous norepinephrine regulates blood flow to the intact rat tibia

The goal of our study was to determine if endogenous norepinephrine (NE) has a role in the regulation of basal blood flow to intact bone. The experimental plan was to measure bone blood flow before and after pharmacological blockade of alpha-adrenergic receptors. A significant increase in blood flow after receptor blockade would suggest that endogenous norepinephrine exerts a tonic constrictor effect on the vessels supplying blood to the bone. Mature, male rats were anesthetized with Inactin. Arterial blood pressure and left tibia blood flow (laser Doppler flowmetry) were measured. A cannula was inserted into the right iliac artery and advanced to the aortic bifurcation to deliver drugs into the left hindlimb circulation, including the left tibia vasculature. Bolus injection of norepinephrine caused a dose-dependent decrease in bone blood flow (30-40%). Blockade of alpha-adrenergic receptors with phentolamine or phenoxybenzamine attenuated by more than 50% the norepinephrine-induced decrease in bone blood flow. In separate rats that had not received exogenous norepinephrine, injection of phentolamine alone decreased bone vascular resistance by 34+/-3%. Similarly, phenoxybenzamine decreased resistance by 25+/-4%. These results are consistent with the conclusion that alpha-adrenergic receptors mediate a significant constriction of blood vessels which participate in the partial control of basal blood flow to the intact rat tibia.

A new in vivo method for the direct measurement of nutrient artery blood flow

A new method of directly measuring nutrient artery blood flow using ultrasonic probes is described. These probes have provided reproducible results in our experiments. Advantages of ultrasonic probes include the direct measurement of blood flow through small arteries, ease of use, accuracy of measurement, applicability to a wide range of vessel diameters, the capability of chronically monitoring blood flow over time using permanently implanted probes, and the ability to use the method in conjunction with previous methods of bone blood flow measurement. The method is limited to the extent that only the contribution of the nutrient artery can be measured and total bone blood flow cannot be assessed. Tibial nutrient arterial flow and cardiac output were measured in adult mongrel dogs. Two experiments were performed: 1) bilateral baseline tibial nutrient artery blood flow measurements over time and 2) tibial nutrient blood flow comparing inhaled anesthesia (halothane/nitrous oxide/oxygen) and intravenous anesthesia (pentobarbital [Nembutal]). In 15 mongrel dogs, tibial nutrient artery blood flow averaged 1.46 +/- 0.72 mL/min (0.09 +/- 0.05 percent of cardiac output and 2.75 +/- 1.95 mL/min/100 g of bone). No significant difference in tibial nutrient artery blood flow was observed between animals given intravenous and inhaled anesthesia (P > .05). As a basic research tool, transit-time ultrasonic blood flow technology may be useful. The method is relatively easy to use and may be applied to experimental models designed to investigate various physiologic and pathologic states frequently encountered in orthopedics (eg, shock, sepsis, fractures).

The relationship between inert gas wash-out and radioactive tracer microspheres in measurement of bone blood flow: effect of decreased arterial supply and venous congestion on bone blood flow in an animal model

Several methods have been employed in the study of bone perfusion. We used a method of determining inert gas wash-out by mass spectrometry in the study of blood flow rates in pigs. The method was validated by comparison of the result obtained with inert gas wash-out to that with measurement by microspheres. Furthermore, the effect of decreased inlet flow and venous congestion on the bone perfusion data was tested. The undisturbed bone blood flow was not significantly different when measured with wash-out of inert gas (7 +/- 0.7 ml/min/100 g) or with microspheres (9 +/- 2.9 ml/min/100 g), and the methods were correlated. Perfusion was reduced significantly, to 20% of the original value, after arterial occlusion. The changes in wash-out curves and accumulation of radioactive tracer provided substantial evidence for impaired intraosseous circulation following venous obstruction also. In conclusion, the study showed that this method of determining inert gas wash-out is feasible for studies of local perfusion rates in bone. The flow rates obtained by wash-out correlated well with the results of microsphere studies. In this animal model, both methods detected a fivefold reduction in flow rate after clamping of the arterial inflow. Obstruction of the venous outflow also impaired blood flow and lowered the cellular supply.

Intraosseous infusion of prostaglandin E2 in the caprine tibia

We evaluated the effects of intraosseously administered prostaglandin E2 (PGE2) within the proximal metaphysis of the goat (caprine) tibia under intraosseous normotensive and hypertensive conditions. PGE2 was administered at 0.5 or 1.0 mg (1 ml vol) twice daily for 10 days via an Osteoport which had been surgically implanted within the proximal tibial metaphysis. Intraosseous hypertension was produced when venous outflow obstruction (VOO) was created by ligation of the popliteal vein, which drained the proximal tibia, and occlusion of the diaphyseal medullary space distally with bone cement. After VOO, the intraosseous pressure measured at the metaphysis increased significantly (p < 0.05) from a baseline mean of 14.9 +/- 4.2 mm Hg to 28.6 +/- 5.3 mm Hg. Serum radioimmunoassays indicated that VOO prolonged the venous drainage of PGE2 from the tibia after an infusion. Static histomorphometric analysis indicated a marked dose-dependent increase in new bone formation in all PGE2 groups at 30 days after the PGE2 infusion. Significant (p < 0.05) formation of new bone occurred, primarily at the subperiosteal and endocortical surfaces, and moderately increased the marrow cavity of cancellous new bone as compared with the VOO-only group and the controls. Bone remodeling indices were also increased by PGE2. The PGE2 infusion, combined with VOO, produced significantly more new bone formation than the PGE2 infusion alone. Intensive marrow fibrosis was associated with the active bone remodeling.

Intraosseous infusion using the osteoport implant in the caprine tibia

We evaluated the in vivo animal tolerance to intraosseous infusion via the Osteoport pediatric implant (model 2005PSO, Lifequest Medical, San Antonio, TX, U.S.A.) into the proximal tibia of immature goats and investigated the osseous effects of intermittent and sustained increases in intraosseous pressure (IOP). In group 1 (n = 3) autogenous whole blood was continuously infused (CI) for 5 days at flow rates producing an IOP of 30-45 mm Hg. Group 2 animals (n = 3) underwent a 5-s high-pressure infusion (HPI) of lactated Ringer solution (LRS) producing an IOP of 90-125 mm Hg twice daily for 10 days. In group 3, the Osteoports were left in place 5 (n = 2) or 10 days (n = 2) and evaluated for patency at 72-h intervals. An IOP > 35 mm Hg produced clinical evidence of bone pain. Bone mineral density was significantly increased (p < 0.05) in all implanted tibias (mean 1.04 g/cm2; range 0.87-1.21 g/cm2) compared with controls (mean 0.67 g/cm2; range 0.65-0.71 g/cm2). A nonsignificant increase (+9% to +31%) in periosteal new bone formation occurred in all implanted tibias. In the continuously infused group, there was a significant increase (p < 0.05) in cancellous new bone formation (+483%), percentage eroded bone surface (+143%), and osteoclast covered bone surface (+255%) compared with controls. HPI of LRS did not produce significant bone changes. Seemingly, the Osteoport provided a ready means of intraosseous infusion and may be associated with less complications than current methods of continual vascular access. Bone changes correlated more with the duration than the magnitude of increased intraosseous pressures.

Vasoactive substances in subchondral bone of the dog knee

The purpose of the present study was to investigate regulatory mechanisms for subchondral bone blood flow. A model including elevation of joint cavity pressure in the immature dog knee was applied. The role of prostaglandins in bone blood flow regulation was indirectly examined by indomethacin blockade. In six puppies, both venous tamponade of the joint cavity [50% of the mean arterial blood pressure (MAP)] and arterial tamponade (150% of MAP) resulted in a significant increase in the intraosseous pressure of the distal femoral epiphyses (p less than 0.05). During venous tamponade no changes were registered in pO2, pCO2, pH, potassium, and lactate in blood withdrawn from the distal femoral epiphyses. Arterial tamponade resulted in hypoxia, a decrease in pH, and increased lactate. Inhibition of the prostaglandin synthesis did not alter this response pattern. Thus, the present study suggests the presence of a regulatory mechanism for subchondral bone blood flow since venous tamponade did not significantly alter intraosseous gas tensions, pH, lactate, or potassium in spite of elevated venous outlet resistance. The study does not allow any conclusion as to the exact nature of the regulatory mechanism, but local metabolic regulation is likely to be involved as indicated by accumulation of vasoactive substances at higher tamponade levels. Prostaglandins are probably of minor importance in this regulation.

Bone marrow embolism following cryosurgery of bone: an experimental study

Cryosurgery is commonly used in medicine for treatment of benign and malignant lesions. We had clinical and experimental data indicating that cryosurgery of intact bone could cause bone marrow intravasation and embolism, i.e., particles of bone marrow entering extraosseous veins and occluding pulmonary vasculature. This study was designed to investigate the pathogenesis of bone marrow intravasation and embolism after cryosurgery. Three hypotheses on the pathogenesis of bone marrow intravasation were tested using a model of cryosurgical continuity lesion in rats and rabbits. Influence of physical and circulatory factors were excluded supporting a mechanical-biological hypothesis; the intravasation of bone marrow after cryosurgery of bone is caused by an increased intramedullary pressure. The increased intramedullary pressure is due to edema in the medullary cavity caused by cryosurgical damage to cell membranes. It is demonstrated that the bone marrow intravasates can embolize to the lungs causing respiratory insufficiency. This can be a serious complication following cryosurgery of intact bone. Prophylactic decompression of the medullary cavity can possibly prevent the rise in intramedullary pressure and thus intravasation and embolisation of bone marrow after cryosurgery of intact bone.

Compartment syndrome delays tibial union

There has been no previous investigation into the association between compartment syndrome and delayed or nonunion of the tibia following fracture. To establish whether such an association might exist, a retrospective survey of the results of the treatment of closed and Grade I tibial fractures complicated by compartment syndrome was undertaken. The survey showed that there was a significant delay in fracture union in patients over 18 years of age, but not in younger patients.

Bone marrow pressure chamber: a permanently inserted titanium implant for intramedullary pressure measurements

We describe a titanium implant for repeated intramedullary pressure measurements. The implant has been inserted permanently in the tibia of rabbits. Pressure is transmitted through a membrane in the chamber to a transducer connected to a meter. During the recordings no penetration of the cortex is necessary. The measured intact intramedullary pressure in the tibia was approximately 12 cmH2O.

Osteotomy of the patella in the patellofemoral pain syndrome. The significance of increased intraosseous pressure during sustained knee flexion

In 40 patients with patellofemoral pain, intra-osseous pressure measurements were recorded under anaesthesia with the knee first in extension and then in flexion prior to performing a longitudinal osteotomy of the patella. There was a statistically significant increase of pressure in painful knees compared with normal knees (29 mm Hg. vs 15 mm Hg.), and a marked increase when compared during sustained flexion (97 mm Hg. vs 60 mm Hg.). However wide variability of individual results made the diagnostic value of a single pressure measurement unreliable. A clinical test, based on reproduction of the characteristic pain by sustained knee flexion, proved to be reliable in predicting a good response to operation. The effect of the operation was encouraging, with significant relief of pain as measured by a visual analogue scale.

Relationship between intraosseous pressures and intra-articular pressure in arthritis of the knee. An experimental study in immature dogs

The influence of chronic synovial inflammation and effusion on the juxta-articular bone haemodynamics in the juvenile knee was studied in 12 immature dogs with Carragheenin-induced unilateral arthritis. Using a fluid filled electromanometric pressure recording system simultaneous pressure measurements were taken from the distal femoral metaphysis, juxta-articular epiphyses and knee joint cavity in general anaesthesia followed by intraosseous phlebographies. During resting conditions the intraosseous pressure of the distal femoral epiphysis and the intra-articular pressure was significantly elevated. The phlebographies showed increased accumulation of contrast in arthritic femoral epiphyses with decreased contrast clearance rate. During increasing intra-articular pressure an augmented vulnerability of the blood supply of the arthritic femoral epiphyses was demonstrated. The results suggests that joint effusion may play an important role in the bone changes in juvenile degenerative arthritis of the knee.

Hemodynamics of the juvenile knee in relation to increasing intra-articular pressure. An experimental study in dogs

The relationships between intraosseous pressure and regional blood flow in the juxta-articular epiphyses were determined in the knees of immature dogs. Intraosseous pressures were continuously registered in one knee. Regional blood flow rates were simultaneously determined by the microsphere technique before and after venous tamponade of both knee joint capsules. During complete venous tamponade the intraosseous pressure of the distal femoral epiphyses rose 268%, while flow increased 122%. A concurrent 20-fold flow increase of the knee capsule and 3-4-fold flow increase of the proximal femoral bone was observed. Evacuation of the knee joints resulted in an immediate drop of the intraosseous pressure of the distal femoral epiphyses, whereas hyperaemia prevailed for at least half an hour and was most pronounced in the distal femoral epiphyses and knee joint capsule. Intraosseous pressure registration did not significantly influence regional blood flow. It is suggested that the changes of intraosseous pressures during knee joint tamponade reflect changes in the venous outlet resistance. The results demonstrate the significance of intra-articular pressure increase on the hemodynamics of the juxta-articular tissues of the knee and proximal femoral bone. These findings may be of importance in the pathogenesis of growth disturbances observed in juvenile degenerative arthritis.

Intraosseous pressure in the patella in relation to simulated joint effusion and knee position: an experimental study in puppies

Simultaneous pressure measurements were carried out in the patella, juxtaarticular epiphyses and the knee joint cavity of six mongrel puppies. The mean intraosseous pressure in the patella was 12.2 mmHg, range 8-15 mmHg. An increase in intraarticular pressure in turn caused an increase in the intraosseous pressure of the patella and juxtaarticular epiphyses. The pressure increase in the patella was the most pronounced. During extension of the knee joint, a significant rise in intraosseous pressure of the tibial epiphysis and patella was observed, whereas during flexion femoral epiphyseal pressure and patellar pressure increased significantly. The introduction of moderate intraarticular effusion amplified intraosseous pressure responses during flexion of the knee joint. The intraosseous pressure changes during knee movement could not be explained solely by the corresponding changes in intraarticular pressure. Intraosseous phlebography revealed a venous drainage system largely parallel to the arterial blood supply. The contrast clearance time was decreased during moderate elevation of the intraarticular pressure, suggesting increased bone blood flow of the patella.

Primary osteoarthritis of the hip. Interrelationship between intraosseous pressure, X-ray changes, clinical severity and bone density

The intraosseous pressure of the femoral head and greater trochanter was measured during 146 Charnley hip replacement operations. In 108 hips with primary osteoarthritis the pressure in the femoral head averaged 49.6 and in the greater trochanter 31.6 mmHg. The pressures in the greater trochanter were significantly lower than those in the femoral head. There was no sex difference, and the pressures were independent of age. The intraosseous pressure in the femoral head varied appreciably with a dispersion which did not significantly differ from the normal distribution. There was a faintly positive correlation between the mean blood pressure and the intraosseous pressure. No relationship was found between the pressure in the femoral head and the radiological severity of the osteoarthritis or between the intraosseous pressure and the duration of symptoms, severity of rest pain, walking ability, range of motion or degree of bone density at the site of measurement. The haemodynamic conditions in bone depend upon blood flow and resistance. Variations in these two factors determine the actual intraosseous pressure. As a consequence intraosseous pressure measurement as the only evaluation of the haemodynamic conditions is of limited value. The vascular factor in osteoarthritis needs further clarification.

The effect of lumbar sympathetic stimulation on the vasculature of bone

1 The nutrient artery to the tibia of anaesthetized dogs was perfused at a constant rate by blood from the femoral artery and the perfusion pressure in the artery, the intramedullary pressure of the bone and the pressure in the nutrient vein recorded. 2 Low frequency stimulation (1 to 5 HZ) of the lumbar sympathetic chain always increased the perfusion pressure but the intramedullary pressure sometimes increased, sometimes decreased and sometimes remained unchanged. 3 The alpha-adrenoceptor blocking agents, phentolamine (1 mg/kg i.v.) and dihydroergotamine (0.5 mg/kg i.v.) reduced or abolished these effects whereas the beta-adrenoceptor blocking agent, propranolol (1 mg/kg i.v.) did not modify them. 4 The nutrient vein end pressure did not differ significantly from the intramedullary pressure and underwent similar variations during stimulation of the lumbar sympathetic chain.

Intramedullary pressure of the patella in Chondromalacia

Degenerative changes in load-bearing joints are often combined with altered intramedullary circulation. This may cause an alteration in intramedullary pressures. It has been said that articular symptoms are connected with a change in intramedullary pressures being high they are suspected to cause pain. In this investigation the intramedullary pressure has been evaluated in chondromalacia and osteoarthrosis of the patella. A comparison has been made with normal patellae. A biopsy needle was drilled into the intramedullary bone of the patella and connected with a registering unit. In a control group an average value of 19 mm Hg was registered. In the condromalacia group the mean intramedullary pressure was 44 mm Hg and in osteoarthrosis 37 mm Hg.

Observations on long bone medullary pressures in relation to arterial PO2, PCO2 and pH in the anaesthetized dog

To investigate the influence of variations in arterial oxygen tensions (PaO2), arterial carbon dioxide tensions (PaCO2), and arterial pH on long bone medullary pressures, seven anaesthetized dogs were investigated. Comparing the control medullary pressures, i.e. the mean medullary pressures obtained at the normal range of PaO2 (75--110 mmHg) with the mean medullary pressures corresponding to the range of PaO2 of less than 75 mmHg, statistically significant (P less than 0.05) decreases were seen in both epiphyseal, metaphyseal and diaphyseal medullary pressures, from 27.6 +/- 5.0 to 15.5 +/- 3.6 mmHg, from 23.5 +/- 2.9 to 13.9 +/- 2.3 mmHg and from 27.7 +/- 3.9 to 18.3 +/- 2.5 mmHg (all mean values +/- s.e. mean), respectively. Hyperoxia, hypocapnia, hypercapnia or metabolic acidosis had no effect on medullary pressures in any of the regions studied.

Observations on long bone medullary pressure in relation to mean arterial blood pressure in the anaesthetized dog

To study the influence of variations in mean arterial pressures (MAP) on long bone medullary pressures, seven anaesthetized dogs were investigated. The medullary pressures were measured in the epiphyseal, the metaphyseal and the diaphyseal regions and remained rather constant when MAP was above 80 mmHg. Below this level of MAP a statistically significant (P less than 0.01) reduction of the medullary pressures was seen. Comparing the mean medullary pressures obtained with ranges of MAP of 81--100 mmHg (the control medullary pressures) and of 61--80 mmHg, the greatest decline was seen in the epiphyseal and the diaphyseal regions, from 25.2 mmHg to 8.1 mmHg and from 26.7 mmHg to 8.3 mmHg, respectively. The corresponding decrease in the metaphyseal region was from 18.9 mmHg to 10.9 mmHg. The mean values of intraosseous pressure measured by our technique were between 20--30 mmHg and this is in accordance with measurements in normal humans found by other authors.

Bone-marrow pressure and bone strength

The pattern of bone-marrow pressure changes differed with the mode of stress application. Intra-medullary pressure remained steady during most of the slow loading. During rapid dynamic loading, however, a slight rise in intra-medullary pressure was observed. Contraction of the femoral muscles also resulted in a greater bone-marrow pressure increase. A correlation of 0.98 (P less than 0.001) between stimulus strength and intra-medullary pressure was obtained. The rise in intra-medullary pressure with femoral muscle contraction is suggested to have a possible role under extreme stresses in living conditions.

The influence of some vasoactive drugs on bone circulation

We have studied the effect of various drugs on the intramedullary pressure in dog tibia after constant-flow autoperfusion of the nutrient artery by femoral arterial blood. The perfusion pressure and carotid arterial pressure were also recorded. Isoprenaline, acetylcholine, histamine, theophylline always lowered the perfusion pressure but had a variable effect on intramedullary pressure. This results from several factors e.g., perfusion pressure and intraosseous vasomotoricity. Adrenaline always caused a rise of the perfusion pressure and lowered the intramedullary pressure in most of the cases. Such effects were reduced or suppressed by alpha-blocking drugs. Isoprenaline caused a lowering of the perfusion pressure which was suppressed by propranolol. A rise of the intramedullary pressure through beta-induced vasodilatation was shown in some experiments. The effect of adrenaline on the perfusion pressure could be reversed after alpha-blockade. These results show the presence of intraosseous vascular alpha- and beta-adrenoceptors.