Intramedullary Pressure Research Articles

Would increased interstitial fluid flow through in situ mechanical stimulation enhance bone remodeling?

Bone accommodates to changes in its functional environment ensuring that sufficient skeletal mass is appropriately positioned to withstand the mechanical loads that result from functional activities. Increasing physical activity will result in increased bone mass, while the removal of functional loading would result in bone loss. Bone is a composite material made up of a collagen-hydroxyapatite matrix and a complex network of lacunae-canaliculi channels occupied by osteocyte and osteoblast processes, immersed in interstitial fluid. There are strong indications that changes in interstitial fluid flow velocity or pressure are the means by which an external load signal is communicated to the cell. In vitro studies indicate that shear stress, induced by interstitial fluid flow, is a potent bone cell behavior regulator. One of the forms of altering interstitial fluid flow is through the mechanical deformation of skeletal tissue in response to applied loads. Other methods include increased intramedullary pressure, negative-pressure tissue regeneration, or external mechanical stimulation. Analysis of these methods poses the question of process effectiveness. The efficacy of each method theoretically will depend on the mechanical efficiency of transmitting an external load and converting it into changes in interstitial fluid flow. In this paper, we combine recent knowledge on the effect of the bone's interstitial fluid flow, different fluid patterns, the role of gap junctions, and the concept of mechanical effectiveness of different methods that influence interstitial fluid flow within bone, and we hypothesize that the efficiency of bone remodeling can be improved if a small mechanical percussion device could be placed directly in contact with the bone, thus inducing local interstitial fluid flow variations. Enhancement of bone repair and remodeling through controlled interstitial fluid flow possesses many clinical applications. Further investigations and in vivo experiments are required. Practical methods and clinical apparatuses need to be conceived and developed to validate and facilitate the clinical use of this technique.

Skeletal nutrient vascular adaptation induced by external oscillatory intramedullary fluid pressure intervention

BackgroundInterstitial fluid flow induced by loading has demonstrated to be an important mediator for regulating bone mass and morphology. It is shown that the fluid movement generated by the intramedullary pressure (ImP) provides a source for pressure gradient in bone. Such dynamic ImP may alter the blood flow within nutrient vessel adjacent to bone and directly connected to the marrow cavity, further initiating nutrient vessel adaptation. It is hypothesized that oscillatory ImP can mediate the blood flow in the skeletal nutrient vessels and trigger vasculature remodeling. The objective of this study was then to evaluate the vasculature remodeling induced by dynamic ImP stimulation as a function of ImP frequency.MethodsUsing an avian model, dynamics physiological fluid ImP (70 mmHg, peak-peak) was applied in the marrow cavity of the left ulna at either 3 Hz or 30 Hz, 10 minutes/day, 5 days/week for 3 or 4 weeks. The histomorphometric measurements of the principal nutrient arteries were done to quantify the arterial wall area, lumen area, wall thickness, and smooth muscle cell layer numbers for comparison.ResultsThe preliminary results indicated that the acute cyclic ImP stimuli can significantly enlarge the nutrient arterial wall area up to 50%, wall thickness up to 20%, and smooth muscle cell layer numbers up to 37%. In addition, 3-week of acute stimulation was sufficient to alter the arterial structural properties, i.e., increase of arterial wall area, whereas 4-week of loading showed only minimal changes regardless of the loading frequency.ConclusionsThese data indicate a potential mechanism in the interrelationship between vasculature adaptation and applied ImP alteration. Acute ImP could possibly initiate the remodeling in the bone nutrient vasculature, which may ultimately alter blood supply to bone.

Noninvasive Assessment of Structural and Mechanical Properties of Trabecular and Cortical Bone by Proton, Deuteron and Phosphorus Magnetic Resonance

Objective. The aim of this study was to evaluate the predictive value of bone mineral density and intracortical porosity measured by micorcomputed tomography for the strength of cortical bone biopsies.Design. Experimental study comparing the predictive value of bone mineral density and of intracortical porosity determined in vitro by microcomputed tomography for the mechanical properties of cortical bone cylinders.Background. The assessment of cortical bone strength might be relevant for the prediction of fracture risk or the choice of suitable therapy strategies in orthopaedic surgery. The predictive value of cortical density for the mechanical properties is discussed controversially. The relevance of intracortical porosity measured by histomorphometry has been established, but the predictive value of porosity determined by microcomputed tomography remains to be explored.Methods. Femoral cortical bone specimens from the mid diaphysis of 24 patients were harvested during total hip replacement procedure at the location, where a diaphyseal hole (∅4.5 mm) was drilled in order to reduce the intramedullary pressure. In vitro intracortical porosity and bone mineral density measurements by microcomputed tomography were compared with strength and elastic modulus assessed by a compression test transverse to the Haversian systems of the same specimens.Results. Significant negative correlations were found between porosity measured by microcomputed tomography scans and yield stress, stiffness and elastic modulus (P<0.001), however, the positive correlations between bone mineral density and mechanical parameters were stronger (P<0.0001). The mechanical parameter best predicted by mineral density as well as by porosity was yield stress (r=0.72,P<0.0001;r=−0.64,P<0.001).Conclusions. Bone mineral density determined by microcomputed tomography imaging in vitro may be a potent method to predict mechanical properties of cortical bone non-destructively. The application in vivo remains to be explored.RelevanceThe relevance of bone mineral density measured by computed tomography for the estimation of the mechanical capacity of cortical bone was confirmed by an in vitro experiment. However, although intracortical porosity measured by microcomputed tomography showed significant correlations with mechanical parameters, it could not improve the prediction of mechanical strength of cortical bone beyond bone mineral density.

In situ permeability measurement of the mammalian lacunar–canalicular system

Bone is capable of adapting its mass and structure under mechanical cues. Bone cells respond to various mechanical stimuli including substrate strain, fluid pressure, and fluid flow (shear stress) in vitro. Although tissue-level strains are well documented experimentally, microfluidic parameters around bone cells are quantified mainly through theoretical modeling. A key model parameter, the Darcy permeability of the bone lacunar–canalicular system (LCS), is difficult to measure using traditional methods due to the co-existence of the larger vascular and smaller LCS porosities. In this paper, we developed a novel method to measure the LCS permeability by rapid compaction of intact mammalian bones and recording the intramedullary pressure (IMP). Six canine metacarpals were subjected to three step compression tests with peak loads of 50, 100, or 200 lbs, while the IMP was simultaneously recorded using a catheter pressure transducer. The loading ramp time was chosen to be ~ 2 ms, which was long enough to allow pressure equilibrium to be established between the marrow cavity and the vascular pores, but short enough to observe the LCS fluid flowing into and out of the vascular pores. This loading scheme permitted us to differentiate the contribution of the two intermingled porosities to the IMP responses. The time constant of the IMP pressurization and relaxation due to the LCS was found to be 8.1 ± 3.6 s ( n = 18). The mid-shaft cortex of the metacarpals mainly consisted of osteons with an average radial thickness of 65 ± 27 µm, which served as the characteristic distance for the LCS fluid to relax. The LCS permeability was obtained via poroelastic analysis to be 2.8 ± 1.8 × 10 − 23 m 2, which was smaller than previous theoretical predictions (order of 10 − 19 to 10 − 22 m 2), but within the range of previous experimentally based estimations (order of 10 − 22 to 10 − 25 m 2). Our results also show that osteoblasts and osteocytes experience hydraulic pressures that differ by three orders of magnitude under physiological compressive strains. These estimates of the in vivo mechanical environments may be used to design in vitro models for elucidating the cellular and molecular mechanisms of bone adaptation and pathological bone loss.

Surgical techniques: how I do it? The Reamer/Irrigator/Aspirator (RIA) System

Although reamed intramedullary nailing has long been considered a safe procedure, pulmonary complications have been reported in some groups of patients. Concerns over fat embolisation, adult respiratory distress syndrome (ARDS), and sudden intraoperative death have prompted some authors to question whether the benefits of reaming are outweighed by its potential adverse effects to the patient. In response to these complications, recent evaluations have focused on alternative systems that reduce intramedullary pressure during reaming. The Reamer/Irrigator/Aspirator (RIA) system (Synthes, Inc., West Chester, PA) was developed as a simultaneous reaming and aspiration system to reduce the intramedullary pressure, heat generation, operating time, and systemic effects of reaming. It was designed with an aggressive one-pass reamer head which is connected to a hand-held reamer via a drive shaft, simultaneously irrigating and aspirating femoral canal contents during reaming, thus preventing thermal necrosis and fat embolisation. After its early use, investigators examined the “aspirate” captured by the RIA which appeared to be loaded with osteogenic substrates. This discovery revealed a second potential use for the RIA-a bone graft harvester. The different design characteristics and technicalities of the RIA system necessitate a deep and clear understanding of its technique, a meticulous preoperative planning and a strict adherence to its principles intraoperatively. We present our current approach to the use of the RIA system, including the preoperative planning, the details of the operative procedure, the pitfalls and the potential complications that could be encountered.

What Is Wrong in the Cava? A Rare Cause of Deep Vein Thrombosis

When using cement in a hip arthroplasty, high intramedullary pressures are generated. This may lead to several complications, ranging from local extravasation to systemic complications such as the implantation syndrome. Until now, venous migration of cement after hip arthroplasty has never been associated with morbidity or mortality. We present a case in which cement pressurization led to migration of cement up to the level of the inferior vena cava with subsequent deep vein thrombosis.

Cortical perfusion and local fat occlusion after intramedullary nailing of the ovine tibia—Comparison of different surgical procedures

The aim of this study was to determine whether reamed or unreamed nailing is more harmful to local bone perfusion and increases fat occlusion of transcortical vessels. Methods After creating a standard fracture of the sheep tibia, reaming was performed in the first group using an experimental optimised reaming system (RE), in the second group with the conventional AO reamer (RC). Unreamed nailing was performed in the third group (UN). UHN 7.5 mm titanium was inserted in all three groups. Intramedullary pressure was measured intraoperatively. Quantitative histological analyses of the bone were performed postoperatively. Results The highest fat occlusion of transcortical vessels occurred in UN (5.7%), the lowest in RE (1.6%). The least harm to intracortical circulation was caused by RE with 28% perfused intracortical vessels compared to 17% (UN) and 18% (RC). Conclusion The experimental optimised reaming system reduces circulatory disturbance and local fat occlusion compared to the existing nailing procedures.

Fat extravasation due to unreamed and experimentally reamed intramedullary nailing of the sheep femur

Aim To compare systemic fat extravasation in unreamed and experimentally reamed nailing. Methods An osteotomy was created in the proximal third of the femoral shaft in 16 sheep, and intramedullary pressure increase and fat extravasation were monitored for the two nailing techniques. Results The highest intramedullary pressures, median 2700 mmHg, and highest percentages of fat extravasation, peaking at almost 90% of fat, were found for the unreamed nailing technique. The values for the reamed group were significantly lower. Conclusions The extravasation of intramedullary fat can be attributed to the great increase in intramedullary pressure that occurs during unreamed nailing. Correctly performed intramedullary reaming with the new reaming system produces lower pressures and much less systemic fat extravasation, reducing the risk for fat embolism.

Cardiopulmonary response to reamed intramedullary nailing of the femur with a traditional reaming system and a one-step reamer-irrigator-aspirator reaming system; an experimental study in pigs

There is general agreement that early internal stabilization in long bone fractures in severely injured patients is advantageous. Intramedullary reaming and nailing, however, include increased intramedullary pressure. This may cause intravasation of bone marrow contents, leading to bone marrow embolisation and altered cardiopulmonary function. Possible beneficial effects of attenuation of the intramedullary pressure increase by the use of a reamer-irrigator-aspirator (RIA) system were studied with the hypothesis that the RIA technique would cause lower numbers of pulmonary embolisms and lesser cardiopulmonary affection than after traditional reaming (TR).

Intramedullary pressure and matrix strain induced by oscillatory skeletal muscle stimulation and its potential in adaptation

Intramedullary pressure (ImP) and low-level bone strain induced by oscillatory muscle stimulation (MS) has the potential to mitigate bone loss induced by disuse osteopenia, i.e., hindlimb suspension (HLS). To test this hypothesis, we evaluated (a) MS-induced ImP and bone strain as function of stimulation frequency and (b) the adaptive responses to functional disuse, and disuse plus 1 and 20 Hz stimulation in vivo. Femoral ImP and bone strain generated by MS were measured in the frequencies of 1–100 Hz in four rats. Forty retired breeder rats were used for the in vivo HLS study. The quadriceps muscle was stimulated at frequencies of 1 and 20 Hz, 10 min/d for four weeks. The metaphyseal trabecular bone quantity and microstructure at the distal femur were evaluated using μCT, while bone formation indices were analyzed using histomorphometric technique. Oscillatory MS generated a maximum ImP of 45±9 mmHg at 20 Hz and produced a maximum matrix strain of 128±19 με at 10 Hz. Our analyses from the in vivo study showed that MS at 20 Hz was able to attenuate trabecular bone loss and partially maintain the microstructure induced by HLS. Conversely, there was no evidence of an adaptive effect of stimulation at 1 Hz on disused skeleton. The results suggested that oscillatory MS regulates fluid dynamics and mechanical strain in bone, which serves as a critical mediator of adaptation. These results clearly demonstrated the ability of MS in attenuating bone loss from the disuse osteopenia, which may hold potential in mitigating skeletal degradation imposed by conditions of disuse, and may serve as a biomechanical intervention in clinic application.

Fatal Fat Embolism following Femoral Head Resection in Total Hip Arthroplasty

We report a rare complication during primary total hip arthroplasty. A fatal fat pulmonary embolism immediately followed removal of the femoral head, prior to further preparation of the acetabulum or femoral shaft. Fat embolism syndrome is a well-known complication during total joint arthroplasty, usually attributed to preparation of the femoral shaft, particularly intramedullary reaming and insertion of the prosthesis. These risk factors have previously been identified in the literature. We believe that this case highlights the need for further research to establish the intramedullary pressures during the processes of dislocation and resection of the femoral neck and the attendant risk.

Osteogenic potential of reamer irrigator aspirator (RIA) aspirate collected from patients undergoing hip arthroplasty

Intramedullary nailing preceded by canal reaming is the current standard of treatment for long-bone fractures requiring stabilization. However, conventional reaming methods can elevate intramedullary temperature and pressure, potentially resulting in necrotic bone, systemic embolism, and pulmonary complications. To address this problem, a reamer irrigator aspirator (RIA) has been developed that combines irrigation and suction for reduced-pressure reaming with temperature modulation. Osseous particles aspirated by the RIA can be recovered by filtration for use as an autograft, but the flow-through is typically discarded. The purpose of this study was to assess whether this discarded filtrate has osteogenic properties that could be used to enhance the total repair potential of aspirate. RIA aspirate was collected from five patients (ages 71-78) undergoing hip hemiarthroplasty. Osseous particles were removed using an open-pore filter, and the resulting filtrate (230 +/- 200 mL) was processed by Ficoll-gradient centrifugation to isolate mononuclear cells (6.2 +/- 5.2 x 10(6) cells/mL). The aqueous supernatant contained FGF-2, IGF-I, and latent TGF-beta1, but BMP-2 was below the limit of detection. The cell fraction included culture plastic-adherent, fibroblastic cells that displayed a surface marker profile indicative of mesenchymal stem cells and that could be induced along the osteogenic, adipogenic, and chondrogenic lineages in vitro. When compared to outgrowth cells from the culture of osseous particles, filtrate cells were more sensitive to seeding density during osteogenic culture but had similar capacity for chondrogenesis. These results suggest using RIA aspirate to develop improved, clinically expeditious, cost-effective technologies for accelerating the healing of bone and other musculoskeletal tissues.

Monitoring and controlling intramedullary pressure increase in long bone instrumentation: A study on sheep

Intramedullary reamed nailing causes elevation in intramedullary pressure and extravazation of intramedullary contents into the venous blood system. This study investigated the effect of an intramedullary suction system, recently developed in our laboratory, on the pressure and fat extravazation in isolated bovine bone and a sheep model. During reaming, the pressure with and without suction was recorded at each step of the procedure. Hemodynamic parameters of mean arterial blood pressure, pulmonary artery pressure, pulmonary arterial CO(2) (PaCO(2)), heart rate, and oxygen saturation were monitored. Blood and lung tissue samples were collected for the examination of medullary fat intravazation. The increases of intramedullary pressure were dramatically reduced in the suction group (p < 0.05) in both in vitro and in vivo experiments. PaCO(2) was significantly lower in the suction group than nonsuction group (32 vs. 40 mmHg, respectively, p = 0.02), while oxygen saturation was higher in the suction group (99 vs. 91 mmHg, respectively, p = 0.009). Histological data revealed a significant higher count of fat emboli in sheep lung tissue in the nonsuction group. Total lipids in lung specimens was lower in the suction group (7.6 mg/g tissue) than in the nonsuction group (13.6 mg/g, p = 0.04). The suction system appears to control the surge in intramedullary pressure and therefore prevent fat embolism.

The Reamer/Irrigator/Aspirator Reduces Femoral Canal Pressure in Simulated TKA

Inserting the femoral intramedullary alignment rod during total knee arthroplasty (TKA) can generate high intramedullary pressure, which increases the risk of intraoperative complications caused by fat embolism. Despite modifications to the surgical procedure, the best method to prevent this increase in pressure remains unknown. The reamer/irrigator/aspirator is a surgical instrument designed for use during femoral canal entry to increase the canal size and remove intramedullary fat and may prevent this pressure increase. We posed two hypotheses: (1) using the reamer/irrigator/aspirator system will result in lower maximum femoral intramedullary pressure than using only conventional instrumentation during the initial steps of a TKA; and (2) using the reamer/irrigator/aspirator system in the initial steps of TKA will result in a mean maximum intramedullary pressure less than 200 mm Hg. We simulated a TKA on 14 cadaveric femurs to compare the femoral intramedullary pressure using both methods. Considerable decreases in femoral intramedullary pressure of 86% proximally and 87% distally were obtained by using the reamer/irrigator/aspirator system. The mean maximum pressure using the reamer/irrigator/aspirator system was less than 200 mm Hg. Additional clinical studies are needed to confirm any reduction in complications using the reamer/irrigator/aspirator system.

Die intraspongiöse Patelladruckmessung in Abhängigkeit von der Funktionsstellung des Kniegelenkes

Degenerative alterations of the patello-femoral joint are often painful and cause an increase of intramedullary pressure. The intraspongious pressure of the patella is measured with a cannula after lateral drilling. Patients with chondromalacia or osteoarthrosis have an increased intramedullary pressure compared with normal patients. The degree of flexion of the knee-joint correlates with the intramedullary pressure. More flexion causes an increase of pressure as well in normal patella as in chondromalacia or in osteoarthrosis.

Experimental studies on the role of intramedullary alignment rods in the etiology of fat embolisms in knee endoprostheses

Fat embolism syndrome (FES) during implantation of an uncemented resurfacing type of total knee replacement is the leading cause of postoperative mortality. A possible explanation might be the insertion of a solid intramedullary alignment rod, resulting in an intrafemoral pressure increase. On 45 cadaveric human femora we measured the resulting intramedullary pressure during insertion of three different alignment rods: a solid rod and a hollow shaped guiding rod, both 10 mm in diameter, and a fluted alignment rod of 8.5 mm in diameter. The highest intramedullary pressures occurred after placement of a solid 10 mm alignment rod (3.77 +/- 0.44 bar), followed by a fluted 8.5 mm rod (2.53 +/- 0.28 bar). In both cases, the increased pressure led to an extrusion of bone marrow contents through the venous system of the proximal femur. The least increase occurred after insertion of a hollow shaped alignment rod (0.26 +/- 0.03 bar) without any fat extrusion. Our study confirms the hypothesis that insertion of solid intramedullary alignment rods during preparation of the femoral shaft results in a dangerous pressure increase, so that embolization can occur. To minimize the risk of a FES, instruments should be modified in a manner, that only hollow shaped alignment rods are used.

Initial stability of an implanted cement-canal prosthesis. Results in experimental studies on human cadaver femurs

Upon implantation of a cement-canal prosthesis in the proximal femur in total hip replacement, the bone cement is injected through the prosthesis via a system of drill holes. A second system of drill holes is used in this endoprosthesis to drain the distal femoral space as well as the cavities within the cement layer which form when the cement is being injected. Since the cement pressure is sustained until the cement has cured, substantial penetration of the cement into the cancellous bone can be achieved by using low intra-medullary cement pressures. Using cadaveric human femurs, the initial stability in the trabecular intertrochanteric region was determined in pull-out experiments for three different curing cement pressures (0.5 bar, 1.0 bar and 1.5 bar). The results were compared to corresponding controls in which a conventional cementation technique was used. With respect to the contact area of the bone/bone-cement interface, the initial stability increased by the factor 2.8 (cement-curing pressure 0.5 bar), 3.7 (cement-curing pressure 1.0 bar) and 2.9 (cement-curing pressure 1.5 bar) compared to the control group.

Chondromalacia of the patella and intraosseous pressure. A study of 43 patients

There are some hints concerning a relationship between the intraosseous pressure and degenerative changes in hyaline cartilage. With a specially constructed cannula we evaluated the intraosseous pressure in 43 patients in relation to the joint position (Extension/Flexion). In two groups we compared patients with and without degenerative changes in the hyaline cartilage, diagnosed by arthroscopy. Our results show, that patients with a chondromalacia have an increase of intramedullary pressure. These changes were discussed in the possible role of the pathology of chondromalacia patellae and retropatellar arthrosis.

Technique and Early Results of Intramedullary Pressure-Guided Core Decompression of the Humeral Head for Nontraumatic Osteonecrosis

The purpose of this study was to describe a modified technique for humeral head core decompression using biplanar fluoroscopy and intraosseous pressure monitoring to identify osteonecrotic regions for targeted decompression. A bone marrow biopsy needle and arterial pressure monitoring equipment were used to locate the region of maximum pressure, and then acorn-style reamers decompressed the osteonecrotic bone. In 12 shoulders (11 patients) evaluated, the peak intramedullary lesion pressure was, on average, 6 times higher than the entry pressure. At 6 months, Visual Analog Scale pain scores had decreased in all shoulders by 70.3% (P < 0.0001) on average. Nine of 12 shoulders, with an average follow-up of 44.2 months (range, 12-72.5 months), were evaluated for pain relief, disease progression, and need for arthroplasty. In that group, Visual Analog Scale pain scores had decreased by 56.8% (P < 0.008) on average. Only 1 patient, despite excellent initial results, had progression of symptoms and required arthroplasty at 12 months. Pressure-guided core decompression provides a technique for directly localizing the osteonecrotic bone and potentially improving decompression outcomes.

Fatal fat embolism following femoral head resection in total hip arthroplasty

We report a rare complication during primary total hip arthroplasty. A fatal fat pulmonary embolism immediately followed removal of the femoral head, prior to further preparation of the acetabulum or femoral shaft. Fat embolism syndrome is a well-known complication during total joint arthroplasty, usually attributed to preparation of the femoral shaft, particularly intramedullary reaming and insertion of the prosthesis. These risk factors have previously been identified in the literature. We believe that this case highlights the need for further research to establish the intramedullary pressures during the processes of dislocation and resection of the femoral neck and the attendant risk.