The uptake by the canine tibia of the bone-scanning agent 99mTc-MDP before and after an osteotomy

Injury of the Tibial Nutrient Artery Canal during External Fixation for Lower Extremity Fractures: A Computed Tomography Study

The tibial nutrient artery (TNA) is the major diaphyseal artery of the tibia supplying two thirds of the inner osseous cortex. Hence, iatrogenic injury of the TNA endangers the integrity of the tibial blood supply and may compromise fracture healing. The incidence of its injury in the setting of external fixation for lower limb fractures has not been previously investigated. The aim of this study was to evaluate the incidence of TNA injury in the context of external fixation and to characterize the topography of the fixator pins in relation to the TNA canal (TNAC). Patients who underwent external fixation for distal femoral fractures and for tibial (proximal, shaft, and distal) fractures and had a postoperative computed tomography study were retrospectively included. The following parameters were retrieved: 1) Pin characteristics (orientation and cortical position of the pins), 2) The anatomic relationship between the TNAC and external fixation pin (topography above/below and at the level of the TNAC, and the distance between the pin and medial tibial plateau and/or the medial malleolus), and 3) The incidence of TNAC injury (complete/partial disruption of TNA lumen). A total of 105 patients with 214 tibial pins were analyzed. In 27 patients (26%), the TNAC was completely injured by the pins of the external fixator. In 13 patients (12%), the TNAC was partially injured. Of the 214 analyzed pins, 85 pins (40%) were located at the level of the TNAC (the TNAC and the pin are seen on the same axial slice). Most pins that were applied at the level of the TNAC belonged to a knee-bridging external fixator. Of those, ninety-three percent of the pins were anteromedially applied according to published surgical guidelines. Six percent of the pins were applied through the tibial crest and 1% anterolaterally. Of those 85 pins, 42 pins (49%) injured the TNAC at least partially. Based on the analyzed pins and the incidence of partial and complete injury of the TNAC, we observed that the tibial segment at which the tibial nutrient artery is endangered was located approximately (95% CI: 13–15 cm) from the medial tibia plateau and (95% CI: 22–25 cm) from the medial malleolus. Thus, TNAC injury by external fixation pins in the context of lower limb fractures can be considered common. Almost half of the pins applied at the middle third of the tibia injured the TNA, despite adherence to published surgical guidelines for external fixation. When possible, pin application at the middle third of tibia should be avoided to circumvent iatrogenic injury of the TNA and to safeguard tibial blood supply.

Implantable hyaluronic acid-deferoxamine conjugate prevents nonunions through stimulation of neovascularization

Approximately 6.3 million fractures occur in the U.S. annually, with 5–10% resulting in debilitating nonunions. A major limitation to achieving successful bony union is impaired neovascularization. To augment fracture healing, we designed an implantable drug delivery technology containing the angiogenic stimulant, deferoxamine (DFO). DFO activates new blood vessel formation through iron chelation and upregulation of the HIF-1α pathway. However, due to its short half-life and rapid clearance, maintaining DFO at the callus site during peak fracture angiogenesis has remained challenging. To overcome these limitations, we composed an implantable formulation of DFO conjugated to hyaluronic acid (HA). This compound immobilizes DFO within the fracture callus throughout the angiogenic window, making it a high-capacity iron sponge that amplifies blood vessel formation and prevents nonunions. We investigated implanted HA-DFO’s capacity to facilitate fracture healing in the irradiated rat mandible, a model whereby nonunions routinely develop secondary to obliteration of vascularity. HA-DFO implantation significantly improved radiomorphometrics and metrics of biomechanical strength. In addition, HA-DFO treated mandibles exhibited a remarkable 91% bone union rate, representing a 3.5-fold improvement over non-treated/irradiated controls (20% bone union rate). Collectively, our work proposes a unique methodology for the targeted delivery of DFO to fracture sites in order to facilitate neovascularization. If these findings are successfully translated into clinical practice, millions of patients will benefit from the prevention of nonunions.

Quantitative analysis of vascular response after mandibular fracture repair using microcomputed tomography with vessel perfusion

BACKGROUND

Poor healing after mandibular fracture repair can be a devastating morbidity with significant clinical consequences. Elucidating the vascular response after mandibular fracture may help determine potential areas for therapeutic interventions for nonunions. The authors performed microcomputed tomographic imaging after vessel perfusion to ascertain objective measures of vascular networks. They hypothesized that despite the haversian-based, highly cortical structure of the mandible, the vascular response after fracture healing will return to nearly normal levels soon after bony union, mirroring the results of endochondral, highly trabecular long bones.

METHODS

Sprague-Dawley rats (n = 12) underwent mandibular osteotomy, and a 2.1-mm fixed gap was set. Animals were euthanized at 40 days after surgery and perfused with Microfil. Specimens underwent microcomputed tomographic analysis for stereologic vascular metrics. Data were compared with nonfractured controls (n = 5). Ninety-five percent confidence intervals and the independent samples t test (p < 0.05) were used to determine statistical differences.

RESULTS

Quantitative measures for mandibular fracture versus control revealed similarities in the following vascular metrics: vessel volume fraction (0.028 percent versus 0.032 percent; 95 percent CI, -0.027 to 0.0169 percent), vessel number (0.497 mm(-1) versus 0.472 mm(-1); 95 percent CI, -0.884 to 0.975 mm(-1)), vessel thickness (0.052 mm versus 0.067 mm; 95 percent CI, -0.037 to 0.008 mm), and vessel separation (2.344 mm versus 2.081 mm; 95 percent CI, -0.752 to 1.278 mm).

CONCLUSIONS

To the authors' knowledge, this is the first study using microcomputed tomography after perfusion to analyze vascular response following mandibular fracture. Their findings establish quantitative similarities and qualitative differences in vascular response to fracture repair of the highly cortical mandible when compared with the highly trabecular long bone.

Intramedullary nailing of the lower extremity: biomechanics and biology

The intramedullary nail or rod is commonly used for long-bone fracture fixation and has become the standard treatment of most long-bone diaphyseal and selected metaphyseal fractures. To best understand use of the intramedullary nail, a general knowledge of nail biomechanics and biology is helpful. These implants are introduced into the bone remote to the fracture site and share compressive, bending, and torsional loads with the surrounding osseous structures. Intramedullary nails function as internal splints that allow for secondary fracture healing. Like other metallic fracture fixation implants, a nail is subject to fatigue and can eventually break if bone healing does not occur. Intrinsic characteristics that affect nail biomechanics include its material properties, cross-sectional shape, anterior bow, and diameter. Extrinsic factors, such as reaming of the medullary canal, fracture stability (comminution), and the use and location of locking bolts also affect fixation biomechanics. Although reaming and the insertion of intramedullary nails can have early deleterious effects on endosteal and cortical blood flow, canal reaming appears to have several positive effects on the fracture site, such as increasing extraosseous circulation, which is important for bone healing.

Effects of acepromazine on three-phase 99mTc-MDP bone imaging in 11 horses

Horses undergoing skeletal scintigraphy can have decreased radiopharmaceutical bone uptake in the limbs. This reduces the diagnostic value of the scan. The aim of the present study was to measure the changes in count density caused by vasodilatation and increased blood flow associated with intravenous injection of acepromazine during bone scintigraphy in normal horses. A three-phase bone scan was performed twice in 11 adult horses to study the effects of acepromazine on the count density of the resultant scintigrams. With acepromazine, there was a statistically significant mean difference of 12 s for initial blood flow and 21 s for peak flow. The time to initial blood flow and time to peak flow occurred earlier for the scans in which acepromazine was used. There were no significant differences in the bone to soft tissue ratios during the soft tissue and bone phases of the scan between procedures. Intravenous administration of acepromazine increases peripheral blood flow causing an earlier onset of the vascular phase during the three-phase bone scan. Acepromazine did not increase the count density of the bone phase scintigrams. As expected, the vasodilatation and increased blood flow associated with intravenous injection of acepromazine affected the count density of the vascular phase of the bone scan.

Dynamic radioisotope bone imaging as a noninvasive indicator of canine tibial blood flow

The relative values of dynamic and static bone imaging with hydroxymethylenediphosphonate technetium 99m (99mTc HDP) as an indicator of bone blood flow was investigated in the tibia of mature dogs. The dynamic bone scan consisted of 60 1-s images formed after the intravenous injection of 99mTc HDP, and the static bone scan was a 45-min uptake image. Blood flow to the tibia was determined by using radioactively labeled microspheres. Studies were carried out in control dogs, in dogs in which blood flow was increased in one leg with ATP, and in dogs in which blood flow was decreased in one leg with norepinephrine. A significant (p less than 0.001) linear relationship between the dynamic scan values and bone blood flow was found at a wide range of blood flow rates. When blood flow increased by more than 50%, the effects of "diffusion limitation" were seen in the static scans: increase in tracer uptake was disproportionately small for a significant increase in blood flow. There is no method currently available for estimating bone blood flow by a noninvasive technique. The method described here may be useful for providing a semiquantitative measure of bone blood flow. This improved versatility of bone imaging may have a role in the management of osteomyelitis or complicated fractures, or in assessing the viability of vascularized bone grafts.

A quantitative study of the routes of blood flow to the tibial diaphysis after an osteotomy

Techniques of tissue exclusion have been used previously in qualitative investigations of the vascularity of long bones, after experimental fracture; we quantified their effects on bone blood flow in rabbits. Thirty-six adult rabbits were divided into three groups in which flow was measured, with the microsphere technique, 1 and 2 weeks after osteotomy. In Group 1, osteotomy of the tibial shaft only was done; in Group 2, osteotomy was done with exclusion of the periosteum and muscle by a silicone rubber sheath; and in Group 3, osteotomy was done with exclusion of the marrow by reaming and insertion of an intramedullary nail. All involved limbs were immobilized in a cast. In Group 1, cortical flow increased but marrow flow did not change, which suggests that the changes in cortical flow were mediated by a supply paralleling that of the marrow. In Group 2, the changes in cortical flow were abolished, which implies that this parallel supply is from the periosteum and extraosseous tissues. In Group 3, cortical flow was not significantly reduced, which demonstrates recruitment of this periosteal and extraosseous supply. These results lend support to the hypothesis that the blood supply to the healing diaphysis is principally from the periosteum and extraosseous tissues during the early peak period of blood flow.

Scintigraphy in the clinical evaluation of disorders of mineral and skeletal metabolism in renal failure

In patients with renal bone disease skeletal and extra-skeletal abnormalities can be visualised using conventional bone scintigraphy. Some of these abnormalities are associated with characteristic scintigraphic appearances, which are reviewed in detail, and the possible mechanisms involved are discussed. Specific imaging with iodine 123 serum amyloid P component and iodine 131 beta 2-microglobulin is also discussed in the diagnosis of beta 2-microglobulin amyloidosis specific to patients on dialysis. In the light of available evidence, it appears that bone scintigraphy plays, so far, a limited role in the clinical evaluation of skeletal and extra-skeletal abnormalities in chronic renal failure. The potential role of bone scintigraphy in identifying patients with aluminium-related bone disease needs to be investigated further, and in this respect special attention must be given to the problem of high soft-tissue activity associated with impaired renal function. Timing haemodialysis sessions before scintigraphic imaging deserves wider recognition as it reduces high soft-tissue activity, thereby allowing bone uptake to be assessed more accurately. Specific imaging of amyloidosis resulting from beta 2-microglobulin deposition is a promising technique, but the relative value of the two proposed radiopharmaceuticals needs further clarification.

Streaming potential of intact wet bone

The conversion of mechanical loads to bioelectrical signals in bone have been suggested to control repair and remodeling. These signals in wet bone are attributed to the electrokinetic behavior where mechanical forces cause electrical signals due to motion of an ion carrying extracellular fluid in the bone matrix (streaming potentials). Streaming potential experiments were performed on control and chemically treated intact wet bone plugs in aphosphate and phosphate buffers to examine the contribution of bone constituents to the electrokinetic behavior of bone tissue. Data indicate that the organic constituents of bone dominate streaming potentials. Slopes of streaming potential vs pressure are related to the electrokinetic (zeta) potential. The slopes should be analyzed in the low pressure region where data is mainly linear. Comparisons of estimated zeta potentials from streaming potentials with existing data obtained by particle electrophoresis showed similar trends.

Omental angiogenic lipid fraction and bone repair. An experimental study in the rat

A lipid material extracted from the omentum has previously been shown to contain a potent angiogenetic activator (20), capable of creating intense vasoproliferation in traumatized tissues (19). This study was undertaken to analyze the efficacy of local administration of this omental lipid fraction on osseous vascularization and bone repair. An osteoperiosteal segmental femoral defect in the rat was replaced by a demineralized allogenic bone graft exposed to continuous local delivery of omental lipid via an implanted miniosmotic pump. Saline solution delivered in the same way served as a control. Neovascularization and bone formation in the transplant were quantitatively evaluated by means of dynamic radioisotopic bone imaging, radiographic photodensitometry, microangiography, and biomechanical testing. Compared with the control group, the omental lipid angiogenic fraction-treated specimens showed an 80% overall increase (p less than 0.001) in bone density as well as a twofold increase (p less than 0.001) in regional blood perfusion, maximal at 2 weeks following surgery. At 12 weeks, biomechanical testing demonstrated significantly higher union rate (p less than 0.05) and strength (p less than 0.01) in the treated specimens as compared with the controls. These data demonstrate that the omental lipid fraction factor has potent angiogenic properties that enhance bone blood perfusion and bone regeneration.

The role of skeletal blood flow in determining the uptake of 99mTc-methylene diphosphonate

The increased uptake of bone-seeking radionuclides following a fracture has been stated to be due to an increase in bone blood flow, resulting in an increase in capillary surface area available for exchange. This paper examines the relationship between the maximum instantaneous extraction of 99mTc-MDP and blood flow in normal canine tibia. The findings, consistent with the model of capillary action proposed for muscle by Renkin and Crone, are applicable to bone. There is no evidence that in normal bone the surface area available for exchange responds to an increase in bone blood flow.

The use of bone scanning for the diagnosis and management of musculoskeletal trauma

Bone scanning provides a unique way of monitoring early metabolic changes in bone and its adjacent soft tissues after trauma. An abnormal scan may often precede radiographic changes by days or weeks. This accounts for its usefulness in the early diagnosis of occult fractures and in fractures not clinically suspected or seen on initial x-ray films in the patient with multiple trauma. Dynamic imaging along with static imaging can be used to evaluate fracture healing and predict delayed union and nonunion. The combined technique is useful in assessing many of the complications arising after trauma and provides a reliable method of observing their treatment. It is also a useful noninvasive technique in the evaluation of pathologic fractures. Bone scanning is becoming an increasingly useful adjunctive procedure in the diagnosis and management of musculoskeletal trauma. However, as with any diagnostic technique, it provides only part of the overall picture and must always be carefully correlated with the history, physical findings, radiographic changes, and other laboratory data.

The role of bone scans in the assessment of prognosis of scaphoid fractures

Fifty patients with radiographic evidence of an acute scaphoid fracture were studied prospectively. Technetium bone scans were performed on all patients soon after injury in an attempt to detect fractures at risk of non-union or avascular necrosis. In three patients the scan showed a focal area of decreased radionuclide concentration in the region of the proximal pole of scaphoid implying avascularity, and each developed the radiographic signs of avascular necrosis. Two of these patients, each with a displaced fracture, developed non-union. Acute fractures of the scaphoid with evidence of avascularity on bone scan are at high risk of developing non-union.

Effects of acute administration of ethane hydroxydiphosphonate (EHDP) on skeletal scintigraphy with technetium-99m methylene diphosphonic acid (Tc-MDP) in the rat

A study has been performed in the rat to assess the effect of EHDP on the distribution of 99Tcm-labelled MDP used for skeletal imaging. Profound alterations in bone, kidney and blood levels were observed. These observations cast doubt on the value of bone scans for monitoring the therapeutic effect of diphosphonates.

Dynamic bone scanning in fractures

In 20 cases routine static bone scans were no value in the detection of delayed fracture healing. Using the 7.5-15 min net uptake of technetium labelled phosphate, disturbed fracture healing was detected in a series, of 37 cases. Normally healing fractures had an increase of 3 per cent per month and delayed unions less than half that amount. Non-unions had no net uptake.

Skeletal blood flow in Paget's disease of bone

Using a modified plasma clearance technique, with 18F as a tracer, it is possible to measure blood flow to bone in man. In the normal adult skeleton, blood flow amounts to about 300 ml/min. In untreated Paget's disease of bone there is a striking increase, which is proportional to the biochemical severity of the disease : total blood flow to the skeleton is approximately doubled at an alkaline phosphatase of 50 KAu/dl (i.e. about four times the normal upper limit). Treatment with calcitonin brings a rapid return to normal, possibly before there is a detectable biochemical response. This may explain the rapid pain relief often reported on starting treatment with calcitonin.

A rabbit model to study the biokinetics of radiopharmaceuticals in bone

A technique is described using the rabbit as the 'animal model' to measure the rate of extraction of the bone-seeking agent, technetium labelled ethane-1-hydroxy-1, 1-diphosphonate (99Tcm-EHDP) following constant-rate infusion into the femoral nutrient artery. The extraction is shown to be approximately linear for a period of 60 min. Washout of the tracer from bone was followed for a further 60 min period and graphical analysis shows that each curve could be resolved into two distinct exponential functions. The 2-h residue of 99Tcm-EHDP in bone has been examined and is found to be dependent upon its route of administration. A high residue (43.7 +/- 5.1%) results when the infusate is delivered directly into the nutrient artery and the single muscular branch is tied off. Retrograde infusion via the femoral artery results in a lower residue (7.8 +/- 2.3%). The close correlation of these results in the rabbit with our previous findings in the dog suggested that the rabbit model described can be used to study the kinetics of other radiopharmaceuticals during their passage through bone.