Comparison of two laser Doppler flowmetry systems for bone blood flow analysis

The influence of expansion on intraoperative bone blood flow in multisegmental maxillary osteotomies: an experimental study

The aim of the presented study was to investigate the effect of maxillary expansion in multisegmental Le Fort I osteotomies on bone blood flow. Five sheep underwent a three-piece total maxillary osteotomy. Bone blood flow was measured intraoperatively by laser Doppler flowmetry in the premaxilla, the lateral segments and the mandible before osteotomy, after osteotomy and segmentation as well as after 4mm, 8mm and 12mm expansion with a Hyrax screw. A significant reduction in blood flow was seen after osteotomy and segmentation with a factor of 3.10 and between 4mm and 8mm expansion with a factor of 1.81. No significant differences could be found between 0mm and 4mm widening or between 8mm and 12mm widening. These results suggest that expansion of more than 4mm in multisegmental osteotomies enhances the risk of avascular sequelae. As greater maxillary widening has been carried out in many cases without avascular complications, further research on additional factors, influencing the recovery of perfusion, is needed.

Changes to patellar blood flow after minimally invasive total knee arthroplasty

Standard surgical exposure reduces blood flow to the patella during total knee arthroplasty (TKA). Reduction of patellar blood flow has resulted in patellofemoral complications including osteonecrosis and patellar fracture, necessitating revision surgery. In TKA, avoiding patellar eversion is one type of minimally invasive surgery (MIS) technique. This study is the first to measure patellar blood flow during MIS TKA with the knee in both extension and 90 degrees of flexion followed by lateral retraction and then eversion of the patella. Patellar blood flow was measured using laser Doppler flowmetry in 40 patients during MIS TKA. A significant reduction in flow was noted when the leg was flexed from full extension to 90 degrees . Eversion of the patella reduced patellar blood flow. MIS TKA without patellar eversion may be useful for preventing a reduction in patellar blood flow.

Role of the extraosseus blood supply in osteoarthritic femoral heads?

Blood perfusion to the femoral head might be endangered during the surgical approach or the preparation of the femoral head or both in hip resurfacing arthroplasty. The contribution of the intramedullary blood supply to the femoral head in osteoarthritis is questionable. Therefore, the contribution of the extraosseous blood supply to osteoarthritic femoral heads was measured intraoperatively to question if there is measurable blood flow between the epiphysis and metaphysis in osteoarthritic hips in case of extraosseus vessel damage. At defined points during surgery we acquired the epiphyseal and metaphyseal femoral head perfusion by high-energy laser Doppler flowmetry. Complete femoral neck osteotomy sparing the retinacular vessels to simulate intraosseous blood disruption showed unchanged epiphyseal blood flow compared to initial measurement after capsulotomy. The pulsatile signal disappeared after transection of the retinacular vessels. Based on these acute measurements, we conclude intramedullary blood vessels to the femoral head do not provide measurable blood supply to the epiphysis once the medial femoral circumflex artery or the retinacular vessels have been damaged. We recommend the use of a safe surgical approach for hip resurfacing and careful implantation of the femoral component to respect blood supply to the femoral head and neck region in hip resurfacing arthroplasty.

Effects of neuropeptides and vasoactive substances on microcirculation of the callus after tibial osteotomy in rabbits

Previous studies have demonstrated a dynamic ingrowth of vessels into the developing callus. In this study, maturation and development of the regulation of microcirculation were followed in the callus of rabbits. In the first series, the effects of vasoactive substances on blood flow velocity, perfusion pressure, duration of effects and peripheral vascular resistance of the bone marrow in the femur and tibia were compared. In the second series, the same parameters were measured in the femur and in the developing callus 10 and 15 days following gap osteotomy of the tibia. There were no significant differences between the microcirculatory reactions of the intact femur and tibia. Basal blood flow could be verified in the callus on the 10th postoperative day. No vascular reactions could be elicited. Basal blood flow velocity was higher on the 15th day, when compared to the measurements on the 10th day. The substances elicited statistically significant differences in flow velocity, resistance and 50% recovery time in the callus on the 15th day. Blood flow reactions of the ipsilateral femoral and tibial bone marrow are identical, thus the femur can serve as a reference site for blood flow measurements in the callus. Regulation and maturation of callus microcirculation develop rapidly between the 10th and 15th days.

Revascularisation during fracture healing with soft tissue injury

INTRODUCTION

The purpose of our study was to quantitatively assess changes in the revascularisation process in the fracture gap and in adjacent regions during the course of healing of diaphyseal fractures with and without closed soft tissue injury.

METHODS

In a rat model (fracture n = 26; fracture with closed soft tissue crush n = 26) revascularisation was assessed in a long-term study with regional mapping by laser Doppler flowmetry, the healing outcome being mechanically tested after 4 weeks. Fracture and soft tissue crush were performed by modified controlled impact device.

RESULTS

No differences in blood circulation were observed at the fracture gap between the study groups up to day 28. In the proximal region of the fracture, the blood circulation in the group with additional soft tissue trauma was down to the baseline throughout the investigation period while the values in the fracture group led to a hyperperfusion after 3 and 7 days. In the distal part at day 1, the blood flow was strongly depressed after fracture, while microcirculation with an additional soft tissue trauma showed only a moderate decline. The reduction of blood circulation in the soft tissue corresponded to the extent of trauma. Mechanical testing demonstrated no significant difference in failure load or in flexural rigidity.

CONCLUSION

Our results indicate that damage severe soft tissue does not adversely affect the fracture healing process. Furthermore, the present findings suggest that a partly destroyed bone-soft tissue interaction resulting in only a temporary and slight reduction of the extraosseous blood supply might have no deteriorating effect on fracture healing outcome. A possible delay in healing is not observed during the first 4 weeks. Therefore, soft tissue damage without destruction of the bone-soft tissue interface is likely to have only a limited effect on fracture healing.

Continual measurement of intramedullary blood perfusion with laser Doppler flowmetry in intact and ostectomized tibiae of rabbits

Blood flow is important for the healing of bone fractures. Until now, however, there have been no publications on the daily, continual measurement of intramedullary blood perfusion using laser Doppler flowmetry (LDF) in the conscious animal. In this study, a model for the daily, continual measurement of intramedullary blood perfusion by LDF and the temperature near the cortex both in intact and ostectomized tibiae in the conscious rabbit is described. The probes for blood perfusion and temperature measurement were implanted permanently at three different localizations into the right tibia of 10 adult New Zealand White rabbits. The probes were held in place by a bilateral, single-plane external fixator. In five of these animals, a midshaft tibial ostectomy was created in order to simulate a fracture. Intramedullary blood perfusion and temperature were measured daily over 49 days.

While in intact tibiae no significant ( P > 0.05) differences were found in blood perfusion readings taken at various time points, for mean values or for blood perfusion over time, in ostectomized tibiae the differences were significant: various time points ( P = 0.0056), mean values ( P = 0.0034) and blood perfusion over time ( P = 0.0337). Blood perfusion readings at the centre probe were elevated compared with those at the proximal and distal probes.

Thus, a revascularization in the ostectomy gap during the fracture healing was proven by means of the LDF. No influence of the blood perfusion on the temperature in the ostectomy area could be determined during healing of the ostectomy. The described model seems suitable for the continual measurement of intramedullary blood perfusion both in intact and ostectomized tibiae in the conscious rabbit.

Acetabular blood flow during Bernese periacetabular osteotomy: an intraoperative study using laser Doppler flowmetry

BACKGROUND

The blood flow to the acetabular fragment is of some concern in juxtaarticular pelvic osteotomies used for the treatment of hip dysplasia. No direct measurements have determined the effect of the Bernese periacetabular osteotomy (PAO) on acetabular perfusion.

METHODS

Acetabular perfusion was measured by means of laser Doppler flowmetry in 10 patients undergoing a PAO for symptomatic acetabular dysplasia. During the surgical procedure, the intraosseous high energy laser Doppler reliably depicts dynamic changes of small vessel blood flow. Measurements were performed after defined surgical steps to obtain sequential information on the blood perfusion of the acetabular fragment.

RESULTS

After complete separation of the acetabular fragment, nine out of 10 patients had pulsatile signals, but the blood flow (BF) significantly decreased by 77%. Corrective positioning of the fragment induced no further drop of the BF signal but a loss of pulsatility in six patients. After a recovery period of about 30 min following preliminary fixation of the fragment, reestablishment of the pulsatile signal and an increase of the BF signal was seen. At termination of the surgical procedure, five out of eight patients, who could be followed throughout the whole procedure, showed a clear pulsatile signal in the supraacetabular area. Bleeding of the supraacetabular cancellous surface could be observed in all acetabula.

CONCLUSION

Despite careful preservation of soft tissues during the surgical procedure, a significant reduction of the blood flow in the supraacetabular region has been observed. Nevertheless, a pulsatile signal in more than 60% of the fragments after fragment correction and an increasing signal during the recovery period showed ongoing blood perfusion indicating reversible changes in the measured supraacetabular area. All osteotomies healed within eight weeks without showing signs of necrosis during a minimum follow up of 1 year.

Laser doppler flow imaging of open lower leg fractures in an animal experimental model

PURPOSE

Open lower leg fractures are frequently associated with severe soft tissue damage, followed by osteomyelitis. Using an animal experimental model, we investigated the effect of timing of coverage of a tibial fracture with a local muscle flap.

METHODS

80 rabbits had a tibial fracture induced in a standardised fashion, which was stabilised by screw osteosynthesis. After 3 (group A; n=40) and 7 days (group B; n=40), respectively, the tissue defect was covered by a local gastrocnemius flap. In increasing intervals from 1 to 2, 4, 8, and 16 weeks, the rabbits from each group were killed and the bone fracture was analysed histomorphologically. Cortical microcirculation was measured by 2-channel laser doppler flowmetry.

RESULTS

Muscle flaps after 3 days improved perfusion significantly as compared with 7 days (24 Flux [standard error, 5 Flux] versus 10 Flux [3 Flux]; baseline, 1.4 Flux). Group A animals also displayed a lower rate of necrosis (0 versus 38). The incidence of osteomyelitis was higher in group B than in group A (24% versus 0%).

CONCLUSION

Laser doppler flowmetry was proven to be a reliable, minimally invasive means for identifying avital tissue, leading to reduction in the loss of vital bone tissue in experimental settings.

Femoral bone blood flow after reaming and intramedullary canal preparation: a canine study using laser Doppler flowmetry

This study was conducted to determine the effect of intramedullary reaming and canal preparation on bone blood flow in the proximal femur. Thirty-five adult dogs were randomly assigned to have their intramedullary canals prepared after reaming in the following manner: group 1, ream only; group 2, lavage; group 3, methylmethacrylate cement introduction; group 4, cement pressurization after placing a cement restrictor; group 5, lavage then cement introduction; and group 6, lavage then cement pressurization. Bone blood flow was measured at both metaphyseal and diaphyseal sites by using laser Doppler flowmetry before reaming, after reaming, after lavage, after cementing, and at 6 weeks after the procedure just before euthanasia. Reaming significantly decreased bone blood flow in the diaphysis (P = .046) but not in the metaphysis. Cement introduction and cement pressurization both significantly decreased bone blood flow in the metaphysis (P = .035, P = .004) and diaphysis (P = .007, P = .029). Pressurization of cement had a significantly greater relative effect than cement introduction alone in the diaphysis (P = .006) but not in the metaphysis. Lavage had no effect on bone perfusion. Bone blood flow was significantly increased at 6 weeks after the initial procedure in both the metaphysis (P = .049) and the diaphysis (P = .004). The results suggest that reaming decreases diaphyseal cortical but not metaphyseal bone blood flow significantly, whereas lavage has no effect. Cement introduction with or without pressurization has a significant detrimental effect on metaphyseal and diaphyseal blood flow. These findings have implications for intramedullary nailing and for canal preparation when performing arthroplasty.

Femoral and cruciate blood flow after retrograde femoral reaming: a canine study using laser Doppler flowmetry

OBJECTIVE

To determine the effect of retrograde femoral reaming on the blood flow of the distal femur and the cruciate ligaments.

DESIGN

Canine experimental study.

SETTING

Tertiary referral and teaching hospital in Toronto, Canada.

PARTICIPANTS

Thirteen skeletally mature, cross-bred dogs.

MAIN OUTCOME MEASURE

Red cell flux (RCF) was measured by using a laser Doppler flowmetry probe at three bone sites in the distal femur (trochlear groove, medial condyle, and lateral condyle) and at the midportion of both the anterior and posterior cruciate ligaments before and after retrograde femoral reaming.

RESULTS

There was a significant increase in the mean postreaming RCF at all the bone sites of the distal femur compared with prereaming values: trochlear groove (p = 0.0247), medial condyle (p = 0.0440), and lateral condyle (p = 0.0042). We also found a significant decrease in the mean postreaming RCF at both cruciate ligament sites compared with prereaming values (anterior cruciate, p = 0.0004; posterior cruciate, p = 0.0006).

CONCLUSIONS

Retrograde femoral reaming and intramedullary nailing has become a popular option for the treatment of distal femoral and some femoral shaft fractures, but concerns regarding the effect of reaming through an intraarticular entry portal have been raised. Our experimental study found that after reaming perfusion of the anterior cruciate ligament decreased by 52 percent and perfusion of the posterior cruciate ligament decreased by 49 percent. Diminished perfusion after reaming may delay healing or exacerbate existing injury to the cruciate ligaments and adversely affect rehabilitation of the knee after femoral fracture.

Assessment of the relationship between standard probe and implantable fiber measurements of cortical bone blood flow: a canine study

Laser Doppler flowmetry (LDF) has been used to assess cortical bone blood flow in various clinical situations, such as osteomyelitis and osteonecrosis. Standard metal-sheathed probes containing optical fibers, applied to cortical bone for perfusion measurements, require direct exposure of the bone surface for each measurement, making nonanesthetized assessments over time impractical. Implantable optical fibers offer a noninvasive method for evaluating cortical bone perfusion without repeated surgical exposure of the bone after initial surgical implantation of the fibers. In vitro studies have shown the reliability of laser Doppler (LD) fibers compared with those of the standard probe. This investigation studied the relationship between measurements of cortical bone perfusion obtained by implanted optical (LD) fibers and standard (LDF) probes in vivo. Midshaft tibial fractures were created in the right hindlimb of 11 adult, large (>25 kg) dogs and stabilized by low contact-dynamic compression plate fixation. Cortical bone blood flow was measured by LDF using standard probes and implantable fibers at five sites along the tibia prefracture, postfracture, immediately postplate application, and at 10 weeks postplating, immediately prior to euthanasia. The implantable fibers were secured onto the cortical bone via the plate and led through a percutaneous exit site. Histological examination of the inguinal and popliteal lymph nodes and soft tissue surrounding the fibers revealed mild inflammation. No significant correlation of blood flow assessed by the implantable fibers and standard probe occurred immediately postfracture (r < 0. 13, p > 0.62). However, a statistically significant correlation was seen postplate application at one of the measurement sites in the distal fracture fragment (r = 0.78, P < 0.003). The fibers remained intact and functional until an average of 3 weeks at which time they either fractured or were removed by the animals. This is the first in vivo study assessing the reliability of implantable fibers for the measurement of cortical bone blood flow. Further modification of the fibers will be necessary to improve their longevity and durability for assessment of cortical bone blood flow.

Comparison of the effect of reamed and unreamed locked intramedullary nailing on blood flow in the callus and strength of union following fracture of the sheep tibia

This study was performed to compare the effects of reamed and unreamed locked intramedullary nailing on blood flow in the callus and early strength of union in a fractured sheep tibia model. After the creation of a standardized short spiral fracture by three-point bending with torsion, each tibia was stabilized by the insertion of a locked intramedullary nail. Ten animals were allocated randomly into two groups: one that had reaming prior to nail insertion and one that did not. Blood flow was measured in real time with use of laser Doppler flowmetry. Endosteal perfusion was determined at the fracture site before and after nail insertion. Perfusion of the callus was measured at three locations (proximal diaphysis, fracture site, and distal diaphysis) and at three time intervals (2, 6, and 12 week follow-up). All animals were killed 12 weeks postoperatively, and the tibiae were tested to failure in four-point bending. Nailing with reaming resulted in a larger decrease in overall endosteal perfusion than nailing without reaming (p < 0.015). The presence or absence of reaming did not affect blood flow within fracture callus. Perfusion of callus was greatest at 6 weeks of follow-up. Bending strength and stiffness were the same in both groups at 12 weeks. The study demonstrated that perfusion of callus and early strength of union are similar following intramedullary nailing with or without reaming.

Circulation in corticocancellous bone grafts measured with laser Doppler flowmetry. An experimental study in rats

Laser Doppler flowmetry has been evaluated for measurement of the microcirculation (flux) in corticocancellous bone grafts. Corticocancellous tibial grafts were transplanted between four donor and eight recipients rats of two histocompatibility-mismatched strains. The microcirculations in the grafted and the intact tibias were measured after 12 weeks. Variation of the method in a single animal was 0.3-0.4 in both normal and grafted bone. The flux variation between the animals was of similar magnitude. The variation did not depend upon the magnitude of the flux values. Grafts had between 26% and 53% lower circulation than normal bone, but the graft bone interface, which contained callus, had a 56% higher flux than normal bone. We conclude that laser Doppler flowmetry might be useful in research into bone grafts.

Evaluation of a laser Doppler flowmetry implantable fiber system for determination of threshold thickness for flow detection in bone

Laser Doppler flowmetry (LDF) with the use of a standard metal shafted probe, has been successfully used to study bone blood flow in a wide variety of settings. The use of the standard probe is limited by the requirement that the probe be replaced onto the bone surface or driven into the bone with a trocar. In response to this, a system of implantable, detachable fibers was developed. This system allows repeated measurement over time without repeated surgical manipulation of the area of interest. This study was performed to evaluate the implantable fiber system by determining threshold thickness for flow detection in bone. A flow chamber with perpendicular and end-on flow was designed to collect results under controlled conditions for flow detection. Threshold thickness for bovine cortical and cancellous bone samples was determined after sequentially grinding the specimens and placing them in the flow chamber. A 2% solution of latex circulated in the chamber and each specimen was exposed to both flow directions and both types of probe. The laser Doppler probe was able to detect flow by resting on top of the sample, with the latex on the other side of the sample. The results showed a significantly greater threshold thickness for the standard probes than for the implantable probes, and a significantly greater threshold thickness for trabecular bone than for cortical bone. Despite the reduced threshold thickness with the implantable fiber, this new system was able to consistently detect depth of perfusion of 80-90% of the values for the standard probe.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of blood flow on the material properties of bone

This project was undertaken to establish if the integral circulation had any effects upon the mechanical behavior of bone. The influence of blood flow in the rabbit tibia on the strain induced at the bone surface when under load was assessed. Recordings were taken from three adult and three immature New Zealand White rabbits which had previously had both their tibiae pinned with modified orthopedic pins. Strain readings were obtained from the exposed mid-shaft of the tibia of both hind legs before, during and after blood flow changes. The loading was static and used to maintain a strain of 250 mu strain in adult animals and 180 mu strain in immature animals prior to variation in blood flow. The blood flow was altered by means of a tourniquet inflated to 80 mm Hg and placed medial to the pinned tibia; it was inflated for a specific time (approximately 40 minutes) during the experimental loading. Reducing the blood flow appeared to alter the strain recorded at the bone surface while the applied load across the pins remained constant. An initial effect when there was reduced perfusion was that the strain increased following a reduction in blood flow. The strain then began to decrease in magnitude on the compressive aspect coincident with release of the cuff to a level below the value of the initial normally perfused bone. Upon return of the blood supply to normal levels following the initial hyperaemic phase, the strain value increased to a value comparable with that of normally perfused bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Sternal blood flow during mobilization of the internal thoracic arteries

A laser Doppler tissue perfusion monitor was used to measure sternal blood flow before, during, and after mobilization of the internal thoracic arteries in 24 patients undergoing coronary artery bypass grafting. To minimize chest wall injury, a narrow pedicle was mobilized. Bilateral flow data were available from 15 of the 24 patients. Analysis of these 39 studies showed no significant reduction of sternal blood flow as a consequence of mobilization of the internal thoracic arteries except in 2 patients who were both diabetic and obese.

Blood flow changes in the tibia during external loading

The influence of external load on the blood flow of the rabbit tibia was assessed by laser Doppler flowmetry (LDF). Blood flow readings were obtained from three adolescent and three adult female New Zealand White rabbits whose tibiae previously had been pinned with modified orthopaedic pins. Readings were obtained from the exposed mid-shaft of the tibia of each hind leg before, during, and after loading. The loading was either static or sinusoidal intermittent. The LDF resulted in a reading from the tibia which was consistent with the recordings of blood flow; the traces were similar to the pulsatile nature of pulse pressure recordings. After loading of the tibia, in both the adolescent and adult rabbits the effects were an increase in blood flow, as measured with LDF, on the tensile aspect, and a decrease in flow on the compressive side. These changes were statistically significant (p < 0.01) as measured by a Student t test. This change in flow reached a plateau with change in strain. Furthermore, the changes in flow produced by loading continued as long as the load was applied. A response similar to reactive hyperaemia occurred on the compressive aspect of the tibia; there was an increase of blood flow above the resting level after removal of the static load. The effect of a sinusoidal intermittent load was less than that of a static load, and the differences in flow between tensile and compressive aspects was not significant. The changes induced offer further insight into factors controlling bone remodelling.

Cortical bone microperfusion: response to ischemia and changes in major arterial blood flow

In order to investigate the effects of short-term ischemia on cortical bone microperfusion, an isolated porcine tibia diaphyseal preparation based on intact nutrient vessels was developed. Laser Doppler flowmetry (LDF) was utilized to assess continuously the cortical microcirculation and the response to short-term ischemia. The femoral artery was isolated and clamped to develop the condition of bone ischemia. On release of the clamp, reactive hyperemia was documented in all animals. Using a roller pump connected to a segment of femoral artery, the same preparation was utilized to investigate the effect of a changing femoral artery flow on the cortical microcirculation. A positive correlation between LDF output and change in arterial inflow (r = 0.64) was defined. This model has the potential for studying the effect of ischemia on bone cell viability.

An in-vitro analysis of two laser Doppler flowmetry systems for evaluation of bone perfusion

Laser Doppler Flowmetry (LDF) has been shown to be a useful tool in the experimental and clinical measurement of bone blood flow. Two LDF receiving fiber channel systems, one with a 2mW He-Ne tube laser source and the other with an infrared diode laser source, were compared with specific reference to their light attenuation through three types of bone as well as their threshold thickness for the same specimens. The threshold thickness was higher for the infrared diode system for all three bone types whereas the attenuation was identical. The demonstrated differences were most likely due to the criteria established for flow detection; the infrared diode system has a greater degree of amplification of the output signal, yielding a higher value at each thickness of bone. The two systems will produce similar output data when used for experimental analysis of bone blood flow.

Effect of internal mammary artery mobilization on sternal blood flow

Use of the internal mammary artery as a conduit for coronary artery bypass has enhanced this procedure in terms of prolonged graft patency. An earlier warning that use of both arteries would devascularize the sternum was based on postmortem radiologic imaging. This was complemented by a subsequent animal study employing isotopic microspheres. In the present clinical study, laser Doppler flowmetry was adapted to identify changes in blood supply to the left half of the divided manubrium sternum during separation of the left internal mammary artery from its chest wall attachment. Our finding of continued blood flow after this event suggests that complete devascularization of the sternum does not take place. Quality of sternal bone and surrounding tissues and clinical indications should remain as factors influencing use of one or both internal mammary arteries.