The influence of the size and condition of the reamers on bone temperature during intramedullary reaming

BACKGROUND: The objectives of this study were to determine whether intramedullary reaming increases bone temperature in vivo to a level that is high enough to produce bone necrosis and to determine the influence of the size and the condition of the reamers on the temperature increase. METHODS: Bone temperature variations were recorded in vivo during intramedullary tibial reaming in fourteen minipigs. The left tibiae were progressively reamed from 6 to 9 mm. The right tibiae were reamed with only 8 and 9-mm reamers. The variables studied were the initial and final temperature and the increase in the temperature. Two weeks after reaming, the tibiae were removed and studied histologically. RESULTS: Intramedullary reaming produced an average increase (and standard deviation) in bone temperature of 6.9 degrees C +/- 4.1 degrees C. The peak temperatures ranged from 34.9 degrees C to 49.4 degrees C. The average maximum bone temperature was 38.1 degrees C +/- 2.8 degrees C when the reaming was done progressively from 6 to 9 mm and 41.1 degrees C +/- 4.4 degrees C when the reaming was done only with the 8 and 9-mm reamers. The mean increase in the temperature in the second group of animals (8.2 degrees C +/- 4.3 degrees C) was greater than that in the first group (5.4 degrees C +/- 3.5 degrees C). Reaming with sharper reamers in the first seven animals resulted in a smaller mean increase in temperature than did reaming with less sharp reamers in the last seven animals (4.6 degrees C compared with 9.2 degrees C; p = 0.001). Histological examination of the tibiae showed periosteal proliferation and an altered disposition of the osteons at the inner cortex with occasional necrotic bone fragments in the medullary canal. CONCLUSIONS: Intramedullary reaming in the minipig increased bone temperature. When the reamer initially used was larger than the diameter of the medullary canal and when the reamers were blunted by repeated use, the maximum temperature reached by the bone was higher. This increase in temperature with use of typical medullary reaming techniques did not exceed the limits that would produce bone necrosis.     

Friction burns within the tibia during reaming. Are they affected by the use of a tourniquet?

We have carried out a prospective, randomised trial to measure the rise of temperature during reaming of the tibia before intramedullary nailing. We studied 34 patients with a mean age of 35.1 years (18 to 63) and mean injury severity score of 10 (9 to 13). The patients were randomised into two groups: group 1 included 18 patients whose procedure was undertaken without a tourniquet and group 2, 16 patients in whom a tourniquet was used. The temperature in the bone was measured directly by two thermocouples inserted into the cortical bone near the isthmus of the tibial diaphysis. Reaming was carried out to at least 1.5 mm above the required diameter of the nail. Blood loss was assessed by recording the preoperative and postoperative haemoglobin (Hb) level. The minimum clinical follow-up was six months. In group 1 (no tourniquet), the mean Hb dropped 2.8 g/dl from 14.3 +/- 1.02 g/dl to 11.5 +/- 1.04 g/dl (p = 0.0001), whereas with the tourniquet, the mean decrease was 1.3 g/dl from 14 +/- 1 g/dl to 12.7 +/- 1.3 g/dl (p = 0.007). This difference was not statistically significant. The mean initial tibial temperature was 35.6 degrees C (SD 0.6) and rose with reaming to levels between 36.3 degrees C and 51.6 degrees C. The highest temperatures were obtained with the largest reamers (11 and 12 mm, p = 0.0001) and the most rapid rise with the smallest diameters of medullary canal (8 or 9 mm). The rise of temperature was transient (20 s). We were unable to identify any effect of the use of a tourniquet on the temperature achieved. Reamed intramedullary tibial nailing induces a transient elevation of temperature which is directly related to the amount of reaming.     

Vascular and structural changes in rat femora following nailing and intramedullary occlusion

The purpose of this study was to evaluate biomechanical, structural, and blood flow changes of the femoral canal in rats 12 weeks after intramedullary reaming, nailing, or occlusion. In one group, reaming alone was performed. In a second group, reaming was followed by use of a tight-fit steel nail. In a third group, reaming was followed by use of inert silicone that totally plugged the medullary cavity. A fourth group served as the control. The acute mechanical and vascular effects caused by reaming and nailing were determined in a separate group. Reaming and nail insertion reduced blood flow in femoral bone to about one-third. Reaming reduced bending moment by approximately 40%, whereas bending rigidity was unchanged. After 12 weeks, the cortical bone blood flow was significantly increased in both the nailed and the silicone-plugged bones compared with the reamed and control groups. The bending moment and energy absorption in the silicone group were inferior to those of the other groups. There were no differences in either the external or internal diameter or the medullary and net bone areas. In the silicone group, both the number and the area of large pores (larger than 10 μm) significantly increased in comparison with the other groups; hence, bone porosity was increased. This increment was confined to large pores. It is concluded that medullary occlusion contributes to structural and blood flow changes in bone.     

Massive fat emboli syndrome after unsuccessful unreamed nailing of the tibia

A patient is presented in whom massive fat emboli syndrome (FES) developed after the unsuccesful treatment of a solitary tibial fracture with an unreamed tibial nail. Ultimately, a reamed tibial nail was inserted. Several risk factors for the development of FES were identified retrospectively in this particular case: a very small medullary canal, a large-diameter unreamed tibial nail, reaming of a small medullary canal and insertion of a thick reamed tibial nail. Even in the presence of patients with solitary lesions and without obvious risks for FES, one should always take this dangerous complication into account.     

Unusual Complications during Removal of Intramedullary Nails after Lower Leg Fractures Tibial Shaft Fissure and Inability to Remove the Nail

Patients and Methods: Between January 1995 and December 1999, 279 fractures of the lower leg were stabilized by crural intramedullary nailing (ACE^® interlocking nails, DePuy). Only under certain circumstances was the medullary cavity reamed. This paper reports on ten patients with whom unusual complications arose during nail removal. Results: In two cases, the nail jammed in the fracture callus during its removal, so that the nail had to be left in place. In eight further cases, the nail could only be removed with extreme difficulty and the use of special instruments; in six of the cases, however, a long fissure in the dorsal tibial shaft was visible under intraoperative X-ray fluoroscopy. Postoperative patient mobilization was achieved using either a brace (allowing full weight bearing on the leg) or crutches (partial weight bearing on the leg). The tibial medullary canal was reamed in nine of the ten patients, and a nail relatively wide in diameter (11-14 mm) was inserted. Conclusions: The ACE^® interlocking nail employed is bent 5° ventrally over the final 50 mm to the tip. This does not only facilitate nail insertion, but the nail also adapts to the physiological anteversion of the distal tibia. As a result of its bent shape and large diameter and in the case of considerable endosteal callus formation with associated narrowing of the medullary cavity the rigid titanium nail can no longer pass through. This may lead to a fissure when removing the nail, or even result in the total inability to remove the nail. Another reason is the dorsal groove in nails S 11 mm in diameter, into which bone grows at the site of callus formation. When removing the nail, the distal end of the nail (with no groove) has to slide over this dorsal bony ridge, thus narrowing the available lumen of the medullary canal by about 20% in the anteroposterior direction. The manufacturer has announced a change in the nail design.     

Effect of re-implanted particles from intramedullary reaming on mechanical properties and callus formation. A laboratory study

This study investigated the quality and quantity of healing of a bone defect following intramedullary reaming undertaken by two fundamentally different systems; conventional, using non-irrigated, multiple passes; or suction/irrigation, using one pass. The result of a measured re-implantation of the product of reaming was examined in one additional group. We used 24 Swiss mountain sheep with a mean tibial medullary canal diameter between 8 mm and 9 mm. An 8 mm 'napkin ring' defect was created at the mid-diaphysis. The wound was either surgically closed or occluded. The medullary cavity was then reamed to 11 mm. The Reamer/Irrigator/Aspirator (RIA) System was used for the reaming procedure in groups A (RIA and autofilling) and B (RIA, collected reamings filled up), whereas reaming in group C (Synream and autofilling) was performed with the Synream System. The defect was allowed to auto-fill with reamings in groups A and C, but in group B, the defect was surgically filled with collected reamings. The tibia was then stabilised with a solid locking Unreamed Humerus Nail (UHN), 9.5 mm in diameter. The animals were killed after six weeks. After the implants were removed, measurements were taken to assess the stiffness, strength and callus formation at the site of the defect. There was no significant difference between healing after conventional reaming or suction/irrigation reaming. A significant improvement in the quality of the callus was demonstrated by surgically placing captured reamings into the defect using a graft harvesting system attached to the aspirator device. This was confirmed by biomechanical testing of stiffness and strength. This study suggests it could be beneficial to fill cortical defects with reaming particles in clinical practice, if feasible.     

Attempted unreamed nailing in tibial fractures: A prospective consecutive series of 55 patients

We evaluated the possibility of unreamed insertion of an intramedullary nail (IMN) in a consecutive series of 55 tibial shaft fractures in 55 patients (30 men). 43 fractures were closed and 12 fractures were open. All surgeons involved were instructed to try unreamed insertion primarily. Selection of nail diameter was based on measurements of the narrowest part of the medullary canal on preoperative AP- and lateral radiographs, with a millimeter-ruler. Of the 25 cases where a 9 mm nail was chosen, 10 were impossible to insert without reaming. An 8 mm nail was selected in the remaining 30 cases, and here 10 required reaming. Mean time-to-union was 4.2 months. Delayed union was noted in 9 patients of whom 6 had been stabilized with an unreamed nail. The concept of unreamed insertion must be questioned since this could be done in only 35 patients and, in addition, we were not able to demonstrate any significant differences in time-to-union in fractures stabilized with an unreamed or a reamed nail. Implant failures were seen in 5 patients, all stabilized with an 8 mm nail. Failure of interlocking screws did not affect the final outcome. However, a possible combination of screw breakage and healing disturbances may lead to the need for more complex surgical procedures. Due to these reasons and the fact that the 8 mm nail could not be inserted unreamed in 10 of 30 patients, we stopped using the 8 mm nail.     

Unusual Complications during Removal of Intramedullary Nails after Lower Leg Fractures Tibial Shaft Fissure and Inability to Remove the Nail

Patients and Methods: Between January 1995 and December 1999, 279 fractures of the lower leg were stabilized by crural intramedullary nailing (ACE^® interlocking nails, DePuy). Only under certain circumstances was the medullary cavity reamed. This paper reports on ten patients with whom unusual complications arose during nail removal. Results: In two cases, the nail jammed in the fracture callus during its removal, so that the nail had to be left in place. In eight further cases, the nail could only be removed with extreme difficulty and the use of special instruments; in six of the cases, however, a long fissure in the dorsal tibial shaft was visible under intraoperative X-ray fluoroscopy. Postoperative patient mobilization was achieved using either a brace (allowing full weight bearing on the leg) or crutches (partial weight bearing on the leg). The tibial medullary canal was reamed in nine of the ten patients, and a nail relatively wide in diameter (11–14 mm) was inserted. Conclusions: The ACE^® interlocking nail employed is bent 5° ventrally over the final 50 mm to the tip. This does not only facilitate nail insertion, but the nail also adapts to the physiological anteversion of the distal tibia. As a result of its bent shape and large diameter and in the case of considerable endosteal callus formation with associated narrowing of the medullary cavity the rigid titanium nail can no longer pass through. This may lead to a fissure when removing the nail, or even result in the total inability to remove the nail. Another reason is the dorsal groove in nails ≥ 11 mm in diameter, into which bone grows at the site of callus formation. When removing the nail, the distal end of the nail (with no groove) has to slide over this dorsal bony ridge, thus narrowing the available lumen of the medullary canal by about 20% in the anteroposterior direction. The manufacturer has announced a change in the nail design.     

Reamed versus minimally reamed nailing: a prospectively randomised study of 100 patients with closed fractures of the tibia

It is generally accepted that in tibial fractures the results of reamed intramedullary nailing are better than those of unreamed. However, it is not known whether the clinical effects of reaming are cumulative or if minimal reaming would induce the same beneficial effects as more extensive reaming. This international multicentre study has investigated the effects of different degrees of reaming. 100 patients with closed diaphyseal tibial fractures were prospectively randomised in two centres. Method of treatment was reamed nailing up to 12 mm inserting an 11 mm tibial nail (n: 50), and minimally reamed nailing up to 10 mm inserting a 9 mm tibial nail (n: 50). All patients included in the study had follow-up studies at 4,8,12,16,26 and 52 weeks after trauma. Sixty-six male and thirty-four female patients with an average age of 37.5 years were included in the study. Gender, age, and injury side were identical in both groups. There was no significant difference of complications in the two methods. The rate of deep wound infections was higher in the reamed group (n: 3) versus the minimally reamed group (n: 1). Union occurred earlier in the reamed group (17 wks) compared to patients with minimally reamed nailing (19 wks), and there were more patients with reamed nails in whom the fracture had healed by 16 weeks (57%) versus the minimally reamed group (43%), however, this was not statistically significant. Pain scales were similar for both groups from week 4 to week 52. A considerable number of outcome parameters including knee and ankle function, as well as the comparison of time intervals to restart certain activities, and return to work showed no significant statistical difference between the two groups. However, patients of the extensive reamed group returned earlier to running, training, and normal sports activities. This study found no significant evidence that more extensive reaming gave better results, however there seemed to be a tendency of more aggressive reaming to induce earlier fracture healing with a tendency of faster recovery times.     

Does graded reaming affect the composition of reaming products in intramedullary nailing of long bones?

Reaming products taken during intramedullary nailing were examined to identify possible differences in their composition depending on the reaming percentage. Reaming products were taken from 39 fresh closed tibial and femoral diaphyseal fractures in patients with an average age of 29 years. According to histology, reaming products mainly consisted of bone trabeculae, viable or nonviable, and bone marrow stroma. A statistically significant reverse correlation exists between viable bone mass percentage and reaming progress. Reaming 1 mm less than the minimum canal diameter provides a higher viable bone mass percentage, which might be an important factor in the bone healing process.     

Periosteal microvascular reorganization after tibial reaming and intramedullary nailing in rats

BackgroundIntramedullary reaming and nailing of long bones impairs the endosteal circulation, often causing necrosis of the inner region of the bone cortex. We hypothesized that compensatory hypertrophy of the periosteal microcirculation may develop in response to mechanical destruction of the endosteum, and that this may affect bone survival in these circumstances. In these studies, nailing was performed with materials that affect regeneration of the endosteum differently, and the effects on the tibial periosteal microvasculatory organization were examined.MethodsIn male Wistar rats, the right tibia was reamed and implanted with an inert titanium nail or a less osseointegrative polyethylene nail; the contralateral tibial endosteum was destroyed by reaming. Reaming without nailing or sham operation was performed on both extremities in two other groups of rats. Twelve weeks later, the anteromedial and anterolateral surfaces of the tibias were exposed by a microsurgical technique. The structural characteristics of the periosteal microcirculation (vessel density and distribution of vessel diameters) were determined by intravital videomicroscopy and computer-assisted analysis. The stability of the implants was assessed on the basis of grades 0–2 on a qualitative scale.ResultsTibial reaming alone caused significant increases in overall blood vessel and capillary densities in the periosteum compared with those of the intact tibias. Implantation with a titanium nail resulted in firm embedding of the nail and caused changes in the periosteal vasculature similar to those after reaming alone. In contrast, implantation of a polyethylene nail was followed by the development of marked instability of the endomedullary implant and significant increases in the percentage of capillaries and the vessel density in the periosteum.ConclusionsDestruction of the endosteal microcirculation per se brings about an increase in periosteal vascular density, which is further augmented if implantation is performed with a material which delays regeneration of the endosteal circulation.     

Intramedullary pressure increase and increase in cortical temperature during reaming of the femoral medullary cavity: the effect of draining the medullary contents before reaming

BACKGROUND:Reaming is regarded as the most adverse aspect of the intramedullary nailing procedure since it leads not only to impairment of the vessels but also to an increase in intramedullary pressure and cortical temperatures which may in turn lead to aseptic cortical necroses and pulmonary dysfunction. Intramedullary pressure increase is considered to be the most detrimental of these factors. METHODS: The aim of this study was to investigate the effect on intramedullary pressure and cortical temperature of removing the medullary fat before reaming. The fat was removed through a suction tube inserted proximally. The measurements were made on pairs of human femora whereby in one group the contents of the medulla were drained by suction before reaming. The pressure was measured in the mid diaphysis and in the metaphysis. The temperature was measured in the mid diaphysis. The femora were reamed in a water bath at 37 degrees C and at a constant insertion force. RESULTS: In comparison to the group which was not drained, the pressure for the 9.0 mm reamer in previously drained femora was reduced as follows: positive diaphyseal pressure by 88% (reamer insertion); positive metaphyseal pressure by 78% (reamer insertion); negative diaphyseal pressure by 84% (reamer withdrawal); negative metaphyseal pressure by 65% (reamer withdrawal). No significant difference was determined for temperature increase (median suction, 39.7 degrees C; median without suction, 39.4 degrees C). CONCLUSION: The removal of the medullary contents by suction before inserting reaming instruments leads to a considerable and statistically significant pressure reduction. If the medullary contents are not sucked out before reaming or insertion of unreamed nails, high intramedullary pressure and the risk of embolization is unaltered. Consequently new instruments should be developed to facilitate the removal of the medullary contents before commencing the reaming procedure or insertion of unreamed nails.     

Effect of unreamed, limited reamed, and standard reamed intramedullary nailing on cortical bone porosity and new bone formation

OBJECTIVE: To compare the effects of unreamed nail insertion and reamed nail insertion with limited and standard canal reaming on cortical bone porosity and new bone formation. DESIGN: A canine segmental tibial fracture was created in fifteen adult dogs. The tibiae were stabilized with a statically locked 6.5-millimeter intramedullary nail without prior canal reaming (n = 5), after limited reaming to 7.0 millimeters (n = 5), or after standard canal reaming to 9.0 millimeters (n = 5). Porosity, new bone formation, and the mineral apposition rate of cortical bone were directly compared between the three nailing techniques. RESULTS: A significant increase in cortical bone porosity and new bone formation was seen in all three groups of experimental animals compared with the control tibiae. The overall lowest porosity levels were measured in the limited reamed group, with similar porosity levels measured in the unreamed and standard reamed groups. Porosity was lower in the limited reamed group in the entire cortex of the segmental and distal cross sections, as well as the endosteal, anterior, and posterior cortices along the length of the tibia. Overall, there was no difference in the amount of new bone formation or the mineral apposition rate between the three groups of animals at eleven weeks after surgery. DISCUSSION: The results of this study suggest that limited intramedullary reaming is a biologically sound alternative for the treatment of tibial diaphyseal fractures in which the circulation is already compromised.     

Destination of debris during intramedullary reaming. An experimental study on sheep femurs

This study was designed to further explain the better fracture healing in fractures treated with a reamed nail. It investigates the location and quantity of the reaming debris in an ex vivo animal model to test the autograft theory. In 10 cadaveric sheep femurs, a 5-mm semicircular gap was created at the midshaft. The medullary cavity was opened and the reaming debris that dropped from the gap during reaming and the debris from the proximal opening were collected and weighed separately. The mean harvest of reaming debris at the gap was 0.99 g +/- 0.12 g (24%) and from the proximal opening at the medullary cavity 3.08 g +/- 0.31 g (76%) (total 4.07 +/- 0.34 g). This study proves that a significant amount of reaming debris collects at an artificial fracture gap during reaming of the medullary cavity. This finding supports the theory of bone autografting.     

The effect on cortical bone of reaming and filling of canine tibial diaphysis with inert bone wax.

In canine studies the effect of intramedullary reaming on tubular bone was investigated in 4 dogs. Intramedullary reaming was further compared with reaming and intramedullary filling with bone wax in 6 dogs. Bone blood perfusion was measured by a microsphere technique and bone remodelling activity by 99mTc-MDP uptake. From histological sections bone necrosis and remodelling activity were estimated. The biological response increased with the surgical trauma. If the medullary cavity was only reamed, endosteal apposition was the predominant reaction. Obturation of the medullary cavity resulted in more vigorous subperiosteal and cortical reaction. It is concluded that the remodelling processes differ significantly between reamed bone and bone where the medullary cavity is reamed and blocked. Thus when testing bone cement the studies should include a control operation with obturation of the medullary canal in a way simulating bone cement.     

A prospective, randomized study of intramedullary nails inserted with and without reaming for the treatment of open and closed fractures of the tibial shaft

OBJECTIVES: To determine if there are differences in healing, complications, or number of procedures required to obtain union among open and closed tibia fractures treated with intramedullary (IM) nails inserted with and without reaming. DESIGN: Prospective, surgeon-randomized comparative study. SETTING: Level One trauma center. PATIENTS: Ninety-four consecutive patients with unstable closed and open (excluding Gustilo Grade IIIB and IIIC) fractures of the tibial shaft treated with IM nail insertion between November 1, 1994, and June 30, 1997. INTERVENTION: Interlocked IM nail insertion with and without medullary canal reaming. MAIN OUTCOME MEASURES: Time to union, type and incidence of complications, and number of secondary procedures performed to obtain union. RESULTS: For open fractures, there were no significant differences in the time to union or number of additional procedures performed to obtain union in patients with reamed nail insertion compared with those without reamed insertion. A higher percentage of closed fractures were healed at four months after reamed nail insertion compared with unreamed insertion (p = 0.040), but there was not a difference at six and twelve months. More secondary procedures were needed to obtain union after unreamed nail insertion for the treatment of closed tibia fractures, but the difference was not statistically significant given the limited power of our study (p = 0.155). Broken screws were seen only in patients treated with smaller-diameter nails inserted without reaming, and the majority occurred in patients who were noncompliant with weight-bearing restrictions. There were no differences in rates of infection or compartment syndrome. CONCLUSION: Our findings support the use of reamed insertion of IM nails for the treatment of closed tibia fractures, which led to earlier time to union without increased complications. In addition, canal reaming did not increase the risk of complications in open tibia fractures.     

Effects of medullary reaming on fracture healing: Tibial osteotomies in rabbits

Unilateral, midshaft tibial osteotomy was made in 16 rabbits. Reaming of the medullary canal was performed in half the animals, while the other half were operated on without reaming. Intramedullary fixation was accomplished with multiple Kirschner pins in both groups. Bone healing occurred with abundant peripheral callus in both groups. Mechanical testing after 6 weeks revealed higher strength of the osteotomized bones where reaming had not been performed compared with bones with reaming.

We conclude that bone healing is delayed by medullary reaming, where-as the pattern of healing is similar in bones with and without reaming.     

Growth factor release following femoral nailing

The aim of this study was to investigate whether growth factors essential for fracture healing are substantially increased in the immediate aftermath following reaming of the intramedullary cavity for stabilisation of femoral shaft fractures. Consecutive adult patients whose femoral shaft fractures stabilised with either reamed (10 patients) or unreamed (10 patients) intramedullary nailing were studied. Peripheral blood samples and samples from the femoral canal before and after reaming and nail insertion were collected. Serum was extracted and using Elisa colorimetric assays the concentration of Platelet Derived Growth Factor-BetaBeta (PDGF), Vascular Endothelial Growth Factor (VEGF), Insulin-like Growth Factor-I (IGF-I), Transforming Growth Factor beta 1 (TGF-beta1) and Bone Morphogenetic Protein-2 (BMP-2) was measured. The mean age of the twenty patients who participated in the study was 38 years (range 20-63). Reaming substantially increased all studied growth factors (p<0.05) locally in the femoral canal. VEGF and PDGF were increased after reaming by 111.2% and 115.6% respectively. IGF-I was increased by 31.5% and TGF-beta1 was increased by 54.2%. In the unreamed group the levels of PDGF-BB, VEGF, TGF-beta1 remained unchanged while the levels of IGF-I decreased by 10%. The levels of these mediators in the peripheral circulation were not altered irrespectively of the nail insertion technique used. BMP-2 levels during all time points were below the detection limit of the immunoassay. This study indicates that reaming of the intramedullary cavity is associated with increased liberation of growth factors. The osteogenic effect of reaming could be secondary not only to grafting debris but also to the increased liberation of these molecules.     

Effects of medullary reaming on fracture healing. Tibial osteotomies in rabbits

Unilateral, midshaft tibial osteotomy was made in 16 rabbits. Reaming of the medullary canal was performed in half the animals, while the other half were operated on without reaming. Intramedullary fixation was accomplished with multiple Kirschner pins in both groups. Bone healing occurred with abundant peripheral callus in both groups. Mechanical testing after 6 weeks revealed higher strength of the osteotomized bones where reaming had not been performed compared with bones with reaming. We conclude that bone healing is delayed by medullary reaming, whereas the pattern of healing is similar in bones with and without reaming.     

Intramedullary pressure and bone marrow fat extravasation in reamed and unreamed femoral nailing.

This study was designed to investigate whether intramedullary pressure and embolization of bone marrow fat are different in unreamed compared with conventional reamed femoral nailing in vivo. In a baboon model, the femoral shaft was stabilized with interlocking nailing after a midshaft osteotomy. Intramedullary pressure was measured in the distal femoral shaft fragment at the supracondylar region. Extravasation of bone marrow fat was determined by the modified Gurd test (range: 0-5) with blood samples from the vena cava inferior. Data were monitored in eight unreamed and eight reamed intramedullary femoral nailing procedures. Intramedullary pressure increased in the unreamed group to 76 +/- 25 mm Hg (10.1 +/- 3.3 kPa) during insertion of 7-mm nails and in the reamed group to 879 +/- 44 mm Hg (117.2 +/- 5.9 kPa) during reaming of the medullary cavity. Insertion of 9-mm nails after the medullary cavity had been reamed to 10 mm produced an intramedullary pressure of 254 +/- 94 mm Hg (33.9 +/- 12.5 kPa) (p < 0.05). Fat extravasation in the unreamed group was recorded with a score of 2.9 +/- 0.4 for the Gurd test during nailing with 7-mm nails, whereas in the reamed group significantly more fat extravasation was noticed during the reaming procedures, with a score of 4.6 +/- 0.1. Liberation of fat during insertion of 9-mm nails after reaming was recorded with a score of 3.5 +/- 0.4. In both groups, a positive correlation of fat extravasation with the rise in intramedullary pressure was found (reamed group: r(s) = 0.868; unreamed group: r(s) = 0.698), resulting in significantly less liberation of bone marrow fat in the unreamed stabilized group than in the reamed control group (p < 0.05). The data indicate that fat embolization during nailing procedures after femoral osteotomy increases with increasing intramedullary pressure and occurs in a lesser degree in unreamed than in reamed intramedullary femoral shaft stabilization.