[Results of follow-up studies on femur fractures in childhood with special reference to femur torsion in relation to conservative types of therapy].
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Adolescent↗
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[Osteosynthesis of femur shaft fractures with the unreamed AO-femur nail. Surgical technique and initial clinical results standard lock fixation].
Nailing technique has changed in recent years in some important aspects which are not limited to the omitted reaming procedure. These changes concern patient positioning, reduction technique and determination of implant length and diameter. Approach and exposure techniques have been modified to new, less invasive procedures, in order to fulfill technical, functional and aesthetic requirements. Techniques and tricks have been developed for avoidance of fragment diastasis, axial and torsional malalignment and leg length differences. Finally, simple algorithms have been elaborated for the management of bilateral femoral shaft or ipsilateral tibial shaft fractures and the number and location of locking bolts. These algorithms, techniques and procedures were developed in a series of 108 femoral shafts, which were stabilized wit the AO unreamed femoral nail (UFN) in a prospective study between 1991 and 1994. Of these, 39 cases with a mean follow-up of 19.3 (range 8-40) months after trauma were reviewed. Fractures were classified according to Müller (1990): 6 type A, 21 type B and 12 type C. Closed soft tissue damage was classified according to our classification: C0/I, n = 14; CII, n = 15 (Tscherne 1982). Among 10 open fractures 4 were OI, 4OII, 1OIIIA and 1OIIIB (Gustilo 1976). The major complications were breakage of locking bolts (n = 2), one nail breakage after 9 weeks and one case of osteitis.
Adolescent↗
[The AO universal femur intramedullary nail: problems and their amelioration. Retrospective quality control study of 57 femur shaft fractures].
Today intramedullary nailing is considered the treatment method of choice in fractures of the femoral diaphysis. In this retrospective quality control study 57 femoral fractures treated with the AO-Universal Femoral Nail have been reviewed. The average follow up time was 2.9 years. Intramedullary nailing was done as a primary procedure in 40 cases and in 17 cases as a secondary procedure following various initial operations. The results were evaluated according to the Stromsoe score. 27 of the 40 primary procedures went on to an uneventful healing and showed good to excellent final result. Technical errors (7), non-unions (4) and 1 deep infection required various secondary procedures. Thereafter the final number of good to excellent results amounted to 35 out of 40 patients. In the group with secondary i.m. nailing 9 out of 17 patients showed a good to excellent final result. 2 non unions persisted. In conclusion the AO-Universal Femoral Nail proved to be suited for the treatment of femoral shaft fractures for both primary and secondary procedures. In this series, however, technical imperfections led to a high rate of secondary procedures. Strict observation of the recommended operative technique is therefore mandatory.
Adolescent↗
In vitro biomechanical comparison of solid and tubular interlocking nails in neonatal bovine femurs.
This study biomechanically evaluates solid and tubular interlocking nails in bovine neonatal femurs. Paired femurs from 40 neonatal dairy calves were obtained for mechanical testing. Intact femurs and four combinations of experimentally manipulated femurs (intact or ostectomized femurs with either a solid or tubular interlocking nail) were tested in craniocaudal and lateromedial bending, eccentric axial compression, and external torsion to evaluate composite rigidity, local/gap stiffness, and load to failure (compression and torsion only). In torsional composite rigidity, femurs with tubular interlocking nails were more complaint than intact femurs or intact femurs with solid interlocking nails (P < .001). Ostectomized femurs with solid interlocking nails were similar to intact femurs with tubular interlocking nails. Within femurs with tubular interlocking nails, ostectomized femurs were more compliant than intact femurs (P < .0001). In craniocaudal and lateromedial bending rigidity, ostectomized femurs were more complaint than intact femurs, regardless of interlocking nail type (P < .001). Within ostectomized femurs, tubular interlocking nails were more complaint than solid interlocking nails in craniocaudal bending (P < .05) and there was a similar trend in lateromedial bending (P = .06). In eccentric axial compression, local/gap stiffness was significantly greater in intact femurs compared with intact femurs with solid (48% of intact bone) or tubular (45% of intact bone) interlocking nails and ostectomized femurs with solid (18% of intact bone) or tubular (11% of intact bone) interlocking nails (P < .0001). In torsional testing, local/gap stiffness was not significantly different between intact femurs and intact femurs with interlocking nails, but was significantly lower in ostectomized femurs with solid (2% of intact bone) and tubular (0.2% of intact bone) interlocking nails (P < .0001).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
An in vitro biomechanical comparison of interlocking nail constructs and double plating for fixation of diaphyseal femur fractures in immature horses.
OBJECTIVE: To compare the biomechanical properties of intact immature horse femurs and 3 stabilization methods in ostectomized femurs. ANIMAL OR SAMPLE POPULATION: Eighteen pairs of femurs from immature horses aged 1 to 15 months, and weighing 68 to 236 kg. METHODS: Thirty-four immature horse femurs were randomly assigned to 1 of 5 test groups: 1) interlocking intramedullary nail (IIN) (n = 6); 2) IIN with a cranial dynamic compression plate (I/DCP) (n = 6); 3) 2 dynamic compression plates (2DCP) (n = 8); 4) intact femurs tested to failure in lateromedial (LM) bending (n = 6); and 5) intact femurs tested to failure in caudocranial (CaCr) bending (n = 8). Mid-diaphyseal ostectomies (1 cm) were performed in all fixation constructs. Biomechanical testing consisted of 4 nondestructive tests: CaCr bending, LM bending, compression, and torsion, followed by bending to failure. All groups were tested to failure in LM bending with the exception of 1 group of intact femurs tested to failure in CaCr bending. Stiffness and failure properties were compared among groups. RESULTS: The 2DCP-femur construct had greater structural stiffness in nondestructive bending than the IIN-femur construct in either LM or CaCr bending, and the I/DCP-femur construct in LM bending. Only the I/DCP and 2DCP fixations were similar to intact bone in nondestructive-bending tests. In addition, the 2DCP-femur construct had greater structural and gap torsional stiffness than the I/DCP-femur construct, and greater gap torsional stiffness than the IIN-femur construct. However, all of the fixation methods tested, including the 2DCP-femur construct, had lower structural stiffness in torsional loading compared with intact bone. No significant differences in structural stiffness were found between intact bones and femur constructs tested nondestructively in compression. In resistance to LM bending to failure, the 2DCP-femur construct was superior to the IIN-femur construct, yet similar to the I/DCP-femur construct. Also, evaluation of yield and failure loads revealed no significant differences between intact bone and any of the femur constructs tested to failure in LM bending. CONCLUSIONS: In general, the 2DCP-femur construct provided superior strength and stiffness compared with the IIN and I/DCP-femur constructs under bending and torsion. CLINICAL RELEVANCE: Double plating of diaphyseal comminuted femoral fractures in immature horses may be the best method of repair, because in general, it provides the greatest strength and stiffness in bending and torsion.
Animals↗
Femur fractures in relatively low speed frontal crashes: the possible role of muscle forces.
In a sample of relatively low speed frontal collisions (mean collision speed change of 40.7 kph) the only major injury suffered by the partly or fully restrained occupant was a femur fracture. However, femur load measurements from standardized barrier crash tests for similar vehicles at a greater speed change (mean of 56.3 kph) showed that in almost all the cases, the occupant's femur would not have fractured because the loads were below fracture threshold. In order to address this discrepancy, the load in the femurs of the occupants in the crash sample were estimated and compared with the femur fracture threshold. Femur load was estimated by inspecting the scene and measuring deformations in each vehicle, defining occupant points of contact and interior surface intrusion, and calculating crash change in velocity and deceleration. From this data, the measured femoral loads from standardized crash test data in a comparable vehicle were scaled to the actual crash by considering crash deceleration, occupant weight, and restraint use. All the occupants (7 males, average age 26.7 years, 13 females, average age 36 years) sustained at least a transverse midshaft fracture of the femur with comminution, which is characteristic of axial compressive impact, causing bending and impaction of the femur. However, the estimated average maximum axial load was 8187 N (S.D. = 4343N), and the average probability for fracture was only 19% (based on the femur fracture risk criteria). In 13 crashes the fracture probability was less than 10%. Two factors were considered to explain the discrepancy. The occupant's femur was out of position (typically the driver's right front leg on the brake) and did not impact the knee bolster, instead hitting stiffer regions of the dashboard. Also, since most victims were drivers with their foot on the brake to avoid the collision, additional compressive force on the femur probably resulted from muscle contraction due to bracing for impact. Adding the estimated muscle load on the femur to the estimated external load increased the femur loads beyond threshold, explaining the fracture in all but one case. Since crash tests using dummies cannot simulate out of position occupants or muscle contraction loading, they may underestimate the total load acting on the femur during actual impacts where the driver is bracing for the crash. These results may have implications for altering knee bolster design to accommodate out of position occupants and the additional load caused by muscle forces during bracing.
Accidents, Traffic↗
Evaluation of fetal femur length to detect Down syndrome in a Thai population.
OBJECTIVE: To assess the value of femur length shortening for prenatal detection of Down syndrome in a Thai population. METHOD: A prospective study was performed by experienced perinatologists on 3137 women undergoing second-trimester amniocentesis, between 16 and 24 weeks of gestation, for the indications of advanced maternal age and past history of chromosomal abnormality. Biparietal diameter and femur length measurements were obtained before the procedures. Regression equations relating biparietal diameter to femur length were used to calculate observed femur length/expected femur length ratio in the chromosomally normal and Down syndrome fetuses. Sensitivity, specificity, false-positive rate and likelihood ratio of a positive test result at various observed femur length/expected femur length ratios for detection of Down syndrome were calculated. A receiver-operator characteristic curve was used to determine threshold screening ratio. RESULTS: There were 3084 chromosomally normal pregnancies, 26 fetuses with Down syndrome (1:118), and 27 other chromosomal abnormalities. The relationship between femur length and biparietal diameter (BPD) was: expected femur length=-7.631+0.814 BPD, R(2)=0.78, P<0.001). Femur length in Down syndrome fetuses was significantly shorter than in normal fetuses (P<0.001). A ratio of 0.91 for observed femur length/expected femur length yielded a sensitivity of 42.3%, specificity of 86.2%, false positive rate of 13.8% and likelihood ratio of a positive test result of 3.07 (95% CI 1.94-4.84) for detection of Down syndrome. CONCLUSIONS: In this study, femur length shortening in the second trimester appears to be a useful screening parameter for fetal Down syndrome in a Thai population.
Adult↗
Maternal ethnicity and variation of fetal femur length calculations when screening for Down syndrome.
OBJECTIVE: To determine whether current methods for detecting Down syndrome based on fetal femur length calculations are influenced by ethnicity. METHODS: The study population consisted of all fetuses scanned between 14 and 20 completed weeks' gestation from April 1, 1997, to January 1, 2000. The expected femur length was calculated from the biparietal diameter. The variance from the expected femur length, compared with the biparietal diameter, was calculated, and the mean variations were compared by maternal race. Ethnic-specific formulas for expected femur length were derived by simple regression. RESULTS: There was a statistically significant difference in femur length in the Asian group compared with all other groups, as well as the white group compared with the black and Asian groups (P < .05). However, there was no significant difference between the black and Hispanic groups or the white and Hispanic groups. The Asian group had the largest variation, with the measured femur length being less than the expected femur length. All groups studied had a mean expected femur length less than the mean measured femur length. On the basis of the ethnic-specific formulas for femur length, there was a significant decrease in patients that would undergo further evaluation for Down syndrome. CONCLUSIONS: There is a significant difference in the mean expected femur length by biparietal diameter among fetuses in the second trimester with regard to ethnicity. Using ethnic-specific formulas for expected femur length can have a considerable impact on the use of sonographic risk factors for Down syndrome screening. Further data are required for use of femur length as a screening tool in the genetic sonogram.
Adult↗
Concept and development of an orthotropic FE model of the proximal femur.
PURPOSE: In contrast to many isotropic finite-element (FE) models of the femur in literature, it was the object of our study to develop an orthotropic FE "model femur" to realistically simulate three-dimensional bone remodelling. METHODS: The three-dimensional geometry of the proximal femur was reconstructed by CT scans of a pair of cadaveric femurs at equal distances of 2mm. These three-dimensional CT models were implemented into an FE simulation tool. Well-known "density-determined" bony material properties (Young's modulus; Poisson's ratio; ultimate strength in pressure, tension and torsion; shear modulus) were assigned to each FE of the same "CT-density-characterized" volumetric group. In order to fix the principal directions of stiffness in FE areas with the same "density characterization", the cadaveric femurs were cut in 2mm slices in frontal (left femur) and sagittal plane (right femur). Each femoral slice was scanned into a computer-based image processing system. On these images, the principal directions of stiffness of cancellous and cortical bone were determined manually using the orientation of the trabecular structures and the Haversian system. Finally, these geometric data were matched with the "CT-density characterized" three-dimensional femur model. In addition, the time and density-dependent adaptive behaviour of bone remodelling was taken into account by implementation of Carter's criterion. RESULTS: In the constructed "model femur", each FE is characterized by the principal directions of the stiffness and the "CT-density-determined" material properties of cortical and cancellous bone. Thus, on the basis of anatomic data a three-dimensional FE simulation reference model of the proximal femur was realized considering orthotropic conditions of bone behaviour. CONCLUSIONS: With the orthotropic "model femur", the fundamental basis has been formed to realize realistic simulations of the dynamical processes of bone remodelling under different loading conditions or operative procedures (osteotomies, total hip replacements, etc).
Absorptiometry, Photon↗
Mismatch of current intramedullary nails with the anterior bow of the femur.
OBJECTIVES: The anterior curvature of the femur affects intramedullary nail insertion, revision prosthesis design, and the biomechanics of the proximal femur. Two previous studies, using small numbers of femurs, determined femoral curvature and showed that it was significantly greater than that of the several intramedullary nails they evaluated. In this study, the curvature of 948 femurs (474 matched pairs) was determined and compared with current intramedullary nails. The correlation of femoral curvature to age, gender, femoral size, and race was also evaluated. SETTING: Museum skeletal collections and a hospital biomechanics laboratory. METHODS: The curvature of 892 femurs (446) from the skeletal collections of 2 museums was measured by processing the digital images of the femurs with a computer curve-fitting program. Fifty-six additional, embalmed femurs (28 pairs) from our collection were also digitally imaged and then radiographed and their medullary curvatures similarly determined for comparison. Curvatures of 8 current antegrade intramedullary nails and 3 long-stemmed femoral hip prostheses were obtained from manufacturers and confirmed by measurements from their templates after digitization. RESULTS: We found the average femoral anterior radius of curvature was 120 cm (+/- 36 cm). There was no effect of age on femoral curvature nor was there a correlation between femoral width or femoral length to curvature. Black donor femurs had less curvature than white donor femurs (P < 0.001). There was close correlation (r = 0.967) between the femoral curvatures determined from the digital images and the radiographs. Radii of curvature of the intramedullary nails ranged from 186 to 300 cm (eg, straighter than the femurs). CONCLUSIONS: There was a large mismatch between the curvature of some current antegrade intramedullary nails and the average femur. Although this is only 1 factor affecting nail insertion, the mismatch warrants a reappraisal of these intramedullary nail designs. CLINICAL RELEVANCE: Because ease of intramedullary nail insertion and possibility of cortical comminution are determined by a number of factors including insertion point and fracture location, it appears that a decrease in radii of curvature (less straight) of current nail designs is warranted, particularly for those larger diameter nails designed for hip fracture stabilization that have greater rigidity due to design or material.
Anthropometry↗
Prophylactic cerclage: a method of preventing femur fracture in uncemented total hip arthroplasty.
The incidence of femur fracture in non-cemented hip arthroplasty has been reported to be between 4.1% and 27.8%. To quantitate the hoop stress generated during insertion of a femoral broach in total hip arthroplasty and determine the effect of cerclage with both braided cable and wire, we harvested 14 pairs of embalmed cadaver femurs. These were reamed and broached to duplicate the surgical technique of inserting a straight non-cemented femoral component. Group one consisted of eight matched cadaver femurs which were tested using a single 2.0 mm chrome-cobalt cable placed around the calcar of one femur, with the other serving as a control. Group two consisted of five matched cadaver femurs which were tested using a single 18 gauge cerclage wire in the same manner. In group one, the femurs serving as controls were found to have a mean microstrain of (1425.00 +/- 1180.19). The eight femurs tested with a 2 mm cable were determined to have a mean microstrain of (4179 +/- 2853.89). In group two, the femurs serving as controls were found to have a mean microstrain of (962.60 +/- 956.78). The five femurs in group two tested with a cerclage wire were determined to have a mean microstrain of (1112.00 +/- 975.66). Using a paired t-test, statistical significance was achieved with a confidence level of P less than or equal to .01 in group one. Prophylactic wiring of the proximal femur with 2 mm cable increases the hoop stress resistance and, therefore, should decrease the incidence of intraoperative femur fractures in uncemented total hip arthroplasty.
Bone Cements↗
[Clinical study on the rotational deformity after interlocking nailing in femur shaft fracture].
OBJECTIVE: To explore the approach to accurately judge the degree of rotational deformity in femur shaft fracture. METHODS: 110 patients with femur shaft fracture were divided into 3 groups: Group A (n = 62) with the distal end of the fractured femur at the traumatic side at neutral position so as to fix the fracture, Group B (n = 27), with both the distal and proximal ends of the fractured femur at the neutral position so as to fix the femur at an antiversion angle of 15 degrees d, and Group C (n = 21), with the degree of antiversion angle to be controlled to that on the intact side. X ray examination and CT scanning were conducted 3 days after intramedullary nailing to measure the degree of the antiversion angle on both sides. The difference between the degrees of antiversion angle at the 2 sides was considered the rotational deformity of the femur shaft after the nailing. The antiversion angles of the femurs at both sides of 11 healthy persons were measured as controls. RESULTS: The biggest value of antiversion angle was 26 degrees , the smallest value was 8 degrees , the average value at the left side was 12.8 degrees , and the average value at the right side was 12.45, and the biggest difference between the 2 side was 7 degrees in the control group. The average antiversion angle of the femur was 14.67 degrees , the biggest value was 51 degrees , and the smallest value was -24 degrees at the traumatic side; and the average antiversion angle of the femur was 14.27 degrees , the biggest value was 40 degrees , and the smallest value was -23 degrees at the intact side in the treatment groups. 53% and 52% of the patients in Groups A and B showed a rotational deformity < 10 degrees , and 9% and 11% of them showed a rotational deformity > 20 degrees , significantly different from those in the control group (all P < 0.05). The rotational deformity was < 10 degrees in all patients of Group C, not significantly different from that of the control group (P > 0.05). CONCLUSION: Clinically about half of the femur shaft fractures are fixed in the position of rotational deformity > 10 degrees after nailing. The rotational deformity of femur shaft fracture should be prevented by comparing the antiversion angle on the intact side so as to achieve more reliable adequate reduction.
Adult↗
Subregion analysis of the rat femur: a sensitive indicator of changes in bone density following treatment with thyroid hormone or bisphosphonates.
Measurement of bone mineral density (BMD) by dual X-ray absorptiometry (DXA) is a precise and accurate way to assess changes in BMD due to a variety of causes. However, the degree of bone loss may vary depending on the skeletal site examined. We postulated that interventions that change bone density would have a different effect on an area rich in trabecular bone, such as the distal femur, than on other subregions of the femur. Male Sprague-Dawley rats (325-350 g) were treated with triiodothyronine (T3), a bisphosphonate (pamidronate), or placebo for 21 days and then sacrificed. Ex vivo BMD of the proximal, distal, mid and total femur were measured by DXA. We found that mean BMD of hyperthyroid rats was significantly lower than controls at all femoral subregions. However, the difference in mean BMD between hyperthyroid and control rats was greatest at the distal femur (8.6%). In rats treated with bisphosphonate, mean BMD was significantly higher than controls at the proximal, distal, and total femur. The difference in mean BMD between controls and rats treated with bisphosphonate was greatest at the distal femur (31.8%). Furthermore, pamidronate (APD)-treated rats had lower mean mid-femur BMD than controls. We conclude that changes in BMD after treatment with bisphosphonate or T3 are greatest at the distal femur subregion, and that treatment with bisphosphonate may cause a slight reduction in mid-femur BMD. Future studies examining changes in BMD in the rat femur after interventions that alter mineral metabolism should include subregion analysis.
Absorptiometry, Photon↗
Femur length shortening in the detection of Down syndrome: is prenatal screening feasible?
The potential utility of screening for femur length shortening in prenatal detection of Down syndrome (trisomy 21) was evaluated by comparing 49 consecutive fetuses with Down syndrome with 572 chromosomally normal fetuses before genetic amniocentesis. Ratios of measured femur length/predicted femur length and biparietal diameter/femur length were calculated for each fetus. The predicted femur length was calculated from a regression equation relating the biparietal diameter and femur length derived from a sample control group. With this normal regression equation, 7 of 49 (14.3%) fetuses with Down syndrome had short femur lengths (measured femur length/predicted femur length ratio of less than or equal to 0.91) compared with 35 of 572 (6.1%) fetuses with a normal karyotype (p less than 0.05). However, the maximum positive predictive value for identification of Down syndrome based on short femur lengths was only 0.93% for a high-risk population (prevalence of Down syndrome, 1:250) and 0.33% for a low-risk population (prevalence of Down syndrome, 1:700). We conclude that ultrasonographic screening of short femur length is less effective for prenatal detection of Down syndrome than initially suggested.
Cephalometry↗
Humerus and femur length shortening in the detection of Down's syndrome.
OBJECTIVE: Our purpose was to determine the utility of screening for humerus and femur length shortening in prenatal detection of Down's syndrome (trisomy 21). STUDY DESIGN: On the basis of the biparietal diameter, predicted humerus and femur lengths were derived from a sample control group of 350 karyotypically normal fetuses. The regression formulas were prospectively applied to 45 consecutive fetuses with Down's syndrome and 942 fetuses with normal karyotypes. Ratios of measured humerus length/predicted humerus length and measured femur length/predicted femur length were calculated for each fetus. RESULTS: Eleven of 45 (24.4%) fetuses with Down's syndrome had short humerus (measured humerus length/predicted humerus length ratio of < or = 0.89), and 11 (24.4%) had short femur (measured femur length/predicted femur length ratio of < or = 0.91. In comparison, among 942 karyotypically normal fetuses only 43 (4.5%) showed short humerus and 44 (4.7%) showed short femur (p < 0.05). Fetuses with both short humerus and short femur carried an 11-fold greater risk of Down's syndrome (risk ratio = 11.1; 95% confidence interval = 5.0 to 25.0). CONCLUSION: Prenatal ultrasonographic detection of short humerus to short femur, or both significantly increase the risk of Down's syndrome; this information may be useful in screening programs.
Bone Lengthening↗
The effect of implant overlap on the mechanical properties of the femur.
BACKGROUND: The most biomechanically stable relationship between the side plate of a compression hip screw (CHS) and retrograde intramedullary (IM) femoral nail has not been described in the literature. This becomes a clinical issue when treating supracondylar femur fractures with a retrograde nail in patients with a history of compression hip screw fixation of intertrochanteric fractures. The proximal end of the nail and the interlocking screws may act as a stress riser in the femoral diaphysis. The purpose of this study is to determine the biomechanical consequences of the amount of implant overlap between a CHS plate and retrograde IM femoral nail. METHODS: Nine paired fresh-frozen cadaver femora from elderly donors were cleaned of soft tissue and fixed with uniaxial strain gauges. Each femur was loaded three times in a fall-loading configuration to 50 kg at a rate of 1 Hz. The study consisted of two phases. In phase 1, six pair were randomly divided into a control and test femur from each pair. Three states were compared on each test femur: uninstrumented, instrumented with CHS, and instrumented with CHS and retrograde nail. The control femur consisted of the matched femur tested in two states: uninstrumented and instrumented with a CHS. The femora were then loaded to failure. The tests were performed with the retrograde nail and CHS gapped 3 cm, kissing, and overlapping by two screw holes (two pair for each state). In phase 2, each of the remaining three pair were instrumented with a CHS and retrograde nail overlapping in one femur and gapped in the matched femur and tested in the same manner. Data analysis was performed using Pearson's correlation coefficients between groups. Paired samples t tests were used to compare differences within test states and independent samples t tests were used to compare differences between femora. Mean strain at 50-kg load, load-versus-strain patterns, failure patterns, and load and strain at failure were recorded. RESULTS; Correlation coefficients were greater than 0.98 within and between pairs (p < 0.001). There were statistically significant differences (p < 0.05) in strain patterns between the uninstrumented, CHS, and CHS/IM test states. The addition of a side plate significantly (p < 0.05) increased lateral compressive strains in the femoral diaphysis. Mean strain at 50-kg load was significantly (p < 0.05) altered by the addition of the retrograde nail in all three implant orientations. Gapped implants failed at lower loads and strains than femurs with kissing and overlapping implants. Gapped constructs failed at lower loads than control states. Overlapped constructs tolerated the highest loads and strains before failure. CONCLUSION: Strain patterns are altered by the degree of implant overlap in the proximal femoral diaphysis. Femora with uninstrumented intervals between retrograde nails and side plates fail at lower loads than femora without retrograde nails and those with kissing or overlapping implants. Kissing or overlapping instrumentation increases load to failure and creates a more biomechanically stable construct than gapped implants. The findings of this study suggest an overlapping implant orientation in the femur increases failure load at the implant interface.
Aged↗
Compression or tension? The stress distribution in the proximal femur.
BACKGROUND: Questions regarding the distribution of stress in the proximal human femur have never been adequately resolved. Traditionally, by considering the femur in isolation, it has been believed that the effect of body weight on the projecting neck and head places the superior aspect of the neck in tension. A minority view has proposed that this region is in compression because of muscular forces pulling the femur into the pelvis. Little has been done to study stress distributions in the proximal femur. We hypothesise that under physiological loading the majority of the proximal femur is in compression and that the internal trabecular structure functions as an arch, transferring compressive stresses to the femoral shaft. METHODS: To demonstrate the principle, we have developed a 2D finite element model of the femur in which body weight, a representation of the pelvis, and ligamentous forces were included. The regions of higher trabecular bone density in the proximal femur (the principal trabecular systems) were assigned a higher modulus than the surrounding trabecular bone. Two-legged and one-legged stances, the latter including an abductor force, were investigated. RESULTS: The inclusion of ligamentous forces in two-legged stance generated compressive stresses in the proximal femur. The increased modulus in areas of greater structural density focuses the stresses through the arch-like internal structure. Including an abductor muscle force in simulated one-legged stance also produced compression, but with a different distribution. CONCLUSION: This 2D model shows, in principle, that including ligamentous and muscular forces has the effect of generating compressive stresses across most of the proximal femur. The arch-like trabecular structure transmits the compressive loads to the shaft. The greater strength of bone in compression than in tension is then used to advantage. These results support the hypothesis presented. If correct, a better understanding of the stress distribution in the proximal femur may lead to improvements in prosthetic devices and an appreciation of the effects of various surgical procedures affecting load transmission across the hip.
Compressive Strength↗
Pediatric reference data for dual X-ray absorptiometric measures of normal bone density in the distal femur.
OBJECTIVE: Many children at risk for osteoporosis have substantial hip and knee contractures that prevent assessment of bone mineral density in the "usual" region, the proximal femur. As an alternative, bone density may be measured in the distal femur projected in the lateral plane. The purpose of this study was to provide normative reference data useful for interpretation of bone density measures in the distal femur of children and adolescents. SUBJECTS AND METHODS: The study was a cross-sectional, single-observational assessment of 256 healthy children and adolescents between the ages of 3 years and 18 years 6 months (mean, 10 years 5 months). Bone mineral density was measured in the nondominant proximal femur, lumbar spine, and both distal femurs using dual X-ray absorptiometry. RESULTS: We found that bone mineral density increases with age in the cortical, cancellous, and mixed regions of the distal femur, similar to the findings with other regional analyses of bone density. Bone density in the distal femur correlates very highly with bone density in the proximal femur and slightly less well with bone density in the lumbar spine. CONCLUSION: In pediatric patients who have deformities, have experienced trauma, or have undergone surgical procedures that prevent reliable measures of bone density in the proximal femur, bone mineral density may be measured in the distal femur and interpreted relative to the bone mineral density findings in healthy age- and sex-matched controls.
Absorptiometry, Photon↗