Mechanical study of the safe distance between distal femoral fracture site and distal locking screws in antegrade intramedullary nailing

Periprosthetic fracture around total knee arthroplasty: What are the advantages of minimal-invasive surgery?

OBJECTIVES

Periprosthetic femur fractures after total knee arthroplasty in older adults are mostly treated by internal fixation. Members of the GETRAUM (French Orthopedic Trauma Society) sought to compare two surgical techniques - conventional open surgery and minimally invasive surgery - with the aim of analyzing the patients' functional recovery. We hypothesized that a minimally invasive technique would produce better early functional outcomes with recovery of independence.

MATERIALS AND METHODS

This retrospective multicenter study of patients treated between 2009 and 2015 consisted of 90 fractures with a follow-up of 1 year. Demographic, preoperative data and the characteristics of fractures, type of fixation and the surgeon's experience level were collected. The endpoints were the Parker Mobility score, Katz ADL, place of residence at the time of fracture and at 6 months and one-year follow-up. All complications and one-year mortality during the follow up were searched.

RESULTS

At 6 months follow-up, the minimally invasive technique contributed to significantly better functional recovery as measured by the Parker (p < 0.05) and Katz scores (p < 0.05). However, there were no differences in these scores at one-year follow-up. The complication rate was 31% at one year follow-up. Mortality rate was 12 % (11 patients).

CONCLUSION

Our hypothesis was confirmed, as there was a difference between techniques that impacted functional recovery and independence, but only in the early postoperative phase. A minimally invasive technique appears to be beneficial in the short term for distal femur fractures after total knee arthroplasty but must be evaluated in a comparative and prospective study to fully confirm its reliability.

"Ratio of fracture site diameter to isthmus femoral canal diameter" as a predictor of complication following treatment of infra-isthmal femoral shaft fracture with antegrade intramedullary nailing

INTRODUCTION

Fixation of infra-isthmus femoral shaft fracture using antegrade intramedullary (IM) nailing is difficult and is associated with a high complication rate. This study aimed to identify risk factors for complications following this procedure. The ratio of the fracture site diameter to the diameter of the femoral intramedullary canal of the isthmus (FI ratio) was evaluated as a novel parameter to predict complication.

MATERIALS AND METHODS

Patients who underwent antegrade IM nailing for infra-isthmus femoral shaft fracture between January 2008 and December 2018 and had a minimum of 12 months of follow-up were retrospectively reviewed. The primary outcome was occurrence of complication, including non-union, mal-alignment, fixation failure, or progressive loss of reduction. Logistic regression analysis was performed to identify risk factors of complication. The sensitivity and specificity of FI ratio as a predictor of complication was calculated. A receiver operating characteristic (ROC) curve was generated to establish an FI ratio threshold to predict occurrence of complication following antegrade IM nailing.

RESULTS

Sixty-five patients with a mean age of 47.1 years were included. Using univariate logistic regression analysis, comminuted fracture pattern (p=0.026), distance from screws to fracture site (< 3cm) (p=0.002), and higher FI ratio (p=0.001) were associated with complication. Using multivariate logistic regression analysis, FI ratio was identified as an independent risk factor for complication following antegrade IM nailing (p=0.038). ROC curve indicated that FI ratio ≥ 2 had sensitivity and specificity of 0.72 and 0.72, respectively, in predicting complication.

CONCLUSIONS

Our study indicates that wider intramedullary diameter at the fracture site was associated with higher complication rate following antegrade IM nailing in distal infra-isthmal femoral fractures. The FI ratio could be a reliable predictor of complication after antegrade IM nailing for such fracture, and alternative strategies should be considered for patients with higher FI ratio (≥ 2).

Comparative analysis of the biomechanical behavior of anterograde/retrograde nailing in supracondylar femoral fractures

Supracondylar femoral fractures account for a noticeable percentage of the femoral shaft fractures, affecting two etiological groups: high energy trauma in young men, with good bone quality, and older women with osteoporotic femur. Surgical treatment of those kind of fractures remains controversial, with different surgical options such as plate and sliding barrel locking condylar plate, less invasive stabilization system (LISS) or intramedullary nailing, which has emerged as a new fixation choice in the treatment of that type of fractures. The present work performs a comparative study about the biomechanical behavior of anterograde and retrograde nailing in supracondylar femoral fractures type A, in order to determine the best choice of nailing and locking configuration. A three-dimensional finite element model of the femur was developed, modeling femoral supracondylar fracture and different nailing configurations, both for anterograde and retrograde nails. The study was focused on the immediately post-operative stage, verifying the appropriate stability of the osteosynthesis. The obtained results show a better biomechanical behavior for anterograde nails, providing a better stability from the point of view of global movements, lower stresses in screws, and less stress concentration in cortical bone. So, for the analyzed fractures and osteosyntheses types, anterograde nailing has demonstrated to be a better surgical option, being an excellent indication in supracondylar fractures of femur, with clear benefits compared to retrograde nailing, providing a better stabilization which enables for a more satisfactory fracture healing.

Influence of gap size, screw configuration, and nail materials in the stability of anterograde reamed intramedullary nail in femoral transverse fractures

Femoral shaft fractures are among the most severe injuries of the skeleton. They are associated with high morbidity and mortality. The most appropriate treatment depending on the type of fracture and location level should be chosen. A finite element model of the femur has been developed, analyzing various types of fractures in the subtrochanteric and diaphyseal supracondylar area, with several gap sizes, being stabilized with a single combination of screws for the intramedullary nail. The mechanical strength of the nail against bending and compression efforts was studied comparing two materials for the nail: stainless steel and titanium alloy. Beside the finite elements (FE) simulations, a clinical follow-up was carried out, considering a sample of 55 patients, 24 males, and 31 females, with mean age of 52.5 years. Localizations of fractures were 22 in the right femur and 33 in the left one, respectively. A good agreement between clinical results and the simulated fractures in terms of gap size was found. Non-comminuted fractures have a mean consolidation time of 4.1 months, which coincides with the appropriate mobility at fracture site obtained in the FE simulations, whereas comminuted fractures have a higher mean consolidation period estimated in 7.1 months, corresponding to the excessive mobility at fracture site obtained by means of FE simulations. The obtained results between both nail materials (stainless steel and titanium alloy) show a higher mobility when using titanium nails, which produce a higher rate of strains at the fracture site, amplitude of micromotions and bigger global movements compared to stainless-steel nails. Steel nails provide stiffer osteosyntheses than the titanium nails. In conclusion, anterograde locked nail is particularly useful in the treatment of a wide range of supracondylar fractures with proximal extension into the femoral diaphysis.

Influence of screw combination and nail materials in the stability of anterograde reamed intramedullary nail in distal femoral fractures

Intramedullary nailing (IM) is a technique universally accepted to treat femoral diaphyseal fractures. The treatment of fractures located in the distal third remains a controversial issue though. A finite element model of the femur has been developed, analyzing distal fractures with several gap sizes combined with different interlocking combinations of distal screws with one oblique screw proximally to stabilize the intramedullary nail. The mechanical strength of the nail against bending and compression efforts was also studied. Beside the FE simulations, a clinical follow-up of 15 patients, 6 males and 9 females, with mean age of 53.2 years was carried out. Localizations of fractures were 10 in the right femur and 5 in the left femur, respectively. A fairly good correspondence agreement between clinical results and the simulated fractures in terms of gap size was found. Non-comminuted fractures had a mean consolidation time of 20.5 weeks (4.8 months), a tendency corresponding well to the mobility obtained in the FE simulations; Comminuted fractures on the other hand exhibited a higher mean consolidation period of 22.2 weeks (5.2 months) secondary to the excessive mobility at fracture site obtained by means of FE simulations. The best stability at fracture site was found for the system with three distal screws and the system with two distal screws placed medial lateral. The highest leverage of distal screws was obtained maximizing the distance between them and choosing the coronal plane for their orientation. The results obtained with both nail materials (stainless steel and titanium alloy) show a higher mobility when using titanium nails. Steel nails provide stiffer osteosyntheses than the titanium nails. In conclusion, the best screw combination in terms of stability to produce fracture healing and the least difficulties during treatment is the one which had one oblique proximal screw with two distal lateral screw implanted in the coronal plane.

Notch sensitivity jeopardizes titanium locking plate fatigue strength

INTRODUCTION

Notch sensitivity may compromise titanium-alloy plate fatigue strength. However, no studies providing head-to-head comparisons of stainless-steel or titanium-alloy locking plates exist.

MATERIALS AND METHODS

Custom-designed identically structured locking plates were made from stainless steel (F138 and F1314) or titanium alloy. Three screw-hole designs were compared: threaded screw-holes with angle edges (type I); threaded screw-holes with chamfered edges (type II); and non-threaded screw-holes with chamfered edges (type III). The plates' bending stiffness, bending strength, and fatigue life, were investigated. The stress concentration at the screw threads was assessed using finite element analyses (FEA).

RESULTS

The titanium plates had higher bending strength than the F1314 and F138 plates (2.95:1.56:1) in static loading tests. For all metals, the type-III plate fatigue life was highest, followed by type-II and type-I. The type-III titanium plates had longer fatigue lives than their F138 counterparts, but the type-I and type-II titanium plates had significantly shorter fatigue lives. All F1314 plate types had longer fatigue lives than the type-III titanium plates. The FEA showed minimal stress difference (0.4%) between types II and III, but the stress for types II and III was lower (11.9% and 12.4%) than that for type I.

CONCLUSIONS

The screw threads did not cause stress concentration in the locking plates in FEA, but may have jeopardized the fatigue strength, especially in the notch-sensitive titanium plates. Improvement to the locking plate design is necessary.

Three-dimensional finite element analysis and comparison of a new intramedullary fixation with interlocking intramedullary nail

This study was set to introduce a new intramedullary fixation, explore its biomechanical properties, and provide guidance for further biomechanical experiments. With the help of CT scans and finite element modeling software, finite element model was established for a new intramedullary fixation and intramedullary nailing of femoral shaft fractures in a volunteer adult. By finite element analysis software ANSYS 10.0, we conducted 235-2,100 N axial load, 200-1,000 N bending loads and 2-15 Nm torsional loading, respectively, and analyzed maximum stress distribution, size, and displacement of the fracture fragments of the femur and intramedullary nail. During the loading process, the maximum stress of our new intramedullary fixation were within the normal range, and the displacement of the fracture fragments was less than 1 mm. Our new intramedullary fixation exhibited mechanical reliability and unique advantages of anti-rotation, which provides effective supports during fracture recovery.

Biomechanical assessment of composite versus metallic intramedullary nailing system in femoral shaft fractures: A finite element study

BACKGROUND

Intramedullary nails are the primary choice for treating long bone fractures. However, complications following nail surgery including non-union, delayed union, and fracture of the bone or the implant still exist. Reducing nail stiffness while still maintaining sufficient stability seems to be the ideal solution to overcome the abovementioned complications.

METHODS

In this study, a new hybrid concept for nails made of carbon fibers/flax/epoxy was developed in order to reduce stress shielding. The mechanical performance of this new implant in terms of fracture stability and load sharing was assessed using a comprehensive non-linear FE model. This model considers several mechanical factors in nine fracture configurations at immediately post-operative, and in the healed bone stages.

RESULTS

Post-operative results showed that the hybrid composite nail increases the average normal force at the fracture site by 319.23N (P<0.05), and the mean stress in the vicinity of fracture by 2.11MPa (P<0.05) at 45% gait cycle, while only 0.33mm and 0.39mm (P<0.05) increases in the fracture opening and the fragments' shear movement were observed. The healed bone results revealed that implantation of the titanium nail caused 20.2% reduction in bone stiffness, while the composite nail lowered the stiffness by 11.8% as compared to an intact femur.

INTERPRETATION

Our results suggest that the composite nail can provide a preferred mechanical environment for healing, particularly in transverse shaft fractures. This may help bioengineers better understand the biomechanics of fracture healing, and aid in the design of effective implants.

Distal femur fractures. Surgical techniques and a review of the literature

Fractures of the distal femur are rare and severe. The estimated frequency is 0.4% with an epidemiology that varies: there is a classic bimodal distribution, with a frequency peak for men in their 30s and a peak for elderly women; however, at present it is found predominantly in women and in the elderly with more than 50% of patients who are over 65. The most common mechanism is an indirect trauma on a bent knee, and more rarely direct trauma by crushing. The anatomy of the distal femur explains the three major types of fracture. Because of the anatomy of the distal femur, only surgical treatment is indicated to stabilize the fracture. A non-surgical treatment is a rare option. The aim of this report was to provide an update on the existing surgical solutions for the management of these fractures and describe details of the surgical technique applicable to these injuries. Recent radiological, clinical and biomechanical data published in the literature are reported to compare different surgical options.

Investigation of creep mechanical characteristics of femoral prostheses by simulated hip replacement

In order to provide creep mechanical parameters for the clinical application of both traditional and reserved anatomy femoral artificial joint replacements, simulated hip replacement femoral stress relaxation and creep experiments were performed. Twenty-four corpse femoral specimens were obtained, with 8 specimens being randomly assigned to the control group and 8 specimens being randomly assigned to the traditional prosthesis group. Our results showed that the retaining femoral neck prosthesis and traditional prosthesis groups have different stress relaxation and creep mechanical properties.

A modified intramedullary nail interlocking design yields improved stability for fatigue cycling in a canine femur fracture model

Intramedullary nailing has evolved to become the standard of care for most diaphyseal femoral and tibial fractures, as well as an expanding number of metaphyseal fractures. Owing to the unstable nature of some fractures, the intramedullary device may be subjected to significant stresses owing to a lack of solid cortical contact after nailing. In such cases, excessive interfragmentary motion (due to construct toggle) has been shown to occur. Such motion increases the likelihood of a non- or delayed-union. In the current study, two versions of a modified, angle stable interlocking design were subjected to fatigue testing in a segmental defect fracture model representing a canine femur. As a control, a third group of constructs were stabilized with a traditional nail that allowed a small amount of toggle. All constructs were subjected to 50,000 fatigue cycles representing 12 weeks of cage activity at physiologic levels of combined axial-torsional loading. Torsional testing pre- and post-fatigue revealed 4.6 +/- 1.3 degrees of toggle in the traditional nail and no toggle with the angle stable nail designs. The stable nails were also significantly stiffer in axial compression and torsion before and after cycling. These data indicate that the enhanced stability of the modified interlocking designs can be maintained throughout fatigue cycling in a challenging fracture model.

Can we trust ex vivo mechanical testing of fresh--frozen cadaveric specimens? The effect of postfreezing delays

BACKGROUND

Because embalming has been demonstrated to decrease the mechanical integrity of bone, most investigators favor fresh-frozen specimens for biomechanical evaluation. However, little is known about how the integrity of fresh--frozen specimens may change during biomechanical testing or may be affected by standard practices in testing.

OBJECTIVE

The purpose of this study was to evaluate how the time after removal from a freezer may affect the mechanical properties of fresh--frozen diaphyseal bone.

METHODS

Matched pairs of nonosteoporotic fresh--frozen human cadaveric femora were thawed before instrumentation with bicortical screws. Matched femora were reserved for either control or delayed use. Each specimen received standard diaphyseal bicortical screws (six or more in each group). At specified time points, screws were axially pulled out following the guidelines of ASTM F543-07. Test groups were stored in air (21 ± 0.5°C) for 16, 50, or 90 hours. In the control group, screws were pulled out at 16 hours, which corresponds to the minimum elapsed time for specimen thawing, instrumentation, potting, and biomechanical test initiation. This represents the baseline mechanical properties of the fresh--frozen bone at the inception of any biomechanical test. The 90-hour group corresponds to the time needed to cycle a construct 300,000 times at a physiological test frequency of 1 Hz. This corresponds approximately to 2 to 4 months of in vivo loading. A midpoint of 50 hours was also tested, representing approximately 180,000 cycles.

RESULTS

Failure for all specimens occurred as a result of bone failure at the screw-to-bone interface. There was a decrease in screw pullout strength as exposure time in air increased. The 50-hour test group showed a 9% decrease in screw pullout strength as compared with the 16-hour control group (P = 0.81). However, the 90-hour test group showed a 30% decrease in screw pullout strength as compared with the 16-hour control group (P = 0.04).

CONCLUSION

This study indicates that when using fresh-frozen cadaveric bone in biomechanical tests to simulate the orthopaedic clinical setting, specimen exposure time should be considered. The timing of testing should be kept constant between specimens to allow for a proper comparison. Furthermore, for fresh--frozen cadavers, the physical properties of bone may be detrimentally affected in biomechanical testing that exceeds the 50-hour time point after removal from the freezer.

A new intramedullary nailing device for the treatment of femoral shaft fractures: a biomechanical study

BACKGROUND

The treatment of choice for early mobilization of femoral fractures is surgery, which traditionally employs plates and screws or intramedullary nails. We examined the biomechanical properties of a new femoral nail system. The new intramedullary propping nailing system, made of a stainless-steel alloy, consists of a nail shaft, inner rod, tensile screw, end cape and two interlocked screws.

METHODS

Intramedullary propping nailing biomechanics was compared with that of the Grosse and Kempf nail when securing transverse fractures in 10 pairs of cadaveric femurs. The axial compressive, bending, torsional stiffness, and strain values were calculated.

FINDINGS

The intramedullary propping nailing system had torsional stiffness (0.50 Nm/ degrees ) and bending stiffness (699.74 and 670.84 N/mm of lateral and frontal bending, respectively) comparable with the Grosse and Kempf nail (0.35 Nm/ degrees , 644.85 and 606.32 N/mm of lateral and frontal bending, respectively). Intramedullary propping nailing system produced a significantly higher compressive stiffness (1.67 and 1.50 x 10(6) N/mm, respectively) than the Grosse and Kempf nail in the medial and anterior aspects (0.86 and 1.32x10(6)N/mm, respectively). Although no significance was found in comparison with Grosse and Kempf of the strain of each aspect, intramedullary propping nailing system yielded a significantly better-distributed strain (F=1.007, P=0.401).

INTERPRETATION

Biomechanically, the intramedullary propping nailing system is safe and able to provide good abutment of the nail to the bone. The intramedullary propping nailing system produces a more extensive and tight contact between the nail and bone than the application of Grosse and Kempf nail.

Influence of muscular contractions on the stress analysis of distal femoral interlocking nailing

BACKGROUND

In the literature, the commonly assumed loading conditions on the proximal femur are hip compression and/or gluteus contractions. However, no study has discussed the influence of muscle forces on failure of distal nail holes and locking screws.

METHODS

This finite-element study analyzed the influence of muscular contractions on stress analysis of distal nail holes and locking screws. Three loading conditions were used for comparison, comprised of either hip compression alone or with muscle contractions. The head displacement of intact and fractured femur, the nail and screw stresses vs. fixation depth, and the stress distribution at the distal nail-screw interfaces were chosen as the comparison indices.

FINDINGS

The addition of trochanteric and diaphysial muscles showed the more physiologically reasonable displacement of the femoral head. However, all loading conditions consistently showed the hole and screw stresses increase as the nail was inserted deeper. The stress distribution at the distal nail-screw interfaces was remarkably different under the condition of with or without the muscular contractions. The exertion of muscles predicted the fatigue cracking originated at the edge of the nail holes on the medial rather than lateral side.

INTERPRETATION

Only hip compression and/or gluteus contraction generated a characteristic bending stress pattern and medially deflected nail curvature. Comparatively, the trochanteric and diaphysial muscles stabilized the femoral head and resulted in the higher stress concentration at the distally medial nail-screw interfaces. However, further experimental and clinical studies, focusing on the failure sites of the distal femoral hardware, should be undertaken to validate such findings.