The effect of locked distal screws in retrograde nailing of osteoporotic distal femur fractures: a laboratory study using cadaver femurs

Current Concepts in Management of Distal Femur Fractures

Recent studies report the overall incidence of distal femur fractures as 8.7/100,000/year. This incidence is expected to rise with high energy motor vehicle collisions and elderly osteoporotic fractures in native and prosthetic knees keep increasing. These fractures are more common in males in the younger age spectrum while females predominate for elderly osteoporotic fractures. Surgical treatment is recommended for these fractures to maintain articular congruity, enable early joint motion and assisted ambulation. Over the last two decades, development of minimally invasive and quadriceps sparing surgical approaches, availability of angle stable implants have helped achieve predictable healing and early return to function in these patients. Currently, laterally positioned locked plate is the implant of choice across all fracture patterns. Retrograde with capital implantation of intramedullary nails with provision for multiplanar distal locking is preferred for extra-articular and partial articular fractures. Even with these advancements, nonunion after distal femur fracture fixation can be as high as 19%. Further recent research has helped us understand the biomechanical limitations and healing problems with lateral locked plate fixation and intramedullary nails. This has lead to development of more robust constructs such as nail-plate and double plate constructs aiming for improved construct strength and to minimise failures. Early results with these combination constructs have shown promise in high risk situations such as fractures with extensive metaphyseal fragmentation, osteoporosis and periprosthetic fractures. These constructs however, run the risk of being over stiff and can inhibit healing if not kept balanced. The ideal stiffness that is needed for fracture healing is not clearly known and current research in this domain has lead to the development of smart implants which are expected to evolve and may help improve clinical results in future.

Comparison of the biomechanical stability of transverse and oblique screw trajectories in retrograde intramedullary nailing of supracondylar femur fractures

BACKGROUND

The goal was to determine the effect of addition of oblique trajectory distal interlock screws to a retrograde intramedullary femoral nail on implant stability (stiffness), cycles to failure and mode of failure. The hypothesis was that addition of oblique screws would increase implant stability and number of loading cycles to failure.

METHODS

Eight matched pairs were tested; one femur implanted with a femoral nail with only transverse distal interlock screws and the other with transverse and oblique interlock screws. Axial compressive load was applied to the femoral head and the gluteal tendon was tensioned vertically to simulate standing or at 45° to the sagittal plane to simulate stair climbing. Loads were cycled to increasing amplitude until failure of fixation (10 mm displacement or 10° rotation).

FINDINGS

In simulated standing, oblique screw specimen had greater sagittal bending (bowing) than transverse only specimen. Transverse (axial) plane motion was higher in simulated stair climbing in oblique screw specimen. Oblique screw specimen had higher sagittal plane translation at 600 N of load. At 300 N, oblique screw specimen had lower internal-external rotation than transverse only specimen. A larger number of cycles to failure were observed in four oblique screw of seven paired specimen. Failure (10 mm or 10 degrees of motion) was only achieved during simulated stair climbing.

INTERPRETATION

Our hypothesis that adding oblique screws improves fixation was rejected. Activities of daily living other than standing may constitute a challenge to fracture fixation; fixation failure occurred at lower loads in simulated stair climbing than standing.

Surgical outcomes of retrograde nailing enhanced with minimally invasive cerclage cable fixation for infra-isthmal femoral fracture

BACKGROUND

Infra-isthmal femoral fracture has been known as one of the risk factors for femoral nonunion. Retrograde intramedullary nailing can provide reliable stability of the distal fragment in infra-isthmal femoral fracture, but adequate reduction is required to achieve a successful outcome. This study aimed to evaluate the surgical outcomes of retrograde nailing enhanced with minimally invasive cerclage cable fixation for infra-isthmal femoral fracture.

METHODS

Between March 2013 and July 2017, 15 patients with infra-isthmal fractures treated with retrograde nailing and minimally invasive cerclage cable fixation were included in this study. Cerclage cable was applied for reduction aid (reduction cable) or prevention of further displacement in non-displaced extension of the distal spiral fracture (prevention cable). Number and function of cerclage cables, operation time, additional surgery, and complications were assessed. Further displacement of the wedge after nailing, coronal and sagittal alignment, displacement of the main fragment, and time from injury to union were evaluated as radiologic outcomes.

RESULTS

Of the 15 patients in this study, 14 were treated with reduction cables. Average postoperative coronal and sagittal angulation was 1.7° (1° varus to 4° valgus) and 1.6° (2° flexion to 11° extension). Mean displacement between the main fragments was 3.5 mm (range 0-22 mm). Four of the 14 cases used additional prevention cables combined with reduction cable. Only one case was treated solely with a prevention cable. A total of five prevention cables were maintained without further displacement. All patients achieved bone union, and the average time to union was 22.7 weeks (range 9-44 weeks). There were no complications as a result of surgery, such as infection or major neurovascular injury.

CONCLUSIONS

The minimally invasive cerclage cable technique could be a useful and safe enhancement in retrograde nailing for infra-isthmal femoral fracture in order to prevent further displacement and to reduce the main fracture.

Boundary Conditions Matter - Impact of Test Setup On Inferred Construct Mechanics in Plated Distal Femur Osteotomies

The mechanics of distal femur fracture fixation has been widely studied in bench tests that employ a variety of approaches for holding and constraining femurs to apply loads. No standard test methods have been adopted for these tests and the impact of test setup on inferred construct mechanics has not been reported. Accordingly, the purpose of this study was to use finite element models to compare the mechanical performance of a supracondylar osteotomy with lateral plating under conditions that replicate several common bench test methods. A literature review was used to define a parameterized virtual model of a plated distal femur osteotomy in axial compression loading with four boundary condition sets ranging from minimally to highly constrained. Axial stiffness, longitudinal motion, and shear motion at the fracture line were recorded for a range of applied loads and bridge spans. The results showed that construct mechanical performance was highly sensitive to boundary conditions imposed by the mechanical test fixtures. Increasing the degrees of constraint, for example by potting and rigidly clamping one or more ends of the specimen, caused up to a 25x increase in axial stiffness of the construct. Shear motion and longitudinal motion at the fracture line, which is an important driver of interfragmentary strain, was also largely influenced by the constraint test setup. These results suggest that caution should be used when comparing reported results between bench tests that use different fixtures and that standardization of testing methods is needed in this field.

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.

Internal fixation of osteoporotic fractures

Osteoporosis leads to bone fragility and increased risk of fracture. Despite advances in diagnosis and treatment, the prevalence continues to rise. Osteoporotic fracture treatment has a unique set of difficulties related to poor bone quality and traditional approaches, and implants may not perform well. Fixation failure and repeat surgery are poorly tolerated and highly undesirable in this patient population. This review illustrates the most recent updates in internal fixation, implant design, and surgical theory regarding treatment of patients with osteoporotic fractures.

Hot topics in biomechanically directed fracture fixation

The evolution of locking plates and modern nail constructs provides the orthopaedic trauma surgeon with a myriad of options with regard to implant selection for common fractures. There is a significant amount of biomechanical literature comparing modern constructs with those conventionally used. A basic understanding of this literature is required to make informed decisions with regard to implant selection in the management of these injuries. This article reviews the most recent biomechanical literature regarding implant selection and application for a variety of commonly treated injuries, including fractures of the clavicle, proximal humerus, distal humerus, intertrochanteric hip region, distal femur, and bicondylar tibial plateau.

Retrograde intramedullary nails with distal screws locked to the nail have higher fatigue strength than locking plates in the treatment of supracondylar femoral fractures

We investigated a new intramedullary locking nail that allows the distal interlocking screws to be locked to the nail. We compared fixation using this new implant with fixation using either a conventional nail or a locking plate in a laboratory simulation of an osteoporotic fracture of the distal femur. A total of 15 human cadaver femora were used to simulate an AO 33-A3 fracture pattern. Paired specimens compared fixation using either a locking or non-locking retrograde nail, and using either a locking retrograde nail or a locking plate. The constructs underwent cyclical loading to simulate single-leg stance up to 125 000 cycles. Axial and torsional stiffness and displacement, cycles to failure and modes of failure were recorded for each specimen. When compared with locking plate constructs, locking nail constructs had significantly longer mean fatigue life (75 800 cycles (sd 33 900) vs 12 800 cycles (sd 6100); p = 0.007) and mean axial stiffness (220 N/mm (sd 80) vs 70 N/mm (sd 18); p = 0.005), but lower mean torsional stiffness (2.5 Nm/° (sd 0.9) vs 5.1 Nm/° (sd 1.5); p = 0.008). In addition, in the nail group the mode of failure was either cut-out of the distal screws or breakage of nails, and in the locking plate group breakage of the plate was always the mode of failure. Locking nail constructs had significantly longer mean fatigue life than non-locking nail constructs (78 900 cycles (sd 25 600) vs 52 400 cycles (sd 22 500); p = 0.04).

The new locking retrograde femoral nail showed better stiffness and fatigue life than locking plates, and superior fatigue life to non-locking nails, which may be advantageous in elderly patients.

Cite this article: Bone Joint J 2014;96-B:114–21.

A three-dimensional comparison of intramedullary nail constructs for osteopenic supracondylar femur fractures

OBJECTIVES

This study developed a new 6 degree-of-freedom, unconstrained biomechanical model that replicated the in vivo loading environment of femoral fractures. The objective of this study was to determine whether various distal fixation strategies alter failure mechanisms and/or offer mechanical advantages when performing retrograde intramedullary nail (IMN) stabilization of supracondylar femur fractures in osteoporotic bone.

METHODS

Forty fresh-frozen human femora were allocated into 2 groups of matched pairs: "locked" (fixed angle locking construct with both distal locking screws rigidly attached to the IMN) versus "unlocked" (conventional locking technique with 2 distal locking screws targeted through the distal locking screw holes of the IMN) and "locked" versus "washer" (fixed angle locking with the most distal screw exchanged for a bolt with condyle washers) distal fixation of a retrograde IM nails. A comminuted fracture (OTA 33-A3) was simulated with a wedge osteotomy. Bone density measurements were completed on all specimens before instrumentation. Instrumented femurs were loaded axially to failure, whereas 6 degree-of-freedom translations and angulations were measured using Roentgen stereophotogrammetric analysis.

RESULTS

Mean (± SD) load born by "locked" specimens (1609 ± 667 N) at clinical failure was 38.1% greater (P = 0.09) than the corresponding mean load born by "unlocked" specimens (1165 ± 772 N). Clinical failure for the "washer" group (1738 ± 772 N) was 29.9% greater (P = 0.07) than the corresponding mean of the "locked" counterparts (1338 ± 822 N). Failure load was most clearly related to bone density in the "unlocked" fixation group.

CONCLUSIONS

Predicting failure load based on bone density using a least squares estimate suggests that the washer construct provides superior fixation to other treatment techniques. The failure mechanism for a comminuted, supracondylar fracture cannot be analyzed accurately with a 1-dimensional measurement. The most common failure mechanism in this model was medial translation and varus angulation.

Retrograde intramedullary nailing for distal femur fracture with osteoporosis

BACKGROUND

The incidence of distal femur fracture in the elderly has been increasing recently, and commonly occurs with osteoporosis. Retrograde intramedullary nailing has been considered a good surgical option for distal femur fracture. The purpose of the present study was to present our surgical results with retrograde intramedullary nailing for distal femur fractures with osteoporosis.

METHODS

Thirteen patients diagnosed with extra-articular distal femur fracture and osteoporosis and managed with retrograde intramedullary nailing were retrospectively reviewed. Cement augmentation was used in four patients, shape memory alloy was used in eight patients and both were used in one patient. All patients were followed up for more than 2 years. Radiologic alignments were scored and Tegner and the Lysholm activity score was used for a functional assessment.

RESULTS

The average time to clinical union was 13 weeks (range, 10 to 15 weeks). In 12 of our cases, the total alignment scores were excellent. At the last follow-up, the mean range of motion was 116° (range, 110° to 125°). The average functional score at postoperative 1 year was 2.6 (range, 1 to 5).

CONCLUSIONS

Retrograde intramedullary nailing is a good surgical option for distal femur fracture with osteoporosis. Cement augmentation and shape memory alloy can also be used for added mechanical stability. This surgical technique is very useful for distal femur fracture with osteoporosis as it promotes fracture healing and early rehabilitation.

Retrograde femoral nailing in elderly patients: outcome and functional results

Functional outcome after retrograde femoral intramedullary nailing was investigated in 35 patients older than 60 years (mean, 86 years) with 36 fractures, comprising 15 (41.7%) shaft and 21 (58.3%) distal fractures; overall, 7 (19.4%) periprosthetic fractures occured. Twenty-two (62.9%) of 35 patients were evaluated at a mean 16.5-month follow-up with the Lyshom-Gillquist score and the SF-8 questionaire. Primary union rate was 97.8%, with no significant differences in duration of surgery, bone healing, mobilization, and weight bearing among different fracture types; periprosthetic fractures revealed a significantly delayed mobilization (P=.03). Complications occured significantly more often among distal femoral fractures (P=.009), including all revision surgeries. The most frequently encountered complication was loosening of distal locking bolts (n=3). Lysholm score results were mainly influenced by age-related entities and revealed fair results in all fractures (mean in the femoral shaft fracture group, 78.1 vs mean in the distal femoral fracture group, 74.9; P=.69), except in the periprosthetic subgroup, which had good results (mean, 84.8; P=.23). This group also had increased physical parameters according to SF-8 score (P=.026). No correlation existed between SF-8 physical parameters and patient age or surgery delay, whereas a negative correlation existed between patient age and SF-8 mental parameters (P=.012). Retrograde femoral intramedullary nailing is commonly used in elderly patients due to reliable bone healing, minimal soft tissue damage, and immediate full weight bearing. It also offers a valid alternative to antegrade nailing in femoral shaft fractures.

Retrograde dynamic locked nailing for valgus knee correction: a revised technique

PURPOSE

Traditionally, valgus knee deformity is predominately corrected by stabilisation with a plate inserted via the medial approach to the supracondylar region of the femur. However, this technique is unfavourable from both a biomechanical and a biological point of view. A revised retrograde dynamic locked nailing was developed to improve correction of this defect.

METHOD

Forty-one knees with valgus deformity (average tibiofemoral angle, 22°; range, 16-29°) in 25 adult patients were treated by oblique femoral supracondylar varus osteotomy and stabilised with retrograde dynamic locked nails. Postoperatively, early ambulation with protected weight bearing and range of motion knee exercises were encouraged.

RESULT

Thirty-five knees of 21 patients were followed-up for an average of 2.6 years (range, 1.1-4.5 years). All osteotomy sites healed with an average union period of 3.4 months (range, 2.5-5.0 months). There were no significant complications. At the latest follow-up, the average tibiofemoral angle was 7.1° valgus (range, 4-10° valgus). For all of the knees, the outcomes were satisfactory (p < 0.001).

CONCLUSION

The technique described here may be a feasible alternative for correction of valgus knee deformity. The advantages of this technique include the use of a biomechanically more appropriate method, a minimal complication rate and a high rate of satisfactory outcomes.

Do locked compression intramedullary nails improve the biomechanical stability of distal femoral fractures?

BACKGROUND

A distal femur nail with fixed-angle locking screws intends to combine the advantages of angular stability and intramedullary stabilization in extraarticular distal femur fractures. The goal of this study was to analyze whether the locked compression distal femur nail (LCN) was biomechanically more stable than a conventional standard distal femur nail (CN).

METHODS

Both nails were compared on a series of 10 matched pairs of human femora. After setting a distal femur defect fracture, the intramedullary stabilized femur was axially loaded starting from 100 N, increasing in steps of 100 N after every 200 cycles with a triangular frequency of 1 Hz, until a predefined point of failure was reached.

RESULTS

The two types of nails showed no significant difference in terms of maximum tolerated load, maximum number of cycles repeated, or axial deformation of the bone-implant construct. The mean load at failure was 2,954 N for the CN and 2,483 N for the LCN. The mean axial deformation for the conventional (14.8 mm) and locked compression nail (15.3 mm) did not differ significantly. Mode of failure was a bony fracture in all specimens predominantly involving the proximal femur.

CONCLUSIONS

No significant difference in stability between the two compared implants could be demonstrated. The LCN showed comparable characteristics under cyclic axial loading as the conventional distal femur nail. No migration into the articular space or implant failure was observed.

Biomechanical strain analysis of the proximal femur following retrograde intramedullary nailing

BACKGROUND: The purpose of this study was to examine the influence of proximal retrograde intramedullary nail position on proximal femoral strain, since stress risers occurring at the end of an implant can increase fracture risk. METHODS: Proximal femoral strains during axial and torsional loading were measured in composite Sawbone femurs after placement of retrograde intramedullary nails that ended at three different locations (2 cm proximal, 4 cm distal, and at the level of the lesser trochanter). RESULTS: No statistically significant difference was found between the axial or torsional strain observed in the intact femur and that seen after placement of a retrograde femoral nail ending at any of the three positions. Gages proximal to the nail tip demonstrated higher strains than the strains for the intact femur when compared with gages distal to the nail tip. CONCLUSION: The ending location of a retrograde nail in the proximal femur does not appear to significantly alter strain in the proximal femur under the axial and torsional loading methods used in the study.

Evaluation of a Customized Artificial Osteoporotic Bone Model of the Distal Femur

In the development of new implants biomechanical testing is essential. Since human bones vary markedly in density and geometry their suitability for biomechanical testing is limited. In contrast artificial bones are of great uniformity and therefore appropriate for biomechanical testing. However, the applied artificial bones have to be proved as comparable to human bone. An anatomical shaped artificial bone representing the distal human femur was created by foaming polyurethane. To get a bone model with properties of osteoporotic bone a foam density of 150 kg/m3 was used. The biomechanical properties of our artificial bones were evaluated against eight mildly osteoporotic fresh frozen human femora by mechanical testing. At the artificial bones all tested parameters showed a very small variation. In contrast significant correlation between bone mass density and tested parameters was found for the human bones. The artificial bones reached 39% of the compression strength and 41% of the screw pullout force of the human bone. In indentation testing the artificial bones reached 27% (cancellous) and 59% (cortical) respectively of the human bones strength. Regarding Shore hardness artificial bone and human bone showed comparable results for the cortical layer and at the cancellous layer the artificial bone reached 57% of human bones hardness. Our described method for customizing of artificial bones regarding their shape and bone stock quality provides suitable results. In relation to the as mildly osteoporotic classified human bones we assume that the biomechanical properties matching to serve osteoporotic bone.

Intramedullary nail fracture compression techniques: when and how to do it?

Fracture compression can be achieved in many ways intraoperatively using either screws in compression plates, compression devices, or using intramedullary nails. The use of locked intramedullary nails combines the advantages of indirect fracture fixation and compression with minimal soft tissue disruption. This article describes the technique, advantages, and limitations of the use of intramedullary nails for compression across fractures, nonunions, and joint arthrodeses.

Temperature influence on DXA measurements: bone mineral density acquisition in frozen and thawed human femora

BACKGROUND

Determining bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA) is an established and widely used method that is also applied prior to biomechanical testing. However, DXA is affected by a number of factors. In order to delay decompositional processes, human specimens for biomechanical studies are usually stored at about -20 degrees C; similarly, bone mineral density measurements are usually performed in the frozen state. The aim of our study was to investigate the influence of bone temperature on the measured bone mineral density.

METHODS

Using DXA, bone mineral density measurements were taken in 19 fresh-frozen human femora, in the frozen and the thawed state. Water was used to mimic the missing soft tissue around the specimens. Measurements were taken with the specimens in standardized internal rotation. Total-BMD and single-BMD values of different regions of interest were used for evaluation.

RESULTS

Fourteen of the 19 specimens showed a decrease in BMD after thawing. The measured total-BMD of the frozen specimens was significantly (1.4%) higher than the measured BMD of the thawed specimens.

CONCLUSION

Based on our findings we recommend that the measurement of bone density, for example prior to biomechanical testing, should be standardized to thawed or frozen specimens. Temperature should not be changed during measurements. When using score systems for data interpretation (e.g. T- or Z-score), BMD measurements should be performed only on thawed specimens.

Biomechanical analysis of retrograde intramedullary nail fixation in distal femoral fractures

This study employed both mechanical testing and finite element analysis to compare the stiffness variations among different intramedullary nail constructs used in the treatment of distal femoral fractures. Compressive and torsional experiments were conducted on a transversely, as well as an obliquely fractured sawbone femur restored with the retrograde intramedullary nail. Corresponding finite element models were established to evaluate the stress distributions around screw holes. The results showed that a perifracture screw could increase stiffness by 40% for the obliquely fractured femur, but that it played an insignificant role in stiffness improvement for the transverse fracture groups. Moreover, compared to proximal-screw fixation, distal-screw fixation could improve construct stiffness by 20%. The absence of one of the two distal screws would increase the screw-hole stress by 70%. Therefore, the distal screw around the metaphyseal region has a more important stabilizing effect in the femur-nail construct than does the proximal screw. A twisting stress pattern occurs on the unused screw holes of the metaphyseal region and induces a higher risk for fatigue fracture. The locking screw at the fracture site would be most effective only if it passed through the fracture gap to integrate the separated femoral pieces.