Forces required to dynamize sliding screws in gamma nail and selfdynamizable internal fixator

BACKGROUND

Single limb support phase of the gait-cycle in patients who are treated for a pertrochanteric fracture is characterized by transversal loads acting on the lag screw, tending to block its dynamization. If the simultaneous axial force overcomes transversal loads of the sliding screw, the dynamization can still occur.

METHODS

Biomechanical investigation was performed for three types of dynamic implants: Gamma Nail, and two types of Selfdynamizable Internal Fixators (SIF) - SIF-7 (containing two 7 mm non-cannulated sliding screws), and SIF-10 (containing one 10 mm cannulated sliding screw). Contact surface between the stem and the sliding screws is larger in SIF implants than in Gamma Nail, as the stem of Gamma Nail is hollow. A special testing device was designed for this study to provide simultaneous application of a controlled sliding screws bending moment and a controlled transversal load on sliding screws (Qt) without using of weights. Using each of the implants, axial forces required to initiate sliding screws dynamization (Qa) were applied and measured using a tensile testing machine, for several values of sliding screws bending moment. Standard least-squares method was used to present the results through the linear regression model.

RESULTS

Positive correlation between Qt and Qa was confirmed (p < 0.05). While performing higher bending moments in all the tested implants, Qa was higher than it could be provided by the body weight. It was the highest in Gamma Nail, and the lowest in SIF-10.

CONCLUSIONS

A larger contact surface between a sliding screw and stem results in lower forces required to initiate dynamization of a sliding screw. Patients treated for a pertrochanteric fracture by a sliding screw internal fixation who have longer femoral neck or higher body weight could have different programme of early postoperative rehabilitation than lighter patients or patients with shorter femoral neck.

Lateral cortical notching facilitates dynamization of proximal femoral nailing - A finite element analysis

INTRODUCTION

Dynamization of proximal femoral nailing by removal of distal interlocking is one of the recommended treatment options for nonunions of femur fractures. However, in certain inter-/subtrochanteric fractures, gliding of the nail along the femoral shaft is blocked by lateral femoral cortical support of the lag screw. For these cases, Biber et al. proposed lateral cortical notching (LCN), in which the supporting lateral bone is removed. This study investigates the biomechanical effect of LCN on gliding of proximal femoral nailing and stress distribution at the bone/implant interface.

MATERIALS AND METHODS

In this finite element analysis a three-dimensional model of an unstable intertrochanteric fracture with proximal femoral nailing without distal interlocking was simulated using the FebioStudio software suite. To simulate LCN, the lag screw hole was lengthened to 15.34 mm at the lateral cortex. Displacement of the nail along the femoral shaft axis and von Mises stress distribution were compared between LCN model and standard implantation model.

RESULTS

Displacement of the nail along the femoral shaft axis was higher in the LCN model than in the standard implantation model (0.48 mm vs. 0.07 mm). Highest von Mises stresses of 176-178 MPa at the implant and of 52-81 MPa at the proximal femur were detected. Maximum von Mises stresses of the implant were comparable at all sides, except for a reduced von Mises stress at the lateral inferior side in the LCN model (80 vs. 102 MPa). At the inferior lateral screw hole and the anterior/posterior lateral screw hole maximum von Mises stress was reduced in the LCN model (2 vs. 49 MPa and 52 vs. 81 MPa), whereas the maximum von Mises stress at the inferior medial screw hole was higher in the LCN model than in the standard implantation model (53 vs. 27 MPa).

CONCLUSIONS

Lateral cortical notching facilitates gliding of a distally dynamized proximal femoral nail along the femoral shaft axis in intertrochanteric fractures. Additionally, the lack of lateral cortical bone support at the lag screw reduces von Mises stress at the bone/implant interface and thus could lower the risk for implant breakage and peri‑implant fractures.

Fixators dynamization for delayed union and non-union of femur and tibial fractures: a review of techniques, timing and influence factors

The optimal balance between mechanical environment and biological factors is crucial for successful bone healing, as they synergistically affect bone development. Any imbalance between these factors can lead to impaired bone healing, resulting in delayed union or non-union. To address this bone healing disorder, clinicians have adopted a technique known as "dynamization" which involves modifying the stiffness properties of the fixator. This technique facilitates the establishment of a favorable mechanical and biological environment by changing a rigid fixator to a more flexible one that promotes bone healing. However, the dynamization of fixators is selective for certain types of non-union and can result in complications or failure to heal if applied to inappropriate non-unions. This review aims to summarize the indications for dynamization, as well as introduce a novel dynamic locking plate and various techniques for dynamization of fixators (intramedullary nails, steel plates, external fixators) in femur and tibial fractures. Additionally, Factors associated with the effectiveness of dynamization are explored in response to the variation in dynamization success rates seen in clinical studies.

The Relation between the Dynamization of Hexapod Circular External Fixator and Tibial Mechanical Properties

OBJECTIVE

Dynamization of the external fixator, defined as gradually decreasing construct-stability of the fixator, is widely accepted as a method for treatment during the late phase of the bone healing process. However, the dynamization is mostly based on the subjective experience of orthopaedists at present, without unified standards and a clear theoretical basis. The objective of the study is to investigate the influence of the dynamization operations on the tibial mechanical properties with a hexapod circular external fixator and standardize the dynamization process.

METHODS

A 3D-printed tibial defects model with Young's modulus of 10.5 GPa and Poisson's ratio of 0.32 simulated the clinically fractured bone. A 10 × ∅ 45 mm silicone sample with Young's modulus of 2.7 MPa and Poisson's ratio of 0.32 simulated the callus in the fracture site. Furthermore, a hexapod circular external fixator whose struts were coded from #1 to #6 was fixed on the model with six half-pins (5 mm diameter). Corresponding to the action of removing and loosening the struts, 17 dynamization operations are designed. For each construct after different dynamization operations, the mechanical environment changes in the fracture site were recorded by a triaxle forces sensor under gradually increasing external load from 0 to 500 N.

RESULTS

The results show that the bone axial load-sharing ratio of each construct in the removal group was generally higher than that in the loosening group. The ratio increased from 92.51 ± 0.74% to 102.68 ± 0.27% with the number of operated struts rising from 2 to 6. Besides, the constructions with the same number of operated struts but with different strut codes such as constructions 3-5, had similar bone axial load-sharing ratios. In addition, the proposed dynamization method of the hexapod circular external fixator can gradually increase the bone axial load-sharing ratio from 90.73 ± 0.19% to 102.68 ± 0.27% and maintain the bone radial load-sharing ratio below 8%.

CONCLUSION

The laboratory study verified the effects of the type of operations and the number of operated struts on the bone axial load-sharing ratio, as well as the slight influence of the choice of the strut code. Besides, a dynamization method of the hexapod circular external fixator was proposed to increase the bone axial load-sharing ratio gradually.

Dynamization-Posterior Lumbar Interbody Fusion for Hemodialysis-Related Spondyloarthropathy: Evaluation of the Radiographic Outcomes and Reoperation Rate within 2 Years Postoperatively

Study Design

Clinical case series.

Purpose

This study aimed to report dynamization-posterior lumbar interbody fusion (PLIF), our surgical treatment for hemodialysisrelated spondyloarthropathy (HSA), and investigate patients' postoperative course within 2 years.

Overview of Literature

HSA often requires lumbar fusion surgery. Conventional PLIF for HSA may cause progressive destructive changes in the vertebral endplate, leading to progressive cage subsidence, pedicle screw loosening, and pseudoarthrosis. A dynamic stabilization system might be effective in patients with a poor bone quality. Thus, we performed "dynamization-PLIF" in hemodialysis patients with destructive vertebral endplate changes.

Methods

We retrospectively examined patients with HSA who underwent dynamization-PLIF at our hospital between April 2010 and March 2018. The radiographic measurements included lumbar lordosis and local lordosis in the fused segment. The evaluation points were before surgery, immediately after surgery, 1 year after surgery, and 2 years after surgery. The preoperative and postoperative radiographic findings were compared using a paired t-test. A p-value of less than 0.05 was considered significant.

Results

We included 50 patients (28 males, 22 females). Lumbar lordosis and local lordosis were significantly improved through dynamization- PLIF (lumbar lordosis, 28.4°-35.5°; local lordosis, 2.7°-12.8°; p<0.01). The mean local lordosis was maintained throughout the postoperative course at 1- and 2-year follow-up (12.9°-12.8°, p=0.89 and 12.9°-11.8°, p=0.07, respectively). Solid fusion was achieved in 59 (89%) of 66 fused segments. Solid fusion of all fixed segments was achieved in 42 cases (84%). Within 2 years postoperatively, only six cases (12%) were reoperated (two, surgical debridement for surgical site infection; two, reoperation for pedicle screw loosening; one, laminectomy for epidural hematoma; one, additional fusion for adjacent segment disease).

Conclusions

Dynamization-PLIF showed local lordosis improvement, a high solid fusion rate, and a low reoperation rate within 2 years of follow-up.

Mechanically-regulated bone repair

Fracture healing is a complex, multistep process that is highly sensitive to mechanical signaling. To optimize repair, surgeons prescribe immediate weight-bearing as-tolerated within 24 hours after surgical fixation; however, this recommendation is based on anecdotal evidence and assessment of bulk healing outcomes (e.g., callus size, bone volume, etc.). Given challenges in accurately characterizing the mechanical environment and the ever-changing properties of the regenerate, the principles governing mechanical regulation of repair, including their cell and molecular basis, are not yet well defined. However, the use of mechanobiological rodent models, and their relatively large genetic toolbox, combined with recent advances in imaging approaches and single-cell analyses is improving our understanding of the bone microenvironment in response to loading. This review describes the identification and characterization of distinct cell populations involved in bone healing and highlights the most recent findings on mechanical regulation of bone homeostasis and repair with an emphasis on osteo-angio coupling. A discussion on aging and its impact on bone mechanoresponsiveness emphasizes the need for novel mechanotherapeutics that can re-sensitize skeletal stem and progenitor cells to physical rehabilitation protocols.

Effectiveness of Nail Dynamization in Delayed Union of Tibial Shaft Fractures: Relationship Between Fracture Morphology, Callus Diameter, and Union Rates

OBJECTIVE

Dynamization has already been described as a secondary intervention for delay unions of tibial shaft fractures treated with intramedullary nailing. Although it's a common procedure, it is not widely supported in the literature. The purpose of this study was to determine the union rate of nail dynamization in cases of delayed union of diaphyseal tibial fractures, and assess the effect of fracture morphology on union rates.

MATERIALS AND METHODS

We retrospectively analyzed a series of 199 consecutive tibial shaft fractures. We recorded the dynamization rate, period from nailing to dynamization, nailing to the union, the fracture pattern (according to AO/ASIF and whether it was closed or open), the callus diameter before dynamization (fracture healing index; FHI) and union/failure rates.

RESULTS

Out of a total of 199 fractures treated during the study period, 41 (20.6%) were dynamized. After applying inclusion and exclusion criteria, 39 patients with 39 fractures were included in the study. The mean time from nailing to dynamization was 18.4 ± 7.2 weeks. The union rate was 92.3% (n = 36) over a mean time of 14.1 ± 5.6 weeks as from dynamization. The overall failure rate was 6.7% (n = 3). There was no significant association between failure and AO/ASIF classification (p > 0.05) or fracture exposure (X ² = 0.19; p = 0.66). The pre-dynamization FHI of ≥ 1.17 was significantly associated with consolidation (p < 0.05).

CONCLUSION

In cases of delayed union of tibial fractures, dynamization offered a high union rate associated with pre-dynamization FHI, while fracture morphology did not affect the failure rate.

The history of intramedullary nailing

PURPOSE

To summarize the evolution of intramedullary nailing, highlight important milestones, introduce the atmosphere of the era concerning the first uses and development of intramedullary nailing, and present the status of nailing in modern international orthopaedics and traumatology.

METHOD

A thorough literature search was undertaken in PubMed and Google Scholar as well as in physical books in libraries to summarize the literature on the history and evolution of intramedullary nailing.

RESULTS

The first use of an intramedullary device was attested in ancient Egypt; however, the first use of intramedullary nailing was reported in 1524 in Mexico, and the first medical journals reported on intramedullary nailing around the mid-1800s. The evolutions of intramedullary nailing including approach, material, cross-section and shape, and reaming technique occurred in the twentieth century. During the 1960s, intramedullary nailing was abandoned in favour of plate and screws osteosynthesis; however, in the 1970s, 1980s, and 1990s, a surge of novelties including flexible reaming, interlocking, and use of image intensification and titanium nails led to the advent of the second-generation intramedullary nailing. Today, intramedullary nailing has become the standard treatment of long bone fractures with low infection rates, small scars, excellent stabilization of the fractures, and immediate mobilization of the patients.

CONCLUSION

Intramedullary nailing has revolutionized the treatment of long bone fractures. However, with numerous nail designs, a lot of information on their efficacy is lacking. Considerably more work will need to be done to determine the optimal nail specifications.

Systematic review of dynamization vs exchange nailing for delayed/non-union femoral fractures

AIM

To analyze the literature on efficacy of dynamamization vs exchange nailing in treatment of delayed and non-union femur fractures.

METHODS

Ultimately, 31 peer-reviewed articles with 644 exchanged nailing patients and 131 dynamization patients were identified and analyzed. The following key words were inputted in different combinations in order to search the field of publications in its entirety: “non-union”, “delayed union”, “ununited”, “femur fracture”, “femoral fracture”, “exchange nailing”, “dynaiz(s)ation”, “secondary nailing”, “dynamic”, “static”, and “nail revision”. The initial search yielded over 150 results, and was refined based on the inclusion criteria: Only studies reporting on humans, non-unions and delayed unions, and the usage of exchange nailing and/or dynamization as a secondary treatment after failed IM nailing. The resulting 66 articles were obtained through online journal access. The results were filtered further based on the exclusion criteria: No articles that failed to report overall union rates, differentiate between success rates of their reported techniques, or articles that analyzed less than 5 patients.

RESULTS

Exchange nailing lead to fracture union in 84.785% of patients compared to the 66.412% of dynamization with statistically comparable durations until union (5.193 ± 2.310 mo and 4.769 ± 1.986 mo respectively). Dynamically locking exchange nails resulted in an average union time of 5.208 ± 2.475 mo compared to 5.149 ± 2.366 mo (P = 0.8682) in statically locked exchange nails. The overall union rate of the two procedures, statically and dynamically locked exchange nailing yielded union rates of 84.259% and 82.381% respectively. Therefore, there was no significant difference between the different locking methods of exchange nailing for union rate or time to union at a significance value of P < 0.05. The analysis showed exchange nailing to be the more successful choice in the treatment of femoral non-unions in respect to its higher success rate (491/567 EN, 24/57 dynam, P < 0.0001). However, there was no significant difference between the success rates of the two procedures for delayed union fractures (25/27 EN, 45/55 dynam, P = 0.3299). Nevertheless, dynamization was more efficient in the treatment of delayed unions (at rates comparable to exchange nailing) than in the treatment of non-unions.

CONCLUSION

In conclusion, after examination of factors, dynamization is recommended treatment of delayed femur fractures, while exchange nailing is the treatment of choice for non-unions.

Distal femur: dynamization of plating

With advances in osteosynthesis technology providing improved stability of fixation and better outcomes, surgical treatment has become the standard of care for distal femur fractures. Pre-contoured distal femoral locking plates are the most commonly used implants for fixation. However, healing problems such as delayed union, failure of fixation, and /or nonunion are not uncommon. The fixation construct being "too stiff" is a commonly quoted reason when nonunion/failure of fixation occurs on distal femur fractures fixed with a plate. A flexible fixation construct allowing controlled axial micromotion could help stimulate the bone healing. In order to achieve this goal, plating construct stiffness can be modified by several methods.

Is nail dynamization beneficial after twelve weeks - An analysis of 37 cases

PURPOSE

Although nail dynamization in femoral and tibial fractures is an effective method of promoting healing, its role beyond twelve weeks is still not clear. It is usually done two to three months following interlocking nailing. This study was done to evaluate the efficacy of late dynamization (after 12 weeks) and factors affecting union.

MATERIALS AND METHODS

In this retrospective study, thirty seven patients who underwent dynamization for reamed intramedullary interlocking nails of femur (18) and tibia (20) after twelve weeks from index surgery and with a minimum followup of six months were included. Fracture healing index was calculated using predynamization radiographs. Radiographic union was defined as osseous bridging of three cortices on followup radiographs. Dynamization failure was defined as fractures not showing progressive increase in callus on followup radiographs and those that required secondary intervention.

RESULTS

Mean age of patients at time of injury was 35.92 years (range: 16-63) with males (86.8%) predominating. Mean time to dynamization from index surgery was 19.11 weeks (range-12-36). Thirty one fractures (81.5%) went onto union after dynamization of which twelve were femoral and nineteen were tibial fractures. Mean time to union after dynamization was 6 months. Communited fractures (6-21) showed poor results with delayed dynamization compared to other anatomical types which was statistically significant (P = 0.05). Predynamization FHI of more than 1.18 had 83% sensitivity and 72% specificity in predicting fracture healing after dynamization.

CONCLUSION

Late dynamization is still beneficial in promoting healing in femoral and tibial fractures. Communited fractures showed poor results with dynamization. Predynamization FHI was an important predictor of fracture healing.

Closed External Fixation for Failing or Failed Femoral Shaft Plating in a Developing Country

INTRODUCTION

Femoral shaft fractures are one of the common injuries that is treated by open reduction, with internal fixation by plate and screws or intramedullary nailing, which can achieve a high union rate.

AIM

To evaluate the outcome of using closed external fixation to augment a failing plate; with signs of screw loosening and increasing bone/plate gap; a failed plate; broken plate; screws completely out of bone with redisplacement of fracture.

MATERIALS AND METHODS

A retrospective study on 18 patients, aged between 17-42 years, who presented between 6-18 weeks after initial surgical fixation, with pain, difficulty in limb function, deformity and abnormal movement at fracture site, was done. X-Rays showed plating failure with acceptable amount of callus, which unfortunately had refractured. Cases associated with infection and no radiological evidence of callus formation were excluded from this study. Closed reduction was done by manipulation, then fracture fixation by AO external fixator. The patients were encouraged for full weight bearing as early as possible with dynamization later on.

RESULTS

Of the 18 patients who underwent external fixation after close reduction, 15 cases showed bone healing in a period between 11-18 weeks (mean of 14.27 weeks) with good alignment (Radiologically). Removal of external fixator was done followed by physical therapy thereafter.

CONCLUSION

Closed external fixation for treatment of failing or failed femoral plating, achieves good success rate and has less complications, is a short time procedure, especially in a hospital with limited resources.

Nonunion of the Femur and Tibia: An Update

Delayed union and nonunion of tibial and femoral shaft fractures are common orthopedic problems. Numerous publications address lower extremity long bone nonunions. This review presents current trends and recent literature on the evaluation and treatment of nonunions of the tibia and femur. New studies focused on tibial nonunion and femoral nonunion are reviewed. A section summarizing recent treatment of atypical femoral fractures associated with bisphosphonate therapy is also included.

Gas nanobubbles and aqueous nanostructures: the crucial role of dynamization

Nanobubbles (NBs) have been a subject of intensive research over the past decade. Their peculiar characteristics, including extremely low buoyancy, longevity, enhanced solubility of oxygen in water, zeta potentials and burst during collapse, have led to many applications in the industrial, biological and medical fields. NBs may form spontaneously from dissolved gas but the process is greatly enhanced by gas supersaturation and mechanical actions such as dynamization. Therefore, the formation of NBs during the preparation of homeopathic dilutions under atmospheric pressure cannot be ignored. I suggested in 2009 the involvement of NBs in nanometric superstructures revealed in high dilutions using NMR relaxation. These superstructures seemed to increase in size with dilution, well into the ultramolecular range (>12c). I report here new experiments that confirm the involvement of NBs and prove the crucial role of dynamization to create superstructures specific to the solute. A second dynamization was shown to enhance or regenerate these superstructures. I postulate that superstructures result from a nucleation process of NBs around the solute, with shells of highly organized water (with ions and silicates if any) which protect the solute against out-diffusion and behave as nucleation centres for further dilution steps. The sampling tip may play an active role by catching the superstructures and thus carry the encaged solute across the dilution range, possibly up to the ultramolecular range. The superstructures were not observed at low dilution, probably because of a destructuring of the solvent by the solute and/or of an inadequate gas/solute ratio.

Biomechanical analyses of static and dynamic fixation techniques of retrograde interlocking femoral nailing using nonlinear finite element methods

Femoral shaft fractures can be treated using retrograde interlocking nailing systems; however, fracture nonunion still occurs. Dynamic fixation techniques, which remove either the proximal or distal locking screws, have been used to solve the problem of nonunion. In addition, a surgical rule for dynamic fixation techniques has been defined based on past clinical reports. However, the biomechanical performance of the retrograde interlocking nailing systems with either the traditional static fixation technique or the dynamic fixation techniques has not been investigated by using nonlinear numerical modeling. Three-dimensional nonlinear finite element models were developed, and the implant strength, fixation stability, and contact area of the fracture surfaces were evaluated. Three types of femoral shaft fractures (a proximal femoral shaft fracture, a middle femoral shaft fracture, and a distal femoral shaft fracture) fixed by three fixation techniques (insertion of all the locking screws, removal of the proximal locking screws, or removal of the distal locking screws) were analyzed. The results showed that the static fixation technique resulted in sufficient fixation stability and that the dynamic fixation techniques decreased the failure risk of the implant and produced a larger contact area of the fracture surfaces. The outcomes of the current study could assist orthopedic surgeons in comprehending the biomechanical performances of both static and dynamic fixation techniques. In addition, the surgeons could also select a fixation technique based on the specific patient situation using the numerical outcomes of this study.

Complex fractures of the tibia and femur treated with static interlocking intramedullary nail

BACKGROUND

Reamed interlocking intramedullary nailing is considered the gold standard treatment for complex fractures of the femoral and tibial shaft. There has been some controversies about dynamization of statically locked nails, and some authors recommended routine dynamization for promotion of healing. This study aims to evaluate treatment of complex fractures in tibia and femur with static interlocking intramedullary nail method.

METHODS

In a retrospective study from January 2003 to April 2008, 173 patients with femoral and tibial shaft fracture that were treated with this method were enrolled. No rod was dynamized in our patients.

RESULTS

All patients with tibial fractures achieved union without any need for dynamization during 12-18 weeks (mean; 13.4 weeks). Four patients developed delayed union but all achieved union without any intervention. In femoral fracture, all but one patient achieved complete union during 10-30 weeks (mean: 18.3 weeks). One patient developed non-union who was treated by an exchange nailing and iliac bone graft method. No significant complication was observed in our patients.

CONCLUSION

It is not necessary to routinely dynamize nails in tibial and femoral shaft fractures as all fractures united in acceptable alignment without any complication.

MANAGEMENT OF UNSTABLE TIBIAL DIAPHYSEAL FRACTURES BY EXTERNAL FIXATION

A group of 30 patients of unstable tibial diaphyseal fractures were managed using unilateral tubular external fixator. The fixator assembly comprised a double stainless steel hollow rod with universal joints and schanz screws as principal implant. Reduction and controlled distraction or compression were achieved by means of distracter/compressor device. Early dynamization was resorted to. The union rate was 100% with average healing time between 20 weeks for closed unstable fractures and 27 weeks for open Gustilo grade-II fractures. Minor pin tract infections accounted for majority of the complications. The unilateral fixator assembly permits early ambulation in unstable tibial diaphyseal fractures without sacrificing a sound anatomical result.