Distal interlocking for short trochanteric nails: static, dynamic or no locking? Review of the literature and decision algorithm

How accurately do finite element models predict the fall impact response of ex vivo specimens augmented by prophylactic intramedullary nailing?

Hip fracture prevention approaches like prophylactic augmentation devices have been proposed to strengthen the femur and prevent hip fracture in a fall scenario. The aim of this study was to validate the finite element model (FEM) of specimens augmented by prophylactic intramedullary nailing in a simulated sideways fall impact against ex vivo experimental data. A dynamic inertia-driven sideways fall simulator was used to test six cadaveric specimens (3 females, 3 males, age 63-83 years) prophylactically implanted with an intramedullary nailing system used to augment the femur. Impact force measurements, pelvic deformation, effective pelvic stiffness, and fracture outcomes were compared between the ex vivo experiments and the FEMs. The FEMs over-predicted the effective pelvic stiffness for most specimens and showed variability in terms of under- and over-predicting peak impact force and pelvis compression depending on the specimen. A significant correlation was found for time to peak impact force when comparing ex vivo and FEM data. No femoral fractures were found in the ex vivo experiments, but two specimens sustained pelvic fractures. These two pelvis fractures were correctly identified by the FEMs, but the FEMs made three additional false-positive fracture identifications. These validation results highlight current limitations of these sideways fall impact models specific to the inclusion of an orthopaedic implant. These FEMs present a conservative strategy for fracture prediction in future applications. Further evaluation of the modelling approaches used for the bone-implant interface is recommended for modelling augmented specimens, alongside the importance of maintaining well-controlled experimental conditions.

Nailing precision: a systematic review and meta-analysis of randomized controlled trials comparing piriformis and trochanteric entry points for femoral antegrade nailing

INTRODUCTION

Entry point selection, a crucial aspect of femoral antegrade nailing, can impact nail fit and consequently fracture reduction. In adults, the standard entry portals used are the piriformis fossa and the tip of the greater trochanter. Previous systematic reviews comparing the two techniques have not been limited to Randomized Controlled Trials (RCTs) and have not consistently included the same available RCTs.

MATERIALS AND METHODS

A systematic search of comparative studies regarding entry portal selection in femoral antegrade nailing was conducted on seven databases. Only Prospective RCTs comparing trochanteric and piriformis entry in the management of trochanteric or diaphyseal femur fractures were eligible for inclusion.

RESULTS

Ultimately, only 6 RCTs were found eligible for inclusion. Five of the six included studies reported on operative time. The resulting mean difference (MD) illustrated a significant decrease in operative time by approximately 21.26 min (95% CI  - 28.60 to  - 13.92, p < 0.001) using trochanteric entry. Fluoroscopy exposure was reported on by four studies, however, only two studies were included in the analysis due to different reporting methods. Trochanteric entry used significantly less fluoroscopy than piriformis entry (MD -50.33 s, 95% CI  - 84.441 to  - 16.22, p = 0. 004). No significant difference in malalignment rates, delayed union rates, nonunion rates, pain scores, or complication rates was found.

CONCLUSION

The significant differences found in operating time and fluoroscopy time align with those in other studies. While we were not able to pool the data on functional outcome scores, none of the included studies found a significant difference in scores by their last follow-up. Both approaches demonstrate comparable functional outcomes and safety profiles, indicating the choice of entry point should be at the discretion of the surgeon based on technique familiarity and fracture characteristics.

[Research progress on distal interlocking screws of cephalomedullary nails in intertrochanteric fractures]

Objective

To summarize the new research progress in distal interlocking screws of cephalomedullary nails for the treatment of intertrochanteric fractures.

Methods

Relevant domestic and foreign literature was extensively reviewed to summarize the static/dynamic types of distal interlocking screw holes, biomechanical studies, clinical studies and application principles, effects on toggling in the cavity, and related complications of distal interlocking screws.

Results

The mode of the distal interlocking screw holes can be divided into static and dynamic. Distal interlocking screws play the role of anti-rotation, maintaining femur length, resisting compression stress, increasing torque stiffness, resisting varus stress, etc. The number of the screws directly affects the toggling of the main nail in the cavity. At present, regardless of whether long or short nails are used, distal interlocking screws are routinely inserted in clinical practice. However, using distal interlocking screws can significantly increase the duration of anesthesia and operation, increase fluoroscopy exposure time, surgical blood loss, and incision length. There is a trend of trying not to use distal interlocking screws in recent years. No significant difference is found in some studies between the effectiveness of dynamic and static interlocking for AO/Orthopaedic Trauma Association (AO/OTA) 31-A1/2 fractures. At present, the selection of the number and mode of distal interlocking screws is still controversial. When inserting distal interlocking screws, orthopedists should endeavor to minimize the occurrence of complications concerning miss shot, vascular injuries, local stress stimulation, and peri-implant fractures.

Conclusion

Distal interlocking screws are mainly used to prevent rotation. For stable fractures with intact lateral walls, long cephalomedullary nails can be used without distal interlocking screws. For any type of intertrochanteric fractures, distal interlocking screws are required when using short cephalomedullary nails for fixation. Different interlocking modes, the number of interlocking screws, and the application prospects of absorbable interlocking screws may be future research directions.

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.

Clinical observation and finite element analysis of femoral stable interlocking intramedullary nail in intertrochanteric fractures

PURPOSE

This study was designed to compare clinical outcomes of the femoral stable interlocking intramedullary nail (FSIIN) with proximal femoral nail anti-rotation (PFNA) for the treatment of intertrochanteric fractures (OTA 31A1 + A2).

METHODS

This study retrospectively analyzed a registered sample of 74 intertrochanteric fractures (OTA 31A1 + A2) surgically treated using FSIIN (n = 36) or PFNA (n = 38) from January 2015 to December 2021. The intra-operative variables (operation time, fluoroscopy time, intra-operative blood loss, length of incision) and fracture healing time were compared between the two groups in this study. Harris hip score (HHS) and visual analog scale (VAS) were used to evaluate the functional states. At the last follow-up, the incidence of related complications in patients was calculated. Eventually, the 3D finite element model was established to analyze the stress of FSIIN and PFNA.

RESULTS

The distribution of all basic characteristics was similar between the two groups (p > 0.05). The operation time, fluoroscopy time, intra-operative blood loss, and length of incision were significantly decreased in the FSIIN group (p < 0.001). The FSIIN group had a shorter fracture healing time than the PFNA group (p < 0.001). There is no significant difference between the two groups in the Harris and VAS (p > 0.05). The incidences of post-operative anaemia, electrolyte imbalance, varus malalignment, and thigh pain were significantly lower in FSIIN than in PFNA groups (all p < 0.05). The finite element results show that the stress shielding effect of FSIIN is smaller.

CONCLUSIONS

Our study revealed that FSIIN seemed to be superior to PFNA in the treatment of intertrochanteric fractures (OTA 31A1 + A2) due to less surgical damage and shorter fracture healing time.

Optimizing fixation methods for stable and unstable intertrochanteric hip fractures treated with sliding hip screw or cephalomedullary nailing: A comparative biomechanical and finite element analysis study

BACKGROUND

Despite recent advances in implants and surgical techniques, catastrophic and clinical failures in the treatment of intertrochanteric fractures continue to occur, with dire consequences in an overall frail population subset. The aim of the current study is to evaluate the effect of the factors under the surgeons' control, namely fracture reduction and implant selection, on the biomechanical behavior of fracture fixation constructs.

MATERIAL-METHODS

An experimental protocol was conducted with the use of instrumented sawbones, in order to validate the finite element models. The implants used were the Gamma3®and DHS systems. Subsequently, a series of scenaria were considered, including various reduction and implant angle combinations. Data were retrieved concerning the peak cancellous bone stresses around the hip screw and the volume of cancellous bone in the femoral head stressed at critical levels, as well as implant stresses and stresses on the cortical bone of the distal fragment.

RESULTS

All stable fracture models displayed significantly decreased cancellous bone stresses and implant stresses compared to their unstable counterparts, regardless of implant used. The effect of increasing implant angle led to a decrease in implant stresses in all models studied, but had a beneficial effect on the stresses in the cancellous bone of the proximal fragment only in the subgroups of stable fractures with both implants and unstable fractures treated with a cephalomedullary nail (CMN). In unstable fractures anatomically reduced, the use of CMN led to significantly lower peak stresses in the cancellous bone and a smaller volume of bone stressed at critical levels. Increasing the reduction angle by 5 ° led to a significant decrease in both peak stresses and volume of bone stressed at critical levels, more prominent in the sliding hip screw (SHS) models. Decreasing the reduction angle into varus by 5 or 10 ° led to a significant increase in bone and implant stresses regardless of implant used.

CONCLUSIONS

In stable two-part (AO31.A2) fractures the use of the SHS appears to be biomechanically equivalent to CMN. In unstable, anatomically reduced fractures, the use of CMN leads to significantly reduced cancellous bone stresses and decreased rotation of the proximal fragment during loading. A reduction in varus should be avoided at all costs. In unstable fractures treated with SHS a reduction in slight valgus appears to be biomechanically beneficial. The highest implant angle that allows for proper screw position and trajectory in the femoral head should be used for stable fractures with both implants and unstable fractures treated with Gamma3®.