The effect of screw thread length on initial stability of Schatzker type 1 tibial plateau fracture fixation: a biomechanical study

Interfragmentary compression force and fixation stability of lateral tibial plateau fractures in normal and osteoporotic bones

Lateral platform collapse in fixations of lateral tibial plateau fractures (TPFs) using either double-lag screws fixation (DSF) or locking-plate fixation (LPF) is not rare. This study aimed to explore the effect of enhancing the interfragmentary compression force (IFCF) on fixation stability in lateral TPFs in normal and osteoporotic bones using finite element analysis. Finite element models of DSF in normal bone and LPF in normal and osteoporotic bones were established to simulate the fixations of lateral TPF. After model validation, axial compressive forces of 500, 1000, 1500, and 2500 N to the tibial plateau along with an IFCF of 0, 100, 200, and 300 N were applied. The maximum axial micromotion of the lateral fragment (MAM-LF), maximal translational micromotion of the lateral fragment (MTM-LF), peak von Mises stress (VMS), and peak equivalent elastic strain of the lateral fragment (EES-LF) were evaluated. The MAM-LF showed a decreasing trend as the IFCF increased in all models. For DSF models, the peak VMS of implants increased as the IFCF increased when the axial loads were 500 and 1000 N. The peak EES-LF decreased as the IFCF increased under axial loads of 1000, 1500, and 2500 N. For the normal and osteoporotic LPF models, the peak VMS of the implants decreased as the IFCF increased. Peak EES-LF decreased as IFCF increased. In conclusion, enhancing IFCF was beneficial in improving the fixation stability of lateral TPF. The optimal IFCF for DSF and LPF should be as high as reasonably feasible.

Application of a combined cancellous lag screw enhances the stability of locking plate fixation of osteoporotic lateral tibial plateau fracture by providing interfragmentary compression force

BACKGROUND

Insufficient interfragmentary compression force (IFCF) frequently leads to unstable fixation of osteoporotic lateral tibial plateau fractures (OLTPFs). A combined cancellous lag screw (CCLS) enhances IFCF; however, its effect on OLTPF fixation stability remains unclear. Therefore, we investigated the effect of CCLS on OLTPF stability using locking plate fixation (LPF).

MATERIALS AND METHODS

Twelve synthetic osteoporotic tibial bones were used to simulate OLTPFs, which were fixed using LPF, LPF-AO cancellous lag screws (LPF-AOCLS), and LPF-CCLS. Subsequently, 10,000 cyclic loadings from 30 to 400 N were performed. The initial axial stiffness (IAS), maximal axial micromotion of the lateral fragment (MAM-LF) measured every 1000 cycles, and failure load after 10,000 cycles were tested. The same three fixations for OLTPF were simulated using finite element analysis (FEA). IFCFs of 0, 225, and 300 N were applied to the LPF, LPF-AOCLS, and LPF-CCLS, respectively, with a 1000-N axial compressive force. The MAM-LF, peak von Mises stress (VMS), peak equivalent elastic strain of the lateral fragment (EES-LF), and nodes of EES-LF > 2% (considered bone destruction) were calculated.

RESULTS

Biomechanical tests revealed the LPF-AOCLS and LPF-CCLS groups to be superior to the LPF group in terms of the IAS, MAM-LF, and failure load (all p < 0.05). FEA revealed that the MAM-LF, peak VMS, peak EES-LF, and nodes with EES-LF > 2% in the LPF were higher than those in the LPF-AOCLS and LPF-CCLS.

CONCLUSION

IFCF was shown to enhance the stability of OLTPFs using LPF. Considering overscrewing, CCLS is preferably recommended, although there were no significant differences between CCLS and AOCLS.

[Research progress on biomechanics for internal fixation in tibial plateau fracture]

Objective

To review the biomechanical research progress of internal fixation of tibial plateau fracture in recent years and provide a reference for the selection of internal fixation in clinic.

Methods

The literature related to the biomechanical research of internal fixation of tibial plateau fracture at home and abroad was extensively reviewed, and the biomechanical characteristics of the internal fixation mode and position as well as the biomechanical characteristics of different internal fixators, such as screws, plates, and intramedullary nails were summarized and analyzed.

Results

Tibial plateau fracture is one of the common types of knee fractures. The conventional surgical treatment for tibial plateau fracture is open or closed reduction and internal fixation, which requires anatomical reduction and strong fixation. Anatomical reduction can restore the normal shape of the knee joint; strong fixation provides good biomechanical stability, so that the patient can have early functional exercise, restore knee mobility as early as possible, and avoid knee stiffness. Different internal fixators have their own biomechanical strengths and characteristics. The screw fixation has the advantage of being minimally invasive, but the fixation strength is limited, and it is mostly applied to Schatzker typeⅠfracture. For Schatzker Ⅰ-Ⅳ fracture, unilateral plate fixation can be used; for Schatzker Ⅴand Ⅵ fracture, bilateral plates fixation can be used to provide stronger fixation strength and avoid the stress concentration. The intramedullary nails fixation has the advantages of less trauma and less influence on the blood flow of the fracture end, but the fixation strength of the medial and lateral plateau is limited; so it is more suitable for tibial plateau fracture that involves only the metaphysis. Choosing the most appropriate internal fixation according to the patient's condition is still a major difficulty in the surgical treatment of tibial plateau fractures.

Conclusion

Each internal fixator has good fixation effect on tibial plateau fracture within the applicable range, and it is an important research direction to improve and innovate the existing internal fixator from various aspects, such as manufacturing process, material, and morphology.

Is there a Difference in Interfragmentary Compression Strength Between Fully or Partially Threaded Screws? Results of an Experimental Biomechanical Pilot Study

Objective  This study assessed differences between fully- and partially-threaded screws in the initial interfragmentary compression strength. Our hypothesis was that there would be an increased loss in initial compression strength with the partially-threaded screw. Methods  A 45-degree oblique fracture line was created in artificial bone samples. The first group (FULL, n  = 6) was fixed using a 3.5-mm fully-threaded lag screw, while the second group (PARTIAL, n  = 6) used a 3.5-mm partially-threaded lag screw. Torsional stiffness for both rotational directions were evaluated. The groups were compared based on biomechanical parameters: angle-moment-stiffness, time-moment-stiffness, maximal torsional moment (failure load), and calibrated compression force based on pressure sensor measurement. Results  After loss of one PARTIAL sample, no statistically significant differences in calibrated compression force measurement were observed between both groups: [median (interquartile range)] FULL: 112.6 (10.5) N versus PARTIAL: 106.9 (7.1) N, Mann-Whitney U-test: p  = 0.8). In addition, after exclusion of 3 samples for mechanical testing (FULL n  = 5, PARTIAL n  = 4), no statistically significant differences were observed between FULL and PARTIAL constructs in angle-moment-stiffness, time-moment-stiffness, nor maximum torsional moment (failure load). Conclusion  There is no apparent difference in the initial compression strength (compression force or construct stiffness or failure load) achieved using either fully- or partially-threaded screws in this biomechanical model in high-density artificial bone. Fully-threaded screws could, therefore, be more useful in diaphyseal fracture treatment. Further research on the impact in softer osteoporotic, or metaphyseal bone models, and to evaluate the clinical significance is required.

The Effects of Different Screw Combinations on the Initial Stability of Ankle Arthrodesis

BACKGROUND

The literature is scanty regarding the biomechanical effects of different thread configurations on the initial stability of ankle arthrodesis. This study aims to compare the initial stability of tibiotalar fusion site in ankle arthrodesis using cannulated screws with different thread designs.

METHODS

We biomechanically tested under cyclic loading the effects of different screw combinations on the initial stability of ankle arthrodesis. A total of 28 synthetic ankle models were divided into four groups: two partially threaded cancellous screws (group A), partially and fully threaded cancellous screws (group B), a partially threaded cancellous screw with a headless compression screw (group C), and a fully threaded cancellous screw and a headless compression screw (group D). Biomechanical variables including ultimate failure load, initial stiffness, ultimate stiffness, and failure angulation were analyzed.

RESULTS

There were no differences in any of the biomechanical variables among the four groups (P = .41 for ultimate failure load, P = .079 for initial stiffness, P = .084 for ultimate stiffness, and P = .937 for failure angulation).

CONCLUSIONS

Combinations of different cannulated screws showed similar results in terms of the stability and stiffness of the tibiotalar fusion site.

Plate-screw and screw-washer stability in a Schatzker type-I lateral tibial plateau fracture: a comparative biomechanical study

The aim of this study was to evaluate the biomechanical role of both a non-locking two-hole small fragment dynamic compression plate with 3.5-mm screws and a 4.5-mm cortical screw with a washer applied to a Schatzker type-I tibial plateau fracture. Sixteen right synthetic tibiae were used to create an anterolateral shear tibial plateau fracture (Schatzker type-I fracture). Eight models were fixed with a small fragment non-locked straight dynamic compression plate with one 3.5-mm bicortical screw (plate-screw construction) and eight models were fixed with a 4.5-mm cortical screw and a washer (screw-washer construction), both inserted at 1.0 mm distal to the apex of the fracture. Specimens were tested up to the onset of yielding at a constant strain rate of 5.0-mm/min. Stiffness ranged from 311.83 N/mm to 199.54 N/mm, with a mean + SD of 260.32 + 33.8 N/mm in the plate-screw construction, and from 290.34 N/mm to 99.16 N/mm, with a mean + SD of 220.46 + 63.12 N/mm in screw-washer construction. There was no significant difference (p=0.172). Use of a two-hole small-fragment non-locked plate with one 3.5-mm cortical screw or a 4.5-mm cortical screw with a washer applied at 1.0 mm distal to the apex of the fracture as buttressing present similar stiffness in terms of preventing axial displacement in synthetic tibiae models tested up to the onset of yielding.

A review of the management of tibial plateau fractures

Tibial plateau fractures form a wide spectrum of injuries presenting varying challenges to the trauma surgeon. The prognosis of this injury spectrum is largely dependent on the management of each particular configuration, and the literature is as a result littered with a number of management strategies with limited consensus. The aim of this review is to provide a concise guide to the trauma surgeon based on newer and classical peer-reviewed publications in international orthopaedic journals. A PubMed search was conducted to identify peer-reviewed publications within the last 10 years and expanded to identify classic papers pertaining to the Schatzker classification. The focus was on articles based on management techniques, controversies and recent developments. The management of specific injury patterns is based on the Schatzker classification which is a widely accepted traditional classification system. Whilst there is a general consensus on the ultimate goal of a stable anatomic reduction in this subset of fractures, there continues to be a number of controversies surrounding issues including pre-operative imaging, initial assessment and definitive management of specific injury patterns, some of which do not conform to the original Schatzker classification. The majority of fractures will require operative management, and with whatever management strategy employed, the main emphasis is on respecting the soft tissue envelope. There remains a paucity of prospective randomised controlled trials comparing the different available operative techniques.

A biomechanical evaluation of different fixation strategies for posterolateral fragments in tibial plateau fractures and introduction of the 'magic screw'

BACKGROUND

Posterior plate fixation is biomechanically the strongest fixation method for posterolateral column fracture (PLCF) of the tibial plateau; however, there are inherent deficiencies and risks of a posterior approach. Thus, the 'magic screw' was proposed to enhance fixation stability of the lateral rafting plate used for PLCF. The purpose of this study was to re-examine and compare the stability of different fixation methods for PLCF.

METHODS

Synthetic tibiae models were used to simulate posterolateral split fractures. The fracture models were randomly assigned into three groups: Group A, fixed with posterolateral buttress plates; Group B, with lateral locking compression plates (LCP); and Group C fixed with lateral LCPs and one 'magic screw'. Gradually increased axial compressive loads were applied to each specimen.

RESULTS

There was a mean subsidence hierarchy of the posterolateral fragment at different load levels: Group A had the least subsidence, followed by Group C, and Group B had the most. There were no significant differences in the mean loads at different displacements between Group A and Group C. Group A had the highest axial stiffness. Additionally, there was a significant difference in axial stiffness between Group B and Group C.

CONCLUSION

Biomechanical stability of the combined fixation of the posteriorly positioned lateral rafting plate with the 'magic screw' was much closer to that of posterior plate fixation for split-type PLCF. The necessity of posterior fixation through a posterior approach may be reduced for selected patients.

A comparison of the biomechanical stability of pedicle-lengthening screws and traditional pedicle screws: an in vitro instant and fatigue-resistant pull-out test

Aims

The aim of this study was to compare the peak pull-out force (PPF) of pedicle-lengthening screws (PLS) and traditional pedicle screws (TPS) using instant and cyclic fatigue testing.

Materials and Methods

A total of 60 lumbar vertebrae were divided into six groups: PLS submitted to instant pull-out and fatigue-resistance testing (groups A1 and A2, respectively), TPS submitted to instant pull-out and fatigue-resistance testing (groups B1 and B2, respectively) and PLS augmented with 2 ml polymethylmethacrylate, submitted to instant pull-out and fatigue-resistance testing (groups C1 and C2, respectively). The PPF and normalized PPF (PPFn) for bone mineral density (BMD) were compared within and between all groups.

Results

In all groups, BMD was significantly correlated with PPF (r = 0.83, p < 0.001). The PPFn in A1 was significantly less than in B1 (p = 0.006) and C1 (p = 0.002). The PPFn of A2 was significantly less than in B2 (p < 0.001) and C2 (p < 0.001). The PPFn in A1, B1, and C1 was significantly greater than in A2 (p = 0.002), B2 (p = 0.027), and C2 (p = 0.003). There were no significant differences in PPFn between B1 and C1, or between B2 and C2.

Conclusion

Pedicle lengthening screws with cement augmentation can provide the same fixation stability as traditional pedicle screws and may be a viable clinical option. Cite this article: Bone Joint J 2018;100-B:516-21.