Experimental in vivo acute and chronic biomechanical and histomorphometrical comparison of self-drilling and self-tapping anterior cervical screws

Immediate and late inflammatory and bone healing response post implantation of self-tapping and self-drilling osteosynthesis screws

The aim of this study was to comparatively analyse osseointegration after the implantation of self-tapping screws (STS) and self-drilling screws (SDS). Thus, 24 four-month-old male Wistar rats, received SDS and STS screws in their left and right tibias, respectively. Sample collection was performed immediately at 0 hours (0h), two, seven, and 21 days after implantation (2d, 7d, 21d). Samples from immediately and 21 days after were analysed by micro computed tomography (MicroCT). All time points were evaluated by histology (Haematoxylin and Eoisin and Goldner's Trichrome) and immunohistochemistry for tartrate-acid resistant phosphatase positive (TRAP+) osteoclasts. MicroCT images revealed an intimate contact between bone and each type of screw at 0h. However, SDS group presented decreased bone volume (BV, mm3) at 21 days in comparison with STS. Both SDS and STS post implantation presented areas of suitable new bone formation surrounding screw threads from seven days, and inflammation decreased from two to 21 days. Also, TRAP+ osteoclasts were mainly identified at seven days in both STS and SDS groups, particularly surrounding areas of pressure, with significant differences between groups. In conclusion, differences in shape and insertion technique for SDS and STS screws did not affect immediate and late inflammatory and bone healing response post implantation in this animal model. Both osteosynthesis screws allowed satisfactory post-surgical outcomes.

Comparative Evaluation of Drill-Free and Self-Tapping Titanium Miniscrews for Semi-Rigid Internal Fixation in Maxillofacial Trauma

Introduction

Conventional semi-rigid fixation systems in maxillofacial trauma use self-tapping titanium miniscrews (STS) that require preliminary drilling of a pilot hole. Although drill-free miniscrews (DFS) accompany these systems, they have not dominated practice despite their allure of improved screw-bone contact and holding power. The COVID-19 pandemic has brought these DFS to light as they avoid aerosol production. The present study has compared DFS to STS in patients being treated with miniplate fixation for maxillofacial trauma to understand their feasibility for maxillofacial fracture fixation.

Methodology

This prospective case–control study sampled 16 patients each with zygomaticomaxillary buttress fracture and parasymphysis fracture of the mandible and grouped alternating patients as case (DFS) and control (STS). Intraoperatively duration of fixation, incidence of screw failures and fragment stability; postoperatively occlusion, neurosensory deficits, teeth vitality and infection and removal rates were evaluated at postoperative week 1, 3, 6, 12 and 24 using Cramer's V test. A P value < 0.05 was considered significant.

Results

In the 32 patients evaluated, DFS reduced internal fixation time at zygomaticomaxillary buttress (P = 0.001) but not at parasymphysis (P = 0.206). No significant difference in screw failures or fragment stability was observed. Stable occlusion was maintained in all groups with vital teeth and intact neurosensory function, but the summative incidence of infection was significant at week 24 when STS was used at parasymphysis (P = 0.019).

Discussion

While DFS may facilitate ease of insertion with a single instrument pick-and-screw-in approach, avoiding thermal osteonecrosis and aerosol production, they fail to confer any other clinical advantage.

A Dual-Motor Drill Reduces Plunge, Simultaneously Gauges Depth, and Saves Time When Placing Orthopedic Screws

The technique for placement of orthopedic hardware remains unchanged despite technological advances. The surgeon controls drill bit speed and advancement, which risks drill bit overpenetration, or plunge. Measurement is performed as an additional step, introducing measurement error and increasing operative time. A dual-motor drill was created to control drill variables and combine drilling and measurement into a single step. The purpose of this study was to determine whether a dual-motor drill could reduce drilling and measurement errors while increasing the speed of placement of orthopedic hardware. Five orthopedic surgeons drilled and measured 10 holes with a standard drill and a dual-motor drill in randomized bicortical bone blocks. The bone blocks were placed on standard ballistic gels, which left a defect from drill bit overpenetration that could be measured with a calibrated gauge. The accuracy of drilling was determined by the depth of the defect in the ballistic gel and was compared between groups. Finally, time for drilling and measurement was collected and compared between groups. Overpenetration for the dual-motor drill (0.5±0.3 mm) was significantly less than for the standard drill (8.4±1.9 mm) (P<.0001). Depth measurement error for the dual-motor drill (0.6±0.3 mm) was significantly less than for the standard drill (2.6±0.5 mm) (P<.0001). Drilling and measurement time for the dual-motor drill (6.0±2.2 seconds) was significantly less than for the standard drill (13.4±3.9 seconds) (P<.0001). Use of a dual-motor drill reduced overpenetration, improved measurement accuracy, and reduced time spent during placement of orthopedic hardware. [Orthopedics. 2020;43(5):e465-e470.].

[Biomechanical changes of sheep cervical spine after unilateral hemilaminectomy and different degrees of facetectomy]

OBJECTIVE

To establish animal models and investigate the impact of unilateral hemilaminectomy (ULHL) and different degrees of facetectomy (FT) on the cervical spinal biomechanics.

METHODS

Twenty sheep were randomly and evenly divided into 4 groups. No operation was performed for group A, right C4-C6 ULHL was performed for group B, right C4-C6 ULHL and 50% ipsilateral C4-C5 FT was performed for group C, right C4-C6 ULHL and 100% ipsilateral C4-C5 FT was performed for group D. Animals of group A, B, C and D were sacrificed 24 weeks after operating and fresh cervical spine specimens were acquired, biomechanically tested and these data were compared to determine whether ULHL and different degrees of FT led to long-term differences in range of motion.

RESULTS

(1) Changes of the total range of motion of cervical spine 24 weeks after surgery: the total range of motion of group D (60.2°±8.6°) was significantly greater than group A (40.7°±6.4°) and group B (41.2°±13.1°) under flexion-extension station, the total range of motion of group D (81.5°±15.7°) was significantly greater than that of group A (56.7°±12.2°) and group B (57.7°±12.8°) under lateral bending station, and the total range of motion of group D (38.5°±17.5°) had no obvious increase compared with group A (26.4°±9.9°) and group B (27.1°±10.9°) under axial rotation station. The total range of motion of group C had no obvious increase compared with group A and group B under flexion-extension station (44.1°±11.7°), lateral bending station (73.6°±11.4°) and axial rotation station (31.3°±11.5°). (2) Changes of the intersegmental motion 24 weeks after surgery: the intersegmental motion of group D (20.3°±4.6°) at C4-C5 was significantly greater than that of group A (11.7°±3.4°) and group B (11.9°±2.1°) under flexion-extension station, the intersegmental motion of group D (26.8°±3.5°) at C4-C5 was significantly greater than that of group A (15.2°±3.1°) and group B (16.2°±3.2°) under lateral bending station, the intersegmental motion of group D (15.2°±3.5°) at C4-C5 was significantly greater than that of group A (6.6°±2.3°) and group B (7.1°±1.9°) under axial rotation station. The intersegmental motion of group C (21.2°±4.1°) at C4-C5 was significantly greater than that of group A and group B under lateral bending station, the intersegmental motion of group C at C4-C5 had no obvious increase compared with group A and group B under flexion-extension station (15.7°±3.7°) and axial rotation station (10.3°±3.1°).

CONCLUSION

ULHL does not affect cervical stability, ULHL and 50% ipsilateral FT does not affect the long-term cervical stability, ULHL and 100% ipsilateral FT can lead to long-term instability under lateral bending and flexion-extension station.

Self-drilling and self-tapping miniscrews for osteosynthesis fixture after LeFort I osteotomy: An ex vivo trial for primary stability and a randomized clinical study

BACKGROUND

Self-drilling osteosynthesis screws (SDS) have a potential higher primary stability together with clinical advantages such as less time effort compared to self-tapping screws (STS). The aims of the study were to compare the primary stability of SDS and STS ex vivo and to analyze of the time-saving effect in vivo.

MATERIALS AND METHODS

Ex vivo, both screws were placed in porcine bone. Torque was measured for insertion and removal. Four specimens were kept in bone for histologic bone-to-implant-contact examination. In vivo, 49 patients who received orthognathic surgery in the maxilla were included in 2 centers. In a split-mouth design, the time for osteosynthesis fixation and perioperative events were recorded.

RESULTS

Ex vivo, insertion and removal torque measurements were higher for SDS, especially in dense bone. Histologic imaging on the exemplary-stained specimens showed higher bone contact and compressed bone matrix for SDS in all bone densities. In vivo, the mean osteosynthesis time in both centers was 5.5 min (±3.03) for SDS and 5.5 min (±2.37) for STS. Separate analysis showed that center I was faster with STS and center II with SDS. Although, in center I a higher rate of failed primary stability of SDS compared to STS was documented.

CONCLUSIONS

SDS showed a partially higher primary stability ex vivo, especially in dense bone. The timesaving effect of SDS is less pronounced than expected, but technically SDS might be favorable where drilling is difficult or even impossible.

Using self-drilling screws in volar plate osteosynthesis for distal radius fractures: a feasibility study

Background

Symptomatic extensor tendon irritation is a frequent complication in volar plate osteosynthesis of distal radius fractures. It is typically caused by dorsal screw protrusion and overdrilling of the dorsal cortex. The use of self-drilling locking screws (SDLS) could overcome both causes. The practical applicability of SDLS depends on two prerequisites: (1) the feasibility of preoperative distal screw length determination, and (2) sufficient primary biomechanical stability of SDLS compared to standard locking screws (SLS).

Methods

We first assessed the feasibility of preoperative screw length determination (1): Distal radius width, depth and distal screw lengths were measured in 38 human radii. Correlations between distal radius width and depth were assessed, a cluster analysis (Ward’s method and squared Euclidean distance) for distal radius width conducted, and intra-cluster screw lengths analyzed (ANOVA). The biomechanical performance of SDLS (2) was assessed by comparison to SLS in a distal radius fracture model (AO-23 A3). 75 % distal screw length was chosen for both groups to simulate a worst-case scenario. Uniaxial compression tests were conducted to measure stiffness, elastic limit, maximum force and residual tilt. Statistics comprised of independent sample t-tests and a Bonferroni correction (p < 0.0125).

Results

(1) Distal radius width and depth showed a high correlation (R² = 0.79; p < 0.001). Three distal radius width clusters could be identified: small <34 mm; medium 34–36.9 mm; large >36.9 mm. ANOVA and Tukey post-hoc analysis revealed significantly different volar-dorsal depths (p < 0.05) for nearly all screws. (2) To assess biomechanical stability nine specimens were tested each; no significant differences were found between the SDLS and SLS groups.

Conclusions

This feasibility study demonstrates that (1) distal radius width can be used as a predictor for distal screw length and (2) that SDLS provides mechanical stability equivalent to SLS. These results highlight the feasibility of applying SDLS screws in volar plate osteosynthesis at least in extraarticular fractures.

Self-tapping ability of carbon fibre reinforced polyetheretherketone suture anchors

An experimental and computational investigation of the self-tapping ability of carbon fibre reinforced polyetheretherketone (CFR-PEEK) has been conducted. Six CFR-PEEK suture anchor designs were investigated using PEEK-OPTIMA® Reinforced, a medical grade of CFR-PEEK. Experimental tests were conducted to investigate the maximum axial force and torque required for self-taping insertion of each anchor design. Additional experimental tests were conducted for some anchor designs using pilot holes. Computational simulations were conducted to determine the maximum stress in each anchor design at various stages of insertion. Simulations also were performed to investigate the effect of wall thickness in the anchor head. The maximum axial force required to insert a self-tapping CFR-PEEK suture anchor did not exceed 150 N for any anchor design. The maximum torque required to insert a self-tapping CFR-PEEK suture anchor did not exceed 0.8 Nm. Computational simulations reveal significant stress concentrations in the region of the anchor tip, demonstrating that a re-design of the tip geometry should be performed to avoid fracture during self-tapping, as observed in the experimental component of this study. This study demonstrates the ability of PEEK-OPTIMA Reinforced suture anchors to self-tap polyurethane foam bone analogue. This provides motivation to further investigate the self-tapping ability of CFR-PEEK suture anchors in animal/cadaveric bone. An optimised design for CFR-PEEK suture anchors offers the advantages of radiolucency, and mechanical properties similar to bone with the ability to self-tap. This may have positive implications for reducing surgery times and the associated costs with the procedure.

Effect of pilot hole on biomechanical and in vivo pedicle screw-bone interface

PURPOSE

To experimentally study the influence of pilot hole diameter (smaller than or equal to the internal (core) diameter of the screw) on biomechanical (insertion torque and pullout strength) and histomorphometric parameters of screw-bone interface in the acute phase and 8 weeks after pedicle screw insertion.

METHODS

Fifteen sheep were operated upon and pedicle screws inserted in the L1-L3 pedicles bilaterally. The pilot hole was smaller (2.0 mm) than the internal diameter (core) of the screw on the left side pedicle and equal (2.8 mm) to the internal diameter (core) of the screw on the right side pedicle. Ten animals were sacrificed immediately (five animals were assigned to pullout strength tests and five animals were used for histomorphometric bone-screw interface evaluation). Five animals were sacrificed 8 weeks after pedicle screw insertion for histomorphometric bone-screw interface evaluation.

RESULTS

The insertion torque and pullout strength were significantly greater in pedicle screws inserted into pilot holes smaller than internal (core) diameter of the screw. Histomorphometric evaluation of bone-screw interface showed that the percentage of bone-implant contact, the area of bone inside the screw thread and the area of bone outside the screw thread were significantly higher for pilot holes smaller than the internal (core) diameter of the screw immediately after insertion and after 8 weeks.

CONCLUSION

A pilot diameter smaller than the internal (core) diameter of the screw improved the insertion torque and pullout strength immediately after screw insertion as well the pedicle screw-bone interface contact immediately and 8 weeks after screw placement in sheep with good bone mineral density.