Self-tapping versus standard tapped titanium screw fixation in the upper extremity

Effect of screw insertion angle and speed on the incidence of transcortical fracture development in a canine tibial diaphyseal model

OBJECTIVE

To assess the incidence of transcortical fracture (TCF) development based on screw insertion angle and screw insertion speed.

STUDY DESIGN

Cadaveric experimental study.

SAMPLE POPULATION

Sixty-six canine tibiae.

METHODS

Sixty-six cadaveric tibiae were randomly assigned to one of six groups that varied based on screw insertion angle relative to the pilot hole (0, 5, or 10°) and screw insertion speed (650 or 1350 revolutions per minute [rpm]). Each tibia was mounted in a custom jig. Locking self-tapping screws (3.5 mm) were inserted at varying speeds and insertion angles, based on group assignment. Orthogonal radiographs were evaluated for TCFs. Fisher's exact tests with a Bonferroni correction were performed to evaluate differences in the frequency of TCF between groups.

RESULTS

In Group A (0°/650 rpm: control), a 0% TCF rate was observed (n = 0/80). Group B (5°/650 rpm) had a 3.75% TCF rate (n = 3/80). Group C (10°/650 rpm) had a 12.5% TCF rate (n = 10/80). Group D (10°/hand insertion) had a 3.75% TCF rate (n = 3/80). Group E (10°/1350 rpm) had a 17.5% TCF rate (n = 14/80). Group F (0°/1350 rpm) had a 0% TCF rate (n = 0/80). Groups C and E had the highest TCF rates with a difference in TCF rates observed between the control group and Group C (p = .001) and between the control group and Group E (p < .001).

CONCLUSION

Increased screw insertion angle and insertion speed appear to be predisposing factors for TCF development in cadaveric bone.

CLINICAL SIGNIFICANCE

Ensuring screw insertion is coaxial with the pilot hole and using slower screw insertion speeds may help reduce the risk of TCF development.

Cutting Flute and Thread Design on Self-Tapping Pedicle Screws Influence the Insertion Torque and Pullout Strength

Self-tapping screws are commonly used in trauma and maxillofacial surgery and are increasingly used for pedicle screw insertions. In order to evaluate how the quantity and length of cutting flutes on self-tapping pedicle screws affect the insertion torque and pullout strength, eight different self-tapping pedicle screw designs were evaluated. All screws had a threaded length of 35 mm and featured variations in the number of leads, as well as the length and quantity of cutting flutes. Five samples of each design were inserted into pre-drilled, untapped holes (ø2.7 mm, length 35 mm) in sawbone blocks of density 20 PCF. The insertion torque and pullout strength were measured according to ASTM F543. The results showed that screws with a longer cutting flute of 9.5 mm had a lower mean maximum insertion torque than screws with shorter 2.9 mm cutting flutes. Pedicle screws with a double-lead thread design had a greater insertion torque than their single-lead counterparts, and the use of three cutting flutes produced a lower torque than two cutting flutes. The results demonstrated a greater pullout strength in screws with a single-lead thread rather than a double-lead, three cutting flutes instead of two, and a longer length for the cutting flute. In conclusion, to provide immediate stability and reduce the surgical insertion time, a single-lead, self-tapping pedicle screw incorporating three long cutting flutes is recommended because of the significantly greater pullout strength. This design could also reduce the risk of implant loosening in comparison to double-lead, self-tapping pedicle screw designs.

The Effect of Coronal Implant Design and Drilling Protocol on Bone-to-Implant Contact: A 3-Month Study in the Minipig Calvarium

Background: Stress concentrated at an implant’s neck may affect bone-to-implant contact (BIC). The objective of this study was to evaluate four different implant neck designs using two different drilling protocols on the BIC. Methods: Ninety-six implants were inserted in 12 minipigs calvarium. Implants neck designs evaluated were: type 1–6 coronal flutes (CFs), 8 shallow microthreads (SMs); type 2–6 CFs,4 deep microthreads (DMs); type 3–4 DMs; type 4–2 CFs, 8 SMs. Two groups of forty-eight implants were inserted with a final drill diameter of 2.8 mm (DP1) or 3.2 mm (DP2). Animals were sacrificed after 1 and 3 months, total-BIC (t-BIC) and coronal-BIC (c-BIC) were evaluated by nondecalcified histomorphometry analysis. Results: At 1 month, t-BIC ranged from 85–91% without significant differences between implant types or drilling protocol. Flutes on the coronal aspect impaired the BIC at 3 m. c-BIC of implant types with 6 CFs was similar and significantly lower than that of implant types 3 and 4. c-BIC of implant type 4 with SMs was highest of all implant types after both healing periods. Conclusions: BIC was not affected by the drilling protocol. CFs significantly impaired the -BIC. Multiple SMs were associated with greater c-BIC.

Effect of insertion factors on dental implant insertion torque/energy-experimental results

Anchorage of dental implants is quantified with a mechanical engagement to insertion, for example maximum insertion torque (MIT) and insertion energy (IE). Good anchorage of dental implants highly correlates to positive clinical outcomes. However, it is still unclear how bone density, drill protocol, surface finish and cutting flute affect anchorage. In this study, effects of the insertion factors on both MIT and IE were investigated using a full-factorial experiment at two levels: bone surrogate density (0.32 g/cm³ versus 0.48 g/cm³), drill protocol (Ø2.4/2.8 versus Ø2.8/3.2 mm), implant surface finish (machined versus anodized surface) and cutting flute (with versus without). Osteotomies were prepared on rigid polyurethane foam blocks with dimensions of 40 × 40 × 8 mm. Screw shaped dental implants with variable tapered body were consecutively inserted into and removed from the polyurethane foam blocks three times under constant axial displacement and rotational speed. Axial force and torque were recorded synchronously. Insertion energy was calculated from the area under the torque-displacement curve. In this study, we found the main insertion mechanics were thread forming for the first insertion. For the second and third insertions, the main mechanics shifted to thread tightening. Maximum insertion torque (MIT) responded differently to the four insertion factors in comparison to IE. Bone surrogate density, drill protocol and surface finish had the largest main effects for first MIT. For the first IE, drill protocol, surface finish and cutting flute were significant contributors. These results suggest that MIT and IE are influenced by different mechanics: the first MIT and the first IE were sensitive to thread tighten and forming, respectively. Together MIT and IE provide a complete assessment of dental implant anchorage.

Pullout Strength After Multiple Reinsertions in Radial Bone Fixation

Background: Due to bone cutting loss from self-tapping screws (STS), progressive destruction of bone can occur with each reinsertion during surgery. When considering the use of jigs that utilize multiple insertions such as those seen in ulnar and radial shortening osteotomy systems, or scenarios where a screw needs to be removed and reinserted due to some technical issue, this can be concerning, as multiple studies examining the effects of multiple reinsertions and the relationship between insertional torque and pullout strength have had mixed results. Methods: Insertional torque and pullout strength were experimentally measured following multiple reinsertions of STS for up to 5 total insertions for various densities and locations along radial sawbone shafts. Results: Torque and pullout strength were significantly greater in middle segments of the radial shaft. Our trials corroborate previous literature regarding a significant reduction in fixation between 1 and 2 insertions; beyond this, there was no significant difference between pullout strength across all segment locations as well as bone densities for 3 to 5 insertions. There was a moderate to high correlation of insertional torque to pullout strength noted across all bone densities and segments (Pearson r = 0.663, P < .001). Conclusion: While reinsertion of STS between 1 and 2 insertions has been shown to significantly differ in pullout strength, beyond this, there does not appear to be a significant difference in up to 5 insertions at any specific region of radial bone across a range of sawbone densities. Further insertions may be considered with caution.

Ten years stable internal fixation of metacarpal and phalangeal hand fractures-risk factor and outcome analysis show no increase of complications in the treatment of open compared with closed fractures

BACKGROUND

: Stable internal screw/plating systems for hand fractures have evolved during the last 20 years. The improved versatility leads to the increased use of these materials in open fractures, with the benefit of early mobilization. The aim of this retrospective study is to discern whether the broadening of the indications for these implants is accompanied by increased complication rates.

METHODS

: Data from 365 patients treated during the last 10 years at our department for metacarpal or phalangeal fractures with stable internal fixation by screw or plate were gathered and analyzed.

RESULTS

: Uneventful bony consolidation was observed in 91.2% (n = 333). The functional results were excellent to acceptable in 85.2%, whereas in 14.8% (n = 54), the result was unsatisfactory, the latter group presenting with concominant soft tissue injury. There was no statistically significant difference in infection and nonunion rates when comparing open and closed fractures.

CONCLUSION

: These results confirm that most patients with open metacarpal and phalangeal fractures can be treated by stable internal fixation.

Fixation of hand fractures with bicortical screws

PURPOSE

Traditionally a compression lag screw technique has been described when screw fixation alone is used to fix phalangeal or metacarpal fractures. The purpose of this retrospective case review was to determine whether there is any disadvantage to using a bicortical screw technique instead of the compression screw technique.

METHODS

Thirty-seven fractures of the phalanges and metacarpals in 36 patients had open reduction and internal fixation. Fixation was achieved with minifragment, self-tapping screws only, which were applied with bicortical fixation rather than a lag technique. Data were obtained through medical record and radiographic review. Intraoperative and immediate postoperative x-rays were compared with final x-rays. Fracture healing, confirmed radiographically, was used to determine whether the bicortical screw technique was adequate for fixation.

RESULTS

All fractures healed by an average of 7 weeks (range, 4-10 wk) without loss of fixation or malunion.

CONCLUSIONS

Based on this experience we believe bicortical fixation is a straightforward technique and provides adequate fracture stability and healing.

Rehabilitation for proximal phalangeal fractures

Proximal phalangeal fracture stability is crucial for the initiation of early and effective exercises designed to recover digital and especially proximal interphalangeal joint motion. Active digital flexion and extension exercises are implemented by synergistic wrist motion. Joint blocking exercises and active tendon gliding exercises in protective blocking splints are instrumental elements of early treatment. Dynamic splinting and serial finger casting are used in recalcitrant, severe, and late presenting cases. Surgical release is a last resort in regaining proximal interphalangeal joint motion. This measure is reserved for a failure of treatment when residual proximal interphalangeal joint contracture is persistent and severe enough to cause serious impairment of digital motion and hand function.

Effect of cutting flute design on cortical bone screw insertion torque and pullout strength

OBJECTIVE

To determine the effect of the number and length of cutting flutes on the insertion torque and pullout strength for self-tapping 4.5-millimeter cortical bone screws.

DESIGN

Screws were self-tapped in the diaphysis of human cadaver femurs. Each of the six screw types studied had different designs with varying cutting flute lengths and numbers. Bone mineral density, insertion torque, and pullout strength were measured.

SETTING

The study was conducted at an experimental biomechanics laboratory associated with a university medical center.

OUTCOME MEASUREMENTS

Insertion torque and pullout strength were normalized by the local bone mineral density.

RESULTS

The mean normalized insertion torque of the design with four full-length cutting flutes was less than the design with three full-length flutes and the two designs with one-third length flutes (p < 0.05). The mean normalized pullout strength of the screw with four full-length flutes was significantly greater than that of all screws with fewer than three flutes (p < 0.05).

CONCLUSIONS

Priorities for a cutting flute design should ideally include ease of screw insertion, minimal soft tissue irritation, and maximal screw holding power. Screws with more than two flutes were easier to insert and did not cause cortical damage during insertion. The screw with four full-length flutes showed a trend toward being the easiest to insert and having the greatest holding strength.