Headless compression screw fixation of scaphoid fractures

Finite Element Analysis of Postoperative Stability of Transverse Scaphoid Waist Fracture

Background and Purpose

Scaphoid waist fractures are often stabilised with compression screws, Kirschner wires (K-wires), or a combination of both. While clinical and bio-mechanical studies evaluating their utility are available, the ideal configuration of implant that would provide adequate stability to permit early use of the hand is debatable. We examined configurations of a single screw, one screw along with a K-wire, and two K-wires used for a transverse scaphoid waist fracture fixation aiming to assess the stability provided by each in the immediate postoperative period.

Methods

Computer-aided design (CAD) models of the scaphoid, K-wire, and headless compression screw were created. A transverse fracture was created at the scaphoid waist, and the CAD models of the screw and K-wire were used to fix the fracture in different configurations in a distal to proximal direction. Finite Element Analysis (FEA) was used to examine the strength of configurations when they were subjected to compression and distraction forces. The total maximum deformation (TDef) and factor of safety (FoS) for each configuration were calculated and used as indirect indicators of postoperative stability.

Results

When a single screw was used, the configurations with the screw directed posteriorly from either centre or anterior had the best combined TDef and FoS values. For one screw and one K-wire, the configuration with screw and K-wire parallel to each other with the screw located along the long axis in the AP projection and anterior to the K-wire in the lateral projection had the best combined TDef and FoS values. When using two K-wires, configurations with the two wires diverging proximally on the lateral projection had the best combined TDef and FoS values.

Conclusions

When fixing a transverse scaphoid waist fracture with a single screw, the screw directed posteriorly from either the centre or anterior aspect of the distal pole has the best stability, a parallel configuration has the best stability when fixing it using a screw and a K-wire, and divergent configuration has the best stability when fixing it with two K-wires only.

Biomechanical Comparison of Double 2.3-mm Headless Cannulated Self-Compression Screws and Single 3.5-mm Cortical Screw in Lag Fashion in a Canine Sacroiliac Luxation Model: A Small Dog Cadaveric Study

OBJECTIVE

 The aim of this study was to evaluate the feasibility of safe positioning of double 2.3-mm headless cannulated self-compression screws (HCS) in a small dog cadaveric sacroiliac luxation model and to compare the static rotational biomechanical properties of fixation repaired using two different screw systems with a minimally invasive osteosynthesis technique: double 2.3-mm HCS and a single 3.5-mm standard cortical screw placed in a lag fashion.

STUDY DESIGN

 A unilateral small dog sacroiliac luxation model was stabilized using double 2.3-mm HCS (n = 11) or a single 3.5-mm cortical screw (n = 11). Radiographic and computed tomography (CT) imaging analyses and biomechanical testing of rotational force on the sacroiliac joint of both fixations were performed. The maximum load at failure and failure modes of each fixation were recorded and compared.

RESULTS

 Fluoroscopically guided percutaneous application of double HCS was safe in a unilateral sacroiliac luxation model in small dogs without violation of the vertebral and ventral sacral foramen. Furthermore, resistance to rotational force applied on fixation of the sacroiliac joint repaired with double 2.3-mm HCS estimated by maximum failure load was significantly higher than that of a single 3.5-mm cortical screw (p < 0.001).

CONCLUSION

 Although this was an experimental cadaveric study, based on our results, the use of smaller double HCS may be beneficial as an alternative to the conventional single lag screw for stabilization of sacroiliac luxation in small dogs.

Evaluation of Cannulated Compression Headless Screw (CCHS) as an alternative implant in comparison to standard S1-S2 screw fixation of the posterior pelvis ring: a biomechanical study

BACKGROUND/PURPOSE

Posterior pelvis ring injuries represent typical high-energy trauma injuries in young adults. Joint stabilization with two cannulated sacroiliac (SI) screws at the level of sacral vertebrae S1 and S2 is a well-established procedure. However, high failure- and implant removal (IR) rates have been reported. Especially, the washer recovery can pose the most difficult part of the IR surgery, which is often associated with complications. The aim of this biomechanical study was to evaluate the stability of S1-S2 fixation of the SI joint using three different screw designs.

METHODS

Eighteen artificial hemi-pelvises were assigned to three groups (n = 6) for SI joint stabilization through S1 and S2 corridors using either two 7.5 mm cannulated compression headless screws (group CCH), two 7.3 mm partially threaded SI screws (group PT), or two 7.3 mm fully threaded SI screws (group FT). An SI joint dislocation injury type III APC according to the Young and Burgess classification was simulated before implantation. All specimens were biomechanically tested to failure in upright standing position under progressively increasing cyclic loading. Interfragmentary and bone-implant movements were captured via motion tracking and evaluated at four time points between 4000 and 7000 cycles.

RESULTS

Combined interfragmentary angular displacement movements in coronal and transverse plane between ilium and sacrum, evaluated over the measured four time points, were significantly bigger in group FT versus both groups CCH and PT, p ≤ 0.047. In addition, angular displacement of the screw axis within the ilium under consideration of both these planes was significantly bigger in group FT versus group PT, p = 0.038. However, no significant differences were observed among the groups for screw tip cutout movements in the sacrum, p = 0.321. Cycles to failure were highest in group PT (9885 ± 1712), followed by group CCH (9820 ± 597), and group FT (7202 ± 1087), being significantly lower in group FT compared to both groups CCH and PT, p ≤ 0.027.

CONCLUSION

From a biomechanical perspective, S1-S2 SI joint fixation using two cannulated compression headless screws or two partially threaded SI screws exhibited better interfragmentary stability compared to two fully threaded SI screws. The former can therefore be considered as a valid alternative to standard SI screw fixation in posterior pelvis ring injuries. In addition, partially threaded screw fixation was associated with less bone-implant movements versus fully threaded screw fixation. Further human cadaveric biomechanical studies with larger sample size should be initiated to understand better the potential of cannulated compression headless screw fixation for the therapy of the injured posterior pelvis ring in young trauma patients.

Surgical outcomes of scaphoid fracture osteosynthesis with magnesium screws

Objectives

This study aims to evaluate the mid-term functional and radiological outcomes of magnesium-based screws in the treatment of scaphoid fractures.

Patients and methods

Between February 2015 and February 2018, a total of 21 patients (18 males, 3 females; mean age: 28.5±5.8 years; range, 19 to 39 years) with acute scaphoid waist fractures who underwent fracture fixation with biologically degradable magnesium-based compression screws were retrospectively analyzed. Fractures were classified according to the Herbert and Fisher classification. The absence of pain on palpation and painless active range of motion were accepted as the signs of union.

Results

The mean follow-up was 43.3±5.3 (range, 36 to 52) months. According to the Herbert and Fisher classification, nine patients had type B1 and 12 patients had type B2 scaphoid fractures. Union was achieved in all cases. The mean time to union was 11.2±1.5 (range, 9 to 14) weeks. The mean grip strength, flexion, and extension were 43.57°, 73.57°, and 76.43°, respectively. The grip strength, pinch strength, and range of motion of the operated side were evaluated at the final follow-up visit and compared with the contralateral side (control group). No complication occurred. Any screw was not removed.

Conclusion

Magnesium-based compression screws can be safely used for acute scaphoid fractures considering their favorable functional and radiological results.

A Mechanical Comparison of the Compressive Force Generated by Various Headless Compression Screws and the Impact of Fracture Gap Size

Background: There is evidence that interfragmentary fracture gap size may affect the compression achievable with a modern headless compression screw (HCS). This mechanical study compared the compression achieved by 3 commercial HCS systems through various fracture gaps: CAPTIVATE Headless (Globus Medical, Inc, Audubon, Pennsylvania), Synthes (DePuy Synthes, Westchester, Pennsylvania), and Acumed Acutrak 2 (Acumed LLC, Hillsboro, Oregon). Methods: Screws were inserted into a custom test fixture composed of polyurethane synthetic bone foam fragments, separated by a layer of easily compressible polyurethane foam simulating a fracture gap. Compression was measured after final insertion and countersinking. The effect of the interfragmentary fracture gap size on the compression generated was also investigated. Results: The CAPTIVATE Headless 3.0 mm screw (70.1 ± 5.7 N) and the Synthes 3.0 mm screw (64.9 ± 7.3 N) achieved similar compressive forces after final countersink. Similar comparisons were found for the CAPTIVATE Headless 2.5 mm and Synthes 2.4 mm screws, and the CAPTIVATE Headless 4.0 mm and Acutrak 2 Standard screws. The final compression of the CAPTIVATE Headless 2.5 mm and Synthes 2.4 mm screws was not significantly affected when the fracture gap was doubled from 2 to 4 mm, but was reduced significantly by 95.9% with the Acutrak 2 Micro screw. Conclusion: When comparing like-sized screws, the CAPTIVATE, Synthes, and Acutrak 2 HCS systems demonstrated similar potential compressive forces. However, compared with the CAPTIVATE Headless and Synthes HCS systems, which are inserted with a compression sleeve that is not gap distance-dependent, the Acutrak 2 HCS system demonstrated less compression when the simulated fracture gap size was increased to 4 mm.

Mid-term follow-up of surgically treated and healed scaphoid fractures

The aim of this study was to evaluate the mid-term results of surgically treated scaphoid fractures since we were concerned that good results might deteriorate over time due to osteoarthritis or functional impairment. Thirty-three out of 121 surgically treated patients (isolated scaphoid fractures n = 23; scaphoid fractures with concomitant injuries n = 10) were evaluated retrospectively (47-138 months). Five patients (4%) had a non-union after internal fixation and were excluded because of additional treatment. The remaining 83 patients were not available for a follow-up examination. Patients with an isolated scaphoid fracture had a mean extension-flexion of 68°-0°-64°, a radial-ulnar deviation of 27°-0°-41° and a grip strength of 39 kg (corresponding to 87-98% of the uninjured contralateral wrist), while patients with concomitant injuries had a mean extension-flexion of 60°-0°-44°, radial-ulnar deviation of 22°-0°-38° and a grip strength of 42 kg (corresponding to 73-98% of the uninjured contralateral wrist). The Michigan Hand Questionnaire score was 85 and 75 and the Patient-Rated Wrist Evaluation score was 8 and 21, respectively. Fifteen patients had radiological signs of radiocarpal osteoarthritis with a significantly higher occurrence in those who had concomitant injuries compared to those with isolated scaphoid fractures (p < 0.01). There was no significant group difference in scaphotrapeziotrapezoid (STT) osteoarthritis (p = 0.968). One STT osteoarthritis case occurred after plate fixation, one after antegrade screw fixation and 10 after retrograde screw fixation. Surgical treatment of an acute isolated scaphoid fracture has excellent clinical, functional, and radiologic mid-term results, while scaphoid fractures with concomitant wrist injuries have slightly inferior results.

Measurement of Scaphoid Bone Microarchitecture: A Computed Tomography Imaging Study and Implications for Screw Placement

PURPOSE

High bone density and quality is associated with improved screw fixation in fracture fixation. The objective of this study was to assess bone density and quality in the proximal and distal scaphoid to determine optimum sites for placement of 2 screws in scaphoid fracture fixation.

METHODS

Twenty-nine cadaveric human scaphoid specimens were harvested and scanned using micro-computed tomography. Bone density (bone volume fraction) and bone quality (relative bone surface area, trabecular number, and trabecular thickness) were evaluated in 4 quadrants within each of the proximal and distal scaphoid.

RESULTS

The proximal radial quadrant of the scaphoid had significantly greater bone volume than the distal ulnar (mean difference, 33.2%) and distal volar quadrants (mean difference, 32.3%). There was a significantly greater trabecular number in the proximal radial quadrant than in the distal ulnar (mean difference, 16.7%) and in the distal volar quadrants (mean difference, 15.9%) and between the proximal ulnar and the distal ulnar quadrants (mean difference, 12%). There was a significantly greater bone surface area in the proximal radial and distal radial quadrants than in the distal ulnar and distal volar quadrants. There were no significant differences in trabecular thickness between the 8 analyzed quadrants CONCLUSIONS: Although there are differences in bone volume, trabecular number, and bone surface area between the proximal pole of the scaphoid and that of the distal pole, there were no significant differences in the bone quality (trabecular thickness, trabecular number, and relative bone surface area) and density (bone volume fraction) between the 4 quadrants of the proximal or distal pole of the cadaveric scaphoids studied.

CLINICAL RELEVANCE

Insertion of 2 headless compression screws can be determined by ease of surgical access and ease of screw positioning and not by differences in bone quality or density of the proximal or distal scaphoid.

Headless screw fixation through the dorsal rough surface for proximal-pole scaphoid-nonunion: a report of 15 patients

Clinical outcomes of the dorsal-retrograde headless screw-fixation technique in 15 patients with proximal scaphoid nonunion are presented. In this technique, screws are inserted from the dorsal rough surface of the scaphoid, located between the dorsal ridge and scaphoid-trapezium-trapezoid joint. Fifteen patients underwent osteosynthesis with this technique with iliac bone graft. Seven patients required primary surgery, and eight patients with a history of failed operation required revision surgery. Among 15 patients, 13 achieved union and two with persistent nonunion were asymptomatic with average follow-up of 24 months (range 14-57). Mean time to union was 20 weeks (range 12-40). Our experience with the dorsal-retrograde headless screw fixation technique has shown encouraging results for the treatment of proximal-scaphoid nonunion, especially in revision surgery wherein secure fixation of the small proximal fragments can be difficult using conventional anterograde techniques.Level of evidence: IV.

Scaphoid waist fractures fixation with staple. Retrospective study of a not widespread procedure

INTRODUCTION

In carpal scaphoid fractures, the surgical treatment with screw is considered the gold standard; shape memory staple however presents substantial advantages. The authors report a study on unstable fractures of the scaphoid waist (type B1, B2, B5, according to Herbert classification) treated with shape memory staple on a large sample of patients, with the aim to confirm the usefulness of this method, the quality of reduction and fixation, the functional results, the time of union and the possible complications.

MATERIALS AND METHODS

A retrospective analysis of 131 patients with scaphoid waist fractures with minimum follow-up 1 year was performed. Staples were used in all cases; technical details are discussed. Outcome measures were: postoperative pain, flexion-extension wrist range, hand grip strength, radiographic consolidation, work absence. Herbert and Fisher Grading System was used to assess subjective, objective and radiographic results.

RESULTS

Consolidation was achieved in all cases of primary fractures (0-30 days) within three months after surgery, and within eight months in all but two cases of delayed unions (operated within 6 months of the injury). Pain was absent at follow-up in 79% of cases, never severe or unbearable, the average flexion-extension range achieved was 112°. Handgrip strength values were comparable to those of contralateral wrist in 75% of cases. Mean time lost at work was 7.4 weeks. No algo-distrophy or malunion were observed. Discussion CONCLUSIONS: Scaphoid waist fractures' treatment with shape memory staple should be considered as an excellent alternative to screw fixation.

Effect of Screw Length and Geometry on Interfragmentary Compression in a Simulated Proximal Pole Scaphoid Fracture Model

Background: The objective of this study was to determine interfragmentary compression forces based on screw length and geometry for simulated proximal scaphoid fractures. Methods: Sixty-four foam model simulated fractures were stabilized with screws of various length (10 mm, 18 mm, 20 mm, or 24 mm) and geometry (central threadless or fully threaded) across a proximal fracture. Interfragmentary compression was measured at the simulated fracture site upon fixation. An independent sample t test and 1-way analysis of variance were performed to assess differences in interfragmentary compression. Results: Fixation utilizing a 10-mm screw generated significantly less interfragmentary compression than fixation utilizing a 20-mm or 24-mm screw. When accounting for both screw length and geometry, an 18-mm central threadless screw generated greater interfragmentary compression than a 20-mm and 24-mm fully threaded screw; there was no significant difference in compression between an 18-mm and 24-mm central threadless screw. Conclusions: The design of headless compression screws allows for maximal interfragmentary compression at the screw midpoint; we questioned whether a short screw centered on the fracture site resulted in superior compression to a longer, noncentered screw. Our data suggest that centering a small screw (10 mm) along a proximal fracture generates significantly less interfragmentary compression than a longer, noncentered screw. Our results demonstrate that balance between maximizing screw length and centering the screw on the fracture is vital toward maximizing interfragmentary compression for the fixation of proximal third scaphoid fractures.

Which Headless Compression Screw Produces the Highest Interfragmentary Compression Force in Scaphoid Fracture?

BACKGROUND

Interfragmentary compression at the fracture site facilitates healing. Headless compression screws used to treat scaphoid fractures can be grouped as shank screws, conical tapered screws and double component screws. There has been no meta-analysis of biomechanical studies to compare interfragmentary compression produced by the above screws.

METHODS

A computerised search of Pubmed, Embase and OVID database was undertaken to identify the studies. We estimated the weighted mean difference of interfragmentary compression (in Newton) with 95% confidence intervals. Random effects model was selected for meta-analysis.

RESULTS

The pooled estimate of nine studies demonstrated that conical tapered screw produced significantly higher interfragmentary compression force compared to the shank screw (WMD 19.96, 95% CI 11.2-28.8, p < 0.0001, I ² = 99%). The pooled estimate of four studies demonstrated that dual component screw produced significantly higher interfragmentary compression force compared to the shank screw (WMD 16.93, 95% CI 12.3-21.6, p < 0.0001, I ² = 97.7%). The pooled estimate of four studies showed that there was no significant difference in the interfragmentary compression force generated by either conical tapered screw or dual component screw (WMD 3.93, 95% CI - 8.3 to 16.2, p = 0.53, I ² = 99.7%). There was evidence of minimal publication bias.

CONCLUSION

Conical tapered screws and dual component screws produced statistically significant higher interfragmentary compression force at the scaphoid fracture site compared to shank screws. There was no difference in the compression force generated by either conical tapered screw or dual component screw.

Impact of Screw Length on Proximal Scaphoid Fracture Biomechanics

Background  Proximal scaphoid fractures display high nonunion rates and increased revision cases. Waist fracture fixation involves maximizing screw length within the cortex; however, the optimal screw length for proximal scaphoid fractures remains unknown. Purpose  The main purpose of this article is to compare stiffness and ultimate load for proximal scaphoid fracture fixation of various headless compression screw lengths. Methods  Eighteen scaphoids underwent an osteotomy simulating a 7 mm oblique proximal fracture. Screws of three lengths (10, 18, and 24 mm) were randomly assigned for fixation. Each specimen underwent cyclic loading with stiffness calculated during the last loading cycle. Specimens that withstood cyclic loading were loaded to failure. Results  No significant difference in stiffness between screw lengths was found. Ultimate load was significantly impacted by the screw length. A significant difference in ultimate load between a 10 and 24 mm screw was found; however, no significant difference occurred in ultimate load between an 18 and 24 mm screw. Conclusions  No significant difference in stiffness between all groups could be due to similarities in purchase in the proximal aspect. The 10 mm screw withstanding less ultimate load compared to the 24 mm screw could be due to the 10 mm screw gaining less purchase on either side of the fracture site compared to the 24 mm screw. Lack of significant difference in ultimate load between the 18 and 24 mm screw could be occurring because the fracture site is closer to the 18 mm screw midpoint, as distal threads are engaged closer to the fracture. Clinical Relevance  Maximizing screw length may not provide superior fixation biomechanically compared with fixation utilizing a 6 mm shorter screw for proximal scaphoid fractures.

Partially threaded headless screw may benefit adequate interfragmentary compression and reduced driving torque for small bone fixation

Headless compression screws (HCSs) are commonly used to fixate small bones and articular fractures. Understanding the biomechanical efficacy of different HCS designs can help surgeons make proper interfragmentary compression when a specific implant is chosen. HCSs with three different central shaft designs (unthreaded, fully threaded, and partially threaded) were studied: the Herbert-Whipple, Mini-Acutrak 2, and headless reduction (HLR). Polyurethane foam blocks were machined with a simulated fracture gap of 0.5 mm and set onto a custom-made jig to simultaneously measure compression force and driving torque during screw insertion. The maximal achievable compression forces and driving torques recorded were 47.4 ± 0.9 N and 145.11 ± 1.65 N mm for the HLR, 50.98 ± 1.29 N and 152.62 ± 2.83 N mm for the Mini-Acutrak 2, and 19.33 ± 1.0 N and 33.4 ± 2.2 N mm for the Herbert-Whipple. Overall, the compression force of the Mini-Acutrak 2 and HLR increased with the torque. Unlike the other screws, the Herbert-Whipple's driving torque increased while the compression force decreased after peak compression force was achieved. The partially threaded shaft design (HLR) demonstrated equivalent biomechanical advantage with the Mini-Acutrak 2 in interfragmentary compression. The HCSs with cone-shaped proximal ends (HLR and Mini-Acutrak 2) maintained their compression force during over-fastening, whereas the unthreaded central shaft of the Herbert-Whipple screw caused it to lose compression force.

[Diagnostics and treatment of acute scaphoid fractures]

BACKGROUND

Fractures of the scaphoid bone are common but can easily be overlooked in standard X‑rays. Inadequate diagnostics and therefore inappropriate treatment of scaphoid fractures often leads to problems in healing with formation of non-union and painful osteoarthritis of the wrist.

OBJECTIVE

This review summarizes the current practical recommendations in the diagnostics and treatment of acute scaphoid fractures.

METHODS

An analysis and review of selected literature including the current S3 guidelines were performed.

RESULTS

The main statements are that in cases of a clinically suspected scaphoid fracture, staged diagnostics including radiographs, computed tomography (CT) and when necessary magnetic resonance imaging (MRI) should be applied to confirm or exclude a fracture. Further treatment in the case of a fracture is planned according to a CT-based classification. There are fracture types that can be treated either conservatively or operatively and there are other fracture types that always require operative fixation. The operative technique depends on the exact fracture geometry. For osteosynthesis, cannulated headless compression screws are mostly used.

Interfragmentary Compression Forces Vary Based on Scaphoid Bone Screw Type and Fracture Location

BACKGROUND

The objective of this study was to determine the interfragmentary compression forces generated in a foam model as a function of headless compression screw type (fully threaded and central threadless) and fracture location.

METHODS

Eighty-eight polyurethane foam models were fixed across a simulated transverse fracture with either a fully threaded screw or a central threadless screw. The location of the transverse fracture varied along the length of the foam model in 2 mm increments for 11 fracture locations. The force generated at the fracture site upon fixation was utilized to determine the interfragmentary compression. Interfragmentary compression was compared using a paired t test and 2-way analysis of variance, with significance set at P < .05.

RESULTS

Interfragmentary compression was found to vary based on fracture location and screw type. The fully threaded screw generated significantly greater compression for fracture locations at 12 mm and 18 mm from the top edge of the foam model, while the central threadless screw generated significantly greater compression for fractures located 2 mm from the top edge of the foam model.

CONCLUSIONS

The central threadless screw and the fully threaded screw had different fracture locations where maximum compression force occurred. The fully threaded screw generated greater compression force toward the screw center due to greater thread purchase. However, the central threadless screw generated greater compression at the most proximal fracture location due to its greater thread pitch toward the screw head. Maximizing interfragmentary compression may aid in reducing nonunion rates associated with the internal fixation of proximal scaphoid fractures.

A comparative study of the effect of drilling depth on generation of compressive force by headless compression screws using conical and cylindrical type of drill bit

Background

This study was conducted to measure the effect of different drilling depths on compression forces generated by two commonly used headless compression screws using the two different types of drill bit, the Acutrak® mini (conical type drill bit) and the Synthes 3.0 HCS® (cylindrical type drill bit).

Methods

A load cell was placed between two Sawbone blocks, which were 12 mm and 40 mm in thickness, respectively. After placing the guide pin into the center of the block, the drilling depth of the Acutrak® mini and Synthes HCS® screws ranged from 16 to 28 mm and 22 to 28 mm, respectively. The 24-mm screws were inserted and the compression force was measured immediately and at 30 min post-insertion.

Results

The Acutrak® mini generated greater compression force compared to the Synthes 3.0 HCS® when drilled to a depth of less than 24 mm. The compression force of the Acutrak® mini showed a strong inverse correlation with the drilling depth. There was no significant inverse correlation observed between the compression force of the Synthes HCS® and the drilling depth.

Conclusions

If the screw length and the drill depth are the same, the Synthes 3.0 HCS® (cylindrical type drill bit) is safer and easier to use as it has no change in the compression force even when over-drilling because the compression force of the two screws is similar. As for the Acutrak® mini (conical type drill bit), while it is technically demanding due to varying compression force according to the drill depth, it can be used in certain cases because it can give stronger compression force through under-drilling.

Micro Screw Fixation for Small Proximal Pole Scaphoid Fractures with Distal Radius Bone Graft

Background  Achieving adequate fixation and healing of small proximal pole acute scaphoid fractures can be surgically challenging due to both fragment size and tenuous vascularity. Purpose  The purpose of this study was to demonstrate that this injury can be managed successfully with osteosynthesis using a "micro" small diameter compression screw with distal radius bone graft with leading and trailing screw threads less than 2.8 mm. Patients and Methods  Patients with proximal pole scaphoid fragments comprising less than 20% of the entire scaphoid were included. Fixation was accomplished from a dorsal approach with a micro headless compression screw and distal radius bone graft. Six patients were included. Average follow-up was 44 months (range, 11-92). Results  Mean proximal pole fragment size was 14% (range, 9-18%) of the entire scaphoid. The mean immobilization time was 6 weeks, time-to-union of 6 weeks, and final flexion/extension arc of 88°/87°. All patients had a successful union, and no patient had deterioration in range of motion, avascular necrosis, or fragmentation of the proximal pole. Conclusion  Small diameter screws with a maximal thread diameter of ≤ 2.8 mm can be used to fix the union of proximal pole acute scaphoid fractures comprising less than 20% of the total area with good success. Level of Evidence  Therapeutic case series, Level IV.

Headless compression screw for horizontal medial malleolus fractures

BACKGROUND

Horizontal medial malleolus fractures are caused by the application of rotational force through the ankle joint in several orientations. Multiple techniques are available for the fixation of medial malleolar fractures.

METHODS

Horizontal medial malleolus osteotomies were performed in eighteen synthetic distal tibiae and randomized into two fixation groups: 1) two parallel unicortical cancellous screws or 2) two Acutrak 2 headless compression screws. Specimens were subjected to offset axial tension loading. Frontal plane interfragmentary motion was monitored.

FINDINGS

The headless compression group (1699 (SD 947) N/mm) had significantly greater proximal-distal stiffness than the unicortical group (668 (SD 298) N/mm), (P = 0.012). Similarly, the headless compression group (604 (SD 148) N/mm) had significantly greater medial-lateral stiffness than the unicortical group (281 (SD 152) N/mm), (P < 0.001). The force at 2 mm of lateral displacement was significantly greater in the headless compression group (955 (SD 79) N) compared to the unicortical group (679 (SD 198) N), (P = 0.003). At 2 mm of distal displacement, the mean force was higher in the headless compression group (1037 (SD 122) N) compared to the unicortical group (729 (SD 229) N), but the difference was not significant (P = 0.131).

INTERPRETATION

A headless compression screw construct was significantly stiffer in both the proximal-distal and medial-lateral directions, indicating greater resistance to both axial and shear loading. Additionally, they had significantly greater load at clinical failure based on lateral displacement. The low-profile design of the headless compression screw minimizes soft tissue irritation and reduces need for implant removal.

Fracture Gap Reduction With Variable-Pitch Headless Screws

PURPOSE

Fully threaded, variable-pitch, headless screws are used in many settings in surgery and have been extensively studied in this context, especially in regard to scaphoid fractures. However, it is not well understood how screw parameters such as diameter, length, and pitch variation, as well as technique parameters such as depth of drilling, affect gap closure.

METHODS

Acutrak 2 fully threaded variable-pitch headless screws of various diameters (Standard, Mini, and Micro) and lengths (16-28 mm) were inserted into polyurethane blocks of "normal" and "osteoporotic" bone model densities using a custom jig. Three drilling techniques (drill only through first block, 4 mm into second block, or completely through both blocks) were used. During screw insertion, fluoroscopic images were taken and later analyzed to measure gap reduction. The effect of backing the screw out after compression was evaluated.

RESULTS

Drilling at least 4 mm past the fracture site reduces distal fragment push-off compared with drilling only through the proximal fragment. There were no significant differences in gap closure in the normal versus the osteoporotic model. The Micro screw had a smaller gap closure than both the Standard and the Mini screws. After block contact and compression with 2 subsequent full forward turns, backing the screw out by only 1 full turn resulted in gapping between the blocks.

CONCLUSIONS

Intuitively, fully threaded headless variable-pitch screws can obtain compression between bone fragments only if the initial gap is less than the gap closed. Gap closure may be affected by drilling technique, screw size, and screw length. Fragment compression may be immediately lost if the screw is reversed.

CLINICAL RELEVANCE

We describe characteristics of variable-pitch headless screws that may assist the surgeon in screw choice and method of use.

Effects of Removal and Reinsertion of Headless Compression Screws

PURPOSE

This study investigates the loss of compression when 3 commonly used headless compression screws are backed out (reversed), and assesses the ability to re-establish compression with screws of greater diameter.

METHODS

Two investigators tested 3 screw designs (Acutrak 2, Synthes HCS, Medartis SpeedTip CCS) in 2 diameters and lengths. Each design had 10 test cycles in a polyurethane foam bone model with compression recorded using a washer load cell. A 28-mm screw of the narrower diameter was inserted until 2 mm recessed and then reversed 30°, 60°, 90°, 180°, 270°, 360°, and 720°. After this the screw was removed completely and a 24-mm screw of greater diameter inserted until recessed 2 mm with the compressive force again recorded.

RESULTS

All screws showed an immediate, statistically significant loss of compression at 30° of reversing. The Acutrak 2 Micro screw demonstrated not only the greatest mean compressive force, but also the fastest compressive loss. Insertion of the shorter screw of greater diameter was associated with re-establishment of compression to levels comparable with the original screw.

CONCLUSIONS

This study reaffirms the importance of establishing the correct screw length before insertion due to the immediate loss of compression with reversal of these devices.

CLINICAL RELEVANCE

If a headless compression screw penetrates the far joint surface, the screw should be completely removed and replaced with a shorter screw of greater diameter.

Effect of interfragmentary gap on compression force in a headless compression screw used for scaphoid fixation

We investigated the effect of an interfragmentary gap on the final compression force using the Acutrak 2 Mini headless compression screw (length 26 mm) (Acumed, Hillsboro, OR, USA). Two blocks of solid rigid polyurethane foam in a custom jig were separated by spacers of varying thickness (1.0, 1.5, 2.0 and 2.5 mm) to simulate an interfragmentary gap. The spacers were removed before full insertion of the screw and the compression force was measured when the screw was buried 2 mm below the surface of the upper block. Gaps of 1.5 mm and 2.0 mm resulted in significantly decreased compression forces, whereas there was no significant decrease in compression force with a gap of 1 mm. An interfragmentary gap of 2.5 mm did not result in any contact between blocks. We conclude that an increased interfragmentary gap leads to decreased compression force with this screw, which may have implications on fracture healing.

Effect of Screw Perpendicularity on Compression in Scaphoid Waist Fractures

Background  Central and perpendicular (PERP) screw orientations have each been described for scaphoid fracture fixation. It is unclear, however, which orientation produces greater compression. Questions/Purposes  This study compares compression in scaphoid waist fractures with screw fixation in both PERP and pole-to-pole (PTP) configurations. PERP orientation was hypothesized to produce greater compression than PTP orientation. Methods  Ten preoperative computed tomography scans of scaphoid waist fractures were classified by fracture type and orientation in the coronal and sagittal planes. Three-dimensional models of each scaphoid and fracture plane were created. Simulated Acutrak 2 (Acumed, Hillsboro, OR) screws were placed into the models in both PERP and PTP orientations. Engagement length and screw angle relative to the fracture were measured. Compression strength was calculated from the shear area, average density, and angle acuity. Results  The PTP angle between screw and fracture ranged from 36 to 84 degrees. By definition, the PERP screw-to-fracture angle was 90 degrees. Perpendicularity of the PTP screw to the fracture was positively correlated to compression strength. PERP screws had greater compression than PTP screws when the PTP screw-to-fracture angle was < 80 degrees (106 vs. 80 N), but there was no difference in compression when the PTP screw-to-fracture angle was > 80 degrees, approximating the PERP screw. Conclusion  Increasing screw perpendicularity resulted in higher compression when the screw-to-fracture angle of the PTP screw was < 80 degrees. Maximum compression was obtained with a screw PERP to the fracture. The increased compression gained from PERP screw placement offsets the decreased engagement length. Clinical Relevance  These results provide guidelines for optimal screw placement in scaphoid waist fractures.

Surgical Treatment of Symptomatic Congenital Type I Lunotriquetral Coalition: Technique and a Report of 4 Cases

Lunotriquetral (LT) synchondrosis is an uncommon variant of congenital LT coalition. Unlike complete LT fusions, this incomplete pseudoarthrosis-like coalition can become symptomatic. Surgical LT arthrodesis is a described treatment for this variant of LT coalition (Minnaar type I). We report 4 patients who underwent LT fusion with a second-generation headless compression screw and distal radius cancellous autograft. Fusion was achieved in all cases at an average of 2.5 months postoperatively. All the patients were satisfied with complete pain relief in 2 patients and minimal pain in 2 patients, and all improved their range of motion. We recommend this procedure, and report the techniques for this limited wrist arthrodesis as treatment for the symptomatic LT synchondrosis.

Tibiotalocalcaneal arthrodesis with headless compression screws

Background

Tibiotalocalcaneal arthrodesis with headless compression screws has not been previously reported. We hypothesized that these screws could be suitable for tibiotalocalcaneal arthrodesis because of their special design. This study aimed to evaluate the clinical outcomes of patients undergoing tibiotalocalcaneal arthrodesis with headless compression screws for the treatment of severe arthropathy of the ankle and subtalar joint.

Methods

From 2010 to 2015, 23 patients with severe ankle and subtalar arthropathy underwent tibiotalocalcaneal arthrodesis. All surgeries were completed by a senior surgeon in the same hospital. These patients were 18~76 years (mean 54.6 years) old; the duration of their disease was 9~38 months (mean 13.2 months). The study population included 12 males and 11 females; 12 patients underwent surgery on the left and 11 on the right. Indications for surgery included avascular necrosis of the talus (n = 14), severe posttraumatic arthritis (n = 4), osteoarthritis (n = 2), terminal tuberculous arthritis (n = 1), rheumatoid arthritis (n = 1) and Charcot neuroarthropathy (n = 1). A lateral oblique incision was performed to expose the subtalar joint, and an anteromedial longitudinal incision was used to expose the ankle joint. After the articular surfaces were removed, the tibia, talus and calcaneus were carefully aligned and fixed with two headless compression screws. Patients were followed up at 6 weeks and 3, 6 and 9 months after surgery; they were evaluated by Roles and Maudsley patient satisfaction scores, the American Orthopaedic Foot & Ankle Society (AOFAS) Ankle-Hindfoot Score, visual analogue scale (VAS) score and radiographic evaluation.

Results

Seventeen patients were studied, with a mean follow-up time of 6.5 months (range 5–24). The mean Roles and Maudsley patient satisfaction score was 1.41 at the last follow-up; most of the patients were satisfied with the surgery results. The mean preoperative AOFAS Ankle-Hindfoot Score was 29.6 (range 18–37), while the mean last follow-up AOFAS Ankle-Hindfoot Score was 68.5 (range 61–80). The VAS score for preoperative functional pain was 6.95 (range 3–10) compared to 1.56 (range 0–3) postoperatively (P < 0.001). The mean surgical duration was 57 (range 42–125) min. The mean time to union was 3.8 months (range 3–12 months); fusion of the ankle and subtalar joint was successful in all patients. One patient experienced delayed wound healing.

Conclusions

Tibiotalocalcaneal arthrodesis with headless compression screws for the treatment of severe arthropathy of the ankle and subtalar joint is an effective treatment that is minimally invasive and is associated with a short operation time, high fusion rate, low incidence of complications and good postoperative recovery.

An Unexpected Complication after Headless Compression Screw Fixation of an Osteochondral Fracture of Patella

This study evaluated complications associated with implant depth in headless compression screw treatment of an osteochondral fracture associated with a traumatic patellar dislocation in a 21-year-old woman. Computed tomography and X-rays showed one lateral fracture fragment measuring 25 × 16 mm. Osteosynthesis was performed with two headless compression screws. Five months later, the screws were removed because of patella-femoral implant friction. We recommend that the screw heads be embedded to a depth of at least 3 mm below the cartilage surface. Further clinical studies need to examine the variation in cartilage thickness in the fracture fragment.

Mechanical Evaluation of Four Internal Fixation Constructs for Scaphoid Fractures

BACKGROUND

The objective of this study was to compare the mechanical performance of 4 different constructs for fixation of oblique scaphoid fractures.

METHODS

Twenty-eight synthetic scaphoids underwent an oblique osteotomy along the dorsal sulcus. Each was randomly assigned to fixation by 1 of 4 methods: two 1.5-mm headless compression screws, one 2.2-mm screw, one 3-mm screw, or a 1.5-mm volar variable-angle plate. After fixation, scaphoids were potted at a 45° angle and loaded at the distal pole by a hydraulically driven mechanical testing system plunger until the fixation failed. Excursion and load were measured with a differential transformer and load cell, respectively. From these data, the stiffness, load-to-failure, and maximum displacement of each construct were calculated.

RESULTS

The 2.2-mm screw demonstrated the highest stiffness and the two 1.5-mm screws had the lowest. However, there were no significant differences among the fixation methods in terms of stiffness. Both 2.2- and 3-mm screw constructs had significantly higher loads-to-failure than two 1.5-mm screws. The maximum load for the plate approached, but did not achieve, statistical significance compared with the 1.5-mm screws. There was no significant difference among constructs in displacement.

CONCLUSIONS

All constructs demonstrated similar mechanical properties that may provide sufficient stability for effective clinical use. Given their significantly higher loads-to-failure, a 2.2- or 3-mm screw may be superior to two 1.5-mm screws for fixation of unstable scaphoid fractures. The volar plate did not have superior mechanical characteristics to the compression screws.

Computed tomography versus magnetic resonance imaging versus bone scintigraphy for clinically suspected scaphoid fractures in patients with negative plain radiographs

BACKGROUND

In clinically suspected scaphoid fractures, early diagnosis reduces the risk of non-union and minimises loss in productivity resulting from unnecessary cast immobilisation. Since initial radiographs do not exclude the possibility of a fracture, additional imaging is needed. Computed tomography (CT), magnetic resonance imaging (MRI) and bone scintigraphy (BS) are widely used to establish a definitive diagnosis, but there is uncertainty about the most appropriate method.

OBJECTIVES

The primary aim of this study is to identify the most suitable diagnostic imaging strategy for identifying clinically suspected fractures of the scaphoid bone in patients with normal radiographs. Therefore we looked at the diagnostic performance characteristics of the most used imaging modalities for this purpose: computed tomography, magnetic resonance imaging and bone scintigraphy.

SEARCH METHODS

In July 2012, we searched the Cochrane Register of Diagnostic Test Accuracy Studies, MEDLINE, EMBASE, the Database of Abstracts of Reviews of Effects, the Cochrane Central Register of Controlled Trials, the NHS Economic Evaluation Database. In September 2012, we searched MEDION, ARIF, Current Controlled Trials, the World Health Organization (WHO) International Clinical Trials Registry Platform, conference proceedings and reference lists of all articles.

SELECTION CRITERIA

We included all prospective or retrospective studies involving a consecutive series of patients of all ages that evaluated the accuracy of BS, CT or MRI, or any combination of these, for diagnosing suspected scaphoid fractures. We considered the use of one or two index tests or six-week follow-up radiographs as adequate reference standards.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened titles and abstracts and assessed full-text reports of potentially eligible studies. The same authors extracted data from full-text reports and assessed methodological quality using the QUADAS checklist. For each index test, estimates of sensitivity and specificity from each study were plotted in ROC space; and forest plots were constructed for visual examination of variation in test accuracy. We performed meta-analyses using the HSROC model to produce summary estimates of sensitivity and specificity.

MAIN RESULTS

We included 11 studies that looked at diagnostic accuracy of one or two index tests: four studies (277 suspected fractures) looked at CT, five studies (221 suspected fractures) looked at MRI and six studies (543 suspected fractures) looked at BS. Four of the studies made direct comparisons: two studies compared CT and MRI, one study compared CT and BS, and one study compared MRI and BS. Overall, the studies were of moderate to good quality, but relevant clinical information during evaluation of CT, MRI or BS was mostly unclear or unavailable.As few studies made direct comparisons between tests with the same participants, our results are based on data from indirect comparisons, which means that these results are more susceptible to bias due to confounding. Nonetheless, the direct comparisons showed similar patterns of differences in sensitivity and specificity as for the pooled indirect comparisons.Summary sensitivity and specificity of CT were 0.72 (95% confidence interval (CI) 0.36 to 0.92) and 0.99 (95% CI 0.71 to 1.00); for MRI, these were 0.88 (95% CI 0.64 to 0.97) and 1.00 (95% CI 0.38 to 1.00); for BS, these were 0.99 (95% CI 0.69 to 1.00) and 0.86 (95% CI 0.73 to 0.94). Indirect comparisons suggest that diagnostic accuracy of BS was significantly higher than CT and MRI; and CT and MRI have comparable diagnostic accuracy. The low prevalence of a true fracture among suspected fractures (median = 20%) means the lower specificity for BS is problematic. For example, in a cohort of 1000 patients, 112 will be over-treated when BS is used for diagnosis. If CT is used, only 8 will receive unnecessary treatment. In terms of missed fractures, BS will miss 2 fractures and CT will miss 56 fractures.

AUTHORS' CONCLUSIONS

Although quality of the included studies is moderate to good, findings are based on only 11 studies and the confidence intervals for the summary estimates are wide for all three tests. Well-designed direct comparison studies including CT, MRI and BS could give valuable additional information.Bone scintigraphy is statistically the best diagnostic modality to establish a definitive diagnosis in clinically suspected fractures when radiographs appear normal. However, physicians must keep in mind that BS is more invasive than the other modalities, with safety issues due to level of radiation exposure, as well as diagnostic delay of at least 72 hours. The number of overtreated patients is substantially lower with CT and MRI.Prior to performing comparative studies, there is a need to raise the initially detected prevalence of true fractures in order to reduce the effect of the relatively low specificity in daily practice. This can be achieved by improving clinical evaluation and initial radiographical assessment.

Metallic artifacts from internal scaphoid fracture fixation screws: comparison between C-arm flat-panel, cone-beam, and multidetector computed tomography

OBJECTIVES

The aim of this study was to compare image quality and extent of artifacts from scaphoid fracture fixation screws using different computed tomography (CT) modalities and radiation dose protocols.

MATERIALS AND METHODS

Imaging of 6 cadaveric wrists with artificial scaphoid fractures and different fixation screws was performed in 2 screw positions (45° and 90° orientation in relation to the x/y-axis) using multidetector CT (MDCT) and 2 flat-panel CT modalities, C-arm flat-panel CT (FPCT) and cone-beam CT (CBCT), the latter 2 with low and standard radiation dose protocols. Mean cartilage attenuation and metal artifact-induced absolute Hounsfield unit changes (= artifact extent) were measured. Two independent radiologists evaluated different image quality criteria using a 5-point Likert-scale. Interreader agreements (Cohen κ) were calculated. Mean absolute Hounsfield unit changes and quality ratings were compared using Friedman and Wilcoxon signed-rank tests.

RESULTS

Artifact extent was significantly smaller for MDCT and standard-dose FPCT compared with CBCT low- and standard-dose acquisitions (all P < 0.05). No significant differences in artifact extent among different screw types and scanning positions were noted (P > 0.05). Both MDCT and FPCT standard-dose protocols showed equal ratings for screw bone interface, fracture line, and trabecular bone evaluation (P = 0.06, 0.2, and 0.2, respectively) and performed significantly better than FPCT low- and CBCT low- and standard-dose acquisitions (all P < 0.05). Good interreader agreement was found for image quality comparisons (Cohen κ = 0.76-0.78).

CONCLUSIONS

Both MDCT and FPCT standard-dose acquisition showed comparatively less metal-induced artifacts and better overall image quality compared with FPCT low-dose and both CBCT acquisitions. Flat-panel CT may provide sufficient image quality to serve as a versatile CT alternative for postoperative imaging of internally fixated wrist fractures.

Nuts and bolts: dimensions of commonly utilized screws in upper extremity surgery

A plethora of screw designs and sizes are available from multiple companies for use in upper extremity surgery. Knowing the dimensions of screws is critical in the treatment of bone of varying dimensions for fractures, osteotomies, or arthrodeses. Although many screws are named by their major thread diameter, this is not always true. Because of this confusing nomenclature and vast number of options, we sought to review the most commonly used screws and codify their dimensions into a readily available article and reference chart. This article highlights the basic dimensions of commonly used headless screws, stand-alone lag screws, non-locking and locking screws for plating, and biocomposite screws. Commonly described treatments using these screws include fixation of elbow, wrist, carpal, metacarpal, and phalangeal fractures and osteotomies, as well as arthrodeses of upper extremity joints. This article and its tables are by no means exhaustive of all commercially available implants. The focus is on the most commonly used implants in the United States as of 2014.

Headless bone screw fixation for combined volar lunate facet distal radius fracture and capitate fracture: case report

We report a case of concomitant fractures of the volar lunate facet of the distal radius and capitate body. Surgical fixation was achieved with open reduction internal fixation using headless compression screws for both fractures. Because of the nature of complications seen after both operative and nonsurgical management, these fractures warrant particular attention.

Scaphoid nonunions treated with 2 headless compression screws and bone grafting

PURPOSE

To evaluate union and complication rates associated with the use of 2 headless compression screws and bone grafting for the treatment of scaphoid nonunions.

METHODS

A total of 19 patients (18 male and 1 female) at an average age of 21 years were treated with open reduction and internal fixation with 2 cannulated, headless, compression screws for scaphoid nonunions. Bone grafting techniques included corticocancellous autograft from the iliac crest in 14 patients, capsular-based vascularized distal radius graft in 3, and medial femoral condyle free vascularized bone graft in 2. Patients were treated an average 19 months after the injury. Fracture nonunions were at the waist (n = 12), proximal third (n = 5), or distal third (n = 2) of the scaphoid. Dorsal (n = 7) and volar (n = 12) surgical approaches were used.

RESULTS

All fractures had clinical and radiographic evidence of bone union at an average of 3.6 months. Postoperative computed tomography scans were available in 13 patients and showed union without evidence of screw penetration of the scaphoid cortex. No complications occurred in this series, and no revision procedures have been necessary.

CONCLUSIONS

Our results indicate that the use of 2 headless compression screws for the treatment of scaphoid nonunions is safe and effective. A variety of bone grafting techniques can be used with this technique. The use of 2 compression screws may provide superior biomechanical stability and ultimately improve outcomes measured with future long-term comparative studies.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Insertion profiles of 4 headless compression screws

PURPOSE

In practice, the surgeon must rely on screw position (insertion depth) and tactile feedback from the screwdriver (insertion torque) to gauge compression. In this study, we identified the relationship between interfragmentary compression and these 2 factors.

METHODS

The Acutrak Standard, Acutrak Mini, Synthes 3.0, and Herbert-Whipple implants were tested using a polyurethane foam scaphoid model. A specialized testing jig simultaneously measured compression force, insertion torque, and insertion depth at half-screw-turn intervals until failure occurred.

RESULTS

The peak compression occurs at an insertion depth of -3.1 mm, -2.8 mm, 0.9 mm, and 1.5 mm for the Acutrak Mini, Acutrak Standard, Herbert-Whipple, and Synthes screws respectively (insertion depth is positive when the screw is proud above the bone and negative when buried). The compression and insertion torque at a depth of -2 mm were found to be 113 ± 18 N and 0.348 ± 0.052 Nm for the Acutrak Standard, 104 ± 15 N and 0.175 ± 0.008 Nm for the Acutrak Mini, 78 ± 9 N and 0.245 ± 0.006 Nm for the Herbert-Whipple, and 67 ± 2N, 0.233 ± 0.010 Nm for the Synthes headless compression screws.

CONCLUSIONS

All 4 screws generated a sizable amount of compression (> 60 N) over a wide range of insertion depths. The compression at the commonly recommended insertion depth of -2 mm was not significantly different between screws; thus, implant selection should not be based on compression profile alone. Conically shaped screws (Acutrak) generated their peak compression when they were fully buried in the foam whereas the shanked screws (Synthes and Herbert-Whipple) reached peak compression before they were fully inserted. Because insertion torque correlated poorly with compression, surgeons should avoid using tactile judgment of torque as a proxy for compression.

CLINICAL RELEVANCE

Knowledge of the insertion profile may improve our understanding of the implants, provide a better basis for comparing screws, and enable the surgeon to optimize compression.

Early results of a new implant: 3.0 mm headless compression screw for scaphoid fracture fixation

There has been a considerable evolution of screws used for internal fixation of scaphoid fractures. We discuss here, early results of a recently introduced implant Synthes 3.0 mm headless compression screw used for scaphoid fracture fixation. Twenty eight patients with scaphoid fractures (five acute and 23 nonunions) were treated with internal fixation by this non-variable pitch screw over a period of 18 months. All nonunions had pedicle vascularized bone grafting. All five patients with acute scaphoid fracture fixation had radiological healing at a mean of 8 weeks. Fifteen of 23 scaphoid fracture nonunions showed definite signs and a further seven showed probable signs of radiological healing at a mean of 8 months. One nonunion has failed to unite after surgery.

Biomechanical analysis of second-generation headless compression screws

INTRODUCTION

Headless Compression Screws (HCS) are commonly utilized for the fixation of small bone and articular fractures. Recently several new second generation HCS (SG-HCS) have been introduced with the purported benefits of improved biomechanical characteristics. We sought to determine and compare the biomechanical efficiencies of these screws.

MATERIAL AND METHODS

Five HCS including four second generation (Mini-Acutrak 2 (Acumed), Twinfix (Stryker), Kompressor Mini (Integra), HCS 3.0 (Synthes)) and one first generation (Herbert-Whipple) were studied. Polyurethane foam blocks that represented osteoporotic cancellous bone (0.16 g/cc) with a simulated transverse fracture at the waist were utilized and five screws of each brand were tested for the generated compression force and fastening torque during insertion with and without pre-drilling.

RESULTS

The generated compression force was highest for Mini-Acutrak 2 (45.41 ± 0.88 N) and lowest for Herbert-Whipple (13.44 ± 2.35 N) and forces of Twinfix, Kompressor Mini, HCS 3.0 were in between in descending order. The compression force of SG-HCS increased slightly without pre-drilling but it was not statistically significant while the fastening torque increased significantly. Slight over-fastening beyond the recommended stage significantly reduced the compression force in Twinfix and Kompressor and had no or moderate effect in other screws.

CONCLUSION

All SG-HCS demonstrated greater biomechanical characteristics than the first generation Herbert-Whipple screw. The Mini-Acutrak 2 with a variable pitch design generated the maximum compression force and showed the most reliability and sustainability. Screws with independently rotating trailing heads (Twinfix and Kompressor Mini) demonstrated loss of compression with extra turns. The increase of fastening torque due to over-fastening and loss of compression at the same time in some screw designs, demonstrated how the fastening torque (applied by the surgeon) can be a misleading measure of the compression force. Application of SG-HCS in osteoporotic bone without pre-drilling can slightly increase the compression force.