Optimal fixation of acute scaphoid fractures: finite element analysis

Comparative Biomechanical Study of Fragment-Specific Plates and Headless Screws for Radial Styloid and Lunate Facet Fixation in Distal Radius Fracture Evaluated in a Synthetic Composite

PURPOSE

To evaluate the compressive stiffness (ability to resist compression under an applied load) of fragment-specific plate and headless screw fixation for radial styloid and volar lunate facet fractures in a synthetic composite distal radius.

METHODS

A simulated radial styloid fracture (AO type B1.1) and simulated volar lunate facet fracture (AO type B3.3) were created in synthetic composite distal radii and fixed with a fragment-specific plate (FSP) using a radial styloid or lunate facet plate or with two- or three-headless screws (2HS, 3HS), creating 6 fixation models: B1.1/FSP, B1.1/2HS, B1.1/3HS, B3.3/FSP, B3.3/2HS, and B3.3/3HS. Compressive stiffness of fixation constructs under initial static load, cyclic load, and final static load was investigated. Nonaxial loadings, including shearing and rotation, were not evaluated.

RESULTS

Regarding AO type B1.1, the mean stiffness of the B1.1/FSP construct was not significantly different from the intact radius, and the mean stiffness was greatest in the B1.1/3HS and lowest in the B1.1/2HS construct. For AO type B3.3, the mean stiffness of the B3.3/3HS construct was not significantly different from the intact radius, and the mean stiffness of the B3.3/FSP and B3.3/2HS construct was greatest and lowest, respectively. Minimal differences in stiffness between initial and final static loads confirmed that there was no evidence of failure implant under cyclic compressive loads.

CONCLUSIONS

Fragment-specific plates and two- or three-headless screw fixation maintained mechanical stability through compressive cyclic loading for radial styloid and volar lunate facet fractures. The FSPs and three-headless screws fixations provided superior stiffness over the two-headless screws fixation. There was no articular fracture failure in all fixation constructs with initial static compression, cyclic loading, and final compression.

CLINICAL RELEVANCE

Fragment-specific plates and headless screws can both be considered as adequate fixation for radial styloid and volar lunate facet 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.

Traditional Bone Grafting in Scaphoid Nonunion

Management of scaphoid nonunion remains challenging despite modern fixation techniques. Nonvascularized bone graft may be used to achieve union in waist and proximal pole fractures with good success rates. Technical aspects, such as adequate debridement and restoration of scaphoid length, and stable fixation are critical in achieving union and functional wrist usage. Rigid fixation can be achieved with compression screws, K-wires, and plate constructs. The surgeon has a choice of various bone graft options including corticocancellous, cancellous, and strut grafts to promote healing and correct the humpback deformity.

Scaphoid numerical simulation of the critical loading until fracture

The numerical study of the scaphoid fracture, although it is relatively unexplored, can be of great clinical interest since it is highly common and can result in temporary or persistent disability. In this manuscript, seven combinations of boundary conditions and contacts between adjacent bones, together with four different loads, simulating real hand movements, are assessed. Three different fracture criteria for bones are employed to study the failure of the scaphoid with the aforementioned combination of interaction conditions. The results offer an interesting view of the accuracy of the possible interaction between adjacent bones. For future calculation, it would be possible to choose a combination of the balance between precision and computational cost savings. This study provides a comprehensive assessment into the modeling of the scaphoid bone and its interactions with adjacent bones. The findings reveal that various choices of interactions can yield similar results, allowing for flexibility in selecting interaction models based on desired accuracy or computational efficiency. Ultimately, this study establishes a foundational understanding for future research on modeling scaphoid motion.

Ultrasound-Based Registration for the Computer-Assisted Navigated Percutaneous Scaphoid Fixation

An ultrasound (US)-based computer-assisted approach has the potential to improve the accuracy and precision of screw placement for the percutaneous fixation of scaphoid fractures and also reduce the radiation dose for patient and clinical staff. Therefore, a surgical plan based on preoperative diagnostic computed tomography (CT) is registered with intraoperative US images, enabling a navigated percutaneous fracture fixation. However, approaches published so far rely on semimanual methods for intraoperative registration and are limited by long computation times. To address these challenges, we propose the employment of deep learning-based methods for US segmentation and registration in order to achieve a fast and fully automated yet robust registration process. For validation of the proposed US-based approach, we first provide a comparison of methods for segmentation and registration, assess their contribution to the overall error throughout our pipeline, and, finally, evaluate navigated screw placement in an in vitro study on 3-D printed carpal phantoms. Successful screw placement has been achieved for all ten screws, with deviations from the planned axis of 1.0 ± 0.6 and 0.7 ± 0.3 mm at the distal and proximal pole, respectively. The complete automation and total duration of about 12 s also allow seamless integration of our approach into the surgical workflow.

The influence of partial union on the mechanical strength of scaphoid fractures: a finite element study

Assessment of scaphoid fracture union on computed tomography scans is not currently standardized. We investigated the extent of scaphoid waist fracture union required to withstand physiological loads in a finite element model, based on a high-resolution CT scan of a cadaveric forearm. For simulations, the scaphoid waist was partially fused at the radial and ulnar sides. A physiological load of 100 N was transmitted to the scaphoid and the minimal amount of union to maintain biomechanical stability was recorded. The orientation of the fracture plane was varied to analyse the effect on biomechanical stability. The results indicate that the scaphoid is more prone to re-fracture when healing occurs on the ulnar side, where at least 60% union is required. Union occurring from the radial side can withstand loads with as little as 25% union. In fractures more parallel to the radial axis, the scaphoid seems less resistant on the radial side, as at least 50% union is required. A quantitative CT scan analysis with the proposed cut-off values and a consistently applied clinical examination will guide the clinician as to whether mid-waist scaphoid fractures can be considered as truly united.

Double-Screw Osteosynthesis in an Unstable Scaphoid Fracture Model: A Biomechanical Comparison of Two Screw Configurations

PURPOSE

Although there is evidence that a single headless compression screw is sufficient for fixation of most scaphoid fractures, double-screw osteosynthesis has been shown to result in higher failure strength and stiffness than a single screw. However, the biomechanical effect of different screw configurations has not been determined.

METHODS

A standardized unstable fracture model was produced in 28 cadaveric scaphoids. Specimens were randomly allocated to 1 of 2 fixation groups using 2 internal compression screws positioned in either the sagittal or coronal plane. A specimen-specific 3-dimensionally-printed customized screw placement and osteotomy device was developed using computer-aided design-generated models derived from computed tomography scan data of each individual scaphoid. Load to failure and stiffness of the repair constructs were evaluated using a mechanical testing system.

RESULTS

There were no significant differences in size, weight, and density between the scaphoid specimens. The average distance between screws was significantly greater in the sagittal group than in the coronal group. There were no significant differences between the coronal and sagittal aligned double screws in load to 2 mm displacement (mean coronal 180.9 ± 109.7 N; mean sagittal 156.0 ± 85.8 N), load to failure (mean coronal 275.9 ± 150.6 N; mean sagittal 248.0 ± 109.5 N), stiffness (mean coronal 111.7 ± 67.3 N/mm; mean sagittal 101.2 ± 45.1 N/mm), and energy absorption (mean coronal 472.6 ± 261.4 mJ; mean sagittal 443.5 ± 272.7 mJ).

CONCLUSIONS

There are no significant biomechanical differences between the sagittal or coronal aligned double headless compression screws in a scaphoid fracture model with bone loss.

CLINICAL RELEVANCE

In cases where double-screw fixation of the scaphoid is being considered, the placement of double screws can be at the discretion of the surgeon, and can be dictated by ease of access, surgical preference, and fracture orientation.

Comparison of conventional and transtrapezial palmar approaches for screw fixation of scaphoid waist fractures: a clinical study

We investigated two palmar approaches for screw fixation of acute scaphoid waist fractures: the conventional percutaneous or transtrapezial approach. Thirty cases who underwent operation from 2013 to 2021 were reviewed (conventional group, 15; transtrapezial approach group, 15). Cross-sections were constructed along the long axis of the scaphoid on postoperative computed tomography to evaluate the screw position, relative to the centre point in the distal-third, midwaist and proximal-third of the bone. The screw could be inserted centrally in the proximal and distal regions using the transtrapezial approach. In the conventional approach, the screw was inserted radially in the distal region, but tended to be positioned centrally in the midwaist and proximal regions. As central placement of the screw in the proximal fragment offers a biomechanical advantage, both approaches can be options for some fracture patterns, while for others, the fracture pattern could influence which approach is better.Level of evidence: IV.

Plate fixation in challenging traumatic carpal scaphoid lesions

BACKGROUND

Complex fractures of the carpal scaphoid with poles fragmentation, edges comminution, bone loss and non-union of fractures previously treated by screw fixation remain challenging for hand surgeons. The authors present the indications, advantages and results of scaphoid plating, underlining the importance of correct plate positioning well shaped onto the bone.

MATERIALS AND METHODS

The study includes 11 patients presenting acute fracture with distal pole fragmentation, acute fracture with comminution and non-union after prior failure of screw fixation. All patients were treated with volar locked plate fixation, adding a cortical bone graft in cases of non-union.

RESULTS

Bone consolidation was achieved in all cases; excellent outcomes in fracture healing and relevant improvement in symptoms and functions were obtained in non-union group that are consistent with the literature. Only one patient underwent early further surgery (first row carpectomy) with poor results.

CONCLUSION

The treatment of the selected scaphoid lesions with volar locked plate is a surely efficient technique. The plate can be easily adjusted to the shape of the scaphoid and can achieve an adequate correction of bone deformity and high degree of stability both in non-union and fractures.

Cannulated compression screw with versus without two K-wire fixation for treatment of scaphoid waist fracture nonunion

Purpose

This study aims to introduce the “tripod” technique using cannulated compression screw and two anti-rotational K-wires for treatment of unstable scaphoid waist fracture nonunion, and to compare it with the single cannulated screw fixation technique in term of scaphoid union and surgical outcomes.

Methods

It was a retrospective study. From January 2014 to March 2020, 103 consecutive patients with scaphoid waist fracture nonunion treated with the tripod fixation and bone grafting (n = 45) or with single cannulated compression screw and bone grafting (n = 58) were included. All the procedures were performed by the same hand surgery team, and autologous cortico-cancellous radius bone graft was used for bony reconstruction. The minimal follow-up period was 12 months. The union rate and the time to union, range of motion (ROM), grip strength, Visual Analogue Scale (VAS), Quick Disabilities of the Arm, Shoulder and Hand (DASH) score and modified Mayo Scores at the last visit were compared.

Results

In tripod fixation group, bony union was achieved in all patients at the mean of 14.8 ± 3.8 weeks, while in the single cannulated screw fixation group the bony union rate was 94.8% (55/58) and the time to union was 17.6 ± 3.6 weeks. The difference of time to union was statistically significant (p = 0.027), but not for bony union rate (p = 0.122). At the last visit, no significant difference was found with respect to any clinical and radiographic outcome measures (all p > 0.05). The overall rate of complications was not significantly different between two groups (15.6% vs 10.3%, p = 0.430).

Conclusions

Tripod fixation technique with headless compression screw and two K-wires is a safe and effective technique for treatment of scaphoid nonunion fixation and can be considered to use in practice, especially for those potentially rotationally unstable cases.

Comparison of Kirschner Wire Versus Screw Fixation in 1,2 Inter-Compartment Supra Retinaculum Artery Pedicle-Vascularized Bone Graft for Scaphoid Fractures

INTRODUCTION

The purpose of the study was to compare the outcomes of the Kirschner wires (k-wires) versus screw fixation in 1,2 inter-compartment supra retinaculum artery (ICSRA) pedicle-vascularized bone graft for scaphoid non-union treatment.

METHOD

A retrospective study that included all patients with scaphoid nonunion underwent pedicle-vascularized bone graft and fixated with either k-wire or screw from 2010 through 2019 in the Department of Plastic and Reconstructive Surgery at Liaquat National Hospital and Medical College. Clinical outcomes were compared between k-wire and screw fixation, which were measured in terms of union rate, time of healing, pre and post-operative Disabilities of the Arm, Shoulder, and Hand (DASH) scores, range of motion at wrist, and grip strength of hand.

RESULTS

A total of 33 patients were included in the study. All of them had scaphoid non-union and were treated with 1,2 ICSRA pedicle-vascularized bone graft; 20 patients had a fixation with k-wire and 13 with a screw. Radiological healing was achieved in 18 patients with k-wire and 11 patients with screw fixation, with healing rates of 90% and 84.6%, respectively. There was a significant decrease in DASH score postoperatively in both groups. Although no significant difference between the outcomes of both groups whether on union rate, DASH score, or range of motion at the wrist.

CONCLUSION

Hence, there is no significant difference in outcome between k-wire and screw fixation methods. We concluded k-wire as a more acceptable option with vascularized bone graft fixation as less technically demanding and low cost as compared to screw fixation.

Scaphoid fracture displacement is not correlated with the fracture angle

Classifications of scaphoid fractures associate the angle of the fracture with its stability. To examine this assumption, we measured acute scaphoid fracture angles and inclinations in relation to different scaphoid axes, using fracture displacement as an indicator of instability. We examined the effect of using different axes on the measurements of angles. CT scans of 133 scaphoid fractures were classified according to the location of the fractures. Using a three-dimensional computer model, we computed four scaphoid axes. For each fracture, we then measured the fracture angle and the direction of the fracture inclination in relation to each one of the axes. We found a correlation between displacement and the angles of proximal fractures using one of these axes (the surface principal component analysis axis). No such correlations were found for waist fractures, which were the majority of fractures. There were significant differences between the measurements made with different axes. The findings indicate that the angle of the fracture and the direction of the fracture inclination are minor factors in the displacement of most scaphoid fractures.Level of evidence: III.

Comparison of two different screw trajectories in the treatment of oblique scaphoid fractures: A mechanical study on composite bone models

Objectives

In this mechanical study, we aimed to compare two different screw trajectories in terms of durability against axial loads on oblique scaphoid fractures using composite bone models.

Materials and methods

Oblique osteotomies were made along the dorsal sulcus of 14 composite scaphoid bone models. Following this, all bone models were randomly classified. One group of bones were fixed with a screw placed perpendicular to the osteotomy line and the other group was fixed with a screw placed centrally down the long axis of the scaphoid bone. Each scaphoid bone model was positioned on a mechanical testing machine. Subsequently, axial loading tests were applied on each bone model to measure the amount of loading required to cause 2-mm displacement and failure on the osteotomy side and maximum displacement at the time of failure on scaphoid bone models.

Results

There was no statistically significant difference in load to 2-mm displacement and failure between the two groups (p>0.05). Also, there was no statistically significant difference between the two groups in terms of maximum displacement seen on failure (p>0.05).

Conclusion

In our study, we found that the stability of the screws which laid perpendicular to the fracture line and parallel to the long axis of the scaphoid was the same in fixing oblique scaphoid fractures.

3D computational anatomy of the scaphoid and its waist for use in fracture treatment

BACKGROUND

A detailed understanding of scaphoid anatomy helps anatomic fracture reduction, and optimal screw position. Therefore, we analysed (1) the size and shape variations of the cartilage and osseous surface, (2) the distribution of volumetric bone mineral density (vBMD) and (3) if the vBMD values differ between a peripheral and a central screw pathway?

METHODS

Forty-three fresh frozen hand specimens (17 females, 26 males) were analysed with high-resolution peripheral quantitative computed tomography (HR-pQCT) and dissected to compute a 3D-statistical osseous and cartilage surface model and a 3D-averaged vBMD model of the scaphoid. 3D patterns were analysed using principal component analysis (PCA). vBMD was analysed via averaging HR-pQCT grey values and virtual bone probing along a central and peripheral pathway.

RESULTS

(1) PCA displayed most notable variation in length ranging from 1.7 cm (- 2SD) to 2.6 cm (mean) and 3.7 cm (+ 2SD) associated with differences of the width and configuration of the dorsal surface (curved and narrow (4 mm) to a wider width (9 mm)). (2) High vBMD was located in the peripheral zone. Lowest vBMD was observed in the centre and waist. (3) Virtual probing along a peripheral pathway near to the cartilage surfaces for the capitate and lunate allowed the center region to be bypassed, resulting in increased vBMD compared to a central pathway.

CONCLUSION

High anatomical variations regarding the osseous and cartilage surfaces were associated with three distinct concentrically arranged zones with notable different vBMD. The complex scaphoid anatomy with its waist might alter the strategy of fracture fixation, education and research.

Treatment of unstable scaphoid waist nonunion with cancellous bone grafts and cannulated screw or Kirschner wire fixation

We compared two methods of fixation for unstable scaphoid waist nonunions regarding rate of scaphoid union, union time, deformity correction, clinical outcomes (pain, range of motion, and grip strength), and QuickDASH scores. Eighty-nine patients who undergo cancellous iliac bone grafting and internal fixation either with a Herbert screw (n = 46) or multiple Kirschner wires (n = 43) were evaluated. The rate of scaphoid union in the K-wire group was 98% (n = 42) versus 89% (n = 41) in the screw group. The mean union time and duration of surgery for K-wire group versus screw group were 12 versus 15 weeks and 45 versus 66 min respectively. There was no significant difference between the two groups with respect to deformity correction, clinical outcomes, and QuickDASH scores. Despite there was no significant difference in the rate of scaphoid union between the two fixation methods, the K-wires procedure had the advantages of short union time, less demanding, and less expensive than the screw implant.

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.

[3D Imaging for the analysis of scaphoid fractures and non-unions]

The aim of the present study is to give an overview over the possibilities of 3D imaging in the analysis of scaphoid fractures and non-unions and to discuss them on the base of case studies and literature.

Kirschner wire versus Herbert screw fixation for the treatment of unstable scaphoid waist fracture nonunion using corticocancellous iliac bone graft: randomized clinical trial

PURPOSE

The study compared the impact of the Kirschner wires versus Herbert screw fixation on the rate of union, time to union, correction of deformity, and clinical outcome in adults with unstable scaphoid waist fracture nonunions without avascular necrosis.

METHODS

We prospectively randomized 122 patients to undergo corticocancellous iliac bone grafting and internal fixation either with multiple Kirschner wires or Herbert screw. Radiographs, clinical outcome measures (pain, range of motion, and grip strength), and the Quick DASH score were taken pre- and post-operatively.

RESULTS

The rate of the scaphoid union in the Kirschner wire group was 91% versus 88% in the Herbert group. No difference was detected between the two groups with respect to the time to union, deformity correction, pain analysis, range of motion, grip strength, return to work, and complications.

CONCLUSION

Using of multiple Kirschner wires as a fixation method for unstable scaphoid waist fracture nonunion that was treated by open reduction and corticocancellous iliac bone grafting had a shorter operative time and lower cost as compared with the Herbert screw fixation. Herbert screw fixation was technically more demanding in terms of technique than K-wires. However, because of easy application of Kirschner wires, and low cost, especially in developing countries, it may be a good alternative to Herbert screw.

Factors Associated with Scaphoid Nonunion following Early Open Reduction and Internal Fixation

Background  Nonunion after open reduction and internal fixation (ORIF) of scaphoid fractures is reported in 5 to 30% of cases; however, predictors of nonunion are not clearly defined. Objective  The purpose of this study is to determine fracture characteristics and surgical factors which may influence progression to nonunion after scaphoid fracture ORIF. Patients and Methods  We performed a retrospective case-control study of scaphoid fractures treated by early ORIF between 2003 and 2017. Inclusion criteria were surgical fixation within 6 months from date of injury and postoperative CT with minimum clinical follow-up of 6 months to evaluate healing. Forty-eight patients were included in this study. Nonunion cases were matched by age, sex, and fracture location to patients who progressed to fracture union in the 1:2 ratio. Results  This series of 48 patients matched 16 nonunion cases with 32 cases that progressed to union. Fracture location was proximal pole in 15% (7/48) and waist in 85% (41/48). Multivariate regression demonstrated that shorter length of time from injury to initial ORIF and smaller percent of proximal fracture fragment volume were significantly associated with scaphoid nonunion after ORIF (63 vs. 27 days and 34 vs. 40%, respectively). Receiver operating curve analysis revealed that fracture volume below 38% and time from injury to surgery greater than 31 days were associated with nonunion. Conclusion  Increased likelihood for nonunion was found when the fracture was treated greater than 31 days from injury and when fracture volume was less than 38% of the entire scaphoid. Level of Evidence  This is a Level III, therapeutic study.

Approach to the Perpendicular Fixation of a Scaphoid Waist Fracture-A Computer Analyzed Cadaver Model

PURPOSE

In scaphoid fracture screw fixation, the screw is commonly placed along the long axis of the bone, without consideration of the fracture plane. This position is not perpendicular to transverse waist fractures or to the more common horizontal oblique fractures. Our aim was to examine the feasibility and describe possible approaches to, placing a screw perpendicular and in the center of the scaphoid waist fracture.

METHODS

Computed tomography of 12 cadaver wrists was performed in 3 positions to examine possible approaches in flexion, neutral, and extension of the wrist. The scans were evaluated using a 3-dimensional model that simulated horizontal oblique (60°) and transverse (90°) fractures. We examined all possible approaches for screw positioning and their deviation from the axis perpendicular to the fracture and in the center of its plane.

RESULTS

The preferred approaches for a perpendicular screw in a horizontal oblique fracture were found to be proximal-dorsal in flexion or transtrapezial in the extended or neutral positions (through the volar-radial trapezium). In transverse fractures, the possible approaches were proximal-dorsal or transtrapezial in the flexed or neutral positions and distal in the extended position (volar to volar-radial trapezium). In these approaches, the screw could be placed perpendicularly (deviating by < 10°) and in the center of the fracture in all specimens.

CONCLUSIONS

According to this model, it appears feasible to place a perpendicular screw in the center of a horizontal oblique waist fracture using a proximal-dorsal approach in flexion or a transtrapezial approach in neutral or extension positions of the wrist. Palpable landmarks may be used as additional guides to direct these approaches according to the clinical setting.

CLINICAL RELEVANCE

Perpendicular screw fixation of horizontal oblique or transverse scaphoid waist fractures is a possible option, if chosen for its biomechanical advantages.

A Cadaveric Study on the Accuracy of an Individualized Guiding Template to Assist Scaphoid Fixation Using Computed Tomography and 3-Dimensional Printing

PURPOSE

The aim of this study was to evaluate the feasibility and accuracy of scaphoid screw guidewire placement using a computer-assisted-designed, and 3-dimensional-printed, surgical guiding template in cadaver wrists.

METHODS

Computed tomography (CT) scans of 12 fresh-frozen cadaver wrists were performed and the data imported into a surgical planning system. A 3-dimensional skin surface template block with a guiding hole was generated from the CT data to allow a screw guidewire to be placed in the central third of the scaphoid. This 3-dimensional model was printed and then put back onto the wrist. A screw guidewire was inserted through the palmar guide hole into the intact scaphoid and then a postprocedure CT scan was obtained. These postprocedure data were introduced into the surgical planning system. Angular and linear deviation between the preprocedural simulation and the image of the guidewire was measured in the system to assess accuracy.

RESULTS

Mean angular deviation was 3.85° ± 1.32° (range, 1.56°-5.35°) and linear deviations of the 12 specimens were less than 1.1 mm. No specimen required a repeat drilling to the scaphoid. All the screw guidewires were considered to be centrally placed in the scaphoid based on our criterion of central placement of the scaphoid screw.

CONCLUSIONS

The use of a computer-assisted 3-dimensional-printed surgical guide template to assist screw guidewire placement into an intact scaphoid, mimicking a nondisplaced scaphoid fracture, showed acceptable accuracy in cadaver wrists.

CLINICAL RELEVANCE

Our technique may provide a simple and effective method for the guidance of screw guidewire insertion in a nondisplaced scaphoid fracture surgery.

How to determine the surgical approach in Hoffa fractures?

Surgical approach selection and fixation of Hoffa fractures is difficult and remains controversial. Evolving trends emphasize the importance of fracture morphology, fracture location, and comminution, all of which guide decisions regarding surgical approach and implant selection. This focused review highlights factors affecting Hoffa fracture available surgical approaches, treatment outcomes, and recommendations for selecting an optimal approach.

Comparison of volar versus dorsal screw fixation for scaphoid waist fractures: A finite element analysis

PURPOSE

Scaphoid waist fractures may be fixed through volar or dorsal screw fixation. However, there is no consensus on which surgical fixation method should be performed. The purpose of this study was to compare volar versus dorsal screw fixation of scaphoid waist fractures under physiological loading conditions utilizing finite element analysis.

METHODS

A transverse scaphoid waist fracture (Herbert type B2) model was fixed with a headless cannulated compression screw using either a volar or dorsal approach. Displacement and rotation of the fragments and stress analysis on the scaphoid bone and screw were analyzed in the models using 3-D finite element analysis in three different wrist positions; total extension (TE), neutral (N) and total flexion (TF).

RESULTS

Displacement of the fracture gap in volar fixation in all planes (x, y, z) was less than in dorsal fixation in the TF and N positions. Furthermore, rotational stability was stronger in volar fixation in all planes and wrist positions. von Mises stress values were concentrated on the proximal fragment in all wrist positions.

CONCLUSIONS

Although both volar and dorsal fixation techniques can be preferred in Herbert type B2 fractures, results of this finite element analysis suggest that centrally placed volar compression screw fixation may be biomechanically advantageous over dorsal screw fixation.

LEVEL OF EVIDENCE

I.

Ideal Starting Point and Trajectory of a Screw for the Dorsal Approach to Scaphoid Fractures

PURPOSE

To determine the screw starting point and trajectory for the dorsal approach to scaphoid fractures that provides a combination of length and compression at the fracture site.

METHODS

Computed tomography scans were obtained of 10 scaphoid fractures for 3 common fracture types. A computerized model was generated for each scaphoid. Screw starting point, length, and angle to the fracture plane were analyzed for starting points and trajectories within a safe zone that protected against cortical penetration. A novel analysis was developed to assess a combination of screw length and angle to fracture plane, termed "effective compression length" (ECL). ECL assessed the screw working distance perpendicular to the fracture. Results were analyzed to determine optimal screw starting point and trajectory.

RESULTS

For proximal pole fractures, a screw perpendicular to the fracture was 9.7 mm from the longitudinal axis starting point (LASP). The screw with the largest ECL was 6.8 mm from the LASP, crossing the fracture at a 67° obliquity. For waist fractures, a perpendicular screw was 7.8 mm from the LASP. The screw with the largest ECL was 6.0 mm away, crossing the fracture at 74°. For distal oblique fractures, a perpendicular screw was 10.2 mm from the LASP. The screw with the largest ECL was 6.4 mm away, crossing the fracture at 70°. A screw with the classic starting point and trajectory crossed the fracture at obliquities of 48°, 51°, and 45° for proximal, waist, and distal fractures, respectively.

CONCLUSIONS

Scaphoid screws placed with the classic starting point and trajectory cross the fracture at an obliquity. By altering the screw starting point and trajectory, screws with adequate length will be more perpendicular to the fracture plane.

CLINICAL RELEVANCE

Screw starting point and trajectory for scaphoid fractures may be altered based on fracture type to obtain a long screw that is closer to perpendicular to the fracture.

A CT-based approach with 3D modeling to determine optimal radiographic views of the scaphotrapezial and scaphotrapezoid joints

PURPOSE

To use a CT-based approach with 3D modeling to determine novel radiographic views of the scaphotrapezial (STl) and scaphotrapezoid (STd) joints.

MATERIALS AND METHODS

Consecutive wrist CT scans excluding those with pathology of the distal radius, scaphoid, trapezium, or trapezoid of subjects between ages 18 and 60 years were retrospectively reviewed. Three-dimensional reconstructions of CT scans were created and best-fit planes of the STl and STd joints were generated. Angles of these planes relative to a distal radial coordinate system were calculated to determine tilt of the wrist and the X-ray beam for novel radiographic views of these joints.

RESULTS

Fifty eligible wrist CT scans were identified. The mean age was 38 years (range, 18 to 59). For the novel STl PA view, the wrist is supinated 17° from the standard PA view and the X-ray beam is canted 6° caudad. In the STl lateral view, the wrist is pronated 17° from the standard lateral view, and the X-ray beam is canted 20° caudad. In the STd PA tilt view, the wrist is supinated 28° from the standard PA view, and the X-ray beam is canted 13° caudad. In the STd joint lateral tilt view, the wrist is pronated 28° from the standard lateral view, and the X-ray beam is canted 29° caudad.

CONCLUSION

We describe novel radiographic views of the STl and STd joints based on 3D modeling of wrist CT scans. Further studies are required to assess the efficacy of these views in detecting joint pathology.

Scaphoid screw fixation perpendicular to the fracture plane: Comparing volar and dorsal approaches

INTRODUCTION

To percutaneously fixate a midwaist scaphoid fracture, both volar and dorsal approaches are considered valid options although they may have different screw insertion angles relative to the scaphoid fracture plane influencing fixation stability. In this virtual simulation study, we investigated the accessibility of placing a screw perpendicularly to the fracture plane in transverse and horizontal oblique scaphoid midwaist fracture models and compared standard volar and dorsal approaches.

MATERIAL AND METHODS

Computed tomography scans of 38 healthy wrists were used to obtain virtual 3-dimensional wrist models in flexion and extension. In case the trapezium in volar approach or the distal radius in dorsal approach obstructed the screw axis perpendicular to the fracture plane, an alternative non-obstructed screw axis was chosen as close as possible to the perpendicular axis. The deviation angle between the best possible non-obstructed screw placement and true perpendicular screw placement was quantified.

RESULTS

For transverse fractures, the average deviation angle (±standard deviation) was 8° (±5°) in volar approach, and 0° (±0°) in dorsal approach. For horizontal oblique fractures, these angles were 40° (±6°) and 14° (±8°), respectively.

DISCUSSION

In our simulations, compared to the volar approach, the dorsal approach provided the most precise screw placement perpendicular to the fracture plane, with the largest differences for horizontal oblique fractures. When taken in addition to screw purchase, thread engagement and protrusion risk, information about screw orientation may help surgeons in deciding between percutaneous approaches in scaphoid surgery on which there is currently no consensus.

LEVEL OF EVIDENCE

N/A.

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.

Three-dimensional comparison of alternative screw positions versus actual fixation of scaphoid fractures

PURPOSE

The recommended technique for the fixation of a scaphoid waist fracture involves a headless compression screw placed in the proximal fragment center. This is usually accomplished by placing a longitudinal axis screw as visualized by fluoroscopy. The screw length has been shown to have a biomechanical advantage. An alternative to these options, which has been debated in the literature, is a screw placed perpendicular to the fracture plane and in its center. The perpendicular screw may have a biomechanical advantage despite the fact that it may be shorter. This study examined the differences in location and length in actual patients between a screw in the center of the proximal fragment with a longitudinal axis screw, and the actual fixating screw. These were then compared to a perpendicular axis screw.

METHODS

Pre- and post-operative CT scans of 10 patients with scaphoid waist fractures were evaluated using a 3D computer model. Comparisons were made between the length, location and angle of actual and virtual screw alternatives; namely, a screw along the central third of the proximal fragment (central screw axis) where the scaphoid longitudinal axis was calculated mathematically (longitudinal screw axis) and a screw placed at 90° to the fracture plane and in its center (perpendicular screw axis).

RESULTS

The longitudinal axis screw was found to be significantly longer than the other axes (28.3mm). There was a significant difference between the perpendicular axis screw and the location and angle of the other screw axis, but it was only shorter than the longitudinal screw (23.6mm versus 25.5mm for the actual screw; ns.).

CONCLUSIONS

A computed longitudinal axis screw is longer than a central or actual screw placed longitudinally by visual inspection by the surgeon. Although it needs to be placed using computer assisted (CAS) techniques, it may have the biomechanical advantages of a longer screw in a similar trajectory. The perpendicular screw was found to be significantly different in position and angle but not shorter than the actually placed screw. It has biomechanical advantages and does not require visualization with CAS methods, making it the more attractive alternative.

Three-Dimensional Analysis of Acute Scaphoid Fracture Displacement: Proximal Extension Deformity of the Scaphoid

BACKGROUND

Our goal was to analyze the movement of acute scaphoid waist fracture fragments and adjacent bones in a common coordinate system. Our hypothesis was that the distal scaphoid fragment flexes and pronates and the proximal fragment extends.

METHODS

Computed tomography (CT) scans of patients diagnosed with an acute scaphoid waist fracture were evaluated using a 3-dimensional (3D) model. The scans of 57 nondisplaced and 23 displaced fractures were compared with a control group of 27 scans showing no pathological involvement of the wrist. Three anatomical landmarks were labeled on the distal and proximal fragments of the scaphoid, the lunate, and the trapezium. Each set of labels formed a triangle representing the bone or fragment. Four landmarks were labeled on the distal radial articular surface and used to create a common coordinate system. The position of each bone or fragment was calculated in reference to these coordinates.

RESULTS

The displaced fracture group showed significant extension, supination, and volar translation of the proximal scaphoid fragment when compared with the other groups. The lunate tended toward a supinated position, which was not statistically significant. The distal scaphoid fragment and the trapezium showed no movement.

CONCLUSIONS

In acute displaced scaphoid fractures, it is the proximal fragment that displaces and should be reduced.

CLINICAL RELEVANCE

The typical "humpback" deformity is actually a "proximal extension" deformity, the consequence of displacement of the proximal fragment of the scaphoid (with the lunate). Manipulating only the proximal fragment (with the lunate) may be technically easier and more effective than manipulating both fragments.

Rotational stability in screw-fixed scaphoid fractures compared to plate-fixed scaphoid fractures

BACKGROUND

The literature describes the treatment of scaphoid fractures comparing the volar and dorsal approaches, the advantages and disadvantages of percutaneous screw fixation, as well as the treatment of scaphoid nonunions using different types of cancellous or corticocancellous bone grafts. Yet, to date no studies are available comparing the outcome of rotational stability in screw-fixed scaphoid fractures to angular stable systems. The purpose of this study is to provide reliable data about rotational stability in stabilised scaphoid fractures and to gain information about the rigidity and the stability of the different types of fixation.

METHODS

Three groups of different stabilisation methods on standardised scaphoid B2 fractures were tested for rotational stability. Stabilisation was achieved using one or two cannulated compression screws (CCS) or angular stable plating. We performed ten repetitive cycles up to 10°, 20° and 30° rotation, measuring the maximum torque and the average dissipated work at angle level.

RESULTS

Our study showed that rotational stability using a two CCS fixation is significantly (p < 0.05) higher than single CCS fixation. Using the angular stable plate system was also superior to the single CCS (p < 0.05). There was, however, no significant difference between two CCS fixation and angular stable plate fixation.

CONCLUSION

Even though indications of using screws or plate systems might be different and plate osteosynthesis may be preferable in treatment of dislocated or comminuted fractures as well as for nonunions, our study showed a better rotational stability by choosing more than just one screw for osteosynthesis. Angular stable plating of scaphoid fractures also provides more rotational stability than single CCS fixation. The authors therefore hypothesise higher union rates in scaphoid fractures using more stable fixation systems.

A finite element analysis of two novel screw designs for scaphoid waist fractures

The scaphoid is the most often fractured carpal bone. Scaphoid fracture repair with a headless compression screw allows for early functional recovery. The rotational stability of a single screw may be limited, having a potential negative impact on the healing process. Two novel screws have been designed to provide improved rotational stability compared to the existing ones. Using a computational finite element model of a scaphoid osteotomy, we compared the efficacy of one simple screw and the two new screws in restricting inter-fragmentary motion (IFM) in three functional positions of the wrist and as a function of inter-fragmentary compression force. The in-plane IFM was primary rotational and was better restricted by the new screws compared to the conventional one when the inter-fragmentary compression force was below 15-20 N, but provided no clear benefit in total flexion independently of the compression force. To better understand the differences in the non-compressed case, we analyzed the acting moments and investigated the effects of the bending and torsional screw stiffness on IFM. By efficiently restricting the inter-fragmentary shear, the new screws may be clinically advantageous when the inter-fragmentary compression force is partially or completely lost and may provide further benefits toward earlier and better healing of transverse waist fractures of the scaphoid.

Dorsal Plating of Unstable Scaphoid Fractures and Nonunions

Achieving stable fixation of displaced acute and chronic nonunited scaphoid fractures continues to be a challenge for the treating surgeon. The threaded compression screw has been the mainstay of treatment of these fractures for the last 3 decades; however, persistent nonunion after screw fixation has prompted development of new techniques. Recent results of volar buttress plating have been promising. We describe a novel technique of dorsal scaphoid plating. In contrast to volar plating, the dorsal plate is biomechanically more favorable as it utilizes the tension side of the scaphoid bone for dynamic compression. Dorsal scaphoid plating provides a more stable construct than the traditional Herbert screw and mitigates the need for vascular or corticocancellous bone grafting in most cases.

Transtrapezial Approach for Fixation of Acute Scaphoid Fractures: Rationale, Surgical Techniques, and Results: AAOS Exhibit Selection

The ideal position for a screw used for scaphoid fixation is central. The purpose of this study was to compare the current volar percutaneous approaches used for scaphoid fracture fixation, explore different options to improve central screw placement, and describe our experience with the transtrapezial approach.

3-dimensional analysis of scaphoid fracture angle morphology

PURPOSE

Scaphoid fractures are classified according to their 2-dimensional radiographic appearance, and transverse waist fractures are considered the most common. Our hypothesis was that most scaphoid fractures are not perpendicular to the longitudinal axis of the scaphoid (ie, not transverse).

METHODS

Computerized 3-dimensional analyses were performed on 124 computed tomography scans of acute scaphoid fractures. Thirty of the fractures were displaced and virtually reduced. The angle between the scaphoid's first principal axis (longitudinal axis) and the fracture plane was analyzed for location and displacement. The distal radius articular surface was used to depict the volar-dorsal vector of the wrist.

RESULTS

There were 86 fractures of the waist, 13 of the distal third, and 25 of the proximal third. The average angle between the scaphoid longitudinal axis and the fracture plane was 53° for all fractures and 56° for waist fractures, both differing significantly from a 90°, transverse fracture. The majority of fracture planes were found to have a volar distal to dorsal proximal (horizontal oblique) inclination relative to the volar-dorsal vector.

CONCLUSIONS

Most waist fractures were horizontal oblique and not transverse. According to these findings, fixation of all fractures along the longitudinal axis of the scaphoid may not be the optimal mode of fixation for most. A different approach may be needed in accordance with the fracture plane.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic II.

Comparison of screw trajectory on stability of oblique scaphoid fractures: a mechanical study

PURPOSE

To determine whether a screw placed perpendicular to the fracture line in an oblique scaphoid fracture will provide fixation strength that is comparable with that of a centrally placed screw.

METHODS

Oblique osteotomies were made along the dorsal sulcus of 8 matched pairs of cadaveric scaphoids. One scaphoid from each pair was randomized to receive a screw placed centrally down the long axis. In the other scaphoid, a screw was placed perpendicular to the osteotomy. Each scaphoid underwent cyclic loading from 80 N to 120 N at 1 Hz. Cyclic loading was carried out until 2 mm of fracture displacement occurred or 4,000 cycles was reached. The specimens that reached the 4,000-cycle limit were then loaded to failure. Screw length, number of cycles, and load to failure were compared between the groups.

RESULTS

We found no difference in number of cycles or load to failure between the 2 groups. Screws placed perpendicular to the fracture line were significantly shorter than screws placed down the central axis.

CONCLUSIONS

A perpendicularly placed screw provides equivalent strength to one placed along the central axis.

CLINICAL RELEVANCE

Compared with a screw placed centrally in an oblique scaphoid fracture, a screw placed perpendicular to the fracture line allows the use of a shorter screw without sacrificing strength of fixation.

Percutaneous antegrade scaphoid screw placement: a feasibility and accuracy analysis of a novel electromagnetic navigation technique versus a standard fluoroscopic method

BACKGROUND

Central screw positioning in the scaphoid provides biomechanical advantages.

METHODS

A prospective randomized study of six fluoroscopically guided and six electromagnetically navigated screw (ENS) placements was performed on human cadavers. Accuracy of screw position was determined. Intraoperative fluoroscopy exposure times, readjustments of drilling directions, complete restarts and complications were documented.

RESULTS

The ENS method provided a mean time benefit of 7.34 min compared with the standard method and the mean screw length ratio (SLR coronar: ENS 0.96 ± 0.04 mm, SFF: 0.92 ± 0.04 mm, P = 0.065; SLR sagittal: ENS 0.98 ± 0.02 mm, SFF: 0.91 ± 0.04 mm, P = 0.009) and the screw axis deviation angle (AD coronar: ENS 3.33 ± 2.34°, SFF: 10.33 ± 2.58°, P = 0.002; AD sagittal: ENS 2.83 ± 0.98°, SFF: 11.00 ± 6.16°, P = 0.002) were lower. Using the electromagnetic navigation procedure no drilling readjustments or restarts were required, no cortical breach occurred.

CONCLUSIONS

Compared with the standard fluoroscopic technique, the ENS method used in this study showed higher accuracy, less complications, required less operation and radiation exposure time.

Pediatric supracondylar humerus fractures: effect of bone-implant interface conditions on fracture stability

BACKGROUND

Closed reduction and percutaneous fixation with Kirschner wires (KWs) is the standard of care of pediatric supra-condylar humerus fractures (SCHFs). Failure modes leading to loss of reduction are not clear and have not been quantified. Multiple factors may weaken the KW-bone interface bonding conditions. To the best of our knowledge, the possible effect of this decrease on different KW configurations and fracture stability has never been studied.

PURPOSE

To investigate the effect of bone-KW friction conditions on SCHF post-operative mechanical stability and to formulate clinical guidelines for KW configuration under different conditions.

METHODS

Finite element-based model of a fixated SCHF was used to simulate structure stability for two lateral divergent versus crossed lateral and medial KW configurations under varying KW-bone friction conditions.

RESULTS

Finite element simulations demonstrated that crossed KWs provide superior stability compared with the divergent configuration when KW-bone bonding is compromised. When KW-bone bonding conditions are adequate, crossed and divergent KW configurations provide similar, sufficient fracture stability.

CONCLUSIONS

Under normal bone-implant interface conditions, the two diverging lateral KW configuration offers satisfactory mechanical stability and may be the preferred choice of SCHF fixation. When KW-bone bonding is suboptimal, as when one or more of the lateral KWs are re-drilled, addition of a medial KW should be considered in order to improve stability despite risk to ulnar nerve.

Establishing a central zone in scaphoid surgery: a computational approach

PURPOSE

Scaphoid fractures are commonly fixed with headless cannulated screws positioned centrally in the scaphoid. Judgement of central placement of the screw may be difficult. We generated a central zone using computer analysis of 3D reconstructions of computed tomography (CT) images. As long as the screw axis is completely contained within this central zone, the screw would be considered as centrally placed.

METHODS

Thirty cases of 3D CT reconstructions of normal scaphoids in a computerised operation planning and simulation system (Vxwork software) were obtained. The central zone was established after some distance shrinkage of the original scaphoid surface reconstruction model using the function "erode" in the software. The shape of the central zone was evaluated, and the width of the central zone in the proximal pole, waist portion and distal pole was measured. We also established the long axis of the scaphoid to see whether it stays in the central zone.

RESULTS

All central zones could be divided into distal, waist and proximal portions according to the corresponding irregular shape of the scaphoid. As the geometry of the central zone was so irregular and its width very narrow, it was possible to completely contain the screw axis either in the proximal portion alone, waist alone or distal central zone alone.

CONCLUSIONS

Establishing the central zone of scaphoid 3D CT images provided a baseline for discussion of central placement of a scaphoid screw. The geometry of the scaphoid central zone determined that the screw could hardly be inserted through entire scaphoid central area during surgery.

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.

Central versus eccentric internal fixation of acute scaphoid fractures

PURPOSE

To accurately calculate the cross-sectional area of typical scaphoid fracture patterns and compare the amount of fracture surface area available for healing when a screw was positioned in the center of the scaphoid (central) versus perpendicular (eccentric) to the fracture plane.

METHODS

We employed a laser scanning technique to create 3-dimensional models of the scaphoid and permit the precise calculation of area along any cross-sectional cut of the bone. We computed approximate bone apposition areas for typical acute Herbert and Fisher fractures for 10 dry bone specimens. Next, we modeled internal fixation for each of these fracture geometries with screws placed either along the central axis of the scaphoid or eccentrically, perpendicular to the fracture plane. We calculated the proportional areas occupied by the screw and remaining area available for fracture healing.

RESULTS

The mean surface area of the simulated distal oblique, complete waist, and proximal pole fractures was 131, 86, and 58 mm(2), respectively. There was little difference in available area for complete waist and proximal pole fractures, but eccentric screw fixation perpendicular to the plane in distal oblique fractures consumed significantly less area than the centrally placed position.

CONCLUSIONS

The area available for apposition is widely variable and depends on each bone's unique morphology, the orientation of the fracture plane, and the design of the screw. Of the 3 fracture patterns studied, the obliquity of the screw with respect to the long axis was greatest for distal oblique fractures where perpendicular (eccentric) placement is preferable to maximize surface area available for healing.

CLINICAL RELEVANCE

Given the poor vascular supply of the scaphoid and morbidity associated with scaphoid fracture nonunions, this study examined a key determinant of bone healing by characterizing the area of these fractures and amount of bone apposition available for blood flow and healing when internally fixed with a compression screw.

Optimal fixation of oblique scaphoid fractures: a cadaver model

PURPOSE

Acute scaphoid fractures are commonly fixed with headless cannulated screws positioned in the center of the proximal fragment. Central placement of the screw may be difficult and may violate the scaphotrapezial joint. We hypothesize that placement of the screw through the scaphoid tuberosity will achieve perpendicular fixation of an oblique waist fracture and result in more stable fixation than a screw in the center of the proximal fragment.

METHODS

We designed oblique osteotomies for 8 matched pairs of cadaver scaphoids and fixed each specimen with a headless cannulated screw. In 1 specimen, we positioned the screw at the center of the proximal fragment; we placed its matched pair perpendicular to the fracture. The perpendicular screw was directed through the scaphoid tuberosity. We placed the specimen under the increasing load of a pneumatically driven plunger. We compared stiffness, load, distance at failure, and mechanism of failure between the central and perpendicular screw groups.

RESULTS

We found no difference between groups. Stiffness was identical in both groups (131 N/mm) and load to failure was similar (central screw, 137 N vs perpendicular screw, 148 N).

CONCLUSIONS

In this biomechanical model of an unstable scaphoid fracture, we found that similar stability of fixation had been achieved with a screw perpendicular to the fracture plane with entry through the tuberosity, compared with a screw in a central position in the proximal fragment. This study suggests that placing the screw through the tuberosity, perpendicular to a short oblique fracture, will not impair fixation stability.

CLINICAL RELEVANCE

Percutaneous fixation of scaphoid fractures has become popular although it is technically challenging. An easier distal approach through the tuberosity, without violating the scaphotrapezial joint, may not impair the fixation stability of an oblique fracture.

Influence of screw design, sex, and approach in scaphoid fracture fixation

BACKGROUND

Screw fixation of scaphoid fractures has gained popularity. A long central screw has been shown to be biomechanically advantageous.

QUESTIONS/PURPOSES

We compared the ability of different screw designs to obtain this goal and determined the influence of sex and approach on screw length.

METHODS

We performed all measurements on three-dimensional reconstructions of 20 CT scans of normal scaphoids (10 men and 10 women) with the use of software. The three-dimensional computer models were analyzed, the central axis was defined, and the screws were placed along this axis. We compared 15 different available screw designs and volar and dorsal screw placement.

RESULTS

The length of the scaphoid along its central axis was longer in men (mean, 27.14 mm; standard error of the mean, 0.97 mm) than in women (mean, 23.86 mm; standard error of the mean, 0.37 mm). The screw length that can be used was longer in the volar approach (mean, 23.72 mm; standard error of the mean, 0.19 mm) than in the dorsal approach (mean, 23.31 mm; standard error of the mean, 0.19 mm) regardless of the screw design. Screws with a trailing thread diameter greater than 3.9 mm and leading thread diameter greater than 3.0 mm were shorter.

CONCLUSIONS

Scaphoids in women are smaller than in men. Theoretically, fixation of scaphoid fractures through a volar approach will allow the surgeon to use longer screws. The screw design has a significant influence on the screw length that can be used in scaphoid fracture fixation. We recommend using a differential pitch screw with a thread diameter of 3.9 mm or less.

Review of treatment of acute scaphoid fractures: R1

Scaphoid fractures are common. Clinical suspicion and early diagnosis and treatment are vital in order to avoid complications such as avascular necrosis. The management of these fractures depends on fracture characteristics, specifically the degree of displacement. With consideration of patient factors, such as occupation, the treatment can be non-operative or operative. There has been much debate in the recent literature regarding the best management of these fractures. The purpose of this review was to identify the current evidence for non-operative and operative treatment. Undisplaced and minimally displaced fractures can be managed non-operatively with a scaphoid cast. Surgical treatment is used for fractures with displacement of >1 mm.