The length and position of the long axis of the scaphoid measured by analysis of three-dimensional reconstructions of computed tomography images

Assessing the risk of re-fracture related to the percentage of partial union in scaphoid waist fractures

Aims

There is ambiguity surrounding the degree of scaphoid union required to safely allow mobilization following scaphoid waist fracture. Premature mobilization could lead to refracture, but late mobilization may cause stiffness and delay return to normal function. This study aims to explore the risk of refracture at different stages of scaphoid waist fracture union in three common fracture patterns, using a novel finite element method.

Methods

The most common anatomical variant of the scaphoid was modelled from a CT scan of a healthy hand and wrist using 3D Slicer freeware. This model was uploaded into COMSOL Multiphysics software to enable the application of physiological enhancements. Three common waist fracture patterns were produced following the Russe classification. Each fracture had differing stages of healing, ranging from 10% to 90% partial union, with increments of 10% union assessed. A physiological force of 100 N acting on the distal pole was applied, with the risk of refracture assessed using the Von Mises stress.

Results

Overall, 90% to 30% fracture unions demonstrated a small, gradual increase in the Von Mises stress of all fracture patterns (16.0 MPa to 240.5 MPa). All fracture patterns showed a greater increase in Von Mises stress from 30% to 10% partial union (680.8 MPa to 6,288.6 MPa).

Conclusion

Previous studies have suggested 25%, 50%, and 75% partial union as sufficient for resuming hand and wrist mobilization. This study shows that 30% union is sufficient to return to normal hand and wrist function in all three fracture patterns. Both 50% and 75% union are unnecessary and increase the risk of post-fracture stiffness. This study has also demonstrated the feasibility of finite element analysis (FEA) in scaphoid waist fracture research. FEA is a sustainable method which does not require the use of finite scaphoid cadavers, hence increasing accessibility into future scaphoid waist fracture-related research.

Clinical outcomes of double-screw fixation with bone grafting for displaced scaphoid nonunions: A series of 21 cases

Purpose

This study reports the clinical outcomes of double-screw fixation with bone grafting for displaced scaphoid nonunions.

Patients and methods

This study was a retrospective survey. From January 2018 to December 2019, 21 patients with displaced scaphoid fractures underwent open debridement and two headless compression screw fixation with bone grafting. The preoperative and postoperative lateral intrascaphoid angle (LISA) and scapholunate angle (SLA) were recorded. Preoperative and postoperative grip strength (% of the healthy side), active range of motion (AROM), visual analogue scale (VAS), and patient-rated wrist evaluation (PRWE) scores at the final follow-up were obtained for all patients for comparison.

Results

Patients were treated for an average of 38.3 months (range 12-250) after the injury. The average time of postoperative follow-up was 30.5 months (range 24-48). All fractures achieved union at a mean of 2.7 months (range 2-4) after surgery, and 14 scaphoids of 21 patients (66.7%) healed by 8 weeks. CT scans showed no evidence of cortical penetration of either screw in all patients. There was a statistically significant improvement in AROM, grip strength, and PRWE. No complications occurred in this study, and all patients returned to work.

Conclusion

This study indicates that double-screw fixation with bone grafting is an effective technique for treating displaced scaphoid nonunions.

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.

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.

[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.

Understanding the Patterns of Deformity of Wrist Fractures Using Computer Analysis

Computer modeling of the wrist has followed other fields in the search for descriptive methods to understand the biomechanics of injury. Using patient-specific 3D computer models, we may better understand the biomechanics of wrist fractures in order to plan better care. We may better estimate fracture morphology and stability and evaluate surgical indications, design more adequate or effective surgical approaches and develop novel methods of therapy. The purpose of this review is to question the actual advances made in the understanding of wrist fractures using computer models.

Deviations in positioning variable pitch screws- scaphoid waist fractures

INTRODUCTION

Operative therapy using a headless cannulated variable pitch compression screw is the gold standard for the treatment of instable scaphoid fractures.

HYPOTHESIS

Deviation from the central placement is associated with a loss of stability and stiffness.

MATERIAL AND METHODS

An artificial bone model was manufactured and different screw positions (central, 10° and 20° to the long axis) were assessed. A shearing test with axial force on the 45° flexed scaphoid was applied.

RESULTS

The inserted variable pitch screw showed the highest stiffness and failure force in a position in the long axis. At 10 degrees, a slight decrease in stiffness (32.7N/mm±9.3N/mm) and failure force (41.6N±13.2N) was observed, while a significant reduction in stiffness (29.3N/mm±4.6N/mm) and failure force (50.3N±19.5N) was measured at 20 degrees.

DISCUSSION

Deviations in the angle of insertion of the compression screw cause loss in failure force, thus deviations from the central placement is associated with less stability and stiffness.

LEVEL OF PROOF

Controlled laboratory study (basic science study, biomechanical testing).

Scapho-Capitate Ratio for Estimation of Scaphoid Length

Background: The failure of scaphoid reconstruction by restoring both length and shape may lead to carpal mal-alignment and progressive degenerative arthritis. The aim of our study is to find a reliable method to find out the scaphoid length without measuring the contralateral scaphoid. Methods: Three X-ray wrist views were collected for 51 patients without any signs suggesting any hand and wrist fractures. The scaphoid, capitate and 3^rd metacarpal bone axes lengths and carpal height were measured by 4 hand surgeons separately. Results: The scapho-capitate ratio was 1.1 ± 0.084, 1.01 ± 0.084 and 0.92 ± 0.109 for lateral, postero-anterior with ulnar deviation and postero-anterior view respectively. The ulnar deviation view had the highest reliability. Conclusions: Scapho-capitate ratio estimation is an easy and accurate measure of normal scaphoid length in situations when the scaphoid is short. It is helpful for the estimation of the size of the bone graft that need for reconstruction of the scaphoid.

A new acute scaphoid fracture assessment method: a reliability study of the 'long axis' measurement

Background

The aim of this study was to assess the inter observer and intra observer reliability of acute scaphoid fracture classification methods including a novel ‘long axis’ measurement, a simple method which we have developed with the aim of improving agreement when describing acute fractures.

Methods

We identified sixty patients with acute scaphoid fractures at two centres who had been investigated with both plain radiographs and a CT (Computed Tomography) scan within 4 weeks of injury. The fractures were assessed by three observers at each centre using three commonly used classification systems and the ‘long axis’ method.

Results

Inter observer reliability: based on X-rays the ‘long axis’ measurement demonstrated substantial agreement (Intraclass Correlation Coefficient (ICC) =0.76) and was significantly more reliable than the Mayo (p < 0.01), the most reliable of the established classification systems with moderate levels of agreement (kappa = 0.56). Intra observer reliability: the long axis measurement demonstrated almost perfect agreement whether based on X-ray (ICC = 0.905) or CT (ICC = 0.900).

Conclusions

This study describes a novel pragmatic ‘long axis’ method for the assessment of acute scaphoid fractures which demonstrates substantial inter and intra observer reliability. The ‘long axis’ measurement has clear potential benefits over traditional classification systems which should be explored in future clinical research.

Estimating Scaphoid Lengths Using Anatomical Measurements in the Wrist

PURPOSE

In reconstructive surgery of scaphoid nonunions with humpback deformity, some surgeons recommend restoration of the normal scaphoid length whereas others overexpand the normal length to ensure carpal realignment and prevent late collapse. To be able to define overexpansion and investigate which levels of overexpansion yield optimal clinical results, a precise method for estimating the original scaphoid length is required. The purpose of this anatomic study was to investigate the precision of estimating normal scaphoid lengths based on intact adjacent bone dimensions, compared with using the contralateral scaphoid length.

METHODS

From bilateral computed tomographic scans of 28 healthy wrist pairs, 3-dimensional virtual bone models were created. The left and right scaphoid lengths were determined at the central axis. The capitate length at the central axis and the distal radius width served to derive an ipsilateral scaphoid length estimate. Estimation precision for individual cases was based on the 95% range (±1.96 × SD) of the observed differences between the actual and estimated lengths.

RESULTS

On average, the capitate length was 10% smaller than the scaphoid length; the radius width was 9% larger. Consequently, we averaged the capitate length and radius width for ipsilateral estimations. The average difference between the scaphoid length and the latter ipsilateral estimate was 0.1 mm. The average contralateral scaphoid length difference was also 0.1 mm. Estimation precisions, however, were ±2.2 and ±1.4 mm, respectively.

CONCLUSIONS

Scaphoid length estimation based on the contralateral scaphoid is more precise than the estimating scaphoid length using the ipsilateral radius and capitate.

CLINICAL RELEVANCE

Scaphoid overexpansion can be ensured if the restored length is at least 1.4 mm longer than the contralateral length. This may be valuable information when establishing a target length for reconstruction and investigating the consequences of scaphoid overexpansion on clinical function, such as range of motion, which are currently unknown.

Reliability of semi-pronated ulnar deviation PA view (billiard view) of the wrist in evaluating the scaphoid

Various methods assessing the scaphoid have been reported because of its unique position. In our hospital, pre- and postoperative evaluation of the scaphoid alignment has been carried out in the billiard view, a combination of 45° pronated oblique with ulnar deviation posteroanterior (PA) view, in addition to 3DCT scan and PA and lateral view. This study compared the intra- and inter-observer reliabilities of the lateral intrascaphoid angle and scaphoid length (SL) and scaphoid height (SH) on the billiard view. A total of 60 patients who underwent surgery for scaphoid nonunion were identified and the preoperative and the final follow-up postoperative plain radiographs were used for measurement. Three observers assessed each image. Intra- and inter-observer reliability was determined using intra-class correlation (ICC) coefficients. Intra-observer reliability was all excellent ranging between 0.855 and 0.992. Inter-observer reliability ranged between 0.292 and 0.983. SL and SH demonstrated excellent agreement, while ISA demonstrated poor to moderate agreement. The best method for assessing the scaphoid in simple radiograph remains debatable, but our current data suggest that measuring SL and SH on the billiard view is reproducible and can be used for evaluating restoration of scaphoid alignment.

Three-Dimensional Assessment of Bilateral Symmetry of the Scaphoid: An Anatomic Study

Preoperative 3D CT imaging techniques provide displacement analysis of the distal scaphoid fragment in 3D space, using the matched opposite scaphoid as reference. Its accuracy depends on the presence of anatomical bilateral symmetry, which has not been investigated yet using similar techniques. Our purpose was to investigate symmetry by comparing the relative positions of distal and proximal poles between sides. We used bilateral CT scans of 19 adult healthy volunteers to obtain 3D scaphoid models. Left proximal and distal poles were matched to corresponding mirrored right sides. The left-to-right positional differences between poles were quantified in terms of three translational and three rotational parameters. The mean (SD) of ulnar, dorsal, and distal translational differences of distal poles relative to proximal poles was 0.1 (0.6); 0.4 (1.2); 0.2 (0.6) mm and that of palmar rotation, ulnar deviation, and pronation differences was −1.1 (4.9); −1.5 (3.3); 1.0 (3.7)°, respectively. These differences did not significantly differ from zero and thus were not biased to left or right side. We proved that, on average, the articular surfaces of scaphoid poles were symmetrically aligned in 3D space. This suggests that the contralateral scaphoid can serve as reference in corrective surgery. No level of evidence is available.

Arthroscopic management of chronic unstable scaphoid nonunions: effects on restoration of carpal alignment and recovery of wrist function

PURPOSE

The purpose of this study was to assess the effects of arthroscopically assisted reduction and osteosynthesis on restoration of carpal alignment and recovery of clinical wrist function in patients with unstable scaphoid nonunion.

METHODS

Thirty-six patients who underwent arthroscopically assisted osteosynthesis with or without bone grafting for unstable scaphoid nonunion between July 2006 and January 2012 were enrolled. The average time from injury to surgery was 51 ± 78.3 months. Radiographic and clinical evaluations were assessed on preoperative and postoperative days, and follow-up evaluation took place at a minimum of 24 months.

RESULTS

Union was achieved in 86% (31 of 36) of patients at a mean of 11 ± 2.7 weeks. Scaphoid axial length (SAL), lateral intrascaphoid angle (ISA), scapholunate angle (SLA), and reversed carpal height ratio (CHR) was significantly improved after surgery, and those correction ratios averaged 66% ± 46.8%, 74% ± 58.2%, 81% ± 59.8%%, and 94% ± 46%, respectively. The range of wrist motion was unchanged after surgery, but the grip strength improved from 74% ± 22.1% preoperatively to 89% ± 13.7% postoperatively compared with the contralateral side (P = .042). Mean Disabilities of the Arm, Shoulder, and Hand (DASH) and Patient-Related Wrist Evaluation (PRWE) scores improved significantly (P < .001) from 44 and 51 preoperatively to 13 and 23 postoperatively, respectively. The radiological parameters of the scaphoid and carpal alignment in patients who achieved bony union did not correlate with clinical wrist function.

CONCLUSIONS

Arthroscopic reduction and osteosynthesis of chronic unstable scaphoid nonunion is limited for restoration of normal carpal alignment but has positive effects on the recovery of clinical wrist function.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

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.

Quantifying scaphoid malalignment based upon height-to-length ratios obtained by 3-dimensional computed tomography

PURPOSE

To determine if 3-dimensional height-to-length (H/L) measurements including coronal plane assessment will improve malalignment detection of scaphoid fractures and to determine if more waist than proximal pole nonunions are malaligned.

METHODS

Computed tomography scans of uninjured wrists (n = 74) were used to obtain 3-dimensional models of healthy scaphoids. These models were used to determine 95% normal ranges of the H/L ratio in standard sagittal and coronal planes in an automated fashion. Subsequently, the H/L ratios of fibrous nonunions (n = 26) were compared with these normal ranges and were classified as either aligned or malaligned.

RESULTS

The mean normal H/L ratio in the sagittal plane was 0.61 (range, 0.54-0.69) and in the coronal plane 0.42 (range, 0.36-0.48). The mean H/L ratios of the nonunions differed from those of the healthy scaphoids in these planes: 0.65 and 0.48, respectively. Based on sagittal plane evaluation of all nonunions, 46% exceeded the normal H/L range versus 54% based on combining sagittal and coronal plane measurements. More waist nonunions (71%) than proximal pole nonunions (22%) exceed the normal H/L range.

CONCLUSIONS

Evaluation of the H/L ratio in the coronal plane provided valuable additional information for the detection of scaphoid deformities. More malaligned cases were found for waist nonunions than for proximal pole nonunions.

CLINICAL RELEVANCE

This method may be a helpful diagnostic tool to detect malalignment and to choose between in situ fixation or reconstruction.

Volar percutaneous screw fixation of the scaphoid: a cadaveric study

PURPOSE

To test the efficacy of a previously described technique of angiocatheter-assisted instrument positioning in achieving a central screw position in a cadaveric model for volar percutaneous screw fixation (PSF) of the scaphoid and to quantify the damage to surrounding soft tissue and articular cartilage associated with the procedure.

METHODS

We performed fluoroscopically guided volar PSF of the scaphoid on 10 fresh cadaveric wrists. We then dissected the specimens, analyzed screw position in cross sections of the scaphoid, and described injury to nearby soft tissue structures as well as articular cartilage of the scaphotrapezial joint.

RESULTS

All 10 screws were positioned within the central third of the scaphoid on at least 2 of 3 cross sections, and 8 of 10 screws were positioned within the central third of the proximal pole. Two wrists required a transtrapezial trajectory for satisfactory screw positioning. None of the specimens sustained visible neurovascular damage, and 2 wrists revealed minor tendon damage. Trajectories involving the scaphotrapezial joint violated, on average, 7% of the scaphoid articular cartilage. With a transtrapezial trajectory, 11% of the trapezial cartilage was violated

CONCLUSIONS

Central positioning of the screw is biomechanically superior, and screw position within the central one third of the proximal pole has been associated with faster time to union. Volar PSF achieved satisfactory screw position in the scaphoid. The majority of wrists were amenable to PSF via the scaphotrapezial joint, though a transtrapezial approach was a viable alternative for wrists with restrictive anatomy. Both approaches minimally disrupted the scaphotrapezial joint and surrounding soft tissues.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

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.

A comparison of the rates of union after cancellous iliac crest bone graft and Kirschner-wire fixation in the treatment of stable and unstable scaphoid nonunion

This study was performed to determine whether pure cancellous bone graft and Kirschner (K-) wire fixation were sufficient to achieve bony union and restore alignment in scaphoid nonunion. A total of 65 patients who underwent cancellous bone graft and K-wire fixation were included in this study. The series included 61 men and four women with a mean age of 34 years (15 to 72) and mean delay to surgery of 28.7 months (3 to 240). The patients were divided into an unstable group (A) and stable group (B) depending on the pre-operative radiographs. Unstable nonunion was defined as a lateral intrascaphoid angle > 45°, or a radiolunate angle > 10°. There were 34 cases in group A and 31 cases in group B. Bony union was achieved in 30 patients (88.2%) in group A, and in 26 (83.9%) in group B (p = 0.439). Comparison of the post-operative radiographs between the two groups showed no significant differences in lateral intrascaphoid angle (p = 0.657) and scaphoid length (p = 0.670) and height (p = 0.193). The radiolunate angle was significantly different (p = 0.020) but the mean value in both groups was < 10°. Comparison of the dorsiflexion and palmar flexion of movement of the wrist and the mean Mayo wrist score at the final clinical visit in each group showed no significant difference (p = 0.190, p = 0.587 and p = 0.265, respectively). Cancellous bone graft and K-wire fixation were effective in the treatment of stable and unstable scaphoid nonunion.

Cite this article: Bone Joint J 2013;95-B:809–14.