Interfragmentary motion in patients with scaphoid nonunion

Quantitative 3-D CT Demonstrates Distal Row Pronation and Translation and Radiolunate Arthritis in the SNAC Wrist

BACKGROUND

In scaphoid nonunion advanced collapse (SNAC) wrist arthritis, we analyzed the 3-dimensional (3-D) deformity patterns of carpal alignment secondary to scaphoid nonunion and quantified subchondral arthritis by investigating alterations in bone density.

METHODS

We constructed 3-D models of the carpal bones and radius from 51 patients with scaphoid nonunion (nonunion group) and 50 healthy controls (control group). We quantified the differences in 3-D geometric position of the distal carpal row relative to the distal radius in SNAC wrists versus controls. In addition, we assessed the bone density of anatomic regions of interest in the radiocarpal and capitolunate joints relative to the pisiform bone density to characterize degenerative changes in SNAC wrists.

RESULTS

The distal carpal row pronated by a difference of 14° (7.2° versus -6.7°; p < 0.001), deviated ulnarly by a difference of 19° (7.7° versus -11.2°; p < 0.001), shifted dorsally by a difference of 17% of the dorsovolar width of the distal radius (21.0% versus 4.4%; p < 0.001), shifted radially by a difference of 8% of the radioulnar width of the distal radius (13.2% versus 5.3%; p < 0.001), and migrated proximally by a difference of 12% of the lunate height (96.3% versus 108.8%; p < 0.001) in the nonunion group compared with the control group. Additionally, it was found that bone density was greater at the capitolunate joint (capitate head: 140.4% versus 123.7%; p < 0.001; distal lunate: 159.9% versus 146.3%; p < 0.001), the radial styloid (157.0% versus 136.3%; p < 0.001), and the radiolunate joint (proximal lunate: 134.8% versus 122.7%; p < 0.001; lunate fossa: 158.6% versus 148.1%; p = 0.005) in the nonunion group compared with the control group.

CONCLUSIONS

Scaphoid nonunion exhibited a unique deformity pattern and alteration in bone-density distributions. The distal carpal row not only shifted dorsally and migrated proximally but also pronated, deviated ulnarly, and shifted radially. Bone density was greater at the capitolunate joint, the radial styloid, and surprisingly, the radiolunate joint. Our findings give insight into the natural history and progression of arthritis of the SNAC wrist. Additionally, future studies may give insight into whether successful treatment of scaphoid nonunion arrests the progression of arthritis.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Double trapezia sign: A new radiologic sign of scaphoid nonunion

In scaphoid nonunion, pseudarthrosis and sclerotic change occur at the nonunion site. These changes make a distal fragment look like a trapezium on plain radiographs and we called this phenomenon the double trapezia sign. The purpose of this study was to estimate the diagnostic reliability of the double trapezia sign and its clinical and prognostic implications for the scaphoid nonunion.A retrospective review of 124 patients who underwent surgical treatment because of scaphoid nonunion between January 2007 and December 2017 was performed. Two hand surgeons and 1 musculoskeletal radiologist reviewed preoperative plain radiographs independently. Each observer evaluated the plain radiographs in 2 separate sessions at least 3 weeks apart to assess intraobserver and interobserver reliabilities of the double trapezia sign. To assess clinical and prognostic implications of the double trapezia sign, the patients were divided into the positive and nonpositive groups, and several variables such as age, sex, duration of nonunion, size of the distal fragment, avascular necrosis (AVN) of the proximal fragment, type of bone graft, healing time, and failure rate were compared between the 2 groups.The kappa values of intraobserver and interobserver reliabilities were >0.8, corresponding to almost perfect agreement. There were 58 patients in the positive group and 66 patients in the nonpositive group. The mean duration of nonunion was 38.5 months in the positive group and 12.2 months in the nonpositive group (P < .001). The size of distal fragment was 49.6% and 60.9%, respectively (P < .001). The AVN of proximal fragment was 24.1% and 54.5%, respectively (P = .001). The mean healing time was 4.1 and 6.4 months, respectively (P < .001). The failure rate was 13.8% and 27.3%, respectively (P = .066).In conclusion, the double trapezia sign is a valuable radiographic sign of scaphoid nonunion. The double trapezia sign is easily identifiable on plain radiographs and has excellent intra- and interobserver reliabilities. The positive double trapezia sign implies mid-waist nonunion, long duration of nonunion, less possibility of AVN, and favorable postoperative prognosis.

[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.

Wrist movements induce torque and lever force in the scaphoid: an ex vivo study

Purpose

We hypothesised that intercarpal K-wire fixation of adjacent carpal bones would reduce torque and lever force within a fractured scaphoid bone.

Methods

In eight cadaver wrists, a scaphoid osteotomy was stabilised using a locking nail, which also functioned as a sensor to measure isometric torque and lever forces between the fragments. The wrist was moved through 80% of full range of motion (ROM) to generate torque and force within the scaphoid. Testing was performed with and without loading of the wrist and K-wire stabilisation of the adjacent carpal bones.

Results

Average torque and lever force values were 49.6 ± 25.1 Nmm and 3.5 ± 0.9 N during extension and 41 ± 26.7 Nmm and 8.1 ± 2.8 N during flexion. Torque and lever force did not depend on scaphoid size, individual wrist ROM, or deviations of the sensor versus the anatomic axis. K-wire fixation did not produce significant changes in average torque and lever force values except with wrist radial abduction (P = 0.0485). Other than wrist extension, torque direction was not predictable.

Conclusion

In unstable scaphoid fractures, we suggest securing rotational stability with selected implants for functional postoperative care. Wrist ROM within 20% extension and radial abduction to 50% flexion limit torque and lever force exacerbation between scaphoid fragments.

Accuracy of manual and automatic placement of an anatomical coordinate system for the full or partial radius in 3D space

Accurate placement of a coordinate system on the radius is important to quantitatively report 3D surgical planning parameters or joint kinematics using 4D imaging techniques. In clinical practice, the scanned length of the radial shaft varies among scanning protocols and scientific studies. The error in positioning a radial coordinate system using a partially scanned radius is unknown. This study investigates whether the imaged length of the radius significantly affects the positioning of the coordinate system. For different lengths of the radius, the error of positioning a coordinate system was determined when placed automatically or manually. A total of 85 healthy radii were systematically shortened until 10% of the distal radius remained. Coordinate systems were placed automatically and manually at each shortening step. A linear mixed model was used to associate the positioning error with the length of the radial shaft. The accuracy and precision of radial coordinate system placement were compared between automatic and manual placement. For automatic placement of the radial coordinate system, an increasing positioning error was associated with an increased shortening of the radius (P = < 0.001). Automatic placement is superior to manual placement; however, if less than 20% of the radial shaft length remains, manual placement is more accurate.

Evaluation of the geometric accuracy of computed tomography and microcomputed tomography of the articular surface of the distal portion of the radius of cats

OBJECTIVE

To evaluate accuracy of articular surfaces determined by use of 2 perpendicular CT orientations, micro-CT, and laser scanning.

SAMPLE

23 cat cadavers.

PROCEDURES

Images of antebrachia were obtained by use of CT (voxel size, 0.6 mm) in longitudinal orientation (CT_LO images) and transverse orientation (CT_TO images) and by use of micro-CT (voxel size, 0.024 mm) in a longitudinal orientation. Images were reconstructed. Craniocaudal and mediolateral length, radius of curvature, and deviation of the articular surface of the distal portion of the radius of 3-D renderings for CT_LO, CT_TO, and micro-CT images were compared with results of 3-D renderings acquired with a laser scanner (resolution, 0.025 mm).

RESULTS

Measurement of CT_LO and CT_TO images overestimated craniocaudal and mediolateral length of the articular surface by 4% to 10%. Measurement of micro-CT images underestimated craniocaudal and mediolateral length by 1%. Measurement of CT_LO and CT_TO images underestimated mediolateral radius of curvature by 15% and overestimated craniocaudal radius of curvature by > 100%; use of micro-CT images underestimated them by 3% and 5%, respectively. Mean ± SD surface deviation was 0.26 ± 0.09 mm for CT_LO images, 0.30 ± 0.28 mm for CT_TO images, and 0.04 ± 0.02 mm for micro-CT images.

CONCLUSIONS AND CLINICAL RELEVANCE

Articular surface models derived from CT images had dimensional errors that approximately matched the voxel size. Thus, CT cannot be used to plan conforming arthroplasties in small joints and could lack precision when used to plan the correction of a limb deformity or repair of a fracture.

Carpal kinematic changes after scaphoid nonunion: an in vivo study with four-dimensional CT imaging

The aim was to evaluate if motion between the scaphoid bone fragments is related to the position of the fracture line and if a scaphoid nonunion results in the uncoupling of the proximal and distal carpal row during wrist motion. The influence of dorsal intercalated segment instability on interfragmentary motion was also analysed. In this study, 12 patients were included with unilateral scaphoid nonunion. Four-dimensional computerized tomography was used to analyse flexion-extension and radioulnar deviation motion of both wrists. We found that an increased instability of the scaphoid fragments is associated with the presence of dorsal intercalated segment instability and is not dependent on the position of the fracture line relative to the scaphoid apex. Additionally, a scaphoid nonunion results in an uncoupling of the carpal rows.

Factors associated with union time of acute middle-third scaphoid fractures: an observational study

Background

The aim of this study was to investigate the union time of acute middle-third scaphoid fractures following treatments and to analyze the effect of different factors on late union.

Patients and methods

We retrospectively reviewed patients with acute middle-third scaphoid fracture at our institution between January 2013 and December 2017. Patient demographics, fracture characteristics, and treatment strategy, such as age, gender, body mass index, habit of smoking, sides of injury, dominant hand, ulnar variance, multiple fractures, and treatment methods, were investigated. Univariate and multivariate analyses were used to identify possible predictive factors.

Results

A total of 132 patients with scaphoid fracture were included in our study. Operation was performed in 67 patients (50.8%), and conservative treatment was performed in the other 65 patients (49.2%). The union time was 7.2±0.5 weeks. In the multivariate logistic regression analysis, late diagnosis (odds ratio, 1.247; 95% CI, 1.022–1.521) and conservative treatment method (odds ratio, 1.615; 95% CI, 1.031–2.528) were identified as 2 independent predictors of late union in scaphoid fractures patients. Other parameters were not demonstrated to be predictive factors.

Conclusion

Late diagnosis and conservative treatment were two factors associated with late union. Long time of follow-up is necessary for patient with these factors.

Analysis of instability patterns in acute scaphoid fractures by 4-dimensional computed tomographic imaging - A prospective cohort pilot study protocol

Introduction

A scaphoid fracture is the most common carpal fracture. When healing of the fracture fails (nonunion), a specific pattern of osteoarthrosis occurs, resulting in pain, restricted wrist motion and disability. Scaphoid fracture classification systems recognize fragment displacement as an important cause of nonunion. The fracture is considered unstable if the fragments are displaced. However, whether and how displaced bone fragments move with respect to one another has not yet been investigated in vivo. With a four-dimensional (4D) computed tomographic (CT) imaging technique we aim to analyze the interfragmentary motion patterns of displaced and non-displaced scaphoid fragments. Furthermore, the correlation between fragment motion and the development of a scaphoid nonunion is investigated. We hypothesize that fragment displacement is not correlated to fragment instability; and concurrent nonunion is related to fragment instability and not to interfragmentary displacement.

Methods

In a prospective single-center cohort pilot study, patients with a one-sided acute scaphoid fracture and no history of trauma to the contralateral wrist are illegible for inclusion. Twelve patients with a non-displaced scaphoid fracture and 12 patients with a displaced scaphoid fracture are evaluated. Both wrists are scanned with 4D-CT imaging during active flexion-extension and radio-ulnar deviation motion. The contralateral wrist serves as kinematic reference. Relative displacement of the distal scaphoid fragment with respect to the proximal scaphoid fragment, is described by translations and rotations (the kinematic parameters), as a function of the position of the capitate. Non-displaced scaphoid fractures are treated conservatively, displaced scaphoid fractures receive intraoperative screw fixation. Follow-up with CT scans is conducted until consolidation at 1½, 3 and 6 months. This trial is registered in the Dutch Toetsingonline trial registration system, number: NL60680.018.17.

Ethics

This study is approved by the Medical Ethics Committee of the Academic Medical Center, Amsterdam.

Current Management of Scaphoid Nonunion Based on the Biomechanical Study

Scaphoid nonunion causes abnormal wrist kinematics and typically leads to carpal collapse and subsequent degenerative arthritis of the wrist. However, the natural history, including carpal collapse and degenerative arthritis of scaphoid nonunion, may vary at different fracture locations. This article reviews recent biomechanical studies related to the natural history of scaphoid nonunion. In the distal-type fractures (type B2 in Herbert classification), where the fracture located distal to the scaphoid apex, the proximal scaphoid fragment and lunate, which are connected through the dorsal scapholunate interosseous ligament (DSLIL) and dorsal intercarpal ligament (DIC), extend together, and the distal fragment of the scaphoid flexes individually. Therefore, untreated type B2 fractures normally show the humpback deformity, resulting in dorsal intercalated segment instability deformity relatively earlier after the injury. In the proximal-type fractures (type B1), where the fracture is located proximal to the scaphoid apex, the connection between the distal fragment and lunate is preserved through the DSLIL and DIC so that the scaphoid-lunate complex remains stable and the carpal collapse is less severe than that in distal-type fractures. The fracture location relative to the apex of the dorsal scaphoid ridge is a reliable landmark in the determination of the natural history of scaphoid nonunion.

Scaphoid nonunion: what is the role of the Zaidemberg 1,2 intercompartmental supraretinacular arterial flap?

The reported results for the treatment of scaphoid nonunions with non-vascularized grafts are based on observational studies with a high variability in union rates from 38%-100% and time to union from 6-18 weeks, and there is also a lack of a standard classification. Meta-analyses and systematic reviews have been presented to better support conclusions from large pools of data (604 to 5246 cases), but their interpretation remains limited because of lack of uniformity in the studies analysed. Several authors have presented results from the Zaidemburg flap, with highly variable outcomes despite using the same technique; union rates have ranged from 27%-100% achieved between 6.5-19 weeks. Technical details that may be responsible for the discrepancies are discussed. There is a need for a validated prognostic classification system for scaphoid nonunions that can allow comparisons between outcome studies.

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.

In vitro experimental investigation of the forces and torque acting on the scaphoid during light grasp

The aim of this study was to measure the magnitude and direction of forces and torque within osteotomized scaphoids within cadaveric wrists during grasping movement of the hand. The mechanical contributions of clinically relevant individual wrist-crossing tendon groups were investigated. Wrists of eight forearms were immobilized in the sagittal, transverse, and coronal plane on a fixation device with unhindered axial gliding. The scaphoid was osteotomized and the fragments stabilized using an interlocking nail. The nail served as a sensor for measurement of inter-fragmentary forces orthogonal and torque around the sensor axis. Thus, torque and cantilever forces were measured which originated between the fragments through co-contraction through the activity of wrist-crossing tendons. Grasping movement of the hand induced a mean maximum torque of 0.038 ± 0.051 Nm and a force of 4.01 ± 1.71 N on the scaphoid. The isolated activation of thumb tendons resulted in a torque of 9.9 E^-3 ± 7.7 E^-3 Nm and a force of 1.42 ± 0.49 N. Despite immobilization of the wrist, grasping movement of the hand caused substantial forces and torque within the osteotomized scaphoid bone in varying directions and severity among different specimens. These factors may contribute to the development of nonunions and malunions in unstable scaphoid fractures through interfragmentary micromotion. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1734-1742, 2016.

Analysis of deformity in scaphoid non-unions using two- and three-dimensional imaging

Pre-operative assessment of the deformity in scaphoid non-unions influences surgical decision-making. To characterize deformity, we used three-dimensional computed tomographic modelling in 28 scaphoid non-unions, and quantified bone loss, dorsal osteophyte volume and flexion deformity. We further related these three-dimensional parameters to the intrascaphoid and capitate-lunate angles, and stage of scaphoid non-union advanced collapse assessed on conventional two-dimensional images and to the chosen surgical procedure. Three-dimensional flexion deformity (mean 26°) did not correlate with intrascaphoid and capitate-lunate angles. Osteophyte volume was positively correlated with bone loss and stage of scaphoid non-union advanced collapse. Osteophyte volume and bone loss increased over time. Three-dimensional modelling enables the quantification of bone loss and osteophyte volume, which may be valuable parameters in the characterization of deformity and subsequent decision-making about treatment, when taken in addition to the clinical aspects and level of osteoarthritis.

TYPE OF STUDY/LEVEL OF EVIDENCE

Level IV.

The Effect of Scaphoid Fracture Site on Scaphoid Instability Patterns

Background Scaphoid fractures are common carpal fractures that are often misdiagnosed as wrist sprains and may go on to nonunion. The location of the fracture site may influence the stability of scaphoid nonunions. Purpose To determine whether the stability of a scaphoid nonunion depends upon the fracture's location, we tested the hypothesis that a simulated fracture distal to the apex of the scaphoid dorsal ridge will have greater interfragmentary motion than proximal. Methods Eleven cadaver wrists were moved through three wrist motions using a wrist simulator. In six wrists, a fracture was created distal to the scaphoid apex, and in five a fracture was created proximal to the apex. Sensors attached to the distal and proximal parts of each scaphoid measured the interfragmentary motion during wrist motion. Results In those wrists in which the scaphoid was sectioned distal to the apex, the distal fragment became significantly more unstable relative to the proximal fragment. It flexed, ulnarly deviated, and pronated. These motion changes were less when the scaphoid was sectioned proximally. Discussion Scaphoid fractures distal to the scaphoid apex will have greater interfragmentary motion. The mobility of the fragments at the fracture site is possibly a more important contributory factor of nonunion in scaphoid waist fractures than for proximal scaphoid fractures. Clinical Relevance Understanding the effect that the location of a scaphoid fracture has on the potential for nonunion may influence the modalities of treatment and follow-up.

Diagnosis of occult scaphoid fractures: a randomized, controlled trial comparing bone scans to radiographs for diagnosis

BACKGROUND

Many patients with suspected scaphoid fractures but negative radiographs are immobilized for ≥ 2 weeks and are eventually found to have no fracture. Bone scans are reportedly 99% sensitive for these injuries if done ≥ 72 hours postinjury.

OBJECTIVE

The purpose of this study was to determine if early bone scans would allow for shorter cast immobilization periods in patients with suspected scaphoid fractures.

METHODS

Twenty-seven patients with clinically suspected scaphoid fractures and negative radiographs were randomized to early diagnosis (bone scan within 3-5 days; n  =  12) or traditional diagnosis (radiographs 10-14 days postinjury; n  =  15). The primary outcome was number of days immobilized in a cast.

RESULTS

The mean number of days immobilized was 26 in the traditional group and 29 in the bone scan group. Overall, 6 patients had scaphoid fractures (2 in the traditional diagnosis group and 4 in the bone scan group; p > 0.05), and 8 had other types of fractures. These other types of fractures included four distal radius fractures, two triquetral fractures, one trapezoid fracture, and one hamate fracture. There was no significant difference in the number of other types of fractures between groups. The Kaplan-Meier survival analysis using the log-rank test revealed that there was no statistically significant difference between days immobilized between the radiograph and bone scan groups (p  =  0.38).

CONCLUSIONS

The current study suggests that the use of bone scans to help diagnose occult scaphoid fractures does not reduce the number of days immobilized and that the differential diagnosis of occult scaphoid fractures should remain broad because other injuries are common.

Radiographic clues for determining carpal instability and treatment protocol for scaphoid fractures

The magnitude of carpal instability following scaphoid fracture is closely related to the fracture location. Middle-third fractures of the scaphoid are classified into B1 (distal oblique fractures) and B2 (complete waist fractures). Deciding preoperatively whether a fracture is B1 or B2 is clinically important, because several studies have revealed that B1 is more stable than B2. Dorsal intercalated segment instability deformity often develops in B2, creating a large, wedge-shaped bone defect, while minimal humpback deformity develops in B1, and the bone defect is much smaller, even after long-standing nonunions. However, determination of the fracture types using X-rays may be less accurate than using three dimensional computed tomography. This article suggests two radiographic clues for estimation of post-fracture carpal instability along with a treatment protocol for each fracture type.

Scaphoid interfragmentary motions due to simulated transverse fracture and volar wedge osteotomy

BACKGROUND

Our goal was to determine 3-dimensional interfragmentary motions due to simulated transverse fracture and volar wedge osteotomy of the scaphoid during physiologic flexion-extension of a cadaveric wrist model.

METHODS

The model consisted of a cadaveric wrist (n = 8) from the metacarpals through the distal radius and ulna with load applied through the major flexor-extensor tendons. Flexibility tests in flexion-extension were performed in the following 3 test conditions: intact and following transverse fracture and wedge osteotomy of the scaphoid. Scaphoid interfragmentary motions were measured using optoelectronic motion tracking markers. Average peak scaphoid interfragmentary motions due to transverse fracture and wedge osteotomy were statistically compared (P<0.05) to intact.

FINDINGS

The accuracy of our computed interfragmentary motions was ± 0.24 mm for translation and ± 0.54° for rotation. Average peak interfragmentary motions due to fracture ranged between 0.9 mm to 1.9 mm for translation and 5.3° to 10.8° for rotation. Significant increases in interfragmentary motions were observed in volar/dorsal translations and flexion/extension due to transverse fracture and in separation and rotations in all 3 motion planes due to wedge osteotomy.

INTERPRETATION

Comparison of our results with data from previous in vitro and in vivo biomechanical studies indicates a wide range of peak interfragmentary rotations due to scaphoid fracture, from 4.6° up to 30°, with peak interfragmentary translations on the order of several millimeters. Significant interfragmentary motions, indicating clinical instability, likely occur due to physiologic flexion-extension of the wrist in those with transverse scaphoid fracture with or without volar bone loss.

The scaphoid

The scaphoid is vitally important for the proper mechanics of wrist function. Its unique morphology from its boat like shape to its retrograde blood supply can present with challenges in the presence of a fracture. Almost completely covered with articular cartilage, this creates precise surface loading demands and intolerance to bony remodeling. Fracture location compounds risk of malunion and non-union. Scaphoid fractures may significantly impair wrist function and activities of daily living, with both individual and economic consequences.

Diagnostic performance of radiographs and computed tomography for displacement and instability of acute scaphoid waist fractures

BACKGROUND

Fracture displacement is the most important factor associated with nonunion of a scaphoid waist fracture.We evaluated the performance characteristics of radiographs and computed tomography (CT) in the diagnosis of intraoperative displacement and instability of scaphoid waist fractures using wrist arthroscopy as the reference standard.

METHODS

During a six-year period (2004 to 2010) at two institutions, forty-four adult patients with a scaphoid waist fracture underwent arthroscopy-assisted operative fracture treatment at a mean of nine days (range, two to twenty-two days) after injury. Subjects included all of those with a displaced scaphoid fracture seen on radiographs and a selection of patients with a nondisplaced scaphoid fracture. All patients had preoperative radiographs and CT. Arthroscopy with up to 5 kg of traction was the reference standard for fracture displacement and instability.

RESULTS

The reference standard (arthroscopy) led to a diagnosis of twenty-two displaced fractures (all unstable) and twenty-two nondisplaced fractures (seven unstable). Displacement was diagnosed in eleven patients (25%) with the use of radiographs and in twenty (45%) with CT. The sensitivity, specificity, and accuracy for diagnosing intraoperative displacement were 45%, 95%, and 70%, respectively, with the use of radiographs and 77%, 86%, and 82%, respectively, with CT. The sensitivity, specificity, and accuracy for diagnosing intraoperative instability were 34%, 93%, and 55%, respectively,with the use of radiographs and 62%, 87%, and 70%, respectively, with CT. Assuming a 10% prevalence of fracture displacement and instability among all scaphoid waist fractures, the positive and negative predictive values for displacement were 53% and 94%, respectively, with the use of radiographs and 39% and 97% with CT whereas the positive and negative predictive values for instability were 36% and 93%, respectively, with radiographs and 34% and 95% with CT.

CONCLUSIONS

Radiographs and CT scans cannot be relied on to accurately diagnose intraoperative scaphoid fracture displacement or instability compared with arthroscopic examination. The influence, with regard to the risk of nonunion, of intraoperative instability of a scaphoid fracture that is seen to be nondisplaced on radiographs or CT is currently unknown.

LEVEL OF EVIDENCE

Diagnostic Level III.

Factors associated with arthroscopically determined scaphoid fracture displacement and instability

PURPOSE

To identify factors associated with arthroscopically diagnosed scaphoid fracture displacement and instability.

METHODS

This was a secondary use of data from 2 prospective cohort studies. The studies included 58 consecutive adult patients with a scaphoid fracture who elected arthroscopy-assisted operative fracture treatment: some for displacement, some as part of a prospective protocol, and others to avoid a cast. All patients had preoperative computed tomography with reconstructions in planes defined by the long axis of the scaphoid.

RESULTS

Arthroscopy revealed 38 unstable fractures (movement between fracture fragments; 66%), 27 of which were also displaced. All arthroscopically determined displaced fractures were unstable, and 11 of the 31 arthroscopically determined, nondisplaced fractures were unstable. There was a significant correlation between radiographic comminution (more than 2 fracture fragments) and arthroscopically determined displacement and instability.

CONCLUSIONS

Radiographic comminution is associated with displacement and instability as determined by arthroscopy.

Carpal and forearm kinematics during a simulated hammering task

PURPOSE

Hammering is a functional task in which the wrist generally follows a path of motion from a position of combined radial deviation and extension to combined ulnar deviation and flexion, colloquially referred to as a dart thrower's motion. The purpose of this study was to measure wrist and forearm motion and scaphoid and lunate kinematics during a simulated hammering task. We hypothesized that the wrist follows an oblique path from radial extension to ulnar flexion and that there would be minimal radiocarpal motion during the hammering task.

METHODS

Thirteen healthy volunteers consented to have their wrist and distal forearm imaged with computed tomography at 5 positions while performing a simulated hammering task. The kinematics of the carpus and distal radioulnar joint were calculated using established markerless bone registration methods. The path of wrist motion was described relative to the sagittal plane. Forearm rotation and radioscaphoid and radiolunate motion were computed as a function of wrist position.

RESULTS

All volunteers performed the simulated hammering task using a path of wrist motion from radial extension to ulnar flexion that was oriented an average of 41 degrees +/- 3 degrees from the sagittal plane. These paths did not pass through the anatomic neutral wrist position; rather, they passed through a neutral hammering position, which was offset by 36 degrees +/- 8 degrees in extension. Rotations of the scaphoid and lunate were not minimal but averaged 40% and 41%, respectively, of total wrist motion. The range of forearm pronation-supination during the task averaged 12 degrees +/- 8 degrees .

CONCLUSIONS

The simulated hammering task was performed using a wrist motion that followed a coupled path of motion, from extension and radial deviation to flexion and ulnar deviation. Scaphoid and lunate rotations were greatly reduced, but not minimized, compared with rotations during pure wrist flexion/extension. This is likely because an extended wrist position was maintained throughout the entire task studied.

In vivo length changes of selected carpal ligaments during wrist radioulnar deviation

PURPOSE

To investigate changes in the lengths of selected carpal ligaments during wrist radioulnar deviation in vivo.

METHODS

We studied in vivo changes in the lengths of fibers of 5 palmar and dorsal intracapsular ligaments of the wrist during radioulnar deviation in 6 wrists of healthy volunteers using a noninvasive approach. Using serial computed tomography scans and volume registration techniques, the carpal kinematics were examined at 4 positions, from 40 degrees ulnar deviation to 20 degrees radial deviation, in 20 degrees increments. The 3-dimensional structures of the carpal bones, distal radius and ulna, and metacarpal bones were reconstructed using customized software. We modeled the paths of fibers of 5 palmar and dorsal carpal ligaments: radioscaphocapitate (RSC), long radiolunate (LRL), ulnocapitate (UC), dorsal intercarpal (DIC), and dorsal radiocarpal (DRC) ligaments. We analyzed changes in the lengths of these ligaments during wrist radioulnar deviation.

RESULTS

During wrist ulnar deviation, the RSC, LRL, and DIC ligaments lengthened significantly. During radial deviation, the UC and DRC ligaments lengthened significantly. Compared with their lengths at the neutral position of the carpus, the LRL ligament showed the greatest elongation rate at wrist ulnar deviation, and the DRC ligament showed the greatest elongation rate at wrist radial deviation among the 5 ligaments studied.

CONCLUSIONS

Among ligaments measured, the RSC, LRL, and DIC ligaments are tensed during wrist ulnar deviation. The UC and DRC ligaments are tensed during wrist radial deviation. Results of this in vivo study suggest that radial or ulnar deviation may predispose some carpal ligaments to excessive tensile load. The finding that the ligaments undergo different elongation rates during wrist motion may also indicate their roles in maintaining normal wrist kinematics.