Intact Wrist Research Articles

Arthroscopic gap distance can predict the degree of scapholunate ligament tears: a cadaver study

BackgroundMidcarpal joint arthroscopy is essential for diagnosing scapholunate (SL) instability, but a discrepancy may exist between the grade of arthroscopic evaluation and the extent of SL ligament tears. This study aimed to investigate whether the magnitude of arthroscopic SL gap distance could predict the extent of ligamentous disruptions in a simulated SL dissociation model. MethodsEight upper extremities of fresh cadavers were analyzed. Static and dynamic SL gap distances were measured with using custom-made probes via midcarpal arthroscopy in intact wrists following sequential sectioning of the SL stabilizing ligaments. Comparisons of static and dynamic SL gaps between stages were conducted using analysis of variance followed by the Games–Howell test. Receiver operating characteristic (ROC) curves were constructed to assess the diagnostic performance of the SL gap distance in identifying simulated ligament tears. ResultsThere were no significant differences between stages in the static SL gap distance. Dynamic SL gap distance increased significantly following SL interosseous ligament (SLIL) sectioning. According to the ROC curve for dynamic SL gap distance, the area under the curve was 0.94 for the assessment of the diagnostic performances in identifying complete SLIL sectioning. A cut-off value of 1.4mm for the dynamic SL gap showed the highest diagnostic accuracy rate (91%). The dynamic SL gap distance showed a high diagnostic performance in the detection of dorsal intercarpal ligament (DICL) sectioning. The highest accuracy rate (85%) was noted when the threshold value was set at 2.8mm. ConclusionThe SLIL is the primary stabilizer of the SL joint in the viewpoint of arthroscopic measurement. Dynamic SL joint widening of more than 1.4mm showed the best predictive ability for complete SLIL tears, while 2.8mm widening made it possible to predict both DICL and SLIL tears.

Simulating Distal Radius Fracture Strength Using Biomechanical Tests: A Modeling Study Examining the Influence of Boundary Conditions

Distal radius fracture strength has been quantified using in vitro biomechanical testing. These tests are frequently performed using one of two methods: (1) load is applied directly to the embedded isolated radius or (2) load is applied through the hand with the wrist joint intact. Fracture loads established using the isolated radius method are consistently 1.5 to 3 times greater than those for the intact wrist method. To address this discrepancy, a validated finite element modeling procedure was used to predict distal radius fracture strength for 22 female forearms under boundary conditions simulating the isolated radius and intact wrist method. Predicted fracture strength was highly correlated between methods (r = 0.94; p < 0.001); however, intact wrist simulations were characterized by significantly reduced cortical shell load carriage and increased stress and strain concentrations. These changes resulted in fracture strength values less than half those predicted for the isolated radius simulations (2274 ± 824 N for isolated radius, 1124 ± 375 N for intact wrist; p < 0.001). The isolated radius method underestimated the mechanical importance of the trabecular compartment compared to the more physiologically relevant intact wrist scenario. These differences should be borne in mind when interpreting the physiologic importance of mechanical testing and simulation results.

Effects of proximal row carpectomy on wrist biomechanics: A cadaveric study

Background Many studies show good clinical results after proximal row carpectomy. Some biomechanical consequences are documented, but to our knowledge muscle moment arm variations have not previously been quantified. Methods In five fresh–frozen wrist, kinematics and tendon excursions were measured using a 3D electrogoniometer and Linear Variable Differential Transformers (SOLARTRON Inc., AMETEK Advanced Measurement Technology, Inc, 801 South Illinois Avenue, Oak Ridge, TN 37831-2011, USA), respectively, in three conditions: intact wrist, after posterior capsulotomy and after proximal row carpectomy. Mean pivot point, defined as the point whose sum of the squared distances to the helical axes is minimum, wrist range of motion and mean moment arms were measured during dorso-palmar flexion, radioulnar deviation and circumduction movements. Findings No alteration of the range of motion was observed. On the other hand, the mean pivot point shifted proximally (6.8–9.1 mm) after proximal row carpectomy (p < 0.05) for all motions tested and most muscle moment arms decreased significantly after proximal row carpectomy. Interpretation The results of this study allow a better understanding of the biomechanical effects of this procedure. The important moment arm reduction and pivot point displacement suggest modifications of joint biomechanical parameters which could influence the functional outcome of PRC.

Scaphoid and Lunate Translation in the Intact Wrist and Following Ligament Resection: A Cadaver Study

To determine the amount of scaphoid and lunate translation that occurs in normal cadaver wrists during wrist motion, and to quantify the change in ulnar translation when specific dorsal and volar wrist ligaments were sectioned. We measured the scaphoid and lunate motion of 37 cadaver wrists during wrist radioulnar deviation and flexion-extension motions using a wrist joint motion simulator. We quantified the location of the centroids of the bones during each motion in the intact wrists and after sectioning either 2 dorsal ligaments along with the scapholunate interosseous ligament or 2 volar ligaments and the scapholunate interosseous ligament. In the intact wrist, the scaphoid and lunate statistically translated radially with wrist ulnar deviation. With wrist flexion, the scaphoid moved volarly and the lunate dorsally. After sectioning either the dorsal or volar ligaments, the scaphoid moved radially. After sectioning the dorsal or volar ligaments, the lunate statistically moved ulnarly and volarly. Measurable changes in the scaphoid and lunate translation occur with wrist motion and change with ligament sectioning. However, for the ligaments that were sectioned, these changes are small and an attempt to clinically measure these translations of the scaphoid and lunate radiographically may be limited. The results support the conclusion that ulnar translocation does not occur unless multiple ligaments are sectioned. Injury of more than the scapholunate interosseous ligament along with either the dorsal intercarpal and dorsal radiocarpal or the radioscaphocapitate and scaphotrapezial ligaments is needed to have large amounts of volar and ulnar translation.

The role of SLIL in 3D movement of scaphoid and lunate during wrist radio-ulnar deviation

Objective To observe the effects of transection of scapholunate interosseous ligament (SLIL)and its subregions on the 3D movement of scaphoid and lunate during wrist radio-ulnar deviation, and study the rule of SLIL subregions in 3D motion of the scaphoid and lunate. Methods Twelve fresh adult cadaver upper extremities (6 left side and 6 right side) were divided to normal control group, proximal SLIL subregion transection group, proximal and dorsal SLIL subregion transection group, proximal and palmar SLIL subregion transection group and entire SLIL transection group (6 each). 3D laser scanning and reconstruction techniques were applied to measure 3D motion of the scaphoid and lunate during wrist radio-ulnar deviation, and data were statistically analyzed, on the normal and sequential sectioning of SLIL subregions during wrist flexion-extension and wrist radlal-ulnar deviation were determined. Results In the intact wrist specimens, the scaphoid and lunate deviated radially and ulnarly during wrist radial-ulnar deviation, along with obvious flexion and extension.At the same time, there was minimal scaphoid and lunate pronation-supination. With sectioning of proximal subregions of the SLIL, no significant kinematics changes were observed in the scaphoid and lunate bones. After sectioning proximal and palmar or proximal and dorsal subregions of the SLIL, kinematics of the scaphoid and lunate were changed. Sectioning the whole SLIL caused increased volar flexion of the scaphoid and decreased volar flexion of the lunate. Conclusion 3D laser scanning and reconstruction can precisely measure 3D motion of the scaphoid and lunate. Kinematic study of SLIL subregions showed that partial or complete sectioning of SLIL led to obvious change in volar flexion of the scaphoid and lunate. However, the proximal subregion of SLIL has no prominent effect on the motion of scaphoid and lunate. Key words: Carpal joints; Scaphoid bone; Lunate bone; Ligaments,articular; 3D movement

Comparison of the “Contact Biomechanics” of the Intact and Proximal Row Carpectomy Wrist

The proximal row carpectomy (PRC) is a clinically useful motion-preserving procedure for various arthritides of the wrist. However, there are few studies on the "contact biomechanics" after PRC. The purpose of this study is to evaluate the contact biomechanics in terms of pressure, area, and contact location of the intact and PRC wrist. Six fresh-frozen cadaver forearms were tested in neutral, 45 degrees of flexion, and 45 degrees of extension. In the intact wrist, Fuji UltraSuperLow pressure contact film was placed in the radioulnocarpal joint. The specimen was loaded to a total force of 200 N. We then performed a PRC, and the experiment was repeated using Fuji Low film. The film was scanned and analyzed with a customized MATLAB program. Multivariable analysis of variance with multiple contrast testing and Student's t-test were performed for statistics. In the intact wrist, scaphoid contact pressure averaged 1.4 megapascals (MPa), and lunate contact pressure averaged 1.3 MPa. In terms of contact location, scaphoid contact in the intact wrist significantly moved dorsal and ulnar in flexion and significantly moved volar and radial in extension. Lunate contact significantly moved dorsal in flexion. PRC wrist contact pressure was 3.8 times that of the intact wrist, and the contact area was approximately 26% that of the intact wrist. Lastly, in terms of the amount of contact translation after PRC, the capitate contact translated (7.5 mm) more than did the scaphoid contact (5.6 mm) and had about equal translation to that of the lunate (7.3 mm). Contact pressure increased significantly and contact area decreased significantly after PRC. There is significant contact translation after PRC (more than scaphoid translation but equal to lunate translation), which provides quantitative support of the theory that translational motion of the PRC may explain its good clinical outcomes.

Proximal Row Carpectomy: Role of a Radiocarpal Interposition Lateral Meniscal Allograft

The purpose of this study was to determine whether use of a lateral meniscal interposition allograft combined with proximal row carpectomy would reduce the peak joint contact pressures and increase the contact area when compared with proximal row carpectomy alone. Six cadaver wrists were cyclically moved through flexion-extension and radioulnar deviation ranges of motion. Joint contact pressure was measured with the carpus intact, after proximal row carpectomy, and after insertion of a lateral meniscal allograft. Contact pressure data were also collected with the wrist in 5 static positions. Proximal row carpectomy caused statistically greater peak pressures and smaller contact areas when compared with the intact wrist. Insertion of the allograft statistically restored the pressures and areas to that observed in the intact wrist. These results support the clinical trial of a lateral meniscal interposition allograft in patients with contraindications for proximal row carpectomy, such as pre-existing arthritis in the capitate head or lunate facet of the radius.

Distal Tunnel Placement Improves Scaphoid Flexion With the Brunelli Tenodesis Procedure for Scapholunate Dissociation

Treatment of scapholunate dissociation remains difficult. The modified Brunelli procedure, a flexor carpi radialis tenodesis through the scaphoid and secured with dorsal wrist ligaments, has shown promising results. This study compares the biomechanical effects on scaphoid flexion and scapholunate gap between proximal and distal tunnel placement in the modified Brunelli procedure. Eight fresh-frozen cadaveric forearms were used. A dorsal approach to the wrist through the floor of the fourth compartment was used. Metallic markers were implanted into the scaphoid and lunate. Tunnels were drilled through the proximal and distal poles of the scaphoid. Wrists were positioned in neutral and loaded to 100 N through the wrist flexor and extensor tendons. Posteroanterior and lateral radiographs were taken with the scapholunate interval intact, with the scapholunate interval sectioned, and after the modified Brunelli tenodesis was performed through the proximal and then distal tunnels using Mersilene tape. Radiographs were analyzed for change in scapholunate angle and scapholunate gap. Multivariate analysis of variance was performed to assess statistical significance for each state compared with the intact wrist. In the intact wrist, the mean scapholunate gap was 1.6 mm +/- 0.1. With the scapholunate interval sectioned, the scapholunate angle increased by 26 degrees +/- 12 and gap increased to 4.2 mm +/- 1.2. With a proximal tunnel for the modified Brunelli procedure, the change in scapholunate angle decreased to 15 degrees +/- 10 and gap decreased to 1.8 mm +/- 0.3. With a distal tunnel for the modified Brunelli procedure, the change in scapholunate angle decreased to 4 degrees +/- 7 and gap decreased to 1.3 mm +/- 0.2. These biomechanical data suggest that a tunnel exiting in the distal pole of the scaphoid results in better correction of scaphoid flexion when performing the modified Brunelli procedure.

RETRACTED ARTICLE: Carpal tunnel syndrome in patients who are receiving long-term renal hemodialysis

The development of a carpal tunnel syndrome has become an increasingly recognized problem in patients who are treated by long-term hemodialysis. Arteriovenous fistula has been identified as one of the possible cause for the development of carpal tunnel syndrome. Wrists of 558 hemodialysis patients who had fistula at least 1 year served as the case group and the other intact wrists of the same patients served as the control group. Carpal tunnel syndrome was diagnosed clinically; however, 232 random patients underwent electrodiagnostic studies the day after hemodialysis. In 170 (30.5%) wrists with arteriovenous fistula developed carpal tunnel syndrome versus 68 (12.2%) in the contralateral wrist. Three patients had a concurrent diagnosed radial steal syndrome. In all three wrists that had radial steal syndrome developed carpal tunnel syndrome. There was a correlation, however, between the development of the carpal tunnel syndrome, and the side of the longest vascular access. Contrary to the clinical assessment, electrodiagnostic studies did not indicate any significant association between the frequency of carpal tunnel syndrome and arteriovenous fistula or its duration. Hemodialysis patients are at considerable risk of developing carpal tunnel syndrome in the wrist with an arteriovenous fistula. Close observation and routine clinical examination is mandatory to prevent further problems.

Carpal Kinematics After Proximal Row Carpectomy

Proximal row carpectomy (PRC) is a clinically useful motion-sparing procedure for the treatment of certain degenerative conditions of the wrist. Clinical outcome studies after PRC have shown that wrist flexion-extension averages approximately 60% of that of the contralateral wrist. The purpose of this study was to determine how the kinematics of the wrist are altered after PRC. Eight fresh-frozen cadaver forearms were scanned with computed tomography before and after PRC. Forearms were scanned in 5 different wrist positions (neutral, extension, flexion, radial deviations, and ulnar deviation). Wrists were positioned dynamically and then held statically in a custom fixture through forces applied to the 4 wrist flexor/extensor tendon groups. Three-dimensional computer models of the radius, lunate, and capitate were generated from the computed tomographic images, and the kinematics of the capitate and lunate were calculated relative to the neutral position. For the intact wrist, the motion of the capitate was calculated relative to both the lunate (midcarpal motion) and the radius (overall wrist motion) and the motion of the lunate was calculated relative to the radius (radiocarpal motion). After PRC, only the movement of the capitate relative to the radius was calculated, which represents radiocapitate and overall wrist motion. All motions were plotted in 3 dimensions for purposes of qualitative visualization. After PRC, the capitate articulated with the lunate fossa of the radius for all positions in all samples. Overall wrist motion decreased 28%, 30%, 40%, and 12% in flexion, extension, radial deviation, and ulnar deviation, respectively. Motion at the radiocarpal joint after PRC, however, was greater compared with motion at the radiocarpal and midcarpal joints of the intact wrist during flexion and extension. This was not the case in radial deviation because of impingement of the trapezoid on the radial styloid. In radial and ulnar deviation, motion of the capitate head changed from predominantly rotational in the intact wrist (midcarpal joint) to a combination of rotation and translation after PRC (radiocarpal joint). Removal of the proximal carpal row decreased normal wrist flexion and extension. Although ulnar deviation was preserved, radial deviation was limited by impingement of the trapezoid on the radial styloid. Radiocapitate range of motion after PRC was greater than capitolunate range of motion in the intact wrists. Compared with previously published requirements, wrist range of motion observed after PRC was sufficient for activities of daily living.

Changes in Patterns of Scaphoid and Lunate Motion During Functional Arcs of Wrist Motion Induced by Ligament Division

To determine the in vitro motion of the scaphoid and lunate during wrist circumduction and wrist dart-throw motions and to see how these motions change after the ligamentous stabilizers of the scaphoid and lunate are sectioned in a manner simulating scapholunate instability. Twenty-one fresh-frozen cadaver forearms were moved through a dart-throw motion and a circumduction motion using a wrist joint simulator. Scaphoid and lunate motion were measured with the wrist ligaments intact and after sectioning of the scapholunate interosseous ligament, the scaphotrapezium ligament, and the radioscaphocapitate ligament. In the intact wrist the scaphoid and lunate moved more during circumduction than during the dart-throw motion. With ligamentous sectioning the scaphoid flexed more and the lunate extended more during both the circumduction and dart-throw motions. During the circumduction motion both before and after sectioning the global motion of the scaphoid was greater than that of the lunate. After sectioning the scaphoid motion increased and the lunate motion decreased. The scaphoid and lunate motions were observed to change remarkably after ligamentous sectioning. The observed changes in carpal motion correlate with the clinical observation that after ligamentous injury arthritic changes occur in the radioscaphoid joint and not in the radiolunate joint. Analysis of the injured wrist in positions that combine flexion-extension and radial-ulnar deviation may allow noninvasive diagnosis of specific wrist ligament injuries.

Association between Carpel Tunnel Syndrome and Arteriovenous Fistula in Hemodialysis Patients

Carpal tunnel syndrome is more common in hemodialysis patients than in the general population. In addition to uremic neuropathy, arteriovenous fistula has been identified as one of the possible causes for the development of carpal tunnel syndrome. Wrists of 279 hemodialysis patients who had arteriovenous fistula for at least 6 months served as the case group and the other intact wrists of the same patients served as the control group. Carpal tunnel syndrome was diagnosed clinically; however, 116 random patients underwent electrodiagnostic studies the day after hemodialysis. Clinically, carpal tunnel syndrome was diagnosed less frequently in the contralateral wrist than in the wrist with arteriovenous fistula (12.2 percent versus 30.5 percent, p < 0.0001). Meanwhile, the authors found a positive correlation between the duration of fistula and the development of carpal tunnel syndrome (p < 0.028). The site of fistula (snuffbox, radiocephalic) used, however, had no effect on the rate of development of carpal tunnel syndrome (p > 0.2). Contrary to the clinical assessment, electrodiagnostic studies did not indicate any significant association between the frequency of carpal tunnel syndrome and arteriovenous fistula or its duration. With the nerve conduction velocity abnormalities observed in patients with uremic polyneuropathy, the authors believe that clinical diagnosis of carpal tunnel syndrome is more indicative of the development of the condition than the electrodiagnostic results. The authors' clinical results have revealed that hemodialysis patients are at considerable risk of developing carpal tunnel syndrome in the wrist with an arteriovenous fistula. These patients should be under close observation and receive routine checkup.

Biomechanical analysis of load transmission characteristics of limited carpal fusions used to treat Kienböck's disease

Although limited carpal fusions used in the treatment of Kienböck's disease are thought to act by decreasing the loads on the lunate, biomechanical studies show that capitohamate fusion acts oppositely to what is expected. This experimental study was designed to resolve this paradox. In a biomechanical cadaveric study, load transmissions at the radioulnacarpal joint were investigated under 140 and 210 newtons of load with three wrist postures, namely, neutral, ulnar and radial deviations, in five intact wrists and after scaphotrapeziotrapezoid, capitohamate, and scaphocapitate fusions. Under 140 newtons of load, the loads imposed to the lunate decreased following scaphotrapeziotrapezoid and scaphocapitate fusions, but increased after capitohamate fusion. However, when the load was increased to 210 newtons, there were no differences between intact wrists and limited carpal fusions in respect to the loads exerted on the lunate. In all the situations, the lunate was subjected to a significantly greater load in ulnar deviation. These results suggest that limited carpal fusions do not alter load transmission characteristics of the wrist joint under 210 newtons of load. The etiology of the Kienböck's disease seems to be related to an overload in ulnar deviation and the beneficial effect of limited carpal fusions seems to be associated with restricted ulnar deviation of the wrist rather than load transmission characteristics.

A morphological study of the scaphoid using a mathematical technique and comparative study of the three-dimensional measurements of the scaphoid.

To guide reconstruction of scaphoid non-union, we attempted to create full-scale models of the scaphoid by three-dimensional computed tomography (3D CT) of the healthy side. In this study, we obtained 3D scans of 51 cadaveric hands and studied the difference in morphology between genders and between the left and right sides. The major axis length on a fixed plane and Fourier transformation curve were examined. Ten scaphoid images were also obtained with 3D CT before and after removal from the cadaveric hands. Our findings suggest good correlation between models produced using 3D CT images of the scaphoid alone, and this could serve as an accurate model if the magnification is corrected using the regression line. However, the model using 3D CT images of the intact wrist joint has a large margin of error and its use will not be practical.

Human motor compensations for thixotropy-dependent changes in resting wrist joint position after large joint movements.

Resting tension of relaxed skeletal muscle fibres held at a given length varies with the immediate previous history of length changes and contractions. The primary aim of this study was to explore the motor control consequences of this history-dependency in healthy subjects. Angular position and passive torque were recorded from the intact wrist joint. Integrated surface electromyography (IEMG) was recorded from wrist extensor and flexor muscles. In relaxed subjects, wrist joint position was displaced towards dorsiflexion after a single high-amplitude dorsiflexion movement combined with a strong flexor/extensor co-contraction (dorsiflexion conditioning), whereas after volarflexion conditioning there was a shift towards volarflexion. These after-effects could be abruptly cancelled by short periods ( approximately 5 s) of rapid flapping hand movements or forceful isometric co-contractions, findings indicative of muscle thixotropy. The IEMG-evaluated motor after-effects were as follows. A slowly subsiding wrist flexor contraction was needed to restore and maintain the original resting wrist position after dorsiflexion conditioning whereas a slowly subsiding extensor contraction was needed for the same goal after volarflexion conditioning. Furthermore, ongoing wrist extensor IEMG activity required to actively hold the wrist in a moderate dorsiflexed position or to resist a constant volar torque at resting position was temporarily reduced after dorsiflexion conditioning and enhanced (not significantly) after volarflexion conditioning. The results provide evidence that during voluntary maintenance of a desired wrist joint position the motor commands to the position-holding muscles are unconsciously adjusted to compensate for thixotropy-dependent variations in the resting tension of the muscles.

Wrist kinetics after luno-triquetral dissociation: the changes in moment arms of the flexor carpi ulnaris tendon

Wrist biomechanics after luno-triquetral (LT) dissociation is important for understanding the clinical sequelae of the disease and for determining its treatment options. The LT interosseous ligament plays an important role in stabilizing the joint and damage to the ligament would be expected to significantly increase moment arms of tendon of the flexor carpi ulnaris (FCU), the principal ulnar wrist flexor. We investigated the changes in moment arms of FCU tendon after various amounts of sectioning of the ligaments proven to be associated with LT dissociation. In six fresh frozen cadaveric upper extremities, excursions of the FCU tendon were recorded simultaneously with wrist joint angulation during wrist flexion-extension and radioulnar deviation. Tendon excursions were measured in intact wrists, in wrists with sectioning of the dorsal portion of the LT interosseous ligament, in wrists with sectioning of the entire LT interosseous ligament, and finally in wrists with further sectioning of the dorsal radiotriquetral and intercarpal ligaments. Moment arms of the tendon were calculated from tendon excursions and joint motion angulations and expressed as percentage changes from those in the intact wrist. During wrist flexion-extension, moment arms of the FCU tendon after sectioning of the entire LT interosseous ligament and after sectioning of the two capsular ligaments were 112±7% and 114±8%, respectively; these values were significantly greater than those in the intact wrist. During radioulnar deviation, the moment arms were 114±11% after sectioning of the dorsal portion of the LT interosseous ligament, 134±15% after sectioning of the entire ligament, and 153±18% after sectioning of the capsular ligaments, again being significantly greater than the normal wrist. Increase in moment arms of the FCU tendon after loss of integrity of the LT interosseous ligament and dorsal capsular ligaments may contribute to clinical sequelae of LT dissociation and difficulty in treating this disorder.

Wrist kinetics after scapholunate dissociation: the effect of scapholunate interosseous ligament injury and persistent scapholunate gaps

The purpose of this study was to investigate the effects of cutting of the scapholunate interosseous ligament (SLIL) and persistent widening of the scapholunate (SL) joint on changes in moment arms of the principal wrist motor tendons. In seven fresh frozen cadaveric upper extremities, excursions of the extensor carpi radialis longus (ECRL) and brevis (ECRB), extensor carpi ulnaris (ECU), flexor carpi radialis (FCR), and flexor carpi ulnaris (FCU) were recorded simultaneously with wrist joint angulation during wrist flexion–extension and radioulnar deviation. Tendon excursions were measured in intact wrists, then in the wrists with complete SLIL sectioning and in those with moderate or severe persistent SL joint widening. The data were converted to moment arms of the tendons. The results showed that moment arms of the ECRL and ECRB tendons after SLIL sectioning were, respectively, 110±6% and 105±3% of those in the intact wrist. In the wrists with moderate or severe SL joint widening, moment arms of the flexors significantly increased ( P<0.01 and P<0.001, respectively). During radioulnar deviation, moment arms of the ECRL, ECRB, ECU, and FCU tendons decreased after SLIL sectioning and the SL joint widening. However, moment arms of the FCR tendon significantly increased 122±23% after the SLIL section, 133±28% after the moderate SL joint widening, and 138±24% after the severe SL joint widening compared with those of the intact wrists. This study demonstrated that integrity of the SLIL and appropriate SL joint space are important for mechanics of wrist motor tendons. Loss of integrity of the SLIL and persistent SL joint widening increase mechanical effects of the radial side wrist motor tendons, which may contribute to the pathomechanics of scaphoid malrotation, scapholunate advanced collapse, and early osteoarthritis in the radioscaphoid joint interface seen in SL dissociation. The results also suggest that reduction of the displaced SL joint is imperative to the recovery of wrist kinetics after SL dissociation.

Biomechanical evaluation of wrist motor tendons after fractures of the distal radius.

We conducted a biomechanical study of changes in parameters of wrist motor tendons in fractures of the distal radius in 7 cadaveric extremities. Extra-articular distal radius fractures were simulated by distal radius osteotomy and fracture angulation was maintained by external fixators. Eight positions of the distal radius fractures were studied: dorsal angulation of 10 degrees, 20 degrees, 30 degrees, and 40 degrees and radial angulation of 5 degrees, 10 degrees, 15 degrees, and 20 degrees. Dorsal and radial angulation of the fractures were measured with respect to the shaft of the radius. Excursions of 5 principal wrist motor tendons extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris were recorded simultaneously with wrist joint angulation using a computer-assisted recording system. Data were collected from intact wrists and from wrists with fractures at each of 8 positions of angulation during wrist flexion and extension and radical and ulnar deviation. Moment arm of the wrist motor tendons was derived from tendon excursion and joint angulation. The results demonstrated that excursions and moment arms of principal wrist motor tendons are significantly affected by dorsal and radial angulation of distal radius fractures. Amplitude of changes in moment arms increased as the deformities became more severe. Statistical analysis revealed that dorsal angulation of 10 degrees or more significantly affected moment arms of all the prime wrist motors. Dorsal angulation of 30 degrees or 40 degrees changed the moment arms greatly. Radial angulation of 5 degrees did not affect moment arms of the tendons and angulation over 10 degrees had a statistically significant effect on the tendons. We conclude that deformities of distal radius fractures have a significant influence on the biomechanics of the wrist motors.

The triangular fibrocartilage complex: An important component of the pulley for the ulnar wrist extensor

The extensor carpi ulnaris (ECU) tendon is the only wrist motor tendon that broadly connects with the triangular fibrocartilage complex (TFCC) of the wrist. The goal of this study was to determine the biomechanical effect of the TFCC on the function of the ECU. The effect of avulsion of the TFCC on the changes in mechanics of the ulnar wrist extensor tendon was investigated in 8 fresh-frozen cadaver forearms. Excursion of the ECU tendon was continuously recorded over the functional range of wrist extension and ulnar deviation in intact wrists, wrists with ulnar styloid fractures, wrists with TFCC release from the distal ulna, and after excising the distal ECU tendon sheath. The ECU tendon demonstrated a 30% increase in excursion during wrist extension after release of the TFCC from its attachment on the distal ulna. During 60 degrees of wrist extension, excursion of the ECU tendon was 4.8+/-1.9 mm in the intact wrists and 6.3+/-2.0 mm after TFCC release. This change in excursion represented 1.4 mm of bowstringing for the ECU tendon during 60 degrees of wrist extension. Further incision of the distal part of the extensor sheath produced only 6% increase in excursion of the ECU. Results of this study suggest that the TFCC is an important component of the pulley for the ulnar wrist extensor. These findings imply that disturbance of the wrist extensor after TFCC injury may potentially contribute to abnormal loading and force transmission through the ulnar wrist and the TFCC, and support the growing consensus that integrity of the TFCC should be restored in the presence of TFCC injuries.

Biomechanical analysis of limited intercarpal fusion for the treatment of Kienböck's disease: a three-dimensional theoretical study.

Although several types of intercarpal fusion have been advocated for the treatment of Kienbock's disease, the clinical outcome of each procedure is still inconclusive. The joint load and ligament tension based on a three-dimensional model were measured to determine which intercarpal fusion procedures unload the lunate and whether they alter the force transmission through the entire wrist joint. Ten theoretical models of wrists were used to simulate three different operative procedures: capitate-hamate fusion, scapho-trapezial-trapezoidal fusion, and scaphocapitate fusion. A discrete element analysis technique was used to perform these investigations. The joint force and ligament tension of normal wrists and of simulated operative procedures were calculated according to the deformation of each spring element, simulating the articular cartilage and the carpal ligaments. Scaphocapitate and scapho-trapezial-trapezoidal fusions significantly decreased the joint force at the radiolunate joint and the lunocapitate joint compared with the intact wrist. In contrast, these fusions significantly increased this value at the radioscaphoid joint in comparison with the intact wrist. In the midcarpal joint, scaphocapitate fusion also increased the joint force at the scapho-trapezial-trapezoidal joints and at the triquetral-hamate joint, whereas scapho-trapezial-trapezoidal fusion increased it at the scapho-capitate joint. Capitate-hamate fusion yielded no significant changes of the joint forces through the entire wrist joint. In the analysis of ligament tension, scaphocapitate and scapho-trapezial-trapezoidal fusions significantly decreased the tension only in the dorsal scapholunate ligament. These findings demonstrate that scaph-ocapitate and scapho-trapezial-trapezoidal fusions are effective in decompressing the lunate. By contrast, capitate-hamate fusion is ineffective in reducing lunate compression. Although scaphocapitate and scapho-trapezial-trapezoidal fusions are recommended for the treatment of Kienbock's disease, clinicians should consider that the increase of force transmission through the radioscaphoid and the midcarpal joints may lead to early degenerative changes after these procedures have been performed.