Dorsal Scapholunate Interosseous Ligament Research Articles

Scaphoid, lunate and capitate kinematics in the normal and ligament deficient wrist: A bi-plane X-ray fluoroscopy study

The ligamentous structures of the wrist stabilise and constrain the interactions of the carpal bones during active wrist motion; however, the three-dimensional translations and rotations of the scaphoid, lunate and capitate in the normal and ligament deficient wrist during planar and oblique wrist motions remain poorly understood. This study employed a computer-controlled simulator to replicate physiological wrist motion by dynamic muscle force application, while carpal kinematics were simultaneously measured using bi-plane x-ray fluoroscopy. The aim was to quantify carpal kinematics in the native wrist and after sequential sectioning of the scapholunate interosseous ligament (SLIL) and secondary scapholunate ligament structures. Seven fresh-frozen cadaveric wrist specimens were harvested, and cycles of flexion–extension, radial-ulnar deviation and dart-thrower’s motion were simulated. The results showed significant rotational and translational changes to these carpal bones in all stages of disruptions to the supporting ligaments (p < 0.05). Specifically, following the disruption of the dorsal SLIL (Stage II), the scaphoid became significantly more flexed, ulnarly deviated, and pronated relative to the radius, whereas the lunate became more extended, supinated and volarly translated (p < 0.05). Sectioning of the dorsal intercarpal (DIC), dorsal radiocarpal (DRC), and scaphotrapeziotrapezoid (STT) ligaments (Stage IV) caused the scaphoid to collapse further into flexion, ulnar deviation, and pronation. These findings highlight the importance of all the ligamentous attachments that relate to the stability of the scapholunate joint, but more importantly, the dorsal SLIL in maintaining scapholunate stability, and the preservation of the attachments of the DIC and DRC ligaments during dorsal surgical approaches. The findings will be useful in diagnosing wrist pathology and in surgical planning.

Dorsal scapholunate interosseous ligament: ultrasound evaluation between dominant and non-dominant wrist in young sports patients.

The dorsal component of the scapholunate ligament, is the strongest component, in fact it has a maximum tensile strength of 300N and mainly controls flexion and extension. In a recent study, the thickness and length of the dorsal component of SLIL was measured using ultrasound image, the length of the dorsal scapholunate ligament was 7.5mm ± 1.4mm and the thickness of 1.8mm ± 0.4mm. We evaluate 60 wrists of 30 young athletic volunteers with ultra-sound image, comparing the thickness variations of the dorsal component of SLIL between the dominant and non-dominant wrist, to confirm our hypothesis that the dorsal component SLIL has proprioceptive activity and therefore the thickness of the ligament increases in following wrist activity. With a high-frequency ultrasound probe > 15MHz (Sonoscape X3 Pro) we evaluated 60 wrists of 30 young men (16 males and 14 females, 20-38years old) manual sports volunteers (10 tennis players, 8 padel players, 7 swimmers, 5 weight lifters) with no recent ligament injuries of the hand or wrist to participate in the study, we compared the dorsal component of SLIL between the dominant and non-dominant wrist. Dorsal SLIL was visualized in all 60 volunteers wrists. We measured an average scapholunate dorsal ligament length 7.7mm and average thickness of 2.3mm in the dominant wrist and average 7.2mm in length and average 1.9mm thickness in the non dominant wrist. The mean dorsal scapholunate interval was average 4.9mm and the mean central interval was average 2.1mm in the dominant wrist and 4.7mm and 1.8mm in the non dominant wrist, so that meas-urements remained unchanged with those reported by previous authors. In our study we ultrasonographically measured an average scapholunate dorsal ligament length 7.7mm and average thickness of 2.3mm in the dominant wrist and average 7.2mm in length and average 1.9mm thickness in the non dominant wrist. This confirms our hypothesis that there is a direct stimulus on the ligamentous component of the dor-sal SLIL in the dominant wrist following repeated uses and activities such as to cause an increase in thickness of the dorsal ligament to highlight the possibility of a proprioceptivity of the ligament if subjected to continuous training. IV.

Changes in Scaphoid and Lunate Position and Loading at Two Wrist Pushup Positions

Scapholunate interosseous ligament (SLIL) injury following a fall on an outstretched hand may lead to carpal instability and in some cases require long-term rehabilitation following repair. Rehabilitation, especially in athletes, may include pushups, but little is known as to what type of pushup may be safer. To determine biomechanical differences between two pushup positions (neutral or extended). Six fresh cadaver wrists with pre-existing SLIL damage were uni-axially loaded in neutral and extension in order to simulate two different pushup styles. The motions of the scaphoid and lunate in relation to the radius were measured. The dorsal, proximal, and volar insertion sites of the SLIL were identified and, using the collected kinematic data, gap distances were calculated for each site. Gap distance between the proximal SLIL insertion points was significantly greater in neutral than in extension. There was a trend that the dorsal and volar SLIL insertion points were also greater in neutral than in extension. After the wrist was extended 90o, the scaphoid extended 70.1o and the lunate extended 28.6o compared to their positions with the wrist in neutral. The larger gap distances between the scaphoid and lunate in neutral suggest that a neutral style pushup could put higher forces on a wrist with pre-existing SLIL damage and may thus hinder recovery for a person with a repaired SLIL. A pushup in extension, in these injured wrists, may be less detrimental.

Multiphasic scaffold for scapholunate interosseous ligament reconstruction: A study in the rabbit knee.

Scapholunate interosseous ligament tears are a common wrist injury in young and active patients that can lead to suboptimal outcomes after repair. This research aims to assess a multiphasic scaffold using 3D-printing for reconstruction of the dorsal scapholunate interosseous ligament. The scaffold was surgically implanted in vivo in the position of the native rabbit medial collateral ligament. Two branches of treatment were implemented in the study. In the first group, the rabbits (n = 8) had the knee joint fixed in flexion for 4 weeks using 1.4 mm K-wires prior to sample harvesting. The second group (n = 8) had the rabbit knee joint immobilized for 4 weeks prior to K-wire removal and mobilization for an additional 4 weeks prior to sample harvesting. Overall, samples were harvested at 4 weeks post-surgery (immobilized group) and eight weeks post-surgery (mobilized group). Mechanical tensile testing (n = 5/group) and histology (n = 3/group) of the constructs were conducted. Tissue integration and maturation were observed resulting in increased mechanical strength of the operated joint at 8 weeks (P < .05). Bone and ligament tissues were regenerated in their respective compartments with structural and mechanical properties approaching those reported for the human dorsal SLIL ligament. Clinical Significance: This proof of concept study has demonstrated that the synthetic multiphasic scaffold was capable of regenerating both bone and ligament while also withstanding the physiological load once implanted in the rabbit knee. The artificial scaffold may provide an alternative to current techniques for reconstruction of scapholunate instability or other ligament injuries in the hand and wrist.

Scapholunate Dissociation: Current Concepts of the Treatments

Scapholunate dissociation is the most common cause of the wrist pain and instability and typically results from scapholunate interosseous ligament (SLIL) injury. It is difficult for surgeons to diagnose the SLIL injury due to its complex anatomy and biomechanics. The natural history of the SLIL injury is still not fully understood as most of the SLIL injuries are not detected in their acute stage. Careful physical examination and radiologic evaluation are essential aspects of SLIL injury diagnosis. We should consider five conditions to evaluate SLIL injuries: the integrity of the dorsal SLIL, the healing potential of the disrupted ligament, the alignment of the scaphoid, the reducibility of the carpal malalignment, and the cartilage condition. In this review, the stages classified based on these conditions and the current treatments according to each stage will be described in detail.

Additively Manufactured Multiphasic Bone-Ligament-Bone Scaffold for Scapholunate Interosseous Ligament Reconstruction.

The scapholunate interosseous ligament (SLIL) is a frequently torn wrist ligament, and current surgical options for SLIL tears are suboptimal. This research aims to develop a novel multiphasic bone-ligament-bone scaffold (BLB) with a porous interface using 3D-printing and cell sheet technology for the reconstruction of the dorsal scapholunate interosseous ligament. The BLB comprises two bone compartments bridged by aligned polycaprolactone fibers mimicking the architecture of the native tissue. Mechanical testing of the BLBs shows their ability to withstand physiological forces. Combination of the BLB with human bone marrow mesenchymal stem cell sheet demonstrates that the harvesting did not compromise cell viability, while allowing homogeneous distribution in the ligament compartment. The BLBs are loaded with cell sheets and bone morphogenetic protein-2 in the ligament and bone compartment respectively prior to ectopic implantation into athymic rats. The histology demonstrates rapid tissue infiltration, high vascularization, and more importantly the maintenance of the compartmentalization as bone formation remains localized to the bone compartment despite the porous interface. The cells in the ligament compartment become preferentially aligned, and this proof-of-concept study demonstrates that the BLB can provide sufficient compartmentalization and fiber guiding properties necessary for the regeneration of the dorsal SLIL.

A four-dimensional-CT study of invivo scapholunate rotation axes: possible implications for scapholunate ligament reconstruction.

Additional fixation of the palmar scapholunate interosseous ligament has been advocated to improve the long-term results of dorsal scapholunate interosseous ligament reconstruction. To investigate the validity of this approach, we determined normal scapholunate motion patterns and calculated the location of the scapholunate rotation axis. We hypothesized that the optimal location of the scapholunate interosseous ligament insertion could be determined from the scapholunate rotation axis. Four-dimensional computerized tomography was used to study the wrist motion in 21 healthy participants. During flexion–extension motions, the scaphoid rotates 38° (SD 0.6°) relative to the lunate; the rotation axis intersects the dorsal ridge of the proximal pole of the scaphoid and the dorsal ridge of the lunate. Minimal scapholunate motion is present during radioulnar deviation. Since the scapholunate rotation axis runs through the dorsal proximal pole of the scaphoid, this is probably the optimal location for attaching the scapholunate ligament during reconstructive surgery.

The Quantitative Anatomy of the Dorsal Scapholunate Interosseous Ligament.

The anatomy of the scapholunate interosseous ligament (SLIL) has been described qualitatively in great detail, with recognition of the dorsal component's importance for carpal stability. The purpose of this study was to define the quantitative anatomy of the dorsal SLIL and to assess the use of high-frequency ultrasound to image the dorsal SLIL. We used high-frequency ultrasound imaging to evaluate 40 wrists in 20 volunteers and recorded the radial-ulnar (length) and dorsal-volar (thickness) dimensions of the dorsal SLIL and the dimensions of the scapholunate interval. We assessed the use of high-frequency ultrasound by comparing the length and thickness of the dorsal SLIL on ultrasound evaluation and open dissection of 12 cadaveric wrists. Student's t test was used to assess the relationship between measurements obtained on cadaver ultrasound and open dissection. In the volunteer wrists, the mean dorsal SLIL length was 7.5 ± 1.4 mm and thickness was 1.8 ± 0.4 mm; the mean scapholunate interval was 5.0 mm dorsally and 2.5 mm centrally. In the cadaver wrists, there was no difference in dorsal SLIL length or thickness between ultrasound and open dissection. The dorsal SLIL is approximately 7.5 mm long and 1.8 mm thick. These parameters may be useful in treatment of SLIL injuries to restore the native anatomy. High-frequency ultrasound is a useful imaging technique to assess the dorsal SLIL, although further study is needed to assess the use of high-frequency ultrasound in detection of SLIL pathology.

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.

Tensile and Torsional Structural Properties oftheNativeScapholunate Ligament.

The ideal material for reconstruction of the scapholunate interosseous ligament (SLIL) should replicate the mechanical properties of the native SLIL to recreate normal kinematics and prevent posttraumatic arthritis. The purpose of our study was to evaluate the cyclic torsional and tensile properties of the native SLIL and load to failure tensile properties of the dorsal SLIL. The SLIL bone complex was resected from 10 fresh-frozen cadavers. The scaphoid and lunate were secured in polymethylmethacrylate and mounted on a test machine that incorporated an x-y stage and universal joint, which permitted translations perpendicular to the rotation/pull axis as well as nonaxial angulations. After a 1 N preload, specimens underwent cyclic torsional testing (±0.45 N m flexion/extension at 0.5 Hz) and tensile testing (1-50 N at 1 Hz) for 500 cycles. Lastly, the dorsal 10 mm of the SLIL was isolated and displaced at 10 mm/min until failure. During intact SLIL cyclic torsional testing, the neutral zone was 29.7° ± 6.6° and the range of rotation 46.6° ± 7.1°. Stiffness in flexion and extension were 0.11 ± 0.02 and 0.12 ± 0.02 N m/deg, respectively. During cyclic tensile testing, the engagement length was 0.2 ± 0.1 mm, the mean stiffness was 276 ± 67 N/mm, and the range of displacement was 0.4 ± 0.1 mm. The dorsal SLIL displayed a 0.3 ± 0.2 mm engagement length, 240 ± 65 N/mm stiffness, peak load of 270 ± 91 N, and displacement at peak load of 1.8 ± 0.3 mm. We report the torsional properties of the SLIL. Our novel test setup allows for free rotation and translation, which reduces out-of-plane force application. This may explain our observation of greater dorsal SLIL load to failure than previous reports. By matching the natural ligament with respect to its tensile and torsional properties, we believe that reconstructions will better restore the natural kinematics of the wrist and lead to improved outcomes. Future clinical studies should aim to investigate this further.

Radiological evaluation of scapholunate intercarpal ligamentoplasty for chronic scapholunate dissociation in cadavers.

We performed a cadaveric study to evaluate radiological performance of a technique for scapholunate intercarpal ligamentoplasty designed for treating reducible scapholunate dissociation. We created scapholunate instability in 12 fresh adult cadaveric forearms by sectioning the dorsal scapholunate interosseous ligament and the dorsal intercarpal ligament. All wrists showed scapholunate diastasis, dorsal intercalated segmental instability and posterior scaphoid subluxation. We performed scapholunate intercarpal ligamentoplasty in six wrists and Garcia-Elias three-ligament tenodesis in another six. Wrists were examined radiographically both after ligament sectioning and after ligamentoplasty to compare static and dynamic scapholunate gaps and scapholunate and capitolunate angles. Improvement was statistically significant in all measurements, reflecting a return to normal values. Posterior scaphoid subluxation was also corrected. There was no significant difference between the two treatment groups. Our findings suggest that ligamentoplasty can restore scapholunate joint stability and normal carpal anatomy.

Length Changes in Scapholunate Interosseous Ligament With Resisted Wrist Radial and Ulnar Inclination.

To investigate the changes in length of the scapholunate interosseous ligament (SLIL) when the wrist is resisting horizontal lateral load and the forearm is in full pronation invivo. We obtained computed tomography scans of the wrists of 6 volunteers in 3 situations: 0° position (0° extension and 0° ulnar inclination) and full forearm pronation without force, and in the same position but with resisted ulnar and radial deviation. Nine zones of 3 subregions of the SLIL were measured and analyzed with computer modeling. Changes in length of the palmar SLIL with resisted ulnar deviation were significantly greater than those without an applied lateral load. In contrast, the changes in length of the dorsal SLIL with resisted radial deviation were statistically greater than those in the 0° position without loading. However, no significant differences in the changes in length of the proximal SLIL werefound in any of 3 situations, except the dorsal zone with resisted radial deviation. Application of lateral load has an effect on the separation of the palmar and dorsal insertions of the SLIL. The palmar subregion of the SLIL was more highly strained with wrist-resisted ulnar deviation. Conversely, the dorsal subregion of the SLIL was under greater tension with wrist-resisted radial deviation. For patients undergoing nonsurgical treatment of SLIL tears, a sudden contraction of ulnar or radial deviation agonist muscles may be harmful and contribute to SLinstability.

Cadaveric Testing of a Novel Scapholunate Ligament Reconstruction.

Background Existing scapholunate interosseous ligament (SLIL) reconstruction techniques include fixation spanning the radiocarpal joint, which do not reduce the volar aspect of the scapholunate interval and may limit wrist motion. Questions/Purpose This study tested the ability of an SLIL reconstruction technique that approximates both the volar and dorsal scapholunate intervals, without spanning the radiocarpal joint, to restore static scapholunate relationships. Materials and Methods Scapholunate interval, scapholunate angle, and radiolunate angle were measured in nine human cadaveric specimens with the SLIL intact, sectioned, and reconstructed. Fluoroscopic images were obtained in six wrist positions. The reconstruction was performed by passing tendon graft through bone tunnels from the dorsal surface toward the volar corner of the interosseous surface. After reduction of the scapholunate articulation, the graft was tensioned within the lunate bone tunnel, secured with an interference screw in the scaphoid, and sutured to the dorsal SLIL remnant. Differences among testing states were evaluated using repeated measures ANOVA. Results There was a significant increase in the scapholunate interval in all wrist positions after complete SLIL disruption. Compared with the disrupted state, there was a significant decrease in scapholunate interval in all wrist positions after reconstruction using a tendon graft and interference screw. Conclusion Our SLIL reconstruction technique reconstructs the volar and dorsal ligaments of the scapholunate joint and adequately restores static measures of scapholunate stability. This technique does not tether the radiocarpal joint and aims to optimize volar reduction. Clinical Relevance Our technique offers an alternative option for SLIL reconstruction that successfully restores static scapholunate relationships.

Biomechanical Evaluation of Scaphoid and Lunate Kinematics Following Selective Sectioning of Portions of the Scapholunate Interosseous Ligament

To determine the relative roles of the dorsal and volar portions of the scapholunate interosseous ligament (SLIL) in the stability of the scaphoid and lunate. Sixteen fresh cadaver wrists were moved through physiological motions using a wrist joint simulator. Electromagnetic sensors measured the motion of the scaphoid and lunate. Data were collected with the wrist intact, after randomly sectioning the dorsal SLIL first (8 wrists) or the volar SLIL first (8 wrists), and after full ligamentous sectioning. Differences in the percent increase in scaphoid flexion or lunate extension were compared using a t test with significance set at P < .05. Sectioning the dorsal SLIL accounted for 37%, 72%, and 68% of the increase in scaphoid flexion in wrist flexion-extension, radioulnar deviation, and dart throw motion as compared with complete SLIL sectioning. Sectioning the volar SLIL accounted for only 7%, 6%, and 14%, respectively. In the same 3 motions, sectioning the dorsal SLIL accounted for 55%, 57%, and 58% of the increase in lunate extension, whereas volar SLIL sectioning accounted for 27%, 28%, and 22%. The dorsal SLIL provides more stability to the scaphoid and lunate in biomechanical testing. The volar SLIL does provide some, although less, stability. Although this study supports the critical importance of dorsal SLIL repairs or reconstructions, it also shows that there may be some value in implementing a volar SLIL repair or reconstruction.

Association of Lesions of the Scapholunate Interval With Arthroscopic Grading of Scapholunate Instability Via the Geissler Classification

To determine whether specific anatomic lesions of the scapholunate supporting structures are associated with the grades of scapholunate instability according to the Geissler classification. Six fresh frozen cadaveric limbs underwent serial arthroscopic sectioning of the scapholunate supporting ligaments. To simulate a progressive scapholunate injury based on the current literature, sectioning occurred as follows: volar scapholunate interosseous ligament (SLIL), membranous SLIL, dorsal SLIL, radioscaphocapitate, long radiolunate, dorsal radiocarpal, dorsal intercarpal, and scaphotrapeziotrapezoid ligaments. We performed arthroscopic examination of the radiocarpal and midcarpal joints after each ligamentous sectioning and recorded the appearance of the scapholunate interval. There was a progressive increase in Geissler grade with sequential sectioning of the scapholunate supporting ligaments. In all specimens, Geissler grade 2 injury was associated with sectioning of intrinsic ligaments only. Geissler grade 3 injury first appeared with sectioning through the dorsal SLIL and continued through sectioning of the volar extrinsic ligaments. Geissler grade 4 injury did not occur until the dorsal extrinsic ligaments were sectioned. Statistical analysis indicated a linear relationship between ligament sectioned and Geissler grade, with deeper sections associated with a higher Geissler grade. In this cadaveric model, arthroscopically determined Geissler grade was associated with specific anatomic lesions of the scapholunate supporting ligaments. Sequential sectioning of the ligaments showed a progressive increase in Geissler grade. Knowledge of the association of Geissler grade with pathoanatomy may aid the surgeon in deciding which reconstructive method is best.

The Scapholunate Ligament Complex (SLLC)

It has become clear that the stability of the scapholunate joint is not dependent wholly upon the scapholunate interosseous ligament (SLIL) but rather upon both primary and secondary stabilizers, which can be thought of as forming a scapholunate ligament complex (SLLC). Each case of SL instability is unique and therefore should be treated with tissue specific repairs, which may partly explain why one procedure cannot successfully restore joint stability in every case. Elsaidi and Ruch sequentially divided the radioscaphocapitate (RSC), long and short radiolunate, the scapholunate interosseous ligament (SLIL), and finally the dorsal capsule insertion on the scaphoid,1 with no appreciable change in the radiographic appearance of the wrist. When the dorsal radiocarpal ligament (DRCL) was then divided, a dorsal intercalated segmental instability (DISI) deformity occurred.2 Short et al determined that the SLIL is the primary stabilizer of the SL articulation and that the DRCL, the dorsal intercarpal (DIC) ligament, the scaphotrapezial (ST) ligaments, and the RSC ligaments are secondary stabilizers.3 Dividing the DRCL alone only caused increased radial deviation of the lunate with the wrist in maximum flexion, whereas dividing the SLIL after any of the ligaments tested produced increased flexion and ulnar deviation of the scaphoid and lunate extension. The scapholunate joint stability is, therefore, dependent on a complex of ligaments, each having a separate role but working in concert. Galley et al published paper on the influence of the lunate type on scaphoid kinematics.4 In a rotating scaphoid, the scaphotrapezial ligaments are distally based and form a V with a narrow scaphoid attachment, and the scaphocapitate ligament is long to allow pronation or supination. When there was a type I lunate with a single facet, there is statistically greater scaphoid translation with radial deviation. In a flexing lunate, the scaphotrapezial ligaments form a proximally based V with a broad scaphoid attachment, and the scaphocapitate ligament is short and along the axis of flexion. When there was a type II lunate with a double facet, there was statistically greater scaphoid flexion with radial deviation. Based on this work, one can surmise that different joint kinematics would require a different type of reconstructive method. Following an injury, the patient with a type I lunate might develop rotational instability and, therefore, require a procedure that effectively limits scaphoid pronation such as a modified Brunelli, whereas the patient with a type II lunate might develop abnormal flexion of the scaphoid and therefore require a procedure that limits scaphoid flexion, such as a dorsal capsulodesis. Any given reconstructive procedure should be designed for one specific function rather than multiple functions, which may be a reason for failure in some cases. Rather than grouping procedures into those that provide sagittal plane stability versus those that provide coronal plane stability, it is preferable to consider the individual subcomponent(s) of the SLLC. The reconstructive procedures can be therefore grouped into those that stabilize the volar components of the SLLC (the palmar SLIL, RSC, ST ligaments), the dorsal components (dorsal capsule, dorsal SLIL, DRCL, DIC), and the interosseous component (SLIL). The dynamic protective role of the musculotendinous SL joint stabilizers should not be underestimated, as discussed in the Perspectives section by Dr. Garcia Elias. This issue explores some of the standard, time-tested techniques for scapholunate joint reconstruction, in addition to a number of new and innovative reconstructive options that signal a change in the conventional thinking regarding the management of scapholunate joint instability.

Desensitizing the Posterior Interosseous Nerve Alters Wrist Proprioceptive Reflexes

The presence of wrist proprioceptive reflexes after stimulation of the dorsal scapholunate interosseous ligament has previously been described. Because this ligament is primarily innervated by the posterior interosseous nerve (PIN) we hypothesized altered ligamento-muscular reflex patterns following desensitization of the PIN. Eight volunteers (3 women, 5 men; mean age, 26 y; range 21-28 y) participated in the study. In the first study on wrist proprioceptive reflexes (study 1), the scapholunate interosseous ligament was stimulated through a fine-wire electrode with 4 1-ms bipolar pulses at 200 Hz, 30 times consecutively, while EMG activity was recorded from the extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris, with the wrist in extension, flexion, radial deviation, and ulnar deviation. After completion of study 1, the PIN was anesthetized in the radial aspect of the fourth extensor compartment using 2-mL lidocaine (10 mg/mL) infiltration anesthesia. Ten minutes after desensitization, the experiment was repeated as in study 1. The average EMG results from the 30 consecutive stimulations were rectified and analyzed using Student's t-test. Statistically significant changes in EMG amplitude were plotted along time lines so that the results of study 1 and 2 could be compared. Dramatic alterations in reflex patterns were observed in wrist flexion, radial deviation, and ulnar deviation following desensitization of the PIN, with an average of 72% reduction in excitatory reactions. In ulnar deviation, the inhibitory reactions of the extensor carpi ulnaris were entirely eliminated. In wrist extension, no differences in the reflex patterns were observed. Wrist proprioception through the scapholunate ligament in flexion, radial deviation, and ulnar deviation depends on an intact PIN function. The unchanged reflex patterns in wrist extension suggest an alternate proprioceptive pathway for this position. Routine excision of the PIN during wrist surgical procedures should be avoided, as it alters the proprioceptive function of the wrist. Therapeutic IV.

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

Evidence of Wrist Proprioceptive Reflexes Elicited After Stimulation of the Scapholunate Interosseous Ligament

Recent publications on the sensory innervation of wrist ligaments have challenged our understanding of ligaments as mere passive restraints in wrist stability. Mechanoreceptors in ligaments have a role in signaling joint perturbations, in which the afferent information is believed to influence periarticular muscles. The scapholunate interosseous ligament is one of the most richly innervated ligaments in the wrist. The purpose of our study was to investigate the possible existence of a wrist proprioceptive reflex, by which afferent information elicited in the scapholunate interosseous ligament was hypothesized to influence the muscles moving the wrist joint. Nine volunteers (4 women and 5 men; mean age, 26 years; range, 21-28 years) participated in this study. Using ultrasound guidance, a fine-wire electrode was inserted into the dorsal scapholunate interosseous ligament and stimulated with four 1-ms pulses at 200 Hz. Electromyographic activities in extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris muscles were recorded using surface electrodes with the wrist actively positioned in isometric extension, flexion, and radial and ulnar deviation. The average EMGs from 30 consecutive stimulations were rectified and analyzed using the Student's t-test to compare the prestimulus (t(1)) and poststimulus (t(2)) EMG activities. Statistically significant changes in poststimulus EMG activity (t(1)- t(2)) were observed at various time intervals. Within 20 ms, an excitation was seen in the flexor carpi radialis and flexor carpi ulnaris in extension, radial and ulnar deviation, and in extensor carpi radialis brevis in flexion. Co-contractions between agonist and antagonist muscles were observed, with peaks around 150 ms after stimulus. We present evidence of wrist ligamento-muscular reactions. The early-onset reactions may serve in a joint-protective manner, and later co-contractions indicate a supraspinal control of wrist neuromuscular stability. These findings contribute new information to the physiologic functions of the wrist joint, which may further our understanding of dynamic wrist stability and serve as a foundation for future studies on proprioceptive dysfunctions after wrist ligament injuries.

Relationship Between the Fracture Location and the Kinematic Pattern in Scaphoid Nonunion

The purpose of this study was to obtain 3-dimensional and quantitative information regarding the pathological kinematics of the wrist with scaphoid nonunion using an in vivo and 3-dimensional motion analysis. We specifically tested the hypothesis that the fracture location is related to the kinematic pattern. We studied wrist kinematics during wrist flexion-extension motion and radioulnar deviation in 13 patients with scaphoid nonunion, using a markerless bone registration technique. Magnetic resonance images or computed tomography (CT) images of the wrist were acquired with the wrist in the neutral and 4 extreme positions of flexion, extension, radial deviation, and ulnar deviation. Three-dimensional animations were created of the carpal motions and interfragmentary motions between the distal and proximal fragments of the scaphoid. Based on the fracture location, accurate estimates of the relative positions and orientations of the carpal bones were analyzed. There were 2 clear patterns of the interfragmentary motions of the scaphoid based on the fracture location. In the mobile type scaphoid nonunion (7 cases), the fracture was located distal to the apex of the scaphoid dorsal ridge (scaphoid apex), and the distal scaphoid was unstable relative to the proximal scaphoid. The distal fragment showed a "book-opening" motion from wrist flexion to extension. In the stable type scaphoid nonunion (6 cases), the fracture was located proximal to the scaphoid apex, and the interfragmentary motion was considerably less than with the distal type. Carpal instability following scaphoid nonunion appears to be related to whether the fracture line passes distal or proximal to the scaphoid apex, where the dorsal scapholunate interosseous ligament and the dorsal intercarpal ligament attach. Three-dimensional imaging should be considered when assessing scaphoid nonunions to identify the exact location of the fracture. This may allow the clinician to choose the best treatment option.