In vivo elongation of the palmar and dorsal scapholunate interosseous ligament

Understanding the biomechanics of the forearm during the dart thrower's motion

This study investigated the contribution of different forearm muscles, namely the flexor carpi ulnaris, extensor carpi radialis longus and brevis, extensor carpi ulnaris and flexor carpi radialis, during the dart thrower's motion. Thirteen healthy participants were recruited. The forearm muscle activation patterns during the dart thrower's motion were measured using surface electromyography. The average root mean square for the extensor carpi ulnaris was found to be the highest during the dart thrower's motion. Muscle activations during the dart thrower's motion were heterogeneous among the participants. The results suggest the rehabilitation protocol for patients with wrist injuries should be reconsidered.

Histomorphology of the Subregions of the Scapholunate Interosseous Ligament and Its Enthesis

Background  The scapholunate interosseous ligament (SLIL) has three subregions: dorsal, proximal, and volar. The SLIL enthesis has not previously been studied despite its important mechanical function in wrist joint biomechanics. Questions/Purposes  This study aims to compare the histomorphological differences between the SLIL subregions, including at their entheses. Three questions are explored: Do the gross dimensions differ between SLIL subregions? Does the enthesis qualitatively, and its calcified fibrocartilage (CF) quantitatively, differ between (a) SLIL subregions and (b) scaphoid and lunate attachments? Methods  Twelve fresh-frozen human cadaveric wrists were dissected and the gross dimensions of the SLIL subregions measured. Subregions were histologically processed for morphological and compositional analyses, including quantification of enthesis CF area. Results  The dorsal subregion was the thickest. The dorsal and volar subregions had fibrocartilaginous entheses, while the proximal subregion was attached to articular cartilage. The dorsal subregion had significantly more CF than the volar subregion. There was no significant difference in the enthesis CF between scaphoid and lunate attachments in the three subregions. Conclusions  There are significant morphological differences between the SLIL subregions. The dorsal subregion has the largest amount of CF, which is consistent with the greater biomechanical force subjected to this subregion. The similar histomorphology of the ligament at the scaphoid and lunate entheses suggests that similar biomechanical forces are applied to both attachments. Clinical Relevance  The histomorphological results confirm that the dorsal subregion is the strongest of the three subregions. The results from the entheseal region may have important implications in the study of graft incorporation during SLIL reconstruction.

Differences in the Rotation Axes of the Scapholunate Joint During Flexion-Extension and Radial-Ulnar Deviation Motions

PURPOSE

To determine the location of the rotation axis between the scaphoid and the lunate (SL-axis) during wrist flexion-extension (FE) and radial-ulnar deviation (RUD).

METHODS

An established and publicly available digital database of wrist bone anatomy and carpal kinematics of 30 healthy volunteers (15 males and 15 females) in up to 8 different positions was used to study the SL-axis. Using the combinations of positions from wrist FE and RUD, the helical axis of motion of the scaphoid relative to the lunate was calculated for each trial in an anatomical coordinate system embedded in the lunate. The differences in location and orientation between each individual axis and the average axis were used to quantify variation in axis orientation. Variation in the axis location was computed as the distance from the closest point on the rotation axis to the centroid of the lunate.

RESULTS

The variation in axis orientation of the rotation axis for wrist FE and RUD were 84.3° and 83.5°, respectively. The mean distances of each rotation axis from the centroid of the lunate for FE and RUD were 5.7 ± 3.2 mm, and 5.0 ± 3.6 mm, respectively.

CONCLUSIONS

Based on the evaluation of this dataset, we demonstrated that the rotation axis of the scaphoid relative to the lunate is highly variable across subjects and positions during both FE and RUD motions. The range of locations and variation in axis orientations in this data set of 30 wrists shows that there is very likely no single location for the SL-axis.

CLINICAL RELEVANCE

Scapholunate interosseous ligament reconstruction methods focused on re-creating a standard SL-axis may not restore what is more likely to be a variable anatomical axis and normal kinematics of the scaphoid and lunate.

A four-dimensional-CT study of in vivo 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.

Computational wrist analysis of functional restoration after scapholunate dissociation repair

The scapholunate ligament stabilizes the scaphoid and lunate of the proximal row in the wrist which allows for proper force transmission with the radius and ulna. Damage to this structure degenerates into arthritis and disability. Controversy exists over the best technique to restore function and reduce pain. A three-dimensional computational model of the wrist and hand was used to investigate the biomechanical effects of scapholunate ligament dissociation and its repair. The model replicated 3D bony anatomy, soft tissue structures, and muscle loading. The model predicted the increased instability caused by the injury, consistent with experimental and clinical evidence, and a return of more healthy kinematics with the repair. Changes to load transmission across the radiocarpal joints were noted with the injury, only some of which were mitigated by the repair. As better understanding of the biomechanics of the wrist joint is achieved, this model could prove to be an important tool to further investigate wrist mechanics and inform the effects of treatment options. Graphical abstract 3D computational model of all bones in the wrist/hand permitted simulation of five major motions-wrist flexion/extension, radial/ulnar deviation, and clenched fist. Shown are the array of tensile elements representing ligaments and capsule, as well as muscle force vectors for the desired motions. SL (scapholunate) separation (interval) predicted by the model for one motion compared well to an experimental study showing the instability induced by an injured (cut) SL ligament and returned stability by a clinical repair procedure, MBT (Modified Brunelli technique).

Yoga-Induced Myositis Ossificans Traumatica of the Scapholunate Ligament

Background  Myositis ossificans traumatica (MOT) involves the heterotopic development of lamellar bone after a traumatic injury. Despite being termed "myositis," MOT is not limited to muscle but rather can involve tendons, fat, and fascia. "Traumatica" reflects that lesions are usually associated with a history of significant trauma, that is, fractures or surgery; however, many reports suggest they can also be linked to repetitive low-energy insults. In both cases, the inflammatory response secondary to tissue injury generates a proliferative osteoblastic cascade. Case Description  We present a case of persistent wrist pain in a 43-year-old woman associated with yoga activities. Her radiographic studies demonstrated partial scapholunate (SL) ligament tear and an associated mass lesion. Surgical pathology revealed MOT involving the SL ligament. Literature Review  MOT lesions in the upper extremity are usually localized around the elbow, and cases in the hand are relatively rare. There are no prior reports of occurrences within the wrist joint or in association with the SL ligament. However, biomechanical studies have quantified significant mechanical strains across the SL interval during various yoga poses. This pattern of microtrauma is capable of generating MOT. Clinical Relevance  Upper extremity weight-bearing positions are common in yoga and subject the wrist, especially the SL interval, to high mechanical strains. This pattern of microtrauma should lead the clinician to suspect MOT when encountering a mass in the wrist, but malignancy and infection must be ruled out.

Lateral epicondylalgia: A primary nervous system disorder

Lateral epicondylalgia (LE) is the most common chronic painful condition affecting the elbow in the general population. Although major advances have been accomplished in recent years in the understanding of LE, the underlying physiopathology is still a reason for debate. Differences in clinical presentation and evolution of the symptoms among patients, suggest the need for revisiting the current knowledge about subjacent mechanisms that attempt to explain pain and functional loss. Previous models have suggested that the condition is mainly a degenerative tendinopathy, associated with changes in pain pathways and the motor system. The hypothesis of this work is that LE is the clinical manifestation of a primary nervous system disorder, characterized by an abnormal increase in neuronal activity and a subsequent loss of homeostasis, which secondarily affects the musculoskeletal tissues of the elbow-forearm-hand complex. A new model for LE is presented, supported by an in-deep analysis of basic sciences, epidemiological and clinical studies.

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

BACKGROUND

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.

OBJECTIVE

To determine biomechanical differences between two pushup positions (neutral or extended).

METHODS

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.

RESULTS

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.

CONCLUSION

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.

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

PURPOSE

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 in vivo.

METHODS

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.

RESULTS

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 were found in any of 3 situations, except the dorsal zone with resisted radial deviation.

CONCLUSIONS

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.

CLINICAL RELEVANCE

For patients undergoing nonsurgical treatment of SLIL tears, a sudden contraction of ulnar or radial deviation agonist muscles may be harmful and contribute to SL instability.

Relative Contributions of the Midcarpal and Radiocarpal Joints to Dart-Thrower's Motion at the Wrist

PURPOSE

To identify the relative contributions of the radiocarpal (RC) and midcarpal (MC) joints to dart-thrower's motion (DTM) of the wrist.

METHODS

Six cadaveric upper extremities were fixed to a custom-designed loading jig allowing for pure moment-rotation analysis in 24 different directions of wrist motion. Each specimen was tested in 3 states: intact, simulated radiocarpal fusion (sRCF) and simulated pancarpal fusion (sPCF). Moments of ± 1.5 Nm were applied at each of 24 directions for each state and the resulting wrist rotation recorded. Data from each specimen were reduced to compute the range of motion (ROM) envelopes and the orientation of the ROM for the 3 different states.

RESULTS

The ROM was significantly decreased in the sRCF and sPCF groups compared with the intact group in the directions of the pure extension, radial extension, ulnar flexion, and ulnar deviation. No significant difference in ROM was detected between the sRCF and sPCF groups in any direction. The ROM envelopes for the intact, sRCF, and sPCF groups were all oriented obliquely to the axis of pure wrist flexion-extension near a path of ulnar flexion-radial extension, consistent with prior reports on DTM.

CONCLUSIONS

Although both simulated fusion types decreased ROM compared with the intact wrist, the principal direction of wrist motion along the path of DTM was not significantly altered by simulated RCF or PCF.

CLINICAL RELEVANCE

These findings suggest that the RC and MC joints can each contribute to a similar mechanical axis of motion located along the path of DTM when the other joint has been eliminated via fusion. Surgical options such as partial wrist fusions may maintain the native wrist's mechanical axis if either the RC or the MC joint is preserved, despite significant reduction in overall ROM.

Scapholunate interosseous ligament dysfunction as a source of elbow pain syndromes: Possible mechanisms and implications for hand surgeons and therapists

Elbow pain syndromes are common upper extremity musculoskeletal disorders, and they are usually associated with repetitive occupational exposure. Ligaments are often one of the sources of musculoskeletal disorders because of their mechanical and neurological properties. The wrist ligaments are some of the ligaments most vulnerable to occupational exposure. Since most occupational tasks require wrist extension for handling tools and loading, the scapholunate interosseous ligament (SLIL) bears greater strain during loading, which results in creep deformation and hysteresis. Ligamentous creep may result in diminished ability to detect signal changes during joint movements, which impairs neuromuscular control established by ligamentomuscular reflex arcs elicited from mechanoreceptors in the ligaments. Changes in muscle activation patterns of forearm muscles due to diminished ligamentomuscular reflexes may initiate a positive feedback loop, leading to musculoskeletal pain syndromes. The relationship between elbow pain syndromes and SLIL injury will be presented through two hypotheses and relevant pain mechanisms: 1. Repetitive tasks may cause creep deformation of the SLIL, which then impairs ligamentomuscular reflexes, leading to elbow pain disorders. 2. Lateral epicondylalgia may increase the risk of SLIL injury through the compensation of the lower extensor carpi radialis muscle activity by higher extensor carpi ulnaris muscle activity, which may alter carpal kinematics, leading to SLIL degeneration over time. The differential diagnosis is usually complicated in musculoskeletal pain disorders. The failure of treatment methods is one of the issues of concern for many researchers. A key element in developing treatment strategies is to understand the source of the disorder and the nature of the injury. We proposed that the differential diagnosis include SLIL injuries when describing elbow pain syndromes, particularly, lateral epicondylalgia.

Arthroscopic Scapholunate Ligament Reconstruction, Volar and Dorsal Reconstruction

Arthroscopic scapholunate volar and dorsal ligament reconstruction achieves an anatomic reconstruction, avoids an open approach and capsular detachment, and provides a strong construct for early mobilization. Clinical results are discussed. Detailed "surgical tips" and technical modifications are provided.

Four-Year Outcomes of Midcarpal Hemiarthroplasty for Wrist Arthritis

PURPOSE

The purpose of this study was to review the average 4-year outcomes of a cohort of patients with wrist arthritis, treated by a single surgeon with a novel prosthetic hemiarthroplasty of the midcarpal joint. We hypothesized that midcarpal hemiarthroplasty would improve range of motion and grip strength of patients with wrist arthritis, with a complication profile comparable with that of alternative solutions for wrist arthritis.

METHODS

We reviewed a series of 20 patients treated with a midcarpal hemiarthroplasty at an average of 4 years following surgery. Patients were evaluated objectively with grip strength, wrist range of motion, serial radiographs, and subjectively surveyed with Disabilities of the Arm, Shoulder, and Hand (DASH) and Mayo scores.

RESULTS

Range of motion increased by a mean 33° in flexion-extension and 10° in radial-ulnar deviation compared with preoperative range of motion. Mean grip strength improved to 20.8 kg from 14.1 kg, and Mayo and DASH scores also significantly improved. Three patients had a manipulation under anesthesia for stiffness. One patient required open reduction internal fixation of an unstable fourth carpometacarpal joint after falling. Two patients were revised to a total wrist arthroplasty and 1 to a wrist fusion.

CONCLUSIONS

Midcarpal hemiarthroplasty provides improved wrist range of motion, grip strength, and patient-reported outcome scores compared with preoperative values, with a complication profile comparable with that of other surgical options for patients with wrist arthritis. Advantages of midcarpal arthroplasty include retention of the native distal carpal row, preservation of midcarpal motion, as well as the option for conversion to a total wrist arthroplasty should revision be required.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Electrogoniometer measurement and directional analysis of wrist angles and movements during the Sollerman hand function test

STUDY DESIGN

Clinical measurement.

INTRODUCTION

To investigate the characteristics of wrist motion (area, axis, and location) during activities of daily living (ADL) using electrogoniometry.

METHODS

A sample of 83 normal volunteers performed the Sollerman hand function test (SHFT) with a flexible biaxial electrogoniometer applied to their wrists. This technique is accurate and reliable and has been used before for assessment of wrist circumduction in normal volunteers. A software package was used to overlay an ellipse of best fit around the 2-dimensional trace of the electrogoniometer mathematically computing the area, location, and axis angle of the ellipse.

RESULTS

Most ADL could be completed within 20% of the total area of circumduction (3686°° ± 1575°°) of a normal wrist. An oblique plane in radial extension and ulnar flexion (dart-throwing motion plane) was used for rotation (-14° ± 32°) and power grip tasks (-29° ± 25°) during ADL; however, precision tasks (4° ± 28°), like writing, were performed more often in the flexion extension plane. In the dominant hand, only 2 power tasks were located in flexion region (cutting play dough [ulnar] and pouring carton [radial]), precision tasks were located centrally, and rotation and other power tasks were located in extension region.

DISCUSSION

This study has identified that wrist motion during the ADL requires varying degrees of movement in oblique planes. Using electrogoniometry, we could visualize the area, location, and plane of motion during ADL. This could assist future researchers to compare procedures leading to loss of motion in specific quadrants of wrist motion and its impact on patient's ability in performing particular ADL. It could guide hand therapists to specifically focus on retraining the ADL that may be affected when wrist range of motion is lost after injury.

LEVEL OF EVIDENCE

Diagnostic level III.

Dart-Splint: An innovative orthosis that can be integrated into a scapho-lunate and palmar midcarpal instability re-education protocol

The Authors describe a novel hinged orthosis that permits selective midcarpal mobilization along the plane of the dart throwing motion. This orthotic device can be used to assist rehabilitation protocols aimed to limit radiocarpal joint mobility and scapho-lunate ligament overload and to accelerate wrist functional recovery after ligamentous injuries around the proximal carpal row. - VictoriaW. Priganc, PhD, OTR, CHT, CLT, Practice Forum Editor.

A study to investigate the intra-rater and inter-rater reliability of goniometric measurements of dart throwers motion of asymptomatic wrists

Introduction

This study investigated the intra-rater and inter-rater reliability of measuring dart throwers motion of asymptomatic wrists with a handheld manual goniometer typical of that used in the clinical setting.

Method

Working in pairs, each rater took three repeated measures of radial extension and of ulnar flexion of both wrists using a goniometer positioned on the radiodorsal aspect of the radius proximally and the second metacarpal distally. Both raters and subjects were blinded, and measurements were read by an independent observer. Subjects were of varied age, gender and with no history of wrist pathology. Subjects rated how difficult they found the dart throwers motion to perform using a 5-point Likert scale.

Results

Measurements were collected from both wrists of 37 subjects (74 wrists). The intraclass correlation coefficient for intra-rater measurements of radial extension was 0.89 (95% CI 0.86–0.92) and for ulnar flexion was 0.92 (95% CI 0.90–0.94). Standard deviation for radial extension was 4.2° and for ulnar flexion 3.6°. The intraclass correlation coefficient for inter-rater measurements of radial extension was 0.83 (95% CI 0.74–0.89) and for ulnar flexion was 0.81 (95% CI 0.72–0.88). Subjects rated the movement more difficult to perform with the non-dominant side (P=0.006), and standard deviation was greater when the subject found dart throwers motion difficult to perform. No significant associations were found (P<0.05) to suggest that reliability is influenced by hand dominance, gender, age, level of perceived difficulty or data collection site.

Discussion

Our study confirms good reliability when using this method to measure dart throwers motion. It is suggested that dart throwers motion can be measured to compare different subjects and monitor change; however, studies need to be undertaken with a symptomatic population.

Scaphoid tuberosity excursion is minimized during a dart-throwing motion: A biomechanical study

PURPOSE

The purpose of this study was to determine whether the excursion of the scaphoid tuberosity and therefore scaphoid motion is minimized during a dart-throwing motion.

METHODS

Scaphoid tuberosity excursion was studied as an indicator of scaphoid motion in 29 cadaver wrists as they were moved through wrist flexion-extension, radioulnar deviation, and a dart-throwing motion.

RESULTS

Study results demonstrate that excursion was significantly less during the dart-throwing motion than during either wrist flexion-extension or radioulnar deviation.

CONCLUSION

If the goal of early wrist motion after carpal ligament or distal radius injury and reconstruction is to minimize loading of the healing structures, a wrist motion in which scaphoid motion is minimal should reduce length changes in associated ligamentous structures. Therefore, during rehabilitation, if a patient uses a dart-throwing motion that minimizes his or her scaphoid tuberosity excursion, there should be minimal changes in ligament loading while still allowing wrist motion.

STUDY DESIGN

Bench research, biomechanics, and cross-sectional.

LEVEL OF EVIDENCE

Not applicable. The study was laboratory based.

The treatment of arthritis of the wrist

Arthritis of the wrist is a painful disabling condition that has various causes and presentations. The traditional treatment has been a total wrist fusion at a price of the elimination of movement. However, forms of treatment which allow the preservation of movement are now preferred. Modern arthroplasties of the wrist are still not sufficiently robust to meet the demands of many patients, nor do they restore normal kinematics of the wrist. A preferable compromise may be selective excision and partial fusion of the wrist using knowledge of the aetiology and pattern of degenerative change to identify which joints can be sacrificed and which can be preserved. This article provides an overview of the treatment options available for patients with arthritis of the wrist and an algorithm for selecting an appropriate surgical strategy.

Scapholunate Interosseous Ligament Anatomy and Biomechanics

Injury to the scapholunate interosseous ligament is one of the most common causes of carpal instability and can impart considerable compromise to the patient's hand function. However, the management of scapholunate ligament injuries remains a dynamic concept, especially with regard to the multitude of options and techniques that exist for its surgical treatment. We present a thorough review of scapholunate anatomy and morphology, and the role of the scapholunate articulations in the kinetics and pathomechanics of wrist instability. We also review the current literature on the biomechanical properties of the scapholunate ligament and its subcomponents. A sound understanding of the anatomy and biomechanics of the scapholunate ligament can clarify its instability and may better orient current reconstructive procedures or pioneer better future techniques.

Length changes of scapholunate interosseous ligament at different wrist positions: an in vivo 3-dimension image study

PURPOSE

The scapholunate interossous ligament (SLIL) has a critical role in maintaining the proper kinematic relationship between the scaphoid and the lunate. We hypothesize that the length of SLIL changes significantly at wrist full extension and during forearm rotation. The aim of this study was to investigate the length changes of SLIL at wrist full extension and forearm rotation in vivo.

METHODS

Twelve volunteers were randomly divided to two groups. We obtained computed tomography scans of the wrists at different wrist positions. The three regions of the SLIL were measured and analyzed with computer modeling.

RESULTS

The results showed that from the neutral to full extension of the wrist, the length of volar SLIL and volar, middle portions of the proximal SLIL increased significantly. The volar and proximal SLIL increased significantly in maximal forearm pronation.

CONCLUSIONS

The lengths of the volar and proximal regions of SLIL increase substantially at wrist full extension, but only slightly at maximal forearm pronation. Clinically, wrist full extension may make the SLIL ligament vulnerable to disruption.

International Federation of Societies for Surgery of the Hand 2013 Committee's report on wrist dart-throwing motion

This report updates information on wrist dart-throwing (DT) motion, based on the most recent research published on the kinematics, kinetics, and clinical applications of DT motion. A wide range of DT planes exists. "Pure" DT motion is done along an oblique plane that intercepts the coronal and sagittal planes at the zero position, and occurs almost exclusively at the midcarpal joint with near zero scaphoid and lunate motion. "Functional" DT motion such as a hammering is done along an oblique plane that is almost parallel to the pure DT plane, but that has an offset toward the dorsal side. Functional DT rotation has greater scaphoid and lunate motion compared with pure DT motion. Midcarpal arthrodesis adversely affects DT motion compared with radiocarpal arthrodesis. During a DT motion, the mean and peak tendon forces of the flexor carpi ulnaris and the extensor carpi radialis longus were the greatest among wrist motors. By performing a task along the plane of DT motion, the scapholunate (SL) joint was stable and SL ligament elongation was minimal in healthy subjects. However, a more recent study of patients with SL dissociation revealed that DT exercises applied tensile forces on the SL ligament and induced an SL gap.

In vivo length changes of wrist ligaments at full wrist extension

The aim of this study was to investigate the length changes of carpal ligaments when loaded in full extension in vivo. We obtained computed tomography scans of the right wrists in three positions for six volunteers: neutral; 75° extension; and 75° extension with a further 10° of radial deviation. Nine ligaments were measured and analysed with computer modelling. The results showed that the radioscaphocapitate, long radiolunate, and ulnolunate ligaments lengthened the most at full wrist extension, suggesting that they were under greatest load. The radioscapholunate, ulnocapitate, and ulnotriquetral ligaments lengthened further with the addition of wrist radial deviation. At full extension, the dorsal intercarpal ligament inserting on the scaphoid was lengthened. The dorsal radiocarpal and dorsal intercarpal ligaments inserting on the trapezoid were shortened, suggesting reduced loading. In conclusion, a number of volar carpal ligaments lengthened significantly in full wrist extension and the ulnar carpal ligaments were further lengthened at wrist radial deviation.

In-vivo confirmation of the use of the dart thrower's motion during activities of daily living

The dart thrower's motion is a wrist rotation along an oblique plane from radial extension to ulnar flexion. We report an in-vivo study to confirm the use of the dart thrower's motion during activities of daily living. Global wrist motion in ten volunteers was recorded using a three-dimensional optoelectronic motion capture system, in which digital infra-red cameras track the movement of retro-reflective marker clusters. Global wrist motion has been approximated to the dart thrower's motion when hammering a nail, throwing a ball, drinking from a glass, pouring from a jug and twisting the lid of a jar, but not when combing hair or manipulating buttons. The dart thrower's motion is the plane of global wrist motion used during most activities of daily living. Arthrodesis of the radiocarpal joint instead of the midcarpal joint will allow better wrist function during most activities of daily living by preserving the dart thrower's motion.

Early results of combined palmar-dorsal scapholunate ligament reconstruction

Isolated dorsal scapholunate reconstruction may be inadequate to stabilize and restore physiological scapholunate kinematics in the setting of combined dorsal and palmar ligamental incompetence. To address this entity, a combined reconstruction that encompass both dorsal and palmar scapholunate reconstruction was performed in 20 patients followed up to 19.8 (6-84) months. Compared to the contralateral wrist, the results were extension (67 ± 1.6 to 85.7%, p < 0.01), flexion (84.5 ± 3.2 to 81 ± 2.3%, p = 0.38), grip strength (62 ± 1.6 to 88.3 ± 1.9%, p < 0.01), and pain score (rest: 1.55 ± 0.26 to 0.2 ± 0.09, p < 0.01; activity: 3.2 ± 0.09 to 0.4 ± 0.17, p < 0.01). Based on Mayo wrist score, five excellent, 13 good, and two fair results were reported.

Arthroscopic ligamentoplasty of the dorsal and volar portions of the scapholunate ligament

Classical arthroscopic techniques for scapholunate instability consist of debridement, thermal shrinkage, and percutaneous pinning. Good results are obtained in acute lesions or in chronic partial tears, but they are less predictable when the lesion is complete, because of the poor healing capacity of the scapholunate ligament and because it is not possible to perform an anatomic ligamentous reconstruction with these techniques. Open techniques are thus required for reconstruction, but they damage the soft tissues. We recently published a description and cadaver study of an arthroscopic ligamentoplasty, trying to combine the advantages of arthroscopic techniques (minimally invasive surgery) and open techniques (reconstruction of the ligament). With this approach, it is possible to reconstruct the dorsal scapholunate ligament and the secondary stabilizers while causing minimal damage to the soft tissues and avoiding injury to the posterior interosseous nerve and detachment of the dorsal intercarpal ligament. The current report describes an additional step to this technique with which it is possible to reconstruct the volar portion of the scapholunate ligament. We also describe an early mobilization postoperative protocol that we believe is equally important.

Prediction of ligament length and carpal diastasis during wrist flexion-extension and after simulated scapholunate instability

PURPOSE

To determine the role of the carpal ligaments during wrist flexion-extension and to understand whether maintaining integrity of only the dorsal scapholunate ligament (SLL) is adequate for maintaining stability of the scapholunate joint.

METHODS

This study combined motion analysis and manual digitization of ligament attachment regions to generate predictions of carpal ligament length and implied strain during wrist motion and length changes after simulated ligamentous injury.

RESULTS

We modeled 13 ligaments and 22 ligament segments (subportions). We measured ligament length change with respect to wrist angle. A total of 11 segments had minimum stretch or elongation from neutral wrist position over the entire wrist range of motion for any ligament cut condition. The remaining 11 segments had more than 10% stretch in some portion of flexion-extension. In general, ligaments had increased stretch during wrist flexion and after cutting the entire SLL and the dorsal intercarpal ligaments off the scaphoid.

CONCLUSIONS

Disruption of the membranous and palmar portions of the SLL and the dorsal intercarpal ligament off the scaphoid did not result in the development of an increased 3-dimensional scapholunate gap, as measured by differences in ligament length calculations between the scaphoid and lunate. This may indicate a predynamic instability condition (before clinical signs and x-ray findings) that is stabilized by the dorsal SLL, preventing the increase in the 3-dimensional scapholunate gap. This may also support surgical treatment recommendations, which suggest that repair of the dorsal component only of the SLL will be effective. Disruption of the dorsal intercarpal ligament off the scaphoid or lunate did not result in further significant changes. Therefore, the dorsal SLL has an important role in preventing scapholunate ligament instability.

CLINICAL RELEVANCE

These results provide insight into the abnormal kinematics as various ligaments are compromised.

Elongation of the dorsal carpal ligaments: a computational study of in vivo carpal kinematics

PURPOSE

The dorsal radiocarpal (DRC) and dorsal intercarpal (DIC) ligaments play an important role in scapholunate and lunotriquetral stability. The purpose of this study was to compute changes in ligament elongation as a function of wrist position for the DRC and the scaphoid and trapezoidal insertions of the DIC.

METHODS

We developed a computational model that incorporated a digital dataset of ligament origin and insertions, bone surface models, and in vivo 3-dimensional kinematics (n = 28 wrists), as well as an algorithm for computing ligament fiber path.

RESULTS

The differences between the maximum length and minimum length of the DRC, DIC scaphoid component, and DIC trapezoidal component over the entire range of motion were 5.1 ± 1.5 mm, 2.7 ± 1.5 mm, and 5.9 ± 2.5 mm, respectively. The DRC elongated as the wrist moved from ulnar extension to radial flexion, and the DIC elongated as the wrist moved from radial deviation to ulnar deviation.

CONCLUSIONS

The DRC and DIC lengthened in opposing directions during wrist ulnar and radial deviation. Despite complex carpal bone anatomy and kinematics, computed fiber elongations were found to vary linearly with wrist position. Errors between computed values and model predictions were less than 2.0 mm across all subjects and positions.

CLINICAL RELEVANCE

The relationships between ligament elongation and wrist position should further our understanding of ligament function, provide insight into the potential effects of dorsal wrist incisions on specific wrist ranges of motion, and serve as a basis for modeling of the wrist.

Biomechanical properties of interosseous proximal carpal row ligaments

The Scapholunate (S-L) and Lunotriquetrum (L-Tr) ligaments have been extensively studied in the literature. A wide range of measurements has been reported for ultimate load and stiffness with different mechanical protocols. In this study, we examined the mechanical properties of both ligaments harvested from the same wrist. Fifteen fresh cadaver wrists were used to harvest eight S-L and four L-Tr. Testing was performed in quasi-static loading in a well defined direction for each ligament system. The ultimate load for S-L was 68-210 N with a mean value of 147 ± 54 N and a stiffness of 35.7 ± 9.6 N/mm. For L-Tr the ultimate load was 122-179 N with a mean value of 150 ± 24 N and a stiffness of 192 ± 60 N/mm. The two ligaments had nearly the same ultimate load, but the L-Tr had a higher stiffness (p = 0.05). These findings could be useful to assess the appropriate autologous autografts for reconstruction of the S-L and L-Tr.

The scapholunate interosseous ligament afferent proprioceptive pathway: a human in vivo experimental study

PURPOSE

To examine the afferent pathways of the scapholunate interosseous ligament (SLIL)-generated stimuli and their contribution to the overall carpal proprioception.

METHODS

We examined 5 selected patients with preganglionic global root avulsion, confirmed by previous brachial plexus exploration, during the initial stage of carpal arthrodesis surgery. Despite their anesthetic-flail extremity, both the distal axon and the ganglionic cell were intact and able to transfer afferent stimuli. We placed electrodes subcutaneously over the adjacent areas of the ulnar, median, and radial nerves at the elbow region and performed an intraoperative neurophysiologic study. We studied the homologous sensory action potentials (SAPs) generated at the wrist in relaxation, flexion, extension, radial deviation, and ulnar deviation positions at each nerve and repeated them in 2 stages. The first took place with the SLIL intact and the second with the SLIL lacerated. The noise from the rest of the wrist elements was digitally eliminated.

RESULTS

After the SLIL laceration, SAP intensities recorded at the median nerve in every wrist position were reduced. The radial and ulnar nerves showed differences of lesser degrees between the recorded SAP intensities before and after the ligament sectioning in every carpal position, with only the radial nerve following a specific pattern. The SAP intensity recorded at the median nerve in every carpal motion after the SLIL laceration was similar to the SAP intensity at relaxation with the SLIL intact, whereas recordings of various intensities were present for the radial and ulnar nerves.

CONCLUSIONS

The SLIL generates proprioceptive stimuli at every wrist position. The main innervation of the whole SLIL derives from the anterior interosseous nerve; a partial contribution of the posterior interosseous nerve focused on the dorsal subregion of the ligament may also be present.

Differential strain of the axially loaded scapholunate interosseus ligament

PURPOSE

To directly measure strain changes in the scapholunate ligament via magnetic resonance imaging (MRI) when axially loading the wrist in the neutral and extended positions.

METHODS

Six asymptomatic male volunteers without known history of previous wrist injury were enrolled in this MRI-based study. Each subject underwent 3 MRI scans in a 3T scanner: in resting neutral position, in neutral with axial load applied, and in extension with axial load applied. Axial load was applied via extension of an elastic band with known force/elongation curve. We analyzed images and converted them to 3-dimensional stereolithographs. Attachment points of the palmar, proximal, and dorsal sections of the scapholunate interosseus ligament (SLIL) were identified. The lengths of the resulting vectors were recorded for each position. Strain, defined as change in length divided by original length, was calculated for the axially loaded neutral and extended wrists. We used the Bonferroni adjusted multiple comparisons from an analysis of variance model, with statistical significance defined as p < .05.

RESULTS

Strains were significantly greater in the palmar (p = .02) and proximal (p = .01) subregions of the SLIL in loaded extension versus loaded neutral positions. In contrast, the strain on the dorsal component in extension was not statistically greater than in the neutral position (p = .45). Axial load in neutral resulted in minimal strain of all 3 components of the SLIL complex, and these were not significantly different from each other (p > .99). With extension, the strains of the palmar (p = .03) and proximal (p = .006) regions were statistically greater than that of the dorsal component.

CONCLUSIONS

In extension, strain is greatest in the palmar and proximal portions of the intact SLIL. Axial load in neutral applies minimal strain to the SLIL complex. Avoiding axial loading in extension and encouraging loading in neutral position may allow for decreased injury and more effective healing of the scapholunate ligament.

The advantage of throwing the first stone: how understanding the evolutionary demands of Homo sapiens is helping us understand carpal motion

Unlike any other diarthrodial joint in the human body, the "wrist joint" is composed of numerous articulations between eight carpal bones, the distal radius, the distal ulna, and five metacarpal bones. The carpal bones articulate with each other as well as with the distal radius, distal ulna, and the metacarpal bases. Multiple theories explaining intercarpal motion have been proposed; however, controversy exists concerning the degree and direction of motion of the individual carpal bones within the two carpal rows during different planes of motion. Recent investigations have suggested that traditional explanations of carpal bone motion may not entirely account for carpal motion in all planes. Better understanding of the complexities of carpal motion through the use of advanced imaging techniques and simultaneous appreciation of human anatomic and functional evolution have led to the hypothesis that the "dart thrower's motion" of the wrist is uniquely human. Carpal kinematic research and current developments in both orthopaedic surgery and anthropology underscore the importance of the dart thrower's motion in human functional activities and the clinical implications of these concepts for orthopaedic surgery and rehabilitation.

Sensory innervation of the subregions of the scapholunate interosseous ligament in relation to their structural composition

PURPOSE

To investigate the different types of innervation and the presence of mechanoreceptors in relation to the structural composition of the scapholunate interosseous ligament and to correlate the findings with the known mechanical properties of the ligament subregions.

METHODS

Six fresh cadaveric scapholunate interosseous ligaments were divided into their 3 subregions: dorsal, palmar, and proximal. The microscopic features were investigated with use of a standard hematoxylin-eosin stain and immunostains for S-100, neurofilaments, neuron-specific enolase, protein gene product 9.5, CD31, and smooth muscle actin. The connective tissue structural composition and the presence of blood vessels and neural structures (myelinated and unmyelinated nerve fibers and mechanoreceptors) were investigated. The macroscopic anatomic details were also noted.

RESULTS

The palmar subregion consists of structured, densely collagenized tissue at the core, surrounded by looser connective tissue. Myelinated nerve fibers forming fascicles accompany the interspersed blood vessels inside the ligament substance. Their concentration is greater in the proximal part of the palmar subregion, reaching a distance of approximately 150 mum from the ligament free surface. The dorsal subregion has similar structure to the palmar one, but the fibrous tissue ratio and density are higher. The proximal subregion consists of chondroid matrix and of loose connective tissue at its core. The radio-scapholunate ligament insertion is noted at the palmar aspect of the proximal subregion. Pacinian and other sensory corpuscles were found mostly at the palmar and proximal subregions.

CONCLUSIONS

The scapholunate interosseous ligament is a richly innervated ligament that contributes to carpal proprioception, a fundamental element of dynamic wrist stability. The palmar subregion, apart from its major mechanical role, contains the greatest amount of the neural structures and mechanoreceptors. The dorsal subregion, with densely packed collagen fibers and limited innervation, functions mainly to constrain the scaphoid-lunate relative motion.

[Rotatory subluxation of the scaphoid: pathology and surgical management]

The interosseous scapholunate ligament (IOSLL) is the main stabilizer of the scapholunate (SL) couple but a static instability can appear only in the event of an associated injury of the extrinsic ligaments. Thus, SL dissociation covers a broad spectrum in which only static instability leads with certainty to osteoarthritis. Classically described as a rotatory subluxation of the scaphoid with DISI collapse, static SL instability manifests itself as a complex deformity with dorsolateral subluxation of the unit formed by the scaphoid and the distal carpal row. This deformity explains the dorsolateral radioscaphoid conflict and capitolunar decentering that is the origin of the radioscaphoid and midcarpal osteoarthritis that later appears. It is only within the first 4 to 6 weeks that a repair of the IOSLL, possibly associated with a capsulodesis, makes it possible to expect a good result and can prevent osteoarthritis. Beyond that time, no soft tissue procedure will modify the natural history of the condition. For us, surgery is indicated only for acute injuries and for symptomatic chronic instabilities. Before the occurrence of osteoarthritis, with new-found knowledge of the medium-term results of capsulodesis, it seems reasonable to favour a limited fusion. But in the event of failure, the patient is likely to remain in pain even after a total fusion. It is thus not aberrant to perform a capsulodesis in a sedentary person but it is necessary to inform the patient that osteoarthritis will occur. After occurrence of osteoarthritis, if it is symptomatic, proximal row carpectomy, SLAC procedure, total wrist fusion and denervation, can be considered, depending on the stage, the mobility of the wrist and the wishes of the patient. Denervation of the wrist can give good results with few risks, and does not jeopardize the results of a subsequent procedure.

Evidence of wrist proprioceptive reflexes elicited after stimulation of the scapholunate interosseous ligament

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

2007 IFSSH committee report of wrist biomechanics committee: biomechanics of the so-called dart-throwing motion of the wrist

The dart-throwing motion (DTM) plane can be defined as a plane in which wrist functional oblique motion occurs, specifically from radial extension to ulnar flexion. Most activities of daily living are performed using a DTM. The DTM utilizes the midcarpal joint to a great extent. Scaphotrapezio-trapezoidal anatomy and kinematics may be important factors that cause a DTM to be a more stable and controlled motion. During a DTM, there is less scaphoid and lunate motion than during pure flexion-extension or radioulnar deviation. Clinically, a DTM at the plane approximately 30 degrees to 45 degrees from the sagittal plane allows continued functional wrist motion while minimizing radiocarpal motion when needed for rehabilitation.