Load transfer characteristics of the wrist. Part II. Perilunate instability

Dynadesis for Treatment of Dynamic Scaphoid Instability with 20-Year Results

Background  Even though the scapholunate interosseous ligament is the most common wrist ligament injury, its treatment remains a challenge for hand surgeons. We report on a surgical treatment (Dynadesis) for dynamic scaphoid instability (DSI) with a 20-year follow-up period. Description of Technique  Dynadesis utilizes antagonist forearm muscles in order to synergistically provide dynamic stabilization to the scaphoid when the wrist is loaded. It is a tendon-to-tendon transfer with the following two components: 1) Dorsal-The extensor carpi radialis longus (ECRL) is passed through a hole in the reduced, distal scaphoid, providing the scaphoid with an independent extension force. 2) Volar-A dynamic checkrein is created by tension-locking the ECRL tendon around the flexor carpi radialis (FCR) tendon. The portion of the FCR distal to the scaphoid tethers and tightens with contracture of the ECRL and FCR muscles. Patients and Methods  Twenty patients (21 wrists) were treated with Dynadesis and reevaluated 20 years later (range: 20-27 years). Results  Average grip strength improved by 8 kg. The average wrist flexion-extension arc decreased by 3 ° . Wrist X-rays showed no radiocarpal arthritis. On the Mayo wrist score, 81% reported excellent to good results (average: 89). Pain levels improved by 90%, with 76% of patients reporting no pain. All patients (100%) were satisfied with their results and would recommend the procedure. Conclusions  Dynadesis is specifically designed for the treatment of DSI. It avoids the eventual complication of osteoarthritis and does not sacrifice wrist motion. A predictable and satisfactory long-term result is obtainable with correct patient selection based on clinical staging and arthroscopic findings.

Functional Outcome of Joshi’s External Stabilization System Fixation in Distal Radius Fractures

Background

Distal radius fractures account for almost one-sixth of all fractures in a casualty setting. The usual aim of distal radius fracture treatment is to restore the function of the wrist joint, of which the distal radius is an important part. There seems to be no consensus regarding which mode of treatment is optimal for managing distal radius fracture, particularly when it is associated with distal radioulnar joint instability.

Objective

To describe the functional outcome in patients presenting with displaced distal radius fractures who undergo Joshi’s external stabilization system (JESS) fixation.

Methods

An observational study was done among 32 working-age (18 to 55 years) patients presenting with unilateral displaced distal radius fractures (excluding volar displaced) and subsequently treated with JESS fixation. The outcomes of the patients were assessed using the Green and O’Brien Scoring System modified by Cooney et al. at six months and one year following the surgery. Radiographs were also taken postoperatively and during follow-up. The data were analyzed (using IBM SPSS software version 22 and Microsoft Excel) in terms of the proportion of patients with acceptable clinical and radiological outcomes.

Results

Acceptable functional outcomes (good and excellent scores in the Green and O’Brien Scoring System) were observed in 78.1% of the study population. Though the functional outcome scores were higher among the younger age group, a statistically significant difference was not obtained. 96.9% of the patients had acceptable radiological reductions, and infection of the pin tracts complicated 9.4% of the cases. A significant improvement in outcome scores (p-value 0.0001) was observed between the outcome scores at six months and one year after surgery.

Conclusions

JESS fixation is an easy and effective method for treating displaced distal radius fractures to achieve good to excellent clinical outcomes. The functional outcome scores were better in the younger age group and male patients, but no statistically significant difference was observed.

Association of the Interfacet Angle and the Lunate Facet Inclination Angle With Kienböck Disease

PURPOSE

The etiology of Kienböck disease remains unclear, although mechanical, vascular, and metabolic risk factors have been suggested. We aimed to investigate the association of the angle between the curvatures of the distal radius and the development of Kienböck disease.

METHODS

The lunate facet inclination (LFI), scaphoid facet inclination, and interfacet angle (IFA) values were measured using posteroanterior plain radiographs of 82 patients diagnosed with Kienböck disease. The results were compared with normative angular reference values published based on an analysis of 400 wrists of Caucasian patients aged between 20 and 45 years. The posteroanterior radiographs were divided into 3 categories: negative, neutral, and positive based on ulnar variance, and the relationship between ulnar variance and facet angles was evaluated.

RESULTS

The IFA value was significantly higher than the normative angular reference value in the patients with Kienböck disease. Conversely, the LFI values were significantly lower in the Kienböck patient group. There were no statistically significant differences in the IFA and LFI values among the ulnar variance groups.

CONCLUSIONS

Measuring IFA and LFI allows the evaluation of the bifacet curvature of the distal radius articular surface in the coronal plane. Steep IFA and shallow LFI are associated with Kienböck disease. Increased IFA may lead to abnormal load transmission to the intermediate column, which might eventually lead to increased stress on the lunate.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

The Biomechanical Effects of Augmentation With Flat Braided Suture on Dorsal Intercarpal Ligament Capsulodesis for Scapholunate Instability

PURPOSE

Selecting treatment for scapholunate (SL) instability is notoriously difficult. Many methods of reconstruction have been described, but no procedure demonstrates clear superiority. New methods proposed use internal bracing (IB) with suture anchors and flat braided suture (FBS), alone or as an augmentation with tendon autograft for SL ligament injuries. Our goal was to use computed tomography (CT) to analyze alignment of the SL joint after 3 different modes of fixation of SL instability: after reconstruction with IB incorporating either tendon autograft or the dorsal intercarpal ligament (DICL), or DICL capsulodesis without FBS.

METHODS

Ten fresh-frozen, matched-pair, forearm-to-hand specimens were used. Serial sectioning of the SL stabilizing ligaments was performed and the SL interval was measured with CT. We reconstructed the SL ligament with DICL capsulodesis alone (DICL) or with IB augmented with either tendon autograft (IB plus T) or DICL (DICL plus IB). The SL interval was measured with CT. Specimens underwent 500 weighted cycles on a jig and were reimaged. Differences in SL interval after repair and cycling were compared.

RESULTS

Dorsal intercarpal ligament capsulodesis augmented with IB best maintained the SL interval before and after cycling. Dorsal intercarpal ligament capsulodesis alone was inferior to DICL plus IB and IB plus T both before and after cycling.

CONCLUSIONS

Dorsal intercarpal ligament capsulodesis augmented with IB appears to maintain better SL joint reduction than IB with tendon autograft.

CLINICAL RELEVANCE

This work serves as a necessary step for further study of the biomechanical strength and clinical application of FBS technology in the reconstruction of SL instability. Flat braided suture augmentation of DICL capsulodesis may provide another option to consider for reconstruction of SL instability.

The Effect of Forearm Position on Wrist Joint Biomechanics

PURPOSE

All active motion wrist joint simulators have been designed to simulate physiologic wrist motion; however, a main difference among them is the orientation of the forearm (horizontal or vertical with respect to gravity). Moreover, the effect of forearm orientation on experimental results has yet to be quantified, but it may be an important variable. Thus, the purpose of this study was to determine the effect of forearm orientation on wrist kinematics and contact mechanics.

METHODS

Eight cadaveric upper limbs were cycled through a flexion-extension motion using an active motion wrist simulator. Motion trials were performed in 3 forearm orientations (gravity-neutral, gravity-flexion, and gravity-extension). A computed tomography-based joint congruency technique was used to examine radiocarpal joint contact and joint contact centroid translation in the 3 tested orientations.

RESULTS

At full wrist extension and wrist flexion, radioscaphoid contact area was greatest in the gravity-extension orientation. Radiolunate contact area was similar among all 3 forearm orientations. The radioscaphoid contact centroid was consistent among the 3 tested positions with the wrist in neutral wrist position. In contrast, the radioscaphoid contact centroid translated radially in the gravity-neutral position relative to the gravity-flexion position in extreme extension. There were no differences in radiolunate centroid contact position in the 3 forearm orientations.

CONCLUSIONS

This study demonstrates that forearm orientation affects contact mechanics and end-range carpal kinematics. Future biomechanical studies should report forearm orientation and discuss the implication of the forearm orientation used on the experimental results.

CLINICAL RELEVANCE

This study provides evidence that the wrist joint is sensitive to forearm positions consistent with activities of daily living and rehabilitation protocols.

The Use of Contact Biomechanics to Study the Intact, Proximal Row Carpectomy and Scaphoid Excision, Four Bone Fusion Wrist

The study of contact biomechanics of the wrist is a challenge. This is partly due to the relatively small size of the joint as well as the lack of space in the radiocarpal joint which makes the delivery of investigative materials such as pressure sensitive film without causing artifact, difficult. Fortunately, a number of authors have studied the intact wrist, the scapholunate ligament injured wrist, the proximal row carpectomy and the scaphoid excision, four bone fusion. Despite some contrasting findings, there are some general concepts that we understand about wrist mechanics.

Arthrokinematics of the Distal Radioulnar Joint Measured Using Intercartilage Distance in an In Vitro Model

PURPOSE

Current techniques used to measure joint contact rely on invasive procedures and are limited to statically loaded positions. We sought to examine native distal radioulnar joint (DRUJ) contact mechanics using nondestructive imaging methods during simulated active and passive forearm rotation.

METHODS

Testing was performed using 8 fresh-frozen cadaveric specimens that were surgically prepared by isolating muscles involved in forearm rotation. A wrist simulator allowed for the evaluation of differences between active and passive forearm rotation. Three-dimensional cartilage surface reconstructions were created using volumetric data acquired from computed tomography. Using optically tracked motion data, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics. The effects of forearm movement method and rotation angle on centroid coordinate data and DRUJ contact area were examined.

RESULTS

The DRUJ contact area was maximal at 10° supination. There was more contact area in supination than pronation for both active and passive forearm rotation. The contact centroid moved volarly with supination, with magnitudes of 10.5 ± 2.6 mm volar for simulated active motion and 8.5 ± 2.6 mm volar for passive motion. Along the proximal-distal axis, the contact centroid moved 5.7 ± 2.4 mm proximal during simulated active motion. These findings were statistically significant. The contact centroid moved 0.2 ± 3.1 mm distal during passive motion (not significant).

CONCLUSIONS

It is possible to examine cartilage contact mechanics of the DRUJ nondestructively while undergoing simulated, continuous active and passive forearm rotation. The contact centroid moved volarly and proximally with supination. There were higher contact area values in supination compared with pronation, with a peak value at 10° supination.

CLINICAL RELEVANCE

This study documented normal DRUJ arthrokinematics using a nondestructive in vitro approach. It further reinforced the established biomechanical and clinical literature on contact patterns at the native DRUJ during forearm rotation.

A biomechanical model of the wrist joint for patient-specific model guided surgical therapy: Part 2

An enhanced musculoskeletal biomechanical model of the wrist joint is presented in this article. The computational model is based on the multi-body simulation software AnyBody. Multi body dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to wrist joint degeneration and restoration. In this study, the simulation model of the wrist joint was used for investigating deeper the biomechanical function of the wrist joint. In representative physiological scenarios, the joint behavior and muscle forces were computed. Furthermore, the load transmission of the proximal wrist joint was investigated. The model was able to calculate the parameters of interest that are not easily obtainable experimentally, such as muscle forces and proximal wrist joint forces. In the case of muscle force investigation, the computational model was able to accurately predict the computational outcome for flexion and extension motion. In the case of force distribution of the proximal wrist joint, the model was able to predict accurately the computational outcome for an axial load of 140 N. The presented model and approach of using a multi-body simulation model are anticipated to have value as a predictive clinical tool including effect of injuries or anatomical variations and initial outcome of surgical procedures for patient-specific planning and custom implant design. Therefore, patient-specific multi-body simulation models are potentially valuable tools for surgeons in pre- and intraoperative planning of implant placement and orientation.

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.

The effect of lunate morphology in Kienböck disease

PURPOSE

To determine if the absence (type I lunate) or presence (type II lunate) of a medial hamate facet on the lunate affects the radiographic characteristics of patients presenting with Kienböck disease.

METHODS

A retrospective review was performed on all patients evaluated at our institution from 2002 to 2010 with a diagnosis of Kienböck disease confirmed on plain radiographs in concert with magnetic resonance imaging (MRI) and/or bone scan. Study groups consisted of patients with type I versus type II lunates, as determined by radiographs, MRI, and/or computed tomography. Measured variables included the modified Lichtman stage on presentation, radioscaphoid angle, presence or absence of a coronal plane fracture of the lunate, modified carpal height, ulnar variance, and ulnar translocation of the carpus at the time of presentation.

RESULTS

A total of 106 wrists were examined, of which 75 were type I (71%) and 31 were type II (29%) lunates. At the time of presentation, there was significantly more advanced disease (stage IIIA or greater) in patients with type I (N = 64, 86%) compared with those with type II lunates (N = 19, 61%). Coronal fractures of the lunate were more prevalent in patients with type I (N = 58, 75%) compared with type II lunates (N = 18, 58%). In the absence of a coronal fracture, radioscaphoid angles were greater in patients with a type I (53°) versus a type II lunate (45°).

CONCLUSIONS

Lunate morphology may affect the severity of Kienböck disease at the time of initial presentation. Type II lunates appear to be protective against coronal fractures and scaphoid flexion deformities. This study provides further evidence that lunate morphology affects carpal pathology and may have implications for treatment options in Kienböck disease.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic III.

Minimal invasive management of scaphoid fractures: from fresh to nonunion

The peculiar shape of scaphoid hinders a precise evaluation of its fracture configuration, displacement and accuracy of screw placement. Its tenuous vascular supply risks the complications of delayed union, nonunion and avascular necrosis. Scaphoid is the focus of ligamentous attachment governing carpal kinematics. Preservation of its anatomy and vascularity is critical for normal wrist function. A new fracture classification clearly denoting every fracture type and guiding the management is introduced. The minimal invasive management of different scaphoid fracture conditions, including acute non-displaced and displaced fracture, delayed presentation, and nonunion are discussed. Role of arthroscopy is emphasized. Detailed surgical techniques are shared here.

A three-dimensional finite element model of maximal grip loading in the human wrist

The aim of this work was to create an anatomically accurate three-dimensional finite element model of the wrist, applying subject-specific loading and quantifying the internal load transfer through the joint during maximal grip. For three subjects, representing the anatomical variation at the wrist, loading on each digit was measured during a maximal grip strength test with simultaneous motion capture. The internal metacarpophalangeal joint load was calculated using a biomechanical model. High-resolution magnetic resonance scans were acquired to quantify bone geometry. Finite element analysis was performed, with ligaments and tendons added, to calculate the internal load distribution. It was found that for the maximal grip the thumb carried the highest load, an average of 72.2 +/- 20.1 N in the neutral position. Results from the finite element model suggested that the highest regions of stress were located at the radial aspect of the carpus. Most of the load was transmitted through the radius, 87.5 per cent, as opposed to 12.5 per cent through the ulna with the wrist in a neutral position. A fully three-dimensional finite element analysis of the wrist using subject-specific anatomy and loading conditions was performed. The study emphasizes the importance of modelling a large ensemble of subjects in order to capture the spectrum of the load transfer through the wrist due to anatomical variation.

Comparison of the "contact biomechanics" of the intact and proximal row carpectomy wrist

PURPOSE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Biomechanical effect of triquetral and scaphoid excision on simulated midcarpal arthrodesis in cadavers

PURPOSE

To examine the biomechanical effects of triquetral and scaphoid excision on wrist motion and radiolunate contact characteristics in a cadaveric model after simulated 4-corner arthrodesis with rigid internal fixation.

METHODS

Ten fresh-frozen cadaveric upper extremities were studied. For all surgical manipulations, the motion was measured and contact characteristics were assessed using ultralow prescale pressure-sensitive film.

RESULTS

Compared with the intact specimen, simple 4-corner arthrodesis with scaphoid retention led to a significant decrease in flexion (-23%), extension (-69%), radial deviation (-129%), and ulnar deviation (-25%), but no significant change in radiolunate contact characteristics. After 4-corner arthrodesis with scaphoid excision, there was a significant increase in radial deviation (+213%) without significant change in radiolunate contact characteristics, but average radial deviation was still less than in the intact specimen. After further excision of the triquetrum, radial deviation increased significantly (+238%), to a mean value 5% greater than that of the intact state, but at the cost of a significant increase in mean radiolunate contact pressure (+44% compared to the intact state).

CONCLUSIONS

When performing 4-corner arthrodesis, scaphoid and triquetrum excision may improve motion at the cost of increased mean radiolunate contact pressure.

Intra-articular pressure measurement in the radioulnocarpal joint using a novel sensor: in vitro and in vivo results

PURPOSE

To determine the amount and distribution of forces transmitted across the human radioulnocarpal joint under physiologic conditions in vivo. We performed an in vitro validation of a specifically developed capacitive pressure-sensor device and an in vivo measurement of force transmission and pressure distribution at the radioulnocarpal joint in a healthy volunteer.

METHODS

A new capacitive pressure-sensor device was adapted for intra-articular pressure measurement in the human radioulnocarpal joint. The technical characteristics of the device were determined and the sensor was validated in fresh-frozen cadaver tests. Force transmission across the radioulnocarpal joint then was measured in healthy volunteers under local anesthesia.

RESULTS

The sensor delivered reproducible measurements of forces across the radioulnocarpal joint and their distribution in the cadaver experiment. In vivo, 2 centers of force transmission were identified. None of these centers correlated with previous findings in the literature. More force is transmitted across the ulnar side of the radioulnocarpal joint than previously thought. The results are consistent with clinical findings.

CONCLUSIONS

The novel sensor device is suitable for intra-articular pressure measurement in the human radioulnocarpal joint in vitro and in vivo.

Three-ligament tenodesis for the treatment of scapholunate dissociation: indications and surgical technique

Different surgical techniques have been proposed to treat traumatic scapholunate instability. Deciding which treatment is best for each individual case is not easy. In this article we report an algorithm of treatment based on a number of prognostic factors that may help in this matter. We also report on the promising results obtained using a new technique, the 3-ligament tenodesis, for the treatment of nonrepairable complete scapholunate ligament rupture, causing a reducible carpal malalignment without secondary osteoarthritis. This technique incorporates features from 3 previously described techniques.

Changes in radiocarpal loading characteristics after proximal row carpectomy

PURPOSE

To document the changes in wrist loading that occur after proximal row carpectomy in a cadaver model.

METHODS

The normal radioulnar carpal pressure distributions of 7 cadaver wrists were measured using super-low-pressure-sensitive film. Proximal row carpectomies were performed and the loading characteristics re-evaluated.

RESULTS

In the lunate fossa the contact area increased 37%, the average contact pressure increased 57%, and the location of the contact moved radially 5.5 mm. With wrist motion between 40 degrees of extension and 20 degrees of flexion the volar/dorsal excursion of the lunate fossa contact point increased by 108%.

CONCLUSIONS

Significant changes in radiocarpal loading occur after proximal row carpectomy. The increased radiocarpal excursion with wrist motion may explain the low incidence of radiocapitate arthritis in patients who have had proximal row carpectomy.

Treatment of Dynamic Scaphoid Instability

BACKGROUND

Chronic wrist pain attributable to scaphoid instability without fixed deformity (dynamic instability) presents a treatment dilemma. The diagnosis usually is delayed, missing the opportunity for direct repair. The intercarpal fusion, tenodesis, and capsulodesis procedures create a fixed deformity. This report presents an outcome study of a new treatment for dynamic scaphoid instability that spanned more than 5 years.

METHODS

Arthroscopic evaluation was used to confirm the diagnosis for 105 wrists of 102 patients who had experienced wrist pain for an average of 24.4 months. The treatment for these patients involved transferring two thirds of the extensor carpi radialis longus through the distal pole of the reduced scaphoid volarly to the intact flexor carpi radialis. The postoperative follow-up period averaged 63 months.

RESULTS

The average grip strength increased by 65%. The average active wrist extension-flexion increased by 9%, with an average radial deviation loss of 6 degrees. The overall results, as measured by the modified Green and O'Brien clinical wrist scale, were as follows: excellent (49%), good (24%), and fair (26%). Good to excellent results were reported by 85% of the patients. Pain relief was reported by 94% of the patients, and 93% of the patients would recommend the procedure to others.

CONCLUSIONS

Scaphoid instability without fixed deformity is a complex problem. Conventional treatments have drawbacks. The new technique produced positive results that are quite promising for the management of dynamic scaphoid instability.

The role of the dorsal intercarpal ligament in dynamic and static scapholunate instability

PURPOSE

Scapholunate instability (SLI) is the most common carpal instability. Recent studies have suggested that the dorsal intercarpal (DIC) and the dorsal radiocarpal ligaments play an important role in stabilization of the scaphoid and lunate. Differences between dynamic SLI and static SLI with a dorsal intercalated segment instability (DISI) are clearly described in the clinical literature; however, there has never been a clear explanation of the anatomic differences. This study describes the role of the DIC in the development of dynamic and static SLI with DISI in a cadaver model.

METHODS

Five fresh cadavers were studied radiographically and by 3-dimensional digitization. Six increasing stages of instability were developed by sectioning progressively the following structures: the dorsal capsule, the palmar and proximal (membranous) portion of the scapholunate interosseous ligament, the DIC from its insertion on the scaphoid and trapezium, the dorsal scapholunate interosseous ligament from the scaphoid, the DIC ligament from its attachment on the lunate, and the lunotriquetral interosseous ligament.

RESULTS

The scaphoid position and the scapholunate gap changed significantly after sectioning the entire scapholunate interosseous ligament and DIC from the scaphoid when a 5-kg load was applied. The lunate position was unchanged in both the loaded and the unloaded conditions. After detaching the DIC from the lunate, both the scaphoid and lunate moved and the scapholunate gap increased significantly in both loaded and unloaded conditions and showed a DISI deformity.

CONCLUSIONS

This study describes an anatomic difference between dynamic and static scapholunate instability. Complete disruption of the scapholunate ligament did not result in the development of a static collapse of the lunate. The DIC had an important role in stabilizing the scaphoid and lunate and preventing DISI deformity. This study suggests that in the clinical setting the DIC ligament should be assessed intraoperatively and consideration should be given to repair and/or reconstruction of the DIC ligament attachments to both the scaphoid and the lunate.

Management of the scaphoid during four-corner fusion-a cadaveric study

PURPOSE

To examine the effects of scaphoid retention, inclusion, and excision on wrist motion and radiolunate contact characteristics in a cadaveric model after simulated 4-corner fusion with rigid internal fixation.

METHODS

Seven fresh-frozen cadaveric upper extremities were examined. For all surgical manipulations the motion was measured and contact characteristics were assessed using ultra-low prescale pressure-sensitive film.

RESULTS

Compared with the intact specimen, simple 4-corner fusion with scaphoid retention led to a significant decrease in extension, radial deviation, and ulnar deviation, but no change in radiolunate contact characteristics. After 4-corner fusion there was no significant difference in motion or radiolunate contact characteristics between scaphoid retention and scaphoid inclusion. After 4-corner fusion scaphoid excision allowed significantly greater radial deviation compared with scaphoid retention and scaphoid inclusion. Compared with the intact specimen 4-corner fusion with scaphoid excision also led to a significant increase in radiolunate contact area and mean contact pressure.

CONCLUSIONS

When performing 4-corner arthrodesis in the absence of radioscaphoid arthritis, scaphoid excision may improve motion at the cost of increased mean radiolunate contact pressure.

The Lichtman classification for Kienböck's disease: an assessment of reliability

PURPOSE

The correct identification of Lichtman stage 3A and 3B Kienböck's disease is crucial for treatment purposes. The present study evaluates the reliability of the Lichtman classification, with specific attention to differentiating stage 3A and 3B.

METHODS

Four reviewers evaluated wrist radiographs from 39 patients with Kienböck's disease. Radiographs were graded according to the traditional Lichtman classification, a modification of the Lichtman classification using a radioscaphoid angle of 60 degrees to subdivide stage 3, and 8 other radiographic measures.

RESULTS

The interobserver reliability of the Lichtman classification was substantial (kappa coefficient 0.63), but Stage 3A was less reliably identified (kappa 0.38). The new modification of the Lichtman classification increased both the overall (kappa 0.81) and the stage 3A (kappa 0.75) interobserver reliability.

CONCLUSION

The use of the radioscaphoid angle increases the interobserver reliability of the Lichtman classification. This should allow a better understanding of the clinically important distinction between stage 3A and 3B disease.

Long-term results after repair and augmentation ligamentoplasty of rotatory subluxation of the scaphoid

Twenty-two patients had scapholunate ligament repairs combined with a new augmentation ligamentoplasty for chronic scapholunate dissociation. All were evaluated by physical and radiologic examination after a mean postoperative follow-up period of 63 months (range, 12-134 mo). According to Green and O'Brien and Johnson and Carrera scores 5/8 had excellent, 13/12 good, and 4/2 fair results. Thirteen were free of pain; 6 had mild pain and 3 had moderate pain. Nineteen returned to their original occupation. There was an average loss of 10 degrees of flexion, 9 degrees of extension, and 11% of grip force compared with the opposite wrist. Radiologic examination showed an average decrease of 12 degrees of the scapholunate and 10 degrees of the radiolunate angles compared with the levels before surgery. No signs of degenerative osteoarthritis were found in 16 (73%) cases. Five wrists showed a distinct pattern of midcarpal degeneration correlating with notable dorsal intercalated segment instability after surgery, and 2 cases had signs of radioscaphoid degeneration.

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.

The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor into the radiocarpal joint on scaphoid and lunate kinematics

The role of the dorsal radiocarpal wrist ligament has been the subject of several investigations. Several biomechanical studies have used sensors inserted dorsally into the wrist joint to evaluate its pressure distribution. The purpose of this study was to evaluate whether a dorsal capsulotomy that sections the dorsal radiocarpal ligament or insertion of a flexible pressure sensor alters scaphoid or lunate kinematics. Eight cadaver upper extremities were instrumented with motion sensors and placed in a wrist joint simulator. Each arm was moved through continual cycles of wrist flexion/extension and radial/ulnar deviation. Motion data were obtained in the intact state, after a capsulotomy, and after insertion of the sensor. We found that either a dorsal capsulotomy sectioning the dorsal radiocarpal ligament or insertion of the pressure sensor alters scaphoid and lunate kinematics during dynamic wrist motion. This study supports the clinical belief that this dorsal wrist ligament should be spared during surgical approaches to the carpus.

Radial styloidectomy: a biomechanical study on stability of the wrist joint

We investigated the influence of radial styloidectomy on carpal alignment and examined translation of the wrist after sequentially increased styloidectomy of 8 cadaver wrists. The radial aspect of the scaphoid fossa of the distal radius was cut obliquely at 3, 6, and 10 mm from the radial styloid guided by real-time fluoroscopy. Radiographic analysis of the changes of carpal alignment was performed with the wrist in neutral position. Force-displacement curves from the neutral to the radioulnar and palmar-dorsal directions were obtained using a multi-axis testing machine. Results demonstrated no significant malalignment of the carpal bones after radial styloidectomy. Significantly increased radial translation (>40% reduction in stiffness), however, was observed due to the loss of radial articular contact after 6- and 10-mm radial styloidectomies. Significant ulnar and palmar carpal displacement also was noted after 6- and 10-mm radial styloidectomies, with 6 specimens demonstrating moderate ulnar and palmar translation and 2 demonstrating notable increased palmar and ulnar translations. We conclude that there is a definite risk of increased carpal instability with radial styloidectomy procedures. A styloidectomy of no more than 3 to 4 mm is recommended.

Constraint and material properties of the subregions of the scapholunate interosseous ligament

The material and constraint properties of the dorsal, proximal, and palmar regions of the scapholunate ligament were studied using isolated bone-ligament-bone preparations from 24 adult intact cadaver wrists. Determinations of constraint to differential rotation and translation as well as failure strength were made using a servohydraulic testing machine incorporating an additional rotatory actuator. The dorsal region of the scapholunate ligament offered the greatest constraint to differential translation, while both the dorsal and palmar regions demonstrated statistically significant combined constraints to differential rotation between the scaphoid and lunate. The greatest yield strength was found in the dorsal region (260.3 N +/- 118.1 N), followed by the palmar region (117.9 N +/- 21.3 N) and the proximal region (62.7 N +/- 32.2 N).

Dorsal intercarpal ligament capsulodesis for scapholunate dissociation: biomechanical analysis in a cadaver model

The purpose of this study was to evaluate in cadavers a new method for treating scapholunate dissociations, dorsal intercarpal ligament capsulodesis (DILC), and to compare its performance with that of a previously described soft tissue reconstruction, Blatt capsulodesis (BC). A cadaver model was used to simulate normal and abnormal wrist motions. The positions of the scaphoid and lunate and their changes with wrist motion and ligament condition were recorded using biplanar radiographs taken posteroanteriorly and laterally. The scapholunate gap was measured on the posteroanterior radiographs and the scapholunate angle was measured on the lateral view radiographs. Following scapholunate interosseous ligament sectioning, a diastasis developed between the scaphoid and lunate that was maximum in the clenched fist position 2.1 +/- 0.33 mm (mean +/- SEM) with the ligament intact versus 8.0 +/- 1.74 mm after the ligament was sectioned. Dorsal intercarpal ligament capsulodesis reduced gap formation more than BC, including when the specimens were in the clenched fist position: increased gap versus intact specimens equals 1.0 mm for DILC versus 3.7 mm for BC. The differences in diastasis were statistically significant between BC and DILC when the wrist was in extension, radial deviation, and clenched fist positions. After the scapholunate interosseous ligament was divided, the scaphoid flexed relative to the lunate. Both capsulodeses improved scapholunate alignment and there was a trend for DILC to correct the scapholunate angle more than BC. The results demonstrate that DILC is an attractive alternative to BC ex vivo. Because DILC does not tether the scaphoid to the distal radius, as BC does, improved wrist motion, especially flexion, might be possible in vivo. The use of DILC in the treatment of scapholunate dissociation warrants further investigation and clinical trials.

Ligamentous injuries of the wrist in the athlete

Wrist instability most commonly results from ligamentous disruption between bones of the proximal carpal row. Scapholunate and lunotriquetral dissociation are forms of this instability pattern. Carpal instability can also occur due to loss of the normal ligamentous restraints between the carpal rows. Ulnar midcarpal instability is an example of this pattern. The treatment of wrist instability depends on the specific type and degree of carpal disruption and the presence or absence of degenerative changes. Options include soft-tissue reconstruction, partial wrist fusion, limited carpal bone excision, or a combination of methods.

Scapholunate interosseous ligament sectioning adversely affects excursions of radial wrist extensor and flexor tendons

Excursions of tendons around the scaphoid were measured in 6 fresh cadaver forearms to evaluate the role of the scapholunate interosseous ligament (SLIL) in wrist joint motion. Excursions of the extensor carpi radialis longus (ECRL) and brevis (ECRB) tendons and the flexor carpi radialis (FCR) tendon were continuously recorded during wrist flexion, extension, and radial and ulnar deviation. Tendon excursions were measured in the intact wrists and after complete sectioning of the SLIL. Tendon excursions were altered significantly in the major ranges of wrist motion after SLIL sectioning. After ligament sectioning, excursions of the ECRL and ECRB tendons increased significantly in wrist flexion and extension. Excursions of the FCR tendon increased significantly during wrist extension and ulnar deviation. These findings support the concepts that integrity of the SLIL plays an important role in wrist function and that injury of the ligament may cause clinical problems.

Radiographic progression to dorsal intercalated segment instability

We present a case of an acute hyper-extension wrist injury that progressed from normal carpal alignment to dorsal intercalated segment instability over a short period of time. Disruption of the scapholunate interosseous and radioscapholunate ligaments was proven arthroscopically, while the intercapsular ligaments were demonstrated to be intact. We have shown that lunate malalignment can occur over time, as secondary lunate ligamentous supports attenuate under abnormal carpal kinetics.

A dynamic biomechanical study of scapholunate ligament sectioning

A biomechanical study was performed on fresh cadaver forearms to investigate the role of the scapholunate interosseous ligament in carpal stability. Scaphoid and lunate motion and radiocarpal and ulnocarpal pressure patterns were continually monitored while the wrist was moved physiologically. Prior to ligament sectioning, it was found that the position of the scaphoid and lunate were dependent on both the wrist position and the direction of wrist motion. Sectioning the scapholunate interosseous ligament caused increased scaphoid flexion, scaphoid pronation, and lunate extension. Pressure in the radiocarpal and ulnocarpal joint was redistributed following ligament sectioning. These findings support the clinical impression that the scapholunate interosseous ligament is an important stabilizer of the scaphoid and lunate.

The scapholunate allograft: a biomechanical feasibility study

The feasibility of a new method for reconstruction of the isolated scapholunate ligament tear with a scapholunate allograft was studied biomechanically using a fresh cadaver upper extremity model. Seven specimens were first tested intact for wrist range of motion, contact characteristics of the radiocarpal articulation, and relative motion of the scaphoid with respect to the lunate. Then a segment consisting of the radial third of the lunate, the adjoining scapholunate interosseus ligament, and the proximal pole of the scaphoid was resected. This segment was matched to a donor allograft of similar size and geometry, which was then placed into the recipient carpus and secured with one central transverse Kirschner wire and two shorter interfragmentary Kirschner wires placed into the lunate and scaphoid. The allografted specimen was subjected to the same tests as the intact wrist. Results showed that there were no significant differences in wrist range of motion, radiocarpal articular surface contact area and pressure, and relative flexion-extension rotation between the scaphoid and lunate during passive radioulnar deviation between the intact and allografted wrists.

Biomechanics of the wrist

This article summarizes six years of studies with an experimental model, which uses a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system, to characterize the biomechanics of the human cadaver wrist by measuring the contact areas and pressures in a variety of normal, simulated traumatic, and surgically treated conditions. The results of these studies have provided clinically relevant information about the normal anatomy and functional mechanics of the wrist, as well as guidelines for the treatment for a number of different fractures and ligament injuries. The results of studies of radial carpal instabilities and fractures have demonstrated an increased load in the areas where degenerative arthritis is seen in these clinical conditions, and have furnished a means by which the biomechanical efficacy of certain surgical treatments can be measured.

Malunited Colles' fracture. Analysis of stress distribution

To try to explain disability in the wrist after malunited Colles' fractures, an experiment was designed to evaluate pressure distribution through the wrist joint with varying degrees of angulation of the distal radius. The results of computer simulation analysis of stress concentration using finite element methods were compared with those of pressure distribution studies on the radial articular surface of cadaveric radii in various positions using pressure-sensitive film. Stress existed in volar regions of the radio-lunate joint under normal pressure in the neutral position, but shifted to dorsal regions of the joint, and was concentrated when dorsal angulation reached 30 degrees. We believe that concentrated loads result in pain and may lead to early degenerative joint disease. Early additional reduction of a displaced fragment or a post-fusion osteotomy should be considered when dorsal angulation exceeds 30 degrees in malunited distal radial fractures to decrease abnormal loading across the wrist joint.

Scapholunate advanced collapse wrist: proximal row carpectomy or limited wrist arthrodesis with scaphoid excision?

Proximal row carpectomy (PRC) and limited intercarpal arthrodesis with scaphoid excision (LWF) are useful alternatives to wrist arthrodesis for treatment of degenerative wrist disorders secondary to scapholunate advanced collapse. Because consensus regarding the ideal motion-preserving option is lacking, we sought to better define the indications for and relative merits of PRC versus LWF. Twenty-four wrists treated for symptomatic scapholunate advanced collapse arthritis between 1980 and 1990 with either PRC or LWF were retrospectively reviewed at an average of 5.5 years postoperatively. At follow-up evaluation, satisfactory pain relief, grip strength, and functional performance were observed except in three patients with PRC, one of whom had developed symptomatic radiocarpal arthritis requiring conversion to arthrodesis. Differences in subjective and objective results between the two treatment groups were not statistically significant except for residual range of motion. Incomplete correction of lunate extension when LWF was performed resulted in diminished wrist extension, compared to PRC. Improvements in grip strength and range of motion were noted for at least 1 year after both procedures, and neither declined with time. A stage-dependent surgical approach to the symptomatic scapholunate advanced collapse wrist is advocated in light of comparable outcomes following both PRC and LWF. For wrists without capitolunate arthritis, PRC avoids the technical demands, lengthy postoperative immobilization, and risk of nonunion associated with LWF, but for stage III disease (capitolunate arthritis) pain relief may be unsatisfactory, and LWF is recommended.

Wrist anatomy: incidence, distribution, and correlation of anatomic variations, tears, and arthrosis

We dissected 393 wrists to evaluate the incidence and distribution of anatomic features, arthrosis, chondromalacia, and soft tissue lesions. The data were then analyzed for any statistically significant associations among the different variables. The most common (73%) lunate morphology had a separate medial facet on its distal surface for the hamate. The capitate had a separate facet for the fourth metacarpal in 86% of the wrists. Fourth metacarpals with a dorsal radial facet, either separate from or connected to the rest of the fourth metacarpal base, were the most common types of fourth metacarpal. Cartilage erosion with exposed subchondral bone was identified in 58% of the wrists. It was most commonly at the proximal pole of the hamate (28%). Tears of the ligaments and/or the triangular fibrocartilage complex were identified in 56% of the wrists. The triangular fibrocartilage complex was found torn in 36% of the wrists. The lunotriquetral interosseous ligament was torn in 36% of the wrists, and the scapholunate interosseous ligament was torn in 28% of the wrists. There was a communication between the proximal wrist joint and the pisotriquetral joint in 88% of the 76 wrists, which were further dissected to assess this issue. Statistical analysis of the data found a significant correlation between the presence of cartilage erosion at the proximal pole of the hamate and the presence of a lunate facet. There was also a significant correlation between the presence of a tear in the scapholunate interosseous ligament and the presence of cartilage erosion in the scaphoid-trapezium-trapezoid joint. Analysis of the paired wrists from 169 cadavers revealed that the same soft tissue tear or combination of tears was present bilaterally in 39% of the pairs. Cartilage erosion was present bilaterally in the same location or locations in 27% of the pairs.

Measurement of carpal bone geometry by computer analysis of three-dimensional CT images

The aim of this project was noninvasively to analyze and quantitate the geometry, load transfer characteristics, and spatial relationships of the carpal bones by using a new three-dimensional CT scan reconstruction technique. The determination of mechanical parameters such as distances between centroids and between bone surfaces, carpal alignment, volumes, surface areas, and contact areas can provide the basis for comparison between normal wrists and wrists with a variety of progressive instability patterns, types of fracture, pathologic and posttraumatic states, and different simulated surgical procedures. This new technology has demonstrated a volumetric accuracy of 94% and a linear accuracy of 97%. Simultaneous analysis of all articulating surfaces of multiple joints can be performed in cadavers and in patients because of the noninvasive nature of the imaging reconstruction technique. This new research offers much more information than has previously been available. It also promises direct application to the clinical setting and eliminates several limitations and questions that were inescapable with previous technology.

Load mechanics of the midcarpal joint

The midcarpal joint was studied in upper extremities of fresh cadavers with the use of a static positioning frame, pressure-sensitive film, and a microcomputer to analyze the contact prints. The contact area on the proximal side of the midcarpal joint was found to consist generally of four areas; the scaphoid-trapezium-trapezoid, the scaphoid-capitate, the lunate-capitate, and the triquetrum-hamate. The contact areas accounted for less than 40% of the available joint surface, even under loads of 118 pounds. The distribution of load through the midcarpal joint was scaphoid-trapezium-trapezoid 23%, scaphoid-capitate 28%, lunate-capitate 29%, and triquetrum-hamate 20%. The midcarpal joint, like the radiocarpal joint, appears to transmit load through distinct areas and through a relatively small portion of the available joint surface.

A comparison of scaphoid-trapezium-trapezoid fusion and four-bone tendon weave for scapholunate dissociation

The contact characteristics of the radiocarpal joint (area, pressure, and ratios of scapholunate area, pressure and force transmitted) were determined with the use of pressure-sensitive film in seven normal wrists after ligament sectioning to create scapholunate instability, with reconstruction involving a scaphoid-trapezium-trapezoid fusion, and with reconstruction involving a four-bone tendon weave procedure. The results demonstrated that the scaphoid-trapezium-trapezoid fusion significantly altered the contact characteristics of the wrist, transferring load, pressure, and area to the radioscaphoid joint, thereby unloading the lunate. In contrast, the tendon weave reconstruction produced characteristics similar to those of the normal joint.

Force distribution across wrist joint: application of pressure-sensitive conductive rubber

A new pressure-sensitive conductive rubber sensor was used for investigation of the pressure distribution through the radio-ulno-carpal joint. Twelve of these transducers were placed in the radio-ulno-carpal joint. Pressure was measured in seven different wrist positions under loads incrementally increasing from 0 to 12 kg. Half of the sensors showed less than 0.5 MPa, even at maximum load, while a high-pressure area was located palmary in each fossa. The peak pressure measured in the wrist neutral position was 2.4 MPa on the scaphoid fossa, 1.5 MPa on the lunate fossa, and 1.1 MPa on the triangular fibrocartilage with a 10 kg load. The peak pressure ratio between the scaphoid and the lunate was 1.7 in the neutral wrist position. This increased in radial deviation to 2.9 and decreased in ulnar deviation to 0.8. The force-transmission ratio was 50% through the scaphoid fossa, 35% through the lunate fossa, and 15% through the triangular fibrocartilage in the neutral position. The advantage of this sensor is that it is thin and flexible and provides reliable reproducible quasi-instantaneous measurements.

Treatment of scapholunate dissociation by ligamentous repair and capsulodesis

We believe that direct scapholunate ligamentous repair, supported by a dorsal radioscaphoid capsulodesis, should be considered for the treatment of most scapholunate dissociations when there is no osteoarthritis, regardless of the time that has elapsed since injury. We treated 24 patients by this technique between 1972 and 1988. The records of 21 were available for study. Average time from injury to surgical treatment was 17 months (range, 1 to 84 months). Results were evaluated clinically and by means of patient questionnaire and x-ray films. The significant change in range of motion was a loss of palmar flexion, which averaged 11.5 degrees. Grip strength, pain, and x-ray appearance improved in all cases. Only one patient had to change occupations after surgery because of wrist symptoms. Three had minimal x-ray degenerative changes, which did not result in increased pain or in loss of motion and grip strength. There were no complications.

Simulated scaphoid proximal pole fracture

Five fresh cadaver upper extremities were studied with use of a static positioning frame, pressure-sensitive film, a microcomputer-based videodigitizing system, and a Sun station image analysis system to assess the load bearing characteristics of the scaphoid in the proximal carpal joint. Specimens were studied in their normal condition, after a proximal pole osteotomy of the scaphoid, and after resection of the proximal pole of the scaphoid. The amount of contact area born through the scaphoid fossa was essentially the same whether the scaphoid was intact, or after a simulated scaphoid fracture of its proximal pole, or after resection of the proximal pole. The scaphoid contact area and pressure, although overall relatively constant, was redistributed after osteotomy, resulting in increased contact area under the distal fragment and no change or a slight decrease in the contact area under the proximal fragment of the scaphoid. After resection of the proximal fragment, all scaphoid contact area and pressure was born by the distal scaphoid fragment. The contact area and pressure characteristics of the lunate remained unchanged in all conditions compared with the normal condition. There were no significant changes in the locations of the centroids of the scaphoid segments and the lunate in any of the conditions tested.

The silicone scaphoid: a biomechanical study

Five fresh cadaver upper extremities were studied by use of a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system, to assess the load-bearing characteristics of a scaphoid silicone implant within the radioulnarcarpal joint. Specimens were studied in their "normal" condition, after resection of the scaphoid, after placement of a scaphoid implant, and with a scaphoid implant and a simulated capitate-lunate-triquetrum-hamate fusion. The scaphoid silicone implant bore significant, although less, load than the normal scaphoid. Decreasing the size of the scaphoid implant decreased the load born by the implant. Decreased load through the scaphoid implant was compensated by the lunate. The addition of a limited carpal fusion did not significantly decrease the load born by a scaphoid implant. Therefore, the silicone scaphoid implant is a load-bearing implant even when undersized or placed in association with a limited carpal fusion.

Wrist injuries: correlation of clinical and arthroscopic findings

Wrist arthroscopy was done for one hundred nine patients with chronic wrist pain, averaging 22.8 months in duration. History regarding mechanism of injury, painful crepitus, pain with activity or at rest, localization of tenderness, visible swelling, and instability with examination was compared with arthroscopic findings of ligament damage, articular cartilage damage, and synovitis. Both pain at rest and swelling correlated significantly with synovitis. Tenderness did not correlate with specific ligament injury. Wrist ligament injuries and/or cartilage damage were noted in 96.3% of these wrists. Ligament injuries were frequently multiple, averaging 2.6 ligament injuries per wrist. No significant association was found between the presence of chondromalacia, synovitis, or specific ligament tears and the mechanism of injury, duration of symptoms, presence of clicking, or pain with activity.