Material properties of the trapezial and trapeziometacarpal ligaments

The passive biomechanics of the thumb carpometacarpal joint: An in vitro study

The thumb carpometacarpal (CMC) joint facilitates multidirectional motion of the thumb and affords prehensile power and precision. Traditional methods of quantifying thumb CMC kinematics have been largely limited to range-of-motion (ROM) measurements in 4 orthogonal primary directions (flexion, extension, abduction, adduction) due to difficulties in capturing multidirectional thumb motion. However, important functional motions (e.g., opposition) consist of combinations of these primary directions, as well as coupled rotations (internal and external rotation) and translations. Our goal was to present a method of quantifying the multidirectional in vitro biomechanics of the thumb CMC joint in 6 degrees-of-freedom. A robotic musculoskeletal simulation system was used to manipulate CMC joints of 10 healthy specimens according to specimen-specific joint coordinate systems calculated from computed tomography bone models. To determine ROM and stiffness (K), the first metacarpal (MC1) was rotated with respect to the trapezium (TPM) to a terminal torque of 1 Nm in the four primary directions and in 20 combinations of these primary directions. ROM and K were also determined in internal and external rotation. We found multidirectional ROM was greatest and K least in directions oblique to the primary directions. We also found external rotation coupling with adduction-flexion and abduction-extension and internal rotation coupling with abduction-flexion and adduction-extension. Additionally, the translation of the proximal MC1 was predominantly radial during adduction and predominantly ulnar during abduction. The findings of this study aid in understanding thumb CMC joint mechanics and contextualize pathological changes for future treatment improvement.

Trapeziometacarpal Dislocations in Pediatric Age, Is There a Better Treatment? Series of Cases and a Systematic Review

(1) Background: Dislocations of the trapeziometacarpal joint (TMC) are uncommon in children and adolescents. Only a few isolated cases are reported in the literature. Therapeutic guidance is minimal and inconclusive. (2) Methods: The authors present four patients treated for this unusual lesion. We evaluated the evolution according to treatment, age, patient activity, and quickDASH. Despite the clear limitation of the small number of patients, it is relevant to try to better understand this lesion and its evolution. A systematic review of the literature was also conducted. (3) Results: This is the largest published series of TMC dislocations in children and adolescents. Patients included a 12-year-old girl treated conservatively with a poor quickDASH; a 9-year-old girl treated surgically with the Eaton-Littler technique for a new dislocation with a partially modified quickDASH; a 13-year-old boy with two necessary closed reductions for a new dislocation and a very good final quickDASH; and a 12-year-old boy treated with closed reduction and percutaneous fixation with excellent final results with quickDASH. (4) Conclusions: In the absence of scientific evidence, conservative treatment and ligament reconstruction did not provide good functionality. In contrast, closed reduction with percutaneous fixation provided excellent results. Therefore, the authors would recommend closed reduction and percutaneous needle fixation as an elective method to treat TMC dislocations in pediatric and adolescent patients.

The effect of trapeziometacarpal joint passive stiffness on mechanical loadings of cartilages

Hypermobility of the trapeziometacarpal joint is commonly considered to be a potential risk factor for osteoarthritis. Nevertheless, the results remain controversial due to a lack of quantitative validation. The objective of this study was to evaluate the effect of joint laxity on the mechanical loadings of cartilage. A patient-specific finite element model of trapeziometacarpal joint passive stiffness was developed. The joint passive stiffness was modeled by creating linear springs all around the joint. The linear spring stiffness was determined by using an optimization process to fit force-displacement data measured during laxity tests performed on eight healthy volunteers. The estimated passive stiffness parameters were then included in a full thumb finite element simulation of a pinch grip task driven by muscle forces to evaluate the effect on trapeziometacarpal loading. The correlation between stiffness and the loading of cartilage in terms of joint contact pressure and maximum shear strain was analyzed. A significant negative correlation was found between the trapeziometacarpal joint passive stiffness and the contact pressure on trapezium cartilage during the simulated pinch grip task. These results therefore suggest that the hypermobility of the trapeziometacarpal joint could affect the contact pressure on trapezium cartilage and support the existence of an increased risk associated with hypermobility.

Ligament reconstruction in thumb carpometacarpal joint instability: A systematic review

In thumb carpometacarpal (CMC) instability, laxity of the ligaments surrounding the joint leads to pain and weakness in grip and pinch strength, which predisposes the patient to developing CMC joint arthritis. Recent advancements in joint anatomy and kinematics have led to the development of various surgical reconstructive procedures. This systematic review outlines the available ligament reconstruction techniques and their efficacy in treating nontraumatic and nonarthritic CMC instability. Additionally, we aimed to provide evidence which specific ligament reconstruction technique demonstrates the best results. Four databases (Embase, MEDLINE, Web of Science, and Cochrane Central) were searched for studies that reported on surgical techniques and their clinical outcomes in patients with nontraumatic and nonarthritic CMC instability. Twelve studies were analyzed for qualitative review, including nine different surgical ligament reconstruction techniques involving two hundred and thirty thumbs. All but one of the reported techniques improved postoperative pain scores and showed substantial improvement in pinch and grip strength. Complication rates varied between 0% and 25%. The included studies showed that ligament reconstruction effectively alleviated the patients' complaints regarding pain and instability, resulting in overall high patient satisfaction. Nevertheless, drawing definitive conclusions regarding the superiority of any ligament reconstruction technique remains challenging owing to the limited availability of homogeneous data in the current literature.

Contribution to the study of stresses in the thumb column during key pinch grip

OBJECTIVES

The aim of this study was to calculate the stress acting on the trapeziometacarpal joint during an key pinch grip.

METHOD

We used profile X-rays of the thumb to measure the various bony and muscle lever arms. We assessed the angles of action of the muscular elements involved in the thumb column. Based on this data, we established a two-dimensional geometric model that enabled us to determine the forces at each joint level, as a function of stresses and muscular contributions. We were also able to calculate the participation of the different muscle groups in obtaining a balanced situation.

RESULTS

Our results, as a function of the degree of flexion of the interphalangeal and metacarpophalangeal joints, show a multiplying factor of 2.9-3.19 in relation to the key pinch grip force.

DISCUSSION

Previous studies modelling a key pinch grip are showed multiplying factors from 6 to 13 in relation to the key pinch grip force. They are not compatible with the characteristics of the polyethylene used for trapeziometacarpal prostheses, whereas numerous articles in the literature show survival rates that are more or less comparable to those of total hip prostheses. These studies required an excessive number of assumptions, which could lead to error. Our results are compatible with the results of trapeziometacarpal prosthesis and with those of a recent study measuring intra-articular trapeziometacarpal pressure in a cadaveric model. Our model allows us to test different configurations of the thumb spine depending on the degree of flexion of the interphalangeal and metacarpophalangeal joints.

Dorsoradial Ligament Reconstruction in Trapeziometacarpal Joint Arthritis

BACKGROUND

The main purpose of the study is to present the alternative novel surgical technique in treating patients with trapeziometacarpal (TMC) joint arthritis using dorsoradial ligament (DRL) reconstruction technique and report the clinical outcomes.

METHODS

Patients who were diagnosed with TMC joint arthritis and underwent DRL reconstruction were evaluated. Visual analog pain score; Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) score; grip, tip pinch, tripod pinch, and key pinch strengths along with range of motion of the thumb; and Kapandji score were recorded in the preoperative period and at follow-up. Stress examination was also performed under a fluoroscope.

RESULTS

Eleven patients were included in the study. Median follow-up time was 13 months. At follow-up, postoperative visual analog scale and QuickDASH score improved in all patients. Grip, tip pinch, tripod pinch, and key pinch strengths also improved. The range of motion and Kapandji score were slightly improved compared with the preoperative period except for the thumb metacarpophalangeal flexion. Two patients had numbness at the thumb and spontaneously recovered after 3 months.

CONCLUSIONS

According to recent evidence which proposed the importance of DRL in TMC joint stability, our DRL reconstruction technique may be an alternative treatment in treating patients presented with TMC joint arthritis. Further study with a longer follow-up period is needed.

Arthroscopic Assisted Treatment of Combined Trapezium and Bennett Fracture-Dislocation

Trapezium fractures are unusual; however, they represent the third most frequent fracture of the carpal bones. As they usually follow a high-energy trauma, they are associated with distal radius, Bennett, or Rolando fractures in 80% of cases. Traditional treatment options include, closed reduction and percutaneous pinning, or open reduction and internal fixation. To minimize the additional surgical trauma, an arthroscopic technique has been developed for safe, minimally invasive management of complex injuries of the first carpo-metacarpal joint. Intra-articular dislocated fracture fragments are reduced under direct visualization and fixed through small incisions. Limiting additional surgical damage on the carpo-metacarpal joint ligaments, capsule, and other soft tissues around the fracture preserves the blood supply to fracture fragments and also the proprioceptive system, which is key for the dynamic stability of such a hypermobile joint. This report confirms that the procedure is feasible, and a complete functional recovery can be expected with reduced postoperative rehabilitation.

Using a finite element model of the thumb to study Trapeziometacarpal joint contact during lateral pinch

BACKGROUND

Finite element (FE) analysis is widely used in different fields of orthopaedic surgery, however, its application to the trapeziometacarpal joint has been limited due to the small size, complex biconcave-convex joint geometry, and complex musculature. The goal of this study was to improve upon existing models by creating a muscle-driven FE thumb model and use the model to simulate the biomechanical effect of hand therapy exercises and ligament reconstructive surgeries.

METHODS

Bone and cartilage geometry were based on a CT dataset of a subject performing a static lateral pinch task. A previously validated musculoskeletal model was utilized to extract electromyography (EMG)-driven muscle forces. Five ligaments with biomechanical significance were modeled as springs using literature values and attached according to their anatomical landmarks.

FINDINGS

The biomechanical consequence of various interventions was proxied as a change in the maximum cartilage stress. The result shows tightening the dorsal ligament complex (dorsal radial ligament, dorsal central ligament, posterior oblique ligament) is the most effective, achieving a stress reduction of 4.8%. Five exercises used in hand therapies were modeled, among which thenar eminence strengthening showed the most prominent stress reduction of 4.0%. Four ligament reconstructive surgeries were modeled, with Eaton-Littler reconstruction showed the most significant stress reduction of 25.0%.

INTERPRETATION

Among the routinely utilized treatment options for early thumb osteoarthritis, we found that three methods: dorsal ligament imbrication, thenar eminence exercise, and the Eaton-Littler method may confer biomechanical advantages cartilage loading. These advantages align with the clinically observed favorable outcomes.

Anatomical 3 Ligaments Reconstruction for Symptomatic Thumb Carpometacarpal Joint Instability

Thumb carpometacarpal (CMC) joint instability is thought to be a debilitating disorder and, if left untreated, develops joint persistent synovitis and osteoarthritis. In this study, we report a novel surgical technique reconstructing the anterior oblique ligament, the dorsoradial ligament, and the intermetacarpal ligament simultaneously using both the transverse carpal ligament, and the palmaris longus tendon. Six patients with a mean age of 44 years showing no osteoarthritic changes by the radiographical examination underwent our anatomical three ligaments reconstruction for persistent painful thumb CMC joint instability. Clinical results with the mean follow-up of 20 months demonstrated that the pain was subjectively improved in all patients, both the grip and the pinch strength were increased significantly and good functional motion of the thumb could be observed after the operation. These findings indicated that our surgical procedure could be one option of treatment of the symptomatic CMC joint instability in early-stage arthritis.

The biomechanics of osteoarthritis in the hand: Implications and prospects for hand therapy

BACKGROUND

The unique anatomy of the human hand makes it possible to carefully manipulate tools, powerfully grasp objects, and even throw items with precision. These apparent contradictory functions of the hand, high mobility for manual dexterity vs high stability during forceful grasping, imply that daily activities impose a high strain on a relatively instable joint. This makes the hand susceptible to joint disorders such as osteoarthritis. Both systemic (eg, genetics, hormones) and mechanical factors (eg, joint loading) are important in the development of osteoarthritis, but the precise pathomechanism remains largely unknown. This paper focuses on the biomechanical factors in the disease process and how hand therapists can use this knowledge to improve treatment and research.

CONCLUSION

Multiple factors are involved in the onset and development of osteoarthritis in the hand. Comprehension of the biomechanics helps clinicians establish best practices for orthotics intervention, exercise, and joint protection programs even in de absence of clear evidence-based guidelines. The effect and reach of hand therapy for OA patients can be expanded substantially when intervention parameters are optimized and barriers to early referrals, access reimbursement, and adherence are addressed. Close and early collaboration between hand therapists and primary care, women's health, rheumatology, and hand surgery providers upon diagnosis, and with hand surgeons pre and postoperatively, combined with advances in the supporting science and strategies to enhance adherence, appear to be a promising way forward.

Anatomy and Biomechanics of the Thumb Carpometacarpal Joint

This review discusses the anatomy and biomechanics of the thumb carpometacarpal (CMC) joint. This articulation between the trapezium and first metacarpal is integral for opposition and other complex movements necessary for pinch and grasp maneuvers. Fortunately, this joint is well equipped to handle the extreme forces imposed by these movements, as it is stabilized by an elaborate arrangement of ligaments and muscles. Without this stability, thumb subluxation would occur with loading during pinch and grasp, and human prehension would be impossible. Understanding the interactions occurring within this joint is essential for adequately treating pathology arising in this crucial joint.

Partial Trapeziotrapezoid Resection and Thumb Range of Movement After Trapeziometacarpal Joint Fusion-A Biomechanical Study

PURPOSE

Trapeziometacarpal (TMC) joint arthrodesis is an effective treatment for stage III osteoarthritis. Although this procedure alleviates thumb pain and restores grip power and pinch strength, persistent limitation of thumb movement is inevitable. This biomechanical study aimed to investigate the altered kinematics of thumb circumduction motion after TMC joint arthrodesis and subsequent excision of the trapeziotrapezoid (TT) and trapezio-second metacarpal (T-2MC) joint spaces.

METHODS

Eight cadaver upper extremities were mounted on a custom testing apparatus. The hand and carpal bones were fixed to the apparatus, except for the first metacarpal bone, trapezium, and trapezoid. A 50-g load was applied at the tip of the first metacarpal head to generate passive thumb circumduction. An electromagnetic tracking system measured the angular and rotational displacement of the first metacarpal. All specimens were tested in 4 conditions: intact, after simulated TMC joint fusion, after subsequent excision of 3 mm of bone at the TT joint space, and after additional 3 mm resection at the T-2MC joint space.

RESULTS

After simulated TMC arthrodesis, the range of angular motion of thumb circumduction decreased to 25% that of the intact thumb. Subsequent resections at the TT and T-2MC joint spaces increased circumduction ranges to 49% (TT joint) and 73% (TT plus T-2MC joints) that of the intact thumb. The range of thumb rotational motion showed a similar trend.

CONCLUSIONS

Trapeziometacarpal arthrodesis decreased the range of both angular and rotational motion during thumb circumduction. Subsequent resections at the paratrapezial space increased the range of thumb motion, suggesting that hypermobility of the paratrapezial joints increases thumb mobility after TMC joint fusion.

CLINICAL RELEVANCE

Patients with hypermobile paratrapezial joints may have larger thumb movement after TMC joint fusion. Additional resections of the TT and T-2MC joint spaces may further mobilize the thumb in patients who complain of stiffness after TMC fusion.

Ligamentous constraint of the first carpometacarpal joint

To examine the role of the ligaments in maintaining stability of the first carpometacarpal (CMC) joint, a sequential ligament sectioning study of sixteen specimens was performed. While a small compressive force was maintained, loads were applied to displace each specimen in four directions - volar, dorsal, radial, and ulnar. Translations of the specimen in both dorsal-volar and radial-ulnar axes were measured. Initially, the tests were conducted with the specimen intact. These tests were then repeated following sectioning of the CMC anterior oblique ligament (AOL), ulnar collateral ligament (UCL), intermetacarpal ligament (IML) and dorsal radial ligament (DRL). The first CMC joint translation was increased in the absence of IML and DRL (p < 0.05). Both IML and DRL were important in constraining the first CMC joint translation against external applied loads. Potential applications of these findings include the treatment of joint hypermobility and the reduction or delay of onset or progression of first CMC joint osteoarthritis.

Comparison of Biomechanical Results about the Effect of Three Surgery Methods in Decompression of Lunate Bone

Objective  Kienbock's disease is an unusual disorder caused by osteonecrosis and the collapse of lunate bone which leads to pain and a chronic decrease in wrist function. The treatments in this disease aim to relieve pain and maintain wrist function and movement. Various surgical procedures have been recommended for the subjects with Kienbock's disease; however, the main question posed here is which of the selected procedures are more successful in relief of the pressure applied on lunate. Methods and Materials  Computed tomography (CT) scan images of a normal subject were used to create a three-dimensional model of the wrist joint. The effects of several surgical procedures, including radial shortening, capitate shortening, and a combination of both radial and capitate shortening, on the joint contact force of the wrist bones were investigated. Results  The pressure applied to the lunate bone in articulation with radius, scaphoid, capitate, hamate, and triquetrum varied between 19.7 and 45.4 MPa. The Von Mises stress, maximum principal stress, and minimum principal stress decreased in the model with a combination of radius and capitate shortening. Conclusion  It can be concluded from the results of this study that the combinations of radius and capitate shortening seem to be an effective procedure to decrease joint pressure, if the combined surgery could not be done, shortening of radius or capitate would be recommended. Level of Evidence  This is a Level III study.

Anatomy and biomechanics of healthy and arthritic trapeziometacarpal joints

Understanding the biomechanics of the trapeziometacarpal (TMC) or first carpometacarpal (CMC1) joint, the pathophysiology of basal thumb arthritis, the design and performance of surgical procedures require a solid anatomical basis. This review of literature summarizes the most recent data on the descriptive, functional, and comparative anatomy of healthy and arthritic TMC joints.

The Effect of the Joint Capsule and Anterior Oblique Ligament on Dorsal Subluxation of the First Metacarpal During Key Pinch

Laxity of the anterior oblique ligament (AOL) and/or the dorsoradial ligament (DRL) are believed to contribute to the progression of osteoarthritis in the trapeziometacarpal joint through increased dorsal subluxation. Stress radiographs during functional tasks, such as key pinch, can be used to evaluate such joint instability. Cadaveric experiments can explore joint contact pressures as well as subluxation under varying conditions, to gain knowledge about joint mechanics. The disturbance of supporting tissues, such as the joint capsule, during experiments may affect the recorded stability of the joint. To evaluate potential effects of opening the joint capsule and severing the AOL, eleven cadaveric specimens were rigged to simulate key pinch. An anteroposterior (AP) radiograph of the hand was recorded for each specimen while intact, after partially opening the joint capsule and after sectioning the AOL. First metacarpal subluxation levels were compared between the intact joint, partially open joint capsule, and sectioned AOL. Neither opening the joint capsule nor cutting the AOL had a statistically significant effect on metacarpal subluxation. The results indicate that partially opening the joint capsule has a negligible effect on joint mechanics and support recent studies that postulate that the AOL plays a less substantial role in preventing subluxation.

Trapeziometacarpal stabilization through dorsoradial ligament reconstruction: An early post-surgery in vivo biomechanical analyses

Ligament reconstruction can provide pain relief in patients with a painful, unstable, pre-arthritic trapeziometacarpal (TMC) joint. Imbrication of the dorsoradial ligament (DRL) has been proposed as a minimal invasive stabilization technique. It requires less invasive surgery than an Eaton-Littler technique and shows promising long-term clinical outcome. We used dynamic CT to objectively review the effects of the imbrication. Four patients with pain and laxity at the TMC joint, but without radiographic signs of osteoarthritis, were recruited. Dynamic CT scans were made during active thumb abduction-adduction, flexion-extension, and two functional grip tasks using a radiolucent jig. Scans of the patients were acquired before and 3 to 6 months after DRL reconstruction. Motion of each bone in the articular chain of the thumb was quantified. In addition, we mapped changes in the contact patterns between the articular facets during the entire thumb motion. After DRL imbrication, we found no overall decrease in MC1 movement in three out of four patients. Furthermore, no increase in TMC joint congruency, defined as proximity area size, was found for three out of four patients. Pre- and post-operative differences in congruency across different tasks were patient-dependent and relatively small. We demonstrated that, from a biomechanical perspective, there is high variability in post-operative outcome between patients that undergo identical surgical procedures performed by the same surgeon. A post-operative decrease in range of motion, increase in joint congruency or decrease in proximity area shift during thumb motion is not omnipresent. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2851-2864, 2018.

Early morphologic changes in trapeziometacarpal joint bones with osteoarthritis

OBJECTIVE

Characterising the morphological differences between healthy and early osteoarthritic (EOA) trapeziometacarpal (TMC) joints is important for understanding osteoarthritis onset, and early detection is important for treatment and disease management. This study has two aims: first, to characterise morphological differences between healthy and EOA TMC bones. The second aim was to determine the efficacy of using a statistical shape model (SSM) to detect early signs of osteoarthritis (OA).

METHODS

CT image data of TMC bones from 22 asymptomatic volunteers and 47 patients with EOA were obtained from an ongoing study and used to generate a SSM. A linear discriminant analysis (LDA) classifier was trained on the principal component (PC) weights to characterise features of each group. Multivariable statistical analysis was performed on the PC to investigate morphologic differences. Leave-one-out classification was performed to evaluate the classifiers performance.

RESULTS

We found that TMC bones of EOA subjects exhibited a lower aspect ratio (P = 0.042) compared with healthy subjects. The LDA classifier predicted that protrusions (up to 1.5 mm) at the volar beak of the first metacarpal were characteristic of EOA subjects. This was accompanied with widening of the articular surface, deepening of the articular surface, and protruding bone growths along the concave margin. These characteristics resulted in a leave-one-out classification accuracy of 73.9% (95% CI [61.9%, 83.8%]), sensitivity of 89.4%, specificity of 40.9%, and precision of 75.9%.

CONCLUSION

Our findings indicate that morphological degeneration is well underway in the EOA TMC joint, and shows promise for a clinical tool that can detect these features automatically.

An anatomical study on the effectiveness of Arthrex Mini TightRope® ligament reconstruction in an unstable trapeziometacarpal joint

INTRODUCTION

Laxity in the trapeziometacarpal (TMC) joint is a debilitating condition usually affecting a young population. It can be treated operatively with ligament reconstruction. The purpose of this study was to determine the effectiveness of the Arthrex Mini TightRope^® in reinforcing the stabilizing ligaments in an unstable TMC joint without decreasing the range of motion of the thumb. This method was compared with the "gold standard" published by Eaton and Littler in 1973.

MATERIALS AND METHODS

Six fresh frozen arms from five cadavers were included. TMC joint laxity was measured on stress view radiographs as the ratio of the radial subluxation (RS) of the first metacarpal in relation to the trapezium, by the first metacarpal articular width (AW) (as described by Wolf in 2009). Measurements of the pre- and post-operative range of motion (ROM) were performed and compared.

RESULTS

Both the Arthrex Mini TightRope^® and the Eaton-Littler stabilization improved the stability of the TMC joint. The pre-operative laxity value (ratio RS/AW) of 0.27 was significantly (P = 0.02) improved by each of the surgical interventions (Eaton-Littler RS/AW = 0.05 and Tightrope RS/AW = 0.09). The pre- and post-operative range of motion was not significantly different by each of the surgical interventions. There were no significant differences between the two stabilizing methods regarding laxity or range of motion.

CONCLUSION

The Arthrex Mini TightRope^® provided a good stabilization method for the TMC joint in this anatomical model without compromising the range of motion.

In Vivo 3-Dimensional Kinematics of Thumb Carpometacarpal Joint During Thumb Opposition

PURPOSE

This study primarily aimed to demonstrate the screw-home rotation of the thumb carpometacarpal (CMC) joint and the function of surrounding ligaments during thumb oppositional motion.

METHODS

A 3-dimensional kinematic analysis of the thumb CMC joint was conducted using data derived from computed tomography of 9 healthy volunteers. Scans were obtained in the neutral forearm and wrist position and the thumb in maximum radial abduction, maximum palmar abduction, and maximum opposition. The movements of the first metacarpal and the palmar and dorsal bases on the trapezium during thumb oppositional motion from radial abduction through palmar abduction were quantified using a coordinate system originating on the trapezium. In addition to the kinematic analyses, the length of virtual ligaments, including the anterior oblique, ulnar collateral, dorsal radial, dorsal central (DCL), and posterior oblique ligament (POL), were calculated at each thumb position.

RESULTS

From radial abduction to opposition of the thumb through palmar abduction, the first metacarpal was abducted, internally rotated, and flexed on the trapezium. The palmar base of the first metacarpal moved in the palmar-ulnar direction, and the dorsal base moved in the palmar-distal direction along the concave surface of the trapezium. Although the DCL and POL lengthened, the lengths of other ligaments did not change significantly.

CONCLUSIONS

During thumb oppositional motion, internal rotation of the first metacarpal occurred, with the palmar base rotating primarily with respect to the dorsal base. The DCL and POL may be strained in thumb functional positions.

CLINICAL RELEVANCE

Kinematic variables indicated a screw-home rotation of the thumb CMC joint and the contribution of the dorsal ligaments to the stability of the rotation on the pivot point.

Biomechanical analysis of the Universal 2 implant in total wrist arthroplasty: a finite element study

Little is known about the mechanics of in vivo loading on total wrist prostheses where many studies have looked at the mechanics of other types of arthroplasty such as for the hip and the knee which has contributed to the overall success of these types of procedures. Currently surgeons would prefer to carry out arthrodesis on the wrist rather than consider arthroplasty as clinical data have shown that the outcome of total wrist arthroplasty is poorer than compared to the hip and knee. More research is needed on the loading mechanisms of the implants in order to enhance the design of future generation implants. This study looks at the load transfer characteristics of the Universal 2 implant using a finite element model of a virtually implanted prosthesis during gripping. The results showed that the loading on the implant is higher on the dorsal and ulnar aspect than on the volar and radial aspect of the implant. The whole load is transmitted through the radius and none through the ulna.

Thumb Injuries in Athletes

Thumb injuries are common in athletes and present a challenging opportunity for upper extremity physicians. Common injuries include metacarpal base fractures (Bennett and Rolando types), ulnar and radial collateral ligament injuries, dislocation of the carpometacarpal and metacarpophalangeal joints, and phalanx fractures. This review, although not exhaustive, highlights some of the most common thumb injuries in athletes. The treating physician must balance pressure from athletes, parents, coaches, and executives to expedite return to play with the long-term well-being of the athlete. Operative treatment may expedite return to play; however, one must carefully weigh the added risks involved with surgical intervention.

Development of a biomechanical model of the wrist joint for patient-specific model guided surgical therapy planning: Part 1

An enhanced musculoskeletal biomechanical model of the wrist joint is presented in this article. The developed computational model features the two forearm bones radius and ulna, the eight wrist bones, the five metacarpal bones, and a soft tissue apparatus. Validation of the model was based on information taken from the literature as well as own experimental passive in vitro motion analysis of eight cadaver specimens. The computational model is based on the multi-body simulation software AnyBody. A comprehensive ligamentous apparatus was implemented allowing the investigation of ligament function. The model can easily patient specific personalized on the basis of image information. The model enables simulation of individual wrist motion and predicts trends correctly in the case of changing kinematics. Therefore, patient-specific multi-body simulation models are potentially valuable tools for surgeons in pre- and intraoperative planning of implant placement and orientation.

Trapeziometacarpal Ligaments Biomechanical Study: Implications in Arthroscopy

Purpose In the presence of early osteoarthritis, changes to the trapeziometacarpal joint (TMJ) often result in pain and is associated with joint instability and a tendency of dorsoradial subluxation. In these instances, arthroscopy may be indicated to: (1) assess the extent of cartilage disease and the laxity of ligaments and to (2) treat TMJ instability. The purpose of our study was to biomechanically analyze which ligaments are the primary stabilizers of the TMJ. Methods Overall, 11 fresh-frozen human cadaver specimens were dissected and attached to a testing device with the thumb positioned in neutral abduction, neutral flexion, and neutral opposition. The four extrinsic and five intrinsic muscle tendons acting on the TMJ were simultaneously loaded with weights proportional to their physiological cross-sectional area. The dorsal, volar, and ulnar groups of ligaments were dissected. A motion-tracking device, FasTrak (Polhemus Inc., Colchester, VT), was used to study the spatial position of the base of the first metacarpal bone (MC1), before and after random sectioning of each of the ligaments. Statistical analysis of the MC1 translation along the transverse XY plane was performed using one-way analysis of variance and a paired t-test, with a significance level of p < 0.05. Results After isolated sectioning of the volar or the ulnar ligaments, the MC1 moved dorsoradially with an average of 0.150 mm (standard deviation [SD]: 0.072) and 0.064 mm (SD: 0.301), respectively. By contrast, the destabilization of the MC1 after sectioning of the dorsal ligaments was substantially larger (0.523 mm; SD: 0.0512; p = 0.004). Conclusion Sectioning of the dorsal ligament group resulted in the greatest dorsoradial translation of the MC1. Consequently, the dorsal ligaments may be regarded as the primary TMJ stabilizers. Clinical Relevance This study suggests that stabilizing arthroscopic shrinkage of the TMJ should be targeted toward the dorsal TMJ ligaments.

Altered Innervation Pattern in Ligaments of Patients with Basal Thumb Arthritis

Purpose The population of mechanoreceptors in patients with osteoarthritis (OA) lacks detailed characterization. In this study, we examined the distribution and type of mechanoreceptors of two principal ligaments in surgical subjects with OA of the first carpometacarpal joint (CMC1). Methods We harvested two ligaments from the CMC1 of eleven subjects undergoing complete trapeziectomy and suspension arthroplasty: the anterior oblique (AOL) and dorsal radial ligament (DRL). Ligaments were divided into proximal and distal portions, paraffin-sectioned, and analyzed using immunoflourescent triple staining microscopy. We performed statistical analyses using the Wilcoxon Rank Sum test and ANOVA with post-hoc Bonferroni and Tamhane adjustments. Results The most prevalent nerve endings in the AOL and DRL of subjects with OA were unclassifiable mechanoreceptors, which do not currently fit into a defined morphological scheme. These were found in 11/11 (100%) DRLs and 7/11 (63.6%) AOLs. No significant difference existed with respect to location within the ligament (proximal versus distal) of mechanoreceptors in OA subjects. Conclusion The distribution and type of mechanoreceptors in cadavers with no to mild OA differ from those in surgical patients with OA. Where Ruffini endings predominate in cadavers with no to mild OA, unclassifiable corpuscles predominate in surgical patients with OA. These findings suggest an alteration of the mechanoreceptor population and distribution that accompanies the development of OA. Clinical Relevance Identification of a unique type and distribution of mechanoreceptors in the CMC1 of symptomatic subjects provides preliminary evidence of altered proprioception in OA.

Radiographic Assessment of the Robert and Lateral Views in Trapeziometacarpal Osteoarthrosis

Background: To evaluate the effectiveness of the Robert view in assessing trapeziometacarpal arthrosis and to compare the accuracy of the Robert and lateral views in staging trapeziometacarpal (TM) joint arthrosis.

Methods: Patient demographics were obtained. Four participating raters reviewed 62 randomly selected thumb x-rays of patients presenting with thumb TM joint pain. Lateral and Robert-hyperpronation views were assessed using an analysis of 13 criteria.

Results: X-rays of 62 thumbs for 58 patients were evaluated. The average patients' age was 64 (47-87) and 51 (80%) were females. The majority of X-rays evaluated fell into stage 3. Stage 2 was the second most common level of arthritis encountered and the least was stage 1. More osteophytes were encountered in the trapezium than metacarpal on both the Robert and lateral views. The Robert view was superior in detecting osteophytes on the trapezium than the lateral view. Osteophyte size varied from 1.7 to 2 mm. The lateral view displayed 61 cases with dorsal metacarpal subluxation (98%). The Robert view displayed 48 cases (77%) with radial metacarpal subluxation and 9 cases (15%) with ulnar metacarpal subluxation. Thumb metacarpal adduction deformity was encountered on the lateral view in 20 cases (32%) whereas on the Robert view it was encountered in 14 cases (23%). Subchondral sclerosis was encountered on the Robert view in 56 thumbs (90%) while it was seen on the lateral view in 52 thumbs (84%). Pantrapezial arthritis involving the STT joint was encountered equally in 16 cases (26%) on the Robert view and the lateral views. The study found a moderate level of interrater reliability on both the lateral and Robert views. With the exception of osteophytes encountered on the trapezium versus the metacarpal, there were no other statistically significant findings.

Conclusions: This study confirms that each of the Robert and lateral views offer unique information and combining both views enhances the ability to assess radiographic disease severity, and should be the recommended set of X-rays for assessing TM osteoarthrosis.

In vivo recruitment patterns in the anterior oblique and dorsoradial ligaments of the first carpometacarpal joint

The anterior oblique ligament (AOL) and the dorsoradial ligament (DRL) are both regarded as mechanical stabilizers of the thumb carpometacarpal (CMC) joint, which in older women is often affected by osteoarthritis. Inferences on the potential relationship of these ligaments to joint pathomechanics are based on clinical experience and studies of cadaveric tissue, but their functions has been studied sparsely in vivo. The purpose of this study was to gain insight into the functions of the AOL and DRL using in vivo joint kinematics data. The thumbs of 44 healthy subjects were imaged with a clinical computed tomography scanner in functional-task and thumb range-of-motion positions. The origins and insertion sites of the AOL and the DRL were identified on the three-dimensional bone models and each ligament was modeled as a set of three fibers whose lengths were the minimum distances between insertion sites. Ligament recruitment, which represented ligament length as a percentage of the maximum length across the scanned positions, was computed for each position and related to joint posture. Mean AOL recruitment was lower than 91% across the CMC range of motion, whereas mean DRL recruitment was generally higher than 91% in abduction and flexion. Under the assumption that ligaments do not strain by more than 10% physiologically, our findings of mean ligament recruitments across the CMC range of motion indicate that the AOL is likely slack during most physiological positions, whereas the DRL may be taut and therefore support the joint in positions of CMC joint abduction and flexion.

In vivo analysis of trapeziometacarpal joint arthrokinematics during multi-directional thumb motions

BACKGROUND

The investigation of the joint arthrokinematics of the trapeziometacarpal joint is critical to comprehend the causative mechanism underlying this common form of osteoarthritis. Therefore, the purpose of this study is to evaluate the arthrokinematics of the trapeziometacarpal joint during thumb postures in vivo.

METHODS

Fifteen healthy participants were enrolled in this study. Static computed tomography images of the 1st metacarpal bone and trapezium were taken at specific thumb postures during thumb flexion-extension, abduction-adduction, and circumduction motions. Images were analyzed to examine the joint gliding, expressed as displacement of the centroid of the articular surface of the 1st metacarpal bone, relative to the trapezium. The gliding ratio, defined as joint gliding in each direction normalized to the dimension of the trapezium joint surface in the given direction, was computed and compared between different thumb motions.

FINDINGS

The results indicate that thumb motions influenced joint gliding. The centroids of the articular surface of the 1st metacarpal bone were primarily located at the central and dorsal-radial regions while executing these motions. The maximum joint gliding of the 1st metacarpal bone occurred in the radial-ulnar direction when performing abduction-adduction, and in the dorsal-volar direction while performing flexion-extension and circumduction, with the gliding ratio values of 42.35%, 51.65%, and 51.85%, respectively.

INTERPRETATION

Activities that involved abduction-adduction in the trapeziometacarpal joint caused greater joint gliding in the ulnar-radial direction, while flexion-extension resulted in greater joint gliding in the dorsal-volar and distal-proximal directions. Understanding normal joint kinematics in vivo may provide insights into the possible mechanism leading to osteoarthritis of the trapeziometacarpal joint, and help to improve the design of implants.

Comparison of the anatomical dimensions and mechanical properties of the dorsoradial and anterior oblique ligaments of the trapeziometacarpal joint

PURPOSE

The respective roles of the dorsoradial (DRL) and anterior oblique (AOL) ligaments in stability of the highly mobile trapeziometacarpal (TMC) joint remain disputed. Earlier publications have pointed to the AOL as the key stabilizing structure; yet, more recent publications have challenged the stabilizing role of the AOL, favoring the DRL as the main TMC joint stabilizer. We executed an anatomical study of the ligaments, including detailed dissection to quantify the length, width, and thickness of the AOL and DRL and tested the material properties of these ligaments.

METHODS

Thirteen fresh frozen cadaveric thumbs from 9 specimens were used. Length, width, and thickness of the AOL and DRL were measured on magnetic resonance imaging and/or after dissection. Next, the first metacarpal and trapezium were isolated together with both ligaments, and both bones were cut sagittally to isolate a first metacarpal-AOL-trapezium and first metacarpal-DRL-trapezium complex from each thumb. These samples were subjected to cyclic loading in displacement-controlled tests. The obtained force-displacement curves were used to calculate stiffness and hysteresis of each sample.

RESULTS

Our results showed that the DRL is significantly shorter and thicker than the AOL, which is thin and ill-defined. Our results also indicate that the DRL has a higher stiffness than the AOL, making it a more likely candidate to provide joint stability.

CONCLUSIONS

Although the AOL has been asserted to be the primary restraint to dorsoradial subluxation, this view has been challenged over the past 10 years by several studies. These studies have shown the AOL to be relatively weak and compliant compared with the intermetacarpal and dorsoradial ligaments and have demonstrated that the DRL is the strongest and stiffest ligament of the TMC joint. Our studies confirm these findings.

CLINICAL RELEVANCE

This study indicates that the DRL is relatively stiff and thick, suggesting it should be repaired or reconstructed when disrupted to restore stability of the TMC joint.

Ultrastructure and innervation of thumb carpometacarpal ligaments in surgical patients with osteoarthritis

BACKGROUND

The complex configuration of the thumb carpometacarpal (CMC-1) joint relies on musculotendinous and ligamentous support for precise circumduction. Ligament innervation contributes to joint stability and proprioception. Evidence suggests abnormal ligament innervation is associated with osteoarthritis (OA) in large joints; however, little is known about CMC-1 ligament innervation characteristics in patients with OA. We studied the dorsal radial ligament (DRL) and the anterior oblique ligament (AOL), ligaments with a reported divergent presence of mechanoreceptors in nonosteoarthritic joints.

QUESTIONS/PURPOSES

This study's purposes were (1) to examine the ultrastructural architecture of CMC-1 ligaments in surgical patients with OA; (2) to describe innervation, specifically looking at mechanoreceptors, of these ligaments using immunohistochemical techniques and compare the AOL and DRL in terms of innervation; and (3) to determine whether there is a correlation between age and mechanoreceptor density.

METHODS

The AOL and DRL were harvested from 11 patients with OA during trapeziectomy (10 women, one man; mean age, 67 years). The 22 ligaments were sectioned in paraffin and analyzed using immunoflourescent triple staining microscopy.

RESULTS

In contrast to the organized collagen bundles of the DRL, the AOL appeared to be composed of disorganized connective tissue with few collagen fibers and little innervation. Mechanoreceptors were identified in CMC-1 ligaments of all patients with OA. The DRL was significantly more innervated than the AOL. There was no significant correlation between innervation of the DRL and AOL and patient age.

CONCLUSIONS

The dense collagen structure and rich innervation of the DRL in patients with OA suggest that the DRL has an important proprioceptive and stabilizing role.

CLINICAL RELEVANCE

Ligament innervation may correlate with proprioceptive and neuromuscular changes in OA pathophysiology and consequently support further investigation of innervation in disease prevention and treatment strategies.

Trapeziometacarpal joint stability: the evolving importance of the dorsal ligaments

BACKGROUND

Trapeziometacarpal (TMC) arthritis of the thumb is a common source of hand pain and disability. TMC ligamentous instability may play a role in TMC degeneration. However, the relative importance of the TMC ligaments in the etiology of degeneration and the use of surgery to treat instability in early-stage arthritis are unclear.

QUESTIONS/PURPOSES

In this review, we addressed several questions: (1) What are the primary ligamentous stabilizers of the thumb TMC joint? (2) What is the evidence for ligament reconstruction or ligament imbrication in the treatment of thumb TMC joint osteoarthritis? And (3) what is the evidence for thumb metacarpal osteotomy in the treatment of thumb TMC joint osteoarthritis?

METHODS

We performed a systematic review of the literature using PubMed (MEDLINE(®)) and Scopus(®) (EMBASE(®)) for peer-reviewed articles published until November 2012. Fifty-two studies fit the inclusion criteria. Twenty-four studies were anatomic, biomechanical, or histopathologic studies on TMC joint ligamentous anatomy, 16 studies were clinical studies concerning ligament reconstruction, and 12 studies were clinical studies on thumb metacarpal osteotomy.

RESULTS

Over the past two decades, increasing evidence suggests the dorsoradial ligament is the most important stabilizer of the TMC joint. Other ligaments consistently identified are the superficial anterior oblique, deep anterior oblique, intermetacarpal, ulnar collateral, and posterior oblique ligaments. Ligament reconstruction and metacarpal osteotomy relieve pain and improve grip strength based on Level IV studies.

CONCLUSIONS

The dorsal ligaments are the primary stabilizers of the TMC joint. Ligament reconstruction and metacarpal osteotomy ameliorate ligamentous laxity and relieve pain based on Level IV studies.

Dorsoradial capsulodesis for trapeziometacarpal joint instability

We describe an alternative method for treating chronic trapeziometacarpal (TM) joint instability after acute injury or chronic repetitive use of the thumb by performing a dorsoradial capsulodesis procedure. The procedure is done by imbricating the redundant TM joint dorsoradial ligament and capsule after reducing the joint by pronating the thumb. The dorsoradial capsulodesis is a reasonable reconstructive option for chronic TM joint instability and subluxation.

An exercise program for carpometacarpal osteoarthritis based on biomechanical principles

A review of the literature was performed to design a hand exercise regimen based on biomechanical principles of the carpometacarpal (CMC) joint and the forces that act upon the joint. Sixteen biomechanical studies were included in the review: four studies developed a mathematical model of the thumb and 12 performed cadaveric dissections to study the CMC joint. Clinical application of the biomechanical findings from the studies was synthesized into specific recommendations for a hand exercise program to preserve CMC joint range of motion and increase the strength of the stabilizing muscles of the thumb. The exercise regimen was developed in accordance with recommendations of the American College of Sports Medicine guidelines for the development of individualized exercise prescriptions.

LEVEL OF EVIDENCE

4.

Functional patterns of thumb key pinch and their influence on thumb strength and stability

Introduction

Trapeziometacarpal osteoarthritis (TMC OA) is a common condition frequently related to instability and hypermobility. Many factors are involved in the development of this degenerative process. Recent research suggests that the position of the metacarpophalangeal (MCP) joint may influence TMC joint contact wear patterns and subsequent development of OA. The aim of this study is to explore the alignment of the MCP joint of the thumb during lateral pinch in order to describe the naturally occurring alignment in a group of healthy volunteers without symptoms.

Methods

One hundred and nine participants were asked to apply a lateral pinch manoeuvre to a pinchmeter, while their thumbs were assessed. Passive hypermobility of the thumb MCP (MCP) joint was assessed, key pinch strength was measured, key pinch position was photographed and the angle of the joints during the assessment was measured.

Results

Four different functional pinch patterns were identified. The most frequent pattern seems to be MCP hyperextension described by Moulton as harmful for the TMC joint. The level of strength obtained did not correspond to the pinch pattern used, and hypermobility of the thumb MCP joint did not determine the position of the thumb during key pinch.

Conclusion

Four different thumb postures were identified during lateral pinch; however, these postures were not associated with any difference in pinch strength. We conclude that the more unstable and mechanically inefficient postures are compensated by functional capacity.

Biomechanical analysis of the wrist arthroplasty in rheumatoid arthritis: a finite element analysis

The total replacement of wrists affected by rheumatoid arthritis (RA) has had mixed outcomes in terms of failure rates. This study was therefore conducted to analyse the biomechanics of wrist arthroplasty using recently reported implants that have shown encouraging results with the aim of providing some insights for the future development of wrist implants. A model of a healthy wrist was developed using computed tomography images from a healthy volunteer. An RA model was simulated based on all ten general characteristics of the disease. The ReMotion ™ total wrist system was then modelled to simulate total wrist arthroplasty (TWA). Finite element analysis was performed with loads simulating the static hand grip action. The results show that the RA model produced distorted patterns of stress distribution with tenfold higher contact pressure than the healthy model. For the TWA model, contact pressure was found to be approximately fivefold lower than the RA model. Compared to the healthy model, significant improvements were observed for the TWA model with minor variations in the stress distribution. In conclusion, the modelled TWA reduced contact pressure between bones but did not restore the stress distribution to the normal healthy condition.

Macroscopic and microscopic analysis of the thumb carpometacarpal ligaments: a cadaveric study of ligament anatomy and histology

BACKGROUND

Stability and mobility represent the paradoxical demands of the human thumb carpometacarpal joint, yet the structural origin of each functional demand is poorly defined. As many as sixteen and as few as four ligaments have been described as primary stabilizers, but controversy exists as to which ligaments are most important. We hypothesized that a comparative macroscopic and microscopic analysis of the ligaments of the thumb carpometacarpal joint would further define their role in joint stability.

METHODS

Thirty cadaveric hands (ten fresh-frozen and twenty embalmed) from nineteen cadavers (eight female and eleven male; average age at the time of death, seventy-six years) were dissected, and the supporting ligaments of the thumb carpometacarpal joint were identified. Ligament width, length, and thickness were recorded for morphometric analysis and were compared with use of the Student t test. The dorsal and volar ligaments were excised from the fresh-frozen specimens and were stained with use of a triple-staining immunofluorescent technique and underwent semiquantitative analysis of sensory innervation; half of these specimens were additionally analyzed for histomorphometric data. Mixed-effects linear regression was used to estimate differences between ligaments.

RESULTS

Seven principal ligaments of the thumb carpometacarpal joint were identified: three dorsal deltoid-shaped ligaments (dorsal radial, dorsal central, posterior oblique), two volar ligaments (anterior oblique and ulnar collateral), and two ulnar ligaments (dorsal trapeziometacarpal and intermetacarpal). The dorsal ligaments were significantly thicker (p < 0.001) than the volar ligaments, with a significantly greater cellularity and greater sensory innervation compared with the anterior oblique ligament (p < 0.001). The anterior oblique ligament was consistently a thin structure with a histologic appearance of capsular tissue with low cellularity.

CONCLUSIONS

The dorsal deltoid ligament complex is uniformly stout and robust; this ligament complex is the thickest morphometrically, has the highest cellularity histologically, and shows the greatest degree of sensory nerve endings. The hypocellular anterior oblique ligament is thin, is variable in its location, and is more structurally consistent with a capsular structure than a proper ligament.

Biomechanical analysis of rheumatoid arthritis of the wrist joint

The wrist is the most complex joint for virtual three-dimensional simulations, and the complexity is even more pronounced when dealing with skeletal disorders of the joint such, as rheumatoid arthritis (RA). In order to analyse the biomechanical difference between healthy and diseased joints, three-dimensional models of these two wrist conditions were developed from computed tomography images. These images consist of eight carpal bones, five metacarpal bones, the distal radius and ulna. The cartilages were developed based on the shape of the available articulations and ligaments were simulated via mechanical links. The RA model was developed accurately by simulating all ten common criteria of the disease related to the wrist. Results from the finite element (FE) analyses showed that the RA model produced three times higher contact pressure at the articulations compared to the healthy model. Normal physiological load transfer also changed from predominantly through the radial side to an increased load transfer approximately 5% towards the ulnar. Based on an extensive literature search, this is the first ever reported work that simulates the pathological conditions of the rheumatoid arthritis of the wrist joint.

Method for the estimation of a double hinge kinematic model for the trapeziometacarpal joint using MR imaging

In this paper, we propose a method to estimate the parameters of a double hinge model of the trapeziometacarpal joint (TMC) by MRI-based motion analysis. The model includes two non-orthogonal and non-intersecting rotation axes accounting for flexion-extension (F-E) and adduction-abduction (A-A). We evaluated the quality of the estimated model parameters in the prediction of the relative motion of the first metacarpal bone with respect to the trapezium. As a result, we obtained that: (a) the estimated location and orientation of the F-E and A-A axes were in agreement with previous in vitro studies, (b) the motion of the first metacarpal predicted by the 2 degrees of freedom (2DoF) model exhibits a maximum surface distance error in the range of about 2 mm and (c) four thumb postures at the boundary of the TMC range of motion are sufficient to provide a good estimation of the 2DoF TMC kinematic model and good reproducibility (~1.7 mm) of the real thumb motion at TMC level.

Current concepts of the anatomy of the thumb trapeziometacarpal joint

This review article describes the anatomy of the thumb trapeziometacarpal joint. In the final phase of opposition screw home torque rotation of the volar beak of the thumb metacarpal in the pivot area of the trapezium recess and tension on the dorsal ligament complex create stability for power pinch and power grip. The resulting compressive shear forces can lead over time to trapeziometacarpal joint osteoarthritis.

Determination of passive moment-angle relationships at the trapeziometacarpal joint

While modeling the trapeziometacarpal (TMC) joint for determination of tendon forces, the TMC has been considered frictionless and passive moments created by soft tissues neglected. This, however, becomes inaccurate when reaching the joint end range of motion and considering that the TMC is entirely crossed by a complex network of skin, ligaments, soft tissues, and tendons. The objective of this study was to evaluate the passive moments with respect to joint posture in order to further include this relationship in biomechanical modeling. An experimental method was proposed to estimate in vivo a global passive moment including the sum of the actions of each passive anatomical structure. An external force was applied at the level of the metacarpophalangeal joint in various directions ranging from neutral position to full extension and full adduction to full abduction. The passive moment was computed and expressed as a function of the adopted joint angles. An exponential regression was then developed to fit the experimental data and to propose a generic passive moment model. Results showed a good agreement between the proposed exponential regression model and the experimental measures. Moreover, it was shown that joint stiffness could represent more than 60% of the net joint moment during a typical pulp grip task. These results showed the necessity to include the data in biomechanical modeling. The results may help predict more realistic tendons force especially in abduction/adduction muscles.

An unusual fracture-dislocation of the trapeziometacarpal joint of the thumb: a case report

Reports describing trapeziometacarpal joint fractures of the thumb have discussed Bennett's fracture or Rolando's fracture primarily. We report a patient with an unusual fracture which could not be classified as a Bennett's-type or Rolando's-type injury. The aetiology of the fracture pattern is proposed and treatment considerations are discussed.

Comparative 3D quantitative analyses of trapeziometacarpal joint surface curvatures among living catarrhines and fossil hominins

Comparisons of joint surface curvature at the base of the thumb have long been made to discern differences among living and fossil primates in functional capabilities of the hand. However, the complex shape of this joint makes it difficult to quantify differences among taxa. The purpose of this study is to determine whether significant differences in curvature exist among selected catarrhine genera and to compare these genera with hominin fossils in trapeziometacarpal curvature. Two 3D approaches are used to quantify curvatures of the trapezial and metacarpal joint surfaces: (1) stereophotogrammetry with nonuniform rational B-spline (NURBS) calculation of joint curvature to compare modern humans with captive chimpanzees and (2) laser scanning with a quadric-based calculation of curvature to compare modern humans and wild-caught Pan, Gorilla, Pongo, and Papio. Both approaches show that Homo has significantly lower curvature of the joint surfaces than does Pan. The second approach shows that Gorilla has significantly more curvature than modern humans, while Pongo overlaps with humans and African apes. The surfaces in Papio are more cylindrical and flatter than in Homo. Australopithecus afarensis resembles African apes more than modern humans in curvatures, whereas the Homo habilis trapezial metacarpal surface is flatter than in all genera except Papio. Neandertals fall at one end of the modern human range of variation, with smaller dorsovolar curvature. Modern human topography appears to be derived relative to great apes and Australopithecus and contributes to the distinctive human morphology that facilitates forceful precision and power gripping, fundamental to human manipulative activities.