Material properties of the trapezial and trapeziometacarpal ligaments

Destabilization of the trapezium from its normal orientation with respect to the trapezoid, second metacarpal, and thumb metacarpal leads to incongruity at the trapeziometacarpal (TMC) joint. Abnormal shear forces may eventually result in TMC joint arthritis. By determining the relative stiffness and strength of the ligaments that stabilize this joint, one may infer their role in providing stability to the TMC joint. This study addresses the material properties of the ligaments stabilizing the trapezium and TMC joint to better understand the mechanics and kinematics of this joint. Fresh-frozen cadaveric hands (10 males and 10 females) were used to obtain bone-ligament-bone complexes from the dorsal and volar trapeziotrapezoid ligaments, dorsal and volar trapezio-second metacarpal ligaments, anterior oblique ligament, dorsoradial ligament, and trapezio-third metacarpal (T-III MC) ligament. The following material properties were derived from our data: ultimate load, ultimate stress (normalized failure load), ultimate strain (percent elongation), stiffness, toughness (energy to failure), and hysteresis. The dorsoradial ligament demonstrated the greatest ultimate load and toughness (energy to failure). The T-III MC ligament demonstrated the greatest ultimate stress (normalized failure load) and stiffness. The anterior oblique ligament demonstrated the least stiffness and the greatest hysteresis. The material properties of capsuloligamentous structures may be a good indicator of their importance to joint stability. Using these criteria we conclude that the T-III MC and dorsoradial ligaments are important stabilizers of the trapezium and TMC joint, respectively. These two ligaments were found to be the strongest, stiffest, and toughest ligaments, while the anterior oblique ligament was relatively weak and compliant. The dorsal trapezio-second metacarpal, volar trapezio-second metacarpal, and T-III MC ligaments were all relatively strong and are anatomically aligned to function as tension bands to restrain the trapezium against cantilever bending forces applied to it by the thumb during key or tip pinch.     

Kinematics of the trapeziometacarpal joint after sectioning of ligaments

This study was designed to examine the roles of ligaments in the maintenance of the articular kinematics of the trapeziometacarpal joint. Circumduction of the trapeziometacarpal joint was studied in 12 hands from fresh human cadavera. With use of a magnetic tracking system, changes in the motion of the base of the first metacarpal after ligament sectioning were analyzed and compared with those of the normal joint. Two sets of ligaments were sectioned: (a) the anterior oblique and ulnar collateral ligaments and (b) the first intermetacarpal ligament and the ulnar joint capsule. Sectioning of the anterior oblique and ulnar collateral ligaments resulted in a significant dorsal-ulnar shift in the path of the base of the first metacarpal. However, sectioning of the first intermetacarpal ligament did not affect the movement pattern of the center of the base. The anterior oblique and ulnar collateral ligaments provided constraint of the trapeziometacarpal joint during circumduction of the thumb.     

Three-dimensional analysis of the ligamentous attachments of the first carpometacarpal joint

PURPOSE: To show the ligamentous locations and attachments of the first carpometacarpal (CMC) joint on a 3-dimensional (3-D) surface model. METHODS: Ten fresh-frozen cadaver wrists were used to dissect and identify the first CMC ligaments. Their ligamentous attachments and whole bone surfaces were digitized 3-dimensionally and their areas were calculated. The attachments of each ligament were represented in a model combining 3-D computed tomography surfaces overlaid by a digitized 3-D surface and also were shown visually by a specific color on 3-D bone images. The superimposed outlines of the ligamentous attachments on both the radial and ulnar base of the first metacarpal (MC) also are described. RESULTS: Seven ligaments of the first CMC joint were identified: the dorsoradial ligament, the posterior oblique ligament, the superficial anterior oblique ligament, the deep anterior oblique ligament, the ulnar collateral ligament, the dorsal first MC ulnar base-second MC radial base intermetacarpal ligament, and the volar first MC ulnar base-second MC radial base intermetacarpal ligament. The detailed locations and areas of the ligamentous attachments of the first CMC joint were determined. The average locations of the centroid of the ligamentous attachments of the ulnar collateral and the dorsoradial ligaments were located ulnovolar and dorsoradial on the first MC base, respectively. CONCLUSIONS: The anatomic 3-D attachment sites of the first CMC ligaments were shown qualitatively and their areas were quantified. The results of this study improve the knowledge and understanding of the normal anatomy and its impact on the mechanics of the first CMC joint. This should help in making an accurate assessment of radiographic images and treating injuries and degenerative changes in the first CMC joint by ligament reconstruction, repair, and arthroscopy.     

Importance of the posteromedial trapezometacarpal ligamentous complex

Pronation and supination of the human thumb has both a practical and a symbolic importance. In supination the thumb caresses but in pronation it grasps. The articular surfaces of the trapezium and first metacarpal are not congruent enough in themselves to assure pronation and supination, but their reciprocal saddle shape causes them to have two distinct orthogonal "fundamental" axes of rotation, and hence two "privileged" planes of rotation. The one corresponds to the movements of the lateral pinch grip and the other to opposition and counter-opposition of the thumb. The important ligaments are situated on both sides of the trapeziometacarpal joint. The posteromedial ligamentous complex is composed of the posterior oblique ligament, the anterior oblique ligament, the intermetacarpal ligament, and a fourth or more anteromedial ligament which we have called the retinaculometacarpal ligament by reason of its proximal insertion. It plays an essential role in suspending and anchoring the base of the first metacarpal. By its action it induces two types of motion: 1) a discrete translation of the metacarpal along the articular concavity of the trapezium in lateral pinch grip; 2) a more important motion characterised by a prosupination of 90 degrees during its rotation in the plane of opposition. The anterolateral ligament's action is restricted to strengthening the action of the posteromedial ligaments in the extreme positions of closing of lateral pinch and thumb opposition. In cases of trapeziometacarpal subluxation it prevents a complete dislocation. These various observations have significant clinical and therapeutic implications.     

Dynamic suspension-sling arthroplasty with intermetacarpal ligament reconstruction for the treatment of trapeziometacarpal osteoarthritis

Our new dynamic suspension-sling arthroplasty of the trapeziometacarpal joint stabilizes the base of the first metacarpal after the removal of the trapezium in patients who have trapeziometacarpal joint osteoarthritis. Other techniques involving ligament reconstruction are accompanied by complications such as proximal migration, dorsal subluxation of the first metacarpal base, and impingement of the first and second carpometacarpal joints. In our technique, the first metacarpal is suspended by using a series of tendon loops derived from one-half of the flexor carpi radialis tendon and, therefore, anatomically reconstructs the intermetacarpal and palmar oblique ligaments. From 1988 to 2000, 197 patients (238 thumbs) underwent this procedure. Follow-up was an average of 1.92 years. After surgery, pain decreased, grip strength increased from 24 to 48.7 lb, key pinch increased from 4 to 7.6 lb, and Kapandji scores increased from 6 to 9.3 (averages). Our technique provides an interposition between the bases of the thumb and index metacarpals, resulting in decreased pain, greater strength, and increased flexibility of the trapeziometacarpal joint.     

Ligament length during circumduction of the trapeziometacarpal joint

The length of the ligaments in the trapeziometacarpal joint in 12 fresh human cadaveric hands was studied with a magnetic tracking system. The location of the insertion and origin of five trapeziometacarpal ligaments was precisely identified and digitized. The distances between the digitized points were calculated throughout the range of motion. The anterior oblique ligament (AOL) and ulnar collateral ligament (UCL) had similar patterns of variation in ligament length during circumduction motion, reaching the maximum length in the extension-abduction position. The first intermetacarpal ligament (IML) and the posterior oblique ligament (POL) exhibited similar patterns of variation in ligament length, reaching their maximum lengths in the flexion-abduction position. The dorsoradial ligament (DRL) had a different pattern, with the maximum length occurring in the adduction position. The ligaments reached their minimum length when the metacarpal head position was nearly opposite the position that produced maximum length. The total variation in length of each ligament in circumduction was about 5%–9% of the maximum length.     

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.     

Contact area of the trapeziometacarpal joint.

Eighteen cadaver hands were studied to determine the contact area of the trapeziometacarpal joint by using silicone rubber casts. Casting material was introduced into the trapeziometacarpal joint during several motions of the thumb and the contact location was observed. The ratios of the contact area to the total joint area were calculated. The contact locations in opposition were the radial, volar, and ulnar segments of the trapezium and the dorsal, radial, and volar segments of the metacarpal. On average, 53% of the trapezium was in contact with 53% of the metacarpal in opposition, while 28% of the trapezium was in contact with 28% of the metacarpal in palmar abduction and 25% of the trapezium was in contact with 25% of the metacarpal in radial abduction. The contact area was the largest in opposition. The trapeziometacarpal joint is stable in opposition and facilitates a strong pinch.     

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.

Electronic supplementary material

The online version of this article (doi:10.1007/s11999-013-2879-9) contains supplementary material, which is available to authorized users.     

Trapeziectomy and intermetacarpal ligament reconstruction with the extensor carpi radialis longus for osteoarthritis of the trapeziometacarpal joint: surgical technique and long-term results

PURPOSE: To report the long-term results of excision of the trapezium and intermetacarpal ligament reconstruction with the extensor carpi radialis longus for thumb trapeziometacarpal osteoarthritis. METHODS: Fourteen women and 5 men were retrospectively reviewed after an average of 9 years of follow-up evaluation. Trapeziectomy was performed and the extensor carpi radialis longus was harvested by a dorsoradial approach to reconstruct the intermetacarpal ligament. All patients wore a below-elbow cast for 6 weeks. Each patient had objective and subjective assessments. Thumb shortening was measured in follow-up radiographs. RESULTS: At the final follow-up evaluation, 16 (84%) patients were free of pain and 17 patients (89%) were satisfied with the results. Grip, key strength, and pinch strength improved compared with preoperative values. The trapezium space lost 14% of its height compared with preoperative values. Thumb motion improved, and there were no cases of instability. CONCLUSIONS: Resection-arthroplasty of the trapezium with intermetacarpal ligament reconstruction with the extensor carpi radialis longus is an effective procedure that permits motion restoration and pain relief in the trapeziometacarpal joint in the long term without affecting thumb stability. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.     

Anatomical study of the ligamentous attachments and articular surfaces of the trapeziometacarpal joint. Consequences on surgical management of its osteoarthrosis

In the goal to optimize conservative surgical techniques of the trapeziometacarpal joint in cases of moderate osteoarthritis, we have defined the relationships between the ligamentous attachments and the articular surfaces onto the trapezium and the first metacarpal bone on the one hand, and the dorsovolar and the transverse diameters of the articular surfaces on the other hand. Thirty-six trapeziometacarpal joints (from 18 fresh cadavers) were studied. They were separated into two groups depending on the macroscopic assessment of chondral disease. Group A included stages I to III (no osteoarthritis or moderate osteoarthritis), group B included stages IV (major cartilage destruction). The dorsovolar and transverse sizes of the articular surfaces were measured. Dorsoradial ligament (DRL), posterior oblique ligament (POL), intermetacarpal ligament (IML), ulnar collateral ligament (UCL) and anterior oblique ligament (AOL) were dissected and the distance between their attachments and the articular surfaces were measured. Group A included 17 joints (71% males) and group B included 19 joints (95% females). For the first metacarpal bone, the average ratio between the dorsovolar diameter and the transverse diameter of metacarpal articular surfaces was significantly higher in group B and the average distance between the ligamentous attachments and the articular surface was more than two millimeters, except for the DRL in group B. For the trapezium, only the posterior ligaments (DRL and POL) of group A were inserted at a mean distance more than two millimeters from the articular surfaces. Dorsovolar length of the metacarpal articular surface was higher for osteoarthritis cases. This difference can be explained by the existence of a palmar osteophyte that was always found in stage IV. Describing a map of the ligamentous attachment distance from the articular surface could help surgeons to avoid the ligamentous injury during minimal osteochondral resection.     

Effects of the deep anterior oblique and dorsoradial ligaments on trapeziometacarpal joint stability

PURPOSE: Osteoarthritis of the trapeziometacarpal (TMC) joint of the thumb affects as many as 25% of postmenopausal women and 5% of middle-aged men. This study investigated the relative contribution of the dorsoradial ligament (DRL) and the deep anterior oblique ligament (dAOL) to the stability of the TMC joint. This knowledge will improve our understanding of the pathomechanics of osteoarthritis at the base of the thumb and may help to design novel reconstructive surgical procedures. METHODS: Seventeen intact cadaver hands were dissected to reveal the DRL and dAOL. Either the DRL or dAOL was transected randomly, physiologic muscle loads were applied to simulate lateral key pinch or thumb opposition, or a 3-dimensional magnetic tracking system was used to record the position of the thumb metacarpal relative to the trapezium. The differences in the 3-dimensional positions between the control and transected states were determined. RESULTS: In lateral pinch, transection of the DRL resulted in a mean increased 3-dimensional translation of 1.3 mm, whereas transection of the dAOL resulted in a mean increased 3-dimensional translation of 0.6 mm. Statistically significant 2-dimensional findings in lateral pinch after transecting the DRL or dAOL included an increased palmar subluxation of 0.3 mm and 0.2 mm, an increased radial (1.0 mm) and ulnar (0.3 mm) translation, and an increased pronation of 4.1 degrees and 2.4 degrees, respectively. In thumb opposition, transection of the DRL resulted in a mean increased 3-dimensional translation of 1.0 mm, whereas transection of the dAOL resulted in a mean increased 3-dimensional translation of 0.5 mm. CONCLUSIONS: In most degrees of freedom of metacarpal movement relative to the trapezium, the DRL is relatively more important than the dAOL in providing stability to the TMC joint.     

Basal joint arthroplasty using the Roosevelt Hospital techniques

Many reconstructive procedures have been developed to treat osteoarthritis of the basal joint of the thumb. The current article describes techniques used at the Hand Surgery Center at Roosevelt Hospital in New York City. A tonometry applanation radiographic staging system is outlined; it serves as a rationale for selecting which form of arthroplasty is appropriate for a particular patient and is predicated on the extent of involvement of the trapezial articulations. Stage 1 disease implies symptomatic laxity of the trapeziometacarpal joint with normal articular surfaces and is most appropriately treated with volar ligament reconstruction. Stage 2 is an intermediate category and amenable to either volar ligament reconstruction or interpositional arthroplasty of the trapeziometacarpal joint, based on the condition of the articular cartilage at surgery. In stage 3 disease there are significant degenerative changes of the trapeziometacarpal joint with preservation of the articular surfaces of the scaphotrapezial joint. Two variations on ligament reconstruction with interpositional arthroplasty of the trapeziometacarpal joint are described; they have consistently good results. Finally, stage 4 is characterized by pantrapezial degenerative disease and necessitates trapezial resection. Reconstruction may be by silicone rubber implant arthroplasty using a stemmed trapezial implant stabilized by an abductor pollicis longus tenodesis. The alternative is a procedure in which the thumb metacarpal is tethered to the index metacarpal by a ligament reconstruction.     

Osteoarthritis of the trapeziometacarpal joint: the pathophysiology of articular cartilage degeneration. I. Anatomy and pathology of the aging joint.

An anatomic study of the trapeziometacarpal joint was conducted on 47 cadaver thumb specimens. The superficial capsule restrained only metacarpal rotation about its long axis. Intracapsular anatomy was notable for a large anterior subthenar recess limited dorsally by the abductor pollicis longus insertion and palmarly by the deep palmar or "beak" ligament. This beak ligament was essential for translational stability of the metacarpal on the trapezium with flexion of the thumb ray. There was a direct correlation between the status of the articular surfaces and the integrity of the beak ligament. Normal surfaces were associated with an intact ligament confluent with the hyaline cartilage of the palmar lip of the metacarpal; degeneration of the palmar lip cartilage was always associated with attritional detachment of the beak ligament. Advanced articular disease occurred only in the palmar contact areas and was predicted by degeneration of the adjacent beak ligament; only nonprogressive chondromalacia was found on the dorsal portions of the articular surfaces.     

An in vitro analysis of ligament reconstruction or extension osteotomy on trapeziometacarpal joint stability and contact area

PURPOSE: Painful instability of the minimally osteoarthritic thumb carpometacarpal (CMC) joint can be treated successfully by either ligament reconstruction or metacarpal extension osteotomy. The purpose of this study was to measure the laxity of cadaveric thumb CMC joints and to determine the influence of ligament reconstruction and metacarpal osteotomy on joint laxity and contact area. METHODS: The baseline laxity of CMC joints from 25 fresh-frozen human cadaveric specimens (average age, 42 y; range, 18-55 y) was measured in the position of lateral pinch on a custom-designed CMC joint laxity tester. Joint laxity was measured again after 2 surgical simulations consisting of either a metacarpal extension osteotomy (at 10 degrees and 15 degrees) or a simulated Eaton-Littler ligament reconstruction (including total, volar, and dorsal ligament reconstructions relative to the plane of the thumbnail). Contact area between the thumb metacarpal and trapezium during testing was determined using stereophotogrammetry. RESULTS: The 15 degrees extension osteotomy significantly reduced CMC joint laxity in the radial-ulnar, dorsal-volar, pronation-supination, and distraction directions in the position of lateral pinch. The 10 degrees osteotomy reduced laxity only in the dorsal-volar direction. The total ligament reconstruction significantly reduced joint laxity in the radial-ulnar, dorsal-volar, and pronation-supination directions. The dorsal ligament reconstruction reduced laxity in the dorsal-volar direction only; the volar ligament reconstruction reduced laxity in both dorsovolar and radioulnar directions. The 10 degrees and 15 degrees osteotomies produced a dorsal shift of the weighted centroid of contact on the metacarpal and trapezium, whereas the ligament reconstruction did not produce such an effect. CONCLUSIONS: In the position of lateral pinch the 15 degrees osteotomy and total ligament reconstruction significantly reduced laxity of the thumb CMC joint in all directions tested. The isolated dorsal or volar ligament reconstructions both reduced dorsal-volar laxity. Metacarpal extension osteotomy may stabilize the thumb CMC joint in lateral pinch to a degree similar to that of a standard ligament reconstruction.     

Immunohistochemical detection of relaxin binding to the volar oblique ligament

PURPOSE: Excess laxity in the volar oblique ligament may predispose the thumb to trapeziometacarpal joint osteoarthritis. A greater prevalence of trapeziometacarpal joint osteoarthritis in women suggests a hormonal cause and relaxin is a hormone that may have some involvement. This conclusion emerges from relaxin's diverse tissue tropism, stimulation of collagenase production in cultured fibroblasts, and reports of increased joint laxity during pregnancy. We used immunohistochemistry to assess the potential of the volar oblique ligament to bind relaxin. METHODS: Eight volar oblique ligaments were obtained intraoperatively from perimenopausal women having basal joint arthroplasty with ligament reconstruction using the flexor carpi radialis tendon. Tissue specimens were snap-frozen in liquid nitrogen and stored at -80 degrees C until processing. Specimens then were cryosectioned, treated with a chelating rinse, incubated overnight with recombinant human relaxin, fixed, blocked, and exposed to antirelaxin antibody. Treatment with a universal aminoethylcarbizole staining kit was used to visualize areas of ligament-ligand binding. Both tissue and procedural controls served to establish binding specificity. RESULTS: Abundant staining was observed with the positive control (cervix) and all 8 volar oblique ligaments. Little or no staining was present in fibrocartilage (negative control) or procedural controls. CONCLUSIONS: Relaxin binds to the volar oblique ligament with specificity, implying a receptor-mediated process. Limitations of the procedure could not confirm binding saturability, necessitating additional study.     

The trapezio-metacarpal joint: the strain of the ligaments as a function of the thumb position. Study on an enlarged model

INTRODUCTION: The aim of this paper was to develop an enlarged anatomical model of the trapezio-metacarpal joint in order to measure the strains on the ligaments when this joint was passively moved in several directions under constant loading. MATERIAL AND METHOD: A model of the two first rays of the hand was made in polystyrene, at a X3 enlargement, and the ligaments substituted by rubber bands with well characterized mechanical properties so as to reproduce the actual ratio of stiffness (approximately = 10) of the different tissues (bones and ligaments) found in real life. The first metacarpal was moved in 6 directions as described by Ebskov (1970) and Pieron (1973, 1980) using a small spring exerting a constant force (1.5 N) tilted at 30 degrees with respect to the transverse plane. The strain was measured between two white marks for each model ligament and each direction respectively, and the percentage of lengthening was calculated. A statistical study was performed using the non-parametrical Test of Wilcoxon in order to compare the ligament strains obtained in the different directions of loading. RESULTS: The largest strains were observed in the intermetacarpal ligament and in the anterior oblique ligament reaching 26 to 39% in direction J (posteromedial) and in direction L (posterolateral). Deformations of the two parts of the dorsoradial ligament and of the posterior oblique ligament were equal or inferior to 12% and were observed in the other 4 directions: D, F, K, I (Anterolateral, maximal anteposition, anteromedial, medial) and their combinations. CONCLUSION:. These data may be useful for helping the understanding of the biomechanics of the basal joint of the thumb. Nevertheless, we are dealing here with a simplified model, which must be considered with caution if the results are to be applied to the living joint.     

MR imaging of thumb carpometacarpal joint ligament injuries

This study describes the MR imaging appearances of the supporting ligaments of the thumb carpometacarpal joint in asymptomatic volunteers and in a group of patients following joint injury. Fourteen patients with 11 acute and three chronic injuries underwent MR imaging. The anterior oblique ligament was the most commonly injured ligament, usually on the metacarpal side where it was disrupted, or allowed dislocation because of subperiosted stripping from the base of the thumb metacarpal. The dorsal radial ligament was occasionally avulsed or partially torn from the trapezoid. Following chronic injury, MR imaging can evaluate ligamentous laxity, ganglion cyst formation or osteoarthritis. Accurate evaluation of ligament injury may identify patients who would benefit from surgery.     

Contact areas in the thumb carpometacarpal joint

The thumb carpometacarpal joint is a common site of osteoarthritis. It has been hypothesized that peaks of localized stress on the dorsoradial or volar-ulnar regions, or both, of the articular surfaces of the trapezium and metacarpal lead to erosion of cartilage and may be responsible for the progression of the disease. The objective of this study was to determine the contact areas in this joint under the functional position of lateral (key) pinch and in the extremes of range of motion of the joint. These contact areas were assessed relative to the observed sites of cartilage thinning. Eight hands from cadavers of women and five from cadavers of men were tested in vitro with the thumb under a 25 N load in the lateral pinch position, and under small muscle loads (0–5 N) with the thumb in flexion, extension, abduction, adduction, and neutral positions. Contact areas of articular surfaces of the thumb carpometacarpal joint were determined for these positions using a stereophotogrammetric technique. The lateral pinch position produced contact areas predominantly on the central, volar, and volar-ulnar regions of the trapezium and the metacarpal. In three specimens, contact areas were distinctly separated between the dorsoradial and volar-ulnar regions, and in one specimen, from a man, contact occurred exclusively on the dorsoradial region of the trapezium. Using stereophotogrammetry, maps of cartilage thickness also were determined for a subset of nine specimens. The volar-ulnar, ulnar, and dorsoradial regions of the trapezium were the most common sites of thin cartilage, and these may be sites of cartilage wear. The results of this study indicate that the lateral pinch position produced stresses in the same regions where cartilage thinning was observed; this lends support to the hypothesis that high stresses can lead to osteoarthritis in this joint.