Beak Ligament Research Articles

Thumb metacarpal dislocation after trapeziectomy with ligamentous reconstruction and tendon interposition: A case report

Thumb carpometacarpal (CMC) arthritis is one of the most common and debilitating pathologies evaluated by the hand surgeon, affecting up to 35% of individuals over 55 years of age. Though multifactorial in etiology, dorsal and radial subluxation of the thumb CMC due to incompetency of the volar beak ligament is thought to be among the most important factors contribution to the arthritis. Multiple operative interventions have been proposed to best address this pathology. In the United States, trapeziectomy with ligament reconstruction and tendon interposition (LRTI) as described by Burton and Pellegrini remains the most widely used technique. As an isolated trauma, dislocation of the thumb CMC joint is a rare injury, only comprising approximately 1% of injuries evaluated by hand surgeons. Typically, thumb CMC dislocations occur due to axial load with the thumb in a flexed position. They are most commonly dorsal dislocations, and are thought to occur due to failure of the dorsoradial ligament. To date, no cases of CMC dislocation after LRTI have yet been described in the literature. Here we present a patient with volar thumb CMC dislocation as a rare complication after LRTI. After percutaneous pinning and immobilization followed by hand therapy, the patient has had a successful return to work with improved pain, restored function, and no further instability.

Bennett Kırığı

Bennett's fracture is the retention of the bone to which the beak ligament is attached, and the dorsoradial and proximal subluxation of the base of the metacarpal detached from this part. Key features are intra-articular fracture, oblique fracture pattern, and volar-dorsal fragment. The medial small piece remains in place and maintains its relationship with the second finger via the volar oblique ligament.

Trapeziectomy and Ligament Reconstruction Tendon Interposition Technique Experience for the First Carpometacarpal Joint Arthrosis

Osteoarthritis of the hand is rare; however, the most retained joint after the distal interphalangeal joint is the first carpometacarpal (1. CMC) joint. Pain in the rest and increased pain with opposition is the most serious symptom, which significantly decreases the quality of life. The aim of these patients is to obtain a painless and stable thumb. Experience of trapeziectomy and ligament reconstruction tendon interposition technique for a Stage III patient was shared and diagnosis and treatment were discussed through the relevant literature. A 53-year-old female patient was admitted with complaints of pain in the right hand thumb root and unable to open the jar lid. In direct radiography, narrowing in the 1. CMC joint space and osteophytes were detected. After the trapeziectomy, 1st and 2nd metacarpals were fixed with K wire. Flexor carpi radialis tendon was passed from the first metacarpal base to the second metacarpal base in the form of a distal-based tendon flap to mimic the beak ligament. There was no pain at the postoperative 6th month, and the Kapandji opposition score was 10. When diagnosing 1. CMC osteoarthritis, pain during opposition and circumduction movements that is not relieved with analgesics and rest is the most important symptom for a clinician to look for. Many treatment principles have been defined according to the staging for the postdiagnosis period, despite the diagnosis is a challenging process.

Ultrasound of Normal and Injured Ligaments and Retinacula of the Hand.

Clinical diagnosis of ligament and retinacular injuries of the hand may be challenging. Ultrasound (US) enables detailed high-resolution, dynamic, and real-time evaluation of these structures. This article is a comprehensive review of the intricate anatomy, optimal imaging technique, and normal US appearances of these ligaments and retinacula. The US features, pertinent biomechanics, clinical presentation, and differential diagnosis of injuries affecting the annular pulleys, differentiating from climber's finger; extensor hood including sagittal band and central slip rupture; proximal interphalangeal and metacarpophalangeal collateral ligaments including the Stener lesion and associated volar plate injury; and the anterior oblique or beak ligament of the trapeziometacarpal joint are reviewed. Emphasis is placed on optimal transducer positioning, value of dynamic US, injury severity, surgical indications, and other US findings with important management implications. US facilitates a timely accurate diagnosis of hand ligament and retinacular injury to ensure optimal patient management and minimize the risk of functional impairment of the hand.

The Pathophysiology of the Osteoarthritis of the Thumb

Introduction: More than 16 ligaments around the joint have been described by Bettinger et al. (1999); four ligaments and the joint capsule are the main stabilizers of the trapeziometacarpal (TM) joint. These ligaments are the dorsoradial (DRL), intermetacarpal (IML), anterior oblique (AOL), and posterior oblique ligaments (POL). The importance of each of these ligaments in the stability of the TM joint is debatable. The purpose of the study was (1) to describe the anatomy and dimension of the thumb carpometacarpal (CMC) joint ligaments, (2) to assess the ligament lesions and the degree of subluxation of the CMC joint, and (3) to measure cartilage thickness in the trapezium and metacarpal and pattern of chondromalacia and osteoarthritis (OA). We investigated the role that these ligament ruptures play in the pathophysiology of the OA. Methods: Twenty-five fresh-frozen cadaver hands were dissected of all soft tissue to expose the joint capsule and ligaments of the TM joint. There were 14 male and 11 female with mean age of 67 years (range, 51-94 years). The dissection was performed under ×4.5 loupe magnification. We showed the main ligaments and also the ligament ruptures in IML, AOL or beak ligament, dorsal oblique ligament (DOL), and DRL. We described the location of the ligament tears and whether these ruptures were partial or total. The ligament ruptures and the metacarpal translation associated with these ruptures were measured (mm). Cartilage thickness in the trapezium and metacarpal of specimens was assessed. We described the degree of degenerative changes using the stanging protocol to describe visual degeneration by Koff et al. (2003). We investigated the relationship between the ligament ruptures and the area of chondromalacia and OA. Statistical analysis of data was performed with the chi-square test, and the level of significance was P < .05. Results: Seven principal ligaments of the thumb CMC joint were identified using Berger’s principles (200s1). Ligament lesions were found in all 25 specimens. Isolated rupture of the AOL was found in 7 (28%), isolated rupture of the DRL was found in 10 (40%), isolated rupture of the IML was found in 2 (8%). Combined rupture of the AOL and IML was found in 2 (8%) and combined rupture of the DRL and IML in 4 (16%) joints. The mean metacarpal displacement due to isolated rupture of the ligaments was DRL 17 mm ( P = .006), AOL 11 mm, POL 0.5 mm, and IML 0.4 mm. We found 2 cases OA stage I, 7 cases OA stage II (1 IIa, 3 lib, and 3 IIc), 9 OA stage III, and 7 OA stage IV. There was a relationship between the presence of a tear in the DRL and the presence of OA in the radial quadrants ( P = .032). Conclusion: These observations suggest a translation of metacarpal on trapezium in the production of arthritic lesions and support a hypothesis that pathologic joint instability could be a cause of CMC OA. This study suggests that repairing the DRL during ligament reconstruction of the CMC joint should be considered.

Idiopathic Trapeziometacarpal Joint Osteoarthritis: Cause, Prevention and Treatment

Background: Idiopathic osteoarthritis of the trapeziometacarpal (TMC) joint is common. Spontaneous attenuation of either the anterior oblique ligament (Beak ligament) or the dorsoradial ligament has been reported as the cause of the joint laxity, resulting in subsequent wear and tear of the articular cartilages. So far, no cause has been reported for the spontaneous attenuation of these key supporting ligaments of the TMC joint and no effective method of prevention or treatment has been reported for the early stages of the condition. Objectives: The authors reported a conservative method for the prevention as well as reversal of the early stages of the joint instability before the process of wear and tear sets in and the condition progresses towards osteoarthritis. Materials and Methods: A retrospective study was performed on 17 patients with early stages of idiopathic TMC joint osteoarthritis. The patients were treated through a conservative management protocol with an average follow-up of 28.4 months. The protocol consisted of performing specifically devised isometric exercises and a functional abduction brace. Results: The result of the conservative treatment was postural correction of the thumb, anatomical stability of the TMC joint and resolution of the symptoms as well as findings including pain, swelling and joint dorsoradial translation. The mean pain score of the patients was 3.6 before the treatment was begun and was zero after the treatment was completed. Conclusions: The presented conservative method is recommended for either prevention or reversal of the early stages of TMC joint instability before the osteoarthritic changes set in.

Can We Really Say That No Patients Benefit from Ligament Reconstruction Tendon Interposition?

Sir:FigureWe read with great interest the article entitled “Comparison of Trapeziectomy and Trapeziectomy with Ligament Reconstruction and Tendon Interposition: A Systematic Literature Review.”1 The article is clear and well designed, incorporating all of the major articles on this controversial topic in hand surgery. Although the authors conclude that “neither procedure produced greater benefit in terms of outcomes investigated,” this is still based on evidence without adequate power or sufficient follow-up. Indeed, patients were followed for an average of only 3 years in their comprehensive review. The insufficient power in assessing outcomes such as pain relief; Disabilities of the Arm, Shoulder and Hand questionnaire score; and grip strength are noted as limitations to the study in their discussion. Indeed, they have attempted to address and improve on the power in this study compared with previous reviews, but the data are still prone to a type II statistical error. These design flaws in the published literature make the surgeon reconsider whether it is the best option to perform trapeziectomy alone on such patients with basal thumb osteoarthritis. Although this is personal experience and more of a hypothesis that still needs to be addressed, we feel using a technique similar to an Eaton-Littler beak ligament reconstruction confers more stability to the thumb and addresses collapse in the long term. Importantly, it also allows the patient by means of the tenodesis effect to dynamically abduct and flex the thumb when the hand is placed into a prehensile position. One prospective study of 56 patients by De Smet et al. compared trapeziectomy with or without ligament reconstruction and tendon interposition; of significance, they noted that trapezial height was preserved much better in the ligament reconstruction and tendon interposition group, and the remaining trapezial height did correlate with key pinch force.2 Pelligrini3 identified that the degeneration of the anterior oblique ligament results in increased joint laxity and dorsal translation of the metacarpal on the trapezium when the thumb is in the position of lateral pinch. Ligament reconstruction and tendon interposition address anterior oblique reconstruction for carpometacarpal joint stability, whereas the tendon interposition addresses axial shortening.4 The volar beak ligament stabilizes the trapeziometacarpal joint; therefore, its reconstruction is important in reestablishing thumb stability.4 The senior author (R.J.) in our department harvests 50 percent of the flexor carpi radialis tendon, passing it through the base of the first metacarpal as a dynamic sling to stabilize the patient's thumb (Figs. 1 and 2).Fig. 1: The senior author's technique for ligament reconstruction and tendon interposition is shown. Fifty percent of the flexor carpi radialis tendon passes through the first metacarpal base, around the abductor pollicis brevis tendon, and back around the flexor carpi radialis tendon. Finally, the flexor carpi radialis tendon is anchored at the base of the first metacarpal.Fig. 2: A tendon interposition is finally constructed with the remaining flexor carpi radialis tendon.There is justification for performing trapeziectomy alone on elderly patients with fewer functional demands. However, there is a strong argument for ligament reconstruction and tendon interposition in the younger patient who remains active and at work. Longer term prospective studies with good follow-up comparing trapeziectomy with or without ligament reconstruction and tendon interposition are needed for more robust evidence. A large multicenter study is needed to compare trapeziectomy with or without ligament reconstruction and tendon interposition to determine which is superior, not just overall but in different patient groups. This question could not be answered in this review. We therefore believe it is more prudent to perform trapeziectomy with ligament reconstruction and tendon interposition to avoid the possibility of poor outcomes in the long term. Dariush Nikkhah, M.R.C.S. Jeremy Rodrigues, M.R.C.S. Plastic Surgery, Bradford Royal Infirmary Daniel B. Saleh, M.R.C.S. Plastic Surgery, Pinderfields General Royal Infirmary, Wakefield, United Kingdom Russell Jeffers, F.R.C.S. Bradford Royal Infirmary, Yorkshire, United Kingdom DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication.

In Vivo Length and Changes of Ligaments Stabilizing the Thumb Carpometacarpal Joint

To investigate the lengths and changes of selected ligaments stabilizing the thumb carpometacarpal (CMC) joint during thumb motion in vivo. We obtained serial computed tomography scans of the thumb CMC joints of 6 healthy volunteers during thumb flexion, abduction, and opposition. We reconstructed the 3-dimensional structures of the bones of the thumb CMC joint using customized software and modeled the paths of fibers of 5 principal ligaments--deep anterior oblique (beak), dorsoradial, posterior oblique, intermetacarpal, and dorsal intermetacarpal--at each of the CMC joint positions studied. We estimated the virtual lengths of these ligaments in neutral position, flexion, abduction, and opposition of the CMC joint by measuring the distances between the origin and the insertion of individual ligaments, and statistically analyzed the length changes. The estimated length of the CMC joint ligaments underwent significant changes during thumb motion in vivo. Thumb flexion led to the greatest changes in ligament lengths. During flexion, all the ligaments lengthened significantly (p < .05 or p < .01), except for the beak ligament, which shortened significantly (p < .001). The lengths of the ligaments changed similarly during thumb abduction and opposition, except for the dorsoradial ligament. In both motions, the posterior oblique and dorsal intermetacarpal ligaments lengthened and the beak ligament shortened significantly (p < .05 or p < .01). During the 3 thumb motions, the beak ligament underwent marked shortening, while the other measured ligaments lengthened to varied extent. The estimated lengths of principal ligaments stabilizing the CMC joint change substantially during thumb motions in vivo. Thumb flexion causes the greatest changes of the ligament lengths; abduction and opposition result in similar changes in the ligament lengths. The beak ligaments shorten while the other ligaments lengthen. This in vivo study suggests that thumb motions expose the CMC joint ligaments to different tensions at these thumb positions, and that the ligaments are under lower tension during thumb opposition and abduction than during flexion.

Thumb Trapeziometacarpal Arthritis: Treatment with Ligament Reconstruction Tendon Interposition Arthroplasty

After studying this article, the participant should be able to: 1. Understand the pathomechanical and biochemical basis for thumb trapeziometacarpal joint degeneration. 2. Diagnose and grade trapeziometacarpal joint disease based on presentation, physical examination (including provocative testing), and radiographic evidence. 3. Understand the principles of ligament reconstruction and tendon arthroplasty procedures. 4. Describe the surgical technique for ligament reconstruction tendon interposition arthroplasty and its variants. Osteoarthritis of the trapeziometacarpal joint is the second most common site of degenerative joint disease in the hand, and mostly affects postmenopausal women. Degenerative arthritis of the thumb trapeziometacarpal joint is associated with a lack of bony constraints and laxity of the supporting ligaments, particularly the anterior oblique ("beak") ligament, which is consistently implicated in disease progression. Resultant increases in joint stress loads leads eventually to metacarpal and trapezial articular destruction, thumb instability, and pain. In this article, the authors review the diagnosis and treatment modalities available to the surgeon in the treatment of patients with trapeziometacarpal osteoarthritis. The technique of ligament reconstruction tendon interposition arthroplasty is discussed in detail. Ligament reconstruction tendon interposition arthroplasty procedures center on three common principles: (1) excision of the diseased trapezium; (2) reconstruction of the beak ligament; and (3) interposition of a tissue substance to maintain metacarpal position. Both conservative and surgical management can be effective in the treatment of trapeziometacarpal arthritis, when properly selected. The success of ligament reconstruction tendon interposition arthroplasty in treating trapeziometacarpal arthritis has withstood the test of time.

THE ABJS 2005 NICOLAS ANDRY AWARD: Osteoarthritis and Injury at the Base of the Human Thumb

The basal joint complex, consisting of four trapezial articulations providing a foundation for the thumb, defines our anatomic evolution from a Simian ancestry by providing an opposable member. Ironically, the trapeziometacarpal joint also is responsible for the most common malady leading to operative reconstruction in the upper limb for arthritic disease. The paradoxic relationship between these two facts has stimulated investigation that has defined the scientific basis for common surgical procedures and provided a foundation for the development of novel treatments for conditions at the base of the thumb. Patterns of articular surface degeneration are determined by areas of contact loading in the joint. Ligament reconstruction, metacarpophalangeal joint flexion splinting, and extension metacarpal osteotomy for early disease resulting from instability all have biomechanical justification for their clinical application. Likewise, percutaneous pinning of Bennett's fracture dislocation is predicated on reestablishing functional continuity of the beak ligament and unloading the palmar joint surfaces. For advanced disease, ligament reconstruction has become the cornerstone of arthroplasty. Perhaps most importantly, the trapeziometacarpal joint as an instability model can provide insight into the interplay of mechanical and biological factors in producing the primary lesion associated with osteoarthritis.

Indications and Techniques for Thumb Carpometacarpal Arthrodesis

Thumb carpometacarpal arthritis is seen commonly in postmenopausal women after attenuation of the volar beak ligament. Less commonly, it may be seen in young men after an intraarticular fracture of the base of the thumb metacarpal. Although most patients respond well to nonoperative measures, two good surgical treatment options exist. Arthroplasty is performed typically in older, low-demand women, and arthrodesis is often recommended in younger patients. Recent studies have demonstrated similar outcomes with these two procedures. Thumb carpometacarpal arthrodesis is a reliable and durable treatment with very good results. It provides excellent strength, satisfactory thumb range of motion, and excellent patient satisfaction. The procedure is contraindicated in patients with arthritis in the scaphotrapeziotrapezoid joint. The surgical technique is straightforward, and fusion is usually performed with either a plate and screw construct or with multiple Kirschner wires. Although failure is rare, good salvage procedures exist. Complications are uncommon but include nonunion in approximately 13% of patients and pain related to prominent hardware.

TREATMENT OF EATON STAGE I TRAPEZIOMETACARPAL DISEASE

Although the cause of TM joint hypermobility may be multifactorial, translational laxity and instability appear to be related to degeneration of the beak ligament. Indeed, the forces experienced at the normal TM joint with grip and pinch are magnified several fold and are concentrated in the palmar aspect of the joint. The TM stress test used in preoperative assessment of thumbs with hypermobile TM joints reflects nonphysiologic dorsal translation and correlates with histologic evidence of detachment of the metacarpal origin of the beak ligament. Ligament reconstruction of the painful TM joint reflects the importance of the beak ligament in providing stability and in limiting dorsal translation of the metacarpal that normally occurs during dynamic pinch activity. Metacarpal extension osteotomy, by contrast, shifts mechanical loading at the TM joint more dorsally and redirects force vectors. Its precise role in the treatment of TM disease has long remained ill-defined because of a lack of correlation between preoperative disease status and postoperative functional result. It appears now, however, that for stage I disease, metacarpal extension osteotomy may result in satisfactory pain relief and improved grip and pinch strength--at least in the short term. Indeed, extension osteotomy may be an efficacious alternative to ligament reconstruction, but long-term follow-up and additional clinical studies will be helpful in shedding additional light on this topic.

Arthritis of the thumb basal joint complex

Osteoarthritis at the base of the thumb is a common and extremely disabling condition that severely compromises function of the entire hand. Successful treatment is based on an understanding of the specific anatomy and the unique functional attributes of the human hand and thumb. Preservation of the web space is a priority in nonsurgical care and splinting as well as a principal goal of surgical reconstruction. Exercise regimens are designed to emphasize thenar strengthening to encourage preservation of the web space. Activity analysis and modification are focused on joint protection and the avoidance of positions that will accentuate the pathologic condition of trapeziometacarpal subluxation accompanying the retropulsion of the thumb that occurs with contracture of the web space. Surgical treatment is directed toward restoring the thumb-index web space and stabilizing the newly fabricated basal joint by reconstructing the beak ligament and providing a suitable interposition material. After-care likewise emphasizes restoration of the thumb web space, joint mobilization, and strengthening of the supporting thenar musculature. A well-integrated surgical and therapy team will produce uniformly good functional results in the treatment of this disabling condition at the base of the thumb that differentiates us from our simian ancestors.

Histopathology of the palmar beak ligament in trapeziometacarpal osteoarthritis.

Eighteen cadaver hands were studied to investigate the relationship between degeneration of the palmar beak ligament and articular disease of the trapeziometacarpal joint. Eight of 18 joints had chondromalacia alone; 10 contained areas of eburnation in the palmar aspect of the joint. Beak ligament degeneration correlated closely with the presence of articular degeneration; all joints with eburnation demonstrated frank detachment of the ligament from its metacarpal insertion site. Histologically, the collagen fibers of the beak ligament were disorganized at the metacarpal attachment. The normal insertional zone of fibrocartilage was often unrecognizable on the metacarpal side and, in more degenerative specimens, an intervening synovial recess appeared at the palmar beak of the metacarpal. The trapezial insertion of the beak ligament showed no degenerative change. Increasingly severe cartilage disease was associated with progressive and selective degeneration of the collagen framework of the beak ligament at its insertion onto the thumb metacarpal. These localized histopathologic findings further support the existence of an anatomically distinct intra-articular beak ligament essential to the normal function of the trapeziometacarpal joint and suggest an etiologic relationship to osteoarthritic disease.

Simulated Bennett fracture treated with closed reduction and percutaneous pinning. A biomechanical analysis of residual incongruity of the joint.

Contact area and contact pressure within the trapeziometacarpal joint were measured during static and dynamic loading in a cadaver model. The measurements were repeated after a Bennett fracture had been simulated with use of an osteotomy of the metacarpal base. The beak fragment was recessed two millimeters and was fixed in close apposition to maintain the integrity of the palmar beak ligament, and contact area and contact pressure were measured during lateral pinch. Despite the resulting articular incongruity, the mean total contact area of the joint surface increased from 15.8 to 25.8 square millimeters (63 per cent) in all specimens after simulation of the Bennett fracture (p = 0.02), and it shifted dorsally in moderately osteoarthrotic and non-osteoarthrotic specimens. The mean contact area in the palmar region of the joint surface decreased, from 58 to 25 per cent of the total area (p = 0.04); that in the central region increased, from 28 to 52 per cent (p = 0.05); and that in the dorsal region increased, but not significantly with the numbers available, from 14 to 24 per cent (p = 0.18). No pathological concentration of contact pressure was seen at the margin of the articular step-off. The changes in area and pressure reflect an unloading of the metacarpal beak, where osteoarthrotic degeneration most commonly occurs. There is no biomechanical basis for predisposition to post-traumatic osteoarthrosis after a Bennett fracture with a small palmar-beak component and a residual two-millimeter articular step-off, provided that the fragments of the shaft and the beak heal in close apposition. This suggests that reduction of the metacarpal shaft relative to the trapezium and the beak fragment, rather than strict anatomical restoration of the joint surface, should be the priority of treatment. Bennett fractures that can be reduced with articular incongruity of no more than two millimeters may be treated satisfactorily with closed reduction and percutaneous pinning without the need for open anatomical reduction and internal fixation of the joint surface.

Contact patterns in the trapeziometacarpal joint: The role of the palmar beak ligament

Twenty-three cadaver forearm specimens were mounted on a Plexiglas acrylic plastic base for study of the trapeziometacarpal joint. Extrinsic and intrinsic motors were loaded to simulate lateral pinch, and pressure-sensitive film was used to record joint contact patterns in various functional positions. The palmar compartment of the trapeziometacarpal joint was the primary contact area during flexion adduction of the thumb ray in lateral pinch. Simulation of dynamic pinch and release produced dorsal enlargement of the contact pattern, suggesting physiologic translation of the metacarpal on the trapezium. Detachment of the palmar beak ligament resulted in dorsal translation of the contact area, producing a pattern similar to that of cartilage degeneration seen in the osteoarthritic joint. End-stage osteoarthritic specimens had a nonfunctional beak ligament and demonstrated a pathologic total contact pattern of joint congruity that was unaffected by further manipulations of the beak ligament. This work defines the contact patterns in the normal and diseased trapeziometacarpal joint and establishes the important influence of the palmar beak ligament on those contact areas.

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.

Osteoarthritis of the trapeziometacarpal joint: The pathophysiology of articular cartilage degeneration. II. Articular wear patterns in the osteoarthritic joint

An anatomic and radiographic study of the osteoarthritic trapeziometacarpal joint was conducted on 27 surgical specimens harvested during basal joint arthroplasty. Surface wear patterns were analyzed by hyaline cartilage staining, and relative involvement of trapezium and metacarpal was calculated as the trapezium/metacarpal eburnation ratio. Eburnation occurred only on facing trapeziometacarpal surfaces in contact areas of the palmar compartment. Metacarpal degeneration began at the palmar joint margin adjacent to the beak ligament and extended dorsally, while trapezial degeneration originated on the central palmar slope and spread centrifugally with more advanced disease. Eburnation consistently involved a greater surface area on the trapezium than on the metacarpal in a ratio of nearly 3:1. A decreasing trapezium/metacarpal eburnation ratio correlated closely with worsening radiographic stage. These observations suggest translation of metacarpal on trapezium in the production of arthritic surface lesions and support a hypothesis of pathologic joint instability as the cause of trapeziometacarpal osteoarthritis.