Anatomy and Biomechanics of the Thumb Carpometacarpal Joint

doi:10.1053/j.oto.2017.12.002

Operative Techniques in Orthopaedics

Volume 28, Issue 1, March 2018, Pages 1-5

https://doi.org/10.1053/j.oto.2017.12.002 Get rights and content

This article describes the anatomy and biomechanics of the thumb CMC joint, which is also often referred as the thumb trapeziometacarpal joint. The complexity of its anatomy, function, kinesiology, and stability allows humans to obtain the unique prehensile ability of thumb opposition with stable pinch. The biconcavoconvex saddle shape joints with offset mechanical axes allows a motion in 3 planes with only 2 axes of control. It is important to appreciate the unique oseous anatomy of the thumb CMC joint and role of supporting ligaments. Although many previous articles reported on the anterior oblique ligament as a primary stabilizer of the thumb CMC joint, increasing evidence has supported the dorsal ligament complex is its primary stabilizer. Understanding those key features of the thumb CMC joint is essential to adequately treat its pathology, such as fracture dislocation, ligamentous injury, and degenerative osteoarthritis.

Section snippets

Osseous Anatomy of the Thumb Carpometacarpal Joint

The increased range of thumb motion in comparison to that of other digits is largely attributable to the unique osseous anatomy of the thumb carpometacarpal (CMC) joint. The CMC joint has inherent bony stability owing to its biconcavoconvex saddle shape (Fig. 1). This semiconstrained and relatively incongruent joint with a relatively loose capsule allows movement described as flexion, extension, adduction, abduction, and ultimately circumduction. Therefore, the articular surface of the joint

Mechanism of 2-Degrees-of-Freedom Joint

The thumb CMC joint has 2 axes of rotation (Fig. 2A): flexion or extension and abduction or adduction. Figure 2B shows a schematic illustration of the CMC joint that is superimposed with an illustration of 2 separate hinge joints, one of which allows only flexion and extension and the other only abduction and adduction.⁴ If both hinges work simultaneously, any angulation is possible as a composite joint of the 2 hinges. If the 2 hinges are placed perpendicular to the anatomical planes, no

Ligamentous Anatomy of the Thumb CMC Joint

Ligaments around the thumb CMC joints play crucial role to provide a static stabilization of the joint during range of motion or pinch motion. Although the anatomy of the ligaments that stabilize the CMC joints has been elucidated by many investigators in the past 40 years,5, 6, 7, 8 there have been some inconsistencies in terms of anatomical description and terminology in the complex ligamentous anatomy of the trapezium and trapeziometacarpal joint. Early studies of CMC joint anatomy defined 4

Dorsal Carpometacarpal Ligaments

The dorsal carpometacarpal ligaments are also collectively called the dorsal ligament complex² or deltoid ligament complex7, 10 (Fig. 3). It is historically described composing of the dosal radial ligament and posterior oblique ligament (POL). Ladd et al⁷ further designated a total of 3 ligaments by additionally describing the dorsal central ligament, which is located in between the dorsal radial ligament (DRL) and POL. The complex has fanlike fibers running from the dorsoradial tubercle of the

Volar Carpometacarpal Ligaments

There are 2 important ligaments on volar aspect of the thumb CMC joint. These ligaments are uniformly thin, fragile, and relatively weaker than dorsal ligament complex (Fig. 4). The AOL; often called the beak ligament extends from the ulnar volar base of the first metacarpal to the trapezium. The AOL is described as an intra-articular ligament. As the closest ligament to the center of the joint, the AOL is a pivot point for pronation as it relates to thumb opposition.11, 12 The intra-articular

Intermetacarpal Ligament

The intermetacarpal ligament is an important ligament in stabilizing the thumb metacarpal. Even when both the dorsal ligament complex and the volar ligaments are cut and the trapezium is removed, the thumb metacarpal remains in contact with the index metacarpal if the intermetacarpal ligament is present.² The reconstructive tenodesis using the FCR tendons after trapezium excision would mimic or reinforce the function of this intermetacarpal ligament, rather than the volar ligaments.

The dorsal

The Stabilizing Role of the Ligaments of the Thumb CMC Joint

Historically, the AOL, or “beak” ligament, had been described as the most important CMC joint stabilizer.6, 9 The AOL’s intra-articular fibers run obliquely to prevent an ulnar shift of the metacarpal. When sectioning the AOL in lateral pinch, Coleman et al¹¹ observed flexion, radial rotation, ulnar shift, and palmar translation of the metacarpal relative to the trapezium.

Recent cadaveric studies indicate that the dorsal ligaments are the principal restraint against dislocation of the CMC joint.

Pinch and Power Grip Motion With Screw Home Torque Rotation

The CMC joint is lax, loose, and unstable. There is a large amount of slack in the joint capsule allowing a wide rang of motion. The mean amount of joint distraction is up to 3 mm.¹ Similar to other joints, stability and close coaptation of the joint surface is dependent on the presence of static stabilizers (ligaments) and dynamic stabilizers (operational muscles and tendon).

Biomechanical studies have shown that up to 120-kg of force is applied to the CMC joint in a 70-kg human during the power

The Pathogenesis of Thumb CMC Joint OA

Although it was previously described that the pathogenesis of thumb CMC joint OA is mainly owing to ligament laxity or degenerative changes of volar ligaments,¹⁶ Edmunds reported that it is owing to the concentration of compressive rotational shear forces in the pivot area in the trapezium recess during power pinch and grip with screw home torque rotation.² The engagement area between the volar beak of metacarpal and trapezium recess is a pivot area where highest shear forces occur. This is in

Innervation Pattern of the CMC Joint Ligaments

Ladd et al reported on the innervation pattern of the CMC ligament by performing immunohistochemistry for sensory nerve endings. The authors found that the dorsal ligament complex had a significantly greater distribution of nerve endings compared to the volar ligament complex. These findings suggest that in addition to providing static joint stability the dorsal ligament complex has a role in neuromuscular and proprioceptive function.

Hormonal Role on the Thumb CMC Joint Ligaments

It has been suggested that physiological hormonal imbalance plays a role in the attenuation of the thumb CMC joint ligament. Relaxin is a member of the insulin-like growth factor family that is produced both in pregnant and nonpregnant women and in men.18, 19 Its mechanism of action is mediated through upregulation of matrix metalloproteases and suppression of tissue inhibitors of metalloproteases within the extracellular matrix, inducing changes in ligament compliance.¹⁹ A mouse model of

References (20)

J.O. Edmunds
Current concepts of the anatomy of the thumb trapeziometacarpal joint
J Hand Surg Am
(2011)
P.C. Bettinger et al.
An anatomic study of the stabilizing ligaments of the trapezium and trapeziometacarpal joint
J Hand Surg
(1999)
J.S. Gluck et al.
Thumb ligament injuries
J Hand Surg Am
(2015)
M. Nanno et al.
Three-dimensional analysis of the ligamentous attachments of the first carpometacarpal joint
J Hand Surg Am
(2006)
M. Colman et al.
Effects of the deep anterior oblique and dorsoradial ligaments on trapeziometacarpal joint stability
J Hand Surg Am
(2007)
R.J. Strauch et al.
Acute dislocation of the carpometacarpal joint of the thumb: An anatomic and cadaver study
J Hand Surg Am
(1994)
P. D’Agostino et al.
Comparison of the anatomical dimensions and mechanical properties of the dorsoradial and anterior oblique ligaments of the trapeziometacarpal joint
J Hand Surg Am
(2014)
L. Xu et al.
Topography of the osteoarthritic thumb carpometacarpal joint and its variations with regard to gender, age, site, and osteoarthritic stage
J Hand Surg Am
(1998)
J. Lubahn et al.
Immunohistochemical detection of relaxin binding to the volar oblique ligament
J Hand Surg Am
(2006)
J.W. Strickland
The Thumb
(1994)

There are more references available in the full text version of this article.

Cited by (19)

The trapeziometacarpal screw home torque mechanism as a clinical indicator of the posterior joint ligament complex integrity: A cadaveric investigation
2023, Journal of Hand Therapy
To date, no clinical test provides specific objective information on the integrity of key ligamentous support of the trapeziometacarpal (TMC) joint.
To examine the potential of the TMC joint screw home torque mechanism (SHTM) in estimating the integrity of the posterior ligament complex in older adult population.
Cross-sectional laboratory-based study.
Twenty cadaver hands presenting with various degrees of TMC joint degradation ranging from none to severe osteoarthritis (OA) were radiographed in multiple positions to establish their degeneration status, joint mobility, and amount of dorsal subluxation at rest and with the application of the SHTM. Comparisons and correlations between degeneration status, joint mobility, subluxation reduction and ligament status obtained from dissection were calculated.
No significant statistical correlation was demonstrated with the subluxation reduction ratio of the SHTM and the combined ligament complex value however, a moderate negative correlation was found with dorsal central ligament injury at 21 Nm (τb = −0.46, p < 0.05) and 34 Nm (τb = −0.45, p < 0.05). A statistically significant reduction of radial subluxation of the TMC joint was observed between the subluxation at rest (M = 5.2, SD = 1.9) and subluxation with SHTM of 21 Nm (M = 4.4, SD = 2.4), t (19) = 3.2, p = 0.01, 95% CI [0.3, 1.4] and subluxation with SHTM of 34 Nm (M = 4.3, SD = 2.6), t (19) = 2.6, p = 0.02, 95% CI [0.2, 1.5].
Our results did not support the SHTM as indicator of the TMC posterior ligament complex integrity however, it demonstrated 100% stabilization effect with non-arthritic TMC population.
Using a finite element model of the thumb to study Trapeziometacarpal joint contact during lateral pinch
2023, Clinical Biomechanics
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.
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.
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%.
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.
In vivo quantification of the 3D kinematics and coupling of the thumb base joints
2022, Medical Engineering and Physics
Full thumb mobility is required to execute tasks of daily living and results from the combined motions of the thumb joints. In this study, we focus on the coupling between the proximal joints of the thumb, the radioscaphoid (RS), scaphotrapezial (ST) and trapeziometacarpal (TMC) joints. We quantified the 3D kinematics of these joints during maximal thumb extension and abduction in a group of healthy volunteers using an image-based technique. Semi-dynamic CT scans of the dominant hand of 36 healthy subjects with the thumb in different standardized positions were used. The maximal range of motion of each joint in the different planes was calculated using a markerless bone registration method. Inter-joint coupling was assessed by performing a regression analysis between the range of motion of the joints during both thumb movements. Strong inter-joint coupling was found between the RS and ST joints during thumb extension and abduction, whereas coupling between the other joints was moderate to weak. This study provides valuable information on the in vivo 3D kinematics of the RS, ST and TMC joints during thumb movement. This can be used as input for modeling studies, where the coupling between the joints can decrease the degrees of freedom of the model. Moreover, these baseline data of a healthy cohort can be used for comparison with the kinematics of patients with TMC osteoarthritis or other pathologies and aid our understanding of motion deficits resulting from these joint disorders.
Anatomy and Biomechanics of the Thumb Carpometacarpal Joint
2022, Hand Clinics
Citation Excerpt :
They subsequently concluded that these ligaments must play a key role in proprioceptive function of the thumb.66 Owing to the arrangement of the 4 joints of the thumb, the thumb is not located in the same plane as the other fingers while resting, opening 45° laterally in the frontal plane and 30° anteriorly in the sagittal plane.4,13 The thumb CMC joint, which sits at 80° of pronation, 40° of abduction, and 50° of flexion in relation to an axis passing through the stable second and third CMC joints, is instrumental in determining this resting position.
Saddle Hemiarthroplasty for CMC Osteoarthritis
2020, Operative Techniques in Orthopaedics
Citation Excerpt :
It functions as 2 separate hinge joints allowing flexion-extension and abduction-adduction.8 A third motion, axial thumb rotation, occurs passively as the thumb pronates with CMC flexion.8,9 Soft tissue structures play an important role in stabilizing the thumb CMC joint.
Carpometacarpal (CMC) osteoarthritis is an exclusively human disease. It occurs because of recent modifications to basic primate hand anatomy that resulted in our modern dexterous hand. This debilitating condition is common and may cause severe pain and loss of hand function. Various surgical procedures aim at providing pain relief and restoring satisfactory function. However, the CMC joint is a challenging joint to reconstruct and the root cause of its degeneration is not well understood, resulting in the development of a wide range of surgical options. This article analyzes the basic biomechanical disorder in thumb CMC joint disease, presents a stabilized saddle CMC hemiarthroplasty as a treatment option, and describes the surgical technique.
Relaxin and fibrosis: Emerging targets, challenges, and future directions
2019, Molecular and Cellular Endocrinology
The peptide hormone relaxin is well-known for its anti-fibrotic actions in several organs, particularly from numerous studies conducted in animals. Acting through its cognate G protein-coupled receptor, relaxin family peptide receptor 1 (RXFP1), serelaxin (recombinant human relaxin) has been shown to consistently inhibit the excessive extracellular matrix production (fibrosis) that results from the aberrant wound-healing response to tissue injury and/or chronic inflammation, and at multiple levels. Furthermore, it can reduce established scarring by promoting the degradation of aberrant extracellular matrix components. Following on from the review that describes the mechanisms and signaling pathways associated with the extracellular matrix remodeling effects of serelaxin (Ng et al., 2019), this review focuses on newly identified tissue targets of serelaxin therapy in fibrosis, and the limitations associated with (se)relaxin research.

View all citing articles on Scopus

View full text

Anatomy and Biomechanics of the Thumb Carpometacarpal Joint

Section snippets

Osseous Anatomy of the Thumb Carpometacarpal Joint

Mechanism of 2-Degrees-of-Freedom Joint

Ligamentous Anatomy of the Thumb CMC Joint

Dorsal Carpometacarpal Ligaments

Volar Carpometacarpal Ligaments

Intermetacarpal Ligament

The Stabilizing Role of the Ligaments of the Thumb CMC Joint

Pinch and Power Grip Motion With Screw Home Torque Rotation

The Pathogenesis of Thumb CMC Joint OA

Innervation Pattern of the CMC Joint Ligaments

Hormonal Role on the Thumb CMC Joint Ligaments

J Hand Surg Am

J Hand Surg

J Hand Surg Am

J Hand Surg Am

J Hand Surg Am

J Hand Surg Am

J Hand Surg Am

J Hand Surg Am

J Hand Surg Am

The Thumb