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Received October 23, 2024, accepted February 21, 2025, date of publication March 25, 2025.

Letter

Navigating Thumb Ligament Pathology: From Injury to 
Recovery

Roberto Tedeschi1, Paolo Boccolari2 and Danilo Donati2,3,4

1 Department of Biomedical and Neuromotor Sciences, Alma Mater Studiorum, University of Bologna, Bologna, Italy.
2 Clinical and Experimental Medicine PhD Program, University of Modena and Reggio Emilia, 41121 Modena, Italy.
3 Physical Therapy and Rehabilitation Unit, Policlinico di Modena, 41125 Modena, Italy.
4 Azienda Ospedaliero, Universitaria di Modena Policlinico.

* Corresponding Author Email: roberto.tedeschi2@unibo.it

Dear Editor, 

The metacarpophalangeal (MP) joint of the thumb functions predominantly as a hinge, facilitating flexion and 
extension while also allowing limited abduction–adduction and rotational movements. Both active and passive stabi-
lizers contribute to its overall stability, with joint morphology playing a secondary role in this function.1 The passive 
stabilizers include the volar plate (VP), which integrates two sesamoid bones, and the main and accessory collateral 
ligaments. The active stabilizers are classified into intrinsic muscles—abductor pollicis brevis (APB), flexor pollicis 
brevis (FPB), and adductor (ADD), and extrinsic muscles—long extensor of the thumb (LET), short extensor of the 
thumb (SET), and long flexor of the thumb (LFT).

The ulnar collateral ligament (UCL) of the thumb comprises two components: the primary and accessory liga-
ments. The primary ligament runs obliquely, from the dorsal side of the metacarpal head to the volar base of the first 
phalanx.2 In contrast, the accessory ligament, which lies more superficially and volarly, merges with the volar plate 
and inserts at the base of the first phalanx. In extension, the accessory ligament becomes taut, while the primary 
ligament tightens during flexion, particularly around 30°. As the joint flexes, the accessory ligament slides proximally 
alongside the volar plate, allowing some degree of joint laxity—approximately 6° in extension and 12° in flexion dur-
ing the varus–valgus stress test. The management of thumb ligament pathologies can significantly benefit from the 
integration of advanced clinical engineering technologies. These technologies offer tools to improve diagnostic ac-
curacy, personalize treatment plans, and monitor recovery progress with greater precision. This document explores 
how advanced imaging, biomechanical modeling, and wearable devices can support the recovery process, enhancing 
diagnostic accuracy and therapeutic effectiveness.

Injuries to the MP joint frequently occur as a result of hyperabduction or hyperextension, often leading to UCL 
damage. Such trauma may also involve the dorsal capsule and volar plate, potentially causing volar subluxation of the 

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69 J Global Clinical Engineering Vol.7 Issue 1: 2025

Tedeschi, Boccolari, Donati: Navigating Thumb Ligament Pathology: From Injury to Recovery

joint. Chronic UCL insufficiency, because of its dorsal location relative to the joint’s center of rotation, can result in a 
supination deformity of the first phalanx as it rotates around the intact radial collateral ligament (Figure 1).

   

FIGURE 1. Management and evaluation of ulnar collateral ligament injuries of the thumb.

Hyperabduction of the thumb MP joint can result in UCL injuries, as shown in the series from normal anatomy 
(Figure 1A), through ligament rupture (Figure 1B), to the development of a stener lesion (Figure 1C). The figure also 
illustrates the use of an orthosis for conservative or postoperative care, alongside the proper technique for perform-
ing a collateral ligament stress test.

Ulnar collateral ligament injuries commonly involve its distal insertion, occasionally accompanied by an avulsion 
fracture at the base of the phalanx.3 Injuries can also occur in the ligament’s central or proximal regions. In case of 
ligament discontinuity, the interposition of the adductor aponeurosis between the torn ligament ends can prevent 
healing, leading to a Stener lesión.4 

Clinical evaluation begins with an examination of the trauma history and physical appearance, where swelling 
and bruising are commonly observed. In severe cases, volar–radial subluxation of the first phalanx may be evident. 
Tenderness is typically present over the ulnar aspect of the MP joint. 

The varus–valgus stress test is essential for determining ligament integrity. This test should always be compared 
with the contralateral hand and performed in both extension and 30° of flexion. Stabilization of the metacarpal neck 
is necessary while lateral stress is applied to the phalanx. Any phalanx rotation can obscure a ligament injury. Biome-
chanical modeling and simulation play a crucial role in understanding ligament stress in the thumb. Using Finite Ele-
ment Modeling (FEM) techniques, researchers can digitally recreate anatomical structures and evaluate how the UCL 
responds to varying degrees of stress. These models support the planning of therapeutic, surgical, and conservative 
interventions by providing an accurate forecast of post-treatment joint stability. Laxity exceeding 30°, or more than 
15°, compared to the unaffected side, strongly suggests UCL rupture. Laxity in flexion alone points to the involvement 
of primary ligament, while laxity in both flexion and extension indicates a more extensive injury to both ligament 
portions. Laxity only in extension may suggest an isolated volar plate injury.



Tedeschi, Boccolari, Donati: Navigating Thumb Ligament Pathology: From Injury to Recovery

J Global Clinical Engineering Vol.7 Issue 1: 2025 70

Advanced imaging technologies, such as high-resolution ultrasound and three-dimensional (3D) magnetic reso-
nance imaging (MRI), allow for a more precise evaluation of ligament structures. These tools can be paired with digital 

stress tests, which quantify the biomechanical response of the ligament. Such technologies, supported by 3D models, 
offer clinical engineers the opportunity to simulate specific thumb movements and predict ligament behavior under 
various stresses, thereby enhancing diagnostic assessments and reducing the risk of diagnostic errors.5

Ulnar collateral ligament injuries are categorized into three grades. Grade 1 involves ligament strain with no detect-
able laxity; Grade 2 presents with some laxity but a firm end point during the stress test, indicating a partial tear; and 
Grade 3 is characterized by significant laxity with a soft end point, suggesting complete rupture. Engineered orthoses 
represent an evolving therapeutic solution. With the development of adaptive designs and advanced materials, these 
orthoses can accommodate progressive changes in thumb stability, providing targeted support and comfort without 
restricting essential movements for rehabilitation. Advances in orthotic engineering allow for lighter and more du-
rable devices that can be customized to support each stage of recovery. Looking forward, the integration of artificial 
intelligence (AI) algorithms with engineering technologies promises to further enhance the management of ligament 
injuries. Predictive systems powered by AI would identify individuals at the risk of injury and optimize rehabilitation 
plans by automatically monitoring patient progress. Such integrated approaches represent an exciting prospect for 
rehabilitation medicine and clinical engineering.

AUTHOR CONTRIBUTIONS

Conceptualization, P.B.; Validation, D.D.; Data Curation, P.B.; Writing–Original Draft Preparation, P.B.; Writing–Re-
view & Editing, D.D. and R.T.

FUNDING
This research received no external funding.

DATA AVAILABILITY STATEMENT
Not applicable.

CONFLICTS OF INTEREST
The authors declare they have no competing interests.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE
Not applicable.

CONSENT FOR PUBLICATION
Not applicable. 

FURTHER DISCLOSURE
Not applicable. 



71 J Global Clinical Engineering Vol.7 Issue 1: 2025

Tedeschi, Boccolari, Donati: Navigating Thumb Ligament Pathology: From Injury to Recovery

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