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The multidirectional biomechanics of the thumb carpometacarpal (CMC) joint underlie the remarkable power and precision of the thumb. Because of the unconfined nature of thumb CMC articulation, these biomechanics are largely dictated by ligaments, notably the anterior oblique ligament (AOL) and the dorsoradial ligament (DRL). However, the rotational and translational stabilizing roles of these ligaments remain unclear, as evidenced by the variety of interventions employed to treat altered pathological CMC biomechanics. The purpose of this study was to determine the effects of sectioning the AOL (n = 8) or DRL (n = 8) on thumb CMC joint biomechanics (rotational range-of-motion [ROM] and stiffness, translational ROM) in 26 rotational directions, including internal and external rotation, and in eight translational directions. Using a robotic musculoskeletal simulation system, the first metacarpal of each specimen (n = 16) was rotated and translated with respect to the trapezium to determine biomechanics before and after ligament sectioning. We observed the greatest increase in rotational ROM and decrease in rotational stiffness in flexion directions and internal rotation following DRL transection and in extension directions following AOL transection. The greatest increase in translational ROM was in dorsal and radial directions following DRL transection and in volar directions following AOL transection. These data suggest the AOL and DRL play complementary stabilizing roles, primarily restraining translations in the direction of and rotations away from the ligament insertion sites. These findings may inform future interventions or implant designs for pathological CMC joints.

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OBJECTIVE: This study aims to evaluate the possibility of characterizing an extra-articular thickening in the knee anteromedial quadrant in routine MRI scans. MATERIALS AND METHODS: Firstly, in a pilot study, for a better understanding of this extra-articular thickening trajectory in MRI, polytetrafluoroethylene (PTFE) tubes were attached to the ligament structure topography in two dissected pieces. Afterward, 100 knee MRI studies were randomly selected from our database, and 97 met the inclusion criteria. Two musculoskeletal radiologists interpreted the exams separately. Both had previously studied the ligament in the cadaveric knee MRI with the PTFE tube. RESULTS: The intraobserver and interobserver agreement for the ligament identification was calculated using Cohen's Kappa coefficient. The first radiologist identified the structure in 41 of the 97 scans (42.2%), and the second radiologist in 38 scans (39.2%). The interobserver agreement was substantial, with a Kappa of 0.68 and an agreement of 84.5%. The results suggest that this extra-articular thickening, recently called Anterior Oblique Ligament (AOL) in the literature, is a structure that can be frequently visualized on MRI scans with a high level of interobserver agreement in a relatively large number of exams. CONCLUSION: Therefore, this study indicates that MRI is a promising method for evaluating this anteromedial thickening, and it may be used for future studies of the Anterior Oblique Ligament.

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The purpose of this study was to evaluate the prevalence of ligament pathology around the first carpometacarpal joint in an asymptomatic population. We used a compact office-based MRI system and examined the hands of 117 healthy volunteers. We checked the competence of the anterior oblique ligament and of the posterior ligament complex on the MRI images. Our results showed that, in 82% of the study population, both ligaments could be perfectly visualized, with consistent signal from origin to insertion. Examination found signal changes indicating a damaged or torn ligament in the other cases. This study suggests that ligament pathology seen on MRI should be interpreted with caution. In symptomatic patients, pathologic images are to be interpreted in the light of the relevant clinical context. LEVEL OF EVIDENCE: III.

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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.

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BACKGROUND: The ulnar collateral ligament (UCL) complex of the elbow plays a primary role in valgus and posteromedial stability of the elbow. The anterior oblique ligament (AOL) of the UCL is believed to provide the majority of resistance to external forces on the medial elbow. The transverse ligament (TL) of the UCL is generally thought to have minimal contribution to the elbow's overall stability. However, recent studies have suggested a more significant role for the TL. The primary aim of this study was to identify the TL's contribution to the stability of the elbow joint in determining the joint stiffness and neutral zone variation in internal rotation. METHODS: Twelve cadaveric elbows, set at a 90° flexion angle, were tested by applying an internal rotational force on the humerus to generate a medial opening torque at the level of the elbow. The specimens were preconditioned with 10 cycles of humeral internal rotation with sinusoidal torque ranging from 0 to 5 Nm. Elbow stiffness measures and joint neutral zone were first evaluated in its integrity during a final ramp loading. The test was subsequently repeated after cutting the TL at 33%, 66%, and 100% followed by the AOL in the same fashion. RESULTS: The native UCL complex joint stiffness to internal rotation measured 1.52 ± 0.51 Nm/°. The first observable change occurred with 33% sectioning of the AOL, with further sectioning of the AOL minimizing the joint stiffness to 1.26 ± 0.32 Nm/° (P = .004). A 33% resection of the TL found an initial neutral zone variation of 0.376 ± 0.23° that increased to 0.771 ± 0.41° (P < .01) at full resection. These values were marginal when compared with the full resection of the AOL for which we have found 3.69 ± 1.65° (P < .01). CONCLUSION: The TL had no contribution to internal rotation elbow joint stiffness at a flexion angle of 90°. However, sequential sectioning of the TL was found to significantly increase the joint neutral zone when compared with the native cadaveric elbow at a flexion angle of 90°. This provides evidence toward the TL having some form of contribution to the elbow's overall stability.

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The first carpometacarpal (CMC) joint consists of seven ligaments. The magnetic resonance imaging (MRI) examination of the first CMC joint should be performed in a high field 1.5/3 T MRI with a dedicated hand coil for high-resolution images. Degeneration of anterior oblique ligament (AOL) is the most important cause for the development of osteoarthritis of first CMC joint. Since the AOL undergoes a predictable pattern of alteration at its metacarpal attachment as degeneration proceeds, MRI imaging can provide an accurate assessment of this ligament.

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BACKGROUND: The ulnar collateral ligament complex, particularly the anterior oblique ligament (AOL), is mainly a static stabilizer controlling valgus. Various studies have been conducted on the kinematics of elbow joints after ligament cutting; however, no biomechanical studies have measured the tension applied to the ligament. Finite element modeling (FEM) is a very useful tool for biomechanical evaluation of the elbow. However, an accurate FEM of elbow joints cannot be developed without information on the potential tension of ligaments applied during the flexion and extension of elbow joints. We believe that FEM of the elbow joint could be obtained by measuring the material properties and potential tension of the ligament applied during the flexion and extension of the elbow joint. This study aimed to measure the potential tension and material properties of the ligament during the flexion and extension of the elbow, by identifying the relation between ligament length and tension using mechanical testing. METHODS: We included 10 elbows harvested from 7 fresh-frozen cadavers. The average age of the cadavers was 83.7 ± 5.65 years, and the samples included 8 elbows from 6 male cadavers and 2 elbows from 1 female cadaver. We measured the ligament length at each elbow angle by changing the elbow joint from 0° to 120° in 15° intervals. Thereafter, we extracted the AOL and divided into an anterior band (AB) and a posterior band (PB) and performed a mechanical test to calculate ligament stress. RESULTS: The ligament length of the AB gradually decreased as the flexion angle increased. Conversely, the ligament length of the PB gradually increased as the flexion angle increased. AB and PB lengths were approximately the same between 60° and 75°. The average ligament tension and stress of the AB gradually increased with elbow extension. In contrast, the average ligament tension and stress of the PB gradually increased with elbow flexion. The tension and stress of the AB and PB were balanced around the elbow joint at 60°. CONCLUSION: The AB was tenser on elbow extension, and the PB was tenser following elbow flexion. Also, the angle at which the AOL stress was equalized was 60°, suggesting that ∼60° is the angle at which the AOL is unlikely to be damaged.

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Trapeziometacarpal joint instability is a well-recognised but under-diagnosed cause of basal thumb pain. A systematic approach with sound understanding of anatomy and clinico-pathological correlation is required to make a diagnosis. We discuss an overview of the principles of diagnosis and management of basal thumb joint instability. An evaluation algorithm for Eaton's injury of the thumb is proposed for clinical application with evidence in literature.

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OBJECTIVE: We used magnetic resonance imaging (MRI) to evaluate where articular degeneration begins and which ligaments are most often involved in the early clinical stage first carpometacarpal joint (CMCJ-1) osteoarthritis. MATERIALS AND METHODS: We retrospectively analyzed the MRI findings of 26 patients with early clinical stage CMCJ-1 osteoarthritis and no radiologic abnormalities and 19 control patients without CMCJ-1 pain or osteoarthritis who underwent MRI for dorsal or ulnar wrist pain. Two observers blinded to group and clinical findings independently assessed the presence of chondral defects in four quadrants of the CMCJ-1: volar-ulnar (VU), volar-radial (VR), dorso-ulnar (DU), and dorso-radial (DR). The integrity of the four major ligaments of the CMCJ-1, i.e., the anterior oblique ligament (AOL), the intermetacarpal ligament (IML), the posterior oblique ligament (POL), and the dorsal radial ligament (DRL), was assessed. The observer reliability was analyzed using Cohen's kappa coefficient. The prevalence of cartilage lesions and ligament abnormalities in the osteoarthritic and control patients was compared using Fisher's exact test. RESULTS: Cartilage lesions were significantly more common in the VU quadrant of the trapezium in the osteoarthritic patients than in the control patients (17/26 vs. 2/19; P = 0.002). AOL abnormalities were more common in the osteoarthritic patients than in the control patients (14/26 vs. 3/19; P = 0.009). CONCLUSION: The MRI findings of early clinical stage CMCJ-1 osteoarthritis commonly demonstrated cartilage lesions in the VU quadrant of the trapezium and ligament abnormalities in the AOL.

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BACKGROUND: The medial collateral ligament of the elbow joint consists of the anterior oblique ligament (AOL), posterior oblique ligament (POL), and transverse ligament (TL). This study aimed to clarify the structure of the TL, with a focus on the continuity between the TL and AOL. METHODS: A total of 42 cadavers (18 males, 24 females) were dissected at Aichi Medical University between 2016 and 2018. Cases of elbow deformity or atrophy were excluded, and 60 elbows (15 males, 15 females) were dissected to assess the fibers of both the TL and AOL using a stereomicroscope. RESULTS: The TL could be detected in all elbows and always continued to the AOL. The TL was classified into 2 types. The TLs continuing to the distal half of the AOL (type I) were observed in 44 elbows (73.3%), whereas the TLs continuing to the entire AOL (type II) were found in 16 elbows (26.7%). Type II TLs were significantly more frequently observed in the elbows of females than in those of males (P = .041). Stereomicroscopic observation revealed that the TL fibers entered perpendicularly to the distal half of the AOL in both types. CONCLUSIONS: The TL frequently continues to the distal half of the AOL, but rarely continues to the entire AOL. The TLs continuing to the entire AOL were more frequently detected in the elbows of females than in those of males. The TL possibly contributes to medial elbow stability via its continuity to the AOL.

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The purpose of this study was to define the normal thumb carpometacarpal joint kinematics in-vivo during opposition and abduction using four-dimensional computed-tomography in four volunteers. Movement of the metacarpal relative to the trapezium was quantified using both Euler and helical axis representations. Articular surface contact patterns were also analysed. The overall axis of rotation for the movement of opposition and abduction passes through the trapezium and the base of the proximal phalanx, respectively. An abrupt change in instantaneous axis of rotation at terminal opposition was found. Ligament modelling shows dorsoradial ligament becomes tauter towards terminal opposition, whereas anterior oblique ligament becomes more slack. These results support the existence of the 'screw-home' pivot at terminal opposition and the importance of the dorsoradial ligament for stability in this position. The normal reference set in this study can help establish a diagnostic tool for subtle carpometacarpal instability, or for evaluating efficacy of surgery.

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BACKGROUND: The trapeziometacarpal joint (TMCJ) is inherently unstable, relying on ligament restraint to prevent subluxation. Subluxation of the thumb in a dorsoradial direction is often observed in clinical practice, either after acute ligament injury or more commonly with osteoarthritis (OA). This subluxation follows loss of function of trapeziometacarpal ligaments that stabilise this joint, resisting the deforming force of abductor pollicis longus (APL). The exact ligaments that stabilise and prevent the thumb from the pull of APL causing dorsoradial subluxation remain unknown, although the anterior oblique ligament (AOL) has been implicated. The aim of this study was to measure the direction of subluxation resisted by the AOL. METHODS: In this study we used cadaveric limbs and custom made biomechanical testing to measure the influence AOL has in stabilising the thumb against subluxation in three planes: radial, dorsal and dorsoradial. Three fresh frozen hands were dissected to expose the TMCJ, leaving all ligaments, capsule and APL attachment in place. The force required to create a displacement of 5mm between the first metacarpal and the trapezium in these three planes was measured before and after AOL division. RESULTS: The average force to displace in the dorsoradial plane prior to division was 6.68N, and a statistically significant reduction to 1.15N (P<0.001) was found after division of the AOL. A statistically significant increase in force (P<0.001) from 2.89N to 4.04N was seen in the radial plane, while no change was seen dorsally (P=0.98), with average forces of 2.74N and 2.62N found pre and post division. CONCLUSION: There is clinical significance in reporting quantifiable data in this field, as subluxation of the thumb is often seen with OA. The results of our study provide support for surgical reconstruction of the AOL as the primary surgical stabilizer against dorsoradial subluxation of the thumb.Level of evidence: III.

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Posttraumatic instability of the carpometacarpal joint of the thumb are rarely reported. Consequently little is known about clinical and radiologic diagnosis, natural progress or treatment method. We report three cases of chronic instability of the carpometacarpal joint of the thumb treated with Eaton and Littler's ligament reconstruction. Satisfactory thumb functions were restored without arthritic change or recurrent subluxation.

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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.

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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.

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Isolated traumatic dislocation of the carpometacarpal joint of the thumb is an uncommon injury. Left untreated, resulting mechanical instability of this joint interferes with normal function of the hand and can lead to articular degeneration of the joint. Most are amenable to closed reduction with or without supplementary pinning. We present a case of a 21 year old female patient with continual instability of the carpometacarpal joint of her right thumb, following closed reduction and pinning. Surgical stabilization was achieved by anterior oblique ligament reconstruction using a Modified Eaton- Littler's technique. At 1 year follow-up evaluation the patient was pain free with no clinico-radiological evidence of instability.

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This investigation examines the reliability and reproducibility of magnetic resonance imaging (MRI) technology in evaluating the anterior oblique ligament (AOL) of the trapeziometacarpal joint (TMC) of the thumb, in order to establish an effective imaging protocol to use in the early identification of conditions leading to degenerative arthritis. We used cadaver specimens, three hand surgeons independently rated from X-rays each specimen. The specimens were then scanned in a General Electric MRI machine with a standard wrist coil. An effort was made to reproduce the image of the AOL - with a unique technique to obtain images of the obliquely oriented thumb and its ligaments. Following the MRI, the specimens were dissected to expose the AOL and visualize the TMC joint. A standard MRI fiducial was sewn to the proximal and distal extent of the volar side of the AOL. The soft tissues were replaced and the skin was closed. They were then rescanned following the same protocol, and pre and post-dissection ligament-labeled specimens were compared. Following dissection and tagging of the AOL ligament, a repeat MRI confirmed its location and validated the protocol in all cases. The open dissection and ligament tagging confirmed that what was visualized was in fact the structure of interest. This investigation demonstrated that with an appropriate MRI protocol it is feasible to guide the scanner to catch appropriate images of a ligament that is closely correlated with degenerative arthritis.

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Eaton and Littler's ligament reconstruction is used to treat carpometacarpal instability of the thumb using the flexor carpi radialis tendon. This procedure involves a reconstruction of the deep anterior oblique ligament in patients with post-traumatic prearthritic unstable joints. According to a recent paper, the dorsoradial ligament as well as the deep anterior oblique ligament plays an important role in stabilizing the trapeziometacarpal joint. We report three cases of post-traumatic instability in a prearthritic thumb that was treated with Eaton and Littler's reconstruction using the flexor carpi radialis tendon.

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