Anteroinferior bundle of the acromioclavicular ligament plays a substantial role in the joint function during shoulder elevation and horizontal adduction: a finite element model

Clavicular tunnel widening after coracoclavicular stabilization surgery: a systematic review and meta-analysis

BACKGROUND

This systematic review and meta-analysis aimed to (1) estimate the prevalence of clavicular tunnel widening (TW) after coracoclavicular stabilization surgery and its risk factors and (2) assess whether TW is correlated with clavicle fracture or loss of reduction of the acromioclavicular joint (ACJ).

METHODS

In January 2023, 3 electronic databases were searched to collect data on postoperative clavicular TW, its prevalence, magnitude, and correlation with fracture and ACJ loss of reduction. Studies were classified according to the time of surgical intervention, and the clavicular tunnels were categorized by their anatomic location. Mean differences were calculated using a DerSimonian-Laird random-effects model, while binomial outcomes were pooled using the Freeman-Tukey double arcsine transformation. Univariate and multivariate meta-regression analyses were performed to determine the effect of several variables on the proportion of cases with TW.

RESULTS

Fifteen studies (418 shoulders) were included. At the final follow-up, evidence of clavicular TW was found in 70% (95% confidence interval [CI]: 70%-87%; I2 = 89%) of 221 shoulders. Surgeries in acute cases had a lower prevalence of TW (52%) compared to chronic cases (71%) (P < .001). Significant TW was found in the central tunnel (3.2 mm; 95% CI: 1.8-4.6 mm; P < .001; I2 = 72%) for acute injuries and in the medial (1.2 mm; 95% CI: 0.7-1.7 mm; P < .001; I2 = 77%) and lateral (1.5 mm; 95% CI: 0.7-2.3 mm; P < .001; I2 = 77%) tunnels for chronic cases. Single central-tunnel techniques were positively associated with the prevalence of TW (P = .046), while biotenodesis screw fixation was associated with a lower prevalence (P = .004) in chronic cases. Reconstruction of the ACJ ligament complex with tendon grafts or sutures was associated with a higher prevalence of TW (P < .001). Drill sizes between 2.5 and 5 mm were significantly associated with a lower prevalence of TW, regardless of injury chronicity (P = .012). No correlation was found between TW and the loss of ACJ reduction or clavicle fractures.

CONCLUSIONS

This systematic review and meta-analysis explored TW occurrence following coracoclavicular stabilization surgery. TW was observed in 70% of patients at final follow-up, with a higher prevalence in chronic than in acute cases. Modifiable surgical variables, such as single-tunnel tendon graft constructs for acute or chronic injuries and knotted graft procedures for chronic injuries, were significantly associated with TW. Furthermore, the prevalence of TW increased with concomitant surgical treatment of the ACJ ligament complex, and decreased with drill sizes between 2.5 and 5 mm, regardless of lesion chronicity. These surgical variables should be considered when establishing transosseous tunnels for coracoclavicular stabilization. Clavicle fractures and TW mechanisms require further investigation.

Acromioclavicular Joint Anatomy and Biomechanics: The Significance of Posterior Rotational and Translational Stability

The shoulder girdle extends from the sternoclavicular joint to the scapular stabilizing muscles posteriorly. It consists of 3 joints and 2 mobile regions. The shoulder girdle is statically stabilized by the acromioclavicular and coracoclavicular capsuloligamentous structures and dynamically stabilized by the trapezius, deltoid, and deltotrapezial fascia. During humerothoracic elevation, the clavicle elevates, protracts, and rotates posteriorly through the sternoclavicular joint while the scapula tilts posteriorly and rotates upward. The purpose of this article is to review the anatomy and biomechanics of the acromioclavicular joint and the shoulder girdle.

ANATOMICAL AND BIOMECHANICAL ROLE OF STATIC STABILIZERS OF THE ACROMIOCLAVICULAR JOINT

OBJECTIVE

The aim: To determine the anatomical and biomechanical significance of the static stabilizers of the acromioclavicular joint by conducting numerical modeling using the finite element method and experimental investigation.

PATIENTS AND METHODS

Materials and methods: To ensure the study, modeling of the deformation processes of the clavicle and scapula systems with various combinations of ligament damage was conducted. The COMPAS-3D software package was used to build the simulation model, which allowed obtaining models that are closest to reality. To verify the results of the numerical modeling, corresponding studies of the mechanical characteristics and determination of the stiffness of the investigated systems were carried out using the upgraded TIRAtest-2151 testing stand.

RESULTS

Results: The stiffest system is the system in which all ligaments are intact, and the sequence of decreasing stiffness of the system is presented in the following order: damage to lig. trapezoideum; lig. conoideum; lig. claviculo-acoacromiale inferior; lig. claviculo-acoacromiale superior; the coracoclavicular ligament complex; the acromioclavicular ligament complex.

CONCLUSION

Conclusions: Static stabilizers in general, and their components in particular, are characterized by significant anatomical and functional features. The natural stabilization of the acromioclavicular joint is provided by their synergistic interaction, which is the basis for the development and implementation of surgical interventions, the scope of which includes the restoration of both ligament complexes. The loss of stiffness in the «clavicle-scapula» system is significantly more pronounced when lig. acromioclaviculare superior and inferior are damaged (8.5 N/mm) than when lig. conoideum and lig. trapezoideum are damaged (11.6 N/mm).

The stress and strain pattern in the ligaments of the acromioclavicular joint using a quasi-static model

BACKGROUND

The precise role of the acromioclavicular and coracoclavicular ligaments during shoulder motion is unclear. We evaluate changes in the stress-strain distribution of the acromioclavicular joint's ligaments during different shoulder passive motion positions.

METHODS

A 3D acromioclavicular joint model was reconstructed. A constitutive hyperelastic model was used for the ligaments. The kinematics of the shoulder girdle was taken to simulate shoulder abduction (Motion 1) and horizontal adduction (Motion 2). A computer-generated quasi-static and non-linear finite element model was used to predict the 3D stress-strain distribution pattern of the acromioclavicular ligament and the coracoclavicular ligament complex.

FINDINGS

In motion 1, from 20 to 90° the peak von Mises stress was found in the conoid (4.14 MPa) and the anteroinferior bundle (2.46 MPa), while from 90 to 120° it was found in the conoid and the trapezoid. However, there were no significant differences between the mean stress values between anteroinferior bundle and trapezoid throughout the motion (p = 0.98). In Motion 2, from 20 to 80° the maximum equivalent elastic strain was found in the anteroinferior bundle (0.68 mm/mm) and the conoid (0.57 mm/mm), while from 80 to 100° it was higher in the conoid (0.88 mm/mm) than in the anteroinferior bundle (0.77 mm/mm).

INTERPRETATION

The coracoclavicular ligament complex demonstrated a high stress-strain concentration during simulated passive shoulder abduction. Additionally, it was shown that the acromioclavicular ligament plays an important role in joint restraint during passive horizontal adduction, changing the primary role with the trapezoid and conoid at different motion intervals.

The three-dimensional displacement tendency of teeth depending on incisor torque compensation with clear aligners of different thicknesses in cases of extraction: a finite element study

Background

Despite the popularity of clear aligner treatment, the effect of the thickness of these aligners has not been fully investigated. The objective of this study was to assess the effects of incisor torque compensation with different thicknesses of clear aligner on the three-dimensional displacement tendency of teeth in cases of extraction.

Methods

Three-dimensional finite element models of the maxillary dentition with extracted first premolars, maxilla, periodontal ligaments, attachments, and aligners were constructed and subject to Finite Element Analysis (FEA). Two groups of models were created: (1) with 0.75 mm-thick aligners and (2) with 0.5 mm-thick aligners. A loading method was developed to simulate the action of clear aligners for the en masse retraction of the incisors. Power ridges of different heights were applied to both groups to mimic torque control, and the power ridges favoring the translation of the central incisors were selected. Then, we used ANSYS software to analyze the initial displacement of teeth and the principle stress on the PDL.

Results

Distal tipping, lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, and mesial tipping and intrusion of the posterior teeth were all generated by clear aligner therapy. With the 0.5 mm-thick aligner, a power ridge of 0.7 mm could cause bodily retraction of the central incisors. With the 0.75 mm-thick aligner, a power ridge of 0.25 mm could cause translation of the central incisors. Aligner torque compensation created by the power ridges generated palatal root torque and intrusion of the incisors, intrusion of the canines, mesial tipping and the intrusion of the second premolar; these effects were more significant with a 0.75 mm-thick aligner. After torque compensation, the stress placed on the periodontal ligament of the incisors was distributed more evenly with the 0.75 mm-thick aligner.

Conclusions

The torque compensation caused by power ridges can achieve incisor intrusion and palatal root torque. Appropriate torque compensation with thicker aligners should be designed to ensure bodily retraction of anterior teeth and minimize root resorption, although more attention should be paid to the anchorage control of posterior teeth in cases of extraction.