The Orientation and Variation of the Acromioclavicular Ligament: An Anatomic Study

ArUco-based stylus reliability for reproductible 3D digitalisation of shoulder cartilage contours

Imaging techniques in anatomy have developed rapidly over the last decades through the emergence of various 3D scanning systems. Depending on the dissection level, non-contact or tactile contact methods can be applied on the targeted structure. The aim of this study was to assess the inter and intra-observer reproducibility of an ArUco-based localisation stylus, that is, a manual technique on a hand-held stylus. Ten fresh-frozen, unembalmed adult arms were used to digitalise the glenoid cartilage related to the glenohumeral joint and the contour of the clavicle cartilage related to the acromioclavicular joint. Three operators performed consecutive digitalisations of each cartilage contour using an ArUco-based localisation stylus recorded by a single monocular camera. The shape of each cartilage was defined by nine shape parameters. Intra-observer repeatability and inter-observer reproducibility were computed using an intra-class correlation (ICC) for each of these parameters. Overall, 35.2 ± 2.4 s and 26.6 ± 10.2 s were required by each examiner to digitalise the contour of a glenoid and acromioclavicular cartilage, respectively. For most parameters, good-to-excellent agreements were observed concerning intra-observer (ICC ranging between 0.81 and 1.00) and inter-observer (ICC ranging between 0.75 and 0.99) reproducibility. To conclude, through a fast and versatile process, the use of an ArUco-based localisation stylus can be a reliable low-cost alternative to conventional imaging methods to digitalise shoulder cartilage contours.

Current Concepts in Management of Acromioclavicular Joint Injury

Background: The management of acromioclavicular joint injuries requires a thorough understanding of the anatomy and biomechanics of the joint, as well as knowledge of the pertinent physical exam findings and classification to determine an appropriate treatment approach, whether operative or nonoperative. In this article, we present a narrative review of the current state of understanding surrounding these issues. Although there are a large number of options for operative intervention, we additionally present our experience with anatomic coracoclavicular ligament reconstruction (ACCR) with imbrication of the deltoid fascia. Methods: A retrospective review of prospectively collected data on a total of 45 patients who had undergone ACCR between 2003 and 2016 were collected. Results: We found that improvements were seen in American Shoulder and Elbow Surgeons Score (ASES) (53 ± 19 to 81 ± 23), Simple Shoulder Test (SST) (6 ± 3 to 12 ± 13), Constant-Murley (CM) (60 ± 18 to 92 ± 8), and Rowe (67 ± 14 to 89 ± 11) and the mean post-operative SANE score was 86 ± 17. Conclusions: ACCR has the advantage of addressing both horizontal and vertical stability with good outcomes.

In Vivo Analysis of Acromioclavicular Kinematics and Distance During Multiplanar Humeral Elevation

BACKGROUND

Knowledge of acromioclavicular (AC) joint kinematics and distance may provide insight into the biomechanical function and development of new treatment methods. However, accurate data on in vivo AC kinematics and distance between the clavicle and acromion remain unknown.

PURPOSE/HYPOTHESIS

The purpose of this study was to investigate 3-dimensional AC kinematics and distance during arm elevation in abduction, scaption, and forward flexion in a healthy population. It was hypothesized that AC kinematics and distance would vary with the elevation angle and plane of the arm.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 19 shoulders of healthy participants were enrolled. AC kinematics and distance were investigated with a combined dual fluoroscopic imaging system and computed tomography. Rotation and translation of the AC joint were calculated. The AC distance was measured as the minimum distance between the medial border of the acromion and the articular surface of the distal clavicle (ASDC). The minimum distance point (MDP) ratio was defined as the length between the MDP and the posterior edge of the ASDC divided by the anterior-posterior length of the ASDC. AC kinematics and distance between different elevation planes and angles were compared.

RESULTS

Progressive internal rotation, upward rotation, and posterior tilt of the AC joint were observed in all elevation planes. The scapula rotated more upward relative to the clavicle in abduction than in scaption (P = .002) and flexion (P = .005). The arm elevation angle significantly affected translation of the AC joint. The acromion translated more laterally and more posteriorly in scaption than in abduction (P < .001). The AC distance decreased from the initial position to 75° in all planes and was significantly greater in flexion (P < .001). The MDP ratio significantly increased with the elevation angle (P < .001).

CONCLUSION

Progressive rotation and significant translation of the AC joint were observed in different elevation planes. The AC distance decreased with the elevation angle from the initial position to 75°. The minimum distance between the ASDC and the medial border of the acromion moved anteriorly as the shoulder elevation angle increased.

CLINICAL RELEVANCE

These results could serve as benchmark data for future studies aiming to improve the surgical treatment of AC joint abnormalities to restore optimal function.

Management of Acromioclavicular Joint Injuries: A Historic Account

There has been a rapid evolution in best practice management of acromioclavicular (AC) joint injuries. AP, Zanca, scapular Y, and dynamic axillary radiographic views provide optimal visualization of the joint and may assess for the presence of horizontal AC instability. Severity of AC joint pathology is classified according to the 6-tier Rockwood scoring system. Over 160 surgical techniques have been described for AC joint repair and reconstruction in the last decade; as a result, determining the optimal treatment algorithm has become increasingly challenging secondary to the lack of consistently excellent clinical outcomes.

Operative Management for Displaced Distal Clavicle Fractures

This article reviews techniques and outcomes of surgical fixation for distal clavicle fractures. Near 100% union has been reported for several techniques. The most common are locked plating, coracoclavicular fixation and a combination of plating with CC fixation. Hook plates are useful for particular fracture patterns, but there can be complications specific to this implant. Low-profile constructs are favored due to the high rates of symptomatic hardware. Fixation of subacute and chronic injuries can provide reliable functional improvements, but is inferior to acute fixation. Surgery is generally the treatment of choice for displaced fractures in athletes.

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.

Acromioclavicular Joint Injury and Repair

The acromioclavicular (AC) joint is commonly injured in athletes participating in contact and overhead throwing sports. Injuries range from simple sprains to complete ligamentous disruption, and they are classified by the established Rockwood grading system. High-grade injuries are associated with fractures around the AC joint and disruption of the superior shoulder suspensory complex, a ring of osseous and ligamentous structures at the superior aspect of the shoulder. Radiographs are the mainstay of imaging of the AC joint, with magnetic resonance imaging reserved for high-grade injuries to aid classification and plan surgical management. Low-grade AC joint injuries tend to be managed conservatively, but a wide range of surgical procedures have been described for higher grade injuries and fractures around the AC joint. This review illustrates the anatomy of the AC joint and surrounding structures, the imaging features of AC joint injury, and the most commonly performed methods of reconstruction and their complications.

Qualitative and Quantitative Anatomic Descriptions of the Coracoclavicular and Acromioclavicular Ligaments: A Systematic Review

Purpose

Methods

Results

Conclusions

Clinical Relevance

All-Arthroscopic Coracoacromial Ligament Transfer: The Modified Neviaser Procedure for Acromioclavicular Dislocations

Over the course of the years, the topic of optimizing the management of acromioclavicular joint dislocations has gained popularity, remaining a subject of debate. It has been determined that posterior horizontal instability appears to be one of the factors influencing both clinical and radiographic outcomes, postsurgical reconstructions with coracoclavicular techniques. In contrast, the acromioclavicular ligament complex (ACLC) has been experimentally demonstrated to play a crucial role in horizontal translation and rotational stability of the clavicle. Although several strategies have been established, perfect surgical timing, and its potential impact during the healing process, remain poorly defined. Furthermore, appropriate surgical techniques to restore normal acromioclavicular joint kinematics while ensuring an adequate biological environment remain unclear. Due to the existence of multiple features present in acromioclavicular joint reconstruction techniques, an ideal approach involves ACLC and coracoclavicular combination reconstruction, minimal clavicular drilling, and biological enhancement to ensure anatomical reduction and an adequate process of ligament healing. The purpose of this Technical Note is to present a modified surgical technique of the Neviaser procedure. This modified surgical technique combines an all-arthroscopic single tunnel coracoclavicular fixation with the transfer of the coracoacromial ligament to reconstruct the ACLC.

Acromioclavicular joint instability on cross-body adduction view: the biomechanical effect of acromioclavicular and coracoclavicular ligaments sectioning

Background

The acromioclavicular (AC) and coracoclavicular (CC) ligaments are important stabilizers of the AC joint. We hypothesized that AC and trapezoid ligament injuries induce AC joint instability and that the clavicle can override the acromion on cross-body adduction view even in the absence of conoid ligament injury. Accordingly, we investigated how sectioning the AC and CC ligaments contribute to AC joint instability in the cross-body adduction position.

Methods

Six fresh-frozen cadaveric shoulders were used in this study, comprising five male and one female specimen, with a mean age of 68.7 (range, 51–87) years. The left side of the trunk and upper limb, and the cervical and thoracic vertebrae and sternum were firmly fixed with an external fixator. The displacement of the distal end of the clavicle relative to the acromion was measured using an electromagnetic tracking device. We simulated AC joint dislocation by the sequential resection of the AC ligament, AC joint capsule, and CC ligaments in the following order of stages. Stage 0: Intact AC and CC ligaments and acromioclavicular joint capsule; stage 1: Completely sectioned AC ligament, capsule and joint disc; stage 2: Sectioned trapezoid ligament; and stage 3: Sectioned conoid ligament. The superior clavicle displacement related to the acromion was measured in the horizontal adduction position, and clavicle overriding on the acromion was assessed radiologically at each stage. Data were analyzed using a one-way analysis of variance and post-hoc tests.

Results

Superior displacement was 0.3 mm at stage 1, 6.5 mm at stage 2, and 10.7 mm at stage 3. On the cross-body adduction view, there was no distal clavicle overriding at stages 0 and 1, and distal clavicle overriding was observed in five cases (5/6: 83%) at stage 2 and in six cases (6/6: 100%) at stage 3.

Conclusion

We found that AC and trapezoid ligament sectioning induced AC joint instability and that the clavicle could override the acromion on cross-body adduction view regardless of conoid ligament sectioning. The traumatic sections of the AC and trapezoid ligament may lead to high grade AC joint instability, and the distal clavicle may subsequently override the acromion.

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

Background

Postoperative acromioclavicular (AC) ligament deficiency has been identified as a common cause of failure after isolated coracoclavicular reconstruction. The two-bundle arrangement of the acromioclavicular ligament has recently been reported in histological and anatomical research. In addition, a clear structural advantage of the superoposterior bundle (SPB) over the less consistent anteroinferior bundle (AIB) was also found. However, the current understanding of the function of the acromioclavicular ligament in joint stability is based on uniaxial bone loading experiments and sequential ligament sectioning. Consequently, these rigid biomechanics models do not reproduce the coupled physiological kinematics, neither in the normal joint nor in the postoperative condition. Therefore, our goal was to build a quasi-static finite element model to study the function of the acromioclavicular ligament based on its biomechanical performance patterns using the benefits of computational models.

Methods

A three-dimensional bone model is reconstructed using images from a healthy shoulder. The ligament structures were modeled according to the architecture and dimensions of the bone. The kinematics conditions for the shoulder girdle were determined after the osseous axes aligned to simulate the shoulder elevation in the coronal plane and horizontal adduction. Three patterns evaluated ligament function. The peak von Mises stress values were recorded using a clock model that identified the stress distribution. In addition, the variation in length and displacement of the ligament during shoulder motion were compared using a two-tailed hypotheses test. P values < 0.01 were considered statistically significant.

Results

The peak von Mises stress was consistently observed in the AIB at 2:30 in coronal elevation (4.06 MPa) and horizontal adduction (2.32 MPa). Except in the position 2:00, statistically significant higher deformations were identified in the two bundles during shoulder elevation. The highest ligament displacement was observed on the Y- and Z-axes.

Conclusions

The AIB has the primary role in restricting the acromioclavicular joint during shoulder motion, even though the two bundles of the AC ligament have a complementary mode of action. During horizontal adduction, the SPB appears to prevent anterior and superior translation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-02966-0.

The reverse coracoacromial ligament transfer for "horizontal" acromioclavicular joint instability

Background

Acromioclavicular (AC) horizontal instability is a problem affecting not only young athletic patients after a trauma to the AC joint but also older patients who have undergone distal clavicle resection. It may cause pain and poor functional outcomes unless the reconstruction technique specifically addresses the horizontal instability of the clavicle, in addition to the well-known superior instability.

Methods

Three cadaveric specimens underwent dissection of the AC joint capsule to determine the superior attachments of the AC joint capsule. These shoulders subsequently underwent distal clavicle resection and were loaded to a 7-kg weight in the horizontal plane. The horizontal displacement of the clavicle was measured and resection continued to the point of horizontal instability of the clavicle. Thereafter, the reverse coracoacromial ligament reconstruction technique was performed and recreation of horizontal stability assessed. Utilization of the reverse coracoacromial ligament transfer in two clinical cases will also be presented.

Results

The AC joint capsule is continuous with trapezius and deltoid insertions. The average distance between the articular surface and insertion of the capsule on the clavicle is 10 mm and on the acromion is 14.8 mm. Horizontal clavicular translation increased from 2.3 mm when intact to 3.3 mm with capsular transection, 8.7 mm with 5 mm clavicle resection, and finally 15 mm with a 10-mm clavicle resection. Horizontal instability of the clavicle was demonstrated with a 10-mm clavicle resection.

Conclusion

Horizontal instability of the clavicle is evident with distal clavicle resection of greater than 10 mm. A reverse coracoacromial ligament transfer may be a reasonable technique to address horizontal stability of the clavicle during AC joint reconstruction in the context of painful instability.

Additional acromioclavicular cerclage limits lateral tilt of the scapula in patients with arthroscopically assisted coracoclavicular ligament reconstruction

INTRODUCTION

The current treatment for acromioclavicular (AC) dislocation lacks a gold standard and previous literature concludes that coracoclavicular (CC) fixation with additional AC cerclage fixation adds stability and is a useful adjunct to augment these repairs.

AIM

The purpose of this study was to investigate the clinical and radiological value of an additional AC cerclage. It was hypothesised that an additional AC cerclage would show better clinical results. We further expected the additional AC cerclage to result in lower radiological loss of reduction compared to the technique relying on CC-fixation only.

METHODS

A total of 30 male patients with acute (less than 3 weeks) AC-dislocations Rockwood grade IV and V from 2013 to 2014 underwent arthroscopic bi-cortical CC-ligament reconstruction. Patients were assigned to a surgeon depending on the day of clinical presentation. One surgeon used only bi-cortical CC-ligament reconstruction (no-PDS group); the other surgeons used an additional PDS cerclage with an 8-loop configuration over the AC joint (PDS group). Clinical data (Constant Shoulder Score, ASES Score, DASH Score, VAS pain) were assessed 24 months post-operatively, and AP shoulder radiographs used to measure the AC and CC distances.

RESULTS

No significant differences in the Constant (Z = - 0.498, p = 0.624), ASES (Z = 0.263, p = 0.806) and DASH (Z = 1.097, p = 0.305) score as well as VAS pain (Z = 0.498, p = 0.624) were seen for both groups. Factorial ANOVA showed a significant effect of "time" [F(1,28) = 17.54, p < 0.001, r = 0.62], reflecting a significant radiological increase of AC distances over time for both groups. Comparing CC and CC + AC groups, the effect of "OP technique" was significant [F(1,28) = 4.67, p = 0.039, r = 0.38], with AC distances obtained in the PDS group being statistically lower than in the No-PDS group, whereas CC distances did not significantly increase in both groups [F(1,28) = 0.07, p = 0.791]. "Time × OP technique" interaction effects were non-significant [F(1,28) = 0.38, p = 0.545], which reflects similar changes in AC distances over time in both groups. For the CC distances, neither main nor interaction effects were significant (all p > 0.05).

CONCLUSION

Both the isolated CC reconstruction and the CC reconstruction with an additional AC cerclage showed good clinical results at 2 years' follow-up. AC distances increased in both groups from the post-surgery measurement to the 2-year follow-up, but were generally lower with an additional AC cerclage. CC distances did not increase significantly over time in both groups. Therefore, the presented data suggest adding a fixation of the AC joint.

Anatomic reconstruction of the coracoclavicular and acromioclavicular ligaments with semitendinosus tendon graft for the treatment of chronic acromioclavicular joint dislocation provides good clinical and radiological results

PURPOSE

To evaluate clinical and radiographic outcomes of anatomical reconstruction of the coracoclavicular and acromioclavicular ligaments with single-strand semitendinosus tendon graft for the treatment of chronic acromioclavicular joint dislocation.

METHODS

Patients affected by chronic type III-V acromioclavicular joint dislocations were included. Exclusion criteria were: age under 18 years, concomitant rotator cuff tears, previous surgery to the same shoulder, degenerative changes of the glenohumeral joint, infections, neurologic diseases, patients with a previous history of ligament reconstruction procedures that had required harvesting of the semitendinosus tendon from the ipsilateral or contralateral knee. All patients underwent the same surgical technique and rehabilitation. Primary outcome was the normalized Constant score. Secondary outcomes were: DASH score, radiographic evaluation of loss of reduction and acromioclavicular joint osteoarthritis.

RESULTS

Thirty patients with a mean age of 28.9 ± 8.3 years were included. Mean time to surgery was 12.8 ± 10 months. Mean follow-up was 28.1 ± 2.4 months (range: 24-32). Comparison between pre- and postoperative functional scores showed significant clinical improvement (p < 0.001). Time to surgery was independently associated with a poorer Constant score (p < 0.0001). On radiographs, 4 patients (13.3%) showed asymptomatic partial loss of reduction.

CONCLUSION

Anatomic reconstruction of coracoclavicular and acromioclavicular ligaments using a semitendinosus tendon graft for the treatment of chronic acromioclavicular joint dislocation provided good clinical and radiological results at minimum 2-year follow-up.

LEVEL OF EVIDENCE

Level III.

Ligamentous and capsular restraints to anterior-posterior and superior-inferior laxity of the acromioclavicular joint: a biomechanical study

BACKGROUND

Approximately 9% of shoulder girdle injuries involve the acromioclavicular joint (ACJ). There is no clear gold standard or consensus on surgical management of these injuries, in part perpetuated by our incomplete understanding of native ACJ biomechanics. We have therefore conducted a biomechanical study to assess the stabilizing structures of the ACJ in superior-inferior (SI) translation and anterior-posterior (AP) translation.

METHODS

Twenty fresh frozen cadaveric specimens were prepared and mounted onto a robotic arm. The intact native joint was tested in SI translation and AP translation under a 50-N displacing force. Each specimen was retested after sectioning of its stabilizing structures in the following order: investing fascia, ACJ capsular ligaments, trapezoid ligament, and conoid ligament. Their contributions to resisting ACJ displacements were calculated.

RESULTS

In the intact native ACJ, mean anterior displacement of the clavicle was 7.9 ± 4.3 mm, mean posterior displacement was 7.2 ± 2.6 mm, mean superior displacement was 5.8 ± 3.0 mm, and mean inferior displacement was 3.6 ± 2.6 mm. The conoid ligament was the primary stabilizer of superior displacement (45.6%). The ACJ capsular ligament was the primary stabilizer of inferior displacement (33.8%). The capsular ligament and conoid ligament contributed equally to anterior stability, with rates of 23% and 25.2%, respectively. The capsular ligament was the primary contributor to posterior stability (38.4%).

CONCLUSION

The conoid ligament is the primary stabilizer of superior displacement of the clavicle at the ACJ and contributes significantly to AP stability. Consideration should be given to reconstruction of the ACJ capsular ligament for complete AP stability in high-grade and horizontally unstable ACJ injuries.

Quantitative and Qualitative Surgical Anatomy of the Acromioclavicular Joint Capsule and Ligament: A Cadaveric Study

BACKGROUND

The acromioclavicular (AC) capsule and ligament have been found to play a major role in maintaining horizontal stability. To reconstruct the AC capsule and ligament, precise knowledge of their anatomy is essential.

PURPOSE/HYPOTHESIS

The purposes of this study were (1) to determine the angle of the posterosuperior ligament in regard to the axis of the clavicle, (2) to determine the width of the attachment (footprint) of the AC capsule and ligament on the acromion and clavicle, (3) to determine the distance to the AC capsule from the cartilage border of the acromion and clavicle, and (4) to develop a clockface model of the insertion of the posterosuperior ligament on the acromion and clavicle. It was hypothesized that consistent angles, attachment areas, distances, and insertion sites would be identified.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 12 fresh-frozen shoulders were used (mean age, 55 years [range, 41-64 years]). All soft tissue was removed, leaving only the AC capsule and ligament intact. After a qualitative inspection, a quantitative assessment was performed. The AC joint was fixed in an anatomic position, and the attachment angle of the posterosuperior ligament was measured using a digital protractor. The capsule and ligament were removed, and a coordinate measuring device was utilized to assess the width of the AC capsule footprint and the distance from the footprint to the cartilage border of the acromion and clavicle. The AC joint was then disarticulated, and the previously marked posterosuperior ligament insertion was transferred into a clockface model. The mean values across the 12 specimens were demonstrated with 95% CIs.

RESULTS

The mean attachment angle of the posterosuperior ligament was 51.4° (95% CI, 45.2°-57.6°) in relation to the long axis of the entire clavicle and 41.5° (95% CI, 33.8°-49.1°) in relation to the long axis of the distal third of the clavicle. The mean clavicular footprint width of the AC capsule was 6.4 mm (95% CI, 5.8-6.9 mm) at the superior clavicle and 4.4 mm (95% CI, 3.9-4.8 mm) at the inferior clavicle. The mean acromial footprint width of the AC capsule was 4.6 mm (95% CI, 4.2-4.9 mm) at the superior side and 4.0 mm (95% CI, 3.6-4.4 mm) at the inferior side. The mean distance from the lateral clavicular attachment of the AC capsule to the clavicular cartilage border was 4.3 mm (95% CI, 4.0-4.6 mm), and the mean distance from the medial acromial attachment of the AC capsule to the acromial cartilage border was 3.1 mm (95% CI, 2.9-3.4 mm). On the clockface model of the right shoulder, the clavicular attachment of the posterosuperior ligament ranged from the 9:05 (range, 8:00-9:30) to 11:20 (range, 10:00-12:30) position, and the acromial attachment ranged from the 12:20 (range, 11:00-1:30) to 2:10 (range, 13:30-14:40) position.

CONCLUSION

The finding that the posterosuperior ligament did not course perpendicular to the AC joint but rather was oriented obliquely to the long axis of the clavicle, in combination with the newly developed clockface model, may help surgeons to optimally reconstruct this ligament.

CLINICAL RELEVANCE

Our results of a narrow inferior footprint and a short distance from the inferior AC capsule to cartilage suggest that proposed reconstruction of the AC joint capsule should focus primarily on its superior portion.

The Role of the Acromioclavicular Ligament in Acromioclavicular Joint Stability: A Cadaveric Biomechanical Study

Background:

Acromioclavicular (AC) joint dislocation is evaluated using the radiologically based Rockwood classification. The relationship between ligamentous injury and radiological assessment is still controversial.

Purpose/Hypothesis:

To investigate how the AC ligament and trapezoid ligament biomechanically contribute to the stability of the AC joint using cadaveric specimens. The hypothesis was that isolated sectioning of the AC ligament would result in increased instability in the superior direction and that displacement >50% of the AC joint would occur.

Study Design:

Controlled laboratory study.

Methods:

Six shoulders from 6 fresh-frozen cadavers were used in this study. Both the scapula and sternum were solidly fixed on a customized wooden jig with an external fixator. We simulated distal clavicular dislocation with sequential sectioning of the AC and coracoclavicular (CC) ligaments. Sectioning stages were defined as follows: stage 0, the AC ligament, CC ligament, and AC joint capsule were left intact; stage 1, the anteroinferior bundle of the AC ligament, joint capsule, and disk were sectioned; stage 2, the superoposterior bundle of the AC ligament was sectioned; and stage 3, the trapezoid ligament was sectioned. The distal clavicle was loaded with 70 N in the superior and posterior directions, and the magnitudes of displacement were measured.

Results:

The amounts of superior displacement averaged 3.7 mm (stage 0), 3.8 mm (stage 1), 8.3 mm (stage 2), and 9.5 mm (stage 3). Superior displacement >50% of the AC joint was observed in stage 2 (4/6; 67%) and stage 3 (6/6; 100%). The magnitudes of posterior displacement were 3.7 mm (stage 0), 3.7 mm (stage 1), 5.6 mm (stage 2), and 9.8 mm (stage 3). Posterior displacement >50% of the AC joint was observed in stage 3 (1/6; 17%).

Conclusion:

We found that the AC ligaments contribute significantly to AC joint stability, and superior displacement >50% of the AC joint can occur with AC ligament tears alone.

Clinical Relevance:

The AC ligament plays an important role not only in horizontal stability but also in vertical stability of the AC joint.

Imaging of the Acromioclavicular Joint: Anatomy, Function, Pathologic Features, and Treatment

The acromioclavicular joint is an important component of the shoulder girdle; it links the axial skeleton with the upper limb. This joint, a planar diarthrodial articulation between the clavicle and the acromion, contains a meniscus-like fibrous disk that is prone to degeneration. The acromioclavicular capsule and ligaments stabilize the joint in the horizontal direction, while the coracoclavicular ligament complex provides vertical stability. Dynamic stability is afforded by the deltoid and trapezius muscles during clavicular and scapular motion. The acromioclavicular joint is susceptible to a broad spectrum of pathologic entities, traumatic and degenerative disorders being the most common. Acromioclavicular joint injury typically affects young adult males and can be categorized by using the Rockwood classification system as one of six types on the basis of the direction and degree of osseous displacement seen on conventional radiographs. MRI enables the radiologist to more accurately assess the regional soft-tissue structures in the setting of high-grade acromioclavicular separation, helping to guide the surgeon's selection of the appropriate management. Involvement of the acromioclavicular joint and its stabilizing ligaments is also important for understanding and classifying distal clavicle fractures. Other pathologic processes encountered at this joint include degenerative disorders; overuse syndromes; and, less commonly, inflammatory arthritides, infection, metabolic disorders, and developmental malformations. Treatment options for acromioclavicular dysfunction include conservative measures, resection arthroplasty for recalcitrant symptoms, and surgical reconstruction techniques for stabilization after major trauma.

Posterior Rotational and Translational Stability in Acromioclavicular Ligament Complex Reconstruction: A Comparative Biomechanical Analysis in Cadaveric Specimens

BACKGROUND

Persistent posterior instability of the acromioclavicular (AC) joint is a reported complication after isolated coracoclavicular (CC) reconstruction. Thus, multiple techniques have been proposed attempting to restore biomechanics of the AC ligament complex (ACLC).

PURPOSE/HYPOTHESIS

The purpose was to evaluate the posterior translational and rotational stability of an ACLC reconstruction with a dermal allograft (ACLC patch) as compared with 3 suture brace constructs. It was hypothesized that the ACLC patch would better restore AC joint posterior stability.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 28 cadaveric shoulders (mean ± SD age, 57.6 ± 8.3 years) were randomly assigned to 1 of 4 surgical techniques: ACLC patch, oblique brace, anterior brace, and x-frame brace. The force and torque to achieve 10 mm of posterior translation and 20° of posterior rotation of the AC joint were recorded in the following conditions: intact, transected ACLC, ACLC patch/brace repair, ACLC patch/brace repair with dissected CC ligaments, and ACLC patch/brace repair with CC ligament repair.

RESULTS

For posterior translation, transection of the ACLC reduced resistance to 16.7% of the native. With the native CC ligaments intact, the ACLC patch (59.1%), oblique brace (54.1%), and anterior brace (60.7%) provided significantly greater stability than the x-frame brace (33.2%; P < .001, P = .008, P < .001, respectively). ACLC patch, oblique brace, and anterior brace continued to have significantly higher posterior translational resistance than the x-frame (35.1%; P < .001, P = .003, P < .001) after transection and subsequent CC ligament repair. For posterior rotation, transection of the ACLC decreased the resistance to 5.4% of the intact state. With the CC ligaments intact, the ACLC patch (77.1%) better restored posterior rotational stability than the oblique (35.3%), anterior (48.5%), and x-frame (23.0%) brace repairs (P < .001, P = .002, P < .001). CC ligament transection and subsequent repair demonstrated the ACLC patch (41.0%) to have improved stability when compared with the oblique (16.0%), anterior (14.0%), and x-frame (12.7%) repairs (P = .006, P = .003, P = .002).

CONCLUSION

ACLC reconstruction with a dermal allograft better restored native posterior rotational stability than other brace constructs, with translational stability similar to the oblique and anterior brace technique at the time of surgery.

CLINICAL RELEVANCE

Horizontal stability of the AC joint is primarily controlled by the ACLC. Inability to restore AC joint biomechanics can result in persistent posterior instability and lead to functional impairment.

Biomechanical evaluation of an independent acromioclavicular ligament repair for acromioclavicular joint reconstruction

BACKGROUND

A number of surgical techniques for the treatment of acromioclavicular joint separations have been described; however, few have been able to create a strong intra-operative construct that provides minimal joint translation. A biomechanical study was conducted to examine joint translation in an independent acromioclavicular ligament repair.

METHODS

Three variations of a novel independent acromioclavicular ligament repair technique underwent testing using a Sawbones model. The technique involves threading sutures through two acromial bone tunnels in a suture-bridge configuration and anchoring them into the distal clavicle. Three groups of eight specimens underwent reconstruction; group 1 using FiberTape, group 2 using FiberWire and group 3 using FiberTape in a modified (under-over) suture-bridge configuration. Superior, anterior and posterior translation was tested at loads of 10, 20 and 30 N.

RESULTS

Group 3 repair yielded the least translation in both anterior-posterior and superior-inferior planes, with a two-fold decrease in superior translation compared to groups 1 and 2 (P < .05). Both groups 1 and 3 using FiberTape resulted in significantly less anterior and posterior translation compared to the FiberWire group (P < .05).

DISCUSSION

The independent acromioclavicular ligament repair, without repair of the coracoclavicular ligament, demonstrated significant translational stability in the anterior-posterior and superior-inferior planes.

Optimal Management of Acromioclavicular Dislocation: Current Perspectives

Injuries to the acromioclavicular (AC) joint are common and mostly involve younger, male individuals. Whereas the majority of AC joint dislocations can be treated nonoperatively with a trial of immobilization, pain medication, cryotherapy, and physiotherapy, there are patients that do not respond well to conservative management and may require surgical treatment. Identifying and treating these patients according to the type and chronicity of AC joint dislocation is paramount. To date, a myriad of surgical techniques have been proposed to address unstable AC joint dislocations and are indicative of the uncertainty that exists in optimal management of these injuries. Historically research has focused on the restoration of the coracoclavicular ligament complex. However, recently the importance of the acromioclavicular capsule and ligaments has been emphasized. This review aims to provide the reader with an overview of current treatment strategies and research, as well as future perspectives.

Reconstruction of the Acromioclavicular Ligament Complex Using Dermal Allograft: A Biomechanical Analysis

PURPOSE

To analyze the posterior translational and rotational stability of the acromioclavicular (AC) joint following reconstruction of the superior acromioclavicular ligament complex (ACLC) using dermal allograft.

METHODS

Six fresh-frozen cadaveric shoulders were used (mean age of 65.3 ± 6.9 years). The resistance force against posterior translation (10 mm) and torque against posterior rotation (20°) was measured. Specimens were first tested with both the intact ACLC and coracoclavicular ligaments. The ACLC and coracoclavicular ligaments were then transected so simulate a Type III/V AC joint dislocation. Each specimen then underwent 3 testing conditions, performed in the following order: (1) ACLC patch reconstruction alone, (2) ACLC patch with an anatomic coracoclavicular reconstruction (ACCR) using semitendinosus allograft, and (3) the transected ACLC with an ACCR only. Differences in posterior translational and rotational torque across testing conditions were analyzed with a one-way repeated analysis of variance analysis.

RESULTS

Mean resistance against posterior translation in the intact condition was 65.76 ± 23.8 N. No significant difference found between the intact condition compared with specimens with the ACLC-patch only (44.2 ± 11.3 N, P = .06). The ACCR technique, when tested alone, had significantly less posterior translational resistance compared with the intact condition (38.5 ± 8.94 N, P = .008). ACLC patch in combination with an ACCR was closest in restoring native posterior translation (57.1 ± 19.2 N, P = .75). For rotational resistance, only the addition of the ACLC patch with an ACCR (0.51 ± 0.07 N-m) demonstrated similar torque compared with the intact joint (0.89 ± 0.5 N-m, P = .06).

CONCLUSIONS

The ACLC-patch plus ACCR technique was able to closest restore the percent of normal posterior translational and rotational stability.

CLINICAL RELEVANCE

Recurrent posterior instability of the AC joint is a potential complication after coracoclavicular reconstruction surgery. In the in vitro setting, this study demonstrated increased AC joint stability with the addition of an ACLC reconstruction using dermal allograft.

Repair of the entire superior acromioclavicular ligament complex best restores posterior translation and rotational stability

PURPOSE

The acromioclavicular ligament complex (ACLC) is the primary stabilizer against horizontal translation with the superior ACLC providing the main contribution. The purpose of this study was to evaluate the specific regional contributions in the superior half of ACLC, where the surgeon can easily access and repair or reconstruct, for posterior translational and rotational stability.

METHODS

The superior half of ACLC was divided into three regions; Region A (0°-60°): an anterior 1/3 region of the superior half of ACLC, Region B (60°-120°): a superior 1/3 region of the superior half of ACLC, and Region C (120°-180°): a posterior 1/3 region of the superior half of ACLC. Fifteen fresh-frozen cadaveric shoulders were used. Biomechanical testing was performed to evaluate the resistance force against passive posterior translation (10 mm) and the resistance torque against passive posterior rotation (20°) during the following the four conditions. (1) Stability was tested on all specimens in their intact condition (n = 15). (2) The ACLC was dissected and stability was tested (n = 15). (3) Specimens were randomly divided into three groups by regions of suturing. Stability was tested after suturing Region A, Region B, or Region C (n = 5 per group). (4) Stability was tested after suturing additional regions: Region A + B (0°-120°), Region B + C (60°-180°), or Region A + C (0°-60°, 120°-180°, n = 5 per group).

RESULTS

The translational force increased after suturing Region A when compared with dissected ACLC (P = 0.025). The force after suturing Region A + B was significantly higher compared to the dissected ACLC (P < 0.001). The rotational torque increased after suturing Region A or Region B compared with dissected ACLC (P = 0.020, P = 0.045, respectively). The torque after suturing the Region A + C was significantly higher compared to the dissected ACLC (P < 0.001).

CONCLUSION

The combined Region A + B contributed more to posterior translational stability than Region B + C or Region A + C. In contrast, combined Region A + C contributed more to posterior rotational stability than Region A + B or Region B + C. Based on these findings, surgical techniques restoring the entire superior ACLC are recommended to address both posterior translational and rotational stability of the AC joint.

Distal Clavicular Augmentation with Acromioclavicular and Coracoclavicular Ligament Reconstruction in the Setting of Iatrogenic Induced Acromioclavicular Instability

Although chronic pain and dysfunction of the acromioclavicular (AC) joint can reliably be treated with distal clavicle excision, disruption of the local stabilizing ligamentous structures may result in iatrogenic instability of the joint. Iatrogenic AC joint instability is a rare condition caused by over resection of the distal clavicle with unintended injury to the stabilizing ligaments in the treatment of AC joint pain. Addressing postresection instability can prove to be difficult because most reconstruction techniques are intended for patients with traumatic AC joint instability with the goal of creating an anatomically stable joint. However, in the setting of iatrogenic instability, the decreased bone stock of the distal clavicle results in instability of the AC joint, especially in the horizontal plane, and may cause these techniques to fail. Thus, operative management must aim to correct both the osseous and ligamentous deficits responsible for the genesis of this instability. In this Technical Note, we describe bony augmentation of the distal clavicle with an iliac crest bone autograft for chronic iatrogenic acromioclavicular joint instability with concomitant reconstruction of the AC and coracoclavicular ligaments.

The Integrity of the Acromioclavicular Capsule Ensures Physiological Centering of the Acromioclavicular Joint Under Rotational Loading

BACKGROUND

The acromioclavicular (AC) capsule is an important stabilizer against horizontal translation and also contributes to the strut function of the clavicle, which guides rotation of the scapula. To best reproduce the biomechanical properties and the complex 3-dimensional (3D) guidance of the AC joint, detailed knowledge of the contribution of each of the distinctive capsular structures is needed. Purpose/Hypothesis: To perform a detailed biomechanical evaluation of the specific capsular structures of the AC joint and their contribution to translational and rotational stability. The hypothesis was that successive cutting of each quadrant of the AC capsule would result in increased instability and increased amplitude of the clavicle's motion in relation to the acromion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-two fresh-frozen human cadaveric shoulders were used. Each scapula was fixed to a swivel fixture of a servohydraulic materials testing system. The AC capsule was dissected in serial steps with immediate rotational and horizontal testing after each cut. A 3D optical measuring system was used to evaluate 3D movement. Posterior translation, rotation, and displacement of the lateral clavicle in relation to the center of rotation were measured. Torques and axial forces required to rotate and translate the clavicle were recorded.

RESULTS

When posterior translational force was applied, all specimens with a completely cut AC capsule demonstrated a significant loss of resistance force against the translational motion when compared with the native state ( P < .05). The resistance force against posterior translation was reduced to less than 27% of the native state for all specimens. Sequential cutting of the AC capsule resulted in a significant reduction of resistance torque against anterior rotation for all specimens with less than 22% of resistance force compared with the native state. Cutting 50% of the capsule reduced the resistance torque for all segments and all testing modalities (posterior translation as well as anterior and posterior rotation) significantly compared with the native state ( P < .05). Cutting the entire AC capsule resulted in a significant increase in motion within the joint as a sign of decentering of the AC joint when torque was applied. All groups demonstrated a significant increase of motion in all directions when the AC capsule was cut by 50%.

CONCLUSION

Cutting the entire capsule (with intact coracoclavicular [CC] ligaments) reduced the resistance force to less than 25% compared with the native state during translational testing and less than 10% compared with the native state during rotational testing. However, the anterior segments of the capsule provided the greatest stability under rotational loading. Second, the amplitude of the joint's motion significantly increased under rotational stress, indicating increased amplitude of the clavicle's motion in relation to the acromion when the ligamentous structures of the AC capsule are dissected.

CLINICAL RELEVANCE

To best restore stability to the AC joint, the relevance and function of each section of the circumferential AC capsule need to be understood. Our findings support the synergistic contribution of the CC ligaments and AC capsular structures to AC joint stability. This synergy supports the need to address both structures to achieve anatomic reconstruction.

Acromion morphology and bone mineral density distribution suggest favorable fixation points for anatomic acromioclavicular reconstruction

PURPOSE

Recent techniques for acromioclavicular (AC) joint reconstruction focus on additional AC cerclage to coracoclavicular (CC)-reconstructions. Due to the specific slim bone morphology at the acromion, there are concerns regarding these additional bone tunnels, as they may predispose to fracture and break out. The purpose of this study was to investigate anatomic properties of the acromion which may help improve surgical techniques directed at injuries to the AC joint. It was hypothesized that via measurements of thickness and density points of increased strength and support could be identified on the acromion.

METHODS

Eighty-five fresh frozen cadaveric shoulders were used for this study. A standardized 3D-net was developed and thicknesses of the acromion were taken from defined points using a certified caliper. To define the acromial arch, the angle and radius of curvature between the antero-lateral, the highest point of the acromial arch and the postero-lateral aspect of the acromion were measured. Additional bone mineral density (BMD) evaluation was performed on 43 specimens in an anterio-posterior and latero-medial direction using 5-mm slices with a maximum of 10 and 6 slices, respectively.

RESULTS

Median specimen age was 63.0 (range 36) years (55 female, and 30 male). There was no statistical significance between male (62.0, range: 35 years) and female (64.5, range 32 years) regarding age (n.s.). Thickness of acromion points of interest were ranging from 3.5 to 24.3 mm. Median radius of curvature of acromial arch for female was 48.2 (range 92.7) mm and 66.2 (range 85.6) for male (p = 0.019). The median angle for female specimens was 21.4° (range: 44.6°) and 23.3° (range 51.7°) for male (p = 0.047). The latero-medial measurements showed significant difference between the region of interest (ROI): 1 and 4, 5, 6 (p = 0.001, p = 0.001, p = 0.001), 2 and 4, 5, 6 (p = 0.007, p = 0.001, p = 0.001), 3 and 5, 6 (p = 0.001, p = 0.001), 4 and 5, 6 (p = 0.010, p = 0.001). Antero-posterior measurements showed significant difference between the ROI: 1 and 8 (p = 0.031).

CONCLUSION

The posterior-medial acromion close to the AC joint revealed the highest BMD with an increasing density from lateral to medial. In combination with thickness measurements this region would support additional anatomical fixation of the AC joint using bone tunnels if necessary.

CLINICAL RELEVANCE

To anatomically reproduce the insertions of the AC ligaments at the acromion, either bone tunnels or anchors are needed. Therefore, several techniques have been developed. This study provides the anatomical data for these techniques and confirms the reconstructive approach of techniques using anatomical points of fixation and orientation.

Injury patterns of the acromioclavicular ligament complex in acute acromioclavicular joint dislocations: a cross-sectional, fundamental study

BACKGROUND

Horizontal instability impairs clinical outcome following acute acromioclavicular joint (ACJ) reconstruction and may be caused by insufficient healing of the superior acromioclavicular ligament complex (ACLC). However, characteristics of acute ACLC injuries are poorly understood so far. Purposes of this study were to identify different ACLC tear types, assess type-specific prevalence and determine influencing cofactors.

METHODS

This prospective, cross-sectional study comprised 65 patients with acute-traumatic Rockwood-5 (n = 57) and Rockwood-4 (n = 8) injuries treated operatively by means of mini-open ACJ reduction and hook plate stabilization. Mean age at surgery was 38.2 years (range, 19-57 years). Standardized pre- and intraoperative evaluation included assessment of ACLC tear patterns and cofactors related to the articular disc, the deltoid-trapezoidal (DT) fascia and bony ACJ morphology. Articular disc size was quantified as 0 = absent, 1 = remnant, 2 = meniscoid and 3 = complete.

RESULTS

All patients showed complete ruptures of the superior ACLC, which could be assigned to four different tear patterns. Clavicular-sided (AC-1) tears were observed in 46/65 (70.8 %), oblique (AC-2) tears in 12/65 (18.5 %), midportion (AC-3) tears in 3/65 (4.6 %) and acromial-sided (AC-4) tears in 4/65 (6.1 %) of cases. Articular disc size manifestation was significantly (P < .001) more pronounced in patients with AC-1 tears (1.89 ± 0.57) compared to patients with AC-2 tears (0.67 ± 0.89). Other cofactors did not influence ACLC tear patterns. ACLC dislocation with incarceration caused mechanical impediment to anatomical ACJ reduction in 14/65 (21.5 %) of cases including all Rockwood-4 dislocations. Avulsion "in continuity" was a consistent mode of failure of the DT fascia. Type-specific operative strategies enabled anatomical ACLC repair of all observed tear types.

CONCLUSIONS

Acute ACLC injuries follow distinct tear patterns. There exist clavicular-sided (AC-1), oblique (AC-2), midportion (AC-3) and acromial-sided (AC-4) tears. Articular disc size was a determinant factor of ACLC tear morphology. Mini-open surgery was required in Rockwood-4 and a relevant proportion of Rockwood-5 dislocations to achieve both anatomical ACLC and ACJ reduction. Type-specific operative repair of acute ACLC tears might promote biological healing and lower rates of horizontal ACJ instability following acute ACJ reconstruction.