Relevant anatomy, biomechanics, and classification of sternoclavicular joint disorders





Surgical anatomy of the sternoclavicular joint


The sternoclavicular (SC) joint is a diarthrodial joint and is the only true articulation between the upper extremity and axial skeleton. Because less than half of the medial clavicle articulates with the upper angle of the sternum, the SC joint has the distinction of having the least amount of bony stability of the major joints of the body. The enlarged bulbous medial end of the clavicle is concave front to back and convex vertically and thus creates a saddle-type joint with the clavicular notch of the sternum. The clavicular notch of the sternum is curved, and the joint surfaces are not congruent. Van Tongel and colleagues evaluated the relationship of the medial clavicular head and the manubrium in a normal population (25 females and 25 males; bilateral measurements) using three-dimensional computed tomography. In the axial plane, the superomedial aspect of the medial clavicle was 17.6 mm (standard deviation, 3.9 mm) above the manubrium. In the frontal plane, the anterior aspect of the medial end of the clavicle was 0.8 mm (standard deviation, 2.6 mm) anterior to the manubrium ( Fig. 25.1 ).




Fig. 25.1


(A) Normal relationship between the superior aspect of the medial clavicle (point S) and the sternum in the axial plane. (B) Normal relationship between the anterior aspect of the medial clavicle (point A) and the sternum in the frontal plane. SC, Sternoclavicular.

(From Van Tongel A, Valcke J, Piepers I, et al. Relationship of the medial clavicular head to the manubrium in normal and symptomatic degenerated sternoclavicular joints. J Bone Joint Surg Am . 2014;96[13]:e109.)


The articular surface of the medial clavicle is much larger than that of the sternum, and both are covered with hyaline cartilage. Articular cartilage covers approximately 67% of the medial end of the clavicle, with coverage only on the anteroinferior aspect of the clavicle and on the underside of the clavicle at its articulation with the manubrial cartilage and first-rib costal cartilage ( Fig. 25.2 ). In 2.5% of patients, there is a small facet on the inferior aspect of the medial clavicle that articulates with the superior aspect of the first rib at its synchondral junction with the sternum.




Fig. 25.2


Anatomy of the medial end of the clavicle (right) with clock face positions indicated (lateral view). (A) The most anatomically superior point is at 12 o’clock, and 9 o’clock faces anteriorly. (B) Anatomic illustration of the medial end of the clavicle showing the extent of the articular surface and the attachment locations of the sternoclavicular (SC), interclavicular, and costoclavicular ligaments. Note the limited articular cartilage coverage and the large attachment area of the intra-articular disk.

(From Lee JT, Campbell KJ, Michalski MP, et al. Surgical anatomy of the sternoclavicular joint: a qualitative and quantitative anatomical study. J Bone Joint Surg Am . 2014;96[19]:e166.)


Ligaments of the sternoclavicular joint


The SC joint has so much incongruity that integrity of the joint must come from its surrounding ligaments (i.e., the intra-articular disk ligament, extra-articular costoclavicular ligament [rhomboid ligament], the capsular ligaments, and interclavicular [IC] ligament).


Intra-articular disk ligament


The intra-articular disk ligament is a very dense, fibrous structure that arises from the synchondral junction of the first rib with the sternum and passes through the SC joint. This ligament divides the joint in the sagittal-oblique plane to create two separate joint spaces (medial or sternal and lateral) ( Fig. 25.3 ). Anatomic studies have shown that the disk has a robust insertion on the posterosuperior aspect of the clavicle (see Fig. 25.2 B). Anteriorly and posteriorly, the disk blends into the fibers of the capsular ligaments; inferiorly, the disk has a less robust attachment ( Fig. 25.4 ). The diameter and thickness of the articular disk, on average, are 18 and 5.4 mm, respectfully. DePalma has shown that the disk is perforated only rarely; the perforation allows free communication between the two joint compartments (see Figs. 25.3 A and 25.4 ).




Fig. 25.3


(A) Anterior view of the sternoclavicular (SC) joint after removal of the covering capsule. The clavicular side of the SC joint space is visualized (arrow) . To the right of the arrow is the intra-articular disk. The anterior SC joint ligament is well defined and visualized to the right of the intra-articular disk. (B) The medial end of the clavicle is visualized with the limited anteroinferior articular surface and broad attachment of the capsule (outlined in blue ).

(From Van Tongel A, MacDonald P, Leiter J, et al. A cadaveric study of the structural anatomy of the sternoclavicular joint. Clin Anat . 2012;25[7]:903–910.)



Fig. 25.4


(A) Normal-appearing articular disk ligament of the right sternoclavicular joint (held by forceps). (B) Degenerative articular disk ligament with a central perforation (left sternoclavicular joint). (C) Intraoperative photograph demonstrating excision of a symptomatic articular disk ligament (held by forceps). (D) Surgical specimen of excised articular disk ligament.


The intra-articular disk acts as a checkrein against medial displacement of the medial clavicle. Histologic studies have demonstrated that the sternal side of the disk is composed of fibrocartilage and dense connective tissue, whereas the clavicular side of the disk is composed of only fibrocartilage. Therefore it is likely that the clavicular side of the articular disk has the function of resisting the compressive load to the clavicular surface. In a recent cadaveric study evaluating the intra-articular disk of 25 SC joints, Van Tongel et al. demonstrated that, when the articular disk was “incomplete” (i.e., signs of degeneration/fraying and loss of a sharp peripheral rim), there was a high prevalence of severe cartilage damage in 71% of specimens (10 of 14 specimens with an incomplete disk). In contrast, when the disk was “complete,” severe damage to the articular surface of the clavicle was detected in only 27% (3 of 11 specimens with a complete disk). This study reinforces that the articular disk helps to protect the articular surfaces of the joint.


Costoclavicular ligament


The costoclavicular ligament, also called the rhomboid ligament , is composed of an anterior and a posterior fasciculus and is the largest ligament of the SC joint. The fibers of the anterior fasciculus arise from the anteromedial surface of the first rib and are directed upward and laterally. The fibers of the posterior fasciculus are shorter and arise lateral to the anterior fibers on the rib and are directed upward and medially. The costoclavicular ligament attaches superiorly to the margins of an impression on the inferior surface of the medial end of the clavicle, sometimes referred to as the rhomboid fossa . , Cave showed, in a study of 153 clavicles, that the attachment point of the costoclavicular ligament to the inferior clavicle can be one of three types: (1) a depression, the rhomboid fossa (30%); (2) a flat surface (60%); or (3) an elevation or prominence (10%). More recently, Lee et al. observed that the costoclavicular ligament consistently attached to a palpable tubercle in all of the 11 cadaveric specimens studied, known as the costoclavicular tubercle , which likely corresponds to the “elevation” described by Cave in 1961. The anatomy of the costoclavicular ligament is in many ways similar to the structural configuration of the coracoclavicular ligament on the outer end of the clavicle ( Fig. 25.5 ).




Fig. 25.5


Left medial clavicle demonstrating the rhomboid appearance of the costoclavicular ligament and the anterior sternoclavicular capsular ligament.


The dimensions of the costoclavicular ligament have also been described. Cave reported that the average length is 1.3 cm, maximum width is 1.9 cm, and average thickness is 1.3 cm. Lee et al. found that on the clavicle, the center of the costoclavicular ligament is on an average 13.8 mm lateral to the inferior SC articular margin, while the most medial fibers are 10.3 mm lateral to the same point of reference. On the first rib cartilage, the center of the insertion was 14.8 mm lateral to the inferior manubrial articular cartilage margin, and the most medial fibers of the ligament were 8.3 mm.


The fibers of the anterior and posterior components cross and allow stability of the joint during rotation and elevation of the clavicle. Bearn has shown experimentally that the anterior fibers resist excessive upward rotation of the clavicle and that the posterior fibers resist excessive downward rotation. In addition, the anterior fibers resist lateral displacement and the posterior fibers resist medial displacement ( Fig. 25.6 ).




Fig. 25.6


The importance of the various ligaments around the sternoclavicular joint in maintaining normal shoulder poise. (A) The lateral end of the clavicle is maintained in an elevated position through the sternoclavicular ligaments. The arrow indicates the fulcrum. (B) When the capsule is divided completely, the lateral end of the clavicle descends under its own weight without any loading. The clavicle seems to be supported by the intra-articular disk ligament. (C) After division of the capsular ligament, it was determined that a weight less than 5 lb was enough to tear the intra-articular disk ligament from its attachment on the costal cartilage junction of the first rib. The fulcrum was transferred laterally so that the medial end of the clavicle hinged over the first rib in the vicinity of the costoclavicular ligament. (D) After division of the costoclavicular ligament and the intra-articular disk ligament, the lateral end of the clavicle could not be depressed as long as the capsular ligament was intact. (E) After resection of the medial first costal cartilage along with the costoclavicular ligament, there was no effect on the poise of the lateral end of the clavicle, as long as the capsular ligament was intact.

(From Bearn JG. Direct observation on the function of the capsule of the sternoclavicular joint in clavicular support. J Anat . 1967;101:159–170.)


Interclavicular ligament


The IC ligament connects the superomedial aspect of each clavicle with the capsular ligaments and the upper part of the sternum ( Figs. 25.7 and 25.8 ). Lee et al. found that the IC ligament was the “most readily identified of the SC-associated joint ligaments as a discrete ligament between the two clavicle heads.” The IC ligament attachment is located at the posterior-superior aspect of the medial clavicle (i.e., 1:30 o’clock position, right clavicle) (see Fig. 25.2 ).


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Aug 21, 2021 | Posted by in ORTHOPEDIC | Comments Off on Relevant anatomy, biomechanics, and classification of sternoclavicular joint disorders

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