4.1
Introduction
The sternocostoclavicular (SCC) region is part of the chest wall (Fig. 4.1) and thereby contributes to respiratory movements. In addition, the sternoclavicular joints are the only synovial joints between the upper extremity and the trunk.
4.2
Sternoclavicular Joints
The sternoclavicular joint is a non-weight-bearing joint, but one of the most fre- quently used joints in the trunk. It accompanies every movement of the arm, and functions like a ball-and-socket joint permitting motion in all planes [2, 3]. With movement of the arm its movements consist of a cone of 60 degrees with the tip in the middle of the clavicular head. Movement in the sternoclavicular joint con- tributes to shoulder abduction and flexion via elevation of the lateral end and rota- tion of the clavicle. In the first 90 degrees of abduction, the clavicle raises approxi- mately 30 degrees. With abduction beyond 90 degrees, the clavicle rotates about its
Contents
4.1 Introduction . . . 39
4.2 Sternoclavicular Joints . . . 39
4.3 Manubriosternal Joint . . . 40
4.4 Sternocostal Joints . . . 41
4.5 Conclusions . . . 42
References . . . 42
4 Biomechanics of Joints and Cartilages
Anne Grethe Jurik
Anne Grethe Jurik
longitudinal axis. Due to the crankshaft shape of the clavicle, this rotation elevates the lateral end, but also implies rotation at the sternoclavicular joint. Moreover, the sternoclavicular joint moves slightly during respiration contributing to con- tinuous strain, although to a lesser degree. It seems there is always some strain on the joint especially in the upright position, and it is apparently only relaxed in the supine position. This may explain the frequent occurrence of degenerative changes (Fig. 3.3) (Chapter 15) [4, 5].
4.3
Manubriosternal Joint
The manubriosternal joint (MSJ) is located between the manubrium sterni and the sternal body. It is slightly moveable and contributes to the mobility of the SCC region; it thus has a function during respiration. During inspiration, the ribs move upward and forward to expand the thoracic cavity. The first rib is much shorter than the succeeding ribs. Therefore, the upward and forward excursion of its an- terior end is lesser, and the adjacent manubrium sterni is only slightly raised for- ward. The greater excursion, especially in the forward direction, imposed upon the rest of the sternum by the longer ribs causes a bending at the MSJ. An opposite
Fig. 4.1 Computed tomography, 3D recon- struction of the thoracic cage in a 58-year-old woman shows the intimate relation of the SCC region and the rest of the thoracic cage
Chapter 4 Biomechanics of Joints and Cartilages
movement occurs during expiration [1]. The forces thus imposed on the joint may cause degenerative changes (Fig. 2.8).
4.4
Sternocostal Joints
The first costal cartilages and sternocostal joints have a special function. The carti- lages are originally united directly to the sternal bone forming synchondrotic first sternocostal joints. However, mineralisation occurs early in these cartilages, but often a non-calcified cleavage will persist between the cartilages and the sternum.
During each respiration the torsion of the cartilages is made possible by these joint-like cleavages. Due to a nearly continuous strain imposed on the region os- teoarthritis-like changes can occur with osteophyte formation, sometimes appear- ing as a pseudoarthrosis (Fig. 4.2).
The second sternocostal joints are intimately related to the MSJ and adjacent cartilages and contribute to the extension during inspiration [1]. Similarly, the third to the seventh sternocostal joints will move during respiration, and the strain thereby imposed on the joints may cause degenerative changes in addition to cal- cification of the adjacent costal cartilages (Fig. 4.2).
Fig. 4.2 Computed tomography, 3D recon- struction of the SCC region in a 63-year-old man. There is pro- nounced calcification of the first costal car- tilages with a cleft-like space and osteophytes on the right side (ar- rows). There are also degenerative changes at other sternocostal joints most pro- nounced correspond- ing to the left-sided second and fourth to seventh joints
Anne Grethe Jurik
4.5
Conclusions
The sternoclavicular, manubriosternal and sternocostal joints are important for the biomechanics of the chest during respiration. This implies a nearly constant strain on the joints, which may result in degenerative changes. In addition, the sternoclavicular joints accompany every movement of the arms being the only joints between the trunk and the upper extremities.
References
1. Asley GT (1954) The morphological and pathological significance of synostosis at the manubrio-sternal joint. Thorax 9:159–166
2. DePalma AF (1957) Degenerative changes in the sternoclavicular and acromioclavicu- lar joints in the various decades. Thomas, Springfield, Illinois
3. DePalma AF (1963) Surgical anatomy of acromioclavicular and sternoclavicular joints.
Surg Clin North Am 43:1541–1550
4. Hagemann R, Ruttner JR (1979) [Arthrosis of the sternoclavicular joint.] Z Rheumatol 38:27–38
5. Langen P (1934) Untersuchungen űber Altersveränderungen und Abnutzungserchei- nungen am Sternoclaviculargelenk. Virchows Arch Pathol Anat 293:381–408
