The sternoclavicular joint is the only true joint between the upper shoulder strap and the trunk [12]. The clavicular notch of the manubrium is less than half the inner end of the clavicle; therefore, it is potentially uncoordinated and unstable. Its stability mainly depends on the reinforcement of the surrounding ligaments, which makes it the smallest bone-stable joint in the body. SCD is a relatively rare dislocation in clinical practice [13]. It is mostly caused by a large external force applied directly to the anterior part of the clavicle, pushing the proximal part of the clavicle behind the sternum and resulting in posterior SCD. Posterior dislocations are less common than anterior dislocations [2, 14]. However, because of the proximity of important structures to the medial posterior clavicle, accurate identification of posterior dislocations is important. Diagnosis is based on three aspects: medical history, clinical manifestations, and auxiliary examination.

Some studies [15, 16] have reported that early surgical treatment was adopted for posterior SCD, and that open reduction and internal fixation became the preferred treatment for this fracture type for young patients and patients requiring high activity [17]. While there are numerous surgical techniques, including large Kirschner wire, cannulated screws, suture anchor fixation or plate fixation [18,19,20,21,22], it is worth noting that operative methods utilizing metallic pin fixation with K-wires, Steinmann pins, and threaded pins with bent ends are associated with severe complications, including fatalities, across all age groups and are now contraindicated [23]. Georgios et al. used suture buttons to reduce and fix the sternoclavicular joint, with one button on the superior surface of the medial end of the clavicle and the other button on the anterior surface of the sternum; function was good at the 12-month follow-up. The use of suture buttons was also reported for superior dislocation, but its efficacy on posterior sternoclavicular joint dislocation remains uncertain [24]. Wire cerclage techniques were used to stabilize sternoclavicular joints during open reduction, resulting in satisfactory shoulder motion range. However, chronic mild pain was reported [25]. Alternative approaches involve resecting the medial part of the clavicle [21, 26] and employing various soft tissue methods for costoclavicular ligament reconstruction, such as suture repair of the costoclavicular or sternoclavicular ligaments [27], costoclavicular tenodesis using the subclavius muscle, sternoclavicular tenodesis using the sternal head of the sternocleidomastoid muscle [27] and sternoclavicular joint reconstruction with the semitendinosus, hamstrings, palmaris longus, or allograft tendon [28,29,30]. In these surgeries, either the amphiarthrodial function of the sternoclavicular joint is sacrificed to achieve adequate fixation, or postoperative complications, such as internal fixation displacement, reduction loss, and infections, are usually observed because of complex surgical manipulation. Currently, there is no well-recognized internal fixation equipment suitable for posterior sternoclavicular dislocation and medial clavicle fractures.

Behind the proximal clavicle are important structures such as the apex pulmonis, mediastinum, and the subclavian artery and vein; thus, surgeries in this area are high-risk. In addition, SCD treatment does not use a special steel plate, and it usually uses internal fixation instruments designed for other diseases [31]. Generally, the risk for surgical complications is high; therefore, safe and effective internal fixation devices and surgical procedures for SCD are required. Alternatively, an external force is directly applied to the front of the proximal clavicle, which is pushed behind the sternum, resulting in posterior dislocation of the proximal clavicle within the sternoclavicular joint. Because closed reduction of posterior SCD mostly requires general anesthesia and that patients’ CT scans indicated that neurovascular structures are in close proximity to the dislocated clavicle, we did not attempt closed reduction in patients with posterior SCD, instead opting for open reduction.

The sternoclavicular hook plate is a special type of steel plate designed to treat SCD; the treatment of posterior SCD has obtained a good curative effect, as follows: (1) The sternoclavicular hook plate’s mechanical stability is adequate due to its sternal bone hole activity while preserving the sternoclavicular joint micro-motion; thus, patients can perform early functional exercises. Iin this study, both the Constant–Murley and Rockwood sternoclavicular joint scores suggested that postoperative acromioclavicular and sternoclavicular joint functions could be effectively restored. (2) When a sternoclavicular hook plate was used, the surgical incision exposed only a third of the medial clavicle and a part of the sternum, and the insertion point of the sternocleidomastoid muscle was well preserved. Furthermore, it had less interference on soft tissues and blood vessels around the joint; therefore, the sternoclavicular hook plate was beneficial for dislocation healing after surgery. (3) The hook part of the sternoclavicular hook plate is close to the rear of the sternoclavicular joint in an arc, effectively avoiding injury to important blood vessels and organs behind the proximal clavicle. The threaded head of the hook can be effectively fixed on the anterior edge of the sternum by adding nuts and spacers to avoid complications such as posterior loosening and displacement of the internal fixation.

Attention should be paid when using internal fixation in elderly patients with osteoporosis. When the sternal end is drilled and inserted into the hook part of the plate, the activity of the upper limb is transmitted to the hook plate through the clavicle. The hook head becomes a major force release point that forms an axis of activity, and bone absorption occurs around the hook head on the sternal side. If vigorous activity is performed early, the loose sternum may not be strong enough to block the trending force of clavicle dislocation, which can lead to a cut and result in failure of internal fixation.

Posterior SCD often occurs in highly violent injuries during athletic events or motor vehicle accidents [13, 32]. Most commonly, an indirect force on the posterolateral shoulder forces the lateral clavicle anteriorly and levers the medial clavicle posteriorly. Less commonly, a significant posterior force is applied to the medial clavicle [33, 34]. Early diagnosis of this disease is often obscured by the presence of other sites such as the head, chest, and abdomen. After the patient’s condition is stabilized, further comprehensive examination is necessary. Traditional internal fixation methods are prone to losses, which can lead to fixation failure. The end of the sternoclavicular hook plate was inserted from the rear of the sternum through a sternal hole and was hooked to the sternum. After completion of internal fixation, the entire structure maintains the original micro-dynamic environment of the sternoclavicular joint and meets the biomechanical requirements. Treatment experiences are as follows: (1) When the hook part of the sternal hook plate is used to enter the sternum, the lymph and veins behind the sternum should be gently separated with a long and bent nerve dissector. (2) When drilling the sternum and clavicle, our specially made drill jig should be used to avoid excessive drilling and damage to the nerves, blood vessels, and organs behind the bone. (3) In the treatment of posterior dislocation, a thin spacer and locking nut must be installed at the head of the thoracic hook plate to prevent backward displacement.

The clinical incidence of posterior SCD is low. This study did not compare the sternoclavicular hook plate internal fixation method with other internal fixation methods. At the same time, prevention of posterior SCD with sternoclavicular hook plates in patients with osteoporosis requires further investigation. With further research, better results could be achieved in patients with posterior SCD.