Transitory inferior subluxation of the humeral head is a well documented phenomenon that can occur after shoulder trauma or surgery in adults.^1,2,6,7 The etiology is either from a large joint effusion, or more likely, from temporary atony of the deltoid and rotator cuff muscles secondary to axillary neuropraxia. This subluxation is characterized by a mid point of the humeral head which lies at the inferior lip of the glenoid, rather than at its center. In adults, the incidence of inferior shoulder subluxation ranges from 10% to 60%, depending on the mechanism of injury.⁶

To date, however, inferior subluxation of the humeral head has not been reported in children. Furthermore, transitory inferior dislocation of the humeral head as a sequela to trauma has not been described. This article is a case report of a 14-year-old girl who developed a transitory inferior shoulder dislocation after sustaining a proximal humerus fracture. Unlike true traumatic fracture dislocations, it required only support of the arm in order to "reduce" the joint and maintain its position within the glenoid.

A 14-year-old African-American female who was involved in a motor vehicle accident impacting the right side where she was a belted passenger. She sustained a right proximal humerus fracture with angulation and displacement. Her neurovascular status demonstrated a slight decrease in sensation over the axillary nerve distribution. With open physis, her fracture position was considered acceptable (Figure 1) and she was placed into a coaptation splint.

Figures 1A & B (A) AP and (B) lateral radiographs of the proximal right humerus showing a fracture with an acceptable amount of displacement in a skeletally immature individual. Note the reduced position of the humeral head within the glenoid.

She returned for follow-up 5 days later where repeat radiographs showed inferior dislocation of the humeral head (Figure 2). She was taken to the fluoroscopic suite, where the fracture was examined and noted to be unstable with manipulation, while the "dislocation" could be "reduced" by mere support of the arm. She underwent percutaneous pin stabilization of the shoulder the following day, with intraoperative images demonstrating a stable, located shoulder joint to all ranges of motion (^{Figure 3A}).

Figure 2 Follow-up radiograph 5 days later showing a dislocated right shoulder joint.

In the PACU, postoperative pinning radiographs again demonstrated inferior dislocation (^{Figure 3B}) and she was placed into a two arm shoulder spica cast with good support under the right elbow. This completely reduced the glenohumeral joint (^{Figure 3C}). She maintained reduction of the humeral head within the glenoid fossa with the cast and was kept in the shoulder spica for a total of six weeks.

The pins were removed in the operating room without complications after complete healing and postoperative radiographs demonstrated maintenance of the reduced position of the humeral head. She was stiff in the shoulders as anticipated and was started on physical therapy. At final follow-up 10 months later, she has full range of motion and strength. She also has a well reduced shoulder joint without delayed sequelae (Figures 4A-D).

Figures 4 A-D Final follow-up 10 months later. A & B show a well-healed fracture with a well-reduced joint. C & D are clinical photographs showing full range of motion.

Trauma to the shoulder may result in injuries that can range from rotator cuff strain and glenohumeral subluxation to proximal humerus fractures and joint dislocations. The most common direction for traumatic shoulder dislocations is anterior, however, luxatio erecta may rarely occur.^3,5 The incidence of luxatio erecta, or inferior shoulder dislocation, is less than 1% of all shoulder dislocations, but it has a pathognemonic history and presentation with the shoulder in abduction, the elbow flexed and the forearm held behind the head. Luxatio, as with any traumatic shoulder dislocations, requires a closed reduction under sedation or anesthesia in order to obtain alignment and avoid complications, such as avascular necrosis.

Transitory inferior dislocation is an even more rare condition that can also occur after shoulder trauma in patients of any age. We report a case occurring in a 14-year-old girl. In contrast to the traumatic fracture dislocation, transitory inferior dislocation is not likely to result in an unstable joint or any other complications if properly supported. This is a more exaggerated presentation of the well know transient inferior subluxation phenomenon that can occur after proximal humerus trauma or rotator cuff surgery in adults.

The etiology of this transient subluxation or dislocation at the glenohumeral joint is hypothesized to be either from a large joint effusion or, more likely, from partial atony of the deltoid and rotator cuff muscles.^4,7 The weakened muscles are subjected to a stretching force which they may be unable to withstand. The result is subluxation, or to the extreme, complete dislocation out of the glenohumeral joint.

Transient subluxation or dislocation of the shoulder may exist without giving rise to symptoms. This subluxation or dislocation usually does not occur immediately following the injury. It typically occurs a few days or weeks following the injury. In this case, it was noted on the patient's first follow up 3 days after the injury. When mildly subluxed, the shoulder recovers on its own after the muscle tone is restored. This usually takes 4 to 6 weeks. Even when overlooked, mild subluxation usually will not result in persistent subluxation or loss of function directly attributable to this lesion. With complete, although transient, inferior dislocations, the shoulder should be more aggressively treated with support to maintain reduction for the duration of the 4 to 6 weeks. This may be in the form of a sling or shoulder spica cast. End results are uniformly good.

In summary, we present a case of an adolescent with an extreme form of transitory inferior subluxation, (i.e. transitory inferior dislocation), after a proximal humerus fracture with axillary neuropraxia. Unlike traumatic fracture dislocations of the proximal humerus, it occurred a few days after the initial injury and required only the support of the arm for 6 weeks in order to "reduce" the dislocation. This is a phenomenon that can happen after injury and an awareness of its presence may avoid more aggressive "reductions" and anesthesia than is really necessary.