In the acute setting, a thorough history and physical examination must be done. Mechanism of injury information should be obtained, as it can help predict the spectrum of injuries that may have occurred. The neurovascular structures need to be completely and thoroughly evaluated. Additionally, the shoulder and distal forearm should be examined as these structures may be injured concomitantly.

AP and lateral radiographs should be obtained to evaluate the spectrum of injury. Gentle closed reduction of the fracture-dislocation should be attempted, and use of sedation with muscle relaxation can minimize patient discomfort. Generally, in-line traction followed by elbow flexion will reduce the elbow. A post-reduction neurovascular exam should be performed. Post-reduction radiographs should also be scrutinized for widening or nonconcentric reduction, which may represent an entrapped osteochondral fragment. CT scans are extremely valuable for both injury evaluation and surgical planning.

Patients with a history of chronic elbow instability should have a similar initial evaluation of patients with acute instability. A thorough history should be performed focusing on possible missed or unrecognized injury. Additionally, any history of prior procedures attempted at stabilizing the elbow joint should be sought. Physical exam should focus on range of motion of the elbow joint and provocative maneuvers to elucidate any instability. A thorough neurovascular exam should also be performed. AP and lateral radiographs should also be obtained to evaluate if the elbow has a concentric reduction and to evaluate the presence of any arthritis. CT scans are routinely obtained as there are often chronic bony injuries resulting in persistent instability. MRI may also be useful if there is concern for an associated tendon injury or there is a question regarding the status of the ligamentous stabilizers. More information is better in the management of these difficult injuries since the chance for a successful result is completely dependent on the full understanding of the injury spectrum prior to treatment.

In general, the use of an external fixator , either static or hinged, remains a rare, but useful option for the treatment of acute elbow instability . Surgeons should first determine if they could achieve stability through nonoperative care. If surgical intervention is warranted, surgeons should make all attempts to address all components of bony and soft tissue instability. This includes fixation or replacement of the radial head, fixation of the coronoid, and repair of the lateral and, if needed, medial ligaments. If the elbow remains unstable following surgical fixation, techniques of which are addressed in other chapters, then the surgeon should proceed with placement of an external fixator [2–4]. Persistent instability is most commonly encountered in the acute setting when fracture fixation of the coronoid or proximal ulna is tenuous or coronoid process fragments are irreparable. External fixation may be utilized to stabilize the elbow in the setting where the coronoid is not repaired due to severe comminution or to protect the elbow in cases where the coronoid process is grafted.

For patients with acute gross elbow instability who have sustained poly-trauma or are in a medical condition that prohibits them from undergoing an extensive elbow repair, it is reasonable to proceed with using an external fixator for temporary or definitive stabilization of the elbow [3, 4].

Similarly, for patients with chronic instability, surgeons must first determine if the elbow is salvageable for reconstruction or if they should proceed with arthroplasty. If reconstruction is chosen, surgeons should again attempt to reconstruct all bony and ligamentous components that are responsible for instability. Similarly, if the elbow is not stable through full range of motion after surgical reconstruction, then an external fixator should be placed for added stability. In the chronic setting, fixators are typically adjuncts to when bony stabilizers are compromised, as in the acute setting, and/or the ligamentous stabilizers are compromised and require reconstruction. External fixators can also be used for added stability following total elbow arthroplasty in the setting of chronic instability [3].

Placement of a uniplanar static external fixator in the setting of surgical management for either acute or chronic instability is relatively straightforward, but certain pitfalls may still occur. In general, most surgeons recommend placement of two humeral and two ulnar pins.

Lateral humeral pins are most commonly used as they are easier to place based on patient positioning, and are generally placed first. Half pins should be placed without impaling any major muscle-tendon units or jeopardizing neurovascular structures, and should have bicortical purchase. The proximal lateral pin should be placed very carefully, as it will usually be in the vicinity of the radial nerve. Some surgeons recommend making a small incision laterally to ensure that the radial nerve is not injured for humeral pins [13]. In terms of radial nerve location, Kamineni et al. have evaluated the location of the radial nerve in reference to the lateral epicondyle as it exits the posterior compartment of the arm in relation to the transepicondylar axis distance [14]. The average transepicondylar axis distance was 62 mm and the average distance from the lateral epicondyle to the radial nerve was 102 mm. The transepicondylar distance was highly correlated to the distance from the lateral epicondyle to the radial nerve (Pearson correlation coefficient, r = 0.95). The authors recommended that the absolute safe zone for pin entry into the lateral distal humerus is the area lying within the caudad 70 % of a line, equivalent in length to the patients own transepicondylar axis distance, when projected proximally from the lateral epicondyle. If medial pins are placed, an open incision should be made to protect the ulnar nerve [3]. The safest location for pins is likely directly posterior through the triceps muscle (Figure of the static fixator with posterior pins). Carlan et al. evaluated the location of the radial nerve as it crosses the posterior humeral shaft and determined that the nerve as it crosses is within 0.1 mm of the most distal aspect of the deltoid tuberosity [15]. Consequently, the distal aspect of the deltoid tuberosity can be used as a landmark for the location of the radial nerve as it crosses the posterior aspect of the humeral shaft and direct posterior pins should be placed distal to this landmark.

Ulnar pins can be placed in either a dorsal-to-volar or lateral-to-medial direction based on surgeon preference, and should be placed with the elbow concentrically reduced. Again, care should be made to not violate any important neurovascular structures. Half-pins should be bicortical. In general, 4 mm pins are placed in the ulna with the goal of 4–5 cm of spread between the pins. On the humeral side, care must be taken to avoid the radial nerve, and 5 mm pins are generally placed above the radial nerve in the anterolateral aspect of the humerus with the goal of attaining 4–5 cm of spread. Pins can also be placed posteriorly on the humerus (Fig. 15.2). The frame should be applied to the half-pins with the elbow concentrically reduced in its most stable position (generally 90° of flexion and pronation). With a highly unstable reduction, the joint may be temporarily pinned with a stout Kirschner wire [2, 3, 16]. Ring et al. demonstrated equivalent outcomes following cross pinning of a joint compared to external fixation with less device related complications [16]. Caution still needs to be exercised with cross pinning of the joint as the articular cartilage can be injured, the cross pins can break and make removal very difficult and infection can be devastating therefore static external fixation is preferred over cross pinning.

Placement of a hinged external fixator may depend on the company specifications of fixator used, but certain general principles still apply. All hinged external fixators utilize a central axis pin to center the hinge. This pin must be collinear with the center of rotation of the elbow joint in order to minimize excess forces about the fixator and prevent pin loosening. The center of rotation of the elbow lies in the center of the capitellar circumference on the lateral condyle and just distal and anterior to the medial epicondyle [3, 4, 8, 9]. This should be verified under direct fluoroscopic visualization on the lateral view. On the AP view, the pin should be traversing parallel to the elbow joint line [3, 8, 9]. Perfect placement of the axis pin is very technically challenging, and improper placement can cause more instability. Madey et al. reported misalignment of 5° caused a 3.7-fold increase in motion energy, and a 10° mismatch yielded a 7.1-fold increase in energy [10]. Based on the system used, the axis pin may require unicortical or bicortical fixation .

Once the axis pin has been placed and perfect placement confirmed, placement of humeral and ulnar half-pins follow similar fashion as static fixators. Lateral humeral pins are most common type with each system, and ulnar pins depend on the type of fixator used. Again, it is important to have the elbow concentrically reduced once the frame is applied, and range of motion should be checked under fluoroscopic guidance to ensure that the elbow remains stable throughout [3, 6, 9].

The authors’ prefer to address all bony and ligamentous repairs/reconstructions prior to placing any pins needed for the external fixator. Patients are usually supine with the arm on a hand table. Placing the axis pin remains the most technically challenging step in placement of a hinged external fixator. Intra-operative fluoroscopy is needed to ensure proper placement of the pin. In general, we aim to place pins lateral to medial, with the pin centered on the axis of rotation on the lateral epicondyle. Fluoroscopy is then used to confirm placement and ensure that the pin is parallel to the articular surface. We currently have no specific preference on commercial manufacturer of the frame.

Acute simple elbow dislocations are generally treated with closed means and early return to motion [17]. There is however a small subset of patients that have significantly persistent instability, especially posterolateral rotatory instability [18, 19]. Hopf et al. investigated the outcomes of using a hinged external fixator to help stabilize acute simple dislocations . In this series, a specific subset of 26 patients with simple dislocations, who were felt to be at high risk for recurrent instability due to subluxation seen on fluoroscopic exam or provocative physical exam maneuvers following initial closed reduction were included for evaluation. At a mean of 2.5 days from injury, a hinged external fixator was placed without any ligament repair for a total of 6 weeks. The authors found excellent outcomes with an average Mayo Elbow Performance Score (MEPS) of 93.5. They found minimal loss of range of motion compared to the patients’ normal contralateral elbow. Overall, 18 joints were found to be clinically stable, and eight had mild evidence of clinical instability. Radiographically, patients were found to have significantly increased varus and valgus instability on dynamic ultrasound examination. Pin site infection occurred in four patients (15.4 %), and one patient required surgical debridement of a pin site infection. One patient did sustain an ulnar fracture through a pin site that did not require surgical intervention. Overall, the authors concluded that external fixator placement in unstable simple elbow dislocations provides patients with excellent results. This study is limited, in that they did not have a control group of patients treated by closed means, and not all of these patients were simple dislocations as they found evidence of 3 type I coronoid fractures in their cohort.

The majority of case series investigating the use of hinged external fixators about the elbow focuses on their use in the setting of elbow fracture-dislocations, most commonly terrible triad injuries . The results are all generally good to excellent in regard to clinical outcomes and stability of the joint. Common complications reported include pin site infection and loosening, fracture through pin sites, recurrent instability, and neurovascular injury. Due to the low number of patients, the studies present a fairly mixed cohort of patients in terms of the spectrum of injuries treated.

Early reports of the use of hinged external fixators focused on fixators in the setting of recurrent complex instability following prior surgical management. McKee et al. investigated 16 patients who had all failed prior open repair of their complex instability injuries [20]. Patients averaged 2.1 unsuccessful surgeries before placement of a fixator occurred at an average of 4.8 weeks after injury. Initial surgeries attempted to repair or reconstruct all bony and ligamentous injuries. Fourteen patients had fixators as a subsequent procedure following initial surgical fixation. Two patients had frames placed at the time of their initial surgical repair. They found mixed results with an average flexion–extension range of 105° (65–140). At average 23-month follow-up, MEPS scores ranged from 49 to 96, with 12 patients obtaining good or excellent results. This small cohort had six complications, but only one episode of recurrent instability.