INTRODUCTION

By definition, a dynamic hinged external fixation allows for an axis of rotation to provide elbow stability and motion following trauma or reconstruction.³⁰ With a properly constructed device, the ulna may be separated or distracted from the humerus and still allow physiologic flexion and extension. The mechanics and anatomic landmarks for the application of several fixator devices have been well defined.^6,^20,²⁸ The axis of rotation of the distal humerus passes through the tubercle of origin of the lateral collateral ligament and through the anteroinferior aspect of the medial epicondyle (Fig. 33-1). Replication of the axis of rotation is essential to avoid pin loosening, persistent stiffness, or instability. In cadaver models, 5 mm of translation or 5 degrees of angulation results in a fourfold increase in resistance to elbow flexion.¹⁵

FIGURE 33-1 On the medial side, placement of the axis pin is at the anteroinferior aspect of the medial epicondyle. On the lateral side, the center of rotation is at the tubercle of the lateral epicondyle, which is at the center of the projection of the curvature of the capitellum.

INDICATIONS

External fixation allows for flexion of the elbow to prevent contracture while still maintaining joint space and appropriate coronal alignment (Fig. 33-2).¹⁸ The hinged fixator, when properly applied, maintains a reduced and balanced ulnohumeral joint during motion, thereby protecting repaired or reconstructed collateral ligaments. In trauma, fixators may be used to protect operative fixation of unstable fractures and ligament repair in cases of persistent postoperative instability and for longstanding elbow dislocation or recurrent instability.⁹ In reconstruction of the elbow, hinged fixators can also be used in the treatment of instability, following ligamentous repair, or with interposition arthroplasty.^3,¹⁹

FIGURE 33-2 An articulated external fixator (1) allows flexion motion, (2) protects the ligaments from varus and valgus stress, and (3) separates the joint.

Although goals of treatment may be attained with relatively simple designs, greater flexibility and broader utility have been introduced by Hotchkiss with a more complex fixation. Although several designs are currently available (Fig. 33-3), only the Mayo dynamic joint distractor (DJD)¹⁹ and the Hotchkiss Compass Hinge¹² are discussed in this chapter because they represent the spectrum from simple to complex.

FIGURE 33-3 A variety of articulated external fixators are currently available. Note: All are based on identity of the axis of rotation with variable means of skeletal attachment and distraction. Illustrated here in increasing order of complexity: DJD II (Stryker, Kalamazoo, MI) (A), Orthofix Inc. (McKinney, Texas) (B), OptiROM (EBI, Parsipanny, New Jersey) (C); and Compass (Smith & Nephew, Mississauga, Ontario, Canada) (D).

TRAUMA

In many traumatic circumstances, the goal is to “neutralize” the forces across the joint while elbow motion is maintained. The fixator can be applied acutely as an adjunct to operative repair or as a secondary measure in case of reduction failure. The specific indications for dynamic external fixators of the elbow in acute trauma include the following: (1) instability, (2) articular injury, and (3) residual or recurrent subluxation.

Instability

Elbow dislocation with extensive soft tissue injury results in gross instability, even after reduction or repair of involved structures.⁵ Adjunctive management of late untreated elbow dislocations involve the use of an external fixator.⁹

Articular Injury (Fracture-Dislocation)

This category includes instability with fractures of the radial head,^17,²¹ some olecranon fractures (Mayo type III)¹⁶ as well as Regan-Morrey type II and III coronoid fractures.^13,²³ Use of a hinged fixator for complex, unstable distal humerus fractures has also been described.⁷ Open fixation is the primary treatment modality. When gross instability persists or when fixation is deemed vulnerable, an external fixator can be added to allow for immediate postoperative motion and neutralization or unloading of the stresses placed on the fracture fixation (Fig. 33-4).

FIGURE 33-4 Fracture-dislocation in 38-year-old radiologist involving the comminution of the coronoid. Anteroposterior (A), lateral (B). After fixation with screws and a buttress plate the elbow was stabilized and neutralized with the DJD external fixator. Note position of the pins referable to the intercondylar distance. C, Lateral projection with external fixator. Note replication of axis of rotation by the fixator (D). At 8 weeks the patient has virtually extension (E) and full flexion (F) and has returned to work.

Residual or Recurrent Subluxation

Residual or recurrent subluxation after simple or complex fracture-dislocation is the third indication for use of a fixator.²⁴ In this setting, percutaneous fixator application can assist in reducing a subluxated joint without having to revert to an open procedure. Maintenance of the device allows for early motion with minimal risk of frank redislocation or continued subluxation. The added stability facilitates proper healing of the capsule and soft tissue restraints.

RECONSTRUCTION

The same basic goals obtain for the use of the fixator after reconstructive interventions.

Ankylosis

When arthrolysis for the post-traumatic joint stiffness is carried out, release of the collateral ligament is sometimes necessary, as well as excision of capsular and bone restraints.^8,¹⁹ These releases can result in instability. Application of the device protects the repaired collateral ligaments after the arthrolysis while allowing immediate motion of the stabilized concentric joint.

CONTRAINDICATIONS

RELATIVE CONTRAINDICATIONS

1. Local sepsis at desired site of pin insertion. The external fixation pins should not be placed through infected bone or skin. They may be placed through areas of exposed tissue, although this is clearly less desirable. In trauma cases, ideally they are placed outside of the zone of injury and ideally should be located away from areas of anticipated hardware or prostheses placement. The fixators can be used to stabilize a septic joint, which on occasion is helpful. However, care must be taken to ensure that the pins of the device are fixed to bone in areas free of infection or local cellulitis.

2. Altered anatomy. When uncertainty exists regarding the anatomic location of the neurovascular structures due to post-traumatic or postoperative disturbance of the anatomy, a careful dissection with protection of the vulnerable nerves (usually the ulnar and radial) must be made when fixator placement is necessary.

3. The presence of fracture fixation devices in the humerus or proximal ulna, making pin placement impossible. (There is some flexibility for pin placement. The presence of internal fixation does not absolutely preclude use.)

4. Inexperience with the use of external fixation devices.

5. Patient inability to comply with pin site care or rehabilitation program.

SELECTION OF FIXATOR CONFIGURATION

Over the last several years, a number of experiments have been conducted in our laboratory to better understand the function and indications for external fixator configuration. One such assessment demonstrated that compression across the joint with the half-pin lateral application of an external fixator doubles the stiffness of the system in varus load when in extension but had much less effect otherwise. Thus, distraction, one of the recommended applications of the articulated external fixator, does render this system less stable than when the articulation is compressed.²⁷ Of particular importance is the study of Kamineni et al.¹⁰ which released the medial and lateral collateral ligaments and assessed the kinematic pattern with a half-pin laterally applied external fixator. In this experiment, it was demonstrated that both varus and valgus stability was restored even with the half-pin lateral configuration and even with up to 7 N out of plane load applied to the forearm (Fig. 33-6). Rotational stability, however, was not as reliably restored (Fig. 33-7). An additional clinical relevant experiment sought to assess the sensitivity of pin placement approximating the axis of rotation. It has been shown that increased energy is needed to move the elbow if a nonoptimum application of the articulated external fixator occurs.¹⁵ A subsequent assessment in our laboratory demonstrated that the nonoptimum placement of an external fixator, however, did not alter the kinematics as much as had been anticipated (Fig. 33-8). Based on these data, it was concluded that a slight proximal placement of the axis of the external fixator actually enhances the rigidity of the elbow in a manner that would favor reconstruction of the lateral ulnar collateral ligament. Thus, there may be instances in which slight nonanatomic axis placement is clinically acceptable.²

FIGURE 33-6 Analysis of varus/valgus stability in a normal elbow and following medial and lateral collateral ligament disruption. Note that half-pin configuration applied laterally restores stability even when both medial and lateral collateral ligaments have been disrupted and with both varus and valgus loading conditions.

(After Kamineni, S., Hirahara, H., Neale, P., O’Driscoll, S. W., An, K-N., and Morrey, B. F.: Effectiveness of the lateral unilateral dynamic external fixator after elbow ligament injury. J. Bone Joint Surg. Am. 89:1802, 2007.) (With permission, Mayo Foundation.)