Hinged External Fixators of the Elbow

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CHAPTER 33 Hinged External Fixators of the Elbow

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

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

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.

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).

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.

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

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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.)

Hence, based on these experiments, our current practice is to employ the lateral half-pin application of the DJD II in virtually all clinical settings in which the fixator is believed to be necessary.

TECHNIQUE

MAYO DYNAMIC JOINT DISTRACTOR

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