Limitations of Ligamentotaxis

Ligamentotaxis has a number of shortcomings when applied to the treatment of displaced intra-articular fractures of the distal radius. First, since ligaments exhibit viscoelastic behavior, there is a gradual loss of the initial distraction force applied to the fracture site through stress relaxation. The immediate improvement in radial height, inclination, and volar tilt are significantly decreased by the time of fixator removal ( Fig. 9-2 A and B).

Limitations of ligamentotaxis . A, Marked radial shortening. B, Initial overdistraction restores radial length. C , Note the persistent dorsal tilt of the articular surface even with maximum distraction.

Traction does not correct the dorsal tilt of the distal fracture fragment. This is because the stout volar radiocarpal ligaments are shorter and they pull out to length before the thinner dorsal radiocarpal ligaments exert any traction. Excessive traction may actually increase the dorsal tilt ( Fig. 9-3 A–C). A dorsally directed vector is still necessary to restore the normal volar angulation. This is usually accomplished by applying manual thumb pressure over the dorsum of the distal fragment. With intra-articular fractures, ligamentotaxis reduces the radial styloid fragment, but for the above reasons it does not reduce a depressed lunate fragment. When there is a sagittal split of the medial fragment, traction causes the volar medial fragment to rotate, which often necessitates an open reduction. External fixation cannot control radial translation and therefore cannot be used with an unstable distal radioulnar joint (DRUJ) ( Fig. 9-4 A and B).

Stress relaxation . A, Note the overdistraction of the radiocarpal joint and the restoration of radial length. B, Two weeks later, there is a loss of radial length, and the joint space is no longer overdistracted.

Unstable distal radioulnar joint . A, Unstable distal radius fracture with disruption of the distal radioulnar joint. B , The medial (sigmoid notch) fragment follows the ulnar head owing to the intact radioulnar ligaments and cannot be stabilized with K wires and bridging external fixation.

Fracture Site Loads

External fixation is considered flexible fixation. The biomechanical requirements of external fixation for fractures of the distal radius have not been ascertained until recently; the magnitude and direction of the physiologic loads on the distal radius were dynamic and unknown. Recent work by Rikli and colleagues, however, has shed new light on this point. Using a new capacitive pressure-sensory device, this group measured the in vivo dynamic intra-articular pressures under local anesthesia in the radioulnocarpal joint of a healthy volunteer. With the forearm in neutral rotation, the forces ranged from 107 N with wrist flexion to 197 N with wrist extension. The highest forces of up to 245 N were seen with the wrist in radial deviation and the forearm in supination. Presumably, any implant or external fixator would need to be strong enough to neutralize these loads to permit early active wrist motion. Rikli and colleagues also identified two centers of force transmission. The first center was opposite the scaphoid pole, which would represent the radial column. The second center, which would represent the intermediate column of the wrist, took a considerable amount of the load and was opposite the lunate, extending ulnarly over the triangular fibrocartilaginous complex (TFCC).

Fixator Frame Rigidity

The strength of the fixator depends on the rigidity of the connecting rods and the clamps. Many external fixator rods are 0.5 to 1.0 cm in diameter, although radiolucent rods made from PEEK (polyetheretherketone), Ultem (polyetherimide), or carbon fiber may be larger. Increasing the diameter of the rods increases the rigidity by a factor of 4. Uniplanar fixators are common, but the rigidity of the construct can be increased by adding a second parallel rod. Placing the rod as close to the skin as possible also increases the stability against bending loads by reducing the lever arm from the neutral joint axis. Most distal radius external fixators use 3.0- or 4.0-mm threaded half-pins. Modern threaded pins are hence designed with a larger-core diameter and smaller-core thread diameter. If the pin threads are buried, the larger pin diameter at the near bone interface resists bending forces, whereas the small-core thread resists pullout forces at the far cortex. A bicortically inserted pin with a very short thread provides the best pin-bone fixation. Theoretically, underdrilling the pin hole by 0.1 mm provides the best pin fixation with the least risk of bone resorption and pin loosening. It is also desirable to spread the force evenly across the entire shaft of the bone by creating a wide separation of the fixator pins. To achieve stable fixation and reduce the lever arm of displacing forces, the pins should be inserted close to the fracture site. One pin is therefore inserted close to the fracture site, and the second pin is placed as far away as possible.

Construct Rigidity

Increasing the rigidity of the fixator does not appreciably increase the rigidity of fixation of the individual fracture fragments. However, there are a number of ways in which to augment the stability of the construct. After restoration of radial length and alignment by the external fixator, percutaneous pin fixation can lock in the radial styloid buttress and support the lunate fossa fragment. A fifth radial styloid pin attached to the frame of a spanning AO (Synthes, Paoli, PA) external fixator prevents a loss of radial length through settling and leads to improved wrist range of motion compared with a four-pin external fixator. The addition of a dorsal pin attached to a sidebar easily corrects the dorsal tilt found in many distal radius fractures.

Kirschner (K)-wire fixation enhances the stability of external fixation. The combination of an external fixator augmented with 0.62-inch K wires approaches the strength of a 3.5-mm dorsal AO plate. Supplemental K-wire fixation is more critical to the fracture fixation than the mechanical rigidity of the external fixator itself. Stabilizing a fracture fragment with a nontransfixing K wire that is attached to an outrigger is just as effective as a K wire that transfixes the fracture fragments.

Temporary External Fixation: Indications

Compared with conventional plate fixation, bridging external fixation may be used in a temporary manner, or it may be used for definitive management of the distal radius fracture. Bindra has listed the following indications for this technique:

• 1.
  

  Initial management of severe-grade open fractures with extensive soft tissue loss ( Fig. 9-5 A–C)

  
  

  
  

  
  

  

  
  

  
  

  A, Open distal radius fracture. B, X-ray appearance. C , Temporary stabilization with a bridging external fixator.

  
  
  
  
• 2.
  

  Temporizing measure to resuscitate a polytraumatized patient

  
  
• 3.
  

  Pending transfer to a tertiary referral facility for definitive fracture management

Rikli and colleagues use temporary bridging external fixation for complex fractures both to aid in the provisional fracture reduction and to allow a better computed tomography (CT) evaluation of the fracture characteristics prior to double-plate fixation.

Definitive External Fixation: Indications

The following are indications for use of a definitive external fixation:

• 1.
  

  Unstable extra-articular distal radius fractures

  
  
• 2.
  

  Two-part and selected three-part intra-articular fractures without displacement

  
  
• 3.
  

  Combined internal and external fixation

Contraindications

Bridging external fixation should not be used as the sole method of stabilization in the following situations:

• 1.
  

  Ulnar translocation due to an unstable DRUJ

  
  
• 2.
  

  Intra-articular volar shear fractures (Barton’s and reverse Barton’s fractures)

  
  
• 3.
  

  Disrupted volar carpal ligaments/radiocarpal dislocations

  
  
• 4.
  

  Marked metaphyseal comminution

Combined index and middle finger metacarpal fractures preclude the use of this technique owing to the interference with distal pin site placement.

Surgical Technique

The patient is positioned supine on the operating table with the arm abducted on an arm board. Finger traps with some type of traction either with weights and an overhead arm holder or an arthroscopy tower may be used unless the fixator has distraction capabilities. A tourniquet facilitates pin insertion, but it is not mandatory, especially in the face of massive soft tissue swelling, vascular impairment, or marked infection. The fixator is applied under fluoroscopic control. A 2-cm incision is made over the radial aspect of the index metacarpal base, although the middle finger metacarpal may be substituted. The interosseous fascia overlying the metacarpal is incised and reflected laterally. The extensor tendon(s) are identified and protected as well as the branches of the superficial radial nerve. Hohmann spike retractors simplify soft tissue retraction. The fixator pin hole is predrilled with a smaller drill diameter to increase the friction fit. The pin is then inserted by hand to minimize the risk of thermal bone necrosis and subsequent pin loosening or infection. A double-pin clamp or any supplied pin guides are then used to insert the second pin, parallel with the first pin. Pin convergence or divergence makes double-pin clamp application laborious, but does not interfere with single-pin clamp application.

It is my preference to apply the distal pin clamp and provisionally attach the fixator frame to gauge the proper site for placement of the proximal pins. It is desirable to place the proximal pins near the mid forearm, since more proximal placement becomes exceedingly difficult because of interposed muscle and the branches arising from the posterior interosseous nerve. If the fixator is used to restore radial length, the distractor module should be prepositioned close to its starting point to allow the maximum potential amount of elongation. Alternatively, the fracture can be distracted with longitudinal traction, which simplifies the fixator application. A 3-cm incision is made over the mid lateral line of the radius shaft. The brachioradialis tendon is identified and retracted along with the superficial radial nerve. The proximal pins can be inserted in the standard dorsoradial position, or they may be inserted dorsally between the extensor carpi radialis brevis and the extensor digitorum with less risk of injury to the superficial radial nerve. The pins holes are also pre-drilled and inserted by hand.

The fracture is distracted under fluoroscopic control. Overdistraction of the carpus should be avoided, since this leads to extensor tendon tightness and intrinsic muscle contraction. The wrist should be placed in neutral or slight extension. Full passive flexion of all the fingers should be possible. The index is the most sensitive to traction and can be used to gauge this.

Complications

Fixator loosening with loss of fracture position can be prevented by periodically checking and tightening the fixator connections. Fixator failure by itself is uncommon, but many commercially available fixators are approved for single use only, because of the risk of unrecognized material fatigue or failure of any locking ball joints. Pin site complications include infection, loosening, and interference with extensor tendon gliding. The risk of injury to branches of the superficial radial nerve mandates open pin site insertion. Bad outcomes associated with external fixation are often related to overdistraction. One biomechanical study documented the effect of distraction of the wrist on metacarpophalangeal (MCP) joint motion. More than 5 mm of wrist distraction increases the load required for the flexor digitorum superficialis (FDS) to generate MCP joint flexion for the middle, ring, and small fingers. For the index finger, however, as much as 2 mm of wrist distraction significantly increases the load required for flexion at the MCP joint. Many cases of intrinsic tightness and finger stiffness that are attributed to reflex sympathetic dystrophy are a consequence of prolonged and excessive traction, which can be prevented by limiting the duration and amount of traction and by instituting early dynamic MCP flexion splinting even while in the fixator ( Fig. 9-6 ).

The degree and duration of distraction correlate with the amount of subsequent wrist stiffness. Distraction, flexion, and locked ulnar deviation of the external fixator encourage pronation contractures ( Fig. 9-7 ). Distraction also increases the carpal canal pressure, which may predispose to acute carpal tunnel syndrome. Metaphyseal defects should be grafted to diminish bending loads and to allow fixator removal after 6 to 7 weeks, which minimizes the fixator-related complications.

Dynamic metacarpophalangeal flexion splints are applied while the fixator is still in place.

The fixator frame is improperly applied with the wrist in marked flexion.

Results

Margaliot and colleagues performed a meta-analysis of 46 articles with 28 (n = 917) external fixation studies and 18 (n = 603) internal fixation studies. They did not detect a clinically or statistically significant difference in pooled grip strength, wrist range of motion, radiographic alignment, pain, and physician-rated outcomes between the two treatment arms. There were higher rates of infection, hardware failure, and neuritis with external fixation and higher rates of tendon complications and early hardware removal with internal fixation. Considerable heterogeneity was present in all the studies, which adversely affected the precision of the meta-analysis.

Westphal and colleagues performed a retrospective comparative study of 166 out of 237 patients who underwent surgery for AO/ASIF A3 or C2 distal radius fractures. The fractures were treated with either external fixation or open reduction and internal fixation using palmar or dorsal plates. Open reduction and internal fixation, particularly palmar plate fixation, demonstrated the best radiologic and functional results. External fixation falls short when used as the sole treatment for displaced intra-articular fractures. In a study of 27 patients with comminuted, displaced intra-articular fractures of the distal radius who were treated exclusively by external fixation, Arora and co-authors concluded that although external fixation is reliable in maintaining the reduction in displaced comminuted intra-articular fractures, in many cases it is inadequate in restoring articular congruity.

Indications

The following are indications for use of augmented external fixation:

• 1.
  

  Intra-articular radial styloid fractures

  
  
• 2.
  

  Three-part intra-articular fractures

  
  
• 3.
  

  Following percutaneous reduction of a depressed lunate fragment

  
  
• 4.
  

  Arthroscopic-aided reduction of distal radius fractures

Contraindications

The following types of fractures are contraindications to augmented external fixation: (1) marked metaphyseal comminution and (2) volar/dorsal intra-articular shear fractures.

Surgical Technique (Three-Part Intra-articular Fracture)

The augmented surgical technique is similar to that of straightforward external fixation. A 1-cm incision is made over the radial styloid, and the superficial radial nerve branches and the thumb extensor tendons are retracted. By means of a drill guide, an oblique and a horizontal subchondral 0.62-inch K wire are pre-positioned in the radial styloid fragment under fluoroscopic control. Ligamentotaxis is used to obtain a reduction of the radial styloid fragment. The K wire is then driven obliquely across the radial styloid fragment to capture the reduction and engage the proximal ulnar shaft. A small dorsal incision is made underneath the medial fragment, and a Free elevator is used to elevate a depressed articular fragment and to correct any abnormal dorsal tilt. The reduction is then captured by advancing the subchondral K wire. Care is taken to prevent penetration of the DRUJ, which can be detected by DRUJ crepitus with passive pronation and supination. Once the reduction is obtained, the traction is diminished and the fixator is applied as previously described. The wrist is then positioned in neutral or slight extension. The index extensor tendon is the most sensitive to traction. Since ligamentotaxis is no longer crucial to maintain the reduction, the traction is reduced until full passive combined flexion of the index MCP, proximal interphalangeal, and distal interphalangeal joints is easily obtained. Any metaphyseal bone defect is then grafted percutaneously through a small dorsal incision. If desired, percutaneous 3.0-mm screws can be substituted for the K wires ( Fig. 9-10 A–J).

Limited internal fixation . A , Anteroposterior x-ray of a displaced four-part fracture. B, Lateral view demonstrates a sagittal split of the medial fragment. C, Internal fixation of medial fragment through a limited volar ulnar approach. D, Fluoroscopy demonstrates the reduction of the medial fragment. E, Radial styloid is reduced with ligamentotaxis and held with an oblique percutaneous K wire. F, Percutaneous screw fixation replaces the oblique radial styloid K wire. G, Subchondral K wire is inserted to support the joint surface. H, Percutaneous bone grafting of metaphysis. I, Second K wire is replaced by a percutaneous screw, which stops short of the distal radioulnar joint. J, Lateral view demonstrates restoration of normal tilt and reduction of the sagittal split.

Results

Kreder and colleagues compared the results from open reduction and internal fixation (ORIF) with the results from external fixation and pinning. A total of 179 adult patients with displaced intra-articular fractures of the distal radius were randomized to receive indirect percutaneous reduction and external fixation (n = 88) or ORIF (n = 91). No statistically significant difference was found in the radiologic restoration of anatomic features or the range of movement between the groups at 2 years’ follow-up. The patients who underwent indirect reduction and percutaneous fixation, however, had a more rapid return of function and a better functional outcome than those who underwent ORIF, provided that the intra-articular step and gap deformity were minimized.

Grewal and co-authors noted the superiority of external fixation and K-wire fixation over internal fixation with a dorsally placed Pi plate for displaced intra-articular fractures of the distal radius. The plate group also had higher levels of pain at 1 year compared with the external fixator group; however, this equalized after hardware removal. The external fixator group showed an average grip strength of 97% compared with the normal side versus 86% in the dorsal plate group.

Complications

In one study of 70 cases of external fixation and percutaneous pinning, 49% of cases lost more than 5 degrees of volar tilt following reduction at the 6-month follow up despite the use of pinning. Initial deformity, patient age, bone graft, and duration of external fixation were not predictors of loss of reduction. No specific predictor of loss of reduction was noted, although there was a trend toward a loss of reduction in younger patients.