The halo skeletal fixator. Principles of application and maintenance

The halo skeletal fixator, originally developed for use in patients with poliomyelitis, is now widely used with many types of cervical spine instabilities. Despite its demonstrated effectiveness, certain problem areas, including pin loosening and infection, have been identified. These problems have subsequently inspired detailed studies of skull osteology, biomechanics of pin fixation, and comparisons of techniques of application. Based on these studies, specific recommendations concerning the application and maintenance of the halo have developed. Anterior pin sites should be located in the safe zone approximately 1 cm superior to the orbital rim, cephalad to the lateral two-thirds of the orbit, and below the greatest circumference of the skull. The optimal posterior pin sites are located posterolaterally, diagonal to the corresponding contralateral anterior pins. Pins should be inserted perpendicular to the skull, tightened to eight inch/pounds (0.90 Newton-meter), and retightened once at 48 hours. A subsequent loose pin may be retightened once to eight inch/pounds if resistance is met; otherwise, it should be removed and a new one placed in a different location. Infected pins require antibiotic therapy, wound care, and possibly pin-site change and wound debridement.     

The effect of pin location on the rigidity of the halo pin-bone interface

Optimal insertion of halo fixation pins to maximize the rigidity of the interface between the halo pins and the outer table of the skull is important in reducing the incidence of pin loosening. An in vitro biomechanical study was performed using cadaver skulls to investigate the effects of pin location on the rigidity of this pin-bone interface. Halo pins were inserted at nine positions within a recommended "safe zone" for pin insertion. It was found that the rigidity of the pin-bone interface progressively decreased as pins were inserted more superiorly on the calvaria. The rigidity of the interface did not change significantly when the location of the pins was varied in the horizontal axis. This reduction in interface rigidity associated with inserting pins more superiorly on the skull may be related to an increase in the angle of insertion of the pins with respect to the surface of the calvaria. Based on this study, a change in the technique of halo pin insertion is recommended. Pins should be placed as inferiorly as possible, close to the supraorbital ridge, to achieve the most perpendicular angle of insertion and thus the most rigid fixation. The improved rigidity obtained with perpendicular pin insertion may minimize the rate of pin loosening and other complications associated with use of the halo orthosis.     

Structural behavior of the halo orthosis pin-bone interface: biomechanical evaluation of standard and newly designed stainless steel halo fixation pins

The structural response of the halo orthosis pin-bone interface to transverse loading was evaluated on an Instron testing machine using fresh cadaver calvarium sections. Commercially available stainless steel (control) pins and newly designed stainless steel experimental pins were evaluated. Cyclic loading tests and load-to-failure tests were performed. Of the many designs tested, one pin demonstrated an improvement in structural properties at the pin-bone interface compared with the control pin. Furthermore, the new pin design was more resistant to insertional torque reduction when subjected to cyclic loading after insertions at 4 and 6 in-lb. Both the control and experimental pins exhibited improved structural behavior at 8 in-lb of insertional torque compared to the currently recommended 6 in-lb.     

Halo pin intracranial penetration and epidural abscess in a patient with a previous cranioplasty: case report and review of the literature.

STUDY DESIGN: Report of a patient with an epidural abscess after halo pin intracranial penetration at the site of a previous cranioplasty. OBJECTIVES: To report a rare case of intracranial penetration at the site of a previous cranioplasty associated with epidural abscess, and to discuss the diagnostic and therapeutic approach to its management. SUMMARY OF BACKGROUND DATA: The most serious complications associated with use of halo device occur when pins penetrate the inner table of the skull, resulting in cerebrospinal fluid leak and rarely in an intracranial abscess. However, no mention of intracranial halo pin penetration at the site of a previous cranioplasty was found in the literature. METHODS: A 64-year-old man with ankylosing spondylitis had a halo vest placed for management of a fracture dislocation through the C5-C6 intervertebral disc space associated with left C6 radiculopathy. One week later, the patient experienced fever and headache associated with pain, redness, and drainage at the site of the insertion of the left posterior pin. Computed tomography of the brain showed a 1.5-cm intracranial penetration of the halo pin through a previous cranioplasty of the temporal bone, associated with epidural abscess and cerebral edema in the left temporoparietal lobe. The pins and the halo vest were removed, the pin site was cleaned, and a Philadelphia cervical collar was applied. Staphylococcus epidermidis grew on the culture of drainage from the pin site. The patient started immediate intravenous antibiotic treatment for 2 weeks, followed by oral antibiotics for 2 additional weeks. RESULTS: The patient had gradual improvement of his symptoms within the first 48 hours. At the latest follow-up visit, he had fully recovered and his fracture had healed. CONCLUSIONS: The halo device should not be used for patients with a previous cranioplasty, especially if the pins cannot be inserted at other safe areas of the skull. A thorough medical history and physical examination of the skull are important before the application of a halo device. Computed tomography of the skull may be necessary before elective halo application for patients with concomitant head trauma, confusion, or intoxication and for patients with a previous cranioplasty to ascertain the safest pin sites.     

Das besondere Instrument Der Halo-Fixateur

OBJECTIVE: Installation of an external fixator in combination with a body cast for temporary or definitive immobilization and retention of unstable fractures of the craniocervical junction and upper part of the cervical spine. Further established applications include presurgical extension treatment of paralytic scoliosis and temporary retention within complex spine deformity operations after ventral release or mobilized osteotomies. INDICATIONS: Closed reposition and temporary retention of unstable injuries of the cervical spine up to operation. Extension treatment for careful reposition of fresh or dated malpositions of the cervical spine. Conservative treatment of injuries of the craniocervical junction and the upper part of the cervical spine. Presurgical extension of paralytic scoliosis. Temporary extension after ventral release. CONTRAINDICATIONS: Cranial fractures and intracranial injuries. Soft-tissue infections of the skull. Children < 3 years. Adiposity, chest injuries and paraplegia as relative contraindications using the halo body cast. SURGICAL TECHNIQUE: Halo traction is applied in two stages; first, the head ring is attached to the skull, then, the body cast and suspension assembly are added. Local anesthesia, depending on circumstances. Sizing of the components; the optimal size of the ring is about 1.5" larger than the circumference of the patient's head. Patient in sitting or supine position. The halo ring is held in proper position by stabilizer plates; the lower margin of the ring should be just above the ears and about 0.4" above the eyebrows. The anterior pins are placed in shallow groove on the forehead between supraorbital ridges and frontal protuberances. Threaded skull pins are screwed with defined torque (4-8"/pounds) in the lamina externa of the cranial calotte without perforating the lamina interna. To avoid side-to-side drifting, the diagonally opposite pins should be tightened simultaneously. Finally, connection of the halo ring with a body cast or putting on an extension device. RESULTS: Secure external stabilization of unstable injuries of upper cervical spine. Improvement of correction results of patients with neuromuscular scoliosis who underwent surgical treatment. Disadvantages are procedure-specific complications (infection and loosening of head pins) with different published frequencies and decreased patient's acceptance at longer therapy duration.     

Evaluation of skull thickness and insertion torque at the halo pin insertion areas in the elderly: a cadaveric study

BACKGROUND CONTEXT: The halo skeletal fixator provides the most rigid type of immobilization of all the orthoses that stabilize the cervical spine. Sometimes with older patients (>70 years old), the pin penetrates the cortical and cancellous bone of the skull and enters the intracranial space, which can result in serious complications such as brain injury, infection, hematoma, and loss of cerebrospinal fluid from the subarachnoid space. Currently, there is a lack of relevant literature that examines these concerns. PURPOSE: To evaluate the thickness of the outer table, diploe, and inner table at the anterolateral and posterolateral pin insertion areas of the skull in elderly cadavers by using computed tomography (CT) scans. In addition, insertion torques at the four standard pin insertion areas was determined by applying halo pins at incremental torque in an effort to suggest safe torque levels for the anterolateral and posterolateral pins. STUDY DESIGN/SETTING: A human cadaveric anatomical and biomechanical study relating to thickness and insertion torques at standard pin areas in the elderly. PATIENT SAMPLE: Twenty-one elderly cadaveric skull specimens. OUTCOME MEASURES: Thickness of cortices (tables) and diploe of skull and insertion torque at halo pin insertion areas. METHODS: Aquarius Image software at the CT scanner's TeraRecon Aquarius Workstation was used to make the necessary skull thickness measurements at the pin insertion areas. Six, 8, 12, 18, and 36 inch lb of torque were used to determine penetration of the pins through the inner table at each of the four locations (two anterolateral and two posterolateral). RESULTS: The mean anterolateral thickness was 7.36+/-1.57 mm. The average thickness of the outer table, diploe, and inner table were 2.24+/-0.44 mm, 1.52+/-0.41 mm, and 3.59+/-1.70 mm, respectively. The mean posterolateral thickness was 9.47+/-1.12 mm. The average thickness of the outer table, diploe, and inner table were 4.32+/-0.92 mm, 1.88+/-0.35 mm, and 3.27+/-1.21 mm, respectively. No pin penetration was seen at the traditional 8 inch lb of insertion torque in both the anterolateral and posterolateral pin insertion areas. Eighteen inch lb of torque resulted in penetration in 90.48% (19/21) and in 85.71% (18/21) of specimens in the left anterolateral and right anterolateral pin insertion areas, respectively. No penetration was seen even at 36 inch lb of torque in 80.95% (17/21) of the cadavers in both the left and right posterolateral pin insertion areas. CONCLUSIONS: The current study supported previous research that 8 inch lb of torque is safe for application of halo pins in the elderly. The posterolateral skull is thicker and stronger than the anterolateral skull. The safe maximum torque is 8 inch lb for anterolateral pin insertion area and 18 inch lb for the posterolateral pin insertion area.     

Comparative theoretical study of various external fixation devices for the stabilization of distal radius fractures

In the treatment of comminuted Colles' fractures different types of external fixation devices are used. Three main types are compared: (1) Fixation with two pins in each plane: Ace-Colles' type; (2) fixation with four or more parallel pins in one plane: Wagner/Hoffmann type; (3) fixation with four pins in one plane, two pins on each side of the fracture forming an angle of 60 degrees: ASIF-type fixator. These three types are compared with reference to the different forces that have to be neutralized by the seating of the pin in the bone. To minimize these forces with the aim of preventing pin-loosening, the theoretical results are used as the basis of practical surgical advice: (1) The distance between skin and fixator should be as short as possible. (2) The fixator should be fixed as close as possible to the fracture. (3) The diameter of the pins should be as great as possible. (4) If more than two pins per plane are used (Hoffmann/Wagner type), the pins should be wide apart. (5) If only two pins per plane are used (Ace-Colles Type) the bending stress on each pin is high (6) If more than two parallel pins per plane are used (Hoffmann/Wagner type), the axial forces on each pin are high. (7) The pins should be fixed at right angles to the fractured bone. Pins at other angles do more harm than good.     

Halo application in the infant

The technique for halo application in very young children is described, with case presentations of three children aged less than 2 years who underwent successful cervical fusion with halo immobilization. Our multiple pin technique for very small children diverges significantly from previously accepted recommendations. With multiple pins, significantly less torque is required to provide stability, allowing a greater range of pin placement sites in areas where the infant skull might otherwise be considered too thin. This technique of halo application provides a safe and effective method of cervical immobilization for infants.     

The halo fixator

The halo fixator may be used for the definitive treatment of cervical spine trauma, preoperative reduction in the patient with spinal deformity, and adjunctive postoperative stabilization following cervical spine surgery. Halo fixation decreases cervical motion by 30% to 96%. Absolute contraindications include cranial fracture, infection, and severe soft-tissue injury at the proposed pin sites. Relative contraindications include severe chest trauma, obesity, advanced age, and a barrel-shaped chest. In children, a computed tomography scan of the head should be obtained before pin placement to determine cranial bone thickness. Complications of halo fixation include pin loosening, pin site infection, and skin breakdown. A concerning rate of life-threatening complications, such as respiratory distress, has been reported in elderly patients. Despite a paucity of contemporary data, recent retrospective studies have demonstrated acceptable results for halo fixation in managing some upper and lower cervical spine injuries.     

Osteomyelitis in burn patients requiring skeletal fixation

Deep and severe burns often present with the exposure of musculoskeletal structures and severe deformities. Skeletal fixation, suspension and/or traction are part of their comprehensive treatment. Several factors put burn patients at risk for osteomyelitis, osteosynthesis material being one of them. In order to determine the safety of skeletal fixation, we reviewed all pediatric patients treated with pin insertion during the past 10 years. Forty-one severely burned children (61+/-3% TBSA full thickness burns), had a total of 357 skeletal fixation procedures. Pins were maintained an average of 25.3+/-1.7 days. Thirteen pins (3. 6%) were loose before the expected time of removal, two patients (4. 8%) presented with cellulitis of the pin site and two patients (4. 8%) presented with osteomyelitis. Loose pins, pin site cellulitis, burn wound infection and sepsis were not associated with osteomyelitis. Skeletal fixation in severely burned patients presents with a low incidence of infectious complications. Its use should be considered in patients affected by severe burns that present with exposed deep structures and for positioning purposes. The exact timing for pin removal in burned patients is still to be defined.     

Application of the halo device for immobilization of the cervical spine utilizing an increased torque pressure

The rates for loosening and infection of the pins used in the halo apparatus are unfortunately high. The commonly recommended amount of torque to be used in applying the pins is 0.68 newton-meter (six inch-pounds). Forty-two adult patients underwent application of a halo device for immobilization of the cervical spine using an increased torque of 0.90 newton-meter (eight inch-pounds). The rate for loosening of the pins and the rate for infection at the pin site dropped from 36 per cent to 7 per cent and 20 per cent to 2 per cent, respectively.     

Use of skin incisions in the application of halo skeletal fixator pins

A halo skeletal fixator was studied prospectively in 51 patients using two different pin insertion techniques. One technique consisted of a stab incision prior to pin placement and the second technique used no incision. There was no difference in infection, loosening, or resultant scars between the two groups. Incision for halo pins may increase initial bleeding and seems unnecessary.     

Soft tissue injuries with the use of safe corridors for transfixion wire placement during external fixation of distal tibia fractures: an anatomic study.

OBJECTIVES: To determine which soft tissue structures are at risk and when joint violation can occur during small wire placement for hybrid external fixation of distal tibial fractures while adhering to published guidelines. DESIGN: Cadaver anatomic experiment. SETTING: University orthopaedic program. SUJBECTS: Five embalmed cadavers. INTERVENTION: Placement of small wire transfixion pins in the distal tibia. MAIN OUTCOME MEASUREMENTS: Dissection and measurements. METHODS: Four orthopaedic surgeons were shown diagrams that have been widely accepted as allowing for placement of transfixion pins in the distal tibia through safe corridors. Each of the orthopaedic surgeons was then asked to place two transfixion pins into each of five cadaver legs in a position that would provide stable external fixation of the metaphysis to the diaphysis with a circular fixator (forty pins total) for a distal tibial fracture within five centimeters of the plafond. The specimens were dissected, and pins impaling neurovascular structures, tendons, or the ankle capsule were recorded. The superior capsular synovial reflections were measured from the anterior joint line and the tip of the medial malleolus. These measurements were also performed on arthrograms of two extremities before their dissection. RESULTS: Fifty-five percent of the pins placed impaled at least one tendon that crosses the ankle joint. Neurovascular structures that were impaled included the saphenous vein (+/-10.5 percent) and the superficial peroneal nerve (+/-7.5 percent). One pin violated the superior capsular synovial reflection, which was an average of thirty-two millimeters (+/-1.58 millimeters) from the tip of the medial malleolus and twenty-one millimeters (+/-1.63 millimeters) from the anteromedial joint line. CONCLUSIONS: This study shows that tendons and neurovascular structures above the ankle are at risk during small transfixion pin placement, even when using safe corridors. Pins placed within two centimeters of the anterior joint line or three centimeters from the medial malleolus may be intracapsular.     

A comparison of various angles of halo pin insertion in an immature skull model.

STUDY DESIGN: A basic science biomechanical study involving an animal model. OBJECTIVES: To evaluate the effect of varying angles of halo pin insertion on the force generated at the pin-bone interface, and thereby the stability of the halo pin-bone interaction during insertion. BACKGROUND DATA: Because of variations in the shape and size of the pediatric skull, halo pins often are inserted at various angles rather than perpendicular to the skull. Concern exists that the high complication rate associated with pediatric halo use may result in part from less than ideal structural properties at the halo pin-bone interface. METHODS: The authors used a fetal calf skull model to simulate the thickness and structural properties of the pediatric skull. Halo pins were inserted at angles of 0 degree (perpendicular), 10 degrees, 15 degrees, and 30 degrees into skull segments via a halo ring. Load generated at the pin-bone interface was measured using a modified mechanical testing device. Twenty trials were conducted per angle, with the endpoint being specimen failure, pin penetration, or maximum load. RESULTS: Mean maximum loads per unit thickness were 82.15 +/- 7.54 N/mm at 0 degree, 68.80 +/- 4.79 N/mm at 10 degrees, 51.49 +/- 5.08 N/mm at 15 degrees, and 42.38 +/- 3.51 N/mm at 30 degrees, There was a significant difference between perpendicular insertion (0 degree) and 15 degrees angles of insertion. There was also a significant difference between the 10 degrees and 30 degrees angles of insertion. CONCLUSIONS: Perpendicular halo pin insertion in an immature skull model was shown to result in increased load at the pin-bone interface. This improved structural behavior may help to reduce the incidence of complications of halo application in children.     

Supra-acetabular placement of external fixator pins: a safe and expedient method of providing the injured pelvis with stability

Applying a stable anterior pelvic external fixator frame is a skill that should be mastered by all orthopedic surgeons who treat acutely injured patients. Splinting of an unstable pelvis during resuscitation can help to reduce the volume of the true pelvis, pending definitive surgical stabilization of the pelvic ring. Supra-acetabular pin placement, less familiar to most surgeons than iliac wing pin placement is, can provide a more reliable pin-bone interface and thus allow improved reduction ability with fewer soft-tissue complications. Because of their location, supra-acetabular pins also seem to be better tolerated than iliac crest pins when used for definitive management of the pelvic ring disruption. A young man who sustained a type II anteroposterior compression injury in a motor vehicle accident presented with symphyseal disruption (7 cm wide) and left anterior sacroiliac joint disruption. During resuscitation, the pelvis was anatomically reduced and stabilized with a supra-acetabular pin-based external fixator. Pin locations, chosen using palpable and cutaneous landmarks, were inserted without additional imaging guidance. The fracture was reduced anatomically, and the frame was used for definitive management of the pelvic ring injury.     

Complications of halo treatment for cervical spine injuries in patients with ankylosing spondylitis--report of three cases

BACKGROUND: Patients suffering from ankylosing spondylitis are prone to injuries of the cervical spine even with minor trauma. Although the fractures are markedly unstable, nonsurgical treatment using a halo-thoracic plaster or jacket is a common approach. METHODS: We present three patients with cervicothoracic fractures of the ankylosed spine to describe problems and complications inherent in this type of treatment. In two, pin track infections and pin protrusion through the skull occurred, leading in one case to an intracerebral hemorrhage. In the third patient, the halo had to be removed after 8 months, just early enough to prevent the pins from cutting through. RESULTS: One patient required craniotomy. The second one could be resolved by local revision. In the third case, the fracture eventually united after using a stiff collar for 2 years. CONCLUSION: Halo treatment for cervical spine fracture in patients with ankylosing spondylitis is a challenging task for orthopedic surgeons and neurosurgeons.     

Six-pin halo fixation and the resulting prevalence of pin-site complications

BACKGROUND: In spite of the many advances in halo application technique, the prevalence of complications associated with the use of halo fixation remains high, particularly at the pin sites. Many practitioners do not use more than four pins for halo application in adults because they believe that it increases the risk of complications. The purpose of this study was to investigate the use of six pins in halo application, in order to determine if the extra pins increased fixation strength without increasing the overall pin-site complication rate. METHODS: The first part of our study consisted of force-deflection tests conducted on models of the skull fitted with either a four or a six-pin halo to determine if the six-pin halo provided greater fixation strength. Each skull model was placed in a servocontrolled hydraulic test machine; an axial distraction force was then applied until failure occurred. The second part of the study was a retrospective analysis of sixty-three patient records to document the prevalence of pin-site complications in patients treated with a six-pin halo system; these findings were then compared with established complication rates associated with four-pin halos. RESULTS: In the force-deflection tests, the mean load to failure of the six-pin halo construct (2879 N [647 lb]) showed the system to be significantly stronger (p = 0.0033) than the four-pin halo construct (1681 N [378 lb]). Of the sixty-three patient records reviewed, five (8% [95% confidence interval, 1% to 15%]) revealed pin-loosening; no infection was recorded for these five patients. One of the sixty-three patients had redness and erythema at "multiple sites," but these areas healed well. Another presented with infection at all six sites; this was recorded as an allergic reaction. CONCLUSIONS: Six-pin halo fixation results in greater halo strength and cervical spine stabilization without increasing the risk of pin-site complications. Clinical Relevance: Our findings are relevant for current clinical practice as the high complication rates associated with halo application have deterred some practitioners from using this type of fixation. The use of six pins, along with an improved protocol for halo application and care, may contribute to a more successful treatment outcome with fewer complications.     

Complications of hinged external fixators of the elbow

Despite the growing use of hinged external fixators of the elbow, there are no studies regarding the complications associated with their application. The purpose of this study is to report our experience with complications with this procedure. Between 1998 and 2005, we reviewed the records of 100 consecutive patients who were treated with hinged external fixators (including 433 pin sites). Complications specifically related to pin placement were recorded. There were 15 patients with minor complications (15%) involving 21 pins (4.8%) and 10 patients with major complications (10%) involving 29 pins (6.7%). Minor complications included local erythema and nonpurulent drainage lasting greater than 5 days in 9 patients (21 pins) and the need for skin release to decrease tension adjacent to pins in 6 patients (9 pins). Major complications included purulent pin site drainage in 1 patient (2 pins), fixator malalignment in 1, pin loosening in 4 (11 pins), and deep infection in 4. There were no fractures around the pin sites or nerve injuries associated with pin placement. With care, articulated external fixators can be used without a high incidence of major complications. Most of the complications were attributed to local pin site infection. Factors clinically associated with an increased risk of deep infection include a history of prior procedures in the post-traumatic elbow and the complexity of the operative technique.     

A study of external skeletal fixation systems for unstable pelvic fractures

This study was undertaken to determine the feasibility of constructing an anterior pelvic external fixator capable of resisting displacement of vertical shear fractures. Newly designed tapered thread pins for cancellous bone had better bone pin fixation and their greater 6-mm diameter provided more than twice the stiffness of Hoffmann 4-mm pins when tested in clusters. Using these pins and a more rigid anterior frame as one model, various pelvic fixators were tested to determine their resistance to vertical shear forces. These tests determined that this new fixator was 16 times stiffer than a Bonnel single anterior frame and five times stiffer than a double anterior frame (both constructed of Hoffmann components). Extrapolation from the data shows that 13 mm of posterior fracture displacement would occur with loads of one half body weight using the new fixator. Additionally it was noted that Hoffmann frames constructed with two 5-mm pins performed as well as those using three 4-mm pins.     

Brain abscess complicating the use of a halo orthosis

We report a case of brain abscess complicating the use of a halo orthosis in the treatment of a cervical spine injury suffered during wrestling. Four previous brain abscesses complicating the use of halo orthoses have been reported. All cases of abscess have been associated with overlying infection at the site of pin insertion. Our case and at least one of those previously reported may have been related to tightening of the halo pins after placement. Serious spine injuries occur rarely in wrestlers and are associated with the use of illegal holds and maneuvers in which one athlete is thrown to the mat. The pathophysiology and radiographic appearance of a unilateral facet dislocation are reviewed.