An <Emphasis Type="Italic">in Vivo</Emphasis> Experimental Comparison of Stainless Steel and Titanium Schanz Screws for External Fixation

Abstract Objective: To compare the clinical benefits of stainless steel (SS) to titanium (Ti) on reducing pin track irritation/infection and pin loosening during external fracture fixation. Methods: A tibial gap osteotomy was created in 17 sheep and stabilized with four Schanz screws of either SS or Ti and an external fixation frame. Over the 12 week observation period, pin loosening was assessed by grading the radiolucency around the pins and measuring the extraction torque on pin removal at sacrifice. Irritation/infection was assessed with weekly clinical pin track grading. A histological analysis of the tissue adjacent to the pin site was made to assess biocompatibility. Results: A statistically non-significant trend for less bone resorption around Ti pins was found during the early observation period. However, at sacrifice, there was no difference between the two materials. Also, there was no difference in the extraction torque, and there was similar remodeling and apposition of the bone around the pins. A statistically non-significant trend for more infection about SS pins at sacrifice was found. Histology showed a slightly higher prevalence of reactionary cells in SS samples, but was otherwise not much different than around Ti pins. Conclusions: There is no clinically relevant substantial advantage in using either SS or Ti pins on reducing pin loosening or pin track irritation/infection.     

Hydroxyapatite-coated Schanz pins in external fixators used for distraction osteogenesis : a randomized,controlled trial

BACKGROUND: Complications of external fixation include loosening of the fixation pins and pin-track infection. Laboratory studies and clinical trials have suggested that hydroxyapatite coating improves the osteointegration of various orthopaedic implants. The purpose of this study was to determine whether the prevalence of pin-related complications can be reduced by the use of hydroxyapatite-coated pins in fixators applied for distraction osteogenesis. METHODS: Forty-six consecutive patients undergoing segmental transport or lengthening of the tibia were randomized to the use of either standard titanium Schanz pins or hydroxyapatite-coated stainless-steel Schanz pins. The fixators were used for an average of thirty-eight weeks (range, fourteen to seventy-two weeks). All patients were closely monitored for pin loosening and infection, and digitized radiographs were assessed for bone resorption around all pins. When the external fixator was removed, the torque required to extract the pins was determined with use of an electronic torque wrench. RESULTS: In the control group (titanium pins), twenty-two pins (13%) loosened and an infection occurred at the site of twenty pins. An extensive infection of the canal developed in one patient. Twenty-two pins were removed or replaced because of these complications. In the hydroxyapatite group, no clinical or radiographic signs of pin loosening or infection were observed and no pins required early removal or exchange. The mean torque (and standard deviation) required to remove the hydroxyapatite-coated pins was 0.43 0.18 N-m compared with 0.10 0.09 N-m for the uncoated pins (p < 0.001). CONCLUSION: Coating pins with hydroxyapatite increases their fixation to bone and reduces the rate of infection and loosening during external fixation for distraction osteogenesis. Use of hydroxyapatite-coated pins should be considered in clinical situations requiring prolonged external fixation.     

Thermal response and torque resistance of five cortical half-pins under simulated insertion technique

A model was developed that can quantitate heat generation during placement of half-pins in cortical bone. Five half-pins were tested to assess differences in insertion torque, heat generation, and microdamage at the pin-bone interface. Thin thermocouple probes were placed 0.5 mm from the track of the pin and within the pin to measure its temperature during insertion. Scanning electron microscopy was used to view the pin-bone interface to assess the microdamage during placement. The design of the tip of the pin influenced insertion torque and heat generation. Higher heat generation was measured when a thermocouple was placed within the pin itself and less was measured when thermocouple probes were placed within bone samples 0.5 mm from the impending pin track. Furthermore, insertion torque and thermal responses were related, but there were no significant differences in microdamage to bone when different pins and drilling/tapping techniques were used. Due to the significant heat generation at the pin-bone interface, proper cooling with saline irrigation should be applied during pin insertion regardless of the design of the pin. The microdamage observed at the surface of the pin track may have significant implications with regard to loosening of pins, but such effects must be studied with in vivo models.     

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.     

Hydroxyapatite-coated external-fixation pins. The effect on pin loosening and pin-track infection in leg lengthening for short stature

Pin loosening and infection are inherent complications of external fixation. This study deals with their effects of using either hydroxyapatite (HA)-coated or uncoated external fixation pins in leg-lengthening procedures on patients of short stature. We used HA-coated pins on one side and uncoated pins on the other (randomly determined) in 28 bilateral lengthenings undertaken in 23 patients. A total of 322 pins was used. The mean implantation time was 530 days and the mean lengthening achieved was 78% of initial bone length. Mean extraction torque was 7611.6 Nmm degree(-1) for HA-coated and 85.4 Nmm degree(-1) for uncoated pins (p < 0.001). The rate of pin loosening was 4% (7/161) for HA-coated and 80% (129/161) for uncoated pins (p < 0.001). There was no statistically significant difference in the incidence of pin-track infection between the two groups. The use of HA coating appears to be an effective method of reducing the incidence of pin loosening in external fixation with a long implantation time and for mechanically highly stressed procedures such as leg lengthening for short stature.     

No clinical benefits using a new design of pins for external fixation: a randomized study in 50 patients operated on by the hemicallotasis technique

BACKGROUND: Pin-site infection and pin loosening are complications that can cause discomfort to the patients. The purpose of present study was to evaluate pin-site infection, pain, and the use of medications using the XCaliber pin (Orthofix((R))) with optimized thread and tip design, and the commonly used standard pin (Orthofix((R))) during the procedure of hemicallotasis osteotomy (HCO). MATERIAL AND METHODS: Fifty patients of mean age 51 (35-66) years treated with HCO were randomized to standard pins (Orthofix((R))) or XCaliber pins (Orthofix((R))). Hydroxyapatite-coated pins were used in the metaphyseal bone and non-coated pins in the diaphyseal bone in both groups. Pin sites, pain, and the use of medications were evaluated weekly during the HCO. RESULTS: At week 7 the patients in the XCaliber group had more pain at rest [19 (22) vs. 5 (5) mm, P = 0.01] and during activity [32 (32) vs. 12 (13) mm, P = 0.02] and used more paracetamol (2,100 vs. 925 mg, P = 0.04) than those in the standard group, with similar differences, until the extraction of the pins. There was no difference in the use of antibiotics [10.5 (14.5) days (XCaliber) vs. 7 (7.5) days (standard) (P = 0.16)]. CONCLUSION: The commonly used standard pin has important clinical- and patient-related benefits.     

Increased insertion torque delays pin-bone interface loosening in external fixation with tapered bone screws

OBJECTIVE: To test the null hypothesis that osseomechanical integration is not related to the maximum insertion torque of tapered external fixation pins. DESIGN: Prospective in vivo study in a functionally loading ovine model. In 12 animals, tapered commercial external fixation pins were inserted at predefined locations with measured insertion torques and extraction torque measured at 10 weeks postoperatively. SETTING: Unrestricted stall activity under veterinary supervision. INTERVENTIONS: Under general anesthesia and aseptic conditions, mid-diaphyseal tibial osteotomies were created and a 3-mm gap width stabilized with a custom-made, high-precision, single-sided external fixator, in compliance with United Kingdom government regulations [Animals (Scientific Procedures) Act 1986]. MAIN OUTCOME MEASUREMENTS: Primary pin site stability and interface load were assessed by measuring maximum insertion torque (Nm). At a 10-week postoperative end point, osseomechanical stability was assessed by measuring the extraction torque and a pin performance index determined from the insertion/extraction torque ratio. RESULTS: A positive correlation was found between extraction torque and insertion torque (R2 = 0.322, P < 10(-6)). All pins with an insertion torque equal to or greater than 7 Nm had a measurable extraction torque, as did 98% of the pins with an insertion torque above 5 Nm. Extraction torque decreased both as a function of pin site position by the postoperative end point. High insertion torques were found to enhance end point stability in both diaphyseal and metaphyseal bone. CONCLUSION: The data from this study indicate that tapered external fixation pins should be inserted with a high torque to enhance the long-term integrity of the pin-bone interface.     

The influence of hydroxyapatite coating of external fixator pins on pin loosening and pin track infection: A systematic review

Objective

The primary objective of this systematic review of published randomised controlled trials was to evaluate whether there was a clinical benefit in terms of pin loosening and pin track infection, or deep infection, associated with hydroxyapatite coating of external fixator pins. The secondary objective was to evaluate whether there was a clinical benefit in terms of loss of alignment or malunion associated with hydroxyapatite coating of external fixator pins.

Methods

Studies included were identified by a PubMed search for relevant randomised controlled trials on the 20th of December 2007. A systematic review was performed.

Results

All of the studies concluded that there was significantly less pin loosening in the HA-coated groups although the definition of loosening was based on different criteria. However, there was insufficient evidence to properly evaluate the clinical benefit in terms of the numbers needed to treat to avoid premature pin removal. There was also insufficient evidence to evaluate whether any clinical benefit is gained by using HA-coated pins with respect to deep infection and malunion.

Conclusion

A well designed large randomised controlled trial is required to determine the numbers needed to treat with HA-coated pins to reduce the incidence of clinically relevant pin loosening, axial deformity and pin track or deep infection.     

Improvement of the bone-pin interface strength in osteoporotic bone with use of hydroxyapatite-coated tapered external-fixation pins. A prospective, randomized clinical study of wrist fractures

BACKGROUND: Achieving adequate fixation strength in osteoporotic bone is a challenge. In this study, we examined the use of hydroxyapatite-coated tapered external-fixation pins for the fixation of wrist fractures in patients with osteoporosis. METHODS: Twenty female patients with osteoporosis and a fracture of the wrist were divided into two paired groups and randomized to receive either standard tapered pins or hydroxyapatite-coated tapered pins. Two pins were inserted in the distal part of the radius, two pins were inserted in the second metacarpal, and an external fixation device was mounted. All fixation devices were removed six weeks after surgery. RESULTS: The mean pin-insertion torque (and standard deviation) was 461 +/- 254 Nmm in the group managed with standard pins and 332 +/- 176 Nmm in the group managed with hydroxyapatite-coated pins (p = 0.01). The mean pin-extraction torque was 191 +/- 155 Nmm in the group managed with standard pins and 600 +/- 214 Nmm in the group managed with hydroxyapatite-coated pins (p < 0.0001, power 95%). The mean extraction torque was lower than the corresponding insertion torque at each pin position in the group managed with standard pins (p < 0.05), whereas the mean extraction torque was higher than the corresponding insertion torque at each pin position in the group managed with hydroxyapatite-coated pins (p = 0.001). Two patients managed with standard pins and no patient managed with hydroxyapatite-coated pins had a pin-track infection. Pain during pin removal did not differ between the two groups. CONCLUSIONS: The present study showed that hydroxyapatite-coated tapered external-fixation pins provided improved fixation in the treatment of wrist fractures in patients with osteoporosis.     

Modulation of the soft tissue reactions to percutaneous orthopaedic implants.

To evaluate soft tissue reactions and biofilm formation on percutaneous external fixator screws coated with diamond-like carbon (DLC) and hydroxyapatite (HA) coatings on stainless-steel (SS) pins in an ovine loaded osteotomy model, an Orthofix external fixator was used to stabilize a 3-mm tibial midshaft osteotomy with six tapered pins inserted into the right tibia of 32 skeletally mature Friesland ewes. Animals were divided into four groups; SS, fully coated HA, DLC, and HA-coated threads. At 10 weeks, specimens were harvested and the pins were removed en bloc to examine the interfaces between the surface coatings and the tissues. Fully coated HA pins had a significantly higher percentage of dermal contact with the pin surface than HA-coated threads (p=0.028). The presence of a biofilm was evident on all pin surfaces except DLC-coated pins. Significantly greater numbers of bacteria were present on fully coated HA and plain stainless-steel pins compared with DLC. The surface of DLC-coated pins had a significantly lower number of bacterial colonies compared to SS (p=0.028) and fully coated HA pins (p=0.005). Fully coated HA pins have greater dermal attachment to the pin surface than the other pin coatings investigated. DLC-coated pins have the potential to prevent biofilm formation and bacterial colonization that may reduce infection and consequent pin loosening. An external fixator pin that is partially coated with HA to encourage bone and soft tissue integration and with DLC to reduce biofilm formation is advocated.     

Antimicrobial efficacy of external fixator pins coated with a lipid stabilized hydroxyapatite/chlorhexidine complex to prevent pin tract infection in a goat model.

BACKGROUND: Pin tract infection is a common complication of external fixation. An antiinfective external fixator pin might help to reduce the incidence of pin tract infection and improve pin fixation. METHODS: Stainless steel and titanium external fixator pins, with and without a lipid stabilized hydroxyapatite/chlorhexidine coating, were evaluated in a goat model. Two pins contaminated with an identifiable Staphylococcus aureus strain were inserted into each tibia of 12 goats. The pin sites were examined daily. On day 14, the animals were killed, and the pin tips cultured. Insertion and extraction torques were measured. RESULTS: Infection developed in 100% of uncoated pins, whereas coated pins demonstrated 4.2% infected, 12.5% colonized, and the remainder, 83.3%, had no growth (p < 0.01). Pin coating decreased the percent loss of fixation torque over uncoated pins (p = 0.04). CONCLUSION: These results demonstrate that the lipid stabilized hydroxyapatite/chlorhexidine coating was successful in decreasing infection and improving fixation of external fixator pins.     

Internal stabilization after external fixation of fractures of the shaft of the tibia: sense or nonsense?

A series of 95 patients with fresh fractures of the shaft of the tibia, treated primarily with a Vidal-Adrey transfixation frame, was studied retrospectively. Only 20 fractures (21.0 per cent) attained clinical and radiological consolidation within 4 months after injury. Pseudarthrosis was seen in 12 patients (12.9 per cent). The external fixator was attached for an average time of 25.0 weeks. Pin loosening was seen in seven patients (7.3 per cent), minor pin track infection in nine (9.4 per cent) and major pin track infection in three (3.1 per cent). In 31 patients (32.6 per cent) a second operative procedure was necessary to accelerate fracture healing. In 17 patients an autologous bone graft was carried out with the external fixator in place. Internal stabilization was performed after removal of the external fixator frame in 14 cases, at an average time of 9.4 months after injury. In difficult fractures we feel that change from external to internal fixation should be performed earlier; it makes early removal of the fixator pins possible and prevents the problems associated with prolonged use of fixator frames. The internal fixation, eventually combined with a transplantation of cancellous autografts, creates a mechanical and biological stimulus for bone consolidation. Functional recovery may also be improved because of a shorter healing time.     

The effect of angled insertion on halo pin fixation

This study evaluated the effect of angled insertion of halo pins on the biomechanical characteristics of the halo pin-calvarium complex. Halo pins were inserted into isolated calvarium sections at 90 degrees, 75 degrees, and 60 degrees to the surface of the bone at an insertional torque of 0.68 N-m (6 inch-pounds). Initial rigidity, load at failure, and deformation at failure of the pin-bone complex were assessed during transverse shear loading. The structural properties of the pin-bone complex were maximized at loads approaching failure when pins were inserted perpendicular (90 degrees) to the bony surface and significantly decreased at more acute angles of insertion. Perpendicular insertion of halo pins maximizes the structural properties of the complex formed by the halo pin and the calvarium. This improved structural behavior may minimize the incidence of pin loosening clinically, and may reduce the frequency of other complications currently associated with the use of the halo orthosis.     

混合式单臂外固定架骨延长术治疗感染性骨不连

目的评价混合式单臂外固定架骨延长术治疗长骨干骺端感染性骨不连的初步临床结果。方法2003年1月至2006年2月采用混合式单臂外固定架固定、局部清创和截骨延长法治疗感染性骨不连21例,男17例,女4例;年龄18～48岁,平均31.5岁。16例为开放骨折内固定术后感染,5例为闭合骨折内固定术后感染。胫骨近端12例,胫骨远端6例,股骨远端3例。12例行骨折端植骨,其中2例二次植骨。结果21例术后随访10～36个月,平均18个月。18例骨折获得初期愈合,3例骨折愈合时仍有局部窦道和渗液,2例骨折尚未完全愈合,1例行截肢术,20例感染得到控制。改良ASAMI骨评定结果为优良13例,中4例,差4例;功能评定结果为优良11例,中6例,差4例。平均骨延长5.6cm,平均愈合时间为11个月。15例发生钉道感染。结论对长骨干骺端感染性骨不连可使用混合式单臂外固定架骨延长术、骨折端开放换药的方法。该方法控制感染好,可自体修复骨缺损,供区畸形发生率低。但固定需采用HA涂层螺钉,严格控制延长速度,一般在1mm/d以内,分次进行延长,手术风险小。     

Stability at the half pin–frame interface on external fixation constructs

A mechanical study investigating the use of two different methods (grub and bolt screws) to secure external fixation half pins to circular frames. A four part experiment: (1) Grub and bolt screws were used to secure half pins in Taylor Spatial frames. Loosening torques were measured using a calibrated torque wrench. (2) Using universal testing machine (UTM), axial loading was applied to establish thresholds for loosening in grub and bolt screw constructs. (3) We established the application torque to produce failure at the head–driver interface using these two methods. (4) Grub and bolt screw constructs were created controlling torque. Using UTM, axial loading was applied to establish thresholds for loosening. Statistical analysis was conducted using SPSS v20.0.0. (1) Higher torque is employed when bolt rather than grub screws is used to secure half pins on Rancho cubes (p < 0.05). (2) Loading threshold for loosening is higher in bolt screw constructs when the torque applied to secure the constructs is not controlled (p < 0.05). (3) Torque required for failure at the head–driver interface was 5.3 Nm for grub screws and 9.9 Nm for bolts. (4) Loading threshold for loosening is higher in grub screw constructs when the same torque was applied to secure them (p < 0.05). Bolt screws can be employed to secure the half pin–frame interface. They offer good stability and reduce failure at the head–driver interface. Further research is needed to determine the mechanical properties of such constructs in vivo.     

Induction and prevention of pin loosening in external fixation: an in vivo study on sheep tibiae.

In external fixation of fractures, pin loosening is a major concern. Preloading the pins is generally done to ensure their stability within the bone cortex. The effect of radial preload and bending preload in reducing resorption at the pin/bone interface was tested. Schanz screws were fixed to live sheep tibiae using a pneumatically operated external fixator frame. Evaluation was based on radiological observation and fluorochrome histology using sequential labels. Though not completely absent, bone resorption was minimal in the radial preload group, compared with the two other groups. More important, the bone-to-pin contact surface in the radial preload group was found to be almost intact after 5 weeks. In this study, radial preload appears to be superior to bending preload in terms of minimizing the problems of pin loosening.     

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.     

Gradual reduction of distal radial malunion using distraction osteogenesis

PURPOSE: To evaluate gradual distraction lengthening or distraction osteogenesis as a technique for treating malunions of the distal radius. METHODS: Twenty patients with clinical and radiographic evidence of distal radius malunion were treated with osteotomy of the distal radius using distraction osteogenesis. At the follow-up evaluation each patient was evaluated for healing rates, complications, resolution of pain, and radiographic alignment. Surgical treatment consisted of an application of a nonbridging external fixator that could be distracted to correct the deformity. A loosely set screw that connected the distal pins to the fixator served as a hinge and allowed the distal radius to rotate into a corrected position. Gradual distraction via distraction osteogenesis was initiated 1 week after surgery. RESULTS: Seventeen osteotomies healed uneventfully in an average of 9 weeks. Complications included 9 pin track infections. Two nonunions required bone grafting. One patient inadvertently compressed rather than distracted the fixator, leading to premature healing of the osteotomy. One patient ruptured the extensor pollicis longus. All complications resolved with additional intervention. Overall the patients showed radiographic and symptomatic improvement. CONCLUSIONS: An external fixator and distraction lengthening through distraction osteogenesis is a viable alternative to plate fixation and bone grafting. In 18 of 20 of our patients, the technique eliminated the need for bone grafting and the need for a second surgical procedure to remove a dorsal plate.     

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.