Use of a CEPH meiotic breakpoint panel to refine the locus of limb-girdle muscular dystrophy type 1A (LGMD1A) to a 2-Mb interval on 5q31

BACKGROUND: Cortical reaming and intramedullary nail insertion injure the medullary vascular system. Little attention has been directed toward quantitative assessment of bone injury and repair after locked intramedullary nailing of long-bone fractures with and without reaming. The effects of reamed versus unreamed locked intramedullary nailing on cortical porosity and new bone formation were compared in a sheep fractured tibia model. METHODS: After creation of a standardized spiral fracture by three-point bending with torsion, each tibia was stabilized by insertion of a locked intramedullary nail. Ten sheep were randomized into two groups, one that had reaming before nail insertion and one that did not. Fluorochromes were given 2 weeks (xylenol orange), 6 weeks (calcein green), and 12 weeks (tetracycline) postoperatively. All animals were killed at 12 weeks postoperatively. Cortical porosity and new bone formation were determined for the proximal diaphysis, fracture site, and distal diaphysis. RESULTS: Overall cortical porosity was greater with reamed nails than with unreamed nails (p = 0.02). Porosity in the inner cortex (18.3% (reamed) vs. 14.3% (unreamed); p = 0.09) and outer cortex (16.8% (reamed) vs. 12.2% (unreamed); p = 0.04) was greater in the reamed group. With reamed nails only, there was less new bone formation at 2 (p = 0.04) and 12 (p = 0.05) weeks in the inner cortex compared with the central cortex and outer cortex. Overall, there was no difference between reamed and unreamed nails in the amount of new bone formation at 2, 6, or 12 weeks. CONCLUSIONS: This study demonstrates that greater injury or overall cortical porosity is associated with reamed nail insertion. There is no difference, however, between the amount of new bone formation after reamed and unreamed nail insertion. Nail insertion without reaming may be initially advantageous when tibial cortical vascularity is compromised, by limiting further injury to cortical bone. This may be important with open tibial fractures in which there is a significant risk of infection after injury. Between 2 and 12 weeks after injury, neither reamed nor unreamed nail insertion seems to have a significant advantage with respect to the amount of new bone formation that occurs.     

Biomechanics of rigid tibial nail insertion sites

The use of a very proximal insertion site for rigid intramedullary nailing was evaluated in a biomechanical study. The purpose of this study was to compare the bursting strains generated in a proximal tibia fracture fragment during rigid nailing, using the recommended insertion sites versus a more proximal site just anterior to the tibial plateau in the midline. Proximal one-third tibia fractures were created in 12 pairs of fresh cadaver specimens. Strain gauges were applied to the medial and lateral cortices of the proximal fragments. Lottes nails, Grosse-Kempf nails, and unreamed Russell-Taylor nails were inserted in four successive pairs of specimens. In each pair, one side used the recommended starting point, and the other side used the proximal insertion site. The strain was recorded at successive 2- to 4-cm depth intervals during nail insertion. In the Lottes group, much larger bursting strains were generated in the lateral cortex when using a distal starting point (P < 0.05). In the unreamed Russell-Taylor group, the anteromedial surface strains were significantly increased using a distal starting point (P < 0.05). The Grosse-Kempf group showed no significant difference in strains associated with any insertion point during tibial intramedullary nailing.     

Intramedullary boring in infected intramedullary nail osteosyntheses of the tibia and femur

The infection after intramedullary nailing is a severe complication, which is hard to eradicate. The results of reaming the intramedullary canal after removal of the infected nail were evaluated in our investigation. From 1984 to 1991 fifty-five patients with infected intramedullary nails of the lower extremity were included in this trial. Twenty-one patients had an infection of the femur. Thirty-four patients had a primary infection of the nail, twenty-one patients had multiple operations with periods of infection prior to nailing. All patients had signs of a chronic osteitis and sinus formation. At the time of the follow-up the success of the procedure was evaluated regarding recurrence of infection, range of motion of the extremity and patient comfort. The mean time of observation was 10.1 +/- 4.9 years. All patients with initially infected intramedullary nails had no recurrence of the infection, compared to 62% of those with multiple operations prior to nailing. At the time of the follow up all fractures had healed. 85% of the patients performed full weight bearing. 32 patients (91%) had good or excellent ROM of the adjacent joints. CONCLUSION: Intramedullary reaming after infected nails is a successful procedure and results in infect healing in the majority of patients.     

Intramedullary pressure and bone marrow fat intravasation in unreamed femoral nailing

OBJECTIVE: To investigate whether intramedullary pressure and bone marrow fat embolization are different in unreamed compared with conventional reamed femoral nailing. The null hypothesis is that there is no difference between the two techniques. DESIGN: A prospective consecutive nonrandomized clinical trial. METHODS: Intramedullary pressure was measured in the distal femoral fracture fragment at the supracondylar region. Bone marrow fat intravasation was measured by means of the modified Gurd-test. Monitoring was carried out in 31 unreamed and eight reamed intramedullary femoral nailing procedures. RESULTS: Intramedullary pressure increased in the unreamed group to 82 +/- 11 mm Hg during the insertion of 9-mm and 10-mm nails and in the reamed group to 396 +/- 85 mm Hg during reaming of the medullary cavity. Insertion of nails after reaming led to an increase in intramedullary pressure of 79 +/- 13 mm Hg. A positive correlation between fat intravasation and intramedullary pressure was found in each group (rs = 0.73), resulting in less liberation of bone marrow fat in the unreamed group than in the reamed group. CONCLUSIONS: Intramedullary pressure increased significantly in the reamed more than in the unreamed group. Bone marrow fat intravasation depended on the rise in intramedullary pressure, and occurred less frequently in unreamed than in reamed intramedullary femoral fracture stabilization.     

Hydroxyapatite coating of threaded pins enhances fixation

We measured the insertion and extraction torque forces in a randomised study of 76 external fixation screws in 19 patients treated by hemicallotasis for osteoarthritis of the medial side of the knee. The patients were randomised to have either standard tapered screws (Orthofix 6/5 mm) or the same screws with hydroxyapatite (HA) coating. One patient had two standard and two HA-coated screws. All patients had an anterior external fixator (Orthofix T-garche), with two screws in the proximal tibial metaphysis parallel to and about 2 cm below the joint surface and two in the tibial diaphysis. The mean torque forces for insertion of the standard screws were 260 Ncm for the proximal to medial screw, 208 for the proximal to lateral screw and 498 and 546 Ncm for the diaphyseal pins. The corresponding forces for the HA-coated pins were not significantly different. The torque forces for the extraction of the standard pins were 2 Ncm for the proximal pins, 277 and 249 Ncm for the distal pins and 482, 478, 585 and 620 Ncm, respectively (p < 0.005) for the HA-coated pins. All 18 of the metaphyseal standard screws were loose at extraction (extraction force < 20 Ncm), but only one of the HA screws in the metaphysis was loose. In the diaphysis the standard screws lost about 40% of their fixation in contrast to the HA-coated screws which retained full fixation strength.     

Breaking strength retention and histologic effects around 1.3-mm. ORTHOSORB polydioxanone absorbable pins at various sites in the rabbit

Absorbable 1.3-mm polydioxanone (ORTHOSORB) pins were implanted in 75 New Zealand White rabbits in three sites: within the lateral subcutaneous tissue parallel to the femur, down the femoral intramedullary canal, and mediolaterally across the femoral condyles (transcondylar). Pins were harvested at periodic intervals up to 56 and 365 days for mechanical and histologic analyses, respectively. Mechanical analyses were performed by loading the pin in double shear. Histologic analyses were performed on the pin and surrounding tissue. Histologic observations revealed a typical nonspecific foreign-body reaction at all implant sites that resolved at 1 year after resorption of the pin. On histologic examination, there was complete resorption of the pin material in the subcutaneous site by day 182, and there was complete resolution of all response to the pin in six of nine rabbits by day 365. In the intramedullary site, pin material was completely resorbed, based on histologic examination, in five of six rabbits by day 182, and there was complete resolution of the response to the pin in eight of nine rabbits by day 365. The pin material was completely resorbed based on histologic examination of the transcondylar site by day 210, and there was complete resolution of the response to the pin in four of six rabbits by day 270 and in four of nine rabbits by day 365. No enlarged pin tracks or sinus formations were observed in or near the implants sites. The average initial shear strength as 171.4+/ 5.1 MPa, and the breaking strength retention decreased with increasing implantation time. Pins from the subcutaneous regions maintained above 97% of their initial strengths at 28 days, and those from the intramedullary canals maintained above 92%. At later times the strength of the pins implanted in the intramedullary canal decreased more rapidly than those from the subcutaneous region. Overall, the average breaking strength of the subcutaneous pins was significantly greater than that of the intramedullary pins at all time points beyond 14 days. These data indicate that the pins exhibited a strength retention profile sufficient to allow normal healing of bone without enlarged pin tracts, allergic reactions, or sinus formations.     

Mechanical characterization of a totally intramedullary gradual elongation nail

An intramedullary gradual elongation nail (Albizzia) capable of fulfilling the function of traditional intramedullary nails while providing the gradual, controlled distraction of an external fixator was designed for progressive lengthening of lower limbs. In this study, the biomechanics of the gradual elongation nail were compared with several intramedullary nails: Grosse & Kempf, Russell-Taylor, AO, and Laffay. Bending stiffness, torsional stiffness, ultimate bending strength, and torsional strength were determined using the American Society for Testing and Materials standard F383-73 as a guide. The results show that in unextended and elongated conditions, the gradual elongation nail has torsional stiffness (1-5 Nm2) comparable with the AO nail (2 Nm2) and bending stiffness (41-89 Nm2), ultimate bending (246 Nm), and torsional (28-37 Nm) strengths within the ranges obtained for other intramedullary nails (27-105 Nm2, 167-298 Nm, and 2-100 Nm, respectively). Additionally, the low torque required to lengthen the device under a 500 N load (3 Nm) and the low longitudinal stiffness because of the active dynamization system with bimodal load deformation characteristics (80-120 N/mm initial, 600-800 N/mm secondary) produce a device with almost no torsional and longitudinal stress shielding. From a biomechanical point of view, this single, completely implantable device is a safe, viable, and efficacious alternative to external fixation for progressive lengthening of lower limbs.     

Bioabsorbable rods and pins for fixation of metacarpophalangeal arthrodesis of the thumb

We report results on the use of bioabsorbable pins and intramedullary rods made of high-molecular-weight polylactic acid in both experimental and clinical conditions. In the experimental study, bioabsorbable rods were implanted in rabbit femora. Histologic assessment on nondecalcified bone showed that resorption of the material began at 4 months after implantation and gradually fragmented over a period of 3 years. In 12 patients 13 metacarpophalangeal joints of the thumb were arthrodesed by using one bioabsorbable intramedullary rod with one or two oblique pins. All joints fused within 6 to 8 weeks. During that period there was no sign of inflammation, and there were no nonunions. Postoperative magnetic resonance imaging assessment was done in all rabbits and eight patients. This modality is a useful tool in postoperative evaluation of the position and shape of the rod but is not sufficiently sensitive to assess the presence of local inflammation and the rate of resorption of the rods.     

Enhanced fixation with hydroxyapatite coated pins

Three groups of seven patients had external fixation of middiaphyseal tibial fractures using uncoated pins, uncoated bicylindrical pins, and hydroxyapatite coated bicylindrical pins, respectively. All fractures were fixed with six pins, and all fractures united. Median pin insertion torque was 0.6, 1.2, and 1.3 Nm in the three groups, respectively. Median extraction torque was 0.1, 0.1, and 2.1 Nm, respectively. Both types of stainless steel pins showed a lower extraction torque than insertion torque in all cases, whereas the mean extraction torque in the hydroxyapatite coated pins was unchanged. Seven of the 14 patients receiving uncoated pins had pin tract infection, compared with none of the patients receiving hydroxyapatite coated pins. Hydroxyapatite coating of external fixation pins increases stability and thereby reduces the risk for pin tract infection and mechanical failure of fracture fixation.     

Loosening of Schanz screws in external fixator montage of the lower extremity

We analyzed the failure of Schanz pins in 234 patients with fractures of the lower extremity. All patients had the AO external fixator and stainless steel pins (ISO 58/32-1). The mean duration of treatment was 14 weeks. During this time 88 of a total of 1147 pins became loose. The first failures occurred 2 weeks after insertion. Most pins failed after 5-6 weeks. Early loosening was not accompanied signs of local infection, while late failures regularly developed pintract infections. Pins next to the fracture gap exhibited the highest rate of loosening. Intermediate pins had the lowest one. We could not detect an effect of the configuration of the external fixation. Eighty-one percent of the failed pins were exchanged consequently. We conclude that the early occurrence of pin loosening is due to mechanical reasons. Significant factors for this complications were the location close to the fracture gap and the number of pins in that segment.     

Forces required to initiate sliding in second-generation intramedullary nails

Second-generation intramedullary nails, which allow the fixation screw that is placed in the femoral head to slide distally and thus allow compression of the fracture of the femoral neck, have become a popular option for the treatment of ipsilateral fractures of the femoral neck and shaft. However, the sliding characteristics of the screw within the barrel of the nail or the side-plate have not been assessed biomechanically, to our knowledge. The goal of the current study was to investigate the forces required to initiate sliding of the proximal screw in intramedullary devices and to compare these forces with those required to initiate sliding of hip screws. The loading configuration simulated the typical angle of 135 degrees between the intramedullary nail and the proximal screw. The forces required to initiate sliding of the proximal screw, with the screw extended fifty-one, seventy-six, eighty-six, and 102 millimeters beyond the proximal end of the barrel, were measured for three different types of second-generation intramedullary nails (Recon, ZMS, and Gamma), a sliding compression hip screw, and an intramedullary hip screw, and these forces were then compared. With each amount of extension of the screw, the hip screws required lower forces to initiate sliding than did the second-generation intramedullary devices. Of the second-generation devices, the Gamma nail required the highest forces to initiate sliding; the Recon and ZMS nails required 20 to 40 percent lower forces compared with the Gamma nail. None of the devices jammed in any of the loading configurations that were tested. When the extension of the screw was increased, higher forces were required to initiate sliding.     

Ender nailing of acute humeral shaft fractures in multiple injuries

From January 1987 to April 1993, 25 multiply injured patients were treated with closed intramedullary Ender nail fixation of the humeral shaft. Criteria for the procedure were humeral diaphyseal fractures with associated multiple injuries. Seventeen distal and mid-shaft fractures were treated via a modified anterograde approach in which the rotator cuff is not violated. Eight proximal third fractures were treated via the standard retrograde approach. Postoperative follow-up averaged 36 months. Full range of motion was attained 17 of the 25 patients. Of the eight remaining patients, three with a slightly limited range of motion achieved full range of motion following nail removal; three had preoperative radial nerve palsy which resolved within 1 year, and two patients required follow-on plating. In 92 per cent (23 of 25) there were no incidences of infection or non-union. Flexible nails avoid complications of reaming. The modified anterograde approach allows excellent shoulder motion since it does not violate the rotator cuff. Ender nails provide excellent fixation and clinical outcome in the multiply injured patient and are cost effective compared with interlocking nails.     

The use of heterologous promoters for adeno-associated virus (AAV) protein expression in AAV vector production

OBJECTIVE: There are few nonproprietary papers addressing the mechanical strength of intramedullary nails; none address the characteristics of the proximal and distal ends of these devices. Our objective was to provide such data. DESIGN: Independent testing of eight femoral intramedullary nail systems at the proximal, middle, and distal regions was undertaken to evaluate strength and flexural rigidity (stiffness). METHODS: Each device, usually a reconstruction nail, was forty-two to forty-six centimeters in length. Four or five nails of each available size (range 9 to 13 millimeters in diameter) were tested for each system. The nails were cut into proximal, middle, and distal thirds. Each nail section was loaded to failure using a four-point bend test on a custom fixture (modification of the American Society of Testing Materials standard test). RESULTS: Significant variations (p < 0.05) were found in strength and stiffness between the middle and the proximal or distal aspects of some rods. A significant difference (p < 0.05) was observed when comparing the properties of earlier designs with the properties of more recent designs. Newer rod designs all performed in a similar manner with regard to strength. Strength and rigidity increased with increasing rod diameter in some but not all systems. CONCLUSIONS: Although none of the newer designs appeared to have superior static strength, the individual systems had significant variations in their mechanical properties (bending rigidity), particularly in the proximal and distal sections. It is important that the surgeon become familiar with the individual characteristics of strength and rigidity for the particular devices available and how these might impact fracture healing. Consideration of this information could alter the decision to select one system over another in a complex fracture situation.     

A simple jig to ease the insertion of distal screws in intramedullary locking nails

Distal locking of closed intramedullary nails can be time consuming and expose the surgeon to unnecessary increased ionization radiation. A simple jig is described which facilitates the insertion of the second distal locking screw, using the first drill hole as a pilot. This tool reduces the operating and the ionizing radiation exposure time.     

Retrograde intramedullary nailing of femoral diaphyseal fractures

OBJECTIVES: To prospectively evaluate the results of retrograde intramedullary nailing of femoral shaft fractures. DESIGN: Prospective, consecutive series. PATIENTS AND SETTING: All patients with a femoral shaft fracture admitted at an urban Level 1 trauma center from December 1995 to December 1996 were treated with a retrograde femoral intramedullary nail. INTERVENTION: Retrograde femoral intramedullary nailing was performed on a radiolucent operating room table. Through a three-centimeter medial parapatellar incision, a reamed ten-millimeter retrograde nail was inserted. METHODS: From the time of injury until union, the following parameters were assessed: operative time, blood loss, extent of comminution, open grade, associated injuries, Injury Severity Score, body mass index, time to union, secondary procedures, range of motion in the knee. and complications. RESULTS: Fifty-seven patients with sixty-one fractures were available for follow-up, which averaged 43.1 weeks. Fifty-two percent of fractures demonstrated Winquist Type 3 or 4 comminution. Twenty-six percent of the fractures were open. Fifty-two fractures healed after the initial nailing, five of seven dynamized nails healed, and one patient with bone loss requiring bone graft united yielding a final union rate of 95 percent. Of the three nonunions (5 percent), two healed with exchange nailing and one remains asymptomatic at seventy-one weeks. One patient developed a late septic knee that resolved with treatment. Excellent range of motion in the knee was obtained by those patients who did not have other ipsilateral limb injuries. CONCLUSIONS: This consecutive series had a 95 percent union rate after nailing and dynamization as necessary. No knee problems were associated with the retrograde femoral intramedullary nailing technique. The one septic knee raises concerns about the use of retrograde nailing in severe open femoral shaft fractures. Retrograde femoral nailing should be given serious consideration as an alternative to antegrade femoral nailing.     

How many severely injured multiple-trauma patients can benefit from the biomechanical advantage of early mobilization following femoral intramedullary nailing?

The benefit of early operative stabilization of femoral fractures is established in patients with multiple injuries. In the last few years the unreamed femoral nail is favoured for internal fixation of femoral fractures despite pathophysiological concerns. The foremost advantage of femoral nails compared with plate fixation is the possibility of early full weight bearing. The aim of this retrospective study was to investigate, under consideration of the severity of injury, the extent of injury, and the clinical course, if multiple injured patients with concomitant femoral fractures benefit from the preferred intramedullary nailing with early weight bearing. Three hundred and two (23.8%) out of 1271 multiple injured patients (ISS > 17) had a concomitant femoral fracture. Fourty-seven out of 302 patients were children under 16 years of age, remaining 255 patients. Eighteen out of 255 patients died within the first 21 days after trauma and 66 patients required mechanical ventilation for more than three weeks (171/255). Thirty patients suffered from severe head injury (AIS-head > 3) and seven from severe pulmonary contusion with concomitant abdominal injury (134/255). Two patients had grade III open femoral fractures with vascular injury. Ipsilateral unstable pelvic fractures were seen in 11 patients, seven patients had ipsilateral intraarticular femoral fractures, and ipsilateral intraarticular fractures of the lower leg or foot were observed in 40 patients (74/255). The results demonstrate, that only 74 (29%) out of 255 multiple injured patients (> 16 years of age) had a theoretical benefit of early weight bearing. Seventy percent of the patients did not benefit from intramedullary nailing considering full weight bearing. With regard to pathophysiological concerns alternative methods of fracture fixation should be discussed for these patients. Primary fracture fixation with external fixators and secondary internal fixation proved to be a save alternative method. The complication rate of plating is comparable to intramedullary nailing but associated with less severe systemic risks. Primary plating of femoral fractures would not delay mobilization of most multiple injured patients.     

Reamed femoral nailing in patients with multiple injuries. Adverse effects of tourniquet use

Limb reperfusion after tourniquet ischemia causes pulmonary microvascular injury. Similarly, microembolization, like that associated with reamed femoral nailing, can induce pulmonary microvascular injury. Both processes result in increased pulmonary capillary membrane permeability and edema. However, the association between femoral nailing followed by tourniquet ischemia and clinical lung injury has not been described. The authors reviewed 72 patients with femoral shaft fractures and tibial or ankle fractures requiring internal fixation between 1987 and 1993. All femoral shaft fractures were treated with reamed intramedullary nails. Patients were divided into groups, based on whether the tibial or ankle injury was managed surgically with (Group T, 34 patients) or without (Group NT, 38 patients) a tourniquet. Group T was subdivided based on tourniquet time: T1, less than or equal to 90 minutes; T2, greater than 90 minutes. Groups were matched for injury severity. Group NT had fewer ventilator dependent days and intensive care days than Group T (NT: ventilator dependent days, 2.5 +/- 5.2; intensive care days, 3.9 +/- 6.5; T: 5.1 +/- 6.4; intensive care days, 6.7 +/- 6.6). Ventilator dependent days and intensive care days increased with increasing tourniquet time (T1: ventilator dependent days, 3.2 +/- 3.6; intensive care days, 5.4 +/- 4.6; T2: ventilator dependent days, 7.5 +/- 8.5; intensive care days, 8.5 +/- 8.5), suggesting that in patients with multitrauma, combining reamed femoral nailing with fracture fixation under tourniquet control increases pulmonary morbidity. Further investigation to measure pulmonary injury associated with ischemia reperfusion and intramedullary nailing in patients with multitrauma is warranted.     

Open reduction and internal fixation of forearm fractures in children

We retrospectively reviewed 16 children younger than 13 years with 17 fractures of the shafts of the radius or ulna or both who had undergone an open reduction-internal fixation (ORIF). ORIF was performed when a closed reduction was deemed unacceptable in 14 radius fractures and for three unstable open fractures of the radius. The average age was 9.4 +/- 2.3 years (range, 5.0-12.5). Of the 14 fractures with an unacceptable closed reduction, soft-tissue interposition was encountered in seven. Fixation was secured by plates and screws, percutaneous Steinmann pins, or intramedullary Steinmann pins. There were no delayed unions or nonunions, no infections, and no neurovascular injuries. The average follow-up was 12.3 months; all 17 fractures had excellent results (forearm rotation loss of < 10 degrees). Our study indicates that excellent results can be expected with no increased risk of complications if the treating physician elects to proceed with an ORIF in a pediatric forearm fracture with proper indications.     

Intramedullary pressure and pulmonary function during total knee arthroplasty

Twenty-eight patients who underwent unilateral total knee arthroplasty and 20 patients who underwent simultaneous bilateral total knee arthroplasties participated in this study and were randomized to have either a fluted or round 10-mm diameter femoral intramedullary alignment rod used during surgery. The intramedullary rods were cannulated and connected with pressure tubing to a monitor which provided measurements of pressure at the tip of each rod. Arterial blood gas measurements on room air were obtained before and on the morning after surgery. An arterial line was placed and an arterial blood gas measurement was obtained at the time of skin incision and again after tourniquet release. Pulmonary shunt was calculated from the arterial blood gas measurements. Intramedullary pressure during rod insertion was significantly higher for the groups of patients having the round compared with the fluted rod. The change in pulmonary shunt during surgery was lowest for the patients in the unilateral group having the fluted rod and highest for the patients in the bilateral group having the round rod. A fluted rather than a round intramedullary alignment rod should be used to minimize intramedullary pressure and pulmonary shunting during unilateral and bilateral total knee arthroplasties.     

Hydroxyapatite coated external fixation pins: an experimental study

A sheep model was developed for the implantation of 84 bicylindrical stainless steel external fixation pins. One-half of the pins were coated with hydroxyapatite, and the rest remained uncoated. A set of 6 pins with the same coating was implanted in the lateral side of the left tibias of 14 sheep, the final insertion torque was measured, and a monolateral external fixator was assembled on the pins. The medial tibial middiaphysis then was exposed and a 5-mm resection osteotomy was done. Sheep were euthanized 6 weeks after surgery, radiographs were taken, and the initial extraction torque was measured on 4 pins from each sheep. Undecalcified sectioning and histologic and histomorphometric analyses were done on the remaining 2 pins. Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins compared with the uncoated pins. Group average insertion torque was 960 +/- 959 Nmm in the hydroxyapatite coated pins and 709 +/- 585 Nmm in the uncoated pins. Group average initial extraction torque was 1485 +/- 1308 Nmm and 298 +/- 373 Nmm, respectively. Bone pin contact was 85.7% +/- 8.9% and 50.3% +/- 20.4%, respectively, in hydroxyapatite coated and uncoated pins. Bone between the threads was 95.6% +/- 5.7% and 80% +/- 8.7%, respectively, in hydroxyapatite coated and uncoated pins. Hydroxyapatite coating was effective for improving the bone-to-pin interface.