The Effect of Axial Tension on the Load Bearing Capacity of Traction Pins

Skeletal traction is often used in the conservative treatment of fractures. Although a small diameter traction pin causes less trauma, its use is limited by the strength of the pin and the holding power of the bone. Both theoretical analysis and in vitro experiments were conducted to investigate the bending resistance of traction pins subjected to an applied traction force. the results of this study indicate that thin K-wires could be used successfully as traction pins. Excessive bending of these wires could be prevented by applying tension. the possibility of a pin cutting through bone is minimal if the cortical bone structure of the patient is normal. However, further in vivo study is necessary to ascertain whether necrosis might occur due to excessive contact stress between the pin and the bone.     

刻槽针内固定治疗股骨颈骨折生物力学研究与临床应用

目的：验证刻槽针治疗股骨颈骨折较普通斯氏针更具有锚固性，方法：通过生物力学试验，采用均质木块与牛股骨按骨折固定方式钉入直径4mm斯氏针与刻槽针，置弹簧拉力试验机上进行拔出力对比，并将刻槽针临床应用于50例股骨颈骨折的治疗，结果：斯氏针在木块上平均拔出力为10．2kg，刻槽针为21．00kg，为斯氏针的2倍，斯氏针在牛股骨上的平均拔出力为5．7kg,刻槽针为14．5kg，为斯氏针的2．45倍，刻槽针临床应用效果良好，结论：刻槽针治疗股骨颈骨折较斯氏针固定牢固，临床应用证实无脱针，折针发生。     

Migration of Kirschner pin from clavicle into ascending aorta

Kirschner pins are widely used for fixation of bone, with few and very rarely serious complications. A case is described in which a Kirschner pin migrated in 10 days from the sternal end of the left clavicle into the lumen of the ascending aorta. The exact location of the pin remained unknown until right thoracotomy, during which X-ray examination revealed the unexpected situation. The pin was simply extracted by pushing it through the vessel wall. The patient recovered uneventfully. The complication could have been prevented by bending the outer part of the pins. The possible route of migration is discussed.     

Stiffness of small-bone external fixation methods: an experimental study

A variety of small-bone external fixation methods were evaluated to determine bending and torsional stiffness. Several methods of external pin stabilization with bone cement and with a commercial device were used. Among experimental variables examined were: the number of pins, pin diameter, pin length, pin spacing, and pin threading. The most rigid fixation was achieved with four pins held with a wire-reinforced bone cement fixator. Pin diameter was the most significant variable in the determination of stiffness with this configuration.     

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.     

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.     

Experimental analysis of effects of pin pretensioning on external fixator rigidity

The effects of same-fragment pin pretensioning on the rigidity of a simple fixator system were investigated. An external fixator device constructed to apply same-fragment pin pretensioning of a defined amount was applied to a bone model made of pedilen cylinders. System rigidity was tested for varying degrees of pin pretensioning in axial compression and AP bending. Pin pretensioning, bringing transfixing pins together, tended to weaken the system in both modalities tested. Tensioning by bringing the pins apart increased the rigidity of the system in AP bending and axial compression.     

Experimental analysis of effects of pin pretensioning on external fixator rigidity

Summary The effects of same-fragment pin pretensioning on the rigidity of a simple fixator system were investigated. An external fixator device constructed to apply same-fragment pin pretensioning of a defined amount was applied to a bone model made of pedilen cylinders. System rigidity was tested for varying degrees of pin pretensioning in axial compression and AP bending. Pin pretensioning, bringing transfixing pins together, tended to weaken the system in both modalities tested. Tensioning by bringing the pins apart increased the rigidity of the system in AP bending and axial compression.     

The misuse of skeletal traction

The misuse of skeletal traction rather than the application of the method itself leads to most of the difficulties associated with it.The greatest danger of the method is infection, which may result from improper surgical technique at the time of application or from subsequent motion of the metal agent used for traction. A method of preventing longitudinal axis motion of skeletal pins is described.The complications of infection are most severe when a hematoma, joint or linear fracture communicating with a major fracture are traversed by a traction pin.Improperly placed pins may result in inefficient traction, pressure necrosis of soft tissues or severe damage to the bone or neighboring epiphyseal areas and joints.The use of metal tongs is condemned, except for traction on the skull.The problem of distraction resulting in delayed union and nonunion is discussed.The hazards associated with the use of multiple points of skeletal fixation and distraction types of apparatus are emphasized. The ambulatory management of patients treated by the incorporation of skeletal pins in plaster is considered dangerous, particularly when weight bearing on the skeletal pins is allowed.     

Biomechanical evaluation of Hackethal's intramedullary bundle pin fixation of humeral neck fractures

Humeral neck fractures can be stabilized using a bundle of intramedullary pins as described by Hackethal. In order to decrease the risk of pin migration, packing of the medullary cavity with as many pins as possible is sometimes recommended, but others believe that stability can be decreased by destruction of cancellous bone in the humeral head by a large bundle of pins. A surgical neck fracture was created with a saw in 30 frozen cadaveric humeri. Bone quality was evaluated by radiography and densitometry. Fractures were stabilized using Hackethal's technique of retrograde intramedullary pinning with varying numbers of 2.5-mm diameter pins; increasing torsion or bending moments of force were then applied to the bones studied. Stability was found to improve with an increasing number of pins and with higher humeral head density. Based upon these findings, the use of a large number of pins is recommended to reduce the risk of pin migration. Up to eight pins, the risk of destruction of cancellous bone in the humeral head appears very low.     

Biomechanical analysis of pin placement and pin size for external fixation of distal radius fractures

A series of biomechanical analyses were performed to explain the recent reduction in treatment-related complications of external fixation of distal radius fractures using a limited open approach for pin placement and larger 4-mm self-tapping half pins. A comparison of pull-out strength, stress concentration effect, and inherent bending strength of 3- and 4-mm half pins was performed. The effect of proximal pin placement in the radius or in the ulna and the effect of distal pin placement in four, six, or eight metacarpal cortices were determined. These analyses demonstrate that the 4-mm self-tapping half pins result in a significantly higher pull-out strength and only a small decrease in torsional load strength of the bone. They also demonstrate that proximal pin fixation in the radius produces the most stable fixation and that distal pin fixation into six metacarpal cortices produces a strong configuration that does not violate the interosseous muscles of the second intrinsic compartment. The rate of treatment-related complications in the external fixation of distal radius fractures (specifically, pin loosening, bending and breakage, fracture through pin sites, collapse at the fracture site, and intrinsic contracture) are addressed in this study. Such complications can be minimized by using 4-mm pins after central predrilling, with proximal placement in the radius and distal placement through six cortices of the bases of the second and third metacarpals.     

生理盐水在儿童骨牵引针道护理中的应用研究

目的探讨生理盐水在儿童骨牵引针道护理应用的可行性。方法将2017年1月至2018年12月华中科技大学同济医学院附属武汉儿童医院小儿骨科收治的208例骨牵引患儿,根据入院时间段分为对照组(113例)和观察组(95例)。对照组使用75%乙醇对骨牵引针道进行常规护理(2次/d),观察组按需使用生理盐水对骨牵引针道进行护理。采用中文版儿童疼痛行为量表(FLACC)评估患儿针道护理时的疼痛情况,Checketts Otterburns感染分级系统评估患儿针道感染情况。结果针道护理时,观察组的FLACC评分为(1.58±0.71)分,优于对照组的(2.06±0.86)分,差异有统计学意义(t=4.280,P<0.001)。观察组发生针道Ⅰ度感染2例,感染发生率为2.11%(2/95);对照组发生针道Ⅰ度感染4例,Ⅲ度感染1例,感染发生率为4.42%(5/113);两组针道感染发生率比较,差异无统计学意义(Z=-1.15,P=0.248)。结论儿童骨牵引针道采用生理盐水按需护理,可预防针道感染发生,减轻针道护理时的疼痛刺激,提高患儿舒适度。     

The small pin circular fixator for distal tibial pilon fractures with soft tissue compromise

A Monticelli-Spinelli small pin circular external fixator was used in combination with closed reduction or a limited open reduction internal fixation in five cases in an attempt to salvage a satisfactory result in distal tibia pilon fractures when associated soft tissue compromise prevented standard fixation with plates and screws. The small pin fixator enhances the ability to perform a closed reduction through a technique that uses distraction with pins in the tibia and calcaneus, combined with correction of angulation by tensioning wires with a stop nut. Small pin stabilization of these comminuted fractures allows early patient mobilization. The small diameter pins support the soft cancellous bone fragments. This technique attempts to combine the benefits of traction, external fixation, and limited internal fixation. We recommend this technique as a salvage procedure when plates and screws are contraindicated because of poor bone and soft tissue conditions.     

Behavior of an external fixation frame incorporating an angular separation of the fixator pins. A finite element approach

A finite element model has been developed to simulate the deformation that occurs at the fracture site of an externally fixed bone as a result of applied bending, compression, and torsional loads. The pin configuration in this model is constructed to allow an angular separation of the fixator pins. The mechanical effect of this angular separation and of the distribution of the pins along the fixator bar is examined. The model shows that an angular separation of the pins provides a more symmetric deformation of the fracture site when a bending load is applied in different directions to the bone and thereby protects a fracture from excessive movement in any direction. The torsional stability of an external fixation frame is considerably increased by incorporating an angular separation of the pins. The model also shows that the most stable configuration for the fixator uses a wide separation of the pins along the fixator bar.     

Insertion force measurement of cervical traction tongs: a biomechanical study

OBJECTIVES: To measure the insertion forces for various cervical traction tong pins and the force required to penetrate cadaveric skull specimens. DESIGN: Cadaveric study testing tong pin forces. METHODS: Insertion force and pin indicator displacement were measured in three tongs from each of three manufacturers (PMT, Depuy Ace, Gardner-Wells) after tightening pins per the manufacturer's recommendations and beyond. The force required for skull penetration was measured by driving each pin into cadaveric temporal specimens until the specimen failed or was penetrated. RESULTS: Forces generated at the recommended pin settings were: PMT, 141 +/- 12 newtons; Ace, 0 +/- 0 newtons; Gardner-Wells, 132 +/- 9 newtons. The Ace tong required 1.0-millimeter indicator protrusion beyond manufacturer's recommended setting before generating clinically significant forces (120 +/- 8 newtons). Unlike the PMT and Ace pins, overtightening of the Gardner-Wells pins (by as little as 0.3 mm beyond recommended indicator displacement) resulted in substantially larger pin force (>448 newtons). Average failure loads of the temporal bone specimens were: PMT, 721 +/- 298 newtons; Ace, 636 +/- 351 newtons; Gardner-Wells, 965 +/- 227 newtons. CONCLUSIONS: Although pin forces generated at the recommended end point for PMT and Gardner-Wells tongs appear safe, insufficient force was generated for Ace tongs. Furthermore, overtightening of the Gardner-Wells pins generated loads in excess of those that may be required to penetrate the skull.     

The small pin circular fixator for proximal tibial fractures with soft tissue compromise

We used a Monticelli-Spinelli small pin circular external fixator in five cases, in combination with closed reduction or limited open reduction internal fixation, to salvage a satisfactory result in juxtaarticular, intraarticular fractures of the proximal tibia, when associated soft tissue compromise prevented standard fixation with plates and screws. The small pin circular fixator allows juxtaarticular placement of the small pins, enhancing stabilization of the comminuted fractures, allowing early range of motion of the joint and early patient mobilization. The small diameter pins support the soft cancellous bone fragments. This technique attempts to combine the benefits of traction, external fixation, and limited internal fixation. We recommend this method as a salvage procedure when plates and screws are contraindicated because of poor bone and soft tissue conditions.     

Experimental study on internal fixation of femoral neck fractures.

The relative strength and the failure mode of internal fixation by multiple pinning and nailing was investigated on 35 specimens. Internal fixation consisted of 3, 5 and 7 Knowles pins, a Smith-Petersen nail or a sliding nail plate. The strength of a specimen with a triflanged nail is only half of that with multiple Knowles pins. There is no significant difference in strength of 3, 5, or 7 pin specimens. The strength of an internal fixation with a sliding nail plate is not superior to the strength of multiple pinning. The mode of failure for the different types of internal fixation is primarily a crush fracture of the supporting trabecular bone at the femoral neck with downward and outward migration of the pins or nail. Except with the fixation with 3 pins where an initial bending could be observed, failure is not a plastic deformation of the internal fixation device.     

可吸收锥形针固定手部骨折的生物力学研究

目的 研究可吸收锥形针的生物力学性能,探讨其在手部骨折中应用的可行性.方法 取新鲜冰冻尸体掌、指骨共32根,左右配对,斜形截骨后分别用2根1.0 mm克氏针和2根1.3 mm 可吸收锥形针固定,通过折弯试验和疲劳试验对两种材料进行生物力学测试.结果 可吸收锥形针的抗弯刚度和最大载荷均显著小于克氏针;疲劳试验后两种材料的抗弯刚度差异无统计学意义,克氏针的最大载荷显著大于可吸收锥形针,而可吸收锥形针经疲劳试验后形变显著小于克氏针;疲劳试验后可吸收锥形针与克氏针的最大载荷比大于折弯试验中两者的最大载荷比,差异有统计学意义,而抗弯刚度比差异无统计学意义.结论 可吸收锥形针强度小于克氏针,但足以对抗术后功能锻炼时的应力,由于具有良好的弹性,在术后功能锻炼方面比克氏针更优越.     

Anodic plasma chemical treatment of titanium Schanz screws reduces pin loosening

OBJECTIVE: This study was designed to assess the benefits of a new Anodic Plasma Chemical calcium-phosphate (APC-CaP) surface treatment on reducing pin track infection and pin loosening in comparison to anodized titanium (Ti) during external fracture fixation. METHODS: A tibial midshaft, transverse, 6-mm gap osteotomy was created in 17 adult female Swiss alpine sheep. The tibia was stabilized with an external fixator and 4 Schanz screws of Ti or APC-CaP-treated Ti. The sheep were examined during a 12-week observation period. Infection was assessed with weekly clinical pin track grading and microbiologic assessment at sacrifice. Pin loosening was assessed by grading for radiolucency on biweekly radiographs and by measuring extraction torque on pin removal. In vivo bending stiffness measurements were performed to determine gap healing. A qualitative histologic assessment of the tissue adjacent to pin sites was also performed. RESULTS: A trend (P = 0.056) for less infection around APC-CaP pins was found at 6 weeks, but the strength of this difference diminished with time. Significantly more radiolucency was found around Ti pins after 8 (P = 0.011) and 12 (P < 0.001) weeks. At all pin sites, the extraction torque for APC-CaP pins was higher than for Ti pins (P = 0.007). No difference in the progression of gap healing was found. Histology showed bone growth at the implant surface in the form of distance osteogenesis for Ti and contact osteogenesis for APC-CaP. CONCLUSIONS: This study has shown that the APC-CaP surface improves the clinical performance of Ti pins with respect to pin loosening and pin track infection.