Locking Screws Research Articles

Analysis of risk factors for failure of locked plate fixation of distal femur fracture

Background: It is quite rare as well as severe to seen commonly distal femur fractures. 0.4% and 3% is the estimated frequency of all fractures and femoral fractures. The gender ratio has changed and today there is a majority of women, and the population is also increasingly older; mean 61 years old at fracture and over 65 in more than half the cases. Hence; we planned this study to examine patients with distal femoral fractures which were treated with locked plates, to assess the various risk factors responsible for complications. Materials & Methods: The present study was carried out in department of orthopaedics and included 400 patients who were treated with open reduction internal fixation (OIF) using a lateral distal femoral locked plate construction. Prospective institutional databases were used to gather information on the fixation which included locked screws in the distal fragment and non-locked, locked, or a combination of locked and non-locked screws in the proximal fragment of the bone. Only the patients with unilateral fracture were included for the present study. All the patients were divided into three predominant groups for the sake of convenience of description, namely; the entire cohort group, group with closed fractures, and group with open fractures. Primary outcome measures included reoperation to promote union, deep infection, and construction failure. These dependent variables were used in statistical analyses. For the identification of the risk factors, the 3 separate groups (entire cohort, closed fractures, and open fractures) were used for each of these populations. Results: A little of 20% of the total fractures required re-operation. Diabetes and open fractures were found to be the independent risk factors for reoperation to promote union and deep infection. For implant failure, risk factors included open fracture, smoking and shorter plate length. Conclusion: It is more advantageous to use relatively long constructs for the treatment of supracondylar femur fractures

A hybrid approach to mid-shaft clavicle fixation

BackgroundThe purpose of this study was to demonstrate the strength characteristics of a hybrid uni-cortical construct for clavicle fixation. The technique reported aims to combine benefits of uni-cortical fixation with stability comparable to traditional bi-cortical fixation. The approach utilises long, oblique uni-cortical screws at the distal ends of the plate acting as surrogate bi-cortical screws. Locked uni-cortical screws positioned centrally provide bending and torsion strength to the construct. This alternative hybrid uni-cortical technique does not require far cortex screw or drill penetration required in bi-cortical fixation techniques, thus avoiding potentially catastrophic vascular and or neurologic injury. The purpose of this study was to compare the mechanical behaviour of the hybrid uni-cortical construct to standard bi-cortical fixations under both torsion and bending loads. MethodThirty osteotomized human cadaveric clavicles were randomly allocated to three surgical fixation techniques: bi-cortical locked screw fixation, bi-cortical non-locked screw fixation and hybrid uni-cortical screw fixation. Each clavicle construct was tested non-destructively under torsional loading, and then under cantilever bending to failure. Construct bending and torsional stiffness, as well as ultimate failure strength, were measured. ResultsThere were no significant differences between uni-cortical or bi-cortical fixation constructs in either bending stiffness or ultimate bending moment (p>0.05); however, there was a trend towards greater bending stiffness in the hybrid construct. The uni-cortical hybrid fixation technique displayed a significantly lower mean torsional stiffness value when compared with the bi-cortical locked screw fixation (mean difference: 134.4Nmm/degrees, 95% confidence interval [32.3, 236.4], p=0.007). ConclusionA hybrid uni-cortical approach to clavicle plate fixation that may improve screw purchase and reduce risk of intra-operative vascular damage demonstrates comparable bending strength to current bi-cortical approaches.

Reducing Fracture Risk Adjacent to a Plate With an Angulated Locked End Screw.

Locking screws often are used in the treatment of osteoporotic fractures. Studies show that locking screws can increase bone stresses at the plate end, which increases the possibility of peri-implant fracture. This study evaluates whether the technique used to insert the end screw is related to the fracture tolerance adjacent to the plate. Twelve groups of plate constructs were evaluated using a fibular diaphyseal surrogate with mechanical properties similar to osteoporotic bone. All inboard screws were nonlocked with only the end screw fixation differing among groups. The end screws were inserted either perpendicularly to the plate or at an angle of 30 degrees for 6- and 12-hole plates. For both orientations, the end screws were inserted nonlocked, locked, or by a locked overdrilling technique, resulting in 6 groups per plate length. The perpendicular nonlocked screws represented a control group. The constructs were tested to failure in 4-point bending to determine peak load, failure energy, and stiffness. All constructs failed by peri-implant fracture along a plane through the 2 cortical holes of the end screw. Compared with the control group, an angulated locked screw at the plate end significantly increased the peak bending moment and energy required to produce a fracture for both plate lengths (6-hole, P = 0.008, P < 0.001; 12-hole, P = 0.006, P < 0.001). The use of an angulated locked end screw may enhance the resistance of osteoporotic bone to peri-implant fractures caused by bending forces.

Tangential Bicortical Locked Fixation Improves Stability in Vancouver B1 Periprosthetic Femur Fractures: A Biomechanical Study.

The biomechanical difficulty in fixation of a Vancouver B1 periprosthetic fracture is purchase of the proximal femoral segment in the presence of the hip stem. Several newer technologies provide the ability to place bicortical locking screws tangential to the hip stem with much longer lengths of screw purchase compared with unicortical screws. This biomechanical study compares the stability of 2 of these newer constructs to previous methods. Thirty composite synthetic femurs were prepared with cemented hip stems. The distal femur segment was osteotomized, and plates were fixed proximally with either (1) cerclage cables, (2) locked unicortical screws, (3) a composite of locked screws and cables, or tangentially directed bicortical locking screws using either (4) a stainless steel locking compression plate system with a Locking Attachment Plate (Synthes) or (5) a titanium alloy Non-Contact Bridging system (Zimmer). Specimens were tested to failure in either axial or torsional quasistatic loading modes (n = 3) after 20 moderate load preconditioning cycles. Stiffness, maximum force, and failure mechanism were determined. Bicortical constructs resisted higher (by an average of at least 27%) maximum forces than the other 3 constructs in torsional loading (P < 0.05). Cables constructs exhibited lower maximum force than all other constructs, in both axial and torsional loading. The bicortical titanium construct was stiffer than the bicortical stainless steel construct in axial loading. Proximal fixation stability is likely improved with the use of bicortical locking screws as compared with traditional unicortical screws and cable techniques. In this study with a limited sample size, we found the addition of cerclage cables to unicortical screws may not offer much improvement in biomechanical stability of unstable B1 fractures.

Is There an Optimal Proximal Locking Screw Length in Retrograde Intramedullary Femoral Nailing? Can We Stop Measuring for These Screws?

Insertion of locking screws through the proximal thigh while locking retrograde femoral nails is arguably more difficult and traumatic to local tissues than locking at other intramedullary nail sites. The purpose of this study was to evaluate whether a "standard" screw length for proximal interlocking of retrograde nails is possible, therefore assessing whether the act of measuring for these screws can be omitted. This article retrospective evaluates screw position and estimated proximal locking screw length in patients undergoing retrograde nailing using a large radiographically measured computed tomography cohort, with validation through a smaller clinical cohort. According to these data, it seems reasonable to skip depth gauge measurement during anteroposterior interlocking of retrograde femoral nails and insert a standard length screw based on location relative to the lesser trochanter. This should decrease the amount of local trauma to the patient at the locking screw site while increasing operating room efficiency by avoiding what can often become a difficult step during the procedure.

Training Distal Locking Screw Insertion Skills to Novice Trainees

To compare the effect fluoroscopy or electromagnetic (EM) guidance has on the learning of locking screw insertion in tibial nails in surgical novices. A randomized, prospective, controlled trial was conducted involving 18 surgical trainees with no prior experience inserting locking screws in intramedullary nails. After a training session using fluoroscopy, participants underwent a pretest using fluoroscopic guidance. Participants were then randomized into either the fluoroscopy or EM group and were further trained using their respective technique. Post, retention, and transfer tests were conducted. Outcomes included task completion, drill attempts, screw changes, and radiation time. Intragroup comparisons revealed that the EM group used significantly less drill attempts during the post and retention tests compared with the pretest (P = 0.016 and P = 0.016, respectively). Intergroup comparisons revealed that the EM group was (1) more likely to complete the task during the retention test (P = 0.043) and (2) had significantly less radiation time during the post and retention tests (P = 0.002 and P = 0.003, respectively). Radiation time in the EM group during the transfer test increased to a level equal to what the fluoroscopy group used during the post and retention tests (P = 0.71 and P = 0.92, respectively). No other significant between-group differences occurred. EM guidance may be safely used to assist in the training of surgical novices in the skill of distal locking screw insertion. Not only does this technology significantly improve the ability to complete the task and decrease radiation use but also it does so without compromising skill acquisition. Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

Est-il avantageux d’ajouter une vis supplémentaire au travers du calcar dans l’enclouage verrouillé de l’humérus proximal ?

BackgroundThe objective of this study was to evaluate the biomechanical effect of an additional unlocked calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck. HypothesisThe additional calcar screw improves stiffness and failure load. MethodsFourteen fresh-frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc®-nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load to failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α=0.05). ResultsNo significant differences was observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases. DiscussionThe use of an additional unlocked calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck. Level of evidenceLevel III. Experimental biomechanical study with human specimen.

Avoiding complication of volar locked plates

Volar locking plates are designed to improve and maintain anatomic alignment, even in patients with dorsal comminution and poor metaphyseal bone quality. Its widespread use led to specific complications. Most part is related to tendon, nerve and complex regional pain syndrome [1] and could be avoided by meticulous attention to detail and surgical experience [2]. Tendon and articular injury complications can be prevented by careful avoidance of dorsal cortex and intraarticular screw penetration, use of the low profile plates, and careful placement of the plate proximal to the watershed line. Most frequent tendons affected are Extensor Policis Longus (EPL) and Flexor Policis Longus (FPL). EPL tendon rupture can occur after a distal radius fractures even when not fixed by a plate [3]. Use of standard intraoperative fluoroscopy imaging is crucial to assess dorsal cortex screw penetration. Lister tubercle can mask prominent screws tips and lateral images have limited sensibility particularly among less experienced observers and for the evaluation of the most ulnar screw positions [4]. Irritation or rupture of flexor tendons, especially the FPL, depends on the position of the plate [5]. Assessment of articular penetration of the screws is critical. Routine use of articular views [6], as well as a 45° pronated oblique view [7] in doubtful cases, is mandatory during placement of each screw. Postoperative nerve dysfunction is one of the most common complications, especially median nerve dysfunction [1]. K-wires used for provisional and supplementary fixation can be a source of complications. Such complication may be caused by superficial radial nerve irritation due to K-wire placement during fracture reduction. Finally, loss of reduction due to inadequate screw length or very osteoporotic bone may lead to symptomatic malunion. In extra-articular fractures, a minimum of four locked unicortical distal screws [8] of at least 75% length produce construct stiffness similar to bicortical fixation and should be considered to avoid extensor tendon injury [9]. This is not the case when there are dorsal unstable articular fragments that can displace afterwards. Once the fracture is healed, plates and screws are not necessary anymore and their removal can be indicated or suggested as a prophylactic measure, as this procedure is usually not associated with complications [10].

Is there any advantage in placing an additional calcar screw in locked nailing of proximal humeral fractures?

BackgroundThe objective of this study was to evaluate the biomechanical effect of an additional unlocked calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck. HypothesisThe additional calcar screw improves stiffness and failure load. MethodsFourteen fresh frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc®-nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load-to-failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α=0.05). ResultsNo significant differences were observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases. DiscussionThe use of an additional unlocked calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck. Level of evidenceLevel III. Experimental biomechanical study with human specimen.

Far cortical locking screws in distal femur fractures.

Distal femur fractures routinely heal by secondary bone healing, which relies on interfragmentary motion. Periarticular locking plates are commonly used for fixation in distal femur fractures but are associated with a high nonunion rate, likely due to the stiffness of the constructs. Far cortical locking (FCL) screws are designed to allow micromotion at the near cortex while maintaining purchase in only the far cortex. Although clinical data are limited, these screws have been shown in biomechanical studies to provide excellent interfragmentary motion, and animal models have shown increased callus formation compared with traditional locking screws. The purpose of this study was to examine the clinical effects that FCL screws have on healing in distal femur fractures treated with locked constructs. In this retrospective case series, 15 patients with a distal femur fracture treated with MotionLoc screws (Zimmer, Warsaw, Indiana) were analyzed. Serial radiographs were evaluated for callus presence and time to union. All fractures were either 33-A3 or 33-C2 according to the AO classification system, and 5 (33%) were open. Bone loss was recorded in 2 patients. There were no nonunions, and average time to union was 24 weeks. There were no implant failures, and all 5 open fractures, including the 2 with bone loss, healed without intervention. There was 1 reoperation due to painful hardware. Although this is a small case series, these results are promising. Far cortical locking screws may provide the answer to the high nonunion rate associated with distal femur fractures treated with traditional locked constructs.

Dynamization at the near cortex in locking plate osteosynthesis by means of dynamic locking screws: an experimental study of transverse tibial osteotomies in sheep.

Locking plates are widely used in fracture fixation, mainly for meta-diaphyseal fractures, comminuted fractures, fractures with a critical-size bone defect, periprosthetic fractures, osteotomies, and fractures in osteoporotic bone. The aim of this animal study was to evaluate the effect on bone-healing of dynamization of locking plate constructs by means of new 5.0-mm dynamic locking screws (in the DLS group), which allow near-cortex micromotion, compared with a more rigid construct utilizing standard bicortical locking-head screws (in the LS group). Use of dynamic locking screws allows modulation of the stiffness of existing locking compression plate systems via parallel interfragmentary micromotion. A standardized diaphyseal tibial osteotomy (90°, 3-mm fracture gap) was performed and stabilized with a six-hole large-fragment locking compression plate in twelve female sheep (six in each group). Radiographs were made postoperatively and then weekly from week three until sacrifice at nine weeks. Macroscopic, biomechanical, histologic, and radiographic assessments and microcomputed tomography were performed. The callus in the tested specimens in the DLS group had better biomechanical stability, with a significantly greater maximum failure moment (mean and standard deviation [SD] as a percentage of intact, 55.15 ± 20.65 compared with 26.80 ± 14.96 in the LS group; p = 0.021). The DLS group also had greater periosteal callus volume at the near cortex (mean volume and SD as a percentage of the tibial shaft volume, 36.21% ± 10.08% compared with 18.98% ± 8.61% in the LS group; p = 0.026) and in the intercortical region (mean volume and SD as a percentage of the bone volume of the tibial shaft, 3.56% ± 0.52% compared with 2.64% ± 0.98% in the LS group; p = 0.045), as shown by microcomputed tomography. The DLS group also had significantly greater torsional stiffness (mean and SD as a percentage of intact, 84.88 ± 13.51 compared with 58.89 ± 20.61 in the LS group; p = 0.027). Controlled micromotion and nearly homogeneous interfragmentary strain at the fracture site, together with the stable bicortical fixation achieved by the new dynamic locking screw, led to more uniform callus formation, significantly more callus formation at the near cortex, and biomechanically more competent bone-healing compared with use of rigid locking plate constructs with locking-head screws.

Reliability of threaded locking screws.

A frequent problem for interlocking nailing that affects the treatment of the fracture is locking screw deformation. The aim of this study is to determine whether bending resistance is different between high, low, and unthreaded locking screws of interlocking femoral nails. Ninety screws were used in this experimental study, with 10 screws used in each of 9 groups. Three-point bending tests were performed on 6 groups of 5 mm screws (titanium, stainless steel, crossed with unthreaded, low threaded, and high threaded) and the same 3 thread types of 5.5 mm stainless steel screws in a 30-mm inner diameter steel tube, imitating the level of the lesser trochanter. An axial compressor was used to determine the yield points for permanent deformation in the locking screws by way of 3-point bending tests. The mean yield point value of the 3-point bending tests of 5-mm low threaded stainless steel locking screws was 2071 N, 53% less than that of unthreaded screws (3169 N). The mean yield point value of 5-mm high threaded stainless steel locking screws was 556 N, 272% less than that of low threaded screws (2071 N). To avoid locking screw deformation, high threaded screws must not be used as locking screws. In cases of unreliable patients, 5-mm low threaded screws should not be used in the nailing of comminuted or oblique femur shaft fractures. All 5-mm unthreaded screws and 5.5-mm low threaded stainless steel screws can be used safely in full weight-bearing conditions of unreliable patients.

A New Femoral Nail with Single Distal Locking Screw for Maximum Inter Fragment Rotational Stability

A New Femoral Nail with Single Distal Locking Screw for Maximum Inter Fragment Rotational Stability

Full weight bearing and dynamisation with Limmed® locked plate fixation accelerates bone regeneration in the volume of opening wedge high tibial osteotomy.

The efficacy of immediate full weight bearing in accelerating bone regeneration after medial opening wedge high tibial osteotomy (HTO) was evaluated in patients operated with the Limmed system (locked plate fixation) that allows dynamisation of the site of the osteotomy. A case series of 50 consecutive osteotomies performed with Limmed locked plate fixation for medial opening wedge HTO had full weight bearing immediately after the HTO; they were compared to a case-matched control series of 50 HTOs (50 patients) performed using the same implant without locked screws. Radiographs were observed at 30days and two, three, four, five and sixmonths after surgery. The osteotomy gap was only partially filled by a medial bone substitute leaving the lateral part unfilled. Bone surface areas of osteotomy planes were quantified and opening volumes were determined applying wedge heights. End points for evaluation included radiographic evidence of bone regeneration in the volume created by the opening of the osteotomy. Statistically significant differences were seen between the groups in terms of radiographic union and radiographic stability between the two groups. Patients of the Limmed group reported a shorter time for union (average fourweeks difference) without loss of correction during healing. At the radiographic evaluation, there was a significant increase in osseointegration in the group with weight bearing compared to the control group without weight bearing with increased rate of speed to fill the void volume of the osteotomy. The computed tomography scan of the grafted area at fourmonths after surgery showed no significant difference in the quality of the newly formed bone between the two groups. The Limmed medial opening wedge HTO system with immediate full weight bearing accelerates bone graft substitute osseointegration and bone healing as compared with controls without full weight bearing.

A Technique to Remove Stripped Star-recess Locking Screws

A Technique to Remove Stripped Star-recess Locking Screws

Effect of Off-Axis Screw Insertion, Insertion Torque, and Plate Contouring on Locked Screw Strength

This study quantifies the effects of insertion torque, off-axis screw angulation, and plate contouring on the strength of locking plate constructs. Groups of locking screws (n = 6-11 screws) were inserted at 50%, 100%, 150%, and 200% of the manufacturer-recommended torque (3.2 Nm) into locking compression plates at various angles: orthogonal (control), 5-degree angle off-axis, and 10-degree angle off-axis. Screws were loaded to failure by a transverse force (parallel to the plate) either in the same ("+") or opposite direction ("-") of the initial screw angulation. Separately, locking plates were bent to 5 and 10-degree angles, with the bend apex at a screw hole. Locking screws inserted orthogonally into the apex hole at 100% torque were loaded to failure. Orthogonal insertion resulted in the highest average load to failure, 2577 ± 141 N (range, 2413-2778 N), whereas any off-axis insertion significantly weakened constructs (165-1285 N, at 100% torque) (P < 0.05). For "+" loading, torque beyond 100% did not increase strength, but 50% torque reduced screw strength (P < 0.05). Loading in the "-" direction consistently resulted in higher strengths than "+" loading (P < 0.05). Plate contouring of 5-degree angle did not significantly change screw strength compared with straight plates but contouring of 10-degree angle significantly reduced load to failure (P < 0.05). To maximize the screw plate interface strength, locking screws should be inserted without cross-threading. The mechanical stability of locked screws is significantly compromised by loose insertion, off-axis insertion, or severe distortion of the locking mechanism.

Dynamic-locking-screw (DLS)-leads to less secondary screw perforations in proximal humerus fractures.

BackgroundLoss of reduction and screw perforation causes high failure rates in the treatment of proximal humerus fractures. The purpose of the present study was to evaluate the early postoperative complications using modern Dynamic Locking Screws (DLS 3.7) for plating of proximal humerus fractures.MethodsBetween 03/2009 and 12/2010, 64 patients with acute proximal humerus fractures were treated by angular stable plate fixation using DLSs in a limited multi-centre study. Follow-up examinations were performed three, six, twelve and twenty-four weeks postoperatively and any complications were carefully collected.Results56 of 64 patients were examined at the six-month follow-up. Complications were observed in 12 patients (22%). In five cases (9%), a perforation of the DLS 3.7 occurred.ConclusionsDespite the use of modern DLS 3.7, the early complications after plating of proximal humerus fractures remain high. The potential advantage of the DLS 3.7 regarding secondary screw perforation has to be confirmed by future randomized controlled trials.

Computational Simulation of Mechanical Microenvironment of Early Stage of Bone Healing under Locking Compression Plate with Dynamic Locking Screws

It is well known that bone healing outcomes highly depend on the mechanical microenvironment of the fracture site, and a certain degree of interfragmentary movement (IFM) is essential for indirect (i.e. natural) bone healing. The application of locking compression plate (LCP) internal fixation in the treatment of bone fracture is a common practice which leads to early mobility and full function of the fractured extremity. However should the fixation configuration be too stiff, it might result in delayed healing or asymmetric tissue development across the fracture site due to the fact that IFM in near cortex area is too small to promote healing. Dynamic locking screw (DLS) has been recently designed to tackle this problem by reducing the stiffness of LCP fixation. However, the actual mechano-regulation mechanisms in which DLS uses to regulate the healing process are still not fully understood. The objective of this paper is to develop a computational model to understand the change of mechanical microenvironment of fracture site under LCP with dynamic locking screw in comparison to standard locking screw, and how this change could potentially regulate tissue development within the fracture callus during the healing process.Keywords: bone healing, locking compression plate, dynamic locking screw, finite element modelling

A novel micro-controlled dynamic intramedullary nail for tibial middle fracture in Tibet mini-pigs

Objective To explore the effect on the fracture union in Tibet mini-pigs of a novel micro-controlled dynamic intramedullary nail which was self-designed on the basis of anatomic parameters of the animal tibia.Methods We measured the length,arc and inner diameters of the starting,narrowest and ending points of the bilateral tibial medullary cavities on the X-ray films of 20 Tibet mini-pigs.We designed and manufactured a new micro-controlled intramedullary nail using UG software on the basis of the anatomic measurements and CT 3D reconstructions of the animal tibia.The new fixation nails were tested in the animal models of left tibial middle fracture in 10 Tibet mini-pigs which were randomized into 2 groups (n =5).The experiment group was treated with the novel micro-controlled dynamic intramedullary nail and the control group with the static interlocking intramedullary nail.The fracture union was evaluated and compared between the 2 groups by X-ray,gait analysis and micro CT.Results Of the medullary cavity,the triangle proximal end was expansive,the middle segment was narrow and the oval distal end was also expansive in the Tibet mini-pigs.The length of medullary cavity averaged 113.31 ± 9.56 mm and the cavity arc 25.66° ± 3.37°.The nail length was 90 to 130 mm,the nail diameter 6 to 9 mm,the arc 15° to 25°,and the diameter of both locked screw and bioresorbable material 4.0 mm.The micro CT showed that the experimental group had significantly higher volume bone density (555.47 ± 23.49 mg/mm3) and bone volume fraction (0.84 + 0.04) than the control group (494.45 ± 16.62 mg/mm3 and 0.78 ± 0.03 respectively) (P ＜ 0.05).Conclusion It may help fracture union to design a novel micro-controlled dynamic intramedullary nail based on the theory of micro-controlled motion in clinic research. Key words: Bone nails; Fracture fixation, intramedully; Fracture healing; Imaging,three-dimensional

Do Locking Screws Work in Plates Bent at Holes?

To assess whether plate bending at a hole significantly changes the biomechanical properties of a locked screw. Coronal plane bends of 5-, 15-, or 45-degree angles were placed in 3.5-mm locking compression plates with the apex at a locking hole. An additional 45-degree angle test group was created in which a threaded screw head insert was placed before bending. Ten plates were tested in each group and compared with nonbent controls in a stepwise cyclic loading protocol. Statistically significant differences in protocol survival were shown between the control group and the 15-degree angle (P = 0.006) and 45-degree angle (P = 0.0007) groups. An apparent decrease in protocol survival in the 5-degree angle group did not reach statistical significance (P = 0.17). The average number of cycles survived was significantly different between the control group and the 15-degree angle (P = 0.027) and 45-degree angle (P = 0.0002) groups. The mean cycles to failure for the 5-degree angle group was 16% lower than for controls but did not reach statistical significance (P = 0.37). The test group bent to an angle of 45 degrees after placement of a threaded screw head insert showed no difference in protocol survival or in mean number of cycles survived compared with the regular 45-degree angle group. Bending of a 3.5-mm locking compression plate by more than 5 degrees at a locking hole results in a statistically significant decrease in survival of the corresponding locked screw. This effect cannot be prevented by the placement of a threaded screw head insert before bending.