Biomechanical evaluation of locking plate fixation with hybrid screw constructs in analogue humeri

Locking plates are well suited to complex fracture patterns and weak bone. In the study reported here, we compared the structural stability of 3 different locking compression plate (LCP) constructs using composite analogue humeri. Eighteen analogue composite humeri were used as bone models. A 6.5-mm osteotomy gap was stabalized with a 9-hole 3.5-mm narrow LCP using four 3.5-mm self-tapping screws on each side of the fracture with the middle hole empty. Three construct configurations were studied: B (all screws bicortical), BU (bicortical screw on each side of fracture gap and remaining screws unicortal), and U (all screws unicortal). Each bone model was fixed in a customized jig and subjected to mediolateral and anteroposterior 4-point bending and external rotational torque to assess rigidity, stiffness, and failure. There was significant (P<.05) differences in torsional stiffness but no significant differences in terms of flexural rigidity between each of the constructs. The results also indicated that construct BU provided as much stability as the other constructs. Therefore, consideration should be given to type of fixation construct, especially when torsional stability is required. Replacing a single set of unicortal locking screws with bicortical locking screws closer to the fracture site improved construct stability compared with any unicortal screw construct. A hybrid fixation construct that provides bicortical screws at any location may provide equivalent construct stability in this model. Hybrid fixation constructs may provide adequate fracture stabilization for a fracture pattern that would typically be considered unstable.     

无头加压螺钉联合PHILOS钢板固定在胫距跟关节融合中的应用

目的探讨应用无头加压螺钉联合PHILOS钢板行胫距跟关节融合术治疗胫距、距下关节严重病变的临床疗效。方法笔者自2011-02—2014-02采用经外踝截骨入路、无头加压螺钉联合PHILOS钢板行胫距跟关节融合术治疗13例胫距、距下关节病变患者。所有患者均有足踝部疼痛,功能受限。术后功能评价采用美国骨科足踝协会(AOFAS)踝和后足评分系统。结果 1例失访,12例获得随访12~24个月,平均16.7个月。切口均一期愈合,术后平均11.3(8~16)周达骨性愈合。末次随访患者关节疼痛完全缓解,无内固定失败及融合失败等并发症发生,末次随访所有患者踝关节疼痛均得到明显缓解,无行走痛,步态基本正常。术前AOFAS评分为(48.75±6.8)分,末次随访AOFAS评分为(83.5±8.4)分,术后AOFAS评分优于术前,差异有统计学意义(t=18.790,P0.001)。2例出现足背外侧皮肤感觉减退,末次随访未恢复。结论经外踝截骨无头加压螺钉联合PHILOS钢板行胫距跟关节融合术,固定强度可靠,融合率高,是临床治疗踝关节和距下关节严重关节疾病的一种有效方法。     

Clinical results of minimal screw plate fixation of forearm fractures.

Traditional plating technique for forearm fractures specifies implant selection based on achieving a minimum number of "cortices" of screw fixation on either side of the fracture. Recent biomechanical data suggest that plates with fewer screws provide equivalent strength of fixation compared with standard compression plating techniques in forearm fractures. As described in this article, we retrospectively reviewed a surgeon's experience at a regional level I trauma center to evaluate the clinical outcome of this newer fixation strategy. Seventy-eight fractured bones were plated using "minimal" screw technique--less than the traditionally recommended 6 cortices of screw purchase. Nonunion or fixation failure occurred in 7 fractures (5 patients), producing a union rate of 91% (71/78). All nonunions were atrophic and occurred in open fractures with bone loss. No construct failed because of fixation loss caused by having too few screws. Minimal screw plate technique was stable fixation, despite not having 6 cortices on both sides of the fracture. Technical emphasis should be on adequate plate length rather than number of cortices of fixation in each segment.     

Valgus osteotomy in delayed presentation of femoral neck fractures using fixed angle simple dynamic hip screw and plate

Purpose

Reduction and fixation in femoral neck fracture in young patients have a problem of nonunion requiring additional procedure like valgus osteotomy but fixation devices are technically difficult for inexperienced surgeons. We aims to assess the results of valgus osteotomy in femoral neck fracture in our setup.

Influence of the number of cortices on the stiffness of plate fixation of diaphyseal fractures

OBJECTIVE: To determine the influence of the number of cortices of fixation on the stiffness of plate fixation of diaphyseal fractures. DESIGN: Canine experimental study. SETTING: Tertiary referral and teaching hospital in Toronto, Canada. PARTICIPANTS: Paired radii from fourteen skeletally mature, cross-bred dogs. MAIN OUTCOME MEASURE: One member of each pair of radii was tested intact as a control, and the other had a transverse osteotomy plated sequentially with five to ten cortices of fixation on either side of the simulated fracture. Dynamic compression plates and limited contact dynamic compression plates were used in two groups with seven paired radii each. Normalized torsional stiffness and four-point bending stiffness were determined in the elastic range for the control and each of the plated constructs in both groups, using a materials testing machine. RESULTS: The authors found no significant difference between the stiffness of the dynamic compression plates and limited contact dynamic compression plates. With either plate of a given length, significantly increased torsional stiffness is achieved with end bicortical screws. For bending stability with the plate at right angles to the bending plane, even short plated constructs have a stiffness exceeding that of intact bone. CONCLUSIONS: For a transverse osteotomy with no fracture interdigitation, the bending rigidity with the plate at right angles to the bending plane is greater than the original stiffness of the bone for all constructs tested, with the exception of the limited contact dynamic compression plate with five cortices of fixation. The torsional rigidity of fixation only approaches the original rigidity of the bone for ten cortices of fixation with the dynamic compression plate and the limited contact dynamic compression plate.     

骨质疏松性肱骨近端骨折PMMA骨水泥强化螺钉钢板固定的有限元分析

目的：借助有限元分析的方法探讨肱骨近端聚甲基丙烯酸甲酯（polymethyl methacrylate,PMMA）骨水泥强化螺钉钢板固定对骨质疏松性肱骨近端骨折内固定稳定性的影响。方法：制作肱骨近端2部分骨折伴干骺端骨缺损的不稳定肱骨近端骨折数字化模型,分别建立肱骨近端骨水泥强化螺钉钢板固定及普通螺钉钢板固定的有限元模型,分析螺钉周围松质骨应力、整体刚度、钢板最大应力及螺钉最大应力。结果：肱骨近端骨水泥强化螺钉钢板固定的头端6枚螺钉周围松质骨最大应力分别为：1号钉1.07 MPa,2号钉0.43 MPa,3号钉1.16 MPa,4号钉0.34 MPa,5号钉1.99 MPa,6号钉1.57 MPa,普通螺钉钢板固定为：1号钉2.68 MPa,2号钉0.67 MPa,3号钉4.37 MPa,4号钉0.75 MPa,5号钉3.30 MPa、6号钉2.47 MPa。两组模型的整体刚度分别为：骨水泥结构448 N/mm、普通结构434 N/mm。钢板的最大应力均出现在结合孔：骨水泥结构701 MPa、普通结构420 MPa。螺钉的最大应力均出现在4号钉的尾端：骨水泥结构284 MPa、普通结构...     

Bone healing after metal plate fixation and external fixation of the osteotomized rabbit tibia

Controversy still exists as to the best method of treatment of long bone fractures. The purpose of the present study was to compare the effects on the healing bone of external fixation and metal plate fixation. In an experimental model on the rabbit tibia the stiffness of the fixation corresponded intentionally to that of the same methods in human fracture treatment.

A transverse, midshaft osteotomy was made on one tibia, and fixed with a steel plate (45 × 5 × 1 mm) or external mini-fixation. The animals were killed after 4, 6 or 12 weeks. The bone healing was evaluated by radiography, histology and biomechanical testing in three-point bending. There were no significant differences between plate fixation and external fixation in the pattern of bone healing, as it occurred by periosteal, in-tramedullary and intercortical callus after both methods. The stiffness increased more rapidly than the strength, and reached normal values after about 6 weeks. No significant differences in stiffness between the two methods were found. The strength was significantly greater after plate fixation than after external fixation at 6 weeks, while no significant differences were found at either 4 or 12 weeks.

It is concluded that the speed of bone healing was more rapid after plate fixation. However, in the later stages of healing the plated bones were secondarily weakened because of the stress-protecting effect of the plate.     

Fatigue subcapital fracture of the femur after the removal of the hip plate in transtrochanteric rotational osteotomy

We report two cases of fatigue subcapital fracture of the femur after the removal of the hip plate used for fixation in transtrochanteric rotational osteotomy for osteonecrosis. Two patients, a 42-year-old man and a 43-year-old man, underwent transtrochanteric rotational osteotomy, and bony union was achieved in both patients. However, fatigue subcapital fracture of the femur occurred in both patients 15 months after the removal of the hip plate. Transtrochanteric rotational osteotomy greatly changes the trabecular bone structure in the proximal femur, thus affecting the strength of the femoral neck. Therefore, for the trabecular bone to be remodeled and for the proximal femur to achieve sufficient strength, a sufficient period is necessary after complete bony union has occurred in the transtrochanteric lesion, before removal of the plate. Received: March 29, 2001 / Accepted: August 26, 2001     

Clinical results of minimal screw plate fixation of forearm fractures

Traditional plating technique for forearm fractures specifies implant selection based on achieving a minimum number of "cortices" of screw fixation on either side of the fracture. Recent biomechanical data suggest that plates with fewer screws provide equivalent strength of fixation compared with standard compression plating techniques in forearm fractures. As described in this article, we retrospectively reviewed a surgeon's experience at a regional level I trauma center to evaluate the clinical outcome of this newer fixation strategy. Seventy-eight fractured bones were plated using "minimal" screw technique--less than the traditionally recommended 6 cortices of screw purchase. Nonunion or fixation failure occurred in 7 fractures (5 patients), producing a union rate of 91% (71/78). All nonunions were atrophic and occurred in open fractures with bone loss. No construct failed because of fixation loss caused by having too few screws. Minimal screw plate technique was stable fixation, despite not having 6 cortices on both sides of the fracture. Technical emphasis should be on adequate plate length rather than number of cortices of fixation in each segment.     

Comparison of plate and screw fixation and screw fixation alone in a comminuted talar neck fracture model

BACKGROUND: Talar neck fracture fixation has been studied in noncomminuted fracture models, but no large clinical series of comminuted fracture patterns have been published and no biomechanical studies have compared plate fixation with screw fixation in comminuted talar neck fractures. METHODS: Nine matched pairs of fresh frozen talar specimens were stripped of soft tissue and mounted in a cylindrical jig. The talar neck was fractured using a dorsally directed shear force at a rate of 200 mm/min, and dorsal comminution was simulated by removing a 2-mm section of bone from the distal fracture fragment. One specimen from each pair was fixed with either two solid 4.0-mm partially threaded cancellous screws posterior-to-anterior just lateral to the posterior process of the talus or with a four-hole 2.0-mm minifragment plate contoured to the lateral surface of the talar neck and secured with 2.7-mm screws. A 2.7-mm fully threaded cortical screw was placed medially using a lag technique. The specimens were then loaded to failure with a dorsally directed force at a rate of 200 mm/min. Failure was defined as the load producing 2 mm of displacement. A Student's t-test analysis was used with significance set at p < or = 0.05. RESULTS: Posterior-to-anterior screw fixation had a statistically significant higher load to failure than plate fixation (p < 0.05). Mean load to failure for the screw group was 120.7 +/- 68.5 N and 89.7 +/- 46.6 N for the plating group. CONCLUSIONS: Plate fixation may offer substantial advantages in the ability to control the anatomic alignment of comminuted talar neck fractures, but it does not provide any biomechanical advantage compared with axial screw fixation. Further, the fixation strength of both methods was an order of magnitude lower than those found in previous studies of noncomminuted fractures.     

Salvage of failed dynamic hip screw fixation of intertrochanteric fractures

Twenty-six patients with failed dynamic hip screw fixation of intertrochanteric fractures were included in this study. The mean age of the patients was 61 years (range, 38-84 years). Average limb shortening was 2.4 cm; 18 patients were treated with revision internal fixation and eight patients with prosthetic replacement. The decision depended on the physiological age of the patient, quality of bone, and condition of the femoral head and the acetabulum. The revision internal fixation group included DHS reinsertion in eight patients, valgus osteotomy and revision DHS fixation in six, while four patients were treated by valgus osteotomy and insertion of single-angled 130 degrees plate. The prosthetic replacement group included cemented Thompson endoprothesis in five patients and cemented total hip arthroplasty in three. The mean follow-up period was 31 months (range, 15-72 months). All patients of revision internal fixation group achieved fracture healing without bone grafting. Time to union averaged 17 weeks. Average gain in length was 2 cm Avascular necrosis of the femoral head occurred in one patient. Six patients of the prosthetic replacement group achieved good functional outcome and pain-free gait. The remaining two had unsatisfactory result.     

Semitubular blade plate for fixation in the proximal humerus

Rigid internal fixation is frequently difficult to obtain in the proximal humerus, as osteoporotic bone and small fracture fragments may preclude firm purchase of plates and/or screws. We describe our clinical results using a semitubular plate, fashioned into a blade plate device, for fixation of four displaced fractures and three osteotomies of the proximal humerus. All patients were clinically and radiographically united by 4 months postoperatively and had a functional range of motion. The strength of this fixation was compared to that of an AO "T" plate in an oblique subcapital osteotomy model using 10 matched pairs of human humeri. No statistically significant difference could be demonstrated between the two fixation methods with regard to load to failure, yield load, energy absorbed to failure, or stiffness. As a consequence of these studies, we believe the semitubular blade plate expands the options available for challenging fixations in the proximal humerus.     

Hip fusion utilizing the cobra head plate.

Sixteen consecutive patients underwent hip fusion with fixation by a cobra head compression plate. In six patients on osteotomy of the innominate bone also was done. Four patients had no osteotomy whatsoever, while in six patients medial displacement of the femur was accomplished by centrally dislocating the femoral head through the acetabulum. This modification made the surgical procedure and postoperative care simpler, and rehabilitation was easily accomplished. All of the hips treated in this series had successful bone fusion. All of the patients were out of bed within the first postoperative week, and ambulation with crutches was begun after the second week.     

Role of valgus osteotomy and fixation with dynamic hip screw and 120° double angle barrel plate in the management of neglected and ununited femoral neck fracture in young patients

Background  Head preservation is the mainstay of management in younger patients with neglected or ununited intracapsular fracture neck of femur. Very few reports have dealt with the results of valgus intertrochanteric osteotomy and fixation with dynamic hip screw in such cases. In this prospective study, we have tried to evaluate the role of valgus osteotomy and fixation with dynamic hip screw and 120° double angle barrel plate in neglected or ununited intracapsular fracture neck of femur in patients below 60 years of age and whose time since injury is equal to or more than 3 weeks. Materials and methods  We treated 16 such cases with valgus intertrochanteric osteotomy and fixation achieved with dynamic hip screw and 120° double angle barrel plate, with mean age of 36.4 years. The cases were evaluated radiologically and clinically at a mean of 19 months. Results  In 14 of the 16 patients, the fracture went on to satisfactory union after an average of 14.7 weeks (10–26.7 weeks). The average Harris hip score increased from 66.6 points (range 55–75 points) before surgery to 88 points (range 75–95 points). All the patients with united fractures were able to sit cross-legged, squat and do one-leg stance. Pain and limitation of motion improved remarkably. Two patients had unfavourable outcome; both had cut-through of the implant, out of the head. Conclusions  Valgus intertrochanteric osteotomy is a very cheap and effective procedure to achieve union in neglected and ununited fracture neck femur in young patients. We propose fixation with dynamic hip screw and 120° double angle barrel plate as it provides additional compression and, with valgus osteotomy, improved stability of internal fixation, with few complications.     

Salvage of a failed valgus osteotomy for non-union of an unstable pertrochanteric fracture

Salvage of a failed valgus osteotomy for nonunion of an unstable pertrochanteric fracture is reported. A valgus intertrochanteric osteotomy was performed for a failed sliding hip screw fixation of an unstable pertrochanteric fracture at another institution. Four months following osteotomy, the fracture was still un-united with two distal screws of the hip plate broken and a coxa vara deformity. Reconstruction was performed with a nine-hole 95° angle blade plate and cancellous bone graft, because the insufficient fixation of the distal fragment was considered to be the main reason for failure. The osteotomy was healed at six months post-surgery and the patient reported complete resolution of symptoms. Intertrochanteric valgus osteotomy is an effective procedure for mal-union and non-union of pertrochanteric fracture but stable fixation is required for a good result. The blade of the angle plate offers good purchase of the proximal fragment and secures it under rotational and bending stresses. We recommend that distal fragments should be fixed with at least seven cortices for this type of osteotomy.     

应用异体腓骨结构性植骨结合钢板螺钉内固定治疗肱骨近端骨折的疗效

目的探讨应用异体腓骨结构性植骨结合钢板螺钉内固定治疗肱骨近端骨折的疗效。方法回顾性分析2014年7月至2017年9月在首都医科大学附属北京朝阳医院骨科应用异体腓骨结构性植骨结合钢板螺钉内固定治疗的11例肱骨近端骨折患者的病历资料。其中,男4例,女7例;平均年龄68(47~81)岁。Neer分型:3部分骨折8例,4部分骨折3例。采用Constant-Murley肩关节评分量表(CMS)对患者的肢体功能进行评定,并评估治疗效果及并发症发生情况。结果术后所有患者均获得随访,平均随访时间14.6(13~17)个月。所有患者均达到骨性愈合,未见内固定失效及骨折移位。CMS评分:优3例,良7例,一般1例。随访期间,有1例患者发生伤口感染。结论应用异体腓骨结构性植骨结合钢板螺钉内固定治疗肱骨近端骨折能提供更牢固的稳定性,满足患者早期功能锻炼需求,可提高预后效果。     

A comparison of plate versus staple-and-cast fixation in maintaining femoral tibial alignment after valgus tibial osteotomy.

PURPOSE: To compare 2 methods of fixation for maintenance of alignment during healing of valgus tibial osteotomies. METHODS: We performed a retrospective chart and radiographic review of valgus tibial osteotomy cases of staple fixation supplemented by a postoperative cast and of blade plate fixation for maintenance of femoral-tibial alignment during healing of the osteotomy. RESULTS: Both groups (staple-and-cast, n = 16; plate, n = 28) were similar in terms of age, preoperative alignment, extent of osteoarthritis and degree of intra-operative correction. Between-group differences in the maintenance of femoral-tibial alignment during healing were not significant. In both groups there was a strong correlation between degree of bone contact at the osteotomy site and maintenance of alignment (p < 0.005). In cases done with the plate, 90% of osteotomies with good or excellent bone contact maintained alignment during healing; with poor or fair bone contact, 75% had loss of alignment > 5 degrees during healing. There was a trend toward a greater incidence of delayed or non-union with plate fixation compared with staple fixation that did not reach statistical significance. All of these cases of delayed/non-union had loss of femoral-tibial alignment > 5 degrees during healing. CONCLUSION: As a result of this study, we have modified our surgical technique. We now use intra-operative fluoroscopy for optimization of bone contact, and we have reverted to the less invasive staple method for fixation of tibial osteotomies.     

Schuhli augmentation of plate and screw fixation for humeral shaft fractures: a laboratory study

OBJECTIVES: Schuhli locking nuts provide a mechanism to lock 4.5-millimeter bone screws to a standard dynamic compression plate (DCP plate). It has been proposed that Schuhlis can provide increased fixation stability in areas of a proximal cortical defect or osteopenic bone and may keep screws from loosening and backing out from the plate. A biomechanical study was performed to investigate the effect of Schuhli augmentation of a ten-hole broad DCP plate for fixation of a simulated humeral shaft fracture versus standard DCP plate fixation. DESIGN: Biomechanical cadaver study. INTERVENTION: Six pairs of cadaveric humeri from elderly individuals were tested in offset axial loading, torsion, and four-point bending to obtain load versus deformation curves and baseline mechanical properties. Each pair of humeri was then instrumented with a ten-hole broad DCP plate on one side and a DCP plate augmented with Schuhlis at each screw hole on the contralateral side. All screws were placed in cortical bone. The constructs were retested in all three modalities. The humeri were then cycled in torsion for 1,000 cycles and retested in all three modalities. Each humerus was then loaded to failure in torsion to determine the ultimate load and rotational displacement. MAIN OUTCOME MEASUREMENTS: Resistance to displacement was determined from the load versus deformation curves in each testing modality before and after cycling; these data were normalized to the intact values determined prior to instrumentation. Paired Student's t tests were performed to determine statistically significant differences between the two modes of fixation. RESULTS: There were no significant differences in stability between the two fixation techniques in all three testing modalities both before and after cycling. However, the Schuhli augmented constructs sustained significantly greater loads and rotational deformations prior to failure. CONCLUSIONS: In this model of humeral shaft fractures in the elderly, the addition of Schuhlis did not significantly change the mechanical stability of plate and screw fixation. However, load and angular deformation at failure were significantly greater in the Schuhli augmented specimens.     

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

Screw loosening is a common complication in plate fixation. However, the underlying mechanism is unclear. This study investigated screw loosening mechanisms by finite element analysis (FEA) simulation and clinical X‐ray feature analysis. Two FEA models incorporated bone heterogeneity and orthotropy, representing fracture fixation using dynamic compression plate (DCP) and locking compression plate (LCP), were developed. These models were used to examine the volume of bone exceeding a certain stress value around each screw under physiologically‐relevant loading conditions. These damaged bone was then separated and compared by the axial stress and radial stress of each screw. In addition, features of patients’ X‐ray images showing screw loosening were analyzed to validate the loosening features simulated by the models. The FEA study showed that more damaged bone was found at the central two screws which gradually decreased toward the two end screws in all groups. More bone was damaged by the radial stress of each screw than by the axial stress. The radiological analysis of screw loosening showed that bone loss occurred at the screw closest to the fracture line first then subsequent bone loss at the screws further away from the fracture line occurred. This study found that the two screws nearest to the fracture line are more vulnerable to loosening. The radial stress of the screw plays a larger role in screw loosening than the axial stress. Bone resorption triggered by the high radial stress of screws is indicated as the mechanism of screw loosening in the diaphyseal plate fixation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1498–1507, 2019.     

Locking plate fixation of humeral head fractures with a telescoping screw. A comparative biomechanical study versus a standard plate

ObjectivesLocking plate fixation of humeral head fractures bares the risk of glenohumeral screw penetration. In order to circumvent this problem it is recommended to insert shorter locking screws having at least a 6 mm distance to the humeral head cortex. This in turn may reduce fixation stability and may lead to early varus displacement. One second frequent failure mechanism is cranial displacement of the greater tubercle. The study evaluates the biomechanical properties of a locking plate employing an additional telescoping screw that may enhance resistance to varus displacement. Screw in screw fixation of the greater tubercle may reduce the rate of cranial displacement.MethodsIn four paired fresh-frozen human cadaver humeri (age > 70 years) a Neer IV/3 fracture was created with a 5 mm osteotomy gap simulating metaphyseal comminution. Limbs were randomly assigned to receive plate fixation with an additional telescoping screw (Humerus Tele Screw: HTS) and on the contralateral limb Philos plate fixation before biomechanical evaluation (MTS-Bionix 858.2). Standard locking screws were placed in both groups 6 mm below the radiological head circumference; the telescoping screw was placed in the subchondral layer. The greater tubercle was fixed with an additional screw in both techniques, in the HTS group the screw was anchored in the sleeve of the telescrew (screw in screw fixation).FindingsFixation stability with a mean stiffness of 300.9 ± 28.8 N/mm in the HTS plate group proved to be significantly higher than in the Philos plate group (184.2 ± 23.4 N/mm; p = 0.006). The HTS plate also resisted higher loads in terms of fixation failure with loss of reduction at 290 ± 58.6 N in comparison to 205 ± 8.6 N for the Philos plate (p = 0.2). Displacement of the greater tubercle occurred in no case of the HTS plate group and in two out of four cases in the Philos plate group.InterpretationThe HTS plate provides high fixation stability in an in vitro humeral head fracture model and securely prevents displacement of the greater tubercle.