Unicortical Screws Research Articles

Treatment of Proximal Phalangeal Fractures by Plate and Angular Stable Unicortical Screws

Objective/Hypothesis: Fractures of the proximal phalanges are the most common phalangeal fractures. The current state-of-the-art treatment is open reduction and internal fixation with a dorsal plate. Immobilization is not required. Immediate digital motion is possible, thus preventing peritendinous adhesions as well as arthrofibrosis. Bicortical plate fixation is a commonly used procedure. However, it is known to cause irritation of flexor tendons and consequent limitation of motion. The difference between unicortical and bicortical screws has been addressed in a small number of studies. In metacarpal bones, Dona et al. found no difference between unicortical and bicortical locking screws in terms of load failure and stiffness. They also observed no screw pullout. In a biomechanical study, Khalid et al. investigated the pullout force of unicortical and bicortical screws in proximal phalanges and found that unicortical screws have significantly higher pullout strength in the mid diaphysis, but less in the proximal and distal metaphysis. However, they only used screws without a locking plate system. The principal aim of the present study was to investigate the outcome after proximal phalangeal fractures treated by open reduction and dorsal stable fixation with angular stable locking screws. Material and Methods: All proximal phalangeal fractures from 2011 to 2012, treated by open reduction and internal fixation with plate and unicortical angular stable locking screws, were analyzed retrospectively. Data concerning age, sex, follow-up interval, range of motion (ROM) of the metacarpophalangeal (MCP), the proximal interphalangeal (PIP), and the distal interphalangeal (DIP) joint were collected for statistical analysis. To assess functional outcome, the Buck-Gramcko score was calculated for the range of motion. The last x-ray examination was analyzed in respect to screw or plate loosening. Fractures were assigned to the following categories: open, closed, transverse, oblique, comminuted, intra-articular, or extra-articular. Results: In all, 15 proximal phalangeal fractures were analyzed retrospectively. Union was achieved in all cases. Eleven patients (73%) were men and 4 (27%) were women. Their mean age was 35 ± 11 years and the mean duration of follow-up was 7 ± 5 months. Triple-joint fingers were involved in 80% and the thumb in 20%. The mean ROM of triple-joint fingers in MCP was 92° ± 10°, PIP 76° ± 20°, and DIP 72° ± 20°. For the thumb, the average ROM of the MCP was 67° ± 15° and the IP 53° ± 15°. The mean Buck-Gramcko score was 14 ± 1, which indicates an excellent outcome. No complication related to the osteosynthesis equipment was observed. Conclusion: Dorsal plating with unicortical angular stable screws is suitable for proximal phalangeal fractures. It is associated with a low complications rate and excellent clinical outcome.

Investigation of Kryptonite™ bone cement in hybrid screw configurations of locking plate humeral midshaft fixation: A study of surrogate bone model

PurposeLocking compression plates (LCP) allow trauma and orthopedic surgeons to have a variety of options for utilizing locking and non-locking screw features. In this study, the hybrid constructs of mixed unicortical and bicortical screws were investigated for humerus midshaft fractures. The locking and non-locking features were also incorporated into the hybrid LCP constructs. Kryptonite™ bone cement is biocompatible with low exothermic properties and strong metal adhesion. This novel bone cement was incorporated into the non-locking screw feature to compare its mechanical effect with that of a traditional locking screw feature. MethodsA total of 24 synthetic bones (Sawbones® Inc., USA) were equally divided into three groups (n=8). The control group obtained traditional LCP fixation (JSM Medimax Inc., India) with bicortical screws, while the hybrid locking constructs employed a mix of bicortical and unicortical screws. The two bicortical screws in hybrid constructs were placed at the end holes of the LCP constructs and the unicortical screws were placed into the remaining holes. The hybrid locking (HL) group contained locking unicortical screws, whereas the hybrid non-locking group (HNK) utilized non-locking screw features incorporating the Kryptonite™ bone cement in the plate/screw bone construct. Specimens were tested by dynamic and static analysis. The eight total constructs were equally divided into two subgroups (n=4) to conduct axial compression and torsion test individually. The low cyclic test was conducted for dynamic analysis, which included 10,000 cycles at 1Hz frequency with a cyclic loading of 0–500N of axial force for the axial compression test and 0–20° of angular displacement for the torsion test. The static analysis was run by a failure test with a nondestructive strain rate of 0.1mm/s for the axial compression test and 0.5°s−1 for the torsional test. The construct stiffness of axial compression and torsion were derived from the linear portion of the load-displacement curves. The yield strength of axial compression and torsion was determined by using offset methods. The results of stiffness and yield strength were compared by using both one-way ANOVA and Scheffe and Games-Howell post hoc tests to analyze statically significant differences among the three groups. ResultsSpecimens completed 10,000 cycles in the dynamic analysis of axial and torsional cyclic tests without major deformation. To compare with the control group in static analysis, the HL and HNK groups achieved positive effect in axial stiffness, 12.3% and 10.5% greater than the control group respectively. HL obtained axial yield strength about 12% less than the control group. The HNK group was equivalent with the control group in axial yield strength. The torsional stiffness and yield strength were found similar in three groups, which indicated torsional equivalence among them. The stiffness and yield strength from axial compression and torsion were found statically non-significant among three groups. ConclusionsHybrid LCP constructs were initially showed to maintain equivalent axial and torsional stability with the traditional method. Kryptonite™ hosted mechanical and biological advantages for internal plate/screws (PLT) fixation.

Augmentative plating for treatment of nonunion of femoral shaft fracture after intramedullary nailing: a biomechanical study

Objective To compare biomechanical effects of augmentative plating assisted by different types and numbers of intramedullary nails in the treatment of nonunion of femoral shaft fracture after intramedullary nailing. Methods Twenty-five specimens of synthetic femur were randomly divided into an experimental group (20 bones) and a control group (5 bones) . All the bones were made into models of nonunion of femoral shaft fracture after intramedullary nailing. The control group was subjected to no augmentative plating. The experimental group was further divided into 4 subgroups (n=5) which were subjected to fixation respectively by: a 7-hole plate with 3 bicortical screws on each side, a 7-hole plate with 3 unicortical screws on each side, a 5-hole plate with 2 bicortical screws on each side, and a 5-hole plate with 2 unicortical screws on each side. The torque values of all the subgroups were measured and compared when the models were subjected to torsional angles of 5°, 10°, 15°, 20° and 25°. Results The anti-torsional strengths at torsional angles of 5°, 10°, 15°, 20° and 25° in the 4 experimental groups were all significantly greater than in the control group (P<0.05) . At a torsion angle of 25°, the mean torque value in the 3-bicortical-screw group (46.51±6.66 nm) was significantly greater than in the 2-bicortical-screw group (39.03±8.52 nm) (P<0.05) . At torsion angles of 5°, 10° and 25°, the mean torque values in the 3-unicortical-screw group (13.48±1.68 nm, 23.29±3.72 nm and 48.19±5.34 nm, respectively) were significantly greater than in the 3-unicortical-screw group (9.56±3.62 nm, 16.99±5.49 nm and 38.69±6.56 nm, respectively) (P<0.05) . At torsion angles of 20° and 25°, the mean torque values in the 3-unicortical-screw group (39.15±5.07 nm and 48.19±5.34 nm) were significantly greater than in the 2-bicortical-screw group (32.50±5.65 nm and 39.03±8.52 nm) (P<0.05). Conclusions The anti-torsional strength of fixation by 3 screws on each side is significantly greater than by 2 screws on each side. When the number of screws is the same, there is no significant difference between fixation by unicortical locking screws and that by bicortical conventional screws. Augmentative plating with 3 unicortical screws or 3 bicortical conventional screws on each side is recommended for treatment of nonunion of femoral shaft fracture after intramedullary nailing. Key words: Femoral fractures; Fractures, ununited; Bone plates; Fracture fixation, internal; Biomechanics

Comparison of the Mechanical Characteristics of a Universal Small Biplane Plating Technique Without Compression Screw and Single Anatomic Plate With Compression Screw

To better understand the mechanical characteristics of biplane locked plating in small bone fixation, the present study compared the stability under cyclic cantilever loading of a 2-plate locked biplane (BPP) construct without interfragmentary compression with that of a single-plate locked construct with an additional interfragmentary screw (SPS) using surrogate bone models simulating Lapidus arthrodesis. In static ultimate plantar bending, the BPP construct failed at significantly greater load than did the SPS construct (556.2 ± 37.1 N versus 241.6 ± 6.3 N, p = .007). For cyclic failure testing in plantar bending at a 180-N starting load, the BPP construct failed at a significantly greater number of cycles (158,322 ± 50,609 versus 13,718 ± 10,471 cycles) and failure load (242.5 ± 25.0 N versus 180.0 ± 0.0 N) than the SPS construct (p = .002). For cyclic failure testing in plantar bending at a 120-N starting load, the results were not significantly different between the BPP and SPS constructs for the number of cycles (207,646 ± 45,253 versus 159,334 ± 69,430) or failure load (205.0 ± 22.4 N versus 185.0 ± 33.5 N; p = .300). For cyclic testing with 90° offset loading (i.e., medial to lateral bending) at a 120-N starting load, all 5 BPP constructs (tension side) and 2 of the 5 SPS constructs reached 250,000 cycles without failure. Overall, the present study found the BPP construct to have superior or equivalent stability in multiplanar orientations of force application in both static and fatigue testing. Thus, the concept of biplane locked plating, using 2 low profile plates and unicortical screw insertion, shows promise in small bone fixation, because it provides consistent stability in multiplanar orientations, making it universally adaptable to many clinical situations.

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.

Antiglide plating of vertical medial malleolus fractures provides stiffer initial fixation than bicortical or unicortical screw fixation

BackgroundVertical shear fractures of the medial malleolus (44-A2 ankle fractures) occur through a supination–adduction mechanism. There are numerous methods of internal fixation for this fracture pattern. MethodsVertical medial malleolus osteotomies were created in synthetic distal tibiae. The models were divided into four fixation groups: two parallel unicortical cancellous screws, two divergent unicortical cancellous screws, two parallel bicortical cortical screws, or an antiglide plate construct. Specimens were subjected to offset axial loading and tracked using high-resolution video. FindingsThe antiglide plate construct was stiffer (P<0.05) than each of the other three constructs, and the bicortical screw construct was stiffer (P<0.05) than both unicortical screw constructs. The mean stiffness (standard deviation) was 111 (SD 35) N/mm for the parallel unicortical screw construct, 173 (SD 57) N/mm for the divergent unicortical screw construct, 279 (SD 30) N/mm for the bicortical screw construct, and 463 (SD 91) N/mm for the antiglide plate construct. The antiglide plate construct resisted displacement better (P<0.05) than each of the other three constructs. The mean force for 2mm of articular displacement was 284 (SD 51) N for the parallel unicortical screw construct, 339 (SD 46) N for the divergent unicortical screw construct, 429 (SD 112) N for the bicortical construct, and 922 (SD 297) N for the antiglide plate construct. InterpretationAn antiglide plate construct provides the stiffest initial fixation while withstanding higher load to failure for vertical medial malleolus fractures when compared to unicortical and bicortical screw fixation.

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.

The influence of distal screw length on the primary stability of volar plate osteosynthesis--a biomechanical study.

BackgroundExtensor tendon irritation is one of the most common complications following volar locking plate osteosynthesis (VLPO) for distal radius fractures. It is most likely caused by distal screws protruding the dorsal cortex. Shorter distal screws could avoid this, yet the influence of distal screw length on the primary stability in VLPO is unknown. The aim of this study was to compare 75 to 100 % distal screw lengths in VLPO.MethodsA biomechanical study was conducted on 11 paired fresh-frozen radii. HRpQCT scans were performed to assess bone mineral density (BMD) and bone mineral content (BMC). The specimens were randomized pair-wise into two groups: 100 % (group A) and 75 % (group B) unicortical distal screw lengths. A validated fracture model for extra-articular distal radius fractures (AO-23 A3) was used. Polyaxial volar locking plates were mounted, and distal screws was inserted using a drill guide block. For group A, the distal screw tips were intended to be flush or just short of the dorsal cortex. In group B, a target screw length of 75 % was calculated. The specimens were tested to failure using a displacement-controlled axial compression test. Primary biomechanical stability was assessed by stiffness, elastic limit, and maximum force as well as with residual tilt, which quantified plastic deformation.ResultsNine specimens were tested successfully. BMD and BMC did not differ between the two groups. The mean distal screw length of group A was 21.7 ± 2.6 mm (range: 16 to 26 mm), for group B 16.9 ± 1.9 mm (range: 12 to 20 mm). Distal screws in group B were on average 5.6 ± 0.9 mm (range: 3 to 7 mm) shorter than measured. No significant differences were found for stiffness (706 ± 103 N/mm vs. 660 ± 124 N/mm), elastic limit (177 ± 25 N vs. 167 ± 36 N), maximum force (493 ± 139 N vs. 471 ± 149 N), or residual tilt (7.3° ± 0.7° vs. 7.1° ± 1.3°).ConclusionThe 75 % distal screw length in VLPO provides similar primary stability to 100 % unicortical screw length. This study, for the first time, provides the biomechanical basis to choose distal screws significantly shorter then measured.Electronic supplementary materialThe online version of this article (doi:10.1186/s13018-015-0283-8) contains supplementary material, which is available to authorized users.

Unicortical fixation of metacarpal fractures: is it strong enough?

Unicortical fixation has some practical and theoretical advantages over bicortical fixation. Questions have been raised to its adequacy for post-operative mobilization. We hypothesized that fixation using a plate and eight unicortical screws would be as strong as using a plate and four bicortical screws. A total of 40 unicortical and 40 bicortical fixations were compared using a cadaveric metacarpal model. Unicortical fixation was performed using an eight-hole parallel plate and bicortical fixation with a four-hole straight plate. Fixations were tested to failure using four-point bending load. The mean load to failure was 414 N SD 38(SE) for the unicortical group and 296 N SD 29(SE) for the bicortical group. Significant differences between these two constructs were observed. The mean stiffness of the fixation was higher for the bicortical group than the unicortical, although this difference did not reach significance. Unicortical fixation alone is sufficient to enable early post-operative mobilization in a live model.

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].

Locking plate placement with unicortical screw fixation adjunctive to intramedullary rodding in long bones of patients with osteogenesis imperfecta.

Intramedullary rodding has been the mainstay of long-bone stabilization in osteogenesis imperfecta. However, in some cases, intramedullary rodding cannot provide adequate fixation because of a lack of rotational control and thin diameter of long bones. We have applied adjunctive unicortical locking plate fixation in selected cases of osteogenesis imperfecta to address these biomechanical issues. Thirty-seven bone segments of twenty-four patients with osteogenesis imperfecta (ten type III, nine type IV, three type I, and two type V), in which unicortical locking plate fixation was applied adjunctive to intramedullary rodding and was later removed after union had been achieved, were the study subjects. The mean patient age at the time of surgery was 15.5 years (range, 6.2 to 39.8 years). Medical records and follow-up radiographs were reviewed to evaluate healing, complications, and the fates of screw holes after plate removal. All fractures or osteotomies healed completely. Locking plates were removed postoperatively at a mean time (and standard deviation) of 1.8 ± 0.9 years (range, 0.3 to 3.8 years). In seven of the thirty-seven cases, fractures through the screw hole occurred; all of these were treated conservatively. In eighteen of nineteen cases that were followed for more than a year after plate removal without screw hole-related complication, screw holes healed and were no longer visualized by radiography. Unicortical locking plate fixation effectively supplements intramedullary rod fixation in selected cases of osteogenesis imperfecta. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Comparative failure analysis of allograft constructs stabilized with compression plates utilizing unicortical versus bicortical screws with or without PMMA

Orthopaedic internal fixation is subject to high stress concentration around screw holes leading to screw loosening. We compared the screw pullout strength (n=8), and bending and torsional stiffness (n=6) for cadaveric (young adult donors age 45years or less) diaphyseal bone constructs with a gap and stabilized with Zimmer 4.5 narrow stainless steel dynamic compression plates with 4.5mm cortical stainless steel screws placed in a unicortical or bicortical manner with and without intramedullary PMMA. The pullout strength for unicortical fixation with PMMA (4.3±.6kN) was not significantly different with bicortical fixation with PMMA (5.3±1.5kN), n=8, P>.5; and for the group with bicortical fixation without PMMA (4.3±1.1kN), n=8, P>.5. The difference in bending stiffness for the group with two unicortical screws fixation with PMMA (324.1±59.7kN/m) was also not statistically significant when compared with the groups with four bicortical screws fixation without PMMA (278.7±89.6kN/m) and two bicortical screws fixation with PMMA (347.9±66.7kN/m), n=6, P>.1. The difference in torsional stiffness for the group with two unicortical screws fixation with PMMA (173±44Nm/deg) was not statistically significant when compared with the groups with four bicortical screws fixation without PMMA (190±22Nm/deg), two bicortical screws fixation with PMMA (179±36Nm/deg), and two bicortical screws fixation with PMMA (193±31Nm/deg), n=6, P>.5. The use of PMMA in allograft fixation appears to allow the use of fewer screws, and perhaps unicortical fixation without significant compromise of strength. Clinically, two unicortical screws with PMMA may replace the use of two bicortical screws without PMMA, or two bicortical screws with PMMA may replace four bicortical screws. The clinical relevance would be the ability to use fewer screws and reduce violation of the far cortex of the allograft.

Angular stable lateral plating is a valid alternative to conventional plate fixation in the proximal phalanx. A biomechanical study

BackgroundDorsal plating is commonly used in proximal phalanx fractures but it bears the risk of interfering with the extensor apparatus. In this study, dorsal and lateral plating fixation methods are compared to assess biomechanical differences using conventional 1.5mm non-locking plates and novel 1.3mm lateral locking plates. MethodsTwenty-four fresh frozen human cadaveric proximal phalanges were equally divided into four groups. An osteotomy was set at the proximal metaphyseal–diaphyseal junction and fixed with either dorsal (group A) or lateral (group B) plating using a 1.5mm non-locking plate, or lateral plating with a novel 1.3mm locking plate with bicortical (group C) or unicortical (group D) screws. The specimens were loaded in axial, dorsovolar and mediolateral direction to assess fixation stiffness followed by a cyclic destructive test in dorsovolar loading direction. FindingsAxial stiffness was highest in group D (mean 321.02, SEM 21.47N/mm) with a significant difference between groups D and B (P=0.033). Locking plates (groups C and D) were stiffer than non-locking plates under mediolateral loading (P=0.007), no significant differences were noted under dorsovolar loading. Furthermore, no significant differences were observed under cyclic loading to failure between any of the study groups. InterpretationNo considerable biomechanical advantage of using a conventional 1.5mm dorsal non-locking plate was identified over the novel 1.3mm lateral locking plate in the treatment of proximal phalanx fractures. Since the novel low-profile plate is less disruptive to the extensor mechanism, it should be considered as a valid alternative.

Biomechanical design of less invasive stabilization system femoral plates: computational evaluation of the fracture environment.

Less Invasive Stabilization System femoral plates are currently accepted as a suitable fixation technique for supra-intercondylar femoral fractures. However, general agreement does not exist regarding the optimum design of this fixator type. Therefore, the aim of this article is to reduce the intrinsic Less Invasive Stabilization System complications by clarifying, from a biomechanical point of view, how the number of screws, the screw connection type (unicortical or bicortical), or the structured position of the screws can influence the outcome of the fracture site. These studies include a specific finite element analysis that determines how several biomechanical variables, such as the movement at the fracture site, are influenced by the preconditions of bone healing. The results of this study show that the screw type affects the mechanical stabilization of the femur to a greater extent than the material type of the Less Invasive Stabilization System femoral plates. The most significant differences among all the analyzed configurations are observed in the shear interfragmentary strain between screw types. Values are approximately 50% higher with unicortical screws than with bicortical ones.

Biomechanical Comparison of Bicortical Locking Versus Unicortical Far-Cortex–Abutting Locking Screw-Plate Fixation for Comminuted Radial Shaft Fractures

To provide comparative biomechanical evaluation of bicortical locking versus unicortical-abutting locking screw-plate fixation in a comminuted radius fracture model. A validated synthetic substitute of the adult human radius with a 1.5-cm-long segmental mid-diaphyseal defect was used in the study to simulate a comminuted fracture. Stabilization was achieved with an 8-hole locking plate and either bicortical screws or unicortical-abutting screws. The specimens were tested using nondestructive cyclical loading in 4-point bending, axial compression, and torsion to determine stiffness and displacement and subsequently in 4-point bending to assess load to failure. There were no statistically significant differences between bicortical versus unicortical-abutting locking screw fixation in nondestructive 4-point bending, axial compression, and torsion. Both locking screw constructs also demonstrated comparable 4-point bending loads to failure. The biomechanical equivalence between bicortical locking versus unicortical-abutting locking screw-plate fixation suggests that adequate locking plate fixation can be achieved without perforation of the far cortex. The abutment of the screw tip within the far cortex enhances the unicortical screw positional stability and thereby effectively opposes the displacement of the screw when subjected to bending or axial or rotational loads. Unicortical-abutting screws potentially offer several clinical advantages. They eliminate the need for drilling through the far cortex and thereby a risk of adjacent neurovascular injury or soft tissue structure compromise. They eliminate the issues associated with symptomatic screw prominence. They can decrease risk of refracture after screw-plate removal. In case of revision plating, they permit conversion to bicortical locking screws through the same near-cortex screw holes, which eliminates the need for a longer or repositioned plate.

HYBRID PLATING SHOWS EQUIVALENT BIOMECHANICAL BENDING STRENGTH TO UNICORTICAL LOCKED PLATING

Locking unicortical screw fixation of diaphyseal fractures may be clinically necessary due to internal constructs or prosthetic implants. The biomechanical effects of substituting one or more bicortical nonlocking screws to create a "hybrid" construct are unknown. Use of an initial nonlocking screw may be clinically desirable for creating initial plate-to-bone fixation prior to locking. A validated transverse fracture model was used with eighteen synthetic humerus models. Plate and screw fixation was performed in three treatment groups (n = 6): Unicortical locking screws only, fixation with two unicortical locking screws and one bicortical nonlocking screw on either side of the fracture and fixation with one unicortical locking screw and two bicortical locking screws on either side of the fracture. Displacement and gap strain measurements were made with a cyclic 4-point bending test. No significant differences were noted for construct stiffness or gap micromotion among the three groups on cyclic testing. Measurements at 1000, 5000, and 10,000 cycles showed stable fixation of all construct types with no significant changes in stiffness or micromotion. Substitution of one or more bicortical nonlocking screws in a unicortical locked construct does not affect construct stiffness or fracture gap strain. Data proven through controlled laboratory study.

Errors in Treatment of Fractures of Distal Femur by LISS Method (Less Invasive Stabilization System) - Single-centre Experience.

LISS, the newest surgical method, makes it possible to completely regain knee function after knee fractures. We share our experience of the most frequently occurring errors during LISS-based treatment and ways of avoiding them. Our sample consisted of patients treated with the LISS method between 2007 and 2012 in the Department of Orthopedics and Traumatology of the 4th Military Hospital in Wroclaw, Poland. We analysed the patients' radiographic records. We analysed follow-up radiographs of 28 patients with fractures of the distal femur. We identified the following seven errors in reduction and fixation of fractures of the distal femur occurring during treatment using the LISS method: 1. Valgus or varus fracture fixation. 2. Malrotation of the fracture fragments. 3. Fixation in malrotation in the sagittal plane. 4. Non-axial placement of the LISS plate in the sagittal plane. 5. The use of K wires not recommended in the LISS method. 6. Screws penetrating into the joint. 7. Drilling holes for unicortical screws. 1. The most common errors in the treatment of fractures of the distal femur by LISS method relate to inadequate reduction of the fracture. 2. Intraoperative fluoroscopy should be used at all stages of the surgical procedure. 3. The surgical technique recommended by the creators of the LISS method must be strictly followed.

Biomechanical evaluation of fracture fixation constructs using a variable-angle locked periprosthetic femur plate system

BackgroundIn the United States there are more than 230,000 total hip replacements annually, and periprosthetic femoral fractures occur in 0.1–4.5% of those patients. The majority of these fractures occur at the tip of the stem (Vancouver type B1). The purpose of this study was to compare the biomechanically stability and strength of three fixation constructs and identify the most desirable construct. MethodsFifteen medium adult synthetic femurs were implanted with a hip prosthesis and were osteotomized in an oblique plane at the level of the implant tip to simulate a Vancouver type B1 periprosthetic fracture. Fractures were fixed with a non-contact bridging periprosthetic proximal femur plate (Zimmer Inc., Warsaw, IN). Three proximal fixation methods were used: Group 1, bicortical screws; Group 2, unicortical screws and one cerclage cable; and Group 3, three cerclage cables. Distally, all groups had bicortical screws. Biomechanical testing was performed using an axial–torsional testing machine in three different loading modalities (axial compression, lateral bending, and torsional/sagittal bending), next in axial cyclic loading to 10,000 cycles, again in the three loading modalities, and finally to failure in torsional/sagittal bending. ResultsGroup 1 had significantly greater load to failure and was significantly stiffer in torsional/sagittal bending than Groups 2 and 3. After cyclic loading, Group 2 had significantly greater axial stiffness than Groups 1 and 3. There was no difference between the three groups in lateral bending stiffness. The average energy absorbed during cyclic loading was significantly lower in Group 2 than in Groups 1 and 3. ConclusionsBicortical screw placement achieved the highest load to failure and the highest torsional/sagittal bending stiffness. Additional unicortical screws improved axial stiffness when using cable fixation. Lateral bending was not influenced by differences in proximal fixation. Clinical relevanceTo treat periprosthetic fractures, bicortical screw placement should be attempted to maximize load to failure and torsional/sagittal bending stiffness.

Biomechanical Evaluation of Anterior Thoracic Salvage Screws in the Osteoporotic Thoracic Spine

Controlled, cadaveric implantation trial. Evaluation of revision thoracic screw fixation: with revision from unicortical screws to bicortical screws, to larger diameter screws, and the addition of bone cement. Limited data is available regarding the effect of salvage screws on fixation quality in the anterior thoracic spine. Biomechanical studies in the cervical spine and the lumbar spine demonstrate dramatic decreases in fixation in salvage situations. Seventy-two cadaveric thoracic vertebrae from 6 specimens were DEXA scanned at T1-T12. A control screw and a second identical screw were placed in each segment. One screw was then removed and replaced with a revision screw. Varying screw diameter, the number of cortices, and the addition of 1.5 cm of bone cement was evaluated in a pairwise fashion. Comparisons were made using descriptive statistical analysis and a general linear statistical model. Bone mineral density had a significant effect on the pullout force. Pullout force did not vary significantly with control screw diameter. Revision of a smaller diameter bicortical to a larger diameter bicortical screw resulted in a decrease in pullout strength for 4-5 mm screws by 40.1% (P=0.02) and 5-7 mm screws by 63.7% (P=0.05). When a 4 mm bicortical screw is revised to a 5 mm unicortical screw, the pullout force decreases by 67.7% (P<0.001). There was a nonsignificant increase (44%) in pullout with revision of a unicortical 4 mm screw to a bicortical 4 mm screw. If a bicortical screw is revised to a unicortical screw with 1.5 cm of cement, the pullout strength is increased by 240% (P<0.001). When the use of salvage screws is required, the surgeon should anticipate a significant decrease in the holding force compared with the original screw regardless of screw size unless a unicortical screw is revised to a bicortical screw or cement is added to the construct.

Bicortical Versus Unicortical Pedicle Screws in Direct Vertebral Rotation

In vitro experimental study. This study aimed to evaluate the biomechanical properties of bicortically placed and laterally oriented screws, which may represent an alternative approach for challenging sites during direct vertebral rotation (DVR). DVR corrects the transverse plane deformity and the thoracic hump in idiopathic scoliosis. However, instrumentation of the convex side of the scoliosis apex may pose a challenge, not allowing the placement of suitable sized screws in adequate direction. Forty-eight calf vertebrae were used and each vertebral body was instrumented with 1 pedicle screw as follows: unicortical group (n=16), a short screw was unicortically placed and directed laterally; bicortical group (n=16), a short screw was bicortically placed again in lateral direction; control group (n=16), a screw with ideal length and direction was placed. Vertebral bodies were rigidly anchored in a custom device. Each screw was rotated using a constant length lever arm while collecting "force to failure" data. Significantly better results were obtained with bicortical screwing when compared with unicortical screwing (335.4±45.6 vs. 239.5±58.50 N, P<0.001). However, mean "force to failure" was significantly higher in the controls than in the bicortical group (415.8±49.2 vs. 335.4±45.6 N, P<0.001). Bicortical screw placement may provide a biomechanically superior construct than unicortical screw placement for resisting DVR maneuver during scoliosis correction. This technique may represent an effective and safe approach, particularly for the convex side of the scoliosis apex, with increased resistance to derotational forces and decreased risk of bone failure. Further clinical studies are warranted for firmer conclusions.