Biomechanical evaluation and comparison of polyetheretherketone rod system to traditional titanium rod fixation on adjacent levels

PurposeAdjacent segment degeneration or fracture of the vertebral body was commonly reported in rigid fusion. Use of semirigid instruments such as PEEK rod system could be an alternative treatment. However, the biomechanical implications of using PEEK rod systems are not well understood. Purpose of this study was to compare a PEEK rod fixation system to traditional titanium rod fixation via a finite element analysis.MethodsA lumbar spine model from L2–L5 vertebral bodies was constructed. A fusion model, created by modifying the intact lumbar model, was used to simulate anterior interbody and posterolateral lumbar fusion. Loading was applied through flexion, extension, lateral bending, torsion.ResultsThe greatest increase in stress was estimated at the upper disc adjacent to the titanium rod with interbody fusion. The lower increase in stress on adjacent segments occurred with PEEK rod fixation without fusion and noninstrumented posterolateral lumbar fusion models. With the same fusion or nonfusion procedures, the stress on discs and facet joints of adjacent segments in the PEEK rod group decreased by 5–25% of that in the titanium rod group for all loading conditions.ConclusionIn comparison with rigid fixation, some potential advantages of using PEEK rod systems include a reduced stress on adjacent segment disc and facet joint, and the elastic ability of PEEK rod fixation allows for a greater range of motion, which may reduce the incidence of clinical complications seen with rigid fusion devices.     

Biomechanical rigidity of an all-polyetheretherketone anterior thoracolumbar spinal reconstruction construct: an in vitro corpectomy model

Background contextPolyetheretherketone (PEEK) is gaining favor as a spinal implant material for interbody and corpectomy cages as well as stabilizing rods. However, there has been little correlation to a relevant and reproducible clinical model. Biomechanical data on PEEK rod constructs have not been reported.PurposeTo quantify the stabilizing effects of PEEK versus titanium (Ti) instrumentation in a thoracolumbar corpectomy model.Study designCorpectomy and randomized instrumentation with an all-Ti, all-PEEK, and hybrid cage/rod construct were performed on cadaveric spines to assess biomechanical differences.MethodsPure unconstrained bending moments were applied to the intact spine and subsequent test constructs in the three physiologic planes using a load control protocol. Motion tracking and analysis were carried out to quantify and compare the range of motion (ROM) between different test constructs in each plane.ResultsFlexion ROM did not show significant changes compared with intact, whereas the all-Ti and hybrid construct reduced ROM significantly in extension. Lateral bending was significantly reduced in all the treatment groups. Rotational stability of the construct was significantly compromised by an all-PEEK spinal construct.ConclusionThe rigidity of the corpectomy construct increased as the amount of Ti in the construct increased. A hybrid construct incorporating a PEEK corpectomy cage and Ti rods may provide adequate stability for an anterior thoracolumbar reconstruction in the sagittal and coronal planes. An all-PEEK construct may provide adequate stability in the coronal and sagittal planes but may compromise the stability significantly in axial rotation. Consideration should be given for supplemental posterior instrumentation if an all-PEEK construct is used in an anterior thoracolumbar spinal reconstruction procedure.     

Lumbar curve response to selective thoracic fusion in adult idiopathic scoliosis

Background contextTo date, no study has critically examined the radiographic characteristics of the lumbar curve after selective thoracic fusion for the adult idiopathic scoliosis patient population.PurposeTo evaluate the radiographic response of the lumbar curve to selective thoracic fusion in the adult scoliosis population with correlative clinical outcomes.Study designRetrospective case series.Patient sampleThirty patients with idiopathic scoliosis surgically treated at a mean age of 40 years (range, 20–66) using a posterior translational technique.Outcome measuresRadiographic review and functional outcome assessment.MethodsA retrospective, minimum 2-year follow-up, radiographic, and clinical review. All patients underwent selective thoracic posterior fusion with end-instrumented vertebra at T11 (1), T12 (7), L1 (14), and L2 (8).ResultsAt a mean follow-up of 39 (range, 24–87) months, spontaneous lumbar curve Cobb improvement (36°–18°=50% correction) was less than the bending radiograph (12°, 68% correction). Lowest-instrumented vertebra (LIV) tilt angle improved from 24 to 9 degrees and LIV disc angle improved from 8 to 4 degrees (p<.001). Lumbar apical disc angle improved from 10 to 7 degrees (p<.001). Lumbar apical vertebral translation remained unchanged from pre-op (17 mm) to latest follow-up (17 mm) (p=.23). Lumbar curve rotation increased from 8 to 10 degrees (p=.11). One patient had coronal imbalance of greater than 3 cm and two patients had greater than 3 cm of negative sagittal imbalance. Mean subgroup scores of the Scoliosis Research Society-22 questionnaire improved (p<.01) for pain (3.0–3.8) and self-image (2.5–4.0) but remained the same for function and mental health. Only one patient required extension of fusion to include the lumbar curve 6 years postoperatively.ConclusionsThe lumbar curve response in adult, selective thoracic scoliosis surgery is characterized by 1) moderate correction but less than the bending film Cobb; 2) greater change in LIV tilt and disc angle than apical vertebra disc angle; 3) no change in lumbar apical translation or rotation; 4) more significant disc height preservation at the LIV compared with lumbar apex. Good clinical outcomes can be achieved with posterior translational instrumentation in adult scoliosis patients.     

Use of instrumented pedicle screws to evaluate load sharing in posterior dynamic stabilization systems

Background contextDynamic stabilization is an alternative to fusion intended to eliminate or at least minimize the potential for adjacent level degeneration. Different design approaches are used in pedicle screw-based systems that should have very different effects on the loading of the posterior column and intervertebral disc. If the implant system distributes these loads more evenly, loads in the pedicle screws will be reduced, and screw loosening will be prevented.PurposeThe purpose of this study was to determine how two different design approaches to dynamic stabilization systems, Dynesys System and the Total Posterior Spine (TOPS) System, affect the load carried by the pedicle screws.Study design/settingA controlled laboratory study in which the magnitude of the moments on pedicle screws during flexion–extension and lateral bending were measured after implantation of two posterior dynamic stabilization devices into cadaveric spines.MethodsFive lumbar spines were tested in flexion–extension and lateral bending. Specimens were tested sequentially: first intact, then with the Dynesys system implanted, and finally with the TOPS system implanted. Range of motion (ROM) for each construct was measured with a 210 N and 630 N compressive load. The pedicle screws were instrumented with strain gages, which were calibrated so that the moments on the screws could be determined from the strain measurements.ResultsCompared with intact values, ROM decreased in flexion–extension and lateral bending when the Dynesys System was implanted. With implantation of the TOPS System, ROM returned to values that were not significantly different from the intact values. The moments in the screws with the Dynesys System were significantly higher than with the TOPS System with increases of as much as 56% in flexion–extension and 86% in lateral bending.ConclusionsThe design of the posterior stabilization device influences the amount of load seen by the pedicle screws and therefore the load sharing between spinal implant and bone.     

聚醚醚酮棒杂交手术治疗腰椎退行性疾病的中长期疗效

目的 探讨聚醚醚酮（PEEK）棒杂交手术治疗腰椎退行性疾病的中长期临床疗效。方法 回顾性分析2014年4月—2016年1月在中国人民解放军联勤保障部队第九六〇医院因腰椎退行性疾病接受PEEK棒杂交手术治疗的27例患者临床资料,术前与末次随访时采用疼痛视觉模拟量表（VAS）评分和Oswestry功能障碍指数（ODI）评估腰腿痛程度及腰椎功能,记录并发症发生情况,在术前及末次随访时的影像学资料上测量相关参数评估临床疗效。结果 所有手术顺利完成,患者随访60～89(77.2±9.8)个月。27例患者共59个节段行手术治疗,其中非融合节段32个,融合节段27个。末次随访时腰腿痛VAS评分、ODI及影像学指标与术前相比明显改善,差异均有统计学意义（P <0.05）。27个融合节段中有23个获得骨性融合,融合率为85.2%。27例患者共置入172枚椎弓根螺钉及54根PEEK棒,1例发生L5左侧椎弓根螺钉断裂,其余未发生螺钉松动或PEEK棒断裂等并发症。结论 PEEK棒杂交手术治疗腰椎退行性疾病的中长期临床疗效满意,更好地保留了固定节段活动度及非融合节段的椎间高度,融合率高且并发症少,可有效保...     

Comparative effectiveness of PEEK rods versus titanium alloy rods in lumbar fusion: A preliminary report

Background

Posterior lumbar instruments made of titanium and its alloys could change the physiological distribution of load at the instrumented and adjacent segments, which is a main cause of implant failure, non-fusion and adjacent segment degeneration. Posterior lumbar rods made of polyetheretherketone (PEEK) which is a semirigid alternative to titanium and its alloys have been introduced in lumbar fusion. This prospective study compared the radiological and clinical outcomes of patients undergoing lumbar fusion with PEEK rods versus titanium alloy rods.

Methods

Using transpedicular fixation and lumbar fusion, 21 patients were treated with titanium alloy rods (TI group), and 20 patients with PEEK rods (PEEK group). Radiological and clinical outcomes were evaluated, including the status of the implanted instruments, fusion rate, lumbar lordosis angle (LA), disc space height (DH), visual analog score (VAS) for lower back pain (VAS-BP) and leg pain (VAS-LP), Japanese Orthopedic Association scoring system (JOA score) and complications.

Results

Clinical VAS-BP, VAS-LP and JOA scores were significantly improved at 3 months, 6 months, and 1 year postoperatively as compared with preoperative scores in both groups (p?<?0.05), with similar levels of improvement observed at the same time points postoperatively between the two groups. The overall fusion rate was 100 % at the 1-year follow-up for both groups. No significant differences in lumbar lordosis angle were found preoperatively, 1 week and 1 year postoperatively in both groups (p?>?0.05). The postoperative increase of disc space height and loss of disc space height during the follow-up showed a similar extent of change between both groups (p?>?0.05).

Conclusions

PEEK rods offer a similar radiological and clinical efficacy as titanium alloy rods. PEEK rods, as a semirigid implant with unique characteristics, may be an effective alternative treatment for patients with degenerative lumbar disease in lumbar fusion.     

Overtightening of the syndesmosis revisited and the effect of syndesmotic malreduction on ankle dorsiflexion

BackgroundAnkle syndesmotic injuries are a significant source of morbidity and require anatomic reduction to optimize outcomes. Although a previous study concluded that maximal dorsiflexion during syndesmotic fixation was not required, methodologic weaknesses existed and several studies have demonstrated improved ankle dorsiflexion after removal of syndesmotic screws.The purposes of the current investigation are: (1) To assess the effect of compressive syndesmotic screw fixation on ankle dorsiflexion utilizing a controlled load and instrumentation allowing for precise measurement of motion. (2) To assess the effect of anterior & posterior syndesmotic malreduction after compressive syndesmotic screw fixation on ankle dorsiflexion.Material and methodsFifteen lower limb cadaveric leg specimens were utilized for the study. Ankle dorsiflexion was measured utilizing a precise micro-sensor system after application of a consistent load in the (1) intact state, (2) after compression fixation with a syndesmotic screw and (3) after anterior & (4) posterior malreduction of the syndesmosis.ResultsFollowing screw compression of the nondisplaced syndesmosis, dorsiflexion ROM was 99.7 ± 0.87% (mean ± standard error) of baseline ankle ROM. Anterior and posterior malreduction of the syndesmosis resulted in dorsiflexion ROM that was 99.1 ± 1.75% and 98.6 ± 1.56% of baseline ankle ROM, respectively. One-way ANOVA was performed showing no statistical significance between groups (p-value = 0.88).Two-way ANOVA comparing the groups with respect to both the reduction condition (intact, anatomic reduction, anterior displacement, posterior displacement) and the displacement order (anterior first, posterior first) did not demonstrate a statistically significant effect (p-value = 0.99).ConclusionMaximal dorsiflexion of the ankle is not required prior to syndesmotic fixation as no loss of motion was seen with compressive fixation in our cadaver model. Anterior or posterior syndesmotic malreduction following syndesmotic screw fixation had no effect on ankle dorsiflexion. Poor patient outcomes after syndesmotic malreduction may be due to other factors and not loss of dorsiflexion motion.Level of Evidence: IV     

Effect of the Total Facet Arthroplasty System after complete laminectomy-facetectomy on the biomechanics of implanted and adjacent segments

Background contextLumbar fusion is traditionally used to restore stability after wide surgical decompression for spinal stenosis. The Total Facet Arthroplasty System (TFAS) is a motion-restoring implant suggested as an alternative to rigid fixation after complete facetectomy.PurposeTo investigate the effect of TFAS on the kinematics of the implanted and adjacent lumbar segments.Study designBiomechanical in vitro study.MethodsNine human lumbar spines (L1 to sacrum) were tested in flexion-extension (+8 to ?6 Nm), lateral bending (±6 Nm), and axial rotation (±5 Nm). Flexion-extension was tested under 400 N follower preload. Specimens were tested intact, after complete L3 laminectomy with L3–L4 facetectomy, after L3–L4 pedicle screw fixation, and after L3–L4 TFAS implantation. Range of motion (ROM) was assessed in all tested directions. Neutral zone and stiffness in flexion and extension were calculated to assess quality of motion.ResultsComplete laminectomy-facetectomy increased L3–L4 ROM compared with intact in flexion-extension (8.7±2.0 degrees to 12.2±3.2 degrees, p<.05) lateral bending (9.0±2.5 degrees to 12.6±3.2 degrees, p=.09), and axial rotation (3.8±2.7 degrees to 7.8±4.5 degrees p<.05). Pedicle screw fixation decreased ROM compared with intact, resulting in 1.7±0.5 degrees flexion-extension (p<.05), 3.3±1.4 degrees lateral bending (p<.05), and 1.8±0.6 degrees axial rotation (p=.09). TFAS restored intact ROM (p>.05) resulting in 7.9±2.1 degrees flexion-extension, 10.1±3.0 degrees lateral bending, and 4.7±1.6 degrees axial rotation. Fusion significantly increased the normalized ROM at all remaining lumbar segments, whereas TFAS implantation resulted in near-normal distribution of normalized ROM at the implanted and remaining lumbar segments. Flexion and extension stiffness in the high-flexibility zone decreased after facetectomy (p<.05) and increased after simulated fusion (p<.05). TFAS restored quality of motion parameters (load-displacement curves) to intact (p>.05). The quality of motion parameters for the whole lumbar spine mimicked L3–L4 segmental results.ConclusionsTFAS restored range and quality of motion at the operated segment to intact values and restored near-normal motion at the adjacent segments.     

Use of the dual construct lowers rod strains in flexion-extension and lateral bending compared to two-rod and two-rod satellite constructs in a cadaveric spine corpectomy model

BACKGROUND CONTEXTComplex spinal reconstructions involving corpectomies, or osteotomies, place spinal implants at extremely high stresses that can lead to pseudoarthrosis and ultimately to rod failure, resulting in revision surgery. Current clinical options to increase the biomechanical strength of a construct include increasing rod diameter, changing rod material, or placing an additional satellite/outrigger rod on a standard two rod construct. Fundamentally, all of these constructs still rely on two longitudinal rods across the reconstruction site and are therefore at risk for rod fracture and loss of alignment. Initially described in 2006, the Dual Construct was developed to address this limitation by utilizing four distinct mechanically independent rods, which allowed for the creation of two separate, and distinct, constructs within each patient. Although there is early clinical evidence to support its efficacy, this is the first biomechanical study to compare the Dual Construct to the two-rod and two-rod with satellite configurations in a cadaveric study.PURPOSETo assess the biomechanical impact of the Dual Construct technique to traditional two-rod and two-rod with satellite rod construct in a cadaveric model.STUDY DESIGN/SETTINGBiomechanical cadaveric studyMETHODSNine fresh-frozen human cadaveric spines (6 males, 3 females, 56 year +/- 9 years) from T9-pelvis were instrumented and tested utilizing all three configurations including two-rod construct, two-rod with satellite construct, and the Dual Construct technique. Biomechanical testing order of the various constructs was randomized to reduce potential effects of order bias. Strain gauges were placed in both the coronal and sagittal planes of the rods to track the strains during flexion-extension and lateral bending while undergoing range of motion testing. Testing was performed using pure-moment flexibility testing protocols.RESULTSIn flexion-extension, the resultant strain in the two-rod construct was an average 600±228 microstrain, the two-rod with satellite rod strain averaged 603±237 microstrain, and the Dual Construct averaged 403±149 microstrain. In lateral bending, the resultant strain in the two-rod construct was an average of 266±134 microstrain, the satellite rod strain was an average of 310±158 microstrain, and the Dual Construct averaged 118±51 microstrain. In both flexion extension and lateral bending, a significant reduction in strain was observed between the Dual Construct condition compared to both the two-rod and satellite configurations. No significant difference was found between the two-rod and two-rod with satellite rod configurations.CONCLUSIONSThe increase in load sharing significantly decreases the strain experienced across the Dual Construct compared to traditional two-rod and two-rod with satellite constructs. Global rod strains on primary rods cannot be reduced by simply increasing the number of satellite rods, but can only be reduce by increasing the actual number of primary rods.     

Clinical and biomechanical researches of polyetheretherketone (PEEK) rods for semi-rigid lumbar fusion: a systematic review

Lumbar spinal fusion using rigid rods is a common surgical technique. However, adjacent segment disease and other adverse effects can occur. Dynamic stabilization devices preserve physiologic motion and reduce painful stress but have a high rate of construct failure and reoperation. Polyetheretherketone (PEEK) rods for semi-rigid fusions have a similar stiffness and adequate stabilization power compared with titanium rods, but with improved load sharing and reduced mechanical failure. The purpose of this paper is to review and evaluate the clinical and biomechanical performance of PEEK rods. A systematic review of clinical and biomechanical studies was conducted. A literature search using the PubMed, EMBASE, and Cochrane Library databases identified studies that met the eligibility criteria. Eight clinical studies and 15 biomechanical studies were included in this systematic review. The visual analog scale and the Oswestry disability index improved significantly in most studies, with satisfactory fusion rates. The occurrence of adjacent segment disease was low. In biomechanical studies, PEEK rods demonstrated a superior load-sharing distribution, a larger adjacent segment range of motion, and reduced stress at the rod-screw/screw-bone interfaces compared with titanium rods. The PEEK rod construct was simple to assemble and had a reliable in vivo performance compared with dynamic devices. The quality of clinical studies was low with confounding results, although results from mechanical studies were encouraging. There is no evidence strong enough to confirm better outcomes with PEEK rods than titanium rods. More studies with better protocols, a larger sample size, and a longer follow-up time are needed.     

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: 134.4 Nmm/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.     

“Anterior subcutaneous pelvic internal fixator (INFIX), Is it safe?” A cadaveric study

IntroductionAnterior pelvic internal fixator (INFIX) is used to treat unstable pelvic ring injuries. Nerve injury complications with this procedure have been reported.ObjectivesThis anatomic study attempted to identify structures at risk after application of INFIX.Materials and methodsINFIX was applied in fifteen fresh, frozen, anatomical specimens using polyaxial pedicular screws and subcutaneous rods. Surgical dissection was done to identify the structures at risk including the femoral nerve (FN), femoral artery (FA), femoral vein (FV) and the lateral femoral cutaneous nerve (LFCN) related to which are potentially affected by the implant.ResultsAll structures at risk were closer to the rod than to the pedicular screw. Measurements were made between the rod and the structures at risk. The LFCN was an average of 13.49 ± 1.65 mm (95% CI 12.871–14.103) from the lateral end of the rod. The FN was an average of 12.43 ± 3.42 mm (95% CI 11.151–13.709), the FA was an average of 12.80 ± 3.67 (95% CI 11.430–14.173) and the FV was an average of 13.48 ± 3.73 (95% CI 12.082–14.871) below the rod. No direct compression of the rod to the structure at risk was observed.ConclusionsThe femoral nerve is the structure most at risk of compression by the INFIX rod. Careful surgical technique is required in every step of this surgery. We suggest using polyaxial screws and recommend that during screw insertion the surgeon should leave some space between the screw and rectus fascia. The the rod should be trimmed as short as possible to reduce LFCN irritation.     

Internal tibial torsion is related to syndesmosis injury in a large osteological collection

BackgroundThe long-term consequences of tibial torsion remain unclear. This study evaluated whether syndesmotic injuries are associated with tibial torsion.MethodsA collection of over 3000 cadaveric skeletons was screened for irregular bony prominence along the lateral distal tibia, consistent with previous syndesmosis injury. Tibial torsion was measured and compared to 1034 control cadaveric tibiae.ResultsMean torsion of 236 specimens with syndesmotic injury was 6.2 ± 8.9 degrees, while that of control specimens was 7.9 ± 8.8 degrees (P = 0.008). Multiple regression analysis showed a non-statistically significant trend toward internal torsion and syndesmotic injury (standardized beta = −0.051, P = 0.059). Syndesmosis injury was present in 48/200 specimens (24.0%) with internal torsion and 31/199 specimens (15.6%) with external torsion (P = 0.035).ConclusionThis association between internal tibial torsion and syndesmotic injury suggests that internal tibial torsion might not be an entirely benign condition and merits further study.     

Biomechanical characterization of an annulus-sparing spinal disc prosthesis

Background contextCurrent spine arthroplasty devices require disruption of the annulus fibrosus for implantation. Preliminary studies of a unique annulus-sparing intervertebral prosthetic disc (IPD) found that preservation of the annulus resulted in load sharing of the annulus with the prosthesis.PurposeDetermine flexibility of the IPD versus fusion constructs in normal and degenerated human spines.Study design/settingBiomechanical comparison of motion segments in the intact, fusion and mechanical nucleus replacement states for normal and degenerated states.Patient settingThirty lumbar motion segments.Outcomes measuresIntervertebral height; motion segment range of motion, neutral zone, stiffness.MethodsMotion segments had multidirectional flexibility testing to 7.5 Nm for intact discs, discs reconstructed using the IPD (n=12), or after anterior/posterior fusions (n=18). Interbody height and axial compression stiffness changes were determined for the reconstructed discs by applying axial compression to 1,500 N. Analysis included stratifying results to normal mobile versus rigid degenerated intact motion segments.ResultsThe mean interbody height increase was 1.5 mm for IPD reconstructed discs versus 3.0 mm for fused segments. Axial compression stiffness was 3.0±0.9 kN/mm for intact compared with 1.2±0.4 kN/mm for IPD reconstructed segments. Reconstructed disc ROM was 9.0°±3.7° in flexion extension, 10.6°±3.4° in lateral bending, and 2.8°±1.4° in axial torsion that was similar to intact values and significantly greater than respective fusion values (p<.001). Mobile intact segments exhibited significantly greater rotation after fusion versus their more rigid counterparts (p<.05); however, intact motion was not related to motion after IPD reconstruction. The NZ and rotational stiffness followed similar trends. Differences in NZ between mobile and rigid intact specimens tended to decrease in the IPD reconstructed state.ConclusionThe annulus-sparing IPD generally reproduced the intact segment biomechanics in terms of ROM, NZ, and stiffness. Furthermore, the IPD reconstructed discs imparted stability by maintaining a small neutral zone. The IPD reconstructed discs were significantly less rigid than the fusion constructs and may be an attractive alternative for the treatment of degenerative disc disease.     

Influence of plate material and screw design on stiffness and ultimate load of locked plating in osteoporotic proximal humeral fractures

IntroductionThe main purpose was to compare the biomechanical properties of a carbon-fibre reinforced polyetheretherketone (CF-PEEK) composite locking plate with pre-existing data of a titanium-alloy plate when used for fixation of an unstable 2-part fracture of the surgical neck of the humerus. The secondary purpose was to compare the mechanical behaviour of locking bolts and conventional locking cancellous screws.Methods7 pairs of fresh frozen human humeri were allocated to two equal groups. All specimens were fixed with the CF-PEEK plate. Cancellous screws (PEEK/screw) were compared to locking bolts (PEEK/bolt) for humeral head fixation. Stiffness, fracture gap deflection and ultimate load as well as load before screw perforation of the articular surface were assessed. Results were compared between groups and with pre-existing biomechanical data of a titanium-alloy plate.ResultsThe CF-PEEK plate featured significantly lower stiffness compared to the titanium-alloy plate (P < 0.001). In ultimate load testing, 6 out of 14 CF-PEEK plates failed due to irreversible deformation and cracking. No significant difference was observed between results of groups PEEK/screw and PEEK/bolt (P > 0.05).DiscussionThe CF-PEEK plate has more elastic properties and significantly increases movement at the fracture site of an unstable proximal humeral fracture model compared to the commonly used titanium-alloy plate. The screw design however does neither affect the constructs primary mechanical behaviour in the constellation tested nor the load before screw perforation.     

Arthroscopic triple fusion joint preparation using two lateral portals: A cadaveric study to evaluate efficacy and safety

BackgroundArthroscopic triple fusion has several advantages over open techniques, but its use has yet to become widespread. Preliminary published techniques use five portals with neurovascular risk. Our aim was to assess the safety and efficacy of an alternative lateral two portal technique.MethodsFour cadaveric hindfeet were arthroscopically prepared for a triple fusion using two lateral portals. The distance to relevant subcutaneous nerves was measured as well as the prepared joint surface percentage.ResultsMean distance from mid-lateral portal to the nearest sural nerve branch was 22.3 mm (range 20–24 mm) and from the dorsolateral portal to the intermediate branch of the superficial peroneal nerve was 7.8 mm (range 4–11 mm). Mean percentages of joint preparation were 63% (talar head), 62% (navicular), 75% (calcaneum) and 74% (cuboid).ConclusionsTwo lateral arthroscopic portals allow adequate joint preparation for triple fusion procedures. The proximity of subcutaneous nerves is important to appreciate when using these portals.     

Impact of cement-augmented condylar screws in locking plate osteosynthesis for distal femoral fractures — A biomechanical analysis

IntroductionCompromised bone quality and the need for early mobilization continue to lead to implant failure in elderly patients with distal femoral fractures. The cement augmentation of screws might facilitate improving implant anchorage. The aim of this study was to analyse the impact of cement augmentation of the condylar screws on implant fixation in a human cadaveric bone model.Material and methodsTen pairs of osteoporotic femora (mean age: 90 years, range: 84–99 years) were used. A 2-cm gap osteotomy was created in the metaphyseal region to simulate an unstable AO/OTA 33-A3 fracture. All specimens were treated with a polyaxial locking plate. Specimens randomly assigned to the augmented group received an additional cement augmentation of the condylar screws using bone cement. A servohydraulic testing machine was used to perform incremental cyclic axial loading using a load-to-failure mode.ResultsAll specimens survived at least 800 N of axial compressive force. The mean compressive forces leading to failure were 1620 N (95% CI: 1382–1858 N) in the non-augmented group and 2420 N (95% CI: 2054–2786 N) in the group with cement-augmented condylar screws (p = 0.005).Deformation with cutting out of the condylar screws and condylar fracture were the most common reasons for failure in both groups. Whereas axial stiffness was comparable between both osteosyntheses (p = 0.508), significant differences were observed for the plastic deformation of the constructs (p = 0.014).ConclusionThe results of the present study showed that the cement augmentation of the condylar screws might be a promising technique for the fixation of distal femoral fractures in elderly patients with osteoporotic bones.     

Biomechanical comparison of plate and screw fixation in anterior pelvic ring fractures with low bone mineral density

IntroductionOsteosynthesis of anterior pubic ramus fractures can be challenging, especially in poor bone quality. The aim of the present study was to compare plate and retrograde endomedullary screw fixation of the superior pubic ramus with low bone mineral density (BMD).Materials and methodsTwelve human cadaveric hemi-pelvises were analyzed in a matched pair study design. BMD of the specimens was 35 ± 30 mgHA/cm³, as measured in the fifth lumbar vertebra. A simulated two-fragment superior pubic ramus fracture model was fixed with either a 7.3-mm cannulated retrograde screw (Group 1) or a 10-hole 3.5-mm reconstruction plate (Group 2). Cyclic progressively increasing axial loading was applied through the acetabulum. Relative interfragmentary movements were captured using an optical motion tracking system.ResultsInitial axial construct stiffness was 424 ± 116.1 N/mm in Group 1 and 464 ± 69.7 N/mm in Group 2, with no significant difference (p = 0.345). Displacement and gap angle at the fracture site during cyclic loading were significantly higher in Group 1 compared to Group 2. Cycles to failure, based on clinically relevant criteria, were significantly lower in Group 1 (3469 ± 1837) compared to Group 2 (10,226 ± 3295) (p = 0.028). Failure mode in Group 1 was characterized by screw cutting through the cancellous bone. In Group 2 the specimens exclusively failed by plate bending.ConclusionsFrom biomechanical point of view, pubic ramus stabilization with plate osteosynthesis is superior compared to a single retrograde screw fixation in osteoporotic bone. However, the extensive surgical approach needed for plating must be considered.     

Biomechanical analysis of locked and non-locked plate fixation of the clavicle

IntroductionDuring plate fixation of clavicular fractures the brachial plexus and subclavian vessels are vulnerable to injury beneath the clavicle. Locking plate fixation allows for mono-cortical fixation, theoretically reducing the risk of injury to these structures. Biomechanical analysis of the performance of such fixation is limited, and this study was designed to explore this further as a treatment option in clavicle fractures.Materials and methodsFixation of fifteen simulated mid-shaft fractures was undertaken using a combination of mono-cortical locked, bicortical locked and bicortical non-locked plating methods in cadaveric clavicles. Samples were then tested via three-point bending to destruction, and the performance of each with respect to failure load, bending stress, bending stiffness and Young's modulus was then analysed. The influence of the number of cortices engaged and locking was also assessed.ResultsClavicles fixed with monocortical locking plates displayed a significantly lower bending stress (12 ± 1 MPa) than both the bicortical locking (28 ± 3 MPa, p = 0.015) and non-locking specimens (24 ± 3 MPa, p = 0.002). Engaging two cortices with the fixation produced a significant increase in failure load (291 ± 28 N vs 138 ± 48 N, p = 0.018) and bending stress (26 ± 2 MPa vs 9.9 ± 3.5 MPa, p = 0.002) compared to single cortex fixation.DiscussionThe greatest influence upon the performance of the fixation was the number of cortices engaged, with bicortical fixation performing significantly better than mono-cortical. Whether or not the fixation device was a locking one did not have a significant bearing upon the performance.ConclusionThis in vitro biomechanical analysis demonstrates that mono-cortical locked plating fails at significantly lower levels of load and stress than bicortical locked and non-locked plating in mid-shaft fractures of the clavicle, and caution would therefore be advised in its use as a fixation modality for these injuries.     

Intrasacral rod fixation for pediatric lumbopelvic fusion

Purpose

This paper reports the authors’ 19 years experience with pediatric intrasacral rod fixation.

Methods

After insertion of two cannulated screws in S1 with and an original template guiding them into the anterior third of the endplate, two short fusion rods were inserted into the sacrum according to Jackson’s technique distally to S3. In neuromuscular scoliosis, pelvic obliquity was reduced by connecting the proximal and distal constructs, distraction or compression, and in situ rod bending. In children with high-grade spondylolisthesis, lumbosacral kyphosis was reduced by rotation of the sacrum and in situ bending.

Results

There were no direct neurological or vascular injuries. The main complication was infection (7 %). No pseudarthrosis or significant loss of correction at the lumbosacral junction was observed during follow-up.

Conclusions

Intrasacral rod fixation appears to be safe and reliable for lumbopelvic fusion in pediatric patients.