The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping

Clinical studies reported frequent failure with anterior instrumented multilevel cervical corpectomies. Hence, posterior augmentation was recommended but necessitates a second approach. Thus, an author group evaluated the feasibility, pull-out characteristics, and accuracy of anterior transpedicular screw (ATPS) fixation. Although first success with clinical application of ATPS has already been reported, no data exist on biomechanical characteristics of an ATPS-plate system enabling transpedicular end-level fixation in advanced instabilities. Therefore, we evaluated biomechanical qualities of an ATPS prototype C4–C7 for reduction of range of motion (ROM) and primary stability in a non-destructive setup among five constructs: anterior plate, posterior all-lateral mass screw construct, posterior construct with lateral mass screws C5 + C6 and end-level fixation using pedicle screws unilaterally or bilaterally, and a 360° construct. 12 human spines C3–T1 were divided into two groups. Four constructs were tested in group 1 and three in group 2; the ATPS prototypes were tested in both groups. Specimens were subjected to flexibility test in a spine motion tester at intact state and after 2-level corpectomy C5–C6 with subsequent reconstruction using a distractable cage and one of the osteosynthesis mentioned above. ROM in flexion–extension, axial rotation, and lateral bending was reported as normalized values. All instrumentations but the anterior plate showed significant reduction of ROM for all directions compared to the intact state. The 360° construct outperformed all others in terms of reducing ROM. While there were no significant differences between the 360° and posterior constructs in flexion–extension and lateral bending, the 360° constructs were significantly more stable in axial rotation. Concerning primary stability of ATPS prototypes, there were no significant differences compared to posterior-only constructs in flexion–extension and axial rotation. The 360° construct showed significant differences to the ATPS prototypes in flexion–extension, while no significant differences existed in axial rotation. But in lateral bending, the ATPS prototype and the anterior plate performed significantly worse than the posterior constructs. ATPS was shown to confer increased primary stability compared to the anterior plate in flexion–extension and axial rotation with the latter yielding significance. We showed that primary stability after 2-level corpectomy reconstruction using ATPS prototypes compared favorably to posterior systems and superior to anterior plates. From the biomechanical point, the 360° instrumentation was shown the most efficient for reconstruction of 2-level corpectomies. Further studies will elucidate whether fatigue testing will enhance the benefit of transpedicular anchorage with posterior constructs and ATPS.     

Evaluation of a new type of titanium mesh cage versus the traditional titanium mesh cage for single-level, anterior cervical corpectomy and fusion

Study design

A retrospective review of prospectively collected data in an academic institution.

Objective

To evaluate the safety and efficacy of a new type of titanium mesh cage (TMC) in single-level, anterior cervical corpectomy and fusion (ACCF).

Methods

Fifty-eight patients consecutive with cervical spondylotic myelopathy (CSM) from cervical degenerative spondylosis and isolated ossification of the posterior longitudinal ligament were treated with a single-level ACCF using either a new type of TMC (28 patients, group A) or the traditional TMC (30 patients, group B). We evaluated the patients for TMC subsidence, cervical lordosis (C2–C7 Cobb and Cobb of fused segments) and fusion status for a minimum of 30 months postoperatively based on spine radiographs. In addition, neurologic outcomes were evaluated using the Japanese Orthopedic Association (JOA) scores. Neck pain was evaluated using a 10-point visual analog scale (VAS).

Results

The loss of height of the fused segments was less for group A than for group B (0.8 ± 0.3 vs. 2.8 ± 0.4 mm) (p < 0.01); also, there was a lower rate of severe subsidence (≥3 mm) in group A (4 %, 1/28) than in group B (17 %, 5/30) (p < 0.01). There were no differences in the C2–C7 Cobb and Cobb of fused segments between the groups preoperatively or at final follow-up (p > 0.05), but the Cobb of fused segments immediately postoperative were significantly less for group B than for group A (p < 0.01). All patients, however, had successful fusion (100 %, each). Both groups had marked improvement in the JOA score after operation (p < 0.01), with no significant differences in the JOA recovery ratio (p > 0.05). The postoperative VAS neck pain scores for group A were significantly less than that for group B (p < 0.05); severe subsidence was correlated with neck pain.

Conclusions

The new type of TMC provides comparable clinical results and fusion rates with the traditional TMC for patients undergoing single-level corpectomy. The new design TMC decreases postoperative subsidence (compared to the traditional TMC); the unique design of the new type of TMC matches the vertebral endplate morphology which appears to decrease the severity of subsidence-related neck pain in follow-up.     

保留椎体后壁的椎体次全切除术治疗多节段颈椎病的前瞻性研究

目的 报告一种改良椎体次全切除术术式,并与传统的椎体次全切除术比较。方法2003年3月—2005年1月,84例多节段颈椎病患者随机行保留椎体后壁的椎体次全切除术（PWCF）和经典的椎体次全切除术（ACF）各42例,比较两组手术时间、出血量、住院时间、住院费用、并发症、术后JOA评分、植骨融合率、节段高度、颈椎曲度等多项指标。结果两种术式术后短期JOA评分无明显差异。PWCF组较ACF组手术时间短、出血量少。术后3个月两组植骨融合率均为100％。颈椎曲度和节段高度两组无差异。结论PWCF是一种切实有效的颈椎前路减压植骨融合术式,具有简便、风险小和植骨融合率高的优点。     

两种长度的颈椎椎弓根螺钉和侧块螺钉钢板系统的稳定性比较

目的比较两种长度的颈椎椎弓根螺钉和侧块螺钉钛板系统固定的三维稳定性,探讨颈椎椎弓根螺钉的适宜长度。方法18具新鲜颈椎标本,制成C4-5节段三柱损伤模型,分别用长度为20mm、28mm的椎弓根螺钉,以及AXIS侧块螺钉钢板系统三种方法固定,测试它们在前屈、后伸、左右侧弯和轴向旋转运动状态的稳定性。结果两种长度的颈椎椎弓根螺钉钢板系统的稳定性无明显差异,但20mm的椎弓根螺钉固定的稳定性显著高于侧块螺钉固定。结论颈椎经椎弓根固定,选择20mm长度的螺钉,即可提供足够的稳定性,同时安全性相对较高。     

枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定的有限元分析

目的分析枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定在寰枢和枕颈固定中的生物力学稳定性。方法构建正常枢椎解剖、椎板薄和椎动脉变异椎弓根细小3种不同解剖状态下的完整上部颈椎有限元模型作为完整模型组,然后分别模拟齿状突骨折进行寰枢固定和寰椎骨折进行枕颈固定。在寰枢固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(椎弓根螺钉组);在枕颈固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+枕骨螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+枕骨螺钉固定组(椎弓根螺钉组)。枢椎棘突螺钉分别测试水平、斜向、垂直置钉3种不同的固定技术。模拟颈椎运动,测量枕颈的屈伸、侧屈、旋转的关节活动范围(ROM)。结果在寰枢和枕颈固定中,棘突螺钉组和椎弓根螺钉组的C1~C2屈伸、侧屈、旋转ROM均较完整模型组均明显下降。在寰枢固定中棘突螺钉组C0~C2屈伸、侧屈、旋转的ROM大于椎弓根螺钉组;在枕颈固定中,棘突螺钉组C1~C2侧屈的ROM大于椎弓根螺钉组,棘突螺钉组的C0~C2旋转的ROM大于椎弓根螺钉组。枢椎棘突螺钉分别测试水平、斜向、垂直固定间有差异,但不明显。结论在寰枢和枕颈固定中,枢椎双侧椎弓根螺钉固定和枢椎单侧棘突螺钉联合对侧椎弓根螺钉组合式固定方法均具有良好的稳定性。在寰枢固定中,相对于枢椎棘突螺钉组合式固定,枢椎双侧椎弓根螺钉固定具有更好的寰枢稳定性。在枕颈固定中,枢椎双侧椎弓根螺钉固定在侧屈和旋转活动上较枢椎棘突螺钉组合式固定稳定性更好。枢椎三种棘突螺钉置钉技术间的稳定性差异并不明显。     

经前后路联合椎弓根钉内固定治疗67例颈椎骨折脱位的疗效评价

目的 评价前后路联合椎弓根钉固定术治疗颈椎骨折脱位伴脊髓损伤的疗效。方法 选择符合诊断标准的颈椎骨折脱位67例,随机分为实验组和对照组,实验组采用前后路联合椎弓根钉固定术,对照组采用传统椎弓根固定术。结果2组获得6-38个月,平均19.7个月的随访。2组ASIS评分和JOA评分术后第3、6个月与术前相比,差异有统计学意义（P〈0.05）。术后6个月随访时,实验组的ASIS评分和JOA评分改善要优于对照组（P〈0.05）。结论 采用前后路联合椎弓根钉固定术治疗颈椎骨折脱位伴脊髓损伤的疗效要优于传统椎弓根固定术。     

Biomechanical evaluation of a new modular rod-screw implant system for posterior instrumentation of the occipito-cervical spine: in-vitro comparison with two established implant systems

Posterior instrumentation of the occipito-cervical spine has become an established procedure in a variety of indications. The use of rod-screw systems improved posterior instrumentation as it allows optimal screw positioning adapted to the individual anatomic situation. However, there are still some drawbacks concerning the different implant designs. Therefore, a new modular rod-screw implant system has been developed to overcome some of the drawbacks of established systems. The aim of this study was to evaluate whether posterior internal fixation of the occipito-cervical spine with the new implant system improves primary biomechanical stability. Three different internal fixation systems were compared in this study: the CerviFix System, the Olerud Cervical Rod Spinal System and the newly developed Neon Occipito Cervical System. Eight human cervical spine C0/C5 specimens were instrumented from C0 to C4 with occipital fixation, transarticular screws in C1/C2 and lateral mass or pedicle screws in C3 and C4. The specimens were tested in flexion/extension, axial rotation, and lateral bending using pure moments of ± 2.5 Nm without axial preload. After testing the intact spine, the different instrumentations were tested after destabilising C0/C2 and C3/C4. Primary stability was significantly increased, in all load cases, with the new modular implant system compared to the other implant systems. Pedicle screw instrumentation tended to be more stable compared to lateral mass screws; nevertheless, significant differences were observed only for lateral bending. As the experimental design precluded any cyclic testing, the data represent only the primary stability of the implants. In summary, this study showed that posterior instrumentation of the cervical spine using the new Neon Occipito Cervical System improves primary biomechanical stability compared to the CerviFix System and the Olerud Cervical Rod Spinal System. Received: 31 December 1999/Revised: 4 April 2000/Accepted: 28 April 2000     

Biomechanical evaluation of posterior lumbar dynamic stabilization: an in vitro comparison between Universal Clamp and Wallis systems

Treatment of chronic low back pain due to degenerative lumbar spine conditions often involves fusion of the symptomatic level. A known risk of this procedure is accelerated adjacent level degeneration. Motion preservation devices have been designed to provide stabilization to the symptomatic motion segment while preserving some physiologic motion. The aim of this study was to compare the changes in relative range of motion caused as a result of application of two non-fusion, dynamic stabilization devices: the Universal Clamp (UC) and the Wallis device. Nine fresh, frozen human lumbar spines (L1–Sacrum) were tested in flexion–extension, lateral bending, and axial rotation with a custom spine simulator. Specimens were tested in four conditions: (1) intact, (2) the Universal Clamp implanted at L3–4 (UC), (3) the UC with a transverse rod added (UCTR), and (4) the Wallis device implanted at L3–4. Total range of motion at 7.5 N-m was determined for each device and compared to intact condition. The UC device (with or without a transverse rod) restricted motion in all planes more than the Wallis. The greatest restriction was observed in flexion. The neutral position of the L3–4 motion segment shifted toward extension with the UC and UCTR. Motion at the adjacent levels remained similar to that observed in the intact spine for all three constructs. These results suggest that the UC device may be an appropriate dynamic stabilization device for degenerative lumbar disorders.     

Biomechanical comparison of laminectomy, hemilaminectomy and a new minimally invasive approach in the surgical treatment of multilevel cervical intradural tumour: a finite element analysis

Purpose

The objective of this study was to investigate the impact of the less invasive procedures of hemilaminectomy and unilateral multilevel interlaminar fenestration (UMIF) on the cervical spinal biomechanics.

Methods

A validated nonlinear finite element model of the intact cervical spine (C2–C7) was modified to study the biomechanical changes as a result of surgical alteration for treatment of intradural tumours at C3–6 using multilevel laminectomy (ML), multilevel hemilaminectomy (MHL) and UMIF with or without unilateral graded facetectomy.

Results

Under the load-controlled method, the greatest biomechanical changes occurred at the surgical segments. The largest increases occurred in flexion motions following ML approach with 70, 62 and 60 % increase at C3–4, C4–5 and C5–6, respectively. The increases were significantly reduced to no more than 14 % under MHL and UMIF. When combined with graded facetectomy, the changes in flexion under ML approach have a significantly further increase, up to 110 % at C3–4. The further increase was not significantly following MHL and UMIF, with no more than 31 % increase at C3–4, C4–5 and C5–6. The motion following UMIF was only slightly smaller in axial rotation than MHL. The maximum stresses in the annulus occurred during flexion in ML model, with 39, 34 and 38 % more stress than the intact at C3–4, C4–5 and C5–6, respectively. The increases of stress were significantly reduced to 5–7 % under MHL and UMIF.

Conclusions

The less invasive approaches of UMIF and MHL greatly preserved the flexion motion (more than 48 %) of the cervical spine compared with laminectomy, and the preserved motion mean the low-risk of postoperative spinal instability. UMIF and MHL also reduced the increased stress of annulus caused by ML, and the lesser stress will lower the risk of postoperative disc degeneration. The posterior bone elements play a slight role in spinal stability after removal of the attached ligaments.     

Effect of design on the initial stability of press-fit cups in the presence of acetabular rim defects: experimental evaluation of the effect of adding circumferential fins

Purpose

This experimental study was undertaken to examine the fixation characteristics of a six-finned acetabular cup in both primary and revision arthroplasty in comparison with two other commonly used cup designs without fins.

Methods

All three cup designs (Ananova® [Intraplant], Plasmacup® NSC [Aesculap]; Exceed ABT™ [Biomet]) were implanted into validated models of normal and revision acetabula. The defect models were designed to simulate a dorso-cranial rim defect of 90° width and 10 mm in depth (moderate rim defect) and a dorso-cranial rim defect of 130° width and 15 mm in depth (severe rim defect). The fixation strength of the three cup designs was tested by cyclically edge-loading the implanted cups using a mechanical testing machine.

Results

The six-finned Ananova implant exhibited greater resistance to foam-cup interface motion than both the Plasmacup and Exceed ABT implants. The largest average differences were observed in the resistance to ultimate spin-out, with Ananova outperforming Exceed ABT and Plasmacup by 26 % and 17 % in the moderate and by 36 % and 38 % in the severe defect models, respectively.

Conclusions

The six-finned Ananova cup was significantly more resistant to edge loading both in the normal acetabulum and in acetabula with moderate to severe dorso-cranial rim defects than cup designs without fins, indicating that it may cover a wider range of clinical indications than conventional press-fit cups and provide clinicians with the confidence that, in primary and simple revision arthroplasty, adequate fixation strength can be obtained.     

Primary stabilizing effect of interbody fusion devices for the cervical spine: an in vitro comparison between three different cage types and bone cement

Interbody fusion cages are small hollow implants that are inserted into the intervertebral space to restore physiological disc height and to allow bony fusion. They sometimes cause clinical complications due to instability, subsidence or dislocation. These are basic biomechanical parameters, which influence strongly the quality of a fusion device; however, only few data about these parameters are available. Therefore, the purpose of the present study was to investigate the primary stabilizing effect of four different cervical fusion devices in in vitro flexibility tests. Twenty-four human cervical spine segments were used in this study. After anterior discectomy, fusion was performed either with a WING cage (Medinorm AG, Germany), a BAK/C cage (Sulzer SpineTech, USA), an AcroMed cervical I/F cage (DePuy AcroMed International, UK) or bone cement (Sulzer, Switzerland). All specimens were tested in a spine tester in the intact condition and after implantation of one of the four devices. Alternating sequences of pure lateral bending, flexion-extension and axial rotation moments (+/- 2.5 Nm) were applied continuously and the motions in each segment were measured simultaneously. In general, all tested implants had a stabilizing effect. This was most obvious in lateral bending, where the range of motion was between 0.29 (AcroMed cage) and 0.62 (BAK/C cage) with respect to the intact specimen (= 1.00). In lateral bending, flexion and axial rotation, the AcroMed cervical I/F cages had the highest stabilizing effect, followed by bone cement, WING cages and BAK/C cages. In extension, specimens fused with bone cement were most stable. With respect to the primary stabilizing effect, cages, especially the AcroMed I/F cage but also the WING cage and to a minor extent the BAK/C cage, seem to be a good alternative to bone cement in cervical interbody fusion. Other characteristics, such as the effect of implant design on subsidence tendency and the promotion of bone ingrowth, have to be determined in further studies.     

Multidirectional flexibility analysis of anterior and posterior lumbar artificial disc reconstruction: in vitro human cadaveric spine model

The in vitro multidirectional flexibility analysis was conducted to investigate the initial biomechanical effect of biomimetic artificial intervertebral disc replacement from either anterior or posterior approach in a cadaveric lumbosacral spine model. Two designs of anterior total and posterior subtotal artificial discs were developed using bioactive three-dimensional fabric and bioresorbable hydroxyapatite/poly-l-lactide material (3DF disc). Both models were designed to obtain the stable interface bonding to vertebral endplates with maximum surface area occupation. Using seven cadaveric lumbosacral spines, the following three anterior reconstruction methods were sequentially performed at L4–5 level: anterior 3DF disc replacement; anterior BAK cages (BAK); and posterior pedicle screw fixation and anterior BAK cages combined (BAK + PS). The L2–3 level received two methods of posterior reconstructions: subtotal 3DF disc replacement (two implants), and posterior interbody cages and pedicle screw fixation (PLIF). Six unconstrained pure moments were applied and three-dimensional segmental motions were measured with an optoelectronic motion measurement system. The center of rotation (COR) calculation was conducted radiographically using flexion-extension films. Both anterior and posterior 3DF replacements statistically demonstrated equivalent range of motions (ROMs) in all loading modes compared to intact segment. Anterior BAK, BAK + PS, and PLIF demonstrated significantly lower ROMs when compared to intact and 3DF groups (P<0.05). The 3DF reconstruction tended to realign the COR to the posterior third or surrounding position at the operative disc level. The stand-alone lumbar 3DF disc replacement demonstrated biomechanical characteristics nearly equivalent to the intact spinal segments even through anterior or posterior approach in vitro, suggesting an excellent clinical potential.     

Spinal implants and radiation therapy: the effect of various configurations of titanium implant systems in a single-level vertebral metastasis model

BACKGROUND: The combination of surgery and radiation therapy is a common clinical practice in the treatment of spinal tumors. Although it is known that metallic implants disturb radiation therapy beams, it is not known what kind of dose distributions appear with spinal irradiation in the presence of a spinal implant. The aim of the present study was to investigate the effect of various spinal implant constructs on the dose of radiation delivered to the spinal canal in a single-level metastasis model. METHODS: We performed four spinal implant reconstructions on standard sawbones spine models: posterior instrumentation without anterior column reconstruction, posterior instrumentation with anterior column reconstruction with use of a titanium cage, anterior instrumentation with anterior column reconstruction with use of a titanium cage, and anterior instrumentation with anterior column reconstruction with use of chest tubes filled with bone cement. Irradiation with two different radiation therapy units (a cobalt-60 teletherapy unit and a linear accelerator) was performed twice for each model in a posterior-to-anterior direction, and thermoluminescent dosimeters were used to measure the dose changes in the anterior, middle, and posterior portions of the spinal canal. RESULTS: Compared with the sawbones-only model, the posterior instrumentation reconstructions resulted in a 5% to 7% decrease in the radiation dose delivered to the spinal canal with both radiation therapy units, whereas the anterior instrumentation reconstructions resulted in a 1% decrease in the dose delivered with the linear accelerator unit and a < or = 2% increase in the dose delivered with the cobalt-60 teletherapy unit. When thermoluminescent dosimeters in the middle of the spinal canal were evaluated individually, anterior instrumentation with anterior column reconstruction with use of bone cement-filled chest tubes resulted in a 5.5% increase in the radiation dose delivered with the cobalt-60 teletherapy unit, whereas all of the other instrumentation models resulted in a <1% disturbance in the radiation dose delivered with both radiation therapy units. CONCLUSIONS: The posterior instrumentation systems did not result in the delivery of an increased dose of radiation to the spinal cord, suggesting that current radiation therapy regimens may be performed without additional harm. The anterior instrumentation systems also appeared to be relatively safe when irradiation was performed with the linear accelerator unit. However, when irradiation was performed with use of the cobalt-60 teletherapy unit, there was an increase in the dose of radiation delivered to the spinal canal in the presence of the anterior instrumentation systems, particularly the anterior column reconstruction with use of bone cement-filled chest tubes. These dose-perturbation characteristics might be important to consider during the calculation of radiation therapy protocols for patients who are going to receive high doses or recurrent treatments that would reach the tolerance limits of the spinal cord.     

Biomechanical analysis of an interbody cage with three integrated cancellous lag screws in a two-level cervical spine fusion construct: an in vitro study

Background contextDespite an increase in the clinical use of no-profile anchored interbody cages (AIC) for anterior cervical discectomy and fusion (ACDF) procedures, there is little published biomechanical data describing its stabilizing effect relative to the traditional anterior plating technique over two contiguous levels.PurposeTo biomechanically compare the acute stability conferred by a stand-alone interbody fusion device with three integrated fixation screws (“anchored cage”) with a traditional six-hole rigid anterior plate in a two contiguous levels (C4–C5+C5–C6) fusion construct. We hypothesized that the anchored cage would confer comparable segmental rigidity to the cage and anterior plate construct.Study designA biomechanical laboratory study using cadaveric human cervical spines.MethodsSeven (n=7) cadaveric human cervical spines (C3–C7) were subjected to quasistatic, pure-moment loading (±1.5 Nm) in flexion-extension (flex/ext), right/left lateral bending (RB/LB), and right/left axial rotation (RR/LR) for the following test conditions: intact; after discectomy and insertion of the AIC at C4–C5 and C5–C6 with anchoring screws engaged; after the removal of the integrated anchoring screws and instrumentation of an anterior locking plate (ALP) over both levels; and cage-only (CO) configuration with screws and anterior plate removed. Intervertebral range of motion (ROM) at the instrumented levels was the primary biomechanical outcome.ResultsFlex/ext, RB/LB, and RR/LR ROMs were significantly reduced (p<.001) over both levels by AIC and ALP constructs relative to the CO construct. Significant reduction in flex/ext motion was achieved with the ALP (6.8±3.7) relative to the AIC (10.2°±4.6°) (p=.041) construct. No significant differences were seen in ROM reductions over the two levels between the AIC and APL groups in lateral bending or axial rotation (p>.826).ConclusionsThe anchored cage fusion construct conferred similar acute biomechanical stability in lateral bending and axial rotation ROMs relative to rigid anterior plating. We identified a statistically significant reduction (Δ=3.4°, combined over two levels) in sagittal plane ROM conferred by the ALP relative to the AIC construct. Our biomechanical findings may support the clinical use of no-profile integrated interbody devices over two contiguous levels in ACDF.     

颈椎前路椎间盘切除融合术与人工颈椎椎间盘置换术治疗跳跃型颈椎椎间盘突出症的生物力学效应有限元分析

目的 探讨颈椎前路椎间盘切除融合术(ACDF)和人工颈椎椎间盘置换术(CDA)治疗跳跃型颈椎椎间盘突出症的生物力学改变情况.方法 建立正常人颈椎(C2～7)三维有限元模型,并与既往研究数据进行对比,验证模型的有效性.选择C3/C4和C5/C6建立节段跳跃ACDF(Zero-P系统)、跳跃CDA(Prestige-LP假...     

Biomechanical comparison of dynamic condylar screw and locking compression plate fixation in unstable distal femoral fractures: An in vitro study

Background:

Distal femur fractures are difficult to manage and the selection of implant for internal fixation remains controversial. The objective of this study is to establish the relative strength of fixation of a distal femoral locking plate (DFLP) compared with the dynamic condylar screw (DCS) in the distal femur fractures.

Materials and Methods:

Study was conducted on 16 freshly harvested cadaveric distal femoral specimens, eight implanted with DCS and other eight with DFLP. The construct was made unstable by removing a standard sized medial wedge of 1 cm base (gap-osteotomy) beginning 6 cm proximal to the lateral joint line in distal metaphyseal region with the loss of medial buttress. Fatigue test was conducted under load control mode at the frequency of I Hz. Specimens were subjected to cyclic loading of 2 kN, under observation for 50,000 cycles or until failure/cutout, which ever occurred earlier.

Results:

In DFLP group, there was no implant failure and the average number of cycles sustained was 50,000. Six out of eight specimens completed 50,000 cycles and two failed in DCS group. The average number of cycles sustained by DCS was 46150. Though the bone quality as assessed by dual energy X-ray absorptiometry DEXA was comparable in both DFLP and DCS group (P = 0.06), none failed in DFLP group and subsidence was 1.02 ± 0.34 mm (range: 0.60-1.32 mm), which was significantly 43% lower (P = 0.006) than subsidence in DCS group (1.82 ± 0.58; range: 1.20-3.08 mm). The average stiffness of DCS group was 52.8 ± 4.2 N/mm, which was significantly lower than average stiffness of locked condylar plate group (71.2 ± 5.1 N/mm) (P = 0.02).

Conclusions:

DFLP fixation of the distal femur fractures resulted in stronger construct than the DCS fixation in both cyclic loading and ultimate strength in biomechanical testing of a simulated A3 distal femur fracture.     

Biomechanical evaluation of a newly developed monocortical expansion screw for use in anterior internal fixation of the cervical spine. In vitro comparison with two established internal fixation systems

STUDY DESIGN: The primary biomechanical stability of anterior internal fixation of the cervical spine obtained with a new monocortical expansion screw in vitro was evaluated. OBJECTIVES: To determine whether the anterior internal fixation of the spine obtained with the new monocortical expansion screw provides biomechanical stability comparable with that obtained with bicortical fixation. SUMMARY OF BACKGROUND DATA: The anterior plate instrumentation used with bicortical screw fixation in the cervical spine provides a primary stability superior to that associated with monocortical screw fixation. However, bicortical screws have the potential to perforate the posterior cortex. Therefore, monocortical instrumentation systems were developed, but without the biomechanical stability associated with bicortical systems. A new expansion screw for monocortical fixation was developed to improve biomechanical stability of monocortical systems. METHODS: Three different internal fixation systems were compared in this study: 1) H-plate with AO 3.5-mm bicortical screws, 2) cervical spine locking plate with monocortical screws, and 3) H-plate with the new monocortical expansion screws. Eight fresh human cadaver spine segments from C4 to C7 were tested in flexion-extension, axial rotation, and lateral bending using pure moments of +/- 2.5 Nm without axial preload. Five conditions were investigated consecutively: 1) intact spine; 2) uninstrumented spine with the segment C5-C6 destabilized; 3-5) instrumentation of the segment C5-C6 with the three implants mentioned above after removal of the disc and insertion of an interbody spacer. RESULTS: Between bicortical and monocortical expansion screw H-plate fixation, no significant differences were observed in all load cases concerning range of motion and neutral zone. The neutral zone and range of motion were significantly larger for the cervical spine locking plate than for bicortical and monocortical expansion screw fixation in all load cases, except neutral zone for axial rotation versus bicortical screw fixation. The instrumented cases only had a significantly lower range of motion and neutral zone than the intact cases in extension-flexion, whereas for lateral bending and axial rotation no significant differences could be observed. Because the experimental design precluded any cyclic testing, the data represent only the primary stability of the implants. CONCLUSIONS: In anterior instrumentation of the cervical spine using a H-plate, the new monocortical expansion screw provides the same biomechanical stability as the bicortical 3.5-mm AO screw and a significantly better biomechanical stability than the cervical spine locking plate. Therefore, the expansion screw may be an alternative to the bicortical fixation and does not involve the risk of penetration of the posterior vertebral body cortex.