Ankle joint contact loads and displacement in syndesmosis injuries repaired with Tightropes compared to screw fixation in a static model

BackgroundThe effect of syndesmotic fixation on restoration of pressure mechanics in the setting of a syndesmotic injury is largely unknown. The purpose of this study is to examine the contact mechanics of the tibiotalar joint following syndesmosis fixation with screws versus a flexible fixation device for complete syndesmotic injury.MethodsSix matched pairs of cadaveric below knee specimens were dissected and motion capture trackers were fixed to the tibia, fibula, and talus and a pressure sensor was placed in the tibiotalar joint. Each specimen was first tested intact with axial compressive load followed by external rotation while maintaining axial compression. Next, syndesmotic ligaments were sectioned and randomly assigned to repair with either two TightRopes® or two 3.5 mm cortical screws and the protocol was repeated. Mean contact pressure, peak pressure, reduction in contact area, translation of the center of pressure, and relative talar and fibular motion were calculated. Specimens were then cyclically loaded in external rotation and surviving specimens were loaded in external rotation to failure.ResultsNo differences in pressure measurements were observed between the intact and instrumented states during axial load. Mean contact presure relative to intact testing was increased in the screw group at 5 Nm and 7.5 Nm torque. Likewise, peak pressure was increased in the TightRope group at 7.5 Nm torque. There was no change in center of pressure in the TightRope group at any threshold; however, at every threshold tested there was significant medial and anterior translation in the screw group relative to the intact state.ConclusionEither screws or TightRope fixation is adequate with AL alone. With lower amounts of torque, the TightRope group appears to have contact and pressure mechanics that more closely match native mechanics.     

Motion of the fibula relative to the tibia and its alterations with syndesmosis screws: A cadaver study

BackgroundThe motion of the fibula in relation to the tibia is coupled on the motion of the talus in the ankle joint. Several authors investigated this motion with different methods. An injury of the elastic fixation of the fibula to the tibia and its treatment with the syndesmotic set screw has an impact on this motion.MethodsThe motion of the fibula relative to the tibia was measured in eight embalmed human above the knee amputated cadaver specimens using a 3D-motion analysis system. The relative motion was measured from 50° of plantar flexion to 30° of dorsiflexion. Experiments were performed in the following conditions: without fixation and intact ligaments, after sectioning of the four syndesmotic ligaments and the interosseous membrane, and application of either a tricortical screw, or a quadricortical screw or two quadricortical screws.ResultsConcordant movements of the lateral malleolus were a medial translation during plantar flexion, external rotation around the sagittal axis during plantar and dorsiflexion. The motion of the proximal fibula was smaller and more variable than in the distal part. After sectioning of the syndesmosis the range of motion, compared to the intact state increased, particularly in translation along the transversal (118%), sagittal (160%) and the longitudinal (136%) axis and in axial rotation (145%). Syndesmotic screws reduced the range of motion in transversal (p < 0.006) and sagittal translation (p < 0.011) and axial rotation.ConclusionThe small relative motion of the tibia and fibula is increased by syndesmotic injuries. Syndesmosis screws significantly limit this increased relative motion below physiologic values, which makes it necessary to remove the screws before flexion in the ankle joint is performed.     

Novel metallic implantation technique for osteochondral defects of the medial talar dome

Background and purpose A metallic inlay implant (HemiCAP) with 15 offset sizes has been developed for the treatment of localized osteochondral defects of the medial talar dome. The aim of this study was to test the following hypotheses: (1) a matching offset size is available for each talus, (2) the prosthetic device can be reproducibly implanted slightly recessed in relation to the talar cartilage level, and (3) with this implantation level, excessive contact pressures on the opposite tibial cartilage are avoided.

Methods The prosthetic device was implanted in 11 intact fresh-frozen human cadaver ankles, aiming its surface 0.5 mm below cartilage level. The implantation level was measured at 4 margins of each implant. Intraarticular contact pressures were measured before and after implantation, with compressive forces of 1,000–2,000 N and the ankle joint in plantigrade position, 10? dorsiflexion, and 14? plantar flexion.

Results There was a matching offset size available for each specimen. The mean implantation level was 0.45 (SD 0.18) mm below the cartilage surface. The defect area accounted for a median of 3% (0.02–18) of the total ankle contact pressure before implantation. This was reduced to 0.1% (0.02–13) after prosthetic implantation.

Interpretation These results suggest that the implant can be applied clinically in a safe way, with appropriate offset sizes for various talar domes and without excessive pressure on the opposite cartilage.     

Comparison of clinically used bilayer collagen membrane and trilayer collagen prototype fixation stability in chondral defects at the talus — An experimental human specimen study

BackgroundThe purpose of this human specimen experimental study was to compare the fixation stability of clinically used bilayer collagen membrane with fibrin glue with trilayer collagen prototype without fibrin glue in chondral defects at the medial or lateral talar shoulder (both matrices from Geistlich Pharma AG, Wollhusen, Switzerland).MethodsEleven human specimens were used. The membranes were implanted in standardized chondral defects at the medial and lateral talar shoulder randomized. All tests were performed in load-control 15 kg. Range of motion ROM of each ankle was examined individually before testing. The average ROM was 10° dorsiflexion range 0°–20° and 30° plantarflexion range 20°–45°. 1,000 testing cycles with the defined ROM were performed. Two independent investigators, blinded to membrane and fixation type, visually assessed the membrane fixation integrity for peripheral detachment, area of defect uncovered, membrane constitution and delamination.ResultsThe clinically used bilayer collagen membrane plus fibrin glue showed higher fixation stability than the trilayer prototype (all p < 0.05). No significant differences occurred between medial and lateral talar shoulder location (all p > 0.05).ConclusionsThe fixation stability of the trilayer collagen prototype without fibrin glue is lower than of the clinically used bilayer membrane with fibrin glue in chondral defects at the medial and lateral talar shoulder in an experimental human specimen test. Clinical use of trilayer collagen prototype without fibrin glue has to be validated by clinical testing to evaluate if the lower stability of fixation is still sufficient.     

全膝关节置换术后股胫关节运动学轨迹的数字化模型研究

 目的 通过透视技术结合数字化模型注册技术分析全膝关节置换术后股骨假体与胫骨垫片之间的相对运动和接触位置。方法 2007年7月至2008年6月,接受GENESISⅡ假体全膝关节置换术患者16例,均为女性;年龄56～76岁,平均66.4岁。随访48～60个月,平均(56±3)个月。采用膝关节学会评分(Knee Society Score,KSS)评价膝关节功能;采用循环透视方法获取影像学数据,对假体逆向数字建模,进行数字模型和影像学数据的匹配,重建膝关节的三维运动;测量股骨内、外髁接触位置的移动,计算胫骨内旋角度,测量股骨凸轮和胫骨立柱的接触时相和范围。结果 末次随访时KSS膝评分(93±5)分,功能评分(88±13)分,与术前比较差异有统计学意义。股骨内髁的移动范围(8.5±2.5) mm,外髁的移动范围(9.5±4.8) mm,胫骨内旋角度2.5°±8.4°。屈膝约30°～40°时凸轮和立柱发生接触,立柱后方的接触范围(8.0±1.8) mm。胫骨平台后倾角度越大,凸轮和立柱的接触越晚。结论 全膝关节置换术后股胫关节的运动学特征与正常膝关节不同,膝关节屈曲10°~30°时股骨内髁前移,屈曲大于40°后股骨内、外髁后移,胫骨平台后倾与凸轮和立柱的接触时相有相关性。     

Adequate Positioning of the Tibial Component Is Key to Avoiding Bearing Impingement in Oxford Unicompartmental Knee Arthroplasty

BackgroundBearing dislocation is a serious complication of unicompartmental knee arthroplasty (UKA) with the Oxford knee prosthesis equipped with a mobile bearing. We aimed to clarify the extent of intraoperative movement of the mobile bearing and its relationship with the positioning of prosthesis components in patients undergoing Oxford UKA.MethodsThis retrospective study included 50 patients (50 knees) who underwent Oxford UKA for anteromedial osteoarthritis or osteonecrosis of the knee. Intraoperative bearing movement was assessed at various angles of knee flexion (0°, 30°, 60°, 90°, and 120°). We stratified patients according to the extent of bearing movement posteriorly during intraoperative knee flexion, with or without contacting the lateral wall of the tibial component (with contact, 20 knees; without contact, 30 knees). Postoperative radiographic evaluations were conducted at 1 week postoperatively to assess the positional parameters of the tibial and femoral components (varus/valgus alignment, rotation, mediolateral position). Clinical evaluations were conducted at 1 year postoperatively (maximum flexion angle, Oxford Knee Score).ResultsAbnormal intraoperative movement of the mobile bearing resulting in contact with the lateral wall of the tibial component was associated with a significantly more medial position and external rotation of the tibial component, as well as poorer improvement in knee flexion angle at 1 year postoperatively.ConclusionIn Oxford UKA recipients, the bearing may impinge on the lateral wall of the tibial component during flexion above 60° if the tibial component is placed too medially or exhibits pronounced external rotation, which may limit knee function improvement postoperatively.     

Periphere Talusfrakturen

Objective

Open reduction and internal fixation with screw(s) for fragments with sufficient size, and resection of smaller fragments.

Indications

Displaced fragments with (typical) involvement of joint surface.

Contraindications

Active infection and severe peripherial vascular disease.

Surgical technique

Positioning and approach are adapted to the fracture location. Fractures of the talar head and talar shoulders, supine position and anteromedial/-lateral approach. Fractures of the lateral talar process, lateral position on contralateral side and lateral approach. Fractures of the posterior talar process, prone position and posterolateral approach. Fractures of the medial, supine position and medial approach. Open reduction and internal screw fixation. Cartilage-surgical procedures for concomitant chondral defects.

Postoperative management

For the first 6 weeks, 15 kg partial weight bearing without orthosis in a standard shoe. Thrombosis prophylaxis following the local standard during the time of partial weight bearing.

Results

At a specialized orthopedic hospital with a supraregional frequented department for foot and ankle surgery, 8 patients with peripherial talar fractures were treated in 2012 (medial/posterior talar process, each n?=?1, lateral talar process, n?=?2, medial and lateral talar shoulder, each n?=?2). One fragment was fixed with 1–3 screws, and additional cartilage reconstruction with matrix-associated stem cell transplantation was performed in 4 cases (lateral talar process, n?=?2, medial and lateral talar shoulder, each n?=?1). Bony fusion was registered at the 6-week follow-up in all cases. Further follow-up is not completed. Complications have not been registered so far.     

Effects of the tibial tunnel position on knee joint stability and meniscal contact pressure after double-bundle anterior cruciate ligament reconstruction

BackgroundTo investigate the effect of the tibial tunnel position on knee stability and the maximum contact area and peak contact pressure on the menisci after double-bundle anterior cruciate ligament (ACL) reconstruction.MethodsTen human knee specimens (mean age: 74.1 ± 15.8 years) were used in this study. The anterior tibial loading test was conducted using a material testing machine at 30°, 60°, and 90° of knee flexion, with the anterior tibial translation (ATT) and the maximum contact area and peak contact pressure on the menisci measured. Outcome measures were compared between the following groups: 1) intact ACL (intact group); 2) anatomical tibial tunnel position (anatomical group) and 3) posterior tibial tunnel position (posterior group) with double-bundle reconstruction, and 4) ACL-deficient (deficient group).ResultsIn response to a 100 N anterior tibial load, the ATT was greater for the posterior and ACL-deficient groups compared to that in the intact group. The normalized maximum contact area of the medial meniscus significantly decreased for the posterior group compared to that in the intact group. The normalized peak contact pressure on the medial meniscus increased in all groups compared to that in the intact group, but with no between-group differences in pressure applied to the lateral meniscus.ConclusionsATT and contact pressure on the medial meniscus increased, concomitant with a decrease in contact area of the medial meniscus, as the position of the tibial tunnel position moved towards a posterior position.     

Solid Bolt Fixation of the Medial Column in Charcot Midfoot Arthropathy

Charcot medial column and midfoot deformities are associated with rocker bottom foot, recurrent plantar ulceration, and consequent infection. The primary goal of surgical intervention is to realign and stabilize the plantar arch in a shoe-able, plantigrade alignment. Different fixation devices, including screws, plates, and external fixators, can be used to stabilize the Charcot foot; however, each of these methods has substantial disadvantages. To assess the effectiveness of rigid, minimally invasive fixation of the medial column and midfoot, 8 cases of solid intramedullary bolt fixation for symptomatic Charcot neuroarthropathy were reviewed. The patients included 6 males (75%) and 2 females (25%), with a mean age of 63 (range 46 to 80) years. The Charcot foot deformity was caused by diabetic neuropathy in 7 cases (87.5%) and alcoholic neuropathy in 1 (12.5%). The mean duration of postoperative follow-up period was 27 (range 12 to 44) months. The mean radiographic correction of the lateral talar–first metatarsal angle was 15° (range 3° to 19°), and the mean radiographic correction of the dorsal midfoot dislocation was 9 (range ?4 to 23) mm. The mean loss of correction of the lateral talar–first metatarsal angle and midfoot dislocation after surgery was 7° (range 0° to 26°) and 1 (range 0 to 7) mm, respectively. No bolt breakage was observed, and no cases of recurrent or residual ulceration occurred during the observation period. Bolt removal was performed in 3 cases (37.5%), 2 (25%) because of axial migration of the bolt into the ankle joint and 1 (12.5%) because of infection. The results of the present review suggest that a solid intramedullary bolt provides reasonable fixation for realignment of the medial column in cases of Charcot neuroarthropathy.     

Quantitative assessment of the subchondral vascularity of the talar dome: A cadaveric study

BackgroundThe arterial supply to the talus has been extensively studied previously but never to specifically examine the subchondral region of the talar dome, a frequent site of localised pathology. This study aims to analyse and quantify the subchondral vascularity of the talar dome.MethodsWe performed cadaveric arterial injection studies. After processing, the vascularity to the subchondral region of the talar dome was visualised and mapped using three-dimensional computer technology, then quantified and reported using a nine-section anatomical grid.ResultsThe areas of relative poor perfusion across the talar dome are the posterior/medial, posterior/lateral and middle/medial sections of a nine-section grid. The rest of the subchondral region shows more richly vascularised bone.ConclusionsThe vascularity of the subchondral surface of the talar dome is not uniformly distributed. This may be relevant to the aetiology and management of osteochondral lesions and shows some correlation with their more frequent locations.     

Simulating clamp placement across the trans-syndesmotic angle of the ankle to minimize malreduction: A radiological study

BackgroundAnkle fractures associated with syndesmotic injury have a poorer prognosis than those without such an injury. Anatomic reduction of the distal tibiofibular joint restores joint congruency and minimizes contact pressures, yet operative fixation of syndesmotic ankle injuries is frequently complicated by malreduction of the syndesmosis. Current methods of assessing reduction have been shown to be inadequate. As such, additional methods to judge the accuracy of syndesmotic reduction are required.Questions/PurposesThe purposes of our study were (1) to determine the anatomic axis of the syndesmosis, or the trans-syndesmotic angle (TSA), and (2) to describe the intraoperative fluoroscopic appearance of syndesmotic clamp reduction oriented along the anatomic syndesmotic angle.MethodsComputed tomography (CT) scans of 45 uninjured adult ankles were analyzed to measure the TSA, defined as the angle between the plane of a lateral ankle radiograph and a line drawn perpendicular to the fibular incisura. Three-dimensional reconstructions of CT scans were then used to demonstrate clamp placement collinear with the TSA as would be seen on an intraoperative lateral ankle radiograph.ResultsThe average TSA measured 21 ± 5° anterior to the plane of a lateral radiograph. When a simulated reduction clamp tine was placed on the fibular ridge and the clamp oriented along the TSA, the medial tine, as seen on a lateral radiograph, was within the anterior one-third of the tibia 93% of the time. It was, on average, 23 ± 7% of the distance from the anterior to the posterior tibial cortex, with tine placement occurring in this range in 73% of ankles. The medial tine rested 53 ± 17% of the distance between the anterior cortices of the tibia and fibula, with 71% of tines placed in this range.ConclusionsReduction clamp placement oriented along the TSA has a predictable appearance on lateral ankle imaging and can guide clamp positioning during syndesmotic reduction. With one tine placed on the fibular ridge, placing the medial clamp tine in the anterior third of the tibia, or halfway between the anterior cortices of the tibia and fibula is the most accurate position for reduction in line with the TSA.Level of evidence2 (Retrospective diagnostic).     

Biomechanical study of four kinds of percutaneous screw fixation in two types of unilateral sacroiliac joint dislocation: A finite element analysis

ObjectiveTo compare the biomechanical stability of four different kinds of percutaneous screw fixation in two types of unilateral sacroiliac joint dislocation.MethodsFinite element models of unstable Tile type B and type C pelvic ring injuries were created in this study. Modelling was based on fixation with a single S1 screw (S1-1), single S2 screw (S2-1), two S1 screws (S1-2) and a combination of a single S1 and a single S2 screw (S1–S2). The biomechanical test of two types of pelvic instability (rotational or vertical) with four types of percutaneous fixation were compared. Displacement, flexion and lateral bend (in bilateral stance) were recorded and analyzed.ResultsMaximal inferior translation (displacement) was found in the S2-1 group in type B and C dislocations which were 1.58 mm and 1.90 mm, respectively. Maximal flexion was found in the S2-1 group in type B and C dislocations which were 1.55° and 1.95°, respectively. The results show that the flexion from most significant angulation to least is S2-1, S1-1, S1-2, and S1–S2 in type B and C dislocations. All the fixations have minimal lateral bend.ConclusionOur findings suggest single screw S1 fixation should be adequate fixation for a type B dislocation. For type C dislocations, one might consider a two screw construct (S1–S2) to give added biomechanical stability if clinically indicated.     

Effect of Medial Soft Tissue Releases During Posterior-Stabilized Total Knee Arthroplasty on Contact Kinematics and Patient-Reported Outcomes

BackgroundMinimal to extensive medial soft tissue releases are part of the exposure and achieving adequate varus knee balance in total knee arthroplasty (TKA). However, the effect of these releases on knee kinematics and patient-reported outcomes is unclear. Our objective was to compare the postoperative in vivo tibiofemoral contact kinematics of a posterior-stabilized TKA between patients who received minimal medial soft tissue releases intraoperatively to those who received extensive releases. We also compared these groups using patient-reported outcomes.MethodsA prospective imaging study was performed in a single-center over a 14-month period. Patients with end-stage osteoarthritis and varus deformity undergoing primary TKA were included. Baseline data were collected 1 month before surgery. The radiostereometric analysis imaging took place at least 1 year postoperatively and composed of weight-bearing radiographic stereo examinations of knee flexion starting in full extension and in 20° increments of flexion to a maximum of 120°. Intraoperative medial soft tissue releases were recorded. Patient-reported outcomes used included Short-Form 12, Western Ontario and McMaster Osteoarthritis Index, and Knee Society Score.ResultsFifty-one patients were included in the statistical analysis. Demographic characteristics were similar between all. Patients were divided into 3 groups depending on the amount of releases they received. No statistically significant differences in tibiofemoral contact positions or excursions on the medial or lateral condyles were found throughout flexion from 0° to 120°. Postoperative patient-reported outcome scores were not different.ConclusionCorrecting severe varus deformities with extensive medial soft tissue release largely did not alter knee kinematics or clinical outcome scores compared to those with minimal soft tissue release.     

Angle bisector method to determine the accurate angle for tibiofibular syndesmotic fixation: A validation study with 3D-printed anatomical models

PurposeThis study aimed to validate the angle bisector method on 3D-printed ankle models to reveal whether it aids in placing syndesmotic screws at an accurate trajectory that is patient- and level-specific and also not surgeon-dependent.MethodsDICOM data of 16 ankles were used to create 3D anatomical models. Then the models were printed in their original size and two trauma surgeons performed the syndesmotic fixations with the angle bisector method at 2 cm and 3.5 cm proximal to joint space. Afterward, the models were sectioned to reveal the trajectory of the screws. The photos of the axial sections were processed in a software to determine the centroidal axis which is defined as true syndesmotic axis and analyze its relationship with the screws inserted. The angle between the centroidal axis and syndesmotic screw was measured by two-blinded observers 2 times with 2 weeks interval.ResultsThe average angle between the centroidal axis and screw trajectory was 2.4° ± 2° at 2 cm-level and 1.3° ± 1.5° at 3.5 cm-level, indicating a reliable direction with minimal differences at both levels. The average distance between fibular entry points of the centroidal axis and screw trajectory was less than 1 mm at both levels indicating that the angle bisector method can provide an excellent entry point from fibula for syndesmotic fixation. The inter- & intra-observer consistencies were excellent with all ICC values above 0.90.ConclusionThe angle bisector method provided an accurate syndesmotic axis for implant placement which is patient- & level-specific and not surgeon-dependent, in 3D-printed anatomical ankle models.     

松质骨螺钉与加压螺栓在微创钢板治疗跟骨骨折中应用的病例对照研究

目的:探讨采用斯氏针撬拨复位,足跟外侧微创小切口钢板全螺纹松质骨钉内固定治疗跟骨关节内移位骨折的临床疗效。方法:2009年9月至2012年6月共收治80例闭合性跟骨关节内移位骨折患者,分为对照组和治疗组,每组40例。对照组:男21例,女19例;年龄23～64岁,平均(39.1±11.7)岁;采用自断型加压螺栓钢板内固定。治疗组:男24例,女16例;年龄21～67岁,平均(39.6±14.3)岁;应用全螺纹松质骨螺钉钢板内固定。记录术中松质骨螺钉与加压螺栓进行固定的时间及手术的出血量,观察术后足底内侧神经的损伤例数,术后1年复查时测量B觟hler角和Gissane角以及跟骨的宽度的矫正度数,1年后行内固定物取出,应用AOFAS踝-后足评分标准评定疗效。结果:患者术后均获得随访,时间9～32个月,平均16个月。治疗组手术时间短、创伤小,术后B觟hler角及跟骨宽度恢复满意,减少了足内侧神经血管损伤,骨折愈合后易于取出,与对照组比较差异有统计学意义。结论:全螺纹松质骨螺钉替代自断型加压螺栓固定跟骨骨折临床疗效相同,但手术时间缩短、出血少、易于取出,避免了内侧神经血管的损伤,降低了并发症的发生。     

A lateral fracture step-off of 2mm increases intra-articular pressure following tibial plateau fracture

IntroductionThe aim of this study was to evaluate the effects of increasing posttraumatic step-offs after lateral tibial plateau fracture reduction on the intra-articular pressure.Materials and MethodsIn eight fresh-frozen human cadaveric knees with intact menisci, a standardized sagittal osteotomy of the lateral tibial condyle was performed as an OTA/AO type 41-B1 fracture-model. The fragment was fixed by a customized sled including an angular stable tibia plate to evaluate step-offs from 0 mm to 8 mm in 1mm increments. In a servo-hydraulic testing machine, an axial force was applied to the tibial plateau in 0° (700N), 15° (700N), 30° (700N), 60° (350N), and 90 ° (350N) of flexion while the joint pressure was recorded by two pressure sensors.ResultsA 1mm step-off did not result in an increased joint pressure. At 60° of flexion a 2mm step-off increased the lateral joint pressure by 61.84kPa (P = 0.0027). In 30° of flexion, a 3mm step raised the lateral joint pressure by 66.80kPa (p = 0.0017), whereas in 0°, 15° and 90° of flexion, a 4mm step increased the pressure by >50kPa (P < 0.05). Concomitant medial joint pressure increments were lower than those in the lateral plateau. A significant increase of 19-24kPa in the medial joint pressure was detected in 90° of flexion with a 1mm lateral step (P = 0.0075), in 15° and 60° of flexion with a 2mm step (P < 0.05), in 0° of flexion with a 4mm step (P = 0.0215) and in 30° of flexion with a 7mm step (P = 0.0487).ConclusionLateral fracture step-offs of 2mm or larger should be reduced intraoperatively to avoid large increases in lateral joint pressure.     

Biomechanical comparison of transfacet screws to lateral mass screw-rod constructs in the lower cervical spine

Purpose

Transfacet screws have been used as an alternative posterior fixation in the cervical spine. There is lack of spinal stability of the transfacet screws either as stand-along constructs or combined with anterior plate. This study was designed to evaluate spinal stability of transfacet screws following posterior ligamentous injury and combined with anterior plate, respectively, and compare transfacet screws to lateral mass screw-rod constructs.

Methods

Flexibility tests were conducted on eight cadaveric specimens in an intact and injury, and instrumented with the transfacet screw fixation and lateral mass screw-rod construct at C5–C7 levels either after section of the posterior ligamentous complex or combined with an anterior plate and a mesh cage for C6 corpectomy reconstruction. A pure moment of ±2.0 Nm was applied to the specimen in flexion–extension, lateral bending, and axial rotation. Ranges of motion (ROM) were calculated for the C5–C7 segment.

Results

ROM with the transfacet screws was 22 % of intact in flexion–extension, 9 % in lateral bending and 11 % in axial rotation, while ROM with the lateral mass screw-rod construct was 9 % in flexion–extension, 8 % in lateral bending and 22 % in axial rotation. The only significant difference between two constructs was seen in flexion–extension (5.8 ± 4.2° vs. 2.4 ± 1.2°, P = 0.002). When combined with an anterior plate and mesh cage, the transfacet screw fixation reduced ROM to 3.0° in flexion–extension, 1.2° in lateral bending, and 1.1° in axial rotation, which was similar to the lateral mass screw-rod construct.

Conclusions

This study identified the transfacet screw fixation, as stand-alone posterior fixation, was equivalent to the lateral mass screw-rod constructs in axial rotation and lateral bending except in flexion–extension. When combined with an anterior plate, the transfacet screw fixation was similar to the lateral mass screw-rod construct in motion constraint. The results suggested the transfacet screw fixation a biomechanically effective way as supplementation of anterior fixation.

     

Radiological indicator of reduction adequacy during ankle syndesmosis surgery: A computational cadaveric study

PurposeWe introduced the intraoperative radiological indicator to assess the reduction adequacy without additional procedure or instrument, and propose the optimal syndesmotic screw trajectory.MethodsThirty adult cadavers (15 males and 15 females) without ankle problems were enrolled and subjected to continuous 0.75 mm-slice computed tomography (CT) scans. CT images were imported into Mimics^® software to reconstruct three-dimensional (3D) model of ankle. Using free 360° rotations with magnification, the 3D mutual relationships of ankle syndesmosis were assessed, and the fibular congruency of incisura was evaluated to determine the optimal screw trajectory. By reformatting the CT scanning plane along the screw direction, the coronal relation of ankle syndesmosis was evaluated to verify the distance between the adjacent bones.ResultsThe fibula was placed in the concentric position of fibular incisura in the 20 models (concentric group) and 40 models, in an eccentric position (eccentric group). Despite this variant, all fibulas were changed into the concentric position in the proximal part of syndesmotic footprint, which might be the ideal height for syndesmotic screw in our study. The fibular bisecting screw trajectory associated with the ideal height of screw was parallel to the ground if the tibial tubercle was directed to the superior and nearly vertical to the ground floor (TT view). Through the reformatted scanning plane parallel to the screw, the lateral border of talus was always placed more medial than the lateral border of distal tibia in the coronal image. All models had a perfectly equidistant and parallel joint space except the medial aspect.ConclusionThe lateral border of talus in the TT view was intraoperatively used as the radiological indicator for ankle syndesmosis widening because it was always placed more medial than the lateral border of distal tibia. The optimal syndesmotic screw trajectory was placed around the proximal syndesmotic footprint and parallel to the ground via the TT view.     

胫腓下联合分离的生物力学研究

目的分析踝关节内、外侧结构和胫腓下联合损伤对踝关节稳定性的影响,探讨胫腓下联合固定的指征。方法12具新鲜膝关节以下下肢标本,随机分为a、b两组,分别模拟内踝骨折和三角韧带撕裂的旋前-外旋型踝关节骨折,按该型骨折加重顺序依次切断周围韧带,用压敏片和位移传感器分别测定每次处理后的关节接触面积和胫腓下联合分离距离。分析各操作步骤对关节接触面积、胫腓下联合分离距离的影响。结果a组切断三角韧带、b组切断骨间韧带后,关节接触面积及胫腓下联合分离距离较基线状态均有明显改变,差异有极显著性意义(P<0.01)。关节接触面积和下联合分离距离呈线性回归关系。结论踝关节的稳定性主要由踝关节内、外侧结构和中间的胫腓下联合共同维持,只有当三者中两处以上发生不可逆性损伤时,踝关节的稳定性才会发生根本性改变。因此,胫腓下联合分离时,下联合固定应选择性地使用。     

固定平台后稳定型假体全膝关节置换术后的运动学研究

 目的 探讨固定平台后稳定型假体全膝关节置换(total knee arthroplasty,TKA)术后膝关节在负重屈膝下蹲时的运动学特征。方法 选取10名健康志愿者和10例固定平台后稳定型假体TKA术后患者。制作骨骼及膝关节假体三维模型,在持续X线透视下完成负重下蹲动作,膝关节屈曲度每增加15°截取一幅图像。通过荧光透视分析技术完成三维模型与二维图像的匹配,再现股骨与胫骨在屈膝过程中的空间位置,通过连续的图像分析比较正常与固定平台后稳定型假体TKA术后膝关节在负重下蹲时股骨内、外髁前后移动及胫骨内外旋转幅度。结果 负重下蹲时,正常膝关节平均屈曲136°,股骨内、外髁分别后移(7.3±1.2) mm和(19.3±3.1) mm,胫骨平均内旋23.8°±3.4°;TKA术后膝关节平均屈曲125°,股骨内、外髁分别后移(1.4±1.6) mm和(6.4±1.7) mm,胫骨平均内旋8.5°±3.4°。结论 固定平台后稳定型假体TKA术后膝关节运动与正常膝关节相似,均表现出股骨内、外髁后移及胫骨内旋运动,但幅度小于正常膝关节,且在屈膝过程中存在股骨矛盾性前移及胫骨外旋现象。