Radiology of postnatal skeletal development

Thirty-one pairs of distal humeri were obtained from human cadavers ranging in age from full-term neonates to fourteen years. These were studied morphologically and roentgenographically. Specimen roentgenography using air/cartilage interfacing demonstrated both osseous and cartilaginous components of the epiphyses. These roentgenographic aspects of development are discussed and illustrated to provide a basic reference index.The supracondylar region is characterized by a fossa which initially is in both metaphysis and epiphysis, but migrates to the metaphysis completely within the first year. On either side of the fossa are osseous columns, which contrast with the broad metaphyseal bone above the columns. Within the fossa, anteriorly and posteriorly, are fat pads which may be elevated by intraarticular hematoma or reactive joint fluid. The physeal contour initially is transverse and smooth. Lappet formation progressively demarcates the epicondylar physeal regions, with the medial one becoming a functionally, but not histologically separate region.The capitellum is the first region to develop a secondary ossification center. This progressively expands into the trochlear portion of the epiphysis, a factor which predisposes to lateral condyle fracture propagation across the trochlear articular surface. The trochlea characteristically ossifies by multiple foci which fuse over time, often creating an irregular appearance to the developing ossification center. Epicondylar ossification tends to be from solitary foci. The lateral epicondylar center fuses with the capitellar center, whereas the medial epicondyle tends to be a functionally separate entity throughout development and does not normally fuse to the trochlear ossification center.     

Radiology of postnatal skeletal development

Thirty-one pairs of distal radioulnar units were obtained from human cadavers ranging in age from full-term neonates to fourteen years. These were studied morphologically and radiographically. Specimen roentgenography using air/cartilage interfacing demonstrated the osseous and cartilaginous portions of the epiphyses. These roentgenographic aspects of development are discussed and illustrated to provide a reference index.The radial and ulnar physeal/metaphyseal contours initially are transverse. Progressively the distal radius develops a proximally directed curve adjacent to the radioulnar joint. Both physes subsequently develop a convex contour with mild undulations, and a central concavity associated with the secondary ossification center. Longitudinal ossification striations were observed crossing the distal ulnar physis. These appear to be normal.At no time during postnatal development did the distal ulna ever articulate directly with the carpus. It was always separated by a segment of triangular fibrocartilage connecting the ulnar styloid to the distal radial epiphysis. This was never perforated. this discoid cartilaginous structure is the anatomic cause of the concomitancy of ulnar styloid fractures with distal radial epiphyseal injuries, an injury pattern which may occur prior to ossification in the ulnar styloid, and which may lead to non-union of the styloid when ossification eventually occurs. In none of the specimens was an accessory ossification center present in either the radial or ulnar styloid process.     

Radiology of postnatal skeletal development

The development of the second cervical vertebra is complex. The dens (odontoid process) develops two primary ossification centers that usually coalesce within three months following birth. These centers are separated from the primary ossification center of the vertebral centrum by a cartilaginous region—the dentocentral synchondrosis. This synchondrosis is a slow growing, bipolar physis similar to the triradiate catilage of the acetabulum. It contributes to the overall heights of both the dens as well as the vertebral body. Anatomically the dentocentral synchondrosis is below the level of the C1–C2 articulations. This cartilaginous structure is continuous throughout the vertebral body with similar cartilage in both the facet regions as well as the neurocentral synchondroses. These various carulaginous continuities progressively close—first, the connections to the facet regions, next the neurocentral synchondroses, and finally the dentocentral synchondrosis. Remnants of the incompletely closed dentocentral synchondrosis must be distinguished from a fracture, which usually propagates along this structure as a physeal injury in infants and children. The cartilaginous epiphysis at the tip of the dens may be transverse or may form a cleft (V) shape. At eight to ten years, a secondary ossification center—the ossiculum terminale—develops in this proximal dens epiphysis. Fusion of the ossiculum terminale with the rest of the dens occurs between ten and thirteen years.     

Radiology of postnatal skeletal development

Thirty-six pairs of proximal radioulnar and elbow units from cadavers and prepared skeletons ranging in age from full-term neonates to fourteen years, were studied morphologically and roentgenographically. Air/cartilage interfacing was used to demonstrate the osseous and cartilaginous portions of the developing epiphyses. These roentgenographic aspects are discussed and illustrated to provide a reference index.The articular interrelationships and basic contours of the distal humerus, proximal ulna, and proximal radius are the same throughout postnatal development. The major changes are proportional volume increase and the progressive development of the secondary ossification centers. Because of overlap of the developing secondary ossification centers, roentgenographic interpretation may be difficult. Awareness of the developmental stages and variations should assist in the diagnosis of trauma to the immature elbow.During the first few years the proximal ulnar metaphysis is usually at the midpoint of the ulnohumeral joint in a lateral roentgenogram with the elbow flexed at 90°. With further growth and maturation this region of the metaphysis extends proximally. However, such extension is quite variable. The secondary ossification center, which will form most of the olecranon at skeletal maturity, initially forms adjacent to the dorsal side of the metaphysis. Multifocal ossification, while a relatively common clinical observation, was not seen in any of the specimens.The radial head is intra-articular, as is part of the neck (metaphysis). However, attachments of the capsule are such that none of the ulnar metaphysis is intra-articular. The proximal radius has the same contours and relative proportions of head and neck throughout postnatal development. The head is always larger than the neck. However, the contours of the sides of the radial head are of variable obliquity, allowing different degrees of excursion of the annular ligament during rotation (supination-pronation), a factor that anatomically predisposes young children to nursemaid's elbow.The secondary ossification center of the proximal radius initially appears as a linear focus centrally located adjacent to the metaphysis. This progressively expands, but not always symmetrically. The concavity of the articular cartilage may be reflected in a central identation of the ossification center, but this is not usually evident until ten to eleven years. The plane of the articular surface is not at a right angle relative to the longitudinal axis of the radius; instead, there is an increased angulation toward the bicipital tuberosity. This also is a factor predisposing to nursemaid's elbow in the young child.     

Radiology of postnatal skeletal development

The patella initially ossifies at between three and five years, commencing as multiple foci that rapidly coalesce. As the patellar ossification center enlarges the expanding margins may be irregular and associated with accessory ossification centers. These are most common superolaterally and may lead to the development of a bipartite patella. The bipartite patella has cartilaginous continuity despite the appearance of osseous discontinuity. The patella expands to all cartilaginous contours during late adolescence when the epiphyseal ossification centers around the knee are also in the final stages of maturation. The only cartilage not replaced is that occupying the superior twothirds of the articular surface (the lower one-third is covered by the fat pad). The subchondral plate does not assume the actual articular contours until the late stages of osseous maturation (after ten to twelve years). Accordingly, typical measurements such as medial and lateral angulation cannot be accurately done prior to the final stages of patellar ossification expansion and maturation.The tibial tuberosity begins ossification at between seven and nine years as a distal focus. This progressively enlarges proximally and anteriorly, while the main tibial ossification center concomitantly expands downward into the tuberosity. A section of epiphyseal cartilage usually remains between these two ossification centers until close to physeal maturity. The anterior chondro-osseous region at the site of patellar tendon attachment is a biomechanically susceptible region that may be acutely or chronically traumatized to create an Osgood-Schlatter lesion. The physis associated with the tibial tuberosity is histologically modified in a proximal to distal gradation of columnar adaptation to specific biomechanical demands in this region. Closure of the tuberosity physis occurs in a proximal to distal direction.     

Radiology of postnatal skeletal development

Forty-four first cervical vertebra were removed from cadavers and skeletons ranging in age from full-term neonates to 14 years. These were studied roentgenographically to duplicate anteroposterior and transverse appearances without superimposition of the skull or other vertebra.Ossification was present in both posterior (neural) arches at birth. These ossification centers extended toward the rudimentary spinous process to form the posterior synchondrosis. Each also extended anteriorly into the articular facet region. The posterior ossification centers formed all the bone present in the facets. Anteromedial to each facet a neurocentral synchondrosis formed on each side of the expanding anterior ossification center. The anterior ossification center appeared between six months and two years. Normally a single center formed. However anterior ossification was sometimes multifocal. Infrequently the posterior centers extended into the anterior arch and met as a single anterior synchondrosis. By four to six years the posterior synchondrosis and the anterior neurocentral synchondroses were fused. All three synchondroses fused at approximately the same time, although the posterior one often slightly preceded the anterior ones. Accordingly, the spinal canal of C1 reached maximum size at this stage of development. Further growth was then limited to periosteal addition on the external surface, leading to thickening and increased height, but without significantly altering the size of the spinal canal.     

Radiology of postnatal skeletal development

Thirty-one pairs of clavicles obtained from human cadavers ranging in age from full-term stillborn to fourteen years were studied morphologically and radiographically. Specimen roentgenography using air/cartilage interfacing demonstrated the osseous and cartilaginous portions of the epiphyses. Overall longitudinal growth appeared to occur to a greater degree in the sternal end, which also developed a secondary ossification center. No comparable ossification was seen in the acromion. The curve patterns differed in the acromial and sternal ends. The sternoclavicular joint has a meniscus throughout postnatal development. This was demonstrated by air arthrography. Finally, the sternoclavicular joint was dislocated anteriorly and posteriorly to duplicate trauma to this region. Roentgenographic aspects of development are discussed and illustrated to provide a reference index.     

Radiology of postnatal skeletal development

Initially the distal tibial physis is a relatively transverse structure. As the epiphysis matures, undulations develop within the physis and lappet formation occurs peripherally. Within the first two years a significant physeal undulation develops anteriorly above the medial malleolus. This undulation must not be misinterpreted as premature epiphyseodesis following distal tibial fracture. Secondary ossification in the distal tibia begins centrally and initially expands to fill the area over the tibial plafond. At the lateral side of the tibial epiphysis the ossification center may be wedgeshaped. The medial margin adjacent to the medial malleolus is often irregular and may show small peripheral foci of ossification. By seven to eight vears, the secondary center extends into the medial malleolus, with complete distal extension often not occurring until adolescence (although usually complete by ten to eleven years). The malleolar tip may exhibit an accessory ossification center. However, this center also may be a traumatic avulsion in the symptomatic patient. Physiologic epiphyseodesis begins over the medial malleolus and subsequently extends laterally. This pattern of closure appears to predispose to fracture of the lateral portion of the distal tibial epiphysis (fracture of Tillaux), as well as to triplane fractures. The articular surface curves onto the lateral side of the distal tibia to form an articulation with the lateral malleolus (distal tibiofibular joint). A similar extension occurs along the medial side of the fibula. These surfaces extend proximally as a recess to the level of the distal tibial physis, at which point the syndesmosis begins. The initially transverse distal fibular physis becomes a convoluted structure, with extensive peripheral lappet formation. Within these regions of physeal overlap there may be small areas of accessory ossification (both medially and laterally) that should not be misinterpreted as fractures. This overlapping also minimizes specific physeal separation and displacement (especially when compared to the incidence of distal tibial physeal injuries). Stress views may be necessary to show such an undisplaced fracture. The fibular physis normally is level with the tibial articular surface or distal extent of the tibial ossification center, especially after the second year of life (however, it may be more proximal in infants). As in the medial malleolus, there may be accessory ossification at the tip of the fibula. While this usually is a normal variant of secondary ossification, occasionally it also may result from trauma. Extensive porosity of the distal fibular metaphysis predisposes to buckling or torus injuries that may have severe, multiangular deformation.     

Radiology of postnatal skeletal development

Thirty-six manubriosternal composites from skeletally immature cadavers were examined morphologically and radiographically. Sternebral ossification followed certain patterns. The manubrium (first sternebra) usually had one primary ossification center and one or two smaller centers. These usually were caudad to the major center (longitudinally bifid). The second sternebra invariably had only one ossification center. The third and fourth sternebrae had latitudinal (right-left) bifid ossification centers, undoubtedly a result of the original formation of the sternum from two longitudinal mesenchymal anlagen. Occasionly the fourth sternebra exhibited longitudinally bifid ossification. The usual pattern was ossification of four sternebrae, although a fifth was intermittently present. The xiphisternum (not a true sternebra) was infrequently ossified.     

Radiology of postnatal skeletal development

Twenty-four pairs of scapulae from fetal specimens and 35 pairs of scapulae from postnatal cadavers ranging in age from full-term neonates to 14 years, were studied morphologically and roentgenographically. Air-cartilage interfacing was used to demonstrate both the osseous and cartilaginous contours. When the entire chondro-osseous dimensions, rather than just the osseous dimensions, were measured, the scapula had a heightwidth ratio ranging from 1.36 to 1.52 (average 1.44) during most of fetal development. The exceptions were three stillborns with camptomelic, thanatophoric, and achondrogenic dwarfism in which the ratio averaged 0.6. At no time during fetal development was the glenoid cavity convex; it always had a concave articular surface. However, the osseous subchrondral countour was often flat or slightly convex. In the postnatal period the height-width ratio averaged 1.49. The ratio remained virtually unchanged throughout skeletal growth and maturation. In a patient with unilateral Sprengel's deformity the ratio for the normal side was 1.5, while the abnormal was 1.0. The cartilaginous glenoid cavity was always concave during postnatal development, even in the specimens with major structural deformities, although the subchondral osseous contour was usually flat or convex during the first few years of postnatal development. Ossification of the coracoid process began with the development of a primary center at three to four months. A bipolar physis was present between the primary coracoid center and the primary scapular center until late adolescence.     

The normal posterior atlantoaxial relationship

The relationship of the posterior aspects of the atlas and the axis were studied in 100 normal adult volunteers. The ratio of the height of the atlantal spinolaminar line to the atlantoaxial interspinous distance was found to be remarkably constant and was less than 2.0 in all men and women. This ratio should prove helpful in detecting hyperflexion injuries isolated to the atlantoaxial level.     

经口寰枢椎复位内固定钢板-Ⅲ系统在复杂寰枢椎脱位中的应用

目的 评估经口寰枢椎复位内固定钢板(transoral atlantoaxial reduction plate,TARP)-Ⅲ系统设计的生物力学特点及其临床应用疗效.方法 在TARP-Ⅱ的基础上设计改良TARP-Ⅲ:将钢板的枢椎螺孔向上向内各移1～2 mm,使固定的枢椎椎体钉改成椎弓根钉固定或关节突钉固定;将钢板的螺孔增设一个可万向活动的自锁环和万向导钻;进行枢椎三种螺钉固定的抗拔出力试验;并将TARP-Ⅲ应用于44例复杂难复性寰枢椎脱位患者.枢椎采用经口椎弓根固定或关节突固定.结果 (1)枢椎三种螺钉固定的最大拔出力分别为:枢椎前路椎弓根螺钉(593.1±97.8)N、枢椎关节突螺钉(469.9±73.3)N和枢椎椎体螺钉(395.2±75.1)N.结果 显示,三种固定方式的最大拔出力进行两两比较,差异有统计学意义(P＜0.05).(2)临床应用44例,获得5～38个月随访,平均18个月,观察寰枢复位、寰枢节段椎管减压,神经功能恢复及并发症的情况.本组有36例达解剖复位,8例接近解剖复位,脑干脊髓角基本纠正,颈髓均得到充分减压.按尹氏颈髓受压减压效果评估方法 评估,颈髓减压改善率平均88.2%.脊髓功能按日本骨科学会(JOA)评分,脊髓功能平均改善率达76.6%.结论 TARP-Ⅲ及其枢椎椎弓根钉或关节突钉固定的生物力学等性能明显优于TARP-Ⅱ的枢椎椎体钉固定,加之钢板螺钉和螺钉的万向自锁机制的设计使之更加完善,经临床应用疗效显著.

Abstract：

Objective To evaluate the biomechanical characteristics and the clinical advantage of transoral atlantoaxial reduction plate(TARP)Ⅲ.Methods Design of TARP-Ⅲ was based on TARP-Ⅱ.The screw hole in the axis was moved 1-2 mm upwards and inwards in a plate which turned a vertebral screw into a pedicle screw or an articular process screw.A polyaxial self-lock ring and polyaxial guiding drill were added to the crew hole of the plate.Finally,the withdrawal resist ence force of the three axis screws was tested and TARP-Ⅲ was used in 44 patients with complicated irreducible atlantoaxial dislocation.The axis was fixed with the pedicle screw or the articular process screw.Results The maximum withdrawal resist ence force of the anterior pedicle screw,the articular process screw and the vertebral screw in the axis was(593.1 ± 97.8)N,(469.9 ± 73.3)N and(395.2 ± 75.1)N respectively,with statistical difference between groups among three fixation methods(P ＜ 0.05).All 44 patients were followed up for 5-38 months(average 18 months),which showed complete anatomic reduction in 36 patients and appropriate anatomic reduction in eight,with basic correction of the angles between the brain stem and the spinal cord and sufficient decompression of the spinal cord.The decompression rate of the cervical spinal cord was average 88.2% according to the Yin evaluating method of cervical cord decompression.The improvement rate of spinal cord function was average 76.6% according to Japanese Orthopaedic Association(JOA)score.Conclusion With the design of polyaxial self-lock mechanism,TARP-Ⅲ with the pedicle screw or the articular process screw surpasses TARP-Ⅱ with vertebral screw in aspect of biomechanics.     

寰枢椎损伤的CT诊断(附50例分析)

目的 探讨ＣＴ对寰枢椎损伤的诊断价值。方法 回顾性分析５０例寰枢椎损伤４ ＣＴ扫描资料。结果 寰椎骨折８例,齿状突骨折２４例,枢椎椎体骨折４例,枢椎椎弓骨折１１例,单纯性寰枢关节间脱位３例。ＣＴ全部诊断正确;Ｘ线平片诊断正确３４例。结论 ＣＴ能够清楚地显示寰枢椎骨折和脱位的情况,能准确确定骨折的类型和骨折的稳定性。ＣＴ是寰枢椎损伤最好的检查方法,应该常规应用。     

经寰枢椎椎弓根钉内固定治疗儿童寰枢椎难治性脱位

目的 探讨应用后路经寰枢椎椎弓根螺钉固定融合治疗儿童难治性脱位的临床疗效.方法 2002年6月-2007年1月,对7例寰枢椎难治性脱位的患儿采用后路经寰枢椎椎弓根螺钉固定,同时辅以寰枢椎间植骨.结果 7例患儿寰枢椎脱位得到复位,无并发症发生,随访8～14个月(平均10个月),影像学显示患儿均获骨性融合.结论 经后路寰枢椎椎弓根螺钉固定融合术是一种有效的治疗儿童寰枢椎难治性脱位的方法.     

寰枢椎椎弓根螺钉棒内固定技术治疗寰枢椎失稳

目的：探讨经寰枢椎椎弓根螺钉棒内固定技术治疗寰枢椎失稳的可操作性和临床疗效。方法对20例寰枢椎不稳的患者应用寰枢椎椎弓根螺钉内固定技术治疗,术前均行X线、CT、MRI等影像学检查;术中在直视下行寰枢椎椎弓根置钉,复位固定,椎板后弓植骨;术后颈托固定3个月。结果全组病例未发生椎动脉,脊髓损伤,术后临床症状得到不同程度的改善,随访6～34个月随访,平均20．4个月,患者均在3～6个月时寰枢椎骨性融合,未发现螺钉松动、断钉和寰枢椎再移位现象。结论经寰枢椎椎弓根螺钉内固定技术是治疗寰枢椎失稳的有效方法。     

后路寰枢椎固定融合治疗陈旧性寰枢椎损伤

目的 探讨后路寰枢椎固定融合治疗陈旧性寰枢椎损伤继发寰枢椎脱位的临床疗效. 方法 回顾性分析2008年3月-2012年3月采用寰枢椎后路固定融合术治疗的陈旧性寰枢椎损伤继发寰枢椎脱位患者16例,其中男14例,女2例.受伤至手术时间3～36个月,平均10.5个月.其中采用寰枢椎后路椎弓根钉板系统治疗13例,包括陈旧性齿状突骨折10例,陈旧性创伤性寰椎横韧带断裂合并寰枢椎脱位3例.采用经寰椎后弓椎弓根钉板联合枢椎椎板螺钉固定治疗3例,均为陈旧性齿突骨折合并寰枢关节脱位.全部患者在复位固定的同时行椎板间自体骨植骨.比较术前、术后日本骨科学会(JOA)评分变化,术后随访X线片及CT,观察寰枢椎复位及融合情况. 结果 所有患者均获随访,随访时间9 ～18个月,平均13个月.全组患者无一例发生脊髓或椎动脉损伤.复查CT显示2例一侧枢椎椎弓根螺钉部分进入横突孔,但无神经或血管损伤并发症,临床症状得到不同程度改善.术后JOA评分13 ～16分,平均14.8分,术前、术后JOA评分改善率为71％ ～92％,平均82％.复查X线片、CT显示骨性融合好,未见寰枢椎失稳或复位丢失征象,固定螺钉位置良好,无松动或断钉发生. 结论 后路寰枢椎固定融合可有效重建寰枢椎稳定性,并能改善脊髓神经功能,疗效可靠.     

寰枢椎结合性骨折的临床分析

目的 总结寰枢椎结合性骨折临床特点、损伤机制和外科治疗方法。方法 对15例单纯性寰枢椎结合性骨折患者的致伤原因、并发的脊髓损伤情况、合并伤和影像学表现等进行总结，分析其损伤类型和机制。对不同的损伤类型选择不同的治疗方法，其中非手术治疗3例，手术治疗12例。对所有患者进行随访，评价并发症和预后情况。结果 寰枢椎结合性骨折占我院同期颅颈交界区损伤患者的12％(15／125)；所有的寰枢椎结合性骨折均为混合性外力机制，常见的外力形式有压缩、后伸和侧屈；5例寰枢椎结合性骨折并发有脊髓损伤，均有齿状突骨折并发寰枢椎脱位；所有患者均骨性愈合或融合，自觉症状均有改善，未发生脊髓损伤、椎动脉损伤、脑脊液漏等手术并发症。结论 寰枢椎结合性骨折常见的基本损伤机制可分为过伸 压缩机制和侧屈 压缩机制两类；寰枢椎结合性骨折并发脊髓损伤的主要机制为寰枢椎脱位继发的椎管狭窄；寰枢椎结合性骨折导致的脊柱失稳可分为寰枢关节和颈2／3关节两个节段；积极的适当的手术治疗有助于提高疗效。     

“V” shaped predens space

V shaped widening of the predens space (PDS) in flexion can be a worrisome finding in trauma patients, possibly representing injury to the transverse ligament. These patients may also show widening of the C-1/C-2 interspinous distance. We think this appearance is usually due to increased flexion mobility at the atlantoaxial level with developmental elongation or laxity of the cranial end of the transverse ligament and/or the posterior ligamentous complex. Tearing of only the cranial end of the transverse ligament must be extremely rare, if it occurs at all; there is no reported proven case. Tearing of only posterior ligaments seems possible and should be evaluated clinically.     

寰枢椎椎弓根螺钉技术治疗陈旧性齿状突骨折并寰枢椎失稳

目的 探讨后路寰枢椎椎弓根钉技术治疗陈旧性齿状突骨折并寰枢椎失稳的疗效.方法 2005年1月-2010年1月,对48例陈旧性齿状突骨折并寰枢椎失稳患者行后路寰枢椎椎弓根钉复位固定,其中男30例,女18例;年龄19～56岁,平均45.1岁.本组术前均行颅骨牵引.结果 本组48例患者共置入寰椎和枢椎椎弓根螺钉各96枚,寰枢椎复位满意,术中无脊髓损伤.术中出血250～900 ml,平均370 ml,手术时间110～280 min,平均155 min.术中3例出现椎动脉损伤,3例出现寰椎后弓下壁破裂.术后均获随访9～64个月,平均46.6个月.所有患者均在术后6个月获得骨性融合,未发现螺钉松动、移位、螺钉断裂和寰枢椎再移位、失稳现象.日本骨科学会(JOA)评分由术前的(7.1±2.8)分改善至术后的(13.3±2.1)分(P＜0.05).结论 寰枢椎椎弓根螺钉内固定技术具有良好的复位效果,为寰枢椎不稳患者治疗提供了一种较好的内固定术式.

Abstract：

Objective To explore the clinical effect of the trans-atlantoaxial pedicle screw-rod internal fixation and fusion in treatment of old odontoid fracture combined with atlantoaxial instability.Methods The study involved 48 patients with old odontoid fractures combined with atlantoaxial instability treated with trans-atlantoaxial pedicle screw-rod internal fixation and fusion from January 2005 to January 2010.There were 30 males and 18 females,at average age of 45.1 years old(19-56 years).All the patients underwent the skull traction preoperatively.Results A total of 192 pedicle screws(96 screws for the atlas and another 96 for the axis)were implanted in all the 48 patients who obtained satisfactory atlantoaxial reduction,with no spinal cord injuries.The operation lasted for average 155 min,with blood loss for average 370 ml.There were three patients with vertebral artery injury and three with inferior posterior arch fracture of the atlas during operation.All the patients were followed up for average of 46.6 months(range,9-64 months),which showed bone fusion at 6 months after operation,with no loosening,displacement,instability or breakage of the screws.The JOA score was improved from preoperative 7.1 ±2.8 to postoperative 13.3 ± 2.1(P ＜ 0.05).Conclusion Atlantoaxial pedicle screw fixation is a reliable and effective method for the treatment of the atlantoaxial instability.     

MRI of atlanto-odontoid osteoarthritis

We present the MRI appearances of advanced degenerative changes at the atlanto-odontoid (AO) joint. Changes including obliteration of the joint space, subchondral sclerosis and osteophytosis were clearly depicted on fast gradient-echo T1-weighted MRI images. Recognition of these changes may be helpful in the diagnosis in patients with suboccipital pain. Received: 11 January 1996 Accepted: 2 July 1996