Comminuted talar neck fractures: a mechanical comparison of fixation techniques

OBJECTIVE: To compare the mechanical performance of 3 fixation techniques for comminuted talar neck fractures. DESIGN: In vitro biomechanical study. SETTING: Bioengineering research laboratory. PARTICIPANTS: Thirty previously frozen human cadaveric tali were osteotomized across the talar neck. A wedge of bone 2 cm long and extending 50% of the medial to lateral and superior to inferior dimension of the talus was removed to create an unstable, comminuted fracture. INTERVENTION: The specimens were randomized to one of 3 fixation groups. The first group was fixed with 3 anterior-to-posterior screws. The second group was fixed with 2 cannulated screws inserted from posterior to anterior. The third group was fixed with 1 screw from anterior to posterior and a medially applied blade plate. Specimens were embedded in acrylic cement and mounted on an Instron mechanical testing machine. Loading was applied in the dorsal-medial direction to failure. MAIN OUTCOME MEASURES: For each specimen, the load-displacement curve, yield point, and 3 mm displacement point were recorded in response to controlled dorsal-medial loading to failure. Stiffness was calculated as the linear portion of the slope of the load (kN) versus displacement (mm) curve. Statistical analysis of the data was conducted using analysis of variance. RESULTS: The mean yield point of each of the fixation techniques tested exceeded 1.4 kN. No statistically significant difference was found between the fixation methods, even when variations in age and sex were considered. CONCLUSIONS: The mean yield point of the fixation techniques tested exceeds the theoretical stress across the talar neck during active motion. Anterior plate fixation provided equivalent stability to posterior screw fixation.     

Safe zone for the placement of medial malleolar screws

BACKGROUND: Hardware placement for fracture fixation can put soft-tissue structures at risk for injury or abutment. The prominence of the hardware is a frequent cause of pain after the fixation of ankle fractures. This study was designed to assess the risk of injury or abutment of the posterior tibial tendon with the placement of medial malleolar screws. METHODS: Ten unmatched cadaveric limbs that had been disarticulated at the knee were used, and the medial malleolus was exposed by dissection of the skin. With use of fluoroscopy and direct visualization of the deep fascia, three Kirschner wires were placed through the tip of the medial malleolus and directed parallel to the medial articular surface. The first wire was placed in the center of the anterior colliculus. Two additional wires were placed parallel and posterior to the initial wire at 5-mm intervals. The wires were overdrilled, and 4.0-mm screws were inserted over the Kirschner wires. The specimens were dissected to inspect for trauma and the proximity of the screws to the posterior tibial tendon. The medial malleolus was divided into three zones on the basis of anatomic landmarks. Zone 1 is the anterior colliculus; Zone 2, the intercollicular groove; and Zone 3, the posterior colliculus. RESULTS: Screws placed in Zone 1 (the anterior colliculus) did not contact the posterior tibial tendon in any specimens. Screws placed in Zone 2 (the intercollicular groove) were, on the average, 2 mm from the posterior tibial tendon. Screws placed in Zone 3 (the posterior colliculus) resulted in tendon abutment in all ten specimens and in tendon injury in five of the ten specimens. CONCLUSIONS: Screws inserted posterior to the anterior colliculus place the posterior tibial tendon at significant risk for injury or abutment.     

Internal fixation of femoral neck fractures with posterior comminution: a biomechanical study

OBJECTIVES: This study was performed to determine whether four cancellous lag screws provide significantly improved rigidity and fixation strength compared with three screws for fixation of displaced femoral neck fractures with posterior comminution. DESIGN: Biomechanical cadaver study. INTERVENTION: Eight pairs of mildly osteopenic femurs were selected, and each pair was fixed with three or four cancellous lag screws (randomly assigned) after the creation of a simulated femoral neck fracture with posterior comminution. A separate comparison with an unmatched group of six similar femurs with a simulated femoral neck fracture without posterior comminution and instrumented with three screws was performed to investigate the effect of posterior comminution. MAIN OUTCOME MEASUREMENT: The specimens were non-destructively tested to determine fixation rigidity in axial and anterior loading. Cyclic axial loading was then performed for 10,000 cycles; the femurs were retested for rigidity and finally were axially loaded until failure. RESULTS: The femurs with a posterior defect stabilized with three screws had significantly less resistance to axial and anterior displacement and sustained significantly lower axial loads to failure than those stabilized with four screws. The specimens instrumented with three screws without a posterior defect exhibited greater resistance to displacement in anterior loading and sustained greater axial loads to failure than those with a posterior defect stabilized with three screws. CONCLUSION: This study suggests that there are benefits to using four screws for fixation of femoral neck fractures with posterior comminution.     

Comparison of internal fixation techniques in metacarpal fractures

A biomechanical study assessed quantitative differences in the stability that was obtained by five commonly used types of internal fixation employed in metacarpal fractures. The techniques included dorsal plating, dorsal plating combined with an interfragmentary lag screw, crossed Kirschner wires, a single intraosseous wire combined with a single oblique Kirschner wire, and a single intraosseous wire alone. Rigidity and strength in torsion and bending were determined after transverse osteotomy and fixation of the metacarpal were performed. The failure modes for each fixation technique were also observed and described. Significant differences in rigidity were found between the plated configurations (with or without an interfragmentary lag screw) and the wired configurations in both apex dorsal bending and axial torsion. The three wired configurations were not significantly different from each other except in torsion. Analysis of the bending moments that were required to produce both yield and failure in apex dorsal bending and also the energy absorbed to yield showed similar disparity between plated and wired techniques. For metacarpal fixation, dorsal plating with or without lag screws provides significantly more stability than do wired techniques and approaches that provided by intact bones.     

Die Arthrodese des oberen Sprunggelenks über den sog. transfibularen Zugang

OBJECTIVE: Bony fusion between tibia and talus in neutral position of foot. Return to a pain-free function of the lower limb. INDICATIONS: Extensive loss of articular cartilage accompanied by a painful and considerably limited motion with or without malalignment. Partial avascular necrosis of talar dome or distal tibial epiphysis. Neuroarthropathy (Charcot joint) with progressive malalignment of ankle. Revision surgery after failed total ankle arthroplasty. CONTRAINDICATIONS: Acute purulent joint infection. Total avascular necrosis of talus. SURGICAL TECHNIQUE: Posterolateral approach to the distal fibula taking care to preserve the periosteal vessels. Fibular osteotomy from proximal lateral to distal medial. Division of the anterior tibiofibular, anterior fibulotibial, and fibulocalcaneal ligaments. Division of posterior tibiofibular ligament. Transverse planar resection of tibial and talar articular surfaces. Freshening of the medial malleolus. Resection of the tip of medial malleolus through a medial incision. Positioning of talus perpendicular to the tibia, paying attention to the valgus of the hindfoot and external rotation. Temporary fixation with Kirschner wires. Radiographic control in two planes followed by fixation with two or three lag screws. Removal of the medial fibular cortex, freshening of the lateral gutter, and fixation of the distal fibular fragments to tibia and talus with cortical screws. RESULTS: 20 arthrodeses in 19 patients were followed up for an average of 39 months (12-69 months). All arthrodeses were fused. In one patient a fibular pseudarthrosis was encountered. All arthrodeses healed in a correct position but one that consolidated with a pes equinus of 3 degrees . The average AOFAS (American Orthopedic Foot and Ankle Society) hindfoot score reached 78.5 points (40-86 points). A marked reduction of symptoms and satisfactory function were reported postoperatively by all patients. All would be willing to undergo surgery again.     

Talus fractures: a current concepts review of diagnoses, treatments, and outcomes

The talus is the key articular segment linking the leg and foot, and as such, is subject to complex loads and may occasionally fracture. Fracture patterns provide clues to the underlying pathomechanics and energy of the injury, both of which can help guide treatment and suggest prognosis. Talus fractures have a wide variety of presentation from low-energy avulsion fractures of the lateral or posterior processes, to high-energy comminuted talar body fractures. Appropriate, expedient treatment provides the patient the best chance of obtaining a good functional outcome. Treatment relies on appropriate diagnosis, which hinges on clinical suspicion provided by the patient's account of pathomechanics, clinical examination, and radiological workup. This current concepts review discusses the pathomechanics, presentation, workup, treatment, and prognosis of fractures of the talar head, neck, body, lateral process, posterior process, and talar extrusions. Key words: talus, fracture, talar neck, talar head, talar body, lateral process, posterior process, talar extrusion, orthopaedic surgery, review.     

Mechanical Testing of Seven Fixation Methods for Generation of Compression Across a Midtarsal Osteotomy: A Comparison of Internal and External Fixation Devices

The purpose of this study was to assess 7 methods of fixation for a midtarsal osteotomy. Polyurethane foam models (N = 6) and cadaver specimens (N = 4-7) were used to examine the force generated by the different constructs of fixation. A midtarsal osteotomy was performed on each specimen in the test groups. The osteotomies were fixated either with 2 parallel 0.062-in Kirschner wires and 40-mm-long, 4-mm partially threaded, cancellous, cannulated titanium screws, an external ring fixator (frame), a frame with wires tensioned (tension), a frame with wires tensioned and compressed toward the osteotomy (tension and compression), a frame with tension, compression, and parallel Kirschner wires, or a frame with tension, compression, and two 4.0 cannulated parallel screws, respectively. Each model was fixated, and the force generated by the construct across the osteotomy was recorded via the use of pressure-sensitive film. Statistical analysis of the data in the polyurethane foam group determined that the use of frame with tension, compression, and two 4.0 parallel cannulated screws was statistically superior to 1) frame, 2) frame with tension, 3) 2 parallel Kirschner wires, 4) two 4.0 cannulated parallel screws, and 5) frame with tension and compression. A cadaver study determined that the frame with tension, compression, and 2 parallel Kirschner wires was statistically superior to 1) frame and 2) two parallel Kirschner wires. These findings suggest that there is a difference in the force generated by the type of fixation construct across a midtarsal osteotomy.     

Stabilization of Lisfranc joint injuries: a biomechanical study

BACKGROUND: Lisfranc joint injuries are often misdiagnosed, leading to significant morbidity. Methods for anatomic reduction of the tarsometatarsal joint include closed reduction with casting or surgical stabilization with either Kirschner wires and/or cortical screw fixation. Controversy exists as to which fixation technique offers optimal stability. In the present study, the biomechanical stability of three fixation methods was tested: (1) four Kirschner wires, (2) three cortical screws plus two Kirschner wires, and (3) five cortical screws. METHODS: Ten matched pairs of fresh-frozen cadaveric feet were dissected to their ligamentous and capsular elements. The tarsometatarsal ligaments were completely transected to replicate a Lisfranc dislocation; the "injury" was reduced and stabilized using one of the three methods. Biomechanical studies were performed by applying a 100-N cyclic load physiologically distributed to the plantar aspect of the metatarsal heads. Displacement and force measurements were taken from the first and fifth metatarsal heads. Average stiffness of each construct was calculated from the force displacement curves. RESULTS AND CONCLUSIONS: Method 2 provided significantly more stability than Kirschner wire fixation. Method 3 created more stiffness than method 2 at the medial portion of the foot; no statistical difference between the two methods was evident at the lateral foot. CLINICAL RELEVANCE: Cortical screw fixation provides a more rigid and stable method of fixation for Lisfranc injuries as compared to Kirschner wire fixation. This fixation method allows maintenance of anatomic reduction and possibly earlier mobilization with a decreased risk of posttraumatic arthrosis.     

Biomechanical comparison for different configurations of tension band wiring techniques in treating an olecranon fracture

BACKGROUND: The aim of this study was to compare the superiority between the newly designed modified AO tension band wiring technique and the traditional modified AO tension band wiring technique in treating an olecranon fracture. METHODS: Eight pairs of fresh cadaveric ulnae were tested biomechanically. After transverse osteotomy of the olecranon, all left ulnae were fixed by the traditional modified AO technique with two Kirschner wires inserted through the anterior ulnar cortex and all right ulnae by the new technique with two Kirschner wires inserted into the marrow cavity from the olecranon to the ulnar styloid process. All specimens were tested by the Material Testing System machine to evaluate fragment displacement and the maximal failure load. A dual linear variable displacement transducer was used to measure relative minimal displacement. RESULTS: There was no significant difference between the techniques. The maximal failure load by either technique was more than 80 kg. Even at testing failure, no Kirschner wires migrated proximally. CONCLUSION: The new technique may be applied widely to treat all olecranon fractures, because it is a technically easier and safer technique. Less than 5.5-kg loads could be permitted in daily activity postoperatively. A single tolerable loading weight should not exceed 8 kg. Kirschner wires will not migrate proximally, despite increased joint loading. Clinically, this study may confirm indirectly the hypothesis that proximal migration of Kirschner wires was mainly due to triceps traction.     

Contact characteristics of the subtalar joint: the effect of talar neck misalignment.

In this study we determined the effects of misalignment of the talar neck on the contact characteristics of the subtalar joint. Each of seven fresh cadaver lower extremities was mounted in a loading jig and a vertical load was applied, 90% of which was directed through the tibia and 10% through the fibula. The foot was allowed to displace freely in the horizontal plane so that relative rotations, known to occur in the subtalar joint, would not be prevented. Pressure-sensitive film, inserted into the posterior and anterior/middle articulations, was used to quantify changes in contact characteristics. After testing in the normal condition, the talar neck was osteotomized and stabilized with internal and external skeletal fixation. Contact characteristics were then determined in each of the following stages: anatomic realignment, or with 2-mm displacement of the talar neck either dorsally, medially, laterally, or complex (dorsal and varus) with respect to the body of the talus. Measurements showed no significant changes in overall contact area or high pressure area in the posterior facet, although four of the seven specimens demonstrated increased localization of the contact area into two discrete regions. The combined anterior/middle facet, on the other hand, was significantly unloaded by all but medial displacement of the talar neck. An extraarticular load path and/or increased loading directly on the talonavicular joint was presumed to account for the loss of load transfer in the talocalcaneal joint.     

早期切开复位无头加压空心螺钉及克氏针治疗经舟骨月骨周围脱位

目的探讨早期切开复位无头加压空心螺钉及克氏针内固定治疗经舟骨月骨周围脱位的临床疗效。方法17例经舟骨月骨周围脱位患者,均行早期切开复位,克氏针固定月骨和头状骨,无头加压空心螺钉对舟骨骨折端进行加压固定,同时修复关节囊和韧带。结果17例均获随访,平均10（3-12）个月,腕关节活动范围在106°-128°之间。X线片示舟骨完全愈合,腕关节轴线恢复好。根据Cooney评定标准,本组优11例,良4例,中2例,优良率88．2％。结论无头加压空心螺钉及克氏针内固定能达到舟骨解剖复位,恢复腕关节轴线,术后腕关节功能恢复较好,是治疗经舟骨月骨脱位的有效方法。     

Computer-assisted surgery in posterior instrumentation of the cervical spine: an in-vitro feasibility study

Transarticular C1/2 screws are widely used in posterior cervical spine instrumentation. The use of pedicle screws in the cervical spine remains uncommon. Due to superior biomechanical stability compared to lateral mass screws, pedicle screws can be used, especially for patients with poor bone quality or defects in the anterior column. Nevertheless there are potential risks of iatrogenic damage to the spinal cord, nerve roots or the vertebral artery associated with both posterior cervical spine instrumentation techniques. Therefore, the aim of this study was to evaluate whether C1/2 transarticular screws as well as transpedicular screws in C3 and C4 can be applied safely and with high accuracy using a computer-assisted surgery (CAS) system. We used 13 human cadaver C0-C5 spine segments. We installed 1.4-mm Kirschner wires transarticular in C1/2, using a specially designed guide, and drilled 2.5-mm pedicle holes in C3 and C4 with the assistance of the CAS system. Hole positions were evaluated by palpation, CT and dissection. Forty-eight (92%) of the 52 drilled pedicles were correctly positioned after palpation, imaging and dissection. The vertebral artery was not injured in any specimen. All of the 26 C1/2 Kirschner wires were placed properly after imaging and dissection evaluations. No injury to vascular or bony structures was observed. C1/2 transarticular screws as well as transpedicular screws in the cervical spine can be applied safely and with high accuracy using a CAS system in vitro. Therefore, this technique may be used in a clinical setting, as it offers improved accuracy and reduced radiation dose for the patient and the medical staff. Nevertheless, users should take note of known sources of possible faults causing inaccuracies in order to prevent iatrogenic damage. Small pedicles, with a diameter of less than 4.0 mm, may not be suitable for pedicle screws.     

基于数字化技术建立距骨颈骨折螺钉固定安全通道的研究

 目的 探讨距骨颈骨折螺钉自距骨内侧壁安全固定时螺钉安全通道的建立。方法 限定志愿者年龄20~60岁,男性身高165~185 cm,女性身高155~175 cm,体质指数(BMI)< 25,既往踝、足部无骨折病史,非重体力劳动及长期站立工作者,X线片证实无关节退行性改变等。共获得男性33名,年龄21~59岁,平均43.7岁,身高168~184 cm,平均176.0 cm;女性22名,年龄22~60岁,平均43.2岁,身高158~172 cm,平均165.4 cm。对所有志愿者的踝部及足部进行CT扫描,将重建层厚为0.75 mm的图像数据以DICOM格式存入光盘,使用SuperImage^TM Orthopedics Edition1.1软件对图像进行显示和三维重建。测量距骨颈和跗骨管的高度,建立螺钉进入跗骨管的模型;模拟螺钉自距骨内侧壁远端中1/3和下1/3两点置入,并沿两条不同的方向走行,测量螺钉的最大长度及角度;最后使用SPSS 13.0软件对以上数据进行比较分析。 结果 获得距骨颈和跗骨管的高度值,同性别左右侧的差异无统计学意义;男性距骨颈和跗骨管高度均大于女性;获得螺钉自距骨颈穿出进入跗骨管的模型;获得以距骨内侧壁远端中1/3和下1/3为入点、自不同方向置入时螺钉的长度值和角度值;以距骨内侧壁远端中1/3为入点时螺钉固定的夹角较以距骨内侧壁远端下1/3为入点时明显更大;;计算出螺钉不同固定方向的长度、角度的安全范围。 结论 螺钉固定时应避免对距骨血运造成进一步破坏;距骨内侧壁中1/3是螺钉固定的良好入点;计算机数字化技术与距骨颈骨折内固定方式相结合可以提高手术安全性和可行性。     

Computer-assisted surgery in posterior instrumentation of the cervical spine: an in-vitro feasibility study

Transarticular C1/2 screws are widely used in posterior cervical spine instrumentation. The use of pedicle screws in the cervical spine remains uncommon. Due to superior biomechanical stability compared to lateral mass screws, pedicle screws can be used, especially for patients with poor bone quality or defects in the anterior column. Nevertheless there are potential risks of iatrogenic damage to the spinal cord, nerve roots or the vertebral artery associated with both posterior cervical spine instrumentation techniques. Therefore, the aim of this study was to evaluate whether C1/2 transarticular screws as well as transpedicular screws in C3 and C4 can be applied safely and with high accuracy using a computer-assisted surgery (CAS) system. We used 13 human cadaver C0-C5 spine segments. We installed 1.4-mm Kirschner wires transarticular in C1/2, using a specially designed guide, and drilled 2.5-mm pedicle holes in C3 and C4 with the assistance of the CAS system. Hole positions were evaluated by palpation, CT and dissection. Forty-eight (92%) of the 52 drilled pedicles were correctly positioned after palpation, imaging and dissection. The vertebral artery was not injured in any specimen. All of the 26 C1/2 Kirschner wires were placed properly after imaging and dissection evaluations. No injury to vascular or bony structures was observed. C1/2 transarticular screws as well as transpedicular screws in the cervical spine can be applied safely and with high accuracy using a CAS system in vitro. Therefore, this technique may be used in a clinical setting, as it offers improved accuracy and reduced radiation dose for the patient and the medical staff. Nevertheless, users should take note of known sources of possible faults causing inaccuracies in order to prevent iatrogenic damage. Small pedicles, with a diameter of less than 4.0 mm, may not be suitable for pedicle screws.     

Utility of new bioabsorptive screws in cervical anterior fusion

BACKGROUND: The aim of this study is to report our use of new bioabsorbable screws in cervical anterior fusion. These screws need not be removed because they are completely absorbed by resolution in vivo. We describe our method and the new bioabsorbable screws. METHODS: We used PLLA screws until September 2004 and uncalcined uHA-PLLA screws thereafter. They are completely absorbed by resolution to water and carbon dioxide upon in vivo hydrolysis. The uHA-PLLA screws are x-ray impenetrable, and their uHA content renders them osteoconductive. In cervical anterior fusion, the graft is inserted in the area of deletion resulting from decompression. The screws are inserted in the 4 corners of the vertebral body and graft. In long fusion, they are introduced in the 2 lateral wings of the bone graft on each vertebral body and in the 4 corners. Our method eliminates the need for plates or mesh. RESULTS: We have used this method in 62 patients and encountered no complications. There were no screw or graft extrusions and no surgery-related infections. The patients were able to walk a few hours after the operation and wore a simple neck collar for a few days. CONCLUSIONS: This safe and easy method shortens the hospital stay and reduces the risk of graft extrusion and complications associated with the use of nonabsorbable devices.     

Comparative strength of three methods of fixation of transverse acetabular fractures.

With the advent of percutaneously placed lag screws for fixation of acetabular fractures, this study evaluated the strength of lag screw fixation compared with traditional fixation techniques of transverse acetabular fractures. Ten formalin-treated human, cadaveric pelvic specimens with bilateral, transtectal transverse acetabular fractures were used for this study. The right acetabular fractures were fixed with a five-hole plate and four screws with the central hole spanning the posterior fracture site. The left acetabular fractures were fixed with two lag screws, one each in the anterior and posterior columns, or with a screw and wire construct stabilizing both columns. The specimens were loaded to implant failure. Stiffness, yield strength, maximum load at failure, and site of failure was recorded. The plate and screw construct showed significantly greater yield and maximum strength when compared with the two lag screws. The stiffness of the lag screw method was 39% higher than that of the plating method, but this result was not statistically significant. In addition, the plate and screw method provided significantly greater maximum strength than the screw and wire technique. The quadrilateral plate seemed to be the weakest area of fixation because 83% of the implant failures occurred in this region. In patients in whom the risks of formal open reduction and internal fixation of acetabular fractures outweigh the possible benefits, such as in patients with burns or degloved skin, the advent of computer-assisted and fluoroscopically guided percutaneous surgical techniques have been instrumental. This study showed there is greater strength of fixation with a plate and screw construct, possibly secondary to supplementary fixation distal to the quadrilateral plate. However, lag screw fixation provided relatively greater stiffness, which may account for its clinical success. Percutaneous lag screw fixation of appropriate transverse acetabular fractures is a viable option.     

The risk of injury to the axillary nerve, artery, and vein from proximal locking screws of humeral intramedullary nails.

An elderly female cadaver fore-quarter amputation was dissected, and a custom straight intramedullary nail with a 55 degrees oblique downward lateral to medial proximal screw was inserted with a trocar protruding beyond the medial cortex of the humeral surgical neck. The main trunk of the axillary nerve was found to be at risk with any penetration from anterior to posterior and any screw penetration beyond the medial cortex with internal rotation. The axillary artery and vein were at risk with penetration of over 3 cm by a drill point or screw tip whether a transverse or oblique downward screw was used. Transverse screws inserted through the humeral neck from lateral to medial have the potential for damaging a small branch of the axillary nerve laterally, and care must be taken of the lateral humerus while inserting these screws. Screws inserted in a downward direction near the greater tuberosity, if originating above the equator of the humeral head, may cause impingement.     

Posterior plating of the cervical spine. A biomechanical comparison of different posterior fusion techniques

Posterior arthrodesis is a preferred treatment for posttraumatic instability of the cervical spine. While most surgical constructs yield predictably high rates of fusion in satisfactory alignment, certain injury patterns involving fractures of the lamina or spinous processes may preclude rigid immobilization by simple wiring techniques. Plate fixation of the posterolateral masses has been advocated for such injuries. The purpose of this biomechanical study was to test the relative stiffness provided by different posterior fusion constructs, including lateral mass plating. All testing was performed on fresh, unembalmed cadaveric spines divided into two vertebral segment units. Muscular tissue was stripped from the specimens, but all discal and ligamentous structures were preserved. Four different posterior fixation constructs were tested. These included 1) Rogers interspinous wiring, 2) Halifax laminar clamps, 3) bilateral 1/3 tubular plates on the lateral masses, using unicortical screws, and 4) bilateral 1/3 tubular plates on the lateral masses, using bicortical screws. Stiffness measurements were taken in both flexion and extension on all specimens. Yield strength and fatigue strength of the spines were not measured. It was found that 1/3 tubular plates secured with bicortical screws to the lateral masses provided the highest mean stiffness. Less stiffness was found in spines stabilized by Halifax clamps, interspinous wiring, and plates secured with unicortical screws. There was, however, no statistically significant difference in stiffness provided by any of these four implants. It was concluded that there is no advantage in plate fixation over standard fusion constructs in augmenting the stiffness of posterior fixation of the cervical spine.     

The stability of internal fixation in the proximal phalanx

A biomechanical study was performed to assess quantitative differences in the stability obtained with five commonly used types of internal fixation used in proximal phalangeal fractures. The techniques included dorsal plating, dorsal plating combined with an interfragmentary lag screw, two interfragmentary lag screws, tension-band technique, and crossed Kirschner wires. Rigidity and strength in apex palmar bending were determined after oblique osteotomy and fixation of the proximal phalanx. The failure modes for each fixation technique were also observed and described. The results showed that both of the techniques that used interfragmentary lag screws across the oblique osteotomies provided significantly more rigidity than did dorsal plating alone or the wired configurations but that measurements of strength were similar between all techniques tested. Dorsal plates were at a mechanical disadvantage on the compression surface in our apex palmar bend test and consequently provided no more rigidity and strength than did the wired techniques. The tension band technique represented a combination of stiff and flexible intraosseous wires without strict application of tension band principles and provided intermediate rigidity and strength. Rigidity and strength in intact proximal phalanges in the controls were significantly greater than in all techniques tested.     

Radiological evaluation of unstable (acute) slipped capital femoral epiphysis treated by pinning with Kirschner wires

Treatment of slipped capital femoral epiphysis is still controversial with regard to the implants used for stabilization and the need for prophylactic treatment of the contralateral, unaffected, side. The objective of this study was to ascertain whether prophylactic transfixation of the epiphysis with Kirschner wires in patients with unstable slipped capital femoral epiphysis resulted in significant disturbance of the growth plate and impairment of further growth of the femoral neck and head. Between 1990 and 1999, 29 patients with unstable slipped capital femoral epiphysis were simultaneously treated with internal fixation of the epiphysis and metaphysis with 3-4 Kirschner wires on the affected and the not (yet) affected side. After a mean follow-up of 3.5 years, we evaluated the hip joints radiologically, analysing different roentgenological parameters (CCD angle, femoral head diameter, length of the femoral neck and sphericity of the femoral head). CCD angle, femoral head diameter and length of the femoral neck showed statistically significant (P<0.001, Student's t-test) differences between the affected and unaffected, but prophylactically pinned, sides. Asphericity of the femoral head was found in six cases only on the affected side, whereas all hips, which were operated prophylactically, showed spherical femoral heads at follow-up (P<0.02, Pearson's chi test). These results indicate that the slip itself may cause impairment of the femoral growth plate in patients with unstable slipped capital femoral epiphysis and not stabilization with Kirschner wires. Compared with other series from the literature using different implants (screws, nails), prophylactic transfixation of the epiphysis and metaphysis with Kirschner wires is less compromising to the growth plate on the not (yet) affected side.