Comparison of metacarpal plating methods

PURPOSE: Most metacarpal fractures are stable and can be treated with nonsurgical stabilization. However, some metacarpal fractures are treated with open reduction and internal fixation because of an open fracture, instability, or multiple fractures. Newer plate designs have emerged that allow a shorter plate and screw construct. We sought to determine the relative strength of 3 different methods of metacarpal plating for unstable fractures. METHODS: We tested our hypothesis in a transverse metacarpal fracture model using fourth-generation, biomechanical testing grade composite sawbones (Sawbones; Pacific Research Laboratories, Vashon, WA). The metacarpals were divided into 3 groups of 15 bones. Group 1 was plated with a standard 6-hole, 2.3-mm plate with 6 nonlocking bicortical screws in standard AO fashion. Group 2 was plated with a 6-hole, double-row, 3-dimensional (3D) plate with 3 nonlocking screws on either side of the fracture aiming for convergence of the screws. Group 3 was plated with a 2.4-mm plate using 6 nonlocking screws and standard AO technique. The metacarpals were then tested to failure in cantilever bending mode. RESULTS: All constructs broke through the bone. No plate failure or screw pullout was seen. Group 1 had a load to failure of 264 N +/- 14. Group 2 had a load to failure of 302 N +/- 17. Group 3 had a load to failure of 274 N +/- 20. The load to failure was highest in group 2 (3D plate). All differences were statistically significant. CONCLUSIONS: All 3 methods produced a strong construct. The load to failure was highest in group 2 (3D plate). Double-row plates with converging screws provide adequate or superior strength of fixation when compared with standard plate constructs.     

Shoulder arthrodesis with plate fixation. Special features in cases of resection and defects

AIM: Shoulder arthrodesis following prosthesis explantation or resection of the acromion has not often been described in the literature. The presented article analyses the special features and problems of these preoperative circumstances in 4 cases and discusses them within the entire group. PATIENTS AND METHOD: Between 06/1987 and 02/2001, a total of 30 shoulder arthrodeses using plate fixation were performed in our clinic and then analysed after an average of 2.7 (0.5 - 8.7) years. Surgery was carried out on 5 (17 %) females and 25 (83 %) males with a mean age of 37 (17 - 82) years. Two patients underwent shoulder arthrodesis as a salvage operation following unsatisfactory arthroplasty, or after trapezius transfer with corresponding reduced bony conditions, respectively. RESULTS: The active extent of movement following arthrodesis was 56 degrees (20 degrees - 90 degrees ) abduction, and 60 degrees (20 degrees - 105 degrees ) anteversion. The most frequent complications following arthrodesis included pseudarthroses (3/10 %), infections (4/13 %), and fractures of the humerus (4/13 %). The rate of complications was especially high in the cases after explantation of a shoulder prosthesis and resection of the acromion. In two of the four patients, three or five revision operations, respectively, were necessary. Two of the three pseudarthroses of the entire group occurred in these two cases. CONCLUSION: Complications of shoulder arthrodesis after resection of the acromion or the proximal humerus are especially frequent. To avoid pseudarthrosis in such cases, primary spongioplasty is advantageous. A fixation with plates is superior to a simple screw arthrodesis. For postoperative immobilization a plaster cast instead of an orthotic device should be taken into consideration.     

Schraubenarthrodese der Schulter

Objective

The aim of the procedure is arthrodesis of the shoulder by osteosynthesis of the glenohumeral and the acromiohumeral joint each with three screws, which results in preservation of scapulothoracic motion and pain relief.

Indications

Traumatic brachial plexus lesions, palsy in infancy, poliomyelitis with preserved or restorable function of the elbow and the hand. Paralysis of the deltoid muscle and the rotator cuff. Nonrestorable vast defect of the rotator cuff with pseudoparalysis. Chronic infectious arthritis resistant to therapy. Unsuccessful attempts to treat glenohumeral instability. Alternative procedure to shoulder arthroplasty in young patients with omarthrosis, who perform hard physical work.

Contraindications

Insufficient strength of the scapular muscles (< grade?4, <75% of normal strength). Insufficient scapulothoracic passive motion. Inadequate soft tissue coverage after burns, excessive previous surgery or radiotherapy. Incomplete rehabilitation (<3?years) after neurosurgical interventions (neurolysis, nerve transplantation). Cases of resection of the proximal humerus.

Surgical technique

Acampsia of the shoulder joint in 20° of abduction, 30° of anteversion, and 40° of internal rotation using three glenohumeral and three acromiohumeral spongiosa screws as a compression arthrodesis.

Postoperative management

Thorax?Carm?Cabduction splint (20° of abduction, 30° of anteversion, and 40° of internal rotation) until the week?6 postoperatively with removal for physiotherapy and personal hygiene. Assisted active and passive motion exercises for the elbow, hand, and fingers after the postoperative day?1. Weaning from the splint after the end of the week?6 postoperatively, full range of motion allowed.

Results

In a prospective study from January 2007 to September 2008, 4?patients with a medium age of 35.7?years underwent screw arthrodesis of the shoulder with a follow-up of 1.0 (0.6?C1.5)?year. Primary fusion of all arthrodesis surfaces was achieved in all patients; no revision surgery was necessary. All patients improved in shoulder function with an average range of motion of 60° abduction and 40° anteversion.     

The effect of bone quality on the stability of ankle arthrodesis. A finite element study

BACKGROUND: Despite uniform operating techniques, lack of fusion still occurs after ankle arthrodesis. Differences in the biological healing potential may be a factor but the mechanical performance of the arthrodesis construct because of varying bone quality also may be important. Internal compression techniques are preferred because of higher union rates, shorter fusion times, and fewer complications. A three-screw configuration has been shown to be more stable than a two-screw configuration, but it is not obvious when it should be used. METHODS: Three-dimensional finite element models of intact and flat-cut ankle arthrodeses were built, using two and three screws in different configurations. Poor bone quality was simulated by decreasing Young's modulus of the bone. The constructs were loaded in torsion and dorsiflexion, and micromotions at the fusion site were measured. RESULTS: Bone quality had a marked effect on the stability at the arthrodesis site. Inserting two screws at 30 degrees relative to the longitudinal axis of the tibia in an intact arthrodesis seemed the best option, especially as bone quality worsened. The addition of a third screw increased the stability at the arthrodesis site. CONCLUSIONS: Overall, intact joint surfaces and three-screw fixation, with the lateral and medial screws inserted produced the most stable arthrodesis constructs when bone quality was poor. CLINICAL RELEVANCE. Ankle arthrodeses are technically demanding because of the shape and small size of the talus. Preoperative planning is an absolute necessity to determine placement and number of screws. This study shows that poor bone quality decreases the stability of the arthrodesis constructs, suggesting that an attempt should be made to create the most stable three-screw configuration. Finite element models can be used as an effective preoperative tool for planning screw number and placement.     

Cost Comparison of Crossed Screws versus Dorsal Plate Construct for First Metatarsophalangeal Joint Arthrodesis

Expensive surgical implants can significantly add to the cost of a procedure. We performed a crude cost analysis to evaluate and compare the crossed screw technique versus dorsal plating for first metatarsophalangeal arthrodesis. First metatarsophalangeal arthrodeses performed over a 20-month period were selected. Exclusion criteria included diabetes, neuroarthropathy, revision surgery, or alternate fixation. Hospital records were reviewed for each case to determine implant charges. Patient charts and radiographs were also reviewed to determine time to fusion, delayed union/nonunion, revision surgery, or hardware removal. Fifty-five first metatarsophalangeal arthrodeses were performed during the study period. Ten fusions were excluded, leaving 45 fusions for review. The overall fusion rate was 91.1%. The average time to fusion in crossed screw versus plating technique was 73.2 +/- 32.5 days (range, 43 to 162) and 69.3 +/- 37.3 days (range, 44 to 238), respectively, and not statistically significant. The mean implant cost in the crossed screw versus dorsal plating technique was $374.05 +/- 76.3 (range, 278.72 to 530.00) and $603.57 +/- 234.7 (range, 543.40 to 1677.00) respectively and was strongly significant (P = .0002). Complications included 2 delayed unions (1 screw, 1 plate), 4 nonunions (1 screw, 3 plate), 2 revisions (1 screw, 1 plate), and 2 hardware removals (1 screw, 1 plate). SUMMARY: A cost comparison of crossed screws versus dorsal plate construct for first metatarsophalangeal arthrodesis is performed. No statistical difference was found in the time to fusion between the 2 constructs but there was strong statistical difference in hardware cost. This information may aid in the cost management of this procedure without compromising clinical results. ACFAS Level of Clinical Evidence: 2c.     

经口咽前路寰枢椎蝶形钢板系统的设计及生物力学评估

目的　设计经口咽前路寰枢椎蝶形钢板内固定系统 ,评价其生物力学性能。方法　设计研制各种型号经口咽前路寰枢椎蝶形钢板、自锁螺钉和复位器等配套器械。选 12具新鲜成年颈椎标本 ,分别进行三维运动范围实验和螺钉拔出力实验。与其他内固定方法作比较分析。结果三维运动范围 ,TARP、Brooks、Magerl、前路经枢椎体寰椎侧块螺钉和Magerl Brooks组的屈伸方向的运动范围分别为平均 4.0、6.2、5 .1、6.6和 3 .7度 ;在侧屈方向的活动范围分别为平均 2 .3、3 .6、2 .7、4.2和 1.8度 ;在旋转活动范围分别为平均 7.4、8.9、8.6、10 .7和 6.0度。结果显示该蝶形钢板固定和Magerl Brooks固定在各个方向上差异均无显著性 (P >0 .0 5 )。其抗屈伸、侧屈和旋转均强于其他 3种内固定方法。寰椎、枢椎和第 3颈椎组的螺钉固定的最大拔出力分别为平均491.5 8、3 96.73和 3 85 .5 3N。结果显示寰椎螺钉的最大拔出力显著高于枢椎和C3 椎体固定螺钉 ,枢椎螺钉与C2 螺钉等效。结论　经口咽前路蝶形钢板系统设计新颖、独特 ,具有良好的生物力学性能。为临床应用提供了生物力学依据。     

Shoulder arthrodesis: indications, technique, results, and complications

Complications after shoulder arthrodesis are frequent. Through results and comparisons with the literature, the presented article analyzes the correlation of complications with the specific operative techniques, indications, and postoperative treatment. Between 1964 and 2001, a total of 43 cases of shoulder arthrodesis (13 screw and 30 plate arthrodeses) were performed and then analyzed after a mean of 6.7 years (range, 0.5-36 years). Surgery was carried out on 10 female patients (23%) and 33 male patients (77%) with a mean age of 35 years (range, 11-82 years). These patients had the following indications: paralysis (32 [74%]), osteoarthritis or humeral head necrosis (15 [35%]), infection (7 [16%]), and persistent shoulder instability (6 [14%]). The extent of active movement after arthrodesis was 56 degrees abduction (range, 20 degrees - 90 degrees) and 60 degrees forward flexion (range, 20 degrees - 105 degrees), with an increase in the Constant score in all cases, from a mean of 27 points preoperatively to 57 points postoperatively (difference, 30 points). The patients rated the outcome of surgery as excellent, good, or satisfactory in 91% of cases. Complications after shoulder arthrodesis were noted in 12 of 43 patients (28%). The most frequent complications after screw/plate arthrodesis included pseudarthrosis, 2 (15%)/3 (10%); infection, 1 (8%)/4 (13%); and fracture of the humerus, 0/4 (13%). No specific judgment can be attributed to the different osteosynthesis techniques used in shoulder arthrodesis, either in the cases presented at our clinic or in the literature. Pseudarthrosis appeared to be less frequent in cases of plate arthrodesis compared with screw arthrodesis. However, the application of plates resulted more often in infection, postoperative fractures of the humerus, and the necessity for removal of material. Particularly in patients with paralysis, a shoulder arthrodesis resulted in an improvement in postoperative active function and presented a suitable operative option.     

Schulterarthrodese

Besides the paralysis of shoulder muscles, large rotator cuff tears beyond repair, persistent shoulder instability with repeat dislocations and resection cases are recent indications for shoulder arthrodesis.The fusion of the shoulder is particularly useful since, despite immobilization of the glenohumeral and acromiohumeral joints, no loss of function is experienced; on the contrary, in many cases an increase of active total mobility may occur. According to the functional outcome, the majority of reports vary between 30 degrees and 90 degrees of active abduction and forward flexion with a mean value of about 60 degrees The most generally accepted arthrodesis position is 20 degrees -40 degrees abduction, forward flexion and internal rotation in relation to the trunk. This position results in a maximum development of muscle power and ensures that the arm will rest comfortably at the side, and that the scapula will not protrude. This also allows the hand to reach the head and facial region.The literature is not confined to any uniform type of arthrodesis and it would appear that the techniques and configurations of material vary considerably. A general advantage of any one particular form of arthrodesis, and the use of plates, screws or external fixators, cannot be deduced.Pseudarthrosis appears to be less frequent in cases of plate arthrodesis compared to screw arthrodesis. However, the application of plates more often results in infections, postoperative fractures of the humerus and the necessary removal of material. Screw arthrodesis is more beneficial in that the exposed area to be operated is smaller than in plate arthrodesis. Postoperative immobilization is more time consuming and, therefore, constitutes one of the disadvantages of screw fixation.     

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.     

寰枢椎前路复位钢板系统的研制及其生物力学

目的研制一种经口咽前路寰枢椎复位钢板内固定系统,评价其生物力学性能。方法研制各种型号经口咽前路寰枢椎复位钢板和复位器等配套器械。选12具新鲜成年颈椎标本,分别进行三维运动范围实验和螺钉拔出力实验。与其它内固定方法作比较分析。结果生物力学测试表明,三维运动范围,该钢板固定和Magerl Brooks固定在各个方向上均无显著差异(P>0.05)。其抗屈伸、侧屈和旋转均强于其它三种内固定方法。寰椎螺钉的最大拔出力显著高于枢椎和C3椎体固定螺钉,枢椎螺钉与C2螺钉等效。结论寰枢椎前路复位钢板系统设计新颖,具有良好的生物力学性能。能满足临床内固定需要。     

Biomechanical testing of bioabsorbable cannulated screws for slipped capital femoral epiphysis fixation

This study compared cannulated 4.5-mm bioabsorbable screws made of self-reinforced poly-levolactic acid to cannulated 4.5-mm steel and titanium screws for resistance to shear stress and ability to generate compression in a polyurethane foam model of slipped capital femoral epiphysis fixation. The maximum shear stress resisted by the three screw types was similar (self-reinforced poly-levolactic acid 371 +/- 146 MPa, steel 442 +/- 43 MPa, and titanium 470 +/- 91 MPa). The maximum compression generated by both the self-reinforced poly-levolactic acid screw (68.5 +/- 3.3 N) and the steel screw (63.3 +/- 5.9 N) was greater than that for the titanium screw (3 +/- 1.4 N, P <.05). These data suggest cannulated self-reinforced poly-levolactic acid screws can be used in the treatment of slipped capital femoral epiphysis because of their sufficient biomechanical strength.     

Biomechanical Evaluation of Subtalar Fusion: The Influence of Screw Configuration and Placement

Common surgical procedures for subtalar fusion include joint resection, autologous bone grafting, and osteosynthesis with screws in a parallel screw configuration. Although fusion is a routine procedure, the reported rates of nonunion have been high. The present study assessed different screw configurations in terms of their rotational and bending stability in an artificial bone model and cadaver bone. Arthrodesis was always performed with 2 screws. Three different screw configurations were tested: parallel, counter-parallel, and a delta configuration. Two different screw designs were used: a cannulated, partially threaded screw (6.5-mm and 8.0-mm diameter) and a solid screw with a different thread design. Eight experimental groups were investigated as pilot studies in artificial bones and then 3 groups in cadaver bones. The parameters were the primary stiffness and deflection of the construct for loads simulating the internal–external rotation and supination–pronation. Delta positioning of the screws resulted in the greatest biomechanical stiffness and the lowest degrees of deflection of the arthrodesis in the artificial bones and cadaver bones. Increasing the screw diameter from 6.5 to 8.0 mm resulted in no additional stability of the arthrodesis in the artificial bones. The results of the present study have indicated that the delta configuration for arthrodesis results in the greatest construct stiffness and lower relative deflection between the talus and calcaneus in the positions tested.     

Rekonstruktion einer iatrogenen Akromionpseudarthrose

Acromial fractures are rare but severe complications which can occur during subacromial decompression. We report a case of acromial pseudarthrosis which was discovered belatedly due to persistent pain after several operations. The pseudarthrosis was successfully treated by osteosynthesis with a distal radius plate and implantation of a monocortical bone graft from the iliac crest. Two years after surgery, the fracture has healed and the patient's pain improved significantly. In the constant score the patient achieved postoperatively 58?points compared to 25?points before surgery and 65?points compared to 25?points preoperatively in the subjective shoulder rating system (SSRS). Postoperatively, the patient had a better range of motion with active abduction/adduction of 50/0/25o (30/0/20° preoperatively), outward rotation/inward rotation of 35/0/45o (30/0/30° preoperatively) and anteversion/retroversion of 60/0/35° (35/0/20° preoperatively).     

Intramedullary nail fixation with posterior-to-anterior compared to transverse distal screw placement for tibiotalocalcaneal arthrodesis: a biomechanical investigation

BACKGROUND: Biomechanical studies on retrograde intramedullary fixation for tibiotalocalcaneal fusion have been reported, but no studies have investigated dorsiflexion stiffness, load-to-failure, fatigue endurance, and plastic deformation using different distal screw orientations. Also, no studies have examined the effect of bone density on different distal screw orientations while using a fatigue loading mode. METHODS: Eight matched pairs of cadaver legs were used. In one leg from each pair an intramedullary nail was inserted with lateral-to-medial distal screws and in the other with posterior-to-anterior screws. These samples underwent dorsiflexion fatigue testing with determination of initial and final stiffness, load-to-failure, and degree of plastic deformation at failure. DEXA scanning was done of each cadaver specimen to determine bone mineral density. Statistical analysis was performed using the Student t-test and a Pearson correlation. Significance level was set at p < 0.05. RESULTS: The specimens with posterior-to-anterior screws had a significantly higher fatigue endurance load-to-failure (1130.0 +/- 362.0 N compared to 801.0 +/- 227 N, p = 0.01). They also had significantly higher final stiffness (203.1 +/- 23.1 N/mm compared to 146.6 +/- 46.2 N/mm, p = 0.05) and lower plastic deformation (2.4 +/- 1.5 mm compared to 3.8 +/- 2.3 mm, p = 0.04). There was a statistically significant correlation between bone mineral density and the difference in construct deformation with posterior-to-anterior and lateral-to-medial screw orientation (r = 0.76, p = 0.03). CONCLUSIONS: In this biomechanical investigation of tibiotalocalcaneal arthrodesis with intramedullary nail fixation, posterior-to-anterior distal screw orientation provided more stable fixation than lateral-to-medial screw orientation.     

The Lapidus Arthrodesis: Examining the Effect of the Metatarsal Base Transfixion Screw

The modified Lapidus bunionectomy is a useful and highly powerful procedure for correcting hallux abducto valgus. Traditionally reserved for “severe” deformities, this procedure has seen a recent resurgence in the podiatric community for its unique ability to achieve tri-planar correction of this challenging deformity. Although this procedure has been extensively studied in both biomechanical labs and the clinical arenas, no clear consensus has been achieved regarding optimal fixation for this thought-provoking procedure. The current study examined the differences in strength between commercially available 5-hole locking plates with interfragmentary compression vs a crossed-screw with a third “transfixation” screw construct in a controlled setting. Ten fresh-frozen cadaveric match pair limbs (20 total limbs) were used to complete this study. Ten limbs were randomly assigned to a 3-screw construct. The other 10 contralateral limbs were assigned to a commercially available 5-hole locking plate (5 stainless steel and 5 titanium alloy) with an interfragmentary lag screw construct. The first rays were then isolated and potted into a 4-point bending device. The specimens were loaded to failure in a servohydraulic load frame at a controlled rate. Failure was defined as catastrophic or 3 mm of plantar gapping at the arthrodesis site. The mean maximal load to failure was 310.9 ± 109.4 N for the 3-screw construct. The mean maximal load to failure for the locking plate constructs was 264.1 ± 100.9 N. This difference was not statistically significant (p = .328). These results suggest that a 3-screw construct for Lapidus arthrodesis is as strong as commercially available locking plate constructs.     

Biomechanical Comparison of a Locking Plate with Intraplate Compression Screw Versus Locking Plate with Plantar Interfragmentary Screw for Lapidus Arthrodesis: A Cadaveric Study

Lapidus arthrodesis (first metatarsal cuneiform arthrodesis) has become an accepted procedure for hallux abducto valgus. Several variations of fixation have been described. Earlier weightbearing postoperatively has been one reported benefit of using locking plates for fixation. Additionally, studies have demonstrated that fixation placed on the plantar or tension side of the arthrodesis increases the biomechanical advantage. We performed a biomechanical cadaveric study of the Lapidus procedure, comparing a previously reported technique using a low profile locking plate with an intraplate compression screw versus the same locking plate with a plantar interfragmentary screw (PIFS) placed on the tension side of the arthrodesis in 10 fresh, paired, cadaver limbs. The mean ultimate load of the plate with a PIFS was 383.2 ± 211.5 N, and the mean ultimate load of the plate with an intraplate compression screw was 205.5 ± 97.2 N. The mean ultimate load of the LPS Lapidus plate with a PIFS was statistically greater (p = .027) than that with the plate intraplate compression screw. Our results indicated that changing the orientation of the compression screw to a PIFS significantly increased the stability of the Lapidus arthrodesis fixation construct. The modified construct with the PIFS might decrease the incidence of nonunion and, ultimately, allow patients to bear weight faster postoperatively.     

Biomechanical investigation of optimal fixation of isolated talonavicular joint fusion

Despite reports of high nonunion rates for isolated talonavicular fusion, this procedure may be indicated for some patients, including those for whom increased stability of the talonavicular joint in triple arthrodesis is needed. In the biomechanical cadaveric study reported here, we evaluated fixation methods used to provide optimal stability of talonavicular arthrodesis. A physiologic 3-point loading model was used to measure dorsal displacement of the navicular on the talus with 1 or 2 cannulated 4.5-mm screws across the talonavicular joint both with and without one 7.3-mm cannulated screw across the subtalar joint. Statistically significant differences in displacement under cyclic loading to one-half body weight were found. Use of 2 talonavicular screws and no subtalar screw or 1 talonavicular screw plus 1 subtalar screw decreased the motion, as compared with use of 1 talonavicular screw and no subtalar screw.     

经口咽前路寰枢椎复位钢板内固定的生物力学研究

目的 研究经口咽前路寰枢椎复位钢板(TARP)的三维运动范围和螺钉拔出力的生物力学. 方法 12例C0～C3新鲜标本,6例用于三维运动测试,分七组:①完整标本(对照)组,②损伤组(去除C1前弓、C2齿突,破坏关节囊和横韧带等),③TARP组,④后路Brooks钢丝组,⑤Magerl经关节螺钉组,⑥Magerl+Brooks组,⑦前路经枢椎体寰椎侧块螺钉组,分别测量其三维运动范围(ROM).另6例(双侧,n=12)分解为单个椎体后用于螺钉拔出力测试,分三组:①寰椎组,②枢椎组,③C,(对照)组,测定最大拔出力、钉道长度和屈服长度.结果 TARP组和Magerl+Brooks组在各个方向上差异均无统计学意义(P>0.05),前者的ROM值略大于后者,二者抗屈伸、侧屈和旋转均强于其他三种内固定方法(P<0.05).寰椎与枢椎、寰椎与C3的最大拔出力之间差异均有统计学意义(P<0.05),枢椎和c3椎体最大拔出力之间差异无统计学意义(P>0.05)[最大拔出力分别为C1=(491.58 4±67.92)N,C2=(396.73±60.99)N,C3=(385.53±96.77)N].寰椎与枢椎、寰椎与C3椎体的钉道长度之间差异均有统计学意义(均为P<0.05),枢椎和C3椎体钉道长度之间差异无统计学意义(P>0.05).三组的屈服长度之间差异.无统计学意义(P>0.05).C1～C3的螺钉最大拔出力与钉道长度和屈服长度均呈显著正相关(P<0.05,r分别为0.810和0.652),但与钉道长度的相关性更高(P<0.05). 结论 TARP与目前临床应用的后路Magerl+Brooks术式等效,较其他三种固定方式(前路经枢椎体寰椎侧块螺钉、后路Magerl经关节螺钉和后路Brooks钢丝固定)具有更坚强的固定作用.TARP的寰椎和枢椎固定螺钉固定牢靠,钉道长度即进钉深度是影响螺钉抗拔出力的主要因素,屈服长度是影响螺钉拔出力的次要因素.     

The effect of humeral component anteversion on shoulder stability with glenoid component retroversion

BACKGROUND: Posterior glenoid bone loss is often seen in association with glenohumeral osteoarthritis. This posterior asymmetric wear can lead to retroversion of the glenoid component and posterior instability after total shoulder arthroplasty. Options for the treatment of this asymmetric wear include eccentric reaming of the so-called high side, bone-grafting, and/or anteverting the humeral component. Although anteverting the humeral component has been advocated by many, it has not been substantiated on the basis of biomechanical data. The purpose of the present study was to determine whether anteverting the humeral component increases the stability of a total shoulder replacement with a retroverted glenoid component. METHODS: A total shoulder arthroplasty was performed in eight human cadaveric shoulders. The glenoid component was placed in 15 degrees of retroversion. Two humeral versions were tested for each specimen: anatomic version and 15 degrees of anteversion relative to anatomic version. The specimens were mounted supine in a custom fixture on a servohydraulic testing system. The humerus was translated posteriorly by one-half of the width of the glenoid. Three positions of humeral rotation were tested for each position of humeral version. Both the energy and the peak load were analyzed as measures of joint stability. RESULTS: There was no significant difference in either energy or peak load between the tests performed with the humeral component in 15 degrees of anteversion and those performed with the component in anatomic version in any of the three rotational positions (p > 0.05). CONCLUSIONS: Although anteverting the humeral component during total shoulder arthroplasty to compensate for glenoid retroversion has been advocated, these data suggest that compensatory anteversion of the humeral component does not increase the stability of a shoulder replacement with a retroverted glenoid component.     

Interfragmental compression of the Zespol osteosynthesis system. Experimental biomechanical studies

Apart from the advantages of plate osteosynthesis, like primary bone healing and immediate post-operative mobilisation treatment, the disadvantages of this method must be mentioned. First of all these are the high pressure on the surface of the bone by the plate and the high tension stress on the bone by the thread of the screws, which can lead to bone atrophy. Besides the splinting by the plate is accompanied by a functional lack of the bone. The bone reacts on this "stress protection" by reduction of material, especially under the plate. These disadvantages shall be avoided by a new osteosynthesis system, called ZESPOL, which has been developed in Poland. Here the plate does not contact directly the bone, but is fixed above the periost by special screw bolts. Although this method is used in Poland clinically with success, until now no experimental examinations concerning the stability of this osteosynthesis have been published. In the following biomechanical tests we examined, whether the new method achieves a comparable interfragmental compression like common selfcompressing plate systems. We measured the maximal interfragmental compression with an interposed piezo-electric element on human cadaver tibiae. Because the original ZESPOL plates have greater dimensions than common plates, we did not use these original plates. In order to get a comparability between the two systems, we modified small Autocompression plates (ACP) by milling a slot in the underside, so that they could be used with the original ZESPOL screw bolts. These modified ZESPOL plates we compared with common 6-hole Autocompression plates and cortical screws.(ABSTRACT TRUNCATED AT 250 WORDS)