Biomechanical comparison of cannulated small bone screws: a brief follow-up study.

The compressive forces generated by the ASIF and Herbert small bone cannulated screws were measured in the laboratory with the use of simulated bones and a custom-designed load washer as a means of quantifying their fixation capabilities. Comparative data were also generated for the Herbert scaphoid bone screw and the ASIF 4 mm cancellous screw. The cannulated Herbert bone screw and the ASIF 4 mm cancellous screw were found to have nearly identical compression capabilities. Both generated compression forces approximately five times those of the Herbert scaphoid bone screw. The ASIF small cannulated screw demonstrated a compressive capacity 2 1/2 times that of the Herbert screw.     

A biomechanical evaluation of a cannulated compressive screw for use in fractures of the scaphoid.

The compressive force generated by a 3.5 mm ASIF cannulated cancellous screw with a 5 mm head was compared with that generated by a standard 3.5 mm ASIF screw (6 mm head), a 2.7 mm ASIF screw (5 mm head), and a Herbert screw. The screws were evaluated in the laboratory with the use of a custom-designed load washer (transducer) to the maximum compressive force generated by each screw until failure, either by thread stripping or by head migration into the specimen. Testing was done on paired cadaver scaphoids. To minimize the variability that occurs with human bone, and because of the cost and difficulty of obtaining human tissue specimens, a study was also done on polyurethane foam simulated bones. The 3.5 cannulated screw generated greater compressive forces than the Herbert screw but less compression than the 2.7 mm and 3.5 mm ASIF cortical screws. The 3.5 mm cannulated screw offers more rigid internal fixation for scaphoid fractures than the Herbert screw and gives the added advantage of placement over a guide wire.     

Aktueller Stand der Kahnbeinchirurgie

Conservative and various operative treatment options are available for fractures of the scaphoid. Nonunion of the scaphoid requires an operative treatment. Of the patients who underwent surgery for fractures of the scaphoid from 1999 to 2001, 74 were treated with Herbert screw fixation. Nonunion of the scaphoid in 52 cases was treated by iliac crest bone grafting and Herbert screw implantation following resection of the affected bony parts. The cannulated, self-tapping headless bone screw system (cannulated Herbert screw) was used, which allows for easier implantation of the screw. Bony consolidation was achieved in a high proportion of these cases; bony fusion was achieved in all cases of scaphoid fracture. Operative treatment was followed by healing in 47 cases of scaphoid nonunions.     

Biomechanical evaluation of osteosynthesis with cannulated screws for Ponteau-Colles fractures in a bird model

INTRODUCTION: The use of cannulated screw without protrusive head in Colles fractures could avoid some of the drawbacks of conventional pinning. In order to compare the mechanical resistance of Kirshner wires versus cannulated screws we designed a animal model of Colles fractures and tested three types of osteosynthesis: A: K-wires, B: Herbert cannulated screw, C: specific cannulated screws. METHOD: After creating a 10 mm defect in three sets of 10 fresh turkey tibia, 3 types of osteosynthesis were done and tested in compression with an Adamel Lhomargy machine: set A: K-wire fixation, set B: Herbert screws fixation and set C: specifics screws fixation. RESULTS: The compression strength needed for failure of the fixations were: for the K-wires (set A): 52 N +/- 17; for the Herbert screws (set B): 93 N +/- 39; for the specifics screws (set C): 160 N +/- 48; (p < 0.0001). DISCUSSION: The use of an animal model makes the experimentation easier and the sampling more homogeneous. In this model, resistance to compression of the cannulated screw was better than K-wires and the specific cannulated screw better than Herbert screw. Therefore clinical trial of osteosynthesis with cannulated screw in Colles fracture could be considered.     

Anterior odontoid fixation using a 4.5-mm Herbert screw: The first report of 20 consecutive cases with odontoid fracture

BACKGROUND: Anterior screw fixation provides the best anatomical and functional results for odontoid process fracture (type II and "shallow" type III) with intact transverse ligament. The purpose of this study is to evaluate the clinical results of the 4.5-mm-diameter cannulated Herbert screw in the anterior odontoid fixation. METHODS: From May 2003 to November 2005, 20 consecutive cases of types II and III odontoid process fractures were treated with anterior screw fixation using a 4.5-mm Herbert screw. The Herbert screw has double threads, with different pitches on the distal and proximal ends. It has no head, so it can be inserted through articular cartilage and buried below bone surface. RESULTS: There were 16 male and 4 female patients whose ages ranged from 15 to 76 years (mean, 43.7 years). The fracture type was type II-A in 4 patients, II-N in 9 patients, II-P in 5 patients, and III in 2 patients. The range of follow-up was 3 to 36 months (mean, 18.6 months). There were an overall bone fusion rate in 17 cases (85%), fibrous union in 1 (5%), and nonunion in 2 (10%). Overall, complication unrelated to hardware occurred in the one (postoperative dysphagia) without complication-related hardware failure. CONCLUSIONS: The Herbert screw is very useful in anterior fixation for types II and III odontoid process fractures. This series showed successful clinical results comparable with that of the 3.5-mm cannulated cancellous screw and distinct advantages over conventional screws in the aspect of biomechanical properties and less invasiveness.     

Compression forces generated by Mini bone screws--a comparative study done on bone model

The compressive forces generated by the AO/ASIF 3.0 mm cannulated cancellous and 2.0 mm cortical screws, Mini-Acutrak and Herbert/Whipple small bone cannulated screws were measured in the laboratory with the use of simulated cancellous bone and a load cell washer as a means of quantifying their fixation capabilities. The Herbert/Whipple screw and the Mini-Acutrak screw were found to have nearly identical compression capabilities and provided more compression than the cortical screw. The AO/ASIF cannulated screw when used with a support screw demonstrated a compressive capacity twice that of the 2.0 mm cortical screw and higher than the headless Mini-Acutrak and Herbert/Whipple screws. The Mini-Acutrak screw produced about 70% of compression of the cancellous screw in spite of having a diameter almost half that of the cancellous screw. The Herbert/Whipple screw in spite of its larger size compared to the Mini-Acutrak produced almost the same amount of compression.     

Current Concepts in the Treatment of Scaphoid Fractures

Abstract Fractures of the carpus are frequent injuries and typically result from of a fall onto the outstretched hand. Scaphoid fractures are the second most frequent fracture type of the hand (80%). 95% of the patients with acute scaphoid fractures are male, and the average age is approximately 25 years. Conservative treatment of acute scaphoid fractures with immobilization in a plaster cast was the therapy of choice for a long time. Surgical treatment was reserved to severe dislocated fractures only. A progress could be obtained by the principle of intramedullary fixation, whose forerunner is represented by the Herbert screw, and the introduction of cannulated screws guaranteed a continuous improvement. The decision to treat the fracture by surgery requires a clear definition of the fracture type. Therefore, precise radiologic technique is mandatory to detect the fracture and to analyze the pathomorphological circumstances. In order to get an exact classification for the decision on how to proceed, three standard X-ray projections (posteroanterior [PA], lateral and Stecher projection) and a CT scan have to be performed. The most well-known classification has been defined by Herbert & Fisher which combines fracture anatomy, stability and disease history in order to derive prognostic and therapeutic criteria. Also, delayed healings and nonunions are considered. To decide on the adequate treatment, a prerequisite for conservative therapy of acute scaphoid fractures is the anatomic position of the scaphoid. Conservative therapy should be reserved to fracture types, which are stable and heal reliably in the lower-arm plaster cast within 6 weeks. All displaced and unstable acute scaphoid fractures should be operated, and whenever possible, rigid internal fixation should be achieved because of interfragmentary compression. Therefore, several intramedullary implants are available for surgical treatment of acute scaphoid fractures, e. g., Herbert screw, Mini Herbert screw, AO screw (cannulated), Acutrac screw (cannulated), or Twin-fix screw (cannulated). With improved surgical and radiologic techniques, most scaphoid fractures are amenable to minimally invasive fixation. The dorsal approach guarantees a good overview in treating proximal pole fractures. Yet, not all types of fractures can be treated in this way. Severely displaced fractures require the classic open palmar approach. In order to prevent the development of a scaphoid nonunion or an advanced carpal collapse (SNAC-wrist), an early and sufficient diagnostic algorithm is necessary. We recommend internal fixation with a cannulated Herbert screw in B1 and B2 fractures and a Mini Herbert screw in fractures of the proximal third (B3). A2 fractures can be treated conservatively. Early diagnosis and operative treatment will shorten the time off work, minimize the risk of nonunion, and reduce the costs of health care in the long term.     

Biomechanical comparison of fixation devices in experimental scaphoid osteotomies

This study determined the force, bending rigidity, and bending moment at failure of three types of internal fixation systems for the scaphoid bone. A pair of parallel, 0.045-inch Kirschner wires were compared on a paired, bilateral basis with either a Herbert screw or a 3.5 millimeter cannulated screw in repairing a transverse waist osteotomy in cadaver scaphoids. The mean values at failure of the Herbert screw and the cannulated screw versus the paired, parallel Kirschner wires for force (65 N and 77 N versus 23.7 N), rigidity (0.47 Nm2 and 0.54 Nm2 versus 0.16 Nm2) and bending (0.98 Nm and 1.15 Nm versus 0.36 Nm) were approximately three times greater. These differences were statistically significant when compared on a paired basis. This experiment demonstrates that the Herbert screw and cannulated screw are significantly stronger in resisting bending forces than paired, parallel Kirschner wires.     

3.0 mm AO空心松质骨螺钉治疗腕舟骨骨折

目的 总结应用3．0mm AO空心松质骨螺钉对9例舟骨骨折病人进行治疗的经验。方法 骨折按Herben分型，A2型5例，B2型2例，B4型1例，D1型1例。A2型及B2型7例骨折经皮穿钉进行内固定。B4型1例伴有舟月骨分离，在切开复位固定的同时进行了舟月韧带重建。D1型1例在切开复位的同时进行了骨移植。患者手术时平均年龄为33岁。结果 术后平均随访12个月。9例均获得了骨性愈合。结论 3．0mm AO窄心钉对骨折端可产牛良好的加压效果，并获得较好的治疗效果。     

The Herbert screw for scaphoid fractures. A multicentre study

The results of a prospective multicentre study of the Herbert differential pitch bone screw used to treat 50 scaphoid fractures and non-unions are presented. All fresh fractures and four of the five fracture-dislocations united, an overall union rate of 92%. Although the technique is demanding, the Herbert screw can achieve excellent results in the management of scaphoid fractures.     

Interfragmentary compression forces of scaphoid screws in a sawbone cylinder model

Various screws have been developed to stabilise fractures of the scaphoid. Commonly used are the Herbert, the HBS, the 3-mm AO and the Acutrak screws. Not long ago a new screw, the Twin Fix, was introduced. This is cannulated and similar in shape and appearance to the classical Herbert screw. In our test series we compared the maximum achievable compression forces of the Twin Fix screw with that of three other screws (AO, HBS and Acutrak screws). To avoid the variations of density, stiffness and rigidity in natural bone, a polyurethane sawbone-based test setup was used. The test series included 10 screws of each type. The compression force was measured using a special strain gauge. The mean compression force was significantly higher for the Twin Fix screw (8+/-1N) and the Acutrak screw (7.6+/-0.4/0.6N) in relation to the AO screw (6.8+/-1.0/1.4N) and HBS screw (2+/-1N). We found the Twin Fix and Acutrak screws to be promising in the treatment of scaphoid fractures.     

Biomechanical evaluation of a new composite bioresorbable screw

A new bioresorbable composite cannulated screw has been developed for small bone fracture fixation. The LG ("Little Grafter") screw is manufactured from Biosteon, which is a composite of poly L-lactic acid and hydroxyapatite. This study aimed to compare interfragmentary compression generated by this new screw with conventional metal screws commonly used in scaphoid fracture fixation. Four small metallic screws were compared with the LG screw, using a bone model produced from rigid polyurethane foam. The screws included the Acutrak, Asnis III, Herbert and Herbert-Whipple screws. The mean maximum compression forces for the LG screw, the Asnis and the Acutrak were comparable (LG 32.3 N, Asnis 32.8 N, Acutrak 38.3 N), whereas those using the Herbert and the Herbert-Whipple screw were significantly lower (Herbert 21.8 N, Herbert-Whipple 19.9 N). The bioresorbable LG screw has been shown to have good compressive properties compared to commonly used small bone fragment compression screws.     

Delayed surgical treatment of displaced midshaft clavicle fracture using Herbert cannulated screw with intramedullary bone graft

There is an increasing trend towards operative treatment for displaced midshaft clavicle fractures. This retrospective study was performed to assess the outcome of delayed fixation of displaced midshaft clavicle fractures and test the null hypothesis that there is no difference in results between early and delayed surgical treatment for displaced midshaft clavicle fractures. Using the hospital database, two groups of patients who were surgically treated using Herbert cannulated screw for displaced midshaft clavicle fractures were identified. There were 114 cases in acute (median time to operation of 5?days) and 21 cases in delayed groups (median time to operation 10.5?weeks). Thirty-five cases were available for follow-up in the acute and 16 cases in the delayed series. The primary outcome was assessed by the Disabilities of the Arm, Shoulder and Hand (DASH) score, American Shoulder and Elbow Surgeons score (ASES) and Constant-Murley score. Union occurred in 14 cases in the delayed group. The median DASH, mean ASES and Constant-Murley scores were 4.1, 97 and 88.7, respectively. Compared with the delayed group, the early group had a higher union rate (P?=?0.033), trend towards lower DASH score (P?=?0.051), and higher ASES score (P?=?0.047). The delayed group had significantly more problems with prominent, symptomatic screws that required removal (P?=?0.002). There were no significant differences in union time and complication rate. Delayed fixation of displaced midshaft fractures using the Herbert cannulated bone screw and bone graft is effective and provides a good functional outcome that only slightly reduced from that recorded for early fixation.     

Clavicular anatomy and the applicability of precontoured plates

BACKGROUND: Plate fixation of clavicular fractures is technically difficult because of the complex anatomy of the bone, with an S-shaped curvature and a cephalad-to-caudad bow. The purpose of the present study was to characterize variations in clavicular anatomy and to determine the clinical applicability of an anatomic precontoured clavicular plate designed for fracture fixation. METHODS: One hundred pairs of clavicles were analyzed. The location and magnitude of the superior clavicular bow were determined with use of a digitizer and modeling software. Axial radiographs were made of each clavicle and the precontoured Acumed Locking Clavicle Plate, which is designed to be applied superiorly. With use of Adobe Photoshop technology, the plates were freely translated and rotated along each clavicle to determine the quality of fit and the location of the "best fit." RESULTS: The location of the maximum superior bow was lateral, with a mean distance of 37.2 +/- 18.4 mm from the acromial articulation and with a mean magnitude of 5.1 +/- 5.9 mm. There was no significant difference in the location or magnitude of the apex of the bow between specimens from male and female donors. The anatomic precontoured clavicular plate had the best fit in specimens from black male donors and the worst fit in specimens from white female donors, with a poor fit being seen in 38% (nineteen) of the fifty specimensfrom white female donors. The best location for superior plate application was along the medial aspect of the clavicle. CONCLUSIONS: The apex of the superior bow of the clavicle is typically located along the lateral aspect of the bone, whereas the medial aspect of the superior surface of the clavicle remains relatively flat, making it an ideal plating surface. The precontoured anatomic clavicular plate appears to fit the S-shaped curvature on the superior surface of the majority of clavicles in male patients but may not be as conforming in white female patients. While this plate fits in the medial three-fifths of the clavicle, it does not fit as well laterally.     

Closed reduction and internal fixation for acute midshaft clavicular fractures using cannulated screws

BACKGROUND: Although most acute midshaft clavicular fractures can be successfully treated nonsurgically, surgery is more appropriate for cases with severe displaced fractures, skin tenting, initial shortening of fracture ends, and associated with multiple injuries. However, methods of surgical treatment for such fractures remain controversial. This study discusses a closed reduction and internal fixation technique for midshaft clavicular fracture. METHODS: Between 2000 through 2003, 34 acute midshaft clavicular fractures were operatively treated with cannulated screws using closed reduction technique by one surgeon. The follow-up and clinical evaluation was performed by another surgeon. RESULTS: Thirty-one patients were followed for an average of 27.4 months (range, 24-37 months). Thirty (96.8%) fractures healed within 12 weeks, and one fracture healed at 18 weeks. No major surgical complications occurred, although superficial wound infection occurred in one patient. No implants needed to be removed. The final union rate was 100%. CONCLUSIONS: Closed reduction and internal fixation with cannulated screw is an alternative choice for treating acute midshaft clavicular fracture in selected cases where surgery is indicated and should be done cautiously.     

Midshaft clavicular non-unions treated with the Herbert cannulated bone screw

PURPOSE: To assess an alternative technique for the treatment of midshaft non-unions of the clavicle. METHODS: Five patients with symptomatic non-unions of the clavicle were treated with open reduction and intramedullary fixation by using a Herbert cannulated bone screw. Autogenous bone grafting was applied in one case and decortication in the other 4 cases. RESULTS: Review of the clinical and radiological documentation at a mean time of 13 months (range, 9-26 months) postoperatively shows that union was achieved in all 5 cases. There were no complications related to the operation, and no patient needed removal of the implant for protrusion, loosening, or any other cause. CONCLUSION: Midshaft non-unions of the clavicle can be treated successfully using the Herbert cannulated bone screw, which avoids the need for a second operation to remove the implant after bone union.     

Management of acute displaced midshaft clavicular fractures using Herbert cannulated screw: Technique and results in 114 patients

Purpose:

A new and simple operative technique has been developed to provide internal fixation for midshaft clavicle fractures. This involves the use of a large fragment Herbert Screw that is entirely embedded within the bone. Screw fixation is combined with bone grafting from intramedullary reamings of the fracture fragments. The purpose of this report is to assess the outcomes following treatment of midshaft clavicular fracture using this method.

Materials and Methods:

One hundred and fourteen patients with acute displaced midshaft fracture were identified between 2002 and 2007. All patients were followed until fracture union. Patients’ medical records were reviewed. Disability of the Arm, Shoulder, and Hand questionnaire (DASH), and American Shoulder and Elbow Surgeons Elbow form (ASES) were posted to all patients. Outcome measures included union rate, time to union, implant removal rate, DASH, and ASES scores.

Results:

Patients’ median age was 29.5 years (interquartile range, 19-44 years). The most common injury mechanism was sports injury (28%). The median time from injury to surgery was 5 days (interquartile range, 2-9 days). Union occurred in an average of 8.8 weeks. Non-union occurred in three cases (2.6%). The re-operation rate for symptomatic hardware prominence screw was 1.7%. The median DASH score was 0.83 and the median ASES was 100 (n = 35).

Conclusions:

Intramedullary fixation using cannulated Herbert screw can be used as an effective approach for operative management of midshaft clavicular fractures. Using this method, an appropriate outcome could be achieved and a second intervention for implant removal could be avoided in great majority of cases.

Level of Evidence:

Level III     

Vascularised bone graft for the treatment of non-union of the scaphoid.

A 4/5 compartment pedicled vascularised bone graft from the distal radius combined with internal fixation with a Herbert type cannulated screw was used to treat non-union fractures of the proximal pole of the scaphoid in 13 patients. Non-union was identified on plain radiographs alone. Uneventful clinical and radiological healing was achieved in 11 patients. One patient had progressive signs of failure of the fixation of the screw at the proximal pole; the screw was changed and the fracture was stable at reoperation. One patient had a fall postoperatively, radiographs taken at follow-ups showed only partial healing, and he had a bone graft 12 months later. Twelve patients had clinical and radiological union of the fracture, and one patient fibrous healing alone. The technique may improve healing of non-union of fractures of the proximal pole of the scaphoid, but it is still a technical challenge.     

Internal fixation of scaphoid non-union: a comparative study of three methods

In this study we compared the results of three methods of fixation for scaphoid non-union. The implants used were the AO 2 mm mini-fragment screw, the Herbert screw and the Kirschner (K) wires. Between 1990 and 1999, 132 patients underwent surgery for scaphoid fractures. We used the modified Filan and Herbert classification. Patients with acute fractures and patients requiring vascularised bone grafts were excluded. Twenty-six non-unions were fixed with an AO mini-fragment screw, 58 with a Herbert screw, and nine with K-wires. Radiological union was achieved in 85% of cases using the AO screw, 77% using the Herbert screw and 55% using the K-wire fixation. Statistically there was no significant difference between the AO and Herbert screw groups in terms of rate and speed of radiological union. The mechanical strength of the implant and the compression achieved did not seem to influence the union rate and speed. The type of bone graft (iliac crest or distal radius) did not significantly affect the union rates. Finally, K-wire fixation, either as a primary method or as a salvage procedure, produced inferior results and required prolonged immobilisation in plaster.     

Vertically oriented femoral neck fractures: mechanical analysis of four fixation techniques

OBJECTIVE: Femoral neck fractures in young individuals are typically high angled shear fractures. These injuries are difficult to stabilize due to a strong varus displacement force across the hip with weight bearing. The purpose of this study was to compare the biomechanical stability of four differing fixation techniques for stabilizing vertical shear femoral neck fractures. METHODS: Vertical femoral neck fracture stability was assessed using 4 surgical constructs in 32 cadaveric femurs: 7.3 mm cannulated screws placed in a triangular configuration (group 1), a 135-degree dynamic hip screw (group 2), a 95-degree dynamic condylar screw (group 3), and a locking proximal femoral plate (group 4). The 4 groups were matched for mean bone density and each specimen was tested under incremental loading, cyclical loading, and loading to failure. The modes of fixation failure were recorded for each specimen and the mean group stiffness, failure loads, and failure energies were calculated. RESULTS: All 8 specimens failed during incremental loading in group 1. Five of 8 constructs failed with incremental loading, and 3 failed with cyclical testing in group 2. The combined 16 specimens in groups 3 and 4 survived both incremental and cyclical loading. The differences in stiffness, failure loads, and failure energies between the 4 groups were statistically significant (P < 0.001). The strongest construct was the locking plate and the weakest construct was the 7.3-mm cannulated screw configuration. The cannulated screw configuration group failed as the screws backed out of the femoral head and by varus collapse of the osteotomy; the fixed angled devices all failed at the bone-implant interface. CONCLUSIONS: The strongest construct for stabilizing a vertical shear femoral neck fracture is the proximal femoral locking plate, followed in descending order by the dynamic condylar screw, the dynamic hip screw, and the 3 cannulated screw configuration.