Predicting the fatigue life of internal fracture fixation plates

Failures of fracture fixation plates, often related to fatigue fractures of the implants, have been reported (Banovetz et al, 1996). While metallurgical defects can usually be excluded, many of these fractures can be explained with the biomechanical situation. This study investigated the biomechanics of two clinical cases, both of which used a 14-hole locking compression plate. In the first case, a titanium plate was used in a rigid configuration with 12 screws resulting in plate breakage after 7 weeks (Sommer et al, 2003). In the second case, a stainless steel plate, which endured the entire healing process, was used in a flexible application with only 6 screws.

Cement-augmented anterior screw fixation of Type II odontoid fractures in elderly patients with osteoporosis

BACKGROUND CONTEXT: Closed reduction and internal fixation by an anterior approach is an established option for operative treatment of displaced Type II odontoid fractures. In elderly patients, however, inadequate screw purchase in osteoporotic bone can result in severe procedure-related complications. PURPOSE: To improve the stability of odontoid fracture screw fixation in the elderly using a new technique that includes injection of polymethylmethacrylat (PMMA) cement into the C2 body. STUDY DESIGN: Retrospective review of hospital and outpatient records as well as radiographs of elderly patients treated in a university hospital department of orthopedic surgery. PATIENT SAMPLE: Twenty-four elderly patients (8 males and 16 females; mean age, 81 years; range, 62-98 years) with Type II fractures of the dens. OUTCOME MEASURES: Complications, cement leakage (symptomatic/asymptomatic), operation time, loss of reduction, pseudarthrosis and revision surgery, patient complaints, return to normal activities, and signs of neurologic complications were all documented. METHODS: After closed reduction and anterior approach to the inferior border of C2, a guide wire is advanced to the tip of the odontoid under biplanar fluoroscopic control. Before the insertion of one cannulated, self-drilling, short thread screws, a 12 gauge Yamshidi cannula is inserted from anterior and 1 to 3 mL of high-viscosity PMMA cement is injected into the anteroinferior portion of the C2 body. During polymerization of the cement, the screws are further inserted using a lag-screw compression technique. The cervical spine then is immobilized with a soft collar for 8 weeks postoperatively. RESULTS: Anatomical reduction of the dens was achieved in all 24 patients. Mean operative time was 64 minutes (40-90 minutes). Early loss of reduction occurred in three patients, but revision surgery was indicated in only one patient 2 days after primary surgery. One patient died within the first eight postoperative weeks, one within 3 months after surgery. In five patients, asymptomatic cement leakage was observed (into the C1-C2 joint in three patients, into the fracture in two). Conventional radiologic follow-up at 2 and 6 months confirmed anatomical healing in 16 of the19 patients with complete follow-up. In two patients, the fractures healed in slight dorsal angulation; one patient developed a asymptomatic pseudarthrosis. All patients were able to resume their pretrauma level of activity. CONCLUSIONS: Cement augmentation of the screw in Type II odontoid fractures in elderly patients is technically feasible in a clinical setting with a low complication rate. This technique may improve screw purchase, especially in the osteoporotic C2 body.

Treatment of posttraumatic cubitus varus in children and adolescents. Supracondylar humeral osteotomy using radial external fixation

OBJECTIVE Precise adaptable fixation of a supracondylar humerus osteotomy with a radial/lateral external fixator to correct posttraumatic cubitus varus. INDICATIONS Acquired, posttraumatic cubitus varus as a result of a malhealed and unsatisfactorily treated supracondylar humerus fracture. Idiopathic, congenital cubitus varus (very seldom) if the child (independent of age and after complete healing) is cosmetically impaired; stability of the elbow is reduced due to malalignment (hyperextension); secondary problems and pain (e. g., irritation of the ulnar nerve) are expected or already exist; or there is an explicit wish of the child/parents (relative indication). CONTRAINDICATIONS In principle there are no contraindications provided that the indication criteria are filled. The common argument of age does not represent a contraindication in our opinion, since angular remodeling at the distal end of the humerus is practically nonexistent. SURGICAL TECHNIQUE Basically, the surgical technique of the radial external fixator is used as previously described for stabilization of complex supracondylar humeral fractures. With the patient in supine position, the arm is placed freely on an arm table. Using a 4-5 cm long skin incision along the radial, supracondylar, the extracapsular part of the distal humerus is prepared, whereby great caution regarding the radial nerve is advised. In contrast to the procedure used in radial external fixation for supracondylar humeral fracture treatment, two Schanz screws are always fixed in each fragment at a distance of 1.5-2 cm. The osteotomy must allow the fragment to freely move in all directions. The proximal and distal two Schanz screws are then connected with short 4 mm carbon or stainless steel rods. These two rods are connected with each other over another rod using the tub-to-tub technique. Now the preliminary correction according the clinical situation can be performed and the clamps are tightened. Anatomical axis and function are checked. If these are radiologically and clinically perfect, all clamps are definitively tightened; if the alignment or the function is not perfect, then further adjustments can be made. POSTOPERATIVE MANAGEMENT Due to the excellent stability, further immobilization not necessary. Immediate functional follow-up treatment performed according to pain. RESULTS Adequate healing is usually expected within 6 weeks. At this time the external fixator can be removed in the fracture clinic. Because the whole operation is performed in an extraarticular manner and the mobility of the elbow is not affected, deterioration of function has never been observed. Also regarding the cosmetic/anatomical situation, good results are expected because they were already achieved intraoperatively.

Prolonged Rehabilitation of Jones Fracture in Division I-A Collegiate American Football Player: A Case Report

Objective: To describe the prolonged rehabilitation program for a Jones fracture in a Division I-A American football player. Background: A 21 year old, African American, collegiate football player (body mass= 264 lb; height= 76.5 in; body fat= 16.0%) complained of a sharp pain at the dorsal aspect of the left foot. The athlete experiences a compressive force to the fifth metatarsal and upon evaluation, mild swelling was present along the lateral aspect of the foot. Differential Diagnosis: Jones fracture, metatarsal fracture, bone contusion. Treatment: An intramedullary fixation surgery was scheduled two weeks post injury, to correct and stabilize the fracture. Intramedullary fixation is a method of mending the bone internally with a screw, wire, or metal plate along the fractured bone length wise. Following surgery the athlete continued use of crutches for ambulation and was placed in a removable walking boot for 5 weeks. Uniqueness: This case presented a unique challenge in the rehabilitation program, as the athlete experienced slow formation of the bone callus and therefore a prolonged rate of recovery. The athlete was in a walking boot longer than expected (2 weeks longer than anticipated) which inhibited advancement in his rehabilitation due to a slow bone callus formation. A soft callus usually begins to form at day 5 following injury, but documentation was incomplete, and a hypothesis for slow bone callus formation could be secondary to lengthened time between injury occurrence and injury reporting. The athlete may have been weight bearing during the early callus formation, but healing may have been prohibited. Also, vascularization in the area is already limited and may also have played a role in delayed bone growth. Conclusions: Although the return to participation was longer than expected, the rehabilitation program was successful in returning the athlete to competition.

Quantitative fit assessment of a precontoured fracture fixation plate : its automation and an investigation on the borderline cases

Virtual methods to assess the fitting of a fracture fixation plate were proposed recently, however with limitations such as simplified fit criteria or manual data processing. This study aims to automate a fit analysis procedure using clinical-based criteria, and then to analyse the results further for borderline fit cases. Three dimensional (3D) models of 45 bones and of a precontoured distal tibial plate were utilized to assess the fitting of the plate automatically. A Matlab program was developed to automatically measure the shortest distance between the bone and the plate at three regions of interest and a plate-bone angle. The measured values including the fit assessment results were recorded in a spreadsheet as part of the batch-process routine. An automated fit analysis procedure will enable the processing of larger bone datasets in a significantly shorter time, which will provide more representative data of the target population for plate shape design and validation. As a result, better fitting plates can be manufactured and made available to surgeons, thereby reducing the risk and cost associated with complications or corrective procedures. This in turn, is expected to translate into improving patients' quality of life.

A new model to study healing of a complex femur fracture with concurrent soft tissue injury in sheep

High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. There is evidence that such closed soft tissue injuries affect the healing of bone fractures, and vice versa. Despite this knowledge, most impact trauma studies in animals have focussed on bone fractures or soft tissue trauma in isolation. However, given the simultaneous impact on both tissues a better understanding of the interaction between these two injuries is necessary to optimise clinical treatment. The aim of this study was therefore to develop a new experimental model and characterise, for the first time, the healing of a complex fracture with concurrent closed soft tissue trauma in sheep. A pendulum impact device was designed to deliver a defined and standardised impact to the distal thigh of sheep, causing a reproducible contusion injury to the subcutaneous soft tissues. In a subsequent procedure, a reproducible femoral butterfly fracture (AO C3-type) was created at the sheep’s femur, which was initially stabilised for 5 days by an external fixator construct to allow for soft tissue swelling to recede, and ultimately in a bridging construct using locking plates. The combined injuries were applied to twelve sheep and the healing observed for four or eight weeks (six animals per group) until sacrifice. The pendulum impact led to a moderate to severe circumferential soft tissue injury with significant bruising, haematomas and partial muscle disruptions. Posttraumatic measurements showed elevated intra-compartmental pressure and circulatory tissue breakdown markers, with recovery to normal, pre-injury values within four days. Clinically, no neurovascular deficiencies were observed. Bi-weekly radiological analysis of the healing fractures showed progressive callus healing over time, with the average number of callus bridges increasing from 0.4 at two weeks to 4.2 at eight weeks. Biomechanical testing after sacrifice showed increasing torsional stiffness between four and eight weeks healing time from 10% to 100%, and increasing ultimate torsional strength from 10% to 64% (relative to the contralateral control limb). Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries.

A novel iterative method for simulating patient-specific optimal deformation and fit of fracture fixation plates

This paper proposes a new iterative method to achieve an optimally fitting plate for preoperative planning purposes. The proposed method involves integration of four commercially available software tools, Matlab, Rapidform2006, SolidWorks and ANSYS, each performing specific tasks to obtain a plate shape that fits optimally for an individual tibia and is mechanically safe. A typical challenge when crossing multiple platforms is to ensure correct data transfer. We present an example of the implementation of the proposed method to demonstrate successful data transfer between the four platforms and the feasibility of the method.

Primary stability of two uncemented acetabular components of different geometry : hemispherical or peripherally enhanced?

Objective This study compared the primary stability of two commercially available acetabular components from the same manufacturer, which differ only in geometry; a hemispherical and a peripherally enhanced design (peripheral self-locking (PSL)). The objective was to determine whether altered geometry resulted in better primary stability. Methods Acetabular components were seated with 0.8 mm to 2 mm interference fits in reamed polyethylene bone substrate of two different densities (0.22 g/cm3 and 0.45 g/cm3). The primary stability of each component design was investigated by measuring the peak failure load during uniaxial pull-out and tangential lever-out tests. Results There was no statistically significant difference in seating force (p = 0.104) or primary stability (pull-out p = 0.171, lever-out p = 0.087) of the two components in the low-density substrate. Similarly, in the high-density substrate, there was no statistically significant difference in the peak pull-out force (p = 0.154) or lever-out moment (p = 0.574) between the designs. However, the PSL component required a significantly higher seating force thanthe hemispherical cup in the high-density bone analogue (p = 0.006). Conclusions Higher seating forces associated with the PSL design may result in inadequate seating and increased risk of component malpositioning or acetabular fracture in the intra-operative setting in high-density bone stock. Our results, if translated clinically, suggest that a purely hemispherical geometry may have an advantage over a peripherally enhanced geometry in high density bone stock.

Clinically-based automatic implant fitting for shape optimization of fracture fixation plates

Complex bone contour and anatomical variations between individual bones complicate the process of deriving an implant shape that fits majority of the population. This thesis proposes an automatic fitting method for anatomically-precontoured plates based on clinical requirements, and investigated if 100% anatomical fit for a group of bone is achievable through manual bending of one plate shape. It was found that, for the plate used, 100% fit is impossible to achieve through manual bending alone. Rather, newly-developed shapes are also required to obtain anatomical fit in areas with more complex bone contour.

A method for optimal fit of patient-specific fracture fixation plates

Anatomically pre-contoured fracture fixation plates are a treatment option for bone fractures. A well-fitting plate can be used as a tool for anatomical reduction of the fractured bone. However, recent studies showed that some plates fit poorly for many patients due to considerable shape variations between bones of the same anatomical site. Therefore, the plates have to be manually fitted and deformed by surgeons to fit each patient optimally. The process is time-intensive and labor-intensive, and could lead to adverse clinical implications such as wound infection or plate failure. This paper proposes a new iterative method to simulate the patient-specific deformation of an optimally fitting plate for pre-operative planning purposes. We further demonstrate the validation of the method through a case study. The proposed method involves the integration of four commercially available software tools, Matlab, Rapidform2006, SolidWorks, and ANSYS, each performing specific tasks to obtain a plate shape that fits optimally for an individual tibia and is mechanically safe. A typical challenge when crossing multiple platforms is to ensure correct data transfer. We present an example of the implementation of the proposed method to demonstrate successful data transfer between the four platforms and the feasibility of the method.

Mechanical testing of internal fixation devices: A theoretical and practical examination of current methods

Successful healing of long bone fractures is dependent on the mechanical environment created within the fracture, which in turn is dependent on the fixation strategy. Recent literature reports have suggested that locked plating devices are too stiff to reliably promote healing. However, in vitro testing of these devices has been inconsistent in both method of constraint and reported outcomes, making comparisons between studies and the assessment of construct stiffness problematic. Each of the methods previously used in the literature were assessed for their effect on the bending of the sample and concordant stiffness. The choice of outcome measures used in in vitro fracture studies was also assessed. Mechanical testing was conducted on seven hole locked plated constructs in each method for comparison. Based on the assessment of each method the use of spherical bearings, ball joints or similar is suggested at both ends of the sample. The use of near and far cortex movement was found to be more comprehensive and more accurate than traditional centrally calculated inter fragmentary movement values; stiffness was found to be highly susceptible to the accuracy of deformation measurements and constraint method, and should only be used as a within study comparison method. The reported stiffness values of locked plate constructs from in vitro mechanical testing is highly susceptible to testing constraints and output measures, with many standard techniques overestimating the stiffness of the construct. This raises the need for further investigation into the actual mechanical behaviour within the fracture gap of these devices.