Long-Term Function following Periprosthetic Fractures.

PURPOSE OF THE STUDY Clinical results of long-term follow-up after traumatic periprosthetic femur fractures and different therapies (ORIF vs. revision arthroplasty) MATERIAL AND METHODS The Visual Analog Scale (VAS), Harris-Hip-Score (HHS), Oxford-Hip-Score (OHS), Oxford-Knee-Score (OKS), Knee-Society-Score (KSS), SF-36 Questionnaire and Funktionsfragebogen Hannover (FFH) were used to evaluate outcome and functionality. Radiological examinations were performed and the Vancouver (THA) and Lewis and Rorabeck (TKA) classifications used. RESULTS 70 patients suffered a periprosthetic hip fracture (29× revision prosthesis, 41x ORIF), 23 patients underwent an ORIF due to periprosthetic fracture of a TKA (total mean age 75.2 years). 47 patients (follow-up rate 51%) were examined 40 months after surgery (mean age 72 years) (THA: 16× revision, 23× ORIF, TKA: 8× ORIF). The VAS revealed significant less pain in the group that had undergone revision hip arthroplasty than in the ORIF group: 3.9±1 vs. 5.1±1.7 (p<0.05), respectively. 5/16 patients with revision arthroplasty had excellent or good results in the HSS compared to 3/23 patients after ORIF. The OHS yielded excellent or good results in 12/16 patients after revision arthroplasty vs. 10/23 after ORIF. The VAS after ORIF in patients who suffered periprosthetic knee fractures was 4.9±2.1. 3/8 patients achieved excellent or good results according to the OKS. CONCLUSION Every functional score (HSS, OHS, FFH, SF-36) of those patients who had undergone revision arthroplasty was slightly higher and their VAS significantly lower than the scores of the patients after ORIF. Key words: periprosthetic fractures, trauma, open reduction and internal fixation, revision arthroplasty.

Relationship between autologous bone graft osteointegration and correction loss after antero-posterior spondylodesis of traumatic vertebral body fracture.

BACKGROUND: A common method to restore the sagittal alignment and stabilize the spinal column is a dorso-ventral spondylodesis. It is assumed that correction loss after posttraumatic spondylodesis results from inadequate incorporation of the autologous iliac crest graft. MATERIALS AND METHODS: Retrospective documentation of patients with unstable vertebral body fractures of the thoracic or lumbar spine with concomitant rupture of at least one adjacent intervertebral disk who received surgical treatment at our institution from 2000 to 2006. Followed by analysis of the computer tomography documentation of a total of 142 patients with unstable vertebral body fracture stabilized by posterior internal fixator and anterior iliac crest spondylodesis. RESULTS: The following mean angle changes were derived from the second series of CT scans performed on average 283 days after anterior spondylodesis: vertebral wedge angle (VWA): 2.1°; segmental kyphotic angle: 4.9°; adjusted-SKA: 4.8°; sagittal index (SI): -0.04; segmental-scoliotic-angle (SSA): 0°; adjusted-SSA: 0°. Changes in VWA, both SKAs and SI postoperatively and prior to ME, were statistically significant (P<0.05). The McAfee fusion assessment of the graft showed: full fusion: cranial 64%, caudal 47%; partial fusion: cranial 20.5%, caudal 29%; lysis: cranial 8.5%, caudal 17%; graft resorption: 7%. No correlation was found between the above-mentioned angle changes and fusions grade. DISCUSSION: The importance of radiological evidence of fusion deficiency is questionable, because the extent of fusion only has a minimal effect on correction loss. LEVEL OF EVIDENCE: Level IV.

Minimally invasive stabilization of distal humerus fractures: a pilot study with biomechanical evaluation.

BACKGROUND: Fracture of the distal humerus is a fairly rare injury and makes high demands on the treating surgeon. Prerequisites for a good outcome are anatomical reconstruction and osteosynthesis stable enough for exercises. A method permitting early restoration of function is especially important for patients with osteoporosis. The extensive surgical approach necessary for open reduction is associated with a high number of wound healing disorders and infections with a frequency of 11% being reported in the literature. Although open reduction and internal fixation in double-plating technique is unavoidable for complex intraarticular fractures, an alternative, minimally invasive and, consequently, tissue-preserving procedure is desirable for simpler fractures. OBJECTVE: To investigate this issue further an angular stable nail system developed for the distal radius was implanted as a stabilizer and the construct tested biomechanically as part of a feasibility study. METHODS: Distal humerus fractures were stabilized by insertion of a distal radius nail, namely, the Targon DR (Aesculap, Tuttlingen) and a K-wire. To test the hypothesis six cadaveric bones fixed in formalin were tested biomechanically for displacement, implant failure, and stiffness. Displacement was determined by means of an ultrasound-based system. RESULTS: An average displacement of 1.6 mm ± 0.7 was recorded at a maximum compression force of 100 N in extension and an average displacement of 1.4 mm ± 0.9 in flexion. Implant failure was not observed for any of the constructs. CONCLUSIONS: The study presented here permits the conclusion that a minimally invasive procedure is possible at the distal humerus and does ensure adequate stability. Although the nail was not specifically designed for the humerus, current findings form the basis for a promising approach that will be pursued further after modification of the nail design.

Failure after osteosynthesis of trochanteric fractures. Where is the limit of osteoporosis?

SUMMARY: The aim of this study is to identify osteoporosis values, beyond which there is a high risk of osteosynthesis failure. Bone mineral density (BMD) of 30 cadaveric femora with a pertrochanteric fracture osteotomy was correlated to the risk of cut out after osteosynthesis on a biomechanical testing approach. For a BMD less than 250 mg/cm(3), there is a high risk of fixation failure after surgical treatment of pertrochanteric fractures. This value can be regarded as a reference value for future experimental and clinical studies. INTRODUCTION: Despite continuous modification of intramedullary load carriers for the surgical stabilization of trochanteric fractures, cut out remains the most frequent complication. The aim of this experimental study was to identify threshold osteoporosis values, beyond which there is a high risk of osteosynthesis failure. METHODS: Bone mineral density (BMD) of 30 cadaveric femora was recorded for the femoral head by QCT measurement. Subsequently, a standardized osteotomy mimicking an unstable trochanteric type fracture was stabilized by intramedullary nailing. The constructs were loaded axially at a force of 2,100 N up to 20,000 cycles. Cut out at the femoral head was documented by radiograph. Statistical evaluation of the cohort group was performed by calculation of relative risk in relation to the BMD values. RESULTS: In total, there were six cases of cut out after 10,000 cycles. The incidence of cut out for BMD less than 250 mg/cm(3) was 0.55 (5 of 9) and for BMD greater than 250 mg/cm(3), it was 0.05 (1 of 21). Therefore, the relative risk of cut out for BMD <250 mg/cm(3) is 11× greater than for a BMD >250 mg/cm(3). After 20,000 cycles, an additional test caused one cut out (relative risk of cut out for a BMD <250 mg/cm(3) 5.8). CONCLUSIONS: For a BMD less than 250 mg/cm(3), there is a high risk of fixation failure after surgical treatment of pertrochanteric fractures. Although this value is based on an experimental in vitro study design with all its associated limitations, it can be regarded as a reference value for future experimental and clinical studies.

Intramedullary nailing of trochanteric fractures: central or caudal positioning of the load carrier? A biomechanical comparative study on cadaver bones.

BACKGROUND: Current recommendations with regard to central or caudal positioning of the femur head carrier in the management of trochanteric fractures are contradictory. METHODS: A standardised pertrochanteric osteotomy was stabilised in 15 pairs of cadaver femurs by means of intramedullary osteosynthesis (5xPFN-A-Synthes, 5xIntertan-Smith&Nephew, 5xTargon-PF-Aesculap). For each pair randomised central (group A) or caudal (group B) implantation of the femoral neck component was performed. Subsequently, the constructs were axially loaded to 2100N. In the absence of cut out after 20,000 cycles, load was increased to a maximum force of 3100N. Angular displacement was recorded based on ultrasound. Migration of the load carrier in the femoral head was monitored radiologically. FINDINGS DISPLACEMENT: No significant difference between groups (p>0.15) was found for the first 50 load cycles. A significantly greater degree of varus deformity was observed in group A (p=0.049) after 2000 load cycles and became more apparent as the number of load cycles increased (after 6000 cycles p=0.039, after 20,000 cycles p=0.034, after 22,000 cycles p=0.016). Angular displacement in the other two planes did not differ significantly across groups. CUT OUT: Migration of the load carrier in the femoral head was not significantly different for the two groups. Overall cut out occurred in 9 constructs, 3 in group A and 6 in group B. The difference in cut-out rate was not significant (p=0.213, chi-squared test). CONCLUSION: Biomechanical superiority can be shown for caudal positioning of the femoral neck load carrier in terms of reduced varus deformity. The incidence of cut out is however unaffected by the position of the load carrier.

A femoral model with all relevant muscles and hip capsule ligaments.

In order to evaluate stabilisation systems in trochanteric femoral fractures with finite element (FE) analysis, a realistic model is required. For this purpose, a new model of a femur with all the relevant muscles and the hip capsule ligaments is set up. The pelvic and tibial bones are modelled as rigid bodies so as to take all the muscles attached to the femur into account. Fracture zones in the proximal femur are defined. Following the modelling of the geometry, the isotropic material behaviour and the load application, a numerical calculation of the femur is carried out. The static iterated FE simulation shows good agreement with in vivo data for the one-leg-stance phase during walking and Pauwels' one-leg stance regarding the displacement of the femoral head (2.9 and 5.2 mm, respectively) and the resulting hip force (253% and 294% bodyweight, respectively). In the modelled fracture zones without osteosynthesis, shear is higher than axial strain. The reduction of shear among others could be a criterion for judging the quality of a stabilisation implant.

Osteoid osteoma of the femoral neck mimicking monarthritis and causing femoroacetabular impingement.

Different aetiologies including the femoroacetabular impingement (FAI) may cause a painful hip, especially in young pa - tients. Two general types of femoroacetabular impingement have been described, the pincer- and the cam type impingement. The latter is characterized by a femoral deformity, usually a bump on the head-and-neck junction that impinges on the acetabular rim. The authors describe the case of a 21-year-old male, bodybuilder, suffering from progressive hip pain with impairment of exercise tolerance, gait and other daily activities. Besides limitation of hip internal rotation physical examination was normal. He had a transitory response to non-steroid anti-inflammatory drugs. Initially performed MRI of the pelvis shows predominant inflammation of the hip joint. In external performed arthroscopy the biopsies of the capsule demonstrated chronic synovitis. In the follow up hip pain remains, however, diagnosis was still unclear. Re-evaluation of the formerly performed and a follow up MRI, and of an additional CT, the findings were compatible with an osteoid osteoma in the femoral cervico-cephalic transition causing itself a cam impingement and monarthritis. The adopted therapeutic strategy consisted on arthroscopic excision of the nidus and trimming of the femoral neck, with clinical recovery after surgical intervention.

Salvage procedures for trochanteric femoral fractures after internal fixation failure: biomechanical comparison of a plate fixator and the dynamic condylar screw.

The aim of this study was the biomechanical evaluation of the reversed less invasive stabilization system (LISS) internal fixation as a joint-preserving salvage procedure for trochanteric fractures. Five LISS plates and five dynamic condylar screws (DCS) were tested using synthetic femora (Sawbones) with an osteotomy model similar to a type-A2.3 pertrochanteric fracture. The constructs were subjected to axial loading up to 1000 N for five cycles. Then, the force was continuously increased until fixation failure. For the evaluation of the biomechanical behaviour, the stiffness levels were recorded and the osteotomy gap displacement was mapped three-dimensionally. The average stiffness for the constructs with LISS plates was 412 N/mm (with a standard deviation (SD) of 103N/mm) and 572N/mm (SD of 116 N/mm) for the DCS constructs (p=0.051). Local displacement at the osteotomy gap did not yield any significant differences. The LISS constructs failed at a mean axial compression of 2103N (SD of 519N) and the DCS constructs at a mean of 2572N (SD of 372N) (p=0.14). It is concluded that the LISS plate offers a reliable fixation alternative for salvage procedures.

Clinical effectiveness of customised sport shoe orthoses for overuse injuries in runners: a randomised controlled study.

BACKGROUND AND OBJECTIVES: Treatment of chronic running-related overuse injuries by orthopaedic shoe orthoses is very common but not evidence-based to date. HYPOTHESIS: Polyurethane foam orthoses adapted to a participant's barefoot plantar pressure distribution are an effective treatment option for chronic overuse injuries in runners. DESIGN: Prospective, randomised, controlled clinical trial. INTERVENTION: 51 patients with running injuries were treated with custom-made, semirigid running shoe orthoses for 8 weeks. 48 served as a randomised control group that continued regular training activity without any treatment. MAIN OUTCOME MEASURES: Evaluation was made by the validated pain questionnaire Subjective Pain Experience Scale, the pain disability index and a comfort index in the orthoses group (ICI). RESULTS: There were statistically significant differences between the orthoses and control groups at 8 weeks for the pain disability index (mean difference 3.2; 95% CI 0.9 to 5.5) and the Subjective Pain Experience Scale (6.6; 2.6 to 10.6). The patients with orthoses reported a rising wearing comfort (pre-treatment ICI 69/100; post-treatment ICI 83/100) that was most pronounced in the first 4 weeks (ICI 80.4/100). CONCLUSION: Customised polyurethane running shoe orthoses are an effective conservative therapy strategy for chronic running injuries with high comfort and acceptance of injured runners.

[Achilles tendon power Doppler sonography in 953 long distance runners - a cross sectional study]. / Powerdopplersonografische Befunde der Achillessehnen von 953 Langstreckenläufern - eine Querschnittsstudie.

AIM: The aim of this cross-sectional study was to assess the frequency of tendinopathy-typical Doppler sonographic changes in the Achilles tendons of long distance runners and to correlate these findings with anamnestic and anthropometric data of the subjects. MATERIALS AND METHODS: 1906 Achilles tendons of 953 long distance runners were examined by ultrasound and power Doppler (Toshiba Aplio SSA-770A/ 80 12 MHz). Ultrasound images (spindle-shaped thickening, hypoechoic/hyperechoic lesions, neovascularizations) were analyzed in relation to the runners' anthropometrical data and history of Achilles tendon complaints. RESULTS: In asymptomatic runners as well as in the overall group, there was a statistically significant correlation between tendon thickness and age, height and weight (CC 0.24 - 0.38, p < 0.001). Runners with current or healed Achilles tendon complaints displayed a statistically significant thickening of the tendons, as well as an increase in hypoechoic lesions and neovascularizations (p < 0.001). While grayscale abnormalities were rarely found in asymptomatic runners (< 10 %), neovascularization was detected in 35 % of healthy test persons using the high-resolution power Doppler "Advanced Dynamic Flow". CONCLUSION: Contrary to frequent assumption, neovascularization is often found in tendons of asymptomatic runners, using modern power Doppler equipment. The pathological relevance of single microvessels in asymptomatic tendons must, therefore, be critically discussed.

Treatment of periprosthetic femoral fractures with two different minimal invasive angle-stable plates: Biomechanical comparison studies on cadaveric bones.

INTRODUCTION: The introduction of fixed-angle plate osteosynthesis techniques has provided us a further means to treat periprosthetic femoral fractures. The goal of this experimental study is to evaluate the biomechanical properties and stability of treated periprosthetic fractures when using two different plate systems, which vary in the locking mechanism and the screw placement (monocortical or bicortical) with respect to the prosthesis stem. MATERIALS AND METHODS: Using five pairs of formalin-fixed femora, a Vancouver B1 periprosthetic fracture was treated either with a 13-hole LISS(®) titanium plate using four monocortical periprosthetic screws or with a non-contact bridging plate (NCB) DF(®) plate using bicortical angle-stable blocked screws positioned ventrally or dorsally to the prosthesis stem. Bones were loaded under axial and cyclic compression with a progressively increased load until failure. Displacement at the osteotomy gap was measured during loading using an ultra-sound measuring system. RESULTS: The mean displacement in the region of the fracture gap was not significantly different at any time during the experiments for the two models. The mean force resulting in subsequent model failure was similar in both models; the failure morphology varied slightly between the models, however. Four of the five LISS(®) models exhibited either a tear-out of the monocortical screws or a decortication from the bony shaft of the cortical lamella surrounding the screws. On the other side, two of the NCB models showed macroscopically visible fissures along the osteosynthesis plates at the height of the osteotomy gap, and were hence considered implant failures. Only one NCB model showed tear-out of the bicortically placed screws. CONCLUSION: Bicortical screw placement provides more stable anchoring when compared to monocortical screw fixation. However, in relation to the amount of motion at the osteotomy gap and to failure loads, stabilisation of periprosthetic femoral fractures can be equally well achieved using either the LISS(®) plate with periprosthetic monocortical screws or the NCB plate with poly-axially placed bicortical screws.

Reliability of leg alignment using the OrthoPilot system depends on knee position: a cadaveric study.

Despite the increase in clinical use of navigation systems in total knee arthroplasty, few studies have focused on the reproducibility of these systems. The aim of the present study was to assess the influence of knee position and observer experience on intra- and inter-observer agreement in limb alignment assessment with the OrthoPilot system. Limb alignment in the coronal plane and extension range of the knee were assessed in four embalmed cadaveric specimens by five independent observers and measurements were repeated four times to determine intra- and inter-observer agreement, expressed as intraclass correlation coefficients (ICCs). Additionally, navigation results were compared against figures from conventional measurement of leg alignment (ground truth). Intra- and inter-observer agreements were excellent for assessing the extension range (ICC, 0.97 and 0.95) and the coronal femuro-tibial axis in knee extension (ICC, 0.92 and 0.88) but were generally worse in knee flexion (ICC, 0.62 and 0.55). There was an increased tendency of intraobserver errors in observers with less clinical experience. Mean correlation with conventional measurements was fair (Spearman's rho 0.61). The OrthoPilot system showed excellent reproducibility for assessment of extension range and coronal limb alignment. However, assessments of coronal limb alignment in flexion were prone to error and caution should be taken when relying on these measurements.

[Treatment options for perioperative hemorrhage: interventional angiography to control bleeding complications after total hip arthroplasty]. / Therapieoption perioperativer Blutungskomplikationen: interventionelle Angiographie zur Blutungskontrolle nach hüftendoprothetischen Eingriffen.

Perioperative hemorrhage after total hip arthroplasty is a rare but life-threatening complication. The aim of the current retrospective analysis of five cases was to answer the question of whether bleeding can be controlled by angiography and catheter embolization.A retrospective analysis of five patients with perioperative bleeding complications after hip surgery was done. Bleeding occurred in one case after implantation of an acetabular revision cup, in three cases in association with implantation of a bipolar prosthesis, and in one case in conjunction with a Girdlestone procedure due to septic femoral head necrosis. In four cases we detected arterial bleeding with angiography, all of which were controlled during angiography; one case was complicated by bleeding after a few days. One patient died from multiorgan failure after control of peracute hemorrhage. Subacute hemorrhage after hip surgery can be controlled by angiography. In peracute situations clamping of the external iliac artery is an alternative procedure.

3-Dimensional ultrasound imaging for meniscal lesions.

PURPOSE: The aim of this prospective study was to evaluate preoperative three-dimensional ultrasound scans for the detection of meniscal lesions with a special focus on interobserver reliability. METHODS: Forty one patients with clinical signs of meniscal lesions were preoperatively examined by ultrasound using the 3-D technique (11.7 MHz linear transducer). The 3-D dataset was stored and examined by a second orthopaedic surgeon. The second ultrasound examiner was blinded to the results of the first. Any meniscal pathology was confirmed arthroscopically and documented. RESULTS: At arthroscopy eight lateral meniscal lesions and 57 medial meniscal lesions were detected at different locations. The sensitivity and specificity of the original ultrasound examination was acceptable whereas the results of the second ultrasound session were not as sensitive. CONCLUSION: Three-D-ultrasound with a high resolution transducer, in the hands of an experienced operator, provides acceptable results in the detection of meniscal lesions, however, analysis of the volume dataset from the 3-D ultrasound investigation indicates that it does not offer sufficient accuracy for clinical use.

[Is the locking, 3.5 mm Palmar T-Plate the implant of choice for displaced distal radius fractures?]. / Ist die winkelstabile, palmare 3,5-mm-T-Platte die Lösung für dislozierte, distale Radiusfrakturen?

BACKGROUND: There are many different possibilities for the treatment of the distal radial fracture. According to evidence-based medicine there is no gold standard for the treatment of this fracture. With the development of locking plates, the spectrum of indications for plate osteosynthesis has possibly increased. The aim of our investigation was the evaluation of the clinical results after stabilisation of distal radial fractures with the locking, 3.5 mm T-LCP. MATERIAL AND METHODS: In a retrospective study we analysed all patients with distal radial fractures treated with a 3.5 mm T-LCP between 05/02 and 05/04. The complete medical histories and X-rays were analysed and a clinical follow-up examination with the Martini score was performed. RESULTS: 76 from 93 patients (82%) could be examined for the follow-up, the average age was 59 years (17/88). According to the AO classification of Mueller and Nazarian we had 23 A-fractures, 7 B-fractures and 73 C-fractures. After reduction and plate osteosynthesis we found no secondary displacement. The median of the overall results according to the Martini score was 33 from 38 points (9/38). As far as complications were found 1 CRPS, 3 CTS, 2 pseudarthroses, 1 wound infection, 1 delayed bony union, 3 implant failures, and 1 broken plate (after a new injury). In one case the median nerve was cut during operation and a suture was performed. CONCLUSION: According to our results the 3.5 mm T-LCP is a good implant for the stabilisation of displaced distal radius fractures if the fragments are not too small for the 3.5 mm screws. The anatomic reduction is maintained and the X-rays show very good results. Compared with other investigations we must ask ourselves if the benefit of the locking plates justifies its use as compared with non-locking (conventional) plates.

[T-plate osteosynthesis--an obsolete osteosynthesis procedure for proximal humeral fractures? Middle-term clinical and radiological results]. / Die T-Platten-Osteosynthese - ein überholtes Osteosyntheseverfahren für proximale Humerusfrakturen? Mittelfristige klinisch-radiologische Ergebnisse.

AIM: The present clinical trial was performed to assess the clinical and radiological outcome after operative treatment of proximal humeral fractures using the T-plate. METHODS: All patients who were treated with the T-plate were included into the study. Patient satisfaction,complications and radiological findings were assessed. The clinical results were evaluated using the Constant-Murley score, the UCLA score, and the DASH score. Between December 1996 and October 2003, 74 patients (with 76 fractures)were treated with the T-plate. Surgically treated complications were 2 hematomas and 3 failures of the osteosynthesis under functional physiotherapy. In 19 patients the implants were removed because of persisting complaints. RESULTS: After an average follow-up period of 67 months 52 patients (54 fractures) were examined. According to the Neer classification there were 34 2-part, 15 3-part and 5 4-part fractures.80% of the patients were satisfied with the result. According to the evaluated scores, 74 to 89% of the patients had an excellent to satisfactory outcome. CONCLUSION: The T-plate enables the stable fixation of complex proximal humeral fractures and permits even in the elderly patient an early functional treatment. Anatomical reconstruction and stable fixation followed by early rehabilitation are most important to achieve a good functional outcome in the patient.

Locking plates in proximal humerus fractures.

It is well known that proximal humerus fractures are among the three most frequent fracture types. Epidemiological invetsigations show that in people elder than 60 years the fracture of the proximal humerus is more frequent than fractures of the hip region (17). Over the last decades several techniques have been applied for treatment of proximal humerus fractures. Widely accepted is the initiation of a conservative treatment regimen for undisplaced fractures, however, the standard treatment for displaced fractures, especially three and four part fractures, is still the center of scientific debate. Many different implants have been tested and investigated, thus demonstrating lack of sufficient results. Over the last years the development of angle stable, locking implants started and clinical studies demonstrated encouraging results. In our clinic the locking proximal humerus plate and the PHILOS plate advanced to the implant of choice for treatment of displaced proximal humerus fractures. There are still cases of implant failure and humerus head necrosis, but most of these complications were caused by the fracture type and not an implant specific problem. However the overall results with these new implants are encouraging. Key words: locking plates, proximal humerus fracture, humerus, humerus fracture, PHILOS, PHP.

[Biomechanical evaluation of the gliding nail in trochanteric fractures]. / Biomechanische Evaluation des Gleitnagels in der Versorgung pertrochantärer Frakturen.

AIM: The purpose of the present study is to evaluate wether the gliding nail with it's double-t-shaped geometry is appropriate in the stabilization of unstable trochanteric fractures or not and if this evaluation can be performed with a static finite element simulation. METHODS: Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. After modelling of geometry, isotropic material behaviour and load application during one leg standing in slow walking was done with a limited dataset of relevant muscles. Two relevant fractures are modelled. RESULTS: FE-simulation shows a movement of the femoral head distally, medially and posteriorly. Maximum bending strain is in the femoral diaphysis medial compression and lateral tension strain. In the proximal part we find a nearly homogeneous strain distribution. The clinical effect of lateralization of the proximal main fragment is also result of the simulation. In the area of the modelled fractures there is much more compressive stress than shear stress. CONCLUSION: Elastomechanical behaviour of the gliding nail is demonstrated with correlation of clinical observed effects. In both simulated fracture areas there is a bone union supporting compressive stress. This means in the FE-simulation the gliding nail is appropriate in the stabilization in unstable trochanteric fractures.

Finite element analysis of a bone-implant system with the proximal femur nail.

Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary.