Magnesium calcium alloys are promising candidates for an application as biodegradable osteosynthesis implants [1,2]. As the success of most internal fracture fixation techniques relies on safe anchorage of bone screws, there is necessity to investigate the holding power of biodegradable magnesium calcium alloy screws. Therefore, the aim of the present study was to compare the holding power of magnesium calcium alloy screws and commonly used surgical steel screws, as a control, by pull-out testing.

Magnesium calcium alloy screws with 0.8wt% calcium (MgCa0.8) and conventional surgical steel screws (S316L) of identical geometries (major diameter 4mm, core diameter 3mm, thread pitch 1mm) were implanted into both tibiae of 40 rabbits. The screws were placed into the lateral tibial cortex just proximal of the fibula insertion and tightened with a manual torque gauge (15cNm). For intended pull-out tests a 1.5mm thick silicone washer served as spacer between bone and screw head. Six animals with MgCa0.8 and four animals with S316L were followed up for 2, 4, 6 and 8 weeks, respectively. Thereafter the rabbits were sacrificed. Both tibiae were explanted, adherent soft tissue and new bone was carefully dissected around the screw head. Pull-out tests were carried out with an MTS 858 MiniBionix at a rate of 0.1mm/sec until failure of the screw or the bone. For each trial the maximum pull-out force [N] was determined. Statistical analysis was performed (ANOVA, Student's t-test).

Both implant materials were tolerated well. Radiographically, new bone was detected at the implantation site of MgCa0.8 and S316L, which was carefully removed to perform pull-out trials. Furthermore, periimplant accumulations of gas were radiographically detected in MgCa0.8. The pull-out force of MgCa0.8 and S316L did not significantly differ (p = 0.121) after two weeks. From 6 weeks on the pull-out force of MgCa0.8 decreased resulting in significantly lower pull-out values after 8 weeks. Contrary, S316L pull-out force increased throughout the follow up. Thus, S316L showed significantly higher pull-out values than MgCa0.8 after 4, 6 and 8 weeks (p<0.001).

MgCa0.8 showed good biocompatibility and pull-out values comparable to S316L in the first weeks of implantation. Thus, its application as biodegradable osteosynthesis implant is conceivable. Further studies are necessary to investigate whether the reduced holding power of MgCa0.8 is sufficient for secure fracture fixation. In addition, not only solitary screws, but also screw-plate-combinations should be examined over a longer time period.

Introduction

The treatment osteonecrosis of the femoral head remains uncertain. Core decompression is the standard technique for the early stages (ARCO I and II). A new alternative is core decompression combined with the insertion of an osteonecrosis rod. This implant is supposed to reduce the intraosseous pressure and to give additional structural support. The aim of this study was to evaluate the clinical and radiological outcome via magnetic resonance imaging (MRI) of this new technique.

Introduction: Fractures in long bones are frequently managed with intramedullary implants, plates ore external fixators. X-ray images are normally used to determine the point of full weight bearing and implant removal. Plain radiographs give only poor information about the mechanical properties of the healing callus. Several quantitative Methods: like QCT and DEXA provide information about the density of the new bone, but the mechanical properties remain unknown. For direct monitoring of the mechanical properties of the healing callus a 4-point-stiffness device for small animals was constructed. This devise is used to detect the influence of degradable implants on bone healing. Long term aim is to develop “smart” implants that degrade during healing and speed up the healing process.

Materials and Methods: An uniplanar, bilateral external fixator was mounted on the tibiae of New Zealand White Rabbits after osteotomy and introduction of different degradable, intramedullar implants. The 4-point-bending measurement unit was temporarily fixed to record deflection with a non-contact displacement transducer. Load cells were instrumented to record the stepwise load increase (25g). The max. bending moment was only 0.14 Nm to avoid bending of the implant. Additional μ-CT analysis was conducted on the stiffness measurement days to quantify bone healing. After the in-vivo tests the stiffness measurement device was validated with ex-vivo measurements of bone models in a Material Test System (MTS).

Results: The bending stiffness unit showed a high precision with a standard deviation of 5.55E-04 N/μm and a mean deviation error of all models of 1.74E-04 N/μm. We found a significant non-linear correlation between the measured stiffness and the diameter of the models (p< 0.05, r2=0.96). Furthermore a significant correlation between the stiffness device and the MTS in vitro was shown (r2=0.96, p< 0.005). A significant correlation between the data of the bending stiffness device and the MTS was found for all animals (r2=0.64, p< 0.01). μ-CT analysis showed an increase in callus formation and density during the increase in bending stiffness.

Discussion: In this study a precise measurement unit to mirror the mechanical properties of healing bone is presented. The device was successfully tested in an in-vivo model of fracture healing. The healing of callus around different degradable implants can be monitored to develop implants that degrade during fracture healing to avoid stress shielding or implant removal. Not only data about the healing bone can be gatherd with the μ-CT analysis, but also processes around the implants can be well monitored to evaluate degradation and quality of the implants.

Today the use of pneumatic tourniquet is commonly accepted in total knee arthroplasty (TKA) to reduce perioperative blood loss. There are a few prospective randomised and nonrandomised studies that compare the effect of tourniquet release timing in cementless or cemented unilateral TKA. However, many of these studies show an inadequate reporting and methodology. This randomized prospective study was designed to investigate the efficiency of tourniquet release timing in preventing perioperative blood loss in a simultaneous bilateral TKA study design. To our knowledge, this is the first study of its kind, in which the effect of tourniquet release timing on perioperative blood loss was investigated in simultaneous bilateral cemented TKA.

In 20 patients (40 knees) one knee was operated with tourniquet release and hemostasis before wound closure, and the other knee with tourniquet release after wound closure and pressure dressing. To determine the order of tourniquet release technique for simultaneous bilateral TKA, patients were randomized in two groups: ‘Group A’ first knee with tourniquet release and hemostasis before wound closure, and ‘Group B’ second knee with tourniquet release and hemostasis before wound closure. The blood loss was recorded 48 hours postoperative for each technique.

We found no significant difference in total blood loss between both techniques (p =.930), but a significant difference in operating time (p =.035). There were no postoperative complications at a follow-up of 6 month. Other studies report an increase the blood loss in early tourniquet release and an increase the risk of early postoperative complications in deflation of tourniquet after wound closure. In this study we found no significant difference in perioperative blood loss and no increase of postoperative complications. Therefore, we recommend a tourniquet release after wound closure to reduce the duration of TKA procedure and to avoid possible risks of extended anaesthesia.

Introduction: High developmental hip dislocation is the most severe anatomic constitution type in developmental dysplasia of the hip (DDH). After the age of 30–40 years the pseudo-articulation often becomes painful and requires advanced treatments. To restore limb length dislocation must be reduced by soft tissue release. If the reduction overreaches 40 mm the risk for nerve-damage increases dramatically. Reducing the dislocation, one-step soft tissue releases and slow release by continuous iliofemoral distraction were invented. In this study we report a combination of a one-step soft tissue release and slow continuous iliofemoral distraction in patients requiring over 40 mm distraction for uncemented THA.

Material and Methods: Between 1998 and 2007 20 procedures in 19 patients with an age of 42.5 years (18–69 years) and a leg-length discrepancy of > 4 cm were performed. For 5.6 years (1–12 years) patients were followed-up clinically and radiographically. The treatment consisted of a two-step procedure. 1st operation: Soft tissue releases combined with the implantation of the THA components and placement of the external distraction apparatus. In the interval period slow iliofemoral distraction of 1mm–1.5 mm per day was conducted. Neurovascular signs and distraction was regularly monitored until the desired length was achieved. 2nd operation: the external fixation device was removed before applying the acetabular PE-inlay and the femoral head. Subsequent reduction was easy in most cases.

Results: A distraction of 51 mm (41 mm–75 mm) in 61 days (32–94 days) with an indicated speed of 1–1.5 mm/d and an effective speed of 0.8 mm (0.4 mm/d–1.8 mm/d) was achieved. Treatment time was 86 days (50–210 days). Patients had to maintain 132 days (40–300 days) restricted weight bearing. 2.6 (2–6) interventions were performed until final reduction. Harris Hip Score increased by 43 points [44 (22–65) to 83 points (66–98)]. The patients showed satisfying increases in all dimensions of the SF-36 health score. In the course of treatment pin-instability was seen in 6 cases, 3 minor intraoperative femoral fractures, 3 infections and 3 nerve damages occurred.

Discussion: The experiences of this study state the difficulties in the treatment of high DDH. The complication rate was high, but patients seemed to be satisfied finally. However, final scores were lower than in patients undergoing hip arthroplasties for degenerative osteoarthritis. Results of this treatment can be improved by avoiding certain pitfalls like insufficient soft tissue release, trans-cortical placement of the iliac screws or fast distraction. Nevertheless, soft tissue release and continuous iliofemoral distraction is the only option to restore limb-length and to preserve neurologic structures in cases with a dislocation over 40 mm.

Introduction: Besides other techniques to reduce blood loss, the use of pneumatic tourniquet is commonly accepted in total knee arthroplasty (TKA). Furthermore it is used to maintain a clean and dry operative field to improve visualization, to use a better cementing technique, and to reduce operating time. The time of tourniquet release is discussed controversially in literature. However, there are only a few prospective randomised studies that compared the effect of timing of tourniquet release in cementless or cemented TKA. To our knowledge, this is the first study that investigated the influence of tourniquet release on blood loss in a randomized prospective study in simultaneous bilateral cemented TKA.

Methods: 20 patients (40 knees) underwent simultaneous bilateral cemented TKA with the cemented Triathlon Knee System (Stryker) between February and May 2006. The mean age of the patients was 67 years (67+/−11 years). 7 males and 13 females were treated with TKA (mean tourniquet pressure: 282.5+/−33.5 mm Hg). In 20 patients one knee was operated with tourniquet release and hemostasis before wound closure (“Technique A”), and the other knee with tourniquet release after wound closure and pressure dressing (“Technique B”). To determine the order of tourniquet release technique in simultaneous bilateral TKA, the patients were randomized in two groups: “Group A” (20 knees) first knee with tourniquet release and hemostasis before wound closure, and “Group B” (20 knees) second knee with tourniquet release and hemostasis before wound closure. The patients were given low molecular weight heparin and a leg dressing to prevent deep vein thrombosis. The blood loss was monitored two days after surgery till removal of the wound drains.

Results: We found no significant difference in total blood loss between “Technique A” (753+/−390 ml) and “Technique B” (760+/−343 ml) (p=.930). Furthermore there was no significant difference in total blood loss between both techniques after randomizing in “Group A” (“Technique A” 653+/−398 ml; “Technique B” 686+/−267 ml; p=.751) and “Group B” (“Technique A” 854+/−374 ml; “Technique B” 834+/−406 ml; p=.861). However, the operating time showed a significant difference between “Technique A” (58+/−18 minutes) and “Technique B” (51+/−17 minutes) (p=.035).

Discussion: In this study we compared the effect of timing of tourniquet release on perioperative blood loss in a randomized prospective study in simultaneous bilateral cemented TKA. Our results showed no significant difference of blood loss but a significant difference of operation time. Therefore, we recommend a tourniquet release after wound closure to reduce operating time and to minimize the risk of peri- and postoperative complications at approximately similarly blood loss between both techniques.

Introduction: Non-invasive prediction of load bearing capacity during consolidation of distraction osteogenesis and fracture healing would represent a significant advance in the treatment of patients by defining the appropriate point of time for the removal of the fixator externe. Thereby the risk of refracture, malunion and infection could be reduced. Several methods have been proposed in the past to predict the load bearing capacity: dual-energy x-ray absorptiometry (DEXA), stiffness measurements, quantitative computed tomography, quantitative radiography and ultrasound. In this ex-vivo study stiffness- and DEXA-measurements were compared regarding their suitability to predict the load bearing capacity of bone regenerate.

In addition this study analysed how compressive, bending and torsional stiffness as suitable tools were related to the torsional load bearing capacity using a common set of bone regenerate samples of 26 sheep treated with distraction osteogenesis.

Material and Methods: After osteotomy the sheep tibiae were stabilized using an external half-ring Ilizarov fixator. Followed by a 4-day latency period the tibiae were distracted at a rate of 1.25 mm per day in two increments for 20 days. On the 74th day the sheep were sacrificed and tibiae were harvested. The ends of the specimens were embedded in PMMA for further biomechanical testing. Therefore, the specimens were mounted to a sequence of special costume made jigs for compressive testing, 4-point bending and torsional testing in a material testing machine. Stiffness was calculated by regression of the linear part of the load-displacement curves. The maximum torsional moment of the specimens was determined in a final experiment. In addition the bone mineral density (BMD) of the distracted bone tissue was measured using DEXA. The correlation between the maximum torsional moment and the various types of stiffness respectively BMD was analysed to gain information about the suitability predicting the load bearing capacity.

Results: Torsional stiffness exhibits the highest correlation with the maximum torsional moment (r2 = 0.77) followed by bending (ap (r2 = 0.70); ml (r2 = 0.66)) and compressive stiffness (r2 = 0.60). The correlation for BMD with the maximum torsional moment was smallest (r2 = 0.39).

Discussion: This ex-vivo study revealed that the stiffness measurements seem to be a helpful tool to predict the load bearing capacity of bone regenerate. The results of this study showed stiffness measurements as a more suitable mean to determine the load bearing capacity. Within the various types of stiffness measurements torsional stiffness measurements perform slightly better than bending and compressive stiffness measurements. Nevertheless, further studies are necessary to support the results of this study since the specimens failed applying torsional stress.

Introduction: The number of revision Total Hip Arthroplasties (rTHA) continues to rise in an ageing population. High fracture rates reported point out that stem removal is associated with substantial surgical complications. Extensive Trochanteric Osteotomies (ETO) may facilitate stem removal; however, it has also been associated with hazards like increased incidence of non-union, fracture of the osteotomy fragment and stem subsidence. It is not yet clear if a permissive indication for ETO may lead to better postoperative results, than removing stem and cement from the top of the femur eventually causing fractures.

This study describes our experience, comparing peri-operative femoral fractures during stem removal with ETOs in rTHA.

Patients & Methods: Between 1992 and 2004 45 perioperative fractures during rTHA were compared to a collective of 28 ETOs. Pre-Op and after a follow-up period of 32 months (range, 21.6 – 76 months) patients were examined clinically and radiographically. Investigation parameters were Harris-Hip score, SF-36 health score, function (0 – 6) and pain (0 – 10) score, limp, postoperative complications, implant survival and radiographic parameters (stem and trochanter migration, stem alignment, bone union). Fractures were graded using the Vancouver classification.

Results: Harris hip score increase was 31 points (p = 0.004) in ETO patients and 17 points in patients with femoral fractures during stem removal. Increase for function and pain was 1.5 points and 4.4 points in ETO patients and 2 points and 3 points in patients with perioperative femoral fractures. SF-36 health score showed better increases in patients with ETOs. Joint luxation occurred in 3 (6.7%) patients with perioperative fractures and once (3.6%) in the osteotomy group. Infections were more frequently after ETO. 2 patients showed Trendelenburg gait after ETO, but were satisfied with the operation. 1 (3.6%, 12 mm) stem in the ETO group and 3 (6.7%, mean 15 mm) stems in the fracture group subsided slightly. No cable failure was detected in the ETO group, but 2 (4.4%) in the fracture group. 1 osteotomy fragment and 3 femoral fractures showed nonunion and needed re-revision. Every implanted stem had excellent alignment within standard error of ± 3°.

Discussion: Our results suggest that permissive indication for ETO in rTHA may lead to better postoperative results. Especially in patients with poor bone stock, where intraoperative fractures may likely occur, proper implant exposure and rigid fragment fixation may be crucial for success. Although the ETO might be associated with nonunion and limp, this study, as well as others, demonstrates that these observations do not necessarily compromise patient satisfaction. Conclusively, risking femoral fractures during stem removal is prejudicially, compared to proper, extensive femoral osteotomies in rTHA.

Introduction: Revision in total hip arthroplasty (THA) continues to be a technical challenge because of difficulties in fixation of the femoral component in mostly deficient bone in the proximal femur. In the past, the use of primary stems in revision surgery has also been described by many authors. Very often, the cortical bone is not sufficient enough for torsional or axial load bearing. In this retrospective study we present our clinical results of femoral component revision surgery using the uncemented primary BiCONTACT stem (Aesculap).

Methods: In this study, seventy-nine patients were examined who underwent a revision of the femoral component in total hip arthroplasty (THA) with the uncemented primary BiCONTACT stem between December 1991 and April 2004 (mean follow-up 6.8+/−3.9 years). Only patient with a defect classification of Paprosky I–II were analysed. The average patient age was 67.1+/−10.1 years (range from 34–87 years). Forty-six female and thirty-three male patients (168+/−10 cm mean height, 75+/−12 kg mean weight, mean Body Mass Index: 26.4+/−2.5) were included in the study. All patients were clinically evaluated both preoperatively and postoperatively using the Harris Hip Score (HHS), a pain score (from 0 [no pain], to 10 [max. pain]) and a motion score (from 0 to [no flexion], to 10 [max. flexion]). Furthermore, the radiographs (anteroposterior and axial) before, after surgery and at follow-up were analysed concerning femoral defects, proximal bone loss, and to determine the quality of bony fixation. The defects were classified using the Paprosky classification. For statistical analysis, the paired Student t-test was used for preoperative and postoperative data.

Results: The postoperative Harris Hip Score (78.9+/−12.5, p < 0.001), Range of Motion Score (p < 0.05) and Pain Score (p =0.005) improved significantly. During follow-up there were only four re-revisions within two years after revision surgery: two re-infections in the first year, two aseptic loosening in the second year. There were only two cases of mild stress shielding. The survival curve (Kaplan-Meyer) showed a 10-years survival rate of 96.2 %. In two cases we found intraoperative periprosthetic fractures and in fourteen cases small fissures during removal or implantation of the stem.

Discussion: The primary uncemented BiCONTACT stem appears to be a good alternative to other revision systems in well-selected femoral revision cases with minor defects. The results of this study correspond to those published before, using a primary cementless stem in cases of revision. Therefore, in cases of minor proximal and metaphyseal bone defects (Paprosky I–II) the use of a primary stem in femoral revision should be considered. However, an exact preoperative planning, intraoperative assessment of bone stock, and experienced surgeon is necessary.

Introduction Non-invasive prediction of load bearing capacity is an important issue in the advanced clinical treatment of distraction osteogenesis in order to define the appropriate point of time for the removal of the external fixateur. Therefore, non-invasive stiffness measurements were recommended as a promising tool due to the high correlation between strength and various kinds of stiffness: Torsional, bending and compressive.

However, previous experiments only analysed the relationship between a single type of stiffness. This approach neglects the multi-dimensional characteristics of bone loading in compression, bending and torsion.

This study investigates how compressive, bending (ap and ml) and torsional stiffness are related to the torsional load bearing capacity of healing callus tissue using a common set of bone regenerate samples of sheep treated with distraction osteogenesis. In addition, this study compares the evolution of the various kinds of stiffness.

This study provides insight into how the various stiffness modes are suited to predict the load bearing capacity by in-vivo stiffness measurement.

Material and Methods Mid-diaphyseal osteotomies were performed in 26 right tibiae of mature, female domestic sheep. Tibiae were then stabilized using an external half-ring Ilizarov fixator. After a 4-day latency period the tibiae were distracted at a rate of 1.25 mm per day in two increments for 20 days. As a result of a parallel study, the callus was treated with different combinations of growth factors and carrier material resulting in four treatment groups plus a contralateral control group. The sheep were sacrificed and the tibiae were harvested on the 74th day.

The ends of the tibiae were embedded in PMMA and mounted to a sequence of special custom made jigs for compressive testing, 4-point-bending and torsion in a material testing machine.

Stiffness was calculated by regression of the initial linear part of the load-displacement curves.

In a final experiment, the specimens were loaded in torsion until failure to record the ultimate torsional moment.

Results Torsional stiffness exhibits the highest correlation with the ultimate torsional moment (r2 = 0.77), while the ones for compressive (r2 = 0.60) and bending (ap (r2 = 0.70); ml (r2 = 0.66)) are only slightly lower.

Discussion This ex-vivo study in sheep shows that torsional, bending (ap and ml) and compressive stiffness measurements are all suitable means to predict the load bearing capacity of healing callus tissue. Our results show that torsional stiffness measurements perform slightly better than compressive and bending stiffness measurements. However, further studies are necessary to underline the superior performance of torsional stiffness measurements, since the sheep-tibiae were failed by applying torsional stress.

Introduction High precision of axis alignement in Total Knee Arthroplasty by usage of navigation tools is a known fact. However, a common disadvantage of navigation tools is the additional time needed for calibration. Especially in time/cost-sensitive hospital environments this can lead to a neglection of navigation tools usage. In this study we address work-economics during navigation assisted total knee arthroplasty. Specifically, we introduce the concept of a well-trained navigator assistant who performs navigation related work steps during surgery while the primary surgeon concentrates on the remaining work-steps.

In a prospective study of primary TKA we compared environmental parameters of surgeries performed with and without the Navigator Concept.

Materials and Methods 60 Total Knee Arthroplasties were performed using an active navigation system (Stryker Navigation System) (40) or a conventional internal/external alignement jig for implantation of the Interax Knee endoprostheses. Half of the navigated knee arthroplasties were performed using a conventional set-up with a primary surgeon and two assistants serving the navigation system and performing the relevant surgical steps. The other half was done by surgeon teams of a primary surgeon, a navigator assistant and a second assistant. The surgical steps were broken down to a complex work-sharing system. The teams were intensively trained in their work-share by simulating an artificial TKA in a specially designed TKA-Navigation lab. During surgery, the timing of individual steps was recorded. Pre- and postoperative x-rays of the limbs were taken and digitized to an computerized axis-measurement system. Data of both groups were compared using ANOVA and Tuckey post-hoc tests.

Results Results showed a significant difference in surgery time between the three groups (p=0,01) with equivalent surgery times of the conventional and navigator concept group, while the remaining navigated group showed longer surgery times. Axis alignments were statistically not influenced, however demonstrated a tendency to higher precision in the navigator concept group.

Discussion This study is the first to address work-economics in navigated TKA. With the introduction of a specifically trained navigator assistant, a precise work-sharing plan and an intensive training lab, high precision in TKA can be achieved by navigation usage even in a highly cost-sensitive environment. The basis for success, however, is support and investment in training of team surgeons. This concept may provide the basis for other musculoskeletal surgeries demanding both high-tech for precision and time-effectiveness for cost reduction.

Introduction: There is a need for new non-invasive, predictable and quantifiable techniques to assess the process of fracture healing and remodelling in bone. There are several methods to monitor the bone healing in-vivo. But these methods either fail as quantitative predictors of the healing process (X-ray) or exhibit complicated and expensive measurement principles. Some known in-vivo stiffness measurement methods have several disadvantages including the risk of bone malalignment. Therefore we compared ex-vivo torsional strength of bone with in-vivo torsional stiffness under minimal load in two animal model of distraction osteogenesis. Additionally the device was tested in an ex-vivo model.

Methods: An external fixator was combined with a rotating double half-ring. The measurement device was fixed to the half-ring during measurements. It was equipped with a linear variable differential transducer, a load cell, and a stepper motor. During measurements the two parts of the half-ring were rotated against each other and the load and displacement were recorded. The slope coefficient after performing a linear regression between data points of moment and displacement curve was defined as stiffness. Afterwards all models were tested in a material testing system as gold standard. This was tested in an in-vivo animal study of tibial distraction (minipigs time of consolidation 10 days/sheeps time of consolidation 50 days).

Results: Between in-vivo initial torsional stiffness and torsional strength in minipigs we found a highly significant (p=0.001) coefficient of determination of 0.82, but we found only a poor correlation (p> 0.05) in sheeps. However, the results of the ex-vivo model showed a high precision and accuracy.

Discussion: The results of this study suggest that the bone regenerate strength of healing bones can be assessed in-vivo by the presented inital stiffness measurement method in the beginning of an early stage of healing as shown in minipigs. But at the end of the healing period the correlation of strength and stiffness leveled off. There is a similar model showing an excellent correlation, that agree with our data. They explained the weakening of the correlation at the end of healing by a transformation of early bone to lamellar bone after a 2/3 consolidation. In summary, the presented device could be a reliable future tool to monitor the healing progress in patients with bone malalignement or fractures in the beginning of the healing period.

Introduction: Periprosthetic fractures occurring during implantation of non-cemented Total Hip Arthroplasty (THA) are considered major surgical complications. As a shot-term disadvantage, patients are required to partially weight-bear. Additionally, high risks of stem migration and joint luxation can be assumed. On the other hand, in fear of fracture surgeons may undersize stems and subsequently trigger failure rates in THA.

As the long-term consequences of Vancouver A and B1 fractures are not fully known, the goal of this study now was to analyze the postoperative performance of non-cemented THA with respect to perioperative fractures.

Materials and Methods: Between 1997 and 2003 41 peri-operative hip fractures were monitored in 1216 primary Total Hip Arthroplasties using the non-cemented Bicon-tact THA stem. Pre-OP and after a follow-up period of 2,2 (+−3,1) years patients were examined clinically and radiographically. Investigation parameters were Harris-Hip-Scores, SF-36 scores, function score, hospitalization, implant survival /revisions and radiographic parameters (stem migration, trochanter migration, osteolysis, bone union, callus formation and bone quality). Fractures were graded using the Vancouver and Mont+Maar classifications. Patients were compared to a comparable collective of THA patients without perioperative fractures. Pooled data of both groups were compared using non-parametric Kruskal-Wallis tests.

Results: Results showed a significant increase in Harris-Hip scores for all THA of 36 (+−17,7) points. There were no differences in function scores (2,3; score 1–6), postoperative pain (4,8; score 1–10), and time of hospitali-sation (21,3d; +−3,7 range, 14 – 32). The non-union rate was 13%, with 85% of trochanteric fractures showing migration. 47% of the Patients in the fracture group were instructed to maintain restricted weight bearing for 6 weeks. No Trendelenburg signs were observed in the fracture group. Stem migration of mean 0,6 cm (+−0,4) was observed in 13% of Vancouver A and B1 patients (6,4% of A, 20,1% of B1). Long-term cerclage wire failure was observed in 20%. Joint luxation was observed in 1 patient. No hips were revised during the follow-up period.

Discussion: Follow-ups of perioperative fractures classes Vancouver A and B1 during non-cemented THA using the Bicontact stem show associations with stem migration, long-term stabilization implant failure and non-union. However, none of these observations seem to be influencing the overall THA performance and patient satisfaction. Specifically, complications commonly associated with perioperative primary prosthetic fractures as luxation and limping were not signifi-cant. At a short-term perspective, perioperative THA fractures prohibit early weight-bearing. However at a mid to long-term perspective, no disadvantages were apparent in comparison to primary THA without fracture complications.

Introduction: Despite advances in endoprosthesis fixation by implant surface alteration, the problem of aseptic implant loosening still exists. Especially in patients with revisions osseointegration and filling of gaps at the bone-implant interface is mandatory for implant survival. Simple BMP-2 immersion has been introduced previously to act as an osteoinductive coating for advanced osseointegration. However, because of the uncontrolled release kinetics and subsequent molecular action and activity of BMP-2, purely osteoinductive actions are hard to differentiate from osteoclastic BMP-actions leading to bone remodelling, which could counteract the implant fixation process and might be the reason for failed attempts to use BMP-2 for implant fixation. In this study we investigated the osteoinductive potency of BMP-2 bound to titanium surfaces by a highly controlled molecular coupling with specifically designed polymers, allowing a slow controlles release kinetics. We present the first results of two different polymers that were implanted in the tibia and femora of New Zealand White Rabbits.

Methods: In this study we designed cylindrical titanium-implants with an inner thread (Ti6-Alï·& #8220;4V, 3 mm hight x 3 mm diameter) and an electropolished outer surface that were coated with different polymers. The polymers were fixed to the surface using the photochemical method of grafting. The implants were implanted in the proximal tibia and distal femora of New Zealand White Rabbits. The anatomical locations of the implants were alternated to test their osseointegration in different quality of bone (cancellous vs. cortical bone). After 4 weeks the animals were sacrificed and DEXA-scans (Dual-energy X-ray absorptiometry), micro-CT and histological analysis were performed. ANOVA and t-test were used for statistic analysis.

Results: In high-resolution DEXA-scans we found a difference in bone mineral density (BMD) between PVBP and a control implant in the distal femora (PVBP 0,720 g/cm², control 0,661 g/cm²) and in the proximal tibia (PVBP 0,633 g/cm², control 0,431 g/cm²) with an increase of bone mineral density. In the histological investigation we found an increase of osteoblasts around the implants coated with PVBP and PVBP-Co-Acryloxysuccimid. Furthermore, the micro-CT scans showed an increase of BV/TV (bone volume/total volume) for both polymers.

Discussion: In this study we present the first results of the investigation of polymer-coated titanium-implants implanted in the proximal tibia and distal femora of New Zealand White Rabbits. The results of DEXA-scans, micro-CT and histological analysis showed an increase of osseointegration. We suggest that controlled release kinetics after coupling of these polymers with BMP-2 can additionally increase osseointegration. To get a closer look on the polymers, their characteristics in-vivo, and coupling with BMP-2 further investigations are conducted.

The ability to predict load-bearing capacity during the consolidation phase in distraction osteogenesis by non-invasive means would represent a significant advance in the management of patients undergoing such treatment. Measurements of stiffness have been suggested as a promising tool for this purpose. Although the multidimensional characteristics of bone loading in compression, bending and torsion are apparent, most previous experiments have analysed only the relationship between maximum load-bearing capacity and a single type of stiffness. We have studied how compressive, bending and torsional stiffness are related to the torsional load-bearing capacity of healing callus using a common set of samples of bone regenerate from 26 sheep treated by tibial distraction osteogenesis.

Our findings showed that measurements of torsional, bending and compressive stiffness were all suitable as predictors of the load-bearing capacity of healing callus. Measurements of torsional stiffness performed slightly better than those of compressive and bending stiffness.