Aims

Periacetabular osteotomy (PAO) is widely recognized as a demanding surgical procedure for acetabular reorientation. Reports about the learning curve have primarily focused on complication rates during the initial learning phase. Therefore, our aim was to assess the PAO learning curve from an analytical perspective by determining the number of PAOs required for the duration of surgery to plateau and the accuracy to improve.

There are no efficient treatment options for osteoarthritis (OA) that delay further progression. Besides osteoinduction, there is growing evidence of also anti-inflammatory, angiogenetic and neuroprotective effects of biodegradable magnesium-based biomaterials. Their use for the treatment of cartilage lesions in contrast is not well-evaluated yet.

Mg-cylinders were analysed in an in vitro and in vivo OA model. In vitro, SCP-1 stem cell line was analysed under inflammatory conditions and Mg-impact. In vivo, small Mg- and WE43 alloy-cylinders (1mm × 0,5mm) were implanted into the subchondral bone of the knee joint of 24 NZW rabbits after establishment of OA. As control, another 12 rabbits received only drill-holes. µCT-scan were performed and assessed for changes in bone volume and density. After euthanasia, cartilage was evaluated macroscopically and histologically after Safranin-O-staining. Furthermore, staining with CD271 directed antibody was performed to assess neuro-reactivity.

In vitro, an increased gene expression of extracellular matrix proteins as collagen II or aggrecan even under inflammatory conditions was observed under Mg-impact. In vivo, µCT evaluation revealed twice-elevated values for bone volume in femoral condyles with Mg-cylinders compared to controls while density remained unchanged. Cartilage showed no significant differences between the groups. Mg- and WE-samples showed significantly lower levels of CD271+ cells in the cartilage and bone of the operated joints than in non-operated joints, which was not the case in the Drilling-group. Furthermore, bone in operated knees of Drilling-group showed a strong trend to an increase in CD271+ cells compared to both Cylinder-groups. Counting of CD271+ vessels revealed that this difference was attributable to a higher amount of these vessels.

The in vitro results indicate a potential cartilage regenerative activity of the degradable Mg-based material. While so far there was no positive effect on the cartilage itself in vivo, implantation of Mg-cylinders seemed to reduce pain-mediating vessels.

Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 404534760). We thank Björn Wiese for production of the cylinders.

According to the latest report from the German Arthroplasty Registry, aseptic loosening is the primary cause of implant failure following primary hip arthroplasty. Osteolysis of the proximal femur due to the stress-shielding of the bone by the implant causes loss of fixation of the proximal femoral stem, while the distal stem remains fixed.

Removing a fixed stem is a challenging process. Current removal methods rely on manual tools such as chisels, burrs, osteotomes, drills and mills, which pose the risk of bone fracture and cortical perforation. Others such as ultrasound and laser, generate temperatures that could cause thermal injury to the surrounding tissues and bone. It is crucial to develop techniques that preserve the host bone, as its quality after implant removal affects the outcome of a revision surgery.

A gentler removal method based on the transcutaneous heating of the implant by induction is proposed. By reaching the glass transition temperature (T_G) of the periprosthetic cement, the cement is expected to soften, enabling the implant to be gently pulled out. The in-vivo environment comprises body fluids and elevated temperatures, which deteriorate the inherent mechanical properties of bone cement, including its T_G. We aimed to investigate the effect of fluid absorption on the T_G (ASTM E2716-09) and Vicat softening temperature (VST) (ISO 306) of Palacos R cement (Heraeus Medical GmbH) when dry and after storage in Ringer's solution for up to 8 weeks.

Samples stored in Ringer's solution exhibited lower T_G and VST than those stored in air. After 8 weeks, the T_G decreased from 95.2°C to 81.5°C in the Ringer's group, while the VST decreased from 104.4°C to 91.9°C. These findings will be useful in the ultimate goal of this project which is to design an induction-based system for implant removal.

Acknowledgements: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – SFB/TRR-298-SIIRI – Project-ID 426335750

There is no optimal therapy to stop or cure chondral degeneration in osteoarthritis (OA). Beside cartilage, subchondral bone is involved. The often sclerotic bone is mechanically less solid which in turn influences negatively chondral quality. Microfracturing as therapeutic technique aims to enhance bone quality but is applied only in smaller cartilage lesions. The osteoproliferative properties of Magnesium (Mg) have been shown repeatedly^1-3. The present study examined the influence of micro-scaled Mg cylinders compared to sole drilling in an OA model.

Ten New Zealand White rabbits underwent anterior crucial ligament transection. During 12 weeks after surgery, the animals developed OA as previously described⁴. In a second surgery, half of the animals received 20 drill holes (ø 0.5mm) and the other half received 20 drill holes, which were additionally filled with one Mg cylinder each. Extracapsular plication was performed in all animals. During the follow-up of 8 weeks three µ-computed tomographic (µCT) scans were performed: immediately after surgery and after four and eight weeks. Changes of bone volume, trabecular thickness and bone density were calculated and compared.

µCT evaluation showed an increase in bone volume and trabecular thickness in both groups. This increase was significantly higher in rabbits which received Mg cylinders showing thrice as high values for both parameters (bone volume: Mg group +44.5%, drilling group +15.1%, p≤0.025; trabecular thickness: Mg group +53.2%, drilling group +16.9%, p≤0.025). Also bone density increased in both groups, but on a distinctly lower level and with no significant difference.

Although profound higher bone volume was found after implantation of Mg cylinders, µCT showed similar levels of bone density indicating adequate bone quality in this OA model. Macroscopic and histological evaluation of cartilage condition have to reveal possible impact on OA progression. Additionally, current examination implement different alloys and influence on lameness.

Aim

The aim of this study was to establish an implant-associated osteomyelitis model in rats with the ability to quantify biofilm formation on implants for prospective evaluation of antibacterial effects on micro-structured implant surfaces.

Understanding the cause of failure of total knee arthroplasties (TKA) is essential in guiding clinical decision making and adjusting treatment concepts for revision surgery. The purpose of the study was to determine current mechanisms of failure of TKA and to describe changes and trends in revision surgery over the last 10 years.

A retrospective review was done on all patients who had revision total knee arthroplasty during a 10-year period (2000–2009) at one institution. The preoperative evaluation in conjunction with the intraoperative findings was used to determine causes of failure. All procedures were categorizes as Sharkey et al. described previously. The data was analyzed regarding the cause of failure and displaying the incidence and trends over the last 10 years.

1225 surgeries were done in the time period with a steady increase of procedures per year (34 procedures in 2000 to 196 in 2009). The most common cause of revision TKA was aseptic failure in 65% and septic failure in 31% of the reviewed cases. However, we could observe a steady proportional increase of the septic classified revisions over the time. Both categories could be subdivided to specific causes of failure including aseptic loosening (24%), anterior knee pain (20%), instability (6,4%), arthrofibrosis (4,9%), PE wear (3,6%), malpositioning/malrotation (2,7%) periprosthetic fracture (2,0%) and other (4,6%), or in early (12,9%), late (15,4%) or low-grade infection (3,3%), respectively. Complementary to the classification Sharkey et al. described in 2002 we identified new subcategories of failure: malrotation (since 2003), Low-Grade-Infection (since 2006), allergic failure/loosening (since 2006), Mid-Flexion-Instability (since 2007), soft tissue impingement (since 2009). The incidence of the classic aseptic loosening due to PE wear shows a clear decrease in the last 10 years whereas we could observe an increase of the new diagnosis of instability, malrotation or low-grade-infection as determined cause of failure.

The detailed analysis of the failure mechanism in total knee arthroplasty is important to understand the clinical problem and to adjust treatment strategies. We were able to complement present classifications and give a first overview on the incidence for specific causes of failure. Our data shows changes in the indication for surgery over the time and compared to the collective of Sharkey et al. from 1997–2000. This might be due to new diagnostic methods and better implant materials as well as to a generally increased awareness of the specific mechanism of TKA failure.

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.

Degradable implants made of magnesium alloys as osteosynthesis material for weight-bearing bone are at present a main research area. With regards to biocompatibility, a MA with 0.8 wt.

% Calcium (MgCa(0.8)) has been shown to possess advantageous qualities. Long-term investigations in animal models however, showed that the degradation rate of this magnesium alloy was relatively rapid and therefore the mechanical properties decreased early during the implantation period. An implant for osteosynthesis in weight-bearing bones however needs to exhibit adequate stability during the first few weeks of fracture healing. This cannot sufficiently be assured by the MgCa(0.8) alloy. It has been suggested in the literature, that the degradation rate of MA could be reduced using a fluoride coating. Therefore it was the aim of this study to investigate, whether the coating of degradable MA MgCa(0.8) implants with magnesium fluoride layer leads to decreased degradation rate and in consequence to an improvement of the mechanical properties using an animal model.

Extruded pins (2.5 mm x 25 mm) of MgCa(0.8) were produced. Twenty of these pins were coated with a fluoride layer by submerging the implants in a bath with 40% hydrofluoric acid. With this procedure, the pins were covered with a thin (150–200μm thickness) MgF2 layer. Coated and uncoated pins were intramedullary implanted into both tibiae of ten New Zealand White Rabbits. Three and six months after surgery five animals of each group were euthanized and the tibiae were explanted for further analysis. Micro-computed tomography (μCT) and scanning electron microscopy (SEM) were performed of the explanted pins. In order to investigate changes of the mechanical properties, 3-point bending tests were carried out with MgCa(0.8) pins at the initial state and with the explanted pins, with and without the fluoride layer at both times. In addition, the mass loss of the pins was determined. To evaluate the degradation process of the MgCa(0.8) pins with the MgF2 layer, micrographs and element analyses (EDX) were accomplished after the three point bending tests.

During the investigation period, the rabbits showed no signs of lameness or pain. The MgCa(0.8) alloy and the MgCa(0.8) alloy with the MgF2 layer showed significant differences regarding the mechanical properties in dependence of the implantation duration. Generally, the mechanical resistance decreases with increasing implantation time. The 3-point bending test showed, that the values of maximal force of the coated MgCa(0.8) implants after three month implantation duration were lower than those of the uncoated implants. After an implantation duration of six months, the values of maximal force of the implants coated with MgF2 were higher than those of the uncoated implants. Regarding the implant mass, the coated and uncoated MgCa(0.8) implants showed a loss of mass during the implantation period. The mass loss of the coated implants was only slightly lower. This difference was minor after three months and more obviously after six months. With μCT new endosteal bone formation could be seen close to all implants. A decrease of the cross section dimension could be demonstrated with μCT and SEM and changes of the surfaces due to pitting corrosion could be demonstrated in both the coated and uncoated MgCa(0.8) implants on the whole length, which was more obvious after six months. The micrographs showed corroded surfaces but not preferred corrosion on the grain boundaries. The element analysis showed a degradation layer on the implant surface, which was more bulky on implants after six month implantation duration. The mapping shows, that the fluoride molecules are clearly visible after three and six months around the margin of the implant.

With the results of this study it could be demonstrated, that the coating of the MgCa(0.8) implants with a flouride layer did not have a positive influence on the mechanical properties and the degradation rate of the implant in the bone. This leads to the conclusion that MgF2-coated MgCa(0.8) implants are also not suitable for osteosynthesis in weightbearing bones.

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 ability to evaluate the alignment of total knee arthroplasty using postoperative radiographs might be confounded by limb rotation. The aim of the presented study was therefore to measure the effect of limb rotation on postoperative radiographic assessment and to introduce a mathematical correction to calculate the true axial alignment in cases of a confounded radiograph.

METHODS A synthetic lower left extremity (Sawbones®, Inc,Vashon Island, WA) was used to create a total knee arthroplasty of the Interax I.S.A.® knee prosthesis system (Stryker, Limerick, Ireland). Laser guided measurement of the tibia showed a femoral valgus angle of 6.5° postoperatively. The model was fixed in an upright stand which positioned the limb in varying degrees of rotation. Four series of 10 antero-posterior (AP) radiographs were taken with the knee in full extension, with femoral limb rotation ranging from 20° external rotation to 20° internal rotation in respect to the x-ray beam, in 5° increments. After digitizing each radiograph, four observer independently measured the femoral valgus angle for each series of the long leg radiographs using a digital measurement software (MEDICAD®, Hectec, Altfraunhofen, Germany). Each observer was instructed to determine the femoral valgus angle following the software’s guidelines. In addition each observer measured the geometrical distances of the femoral component figured on the radiographic film. Using a student t-test, the effect of femoral limb rotation on the measured femoral valgus angle and a correlation between femoral rotation and femoral valgus angle was established. Then for each limb rotation the distances ratio was determined to calculate the limb rotation.

RESULTS Without an application of femoral rotation the femoral valgus angle was measured radiographically to be 6.5° (SD 0.4°). With external femoral rotation the measured femoral valgus angle linearly decreased to a minimum of 4.5° (SD 0.2°) at 20° femoral rotation. The linear regression (R2=0.94) calculated a 0.09° change of radiographically measured femoral valgus angle per femoral rotation angle. With the femoral rotation the radiographically measured ratio decreased linearly (R2=0.98) with further internal rotation.

DISCUSSION The results of the presented study suggest a significant influence of femoral rotation during radiographic evaluation of limb alignment after total knee arthroplasty. With further external femoral rotation the radiographically apparent femoral valgus angle decreases. As the apparent femoral valgus angle changes linearly, a calculation of the distances of the particular femoral component could be used to determine the real femoral valgus angle in cases of femoral limb rotation.

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: The long consolidation phase of patients undergoing distraction osteogenesis (DO) causes a high risk of side effects and contributes to high costs. Thus, the development and evaluation of treatments that accelerate the bone consolidation process is of great interest. Evidence suggests that recombinant human bone morphogenetic protein 2 (rhBMP-2) increases the mechanical integrity of the callus. However, the potential benefits of rhBMP-2 on trabecular microarchitecture during DO have not been investigated up to date. In this study the regenerate microarchitecture was assessed using 3D micro-computed tomography (CT).

Methods: Mid-diaphyseal osteotomies were created in the right limb of twenty-four skeletally mature sheep, which were stabilized with an external fixator. After a latency period of 4 days, the tibiae were distracted at a rate of 1.25 mm daily over a period of 20 days. The operated limbs were randomly assigned to three treatment groups and one control group: (A) triple injection of rhBMP-2/NaCl, (B) single injection of rhBMP-2/Hydroxylapatite, and (C) single injection of buffer/Hydroxylapatit, (D) no injection. Groups A and C were injected at day 27. Group B was injected on days 3, 10 and 17. The animals were sacrificed after 74 days. The tibiae were analyzed by CT and for bone volume/total volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th.), trabecular separation (Tb.Sp.) and Connectivity. The BV/TV was maesured for the total volume of the distraction zone (BV/TVtotal) respectively in a subvolume with emphasize on the cortical bone region (BV/TVcortical). All other microarchitecture parameters were measured in the cortical weighted subvolume.

Results: The stereologic evaluation revealed a significant higher BV/TVcortical, Tb.N and Connectivity in the triple rhBMP-2 injected group A than in the control (D). Furthermore, the Tb.Sp. in group A was significant lower than in group D. The single injections of rhBMP-2/carrier in group B showed a significant higher BV/TVcortical, Tb.N and Connectivity than the control (D). Although the BV/TVcortical was increased in group A and B, there was no significant difference in BV/TV total between the rhBMP-2 treated groups (A, B) and the control (D).

Discussion: In this DO model a triple injection of rhBMP-2 has been demonstrated to induce significant changes in trabecular microarchitecture. RhBMP-2 does not increase the total amount of newly formed bone, but it enhances the formation of the corticalis. The microstructural changes in the cortical volume: increase of Tb.N and Connectivity, decrease of Tb.Sp., are discussed to be biomechanically highly relevant. This study suggests that rhBMP-2 optimizes the trabecular microarchitecture, which might explain the advanced mechanical integrity of newly formed bone under rhBMP-2 treatment.

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.