Objectives

Restoring more natural kinematics is crucial for the success of knee TKA. The relative size of the tibia to the femur may differ in each patient and requires the possibility to combine different tibia sizes for a given femur size. Therefore, TKA systems need to be designed to allow for different size combinations. In literature some report higher revision rates when the femoral size is greater than the tibia, while others find no impact of the size mismatch on the clinical outcome. The tibio-femoral kinematics resulting from different size combinations has not been analyzed yet. The Columbus Deep Dish implant (Aesculap, Tuttlingen, Germany) is designed to allow a full size compatibility. Therefore we hypothesized that the kinematics would not be affected by the different size combinations. The goal of this study was to investigate the impact on kinematics of different tibio-femoral size combinations with the Columbus Deep Dish implant.

Introduction

Revision total hip arthroplasty is often associated with acetabular bone defects. In most cases, assessment of such defects is still qualitative and biased by subjective interpretations. Three-dimensional imaging techniques and novel anatomical reconstructions using statistical shape models (SSM) allow a more impartial and quantitative assessment of acetabular bone defects [1]. The objectives of this study are to define five clinically relevant parameters and to assess 50 acetabular bone defects in a quantitative way.

Introduction

It is well-known that wear debris generated by metal-on-metal hip replacements leads to aseptic loosening. This process starts in the local tissue where an inflammatory reaction is induced, followed by an periprosthetic osteolysis. MOM bearings generate particles as well as ions. The influence of both in human bodies is still the subject of debate. For instance hypersensitivity and high blood metal ion levels are under discussion for systemic reactions or pseudotumors around the hip replacement as a local reaction. The exact biopathologic mechanism is still unknown. The aim of this study was to investigate the impact of local injected metal ions and metal particles.

Wear is an important factor in the long term success of total knee arthroplasty. Therefore, wear testing methods and machines become a standard in research and implant development. These methods are based on two simulation concepts which are defined in standards ISO 14243-1 and 14243-3. The difference in both concepts is the control mode. One is force controlled while the other has a displacement controlled concept.

The aim of this study was to compare the mechanical stresses within the different ISO concepts. Furthermore the force controlled ISO was updated in the year 2009 and should be compared with the older which was developed in 2001.

A finite element model based on the different ISO standards was developed. A validation calculated with kinematic profile data of the same implant (Aesculap, Columbus CR) in an experimental wear test setup (Endolap GmbH) was done. Based on this model all three different ISO standards were calculated and analysed.

Validation results showed Pearson correlation for anterior posterior movement of 0.3 and for internal external rotation 0.9. Two main pressure maximums were present in ISO 14243-1:2001 (force controlled) with 17.9 MPa and 13.5 MPa for 13 % and 48 % of the gait cycle. In contrast ISO 14243-1:2009 (force controlled) showed three pressure maximums of 18.5 MPa (13 % of gait cycle), 16.4 MPa (48 % of gait cycle) and 13.2 MPa (75 % of gait cycle). The displacement controlled ISO (14243-3:2014) showed two pressure maximums of 16.0 MPa (13 % of gait cycle) and 17.2 MPa (48 % of gait cycle).

The adapted force controlled ISO of the year 2009 showed higher mechanical stress during gait cycle which also might lead to higher wear rates. The displacement controlled ISO leads to higher mechanical stress because of the constraint at the end of the stance phase of the gait cycle. Future studies should analyse different inlay designs within these ISO standards.

Introduction

Metal on metal bearings are used especially in hip resurfacing. On the one hand, small bone preserving implants can be used. On the other hand recent studies found a variety of local and systemic side effects, for instance the appearance of pseudotumors, that are explained by pathologic biological reaction of the metal wear debris. The detailed mechanisms are still not understood until now. Thus it was the aim of this study to investigate the local reaction of metal wear particles and metal ions in a murine model. The hypothesis was that mainly metal ions provoke adverse histopathological reactions in vivo.

Introduction

The complex process of inflammation and osteolysis due to wear particles still is not understood in detail. So far, Ultra-high-molecular-weight-polyethylene (UHMWPE) is the bearing material of choice in knee arthroplasty and revision knee arthroplasty, but there is a growing demand for alternative bearing materials with improved wear properties. Lately, increasing interest developed in the use of natural and carbon-fiber-reinforced-poly-ether-ether-ketones (CFR-PEEK).

While there is a lack of data concerning the effects of CFR-PEEK particles on human tissue, the effects of such wear debris in vitro and in animal studies is controversially discussed.

The aim of this study was to analyze human tissue containing CFR-PEEK as well as UHMWPE wear debris.

The authors hypothesized no difference between the used biomaterials because of similar size parameters of the wear particles in a prior knee simulator study of this implant.

Introduction

Despite consequent advancement in Total Knee Arthroplasty (TKA) up to 20% of patients are not satisfied after having been operated. Beside correct implantation, the design of the TKA-system is supposed to be a key factor of a successful TKA. Consequently it has been tried to restore natural kinematics by the design of the prosthesis. A medially stabilized design therefore is supposed to allow a lateral translation with a medial pivot.

Introduction

The complex cellular mechanisms of the aseptic loosening of total joint arthroplasties still remain not completely understood in detail. Especially the role of adherent endotoxins in this process remains unclear, as lipopolysaccharides (LPS) are known to be very potent modulators of the cell response on wear particle debris. Contributing factors on the LPS affinity of used orthopedic biomaterials as their surface roughness have to be investigated. The aim of this study was to evaluate the affinity of LPS on the surface roughness of different biomaterials in vitro. The hypothesis of the study was that rough surfaces bind more LPS than smooth surfaces.

A pain free motion of the patella after total knee arthroplasty (TKA) is still a challenge for surgeons and TKA-designers today. After TKA, the restricted guidance of the patella and kinematic alterations of the femorotibial joint results in increased retropatellar pressure and unphysiological patellar tracking. The alignment of the prosthetic components can influence patellofemoral stresses and tracking of the patella. The aim of this study was to demonstrate the consequences of different alignments of the tibial baseplate on patellar stress and knee kinematics.

Different alignments of the tibial baseplate were simulated with five different UHMWPE-Inlets. Inserts with medial and lateral translation (±3mm; Figure 1A) as well as internal and external rotation (±3°; Figure 1B) were manufactured. Original inlays were used to define the neutral position. Eight human knee specimens without TKA were tested in a custom made knee rig. This rig mimics a loaded squat from approximately 20°−120° of flexion under six degrees of freedom in the knee joint. Retropatellar pressure (IScan, Tekscan, USA) as well as knee kinematics (CMS 20, Zebris, Germany) were recorded during squatting. Afterwards, TKA components were implanted in a neutral position via subvastus approach in tibia first technique. Each of the 5 tibial inlets was tested consecutively with the knee rig under the same conditions. Results were compared using mixed effects models with a random intercept per specimen. Component alignment as well as moving direction (flexion/extension) and flexion degree were defined as fixed effects in our model (SPSS, IBM, USA).

After TKA in neutral position, retropatellar peak pressure increased by 0.71MPa (p<0.01), femorotibial rollback was reduced (−2.24mm; p<0.01) and the patella kinematics, in particular patella flexion (−2.02°; p<0.01) and rotation (−0.97°; p<0.01), were changed during squatting. Compared to the neutral position, internal rotation of the tibial baseplate increased retropatellar pressure by 0.20 MPa, while an external rotation provided a reduction of −0.24 MPa (p<0.01). In contrast a medialization or lateralization showed no effect on retropatellar pressure (p=0.09). Both, rotation and translation of the tibial baseplate influenced tibiofemoral kinematics significantly. A reduction of the femorotibial rollback was measured in external alignment (rotation and lateral translation; both p<0.01). An internal rotation showed more femoral rollback (0.93mm p<0.01). Patellar kinematics was changed primarily by component translation rather than rotation. A lateralisation of the tibial baseplate resulted in a medial shift of the patella by −0.43mm and vice versa (p<0.01). Rotation of the tibial baseplate had no influence on the patella shift (p=0.8)

The findings in this study suggest that the alignment of the tibial baseplate influences patellar biomechanics significantly in vitro. An external rotation of the tibial baseplate decreased retropatellar pressure and patella kinematics tend more to the in situ situation of a natural knee. An internal alignment of the tibial baseplate seems to reconstruct natural tibiofemoral rollback in parts. However, studies (i.e. Nicoll et al.) show higher anterior knee pain by an internal alignment and a higher rollback after TKA might lead to higher wear.

Summary Statement

To evaluate carbon-fiber-reinforced PEEK as alternative biomaterial for total disc arthroplasty a closed loop between biotribology (in vitro), application of sterile particle suspensions in the epidural space of rabbits and biological response in vivo was established.

Common cell based strategies for treating bone defects require time-consuming and expensive isolation and expansion of autologous cells. We developed a novel expedited technology creating gene activated muscle grafts. We hypothesized that BMP-2 activated muscle grafts provide healing capabilities comparable to autologous bone grafting, the clinical gold standard.

Two male, syngeneic Fischer 344 rats served as tissue donors. Muscle tissue was harvested from hind limbs and incubated with an adenoviral vector carrying the cDNA encoding BMP-2. Bone tissue was harvested from the iliac crest. Segmental bone defects were created in the right femora of 12 rats and were filled with either BMP-2 activated muscle tissue or bone grafts. After 8 weeks, femora were evaluated by radiographs, microCT, and biomechanical tests.

BMP-2 activated muscle grafts and autologous bone grafts resulted in complete mineralization and healing, as documented by radiographs and microCT. Bone volume in the muscle graft defects (33+/-12mm3) was similar to autologous bone graft defects (39+/-5mm3). Torque at failure of the two groups was statistically indistinguishable (240+/-115 Nmm vs. 232+/-108Nmm).

In previous experiments we demonstrated that the large segmental defect model in this study will not heal with either empty defects or non-activated muscle grafts. Our findings therefore demonstrate that BMP-2 gene activation of muscle tissue effectively stimulates defect healing similar to autologous bone grafts.

Periprosthetic osteolysis depends on the biological activity of wear particles, but there is little known about the distribution of polyethylene wear particles (PE) in the surrounding joint tissue. The purpose of this study was to examine the localisation of wear particles of six different PEs, including four crosslinked polyethylenes (XPE), as well as their biological activity in the murine knee.

Introduction

Minimally invasive implanted unicompartmental knee arthroplasty (UKA) leads to excellent functional results. Due to the reduced intraoperative visibility it is difficult to remove extruded bone cement particles, as well as bone particles generated through the sawing. These loose third body particles are frequently found in minimally invasive implanted UKA.

The aim of this study was to analyse the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro.

Introduction

Unicompartmental knee arthroplasty (UKA) in patients with isolated medial osteoarthritis of the knee is nowadays a standard procedure with good results, especially with the minimally-invasive approach. However, the survival rate of the unicompartmental knee prostheses is inferior to that of total knee prostheses. Therefore, further studying of UKA is still necessary. In most mobile bearing designs the femoral component has a spherical surface and therefore its positioning is not crucial. The role of the tibial slope in UKA has not been investigated so far. The manufacturers recommend tibial slopes with values between 10° positive slope and 5° negative slope. Most surgeons try to reconstruct the anatomical slope with a high failure by measuring the slope on x-rays. The aim of this study was to investigate the influence of the tibial slope on the wear rate of a medial UKA.

Objectives: The aim of this study was a clinical and radiological evaluation of 68 shoulders operated with the Delta reverse-ball-and-socket total shoulder prosthesis by the senior author with a mean follow-up of 42 months.

Methods: This is a retrospective study in one consecutive series of 68 shoulders, operated by the senior author, which were clinically assessed using the Constant score for pain, Constant Shoulder Score, Oxford Shoulder Score, UCLA Shoulder rating scale, DASH Score, Rowe Score for Instability and Oxford Instability Score. Radiological evaluation was graded by the classification according to Nerot et al. and complications were analysed according to Goslings and Gouma. Patients were evaluated before surgery and at a mean clinical follow-up of 42 months.

Results: There was a significant improvement in all clinical and stability scores. On the average, the Constant score for pain increased from 4.62 to 11.08 points (p< 0.05); the Constant Shoulder Score from 32.65 to 60.31 (p> 0.05); the Oxford Shoulder Score increased from 32.65 to 60.31 (p< 0.05) and the UCLA Shoulder rating scale increased from 15.08 to 27.42 (p< 0.05). The evaluation of stability showed an increase from 49.42 to 80.19 points in the Rowe Score for Instability and from 22.04 to 37.62 in the Oxford Instability score (p< 0.05). According to the Nerot classification, 65 percent of patients were graded as “0”, 20 percent as “1”, 3 percent as “2”, 6 percent as “3” and 6 percent as “4”. Eight complications occurred in terms of a nerve lesion which was graded according to Goslings and Gouma as “1” once, loosening of the humeral stem which was graded as “2” three times and loosening or fracture of the glenoid component which was graded as “2” in five times. At mean follow-up of 42 months, one patient of this series had died of decrepitude which was graded as “4” and one patient was lost of follow-up.

Conclusions: We summarize, that there were significant advantages identified in terms of the Constant score for pain, all clinical scores and the instability scores. Radiological analyses showed 85 percent of patients without or with a small notch only. On the other hand, the rate of complications should be taken into account. We conclude that shoulder arthroplasty with the Delta prosthesis shows significant benefits in terms of less shoulder pain, a higher stability and a gain of range of motion but on the other hand, we emphasize that this treatment remains a salvage procedure in the elderly only.

In recent years UHMWP sutures have gained more and more popularity in shoulder surgery. They have an increased tensile strength but were shown to have a higher rate of knot slippage due to their smooth surface. There exist different testing protocols on suture testing in dry or in wet conditions.

The purpose of this study was to gain some inside as to whether or not the knot security of sliding and non-sliding knots with different suture materials is influenced by dry or wet testing conditions.

We tested five common suture materials, all of them USP #2. The PDSII, the Ethibond and three ultra high molecular weight polyethylene (UHMWPE) sutures: Fiber Wire, Orthocord and Herculine. As non-sliding knots we used Square knot and Revo knot and for sliding knots we used Fisherman and Roeder knot. 10 samples of each knot type were tested. In the first group knot tying and biomechanical testing were performed under dry conditions. In the second group the sutures were soaked in saline solution for 3 min. before knot tying and afterwards tested in saline bath. Cyclic loading was performed to simulate the physiological conditions. We started with a tensile load of 25 N. After 100 cycles, the load was increased to 50 N for another 100 cycles. Until suture rupture or knot slippage of 3 mm the tensile load was gradually increased by 25 N per 100 cycles. Under dry conditions 170 suture ruptures and 30 knot slippages were recorded. Under wet testing conditions 186 suture ruptures and 14 knot slippages were seen, which tested statistically significant. Failure by knot slippage (n=44) was seen under dry and saline testing conditions mainly with UHMWPE sutures particularly with Herculine suture. Knot slippage occured only with sliding knots. With the Ethibond suture no knot slippage was found regardless of the testing conditions and applied knot type. Across all knot types the UHMPE-sutures were significantly stronger in ultimate load to failure than Ethibond and PDSII under dry and wet testing conditions.

Is the information we get from testing dry suture material reliable and helpful for our daily practice? Our study clearly showed: No! The mode of failure and the number of knot-failure differs significantly in wet testing conditions compared to dry testing. We found that the number of knot-failures is higher when tested with dry sutures than in wet testing conditions. The soaking of the suture material with fluid improves its “skid-resistance”. As we expected showed the UHMWP sutures with their smooth surface a high number of knot-failures compared to polyethylen suture Ethibond, which did not show a single knot-failure in dry or wet tesing conditions. The maximum failure load showed clearly the superiority of the new UHMWP suture material, with around 300 N being double as high as for polyethylen and polydioxone sutures.

The incidence of rotator cuff tears increases with age, thus the rotator cuff tear is often associated with osteoporotic or osteopenic bone in the proximal humerus, especially with female patients. For testing of fixation devices such as suture anchors used in rotator cuff repair often animal bones are used. They are easily to obtain, inexpensive and some have been found to be similar to human bone. But can we rely on the results drawn from these studies in our daily surgical practice?

The purpose of this study was to compare the trabecular bone mineral density, the trabecular bone volume fraction and the cortical layer thicknes in the greater tubercle in different species to evaluate their infiuence on primary stability of suture anchors under a cyclic loading protocol representing the physiologic forces placed on rotator cuff repairs in vivo. We hypothezised that maximum pullout forces as well as the modes of failure are different for a suture anchors in different humeri. The available three different types of anchor fixation design (screw: Spiralok 5mm, Super Revo 5mm, press-fit: Bioknotless RC, wedging: Ultrasorb) were tested. The bone mineral density (BMD) of the humeri was measured by a 64-slice-computed tomography system. Each anchor was tested individually until failure. The sutures were pulled at 135° to the axis of the humeral shaft, simulating the physiological pull of the supraspinatus tendon. Starting with 75 N the tensile load was gradually increased by 25 N after everey 50 cycles until failure of the anchor fixation system occurred. The ultimate failure load, the system displacement after the first pull with 75 N and the mode of failure were recorded.

The ultimate failure loads of each anchor were different in the human osteopenic, human healthy, ovine and bovine humeri. The statistical significancies for pull out forces between the anchors varied from species to species. The biomechanical testing of suture anchors for arthroscopic rotator cuff repair in ovine and bovine humeri does not give reliable data that can be transferred to the human situation. The significances between the suture anchors found in ovine and bovine humeri are different from the results in human humeri. When taking the impaired bone quality of older patients into account the results from ovine and bovine humeri are even less predictable. We found a positive correlation between maximum failure load and cortical layer thickness for the Super Revo and the Ultrasorb anchor. The ultimate failure load seems to depend mainly on the cortical thickness and on the subcortical trabecular bone quality.

Crosslinked polyethylene (XPE) was developed to reduce wear in hip and knee arthroplasty. Periprosthetic osteolysis depends on many factors including biological activity of wear particles. This study examines the relative inflammatory effect of different crosslinked polyethylenes compared to ultra-high-molecular-weight-polyethylene (UHMWPE) particles in vivo.

Materials and Methods: Wear particles of 3 XPE- (1 sequential irradiated/annealed; 2 remelted inserts) and 1 UHMWPE-insert were isolated from a knee joint simulator (20nm-nucleopore-filter;acid digestion method;ISO). Particles were analysed by scanning electron microscopy (n=66000). For all groups the particles were smooth, granular, irregular and less fibrillar. More than 85% of the particles were submicron. After removal of endotoxin the particles were suspended in a phosphate buffered saline solution (0.1% vol/vol (particle volume/PBS volume)). Endotoxin levels were controlled using standardised endotoxin detection tests (Lonza) in all samples.

40 female Balb/c mice were randomly assigned to one of five treatment groups (according to the national guidelines of animal protection laws): control (n=8); XPE1 (95 kGy E-beam, remelted; n=8); XPE2 (65 kGy E-beam, remelted; n=8), XPE3 (3x30 kGy Gamma, annealed and sequential irradiated; n=8) and UHMWPE particles (n=8). 50 μl of the particle suspension were injected into the murine left knee under sterile conditions. The leukocyte–endothelial cell interactions and the synovial microcirculation were performed by intra-vital fluorescence microscopy one week after particle injection to assess the inflammatory reaction to the particles (by measuring the rolling fraction of leukocytes, the adherent cells and the functional capillary density (FCD)). Data analysis was performed using a computer-assisted microcirculation analysis system (Cap-Image).

For the statistical analysis the Kruskal-Wallis test was used to determine differences within the groups, followed by an all pairwise multiple comparison procedure with a Bonferoni correction. The level of significance was set at p< 0.05.

Results: The fraction of the rolling leukocytes, adherent cells and FCD increased significantly (p< 0.05) in all bio-materials compared to control group. However, there was no significant difference between the UHMWPE and the XPE particle groups (p> 0.05).

Conclusion: Our data suggest that crosslinked polyethylene wear particles do not lead to a higher inflammatory reaction in vivo compared to UHMWPE particles.

Introduction: Knotless Suture Anchors provide numerous advantages in arthroscopic rotator-cuff (RC) repair such as, reducing the difficulties of knot tying, reducing surgical exposure, thus decreasing morbidity. The purpose of this in-vitro study was to compare the pull-out strength of three new knotless suture anchors in correlation with bone quality using the following anchors: Opus Magnum 2 -ArthroCare Co., USA; Push Lock and Swivel Lock -Arthrex Inc., USA.

Material & Methods: Ten healthy and ten osteopenic macroscopically intact humeri with an average age of 51.7 and 79.5 years, respectively, were loaded with the three knotless suture anchors according to the manufacturers’ description. The healthy humeri had a mean trabecular BMD of 152.77 mgCa-HA/ml. The osteopenic humeri had a mean trabecular bone mineral density of 54.02 mgCa-HA/ml. The humeri were positioned in a custom - engineered adjustable fixation device, stabilising the direction of the pull of the sutures at an angle of 135° to the axis of the humeral shaft (Universal testing device Z010/TN2A – Zwick GmbH, Ulm, Germany). The anchors were cyclically loaded to simulate postoperative conditions.

The ultimate pull-out strenngth, the initial displacement in millimeters after the first pull with 75 N and the modes of failure were recorded.

Results: The mean ultimate failure loads of the Opus Magnum 2, PushLock and SwiveLock anchors in osteopenic humeri were 135.0, 102.5 and 130.0 N (p> 0.05), respectively, and in healthy humeri 142.5 N, 182.5 N and 202.5 N (p> 0.05), respectively. The initial system displacement in osteopenic humeri of the Opus Magnum 2, PushLock and SwiveLock anchors were 3.53 mm, 16.11 mm and 3.23 mm (p< 0.01), respectively, and in healthy humeri 3.71 mm, 1.98 mm, and 1.96 mm (p> 0.05), respectively.

Discussion: The results of this study show that in osteopenic humeri, the Opus Magnum 2 and SwiveLock anchors display significant superiority in system displacement with an initial pull of 75N compared to the PushLock anchor in osteopenic bone, but all three anchors fail to provide significance in the ultimate failure load. PushLock anchor might cause a greater gap formation between the RC-tendon and greater tubercle interface in osteopenic humeri due to inferior gripping and therefore should not be used solely for RC repair. Due to a manufacturing flaw the suture holding fixture of the Opus Magnum 2 anchor “breaks” when a mean force of 138.75 N is applied to the system, regardless of the bone quality, thus disabling the anchor to unfold it’s properties in healthy bone. Whereas the results in osteopenic bone are comparable to the other two anchors. SwiveLock provides the best support of all three anchors in healthy humeri.

Background: In regenerative medicine the autologous cartilage implantation (ACI) has been used for the repair of cartilage defects. As modification of ACI, the matrix assisted ACI is used nowadays with varying results. There is a general discussion about whether supporting scaffolds should be used or whether a scaffold-free cartilage repair is the method of choice. The major problem of scaffold-free regenerates is how to keep the cells in place after transplantation. Aim of this study was to examine a new scaffold-free diffusion-culture model, which uses a mega-congregate of chondrocytes cultured at an air-medium interface. This scaffold-free high-density diffusion culture could be used to repair cartilage defects.

Material and methods: Human chondrocytes from passage 1–7 were expanded in monolayer and transferred to pellet-culture or diffusion-culture. After one week cultures were stained with toluidine blue and safranin-O and evaluated by immunohistochemical staining for type II collagen. Quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) was performed for the mRNAs of cartilage markers.

Results: Positive alcian blue staining was detectable in diffusion-culture for human chondrocytes up to passage 7. Within passages the amount of proteoglycan production in relationship to the number of cells increased. There was a positive signal for Collagen type II in diffusion-cultures up to passage 7.

In qRT-PCR a redifferentiation of human chondrocytes was shown by the transfer into diffusion-culture. Within passage 1 to 3 human chondrocytes which were cultured in monolayer lost the ability to express Collagen Type II but could regain it if they were transferred to diffusion-culture. At diffusion-culture chondrocytes showed the highest expression of Collagen type II at passage 1 when compared to monolayer or to pellet-culture.

Conclusion: It could be shown that the cultivation in a scaffold-free diffusion-culture can lead to redifferentiation of human chondrocytes Chondrocytes in diffusion-cultures tend to form their own matrix and produce Collagen type II at higher amounts than in monolayer or in normal pellet-cultures. Therefore diffusion-culture congregates might be an appropriate tool to be used for a new scaffold-free cartilage regeneration approach.