Primary bone graft stability after Latarjet surgery: biomechanical evaluation of a fixation technique with metal-free all-suture cerclage vs. cortical screws.

BACKGROUND: To reduce hardware-related complications in coracoid graft fixation to the anterior aspect of the glenoid, a metal-free Latarjet technique was recently introduced. The aim of this study was to compare the primary stability of a classic Latarjet procedure with 2 metal screws to a novel metal-free, all-suture cerclage method. It is hypothesized that fixation of the coracoid graft with 2 malleolar screws will provide higher primary stability compared with an all-suture cerclage technique. METHODS: This biomechanical in vitro study was conducted on 12 fresh-frozen cadaveric shoulders (6 matched pairs) with a mean donor age of 80 years (range, 67-89 years). Coracoid graft fixation was performed using a recently introduced all-suture cerclage technique (group A) or a classic Latarjet technique with two 4.5-mm malleolar screws (group B). The conjoint tendon was loaded with a static force of 10 N to simulate the sling effect. Graft loading with a probe head consisted of 6 ascending load levels (10-50 N, 10-100 N, 10-150 N, 10-200 N, 10-250 N, and 10-300 N) with 100 cycles each at 1 Hz. Relative motion of the bone graft to the glenoid was measured using an optic 3-dimensional system. RESULTS: While loading the conjoint tendon with 10 N, no difference in mean displacement of the bone-graft was found between both groups (P = .144). During cyclic loading, a significant difference in relative displacement for both groups was already detected in load level 1 (group A: 2398.8 µm vs. group B: 125.7 µm; P = .024), and this trend continued with the following load levels (P < .05). DISCUSSION AND CONCLUSION: The study demonstrated that the innovative metal-free, all-suture cerclage fixation technique results in higher micromotion than the classic coracoid graft fixation with 2 malleolar screws. According to the present biomechanical investigation, shoulders treated with a metal-free all-suture cerclage technique might need adapted rehabilitation protocols to protect the construct and allow for graft healing.

Is TKA femoral implant stability improved by pressure applied cement? a comparison of 2 cementing techniques.

BACKGROUND: The majority of knee endoprostheses are cemented. In an earlier study the effects of different cementing techniques on cement penetration were evaluated using a Sawbone model. In this study we used a human cadaver model to study the effect of different cementing techniques on relative motion between the implant and the femoral shaft component under dynamic loading. METHODS: Two different cementing techniques were tested in a group of 15 pairs of human fresh frozen legs. In one group a conventional cementation technique was used and, in another group, cementation was done using a pressurizing technique. Under dynamic loading that simulated real life conditions relative motion at the bone-implant interface were studied at 20 degrees and 50 degrees flexion. RESULTS: In both scenarios, the relative motion anterior was significantly increased by pressure application. Distally, it was the same with higher loads. No significant difference could be measured posteriorly at 20°. At 50° flexion, however, pressurization reduced the posterior relative motion significantly at each load level. CONCLUSION: The use of the pressurizer does not improve the overall fixation compared to an adequate manual cement application. The change depends on the loading, flexion angle and varies in its proportion in between the interface zones.

[Tribology in hip arthroplasty : Benefits of different materials]. / Tribologie in der Hüftendoprothetik : Welches Material hat welchen Nutzen?

When it comes to total hip replacements, choosing the suitable material combination is of clinical relevance. The present review article examines the technical differences in wear and corrosion of the relevant material combinations of ceramics, metals, ceramized metals and various types of polyethylene. The material characteristics, which were often tested under standardized conditions in the laboratory, are compared with clinical results on the basis of evidence-graded clinical studies and on the basis of register studies. This article thus represents an up-to-date snapshot of the expectations and actual clinical outcomes of the present choice of material combinations. It shows that some tendencies from the field of materials research, e.g. with regard to cross-linked polyethylene, coincide with observations from practical clinical experience, while for other materials, a proven technical superiority has not yet been confirmed as an evident advantage in clinical practice.

Bone morphogenetic proteins - 7 and - 2 in the treatment of delayed osseous union secondary to bacterial osteitis in a rat model.

BACKGROUND: Bone infections due to trauma and subsequent delayed or impaired fracture healing represent a great challenge in orthopedics and trauma surgery. The prevalence of such bacterial infection-related types of delayed non-union is high in complex fractures, particularly in open fractures with additional extensive soft-tissue damage. The aim of this study was to establish a rat model of delayed osseous union secondary to bacterial osteitis and investigate the impact of rhBMP-7 and rhBMP-2 on fracture healing in the situation of an ongoing infection. METHODS: After randomization to four groups 72 Sprague-Dawley rats underwent a transverse fracture of the midshaft tibia stabilized by intramedullary titanium K-wires. Three groups received an intramedullary inoculation with Staphylococcus aureus (103 colony-forming units) before stabilization and the group without bacteria inoculation served as healing control. After 5 weeks, a second surgery was performed with irrigation of the medullary canal and local rhBMP-7 and rhBMP-2 treatment whereas control group and infected control group received sterile saline. After further 5 weeks rats were sacrificed and underwent biomechanical testing to assess the mechanical stability of the fractured bone. Additional micro-CT analysis, histological, and histomorphometric analysis were done to evaluate bone consolidation or delayed union, respectively, and to quantify callus formation and the mineralized area of the callus. RESULTS: Biomechanical testing showed a significantly higher fracture torque in the non-infected control group and the infected rhBMP-7- and rhBMP-2 group compared with the infected control group (p < 0.001). RhBMP-7 and rhBMP-2 groups did not show statistically significant differences (p = 0.57). Histological findings supported improved bone-healing after rhBMP treatment but quantitative micro-CT and histomorphometric results still showed significantly more hypertrophic callus tissue in all three infected groups compared to the non-infected group. Results from a semiquantitative bone-healing-score revealed best bone-healing in the non-infected control group. The expected chronic infection was confirmed in all infected groups. CONCLUSIONS: In delayed bone healing secondary to infection rhBMP treatment promotes bone healing with no significant differences in the healing efficacy of rhBMP-2 and rhBMP-7 being noted. Further new therapeutic bone substitutes should be analyzed with the present rat model for delayed osseous union secondary to bacterial osteitis.

Mixing of Head-Stem Components in Total Hip Arthroplasty.

BACKGROUND: Implant manufacturers proclaim that the tapers of modular total hip arthroplasty are not standardized and can vary from manufacturer to manufacturer. That is why the combination of various components from different manufacturers ("Mix and Match") is not permitted. In this study, different taper combinations were investigated experimentally to assess the effect of "Mix and Match" regarding the taper connection strength. METHODS: Torque-off tests using hip stems and metal femoral heads from 6 different implant manufacturers were performed. First the components were tested as intended and afterwards the stems were combined with metal heads from other manufacturers. RESULTS: There was no significant difference in taper connection strength when stems from the manufacturers Link, Smith & Nephew, and Zimmer were combined with heads from other manufacturers. The Biomet stems showed a significantly reduced taper connection strength if femoral heads of Aesculap, DePuy, or Smith & Nephew were used. On the contrary, the DePuy stems in combination with the originally intended femoral heads showed a significantly lower taper connection strength compared to the use of heads from Link, Biomet, and Zimmer. The same was observed for the Aesculap stems in combination with Zimmer heads. CONCLUSION: The results of this study suggest that mixing components from different manufacturers may affect the taper connection strength and could reduce the stability. As safety should be a high priority in patient treatment, any potential risks should be avoided. Therefore, mixing and matching of heads and femoral stems from different manufacturers cannot be recommended.

Surface and form alterations in retrieved shoulder hemiarthroplasty.

BACKGROUND: Shoulder hemiarthroplasty is a viable treatment for shoulder arthritis, particularly if the natural glenoid is still intact. One of the most common reasons for revision surgery is glenoid erosion, where the cartilage or bone is worn. The aim of the current study was to analyze whether the metallic articular surface of retrieved shoulder hemiarthroplasty is different from new implants. We hypothesized that the surface roughness would increase as a result of the articulation and that metallic wear would be detectable on the implants. METHODS: Included were 13 retrieved and 3 new shoulder hemiarthroplasties. The surface roughness was measured on different sites of the surface (dome of the head and the rim). The implants were further measured using a coordinate measuring machine to gain information on volumetric wear and geometric alterations. The surface was analyzed with a scanning electron microscope to see marks of wear. RESULTS: Compared with new implants, the surface roughness on the retrievals was significantly increased. The roughness parameters within the retrieval group were generally higher at the dome of the head than at the rim; however, this difference was not significant. Apart from shape deviations caused by deformation of the retrievals, no volumetric wear was detectable on the heads. CONCLUSIONS: The current results indicate that the roughness of the surface of the implant and the shape changes occur in vivo and that the material incurs damaged caused by the articulation against the softer cartilage or bone. Increasing roughness of the humeral component may be one cause for glenoid erosion over time.

Same Same but Different? 12/14 Stem and Head Tapers in Total Hip Arthroplasty.

BACKGROUND: Taper corrosion has been identified to be a major concern in total hip arthroplasty during the past years. So far, the mechanisms that lead to taper corrosion in modular taper junctions are not fully understood. However, it has been shown that corrosion is also influenced by the geometry and topography of the taper, and these parameters vary among the implant manufacturers. The purpose of this study was to investigate the variations of common stem and head tapers regarding design and surface characteristics. METHODS: An analysis of selected commercially available 12/14 stem and head tapers was performed. As geometric parameters, the taper angle, the opening taper diameter, and the taper length were measured using a coordinate measuring machine. Several topographic parameters were determined using a tactile roughness measurement instrument. RESULTS: Although all investigated tapers are so-called 12/14 tapers, this study showed that the stem and head tapers differ among the manufacturers. The stem tapers were clearly different in both geometry and topography, and the range in variation of the topographic parameter was greater than it was for the geometric parameter. In contrast, the head tapers were different in their geometry, although not in topography. CONCLUSION: Ultimately, this study provides an overview on the characteristics and variations of modular hip taper connections, and in addition, a new classification system regarding the surface finish is presented. These findings could be further considered in experimental corrosion or retrieval studies.

Long-term durability of alumina ceramic heads in THA.

BACKGROUND: The optimal type of bearing for hip arthroplasty remains a matter of debate. Ceramic-on-polyethylene (CoP) bearings are frequently used in younger and more active patients to reduce wear and increase biocompatibility compared to Metal-on-Polyethylene (MoP) bearings. However, in comparison to metal heads, the fracture risk of ceramic heads is higher. In addition, ceramic head fractures pose a serious complication which often necessitates major revision surgery. To date, there are no long-term data (>20 years of follow-up) reporting fracture rates of the ceramic femoral heads in CoP bearings. The purpose of this research was to investigate long-term CoP fracture rate. METHODS: We evaluated the clinical and radiographic results of 348 cementless THAs treated with 2nd generation Biolox Al2O3 Ceramic-on-Polyethylene (CoP) bearings consecutively implanted between January 1985 and December 1989. The mean age at implantation was 57 years. The patients were followed for a minimum of 20 years. At the final 111 had died, and 5 were lost to follow-up. The cumulative incidence of ceramic head fractures in the long-term was estimated using a competing risk analysis. RESULTS: The cumulative incidence of ceramic head fracture after 22-years was estimated with a competing risk analysis at 0.29% after 22-years (SE = 2.09%; 95% - CI: 0.03-1.5%). The radiographic analysis revealed no impending failures at final follow-up. DISCUSSION/CONCLUSION: The fracture rate of second-generation ceramic heads using a CoP articulation remains very low into the third decade after cementless THA.

Cortical hypertrophy with a short, curved uncemented hip stem does not have any clinical impact during early follow-up.

BACKGROUND: Short stems have become more and more popular for cementless total hip arthroplasty in the past few years. While conventional, uncemented straight stems for primary total hip arthroplasty (THA) have shown high survival rates in the long term, it is not known whether uncemented short stems represent a reasonable alternative. As cortical hypertrophy has been reported for short stems, the aim of this study was to determine the radiographic prevalence of cortical hypertrophy and to assess the clinical outcome of a frequently used short, curved hip stem. METHODS: We retrospectively studied the clinical and radiographic results of our first 100 consecutive THAs (97 patients) using the Fitmore® hip stem. Mean age at the time of index arthroplasty was 59 years (range, 19 - 79 years). Clinical outcome and radiographic results were assessed with a minimum follow-up of 2 years, and Kaplan-Meier survivorship analysis was used to estimate survival for different endpoints. RESULTS: After a mean follow-up of 3.3 years (range, 2.0 - 4.4 years), two patients (two hips) had died, and three patients (four hips) were lost to follow-up. Kaplan-Meier analysis estimated a survival rate of 100 % at 3.8 years, with revision for any reason as the endpoint. No femoral component showed radiographic signs of loosening. No osteolysis was detected. Cortical hypertrophy was found in 50 hips (63 %), predominantly in Gruen zone 3 and 5. In the cortical hypertrophy group, two patients (two hips; 4 %) reported some thigh pain in combination with pain over the greater trochanter region during physical exercise (UCLA Score 6 and 7). There was no significant difference concerning the clinical outcome between the cortical hypertrophy and no cortical hypertrophy group. CONCLUSIONS: The survival rate and both clinical and the radiographic outcome confirm the encouraging results for short, curved uncemented stems. Postoperative radiographs frequently displayed cortical hypertrophy but it had no significant effect on the clinical outcome in the early follow-up. Further clinical and radiographic follow-up is necessary to detect possible adverse, long-term, clinical effects of cortical hypertrophy.

The protective effect of pulsed lavage against implant subsidence and micromotion for cemented tibial unicompartmental knee components: an experimental cadaver study.

Cemented UKAs were performed in 12 pairs of human cadaver legs and the bone bed was cleansed using pulsed lavage (group A) and conventional syringe lavage (group B). Subsidence and micromotion of the loaded tibial trays were measured. There was a significant effect of BMD on subsidence (P = 0.043) but not on micromotion. Cement penetration of group A was significantly increased (P = 0.005). Group A showed a reduced implant subsidence (P = 0.025) and micromotion (P = 0.026) compared to group B. The group differences in micromotion and implant subsidence of UKA tibial components were statistically significant but rather small and might clinically be of minor importance. Nevertheless a worse bone quality adversely affected implant subsidence and pulsed lavage had a protective effect in these specimens.

Primary stability of the Fitmore stem: biomechanical comparison.

PURPOSE: After clinical introduction of the Fitmore stem (Zimmer), we noticed the formation of cortical hypertrophies in a few cases. We questioned whether (1) the primary stability or (2) load transfer of the Fitmore stem differs from other stems unassociated with the formation of hypertrophies. We compared the Fitmore stem to the well-established CLS stem. METHODS: Four Fitmore and four CLS stems were implanted in eight synthetic femurs. A cyclic torque around the stem axis and a mediolateral cyclic torque were applied. Micromotions between stems and femurs were measured to classify the specific rotational implant stability and to analyse the bending behaviour of the stem. RESULTS: No statistical differences were found between the two stem designs with respect to their rotational stability (p = 0.82). For both stems, a proximal fixation was found. However, for the mediolateral bending behavior, we observed a significantly (p < 0.01) higher flexibility of the CLS stem compared to the Fitmore stem. CONCLUSION: Hip stem implantation may induce remodelling of the periprosthetic bone structure. Considering the proximal fixation of both stems, rotational stability of the Fitmore® stem might not be a plausible explanation for clinically observed formation of hypertrophies. However, bending results support our hypothesis that the CLS stem presumably closely follows the bending of the bone, whereas the shorter Fitmore stem acts more rigidly. Stem rigidity and flexibility needs to be considered, as they may influence the load transfer at the implant-bone interface and thus possibly affect bone remodelling processes.

10-year results of the uncemented Allofit press-fit cup in young patients.

BACKGROUND AND PURPOSE: Uncemented acetabular components in primary total hip arthroplasty (THA) are commonly used today, but few studies have evaluated their survival into the second decade in young and active patients. We report on a minimum 10-year follow-up of an uncemented press-fit acetabular component that is still in clinical use. METHODS: We examined the clinical and radiographic results of our first 121 consecutive cementless THAs using a cementless, grit-blasted, non-porous, titanium alloy press-fit cup (Allofit; Zimmer Inc., Warsaw, IN) without additional screw fixation in 116 patients. Mean age at surgery was 51 (21-60) years. Mean time of follow-up evaluation was 11 (10-12) years. RESULTS: At final follow-up, 8 patients had died (8 hips), and 1 patient (1 hip) was lost to follow-up. 3 hips in 3 patients had undergone acetabular revision, 2 for deep infection and 1 for aseptic acetabular loosening. There were no impending revisions at the most recent follow-up. We did not detect periacetabular osteolysis or loosening on plain radiographs in those hips that were evaluated radiographically (n = 90; 83% of the hips available at a minimum of 10 years). Kaplan-Meier survival analysis using revision of the acetabular component for any reason (including isolated inlay revisions) as endpoint estimated the 11-year survival rate at 98% (95% CI: 92-99). INTERPRETATION: Uncemented acetabular fixation using the Allofit press-fit cup without additional screws was excellent into early in the second decade in this young and active patient cohort. The rate of complications related to the liner and to osteolysis was low.

Is taper corrosion in modular revision hip stem junctions associated with patient or implant specific factors? A retrieval analysis.

Implant modularity within revision total hip arthroplasty (THA) offers multiple implant configurations and allows surgeons a high intraoperative flexibility to restore functionality to the patients joint, even in complex revision cases. However, a rare but devastating complication for patients, clinicians and manufacturers presenting a breakage of the taper junction between the distal stem and the proximal implant part. Aside from implant and patient specific risk factors, corrosion and fretting at the stem junctions have been associated with taper failure. Whether corrosive processes are a precursor of failure or rather an accompaniment of material fatigue is thereby still unclear. Therefore, this study aims to investigate the incidence of taper corrosion in a collection of 17 retrievals from a single type (MRP-Titan, Peter Brehm GmbH) and on the correlation of taper corrosion to implant and patient specific factors. None of the implants was revised for problems related to the taper junction, corrosion or the implant itself. The modular stem junction of all retrievals was visually rated with respect to corrosion, fretting and surface contamination. Additionally, the stability of taper junctions of retrievals where the proximal part with the neck was still assembled to the stem was determined by measuring the loosening moment of the securing screw and the push-out-force for taper dissociation. There was no difference between the mean push-out-force of the retrievals (14 kN ± 1.2 kN) and new reference samples (12.6 kN ± 0.5 kN). Approximately one third of the investigated retrievals showed considerable taper corrosion. The extent of corrosion increased with time in vivo and contamination of the neck piece, while it decreased with the loosening moment of the locking screw. The parameters femoral head offset, neck piece length, lateralized neck pieces, obesity of patients and septic/aseptic revision were not correlated to taper corrosion. Taper corrosion seems to occur regularly in modular taper junctions and is not necessarily connected to taper failure. A correct assembly of the junction and avoiding taper surface contamination during revision surgery is mandatory.

Capsule elongation occurs after first time shoulder dislocation A biomechanical in-vitro investigation on human cadaveric specimen.

Purpose: As capsule elongation is assumed to weaken the static stability of the shoulder joint, the purpose of this biomechanical study was to demonstrate that capsule elongation occurs immediately after a first-time shoulder dislocation and not just after recurrent dislocation events. We hypothesize an increment in joint clearance due to joint capsule elongation after a first-time dislocation. Methods: An experimental in-vitro study was conducted on 6 paired fresh frozen human shoulders (4 females; 2 males; 12 specimen) with a mean age of 80 (Range 67-89) years. The shoulder joint with the articular capsule was exposed and an inferior static tension force of 2.5 N was applied to the humerus prior to dislocation. Next, the humeral head was dislocated and was then immediately reduced back into the start position. The joint gap as well as joint capsule deformation was assessed using optical techniques. Results: The radiographic joint gap increased from 13.7 ± 6.9 mm (prior to dislocation) to 18.1 ± 6.5 mm (post dislocation) (p < .001). The increase in joint clearance was 4.4 mm. The joint capsule elongated from 5.9 ± 0.005 % (prior to dislocation) to 9.4 ± 0.007 % (post dislocation) (p < .001). The mean increase in joint capsule elongation was 3.5 %. Conclusions: Capsule elongation was observed immediately after a simulated first-time shoulder dislocation in an in-vitro model of elderly human cadavers. It might therefore not only be a phenomenon of recurrent dislocation events.

Stability of ceramic coatings on retrieved knee prostheses.

BACKGROUND: In total knee arthroplasty, femoral components with coated or oxidized surfaces are commonly used as alternative to CoCrMo in metal sensitive patients. Data on the in vivo behaviour of different coating types is, however, rare. Aim of the study was the investigation of coating stability with respect to implant and patient specific parameters. METHODS: Coating thickness and coating thickness reduction, respectively, was measured at 37 retrieved femoral components with TiNbN, TiN, ZrN or oxidized zirconium (OxZr) surface by the crater grinding method. The results were correlated to surface type, manufacturer, time in vivo of the implant, patient body weight and patient activity. RESULTS: Mean coating thickness reduction in the overall retrieval collection was 0.6 µm ± 0.8 µm. There was no correlation between coating thickness reduction and coating type, time in vivo, patient body weight, and patient activity. If grouped according to manufacturers, implants of one manufacturer showed an increased coating thickness reduction. 10 of 37 retrievals exhibited coating abrasion with exposure of the underlying alloy. TiNbN coatings showed the highest incidence (9/17) of coating abrasion. No coating breakthrough was observed in the ZrN or OxZr surfaces. CONCLUSION: Our results indicate that TiNbN coatings should be optimized to improve their wear resistance in the long-term.

Precision of slot widths and torque transmission of in-office 3D printed brackets : An in vitro study.

PURPOSE: To investigate a novel in-office three-dimensionally (3D) printed polymer bracket regarding slot precision and torque transmission. METHODS: Based on a 0.022″ bracket system, stereolithography was used to manufacture brackets (N = 30) from a high-performance polymer that met Medical Device Regulation (MDR) IIa requirements. Conventional metal and ceramic brackets were used for comparison. Slot precision was determined using calibrated plug gages. Torque transmission was measured after artificial aging. Palatal and vestibular crown torques were measured from 0 to 20° using titanium-molybdenum (T) and stainless steel (S) wires (0.019â€³â€¯× 0.025″) in a biomechanical experimental setup. The Kruskal-Wallis test with post hoc test (Dunn-Bonferroni) was used for statistical analyses (significance level p < 0.05). RESULTS: The slot sizes of all three bracket groups were within the tolerance range according to DIN 13996 (ceramic [C]: 0.581 ± 0.003 mm; metal [M]: 0.6 ± 0.005 mm; polymer [P]: 0.581 ± 0.010 mm). The maximum torque values of all bracket-arch combinations were above the clinically relevant range of 5-20 Nmm (PS: 30 ± 8.6 Nmm; PT: 27.8 ± 14.2 Nmm; CS: 24 ± 5.6 Nmm; CT: 19.9 ± 3.8 Nmm; MS: 21.4 ± 6.7 Nmm; MT: 16.7 ± 4.6 Nmm). CONCLUSIONS: The novel, in-office manufactured polymer bracket showed comparable results to established bracket materials regarding slot precision and torque transmission. Given its high individualization possibilities as well as enabling an entire in-house supply chain, the novel polymer brackets bear high potential of future usage for orthodontic appliances.

Taper corrosion in total hip arthroplasty - How to assess and which design features are crucial?

BACKGROUND: In total hip replacement, wear and corrosion arising from modular taper connections have increasingly become a serious clinical concern. Previous studies led to confounding results regarding the role of specific taper design features, likely due to the application of different analytical approaches. Accordingly, this study has two major objectives: first, to evaluate different analytical approaches to evaluate the fretting-corrosion behavior; and secondly to determine the effect of four specific design variables: the taper engagement situation, the stem taper length and surface topography in terms of roughness and contact ratio. METHODS: An in vitro fretting-corrosion test setup was used including an aggressive solution. Cyclic loading was applied, varying from 300 N to 2500 N at a frequency of 3 Hz. Taper dummies covering different implant designs were tested in seven different test groups. Different quantitative and qualitative analytical test methods such as electrochemical characterization, ion analysis, gravimetry and corrosion scoring were applied in order to quantify the material degradation. RESULTS: A stepwise linear regression analysis showed that the taper engagement situation is the predominant factor that predicts the metal ion release from the taper connection, followed by the contact ratio of the taper surface and subsequently the taper length. A distal taper engagement situation, as well as a high contact ratio and a short taper length are the relevant parameters that decrease the metal ion release. Hereby, metal ion analysis turned out to be the most precise and reliable method for determining corrosive driven material loss, followed by gravimetry. CONCLUSION: It was found that the taper engagement length is the major design parameter that influences the total ion release. It further turned out, that the selection of an appropriate analytical approach is essential for the evaluation of the corrosion behavior of taper connections in an experimental setting.

Influence of FeCl3 and H2O2 in corrosion testing of modular taper connections in total hip arthroplasty: An in vitro study.

Corrosion at the modular taper junctions in total hip arthroplasty is clinically relevant because wear particles and ions generated at this interface can lead to adverse local tissue reactions or even implant failure. In vitro tribo-corrosion tests are usually accomplished in saline solutions or calf serum (CS), but the addition of H2O2 and FeCl3 have been suggested to mimic inflammatory conditions in the joint. Inflammatory conditions may aggravate corrosive processes and, therefore, should lead in vitro to a more severe and realistic tribo-corrosive material attack. Corrosion testing at 12/14 tapers comprising a CoCrMo head taper and a Ti6Al4V trunnion was accomplished in five electrolytes (Ringer's solution (RS), RS with 30 mM H2O2 and/or 0.7 mM FeCl3 and CS) under dynamical loading for five million cycles. Resulting material loss was determined gravimetrically and by ion analysis. The tribo-corrosive material degradation was investigated by light and electron microscopy. FeCl3 enhanced the material loss from taper connections while H2O2 did not lead to a significant alteration of total material loss. In comparison to pure RS, corrosion testing in CS decreased material loss at the head taper while it increased material loss at the trunnion. The combination of FeCl3 and H2O2 led to an enhanced occurrence of micro cracks at the trunnion surface. Adding FeCl3 and optionally also H2O2 aggravates material loss in in vitro corrosion testing of taper junctions and leads to harsher and probably more realistic testing conditions. STATEMENT OF SIGNIFICANCE: Tribo-corrosive processes at taper connections in hip implants are complex and can lead to major clinical implications. Joint inflammation is assumed to aggravate taper corrosion in vivo, why FeCl3 and H2O2 have been proposed as additives to electrolytes to simulate inflammatory conditions in vitro. Often used fretting test setups, however, do not involve real taper geometries. Besides, testing is often accomplished in saline solutions or calf serum, which do not induce a clinically significant amount of corrosive material degradation. This study presents an approach to increase tribo-corrosive processes at realistic taper connections by adding FeCl3 and/or H2O2. Unlike H2O2, FeCl3 increased material loss from taper connections. The combination of both additives enhanced micro crack formation at the trunnion surfaces.

Does tibial design modification improve implant stability for total knee arthroplasty? An experimental cadaver study.

AIMS: One of the main causes of tibial revision surgery for total knee arthroplasty is aseptic loosening. Therefore, stable fixation between the tibial component and the cement, and between the tibial component and the bone, is essential. A factor that could influence the implant stability is the implant design, with its different variations. In an existing implant system, the tibial component was modified by adding cement pockets. The aim of this experimental in vitro study was to investigate whether additional cement pockets on the underside of the tibial component could improve implant stability. The relative motion between implant and bone, the maximum pull-out force, the tibial cement mantle, and a possible path from the bone marrow to the metal-cement interface were determined. METHODS: A tibial component with (group S: Attune S+) and without (group A: Attune) additional cement pockets was implanted in 15 fresh-frozen human leg pairs. The relative motion was determined under dynamic loading (extension-flexion 20° to 50°, load-level 1,200 to 2,100 N) with subsequent determination of the maximum pull-out force. In addition, the cement mantle was analyzed radiologically for possible defects, the tibia base cement adhesion, and preoperative bone mineral density (BMD). RESULTS: The BMD showed no statistically significant difference between both groups. Group A showed for all load levels significantly higher maximum relative motion compared to group S for 20° and 50° flexion. Group S improved the maximum failure load significantly compared to group A without additional cement pockets. Group S showed a significantly increased cement adhesion compared to group A. The cement penetration and cement mantle defect analysis showed no significant differences between both groups. CONCLUSION: From a biomechanical point of view, the additional cement pockets of the component have improved the fixation performance of the implant. Cite this article: Bone Joint Res 2022;11(4):229-238.