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.

Soft-tissue fixation is not inferior to suture-anchor fixation in reconstruction of the medial patellofemoral ligament using a nonresorbable suture tape.

PURPOSE: Reconstruction of the medial patellofemoral ligament (MPFL-R) with nonresorbable suture tape (FiberTape®, FT) is becoming popular. Patella-side fixation of the FT can be performed with suture anchors or via soft-tissue fixation. The aim of this study was to investigate whether patella-side soft-tissue fixation can achieve equivalent primary stability compared to suture-anchor fixation. METHODS: In ten human, fresh-frozen knee joint specimens (m/f 6/4; age 74 ± 9 a), the MPFL was identified and dissected near the femoral insertion site. In five knee joints, the MPFL-R using FT was performed with soft-tissue fixation at the patella (study group; SG), and in five knee joints, the FT was fixed via suture anchors (control group, CG). All reconstructions were evaluated until load to failure of the patella-side fixation with a displacement rate of 200 mm/min. RESULTS: The mean maximum load to failure in the SG was 395.3 ± 57.9 N. All reconstructions failed by complete tearing off the medial patellar retinaculum from its medial patellar margin, but fixation of the FT remained stable. In the CG, the mean maximum load to failure was 239.4 ± 54.5 N and was significantly different compared to the SG (p = 0.04). All reconstructions failed via pullout of the suture anchors. Stiffness and elongation did not differ between the groups, and no failure of the FT was observed in any of the specimens. CONCLUSION: Primary stability of soft-tissue MPFL-R using FT was superior to suture-anchor fixation. Both fixation techniques provided sufficient primary stability, superior to previously reported native MPFL tensile strengths. MPFL-R with FT could be a possible alternative procedure for MPFL-R, eliminating potential complications due to autologous tendon graft harvesting.

Enhanced antibiotic release from bone cement spacers utilizing dual antibiotic loading with elevated vancomycin concentrations in two-stage revision for periprosthetic joint infection.

PURPOSE: Antibiotic loaded bone cement spacers provide high local antibiotic concentrations, preserve bone stock, and reduce soft tissue contractions. The objective of this in-vitro study was to compare antibiotic release from spacers, aiming to discover the most optimal preparation and identify modifiable factors that can further enhance antibiotic release. METHODS: Six distinct spacer preparation were created using three different bone cements and manual incorporation of antibiotics. During a six-week period, the release of antibiotics from each spacer was measured individually at ten predetermined time points using a chemiluminescent immunoassay. RESULTS: Manually adding 4 g of vancomycin to every 40 g of "Palacos R + G" yielded the most favorable release profile. Throughout all preparations, antibiotic release consistently and significantly decreased over the six-week period. When incorporating a higher concentration of vancomycin, a significantly higher cumulative release of vancomycin was observed, with varying effects on the release of gentamicin. The choice of bone cement had a significant impact on antibiotic release. CONCLUSION: To enhance antibiotic release from spacers, surgeons should manually incorporate high antibiotic concentrations into the most appropriate bone cement and keep the interim period as short as possible. Specifically, we suggest manual incorporation of 4 g of vancomycin to every 40 g of gentamicin premixed "Palacos R + G" to create bone cement spacers.

Dissociation of liner from cup in THA: does liner damage affect the risk of dissociation?

INTRODUCTION: A rare catastrophic failure of modular component Total Hip Arthroplasty is dissociation between liner and cup, which has been associated with component malposition and/or impingement and seems to be more frequently associated with the Pinnacle system. The goal of this study was to evaluate the resistance of a polyethylene liner to lever-out-forces of the Pinnacle locking mechanism and the locking mechanisms of two other current cup/liner systems using a standardized testing method (ASTM). MATERIALS AND METHODS: Five of each of the following cups were evaluated with their corresponding polyethylene liners: Pinnacle Multihole cup with and without intact anti-rotation tabs (ART's); Allofit-S-Alloclassic and Plasmafit Plus7 cups. The ASTM test set-up was used to evaluate the lever-out force resulting in liner dissociation for each construct. RESULTS: The Pinnacle construct with intact ARTs required the greatest force (F) to achieve dissociation (263.2 ± 79.2 N) followed by the Plasmafit Plus7 (185.8 ± 36.9 N) and the Allofit-S (101.4 ± 35.3 N) constructs, respectively. However, after removal of the ARTs, the Pinnacle system required the least force to achieve dissociation (75.1 ± 22.2 N) (p < 0.001). CONCLUSIONS: The intact Pinnacle system appeared the most stable in lever-out tests when compared to the other systems. However, after removal of the ARTs, the Pinnacle system required the least force for dissociation, consistent with locking mechanism failure, and suggesting that the ARTs are a critical component of the locking mechanism. Our findings are consistent with the clinical experience of dissociated Pinnacle constructs displaying damaged or missing ARTs, and that damage to these may increase risk of liner dissociation.

Does Kinematic Alignment Increase Polyethylene Wear Compared With Mechanically Aligned Components? A Wear Simulation Study.

BACKGROUND: Kinematic alignment is an alternative approach to mechanical alignment. Kinematic alignment can restore the joint line to its prearthritic condition, and its advocates have suggested it may be associated with other benefits. But this alignment approach often results in tibial components that are placed in varus and femoral components that are placed in valgus alignment, which may result in an increased risk of component loosening because of wear. Like malaligned implant components, kinematically aligned knee implants could increase wear in vivo, but we lack comparative data about wear behavior between these approaches. QUESTIONS/PURPOSES: (1) Do the different alignment approaches (kinematic, mechanical, and purposefully malaligned components) result in different wear rates in a wear simulator? (2) Do the different alignment approaches lead to different worn areas on the polyethylene inserts in a wear simulator? (3) Do the different alignment approaches result in different joint kinematics in a wear simulator? METHODS: Mechanical alignment was simulated in a force-controlled manner with a virtual ligament structure according to the International Organization for Standardization (ISO 14243-1) using a knee wear simulator. To simulate kinematic alignment, flexion-extension motion, internal-external torque, and the joint line were tilted by 4°, using a novel mechanical setup, without changing the force axis. The setup includes bearings with inclinations of 4° so that the joint axis of 4° is determined. To verify the angle of 4°, a digital spirit level was used. To simulate malalignment, we tilted the implant and, therefore, the joint axis by 4° using a wedge with an angle of 4° without tilting the torque axes of the simulator. This leads to a purposefully malaligned tibial varus and femoral valgus of 4°. For each condition, three cruciate-retaining knee implants were tested for 3.0 x 10 6 cycles, and one additional implant was used as soak control. Gravimetric wear analyses were performed every 0.5 x 10 6 cycles to determine the linear wear rate of each group by linear regression. The wear area was measured after 3.0 x 10 6 cycles by outlining the worn areas on the polyethylene inserts, then photographing the inserts and determining the worn areas using imaging software. The joint kinematics (AP translation and internal-external rotation) were recorded by the knee simulator software and analyzed during each of the six simulation intervals. RESULTS: Comparing the wear rates of the different groups, no difference could be found between the mechanical alignment and the kinematic alignment (3.8 ± 0.5 mg/million cycles versus 4.1 ± 0.2 mg/million cycles; p > 0.99). However, there was a lower wear rate in the malaligned group (2.7 ± 0.2 mg/million cycles) than in the other two groups (p < 0.01). When comparing the total wear areas of the polyethylene inserts among the three different alignment groups, the lowest worn area could be found for the malaligned group (716 ± 19 mm 2 ; p ≤ 0.003), but there was no difference between kinematic alignment and mechanical alignment (823 ± 19 mm 2 versus 825 ± 26 mm 2 ; p > 0.99). Comparing the AP translation, no difference was found between the mechanical alignment, the kinematic alignment, and the malalignment group (6.6 ± 0.1 mm versus 6.9 ± 0.2 mm versus 6.8 ± 0.3 mm; p = 0.06). In addition, the internal-external rotation between mechanical alignment, kinematic alignment, and malalignment also revealed no difference (9.9° ± 0.4° versus 10.2° ± 0.1° versus 10.1° ± 0.6°; p = 0.44). CONCLUSION: In the current wear simulation study, the wear rates of mechanical alignment and kinematic alignment of 4° were in a comparable range. CLINICAL RELEVANCE: The results suggest that kinematic alignment with up to 4° of component inclination may give the surgeon confidence that the reconstruction will have good wear-related performance when using a modern cruciate-retaining implant. The malaligned group had the lowest wear rate, which may be a function of the smaller worn area on the inserts compared with the other two alignment groups. This smaller articulation area between the femoral condyles and polyethylene insert could increase the risk of delamination of malaligned components over longer test durations and during high-load activities. For that reason, and because malalignment can cause nonwear-related revisions, malalignment should be avoided. Further in vitro and clinical studies must prove whether the wear simulation of different alignments can predict the wear behavior in vivo.

Mechanical strength of antibiotic-loaded PMMA spacers in two-stage revision surgery.

BACKGROUND: Antibiotic-loaded polymethylmethacrylate (PMMA) bone cement spacers provide high local antibiotic concentrations and patient mobility during the interim period of two-stage revision for periprosthetic joint infection (PJI). This study compares mechanical characteristics of six dual antibiotic-loaded bone cement (dALBC) preparations made from three different PMMA bone cements. The study`s main objective was to determine the effect of time and antibiotic concentration on mechanical strength of dALBCs frequently used for spacer fabrication in the setting of two-stage revision for PJI. METHODS: A total of 84 dual antibiotic-loaded bone cement specimens made of either Copal spacem, Copal G + V or Palacos R + G were fabricated. Each specimen contained 0.5 g of gentamicin and either 2 g (low concentration) or 4 g (high concentration) of vancomycin powder per 40 g bone cement. The bending strength was determined at two different timepoints, 24 h and six weeks after spacer fabrication, using the four-point bending test. RESULTS: Preparations made from Copal G + V showed the highest bending strength after incubation for 24 h with a mean of 57.6 ± 1.2 MPa (low concentration) and 50.4 ± 4.4 MPa (high concentration). After incubation for six weeks the bending strength had decreased in all six preparations and Palacos R + G showed the highest bending strength in the high concentration group (39.4 ± 1.6 MPa). All low concentration preparations showed superior mechanical strength compared to their high concentration (4 g of vancomycin) counterpart. This difference was statistically significant for Copal spacem and Copal G + V (both p < 0.001), but not for Palacos R + G (p = 0.09). CONCLUSIONS: This study suggests that mechanical strength of antibiotic-loaded PMMA bone cement critically decreases even over the short time period of six weeks, which is the recommended interim period in the setting of two-stage revision. This potentially results in an increased risk for PMMA spacer fracture at the end of the interim period and especially in patients with prolonged interim periods. Finally, we conclude that intraoperative addition of 4 g of vancomycin powder per 40 g of gentamicin-premixed Palacos R + G (Group D) is mechanically the preparation of choice if a dual antibiotic-loaded bone cement spacer with high antibiotic concentrations and good stability is warranted. In any case the written and signed informed consent including the off-label use of custom-made antibiotic-loaded PMMA bone cement spacers must be obtained before surgery.

[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.

Computer-simulated TOUCH prosthesis cup malposition and solutions.

INTRODUCTION: Total joint replacement has become significantly more common as a treatment for advanced trapeziometacarpal joint osteoarthritis in recent years. The latest generation of prostheses with dual-mobility designs leads to very good functional results and low rates of loosening and dislocation in the short and medium term. Biomechanical studies showed that central placement and parallel alignment of the cup with respect to the proximal articular surface of the trapezium are crucial for both cup stability and prevention of dislocation. Despite correct positioning of the guidewire, incorrect placement or tilting of the inserted cup may occur, requiring immediate intraoperative revision. METHODS: The existing spherical and conical cup models in sizes 9 mm and 10 mm were transferred to a computer-aided design dataset. Depending on the intraoperative complication (tilting or incorrect placement), the revision options resulting from the various combinations of cup type and size were simulated and analyzed according to the resulting defect area and bony contact area. RESULTS: In well centered cups, a size 9 conical cup could be replaced by a size 9 spherical cup and still be fixed by press-fit. Conversely, a size 9 spherical cup could not be replaced by a size 9 conical cup, but only by a size 10 cup, of whatever shape. When a size 9 conical cup was tilted up to 20°, the best revision option was to resect the sclerotic margin and insert a size 10 conical cup deeper into the cancellous bone, to achieve the largest contact area with the surrounding bone. When a size 9 cup of whatever shape was poorly centered (misplaced with respect to the dorsopalmar or radioulnar line of the trapezium), placement should be corrected using a size 10 cup, combined with autologous bone grafting of the defect. Again, the size 10 conical cup showed the largest bony contact area. CONCLUSION: Our computer-based measurements suggested options for intraoperative cup revision depending on cup shape and size and on type of misalignment with resulting bone defects. These suggestions, however, need to be confirmed in anatomic specimens before introducing them into clinical practice.

[Implant anchorage: In vivo and in vitro analyses : Clusters for implant anchorage and safety]. / Implantatverankerung: In-vivo- und In-vitro-Analysen : Cluster Implantatverankerung und -sicherheit.

Aseptic implant loosening is the primary cause of revisions in arthroplasty. Various in vitro and in vivo methods are available for assessing implant fixation and stability. The aim of the Musculoskeletal Biomechanics Research Network (MSB-NET) is to continuously improve or develop these methods. In vitro analyses are often conducted using static and dynamic ISO and ASTM standards, while RSA, DXA, and EBRA analyses are established in vivo methods for evaluating implant fixation. Primary stability analyses, as well as acoustical methods, provide additional opportunities to detect loosening early and precisely evaluate implant stability. The cluster serves as a link between basic research, clinical practice, and end users to promote in vitro and in vivo methods to improve implant safety.

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.

Pulsatile lavage systems and their potential to penetrate soft tissue.

BACKGROUND: In orthopedic and trauma surgery, pulsatile lavage systems are used to clean soft tissue. This may be necessary in septic surgeries or in case of contaminated wounds after trauma. Positive features such as reduction of bacterial contamination and removal of foreign particles are counterbalanced by negative aspects such as bacterial seeding in deeper tissue layers, damage to various tissues and even cases of air embolism. PURPOSE: The aim of this prospective experimental in vitro study was to compare impact pressure and flow rate in three different pulsatile lavage systems and to determine, whether these parameters alter their ability to reach deeper soft tissue layers. METHODS: To test the penetration of soft tissue, the muscle tissue was flushed with contrast medium instead of saline fluid and afterwards scanned by computed tomography. RESULTS: Impact pressure and flow rate showed significant differences between the different systems. There were no significant differences between the three devices in terms of total penetration volume, but there were significant differences in penetration depth. CONCLUSION: In this study, we found that higher impact pressure leads to deeper penetration and therefore bacteria are likely to be transferred to deeper tissue layers.

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.

Cement debonding behaviors of the various tibial components of the ATTUNE knee system and its predecessors: Is a cement-in-cement revision an alternative?

BACKGROUND: Aseptic loosening remains one of the most common causes of revision of the tibial component for total knee arthroplasty. A stable bond between implant and cement is essential for appropriate long-term results. The aim of our in vitro study was to investigate the maximum failure load of tibial ATTUNE prosthesis design alternatives compared with a previous design. In addition, cement-in-cement revision was considered as a potential strategy after tibial component debonding. METHODS: The experimental investigations of the maximum failure load of the implant-cement interface were performed under optimal conditions, without potential contamination. We compared the designs of the tibial components of the ATTUNE, ATTUNE S+ and P.F.C. Sigma. In addition, we investigated the cement-in-cement revision for the ATTUNE knee system replacing it with an ATTUNE S+. RESULTS: The maximum failure load showed no significant difference between P.F.C. Sigma and ATTUNE groups (P = 0.087), but there was a significant difference between the P.F.C. Sigma and the ATTUNE S+ groups (P < 0.001). The analysis also showed a significant difference (P < 0.001) between the ATTUNE and the ATTUNE S+ groups for the maximum failure load. The ATTUNE S+ cement-in-cement revision group showed a significant higher failure load (P < 0.001) compared with the P.F.C. Sigma and ATTUNE groups. No significant differences (P = 1.000) were found between the ATTUNE S+ cement-in-cement and ATTUNE S+ group. CONCLUSION: Based on these results, we found no design-specific evidence of increased debonding risk with the ATTUNE and ATTUNE S+ components compared with the P.F.C Sigma. Furthermore, the cement-in-cement revision seems to be an alternative for the revision surgery.

Does Additive Pressurized Carbon Dioxide Lavage Improve Cement Penetration and Bond Strength in Cemented Arthroplasty?

The modern cementing technique in cemented arthroplasty is a highly standardized and, therefore, safe procedure. Nevertheless, aseptic loosening is still the main reason for revision after cemented total knee or cemented total hip arthroplasty. To investigate whether an additional carbon dioxide lavage after a high-pressure pulsatile saline lavage has a positive effect on the bone-cement interface or cement penetration, we set up a standardized laboratory experiment with 28 human femoral heads. After a standardized cleaning procedure, the test implants were cemented onto the cancellous bone. Subsequently, the maximum failure load of the bone-cement interface was determined using a material testing machine to pull off the implant, and the cement penetration was determined using computed tomography. Neither the maximum failure load nor cement penetration into the cancellous bone revealed significant differences between the groups. In conclusion, according to our experiments, the additive use of the carbon dioxide lavage after the high-pressure pulsatile lavage has no additional benefit for the cleaning of the cancellous bone and, therefore, cannot be recommended without restrictions.

Pulsatile Lavage Systems with High Impact Pressure and High Flow Produce Cleaner Cancellous Bone Prior to Cementation in Cemented Arthroplasty.

In cemented joint arthroplasty, state-of-the-art cementing techniques include high-pressure pulsatile saline lavage prior to cementation. Even with its outstanding importance in cementation, there are surprisingly few studies regarding the physical parameters that define pulsatile lavage systems. To investigate the parameters of impact pressure, flow rate, frequency and the cleaning effect in cancellous bone, we established a standardized laboratory model. Standardized fat-filled carbon foam specimens representing human cancellous bone were cleaned with three different high-pressure pulsatile lavage systems. Via CT scans before and after cleaning, the cleaning effect was evaluated. All systems showed a cleaning depth of at least 3.0 mm and therefore can be generally recommended to clean cancellous bone in cemented joint arthroplasty. When comparing the three lavage systems, the study showed significant differences regarding cleaning depths and volume, with one system being superior to its peer systems. Regarding the physical parameters, high impact pressure in combination with high flow rate and longer distance to the flushed object seems to be the best combination to improve the cleaning of cancellous bone and therefore increase the chances of a deeper cement penetration that is required in cemented joint arthroplasty. In summary, this study provides the first standardized comparison of different lavage systems and thus gives initial guidance on how to optimally prepare cancellous bone for cemented joint arthroplasty.

Early tibial loosening of the cemented ATTUNE knee arthroplasty - Just a question of design?

BACKGROUND: Total knee arthroplasty is a very successful standard treatment for severe osteoarthritis. Nevertheless, the literature reports tibial debonding between implant and bone cement as well as radiolucent lines related to the tibial components of different knee systems. Regardless of cementing techniques and the influences during surgery, we examined the design of a newly developed knee system and its predecessors (Attune, Attune S+, P.F.C. Sigma, P.F.C. Sigma RP/M.B.T., all DePuy). METHODS: We investigated the dimensions of the tibial components and the fit between them and their bone bed after instrumentation in a foam material. RESULTS: Our results showed considerable differences for the used knee prostheses as well as their tibial instrumentation options with a corresponding risk for incomplete seating. CONCLUSION: The orthopedic surgeons need to be aware of these design features and the resulting increased seating resistance especially in hard and sclerotic bone. ARTICLE FOCUS: Comparison of the tibial instruments and the different design options of the Attune knee system and its predecessor knee prostheses. KEY MESSAGES: The Attune implant showed incomplete seating because of too much press fit and an uneven bone quality or sclerosis can result in tilting of the tibial component. STRENGTHS AND LIMITATIONS: This is the first study investigating the Attune knee and its predecessor in terms of implant seating and press fit. The foam material is a limitation.

Primary Stability in Hip Revision Arthroplasty: Comparison of the Stability of Cementless Fixed Augments on a Modular Acetabular Cage System with and without Cranial Straps.

The goal of this study is to evaluate the primary stability of a cementless augment-and-modular-cage system with and without the addition of cranial straps in a standardized in vitro setting. As the surrogate parameter for the evaluation of primary stability, the measurement of relative motion between the implant components themselves and the bone will be used. Acetabular revision components with a trabecular titanium augment in combination with a large fourth-generation composite left hemipelvis were assembled. These constructs were divided into two groups with (S) and without cranial straps (nS). A total of 1000 cycles was applied at each of three load levels. Relative movements (RM) between the components were measured. Load levels display a significant effect on the amount of RM at all interfaces except between shell/augment. The group assignment appears to have an effect on RM due to significantly differing means at all interfaces. Between bone/shell RM increased as load increased. NS displayed significantly more RM than S. Between shell/augment RM remained constant as load increased. Between shell/cup S showed more RM than nS while both groups' RM increased with load. We conclude a significant increase of primary stability between the shell and the bone through the addition of cranial straps. Relative motion between components (shell/cup) increases through the addition of cranial straps. A clinical impact of this finding is uncertain and requires further investigation. Finally, the cementless fixation of the augment against the rim-portion of the shell appears stable and compares favorably to prior investigation of different fixation techniques.

Comparison of the Primary Stability of Porous Tantalum and Titanium Acetabular Revision Constructs.

Adequate primary stability of the acetabular revision construct is necessary for long-term implant survival. The difference in primary stability between tantalum and titanium components is unclear. Six composite hemipelvises with an acetabular defect were implanted with a tantalum augment and cup, using cement fixation between cup and augment. Relative motion was measured at cup/bone, cup/augment and bone/augment interfaces at three load levels; the results were compared to the relative motion measured at the same interfaces of a titanium cup/augment construct of identical dimensions, also implanted into composite bone. The implants showed little relative motion at all load levels between the augment and cup. At the bone/augment and bone/cup interfaces the titanium implants showed less relative motion than tantalum at 30% load (p < 0.001), but more relative motion at 50% (p = n.s.) and 100% (p < 0001) load. The load did not have a significant effect at the augment/cup interface (p = 0.086); it did have a significant effect on relative motion of both implant materials at bone/cup and bone/augment interfaces (p < 0.001). All interfaces of both constructs displayed relative motion that should permit osseointegration. Tantalum, however, may provide a greater degree of primary stability at higher loads than titanium. The clinical implication is yet to be seen.