Comparison of the Primary Stability of a Porous Coated Acetabular Revision Cup With a Standard Cup

Early Radiographic and Clinical Outcomes of an Additive-Manufactured Acetabular Component

Background

Additive manufacturing has recently gained popularity and is widely adopted in the orthopaedic industry. However, there is a paucity of literature on the radiographic and clinical outcomes of these relatively novel components. The aim of this study was to assess the 2-year clinical and radiographic outcomes of a specific additive-manufactured acetabular component in primary total hip arthroplasty.

Methods

We performed a retrospective review of 60 patients who underwent primary total hip arthroplasty with the use of the Stryker's TRIDENT II acetabular component. Evaluation of radiographs was performed at 6 weeks, 1 year, and 2 years postoperatively. Radiographs were evaluated for radiolucencies in Charnley and DeLee zones, signs of biologic fixation, and acetabular inclination and anteversion measurements. Patient-reported outcomes and complications were also obtained.

Results

There were no cases of component loosening or changes in component position during follow-up, with an average follow-up time of 1.7 years. A radiolucent line was identified in one patient in zone 1 at 6 weeks; this was absent at 1 year. Radiographic signs of cup biologic fixation were present in 85% of cases by final follow-up. The average inclination was 45.1 (SD = 4.0), and the average anteversion was 26.9 (SD = 5.2). Patient-Reported Outcomes Measurement Information System scores significantly increased at the final follow-up, and there were no complications in this cohort.

Conclusions

This study demonstrated excellent radiographic and clinical outcomes with this novel additive-manufactured acetabular component at early follow-up. Although longer-term follow-up is warranted, this additively manufactured highly porous titanium acetabular component demonstrated excellent biologic fixation and reliable fixation at mid-term follow-up.

Cup positioning and its effect on polyethylene wear of vitamin E- and non-vitamin E-supplemented liners in total hip arthroplasty: radiographic outcome at 5-year follow-up

BACKGROUND

Aseptic loosening remains a challenging problem after total hip arthroplasty. Accurate cup placement and supplementation of antioxidants in acetabular liners might reduce material failure rates. The aim of this study is to assess the effect of the cup position on the wear behaviour of UHMWPE-XE and UHMWPE-X liners in vivo using virtual radiographs.

METHODS

We conducted a prospective, randomized, controlled, multicenter trial. Clinical data of 372 probands were analyzed. Anteroposterior pelvic X-rays of 324 patients immediately postoperatively and after 1 and 5 years were evaluated by the RayMatch® analysis software regarding cup position and wear behaviour.

RESULTS

Mean cup anteversion was 20.3° (± 7.4) and inclination was 41.9° (± 7.0) postoperatively. 62.3% of all patients had an anteversion and inclination within the Lewinnek safe zone. Anterior and anterolateral approaches led to significantly higher cup anteversion compared to lateral approaches (27.3° ± 5.5; 20.9° ± 7.2; 17.5° ± 6.6; p < 0.001 and p = 0.001, respectively). Mean anteversion increased to 24.6° (± 8.0) after 1 year (p < 0.001). Only one revision occurred because of implant dislocation. Wear rates from UHMWPE-X and UHMWPE-XE did not differ significantly. Anteversion angles ≥ 25° correlated to increased polyethylene wear (23.7 µm/year ± 12.8 vs. 31.1 µm/year ± 22.8, p = 0.012) and this was amplified when inclination angles were ≥ 50° (23.6 µm/year ± 12.8 vs. 38.0 µm/year ± 22.7, p = 0.062).

CONCLUSION

Anterior approaches lead to the highest inaccuracy of cup placement, but cup positioning outside the Lewinnek safe zone does not necessarily cause higher dislocation rates. Moreover, mean anteversion increased by approximately four degrees within the first year after operation, which is expected to be functional due to a regularization of pelvic tilt after intervention. Mid-term wear rates of UHMWPE-X and UHMWPE-XE liners are comparable, but steep cup positions lead to significantly increased polyethylene wear. In summary, a re-evaluation of target zones for intraoperative cup positioning might be considered. In the long-term reduced oxidative embrittlement could lead to superior wear behaviour of vitamin E-blended liners.

Irregular porous titanium enhances implant stability and bone ingrowth in an intra-articular ovine model

Two commercially available porous coatings, Gription and Porocoat, were compared for the first time in a challenging intra-articular, weight-bearing, ovine model. Gription has evolved from Porocoat and has higher porosity, coefficient of friction, and microtextured topography, which are expected to enhance bone ingrowth. Cylindrical implants were press-fit into the weight-bearing regions of ovine femoral condyles and bone ingrowth and fixation strength evaluated 4, 8, and 16 weeks postoperatively. Biomechanical push-out tests were performed on lateral femoral condyles (LFCs) to evaluate the strength of the bone-implant interface. Bone ingrowth was assessed in medial femoral condyles (MFCs) as well as implants retrieved from LFCs following biomechanical testing using backscattered electron microscopy and histology. By 16 weeks, Gription-coated implants exhibited higher force (2455 ± 1362 vs. 1002 ± 1466 N; p = 0.046) and stress (12.60 ± 6.99 vs. 5.14 ± 7.53 MPa; p = 0.046) at failure, and trended towards higher stiffness (11,510 ± 7645 vs. 5010 ± 8374 N/mm; p = 0.061) and modulus of elasticity (591 ± 392 vs. 256 ± 431 MPa; p = 0.061). A strong, positive correlation was detected between bone ingrowth in LFC implants and failure force (r = 0.93, p < 10^-13 ). By 16 weeks, bone ingrowth in Gription-coated implants in MFCs was 10.50 ± 6.31% compared to 5.88 ± 2.77% in Porocoat (p = 0.095). Observations of the bone-implant interface, made following push-out testing, showed more bony material consistently adhered to Gription compared to Porocoat at all three time points. Gription provided superior fixation strength and bone ingrowth by 16 weeks.

Measurement of safe acetabular medial wall defect size in revision hip arthroplasty with a porous cup

INTRODUCTION

The majority of acetabular revisions can be performed with an uncemented, porous acetabular component with or without bone grafting. These are contained acetabular defects, with an intact acetabular rim (Paprosky type I and II). As defects of the medial wall of the acetabulum are a challenge situation revision surgery, we performed this biomechanical study on a pig pelvis model with contained acetabular defects to determine the size of medial wall defect at which the acetabular cup will have sufficient primary stability.

MATERIALS AND METHODS

In 24 pig pelvis models, different diameter of medial wall defects were created, followed by acetabular component placement. The acetabulum externally loaded, and the force at a level in which the acetabular component remains stable for each diameter of defect, or at which point the acetabular cup moves into the pelvis for >2 mm.

RESULTS

In the models with acetabular medial wall defects of 10 and 20 mm, 2 mm acetabular displacement occurred under a force between 1000 and 1500 N. In those with a medial wall defect of 25 mm, the force that caused acetabular instability was between 700 and 1000 N. In the models with 30 mm of medial wall defect all acetabular components were unstable under a force of 700 N.

CONCLUSIONS

According to our results, acetabular component should be stable if the defect of the medial wall of the acetabulum is less than 68% of the diameter of the acetabular component or if the uncovered surface area of the acetabular component is not greater than 27%, and the force <700 N. For a load of 1000 N, the medial wall defect should not exceed 45% of acetabular component diameter or 18% of uncovered acetabular component surface.

Clinical Application and Biological Functionalization of Different Surface Coatings in Artificial Joint Prosthesis: A Comprehensive Research Review

With advances in materials science and biology, there have been continuing innovations in the field of artificial joint prostheses. Cementless prostheses have the advantages of long service life, easy revision, and good initial stability and are widely used in artificial joint replacement. Coatings are the key to cementless prostheses and are at the heart of their excellent functionality. This article mainly studies the clinical application of hydroxyapatite (HA) coating, standard porous coating represented by Porocoat coating, and new high-porosity coating represented by Gription coating. The clinical application and biological functionalization of different artificial joint prosthesis surface coatings are clarified, and it provides a reference for the clinical selection and development of different prosthesis surface coating materials.

Evaluation of the feasibility of acetabular cup pre-determination in revision total hip arthroplasty via X-ray of the bone stock of the anterosuperior acetabulum

Purpose

This study was aimed to explore (1) location on AP pelvic X-ray that displayed bone stock in anterosuperior acetabulum; (2) whether X-ray could provide enough evidence to evaluate whether bone stock could provide support for acetabular cup; (3) criteria to determine whether anterosuperior bone stock could provide sufficient support for cup on X-ray.

Methods

Our study retrospectively collected 43 patients who underwent revision THA for cup loosening from 2014 to 2019. The position of anterosuperior acetabular bone stock was compared between X-ray and CT-based 3-D reconstruction. Seventy-millimeter acetabular cup was implanted simulatively to obtain the contact line between acetabular cup and superolateral remaining bone stock. The contact line length and the angle were measured. Patients were divided into cup group and cage group, and ROC curves of both contact line length and angle were drawn.

Results

The superolateral part of acetabulum on X-ray could reflect the anterosuperior host bone stock of acetabulum according to the comparison of anteroposterior pelvic X-ray and 3-D reconstruction. Critical point was chosen when we got the highest sensitivity with a 100% specificity in ROC curves. The critical values of contact length and angle were 15.58 mm and 25.5°.

Conclusions

Surgeons could assess the anterosuperior bone stock of acetabulum by AP pelvic X-ray to decide whether revision could be done merely using cup or need customized cage. Clinically, when contact line length was larger than 16 mm or contact angle was larger than 25.5°, adoption of cup could obtain primary stability in the revision surgery in most cases.

The use of acetabular screws in total hip arthroplasty and its influence on wear and periacetabular osteolysis in the long-term follow-up

Purpose

The cementless implantation of hip replacement cups may be performed with and without the additional use of acetabular screws. If the surgeon uses screws or not depends on variable factors. In general, the use of screws is intended to increase the primary stability of the cup. Whether screws increase the initial stability of the cup construct, or even reduce it in part, is the subject of considerable debate in the literature. It is also unclear whether the additional screws lead to increased wear or increased periacetabular osteolysis over the long-term course.

Methods

Two hundred eleven patients from a previous study with a minimum follow-up of 10.7 years were included. Of these, 68 patients with 82 total hip arthroplasties (THA) were given clinical and radiological follow-up examinations. Of these, 52 had been fitted without screws and 30 with screws. On the basis of radiographs, annual wear and osteolysis were quantified. The clinical results were recorded by means of VAS, HHS, and WOMAC scores.

Results

Significantly more periacetabular osteolysis was found if additive acetabular screws had been used. No difference was found in relation to the volumetric wear per year. Likewise, no difference was found with regard to the clinical scores.

Conclusions

The use of additive acetabular screws leads to increased osteolysis in the periacetabular bone stock. Insofar as the primary stability of the cementless cup construct allows it, no additional acetabular screws should be used.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00264-021-05219-7.

Osseointegration of retrieved 3D-printed, off-the-shelf acetabular implants

Aims

The main advantage of 3D-printed, off-the-shelf acetabular implants is the potential to promote enhanced bony fixation due to their controllable porous structure. In this study we investigated the extent of osseointegration in retrieved 3D-printed acetabular implants.

Methods

We compared two groups, one made via 3D-printing (n = 7) and the other using conventional techniques (n = 7). We collected implant details, type of surgery and removal technique, patient demographics, and clinical history. Bone integration was assessed by macroscopic visual analysis, followed by sectioning to allow undecalcified histology on eight sections (~200 µm) for each implant. The outcome measures considered were area of bone attachment (%), extent of bone ingrowth (%), bone-implant contact (%), and depth of ingrowth (%), and these were quantified using a line-intercept method.

Results

The two groups were matched for patient sex, age (61 and 63 years), time to revision (30 and 41 months), implant size (54 mm and 52 mm), and porosity (72% and 60%) (p > 0.152). There was no difference in visual bony attachment (p = 0.209). Histological analysis showed greater bone ingrowth in 3D-printed implants (p < 0.001), with mean bone attachment of 63% (SD 28%) and 37% (SD 20%), respectively. This was observed for all the outcome measures.

Conclusion

This was the first study to investigate osseointegration in retrieved 3D-printed acetabular implants. Greater bone ingrowth was found in 3D-printed implants, suggesting that better osseointegration can be achieved. However, the influence of specific surgeon, implant, and patient factors needs to be considered.

Cite this article: Bone Joint Res 2021;10(7):388–400.

Primary stability of a press-fit cup in combination with impaction grafting in an acetabular defect model

The objectives of this study were to (a) assess primary stability of a press-fit cup in a simplified acetabular defect model, filled with compacted cancellous bone chips, and (b) to compare the results with primary stability of a press-fit cup combined with two different types of bone graft substitute in the same defect model. A previously developed acetabular test model made of polyurethane foam was used, in which a mainly medial contained defect was implemented. Three test groups (N = 6 each) were prepared: Cancellous bone chips (bone chips), tricalciumphosphate tetrapods + collagen matrix (tetrapods + coll), bioactive glass S53P4 + polyethylene glycol-glycerol matrix (b.a.glass + PEG). Each material was compacted into the acetabulum and a press-fit cup was implanted. The specimens were loaded dynamically in the direction of the maximum resultant force during level walking. Relative motion between cup and test model was assessed with an optical measurement system. At the last load step (3000 N), inducible displacement was highest for bone chips with median [25th percentile; 75th percentile] value of 113 [110; 114] µm and lowest for b.a.glass + PEG with 91 [89; 93] µm. Migration at this load step was highest for b.a.glass + PEG with 868 [845; 936] µm and lowest for tetrapods + coll with 491 [487; 497] µm. The results show a comparable behavior under load of tetrapods + coll and bone chips and suggest that tetrapods + coll could be an attractive alternative to bone chips. However, so far, this was found for one specific defect type and primary stability should be further investigated in additional/more severe defects.

Osseointegration of porous titanium and tantalum implants in ovariectomized rabbits: A biomechanical study

BACKGROUND

Today, biological fixation of uncemented press-fit acetabular components plays an important role in total hip arthroplasty. Long-term stable fixation of these implants depends on the osseointegration of the acetabular cup bone tissue into the acetabular cup implant, and their ability to withstand functional loads.

AIM

To compare the strength of bone-implant osseointegration of four types of porous metal implants in normal and osteoporotic bone in rabbits.

METHODS

The study was performed in 50 female California rabbits divided into non-ovariectomized (non-OVX) and ovariectomized groups (OVX) at 6 mo of age. Rabbits were sacrificed 8 wk after the implantation of four biomaterials [TTM, CONCELOC, Zimmer Biomet's Trabecular Metal (TANTALUM), and ATLANT] in a 5-mm diameter defect created in the left femur. A biomechanical evaluation of the femur was carried out by testing implant breakout force. The force was gradually increased until complete detachment of the implant from the bone occurred.

RESULTS

The breakout force needed for implant detachment was significantly higher in the non-OVX group, compared with the OVX group for all implants (TANTALUM, 194.7 ± 6.1 N vs 181.3 ± 2.8 N; P = 0.005; CONCELOC, 190.8 ± 3.6 N vs 180.9 ± 6.6 N; P = 0.019; TTM, 186.3 ± 1.8 N vs 172.0 N ± 11.0 N; P = 0.043; and ATLANT, 104.9 ± 7.0 N vs 78.9 N ± 4.5 N; P = 0.001). In the OVX group, The breakout forces in TANTALUM, TTM, and CONCELOC did not differ significantly (P = 0.066). The breakout force for ATLANT in the OVX group was lower by a factor of 2.3 compared with TANTALUM and CONCELOC, and by 2.2 compared with TTM (P = 0.001). In the non-OVX group, the breakout force for ATLANT was significantly different from all other implants, with a reduction in fixation strength by a factor of 1.9 (P = 0.001).

CONCLUSION

TANTALUM, TTM, and CONCELOC had equal bone-implant osseointegration in healthy and in osteoporotic bone. ATLANT had significantly decreased osseointegration (P = 0.001) in healthy and in osteoporotic bone.

A New Additive-Manufactured Cementless Highly Porous Titanium Acetabular Cup for Primary Total Hip Arthroplasty-Early Two-Year Follow Up

INTRODUCTION

Additive-manufacturing technologies are increasingly being used, not only to create acetabular components with porous coating architecture very similar to the complex trabecular structure of cancellous bone, but also for producing the entire implant in a single step. The aim of this study is to assess two-year clinical and radiological outcomes of a new additive-manufactured cup in primary total hip arthroplasty (THA).

MATERIALS AND METHODS

We reviewed 266 primary THAs (254 patients) performed in our institution between December 2016 and December 2018 using a new highly porous titanium acetabulum shell fabricated via additive manufacturing. Clinical and functional outcomes were measured using SF/VR-12 and HOOS JR to determine patient satisfaction with surgery. Radiographs were assessed to determine the presence of migration, radiolucency, and loosening. Patients records were reviewed to assess cup survivorship in terms of all-cause revisions and revision for aseptic cup loosening.

RESULTS

At a minimum of two-year follow up (range: 2-3.45 years), the patient cohort demonstrated significant improvement in postoperative functional scores (hip disability and osteoarthritis outcome score for joint replacement [HOOS JR.] and clinical scores (12-item short-form health survey [SF/VR-12]) (p<0.001). One cup developed progressive radiolucent lines at the prosthesis-bone interface consistent with loosening and was revised. The overall acetabular component two-year survivorship free of all-cause failure was 97.4% (95% confidence interval [CI]: 95.5-99.4%). When aseptic loosening of the acetabular component was used as the failure endpoint, the two-years survivorship rate was 99.6% (95% CI: 98.9-100%).

CONCLUSION

Highly porous titanium cementless acetabular cups produced via additive-manufacturing showed promising early clinical and radiological results in primary THA with low rates of aseptic loosening. Further follow-up studies are needed to assess the long-term survivorship and outcomes of this new acetabular component.

Vitamin E-blended highly cross-linked polyethylene liners in total hip arthroplasty: a randomized, multicenter trial using virtual CAD-based wear analysis at 5-year follow-up

BACKGROUND

Progressive oxidation of highly cross-linked ultra-high molecular weight (UHMPWE-X) liners is considered to be a risk factor for material failure in THA. Antioxidants such as vitamin E (alpha-tocopherol) (UHMWPE-XE) were supplemented into the latest generation of polyethylene liners. To prevent inhomogenous vitamin E distribution within the polymer, blending was established as an alternative manufacturing process to diffusion. The purpose of the present study was to investigate the in vivo wear behavior of UHMWPE-XE in comparison with conventional UHMWPE-X liners using virtual CAD-based radiographs.

METHODS

Until now, 94 patients from a prospective, randomized, controlled, multicenter study were reviewed at 5-year follow-up. Of these, 51 (54%) received UHMWPE-XE and 43 (46%) UHMWPE-X liners. Anteroposterior pelvic radiographs were made immediately after surgery and at 1 and 5 years postoperatively. The radiographs were analyzed using the observer-independent analysis software RayMatch^® (Raylytic GmbH, Leipzig, Germany).

RESULTS

The mean wear rate was measured to be 23.6 μm/year (SD 13.7; range 0.7-71.8 μm). There were no significant differences between the two cohorts (UHMWPE-X: 23.2 μm/year vs. UHMWPE-XE: 24.0 μm/year, p = 0.73). Cup anteversion significantly changed within the 1st year after implantation independent from the type of polyethylene liner [UHMWPE-X: 18.2-23.9° (p = 0.0001); UHMWPE-XE: 21.0-25.5° (p = 0.002)]. No further significant changes of cup anteversion in both groups were found between year 1 and 5 after implantation [UHMWPE-X (p = 0.46); UHMWPE-XE (p = 0.56)].

CONCLUSION

The present study demonstrates that the addition of vitamin E does not adversely affect the midterm wear behavior of UHMWPE-X. The antioxidative benefit of vitamin E is expected to become evident in long-term follow-up. Cup anteversion increment by 5° within the 1st year is likely a result of the released hip flexion contracture resulting in an enhanced posterior pelvic tilt. Therefore, a reassessment of target values in acetabular cup placement might be considered.

A method to assess primary stability of acetabular components in association with bone defects

The objectives of this study were to develop a simplified acetabular bone defect model based on a representative clinical case, derive four bone defect increments from the simplified defect to establish a step-wise testing procedure, and analyze the impact of bone defect and bone defect filling on primary stability of a press-fit cup in the smallest defined bone defect increment. The original bone defect was approximated with nine reaming procedures and by exclusion of specific procedures, four defect increments were derived. The smallest increment was used in an artificial acetabular test model to test primary stability of a press-fit cup in combination with bone graft substitute (BGS). A primary acetabular test model and a defect model without filling were used as reference. Load was applied in direction of level walking in sinusoidal waveform with an incrementally increasing maximum load (300 N/1000 cycles from 600 to 3000 N). Relative motions (inducible displacement, migration, and total motion) between cup and test model were assessed with an optical measurement system. Original and simplified bone defect volume showed a conformity of 99%. Maximum total motion in the primary setup at 600 N (45.7 ± 5.6 µm) was in a range comparable to tests in human donor specimens (36.0 ± 16.8 µm). Primary stability was reduced by the bone defect, but could mostly be reestablished by BGS-filling. The presented method could be used as platform to test and compare different treatment strategies for increasing bone defect severity in a standardized way.

Characterization of dimensional, morphological and morphometric features of retrieved 3D-printed acetabular cups for hip arthroplasty

Background

Three-dimensional (3D) printing of porous titanium implants is increasing in orthopaedics, promising enhanced bony fixation whilst maintaining design similarities with conventionally manufactured components. Our study is one of the first to non-destructively characterize 3D-printed implants, using conventionally manufactured components as a reference.

Methods

We analysed 16 acetabular cups retrieved from patients, divided into two groups: ‘3D-printed’ (n = 6) and ‘conventional’ (n = 10). Coordinate-measuring machine (CMM), electron microscopy (SEM) and microcomputed tomography (micro-CT) were used to investigate the roundness of the internal cup surface, the morphology of the backside surface and the morphometric features of the porous structures of the cups, respectively. The amount of bony attachment was also evaluated.

Results

CMM analysis showed a median roundness of 19.45 and 14.52 μm for 3D-printed and conventional cups, respectively (p = 0.1114). SEM images revealed partially molten particles on the struts of 3D-printed implants; these are a by-product of the manufacturing technique, unlike the beads shown by conventional cups. As expected, porosity, pore size, strut thickness and thickness of the porous structure were significantly higher for 3D-printed components (p = 0.0002), with median values of 72.3%, 915 μm, 498 μm and 1.287 mm (p = 0.0002). The median values of bony attachment were 84.9% and 69.3% for 3D-printed and conventional cups, respectively (p = 0.2635).

Conclusion

3D-printed implants are designed to be significantly more porous than some conventional components, as shown in this study, whilst still exhibiting the same shape and size. We found differences in the surface morphologies of the groups, related to the different manufacturing methods; a key finding was the presence of partially molten particles on the 3D-printed cups.

Two Different Methods to Measure the Stability of Acetabular Implants: A Comparison Using Artificial Acetabular Models

The total number of total hip arthroplasties is increasing every year, and approximately 10% of these surgeries are revisions. New implant design and surgical techniques are evolving quickly and demand accurate preclinical evaluation. The initial stability of cementless implants is one of the main concerns of these preclinical evaluations. A broad range of initial stability test methods is currently used, which can be categorized into two main groups: Load-to-failure tests and relative micromotion measurements. Measuring relative micromotion between implant and bone is recognized as the golden standard for implant stability testing as this micromotion is directly linked to the long-term fixation of cementless implants. However, specific custom-made set-ups are required to measure this micromotion, with the result that numerous studies opt to perform more straightforward load-to-failure tests. A custom-made micromotion test set-up for artificial acetabular bone models was developed and used to compare load-to-failure (implant push-out test) with micromotion and to assess the influence of bone material properties and press-fit on the implant stability. The results showed a high degree of correlation between micromotion and load-to-failure stability metrics, which indicates that load-to-failure stability tests can be an appropriate estimator of the primary stability of acetabular implants. Nevertheless, micromotions still apply as the golden standard and are preferred when high accuracy is necessary. Higher bone density resulted in an increase in implant stability. An increase of press-fit from 0.7 mm to 1.2 mm did not significantly increase implant stability.

Titanium Acetabular Component Deformation under Cyclic Loading

Acetabular cup deformation may affect liner/cup congruency, clearance and/or osseointegration. It is unclear, whether deformation of the acetabular components occurs during load and to what extent. To evaluate this, revision multi-hole cups were implanted into six cadaver hemipelvises in two scenarios: without acetabular defect (ND); with a large acetabular defect (LD) that was treated with an augment. In the LD scenario, the cup and augment were attached to the bone and each other with screws. Subsequently, the implanted hemipelvises were loaded under a physiologic partial-weight-bearing modality. The deformation of the acetabular components was determined using a best-fit algorithm. The statistical evaluation involved repeated-measures ANOVA. The mean elastic distension of the ND cup was 292.9 µm (SD 12.2 µm); in the LD scenario, 43.7 µm (SD 11.2 µm); the mean maximal augment distension was 79.6 µm (SD 21.6 µm). A significant difference between the maximal distension of the cups in both scenarios was noted (F(1, 10) = 11.404; p = 0.007). No significant difference was noted between the compression of the ND and LD cups, nor between LD cups and LD augments. The LD cup displayed significantly lower elastic distension than the ND cup, most likely due to increased stiffness from the affixed augment and screw fixation.

Effect of different motor tasks on hip cup primary stability and on the strains in the periacetabular bone: An in vitro study

BACKGROUND

Excessive prosthesis/bone motions and the bone strains around the acetabulum may prevent osteointegration and lead to cup loosening. These two factors depend on post-operative joint loading. We investigated how Walking (which is often simulated) and Standing-Up from seated (possibly more critical) influence the cup primary stability and periacetabular strains.

METHODS

Twelve composite hemipelvises were used in two test campaigns. Simplified loading conditions were adopted to simulate Walking and Standing-Up. For each motor task, a single-direction force was applied in load packages of increasing amplitude. Stable and unstable uncemented cups were implanted. Digital image correlation was used to measure implant/bone motions (three-dimensional translations and rotations, both permanent and inducible), and the strain distribution around the acetabulum.

FINDINGS

When stable implants were tested, higher permanent cranial translations were found during Walking (however the resultant migrations were comparable with Standing-Up); higher rotations were found for Standing-Up. When unstable implants were tested, motions were 1-2 order of magnitude higher. Strains increased significantly from stable to unstable implants. The peak strains were in the superior aspect of the acetabulum during Walking and in the superior-posterior aspect of the acetabulum and at the bottom of the posterior column during Standing-Up.

INTERPRETATION

Different cup migration trends were caused by simulated Walking and Standing-Up, both similar to those observed clinically. The cup mobilization pattern depended on the different simulated motor tasks. Pre-clinical testing of new uncemented cups could include simulation of both motor tasks. Our study could also translate to indication of what tasks should be avoided.

In vitro examination of the primary stability of three press-fit acetabular cups under consideration of two different bearing couples

BACKROUND

For preclinical statements about the anchoring behavior of prostheses, the primary stability of the prosthesis is of special importance. It was the aim of this study to examine and compare the relevant relative micromotions of three different acetabulum prostheses by introducing three-dimensional torques.

METHODS

The cups were implanted under standard conditions into an anatomical artificial bone model. Three-dimensional torques were applied to the acetabular cups. Taking into account the resulting frictional moments of two different bearing couples, ceramic-on-ceramic and ceramic-on-polyethylene, the relative micromotions of the cups were recorded as maximum total micromotion, translational and rotational micromotion, and the primary stability values of the three cups were compared.

RESULTS

Relative micromotion of all cup models was always significantly smaller with the CoC bearing couples than with the CoP bearing couples (p < 0.001). The rotational micromotion was always lower (p < 0.001) than the translational micromotion, and the rotational as well as the translational micromotions were each always lower than the maximum total micromotion (p < 0.001, p < 0.010). The thinnest-walled cup system always showed the largest relative micromotions.

CONCLUSION

The results of our study can be interpreted as indicating that the low relative micromotions of all cups - irrespective of the use of CoC or CoP bearing couples - are within an acceptable range favoring secondary osseointegration of the implants. Furthermore, we were able to show that the cup wall thickness and the surface quality of the cup systems have an influence on the primary stability and the elastic deformability of the examined cup systems.

Treatment of High-Grade Acetabular Defects: Do Porous Titanium Cups Provide Better Stability Than Traditional Titanium Cups When Combined With an Augment?

BACKGROUND

Revision total hip arthroplasty frequently faces challenges associated with deficient bone stock. Porous metal implants were developed to meet the challenge, but require rapid osseointegration for ultimate success. This study aims to assess relative motion as an indicator for primary stability and osseointegration of two different titanium cups each combined with a titanium augment.

METHODS

In 14 cadaver hemipelvises, 2 types of titanium acetabular cups, a traditional sintered-bead cup (POROCOAT Acetabular Cup [PAC]) and a newer porous-coated cup (GRIPTION Acetabular Cup [GAC]) each associated with a porous augment, were subjected to 3-dimensional varying loads, replicating 30% of loads experienced during normal gait. Relative motion was measured at the cup/bone, augment/bone, and cup/augment interfaces.

RESULTS

Only at the cup/bone interface was there a statistically significant difference in relative motion between the traditional PAC and the newer GAC, with PAC showing less relative motion (P = .0037). Bone mineral density (BMD) had a significant effect on relative motion (P = .0019) at the cup/bone interface of both cup types, with low BMD specimens showing more relative motion.

CONCLUSION

Both cup types combined with augments displayed minimal relative motion that was within the accepted range thought to allow osseointegration, although the traditional surface proved superior to the newer surface. This difference was more pronounced at low BMD, with the well-established PAC cup displaying less relative motion than the more porous GAC cup, consistent with better osseointegration than the more porous cup. This suggests that the more porous implant may be less advantageous than traditional PAC cups, particularly in cases with poorer bone stock.

Comparison of the stability of three fixation techniques between porous metal acetabular components and augments

Objectives

In order to address acetabular defects, porous metal revision acetabular components and augments have been developed, which require fixation to each other. The fixation technique that results in the smallest relative movement between the components, as well as its influence on the primary stability with the host bone, have not previously been determined.

Methods

A total of 18 composite hemipelvises with a Paprosky IIB defect were implanted using a porous titanium 56 mm multihole acetabular component and 1 cm augment. Each acetabular component and augment was affixed to the bone using two screws, while the method of fixation between the acetabular component and augment varied for the three groups of six hemipelvises: group S, screw fixation only; group SC, screw plus cement fixation; group C, cement fixation only. The implanted hemipelvises were cyclically loaded to three different loading maxima (0.5 kN, 0.9 kN, and 1.8 kN).

Results

Screw fixation alone resulted in up to three times more movement (p = 0.006), especially when load was increased to 100% (p < 0.001), than with the other two fixation methods (C and SC). No significant difference was noted when a screw was added to the cement fixation. Increased load resulted in increased relative movement between the interfaces in all fixation methods (p < 0.001).

Conclusion

Cement fixation between a porous titanium acetabular component and augment is associated with less relative movement than screw fixation alone for all implant interfaces, particularly with increasing loads. Adding a screw to the cement fixation did not offer any significant advantage. These results also show that the stability of the tested acetabular component/augment interface affects the stability of the construct that is affixed to the bone.Cite this article: N. A. Beckmann, R. G. Bitsch, M. Gondan, M. Schonhoff, S. Jaeger. Comparison of the stability of three fixation techniques between porous metal acetabular components and augments. Bone Joint Res 2018;7:282-288. DOI: 10.1302/2046-3758.74.BJR-2017-0198.R1.