Introduction. Femoral neck impingement occurs clinically in total hip replacements (THR) when the acetabular liner articulates against the neck of a femoral stem prosthesis. This may occur in vivo due to factors such as prostheses design, patient anatomical variation, and/or surgical malpositioning, and may be linked to joint instability, unexplained pain, and dislocation. The Standard Test Method for Impingement of Acetabular Prostheses, ASTM F2582 −14, may be used to evaluate acetabular component fatigue and deformation under repeated impingement conditions. It is worth noting that while femoral neck impingement is a clinical observation, relative motions and loading conditions used in ASTM F2582-14 do not replicate in vivo mechanisms. As written, ASTM F2582-14 covers failure mechanism assessment for acetabular liners of multiple designs, materials, and sizes. This study investigates differences observed in the implied and executed kinematics described in ASTM F2582-14 using a Prosim electromechanical hip simulator (Simulation Solutions, Stockport, Greater Manchester) and an AMTI hydraulic 12-station hip simulator (AMTI, Watertown, MA). Method. Neck impingement testing per ASTM F2582-14 was carried out on four groups of artificially aged acetabular liners (per ASTM F2003-15) made from GUR 1020 UHMWPE which was re-melted and cross-linked at 7.5 Mrad. Group A (n=3) and B (n=3) consisted of 28mm diameter femoral heads articulating on 28mm ID × 44mm OD acetabular liners. Group C (n=3) and D (n=3) consisted of 40mm diameter femoral heads articulating on lipped 40mm ID × 56mm OD 10° face changing acetabular liners. All acetabular liners were tested in production equivalent shell-fixtures mounted at 0° initial inclination angle. Femoral stems were potted in resin to fit respective simulator test fixtures. Testing was conducted in bovine serum diluted to 18mg/mL protein content supplemented with sodium azide and EDTA. Groups A and C were tested on a Prosim; Groups B and D were tested on an AMTI. Physical examination and coordination measurement machine (CMM) analyses were conducted on all liners pre-test and at 0.2 million cycle intervals to monitor possible failure mechanisms. Testing was conducted for 1.0 million cycles or until failure. An Abaqus/Explicit model was created to investigate relative motions and contact areas resulting from initial impingement kinematics for each test group. Results. Effects of kinematic differences in the execution of ASTM F2582-14 were observed in the four groups based on simulator type (Figure 1) and liner design. The Abaqus/Explicit FEA model revealed notable differences in relative motions and contact points (Figure 2) between specimen components i.e. acetabular liner, femoral head, and femoral stem throughout range of motion. Acetabular liner angular change within shell-fixtures, rim deformation, crack propagation, and metal-on-metal contact between acetabular shell-fixtures and femoral stems were observed as potential failure mechanisms (Figure 3) throughout testing. These mechanisms varied in severity by group due to differing contact stresses and simulator constraints. Significance. Investigating failure mechanisms caused by altered kinematics of in-vitro neck impingement testing, due to influences of simulator type and acetabular liner design, may aid understanding of failure mechanisms involved when assessing complaints/retrievals and influence future prosthetic designs. For any figures or tables, please contact the authors directly

Polyethylene contact stresses have been shown to correlate with wear in total hip arthroplasty (THA). Several liner designs have been introduced in an attempt to increase stability or reduce impingement and increase range of motion. This study analyzed the effect of liner design on range of motion (ROM) and PE contact stresses in a finite element model (FEM). FEMs of four liner designs were generated: Generic was modelled as a simple hemisphere, Chamfer had a wide chamfer on the inner edge of the liner to increase ROM, Highwall had an extended lip to increase stability, and Anteverted created a 20° anteversion with lat-eralisation of the centre of rotation. With the liners in varying positions of abduction and anteversion, physiologic loads were applied through the femoral head. Hip ROM was measured by rotating the head and neck in different directions until prosthetic impingement. Significant differences in ROM were seen relative to the Generic liner. Chamfer increased ROM by mean 16%. Highwall reduced ROM by mean 12%. Anteverted increased flexion by 17% but decreased extension, abduction, and external rotation. Contact stresses were also significantly affected by liner design and acetabular orientation. Overall for the same acetabular position, contact stresses were higher for Chamfer and lower for Highwall and Anteverted. These results underline the complex interaction between cup design, hip stability, range of motion and contact stresses. Design features that increase stability tend to reduce contact stresses and ROM, while those features that increase ROM, tend to increase contact stresses. This data can help the surgeon match liner design to specific patient requirements

Aims. Registry studies on modified acetabular polyethylene (PE) liner designs are limited. We investigated the influence of standard and modified PE acetabular liner designs on the revision rate for mechanical complications in primary cementless total hip arthroplasty (THA). Methods. We analyzed 151,096 primary cementless THAs from the German Arthroplasty Registry (EPRD) between November 2012 and November 2020. Cumulative incidence of revision for mechanical complications for standard and four modified PE liners (lipped, offset, angulated/offset, and angulated) was determined using competing risk analysis at one and seven years. Confounders were investigated with a Cox proportional-hazards model. Results. Median follow-up was 868 days (interquartile range 418 to 1,364). The offset liner design reduced the risk of revision (hazard ratio (HR) 0.68 (95% confidence interval (CI) 0.50 to 0.92)), while the angulated/offset liner increased the risk of revision for mechanical failure (HR 1.81 (95% CI 1.38 to 2.36)). The cumulative incidence of revision was lowest for the offset liner at one and seven years (1.0% (95% CI 0.7 to 1.3) and 1.8% (95% CI 1.0 to 3.0)). No difference was found between standard, lipped, and angulated liner designs. Higher age at index primary THA and an Elixhauser Comorbidity Index greater than 0 increased the revision risk in the first year after surgery. Implantation of a higher proportion of a single design of liner in a hospital reduced revision risk slightly but significantly (p = 0.001). Conclusion. The use of standard acetabular component liners remains a good choice in primary uncemented THA, as most modified liner designs were not associated with a reduced risk of revision for mechanical failure. Offset liner designs were found to be beneficial and angulated/offset liner designs were associated with higher risks of revision. Cite this article: Bone Joint J 2022;104-B(7):801–810

Aims. The liner design is a key determinant of the constraint of a reverse total shoulder arthroplasty (rTSA). The aim of this study was to compare the degree of constraint of rTSA liners between different implant systems. Methods. An implant company’s independent 3D shoulder arthroplasty planning software (mediCAD 3D shoulder v. 7.0, module v. 2.1.84.173.43) was used to determine the jump height of standard and constrained liners of different sizes (radius of curvature) of all available companies. The obtained parameters were used to calculate the stability ratio (degree of constraint) and angle of coverage (degree of glenosphere coverage by liner) of the different systems. Measurements were independently performed by two raters, and intraclass correlation coefficients were calculated to perform a reliability analysis. Additionally, measurements were compared with parameters provided by the companies themselves, when available, to ensure validity of the software-derived measurements. Results. There were variations in jump height between rTSA systems at a given size, resulting in large differences in stability ratio between systems. Standard liners exhibited a stability ratio range from 126% to 214% (mean 158% (SD 23%)) and constrained liners a range from 151% to 479% (mean 245% (SD 76%)). The angle of coverage showed a range from 103° to 130° (mean 115° (SD 7°)) for standard and a range from 113° to 156° (mean 133° (SD 11°)) for constrained liners. Four arthroplasty systems kept the stability ratio of standard liners constant (within 5%) across different sizes, while one system showed slight inconsistencies (within 10%), and ten arthroplasty systems showed large inconsistencies (range 11% to 28%). The stability ratio of constrained liners was consistent across different sizes in two arthroplasty systems and inconsistent in seven systems (range 18% to 106%). Conclusion. Large differences in jump height and resulting degree of constraint of rTSA liners were observed between different implant systems, and in many cases even within the same implant systems. While the immediate clinical effect remains unclear, in theory the degree of constraint of the liner plays an important role for the dislocation and notching risk of a rTSA system. Cite this article: Bone Jt Open 2024;5(10):818–824

Introduction. Instability continues to be the number one reason for revision in primary total hip arthroplasty (THA). Commonly, impingement precedes dislocation, inducing a levering out the prosthetic head from the liner. Impingement can be prosthetic, bony or soft tissue, depending on component positioning and anatomy. The aim of this virtual study was to investigate whether bony or prosthetic impingement occurred first in well positioned THAs, with the hip placed in deep flexion and hyperextension. Methods. Twenty-three patients requiring THA were planned for a TriFit/Trinity ceramic-on-poly cementless construct using the OPS. TM. dynamic planning software (Corin, UK). The cups were sized to best fit the anatomy, medialised to sit on the acetabular fossa and orientated at 45° inclination and 25° anteversion when standing. Femoral components and head lengths were then positioned to reproduce the native anteversion and match the contralateral leg length and offset. The planned constructs were flexed and internally rotated until anterior impingement occurred in deep flexion [Fig. 1]. The type (bony or prosthetic), and location, of impingement was then recorded. Similarly, the hips were extended and externally rotated until posterior impingement occurred, and the type and location of impingement recorded [Fig. 2]. Patients with minimal pre-operative osteophyte were selected as a best-case scenario for bony impingement. Results. 6/23 (26%) patients were planned with only a 32mm articulation (<50mm cup size), with the remaining 17 patients all planned with both 32mm and 36mm articulations (≥50mm cup size). Anterior impingement was 26% prosthetic and 74% bony with the 32mm articulations, and 100% bony with the 36mm articulations. Bony impingement in deep flexion was exclusively anterior neck on anterior inferior iliac spine. Posterior impingement was 57% prosthetic and 43% bony with the 32mm articulations, and 41% prosthetic and 59% bony with the 36mm articulations. Bony impingement in hyperextension was exclusively lesser trochanter (LT) on ischium. Of the patients planned with both 32mm and 36mm articulations, there was a 14% increase in prosthetic impingement when a 32mm head was planned (35% and 21% respectively). Discussion. Impingement in THA usually precedes dislocation and should be avoided with appropriate component positioning. We found that in hyperextension, prosthetic and bony impingement were equally common. In deep flexion, impingement was almost exclusively bony. Further studies should investigate the effects of stem version, cup orientation, liner design, cup depth, native offset and retained osteophytes on the type of impingement in THA. For any figures or tables, please contact the authors directly

Introduction. Lipped liners have the potential to decrease the rate of revision for instability after total hip replacement since they increase the jumping distance in the direction of the lip. However, the elevated lip also may reduce the Range of Motion and may lead to early impingement of the femoral stem on the liner. It is unclear whether the use of a lipped liner has an impact on the level of lever-out moments or the contact stresses. Therefore, the aim of the current study was to calculate these values for lipped liners and compare these results to a conventional liner geometry. Materials and Methods. 3D Finite Element studies were conducted comparing a ceramic lipped liner prototype and a ceramic conventional liner both made from BIOLOX. ®. delta. The bearing diameter was 36 mm. To apply loading, a test taper made of titanium alloy was bonded to a femoral head, also made from BIOLOX. ®. delta. Titanium was modeled with a bilinear isotropic hardening law. For the bearing contact a coefficient of friction of both 0.09 or 0.3 was assumed to model a well and poorly lubricated system. Frictionless contact was modeled between taper and liner. Pre-load was varied between 500 N and 1500 N and applied along the taper axis. While keeping pre-load constant, lever-out force was applied perpendicular to the taper axis until subluxation occurred. Liners were fixed at the taper region. Lever-out moment, equivalent plastic strain and von Mises stress of the taper, bearing contact area and contact area between taper and liner was evaluated. Results. With increasing pre-load, larger lever-out moment, equivalent plastic strain, contact area between taper and liner and bearing contact area was found for both liner designs. However, von Mises stresses were nearly constant but slightly exceeded yield strength of titanium. For all evaluated parameters almost no differences were found between the liner designs. Lever-out moments were comparable for both designs ranging from 4.5–10.5 Nm for the lipped liner and 4.4–10.2 Nm for the conventional liner. The increase of the coefficient of friction strongly affected lever-out moments, equivalent plastic strain and contact area between taper and liner. The other parameters were not affected by varying the coefficient of friction. Discussion. This study did not find significant differences in the lever-out behavior of the lipped acetabular liner compared to the conventional liner design. The inner geometry of the lipped liner is comparable to the conventional liner inner geometry. Therefore, contact area showed no significant differences and contact mechanics are identical in the current setup leading to similar results of both liner designs. For both designs small plastic deformations in the contact point of the taper were found at the contact region between liner and taper. However, the investigated mechanical parameters did not differ between the two investigated liner types. For any figures or tables, please contact authors directly

Introduction. Dual-mobility (DM) liners provide increased range of motion and stability. However, large head diameters have been associated with anterior hip pain due to impingement with surrounding soft-tissues, particularly the iliopsoas. Further, during hip extension the liner can get trapped due to anterior soft-tissue impingement that resists rotation being imparted to the liner from posterior stem-liner contact. Over time this can cause liner rim damage, leading to intra-prosthetic dislocation of the small diameter inner head. To address this, an anatomically contoured dual mobility (ACDM) liner was designed to reduce the volume of the liner below the equator that can interact with soft-tissues (Fig. 1). In this study, we utilized finite element analysis to evaluate tendon-liner contact pressure and tendon stresses with ACDM and conventional designs during hip extension, wherein the posterior edge of liner is in contact with the stem while the anterior edge is exposed to the soft-tissue. Methods. The average uniaxial stiffness (350 N/mm), and average dimensions (width × thickness = 14mm × 4mm) of 10 cadaver psoas tendon samples were determined in a separate study. The iliopsoas tendon was modelled as a Yeoh hyper-elastic material, and the material constants were tuned to match the experimental uniaxial test data. Cadaver specific FEA models were created for 5 specimens (10 hips) using computed tomography (CT) scans. The implant components were modeled as being rigid relative to the iliopsoas tendon. The iliopsoas tendon was modelled as extending from its insertion point on the lesser trochanter to the psoas notch on the pelvis for hip flexion angles of −15°, 0°, 15° and 30°. Appropriately sized DM components were implanted virtually for each specimen. Once placed in its proper position, the liner was rotated about the flexion axis until it contacted the stem posteriorly to represent its orientation during hip extension (Fig. 2). A 500N tensile load was applied to the iliopsoas tendon and the average/max stresses within the tendon, and average/max contact pressures between the tendon and liner were measured. Results. At all hip flexion angles from −15° to 30°, the tendon-liner contact pressure and tendon stresses were lower with the ACDM liners compared to the conventional liner. Contact pressure and tendon stress decreased for both liner designs with increasing hip flexion angle. At −15° flexion angle, the average contact pressure was 42.3% lower (0.36Mpa), and the maximum contact pressure was 45.1% (8.5Mpa lower), with the ACDM compared to conventional liner design. Similarly, at −15° flexion angle the average vonMises pressure in the tendon was 32.5% lower (14.8Mpa), and the maximum vonMises stress in the tendon was 55.7% (159Mpa lower) with the ACDM design. (Fig 3). Discussion. This study utilized cadaver specific FEA models to evaluate interaction between the iliopsoas tendon and conventional and ACDM liners during hip extension. The results showed a notable reduction in contact pressure and tendon stress resulting from reduced volume and more soft-tissue friendly profile of the ACDM design. Thus, the ACDM design may be able to reduce undesirable soft-tissue interaction with dual mobility liners

Introduction. Impingement of total hip arthroplasties (THAs) has been reported to cause rim damage of polyethylene liners, and in some instances has led to dislocation and/or mechanical failure of liner locking mechanisms in modular designs. Elevated rim liners are used to improve stability and reduce the risk of dislocation, however they restrict the possible range of motion of the joint, and retrieval studies have found impingement related damage on lipped liners. The aim of this study was to develop a tool for assessing the occurrence of impingement under different activities, and use it to evaluate the effects a lipped liner and position of the lip has on the impingement-free range of motion. MATERIALS & METHOD. A geometrical model incorporated a hemi-pelvis and femur geometries of one individual with a THA (DePuy Pinnacle® acetabular cup with neutral and lipped liners; size 12 Corail® stem with 32mm diameter head) was created in SOLIDWORKS (Dassault Systèmes). Joint motions were taken from kinematic data of activities of daily living that were associated with dislocation of THA, such as stooping to pick an object off the floor and rolling over. The femoral component was positioned to conform within the geometry of the femur, and the acetabular component was orientated in a clinically acceptable position (45° inclination and 20° anteversion). Variation in orientation of the apex of the lip was investigated by rotating about the acetabular axes from the superior (0°) in increments of 45° (0°−315°), and compared to a neutral liner. Results. When a lipped liner was used, implant (neck on acetabular rim) impingement was found to occur when performing sit-to-stand from a normal seat, leg cross and pivot, whereas no impingement occurred with a neutral liner. The presence and position of the lip reduced the impingement-free range of motion, compared to the neutral liner. Impingement occurred when the lip was positioned superiorly and anteriorly, when performing most of the activities that were prone to posterior dislocation, and posteriorly, posterior-superiorly and posterior-inferiorly when performing activities prone to anterior dislocation. During sit-to-stand from a normal seat no impingement occurred when a lipped or neutral liner was used. Bone impingement was observed when the performing the roll activity with both lipped and neutral liners. DISCUSSION. Impingement was observed more with lipped liners compared to neutral liners, this agrees with the findings of some clinical studies. The results indicate that the positioning of the lip influences the possible range of impingement-free motion. Considering this and the improved joint stability of using a lipped liner, a balance is required to achieve an optimal range of motion without increasing the risk of dislocation. This tool could potentially to be used to optimise lipped liner design and position, and could assist with the liner selection for patients based on their activities

Aims

Several short- and mid-term studies have shown minimal liner wear of highly cross-linked polyethylene (HXLPE) in total hip arthroplasty (THA), but the safety of using thinner HXLPE liners to maximize femoral head size remains uncertain. The objective of this study was to analyze clinical survival and radiological wear rates of patients with HXLPE liners, a 36 mm femoral head, and a small acetabular component with a minimum of ten years’ follow-up.

Young patients have been reported to have a higher risk of revision following total hip arthroplasty than older cohorts. This was attributed to the higher activity level which led to increased wear, osteolysis, and component fracture. We prospectively assessed the clinical results, wear and osteolysis, the incidence of squeaking, and the survivorship of ceramic on ceramic THA in patients younger than 50 years (mean age of 42 [18–50] years). The series included 425 THAs in 370 patients with 368 hips followed for a minimum of 2 years (mean 7.1 years, range 2–14 years). All patients received uncemented acetabular components with flush-mounted acetabular liners using an 18 degree taper. No osteolysis was observed in any uncemented construct. There was osteolysis around one loose cemented femoral component. The survivorship for reoperation for implant revision was 96.7%. There were only two acetabular liner fractures (0.47%) and one femoral head fracture (0.24%). Two of the three fractures involved a fall from a significant height. There were no hip dislocations. Five patients (1.17%) noted rare or occasional squeaking. None had reproducible squeaking. In summary, the current study shows that ceramic-on-ceramic THAs in the young patient population are extremely reliable with a very low revision rate and an absence of wear-induced osteolysis. In addition, it shows that both bearing fracture in this young patient population typically occurs with polytrauma and squeaking issues that have been raised relative to ceramic bearings occur very rarely with the flush-mounted ceramic liner design used in this study

Introduction. Dual Mobility (DM) implants have gained popularity for the treatment and prevention of hip dislocation, with increased stability provided by a large diameter mobile liner. However, distal regions of the liner can impinge on soft-tissues like hip capsule and iliopsoas, leading to anterior hip pain. Additionally, soft-tissue impingement may trap the mobile liner, leading to excessive loading of the liner rim, from engagement with the femoral stem, and subsequent intra-prosthetic dislocation. The hypothesis of this study was that reducing the liner profile below the equator (contoured design) can mitigate soft-tissue impingement without compromising inner-head pull-out resistance and overall hip joint stability (Fig. 1). Methods. The interaction of conventional and contoured liners with anterior soft-tissues was evaluated in 10 cadaveric hips (5 specimens; 2 male, 3 female; age 65 ± 10 yrs; liner diameter 42–48mm) via visual observation and fluoroscopic imaging. A metal wire was sutured to the deep fibers of the iliopsoas tendon/muscle, and metal wires were embedded in the mobile liners for fluoroscopic visualization (Fig. 2). All soft-tissue except the anterior hip capsule and iliopsoas was removed, and a rope was attached to the iliopsoas to apply tension along its natural orientation. Resistance to inner-head pull-out was evaluated via Finite Element Analysis (FEA) by simulating a full cycle of insertion of the inner head into the mobile liner and subsequent pullout. The femoral head, acetabular shell, and stem were modeled as rigid, while the mobile liner was modeled as plastically deformable. Hip joint stability was evaluated by dynamic simulations in for two dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal hip rotation; (B) Posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction. A 44 mm diameter conventional and a 44 mm contoured liner were evaluated during these tests. Results. The cadaver experiments showed that distal portion of conventional liners impinge on anterior hip capsule and iliopsoas at low flexion angles (<30°). Additionally, when the hip moved from flexion into extension, the liner motion was blocked between posterior neck engagement, and anterior soft-tissue impingement. In all hips, the soft-tissue impingement / tenting was significantly reduced with contoured liners (Fig. 7). The change in tenting could be visualized as change in distance between the iliopsoas wire, and the contoured/conventional liners on sequential fluoroscopic images. The maximum reduction in iliopsoas tenting for a given specimen ranged from 1.8 mm to 5.5 mm. Additionally, the contoured and conventional liners had identical inner-head pull-out resistance (901N vs. 909N), jump distance (9.4 mm mode-A, 11.7 mm mode-B) and impingement-free range of motion (47° mode-A, 29° mode-B). Conclusion. This study showed that distal portions of conventional DM liners can impinge against iliopsoas and hip capsule in low flexion leading to functional impediment of liner motion. Additionally, reducing the liner profile below the equator led to significant reduction in soft-tissue impingement/tenting without affecting mechanical performance. Thus, a contoured dual mobility liner design may reduce the risk of anterior hip pain and intra-prosthetic dislocation resulting from soft-tissue impingement and liner entrapment. To view tables/figures, please contact authors directly

Previous studies suggested that the shallow Ultra High Molecular Weight Polyethylene (UHMWPE) acetabular socket liner or the liner with no head centre inset can significantly increase the risk of hip joint dislocation. Independent to the traditional neck impingement models, the purpose of this study was to investigate an additional dislocation force pushing the femoral head out of UHMWPE acetabular liner bearing under direct hip joint loading and the factors including the head centre inset affecting the magnitude of this force. The 3 D Finite Element Analysis (FEA) models were constructed by (30) 10 mm thick UHMWPE liners with six inner bearing diameters ranging from 22 mm to 44 mm and five head centre insets in each bearing size from 0 mm to 2 mm. A load of 2 446 N was applied through the corresponding CoCr femoral head to the rim of the liner. The DF was recorded as a function of head centre inset and head diameter. The results were verified by the physical tests of two 28 mm head bearing liners with 0 and 1.5 mm head centre insets respectively. The results showed that the highest DF was 1 269N in 0 mm head centre inset and 22 mm head. The lowest DF was 171 N in 2 mm head centre inset and 44 mm head. The DF decreased as the head centre inset and head size increased. When head centre inset increased from 0 mm to 1 mm, the DF was reduced more than 50%. Two experimental data points were consistent with the trend of DF curve found in the FEA. We concluded that the new intrinsic dislocating force DF can be induced by the rim directed joint loading force alone and can reach as high as 51% of the femoral loading force. This can be the addition to the dislocating moment generated by the neck impingement. A head inset above 1mm can effectively reduce DF to less than 25% of the joint force. Furthermore, the larger head diameter generates less DF. The DF is likely caused by the wedge effect between the deformed polyethylene bearing and the femoral head. The inset allows the femoral head to be separated from the spherical bearing surface, thus reducing the wedge effect. Our observation of the stabilizing effect trend of the head centre inset was consistent with reported clinical data. However, the increased height of the capture wall also reduces the range of motion. It is therefore necessary to minimize the inset height with the maximum benefit of the stabilize effect. This study suggested the larger femoral head has the advantage of reducing the DF and the stabilizing effect is more effective when combining with the inset wall. The result of this study should provide the guidance to improve acetabular poly liner design for better joint stability

Aims

The aim of our study was to investigate the effect of asymmetric crosslinked polyethylene liner use on the risk of revision of cementless and hybrid total hip arthroplasties (THAs).

Introduction. Dual-mobility (DM) liners have increased popularity due to the range of motion and stability provided by these implants. However, larger head diameters have been associated with anterior hip pain, due to surrounding soft-tissue impingement, particularly the iliopsoas. To address this, an anatomically contoured dual mobility (ACDM) liner was designed by reducing the volume of the liner below the equator (Fig1). Previous cadaver studies have shown that the ACDM significantly reduces iliopsoas tenting and trapping of the liner compared to conventional designs. We created a finite element study based on previous cadaver testing to further analyze the effectiveness of the ACDM design in reducing soft-tissue impingement, specifically the tendon-liner contact pressure and the tendon stress. Methods. The finite element model was developed within COMSOL 4.3b. The psoas tendon was modelled as a Yeoh hyper-elastic Material, which uses 3 constants (c1-c3), density (1.73g/cm3) and a bulk modulus (26GPa)[Hirokawa,2000]. In a previous, separate study, the average stiffness of 10 psoas tendon samples (5 cadavers), were measured to be 339[N/mm] in the linear region with average width and thickness of 14mmX4mm. The 3 constants were tuned to match experimental uniaxial test data, and were 5[GPa], 0[Gpa], and 46[GPa] for c1, c2, and c3 respectively. The implant components were rigidly modeled relative to the psoas. Cadaver specific CT models were used to create the FEA geometry. The insertion points for the Psoas were digitally determined on the proximal end of the lesser trochanter, and the psoas notch on the pelvis for hip flexion angles of −15°, 0°, 15° and 30°. These insertion points determined the length of the psoas and its relative position to the femoral head in 3D. The specific liner size and position for each cadaver was determined by implant planning with the CT models. In this abstract, we only present data for 2 specimens (left/right hips) with 44mm conventional DM, and 44mm ACDM, matching specimen anatomy. A 500N tensile load was applied to the psoas tendon proximally to simulate moderate physiological loading, the average/max stresses and contact pressures between the psoas and the two liner designs were determined. Results. At all flexion angles from −15° to 30°, the ACDM had lower psoas-liner contact pressure and stress compared to the conventional liner. Both contact pressure and tendon stress decreased for both liners with increasing hip flexion. At −15° flexion angle, there was an average contact pressure difference of .51MPa between the conventional and ACDM designs, or 37% decrease in pressure when using the ACDM. The average difference in tendon stress was 67.9MPa, or a 59% decrease in stress when using the ACDM (fig2, fig3). Conclusion. This study utilized cadaver specific FEA models to evaluate interaction between the iliopsoas tendon and conventional and ACDM liners. Although this abstract presented FEA models for only four hips (two specimens), the results show a notable reduction in contact pressure and tendon stress with ACDM designs. This validates findings from previous cadaver studies, suggesting that anatomically contoured designs could reduce anterior hip pain and soft tissue impingement

Aims

Dislocation is the most common indication for further surgery following total hip arthroplasty (THA) when undertaken in patients with a femoral neck fracture. This study aimed to assess the complication rates of THA with dual mobility components (THA-DMC) following a femoral neck fracture and to compare outcomes between THA-DMC, conventional THA, and hemiarthroplasty (HA).

We compared the rate of revision for instability after total hip replacement (THR) when lipped and non-lipped acetabular liners were used. We hypothesised that the use of a lipped liner in a modular uncemented acetabular component reduces the risk of revision for instability after primary THR. Using data from the New Zealand Joint Registry, we found that the use of a lipped liner was associated with a significantly decreased rate of revision for instability and for all other indications. Adjusting for the size of the femoral head, the surgical approach and the age and gender of the patient, this difference remained strongly significant (p < 0.001).

We conclude that evidence from the New Zealand registry suggests that the use of lipped liners with modular uncemented acetabular components is associated with a decreased rate of revision for instability after primary THR.

Cite this article: Bone Joint J 2014;96-B:884–8.

We report the clinical and radiological outcomes of a series of contemporary cementless ceramic-on-ceramic total hip replacements (THRs) at ten years in patients aged ≤ 55 years of age. Pre- and post-operative activity levels are described. A total of 120 consecutive ceramic cementless THRs were performed at a single centre in 110 patients from 1997 to 1999. The mean age of the patients at operation was 45 years (20 to 55). At ten years, four patients had died and six were lost to follow-up, comprising ten hips. The mean post-operative Harris hip score was 94.7 (55 to 100). Radiological analysis was undertaken in 90 available THRs of the surviving 106 hips at final review: all had evidence of stable bony ingrowth, with no cases of osteolysis. Wear was undetectable. There were four revisions. The survival for both components with revision for any cause as an endpoint was 96.5% (95% confidence interval 94.5 to 98.7). The mean modified University of California, Los Angeles activity level rose from a mean of 6.4 (4 to 10) pre-operatively to 9.0 (6 to 10) at the ten-year post-operative period.

Alumina ceramic-on-ceramic bearings in cementless primary THR in this series have resulted in good clinical and radiological outcomes with undetectable rates of wear and excellent function in the demanding younger patient group at ten years.

Cite this article: Bone Joint J 2013;95-B:1603–9.

Cementless acetabular fixation has demonstrated superior long-term durability in total hip replacement, but most series have studied implants with porous metal surfaces. We retrospectively evaluated the results of 100 consecutive patients undergoing total hip replacement where a non-porous Allofit component was used for primary press-fit fixation.

This implant is titanium alloy, grit-blasted, with a macrostructure of forged teeth and has a biradial shape. A total of 81 patients (82 hips) were evaluated at final follow-up at a mean of 10.1 years (8.9 to 11.9). The Harris Hip Score improved from a mean 53 points (23 to 73) pre-operatively to a mean of 96 points (78 to 100) at final review. The osseointegration of all acetabular components was radiologically evaluated with no evidence of loosening. The survival rate with revision of the component as the endpoint was 97.5% (95% confidence interval 94 to 100) after 11.9 years. Radiolucency was found in one DeLee-Charnley zone in four acetabular components. None of the implants required revision for aseptic loosening. Two patients were treated for infection, one requiring a two-stage revision of the implant. One femoral stem was revised for osteolysis due to the production of metal wear debris, but the acetabular shell did not require revision.

This study demonstrates that a non-porous titanium acetabular component with adjunct surface fixation offers an alternative to standard porous-coated implants.

This systematic review of the literature summarises the clinical experience with ceramic-on-ceramic hip bearings over the past 40 years and discusses the concerns that exist in relation to the bearing combination. Loosening, fracture, liner chipping on insertion, liner canting and dissociation, edge-loading and squeaking have all been reported, and the relationship between these issues and implant design and surgical technique is investigated. New design concepts are introduced and analysed with respect to previous clinical experience.