Impingement In Total Hip Arthroplasty Research Articles

Phantom validation of a novel RSA-based impingement metric to assess component-on-component impingement risk.

Component-on-component impingement in total hip arthroplasty may lead to post-operative complications including dislocation. Despite numerous clinical studies focusing on reducing this risk, assessment methods remain limited to qualitative radiography, finite element analysis, and cadaver studies. There is a need for more precise measurements of impingement in the research setting. We aimed to validate a novel RSA-based impingement metric to measure component-on-component impingement in vivo. A phantom experiment of a standard metal-on-polyethylene total hip system was performed. RSA examinations were performed as typical for a traditional weight-bearing RSA exam for large joints. The phantom was placed in 10 possible impinged positions and one neutral position. Double exposure radiographs were taken to measure repeatability. The closest distance between the skirt of the head and the inner circumference of the acetabular cup liner was measured to assess impingement risk. Distances between the closest point of the hood to the edge of the cup in 10 impinged positions ranged from 0.05 to 1.03 mm, with the average being 0.67 mm. In the neutral position, the distance measured is 11.02 mm. Excellent repeatability was observed, with a standard deviation of 0.03 mm with an r value of 0.09. A validated RSA-based risk metric was established to evaluate in vivo hip impingement. A 1 mm threshold may be proposed to define impingement where distances approaching 1.00 mm are at a greater risk of impingement. This simplified metric holds promise for upcoming clinical studies on component-on-component impingement.

Impingement in total hip arthroplasty: A geometric model.

Total Hip Arthroplasty (THA) is one of the most common and successful surgical interventions. The survivorship at 10 years for the most commonly used systems is over 95%. However, the incidence of revision is usually much higher in the 0–1 year time period following the intervention. The most common reason for revision in this early time period is dislocation and subluxation, which may be defined as complete or permanent, and partial or temporary loss of contact between the bearing surfaces respectively. This study comprises the development of a geometric model of bone and an in situ total hip replacement, to predict the occurrence and location of bone and component impingement for a wide range of acetabular cup positions and for a series of frequently practiced activities of daily living. The model developed predicts that anterior-superior component impingement is associated with activities that result in posterior dislocation. The incidence may be reduced by increased cup anteversion and inclination. Posterior-inferior component impingement is associated with anterior dislocation activities. Its incidence may be reduced by decreased cup anteversion and inclination. A component impingement-free range was identified, running from when the cup was positioned with 45° inclination and 25° anteversion to 70° inclination and 15°–20° anteversion.

The impact of functional combined anteversion on hip range of motion: a new optimal zone to reduce risk of impingement in total hip arthroplasty.

AimsPelvic tilt (PT) can significantly change the functional orientation of the acetabular component and may differ markedly between patients undergoing total hip arthroplasty (THA). Patients with stiff spines who have little change in PT are considered at high risk for instability following THA. Femoral component position also contributes to the limits of impingement-free range of motion (ROM), but has been less studied. Little is known about the impact of combined anteversion on risk of impingement with changing pelvic position.MethodsWe used a virtual hip ROM (vROM) tool to investigate whether there is an ideal functional combined anteversion for reduced risk of hip impingement. We collected PT information from functional lateral radiographs (standing and sitting) and a supine CT scan, which was then input into the vROM tool. We developed a novel vROM scoring system, considering both seated flexion and standing extension manoeuvres, to quantify whether hips had limited ROM and then correlated the vROM score to component position.ResultsThe vast majority of THA planned with standing combined anteversion between 30° to 50° and sitting combined anteversion between 45° to 65° had a vROM score > 99%, while the majority of vROM scores less than 99% were outside of this zone. The range of PT in supine, standing, and sitting positions varied widely between patients. Patients who had little change in PT from standing to sitting positions had decreased hip vROM.ConclusionIt has been shown previously that an individual’s unique spinopelvic alignment influences functional cup anteversion. But functional combined anteversion, which also considers stem position, should be used to identify an ideal THA position for impingement-free ROM. We found a functional combined anteversion zone for THA that may be used moving forward to place total hip components.Cite this article: Bone Jt Open 2021;2(10):834–841.

Prosthetic Impingement in Total Hip Arthroplasty—The Trigger for Adverse Wear

Development of total hip arthroplasty (THA) now spans more than 5 decades encompassing combinations of metal-on-metal (MOM), ceramic-on-metal (COM), metal-on-plastic (MOP), ceramic-on-plastic (COM), and ceramic-on-ceramic (COC). In every arena of extensive technical development, there exists a data set that when viewed in isolation seemed of little import, but when assembled in-toto may produce a generational shift in perception. Our review focused on two such THA events. Firstly, COC retrieval studies (1999-2001) noted habitual wear patterns on heads and peripheral wear stripes, along with femoral-neck impingement, and ceramic surfaces stained gray by metal debris. These COC data indicated THA risks included, 1) cup edge-loading (E/L) on heads producing “stripe wear”, 2) component impingement releasing metal particles resulting in 3) tissues contaminated by metal debris. A corresponding MOM impingement-debris mechanism was only perceived by Howie (2005) in a McKee-Farrar retrieval study. Our anticipation at LLUMC was that MOM retrievals would provide superior wear details to those seen on COC retrievals. We noted stripe wear in the polar zone of CoCr heads and basal stripes in the non-wear areas. The basal-polar stripe combinations were found in all MOM retrievals. Basal-polar stripe combinations followed cup-rim profiles in our LLUMC simulations of prosthetic impingement. LPUH videos demonstrated the formation of stripe wear in functional-standing and functional-sitting postures for both impingement and subluxation episodes using THA and RA designs. The stripes on CoCr heads revealed the large scratches we now term “microgrooves”. Microgroove width varied from 40 - 400 um with 100 um being typical. The longitudinal striations in microgrooves, the raised jagged lips, scratches with shallow entry and exit termini, were all indicative of a classic 3rd-body wear mechanism. The THA impingement simulations denoted four sites of edge-loading, i.e. neck-E/L, inferior cup-E/L, superior cup-E/l and head-E/L, and ingress of Ti64 particles as a contaminating-roughness effect. Individual MOM cases referred to LLUMC demonstrated dramatic evidence of neck notching. At one end of the debris spectrum, a Ti64-notch model predicting a 6 mm3 annual wear-rate represented the release of 5700 particles of 126 um-size (approximating daily release of 16 particles). At the other end of the spectrum, if metal particles were crushed between MOM surfaces to the equivalent nanometer size found in tissues, our notch model represented approximately 22-trillion Ti64 particles annually deposited in tissues. The anatomical THA models represented in LPUH videos demonstrated that even 1-degree of head subluxation from a rigid cup created a cup “lift-off” scenario (CLO) that would open a gap of 250 - 400 microns between femoral head and cup. This would void all lubrication potential and focus the total hip-joint force along the beveled cup rim, i.e. stripe wear. It is therefore interesting that MOM impingement/debris predictions by Howie et al. have not been confirmed until now or discussed in contemporary literature. Therefore, this review of 50 years of THA data demonstrated that hip impingement was always the trigger for adverse wear and that metal-backed cups represent the potential for release of metal debris at extremes of functional standing and sitting postures.

Effects of Acetabular Cup Orientation and Implant Design on Psoas Impingement in Total Hip Arthroplasty

Background: Durable fixation has been demonstrated with use of large (jumbo) cementless cups in revision total hip arthroplasty (THA). However, anterior protrusion of the cup rim may impinge on the iliopsoas tendon and cause groin pain. The purpose of this study was to assess the effect of cup position and implant design on iliopsoas impingement.Methods: THA was performed on six cadaver hips using oversized (jumbo) acetabular components, 60 to 66mm. A stainless steel cable was inserted into the psoas tendon sheath to identify the location of the psoas muscle. CT scans were performed on each cadaver and imported in an imaging software. The acetabular shells, cables, and pelvi were segmented to create separate solid models of each. The shortest distance between each shell and cable was measured. To determine the influence of cup inclination and anteversion, the inclination (30°/40°/50°) and anteversion (10°/20°/30°) angles were varied in the virtual model for both a hemispheric and offset head center shell design. Results: The shell to wire distance increased linearly with greater cup anteversion (R2>0.99) while inclination had less effect. The distance was greater for the offset head center cup in comparison to the hemispheric cup. Our results indicate that psoas impingement is related to both cup position and implant geometry. Conclusions: For an oversized jumbo cup, psoas impingement is reduced by greater anteversion while cup inclination has little effect. An offset head center cup with an anterior recess was helpful in reducing psoas impingement in comparison to a conventional hemispherical geometry.

Anatomic stem inserted according to native anteversion could reproduce the native anterior distance of the femoral head and decrease bony impingement in total hip arthroplasty.

To investigate whether anatomic and straight stems could reproduce the anteroposterior distance (AD) of the native femoral head and evaluate the effect of AD of the femoral head on range of motion (ROM) and bony impingement. This retrospective simulation study included 64 patients who had undergone primary total hip arthroplasty between 2012 and 2014. Using computed tomography (CT)-based templating software, anatomic and straight stems were inserted with same alignment. AD of the head centre was compared between the two stems and native anatomy. Furthermore, post-operative ROM was calculated, and correlation between AD and ROM was assessed. There was a strong positive correlation between native anteversion (mean 21.9°) and anatomic stem anteversion (mean 22.5°) (R = 0.975, P < 0.001). There was no significant difference in AD between the native and anatomic stems (mean 37.7 and 38.8mm, respectively), but AD of the straight stem was significantly lower than that of the native and anatomic stems. The straight stem showed a significantly lower ROM in flexion and internal rotation angles with 90° flexion (IR) than the anatomic stem (P < 0.05 and P < 0.001, respectively). AD showed a stronger correlation with ROM of IR than with stem anteversion. The anatomic stem could reproduce AD of the native femoral head centre, but the head centre of the straight stem in the same anteversion with anatomic stem translated significantly posterior, significantly decreasing the ROM of flexion and IR and increasing bony impingement of IR. To avoid bony impingement and acquire sufficient ROM, reproducing AD was important.

Spinopelvic Motion and Impingement in Total Hip Arthroplasty

The stability of a total hip arthroplasty relies on proper positioning of the acetabular cup. Recent research has shown that this cup position is more dynamic than previously thought. The 3-dimensional orientation of the acetabular cup changes when the pelvis tilts anteriorly or posteriorly. These changes in pelvic tilt are directly related to the biomechanics of the lumbosacral junction. In normal physiology, the lumbar spine straightens with sitting and becomes more lordotic with standing. This directly translates to posterior or anterior pelvic tilt due to the rigid sacroiliac attachments. During sitting, increased posterior pelvic tilt opens the acetabulum to accommodate flexion and internal rotation of the hip. This helps prevent anterior impingement and posterior hip dislocation. During standing, anterior pelvic tilt increases superior coverage of the acetabulum. This helps prevent posterior impingement and anterior hip dislocations. When lumbosacral motion becomes pathologic, spinopelvic motion changes and acetabular cup orientation is affected. In cases of decreased lumbosacral motion, patients rely on greater hip motion to reach standing or sitting positions. This can cause pathologic impingement. In addition, traditional safe zones for cup position may not apply in the presence of pathologic spinopelvic motion. This article discusses the normal physiology of spinopelvic motion, the patterns of pathologic change, and the clinical implications therein.

Variations in sagittal and coronal stem tilt and their impact on prosthetic impingement in total hip arthroplasty.

Optimization of the combined anteversion of cup and stem has been emphasized to avoid prosthetic impingement in total hip arthroplasty (THA). However, no study has focused on the impact of variations in sagittal and coronal stem tilt against the whole femur on prosthetic range of motion. The purposes of the present study were a) to quantify the anatomical variation of sagittal and coronal tilt of the proximal canal axis against the femoral retrocondylar coordinate system, that is variation of sagittal and coronal stem tilt and b) to determine their impact on the zone of impingement-free cup position using computer simulation. Preoperative computed tomography images of 477 femurs from 409 consecutive patients who underwent THA using computed tomography-based computer navigation were stored. Virtual implantation of an anatomical stem was performed on the navigation workstation. The safe zone of the cup position with regard to prosthetic impingement was determined by motion simulation in the range of sagittal and coronal stem tilt of the subjects. The sagittal and coronal stem tilt varied by 10°, which was smaller than the stem anteversion variation. However, there was about 3 times the difference in the impingement-free zone of cup position in the ranges of sagittal and coronal stem tilt. The safe zone was significantly decreased by posterior tilt and valgus tilt of the stem. Range of motion simulation revealed that the variations in sagittal or coronal stem tilt significantly influenced the safe zone of the cup. In conclusion, although the variations in sagittal and coronal stem tilt against the femoral retrocondylar coordinate system were small, their impact on prosthetic impingement was significant.

Have large femoral heads reduced prosthetic impingement in total hip arthroplasty?

Prosthetic impingement is implicated in dislocation after total hip arthroplasty (THA). While use of larger diameter femoral heads reduces the incidence of dislocation, the effect of larger heads upon impingement rate is unknown. We assessed retrieved THA components for evidence of impingement to determine if large femoral heads reduced the rate of impingement in primary THA and what factors might influence impingement. Liners from 97 primary THAs retrieved at revision arthroplasty were scored for evidence of impingement, defined as wear or deformation on the rim of the component. Component inclination and version were measured from anteroposterior and cross-table lateral radiographs. Independent of revision diagnosis, 77% of liners demonstrated evidence of impingement. Impingement was less prevalent and less severe as head size increased. Severe impingement was observed in 50% of the liners with 28-mm heads, 15% of liners with 32-mm heads, and 21% of liners with 36-mm heads. Regardless of head size, 76% of liners revised for instability demonstrated impingement. Decreased head-neck ratio, use of an elevated liner, increased length of implantation, and increased version were associated with increased severity of impingement. We showed that larger head sizes are associated with decreased incidence of impingement on retrieved acetabular liners when compared to smaller head sizes. Larger heads have reduced but not eliminated impingement, which remains a potential source of instability.

Femur First navigation can reduce impingement severity compared to traditional free hand total hip arthroplasty

Impingement is a major source of dislocation and aseptic loosening in total hip arthroplasty (THA). We compared impingement free range of motion (ROM) using a novel computer navigated femur first approach to conventional THA. In addition, impingement between genders was also explored. In a retrospective analysis of 121 THA patients, subject-specific post-operative ROM was simulated using post-operative 3D-CT data, and compared with the benchmark ROM, essential for activities of daily living. Three parameters were defined to express both implant-to-implant (ITI) and bone-to-bone (BTB) impingement - coverage percentage, third angle, and impingement severity. Although coverage percentage was similar between the navigated and conventional group for both ITI (p = 0.69) and BTB (p = 0.82) impingement, third angle was significantly reduced in the navigation group for both ITI (p = 0.02) and BTB (p = 0.05) impingement. Impingement severity for both ITI (p = 0.01) and BTB (p = 0.05) was significantly decreased in the navigation group compared to the conventional. Impingement severity in men was considerably higher compared to women for both ITI (p = 0.002) and BTB (p = 0.02). Navigation guided femur first THA is able to improve alignment of ROM axis, and consequently, to reduce impingement in THA. Men seem to be more prone to impingement than women.

Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty

BackgroundIn this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM). MethodsAfter navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position. ResultsWe found a lower flexion of 8.3° (8.8°, P < .001) and lower internal rotation of 9.2° (9.5°, P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8° (11.8°, P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group. ConclusionFor implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning.

Current standard rules of combined anteversion prevent prosthetic impingement but ignore osseous contact in total hip arthroplasty.

In this prospective study of 135 patients undergoing cementless total hip arthroplasty (THA) we asked whether six current definitions of combined anteversion prevent impingement and increase postoperative patient individual impingement-free range-of-motion (ROM). Implant position was measured by an independent, external institute on 3D-CT performed six weeks post-operatively. Post-operative ROM was calculated using a CT-based algorithm detecting osseous and/or prosthetic impingement by virtual hip movement. Additionally, clinical ROM was evaluated pre-operatively and one-year post-operatively by a blinded observer. Combined component position of cup and stem according to the definitions of Ranawat, Widmer, Dorr, Hisatome and Yoshimine inhibited prosthetic impingement in over 90%, while combined osseous and prosthetic impingement still occurred in over 40% of the cases. The recommendations by Jolles, Widmer, Dorr, Yoshimine and Hisatome enabled higher flexion (p ≤ 0.001) and internal rotation (p ≤ 0.006). Clinically, anteversion rules of Widmer and Yoshimine provided one-year post-operatively statistically but not clinically relevant higher internal rotation (p ≤0.034). Standard rules of combined anteversion detect prosthetic but fail to prevent combined osseous and prosthetic impingement in THA. Future models will have to account for the patient-individual anatomic situation to ensure impingement-free ROM.

True Angle between Anterior-Posterior Impingement in Total Hip Arthroplasty: Why Common Constrained Cups have to Fail

Background: Dislocation after total hip arthroplasty is a common complication and partially based on impingement. Questions/purposes: (1) The purpose of this study was to investigate the angle between anterior and posterior impingement in current hip cup designs. (2) Furthermore, the aim was to design a model of an acetabular cup with sparing gaps that match to impact areas. Methods: The range of motion was simulated with Maple R8 software using standard parameters in hip arthroplasty. Afterwards, a preliminary model for an optimized acetabular cup was designed in order to avoid impingement and dislocation. Results: (1) Anterior and posterior areas of impingement were not opposite but twisted by an angle of 108.3°. (2) The two main trajectories of motion were identified and areas with corresponding reductions and elevations were appropriate modified. The improvement resulted in a “bidirectional total hip prosthesis” with a combination of a snapfit acetabular cup and a reduced cup profile. Conclusion: The improvements of the described hip prosthesis are based on a simulation and are most likely to prevent impingement and subsequent dislocation. In addition, simulation with standard implantation parameters resulted in a rotational asymmetric implant design. Clinical relevance: Our data provide evidence that conventional hip cup designs fail to prevent impingement due to (1) The incorrect assumption of diagonally arranged impingement areas and the diagonal arranged sparing gaps (2) The sparing gap design itself that technically is not reducing the rim of the cup but instead only has an elevated coverage relative to the center of motion.

Three-dimensional in vivo difference between native acetabular version and acetabular component version influences iliopsoas impingement after total hip arthroplasty.

The potential influence of acetabular component orientation on iliopsoas impingement in total hip arthroplasty (THA) has not been previously quantified. The aim of the present study was to utilize pre- and post-operative CT-based 3D models to quantify iliopsoas impingement on acetabular components, and to identify any potential factors associated with iliopsoas impingement. Iliopsoas muscle was modelled from pre-operative CT scans and transferred to the post-operative 3D models in 19 THAs. The volume and the area of the overlap between iliopsoas muscle and acetabular cup (iliopsoas volume & area) was measured on axial and sagittal images. Most protruded lengths of cup uncovered by acetabular bone were measured on axial sagittal scan of CT scans. Version of acetabulum, acetabular cup, and the difference between the two (version difference) were also measured with cup inclination and size. Linear regression analysis was performed to identify any factor influencing iliopsoas impingement. Iliopsoas impingement volume and area were 100.6 ± 226.1 (range, 0.0-663.9) mm³ and 52.6 ± 102.0 (0.0-342.3) mm³, respectively. The protruded lengths on axial and sagittal view were 6.9 ± 5.3 (0.0-16.0) and 2.1 ± 2.7 (0.0-8.0). Linear regression model showed that version difference was significantly related to the iliopsoas impingement volume and area (beta = -0.709, p = 0.041 for volume, and beta = -0.684, p = 0.047 for area). The results of this study demonstrate that iliopsoas impingement on acetabular components was influenced by the version difference between pre-operative acetabular bone and acetabular component rather than the magnitude of post-operative cup version alone.

The influence of stem offset and neck shaft angles on the range of motion in total hip arthroplasty.

To evaluate the influence of stem offset and neck shaft angles on the range of motion before component impingement (ROMCI) and bony impingement (ROMBI), and the types of impingement in total hip arthroplasty (THA). Using the computed tomography data of 101 patients who underwent THA, three-dimensional dynamic motion analysis was performed using a modular implant (Kinectiv(®) stem) that enabled adjustment of offset and leg length independently. We defined offset as horizontal offset (HO) and leg length as vertical offset (VO), and measured the ROMCI and ROMBI in flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) with the configuration of each horizontal/vertical offset. We found that HO lengthening increased the ROMCI and ROMBI in Flex and Int-R by delaying bony impingement, although excessive lengthening had minimal effect. On the contrary, VO lengthening decreased the ROMCI and ROMBI in Flex and ROMCI in Int-R. As for Ext-R, VO lengthening had positive effects on the ROMCI and ROMBI, whereas lengthening of HO had negative effects on the ROMCI and ROMBI. We demonstrated that the appropriate long offset with a low shaft angle increased the ROM in Flex and Int-R, and a high neck shaft angle increased the ROM in Ext-R. We should use implants properly in accordance with the types of impingement for avoiding dislocations in THA.

Ceramic liner fracture and impingement in total hip arthroplasty.

Ceramic-on-ceramic bearing surfaces were developed to provide an alternate to metal-on-polyethylene to decrease wear-induced osteolysis in total hip arthroplasty patients. In an effort to decrease the risk of ceramic acetabular component fracture or damage during implantation, a raised metal rim was added. How many fractures or impingements have occurred in our population of patients with ceramic liners with raised rims? With IRB-approved consent, a case series was reviewed from a single center registry and 4 of 169 patients were identified who had revision hip surgery with the ceramic liner with a raised metal rim: one for ceramic liner fracture and three for metallosis, pain, and squeaking. Implant alignment and operative findings were reviewed. One ceramic liner fracture and three cases of metallosis from impingement of the femoral neck on the posterior elevated metal rim of the acetabular liner were observed at revision. The femoral neck in each patient had a divot that corresponded to a divot in the posterosuperior liner rim. Three of the four patients had audible squeaking or clicking prior to revision. A total of 3% of patients in this series had clinically significant impingement with this implant type. Acoustic phenomenon in a ceramic on ceramic bearing surface should be investigated with a cross-table lateral radiograph to evaluate component position. If symptomatic impingement is demonstrated, revision should be considered to avoid failure from metallosis or fracture.

Risk of edge-loading and prosthesis impingement due to posterior pelvic tilting after total hip arthroplasty

BackgroundProper implant orientation is essential for avoiding edge-loading and prosthesis impingement in total hip arthroplasty. Although cup orientation is affected by a change in pelvic tilt after surgery, it has been unclear whether surgeons can prevent impingement and edge-loading by proper positioning by taking into account any change in pelvic alignment associated with alteration of hip range of motion. MethodsWe simulated implant orientation without edge-loading and prosthesis impingement, even with a change in pelvic tilt and associated change in hip range of motion after surgery, by collision detection using implant models created with computer-aided design. FindingsIf posterior pelvic tilting with a corresponding hyperextension change in hip range of motion after surgery remains within 10°, as occurs in 90% of cases, surgeons can avoid edge-loading and impingement by correctly orienting the implant, even when using a conventional prosthesis. However, if a 20° change occurs after surgery, it may be difficult to avoid those risks. InterpretationAlthough edge-loading and impingement can be prevented by performing appropriate surgery in most cases, even when taking into account postoperative changes in pelvic tilt, it may also be important to pay attention to spinal conditions to ensure that pelvic tilting is not extreme because of increasing kyphosis.

Future Bearing Surfaces in Total Hip Arthroplasty

One of the most important issues in the modern total hip arthroplasty (THA) is the bearing surface. Extensive research on bearing surfaces is being conducted to seek an ideal bearing surface for THA. The ideal bearing surface for THA should have superior wear characteristics and should be durable, bio-inert, cost-effective, and easy to implant. However, bearing surfaces that are currently being implemented do not completely fulfill these requirements, especially for young individuals for whom implant longevity is paramount. Even though various new bearing surfaces have been investigated, research is still ongoing, and only short-term results have been reported from clinical trials. Future bearing surfaces can be developed in the following ways: (1) change in design, (2) further improvement of polyethylene, (3) surface modification of the metal, (4) improvement in the ceramic, and (5) use of alternative, new materials. One way to reduce wear and impingement in THA is to make changes in its design by using a large femoral head, a monobloc metal shell with preassembled ceramic liner, dual mobility cups, a combination of different bearing surfaces, etc. Polyethylene has improved over time with the development of highly crosslinked polyethylene. Further improvements can be made by reinforcing it with vitamin E or multiwalled carbon nanotubes and by performing a surface modification with a biomembrane. Surface modifications with titanium nitride or titanium niobium nitride are implemented to try to improve the metal bearings. The advance to the fourth generation ceramics has shown relatively promising results, even in young patients. Nevertheless, further improvement is required to reduce fragility and squeaking. Alternative materials like diamond coatings on surfaces, carbon based composite materials, oxidized zirconium, silicon nitride, and sapphire are being sought. However, long-term studies are necessary to confirm the efficacy of these surfaces after enhancements have been made with regard to fixation technique and implant quality.

Bony impingement depends on the bone morphology of the hip after total hip arthroplasty

The purpose of this study was to evaluate whether the bone morphology of the hip affects the range of motion (ROM) in total hip arthroplasty (THA). Using the CT data of 63 patients who underwent THA, we calculated the ROM of flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) using 3D dynamic analysis software. We measured the distance between the anterior surface of the stem and anterior aspect of the greater trochanter (GTa length) at the cutting point and between the tip of the antero-inferior iliac spine (AIIS) and coronal plane of both femoral heads (AIIS length), as a parameter of the femur and pelvis, respectively. The relationship between the ROM, bone anatomy and impingement site was evaluated. We found a significant decrease in the ROM of Flex and the Int-R to be inversely proportional to the GTa and AIIS length. In Flex and Int-R, the anterior intertrochanteric region often impinges on the AIIS in patients with larger bone anatomy. We demonstrated that the bone morphology of the hip substantially affects the ROM of Flex and Int-R, especially in patients with large bone anatomy. For these patients we should consider bony impingement in THA.

Evaluation of range of motion restriction within the hip joint

In total hip arthroplasty, determining the impingement free range of motion requirement is a complex task. This is because in the native hip, motion is restricted by both impingement as well as soft tissue restraint. The aim of this study is to determine a range of motion benchmark which can identify motions which are at risk from impingement and those which are constrained due to soft tissue. Two experimental methodologies were used to determine motions which were limited by impingement and those motions which were limited by both impingement and soft tissue restraint. By comparing these two experimental results, motions which were limited by impingement were able to be separated from those motions which were limited by soft tissue restraint. The results show motions in extension as well as flexion combined with adduction are limited by soft tissue restraint. Motions in flexion, flexion combined with abduction and adduction are at risk from osseous impingement. Consequently, these motions represent where the maximum likely damage will occur in femoroacetabular impingement or at most risk of prosthetic impingement in total hip arthroplasty.Electronic supplementary materialThe online version of this article (doi:10.1007/s11517-012-1016-3) contains supplementary material, which is available to authorized users.