INTRODUCTION. Adverse local tissue reactions (ALTR) and elevated serum metal ion levels secondary to fretting and corrosion at head-neck junctions in modular total hip arthroplasty (THA) designs have raised concern in recent years. Factors implicated in these processes include trunnion geometry, head-trunnion material couple, femoral head diameter, head length, force of head impaction at the time of surgery, and length of implantation. Our understanding of fretting and corrosion in vivo is based largely on the analysis of retrieved prostheses explanted for reasons related to clinical failure. Little is known about the natural history of head-neck tapers in well-functioning total hip replacements. We identified ten well-functioning THA prostheses retrieved at autopsy. We sought to determine the pull-off strength required for disassembly and to characterize fretting and corrosion apparent at the head-neck junctions of THAs that had been functioning appropriately in vivo. METHODS. Ten cobalt-chromium femoral stems and engaged cobalt-chromium femoral heads were retrieved at autopsy from 9 patients, after a mean length of implantation (LOI) of 11.3 ± 8 years (range 1.9–28.5). Trunnion design and material, femoral head material, size, and length, LOI, and patient sex were recorded (Table 1). Femoral heads were pulled off on a uniaxial load frame according to ASTM standards under displacement control at a rate of 0.05mm/s until the femoral head was fully disengaged from the trunnion. Mating surfaces were gently cleaned with 41% isopropyl alcohol to remove any extraneous debris. Femoral trunnions and head tapers were examined under a stereomicroscope by two independent graders to assess presence and severity of fretting and corrosion (method previously established). Trunnions and tapers were divided into 8 regions: anterior, medial, posterior, and lateral in both proximal and distal zones. Minimum possible damage score per hip was 32 (indicating pristine surfaces). The total possible score per hip was 128 (2 damage modes × 2 mating surfaces × 8 regions × max score of 4 per region). RESULTS. Mean pull-off force among all retrievals was 2446 ± 841 N (1655 – 4246 N). Mean pull-off force for 14/16 tapers (2998 ± 1298 N) was larger than for 12/14 tapers (2210 ± 531 N). Seven retrievals (70%) had no evidence of damage on either the stem or head component (Fig. 1). Three retrievals showed evidence of damage: (1) corrosion in one zone of the femoral head taper (score 33); (2) a circumferential ring of fretting in one zone of the stem trunnion (score 36); (3) circumferential rings of minor fretting in two regions of the stem trunnion (score 40). LOI for damaged retrievals was 16.3 ± 6 years, longer than that for undamaged retrievals (9.1 ± 9.1 years). CONCLUSION. THAs that had been well-functioning in vivo showed little evidence of fretting and corrosion. The presence of minor fretting and corrosion correlated with increased LOI. Mean pull-off force was 2446 +/- 841 N among the complete sample of ten THAs. Larger tapers were associated with greater average pull-off strength. Further investigation is required in order to clarify the clinical implications of these results

Introduction: Whereas in traumatic avascular necrosis of the femoral head (ANFH) loss of the femoral head’s blood supply is due to a mechanical event, in non-traumatic AFNH it is the result of a wide variety of etiologies (e.g. alcoholism, hypercortisonism, etc.), which have in common that they lead to an intravascular complication with subsequent malperfusion of the femoral head. Additionally, for part of non-traumatic ANFH no causative factors are known, why they are called idiopathic. A mechanical cause for nontraumatic ANFH – as e.g. a repetitive trauma of the femoral head supplying deep branch of the medial femoral circumflex artery and its terminal branches by abutment of the femur against the acetabulum as in femoroacetabular impingement (FAI) – has not been discussed so far. Methods: The anteroposterior and lateral radiographs of 118 hips in 77 patients, who were operated in our institution between January 1995 and December 2005 because of nontraumatic ANFH, were evaluated with respect to the configuration of the head-neck junction. In a qualitative analysis the head-neck contour of all femora was assigned to one of the following four groups: regular waisting, mildly reduced waisting, reduced to distinctly reduced waisting or completely lacking waisting. In a quantitative analysis, angle alpha according to Nötzli et al. (2002) was measured. Furthermore, the CCD angle was measured to assess the orientation of the femoral neck in the frontal plane as well as the LCE-angle according to Wiberg and the acetabular index of the weightbearing zone to rule out any acetabular anomalies. Results: In this retrospective analysis, for 44.1% of the hip joints hypercortisonism, for 40.7% alcoholism, for 12.7% hypercholesterinemia and for 11.0% no risk factors were found documented in the patients’ files. In AP and lateral radiographs a regular waisting was found in 60.2% and 9.3%, a mildly reduced waisting in 32.2% and 37.3%, a reduced waisting or distinctly reduced waisting in 7.6% and 35.6%, and a completely lacking waisting in 0% and 16.9%, respectively, and the mean angle alpha was 63° ± 18° and 67° ± 14°, respectively. On average, the (frontally projected) CCD angle was 133° ± 6°, the LCE angle 30° ± 7° and the acetabular index of the weightbearing zone 4° ± 5°. Conclusion: Nötzli et al. found an angle alpha of 42° ± 2° for healthy individuals. A markedly increased angle alpha in both radiographic planes of the 118 investigated hips with nontraumatic ANFH was found, demonstrating a reduced shape of their head-neck junction in the anterior and lateral aspect. Together with the fact that no gross pathological deviations for the orientation of the femoral neck and the acetabulum were found, this may hint at cam-type FAI to occur in this hips and thus potentially at a mechanical (co-) factor in developing non-traumatic ANFH

Femoroacetabular impingement (FAI) results from a morphological deformity of the hip and is associated with osteoarthritis (OA). Increased bone mineral density (BMD) is observed in the antero-superior acetabulum rim where impingement occurs. It is hypothesized that the repeated abnormal contact leads to damage of the cartilage layer, but could also cause a bone remodelling response according to Wolff's Law. Thus the goal of this study was to assess the relationship between bone metabolic activity measured by PET and BMD measured in CT scans. Five participants with asymptomatic cam deformity, three patients with uni-lateral symptomatic cam FAI and three healthy controls were scanned in a 3T PET-MRI scanner following injection with [18F]NaF. Bone remodelling activity was quantified with Standard Uptake Values (SUVs). SUVmax was analyzed in the antero-superior acetabular rim, femoral head and head-neck junction. In these same regions, BMD was calculated from CT scans using the calibration phantom included in the scan. The relationship between SUVmax and BMD from corresponding regions was assessed using the coefficient of determination (R. 2. ) from linear regression. High bone activity was seen in the cam deformity and acetabular rim. SUVmax was negatively correlated with BMD in the antero-superior region of the acetabulum (R. 2. =0.30, p=0.08). SUVmax was positively correlated with BMD in the antero-superior head-neck junction of the femur (R. 2. =0.359, p=0.067). Correlations were weak in other regions. Elevated bone turnover was seen in patients with a cam deformity but the relationship to BMD was moderate. This study demonstrates a pathomechanism of hip degeneration associated with FAI deformities, consistent with Wolff's law and the proposed mechanical cause of hip degeneration in FAI. [18F]-NaF PET SUV may be a biomarker of degeneration, especially in early stages of degeneration, when joint preservation surgery is likely to be the most successful

Cam type femoro-acetabular impingement is defined by a reduced femoral head-neck offset and by excessive bone at antero-lateral femoral head-neck junction. Reconstruction of the femoral head-neck offset by removing the femoral bony prominence is a common treatment for cam type impingement. In many cases, the goal of this treatment is to make the antero-lateral head-neck offset symmetrical to the postero-lateral offset. However, guidelines for bony removal are not well established. The objective of this study is to examine if the antero-lateral and postero-lateral femoral offsets are symmetrical in normal healthy hips. CT analyses of the anatomic geometry of the femoral head and neck were performed. Hip joints with any evidence of cartilage defects and impingement were excluded. Eight cadaveric hips (3 right and 5 left hips) were examined. The average age of the cadavers was 65.1±15.1 years. A peripheral QCT scanner was used which provided 0.2 x 0.2 x 2 mm resolution. To improve the resolution of the final result, each hip joint was scanned in three different scanning directions (sagittal, coronal, and axial scanning planes). A custom imaging fixture was built to position a joint sample in three different scanning planes and a custom irrigation system supplied saline to protect the sample from dehydration. A custom segmentation program was developed to delineate the bony contours of the femoral head and neck in a fully automated manner. The segmentation data from the three differenent imaging planes were merged and a 3D solid model of each hip joint was created. The prominence of the femoral head was determined by the distance of the 3D head from an ideal sphere fitted into the 3D model. All the femoral heads were found to be asymmetric. Prominence of posteromedial femoral head averaged 0.105 mm more than the antero-medial femoral head. The antero-lateral head-neck junction was also found to be more prominent than the postero-lateral head-neck junction by an average of 1.09 mm. Asymmetry in the femoral head and femoral head-neck junction was a general finding in normal hip joints. The conventional approach of symmetric reconstruction of femoral head-neck junction may result in unnecessary removal of bone at the antero-lateral head-neck junction and potentially increase the risk of femoral neck fracture

Introduction. The process of wear and corrosion at the head-neck junction of a total hip replacement is initiated when the femoral head and stem are joined together during surgery. To date, the effects of the surface topography of the femoral head and metal stem on the contact mechanics during assembly and thus on tribology and fretting corrosion during service life of the implant are not well understood. Therefore, the objective of this study was to investigate the influence of the surface topography of the metal stem taper on contact mechanics and wear during assembly of the head-neck junction using Finite Element models. Materials and Methods. 2D axisymmetric Finite Element models were developed consisting of a simplified head-neck junction incorporating the surface topography of a threaded stem taper to investigate axial assembly with 1 kN. Subsequently, a base model and three modifications of the base model in terms of profile peak height and plateau width of the stem taper topography and femoral head taper angle were calculated. To account for the wear process during assembly a law based on the Archard equation was implemented. Femoral head was modeled as ceramic (linear-elastic), taper material was either modeled as titanium, stainless steel or cobalt-chromium (all elastic-plastic). Wear volume, contact area, taper subsidence, equivalent plastic strain, von Mises stress, engagement length and crevice width was analyzed. Results. Titanium tapers showed largest wear volume throughout all simulations, followed by stainless steel and cobalt-chromium. A larger head taper angle resulted in an increase of the wear volume for all taper materials while the increase of the plateau width resulted in a decrease of the wear volume. Taper subsidence, von Mises stress and equivalent plastic strain followed the same trends. Contact area was largest for the models with a large plateau width for all taper materials. Other taper parameters had little effect on contact area. A pure increase of the angular mismatch (AM) resulted in the strongest decrease of the engagement length, while a combined increase of the AM and plateau width showed only a moderate decrease. The smallest effect concerning the engagement length was found when a combined increase of the profile peak height and AM was simulated. Crevice width was largest for a pure increase of the AM and for a combined increase of the AM and profile peak height for all taper materials. Discussion. This study showed that depending on the surface topography and material of the stem taper, wear and taper mechanics during assembly could be affected. For the examined surface topographies wear is distinctively elevated by increasing the AM and the profile peak height due to the resulting higher mechanical loading. More parameter studies under in vivo loading and the study of other taper surface parameters like the peak-to-peak distance have to be conducted to get a deeper insight into taper mechanics and wear effects. However, this study demonstrates the importance of good manufacturing practice of components for hip replacement systems to guarantee reproducible taper mechanics. For any figures or tables, please contact authors directly

Introduction. Numerous factors have been hypothesized as contributing to mechanically-assisted corrosion at the head-neck junction of total hip prostheses. While variables attributable to the implant and the patient are amenable to investigation, parameters describing assembly of the component parts can be difficult to determine. Nonetheless, increasing evidence suggests that the manner of intraoperative assembly of modular components plays a critical role in the fretting and corrosion of modular implants. This study was undertaken to measure the magnitude and direction of the impaction forces applied by surgeons in assembling modular head-neck junctions under operative conditions where both the access and visibility of the prosthesis may potentially compromise component fixation. Methods. A surrogate consisting of the lower limb with overlying soft tissue was developed to simulate THR performed via a 10cm incision using the posterior approach. The surrogate was modified to match the resistance of the body to retraction of the incision, mobilization of the femur and hammering of the implanted femoral component. An instrumented femoral stem (SL PLUS) was surgically implanted into the bone after attachment of 3 miniature accelerometers (Dytran Inc) in an orthogonal array to the proximal surface of the prosthesis. A 32mm cobalt chrome femoral head was mounted on the trunnion (12/14 taper, machined) of the femoral stem. 15 Board-certified and trainee surgeons replicated their surgical technique in exposing the femur and impacting the modular head on the tapered trunnion. Impaction was performed using an instrumented hammer (5000 Lbf Dytran impact hammer) that provided measurements of the magnitude and temporal variation of the impact force. The components of force acting along the axis aof the neck and in the AP and ML directions were continuously samples using the accelerometers. Results. For all surgeons, the average value of the peak impaction force was 3765±1094N (range: 2358 to 6225N). Head impact was delivered in an average direction of 24.4±7.5 degrees more vertical than the trunnion axis, though this value varies from 14 to 43 degrees between individual surgeons. On average, the off-axis force perpendicular to the trunnion axis was 1586±736N, however, this value ranged from 634 to 2895N with peak loading of both the head and the implant in varus. Almost all of the applied impact was directed within 10 degrees of the mid-plane of the stem (average deviation: 2.5±5.9 degrees of with only a small force directed anteriorly or posteriorly (average force: 140±396N, anterior). The variability in the magnitude and direction of the impaction force was not associated with the level of training or the surgical experience of the participants (p>0.05). Conclusions. This study shows that large off-axis forces are developed during manual impaction of modular heads onto stem trunnions via the posterior approach. The variation in magnitude and direction of these forces varies between individual surgeons and is not systematically related to the training or experience of each surgeon in joint replacement. This variability in intraoperative assembly of head-neck junctions may contribute to the severity and incidence of mechanically assisted corrosion in total hip replacement

It has been reported that 60-85% of patients who undergo PAO have concomitant intraarticular pathology that cannot be addressed with PAO alone. Currently, there are limited diagnostic tools to determine which patients would benefit from hip arthroscopy at the time of PAO to address intra-articular pathology. This study aims to see if preoperative PROMs scores measured by IHOT-33 scores have predictive value in whether intra-articular pathology is addressed during PAO + scope. The secondary aim is to see how often surgeons at high-volume hip preservation centers address intra-articular pathology if a scope is performed during the same anesthesia event. A randomized, prospective Multicenter trial was performed on patients who underwent PAO and hip arthroscopy to treat hip dysplasia from 2019 to 2020. Preoperative PROMs and intraoperative findings and procedures were recorded and analyzed. A total of 75 patients, 84% Female, and 16% male, with an average age of 27 years old, were included in the study. Patients were randomized to have PAO alone 34 patients vs. PAO + arthroscopy 41 patients during the same anesthesia event. The procedures performed, including types of labral procedures and chondroplasty procedures, were recorded. Additionally, a two-sided student T-test was used to evaluate the difference in means of preoperative IHOT score among patients for whom a labral procedure was performed versus no labral procedure. A total of 82% of patients had an intra-articular procedure performed at the time of hip arthroscopy. 68% of patients who had PAO + arthroscopy had a labral procedure performed. The most common labral procedure was a labral refixation which was performed in 78% of patients who had a labral procedure performed. Femoral head-neck junction chondroplasty was performed in 51% of patients who had an intra-articular procedure performed. The mean IHOT score was 29.3 in patients who had a labral procedure performed and 33.63 in those who did not have a labral procedure performed P- value=0.24. Our findings demonstrate preoperative IHOT-33 scores were not predictive in determining whether intra-articular labral pathology was addressed at the time of surgery. Additionally, we found that if labral pathology was addressed, labral refixation was the most common repair performed. This study also provides valuable information on what procedures high-volume hip preservation centers are performing when performing PAO + arthroscopy

Purpose of the study: Although the association between femoroacetabular impingement and degenerative hip disease has been well established, there is no way to detect a subgroup of hips with radiographic signs of impingement which will progress to degeneration. In addition, the majority of publications on the topic have been conducted in populations of patients with an overtly degenerative hip, where the incidence of signs of impingement is higher. There has not been any study searching for the presence of signs of impingement in a symptom free population. For this reason, we searched for signs of femoroacetabular impingement in a general population and attempted to find correlations with degenerative hip disease. Material and method: We examined 200 computed tomography (CT) series of the pelvis performed for reason other than an orthopaedic indication. Four hundred hips were thus analysed with the Amira 4.1 3D software. We measured the classical coxometric parameters, orientation of the acetabulum, alpha angle, and presence or not of a bulge at the head-neck junction. Cartilage thickness was also mapped using a precise protocol. Cartilage thickness less than 0.25mm was considered for the purpose of this study to indicate degenerative disease. All data were processed with SPPS 17.0. Results: There were 103 men and 97 women, mean age 58 years and 59 years respectively. The mean alpha angle was 55.7. Retroversion was noted in 20% of hips and 28% exhibited an anterior bulge at the head-neck junction. The mean cartilage thickness at the anterosuperior part of the hip was 37mm. Degenerative disease was present in 28 patients (14%) whose mean cartilage thickness at the anterosuperior portion of the joint was 21 mm. There was no significant correlation between cartilage thickness and acetabular orientation, alpha angle, presence of a bulge at the head-neck junction. Only age was significantly correlated with degenerative disease r=−0.158 [p< 0.0]. Discussion: Among the parameters currently considered to be risk factors for degenerative disease of the hip joint, age alone was statistically linked with reduced cartilage thickness in our symptom-free population. This would suggest that the essential mechanism underlying degenerative disease remains to be discovered. Conclusion: Our findings suggest we should be prudent when proposing corrective surgery for femoroacetabular impingement. Such surgery should be reserved for symptomatic patients

INTRODUCTION. Understanding bone morphology is essential for successful computer assisted orthopaedic surgery, where definition of normal anatomical variations and abnormal morphological patterns can assist in surgical planning and evaluation of outcomes. The proximal femur was the anatomical target of the study described here. Orthopaedic surgeons have studied femoral geometry using 2D and 3D radiographs for precise fit of bone-implant with biological fixation. METHOD. The use of a Statistical Shape Model (SSM) is a promising venue for understanding bone morphologies and for deriving generic description of normal anatomy. A SSM uses measures of statistics on geometrical descriptions over a population. Current SSM construction methods, based on Principal Component Analysis (PCA), assume that shape morphologies can be modeled by pure point translations. Complicated morphologies, such as the femoral head-neck junction that has non-rigid components, can be poorly explained by PCA. In this work, we showed that PCA was impotent for processing complex deformations of the proximal femur and propose in its place our Principal Tangent Component (PTC) analysis. The new method used the Lie algebra of affine transformation matrices to perform simple computations, in tangent spaces, that corresponded to complex deformations on the data manifold. RESULTS. Both PCA and PTC were applied to the proximal femur dataset, from which selected femurs were reconstructed using the accumulation of components. PCA was deemed to have failed to reconstruct the surfaces because it required 65 components to achieve high coverage of the dataset. An important observation was that the head-neck junction was the most difficult section in the femur, requiring more components than other anatomical regions to reconstruct. This finding is consistent with the surgical observation that deformations occur in this junction for abnormal hip morphologies. PTC was successful in recovering 100% of the medical data using the only the first 5 components. We note that the encoding of deformation in PTC accounting for the performance increase. PTC outperformed PCA on the dataset in descriptive compactness. CONCLUSION. A standard SSM construction method was not adequate for analysing proximal femur surfaces because it could not easily model the complexity of non-rigid deformations at the head-neck junction. Principal tangent components, a novel method for using exponential maps on manifolds, accurately reconstructed the anatomical surfaces with very few components. Future work may include extending these concepts to describe joint diseases based on the shape of surfaces derived from volumetric data, such as CT or MRI. In conclusion, we have shown that differential geometry may be provide new insights to computational anatomy applications

Hip impingement is a diagnosis that has been increasingly recognized among young patients with hip pain. Two different types of impingement have been described. Over coverage impingement, or a “pincer” effect, occurs between the anterior wall or labrum of the acetabulum and the femoral head. This is typically due to a decrease in anteversion of the acetabulum or over-coverage of the femoral head (coxa profunda or protrusio). A so-called cam-effect impingement occurs when the femoral head-neck junction has an abnormally large radius resulting in insufficient offset. Widening of the femoral neck reduces its concavity, creating an impingement over the acetabular rim. Thus, the anterolateral junction is forced under the acetabular rim, resulting in labral injury and deterioration of the cartilage. Options for treatment of impingement include non-operative management, arthroscopic débridement, trimming of the anterior aspect of the acetabular rim after surgical dislocation of the hip, periacetabular osteotomy when impingement is secondary to an acetabular torsion abnormality, and surgical resection of a femoral neck bump and/or part of the anterolateral aspect of the neck when the primary anatomic abnormality is secondary to insufficient head-neck offset. Resection of a portion of the anterolateral aspect of the femoral head-neck junction improves the femoral head-neck ratio, increasing the range of motion before impingement occurs. Recently, surgical dislocation has been used for achieving full access to the femoral head and the acetabulum. Surgical dislocation and resection osteochondroplasty were performed in 22 hips from January 2001 to Decem-ber 2004 because of anterior impingement resulting from an idiopathic nonspherical femoral head, mild slipped capital femoral epiphysis, or poor offset at the head-neck junction. Osteonecrosis was not observed in the hips treated with this method. Pain and function markedly improved after the index operation. Two patients required hardware removal. Treatment goals in young patients with hip impingement should be pain relief and, prevention of further damage to the cartilage and subsequent osteoarthritis. Surgeons using this technique need to know the amount of bone that can be removed safely before catastrophic weakening of the femoral neck occurs

Introduction:. Femoro-acetabular impingement reduces the range of motion of the hip joint and is thought to contribute to hip osteoarthritis. Surgical treatments attempt to restore hip motion through resection of bone at the head-neck junction. Due to the broad range of morphologies of FAI, the methodology of osteochondroplasty has been difficult to standardize and often results in unexpected outcomes, ranging from minimal improvement in ROM to excessive head resection with loss of cartilage and even neck fracture. In this study we test whether a standardized surgical plan based on a pre-determined resection path can restore normal anatomy and ROM to the CAM-impinging hip. Methods:. Computer models of twelve femora with classic signs of cam-type FAI were reconstructed from CT scans. The femoral shaft and neck were defined with longitudinal axes and the femoral head by a sphere of best fit. Boundaries defining the maximum extent of anterior resection were constructed: (i) superiorly and inferiorly along the anterior femoral neck at 12:30 and 5:30 on the clock face, approximating the locations of the vascularized synovial folds; (ii) around the head-neck junction along the edge of the articular cartilage; and (iii) at the base of the neck, perpendicular to the neck axis, 20–30 mm lateral to the articular edge. All four boundaries were used to form 3 alternative resection surfaces that provided resection depths of 2 mm (small), 4 mm (medium), and 6 mm (large) at the location of the cam lesion. Solid models of each femur after virtual osteochondroplasty were created by Boolean subtraction of each of the resection surfaces from the original femoral model. For each depth of neck resection, we measured the following: (i) alpha angle, (ii) anterior offset of the head-neck junction, and (iii) volume of bone removed. Before and after each resection, we also measured the maximum internal rotation of the hip in 90° flexion and 0° abduction. Results:. The initial alpha angles of the twelve femora averaged 63.8°, with corresponding average anterior head-neck offset of 5.8 mm and average maximum internal rotation of 16.3°. Impingement prevented one specimen from attaining the initial position of 90° flexion and 0° abduction. Implementation of pre-operative plans demonstrated that normal alpha angles (<55°) could be achieved using resection depths of 2 mm, 4 mm, and 6 mm (small: 48.8°, medium: 40.8°, large: 35.3°). The corresponding changes in internal rotation were +7.7° (to 24.0°; p < 0.001), +11.8° (to 28.1°; p < 0.001), and +14.7° (to 31°; p < 0.001), with anterior offsets of 8.0 mm, 9.9 mm, and 11.2 mm, respectively. The corresponding volume of resected bone ranged from 0.57 cm. 3. to 3.20 cm. 3. . Conclusions:. Our study shows that a standardized method of pre-operative planning may enable surgeons to restore normal hip ROM, alpha angles, and anterior offsets through pre-determined bony resection. This method shows how osteochondroplasty can be customized to each deformity, thus removing only the necessary amount of bone to correct each abnormality. We believe implementation of our boundaries and method will enable surgeons to consistently and quantitatively reproduce and teach osteochondroplasty, and that this method is readily adaptable to computerized machining of the femur

In 12 patients, we measured the oxygen concentration in the femoral head-neck junction during hip resurfacing through the anterolateral approach. This was compared with previous measurements made for the posterior approach. For the anterolateral approach, the oxygen concentration was found to be highly dependent upon the position of the leg, which was adjusted during surgery to provide exposure to the acetabulum and femoral head. Gross external rotation of the hip gave a significant decrease in oxygenation of the femoral head. Straightening the limb led to recovery in oxygen concentration, indicating that the blood supply was maintained. The oxygen concentration at the end of the procedure was not significantly different from that at the start. The anterolateral approach appears to produce less disruption to the blood flow in the femoral head-neck junction than the posterior approach for patients undergoing hip resurfacing. This may be reflected subsequently in a lower incidence of fracture of the femoral neck and avascular necrosis

Objectives. Modern metal-on-metal (MoM) hip resurfacing arthroplasty (HRA), while achieving good results with well-orientated, well-designed components in ideal patients, is contraindicated in women, men with head size under 50 mm, or metal hypersensitivity. These patients currently have no access to the benefits of HRA. Highly crosslinked polyethylene (XLPE) has demonstrated clinical success in total hip arthroplasty (THA) and, when used in HRA, potentially reduces metal ion-related sequelae. We report the early performance of HRA using a direct-to-bone cementless mono-bloc XLPE component coupled with a cobalt-chrome femoral head, in the patient group for whom HRA is currently contraindicated. Methods. This is a cross-sectional, observational assessment of 88 consecutive metal-on-XLPE HRAs performed in 84 patients between 2015 and 2018 in three centres (three surgeons, including the designer surgeon). Mean follow-up is 1.6 years (0.7 to 3.9). Mean age at operation was 56 years (. sd. 11; 21 to 82), and 73% of implantations were in female patients. All patients were individually counselled, and a detailed informed consent was obtained prior to operation. Primary resurfacing was carried out in 85 hips, and three cases involved revision of previous MoM HRA. Clinical, radiological, and Oxford Hip Score (OHS) assessments were studied, along with implant survival. Results. There was no loss to follow-up and no actual or impending revision or reoperation. Median OHS increased from 24 (interquartile range (IQR) 20 to 28) preoperatively to 48 (IQR 46 to 48) at the latest follow-up (48 being the best possible score). Radiographs showed one patient had a head-neck junction lucency. No other radiolucency, osteolysis, component migration, or femoral neck thinning was noted. Conclusion. The results in this small consecutive cohort suggest that metal-on-monobloc-XLPE HRA is successful in the short term and merits further investigation as a conservative alternative to the current accepted standard of stemmed THA. However, we would stress that survival data with longer-term follow-up are needed prior to widespread adoption. Cite this article: R. B. C. Treacy, J. P. Holland, J. Daniel, H. Ziaee, D. J. W. McMinn. Preliminary report of clinical experience with metal-on-highly-crosslinked-polyethylene hip resurfacing. Bone Joint Res 2019;8:443–450. DOI: 10.1302/2046-3758.810.BJR-2019-0060.R1

Introduction. Relative motion at the modular head-neck junction of hip prostheses can lead to severe surface damage through mechanically-assisted corrosion. One factor affecting the mechanical performance of modular junctions is the frictional resistance of the mating surfaces to relative motion. Low friction increasing forces normal to the head-neck interface, leading to a lower threshold for slipping during weight-bearing. Conversely, a high friction coefficient is expected to limit interface stresses but may also allow uncoupling of the interface in service. This study was performed to examine this trade-off using finite element models of the modular head-neck junction. Methods. A finite element model (FEM) of the trunnion/ head assembly of a total hip prosthesis was initially created and experimentally validated. CAD models of a stem trunnion (taper size: 12/14mm) and a prosthetic femoral head (diameter: 28mm) were discretized into elements for finite element analysis (FEA). The trunnion (Ti6Al4V) was modelled with a hexahedral mesh (33,648 elements) and the femoral head (CoCrMo) with a tetrahedral mesh (51,182 elements). A friction-based sliding contact interface was defined between the mating surfaces. The model was loaded in 2 stages: (i) an assembly load of 4000N applied along the trunnion axis, and (ii) 500N applied along the trunnion axis in combination with a torque of 10Nm. A linear static solution was set up using Siemens NX-Nastran solver. Multiple simulations were executed by modulating the frictional coefficient at the taper-bore interface from 0.05 to 0.15 in increments of 0.01, the coefficient of 0.1 serving as the control case (Swaminathan and Gilbert, 2012). Results. The vertical and tangential displacements of the nodes on the taper of the trunnion relative to the femoral head demonstrated a strong inverse dependence upon the coefficient of friction at the interface (Fig. 1). A similar trend was observed with respect to the peak interface pressure (Fig. 2). The peak von Mises stress, however, increases with increasing coefficient of friction (Fig. 2). A Fisher's R to Z correlation test was performed on each output variable to determine its correlation with coefficient of friction. The coefficient of friction correlated significantly (p<0.0001) with both tangential displacement (r = −0.990) and vertical displacement (r = −0.974). Peak von Mises stress (r = 0.995) and peak contact pressure (r = −0.984) were also found to be significantly (p<0.0001) correlated to the coefficient of friction. Discussion. A higher coefficient of friction at the taper-bore interface led to lower contact pressure and sliding at the modular junction. However, higher coefficients of friction also led to increased von Mises stresses within the bore and the trunnion increasing the risk of yielding and fatigue failure. The current results strongly indicate that factors affecting the frictional coefficient at the interface likely influence the occurrence of and severity of mechanically-assisted corrosion in THA. Significance. The results from this study will help us set tolerances for the interlocking mechanism, identifying the minimum frictional coefficient required to obtain stable implant mechanics

Purpose. To evaluate the radiological changes after metal on metal resurfacing arthroplasty. Materials and Methods. Between December 1998 and August 2004, 166 hips in 150 patients who underwent metal resurfacing arthroplasty and followed up more than 4 years. Their mean age at the time of operation was 37.3 years(range, 15–68 years) and mean period of follow-up was 6.1 years(range, 48–95 months). The cause of arthroplasty included 115 avascular necrosis, 43 osteoarthritis, 7 ankylosing spondylitis, 1 haemophilic arthropathy. All patients had anteroposterior, translateral radiographs of the hip made preoperatively and each follow-up visit, and we analyzed radiographic findings such as radiolucencies or impingement signs around implant, neck narrowing and heterotopic ossification. Results. There was a no significant difference between preoperative and postoperative Harris hip score and range of motion. The mean stem-shaft angle was 137.4°, and 55.4% were ranged 130° to 140°. The mean inclination of acetabular component was 44.9°. There were no radiolucent lines or osteolytic lesion around the acetabular components, but 3 hips showed radiolucency around the head-neck junction(1.8%) and 4 hips showed radiolucent line around the stem (2.4%). 12 hips had impingement signs around the head-neck junction (7.2%), and 2 cases showed neck narrowing (1.2%). 3 cases had some heterotopic ossification (1.8%). In 12 cases with impingement signs, the stem-shaft angle and inclination of acetabular component were lower than control group. Pseudotumor was not found in this cohort. Conclusions. This study demonstrates no serious radiological problems till the midterm follow-up after resurfacing arthroplasty, but osteolytic lesion such as radiolucent line around head-neck junction, neck narrowing can be a potential cause of failure in future. Even though the radiolucent line around stem of femoral component revealed no subjective symptom yet, it suggests the micromotion of femoral component which can lead to femoral component loosening. The most common radiological findings, impingement signs, seem not to have clinical significance

Introduction. Mechanically-assisted corrosion of the head-neck junction present a dilemma to surgeons at revision THR whenever the femoral component is rigidly fixed to the femur. Many remove the damaged femoral head, clean the femoral taper and fix a new head in place to spare the patient the risks associated with extraction and replacement of the well-functioning femoral stem. This study was performed to answer these research questions:. Will new metal heads restore the mechanical integrity of the original modular junction after impaction on corroded tapers?. Which variables affect the stability of the new interface created at revision THR?. Materials and Methods. Twenty-two tapers (CoCr, n=12; TiAlV, n=10) were obtained for use in this study. Ten stems were in pristine condition, while 12 stems had been retrieved at revision THR and with corrosion damage to the trunnion (Goldberg scale 4). Twenty-two new metal heads were obtained for use in the study, each matching the taper and manufacturer of the original component. The following test states were performed using a MTS Machine: 1. Assembly, 2. Disassembly, 3. Assembly, 4. Toggling and 5. Disassembly. All head assemblies were performed wet using 50% calf serum in accordance to ISO 7206-10. During toggling, each specimen's loading axis was aligned 25° to the trunnion axis in the frontal plane and 10° in the sagittal plane (Figure 1). Toggling was performed at 1Hz for 2,000 cycles with a sinusoidal loading function (230N–4300N). During loading, 3D motion of the head-trunnion junction was measured using a custom jig rigidly attached to the head and the neck of each prosthesis. Relative displacement of the head with respect to the neck was continuously monitored using 6 high resolution displacement transducers with an accuracy of ±0.6µm. Displacement data was independently validated using FEA models of selected constructs. Results. The average micromotion of the head vs trunnion interface was greatest at the start of loading and stabilized after approximately 50 loading cycles at an average of 30.6±3.2µm (Figure 2). For CoCr couples, interface motion dropped by 17% when a pristine head was mounted on a corroded stem compared to a new stem (25.7±2.7µm (pristine stem), vs. 30.1±4.6µm (corroded stem), p= 0.4023) (Figure 3). However, addition of a new CoCr head with a corroded titanium stem led to an 73% increase in interface motion after assembly with a new CoCr head (Corroded: 43.4±9.8µm, Pristine: 25.2±7.0µm, p=0.1661). The resistance to head-neck disruption was 15% higher in TIALV/CoCr couples compared to CoCr/CoCr (TiAlV: 2558 ±63N, CoCr: 2226±99N, p=0.0111) and was not affected by the presence of corrosion of the trunnion (1% loss of strength in each case). Discussion. Corrosion at the trunnion does not disrupt the mechanical integrity of the junction when a CoCr head is replaced on a CoCr taper. We are less sure about the mechanical integrity of a TiAlV taper demonstrated by a trend towards increased micromotion at this junction. Further work is required to better elucidate the role of dissimilar metals in the mechanical integrity of the head-neck junction

Purpose: A growing body of literature confirms that idiopathic OA is frequently caused by subtle, and often radiographically occult, abnormalities at the femoral head-neck junction or acetabulum that result in abnormal contact between the femur and acetabulum. This condition, known as femoroacetabular impingement, is a widely accepted cause of early OA of the hip. MRI is the imaging modality that is most sensitive in detecting cam morphology. There is currently little published data regarding the prevalence of abnormalities of the femoral head-neck junction in patients without hip pain or previous hip pathology. The primary aim of this project is to examine the incidence of cam morphology in a population without hip pain or pre-existing hip disease using non-contrast MRI. Method: Two hundred asymptomatic volunteers underwent magnetic resonance imaging targeted to both hips. Subjects were examined at the time of MRI to document internal rotation of the hips at 90 degrees flexion and to assess for a positive impingement sign. The mean age was 29.4 years (range 21.4–50.6); 77.5% were Caucasian and 55.5% female. The Nötzli alpha angle was measured on oblique axial images through the middle of the femoral neck for each hip. A value greater than 50 degrees was considered consistent with cam morphology. Measurements were performed independently by two musculoskeletal radiologists. Results: Twenty-six percent of volunteers had at least one hip with cam morphology: 20% had an elevated alpha angle on either the right or the left side, and 6% had bilateral deformity. The average alpha angle was 42.6 degrees on the right (SD=7.9) and 42.4 degrees on the left (SD=7.7). Internal rotation was negatively correlated with alpha angle (p< .05). Patients with an elevated alpha angle on at least one side tended to be male (p< .01). Conclusion: The high prevalence of cam morphology in asymptomatic individuals is critical information in determining the natural history of FAI as well as establishing treatment strategies in patients presenting with pre-arthritic hip pain

Introduction: The anterior femoroacetabular impingement syndrome has so far been a great unknown in orthopedic surgery. It is typically characterized by pain when the hip is subjected to the flexion – adduction – internal rotation movement. This pain is provoked by the impaction of the head-neck interface on the anterior wall of the acetabulum. The reason for this may be a retroverted acetabulum, an excessively prominent anterosuperior femoral head-neck junction or a combination of both. For many years, patients have been diagnosed with “adductor tendinopathy” or “inguinal herniations”, when in fact they had a coxofemoral problem. Materials and methods: The first 14 cases operated were analyzed; all of them were young patients who played sports regularly. Using the modified Smith-Petersen approach, an osteoplasty was made in order to resect in the anterior wall and the superior walls of the acetabulum – the latter only in part – and the prominent head-neck junction of the femur. The result was an improvement in the joint balance and the disappearance of impingement. Unlike other authors (Ganz, Trousdale), we avoided an osteotomy of the greater trochanter as a surgical approach. Results: In 13 of the first 14 cases operated with the technique described, immediate pain relief was achieved on internal flexorotation. ROM went from −17 ° mean internal rotation (range: −14°–−28°) in one 80 ° flexion to +23° after one month postop (range: 14°–32°). After two months, there were no instances of Trendelemburg sign or osteonecrosis of the femoral head. Conclusions: We should wait to assess the pre-osteoarthritic development of these patients, although their clinical and functional improvement is evident

Introduction. Modularity is being increasingly used throughout the world for both primary and revision total hip arthroplasty. Recently there have been concerns of increased corrosion and fretting at the modular junctions. In the SROM® modular hip system, two modular junctions are the head-neck taper junction and the stem-sleeve taper junction. The aim of this study was to investigate corrosion at these junctions with the use of different bearing materials. Methods. Between 1994 and 2012, fourty-two patients were revised with SROM® stems. Reasons for revision included aseptic loosening of the cup or stem (11), periprosthetic fracture (2), osteolysis (8), dislocation (13) and other reasons (7). One was revised for stem breakage, and this was excluded from this study. We examined 41 retrieved S-ROM® comprised of 6 metal-on-metal (MOM), 12 metal-on-polyethylene (MOP), 7 ceramic-on-polyethylene (COP) and 16 ceramic-on-ceramic (COC). The orientation for all components was marked at the time of revision surgery. Both the proximal sleeve/stem and the femoral head-neck modular junctions were examined under 10X magnification, and graded by two independent observers. The head tapers were divided into 4 regions, and graded using a previously published 3 point scoring system for fretting and corrosion damage (Goldberg et al, Kop et al), for a total corrosion damage score of 12. The SROM stems were also assessed at the sleeve/stem taper junction. Each stem was divided into 8 quadrants, and graded for corrosion and fretting using the same system as the taper. In addition to severity, we also quantified area of corrosion damage of the stem at the sleeve-stem junction from 0–3, which was multiplied by the severity of damage, to give a score out of 9 for each quadrant (maximum total score of 72 for the stem). The bearing type was unknown to the investigators, so the grading was done in a blinded fashion. Corrosion scores were divided by time to account for differences in time to revision. Results. Corrosion at the head-neck taper junction was higher for 17 stems with metal heads compared to 23 stems with ceramic heads (p=0.008). The average corrosion rate at the stem-sleeve taper junction in hips with hard-on-hard bearings (COC and MOM) was higher than polyethylene (MOP and COP) bearings, but this was not significant (p=0.07). Conclusions. Corrosion at the head-neck modular junction of hips with metal heads was greater than ceramic heads, likely due to galvanic corrosion in a mixed-metal system. Greater corrosion was found at the stem-sleeve taper junction in stems with hard-on-hard bearings. This may be related to friction in the bearings

Introduction:. A surgical hip dislocation provides circumferential access to the femoral head and is essential in the treatment pediatric and adult hip disease. Iatrogenic injury to the femoral head blood supply during a surgical may result in the osteonecrosis of the femoral head. In order to reduce vessel injury and incidence of AVN, the Greater Trochanteric Osteotomy (GTO) was developed and popularized by Ganz. The downside of this approach is the increased morbidity associated with the GTO including non-union in 8% and painful hardware requiring removal in 20% of patients. (reference) Recent studies performed at our institution have mapped the extra-osseous course of the medial femoral circumflex artery and provide surgical guidelines for a vessel preserving posterolateral approach. In this cadaveric model using Gadolinium enhanced MRI, we investigate whether standardized alterations in the postero-lateral surgical approach may reliably preserve femoral head vascularity during a posterior surgical hip dislocation. Methods:. In 8 cadaveric specimens the senior author (ES) performed a surgical hip dislocation through the posterolateral approach with surgical modifications designed to protect the superior and inferior retinacular arteries. In every specimen the same surgical alterations were made using a ruler: the Quadratus Femoris myotomy occurred 2.5 cm off its trochanteric insertion, the piriformis tenotomy occurred at its insertion and extended obliquely leaving a 2 cm cuff of conjoin tendon (inferior gemellus), and the Obturator Externus (OE) was myotomized 2 cm off its trochanteric insertion. (Figure 1) For the capsulotomy, the incision started on the posterior femoral neck directly beneath the cut obturator externus tendon and extending posteriorly to the acetabulum. Superior and inferior extensions of the capsulotomy ran parallel to the acetabular rim creating a T-shaped capsulotomy. After the surgical dislocation was complete, the medial femoral circumflex artery (MFCA) was cannulated and Gadolinium-enhanced MRI performed in order to assess intra-osseous femoral head perfusion and compared to the gadolinium femoral head perfusion of the contra-lateral hip as a non-operative control. Gross-dissection after polyurethane latex injection in the cannulated MFCA was performed to validate MRI findings and to assess for vessel integrity after the surgical dislocation. Results:. In 8 cadaveric specimens MRI quantification of femoral head perfusion was 94.3% and femoral head-neck junction perfusion was 93.5% compared to the non-operative control. (Figure 2) Gross dissection after latex injection into the MFCA demonstrated intact superior and inferior retinacular arteries in all 8 specimens. (Figure 3). Discussion and Conclusions:. In this study, perfusion to the femoral head and head-neck junction is preserved following posterior surgical dislocation through the postero-lateral approach. These preliminary findings suggest that specific surgical modifications can protect and reliably maintain vascularity to the femoral head after surgical hip dislocation. This approach may benefit hip resurfacing and potentially decease risk of femoral neck fracture secondary to osteonecrosis. In addition this may allow a vascular preserving surgical hip dislocation to be performed without the need for a GTO