Key Points:. Historically, 22.25, 26, 28, or 32 mm metal femoral heads were used in primary total hip arthroplasty, but innovations in materials now permit head sizes 36 mm or larger. Stability and wear of primary total hip arthroplasty are related to the diameter and material of the femoral head. Larger diameter femoral heads are associated with increased joint stability through increases in arc range of motion and excursion distance prior to dislocation. Fixation of the acetabular component may be related to the size of the femoral head, with increased frictional torque associated with large diameter heads and certain polyethylene. Linear wear of highly crosslinked polyethylenes seems unrelated to femoral head diameter, but larger heads have been reported to have higher volumetric wear. Mechanically assisted crevice corrosion at the connection between the modular femoral head and neck may be associated with the femoral head size and material. Cobalt chromium alloy, alumina ceramic composite, or oxidised zirconium femoral heads on highly crosslinked polyethylene are the most commonly used bearing surfaces, but each may have unique risks and benefits. Conclusions. At present, there is a wave of enthusiasm for the routine use of “large” (32, 36 mm, or larger) femoral heads with highly crosslinked polyethylene for the vast majority of patients having a primary THA. It may be reasonable to consider the “graduated femoral head-outer acetabular diameter system”, using 28 mm femoral heads with “smaller” acetabular components (<50 mm), 32 mm femoral heads with acetabular components 50 – 56 mm outer diameter, and 36 mm or larger femoral heads with acetabular components 58 mm or larger in diameter, to minimise both the risk of dislocation and the frictional torque. Although the linear wear of highly crosslinked polyethylene appears to be independent of head size, the reported increase in volumetric wear with large femoral heads and highly crosslinked polyethylene requires further study, and should temper the use of femoral heads 36 mm or larger in younger and more active patients. With its long and successful history, it is difficult to recommend the complete abandonment of the cobalt chromium alloy femoral head in all patients having a primary THA. Alumina ceramic or oxidised zirconium heads may be considered for younger, heavier, and more active patients, who seem to have the highest risk of trunnion corrosion. Surgeons and patients should be aware of the unique possible complications of these two newer femoral head materials

Dynamic 2D sonography of the infant hip is a commonly used clinical procedure for developmental dysplasia of the hip (DDH) screening. It however has been found to be unreliable with some studies reporting associated misdiagnosis rates of up to 29%. In a recent systematic review, Charlton et al. examined dynamic ultrasound (US) screening for hip instability in the first six weeks after birth and found current best practices for such early screening techniques to be divergent between international institutions in terms of clinical scanning protocols. Such protocols include: the appropriate scanning plane and US probe position (e.g. coronal, transverse, lateral, anterior), DDH diagnostic metrics (e.g. femoral head coverage, alpha angle), appropriate patient age when scanning, and follow up procedures. To improve reliability of diagnosis and to help in standardizing diagnosis across different raters and health-centers, we propose an automated method for dynamically assessing hip instability using 3D US. 38 infant hips from 19 patients were scanned with B-mode 3D US by a paediatric orthopaedic surgeon and two technologists from the radiology department at a paediatric tertiary care centre. To quantify hip assessment, we proposed the use of femoral head coverage variability (ΔFHC3D) within 3D US volumes collected during a sequence of US scans (one at rest, and another with posterior stress applied to the joint as maneuvered during a dynamic assessment). We used phase symmetry image features to localize the ilium's vertical cortex and a random forest classifier to identify the location of the femoral head. The proposed ΔFHC3D provided good repeatability with an average test-retest ICC measure of 0.70 (95% confidence interval: 0.35 to 0.87, F(21,21) = 7.738, p<.001). The mean difference of ΔFHC3D measurements was 0.61% with a SD of 4.05%. Since the observed changes in ΔFHC3D start near 0% and range up to about 18% from stable to mildly unstable hips in this cohort, the mean difference and standard deviation of ΔFHC3D measurements observed suggest that the proposed metric and technique likely have sufficient resolution and repeatability to quantify differences in hip laxity. The long-term significance of this approach to evaluating dynamic assessments may lie in increasing early diagnostic accuracy in order to prevent dysplasia remaining undetected prior to manifesting itself in early adulthood joint disease

Introduction. Corrosion products from modular taper junctions are a potent source of adverse tissue reactions after THR. In an attempt to increase the area of contact and resistance to interface motion in the face of taper mismatches, neck trunnions are often fabricated with threaded surfaces designed to deform upon assembly. However, this may lead to incomplete contact and misalignment of the head on the trunnion, depending upon the geometry and composition of the mating components. In this study we characterized the effect of different femoral head materials on the strength and area of contact of modular taper constructs formed with TiAlV trunnions. Materials and Methods. Three groups of 36mm femoral heads (CoCr, Biolox ceramic; Oxinium) and matching Ti-6Al-4V rods with 12/14 trunnions were selected for use in this study. The surface of each trunnion was coated with a 20nm layer of gold applied by sputter-coating in vacuo. Each head/trunnion pair was placed in an alignment jig and assembled with a peak axial impaction force of 2000N using a drop tower apparatus. After assembly, each taper was disassembled in a custom apparatus mounted in a mechanical testing machine (Bionix. MTS. After separation of the components, the surface of each trunnion was examined with backscattered electron microscopy to reveal the area of disruption of the original gold-coated surface. Images encompassing the entire surface of the trunnion were collected and quantified by image processing. Results. The force required to disassemble the Oxinium and Biolox heads from their mating tapers were 2153±104N and 2200±145N, respectively (p-=0.5359). In contrast, the average disassembly force of the CoCr-TiAlV couples was 47% less (1165±156N, p<0.0001). Direct contact between the trunnion and the femoral head was only present over 3.7±0.3% of the nominal surface area of the modular junctions and was limited to the crests of the threads. Contact area did not vary as a function of head composition (p>0.4). However, there were noticeable differences in terms of the distribution of contact between the head and the trunnion. CoCr heads typically had large spans of noncontact immediately below the apex of the taper and opposite each other at the trunnion base. Biolox heads tended to have complete contact at the apex but only extended down 30% of the taper and intermittently at the base. Oxinium heads had comparable complete contact areas to Biolox at the apex but unlike Biolox and CoCr, a uniform band of contact existed at the base. Conclusions. CoCr heads provided only half the resistance to disassembly of Biolox and Oxinium heads. The total area of direct head-trunnion contact is minimal and is not affected by head composition. The heads studied had characteristic patterns of interface contact. This may be due to variations in the geometry of the bores within each head combined with cocking of the femoral head during seating as the thread peaks are being deformed. For any figures or tables, please contact authors directly

Introduction. Up to 60% of total hip arthroplasties (THA) in Asian populations arise from avascular necrosis (AVN), a bone disease that can lead to femoral head collapse. Current diagnostic methods to classify AVN have poor reproducibility and are not reliable in assessing the fracture risk. Femoral heads with an immediate fracture risk should be treated with a THA, conservative treatments are only successful in some cases and cause unnecessary patient suffering if used inappropriately. There is potential to improve the assessment of the fracture risk by using a combination of density-calibrated computed tomographic (QCT) imaging and engineering beam theory. The aim of this study was to validate the novel fracture prediction method against in-vitro compression tests on a series of six human femur specimens. Methods. Six femoral heads from six subjects were tested, a subset (n=3) included a hole drilled into the subchondral area of the femoral head via the femoral neck (University of Leeds, ethical approval MEEC13-002). The simulated lesions provided a method to validate the fracture prediction model with respect of AVN. The femoral heads were then modelled by a beam loaded with a single joint contact load. Material properties were assigned to the beam model from QCT-scans by using a density-modulus relationship. The maximum joint loading at which each bone cross-section was likely to fracture was calculated using a strain based failure criterion. Based on the predicted fracture loads, all six femoral heads (validation set) were classified into two groups, high fracture risk and low fracture risk (Figure 1). Beam theory did not allow for an accurate fracture load to be found because of the geometry of the femoral head. Therefore the predicted fracture loads of each of the six femoral heads was compared to the mean fracture load from twelve previously analysed human femoral heads (reference set) without lesions. The six cemented femurs were compression tested until failure. The subjects with a higher fracture risk were identified using both the experimental and beam tool outputs. Results. The computational tool correctly identified all femoral head samples which fractured at a significantly low load in-vitro (Figure 2). Both samples with a low experimental fracture load had an induced lesion in the subchondral area (Figure 3). Discussion. This study confirmed findings of a previous verification study on a disease models made from porcine femoral heads (Preutenborbeck et al. I-CORS2016). It demonstrated that fracture prediction based on beam theory is a viable tool to predict fracture. The tests confirmed that samples with a lesion in the weight bearing area were more likely to fracture at a low load however not all samples with a lesion fractured with a low load experimentally, indicating that a lesion alone is not a sufficient factor to predict fracture. The developed tool takes both structural and material properties into account when predicting the fracture risk. Therefore it might be superior to current diagnostic methods in this respect and it has the added advantage of being largely automated and therefore removing the majority of user bias. For any figures or tables, please contact the authors directly

Orthopaedic implants, such as femoral heads, sockets and stems, are manufactured with a high degree of smoothness and very low form error in order to function as low wear bearings. The surfaces are subject to both wear and damage during in vivo use. Articulating surfaces naturally wear during normal use. Aseptic loosening associated with osteolysis and release of wear particles is the main reason for revision of total hip arthroplasty (THA). Damage of femoral heads is well known to increase the wear rate at the articulating surface and is vulnerable to scratching during the maneuver of positioning the femoral component into the acetabulum component either in primary as in revision total hip arthroplasties. The findings emphasize the importance of achieving and maintaining good surface finish of the femoral head component. The author presents a very simple and “zero cost” method of preventing scratching of the femoral head of any kind of total hip prosthesis (ceramic on ceramic, ceramic on poly, metal on metal, metal on poly and even metal on ceramic) when the reduction of the femoral head prosthesis is done inside the new acetabular component with metal, ceramic liner or poly liner with metal back (where the scratching can also occur) as one of the final stages of the surgical procedure which can be crucial to the long survival of the hip prosthesis. A short one minute video on an e-poster will show how this can be done being an easy, reproducible, safe and reliable technique to prevent femoral head scratching

Introduction. To control anteversion of the acetabular cup and femoral stem within an appropriate angle range is extremely important in total hip arthroplasty. The sum of these angles is called the “combined anteversion” (CA), and a navigation system is necessary for its accurate intraoperative evaluation. However, navigation is too expensive and time-consuming to be commonly used. Therefore, a cheaper and easier tool for intraoperative CA evaluation is desired in the clinical field. I had an idea of marking ruler-like scales on a trial femoral head ball for this purpose. The purpose of this study was to introduce the idea in a computer simulation. Materials and Methods. An acetabular cup, a femoral head, and a femoral stem were designed virtually using three- dimensional computer graphics software (FreeCAD). The head was assembled with the femoral stem, and the axis of the stem was tilted 7 degrees to the vertical axis, referring the angle between mechanical and anatomical axes of the femur. Ruler-like scales and a horizontal line were marked on the surface of the head. The cup inclination angle was fixed at 40 degrees and paired with the head and stem assembly. The cup axis was on the stem–neck plane, which meant that CA was zero before rotating the cup and the stem. The scale at an intersecting point of the inner edge of the cup and the horizontal line was read before and after rotating the cup and the stem. I confirmed if the sum of the rotated angles of the cup and stem and the angle indicated by the scales were consistent when they were rotated at an arbitrary angle. Results. CA was successfully evaluated by the difference in angle indicated by the scales before and after rotation. Discussion. There are several definitions for cup and stem anteversion. The CA evaluated in this study was the sum of anatomical anteversion of the cup and the angle between the neck axis and epicondylar or posterior-condylar axes of the knee projected on the horizontal plane. There are several factors that make the CA evaluation by this method inaccurate. For example, when the cup inclination angle is not 40 degrees, or the pelvis or the femur are not held at the intended position, the CA indicated by the scales is not accurate. It is my future work to assess whether this method is accurate enough to be used in the clinical situation. Conclusion. Marking ruler-like scales on the femoral head would be a low-cost and effective method for rough intraoperative evaluation of CA

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in the human body after total joint replacement causes serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE is now recognized as one of the major factors restricting the longevity of artificial joints. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. In a previous study (Cho et al., 2016), it was found that roundness (out-of-roundness) of the retrieved UHMWPE acetabular cup liner [Figure 1(a)] had a tendency to increase with increasing roundness of the retrieved metal femoral head [Figure 1(b)]. It appears that roundness of the femoral head contributes to increase of wear of the polyethylene liners. We focused on the roundness of femoral head as a factor influencing the wear of polyethylene liner in hip prosthesis. In this study, further roundness measurements for 5 retrieved metal femoral heads were performed by using a coordinate measuring machine. The elasto-plastic contact analyses between femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the influence of femoral head roundness on the mechanical state and wear of polyethylene liner in hip prosthesis. Results. The range of roundness of the 5 retrieved metal femoral heads measured in this study was 14.50∼44.70 µm. Two examples of the results of FEM contact analyses are shown in Figure 2. Figure 2(a) is the results of the repeated contact analysis between femoral head and polyethylene liner under constant axial loading of 1000 N. Figure 2(b) is the results of the repeated contact analysis between femoral head and polyethylene liner under hip joint loading during normal gait. These figures show the distribution of the contact stress (von Mises equivalent stress) in the polyethylene liner. The graph in Figure 3 shows the changes in the maximum contact stress in the polyethylene liner with the flexion/extension angle of femoral head. Discussion and Conclusions. As the results of a series of the FEM contact analyses, it was found that repeated high contact stresses which exceed the yield stress of UHMWPE caused by roundness of the metal femoral head occurred in the polyethylene liner as shown in Figures 2 and 3. It was also found that the magnitude and amplitude of the repeated contact stresses had a tendency to increase with increasing roundness of the femoral head and axial loading applied to the femoral head. The results of this analytical study suggest that the roundness (out-of- roundness) of the femoral head is associated with accelerating and/or increasing wear of the UHMWPE acetabular cup liner in a hip prosthesis after total hip replacement. For any figures or tables, please contact authors directly

Introduction. Cobalt chrome femoral head has been used widely in total hip arthroplasty and has shown favorable outcome. However, there is still of concern of potential metal toxicity from the wear debris. In the other hand, titanium is well known for its biocompatibility but it is not used in bearing surface of arthroplasty due to its brittleness. Recently, coating of the prosthesis using plasma electrolytic oxidation (PEO) has shown favorable surface protection. Thus, in this study, we tried to find out whether the PEO coating on the titanium surface would provide surface protection. Materials and methods. Five Titanium alloy (Ti-6Al-4V) ball mimicking femoral head was manufactured and was coted using plasma electrolytic oxidation. Wear rate was tested using validated wear tester with 10N compression force at 80rpm. The amount of wear was detected by measuring change of weight after wear test was completed. This was compared with femoral head manufactured with titanium alloy without PEO coating. Toxicity of the debris was also tested using MTT assay with human osteoblast cell line. Results. Compare to the base titanium metal, PEO coated metal head has shown to provide surface protection. The wear rate has significantly decreased with PEO coating (median value : 0.00015g/mm. 2. vs 0.00006 g/mm. 2. ). MTT assay revealed no cytotoxicity with the amount of debris generated from the wear test. Conclusion. The result of the current study indicate that the PEO coating on the titanium femoral head can significantly decrease the wear rate and is non cytotoxic. This indicates that the femoral head manufactured with titanium alloy and PEO coating maybe a potential alternative to be used in total hip arthroplasty

Introduction. Acetabular revision surgery is challenging due to severe bone defects. Burch-Schneider anti-protrusion cages (BS cage: Zimmer-Biomet) is one of the options for acetabular revision, however higher dislocation rate was reported. A computed tomography (CT)-based navigation system indicates us the planned direction for implantation of a cemented acetabular cup during surgery. A large diameter femoral head is also expected to reduce the dislocation rate. The purpose of this study is to investigate short-term results of BS cage in acetabular revision surgery combined with the CT-based navigation system and the use of large diameter femoral head. Methods. Sixteen hips of fifteen patients who underwent revision THA using allografts and BS cage between September 2013 and December 2017 were included in this study with the follow-up of 2.7 (0.1–5.0) years. There were 12 women and three men with a mean age of 78.6 years (range, 59–61 years). The cause of acetabular revision was aseptic loosening in all hips. The failed acetabular cup was carefully removed, and acetabular bone defect was graded using the Paprosky classification. Structural allografts were morselized and packed for all medial or contained defects. In some cases, solid allograft was implanted for segmental defects. BS cage was molded to optimize stability and congruity to the acetabulum and fixed with 6.5 mm titanium screws to the iliac bone. The inferior flange was slotted into the ischium. The upside-down trial cup was attached to a straight handle cup positioner with instrumental tracker (Figure 1) and placed on the rim of the BS cage to confirm the direction of the target angle for cement cup implantation under the CT-based navigation system (Stryker). After removing the cement spacer around the X3 RimFit cup (Stryker) onto the BS cage for available maximum large femoral head, the cement cup was implanted with confirming the direction of targeting angle. Japanese Orthopedic Association score (JOA score) of the hip was used for clinical assessment. Implant position, loosening, and consolidation of allograft were assessed using anterior and lateral radiographies of the pelvis. Results. Fifteen hips had a Paprosky IIIB defect, and one hip had a pelvic discontinuity. JOA score significantly improved postoperatively. No radiolucent lines and no displacement of BS cage could be found in 9 of 15 hips. Consolidation of allografts above the protrusion cage was observed in these patients. Displacement of BS cage (>5mm) was observed in 6 hips and displacement was stopped with allograft consolidation in 5 of 6 hips. The other patient showed lateral displacement of BS cage and underwent revision surgery. Average cup inclination and anteversion angles were 37.7±5.0 degree and 24.6±7.2 degree, respectively. 12 of 16 patients were included in Lewinnek's safe zone. One patient with 32 mm diameter of the femoral head had dislocation at 17 days postoperatively. All patients who received ≥36mm diameter of femoral head showed no dislocation. Conclusions. CT-based navigation system and the use of large femoral head may influence the prevention of dislocation in the acetabular revision surgery with BS cage for severe acetabular bone defects

Introduction. To control implant alignments (anteversion and abduction angle of the acetabular cup and antetorsion of the femoral stem) within an appropriate angle range is essentially important in total hip arthroplasty to avoid implant impingement. A navigation system is necessary for accurate intraoperative evaluation of implant alignments but is too expensive and time-consuming to be commonly used. Therefore, a cheaper and easier tool for intraoperative evaluation of the alignments is desired in the clinical field. I presented an idea of marking ruler-like scales on a trial femoral head in the last ISTA Congress. The purpose of this study is to introduce an idea further improved in evaluating the combined implant alignment intraoperatively. Materials and Methods. We can evaluate the combined anteversion (sum of cup anteversion and stem antetorsion) and cup abduction angle by reading the scales at the most proximal point of inner edge of the liner when horizontal and vertical scales are marked on the femoral head appropriately and the hip joint is kept at the neutral position after implant settings and trial reduction. Whether the impingement occurred within the target ROM (Flx 130, IR40@Flx90, Ext 40, ER 40) was judged under specific conditions of the oscillation angle (139), neck-shaft angle of the stem (130), stem adduction angle (7), stem antetorsion (20 or 30), and cup anteversion and abduction angles. Cup anteversion and abduction angles were changed from 0 to 40 and 30 to 50 degrees in 1-degree increments, respectively. Impingement judgment was performed mathematically for each combination of implant alignment based on matrix transformations and trigonometric formulas. Results. Impingement-free combinations of implant alignments were identified using spreadsheet software. Points which indicated impingement-free when they matched with the most proximal point of the inner edge of the liner when the hip joint was kept neutral were plotted on the surface of the head on a 3-dimensional computer graphic software. Thus, the safe zone could be indicated visually on the trial head by a collection of these points. Discussion. We can easily judge whether the implant impingement occurs or not by using this trial head intraoperatively. However, there are several factors which make the judgment inaccurate. First, the safe zone varies according to the stem antetorsion. Second, the position at which the hip is kept intraoperatively is not necessarily neutral. Third, stem adduction angle varies according to the length of the femur. Conclusion. Safe zone mapping on the trial femoral head is low cost and easy method to be introduced in the clinical practice for the purpose of a rough judgment of implant impingement

Recent issues related to trunionosis have created a new paradigm in choosing femoral head material in total hip arthroplasty. While many consider highly-crosslinked polyethylene (XLPE) to be the gold standard currently in acetabular liner bearing surface, the debate remains whether metal or ceramic heads are best paired with XLPE. Wear characteristics are similar within an order of magnitude when comparing cobalt chrome femoral heads with ceramic when used in combination with XLPE. Therefore, discernable differences between the two femoral head materials with respect to outcomes would be the result of other biomechanical factors. Notably the fretting and corrosion of metal heads at the modular taper of femoral components is a serious concern and represents a significant deterrent when considering this material. The fretting corrosion that occurs with metal femoral heads has recently been well documented in multiple reports, and can be associated with adverse local tissue reactions necessitating revision hip arthroplasty. Frictional torque has recently been implicated in taper corrosion at modular junctions. In a recent simulated in vivo study, large diameter CoCr femoral heads were associated with increased frictional torque compared to smaller metal heads, supporting recent taper corrosion retrieval studies. In one recent series, a 1.1% incidence of head-neck taper corrosion with a metal head was reported and the authors recommended use of ceramic femoral heads. The notable downside of ceramic femoral heads is the implant cost and potential for fracture. However, the incidence of femoral head fracture with the newer mixed delta ceramic heads is exceptionally low and infrequent (rate 1.7 per 100,000). Furthermore, the incidence of taper corrosion is negligible with ceramic heads, making it the bearing couple of choice among many surgeons in combination with XLPE

There are numerous benefits of femoral head/neck modularity in both primary and revision surgery. Taper corrosion necessitating revision surgery was recognised decades ago, and there are concerns that the incidence is increasing. Variables in design, manufacturing, biomechanics, and modular head assembly have all been implicated. While the incidence of clinically significant taper corrosion is unknown, the adverse local tissue reaction (ALTR) does not appear to occur absent a cobalt chromium interface. The utilization of ceramic heads has increased in recent years. Domestically, more than 50% of femoral heads are now ceramic. This is due, at least in part, to a reduction in patient age at the time of surgery. A stronger influence, however, may be the concern for an adverse local tissue reaction (ALTR) due to taper corrosion with a cobalt chromium femoral head. Ceramic heads have a small risk of in-vivo fracture and cost more. Compared to cobalt chromium alloy, ceramic femoral heads wear less against UHMWPE, although the reduction may not be clinically significant when paired with a crosslinked polyethylene. In the Australian National Joint Replacement Registry, of the five bearing combinations with 14-year cumulative percent revision (CPR) data, the lowest is metal femoral heads with crosslinked polyethylene (5.4%). In-vivo taper assembly technique is variable and can play a role in clinical success or failure, regardless of the head material: taper corrosion with cobalt chromium heads, or fracture of ceramic heads. Standardization of head-neck taper assembly is desirable

Introduction. Collapse of femoral head associated with end-stage arthritis form hallmark of osteonecrosis of femoral head. Purpose was to assess efficacy of platelet rich plasma following core decompression in early stage of osteonecrosis of femoral head. Methods. Forty consecutive age, sex and BMI-matched patients of osteonecrosis were enrolled for this prospective randomized comparative double blinded clinical study. 19 patients belonged to intervention group (PRP with Core decompression) and 21 to control (Core decompression) group. 8ml of autologous PRP was injected into channels alongwith Calcium Chloride (4:1) after core decompression. Patients were assessed for outcome measures by pain score, functional and Harris Hip scores, Modified Kerboul angle (combined necrotic angle) in MRI. Patients were followed up after 6, 24 weeks and final follow up (mean 10.33 months). Results. There was statistically significant difference in pain score in two groups at different follow ups (p: 0.002, 0.00; 0.001). The difference in function scores in two groups was statistically significant (p: 0.001). There was statistically significant difference in Harris Hip score in two groups at different follow ups (p: 0.021, 0.001; 0.003). Mean increase in modified Kerboul angle in group A was 11.32 (SD±13.00) and in group it was 18.33 (±14.347). 6 (24%) hips in group A and 12 (42%) hips in group B had progression of disease upto final follow up. Conclusions. Core decompression augmented with platelet rich plasma is effective in providing pain relief, improving the functional status and delaying or cessation of progression in early stage of osteonecrosis of hip

Post-traumatic avascular necrosis of the femoral head usually occurs after hip dislocation and femoral neck fracture. Recently along the development of hip arthroscopy, early stage of avascular necrosis of the femoral head can be treated rthroscopically. We hereby present two cases of post-traumatic avascular necrosis patients treated with hip arthroscopy. Case 1. Twenty one year old female patient came to the hospital because of fall from height of 3 floors. Left acetabular fracture, both superior pubic rami fractures and severely displaced left femoral neck fracture were identified at the emergency department (Fig. 1-A). She underwent surgery at the injury day. After the repair of ruptured urinary bladder, internal fixation of the femoral neck was done. Four cannulated screws with washers were inserted for displaced femoral neck fracture, consistent with garden stage IV (Fig. 1-B). Skeletal traction of ipsilateral lower extremity was applied four weeks after the surgery for acetabular fracture. She visited us for painful limitation of motion on left hip at eight months postoperatively. Plain radiograph showed collapse of femoral head and osteophyte formation which were caused by post-traumatic avascular necrosis (Fig. 1-C,D). Femoral head was perforated by a screw. She was planned to remove the screw and resect the osteophyte arthroscopically. On arthroscopic examination, severe synovitis and folded, collapsed femoral cartilage were identified (Fig. 1-E). Screws were removed and osteophyte were also resected (Fig. 1-F). We filled the cavity caused by the screws with allogenic strut graft for structural support. After the surgery, pain was relieved and she came back to her active daily living and for six months, no other complication nor further collapse were identified postoperatively. Case 2. Fourty year old male patient was admitted to the hospital for fall from height about fifteen feet from the ground. Left femoral neck fracture was identified on the emergency department. Previously he had underwent intramedullary nailing for the femoral shaft fracture about five years ago. Urgent internal fixation with four cannulated screws was done on the day of injury. The fixation was unsatisfactory because previously inserted intramedullary nail hindered the proper trajectory of screws. Furthermore, direction of cephalad interlocking holes of the nail were not consistent with the anteversion of femoral neck, we could not place the screws through the nail. Four months after the index surgery, collapse of femoral head and loosening of screws have occurred. MRI showed the collapse of femoral head and posttraumatic avascular necrosis. Prominent bony beak of femoral neck were identified and he complained difficulty and pain on his hip during abduction. We left two screws for secure fixation and resected the bony beak using arthroscopic burr. After the surgery, he felt free from the pain on abduction of hip. Discussion. Even though collapse of the femoral head is identified, early intervention by the arthroscopy could minimize pain or delay the progression of arthritic change. Authors think that it might be helpful for the young adult patients in terms of pain relief and potential delay of the total hip arthroplasty

Background. The femoral head center shift on reduction time in total hip arthroplasty (THA) causes alteration of the muscle tension around the hip joint. Many studies about the shift of the femoral head in the cranio-caudal direction or medio-lateral direction on coronal plane have been reported. It has been known widely that the shift on these directions influence tension of the abductor muscle around the hip joint. Nevertheless few studies about the three-dimensional shift including the antero-posterior direction have been reported. Purpose. The purpose of this study is to evaluate the three-dimensional shift of the femoral head center in THA using three-dimensional THA templating software. Subjects & Methods. The subjects of this study were 156 primary THA cases of 143 patients. Using CT-based three-dimensional THA templating software ZedHip® (LEXI, Tokyo Japan), simulation of optimal implantation was performed on each THA case. On case which has over anteverted or less anteverted femoral neck, a stem which has modular neck system was selected to adjust anteversion of the femoral neck. The three-dimensional shift of the femoral head center on reduction time was calculated with ZedHip®. The three-dimensional shift was resolve into cranio-caudal, medio-lateral and antero-posterior direction (Fig. 1). Furthermore the correlation between the amount of the shift and hip joint deformity was investigated. Results. The average amount of the shift on cranio-caudal direction was 9.9mm to caudal side, on medio-lateral direction was 3.1mm to medial side and on antero-posterior direction was 2.6mm to posterior side. The average total amount of three-dimensional shift was 12.9mm (Fig. 2). On Crowe type 1 hips in 88 cases, the average shift to posterior side was 3.2mm, on Crowe type 2 in 20 cases was 3.7mm and on Crowe type 3 in 13 cases was 4.0mm. Among them there was no significant difference (Fig. 3). Conclusion. At THA surgery, the femoral head center shifted three-dimensionally and the maximum amount of shift on antero-posterior direction was 16.6mm to posterior side. There was no correlation between these amounts of the shift on antero-posterior direction and anatomical deformity of the hip joint. It is important to understand the shift of the femoral head center for predicting the alteration of muscle tension around the hip joint. The shift on antero-posterior direction influences the tension of iliopsoas muscle and there is a possibility that the shift to posterior side causes anterior iliopsoas impingement after THA surgery

Purpose. The aim of this study was to compare the clinical outcomes of the revision TKA in which trabecular metal cones and femoral head allografts were used for large bone defect. Method. Total 53 patients who have undergone revision TKA from July 2013 to March 2017 were enrolled in this study. Among them, 24 patients used trabecular metal cones, and 29 patients used femoral head allografts for large bone defect. There were 3 males and 21 females in the metal cone group, while there were 4 males and 25 females in the allograft group. The mean age was 70.2 years (range, 51–80) in the femoral head allograft group, while it was 79.1 years (range, 73–85) in the metal cone group. Bone defect is classified according to the AORI classification and clinical outcomes were evaluated with Visual Analogue Scale (VAS), Hospital Special Surgery-score (HSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), and ROM. Operation time was also evaluated. We used radiographs to check complications such as migration or loosening. We took follow-up x-rays and 3D CT of the patients, to assess the mean bone union period. Shapiro-Wilk test was done to check normality and Student T-test and Mann Whitney U-test were done for comparison between two groups. Result. The mean follow-up period was 3 .75 years (Range; 2.1 ∼ 5.75). The pre-op scores did not show significant difference. The mean VAS in the allograft and trabecular metal cone groups was 2.1 ± 0.87 and 1.8 ± 0.53, respectively (p = 0.16). The mean HSS score were 76.3 ± 5.51 and 79.2 ± 4.12 respectively (p = 0.13) and the mean WOMAC scores were 15.1 ± 3.25 and 14.8 ± 3.31 respectively (p = 0.06), and the mean KOOS scores were 27.8 ± 4.77 and 25.5 ± 4.84, respectively (p = 0.07). The mean ROM ranges were 100.6 ± 17.54 and 101.3 ± 19.22, respectively (p = 0.09). But the mean operation time of the allograft and trabecular metal cone groups was 137 minutes (Range; 111–198) and 102minutes (Range; 93 −133) (p=0.02) respectively, which showed statistical significance. In follow-up x-rays, no migration or loosening of the implants, osteolysis and other complications were found in both groups. In follow-up 3D CT, osteointegration was seen at the trabecular metal cone site, host bone being interpreted to the host bone. The allograft group showed fibrous and stable union in follow-up 3D CT. Conclusion. According to this study, in case of revision TKA with large bone defect, using whether allograft or trabecular metal cones did not affect the clinical outcomes. However, operation time was significantly shorter in trabecular metal cone group, therefore, in patients with poor general condition along with severe underlying diseases, usage of trabecular metal cone would be a better choice to shorten operation time and ease postoperative care. Keywords. Revision TKA, metal cone, allograft, bone defect. For any figures or tables, please contact authors directly

A multitude of different bearing combinations exist to recreate the artificial hip joint. To date, there is no particular ‘gold-standard’ total hip arthroplasty (THA) couple since none is faultless. Strategies to improve performance are aimed either at modifying the shape and design of components or their material properties. Wear particle generation is now well recognised as a cause of aseptic loosening which consistently features amongst the most common indication for revision THA and thus minimising wear lies at the cornerstone of developing bearing couples. However, history has shown the use of supposed newer and improved materials have not been without occasional catastrophic failure. Hard-on-hard bearings are theoretically more resistant to wear but component fracture and squeaking has been witnessed with ceramic-on-ceramic articulations whilst metal-on-metal articulations have been plagued by reports of pseudotumor and ALVAL formation. This has all led to resurgence in the hard-on-soft couple. More recently, corrosion at taper junctions has been identified as a significant factor in hip arthroplasty failure. Femoral head materials, surface changes or coatings may therefore have an increasing role to play. In 2005, a multi-center, prospective, assessor and patient-blinded, randomised control trial was initiated. This was designed as a three armed study with either cobalt-chrome or oxidized zirconium femoral heads articulating against highly cross-linked polyethylene (XLPE) liners and oxidized zirconium articulating against ultra-high molecular weight polyethylene (UHMWPE). Early reports that XLPE was significantly superior to UHMWPE when coupled with cobalt-chrome meant no patient involved in the study was approved to receive a couple of cobalt-chrome and UHMWPE since it was deemed to be a high wear group. We hypothesised that oxidized zirconium femoral heads would produce less linear wear than cobalt- chrome femoral heads at mid-term evaluation, whilst maintain similar outcomes when recording WOMAC, SF-36 and pain scores, and complication rates. All three groups were statistically comparable preoperatively and at five years when measuring normalised WOMAC, SF-36 and pain scale scores; all groups showed a statistically significant improvement in scores from baseline compared to at five years (p<0.001). There was no significant difference in mean femoral head penetration when either oxidized zirconium or cobalt-chrome where articulated with XLPE (p=0.1533) but a significant difference in mean femoral head penetration was observed between the group that had used UHMWPE and both the other groups which had used XLPE (p<0.001). There were no hips in which either acetabular or femoral osteolysis was observed. We have demonstrated that oxidized zirconium femoral heads are safe with low rates of wear when coupled with XLPE. However at five year follow-up, it appears that the choice of material of the acetabular bearing is more important than the choice of femoral head bearing. Further follow-up is needed in order to see if femoral head choice leads to a difference in outcome beyond 5 years as laboratory data suggests. Moreover the potential reduction of corrosion with ceramic or oxidized zirconium heads may yet also prove to be significant. It is likely that current and future data will lead us away from the use cobalt chrome heads towards alternatives that are less likely to be associated with corrosion or wear and osteolysis

INTRODUCTION. Femoral stem impingement can damage an acetabular liner, create polyethylene wear, and potentially lead to dislocation. To avoid component-to-component impingement, many surgeons aim to align acetabular cups based on the “Safe Zone” proposed by Lewinnek. However, a recent study indicates that the historical target values for cup inclination and anteversion defined by Lewinnek et al. may be useful but should not be considered a safe zone. The purpose of this study was to determine the effect of altering femoral head size on hip range-of-motion (ROM) to impingement. METHODS. Ten healthy subjects were instrumented and asked to perform six motions commonly associated with hip dislocation, including picking up an object, squatting, and low-chair rising. Femur-to-pelvis relative motions were recorded throughout for flexion/extension, abduction/adduction, and internal/external rotation. A previously reported custom, validated hip ROM three-dimensional simulator was utilized. The user imports implant models, and sets parameters for pelvic tilt, stem version, and specific motions as defined by the subjects. Acetabular cup orientations for abduction and anteversion combinations were chosen. The software was then used to compute minimum clearances or impingement between the components for any hip position. Graphs for acetabular cup abduction vs. anteversion were generated using a tapered wedge stem with a 132º neck angle, a stem version of 15°, and a pelvic tilt of 0°. The only variable changed was femoral head size. Head sizes reviewed were 32mm, 36mm, and a Dual-Mobility liner with an effective head size of 42mm. All femoral head sizes can be used with a 50mm acetabular cup. RESULTS. We found that the “Safe Zone” varies considerably depending on the size of the femoral head used for all subjects. A typical plot illustrating the ROM to impingement is presented in Figures 1a-1c. The area to the left of each curve represents an impingement zone for that motion, and to the right, a non-impingement zone. In all cases the non-impingement area is smaller than the Lewinnek safe zone. Motions like picking up an object and squatting had the greatest influence on impingement. CONCLUSIONS. The true acetabular target for impingement-avoidance motion is much smaller than previously believed and identifies the need to take into account the size of the femoral head to be used. This may explain why approximately 70% of dislocations have been reported to be found even when cups were placed within the Lewinnek safe zone. Certain activities, such as picking up an object and squatting reduce the size of the safe zone. This study supports the need for better patient planning and intraoperative execution for placement of the acetabular component

Objective. To define the common pathology of the hips with irreducible posterior dislocation combined with femoral head fracture and the outcome of surgical treatment using surgical hip dislocation technique. Design: retrospective observational clinical study. Setting: Level III referral trauma center. Patients/Participants: from January 2011till February 2014 five patients with irreducible posterior hip dislocation and femoral head fracture who underwent operation were included and they followed for at least 18 months. Intervention. Open reduction and internal fixation of fractured femoral head and labral repair by suture anchors using surgical hip dislocation through trochanteric flip osteotomy approach. Main Outcome Measures: Clinical and radiographical findings of the irreducible posterior hip dislocation, intraoperative findings, clinical outcomes using Merle d'Aubigné & Postel and Thompson & Epstein scores, and radiological outcome. Results. All patients presented clinically with a shortened lower limb in neutral or external rotation of the hip (not in Internal rotation). All were Pipkin type II fracture of femoral head with the intact part of the head buttonholed on the posterior wall of the acetabulum through a capsule-labral flap. Postoperative computed tomography revealed perfect reduction except one case with severe comminution with good reduction. Only one patient with delayed operative management developed avascular necrosis and underwent total hip arthroplasty. Conclusion. Irreducible femoral head fracture-dislocation is rare injury with different clinical presentation that shows neutral or externally rotated limb and optimal surgical management is not clear. Surgical hip dislocation gives full access to the femoral head for reconstruction and opportunity to direct repair of the labral tears

Background. The advent of highly cross-linked polyethylene has resulted in improved wear rates and reduced osteolysis with at least intermediate follow-up when compared to conventional polyethylene. However, the role of alternative femoral head bearing materials in decreasing wear is less clear. The purpose of this study was to determine in-vivo polyethylene wear rates across ceramic, Oxinium, and cobalt chrome femoral head articulations. Methods. A review of our institutional database was performed to identify patients who underwent a total hip arthroplasty using either ceramic or oxidized zirconium (Oxinium) femoral head components on highly cross-linked polyethylene between 2008 and 2011. These patients were then matched on implant type, age, sex and BMI with patients who had a cobalt chrome bearing implant during the same time period. RSA analysis was performed using the center index method to measure femoral head penetration (polyethylene wear). Secondary quality of life outcomes were collected using WOMAC and HHS Scores. Paired analyses were performed to detect differences in wear rate (mm/year) between the cobalt chrome cohorts and their matched ceramic and Oxinium cohorts. Additional independent group comparisons were performed by analysis of variance with the control groups collapsed to determine wear rate differences between all three cohorts. Results. A total of 75 patients underwent RSA analysis. 20 patients with a ceramic femoral head component and 16 patients with an Oxinium femoral head component along with the same number of matched patients with cobalt chrome femoral head component were included in the analysis. The time in vivo for the Oxinium (5.17 +/− 0.96 years), Oxinium matched cohort (5.13 +/− 0.72 years), ceramic (5.15 +/− 0.76 years) and ceramic matched cohort (5.36 +/− 0.63 years) were comparable. The demographics of all bearing surface cohorts were similar. The paired comparison between the Oxinium and cobalt chrome cohorts (0.32 vs. 0.28 mm/year, p=0.427) and ceramic vs cobalt chrome cohorts (0.28 vs. 0.22 mm/year, p=0.202) did not demonstrate a significant difference in wear rate. The independent groups analysis revealed a significantly higher wear rate of Oxinium (0.33 mm/year) compared to cobalt chrome (0.24 mm/year) (p = 0. 038). There were no differences in HHS and WOMAC scores between the Oxinium and cobalt chrome cohorts (HHS: p = 0.71, WOMAC: p=0.08) or the ceramic and cobalt chrome cohorts (HHS: p=0.15, WOMAC: p =023). Conclusion. This study presents evidence of a greater wear rate (mm/year) of the Oxinium femoral head component compared to a cobalt chrome femoral head component. This difference was not demonstrated in the ceramic femoral head component. Despite this difference, there were no clinical differences as measured by the HHS and WOMAC. Future research should focus on factors that may contribute to the higher wear rate seen in the Oxinium cohort. Level of Evidence – Level II. Disclosures - Institutional support provided by Depuy, Stryker, and Smith and Nephew