Introduction. We have been developed lateral flare stem and have been using it since 1989. It was custom stem at first. After being experienced, using the same software, off-the-shelf version lateral flare stem (Revelation) was developed in 1996 in the U.S. We could start using it since 2001 in our country. Lateral flare stems are designed to reproduce physiological proximal load transfer lateral side as well as medial side. It was obtained by having bigger and more accurate proximal part with lateral flare. The design is optimized by matching with 3D insertion path. Using many custom stems including different length and off-the-shelf standard stems, we have come to feel that as for this high proximal fit and load transfer design, it is not necessary to having long distal part and sometimes it is harmful to obtain good proximal load transfer in some situation such as type A (champagne flute) canal. So we have developed short version of the stem. Many makes of the hip stems have included short stems recently. Some aimed to improve easier insertion, some aimed to improve the volume of residual bone quantity. We have aimed to improve proximal fit expecting more proximal and more physiological load transfer to the femur. Objectives. Our objectives are to comare standard stem and short stem from biomechanical aspect and clinical aspect. Materials and methods. As for the biomechanical aspect, finite element analyses were done with standard and short stem. As for the clinical aspect, the very last 25 cases of the standard stems; which we have 12 years clinical experience; done at Nagoya City University, the very first 25 cases of the short stems, and the next 25 cases were examined. The distance between stem and cortical bone on medial and lateral side at lateral flare hight of the stem and the bottom of arc deposite coated area. Alignment was assessed by the angle of the stem and canal axis. Result. By the FEA, small stress point was observed at the tip of the standard stem which pushes canal wall from inside (Fig. 1), which was disappeared at the tip of the short stem. Less micromotion was observed in short stem too. No significant difference was observed in the stem cortical distance. No significant difference of stem alignment was observed between standard stem and all 50 short stems but better alignment (p = 0.07) was seen in the second 25 cases of the short stem than standard stem. Between the first 25 and the second 25 case high difference (p = 0.01) was seen. (Fig. 2). Discussion. The standard lateral flare stem has very physiological proximal load transfer in most of the cases, sometimes longer distal part could effect to the alignment because of the femoral bending. Short stem could be expected have better alignment being free from femoral bending. On the contrary, distal part could be the insertion guide during the surgery. For the short stem, learning curve exists to realize potentially better alignment

Introduction. Total hip arthroplaty (THA) using direct anterior minimal invasive (AMI) surgery is an attractive option to achieve a quicker habilitation. However, high complication rates were reported and very often related to technical difficulties at the time of surgery. We hypothesized that 3D preoperative planning may allow to anticipate these difficulties and to decrease the complications rates when using an AMI approach. Material and methods. A prospective observational study included 191 consecutive patients who underwent a primary cementless THA using an AMI. A 3D CT-scan based pre-operative planning was performed in order to anticipate the potential difficulties that may be encountered especially regarding the hip anatomy reconstruction and the implants stability. The components size and position were planned in order to restore the leg length, the offsets, and the anteversions. Postoperatively, a CT scan was performed in order to compare the final anatomy to the planning. Results. The real implants were the same than the ones planned in 94% for the cup, 96% for the stem and 100% for the neck. The hip anatomy was restored with a high accuracy: 0.1±3mm for the hip rotation centre, −1.6±3 mm for the leg length and 0.1±2.5mm for the femoral offset. All the surgical difficulties were anticipated. No false route and no dislocation occurred. A motorized reaming procedure of the femur was required in 6 patients because a very dense bone associated to a narrow femoral diaphysis. A varus neck was used in 60 % of cases mainly in order to compensate a decrease in the acetabular offset generated by the reaming procedure imposed by the acetabular dysplasia. A retroverted neck was used in 8% of patients because of a torsional abnormality and allowed to increase the stability (Figure 1). A severe femoral dysplasia was treated with a custom stem in 7% of cases in order to avoid a rotational osteotomy of the femur a trochanteromy (Figure 2). Discussion. No complication happened at the time of surgery and no dislocation occurred afterwards. False routes were avoided probably also thanks to the shape of the anatomic stem which presents an anterior sagittal curvature. This shape allowed an easier rasping procedure despite the limited exposure of the femur. Conclusion. 3D planning anticipates the potential surgical difficulties at the time of THA, and allow to increase the safety and the accuracy of the surgical procedure

Improving the adaptation between the implant and the patient bone during total hip arthroplasty (THA) may improve the survival of the implant. This requires a perfect understanding of the tridimensional characteristics of the patient hip. The perfect evaluation of the tridimensional anatomy of the patient hip can be done pre-operatively using X-rays and CT-scan. All patients underwent a standard x-rays evaluation in the same center according to the same protocol. Pre-operatively, the frontal analysis of the hip geometry was performed and the optimal center of rotation, CCD angle, neck length and lever arm was analyzed to choose the optimal solution for proper balance of the hip in order to obtain adequate range of motion, appropriate leg length, and correct tension of the abductors muscles. Standard or lateralized monoblock stems can be valid or modular neck shape can be choosen among 9 available shape. These 9 frontal shapes are available in standard, anteverted or retroverted shapes, leading to 27 potential neck combinations. In case of important hip deformation, a custom implant can be used in order to balance the extra-medullar geometry without compromising the intra-medullary adaptation of the stem. We prospectively included 209 hips treated in our institution with total hip arthroplasty performed using a supine Watson-Jones approach and the same anatomic stem. The mean patient age was 68 years and the mean BMI 26 Kg/m². Intra-operatively the sagittal anatomy of the hip was analyzed and standard, ante or retro modular necks were tested for the frontal shape defined pre-operatively. According to the pre-operative frontal planning, non-standard necks were required in 24 % of the cases to restore the anatomy of the hip. Intra-operatively, a sagittal correction using anteverted neck was required in 5% of the cases and retroverted necks in 18% of the cases. Harris hip score improved from 56 to 95 points at min. 5 year follow-up. No leg length discrepancy greater than 1 cm was observed. Restoration of the lever arm (mean 39.3 mm, range 30 to 49 mm) and of the neck length (55.2, range 43 to 68 mm) was adapted for 95% compared to the non operate opposite side. Disturbed anatomy like in DDH or post-traumatic cases may require additional solutions to balance the hip such combined osteotomy or customized stem and neck

Introduction. Since 1989, we have been developing lateral flare stem. The concept of lateral flare stem is to deliver proximal part big enough to fill the proximal cavity that most of the cement stems can fill and most of the cementless stems cannot. Also having distal part polished, much less distal load transfer occurs than cement stem. Thus, we can expect high proximal load transfer to prevent stress shielding. To deliver lateral flare stem, straight insertion path cannot be available, as proximal lateral part to fill inside the greater throchanter collides to the greater trochanter. So 3-Dimension insertion path was calculated to deliver that part through the narrow made by neck osteotomy. The first generation of the lateral flare stem was custom made. The second generation was designed as an off-the-shelf stem from what we have learned by the experience of custom stems. With the third generation, the stem was shortened to achieve more proximal load transfer. Direct Anterior Approach (DAA) developed by Judet is one of less invasive hip approach. With a stem with straight insertion path, the extended line of proximal femoral axis should come out of the skin. To achieve this position, proximal end of the femur has to be fully pulled up. (Fig.1) Some of the cases would be able to be lifted up but some have difficulty. Using lateral flare stem with curved 3 dimensional insertion path, even the axis extension does not come out of the skin, it would be expected to be inserted. In the present study, 3D insertion path of the lateral flare short stem for DAA was analyzed. Materials and methods. Preoperative CAT scan data were transferred to STL data by Mimics®. The procedures after that were done by Magics®. First, neck osteotomy was done, externally rotated, and mild extension that doesn't make the axis come out of the skin was added. Then insertion path was verified keeping the stem attached medial sidewall of the canal (Fig. 2). In actual case, skin translation and pelvis rotation was assessed by 3D scanner. (Fig. 3). Results. Three D scanner revealed that the pelvis rotation is less than detective limit, and the upper skin incision where the stem passes remains almost the same place by dropping the leg. Lateral flare short stem could be inserted without lifting the femur out of the skin. So it was expected that lateral flare short stem has high applicability for DAA. Discussion. We can expect less invasive THA with DAA. However, once we have problem during surgery such as hard insertion or fracture and so forth, it is very hard to recover from those difficulties, because with supine position we cannot access posterior side of the leg. By easier insertion, less stress for bone and other tissues, we can reduce the risks. Even cases with easier femoral lift up, pulling femur less can reduce those risks

Introduction. To obtain a better range of motion and to reduce the risk of dislocation, neck and cup anteversion are considered very important. Especially for the reduction of the risk of dislocation, the mutual alignment between neck and cup anteversion (combined anteversion) is often discussed. A surgeon would compare the neck direction to the calf direction with the knee in 90 degrees flexion. When an excessive anteversion was observed, the neck anteversion would be reduced using modular neck system or setting the stem a little twisted inside the canal with the tradeoff of the stem stability. Another choice would be the adjustment of cup alignment. Combined anteversion is defined the summation of cup anteversion in axial plane and stem anteversion in axial plane. But in realty the impingement occurs with 3 dimensional relationships between neck and cup with very complicated geometries. In that meaning, the definition of the angles could be said ambiguous too. The bowing of the femur also makes the relationships more complicated. Upon those backgrounds, we have been performing 3D preoperative planning for total hip arthroplasty on every case. In the present study, in vivo position of the stem in each case was determined then the anteversion observed on surgical view and anteversion around femoral mechanical axis are compared using 3D CAD software. Materials and Methods. Ten recent cases from our hip arthroplasty with 3D preoperative planning were reviewed for this purpose. The bone geometries were obtained from CAT scans with very low X-ray dose using Mimics® (Materialize, Belgium). Preoperative planning for Revelation stem® (DJO, USA) was performed using Mimics® (Materialize, Belgium). Femoral mechanical axis was defined as a line between center of femoral head and the middle point of medial and lateral epicondyle of the femur. Then mechanical anteversion is assessed from posterior condylar line. On the other hand, the calf was rotated 90 degrees around epiconlylar axis of each femur, and in vivo stem position was estimated then, stem axis was aligned perpendicular to the view. The anteversion in the surgical view was assessed from that view as the angle toward the calf. (Fig. 1) Using in vivo stem alignment, the impingement angle was also assessed. Results. Anteversion was in average 10 degree overestimated in the surgical view. Only one case was considered to have impingement risk and reduction of the anteversion was performed using custom stem. Discussion. In real surgical view, the anteversions are often observed to be more. In the present study instability of the knee was not considered. If the surgeon has performed inappropriate modification of the stem and cup anteversion, it can increase the risk of the dislocation and worse mechanical conditions. The in vivo prosthesis alignment should not be discussed with the angles from surgical view, but should be well planed 3 dimensionally preoperatively

The rate of periprosthetic joint infections (PJI) after primary total hip arthroplasty (THA) is approximately 1%. As the number of THAs performed each year continue to increase (550,000 by 2030), a corresponding increase in the number of hip PJI cases is likely to occur. A chronic deep infection may be treated by either chronic suppression, irrigation and debridement, single-stage exchange, or two-stage exchange. In the United States, the gold standard for chronic PJI continues to be a two-stage exchange. The benefit of an antibiotic impregnated cement is that they produce higher local concentrations of antibiotics than systemic intravenous administration. Hip spacers may be either static or articulating. Static spacers are reserved for cases of massive acetabular bone loss in which an articulating spacer is not feasible. A static spacer consists of a block of antibiotic cement in the native acetabulum and antibiotic coated rod in the femoral canal. Limb shortening, loss of soft tissue planes, and disuse osteopenia and muscle atrophy are all limitations of static spacers. In contrast, articulating spacers fulfill the goals of the interim construct during two-stage exchange which is to enhance eradication of the infecting organism through drug elution, to maintain limb length, to facilitate exposure during revision surgery, and to improve functional mobilization. Articulating spacers may be divided into three general categories based on method of spacer creation: Handmade custom spacers, prefabricated spacers, custom molded spacers (hemiarthroplasty molds and molded stem with cemented all-polyethylene cup). Handmade custom spacers are usually created with K-wire or rush rods coated with antibiotic cement. Handmade spacers are relatively simple to make, they are economical, and the amount and type of antibiotics incorporated can be customised for the infecting organism. Commercially available hemiarthroplasty spacers can be either prefabricated (Spacer G, Exactech, Gainesville. FL) or made intraoperatively (Stage One, Zimmer Biomet, Warsaw, IN) are available in several head and stem sizes. The advantage of prefabricated spacers is that they do not require additional time to mold in the operating room. The downside of prefabricated spacers is that the antibiotic concentration and type is predetermined. A custom molded stem with cemented all-polyethylene cup can be made with off the shelf implants or used as part of a commercially available spacer (PROSTALAC, DePuy Synthes, Warsaw, IN). A common antibiotic/cement combination includes Tobramycin (3.6 g/40 g of cement) and vancomycin (1.5 g/40 g of cement). In all of these spacer constructs, the principles of using a high-elution cement mixed without a vacuum and with high doses of heat stable antibiotics are consistent. Tobramycin works synergistically to improve Vancomycin elution properties and is usually added in higher doses. Overall infection eradication is similar between all categories of spacers and range between 90–97%. Complications after placement of an articulating spacer are often specific to the type of spacer used. Handmade spaces that have K-wires for support are at risk for spacer cement fracture. Spacer dislocation is also a common complication in up to 15% of cases with all types of spacers. In addition, periprosthetic fractures can occur postoperatively in up to 10% of patients. Overall, despite this complication profile, articulating antibiotic spacers have excellent rates of infection eradication and offer improved mobilization in the interim two stage period and reduce operative time, complexity, and morbidity during reimplantation

Introduction. Since 1989 we have been using custom lateral-flare stems. Using this stem, its lateral flare can produce high proximal fit and less fit in distal part. Applying this automatic designing software to the average femoral geometries, we can make off the shelf high proximal fit stem (Revelation ®). Putting the off the shelf stem, the original center of the femoral heads were well reproduced. But in DDH cases, severe deformities around hip sometimes make complicated difficulty for better functional reconstruction. They are high hip center such as Crowe II-IV, shortening of the femoral neck, high anteversion etc. DDH cases are well known to have higher anteversion than non DDH cases. There would be no definite explanations for it. The high anteversion would not always be harmful for the preoperative patients. But in some cases, osteophytes are observed at posterior side of the femoral head which make another sphere with different centre. We can guess that the patient's biomechanics had not been matched with the original anteversion. Then posterior osteophytes can correct inappropriate anteversion (self-reduction.) (Fig.1) In those patients, reduction of the anteversion by putting stems twisted into the canal or using modular stems are sometimes done by the surgeons' decision. Younger DDH cases can also be treated with THA, because of the complicated deformities or biomechanical disorders. Short stems are expected to reduce operative invasion and stress shielding then can reserve bone quality and quantity. From these point of view to improve the understanding of the characteristics of the DDH anteversion, and design a DDH oriented short stem could be one of good solution for those cases. Method. For the better understanding of the high anteversion 57 femora (mean anteversion: 34.4 deg.) were analyzed slice by slice. The direction of femoral head centre, lesser trochanter (LTR), linea aspera (aspera) just below LTR, aspera in the middle of the femur and aspera between the last 2 sections. All of the directions were assessed from PC line. To clarify the meaning of the head osteophytes, 35 operated cases were analyzed the extent of the head osteophytes. According to the results, a DDH oriented short stem was designed. Results. Even with the different anteversion, femoral head centres and LTRs were located within limited angle (51.4 +/−7.9 deg.) But aspera just below the LTR had no relation to the LTR direction, but always kept within limited angle (102.0 +/− 4.5) to the PC line. This means that DDH cases have proximal femurs of normal shape. But they are only twisted around the level just below the LTR. From this result, stems for DDH cases can have the same shape with normal stem inside the canal. The posterior osteophytes had reduced 4.6+/− 3.0 degree in average independently to the extent of anteversion. There was no tendency that higher anteversion cases have higher self-reduction angle. the stems were give the same shape inside the canal with stems for non DDH cases but its femoral head center was located with 5 degrees less anteversion

Published investigations with custom short stems have reported very encouraging results (Walker, et al, 1). However, off-the-shelf (OTS) versions of shorter length prostheses has not met with the same success. Several basic questions must be addressed. First, what is the purpose of a stem? Second, can stem length be reduced and if so by how much can this be safely done. Third, what are the effects of stem shortening and are there other design criteria which must take on greater importance in the absence of a stem to protect against implant aseptic failure. To examine these issues a testing rig was constructed which attempts to simulate the in vivo loading situation of a hip, Fig. 1 (Walker, et, al.). Fresh cadaveric femora were tested with the femora intact and then with femoral components of varying stem length implanted to examine the distribution of stresses within the femur under increasing loads as a function of stem length. This was correlated with observations of prospective DEXA measurement of proximal femoral bone mass and implant migration following THR (Leali, 3). We then initiated a prospective multi-center study of a specific short stem design which included three geometric features to ensure initial implant stability. This report documents that after 2 years, in the first 200 stems implanted, this design has been shown to provide stability against subsidence, flexion/extetnsion and rotational forces. This is consistent with the findings of the in-vitro studies and identical to the previously published clinical results of a similarly designed full length version of this same stem. Our studies indicated that a stem is not an absolute requirement in order to achieve a well functioning, stable implant. Initial stability can be achieved in the absence of a stem, by a “rest fit,” if adequate design features are incorporated. These studies also demonstrated that simply reducing the length of an existing implant to accommodate changes in surgical techniques may not be a reasonable or safe design change. Such shortened versions of existing stem designs must undergo rigorously in-vitro testing and clinical validation before being released for implantation

Recent trends in surgical techniques for THR, i.e. MIS and anterior approaches, have spawned an interest in and possible need for shorter femoral prostheses. Although, early clinical investigations with custom short stems have reported very encouraging results, the transition to off-the-shelf (OTS) versions of shorter length prostheses has not met with the same degree of success. Early reports with OTS devices have documented unacceptably high and significant incidences of implant instability, migration, mechanical/aseptic failure, and technical difficulty in achieving reproducible implantation outcomes. They have highlighted the absolute need for a better understanding of the consequences of changes in implant design as well as for improvements in instrumentation and surgeon training. Two basic questions must be addressed. First, what is the purpose of a stem? And second, can stem length be reduced and if so by how much can this be safely done. What are the effects of stem shortening and are there other design criteria which must take on greater importance in the absence of a stem to protect against implant failure. To examine these questions a testing rig was constructed which attempts to simulate the in vivo loading situation of a hip, fig. 1. Fresh cadaveric femora were tested with the femora intact and then with femoral components of varying stem length implanted to examine the distribution of stresses within the femur under increasing loads as a function of stem length. Our studies indicated that a stem is not an absolute requirement in order to achieve a well functioning, stable implant. However in order to reduce the possibility of mechanical failure a reduced stem or stemless implant absolutely must have three important characteristics to its design. First, it must have sufficient medial/lateral dimension to provide stability against subsidence and varus stress; second it must have a flat posterior surface, parallel and in contact with the posterior endosteal surface of the proximal femur with which to maximize A/P stability against flexion/extension forces (As a consequence of this design feature, appropriate anteversion must be achieved in the neck region of the prosthesis and not by rotation of the implant within the proximal metaphyseal cavity of the femur); and third, the implant must also have a cross-sectional geometry that will stabilize against torsional loading about the long axis of the femur. Therefore, simply reducing the length of an existing implant to accommodate changes in surgical techniques may not be a reasonable or safe design change. Such shortened versions of existing stem designs must be rigorously tested before being released for general use. The required design parameters outlined above have been clinically validated in custom fabricated implants. They have been shown to reduce aseptic loosening and migration of a short stem femoral implant. This report will provide the clinical review of a multi-center experience with the first 200 off-the-shelf “Lateral Flare” short stem implants

Recent trends in surgical techniques for THR, i.e. MIS and anterior approaches, have spawned an interest in and possible need for shorter femoral prostheses. Although, early clinical investigations with custom short stems have reported very encouraging results, the transition to off-the-shelf (OTS) versions of shorter length prostheses has not met with the same degree of success. Early reports with OTS devices have documented unacceptably high and significant incidences of implant instability, migration, mechanical/aseptic failure, and technical difficulty in achieving reproducible implantation outcomes. They have highlighted the absolute need for a better understanding of the consequences of changes in implant design as well as for improvements in instrumentation and surgeon training. Two basic questions must be addressed. First, what is the purpose of a stem? And second, can stem length be reduced and if so by how much can this be safely done. What are the effects of stem shortening and are there other design criteria which must take on greater importance in the absence of a stem to protect against implant failure. To examine these questions a testing rig was constructed which attempts to simulate the in vivo loading situation of a hip, fig. 1. Fresh cadaveric femora were tested with the femora intact and then with femoral components of varying stem length implanted to examine the distribution of stresses within the femur under increasing loads as a function of stem length. Our studies indicated that a stem is not an absolute requirement in order to achieve a well functioning, stable implant. However in order to reduce the possibility of mechanical failure a reduced stem or stemless implant absolutely must have three important characteristics to its design. First, it must have sufficient medial/lateral dimension to provide stability against subsidence and varus stress; second it must have a flat posterior surface, parallel and in contact with the posterior endosteal surface of the proximal femur with which to maximize A/P stability against flexion/extension forces (As a consequence of this design feature, appropriate anteversion must be achieved in the neck region of the prosthesis and not by rotation of the implant within the proximal metaphyseal cavity of the femur); and third, the implant must also have a cross-sectional geometry that will stabilize against torsional loading about the long axis of the femur. Therefore, simply reducing the length of an existing implant to accommodate changes in surgical techniques may not be a reasonable or safe design change. Such shortened versions of existing stem designs must be rigorously tested before being released for general use. The required design parameters outlined above have been clinically validated in custom fabricated implants. They have been shown to reduce aseptic loosening and migration of a short stem femoral implant. This report will provide the clinical review of a multi-center experience with the first 150 off-the-shelf “Lateral Flare” short stem implants

Total hip replacements have shown great benefits to patients through relief of pain and restoration of function. However, because of the extensive variation in the size and shape of the femoral canal, especially for the situation encountered in the revision hip arthroplasty, standard uncemented hip systems with a limited number of sizes are unable to provide an accurate fit in every case. This study showed clinical results of 112 primary total hip replacements and 158 revision total hip replacements, using custom made CAD-CAM (Computer Aided Design-Computer Aided Manufactured) hip prostheses inserted between 1992 and 1998. For primary hip replacements, the implants were designed to produce proximal line-to-line fit with the femoral bone and to provide optimal biomechanical environment of the hip. The stem was HA coated, 53 males and 58 females were included. Mean age was 46.2 years (range 24.6yrs - 62.2 yrs). The average duration of the follow up was 24 years (10 – 17 years). The mean Harris Hip Score (HHS) was improved from 42.4 to 90.3, mean Oxford Hip Score (OHS) was improved from 43.1 to 18.2 and the mean WOMAC hip score was improved from 57.0 to 11.9. There was 1 revision due to failure of the acetabular components but there were no failures of the femoral components. In the whole follow-up period, the survival of the femoral stem alone was 100%. For revision hip replacements, the implants were designed using our design strategies of graduate approach to different revision situation based on Paprosky's classification of femoral bone defect. The implants were HA coated; some of them had distal cutting flutes. A total of 158 patients (97 males and 61 females) who had operation between 1991 and 1998 were followed up, among them 138 cases were due to aseptic loosening, 6 cases were periprosthetic fractures and 14 cases were infection. The average age was 63.1 years (range 34.6 – 85.9 years). The minimum follow up was 10 years (range 10 – 12 years). The mean Harris Hip Score was improved from 44.2 to 89.3, mean Oxford Hip Score was improved from 41.1 to 18.2 and the mean WOMAC hip score was improved from 52.4 to 12.3 respectively. 6 cases required further revision surgery, among them 3 were due to aseptic implant loosening, the overall survivorship at ten years was 97%. The CAD-CAM hip stems are able to provide optimal implant fixation and restore hip function for every patient regardless their original femoral shape, bone condition and biomechanics of the hip. The excellent medium to long term clinical results justifies the use of CAD-CAM custom hip stems