Introduction

Although total knee arthroplasty (TKA) in end-stage hemophilic arthropathy can reduce the severe joint pain and improve the functional disability, it is technically demanding. In addition, it has generally reported a high rate of complication including periprosthetic joint infection (PJI) and component loosening up to 20%. Although the Knee Society classification system of TKA complication was introduced, the complications of TKA in hemophilic arthropathy has not stratified using this classification system in previous articles to the best of our knowledge.

The purpose of this study was to evaluate the mid-term outcomes and complications of TKA in hemophilic arthropathy.

Purpose

There are some concerns about doing hip resurfacing arthroplasty in ONFH due to bone defect which can cause mechanical weakness of femoral component and highly active young age of patients which can cause high wear rate and failure rate. The purpose of this study is to verify the HRA is safe procedure in ONFH in the aspect of mechanical and biological issue.

Purpose

To evaluate the radiological changes after metal on metal resurfacing arthroplasty.

Purpose

In general, the amount and rate of linear wear are associated with femoral head size in the conventional UHMWPE acetabular liner. The smaller the femoral head, the higher the linear wear rate. The aim of this study is to verify the relationship between wear rate and femoral head size and the polyethylene cup thickness.

We wanted to evaluate the clinical and radiological results of acetabular revision using the acetabular reinforcement ring and allograft impaction in patients with severe acetabular bony defect.

41 hips revision arthroplasty using reinforcement ring were performed between April 1997 and October 2005 and were followed up for more than two years. The cause of primary arthroplasty was AVN in 18 cases, secondary osteoarthritis (OA) in 17 cases, fracture in cases and primary OA in 1 case. The cause of revision arthroplasty was acetabular cup loosening in 20 cases, massive osteolysis in 14 cases, infection in 4 cases, liner dissociation in 2 cases, and recurrent dislocation in 1 case. The average period between primary and revision arthroplasty was 11.4 years (range 0.6 to 29.1 years). Acetabular defects were classified based on the AAOS classification and Paprosky classification system. All were treated with autografts or allografts. Muller ring was used in 18 cases, Burch-Schneider ring was used in 14 cases, and Ganz ring in 9 cases. Clinical evaluations were performed according to the Harris hip score (HHS), and the radiographic results were evaluated by progression of acetabular component loosening, union of bone grafts, periacetabular osteolysis, and migration of the hip center.

The mean preoperative Harris hip score of 64.9 was improved to 91.8 points at the latest follow-up. There were 39 cases of type 3 defect, 2 cases of type 4 defect according to the AAOS classification and 8 cases of type 2B defect, 3 cases of type 2C defect, 28 cases of type 3A defect, and 2 cases of type 3B defect according to Paprosky classification.

Radiographically, the bone grafts were well united except one case. The mean preoperative hip center of rotation which was vertically 32.3mm, horizontally 33.2 mm migrated to vertically 26 mm, horizontally 33.2 mm postoperatively and it was statistically significant.

The mean preoperative abductor lever arm of 41.7 mm changed to 45 mm postoperatively which was statistically insignificant. However the mean preoperatiave body lever arm of 89.4 mm changed to 96.9 mm postoperatively which was statistically significant. Postoperative complications were cup loosening in 1 case, dislocation in 2 cases, and recurrence of deep infection in 1 case.

Clinically and radiographically, acetabular reconstruction using reinforcement ring showed very promising short term result. We conclude that reinforcement ring can provide stable support for grafted bone in severe bone defect. But meticulous surgical technique to get initial firm stability of ring and optimal indication in mandactory for the successful result.

Reconstructive acetabular osteotomy is a well established and effective procedure in the treatment of acetabular dysplasia. However, the dysplasia is frequently accompanied by intra-articular pathology such as labral tears. We intended to determine whether a concomitant hip arthroscopy with peri-acetabular rotational osteotomy could identify and treat intra-articular pathology associated with dysplasia and thereby produce a favourable outcome. We prospectively evaluated 43 consecutive hips treated by combined arthroscopy and acetabular osteotomy. Intra-operative arthroscopic examination revealed labral lesions in 38 hips. At a mean follow-up of 74 months (60 to 97) the mean Harris hip score improved from 72.4 to 94.0 (p < 0.001), as did all the radiological parameters (p < 0.001). Complications included penetration of the joint by the osteotome in one patient, a fracture of the posterior column in another and deep-vein thrombosis in one further patient. This combined surgical treatment gave good results in the medium term.

We suggest that arthroscopy of the hip can be performed in conjunction with peri-acetabular osteotomy to provide good results in patients with symptomatic dysplasia of the hip, and the arthroscopic treatment of intra-articular pathology may alter the progression of osteoarthritis.

The exact alignment of the femoral component is crucial for the success of hip resurfacing arthroplasty. This prospective study was performed to find whether the imageless computer-assisted navigation surgery can improve the accuracy during hip resurfacing arthroplasty by comparing the alignment of the femoral component implanted with navigation system and conventional-mechanical guided system.

Forty patients were randomly allocated into 2 groups for resurfacing hip arthroplasty using Birmingham hip resurfacing system. In the conventional group, femoral component positioning was assisted by mechanical alignment guides. In the navigation group, it was assisted by an imageless computer-assisted surgical system of Vectorvision^® (BrainLAB, Germany). We measured the difference between the preoperative plan of femoral component’s position and postoperative results on radiographs in the 2 groups

In the conventional group, a median difference of the stem alignment was 5.4° (range, 0.2°–10.9°) and a median difference of the stem anteversion was 2.6° (range, 0°–6.5°). In the navigated group, a median difference of the stem alignment was 2.3° (range, 0.2°–4.9°) and a median difference of the stem anteversion was 1° (range, 0°–3.6°). These differences between the 2 groups were statistically significant (P< 0.05).

In resurfacing arthroplasty with a hip navigation, the procedure showed a good performance and reliability. It is achieved with greater precision with a navigation system than a mechanical alignment system.

The ultimate goal for treatment of osteonecrosis of femoral head (ONFH) is preserving the femoral head. We have tried to manage the patient who received failed joint preserving procedures with resurfacing arthroplasty if they fit the indicati385on. In this brief review, we wanted to clarify the role and technical concern of resurfacing arthroplasty as a salvage procedure after failed joint preserving operations for ONFH.

Among 556 hips underwent resurfacing arthroplasty from September 1998 to October 2007, sixteen resurfacing arthroplasties (13 patients) were performed after failed joint preserving procedures for ONFH. Mean age at the operation was 39 years old. Seven vascularized fibular grafts, 3 multiple drillings, 3 core decompressions and 3 combined procedures were performed as initial operations. Mean duration from the index operation and resurfacing was 95 months. Mean follow up was 14 months. The patients were clinically evaluated with the Harris hip score, hip or thigh pain, and range of motion. As a radiological evaluation, we measured positions of the acetabular cup and femoral stem, radiographic changes at the neck and complications. The Harris hip score increased from 69.2 preoperatively to 89.5 at the final visit. Hip range of motions other than sagittal directions significantly improved after the operation. No patient complained of limb length discrepancy. One patient complained of unexplained hip pain, and another patient had trochanteric pain. Other than those two cases, all patients regained their pre-morbid activity level uneventfully. Radiologically, eleven femoral stems in anteroposteior and lateral radiographs were exactly aligned along the previous operative tracts. However, there were no clinical complications related to the position of femoral component. The only case that the acetabular cup was implanted in high inclination (60 degrees) experienced sustained unexplained hip pain. There was no another complications.

Our experience suggests that even for the case of failed hip preserving procedures in ONFH, resurfacing arthroplasty can play a successful role as a salvage operation. Furthermore, this can be an excellent alternative between joint preserving procedures and conventional THA.

The purpose of this study is to evaluate short to mid-term clinical and radiological results of metal on metal resurfacing arthroplasty in osteonecrosis of the femoral head (ONFH).

185 hips of 169 patients who underwent metal on metal resurfacing arthroplasty using Birmingham Hip Resurfacing system (Midland Medical Technololgies, Birmingham, UK) between December 1998 and May 2005 were available for this study and all cases were followed up over 3 years. All preoperative diagnoses were ONFH. The extents of necrotic area were analyzed by preoperative MRI scanning. Their mean age at the time of operation was 37.7(range, 16–67) years old and mean period of follow-up was 88(range, 36–113) months. For the clinical assessments, Harris hip scores, UCLA activity scores, pain and ROM were evaluated. Radiological changes such as radiolucencies around the stem, impingement sign, neck narrowing, osteolysis around head and neck junction, loosening of implants, heterotopic ossifications were evaluated in the serial antero-posterior, translateral radiographs of the hip joint.

Preoperative necrotic area was average 42.7(range, 11.5–60) %. Clinically, the average Harris hip score was improved from 85.2 points to 97.1 points at final follow-up. Average UCLA activity scores at the last follow-up was 8.8 and almost of the patients showed high activity and returned to their original job. ROM were very satisfactory. Radiologically, the mean inclination of acetabular component was 48.0°. There were no radiolucent lines around the acetabular components, but 3 cases showed radiolucent lines around the stem of femoral components. Osteolytic lesions were noticed in 10 cases around head-neck junction. Nine hips had impingement signs around the head-neck junction. There was no case which showed evidence of stress shielding. Moderate neck narrowing were shown in 3 cases. There were 6 cases of heterotopic ossification. One hip had a revision surgery to a total hip arthroplasty using big metal ball because of loosening of acetabular component. There was no patient complained limb length discrepancy and no infection, dislocation, thigh pain.

The midterm performance of metal on metal resurfacing arthroplasty in ONFH was very excellent in the aspects of pain relief, ROM of hip joints, rehabilitation and return to preoperative activity and minimization of common complications of conventional total hip arthroplasty. There was no mechanical failure related to the osteonecrosis and we can conclude that performing resurfacing arthorplasty in osteonecrosis less than 50% of extent can be justified. However, performing resurfacing arthroplasties in osteonecrosis of femoral heads needs meticulous surgical techniques and longer learning curve to prevent early failure. Even though our midterm follow-up study revealed excellent results, more long-term follow-up studies are mandatory to determine the survivorship and to verify the problems related to the increased serum metal ion and metal ion toxicity after resurfacing arthroplasty.

For radiographic assessment of THA, we must estimate a 3-D structure with 2-D images. Basically, it has been good. But even after a successful surgery, sometimes we encountered an undersized stem in radiograph. Interestingly, it was more frequent after we introduced surgical robot for primary THA. It sometimes brought a huge dilemma during planning and evaluating the surgery. We performed this study to elucidate the cause of this problem.

We used image data of 30 consecutive THAs using ROBODOC (ISS, USA). The measurement was made with the built-in tool in the Orthodoc, which is for the CT-based preoperative planning, and digital imaging system (PiView, Infinitt, Korea). We measured femoral anteversion, tilting angle at corresponding level, the longest and shortest diameters of femoral canal and their ratio. Also we measured anteversion and alignment of the stem. The canal filling of the stem was measured in projected images with CT and postoperative radiographs.

The mean femoral anteversion was 21.1±10.2°. The canal tiling angle was 39.3±7.9°(p< 0.01). The long and short diameters were 19.3±2.6° and 14.3±1.8°. The mean ratio between them was 0.8±0.08°. Canal filling at AP and lateral dimensions were 88.25±9.8% and 85.7±6.9%. In postoperative radiographs, they were 85.4±7.3%(p=0.05) and 88.0±6.1%(p=0.06).

This result suggests that the femoral canal at this particular or more distal level is elliptically shaped constantly. It tilts (in axial plane) to the same direction but not to the same degrees with femoral anteversion. Because of this tilt, relatively well-fixed round femoral stem can be considered as undersized in plane radiograph. Therefore, rather than using two plain radiographs alone for postoperative evaluation, adding postoperative CT may provide appropriate accuracy for assessment. And surgeon should keep in mind this axial tilt during planning and evaluating a robotic THA, especially not to remove too much healthy cortical bones to obtain full distal filling.

The purpose of this study is to analyze clinical and radiological results of total hip arthroplasty using the 3rd generation ceramic on ceramic articular surface.

Between July 1999 and May 2005, 339 hips of 250 patients had primary cementless total hip arthroplasty with the 3rd generation ceramic on ceramic bearing implants. And 325 hips of 236 patients were followed up over 3 years. Male were 168 patients(237 hips) and female were 68 patients(88 hips). The mean age at the time of operation was 47.3(range, 25~76) years old and the mean follow up period was 62.4(range, 36~107.6) months. The preoperative diagnoses were osteonecrosis of the femoral head (ONFH) in 250 hips, secondary osteoarthritis in 55 hips(dysplasia in 35, infection sequalae in 12, LCP in 2, CDH in 2), hemophilic arthropathy in 9 hips, ankylosing spondylitis in 7 hips etc.

We used Bicontact system(Aesculap, Germany) in 65 hips, Secur-FitTM(Stryker Howmedica Osteonics, USA) in 206 hips, Trilogy ABTM (Zimmer, USA) in 54 hips. Clinically, Harris Hip Score, thigh pain, squeaking and other complications were evaluated. Radiologically, the serial radiographs were analyzed.

Clinically, the Harris hip score was improved from preoperative 66.0(19~91) to 96.2(58~100) at the last follow-up. Radiologically, there was no loosening of implants and visible wear and osteolysis. Heterotopic ossifications were noted in 5 cases. In complications, there was dislocation in one case, periprosthetic fracture in 2 cases and thigh pain in 9 cases. Intermittent squeaking sound has occurred in 8 cases(2.5%). Among these, one case of loud squeaking which happened after fall down had revision surgery. There was no infection and fracture of ceramic implant.

Our midterm results of THA with the 3rd generation ceramic bearing system were very satisfactory and demonstrated that the 3rd generation ceramic bearings remain as an excellent bearing choice because of their superior wear characteristics. However, the results of this study suggests that the squeaking would be one of strong potential risk factors for failure of ceramic on ceramic total hip arthroplasty and we must be very cautious to prevent squeaking.

The aim of this study is to analyse the mid to long term results of cementless total hip arthroplasty (THA) performed in hemophilic coxarthrosis. Twenty-seven consecutive cementless THAs (23 patients) were performed at our institute for hemophilic coxarthrosis between June 1995 and June 2003. All these patients were followed up regularly for minimum 5 years and were included in this study. The average age at the time of surgery was 36 years (± 8.1) (range, 24–52 years). All the patients had hemophilia A. Twelve patients (52%) had more than 1 joint affected by hemophilic arthropathy. The mean follow-up period was 92 months (± 31.4) (range, 60–156 months). For clinical assessment we evaluated Harris hip score, range of motion, amount of transfusion and factor replacement, perioperative bleeding and the problems associated with the use of coagulation factors. For radiographic assessment, we evaluated the stability and fixation of components, various bone responses around the implants and complications such as loosening and osteolysis.

The average Harris hip score improved from 60.7 (± 19.3) (range, 30–89) before surgery to 95.9 (± 3) (range, 90–100) at the latest follow-up. The hip range of motion increased in all planes of motion after the operation. The mean factor VIII requirement per THA was 37 500 units (± 18 500) (range, 19 000–90 000 units). During surgery and post operative period mean 1.5 units (± 1.5) (range, 0–5 units) of packed cells and 0.5 units (± 1.4) (range, 0–5 units) of fresh frozen plasma was required. There was episode of re-bleeding in 4 cases. In one of them, severe osteolysis around pelvis and femoral stem was noted due to pseudotumor. Radiographically, except 1 loosened cup, the fixation was stable in all cases at the latest follow-up. Heterotopic ossification was noted in 2 hips. Osteolysis was noted in 4 femurs and 5 acetabulae. In 1 case of severe osteolysis around the stem, morsellised bone graft was performed at 144 months after the index operation. One case of pseudotumor was waiting for surgery. One loosened cup was revised to a cemented cup.

Unlike worrisome results of cemented THA, meticulously performed cementless THA for moderate or severe hemophilic arthropathy is safe and greatly effective in reducing pain, increasing the range of motion and improving the walking ability. However, special attention must be paid to the possible complications associated with re-bleeding such as pseudotumor around the hip. To obtain the best results multidisciplinary team comprising of pediatrician, hematologist, rehabilitation therapist and orthopaedic surgeon should be needed.

We performed 52 total hip replacements in 52 patients using a cementless acetabular component combined with a circumferential osteotomy of the medial acetabular wall for the late sequelae of childhood septic arthritis of the hip. The mean age of the patients at operation was 44.5 years (22 to 66) and the mean follow-up was 7.8 years (5 to 11.8). The mean improvement in the Harris Hip Score was 29.6 points (19 to 51) at final follow-up. The mean cover of the acetabular component was 98.5% (87.8% to 100%). The medial acetabular wall was preserved with a mean thickness of 8.3 mm (1.7 to 17.4) and the mean length of abductor lever arm increased from 43.4 mm (19.1 to 62) to 54.2 mm (36.5 to 68.6). One acetabular component was revised for loosening and osteolysis 4.5 years postoperatively, and one had radiolucent lines in all acetabular zones at final review. Kaplan-Meier survival was 94.2% (95% confidence interval 85.8% to 100%) at 7.3 years, with revision or radiological loosening as an end-point when two hips were at risk.

A cementless acetabular component combined with circumferential medial acetabular wall osteotomy provides favourable results for acetabular reconstruction in patients who present with late sequelae of childhood septic hip arthritis.

Positioning and secure fixation of the acetabular component without bone cement in dysplastic and deficient acetabulum is technically challenging because of the distorted anatomy of the acetabulum such as shallow and very thin medial and anterior wall, deficient super-olateral dome. Several treatment options have been reported to solve these problems when total hip arthroplasty is needed.

The author developed a new technique of circumferential acetabular medial wall displacement osteotomy to get secure fixation of the cementless hemispherical acetabular component at the site of the original acetabulum. This technique preserves the thin medial wall, deepens, and enlarges the acetabulum without additional structural bone graft. The procedure can also provide appropriate positioning and sufficient coverage of the acetabular cup.

From October 1989 to October 1995, we analyzed 84 hips in 80 patients who had a cementless total hip replacement with circumferential acetabular medial wall osteotomy at the Kyung Hee University Hospital. There were 28 male and 52 female patients with an average age of 49 years (range 25–71). Initial diagnoses were congenital dislocation, severe dysplasia, infection sequelae, and secondary osteoarthritis. The follow-up period ranged from 5 years to 11 years, the average being 7.2 years. All acetabular components used in this procedure were cementless porous coated hemispherical Harris-Galante (HG) I or II cup. The acetabular cup had secure fixation at the site of the original acetabulum without bone cement in all cases. Cup coverage ratio has become 97.7% in average. There was no radiolucent line around the cup or loosening. None of the acetabular cups with circumferential acetabular medial wall osteotomy had signs of medial migration. Bone union at the site of osteotomy was achieved in all cases. Bony ingrowth into the porous surface and remodeling around osteotomized acetabular medial wall was excellent. Technical pitfalls and advantages in biomechanical viewpoint of the procedure will be discussed.

Introduction: Resurfacing arthroplasty of the hip joint has advantages of minimal bone resection, restoration of normal anatomy, and biomechanical circumstances. This study was undertaken to analyze the clinical and radiographic results of the resurfacing arthroplasty in patients with osteonecrosis of the femoral head (ONFH).

Materials and Methods: Between September 1998 and September 2001, 40 hips in 39 patients with ONFH had a resurfacing arthroplasty with the Birmingham Hip Resurfacing (BHR) system. The mean age at the time of operation was 38.3 years. The average follow-up period was 36.8 months after operation. The patients were clinically evaluated by hip pain, Harris hip scores, range of motion, and radiographically evaluated for wear, change of cup position, loosening, and osteolysis.

Results: The preoperative Harris hip score averaged 70.4 points and the degrees of flexion and internal rotation were 94° and 8°, respectively. The average Harris hip score at the last follow-up was 95.4 points. The degrees of flexion and internal rotation at last follow-up were 120°, and 20°, respectively. No patient complained of limb length discrepancy or pain in the hip or thigh. Rehabilitation programs and return to normal activities were earlier than that of conventional total hip arthroplasty (THA). There was no osteolysis, change of cup position, loosening, or detectable wear on the latest radiographic evaluation.

Conclusions: Our experience with resurfacing arthroplasty for ONFH indicates that the overall results are superior than conventional THA with respect to pain relief, range of hip motion, earlier rehabilitation, and early return to preoperative activity. This procedure with BHR could be an alternative between joint preserving procedure and conventional THA in ONFH especially in younger patients.

Introduction: The purpose of this study was to evaluate the clinical and radiographic long term follow-up results of vascularized fibular grafting (VFG) as a joint preserving procedure for osteonecrosis of the femoral head (ONFH).

Materials and Methods: Between October 1979 and December 1992, 97 hips in 89 patients with ONFH that had follow-up for at least 10 years (range: 10 years – 21 years) were evaluated. The mean age at the time of operation was 34 years. There were 49 hips with Ficat stage II radiographic changes and 48 hips with stage III disease. The disease was associated with consumption of alcohol in 19 hips, trauma in 17, and the use of steroids in 7. In the remaining 54 patients, the condition was idiopathic.

Results: Overall satisfactory results, including excellent, good or improved by 10 points, were seen in 78 hips (80.4%) clinically, and 63 hips (64.9%) showed radiographic improvement or no change.†Radiographically, new bone formation and remodeling was found in 32 hips; and no further progression of necrosis in 31 hips while progression of collapse was found in 34 hips. There were only 9 conversions to total hip anthroplasty (THA) at the last follow-up. By Kaplan-Meier survivorship analyses, there was a significant lower rate of conversion to THA in patients who were less than 35 years. The probability of conversion to THA was not significantly related to etiology, radiologic stage, or location of involvement of the necrosis.

Discussion: VFG not only has an excellent new bone formation and remodeling capacity, but also is one of the highly recommended joint preserving procedures in symptomatic ONFH in younger patients with early collapsed disease. Furthermore, femoral head replacement can be avoided or at least postponed in advanced stages of disease in the younger population.

Introduction: The purpose of this prospective study was to evaluate the therapeutic value of Pulsed Electromagnetic Fields (PEMF) in the treatment of the osteonecrosis of the femoral head (ONFH).

Materials and Methods: One hundred-eight consecutive hips with ONFH (80 patients) treated with PEMF between June 1990 and June 1998 were analyzed. The average age was 37 years. The average follow-up period was 6.9 years. According to the ARCO staging system, 3 hips were stage I, 85 hips stage II, and 20 hips stage III. Hips were evaluated clinically with a modified Harris hip scoring system and degree of pain relief. Radiographic progression was defined as either an advance in ARCO stage or progressive collapse of the femoral head more than 2 mm.

Results: Clinical improvement was achieved in 81 hips (75%). Hip pain was relieved or decreased at an average of six months following initiation of PEMF therapy in the 81 hips with clinical improvement as well as some radiographically progressed hips. Radiographic progression was seen in 35 hips (32.4%). Total hip arthroplasty (THA) had been performed in 20 hips (18.5%). Kaplan-Meier survivorship analysis demonstrated that the probability of conversion to THA within 5 years after PEMF was 16% overall. Conversion to THA was significantly higher in patients who had the necrotic lesion laterally, in the subgroup C (more than 30% involvement of necrosis), and in patients older than the mean age.

Discussion: These results demonstrate that PEMF can modifiy the natural course of ONFH. PEMF is recommended in patients who are less than forty years old with early stage disease with small necrotic involvement. Refinement of PEMF could make it a more efficacious non-invasive method of treatment.

We report the long-term radiographic results of the total hip arthroplasty with use of the cementless porous coated Harris-Galante (H-G) stem. Seventy-five consecutive patients, eighty-eight hips formed the basis of this study. Fifty patients were male, twenty-five patients were female, and thirteen patients were bilateral. The mean age of patients at operation was 42 years. They were followed up for an average of thirteen years four months (ten years two months to fourteen years four months). The diagnosis was avascular necrosis of the femoral head in 49 cases, degenerative osteoarthritis in 32 cases. Clinical results were estimated by modified Harris hip score and thigh pain, and radiographic results by periodically checked plain X-ray film. The average Harris hip score increased from 60 points preoperatively to 83 points at the most recent follow-up examination. The hip pain score increased from 31 points to 41 points. Clinically severe thigh pain was observed in 3 cases (4%). In radiographic evaluation, subsidence more than 5mm was seen in 2 cases (2%). Periprosthetic osteolytic lesion was observed in 15 cases (17%), but the lesions do not influence stability of the stem. Femoral stem stability by Engh was stable in 72 cases, fibrous stable in 12 cases, unstable in 4 cases. Pedestal formation, cortical hypertrophy of the distal femur, and stress shielding was observed more than 40%. Subcollar resorption was identified in 29% and ectopic ossification in 15%. Revision of the femoral stem was needed in 4 cases for aseptic loosening. At 10 years probability of survival of the stem using Kaplan-Meyer method was 95.5%. Use of the cementless H-G stem yielded the excellent long-term outcome, but osteolysis and stress shielding would be the main problems to solve.