Osteonecrosis of the femoral head (ONFH) is a painful and disabling condition, which most commonly involves the hips of young patients. But despite of the high incidence, treatment is still has not been definitely identified. We performed a modified muscle pedicle bone graft (MPBG) technique using anterior one-third of gluteus medius (GM) attached to the greater trochanter (GT) in ONFH. The purpose of this study was to evaluate the effectiveness of our technique on ONFH in ARCO stage II and III patients.

Between June 2007 and March 2015, 24 hips were treated by our technique, who were able to follow up at least 2 years. The group was consisted of 15 men and 8 women, mean age of 36 years at the time of surgery. Mean follow-up was 5 years.

Twenty of 24 hips hips had no progression of necrotic lesions. The postoperative scintigrams showed increased blood flow in the 3 month follow up evaluation. But 4 hips underwent THA at the mean follow-up of 6 years after the surgery, and considered as “failure”. Excluding the 4 failed cases, the mean Harris hip score was improved from 54 points to 85 points at the last follow up.

Through our new technique, we showed 83% of survival rate by average of 5 year follow up. And compared to other reports, our technique showed relatively good survival rate and clinical outcomes. Therefore, we suggest this modified technique as one of promising treatment of choices for young patients with ARCO stage II or III ONFH.

Aim

Identification of the causal pathogen is crucial in the management of periprosthetic joint infection (PJI) of the hip. Unfortunately, it was often difficult and negative culture could be a common findings. This situation made the treatment of PJI of the hip became more challenging. The negative culture finding resulted in a doubtful diagnosis of infection, and poses difficulty in choosing the appropriate antibiotics. Here we compared the treatment outcome of two-stage revision arthroplasty for culture-negative versus culture-positive PJI of the hip.

Background

Need for hip or knee arthroplasty is rapidly increasing in aging society nowadays. Accordingly, orthopedic surgeries for patients with various diseases of high mortality rates are becoming indispensable. Patients with liver cirrhosis undergoing major orthopedic surgery like joint arthroplasty are at risk of many complications including infection and excessive bleeding. In this study, we want to present helpful measures to prevent expected complications that can occur with hip or knee arthroplasty performed on patients with liver cirrhosis through comparative analysis on the prognosis of relevant patients studied at our hospitals.

Background

The patients with high hip dislocation due to the sequelae of septic hip or neglected Developmental Dysplasia of the Hip (DDH) show severely impaired gait pattern. Total hip arthroplasty (THA) for these patients are expected to restore gait pattern by establishing better joint stability and biomechanics. To our knowledge, no study have investigated about objective change in gait parameters after total hip arthroplasty (THA) for these patients. So, we are to prospectively evaluate change in gait patterns after THA.

We performed this study to evaluate the clinical and radiological results of metal on metal articulation change for the treatment of ceramic liner or head fractures in total hip arthroplasty (THA).

We retrospectively reviewed 8 patients with revision THA using liner cementation (metal on metal) due to ceramic fracture (liner fracture; 5 cases, head fracture; 3 cases).

They were followed up for an average of 30 months (range 12 to 68 months). At the surgery, we removed ceramic liner and head, the joint cavity was irrigated with saline to remove remnants of ceramic particles. After that, the inner surface of the metal shell was roughened with a high-speed diamond burr to improve the fixation strength of the liner.

Metal inlay polyethylene (Metasul^®, Centerpulse Orthopedics, Austin, TX) liner was used and the back surface of the liner was routinely down sized and roughened like spider web with an electrical burr to ensure stable fixation with bone cement.

We evaluated clinical result using Harris Hip Score (HSS) and the Western Ontario and McMaster Universities Osteoarthritis index (WOMAC) score and radiological evaluation was done using the mothod of DeLee and Charnley for the acetabular osteolysis and method of Gruen et al. for the femoral osteolysis.

The mean Harris hip scores improved from 65.3 pre-operatively to 93.8 at the final follow-up. There were no changes in cup position, no progression of osteolytic lesion around the femoral and acetabular components and no measurable wear of metal on metal bearing articulation at the last follow-up radiographs. There was one case of recurrent dislocation after surgery and the patient treated with greater trochanter distal advancement.

This study showed that for the treatment of ceramic liner or head fractures, after thorough removal of ceramic particles, cementation into a metal shell and changing the articulation to metal-on-metal provided good clinical and radiological results.

The aim of the present study was to report the midterm follow up results of second generation metal-on-metal cementless total hip arthroplasties in patients younger than 50 years.

From December 1997 and January 2003, 91 metal-on-metal cementless primary total arthroplasties in 77 patients (who were younger than 50 years) were performed in our institution. Among them 72 hips in 63 patients could be followed more than 5 years. There were 18 women (22 hips) and 44 men (50 hips) with a mean age at surgery of 39 years (range 22 to 49 years) and a mean follow up of 7 years (range 5 to 10 years).

The most common cause of total hip replacement were avascular necrosis of femoral head (37 hips in 28 patients, 51%) and second one was osteoarthritis (13 hips in 13 patients, 18%). We used Fitmore (Zimmer, Winterthur, Switzerland) cup in all cases and used 28mm Metasul femoral head. About the femoral stem, CLS (Protek AG/Zimmer, Bern, Switzerland) stems were used in 48 hips and Cone prosthesis^® (Protek AG, Berne, Switzerland) were used in 24 hips.

We evaluated clinical result using Harris hip score (HSS) and the Western Ontario and McMaster Universities Osteoarthritis index (WOMAC) score and radiological evaluation was done using the method of DeLee and Charnley for the acetabular osteolysis and method of Gruen et al. for the femoral osteolysis.

The mean HSS improved from 58.9 (range 35 to 69) preoperatively to 92.2 (range 82 to 100) postoperatively. The mean WOMAC score improved from 72.2 (range 63 to 94) preoperatively to 29.2 (range 17 to 51) postoperatively. In radiological evaluation, all femoral and acetabular component were well fixed without loosening or subsidence. But osteolysis was observed in 10 (14%) of total 72 hips (Acetabular osteolysis in 5 cases-Zone 2; 2, Zone 3; 3, Femoral osteolysis in 6 cases-Zone 1; 6, Zone 7; 1).

About the major complications, there were immediate postoperative deep infection 1 case, delayed infection 1 case and recurrent dislocation 1 case. There was no revision case due to aseptic loosening.

The treatment of second generation metal-on-metal cementless total hip arthroplasties in patients younger than 50 years showed favorable midterm results.

The two-incision technique uses strategically located incisions to insert the prosthesis components in to specific intermuscular or internervous planes in an effort to minimize damage to these tissues. Even though there are many reports about safety and benefits of bilateral simultaneous total hip arthroplasty (THA), none of them has reported about either one-incision or two-incision bilateral simultaneous minimally invasive (MI) THA. This study aimed to assess the feasibility of bilateral simultaneous MI two-incision THA in terms of clinical, radiological and functional outcomes.

Sixty two patients, in the age of 24 to 69 years were operated for bilateral simultaneous THA using modified two-incision technique and followed for average 41 months. In the technique of two-incision THA described by Mears, they used modification of Smith Peterson approach for insertion of acetabular component and femoral component is inserted through a small incision situated between greater trochanter and iliac crest, centered directly in line with the femoral shaft. We modified this technique and used part of Watson Jones approach for insertion of acetabular component with patient in lateral position. The posterior incision for insertion of femoral component is through intermuscular interval between gluteus medius and piriformis.

The average Harris Hip score improved from 41.8 (range 10 to 59) preoperatively to 95.3 (range 73 to 100) postoperatively (P < 0.05). WOMAC score improved from median of 66.2 (range 31 to 96) preoperatively to 5.0 (range 0 to 19) postoperatively (P < 0.05). Forty-nine (79.03%) patients were pain-free at the time of first follow up (6 weeks after surgery) and remained pain-free till the last follow up, while remaining 13 (20.97%) had only slight pain. Out of those 13, 3 patients complained of occasional mild pain at last follow up. Fifty (80.64%) patients were walking without limp, while remaining 12 (19.35%) had only slight limp at 6 months. Out of those 12, 2 patients had persistent limp at final follow up. Fifty-eight (93.53%) patients were walking without support, 56 (90.32%) were able to walk unlimited distance and 55 (88.70%) were able to climb stairs without using a railing. Walking with walker was started on average 3.7 days (range 1 to14 days) and walking with crutches was started on average 10.3 days (range 1 to 49 days) postoperatively. Patients were able to walk without support on an average 48 days (range 14 to 120 days) and use stairs without support and without any discomfort on an average of 50 days (range 5 to 150 days). The average lateral opening angle of acetabulum was 40 ° and anteversion was 12 °. All femoral components were implanted in neutral to 5 ° valgus position. None of the femoral component showed subsidence of more than 3 mm. The filling of the femoral canal by the prosthesis was excellent in all cases. Post-operative periprosthetic fracture occurred in 2 patients and delayed infection occurred in 1 patient.

In conclusion, bilateral simultaneous two-incision minimally invasive THA gives satisfactory clinical and radiological results in comparison with conventional THA. It is safe in experienced hands, without any additional risk of complications. It provides excellent functional outcome and patient satisfaction.

A consecutive series of patients who underwent 113 total hip arthroplasty (THA) with minimally invasive surgery (MIS) (63 one-, 50 two-incision cases) were studied. One-incision THA was performed with a posterolateral approach. For the two-incision, the first incision for cup insertion was made over the anterolateral side of the hip and intermuscular dissection was performed between the gluteus medius and the tensor fascia lata. The second incision for stem insertion was made on the posterolateral side along the fiber of the gluteus maximus and intermuscular dissection was made between the gluteus medius and the piriformis.

The average length of the skin incision and standard deviation (SD) in the one- and two-incision group was 7.5 ± 0.54 cm and 12.1 ± 0.93 cm (p < 0.001). Average surgical time for the two groups (and SD) was 52 ± 8.5 minutes and 70 ± 10.2 minutes (p = 0.042) in the one and two incision groups respectively. Fluoroscopy was used in the two-incision group for an average 6.0 ± 5.3 seconds. In the one-incision group, the average time was 1.3 ± 2.1 seconds.

The patients in the one-incision group could walk on crutches at postoperative 3.7 days on average, and in the two-incision group at 1.6 days on average (p = 0.000). In the one-incision group, patients used crutches for 6 weeks on average, and in the two-incision group, patients used crutches for 3 weeks on average (p = 0.042).

Complications that developed within 1 month of surgery in the one-incision group were: 1 case of DVT, 1 case of intra-operative fracture and 1 case of dislocation; for the two incision group there were: 1 case of DVT, 1 case of intra-operative fracture and 1 case of femoral nerve entrapment.

Before surgery, the HHS for the one-incision group was 49.8 points, and for the two-incision group it was 49.6 points (p > 0.05). At the time of the follow up review conducted postoperatively 1 year, the average HHS was not significantly different (p > 0.05). However, the average function score in HSS for the two-incision group was superior to that of the one-incision group (p = 0.045). Preoperative WOMAC scores were not different for the two groups (68.7 in one-incision group and 70.9 in two-incision group, respectively, p > 0.05). However, the average WOMAC score for the two-incision group was better, especially for the function score (p = 0.001). The other hip functions, common in oriental persons, were also better in the two-incision group compared to the one-incision group.

On the radiographs, the location of the femoral prosthesis inserted in the medullary cavity was usually central in both groups; only 4 cases showed varus in the one-incision group and 2 cases in the two-incision group. The opening angle of the acetabular component was 38.1° in the one-incision group and 39.2° in the two-incision group (p > 0.05). The anteversion of the acetabular component was 21.0° in the one-incision group and 22.2° in two-incision group (p > 0.05).

As compared with one-incision MIS-THA, two-incision MIS-THA, although it is a more difficult procedure, produces superior results, recovery was faster and patient satisfaction was higher due to early rehabilitation and reduced soft tissue damage without increasing the complication frequency.

Audible squeaking following ceramic-on-ceramic total hip arthroplasty (THA) is a rare but troublesome problem. We retrospectively reviewed records of 1002 patients where a ceramic-on-ceramic THA had been done during the study period. Fifteen patients complained of squeaking, at any time following their arthroplasty. Fourteen of these 15 patients were evaluated clinically and radiologically. The demographics of these patients were compared to that of all the other patients who did not have squeaking following ceramic-on-ceramic THA. The radiographic data was compared to a control group matched for age, sex, body mass index (BMI), primary diagnosis, type of implant, date of surgery and length of follow-up.

There were 12 males and 2 females of a mean age of 44.5 years (range, 25–65 years). These 14 patients were found to have significantly higher BMI of 25.98 kg/m2 (range, 21.6–32.3 kg/m2) as compared to the other patients who had ceramic-on-ceramic THA (mean, 23.61 kg/m2; range, 15.8 –30.3 kg/m2) (p=0.005). The lateral opening angle was found to be significantly lower (mean, 34°; range 29°–40°) in these patients than the matched control group (mean, 38°; range 30°–41°) (p=0.016). Mean acetabular anteversion was 22° (range 9°–37°), which was not significantly different to that of the matched controls (mean 23°; range 2°–33°) (p=.957). Limb length shortening of more than 5mm was observed in 12 of the 14 (85.7%) patients as compared to only 4 of 14 (28.6%) patients in the matched control group. Two patients had intermittent squeaking while the other 12 had continuous squeaking. Flexion and sitting cross legged were identified as the movements which most commonly (11 of 12) resulted in squeaking. Mean Harris hip score (HHS) improved from 44 (range, 19–66) to 94 (range, 88–100) and most patients (13 of 14) were satisfied with the outcome of the surgery.

Thus the incidence of squeaking was found to be low (1.5%, 15 of 1002) in our series. We identified high BMI, decreased lateral opening angle and limb length shortening as factors associated with occurrence of squeaking. Proper patient selection, implant placement, and avoidance of limb length discrepancy are likely to further reduce the incidence of this complication of ceramic-on-ceramic THA.

This study was undertaken to assess the feasibility of a new subtrochanteric osteotomy technique for total hip arthroplasty (THA) in cases with a high dislocated hip secondary to the sequelae of a septic hip in childhood. Eighteen patients (20 hips), aged 25 to 65 years (average 47.3 years), underwent THA using a cement-less conical stem (Cone prosthesis^®; Protek AG, Berne, Switzerland) with a new subtrochanteric osteotomy technique and were followed for an average of 23.6 months. All patients were graded as type III (high dislocation) according to the Hartofilakidis classification, and according to the Crowe classification 3 cases were of type III and 17 were of type IV.

The procedure was performed through a posterolateral approach and a provisional osteotomy was usually performed at the inferior half of the lesser trochanter. All acetabular component was inserted at the true acetabular and the acetabular cup was inserted in 5 cases and only a liner was inserted after cementing in 15 cases. The stem size and the amount of stem insertion was decided according to the preoperative planning and soft tissue tension. After final reduction, the greater trochanter was re-attached to the proximal femur with the hip in the abducted position. Cables or a grip system (Dall Miles^®, Stryker Orthopaedics Inc., Mahwah, NJ, USA) were used for fixation, and if possible, additional screws were inserted.

Postoperatively, range of motion exercises were encouraged after 2 to 3 weeks of bed rest and non-weight bearing crutch ambulation followed. Weight bearing was permitted only after obtaining radiological confirmation of bone union, but then active exercises were strongly encouraged to stretch abductors. Mean duration of surgery was 180.6 minutes, and mean perioperative blood loss was 1424.1ml. There were no intra-operative complications. Post-operative dislocation occurred in 2 cases and partial femoral nerve palsy developed in 1 case. Mean Harris Hip Score improved from 42.4 to 84.2. Mean lateral opening angle of acetabular cup and liner was 34.7 0 and mean anteversion was 20.8 0. All femoral components were implanted in neutral to 5 degrees of valgus, and mean leg lengthening was 36.5mm. The mean time to greater trochanter union was 3.72 months.

Primary THA in highly dislocated hips due to the sequelae of septic hip in childhood using the described subtrochanteric osteotomy and a cone prosthesis was found to be safe and effective at restoring leg length and trochanteric rotation. But more follow-up is required to more comprehensively establish the long-term results of the described procedure.

Only limited data exists concerning outcomes after total knee arthroplasty (TKA) using a surgical robot. We conducted this study to evaluate the clinical and radiographical results in robotic-assisted implantation of TKAs with a minimum follow-up of two years.

A total of 50 primary TKAs using ROBODOC were included in this study. The mean duration of follow-up was 28.3 months. The radiographic measurement with regard to the change of mechanical axis, and the inclination of the femoral and tibial components were assessed. The value within ± 3° of optimum was classified to be “acceptable”, and the value exceeding more than ± 3° to be “outlier” results. Also we evaluated clinical results with the range of motion (ROM), Hospital for Special Surgery (HSS) scores, and Western Ontario and McMaster University (WOMAC) scores.

The mechanical axis was changed from 6.57 varus to 0.81 valgus. Mean coronal inclination of the femoral and tibial component were 88.61 and 89.76 at the last follow up. Also, mean sagittal inclination of the femoral and tibial component were 0.82 and 85.49. On the other hand, all prostheses had no radiolucent lines. On the clinical assessment, the range of motion improved from 124.9 to 128.4, and the improvement of HSS score and Womac score were 70.06 to 95.72 and 65.64 to 28.92 in each. No major adverse events related to the use of the robotic system have been observed. However, one case of the formation of seroma around the pin track and two cases of the partial abrasion of patellar tendon occurred in relation to procedures.

A surgical robot system in TKAs provides good clinical and radiographical results at least 2 years follow-up, however further study for the long term follow-up may be needed. A clear advantage of robot-assisted TKA seems to be ability to execute a highly precise preoperative planning and intraoperaive procedures. But current disadvantages such as increased operating times and inability of adjusting the preoperative planning during the procedure have to be resolved in the future.

Navigation was used to achieve a balanced flexion-extension gap for total knee arthroplasty and it’s 3 years clinical results were reported.

From 112 osteoarthritic knees with varus deformity the flexion and extension gap were measured with distraction of 50 lb/inch using special torque wrench following completion of controlled medial release with guidance of navigation system & tibial bone cut. Distal & AP femoral bony cut were finished according to the data of measurement of flexion-extension gap. After confirmation of the balanced flexion-extension gap by navigation total knee arthroplasty was completed.

The differences between flexion and extension gap varied from case to case, and could be classified into 3 kinds; balanced, tight flexion gap and tight extension gap.

HSS score was 96.7, ROM was 128.5 degree. 39 patients (35%) can have comfortable kneeling 75 patients(67%) can sit with cross leg. Gap technique with navigation could provide excellent clinical results of total knee arthroplasty and 3 classifications of flexion and extension gap should be taken into considerations for balanced total knee arthroplasty

Long term successful results of high tibial osteotomy (HTO) strongly depend on the degree of correction, and inadequate intraoperative measurements of the leg axis can lead to under or over correction, and surgeons have to solve these problems based on personal experience.

This study was undertaken to investigate and compare the clinical and radiological results of navigation assisted open wedge high tibial osteotomy (HTO) versus conventional HTO at 12 months after surgery, for unicompartmental gonarthrosis.

Forty navigated open HTOs with an anterior opening gap of approximately 70% of the posterior gap were included and compared with forty open HTOs performed using the conventional cable technique in terms of intraoperative leg axis assess.

Navigated HTOs corrected mechanical axes to 2.9° valgus (range 0.5–6.2) with few outliers (12.5%), and maintained posterior slopes (7.9±2.3° preoperatively and 8.3±2.8° postoperatively) (P> 0.05). However, in the conventional group, only 63% of cases were within the satisfactory range (valgus 2–5°), and tendencies toward undercorrection and an increase in posterior slope were observed. Clinically both groups showed satisfactory results.

Navigated HTO significantly improved the accuracy of postoperative mechanical axis and decreased correction variabilities with fewer outliers.

The navigation system recently introduced in an ACL reconstruction is reported that it would be helpful for determining the accurate tunnel position and better clinical results in. It also provides intra-operative information such as knee kinematics and anteroposterior translation and internal-external rotation of the tibia during the reconstruction. Our hypothesis was that a double bundle reconstruction would provide better anteroposterior and rotational stabilities than a single bundle reconstruction.

The aim of this study was to assess the changes of anteroposterior and rotational stabilities using a navigation system achieved by double bundle reconstruction (20 knees) and compare them with those by single bundle reconstruction (20 knees).

After registering the reference points, anteroposterior ad rotational stability test with 30° knee flexion using a navigation system was carried out and measured before and after reconstruction on both groups.

The anteroposterior stability showed significant improvement from 17.5 mm before the reconstruction to 5.1 mm after the reconstruction in the double bundle group and from 16.6 mm to 6.1 mm in the single bundle group, showing a significant inter-group differences (p< .05). The mean rotation stability of the double bundle group showed more significant improvement after reconstruction than those of the single bundle group (9.8° in single and 6.1° in double bundle group, p< .05).

The double bundle ACL reconstruction tends to be more stable in rotational stability than the single bundle reconstruction, but not so much in anteroposterior stability. Clinically the double bundle ACL reconstruction may provide better rotational stability reducing residual pivot shift phenomenon after reconstruction.

Unexpected findings were sometimes observed such as hyper extension, oversize of femoral component, or anterior notching of anterior femoral cortex in total knee arthroplasty (TKA) using computer system. We conducted this study to evaluate these findings by a virtual simulation using ORTHODOC and then confirmed them on real patients with TKA.

Virtual simulations of distal femoral cut in 50 patients using ORTHODOC system were made by way of being perpendicular to mechanical axis (CAOS way) and to intramedullary guide (manual way) in the same knee and measured the difference of sagittal cutting planes. We compared the maximum AP dimensions of femoral condyle parallel to distal cut plane. We also compared sagittal alignment and size of the femoral component in 30 bilateral TKAs, one side using ROBODOC (CAOS way) and the other side using IM guide (manual way).

On virtual simulation, distal femoral cut was more extended (3.1±1.6°) in CAOS than in manual way and anteroposterior size of the femoral condyle in CAOS way was also larger than in manual way (p=0.001). Radiographic sagittal alignment of femoral component performed using CAOS way was slightly more extended than those using manual way, showing a significant difference (p=0.024). The larger femoral components were required in six patients on CAOS and in two patients on manual way, whereas twenty-two patients showed same size on both side.

CAOS can provide more accurate sagittal cut perpendicular to mechanical axis than manual system, which may lead to slightly extended position or larger femoral component.

In total knee arthroplasty, navigation systems that help achieve accurate alignment of the lower limbs have been applied widely, and these techniques are currently being used in minimally invasive unicondylar knee arthroplasty (MIS UKA) with good alignment results. To the best of our knowledge, there are no studies showing whether or not MIS UKA using a navigation system has a significant influence on the clinical results. This prospective study investigated the hypothesis that minimally invasive uni-compartmental knee arthroplasty using navigation system (NA-MIS UKA) will produce better short-term clinical results than MIS UKA without navigation system.

After a minimum two-year follow-up, the short-term functional results included the ranges of motion, Hospital for Special Surgery (HSS) scores, and WOMAC scores and the alignment accuracy of the components of 31 NA-MIS UKAs (NA-MIS group) compared with those of 33 MIS UKAs without a navigation system (MIS group). The surgery time was also recorded and compared.

The HSS and WOMAC scores showed significant improvement at the final follow-up in both groups, showing no significant inter-group difference (p=0.071, p=0.096, respectively). The ranges of motion also showed significant improvements in both groups, but there was no significant difference between two groups (p=.687). However, the surgery time was longer in MIS group than in NA-MIS group. NA-MIS UKA produces significant improvement in the desired mechanical axis with prosthetic alignment outliers compared with that without the navigation system.

However, at the final follow-up, there were no significant differences in any of the functional parameters between the two groups.

This prospective study was undertaken to compare the clinical and radiological results achieved using navigation assisted minimally invasive (NA-MIS) and conventional (CON) techniques in bilateral total knee arthroplasty (TKA).

Forty-two bilateral patients with a minimum 2-year follow-up who were available for study after NA-MIS TKA were included in this study. Clinical evaluations (ROM, HSS and WOMAC scores) were performed at 3 and 6 months and at 1 & 2 year postoperatively. Patient subjective preferences and radiological accuracies were compared at 1 year postoperatively.

Preoperative HSS scores were 68.5 in the NA-MIS group and 66.5 in the CON group, and these scores improved to 93.6 and 92.5 at 1 year postoperatively, respectively. Knees had a higher average HSS score in NA-MIS group than in the CON group till six months, but not after nine months postoperatively. In terms of WOMAC scores, pain scores in the NA-MIS group were better up to nine months postoperatively, but not at one & 2 year postoperatively, and total WOMAC scores were better up to six months, but not after nine months postoperatively. ROM was comparable in both groups at all times. However, more patients preferred NA-MIS sides than CON sides. Radiological results demonstrated no difference between the mean values of the two groups, although the NA-MIS group contained fewer outliers than the CON group.

NA-MIS TKA results in better functional scores than CON-TKA over the first or nine months postoperatively. However, no differences in any functional parameters were evident at one & two year postoperatively.

Computer based navigation system improved the accuracy of limb and component alignment and decreased the incidence of outliers. The majority of previous studies were based on the infrared navigation system. We evaluate the availability and accuracy of the electromagnectic(EM) navigation system in total knee arthroplasty

From July 2006 to January 2007, 40 patients (50 TKAs) with osteoarthritis were participated in this study. AxiEM(Medtronics) was used and Nexgen CR(26 cases), and Nexgen CR flex(24 cases) were used. We analyzed the failure mode of navigation (7 cases), operation time and radiologic results (limb and component alignment)

Total registration time was 4 minutes 45 seconds in average (Range : 3 minutes 45 seconds ~ 6 minutes 55 seconds). Failures in clinical applications resulted from non-recognition of EM tracker or paddle by metallic interference in 4 cases and from informational changes during surgery by fixation loss or loosening of the tracker in 3 cases. Radiologically, the mechanical axis changed from −11.2±7.21 (Range : −25.8~3.1) to 1.0±1.25(Range : −2.1~4.0) and 1 case of outlier occurred (valgus 4°). Component alignment is measured as followed: 89.3±1.6° of Theta angle, 89.9±1.5° of Beta angle, 1.8±2.5° of Gamma angle, 86.1±2.9 of Delta angle°. There were no complications related to the EM navigation.

The EM navigation system helped to achieve accurate alignment of component and lower leg axis without any complications. It had several advantages such as relatively less invasiveness in fitting small instruments, not disturbing operation field, no interrupted line of sight, portable use, and applicability to any implant. However, metallic interference may be still problematic.

The EM navigation had advantages; less invasiveness, no disturbing operation field, no interrupted line of sight, portable use and applicability to any implants. But metallic interference may be still problematic.

Correct alignment of the leg and positioning of the implant has shown to be an important factor in the successful long term outcome of total knee arthroplasty and navigation systems enable an accuracy of corrections and alignment within intervals of 1 mm or 1 degree. This study is to test if there is any discrepancy in accuracy which was sometimes observed in clinical trials between Orthopilot (Aesculap, Tuttlingen, German) and AxiEM (Medtronic Navigation, CoalCreek, Colo., USA).

A synthetic bone model (Sawbones, Pacific Laboratories, Vashon, Washington) including pelvis and leg with mobile joint made up of titanium which does not affect the electromagnetic field was constructed. Mechanical axis was checked by ORTHODOC system (Integrated Surgical System, CA, USA) that is a preplanning system for ROBODOC (ISS, CA, USA) assisted total knee arthroplasty (TKA) and total hip arthroplasty (THA). The CT images were scanned with 1.25 mm or less slice interval. The CT images were converted to 3-dimensional (3D) volume-rendered model in ORTHODOC. Two orthopaedic surgeons measured it ten times independently.

For the measurement of mechanical axis using navigation, 4 orthopaedic surgeons (two experts having more than 100 navigation experiences and two residents) registered anatomical landmarks and kinematic center of bone model ten times using Orthopilot as well as AxiEM. After that, one surgeon intentionally registered the wrong anatomical landmarks (10 mm medial and lateral to the center of distal femur, proximal tibial and ankle, and both malleoli) in both navigation system and observed the change of mechanical axis.

True mechanical axis was varus 1.25° using Orthodoc, Orthopilot displayed varus 1.10±0.64° and AxiEM did varus 1.78±0.79°. The difference of mechanical axis between two navigations was not observed (P=0.12) and there were no intra and inter-observer variation in statistical analysis (Correlation=0.934, P=0.00). In the case of erroneous identification of the anatomical landmarks, Orthipilot showed much less variation compared to AxiEM. AxiEM altered the mechanical axis more in palpating center of the distal femur and ankle center and Orthopilot did in palpating the center of ankle.

Both navigation systems provide high accuracy and reproducibility of mechanical axis of lower limb in experimental condition. But both were affected by the wrong identification of the anatomical landmarks. AxiEM had more variations. So surgeon should pay attention to register the precise anatomical landmarks.

Bilateral sequential total knee replacement with a Zimmer NexGen prosthesis (Zimmer, Warsaw, Indiana) was carried out in 30 patients. One knee was replaced using a robotic-assisted implantation (ROBOT side) and the other conventionally manual implantation (CON side). There were 30 women with a mean age of 67.8 years (50 to 80).

Pre-operative and post-operative scores were obtained for all patients using the Knee Society (KSS) and The Hospital for Special Surgery (HSS) systems. Full-length standing anteroposterior radiographs, including the femoral head and ankle, and lateral and skyline patellar views were taken pre- and post-operatively and were assessed for the mechanical axis and the position of the components. The mean follow-up was 2.3 years (2 to 3).

The operating and tourniquet times were longer in the ROBOT side (p < 0.001). There were no significant pre- or post-operative differences between the knee scores of the two groups (p = 0.288 and p = 0.429, respectively). Mean mechanical axes were not significantly different in the two groups (p = 0.815). However, there were more outliers in the CON side (8) than in the ROBOT side (1) (p = 0.013). In the coronal alignment of the femoral component, the CON side (8) had more outliers than the ROBOT side (1) (p = 0.013) and the CON side (3) also had more outliers than the ROBOT side (0) in the sagittal alignment of the femoral component (p = 0.043). In terms of outliers for coronal and sagittal tibial alignment, the CON side (1 and 4) had more outliers than the ROBOT side (0 and 2).

In this series robotic-assisted total knee replacement resulted in more accurate orientation and alignment of the components than that achieved by conventional total knee replacement.