Simultaneous Post and Cone Fractures of a Polyethylene Insert in a Mobile-Bearing Posterior-Stabilized Total Knee Arthroplasty.

We report a novel case of the simultaneous post and cone fractures of a polyethylene (PE) insert in a mobile-bearing posterior-stabilized total knee arthroplasty. Twelve years after the primary total knee arthroplasty, the 72-year-old male patient presented with a recurring right knee instability and was diagnosed with the wear of the PE insert based on physical and radiological examinations. Revision surgery was performed. The post and cone of the PE insert had fractured simultaneously. Moreover, the femoral and tibial components were in direct contact with each other. One year post-revision, knee function had improved. To diagnose a PE breakage, such as a post or cone fracture, surgeons should consider the possibility of PE breakage even in the absence of pain since patients might complain of subjective instability only.

Improvement of rotational arc during deep flexion range of a novel designed polyethylene insert for posterior-stabilised total knee arthroplasty.

BACKGROUND: One of the remaining issues in total knee arthroplasty (TKA) is achieving sufficient rotational arc during deep flexion range of the knee for specific postures such as the 'seiza' or cross-legged sitting. This study aimed to evaluate whether there was a change in the actual in vivo rotational arc during deep flexion range before and after a design change of polyethylene (PE) inserts. METHODS: In 50 posterior-stabilised TKA cases, knee kinematics, including rotational movement, were measured intraoperatively using an image-free navigation system to compare a newly designed PE insert with reduced the posterior lip with a conventional PE insert. Femoral-tibial rotational angles at 30°, 45°, 60°, 90°, 120°, and 130° knee flexion were evaluated. Varus/valgus instability, knee range of motion, and femoral rollback were also measured. Obtained parameters were compared between new and conventional PE inserts. The independent factors associated with rotational arc during deep flexion range (120° and 130° knee flexion) were analysed using multivariate analysis. RESULTS: The newly designed PE insert demonstrated a significant increase in the rotational arc at 120° (22.9 ± 8.7° vs. 30.1 ± 11.9°, P < 0.001) and 130° (24.3 ± 9.5° vs. 32.5 ± 12.4°, P < 0.001) knee flexion compared with that with the conventionally designed posterior-stabilised insert. Multivariate analysis demonstrated that using the newly designed PE insert was an independent predictor of improved rotational arc during deep flexion range: regression coefficient was 11.2 (95% confidence interval 7.1-15.3, P < 0.001). CONCLUSION: The design change, which reduced the posterior lip of the PE insert, contributed to improved rotational arc in 120° and 130° deep flexion ranges.

Long-term clinical results of alumina ceramic medial pivot total knee arthroplasty: a 10-year follow-up study.

BACKGROUND: The newly-designed alumina ceramic medial pivot total knee prosthesis was introduced to reduce polyethylene wear and better fit the anatomical morphology of the Asian population. This study aimed to clarify the long-term clinical results of alumina medial pivot total knee arthroplasty over a minimum follow-up period of 10 years. METHODS: The data of 135 consecutive patients who underwent primary alumina medial pivot total knee arthroplasty were analyzed in this retrospective cohort study. Patients were examined over a minimum 10-year follow-up period. The knee range of motion, Knee Society Score (KSS) knee score, Knee Society Score function score, and radiological parameters were assessed. The survival rate was also evaluated by using reoperation and revision as endpoints. RESULTS: The mean follow-up period lasted 11.8 ± 1.4 years. Patients who were not followed accounted for 7.4% of the total cohort. Knee and function scores of KSS improved significantly following total knee arthroplasty (P < 0.001). In 27 individuals (28.1%), a radiolucent line was observed. Aseptic loosening occurred in three cases (3.1%). The survival rates for reoperation and revision were 94.8% and 95.8% 10 years after the operation, respectively. CONCLUSIONS: During a minimum 10-year follow-up period, the present model of alumina medial pivot total knee arthroplasty showed good clinical outcomes and survival rates.

Chronological Changes in Axial Alignment of the Ipsilateral Hip and Knee After Total Hip Arthroplasty.

BACKGROUND: Internal rotation of the hip and lateral patellar tilt increases after total hip arthroplasty (THA). However, it remains unknown whether these parameters change with time after the index THA. METHODS: A total of 91 patients undergoing 2-stage bilateral primary THAs between January 2008 and May 2014 were included to assess the association of chronological changes in internal rotation of the hip or lateral patellar tilt with anthropometric and perioperative parameter and changes in alignment after the index THA. Chronological changes were assessed as changes between postoperative computed tomography on the index surgery and the preoperative computed tomography on the contralateral THA. Internal rotation of the hip was defined as the angle between the posterior intercondylar line and a line passing through the posterior inferior iliac spines. Lateral patellar tilt was defined as the angle between the posterior intercondylar line and a line joining the medial and lateral edges of the patella. RESULTS: Internal rotation of the hip and lateral patellar tilt changed until 2 years after the index surgery by a mean of -2° (range -17.3° to 17.7°) and -2° (range -18.2° to 5.3°), respectively. Adductor tenotomy was associated with increasing internal rotation of the hip with time (adjusted R2 0.076); leg lengthening and larger preoperative femorotibial angle were associated with decreasing lateral patellar tilt with time (adjusted R2 0.159). CONCLUSION: Both internal rotation of the hip at rest and lateral patellar tilt decreased by approximately 2° until 2 years after surgery and there was a large variation in chronological change.

Cement Removal from the Femur Using the ROBODOC System in Revision Total Hip Arthroplasty.

Introduction. The perforation and fracture of the femur during the removal of bone cement in revision total hip arthroplasty (THA) are serious complications. The ROBODOC system has been designed to selectively remove bone cement from the femoral canal, but results have not been reported yet. The purpose of our study was to evaluate the clinical and radiographic results of revision THA using the ROBODOC system for cement removal. Materials and Methods. The subjects comprised 19 patients who underwent revision THA using the ROBODOC system. The minimum duration of follow-up was 76 months (median, 109 months; range, 76-150 months). The extent of remaining bone cement on postoperative radiography, timing of weight bearing, and the complications were evaluated. Results. The mean Merle d'Aubigne and Postel score increased from 10 points preoperatively to 14 points by final follow-up. Bone cement was completely removed in all cases. Full weight bearing was possible within 1 week after surgery in 9 of the 19 cases and within 2 months in all remaining cases. No instances of perforation or fracture of the femur were encountered. Conclusions. Bone cement could be safely removed using the ROBODOC system, and no serious complications occurred. Full weight bearing was achieved early in the postoperative course because of circumferential preservation of the femoral cortex.

Robot-assisted primary cementless total hip arthroplasty using surface registration techniques: a short-term clinical report.

PURPOSE: The purpose of this study was to compare non-fiducial based surface registration technique (DigiMatch) with the conventional locator pin-based registration technique in performing cementless total hip arthroplasty (THA) using ROBODOC system. METHODS: Eighty-one THA were performed using pin-based technique and forty-three were performed using the DigiMatch technique. The average follow-up term was 38 months. RESULTS: Postoperatively, the Japanese Orthopedic Association hip scores were significantly better in the DigiMatch group than in pin-based group. The accuracy of postoperative stem alignment of the DigiMatch technique was comparable with that of pin-based method. CONCLUSIONS: No need for prior pin implantation surgery and no concern for pin related knee pain were the advantages of DigiMatch technique. Short-term follow-up clinical results showed that DigiMatch ROBODOC THA was safe and effective.

Hip motion analysis using multi phase (virtual and physical) simulation of the patient-specific hip joint dynamics.

In total hip arthroplasty (THA), the patient-specific bone geometry or the characteristics of the skeletal movement should be considered during treatment in order to prevent complications. In this paper, we propose a novel approach for the analysis of joints which combines the patient-specific virtual and physical simulation. The patient-specific anatomical structure and hip motion was obtained from CT and optical motion capture. The virtual simulation was conducted by integrating these data using virtual reality technique. The physical simulation was achieved by using plaster models of the patient's pelvis and femur and robotic manipulator. The plaster models were driven by two robotic manipulators to reproduce the hip motion. The accuracy of the robot movement was 0.245 mm over the working area according to the validation by an optical tracking system. By combining this system with linear actuators that reproduce the muscle functions, patient-specific muscle function can be simulated, thereby helping clinicians to diagnose and make a treatment plan.

Open-configuration MRI study of femoro-acetabular impingement.

Femoro-acetabular impingement has been proposed as a causative factor of primary hip osteoarthritis. However, primary osteoarthritis of the hip is infrequent in Japan and other Asian countries, even though the hips of Asians frequently sustain impingement, since the Asian lifestyle commonly requires a larger range of hip motion than the Western lifestyle. Therefore, using open-configuration MRI, we investigated whether impingement actually occurs during some traditional Japanese hip positions. The hips of 5 healthy Japanese females were examined in 5 sitting postures: 1) sitting straight; 2) bowing while sitting straight; 3) sitting cross-legged; 4) W-sitting; and 5) squatting. The impingement point was detected by multiple plane reconstructed (MPR) views along with the acetabular rim depicted circumferentially. Impingement was considered to have occurred when, on MRI, the anterior femoral head-neck junction approached the acetabular rim and the femoral head was seen to float from the bottom of the acetabulum with the acetabular rim acting as a fulcrum. Impingement was observed in all volunteers in the W-sitting position, and in 2 of 5 volunteers during squatting. These findings show that impingement occurs frequently during daily Japanese activities. Thus, depending on race, femoro-acetabular impingement might not always cause primary osteoarthritis of the hip. (c) 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1582-1588, 2007.

Preoperative templating of femoral components on plain X-rays. Rotational evaluation with synthetic X-rays on ORTHODOC.

INTRODUCTION: Preoperative femoral templating for total hip arthroplasty (THA) has been performed by antero-posterior radiographs of both hips which should be taken with the femur rotated internally to reduce the effect of femoral anteversion. However, there is no criterion to evaluate the optimal rotated radiograph. Here, we quantitatively investigated 50 femora whether the thickness of the lesser trochanter (TLT) was useful when evaluating the femoral rotation, and assessed the effect of prosthetic templating on the inappropriate rotated radiographs. MATERIALS AND METHODS: We assessed 50 femora of 46 consecutive osteoarthritic patients using "synthetic X-ray" based on computer tomography (CT) images, which can be displayed as virtual plain radiographs with any magnification and any projected direction such as plain radiographs. We made four femoral radiograph groups of different rotation prepared (neutral, 15 degrees, 30 degrees, and 45 degrees external rotation), and measured the TLT. We also templated femoral stem on the different rotated synthetic X-ray of each patient, and investigated the effect of inappropriate rotated radiograph by the measurement of the position and the size of the stem. RESULTS: Seventy-four percent of the neutral rotational group had less than 5 mm of the TLT. While 30 degrees and 45 degrees external rotation group had few cases with less than 5 mm of the TLT. Compared to the neutral group, smaller stem size was selected in more than 80% cases of 30 degrees and 45 degrees external rotational group, and the stem position in these two groups was more than 5 mm proximally. CONCLUSION: We suggest that when templating femoral stem, this criterion "the TLT is less than 5 mm" reduces some risks by inappropriate rotated radiograph.

Effect of robotic milling on periprosthetic bone remodeling.

The ROBODOC system has provided better fit and fill of the stem and less destruction of the bony architecture than with manual surgery. These benefits might affect femoral periprosthetic bone remodeling. We evaluated the effects of robotic milling in cementless total hip arthroplasty (THA) in a longitudinal 24-month follow-up study using dual energy X-ray absorptiometry (DEXA) and plain radiographs of 29 patients (31 hips) after ROBODOC THA and 24 patients (27 hips) after manual THA with the same stem design. To minimize the influence of other factors on bone remodeling, only female osteoarthritis patients, who had no drugs that might affect bone metabolism were enrolled. Significantly less bone loss occurred at the proximal periprosthetic areas in the ROBODOC group. In zone 1, the decrease was 15.5 versus 29.9% using conventional rasping; in zone 7, the loss was 17.0% with ROBODOC compared to 30.5% with conventional rasping (p < 0.05). On radiographs, endosteal spot welds in the proximal medial portion were more pronounced in the ROBODOC group (48 vs. 11% in the conventional group, p < 0.05). Our results suggest that robotic milling is effective in facilitating proximal load transfer around the femoral component and minimizing bone loss after cementless THA.

System for intraoperative evaluation of soft-tissue-generated forces during total hip arthroplasty by measurement of the pressure distribution in artificial joints.

A system for evaluating the soft-tissue-generated forces at the hip joint was developed. The system enabled measurement of contact pressure distribution at hip joint surfaces, as well as evaluation of the artificial hip joint condition during total hip arthroplasty (THA). First, a pressure sensor module that forms part of the artificial joint was constructed. Eight small pressure sensors were installed in the spherical head component of the ball-and-socket joint. Next, software for recording and visualizing the detected pressures at 1-millisecond intervals was developed. The pressure distribution was displayed in real time via 3D computer graphics on a monitor. The system enabled intuitive recognition of the direction of soft-tissue-generated forces and pressure distribution in three dimensions. Accuracy tests were conducted using a high-accuracy 6-degree-of-freedom positioning device and digital force gauge. The error between the applied loads and measured forces was 3.42 +/- 3.26 N (mean +/- standard deviation) for each coordinate in 10 trials involving load application from 10 different directions. Next, a clinical evaluation was conducted during THA. The relative positions of the cup and stem component were measured using a surgical navigation system simultaneously with the pressure measurement. The system allowed real-time acquisition of information regarding the artificial hip joint, as well as comparison of the differences in the hip condition when several types of neck were used. Further improvements to the calibration method should enable more accurate measurements. We believe this system will be a useful tool for selecting an appropriate implant that fits a patient's hip joint or for estimating the risk of complications following surgery.

Serious metallosis of a metal head due to fragmented ceramic screws in a cemented THA.

We reported a rare revision case necessitated by massive metallosis of a metal head due to a fragmented ceramic screw which had been extraarticularily used in the primary THA here and reviewed previous literature about metallosis of metal heads associated with ceramic materials. The ceramic screw had been used for the fixation of a bone graft and reattachment of the greater trochanter in the primary THA. Scanning electron microscope analysis revealed large alumina ceramic particles embedded on the bearing surface of the polyethylene. It has previously been pointed out that metallosis of an inner head occurred in bipolar case due to a fracture of the ceramic screws in contact with a proximally migrated outer head. However, this case showed that if a ceramic screw fragmented even though it was used outside of the hip joint, the fragments could migrate into bearing surface and cause serious metallosis of the metal head. Thus, we recommend that surgeons should pay special attention to the radiographic signs of ceramic failure or metallosis such as a change of the metal head contour, if an aseptic loosening or severe osteolysis is observed in a THA in which ceramic materials were used near the hip joint. And, when a surgical revision is planned, the surgeon should be prepared to exchange with a new ceramic head.

Soft-tissue balance evaluation system for total hip arthroplasty by intraoperative contact pressure measurement at the hip joint.

We developed a system for measurement of contact pressure at the hip joint surfaces that enables checking of the artificial hip joint condition during surgery. First, we constructed the pressure sensor that forms the artificial joint. We installed eight small pressure sensors to the spherical head component, a part of the ball-socket joint. Next, we developed software for recording and visualizing the detected pressures that were recorded every 1 ms. The pressure distribution was displayed with the 3D computer graphics in real-time. The system enabled intuitive recognition of pressure direction 3-dimensions. Next, using the system, we conducted measurements during total hip arthroplasty. Although it requires some improvements in its measurement accuracy, the system allows real-time acquisition of information on the artificial hip joint in real-time. Further improvements of the calibration method should enable more accurate measurements. As a complete system, it will be a useful tool for selecting an appropriate implant that fits a patient's hip joint or for estimating the risk of complications after surgery.

Estimation of dislocation after total hip arthroplasty by 4-dimensional.

We constructed a 4-dimensional musculoskeletal model for patients who have undergone total hip arthroplasty (THA), which aimed to simulate the movement of the patient's inner body structure and estimate the complications that can arise with THA. The model reflects patient-specific characteristics of the bone geometry, implant alignment and hip movement. In order to estimate the direction of the muscle force and the length of the muscles, we developed a string-type muscle model that represents the route of the muscles. The strings expand and contract according to the movement of the origin and insertion location of the muscle. We developed models for the seven muscles related to movement of the hip joint. By using this model, clinicians will be able to predict the possibility of dislocation or recognize the actual causes of dislocation, as well as any possible influences the muscle may have on dislocation.