Recently, as the number of total knee arthroplasty (TKA) is increasing, the number of revision TKA due to loosening or osteolysis is rapidly increasing. Large bone defect is one of the most critical issues during revision TKA. Therefore, early detection of bone loss around the TKA prosthesis before bone loss has been enlarged is very important. However, it is difficult to detect the loosening or ostolysis at the early stage around the femoral component even using fluoroscopically guided plain radiograph. A novel technique of tomography (Tomosynthesis; Shimazu Corporation, Kyoto, Japan) was introduced to detect the small bone loss. The purpose of this study was to examine, in a pig model of radiolucent line and osteolysis around TKA, the sensitivity and specificity of detection of radiolucent line and osteolysis using fluoroscopically guided plain radiographs and a novel technique of tomography. Six cemented femoral components (PFC Sigma; DePuy, Warsaw, IN, USA) were implanted in pig knees. Two components were implanted with standard cement technique (Standard model). Two components were implanted with 2 mm-thick defect between the cement and bone (Radiolucent line model). Two components were implanted with cystic defects (mean size = 0.7 cm3) in femoral condyles (Osteolysis model). The simulated bone lesions were filled with agarose to simulate granuloma tissue and to reduce the air artifact around the bone lesions, which can interfere with imaging techniques (Figure 1). Fluoroscopically guided plain radiographs (63 kV, 360 mA, 50 msec) were taken in 4 postures (antero-posterior, lateral, and +/−45 degrees oblique views) for each specimen (Figure 2). For Tomosynthesis, 74 frames were acquired in the rate 30 frames/sec with fixed X-ray condition (65 kV 1.25 mAs) and were reconstructed (Figure 3). Seven blinded assessors experienced in clinical radiographic analysis examined. The sensitivities, specificities and accuracy of the two imaging techniques were compared.INTRODUCTION
METHODS
In previous congress of ISTA in Hawaii, we reported the results about accuracy of the cup center position in our image-free navigation system. In the new version of our navigation system, leg elongation and offset change as well as cup center position can be navigated. In this study, we therefore investigated the accuracy of cup center position, leg elongation and offset change. Twenty four THA operations were performed with using the image-free OrthoPilot THA3.1 dysplasia navigation system (B. Braun Aesculap, Tuttlingen, Germany) between August 2009 and December 2009 by three experienced surgeons. In this system, cup center height was shown as the distance from tear drop, and cup medialization was shown as horizontal distance from inner wall of acetabulum. Leg elongation and offset change were navigated by comparing the two reference points in femur between registration before neck resection and that after inserting the trial implant. After operation, the cup angles were measured on CT image, and cup center position, leg elongation and offset change were measured on plain radiography. We compared these values that indicated by the navigation system to those measured on the CT image and the plain radiography. The average cup inclination was 37.5 ± 7.0 degree and anteversion was 22.2 ± 4.7 degree. The average absolute difference between navigation and measured angles were 5.2 ± 4.0 degree in inclination, 5.9 ± 4.0 degree in anteversion. The difference of cup height was 5.8 ± 3.9 mm, cup medialization was 3.8 ± 2.7 mm, leg elongation was 4.3±3.3mm, and offset was 5.4±4.1mm, respectively. By using this new version navigation system, we can plan the cup center position and navigate it within smaller error of vertical and horizontal direction than the previous system. Moreover, leg elongation and offset change can be satisfactory navigated during operation. However surgeon's skill and learning curve might have influence the accuracy. We have to continue to evaluate this system and make effort to further improvement.
Nowadays navigation system for THA is widespread and contributes to accurate cup installation as for cup abduction and anteversion angles. On the other hand, cup center position is very important to prevent leg length discrepancy and to acquire appropriate muscle tension especially for DDH cases. However planning and accuracy of cup center position was rarely mentioned when the efficacy of navigation systems were discussed. We therefore examined not only accuracy of cup angles, but also of cup center position in our image-free navigation system for DDH. One hundred three THA operations were performed with using the image-free OrthoPilot hip navigation system (B. Braun Aesculap, Tuttlingen, Germany) between May 2006 and July 2008 by three experienced surgeons. In this system, we can measure the length between two different points marked by special pointer during surgery. Thus we pointed the upper rim of obturator foramen (this mark was estimated the lower tip of tear drop, and the bottom of reaming hole (this mark was estimated same height from cup center position) before cup installation and measured the vertical length between them(op length). After operation, we measured the vertical length from tear drop to cup center on the x-ray film (xp length), and compared these two values. The average difference of two values were 6.41±4.17 mm ((op length)-(xp length)). Secondly we divided them into two groups, large error group (>
0.7mm) and small error group (<
0.6mm) and investigated the cause of large error. As result, large error was influenced by difference of surgeons, whereas not influenced by patient’s etiology and BMI. By using image-free navigation system for DDH, we can plan the cup center position and install it within the error of 6.4mm. This will contribute to avoid a lot of hesitations during surgery. However surgeon’s skill and habitants have influence on this technique. We have to investigate this system and make effort to further improvement continuously.
In image-free navigation system, three bony landmarks (typically both anterior superior iliac spines (ASIS) and pubic symphysis) are registered intraoperatively by manual palpation. If the registration of bony landmarks is inaccurate, the final orientation of the cup determined by the navigation system will also be inaccurate. We therefore examined intra-and intersurgeon variability in registration and the distance between registration points in each bony landmark with two surgical positions. Thirty-seven THAs were performed in the lateral position and 15 THAs were performed in the supine position. The cup was fixed using the image-free Ortho-Pilot hip navigation system (B. Braun Aesculap, Tuttlingen, Germany). The registration was repeated two more times by operator and assistant, and the intra-and intersurgeon variability of cup abduction angle and anteversion was analyzed by ICC (intraclass correlation coefficients). In 25 hips, the distance between intrasurgeon registration points and that between intersurgeon registration points in each landmark were calculated. The ICC in the lateral position ranged between 0.59 and 0.81, and between 0.85 and 0.95 in the supine position. The ICCs of cup abduction angle for the intra-and intersurgeon variability were 0.92 and 0.95 for the supine position and 0.65 and 0.59 for the lateral position. Those of anteversion were 0.93, 0.85, and 0.81, 0.72, respectively. The variability of registration of collateral and contralateral ASIS in the lateral position was greater than that in the supine position. In image-free navigation system, the variability of registration points depended on bony landmarks and patient position. The registrations of pubic symphysis in the supine position and all bony landmarks in the lateral decubitus position are standing further improvement.
Pelvic inclination angle (PIA) and lumbar lordotic angle (LLA) were measured on the standing lateral X-rays before operation and 1-month, 6-month and 1-year post-operation. The effects of patient age, BMI, ROM of the hip, preoperative PIA and LLA on the changes of PIA were statistically investigated using multiple linear regression analysis. We divided the patients into three groups with regard to pre-operative PIA (anterior group: PIA <
0, intermediate group: 0 <
PIA <
10, posterior group: PIA >
10) and with regard to pre-operative LLA (insufficient group: LLA <
20, moderate group: 20 <
LLA <
40, severe group: LLA >
40).
The introduction of porous tantalum metal (Trabecular Metal; Zimmer, Warsaw, IN) for acetabular component fixation in total hip arthroplasty has shown optimum fixation qualities and “gap filling” effect. Recently, trabecular metal was introduced in tibial component for total knee prosthesis, however its effect on the bone mineral density (BMD) was not reported. The purpose of this study was to compare the BMD of proximal part of the tibia between trabecular metal and another cemented tibial component. 31 knees receiving trabecular metal tibial component and 33 knees receiving cemented tibial component (PFC Sigma RP, Depuy, Warsaw, IN) had dual energy x-ray absorptiometry (DEXA) scans at preoperatively and 3 weeks, 3, 6, 12, 18, 24 months post-operatively. To assess peri-prosthetic BMD, three regions of interest (ROI) were measured for each case. They were medial aspect (ROI 1), center aspect (ROI 2) and lateral aspect (ROI 3) of tibia. Average follow up period was 1.8 (range: 1.5 to 2) years. In both groups, BMD in tibia decrease postoperatively. Comparing postoperative decrease of BMD in lateral aspect of tibia (ROI 3) between both groups, it was significantly less in trabecular metal component (−0.09 g/cm2 +/−0.27) than cemented tibial component (−0.31 g/cm2 +/− 0.21) (p=0.0007). We conclude that trabecular metal tibial component showed a favorable effect on BMD of proximal part of the tibia after total knee arthroplsaty.
