Buechel and Pappas invented a modified version of LCS RP system (Co-Cr) with light material (Titanium), axial rotation limiting bar and improved conformity. The purpose of this prospective randomized study was to compare the minimum 3-year clinical outcomes including lightness, preference, and instability between the Co-Cr implant system and the Titanium implant system in bilateral total knee arthroplasty.

We prospectively enrolled 108 patients and 20 patients were lost to follow-up. Therefore, 88 patients (176 knees; mean age, 69.9±6.0years) were included in the study. The range of motion and clinical scores such as Knee Society score (KSS), Hospital for Special Surgery score (HSS) and Western Ontario and McMaster University (WOMAC) scores were measured preoperatively and postoperatively. At each follow-up, patients also complete a Likert scale questionnaire regarding subjective pain, lightness, left-right side preference (naturalness and satisfaction) and subjective instability.

There were no significant differences in all preoperative variables between two groups (p>.05). Mean follow-up period was 46.3±8.8 (36 to 72) months. The mean weight of Titanium implants was three times lighter than that of Co-Cr implants (133.9g versus 390.1g, p<.01). At the minimum of 3-year follow-up, there were no significant differences in pain, range of motion (ROM), clinical scores including KSS, HSS, and WOMAC between both groups. Also, the study showed no significant differences with subjective pain, lightness, preference (convenience, naturalness, and satisfaction), and subjective instability between the Co-Cr protheses and the Titanium protheses (p>.05).

No differences in clinical outcomes as well as subjective side-to-side differences between the Co-Cr prostheses and the Titanium prostheses were observed in the minimum 3-year follow-up. This implies that patients do not feel differently with two different weighted implants in mid-term follow-up.

Recently, several preliminary reports have been issued on the application of computer assistance to bone tumour surgery. Surgical navigation systems can apply three-dimensional images such as CT and MR images to intraoperative visualization. Although CT is better at describing cortical bone status, MRI is considered the best method for defining the extent of marrow involvement for bone tumours and for planning surgical resection in bone tumour surgery. There have been a few reports on the application of MR imaging to navigation-assisted bone tumour surgery through CT–MR image fusion. However, the CT–MRI fusion technique requires additional costs and exposure of the patient to radiation from the preoperative CT, as well as additional time for image fusion. Above all, the image fusion process is a kind of registration (image to image registration) that inevitably leads to registration error. Herein we describe a new method for the direct application of MR images to navigation-assisted bone tumour surgery as an alternative to CT–MRI fusion.

Six patients with an orthopaedic malignancy were employed for this method during navigation-assisted tumour resection. Resorbable pin placement and rapid 3-dimensional spoiled gradient echo sequences made the direct application of MR images to computer-assisted bone tumour surgery without CT–MR image fusion possible. A paired-point registration technique was employed for patient-image registration in all patients. It took 20 min on average to set up the navigation (range 15 to 25 minutes). The mean registration error was 0.98 mm (range 0.4 to 1.7 mm). On histologic examination, distances from tumours to resection margins were in accord with preoperative plans. Mean duration of follow-up was 25.8 months (range 18 to 32 months). No patient had a local recurrence or distant metastasis at the last follow-up.

Direct patient-to-MRI registration is a very useful method for bone tumour surgery, permitting the application of MR images to intraoperative visualization without any additional costs or exposure of the patient to radiation from the preoperative CT scan.