Tibial component rotation assessment using CT scan in medial and lateral unicompartmental knee arthroplasty.

BACKGROUND: Rotation of tibial component has not been analysed in literature for unicompartmental knee arthroplasty. The purpose of the study was to determine and compare the rotation of medial and lateral unicompartmental knee arthroplasty (UKA) tibial components. We assumed both components (lateral and medial) were positioned with external rotation. PATIENTS AND METHODS: Eighteen lateral and 19 medial UKA patients were scanned postoperatively in neutral position with computed tomography enabling lower extremity three-dimensional image acquisition from the hip to the ankle. All the patients were operated by three different senior surgeons using the same surgical technique. From the reconstructions we measured the two-dimensional (2D) rotation of the tibial components. RESULTS: The rotation of the tibial component was external (mean 6.5°, SD 5.1°) for the medial UKA and external (mean 7.3°, SD 10.3°) as well for the lateral UKA. The difference was statistically insignificant (P=0.717). DISCUSSION: This study presents the first 2D in vivo analysis accurately determining and comparing medial and lateral UKA component rotation. Despite a wide range of value, we found both components were indeed externally rotated. The variability in implant positioning was observed despite the rigorous performance of an experienced surgeon using routine techniques in patients selected under routine criteria. Further analysis of these patients for satisfaction and implant survivorship in relation to implant rotation may give us an optimal range for the tibial component. If it is found that this ideal range cannot be consistently obtained with current surgical techniques then there may be a case for the use of a navigation system.

Lateral versus medial tibial plateau: morphometric analysis and adaptability with current tibial component design.

The purpose of this study was to analyze the in vivo dimensions of each tibial plateau for planning of unicompartmental knee arthroplasty (UKA), and to compare the morphometric data to the dimensions of nine current designs of UKA tibial components. Thirty-seven knees (31 females and 6 males) operated on with UKA were studied. All patients were examined postoperatively using computed tomography (CT). There were 18 lateral and 19 medial UKAs. On the CT scan, each operated tibial plateau was measured in the transverse plane at the resection level, just below the full polyethylene tibial component. We measured the length of the anteroposterior (AP) cut as well as the maximal mediolateral dimension of the resected plateau (perpendicular to the AP cut). We compared the measurements with nine current UKA systems: Accuris (Smith and Nephew), Advance (Wright Medical), HLS Uni Evolution (Tornier), Miller-Galante and "ZUK" (Zimmer), Oxford and Oxford alpha (Biomet), Preservation (DePuy) and Unix (Stryker). There was good correlation between patient height and mediolateral dimension (r=0.6), and between patient height and area of total tibial plateau (r=0.7). The anteroposterior dimension was greater for the medial plateau (mean 50.8 mm, SD 3.3) than for the lateral plateau (mean 47.2 mm, SD 3.3). This difference was statistically significant (P=0.0016). Some UKA implants are designed with an asymmetric femoral component, but none have an asymmetric tibial component. The present study suggests, however, that the shape of the medial tibial plateau differs from that of the lateral plateau. This difference can lead to mediolateral overhang for medial UKA, if the surgeon aims for optimal anteroposterior coverage.

[French Guyana's case of renal pseudotumor caused by actinomycosis]. / Un cas guyanais d'actinomycose rénale pseudotumorale.

We report one case of renal pseudotumor caused by actinomycosis with cutaneous fistula in a young French Guyana's boy. Diagnosis before surgery and histology is difficult. CT is the best examination to evaluate the extent of the disease. A short review of the literature is presented.