title: Tibial component coverage based on bone mineral density of the cut tibial surface during unicompartmental knee arthroplasty: clinical relevance of the prevention of tibial component subsidence.
abstract: BACKGROUND
  An optimally implanted tibial component during unicompartmental knee arthroplasty would be flush with all edges of the cut tibial surface. However, this is often not possible, partly because the tibial component may not be an ideal shape or because the ideal component size may not be available. In such situations, surgeons need to decide between component overhang and underhang and as to which sites must be covered and which sites could be undercovered. The objectives of this study were to evaluate the bone mineral density of the cut surface of the proximal tibia around the cortical rim and to compare the bone mineral density according to the inclusion of the cortex and the site-specific matched evaluation.
  
  
  METHODS
  One hundred and fifty consecutive patients (100 men and 50 women) were enrolled in this study. A quantitative computed tomography was used to determine the bone density of the cut tibial surface. Medial and lateral compartments were divided into anterior, middle, and posterior regions, and these three regions were further subdivided into two regions according to containment of cortex. The site-specific matched comparison (medial vs. lateral) of bone mineral density was performed.
  
  
  RESULTS
  In medial sides, the mid-region, including the cortex, showed the highest bone mineral density in male and female patients. The posterior region showed the lowest bone mineral density in male patients, and the anterior and posterior regions showed the lowest bone mineral density in female patients. Regions including cortex showed higher bone mineral density than pure cancellous regions in medial sides. In lateral sides, posterior regions including cortex showed highest bone mineral density with statistical significance in both male and female patients. The anterior region showed the lowest bone mineral density in both male and female patients.
  
  
  CONCLUSIONS
  The mid-region of the medial side and the posterior region of the lateral side are relatively safe without cortical coverage when the component is not flush with all edges of the tibia. Cortical coverage is strongly recommended for the prevention of subsidence of the tibial component in the posterior region of the medial side, and in the anterior region of the lateral side.
authors.affiliation: Department of Orthopaedic Surgery, Gil Medical Center, Gachon University School of Medicine, Gil Hospital, 1198 Guwol-dong, Namdong-gu, Incheon, 405-760, Korea, smcos1@hanmail.net.
authors.forename: Yong Seuk
authors.initials: YS
authors.lastname: Lee
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Yun
authors.forename: Beom Koo
authors.initials: BK
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D015519:Bone Density; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed