title: Effect of Femoral Component Flexion Implantation on the Mediolateral Bone-prosthetic Fit in Total Knee Arthroplasty.
abstract: OBJECTIVE
  Femoral component overhang in total knee arthroplasty (TKA) has been reported in previous studies. The purpose of this study was to evaluate the effect of femoral component flexion implantation on mediolateral bone-prosthetic fit in TKA.
  
  
  METHODS
  Virtual prosthesis implantations were performed on computed tomographic models of 10 Chinese knees with femoral prostheses of the Advance Medial-Pivot knee system (MicroPort Orthopedics, Arlington, TN, USA), with the femoral component positioned at 0°, 3°, or 6° of flexion in the sagittal plane. For each degree of flexion implantation, the differences between the knee and femoral component models on the lateral and medial sides at trochlea (zone 1), anterior-distal condyle (zone 2), posterior-distal condyle (zone 3), and posterior condyle (zone 4) were measured. Positive difference values indicate component overhang, and negative difference values indicate component underhang. The values of component overhang (underhang) in each zone were statistically analyzed across the 3° of flexion implantation.
  
  
  RESULTS
  With a greater degree of flexion implantation, overhang was reduced and even changed to underhang. With 0° of flexion implantation, an overhang exceeding 3 mm existed mainly on the medial side of zone 1 (5.81 mm) and the lateral side of zone 2 (3.39 mm). With 3° of flexion, overhang exceeding 3 mm was observed only on the medial side of zone 1 (3.10 mm), and underhang was observed only on the medial side of zone 4 (-0.32 mm). No overhang exceeding 3 mm was observed for 6° of flexion, while underhang was observed except on the lateral sides of zone 2 (1.32 mm) and zone 4 (1.10 mm) and on the medial side of zone 1 (1.54 mm). A significant difference in overhang values on the lateral and medial sides of zone 1 was observed between 0 and 6° of flexion (P < 0.05).
  
  
  CONCLUSIONS
  The present study demonstrated that femoral component flexion implantation by 3° can reduce excessive overhang, although 3.10 mm of overhang remained at the medial side of zone 1. Conversely, 6° of flexion implantation can avoid 3 mm of overhang for any zone, but increases the risk of underhang. Slight flexion implantation may be an effective alternative technique to prevent excessive component overhang, especially in the trochlea and anterior region of the distal condyle, in Chinese patients with standard TKA prostheses.
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Shi-Chang
authors.initials: SC
authors.lastname: Chen
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Yi-Ming
authors.initials: YM
authors.lastname: Zeng
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Meng-Ning
authors.initials: MN
authors.lastname: Yan
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Yue
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: You
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000328:Adult; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D017755:Prosthesis Fitting; D014057:Tomography, X-Ray Computed
keywords: Component overhang; Femoral component; Flexion implantation; Morphometry; Total knee arthroplasty