title: Autologous chondrocyte implantation in knee joint: MR imaging and histologic features at 1-year follow-up.
abstract: OBJECTIVE
  To evaluate magnetic resonance (MR) imaging features of autologous chondrocyte implantation (ACI) grafts and compare these with graft histologic features 1 year after ACI for treatment of femoral condylar defects.
  
  
  METHODS
  This study was approved by the regional ethics committee, and all patients gave informed consent. Forty-one patients (mean age, 35 years; 30 men, 11 women) underwent ACI for treatment of femoral condylar defects. One year later, knee joint MR imaging and graft biopsy were performed. Graft biopsy results were categorized into those showing hyaline, mixed fibrohyaline cartilage, fibrocartilage, and fibrous tissue. Standard T1-, T2-, T2*-, and intermediate-weighted sequences were performed, as well as three-dimensional (3D) fast low-angle shot (FLASH) and double-echo steady-state sequences for cartilage assessment. ACI grafts were assessed for signal intensity (with FLASH sequence), thickness, overgrowth, surface smoothness, integration to adjacent cartilage and underlying bone, bone marrow edema underneath graft, and contour of bone underneath graft. MR images were assessed by two observers, first independently and then in consensus. MR imaging findings were correlated with histologic findings.
  
  
  RESULTS
  All 41 grafts were present at 1-year follow-up. The graft consisted of hyaline cartilage in four, mixed fibrohyaline cartilage in 10, fibrocartilage in 25, and fibrous tissue in two cases. Graft signal intensity was virtually always lower than adjacent normal cartilage signal intensity, and there was no relationship between graft signal intensity and histologic appearance (P = .34). Graft thickness (P = .83), overgrowth (P = .69), surface smoothness (P = .28), and integration with adjacent cartilage and underlying bone (P = .90); edema in bone marrow underneath graft (P = .63); and bone contour underneath graft (P = .94) at MR imaging had no correlation with graft histologic appearance. Graft overgrowth (n = 16; 39%) and edema-like signal in bone marrow underneath graft (n = 23; 56%) were common. The origin of graft overgrowth remains unclear.
  
  
  CONCLUSIONS
  With the methods presented here, MR imaging findings cannot predict ACI graft histologic features, and graft histologic appearance determined at biopsy was not related to graft signal intensity, graft thickness, overgrowth, surface smoothness, integration with adjacent cartilage or underlying bone, signal intensity change in underlying bone marrow, or underlying bone contour. Overgrowth and bone marrow changes underneath the graft were common.
authors.affiliation: Department of Radiology, Robert Jones and Agnes Hunt Orthopaedic and District Hospital, Oswestry SY10 7AG, England. bernhard.tins@rjah.nhs.uk
authors.forename: Bernhard J
authors.initials: BJ
authors.lastname: Tins
authors.forename: Iain W
authors.initials: IW
authors.lastname: McCall
authors.forename: Tomoki
authors.initials: T
authors.lastname: Takahashi
authors.forename: Victor
authors.initials: V
authors.lastname: Cassar-Pullicino
authors.forename: Sally
authors.initials: S
authors.lastname: Roberts
authors.forename: Brian
authors.initials: B
authors.lastname: Ashton
authors.forename: James
authors.initials: J
authors.lastname: Richardson
mesh_terms: D000328:Adult; D001706:Biopsy; D002358:Cartilage, Articular / Q000473:pathology; D019902:Chondrocytes / Q000473:pathology / Q000637:transplantation*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D014182:Transplantation, Autologous