• The time between injury and surgery can affect the efficiency of the procedure. Although microfracture is successful with degenerative lesions, defects treated within 12 weeks of injury have significantly better results. (7, 14)
• A patient unwilling to follow the strict and rigorous rehabilitation schedule will not be offered microfracture. The healing process and the formation of the regenerated tissue is advanced by proper rehabilitation. (21)
• The age of the patient can affect the outcome of the surgery as it affects both recovery and the procedure. The general rule is that patients older than 60 should not consider microfracture. In one study, athletes who returned to high-impact sports after microfracture were younger than those who did not return. Sixty-five percent of athletes younger than 40 returned to sports, while only 20% of athletes older than 40 returned. There is a decline in the amount of mesenchymal stem cells available for repair due to an increase in age of the patient, osteoporosis, or other metabolic issues. Since microfracture knee surgery depends on the presence of mesenchymal stem cells, patients with these conditions are not candidates for this procedure. (3, 10, 15, 21)
• Although size generally does not limit a patient's candidacy for this procedure, chondral defects greater than 5 to 10 mm deep can cause the procedure to be unsuccessful. A mosaic-plasty or autologous chondrocyte transplantation may be used instead. (7)
• The presence of an axial malalignment is the most significant contraindication as it can limit the success of the procedure. Normal knee alignment is considered to be between 1 degree and 7 degrees of anatomic valgus alignment. Microfracture of the medial compartment of varus alignment will fail. In these cases, a microfracture should be used in combination with a high tibial osteotomy to reneutralize the mechanical axes. Lateral patellofemoral lesions have a worse prognosis in the area of patellar maltracking. The tracking must be corrected at the same time as the treatment for the chondral injury. (7, 8)
  

Example of a properly aligned knee
Permission granted by Mr. Dunlop of Spire Southampton Hospital

• Lesions less than 400 mm in area are less painful than larger lesions, although there is no significant difference in the success of the treatment based upon size. For lesions greater than 3 cm in diameter, second-look arthroscopy may be helpful after the initial microfracture procedure. (7)
• Although location of the injury does not statistically effect the outcome of the procedure, femoral and trochlear lesions have more predictable and favorable regrowth than tibial or patellar defects. This is even more important when performed on arthritic knees. (7)
• Studies have shown that poor outcomes occur when body mass index is higher than 30. Also due to weight-bearing restrictions, the inability to use the non-operative leg during the rehabilitation time limits a patients candidacy. (14, 15, 17)
• Specific cases for not having the surgery include, systemic immune-mediated disease, disease-induced arthritis, or cartilage disease. (21)
  
  
  

  Factors Affecting Outcome After Microfracture
  Factors                                                                                              Better Results With

  Age                                                                                                 <40 years
  Duration of symptoms                                                                      <12 months
  Lesion size                                                                                       < 4 cm2
  Body mass index                                                                              < 30 kg/m2
  Preoperative activity level                                                              Tegner score >4
  Previous surgery                                                                            Primary microfracture
  Repair cartilage volume                                                                  Good defect fill (>66%)

  Table 5- Identifies the features of a strong candidate
  Adapted from Dr. Kai Mithoefer, (16)
  
  
  

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