Several attempts have been made to establish a classification of bone deficiencies for both primary and revision knee replacement surgery. In general, these schemes try to either categorize defects with similarities into a small number of defect types, or separate defects into a larger number of more specific groups.
Dorr's classification1 is the most straightforward; defects are defined as either central or peripheral and cases are separated as primary or revision procedures. No attempt is made to define the size and location of the defect.
Insall2 uses similar terminology in primary cases of central and peripheral bone defects. His classification is based on how to treat the defect: cement alone (stage 1); cement or augmentation plus a stemmed component (stage 2); or massive defects that require block augmentation and stem extension (stage 3).
In revision surgery, Insall's classification is primarily a visual description of bone defects that describes patterns of bone loss in both the femur and tibia. Femoral defects are categorized as symmetrical and asymmetrical distal loss, central and medial or lateral peg hole defects, distal ice cream cone, and asymmetrical ice cream cone deficiencies. Tibial deficiencies are categorized as proximal loss, asymmetrical loss, full slope, ice cream cone, asymmetrical ice cream cone, and contained defects.
Rand's classification is also based solely on the appearance of the defect at surgery. Rand's classification3 differentiates three types of defects based on a combination of the depth of the defect and the percentage of the condyle involved. The most severe cavitary defect is further subdivided according to the integrity of the peripheral rim.
A comprehensive classification of bone deficiencies, which covers any and all defects of the femur, tibia, or patella, has been proposed by Bargar and Gross.4 Four types of defects are defined for the femur and tibia and three types for the patella. Segmental, cavitary, and discontinuity defects can occur in any of the three locations, with intercalary defects as a fourth category for the tibia and femur. This scheme is similar to a classification system recommended by the Hip Society for defects adjacent to failed total hip implants. The large number of defects makes this classification cumbersome and somewhat impractical.
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