Understanding the Dorr Classification of the Femoral Bone
The Purpose of the Dorr Classification
Orthopedic surgeons widely use the Dorr classification to assess the quality of the proximal femur before total hip arthroplasty (THA). Its primary purpose is to help determine whether to use a cemented or cementless femoral component for the replacement implant. A cementless implant relies on bone ingrowth for stability, while a cemented implant uses bone cement. The success of each method depends on bone quality.
This radiographic classification examines the femoral bone's cortex and medullary canal to categorize bone quality into Type A, B, or C. Each type represents different bone density and morphology, often related to age and conditions like osteoporosis. Identifying the bone type helps surgeons anticipate complications and tailor the surgical plan.
Dorr Type A: The "Champagne Flute" Femur
Dorr Type A indicates high-quality femoral bone, common in younger, active patients, often men. It has thick cortical walls and a narrow, tapering medullary canal, resembling a champagne flute. This type is ideal for cementless fixation due to good bone stock. However, the narrow canal can make implantation technically challenging, risking distal stem impingement or fracture.
Dorr Type B: The Intermediate Femur
Dorr Type B represents intermediate bone quality with moderate cortical thinning and a wider canal, the most common type. The cortex is thinner than Type A, and the medullary canal is wider with less tapering. Some proximal bone loss is present. Surgeons may use either cementless or cemented fixation depending on the degree of thinning and patient bone health.
Dorr Type C: The "Stovepipe" Femur
Dorr Type C is characterized by poor bone quality, with significant cortical thinning and a wide, straight medullary canal. This type is frequent in elderly, osteoporotic women. The cortical bone is thin, and the canal lacks the normal funnel shape, appearing like a stovepipe. Cementless fixation is less reliable here due to poor support and increased fracture risk. Cemented fixation is often preferred for better stability.
Dorr Classification for Total Hip Arthroplasty (THA) Planning
| Feature | Dorr Type A | Dorr Type B | Dorr Type C |
|---|---|---|---|
| Appearance | "Champagne Flute" | Transitional (Tapered) | "Stovepipe" |
| Cortical Bone | Thick and Robust | Moderate Thinning | Extremely Thin |
| Medullary Canal | Narrow, Tapered | Wider | Wide and Straight |
| Canal Flare Index | Higher Index | Moderate Index | Lower Index |
| Common Patients | Younger, Active Men | Average Population | Elderly, Osteoporotic Women |
| Preferred Fixation | Cementless | Cementless or Cemented | Cemented |
| Fixation Reliability | Excellent for Cementless | Variable | Poor for Cementless |
| Fracture Risk | Low (except during impaction) | Moderate | High |
Conclusion
The Dorr classification is a foundational tool in orthopedic surgery, particularly for total hip arthroplasty. By providing a standardized method for assessing the quality and morphology of the proximal femur, it allows surgeons to anticipate potential challenges and customize the surgical approach for each patient. Whether using cementless fixation in a robust Dorr A femur or opting for a cemented implant in a fragile Dorr C bone, the classification guides critical decisions that directly impact implant stability, surgical risks, and long-term outcomes. While modern implant designs have expanded the possibilities, a thorough understanding of the Dorr classification remains an essential component of preoperative planning and successful hip replacement surgery.
