In the Dorr classification of femoral canal morphology relevant to cementless THA, a Dorr Type C canal is characterised by which morphological feature and its implication for stem choice?

• A Narrow, funnel-shaped ('champagne-flute') canal with thick cortices; excellent press-fit is easily achieved
• B Wide, cylindrical ('stovepipe') canal with thin cortices and minimal endosteal definition; poor press-fit for cementless stems, cemented fixation may be preferred ✓
• C Intermediate canal morphology; suitable for either cemented or cementless stems
• D Sclerotic canal with obliterated medullary cavity due to metabolic disease; requires femoral canal perforation before stem insertion

Explanation

Dorr classification describes three canal types based on cortical index (cortical thickness/total canal width) on AP femoral X-ray. Dorr A: narrow, funnel-shaped with thick cortices (young, male pattern) — ideal for cementless press-fit. Dorr B: intermediate morphology — both cemented and cementless acceptable. Dorr C: wide 'stovepipe' canal with thin cortices and poor corticomedullary differentiation (older, osteoporotic, female pattern) — poor mechanical environment for press-fit cementless stems; cemented long-stemmed fixation or calcar-replacing stems may be preferred to achieve reliable initial stability.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.