A 70-year-old man with total hip arthroplasty 8 years ago presents with thigh pain. Radiograph shows a radiolucent line around the femoral stem in the region of the calcar. According to Gruen's classification of periprosthetic femoral zones, which zone is involved?

• A Zone 1
• B Zone 3
• C Zone 5
• D Zone 7 ✓

Explanation

Gruen zones divide the periprosthetic femur into 7 zones on the AP radiograph, numbered sequentially from lateral to medial. Zone 1 corresponds to the greater trochanter, and Zone 7 corresponds to the calcar femorale. These zones are used to describe radiolucent lines and loosening around femoral stems. Zone 1 is the most common site for loosening, but the calcar is specifically Zone 7. Zones 1, 3, and 5 represent other regions of the periprosthetic femur.

Reference: Campbell's Operative Orthopaedics, 14th ed.

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