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Calcar Femorale

calcar femorale

The calcar femorale (Merkel spur) is the dense vertical plate of cortical bone within the proximal femur at the posteromedial femoral neck-shaft junction, running from the lesser trochanter superiorly toward the greater trochanter. It is the principal structural reinforcement of the medial femoral neck, transferring compressive loads from the femoral head through the calcar to the femoral shaft. The calcar density and architecture is critical for hip arthroplasty fixation.

Region: Pelvis & Hip

Clinical Relevance

Clinical Notes

The calcar femorale is the key structural reference for hip arthroplasty stem insertion and femoral neck resection. The calcar is preserved in stemmed arthroplasty to support the prosthetic collar and resist torsional loads; calcar deficiency from previous fracture or resorption requires extended metaphyseal fixation or proximal femoral replacement. In femoral neck fractures, Garden's valgus impaction fractures preserve calcar integrity; fully displaced fractures disrupt the calcar, reducing fixation options. Calcar resorption from stress shielding after cementless hip arthroplasty weakens medial proximal femoral bone stock.

Pathology

Common Injuries & Conditions

Calcar Resorption from Stem Stress Shielding in Total Hip Arthroplasty

Cementless femoral stems with distal fixation bypass the proximal femoral calcar, reducing mechanical loading and causing stress-shielding calcar resorption visible on serial radiographs as proximal medial bone loss; this weakens the proximal femoral envelope and makes future revision surgery more complex, favouring proximally-fixed short stems that maintain calcar loading.