What is a Heel Spur?
A heel spur (calcaneal spur) is a bony outgrowth or projection that develops from the calcaneal tuberosity (heel bone), most commonly on the inferior (plantar) surface where it forms on the deep surface of the plantar fascia, though it can also occur posteriorly at the Achilles tendon insertion. 1, 2
Anatomical Characteristics
The spur develops on the deep surface of the plantar fascia, not within the fascia itself, contrary to the common misconception that it is a "traction spur" caused by pulling forces from the plantar fascia. 2
The bony trabeculae within the spur are aligned in the direction of stress on the calcaneus during walking and standing, rather than in the direction of soft tissue traction, suggesting the spur forms as a skeletal response to mechanical stress. 3
Heel spurs are variably associated with surrounding soft tissues including loose connective tissue, fibrocartilage, muscle, and aponeurosis, with greater anatomical variability than previously recognized. 3
The spur is a fibrocartilaginous triangular projection that grows by a combination of intramembranous and chondroidal ossification. 2, 4
Development and Formation
Spur formation is heralded by degenerative changes within the plantar fascia enthesis (insertion point), progressing through three stages: (1) initial formation of cartilage cell clusters and fissures at the enthesis; (2) thickening of the subchondral bone plate as small spurs form; (3) development of vertically oriented trabeculae buttressing larger spurs. 2
The spur may serve to protect the bone against the development of microfractures in response to repetitive stress. 3
Spurs are typically detected on plain radiographs as bony projections from the calcaneal tuberosity. 5, 6
Clinical Associations and Risk Factors
Heel spurs are present in approximately 12.4% of the general population, with higher prevalence in women and older patients. 7
Key risk factors include: advanced age, increased body weight/BMI, female gender, diabetes mellitus (4 times more likely), lower-limb osteoarthritis (10 times more likely), arthritides, and foot position abnormalities (pes cavus, pes planus). 1, 6, 7
Patients with heel spurs have significantly more foot pain and poorer functional outcomes compared to matched controls without spurs, even when plantar fasciitis is excluded, indicating that spurs may be an indicator of foot pain independent of plantar fasciitis. 7
Ultrasound has only 56% diagnostic accuracy for detecting calcaneal spurs when using MRI as the reference standard. 5
Relationship to Heel Pain
The classic symptom associated with calcaneal spurs is talalgia (heel pain), though spurs can be asymptomatic in some individuals. 6, 4
Historically, plantar calcaneal spurs were considered the cause of plantar fasciitis, but they are now regarded by most authors as an incidental finding that may coexist with plantar fasciitis rather than directly causing it. 7, 8
The presence of a spur may be an indicator of other associated conditions that contribute to heel pain, rather than being the direct pain generator itself. 7
Tenderness at the medial calcaneal tubercle on examination is characteristic of plantar fasciitis, which may or may not be associated with a visible spur. 9
Clinical Pitfalls
Do not assume that the presence of a heel spur on radiograph is the definitive cause of a patient's heel pain, as spurs are common incidental findings in asymptomatic individuals. 7
Heel spurs can fracture with trauma (such as falls from height), particularly in patients with pre-existing chronic plantar fasciitis, presenting as a differential diagnosis for acute heel pain following injury. 10
Radiographs are the first-line imaging modality for identifying heel spurs, but MRI or ultrasound may be needed when the diagnosis is unclear or to evaluate associated soft tissue pathology. 9