Donner Bursa: Anatomy, Function, and Deep Retrocalcaneal Bursitis

What is a Donner Bursa?

The "Donner bursa," more commonly and precisely known as the deep retrocalcaneal bursa, is a small, fluid-filled sac located at the back of the ankle, positioned between the Achilles tendon and the calcaneus (heel bone). Its essential role is to reduce friction and facilitate the smooth gliding of the Achilles tendon during ankle movements.

Understanding Bursae: A Quick Primer

To understand the Donner bursa, it's helpful to first grasp the general concept of a bursa. Bursae (plural of bursa) are small, flattened, fluid-filled sacs lined with synovial membrane, similar to the lining of a joint capsule. They are strategically located throughout the body where tendons, muscles, or skin glide over bones. Their primary function is to reduce friction between these structures, acting as a cushion and facilitating smooth, unimpeded movement. When a bursa becomes inflamed, a condition known as bursitis occurs, leading to pain, swelling, and restricted movement.

The Donner Bursa: Anatomical Location and Function

The term "Donner bursa" is an anatomical descriptor, sometimes used synonymously with or to specifically highlight the deep retrocalcaneal bursa. It is distinct from the superficial calcaneal bursa (often called the Achilles bursa or adventitious bursa), which lies between the Achilles tendon and the skin.

• Location: The Donner bursa is situated deep within the heel region, specifically nestled between the anterior surface of the Achilles tendon (the large tendon connecting the calf muscles to the heel bone) and the posterior superior aspect of the calcaneus (heel bone). This precise location is crucial for its function.
• Function: Its main physiological role is to minimize friction and absorb shock during ankle movements. As the ankle moves through dorsiflexion (toes moving towards the shin) and plantarflexion (toes pointing away), the Achilles tendon glides over the calcaneus. The Donner bursa provides a lubricated cushion, ensuring this movement is smooth, efficient, and pain-free, preventing wear and tear on the tendon and bone.

Clinical Relevance: Bursitis of the Donner Bursa

Inflammation of the Donner bursa, or deep retrocalcaneal bursitis, is a common cause of posterior heel pain, particularly among athletes and individuals engaging in activities involving repetitive ankle motion.

• Causes:

  • Overuse and Repetitive Stress: Activities like running, jumping, and prolonged walking, especially on inclines, can lead to repetitive compression and friction on the bursa.
  • Inappropriate Footwear: Shoes with a rigid or high heel counter that rubs against the Achilles tendon insertion can irritate the bursa.
  • Haglund's Deformity: Also known as "pump bump," this is a bony prominence on the posterior aspect of the calcaneus. It can mechanically impinge on the b Donner bursa and Achilles tendon, leading to chronic irritation.
  • Biomechanical Issues: Foot imbalances, such as excessive pronation or a tight Achilles tendon, can alter the mechanics of the ankle joint and increase stress on the bursa.
  • Direct Trauma: A direct blow to the back of the heel.
  • Systemic Inflammatory Conditions: Less commonly, conditions like rheumatoid arthritis, gout, or spondyloarthropathies can cause bursitis.

• Symptoms:

  • Pain: Localized pain at the back of the heel, particularly noticeable during or after activity. The pain often worsens with dorsiflexion of the ankle.
  • Tenderness: Palpable tenderness directly anterior to the Achilles tendon insertion, between the tendon and the bone.
  • Swelling: Localized swelling may be present, though it can be subtle due to the deep location of the bursa.
  • Redness and Warmth: In acute or severe cases, the skin over the affected area may appear red and feel warm to the touch.
  • Limping: Patients may alter their gait to avoid pain.

• Diagnosis:

  • Clinical Examination: A thorough physical examination involving palpation of the heel, assessment of ankle range of motion, and observation of gait. Pain elicited by squeezing the Achilles tendon just above its insertion, or with passive dorsiflexion, is often indicative.
  • Imaging Studies:
    • X-rays: Primarily used to rule out bony abnormalities like Haglund's deformity or stress fractures.
    • MRI (Magnetic Resonance Imaging): The gold standard for visualizing soft tissue structures. An MRI can clearly show fluid accumulation within the bursa (indicating inflammation) and assess the condition of the Achilles tendon.
    • Ultrasound: Can also be used to visualize fluid within the bursa and assess soft tissues.

• Treatment and Management:

  • Conservative Management: The initial approach for most cases of Donner bursa bursitis.
    • RICE Protocol: Rest from aggravating activities, Ice application to reduce inflammation, Compression (light bandaging), and Elevation.
    • NSAIDs: Non-steroidal anti-inflammatory drugs (e.g., ibuprofen, naproxen) to manage pain and inflammation.
    • Activity Modification: Temporarily reducing or avoiding activities that exacerbate symptoms.
    • Footwear Modifications: Wearing shoes with soft, open backs or a heel lift to reduce tension on the Achilles tendon. Avoidance of tight-fitting shoes.
    • Physical Therapy: Stretching exercises for the calf muscles and Achilles tendon, strengthening exercises for surrounding muscles, and modalities like ultrasound or phonophoresis. Addressing biomechanical imbalances.
  • Medical Interventions:
    • Corticosteroid Injections: In some cases, a corticosteroid injection into the bursa may be considered to reduce inflammation. This must be done with extreme caution due to the proximity to the Achilles tendon, as injections directly into or around the tendon can increase the risk of tendon rupture.
    • Aspiration: Rarely, if the bursa is significantly distended with fluid, aspiration (drawing out the fluid) may provide temporary relief.
  • Surgical Intervention: Reserved for chronic, severe cases that do not respond to conservative measures. Surgical options may include bursectomy (removal of the bursa) or removal of a bony prominence (like a Haglund's deformity) that is irritating the bursa.

Differential Diagnosis

It's important to differentiate Donner bursa bursitis from other conditions that cause heel pain, as treatment approaches vary:

• Achilles Tendinopathy/Tendinitis: Inflammation or degeneration of the Achilles tendon itself.
• Plantar Fasciitis: Pain on the bottom of the heel, usually worse with the first steps in the morning.
• Achilles Tendon Rupture: Acute, severe pain and inability to push off the foot.
• Stress Fracture of the Calcaneus: Pain that worsens with weight-bearing.
• Sever's Disease (Calcaneal Apophysitis): Heel pain in growing children, related to inflammation of the growth plate.

When to Seek Medical Attention

While many cases of Donner bursa bursitis resolve with conservative care, it's advisable to seek medical attention if:

• Pain is severe or persists despite rest and home care.
• You experience significant swelling, redness, or warmth, which could indicate infection.
• You are unable to bear weight on the affected heel.
• Symptoms recur frequently.

Conclusion

The Donner bursa, or deep retrocalcaneal bursa, is a small but vital anatomical structure that plays a crucial role in the smooth functioning of the ankle and Achilles tendon. While often overlooked until it becomes problematic, understanding its location, function, and the implications of its inflammation (bursitis) is key for effective diagnosis and management of posterior heel pain. Proper footwear, gradual increases in activity, and addressing any underlying biomechanical issues are fundamental in both treating and preventing this condition.