Understanding Patellar Tendinitis: Mechanisms, Clinical Features, and Evidence-Based Management

What is patellar tendinitis?

Patellar tendinitis is an overuse injury of the patellar tendon, the strong connective tissue that links the patella (kneecap) to the tibia (shinbone). This tendon plays a central role in knee extension by transmitting force from the quadriceps muscles at the front of the thigh to the lower leg. It is essential for activities such as walking, running, jumping, climbing stairs, and rising from a seated position.

Patellar tendinitis is commonly referred to as “jumper’s knee” because it frequently affects athletes involved in sports that require repetitive jumping, rapid acceleration, and abrupt changes in direction. Basketball, volleyball, athletics, and football are classic examples. However, the condition is not limited to athletes. It can also occur in physically active individuals, workers exposed to repetitive knee loading, or people who suddenly increase their level of physical activity.

Although the term “tendinitis” suggests inflammation, current evidence indicates that chronic patellar tendinitis is more accurately described as a tendinopathy, characterized by degenerative changes in the tendon rather than acute inflammation.

Pathophysiology

Patellar tendinitis develops as a result of repeated mechanical overload of the tendon without sufficient time for recovery. Recurrent stress causes microscopic tears within the tendon fibers. When the repair process is overwhelmed, the tendon structure becomes disorganized, thicker, and weaker.

Key pathological changes include:

• Collagen fiber disruption

• Increased tendon thickness

• Reduced tendon elasticity

• Altered blood vessel growth

• Increased pain sensitivity

These changes reduce the tendon’s ability to tolerate load, creating a cycle of pain, further injury, and functional limitation.

Symptoms of patellar tendinitis

Pain is the hallmark symptom and typically develops gradually. Clinical manifestations include:

• Pain localized between the lower edge of the kneecap and the upper part of the shinbone

• Discomfort during or after physical activity, especially jumping or running

• Pain that initially appears only after exercise but later occurs during activity

• Stiffness or aching in the knee, particularly after rest

• Difficulty climbing stairs, squatting, kneeling, or rising from a chair

In advanced stages, pain may persist even at rest and significantly interfere with daily activities and athletic performance.

When to seek medical evaluation

Medical consultation is recommended when knee pain:

• Persists despite rest and self-care

• Gradually worsens over time

• Limits daily activities or sports participation

• Is accompanied by swelling, redness, or warmth around the knee

Early evaluation improves outcomes and reduces the risk of long-term tendon damage.

Causes of patellar tendinitis

The primary cause of patellar tendinitis is repetitive mechanical overload. Contributing factors include:

• Frequent jumping, sprinting, or abrupt stopping and starting

• Sudden increases in training intensity, duration, or frequency

• Insufficient recovery between training sessions

• Poor biomechanics or improper technique

• Hard playing surfaces or inadequate footwear

The tendon becomes vulnerable when cumulative stress exceeds its capacity to repair itself.

Risk factors

Several intrinsic and extrinsic factors increase susceptibility to patellar tendinitis:

• Male sex, with higher incidence observed in men

• High-impact sports involving jumping or running

• Training volumes exceeding 20 hours per week

• Tight quadriceps or hamstring muscles, increasing tendon strain

• Muscle imbalances between quadriceps and hamstrings

• Reduced flexibility or poor core stability

• Chronic medical conditions affecting blood flow or tissue healing, such as diabetes, autoimmune diseases, or chronic kidney disease

These factors often interact, compounding stress on the patellar tendon.

Complications

If ignored or managed inadequately, patellar tendinitis may lead to:

• Progressive tendon degeneration

• Chronic pain and long-term functional impairment

• Partial or complete patellar tendon rupture, a rare but serious complication

• Prolonged absence from sports or physically demanding work

Continuing physical activity despite pain significantly increases the risk of these complications.

Diagnosis

Diagnosis is primarily clinical and based on:

• Patient history and activity level

• Localized tenderness over the patellar tendon

• Pain reproduced by resisted knee extension

Imaging studies may be used to confirm the diagnosis or assess severity:

• Ultrasound can show tendon thickening and structural changes

• Magnetic resonance imaging (MRI) provides detailed evaluation of tendon degeneration and tears

Treatment of patellar tendinitis

Treatment is usually conservative and focuses on reducing tendon load while restoring strength and function.

Activity modification

Reducing or temporarily avoiding activities that aggravate symptoms is essential. Complete rest is rarely recommended, but controlled loading is important.

Physical therapy

Structured rehabilitation is the cornerstone of treatment and typically includes:

• Eccentric strengthening exercises for the quadriceps

• Gradual progressive loading of the tendon

• Stretching of tight quadriceps and hamstrings

• Core and hip strengthening to improve biomechanics

Eccentric exercises, which involve slow muscle lengthening under load, have shown strong evidence for improving tendon structure and reducing pain.

Pain management

Short-term use of ice and nonsteroidal anti-inflammatory drugs may help relieve symptoms, although they do not address the underlying tendon degeneration.

Advanced therapies

In refractory cases, additional options may include:

• Shockwave therapy

• Injection-based treatments under specialist guidance

• Bracing or patellar straps to reduce tendon strain

Surgery is rarely required and reserved for severe, persistent cases unresponsive to prolonged conservative treatment.

Prevention

Preventive strategies focus on reducing excessive tendon load and improving tissue resilience:

• Avoid training through pain

• Increase training intensity gradually

• Incorporate regular strength and flexibility exercises

• Emphasize proper technique and movement patterns

• Use appropriate footwear and training surfaces

• Ensure adequate rest and recovery between sessions

Early attention to knee discomfort can prevent progression to chronic tendinopathy.

Scientific references

1. Cook JL, Purdam CR. Is tendon pathology a continuum? British Journal of Sports Medicine. 2009;43(6):409–416.

2. Khan KM, Cook JL, Bonar F, Harcourt P, Astrom M. Histopathology of common tendinopathies. Sports Medicine. 1999;27(6):393–408.

3. Malliaras P, Cook JL, Purdam CR, Rio E. Patellar tendinopathy: clinical diagnosis, load management, and advice for challenging case presentations. Journal of Orthopaedic & Sports Physical Therapy. 2015;45(11):887–898.

4. Visnes H, Bahr R. Training volume and body composition as risk factors for developing jumper’s knee. Scandinavian Journal of Medicine & Science in Sports. 2013;23(5):607–613.

5. Lian Ø, Engebretsen L, Bahr R. Prevalence of jumper’s knee among elite athletes. American Journal of Sports Medicine. 2005;33(4):561–567.