Rabbit Knee: Understanding Patellar Tendinopathy, Causes, Symptoms, and Treatment

What is rabbit knee?

The term "rabbit knee" is a colloquial and non-medical phrase often used to describe patellar tendinopathy, commonly known as "jumper's knee." This condition involves pain and degeneration of the patellar tendon, which connects the kneecap (patella) to the shinbone (tibia), primarily due to repetitive stress and overuse.

Introduction to "Rabbit Knee"

While not a formal medical diagnosis, the expression "rabbit knee" vividly describes the discomfort and impaired function associated with patellar tendinopathy. This condition typically manifests as pain just below the kneecap, especially during activities that involve repetitive jumping, running, or squatting. It is an overuse injury, meaning it develops gradually over time due to chronic strain on the patellar tendon, leading to micro-tears and degenerative changes rather than acute inflammation.

Understanding the Anatomy of the Knee

To grasp patellar tendinopathy, it's crucial to understand the relevant knee anatomy. The patella (kneecap) is a small, triangular bone embedded within the quadriceps tendon. This tendon, originating from the quadriceps muscles in the thigh, attaches to the top of the patella. From the bottom of the patella, the patellar tendon extends downwards, attaching to the tibial tuberosity (a bony prominence on the front of the shinbone).

Together, the quadriceps muscles, quadriceps tendon, patella, and patellar tendon form the extensor mechanism of the knee. This system is vital for straightening the leg, absorbing impact during landing, and generating power for activities like jumping and running. When the patellar tendon is repeatedly overloaded, particularly during eccentric contractions (muscle lengthening under tension, like landing from a jump), it can lead to the microscopic damage characteristic of patellar tendinopathy.

Common Causes of "Rabbit Knee" (Patellar Tendinopathy)

Patellar tendinopathy is primarily an overuse injury, stemming from a combination of factors that place excessive stress on the patellar tendon.

• Repetitive High-Impact Activities: Sports or activities involving frequent jumping (basketball, volleyball, track and field), running (especially downhill or on hard surfaces), and deep squatting are common culprits.
• Sudden Increase in Training Load: Rapidly increasing the intensity, duration, or frequency of exercise without adequate progression can overload the tendon.
• Improper Biomechanics:
  • Poor Landing Mechanics: Landing stiff-legged or with excessive knee valgus (knees caving inward).
  • Muscle Imbalances: Weakness in the glutes, hamstrings, or core, forcing the quadriceps and patellar tendon to work harder. Tight quadriceps, hamstrings, or calf muscles can also alter forces across the knee joint.
  • Foot and Ankle Issues: Overpronation or limited ankle dorsiflexion can affect the kinetic chain and increase knee stress.
• Inadequate Warm-up and Cool-down: Failing to prepare the muscles and tendons for activity or neglecting post-exercise recovery can contribute to injury.
• Equipment and Surface: Worn-out footwear that lacks cushioning or training on excessively hard surfaces can increase impact forces on the knee.
• Obesity: Increased body weight places greater strain on the knee joint and surrounding tendons.

Symptoms and Clinical Presentation

The symptoms of "rabbit knee" typically develop gradually and worsen over time if not addressed.

• Pain Below the Kneecap: The hallmark symptom is localized pain at the inferior pole of the patella, where the patellar tendon originates.
• Activity-Related Pain: Pain is often exacerbated by activities that load the extensor mechanism, such as jumping, running, squatting, kneeling, or ascending/descending stairs.
• Pain Progression:
  • Initially, pain may only occur after activity.
  • As the condition progresses, pain may be present during and after activity.
  • In severe cases, pain can be constant, even at rest, and significantly interfere with daily life.
• Tenderness to Touch: The area just below the kneecap is often tender when pressed.
• Stiffness: The knee may feel stiff, especially after periods of rest (e.g., in the morning or after prolonged sitting).
• Mild Swelling: Localized swelling around the patellar tendon may be present, though it's less common than in acute inflammatory conditions.
• Reduced Performance: Athletes may notice a decline in their ability to jump, sprint, or perform certain movements.

Potential Risks and Complications

If left unaddressed, patellar tendinopathy can lead to chronic pain and significant limitations.

• Chronic Pain: The condition can become persistent and difficult to resolve, impacting quality of life.
• Activity Limitation: Individuals may be forced to reduce or completely cease participation in sports or activities they enjoy.
• Tendon Rupture: While rare, severe, long-standing degeneration of the patellar tendon can theoretically increase the risk of a partial or complete tendon rupture, requiring surgical repair.
• Psychological Impact: Chronic pain and inability to participate in desired activities can lead to frustration, anxiety, and depression.

Diagnosis

Diagnosing patellar tendinopathy typically involves a comprehensive approach by a healthcare professional, such as a physician, physical therapist, or sports medicine specialist.

• Clinical Examination:
  • Patient History: The clinician will ask about the onset of pain, aggravating and alleviating factors, activity levels, and any previous injuries.
  • Physical Assessment: This includes palpating the patellar tendon for tenderness, assessing range of motion, strength of the quadriceps and surrounding muscles, and evaluating lower limb biomechanics.
  • Special Tests: While no single test is definitive, specific movements that load the patellar tendon (e.g., single-leg squat, hop tests) can reproduce symptoms.
• Imaging Studies: Imaging is often used to confirm the diagnosis, assess the severity of tendon changes, and rule out other conditions.
  • Ultrasound: This is often the preferred initial imaging modality as it can show tendon thickening, hypoechoic areas (indicating degeneration), and sometimes neovascularization (new blood vessel growth, associated with chronic tendinopathy). It can also be used for dynamic assessment.
  • Magnetic Resonance Imaging (MRI): Provides a more detailed view of the tendon and surrounding structures, helping to confirm the diagnosis, assess the extent of degenerative changes, and rule out other knee pathologies like patellofemoral pain syndrome, Osgood-Schlatter disease (in adolescents), or meniscal tears.
  • X-rays: Primarily used to rule out bony abnormalities, fractures, or conditions like calcific tendinitis, rather than directly visualizing the tendon itself.

Management and Treatment Strategies

Effective management of "rabbit knee" focuses on reducing pain, restoring tendon strength and function, and addressing underlying biomechanical issues. A multi-faceted approach, often guided by a physical therapist, is key.

• Relative Rest and Activity Modification:
  • Reducing or temporarily avoiding activities that provoke pain is crucial for allowing the tendon to heal. This doesn't mean complete inactivity but rather smart modification.
• Pain and Symptom Management:
  • Ice Application: Applying ice packs to the affected area for 15-20 minutes several times a day can help manage pain and localized swelling.
  • Over-the-Counter Pain Relievers: Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen may provide short-term pain relief, but they do not address the underlying tendon degeneration. Use under medical guidance.
• Physical Therapy: This is the cornerstone of treatment.
  • Eccentric Loading Exercises: These are the most evidence-based exercises for patellar tendinopathy. Examples include decline squats or calf raises where the emphasis is on the lowering (eccentric) phase. These exercises help stimulate tendon remodeling and strengthen the tendon's capacity to tolerate load.
  • Progressive Strengthening: Strengthening the quadriceps, hamstrings, glutes, and calf muscles is vital for improving overall lower limb stability and distributing load more effectively.
  • Flexibility and Mobility: Addressing tightness in the quadriceps, hamstrings, hip flexors, and calf muscles can improve biomechanics and reduce stress on the patellar tendon.
  • Proprioception and Balance Training: Exercises that improve balance and joint awareness help refine movement patterns and reduce injury risk.
  • Biomechanical Correction: A physical therapist can analyze movement patterns (e.g., running gait, jumping technique) and provide cues and exercises to correct inefficiencies.
• Adjunctive Therapies:
  • Patellar Strap (Cho-Pat Strap): A strap worn just below the kneecap can help alter the forces on the patellar tendon, providing some immediate pain relief for certain individuals.
  • Taping: Kinesiology taping may be used to provide support or facilitate muscle activation.
  • Manual Therapy: Techniques like soft tissue mobilization or joint mobilizations may be used by a physical therapist to address muscle tightness or joint restrictions.
• Injections (Less Common and Specific Cases):
  • Corticosteroid Injections: Generally avoided for patellar tendinopathy due to potential negative effects on tendon integrity and long-term outcomes, though they may be used in rare, specific cases for severe pain.
  • Platelet-Rich Plasma (PRP) Injections: Involves injecting concentrated platelets from the patient's own blood into the injured tendon. Research on its effectiveness for patellar tendinopathy is ongoing and results are mixed.
• Surgery (Rare): Surgical intervention is considered only in chronic, severe cases that have failed to respond to at least 6-12 months of consistent, high-quality conservative treatment. Procedures typically involve debridement (removal of diseased tissue) or longitudinal tenotomies.

Prevention

Preventing "rabbit knee" involves a proactive approach to training and body maintenance.

• Gradual Progression of Training: Avoid "too much, too soon." Gradually increase the intensity, duration, and frequency of your workouts to allow your body (and tendons) to adapt. The 10% rule (not increasing volume by more than 10% per week) is a good guideline.
• Thorough Warm-up and Cool-down: Always start with a dynamic warm-up to prepare muscles and tendons for activity, and finish with a static cool-down to improve flexibility and aid recovery.
• Strength and Conditioning:
  • Balanced Leg Strength: Ensure adequate strength in the quadriceps, hamstrings, glutes, and calves.
  • Core Stability: A strong core contributes to overall body control and efficient movement.
  • Eccentric Training: Incorporate eccentric exercises (e.g., controlled lowering during squats or calf raises) into your routine to build tendon resilience.
• Flexibility and Mobility: Regularly stretch tight muscles, particularly the quadriceps, hamstrings, hip flexors, and calves, to maintain good range of motion and reduce biomechanical stress on the knee.
• Proper Technique and Biomechanics: Learn and practice correct form for sports-specific movements, especially jumping and landing. Consider working with a coach or physical therapist for gait analysis if you're a runner.
• Appropriate Footwear and Surfaces: Wear supportive shoes that are appropriate for your activity and replace them regularly. Avoid training excessively on very hard or uneven surfaces.
• Listen to Your Body: Pay attention to early signs of pain or discomfort. Do not push through pain, as this can worsen the condition. Incorporate rest days into your training schedule.

When to Seek Professional Help

If you experience pain below your kneecap that fits the description of "rabbit knee," it's advisable to consult a healthcare professional, especially if:

• The pain is persistent and does not improve with rest or activity modification.
• The pain worsens or significantly interferes with your daily activities or athletic performance.
• You experience sudden, severe pain, swelling, redness, or warmth around the knee.
• You are unable to bear weight on your leg.

Early diagnosis and intervention can significantly improve outcomes and prevent the condition from becoming chronic.

Conclusion

"Rabbit knee," or patellar tendinopathy, is a common overuse injury that can significantly impact athletic performance and daily life. While the term is informal, the condition it describes is a legitimate and often challenging issue rooted in repetitive stress on the patellar tendon. Understanding its causes, symptoms, and the importance of a structured, progressive rehabilitation plan is crucial for recovery. By prioritizing proper training progression, balanced strength, flexibility, and seeking professional guidance when needed, individuals can effectively manage and prevent patellar tendinopathy, allowing them to return to the activities they love with stronger, more resilient knees.