PES Syndrome of the Knee: Understanding, Causes, Symptoms, and Treatment

What is PES syndrome of the knee?

PES syndrome, also known as pes anserine bursitis or pes anserine tendinopathy, is a common cause of pain on the inner (medial) side of the knee, resulting from irritation or inflammation of the pes anserinus bursa or the tendons that attach there.

Understanding Pes Anserinus Syndrome

Pes anserinus syndrome refers to a condition characterized by pain and tenderness over the medial (inner) aspect of the knee, approximately 2-3 inches below the joint line. This area is the insertion point for three distinct muscles – the sartorius, gracilis, and semitendinosus – whose combined tendons form a structure resembling a goose's foot, hence the Latin term "pes anserinus." Beneath these tendons lies the pes anserinus bursa, a small fluid-filled sac designed to reduce friction. When this bursa or the overlying tendons become irritated or inflamed due to overuse, repetitive stress, or biomechanical imbalances, it leads to the symptoms associated with PES syndrome.

Anatomy and Biomechanics of the Pes Anserinus

To understand PES syndrome, it's essential to grasp the anatomy and function of the structures involved:

• Sartorius: The longest muscle in the body, originating from the anterior superior iliac spine (ASIS) of the pelvis. It contributes to hip flexion, abduction, and external rotation, as well as knee flexion.
• Gracilis: A long, slender muscle originating from the pubic bone. It primarily acts as a hip adductor and assists in knee flexion.
• Semitendinosus: One of the three hamstring muscles, originating from the ischial tuberosity (sit bone). It functions in hip extension and knee flexion, as well as internal rotation of the tibia.

These three muscles converge to insert via a common tendon onto the superomedial surface of the tibia, just below the knee joint. The pes anserinus bursa lies between this common tendon and the underlying tibia. Its primary role is to facilitate smooth gliding of the tendons over the bone, minimizing friction during knee movement.

Collectively, these muscles contribute to knee flexion, internal rotation of the tibia, and various hip movements. Any activity involving repetitive knee flexion and extension, or stress on the medial knee, can potentially irritate this complex.

Causes and Risk Factors

PES syndrome typically arises from overuse or repetitive stress rather than a single traumatic event. Several factors can contribute to its development:

• Overuse and Repetitive Stress: Common in athletes, particularly runners, cyclists, swimmers, and those involved in sports requiring sudden changes of direction or pivoting (e.g., basketball, soccer).
• Biomechanics:
  • Tight Hamstrings and Adductors: Increased tension from these muscle groups can pull on the pes anserinus tendons, leading to irritation.
  • Valgus Knee Alignment ("Knock-knees"): This alignment places increased stress and strain on the medial knee structures.
  • Pes Planus ("Flat Feet"): Can alter lower limb mechanics and contribute to increased medial knee stress through overpronation.
  • Gait Abnormalities: Any deviation in walking or running patterns that disproportionately loads the medial knee.
• Muscle Imbalances: Weakness in hip abductors (e.g., gluteus medius) or external rotators can lead to compensatory overuse of the pes anserinus muscles.
• Sudden Increase in Activity Level: Rapidly increasing the duration, intensity, or frequency of exercise without proper conditioning.
• Direct Trauma: While less common, a direct blow to the medial knee can sometimes trigger inflammation.
• Obesity: Increased body weight places greater compressive and shear forces on the knee joint and surrounding structures.
• Osteoarthritis of the Knee: Degenerative changes in the knee joint can alter biomechanics and contribute to inflammation of the bursa or tendons.
• Diabetes: Individuals with diabetes may have a higher predisposition to tendinopathies and bursitis due to metabolic factors.

Common Symptoms

The symptoms of PES syndrome are generally localized and characteristic:

• Pain: The primary symptom is pain on the inner (medial) side of the knee, typically 2-3 inches below the joint line.
• Tenderness: The area over the pes anserinus insertion is usually tender to the touch upon palpation.
• Aggravating Factors: Pain is often worse with activities that involve repetitive knee flexion and extension, such as:
  • Ascending or descending stairs.
  • Getting up from a seated position.
  • Running, cycling, or swimming (breaststroke kick).
  • Prolonged sitting or standing.
  • Night pain may occur, especially when sleeping with knees touching.
• Swelling: May or may not be present; if so, it's usually mild and localized.
• Stiffness: Especially noticeable after periods of rest or in the morning.
• No Mechanical Symptoms: Unlike some other knee injuries (e.g., meniscal tears), PES syndrome typically does not cause mechanical symptoms like locking, catching, or a sensation of the knee "giving way."

Diagnosis

Diagnosis of PES syndrome is primarily clinical, based on a thorough history and physical examination.

• Clinical Examination:
  • History Taking: The healthcare professional will ask about the onset of pain, aggravating and relieving factors, activity levels, and any relevant medical history.
  • Palpation: Direct palpation of the pes anserinus insertion point will elicit tenderness, confirming the location of pain.
  • Physical Tests: Resisted knee flexion and internal rotation of the tibia against resistance may reproduce the pain. The clinician will also assess for lower limb alignment, muscle flexibility, strength, and gait abnormalities.
• Imaging Studies:
  • X-rays: Generally not diagnostic for PES syndrome itself, but may be used to rule out other bone pathologies or identify coexisting knee osteoarthritis.
  • Ultrasound: Can be helpful in visualizing inflammation or fluid within the pes anserinus bursa (bursitis) or thickening/degeneration of the tendons (tendinopathy).
  • MRI (Magnetic Resonance Imaging): Rarely necessary for a straightforward diagnosis of PES syndrome, but may be used to rule out other soft tissue injuries such as meniscal tears or medial collateral ligament (MCL) sprains, which can present with similar pain patterns.

Treatment and Management

Treatment for PES syndrome is predominantly conservative, focusing on reducing pain and inflammation, addressing underlying causes, and restoring function.

• Conservative Management (First Line):

  • Rest and Activity Modification: Temporarily reduce or avoid activities that aggravate the pain. This doesn't necessarily mean complete immobilization, but rather modifying movements to reduce stress on the affected area.
  • Ice Application: Apply ice packs to the medial knee for 15-20 minutes several times a day to help reduce pain and inflammation.
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Over-the-counter NSAIDs like ibuprofen or naproxen can help manage pain and inflammation.
  • Physical Therapy: This is a cornerstone of effective treatment. A physical therapist will design a program that includes:
    • Stretching: Targeting tight muscles such, as hamstrings, adductors, and quadriceps.
    • Strengthening Exercises: Focusing on muscles that support the knee and improve lower limb mechanics, including hip abductors (e.g., gluteus medius), quadriceps, and core stabilizers. Eccentric hamstring exercises may be particularly beneficial.
    • Gait Analysis and Correction: Identifying and correcting any biomechanical inefficiencies during walking or running.
    • Proprioception and Balance Training: To improve neuromuscular control around the knee.
  • Corticosteroid Injections: In cases of persistent pain, a physician may administer a corticosteroid injection directly into the bursa. This can provide significant short-term pain relief but is not a long-term solution and should be used judiciously.
  • Orthotics: If flat feet or other foot biomechanical issues contribute to the condition, custom or over-the-counter orthotics may be recommended.

• Advanced/Surgical Intervention:

  • Surgery: Surgical intervention for PES syndrome is extremely rare. It is typically considered only in very recalcitrant cases where extensive conservative treatment has failed. Procedures may involve bursectomy (removal of the bursa) or, in rare instances, release of a portion of the tight tendons.

Prevention Strategies

Preventing PES syndrome involves addressing risk factors and adopting healthy exercise habits:

• Gradual Progression: When starting a new exercise program or increasing activity levels, do so gradually (e.g., following the "10% rule" for increasing mileage in running).
• Proper Warm-up and Cool-down: Always include dynamic stretches before exercise and static stretches (especially for hamstrings and adductors) after.
• Strength and Flexibility Training: Maintain balanced strength in the lower kinetic chain, including quadriceps, hamstrings, glutes, and core. Incorporate regular stretching to improve flexibility.
• Proper Footwear: Wear supportive shoes appropriate for your activity, and consider consulting a specialist for gait analysis if you suspect biomechanical issues.
• Address Biomechanical Issues: If you have flat feet, knock-knees, or other alignment issues, consult a physical therapist or podiatrist for guidance on corrective exercises or orthotics.
• Listen to Your Body: Do not push through pain. If you experience discomfort, reduce your activity level and allow time for recovery.

Prognosis and Outlook

The prognosis for PES syndrome is generally very good with appropriate conservative treatment. Most individuals experience significant improvement and a full return to activity within weeks to a few months. However, recurrence is possible if the underlying biomechanical issues, training errors, or muscle imbalances that contributed to the condition are not adequately addressed. Adherence to a prescribed rehabilitation program and continued attention to preventive strategies are key to long-term success.

When to See a Professional

While many mild cases of PES syndrome can improve with rest and home care, it's advisable to seek professional medical attention if you experience any of the following:

• Persistent pain despite rest and home remedies.
• Pain that worsens or significantly interferes with your daily activities or sleep.
• Sudden onset of severe pain or swelling in the knee.
• Inability to bear weight on the affected leg.
• Symptoms accompanied by fever, redness, or warmth around the knee, which could indicate an infection.

A healthcare professional, such as a physician, physical therapist, or sports medicine specialist, can accurately diagnose the condition and develop an individualized treatment plan.