🦴 Fabella Syndrome: The Hidden Cause of Outer Knee Pain

What Is the Fabella?

The fabella is a small sesamoid bone — similar to a tiny kneecap — that sits within the tendon of the lateral gastrocnemius (outer calf muscle), just behind the knee. Not everyone has one; it’s present in around 10–30% of the population. In most people, it causes no issues.

However, when this small bone becomes compressed between the femur (thigh bone) and the tendon during knee extension, it can irritate surrounding soft tissue and cause posterolateral knee pain — a condition known as Fabella Syndrome.

Typical Symptoms

• Pain or tenderness behind and to the outer side of the knee

• Discomfort when fully straightening the knee or after long runs

• Snapping or clicking sensations at the back of the knee

• Pain reproduced by knee extension against resistance

• Occasionally mild swelling or tightness in the upper calf region

  
  

Because the pain is deep and posterior, Fabella Syndrome is frequently mistaken for a lateral meniscal tear, hamstring tendinopathy, or popliteus strain.

Common Causes

• Repetitive loading in running, jumping, or cycling

• Tight or overactive gastrocnemius (outer calf)

• Reduced hamstring or glute control, leading to excess posterior knee compression

• Previous knee surgery or trauma that altered local mechanics

• Hyperextension postures or overstriding when running

  
  

Athletes who increase mileage or plyometric training rapidly may develop irritation due to increased posterior compression.

Diagnosis: Identifying the Hidden Source

Diagnosis can be challenging because the fabella is small and often overlooked. A skilled physiotherapist can suspect it through palpation of the posterolateral knee and reproduction of pain during resisted extension or end-range straightening.

X-ray or MRI can confirm its presence and rule out other pathologies.

At The Knee Physio in Bury St Edmunds, we combine detailed clinical testing with VALD force-platform assessment to identify asymmetries in lower-limb strength or landing mechanics that may be increasing stress around the fabella.

Current Management and Rehabilitation Strategies (2025)

Conservative physiotherapy remains the first-line treatment for Fabella Syndrome, with excellent outcomes when managed early.

1. Load Modification and Symptom Relief

The first step is reducing activities that provoke posterior compression:

• Limit deep knee extension, sprinting, and downhill running temporarily.

• Apply ice or compression post-training.

• Use soft-tissue release to relax the lateral calf and hamstring.

• Avoid hyperextension standing postures.

  
  

A short course of anti-inflammatories may help if irritation is acute.

2. Restore Mobility and Muscle Balance

Gentle mobility work through the calf, hamstrings, and lateral thigh improves tissue compliance and reduces compression. Incorporate:

• Foam rolling to the lateral calf

• Dynamic calf and hamstring stretching

• Hip mobility drills to normalise stride and knee drive

  
  

3. Strength and Control Training

The goal is to improve lower-limb strength balance and posterior chain coordination.

Focus on:

• Glute strengthening (bridges, hip thrusts, single-leg RDLs)

• Hamstring control through eccentric loading (Nordic curls, sliders)

• Calf endurance and soleus strength to share load across the posterior knee

• Controlled squats and split squats within pain-free range

  
  

At Knee Physio, VALD testing quantifies force and asymmetry, ensuring load is reintroduced safely and progressively.

4. Running Retraining (if applicable)

Runners often benefit from stride-length and cadence adjustments to minimise knee hyperextension at push-off. Video analysis helps identify gait mechanics that might be irritating the fabella region.

5. Adjunct Therapies

• Taping or strapping can off-load the posterior knee temporarily.

• Manual therapy to the lateral calf and popliteal region can reduce local tension.

• Persistent cases may consider ultrasound-guided corticosteroid injection to calm inflammation. Surgical excision (fabellectomy) is rare and reserved only for chronic, refractory cases.

  
  

Return-to-Sport Guidelines

Before full return to sport or heavy training:

• Pain-free end-range extension and resisted knee movements

• Symmetrical quadriceps and hamstring strength (verified by VALD)

• Normal gait and running mechanics

• Confidence in sport-specific drills (acceleration, deceleration, cutting)

  
  

When to Seek Specialist Help

If posterior or outer-knee pain persists despite standard stretching or rest, or if imaging has revealed a fabella, book a specialist physiotherapy assessment. Early, data-driven intervention prevents chronic irritation and unnecessary surgery.

The Takeaway

Fabella Syndrome may be rare, but it’s a real and often-overlooked cause of persistent posterior knee pain. By combining precise diagnosis, progressive rehabilitation, and objective strength tracking, athletes can return to running and sport pain-free — without invasive procedures.

At Dominic Richmond - Knee Physio in Bury St Edmunds & Cambridge (Sawston), we specialise in identifying these subtle biomechanical contributors using VALD-based testing and tailored rehabilitation — because every knee deserves individualised, evidence-based care.

For more information on knee pain management, visit Dominic Richmond - Knee Physio.