Fibular Head Subluxation: Symptoms, Causes, and Diagnosis

What are the symptoms of a fibular head subluxation?

A fibular head subluxation typically presents with localized pain over the outside of the knee, often accompanied by a sensation of instability, clicking or popping during movement, and tenderness to touch.

Understanding the Proximal Tibiofibular Joint

The fibular head is the enlarged, uppermost part of the fibula, the smaller of the two bones in the lower leg. It articulates with the lateral condyle of the tibia, forming the proximal tibiofibular joint (PTFJ). While often overlooked, this joint plays a crucial role in knee and ankle biomechanics, contributing to the stability of the knee and acting as an attachment point for several muscles and ligaments, including the biceps femoris tendon and the lateral collateral ligament (LCL). A subluxation refers to a partial dislocation, where the joint surfaces lose their normal alignment but remain in partial contact, unlike a full dislocation.

Recognizing the Symptoms of Fibular Head Subluxation

The symptoms of a fibular head subluxation can vary in intensity depending on the degree of displacement and whether associated structures are also injured. Common symptoms include:

• Localized Pain: The most prominent symptom is pain experienced on the lateral aspect of the knee, specifically over the fibular head itself. This pain can be:
  • Sharp and acute immediately after an injury.
  • Aching or dull with chronic subluxations.
  • Worsened by specific movements, such as squatting, kneeling, twisting the knee, or performing ankle movements like dorsiflexion (pulling the toes up) or plantarflexion (pointing the toes down).
  • Pain may also radiate down the lateral calf or into the ankle.
• Sensation of Instability or Laxity: Individuals often describe a feeling that the knee is "giving way" or that the fibular head is "moving out of place." This instability is particularly noticeable during weight-bearing activities, pivoting, or sudden changes in direction.
• Clicking, Popping, or Clunking Sensation: A distinct audible or palpable click or pop may occur as the fibular head shifts during knee flexion and extension, or during ankle movements. This sensation is due to the abnormal movement of the joint surfaces.
• Tenderness to Palpation: The area directly over the fibular head will be tender to touch, and direct pressure may reproduce the pain or the sensation of instability.
• Localized Swelling: Depending on the severity and chronicity of the injury, there may be mild to moderate localized swelling around the proximal tibiofibular joint.
• Limited Range of Motion: While not always severe, some individuals may experience restricted or painful end-range knee flexion or extension, or difficulty with full ankle dorsiflexion.
• Altered Gait: To avoid pain or instability, an individual may adopt an altered walking pattern (limp), favoring the affected leg.
• Weakness or Numbness (Rare but Possible): In rare cases, severe subluxation or chronic instability can irritate the common peroneal nerve, which wraps around the fibular neck. This can lead to symptoms such as:
  • Foot drop (difficulty lifting the front part of the foot).
  • Numbness or tingling along the top of the foot or outer shin.
  • Weakness in the muscles that dorsiflex the ankle or evert the foot.

Common Mechanisms of Injury

Fibular head subluxation can result from various mechanisms, including:

• Direct Trauma: A direct blow to the lateral aspect of the knee or fibular head.
• Twisting Injuries: Sudden, forceful twisting movements of the knee or ankle, especially when the foot is planted.
• Sudden Muscle Contraction: Strong, sudden contraction of the biceps femoris muscle, which attaches to the fibular head, can exert traction and cause subluxation.
• Chronic Ligamentous Laxity: Repeated stress or underlying hypermobility can lead to chronic instability of the joint.
• Ankle Sprains: Severe ankle inversion sprains can sometimes transmit force up the fibula, affecting the proximal joint.

When to Seek Professional Medical Attention

If you experience persistent pain, instability, or any of the symptoms described above, especially after an acute injury, it is crucial to consult a healthcare professional. Early and accurate diagnosis is important to differentiate fibular head subluxation from other knee or ankle pathologies, such as:

• Lateral collateral ligament (LCL) sprain
• Meniscus tear
• Distal fibula fracture
• Peroneal nerve entrapment

Diagnostic Considerations

Diagnosis typically involves a thorough physical examination, where a clinician will assess tenderness, joint stability, and perform specific provocative tests to reproduce symptoms. While X-rays may be taken to rule out fractures, dynamic ultrasound or MRI may sometimes be used to visualize the joint more clearly and assess soft tissue involvement, though the diagnosis is often made clinically based on symptoms and physical findings.