Causes of Pain in Back of Knee When Straightening Leg

Causes of Pain in the Back of the Knee When Straightening the Leg

Feeling pain in the back of your knee when straightening your leg can be caused by a variety of conditions. The knee joint is complex and many structures can contribute to discomfort.

Typically, pain behind the knee that worsens with leg straightening indicates an issue with the musculoskeletal structures. Identifying the specific cause is key to finding the right treatment.

Common Causes

Some of the most common reasons for having knee pain when straightening the leg include:

• Baker's cyst - fluid-filled swelling behind the knee
• Hamstring tendinopathy - inflammation of the hamstring tendons
• Popliteus tendinopathy - inflammation of the popliteus tendon
• Gastrocnemius muscle strain - calf muscle tear or pull
• Arthritis - osteoarthritis or rheumatoid arthritis in the knee joint
• Meniscal injury - torn cartilage in the knee
• Loose bodies - fragments of cartilage or bone floating in the knee

Less Common Causes

Less frequent reasons for pain behind the bent knee:

• Popliteal artery entrapment - compression of the artery behind the knee
• Cystic adventitial disease - cyst in the popliteal artery
• Deep vein thrombosis - blood clot in the leg vein
• Infected bursa - septic prepatellar bursitis behind the knee cap
• Referred pain - from nerve compression in the back or hip

Common Knee Conditions Causing Pain When Straightening

Here is more detail on some of the most frequent knee problems that can cause pain in the back of the knee when straightening the leg:

Baker's Cyst

A Baker's cyst refers to a fluid-filled swelling that develops behind the knee, in the popliteal space. It is caused by a buildup of synovial fluid inside the gastrocnemius-semimembranosus bursa.

As the knee straightens, the cyst can become compressed and produce symptoms. Pain results from inflammation or direct compression on the surrounding tissues.

Hamstring Tendinopathy

The hamstring muscle group located behind the thighs connects to the knee via tendons. Irritation and inflammation of these hamstring tendons is called tendinopathy.

As the knee straightens, the inflamed and painful tendons get pulled taut over the joint. This aggravates the condition and triggers pain.

Popliteus Tendinopathy

The popliteus muscle spans the back of the knee joint.Inflammation of its connecting tendon, called popliteus tendinopathy, can cause back of knee pain when straightening.

Stretching of the damaged tendon with leg extension elicits pain and discomfort behind the knee.

Gastrocnemius Strain

The gastrocnemius muscles make up the bulk of the calf muscles. A tear or strain of these muscles can occur when sprinting or jumping.

Straightening the knee fully stretches the torn gastrocnemius fibers, producing pain at the back of the knee. The pain worsens when standing on tip-toes.

Arthritis

Osteoarthritis and rheumatoid arthritis commonly affect the knee joint. As the cartilage wears down and the joint space narrows, knee arthritis can develop.

Full knee extension compresses the inflamed joint surfaces together, which causes pain in the back of the knee.

Less Common Conditions Behind Knee Pain When Straightening

Here are some less frequent, but possible, reasons for pain behind the knee when the leg straightens:

Popliteal Artery Entrapment Syndrome

In some people, the popliteal artery that runs behind the knee can get compressed. Certain leg positions constrict this major blood vessel.

As the knee extends, the popliteal artery becomes further compressed, restricting blood flow. This elicits cramping pain in the calf that extends behind the knee.

Cystic Adventitial Disease

A rare condition called cystic adventitial disease results from a cyst forming in the outer wall of the popliteal artery. The growing cyst can eventually compress the artery.

Straightening the leg fully constricts the encroached artery, causing ischeamic pain behind the knee. Symptoms resemble those of popliteal entrapment.

Deep Vein Thrombosis

A blood clot in one of the major deep veins of the leg constitutes deep vein thrombosis or DVT. The clot usually forms in the calf veins.

Fully extending the knee helps pull on the thrombosed vein, creating pain and discomfort in the back of the knee.

Diagnosing the Cause of Knee Pain When Straightening

To properly diagnose the underlying cause of pain in the back of your knee when straightening the leg, the doctor will typically perform:

• Medical history assessment
• Physical examination of the knee
• Range of motion testing
• Muscle strength evaluation
• Palpation to pinpoint tender areas
• Special tests like the Apley's compression test
• Neurological testing
• Vascular assessment
• Imaging tests - x-rays, MRI, CT scan, ultrasound
• Laboratory tests on blood or fluid samples

Based on the findings from these diagnostic procedures, the doctor can determine the specific structural problem behind the knee pain.

Treatments for Pain Behind the Knee When Straightening

The appropriate treatments for pain in the back of the knee when straightening the leg depends on the underlying diagnosis. Some general treatment approaches include:

Rest and Activity Modification

Refraining from activities that aggravate symptoms allows healing. Use crutches or knee braces to immobilize the joint temporarily.

Ice and Heat

Applying ice packs can alleviate swelling and pain, while heat relaxes muscles. Use them carefully for 10-15 minutes at a time.

Compression

Wrapping an elastic bandage around the knee can provide compression to minimize swelling and support the structures.

Medications

Non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, help relieve pain and decrease inflammation.

Physical Therapy

Specific PT exercises can strengthen the knee, improve flexibility, and restore proper function.

Knee Bracing

Custom or over-the-counter braces provide additional knee support and stability.

Injections

Corticosteroid injections into the knee may reduce inflammation and pain.

Draining fluid

With a Baker's cyst, draining off excess fluid using a needle can provide relief.

Surgery

If conservative treatments fail, surgery may be needed to repair damaged structures in the knee.

Prevention of Knee Pain When Straightening

You can help prevent problematic knee pain when straightening your leg by:

• Maintaining a healthy body weight
• Wearing proper footwear with adequate support
• Avoiding high-impact activities
• Stretching and warming up muscles before exercise
• Strengthening the leg and core muscles
• Using proper form when lifting objects or exercising
• Taking frequent breaks when engaged in repetitive bending tasks
• Wearing knee pads when kneeling

When to See a Doctor

You should consult a doctor promptly if you have:

• Severe or worsening knee pain
• Swelling in the knee
• Knee pain combined with calf swelling
• Inability to fully straighten the knee
• Significant knee stiffness
• Leg numbness, tingling or weakness
• Trauma such as a fall or blow to the knee
• Persistence of symptoms beyond a few days

Diagnosing and addressing the underlying cause of any unexplained knee pain is important for proper management.

Conclusion

If you experience pain in the back of your knee when straightening your leg, don’t ignore it. Seeking an accurate diagnosis allows targeted treatment of the issue.

With rest, medications, physical therapy, bracing, injections or surgery, most causes of knee pain when straightening can be resolved effectively. Proper attention and care promotes full restoration of knee function.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.