Knee pain is a common problem that affects millions of people worldwide. Knee pain can arise from various sources, ranging from injuries and overuse to underlying medical conditions such as osteoarthritis. While muscular and skeletal factors often take the spotlight, vascular causes of knee pain are equally significant yet frequently overlooked. Part of this has to do with the physician referral pattern for knee pain. Typically, if a primary care physician cannot find and/or treat the cause of a patient’s knee pain, the patient is referred to an orthopedic surgeon since the majority of knee pain is musculoskeletal in origin. If no musuloskeletal cause of knee pain is found by the orthopedic expert, the patient is often left with ongoing knee pain and no answer as to its cause. In this article, we will discuss the vascular causes of knee pain that may be key in helping you or a loved one get the care that you need.
Vascular Anatomy of the Knee
The knee joint is a marvel of biomechanical engineering, connecting the thigh bone (femur) to the shinbone (tibia) and facilitating a wide range of movements. Within this complex joint, an extensive network of blood vessels plays a crucial role in nourishing the surrounding tissues to ensure that the knee works optimally.
Arteries and veins, such as the popliteal artery and vein, supply blood to the knee joint and surrounding structures. Any disruption to the normal functioning of these vessels can lead to vascular-related knee pain.
Common Vascular Causes and Treatments of Knee Pain
1. Peripheral Arterial Disease (PAD):
- PAD is a condition characterized by the narrowing of arteries due to the accumulation of plaque called atherosclerosis which reduces blood flow to the knee, calf, and foot.
- Inadequate blood supply to the knee joint can result in pain, especially during physical activity.
- Treatment involves conservative therapy such as quitting smoking, exercise, statin therapy (medication to decrease cholesterol) and other vascular medicines, weight loss, and blood sugar control. When conservative therapy fails, endovascular procedures such as angioplasty and stenting can be performed. In some cases, bypass surgery may be needed.
2. Deep Vein Thrombosis (DVT):
- DVT is a blood clot that forms in the deep veins of the leg. When a DVT occurs in the popliteal vein that runs behind the knee, pain and swelling occurs in the knee and calf.
- DVT in the popliteal vein can often turn into scar tissue leading to chronic knee pain and calf/ankle swelling. This is known as post thrombotic syndrome (PTS).
- Standard of care treatment starts with anticoagulation (blood thinners), compression stockings, and exercise. In some cases, endovascular procedures to remove fresh clot can be performed if the clot extends beyond the popliteal vein into the femoral vein. In cases of chronic DVT in which scar tissue has developed in the popliteal vein causing chronic knee pain, Deep Venous Recanalization (DVR) can be performed to reopen the popliteal vein.
3. Popliteal Artery Entrapment Syndrome (PAES):
- PAES is a rare condition where the popliteal artery is compressed by the gastrocnemius muscle in the calf. Compression of the popliteal artery results in decreased blood flow down the leg, often during exercise such as walking or flexing the knee. This leads to pain and cramping behind the knee and calf.
- PAES occurs more commonly in young athletic males and the affected calf may be larger than normal.
- The popliteal vein can also be entrapped with the artery leading to knee pain and calf swelling.
- Treatment is surgical and involves release of the calf muscle so that there is more room, thereby preventing the muscle from compressing the artery.
4. Chronic Venous Insufficiency (CVI):
- CVI is a commonly overlooked cause of knee pain that is due to blood pooling in the veins of the leg, especially with prolonged sitting or standing.
- CVI leads to leg heaviness, fatigue, cramps, restless legs, varicose veins, skin discoloration and knee pain.
- The small saphenous vein (SSV) courses behind the knee and sometimes extends up the back of the thigh. If this vein is malfunctioning, this can result in pain behind the knee, thigh, and calf.
- Treatment is initially conservative with leg elevation, compression stockings, weight loss, and exercise. If conservative therapy fails, endovenous laser treatment (EVLT) is performed to close off the malfunctioning SSV and resolve symptoms.
Non-Vascular Causes of Knee Pain with a Vascular Treatment
- OA is degenerative joint disease that often occurs with age resulting in the breakdown of cartilage (the cushioning between bones). This leads to joint inflammation and pain.
- OA affects men and women and commonly affects the hands, hips, knees and spine.
- Treatment is initially conservative with pain medication, weight loss, and less rigorous exercise. With moderate OA, steroid injections of the knee are performed to reduce pain and swelling. More recently, geniculate artery embolization (GAE) is being performed, resulting in significant improvement in knee pain and swelling. GAE often serves as a bridge to knee replacement, especially in those individuals who are too young or not ready to undergo knee replacement.
Non-Vascular Causes of Knee Pain
- A Baker’s cyst is a fluid-filled swelling at the back of the knee, often associated with conditions like arthritis.
- Rupture of the cyst can cause localized swelling and discomfort, resembling knee pain of vascular origin.
For physicians and other healthcare providers, understanding the vascular causes of knee pain is important to provide a comprehensive approach to the diagnosis and treatment of chronic knee pain. For patients, having a basic knowledge of the vascular network around the knee can be beneficial so that you can be a better advocate for your own healthcare.