Lower back pain can be caused by many different conditions including a herniated disc or sciatica. The Journal of the American Academy of Orthopaedic Surgeons recently published an excellent article on the common causes of lower back pain. This included lower back pain that radiates into the lower extremity. Dr. Bennett Douglas Grimm is the lead author of the Jan 2015 article. A summary of this very informative article is below.
Lower back pain that radiates into the leg is known as lumbar radiculopathy. The prevalence of true lumbar radiculopathy in the general population is approximately 3–5%. The two most common causes for these symptoms are a herniated disc or, less commonly, spinal stenosis.
A lumbar disc herniation most frequently occurs in patients younger than age 50. Symptoms of a herniated disc typically start with severe low back pain that will then radiate into the lower extremity. There may or may not be a traumatic or inciting event that causes the symptoms to start. Initially the low back pain occurs because a tear in the annulus surrounding the disc occurs.
The annulus is richly innervated by nerves which will cause severe pain when torn. After the annulus tears, disc material leaks out and compresses the nerve root going to the lower extremity causing leg pain. It is typically a two-step process. Some people hear or feel a pop at the time of injury which is the annulus tearing.
Once the nerve root is compressed, there may be symptoms of numbness, tingling and weakness involving the lower extremity. Symptoms usually worsen from sneezing or bending forward. Any action that increases intradiscal pressure will cause increased pain such as listed above.
The Physical Exam for Lower Back Pain
An important portion of the physical examination for low back pain is a positive nerve root tension test, also known as a straight leg raise test. This will be present 60% of the time in people who have disc herniation at L4-L5 and L5 and S1. A femoral stretch test may be positive for this condition at L2-3 and L3-4. There may be a decrease in reflexes at the patella tendon or Achilles’ tendon. The patellar tendon represents L4 and the Achilles tendon represents S1.
If there is bowel or bladder dysfunction, or saddle anesthesia is present, there is concern for cauda equina syndrome. This occurs with a very large disc herniation. This is a surgical emergency and requires urgent surgical decompression or permanent nerve damage can occur.
An MRI scan is the best imaging study for the above-mentioned diagnoses.
Spinal Stenosis and Lower Back Pain
Spinal stenosis is another common cause of low back pain and this typically occurs in patients older than 65. Spinal stenosis is caused from osteoarthritis involving the lumbar spine. Typically there is a history of chronic low back pain that radiates into the buttuck and legs.
With spinal stenosis, it is not as common to have only one leg affected, which is typically seen with the disc herniation. Only 20% of the people that present with spinal stenosis would have a positive straight leg raise test. People will complain of pain with ambulation. Their pain will typically stop when they bend forward or sit down. Plain X-rays and an MRI scan are used to help to diagnose this condition.
Additional Causes of Lower Back Pain
There are other causes of lower back pain that occur that have nothing to do with the anatomy of the back but can cause pain in that region of the body. This can be caused from other anatomical structures in the body that are near the low back such as the pelvis and the hip joint.
Conditions such as hip osteoarthritis, osteonecrosis, femoral acetabular impingement, femoral neck stress fractures, pelvic insufficiency fractures, trochanter bursitis of the hip, and sacroiliac joint pain can mimic low back pain.
Osteoarthritis of the hip is the most common hip condition in patients older than 65 years of age. It can affect up to 10% of the general population. Plain X-rays will diagnose hip osteoarthritis.
If your healthcare provider is still unsure of whether your lower back pain is coming from the hip or the lumbar spine, a diagnostic and therapeutic injection of cortisone and numbing medicine can be given in the hip under ultrasound guidance to help determine if the pain is being generated from the hip joint or the low back.
Osteonecrosis is caused by lack of blood flow to the head of the hip, also known as the femoral head. This can be caused from several factors. Most commonly patients affected by osteonecrosis of the femoral head are between ages 20 and 50 years of age. There can be a history of alcoholism, chronic steroid use, or sickle cell disease. Plain X-rays of the hip are initially obtained which may reveal a crescent sign which represents collapse of the femoral head. MRI scan is most diagnostic in the early phases of the disease where the plain X-rays may look normal.
Femoral acetabular impingement (FAI) is a more recent diagnosis in the hip. This is a hotly studied topic right now in orthopedics. This typically occurs from an abnormality of the growth plate in the femoral neck. There can be two types of femoral acetabular impingement (FAI). There is the cam impingement and the pincer impingement. Plain X-rays are diagnostic. If a patient has femoral acetabular impingement they are predisposed to labral pathology and maybe predisposed to early onset osteoarthritis. An MRI arthrogram of the hip is diagnostic for labral pathology which may be a result of the femoral acetabular impingement.
Another cause of pain in the pelvis region can be a stress fracture the femoral neck. This is most common in long-distance athletes and also in patients with an eating disorder. The problem occurs as a result of repetitive stressed to the bone which exceeds the body’s ability to remodel the bone secondary to the activity. This can be a surgical emergency in young patients. If the fracture occurs on the outer half of the hip, also known as the tension side of the hip, surgical intervention is needed. If the stress fracture occurs on the compressive side of the hip also known as the inner side of the hip: non-weight bearing can be used to treat the fracture as opposed to surgical intervention. Plain X-rays are typically obtained but may or may not be diagnostic. An MRI scan will be diagnostic.
Greater trochanteric bursitis of the hip can also cause hip and lower back pain. This is typically found in middle-aged patients. Their pain tends to be located laterally or over the trochanteric region of the hip. People will complain of pain with resting on that side at night or sitting with their leg in a crossed over position. Women are affected twice as much is men.
Sacral or pelvis insufficiency fractures can occur as a result of normal activity in a patient with osteoporosis. This can be seen in the elderly, patients with chronic steroid use, or in patients with a history of pelvic irradiation. People typically report vague lower back pain. Typically there is no history of trauma, and pain can be debilitating to the point where they cannot ambulate and have to use a wheelchair. The most common finding during a physical examination is tenderness to palpation around the sacrum. An MRI scan is the best imaging study. If the patient cannot undergo an MRI scan, a three phase bone scan would be indicated. Plain X-rays do not typically show these fractures and a CT scan will commonly miss this pathology.
Sacroiliac pain presents as buttock pain. It is typically a diagnosis of exclusion when all other diagnoses have been ruled out. The physical examination would include a positive Faber test which is pain with hip flexion, abduction and external rotation.
Another cause of lower extremity pain can be peripheral artery disease. People who are smokers, have diabetes, hyperlipidemia and hypertension are at risk. A person does not have to be currently smoking. They could have a history of smoking that resulted in peripheral artery disease. This occurs when there is a buildup of atherosclerosis plaque in the arteries decreasing the amount of blood flow to the muscles.
When the person goes to ambulate or exercise there’s not enough blood being delivered to the muscle which causes significant pain. The pain is relieved with rest. As soon as the patient stops exercising or walking, the pain will subside. A physical examination would include diminished or asymmetrical pulses in the feet, and the presence of shiny, hairless or very thin appearing skin. There is also redness of the lower extremity that is relieved by elevation, also known as dependent rubor.
Diagnostic studies for peripheral artery disease would include an ankle brachial indices (ABI). If the ABI ratio is less than 0.9, the patient has peripheral artery disease.
Tumors, both benign and malignant, can cause pelvis pain. A patient with a tumor in the pelvis may have insidious onset of symptoms, pain primarily at night, no change in pain pattern with activity or position, constitutional type symptoms which include weight loss, fever, and night sweats, and they may have cancer risk factors. Cancer risk factors would include a prior diagnosis of cancer, tobacco use, and prior radiation to the pelvis. A work up would include plain X-rays, MRI scan, bone scan and possibly a pet scan.
Peripheral neuropathy, which is loss of normal sensation, most commonly from diabetes, can cause numbness and tingling in the lower extremities. This is sometimes confused with disc pathology. Up to 66% of patients with diabetes also experience peripheral neuropathy.
Compressive neuropathy can also be confused with a disc herniation. Compressive neuropathy is when one of the nerves in the lower extremity is damaged from some type of compression either from trauma or a mass effect.The peroneal nerve is the most common lower extremity nerve that is affected. This causes weakness in the tibialis anterior muscle and is most commonly known as a footdrop.
An MRI scan of the lumbar spine is the first imaging study to obtain if there is no disc pathology. An EMG should be obtained to document peroneal nerve compression. Peroneal nerve compression most commonly occurs at the knee near the fibular head where the peroneal nerve is very superficial and at risk.
Another common compressive neuropathy affecting the lower extremity is compression of the lateral femoral cutaneous nerve also known as meralgia paresthetica. This most commonly occurs in middle age men. It occurs from the L1, L2 or L3 nerve roots being compressed. It may be caused from tight-fitting pants, belts, or girdles. Obesity, diabetes and pregnancy are risk factors for this condition. This also may occur if a person has undergone surgery and they are lying in a prone position.
Piriformis syndrome can also be a compressive neuropathy. The piriformis muscle is a hip external rotator. If it becomes inflamed, irritated, or enlarged it can compress on the sciatic nerve reproducing symptoms that are very similar to a disc herniation. It also is a diagnosis of exclusion after all other causes of radiculopathy have been ruled out. There is not a specific diagnostic test that can confirm the condition. An EMG may suggest the diagnosis.
Infectious and autoimmune disorders may also cause low back pain and radiculopathy. Osteomyelitis and discitis are causes of lower back pain that are nonradicular. The pain is localized in the lower back region. It does not radiate into either lower extremity. They are typically associated with a fever. The most common bacterial organism is Staphylococcus aureus. Laboratory studies would be elevated which identify infections. Lab values that would be elevated would be a sed rate, C- reactive protein and a white blood cell count. An MRI scan with contrast would be the imaging study of choice.
Shingles, also known as herpes-zoster, can also cause severe pain radiating down one lower extremity. It is caused from the dormant varicella zoster virus in nerve cell bodies of the dorsal root ganglia. It may cause a rash in a dermatomal pattern. Patients older than 60 years of age and immunosuppressed patients, patients with cancer, HIV, or diabetes are particularly susceptible.
HIB can cause a lower extremity symmetrical polyneuropathy similar to diabetic neuropathy. It is typically found in patients with advanced stages of HIV. It is the most common neuropathy associated with a virus.
In summary, the most common cause of lower back pain radiating into the lower extremity is a disc herniation, but there are many other conditions that may cause similar symptoms. If you are suffering from lower back pain, it is advisable that you contact a qualified medical professional or a thorough examination and diagnosis.