Iliopsoas syndrome, which is also called psoas syndrome or iliopsoas tendonitis, occurs when the iliopsoas muscles are injured. Lower back pain is the most common symptom; however, pain can also occur in the hip, thigh, or leg. The iliopsoas bursa, which is a fluid-filled sac located on the inside of the hip that reduces rubbing and friction, is also likely to become inflamed due to the proximity of the two structures. When this happens, the inflamed bursae will make it difficult to move. 

There are many causes of hip joint pain. Some hip pain is temporary, while other hip pain can be long-standing or chronic. Causes of hip pain include arthritis, inflammatory and noninflammatory arthritis, fracture, sprain, infectious arthritis (septic arthritis), avascular necrosis, Gaucher's disease, sciatica, muscle strain, iliotibial band syndrome (IT band syndrome), and hematoma.
True numbness is not just a dead/heavy feeling (which is common, and caused even by minor muscular dysfunction in the area), but a significant or complete lack of sensitivity to touch. You have true numbness when you have patches of skin where you cannot feel light touch. Such areas might still be sensitive to pressure: you could feel a poke, but as if it was through a layer of rubber. Most people have experienced true numbness at the dentist. BACK TO TEXT
Endometriosis (when the uterus lining grows somewhere else) can cause pelvic tenderness, which some women describe as hip pain. Pain from the back and spine also can be felt around the buttocks and hip, Siegrist says. Sciatica, a pinched nerve, typically affects one side of the body and can cause pain in the back of the right or left hip — the pain from sciatica can start in your lower back and travel down to your buttocks and legs.
Sacroiliac joint dysfunction. The sacroiliac joint connects the sacrum at the bottom of the spine to each side of the pelvis. It is a strong, low-motion joint that primarily absorbs shock and tension between the upper body and the lower body. The sacroiliac joint can become painful if it becomes inflamed (sacroiliitis) or if there is too much or too little motion of the joint.
Magnetic resonance imaging (MRI) uses a magnetic force instead of radiation to create a computer-generated image. Unlike x-ray, which shows only bony structures, MRI scans also produce images of soft tissues such as muscles, ligaments, tendons, and blood vessels. An MRI may be ordered if a problem such as infection, tumor, inflammation, disc herniation or rupture, or pressure on a nerve is suspected. MRI is a noninvasive way to identify a condition requiring prompt surgical treatment. However, in most instances, unless there are “red flags” in the history or physical exam, an MRI scan is not necessary during the early phases of low back pain.
The presence of certain signs, termed red flags, indicate the need for further testing to look for more serious underlying problems, which may require immediate or specific treatment.[5][36] The presence of a red flag does not mean that there is a significant problem. It is only suggestive,[37][38] and most people with red flags have no serious underlying problem.[3][1] If no red flags are present, performing diagnostic imaging or laboratory testing in the first four weeks after the start of the symptoms has not been shown to be useful.[5]

Brace your core and bend your knees to lower down into a split squat. Your left knee should ideally form a 90-degree angle so that your thigh is parallel to the ground, and your right knee is hovering above the floor. (Quick position check: your left foot should be stepped out far enough that you can do this without letting your left knee go past your left toes—if you can't, hop your left foot out a bit farther away from the bench.)
Doing the bridge exercise in the morning gets your muscles working, activated, and engaged and will help support you the rest of the day, says Humphrey. Lie on your back with your legs bent and your feet flat on the floor, hip-width apart. Press down through your ankles and raise your buttocks off the floor while you tighten your abdominal muscles. Keep your knees aligned with your ankles and aim for a straight line from knees to shoulders, being sure not to arch your back; hold this position for three to five seconds and then slowly lower your buttocks back to the floor. Start with one set of 10 and build up to two or three sets.
While a sharp pain in the hip, groin, pelvis, or thigh is an obvious sign of a hip flexor injury, pain in the lower back and leg are easy to misdiagnose. After all, it’s natural to assume that radiating pain in the leg or lower back originate from these areas. Unfortunately, diagnosing the source of a patient’s pain is not always straightforward. In fact, it’s possible for patients to go years with a misdiagnosed injury.

2016 — More editing, more! Added some better information about pain being a poor indicator, and the role of myofascial trigger points. This article has become extremely busy in the last couple months — about 4,000 readers per day, as described here — so I am really polishing it and making sure that it’s the best possible answer to people’s fears about back pain.
Shingles (herpes zoster) is an acute infection of the nerves that supply sensation to the skin, generally at one or several spinal levels and on one side of the body (right or left). Patients with shingles usually have had chickenpox earlier in life. The herpes virus that causes chickenpox is believed to exist in a dormant state within the spinal nerve roots long after the chickenpox resolves. In people with shingles, this virus reactivates to cause infection along the sensory nerve, leading to nerve pain and usually an outbreak of shingles (tiny blisters on the same side of the body and at the same nerve level). The back pain in patients with shingles of the lumbar area can precede the skin rash by days. Successive crops of tiny blisters can appear for several days and clear with crusty inflammation in one to two weeks. Patients occasionally are left with a more chronic nerve pain (postherpetic neuralgia). Treatment can involve symptomatic relief with lotions, such as calamine, or medications, such as acyclovir (Zovirax), for the infection and pregabalin (Lyrica) or lidocaine (Lidoderm) patches for the pain.
If you’re worried you’re headed toward a surgeon’s office, there might be hope. According to the Arthritis Foundation, the best way to avoid hip replacement surgery is to get active in an exercise program. In a study, people who participated in an exercise program for 12 weeks were 44 percent less likely to need joint-replacement surgery six years later than those who did not exercise.
Foraminotomy is an operation that “cleans out” or enlarges the bony hole (foramen) where a nerve root exits the spinal canal. Bulging discs or joints thickened with age can cause narrowing of the space through which the spinal nerve exits and can press on the nerve, resulting in pain, numbness, and weakness in an arm or leg. Small pieces of bone over the nerve are removed through a small slit, allowing the surgeon to cut away the blockage and relieve pressure on the nerve.
If low back pain gets worse or does not improve after two to three days of home treatment, contact a primary-care physician. The physician can evaluate the patient and perform a neurological exam in the office to determine which nerve root is being irritated, as well as rule out other serious medical conditions. If there are clear signs that the nerve root is being compressed, a physician can prescribe medications to relieve the pain, swelling and irritation; he or she also may recommend limitation of activities. If these treatment options do not provide relief within two weeks, it may be time to consider other diagnostic studies and possibly surgery. 
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