Hip arthritis is a common condition affecting hundreds of thousands of people in the United States. The hip is a ball and socket joint that can wear out over time leading to pain, shortening of the leg and difficulty walking. Most patients develop the condition in their 50’s and 60’s but it can develop much earlier. The most common cause of arthritis in men is a condition called impingement in which there is a slight discrepancy in the shape of the ball and socket (egg shaped ball in a round socket). This can eventually lead to degeneration in the cartilage in the hip joint. In women, the most common cause is dysplasia or a misshapen and, most commonly, shallow hip socket that causes damage to the cartilage. Previous trauma and avascular necrosis are the most common cause in younger patients. Any fracture that involves the joint surface causes some damage to the cartilage. When the joint surface is not perfectly aligned excessive stress and shear is placed on the gliding surface of the joint and this accelerates joint degeneration. This type of arthritis is referred to as secondary osteo-arthritis or post-traumatic arthritis.
Finally, the blood supply to the femoral head (the ball of the hip joint) is easily damaged from fracture or dislocation. Injury to the blood supply leads to a condition called osteo-necrosis or avascular necrosis in which the bone softens and often collapses leading to hip arthritis.
Unlike many other joints in the body, the hip joint is fairly deep and covered by a thick layer of tissue and muscle. Because of the hip’s anatomic position, injections require the use of live x-ray to ensure the needle is in the correct position. This is best performed in an operating or special procedure setting.
Pain in the hip can mimic other conditions such as sciatica or pinched nerves in the lower back. Although many patients have MRI scans performed to assess the condition of the joint, high quality x-rays are sufficient to make the diagnosis of arthritis.
The surgical options for hip arthritis are limited to hip replacement and resurfacing and each procedure has pluses and minuses. In general, the number of patients who are candidates for hip resurfacing surgery are limited. The best long term data from European and Australian national joint registries (we don’t have a nation joint registry in the U.S.) keep track of the outcomes of every joint replacement done in these countries. This data demonstrates about equal functional outcome between joint replacement and joint resurfacing but a significantly higher revision rate (need for another surgery) at 10 years in patients who undergo resurfacing. Based in large part on this data, total joint replacement is the treatment of choice unless there is a compelling reason to perform resurfacing.
Primary total hip replacement is considered the most successful surgery (for both the patient and the surgeon) in Orthopaedics. The indications are severe osteo-arthritis, hip dysplasia, rheumatoid arthritis and avascular necrosis (AVN) of the femoral head with collapse. Even though these entities have differing causes, the end clinical picture is the same: loss of cartilage in the joint causing pain, limitation of motion and impairment of activity. Most patients with severe arthritis have progressively incapacitating groin and thigh pain, limping and restricted range of motion.
There are several different implants available on the market and many manufacturers have started using direct to consumer (DTC) advertising. The basic choices for implants depend on the bearing surface of the implant (outlined below). Hip resurfacing surgery (also outlined below) is an option for younger patients but represents a much larger surgical procedure.
There surgical approaches used to perform total hip replacements are outlined below. Each one has benefits and drawbacks. The anterior approach allows excellent access to the socket and the posterior approach is favored for revision surgery or in heavier patients. Although many patients focus on the length of the incision, this is probably the least important aspect of the operation. The surgical dissection is kept to the least amount possible while focusing on implanting the components in the best possible position. Implant position has been shown to be the most important factor influencing the longevity of the implants. So if you have a hip replacement performed through a 3 inch incision you may recover faster than if you have a 6 inch incision, but if the components are not placed properly and you require a revision surgery in three years, this is a much worse outcome than if the hip were to last 20-25 years.
The length of the incision depends on weight of the patient, history of previous surgeries and type of replacement surgery. Patients with several surgeries in the past require larger incisions to compensate for scar tissue and to protect the nerves and arteries in the area. After surgery all patients are given a low molecular weight heparin medication to prevent blood clots in the veins of the pelvis and leg. This is the single most common complication after surgery. Most patients stand the night of surgery and then physical therapy starts more aggressively on the first day after surgery. Typically, patients are comfortable and go home with a walker on the 3rd day after surgery. Patients may shower after the 5th day and walk as much as possible after returning home. Most patients are able to walk comfortably with a cane after about 2 weeks and without a cane after 6 weeks.
This surgical approach has been popularized in the last 5-7 years with the introduction of specialized operating room tables which assist in the exposure of the joint during the procedure. This is the most commonly used approach in our practice. The surgery takes approximately 1 and a half hours and is done through a 3-5 inch incision in the side of the hip. Patients with a BMI (body mass index) over 30 are better treated through a posterior approach because of an increased risk of complications with the anterior surgical approach. After surgery all patients are given a low molecular weight heparin medication to prevent blood clots in the veins of the pelvis and leg. This is the single most common complication after surgery. Most patients stand the night of surgery and then physical therapy starts more aggressively on the first day after surgery. Typically, patients are comfortable and go home with a walker on the 3rd day after surgery. Patients may shower after the 5th day and walk as much as possible after returning home. Most patients are able to walk comfortably with a cane after about 2 weeks and without a cane after 6 weeks.
Types of Implants
Metal on Plastic -The most common type of bearing surface re-approximating the characteristics of normal bone and cartilage fairly well. The cup component contains a plastic liner made of high molecular weight polyethylene while the ball component is constructed of metal alloy such as cobalt chrome. This bearing surface is both durable and flexible and allows the surgeon a wide variety of combinations of head size, neck length and cup size and shape to allow me to re-create normal hip mechanics in most people.
Metal on Metal -This is the main bearing surface on resurfacing implants. There has been a large amount of negative press recently with several reports of catastrophic failure. The mechanism for this is still largely unknown. Currently, there is a moratorium on the use of metal on metal components in the UK. We do not currently implant this bearing surface. Metal on metal prostheses have larger femoral head diameters which clinically translates into a lower risk of dislocation. The bearing surface is very durable. However, it is unclear whether these prosthesis designs offers an advantage over the newer plastic designs. Other issues include the elevated concentration of metal ions in the blood samples from patients with metal prostheses, but it is unclear whether this leads to any long term problems. Although this is a good implant bearing surface, the press and plaintiff attorneys have severely damaged the reputation of this prosthesis. This type of prosthesis should be avoided in any patient with a metal allergy.
Ceramic on Ceramic – This type of bearing surface has the lowest wear rate of any bearing surface by a factor of 10. The ceramic, not unlike a ceramic tile, is extremely hard and durable; however, they are also brittle and have been reported to crack or fracture with hard falls. Other problems reported with this prosthesis are “squeaking” in which the bearing surface makes a noise when the hip is flexed. Although painless, this problem can be troublesome. Ceramic prostheses are reasonable options in younger patients (under 45 years of age) with degenerative arthritis of hip.
We currently use two manufacturers (Zimmer and Stryker) of prostheses for primary total hip replacement. Implant choice depends on the age of the patient and the anatomy of the proximal femur (which can be quite variable) listed below. Both implants use a cobalt chrome head on a highly cross-linked poly-ethylene liner. In certain situations, a ceramic liner may be appropriate.
After surgery, you will be admitted to the hospital and for approximately 3 days. Anesthesia is a combination of general and epidural. The epidural is very effective in controlling post-operative pain and allows lower use of narcotics in the first few days after surgery. Depending on the surgical approach, your therapist will go over anterior or posterior hip precautions (positions to avoid for the first 6 weeks after surgery). The three most common complications after surgery are infection (0.5-1.0%), dislocation (0.1-0.4%) and deep venous thrombosis (blood clots in the leg 2.0-5.0%). All patients receive intravenous antibiotics for the first 24 hours to minimize the risk of infection and low-molecular weight heparin (lovenox) to reduce the risk of blood clots after surgery. You will continue on this medication for 10-14 days after leaving the hospital and the nurse will show you or a family member how to administer this medication.
By the time you leave the hospital you should be able to get out of bed on your own, stand and walk with a walker, and get on and off the toilet without assistance. Most people will get a shower chair and elevated toilet seat to take home or have them delivered. You will start physical therapy in the hospital and continue at home. Your first post-surgery office visit is generally 10-14 days to have the stitches or staples removed and to go-over your therapy and progress. Most patients transition to a cane at 2-4 weeks and can walk without a cane at 4-6 weeks. Hip replacement instruction are listed below