Some patients in need of a hip replacement will ask me if they are candidates for a partial rather than a total hip replacement because it sounds “less invasive.” Unlike the knee (which has three distinct compartments and when one wears out there’s a good chance that only that compartment needs to be replaced), the hip is a single ball (femoral head) and joint socket (acetabulum) and a partial hip replacement often isn’t the optimum choice.
A partial hip replacement (hemiarthroplasty) is the replacement of only the patient’s femoral head. The new prosthetic femoral head (metal ball) then rotates inside the natural body socket. However, the artificial metal ball is placed directly next the body’s natural hyaline cartilage and unfortunately, this cartilage doesn’t do well or remain healthy when compressed against a metal surface.
A total hip involves the replacement of the femoral head and the resurfacing of the socket. With this procedure, the prosthetic femoral head moves within the prosthetic socket.
Each procedure has advantages and disadvantages but as a rule, the best results for longevity and consistent pain relief are attained with a total hip replacement.
Fracturing or breaking a hip refers to a break occurring through the upper femur (thigh bone), which often displaces the femoral head. If the fracture occurs within the hip joint capsule, we refer to this as a “femoral neck fracture.” An “intertrochanteric” fracture is when the fracture occurs just outside of the hip joint capsule. Because the upper femur bone – located just below the hip capsule – is surrounded by muscle, it has a much better blood supply and therefore, these types of fractures usually heal when they are realigned and the alignment is held in that position with plates, screws or a rod. This is called an internal fixation. On the other hand, the femoral neck within the hip joint capsule is bathed in synovial fluid and has a precarious blood supply. Because of this, fractures through the neck region often don’t heal. If a fracture occurs though the neck and the neck fragments displace, the blood supply usually is compromised and then even if internally fixed, leads to a fracture that either doesn’t heal or heals but subsequently the head collapses because of lost blood supply.
Historically, femoral neck fractures left patients crippled or even caused death due to lack of mobility and all its associated complications. During the 1960s, the one-piece partial hip replacement was introduced. The Austin Moore and Thompson are classic examples of these revolutionary prosthetics. For the first time, physicians could replace a broken femoral head with an artificial one. The stem, which was inserted down through the upper femur bone, was constructed from the same piece of metal as the ball (monoblock). This was a dramatic move forward, saving countless lives and greatly improving mobility and quality of life for many. Although a quantum leap in hip replacement surgery, most patients still had a less than a perfect result, experiencing pain either from the stem not being stable within the femur or the new ball wearing away the natural cartilage.
Today, many people who fracture their femoral necks still are treated with partial hip replacements. Now, almost all prosthetics have a modular head that fits on the stem. A further refinement to the partial hip is the “bipolar” hip replacement. Imagine a standard sized ball, often used in total hip replacement, first being impacted on the new stem and then a bigger ball inserted over the smaller ball and placed inside the natural socket. It’s referred to as bipolar because it can move in two planes: between the little ball and the big ball and between the big ball and the natural socket, as opposed to the original “monopolar” ball. Some studies suggest that the body’s natural cartilage within the acetabulum is worn away more quickly and there is less relief from pain when a monopolar rather than a bipolar ball is implanted. The main reasons that monopolars still are used today are because they usually are less expensive and some surgeons prefer them because of their simplicity and lack of modularity.
Usually the only patients still considered good candidates for a partial hip replacement are those who do not have underlying arthritis and have healthy acetabular cartilage. This is often the case for someone who has fractured the femoral neck but did not have hip symptoms or hip arthritis prior. One of the main advantages for performing a partial hip rather than a total hip replacement is that partial hips are inherently more stable. Because the balls are larger they are less prone to dislocation. The Bipolar also is thought to be slightly more stable or resistant to dislocation than the monopolar due to its increased range of motion. Another advantage is that significantly less surgery is required to replace only the ball of femur and not the socket as well. Less skill is required when only preforming a partial hip and less surgical dissection is needed which often results in less blood loss.
The main disadvantage in performing a partial hip replacement is that the final results are not as consistently perfect. Without question, the gold standard is the total hip replacement. More and more recent studies are showing better results with total versus partial, even among the “fracture” population.
As a result, I seldom perform partial hip replacements. Yet, even for me, there are a small number of patients for whom this is the best course of action, for example, an elderly patient who prior to a fracture had no hip arthritis. I recently was asked to help an older gentleman who had fallen and fractured his femoral neck. I was told that he had fallen multiple times over the past year and ultimately sustained a fracture. This, unfortunately, is a common story: multiple falls before a fracture finally occurs, particularly in some elderly patients. This patient also had severe Parkinson’s disease and had developed some cognitive demise. Although he was living independently with his spouse, he required the use of a walker even around the house and was not very active. For this patient, a partial hip replacement (bipolar) was most appropriate, because he was not very active, had a high probability of future falls and performing less surgery to fix the fracture was safer for him. Also, he did not have hip disease or any arthritic symptoms prior to fracturing his hip. Fortunately, he did very well and after a short stay in the hospital was again able to go home with his wife and resume his prior level of independence.
Another much less common indication to use a bipolar hip replacement is when a patient already has had a total hip, but is suffering recurring dislocations. In some cases, I add a bipolar cap over the ball and then place the large ball into the patient’s fixed cup. This creates a “tripolar” construct and has helped me to solve some very difficult instability problems for patients.
Because of the specialty nature of my practice, I occasionally see patients who already have been reconstructed with a partial hip replacement but are still in pain and not doing well. I convert their partial hip to a total hip by implanting a new socket and changing the ball if the stem is satisfactory. These surgeries tend to be very successful.
For patients who are active and have higher lifestyle demands (want to play golf, tennis, walk for exercise, ride a bike, etc.) I perform total hip replacements, even for a fracture without prior disease. The results are consistently more perfect. It’s a fact that the vast majority of patients who come to me with hip problems have degenerative osteoarthritis. Their femoral head and socket have cartilage loss and degeneration, so a partial hip simply is inappropriate.
The key to successful joint replacement surgery is having the right surgeon with enough experience to choose the best prosthesis and procedure for you. An orthopedic surgeon who is highly experienced in hip replacement surgery brings valuable expertise and typically has built an experienced team ready to assist. Your surgeon also should know from personal experience with and repeated use of any prostheses, which are optimal, safe, long lasting and provide the best results.
During my more than 20-year career, I have helped thousands of people from around the world. At The Leone Center for Orthopedic Care, we offer both the latest and most time-tested innovations in joint replacement.