Click a heading below to learn more about different risks and complications that can happen with hip replacement and how Dr. Gross uses his expertise and experience to minimize each one.
All surgeries have risks, so the potential benefits must be carefully weighed. Some complications are directly related to the surgical procedure and I call these surgical complications. Some are related to the stress we place on the body by the trauma of surgery, I call these medical complications.
Medical complications include but are not limited to: heart attack, stroke, kidney bladder dysfunction, and bowel dysfunction. I am unable to quantitate these for you. If you have significant underlying medical conditions, you should consult with your medical doctor or medical specialist (e.g. cardiologist) about your risk and how to best limit it. We recommend a complete physical by your personal physician and medical clearance in writing prior to surgery.
Medical clearance does not mean that your medical doctor or I can predict or prevent a major medical complication. It means that your doctor feels your medical condition has been optimized prior to surgery. I am a surgical specialist and not a medical specialist; therefore I need your personal physician to make this call. I want to avoid any surprises during or after the operation. For example it has been shown that people who have had a heart attack should ideally wait for 6 months to have elective surgery to minimize risk. Also people over 80 years age have a 25% risk of major medical complication with joint replacement surgery.
General and spinal anesthesia seem to be equally safe and effective for most people. The early recovery process is better with spinal anesthesia plus sedation; we therefore recommend it for most patients. We usually only use general anesthesia for the rare patients in whom spinal fails to work. However, the final choice is yours to make. Prior to the surgery, the anesthesiologist will discuss the options with you and help you to decide which type is best for you.
Using a comprehensive blood management program, my transfusion rate for hip replacement and resurfacing is less than 0.1%. If you have bilateral surgery the same week the transfusion rate is still less than 1%. For purposes of comparison, the national transfusion rate for hip replacement is 20-30 %.
If a blood transfusion is required, there is a potential risk for a transfusion reaction or disease transmission (e.g. hepatitis, AIDS). The risk of contracting AIDS from a blood transfusion is now estimated at one in a million. The risk of contracting hepatitis is approximately one in two thousand.
If your hemoglobin is low prior to surgery, you should take iron supplements and possibly a series of erythropoietin injections (Procrit) to build up your hemoglobin level. Using autologous blood is costly, inconvenient, and of questionable value. With my track record, it is unnecessary, however it can be arranged if you desire.
Our blood management protocol is as follows:
- Measure preop Hg
- If Hg < 15, start prescription iron
- If Hg < 13, recheck Hg 1 month preop
- If Hg < 13 again, administer procrit
- Auquamantys tissue sealer used in surgery to limit bleeding
- Minimally invasive surgery; average blood loss is less than 150ml. (Compare this to the literature 500-1000ml)
- Platelet concentrate
My rate of early postoperative (within 3 months) deep hip infection is 0.1%. These can usually be cured with aggressive treatment without loosing your implant as long as you keep me informed about problems. If you live out of state and let someone else manage your care, the result may not be as good. For comparison purposes, the national infection rate is 1-2%.
Higher risk patients are those with:
- other immune suppressive conditions
- previous hip surgery
I believe our results are superior because we have developed a comprehensive program to prevent infections including the following:
- Preop evaluation
- No active infection
- Medical clearance
- Hg A1c< 7 (if diabetic)
- normal prealbumin
- Preop Hibiclens shower
- Shave surgical site
- Mupirocin into nostrils
- IV antibiotics for 24º
- Duraprep and plastic adhesive
- Clean air OR + body exhaust suits
- Efficient minimally invasive surgery
- Intraarticular Vancomycin
- Betadine jet lavage irrigation
- Gentamicin loaded cement
- Quill barbed suture closure
- Dermabond (superglue) skin seal
- Acticoat silver dressing (antibacterial) for 7 days
- No dressing changes or wound checks
- Daily mupirocin on incision after acticoat is removed.
Although only some of these measures have been individually proven to decrease infection, we think the combined use of all of them has driven our infection rate more than ten times below the national average.
Most infections in total hip replacements occur either due to contamination at thetime of surgery or from bacteria that invade from the skin through the incision before it is fully sealed within the first few weeks after the operation. It is a myth that surgery can be a truly sterile procedure. The wound also does not become completely sealed for at least one month after surgery. The program works because we address the problem of potential infection from multiple angles: optimize the patient, clean the skin, keep the OR contamination to a minimum, provide antiseptics and antibiotics to kill any residual bacteria, and prevent any bacterial access to the wound postoperatively.
We do not keep track of minor wound problems in a systematic way in our database. I estimate that they occur in less than 5% of patients. Bruising is normal. If you keep me informed about redness, drainage or any wound separation, these can usually be managed without resulting in deep infection.
In the rare case where deep infection occurs, these can usually be cured without loss of implants if treated aggressively with debridement and intraarticular antibiotics.
Late infections (after 3 months) are not directly related to the surgery. Lifetime risk is far less than 1%. Usually the implant has to be removed to cure these. For the rest of your life, cleaning all cuts with an antiseptic like betadine, treating any bodily infections promptly and taking a single dose of preventative antibiotics prior to any invasive procedures as well as prior to teeth cleaning are unproven, but prudent precautions.
(0.2% DVT, 0 PE)
When we perform hip or knee replacement operations we create tissue trauma that naturally cause the body to respond with a clotting response. Patients who have a defective clotting system such as hemophilia would bleed to death with these operations if we did not artificially supplement their clotting system. I use careful surgical technique, electrocautery, the Aquamantyss tissue sealer and platelet concentrates with Thrombin to minimize perioperative bleeding. But this is not enough. We depend on the patient’s normally functioning clotting system to do the rest. Clotting in the wound is natural and absolutely necessary. But sometimes the patient’s clotting system over reacts and clots are formed in the veins of the legs and pelvis.
This can lead to problems. Especially when these clots break off and travel to the lungs (pulmonary embolus). Preventative measures include rapid mobilization of the patient, pneumatic compression devices (SCD) and use of drugs that impair the clotting mechanism commonly referred to as anticoagulants or “blood thinners”. Although these drugs can reduce the chance that abnormal clots form in the veins, they also reduce the desirable clotting that occurs in the wound itself. This leads to more bleeding for up to several days postoperative.
This may then lead to more pain as well as wound drainage. The more the wound drains, the higher the chance of infection. Rarely they can cause a stroke or subdural hematoma. Therefore anticoagulants have two effects: they decrease thromboembolic events (undesirable vein clots) but they increase the rate of infection. Every persons clotting system is different. But efforts to quantitate this so far have been ineffective. We are unable to predict how strongly an individual’s clotting system will respond. The best risk-benefit ratio therefore seems to some form of limited anticoagulation for most patients.
Without any preventative measure, the incidence blood clots in the legs or pelvis (deep venous thrombosis, DVT) is approximately 50% to 60% and the incidence of blood clots traveling to the lungs (pulmonary embolus, PE) is 10%. The risk is higher in patients who are obese or who have a know hypercoaguable state. In and of themselves DVTs are not a great threat; they can be treated with blood thinners and will ultimately resolve. The patient may, however, be left with some permanent swelling of the leg due to destruction of some of the valves in the veins. But PE carries a 1% chance of death.
The protocol that we are currently using has resulted in a < 1% chance of DVT and no PE in over 1000 patients.
- Avoidance of entering marrow canal: resurfacing
- SCD for 24º, beginning in the operating room
- Spinal anesthesia
- Rapid mobilization
- Xarelto for 2 weeks/ 4weeks for high risk patients
(once a day oral medication, no injections or blood monitoring needed)
The sciatic nerve is at risk in hip replacement. It can be cut accidentally, but typically it is stretched excessively during surgery causing numbness in the foot and a foot drop. If this does occur, the foot of the operated leg remains numb after the spinal anesthesia wears off and it is difficult to pull the toes towards the head. This can only occur immediately after the surgery (If you develop numbness or foot drop a week or month after surgery, it is probably being caused by a separate back problem). The deficit may be minor a transient or more complete.
There is no known treatment to make the nerve recover. Younger patients have a higher chance of nerve recovery. Nerves regrow at a rate of 1mm/ day. Therefore if recovery occurs, it may take up to 18 months. Early in the process there may be a burning pain that can be treated with nerve agents such as Lyrica. A brace (spring loaded sports ankle foot orthotic) can be prescribed to help prevent toe dragging. Usually partial recovery occurs. After 18 months, consideration can be given to a tendon transfer operation to return foot function.
The national rate of sciatic injury in THR is 1-2%. During my first 500 HRA I had a 1% rate of this problem. During the last 2500 case we have had none. In THA my rate is 0.1%.
This is the single biggest problem with hip replacements. This is when the ball comes completely out of the socket. A normal hip is held in place by ligaments as well as muscles around the hip. The normal femoral head is quite large and difficult to dislocate. It requires a fall from 2 stories or a blow of knee onto the dashboard of a car at 30 mph to do this. Usually a bone will break first.
Most total hip replacements (THR) have a smaller head than the normal hip. The smaller the artificial head, the higher the risk of dislocation. Also in THA a metal stem replaces the top of the femur. The stem imperfectly reproduces the natural anatomy of this bone. This is also a factor in instability. Also, during the operation, the major stabilizing hip ligaments (hip capsule) are cut. If the patient bends the hip too far, the hip may dislocate. It requires no significant force as with a normal hip.
The risk of dislocation is approximately 5% within the first year after surgery if a standard 28mm bearing is used. If a 36mm bearing is used, the risk is 1%, if anatomic sized metal bearings are used the risk is < 0.2%. When the risk of dislocation over 10 years is considered, it doubles. When a hip dislocates, you can’t walk and you need to go under anesthesia to have it manipulated back into place by your surgeon.
About half of all people who dislocate a hip end up having repeated dislocations and require surgery to try to correct this. This is the most common cause for revision hip surgery in the US. It accounts for over 22% of all revisions. Patients with the following conditions are at higher risk: dysplasia, obese, neuromuscular conditions such as MS or Parkinson’s disease. The risk is somewhat influenced by the type of surgical approach (anterior vs. posterior) implant design features other than the head size (lateral offset, neck diameter) and implant position (primarily of the acetabular component). But bearing size is by far the most critical factor. Although surgeons often speak of ideal component positions, attempts to define a safe zone for implant positioning has so far been unsuccessful with these smaller bearings.
When larger bearing sizes are used with a plastic socket liner, the liner has to be made thinner. When this was tried 20 years ago, plastic wear increased dramatically causing extensive bone destruction (osteolysis). We had to abandon this idea and return to smaller bearings and accept a higher dislocation risk. Metal bearings became available 10-15 years ago. In the laboratory they produced very low wear rates even with larger bearing sizes. Because large metal bearings are obviously more stable, these became very popular a few years ago.
However we have learned that they do have a different set of problems. When implanted into people, large metal bearings sometimes produced higher wear rates than expected and this metal debris caused swelling, pain, and eventually soft tissue destruction that I have named an adverse wear failure (AWF). In addition, all larger bearings (including plastic and ceramic ones) may put excess stress on the stem trunion (where the head attaches to the neck of the metal stem) resulting in corrosion and also AWF.
Therefore the downside of more stable larger bearings is AWF produced by excess metallic debris. But we have found that this problem is related to specific implant design (brand) and acetabular component position. I will explain this in more detail in the section on AWF. In addition there may be very rare patients with allergy to metal, but we have no reliable test for this and the rate appears to be less than 0.025%.
My solution to the problem is to use a proven well-designed metal bearing with precise positioning of the acetabular component. There is only one design that has been recalled for bearing wear problems, the DePuy ASR total hip and resurfacing system. For hip resurfacing I use either the Biomet or Wright system because their bearings are sound and they are the only companies to offer an uncemented femoral component (different discussion). For total hip systems we must not only consider the bearing design, but also the trunion design.
It is still not entirely clear what trunion design is optimal for large heads. But I am strongly suspicious that the Biomet design is superior for several reasons. Again, it appears that DePuy had serious flaws with their trunion and had the worst problems. Biomet has a completely different trunion than DePuy and most other companies. The stem is titanium and the neck adapter is titanium. The attachment of the neck adaptor to the cobalt-chrome head is at a massive trunion. One comparative study has shown that this unique design releases significantly lower amounts of metal ions than other trunion designs.
In addition, many companies added grooves to their stem trunions over the last 10 years to better accommodate ceramic heads. They also made them smaller to reduce the risk of impingement and dislocation. Biomet did not do this. I have not seen any trunion failures with the Biomet implants over 7 years of use. We are in the process of compiling a formal study with metal ion levels to assess this more carefully.
For hip resurfacing and large bearing THR, my risk of dislocation has historically been less than 0.2 % and AWF rate has been 1% at 10 years. Both of these are falling further now that we have finally discovered a “Safe Zone” for acetabular component positioning for large metal bearings. In a study of 761 cases we found that the dislocation rate and the AWF rate was ZERO if we placed the acetabular component within a certain range that we named RAIL (Relative acetabular inclination Limit).
In the last 2 years we have been able to place 100% of all implants within RAIL. I believe the risk of dislocation and AWF is now negligible for HSR and THR. For rare patients who cannot tolerate cobalt chrome, I think the best solution is a 36mm Biolox ceramic head on a Biomet titanium stem against vitamin E doped cross-linked polyethelene. I only rarely use this implant and can therefore not give you my personal stats. But this carries a 1% theoretical risk of dislocation, and probably little risk of trunion corrosion. The plastic liner is thin and therefore carries some as of yet unknown risk of breakage by 10 years. Impact activities should be avoided.
To prevent dislocation, patients with THR using smaller bearings need to follow lifelong restrictions. They should never bend their hip into extreme positions as required in ballet, palates, yoga and kayaking and squats. The risk is less with a 36mm bearing than the standard 28mm bearing. Patients with large metal bearings with HRA or THA have to limit extreme positions for 6 months until the hip capsule has healed, them they no longer have position restrictions.
Leg Length Inequality
Lengthening up to 5mm is typical as lost cartilage is replaced. Patients will accommodate to lengthening up to 1 cm by pelvic tilt within 6 months after surgery. Lengthening greater than this is only rarely possible in certain cases of deformity.
Significant leg lengthening is defined as increasing the length of the leg more than 1 cm (3/8 inch) in surgery. This occurs in about 5% of stemmed THR. Most patients accommodate well to such minor changes in length. 1 cm is only 1% of the length of the leg. The pelvis is designed to shift and tilt over 2 cm from side to side to make up for minor leg length differences. No person is born with exactly equal leg lengths. In a study of healthy military recruits it was found that 25% have a difference of over 1cm from side to side.
There is no scientific evidence that a difference in leg lengths causes problems in other joints including in the back. Nevertheless chiropractors and physical therapist are prone to diagnose misalignment and prescribe lifts. There is no scientific basis for this. Just as there was no scientific basis for all the braces orthopedic surgeons historically used to prescribe kids with various deformities. It kind of made sense so it was done- but it has been largely abandoned by our profession because evidence of its ineffectiveness has accumulated.
Occasionally the length of a leg is inadvertently lengthened during standard stemmed total hip replacement surgery, especially in a patient with loose ligaments. Often the surgeon plans to slightly (<1cm) lengthen the leg to increase tissue tension and thereby reduce the chance of dislocation in a small bearing total hip replacement. If length is increased by more than 2 cm beyond the opposite leg, patients will often not accommodate to it with time and find it unpleasant. But it will not hurt other joints. The solution is to wear a 1cm (3/8) lift inside the opposite shoe. This does not affect appearance; other people cannot notice this. If more than 1 cm lengthening is required, the buildup is first put on the shoe, and then additional amount is placed on the sole if necessary.
With hip resurfacing it is only rarely possible to increase the leg length even if the surgeon tries to do it. This is because we are only cutting away a small layer of bone and replacing it with metal on both sides of the joint. Usually the leg is lengthened 0-0.5cm because lost cartilage is replaced. In certain cases of bone deformity length may be increased slightly more as the deformity is corrected. In patients who have a major leg length discrepancy, this cannot be corrected with resurfacing, but may be correctable with a stemmed total hip replacement. The patient must then decide what is more important to them, gaining up to 2 cm in length (THR), or preserving the top of the femur (HRA). We are unable to shorten the leg with either operation, because hip instability may develop.
Before surgery, with an arthritic hip most people have slight shortening due to loss of cartilage or bone. It is not uncommon for people to feel major shortening or even lengthening has occurred because of the arthritis. This sensation can be caused by pelvic tit associated with an arthritic hip. Sometimes this tilt is toward the hip and sometimes it is away. True change in length can be measured on the x-ray. On the other hand, measuring a patient’s leg length lying or standing is completely unreliable. After surgery, for up to 6 months, pelvic tilt as a response to the trauma of surgery can also occur. This can give the patient a false sense that major length change has occurred. The x-ray will again help the patient understand that this has not occurred. This sensation usually resolves by 6 months after surgery.
Abnormal bone may form in the tissues adjacent to the joint as a reaction to surgery. Some patients are more prone to this. This does not cause pain. If it is extensive, it may decrease motion. Most patients with an arthritic hip have loss of motion. After resurfacing the hip returns to near normal motion after 1 year of healing. Exceptions are case with certain deformities, extreme stiffness before surgery, and in rare cases where extensive heterotopic bone forms.
We try to prevent this by the following measures:
- Protective covers over muscle during surgery when bone is reamed.
- Thorough jet lavage of hip prior to closing.
- 2 week course of celebrex or Mobic
- Single doe of x-ray therapy after surgery in high risk patients.
Fractures in Surgery
Occasionally cracks are seen when implants are driven into bone. This is because bone is prepared for a very tight initial fit of the implant.
In hip resurfacing the femoral side never fractures in surgery. It is extremely rare to see a socket wall fracture. These are typically stable and require only that the patient stay on crutches longer after surgery.
In stemmed total hip replacement, 1-2 % of cases suffer a crack around the top of the femur during stem insertion. This can easily be handled with a cable placed in surgery around the crack. These patients usually also need to stay on crutches a little longer after surgery.
Fractures after Surgery
(0.1% HRA, 0.7% THR)
In Hip resurfacing, the femoral neck may fracture during the first 6 months of healing. I have never seen it occur thereafter, even with significant falls. The femoral head can gradually collapse within the first year. Both of these problems combined are called early femoral failure. When I first started doing resurfacing my rate was about 2.5%. We have extensively studied this problem and found a solution. These fractures are related to weak bone and excessive patient weight. We now always measure bone density before surgery with a DEXA scan.
Patients with weak bone or BMI >30 are paced on crutches longer and/or are prescribed a bone strengthening medicine for 6 months. Using this protocol, we have reduced the early femoral failure rate to 0.1% in the last 1000 cases. These fractures can occur gradually as a stress fracture due to early over activity, or from a minor fall during the first 6 months after surgery. If this occurs, we need to revise the femoral side to a stemmed THR.
Femoral trochanteric and shaft fractures occur after stemmed THR. The reported rate is 0.7% in one major study. At this moment I cannot quote my personal rate because we are still compiling the data. Trochanteric fractures are repaired with a clamp, while shaft fractures usually require revision to a longer stem plus cables. We have not studied bone-strengthening agents in THR patients.
Failure of Bone Ingrowth into Implants
(Acetabular 0.2%, Femoral 0/2000 HRA, 0/1000 THR)
Implants need to be firmly attached to bone to function correctly. If they are loose, they rub on the bone causing pain. There are two methods to fix implants to bone: cementing and bone ingrowth. The advantage of cement is immediate fixation, while the disadvantage is lower durability. I strongly favor bone ingrowth implants. The disadvantage they have is a low rate of bone ingrowth failure. Most US surgeons favor bone ingrowth in THA except possibly in very old weak bone, where cement may still have an advantage.
Approximately 90% of all THR implants are bone ingrowth types. The socket component that I use for HRA and THR are the same. We had some problems with bone ingrowth failures in dysplasia case with severely deformed anatomy before 2007. However, since then the introduction of a component with supplemental fixation (Trispike Magnum) that we can use in these deformed cases, has allowed us to decrease the rate of acetabular bone ingrowth failure to 0.2%. We have not had any failure of bone ingrowth into the uncemented femoral component in HRA or THR in 5 years.
(3% @ 10 years for cemented HRA femoral component)
Sometimes implants are initially well fixed to bone, but this bond can break down over time. His process is called loosening. Loose implants rub on bone and hurt. Uncemented implants are initially fixed to bone by a tight press-fit. But they are not truly considered fixed until bone ingrowth occurs. It can be difficult to know for certain if this process has occurred until you see a patient 2 years after surgery and they are without pain and have a stable x-ray. After that, if an implant becomes unstable w.r.t the bone it is thought to have loosened. This is extremely rare. It could possibly be caused by inflammation from excess wear debris (either plastic of metal).
In the Corin Cormet 2000 HRA we have seen 5/373 (1.3%) cases where the porous coating debonded from the uncemented acetabular implant causing loosening after 7 years of implantation. We have not yet seen this in the Biomet Magnum acetabular component, which we started using 7 years ago.
With cemented femoral components of HRA we have seen a 3% rate of loosening @ 10 years. We believe that this will not occur with the uncemented components. We started implanting these in 2007. It is still too early for us to see any difference statistically in the overall patient groups. However, in a small high-risk group of patients with osteonecrosis of the femoral head we have seen better results already.
We have never seen this in HRA, except one broken femoral stem in an implant that is still functioning many years after we saw this on x-ray. The implant is fixed to the bone by cement under the bearing; the stem did not provide any fixation.
Implant breakage was a known cause of failure when THR stems were made of stainless steel. It is rarely seen with cobalt chrome stems. It is exceedingly rare with the titanium stems that I have been using for years. I have never personally seen one fracture. But if young athletic patients run on these for years, it is possible that this may become a late failure mode. Extracting a broken stem is quite difficult. Therefore I recommend no running more than 1-2 miles at a time with a stemmed THR.
Wear Related Failure
(AWR in HRA 1% @ 10 years)
All artificial implants wear and release debris into your body. If the level of debris generation is low, the body can tolerate it well for many years. There are many different bearing surface options. In HRA only cobalt-chrome metal on metal bearings work. There is only one bearing surface and no additional junctions that can wear or corrode.
With stemmed THR there are four bearing options:
- Metal on plastic (polyethelene)
- Ceramic on plastic
- Ceramic on ceramic
- Metal on metal
- Metal on ceramic
The most commonly used are listed first. In addition to the bearing, wear and corrosion can occur at numerous implant junctions in stemmed THR. These include: liner on socket, ball on stem trunion, and modular junctions.
In the past, plastic (polyethelene) wear was a major problem particularly in younger more active patients. Once produced, plastic debris has no way to exit the body. It accumulates around the implant and travels along the lymph channels but it never leaves the body. These bearings carried a 30% failure rate by 8 years in patients under age 50. If a large amount of plastic debris accumulates around the hip, the body’s immune system reacts against it and destroys bone. The result is often extensive bone destruction, which is called osteolysis. There is no way to measure the amount of plastic particles released into the body. Improvements in plastics (cross-linked polyethelene) appear to have solved this problem. The plastic wear rate has been reduced dramatically. But the down side is that these plastics are more brittle, increasing the risk of implant (liner) breakage with impact activity. As the new plastic liners have become more wear tolerant, we have moved into larger bearing sizes to improve stability. In this situation, the liner becomes thinner and breakage becomes a greater concern. These are not suitable for impact activity.
Ceramic on ceramic bearings produce the most benign debris. Cases of adverse reaction to ceramic debris are exceedingly rare. If an implant was chosen based primarily on debris generation, ceramic on ceramic would be the clear favorite. The amount of ceramic debris deposited in the body cannot be measured. Unfortunately these cannot be used for resurfacing. Ceramic fracture is also an exceedingly rare event with current ceramic bearings. But as ceramic bearings are made larger to improve stability, the liner becomes thinner and fracture may become a problem, especially with impact activity. The main problem currently is that larger bearing sizes are not available, making instability a persistent problem.
Metal on metal bearings are unique because very thin one-piece acetabular components can be manufactured in which there is a porous bone ingrowth surface on the outside, and a polished bearing surface on the inside. This allows us to reconstruct the hip of each individual patient with its natural bearing size, providing normal hip stability. This also allows us to preserve the femoral head for resurfacing. Alternatively, a large metal head can be placed into this acetabular component and attached to any standard total hip stem. This results in a very stable hip joint. All metal on metal bearings are made of cobalt chrome. The wear products are cobalt, chromium and traces of nickel and molybdenum, which are also present in the alloys used. In a well functioning metal on metal bearing the amount of wear debris generated is very small and is well tolerated by the body. It is deposited in the tissues around the hip. It is then absorbed into the bloodstream and excreted in the urine. A level can be measured in the blood or urine. I have used over 4000 metal bearings; the vast majority are well tolerated by the body.
If a well-designed metal bearing is implanted in the correct orientation, the wear rate is low and the small amount of wear debris is well tolerated. Numerous large long term studies have been done showing that these particles do not cause cancer. There are a handful of individual case reports of systemic metal toxicity. Most have these have not been in cases of metal bearings. None of the cases that I have treated for adverse wear reaction (AWR) have had any signs of systemic toxicity, despite extremely high metal ion levels being measured.
There is no evidence that the metal ions released form bearing wear cause cancer or kidney damage, and even systemic reactions are rare in cases of excessive bearing wear.
Adverse Wear Reaction (AWR)
Local inflammatory tissue reaction to excess metal wear debris is the problem. I have called this an adverse wear reaction (AWR). In plastic bearings, excess debris tends to cause more bone destruction and less soft tissue inflammation, in metal bearings there tends to be more soft tissue inflammation and less bone destruction. In cases of AWR to metal debris there is fluid collection, metallic staining of tissues, and production of inflammatory masses (not cancer). If severe reactions are not treated for years, muscle destruction can occur. But I have not yet seen any case of muscle damage.
We now recommend measuring blood metal ion levels on all patients at 2 years after surgery to assess their wear rate. We have found that this is an extremely helpful test to discover patients whose wear rate is excessive. Using blood ion level testing, we have found some patients who have an early AWR that is not yet symptomatic and I have revised them. On the other hand, we have found a few cases with high ion levels without AWR and we are monitoring them with yearly levels.
We have done extensive studies on AWR. Based on detailed studies of hundreds of patients with accurate x-rays and ion levels, we have been able to develop a “safe zone” for placing acetabular components to prevent AWR. This paper will be published in Journal of arthroplasty in 2013. This safe zone is based on bearing size. Although safe zones have been published previously for plastic bearings (to prevent dislocations), they are very unreliable. Our safe zone reliably prevents both AWR and dislocation with >99% accuracy. This has never before been achieved for any type of hip replacement type.
The cause of the AWR in metal bearings is now fairly well understood by most hip resurfacing experts. I will try to summarize the problem briefly. AWR occurs when a metal bearing exhibits an abnormal wear pattern called edge loading. When this occurs, the natural fluid lubrication film breaks down and an extremely high wear rate ensues. A large amount of metal is produced and deposited in the surrounding tissue leading to the AWR. Elevated metal levels will be measured in the blood. There are 2 factors that will result in edge loading; an acetabular component that is shallow by design, or a component that is placed in too steep of a position (High inclination angle as measured on a standing pelvis x-ray).
The recalled Depuy ASR implant had an excessively shallow design, this is one reason it had a 30% failure rate within 5 years. It is a quirk in design that in virtually every resurfacing system on the market, the smaller bearing sizes have shallower acetabular components than the larger sizes for the same brand. This is the primary reason why smaller bearing sizes carry a higher risk of AWR than larger bearing sizes in every system. Women tend to have smaller bones and typically require the smaller sizes; therefore they have higher rates of AWR. AWR occurs when an acetabular component is implanted too steeply. The more steep the acetabular inclination angle (AIA), the less well the head is “captured” and the more likely that edge loading and AWR will develop.
In our studies, no components with AIA< 50º on standing pelvis x-ray have developed AWR, while about 5% of those with AIA>50º have had this problem. We have also had no cases of AWR in bearing sizes >48mm. But the AWR can be avoided in smaller sizes, simply by implanting them with lower inclination angles. This allows the shallower component to function well without edge loading. Our paper on safe zones makes this very clear.
In addition to the fiasco with the Depuy ASR (total hip and resurfacing) recalled in 2010, there was a very disturbing report published by the Oxford Group in the JBJS British Journal in 2008. This was the first major clinical series highlighting the problem of AWR. This group found a 4% @ 8 years rate of AWR in a series of 1400 cases while using proven well designed implants. They called these failures “pseudotumors” and speculated that they may be severe allergic reactions to metal. Most disturbingly, they reported that these failures were not related to steeply implanted acetabular components. We have now published a larger report of 2600 cases with a 1% rate of AWR in 10 years in the journal hip international 2013. Our data clearly indicate that AWR is caused by steep component placement, particularly in smaller implant sizes. All 8 of our cases had AIA>50º and bearing size
To make matters worse, the Oxford Group soon published a report on the results of their revision surgery for “pseudotumors”. It showed disastrous outcomes for these patients. I have not yet published my outcomes for revisions of AWR (my own 8 cases plus others referred to me from elsewhere), but can assure you that my results again are diametrically opposed to their report. I have not even transfused any of my cases. The revision surgery for AWR is actually quite straightforward and carries only a slightly higher risk than the original operation.
The combination of the DePuy ASR disaster and the poor results with good implants from the Oxford Group, have scared many surgeons away from large metal bearings for stemmed THR and resurfacing. This is a shame, because we now know that the problem is virtually completely avoidable with proper implant choice and placement. These large metal bearings are the only ones that provide a truly stable hip joint and avoid the most common problem in hip replacement: recurrent dislocation.
Metal Ion Testing
We have made a concerted effort to obtain metal ion testing on all of our patients who are at least 2 years postoperative. It is important to recognize that metal ions found in the blood are not in and of themselves a problem. We use blood ion levels in two ways. First, they are used a screening test to see if AWR are developing in asymptomatic patients. We have found occasional cases where this is true. Secondly, in patients who are having pain, a low ion level is very good evidence to rule out an AWR. If a metal ion level is high we then perform either a metal suppression CT or MRI scan to see if a substantial fluid collection or soft tissue mass (not cancer) is present.
Small amounts of fluid can be normal around well-functioning implants (A hip replacement or resurfacing is not a normal hip). A large collection together with a high ion level is diagnostic of AWR. This is then confirmed at the time of revision surgery with extensive metal staining of the tissues. If the metal level is high but there is no fluid collection we recommend yearly monitoring with ion levels. We are not certain what the long-term outcome will be in these cases, but we don’t think it is dangerous to observe these patients. Sometimes metal levels can be elevated when an implant is loose (this is symptomatic).
There are no accepted guidelines regarding what constitutes an acceptable ion level. We have extensive experience and have developed our own internal guidelines. We consider any level below 10ug/L safe and would only recommend further testing in a significantly symptomatic patient. Patients who have bilateral implants or even joint implants elsewhere in the body may have higher levels, as could patients with kidney dysfunction, or those who are taking vitamins or supplements (they may contain chromium even without listing them).
Normal levels as reported by the labs (for patients without implants) are below 2ug/L. As we are getting better at placing these components, we are seeing a trend of more patients with very low levels, even many in the normal range. There is a period of “run in wear” with these bearings that lasts 1-2 years. Ion levels are somewhat higher during this time. This is why we have chosen 2 years as our starting point for testing. Long-term studies have shown that there is a general trend of ever declining levels out to 10 years.
One study has shown that ion levels for total knee replacement are similar as for a well-functioning metal on metal hip replacement. Knee replacements have a cobalt chrome femoral component that articulates on a plastic liner; they are not metal on metal bearings. About 300,000 of these are done annually in the US. There is no evidence that mildly elevated metal ion levels have caused any clinical problem in TKR over the last 2 decades. This is further evidence that mildly elevated metal ion levels are not harmful.
In conclusion, ion levels will be elevated in HRA, but there is no evidence that this harms the body. Measuring ion levels is primarily useful in diagnosing local (around the hip) adverse wear reactions (AWF).