Background

Proper positioning of the acetabular component is critical for prevention of dislocation and excessive wear for total hip arthroplasty (THA) and hip resurfacing. Consideration of preoperative pelvic tilt (PT) may aid in acetabular component placement. The purpose of this study was to investigate how PT changes after hip resurfacing, via pre and post-operative radiographic analysis of anterior pelvic plane (APP), and whether radiographic analysis of the APP is a reproducible method for evaluating PT in resurfaced hips.

Introduction

Metal-on-Metal (MoM) bearing surfaces were historically used for young patients undergoing total hip arthroplasty, and remain commonplace in modern hip resurfacing. In theory, it has been postulated that metal ions released from such implants may cross the placental barrier and cause harm to the fetus. In light of this potential risk, recommendations against the use of MoM components in women of child-bearing age have been advocated. The purpose of this systematic review was to evaluate: 1) the Metal-on-Metal bearing types and ion levels found; 2) the concentrations of metals in maternal circulation and the umbilical cord; and 3) the presence of abnormalities in the fetus

Introduction

Hip resurfacing arthroplasty (HRA) is an alternative to traditional total hip arthroplasty (THA) in young active patients. While comparative implant survival rates are well documented, there is a paucity of studies reporting the patient mortality rates associated with these procedures. The purpose of this study was to evaluate the mortality rates in patients age 55 years and younger who underwent HRA versus THA and to assess whether the type of operation was independently associated with mortality.

Hip resurfacing presents advantages and disadvantages compared to total hip arthroplasty. Dislocation and leg length discrepancy, common complaints with total hips, are unusual following resurfacing. Bone stock in the proximal femur is retained, and revision options on the femoral side of a resurfacing are much better.

Concerns persist regarding adverse tissue reactions to metal debris.

Conflicting data abounds regarding ultimate hip function, patient satisfaction, durability, etc. Yet all of these would be rendered irrelevant if resurfacing carried with it greater life expectancy. We would not speak of survivorship of the implant, but survival of the patient. Instead of quality of life, let us preserve life itself.

Beginning in 2010, the UK Registry reported improved mortality rates at 90 days and five years after hip resurfacing compared with total hip replacement. This persisted after multivariate analysis for several covariables, including age, gender, health status, type of device, provider, and country. Recently, the 2016 Australian Registry Mortality Supplement showed similar results, corrected for age and gender.

Analysis of UK data by the designing surgeons of the Birmingham device, and an independent group of Oxford statisticians confirmed the lower mortality rate in patients treated with resurfacing vs. total hip replacement. Possible reasons for these differences include greater post-operative activity, longer stride length, less fat and marrow embolism, or perhaps more internet-savvy, health-conscious patients seeking out a resurfacing procedure.

Mid-term data from the US is now starting to come in, and mortality benefits are being confirmed in a series of patients from a large, academic center. Should there be a confirmed mortality advantage of resurfacing over total hip replacement, more surgeons and patients would be interested in this procedure, and new materials and techniques may follow.

Each of the seven cuts required for a total knee arthroplasty has its own science, and can affect the outcome of surgery.

Distal femoral varus osteotomy is a procedure intended to relieve pain, correct valgus deformity, and delay or possibly prevent the progression of lateral compartment osteoarthritis in the knee. It is indicated in patients who are considered too young or are too active to be considered candidates for total knee arthroplasty. It also allows protection of the lateral compartment in cases of meniscal or cartilage allograft. In patients who are a good candidate for total knee replacement, TKR is the procedure of choice.

A sloping joint line requires that the correction be performed above the knee. Several methods of distal femoral varus osteotomy have been proposed. These include a medial closing wedge, a lateral opening wedge, and a dome osteotomy. In the author's experience, the medial closing wedge has proven reliable. This technique uses a 90-degree blade plate, and does not require any angle measurements during surgery. Fixation is secure, allowing early motion. Healing proceeds rapidly in the metaphyseal bone, and non-unions have not occurred. The desired final alignment was zero degrees, which was reliably achieved using this method.

Medium to long-term results are generally satisfactory. When conversion to total knee replacement is required, standard components may generally be used, and function was not compromised by the prior osteotomy.

Distal femoral varus osteotomy is a successful procedure for lateral compartment osteoarthritis in a valgus knee. It is indicated in patients who are too young or active for total knee arthroplasty, and provides an excellent functional and cosmetic result.

It's easy to say that hip resurfacing is a failed technology. Journals and lay press are replete with negative reports concerning metal-on-metal bearing failures, destructive pseudotumors, withdrawals and recalls. Reviews of national joint registries show revision risks with hip resurfacing exceeding those of traditional total hip replacement, and metal bearings fare worst among all bearing couples. Yet, that misses the point. Modern hip resurfacing was never meant to replace total hip replacement (THR). It was intended to preserve bone in young patients who would be expected to need multiple revisions due to their youth and high-demand activities. The stated goal of the developers of the Birmingham Hip Resurfacing (BHR) was to delay THR by 10 years. In the two decades that followed the release of BHR, this goal has been met and exceeded. Much has been learned about indications, patient selection, and surgical technique. We now know that this highly specialised, challenging procedure is best indicated in the young, active male with osteoarthritis, as a complementary, not competitive procedure, to THR.

Resurfacing has many advantages. First and foremost, it saves bone, on the day of surgery, and over the next several years by preventing stress shielding. Dislocations are very rare. Leg length discrepancy and changes in offset are avoided. Post-operative activity, including heavy manual labor and contact sports, is unrestricted. More normal loading of the femur and joint stability has allowed professional athletes to regain their careers. Femoral side revisions, if necessary, are simple total hips, and dual mobility constructs allow one to keep the socket.

Adverse reactions to metal debris (ARMD), including pseudotumors, have generated great concern. Initially described only in women, it was unclear whether the etiology was allergy, toxicity, or inflammation. A better understanding of the wear properties of the bearing, and its relation to size, anteversion, hip dysplasia and metallurgy, along with retrieval analysis, allow us to conclude that it is excessive wear due to edge loading which is the fundamental mechanism for the vast majority of ARMD. Thus, patient selection, implant selection and surgical technique, the orthopaedic triad, are paramount.

What has been most impressive are the truly exceptional results in young, active men. The worst candidates for THR turn out to be the best candidates for resurfacing. The ability to return to full, unrestricted activity is just as important to these patients as the spectacular survivorship in centers specializing in resurfacing. If they are unlucky and face a revision, they are not facing the life-changing outcomes of a long revision femoral stem. So if the best indication for hip resurfacing is the young, active male, let's look at the results of resurfacing these patients in centers with high volumes, using devices with a good track record, such as BHR. Several centers around the world report 10–18 year success rates of BHR in males under 50 at 98–100%. Return to athletics is routinely achieved, and even professional athletes have regained their careers.

Hip resurfacing doesn't have to be better than THR to be popular among patients. Just the idea of saving all that bone makes it attractive. In the young active male, however, the results exceed those of THR, while leaving better revision options for the future. This justifies its continued use in this challenging patient population.

Distal femoral varus osteotomy is a procedure intended to relieve pain, correct valgus deformity, and delay or possibly prevent the progression of lateral compartment osteoarthritis in the knee. It is indicated in patients who are considered too young or are too active to be considered candidates for total knee arthroplasty. It also allows protection of the lateral compartment in cases of meniscal or cartilage allograft. In patients who are a good candidate for total knee replacement, TKR is the procedure of choice.

A sloping joint line requires that the correction be performed above the knee. Several methods of distal femoral varus osteotomy have been proposed. These include a medial closing wedge, a lateral opening wedge, and a dome osteotomy. In the author's experience, the medial closing wedge has proven reliable. This technique uses a 90-degree blade plate, and does not require any angle measurements during surgery. Fixation is secure, allowing early motion. Healing proceeds rapidly in the metaphyseal bone, and non-unions have not occurred. The desired final alignment was zero degrees, which was reliably achieved using this method.

Medium to long-term results are generally satisfactory. When conversion to total knee replacement is required, standard components may generally be used, and function was not compromised by the prior osteotomy.

Distal femoral varus osteotomy is a successful procedure for lateral compartment osteoarthritis in a valgus knee. It is indicated in patients who are too young or active for total knee arthroplasty, and provides an excellent functional and cosmetic result.

When patients present at an early age with osteoarthritis of the hip, there is usually an underlying predisposing cause. In men, a common cause is femoroacetabular impingement (FAI). This is evident as anterior neck osteophytes, with retroversion and varus alignment of the femoral head, most likely the result of subclinical slipped capital femoral epiphysis.

The resulting femoroacetabular cam impingement causes degenerative osteoarthritis (OA) of the hip, at an earlier age than primary OA. Patients present in their 40s and 50s with advanced arthritis, and are faced with the prospect of a total hip arthroplasty. Women may experience this as well, but may present with early hip arthritis as a result of subclinical dysplasia or pincer FAI more often than their male counterparts.

Hip resurfacing has several advantages over traditional total hip replacement for younger patients, especially men. These include bone preservation, less dislocation, thigh pain or leg length inequality, easier return to athletics, and easy revision on the femoral side. It is indicated in young, active patients.

The resurfacing procedure realigns the femoral head on the native and resurfaces the arthritic joint. Anterior neck osteoplasty is performed. Head retroversion is corrected. This restores deep flexion, and eliminates forced external rotation in flexion. Hip resurfacing can be done through either an anterior or posterior approach, although the anterior approach gives easier access to the anterior femoral neck, and preserves the blood supply to the head. This may help prevent femoral neck fractures and late head collapse.

Hip resurfacing has been proposed as an alternative to traditional total hip replacement in young, active patients. Metal-on-metal resurfacing devices were introduced in the 1990's, and a number of them reached the international market. The promise of bone preservation, more normal loading, greater activity, and easier revision led many surgeons to begin implanting these devices.

Over time, lessons have been learned regarding patient selection, implant selection, and surgical technique. Several devices have been withdrawn from the market, and many surgeons have abandoned the procedure. We continue to perform this procedure in substantial numbers, approximately 350 per year. The triad of a well-designed device, implanted accurately, in the correct patient has never been more critical than with these implants.

Following FDA approval in 2006, we studied the safety and effectiveness of one hip resurfacing device at our US institution in a large, single-surgeon series. We report our early to mid–term results in 476 patients who were under the age of 50 years at the time of hip resurfacing. Their average age was 42.8 (12–49) with an average follow-up of 4.8 years (2–8.8). Males represented 76% of the patients, and 91% had osteoarthritis. The average component size was 50.8mm (44–58) in men and 45.3mm (40–50) in women.

All surgery was performed in the lateral position using an anterolateral approach. Patients were allowed 75% weight-bearing for 6 weeks, followed by avoidance of strenuous exertion (running, jumping, heavy lifting) for 12 months. Follow-up intervals were 6 weeks, 1 year, 2 years, and 5 years. Follow-up percentage was 81%.

We measured a number of outcomes scores using a validated prospective observational registry at each follow-up interval. Improvement in HOOS Function was from pre-op of 41.4 + 22.7 to 93.5 + 15.2, Physical Activity Limitation improved from 2.4 + 2.5 to 8.2 + 2.6, and SF-12 Physical Composite Score improved from 31.7 +10.3 to 49.4 + 10.2.

There were no device-related failures in this series. There were no femoral neck fractures, no femoral component loosening, no failure of acetabular ingrowth, and no metal-related complications or pseudotumors. Two male patients, one a known heroin user, and the other with septic discitis, had remote hematogenous sepsis requiring component removal, each at 38 months after resurfacing. One female fell down an escalator 32 months after resurfacing sustaining a fractured acetabulum requiring component revision. Overall survivorship was 99.4%. Aseptic survivorship in males under age 50 was 100%.

We believe that hip resurfacing continues to offer a viable alternative for younger patients who would otherwise be candidates for total hip arthroplasty.

Valgus deformity is less common than varus. There is an associated bone deformity in many cases – dysplasia of the lateral femoral condyle. There are also soft tissue deformities, including tightness of the lateral soft tissues, and stretching of those on the medial side.

Unlike varus, where the bone deformity is primarily tibial, in valgus knees it is most often femoral. There is both a distal and a posterior hypoplasia of the lateral femoral condyle. This results in a sloping joint line, and failure to correct this results in valgus malalignment. Posterior lateral bone loss also results in accidental internal rotation of the femoral component, which affects patellar tracking. Using the trans-epicondylar axis and Whiteside's line helps to position the femoral component in the correct rotation.

Soft tissue balancing is more complex in the valgus knee. Releases are performed sequentially, depending on the particular combination of deformities. It is important to note whether the knee is tight in flexion, in extension, or both. Tightness in extension is the most common, and is corrected by release of the iliotibial band. Tightness in flexion as well as extension requires that the lateral collateral ligament +/− the popliteus tendon be released.

Cruciate substituting designs are helpful in many cases, and in extreme deformity with medial stretching, a constrained or “total stabilised” design is needed. Patellar maltracking is common, and a lateral retinacular release may be needed. Beware of over-releasing the posterolateral corner, as excessive release may cause marked instability. Use the pie-crust technique of Insall.

Hip resurfacing, like other orthopaedic procedures, depends for its success upon the confluence of three factors: a well-designed device, implanted using good technique, in a properly selected patient.

Cleveland Clinic has had good mid-term results in more than 2,200 patients using the Birmingham device since its FDA approval in 2006. These results are quite similar to other reported series from many centers around the world.

All surgery was performed using an anterolateral approach. Males accounted for 72% of the patients, and the average age was 53 years (12‐84). More than 90% of the patients had a diagnosis of osteoarthritis, and femoroacetabular impingement was the predominant pathology. The average component head size in males was 51mm, and in females 45mm.

Complications were few, with no dislocations, no femoral loosening, one socket loosening, one head collapse, 2 femoral neck fractures, and 2 deep infections. There were two patients with metallosis, one due to component malposition, and one in a small, dysplastic female. There were no destructive pseudotumors.

Overall survivorship at up to 8 years was more than 99%. Survivorship in young males, under age 50 with OA was 100%.

New mushroom templates for head size are described. Additional imaging recommendations including a standing lateral of the pelvis, and a CT scan for femoral anteversion may be helpful in patient selection.

Hip resurfacing using metal-on-metal bearings has a number of purported advantages over traditional total hip replacement in the young, active patient. Males in particular can benefit from the bone preservation, stability, and higher activity levels seen with this procedure. As more is learned about the factors affecting long-term outcome of hip resurfacing, component position has emerged as one major predictor of success.

Given a well-selected patient, and a well-designed device, acetabular positioning is perhaps the most important determinant of long-term survivorship in hip resurfacing. One feature of resurfacing socket design which has not been widely disseminated is the sub-hemispheric arc of the bearing surface. While the outer circumference of the socket represents a complete hemisphere, and radiographic evaluation may assume that the apparent socket angle is satisfactory, the actual bearing is less than a hemisphere, so that the true abduction of the bearing is considerably more vertical. This important fact leads to excessive bearing inclination, edge loading, and all that follows, including runaway wear, metallosis, ALVAL, and pseudotumors.

Inadequate socket anteversion can expose the psoas tendon to abrasion and tendonitis. Too much acetabular anteversion, especially when combined with increased femoral neck anteversion, can result in an overall decrease in bearing contact area, and excessive wear.

Femoral component positioning is critical in the prevention of femoral neck fractures, which are a chief cause of early failure. Varus placement increases the tensile stresses on the superior femoral neck. Excessive valgus threatens notching. Both increase femoral neck fractures.

Sufficient malposition will ultimately result in edge loading. Edge wear is incompatible with fluid film lubrication, the key to longevity of these bearings.

Concerns with long-term fixation of cemented all-poly sockets have led to the near-universal acceptance of cementless fixation of the acetabulum.

The sockets most often utilised today are bone-ingrowth porous metal, made of titanium, cobalt-chrome, or hyper-porous materials such as tantalum trabecular metal.

Porous ingrowth sockets are extraordinarily reliable, with reports of 99–100% achieving stable fixation. The problem with sockets is not the fixation, but the bearing. Modular polyethylene liners are most commonly used, but wear on the primary bearing surface as well as backside wear can lead to osteolysis and late failure. Holes in the socket designed for supplemental screws act as a conduit for particles to enter the ace tabular bone where a cascade of inflammatory responses activate osteoclastic activity and bone destruction.

One alternative is a socket without holes, using spikes or fins for additional stability. The concern here is that the socket may not be completely seated and the surgeon is unaware.

Another alternative is the use of a monoblock acetabular component with the polyethylene molded to the metal shell. While excellent results are reported, the downside is an inability to exchange the polyethylene.

Resurfacing sockets are also monoblocks, and some offer peripheral supplemental screws. Here again, incomplete seating may occur, leaving a gap behind the dome. Serial x-rays almost always reveal that this gap gradually fills in.

Improvements in polyethylene, better locking mechanisms and alternative bearing materials such as ceramic and metal are the final steps to ensure acetabular durability.

Acetabular revision surgery can be complex and challenging. The technique selected depends upon the amount of bone deficiency. One of the most useful ways to assess remaining bone stock has been described by Paprosky, based on the location and severity of bone loss, and the likelihood of obtaining a stable construct with a hemispherical cup.

In almost all cases of acetabular revision, the remaining bone is in fact capable of supporting a hemispherical socket, as long as details of technique are followed. The implant is larger than the native acetabulum and the removed socket by several sizes, and may approach quite large proportions, hence the term “Jumbo Cup”. The principle is to gradually enlarge the acetabulum with hemispherical reamers, taking care to protect the posterior and superior bone, at the expense of the less crucial anterior and inferior bone.

As reaming proceeds, there comes a point where the reamer is stable within the acetabulum. High areas have been reamed down, and remaining cavitary defects are then back-filled with autogenous reamings or allograft cancellous chips. This is then re-reamed in reverse to distribute the graft into the defects. A large or “Jumbo” cup, 2–3 mm larger than the last reamer, is then impacted into place, and supplemented with screws.

In many cases, the anterior lip, and to a lesser extent the medial wall, may be sacrificed to obtain stability, without compromising long-term results.

Hip dislocation is one of the most common causes of patient and surgeon dissatisfaction following hip replacement. To correctly treat dislocation, the causes must first be understood.

Patient factors included age greater than 70, medical co-morbidities, female gender, musculo-ligamentous laxity, revision surgery, issues with the abductors and trochanter and education.

Issues related to the surgeon and technique are surgical volume and experience, the surgical approach and repair, adequate restoration of femoral offset and leg length, correct component position, and avoidance of soft tissue or bony impingement.

There are also implant-related factors. Chief among these is the design of the head and neck region. Is the femoral head diameter sufficient, and in concert with the prosthetic neck is there an adequate head-neck ratio? Skirts on longer neck lengths greatly reduce the head-neck ratio and should be avoided if possible. There must be available offset choices in order to restore soft tissue tension. Lipped liners aid in gaining stability, yet if improperly placed may result in impingement and dislocation.

Late dislocation may result from polyethylene wear, soft tissue destruction, trochanteric or abductor disruption and weakness, or infection.

Understanding the causes of hip dislocation allow prevention in a majority of instances. Proper pre-operative planning includes the identification of high-offset patients in whom inadequate restoration of offset will reduce soft tissue tension and abductor efficiency. Component position must be accurate to achieve stability without impingement.

Finally, patient education cannot be over-emphasised, as most dislocations occur early, and are preventable with proper instructions.