The purposes of total hip arthroplasty (THA) are hip pain relief, resumption of range of motion (ROM) with normal ambulation, and long-term implant survival. Results of THA are excellent in elderly patients, whereas in young patients they are poorer. Data from the Emilia-Romagna regional Registry of Orthopedic Prosthetic Implantology (RIPO) show that approximately 24% of THAs are performed in patients younger than 60 years.
Hip pain relief and restoration of ROM is generally obtained in young patients. However, long-term implant survival is not always achieved, with only 72% of THAs still in place at 10-year follow-up.1 This high failure rate may be due to elevated functional demands of younger patients, which may lead to high wear and mobilization of the implant.
During the past 15 years, second-generation hip resurfacing (HR) has been introduced to obtain better functional results and longer implant survival in a population of young and active patients. These implants resurface both the acetabulum and femoral head with a thin metal layer, thus sparing bone stock.
Major advantages of HR include femoral bone stock preservation, which facilitates conversion to a stemmed prosthesis2; low dislocation risk due to the large femoral head diameter; physiological hip loading, thus preventing stress shielding; negligible risk of implant rupture; and the permitted resumption of sporting activities. Hip resurfacing is the only prosthesis that allows almost complete proximal femur preservation—far more than short stems. On the acetabular side, the same amount of bone removal is required compared with THA.3
The ability of HR patients to resume sporting activities is important. Girard et al4 reported that 98% of patients returned to playing sports after HR, of which 82% were involved in high-impact activities such as playing tennis. These results were not achieved with THA. In a similar study, 91.6% of HR patients returned to running practice, including that involving a degree of competition.5 Nevertheless, choosing activities where the cardiovascular system is challenged, such as cycling or backpacking, may be more reasonable choices than distance running or singles tennis, leading to longer implant survival.6
The better functional outcome achievable with HR has been evaluated in gait analysis studies. Aqil et al7 suggested that HR enables superior levels of function when treadmill walking at variable speeds; in particular, the gait cycle of HR-implanted limbs was closer to normal at top walking speed and top walking inclination. Postural balance analysis found identical data for HR patients and healthy individuals: conserved bone capital and numerous intraosseous receptors allow better proprioception and seem to contribute to this advantage.8
Although meeting patients’ expectations is important, implant survival over time is even more crucial. At 10-year follow-up, HR showed a lower revision rate for male patients regardless of age compared with either cemented or uncemented THA.9 In addition, a lower mortality rate for patients with HR compared with THA was observed in a retrospective cohort analysis.10
Hip resurfacing has some disadvantages, such as a more difficult surgery, femoral neck fracture,11 limited ROM due to the high head/neck ratio, higher incidence of groin pain compared with THA,12 and eventual onset of neck narrowing.13 Early femoral neck fracture is a severe complication that requires revision surgery (Figure 1). Shimmin and Back11 reported 50 (1.46%) cases of femoral neck fracture after a mean of 15.4 weeks in a multicentric study on 3429 HR patients. They demonstrated the crucial role of femoral component positioning in the majority of failures. Five degrees of varus (present in 71.1% of cases) or notching of the superior cortical bone of femoral neck (present in 46.6% of cases) were recognized as risk factors. Femoral neck fracture is a relatively rare complication: in most of the cases reported, it was due either to prosthesis malpositioning or inappropriate patient selection (poor bone quality).
Anteroposterior radiographs showing a femoral neck fracture in a 55-year-old man. The acetabular component is slightly steep, whereas the femoral component is well positioned (A). A femoral neck fracture occurred 55 days postoperatively (B).
Metal-on-metal (MoM) coupling is available for HR, and although it indicates a much lower wear rate than metal-on-polyethylene, its disadvantages are now under investigation after the high failure rate of large-diameter MoM THA.14
Increased serum concentrations of chromium (Cr) and cobalt (Co) metal ions,15 pseudotumors,16 peri-implant osteolysis, and tissue reactions, such as aseptic lymphocytic vascular and associated lesions (ALVAL),17,18 are elements that must be considered during implant choice.
Young patients with primary or posttraumatic hip osteoarthritis and high functional demands represent the right indications for HR. Congenital hip dysplasia, rheumatoid arthritis, and avascular necrosis of the femoral head are now recognized as relative contraindications for HR. Generally, congenital hip dysplasia is characterized by a defect in proximal femur anteversion that cannot be corrected using HR. Although Amstutz et al19,20 reported excellent results in grade I and II congenital hip dysplasia treated with HR, the current authors believe that minor deviations in the orientation of components (due to altered hip anatomy) may lead to accelerated wear and an increased failure rate.
Some good results21 have been reported when treating rheumatoid arthritis. However, it is necessary to consider that this autoimmune disease frequently affects the kidneys, which are responsible for filtration and excretion of metal ions. Therefore, Cr and Co serum concentrations may rise, and their long-term effects are still under investigation.
Some satisfactory outcomes have been reported22 in patients with femoral head osteonecrosis treated with HR. However, this disease is considered to progress over time, even below the resurfaced head, leading to inappropriate bone quality and a higher failure rate. For these reasons, some authors suggest performing HR for osteonecrosis only after at least 5 years have elapsed since the cessation of the disease. To overcome this disadvantage, mid-head resection arthroplasty23 was introduced specifically for these patients.
Osteonecrosis of the femoral head may be partially due to the exothermic cement polymerization reaction. For this reason, and considering the concerns about long-term survivorship of cemented stems in THA, cementless head components in HR are an attractive option. Some studies (although with several limitations, such as a small number of patients treated and limited surgeon experience with the operation) have reported encouraging results.24 In the future, cementless fit-and-fill femoral-side fixation may be a viable alternative to fixation with cement in MoM HR.
Materials and Methods
In the first unit of Rizzoli Orthopedic Institute, the authors performed 1417 HRs with a mean follow-up of 4.5 years. The HRs were performed using 1325 BHR (Smith & Nephew, London, United Kingdom), 59 MITCH (Stryker, Kalamazoo, Michigan), and 33 ROMAX (Medacta, Castel San Pietro, Switzerland) implants. Although the BHR was prevalently used, the authors tested different prosthetic devices with specific implant and instrumentations characteristics. The MITCH system has a shorter femoral stem compared with the widely used BHR. The ROMAX HR has an acetabular component with the presence of a notch to reduce groin pain due to the iliopsoas impingement. Considering the increasing concerns regarding MoM and the well-established performance of BHR, both in terms of clinical outcome and implant survival, the authors now perform HR only with the BHR. The MITCH is no longer available, and the ROMAX HR has been temporarily suspended by the manufacturer but not formally withdrawn from the market.
On postoperative day 1, rehabilitation started with passive mobilization. From postoperative day 2, patients were allowed partial weight bearing and walking with 2 crutches. Patients were discharged after a mean of 6 days, when they were able to go up and down stairs.
Twenty-three patients were considered to have failed treatment. The revision rate was 1.35% (18 of 1325) for BHR, 3% (1 of 33) for ROMAX, and 6.8% (4 of 59) for MITCH. Sixteen of these failures were due to femoral neck fractures, 5 to aseptic loosening or metallosis, 1 to avascular necrosis, and 1 to a pseudotumor of the iliopsoas muscle.
For the first 132 patients, mean preoperative Harris Hip Score (HHS) was 58.6 (range, 25–88). This improved to 94.4 (range, 60–100) at a minimum follow-up of 5 years (P<.0005), with an implant survival rate of 97.8% at 6 years.25
Madhu et al26 reported positive clinical results in a series of 117 HRs in 101 patients at a mean follow-up of 7 years. They reported a slightly lower survival rate compared with the current authors’ (91.5%), probably due to the longer average follow-up. Treacy et al27 reported excellent results with 144 BHRs implanted in 130 patients at a minimum follow-up of 10 years. Implant survival was 93.5%, including the septic mobilizations, and 95.5% if these were not considered. Reito et al28 reported similar positive results at a follow-up between 5 and 8 years.
Despite these encouraging results, analysis of data collected from registries shows that HR has a worse survival rate than THA in specific patient populations: females, small-diameter femoral heads (<50–54 mm), patients older than 65 years, and patients affected by specific diseases such as congenital hip dysplasia or osteonecrosis. It is therefore necessary to consider these elements as exclusion criteria for HR. If only BHR prostheses are considered, the survival rate in the registries becomes similar to that reported by Treacy et al.27 On this note, it is important to consider the details of the expertise of Treacy et al27 as surgeons well trained in HR, because they work in Birmingham, United Kingdom, where BHR was first introduced. Correct patient selection, choice of the best implant design, and exact implant positioning are paramount contributory factors for ensuring excellent survival rates.
Data from the British Commonwealth Register show a survival rate of HR at 10-year follow-up similar to or even better than that of THA in males younger than 65 years with a femoral head diameter larger than 50 mm.29 This result was also confirmed in a study from the Australian registry at 7-year follow-up.30
Although the ideal patient for HR is a young, active male affected by primary hip osteoarthritis and with a femoral head larger than 50 mm, the current authors’ experience suggests that other patients can benefit from these prostheses. In these cases, it is necessary to evaluate the advantages and drawbacks of HR, including the theoretically higher failure rate.
To meet patients’ expectations and minimize failure rate, it is mandatory that there is proper patient selection and correct implant positioning, including inclination and version of the shell, avoiding notching of the femoral neck, and varus placement of the femoral component. Considering the differences regarding either tribology or implant design (acetabular coverage angle, radial clearance, cemented or uncemented fixation) between the different HRs available, the choice of a well-established prosthetic model is crucial to achieve a good clinical outcome and long-term survival.
The RIPO data show the use of 10 different HR models in the authors’ region: BHR, ADEPT (Finsbury, London, United Kingdom), ASR (DePuy, Warsaw, Indiana), MRS (Lima, Udine, Italy), MITCH, RECAP (Biomet, Bridgend, United Kingdom), ROMAX, CONSERVE PLUS (Wright Medical Technology, Memphis, Tennessee), ICON (International Orthopedics, Hamburg, Germany), and DUROM (Zimmer, Warsaw, Indiana).31 Different survival rates correspond to different HRs, ranging from 97.1% (better) to 80.9% (worst) at 5-year follow-up. For this reason, concerns have been raised over the safety of some of these implants and the suitability of their use.
In 2010, DePuy withdrew the ASR due to a high failure rate (approximately 13% according to the National Registry of Articulation of England and Wales). The BHR is one of the most widely used HRs and has one of the lowest failure rates. Excluding the ASR, the relative risk of revision surgery of other HRs compared with the BHR is 3.3 times higher (P=.04).The high revision rate of large-diameter femoral head MoM THAs aroused concerns about the long-term survival of HRs; in particular, the possible effect of long-term chronic exposition to Cr and Co needs to be investigated.
The debris products of metal, such as microparticles, ions, and metal-organic compounds, may be responsible for pathological local or systemic disease, including pseudotumor, osteolysis, ALVAL, cobaltism, chromosomal alterations, and, hypothetically, carcinogenesis and teratogenicity. The complication of pseudotumor formation16 may create additional difficulties during revision surgery, with worse clinical and functional results.32
Metal ion serum concentrations and their behavior over time in HR patients have been investigated in the current authors’ clinic in recent years.33–35 Chromium and cobalt tend to decrease up to final follow-up at an average of 9 years postoperatively (Figure 2). At 2-year follow-up, the authors found average metal ion serum concentrations of 2.30 mcg/L (range, 0.69–7.24 mcg/L) and 1.40 mcg/L (range, 0.08–8.96 mcg/L) for Cr and Co, respectively. After 55-month follow-up, mean concentrations were 2.26 mcg/L (range, 0.49–10.47 mcg/L) and 1.13 mcg/L (range, 0.30–5.60 mcg/L) for Cr and Co, respectively. At final follow-up after 9 years, mean concentrations were 1.94 mcg/L (range, 0.56–1.19 mcg/L) and 0.98 mcg/L (range, 0.29–2.45 mcg/L) for Cr and Co, respectively. Possible differences due to patient sex were also considered, and females showed a tendency toward increased Cr ion levels compared with males. It is therefore important to pay particular attention to female patients when proposing HR.
Diagram showing metal ion serum concentrations (ng/mL) of chromium and cobalt at 2-, 5-, and 9-year follow-up in a population of patients who underwent hip resurfacing.
A recent study with an average follow-up of 11 years reported increased serum concentrations of Cr and Co ions during the first 2 years; after this period, the concentrations progressively decreased and remained stable over time.36 In another study by Van Der Straeten et al,37 it was reported that in well-positioned prostheses, the metal ion levels tended to decrease significantly over 10 years.
The current authors’ results are similar to those reported in literature,15 both in terms of ion serum concentrations and their behavior over time. Although consistent data regarding metal ion levels are not available at follow-up longer than 10 years, it may be hypothesized that in well-positioned HRs, a steady state is reached within 2 or 3 years after implantation, and low chronic ion release persists over time. The clinical meaning of this chronic release has not yet been established.
The Italian Society of Orthopedics and Traumatology (SIOT) set a Co level less than 2 mcg/L as a reference value in patients with MoM-bearing prostheses. If Co values are between 2 and 7 mcg/L, strict follow-up is recommended. In cases with Co levels higher than 7 mcg/L, further analysis using computed tomography with contrast and magnetic resonance imaging is recommended even in asymptomatic patients. De Smet et al38 suggested considering revision surgery in cases of elevated ion concentrations (Co >20 mcg/L).
The US Food and Drug Administration established that in asymptomatic patients with BHR, it is not necessary to modify the follow-up protocol without performing metal ion analysis.
The authors’ experience with HR has been extremely positive. The low revision rate and excellent functional results encouraged them to use these prostheses in young and active patients. Implant choice is especially important when dealing with a young patient population, where THA leads to a high revision rate.1 Hip resurfacing is particularly suitable for patients younger than 30 years with an estimated implant survival of 95% at 8-year follow-up (Figure 3).39,40 Recent knowledge of possible complications due to MoM coupling caused the current authors to reconsider the role of HR and suggest restrictions for its use.
Radiographs showing hip resurfacing with the ROMAX (Medacta, Castel San Pietro, Switzerland) in a 30-year-old man with good implant orientation postoperatively (anteroposterior view) (A) and at 5-year follow-up (inguinal view) (B).
Young male patients with a femoral head diameter larger than 50 mm, affected by primary or posttraumatic hip osteoarthritis, and with high functional demand are ideal candidates for HR. Data from the literature and international registries confirm that in this specific patient population, HR survival is equal to or better than THA. However, several factors play a role in determining the success of this implant, such as the precise orientation of components and the correct choice of a well-established HR model. The possible long-term effects of the debris of an MoM bearing must be controlled over time. Finally, the choice of HR must be shared with the patient, who needs to be carefully counseled about the advantages and disadvantages of the procedure.
- Smith AJ, Dieppe P, Howard PW, Blom AWNational Joint Registry for England and Wales. Failure rates of metal-on-metal hip resurfacings: analysis of data from the National Joint Registry for England and Wales. Lancet. 2012; 380(9855):1759–1766. doi:10.1016/S0140-6736(12)60989-1 [CrossRef]
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- Vendittoli PA, Lavigne M, Roy AG, Girard J. Removal of acetabular bone in resurfacing arthroplasty of the hip. J Bone Joint Surg Br. 2006; 88(6):838–839. doi:10.1302/0301-620X.88B6.18085 [CrossRef]
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- Aqil A, Drabu R, Bergmann JH, et al. The gait of patients with one resurfacing and one replacement hip: a single blinded controlled study. Int Orthop. 2013; 37(5):795–801. doi:10.1007/s00264-013-1819-3 [CrossRef]
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- Kendal AR, Prieto-Alhambra D, Arden NK, Carr A, Judge A. Mortality rates at 10 years after metal-on-metal hip resurfacing compared with total hip replacement in England: retrospective cohort analysis of hospital episode statistics. BMJ. 2013; 347:f6549. doi:10.1136/bmj.f6549 [CrossRef]
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- Hing CB, Young DA, Dalziel RE, Bailey M, Back DL, Shimmin AJ. Narrowing of the neck in resurfacing arthroplasty of the hip: a radiological study. J Bone Joint Surg Br. 2007; 89(8):1019–1024. doi:10.1302/0301-620X.89B8.18830 [CrossRef]
- Smith AJ, Dieppe P, Vernon K, Porter M, Blom AWNational Joint Registry of England and Wales. Failure rates of stemmed metal-on-metal hip replacements: analysis of data from the National Joint Registry of England and Wales. Lancet. 2012; 379(9822):1199–1204. doi:10.1016/S0140-6736(12)60353-5 [CrossRef]
- deSouza RM, Parsons NR, Oni T, Dalton P, Costa M, Krikler S. Metal ion levels following resurfacing arthroplasty of the hip: serial results over a ten-year period. J Bone Joint Surg Br. 2010; 92(12):1642–1647. doi:10.1302/0301-620X.92B12.24654 [CrossRef]
- Williams DH, Greidanus NV, Masri BA, Duncan CP, Garbuz DS. Prevalence of pseudotumor in asymptomatic patients after metal-on-metal hip arthroplasty. J Bone Joint Surg Am. 2011; 93(23):2164–2171. doi:10.2106/JBJS.J.01884 [CrossRef]
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- Amstutz HC, Le Duff MJ, Harvey N, Hoberg M. Improved survivorship of hybrid metal-on-metal hip resurfacing with second-generation techniques for Crowe-I and II developmental dysplasia of the hip. J Bone Joint Surg Am. 2008; 90(suppl 3):12–20. doi:10.2106/JBJS.H.00711 [CrossRef]
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