Implant selection in total hip arthroplasty is the prerogative of the operating surgeon and is usually based on patient age, bone quality, local anatomy, experience of the surgeon and scientific evidence. The ideal implant must achieve adequate fixation both in short and long term, must provide the patient with desired function, must have low wear and should be easy to revise should the need arise. The available implants can broadly be classified based on the method of fixation and the bearing couple. The method of fixation can be cemented or uncemented. Bearing options available include the traditional metal on polyethylene or the alternate bearing couples like crosslinked polyethylene with metal or ceramic, metal on metal and ceramic on ceramic. With total hip arthroplasty being offered to younger and more active patients the need to plan for a future revision becomes important and bone conserving options like hip resurfacing, short stems may be considered. However one must understand that until long term (minimum ten year) results of these newer implants are at least as good as the gold standard cemented THA they should not be routinely recommended. Cemented total hip arthroplasty has remained the gold standard for total hip replacement based on excellent results reported in several series and also because of long duration of follow up and easy predictable revision especially when performed early. However most of the long term follow up results of cemented THA are on older patients and although the femoral side has performed reasonably well there is a problem with the acetabular side

especially in young active patients.

Cemented Femoral Implants

 

The goals of fixation in THA can be classified as short-term and long-term. Both short and long-term goals can be achieved with good cementing technique and with any modern cemented stem design in the majority of patients undergoing total hip replacement, regardless of age, weight, activity level, or bone quality. However traditionally cemented stems have been recommended for elderly, light weight, female patients with low demand. The younger patients, heavier, high demand males have been offered cementless stems.

Although some surgeons advocate the use of cementless or cemented fixation in all patients, most surgeons attempt to choose rationally between the two fixation methodologies. It is important to match the patient with the technique most likely to give the most durable and reliable result. To choose the best candidate for a cemented femoral stem in THA, a surgeon must consider cement technique and implant design, the history and evolution of fixation in THA, patient factors, and emerging data on the impact of fixation on the surrounding bone stock.

Total Hip Arthroplasty

Figure 4.1: Collarless Polished Taper designs, note conversion of axial forces to radial compression loading cement in compression

 

Variable survivorship of the cemented stem can be attributed to evolution of cementing techniques and changes in implant designs.1-5 When evaluating the clinical results it is important to determine the cement techniques and criteria for failure. Porosity reduction of cement via vacuum mixing, plugging of medullary canal, pulsatile lavage, retrograde insertion of the cement using cement gun, cement pressurization and use of proximal and distal centralizers can ensure adequate and symmetric cement mantle. For an elderly, low-demand patient, although careful cement technique is critical, pressurization must be carried out with caution, using venting techniques to avoid cardiovascular collapse.

Two divergent philosophies exist on the optimal design of the cemented stem and the way it achieves fixation at the implant cement interface. These are the tapered slip philosophy of which the original flat back Charnley with anteroposterior taper is the prototype. This was followed by the double tapered EXETER® and the triple tapered C STEM® designs. The collarless tapered stems allow for controlled subsidence through the cement mantle thereby converting the shear stresses at the implant cement interface into radial compressive forces and thus favourably loading the bone and preventing stress shielding and also protecting the cement bone interface from loosening (Fig. 4.1). The polished surface ensures that there is no real bonding between the implant and cement.

The benefit of tapered stems was not initially appreciated despite the good long-term results. This led to the development of the composite beam philosophy with introduction of flanges and surface structuring to enable fixation of the implant to the cement and resist subsidence. This leads to shear stress both at implant cement and cement bone interfaces (Fig. 4.2). Hence it is critical to achieve good bond between the implant and cement to ensure long-term success with this design.

Bone quality is an important determinant of fixation technique. Dorr et al6 developed a

classification of bone quality by correlating radiographic appearance of bone and cortical index with bone mineral density and provided a widely used tool for matching fixation to patient. Strong, dense bone with thick cortices (Dorr type A-B) was thought to be a better substrate for cementless fixation, whereas more osteoporotic bone (Dorr type B-C) was thought to provide the ideal substrate for optimum cement technique.

In the Dorr type A, champagne flute femur in which the diaphysis is narrow a cemented stem of sufficient size with adequate offset will not fit without reaming all cancellous bone and removing the endosteum. In this instance, the cement has no microstructure into which to interdigitate, the shear strength of the bone cement interface is compromised. A cementless stem would be better in these patients.

Implant Selection in Total Hip Arthroplasty

Figure 4.2: Composite beam stems transfer stress at the tip of the implant, are subject to shear stresses and lead to stress shielding proximally

 

Elderly patients with Dorr type B femur are ideal candidates for cemented stem. However, attention to surgical technique, proper cementing and choice of stem design is critical to ensure long-term success.

The Dorr type C, stovepipe-shaped femur is poorly suited to a cementless stem. A large cemented stem is required to fill this canal, and even gentle preparation can easily denude the endosteum of remaining cancellous structure. Even when the cancellous bone survives, the severe osteopenia that characterizes this bone type may compromise cement intrusion and interdigitation. A high incidence of loosening has been documented when cementing into this envelope.7 Primary impaction allografting or compaction of the native cancellous bone may facilitate cement fixation in this bone type.8

The use of cemented or cementless fixation in patients younger, high demand patients is the subject of controversy. These patients are expected to outlive any implant and higher activity levels may shorten the life expectancy of an otherwise durable prosthesis. First generation cementing techniques have produced poor results in young active patients.4 This led to the development of cementless implants with potential for biologic in-growth. However improved cementing techniques have resulted in better outcomes even in younger patients owing to improved cement uniformity and mantle thickness.9,10 Also the positive bone remodelling reported with some of the collarless polished taper designs and potential for cement in cement revision in cases of failure has made these viable options in young patients. However problems of cement removal during revision must be considered.

Cemented Acetabulum

 

Most studies of cemented THA show that longevity of cemented acetabulum is more of a problem than cemented femur. This is especially true for the younger patients (<50 years).4,6 Also decreasing use of cemented hip arthroplasty makes it difficult for the younger orthopedic surgeons to be familiar with cementing technique for cemented acetabulum. However the cemented acetabulum when performed properly provides a durable and cost effective solution especially for the elderly low demand patients. Paradoxically even in younger patients cemented acetabulum can provide an easier and more predictable revision option once failure occurs. Furthermore the wear rates of the cemented all polyethylene cup have been superior to the wear rates of metal backed cups (less than 0.1 mm/year).6 Failure to achieve satisfactory initial cement bone interlock is the cause of early failure. Cemented acetabulum is contraindicated in patients with excessive acetabular bleeding after reaming, weak cancellous bone as in inflammatory arthritis, protrusio deformity and with extensive cyst

formation in the acetabulum. 59

Cementless Femoral Component

 

The development of cementless implants and the concept of osseointegration is an offshoot of the late failures of cemented femoral implants due to aseptic loosening especially in young and active patients.

Total Hip Arthroplasty

Modern cementless implants can be classified as non modular and modular. The non modular implants can be extensively coated (Fig. 4.3)or proximally coated (Fig. 4.4), can be anatomical, cylindrical or tapered, short or standard length. Porous coating, hydroxyapatite coating, plasma spray with or without tricalcium phosphate and grit blasted designs are available. All these have shown excellent long-term results namely AML®, CORAIL®, BICONTACT® and ZWEYMULLER®. Traditionally uncemented implants were reserved for younger active patients particularly those with good bone stock or Dorr type A or B femora. Few studies have demonstrated no adverse effects of using cementless implants in elderly patients and those with type C femurs.11 This will make operative procedure faster and eliminate the risk of cement monomer induced hypotension. However, the risk of intraoperative fractures must be kept in mind while using cementless implants in elderly patients with poor bone quality.

Anatomic implants (PCA) due to modular mismatch, endosteal irritation and lack of bony ingrowth resulted in high incidence of symptomatic thigh pain.12

The cylindrical fully porous coated stems like AML® have shown excellent clinical results over twenty years.13 However problems of proximal stress shielding, anterior thigh pain and difficult revision prompted the development of proximally coated stems.13 The second generation of proximally porous coated stems provide circumferential proximal porous coating and aimed to achieve metaphyseal biologic fixation, thereby reducing proximal stress shielding, reduce incidence of thigh pain and distal osteolysis. Midterm data have validated these assumptions but longer follow up is needed to see if these benefits remain in the long-term.14

Figure 4.3: Extensively porous coated stem

 

Figure 4.4: Example of proximally coated tapered stem

 

Implant Selection in Total Hip Arthroplasty

Figure 4.5: Proximally coated tapered cementless stems, reduces stress shielding and thigh pain

 

Tapered uncemented stems (ZEYMULLER®, CLS®, SYNERGY®, SUMMIT®) further reduce the risk of anterior thigh pain compared to cylindrical stem designs. The initial three point fixation followed by in/on growth results in a graduated load transfer to the proximal femur thereby reducing stress shielding and the reduced diameter of the distal part of the stem reduces the incidence of thigh pain15-17(Fig. 4.5).

Poor correlation between proximal and distal femoral anatomy has been demonstrated in cadaver studies.18,19 While the nonmodular femoral implants may suffice in majority of the patients these may not be ideal for patients with deviations from normal anatomy like developmental dysplasia of the hip and previously osteotomized femur with abnormal version. The use of modular stem designs (S- ROM®) allows the surgeon to individualize the proximal and distal implant geometries to optimize component fit and fill and achieve optimal stability irrespective of the femoral geometry. In addition the ability to adjust the neck length, offset and version intraoperatively (with use of modular neck adaptors: ML KINECTIV®, METHA®) helps in recreating a functional, mechanically stable hip with appropriate soft tissue tension. Three main concerns include fretting, dissociation and breakage at the modular interfaces. Although these have not proven valid with either clinical or laboratory studies long term follow up is imperative and the use of modular implants in routine total hip arthroplasty cannot be recommended.

Short neck preserving stems have been around since 1985 with the Mayo hip (Bernard F Morrey) having excellent long term track record.20,21 Not all short stems are similar. Five designs are currently available. These include stems inspired by the Mayo hip (METHA®, NANOS®), short, bulky but not neck preserving stems like PROXIMA®, neck preserving curved stems (CFP: Pipino), shortened tapered stems (taperlock microplasty, trilock) and the so called neck pods like the BMHR and Silent hip.

The role of short stems in total hip arthroplasty is unclear. The obvious comparisons are with hip resurfacing and modern cementless tapered femoral stems with proximal load transfer. While hip resurfacing is bone preserving it can hardly be said as soft tissue preserving, usually the incision and extent of soft tissue dissection needed for exposure is more than that seen in conventional THA. Furthermore resurfacing is restricted to metal on metal articulation which has its own set of problems like hypersensitivity, ALVAL, problems of use in young women of child bearing age and concerns about elevated serum metal ions.

The short metaphyseal fixing implants are bone preserving, they can be implanted with a minimally invasive approach and are can be used with a variety of tribological couplings. As compared to the traditional femoral stems the short stem implants are more physiological

Total Hip Arthroplasty

i.e. proximal loading, do not give rise to thigh pain and are easy to revise to traditional hip replacement. Hence the short metaphyseal loading implant serves as a bridge between hip resurfacing and standard cementless stems and is suitable in young arthritic patients with good quality bone.

Cementless Acetabulum

Long-term follow up of cemented acetabular component has shown radiologic loosening rates between 24-60% in multiple series with 10-25 year follow up.4,6,22-24 Benefits of improved cementation techniques have not been demonstrated on the acetabular side.4,6 Also cemented acetabular reconstruction is technically demanding and does not allow for intraoperative flexibility of changing the cup position and modularity. This led to the development of the cementless acetabular cups with potential for biologic in growth. While choosing a cementless cup one must consider bone quality, the cup design, type of coating and long-term results of the design philosophy.

Most of the modern acetabular components have a hemispherical or modified hemispherical design and are made of cobalt chrome, commercially pure titanium or titanium based alloy (Fig. 4.6A). The most common types of coatings include sintered cobalt chrome beads with or without hydroxyapatite coating, titanium fiber metal, cancellous structured titanium and plasma sprayed titanium. Two basic fixation philosophies include line to line reaming with supplemental screw fixation and under reaming between 1-4 mm and press fit fixation with or without supplemental fixation (Figs 4.6B and C). Problems with screw fixation include risk of neurovascular injury, fretting and corrosion between the screws and shell, wear of polyethylene against the screw heads, migration of polyethylene wear particles along the screw tracks and holes and areas of unsupported polyethylene due to the screw holes. Press fit acetabular components without screw holes have the potential advantage of increasing surface area for bone in growth and polyethylene support. There is no risk of neurovascular injury due to screws, there is no fretting between screws and metal shell and a potential pathway for polyethylene particles along the screw holes can be eliminated.

Modular cementless acetabular fixation offers distinct advantages which include intraoperative flexibility, potential for biologic in growth and ability to exchange the poly-

Figures 4..6A to C: (A) Plasma sprayed acetabular cup with screw option (B and C) Use of cementless cup with and without screws

 

Implant Selection in Total Hip Arthroplasty

ethylene liner without disturbing the biologic bone implant interface in cases of polyethylene damage. However continued clinical use has demonstrated several distinct disadvantages including higher rate of polyethylene wear probably related to both articulating and backside wear, thinner poly, poor locking mechanism and poor cup designs, osteolysis behind the cup and along screw holes and in some cases polyethylene dissociation and catastrophic poly wear.25,26 Most of the available studies on cementless cups were with poorer first generation designs and metal on polyethylene articulation. Also the studies are retrospective, poorly controlled with respect to the patient demographics, femoral implant and head size.

The longest series on porous coated cups is fifteen years27 still 10 years lesser than

published results for the cemented cups. The final verdict on cementless cups is yet to be decided but with better cup designs, coating, improved locking mechanisms and adequate thickness of highly conforming polyethylene and improved articulation via alternate bearings hopefully the long-term performance of cementless sockets will improve.

Both cemented and uncemented fixation methods have shown good medium to longterm results but the limiting factor to long-term success is polyethylene wear and wear induced osteolysis. While conventional metal on polyarticulation may be appropriate for the elderly low demand patients there is a need for a better bearing couple with low wear for the young and more active patients. This has lead to the reintroduction of hard on hard (metal on metal and ceramic on ceramic) bearings and also led to advances in the existing hard on soft bearings. All bearing couples have their strengths and potential weaknesses which must be understood before offering it to individual patients.

The wear of cobalt chrome alloy against UHMWPE is the standard against which the wear of all other components is judged.

Conventional UHMWPE

 

Most UHMPE components are machined by converting the powdered form into solid form. This can be by ram extrusion (rods), or compression moulding (sheets) or direct compression moulding in the shape of the final component. The final step in the manufacturing process is sterilization which is usually with gamma radiation (2.5-4 mrad) in air. Gamma radiation leads to cross linking of polyethylene from interaction of free radicals. Laboratory and clinical studies have shown improved wear resistance of gamma sterilized polyethylene as compared to UHMWPE sterilized using nonionizing radiation (ethylene oxide or gas plasma). However the potential for oxidative damage due to gamma sterilization in air due to residual free radicals was recognized and some manufacturers started gamma sterilization in inert atmosphere (nitrogen, argon and vacuum).

The recognition that cross linking reduces wear and that oxidative damage due to free radicals can compromise wear properties led to the development of highly cross linked poly.

Highly Cross Linked UHMWPE

Highly cross linked poly is manufactured by sterilization with higher doses of radiation to enhance cross linking and heating which reduces free radicals. The key variables to be understood are the radiation dose and process of heating. Heating above the melting point of polyethylene is called remelting and below the melting point is annealing. When making a choice between the different highly cross-linked polyethylenes the compromises inherent to their properties must be considered. Remelted highly cross-linked polyethylenes have lower mechanical and fatigue properties but with no free radicals, while in annealed highly cross-linked polys the mechanical and fatigue properties are maintained at the cost of retaining some free radicals.

Laboratory studies have shown significantly lower wear rates with highly cross-linked poly as compared to conventional poly.28 Early clinical results also indicate in vivo wear reduction with these newer materials.29-31 A wear reduction up to 90% has been shown

with highly cross-linked poly articulating with cobalt chrome metal balls as compared to conventional polyethylene.28 Similar wear reduction has been shown with ceramic ball on highly cross-linked poly as compared to conventional polyethylene.32 This allows for using large diameter femoral heads with highly cross-linked polyethylene. The advantage of large diameter head is a reduction in the incidence of impingement and dislocation. Unlike hard on hard bearings polyethylene is more forgiving and accommodates for some degree of implant malpositioning. This makes highly cross-linked poly with either a metal or ceramic head an attractive and safe option for young and active patients undergoing total hip arthroplasty.

Metal on Metal

 

Polyethylene wear induced osteolysis created a renewed interest in metal on metal bearings. Currently available metal on metal designs are modelled on first generation metal on metal designs which were found to be functioning well after 20-30 years in vivo. Factors to be considered while choosing a metal on metal device include type of cobalt chromium alloy used (wrought or cast), carbide content (low or high), cup design (hemispherical or sector) and type of coating (sintered cobalt chromium beads with or without hydroxyapatite coating, titanium spray). Also bearing size, clearance, sphericity and surface finish determine the wear characteristics of metal on metal bearings. Laboratory studies have shown a 200 fold reduction of volumetric wear with metal on metal bearings as compared to conventional polyethylene. Currently metal on metal bearings are being used as part of hip resurfacing or conventional total hip arthroplasty using large diameter metal on metal couple over cemented or cementless stems. The advantages of metal on metal include large femoral head, low wear and osteolysis33 and amenability to hip resurfacing.

Ten year follow-up studies with hip resurfacing using BHR have shown survival of 93.5% with revision as end point. The results are even better in male patients (98%) and with femoral components more than 50 mm in size (97.7%).34 The revision risk increased by

1.14 times/year with every 4 mm decrease in the component size and 5.78 times/year in female patients.34 Hip resurfacing is a viable alternative in patients who are categorically at higher risk of failure with total hip replacement with favorable proximal femoral anatomy and sufficient acetabular bone stock. This typically includes young adult men with premature osteoarthritis. Resurfacing can also be considered in patients with sub trochanteric deformity which precludes the use of stems. Contraindications to hip resurfacing include limb length discrepancy and offset problems, absent head neck junction, avascular necrosis, severe osteoporosis and loss of more than 30% of femoral head surface.

Continued clinical use of metal on metal hips has shown failure due to unexplained reasons.35 This may be related to higher metal ion concentration (due to component malposition)36 and delayed hypersensitivity reactions. Soft tissue lesions have been noted on MARS (metal artefact reduction sequence) MRI of patients with painful metal on metal hips and have been called as ALVAL (acute lymphocytic vasculitis associated lesion).37 Also the long-term effect of elevated metal ions is poorly understood. Metal on metal is contraindicated in women of child bearing age and patients with renal problems.

Long-term results with large diameter metal on metal total hip replacement are not available. Concern exists regarding the so called trunionitis, between the metallic head, sleeve adaptor and trunion leading to increased risk of fretting and higher metal ion concentrations in large diameter metal on metal total hip arthroplasty. Although hip resurfacing represents an attractive option for young adult males one must understand that the surgical technique is more technically demanding than a standard THR and the bearing less forgiving.

Ceramic on Ceramic

 

The first and second generation ceramic on ceramic bearings were hampered by poor implant design and poor mechanical properties of the ceramic itself. Substantial improvements in

Implant Selection in Total Hip Arthroplasty

implant design, surgical technique and quality of alumina components have led to resurgence in use. Newer alumina ceramic design options have a harder, more resistant surface leading to improved tribologic properties because of its low surface roughness because of low grain size.38 With high density, high purity, and small grains, these designs create less debris, have a lower coefficient of friction, have improved fracture toughness, and are more hydrophilic than either polyethylene or metal.38-40 Hip simulator studies have documented wear rate for alumina on alumina couplings to be between 1 and 2 microns/million cycles which is lower than the metal on metal coupling. Furthermore there is no risk of metal ions and the particles are more biologically inert. This potentially eliminates the risk of osteolysis. However like metal on metal bearings ceramic on ceramic is very technique sensitive and does not tolerate implant malposition. Edge loading due to vertical malposition of cups can lead to stripe wear and in some cases catastrophic failure.

The concern of alumina articular surfaces has been the risk of fracture, which is low with third-generation ceramics but substantial when it occurs.41 The patient must undergo another operation, and the results of the revision arthroplasty can easily be compromised because of retained ceramic fragments. These fragments can enhance wear, further the development of osteolysis, and increase the need for another revision surgery.41 The risk of ceramic femoral head fracture is now considered less than the risk of femoral stem fracture.42 A review of more than 500 000 current-generation alumina ceramic femoral heads indicated a fracture rate of 4:100 000 or 0.004%. This rate is significantly lower than that of femoral stem fracture, which is approximately 270:100 000 or 0.27%.42 However to achieve these low rates one must avoid impingement, femoral head should be carefully placed on a clean taper, perfect seating of the ceramic socket in the acetabular shell must be ensured and taper should not be reused for a ceramic head during revision. Squeaking has been reported with both ceramic on ceramic and metal on metal hips but the incidence is relatively low (1 in 700).

Recent research has been on the development of aluminium Zirconium composite to retain the best properties of both. Currently used ceramic is Biolox Delta (Ceramtec, Plochingen, Germany) which is a transformation-toughened and platelet-reinforced alumina containing 75% alumina, 24% zirconia and 1% chromium oxide and strontium oxide. This exhibits increased strength and wear resistance compared to alumina coupling.

All the modern bearings produce far less wear than the conventional gamma irradiated polyethylene/metal articulation and therefore reduce the risk of particle induced osteolysis. For young and active patients hard on hard bearings produced less wear particles than metal/highly cross-linked poly. However, cup placement is critical to prevent impingement, excessive wear and fracture (especially ceramic on ceramic).

Femoral Heads

 

Femoral heads currently available are made of either cast or forged cobalt chrome, ceramic (aluminium or aluminium Zirconium composite) and oxidized Zirconium (oxynium). The original concept of low friction arthroplasty employed 22.2 mm heads against polyethylene. This ensured adequate thickness of the polyethylene and low volumetric wear rates. However the diameter of femoral head is directly related to the range of motion and stability of the hip. The 22 mm heads had less range of motion and higher risk of instability. The relative risk of dislocation with 22 mm head is 1.7 compared to 1.3 with 28 mm head and 1 with 32 mm head. The head size was subsequently increased to 28 mm as this as thought to be a right balance between linear and volumetric wear. The acetabular component size is a limiting factor for the femoral head in conventional bearings to ensure adequate polyethylene thickness. This implied that young and active patients with smaller acetabular sizes typically less than 52 mm had to have a 28 mm head. With the advent of modern bearings larger diameter heads can be used even with smaller diameter acetabulae. This allows the use of 36 mm femoral heads with 52 mm acetabular shells in ceramic on ceramic and with 54 mm

Total Hip Arthroplasty

Figure 4.7: Multiple head options available

 

shells in ceramic or metal on highly cross-linked polyethylene. A large range of head options are currently available (Fig. 4.7).

With the advent of monoblock ceramic cups like DELTA MOTION®, PLASMA® cup

36 mm femoral head can be used with 46 mm and 48 mm acetabular cups respectively (Figs 4.8 and 4.9). These cups are made of preassembled biolox delta ceramic liner and

Figure 4.8: Mono block ceramic cups, note special introducer needed to insert these, also large diameter of femoral head 44 mm in this case

 

Figure 4.9: Short metaphyseal stem with monoblock ceramic cup, note use of mono block cup allows use of 36 mmfemoral head with acetabular size of 48 mm

 

titanium shell allowing for use of significantly thinner ceramic and titanium shell than seen in traditional systems. The resultant flexibility of the construct allows for adaptability to the form of ceramic liner taper resulting in improved contact between the two components and improved load transfer in use. Also the residual tensile (hoop) stresses in the titanium shell allow the ceramic liner to be held in compression, thereby maintaining each material in its ideal load state. However, long-term follow up is needed to routinely recommend their use.

Implant Selection in Total Hip Arthroplasty

Conclusions

 

1. Both cemented and cementless fixation techniques are successful but have their respective liabilities. Both technologies have a role, and the choice should be based on how effectively the particular fixation technology can be applied to the individual patient and by the individual surgeon, and how well the fixation philosophy satisfies the needs of the individual patient. Individual design philosophies must be understood and the technology must be applied skillfully, meticulously employing the details essential to the success of the chosen technique.

2. Metal on highly cross-linked polyethylene is emerging as a safe and durable bearing even in young and active patients.

3. Hard on hard bearings reduce the wear rate and therefore the incidence of particle induced osteolysis. Alumina on alumina has the lowest wear rates for all available bearing couples and has no concern for metal ions unlike metal on metal bearing. The problems with earlier generation ceramics have been successfully addressed and ceramic on ceramic represents a good option for total hip arthroplasty in active patients with high life expectancy. Accurate component positioning however is mandatory to ensure successful outcome.

4. Hip resurfacing is a viable alternative to conventional total hip arthroplasty in young active, male patients with osteoarthritis. However owing to unexplained failures, ALVAL, concern regarding high metal ions the use of large diameter metal on metal total hip arthroplasty cannot be recommended with the available evidence.

5. Short stems can provide a bone and soft tissue sparing alternative to hip resurfacing with further benefits including amenability to use with multiple bearing options.

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