Bone cement: perioperative issues, orthopaedic applications and future developments.
Abstract: Bone cement has been increasingly used in orthopaedic surgery over the last 50 years. Since Sir John Charnley pioneered the use of polymethylmethacrylate cement in total hip replacements, there have been developments in cementing techniques and an expansion in the number of orthopaedic procedures that use cement. This review covers the perioperative issues surrounding bone cement including storage, cementing techniques and complications. It also discusses specific orthopaedic applications of bone cement and future developments.

KEYWORDS Bone cement / Polymethylmethacralate / Orthopaedics / Developments Provenance and Peer review: Unsolicited contribution; Peer reviewed; Accepted for publication June 2011.
Subject: Implants, Artificial (Usage)
Prosthesis (Usage)
Orthopedic surgery (Health aspects)
Bone cements (Usage)
Authors: O'Dowd-Booth, Christopher John
White, Jonathan
Smitham, Peter
Khan, Wasim
Marsh, David R.
Pub Date: 09/01/2011
Publication: Name: Journal of Perioperative Practice Publisher: Association for Perioperative Practice Audience: Academic Format: Magazine/Journal Subject: Health; Health care industry Copyright: COPYRIGHT 2011 Association for Perioperative Practice ISSN: 1750-4589
Issue: Date: Sept, 2011 Source Volume: 21 Source Issue: 9
Product: SIC Code: 3842 Surgical appliances and supplies
Geographic: Geographic Scope: United Kingdom Geographic Code: 4EUUK United Kingdom
Accession Number: 272168039
Full Text: Bone cement was originally developed in 1943 for use in the field of dentistry (Kuhn 2005). There are now a number of different types of bone cement and these vary in their biomechanical properties. The first and most commonly used bone cement is polymethylmethacrylate (PMMA) acrylic cement. In 1958, Sir John Charnley first used PMMA cement in orthopaedics to create a more secure fixation of the femoral and acetabular components in a total hip replacement (Charnley 1960, 1970). The interface between the stiff metal implant and the more elastic bone was referred to as the weak link due to the difference in mechanical properties, resulting in loosening over time (Gupta et al 2006). PMMA cement has an elasticity value between that of implant and bone, allowing for additional shock absorption and a more even distribution of contact forces between the two materials (Webb & Spencer 2007). Figure 1 shows the radiograph of a cemented total hip replacement. Bone cement acts more like a grouting agent than an adhesive 'cement' (Gupta et al 2006).

PMMA has proved to be one of the most versatile and lasting biomaterials in orthopaedics having an important role in joint replacement, as well as spinal and tumour surgery (Webb & Spencer 2007). It is by far the most common choice of bone cement due to its workability and is widely used in orthopaedic theatres (Wang & Dunne 2008). The addition of chlorophyllin gives bone cement a distinctive green colour, which aids visualisation and correct placement, and allows for a better distinction between the cement and surrounding bone (Hendriks et al 2004). Barium sulphate is also added to allow visualisation on postoperative radiographs and to assess the quality of the cement mantle (Figure 1).

Perioperative issues surrounding bone cement

Storage

PMMA cement is packaged in the form of a liquid monomer and a powder copolymer constituent. These are mixed together at the time of use and undergo polymerisation to form a viscous material which can be moulded and inserted into the required location (Chatterjee & Blunn 2007). It is

vital that the cement curing time is known so that it can be manipulated and inserted before the cement becomes unusable. From the initial mixing of the monomer and activator the time should be monitored. The transition of PMMA from a liquid to a useable paste is quick, and it sets as a solid about nine minutes after mixing (Turner et al 1981). International Standard Organization (ISO) standard 5833 set a limit of 3 to 15 minutes for the working time of bone cement. The storage conditions of these constituents affects the structural properties of the cement, and it is important to ensure storage at an ambient temperature of around 21[degrees]C (Lewis & Son 2008). Cement constituents stored at warmer temperatures set quickly and can cause procedural difficulties.

[FIGURE 1 OMITTED]

When the powder copolymer has been sterilised with ethylene oxide gas, it is thermally stable and available for use immediately. Gamma-irradiated powders however should be stored for a period of at least three weeks in an ambient environment to allow the development of increased stability post-sterilisation (Lewis & Son 2008).

Cementing technique

A satisfactory interface between bone and cement is vital to prevent aseptic loosening, and cementing technique can directly influence the outcome (Ota et al 2005). The process for cement preparation in hip replacement surgery has undergone several generations of development. First generation cementating technique in which the cement was finger-packed, lead to radiographic evidence of aseptic loosening in 19-40% of cases (Ota et al 2005). Results improved with the development of second generation techniques during the 1970s. These included intramedullary canal preparation with pulsatile lavage, use of a cement restrictor, and the introduction of a cement gun to allow a more even distribution of cement, greater pressurisation and better penetration into bone interstices (Ota et al 2005). This promoted a strong bone-cement interface with good stability and greater fixation strength (Jaeblon 2010). Third generation techniques that are currently employed involve the vacuum mixing of cement to minimise any air inclusion and intramedullary pressurisation of cement with a proximal femoral seal (Ota et al 2005). This achieves an adequate level of cement penetration and reduces the degree of cement porosity that may compromise the cement mantle. These techniques have also benefitted the fixation of acetabular components in hip replacement surgery although the use of cemented sockets remains a controversial point and current trends favour an uncemented approach (Corten et al 2009).

Complications

Bone cement implantation syndrome (BCIS) poses a significant risk of morbidity and mortality during cemented procedures. It is usually associated with total hip arthroplasty although it is not restricted to this procedure. The clinical features may include hypoxia, hypotension, cardiac arrhythmias and cardiovascular collapse. There is a wide spectrum of activity that ranges from a non-fulminant reaction characterised by a significant, momentary drop in arterial oxygen saturation and systemic blood pressure, to a profound intraoperative compromise in cardiovascular function and potential arrhythmias, shock and cardiac arrest (Donaldson et al 2009). Problems typically occur shortly after cement insertion; hypotension is common, independent of the anaesthetic technique used and is worsened if there is any degree of hypovolaemia present.

The aetiology and pathophysiology of BCIS is poorly understood. Initial theories proposed direct toxicity of the cement monomer methyl methacrylate (MMA) on the cardiovascular system. Current thinking suggests that the changes observed in BCIS are secondary to the release of microemboli into the systemic circulation secondary to cement pressurisation. These emboli have been shown to include molecules of fat, marrow, cement, air and bone (Donaldson et al 2009). Due to the serious nature of BCIS, the anaesthetic team should be informed prior to cement insertion to ensure frequent and diligent monitoring of blood pressure and cardiorespiratory function. The postoperative team should also be aware of the potential for persistent hypotension, pulmonary emboli, pulmonary hypertension and anaphylactoid reactions (Memtsoudis et al 2007).

Thermal injury poses a risk to both the patient and theatre staff. The polymerisation reaction generated during cement formation is exothermic and temperatures can reach as high as 110[degrees]C (Meyer et al 1973). This can result in tremendous heat transfer to the surrounding tissues with the potential to cause thermal damage to skin, bone and surrounding neurovascular structures (Mjoberg et al 1984). Should the patient or member of the surgical team be exposed such temperatures, thermal damage can result, with less than one second needed to cause transdermal necrosis when exposed to surface temperatures exceeding 70[degrees]C (Dunne & Orr 2007).

PMMA cement is used extensively in orthopaedics, particulary joint arthroplasties, and therefore all members of the surgical team will have a level of occupational exposure to its component monomer methyl methacrylate (MMA) (Leggat et al 2009). Combined inhalational and contact exposure can lead to problems with hypersensitivity, asthmatic reactions, local neurological symptoms, and localised irritation/dermatological reactions. The compound is not currently thought to pose a carcinogenic risk under conditions of normal use. To reduce these potential risks, room ventilation and airflow should be optimised, direct contact should be avoided and latex gloves should be inspected for possible compromise as a result of cement contact (Leggat et al 2009).

Orthopaedic applications of bone cement

Joint reconstruction

Joint reconstruction is the most common orthopaedic application of bone cement. A wide range of procedures utilise cement including hip, knee and shoulder arthroplasties (Schlegel et al 2011). Bone cement is used because of its ability to augment the interface between bone and implant, and to facilitate the transfer of forces. This accounts for the excellent long-term survival of cemented prostheses (Wang & Dunne 2008). Clinical studies and joint registries data strongly support the continued use of cemented prostheses in total hip and knee replacements (Webb & Spencer 2007). According to the National Joint Registry, cemented prostheses comprise 36% of total hip replacements and 83% of total knee replacements respectively in the UK (Hooper et al 2009, Ellams et al 2010). There has been a recent trend towards uncemented techniques for total hip arthroplasty, the reasons for which are not fully understood (Dunbar 2009). There is evidence that cemented techniques are associated with reduced pain postoperatively and improved mobility with no significant difference in perioperative complications (Parker et al 2010). The use of bone cement is likely to continue to play an integral role in primary arthroplasty for the foreseeable future (Dheerendra et al 2010).

It is inevitable that joint arthroplasties will eventually require revision and the use of bone cement adds an extra dimension to the complexity of this procedure. This difficult and time-consuming process requires optimal visualisation of the prosthesis and bone-cement interface (Takaqui et al 2009). Cement removal usually involves curettage through the use of flexible and narrow osteotomes, chisels, high-speed burs and reamers. Ultrasonic extraction systems (e.g. OSCAR, orthosonics) and laser techniques have also been developed to improve cement removal (Birnbaum & Gutknecht 2010). Should these techniques fail or be unavailable, an osteotomy may be needed. In the rare situations that this is required there are associated complications of bone loss, cortical perforation and further fracture (Goldberg et al 2007). The addition of chlorophyllin or methylene blue to the PMMA cement improves visualisation and facilitates cement removal (Graves & Sands 2007).

PMMA cement is also used in two-stage revisions for infected hip and knee arthroplasties. In these cases antibiotic-loaded cement spacers are used. These spacers can either be static or mobile. Static spacers are the traditionally preferred option but mobile, articulating spacers are increasingly being used due to their ability to allow limited weight bearing and hence to facilitate mobility and reduce bone loss (Jacobs et al 2009). The use of these spacers allows local antibiotic delivery though impregnated PMMA cement. Broadspectrum antibiotics such as vancomycin and tobramycin are commonly used however this can potentiate the development of antibiotic resistance and continued infection (Fink 2009). It is therefore advisable to obtain antibiotic sensitivities prior to spacer insertion (Fink 2009).

Spinal surgery

Vertebral crush fractures are one of the most common fractures associated with osteoporosis affecting 20% of those aged over 70 years. Bone cement has been used in the treatment of these fractures (Ghofrani et al 2010).

Percutaneous vertebroplasty and kyphoplasty both aim to stabilise the vertebral body and achieve pain reduction (Dionyssiotis 2010). Percutaneous vertebroplasty is a procedure that involves the injection of PMMA cement into the vertebral body (Hu et al 2006). Kyphoplasty differs in that before the PMMA cement is injected, a balloon is inserted and inflated inside the vertebral body. The aim is to attempt to decompress any existing bone so as to create a larger cavity to inject the cement (Dionyssiotis 2010). This leads to some correction of the deformity and fracture stabilisation (Hu et al 2006). These procedures are performed under radiological control and the cement contains additional opacifiers such as tungsten or barium sulphate, added to aid with radiological monitoring (Prime et al 2010).

Lowering the temperature of the cement prior to insertion has been shown to lead to a significant increase in working time. Cooling the cement-filled syringes to 12[degrees]C increases the working time by more than 30 minutes (James & Connell 2006). Chavali et al (2003) found that cooling the cement to around 0.5[degrees]C can extend its injectability to over two hours. This does however reduce cement viscosity and increases the chance of cement leakage. It is therefore advisable to wait for a sufficient period of time until a suitable viscosity is achieved (James & Connell 2006).

There are a number of disadvantages to using PMMA cement to correct and stabilise vertebral crush fractures. The rigidity caused by the cement can lead to further fractures in the adjacent vertebral bodies due to a difference in biomechanical properties between adjacent bodies (Berlemann et al 2002). There is also a risk of thermal damage to surrounding neurovascular structures as the cement undergoes polymerisation (Ghofrani et al 2010).

Oncology

Bone cement has a significant role in the management of tumours affecting the bone. It is used in massive prostheses that are employed in wide excision, requiring a large portion of bone and joint to be removed. Bone cement also plays a vital role in the treatment of giant cell tumours of bone, where it has been used since 1969 as a packing material after a curettage procedure (Remedios et al 1997). The PMMA cement polymerisation process is exothermic and leads to the destruction of any remaining tumour cells in the cavity. The cement also provides stability to the bone by filling the cavity. It has been shown that the use of cement gives greater mechanical properties than a bone graft in the early stages (Remedios et al 1997).

The principles behind the technique of vertebroplasty or kyphoplasty can also be applied for the treatment of pathological fracture of the vertebral body (Chi & Gokaslan 2008).

Additional applications

Antibiotics were incorporated into PMMA as early as 1970 by Buchholz and Engelbrecht, who used gentamycin to aid in the management of infected arthroplasty (Webb & Spencer 2007). Antibiotic-impregnated bone cements are now commonly used for the prophylaxis and management of infected prostheses, osteomyelitis and infected non-union in conjunction with systemic antibiotics (McKee et al 2010). In total hip replacements, gentamicin-loaded PMMA cement has been shown to reduce deep infection (Josefsson et al 1990). In two-stage hip revision procedures for infection, antibiotic-loaded cement insertion after the first stage results in a 40% reduction in infection (Parvizi et al 2008). Antibiotic-loaded cement beads have also been used in the management of chronic non-haematogenous osteomyelitis to provide localised therapy (McKee et al 2010).

Bone cements are also used in situations where there is a decrease in bone quality, such as in osteoporosis. Augmentation of cancellous bone screws would be one such application, due to the stresses present at the screw-bone interface. Cement is used to increase stability and improve fixation (Al-Rasid et al 2010).

Future developments

Cement contracts as it cools at the end of polymerisation, potentially leading to compromise of the bone-cement interface and aseptic loosening (Webb & Spencer 2007). These factors have generated interest in alternative options. Glass ionomer cements have been used in dental surgery since the 1970s and undergo nonexothermic reactions during curing (Hatton et al 2008). This avoids the risks of cement contracture (Wood & Hill 1991). Unlike PMMA cement, they are adhesive to both bone and metal surfaces resulting in enhanced mechanical interlocking with bone and metal (Hatton et al 2008). Their mechanical properties however are not as ideal as PMMA cement, and they release ions into the biological environment (Hatton et al 2008).

Calcium phosphate cements are also available and have attracted a great deal of attention due to their bioactivity and ability to self-set in vivo (Ginebra et al 2006). Calcium phosphate has a number of advantages over PMMA in terms of biocompatibility and osteoconductivity, and its biomechanical properties are continuing to be improved (Stadelmann et al 2010). Its clinical use so far has been limited to revision operations where a graft layer with bioresorbable cement is desired (Speirs et al 2005).

There remains potential for expansion in the use of cement as a delivery medium for potential therapeutics, including antibiotics (Webb & Spencer 2007). Through the use of calcium phosphate cements it may be possible to impregnate anti-inflammatory drugs, anti-cancer agents, and hormones such as bone morphogenic proteins or transforming growth factors (Ginebra et al 2006). The development of a system that would allow the selection of single or

combined drug options at the time of cement implantation would improve the versatility of bone cement, however the effects of these additions on the physical properties of the cement needs greater research (Ginebra et al 2006).

With continued study and developments in different biomaterials, particularly bioactive materials, we may see the function of PMMA and other bone cements change as we develop our understanding of their mechanical behaviour (Jaeblon 2010). The applications of cement will no doubt increase and provide a continued support in a large number of orthopaedic procedures.

No competing interests declared

Provenance and Peer review: Unsolicited contribution Peer reviewed; Accepted for publication June 2011.

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Correspondence address: Wasim Khan, UCL Institute of Orthopaedics and Musculoskeletal Science, Royal National Orthopaedic Hospital, Stanmore, Middlesex, HA7 4LP. Email: wasimkhan@doctors.org.uk

About the authors

Christopher John O'Dowd-Booth BSc(Hons)

Medical Student, UCL Institute of Orthopaedic and Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore

Jonathan White BSc (Hons), MBBS

FY2 Doctor, Luton and Dunstable NHS Foundation Trust

Peter Smitham MBBS, MRCS, PhD

Clinical Lecturer, UCL Institute of Orthopaedic and Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore

Wasim Khan MBChB, MSc, MRCS, PhD

Academic Clinical Fellow, UCL Institute of Orthopaedic & Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore

David R Marsh

MBChB, FRCS, MD

Professor of Clinical Orthopaedics, UCL Institute of Orthopaedic & Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore
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