Cemented Acetabular Component in Total Hip Arthroplasty
Cemented Acetabular Component in Total Hip Arthroplasty
INTRODUCTION
The popularization of total hip arthroplasty (THA) resulted primarily from the success of the original low-friction arthroplasty (1) in which polymethylmethacrylate (PMMA) bone cement was used for fixation of both implants to the bony skeleton. Despite similar or improved outcomes with cemented THA (2,3,4), as well as lower implant cost, there has been a trend toward the use of uncemented implants. There are still many centers around the world where cemented THA is routinely being performed for all indications with high rates of survivorship of the cemented acetabular component.
The main aim of the different techniques involved in the use of cement for acetabular cup fixation is to achieve mechanical interlock between cement and acetabular bone that is strong and extensive enough to produce an eventual interface in which direct contact between cement and living bone (osseointegration: Brånemark [5]) is the dominant feature. Such an interface represents a reliable basis for long-term socket stability. While this is technically challenging, superior results are achievable with meticulous attention to the details of good cementing technique and the use of a prosthesis design with a proven track record of success.
INDICATIONS FOR THE USE OF A CEMENTED SOCKET
Can be considered for use in all hip arthroplasty procedures for patients of any age.
In young and very active patients in whom polythene wear is an issue, the use of highly cross-linked polythene may lead to improved outcomes.
In the setting of copious bleeding from the prepared acetabular subchondral surface, measures can be taken to reduce accumulation of blood at the interface using a combination of pulsatile lavage and an iliac suction device and paying close attention to the pressurization technique.
In protrusio or cystic sockets, autograft can be impacted into the defects prior to cementation.
In the setting of intensely sclerotic and/or cystic bone, with inability to prepare adequate cancellous bed, one can consider bone grafting the interface with autogenous bone and primarily impaction grafting of the socket.
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In cases with deficient bone stock, morcellized bone graft should be used to augment the defects.
Where there is any type of segmental defect, the defect should be repaired with the use of block bone, rim, or medial wall implants such as meshes or porous metal wedges, as appropriate.
In cases of previous pelvic irradiation, fixation of any type of socket is notoriously unreliable. A cage can be utilized in the pelvis for improved fixation, and the cemented socket can then be implanted into the cage.
In the setting of previous septic arthritis, there is an advantage in using cement for fixation, as cement can be loaded with appropriate antibiotics to reduce risk of recurrence.
CONTRAINDICATIONS
There are no specific contraindications for the use of cemented fixation of an acetabular component in total hip replacement surgery.
PREOPERATIVE PREPARATION/PLANNING
As with all hip replacements, preoperative planning is critical in achieving a near anatomical result and a more favorable outcome for the patient. Planning also ensures that appropriate implants and instruments are available at the time of surgery. The key is to have an appropriate AP and lateral x-ray of the pelvis to ensure good visualization of the acetabular bone stock. This allows identification of any significant acetabular deficiency or bone excess in the form of osteophytes that might cause bony impingement. Using appropriate templating, the size of the component and the center of rotation acetabulum (CRA) are identified. The aim is to establish the center of rotation in an anatomical position with the inferior edge of the implant at the level of the transverse ligament. In the setting of severe acetabular dysplasia, the position of the center of rotation can be estimated using the Muller technique (6). Muller estimated that in the average adult male, the CRA is approximately 14 mm superior and 37 mm lateral to the inferior margin of the teardrop. This allows estimation of the CRA in even the most severe cases of dysplasia. Appropriate femoral templating completes the process so that the biomechanics of the hips are established in terms of offset, leg length, and combined anteversion of the implants.
We utilize a flanged acetabular component. The technique described below can be applied to any cemented acetabular component.
OPERATIVE TECHNIQUE
Acetabulum appropriately exposed with standard approach of choice.
Removal of medial osteophytes with a combination of reamers and gouges, to identify the true medial wall (Fig. 12-1).
Use of power reamers in the axis of the acetabulum. Sequential concentric reaming with the aim of removing subchondral bone and exposing cancellous bone into which polymethylmethylmeth-acrylate bone cement can be pressurized (Fig. 12-2).
Reamers used in 2-mm increments.
Anterior wall most at risk of excessive thinning, so reamer positioned slightly posterior.
Reaming stopped when acetabular rim has been cleared to expose bleeding cancellous bone (Fig. 12-3).
When the last reamer has removed all articular cartilage from the periphery of the acetabulum but subchondral bone remains, multiple drill holes are made through into the cancellous bone to expose a surface for PMMA ingress on pressurization.
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FIGURE 12-1 Identification of true medial wall.
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Occasionally smaller reamers used to further expose trabecular bone in localized areas of subchondral bone, especially in the acetabular rim.
The face of the largest reamer can be used as a guide to removing peripheral osteophyte with a gauge.
Step drill used to make multiple drill holes within the acetabulum (Fig. 12-4).
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FIGURE 12-2 Concentric reaming of subchondral bone.
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FIGURE 12-3 Ream to bleeding cancellous bone.
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FIGURE 12-4 Multiple drill holes created with step drill.
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The smaller part of the drill (4 mm) used to make holes around the rim.
The larger part of the drill (8 mm) used to make holes in the ilium, ischium, and pubis to a depth of about 1.5 to 2 cm.
Care taken to ensure the acetabular wall is not perforated. If this occurs, then autograft packed into hole to prevent egress of cement.
Socket with a diameter of 2 mm smaller than the largest reamer used is usually the appropriately sized implant.
Trial flange is placed on the introducer along with the trial cup, and the flange is trimmed along the line indicating the largest reamer used. The trial cup is then repositioned within the acetabulum and flange retrimmed, if necessary, so it lies just within the mouth of the acetabulum (Figs. 12-5 and 12-6).
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FIGURE 12-5 Trial cup trimmed to appropriate size.
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FIGURE 12-6 Trial cup position assessed.
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Flange of definitive component then trimmed using the trial flange (Fig. 12-7).
Rehearsal of appropriate positioning of the component within the acetabulum (Fig. 12-8)
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FIGURE 12-7 Definitive cup flange trimmed using the trial flange.
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FIGURE 12-8 Cup positioned within the acetabulum.
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The sucker aspirator device is introduced into the superior ilium just above Zone 1 (7) of the component
cement-bone interface (Figs. 12-9 and 12-10).
Autograft reamings are compacted onto the transverse acetabular ligament (TAL) and the smooth medial wall of the acetabulum (Fig. 12-11). This technique prevents cement escaping under the TAL and obviates the possibility of a postoperative radiolucent line in Zone 3 where cement cannot gain fixation against the exposed cortical bone of the true medial wall.
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FIGURE 12-9 Sucker aspirator on pelvis model.
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FIGURE 12-10 Application of the sucker aspirator over Zone 1.
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Graft is protected with a swab and thorough pulsatile lavage of socket is carried out. Fluid is sucked out using the sucker aspirator (Fig. 12-12).
Hydrogen peroxide swabs are applied into the socket with care taken to ensure that the initial swabs are placed into the large drill holes in the acetabulum.
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FIGURE 12-11 Autograft reamings applied to smooth medial wall.
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FIGURE 12-12 Pulsatile lavage of the acetabulum.
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Cement applied into the acetabulum at approximately three and a half minutes after mixing, ensuring any excess bolus is removed. Timings may be slightly different depending on the type of cement used (Fig. 12-13).
Pressurization with a disposable sorbothane disc of the appropriate size ensuring a good seal at the socket rim (Fig. 12-14). Significant force applied to drive the cement into the bone and pressure maintained to reduce risk of back bleeding from host bone. The sucker aspirator assists in reducing any back bleeding (Fig. 12-15).
Pressurizer is removed and the cement surface cleared of any blood with a swab. More cement is applied into the acetabulum if needed.
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FIGURE 12-13 Cement application.
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FIGURE 12-14 Cement pressurizer sizes.
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Acetabular component applied at approximately 5 minutes after mixing (Fig. 12-16).
Placed within the acetabulum using an introducer and an axial pusher
Strong force applied to ensure correct seating inferiorly and medially
Excess cement removed and position checked to ensure appropriate version and abduction angle (Fig. 12-17)
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FIGURE 12-15 Application of cement pressurizer.
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FIGURE 12-16 Application of acetabular component.
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FIGURE 12-17 Removal of excess cement.
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Pressure maintained on the component till the cement polymerization is complete (Fig. 12-18)
Any remaining peripheral osteophyte is now removed from around the edge of the implanted socket. Aim to ensure good cement penetration and no radiolucent lines on the post-op radiograph (Fig. 12-19).
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FIGURE 12-18 Pressure maintained till polymerization complete.
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FIGURE 12-19 Good cement penetration on x-ray.
PEARLS AND PITFALLS
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Thorough assessment of the x-ray films, taking into account component coverage, rim osteophytes, and extent of medial subchondral bone.
Good view of the anterior and posterior walls prior to commencing reaming.
Careful assessment of the acetabular bony rim during reaming to ensure no unnecessary bone loss. Care taken to ensure reaming to medial wall but not any further medial.
Maximum number of drill holes made, and checked to ensure no perforation.
Use a flanged component to enhance cement pressurization and intrusion into bone.
More flange maintained superiorly on the component so that it can sit at the level of the teardrop with minimization of superior cement escape during implantation.
Rehearse the insertion of component to ensure no difficulty in placement in the ideal position. Avoid bottoming out of component by excessive medial pushing.
Avoid releasing pressure before cement polymerization is complete.
POSTOPERATIVE MANAGEMENT
Standard management involves full weight bearing as tolerated with aids commencing day of surgery or day 1 post-op. DVT prophylaxis is agreed with patient after risk assessment and consists of a combination of mechanical and chemical prophylaxis. All patients get AP and lateral x-ray films prior to discharge.
COMPLICATIONS
The common complications of THA have been previously discussed. The complications specific to cemented cups are discussed below in order of occurrence.
Perforation of the acetabulum with drill holes is an uncommon occurrence and can easily be dealt with by impacting autograft from the femoral head or acetabular reamings into the perforated hole.
Cement escape during pressurization can occur inferiorly under the TAL. If easy access, then removal of the cement is considered, but in the setting of difficult access or poor visualization, the cement can be left behind with minimal risk of complications.
Acetabular component can be overmedialized due to overzealous pushing.
High cup position is also a rare occurrence. This can be avoided by using the TAL as a marker for the inferior border of the cup.
Care should be taken to rehearse introducing the cup into the desired position or inadvertent malpositioning of the cup can occur. This can be dealt with by reaming the polyethylene cup out and performing an in-cement revision without disturbing the original cement mantle.
Overreaming the acetabulum leading to compromised medial wall. This is an uncommon problem if care is taken while reaming. However, this can be easily treated with autograft impaction grafting using the available femoral head. In rare situations with a significant defect of the medial wall, a mesh can be utilized with autograft impaction over it.
RESULTS
Cemented THAs have had good results over the last two decades with the various national registry data showing survivorship of between 95% and 98% at 10 years (8,9,10).
REGISTRY DATA
The Swedish joint registry reveals that the 10-year survivorship of cemented THAs for all cause is 94.7%. This compares to 88.2% survivorship for uncemented THAs and 89.8% for hybrid THAs (8).
The Norwegian registry also has similar differences with 10-year survivorship of cemented THAs at 93.5% versus 89.4% for uncemented and 88.4% for hybrid THAs (8).
The National Joint Registry from the United Kingdom quoted a 10-year survivorship of cemented THAs at
96.8% versus 92.3% for uncemented THAs and 96.1% in hybrid THAs (10).
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INDIVIDUAL STUDIES
Comparison of different types of fixation is difficult given the regular changes to implant design and the
improvements in material properties of the prostheses. As the designs of uncemented shells have improved, so
have the techniques used in cementing sockets. The material benefits of the new cross-linked polyethylenes are likely to lead to improvements in outcome no matter the mode of fixation of the implant.
While there is paucity of level 1 randomized clinical trials comparing cemented and uncemented components, there have been many individual studies and some meta-analysis and review articles recently published. There is no significant published literature known to the authors that show significantly improved survivorship of an uncemented acetabular component over a cemented one.
A recently published review article and meta-analysis supported the superiority of cemented cups with an odds ratio of 1.60 of the survivorship of a cemented component versus an uncemented component, suggesting lower revision rates (11). Another older meta-analysis showed no difference between the two types of acetabular fixation for all patients, but in the greater than 55 years of age subgroup, there was superior survival with cemented acetabular fixation (12).
Interestingly, a recently published follow-up of design of flanged acetabular component in patients less than 50 years of age showed an 8-year survivorship with the endpoint for aseptic loosening was 96.4% (13). Given that the younger population usually has lower survivorship, this study certainly showed superior outcomes with the contemporary cup, with results similar to the survivorship of the implant in all age groups in various national registry data.
Another retrospective cohort joint registry study from the United Kingdom showed an overall 7-year revision rate for the contemporary flanged cup for any reason at 1.18%, which is again very comparable to other successful cemented and uncemented cups currently in use (14).
CONCLUSION
Cemented THA has had successful outcomes over the last four decades, and with recent improvements in cementing techniques and acetabular implant quality, there is every indication that there should continue to be further improvements in survivorship of cemented arthroplasty in all age groups.
ACKNOWLEDGMENTS
We wish to thank Sophie Kolowska, Media Manager, Hip Unit, Dept of Orthopaedics, PEOC, Royal Devon and Exeter Hospital, Exeter, UK, for her contribution to this chapter.
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