The Cemented Acetabular Component

RECONSTRUCTION 2023, Jan, 08 | 12:00 am

The Cemented Acetabular Component

P ITFALLS

In order to achieve longevity of the cemented acetabular component, it is important to have adequate cover of the socket by host bone.
If this is not possible, augmentation with structural autograft should be considered.

Cemented Acetabular Component

Indications

Provision of an acetabular bearing for patients undergoing total hip replacement surgery

Examination/Imaging
For the majority of cases, a well-penetrated anteroposterior (AP) pelvis radiograph is all that is required to prepare for the cemented acetabular component.

Controversies
- There has been a cultural shift from cemented to uncemented components among surgeons.
- Advocates of the technique argue that its versatility lends itself better to the wide variety of pathology encountered in the hip than uncemented techniques.
- Surgeons favoring uncemented acetabular components would argue that they offer superior longevity in the younger patient with a wider variety of bearing materials. However, Figure 1 shows the long-term results with cemented components in a 30-year-old cemented total hip replacement performed by Professor Sir John Charnley when the patient was 46 years of age.
In patients with significant deformity or structural anomalies, useful information may be gained about the adequacy of the bone stock from preoperative false profile views or a computed tomography scan, although this is not our usual practice.
On the plain radiograph, an initial assessment should be made of the size of the acetabulum, thickness of the medial wall, and amount of medial osteophyte.
- The preoperative radiograph in Figure 2 demonstrates an adequate medial wall with some associated osteophyte, good superolateral coverage, and an adequate size for a standard socket.
- The preoperative radiograph in Figure 3 demonstrates a good medial wall, a lack of superolateral coverage, and a small diameter in a patient with dysplasia.
Attention should be paid to the amount of superolateral coverage that will be provided for the acetabular component and whether any augmentation is likely to be required.

Treatment Options
- The main variations for the acetabular component include:
  - A cemented polyethylene socket
  - A press-fit uncemented component with various surface finishes and coatings to encourage osseointegration
Cemented Acetabular Component

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FIGURE 1

FIGURE 2

FIGURE 3

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Cemented Acetabular Component

Surgical Anatomy
The hip joint can be adequately approached through a variety of approaches; these are beyond the scope of this chapter.
Once the head is removed and the acetabulum exposed, it is most important to define the inferior margin, the transverse acetabular ligament, and the bony margins of the acetabulum.

Positioning
Other than those using a trochanteric osteotomy or the Smith-Peterson and Watson-Jones approaches, patients are almost universally positioned in a lateral position and held with a positioning device anterior and posterior on the pelvis.

P EARLS
- Exposure of the acetabulum should be possible with the minimum use of force.
- Correct positioning of the retractors, whichever approach is being used, is the secret to clear visualization of the acetabulum.
  
  P ITFALLS
- Try to preserve the integrity of the capsule by using self-retaining retractors rather than excising the tissue. This confers additional stability to the hip in the postoperative period.
Portals/Exposures
For the surgical technique demonstrated here, the patient is positioned supine and a right total hip replacement is being performed via a trochanteric osteotomy approach.
In all of the illustrations, the trochanteric osteotomy is held proximally by a pin retractor in the iliac bone. The cut end of the femur is visible adjacent to the inferior margin of the acetabulum, and the leg being operated upon is crossed over the contralateral side to improve exposure (Fig. 4).

Procedure

Step 1
Any labral remnants and soft tissue falling into the acetabulum should be removed at this stage.

Instrumentation
- For the technique as illustrated, a Charnley initial retractor is placed once the fascia lata is incised.
- Once the osteotomy and neck cut are made, the exposure is improved with a Charnley east-west retractor against the superior pin and the femoral neck as well as an angled self-retaining retractor in the capsule.
The inferior retractor is positioned to allow visualization of the transverse acetabular ligament and to determine the inferior margin of the

acetabulum (Fig. 5). This helps to avoid inadvertently

creating a high hip center by malpositioning the socket.
If there is a significant amount of soft tissue in the floor of the acetabulum, this can be removed at this time.

FIGURE 4

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Cemented Acetabular Component

A

Hip capsule

True floor of acetabulum

Vastus muscle fibers

Capsular retractor

Femoral neck cut

Gluteus medius muscle fibers

Retracted trochanteric osteotomy (exposed cancellous

bone)

Distal portion of trochanteric osteotomy

Charnley bow retractor

B

FIGURE 5

East/West retractor

P EARLS
- Removal of large osteophytes is essential to avoid the possibility of impingement against the femoral neck, which may lead to dislocation.
- When using a flanged cemented component on the acetabular side, an overhanging osteophyte impedes access when implanting the device and may lead to removal of too much of the flange just to allow easy implantation.
  
  P ITFALLS
- Care should be taken to avoid angling the osteotome excessively and removing normal bone, especially from the posterior wall.
Step 2
Where there are significant marginal osteophytes on the acetabular side, a trial socket can be placed in the acetabulum to define the normal margin (Fig. 6A, arrow) and the osteophytes removed (Fig. 6B).
When these osteophytes are less substantial, they can be removed once the definitive socket is cemented

in place.

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Cemented Acetabular Component

FIGURE 6

Step 3

Using the traditional starter drill (Fig. 7A), a pilot hole is made medially to allow an assessment to be made of the thickness of the medial wall (Fig. 7B). While this practice is becoming less frequent, it is our preferred technique to ensure that the medial wall is not over-reamed.

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Cemented Acetabular Component

FIGURE 7

Instrumentation/ Implantation

A curved 2-cm osteotome is ideal at this stage of the procedure.

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Instrumentation/ Implantation

Our preferred technique uses the ½-inch starter drill for the medial pilot hole. The defect is covered with a central mesh as originally described by Charnley.
Others advocate the use of a 2-mm drill and a depth gauge to avoid cement penetration medially.

Cemented Acetabular Component

FIGURE 8

P EARLS

With good-quality, sharp hemispherical reamers, it is possible to achieve even expansion of the cavity quite easily by hand. Many surgeons tend to favor power reaming; however, blunted reamers tend to skip on the bone surface and perform less effectively. There is a surprising amount of proprioceptive feedback possible with hand reaming, and we recommend this technique.

The presence of a medial “collar stud” of cement (Fig. 8) has been thought to be advantageous in resisting migration superolaterally.

Step 4
A small hemispherical reamer is then used, and the direction of reaming is deliberately angled medially

(Fig. 9) and forcibly kept inferior at the level of the transverse acetabular ligament.
Care is taken at this time to ensure that the true floor is identified (Fig. 10) and that any medial osteophyte is removed.

Step 5
After this, reaming is simply a process of expanding this cavity (Fig. 11), taking care not to overmedialize and ream through the medial wall.
Attention should be paid to ensure that expansion is taking place evenly in the AP plane. This will avoid inadvertently reaming out one of the walls.

Cemented Acetabular Component

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FIGURE 9

FIGURE 10

FIGURE 11

Instrumentation/ Implantation
- A mixture of curette spoons, a ring curette, and a set of gouges are ideal for hand finishing the acetabulum and to clear the last tissue remnants.
Step 6

Cemented Acetabular Component
Much has been written about the shape of the acetabulum, and clearly it is not hemispherical. Early acknowledgment of this fact is vital to avoid over-reaming and excessive bone loss in the anterior and posterior walls.
A point will be reached at which the reamer fits the acetabulum well in the AP plane and all articular cartilage is removed from these surfaces.
Attention should then be turned to the superolateral margin of the acetabulum (Fig. 12) to ensure that there is no residual cartilaginous or soft tissue material present. Failure to do so tends to give rise to the telltale lucent line in Charnley and Delee zone 1 on the postoperative radiograph (Fig. 13).
Using a combination of gauges and curettes, this

area can be well cleared.

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FIGURE 12

FIGURE 13

P EARLS
- Care should be taken to ensure that a good cortical bridge remains between each keyhole drilled.
- In areas where there are cysts, the drill can be used straight into the cyst and a curette should be used to clear all remaining tissue.
  
  P ITFALLS
- Keyholes placed too deep and medially lead to excessive cement migration into the pelvis and make for complicated revision surgery if required.
Step 7
- Multiple keyholes are prepared in the acetabular bone using a power drill (Fig. 14A and 14B).
- Historically the large ½-inch starter drill was used for pubic, ischial, and iliac keyholes. We now favor multiple ¼-inch holes throughout the acetabulum with care taken medially.
  
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  Cemented Acetabular Component
  
  A
  
  B
  
  FIGURE 14
  
  P EARLS
  - Rehearsal of the implanting maneuver and awareness of the ﬁnal resting position of the implant are the most important factors at this stage.
  - An excessive residual flange may hamper correct seating of the prosthesis.
    
    P ITFALLS
  - The most common error is inadequate medialization of the socket on insertion; it is important to approach implantation as two moves:
    - First, adequate medially directed pressure with the socket held closed on the holder
    - Second, gradual introduction of the correct inclination and anteversion once the socket is medialized
  Cemented Acetabular Component
  
  Step 8
The socket is sized so that its outer diameter is within 10 mm of the largest reamer used.
The flange is cut to ensure that, when a trial is performed, the flange sits evenly on the acetabular margin (Fig. 15).
The final position of the socket holder is tested to ensure that the definitive component is correctly seated (Fig. 16).
While the cement is being mixed, the cavity is washed and prepared with hydrogen peroxide immediately prior to cementation. This results in a dry field that allows good cement penetration.

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FIGURE 15

FIGURE 16

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P EARLS
- Knowledge of your cement, its working time, and the effect of temperature and humidity is vital to timing insertion correctly.
- If things do not look right, then opt out early. It is possible to remove the majority of the cement well while it is still soft. It is much harder once the cement has cured.
Cemented Acetabular Component

Step 9
- First, the medial cement restrictor is inserted with a small amount of cement on its deep surface to hold it in place.
- While proprietary cement pressurizers are available for the next part of the procedure, in vitro studies using the socket illustrated have demonstrated that the pressure achieved with this well-fitting flange is comparable to that of an acetabular pressurizer. Our preference is to insert the cement as a ball into the acetabulum, gently thumb it toward the superior part of the acetabulum, and then clear the cement inferiorly to allow accurate placement of the socket.
- The socket is then introduced as rehearsed with the
  
  socket holder and a socket pusher.
- Once the final position is achieved, the socket holder is removed, leaving the pusher in place. Further pressure is then applied to the flange at its margin until the cement has cured (Fig. 17). Note that, once the cement has cured, a thin film of blood is apparent beneath the flange.
- The inferior retractor is removed at this time to avoid inadvertent fixation of this device with cement. Care should be taken to avoid excessive changes in position as the cement is curing.
  
  FIGURE 17
  
  Cemented Acetabular Component
  
  FIGURE 18
  
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Finally, once the cement has cured, the margin of the acetabulum should be inspected to look for residual fragments of cement that may get into the articulation and lead to excess wear (Fig. 18). Again, attention should be paid to the bony margin of the acetabulum and excessive osteophytes should be removed.
The aim is for a neutral or slightly anteverted socket with an inclination/angle opening laterally of approximately 40°.

Postoperative Care and Expected Outcomes
In cases where a cemented acetabular component has been chosen, patients are usually encouraged to start full weight bearing on the operated side in the early post-operative period.
Where a more complex acetabular reconstruction has been necessary with either structural or morcellised allograft, a period of partial weight bearing is encouraged postoperatively. In cases where a trochanteric osteotomy has been employed, protected weight bearing is encouraged for 12 weeks.
With care and attention to detail, it is extremely unusual to encounter problems relating to a

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Cemented Acetabular Component

cemented acetabular component in the early postoperative period. The chance of incorrect positioning of the component should be minimized by correct rehearsal of the insertion maneuver. Attention to removing cement debris from the margin of the component should ensure that no retained cement fragments will get into the bearing.
- Radiological follow-up is recommended at one year and every fifth postoperative year routinely to look for signs of wear and progressive lucencies affecting the acetabular component.

Evidence

Levy BA, Berry DJ, Pagnano MW. Long-term survivorship of cemented all polyethylene acetabular components in patients 75 years of age. J Arthroplasy. 2000;15:461–7.

Average follow-up for this series was 8.9 years. Despite the fact that over time many of the original cohort had died, no patient had required revision of an acetabular component for aseptic loosening. This paper demonstrates that survivorship free from revision can be expected with this choice of implant.

Williams HD, Browne G, Gie GA, Ling RS, Timperley AJ, Wendover NA. The Exeter universal cemented femoral component at 8–12 years. A study of the first 325 hips. J Bone Joint Surg Br. 2002;84:324–34.

Three hundred twenty-ﬁve hip replacements performed by surgeons of varying levels of experience followed up at a minimum of 8 years. With revision of the acetabular component for aseptic loosening, the survivorship was 96.86% (95% CI 93.1 to 98.9).

The fall from grace of the cemented acetabular component seems to have stemmed from perceived poorer outcomes relating to younger patients. Diagnoses such as ddh and avn tend to produce patients with single joint pathology who will test their arthroplasties more rigorously. The wish to take advantage of larger bearings is certainly not advantageous to any form of polyethylene acetabulum regardless of the means of ﬁxation. The advent of potentially more wear resistant bearing combinations in these cases has greatly increased the options available to the joint replacement surgeon. We would still advocate the use of this acetabular bearing for a large proportion of our routine workload, but we would not routinely consider bearing sizes above 28 mm in any but the most frail patients.

The Cemented Acetabular Component

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