rates of more than 95% after 10 years can be achieved and even longer term implant survival can be expected ( chapter 9.1, 9.2 ).

Operative Steps:

Acetabulum

Steffen J. Breusch, Henrik Malchau, John Older

rates of more than 95% after 10 years can be achieved and even longer term implant survival can be expected (  chapter 9.1, 9.2 ).

It has become very clear over the last decade that the quality of bone preparation and the cementing technique are the decisive factors influencing outcome significantly more than implant choice (as is the case with femoral components), although the quality of polyethylene is also of particular importance.

The same principles, which are accepted for femo- ral fixation (  chapter 2.2, 5.1, 5.2, 6.4 ) also apply to the socket (  chapter 5.3 ). Modern cementing techniques aim to improve the mechanical interlock between bone and cement in order to establish a durable interface at the time of surgery. With increased depth of cement penetration the strength of the cement-bone interface is enhanced. It is extremely important to accept, that only meticulous bone bed preparation, thorough bone bed cleansing with pulsatile lavage and sustained cement pressurization, as well as accurate implant positioning, will ensure long term success of a cemented acetabular component.

In the following the authors preferred operative tech- nique is outlined on a step-by-step basis.

Surgical Technique

Hypotensive anaesthesia with spinal or epidural injection is preferred. A low systolic blood pressure (<80–90 mmHg) at the time of cement application is considered essential to minimize the extent of bleeding at the interface. In the authors view an anaesthesist with particular arthroplasty interest and experience will significantly contribute to a successful operative procedure.

Summary

In this chapter the operative technique for the cemented socket is described in detail in a step-by-step manner.

Technical considerations, tips and tricks are given to enhance the understanding for this demanding proce- dure. Particular emphasis is given to restoration of the anatomical centre of rotation, meticulous bone prepara- tion and cementing technique. The indications and tech- niques for acetabular floor and roof graft are outlined.

Introduction

Despite some excellent long-term results cemented ace- tabular fixation has become less popular over the years in continental Europe, although it remains the most common procedure in the UK and Scandinavia. In the vast majority of US patients cementless designs are used and indeed in many teaching centres the technique of cemented socket fixation is not part of the trainee’s cur- riculum anymore.

Numerous cementless cup designs are available on the market despite the lack of published data and long term track record. If all reoperations, including liner exchange (wear), bone grafting (osteolysis) and disloca- tion are included, the overall revision rates (which mat- ter to the patient) for most cementless sockets do not favourably compare with those of well-cemented com- ponents (  chapter 9.1 ). Hence there has been a swing back to cemented acetabular fixation in Norway and Sweden.

It is important to realise, that cemented socket fixa-

tion remains an extremely successful procedure, par-

ticularly if performed well. Long term implant survival

Containment

It is a cardinal rule, that the acetabular component (cup) should be completely contained under the roof of the acetabulum. This usually requires the acetabulum (socket) to be deepened a variable amount, thus ensuring me- dial component placement. If the acetabular roof is de- ficient or dysplastic an acetabular roof graft is necessary ( ⊡ Fig. 2.2b, Fig. 2.4a,b,  see chapter 2.3.1 ).

Transverse Deepening

It is of importance to understand the anatomical and bio- mechanical consequences of preparing and reaming of the acetabulum. ⊡ Figure 2.1a outlines the scenario of too later-

al cup placement due to inadequate medial deepening. The most common mistake, however, is made not infrequently by reaming the acetabulum in the natural 45° axis of the acetabulum, which will create a concentric, hemispherical cavity, which is good for cement pressurisation, but unfor- tunately will automatically put the centre of the cup (and rotation) higher than the anatomical level, as simulated in

⊡ Fig. 2.1b and documented radiographically in ⊡ Fig. 2.2 . This is particularly the case when lateral femoral head subluxation is present, which can lead to erosion of the superior lip. This subluxation with outward and upward femoral head migration commonly occurs in advanced OA, and is usually in association with a large central osteo- phyte ( ⊡ Fig. 2.3 ) and developmental dysplasia of the hip (DDH, ⊡ Fig. 2.4 a,b ).

⊡ Fig. 2.2a,b. This postoperative radiograph (left) shows 2 cardinal mistakes: Firstly the transverse deepening was not carried out suf- ficiently and due to reaming only in 45° direction the hip centre is significantly raised (note: relation to tear drop figure!). Secondly, the

cup was not inserted medially first, but pushed superiorly, which has led to a (too) thin cement mantle in DeLee and Charnley Zone I. On the right (b), the correct cup position is superimposed

a b

⊡ Fig. 2.1. TDL = tear drop line, dR = direction of Reamer

a A too lateral cup placement is simulated due too inadequate medial deepening. Note failure to remove central osteophyte lateral to tear drop (true inner floor of pelvis)

b Common mistake of concentric deepening with reamers kept at 45°

thus raising the anatomical centre of rotation

c Correct transverse deepening keeps anatomical centre or rotation, but not infrequently renders socket cavity eccentric, which makes cement containment and pressurisation more difficult

a b c

2

⊡ Fig. 2.3. Lateral subluxation and large central osteophyte in osteo- proliferative OA

⊡ Fig. 2.4. a Acetabular dysplasia with lateral-superior subluxation and bony (distance between two parallel lines) obliteration of the ace- tabular fossa. The preoperative radiograph provides a good guide for the true depth of the fossa. Note subluxation using the Menard-Shen- ton line as reference. b Postoperative radiograph shows autogenous roof graft and inferior cup placement in correct anatomical position with restoration of the Menard-Shenton line. In contrast to ⊡ ^{Fig. 2.2} adequate medial deepening/reaming ensured correct anatomical cup position. This technique will reveal more clearly a roof graft required to archieve full containment.

a

b

In ⊡ Fig. 2.1c the correct method of transverse deep- ening is shown. The reamers are directed horizontally to keep the anatomical centre and level of rotation inferior, thus ensuring preservation of limb length restoration of normal soft tissue tension. Both are important factors for preventing postoperative dislocations.

These circumstances can be mimicked preoperatively by using a hemispheric cup template, which is super- imposed on the preoperative radiograph of the pelvis ( ⊡ Fig. 2.2 ), thus giving a good preoperative understand- ing of any anatomical difficulties to be encountered.

Normally a cup size according to the femoral head size (contralateral hip if deformity is present) or smaller is chosen and placed in the desired anatomical position with adequate medial placement, so that a normal centre of rotation and full containment is achieved. An eroded or deficient roof will be brought to light ( see ⊡ Fig. 2.1c, 2.2b ) by this simple manoeuvre. In difficult circumstances a preoperative drawing is recommended.

Operative Steps

Deepening of Acetabulum and Bone Bed Preparation

Please note: In all intraoperative photographs superior (i.e.

acetabular roof) is right and anterior is top of the images.

Exposure and Access to the Socket

Regardless of which approach is used (  chapter 1 ), three retractors are ideally positioned to allow adaequate access to the socket ( ⊡ Fig. 2.5 ). An angulated Cobra type retractor is placed in the acetabular notch. A narrow, sharp pointed Hohmann and a further curved lever are positioned around the anterior and posterior acetabular margin. If the inferior capsule has not been adequately released access may be difficult.

Rim Osteophytes

To ensure inferior cement containment it is best to pre- serve the transverse ligament. In cases where this is ossified, this has to be recognised as a too vertical cup placement may result if this inferior osteophyte is used a reference for cup alignment.

For the same reason, i.e. for improved cement con- tainment acetabular rim osteophytes should be preserved until the cup has been cemented. However, in some cases with very large osteophytes these have to be partially removed early to facilitate access to the socket.

Identification Inner Floor of Pelvis

It is recommended and considered important to always

identify the true inner floor (lamina interna). If the liga-

mentum teres is not ossified, it can be excised to reveal

⊡ Fig. 2.5a–c. Three retractors ensure adequate exposure of the socket. The central osteophyte and lig. teres are resected prior to reaming using an osteotome (a) and a sharp curette (b). All soft tissue and bone can be easily removed thus exposing the true floor – a step is then visible between the floor and the facies lunata (c) osteotome on acetabular floor after removal of lig. teres and central osteophyte

a

b

c

⊡ Fig. 2.6. The first reamer is directed transversely to reach to the inner floor (a), before the cavity is enlarged and the superior sclerosis is addressed to expose bleeding cancellous bone. Note that an eccentric cavity will result (which is nor- mal!). If immediate upwards reaming is done (b) superior and lateral cup place- ment (see ⊡ Fig. 2.2) with inadequate containment will result

a b

the fossa acetabuli. However, the ligamentous fibres are invariably overgrown by central osteophyte formations and in the extreme case the fossa will be completely obliterated and buried ( ⊡ Fig. 2.3 ). By resecting the cen- tral overhanging osteophyte ( ⊡ Fig. 2.5 ) prior to reaming using an osteotome (a) and a sharp curette (b), all soft tissue and bone can be easily removed thus exposing the true floor (c). This will ensure adequate roof coverage and medialisation of the component ( ⊡ Fig. 2.4 ). In the average patient a step of 0.5 to 1 cm between the fossa and the facies lunata will then be revealed. In large men this distance may be greater than 1.5 cm.

Deepening of Acetabular Cavity

It is a sound principle always to deepen the socket suffi- ciently to contain the cup under the acetabular roof. After the inner floor has been identified, the first small reamer (usually 42–46 mm Ø) is placed horizontally in the unroofed acetabular fossa and directed medially ( ⊡ Fig. 2.6 and 2. 11a ) until the inner floor is reached.

Once the inner floor is reached, the cancellous bone of the facies lunata becomes flush with the cortical surface of the floor, which corresponds radiographically to the lat- eral border of the tear drop figure. In the average patient the depth may vary between 0.5 to 1 cm. The reamer is kept inferior in close contact to the transverse ligament.

In cases with advanced OA and significant peripheral

inferior-posterior osteophyte overgrowth, it sometimes is

difficult to identify the inferior aspect and removal of the

inferior osteophyte may be necessary first. However, as a

rule peripheral osteophytes, which enhance cement con-

tainment and aid cement pressurisation, are only removed

after having cemented the component. The exception to

this rule is the very tight and contracted hip, where only

removal of peripheral osteophytes will allow appropriate

access to the socket.

! ^Cave

Beware of the large man with osteoproliferative OA.

In these patients a central osteophyte of more than 1.5 to 2 cm can obliterate the inner floor and it may be prudent to plan for deliberate conservation of deepe- ning, as full deepening may lead to excessive compo- nent medialisation and loss of offset, thus increasing the risk of dislocation (preoperative planning!). Also it is important to recognise a protrusio type socket.

Protrusio Acetabuli

In protrusio acetabuli ( ⊡ Fig. 2.7 ) no central osteophyte is present and the step of transverse deepening should be avoided to prevent perforation of the thinned lamina interna. In these cases a floor graft from the femoral head ( ⊡ Fig. 2.8, Fig. 2.9 ) is essential to lateralise the cup to restore the anatomy ( ⊡ Fig. 2.7b ). Failure to do so, may result in early loosening and migration ( ⊡ Fig. 2.10a–c ).

2

⊡ Fig. 2.7a,b.

a Protrusio acetabuli with central migration of the femoral head. Note the femoral head is medial to tear drop line

b The postoperative radiograph shows restoration of anatomy with the use of autogenous floor graft from femoral head: Morcellised bone is impacted onto the sclerosed lamina interna, followed by a structural bone slize ( ⊡ ^{Fig. 2.8)}

a b

⊡ Fig. 2.8a,b. Structural autograft taken from femoral head

a b

Enlarging the Socket and Roof Preparation

A large and sharp curette or two handed Volkmann spoon is used to remove all remaining cartilage and to scrape the roof sclerosis. In some cases with soft bone this instrument may be sufficient to roughen the ebonated bone of the roof. However, more commonly a reamer is necessary.

After transverse deepening and medial reaming ( ⊡ Fig. 2.6, Fig. 2.11a ) the next reamers are directed supe- riorly ( ⊡ Fig. 2.11b ) to enlarge the cavity, but no attempt is made to remove the eburnated roof sclerosis. Only partial preservation of the subchondral bone plate will leave the structural support intact.

! ^Cave

Beware of too superior reaming: this may result in loss of roof cover and superior component position- ing (high hip centre, ⊡ Fig 2.2 ).

The final reamer size relates to the anterior-posterior diameter of the acetabulum. If the inferior-superior diam- eter is larger and a corresponding reamer size is used, overreaming may result in thinning or destruction of the anterior and posterior wall.

⊡ Fig. 2.9a,b. Depth of reamer before (a) floor graft in protrusio acetabuli and after (b) impaction of morcellized and structural graft (Fig. ⊡ 2.8b) confirms adequate intraoperative lateralisation. Cave: In protrusio the first reamer is not medialised to avoid perforation of the (thinned) sclerotic lamina interna

a

b

⊡ Fig. 2.10. a Protrusio acetabuli. Note medial head migration well beyond tear drop line. No central osteophyte is present and a floor graft is necessary to lateralise the cup to restore the anatomical centre of rotation and prevent early failure (see ⊡ Fig. 2.10c)

b Immediate postoperative situation with failure to address the pathol- ogy. Note the absence of a floor graft and a very poor cementing technique. c Early failure with central and superior en-bloc migration after 18 months

a

b

c

2

As a rule of thumb, the largest and final reamer size should only exceed the ap-diameter by 2–4 mm and intends to roughen the anterior and posterior bone surfaces. To prepare the roof, finally, a smaller sized reamer, which can easily be manoeuvred in all directions like a burr, is then used to roughen the roof sclerosis to bleeding bone.

> Note: It is the governing principle that cement = can- cellous bone. Bone cement cannot bond to a smooth cortical surface ( see also ⊡ Fig. 2.12c ), but can only maintain long-term function when interdigitated with the cancellous framework (  chapter 3.6, 5.2 and 5.3 ).

Anchoring Holes

Multiple 6–10 mm anchoring holes of approximately 10 mm depth are made in the roof ( ⊡ Fig. 2.12 ) using a flexible drill. Care has to be taken not to perforate the thin anterior and posterior walls. In these areas only grooves and dimples are made with the drill or a sharp small gauge.

We do not recommend the traditional large holes made in

the pubis and ischium as the cup is loaded in compression and therefore fixed to the roof! Inferior cement pegs are loaded in tension and will commonly debond from the bone interface with time, causing unnecessary bone loss.

⊡ Fig. 2.11a,b. Intraoperative photographs to emphasize the direction of reaming. Initially the direction is at 90° until the inner floor has been reached (a) and then the reamer is angulated up to 45° (b) to prepare the acetabular roof sclerosis. Note that when using a short incision the inferior retractor is temporarily removed from the acetabular notch

a

b

a

b

c

⊡ Fig. 2.12. a A flexible drill with drill guide allows the most accurate

placement of the anchoring holes. Partial preservation of subchondral

plate is considered beneficial in cases with significant sclerosis (  ^see

chapter 5.3). b Multiple small drill holes are shown for better clarity

in a cadaver specimen. Please note exposed cancellous bone despite

partial preservation of bone plate. c Inadequate roughening of the

sclerosis carries the risk of radiolucent lines and earlier failure, despite

multiple drill holes

Having made the anchoring holes, frequently sub- chondral cysts will become apparent, especially after pul- satile lavage ( ⊡ Fig. 2.13 ). In cases with radiologically evident cysts, these must be found and removed. Smaller cysts can be simply curetted, but the pericystic sclerotic wall must always be removed to gain access to the adja- cent cancellous honeycombs. A gauge is better than a drill doing this. This may sometimes leave a significant defect, which should then be grafted using the cancellous bone from the femoral neck and head.

Bone Bed Cleansing

The single most important step is copious and thor- ough pulsatile lavage ( ⊡ Fig. 2.14a ). Irrigation not only renders white strands of any soft tissue remnants vis- ible, but also effectively removes blood and bone marrow from the bone intersticies, thus aiding cement penetra- tion. (  chapter 5.2.1 ). A very clean bone bed will result ( ⊡ Fig. 2.14b ). This step is commonly repeated several times

⊡ Fig. 2.13a,b. Multiple anchoring holes have been made and a large roof cysts has been revealed. A sharp, thin walled gauge is best suited to remove the pericystic sclerotic wall. Failure to do so will result in cement pegs with no interdigitation into cancellous bone. Larger cysts should always be bonegrafted

a

b

⊡ Fig. 2.14. a Prior to cement application, again copious lavage is used. Some further bone preparation may be necessary at this stage.

Lavage is repeated and the acetabulum is packed with 3–5% H

O

soaked ribbon gauze. b Immediately prior to cement application the socket is irrigated again thoroughly and packed with dry swabs

a

b

between the steps of bone preparation to facilitate visualisa- tion. Prior to the last wash, a H

O

soaked swap is firmly packed into acetabulum to reduce bleeding and blood loss.

Some surgeons still prefer to use a rotatory brush with stiff nylon bristles. These are particularly useful to remove loose bone and remnant fibrous tissue. However, some bristles may brake from the brush, and since the modern pulsatile lavage is equally powerful in terms of cleansing capabilities, there value is questionable, in particular as no added benefit on long term outcome could be shown (  chapter 6.1 ).

Cement Application and Pressurization

In contrast to the femur a higher cement viscosity at the time of cement application and cup implantation is preferred to reduce the risk of blood laminations at the interface (  chapter 5.1 ). In the acetabulum the cement is applied en bloc, so immediate pressurisation can be implemented ( ⊡ Fig. 2.15 ). Timing is critical and the bone bed should be as clean and dry as possible, even if further lavage and dry swabs are necessary.

Immediately after insertion of the cement ball, pres- surisation is commenced manually using a sterile glove filled and padded with a swab ( ⊡ Fig. 2.16a ). This ensures prompt (counter)pressure to resist the aectabular bleed- ing pressure and cement penetration. The tips of the flat fingers should touch the acetabular floor ( ⊡ Fig. 2.16b ) thus ensuring, that no cement can escape inferiorly during pressurisation.

After manual pressurisation of approximately one to two minutes, a well designed pressurizer ( ⊡ Fig. 2.17 ) is positioned, so that it touches the acetabular floor and seals the entire rim of the acetabulum.

If a simple design is used ( ⊡ Fig. 2.17a ), its diameter should exceed the acetabular diameter at least 4 mm to allow for appropriate sealing and pressurisation. If the water-inflatable Exeter balloon pressurizer is used ( ⊡ Fig. 2.17b ), often wider access to the socket is required to accommodate the device and furthermore some osteo- phytes may need to be trimmed.

Regardless of what design is used it is important to implement sustained pressurisation (  chapter 5.1 and 6.5 ) until the cement has sufficiently penetrated and reached a high enough viscosity, so it cannot be displaced by the

2

⊡ Fig. 2.15a,b. After further lavage and drying, typically the cement is applied at 3,5 to 4 minutes (for Palacos) as a lump en bloc. For the large socket two mixes may be necessary. For the socket cement in a state of higher viscosity is preferred compared to the femur

b a

⊡ Fig. 2.16a,b. Immediate manual cement pressurisation is com- menced using a padded steril glove before the acetabular pressurizer is positioned

b

a

intraosseous bleeding pressure. Care has to be taken, not to bottom the pressurizer, which would lead to a break- down of the pressurisation process.

As a general rule in socket sizes (largest reamer size used!) up to 54 mm one mix of 40 g bone cement may suffice, but in larger socket sizes 60–80 g will be necessary to guarantee effective pressurisation and enough cement to fix the acetabular component.

After cement pressurisation and increase of cement viscosity, the pressurizer can be removed. Commonly no backbleeding at the cement-bone interface will occur ( ⊡ Fig. 2.18 ). The remaining excess inferior cement is removed with a McDonald dissector ( ⊡ Fig. 2.18 ) and the cement is lifted slightly from the sclerotic acetabular floor to place a thin autogenous floor graft from the last ream- ings.

Cup Implantation

Depending on the surgeons’s preference either a standard or a flanged type acetabular component is implanted.

In this chapter the technique with an unflanged cup is described, but in  chapter 7.6 a detailed description of the rationale and technique with a flanged cup is given.

The use of cups with extended posterior lips is generally not advised as these carry the risk of neck-taper impinge- ment, which is associated with a higher risk of polyethyl- ene wear and dislocation.

An acetabular cup size of at least 4 mm smaller in diameter than the largest reamer used, is chosen to ensure a minimum (pure) circumferential cement mantle thick- ness of 2 mm. PMMA spacers may prevent cup superiori-

⊡ Fig. 2.17a–c. Cement is then more effectively pressurised with a well designed pressurizer for a minimum period of 60–120 seconds, depending on the cement type, the timing of cement application and the cement viscosity. Note: Care has to be taken not to bottom the pres- surizer to avoid insufficient pressurisation and cement mantle defects

a

b

c

⊡ Fig. 2.18. After successful and adequate pressurisation the pressu-

rizer is removed and at approx. 6–7 minutes no further bleeding will

occur. Excess inferior cement is removed from the acetabular floor and

notch with a MacDonalds dissector to prevent inferior cement escape

during cup insertion

2

⊡ Fig. 2.21. Postoperative radiograph with correctly implanted ace- tabular component. Note the absence of a lucent lines and the ade- quate degree of cement interdigitation

⊡ Fig. 2.20. An acetabular component with a minimum PE thickness of 8 mm is used. The implant should be downsized at least 4 mm from the last reamer (e.g. Ø 48 mm cup and Ø 52 mm reamer) to guarantee a minimal circumferential cement mantle thickness of 2 mm. Depend- ing on the cup/reamer relation a minimum cement mantle of 2 mm should be visible. This prevents thin cement mantles in Gruen Zone 1 (  chapter 6.5).

The component orientation can be assessed by rotation of the ball headed introducer, using the introducer rod as orientation in space.

Alternatively, a cup inserter with orientation guides can be used initially

⊡ Fig. 2.19. Schematic drawing of cup implantation. With reference to the transverse ligament the component is inserted horizontally and pushed fully medially first, before gradually angulated to the desired inclination of 45°. Pressurisation is maintained using the ball-headed introducer

b a

sation and thin cement mantles in DeLee and Charnley zone I. However it must be realised that these spacers may engage within the trabeculae. Further pressurisation and cup positioning may then become difficult.

After removal of the excess cement ( ⊡ Fig. 2.18 ) the acetabular component is inserted either by hand or using a cup holder. Applying the same principle when pre- paring the socket, the cup is inserted horizontally and pushed fully medially first, before gradually angulated to the desired inclination of 45° ( ⊡ Fig. 2.19 and 2.20 ). Then a cup pressurizer with a ball is inserted to maintain pressure on the cement without the risk of rocking the component.

Also good visualisation of the cup position is possible. By

holding and rotating the cup pressurizer perpendicular to

the cup surface a very accurate account of implant align-

ment can be judged without the use of special alignment

rods or jigs.

Using an unflanged component the proximal cement mantle is not only visible to ensure an adequate thickness of >2 mm, but can also be accessed and pressurised dur- ing final cement curing to prevent a shrinkage gap at the roof interface.

Finally, all remnant cement and all cementophytes are removed with an osteotome to prevent the risk of third body wear. As a last step all acetabular rim osteophytes are removed flush to the component rim to reduce the risk of anterior and posterior femoro-acetabular impingement leading to dislocation.

Take Home Messages I I

▬ Preoperative planning is recommended (e.g. to establish the need for a roof or floor graft and to achieve a norma l hip centre).

▬ Complete containment under the acetabular roof should be achieved.

▬ This usually requires transverse (medial) deepen- ing to the acetabular floor.

▬ Meticulous bone preparation with exposure of the cancellous bone is essential.

▬ Pulsatile lavage for bone bed cleansing is manda- tory.

▬ Sustained cement pressurisation (acetabular pres- suriser) ensures adequate cement interdigitation.

▬ The size of the acetabular component should be at least 4 mm smaller in diameter than the larg- est reamer used to guarantee a minimal cement mantle thickness of 2–3 mm.

▬ The acetabular component is positioned in the high viscosity, late phase of cement polymerisation.

(The cup should not be regarded as a pressuriser)

▬ All osteophytes are finally removed to avoid dislo- cation secondary to impingement.

▬ It is the surgeon at the time of cup implantation

who will determine the success of a cemented

socket.