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Mistakes and Pitfalls with Cemented Hips
Götz von Foerster
Summary
More than any other factor it is the surgeon’s operative performance which has the greatest influence on the long- term fate of a cemented total hip arthroplasty. Although most mistakes are forgiving, at least in the short term, the chances of success are compromised. In this chapter, the most common surgical errors and potential pitfalls, which can occur during the cementing process of stem and cup, are outlined.
Introduction
There is no doubt that when implanted with an optimal cementing technique cemented hip arthroplasties (THA) can achieve excellent long-term results. The surgeon’s experience and technical ability is crucial for the success of the procedure.
Mistakes made during the cementing procedure rarely lead to immediate failure of the implant. This is one of the reasons why mistakes often remain undiscovered for a long time and are difficult to rectify. The weaknesses of faulty cementing technique do not become apparent until revealed by the long-term results of large case num- bers. Although this suggests that even poor cementing techniques are forgiving this should not lead to a false conclusion.
The following questions must be considered:
▬ How long can hip arthroplasties survive when implanted with an optimal cementing technique?
▬ What are the cementing mistakes which shorten the survival of the implants?
▬ How serious must a mistake be in order to shorten the survival of an implant?
It is extremely difficult to pinpoint specific details here, therefore there is only one possible principle:
>
Note: Every mistake in cementing technique short- ens the survival of an implant and must be avoided.We differentiate between two categories of cementing:
▬ primary cementing during primary joint arthroplasty,
▬ secondary cementing during revision surgery (modi- fied bearing, larger implants).
The surgeon must ensure that all steps in the cement- ing procedure, i.e. preparation of the bone, mixing the cement, insertion at the correct time (timing!) and pres- surisation of the cement, are carefully co-ordinated.
The Common Mistakes The Cement Mantle
The aim is to achieve a complete and non-deficient cement mantle encompassing the entire implant. The cement mantle is defined by the correlation between the bone bearing, implant size and the position of the implant after implantation. The most common mistake is that the prosthesis stem is not implanted in a per- fectly centred position. In many cases the implant is in a varus position and often there is contact between the metal tip of the implant and the bone (
⊡Fig. 17.1). The result is that at this point the cement mantle is too thin or not present at all. Osteolysis may result and later the implant tip migrates into the cortical bone and may cause fracture.
Valgus malpositioning is less frequent (
⊡Fig. 17.2),
but is known to be more forgiving.
Another mistake which is often observed is incom- plete filling of the femur with cement. The reason for this mistake is that the surgeon has failed to appropri- ately lavage and suction off all the fluid in the femur or to notice pockets of blood and air remaining in the cavity.
As a consequence, air and blood entrapment with radio- graphically evident voids within the cement mantle or radiolucent lines at the cement-bone interface (visible on the first postoperative X-ray) may occur. This can result in prosthetic stem loosening from distal which leads to instability of the implant. The consequences of this mistake are, however, usually less dramatic than those of malpositioned implants.
If poor cementing technique and stem malpositioning are present as a combined surgical mistake, then early aseptic failure can result (
⊡Fig. 17.3).
⊡Figure 17.3high- lights a number of cardinal mistakes:
▬ The stem is in varus malalignment.
▬ This had led to a deficient cement mantle at the lateral stem tip (direct bone contact).
▬ The rounded distal tip of the cement mantle indicates residual blood entrapment above the cement restric- tor and is evidence for poor intraoperative pressurisa- tion.
Chapter 17 · Mistakes and Pitfalls with Cemented Hips 341
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⊡ Fig. 17.2. Prosthesis in valgus position. Cement mantle incomplete
⊡ Fig. 17.1a–c. Prosthesis in varus position. Contact between metal and bone
a b c
▬ The cement mantle is too thin (implant size!) and has cracked.
▬ At three years there is radiographic loosening with a complete radiolucent line at the cement bone inter- face.
▬ Radiographically the entire stem/cement complex has significantly subsided more than 5 mm (see stem shoulder!).
▬ The explanted specimen shows a smooth entire cement mantle as evidence for poor cementing technique. A smooth cement surface can only result, if no endosteal cancellous bone has been preserved and lavaged and if cement pressurisation was not or insufficiently done.
The Cement Restrictor
The cement restrictor in the distal femur plays a very important role. The restrictor must be inserted at exactly the right point using a longitudinally marked guide and the surgeon must check that it is firmly in position. If the restrictor is incorrectly placed, the cement spreads out over a long distance in the femoral medullary canal.
This causes serious problems if revision is later necessary.
These plugs of cement are extremely difficult to remove (
⊡Figs. 17.4 and 17.5).
Failure of the cement restrictor also results in reduced intramedullary pressure during the cementing process
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⊡ Fig. 17.4a,b. Long cement plug as evidence for failed and migrated cement restrictor
a b
⊡ Fig. 17.3. Early aseptic loosening after 3 years which is unrelated to the implant type, but a consequence of poor surgical technique with
a combination of varus stem malalignment and poor cement mantle (see text)
and thus to reduced penetration of the cement into the cancellous bone (bonding).
Cement Protrusion
There are various reasons for cement protrusion from the femoral medullary canal. During primary cementing, cement may protrude through unnoticed screw holes in patients, who had previous osteosynthesis, and can cause severe pain (
⊡Fig. 17.6).
Otherwise, cement protrusion usually happens dur- ing secondary cementing in revision surgery when corti- cal perforations occur (unnoticed), often in the critical region around the former implant tip (
⊡Fig. 17.7). This is because the affected areas were not sufficiently exposed during the operation. It is essential to ensure that the medullary canal is fully intact before cementing, particu- larly after osteosynthesis and removal of screws or during revision surgery.
For a while, some hospitals used additional material such as the Verhoewe »quiver« or osteosynthesis plating to close large defects at revision arthroplasty with extremely thick layers of cement (
⊡Fig. 17.8). This strategy did not lead to any improvement in the cement anchorage of a large defect. On the contrary, it only produced additional interfaces between the implant, cement, additional mate- rial and then the bone and therefore an increased risk of loosening, for example, when the material was subjected to greater stress than usual.
Chapter 17 · Mistakes and Pitfalls with Cemented Hips 343
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⊡ Fig. 17.7a,b. Cement protrusion through cortical perforation in revi- sion surgery
a b
⊡ Fig. 17.6a,b. Cement protrusion through screw holes
a b
⊡ Fig. 17.5a,b. Distal cement plug specimens, difficult to remove at revision
a
b
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Cementing Cementless Hip Implants
Using cement to fix cementless implants in position is a frequently observed mistake. This happens when a suit- able cemented implant is not available during surgery or when the surgeon is not aware of the consequences of cementing a cementless implant (
⊡Fig. 17.9).
Cementing a cementless implant is in itself an uncompli- cated procedure, but in revision cases removal of the cement is the exact opposite. A cemented cementless implant can only be removed together with the entire cement mantle.
This often means that the femur has to be opened by fenestration or more extensive osteotomy. Cementing a cementless implant is therefore an unforgivable mistake.
Incomplete Removal of Cement at Revision Surgery
In certain situations in revision surgery (excluding infec- tion cases) it is not always necessary to remove a firmly fixed cement mantle completely. It is possible to implant a new prosthesis in a distally well-preserved and firmly fixed cement mantle, especially if the prosthesis has a straight stem. If the surgeon decides to leave the cement mantle in place he must ensure that it really is intact and firm.
In patients with deep periprosthetic infection, how- ever, all cement must be removed completely and thor- oughly. Even the smallest cement fragments are most certainly colonised by bacteria and are bound to cause recurrence of infection (
⊡Fig. 17.10).
When a joint is infected, even a firmly fixed cement mantle and distal cement plugs deep inside the femur must be completely removed. Otherwise, the procedure is doomed to failure with recurrent/persisting infection.
Cementing the Acetabular Cup
The fact that the long-term results of cemented cups are poorer than those of cemented stems could be attributed to the different type of bone bearing. The fact that cementless acetabular cups also have poorer long-term results than cementless stems would seem to confirm this conclusion.
Mistakes during the cementing of acetabular cups occur because the bone has been poorly prepared and/or the cement has been inadequately pressurised into the acetabulum. Correct and adequate pressurisation is only possible with the new instruments now available.
A further mistake is, that defects, especially in the centre of the acetabulum, are either not recognised or not sufficiently covered (with bone graft) and as a result
⊡ Fig. 17.8. Stress fracture of a Verhoewe »quiver« ⊡ Fig. 17.9a,b. Cementing a cementless hip is an unforgivable mistake
a b
Chapter 17 · Mistakes and Pitfalls with Cemented Hips 345
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⊡ Fig. 17.11. Cement protrusion into the pelvis
cement protrudes into the pelvis (
⊡Fig. 17.11). This can lead to serious complications such as vascular erosion and haemorrhaging, especially during later revision.
Inadequate handling and compression of cement also causes dispersion of small fragments of cement especially towards caudal. These are often not visible during surgery and are not discovered until later on the radiograph. For
this reason, meticulous inspection of the acetabulum after cementing is essential (
⊡Fig. 17.12). Protruding cement which is no longer connected firmly to the cement inside the acetabulum can migrate and endanger nerves and blood vessels.
Another cardinal mistake is filling the acetabular roof with cement in an area which is no longer contained.
⊡ Fig. 17.12a,b. Inferior cement escape (a). Migration of disconnected cement fragment (b).
a b
⊡ Fig. 17.10. Incomplete removal of cement in a case with deep infection
In the course of time this cement is destined to fracture and slip away as it has no bone support (
⊡Fig. 17.13).
It goes without saying that after the stem or cup have been cemented in position any surplus cement must be removed, otherwise this cement can later break off during joint movement. Small particles can penetrate into the ace- tabulum between the cup and head of the femoral stem where they can cause serious damage due to three body wear.
Conclusion
For expert cementing, surgeons must have comprehensive knowledge of and ability in the technique of cementing and carry out all the necessary checks to avoid or elimi- nate the mistakes described here.
To conclude, here are two notable examples. In the first case the cemented stem survived twelve years, which could be interpreted as evidence that even small amounts of cement in the right place can hold an implant in posi- tion for quite a long time (
⊡Fig. 17.14).
The second case shows that although it may allow double mobility of the artificial femoral head in the cup and at the same time of the natural femoral head in the natural acetabulum, cementing implant components on an unsuitable base such as the »retained« femoral head after femoral neck fracture does not provide firm fixation for any length of time (
⊡Fig. 17.15).
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⊡ Fig. 17.14. Despite small amounts of cement this implant was in position for 12 years
⊡ Fig. 17.13a,b. Using cement in an uncontained area and roof defect will lead to failure. Cement has fractured and slipped away
a b
Chapter 17 · Mistakes and Pitfalls with Cemented Hips 347
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⊡ Fig. 17.15. »Too much mobility«
Take Home Messages
