Cemented THR, Uncemented THR and Birmingham Hip Replacement outcomes compared for death rate and revision rate

BMJ 2012; 344 doi: (Published 14 June
2012)
Cite this as: BMJ 2012;344:e3319

D J W McMinn, consultant orthopaedic surgeon1,
K I E Snell, PhD student2,
J Daniel, director of research1,
R B C Treacy, consultant orthopaedic surgeon3,
P B Pynsent, director of research and teaching centre3,
R D Riley, reader in biostatistics4

Objectives: To examine mortality and revision rates among patients
with osteoarthritis undergoing hip arthroplasty and to compare these rates
between patients undergoing cemented or uncemented procedures and to compare
outcomes between men undergoing stemmed total hip replacements and Birmingham
hip resurfacing.

Population: About 275 000 patient records.

Main outcome measures: Hip arthroplasty procedures were linked to the time to
any subsequent mortality or revision (implant failure). Flexible parametric
survival analysis methods were used to analyse time to mortality and also time
to revision. Comparisons between procedure groups were adjusted for age, sex,
American Society of Anesthesiologists (ASA) grade, and complexity.

Conclusions: There is a small but significant increased risk of
revision with uncemented rather than cemented total hip replacement, and a small
but significant increased risk of death with cemented procedures. It is not
known whether these are causal relations or caused by residual confounding.
Compared with uncemented and cemented total hip replacements, Birmingham hip
resurfacing has a significantly lower risk of death in men of all ages.
Previously, only adjusted analyses of hip implant revision rates have been used
to recommend and justify use of cheaper cemented total hip implants. Our
investigations additionally consider mortality rates and suggest a potentially
higher mortality rate with cemented total hip replacements, which merits further
investigation.

The evidence in this analysis suggests there are differences between the
outcomes of cemented and uncemented total hip replacements in terms of both
revision and mortality rates. On average across the population, our model
predicts that performing a cemented instead of an uncemented total hip
replacement results in an extra death once in every 77 (95% confidence interval
53 to 143) procedures every eight years for patients who do not undergo revision
before this time; conversely, the disadvantage of uncemented total hip
replacement is that an extra revision is predicted within eight years for every
67 (58 to 84) procedures for patients alive at this time. Secondary analyses in
men showed that the lowest death rate is associated with Birmingham hip
resurfacing. By performing a cemented total hip replacement instead of
resurfacing, our analysis predicts an extra death occurs within six years for
every 23 (17 to 35) operations.

Although the hazard ratios and differences in survival probabilities for
mortality between procedure types are small, a large number of people currently
undergo hip arthroplasty and the number is increasing year on year. Therefore
even small differences, if they are genuine, indicate potentially large numbers
of avoidable deaths. For example, an estimated 1.2 million hip arthroplasties56
were performed worldwide in 2011 alone. If hypothetically 1.2 million planned
cemented procedures were changed to uncemented procedures then, based on our
model estimates, there would be a predicted 15 584 (8392 to 22 641) fewer deaths
by eight years for patients who had not undergone revision by this time. As the
baby-boomer generation ages the number of arthroplasties has been progressively
increasing and therefore the number of potential avoidable deaths could also
progressively increase if cemented hips continue to be used widely. If 40% of
these 1.2 million are assumed to be men then, based on our estimates, switching
0.48 million cemented procedures to Birmingham hip resurfacing would lead to a
predicted 20 869 fewer deaths (13 714 to 28 235) at six years for who had not
undergone revision before this time…

…Over six years’ follow-up, Birmingham hip resurfacing had a significantly
lower mortality rate than uncemented and cemented total hip replacement in men
of all ages, but a higher revision rate than cemented total hip replacement.

Epidemiological magnitude of the problem

Although polymethylmethacrylate (PMMA) bone cement is biocompatible, adverse
cardiopulmonary effects57 58 59 60 61 62 have been widely documented during and
after the cementation period. Modern cement techniques,63 including
pressurisation, which were developed to improve cement penetration and fixation
can exacerbate these events.64 During the reaming and pressurisation processes
fat, marrow, air, particles of bone, cement, and aggregates of platelets and
fibrin are driven into the systemic circulation57 with the potential for
intraoperative and postoperative embolic events and adult respiratory distress
syndrome. Embolic events have been found to correlate with haemodynamic changes
suggesting pulmonary embolism65 and have been observed in over 90% of cases66 by
transoesophageal echocardiography. Furthermore about 10% of normal patients have
right to left shunt, giving the possibility of systemic embolisation with
unknown long term effects.67 68 69 In comparison, the relative rarity of overt
postoperative adult respiratory distress syndrome in patients suggests that the
embolic insult is usually insufficient to cause important clinical symptoms
immediately. The persistence of increased mortality over eight years, however,
raises the question of whether the embolisation has the potential to reduce the
normal respiratory reserve, making the patient prone to succumb to minor
respiratory diseases in the longer term. A long term detrimental effect on other
organ systems from systemic embolisation could also explain the continuing
increased mortality.

We have had the opportunity of studying embolisation intraoperatively after
cemented total hip replacement and Birmingham hip resurfacing using
transoesophageal echocardiography.70 The embolisation of echogenic material into
the right heart and lungs is markedly different with the two different
procedures. With Birmingham hip resurfacing, there is momentary transient
embolisation or no embolisation, whereas with cemented total hip replacement
there is profound embolisation, which can persist for up to 20 minutes.

Furthermore, the potential long term detrimental effects from prolonged
exposure to nephrotoxic agents such as gentamicin from the bone cement cannot be
ruled out, and this matter is being actively investigated.

What is already known on this topic

• Unadjusted and adjusted survival analyses suggest
  cemented total hip replacements are associated with better implant
  survival (improved revision rates) than uncemented total hip
  replacement and hip resurfacings.
• NICE indicate there are no data to support the use of
  generally more costly uncemented total hip replacement, though
  adjusted comparisons of mortality rates have previously been lacking

What this study adds

• In the National Joint Register, there are large
  baseline differences in characteristics of patients undergoing
  cemented, uncemented, or resurfacing procedures, which makes
  unadjusted comparisons inappropriate
• Over eight years’ follow-up uncemented total hip
  replacement was associated with a small but significant increased
  revision rate compared with cemented total hip replacement at any
  time for patients alive and unrevised at that time, and cemented
  total hip replacement was associated with a small but significant
  increased mortality rate compared with uncemented total hip
  replacement at any time for patients without a revision at that time
• Over six years’ follow-up, Birmingham hip resurfacing
  had a significantly lower mortality rate than uncemented and
  cemented total hip replacement in men of all ages, but a higher
  revision rate than cemented total hip replacement