294 Acta Orthopaedica 2010; 81 (3): 292–295 Table 5. Cement mantle thickness on AP and lateral radiographs. Values are percentage with antero-lateral/posterior approach ≥ 2 mm < 2 mm < 1 mm 1 98/99 2/1 0/0 2 98/99 2/1 0/0 3 98/99 2/1 0/0 4 98/99 0/0 2/1 5 97/97 2/2 1/1 6 96/95 3/3 1/2 7 99/99 1/1 0/0 Gruen zone 8 68/79 27/19 5/2 9 72/81 26/15 2/4 10 99/99 1/1 0/0 11 99/99 0/0 1/1 12 97/97 2/3 1/0 13 100/100 0/0 0/0 14 99/99 1/1 0/0 Gruen zone. In Gruen zone 9, 72% in the antero-lateral group and 81% in the posterior approach group had a cement mantle thickness of ≥ 2 mm. In Gruen zone 12 (postero-distally), only 3% in the antero-lateral approach group and 3% in the poste- rior approach group had a cement mantle thickness of < 2 mm. Discussion Evaluation of the cement mantle is an important tool for quality and outcome assessment of cemented total hip arthroplasty. Poor cement mantle quality has been identified as a predictor of worse long-term outcome (Chambers et al. 2001). Most previous studies have only assessed the cement mantle on AP radiographs. It is well documented that if true lateral radiographs are not taken, then the risk of thin cement mantles is underestimated (Breusch et al 2001, Östgaard et al 2001). Östgaard et al. (2001) observed a similar pattern of malaligned Charnley stems in the lateral plane as we did, con- firming previous reports (Crawford et al. 1999, Breusch et al 2001, Valdivia 2001). In a historical comparison to an origi- nal Charnley series, lateral cement mantles were less deficient in cases with trochanteric osteotomy (Garellick et al. 1999). A similar lateral stem malalignment pattern was found with other stem designs and stem-bone contact was noted in Gruen zone 8 in 20% of cases with Charnley stems and 13% with the Spectron stem (Garellick et al 1999). In this context, lower femoral neck osteotomies and more aggressive removal of the posterior femoral neck (Wroblewski et al. 2000) were advo- cated. This allows a more posterior entry point, and as a con- sequence the alignment of a straight stem design is improved. Vaughan et al. (2007) reported a tendency for lateral stem malalignment and posterior stem tip-to-cortex contact, as was also observed in the present study. Little is known regarding the influence of the surgical approach to the hip on the cement mantle, aseptic loosen- ing, and overall revision rates. RSA data have shown a higher incidence of rotational instability with the Exeter stem using the posterior approach than when using the lateral approach (Glyn-Jones et al. 2006). Our results suggest that a posterior approach is associ- ated with a lower risk of thin cement mantles. We can only hypothesize that exposure of the fossa piriformis and canal entry may be easier with a posterior approach. When using an antero-lateral approach in obese or very muscular patients, the broach and stem have a tendency to be pushed anteriorly by the soft tissue, thus providing an explanation for sagittal stem malalignment. In our series, however, a high BMI was not predictive in this context. An efficient distal centralizer appears to eliminate the prob- lem of a distal stem tip-to-cortex contact and its detrimental effect in zone 12 (Berger et al. 1997, Garellick et al. 1999, Breusch et al. 2001), and our findings support this also. How- ever, it has been shown that a distal centralizer cannot pre- vent thin cement mantles in zone 8/9 (Breusch et al. 2001). This has been confirmed in our study, where the distal cen- tralizer did not protect from a thin cement mantle anteriorly in approximately a quarter of the cases. These findings are also in keeping with the results of cadaver studies with Exeter stems (Valdivia et al. 2001, Mayr et al. 2006). The clinical relevance of these thin cement mantles is sub- ject to debate. It is clear from the published outcome data that a thin cement mantle anterior-proximally is a frequent find- ing around Exeter and other straight stems, but with polished, tapered designs this does not seem to adversely affect outcome in the first decade (Berli et al. 2005, Hook et al. 2006, Lewth- waite et al. 2008). In the second decade, when more wear par- ticles may have accumulated, osteolysis is more common and rates of femoral osteolysis from 32–70% have been described (Räber et al 2001, Iwase et al. 2002). Osteolysis-induced periprosthetic fracture then becomes a more frequent failure mechanism (Lindahl et al. 2005). In the presence of polyeth- ylene wear, thin cement mantles may play a future role in fail- ure during the second decade (Kerboull et al. 2004). Stems designed to be implanted with thin cement mantles (line to line) have shown excellent survival after a mean of 14 years (Kerboull et al. 2004). However, the cases that had failed due to aseptic loosening/osteolysis were all in a high wear rate group, thus emphasizing the importance of a non-deficient cement mantle. In this biological context, the integrity of the cement mantle becomes most important. Open access of the bone interface, via mantle defects, to particles and fluid pres- sure has been identified as an important factor for osteolysis (Schmalzried et al. 1997, Bartlett et al. 2008). Although we do not know the long-term implications of our findings, the effect on the cement mantle should also be con- sidered when choosing the approach to the hip. It seems rea- sonable to favor a posterior approach in younger patients, who are likely to survive the first decade after implantation. In older patients, other factors may play a more important role when