We found a number of factors that influenced the risk of reoperation after hemiarthroplasty. The most important findings were the higher risk of reoperation for patients with bipolar implant heads and for those with uncemented implants.
The higher risk for bipolar implant heads might indicate some general problems with these implants. Prolonged surgery time due to assembly of the bipolar head may play a role. This finding could be incidental, or related to some unknown confounder. It is, however, in agreement with previous analyses from the Register on different stem-head combinations (Garellick et al. 2010
), which showed an increased risk of revision for bipolar hemiarthroplasty compared to unipolar, using the same stem (Lubinus and Exeter stems with their unipolar and bipolar heads, respectively). Register analyses have also shown a higher risk of reoperation because of dislocation for the Vario Cup implant head (which accounts for almost half of the bipolar heads) compared to other bipolar implant heads (Garellick et al. 2010
Our results contrast with the experience from the Australian National Joint Replacement Registry, where bipolar implants have had a lower risk of revision than unipolar implants, at least in younger patients after long follow-up (Graves et al. 2011
). This might be attributable to differences between the hemiarthroplasty populations in Australia and Sweden regarding the case-mix in the different age groups.
On the other hand, patients operated with unipolar heads were more likely to undergo reoperation due to acetabular erosion. The total rate of erosion requiring surgery was very low, however, at only 1.7 per thousand. As erosion is mainly a long-term problem, the concern about this complication may be more legitimate in a younger patient group with longer remaining life expectancy. We only assessed acetabular erosions that lead to reoperation, and lack information about patients who might have symptoms from erosion, which for various reasons do not lead to surgery. The total number of patients with erosion may be higher than the rate we observed (Baker et al. 2006
, Hedbeck et al. 2011
). Patient-reported outcomes, e.g. hip function and pain, were not addressed in the present study. In all, based on our findings, unipolar implant heads appear to be the most advantageous ones, at least for the majority of patients, who have a relatively short remaining life expectancy. In Sweden, the retail price of the most common bipolar heads (i.e. Vario Cup and UHR Universal Head) is at least 50% higher than that of the corresponding unipolar heads (Mega Caput and V40 Unipolar). This higher cost might be motivated for patients with a relatively long remaining life expectancy, but this remains to be shown.
In addition to implant heads, the stems also had an influence on the reoperation risk. Uncemented implants had a 50% higher risk of reoperation than cemented matte implants, mainly due to fracture. This is in accordance with reports from the Australian National Joint Replacement Registry (Graves et al. 2011
). There have been few randomized trials comparing cemented and uncemented hemiarthroplasties, and only 3 assessing contemporary uncemented implants. In 2 of these, no statistically significant differences were seen regarding hip function or major complications such as reoperation (Figved et al. 2009
, Deangelis et al. 2012
). One recent study showed higher rates of complications and periprosthetic fractures and also a poorer early functional outcome for uncemented stems (Taylor et al. 2012
). In all 3 studies, mortality was similar in the 2 groups.
The designs of the different brands of cemented polished stems are similar, with a straight stem shape in most cases, whereas the matte ones differ somewhat within the group—with both straight and curved stems. The substantially higher risk of reoperation because of fracture for the polished stems has been reported previously (Lindahl et al. 2005
, Garellick et al. 2010
). Of the matte stems, the curved Lubinus SPII accounted for 78% in the present study. Only 10 of the 10,816 patients operated with this stem sustained periprosthetic fractures that led to reoperation. The lower risk of reoperation because of implant dislocation for polished stems may be related to the distribution of implant heads—which differ between matte and polished stems—rather than being related to the stem design itself.
Hemiarthroplasty surgery performed as a secondary procedure after failed internal fixation was associated with a more than doubled risk of reoperation regardless of reason, as well as when due to dislocation and infection. This is in accordance with the findings of Frihagen et al. (2007)
, although the statistical power in that study was too low to reach significance for the different reasons for reoperation.
The surgical approach had no statistically significant influence on the risk of reoperation in general. However, the anterolateral transgluteal approach had a lower risk of reoperation due to dislocation than the posterior approach, a finding that matches previous reports (Varley and Parker 2004
, Enocson et al. 2008
). Notably, closed reductions of dislocated arthroplasties are not recorded in the SHAR. Thus, the true number of implant dislocations is greater than the number in this study. Recurrent dislocation in particular can affect the elderly patient for a long time, and is a potential cause of persistent reduction in health-related quality of life (Enocson et al. 2009
). Our findings suggest that the anterolateral transgluteal surgical approach should be recommended for hemiarthroplasty procedures.
The younger age groups at the time of fracture had higher risk of reoperation irrespective of cause—and also because of implant dislocation, infection, and acetabular erosion. A younger patient with a more active lifestyle may be more at risk of dislocation and acetabular erosion. Surgeons might also be more inclined to use nonoperative treatment for elderly patients than for younger patients. Apart from this, higher age may protect the patient from complications and reoperation because of shorter remaining lifetime.
Males had a higher risk of reoperation, mainly due to fracture. This is in accordance with reports from Australia, at least for unipolar hemiarthroplasties (Graves et al. 2011
Consistent with previous reports, male hip fracture patients also had higher mortality than female patients (Soderqvist et al. 2009
, Kannegaard et al. 2010
, Sterling 2011
). Even when we adjusted for ASA grade and classification of cognitive impairment, the mortality risk was still higher in men.
The method of fixation was not a risk factor for mortality during the first postoperative year. In a recent registry study, the risk of death was higher with cemented hemiarthroplasties in the first postoperative day, but at 1 week, 1 month, and 1 year postoperatively the risk was higher with uncemented implants (Costain et al. 2011
Altogether, the choice of implant and technique can be somewhat of an orthopedic cruise between Scylla and Charybdis; the choice leading to a lower risk of one complication also leads to a higher risk of another. This means that we need to rank the different complications in terms of importance, taking into account the frequency of the complication, the magnitude of the increase in risk, and how severe the particular complication is to the patient.
One limitation to a nationwide registration is the issue of selection bias, with possible unknown confounders. Also so far no patient-reported outcomes have been registered. There could certainly be a number of patients with complications or symptoms that do not result in surgery. Another type of bias might be related to individual selection of implants and surgical technique at the different hospitals. 30 of 65 hospitals used only either bipolar or unipolar implants; four hospitals accounted for 72% of the total number of uncemented stems, whereas the majority of the units (47) contributed with cases that were operated using either approach (anterolateral or posterior). The observation of diversity related to operating unit is common in registry studies and difficult to handle, because some hospitals may use a uniform treatment algorithm, e.g. the same implant type, fixation, and surgical approach for all patients. The large number of operating units, many of them using several alternatives, should at least partially compensate for this problem. Also, especially after the first 2 years of the registration, completeness of reporting by the different hospitals is highly consistent, with only a few units reporting less than 90% of cases—thus reducing the risk of skewed results due to different reporting rates. Some hospitals may not, however, report all their reoperations even though they do have routines for this. Finally, the classification of cognitive impairment is not done according to a validated form. Instead, the patients are graded by the surgeon based on the patient’s appearance and records of previous investigations of cognitive impairment. There is a risk that some patients may be incorrectly classified as having evident or suspected cognitive impairment as a result of a transient confusion related to the injury.
The strengths of this prospective observational study are the large number of patients and the high degree of completeness.
In summary, we recognize that methodologically, register studies are observational and hypothesis generating. Nonetheless, our findings indicate that there is a problem with bipolar implants, leading to a higher risk of reoperation. The reason for this is currently unclear and requires further investigation. Unipolar hemiarthroplasty appears advantageous, at least for the oldest patients with short remaining life expectancy and thus a minor risk of acetabular erosion. Cemented implants are associated with lower risk of reoperation in hip fracture patients, suggesting that they should be preferred—together with the anterolateral transgluteal surgical approach in order to reduce the risk of dislocation.