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- PATIENTS AND METHODS
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Obesity has been associated with a higher prevalence of symptomatic osteoarthritis of the hip and a subsequent increase in total hip arthroplasty (THA) procedures (1–6). Interestingly, a recent large population-based study (6) did not find an increase in revision procedures among obese patients post primary THA. Prosthetic joint infections, dislocations, and revisions are rare but serious complications after primary THA. There are conflicting results in the current literature concerning the influence of obesity on the occurrence of these complications. A number of studies found an increase in perioperative morbidity (7–9) and complications such as infections or dislocations associated with obesity (8, 10–13), whereas others have reported no differences (14–18). The literature concerning the influence of obesity on revision for aseptic loosening is also inconclusive, which has partially been related to differences in activity level (15, 16, 18–23). However, functional outcome and patient satisfaction after THA have been considered comparable or only slightly lower in obese compared with nonobese patients (11, 13, 17, 24).
In comparison with primary hip arthroplasty, revision hip arthroplasty is a prolonged intervention resulting in more extensive tissue damage and is associated with more short- and long-term complications, as well as a higher mortality rate (25–29). The intervention is considered to be technically challenging, particularly in obese patients probably because of more difficult anatomic conditions. Only a few studies, notably with short-term followup, have reported on the influence of obesity on outcomes after revision THA (12, 30, 31). There is even less literature concerning the effect of obesity on functional outcomes and satisfaction after revision surgery (32, 33).
The aim of this study was first to evaluate the association between obesity and the incidence of main complications (in particular, surgical site infection, dislocation, and re-revision) after revision THA up to 5 years postoperatively. Also, we aimed to determine whether functional outcome, pain, and patient satisfaction at 5 years differed between obese and nonobese patients who underwent revision THA.
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- PATIENTS AND METHODS
- AUTHOR CONTRIBUTIONS
Among the 204 patients, 114 were women and 90 were men, with a mean age of 71.6 years (range 32–94 years) and a mean BMI of 26.7 (range 15–44). Twenty-five percent (n = 52) of the revisions were performed in patients with a BMI ≥30. Table 2 presents the distribution of the baseline characteristics (potential confounders) across obese and nonobese patients. The 2 groups mainly differed with respect to age, ASA score, Charnley classification grade, and indication for revision. Obese participants were younger, more often classified as Charnley grade C, and had higher ASA scores. Moreover, they were revised for aseptic loosening less often overall (less loosening of the cup or of both components, more stem loosening), but more often for recurrent dislocation or technical error.
Table 2. Distribution of baseline characteristics among obese and nonobese patients*
| ||BMI <30 (n = 152)||BMI ≥30 (n = 52)||RR (95% CI)||Mean difference (95% CI)†|
|Female||88 (57.9)||26 (50.0)|| || |
|Male||64 (42.1)||26 (50.0)||1.2 (0.9, 1.7)|| |
|Age at operation, mean ± SD years||72.5 ± 11.8||68.7 ± 9.9|| ||3.7 (0.1, 7.4)|
|Age, years|| || || || |
| <50||8 (5.2)||2 (3.8)|| || |
| 50–59||13 (8.6)||5 (9.6)|| || |
| 60–69||32 (21.1)||14 (26.9)|| || |
| 70–79||56 (36.8)||28 (53.9)|| || |
| ≥80||43 (28.3)||3 (5.8)|| || |
|Reason for revision|| || || || |
| Aseptic loosening total||73 (48.0)||16 (30.8)|| || |
| Stem loosening||19 (12.5)||13 (25.0)|| || |
| Cup loosening||17 (11.2)||2 (3.8)|| || |
| Septic loosening||19 (12.5)||7 (13.5)|| || |
| Recurrent dislocation||12 (7.9)||7 (13.5)|| || |
| Periprosthetic fracture||7 (4.6)||3 (5.8)|| || |
| Technical error||5 (3.3)||4 (7.6)|| || |
|Merle d'Aubigné score, mean ± SD‡||10.5 ± 2.3||10.1 ± 2.2|| ||0.4 (−0.6, 1.3)|
|ASA score|| || || || |
| 1–2||98 (64.5)||22 (42.3)|| || |
| 3–4||51 (33.6)||29 (55.8)||1.7 (1.2, 2.3)|| |
| Missing||3 (1.9)||1 (1.9)|| || |
|Surgery prior to primary THA||8 (5.3)||3 (5.8)|| || |
|Charnley classification|| || || || |
| A||60 (39.5)||6 (11.5)|| || |
| B||52 (34.2)||18 (34.6)|| || |
| C||40 (26.3)||28 (53.9)||2.0 (1.4, 3.0)§|| |
|Hip contralateral|| || || || |
| Normal||74 (48.7)||22 (42.3)|| || |
| Affected unoperated||12 (7.9)||5 (9.6)|| || |
| Operated||66 (43.4)||25 (48.1)|| || |
In obese patients the revision was performed, on average, 92 months after the primary hip THA, compared with 125 months in nonobese patients (mean difference 33 months, 95% CI 9, 58). The 2 groups did not significantly differ with respect to the use of osteotomy. A trochanteric or proximal femoral osteotomy was performed in 31 (60%) obese patients and 79 (52%) nonobese patients. In the obese group, an acetabular ring was used in 17 (43%) of the 40 revisions involving a cup replacement as compared with 89 (66%) of 134 cup replacements in the nonobese group. In the large majority of patients, a 28-mm head was chosen, except for 3 cases from each group with a 22-mm or a 32-mm head. A cemented cup was inserted in 67% of obese patients versus 80% of nonobese patients, and a cemented stem in 83% versus 74%. The groups did not differ with respect to operation time (209 versus 210 minutes).
The followup period for the primary outcome ranged from 3 to 74 months. During followup, 3 (5.8%) of 52 obese patients and 22 (14.5%) of 152 nonobese patients had died, and 4 (7.7%) obese and 6 (3.9%) nonobese patients were lost to followup.
Obese patients contributed a mean ± SD of 33 ± 25 person-months, and nonobese patients contributed a mean ± SD of 41 ± 21 person-months. Overall, 20 complications occurred in 17 (33%) of 52 obese patients compared with 18 events in 13 (9%) of 152 nonobese patients. Surgical site infections were reported in 6 (11.5%) obese patients (3 superficial, 3 prosthetic joint) and 4 (2.6%) nonobese patients (1 superficial, 3 prosthetic joint). The crude incidence rate was 4.6 times higher in obese patients (Table 3). After adjustment for ASA score, the adjusted HR was 4.1 (95% CI 1.1, 15.0). After stratification for sex, we observed a higher incidence rate of infection in obese versus nonobese women (IRR 15.5, 95% CI 1.7, 138.8) but no significant increase in obese versus nonobese men (IRR 2.0, 95% CI 0.3, 12.2). Dislocation was observed in 10 (19.2%) obese patients and 10 (6.6%) nonobese patients. The crude incidence rate was 3.1 times higher in obese individuals. After adjustment for age and ASA score, the adjusted HR was 3.5 (95% CI 1.3, 9.3). Eight re-revisions were undertaken, with 4 re-revisions in each group (7.7% versus 2.6%). In each group, 2 re-revisions were performed for septic loosening; 1 for recurrent dislocation and 1 for early aseptic loosening of the cup. The crude incidence rate of re-revision for any cause was 2.8 times higher in obese patients (95% CI 0.7, 11.1). Loss of fixation of the trochanteric osteotomy was observed in 5 (17.2%) obese patients and 5 (9.3%) nonobese patients.
Table 3. Incidence rates for each of the adverse events across obese and nonobese patients*
| ||BMI <30 (n = 152)||BMI ≥30 (n = 52)||Unadjusted IRR (95% CI)||Adjusted HR (95% CI)|
|Complication (1 event)|| || || || |
| Cases||13||17|| || |
| Person-years||516||145|| || |
| Incidence rate†||2.5||11.7||4.7 (2.3, 9.6)||4.0 (1.8, 8.9)‡|
|Surgical site infection|| || || || |
| Cases||4||6|| || |
| Person-years||543||177|| || |
| Incidence rate†||0.7||3.4||4.6 (1.3, 16.4)||4.1 (1.1, 15.0)§|
|Dislocation|| || || || |
| Cases||10||10|| || |
| Person-years||519||167|| || |
| Incidence rate†||1.9||6.0||3.1 (1.3, 7.5)||3.5 (1.3, 9.3)¶|
|Re-revision|| || || || |
| Cases||4||4|| || |
| Person-years||543||195|| || |
| Incidence rate†||0.7||2.0||2.8 (0.7, 11.1)||-|
The incidence rate for the occurrence of ≥1 adverse event increased with rising BMI (Table 4 and Figure 1). This increase was small between normal and overweight patients (adjusted HR 1.5), but it became significantly greater in the group with a BMI 30–34.9 (adjusted HR 4.5) and was most evident in the group with a BMI ≥35 (adjusted HR 10.9), although the width of the 95% CI increased due to the low patient number in this latter group. Adjustment was performed for age, sex, and ASA score. Further adjustment for indication for revision and Charnley classification grade did not substantially change the results.
Table 4. Occurrence of first primary outcome event (surgical site infection, dislocation, or re-revision) according to 4 BMI categories*
|<25 (n = 83)||25–29.9 (n = 69)||30–34.9 (n = 41)||≥35 (n = 11)|
|Unadjusted IRR (95% CI)||1.0 (Ref.)||1.9 (0.6, 5.8)||5.8 (2.0, 16.4)||10.0 (2.9, 34.7)|
|Adjusted HR (95% CI)‡||1.0 (Ref.)||1.5 (0.5, 4.7)||4.5 (1.4, 14.0)||10.9 (2.9, 41.1)|
Figure 1. Cumulative incidence (one minus survival function) of first primary outcome event (surgical site infection, dislocation, or re-revision) in normal weight (body mass index [BMI] <25), overweight (BMI 25–29.9), obese (BMI 30–34.9), and highly obese (BMI ≥35) patients after revision total hip arthroplasty using the Kaplan-Meier approach.
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Five years after revision, 31 obese and 79 nonobese patients were due for followup. Among the obese group, 2 (6.5%) patients had died, 3 (9.7%) were lost to followup, and 2 (6.5%) were unable to attend. Of the nonobese patients, 13 (16.5%) had died, 5 (6.3%) were lost to followup, and 5 (6.3%) were unable to attend. Of those still alive, 24 (82.8%) obese patients and 56 (84.8%) nonobese patients were seen at the 5-year visit. The mean ± SD time to followup was 57 ± 8 months.
Five years postoperatively, obesity was associated with moderately lower functional status (HHS) and a lower pain subscore, which remained after adjustment for age, sex, preoperative function and pain (Merle d'Aubigné score), ASA score, and Charnley classification grade (Table 5). The association with patient satisfaction was less evident, after adjustment the 95% CI included 0.
Table 5. Harris hip score (HHS), pain, and patient satisfaction at 5 years for obese and nonobese patients*
| ||BMI, mean ± SD||Difference, mean (95% CI)|
|<30 (n = 56)||≥30 (n = 24)||Unadjusted||Adjusted†||Adjusted‡|
|HHS||82.8 ± 14.7||71.4 ± 17.0||11.4 (3.9, 18.9)||9.2 (2.0, 16.7)||8.9 (1.9, 15.9)|
|HHS pain||39.2 ± 7.2||33.9 ± 9.6||5.3 (0.8, 9.7)||5.0 (0.9, 9.1)||5.4 (1.1, 9.8)|
|Satisfaction||8.2 ± 1.8||7.2 ± 2.7||1.0 (−0.2, 2.3)||0.8 (−0.3, 1.9)||1.1 (−0.1, 2.3)|
- Top of page
- PATIENTS AND METHODS
- AUTHOR CONTRIBUTIONS
The primary aim of this study was to determine whether obesity was associated with a higher incidence of major events in patients undergoing revision THA. We found significantly more events, notably surgical site infections and dislocations, in obese patients. Secondarily, we found moderately lower results on the HHS but almost similar satisfaction in obese patients 5 years postoperatively.
In comparison with primary THA, revision surgery is associated with greater soft tissue damage and prolonged operation time, which may explain the increased incidence of superficial and deep infections after revision. Larger soft tissue dissection and subsequent increased muscle weakness in revision THA might be one of the responsible factors for higher dislocation rates (45). In turn, obesity has been associated with higher rates of wound healing complications (46) and higher morbidity. Furthermore, in obese patients the intervention can be more technically challenging with respect to exposure, implant positioning, and soft tissue closure (47).
Literature about the influence of obesity on the occurrence of adverse events after revision THA is sparse. Most studies have reported on small patient groups and short followup periods. Perka et al (31), in a retrospective study including 229 patients of whom 31 had a BMI ≥30, found no increase in perioperative morbidity and mortality within 90 days. Another study (12) evaluated the risk of surgical site infection after revision according to 3 BMI categories. The authors did not observe an increase in infection in obese patients during the study followup, which was limited to the in-hospital postoperative period.
In contrast, a recent matched cohort study (30) reported a much higher risk of dislocation (relative risk 6.3) in morbidly obese patients as compared with a group of normal-weight and overweight patients 12 to 28 months after revision THA. The mean age of their patients was 57 years, compared with 72 years in our study. All patients were operated upon by 1 experienced surgeon. The even higher relative risk for dislocation in obese patients in their study might be due to the low dislocation rate (3%) in their young, nonobese patients.
In a previous study evaluating the effect of obesity on complications after primary THA, we observed a 4-times higher rate of infection similar to our current findings. The only difference is that in the present study, we included both superficial and prosthetic infections (11). However, the increase in dislocation due to obesity was less important after primary THA in that study than it was in this study (2 times versus 3 times higher).
Our findings are also in accordance with several other studies reporting on increased postoperative complications in obese patients after primary THA (7, 8, 12, 13). Two of these studies found higher rates of postoperative infections (8, 12). Stickles et al (13) evaluated 1-year orthopedic complication rates according to 5 BMI categories (<25, 25–29, 30–34, 35–39, and ≥40) using univariate analyses, and they found a significant increase with rising BMI, similar to what we observed in our data. A few studies reported similar short-term (orthopedic) complication rates (14–18), but their numbers of patients, and as a consequence their numbers of adverse events, were small.
Literature about pain and function after revision THA is lacking. Lower functional results (on the HHS score) in obese patients undergoing revision THA have been reported in 2 studies at 3 and 5 years postoperative (32, 33). In contrast to the present study, those analyses were unadjusted. Davis et al (48) analyzed predictors of pain and functional outcomes 2 years after revision THA using the Western Ontario and McMaster Universities Osteoarthritis Index, and they emphasized the importance of preoperative pain and function for the 2-year results. However, they did not include BMI among their predictors.
Previous studies have reported that obesity was associated with greater pain and disability in patients with hip or knee osteoarthritis (49, 50). However, we found similar preoperative Merle d'Aubigné scores (10.5 in nonobese versus 10.1 in obese patients) together with significant differences in Charnley classification grades between the 2 groups. Part of the explanation for this could be that the function domain, which we expect to mainly be related to disability, counts only for one-third of the total Merle d'Aubigné score. An additional subscore analysis of our data revealed that the difference of 0.4 points on the preoperative Merle d'Aubigné score between obese and nonobese patients was mostly due to lower function subscores in the obese group. With respect to the pain issue, we are unable to provide a clear reason why obese and nonobese patients did not differ at baseline in our study.
This prospective, hospital-based study compared the occurrence of several main adverse events in addition to pain, functional outcome, and patient satisfaction 5 years postoperatively in obese and nonobese patients undergoing first revision THA. To our knowledge, the followup period was longer than in any previous study. Analyses were performed for 2 and 4 BMI categories. We used incidence rates and Cox proportional hazards analysis to account for patient differences in length of followup and censoring, and to adjust for baseline differences (confounding) across BMI categories. Data collection and clinical followup were standardized, and the clinical assessment was performed by 2 independent surgeons in order to avoid observer bias.
The study has several weaknesses. First, it was limited by the relatively small number of adverse events resulting in large confidence intervals. For the same reason, we were unable to adjust for all potentially confounding factors. However, adjustment for several confounders was made for the combined complications, and for the complications infection and dislocation alone we adjusted for the most important confounders. Second, obese and nonobese patients differed by several baseline characteristics, which could be due to differences in the adverse events following primary THA and/or differential selection at the time of indication for primary or revision arthroplasty. Because 2 different clinical scores evaluating pain, function, and mobility were used at baseline and at followup, we were unable to analyze score differences. No information on intraoperative bone quality was available, but reports have shown that obese subjects tend to have greater bone mineral density and a lower risk of hip fractures (51–53). In addition, the need for an acetabular ring indicating insufficient acetabular bone stock was higher in the nonobese group, and severity of revision based on bone stock loss was not found to be significantly related to pain and function in the study by Davis et al. Finally, our study was conducted at 1 large academic center; however, baseline characteristics and indications for revisions did not substantially differ from descriptions of other hospital- or community-based revision cohorts in the literature (30, 54–56). Further studies including a larger number of patients are needed to assess external validity and to evaluate the extent to which different techniques and implants can influence the results.
Revision THA is a technically-challenging intervention, particularly in obese patients, probably because of more difficult anatomical conditions. Our results revealed that obesity was associated with higher event rates; notably, surgical site infection and dislocation. Furthermore, we found moderately lower HHS with higher levels of pain 5 years postoperative. Surgeons, patients, and referring physicians should be aware of an increased risk of adverse events in this patient group. Further studies are necessary to evaluate whether changes in medical preparation, surgical technique, and implant choice can help reduce the adverse event rate in obese patients undergoing revision THA.