In this study, we demonstrated that patients over 80 years of age were not at greater risk of developing a severe postoperative complication after surgery of lumbar spinal stenosis. Older patients had more comorbidities and the surgical procedure was different for this category. These parameters influenced the occurrence of a severe postoperative complication.
Complications in elderly patients
We found a 6.9% risk of SC within 30 days following LSS surgery for patients over 80 years of age. For patients over 80s undergone LSS surgery, the complications rate is variable in the literature, according to the definition of a SC. Saleh et al did a retrospective study in US based on national data with 2320 patients over 80 years of age. They found a lower risk of severe complications of 3.23%. However, they did not include revisions as severe complications. Their SC corresponded to our severe medical complications with a similar rate: 3.5%. Contrary to this study, we believe that a surgery revision should be considered as a severe complication. Another French study by Balabaud et al  showed a 13% rate of SC: they counted a higher epidural hematomas and wound infections rate of 3.3% and 4% (against 2.5% and 0.5% respectively for us). Their definition of severe medical complications was larger including new-onset cardiac arrhythmia and SIADH. Wang et al  made a same study with 26 patients over 85 years. Their complication rate was higher: 7.6% of SC. These observations continue to raise the question of the relationship between age and complications.
In our study, we showed that the risk of SC was not increased after surgical management of LSS in patients older than 80. To compare Giannadakis et al  using the same design that us, showed that an age over 80 was not associated with increased complications. Murphy et al  made the same observation in a US national cohort of 8,744 patients divided into four classes: <65, 65-75, 75-85, >85YO. They showed an increased complication rate for patients over 65 years of age. Dividing the cohort into several classes was interesting, nevertheless 58% of patients were under 65 years while the LSS mainly involved older people. Thus, our main question was to know whether in a group of seniors, the oldest patients were more likely to have complications. We also included patients under 65, but they represented only 25%. Li et al  published in 2008 the largest study on this topic with 471,215 patients. They found a direct association between the occurrence of complications and an age above 65. More interestingly, they showed an excess risk for people over 85 to develop a complication after a decompression of the lumbar spine.
Regarding complications in our cohort, the death rate was 0.2%, but no patient died in the older group. Studies with young patients like the studies of Li et al  and Murphy  found a similar death rate. Studies including only elderly patients found a higher number: Gerhardt et al  reached a death rate of 0.8% while Saleh  found a rate of 0.4%. Concerning admission to ICU, Kay et al  reported a 5.1% rate after lumbar spinal surgery, more than ours: 0.3%. However, they included more aggressive procedures: the rates of fusions and length of surgery were higher. In their study, female gender, ASA grade, cardiac comorbidities, age, length of surgery and blood loss were identified as risk factors for ICU admissions.
For unplanned readmissions, 2.6% of patients returned to the neurosurgical unit in our cohort. This rate is low compared to the literature: 6.39% for Saleh et al  with patients over 80 and 4.4% found in the Kim et al study . This last study showed that a high ASA score, venous thromboembolic events, re-operations in the first stay, post operative complications were risk factors. In our cohort, the rate of readmissions was similar between the older and younger groups. Murphy et al  found a higher readmission rate in older people compared to those under 65, but they did not show evidence of an increased risk after 85 years old.
Concerning the LOS, older patients stayed longer in hospital as reported in the literature . Our median length of stay (five days for the youngest and six days for the oldest) could be improved with the introduction of the enhanced Recovery After Surgery: currently four days in hospital for the surgical management of LSS is our daily goal regardless of the age class.
Management of comorbidities
Beyond age, it seems that the postoperative outcome is related to several other factors. To start with the patient’s comorbidities: we noticed that patients over 80 had higher CCI and ASA score meaning more comorbidities. To compare with the literature, the studies of Giannadakis  and Nanjo  found almost the same result (p-value at 0.09 and 0.07 respectively). In the study of Murphy et al , they showed an association between the increasing comorbidities and the aging excepted for high blood pressure. In our cohort, the elderly were significantly more affected by hypertension, the most frequent affection with 69% of cases. In France, hypertension is the leading cardiovascular risk factor. It increases with age and affects more than two-thirds of the population aged 65 to 75 years of age , consistent with our observations.
In our study, the risk of postoperative SC was independently related to heart diseases and to the use of antiaggregants. The management of anticoagulants and platelet antiaggregants must be a compromise between the risk of intraoperative blood loss or epidural hematoma and the risk of arterial thrombosis. Soleman et al  compared the impact of aspirin in 102 patients on the postoperative complications after LSS or herniated disc surgery. They showed no significant difference between the groups. However, they found higher blood loss, lower postoperative haemoglobin, more transfusions in the Aspirin group. Comparing with others studies, the rate of epidural hematoma varies between 0 to 1% . Park et al  made a large retrospective study of 17,549 patients who undergone spinal decompression. They found a 1.15% rate of postoperative epidural hematoma. Risk factors were a high blood loss greater than 500ml, a surgical duration greater than two hours, hypertension. The use of anticoagulants increases the risk, but the result was near significant. Anticoagulants were not considered as a risk factor of SC in our study. Our rate of thromboembolic events was similar to the literature : 0.2% for Ginnadakis , 0.5% for Murphy , 0.4% for Li . In our study, the four patients concerned belonged to the elderly group. We did not perform a subgroup analysis for this risk factor although it appears that age may be a risk factor of thromboembolic events. This observation can be supported by Yoshioka’s prospective study about thromboembolic events after degenerative spine surgery, which showed that advanced age was a risk factor .
Other comorbidities did not play a major role in the occurrence of SC. Regarding diabetes, this condition was slightly increased in patients with SC.. A large study based on data from the Korean National Health Insurance Service, showed that after surgery for LSS, the mortality rate was multiplied by 1.35 for diabetes patients . The criteria of inclusion in the Korean study are less restricted than ours: no exclusion for aggressive surgical procedures. Furthermore, the result was significant in univariate analysis, but diabetic patients had more heart disease and chronic kidney disease which could impact the rate of severe complications. CKD did not appear as a risk factor of severe complications. To talk to diabetes again, its management must involve the anaesthesiologist. The SFAR recommends to look for its complications, to evaluate its control, and to follow the prescription of antidiabetic drugs . The major risk of unbalanced diabetes is the surgical site infection .
Concerning the BMI for the elderly, the standards are different from those for the youth. We talk about undernutrition for patients whose BMI is under 21 and obesity when BMI is over 30. Undernutrition is a known risk for spinal infections and can multiplicate the risk by 2.3 . Like in the study of Giannadakis et al, the BMI was significantly lower for the elderly in our cohort, but no link with SC was noticed. A recent Chinese study made by Kong et al  evaluated the impact of BMI on lumbar arthrodesis for elderly patients: they found that low BMI under 24kg/m² increased the complication rates. The preoperative nutritional evaluation is a way to minimize these risks. This topic is included in our current protocol “enhanced recovery after surgery” and was described in the literature . Patients are assessed by dieticians and receive nutrition therapy if necessary. The rate of serum albumin level was described in the literature to detect undernutrition: low albumin are associated with an increased risk of readmissions, mortality, length of stay, and mortality  . This data was not available. As the undernutrition, obesity also presented risks. Giannadakis et al  found that obesity increases the duration of the surgery. In addition to being a risk factor for LSS , it rises postoperative complications in spine surgery  especially for spinal infections. Beside obesity, other risk factors for wound infections have been described in the literature: blood loss, reoperation, diabetes, duration of the surgery and length of stay at hospital . Age over 80 was not found to be a risk factor of wound infection in our study.
Regarding breathing disorders, no difference was observed between the two groups. These diseases appeared as a risk factor for complications with a p-value close to 0.05. Our broad definition of breathing disorders would allow us to detect a possible risk factor that was not described in the literature. To go on, this study did not evaluate the impact of smoking on SC. Giannadakis et al  found that the proportion of smokers was lower in the older group, but their did not find an increased risk of complications in LSS surgery. Smoking is known to be a risk factor for surgical site infections . It is a target of our enhanced recovery after surgery program, as described in the literature .
Performing the least morbid surgery ?
We have shown in our study that surgical procedures have an impact on the risk of SC. This highlights the issue of the invasiveness of the surgery. We need to propose the least risky surgery with the best benefit-risk ratio. This starts with the selection of the best operative position. In our cohort, the knee-chest position was the most used position for the management of LSS. Some compression complications, unfound in our cohort, have been described in the literature, such as blindness due to eyeball support, limb paralysis and shoulder dislocation . Elderly patients were less likely to be positioned in knee-chest for hemodynamic reasons. The knee-chest position decreases the cardiac ejection fraction due to lack of venous return. It theoretically affects the elderly, who are more likely to suffer from heart disease. This position can lead to hypotension during surgery, which can cause strokes and acute renal failures . However, this position is interesting for the surgeon: this hypotension reduces epidural blood loss during laminectomy and facilitates decompression by reducing the lordosis  leading to faster surgical procedures. In our cohort, the knee-chest position seemed to have a protective effect on the occurrence of serious postoperative complications.
Secondly, regarding durotomy, its rate varies in the literature between 0.5 and 18% . In our study, the occurrence of a durotomy represented a strong risk factor for severe complications. Its rate was high: 17.3%. The Swedish study of Strömqvist et al  evaluated the risk factors for the occurrence of durotomy in 64,431 patients. They found that age and history of lumbar spinal surgery were risk factors. In our cohort, older patients had significantly more durotomies, as shown in the literature . In addition, they have undergone a significantly more extensive decompression that increases the risk to make a durotomy. Anatomically, during LSS decompression, most durotomies occur in the medial part of the joint , where the enlarged ligament sticks  especially for the elderly. Lateral durotomies can be delicate to suture, however no patient over 80 underwent a revision for CSF leakage. Another study from USA  with 766 patients showed a risk of durotomy of 19% in patients over 65 years old. In practice, durotomy will result in the confinement to bed of the patient for 48 hours. This bed rest can cause complications as confusion for the elderly patients. Concerning confusions, its rate was very low and we think that we had a bias of information due to a lack of data in medical records. The rate of confusion after lumbar spinal surgery is variable in the literature: 0.8-13%   . Increased age was found as risk factor in a large study of 578,457 lumbar decompressions . Pernik et al  study the impact of geriatric optimization before spinal surgery on the postoperative delirium. Patients with geriatric assessment were older and had more comorbidities, but they had less delirium in postoperative time. Involving geriatricians in our care could therefore be a way to reduce minor complications for the oldest patients. Finally, Balabaud et al  found an association between instrumentation and the occurrence of delirium.
The question of whether an additional arthrodesis in the elderly should be performed is still being debated. We included in our study only arthrodesis with one level. The WNFS recommends a decompression alone if the patient has a predominantly radicular pain without signs of instability or with stable spondylolisthesis . In our cohort, the prevalence of spondylolisthesis was 23%. The prevalence of degenerative spondylolisthesis was determined in the Kalichman et al. study using the Framingham cohort : 16% for patients over 70 and 16% for patients with low back pain. The use of fusion depends on the preoperative evaluation on the X-ray and on the search for instability . Regarding grade 1 spondylolisthesis, Blumenthal et al  described the criteria for instability: sagittal facet joints with an angle > 50°, a disc height greater than 6.5mm, and a mobile spondylolisthesis of more than 1.25mm on dynamic X-ray. In addition, it is recognised that arthrectomy or isthmus resection creates postoperative instability . In our study, these criteria were not available in all hospital records. Our philosophy on LSS and fusions is to follow guidelines while remaining as minimally invasive as possible. We have to keep in mind that fusion does not improve the functional status at two and five years and increases the blood loss and surgical costs . In our study, fusions were not a risk factor to develop SC. We reported an occurrence of symptomatic screw malposition of 3% comparing with 10% in mean in the literature . These results can be explained by the fact that we excluded patients with posterolateral arthrodesis more than one level. Saleh et al , who did not apply these criteria, found a complication rate twice as high in patients with arthrodesis. The sparing use of fusion reduces the risk of postoperative complications.
Then, the number of decompressed levels was greater in elderly subjects. Contrary to Murphy et al , we did not detect the number of levels as a major complications factor. The length of the surgery was also reported as a risk factor in their study. For Saleh et al , procedures lasting over 180 minutes presented an extra risk. In our cohort, only 1.8% procedures lasted over 180 minutes. Kong et al  reported decompression as risk factor from three levels. In our study, only 46 patients had a more than three levels extension decompression, showing our desire to be less invasive. Continuing with the use of minimally invasive surgery, 9.3% of patients underwent the installation of interspinous device, allowing correction of the hyperlordosis responsible for radicular pain. 9.3% of patients underwent this technique. However, the disadvantage of this technique is its efficiency. Indeed, the decompression may be insufficient with a reoperation rate of up to 27% .
Finally, a more aggressive procedure may be related to increased blood loss during the operation. The postoperative red blood cell transfusion rate was 0.9% in our study. Giannadakis et al.  found an almost similar rate of 1.2% in their cohort. Our transfusion rate was higher in the elderly, but no subgroup analysis was performed in this study. ASA grade, duration of surgery and multilevel fusion were known risk factors of blood transfusion in the study of Morcos et al.  while age did not appear as a risk factor. They did not study the potential association between the operative position of the patient and transfusion. In our study, among nine transfused patients, five were positioned in prone position (55.6%). As we have seen previously, this position could potentially increase blood loss and postoperative transfusions. Only one study by Rigamonti et al  was found in the literature. With only 30 patients undergoing microdiscectomy they compared prone vs knee-chest positions and their impact on blood loss. They reported significantly increased blood loss with knee-chest position. However, when the knee-chest position was contraindicated due to cardiac or renal or respiratory disorders, patients were excluded. Moreover, microdiscectomy frequently involved younger patients with a mean age around 50, not comparable with our cohort. To avoid post-operative transfusions in lumbar spinal surgery, some authors reported the use of tranexamic acid before procedure. This drug should be used with caution in the elderly. CKD, epilepsy, venous and arterial thrombosis contraindicate its use . In addition, minimally invasive techniques reduces intraoperative blood loss . Finally, the search for preoperative anaemia may also have an impact on the transfusion rate. This is a target of our ERAS program: patients with anaemia receive an iron infusion or erythropoietin.
We must point out some boundaries of our study. First, the retrospective design of the study may cause bias. Even though we are in a university hospital, we have to note that the anaesthesia team has performed a first screening of our patients. They rejected patients deemed unfit to receive general anaesthesia, which defines a selection bias in our population.
Secondly, the use of propensity score was very helpful to guarantee a good comparison between groups. It should be highlight that the standardized mean differences were 0.12 for an interspinous device (see table in appendix) and must keep between -0.10 and 0.10 to have good comparison. 0.12 is very close to 0.10 and we considered with statisticians that the model can still be used. Next,
In severe complications, we chose to include the occurrence of severe organ failure. The definition of organ failure can be confusing. These complications are life-threatening for the patient and therefore we have included them.
Thirdly, the age limit of 80 years is an arbitrary limit. Even though it is used frequently in the literature, we find that physiological age is more important than chronological age. For a future study, we could have separated into 2 groups the patients considered fragile versus the others by evaluating the frailty. This corresponds to the reduction of physiological reserves through a multi-organ system that decreases resistance to stress . We can measure this parameter with Fried’s criteria. The review done by Simcox et al  showed a link between frailty and postoperative mortality, postoperative complications, and the risk of prolonged hospitalization. Concerning the impact of heart diseases on postoperative prognosis, anaesthetic score like MET or Lee were interesting to study this link.
Finally, it would be interesting to compare the complication rate per year. This would show the impact of new anaesthesia techniques such as locoregional anaesthesia and new surgical techniques such as the use of minimally invasive surgery.