JONATHAN R. SLOTKIN, M.D.

Plain English
This study looked at older patients (65 and up) who had surgery for a specific type of back problem called grade I degenerative lumbar spondylolisthesis. Researchers found that patients who had additional fusion surgery had significantly better outcomes, with 87% of those in this group reporting meaningful improvements in their pain and mobility after two years, compared to only 49% in a group with less favorable outcomes. These results are important because they can help doctors decide whether to include fusion in surgery for older patients, ultimately improving patient recovery and quality of life. Who this helps: This helps patients with degenerative lumbar spondylolisthesis and their doctors in making informed treatment decisions.

Plain English
This study looked at how body mass index (BMI) affects recovery outcomes after two types of back surgery for a condition called spondylolisthesis. Researchers followed 608 patients over two years and found that obese patients (BMI of 30 or higher) had better recovery results when they underwent minimally invasive (MI) surgery compared to open surgery, with 73.3% of them showing meaningful improvement in disability scores after MI versus 56.3% after open surgery. In contrast, there was no significant difference in outcomes for non-obese patients regardless of the type of surgery. Who this helps: This helps obese patients needing back surgery by providing them with information on the best surgical options for recovery.

Plain English
This study looked at how a new type of bone adhesive, called TTCP-PS, compares to traditional titanium plates and screws (TPS) for fixing skull flaps in sheep. Researchers found that the adhesive did not cause any more harm to the underlying brain tissue than the standard method, with both methods showing minimal tissue changes. This is important because it suggests that TTCP-PS can be a safe alternative to TPS for fixing skulls, possibly reducing complications associated with metal hardware. Who this helps: Patients undergoing cranial surgery.

Plain English
This study looked at 436 patients who had surgery for a specific spinal condition called low-grade spondylolisthesis. The researchers found that while 73% of patients showed significant improvement in their disability scores within three months, about 21% experienced a delay in their improvement but eventually caught up by 12 months. Understanding who might have a slower recovery, such as those with trouble walking before surgery or who still had leg pain at three months, is important for managing patient expectations and care. Who this helps: This helps patients and their doctors by identifying who might need extra support during recovery.

Plain English
This study looked at how often patients with grade 1 spondylolisthesis needed a second surgery within five years of their first surgery, and how that affected their reported outcomes. Out of 608 patients, 13.3% who had decompression only and 9.8% who had decompression and fusion needed revision surgery. Those who required revision generally reported worse outcomes, with an Oswestry Disability Index score of 27.4 compared to 19.4 for those who did not need additional surgery, highlighting the impact of needing a second operation. Who this helps: This benefits patients with grade 1 spondylolisthesis, as well as their doctors, by providing insight into the risks and outcomes of revision surgery.

Plain English
This study looked at how anticipating severe back pain affects patients' recovery after surgery for degenerative lumbar spondylolisthesis, a condition causing back and leg pain. The researchers found that out of 608 patients, 42.8% were classified as "catastrophizing," meaning they expected high levels of pain, but they still showed significant improvement in their pain levels after surgery, achieving better outcomes than those with lower initial pain expectations. This matters because it suggests that fear and anxiety about pain shouldn't stop patients from getting surgery, and emphasizes the importance of clear communication between patients and doctors about what to expect. Who this helps: This helps patients dealing with chronic back pain and their healthcare providers.

Plain English
This study looked at the long-term results of two surgical treatments for grade 1 spondylolisthesis: minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) and decompression alone. After five years, both groups showed significant improvements in pain and disability, but the MIS TLIF group had a much lower reoperation rate of 2.8%, compared to 15.5% for decompression. This is important because it suggests that patients undergoing MIS TLIF are less likely to need additional surgery and report higher satisfaction overall. Who this helps: Patients with grade 1 spondylolisthesis undergoing spinal surgery.

Plain English
This study looked at how some patients' back pain changes after surgery for a specific spinal condition called low-grade spondylolisthesis. Out of 608 patients assessed, most (about 88%) experienced improved or stable back pain two years after surgery, while 12% had worse pain; notably, those who started with lower pain scores were more likely to report worsening pain later on. These findings are important because they help identify which patients might not benefit as much from surgery, particularly those with less severe symptoms or ongoing leg pain. Who this helps: This helps doctors make better decisions about who should undergo surgery for back issues.

Plain English
This study looked at how diabetes affects the outcomes of lumbar spinal surgeries, specifically decompression and arthrodesis. Researchers found that while patients with diabetes had similar outcomes after decompression surgery, those undergoing arthrodesis had significantly higher issues, such as a 15.7% nonroutine discharge rate compared to 13.4% for non-diabetic patients, and a higher reoperation rate of 4.3% versus 3.2%. This matters because it highlights the need for better management of diabetes before surgery to help improve patient outcomes, especially for those having arthrodesis. Who this helps: This helps patients with diabetes who need spinal surgery, especially those undergoing arthrodesis.

Plain English
This study looked at how cervical spondylotic myelopathy (CSM), a condition that can cause problems with driving, affects patients and how surgery can improve driving abilities over time. They found that 31.4% of the 1,128 patients had issues with driving before surgery, but 72% of those patients reported improvements in their driving ability within 24 months after surgery. This is important because better driving ability can lead to a better quality of life for these patients. Who this helps: This helps patients with cervical spondylotic myelopathy.

Plain English
This study compared two types of surgery for patients suffering from neck and arm pain caused by nerve issues: posterior cervical foraminotomy and anterior cervical discectomy and fusion (ACDF). Researchers found that while the foraminotomy surgery led to shorter hospital stays (0.5 days compared to 0.9 days) and similar improvements in quality of life and pain after one year, it also had a higher reoperation rate (4.2% vs. 1.9%) and lower satisfaction rates (65.2% vs. 74.6%) compared to ACDF. This information is important because it helps guide doctors in choosing the right surgical approach for patients based on their specific conditions. Who this helps: Patients with cervical radiculopathy and their doctors.

Plain English
This study looked at how a patient's level of education affects their health before and after surgery for a spine condition called lumbar spondylolisthesis. Researchers found that people with lower educational levels reported worse disease severity and higher disability scores before surgery; for instance, those with only a high school education scored 27.1 on the disability index, while graduates did much better. Even though surgery outcomes were similar for all education levels, patients with lower education had worse overall health ratings afterward, highlighting the need for better patient education to improve health results. Who this helps: This helps patients with lower educational backgrounds who may not be getting the best possible health outcomes.

Plain English
This study looked at the long-term cost-effectiveness of two types of back surgery, PLIF and TLIF, for patients with a specific condition called grade 1 lumbar spondylolisthesis. Researchers analyzed data from 385 patients over five years and found that the average cost of surgery was $31,634, leading to a gain of about 1.07 quality-adjusted life years (QALYs) at a cost of $29,511 per QALY. This is significantly lower than the $100,000 threshold typically considered cost-effective, showing that these surgeries are a good investment in improving patients' lives. Who this helps: This benefits patients suffering from lumbar spondylolisthesis and the doctors treating them.

Plain English
This study looked at 573 patients who had surgery for a specific back condition called grade 1 degenerative spondylolisthesis and tracked their satisfaction five years later. They found that 83.7% of patients were satisfied with their outcomes, and those who could walk independently before surgery were more likely to be happy after the surgery. This is important because it highlights that certain patient characteristics, such as independence and health status, can predict long-term satisfaction after back surgery, helping doctors better understand who might benefit most from the procedure. Who this helps: This helps patients and doctors make informed decisions about surgical options for back pain.

Plain English
This study looked at how having both depression and anxiety affects patients' long-term recovery after spine surgery for a condition called lumbar spondylolisthesis. Researchers analyzed 608 patients and found that, although those with both conditions had lower quality of life scores before surgery, they experienced similar improvements and satisfaction rates after 5 years as those without these mental health issues. Specifically, over 80% of all patients were satisfied with their surgery results, regardless of whether they had depression or anxiety. Who this helps: This information benefits patients dealing with lumbar spondylolisthesis, especially those with depression and anxiety, by showing they can still expect good outcomes from surgery.

Plain English
This study looked at the long-term outcomes (five years) of obese and non-obese patients who had surgery for a specific spine condition called grade 1 spondylolisthesis. They found that while obese patients (those with a BMI of 35 or more) reported worse pain and disability before surgery, at the five-year mark, both obese and non-obese patients had similar rates of needing more surgery and were satisfied with their results. However, obese patients struggled more to improve their leg pain after surgery compared to non-obese patients. Who this helps: This research helps both patients and doctors by showing that surgery can be effective for all patients, regardless of obesity, while also highlighting areas for improvement in leg pain management for obese patients.

Plain English
This study looked at how body mass index (BMI) affects the success of surgery in overweight patients with a spinal condition called lumbar spondylolisthesis. It found that among 282 patients, those with a BMI of 37.5 or lower had better results after surgery, like less pain and higher satisfaction. Understanding this helps doctors determine who might have a better chance of a successful surgery, improving overall patient care. Who this helps: This helps patients with obesity and lumbar spondylolisthesis considering surgery.

Plain English
This study compared two surgical methods for treating grade I lumbar spondylolisthesis: minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) and traditional open TLIF, looking at patient outcomes five years after surgery. While MI-TLIF had significantly less blood loss during surgery—about 108.8 ml compared to 299.6 ml for open TLIF—it didn't result in better long-term outcomes for disability, back pain, or patient satisfaction, with similar rates of reoperations for both methods (5.6% for MI-TLIF and 11.6% for open TLIF). This matters because it helps surgeons and patients choose between two effective surgical options without worrying about significant differences in long-term recovery. Who this helps: Patients with degenerative lumbar spondylolisthesis and their doctors.

Plain English
This study looked at a new type of adhesive, called Tetranite, for fixing skull pieces after brain surgery instead of using traditional titanium plates and screws. The researchers found that the adhesive made the skull flaps hold together better and prevented leaks of cerebrospinal fluid more effectively; 14 out of 16 adhesive-fixated samples showed no leaks even under high pressure. This is important because it reduces the risk of complications like infections and ensures proper alignment, which can improve patient recovery and outcomes. Who this helps: This helps patients undergoing brain surgery by providing a safer and more effective method for securing skull flaps.

Plain English
This study looked at patients with a condition called cervical spondylotic myelopathy (CSM) who had surgery and planned to return to work afterward. Of the 409 patients, 80% were able to go back to work within 3 months of their surgery. However, even those who had good surgical outcomes sometimes struggled, with 11.9% not returning to work; factors like being on short-term disability before surgery or having more neck pain influenced their chances of not going back to work. Who this helps: Patients recovering from cervical spine surgery.

Plain English
This study looked at how different questionnaires, which ask patients about their experiences after cervical spine surgery for myelopathy (a type of spinal cord problem), relate to their overall satisfaction with the surgery. The researchers analyzed data from 1,141 patients and found that satisfaction scores were closely linked to pain ratings for the neck and arms, with correlations ranging from 0.30 to 0.49, and that high levels of neck pain were very common (42.8% of patients). This matters because it shows that patients care more about reducing their pain and disability than about the underlying neurological issues, which can help doctors better assess treatment outcomes. Who this helps: This helps patients who are undergoing cervical spine surgery and their doctors.

Plain English
This study looked at how common sleep problems are among patients with cervical spondylotic myelopathy (CSM) and what factors affect their sleep quality after surgery. Out of 1,135 patients, 79.5% had sleep issues before their surgery, and 72.8% saw an improvement in their sleep 24 months later, with 42.5% reporting that their sleep problems completely went away. Factors like smoking, osteoarthritis, and moderate neck pain were linked to a lower chance of improving sleep. This is important because better sleep is strongly associated with higher satisfaction with surgery results. Who this helps: Patients with cervical spondylotic myelopathy.

Plain English
This research looked at the Quality Outcomes Database (QOD), which has been tracking neurosurgery data since 2012. Over ten years, it produced 94 studies, mostly focusing on spinal surgeries—59 on lumbar and 22 on cervical spine operations. This work is important because it provides trusted information that helps doctors make better decisions for treating patients based on real-life outcomes. Who this helps: This benefits patients undergoing neurosurgery and the doctors treating them.

Plain English
This study focused on figuring out which patients are at higher risk of staying longer in the hospital after spine surgery, specifically for a condition called spondylolisthesis. Researchers developed two machine learning models using data from 544 patients, finding that the models were extremely accurate: one model correctly identified high-risk patients 98.1% of the time, while the other was even better at 99.1%. These results are crucial because they can help doctors predict patient outcomes more effectively, guiding better care and resource allocation. Who this helps: This benefits patients undergoing spine surgery and their doctors.

Plain English
This study looked at whether correcting the slippage in the spine (known as Meyerding grade) during surgery helps patients report better results two years after having surgery for a specific back condition called degenerative lumbar spondylolisthesis. It included 206 patients, and although all saw significant improvements in their symptoms and satisfaction after surgery, there was no difference in outcomes between those who had more than 3 mm of slippage corrected and those who had less. This finding is important because it shows that even a small correction can lead to positive results, helping guide treatment decisions. Who this helps: This helps patients with degenerative lumbar spondylolisthesis and their doctors in understanding the effectiveness of surgery options.

Plain English
This study looked at how different age groups—young adults, early elderly, and late elderly—experienced quality of life after surgery for a spinal condition called cervical spondylotic myelopathy. Researchers found that although younger patients reported worse symptoms before surgery, by 12 months after the operation, all age groups had similar improvements in their quality of life scores. This is important because it shows that older patients can expect similar benefits from the surgery as younger patients, helping to reassure both patients and doctors about the effectiveness of the treatment for seniors. Who this helps: Older patients with cervical spondylotic myelopathy and their healthcare providers.

Plain English
This study looked at how different types of insurance affect the results of surgery for a condition called degenerative lumbar spondylolisthesis, which is a back problem. Researchers found that after 24 months, patients with Medicaid had worse outcomes compared to those with private insurance, with a 10.2 point drop in their disability index and more leg pain. This matters because it highlights disparities in healthcare, showing that those with Medicaid may not benefit as much from surgery as those with other insurance types. Who this helps: This information helps patients and healthcare providers understand the impacts of insurance on treatment outcomes.

Plain English
This study looked at a new, less invasive way to surgically remove large, calcified discs in the thoracic area of the spine that can cause nerve problems. The researchers successfully performed this procedure on patients without the need for hospital stays or complicated surgeries, showing that this approach is safer and easier for patients. This is important because it can lead to faster recovery times and fewer complications for those suffering from this condition. Who this helps: Patients with thoracic disc herniations.

Plain English
This study looked at the genetic factors involved in spondylosis, a common degenerative spine condition. Researchers analyzed data from 16,956 patients and found a significant genetic link to a specific region in the BMP6 gene, with a notable increase in risk (about 3.4% higher odds per variant) for developing spondylosis. The findings suggest that genetics play a role in this condition, which could open up new avenues for treatment and prevention. Who this helps: This helps patients with spondylosis and healthcare providers looking for better treatment options.

Plain English
This study examined whether surgeries performed in July, when new medical trainees start, lead to different long-term health outcomes compared to surgeries done at other times. Researchers analyzed data from 608 patients who had surgery for a specific back condition and found that although surgeries in July took about 22.4 minutes longer on average, there were no significant differences in complications, recovery, or patient satisfaction between the July and other months' surgeries. This indicates that having new trainees does not negatively impact patient outcomes, possibly due to increased supervision and support. Who this helps: Patients undergoing lumbar spondylolisthesis surgery.

Plain English
This study looked at how well patients did after two different surgical treatments for a back condition called grade I lumbar spondylolisthesis. It found that patients who had both decompression and fusion surgery reported a significant improvement in their disability levels 24 months later, with an average change in their disability score of -25.8 compared to -15.2 for those who just had decompression. This matters because it indicates that adding fusion surgery can lead to better outcomes for patients suffering from this condition. Who this helps: Patients with grade I lumbar spondylolisthesis.

Plain English
This study looked at factors that lead some patients to leave the hospital in a way that requires extra care after surgery for cervical myelopathy, a condition affecting the spinal cord in the neck. Out of 1,114 patients studied, 11.2% (or 125 patients) had to go to rehabilitation or another hospital rather than go home. Key findings showed that older patients (65 and up), African American patients, and those with Medicare insurance were more likely to be among these cases, and patients showing motor deficits were also at higher risk. Who this helps: This research benefits patients with cervical myelopathy and their healthcare providers by identifying those who may need additional support after surgery.

Plain English
This study examined patterns among patients who had surgery for a specific type of spine condition called spondylolisthesis. Researchers analyzed data from 608 patients, discovering two main groups: one with a higher disease burden that was younger, heavier, and reported more pain, and another with a lower burden that was older and had less severe symptoms. While the first group started with worse health but showed significant improvements after surgery, they were also less satisfied with their outcomes compared to the second group. Who this helps: This research benefits patients undergoing surgery for spondylolisthesis, as well as the doctors treating them.

Plain English
Researchers tested a new bone glue made from minerals to hold skull bone flaps in place after brain surgery, comparing it to the standard metal plates and screws currently used. In sheep, the new adhesive was stronger than metal fixation from 12 weeks through 2 years after surgery, healed bone faster with better integration, and caused no tissue damage or complications. This bone glue could be a better option for human skull surgery because it's stronger, dissolves naturally over time as new bone grows in, and avoids the problems that can happen when metal hardware shifts or loosens.

Plain English
This study looked at how obesity affects outcomes for patients who had surgery for a back condition called lumbar spondylolisthesis. Researchers analyzed data from 797 patients and found that while obese patients (382) had worse pain and disability scores before surgery compared to non-obese patients (415), both groups showed significant improvements after one year. However, at the end of that year, the obese patients still reported more leg pain and lower quality of life than non-obese patients, even though similar percentages from both groups felt their surgery met their expectations (62.6% for obese vs. 67.4% for non-obese). Who this helps: This research helps both patients and doctors understand the specific challenges faced by obese patients after back surgery.

Plain English
This study looked at how surgery for degenerative lumbar spondylolisthesis affects sexual activity and satisfaction in patients. Of the 218 patients studied, about 82% reported that their sex life was affected before surgery, but 73% experienced improvement two years after surgery. Factors like a lower body mass index (BMI), better health status, and more education were linked to better outcomes. Who this helps: This helps patients undergoing surgery for back issues, especially those concerned about sexual health.

Plain English
This study looked at patients who had surgery for a condition called grade I spondylolisthesis and found that 9.4% of them had to go to a rehabilitation facility instead of going straight home. Key factors that increased the chances of this happening included being older, having a higher body mass index, having depression, facing complications after surgery, and undergoing more complex surgery. Understanding these factors is important because it can help healthcare providers better prepare for and manage the postoperative care of these patients, potentially reducing costs and improving outcomes. Who this helps: This helps patients and doctors by identifying risks that may lead to longer hospital stays and additional care needs.

Plain English
This study looked at how age affects the results and complications for older patients who had surgery for a condition called spondylolisthesis, which affects the spine. Researchers analyzed data from 608 patients and found that older patients are more likely to have health issues like diabetes and heart disease. Despite their age, all patients showed significant improvement in their quality of life after surgery, with no difference in the rates of hospital readmissions or repeat surgeries across different age groups. Who this helps: This helps older patients considering surgery for back issues and their healthcare providers.

Plain English
This study looked at patients with a specific back condition (grade I spondylolisthesis) who had surgery and whether they were still part of the study two years later. Out of 608 patients, 88 (14.5%) were lost to follow-up. The researchers found that those who dropped out were generally younger, had higher levels of back and leg pain, more anxiety, and worse overall functioning compared to those who stayed in the study. Who this helps: This information is useful for doctors and researchers to understand which patients may be more likely to miss follow-up appointments.

Plain English
This study looked at how patients' disability and quality of life changed after spine surgery for a specific back problem across different regions in the United States. Researchers found that patients in the South started with higher disability scores (51.2) compared to other regions, but they also saw the greatest improvement after surgery, with their scores improving by an average of 26.5 points. Meanwhile, while all regions experienced significant improvements, quality of life scores were similar across the board. Who this helps: This information benefits patients undergoing back surgery and their doctors by highlighting regional variations in recovery outcomes.

Plain English
This study looked at the Quality Outcomes Database (QOD) for spine care from 2012 to 2020, which aims to improve the quality and effectiveness of spine surgery across North America. The project has helped create the largest spine registry in the region, allowing healthcare providers to compare their results with national benchmarks, identify which patients benefit most from specific surgeries, and share important data on care quality. These achievements support better decision-making in spine care and enhance the overall safety and effectiveness of neurosurgical procedures. Who this helps: This benefits patients undergoing spine surgery, along with their doctors and healthcare providers.

Plain English
This study looked at how returning to work after surgery for lumbar spondylolisthesis (a spine condition) is related to how satisfied patients feel about their surgery. Out of 608 patients, 85.3% were satisfied with the surgery, and 76.7% were able to return to work. Interestingly, many patients who didn't go back to work (72.1%) were still happy with the surgery, suggesting that satisfaction can exist independently of return to work status. Who this helps: This information benefits both patients and doctors by highlighting that satisfaction can vary regardless of work status.

Plain English
This study looked at two types of surgery for people with a specific spinal condition called low-grade spondylolisthesis and compared their outcomes. Researchers found that while both open surgery and minimally invasive surgery (MIS) led to similar improvements in pain and patient satisfaction over two years, patients who had the open surgery reported higher satisfaction levels. However, those who underwent MIS had significantly shorter hospital stays—about 0.7 days compared to 1.8 days for open surgery. Who this helps: This benefits patients with low-grade spondylolisthesis by providing them with options for treatment that consider both effectiveness and recovery time.

Plain English
This study compared two types of surgery for patients with a specific back condition called grade 1 degenerative lumbar spondylolisthesis: minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) and traditional open TLIF. Out of 297 patients, those who had the MI-TLIF surgery experienced less blood loss and a higher return-to-work rate (100% compared to 80% for open surgery), as well as improved quality of life and lower disability scores. These findings are significant because they show that MI-TLIF can lead to better recovery outcomes, making it a preferable option for certain patients. Who this helps: Patients suffering from grade 1 degenerative lumbar spondylolisthesis.

Plain English
This study looked at a new method for taking tissue samples from spinal tumors using a special endoscopic technique. The researchers treated a patient with a suspected lump in the spine and successfully diagnosed it as large B-cell non-Hodgkin lymphoma after a previous method failed. This new approach minimizes complications and can give doctors the information they need faster, which is crucial for starting the right treatment. Who this helps: This helps patients with spinal tumors, especially those with a history of lymphoma.

Plain English
This study looked at what factors lead to the best results for patients after minimally invasive surgery for a specific back condition called grade 1 degenerative lumbar spondylolisthesis. It involved 259 patients over two years, finding that those who were employed, had fusion surgery, or were older experienced better improvements in disability, back pain, and overall satisfaction. For instance, employed patients reported significantly less disability, while those undergoing fusion surgery also showed notable improvements. Who this helps: This helps patients with grade 1 degenerative lumbar spondylolisthesis and their doctors in making informed treatment choices.

Plain English
This study looked at the impact of depression and anxiety on patients undergoing surgery for a specific lower back condition called grade 1 spondylolisthesis. Of the 608 patients analyzed, 25.6% reported having a depressive or anxiety disorder, and those patients experienced worse short-term outcomes, like higher back pain and a lower quality of life three months after surgery. However, over two years, their overall satisfaction with the surgery was similar to those without these disorders, indicating that while mental health issues can affect recovery initially, they do not seem to change long-term results. Who this helps: Patients with depressive or anxiety disorders undergoing back surgery.

Plain English
This study looked at two types of surgery for grade 1 lumbar spondylolisthesis: laminectomy alone and laminectomy with fusion, involving 426 patients. The researchers found that surgery significantly improved patients’ disability and pain levels after 12 months, with about 80% receiving fusion surgery showing better scores on disability measurements. While the fusion group had a slightly lower reoperation rate, both surgical methods were effective in enhancing quality of life. Who this helps: Patients with lumbar spondylolisthesis seeking surgical treatment options.

Plain English
This study looked at how satisfied patients were two years after having surgery for a specific back condition called grade I lumbar spondylolisthesis. Out of 502 patients, about 82% reported being satisfied with their results. The research found that being older, having a job before surgery, and undergoing a type of surgery called fusion were linked to higher satisfaction levels. Who this helps: This helps patients undergoing back surgery and their doctors.

Plain English
This study compared two types of minimally invasive surgery for a back condition called degenerative lumbar spondylolisthesis. Researchers found that patients who underwent a procedure called MIS transforaminal lumbar interbody fusion (TLIF) had a significantly lower chance of needing another surgery (1.4% versus 14.1% for decompression) and reported better improvements in disability and back pain after 24 months. This is important because it helps doctors decide the best surgical option for patients dealing with this condition. Who this helps: Patients with degenerative lumbar spondylolisthesis.