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CLINICAL RESEARCH

What Are the Patient-reported Outcomes, Complications, and Radiographic Results of Lumbar Fusion for Degenerative Spondylolisthesis in Patients Younger Than 50 Years?

Goh, Graham S. MBBS, MRCS (Edin); Tay, You Wei Adriel MBBS, MRCS (Edin); Yue, Wai-Mun MBBS, FRCS (Edin), FAMS; Guo, Chang-Ming MBBS, MMed (Surg), FRCS (Edin), FAMS; Tan, Seang-Beng MBBS, FRCS (Edin), FRCS (Glas), FAMS; Chen, John Li-Tat MB BCh BAO, FRCS (Edin)

Author Information
Clinical Orthopaedics and Related Research: August 2020 - Volume 478 - Issue 8 - p 1880-1888
doi: 10.1097/CORR.0000000000001252

Abstract

Introduction

Degenerative lumbar spondylolisthesis affects 5% to 7% of the general population, and its prevalence increases with age [12, 16, 17, 20]. Because of its degenerative etiology, the onset of this disease historically was believed to occur only after the fifth decade of life [41], and radiologic studies showed that degenerative changes on lumbar MR images were extremely rare in asymptomatic patients younger than 50 years [48]. Boden et al. [6] reported that only 20% of asymptomatic patients younger than 60 years had herniated discs and only one had spinal stenosis. Furthermore, epidemiologic studies have observed that fewer than 10% of all patients with degenerative lumbar spondylolisthesis are younger than 50 years [17, 20, 25]. Many studies have evaluated the function and quality of life after lumbar spine surgery in patients aged 65 or older [4, 18, 39, 40]. Similarly, population-based studies evaluating trends in degenerative spondylolisthesis have restricted inclusion to patients 65 years and older [10, 47]. In fact, to avoid capturing patients with lumbar disc herniation, degenerative disc disease, or isthmic spondylolisthesis, some studies have arbitrarily excluded patients younger than 50 years [5, 15, 43].

Although many studies have investigated the outcomes of young patients undergoing total joint arthroplasty [24, 31, 49], limited evidence is available about this group in the context of lumbar spine surgery [23]. More recently, data from a multicenter spine registry have suggested that younger age may predict dissatisfaction after lumbar spine surgery [30]. Khan et al. [ 23] also reported the results of 330 young patients aged 18 to 54 years who underwent open posterior lumbar fusion and found that young patients had greater residual disability at a short follow-up of 15.76 months, although there was diagnostic and surgical heterogeneity in the cohort studies. As the number of individuals with obesity increases in the United States, even at younger ages [32], the incidence of degenerative diseases of the lumbar spine will rise concomitantly [17, 28, 51]. Spine surgeons will encounter an increasing number of young patients (younger than 50 years) who will undergo lumbar spinal surgery [11]. It is thus imperative that we evaluate the effectiveness of lumbar fusion in this challenging population.

We therefore asked (1) How likely were patients younger than 50 years to achieve a minimal clinically important difference (MCID) in improvement on any of several validated patient-reported outcomes scores after transforaminal lumbar interbody fusion (TLIF) for degenerative spondylolisthesis at a minimum of 2 years after surgery? (2) What proportion developed complications or underwent reoperations? (3) What proportion achieved radiographic fusion or developed adjacent-segment degeneration?

Patients and Methods

After obtaining approval to perform this study from our institutional review board (CIRB 2018/2356), we reviewed longitudinally gathered and maintained data of patients undergoing minimally invasive TLIF (MIS-TLIF) for degenerative spondylolisthesis at Singapore General Hospital from 2006 to 2013.

Study Inclusions and Exclusions

During the study period, a total of 210 patients younger than 50 years of age underwent MIS-TLIF at our institution after non-surgical attempts to mitigate their symptoms, such as analgesia and physical therapy, did not achieve that goal; all patients underwent a minimum of 12 weeks of non-surgical treatments before undergoing surgery, which is longer than has been advocated by some prior research [44]. The indications for surgery were Meyerding’s Grade 1 or 2 degenerative spondylolisthesis with radiculopathy or neurogenic claudication, although many patients also had low-back pain. From the 210 patients, we excluded 49 patients who had previous lumbar spine surgery, 52 patients who had surgery for isthmic or dysplastic spondylolisthesis, and 13 patients who had a two-level procedure for degenerative spondylolisthesis. This left 96 patients younger than 50 years of age who underwent a primary, single-level MIS-TLIF for degenerative spondylolisthesis and met the inclusion criteria. In this cohort, 86% (83) of patients had complete clinical and radiographic data, 10% (10) had missing clinical data but were included in the radiological analysis, and 3% (three) were missing both clinical and radiological data (Fig. 1).

F1
Fig. 1:
The flow diagram outlining the patient selection process is shown here.

The mean age of the study group was 44 ± 7 years, mean BMI was 25 ± 4 kg/m2 and percentage of females was 65%. There were 61 patients working preoperatively (Table 1). As degenerative spondylolisthesis has been increasingly recognized as a heterogenous disease, we also recorded the radiological parameters for each patient with spondylolisthesis. Specifically, the severity of (1) fixed translation, (2) dynamic translation, (3) angular instability, (4) disc space collapse [38], (5) central stenosis [42], (6) lateral recess stenosis [3] and (7) neuroforaminal stenosis [27] were measured for all patients (Table 2). Outcome scores were assessed preoperatively and at fixed intervals of 1, 3, 6 months and 2 years after surgery. The mean clinical and radiographic follow-up was 5 ± 3 years.

T1
Table 1.:
Preoperative characteristics (n = 96)
T2
Table 2.:
Radiographic parameters

Surgical Technique and Aftercare

The senior authors (CMG, WMY, SBT) performed all procedures. First, the operative level was confirmed using a mobile C-arm radiograph. A surgical incision was then made 3 cm to 5 cm parallel to the midline on the symptomatic side. Tissue dilators were inserted down to the facet complex. Facetectomy was performed to visualize the posterolateral part of the intervertebral disc, after which discectomy was performed and the endplates were prepared. Intradiscal spreaders were used to distract the disc space and an interbody cage filled with autograft and allograft cancellous bone chips was placed. The surgeons confirmed cage position using fluoroscopy. To ensure decompression, the remainder of the ipsilateral facet and lamina was resected and the lateral margin of the ligamentum flavum was removed to expose the ipsilateral exiting and transversing the nerve roots. In patients with bilateral disease, the patient was tilted and the tubular retractor was angled medially to visualize the contralateral side, followed by over-the-top decompression, where indicated. After decompression, a percutaneous pedicle screw and rod were inserted via the same incision and a second construct was inserted via a contralateral incision. Compression was applied and the construct was tightened to restore lordosis. Hemostasis and wound irrigation were performed before closure.

Postoperatively, patients were treated via a standardized clinical protocol. All patients sat up in bed postoperatively and were encouraged to ambulate from the first postoperative day. Patients were deemed fit for discharge to their homes after they successfully ambulated 20 m to 30 m independently and were found to be competent with stair climbing, if required. The length of hospital stay was the number of days needed to achieve sufficient independence to be discharged home. Patients were asked to attend follow-up appointments with the surgeon at 2 weeks, 1, 3 and 6 months, 1 year, and annually thereafter.

Primary and Secondary Study Outcomes

To answer our first research question, an independent healthcare professional who was not involved in clinical care (WY) assessed the patients preoperatively and postoperatively. Patients were assessed using the numeric rating scale (NRS) for back pain and leg pain (scored from 0 to 10, with a lower score representing less pain), the Oswestry Disability Index (ODI) (scored from 0 to 100, with a lower score representing less disability), and the SF-36. The medical outcome study approach proposed by Ware et al. [46] was used to derive two higher-order summary scores from the eight subscales of the SF-36: the physical component summary (PCS) and mental component summary (MCS) (scored from 0 to 100, with a higher score representing better quality of life). The PCS and MCS aggregate the most highly correlated subscales and simplify analyses without substantial loss of information. Clinical improvement was defined using the minimal clinically important difference (MCID), which represents a critical threshold of change in score, compared with the baseline, that is considered meaningful improvement to the patient. Previously published MCID values of 2.1 for NRS-back pain, 2.8 for NRS-leg pain, 14.9 for the ODI [37], and 4.9 for PCS [13] were used.

To answer our second research question, the medical, surgical or wound complications, blood transfusions, 30-day readmissions, and reoperations for any reason were recorded at a mean follow-up of 5 years.

To answer our third research question on radiographic findings, an independent observer (YWAT) who was not involved in clinical care, analyzed for radiographic fusion at mean follow-up of 5 ± 3 years, based on the grading system of Bridwell et al. [7]. We determined radiographic adjacent-segment degeneration by comparing radiographs taken preoperatively and at the most recent follow-up examination, irrespective of clinical symptoms. The following degenerative changes were identified: anterolisthesis or retrolisthesis of more than 3 mm, a decrease in the adjacent-segment disc height of more than 3 mm, or an intervertebral angle of flexion greater than 5° [33, 52]. Signs of implant loosening or cage migration were also recorded.

A secondary outcome of this study was the proportion of patients who were able to return to work among the subgroup of 61 patients who were working preoperatively. We recorded the mean number of days taken to return to work and the proportion of young patients who had successfully returned to work at predefined intervals of 1, 3, 6 months and 2 years postoperatively.

Sample Size and Statistical Methods

All continuous data was expressed in terms of mean and SD and categorical data was expressed in terms of a percentage with the numerator and denominator in parentheses. Improvement in scores over time was analyzed using repeated-measures ANOVA. All statistical analyses were performed using SPSS version 23.0 (SPSS Inc, Chicago, IL, USA). Statistical significance was defined as p ≤ 0.05.

Results

Achieving the MCID After Lumbar Fusion

At 2 years after surgery, the proportions of young patients who achieved the MCID for the various patient-reported outcomes were 82% (68 of 83) for leg pain, 75% (62 of 83) for back pain, 87% (72 of 83) for ODI and 71% (59 of 83) for SF-36 PCS (Table 3). All patient-reported outcomes improved from preoperatively to all postoperative timepoints (Table 4).

T3
Table 3.:
Proportion of patients who attained the MCID and returned to work at different time intervals
T4
Table 4.:
Patient-reported outcomes at different time intervals

Complications and Reoperations

Complications and reoperations in this series were uncommon; we observed two of each: one surgical complication and one medical complication. One young patient experienced radiculopathy on the contralateral side 3 days postoperatively. A repeat MRI was performed and showed that the S1 pedicle screw was near the contralateral S1 nerve root. This was managed non-surgically. Another patient had a postoperative urinary tract infection with Morganella spp. that was treated with ciprofloxacin. In terms of reoperations, one patient had posterior cage migration at L4-L5 and presented with recurrent radiculopathy at 3 months, which was treated with cage removal and packing of the L4-L5 disc space with a bone graft. Another patient showed signs of screw loosening and underwent partial implant removal 5 years after the initial surgery. No patients received a blood transfusion. In terms of 30-day readmissions, one patient was readmitted for poor pain control and another for a right hemothorax for unrelated causes that was managed by cardiothoracic surgeons. One patient died of unrelated causes 8 months after surgery.

Fusion and Adjacent-segment Degeneration

We found that 85% (79 of 93) of patients had achieved a Bridwell Grade 1 or 2 fusion. In addition, 8% (seven of 93) of the younger patients had evidence of radiologic adjacent-segment degeneration, but only one patient required a revision L5-S1 MIS-TLIF 4.3 years after the initial surgery at L4-5.

Secondary Endpoint: Return to Work

Of the 61 patients working preoperatively, 61% (37) returned to work by 3 months (Table 3). The mean number of days to return to work was 84 ± 70 days in the young cohort.

Discussion

As the total number of patients undergoing lumbar spine surgery for degenerative diseases increases [11], more young patients experiencing symptoms from degenerative spinal diseases will seek surgical treatment to improve their quality of life, and these patients often have higher functional demands than older patients [29]. Unfortunately, limited evidence is available on the effectiveness of lumbar spine surgery in this patient group [23], likely because of the extremely low prevalence of degenerative spondylolisthesis in patients younger than 50 years [17]. We assessed the clinical and radiological results of lumbar fusion in a young population and found that a high proportion of patients achieved a clinically important improvement in pain, function, and quality of life that was sustained up to 2 years postoperatively. In addition, we found few complications and reoperations, and a low risk of radiographic nonunion and adjacent-segment disease over a mean follow-up of 5 years.

This study has several limitations. This was a retrospective case series of young patients undergoing lumbar fusion for degenerative spondylolisthesis, hence future comparative studies are needed to confirm if the successful outcomes in the young are indeed comparable to the results of age-appropriate controls. Secondly, there was transfer bias, as 14% of patients (13 of 96) did not complete clinical follow-up. It is plausible that patients who had poorer outcomes scores or complications did not return for follow-up, and so our results may represent a best-case estimate of patients’ results from surgery. Thirdly, we used plain radiographs instead of CT scans to assess postoperative fusion after MIS-TLIF. This could have led to poorer accuracy when determining radiographic fusion or adjacent-segment degeneration. The reason for this was that CT scans were not routinely performed after surgery at our institution due to the additional costs and radiation exposure. Plain radiographs have also been used in other studies reporting the influence of age on the results of lumbar fusion [23], albeit with its shortcomings. Fourthly, the sample size was relatively small and may limit the conclusions that can be drawn. Given the low frequency of complications and reoperations in general, it is possible that larger series might find more or different complications than we did.

We also believe that longer follow-up is needed to understand fully the natural course of adjacent-segment degeneration in this young population, which includes patients whose life expectancy may be measured in decades; our findings at a mean of 5 years are a start, but will not be the last word on this important topic. Finally, we did not have sufficient numbers of patients who were very young to allow comparisons within our study group; most of our patients were between the ages of 40 and 50 years, and we had only 23 patients younger than 40 years in the study group. Further studies are needed to evaluate whether the experiences of very young differ from those who are slightly older.

Achieving the MCID After Lumbar Fusion

Degenerative spondylolisthesis is a disease of aging [17, 20]. A recent systematic review showed that degenerative spondylolisthesis is relatively rare before 50 years of age [45]. In the Copenhagen Osteoarthritis Study, only 4% of all patients had degenerative spondylolisthesis before the age of 50 [17]. To our knowledge, only one study has reported the results of lumbar fusion in young patients [23]. Khan et al. [23] analyzed the clinical and radiological outcomes of open posterior lumbar fusion in 330 patients aged 18 to 54 years at a short follow-up of 15 months and found that these patients had worse final ODI scores compared with middle-aged patients (55-69 years), although there was no difference in the attainment of MCID between the two groups. Specifically, the authors reported an MCID attainment of 43%, 47% and 56% for ODI, leg pain and back pain in the young group, respectively. Our findings differed slightly as we noted that 71% to 82% of patients achieved the MCID for the patient-reported outcome measures of pain, function, and quality of life. The variability of results could be explained by the heterogeneity in the previous study, as multilevel fusions, isthmic spondylolisthesis, and patients who underwent prior lumbar spine surgery were included. Furthermore, given the short follow-up of 15 months, patients may not have experienced full functional recovery, and only 39% of patients in that study had clinical outcomes collected while 38% had radiographic data. We studied patients younger than 50 years undergoing primary, single-level MIS-TLIF for degenerative spondylolisthesis to maintain homogeneity. Young patients experienced substantial pain relief, functional recovery, and quality of life improvement, suggesting that surgical intervention may be an effective treatment even in young patients with degenerative spine disorders who have failed nonoperative treatment.

Complications and Reoperations

We found perioperative complications in this young population to be uncommon; we observed only two: one minor medical complication and one surgical complication because of technical difficulties. These findings were in line with a recent study that reviewed the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database, which reported that younger patients were less likely to have complications than patients older than 65 years (9% versus 14%) [8]. That study evaluated age after controlling for potentially confounding variables, and it found that increasing age was not associated with complications; this suggests that perhaps comorbid medical conditions, rather than age alone, warrant our attention as we try to make these operations as safe as possible. The low frequency of complications in our series was congruous with the low number of comorbidities expected in this age group.

Fusion and Adjacent-segment Degeneration

We found that most patients in our series experienced osseous fusion, and a low proportion developed adjacent-segment degeneration at short-term follow-up. Studies investigating the effect of age on the likelihood of fusion after spine surgery have focused on older patients because age-related changes affect many of the biological processes involved in bone healing [9]. Although one study demonstrated a higher risk of nonunion in older patients than in younger patients [34], another had conflicting results [19]. This study noted stable fusion in 85% of young patients undergoing MIS-TLIF, comparable to that reported in a previous study [36]. As the number of spinal fusions continues to increase annually [11], adjacent-segment degeneration has become a major concern. The reported incidence of adjacent-segment degeneration after lumbar fusion varies greatly among previous studies. A recent meta-analysis of 94 studies and noted an occurrence of 5% to 77% [50]. Likewise, a systematic review reported that the risk of radiologic adjacent-segment degeneration was 8% to 100% during a mean follow-up duration of 36 months to 369 months [35]. Our study found that 8% of patients developed this by a mean of 5 years, and only one patient in the young cohort underwent surgery for adjacent-segment disease. This observation was consistent with another review by Lawrence et al. [26], who reported a mean annual incidence of 0.6% to 3.9% for clinical adjacent-segment disease. The low risk of adjacent-segment degeneration and disease in our young cohort is supported by the findings of both systematic reviews, which noted that the risk of adjacent-segment disease was lower in patients younger than 60 years than in older patients [26, 35].

Return to Work

Return to work is a particularly important consideration for young, working adults; hence, we investigated the likelihood of return to work of a non-workers compensation cohort of patients younger than 50 years undergoing MIS-TLIF. Most of the young patients (61%) were able to return to work within 3 months after surgery. The costs of low back pain are estimated to exceed USD 100,000,000 annually, with two thirds of this cost directly related to decreased productivity and lost income [21]. Older age, permanent disability, and psychological comorbidities have been negatively associated with return to work status in patients receiving workers compensation undergoing lumbar fusion [1]. Although Asher et al. [2] excluded age as a factor in a predictive model of return to work within 3 months after elective lumbar surgery, another study by Khan et al. [22] using the Quality and Outcomes Database found that older patients had a lower odds of returning to work at 1 year. A third study that reviewed the same database reported a 3-month return to work rate of 67% after MIS-TLIF [14].

Conclusions

As the global average life expectancy continues to increase, young patients with degenerative diseases will need to adapt to (or treat) the pain and disability from these conditions over a longer period of time. Although not a panacea, we found that TLIF provided pain relief, restored function, and improved the quality of life of young patients with lumbar degenerative spondylolisthesis, allowing timely return to work for these patients after surgery. Furthermore, complications, reoperations, nonunion, and adjacent-segment degeneration were uncommon in this population. Clinicians may offer surgery to young patients experiencing degenerative spinal conditions who have not benefited from reasonable conservative measures with some confidence that despite greater functional demands, these patients will experience clinical benefits with a low risk of reoperation. Future studies might be conducted to compare the clinical and radiological results in young patients and age-appropriate controls undergoing lumbar spine surgery.

Acknowledgments

We thank Ms. Sarah Boey for assisting with the statistical analysis and presentation of figures in this manuscript. We also thank Mr. William Yeo for the preoperative assessment of all patients.

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