Development of a mapping function ("crosswalk") for the conversion of scores between the Oswestry Disability Index (ODI) and the Core Outcome Measures Index (COMI)

INTRODUCTION

The Oswestry Disability Index (ODI) and the Core Outcome Measures Index (COMI) are two commonly used self-rating outcome instruments in patients with lumbar spinal disorders. No formal crosswalk between them exists that would otherwise allow the scores of one to be interpreted in terms of the other. We aimed to create such a mapping function.

METHODS

We performed a secondary analysis of ODI and COMI data previously collected from 3324 patients (57 ± 17y; 60.3% female) at baseline and 1y after surgical or conservative treatment. Correlations between scores and Cohen's kappa for agreement (κ) regarding achievement of the minimal clinically important change (MCIC) score on each instrument (ODI, 12.8 points; COMI, 2.2 points) were calculated, and regression models were built. The latter were tested for accuracy in an independent set of registry data from 634 patients (60 ± 15y; 56.8% female).

RESULTS

All pairs of measures were significantly positively correlated (baseline, 0.73; 1y follow-up (FU), 0.84; change-scores, 0.73). MCIC for COMI was achieved in 53.9% patients and for ODI, in 52.4%, with 78% agreement on an individual basis (κ = 0.56). Standard errors for the regression slopes and intercepts were low, indicating excellent prediction at the group level, but root mean square residuals (reflecting individual error) were relatively high. ODI was predicted as COMI × 7.13-4.20 (at baseline), COMI × 6.34 + 2.67 (at FU) and COMI × 5.18 + 1.92 (for change-score); COMI was predicted as ODI × 0.075 + 3.64 (baseline), ODI × 0.113 + 0.96 (FU), and ODI × 0.102 + 1.10 (change-score). ICCs were 0.63-0.87 for derived versus actual scores.

CONCLUSION

Predictions at the group level were very good and met standards justifying the pooling of data. However, we caution against using individual values for treatment decisions, e.g. attempting to monitor patients over time, first with one instrument and then with the other, due to the lower statistical precision at the individual level. The ability to convert scores via the developed mapping function should open up more centres/registries for collaboration and facilitate the combining of data in meta-analyses.

Shorter and sweeter: the 16-item version of the SRS questionnaire shows better structural validity than the 20-item version in young patients with spinal deformity

PURPOSE

In patients with adult spinal deformity, it was previously shown that 16 of the non-management items of the SRS-instrument showed a better fit to the theoretical four-factor model (pain, function, self-image, mental health) than did all 20 items. Whether the same phenomenon is observed in data from younger (< 20y) patients, for whom the questionnaire was originally designed, is not currently known.

METHODS

Confirmatory factor analysis was used to evaluate the factor structure of the 20 non-management items of the SRS-instrument completed by 3618 young patients with spinal deformity (75.5% female; mean age, 15.0 ± 2.0 years) and of its equivalence across language versions (2713 English-speaking, 270 Spanish, 264 German, 223 Italian, and 148 French). The root mean square error of approximation (RMSEA) and comparative fit index (CFI) indicated model fit.

RESULTS

Compared with the 20-item version, the 16-item solution significantly increased the fit (p < 0.001) across all language versions, to achieve good model fit (CFI = 0.96, RMSEA = 0.06). For both 16-item and 20-item models, equivalence across languages was not reached, with some items showing weaker item-loading for some languages, in particular German and French.

CONCLUSION

In patients with adolescent idiopathic scoliosis, the shorter 16-item version showed a better fit to the intended 4-factor structure of the SRS-instrument. The wording of some of the items, and/or their equivalence across language versions, may need to be addressed. Questionnaire completion can be a burden for patients; if a shorter, more structurally valid version is available, its use should be encouraged.

Development of a machine-learning based model for predicting multidimensional outcome after surgery for degenerative disorders of the spine

BACKGROUND

It is clear that individual outcomes of spine surgery can be quite heterogeneous. When consenting a patient for surgery, it is important to be able to offer an individualized prediction regarding the likely outcome. This study used a comprehensive set of data collected over 12 years in an in-house registry to develop a parsimonious model to predict the multidimensional outcome of patients undergoing surgery for degenerative pathologies of the thoracic, lumbar or cervical spine.

METHODS

Data from 8374 patients (mean age 63.9 (14.9-96.3) y, 53.4% female) were used to develop a model to predict the 12-month scores for the Core Outcome Measures Index (COMI) and its subdomain scores. The data were split 80:20 into a training and test set. The top predictors were selected by applying recursive feature elimination based on LASSO cross validation models. Based on the 111 top predictors (contained within 20 variables), Ridge cross validation models were trained, validated, and tested for each of 9 outcome domains, for patients with either "Back" (thoracic/lumbar spine) or "Neck" (cervical spine) problems (total 18 models).

RESULTS

Among the strongest outcome predictors in most models were: preoperative scores for almost all COMI items (especially axial pain (back or neck) and peripheral pain (leg/buttock or arm/shoulder)), catastrophizing, fear avoidance beliefs, comorbidity, age, BMI, nationality, previous spine surgery, type and spinal level of intervention, number of affected levels, and surgeon seniority. The R² of the models on the validation/test sets averaged 0.16/0.13. A preliminary online tool was programmed to present the predicted outcomes for individual patients, based on their presenting characteristics. https://linkup.kws.ch/prognostictool .

CONCLUSION

The models provided estimates to enable a bespoke prediction of the outcome of surgery for individual patients with varying degenerative pathologies and baseline characteristics. The models form the basis of a simple, freely-available online prognostic tool developed to improve access to and usability of prognostic information in clinical practice. It is hoped that, following confirmation of its validity and practical utility, the tool will ultimately serve to facilitate decision-making and the management of patients' expectations.

Patient-rated outcome after atlantoaxial (C1-C2) fusion: more than a decade of evaluation of 2-year outcomes in 126 patients

INTRODUCTION

Various surgical techniques have been introduced for atlantoaxial (C1-C2) fusion, the most common being Magerl's (transarticular) or the Harms/Goel screw fixation. Common indications include degenerative osteoarthritis (OA), trauma or rheumatoid arthritis (RA). Only few, small studies have evaluated patient-reported outcomes after C1-C2 fusion. We investigated 2-year outcomes in a large series of consecutive patients undergoing isolated C1-C2 fusion.

METHODS

We analysed prospectively collected data (2005-2016) from our Spine outcomes database, collected within the framework of EUROSPINE's Spine Tango Registry. It included 126 patients (34 (27%) men, 92 (73%) women; mean (SD) age 67 ± 19 y) who had undergone first-time isolated C1-C2 fusion (61% Magerl, 39% Harms(-Goel)) at least 2 years ago for OA (83 (66%)), RA (20 (16%)), fracture (15 (12%)) or other (8 (6%)). Patients completed the multidimensional Core Outcome Measures Index (COMI; 0-10) and various single item outcomes.

RESULTS

Questionnaires were returned by 118/126 (94%) patients, 2 years post-operative. Mean COMI scores showed a significant reduction from baseline: 6.9 ± 2.4 to 2.7 ± 2.5 (p < 0.0001). Overall, 75% patients achieved the MCIC of ≥ 2.2 points reduction in COMI and 88% reported a good global outcome. 91% patients were satisfied/very satisfied with their care. Self-reported complications were declared by 16% patients and further surgery at the same segment, by 2.5%.

CONCLUSION

In this large series with almost complete follow-up, C1-C2 fusion showed extremely good results. Despite the complexity of the intervention, outcomes surpassed those typically reported for simple procedures such as ACDF and lumbar discectomy, suggesting reservations about the procedure should perhaps be reviewed.

Can the Charlson Comorbidity Index be used to predict the ASA grade in patients undergoing spine surgery?

BACKGROUND

The American Society of Anaesthesiologists' Physical Status Score (ASA) is a key variable in predictor models of surgical outcome and "appropriate use criteria". However, at the time when such tools are being used in decision-making, the ASA rating is typically unknown. We evaluated whether the ASA class could be predicted statistically from Charlson Comorbidy Index (CCI) scores and simple demographic variables.

METHODS

Using established algorithms, the CCI was calculated from the ICD-10 comorbidity codes of 11'523 spine surgery patients (62.3 ± 14.6y) who also had anaesthetist-assigned ASA scores. These were randomly split into training (N = 8078) and test (N = 3445) samples. A logistic regression model was built based on the training sample and used to predict ASA scores for the test sample and for temporal (N = 341) and external validation (N = 171) samples.

RESULTS

In a simple model with just CCI predicting ASA, receiver operating characteristics (ROC) analysis revealed a cut-off of CCI ≥ 1 discriminated best between being ASA ≥ 3 versus < 3 (area under the curve (AUC), 0.70 ± 0.01, 95%CI,0.82-0.84). Multiple logistic regression analyses including age, sex, smoking, and BMI in addition to CCI gave better predictions of ASA (Nagelkerke's pseudo-R² for predicting ASA class 1 to 4, 46.6%; for predicting ASA ≥ 3 vs.  < 3, 37.5%). AUCs for discriminating ASA ≥ 3 versus < 3 from multiple logistic regression were 0.83 ± 0.01 (95%CI, 0.82-0.84) for the training sample and 0.82 ± 0.01 (95%CI, 0.81-0.84), 0.85 ± 0.02 (95%CI, 0.80-0.89), and 0.77 ± 0.04 (95%CI,0.69-0.84) for the test, temporal and external validation samples, respectively. Calibration was adequate in all validation samples.

CONCLUSIONS

It was possible to predict ASA from CCI. In a simple model, CCI ≥ 1 best distinguished between ASA ≥ 3 and < 3. For a more precise prediction, regression algorithms were created based on CCI and simple demographic variables obtainable from patient interview. The availability of such algorithms may widen the utility of decision aids that rely on the ASA, where the latter is not readily available.

A novel use of the Spine Tango registry to evaluate selection bias in patient recruitment into clinical studies: an analysis of patients participating in the Lumbar Spinal Stenosis Outcome Study (LSOS)

PURPOSE

Patients enrolled in clinical studies typically represent a sub-set of all who are eligible, and selection bias may compromise the generalizability of the findings. Using Registry data, we evaluated whether surgical patients recruited by one of the referring centres into the Lumbar Spinal Stenosis Outcome Study (LSOS; a large-scale, multicentre prospective observational study to determine the probability of clinical benefit after surgery) differed in any significant way from those who were eligible but not enrolled.

METHODS

Data were extracted for all patients with lumbar spinal stenosis registered in our in-house database (interfaced to Eurospine's Spine Tango Registry) from 2011 to 2013. Patient records and imaging were evaluated in relation to the admission criteria for LSOS to identify those who would have been eligible for participation but were not enrolled (non-LSOS). The Tango surgery data and Core Outcome Measures Index (COMI) data at baseline and 3 and 12 months after surgery were analysed to evaluate the factors associated with LSOS enrolment or not.

RESULTS

514 potentially eligible patients were identified, of which 94 (18%) were enrolled into LSOS (range 2-48% for the 6 spine surgeons involved in recruiting patients) and 420 (82%) were not; the vast majority of the latter were due to non-referral to the study by the surgeon, with only 5% actually refusing participation. There was no significant difference in gender, age, BMI, smoking status, or ASA score between the two groups (p ≥ 0.18). Baseline COMI was significantly (p = 0.002) worse in the non-LSOS group (7.4 ± 1.9) than the LSOS group (6.7 ± 1.9). There were no significant group differences in any Tango surgery parameters (additional spine patholothegies, operation time, blood loss, complications, etc.) although significantly more patients in the non-LSOS group had a fusion procedure (38 vs 18% in LSOS; p = 0.0004). Postoperatively, neither the COMI nor its subdomain scores differed significantly between the groups (p > 0.05). Multiple logistic regression revealed that worse baseline COMI (p = 0.021), surgeon (p = 0.003), and having fusion (p = 0.014) predicted non-enrolment in LSOS.

CONCLUSION

A high proportion of eligible patients were not enrolled in the study. Non-enrolment was explained in part by the specific surgeon, worse baseline COMI status, and having a fusion. The findings may reflect a tendency of the referring surgeon not to overburden more disabled patients and those undergoing more extensive surgery with the commitments of a study. Beyond these factors, non-enrolment appeared to be somewhat arbitrary, and was likely related to surgeon forgetfulness, time constraints, and administrative errors. Researchers should be aware of potential selection bias in their clinical studies, measure it (where possible) and discuss its implications for the interpretation of the study's findings.

[Congenital malformations of the growing spine : When should treatment be conservative and when should it be surgical?]

Congenital malformations of the spine are caused by genetic and teratogenic factors. By means of asymmetrical longitudinal growth of the spine they can lead to deformity, most commonly to scoliosis. The malformations can be classified as failure of formation, failure of segmentation and mixed-type malformations. The extent of the deformity and its progression are determined by the remaining growth potential and the location and type of malformation. Up to one third of such deformities are associated with some sort of cardiac or urogenital malformation. The treatment concept is typically determined on an individual basis. Mild deformities often remain undetected. Conservative treatment using a brace has no substantial effect on the primary curve but might be helpful in the treatment of long sweeping, flexible, secondary curves. If rapid progression is documented or expected, surgical intervention as early as possible is warranted to prevent secondary structural changes. The surgical treatment should be focused on and limited to the site of malformation. The aim of surgery is the correction of the deformity at the site of asymmetrical growth. This can be achieved either by resection of a hemivertebra or by performing a vertebral column resection or other type of osteotomy. If notable compensatory, secondary curves are present, these can be corrected with growing rod constructs. The aim of all types of treatment is the correction of existing deformity or the prevention of its progression, in order to ensure balanced growth of the healthy regions of the spine. The present paper discusses the conservative and surgical treatment modalities available to achieve these aims.

Validity of a single-item measure to assess leg or back pain as the predominant symptom in patients with degenerative disorders of the lumbar spine

PURPOSE

Recent studies suggest that the location of predominant pain (back or leg) can be a significant predictor of the outcome of surgery for degenerative spinal disorders. However, others challenge the notion that the predominant symptom can be reliably identified. This study examined the validity of a single item used to determine the most troublesome symptom.

METHODS

A total of 2,778 patients with degenerative disorders of the lumbar spine scheduled for surgery with the goal of pain relief completed a questionnaire enquiring as to their most troublesome symptom ["main symptom"; back pain (BACK) or leg/buttock pain (LEG)]. They also completed separate 0-10 graphic rating scales for back pain (LBP) and leg/buttock pain (LP) intensity. Receiver operating characteristics (ROC) analysis was used to determine the accuracy with which the "LP minus LBP" score was able to classify patients into their declared "main symptom" group. Sub-studies evaluated the test-retest reliability of the patients' self-rated pain scores (N = 45) and the agreement between the main symptom declared by the patient in the questionnaire and that documented by the surgeon after the clinical consultation (N = 118).

RESULTS

Test-retest reliability of the back and leg pain scores was good (ICC₂,₁ of 0.8 for each), as was patient-surgeon agreement regarding the main symptom (BACK or LEG) (κ value 0.79). In the BACK group, the mean values for pain intensity were 7.3 ± 2.0 (LBP) and 5.2 ± 2.9 (LP); in the LEG group, they were 4.3 ± 2.9 (LBP) and 7.5 ± 1.9 (LP). The area under the curve for the ROC was 0.95 (95 % CI 0.94-0.95), indicating excellent discrimination between the BACK and LEG groups based on the "LP minus LBP" scores. A cutoff score >0.0 for "LP minus LBP" score gave optimal sensitivity and specificity for indicating membership of the LEG group (sensitivity 79.1%, specificity 95.7%).

CONCLUSIONS

The responses on the single item for the "main symptom" were in good agreement with the differential ratings on the 0-10 pain scales for LBP and LP intensity. The cutoff >0 for "LP minus LBP" for classifying patients as LEG pain predominant seemed appropriate and suggests good concurrent validity for the single-item measure. The single item may be of use in sub-grouping patients with the same disorder (e.g. spondylolisthesis) or as an indication in surgical decision-making.

Posterior vertebral column resection in early onset spinal deformities

PURPOSE

Early onset spinal deformities (EOSD) can be life-threatening in very young children. In the growing spine, surgical intervention is often unavoidable and should be carried out as soon as possible. A deformed section of the spine not only affects the development of the remaining healthy spine, but also that of the chest wall (which influences pulmonary function), the extremities and body balance. Posterior vertebral column resection (PVCR) represents an effective surgical solution to address such problems. However, reports in the literature concerning PVCR are mostly limited to its use in adolescents or adults. The purpose of this study was to illustrate our experience with PVCR in EOSD and to describe the surgical technique with respect to the unique anatomy of young children.

MATERIALS AND METHODS

Four children [mean age 3.7 (range 2.5-5.2) years] with severe spinal deformity underwent PVCR through a single approach. Multimodal intraoperative monitoring was used in all cases. Surgery included one stage posterior circumferential resection of one vertebral body along with the adjoining intervertebral discs and removal of all posterior elements. A transpedicular screw-rod system was used for correction and stabilisation. Fusion was strictly limited to the resection site, allowing for later conversion into a growing rod construct at the remaining spine, if necessary. Relevant data were extracted retrospectively from patient charts and long spine radiographs.

RESULTS

The mean operation time was 500 (range 463-541) min, with an estimated blood loss of 762 (range 600-1,050) ml. Mean follow-up time was 6.3 (range 3.5-12.4) years. After PVCR, the mean Cobb angle for scoliosis was reduced from 69° (range 50-99°) to 29° (5-44°) and the sagittal curvature (kyphosis) from 126° (87-151°) to 61° (47-75°). The mean correction of scoliosis was 57 % (18-92°) and of kyphosis, 51 % (44-62°). There were no spinal cord-related complications. In three patients, spinal instrumentation for growth guidance (fusion less growing rod technique) was applied. Two patients had complications: one patient had a complication of anesthesia, halo pin failure, and revision surgery with extension of the instrumentation cranially due to loss of correction; the second patient had a postoperative infection, which required plastic reconstructive measures.

CONCLUSION

PVCR appears to be an effective technique to treat severe EOSD. There are important differences in its use in young children when compared with older patients. In patients with EOSD, additional surgical procedures are often necessary during growth, and hence non-fusion instrumentation beyond the vertebral resection site is advantageous, as it permits spinal growth and the later addition of fusion.

Fusionless posterior hemivertebra resection in a 2-year-old child with 16 years follow-up

PURPOSE

We present the case of a 2-year-old patient with congenital scoliosis due to a lumbar hemivertebra. The current gold standard treatment of such an abnormality would be hemivertebra resection and short level posterior spinal fusion. However, due to the young age of the patient, we considered that application of a fusionless solution might offer advantages in terms of retaining normal segmental motion and the potential for growth.

METHODS

The incarcerated hemivertebra was resected and the facet joints of the neighbouring vertebrae were joined to create a new functional motion segment and correct the kyphoscoliotic deformity. Transpedicular screws were inserted on the convex side in L2 and L3 and a tension band was applied.

RESULTS

16 years after the surgery, the patient was completely pain-free, motion of the lumbar spine was preserved and the physiological curvatures were maintained.

CONCLUSION

To our knowledge a fusionless surgical solution for the treatment of a hemivertebra has never been described before. Although this is only a single case, the good result with a long follow-up suggests the technique is worthwhile considering when planning the treatment of a lumbar hemivertebra in very young children.

To fuse or not to fuse in lumbar degenerative spondylolisthesis: do baseline symptoms help provide the answer?

INTRODUCTION

Clinical symptoms in lumbar degenerative spondylolisthesis (LDS) vary from predominantly radiating pain to severe mechanical low back pain. We examined whether the outcome of surgery for LDS varied depending on the predominant baseline symptom and the treatment administered [decompression with fusion (D&F) or decompression alone (D)].

METHODS

213 consecutive patients (69 ± 9 years; 155f, 58 m) participated. Inclusion criteria were LDS, maximum three affected levels, no previous surgery at the affected level, and D (N = 56) or D&F (N = 157) as the operative procedure. Pre-op and at 12 months' follow-up (FU), patients completed the multidimensional Core Outcome Measures Index (COMI) including 0-10 leg-pain (LP) and LBP scales. At 12 months' FU, patients rated global outcome which was then dichotomised into "good" and "poor".

RESULTS

Pre-operatively, LBP and COMI scores were significantly worse (p < 0.05) in the D&F group than in the D group. The improvement in COMI at 12 months' FU was significantly greater for D&F than for D (p < 0.001) and was not influenced by the patient's declared "main problem" at baseline (back pain, leg pain, or neurological disturbances) (p > 0.05). There was a higher proportion (p = 0.01) of "good" outcomes at 12 months' FU in D&F (86%) than in D (70%). Multiple regression analysis, controlling for possible confounders, revealed treatment group to be the only significant predictor of outcome (adding fusion = better outcome).

DISCUSSION

Our study indicated that LDS patients showed better patient-based outcome with instrumented fusion and decompression than with decompression alone, regardless of baseline symptoms. This may be due to the fact that the underlying slippage as the cause of the stenosis is better addressed with fusion.

Management of fractures of the pedicle after instrumentation with transpedicular screws: A report of three patients

Fracture of a pedicle is a rare complication of spinal instrumentation using pedicular screws, but it can lead to instability and pain and may necessitate extension of the fusion. Osteosynthesis of the fractured pedicle by cerclage-wire fixation and augmentation of the screw fixation by vertebroplasty or temporary elongation of the fixation, allows stabilisation without sacrifice of the adjacent healthy segment. We describe three patients who developed a fracture of the pedicle in the most caudal instrumented vertebra early after lumbar spinal fusion. During revision surgery the pedicles were reduced and secured by a soft cerclage wire bilaterally. Fusion was obtained at the site of the primary instrumentation and healing of the pedicles was achieved. Cerclage wiring of the fractured pedicle seems to be safe and avoids permanent extension of the fusion without the sacrifice of an otherwise healthy segment.