This study was approved by the Ethics Committee of the Keio University School of Medicine (approval no., 20110142). We obtained written informed consent for the use of patient data from each patient or their guardian, according to the hospital’s ethics guidelines.

Approximately 432 consecutive patients who underwent spinal cord tumor resection surgery at Keio University Hospital between 2014 and 2019 were retrospectively reviewed. The clinical data for each patient was collected through medical records in accordance with the institution’s ethical guidelines. Among these cases, 161 patients presented with cervical and thoracic ISCTs. All surgeries for ISCT resection were performed via posterior approach microscopically by the same skilled surgical team under general anesthesia with neuromonitoring. Exclusion criteria included preoperative gait disorder (Functional Independence Measure Locomotor Scale (FIM-L) score of 5 or less [11]), a history of brain disease or lower-limb injury, and postoperative complications that delayed the start of rehabilitation. The reason for excluding nonindependent preoperative ambulators was that preoperative physical function had been reported to affect postoperative function [7,8,12,13]. This study focused on the course of physical function and walking ability after surgery and the effects of rehabilitation in independent preoperative ambulators. Consequently, 79 total independent ambulatory preoperative cases (44 males and 35 females) were eligible for a series of follow-up and neurological examination for 1 year postoperatively. The mean age was 46.8±16.2 years (range, 11–81 years) (Table 1).

On the first day after surgery, the bed angle was up to 30°. The bed angle was then limited to 60° on the second postoperative day, and the wheelchair transfer began on the fourth postoperative day. To prevent rupture of the sutured dura and arachnoid maters, our standard postoperative course after spinal cord tumor resection is to gradually stand for 4 days instead of leaving the bed immediately. The practice in the rehabilitation room began 1 week after surgery. Physical therapy in the rehabilitation room consisted of range-of-motion exercises, muscle strengthening, basic movement exercises, walking exercises, and endurance training according to each patient. Treatment frequency was 20–40 minutes a day, 5 days a week.

Postoperative functional status at 1 and 2 postoperative weeks was evaluated using the following measurements: the American Spinal Injury Association (ASIA) lower extremity motor score (ASIA-LEMS) [14] was used for lower-limb motor function, the ASIA lower extremity sensory score (ASIA-LESS) [14] below the L1 level for lower-limb sensory function, the Walking Index for Spinal Cord Injury II (WISCI II) [15] for walking ability, and the FIM-L score for walking independence [11]. WISCI II was developed for patients with incomplete spinal cord injuries [16] and evaluated walking function on a 21-point scale based on walking aids, orthotics, and physical assistance. However, the definition of the grading of physical assistance is unclear. This is the part where those who do not need a walking aid but need physical assistance are rated higher than those who need a walking aid but do not need physical assistance. Ditunno et al. [17] stated that WISCI II scores should not be dichotomized into dependent and independent levels of physical assistance. Therefore, to assess for physical assistance for walking, FIM-L was used. The FIM-L score is assigned on a 7-point scale based on walking assistance: 1, full assistance; 2, maximum assistance; 3, moderate assistance; 4, minimum assistance; 5, monitoring; 6, modified independence (with equipment); and 7, independence without equipment. In this study, an independent ambulator was defined as FIM-L score of ≥6 and nonindependent as FIM-L score of <5.

First, the above indices collected 1 and 2 weeks after surgery were compared between independent and nonindependent ambulators, whose walking ability was evaluated 1 year postoperatively. Moreover, the above indices were compared using tumor histology and localization (cervical or thoracic spinal cord). For the grouping of tumor histology, ependymoma, astrocytoma, and lipoma were classified as solid tumor group, and hemangioblastoma and cavernous hemangioma were classified as vascular tumor group. We examined changes in walking ability from 2 weeks to 1 year postoperatively in 78 patients who could be assessed with FIM-L and WISCI II at 1 year postoperatively. Then, the cutoff value for the discrimination of walking independence at 1 year postoperatively was calculated using the receiver operating characteristic (ROC) curve from the WISCI II score at 2 weeks postoperatively.

The normality of all data was confirmed using the histogram. The clinical course of all subjects was analyzed, and the results were compared according to walking independence, tumor histology, and tumor location. The Wilcoxon signed rank test was performed to compare continuous variables within a subject, while the Mann-Whitney U test was performed to compare them between subjects. Fisher’s exact test was performed for walking independence at 2 weeks postoperatively. A univariate logistic regression was performed to predict walking independence (independent ambulators defined as FIM-L score of ≥6) at 1 year postoperatively from the WISCI II score at 2 weeks after surgery. The optimal cutoff value of the WISCI II score was calculated based on the Youden’s index of the ROC curve. Then, the sensitivity and specificity were calculated using the optimal cutoff value. For statistical analysis, IBM SPSS ver. 25.0 (IBM Corp., Armonk, NY, USA) was used, and the significance level was set at 5%.

The baseline demographics of the 79 subjects who underwent spinal ISCT resection surgery are summarized in Table 1. The study participants included those who walked independently before the surgery. Therefore, all of the study participants had an FIM-L of at least 6 points and a WISCI II of at least 19 points. The median score of ASIA-LEMS was 50 out of 50. The median score on ASIA-LESS was 33 out of 36. Regarding tumor histology, 46 cases had solid tumors (43 gliomas and three lipomas), and 33 had vascular tumors (23 cavernous hemangiomas and 10 hemangioblastomas) (Table 2).

Fig. 1A–C shows the results for all participants at 1–2 weeks postoperatively. The percentage of nonindependent ambulators decreased from 71% to 43% at 1–2 weeks postoperatively. During this observation period, a significant improvement in lower-limb motor function was observed, but no significant change was found in sensory function. Then, the independent and nonindependent ambulator groups 2 weeks after surgery were compared. Table 3 demonstrated that independent ambulators 2 weeks after surgery showed significantly better lower-limb and sensory functions evaluated by ASIA-LEMS and ASIA-LESS scores at 1 week after surgery than those nonindependent ambulators. At 1 week after surgery, 63% of the nonindependent ambulator group could not walk or could walk only with parallel bars (WISCI II score: 0–4). Conversely, all patients in the independent ambulator group started walking with a walker or a cane (WISCI II score of 8 or higher).

Differences in postoperative walking ability, lower extremity motor function, and sensory function by tumor histopathology are shown in Table 4 (Supplement 1) and Fig. 1D–I. Those with solid tumors exhibited significantly lower walking ability and sensory function than those with vascular tumors, but no statistically significant difference was observed in lower-limb function at 1 and 2 weeks postoperatively (Fig. 1D–I).

The comparison was conducted focusing on tumor location, cervical or thoracic (Table 5, Supplement 2, Fig. 2). Cases with thoracic tumors were found to have significantly lower-limb function than those with cervical tumors 1 week after surgery. However, no statistically significant differences were found in walking ability and sensory function between the cervical and thoracic locations (Fig. 2A–C). At 2 weeks postoperatively, cases with thoracic tumor showed significantly lower walking ability and lower-limb function, except sensory function (Fig. 2D–F).

Finally, the transition of walking ability has been evaluated among 78 individuals who were evaluated by FIM-L and WISCI II, and who were followed 1 year after surgery (Fig. 3). Fig. 3A shows the results at 2 weeks and 1 year follow-up. Nonindependent ambulators decreased from 43% to 10% at 2 weeks and 1 year postoperatively. Fig. 3B shows the change in WISCI II scores from 2 weeks to 1 year postoperatively. At 2 weeks after surgery, 42 patients walked without a cane (WISCI II: 20), 27 patients required assistance or walking aid (WISCI II: 6–19), and nine patients had difficulty walking or walked with parallel bars (WISCI II: 0–2). All 27 patients who needed walking aid or assistance at 2 weeks after surgery recovered as independent ambulators (walking without a cane or without assistance with a cane or brace) 1 year after surgery. Of the nine patients with a WISCI II score of 0–2 at 2 weeks after surgery, one recovered to walk without a cane (WISCI II: 20), one used a cane and no assistance (WISCI II: 19), five used walking aids or assistance (WISCI II: 6–14), one remained with difficulty walking (WISCI II: 0), and one had difficulty walking (WISCI II: 2–0) after reoperation due to recurrence at 1 year after surgery. The cutoff value of the WISICI II score at 2 weeks postoperatively was derived using the ROC analysis to determine the level of walking independence at 1 year postoperatively. The optimal cutoff value of the WISICI II score at 2 weeks postoperatively was 2 points to predict walking independence at 1 year postoperatively according to the Youden index (Table 6, Supplement 3). The area under the curve was 0.99 (95% confidence interval, 0.99–1.00), and the sensitivity and specificity with optimal cutoff value were 100.0% and 97.2%, respectively.