Here, we present a protocol to analyze the posture and the gait of patients after lumbar fusion surgery by means of high-resolution video rasterstereography and a treadmill equipped with an integrated sensor mat. Allowing critical functional postoperative evaluation on a less subjective level may enhance accuracy and reliability of indication for surgery.
This protocol provides guidance on how to perform high resolution video rasterstereography and treadmill gait analysis on patients after lumbar fusion surgery to obtain results about altered variables of gait and posture. These observed changes can then be correlated with the patient-reported outcome measure of pain relief. The rasterstereographic device projects lines of parallel light onto the surface of the tested subject's back. The deformation of these lines is recognized by the device. From these data, a special software then generates a 3-D profile based on the principle of triangulation. With an inaccuracy of only 0.2 mm it can measure changes in posture at very high precision. Gait and stance parameters are recorded using a treadmill equipped with an electric sensor mat that contains 10,200 miniature force sensors in the registering zone under the belt. Initial walking speed on the treadmill is 0.5 km/h. Speed is then gradually increased by increments of 0.1 km/h until each subject reaches his or her individual maximum well tolerable walking speed. At this speed, parameters are recorded during a 20 s measurement interval. Subjects are tested barefoot and without holding a handrail. Among various other parameters, stride width, step length, stance phase and foot rotation are measured. Both methods used reportedly have a high intra- and inter-observer reliability. The advantage of these highly accurate techniques is that they offer an objective and very detailed perspective on changes in the patient's posture and gait. Due to the amount of data generated, these techniques are, however, not so much suitable for everyday routine use, but rather interesting to scientifically evaluate long term alterations in posture and gait in patients like for example after lumbar fusion surgery.
This protocol provides instructions on how to objectively perform a functional posture and gait analysis of patients after lumbar spinal fusion surgery in contrast to subjective evaluation by the examiner or patient reported questionnaires. The setup consists of a high-resolution video rasterstereography for posture analysis, and a pressure-sensor equipped treadmill setup for gait analysis. Results obtained by these techniques from patients after lumbar fusion surgery are compared with subjectively reported pain relief.
Even if spinal surgery techniques and outcomes have vastly improved over the past years, the increase in procedures performed1,2 also leads to a rise in absolute numbers of patients dissatisfied with their individual postoperative results. For surgeons, it is thus crucial to identify those patients who will most likely benefit from surgery. The development of this skill is closely associated with the constant postoperative outcome evaluation and reevaluation of the initial indication for surgery.
To date, the postoperative outcome is mostly judged on subjective patient-reported levels of pain and function by questionnaires3,4,5. These questionnaires are, however, always subjectively affected and not only influenced by the objective physical abnormality but also by the patient's attitudes and beliefs, psychological distress, and illness behavior. Interestingly, even findings in X-ray, computed tomography or magnetic resonance imaging are prone to high inter- and intra-observer variability6,7,8,9,10. The additionally radiologic imaging, however, only offers a static technical evaluation of the surgery. There is a clear lack in means to objectively evaluate the functional outcome after spinal surgery.
A patient's posture and gait are generally supposed to be linked to the perceived level of pain and also to the overall quality of life11,12. Therefore, function can be considered one of the most important elements of postoperative outcome. The overall functional satisfaction of the patient seems to be associated with spinal alignment, kyphosis, lordosis and vertebral rotation13,14,15. As lumbar fusion surgery tries to restore the anatomical curvature of the spine and therefore to balance the muscles, the adaptation of posture is expected16. Restored lumbar lordosis is complementary with pain relief and thus result in the ability to walk painless.
The technique of back surface analysis goes back to the work of Takasaki and Meadows et al., as well as Drerup et al. from the late 1970s and 80s17,18,19,20,21. Based on the principle of triangulation, this technique presents a measurement inaccuracy of only 0.2 mm 22. The technique is widely used and tested for the radiation free diagnosis and follow-up of patient with scoliosis23,24. In the context of evaluation of scoliosis patients, the setup showed good validity and an excellent intra- and interrater reliability25. An even more functional view on the patient offers the analysis of gait. A common technique to register the distinct parameters used to describe a patient's gait is a treadmill experimental setup. Thus stride width, step length, stance phase and foot rotation as well as pressure distribution for each foot can be measured at a very high precision26,27,28,29,30,31. Whereas patients with low back pain seem to use strategies to reduce the impact on the lumbar spine while walking, the treadmill setup offers the advantage to measure a patient's walk while keeping track of every single step32.
The hypothesis is that lumbar fusion surgery changes pathologic patterns in gait or posture and that these changes are in correlation with the detectable alleviation in the patient-reported outcome measure i.e., level of pain. The expected changes can be measured with video rasterstereography and treadmill gait analysis. The additional information about posture and gait can thus be compared with the overall functional status and satisfaction14,15,33.
Full approvals from the Department of Orthopaedic Surgery at the University of Tuebingen and the Ethics Committee at the University Hospital Tuebingen were obtained before the commencement of the study. Written informed consent was received from all subjects before their participation.
1. Patient Recruiting and Preparation
2. Experimental Design
3. Treadmill Gait Analysis and (Optional) Plantar Pressure Measurements
4. Experimental Design - Statistical Analysis
The representative results shown in this protocol come from a previous publication that has been published elsewhere26.
Rasterstereographic analysis
The results of perioperative rasterstereographic analysis of patients who did suffer from chronic lumbar back pain and who were treated with lumbar fusion surgery (n = 59) showed no significant changes in trunk length at the 3 month follow-up in comparison to the preoperative measurements (459 (33) - 448 (40) mm; p = 0.313; Tukey test) (Figure 1A). We however noted a significantly reduced kyphotic angle (vertebra prominens (VP) - thoracic spine vertebrae 12 (Th12), from 52° to 43°; p = 0.014; Tukey test) and lordotic angle (Th12 - dimple medium (DM), from 28° to 11°; p < 0.001; Tukey test) at the first post-operative measurement when compared to the preoperative values (Figure 1B). No differences for the measurements of trunk inclination or lateral tilt were detected at any time point (Figure 1C, D).
Gait and stance analysis
The treadmill gait measurements of the same patient cohort (n = 59) showed a significant reduction in cadence in the course from preoperatively to 3 months postoperatively (pre-OP to 7-days postoperatively: 98 (57-132) - 94 (43-119) steps/minute, p = 0.004; 3-months postoperatively: 91 (54-117) steps/minute, p = 0.006, Wilcoxon-test) (Figure 2A). Over the three postoperative months significant changes were detected for most spatiotemporal parameters (swing phase p = 0.01; stance phase p < 0.001; foot rotation p = 0.001). However, no significant improvements were seen for the symmetry of swing phase (difference-major-minor value (DiffMJMn) 2 (0-8) - 1 (0-6) %), stance phase (DiffMJMn 2 (0-8) - 1 (0-6) %) or foot rotation (DiffMJMn 3 (0-10) - 3 (0-15)°) (Figure 2B,C,D).
Figure 1: Rasterstereographic results. Boxplots displaying measurement changes for (A) trunk length at the 3-months follow-up in comparison to the preoperative measurements (459 (33) - 448 (40)mm; p = 0.313; Tukey test), (B) Lordotic angle at the first postoperative measurement when compared to the preoperative values (thoracic spine vertebra 12 - dimple medium, from 28° to 11°; p < 0.001; Tukey test), and (C-D) trunk inclination and lateral lilt over the course of one year (no significant difference). This figure has been adapted from reference26. Please click here to view a larger version of this figure.
Figure 2: Gait and stance results. (A) Boxplots displaying a reduction in cadence from preoperatively over the postoperative course of 3 months (preoperatively to 7 days postoperatively: 98 (57-132) - 94 (43-119) steps/minute, p = 0.004; 3 months postoperatively: 91 (54-117) steps/minute, p = 0.006, Wilcoxon-test) and the preoperative, 7-days and 3-months postoperative treadmill results for (B) swing phase, (C) stance-phase and (D) foot-rotation grouped according to subjective pain relief after surgery in percentage (<30%, 30-74%, >75%). From preoperatively to 3-months postoperatively we detected significant changes for most spatiotemporal parameters (swing phase p = 0.01; stance phase p < 0.001; foot rotation p = 0.001). No significant improvements were however observed with respect to their effect on gait symmetry (swing phase (difference-major-minor value (DiffMJMn) 2 (0-8) - 1 (0-6)%) stance phase (DiffMJMn 2 (0-8) - 1 (0-6)%, ), or foot rotation (DiffMJMn 3(0-10) - 3(0-15)°)). This figure has been adapted from reference26. Please click here to view a larger version of this figure.
Perioperative surgical outcome-monitoring is a field that is subjectively shaped. First it is affected by the surgeon's experience and secondly by the patient's subjective perception registered by for example questionnaires which also reflect his or her psychological distress and illness behavior. Our presented procedure offers an approach that objectifies crucial parameters regarding functional outcome. The methodical setup presented in this manuscript allows high precision measurements of changes in posture and gait after lumbar surgery18,37,38,39,40, but it can also be applied for other surgical interventions of the musculoskeletal system.
The investigator has to be aware of some method-related pitfalls. The rasterstereographic analysis of the back profile is highly dependent on the precise selection of the anatomical landmarks. If chosen imprecisely, measurement and data calculation will be incorrect as well. In addition, the subject's back must be completely undressed. Even wires of a bra or long scalp hair could disturb the scanning process. As gait measurements are susceptible to limping as a result of a painful hip, knee or ankle joint, the tested subjects need to be well examined before inclusion in the study and also before each follow-up visit to ensure the results are relevant and in correlation to the alterations of the spine. Since both methods have a high intra- and interobserver reliability21,24,41,42, their use in every-day routine can be easily implemented. However, combining both measurement-techniques might make it difficult to keep track of the abundance of data and to interpret these findings in a justifiable time.
One limitation of the technique of back surface measurement in general is that, to date, the data in the literature mostly refer to radiologic parameters obtained from X-rays to interpret postoperative outcome24. Since — due to modality-specific limitations — the definition of parameters used to describe posture differs between rasterstereography and X-rays (for example thoracic angle: rasterstereography thoracic vertebrae 1 to 12, x-ray thoracic vertebrae 4 to 12) it is not yet possible to derive conclusions from absolute values obtained by rasterstereographic analysis. It is rather their changes in the perioperative course that are of interest. Presently this tool is thus best suited for longitudinal analyses.
Other objectifiable data, such as CT (computed tomography imaging) or MRI (magnetic resonance imaging), can help to technically evaluate postoperative outcome, but they only illustrate static anatomical details. In contrast to the non-invasive and radiation-free measurement techniques described in this protocol, these imaging techniques are not able to take function into consideration8,9,10.
Interestingly the changes for gait and posture in our study were not always related with the patients' levels of pain. It thus appears that the postoperative dimension of function is not strictly associated with pain experience. The observed functional results are thus to be considered not contradictory but rather complementary to the patient related outcome measures. These measurements hence offer an additional dimension to critically evaluate postoperative outcome.
The evaluation of gait and posture is still a highly dynamic research field. We are confident that providing data about perioperative development of such functional parameters will improve our understanding of these conditions. In the long run, this may also help to further improve our surgical outcomes.
It is, therefore, important to apply the technique described in detail in this protocol and video on a broader scale to obtain more data about the functional parameters posture and gait in the perioperative course of musculoskeletal surgery.
The authors have no acknowledgements.
Name | Company | Catalog Number | Comments |
Ergo-Run Medical | Daum Electronic GmbH, Germany | NaN | NaN |
formetric 4D | Diers International GmbH, Germany | NaN | NaN |
IBM SPSS version 22 | IBM Inc. | NaN | NaN |
Matlab | MathWorks, Natick/MA, USA | NaN | NaN |
Numeric Pain Rating Scale (NRS) | NaN | NaN | NaN |
Oswestry Disability Index (ODI) questionnaire | NaN | NaN | NaN |
Video camera | Canon MD 216, Japan | NaN | NaN |
WinFDM-T software | Version 2.0.39, zebris medical | NaN | NaN |
Zebris medical system | Zebris, Isny, Germany | NaN | NaN |
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