**4. Discussion**

This manuscript demonstrates missing links between low back pain and orthotic fitting. As a result of these findings, we developed a concept for orthotic selection depending on the pathological source. This could be considered a step towards improving the accompanying treatment options and therapeutic accuracy.

Spinal orthoses can limit range of motion, and can stabilize or reposition spinal segments. In the case of obesity or during pregnancy, the circular design can relieve the spine through targeted application of ventral forces. Other local effects are described, but not well studied. For temporary orthotic treatment, the effects must be consistent with the cause of the complaint.

One prospective study did not show any effectiveness of lumbar supports in 28 assemblyline workers, with respect to low back functionality and disability [1]. In contrast, another reported positive effects of wearing a lumbar belt in workers [4]. An in vitro biomechanical study investigating the effects on posterior pelvis kinematics reported an altered lumbosacral transition and increased movement in the sacroiliac joint by pelvic orthosis [5].

Two prospective reports dealt with postoperative bracing including 119 patients. No indication for postoperative bracing regarding pain relief or quality of life was observed [22,23]. The same was true for 96 patients with conservatively treated thoracolumbar burst fractures [9] or following single-level lumbar discectomy in 54 patients [20].

Regarding low back pain, different study protocols reported a positive effect of lumbar orthosis in 115 patients [2,6,18,21]. In contrast, four different randomized studies did not provide any pain relief after six months observation of 266 patients [8,14,17,30]. No positive effect of wearing a lumbar orthosis on muscle thickness measured by ultrasound was reported in 44 patients [19]. Reduced back muscle fatigue was reported in six healthy participants after wearing a low-profile elastic exosuit [7].

Here we only individually discuss those contributions that describe no effect despite differentiated cause of pain and differentiated orthotic fitting. In total, 30 studies were identified, of which 20 were prospective studies (Table 1) and nine were reviews or meta-analyses (Table 2). The remaining paper was a retrospective analysis of treating chronic lumbar back pain with a rigid lumbar brace [28]. The literature selection process is presented in the flow diagram in Figure 6.

Zoia et al. investigated postoperative orthotic fitting after monosegmental disc surgery. Their highly structured study concluded that after monosegmental disc surgery, the shortterm and mid-term outcomes displayed no difference to orthosis-free care [20].

It should be noted that all patients displayed monoradicular lumboischialgia and were surgically treated by only two surgeons using microscopes. The corresponding pain reduction did not sugges<sup>t</sup> an effect of additional orthoses, since a sufficient postoperative pain treatment would be expected. The question about a possible reduction of pain medication, recurrence frequency or longer-term instability has not been answered.

Fujiwara et al. reported that orthotic fitting after PLIF (posterior lumbar interbody fusion) resulted in no benefit compared to orthotic-free fitting. Severe osteoporosis was mentioned as an exception [23].

Neither a benefit nor a disadvantage in terms of complaints was recorded in the control period of 3 months. In this case, it was also true that drug therapy was not answered. A long-term effect on follow-up degeneration was not discussed.

Orthotic fitting after posterior instrumented fusion did not improve quality of life or complaints, as reported by Soliman. The number of complications and reoperations in the brace group (7 out of 25) and in the control group (5 out of 18) must be seen as a limitation on the outcome [25].

Disc surgery, or segmental fusion, should not require additional external stabilization. However, this only applies to the surgically treated segment. The protection of the adjacent segmen<sup>t</sup> and thus the reduction of connecting degenerations cannot be derived from this.

It must also be considered that a sufficient postoperative medicinal pain treatment excludes the discomfort as a measure for an indication of the orthotic fitting.

From this perspective, local wound treatment, reduction of complications and, in the long term, prevention of follow-up degeneration should be cited as measures of treatment success with spine orthoses.

In a Cochrane Database of Systematic Reviews from 2016, the "Surgical versus nonsurgical treatment for lumbar spinal stenosis" was treated. The authors concluded that they

had very little confidence to confirm whether surgical treatment or a conservative approach is better for lumbar spinal stenosis, and they could not provide any new recommendations to guide clinical practice [29].

The results of the current literature are presented in a structured manner. Overall, there are no general statements for or against treatment with orthoses in low back pain.

The simple systematic structuring of orthoses forms the basis for finding promising treatments, but also forms a basis for contraindications.

Strict scientific statements cannot be provided. The structure of the orthoses is influenced by clinical application, since neither the nomenclature for orthoses nor a recommendation for indications is currently available.

This manuscript highlights the weakness of the current indications for orthotic provision in low back pain.

Accordingly, we can conclude that the current literature gives no recommendations to guide clinical practice.

The effectiveness of spine orthoses cannot be deduced from the current literature. The most serious limitation is the inconsistency of the complaints and orthoses. Furthermore, the imprecise designation of the orthoses is an additional limitation.

## **5. Conclusions**

The effectiveness of spinal orthoses cannot be determined on the basis of the current literature. A major limitation is the lack of standardized nomenclature.

The lack of differentiation of the causes of pain is another weakness in many scientific papers. This limitation cannot be overcome by statistical methods or meta-analyses.

Additionally, in the case of postoperative treatments, pain reduction cannot be applied as a measure of therapeutic success in the presence of sufficient medicinal pain management.

The categorization of spinal orthoses demonstrated in this manuscript should be an impetus for further efforts to standardize products. These suggestions can provide the basis for answering the question of the effectiveness of spinal orthoses in conjunction with a differentiated cause of complaints. Spinal orthoses are an additional treatment option in limited indication of medication or surgery.

We found that articles with a precise allocation of the complaint and a description of the orthosis showed a positive effect. The treatment concept presented here is intended to provide a basis for answering the question concerning the effectiveness of spinal orthoses as an accompanying treatment option.

**Author Contributions:** Conceptualization, F.L. and K.T.; methodology, F.L. and K.T.; validation, F.L. and K.T.; formal analysis, F.L. and K.T.; writing—original draft preparation, F.L. and K.T.; writing— review and editing, F.L. and K.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable for studies not involving humans or animals.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The study did not report any data.

**Conflicts of Interest:** The authors declare no conflict of interest.
