Methods

Study design and acquisition of data

Ethical approval of the study was granted by local authorities (01/034/21). The patients consent to the procedure and the publication of their images. The institutional database of patients with peripheral nerve disease was screened for nTOS cases surgically treated by a single surgeon (NFD) between January 1, 2015 and June 30, 2023. Inclusion criteria were the diagnosis of nTOS according to the following nTOS subclassification that was recently published by the Peripheral Nerve Section of the European Association of Neurosurgical Societies (EANS) (Dengler et al., 2022b):-nTOS 1 - Hypotrophic nTOS: This subgroup comprises patients presenting with muscle weakness, hypotrophy, or atrophy primarily affecting the upper limbs, usually in a distal pattern.-nTOS 2 - Irritative nTOS with anatomical anomaly: Patients in this subgroup exhibit pain or sensory symptoms without motor deficits.-nTOS 3 - Irritative nTOS without anatomical anomaly: This is a diverse subgroup encompassing patients without motor involvement who experience pain or sensory symptoms.

Other inclusion criteria were age ≥ 18 years, failed conservative management by physiotherapy and/or pain medication, surgery via the microsurgical approach, and exclusion of a cervical pathology by cervical MRI or a peripheral pathology (carpal or cubital tunnel syndrome) by electrophysiology. The HRQoL, was assessed using the EQ-5D-5L questionnaire that was sent to all patients. The EQ-5D-5L consists of two sections. Problems in five dimensions of daily living (mobility/self-care/usual activities/pain/anxiety) are quantified on a scale from 1 (no problems) to 5 (not able to perform tasks) within the first section. The individual HRQoL is quantified on a visual analogue scale (VAS) ranging from 0 to 100 within the second section of the EQ-5D-5L (Feng et al., 2021). The following variables were assessed at routine follow-up examinations or by a structured telephone interview: age, sex, duration of symptoms before surgery, intraoperative findings in terms of anatomic abnormalities, self-reported benefit from surgery, pain on the numeric rating scale (NRS, 0-10 points), time to follow-up, HRQoL at follow-up, and work status. Comorbidities and body mass index (BMI) were documented.

Treatment algorithm

Patients were evaluated in our outpatient clinic prior to surgery. All patients underwent an x-ray of the thoracic outlet, an MRI or ultrasound of the thoracic outlet and an MRI of the cervical spine, as recommended (Dengler et al., 2022a, 2022b). Other peripheral nerve pathologies (e.g., carpal or cubital tunnel, loge de Guyon syndrome) were ruled out by electrophysiological examination, or, if present, primarily addressed. In case of nTOS 2 and nTOS 3, patients underwent an initial conservative treatment phase with pain management and/or physiotherapy. In case of persisting symptoms surgery was offered according to recent consensus recommendations (Dengler et al., 2022b; Rochkind et al., 2023). Surgery was performed in a supine position as described elsewhere (Ferrante, 2012; Dengler et al., 2022b). In short, the arm of the affected side is extended and positioned on a side table. The head is turned towards the contralateral side (Fig. 1). Intraoperative electrophysiological monitoring with free-run electromyography EMG) of the M. opponens pollicis, M. flexor digiti minimi, M. deltoideus and M. biceps brachii as well as a monopolar stimulation probe is established. A 3 cm incision approximately two fingers above the clavicle is marked. Preparation based on the important landmarks including the sternocleidomastoid muscle, the supraclavicular fat pad, the omohyoid muscle, the phrenic nerve, and the anterior scalene muscle is performed until the brachial plexus is visualized. Further preparation is performed under microscopic view using a retractor. The superior, medial and inferior trunks are visualized. A three-dimensional decompression is performed by partial anterior scalenectomy, transection of fibrous bands, resection of bony anomalies and decompression of the subclavian artery. The first rib is visualized. Position maneuvers are performed to check for adequate decompression in provocative positions. The first rib is only resected in case where residual compression is detected. Free-run EMGs are constantly checked.

Fig. 1: Intraoperative patient positioning. The arm of the affected side (here left arm) is extended and positioned on a side table. The head is turned against the contralateral side. The incision line (continuous) is approximately two fingers above the clavicle. The sternocleidomastoid muscle is marked by the dashed line.

Statistical analysis

Statistical analysis was performed using SPSS software (Version 25.0. Armonk, NY: IBM Corp.). All values were expressed in numbers and % of patients or median and interquartile range (IQR) and were compared using the non-parametric Mann-Whitney U or Wilcoxon test for metric non-normally distributed variables and Chi (Laulan et al., 2011) test for ordinal or nominal scaled variables. Statistical significance was assumed at p-values of <0.05.