Three rheumatologists who were experts in musculoskeletal ultrasound were trained in synovial biopsy throughout 2022–2023 in different specific training programmes. Each procedure was performed in the presence of 2 rheumatologists and 2 third- and fourth-year rheumatology residents, either from the unit or external rotating personnel. Each procedure was performed at the same time by both an assistant and a resident, so that, between procedures, a team of 2 human resources were preparing the next patient or drafting the surgical report on the previous patient. All residents taking part in the operating theatre work had been through the ultrasound rotation of one month in the second year of residency and 3 months in the third. In the case of external rotations in the Imaging and Ultrasound-Guided Procedures Unit (USGPU), their involvement was in the third month of their rotation.

The surgical sub-directorate at our centre assigned an operating theatre to our unit in the outpatients’ surgical procedures unit, where other specialties such as urology, dermatology or otorhinolaryngology performed procedures. The rheumatology operating theatre had the same facilities as a conventional operating theatre and was assigned to a 7 h anaesthesiology shift in which up to 5 procedures could be performed on the same day. Although the performance of a synovial biopsy did not require the presence of an anaesthesiologist or access to an operating theatre and, according to the literature, this can be performed in a clean room with the assistance of auxiliary personnel,2,7,15 in our unit the use of the operating theatre was chosen for 2 reasons: 1) to offer maximum comfort and for the well-being of the patient during the procedure, and 2) because there was no clean room cleaning staff available between procedures, or auxiliary personnel for exclusive service during synovial biopsies.

The Rheumatology Service provided a portable MyLab Sigma ultrasound machine™ from the commercial company ESAOTE, equipped with a 23 MHz hockey stick probe and an 8−13 MHz linear probe. The operating theatre material included 3 biopsy needle measurements that were selected by the team of rheumatologists responsible for the USGSB after evaluation of different models and brands. The small biopsy needle reserved for metacarpophalangeal and interphalangeal joints was not equipped with a guidewire cannula, while the medium and large needle, which was used in the rest of the joints, had a cannula that was inserted beforehand, was located with the ultrasound guide and enabled the sampling procedure to be repeated without the need for further punctures.

The rheumatology operating theatre shift was coordinated every four months with the immunology and pathology departments. The immunology unit was responsible for the flow cytometry process which, in turn, required prior processing of the tissues by enzymatic digestion to facilitate the exposure of cell receptors. This pre-procedure requires 6 h and should be started immediately after the sample has been obtained. For this reason and with the limitation of the availability of personnel in this laboratory, the last sample had to be processed at 12:00 so, finally, the number of procedures that could be performed in order to obtain a cytometric analysis, were 3 or 4. The pathological anatomy unit was responsible for the conventional histological study of the tissue samples sent. Unless specifically requested, the report included data on architecture and composition (Krenn scale) and specific histochemical or microbiological studies could be requested.

In our unit, the performance of synovial biopsies has been proposed in the following situations: synovitis where the intention is to exclude infections, diagnostic uncertainty between 2 or more probable processes, and synovial study of patients with failure to respond to 3 or more biological therapies.

The proposal of the procedure to the patient is made by the clinician responsible for each case, which includes signing an informed consent. The case is discussed with the rheumatologists who perform the USGSB, and they schedule an ultrasound examination if this has not been previously done or if it has not been undertaken recently. Once the consent has been signed, the patient is scheduled for a pre-anaesthesia consultation (for which it is not necessary to request laboratory tests) and is finally scheduled for the rheumatology operating theatre.

On the day of the procedure, an exploratory ultrasound is performed before entering the operating theatre to ensure the availability of tissue and to plan the procedure between the doctors involved. Once in the operating theatre, the decision is taken as to whether to perform a regional block, or conventional sedation with supervision by the anaesthesiologist in all cases.

The procedure is performed in teams of 2 (one assistant and one resident) and can be conducted by one single or 2 operators in a two- or four-handed procedure, respectively. In the 4-handed procedure, one operator maintains the positioning of the probe while the second manipulates the biopsy needle. In the 2-handed procedure, a single operator is responsible for holding the probe in position and also handling the needle. In all cases, the management of the samples is handled by the surgical nursing staff and the transportation to the corresponding laboratories is done by the operating theatre assistant staff.

Synovial tissue samples sent to the immunology laboratory are inserted into a saline tube, 3 per tube according to the region of interest (usually one region of interest per USGSB). Tissue samples for the study of pathological anatomy are sent in formaldehyde in threes or fours by region of interest.

Immunology results can be available in 48 h and pathological anatomy results in approximately 3–4 weeks.

At the end of the procedures, patients are clinically re-assessed and are given a report with the detail of the procedure performed and analgesic recommendations. After performing the USGSB, the residents taking part contact the patients 72 h after the USGSB to corroborate their general well-being and the absence of complications. Throughout this period, patients can contact the unit in case of urgent assessment needs during working hours and, outside working hours, the emergency department of our centre.

38 USGSBs were performed on 33 patients over the period described, of which 22 were female. The mean age (standard deviation) of the patients was 59 (17) years with a range between 26 and 90 years. Two patients scheduled for USGSB) finally rejected the procedure.

USGSB was performed in all peripheral articular regions with the exception of the coxofemoral joint. Table 1 summarises the characteristics of the procedures performed.

The mean time in the operating theatre per patient was 95 min, taken from the time of entry to the operating theatre until the drafting of the operation report. Approximately, the time spent on the procedure itself ranged from 25 to 45 min (Table 1).

As regards the approaches used to carry out the USGSBs, these were the following: for carpal biopsy, the distal radioulnar joint was targeted, approaching ulnar-dorsally; for the USGSB of the second MCF joint, the approach was radially; for shoulder USGSB, posterior access at the level of the labrum was the approach for the study of the synovium, and lateral anterior access for the study of the bursa; for elbow USGSB, access was posteriorly and laterally, targeting the olecranon fossa, although in one patient the anterior access was adopted, with a lateral approach, bypassing the humeral artery and targeting the condyle-radial synovium; for the knee, the approach was through the external parapatellar recess; and for the ankle, access to the tibiotalar joint was by the lateral approach.

Throughout the period described, there was no loss of samples due to means of transport. In one patient, a sufficient synovial tissue sample could not be obtained for the study.

The motivation or indication for USGSB in the 33 patients was due to diagnostic needs (differential diagnosis, diagnostic confirmation, or diagnostic uncertainty) in 20 cases, and due to poor or insufficient treatment response in 16 cases. Both indications coexisted in 3 patients. Three diagnoses of infectious diseases were reached (2 for chikungunya virus, one diagnosis of microcrystalline arthritis due to hydroxyapatite, one diagnosis of disease due to calcium pyrophosphate crystal deposition, two diagnoses of amyloidosis, and one diagnosis of psoriatic arthritis). A total of 16 diagnoses of seronegative rheumatoid arthritis were ratified.

Table 1 summarises the previous diagnoses, final diagnoses reached, and clinical attitudes after the USGSB results were known. These changes in attitude correspond to the review of the evolutionary changes immediately following the assessment of the result of the USGSB, although the decision may have been taken without considering that result exclusively, but also taking other evaluation parameters, together with the result of the USGSB.

No complications occurred during the performance of the USGSB. No patient required analgesia rescue beyond the regimen performed at discharge, on the day of the procedure. There was no need for prostration or specific rest in the case of any patient. One patient presented with a local haematoma on the ankle, at the level of the puncture site, which was resolved with physical measures and prolongation of analgesia. Table 2 summarises the condition of the patients 72 h after the USGSB had been performed, in line with the further treatment undertaken by the resident physicians who took part in the procedures.

Throughout the period indicated, 16 residents attended the rheumatology operating theatre, 8 of them from the unit and 8 external rotating residents. In all cases, the assistants in charge performed the first approach and, depending on the degree of skill demonstrated, the residents performed the procedure once the catheter and cannula had been placed in the desirable positions, or even from the first incision. This training system was consistent with that proposed in the literature,16 although without reaching the capability of performing the procedure autonomously. Two joint sessions were held along with the Immunology and Pathological Anatomy departments and the unit organised its own sessions on the scope of the usefulness of the procedures.