## 3 Technique Description
The arthroscopy of the first metatarasophalangeal joint was first described by [PERSON] in 1988 during an osteochondritis dissecans treatment [24]. However, this procedure has gained popularity in recent years and has been used to treat osteochondritis dissecans, hallux valgus, and gout, as well as the most common indication, hallux rigidus. Arthroscopic debridement cannot definitively remove the entire bony eminence. Even with extended synovectomy, a collapsing capsule, and often, overgrowth synovonium may deceive the surgeon. Intraoperative sonographic navigation during first metatarasophalangeal joint arthroscopy allows a constant view of osteophyte removal, ensuring complete resection. Furthermore, the first metatarasal joint is relatively small, and navigation over the upper surface of the metatarsal head under both the capsule and the extensor hallucis longus tendon requires excellent orientation. Moreover, US imaging allows surgeons to omit performing an open procedure in numerous cases. Double visualization makes the procedure safer, faster, and more reliable. [PERSON] et al., in their study, suggest sterile draping for the transducer, and additionally, gel was added frequently during visualisation [23]. After the sterile draping of the ultrasound transducer (linear probe: 7.5 cm; frequency: 10-12 MHz), the joint was visualised using the ultrasound scanner by placing the probe longitudinally over the upper surface of the first metatarasophalangeal joint. The authors revealed that all three patients were satisfied with the procedure and the functioning of the treated feet. The average surgery time was 81 min, with no complications having occurred. [PERSON] et al. used sonographic navigation to avoid complications during arthroscopic ganglion resection. The authors emphasized the role of double visualisation and the decreased risk of inadvertent injury to the arteries or nerves surrounding the joint during arthroscopy. Using sonography, the vessels, nerves, and tendons around the ganglion can be easily visualized. In addition, the position of the tip of the shaver can be controlled throughout the all procedures [25]. Hematoma of the calf is a rare complication following anterior cruciate ligament reconstruction, and the golden standard method for its treatment is puncture and aspiration (Figure 5). However, prolonged hematomas may demand more advance procedures, such as surgical evacuation. [PERSON] et al. presented a case study where an open surgery failed, and reoperation using a hybrid-US/endoscopic procedure resolved the  
Figure 4: **(a)** Sonographic visualisation of the arthroscopic cannula introduced the first metatarasal joint between first metatarasal (M) and phalanx (P). The aim of the procedure is the removal of the bony osteophyte (arrowhead). Note hyperechoic artefacts (A) caused by steel cannula (arrow) (**b**) Resection of the first metatarasal (M) head osteophyte using the motorised shaver (S). clinical problem [26]. The authors concluded that the endoscopic and ultrasound-assisted evacuation of the prolonged calf hematoma is an effective, minimally invasive and targeted procedure, even in old hematomas with evident scarring of the soft tissues. Lastly, ultrasound navigation can also be used in mini-invasive, percutaneous Achilles tendon repair. Ultrasound are an adequate tool for assessing the pathological alteration of the Achilles tendon, effectively represents histopathological changes, and moreover, in Europe, it is regarded as a primary imaging method [27]. Achilles tendinopathy with the degeneration of tendinous tissue occurs in 5.9% of seniors and 50% of elite athletes [28]. There are multiple methods of treatment for completely torn Achilles tendons, such as an operative treatment (open, percutaneous, or mini-invasive repair) and a non-operative treatment (cast, brace, or orthosis). Still, no consensus has been reached regarding a universal treatment option.