**5. Discussion**

The US is widely used for diagnosis and treatment in musculoskeletal fields. There have been several studies representing US features of PA tendon or PAB in patients with PATB. Some studies reported that the US is limited in detecting PATB, while others concluded that it can be helpful. Uson et al. [17] assessed the US findings of the PA and the subcutaneous fat of medial knee in clinically diagnosed PATB patients. The diagnostic findings were the thickness of the insertion of the tendons, the presence of fluid collection greater than 2 mm in the bursa, and changes in the subcutaneous fat of the medial aspect of the knee. For a total of 37 participants, PA tendinitis was diagnosed in just one knee and PA bursitis in three knees (two symptomatic and one asymptomatic). From the results, they concluded that it was difficult to detect US findings of PA tendinitis or bursitis in patients diagnosed with PATB syndrome. Unlu et al. [18] examined US evidence of PA tendinitis or bursitis in patients with type 2 diabetes mellitus. Only 8.3% of 48 patients were found to have PA tendinitis findings in the US. Although PA tendinitis or bursitis syndrome is not uncommon in patients with diabetes mellitus, there might be less frequent morphologic US changes of the PA tendons. Yoon et al. [2] prospectively studied the correlation between US findings and response to steroid injection in 26 patients with clinically diagnosed PATB syndrome. Only two patients (8.7%) showed sonographic evidence of PATB. One patient with PA tendinitis showed thickening and loss of normal fibrillar echotexture. The other who had bursitis revealed circumscribed anechoic fluid collection of 2 mm or greater.

Uysal et al. [12] evaluated the prevalence of PA bursitis in OA patients. A total of 170 knees from 85 patients with knee OA were assessed, and 20% (34/170) of the knees showed PA bursitis in US examinations. They suggested that PA bursitis was easily found in the US, and there was a positive correlation between OA grade and PAB size and area. Toktas et al. [19] studied the US findings of PA tendon and bursa in 183 clinically diagnosed PATB among the 314 knees with OA. The results showed that the mean thickness of PA in knees with OA with/without PATB was significantly greater than the controls. US could be a useful diagnostic tool for detecting PATB syndrome in knee OA patients.

The term PATB is generally used to describe the inflammatory condition of PAB; however, the structure associated with symptoms is still not identified. After the intervention in our study, all injectates (25 of 25 subjects) were located accurately in the PAB in the US-guided injection group, whereas just 18% (4 of 22 subjects) were properly located in the blind injection group. The US-guided group revealed greater pain reduction significantly than the blind group. This suggests that the pain might be arisen from the bursa, so a diagnosis of tendinobursitis is more suitable for this condition.

As previous studies have shown, US-guided injections are more accurate than blind injections. Various reviews have recently been reported on the clinical utility of US-guided injections in locations such as shoulder girdles, hip joints, and knee joints. A systematic review of US-guided shoulder girdle injections reviewed four cadaveric studies and nine human studies, and concluded that US-guided injections had greater accuracy for all types of shoulder injections than landmark-guided injections, except subacromial injection. The efficacy for the subacromial and biceps tendon sheath injections was improved [20]. Another systematic review of US-guided hip joint injections showed the improvement of accuracy. They reviewed four US-guided and five landmark-guided studies, and suggested that US-guided hip injections were significantly more accurate than landmark-guided techniques [21].

A review of US-guided intra-articular knee injections revealed that US-guided injections notably improved accuracy in the intra-articular joint injections than conventional palpation-guided injections by analyzing a total of 13 previous studies. US guidance also directly improved patient-reported clinical outcomes and costeffectiveness [15].

PAB injection is usually performed by blind technique in actual clinical settings because PA is located closer to the superficial layer compared to other deep joints. Acromioclavicular joint (AC) is also located superficially, and blind injection is often performed through palpation. Nevertheless, a previous study has shown that the use of US in the AC joint injection is more accurate and effective [22]. They concluded that US-guided AC joint articular injection resulted in better pain and functional status improvement than palpation-guided injection at the 6-month follow-up. Therefore, even in the superficial structures, US-guided injection is recommended for accurate treatment.

For this reason, although the effectiveness of US examination in the PATB diagnosis is controversial, the value of US-guided injection treatment is sufficiently recognized for its accuracy. Overall, the accuracy of blind injections is 40–80%, while that of US-guided injections is approximately 90–100%. In most of these injections, the improved accuracy achieved by US guidance directly enhances clinical outcomes.

Consistent with previous studies, this research observed that US-guided injection was more accurate than the blind injection, and intra-bursal injection had a better clinical result in the treatment of PATB. Although the standardized US-guided injection technique has not yet been established, longitudinal access to the tibia would be appropriate to administer materials. Anatomically, the transducer is positioned in a longitudinal orientation relative to the MCL, oblique transverse access relative to the PA. While monitoring the image, insert the needle through the skin proximal to the transducer and advance in a proximal to the distal direction in a longitudinal plane. According to the physician's preference, a needle can approach the distal to the transducer and advance in the proximal direction in a longitudinal plane. The target of the injection is the space beneath the PA tendon. When the needle tip is visualized in the target space, inject the materials slowly and carefully, since the space is relatively narrow.

The PAB corticosteroid injections are contraindicated in patients with systemic infection states (sepsis, bacteremia, etc.), joint infection (septic arthritis, cellulitis, osteomyelitis, etc.), fracture, osteoporosis, coagulopathy, skin defect, hypersensitivity to the steroid, uncontrolled hyperglycemia; also, some complications such as bleeding, bruising, swelling, infection, post-injection pain (steroid flare), face flushing, skin depigmentation, cutaneous atrophy can occur [23].

There were several limitations of our study. Because of the short-term follow-up period, the long-term clinical effects could not be determined. The morphologic US features of the anserine bursa or tendon were not examined that might help to identify the source of pain in PATB. In addition, potential differences caused by activity levels were not considered even if they had a potential impact on the results of the study.

## **6. Conclusion**

Both US-guided and blind injections significantly reduced pain levels in patients with PATB. In the US-guided injection group, the accuracy was higher than in the blind injection group. Clinical results were more affected in the US group.

All injectates were located in the PAB after the US-guided injections, while only in some cases of the blind approaches, injectates were located in the PAB. This suggests that the optimal source of pain might be associated with the bursa.
