**3. Diagnostic Radiology**

Conventional radiographs usually confirm the diagnosis of OA in advanced stages or provide essential hints for differential diagnosis. The typical findings of OA are narrowing of joint space as an indirect sign of reduction of cartilage, subchondral sclerosis representing an adaptation reaction of the bone, and metaplastic responses known as osteophytes [7]. The extent of these changes is underestimated by plain-film radiography [8]. Computer tomography (CT) could finally increase the accuracy in diagnosis and the prevalence of OA essentially (Figure 1). In 282 patients with unilateral instability without surgery, the rate of OA was 11.3% in conventional radiographic imaging and 31.2% when CT was used. Even small osteophytes can be detected. CT can also detect the loss of the anterior and posterior part of the joint gap when it remains almost unaltered in conventional radiographic approjection [9]. Ogawa et al. [10] reviewed 167 joints of 163 patients undergoing the open Bankart procedure. Preoperative CT showed OA in 44 shoulders (26.3%), among which 12 shoulders (7.2%) showed OA on the preoperative radiographs. Preoperative CT-proven OA in 20 shoulders never became visible on postoperative radiographs. Recent threedimensional computed tomography (3D CT) trends could better define the relationship between the humeral head and the glenoid [11]. Posterior wear after index surgery should be analyzed if the progression of OA is recognized to define new treatment options [12]. Ultrasound is the method to depict intra-articular effusion at early stages. Osteophytes or the degree of synovitis are also visible. Subchondral lesions, changes in cartilage volume, and concomitant soft-tissue alterations were detected earlier using MRI [7,9]. MRI also enables semi-quantitative analysis of the postoperative changes of the subscapularis muscle. The results provide indications of the causes of the clinical dysfunction of the subscapularis musculotendinous unit after open shoulder stabilization [13].

**Figure 1.** Imaging methods for evaluating dislocation arthropathy. Examples of conventional radiographs, MRI, and CT scan showing OA.
