Teaching Case

A 59-year-old woman presented with a 2-month history of right shoulder pain and swelling. The patient reported a traumatic fall 9 months prior. Physical examination revealed a limited and painful active and passive range of motion of the right shoulder.

Plain radiograph of the right shoulder showed significant destruction, deformity, and cranial subluxation of the humeral head. There was also evidence of osteolysis of the acromial end of the clavicle. Intra-articular calcifications were apparent as well (Figure 1a). A shoulder radiograph performed one year earlier did not reveal any of these findings (Figure 1b).

The computed tomography (CT) scan demonstrated extensive destruction of the humeral head, glenoid, and coracoid process. Osteolysis of the inferior surface of the acromion and the lateral end of the clavicle was visible (Figures 2a and 2b). There was a large joint effusion, with extensive areas of synovial proliferation (Figures 3a, 3b and 3c) associated with capsular calcifications and intra-articular amorphous calcium deposition (Figures 2a and 2b). Signs of massive rotator cuff tear were present, with marked atrophy and fatty infiltration of the corresponding muscle (Figure 3c), with consequent migration of the remaining humeral head and reduction of the subacromial space.

Background

Milwaukee shoulder is a rare condition characterised by massive destruction of the shoulder joint due to intra-articular deposition of calcium phosphate crystals [1]. The deposition of these crystals within the joint space triggers the release of lysosomal enzymes, which then degrade the bones and surrounding periarticular structures, including the rotator cuff tendons [2,3].

Clinical Perspective

The disease typically affects elderly women and presents with progressive shoulder pain, joint swelling, and limited range of motion [4].

The insidious onset and progressive nature of the disease often lead to a delayed diagnosis and treatment. Furthermore, symptoms are frequently disproportionate to the advanced state of bone destruction [5].

While unilateral shoulder joint involvement, typically in the dominant side, is more common, Milwaukee shoulder can also present bilaterally in some cases [2]. Predisposing factors include recent trauma, joint overuse, dialysis, and hyperparathyroidism [6].

Imaging Perspective

Since the clinical presentation of Milwaukee shoulder is non-specific and its symptoms overlap with those of other conditions, imaging techniques are crucial for diagnosing and ruling out other potential causes [7].

Plain radiographs often reveal extensive joint space narrowing, subchondral bone destruction with partial bony collapse of the humeral head, intra and peri-articular calcifications, and subchondral sclerosis with cyst formation. The bone destruction can also extend to the acromion, the coracoid process, and the distal clavicle. Pseudoarthrosis involving the humeral head, coracoid, and acromion is common [2,6].

CT is useful for a more detailed evaluation of bone destruction and for pre-operative planning. Magnetic resonance imaging (MRI) provides a better evaluation of soft-tissue-associated changes, such as rotator cuff tears and synovitis, and offers a detailed assessment of cartilage damage [6].

Large joint effusions are frequently observed, with extension to subdeltoid and subacromial regions. There is also a strong association with massive rotator cuff tears [6,8].

A definitive diagnosis is confirmed by detecting hydroxyapatite crystals in synovial fluid, using alizarin red staining [2,5].

Outcome

The treatment is focused on symptomatic relief, with nonsteroidal anti-inflammatory drugs, corticosteroid injections, and physical therapy being the most common conservative strategies. In cases of severe joint destruction or advanced degenerative changes, surgical interventions may be necessary [2].

Take Home Message / Teaching Points

• Milwaukee shoulder is a destructive arthropathy caused by intra-articular calcium phosphate crystals deposition.
• Imaging techniques like plain radiographs, CT, and MRI reveal joint space narrowing, bone destruction, and soft tissue changes.
• Definitive diagnosis is confirmed by detecting hydroxyapatite crystals in synovial fluid.

Written informed patient consent for publication has been obtained.