11.4 Shoulder, Bony Pelvis & Hip CT

Why This Topic Matters

Shoulder, bony pelvis, and hip complete the six Musculoskeletal leaf items in the Procedures outline. These three regions share a recurring exam theme called out explicitly in the blueprint's "Additional Procedures" focus area — trauma and surgical planning — and they also create one of the highest-yield vocabulary traps on the entire exam: the word "pelvis" appears in two different Procedures leaf items with two different meanings.

Core Terms and Rules

• Shoulder CT: used for complex proximal humerus fractures, glenoid fractures, and glenohumeral instability, where surgical planning benefits from 3D reconstruction of fracture fragments and joint congruity. Shoulder CT arthrography (intra-articular contrast injection into the glenohumeral joint) evaluates labral tears — including Bankart lesions after anterior dislocation — and rotator cuff pathology when MRI is contraindicated, following the same intra-articular contrast principle introduced in the previous section.
• Bony pelvis CT: focuses on the osseous pelvic ring — ilium, ischium, pubis, sacrum, and acetabulum — most often in high-energy trauma such as motor vehicle or motorcycle collisions. CT is markedly more sensitive than radiography for occult sacral fractures and posterior ring injuries, and 3D volume-rendered reconstructions are the modern standard for classifying acetabular fractures (historically assessed with Judet oblique radiographic views) and planning operative fixation.
• Hip CT: evaluates occult hip fractures in patients — classically elderly patients — with a negative or equivocal radiograph who remain unable to bear weight, as well as avascular necrosis of the femoral head and preoperative templating before hip arthroplasty. Hip CT arthrography can also assess acetabular labral tears.
• The blueprint vocabulary trap: "bony pelvis" is a Musculoskeletal leaf item describing the pelvic skeleton (fractures, ring injuries), while "pelvis" also appears as a separate Procedures leaf item under Abdomen and Pelvis, describing pelvic organs (bladder, reproductive organs, colorectal structures) — a different subcategory covered in the abdominal/pelvic imaging chapter. Exam questions that mention fracture, ring injury, or acetabulum are testing the musculoskeletal "bony pelvis" item; questions about bladder distension, cystogram, or reproductive-organ imaging are testing the abdomen/pelvis "pelvis" item. Reading the clinical indication in the question stem — not just the word "pelvis" — tells you which content area is being tested.

Table: Region-Specific High-Yield Indications

Acetabular Fracture Classification and Arthroplasty Planning

Acetabular fractures are traditionally described using the Letournel classification, which separates fractures into elementary patterns (such as posterior wall, anterior column, or transverse fractures) and associated patterns that combine two or more elementary types (such as a T-shaped fracture or an associated both-column fracture). CT — especially with 3D volume-rendered and "disarticulated" hip reconstructions that digitally remove the femoral head from the view — has become the standard way surgeons assess which columns and walls of the acetabulum are involved, because this directly determines the surgical approach (anterior, posterior, or combined) and whether the femoral head remains congruently seated in the joint. A similar preoperative logic applies to hip CT ordered purely for arthroplasty templating: thin-section, bone-algorithm images through the proximal femur and acetabulum let surgeons measure femoral canal dimensions and acetabular geometry to select implant component sizes before a scheduled hip replacement, distinct from the trauma indications discussed above.

Exam Scenario

A 78-year-old falls at home, cannot bear weight on the left leg, and has a hip radiograph read as negative. Because occult hip fractures are common in this population and a missed fracture risks further displacement and complication, the ordering provider requests a CT of the hip. The technologist protocols a thin-section acquisition with bone- and soft-tissue-algorithm reconstructions and coronal/sagittal reformats through the proximal femur and acetabulum — the same dual-algorithm, thin-section approach used for every musculoskeletal region in this chapter, applied here to detect a fracture line the radiograph missed.

A second scenario: a 35-year-old motorcyclist arrives after a high-speed collision with an unstable pelvic ring on physical exam. The trauma CT of the bony pelvis shows a complex fracture involving both the anterior and posterior columns of the acetabulum. The trauma surgeon requests 3D volume-rendered reconstructions with the femoral head digitally removed from the view before finalizing the operative approach — a direct application of the surgical-planning focus theme to a Letournel-type acetabular fracture pattern.

Common Traps

• Reading "pelvis" in a question stem and automatically routing it to bladder or reproductive-organ content — check whether the clinical detail is fracture/ring/acetabulum (bony pelvis, Musculoskeletal) or bladder/cystogram/reproductive organ (pelvis, Abdomen and Pelvis).
• Forgetting that "trauma" and "surgical planning" are explicit cross-cutting focus themes the blueprint applies to every study in this chapter — expect scenario questions that combine anatomy recognition with a trauma or preoperative context rather than pure anatomy recall.
• Treating shoulder, bony pelvis, and hip protocols as fundamentally different from each other — in practice, all three share the same thin-section, dual-algorithm, MPR/3D-reconstruction technical approach; what changes is anatomic coverage and clinical indication, not the underlying protocol logic.