Following a motor vehicle accident, a 63-year-old man is scheduled for surgery. The emergency physician notes a posture abnormality in the distal left lower limb and a fracture-dislocation of the right hip and acetabulum based on the radiology report. The senior orthopedic resident mistakenly notes a fracture dislocation of the left hip. The surgeon's examination of the patient in the operating room shows an externally rotated and shortened left lower limb. The surgeon reduces the left hip and inserts a pin in the left tibia. A review of postoperative imaging leads to a second surgery on the fracture-dislocation of the right hip. Which of the following strategies is most likely to prevent the recurrence of this type of error?

Conducting a preoperative time-out

Verifying the patient’s identity

A 54-year-old man presents to his primary care physician for back pain. His back pain worsens with standing for a prolonged period of time or climbing down the stairs and improves with sitting. Medical history is significant for hypertension, type II diabetes mellitus, and hypercholesterolemia. Neurologic exam demonstrates normal tone, 5/5 strength, and a normal sensory exam throughout the bilateral lower extremity. Skin exam is unremarkable and dorsalis pedis and posterior tibialis pulses are 3+. Which of the following is the best next step in management?

Radiography of the lumbosacral spine

A 69-year-old woman presents with pain in her hip and groin. She states that the pain is present in the morning, and by the end of the day it is nearly unbearable. Her past medical history is notable for a treated episode of acute renal failure, diabetes mellitus, obesity, and hypertension. Her current medications include losartan, metformin, insulin, and ibuprofen. The patient recently started taking high doses of vitamin D as she believes that it could help her symptoms. She also states that she recently fell off the treadmill while exercising at the gym. On physical exam you note an obese woman. There is pain, decreased range of motion, and crepitus on physical exam of her right hip. The patient points to the areas that cause her pain stating that it is mostly over the groin. The patient's skin turgor reveals tenting. Radiography is ordered. Which of the following is most likely to be found on radiography?

Loss of joint space and osteophytes

Posterior displacement of the femoral head

A previously healthy 2-year-old boy is brought to the emergency room by his mother because of persistent crying and refusal to move his right arm. The episode began 30 minutes ago after the mother lifted him up by the arms. He appears distressed and is inconsolable. On examination, his right arm is held close to his body in a flexed and pronated position. Which of the following is the most likely diagnosis?

Supracondylar fracture of the humerus

A 25-year-old male presents to his primary care physician for pain in his knee. The patient was in a wrestling match when his legs were grabbed from behind and he was taken to the floor. The patient states that the moment this impact happened, he felt a snapping and sudden pain in his knee. When the match ended and he stood back up, his knee felt unstable. Minutes later, his knee was swollen and painful. Since then, the patient claims that he has felt unstable bearing weight on the leg. The patient has no significant past medical history, and is currently taking a multivitamin and protein supplements. On physical exam you note a tender right knee, with erythema and an effusion. Which of the following is the most likely physical exam finding in this patient?

Anterior translation of the tibia relative to the femur

Clicking and locking of the joint with motion

Posterior translation of the tibia relative to the femur

Musculoskeletal radiologic landmarks for USMLE Step 3: High-Yield Anatomy Lessons

Shoulder & Upper Limb - Arm-ature Hour

Shoulder (AP View):
- Glenohumeral Joint: Normal space 4-5 mm.
- Acromioclavicular (AC) Joint: Normal space < 7 mm.
- Coracoclavicular Distance: Normal 11-13 mm.
- Greater Tuberosity: Lateral projection of humeral head.

Shoulder X-ray AP view with bony landmarks

Elbow (Lateral View):
- Anterior Humeral Line: Should intersect middle third of capitellum.
- Radiocapitellar Line: Line through radial neck should bisect capitellum.
- 📌 CRITOE mnemonic for ossification centers (ages in years): Capitellum (1), Radial head (3), Internal (medial) epicondyle (5), Trochlea (7), Olecranon (9), External (lateral) epicondyle (11).

⭐ A displaced radiocapitellar line is a key sign of elbow dislocation or subtle fracture, especially in pediatric patients (e.g., Monteggia fracture).

Wrist (PA/Lateral View):
- Scapholunate distance: < 3 mm.
- Volar Tilt: 10-15°.
- Radial Inclination: 21-25°.

Hip & Pelvis - Pelvic Power Lines

Shenton's Line: Arc from the medial femoral neck to the inferior pubic ramus.
- Disruption suggests: Femoral neck fracture or developmental dysplasia of the hip (DDH).
Iliofemoral Line: Curve along the outer ilium and superior femoral neck.
- Disruption indicates: Fracture or congenital hip disease.
Klein's Line: Drawn along the superior border of the femoral neck.
- Normal: Intersects the superior femoral epiphysis.
- Abnormal: Failure to intersect indicates Slipped Capital Femoral Epiphysis (SCFE).
Skinner's Line: Line from the greater trochanter to the femoral shaft axis.
- Normal: Fovea capitis lies above this line.

⭐ Klein's Line is the most reliable method for diagnosing Slipped Capital Femoral Epiphysis (SCFE) on an AP hip radiograph, a crucial diagnosis in adolescents presenting with hip or knee pain.

Knee & Ankle - Joint Observations

Knee Joint Effusion
- Best seen on lateral view; soft tissue density in the suprapatellar pouch.
- Lipohemarthrosis (fat-fluid level) suggests an intra-articular fracture.
Key Knee Landmarks
- Fabella: A sesamoid bone in the lateral gastrocnemius head; a common normal variant.
- Segond Fracture: Avulsion of the lateral tibial plateau; pathognomonic for an ACL tear.
Ankle Joint Alignment
- Mortise: Joint space should be uniform. Widening suggests ligamentous injury.
- Tibiofibular Overlap: On AP view, should be >6 mm. Less overlap suggests syndesmotic injury.

⭐ A Segond fracture ("lateral capsular sign") is highly specific for an anterior cruciate ligament (ACL) tear, seen in ~75% of cases.

Ankle Mortise Radiographs with Measurements

Spine & Skull - Vertebral Views

Lateral View: Assesses alignment, vertebral body height, and disc spaces.
- Trace three parallel spinal lines; disruption suggests instability.
Anteroposterior (AP) View: Evaluates coronal alignment and pedicles.
- "Winking owl sign": a missing pedicle suggests metastatic destruction.
Oblique View: Key for pars interarticularis visualization.
- 📌 "Scotty Dog" Sign identifies spondylolysis.
  - Neck: Pars interarticularis (fracture site)
  - Eye: Pedicle
  - Nose: Transverse process
  - Ear: Superior articular process
Odontoid (Open-Mouth) View: For C1-C2 articulation, assessing dens and lateral masses.

Oblique lumbar spine radiograph with Scotty dog sign

⭐ A "collar" on the Scotty dog's neck (oblique view) indicates spondylolysis, a pars interarticularis stress fracture common in young athletes.

High‑Yield Points - ⚡ Biggest Takeaways

The Anterior Humeral Line must intersect the capitellum's middle third; displacement indicates a supracondylar fracture.

A normal Radiocapitellar Line bisects the capitellum, crucial for detecting radial head dislocation.

Shenton's Line disruption suggests a femoral neck fracture or developmental dysplasia of the hip.

Klein's Line is key for diagnosing SCFE; it should intersect the femoral epiphysis.

A Bohler's Angle <20 degrees is highly indicative of a calcaneal fracture.

Increased medial clear space (>4 mm) in the ankle points to a deltoid ligament rupture.

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