Musculoskeletal Imaging Measurements

Standing full-spine PA radiograph. Identify the upper and lower end vertebrae (most tilted at each end of the curve); draw lines along the superior endplate of the upper and the inferior endplate of the lower end vertebra; the angle between them (or their perpendiculars) is the Cobb angle. Use pedicle margins if endplates are unclear. Intra-observer error is about ±3–5°, so only a change ≥ 5° counts as progression; keep the same end vertebrae on follow-up.

Standing full-spine lateral radiograph including both femoral heads and C7. PI: angle between the line from the femoral-head centre (midpoint of both) to the S1 endplate midpoint and the perpendicular to the S1 endplate; PT: that line vs vertical; SS: S1 endplate vs horizontal; PI = PT + SS. LL: L1 superior to S1 superior endplate. SVA: horizontal distance from the C7 plumb line to the posterosuperior corner of S1, anterior positive.

Standing lateral lumbar radiograph (± flexion/extension). Measure the AP width W of the lower vertebra's superior endplate and the slip distance D between the posteroinferior corner of the upper and the posterosuperior corner of the lower vertebra along the endplate. Slip % = D / W × 100. Change > 3–4 mm or > 10° on flexion/extension suggests instability.

Lateral thoracolumbar radiograph or sagittal CT. Measure anterior Ha, middle Hm and posterior Hp heights. Wedge = 1 − Ha/Hp; biconcave = 1 − Hm/Hp; crush (posterior collapse) = 1 − Hp/adjacent normal posterior height. Grade by the largest. Exclude developmental wedging, Schmorl nodes and Scheuermann disease.

Lateral cervical radiograph: canal AP diameter from the mid posterior vertebral body to the spinolaminar line; divided by the vertebral body AP diameter gives the Torg-Pavlov ratio (magnification-independent). Lumbar CT/MRI axial at disc level: canal AP diameter and dural sac CSA; lateral recess height from the anterior superior articular process to the posterior vertebral body; foraminal height on sagittal images. Report with Schizas morphological grade.

Lateral cervical radiograph or sagittal CT. ADI: posterior anterior C1 arch to anterior dens; PADI: posterior dens to anterior posterior C1 arch (space available for the cord). Powers ratio = basion to posterior C1 arch / opisthion to anterior C1 arch. BDI: basion to dens tip. McGregor's line: posterosuperior hard palate to lowest occiput; distance of the dens tip above it (Chamberlain > 3 mm also suggests invagination). Flexion/extension views are more sensitive.

True AP (Grashey) view tangential to the glenohumeral joint. AHI: shortest distance from the acromion undersurface to the humeral head. CSA: angle between the line joining the superior and inferior glenoid rims and the line from the inferior glenoid rim to the inferolateral acromion. Acromion index = glenoid plane to lateral acromion / glenoid plane to lateral humeral head. Bigliani type on the outlet (Y) view. Malrotation strongly affects CSA.

3D CT en-face view of the glenoid with the humeral head subtracted (or oblique sagittal). Fit a circle to the inferior two-thirds; measure diameter D and anterior defect width d; bone loss = d / D. Glenoid track = 0.83 × D − d. Hill-Sachs interval HSI = Hill-Sachs width + bone bridge to the cuff insertion; HSI > track is off-track (high recurrence; address the humeral side, eg, remplissage).

Standard AP pelvis (coccyx tip over the symphysis, 1–3 cm). LCEA: angle between the vertical through the femoral-head centre and the line to the lateral sourcil. Tönnis angle: line across the sourcil vs horizontal. Alpha angle: Dunn 45° view or radial MRI, between the neck axis and the line to where the head loses sphericity. Neck-shaft angle: neck vs shaft axes. Femoral version on CT/MRI (methods differ by up to 10°).

Standard coronal plane in lateral decubitus showing a straight iliac line, the lower limb of the ilium and the labrum. Baseline along the ilium; the bony roof line from the lower ilium tangent to the bony acetabulum gives alpha (bony coverage); the cartilage roof line from the bony rim through the labrum gives beta. Do not classify on a non-standard plane.

Supine standard AP pelvis, legs extended together, patellae forward. Draw Hilgenreiner's line (through triradiate cartilages) and Perkins' line (perpendicular at the lateral acetabular margin). A = head width lateral to Perkins' line, B = total head width, MI = A / B × 100. Acetabular index: angle between Hilgenreiner's line and the line to the lateral acetabular edge.

Lateral radiograph at 30° flexion or sagittal MRI. Insall-Salvati = patellar tendon length (inferior pole to tibial tubercle) / greatest diagonal patellar length. Caton-Deschamps = distance from the lower articular patellar edge to the anterosuperior tibial plateau / articular surface length. TT-TG on axial CT/MRI: distance between perpendiculars from the tubercle apex and the trochlear groove deepest point to the posterior condylar line. Sulcus angle between the highest medial/lateral trochlear points and the groove.

Standing bilateral long-leg AP (patellae forward). Mechanical axis: hip centre to ankle centre. HKA: angle between femoral and tibial mechanical axes, 180° neutral. MAD: perpendicular distance of the knee centre from the mechanical axis (medial positive). mLDFA: lateral angle between femoral mechanical axis and distal femoral joint line; MPTA: medial angle between tibial mechanical axis and proximal tibial joint line; JLCA: angle between the two joint lines. Localize per Paley's malalignment test.

Weight-bearing AP foot. HVA: first metatarsal shaft axis vs proximal phalanx axis. IMA: first vs second metatarsal axes. DMAA: perpendicular to the distal first metatarsal articular line vs the shaft axis. Sesamoid position (Hardy-Clapham 1–7) of the medial sesamoid relative to the first metatarsal axis; ≥ 5 is marked lateral displacement.

Weight-bearing lateral: Meary angle between the talar and first metatarsal axes — plantar apex (flatfoot) positive, dorsal apex (cavus) negative; calcaneal pitch between the inferior calcaneal tangent and the floor. Weight-bearing AP: talonavicular coverage angle between the talar-head and navicular articular lines (forefoot abduction).

Lateral calcaneal radiograph. Böhler angle: acute angle between the line from the tuberosity apex to the posterior facet apex and the line from the posterior facet apex to the anterior process. Gissane angle between the cortical lines of the posterior facet and the anterior/middle facets. Contralateral comparison is more reliable; CT for Sanders classification.

Standard PA (shoulder 90° abducted, elbow 90°, neutral rotation) and lateral wrist. Radial inclination: line from the radial styloid tip to the ulnar sigmoid notch vs the perpendicular to the radial axis; radial height: their distance along the axis; volar tilt: line across the volar and dorsal rims vs the perpendicular (volar positive, dorsal negative); ulnar variance: height difference between the ulnar head and sigmoid notch (ulna longer positive). SL angle between scaphoid and lunate axes on the lateral; SL gap at the mid joint on PA.

DXA: lowest T-score of L1–L4 (exclude fractured / degenerated levels, keep ≥ 2), femoral neck and total hip; T-score for postmenopausal women and men ≥ 50, Z-score for premenopausal women, men < 50 and children. QCT: mean trabecular vBMD of L1–L2 (or L2–L3). Opportunistic CT: oval ROI in mid-L1 trabecular bone (avoid cortex and bone islands), unenhanced or portal venous phase.