MSKbase — MSK Radiology Measurements & Classifications
MSKbase is a reference of radiological measurements and classification systems used in musculoskeletal (MSK) radiology, covering the knee, shoulder, hip and more. Each entry describes how a measurement is performed, its normal values and grading, clinical significance, pitfalls, and key references.
Knee
- TT-TG Distance — Tibial Tubercle–Trochlear Groove Distance: The horizontal offset between the tibial tuberosity and the deepest point of the trochlear groove, measured on superimposed axial images. Quantifies lateralization of the extensor mechanism relative to the trochlea.
- Dejour Classification — Trochlear Dysplasia Grading: A four-tier system grading the severity of trochlear dysplasia, the single strongest risk factor for patellofemoral instability.
- Lateral Trochlear Inclination — LTI: An angle quantifying the inclination of the lateral trochlear facet relative to the posterior condylar line — a simpler, more reproducible surrogate for trochlear dysplasia severity than qualitative classification alone.
- Caton-Deschamps Index — CD Index — Patellar Height: A ratio quantifying patellar height relative to the tibial plateau, independent of patellar tendon length.
- Insall-Salvati Ratio — Patellar Height (tendon-based): A classic index of patellar height using the patellar tendon length relative to patellar length.
- Patellotrochlear Index — PTI: A cartilage-based measure of patellotrochlear engagement on MRI, assessing the functional overlap between patellar and trochlear cartilage rather than bony height alone.
- Meniscal Tear Types — Meniscal Tear Morphology: A description of the morphological pattern of a meniscal tear — independent of its location or size — used to determine reparability and guide treatment.
- Segond Fracture: An avulsion fracture of the lateral tibial condyle at the attachment of the anterolateral ligament/iliotibial band capsule.
- Outerbridge Classification — Chondromalacia Grading: A four-grade system describing the severity of articular cartilage damage, originally described arthroscopically and now commonly adapted for MRI reporting.
Shoulder
- Patte Classification — Rotator Cuff Tear Retraction: A three-stage classification describing the degree of retraction of a torn rotator cuff tendon (classically supraspinatus), graded by how far the proximal tendon stump has pulled back from its footprint.
- Goutallier / Fuchs Classification — Fatty Infiltration Grading: A grading system for fatty infiltration of the rotator cuff musculature, a key marker of chronic tear and muscle quality.
- Tangent Sign: A qualitative sign of severe supraspinatus muscle atrophy, assessed on the sagittal oblique 'Y' image.
- Occupation Ratio — Thomazeau / Zanetti Method: A quantitative ratio of supraspinatus muscle cross-sectional area to its fossa area, used to assess muscle atrophy.
- Snyder Classification — SLAP Tear Classification: A classification of superior labral anterior-to-posterior (SLAP) tears based on the pattern of labral and biceps anchor involvement.
- Glenoid Bone Loss (%) — Bankart Lesion Quantification: Quantification of anteroinferior glenoid bone deficiency following anterior shoulder dislocation, central to choosing between soft-tissue and bony stabilization.
- Hill-Sachs Lesion / Glenoid Track: The Hill-Sachs lesion is a posterosuperior humeral head impaction fracture from anterior dislocation. The 'glenoid track' concept assesses whether that lesion will engage the anterior glenoid rim during abduction and external rotation — an 'off-track' lesion is one that extends medial to the zone of glenohumeral contact and is therefore liable to engage.
- Bigliani Classification — Acromion Morphology: A classification of the shape of the undersurface of the acromion.
- Rockwood Classification — AC Joint Injury Grading: A six-type grading system for acromioclavicular joint injury severity.
Hip
- Alpha Angle: An angle quantifying asphericity of the femoral head–neck junction — the key measure of cam-type morphology.
- Femoral Head–Neck Offset — Offset Ratio: An alternate quantification of cam morphology based on the anterior offset between the femoral head and neck contours.
- Tönnis Angle — Acetabular Roof Angle / Index of the Weight-bearing Zone / HTE Angle: An adult measure of the inclination of the weight-bearing acetabular roof (sourcil), assessing femoral head coverage and structural stability. Distinct from the paediatric acetabular index and from Sharp's angle by virtue of its reference points.
- Acetabular Index — Acetabular Index of Hilgenreiner (paediatric): The paediatric measure of acetabular roof slope, used to diagnose and follow developmental dysplasia of the hip (DDH). Applicable only while the triradiate cartilage is unossified — it depends on a landmark that disappears at skeletal maturity.
- Crossover / Posterior Wall / Ischial Spine Signs — Acetabular Retroversion Signs: A group of radiographic signs on an AP pelvis indicating focal (cranial) or global acetabular retroversion — a form of pincer morphology that predisposes to femoroacetabular impingement.
- Femoral Neck Version — Ante/Retroversion: The angle between the femoral neck axis and the transcondylar (posterior bicondylar) axis of the distal femur, assessing femoral rotational alignment.
- Acetabular Version: An angle assessing anteversion or retroversion of the acetabulum, used together with femoral version for a combined 'hip version' assessment.
- Tibial Torsion — Tibial Rotational Profile: The rotational alignment of the tibia, measured as the angle between its proximal and distal axes. Typically assessed as part of a full CT lower-limb rotational profile alongside femoral and acetabular version.