Ames: Cervical spine deformity classification system

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Classification-Spinal deformity

General

• Similar to SRS-Schwab classification for TL spine

• A modified Delphi approach was used to develop the classification

• Passias 2021 modifiers added further modifiers

 

5 modifiers

C2 SVA

• Measurement
• Global
• Centroid of C2 (or odontoid) plumb line ↔ posterior superior corner of sacrum
• Regional
• C2-7 SVA
• Centroid of C2 (or odontoid) plumb line ↔ posterior superior corner of C7
• Tang 2015: C2–7 SVA threshold of 4 cm was found to correlate with moderate disability based on the NDI

• The T1 slope is a predictor of C2–C7 SVA.

• Has been directly correlated with HRQOL (SF36)
• Larger C2 SVA poorer HRQOL
• Increasing C2 SVA (>40 mm) is correlated with worse outcomes as assessed by the Neck Disability Index (NDI).

• Normal Cervical SVA Values in Asymptomatic Adults

Odontoid marker at C7	15.6 ± 11.2 mm
Odontoid marker at sacrum	13.2 ± 29.5 mm

Horizontal Gaze: Chin-brow vertical angle (CBVA)

• Measurements
• Positioning
• Patient standing with hips and knees extended
• Neck is in a neutral or fixed position.
• Photos
• Angle
• patient’s chin to brow
• vertical line
• Xrays
• Angle
• A line from Chin to forehead
• A vertical line

• CBVA of 10° has been described as an optimal target.
• overcorrection of CBVA had a negative impact,

• Significantly impacts activities of daily living.

• Correction considering CBVA has been linked to positive postoperative outcomes:
• Improved gaze
• Ambulation
• Activities of daily living

• Normal CBVA has not been characterised, but postoperative values of +10 ° to −10 ° have been well tolerated in patients

Tetreault 2017 mJOA

Severity	mJOA
Mild	15-17
Moderate	12-14
Severe	0-11

T1 Slope

• The T1 slope will determine the amount of subaxial lordosis required to maintain the COG of the head in a balanced position

• Varies depending on Global spinal alignment as measured by
• SVA AND
• Inherent upper thoracic kyphosis (TK).

• In patients with scoliosis, the T1 slope has been shown to correlate directly with SVA measured from the C2 odontoid plumb line to provide a measure of overall sagittal alignment.

• Kim 2013: High preoperative T1 slope were more likely to have postoperative (Laminoplasty for cervical myelopathy) kyphotic changes at 2-years

• Tamai 2018: Not easily visualised on xray so use C7 slope as surrogate
• As only 18% of the T1 slope is visible

• T1 Slope - C2-C7 lordorsis
• Similar to PI - LL
Score	TS-CL
0	< 15°
1	15°–20°
2	> 20°
• T1 slope minus Cervical Lordosis (TS-CL)
• Low: <26°
• Moderate: 26° to 45°
• Severe: >45°
• A postoperative T1-CL > 20 degrees correlates with greater postoperative cSVA, indicating higher risk of persistent deformity
• C2–C7 Lordosis
• Low: >3°
• Moderate: -21° to 3°
• Severe: <-21°

Passias 2021 modifiers

• Modifers made because the Ames classification is not built on radiological or clinical severity. Rather it is used as a communication tool to describe cervical deformity. The Passias modifiers aim to correlate the below parameters with mild, moderate and severe scores of the mJOA.

McGregor’s Slope (MGS)

• Measurement
• is the angle between the posterior edge of the hard palate ↔ the caudal aspect of the occiput
• McGregor’s line (number 1)
• extends from the hard palate to the most caudal point of the occipital curve
• dental tip should by less than 5 mm above this line.
• McGregor has modified chamberlain's line for when the opisthion cannot be identified.
• On CT and MRI the normal odontoid tip is 0.8mm (± 2.4) above the line

• A surrogate for CBVA, which can be diffcult to visualize on standing radiographs.

• Clinical significance
• MGS < 2.16 degrees has been suggested as a goal for for CSD correction,
• MGS of < 0 has been proposed as modier for CSD classication.
• A high MGS is pathologic, as MGS ≥ 20 is an inclusion criteria for cervical deformity in ISSG studies.
• Passias 2021 modifier
• Low: >-9° and <0°
• Moderate: -12° to -9° or 0° to 19°
• Severe: <-12° or >19°

C2–T3 SVA Angle

• Measures both cervical and upper-thoracic alignment,
• Unlike the traditional C2-7 SVA

• Higher values corresponding to more lordosis.

• Clinical significance
• Passias 2021
• Low: >-25°
• Moderate: -35° to -25°
• Severe: <-35°
• C2-T3 angle <−25 degrees is associated with more severe myelopathy per the modi ed Japanese Orthopaedic Association (mJOA) scale.
• A high C2-T3 angle may signify compensatory cervical lordosis in the setting of insufficient sagittal correction and may predict DJK.

• C2 Slope
• Passias 2021 modifiers
• Low: <33°
• Moderate: 33° to 49°
• Severe: >49°
• Clinical significance
• Surrogate for T1-CL Mismatch: It acts as a simplified, single-value measure reflecting the degree of T1 slope-cervical lordosis (T1-CL) mismatch.
• Correlation with HQROLs:
• A greater C2 slope (specifically 17–38 degrees) is associated with worse health-related quality of life (HQROLs).
• Classification Modifier:
• It has been proposed as a novel modifier to the Ames classification system for CSD.
• Surgical Target for Correction:
• A goal correction of C2 slope to less than 10 degrees has been proposed as a surgical target.
• Prediction and Prevention of DJK:
• Failure to correct C2 slope to less than 10 degrees is a radiographic predictor of distal junctional kyphosis (DJK).
• Achieving this target is associated with lower rates of DJK.
• Some surgical approaches prioritise correcting C2 slope to less than 10 degrees to achieve optimal clinical outcomes.
• Benzel: when positioning head for CVJ fusion make sure C2 slope is 90 deg to the floor.
• Insight into Deformity Drivers:
• It provides insight into the primary "driver" of the cervical deformity; for example, a low C2 slope with high T1 slope suggests a thoracolumbar issue, while the opposite indicates a primary cervical pathology.

• Frailty - ASD - FI
• Low: <0.18
• Moderate: 0.18 to 0.27
• Severe: >0.27