What Is McNamara Analysis?
McNamara analysis was introduced by James A. McNamara Jr. in 1984 as part of a broader effort to make cephalometric measurements more directly clinically applicable. Where angular analyses like Steiner and Downs express jaw relationships as degree deviations from a population mean, McNamara expresses most measurements as linear distances in millimetres — values that correspond directly to the magnitude of correction needed in treatment.
The central feature of McNamara analysis is the nasion perpendicular: a true vertical line dropped from Nasion (perpendicular to the Frankfort Horizontal). The positions of A point and Pogonion relative to this line give an immediate visual and quantitative sense of whether the maxilla and mandible are appropriately positioned anteroposteriorly. This is particularly intuitive for treatment planning: a mandible 8 mm behind the nasion perpendicular in an adult female has a clearly quantified deficit that can be compared directly against surgical advancement targets or growth modification goals.
McNamara's analysis also includes measurements of absolute jaw lengths — effective maxillary length (Co-A) and effective mandibular length (Co-Gn) — that allow assessment of whether a skeletal discrepancy is primarily a size problem, a position problem, or both. The addition of lower facial height and pharyngeal airway measurements gives McNamara a unique scope among standard cephalometric analyses.
All McNamara Measurements — Norms and Interpretation
McNamara norms are age-dependent for the jaw length measurements. The values below reflect adult (18+) reference ranges. For growing patients, McNamara's original proportional tables (published in 1984) should be consulted for age-adjusted linear norms.
| Measurement | Adult Male Norm | Adult Female Norm | Anterior = | Posterior = |
|---|---|---|---|---|
| A point to Nasion perp. | 0 to +1 mm | 0 to +1 mm | Maxillary prognathism | Maxillary retrusion |
| Pog to Nasion perp. | −4 to 0 mm | −4 to −2 mm | Mandibular prognathism | Mandibular retrusion |
| Effective maxillary length (Co-A) | 95–100 mm | 91–96 mm | Long / prognathic Mx | Short / retrognathic Mx |
| Effective mandibular length (Co-Gn) | 125–135 mm | 118–128 mm | Long / prognathic Mn | Short / retrognathic Mn |
| Lower facial height (ANS-Me) | 65–75 mm | 60–70 mm | Hyperdivergent / open bite | Hypodivergent / deep bite |
| Upper pharyngeal airway width | 15–20 mm | 15–20 mm | Wide / patent airway | Narrow / potential obstruction |
| Lower pharyngeal airway width | 11–14 mm | 11–14 mm | Wide airway | Narrow / potential obstruction |
| Maxillary incisor to A-perp (linear) | 4–6 mm | 4–6 mm | Protruded upper incisors | Retruded upper incisors |
| Mandibular incisor to A-Pog (linear) | 1–3 mm | 1–3 mm | Protruded lower incisors | Retruded lower incisors |
Norms from McNamara (1984), based on the University of Michigan Growth Study and Burlington Growth Study samples. Age-adjusted norms for growing patients vary; consult original reference tables.
Key principle: McNamara analysis assesses position and size independently. A patient can have a normal A-point-to-nasion-perpendicular but a short Co-A, indicating normal maxillary position but deficient maxillary development. This distinction is critical for surgical planning — a retropositioned maxilla needs advancement; an underdeveloped maxilla may need a different intervention strategy.
Landmarks Required for McNamara Analysis
Clinical Interpretation of McNamara Analysis
Nasion Perpendicular: Reading Position
The nasion perpendicular provides an immediately interpretable spatial picture of the anteroposterior jaw relationship. An ideal adult female profile has A point 0–1 mm anterior to the nasion perpendicular and Pog 2–4 mm posterior to it — a slight maxillary protrusion and mild mandibular retrusion that creates the balanced convex profile characteristic of Class I facial balance.
When A point is significantly posterior to the nasion perpendicular (−3 mm or more), maxillary retrusion or deficiency is implicated — a finding relevant to growth modification, BSSO sequencing, and LeFort I planning. When Pog is markedly posterior (−8 mm or more in females), mandibular deficiency is the dominant skeletal issue.
Jaw Lengths: Size vs Position
The Co-A and Co-Gn measurements distinguish between jaw size and jaw position. A patient with retropositioned A point but normal Co-A length has a positioned maxilla in a retruded location — possible causes include a Class III functional shift, maxillary posterior rotation, or a deep palatal vault. A patient with retropositioned A point and a short Co-A has a genuinely underdeveloped maxilla. These two scenarios require different treatment approaches.
The ratio between Co-Gn and Co-A is also informative. McNamara's original work established that in well-balanced Class I adults, mandibular length exceeds maxillary length by approximately 25–30 mm. When the discrepancy is greater than 30 mm, there may be relative mandibular excess; when it is less than 20 mm, there may be relative mandibular deficiency — even if absolute lengths are within normal range.
Lower Facial Height and Vertical Integration
The ANS-Me measurement contextualises the vertical dimension in linear terms. When interpreted alongside the posterior-anterior facial height ratio from Björk-Jarabak analysis, the two measurements provide complementary perspectives: Björk-Jarabak expresses the vertical dimension as a ratio (informing growth rotation tendency); McNamara expresses it as an absolute millimetre value (directly comparable against treatment goals).
Pharyngeal Airway Assessment
McNamara was among the first cephalometric systems to include airway measurements as part of the standard analysis. The upper and lower pharyngeal airway widths are assessed from the posterior pharyngeal wall to the relevant anatomical boundaries. Upper airway width below 10 mm has been associated with increased sleep-disordered breathing risk; lower airway width below 11 mm is considered potentially compromised. These measurements are particularly relevant when planning mandibular setback procedures, where posterior displacement of the tongue base can narrow the airway.
Run McNamara Analysis Free in BCeph
BCeph implements the complete McNamara analysis module including the nasion perpendicular measurements, effective jaw lengths, lower facial height, airway widths, and incisor position measurements. All values are computed from landmark positions and displayed against sex-appropriate adult norms, with deviation indicators for values outside the normal range.
McNamara analysis in BCeph uses the same Condylion landmark required for the Ricketts analysis, and the same Menton and ANS landmarks used across multiple other modules. A full multi-analysis session covering Steiner, Ricketts, McNamara, Downs, and Björk-Jarabak requires only one landmark placement session — BCeph shares landmarks across all active analysis modules simultaneously.