The Haller Index Explained: What Your Number Means

The Haller index is a single number that describes how deep a pectus excavatum is. It is the transverse width of the chest divided by the front-to-back distance at the deepest point of the indentation, measured on a cross-sectional chest image. A chest without pectus excavatum sits around 2.5, and the ratio rises as the sternum sinks. A value of 3.25 has long been the threshold for considering surgical repair.

Key points

  • The Haller index is the transverse width of the chest divided by the front-to-back (anteroposterior) distance at the deepest point of the indentation. A chest without pectus excavatum measures around 2.5.
  • Values are commonly grouped as mild below 3.2, moderate from 3.2 to 3.5, and severe above 3.5, with 3.25 the long-standing threshold for considering surgical repair. There is no band above severe.
  • The index is taken from a cross-sectional chest image at the point of deepest indentation, and the two distances must be measured the same way each time, because the ratio changes with breathing and growth.
  • St. Peter and colleagues showed the Haller index has a known weakness: it overlaps by roughly 48% between those who have pectus excavatum and those who do not, so a single value near the threshold is not decisive on its own.
  • St. Peter and colleagues describe the correction index, an alternative that puts the same 3.25 threshold at 28% or more and stays accurate in non-standard chest shapes, separating affected from unaffected chests more cleanly.
  • Research grades treatment outcomes by change in this ratio. Vacuum bell cohorts use Haller index change as the endpoint, and the patients whose age and consistency favour a response are the ones who record a meaningful correction.

The short answer, expanded

The Haller index, sometimes called the pectus index, was introduced to put a number on a deformity that until then was described in words. It is a ratio, so it has no units. You measure the widest inside-to-inside distance across the chest, then divide it by the distance from the back of the sternum to the front of the spine at the point where the chest is most sunken. A deeper indentation pushes the sternum closer to the spine, the bottom number shrinks, and the ratio climbs.

A chest with no pectus excavatum measures around 2.5. The numbers used to sort severity are covered in the next section, along with the reason a single value near the cut-off should not be read as a verdict on its own. The index is classically taken from an axial CT slice, though the same measurement can be estimated from other cross-sectional images and, less precisely, from external tools. What matters is that the two distances are measured at the same level, in the same phase of breathing, because both change as the chest moves and as a child grows.

What the evidence actually shows

The severity bands

Once the ratio is known, it is commonly sorted into three bands. A value below 3.2 is described as mild, a value from 3.2 to 3.5 as moderate, and a value above 3.5 as severe. A ratio of 3.25 has served for years as the point at which surgical repair is formally considered, and it appears in the eligibility criteria many insurers and surgical centres still use. The minimally invasive repair described by Nuss and colleagues (1998), now the usual surgical approach in adolescents, is generally reserved for the more severe end of that range rather than offered on the number alone. There is no band above severe. A very deep chest simply produces a higher ratio; the categories stop at mild, moderate and severe.

How research uses the index

The index is not only a surgical gate. It is also the yardstick most outcome studies use to measure whether a treatment worked. Vacuum bell cohorts grade results by the change in this ratio: a Swiss cohort at University Hospital Basel reported significant improvement in about 80% of 140 patients, and Scaife and colleagues (2025, n=240) reported a successful outcome in 66%. The important detail for anyone reading such a study is that a headline correction rate depends entirely on which starting and finishing values the authors counted as success, which is one reason two studies of the same therapy can report very different numbers.

The known weakness of the index

The Haller index has a specific and well-documented limitation. St. Peter and colleagues (Annals of Thoracic Surgery) reported that it shows roughly 48% overlap between those who have pectus excavatum and those who do not, so a single value near the threshold does not cleanly separate the two groups. The same team describe an alternative called the correction index, which expresses the depth of the indentation as a proportion of the total chest depth. St. Peter and colleagues put the equivalent correction index threshold at 28% or more, matching the long-standing 3.25 value, and note it stays accurate in unusual chest shapes, better separating those who have pectus excavatum from those who do not. The Haller number is a useful summary, not a diagnosis on its own.

Who this works best for

As a decision aid, the Haller index is most useful in a few clear situations.

  • Clearly severe or clearly mild chests. When the ratio sits well above 3.5 or well below 3.2, it agrees with what the eye and the symptoms already suggest, and it gives clinicians a shared number to plan around.
  • Deciding whether surgery is on the table. A ratio around the 3.25 mark is one of the criteria used to consider minimally invasive repair (Nuss and colleagues 1998), alongside symptoms, cardiac and lung findings, and how the chest looks and feels to the person living in it.
  • Sorting candidates for conservative treatment. Vacuum bell therapy is formally indicated in mild-to-moderate deformity and in patients declining surgery, in a review of 13 studies (Loufopoulos and colleagues 2021), and the band the index falls in helps place a person on that map. Cincinnati Children's Hospital reports the strongest conservative results in children aged 6 to 12 with a mild defect.
  • Tracking change over time. Because it is a single reproducible number, the index is a reasonable way to follow a chest across years, provided the measurement is taken the same way each time.

Who this does not work for

The Haller index is a summary, and there are situations where leaning on the number alone is a mistake.

  • Chests with an unusual shape. A broad or flat chest can produce a reassuring ratio while a real indentation is present, and a narrow chest can inflate it. St. Peter and colleagues developed the correction index precisely because the ratio misclassifies these chests, and they showed the two measures disagree often enough to matter.
  • Borderline values. Because the index overlaps between people with and without pectus excavatum, a value sitting near 3.2 or 3.25 cannot settle a decision by itself. It has to be read next to symptoms, growth stage and how the chest actually functions.
  • Anyone treating the number as a diagnosis or a prognosis. The index describes geometry. It does not measure breathlessness, exercise tolerance, cardiac compression or the social distress that often drives people to seek help, and none of those track the ratio reliably.
  • Home measurement standing in for imaging. External estimates can approximate the index, but a treatment or surgical decision rests on a properly measured cross-sectional image read by a clinician, not on a ruler at the bathroom mirror.

In short, the index earns its place as one input among several. A chest is not a ratio, and no single number should carry a decision this consequential on its own.

What this means in practice

A few practical points follow from all this.

Know your band, not just your number. If you have a measured ratio, place it: below 3.2 is mild, 3.2 to 3.5 is moderate, above 3.5 is severe, and 3.25 is the value around which surgical repair is usually discussed. That band tells you roughly which conversations are relevant, from watchful monitoring to conservative treatment to a surgical opinion.

Ask for the correction index too. If your Haller value sits near the threshold, or if your chest is broad, flat or narrow, the correction index (St. Peter and colleagues) can give a more reliable read, and it is calculated from the same image.

Measure the same way every time. The ratio shifts with breathing and with growth, so a change over months only means something if the two distances are captured at the same level and in the same breathing phase on each image.

Do not let one number frighten or reassure you too much. A single value near the cut-off is not a verdict. Symptoms, function and how the chest is changing over time carry at least as much weight as the ratio.

Not sure whether this applies to you?

The two questions this article cannot answer for you are whether your own chest is a reasonable candidate, and which device size fits it. Both depend on measurements only you can take.

The FormaChest assessment takes about four minutes. It screens your situation against the variables the research identifies as predictive (age, depth of the indentation, chest flexibility and symptoms) and returns an honest read on whether conservative treatment is a reasonable first step. That includes telling you when the answer is to see a surgeon first, which it does for roughly the situations described in the section above.

It also returns a vacuum bell size recommendation based on your own measurements, at no cost.

Sizing is normally not free or simple in this category. The usual process is to email photographs of your bare chest to a company and wait for a reply, or to print paper templates and tape them to yourself, with the manufacturer warning that self-measurement may produce the wrong model. The assessment asks for numbers you can take alone with a ruler. No photographs, no email exchange, no deposit.

Take the free assessment →

What the research does not tell us

The evidence around this measurement has real gaps, and they are worth stating plainly.

The threshold is a convention, not a proven cut-off. The 3.25 value is long-standing and widely used, but it was not derived from a trial showing that people above it do better with surgery than people below it. It is a practical line, and reasonable clinicians place decisions slightly either side of it.

Studies do not measure the same way. Some grade outcomes by change in the Haller index, some by the correction index, some by external depth. Haecker and colleagues (2024) note that these endpoints are not interchangeable, which is a large part of why reported success rates for the same therapy disagree.

The index does not capture what patients feel. There is no clean published relationship between the ratio and symptoms such as breathlessness, exercise tolerance or the psychosocial impact that is documented as a consistent finding in chest wall deformity. Two people with the same number can have very different experiences.

Overlap is under-appreciated. That the Haller index overlaps substantially between affected and unaffected chests (St. Peter and colleagues) is well documented but often ignored in casual use of a single value.

About this guide This article is published by FormaChest, a European manufacturer of vacuum bell correction systems, registered in Romania as AUGUMENTUM SRL. We make the device described above, and every figure quoted is cited to its source so you can verify it independently. Knowing your severity band is only the first step, and turning a measurement into a plan is the harder part. That is why FormaChest ships the bell, brace and gel together rather than a device alone: the vacuum bell, a chest support brace, post-session skin care, the written protocol, and scheduled follow-up. Together, the bell, brace and gel are $461.40 in the men's line and $491.40 in the women's line, where every competitor in this category sells the device by itself. See what is included →Tomas Titus is the founder of FormaChest (AUGUMENTUM SRL, Craiova, Romania). He had pectus excavatum and corrected it without surgery, documenting his own vacuum bell treatment on camera, taking each measurement before a session rather than after. His chest depth went from 25mm to 4mm. That is one person's result at 19; published adult timelines run 12 to 24 months and results vary. He is not a clinician, and nothing in this article is a substitute for assessment by one.

Related questions

References

  1. St. Peter SD, et al. A novel measure for pectus excavatum: the correction index. Annals of Thoracic Surgery.
  2. Scaife ER, et al. Vacuum bell therapy for pectus excavatum. 2025. n=240
  3. Loufopoulos I, Karagiannidis IG, Lampridis S, Mitsos S, Panagiotopoulos N. Vacuum Bell: Is It a Useful Innovative Device for Pectus Excavatum Correction? Turkish Thoracic Journal. 2021. PMID 35110237
  4. Nuss D, Kelly RE, Croitoru DP, Katz ME. A 10-year review of a minimally invasive technique for the correction of pectus excavatum. 1998.
  5. Haecker FM, et al. 20 years clinical application of the vacuum bell for conservative treatment of pectus excavatum. Journal of Thoracic Disease. 2024. PMID 39268139
  6. Cincinnati Children's Hospital Medical Center. Pectus excavatum. Patient education resource.

This article is for information only and is not medical advice. Pectus excavatum should be diagnosed and assessed by a qualified physician. If you have chest pain, breathlessness, palpitations or reduced exercise tolerance, seek medical assessment before beginning any treatment.

Last reviewed: July 2026.

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