For Clinicians

Body mass index is used as a screening tool for weight-related health risk, a criterion for certain interventions (e.g., bariatric surgery eligibility, insurance coverage of medical nutrition therapy), and a metric in research. In people with limb loss, uncorrected BMI systematically underestimates adiposity because the denominator (height²) assumes an intact body while the numerator (weight) reflects only the remaining mass.

Failure to correct can result in:

Delayed referral for weight management in people who would qualify
Inappropriate denial of services tied to BMI thresholds
Underestimation of cardiovascular risk in a population already at elevated risk

The correction method

This calculator applies the Osterkamp (1995) correction, which uses body-segment weight percentages derived from cadaver-based anthropometric studies (Dempster, 1955; Winter, 1990). The formula is:

Corrected BMI = (Measured Weight / Height²) / (1 − Missing Fraction)

Where Missing Fraction is the sum of segment percentages for all absent limb segments. For unilateral amputation, this is the single segment percentage. For bilateral or multi-limb amputation, the fractions are additive.

Segment weight percentages used

Amputation level	Segment terminology	% Total Body Mass (single)
Hand	Partial hand / metacarpal	0.7%
Below-elbow	Transradial	2.3%
Above-elbow	Transhumeral	6.5%
Foot	Partial foot / Syme's	1.5%
Below-knee	Transtibial	5.9%
Above-knee	Transfemoral	16.3%
Hip disarticulation	—	18.5%

Comparison to alternative approaches

Direct segment weighing (Dempster, 1955): Gold standard, requires specialized equipment. Not practical for routine use.
Bioelectrical impedance analysis (BIA): Increasingly used, but accuracy varies by device and amputation level. Not universally available.
Osterkamp correction: Uses published segment percentages. Simple, transparent, reproducible. Best suited for settings where only height and weight are known.
Gallagher et al. adjustment: A more recent method that incorporates both amputation level and body composition estimates. More complex but may be more accurate in people with obesity.

The Osterkamp method is used here because it is the most transparent and widely cited in prosthetics literature, requires no specialized equipment, and is easily verified.

Known limitations

Population averages: Segment percentages are based on cadaver studies of a limited sample. Individual variation in body composition can affect accuracy.
Obesity interaction: The Osterkamp method assumes a constant segment fraction. In people with obesity, the missing limb may have had a higher fat proportion than the population average, potentially overcorrecting.
Height assumption: The calculator uses pre-amputation height (or user estimate). Post-amputation height reduction is not accounted for.
Not validated in pediatric populations: Segment percentages are based on adult cadaver data. Use in children requires caution.

When to use this tool

This calculator is appropriate as a screening aid when:

You need a quick estimate of weight status in a person with limb loss
You are discussing weight management goals and want a more accurate baseline than standard BMI
You are documenting weight status for insurance or program eligibility where corrected BMI is requested

It is not appropriate as a substitute for:

DEXA or other body composition analysis when precise measurement is needed
Professional judgment about individual health risk
Diagnostic criteria that specifically require uncorrected BMI (e.g., some research protocols)

References