Optimizing below knee amputation osteotomy length: a ratio-based approach

To introduce a novel below knee amputation (BKA) ratio and evaluate its potential for tailoring residual tibia length for patients of varying height and sex.

Retrospective, radiographic review.

Level I Trauma Center.

Full-length tibia radiographs in skeletally mature patients, without fracture or osseous abnormality.

Demographic information (age, sex, height), tibial length, and BKA ratio [calculated utilizing a standard, 12-cm osteotomy (from the medial plateau) (12 cm/tibial length)] were recorded for each patient. The mean BKA ratio from the population was then utilized as a reference standard to evaluate the variation in residual tibia length. Mean values were compared using independent t-tests.

In this cohort of 100 patients (50 males, 50 females), mean age was 35.4 ± 18.5 years, with a mean height of 169 ± 9 cm. Mean tibia length was 39.5 ± 2.2 cm for males and 36.5 ± 2.2 cm for females, a difference of 2.9 cm (P < 0.0005), with a nearly 6-cm difference between the means of the shortest and longest tibia quartiles for both males and females. Based on a 12-cm osteotomy, the mean BKA ratio was 0.32 ± 0.02 (0.31 ± 0.02 for males and 0.33 ± 0.02 for females, P < 0.0001). Utilizing this ratio as a reference standard, residual limb lengths varied by 2.9 and 3.3 cm between the shortest and longest tibia for males and females, respectively.

A one-size fits all approach to BKA length predisposes individuals of varying height and sex to substantial variability in the relative length of their residual limb. This pilot study suggests that current practice standards regarding BKA length may be oversimplified. Further investigation is required to determine the clinical relevance of these differences regarding energy expenditure and prosthetic fit and ultimately for determining an ideal BKA ratio.