Challenging the Paradigm of the Parabola Post-Transmetatarsal Amputation
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A recent oral abstract presented at the 2025 American Podiatric Medical Association National conference showcased findings after investigating if the residual parabola post-transmetatarsal amputation truly has an impact on patient function and final outcomes.1 Craig J. Verdin, DPM, DABPM, AACFAS, lead author of the study, shares his team’s thinking, research details, and how they feel this knowledge could impact treatment choices.
The idea of this study was largely inspired by the current paradigm shift we are seeing within the limb salvage literature in which function is becoming recognized as an important tenet in limb salvage and preservation decision making. At Georgetown University, we are beginning to see improved outcomes when decision making is function-driven as opposed to length-driven through the use of patient reported outcome measures (PROMs), gait, and biomechanical assessments. With this in mind, as a fellow, I wanted to replicate landmark articles within the limb salvage literature, but from a functional perspective.
My main inspiration for this article was an article by Bik and colleagues2 that challenged the dogmatic belief that residual parabola shape in transmetatarsal amputations (TMAs) is related to outcomes. While that study found no relationship between residual parabola shape and clinical outcomes, the authors did not evaluate the functional effects of the residual parabolic shape. As a result, we wanted to confirm the findings from the aforementioned paper and challenge the historical and time-tested belief that length and a residual parabola that replicates the normal pedal parabola (Type 1) is superior, functionally and clinically.
Details on the Research Process
To conduct this research, we performed a retrospective analysis over a 2-year period using our available PROM database at Georgetown University. In our study, we included patients with TMAs seen and evaluated at Georgetown University Hospital if they met inclusion criteria. In total, we identified 57 patients with unilateral TMAs who had the targeted functional and clinical complications data. All 57 TMAs were substratified based on parabola shape as demonstrated by Bik and team2 and on length based on if the residual TMA apex was greater than or less than 50% of the preoperative length.
We subdivided clinical outcomes into major and minor complications and the 2 targeted PROMs were function as assessed by the Lower Extremity Function Scale (LEFS) and quality of life (QoL) via the Short Form-12 (SF-12) questionnaire, both routinely administered to every patient seen within our clinic. Our team defined major complications as those requiring a return to the operating room and minor complications as clinically managed scenarios.
With respect to complications, our findings showed that differing parabolic shapes had no significant effect on major complications.1 However, in contrast to the findings by Bik and colleagues, we did find a weak but significant correlation between minor complications with TMAs, in which we noted that the residual second metatarsal was significantly longer than the neighboring metatarsals (Type 4). Based on a few studies within the ray amputation literature, these findings aren't surprising, because there is a poor distribution of residual plantar pressures in the setting of an unbalanced residual parabola, which ultimately results in increased adverse outcomes as shown by Hong and team.3 In addition, we found that length had no significant impact on complications, major or minor. With respect to our targeted PROMs that assessed function and quality of life, it appears there is no relationship between residual TMA shape or length and increased access to function or QoL.
Final Thoughts and Next Steps
Our research challenges the dogmatic and long-held belief that parabolic shape and length is as important as previously believed. As a result of this study, we believe that a "balanced" parabola, regardless of residual length and shape, should be targeted in an effort to encourage optimal functional and clinical outcomes. Even further, these findings raise the question of whether or not TMA variants/alternatives with maximal preservation of musculotendinous insertions such as a pandigital or "ray-preserving" TMAs as proposed by Suh and colleagues would be a more functional and superior means of midfoot amputation as opposed to the traditional technique as proposed by McKitrick and team in 1949.4,5 Regardless, we hope this information will be of value to the limb salvage community and can help shape existing function-based treatment algorithms all in an effort to optimize functional outcomes and help clinicians better understand the functional impact of limb salvaging interventions.
References
1. Verdin CJ, Ply C, Lava C, et al. Radiographic predictors of functional and clinical outcomes in transmetatarsal amputations: Does the residual parabola structure truly matter? Oral abstract presented at the APMA National, July 24-27, 2025, Grapevine, TX.
2. Bik PM, Heineman K, Levi J, Sansosti LE, Meyr AJ. The effect of remnant metatarsal parabola structure on transmetatarsal amputation primary healing and durability. J Foot Ankle Surg. 2022;61(6):1187-1190.
3. Hong CC, Saha S, Pearce CJ. Does a shorter residual first metatarsal length after first ray amputation in diabetic patients leads to poorer outcomes - A risk factor study. Foot Ankle Surg. 2023;29(3):228-232.
4. Suh YC, Kushida-Contreras BH, Suh HP, et al. Is reconstruction preserving the first ray or first two rays better than full transmetatarsal amputation in diabetic foot?. Plast Reconstr Surg. 2019;143(1):294-305.
5. McKittrick LS, McKittrick JB, Risley TS. Transmetatarsal amputation for infection or gangrene in patients with diabetes mellitus. Ann Surg. 1949;130(4):826-842.
