1 Introduction

Tibial shaft fractures are the most common type of long bone fracture, involving 2% of all fractures.¹ Mainly occurring due to injuries sustained in motor vehicle accidents, falls from height, or collisions during sports, they most commonly present in young men.² While various treatment methods exist, intramedullary nailing (IMN) remains the standard of care for most diaphyseal fractures as it provides stability with the potential for early weight bearing.³ As part of the procedure, nail length must be carefully matched to the tibia to adequately stabilize the fracture while avoiding irritation to surrounding structures caused by excessive length. However, no validated method currently exists to preoperatively estimate tibial nail length.

Common intraoperative methods to measure tibial nail length include the use of two guidewires, a nail-against-limb technique, or a radiographic ruler.^4–6 However, these approaches can lead to increased operating times and financial costs, due to the search for suitable nail sizes and unnecessary opening of expensive nail implants.^2,4,7 Thus, preoperative planning for accurate nail lengths may provide simplicity and efficiency intra-operatively.

The use of anthropometric measurements to preoperatively estimate tibial nail length has been described in the literature. Studies have investigated the lengths between the knee joint to ankle joint,^4,8 medial knee joint to medial malleolus,^4,8 tibial tuberosity to medial malleolus,^4,8,9 olecranon to 5th metacarpal head length,^4,8 and forearm length,¹⁰ without finding any predictive power. Body height has also been studied with mixed results, with one previous paper detailing a predictive equation only to be uncorroborated by two later papers.^4,8,11 More recently, body height has been shown to successfully predict femoral nail length,¹² and a similar method for tibial nails has been used at our institution with relative accuracy, improving efficiency in the operating room. Out of all of the described anthropometric measurements, body height displays the most promise due to its ease of measurement and ubiquitous nature in patients’ medical records. Given the dearth of literature regarding the association between body height and tibia length, our objective was to study this association with a larger sample size and develop a predictive equation.

2 Methods

This was an IRB approved retrospective review of patients with tibial fractures managed with IMNs at a single Level 1 trauma center from May 2018 to March 2021. Patients under the age of 18 and who received nonoperative management or treatment with tibial plate or open reduction internal fixation were excluded. We also excluded patients with congenital abnormalities (achondroplasia, dwarfism) as well as post-traumatic deformities. A total of 231 patients were identified, of which 220 were included in the analysis. Of these 11 excluded patients, 9 had no height listed in their chart while a single patient had prior hardware implantation which affected the tibial nail length used, and another patient had no report of the tibial nail length used. Patient data including age, sex, body mass index, height, weight, and tibial nail length were obtained from the patient chart, with postoperative x-rays viewed by a fellowship trained traumatologist. At our institution, for patients who presented through the emergency department with tibia fractures that were unable to stand for height measurement, standing height was obtained from the patient medical record. If the patient's medical record did not include a previous patient height measurement, then a verified state identification (driver's license, state identification) was used to obtain standing height. Standing height was then verified during post-operative clinic visits by a registered nurse with a stadiometer. We found zero discrepancies between listed standing height upon presentation and post-operative standing height confirmed on stadiometer.

A logarithmic regression was then performed to predict tibial nail length based on patient height. This equation was then applied to the 220 patients to estimate the validity of the prediction equation. Of special note was whether the equation would predict tibial nail length within 1 nail length (15 mm) of the actual nail length used.

3 Results

Of the 220 patients included, 161 were male (73.2%), and 59 were female (26.8%) with a mean age of 38.7 (±15.5). Patient height ranged from 154.9 cm to 195.6 cm (174.5 ± 8.7) and tibial nail length ranged from 285 mm to 420 mm (361.1 ± 26.1). The correlation coefficient between both variables was 0.75 (p < 0.001). The logarithmic regression equation for the best fit line was y = 391.02 × ln (patient height in cm) – 1656.9, as seen in Fig. 1. When applied to all 220 patients, this equation successfully predicted tibial nail length within 1 nail size (15 mm) in 180 patients (81.8%). The equation overestimated actual tibial nail length by more than 1 nail length in 21 patients (9.5%), with 15 of these 21 patients (71.4%) having a prediction between 1 and 2 nail lengths greater than the actual nail length used. The equation underestimated actual tibial nail length by more than 1 nail length in 19 patients (8.6%), with 15 of these 19 patients (78.9%) having a prediction between 1 and 2 nail lengths smaller than the actual nail length used, as seen in Table 1.

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Fig. 1 Patient height plotted against tibial nail length for each study patient. Logarithmic regression equation also shown.

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4 Discussion

While body height has been used to accurately predict femoral nail length,¹² there are very few studies using body height to preoperatively predict tibial nail length. Frequently cited, Fischmeister et al.¹¹ developed a predictive equation for tibial nail lengths based on the heights of 59 patients. However, subsequent studies showed this same equation to lack accuracy, predicting an accurate nail size in only 13%⁸ and 5%⁴ of cases. As a result, much of today's literature has focused on other anthropometric measurements including tibial tuberosity to medial malleolus (TT-MM) distance and tibial tuberosity to ankle (TT-A) distance.^4,8,9 Regarding TT-MM distance, its tibial nail length prediction accuracy has been reported ranging from 38% to 71%,^7–9 while TT-A has been reported at 81% in one study.⁴ Complicating the implementation of such measurements, however, Venkateswaran et al.⁷ reported difficulty palpating the tibial tuberosity on female patients as this anatomic landmark was not as prominent. Thus, practicality and accuracy are both important qualities in identifying a suitable anthropometric measurement to preoperatively predict tibial nail length.

This study shows that body height can meet both requirements. Given the ease and frequency of measuring body height during clinic visits, this measurement was almost always present in patient charts. Additionally, this study builds upon previous anthropometric tibial nail length studies by involving a larger number of patients. While previous studies involved 8–14 cadavers^8,9 or 16–100 patients,^{2,4,7,10,11,13} this study involved 220 patients, the largest sample size described in the literature so far. Given the predictive formula's accuracy in 82% of cases, body height easily compares with the reported accuracy of other anthropometric measurements, mirroring its use in predicting femoral nail length with 85% accuracy.¹² Thus, coupled with its practicality, body height displays promise in predicting tibial nail length.

At our institution, this equation increases efficiency in the operating room by allowing for an accurate appraisal of necessary supplies. As a result, personnel are able to concentrate on other tasks, and fewer nail implants are opened and ultimately wasted due to inaccurate sizing. However, we do not recommend only using this anthropometric method for choosing intramedullary nail length. Rather the authors recommend using this anthropometric measurement as a pre-operative guide to provide the surgeon with a ballpark figure of what an appropriate nail length should be for the patient. Surgeons should still confirm nail length intra-operatively under image intensifier and/or the guide wire method.

Some limitations of this study included its retrospective nature and the potential for selection bias. There also exists the potential for inaccuracy in the patient heights that were entered into the chart, however a registered nurse did confirm patient height post-operatively using a stadiometer. Further we excluded patients with congenital and post-traumatic deformities as this was out of the scope of the current study. Thus, this equation lacks external validity when applying it to patients with post-traumatic or congenital deformities and should not be used to predict tibial nail length for these patients. Future studies on the accuracy of this anthropometric method for predicting tibial nail length in patients with congenital and post-traumatic deformities is warranted.

Going forward, efforts are currently underway at our institution to prospectively evaluate the predictive equation. An application-based formula calculator is also being developed, hopefully allowing for easier use and wider implementation.

5 Conclusion

This study presents a novel equation for predicting tibial nail length based on patient body height. Compared to other anthropometric measurements, body height can be easily and consistently measured, allowing for its use in a predictive formula. Surgeons can use this formula in a preoperative setting to help guide their choice of an appropriate tibial nail length.

Patient's consent/institutional review board approval

This study received IRB approval.

Financial disclosures

No author has received financial reward for this work.

Author contributions

PK- Methodology, Formal Analysis, Writing- Original Draft.

HB- Conceptualization, Methodology, Writing- Review & Editing.

DN- Data creation, Methodology, Writing- Review & Editing.

DD- Conceptualization, Methodology, Writing- Review & Editing.

Statements and declarations

This research did not receive any specific grant from funding agencies in the public, commercial, or non-for-profit sectors. The authors have no competing interests to declare.