Improper sized nail, either shorter or larger can cause impingement, soft tissue irritation, patellar tendinitis, joint penetration, mal-reduction, delayed union, stress fractures, and difficulty in dynamization or removal [5-7].
Many methods both preoperative and intraoperative, are mentioned in literature to determine the correct nail size i.e. proper length and diameter of an intramedullary tibial nail to be used. Each method has its merits and demerits, and most are lacking in accuracy.
Intraoperative methods used are nail-against-limb technique, two guide wires technique and by using a radiographic ruler [5-7]. Intraoperative techniques, the guide wire method and use of intraoperative radiographic ruler have an excellent accuracy of 94% according to Galbraith etal [8]. But, inaccuracies may occur due to eccentric C-arm placement, with the measurement being taken from the lowest exposed part of the guide wire or by not holding the radiographic ruler close and paralleled to the tibia [8].
Further, these techniques cannot be utilized in comminuted fractures or bilateral tibial fractures as these use comparisons with the opposite normal side or restoration of normal tibial length as a guide for measurement, which is difficult in bilateral or comminuted fracture cases respectively. Further, these intraoperative techniques take valuable operating time and add radiation exposure to both the patient and the operating room personnel. Two guide wires technique cannot be used when un-reamed nails are used [8].
Intraoperative, primary insertion of inaccurate size nail may need exchange of an incorrect length nail which further increases the radiation and operating time and causes frustration for the surgeon. Hence although, intraoperative measures are considered to be the most accurate methods, they provide no scope for preoperative planning and are not recommended in isolation for estimation of tibial nail length [6,9].
So preoperative planning for tibial interlocking nail should also include estimation and determination of tibial nail length preoperatively in-order to augment the accuracy of intra-operative tibial length estimation, so that we could avoid these intra-operative problems. This also avoids wastage of inaccurate nails which are discarded during the operative procedure [8].
Accurate preoperative nail estimation also can reduce intra-operative errors, operative time and radiation exposure [5-7]. Preoperative estimation of tibial nail length can be done by radiographic assessment or by anthropometric measurements.
The preoperative radiological methods described are krammer splint technique, templating, scanograms, spotograms and direct measurement from radiographs of the contralateral limb. These preoperative methods which rely on conventional radiography can cause inaccuracies due to malrotation in positioning the patient, inadequate exposure and variation and errors in magnification [7].
Krettek etalreported a magnification of 7% in standard tibial radiographs and found templates unreliable in selecting implant length, because magnification varies depending on the splint used, position of limb at time of X rays and distance of the cassette and tube [5].
The problem of magnification can be overruled by use of a radiographic ruler or marker [6].But routinely use of such a radiographic ruler for all cases is not feasible and is difficult especially in a poly trauma patient. Further if the radiographic marker is not kept at proper level it could result in poor accuracy in determining the correct nail length [6].
Digital radiograph although helps to assess the fracture pattern better, but its modularity to change the magnification of the length of tibia to fit the size of X ray film, makes them unsuitable for estimation of tibial nail length. Digital aids and scanogram are not routinely recommended for trauma cases and availability and cost is also an issue.
Anthropometric measurements can be done quickly, easily and freely, even in uncooperative or polytrauma patients. Several anthropometric methods have been described for the preoperative estimation of tibial nail length. Most commonly used anthropometric measurements described for the preoperative estimation of tibial nail length are knee joint line to ankle joint line (K-A), knee joint line to medial malleolus (K-MM), tibial tuberosity to ankle joint line (TT-A), tibial tuberosity to medial malleolus (TT-MM), olecranon to fifth metacarpal head (O-MH) and body height (BH) [9-12].
Existing literature provides varying and contrasting accuracies to each anthropometric parameter used. Hence, in order find out the best anthropometric measure correlating with the tibial nail length, we measured various anthropometric measurements in 100 cases of tibial shaft fracture and compared their proximity to actual size of tibial interlock nail used. We found that in our study the mean nail size was 33.61, whereas mean K-A was 35.61, mean K-MM was 37.16 +1.36, mean TT-A was 33.58, mean TT-MM was 34.40 and mean O-MM was 33.10 ± 1.61.
The mean TT-A and O-MH was the closest length of actual sized tibial nail used. Among the two we found O-MH distance to be the most accurate as the tip of olecranon and metacarpal head are easy to palpate, in comparison to tibial tuberosity, which is difficult to palpate as it may not be prominent or it wide enough to take as a reference point, causing intra observer errors.
Conclusion
Accurate size tibial nail insertion is of paramount importance for satisfactory outcome. Various anthropometric measurements help to assess the tibial length size preoperatively, among which distance between the olecranon tip to 5th metacarpal head, correlates best with the ideal nail size to be used. When, one of the landmarks, for the measurement cannot be easily palpated or to increase the accuracy of nail size prediction, other anthropometric measurements can be used.