This study was designed to corroborate the results of previous studies suggesting that fracture healing is unrelated to IMN diameter and CN difference in patients with femoral shaft fractures treated with IMN. A high union rate was observed at our medical center among patients with simple fracture patterns (AO/OTA 32A and 32B). According to our study results, union time was unrelated to IMN size and CN difference. Multivariate linear regression revealed that, rather than either of these variables, fracture pattern and smoking habits affected time to union.
A larger IMN diameter was previously believed to be more effective at providing adequate stability and promoting healing in the load-sharing device. Press-fit contact between the nail and medullary wall can help to minimize movement of the nail and canal to maintain reduction[6]. Therefore, inserting large-diameter nails is standard care. Using small-diameter nails may increase interfragmentary motion, which creates an unfavorable environment for union. As the load transferred through the nail increase, implant failure becomes increasingly likely. In a biomechanical test, a 12-mm IMN exhibited high endurance. Brumback et al recommended 12-mm nails[7] and Clatworthy et al preferred 13-mm nails for men and 12-mm nails for women[8]. Arazi et al used 12-, 13-, and 14-mm nails in their study, which revealed optimal outcomes [9]. However, these studies were conducted over 2 decades ago. Because of improvements in nail design and metallurgy, newer nails can withstand greater compressive, torsional, and bending loads and thus enable smaller nails to achieve comparable strength to that of older, larger nails [3]. Current guidelines suggest minimal reaming after the occurrence of isthmic cortical chatter (0.5-1 mm). The appropriate nail diameter for a proper fit is 1 to 1.5 mm smaller than that of the largest reamer. The intraoperative midportion and narrowest medullary diameter can also be referenced for nail diameter selection[10].
In this retrospective study, we aimed to provide further evidence that IMN diameter and CN difference do not affect the likelihood of union or time to union. We first compared groups of patients receiving different IMN sizes and found no significant differences in union rate and mean time to union (Fig. 1). We then compared groups with different CN differences at the isthmus. No patients in Group 3 (> 2-mm CN difference) experienced nonunion. Patients in Group 2 and Group 3 who were treated without tight contact between the canal and nail tended to have the more complex fracture pattern in AO/OTA 32B. A complex fracture pattern may prevent physicians from inserting a tight-fitting nail. However, no significant differences were noted in union rate or time to union among the groups. Our result suggests that treating all diaphyseal femoral fractures with simple fracture patterns without tight contact between the nail and canal is reasonable; a 10-mm nail should be suitable in most cases.
Unlike patients in previous studies, all patients in our study received the same implant administered with the T2 Femoral Nailing System. This system adopts the greater trochanter as the starting point, with one proximal and 2 distal interlocking screws, which are all 5.0 mm in size. Because of this uniformity in implants, the strength and design of the nails were consistent.
In our opinion, reduction is the most important surgeon-controlled factor affecting fracture union. According to Millar et al, poor fracture reduction is associated with 11.5-fold greater odds of nonunion. Although this study emphasizes the importance of maximizing nail fit at the isthmus to decrease the risk of fracture non-union [11], we consider that poor nail fit is attributed to inadequate fracture reduction, which renders inserting nail appropriately impossible. The resultant non-union is actually associated with inadequate fracture reduction rather than smaller nail size. Our result further confirmed that nail size is not as important as fracture reduction.
Although reamed IMN is considered the gold standard treatment for femoral shaft fracture because of its high union rate[12]. Inserting smaller nails with limited reaming has some benefits. Limiting the reaming process minimizes alterations of the bony architecture, providing an ideal situation for osteoinduction[13]. Preserving cortical blood flow to reduce thermal necrosis in the cortical bone provides surgeons with numerous options for nail exchange during revision. We avoided excessive reaming, which can elevate intramedullary pressure and lead to marrow debris leakage into the venous system. Fat embolism syndrome, acute respiratory distress syndrome, and even sudden death can occur though some studies have questioned the applicability [14, 15]. Excessive reaming also causes increase operative time and blood loss, reduce bone strength, and lead to cortical thinning [16]. In addition, a large nail can cause iatrogenic fracture propagation, iatrogenic bursting of the femoral canal, insertion difficulties, and implant failure. Finally, the lower cost of smaller nails is another benefit. Similar to a previous study, our study revealed no difference in union rate and time between antegrade and retrograde femoral nailing[17].
Nonetheless, our study has shortcomings. This was a retrospective review. Primarily, postoperative radiographs were used for nail and canal diameter measurement. In addition, reduction quality was not compared. Finally, patients may require different rehabilitation protocols because of their concomitant health status.