Despite subtrochanteric fractures being commonly treated with an IM nail, evidence on the incidence and risk factors of re-operation in this subgroup of fractures is still lacking. In addition, as yet, no studies have compared the outcomes of different nailing systems used to treat subtrochanteric fractures in the same study population.

This study reported a re-operation rate of 22.3% in subtrochanteric fractures treated with a distally locked IM nail. Despite the differences in demographics, injury patterns, comorbidities and complications between patients who required a re-operation against those who did not, following an adjusted analysis, only six factors were found to be associated with re-operation. These include (i) age < 75 years old, (ii) nail type (long Gamma nail), (iii) pre-injury femoral neck shaft angle (coxa vara), (iv) a varus reduction angle > 10°, (v) fracture-related infection, and (vi) non-union.

A better way of understanding these six risk factors for re-operation would be to group them into (i) biological factors (age, infection, non-union) and (ii) anatomical factors (pre-injury femoral neck shaft angle, implant choice, reduction angle). Younger patients are more likely to sustain high-energy injuries, which often result in comminuted fracture patterns and other insults to the zone of injury (e.g. open fracture, vascular injury) [21]. All these deleterious factors ultimately subject the fracture to a higher risk of non-union [21]. Unless the fracture non-union or its causative factor (such as a fracture-related infection) is addressed and treated, the repetitive cyclic loading would, over time, exceed the failure load of the IM nail, resulting in nail failure [22, 23].

From a mechanical perspective, the pre-injury femoral neck shaft angle, reduction angle and nail type were all risk factors for nail failure leading to re-operation. A varus femoral neck shaft angle, whether congenital or secondary to malreduction, subjects the nail/lag screw junction to significant loading and bending stress, risking nail failure [22].

Comparing the use of long Affixus and Gamma nails in subtrochanteric fractures, outcomes of subtrochanteric fractures treated with the two nails in question have been reported in only a few studies [24, 25]. Most studies have only reported on the outcomes of Gamma nail use in intertrochanteric fractures [25,26,27,28]. Surgical time (Gamma nail: 104.1 min; Affixus nail: 114.5 min) and length of stay (Gamma nail: 23.7 days; Affixus nail: 23.6 days) were comparable between the two nails in our study group. This finding is similar to that of Persiani et al., who, to our knowledge, performed the only study that compared the use of Affixus and Gamma nails in the treatment of trochanteric fractures [26]. Mortality rates at 1 year were not significantly different between the two nail groups. On the other hand, the rates of re-operation, nail failure and touching of the anterior cortex in our study cohort were lower in the Affixus nail group when compared against the Gamma nail group (re-operation: p = 0.003; nail failure: p = 0.015; touching of anterior cortex: p < 0.001) (Table 5).

Complications were common with both nails. The two commonest complications in our patient cohort were non-union and fracture-related infection (Table 4). The incidence rates of non-union (25.2% in the Gamma nail group, 19.3% in the Affixus nail group) and fracture-related infection (2.5% in both the Gamma and Affixus nail groups) in our cohort of patients with subtrochanteric fractures were much higher than those reported in proximal femur fractures (non-union: 6.3%; fracture-related infection: 1.1%) [25, 27, 28]. The smaller (albeit not statistically significantly smaller) non-union rates in the Affixus group could be explained by the better lateral cortical reduction demonstrated with this nailing system (Table 4). Failure at the lag screw junction was another common complication, occurring at rates of 9.2% and 5.9% in the Gamma and Affixus nail groups, respectively. The cut-out rate in our Affixus nail group (0.8%) was slightly less than for proximal femur fractures treated with cephalomedullary nails (1.1 to 2.7%) [25, 28], whereas it was notably higher amongst the patients in the Gamma nail group (4.2%). Lastly, peri-implant fractures occurred in 4.2% and 2.5% of the Gamma and Affixus groups, respectively. Individual nail complications were not statistically different between the two nails, as previously mentioned, but the collective risk of nail failure due to all nail complications was significantly lower in the Affixus nail group (5.9% in the Affixus vs 15.1% in the Gamma nail group; p = 0.02).

The Affixus nail was noted to have superior performance, based on our 5-year Kaplan–Meier survival curve analyses (Figs. 3 and 4). The reasons for the improved survivorship of Affixus nails ought, however, to be interpreted with care. It is noteworthy that the Affixus nail was used during the second half of the study, when improvements had been made to the care pathway of patients with fragility fractures (e.g. orthogeriatric input, time to surgery of less than 48 h from the time of injury). Therefore, the improved survivorship of Affixus nails could well be multifactorial, and not attributable to just the nailing system alone.

Lastly, our study has addressed several controversial topics surrounding the use of a proximal anti-rotation screw in the Affixus nail. Implantation of the additional proximal anti-rotation screw did not lead to any statistically significantly different rates of complications, including non-union, infection and nail failure, as well as revision for any cause, therefore allaying the concerns over the additional surgical step and potential complications caused by the implantation of this additional proximal anti-rotation screw, such as the ‘Z-effect’, whereby the inferior lag screw migrates laterally and the superior screw migrates medially, leading to perforation of the femoral head by the superior screw [29].

To date, this study represents the largest series reporting on the incidence and associations of re-operation in subtrochanteric fractures treated with a long cephalomedullary nail. Furthermore, this study also compared the use of Gamma and Affixus nails in subtrochanteric femur fractures, and the effects of a proximal anti-rotation screw in the Affixus nail. One of the strengths of our study design lies in our inclusion criteria, which were generally more inclusive, with no restrictions imposed upon age or comorbidity, therefore allowing for a more accurate representation of the outcomes of these nails when used to treat subtrochanteric fractures. A further strength lies in the random matching of patients by age, gender and mechanism of injury (low energy, high energy and pathological fractures), thus removing any inherent risk of selection bias during statistical analysis. The retrospective nature of our study is a limitation, as data collection could be subject to bias. The analysis of fracture and radiological features could also be subject to inter- and intra-observer bias, which we hope to have addressed by utilising two assessors to analyse the results. Formal intra- and inter-observer reliability testing would help to reduce this risk. Additionally, measurements such as the neck shaft angle can be difficult to capture on plain radiographs, as flexion, abduction or external rotation of the hip can affect them. We assume, however, that the error was similar in the two groups, and therefore the effect of this error is minimised. Another limitation lies in the fact that the Affixus nail and the Gamma nail were used over different periods of the study. A prospective, randomised controlled trial would have been a superior model, providing a more accurate comparison of the survivorship between the two nailing systems.