Neck shaft angle deviation in patients undergoing femoral limb lengthening, a retrospective study

Purpose Previous studies have shown that subtrochanteric femoral fractures treated with intramedullary nails might lead to varus-procurvatum malalignment. Similar results have been reported when using antegrade intramedullary lengthening nails (ILNs). The purpose of our study is to examine if antegrade telescoping intramedullary lengthening nails lead to varus-procurvatum malalignment of the proximal femur and what are possible predictors of that shift. Methods In this retrospective, single centre study, five surgeons performed 537 femoral ILN. 347 antegrade PRECICE nails were selected after applying exclusion criteria. The following exclusion criteria were applied, intentional angular deformity correction, retrograde femoral lengthening and concomitant tibial lengthening. After further exclusion criteria were applied, we retrospectively inspected 201 PRECICE nails inserted in 158 paediatric and adult patients (average age 19.9 years) that underwent IM nail limb lengthening. Follow-up was at least one year by which time all osteotomies were healed. Results Mean lengthening was 4.7 cm per lengthening surgery with some patients needing multiple lengthening for large discrepancies. Of the 201 nails, trochanteric entry was used in 127 procedures and piriformis entry was used in 74 of them. With pre-op Osteotomy Level Coefficient (OLC) of 0.3. The preoperative neck shaft angle (NSA) was significantly reduced from 130.6 to 127.4 degrees at the end of lengthening (P < 0.05). There was no discernible correlation between the OLC and change in NSA. The trochanteric entry point was associated with a greater tendency to reduce the NSA (Mdif = -4.1, SD = 6.5) as compared to the piriformis entry point (Mdif = -3, SD 6.4) (P < 0.05). No significant change in anatomic medial proximal femoral angle (aMPFA) was noted between pre- and postoperative time points, nor between trochanteric and piriformis entry groups. Conclusion Our study investigated the risk of iatrogenic varus deformity of the proximal femur following intramedullary limb lengthening procedures. We identified the osteotomy site as the most significant risk factor for developing iatrogenic varus, while the nail insertion point did not significantly predict this complication, showing comparable results for both trochanteric and piriformis entry points. Additionally, our study is the first to identify a correlation between the level of osteotomy and coxa-valga correction. We hypothesize that a higher osteotomy level might be beneficial for patients undergoing limb lengthening who also present with coxa-valga deformity. Level of evidence IV.