The use of blocking "screws" in retrograde intramedullary nailing for distal femur fractures: A systematic review.

INTRODUCTION: Distal femur fractures present significant challenges when achieving and satisfying alignment due to the wide metaphyseal canal and deforming muscular forces. Retrograde intramedullary nailing (RIMN) is a well-established fixation strategy for extraarticular distal femur fractures; however, malalignment remains a recognized limitation, particularly with metaphyseal comminution. Blocking screws have been introduced to guide nail trajectory and reduce diaphyseal-metaphyseal mismatch, as well as augment mechanical stability. This systematic review examines the indications, technical considerations, postoperative outcomes, and complication profile associated with blocking screw use during RIMN for distal femur fractures.

MATERIALS AND METHODS: A systematic search of PubMed and the Cochrane Library was conducted for studies published between January 1999 and December 2024. The search followed PRISMA guidelines and included randomized trials, comparative cohort studies, retrospective series, and biomechanical analyses evaluating blocking screws used in conjunction with RIMN. Two reviewers independently screened titles, abstracts, and full texts. Eligible studies reported radiographic and/or clinical outcomes related to malalignment, union, or construct stability. Studies without postoperative alignment metrics, those evaluating antegrade nails, open or periprosthetic fractures, pediatric cohorts, or noncomparative descriptions without outcome measures were excluded. Data extraction focused on alignment parameters, union rates, fracture characteristics, and complications.

RESULTS: Across the included studies, blocking screws consistently reduced postoperative coronal and sagittal malalignment by constraining nail position particularly in fractures with metaphyseal comminution, wide canals, or in patients with elevated body mass index. Union rates did not differ significantly between constructs, suggesting that augmentation primarily improves alignment rather than osteogenic potential. Complications were infrequent, typically limited to hardware irritation or interference with locking screws, with neurovascular injury rarely reported.

CONCLUSIONS: Blocking screws are a valuable adjunct to RIMN in complex distal femoral fractures, improving alignment without adversely affecting union. Prospective, high-quality studies are warranted to refine indications, optimize screw placement strategies, and clarify long-term functional outcomes.