Abstract
Internal lengthening nail (ILN) is a recent development in limb lengthening and deformity correction specialty. The ILN has the distinct advantage of combining acute deformity correction with gradual lengthening of bone. While using ILN, the short metaphyseal bone fragment may develop a deformity at the time of osteotomy and nail insertion or during bone lengthening because of the wide medullary canal. These deformities are typically predictable, and blocking screws (Poller screws) are helpful in these situations. This manuscript describes the common deformities that occur in femur and tibia with osteotomies at different locations while using ILN in antegrade and retrograde nailing technique. Also, a systematic approach to the appropriate use of blocking screws in these deformities is described. In addition, the “reverse rule of thumb” is introduced as a quick reference to determine the ideal location(s) and number of blocking screws. These principles are applicable to limb lengthening and deformity correction as well as fracture fixation using intramedullary nails.
Highlights
Limb lengthening and deformity correction is a rapidly evolving orthopedic subspecialty that is gaining international popularity
The Internal lengthening nail (ILN) has the distinct advantage of combining acute deformity correction with gradual lengthening of bone
While using ILN, the short metaphyseal bone fragment may develop a deformity at the time of osteotomy and nail insertion or during bone lengthening because of the wide medullary canal
Summary
Limb lengthening and deformity correction is a rapidly evolving orthopedic subspecialty that is gaining international popularity. The distal fragment could possibly go into varus or valgus during lengthening and may benefit blocking screws This pattern of lengthening-induced deformity is not common. To decide the ideal locations of the blocking screws, the ‘‘reverse rule of thumb’’ is helpful This technique involves three steps: (1) assess or speculate the deformity: understand the direction of existing deformity that will be corrected with nailing or speculate the deformity that could occur later during lengthening; (2) manually correct the deformity: envision trying to manually correct the deformity by holding the bone with both hands. Varus angulation requires a blocking screw medial to the IM nail in the proximal fragment and often in the distal fragment close to the osteotomy site.
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