The use of blocking screws with internal lengthening nail and reverse rule of thumb for blocking screws in limb lengthening and deformity correction surgery

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.

Keywords: Blocking screws; Deformity correction; Intramedullary lengthening nail; Limb lengthening; Reverse rule of thumb.

Fig. 1

a Holding the bone with the thumbs and index fingers of both hands as if you are manually trying to correct the deformity. The thumbs of both hands are placed on the convex side of the deformity near the apex or osteotomy site, and the index fingers are placed away from the apex or osteotomy site on the concave side. b The gray bar with black outline represents nail. The red circles indicate the locations where the blocking screws should be inserted. They are inserted adjacent to the nail on the side that is OPPOSITE to where the thumbs and index fingers are placed on the bone

Fig. 2

a Correction of distal femur varus deformity: The thumbs of both hands are placed laterally over the apex of the deformity, and the index fingers are placed on the concave side away from the apex. The red dotted line indicates the osteotomy site, and the blue arrows indicate the direction of force to correct the deformity. The black dots indicate the locations where the blocking screws should be inserted using the reverse rule of thumb. They are inserted on the side that is OPPOSITE to where the thumbs and index fingers are placed on the bone. b Correction of distal femur procurvatum deformity: The bone is not deformed, but the distal fragment is expected develop procurvatum deformity during lengthening. The thumbs of both hands are placed anteriorly where the apex of the procurvatum deformity would lie. The black dots indicate the locations where the blocking screws should be inserted. c Correction of mid tibia valgus deformity: The black dots indicate the locations of blocking screws. d Correction of proximal tibia procurvatum deformity: The bone is not deformed, but the proximal fragment is expected develop procurvatum deformity during lengthening. The black dots indicate the locations of blocking screws

Fig. 3

Antegrade femoral nail. a, b Represent radiographs taken at early distraction and consolidation phases, respectively. Blocking screws were not needed in the proximal fragment. One medial screw and one lateral screw were inserted in the distal fragment near the osteotomy site to prevent varus or valgus tilt of the fragment

Fig. 4

Retrograde femoral nail with distal femoral osteotomy. Anteroposterior radiograph (a) and intraoperative fluoroscopic anteroposterior view (b) show two medial blocking screws, one in proximal fragment and one in the distal fragment near the osteotomy site used to prevent varus angulation of the proximal and distal fragments, respectively. Lateral radiograph (c) and the intraoperative fluoroscopic lateral view (d) show one posterior blocking screw in the distal fragment near the osteotomy site used to prevent procurvatum deformity

Fig. 5

Antegrade tibial nail with mid-tibial osteotomy. Preoperative anteroposterior (a) and lateral (b) radiographs show preexisting valgus deformity of mid tibia. One lateral blocking screw was inserted near the osteotomy site in the proximal fragment to avoid valgus deformity during lengthening. Also, a blocking screw was inserted posterior to the nail in the proximal fragment before the reaming to guide the nail. Radiographs (c, d) represent post operative anteroposterior and lateral views at the end of distraction, respectively