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.

Total hip arthroplasty and femoral nail lengthening for hip dysplasia and limb-length discrepancy

“…IM lengthening nails provide new opportunities for limb equalization and deformity correction from conventional external fixation [18]. Former generations of nail systems include the Fitbone telescope active actuator system, Albizzia nail, and the IM skeletal kinectic distractor.…”

Effect of lengthening along the anatomical axis of the femur and its clinical impact

“…This may compensate for the limb mechanical axis that lateralization that was proven both theoretically and radiologically[2-4,6], and hence could partially justify the minimal clinical impact of such mechanical angle lateralization after intramedullary lengthening.…”

Use of internal lengthening nails in post-traumatic sequelae

“…Blocking screws are useful adjuncts to stabilise the nail in the desired location. A uniformly straight passageway for the nail may be fashioned in the best favourable direction within the confines of the medullary canal using a rigid reamer guided by preplaced blocking screws, as indicated [2,39]. Correcting rotational deformity can be obtained around the internal lengthening rods as far as the surrounding soft tissues remain unharmed [24].…”

“…Retrograde femoral lengthening tends to develop procurvatum and varus deformity, whereas antegrade tibial lengthening is associated with procurvatum and valgus malalignment [34]. Blocking screws should be placed intra-operatively at the concave side of the IM canal whenever deformity development is anticipated [39].…”

“…Fixator-assisted nailing is recommended during insertion to maintain the proper alignment for bone healing [26]. Blocking screws should be considered selectively wherever deformity potential is a concern [39]. Vigorous nail insertion is harmful to the inner drive mechanism [33].…”