Internal lengthening devices in the femur lengthen along the anatomical axis, potentially creating lateral shift of the mechanical axis. We aimed to determine whether femoral lengthening along the anatomical axis has an inadvertent effect on lower limb alignment. Isolated femoral lengthening using the Intramedullary Skeletal Kinetic Distractor was performed in 27 femora in 24 patients (mean age 32 years (16 to 57)). Patients who underwent simultaneous realignment procedures or concurrent tibial lengthening, or who developed mal- or nonunion, were excluded. Pre-operative and six-month post-operative radiographs were used to measure lower limb alignment. The mean lengthening achieved was 4.4 cm (1.5 to 8.0). In 26 of 27 limbs, the mechanical axis shifted laterally by a mean of 1.0 mm/cm of lengthening (0 to 3.5). In one femur that was initially in varus, a 3 mm medial shift occurred during a lengthening of 2.2 cm.
In a normally aligned limb, intramedullary lengthening along the anatomical axis of the femur results in a lateral shift of the mechanical axis by approximately 1 mm for each 1 cm of lengthening.
The authors would like to thank the following people for their invaluable assistance with the manuscript: A. Ranade, MD, Amanda Chase, MA, A. Lee, D. Kelly, MA, and J. Marlowe, MA. The study was conducted at the International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, Maryland, USA. One author (DP) is a paid consultant and another author is an unpaid consultant (JEH) for Orthofix, Inc. One author (DP) is also a paid consultant for Smith & Nephew and Ellipse Technologies. One author (JEH) is an unpaid consultant for Ellipse Technologies.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
- Received November 9, 2011.
- Accepted April 26, 2012.
- ©2012 British Editorial Society of Bone and Joint Surgery