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.

Patients with diabetes mellitus may develop plantar flexion contractures (equinus) which may increase forefoot pressure during walking. In order to determine the relationship between equinus and forefoot pressure, we measured forefoot pressure during walking in 27 adult diabetics with a mean age of 66.3 years (sd 7.4) and a mean duration of the condition of 13.4 years (sd 12.6) using an Emed mat. Maximum dorsiflexion of the ankle was determined using a custom device which an examiner used to apply a dorsiflexing torque of 10 Nm (sd 1) for five seconds.

Simple linear regression showed that the relationship between equinus and peak forefoot pressure was significant (p < 0.0471), but that only a small portion of the variance was accounted for (R² = 0.149). This indicates that equinus has only a limited role in causing high forefoot pressure. Our findings suggest caution in undertaking of tendon-lengthening procedures to reduce peak forefoot plantar pressures in diabetic subjects until clearer indications are established.