One of the biomechanical implications of mild leg length discrepancy (LLD) is excessive or abnormal mechanical joint loading, which is recognised as a key risk factor for knee osteoarthritis (OA).
As stated by Golightly et al. in their study on the subject, individuals with LLD tend to modify their movement patterns to functionally minimise the inequality by increasing knee flexion or hip adduction of the longer limb.
The authors conducted the first large, community-based study to examine the relationship of LLD with radiographic knee and hip OA and found that the prevalence and severity of knee OA were higher in participants with leg length inequality than those without, even when adjusted for key risk factors.
They attributed this correlation to altered or amplified joint forces in LLD which accelerate degeneration of joint structures and increase OA severity.
The biomechanical effects of mild leg length discrepancy in patients with knee OA during gait were investigated in detail by Resende et al. who measured ankle, knee, hip, pelvis and trunk kinematics and moments in 15 knee osteoarthritic participants.
It was observed that mild LLD affected the biomechanics of the entire kinetic chain during the stance phase of gait of individuals with moderate knee OA.
In addition to this, individuals with knee OA demonstrated increased rearfoot plantar flexion angle, ankle plantar flexion moment and reduced hip adduction angle; the short limb condition increased the knee flexion angle and the flexion and extension moments, which may explain the relationship between mild LLD and OA progression.
The cross-sectional relationship between the two conditions makes it necessary to understand this association clearly to develop a better clinical understanding and to formulate successful treatment and management modalities.
In the case of Structural LLD, orthotics with heel lifts can be used to treat leg length discrepancies of up to 10mm, helping restore alignment and optimal lumbopelvic biomechanics.
Excessive pronation on the long leg side can be treated with corrective orthotics in conjunction with heel lifts on the ipsilateral foot, to balance the sacral base and rectify compensatory scoliosis on the shorter side.
By optimally redirecting the mechanical forces acting on the lower extremity, highly customised orthotics such as MASS4D® can also be used to cause a decrease in the pathological loading forces acting on the affected knee, improving gait function in the patient and protecting the musculoskeletal system from any further damage.
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Repetitive plantarflexion can lead to pain and mechanical limitation in the posterior ankle joint which is known as posterior ankle impingement syndrome. This pathology commonly occurs in ballet dancers and football players.