Some studies offer evidence that leg length discrepancy (LLD) is associated with a variety of musculoskeletal disorders, such as hip or knee OA and chronic low back pain (LBP). One study for instance showed that hip or knee arthroplasty had been done 3 times more often to the longer leg than to the shorter leg (Tallroth et al 2017). LBP though seems to be more common on the side of the shorter leg (Gordon et al 2019).
It has been reported that patients with LLD frequently have increasing pain while standing for 20-30 minutes, and have immediate relief upon sitting. One RCT demonstrated the potential benefits of conservative correction of LLD using shoe inserts (10mm or less) in patients with chronic LBP. They concluded that simple and inexpensive individually fitted shoe inserts appear to reduce chronic LBP and functional disability in patients with LLDs of 10mm or less (Defrin et al 2005).
Interestingly though, LLD has been shown to be present in up to 90% of the population with an average value of 5 ± 4mm as measured by highly precise x-ray methods (Knutson et al 2005). This means only 10% of the population has exactly equal lower limb lengths!
However of the 90%, the vast majority have LLD of less than 1cm (Gordon et al 2019). The incidence of LLD of greater than 2cm was found to be present in 0.1% of the population, which is one in every 1000, with a male-to-female ratio of 2:1 (Guichet et al 1991).
The challenge is that some studies find a definite association between LLD and LBP, whereas others find none.
“There seems to be a consensus that limb length discrepancies of >2cm are frequently a problem.” – Gordon et al 2019
“Correction of LLD with insoles was an effective intervention among workers with LBP and a standing job.” – Rannisto et al 2019
“There is low-quality evidence that shoe lifts reduce pain and improve function in patients with LLD and common painful musculoskeletal conditions.” – Campbell et al 2018