For many years I was honored to be the Military’s expert in lower extremity biomechanics and I’ve made tens of thousands of orthotics in my career and yet I’ve only added a leg length correction in maybe 10-20 instances. The reason this came to mind is that I recently assessed a patient s/p TKA who became one of the very rare patients to add her name to that list. I thought I would share my thoughts on the subject because I certainly have run into no shortage of patients (and providers) who strongly believe in correcting for leg length difference.
- Since Jesus ascended to heaven there hasn’t been another person on the planet whose legs are symmetrical and really how could we be symmetrical? The obvious is the actual length of the femur and tibia, but functional leg length difference is more often due to asymmetry of Coxa, femoral, genu, and tibial varus/valgus alignment
2. Leg length asymmetry is just one part of the picture of frontal plane function…the real culprit is often what’s happening below the ankle and understanding those biomechanics will help you go a long way to deciphering the potential effect of leg length difference on functional biomechanics.
3. The body has numerous mechanisms to cope or compensate for frontal plane deviations and typically it’s been coping well for years or decades.
How do I decide whether or not to correct for a leg length asymmetry?
- Has something changed in the bone? Most of my leg length corrections followed a TKA, THA, or Femur/Tibial fracture. Some change in bone length that the patient’s body hasn’t lived with for decades.
- Is there an observable frontal plane gait deviation? Look for a drop in the pelvis on one side that would indicate an uncompensated leg length difference that might need intervention.
- Does the patient present with chronic or recurrent frontal plane pathology? Unilateral sacroiliac/trochanteric symptoms (bursitis, piriformis, etc), lateral thigh/knee pain (ITB, Vastus Lateralis, and patellofemoral pain).
- You’ve balanced the frontal plane issues below the ankle (typically: rearfoot varus, forefoot varus, and/or unstable midtarsal joint) and the patient’s symptoms have not improved. The foot has so much more leverage to impact the pelvis, you will be amazed how quickly your posterior and lateral hip pain patients recover when you address frontal plane issues below the ankle.
So you might be asking, why not correct for the apparent leg length asymmetry? What’s to lose?
- As noted above, of all the things that could lend to the appearance of a leg length difference, most of them are more variations of angulation (varus or valgus) than a true difference in length of either the femur or tibia (unless something has changed in the bone, see #1 above).
- You might actually be creating a leg length asymmetry. (Whatever the patient has going on, they may have been coping well with it for decades and changing that may cause more problems than it improves).
- Correcting for a leg length difference inside the shoe can significantly change the fit of a shoe far more than treating the frontal plane issues in angulation below the ankle…and if the patient doesn’t like how his/her shoe is fitting, she won’t wear the correction. Typically the most correction you can fit inside a shoe before shoe fit becomes an issue is ¼”, so the picture below is for your entertainment purposes. I was stationed at Brooke Army Medical Center in 1998 when I ordered a “custom shoe modification” for a 2” leg length difference secondary to femur fracture and instead of doing the hard work of adding the correction to the sole of my patient’s shoe, the Orthotist did the ridiculous work of constructing the biggest heel lift I’ve ever seen. I’ve kept it as a souvenir.