Leg Length Discrepancy and Osteoarthritic Knee Pain in the Elderly

To the Editor:

The article by Donald R. Noll, DO, in the September 2013 issue of The Journal of the American Osteopathic Association (JAOA)¹ was an interesting read despite its small database. It addresses 3 questions regarding postural asymmetry:

• How do we, the readers of the JAOA, define a short leg?

• Does a short leg correlate with unilateral knee pain?

• Can we bypass classical standing lumbosacral (SLS) radiographic evaluation of leg length discrepancy (LLD) by use of visual or palpatory physical findings that would allow us to separate functional treatable causes of LLD in a clinically efficacious way?

There is congruency in the osteopathic, orthopedic, chiropractic, and physical therapy literature that the reference standard for measurement of anatomic LLD is SLS radiography. Protocols to optimize the comparison of the standing height of the femoral heads (ΔFHU [femoral head unleveling], where Δ indicates a relative quantitative difference on the low or short side²) and reduce left-right magnification differences date back to Schwab³ in the 1920s. These protocols were formalized by Denslow et al⁴ in the osteopathic literature more than 60 years ago. A unilateral dropped foot arch, severe unilateral hip, or knee arthritis would be considered part of the anatomic LLD, even if such conditions developed over time from functional asymmetry. Anterior or posterior (A-P) rotations of the innominate bones, sacral torsions or shears, tight psoas muscles, or tight quadratus lumborum muscles may affect the apparent LLD in the supine, non–weight-bearing position but do not affect the height of the femoral heads in the standing, weight-bearing position.

It is problematic to define short leg as the leg presenting with superior (cephalic) medial malleolus in the supine position, when apparent short leg is actually more accurate, including functional and anatomic components.

Thirty years ago, Travell and Simons⁵ reviewed a number of studies looking at anatomic LLD in symptomatic and asymptomatic populations. If we assume a similar prevalence of anatomic LLD, then the challenge is to show that some combination of physical findings can identify the functional causes of LLD and that osteopathic manipulative treatment can resolve or stabilize symptoms of unilateral knee pain before obtaining standing lumbar radiographs and managing anatomic LLD with a heel or foot lift.

Irvin⁶ showed more than 20 years ago that patients with chronic low back pain and sacral base unleveling (ΔSBU) and scoliosis convex to the ipsilateral side (the most common compensatory pattern) would have reduced pain and decreased scoliotic curve with leveling of the sacral base by use of a heel lift.

It is difficult to argue that apparent functional factors play a major role in LLD but dismiss ΔSBU, sacral torsion, and sacral shear as “not predominant functional factors influencing LLD.”¹ This interpretation came about by assuming that ΔSBU will result in uneven iliac crests in the supine position.

On standing A-P view of the SLS radiograph, we typically measure the height of the iliac crest on the posterior aspect along the attachment of the quadrate muscle. A left-to-right difference reflects primarily rotation of the innominate bone around a horizontal axis in the sagittal plane but may also reflect an anatomic short leg by relative rotation of the pelvis about an A-P axis in the coronal plane.

With the patient in the standing position, we tend to evaluate iliac crest heights on the lateral aspects, where a difference reflects more of an anatomic LLD. In the supine, non–weight-bearing position, iliac crest height in the coronal plane is more likely to be affected by unilateral spasm or contracture of quadratus/psoas/erector spinae muscle groups in the absence of gravitational loading, exposing more functional causes for LLD and iliac crest height asymmetry.

In a 2004 article in which 421 cases were reviewed,² iliac crest height in SLS radiographs correlated strongly with ΔFHU. Historically, the frequency of ΔFHU for patients with low back pain is higher than that of control patients for cutoffs of 4-, 10-, and 15-mm levels. The type I pattern, in which ΔFHU and ΔSBU are parallel, is the most common compensatory response to a short leg, but as the ΔFHU cutoff increases, the added ΔSBU of type IB overwhelms the prevalence of pure ΔFHU. As the cutoff for ΔLLD increases, the frequency of ΔSBU increases with functional scoliosis tending to be convex to the ΔSBU.

Dott et al⁷ found poor correlation of the iliac crest with ΔSBU, presumably because of functional compensatory mechanisms. The sacrum, which acts as a gear box between the bipedal mechanics of the lower half of the body and the unimodal torso, apparently does not follow the gravitational effect of the ΔFHU with the same regularity as the iliac crest.

According to my personal conversations with Phillip Greenman, DO, it was his opinion that ΔSBU is more important than ΔFHU. Whether ΔSBU is considered anatomic or functional probably does not lessen its importance on spinal mechanics going cephalad or hip or knee mechanics going caudad.

One core question is whether physical examination can distinguish an anatomic short leg from ΔSBU. The standing and seated forward flexion tests and the relative position of inferior lateral angles in the prone position may be useful in this regard, but we cannot know for certain without correlating those physical measurements to SLS radiographic results in a substantial number of cases. We can assume that ΔSBU on standing SLS radiograph, as a result of sacral down sheer or sacral torsion, is a functional LLD, but we also do not have before and after radiologic evidence that classical osteopathic manipulative treatment will reduce or remove ΔSBU.

My unpublished research (recently rejected for publication by the JAOA) confirms and supports classical osteopathic theory that the ipsilateral innominate bone tends to rotate anteriorly on the anatomic short leg side as a compensation for the short leg. My future investigations will attempt to correlate the frontal plane pelvic postural asymmetry patterns with compensatory patterns of somatic dysfunction and visual or palpatory findings on physical examination. An algorithm for the differential diagnosis of apparent short leg is available on http://www.drjuhl.com under “Osteopathy.”

The greater the number of people thinking about these issues, the better. Osteopathy has always been about science—and intuition. A greater unification theory of somatic dysfunction continues to emerge.