Leg length discrepancies (LLD’s) are encountered on a daily basis. They are the root of many ankle, knee, hip and spinal problems. The questions the clinician must ask are “How much is significant?”, “How much do I add?” What are some of the signs and symptoms?” “What is the etiology?” and “How do I detect it?” A literature search (2003) provided the following information and answers.
How much is significant?
Most authorities claim that deficiencies of greater than ¼ inch (6mm) are clinically significant (1, 2) though some sources state that differences as little as 4 mm are significant (5). Subotnick (3) states that because of the threefold increase in ground reactive forces with running, lifts should be used with inequalities of greater than 1/8” inch (3mm).
How much do I add?
One of the easiest ways to determine the amount of lift needed is to examine the person in a weight bearing posture and add lifts under the short leg until the pelvis is even or until the lumbar spine is straight. If using off weight bearing measurements, you need to add 1/3 more height than measured because the talus is positioned 1/3 of the way between the calcaneus and metatarsal heads (4, 13). So, a heel lift placed under the calcaneus will only raise the talus 2/3 of that height. Lifts placed under the calcaneus can shorten the tricep surae muscles (4, 6) and apply increased pressure to the metatarsal heads (12); full length sole lifts are more physiological, though not always practical. Due to the supinatory moment of the short leg on heel strike, a lift may cause overcompensation and increased supination, with a tendency to overweight the lateral column and possibly injure the lateral ankle. Careful observation of gait post addition of a lift is in order and a valgus post running at least the length of the 5th metatarsal along with the lift should be considered (8, 9). Heel lifts also cause EMG changes of leg muscles, with decreased recruitment of gastrocnemius and tibialis anterior directly proportional to the height of the heel lift (18, 19). A lift or LLD changes the ground reactive forces associated with gait, increasing vertical force on the longer leg, along with increased joint stresses along the kinetic chain (14, 20).
Generally speaking, lifts greater than 3/8” (9mm) require extrinsic modifications to footwear (4, 6, 8). Find a competent individual to perform this work for you. Large discrepancies should be treated gradually, at a rate of ¼ inch every 4 weeks, less if symptoms do not permit.
What are signs and symptoms associated with LLD’s?
Compensation comes in many forms, depending whether it is acute (recent injury caused an LLD or compensation resulting in one, or long term. The deficiency can cause injury on the short or long legged side (or both).
The long leg moves through a greater arc during all portions of swing phase (7). The person may flex the knee to compensate and shorten the arc. The individual may also maximally pronate and evert the calcaneus an additional 3 degrees or greater on that side in an attempt to lower the navicular to the ground and shorten that leg. This causes an increased amount of internal rotation of the tibia and thigh causing muscular dysfunction (tightness of the hip flexors, strain of the intrinsic external rotators from eccentric deceleration of the thigh), along with medial knee strain (especially with concomitant genu valgus) (4, 6, 8, 9, 10, 11, 21, 22).
The short leg side will often supinate in an attempt to lengthen and cushion some of the shock of heel strike, since it has a greater vertical distance to travel (14); this often occurs with hyperextension of that knee. This lessens the dampening ability of the knee (since it flexes almost 20 degrees between heel strike and full forefoot load), and speeds the rate of subtalar pronation (since the rear foot is inverted and still must pronate the same amount (4). Many individuals will try and attenuate impact by contracting the contralateral hip abductor muscles and eccentrically lower the shorter extremity (4, 14). This can produce excessive strain of that musculature (trochanteric bursitis) as well as pathomechanical abnormalities of the L4 and L5 motion segments (due to increased body rotation toward the short side and attachments of the iliolumbar ligaments; this can cause degenerative changes if present long term (11, 12)).
What’s the etiology?
LLD’s can be structural (anatomical) or functional (pathomechanics, compensation). LLD’s can be due to foot problems (overpronation/supination, fractures), leg or thigh problems (congenital shortening, deformity, fracture), or pelvic compensation (rotation of ilia, fractures).
So, what is the etiology? A lot can be gleaned from the history. Past trauma is the most obvious so pay close attention. This could result in flattening of the calcaneus or overpronation due to ligamentous laxity; tibial fractures can cause shortening as well as increased or decreased tibial torsion; similar findings can occur in the femur, along with anteversion or retroversion; pelvic trauma can be more subtle and x-ray can often provide the most information (1, 2, 4, 6).
How do you determine a leg length inequality?
There are a number of methods, each with their own merit. X –ray is most accurate, but exposes the patient to ionizing radiation. Weight bearing seems most appropriate, since symptomatology usually presents itself then. Supine measurements are said to be influenced by asymmetrical muscle tension, table pressure on the innominates and hip flexor length (15).
With the patient weight bearing and both feet placed below the trochanters, observe the level of the medial malleoli. Next, compare the heights of the tibial plateaus. Femoral length can be judged by the heights of the greater trochanters, and pelvic alignment judged by the heights of the iliac crests (4, 17).
Alternately, lay the person supine and observe the heels and medial malleoli. If there is noticeable discrepancy, they may have a short leg; if there isn’t, they still may have a discrepancy that they are compensating for. Check the range of motion of the foot and ankle in 6 general directions: plantar flexion (40-45 degrees), dorsiflexion (20-25 degrees, depending on whether the knee is flexed or extended), inversion of the forefoot (3-60 degrees, on average), and eversion of the forefoot (20-45 degrees on average), calcaneal inversion (4-20 degrees) and calcaneal eversion (4-10 degrees). Excessive calcaneal eversion usually means over pronation due to a longer leg on that side; excessive inversion can mean a long leg due to a cavus foot type (2, 4, 6, 8, 9, 12). Lack of flexibility in the posterior compartment of the calf usually causes a greater degree of pronation (16).
Now, perform Allis’s test. Bend both knees to 90 degrees and observe the height of the tibial plateaus. The lower one is usually the side of the discrepancy (which can be in tibial length or due to excessive pronation). Now walk superior to the knees and observe the femurs from more cephalad (4). Is there a discrepancy? If so, the problem may be in the femur length, femoral head angle or pelvis. Extend the knees so that the legs are lying flat on the exam table. Palpate the greater trochanters on both sides. Is one lower than the other? If so, they probably have coxa vara on the short side or coxa valga on the long side. If they are even, you need to look at the pelvis. Does one ASIS palpate more anterior or posterior than the other? This could represent compensation. A posterior or “flexed” ilia, usually causes a short leg on that side; an anterior or extended ilia usually causes a long leg on that side. Now stand the patient up and perform a Gillet Test. Have them stand erect and hold onto something for balance. Palpate the PSIS on one side along with the 2nd sacral tubercle. Have them raise their thigh to 90 degrees on the side you are palpating. The PSIS should nutate backward (flex) and drop .5-1.5 cm on the side of the raised leg. Now have them raise the opposite leg. The sacrum should nutate backward and down. If either of these movements does not occur, consider pelvic pathomechanics and treat accordingly. Recheck for motion as well as leg length when done.
Standing observation often (but not always) reveals overpronation on the long leg side and relative supination on the short leg side. The shoulder is often higher on the short side and the waistline dips to the long side because of posterior rotation of the innominate. The shoulder will dip to the side of the short leg on heel strike during dynamic evaluation (4, 6, 8, 9, 10, 11). Gait observation usually reveals adduction of the pelvis toward the stance phase leg with a lateral sway in excess of 1” during stance phase. The person will seem like they are “stepping into a hole” on the short side.
Leg length inequalities occur due to a variety of anatomical and physiological conditions. Careful analysis and examination can often reveal its etiology. To lift or not to lift is a clinical decision that is left to the clinician and patient, with a careful balance between what is perceived as improved biomechanics and tolerance levels of the patient with regards to their presenting symptomatology.
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