Before discussing our quantitative results and their implications, we must first address certain nomenclatural issues that came up during the execution of this project. Versions of the Allis test, as seen in figure 1, can be found in several textbooks commonly used by chiropractic students: Hoppenfeld p. 165 [21], Haldeman p.294 [22], and Magee p.246 [23] as well as included within innumerable course notes among the chiropractic colleges. The test has been mislabeled and misapplied by a number of authors, producing confusion in the literature which apparently has not been unrecognized. Accordingly, we attempt to document some of these inaccuracies in the following section.
The original test named after the historical Dr. JB Allis (c. 1960) is quite different from the test we modeled, and was apparently restricted to children or even infants, purporting to identify gross deformity such as congenital hip dislocation, hip dysplasia, tibial bowing, or marked anatomical leg length inequality.
According to Stricker and Hunt [1], the Allis test can discriminate between a short femur or tibia in children, if there is a suspicion of aLLI. They write: "If a LLD [leg length discrepancy] is suspected by pelvic tilt during standing, the location of discrepancy may be verified by performing the Allis test and the reverse Allis test. The Allis test (also called Galeazzi test) is performed in the supine patient by noting relative knee heights when both hips and knees are flexed 90°. This will determine how much discrepancy is located in the thigh segment. The patient is then turned prone with the knees and ankles at 90° (and both hips in neutral rotation) to determine how much LLD is present below the knees." Based on our modeling, as well as simple inspection of figure 4, it is not entirely clear why Stricker et al believe that knee height discrepancy assessed from the foot of the table confirms femoral deficiency, as compared with tibial deficiency. In another paper [24], Stricker's depiction of the Allis/Galeazzi test does not conform to his own stipulation that the hip and knee are flexed to 90°; our figure 4 is based on this depiction. A similar illustration appears in an article by Leet and Skaggs [25], who state: "The test is positive when the knees are at different heights as the patient lies supine with ankles to buttocks and hips and knees flexed." Their illustration does not really appear to bring the infant's feet to his or her buttocks.
In neither of these papers do we see any mention of assessing the Y axis location of the knee, as chiropractors performing their version of Allis are wont to do, and as is described in several textbooks commonly used by chiropractors. It might be added that Stricker's ancillary prone, knees-flexed procedure for identifying tibial length discrepancy can also be found in Peterson et al [26], p.322. This is portrayed in figures 5 and 6. Cooperstein has devised a model in which tibial length discrepancy in this position may be apparent (i.e., functional) rather than structural, the result of a difference in the stiffness of the anterior thigh musculature [17, 18].
In the 1987 first edition of Magee's orthopedics textbook [23], the index lists page 225 for the Allis test, but there is nothing on or near that page pertinent to anything like it. Page 255 of the same text depicts "Galeazzi's sign (Allis test)," with an illustration like the left side alone of our figure 1, stating it is "good for assessing unilateral dislocation of the hip only and may be used in children from 3 to 18 months of age. Page 246 of the same text provides an illustration nearly identical to our figure 1 (both left and right sides), purporting to identify "leg length discrepancy." We are not able to easily reconcile the information provided on pages 255 and 246 of this 1987 text. The 2002 4th edition of Magee's text [27] contains the same inconsistency, on pages 627 and 628.
Magee also describes another procedure he calls the "Weber-Barstow maneuver" ([27], p.629) for assessing LLI, that superficially resembles Allis/Galeazzi. We found other internet references to the Weber-Barstow procedure, such as course notes from the University of Minnesota [28] and another from the University of Maryland [29]. (Although these course notes were available when accessed on July 20, 2006 and August 25, 2005 respectively, their URLs had become inoperable by the time the present article was in press.) Further researching showed the proper name for this Allis-like test is the "Wilson-Barstow maneuver," as described by Donatelli ([30] p.412). Dorman portrays and discusses a procedure he also calls the Wilson-Barstow procedure [31], but he adds motion testing and thus winds up showing something quite different from Donatelli.
It is hard to escape the impression that the literature on the Allis/Galeazzi/Wilson-Barstow tests is very confusing and inconsistent. We do not know why, how, or when a simple visual test developed to assess gross structural deformity (such as congenital hip dislocation or dysplasia) mutated into a test for LLI in adults, possibly of small magnitudes. It appears that writers of orthopedic textbooks and their invited authors are making liberal use of each other's writings, without critically evaluating the accuracy of their attributions or validity of the tests. It is common to find discrepancies between the words authors use to describe test procedures, and the illustrations that appear in their texts.
Irrespective of nomenclature, our modeling shows that the test shown in figure 1 (the so-called Allis test in chiropractic, and apparently unnamed in orthopedic medicine) is flawed. Although it may detect aLLI, this test as commonly construed, as a differential diagnosis of short femur vs. short tibia, is not likely valid. It is simply not the case that a low knee seen from the foot of the table suggests a short tibia, whereas a cephalad knee seen from the side suggests a short femur. On the contrary, either a short tibia or a short femur would likely lower the knee as seen from the foot of the table. In addition, a cephalad knee likely suggests a short femur, and a caudad knee a short tibia, when the short leg is sighted from the side of the table. However, the accuracy of such a determination would in turn depend on a series of other factors that would affect the knee position as seen from both from the side and foot of the table:
• The hips would have to be in the same Y axis position. Table 1 shows that cephalad displacement of one hip results in a somewhat lesser degree of cephalad knee displacement. It is not obvious how an examiner would confirm symmetric hip placement on the table.
• The tone and/or stiffness of the gluteal muscles would have to be the same or similar, since this could affect the relative position of the femoral heads. Cooperstein's model of the Derifield pelvic leg check [17, 18] invoked similar differences in the stiffness of the anterior thigh musculature to explain differences in apparent tibial length.
• Equal and opposite differences in tibia and femur lengths would create asymmetry in both the Y axis hip locations and in knee height, as seen in table 1. Thus, the so-called Allis test would suggest anatomic LLI where it is not present, generating a false positive result