Relationship of Functional Leg-Length Discrepancy to Abnormal Pronation: Commentary

Commentary

[Editor’s Note: The following commentary on the preceding article was invited by the Editor to accompany the article. The author of the commentary served as a reviewer of the paper during the prepublication peer-review process.]

The article “Relationship of Functional Leg-Length Discrepancy to Abnormal Pronation” by Brian A. Rothbart, DPM, PhD, is useful, and the model he proposes to link functional limb-length discrepancy and foot pronation is appealing. Limb-length discrepancies are complex and common; at present, however, there is a lack of consensus regarding what degree of discrepancy constitutes a clinically significant condition [1–7]. This disagreement has affected the entity’s proposed prevalence rates, which range from as high as 95% [8]. to as low as 4% [9]. Methodologic protocols are thought to be a key factor contributing to the lack of agreement among clinicians and researchers, with many authors failing to demonstrate how reliability and validity have been established. Common methods for assessing leg-length discrepancy include indirect clinical methods, such as using a pelvic leveling device and blocks; direct clinical methods, such as using a tape measure; and a variety of radiographic techniques, including teleroentgenography, orthoroentgenography, and scanography [10]. I have recently attempted some of the techniques presented in this article and have identified a number of limitations, challenging issues, and key areas for future research.

The author performed the pelvic thrust maneuver to determine functional leg length, which in the author’s words “tended to level the pelvis and legs.” This maneuver is particularly dependent on the strength of the lower spinal musculature (paraspinal muscles), hip flexors (iliopsoas, iliacus, psoas major, rectus femoris), glutei, and hamstrings (semitendinosus, semimembranosus, biceps femoris). Weakness of these muscles could disguise a functional limb-length discrepancy. In addition, limb-length discrepancy has been reported to be a contributing factor in low-back pain [3,6,7]. It could be argued that many patients with low-back pain may find it difficult or impossible to perform the pelvic thrust maneuver, limiting the role of this assessment method.

The author determined hip positions by comparing the relative heights of the posterosuperior iliac spines. Although Dr. Rothbart reportedly has 35 years of clinical experience, this method has inherent limitations and clearly depends greatly on the clinician’s palpation skills. The clinician may have difficulty in performing this technique on patients who are obese or who have hypertrophy of the posterior region of the hip. Furthermore, although clinical experience has been shown to increase the degree of accuracy and reliability of a variety of clinical measures,11]. the techniques used must be easy to perform and master. The author should consider how such techniques could be improved. Perhaps a modified pelvic level could be employed to establish the height (sagittal plane) differences in the posterosuperior iliac spines.

Reliability and validity of clinical measurement techniques are fundamental to clinical practice. Dr. Rothbart did not determine or report the reliability of the techniques. Although previous literature documents a moderate-to-good reliability for the Foot Posture Index, limited information exists on the techniques used for assessing the functional leg-length patterns and hip positions. Furthermore, it would be interesting to know how many practice sessions and repetitions were required. As previously stated, a clinician who learns the motor skill when beginning the test is less skilled than a clinician who has already learned it and has practiced it many times. The concept of reliability (both intratester and intertester) of these techniques requires further investigation.

The author states that one of the overall aims of the study was to correlate abnormal pronation and a functional leg-length discrepancy on the basis of the position of the posterosuperior iliac spine during a weightbearing assessment. The body and foot positions of these two assessments were inconsistent. For example, in the assessment of foot pronation, subjects were asked to position themselves in a modified stance, with both arms extended, leaning forward against a wall with the knees in a flexed position. The author did not provide any rationale for this rather unnatural position, and it seems to differ significantly from traditional protocols employed to assess foot posture, such as the Foot Posture Index and navicular drop. As is evident from Dr. Rothbart’s Figure 3, this position may not only increase the base of gait but also increase the angle of gait, which has also been shown to increase pronation of the foot [12,13]. Many authors suggest that patients be positioned in their natural angle and base of gait, as this position appears to correspond with that of midstance [14–16]. Foot placement and position for the assessment of hip position were established with subjects standing in their own relaxed angle and base of gait. This foot position should have been used for assessing the Foot Posture Index; this would have made the data more convincing.

The emphasis of Dr. Rothbart’s article encompasses his dysfunctional model, the ascending pathway,17]. which is an interesting concept that highlights the role of mechanical coupling. Further research is required to help determine the influence of foot pronation on the innominate bone. This might need to include the use of pins placed directly into the posterosuperior iliac spine to record either two- or three-dimensional kinematics, as well as a series of radiographic and magnetic resonance imaging studies of cadavers.

As a general comment, the author screened 373 Mexican Indians; 61 individuals met the criteria (16.4%) and 56 (15%) of those individuals agreed to participate in the study. Although identifying the prevalence of functional leg-length discrepancy in this population was not a principal aim of the study, these figures are interesting and seem to add to the confusion about prevalence rates of leg-length discrepancy in different populations. In his “Discussion,” the author refers to a study by Keeling,18]. noting the small population size. This same statement can also be applied to Dr. Rothbart’s current study.

Considering these comments, the conclusion that “a positive correlation exists between the most pronated foot and the shortest leg” should be viewed with caution. Further study should be encouraged in the areas previously outlined.