Understanding the Correlation Between Ankle Joint Motion and Functional Short Legs in Chiropractic Practice

Leg length discrepancies often present a challenge in chiropractic, physical therapy, and osteopathic care. Distinguishing between a functional short leg and an anatomical short leg is crucial for accurate diagnosis and effective treatment. The study by Cooperstein and Lisi explores how ankle joint complex range of motion, leg checks, pelvic landmarks, and radiological findings relate to each other, offering insights that can improve clinical assessments.

The Challenge of Measuring Leg Length Differences

Measuring the anatomical length of legs has long been difficult due to natural variations and measurement inconsistencies. Even more complex is identifying a functional short leg, which results from biomechanical or muscular imbalances rather than actual bone length differences. Functional short legs can affect posture, gait, and spinal alignment, making reliable detection essential for practitioners.

The study aimed to develop reliable leg checking methods and examine how these relate to pelvic landmarks such as the posterior superior iliac spines (PSISs) and radiological markers like femur head and sacroiliac joint positions.

Innovative Measurement Tools and Methods

To capture precise ankle joint motion, the researchers created a triaxial foot posturometer. This device combined two inclinometers placed at right angles and a compass, all mounted on a surgical boot fixed to a wooden footprint. This setup allowed measurement of six end ranges of motion—two for each axis of rotation around the foot-ankle joint complex.

The study was divided into four parts:

• Study 1: Looked for covariance among the end range rotations.

• Study 2: Tested interexaminer reliability of two new leg checking methods—compressive and triaxial.

• Study 3: Explored correlations between leg checks and pelvic landmarks (sitting and standing PSIS).

• Study 4: Investigated correlations between leg checks and radiological parameters of femur heads and inferior sacroiliac joints.

  
  

Key Findings on Ankle Joint Motion

The researchers found that three specific ankle joint motions—plantarflexion, abduction, and inversion—tended to occur together. This combination was named the "triaxial foot." The statistical correlations between these motions were strong:

• Inversion and abduction: r = 0.96, p = 0.01

• Inversion and plantarflexion: r = 0.87, p = 0.053

• Plantarflexion and abduction: r = 0.98, p = 0.004

  
  

These results suggest that when assessing ankle motion, these three movements should be considered collectively rather than in isolation.

Reliability of Leg Checking Methods

The study showed high interexaminer reliability for subjective ratings of the triaxial foot by two examiners. This means that trained practitioners can consistently identify the degree of triaxial foot motion without relying solely on instruments.

The two novel leg checking methods—compressive and triaxial—also demonstrated good reliability, supporting their use in clinical settings. Reliable leg checks are essential for distinguishing functional short legs from anatomical ones.

Correlations With Pelvic Landmarks and Radiology

The researchers found meaningful correlations between leg checks and pelvic landmarks, particularly the PSISs in both sitting and standing positions. This supports the idea that pelvic asymmetry can reflect functional leg length differences.

Radiological findings of femur head and inferior sacroiliac joint positions also showed some correlation with leg checks, although these were less consistent. This highlights the complexity of linking functional assessments with imaging and the need for comprehensive evaluation.

Understanding the Correlation Between Ankle Joint Motion and Functional Short Legs in Chiropractic Practice: Practical Implications for Chiropractic Practice

Understanding the relationship between ankle joint motion and leg length discrepancies can improve diagnosis and treatment planning. Here are some practical takeaways:

• Assess the triaxial foot pattern: Look for combined plantarflexion, abduction, and inversion during ankle evaluation.

• Use reliable leg checking methods: Incorporate compressive and triaxial leg checks to improve consistency.

• Consider pelvic landmarks: Evaluate PSIS asymmetry in both sitting and standing to detect functional short legs.

• Integrate imaging cautiously: Use radiological findings as part of a broader assessment rather than sole indicators.

  
  

By focusing on these areas, practitioners can better identify functional short legs, tailor interventions, and monitor progress.

Cooperstein R, Lisi A, Correlation of Ankle Joint Complex Range of Motion, Leg Checks, PSIS Measurements, and Radiological Findings Proceedings of the ACC Conference X,Journal of Chiropractic Education Spr 2003; 17(1): 51.

The chiropractic, physical therapy, and osteopathic professions all use let-checking methods, and each has some concept of distinguishing a functional short leg from an anatomical short leg. Although finding accurate ways of measuring the anatomic length of the legs has not been without difficulties, identifying (i.e., validating) and reliably measuring the functional short leg has been far more difficult. The authors conducted a series of small studies to devise reliable leg checks and determine if their findings correlated with either the sitting or standing PSISs, or the radiological parameters of femur heads or inferior SI joints.

METHODS: A triaxial foot posturometer was constructed, consisting of two orthogonally placed inclinometers and a compass mounted on a surgical boot, screwed to a wood "footprint." This allowed measurement of the six end ranges, two for each direction of rotation around each of three axes for the foot-ankle joint complex. The first study looked for covariance in the end range rotations, the second study investigated the interexaminaer reliability of two novel methods on leg checking (compressive and triaxial), the third evaluated possible correlation of the leg checks with both each other and pelvic landmarks, and the fourth the possible correlation of the leg checks with radiological parameters.

RESULTS: Plantarflexion, abduction and inversion of the foot-ankle joint complex tend to covary; this triad of findings was termed the "triaxial foot." The values were: inversion-abduction r=.96,p=.0`1; inversion -plantarflexion r=.87, p=.0530; and plantarflexion-abduction r=.98, p=.004. Noninstrumented (subjective) ratings of two examiners for degree of triaxial foot were highly correlated (kappa=.85) as were their ratings for compressive leg checking (kappa=.67). The triaxial foot correlated with posterior innominate rotation in the group with a relatively small amount of torsion (r=.58, p=.17). The compressive leg cheek covaried with the difference between sitting and standing PSIS discrepancies, r=.44, p=.07 (a surrogate value for anatomical leg length inequality (LLI). The compressive leg check covaried with the radiological inferior SI joints, r=.87, p=.003, a surrogate for anatomic LLI. Looking at subjects in whom delta PSIS sitting was >3mm, a high torsion group, the triaxial and compressive leg checks were more highly correlated, r=.85, p<.001 and were unrelated in the low torsion group.

DISCUSSION: Using the difference between the sitting and standing delta PSIS as a surrogate measure for anatomic LLI compressive leg checking tends to correlate with the "delta of the deltas," suggesting it detects primarily anatomic LLI. This impression is further supported by the correlation between compressive leg checking and radiographic inferior sacroiliac joints. It was more difficult to determine the significance of the triaxial foot , except to see that in a low torsion group it predicted standing PSIS deltas, occurring on the side of the weightbearing low hip.

CONCLUSION: Since the results of compressive and triaxial leg checking covaried among the 17 subjects, it is reasonable to assume that the triaxial pattern serves as an easily identified surrogate for the more traditional identification of the short leg. We believe the triaxial foot to correspond under some circumstances to what clinicians generally call the function short leg and the compressive short leg more to an anatomic short leg. Having reliable leg checks facilitates the conduct of validity studies, which might determine what pathological significance (if any) leg length asymmetry may denote. Ultimately, we hope to validated or refute the suggestion that leg checks provide clinically useful information about pelvic function.