Elsevier

Manual Therapy

Volume 26, December 2016, Pages 150-157
Manual Therapy

Original article
Regional asymmetry, obesity and gender determines tactile acuity of the knee regions: A cross-sectional study

https://doi.org/10.1016/j.math.2016.08.002Get rights and content

Highlights

  • Two-point discrimination threshold (TPDT) reference values for the knee regions have been reported.

  • Medial knee has better tactile acuity in comparison to the lateral knee region.

  • Knee regions, obesity indices and gender influences the knee TPDT.

Abstract

Background and aims

Alterations in central somatosensory function (e.g. cortical reorganisation) occurs secondary to chronic knee pain. The reorganization can be quantified using a clinical signatory measure, the two-point discrimination threshold (TPDT). In order to differentiate normal variability of TPDT against abnormal thresholds for clinical practice, development of body region specific reference values are required and the factors that determine the TPDT have to be established.

Objective

To establish reference values for TPDT of the knee region in healthy individuals and to determine the factors that influence the TPDT of the knee regions.

Methods

Participants across four decades (18–59 years; n = 79) were recruited. TPDT estimates for medial and lateral knee regions were determined using a mechanical calliper. Descriptive statistics, and linear regression analyses were performed to establish reference TPDT values, and to investigate associations between demographics, anthropometric variables, and TPDT estimates respectively.

Results

Participants' Mean (SD) age = 38.3 (12.2); females (n = 56); and right lower limb dominant (n = 72). Mean TPDT threshold ranges included: lateral right knee, 36.7 (14.3); medial right knee, 28.6 (9.7); lateral left knee, 37.7 (12.9); and medial left knee, 27.9 (11.4). Fifteen percent of the threshold variance (R2 = 0.148) of TPDT estimates was explained by the medial aspect (β = −8.9; p = 0.000) and male gender (β = 3.1; p = 0.057), weighted by anthropometric factors.

Conclusions

Age-stratified knee TPDT estimates have been reported to aid clinical interpretation. Regional asymmetry, gender, and obesity indices are factors that determine the TPDT of the knee. Normal TPDT asymmetry observed at medial aspect of the knee has significantly greater acuity compared to the lateral knee.

Introduction

Knee pain is a common musculoskeletal disorder encountered in clinical practice, contributing to 17.1 million years of life lived with disability among the world-wide population in 2010 (Woolf and Pfleger, 2003, Cross et al., 2014). A range of pathophysiological manifestations affecting the intra-articular, peri-articular, and extra-articular structures include degenerative, inflammatory, and mechanical processes which may contribute to joint pain (Sokolove and Lepus, 2013). Considering the mismatch between medical imaging findings and clinical signs and symptoms, the etiological mechanisms behind joint pain could be partly explained by central neurological adaptive mechanisms (Staud, 2011). These adaptive mechanisms occur secondary to chronic peripheral nociceptive activity at the receptor, dorsal horn, cortical and sub-cortical areas where the sensory information is processed for perception of pain (Haigh et al., 2003, Arendt-Nielsen et al., 2010, Allen, 2011, Murphy et al., 2012, Lluch et al., 2014).

Chronic nociceptive inputs associated with musculoskeletal conditions are associated with changes to the anatomical representation of the sensory and motor cortices of a specific body region (Wand et al., 2011, Catley et al., 2014). The changes in the cortices are observed in individuals with chronic low back pain, chronic knee pain (knee osteoarthritis), complex regional pain syndromes, and limb amputations (Flor et al., 1997, Grüsser et al., 2001, Pleger et al., 2006, Shanahan et al., 2015). The structural changes in the brain, known as cortical reorganization, adapt to the chronic nociceptive inputs (Flor et al., 1997). Cortical reorganisation is generally quantified by using various electrophysiological and brain imaging techniques for research purposes (Flor et al., 1997, Grüsser et al., 2001, Gwilym et al., 2010, Shanahan et al., 2015). However, clinically feasible methods to quantify such adaptive cortical processes secondary to chronic nociceptive inputs for early intervention is minimal. Recent research suggests that the extent of the cortical representation of a body region can be quantified by assessing the magnitude of two-point discrimination threshold (TPDT) of that body region using a mechanical caliper tool (Moseley, 2008, Moseley et al., 2008, Catley et al., 2013).

Two-point discrimination describes a function of touch that has significant peripheral and cortical neural mechanisms and it is a measure of tactile acuity. Traditionally, the TPDT is used as a measure of cutaneous innervation density (i.e. receptive field size) (Lundborg and Rosen, 2004), which can be influenced by sensory ageing (Koltzenburg et al., 1999, Wickremaratchi and Llewelyn, 2006, Decorps et al., 2014), anthropometric factors including body mass index (BMI) (Falling and Mani, 2016) and body fat ratios (Boles and Givens, 2011), and dermatomal organization (Horner and Dellon, 1994). Recent meta-analysis suggests that there is an increased TPDT in individuals with musculoskeletal pain including chronic knee pain (Catley et al., 2014), where the peripheral nervous system organization is unaltered. This indicates the ability of TPDT to identify altered central somatosensory function in chronic musculoskeletal pain, thereby the TPDT has expanded its clinical utility beyond investigating the integrity of peripheral nerve function (Tamura et al., 2003, Maihöfner and DeCol, 2007).

Recent evidence that investigated the TPDT of the knee joint found significant differences in TPDT in a small, non-age stratified clinical population (chronic knee pain) compared against healthy controls (Stanton et al., 2011, Stanton et al., 2013). This evidence clearly articulates the need for clinical assessment of altered central somatosensory function (e.g. cortical reorganization, warranting the need to embrace interventions targeting such adaptive central processes associated with chronic knee pain (Moseley and Flor, 2012)). However, the statistically significant difference in TPDT estimates was not adjusted for common variables that may have positively or negatively confounded the observed differences. A range of demographic and anthropometric factors and the potential interactions among these factors can influence the sensory acuity of the body region. Literature (Nolan, 1983, Bell-Krotoski et al., 1993, Bowden and McNulty, 2013, Catley et al., 2013) addresses the contribution of demographic (age, gender, side, limb dominance) and anthropometric factors on TPDT estimates in regions of high acuity, however, the underlying mechanisms are not completely understood for regions of lower acuity (e.g knee regions). There is a definitive lack of understanding of how these factors may influence the TPDT over peripheral joints, including knee joints. Establishing an improved understanding of those factors may help inform how one (clinicians/researchers) can normalize cortical representation through targeted interventions designed to address modifiable factors (Moseley and Flor, 2012).

A large body of evidence has established TPDT reference values for areas of high functional acuity, including those of the hand and face (Nolan, 1985, Posnick et al., 1990, Bell-Krotoski et al., 1993). However, only few studies have investigated TPDT over joint regions which are the commonly encountered in musculoskeletal clinical practice (Nolan, 1983, Catley et al., 2013). In addition, for clinical practice, normal reference values are needed in order to help clinicians differentiate normal variability of TPDT against abnormal thresholds in symptomatic populations. To the best of our knowledge, no previous studies have developed reference TPDT values or examined the determinants of knee joint organization. Evidence suggests that sensory deficits exist in the contralateral uninjured side, mediated through several mechanisms including altered central neuronal activity (Donaldson, 1999, Koltzenburg et al., 1999, Shenker et al., 2003, Kelly et al., 2007). This suggests the need for establishing reference values for both knee joints which will help clinicians to differentiate from normal against the abnormal thresholds when assessing for altered central somatosensory function in patients with unilateral or bilateral joint pain. Therefore, the aims of this study are to develop age-stratified TPDT reference values for knee (side and regions), and to investigate the associations of demographic (age, gender, body side, knee regions) and anthropometric variables (body mass index (BMI) and waist-height ratio (WHR)) on TPDT (a measure of tactile acuity).

Section snippets

Study design

This study is a part of the larger cross-sectional research that investigated TPDT estimates of the low back regions (Falling and Mani, 2016). This study was granted ethical approval by the University of X Human Ethics Committee. Written consent to participate in the study was obtained from all participants. TPDT was measured at four sites for each participant, including: medial and lateral regions of both knees. Each site was assessed once, in random testing order generated and counterbalanced

Results

A total of 79 participants across four decades: Group I (18–29 years), Group II (30–39 years), Group III (40–49 years), and Group IV (50–60 years), participated in this study. Anthropometric data was used to calculate BMI and WHR for each participant. Baseline characteristics are summarized in Table 1.

Discussion

The following discussion of study findings is organised by study aims, and therefore includes: TPDT estimates of knee regions in healthy individuals and association of variables with TPDT estimates.

Conclusions

Reference TPDT values for knee regions across four decades have been reported in healthy individuals. Current study results indicated regional differences within the knee, with females demonstrating decreased thresholds of the knee region. The observed linear relationships between body mass, waist circumference and threshold estimates, indicates the role played by obesity in threshold determination. Such influences of anthropometric variables stimulates further interest to investigate the

Conflict of interest

There are no known conflicts of interest associated with this study nor any financial support that could have influenced the outcomes.

Ethical approval

The ethical approval was obtained from the University of Otago Human Ethics Committee.

Funding statement

None.

References (74)

  • M. Koltzenburg et al.

    Does the right side know what the left is doing?

    Trends Neurosci

    (1999 Mar)
  • G. Lundborg et al.

    The two-point discrimination test - time for a re-appraisal?

    J Hand Surg

    (2004)
  • C. Maihöfner et al.

    Decreased perceptual learning ability in complex regional pain syndrome

    Eur J Pain

    (2007)
  • J. Medina et al.

    From maps to form to space: touch and the body schema

    Neuropsychologia

    (2010)
  • G.L. Moseley

    I can't find it! Distorted body image and tactile dysfunction in patients with chronic back pain

    Pain

    (2008)
  • G.L. Moseley et al.

    Tactile discrimination, but not tactile stimulation alone, reduces chronic limb pain

    Pain

    (2008)
  • M.L. Peters et al.

    A comparison of two-point discrimination threshold of tactual, non-painful stimuli between chronic low back pain patients and controls

    Pain

    (1991)
  • B. Pleger et al.

    Patterns of cortical reorganization parallel impaired tactile discrimination and pain intensity in complex regional pain syndrome

    Neuroimage

    (2006)
  • J. Reiswich et al.

    Intact 2D-form recognition despite impaired tactile spatial acuity in complex regional pain syndrome type I

    Pain

    (2012)
  • F. Scarpina et al.

    Tactile mental body parts representation in obesity

    Psychiatry Res

    (2014)
  • A.G. Schneiders et al.

    A valid and reliable clinical determination of footedness

    PM&R

    (2010)
  • P. Sörös et al.

    Cortical asymmetries of the human somatosensory hand representation in right-and left-handers

    Neurosci Lett

    (1999)
  • Y. Tamura et al.

    Central mechanisms for two-point discrimination in humans

    Neurosci Lett

    (2003)
  • J.P.M. Vriens et al.

    Extension of normal values on sensory function for facial areas using clinical tests on touch and two-point discrimination

    Int J Oral Maxillofac Surg

    (2009)
  • B.M. Wand et al.

    Cortical changes in chronic low back pain: current state of the art and implications for clinical practice

    Man Ther

    (2011)
  • ACSM's guidelines for exercise testing and prescription

    (2013)
  • K. Allen

    Central pain contributions in osteoarthritis: next steps for improving recognition and treatment?

    Arthritis Res Ther

    (2011)
  • D.B. Boles et al.

    Laterality and sex differences in tactile detection and two-point thresholds modified by body surface area and body fat ratio

    Somatosens Mot Res

    (2011)
  • R.M. Boon et al.

    Validation of the New Zealand Physical Activity Questionnaire (NZPAQ-LF) and the International Physical Activity Questionnaire (IPAQ-LF) with accelerometry

    Br J Sports Med

    (2010)
  • J.L. Bowden et al.

    Age-related changes in cutaneous sensation in the healthy human hand

    Age (Dordr)

    (2013)
  • M.J. Catley et al.

    Assessing tactile acuity in rheumatology and musculoskeletal medicine–how reliable are two-point discrimination tests at the neck, hand, back and foot?

    Rheumatology (Oxford)

    (2013)
  • M. Cross et al.

    The global burden of hip and knee osteoarthritis: estimates from the global burden of disease 2010 study

    Ann Rheum Dis

    (2014 Jul)
  • N.J. Davey et al.

    Somatotopy of perceptual threshold to cutaneous electrical stimulation in man

    Exp Physiol

    (2001)
  • L.F. Donaldson

    Unilateral arthritis: contralateral effects

    Trends Neurosci

    (1999 Nov)
  • W. Dunn et al.

    Measuring change in somatosensation across the lifespan

    Am J Occup Ther

    (2015 May-Jun)
  • W.H. Ehrenstein et al.

    Chapter-43 Psychophysical methods

    (1999)
  • C. Falling

    Two-point discrimination thresholds of back and knee regions: a normative study., in School of Physiotherapy

    (2014)
  • Cited by (4)

    • Tactile acuity is reduced in people with chronic neck pain

      2018, Musculoskeletal Science and Practice
      Citation Excerpt :

      Control group participants were excluded on the basis of history of chronic pain, current pain, or presence of neurological disorder or neurological symptoms/signs such as dysesthesia. Age, height and weight were collected as these factors are purported to have a small impact on tactile acuity (Lourens, 2014; Falling and Mani, 2016). Duration of pain was self-reported and average intensity of pain over the last week was quantified using the visual analogue scale within the McGill pain questionnaire (Melzack, 1987) and the Neck Disability Index was used to categorise disability as mild (<28%), moderate (30–48%), severe (50–68%) or complete (>70%) (Vernon and Mior, 1991).

    The manuscript proposal was approved by the University Human Ethics Committee.

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