Shoulder Joint Position Sense Improves with External Load

1
Shoulder Joint Position Sense Improves with
External Load

• David N. Suprak, PhD
• Louis R. Osternig, PhD
• Paul van Donkelaar, PhD
• Andrew R. Karduna, PhD

2
Introduction

• Joint stability
• Functional activity
• Contributing factors
• Proprioception
• Feedback from limbs to CNS (Sherrington, 1906)
• Joint position sense (JPS) and kinesthesia (Dover
  et al, 2003)
• Muscle stiffness, coordination
• Importance for shoulder function

3
Mechanoreceptors
Introduction

• Capsuloligamentous
• Pacinian
• Ruffini
• Golgi tendon organ-like
• End range (Salo and Tatton, 1993 Vangsness,
  1995 Steinbeck, 2003)
• Musculotendinous
• Muscle spindles
• Golgi tendon organs
• Throughout ROM (Rymer and D'Almeida, 1980)
• Spindle sensitivity modulation (Burke, 1978
  Durbaba, 2001 Jami, 1980)

4
Muscle Spindle
Introduction

• Alpha-gamma linkage (Edin and Vallbo, 1990)
• Increased stimulation and sensitivity w/ muscle
  contraction (Burke, 1978 Durbaba, 2001 Jami,
  1980)

5
JPS and Muscle Activation
Introduction

• Active JPS more accurate than passive (Aydin et
  al, 2001 Edmonds et al, 2003 Potzl et al, 2004)
  
• Knee JPS with weight-bearing (Bullock-Saxton,
  2001)

6
Effect of Elevation Angle
Introduction

• Decreased error approaching 90 deg (Suprak et al,
  2006)
• Torque
• Muscle spindle sensitivity
• Did not assess effect of muscle activation
  directly

7
Purpose
Introduction

• Effect of altering external load at constant
  position on repositioning error
• Hypothesis
• Linear decrease in error with increased load

8
Subjects
Methods

• 24 healthy subjects
• (10 M, 14 F)
• Inclusion
• No hx of shoulder injury requiring surgery or
  rehabilitation
• Exclusion
• Limited elevation ROM
• Diagnosed neuromuscular disorders

9
Experimental Set-up
Methods
Head-mounted display
Humeral cuff and receiver
Load
Thoracic receiver
10
Load Calculation
Methods

• Baseline shoulder torque
• Arm length
• Body mass
• Segment mass, COM estimates (Dempster, 1955)
• 10, 20, 30, and 40 above baseline torque
• 5 Loading conditions

11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
Absolute Error Calculation
Methods
15
Target Positions
Methods
20/70
50/70
35/50
5 trials 2 trials at 35/50 1 trial at distracters
20/30
16
Statistical Analysis
Methods

• Planned linear contrast
• One-way repeated measures ANOVA
• IV External resistance (5 levels)
• DV Vector error
• Analysis repeated for plane and elevation error
• a lt 0.05

17
Vector Error by Resistance
Results
18
Plane Error by Resistance
Results
19
Elevation Error by Resistance
Results
20
Discussion

• Non-linear pattern
• Internal representation
• Sampling variability

21
Discussion

• JPS increases with external load
• Muscle activation receptor sensitivity
• (Durbaba, 2001)
• Only in direction of load
• Role of musculotendinous receptors
• Injury prevention under high forces

22
Thank you