TENS Effectiveness and Knee Osteoarthritis in Humans (TOPS)

• Pressure pain threshold [ Time Frame: 3 hours ] [ Designated as safety issue: No ]
  A handheld digital pressure algometer (Somedic AB, Farsta, Sweden), was used to assess PPT with the 1 cm2 circular probe. Pressure was applied at 40 kPa/s and patients were instructed to press the hand held response switch when the sensation first became painful. Familiarization with the proceedure was accomplished with testing on the non-dominant forearm of each subject. Following this familiarization procedure, PPTs were assessed at the knee and anterior tibialis muscle bilaterally. An average of the three trials at each test site was used for analysis.
  
  
• Timed Up and Go test [ Time Frame: 3 hours ] [ Designated as safety issue: No ]
  The TUG is a standardized test where on command subjects arise from a chair with no arm rest, ambulate 9.8 feet as quickly and safely as possible, turn, ambulate back, turn and return to sitting in the chair. The walking distance was measured in advance and marked on the floor with tape marks well visualized by subjects. Subjects were timed in a standardized fashion from the moment the upper back left the chair until return to full sitting position with back in contact with the chair.
  
  
• Pain Intensity measures [ Time Frame: 3 hours ] [ Designated as safety issue: No ]
  Subjects were asked to rate their pain intensity on a horizontal 100 mm Visual Analog Scale (VAS). The anchors utilized were "no pain" and "worst imaginable pain". VAS measures were taken at rest, during the TUG, during the HTS, and cutaneous mechanical pain testing.
  
  
• Thermal Pain threshold (HPT) and Temporal summation (HTS) [ Time Frame: 3 hours ] [ Designated as safety issue: No ]
  The TSA II NeuroSensory Analyzer was used to assess (HPT)and (HTS). For both measures, the 5 cm2 probe was placed and initial temperature was set at 37oC, and increased at 1 °C/s to a maximum of 52 oC. Subjects indicated when they first felt pain by using the remote patient switch which recorded the temperature . For temporal summation (HTS), a tonic heat stimulus of 45.5 oC was applied for 20 s. After building to the 45.5 oC in the first 5 s, subjects rated pain caused by this stimulus on a 10 cm visual analog scale every 5s for 15s.
  
  
• Cutaneous Mechanical Pain testing [ Time Frame: 3 hours ] [ Designated as safety issue: No ]
  Cutaneous mechanical pain thresholds were assessed with a series of von Frey filaments (North Coast Medical, Gilroy, CA) applied in ascending order from 0.008 to 300 g (0.008, 0.02, 0.04, 0.07, 0.16, 0.4, 0.6, 1.0, 1.4, 2, 4, 6, 8, 10, 15, 26, 60, 100, 180, 300 g). In addition, the subjects rated their pain on a 100 mm VAS in response to application of a 6 g von Frey filament at the six sites bilaterally.
  
  

The following specific aims will address this hypothesis:

Specific Aim 1 will compare the effect of high frequency TENS, low frequency TENS, and placebo TENS in patients with osteoarthritis on a variety of outcome measures: primary and secondary hyperalgesia, subjective pain scores, and function.

Specific Aim 2 will determine the relationships among these multiple pain measures in people with osteoarthritis, and compare to age matched controls.

Specific Aim 3 will determine the genetic variability as it relates to osteoarthritis pain and response to TENS treatment

Specific Aim 4 will determine how body composition (BMI, fat mass, percent fat, lean mass, and bone mass) impacts the effectiveness of TENS

One of the long-term goals of the investigators is to determine the clinical effectiveness of non-pharmacological treatments for pain, like TENS. These studies will begin to address this issue by examining effects of TENS on a variety of outcome measures in patients with a specific controlled condition (i.e., knee osteoarthritis). This research is innovative because it will be the first to systematically examine the effects of TENS on a variety of physiological parameters (primary and secondary hyperalgesia) and clinical outcome measures (resting pain, movement-evoked pain, function) in a common, painful and limiting condition that is frequently seen in physical therapy clinics. These studies will further allow us to translate basic science experiments previously performed in animal models of arthritis to the clinic. This information is expected to assist the clinician in the treatment choice for a particular patient and guide future clinical research.