Background/Purpose:   Osteoarthritis is the most common form of arthritis, and is a major cause of pain and disability. Continuous nociceptive input can influence somatosensory processing, and studies suggest that patients with knee OA have altered somatosensory findings, demonstrated by decreased vibration perception threshold (VPT), pressure pain thresholds (PPTs), and temporal summation (TS) elicited by repeated non-nociceptive stimulation. Here, we further characterize the relationship between these somatosensory measures in knee OA.

Methods:   Persons with moderate to severe radiographic (Kellgren-Lawrence (KL) grade ≥2) and symptomatic (at least 20mm on WOMAC visual analog scale) knee OA were evaluated. In subjects with bilateral OA, the most symptomatic side was considered the “affected” side. VPT was measured using a biothesiometer (Bio-Medical Instrument Co., Newberry, Ohio) that provided vibratory stimulation at multiple predetermined anatomic sites.  VPT was recorded as the first sensation of vibration (volts). TS was assessed by application of a 60g Von Frey monofilament repeatedly (30 times) to various sites. Participants answered the question “do you consider this painful?” (yes/no) and rated the extent of their pain on a scale of 0-10, immediately and after 10 seconds. PPT’s were measured using a pressure algometer applied to pre-defined sites with steadily increasing pressure. Recordings were taken at the first sensation of pain.

Results: 42 OA participants (mean age 54.1 ± 8.1 years) were evaluated. Subjects who demonstrated TS at the ipsilateral tibial tuberosity had significantly lower PPTs at multiple sites compared to those without TS (Table 1). VPT and PPTs were directly correlated at several anatomic sites (Table 2). VPT was lower at the first metatarsophalangeal joint (MTP) in those that demonstrated TS at the ipsilateral tibial tuberosity vs those that did not (8.2±3.3 vs 12.1±4.8 volts, p=0.005).  VPT was also lower at the first MTP in those that sensed/rated pain at the ipsilateral tibial tuberosity 10 seconds post-stimulation (for TS) vs those that did not (7.6±4.2 vs 11.3±4.2 volts, p=0.011). 

Conclusion:   Key measures of central sensitization appear to be well correlated in this group, with lower pain thresholds (PPT) in those that demonstrate TS. Higher pain thresholds and the absence of TS were both associated with decreased vibratory sense acuity (higher VPT).  Thus, the well documented loss of vibratory acuity in patients with knee OA may also be part of an inhibitory pathway reflected in higher pain thresholds and lack of temporal summation.