Experimental Knee Pain Evoke Spreading Hyperalgesia and Facilitated Temporal Summation of Pain

Could emotional and sensitization status affect postural sway in adults with knee osteoarthritis?

BACKGROUND AND PURPOSE

The manipulation of sensory conditions and attentional demand affect the postural sway in older adults with knee osteoarthritis (KOA). However, it is not known if emotional and sensitization status affects postural sway in this population. This study aimed to test if older adults with mild and moderate knee osteoarthritis with symptoms of depression and high sensitization would change the profile of postural sway.

METHODS

Design: A cross-sectional study was undertaken.

PARTICIPANTS

The center of pressure parameters of 30 older adults with mild and moderate knee osteoarthritis and 15 healthy controls were evaluated under different conditions manipulating the visual and attentional demand. We used the pressure pain threshold to measure the sensitization status. Furthermore, we applied the Beck Depression Inventory index to assess emotional status.

RESULTS

Manipulating the visual demand affected the center of pressure parameters for both groups, without differences between them. Compared to the healthy control group, the knee osteoarthritis group presented with worse scores on the Beck Depression Inventory, lower pressure pain threshold scores, and the correlations between the symptoms of depression and sensitization status ranged from weak to moderate. Finally, in the knee osteoarthritis group, we observed few and weak significant associations between the center of pressure parameters and the Beck Depression Inventory and the pressure pain threshold scores.

DISCUSSION

Emotional and sensitization status seem not to be more associated with the center of pressure of older adults with mild to moderate KOA than healthy adults. Thus, it suggests that this population can safely maintain postural sway, irrespective of depression symptoms and high sensitization.

Acid-induced experimental knee pain and hyperalgesia in healthy humans

Inflammation and the related acidity in peri-articular structures may be involved in pain generation and hyperalgesia in knee osteoarthritis. This study investigated pain and associated hyperalgesia provoked by infusion of acidic saline into the infrapatellar fat pad. Twenty-eight subjects participated in two sessions in which acidic saline (AS, pH 5) or neutral saline (NS, pH 7.4) were infused into the infrapatellar fat pad for 15 min. Pain intensity, pain area, mechanical and thermal sensitivity, and maximal voluntary knee extension force were recorded. Repeated infusions were performed in 14 subjects. Infusion of AS caused significantly higher pain intensity, larger pain areas, induced hyperalgesia around the infused knee, and reduced extension force. No significant pain facilitation or spreading of hyperalgesia was found after repeated infusions as compared with single infusions. Acidic saline infused into the infrapatellar fat pad provoked pain and localized mechanical hyperalgesia. Thus, this acid-induced pain model may mimic the early-stage responses to tissue injury of knee osteoarthritis.

Task-Specific Training for Adults With Chronic Knee Pain: A Case Series

Study Design Case series. Background Recent evidence suggests that traditional impairment-based rehabilitation approaches for patients with knee pain may not result in improved function or reduced disability. This case series describes a novel task-specific training approach to exercise therapy for patients with chronic knee pain and reports changes in measures of clinical outcome (pain and physical function) following participation in the training program. Case Description Seven patients with chronic knee pain aged 40 years or older were included. Each reported at least "moderate" difficulty with sit-to-stand transfers, floor transfers, and/or stair negotiation at baseline. Experienced physical therapists provided between 8 and 16 treatment sessions focusing on improving performance of difficult or painful tasks. Outcomes A majority of patients demonstrated clinically important improvements in both patient-rated outcomes (Knee injury and Osteoarthritis Outcome Score, numeric pain-rating scale, modified Arthritis Self-Efficacy Scale) and performance-based outcomes (30-second chair-rise test, timed stair-climb test, floor transfer test, Performance Assessment of Self-Care Skills). Discussion A task-specific training approach for patients with chronic knee pain was described and yielded considerable improvement in pain and function for most of the individuals in this case series. Larger studies are needed to determine how task-specific training compares with more traditional impairment-based exercise approaches for chronic knee pain. Level of Evidence Therapy, level 5. J Orthop Sports Phys Ther 2017;47(8):548-556. doi:10.2519/jospt.2017.7349.

The dynamics of the pain system is intact in patients with knee osteoarthritis: An exploratory experimental study

Background and aims

Despite the high prevalence of knee osteoarthritis (OA) it remains one of the most frequent knee disorders without a cure. Pain and disability are prominent clinical features of knee OA. Knee OA pain is typically localized but can also be referred to the thigh or lower leg. Widespread hyperalgesia has been found in knee OA patients. In addition, patients with hyperalgesia in the OA knee joint show increased pain summation scores upon repetitive stimulation of the OA knee suggesting the involvement of facilitated central mechanisms in knee OA. The dynamics of the pain system (i.e., the adaptive responses to pain) has been widely studied, but mainly from experiments on healthy subjects, whereas less is known about the dynamics of the pain system in chronic pain patients, where the pain system has been activated for a long time. The aim of this study was to assess the dynamics of the nociceptive system quantitatively in knee osteoarthritis (OA) patients before and after induction of experimental knee pain.

Methods

Ten knee osteoarthritis (OA) patients participated in this randomized crossover trial. Each subject was tested on two days separated by 1 week. The most affected knee was exposed to experimental pain or control, in a randomized sequence, by injection of hypertonic saline into the infrapatellar fat pad and a control injection of isotonic saline. Pain areas were assessed by drawings on anatomical maps. Pressure pain thresholds (PPT) at the knee, thigh, lower leg, and arm were assessed before, during, and after the experimental pain and control conditions. Likewise, temporal summation of pressure pain on the knee, thigh and lower leg muscles was assessed.

Results

Experimental knee pain decreased the PPTs at the knee (P <0.01) and facilitated the temporal summation on the knee and adjacent muscles (P < 0.05). No significant difference was found at the control site (the contralateral arm) (P =0.77). Further, the experimental knee pain revealed overall higher VAS scores (facilitated temporal summation of pain) at the knee (P < 0.003) and adjacent muscles (P < 0.0001) compared with the control condition. The experimental knee pain areas were larger compared with the OA knee pain areas before the injection.

Conclusions

Acute experimental knee pain induced in patients with knee OA caused hyperalgesia and facilitated temporal summation of pain at the knee and surrounding muscles, illustrating that the pain system in individuals with knee OA can be affected even after many years of nociceptive input. This study indicates that the adaptability in the pain system is intact in patients with knee OA, which opens for opportunities to prevent development of centralized pain syndromes.

Intra-Articular Analgesia and Steroid Reduce Pain Sensitivity in Knee OA Patients: An Interventional Cohort Study

Objectives. To assess the effects of intra-articular therapy on pain sensitivity in the knee and surrounding tissues in knee OA patients. Methods. Twenty-five knee OA patients with symptomatic knee OA were included in this interventional cohort study. Pressure pain thresholds (PPT) were recorded before, immediately after, and two weeks after ultrasound guided intra-articular injection of lidocaine combined with glucocorticosteroid. Computer-controlled and manual pressure algometers were used to assess PPT on the knee, vastus lateralis, tibialis anterior, and the extensor carpi radialis longus muscles (control site). Results. Significantly increased PPTs were found following intra-articular injection, at both the knee (P < 0.0001) and the surrounding muscles (P < 0.042). The treatment effects were sustained for two weeks, and at some points the effect was even greater at two weeks (P < 0.026). Albeit not statistically significant, a similar trend was observed at the control site. Conclusions. Intra-articular anesthesia, combined with glucocorticosteroid, reduced pain sensitivity in both the knee and surrounding muscles for at least two weeks.

The pain-relieving qualities of exercise in knee osteoarthritis

The purpose of this review article is to explore the role of therapeutic exercise in managing the pain associated with knee osteoarthritis (OA). Therapeutic exercise is often recommended as a first-line conservative treatment for knee OA, and current evidence supports exercise as an effective pain-relieving intervention. We explore the current state of evidence for exercise as a pain-relieving intervention for knee OA. Next, the mechanisms by which knee OA pain occurs and the potential ways in which exercise may act on those mechanisms are discussed. Clinical applicability and future research directions are suggested. Although evidence demonstrates that exercise reduces knee OA pain, optimal exercise mode and dosage have not been determined. In addition, it is not clearly understood whether exercise provides pain relief via peripheral or central mechanisms or a combination of both. Published clinical trials have explored a variety of interventions, but these interventions have not been specifically designed to target pain pathways. Current evidence strongly supports exercise as a pain-relieving option for those with knee OA. Future research needs to illuminate the mechanisms by which exercise reduces the pain associated with knee OA and the development of therapeutic exercise interventions to specifically target these mechanisms.