Many clinical veterinary orthopedic studies assess patient outcomes with subjective measures such as owner questionnaires or veterinarian lameness scores. Although many subjective measures are validated for dogs with osteoarthritis and owner input is undoubtedly useful, these methods of assessing subjects have an additional source of bias: the assessors (owner and veterinarian). A placebo effect is a change in a patient's illness attributable to the symbolic import of a sham treatment perceived by the patient rather than a specific pharmacological or physiologic property.1,2 In situations where patients have no understanding of the efficacy of a treatment given to them by a caregiver, a caregiver placebo effect can develop. A reasonable definition of the caregiver placebo effect for veterinary medicine is a sham medical intervention that causes pet caregivers (owners or veterinarians) to believe the treatment they provided to the pet improved the pet's condition. The caregiver placebo effect may have its greatest influence during evaluation of a single patient and when interpreting results of an uncontrolled study or case series. In these situations, the bias created can artificially inflate the perceived effect of treatment, thereby causing unwarranted changes in clinical practice.
The caregiver placebo effect has been documented in veterinary medicine for the treatment of osteoarthritis for dogs. Review of FDA Freedom of Information summaries of NSAIDs shows that pet owners and veterinarians consistently report improvement in dogs treated with a placebo (reported improvement in dogs treated with the drug was significantly greater than the improvement reported for placebo-treated dogs). In deracoxiba and carprofenb summaries,3,4 the reported percentage of dogs with osteoarthritis treated with placebo that were perceived to improve ranged from 34.1% to 42.1%, depending upon the question asked, the time of the interview (eg, day 14 vs 42 of a study), and who was asked (owner or veterinarian). However, these summaries do not provide all of the necessary information to measure the true caregiver placebo effect because they incompletely describe the questions asked, grading scales, range of responses, and how the caregiver responses compared with an objective measure of patient disease status (eg, limb function measured by force platform gait analysis). These summaries tend to focus on the percentage of caregivers stating the patient was improved and do not mention whether caregivers reported their dog as unchanged when it had actually gotten worse. This would also be evidence of a caregiver placebo effect. In these 2 clinical trials,3,4 when limb function was measured objectively by means of force platform gait analysis and GRFs, a treatment effect was documented when dogs were treated with the active drug but no placebo response was found via measurement of GRFs.
A treatment effect in dogs with lameness from osteoarthritis that received only placebo has been consistently documented in the past.5–12 For example, in an investigation of the safety and efficacy of meloxicam,c both owners and veterinarians reported that, on average, placebo-treated dogs improved.5 During the Liverpool Osteoarthritis in Dogs (elbow) owner questionnaire validation study for dogs with osteoarthritis, Hercock et al6 found that, on average, owners reported their dog's lameness as improved even when treated only with placebo. There was no improvement in lameness when the same placebo-treated dogs were evaluated by use of GRFs. Moreau et al7 reported that veterinarians graded placebo-treated dogs as improved when gait analysis showed no change. In a randomized, double-blinded, placebo-controlled study, Innes et al8 found that mean function in placebo-treated dogs improved when rated by both owners and veterinarians. Again, no change in the mean GRF of these dogs occurred. Similar to FDA Freedom of Information summaries, these papers simply address when the caregiver reported the patient as improved and do not address when a caregiver might have reported the patient as unchanged when it had in fact worsened. In addition, none reported how caregivers' opinions compared with an objective outcome measure of the patient.
Osteoarthritis is a chronic debilitating disease that affects millions of dogs each year. The efficacy of non-surgical and surgical interventions for the treatment of osteoarthritis is commonly determined on the basis of owner interview and examination by a veterinarian. Veterinary patients cannot verbally communicate the effect of an intervention or treatment, so these simple and subjective outcome measures are necessary for routine veterinary care and clinical research. However, correct interpretation of a scientific manuscript, an interview with an owner, or even a veterinary physical examination would be improved with a better understanding of how often caregivers (owners and veterinarians) overestimate or underestimate the efficacy of a potential intervention for osteoarthritis. The objective of the study reported here was to document the caregiver placebo effect in owners and veterinarians in evaluation of dogs with lameness from osteoarthritis.
Ground reaction force
Peak vertical force
Deramaxx, Novartis Animal Health, Greensboro, NC.
Rimadyl, Pfizer Animal Health, New York, NY.
Metacam, Boehringer Ingelheim Vetmedica Inc, St Joseph, Mo.
Advanced Mechanical Technology Inc, Watertown, Mass.
Sharon Software Inc, Dewitt, Mich.
JMP, version 9.0.0, SAS Institute Inc, Cary, NC.
Brody H. Placebo effect: an examination of Grunbaum's definition. In: White L, Tursky B, Schwartz GE, eds. Placebo: theory, research, and mechanisms. New York: Guilford Press, 1985; 37–58.
Turner JA, Deyo RA, Loeser JD, et al. The importance of placebo effects in pain treatment and research. JAMA 1994; 271: 1609–1614.
US FDA. Freedom of Information summary. Rimadyl (carprofen) caplets for dogs. S/NADA 141-053. Available at: www.fda.gov/downloads/…/FOIADrugSummaries/ucm116543.pdf. Accessed Jul 8, 2009.
US FDA. Freedom of Information summary. Deramaxx chewable tablets (deracoxib). Supplemental NADA 141-203. Available at: www.fda.gov/downloads/…/FOIADrugSummaries/ucm117645.pdf. Accessed Jul 8, 2009.
Peterson KD, Keefe TJ. Effects of meloxicam on severity of lameness and other clinical signs of osteoarthritis in dogs. J Am Vet Med Assoc 2004; 225: 1056–1060.
Hercock CA, Pinchbeck G, Giejda A, et al. Validation of a client-based clinical metrology instrument for the evaluation of canine elbow osteoarthritis. J Small Anim Pract 2009; 50: 266–271.
Moreau M, Lussier B, Doucet M, et al. Efficacy of licofelone in dogs with clinical osteoarthritis. Vet Rec 2007; 160: 584–588.
Innes JF, Fuller CJ, Grover ER, et al. Randomised, double-blind, placebo-controlled parallel group study of P54FP for the treatment of dogs with osteoarthritis. Vet Rec 2003; 152: 457–460.
Moreau M, Dupuis J, Bonneau NH, et al. Clinical evaluation of a powder of quality elk velvet antler for the treatment of osteoarthrosis in dogs. Can Vet J 2004; 45: 133–139.
Vasseur PB, Johnson AL, Budsberg SC, et al. Randomized, controlled trial of the efficacy of carprofen, a nonsteroidal antiinflammatory drug, in the treatment of osteoarthritis in dogs. J Am Vet Med Assoc 1995; 206: 807–811.
Brown DC, Boston RC, Coyne JC, et al. Ability of the canine brief pain inventory to detect response to treatment in dogs with osteoarthritis. J Am Vet Med Assoc 2008; 233: 1278–1283.
Roush JK, Cross AR, Renberg WC, et al. Evaluation of the effects of dietary supplementation with fish oil omega-3 fatty acids on weight bearing in dogs with osteoarthritis. J Am Vet Med Assoc 2010; 236: 67–73.
Waschbusch DA, Pelham WE, Waxmonsky J, et al. Are there placebo effects in the medication treatment of children with attention-deficit hyperactivity disorder? J Dev Behav Pediatr 2009; 30: 158–168.
Waxman AW, Robinson DA, Evans R, et al. Relationship between objective and subjective assessment of limb function in normal dogs with an experimentally induced lameness. Vet Surg 2008; 37: 241–246.
Brown DC, Boston RC, Farrar JT. Use of an activity monitor to detect response to treatment in dogs with osteoarthritis. J Am Vet Med Assoc 2010; 237: 66–70.
Budsberg SC, Johnston SA, Schwarz PD, et al. Efficacy of etodolac for the treatment of osteoarthritis of the hip joints in dogs. J Am Vet Med Assoc 1999; 214: 206–210.
Burton NJ, Owen MR, Colborne GR, et al. Can owners and clinicians assess outcome in dogs with fragmented medial coronoid process? Vet Comp Orthop Traumatol 2009; 22: 183–189.
Everitt BS. Response feature analysis of longitudinal data. In: Everitt BS, Pickles A, eds. Statistical aspects of the design and analysis of clinical trials. River Edge, NY: World Scientific Publishing, 2004; 119–132.
Descriptions provided to pet owners to assist them in grading of their pets' degree of lameness in a study of the caregiver placebo effect in evaluation of dogs with lameness from osteoarthritis.
|Mild||Slight stiffness and occasional lameness when walking; minimal licking of the affected joint; does not whimper or cry upon voluntary joint movement; rises from resting position with minimal difficulty; climbs steps or jumps up near normally; mild signs of pain when joint is moved (looking at joint and pulling away of limb)|
|Moderate||Increased stiffness or noticeable limping when walking; shortened steps; some licking of affected joint; occasional whimpering or yelp upon voluntary joint movement; slow to rise from resting position; sitting preferred over standing; reluctant to climb steps or jumps up; increased signs of pain when joint is moved (looking at joint and pulling away of limb)|
|Severe||Will not bear weight (carries affected leg); frequent licking of the affected joint; frequent whimpering or yelp upon voluntary joint movement; increased difficulty in rising from resting position; cannot climb steps or jumps up; will not allow person to handle joint (biting, growling, and pulling away of limb)|
Lameness scoring and criteria used for each grade of lameness.
|1||Mild subtle lameness with partial weight bearing|
|2||Obvious lameness with partial weight bearing|
|3||Obvious lameness with intermittent weight bearing|
|4||Full non–weight bearing|