## 3 Experimental Section  
### Animal Population and Randomization  
The study was designed as a randomized, multicenter, blinded, parallel group, conducted in 3 veterinary hospitals. Dogs, male or female, with lameness of the legs were eligible for inclusion. A complete orthopedic and health history was collected as part of the screening and initial enrollment. Only dogs with hip OA were included in the study. A block randomization to either aMSCs or PRGF group was performed where an independent randomization coordinator, who was not responsible for determining the eligibility of the animals, included the animal and had no information about the dogs in the trial and no influence on the assignment sequence. All assignments were communicated by phone.  
The following diagnostic criteria for patient selection were used: Animals suffering from degenerative joint disease in one or both hips, weighing more than 15 kg and being free of concurrent pathologies apart from OA. Prior to inclusion, a complete clinical evaluation (physical examination and vital signs were taken), complete hematology and serum biochemistry, endocrine and serology panel were performed. Orthopedic radiographs were reviewed to determine the degree of osteoarthritis in the affected area using the Bioarth(r) scale (Bioiberica, S.A. Barcelona, Spain) for the hip joint, where the presence of OA was evaluated and evidenced by subchondral bone sclerosis, bone remodeling, osteophytes, or enthesophytes [82]. Once the animal completed the inclusion criteria, no treatments (non-steroidal anti-inflammatory drugs, analgesics, nutraceuticalals, or adjunctive therapies) could be administered for two months. After this two month period, the animal was evaluated again as at baseline.  
Once the animal started the study, the exclusion criteria included any significant impairment of physical condition or functional status, whether as a result of the treatment, or for reasons beyond those previously mentioned (Figure 5).  
All owners of participating dogs signed a written consent form where they were given relevant information about the study and agreed to the randomization procedure. There was one fixed price for all participants irrespective of the treatment given. The study was approved by the institutional animal care board at the Las Palmas de Gran Canaria School of Veterinary Science.  
After this, dogs were assigned to one of the following groups:  
aMSCs: single intra-articular injection of autologous aMSCs (DogStem(r), Fat-Stem, Aalst, Belgium) (2 mL containing 30 million aMSCs) (\(n=18\)).  
PRGF: single intra-articular injection of autologous PRGF (PRGF-Endoret(r), BTI Biotechnology Institute, Vitoria-Gasteiz, Araba, Spain) (2 mL) (\(n=19\)).  
As some animals were affected bilaterally, the total number of joints studied were 40 and 38 for the aMSCs and PRGF groups, respectively.  
After the injection, the owners of the dogs were instructed to check for any sign of discomfort or pain, and were given instructions on the administration of cephalospororin (20 mg/kg/12 h, PO 7 days), meloxicam (0.1 mg/kg/24 h, PO, 3 days), and tramadol 82.0 mg/kg/12 h, PO, 24 h). Throughout the study the owners could use meloxicam as a rescue analgesic, to be recorded in writing for further assessment.