## 2 Results and Discussion
### Discussion  
The results from this randomized trial show that a single intra-articular injection of aMSCs is significantly more effective than one intra-articular injection of PRGF in reducing pain and improving functional limitation and quality of life in dogs with hip OA. To the author's knowledge, the present study is the first that showed that both treatments reported good results from the first month post-treatment and up to six months, although better results were subjectively observed at 6 months in patients treated with aMSCs. The data obtained in the present study supports the use of these therapies as a treatment for OA. Among the wide variety of sources for adult mesenchymal cells [33] in this study MSCs were obtained from adipose tissue due to the ease of extraction and the absence of complications associated with this process [13,34]. Likewise, adipose tissue is a very rewarding source of mesenchymal cells, which are easily harvested and expanded in culture and have a high proliferation rate [19], capable of differentiation into chondrocytes, osteocytes and adipocytes [20]. The main adipose tissue harvest areas in previous studies in dogs are the falciparum ligament [35], lateral thoracic area [36], caudal scapular region [37], intra-abdominal or subcutaneous fat obtained during ovariohisterectomy surgery [38,39] gluteal fat [40], and inguinal region [41,42]. In the current study fat was harvested from the inguinal area due to easy surgical access, the abundant collection and discrete scarring with no postoperative complications in any patients. The use of PRP products especially PRGF technology has been extended to the treatment of OA in single and in serial repeated injections over time [5,10,31,32,43]. The autologous growth factors and proteins released from the fibrin scaffold may play an important role in the repair or regeneration of the damaged cartilage [5]. In the current study, a single injection of PRGF was opted for, in order to compare results without additional variables in the treatment regimen of the two groups. In OA there is an overproduction of destructive substances and inflammation mediators that give rise to a balance in favor of articular cartilage catabolism [44]. The main problem with OA is pain, being the most common reason for consultation [10,44,45], but patients also present with stiffness, fatigue, walking limitations, discomfort, sleep disturbances, anxiety, and decreased quality of life [46]. Options for the treatment of OA vary considerably among authors [32] although biological therapies are a promising way of treating this disease, providing evident and lasting improvement that preserves tissue, improves the clinical signs and enhances articular function [47, 48, 49, 50]. As mentioned, the objectives of treatment with regenerative therapies are the reduction of this parameter with consequent improvement of the functionality, using less aggressive therapies [51]. Both the application of aMSCs [22,52,53], and PRGF [32,54] demonstrate a decrease in the patient's perception of pain. This effect is very important, as it has been shown that even after a joint replacement, 38% in hip and 53% in knee maintain some degree of pain one year after surgery [55]. Assessing the severity of lameness and pain due to OA is more challenging with canine patients than with human patients. The VAS scale has been used in previous studies [32,56], and are accepted methods for assessing pain. In this study, animals in both groups showed significant improvement in pain scores from the first month post treatment, perceived by both evaluators. So, with both therapies, one of the most important goals in the treatment of OA was achieved, the reduction of the pain experienced by patients in the affected area [10,57].