This prospective study will be quantitatively analyzing the effectiveness of platelet-rich-plasma (PRP) injections into the sacroiliac (SI) joint in relieving sacroiliitis and low back pain originating from the SI joint. The effectiveness of PRP injections on joint pain has been well studied in the knee and shoulder. PRP injections are performed on the SI joint commonly, but there is little research documenting their effectiveness when compared to other interventions. This study will be a small pilot study to aid in closing this knowledge gap. Additionally, these injections will be performed under ultrasound guidance. Ultrasound has been proven to be of equal reliability to fluoroscopy and has the advantage of shorter time to administer and no radiation. There will be one arm to this study. The data collected will be compared to existing studies on corticosteroid SI joint injection. The experimental arm consists of the PRP injection. The PRP will be injected into the joint using the exact same technique via physical exam, special tests, and ultrasound guidance as performed in our previous studies. The outcomes will be measured with the Numeric Rating Scale for Pain (NRS) and the Oswestry Disability Index (ODI) prior to the injection, immediately post-injection, 2 weeks, 4 weeks, 3 months, and 6 months post-injection. The investigators hypothesis is, "Platelet-Rich Plasma Injections in the Sacroiliac Joint using ultrasonography in conjunction with physical examination and Point of Maximal Tenderness will produce statistically significant pain relief for more than 3 months as measured by the Numeric Rating Scale for Pain (NRS) and Oswestry Disability Index (ODI)."

PRP is not just an additional tool for physicians to use, but a potential treatment for underlying joint pathology. PRP is one of the closest treatments that exists for a definitive solution for inflammatory and degenerative joint disease. PRP is currently being used for dysfunction of the shoulder joint, knee joint, sacroiliac joint, facet joints, intervertebral discs, rotator cuff, hamstrings, and others. It has been extensively researched for osteoarthritis, tendon, and ligament injury of the knee, but little research has documented the short or long-term effects on the sacroiliac joint. A brief search on PubMed provides only two articles, one of which is a case study, and neither were performed in the United States. PRP is the future of orthopedics and physical medicine as well as a gateway to curing degenerative and inflammatory joint disease.

Furthermore, the use of ultrasound guided injections has helped increase the success rate because it provides a method for visualizing the path of the needle to a precise location. In recent studies, authors have indicated the use of a curvilinear transducer to be the most successful, as well as injections administered to the lower one third of the sacroiliac joint, to be adequately effective in diagnosing and treating sacroiliac joint pain. Disadvantages surrounding fluoroscopy include inconvenience, cost, radiation, and exposure to contrast media. Arranging the procedure can take extensive time and resources. The procedure can be costly for the patient, especially if it does not produce long-term results, and radiation exposure can have long-term consequences for the patient's health, rendering it a questionable treatment for chronic low back pain. As ultrasound guided and fluoroscopic sacroiliac joint injections present themselves as front-runners for diagnosis and treatment of sacroiliac joint-induced low back pain, the benefits and downsides to both are heavily weighed and compared. The next step moving forward in the treatment of the SI joint is administering PRP injections while utilizing ultrasonography for image guidance. The investigators believe this combination will provide the most immediate and long term benefit to patients as well as fewer risks from medications, corticosteroids, and fewer risks and downsides from fluoroscopy, such as radiation and cost.

Experimental design will be a nonrandomized trial (or quasi-experiment). The specific study design to be used is pretest-posttest design. The independent variable will be the PRP injection. The dependent variables of interest include the NRS and Oswestry Disability Index (ODI) recording pre-injection, immediately post-injection, 2 weeks, 4 weeks, 3 months, 6 months post-injection.

Most studies in the past look at short-term and moderate-term results up to approximately six months to one year. Many studies state a limitation to their data is the lack of long-term investigation into pain, disability, and function more than 12 months. This is partly due to losing patients to follow up. Patients whose pain resolved have no reason to return for further evaluation.

The investigators will take measures to avoid study bias and confounding by ensuring patients have been correctly diagnosed with sacroiliitis via special tests and physical examination as well as PMT. Additionally, to avoid confounding, the investigators will not administer PRP injections to patients who have had a corticosteroid injection in the SI joint within the last three months or received significant benefit from a corticosteroid injection. The efficacy of corticosteroids in the joint begin to dwindle starting at approximately three months.

This information will be recorded in each patient's chart as well as an Excel file only accessible to key personnel working on the study. The following data will be recorded form each patient: current pain scale using the NRS and their functionality using the ODI.

Inclusion Criteria:

• Diagnosis of sacroiliitis
• Age 18 to 80 years old
• Chronic low back pain
• SI joint pathology is the predominant source of pain
• Positive Fortin Finger Test (PMT)
• Joint anatomy is identifiable using ultrasonography
• Patient has no other comorbidities that contraindicate the procedure
• Patient has attempted physical therapy and corticosteroid injections with local anesthetic -Previous injections of lidocaine and corticosteroid provided at least minor immediate relief
• Patient must not have had a corticosteroid injection in the SI joint within the last three months
• Patient must consent to the procedure

Exclusion Criteria:

• Patients under the age of 18 (Subjects under the age of 18 will not be included in this study due to the continued growth and development of their joints and unstudied effects on children.)
• Over the age of 80
• Multiple pain sources and multifactorial pain sources that complicated or confound diagnosing the SI joint as the primary and predominant pain generator that may contribute to low back pain (including but not limited to: lumbar diagnosis, lumbar radiculopathy, intra or extra-articular hip pathology to include acetabulum and femoral head, lumbo-sacral joint pathology, intervertebral disk disease, spondylolisthesis/spondylosis/spondylolysis of lumbar vertebra)
• Immunosuppressed/immune compromised
• Underlying comorbidities that contraindicate the procedure (including but not limited to polycythemia, coagulation disorder, or malignancy).