A Needle in the Wrong Place Is a Negative Study

Two patients get “a PRP injection” for the same diagnosis, in the same year, in the same city. One improves. One does not, and concludes the treatment does not work.

They did not receive the same treatment. They may not have received it in the same anatomical structure.

How often a blind injection lands somewhere else

The accuracy of an unguided injection is worse than most people assume, and it has been measured.

At the hip, a systematic review and meta-analysis found ultrasound-guided injections accurate in 100% of cases against 72% for landmark-guided placement. At the shoulder girdle, another meta-analysis found accuracy of 93.6% versus 68.2% at the acromioclavicular joint, 92.5% versus 72.5% at the glenohumeral joint, and — the number worth sitting with — 86.7% versus 26.7% for the biceps tendon sheath.

The same review is honest about where guidance did not change accuracy: for the subacromial space, guided and unguided placement were comparable. Guidance is not a talisman. It matters most where the target is small, deep, or next to something that must not be injected.

Now apply that to a study. If a trial injects a joint blind and a quarter of the injections miss, the trial is not measuring the treatment. It is measuring the treatment diluted by a delivery failure rate — and that result then gets quoted back at patients as evidence that biologics do not work.

“PRP” is not a description of anything

Written on a bill, PRP is roughly as informative as writing “medication.” The orthopaedic profession has known this for years, which is why it published a minimum reporting standard for studies of biologics — covering platelet dose, leukocyte content, activation, volume, and how the preparation was produced.

Adherence to it is poor. A 2024 systematic review of 25 randomized trials in knee osteoarthritis, covering 2,356 patients, found the trials reported on average 53.1% of the checklist items. Not one reached 80%. The worst-reported category was activation, at 14%.

Those variables are not bookkeeping. A meta-analysis of randomized trials found the clinical effect in knee osteoarthritis influenced by the platelet concentration actually delivered. A meta-analysis of 18 level-1 studies found leukocyte-poor preparations producing better subjective knee scores than leukocyte-rich ones. Two clinics can both say PRP, use materially different products, and get materially different results.

What goes in the record for every injection here

1. The diagnosis, and the test that established it — imaging, electrodiagnostics, or a diagnostic block.
2. The anatomical target, named specifically rather than regionally.
3. The guidance modality used, ultrasound or fluoroscopy, with images retained.
4. The preparation: system used, volume, platelet concentration, leukocyte content, whether activated.
5. The published guidance or consensus scenario the indication maps onto.
6. A validated outcome measure before, and at intervals after.
7. What was done alongside it — loading program, rehabilitation, metabolic care.

Seven lines. They are the difference between a treatment that can be evaluated and a charge that can only be disputed. Why that record is written for a reader you have not met.

When the tendon needs debriding, not filling

Not every damaged structure wants an injection. Chronically degenerated tendon tissue is not inflamed tissue waiting for a signal; it is disorganized tissue occupying space where organized tissue should be.

Percutaneous hydro-resection [ultrasound-guided removal of degenerated tendon tissue] addresses that directly. A fine saline jet, placed under real-time ultrasound, is used to break up and remove diseased tissue while leaving healthy tendon intact, through an opening that needs no stitches. It is a structural correction rather than a biological signal, and choosing between the two is a diagnostic decision, not a preference.

The general principle holds across everything on this page: match the tool to what the tissue is actually doing. An injection into disorganized tissue and a debridement of an inflamed joint are both precise procedures aimed at the wrong problem.

What to ask before you let anyone inject you

What is the target, and what proved it. Under what imaging. What exactly is in the syringe, in numbers. And what measurement will tell us in three months whether this worked. A clinic that answers those four in a sentence each is practicing precisely. A clinic that finds the questions unusual is telling you something.

Frequently asked questions

Does ultrasound guidance really change an injection result?

It changes accuracy, substantially, at targets where accuracy is hard. Meta-analyses found ultrasound guidance accurate in 100% of hip injections versus 72% landmark-guided, and 86.7% versus 26.7% for the biceps tendon sheath — while finding no accuracy difference at the subacromial space. Learn more: how image-guided procedures fit into a treatment plan.

What should the record say about what was injected?

System used, volume, platelet concentration, leukocyte content, and whether the preparation was activated — the variables in the orthopaedic profession’s minimum reporting standard. A 2024 review found randomized trials reported barely half of those items on average, which is why results vary between clinics using the same word. Learn more: what a defensible treatment record contains.

Is leukocyte-rich or leukocyte-poor PRP better?

For knee osteoarthritis, a meta-analysis of 18 level-1 studies found leukocyte-poor preparations produced better subjective knee scores. The relevant point for a patient is that the two are different products, and the difference should appear in your chart. Learn more: what the knee evidence actually shows.

What is percutaneous hydro-resection?

Ultrasound-guided removal of degenerated tendon tissue using a fine saline jet, which breaks up and removes diseased tissue while leaving healthy tendon intact. It treats a structural problem rather than delivering a biological signal, and the choice between them is diagnostic. Learn more: how procedures are selected against the diagnosis.

Why do some studies find PRP ineffective?

Several reasons that are not about the biology: the indication studied, the preparation used, the concentration delivered, and whether the needle reached the target. Blind injections miss often enough to dilute a result, and trials frequently do not report the preparation in enough detail to compare. It is also genuinely negative for some indications. Learn more: where the evidence is positive and where it is not.

Where is Injury Experts located?

Injury Experts is at 4477 Woodson Rd, Suite 202, St. Louis, MO 63134, next to Lambert International Airport, serving the St. Louis region in Missouri and Illinois. Call (314) 887-5866 or text (314) 886-5902.

Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP — Board Certified in Anesthesiology, Pain Medicine, Interventional Pain Management, Addiction Medicine, and Obesity Medicine.

This article is for general education and is not medical advice. It does not create a physician–patient relationship. Do not start, stop, or change any medication — including opioid medication — without consulting your physician.