Diagnostic injections

An intra-articular hip injection can be used for diagnostic localization, treatment, or both. Its strongest diagnostic role is determining whether the joint contributes to a mixed pain presentation. Response to injection is a weak prognostic test and should not be used as a pass/fail criterion for arthroscopy. 1-3

Plan the purpose of the injection

The clinical question should be defined before the procedure. For example, an injection may be used to determine whether the dominant groin pain is intra-articular. Image guidance confirms placement. Protocols vary; local anesthetic permits immediate diagnostic assessment, while corticosteroid may be added when therapeutic benefit is intended. Record the agent, dose and volume, laterality, guidance method, and complications.

Assessing the response

• Record baseline pain and the patient’s familiar provocation before the injection.
• Assess the anesthetic window with the same activity or a safe, predefined functional task; a short diary is often more informative than a telephone estimate.
• Separate immediate anesthetic relief from delayed steroid response. Ask what pain improved, how much, for how long, and what pain did not change.
• Integrate the result with history, examination, and imaging.

In a prospective cohort of 52 patients undergoing arthroscopy for FAI, Ayeni and colleagues used a two-week diary after injection and provocative activity. Eighty-one percent reported partial or complete relief, but a positive response had only a small likelihood ratio for a satisfactory six-month modified Harris Hip Score (LR+ 1.15, 95% CI 0.85 to 1.56). A negative response was more cautionary but imprecise (LR− 0.57, 95% CI 0.10 to 1.73). 1

Timing before surgery

Timing should be discussed when the injection is ordered. Wang et al. found an association between injection within three months and postoperative infection in two administrative cohorts; infection rates were 2.16% versus 1.10% in privately insured patients and 2.80% versus 1.05% in Medicare patients. These data are retrospective, code-based, and do not reliably specify injectate, technique, or indication. They support caution rather than a universal biologic cutoff. Local policy and the surgeon’s practice should govern the interval, particularly if corticosteroids are used. 4

A positive injection localizes a component of pain to the joint. It does not prove that the observed morphology is the surgical pain generator or guarantee a good postoperative outcome.

Important considerations:

An injection should not be ordered solely because an insurer or workflow expects it when the history, examination, and imaging are already concordant and surgery may be imminent. The diagnostic benefit should outweigh the potential scheduling and infection-risk consequences.