Suspected labral tear — shoulder instability or femoroacetabular impingement

ACR AC Chronic Shoulder Pain (2022 rev); ACR AC Chronic Hip Pain; SSR direct MR arthrography white paper (2023)

Radiographs first for the bony morphology, then a direct arthrogram for the labrum itself. MR arthrography is the reference standard; CT arthrography is its genuine substitute — and only its substitute — when the patient cannot go in the magnet or when metalwork makes the MR study non-diagnostic.

A young or middle-aged patient with mechanical symptoms referred from orthopaedics or sports medicine: recurrent shoulder dislocation, subluxation or a painful catching shoulder after a dislocation; or groin pain with impingement signs and a cam or pincer morphology on radiographs.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

MR safety

A non-conditional or unknown implant changes which study is possible, not just which checks apply.

Recent surgery

Days since the relevant operation, where the pathway depends on it.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Limb radiograph — two orthogonal views

Limb radiograph

What we'd amend, and why

Radiographs are the initial study. In the shoulder they show glenoid and humeral head bone loss after recurrent dislocation, which is what decides between a soft-tissue repair and a bone-block procedure; in the hip they show cam and pincer morphology, acetabular dysplasia and joint space loss. Advanced arthritis on either is the finding that most often retires the labral question before any injection is contemplated.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwaystandard — MRI available — no device contraindication or metalwork declared
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.

Worth asking the referrer (4)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Which joint, and is the question instability or impingement rather than the cuff, the meniscus or degenerative pain?
An arthrogram is an invasive procedure and is only justified by a labral, capsular or intrinsic-ligament question. A cuff or degenerative question is answered better, and without an injection, by ultrasound or conventional MRI.
Can this patient actually have an MRI — implanted device, retained metal, or claustrophobia severe enough that a previous scan was abandoned?
It is the single fact that decides between MR and CT arthrography. Implanted-device status travels with the request; severe claustrophobia and previous abandoned scans do not, and the request is the only place they can be stated.
Has this joint been operated on, and is there metalwork — suture anchors, screws, a resurfacing or an arthroplasty — in or adjacent to it?
Metal near the joint is what makes MR arthrography non-diagnostic and CT arthrography the better study. The presence of metal, not the date of the operation, is the deciding fact, and only the referrer can state it.
Is the skin over the planned puncture site intact and uninfected, and what is the anticoagulation status?
Both arthrograms begin with a joint injection. Infected skin over the approach is a contraindication, and anticoagulation changes the plan for the procedure — neither is a contrast-safety question.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

MRI not possible — non-conditional or unknown implanted device

Role	Study & protocol	Why this answers the question
First line	CT Arthrogram CT Arthrogram — Post Intra-Articular Contrast	This is the indication CT arthrography exists for. Dilute iodinated contrast is injected into the joint under fluoroscopic or ultrasound guidance and the joint is then scanned thin-section: distension separates the labrum from the glenoid or acetabular rim exactly as it does in MR arthrography, and multiplanar reformats — radial for the hip labrum, oblique coronal and sagittal for the shoulder — show the labral base, the articular cartilage contour, loose bodies and glenoid or femoral head bone loss. Where the patient cannot enter the magnet it is the genuine substitute for the MR study rather than a compromise, and it quantifies bone loss better than MRI does. Radiographs, if not already available, precede it. The contrast is intra-articular: nothing is given intravenously, so this is not a renal or metformin decision. It is an invasive procedure, and its real safety questions are aseptic technique, image guidance, consent for the small risk of septic arthritis, and intact uninfected skin over the approach.
First line	Limb radiograph Limb radiograph — two orthogonal views	Radiographs remain a correct first move here rather than a hurdle: glenoid and humeral bone loss, cam and pincer morphology, acetabular dysplasia, arthritis and loose bodies all change the operation being planned, and in a patient who cannot have MRI they are also what tells you whether the arthrogram is worth the injection at all. They are listed alongside the arthrogram rather than ahead of it because by the time instability is the referral they have usually already been taken.
Problem solving	CT Extremity / Musculoskeletal CT Extremity — Unenhanced, Thin Section	Unenhanced CT for the patient in whom the joint should not be injected — infected or broken skin over the approach, uncorrected coagulopathy, or a patient who declines the procedure. It answers the bony half of the question well: glenoid and humeral head bone loss for a stabilisation decision, femoral head-neck morphology, and ossified loose bodies. It does not show the labrum, so a negative study does not exclude a tear.

The device status is what routes this patient, and it is a routing decision, not a refusal: the labral question still gets an answer, by a different route.
A device that is merely unknown belongs here too. Characterising it and returning to MR arthrography later is entirely reasonable where the operation is not imminent; what is not reasonable is offering a scan the patient cannot have.
Severe claustrophobia and an abandoned previous MRI are the other legitimate reasons to be on this pathway. The patient model does not carry them, so they have to be stated on the request.
Nothing is injected intravenously anywhere on this pathway. Renal function and metformin do not enter into it.

Post-operative joint — metalwork may defeat MR arthrography

Role	Study & protocol	Why this answers the question
First line	CT Arthrogram CT Arthrogram — Post Intra-Articular Contrast	Where suture anchors, screws, a resurfacing or an arthroplasty sit in or beside the joint, susceptibility artefact from the metal blooms across exactly the structures the MR arthrogram was requested to show, and the study comes back non-diagnostic. CT arthrography is far less troubled by metal: the intra-articular iodine outlines the labral remnant, the repair site and the articular surface, loose bodies and cement or anchor-related lucencies are directly visible, and a dual-energy acquisition allows a virtual unenhanced reconstruction that separates dense contrast from bone. Contrast is intra-articular only — there is no intravenous injection and therefore no renal or metformin consideration — but the injection is invasive, needs image guidance and aseptic technique, and must not be performed through infected skin.
First line	MR Arthrogram (Direct) MR Arthrogram — shoulder	Equally correct, and the better study, where the metal load is small or sits away from the joint — an all-suture repair, a single distant screw, or hardware that has since been removed. Direct MR arthrography still shows the soft tissues, the capsule and the marrow that CT cannot, and a metal-artefact-reduction sequence set recovers a great deal. The question the request has to answer is how much metal there is and where it is, not how long ago the operation was.
First line	Limb radiograph Limb radiograph — two orthogonal views	Radiographs of the operated joint are the study that decides between the two arthrograms, which is why they are a correct first move rather than a formality: they show what metal is present, where it sits relative to the labrum, whether an implant has loosened or migrated, and whether arthritis has overtaken the original question.

All three steps are endorsed first moves. The card deliberately does not rank the two arthrograms against each other, because the ranking depends on a fact the patient model does not carry — how much metal is in the joint — and a false ranking here would send half these patients a correction they should ignore.
This fork is entered on the post-operative flag alone. If the joint was operated on but holds no metal, the ordinary pathway applies and MR arthrography is the study; the radiograph is what settles it.
The flag says nothing about how recent the operation was, and that matters for the injection rather than for the choice of arthrogram. A joint days or a few weeks out from surgery is not an elective arthrography candidate: postoperative marrow and capsular signal, effusion and granulation tissue make the study uninterpretable, and puncturing a recently operated joint carries an infection risk that a non-urgent instability question does not justify. This is a fork for the failed repair months or years later, not for the early postoperative period — and early postoperative pain with fever or raised markers is the septic arthritis question, not this one.
Conventional MRI without intra-articular contrast is the weakest option in an operated joint: the repaired labrum is already irregular, and without distension a re-tear and a healed repair look much the same.

MRI available — no device contraindication or metalwork declared

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Limb radiograph Limb radiograph — two orthogonal views	Radiographs are the initial study. In the shoulder they show glenoid and humeral head bone loss after recurrent dislocation, which is what decides between a soft-tissue repair and a bone-block procedure; in the hip they show cam and pincer morphology, acetabular dysplasia and joint space loss. Advanced arthritis on either is the finding that most often retires the labral question before any injection is contemplated.
Second line	MR Arthrogram (Direct) MR Arthrogram — shoulder	Direct MR arthrography is the reference standard for the labrum once radiographs have set the bony scene. A small volume of dilute gadolinium injected into the joint under image guidance distends the capsule and drives contrast into a tear, and fat-suppressed T1 in the planes aligned to the joint — with radial imaging for the hip labrum — shows the labral base and the capsular structures that lie undetectably flat on an unenhanced study. It is an invasive procedure and is vetted as one: image guidance, aseptic technique and no injection through infected skin.
Second line	MRI Shoulder MRI Shoulder — routine	Conventional shoulder MRI is a reasonable substitute for the arthrogram in an older patient, in a shoulder with an effusion that provides its own distension, and wherever the differential is broad enough that marrow, cuff and extra-articular findings matter as much as the labrum. It under-calls small labral and capsular tears, which is precisely why the arthrogram exists.
Second line	MRI Hip MRI Hip — routine	The equivalent for the hip, and at 3T with a dedicated small field-of-view protocol it is close enough to arthrography for many surgeons that an injection is no longer routinely required. It also covers the alternatives a groin-pain referral has to exclude — stress fracture, osteonecrosis, athletic pubalgia — which an arthrogram-only study does not.
Problem solving	CT Arthrogram CT Arthrogram — Post Intra-Articular Contrast	CT arthrography is on this pathway but is not where a patient with an available magnet should start. Its legitimate triggers are all reasons the MR study cannot be done or cannot be read: a non-conditional or unknown implanted device, claustrophobia severe enough that a previous scan was abandoned, metalwork that will bloom across the labrum, or no realistic MRI access within the timeframe the surgical decision needs. Where none of those applies, MR arthrography answers the same question, shows the marrow and the capsule as well, and does it without ionising radiation. The injection itself is the same procedure with the same procedural safeguards, and the iodine goes into the joint rather than into a vein.

The MR arthrogram is second-line rather than first-line because it is an injection, and the radiograph in front of it genuinely changes whether the injection is worth doing.
If the request states a reason the patient cannot be scanned that the record does not carry — severe claustrophobia, an abandoned previous MRI, no MRI access in the surgical timeframe — read this card on the MR-unsafe pathway instead, where CT arthrography is first-line.

Pitfalls

This card covers the shoulder and the hip, and nothing in a request tells the engine which joint is in question — so the protocol named in the verdict is the shoulder one by convention. For a hip labral question read it as mri-arthrogram-hip: radial imaging around the acetabular rim, a different coil and a different injection route. The named protocol is a label here, not an instruction.
Treating a CT arthrogram as if it were an intravenous contrast study. The iodinated contrast is injected into the joint, there is no systemic vascular load, and asking for an eGFR or worrying about metformin before a joint injection is over-flagging — which trains referrers to ignore the safety panel that will one day matter.
Missing the safety questions that do apply: this is an invasive image-guided procedure needing an aseptic operator, fluoroscopic or ultrasound guidance, and consent covering post-procedural pain and the small risk of septic arthritis. Infected or broken skin over the planned puncture site is a contraindication to the injection.
Requesting a CT arthrogram for a patient who could perfectly well have an MR arthrogram. It adds ionising radiation and answers less, and the only things that justify it are an inability to do or to read the MR study.
Expecting a CT arthrogram to answer a marrow question. Bone oedema, occult fracture and osteonecrosis are MRI diagnoses; a normal CT arthrogram does not exclude any of them.
Requesting an arthrogram of either kind for a degenerative or cuff question, where it adds an injection without adding to the answer.
Scanning late after the injection. Intra-articular contrast is resorbed and diluted, and the delay between the injection list and the scanner is the commonest avoidable cause of a non-diagnostic arthrogram.
Accepting conventional MRI in an operated joint and reading a persistently irregular labrum as a re-tear; without distension a healed repair and a recurrent tear look much the same.
Forgetting that glenoid bone loss, not the labral tear, is often the finding that changes the operation — and that CT quantifies it better than MRI does.

Priors — what to pull first

The operation note is worth more than any previous report in an operated joint: what was repaired, with what, and how much metal was left behind is exactly what decides between the two arthrograms.
Previous radiographs establish whether glenoid or femoral head bone loss is new, and serial loss after repeated dislocations is itself a surgical trigger.
A previous arthrogram of either kind makes today’s study a comparison, and the injected volume and dilution used last time are worth knowing before repeating it.

What makes a good request

This is not the rotator cuff question and it is not degenerative hip pain. The labral question is asked when instability or impingement is the clinical problem and a surgical decision — stabilisation, labral repair, osteochondroplasty — depends on the answer.
Radiographs come first and are rarely wasted: glenoid and humeral bone loss, cam and pincer morphology, joint space loss and a dysplastic acetabulum all change the operation, and advanced arthritis frequently retires the labral question altogether.
Direct arthrography distends the joint and separates structures that lie flat against each other on an unenhanced study. That is the whole mechanism, and it is the same mechanism whether the injected agent is dilute gadolinium (MR) or dilute iodine (CT).
Choose the arthrogram by what will actually be diagnostic in this patient: MR arthrography when the magnet is available to them, CT arthrography when it is not, or when metalwork in or next to the joint would destroy the MR images.
CT arthrography answers the surface questions — labrum, articular cartilage contour, loose bodies, glenoid and femoral head bone loss, which it quantifies very well. It does not answer marrow questions: bone oedema, occult fracture and osteonecrosis are MRI diagnoses and CT arthrography does not substitute for them.
Both arthrograms are image-guided joint injections performed under fluoroscopic or ultrasound guidance by an operator who does them routinely, with aseptic technique and consent covering post-procedural discomfort and the small risk of septic arthritis. Infected or broken skin over the planned approach is a contraindication to the injection, not a caveat on the scan.
The iodinated contrast in a CT arthrogram is injected into the joint, not into a vein. There is no systemic vascular contrast load, so an eGFR is not part of this request and metformin is irrelevant to it — asking for either is over-flagging, and it teaches referrers that the safety panel can be ignored.

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Arthrogram — Post Intra-Articular Contrast Limb radiograph — two orthogonal views CT Extremity — Unenhanced, Thin Section MR Arthrogram — shoulder MRI Shoulder — routine MRI Hip — routine

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

ACR Appropriateness Criteria — Chronic Shoulder Pain: 2022 Update · ACR Appropriateness Criteria
ACR Appropriateness Criteria — Chronic Hip Pain — Suspected labral tear and femoroacetabular impingement variant · ACR Appropriateness Criteria
SSR White Paper — guidelines for utilization and performance of direct MR arthrography. Skeletal Radiol 2023 · Other
Shoulder arthrogram. StatPearls, NCBI Bookshelf. · Primary literature
Dual-energy CT arthrography in shoulder instability: iodine removal and 3D glenoid reformats. Skeletal Radiol 2022. · Primary literature
ACR Manual on MR Safety (2024 update) · ACR MR Safety
Image Gently — child-sizing the CT dose; size-based protocols and accreditation of paediatric CT dose indices · Image Gently
Strauss KJ et al. Image Gently: Ten Steps You Can Take to Optimize Image Quality and Lower CT Dose for Pediatric Patients (AJR) · Image Gently
AAPM Pediatric Routine Abdomen and Pelvis CT Protocol — size-based technique parameters · Other

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.