A marathon training block is a fragile thing. Twelve to sixteen weeks of accumulated fitness can end in a single overtrained week, and the injuries that end it are almost never what a runner expects. They are not muscle tears. They are the small, quiet, load-related failures of bone and cartilage that hide from X-ray, sit under the radar of a physio’s hands, and only show up on MRI. This is the guide to which scan to book, when, and how to time it to a race that is already in the calendar.
The three injuries that most reliably end a training block, in order of how often we see them at Pulse Atlas in the six weeks before a spring or autumn marathon, are patellofemoral pain, hip labral tears and tibial stress fractures. None of these are diagnosed by X-ray. All three are diagnosed by MRI. And all three, if caught four to six weeks before race day, can still leave a viable path to the start line.
One-line answer
If a running injury has changed your gait, woken you at night, or held at rest for more than three days, book an MRI of the specific joint or bone in question - not an X-ray - and do it inside a week, not at taper.
Patellofemoral syndrome and PFJ MRI
Patellofemoral pain, often shortened to PFPS or “runner’s knee”, is the single most common overuse presentation in UK distance runners. The pain sits under or around the kneecap, worsens on downhills and on stairs, and characteristically gets worse the further into a long run you go. It is a real, biomechanical failure of the joint - not a nuisance to be run through.
An X-ray of the knee for suspected PFPS is almost always normal, because the problem is not bony. A good musculoskeletal MRI of the knee shows the four things that actually matter for a runner: cartilage thinning under the patella, bone marrow oedema at the patellofemoral joint (a sign of overload, not damage), patellar tendon signal changes at the lower pole, and any incidental meniscal or ligament involvement that a physio’s hands would miss.
The reason this matters at race build is that a runner with grade 1 chondral change and a hot patellofemoral joint can still race, on a modified plan, with a strength and load rework. A runner with a full-thickness cartilage defect cannot, and needs to know that six weeks out - not on race morning.
Hip labral tears in runners: MRA vs MRI
Hip pain in a marathon runner is under-diagnosed by roughly a decade, because it does not present the way people expect. It is not always groin pain. In the majority of runners it presents as a deep, catching, C-shaped pain around the front of the hip that appears on longer runs and disappears at rest, or as a persistent lower-back or buttock ache that resists every physio intervention. Femoroacetabular impingement and labral tears sit behind most of these cases.
Standard MRI of the hip is not sensitive enough for labral pathology. The accepted gold standard is an MR arthrogram, or MRA - a hip MRI performed after a radiologist injects a small volume of dilute gadolinium contrast directly into the hip joint under ultrasound guidance. The contrast distends the joint capsule, and any tear in the labrum lights up as a bright tracking of dye. Nothing else in imaging can see it as reliably.
The practical implication for runners: if a physio or sports doctor suspects a labral tear, ask for MRA of the hip, not standard MRI. A cheap standard MRI booked online, without a referring clinician who knows to specify MRA, is the single most common wasted scan we see. It reports as “no significant abnormality” and the tear is still there.
| Injury | First-line scan | Typical private wait |
|---|---|---|
| Patellofemoral syndrome | MRI knee | 2 to 5 days |
| Hip labral tear / FAI | MR arthrogram (MRA) hip | 3 to 7 days |
| Tibial stress fracture | MRI lower leg | 2 to 5 days |
| Metatarsal stress fracture | MRI foot | 2 to 5 days |
| Plantar fasciitis (chronic) | MRI foot | 2 to 5 days |
| Achilles tendinopathy | Ultrasound or MRI ankle | Same day / 2 to 5 days |
Tibial and metatarsal stress fractures (invisible on X-ray for 2-3 weeks)
This is the injury that catches the most runners out, and the one where the wrong first scan wastes the most time. A stress fracture is a bone failure caused by cumulative load - a training-volume error, a sudden shoe change, a hard block on concrete. The classic runner presentation is a sharp, focal pain on the shin or on the top of the foot that started as a niggle, got worse over a week, and now hurts to hop on.
X-ray of the affected bone will be normal for the first two to three weeks. That is not radiographer error - it is the biology. Stress fractures only become visible on X-ray once callus has started to lay down, which is well after the injury needs to have been diagnosed. MRI, by contrast, shows the bone marrow oedema of a stress reaction within days of symptoms, before the cortical fracture line appears. The scan grades the injury on the Fredericson scale from 1 (oedema only) to 4 (full cortical fracture), and each grade maps to a well-established return-to-run timeline.
Plantar fasciitis MRI when conservative fails
Most plantar fasciitis does not need an MRI. Six weeks of load management, calf and intrinsic-foot strength, a night splint and shoe changes will resolve the majority of cases. The runners who need imaging are the ones where the pain has held past twelve weeks of good conservative care, or where the pain profile does not fit a straightforward plantar fasciopathy.
An MRI foot in this group serves two purposes. First, it grades the fascia itself - thickening, oedema, partial or full-thickness tear. Second, and more importantly, it rules out the diagnoses that mimic plantar fasciitis and get missed for months: calcaneal stress fracture, tarsal tunnel syndrome, and Baxter’s nerve entrapment. Any of these needs a fundamentally different treatment pathway, and none of them are diagnosed by an X-ray or a physio’s hands.
