Knee MRI: Indications, the examination procedure and interpretation of findings

The knee is one of the most complex and injury-prone joints in the human body. If knee pain persists for a long time, swelling does not subside or joint function is noticeably impaired, magnetic resonance imaging (MRI) is now part of standard diagnostic practice. A knee MRI provides detailed cross-sectional images of all relevant structures – without exposure to radiation and without any invasive procedure. This article explains when a knee MRI is indicated, which structures can be assessed using this technique, how the examination is carried out and what the results mean.

The knee joint is a compound joint consisting of the patellofemoral joint and the tibiofemoral joint. It connects the thigh bone (femur), the shin bone (tibia) and the kneecap (patella), and is stabilised and kept functional by a complex system of ligaments, menisci, cartilage, tendons and bursae.

This anatomical complexity is the reason why conventional X-rays are of limited value for the diagnosis of soft tissue conditions in the knee: X-rays show bones, but not the menisci, cruciate ligaments, articular cartilage or tendon structures. MRI is the method of choice for a reliable assessment of these structures.

The clinical indication for a knee MRI is determined by a combination of medical history, physical examination and the therapeutic context. Common indications include:

Meniscal lesions

Meniscal tears result both from acute trauma – such as twisting injuries during sport – and from degenerative processes associated with osteoarthritis of the knee. MRI can precisely visualise the location, extent and morphology of a meniscal lesion and is therefore crucial for distinguishing between tears that can be treated conservatively and those requiring surgical intervention.

Ligament injuries

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. MRI findings allow for the reliable diagnosis of complete and incomplete ruptures, as well as the assessment of associated injuries – such as collateral ligament or meniscus lesions. Injuries to the posterior cruciate ligament (PCL), the medial collateral ligament (MCL) and the lateral ligament complex are also visualised on MRI.

Cartilaginous and osteochondral lesions

Cartilage damage to the knee joint is not directly visible on an X-ray. MRI reveals cartilage defects, enables grading according to recognised classification systems (e.g. ICRS, Outerbridge) and provides the basis for treatment decisions – whether conservative management, cartilage transplantation or joint-preserving surgery.

Patellofemoral pathologies

Pain beneath and around the kneecap may indicate chondropathia patellae, patellar instability or patellofemoral pain syndrome. MRI enables assessment of the patella’s cartilage layer, the retinacula and the biomechanics of patellar tracking.

Inflammatory joint diseases

Where inflammatory arthropathies are suspected – such as rheumatoid arthritis, reactive arthritis or crystal arthropathies – MRI is more sensitive than X-ray and can detect synovitis, effusion, bone oedema and erosions at an early stage.

Osteochondrosis dissecans and bone oedema

Bone oedema, subchondral insufficiency fractures or osteochondrosis dissecans are often not visible on conventional X-rays or are underestimated. MRI is the only imaging technique that reliably detects these conditions.

Pre-operative planning and post-operative follow-up

Prior to orthopaedic or arthroscopic procedures, MRI provides the necessary basis for planning. Following operations – such as cruciate ligament reconstruction or meniscus suturing – it is used to monitor recovery and assess the progress of healing.

For knee diagnostics, radiological societies recommend high-field scanners with a field strength of at least 1.5 tesla, although 3-tesla scanners are now regarded as the standard in specialist radiology. The higher field strength enables a better signal-to-noise ratio, thinner slice thicknesses and thus higher resolution – which is clinically relevant, particularly in the assessment of cartilage.

Quartz Healthcare uses 3-Tesla high-field scanners that enable this level of diagnostic precision. AI-supported systems further assist with interpretation by identifying pathological patterns more quickly – though the final assessment always rests with the specialist.

A knee MRI is a non-invasive examination that requires no anaesthesia, involves no radiation exposure and generally requires no special preparation.

Preparation

Before the examination, any metal objects – jewellery, watches, belts – must be removed. Metallic implants are not usually a contraindication, but must be discussed with the radiology team in advance. Pacemakers or certain neurostimulators may be a contraindication; in which case an individual assessment is necessary. There is no specific requirement to fast for a knee MRI.

Procedure

The knee is positioned within a special knee coil that encloses the joint and ensures optimal signal acquisition. The upper body remains completely outside the scanner – a significant advantage for patients with claustrophobia. The scan usually takes 20 to 30 minutes. During this time, the knee must be kept still to avoid motion artefacts. Loud tapping and thumping noises from the machine are normal; earplugs are provided.

Contrast agents (gadolinium-containing substances) are not required in most cases for a standard knee MRI. It is used when inflammatory processes, tumours or post-operative vascularisation need to be assessed.

Interpretation of findings

The results are interpreted by a radiologist specialising in musculoskeletal imaging. All relevant structures are assessed systematically: menisci, cruciate ligaments, collateral ligaments, articular cartilage, patellar tendon, quadriceps tendon, bursa, synovial structures and adjacent bone segments.

The radiological report describes the imaging findings in a structured manner and places them in a clinical context. Interpreting the MRI findings within their clinical context – that is, in conjunction with the patient’s medical history, physical examination and level of distress – is crucial for determining the course of treatment.

Meniscal lesions are classified according to their morphology: horizontal, vertical, radial or complex tears, flap tears and basket-handle tears. Degenerative changes (Grade I–III according to Stoller) are distinguished from clinically relevant tears – an aspect that is of central importance when determining the indication for arthroscopy.

Cruciate ligament lesions appear on MRI as signal changes, loss of fibres or a complete interruption of the ligament’s course. A complete rupture can usually be diagnosed unambiguously; partial ruptures sometimes require clinical correlation.

Cartilage lesions are assessed using the ICRS grading system: ranging from superficial tears (Grades I–II) to full-thickness defects with subchondral involvement (Grades III–IV). This grading system has direct implications for treatment planning.

A normal MRI scan of the knee is highly likely to rule out any significant structural injury – and can therefore provide important guidance for both patients and treating doctors.

Quartz Healthcare carries out knee MRI scans at several locations in North Rhine-Westphalia and Bavaria – using 3-Tesla high-field scanners and sub-specialist radiologists who perform these scans on a daily basis. Appointments are often available within two working days; results can be accessed on the same day via the app or a QR code.

Locations for knee MRI scans: Wuppertal, Regensburg, Münster, Düsseldorf and others.

Book an appointment online: termin.quartz-healthcare.com | Hotline: +49 202 24890