Acute patellar luxation with cartilage damage

Anatomy and biomechanics: Why the kneecap can dislocate

The kneecap (patella) slides in the groove of the femur (trochlea femoris). It is stabilized by an interaction between the bony form, the capsular ligament apparatus and the muscles.

• Passive stabilizers: medial patellofemoral ligament (MPFL), retinacula, joint capsule
• Active stabilizers: quadriceps muscle, especially the medial portion (vastus medialis obliquus, VMO)
• Bony guidance: shape and depth of the trochlea, position of the patella (patella alta/normal), leg axis
• Articular cartilage: smooth sliding surface on the patella and trochlea, sensitive to shear forces

In the event of a dislocation, the patella usually jumps out of the groove laterally (outside). This can lead to ligament injuries (often MPFL tears) and cartilaginous or bony-cartilaginous detachments (osteochondral fragments).

What does “acute patellar luxation with cartilage damage” mean?

An acute patellar luxation is the sudden dislocation of the kneecap, usually due to twisting or a misstep during sport. In up to a relevant proportion, cartilage injuries occur - from superficial abrasions to torn pieces of cartilage and bone (osteochondral fragments), which as free joint bodies can cause discomfort or blockages.

• Initial dislocation vs. repeated dislocation (recurrences)
• Cartilage-only lesion (pure cartilage damage) vs. osteochondral fracture (cartilage with bone)
• Concomitant injuries: MPFL tear/overstretching, bone bruises, joint effusion/hematarthrosis

Causes and risk factors

The trigger is often a valgus/external rotation moment of the knee joint with slight flexion, for example when changing direction in sport. Whether the kneecap dislocates and how severely the cartilage is injured depends on individual factors.

• Anatomy: flat trochlea (dysplasia), patella alta, increased TT-TG distance
• Ligament laxity, weak medial thigh muscles (VMO)
• X-leg axis, foot misalignments, neuromuscular deficits
• Youth and young adulthood, contact sports
• Previous dislocations or family history

Symptoms and warning signs

• Acute, stabbing pain in the front of the knee
• Visible or palpable malposition of the patella (often spontaneous reduction)
• Rapid swelling (joint cast/hemarthrosis)
• Feeling of instability, “folding away” or feeling of being blocked
• Cracking/scraping, v. a. with a free joint body

Warnings for rapid evaluation: persistent blockage, significant swelling, inability to perform, numbness, visible deformity, fever or redness.

First aid after the event

A self-performed reduction without experience is not recommended. The patella often springs back on its own; However, a specialist check-up still makes sense.

Diagnostics in practice

The aim is to identify accompanying injuries (especially cartilage/bone fragments and ligament injuries), assess the individual risk of recurrence and create a safe treatment plan.

• History: mechanism of accident, first vs. recurrent dislocation, blockages
• Clinical: Effusion, tenderness on the medial edge of the patella (MPFL), apprehension test, patellar lubrication, leg axis and foot statics
• X-ray (AP, lateral, axial/Merchant): Rule out fractures, assess patellar height and trochlea type
• MRI: Assessment of MPFL, cartilage, bone bruise, size/location of osteochondral lesions, loose joint bodies
• CT (selective): preoperative planning for complex anatomy

Larger, displaced osteochondral fragments or free joint bodies with blockage are important findings that are often relevant to surgery. Smaller, stable cartilage lesions are initially treated conservatively.

Classification and severity

• Initial dislocation without relevant fragments: often conservative approach
• Initial dislocation with osteochondral fracture/free joint body: surgical removal/refixation often makes sense
• High instability (pronounced dysplasia, patella alta, significant ligament injury): increased risk of recurrence
• Cartilage damage severity levels (ICRS 1–4): deeper lesions (3–4) influence prognosis and therapy

Conservative therapy: standard for many first dislocations

For initial dislocations without large osteochondral fragments and without relevant blockage, conservative treatment is the first step in accordance with the guidelines. The aim is to control pain, reduce swelling and restore stable, centered patellar guidance.

• Short-term immobilization in an extension splint/orthotic guide (typically 1–2 weeks, depending on pain/effusion)
• Early, pain-adapted mobilization and partial to full weight bearing after medical approval
• Physiotherapy: Activation VMO, hip and pelvic stability, axis control, proprioception
• Lymphatic drainage/swelling management, if necessary kinesiotaping or patellar stabilization orthosis
• Pain and inflammation management as needed and tolerated

The duration until sport-specific stress depends on the symptoms, stability and cartilage findings. A structured rehabilitation program is crucial to preventing recurrent dislocations.

Surgical options: targeted and with clear indications

Surgery may be considered if conservative measures are not sufficient or if there are findings that make prompt intervention useful. These include, in particular, free, blocking fragments or larger osteochondral fractures.

• Arthroscopy: Removal of free joint bodies, smoothing of unstable cartilage edges, microfracturing procedures for localized defects (depending on the situation)
• Refixation of osteochondral fragments: e.g. B. with absorbable pins/screws if size and quality are suitable
• Cartilage reconstructive procedures (selected cases): OATS/mosaicplasty, AMIC, matrix-associated autologous chondrocyte transplantation (MACT) – only after careful indication
• Soft tissue stabilization: medial patellofemoral ligament reconstruction (MPFL reconstruction) in cases of relevant instability
• Corrections to the bone guidance (recurrence/pronounced dysplasia): tuberosity transfer, trochleoplasty - more likely in cases of repeated dislocations and clear anatomy

Which technique is suitable depends on age, activity level, cartilage quality, defect size and anatomical risk factors. We discuss options transparently and, if necessary, plan interventions in collaboration with experienced partner clinics in Hamburg.

Rehabilitation: Phase-oriented return to stability

Splint times, flexion limits and load release may vary after surgical procedures. The rehabilitation plan is determined individually and adjusted regularly.

Course and prognosis

Many patients with initial dislocations without large fragments achieve good function with conservative therapy. However, the risk of new dislocations is increased - especially in young athletes and unfavorable anatomy. Cartilage damage can influence the long-term prognosis and is a reason for consistent rehabilitation and careful follow-up.

• Risk of recurrence: dependent on age and anatomy; Prevention through stabilization training
• Possible long-term consequences: anterior knee pain, chondromalacia, early osteoarthritis with pronounced cartilage defects
• Regular follow-up care: clinical re-evaluation, if necessary follow-up imaging checks

Prevention: What you can do yourself

• Regular strength training for the quadriceps (VMO), hip abductors and core
• Neuromuscular training: jump-landing technique, balance, axis control
• Adapted training increase, sufficient regeneration
• Have leg axis and foot statics checked; If necessary, insoles/shoe advice
• Sport-specific technical training; If necessary, temporary patella stabilization orthosis when returning from dislocation

When should I see a doctor?

• After every first-time patellar luxation - even if the kneecap has spontaneously sprung back
• If there is severe swelling, a feeling of blockage or persistent pain
• With repeated buckling events or a feeling of insecurity in the knee
• If there is numbness, a feeling of cold or a significant misalignment

Our practice is located at Dorotheenstraße 48, 22301 Hamburg (Winterhude). We will clarify whether a conservative approach is sufficient and accompany you through the rehabilitation.

This is how we support you in Hamburg-Winterhude

As an orthopedic specialist practice, we focus on thorough diagnostics and conservative, function-oriented treatment. In the case of cartilage damage following a patellar luxation, we carefully examine whether purely conservative therapy makes sense or whether additional surgical treatment can be expected to benefit.

• Conservative acute care including swelling management and orthotic advice
• Individual rehabilitation plans with evidence-based stabilization and coordination training
• Imaging clarification (organization MRI) and structured follow-up checks
• Transparent second opinion and surgical indication check; Coordination with experienced partner clinics in Hamburg

The goal is stable knee function that is suitable for everyday use and sports. We provide honest information about expected outcomes and avoid unrealistic promises of healing.