Patellar luxation (kneecap luxation)

What is a patellar luxation?

A patellar luxation is the complete protrusion of the kneecap from the femoral sliding groove (trochlea), usually outwards (laterally). A distinction is made between the initial dislocation and recurring (recurrent) dislocations. Even a single dislocation can damage ligamentous structures and increase the risk of further events.

• First dislocation: often traumatic (e.g. during sports, twisting under stress)
• Recurrent dislocation: repeated episodes, often in the presence of anatomical risk factors
• Subluxation: incomplete slipping out with immediate return to the groove

Anatomy and biomechanics of the patellofemoral joint

The patella transmits the force of the quadriceps through the front knee and runs into the trochlea femoris. Stability is ensured by the shape of the trochlea, the height of the patella, the axis of the leg, the direction of pull of the patellar tendon and soft tissue stabilizers.

• MPFL (medial patellofemoral ligament): most important soft-tissue stabilizer in 0–30° flexion
• Trochlea: bony guide, becomes more important with increasing flexion
• Quadriceps/VMO: muscular guidance and centering of the patella
• TT–TG distance: distance between tibial tuberosity and trochlear center; influences career
• Patella alta (high kneecap): delayed intervention in the trochlea

Causes and risk factors

Often several factors together lead to dislocation. An initially harmless twisting fall can trigger a dislocation if there is an anatomical predisposition.

• Trauma in sports: abrupt braking, change of direction, valgus stress
• Trochlear dysplasia: flat or crested sliding groove
• Increased TT–TG distance or lateralized tibial tuberosity
• Patella alta (high patella) or patellar maltracking
• Joint hypermobility, connective tissue weakness
• X-leg axis, increased Q-angle
• Previous dislocation with MPFL damage

Symptoms and warning signs

The acute dislocation is usually noticeable immediately. Depending on the mechanism and accompanying damage, the symptoms vary.

• Sudden popping out/snapping of the kneecap
• Severe pain, swelling (often hemarthrosis) and restricted movement
• Patella visibly displaced outwards, possibly spontaneous repositioning
• Feeling of instability, buckling, unsteadiness when climbing stairs
• Blockage or sensation of entrapment in osteochondral fragments

Warning signs that require rapid medical evaluation: severe swelling, possible bone or cartilage tear, persistent blockage or sensory disturbances.

First aid for acute dislocation

• Protection and relief: Stop exercising immediately and elevate your leg
• Cooling: at intervals, pay attention to skin protection
• Compression: elastic bandage if possible
• If the misalignment is visible, do not force the reduction; If in doubt, go to the emergency room

After spontaneous repositioning or reduction, an orthopedic assessment should be carried out promptly to identify ligament and cartilage damage.

Diagnostics in our practice

We combine history, careful clinical examination and targeted imaging. The aim is to record the individual risk profile and accompanying damage.

• Clinic: Inspection, pain points, swelling, apprehension test, J-Sign, leg axis
• X-ray: AP, lateral, axial (Merchant/Sunrise) to assess patellar height and axis
• MRI: detection of MPFL lesions, edema, osteochondral injuries
• CT (if necessary): precise measurement of TT–TG distance, trochlear shape, torsion analysis
• Functional diagnostics: muscle status (VMO/external rotators), gait/stair pattern

The diagnosis enables a risk-adapted treatment decision – conservative, surgical or combined.

Classification of the injury and accompanying damage

After an initial dislocation, soft tissue structures, especially the MPFL, are often at least partially torn. It is also crucial whether osteochondral fragments (cartilage-bones) are present.

• MPFL rupture/partial rupture: often located medially patellar or femoral
• Retinacula maceration, hemarthrosis
• Osteochondral flakes on patella or lateral femoral condyle
• Form variants: trochlear dysplasia (Dejour), patella alta, increase in the TT–TG distance

The sum of the factors influences the risk of recurrence and treatment planning.

Conservative treatment: standard for initial dislocation without major fragments

For many initial dislocations without free osteochondral fragments, conservative therapy makes sense. It aims to reduce swelling, stabilize and restore patellar guidance.

• Short-term immobilization/orthosis: e.g. B. Limiting stretching in the first few weeks
• Pain and inflammation management: ice, relief, medication if necessary
• Early, guided physical therapy: VMO activation, quadriceps building, hip and glute muscles
• Coordination/proprioception: sensorimotor training, balance
• Taping/bandages: temporary centering in everyday life and during light activities
• Adaptation to everyday life: avoid stairs, avoid sudden changes of direction at first

The increase in stress occurs gradually and depending on the symptoms. The aim is to have a stable knee position without pain in everyday life - sports development only follows afterwards.

When does an operation make sense?

Surgical stabilization is considered if conservative measures are unlikely to be sufficient or if there are relevant accompanying damages. The decision is made individually and based on the imaging.

• Free osteochondral fragments with risk of entrapment
• Severe trochlear dysplasia, patella alta or significantly increased TT–TG distance
• Persistent instability after adequate conservative therapy
• Recurrent dislocations (see also: Recurrent patellar dislocation)
• Rare special cases with combined axle or torsion problems

Even with a surgical procedure, physiotherapy and a structured rehabilitation program remain the basis for a good functional result.

Common surgical procedures for patellar instability

The choice of procedure depends on the individual findings. Not every procedure is suitable for every patient.

• MPFL reconstruction: Replacement of the torn ligament usually with the body's own tendon; Goal: medial soft tissue stability in the extended position
• Reattachment of the MPFL/medial retinacula: possible in selected recent injuries
• Medializing/distalizing tuberosity transfer osteotomy (TTT): correction of the direction of pull/patellar height with increased TT–TG distance or patella alta
• Trochleoplasty: shape correction for severe trochlear dysplasia in specialized centers
• Cartilage and osteochondral measures: Refixation of larger fragments, cartilage repair techniques according to individual indications
• Lateral release: only selectively and in combination if it can be proven to be useful

The aim of all interventions is to better center the patella and reduce instability. Absolute promises of healing are not possible; Information about benefits and risks is an integral part of the planning.

Rehabilitation and return to sport

Rehabilitation depends on the extent of the injury and therapy. A clear, individually tailored plan increases the chance of resilient function in everyday life and sports.

Timings vary. After a conservative initial dislocation, sporting activities are often possible after several weeks to a few months; After surgery, return may take several months depending on the procedure. Clinical stability, strength symmetry and freedom from pain are crucial.

Preventing relapse: training and everyday tips

• Regular targeted strength training for the quadriceps (VMO), hip abductors and external rotators
• Coordination and balance training, e.g. E.g. one-legged stand, balance boards
• Train movement control during landings and changes of direction
• Consider bandaging or taping in the early loading phase
• Avoid overtiredness and unprepared maximum loads

Course and prognosis

After an initial dislocation, the prognosis is often good with consistent therapy. The risk of recurrent dislocations depends on individual risk factors. Early, structured treatment can reduce feelings of instability and improve function. If there are pronounced anatomical factors or if repeated dislocations occur, targeted surgical stabilization may make sense.

When should you introduce yourself?

• After an acute dislocation or persistent instability
• If there is significant swelling, a feeling of blockage or a snapping phenomenon
• If sports or everyday activities are unsafe or painful
• For a second opinion for planned operations

We clarify whether conservative treatment is sufficient or whether risk factors require stabilization. Transparency about options, benefits and risks is important to us.

Your orthopedics in Hamburg

Our practice at Dorotheenstraße 48, 22301 Hamburg, specializes in conservative and joint-preserving orthopedic treatment. We take the time for diagnostics, advice and an individual therapy plan - from acute care to sport-specific return.