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Patellar Instability

Recurrent patellar dislocation or subluxation due to trochlear dysplasia, MPFL insufficiency, patella alta, or rotational malalignment, often requiring tailored reconstruction.

Written by: Saygı Hospital Health Guide Editorial Board
Published:

This content is for general information; please consult your physician for diagnosis and treatment.

References (5)

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What is Patellar Instability?

The patella is stabilized by static (MPFL, trochlear groove, patellar tendon, retinaculum) and dynamic (vastus medialis obliquus, quadriceps angle) restraints. Lateral patellar dislocation occurs when these restraints fail under valgus, internal tibial rotation, and quadriceps contraction.

Anatomical risk factors (Dejour classification of trochlear dysplasia A–D, patella alta — Caton-Deschamps index >1.2, increased TT-TG distance >20 mm, increased femoral anteversion, external tibial torsion, genu valgum) cumulatively determine instability risk. First-time dislocation has 17–60% recurrence rate depending on these factors.

Clinical assessment: history of giving way, J-sign, apprehension test, glide test, lateral patellar tilt and translation. Imaging: lateral knee radiograph (Insall-Salvati, Caton-Deschamps), Merchant view (sulcus angle, congruence angle), CT or MRI for trochlear dysplasia grading, TT-TG measurement, patella alta, and chondral lesions; MRI evaluates MPFL injury location and any osteochondral fracture.

Symptoms

Acute lateral patellar dislocation with giving way and patellar deviation
Recurrent episodes of patellar dislocation or subluxation
Sensation of patella "slipping out" with twisting movements
Anterior knee pain, catching, or locking
Apprehension when knee is flexed beyond 30°
Effusion and hemarthrosis after dislocation
Lateral retinacular tenderness, MPFL tenderness at medial femoral epicondyle
Functional limitations in sports, stairs, squatting

Risk Factors

Trochlear dysplasia (Dejour classification A–D)
Patella alta (high-riding patella)
Increased TT-TG distance >20 mm
Increased femoral anteversion or external tibial torsion
Genu valgum, increased Q-angle
Generalized ligamentous laxity (Beighton score)
Female gender, adolescent age (peak 15–19 years)
Family history of patellar instability
Previous patellar dislocation (recurrence risk)

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Acute patellar dislocation — emergency reduction (often spontaneous), orthopedic evaluation
  • Recurrent dislocations or subluxations — surgical consultation
  • Apprehension and functional limitation in sports
  • Symptoms of osteochondral fracture after dislocation (mechanical locking, large effusion)
  • Failed non-operative management after 6–12 weeks

Treatment Methods

01
First-time dislocation without osteochondral fracture: brace immobilization 3–6 weeks (some centers use early mobilization), physiotherapy emphasizing VMO strengthening, hip abductor and core strengthening, neuromuscular control
02
Acute MRI to identify MPFL tear location, trochlear injury, and osteochondral fracture; arthroscopic removal/fixation of large osteochondral fragments
03
Recurrent instability: anatomical risk factor analysis (Dejour classification, TT-TG, patellar height, alignment) guides procedure selection
04
MPFL reconstruction (most common): autograft (gracilis, semitendinosus) or allograft, double-bundle technique, anatomic femoral and patellar fixation; success rate 85–95% in patients without major bony abnormalities
05
Tibial tubercle osteotomy (TTO): medialization (Elmslie-Trillat) for TT-TG >20 mm, distalization (Fulkerson) for patella alta, anteromedialization (Fulkerson) for combined patella alta and lateral facet chondrosis
06
Trochleoplasty (Dejour, Bereiter, deepening trochleoplasty): reserved for high-grade trochlear dysplasia (B, C, D) with continued instability after MPFL reconstruction; technically demanding
07
Lateral release: only when lateral retinacular tightness with patellar tilt; avoid as standalone procedure (results in medial instability)
08
Rotational osteotomies (femoral derotation, tibial derotation): for severe rotational malalignment contributing to instability
09
Articular cartilage management for chondral lesions: microfracture, OATS, MACI, particulate juvenile cartilage allograft
10
Postoperative rehabilitation: brace 6 weeks, progressive ROM, weight-bearing as tolerated, return to sport at 6–12 months depending on procedure
11
Pediatric patients with open physes: avoid TTO and trochleoplasty until skeletal maturity; modified MPFL reconstruction techniques
12
Long-term: maintain VMO strength, neuromuscular control, brace for high-risk activities, monitor for chondromalacia progression

Which Department to Visit?

You can visit our Ortopedi ve Travmatoloji department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.