Definition

Abnormal movement of the patella within the trochlea, which is particularly symptomatic at the start of flexion. Various symptoms may occur, particularly retropatellar knee pain, palpable and audible crepitations and a feeling of instability. The condition may be due to purely functional causes, such as excessive tension in the lateralising muscles (vastus lateralis and rectus femoris) and insufficient tension in the vastus medialis (particularly its VMO component), or it may have structural causes such as patellar dysplasia, innervation disorders or insufficient depth of the trochlea. These symptoms occur primarily under load, but also after prolonged sitting, a phenomenon known as the ‘theatre sign’. Misalignment can lead to soft-tissue irritation, as well as changes to the retropatellar cartilage such as PFPS or retropatellar osteoarthritis, and, of course, patellar dislocation. These problems are particularly evident during slight flexion; with further flexion, the patella glides much more smoothly within the trochlea. If symptoms such as a sensation of locking, acute swelling or rest pain occur, this must be investigated; a dislocation must be treated immediately.

Cause

1. Absent or too loose MPFL (transverse medial retinaculum)
2. Imbalance between the lateral and medial (VMO) quadriceps components
3. Trochleodysplasia
4. Patellar dysplasia

Predisposing

1. Torsion of the tibia relative to the femur and a lateral displacement of the tuberosity of the tibia
2. Neuropathic disorders
3. unfavourable Q-angle
4. large distance between the tuberosity of the tibia and the trochlea
5. displaced tuberosity of the tibia
6. Patella high
7. Hyperlaxity, for example in the context of hypermobility
8. previous traumas
9. Movement patterns involving external rotation of the lower leg at the knee joint, such as hip internal rotation / adduction with compensatory lower leg exorotation
10. Kinetics errors when jumping and landing
11. Shortcomings in training, such as technical shortcomings and equipment issues
12. Growth spurts

Symptoms

1. ventral, retropatellar knee pain that is aching or stabbing in nature, particularly during activities such as standing up, going down stairs or squatting
2. palpable and audible crepitations
3. A feeling of instability when bending and stretching
4. swelling, if any
5. where applicable, the ‘giving way’ phenomenon
6. A drop in performance and uncertainty in sport

Diagnosis

1. Test and symbol: J-sign, Apprehension
2. X-rays and MRI to assess bone structures and soft tissues: cartilage, ligaments, in particular MPFL (transverse medial retinaculum) and oedema

Complications

1. Patellaluxation
2. PFPS
3. Retropatellar osteoarthritis
4. Recurrences following conservative treatment due to a deterioration in physical activity patterns

Therapy

1. A conservative approach where possible: improving muscle function, particularly by training the VMO, and reducing tension in the quadriceps fibres that cause the patella to shift laterally. Initial results are often seen after 4–6 weeks, with lasting improvement from 8–12 weeks onwards
2. Load control
3. Sport: Technical training, equipment optimisation
4. If you are prone to hyperpronation: insoles
5. Apply a cold compress if necessary; take NSAIDs for pain
6. more frequent changes of posture
7. where appropriate, MPFL (transverse medial retinaculum) reconstruction
8. if necessary, repositioning osteotomy of the tuberosity of the tibia
9. in cases of trochlear dysplasia-induced instability: trochleoplasty
10. For torsional deformities: derotational osteotomy
11. if necessary, lateral release

DD

1. ITBS (Runner’s knee
2. Patellaspitzensyndrom (Jumper’s knee)
3. Plica Syndrome
4. Hoffa’s syndrome
5. Chondromalazia patellae
6. Retropatellar osteoarthritis
7. Meniscal lesions
8. free joint bodies