What is patella Instability?
Patello-femoral joint (PFJ) instability or dislocation is a common condition that most often presents for the first time during adolescence or early adulthood. It occurs when the patella (kneecap) moves laterally out of its normal groove on the femur, known as the trochlea. Every patello-femoral dislocation results in tearing or rupture of the medial patello-femoral ligament (MPFL), which is the primary stabilising structure of the PFJ. During a dislocation event, the cartilage covering the patella or femur may also be damaged or partially detached, and in some cases this can require urgent surgical treatment.
Causes
PFJ dislocation can occur following a significant laterally directed force to the kneecap, such as during sport or trauma. However, in individuals with underlying instability risk factors, it may also happen during relatively simple twisting movements or changes in direction. Several anatomical and biomechanical factors increase the risk of instability, including a previous history of dislocation, generalised joint hypermobility, valgus alignment (knock knees), patella alta (a high-riding kneecap), and abnormal rotational alignment of the lower limbs.
Symptoms
A first-time patellar dislocation often causes :
- Pain : severe (especially during first-time dislocation). Painful “clunk” sensation in recurrent or secondary dislocations.
- Mobility : Inability to walk (in acute first-time dislocation).
- Visible : displacement of the kneecap to the side of the knee.
- Sensation : of kneecap dislocation or slipping in and out of its groove.
- Instability : during activity.
- Swelling : of the knee.
- Apprehension : or fear with knee movement and reduced confidence during sport or daily activities.
Diagnosis
Diagnosis is usually made clinically following the patient’s history and examination after a dislocation event. During assessment, specific risk factors for recurrent instability are evaluated through a detailed physical examination.
Imaging
X-rays and MRI scans are used to further assess the anatomy of the knee, identify associated injuries, and guide treatment planning. X-rays are important in assessing lower limb alignment and identifying structural factors that may contribute to instability. In many cases, full-length lower limb X-rays from the hip to the ankle are obtained to evaluate overall alignment. MRI scans are particularly valuable for assessing soft tissue and cartilage injuries following dislocation. They can confirm rupture of the MPFL and detect any damage to the cartilage surfaces of the patella or femur, including loose fragments that may require surgical management.
Treatment
Conservative (non-operative)
Treatment depends on the severity of the injury, the presence of cartilage damage, and the patient’s risk of recurrent instability. For first-time dislocations without significant chondral injury, non-operative treatment is often recommended, including physiotherapy, strengthening exercises, and rehabilitation programmes aimed at improving muscular control and patellar stability. In cases of recurrent dislocation, however, surgery may be advised to restore stability, enable return to sport or normal daily activities, and reduce the risk of further cartilage injury and long-term joint degeneration.
Surgical Treatment
The most common surgical treatment for recurrent PFJ instability is a medial patello-femoral ligament (MPFL) reconstruction. This procedure typically involves using one of the patient’s own hamstring tendons, similar to techniques used in ACL reconstruction, to recreate the torn ligament and restore stability to the kneecap. In some patients, an isolated MPFL reconstruction may not be sufficient due to underlying anatomical factors. In these cases, the procedure may be combined with a Tibial Tubercle Transfer (TTT), where the attachment of the patellar tendon on the tibia is repositioned and secured to improve the alignment and stability of the patello-femoral joint and function.
Recovery
Recovery after medial patellofemoral ligament (MPFL) reconstruction is a gradual process that typically takes several months. In the early phase, the focus is on protecting the surgical repair, reducing pain and swelling, and restoring gentle knee movement, often with the use of a brace and crutches. Weight-bearing is usually progressed as tolerated, according to the surgeon’s protocol. Physiotherapy is essential throughout recovery to rebuild quadriceps strength, improve patellar control, and restore normal knee function. As healing progresses, patients gradually return to daily activities, followed by more demanding exercises such as running and sport-specific training. Full recovery and return to sport commonly take around 4 to 6 months, although this may vary depending on individual progress and associated knee injuries.