Patellar Instability

What is patellar instability?
Instability of the patella (knee joint) may occur in two ways.

It often develops after a dislocation of the patella in which the medial stabilizers of the knee are stretched or ruptured, which can eventually lead to recurrent dislocations of the patella.
Also, in some cases it is due to an anatomical anomaly of the knee joint (most commonly orbital dysplasia, high patella, bunion and outward displacement of the tibial tuberosity).
Important predisposing factors that contribute to patellofemoral instability are recumbent knees and syndromes of ligamentous hyperextension such as Ehlers-Danlos syndrome and Marfan syndrome. Chronic instability of the patellofemoral joint and dislocations can lead to progressive cartilage damage and arthritis.

More specifically, the patella is the largest sesamoid bone in the human body and connects the quadriceps tendon and patellar tendon. Through its articulation with the femoral condyle, the patellofemoral joint is formed, which is stabilised by ligaments, the synovial bursa and adjacent muscle groups.

What are the symptoms of patellar instability?
Patients with patellofemoral instability suffer from pain in the anterior part of the knee and episodes of mechanical instability. The pain can be aggravated by activities such as climbing up and down stairs, sports involving running, jumping and changes of direction.

What is the process of diagnosis?
Diagnosis is made by taking a history, clinical examination and imaging tests such as x-rays, CT scans and MRI of the knee.

Conservative treatment
Initial conservative treatment usually lasts for 3 to 6 months. It mainly involves physiotherapy aimed at strengthening the quadriceps muscle (mainly the medial pectoralis major muscle) and developing proprioception.

Surgical interventions
If conservative treatment fails, surgical options can be implemented. Indicative surgical interventions are as follows:

Surgical release of the external catheter ligaments (lateral release): the aim of this operation, which is performed arthroscopically, is to release the tight external patellofemoral ligaments that pull the patella from the femoral orbit causing increased pressure on the cartilage and dislocation.
MPFL (medial patellofemoral ligament) reconstruction: in this arthroscopic procedure, the torn MPFL is removed and reconstructed using autografts from the posterior femurs, which are fixed to the patellar tendon with screws.
Tibial tubercle transfer osteotomy: A tibial tubercle is a bony lump of the tibia on which the patellar tendon is lodged. In this surgery, the tibial tubercle is moved to the centre of the tibia and reattached with two screws. The screws hold the bone in place and allow faster healing and prevent the patella from slipping out of the groove.
In the rare case where the femoral orbit is too shallow, it can be treated by plastic surgery of the femoral orbit to deepen it.

All these surgical procedures can be performed under general or regional anaesthesia. A thigh splint is applied postoperatively. The sutures are cut 15 days after surgery. Complications are rare and do not exceed 1% of cases.

The orthopaedic surgeon, Dr. Antonios Pettas, was responsible for the foot and ankle surgeries at Norrtälje Hospital in Stockholm. He has many years of experience, with a high success rate of operations. Contact him for an early diagnosis and treatment.