Patellar (Kneecap) Instability / Dislocations / Malalignment
What is patellar instability?
The patella (kneecap) is attached by tendons to the femur (thigh bone) and the tibia (shin bone). The patella fits into a grove at the end of the femur called the trochlear groove. When the knee bends or straightens, the patella slides up and down. Patellar instability occurs when the patella moves outside of the trochlear groove. Patellar instability is almost always due to a dislocation of the kneecap. When the kneecap dislocates it can tear the structures on the inside of the knee, with the medial patellofemoral ligament (MPFL) being the most commonly injured.
What causes patellar instability?
There are two main causes commonly associated with patellar instability:
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Acute traumatic injuries – typically the result of a sports-related trauma or direct blow to the knee. may result from a specific injury or trauma, such as a direct blow to the knee. Traumatic dislocations of the kneecap can stretch or rupture the stabilizing structures on the inside of the knee, which can eventually lead to recurrent dislocations of the patella.
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Chronic subluxations – usually associated with malalignment or anatomic anomalies. Chronic subluxation is considered an atraumatic injury and occurs when the kneecap due to the patient’s anatomy, even during their everyday activities.
What are the symptoms of patellar instability?
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Sensation of the kneecap slipping or moving with turning or rotating movements
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Pain in the kneecap, especially with activity or when being palpated
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Swelling and stiffness in the knee, especially following a traumatic incident
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Weakness and limited range of motion in the joint
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Hearing a popping sound when the patella dislocates
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A change in the knee’s appearance with the knee looking misshapen or malformed
How is patellar instability Diagnosed?
Dr. Wusu will want to assess the degree of injury and determine the cause leading up to the patellar instability and/or dislocation. He will perform a thorough medical history review and physical examination to determine the level of instability, and will likely order x-rays to evaluate for patellar alignment and evidence of any bone injury from a previous dislocation. An MRI may be also be ordered to evaluate possible ligament and cartilage damage in the case of a traumatic dislocation.
What is the treatment for patellar instability and malalignment?
In most cases, patellar instability can be treated without surgery in patients at low risk for recurrent patellar instability. Patients with recurrent instability, dislocations, or malalignment may require surgery to restore the stabilizing ligaments of the knee and correct their anatomy.
The type of surgery required will depend on the cause of the instability. Surgical treatment options often include MPFL reconstruction to rebuild the ligament that holds the patella in place, or tibial tubercle osteotomy (TTO), to realign the patella by relocating the attachment of the patellar tendon just below the knee joint.
What is a knee dislocation?
A knee dislocation is an uncommon but extremely serious injury in which the femur (thigh bone) and tibia (shin bone) lose contact with each other. A dislocated knee is different than a dislocated kneecap, which occurs when the kneecap slips out of place. Knee dislocation can damage several important ligaments, blood vessels, and nerves, and the entire health and integrity of the joint and leg may be at risk.
A knee dislocation typically happens after a traumatic fall, high-speed motor vehicle accident, or a severe sports-related injury. Sometimes, a dislocated knee will go back into place on its own or with assistance, but this is a very painful and complex process. Patients will often need to be put under anesthesia or given a pain block in order to reduce the dislocated knee.
What are the symptoms of a dislocated knee?
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Hearing a “popping” sound at the time of injury
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Visible deformity and swelling of the knee joint
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Severe pain with any movement of the joint
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Numbness below the knee
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Absent or diminished pulses in some cases
What happens during a knee dislocation?
Most knee dislocations involve injuries to three or four of the major knee ligaments, including the ACL, PCL, MCL, and posterolateral corner (PLC). In addition, there may also be injuries to the medial or lateral meniscus, the articular cartilage, fractures, or patellar tendon injury. It is very important to carefully assess the injury.
It is also extremely important to examine vascular and nerve function at the time of injury. To evaluate vascular obstruction, your doctor may order a CT angiogram in which an iodine-based dye is injected into a vein to map the blood flow. A Doppler ultrasound can also be used to assess arterial blood flow.
What is the treatment for a dislocated knee?
Reduction, or repositioning of the injured joint, is the first and most crucial step in treating a knee dislocation in order to in order to reduce any further damage to blood vessels, nerves, or any other internal structures. In almost all cases, surgery will be required – often to repair multiple ligament injuries, meniscus tears, and cartilage damage. In the early stages of treatment, the medical priority is to minimize any damage caused to the blood vessels or nerves. When these issues have been addressed and stabilized, attention can be turned to the structural tissue damage. In general, the results of a dislocated knee are best if they are treated as soon as possible.
What is knee malalignment?
There arIn a normal leg, an imaginary straight line drawn from the center of the hip to the center of the ankle will pass through the center of the knee. This straight line, called the mechanical axis, illustrates the way our bodies bear weight when standing. Even a tiny variance of a few millimeters can make a huge difference in the wear-and-tear on a knee joint. Malalignment of the bones that form the knee joint may be present at birth or may develop following trauma or arthritis.
What are the types of malalignment?
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Genu varum:
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Tibia turns inwards in relation to the femur causing a bow-legged deformity
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Tend to have more wear on the inside (medial side) of their knees
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High tibial osteotomy (HTO) is more often recommended in these cases
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Genu valgus:
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Tibia turns outwards in relation to the femur causing a knock-knee deformity
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Tend to have more cartilage wear in the outside (lateral side) of their knees
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Distal femoral osteotomy (DFO) is more often recommended in these cases
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How are varus and valgus deformities treated?
Knee osteotomy is the cutting of bone to correct the knee’s alignment and improve its function with the goal of reducing the development of osteoarthritis. The primary objective of the surgery is to shift weight away from the painful, damaged side of the knee joint and onto the healthy side of the knee joint. This is made possible by strategically repositioning the bones and then securing them in proper alignment.
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High Tibial Osteotomy (HTO) – most commonly performed to correct genu varum (bow-legged deformity). A wedge of bone is added or removed to an area of the tibia just below the knee
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Distal Femoral Osteotomy (DFO) – most commonly performed to correct genu varum (knock-knee deformity). A wedge of bone is added or removed to the femur, just above the knee. Less common than tibial osteotomies
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Closed osteotomy – A wedge of bone is cut and removed. The resulting gap in the bone is closed by bringing the two sides together and securing them with a plate and screws.
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Open osteotomy – A cut is made about three-quarters of the way across the bone. A wedge-shaped bone graft is inserted into the cut. The wedge is secured to the bone with a plate and screws. There are three types of bone graft: autograft, allograft, and artificial graft.
