Patellar dislocation

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Patellar dislocation
Other namesKneecap dislocation, dislocated kneecap
PetellardislocationChildMark.png
X-ray showing a patellar dislocation, with the patella out to the side.
Specialty Emergency medicine, orthopedics
Symptoms Knee is partly bent, painful and swollen [1] [2]
Complications Patella fracture, arthritis [3]
Usual onset10 to 17 years old [4]
DurationRecovery within 6 weeks [5]
CausesBending the lower leg outwards when the knee is straight, direct blow to the patella when the knee is bent [1] [2]
Risk factors High riding patella, family history, loose ligaments [1]
Diagnostic method Based on symptoms, X-rays [2]
TreatmentReduction, splinting, physical therapy, surgery [1]
Medication Pain medication [3]
Prognosis ~30% risk of recurrence [4]
Frequency6 per 100,000 per year [4]

A patellar dislocation is a knee injury in which the patella (kneecap) slips out of its normal position. [5] Often the knee is partly bent, painful and swollen. [1] [2] The patella is also often felt and seen out of place. [1] Complications may include a patella fracture or arthritis. [3]

Contents

A patellar dislocation typically occurs when the knee is straight and the lower leg is bent outwards when twisting. [1] [2] Occasionally, it occurs when the knee is bent and the patella is struck directly. [1] Commonly associated sports include soccer, gymnastics, and ice hockey. [2] Dislocations nearly always occur away from the midline. [2] Diagnosis is typically based on symptoms and supported by X-rays. [2]

Reduction is generally done by pushing the patella towards the midline while straightening the knee. [1] After reduction, the leg is generally splinted in a straight position for a few weeks. [1] This is then followed by physical therapy. [1] Surgery after a first dislocation is generally of unclear benefit. [6] [4] Surgery may be indicated in those cases where a fracture occurs within the joint or where the patella has repeatedly dislocated. [3] [4] [5]

Patellar dislocations occur in about 6 per 100,000 people per year. [4] They make up about 2% of knee injuries. [1] It is most common in those 10 to 17 years old. [4] Rates in males and females are similar. [4] Recurrence after an initial dislocation occurs in about 30% of people. [4]

Signs and symptoms

People often describe pain as severe and being "inside the knee cap". [3] The leg tends to flex even when relaxed. In some cases, the injured ligaments involved in patellar dislocation do not allow the leg to flex. [2]

Risk factors

A predisposing factor is tightness in the tensor fasciae latae muscle and iliotibial tract in combination with a quadriceps imbalance between the vastus lateralis and vastus medialis muscles can play a large role, found, mainly, in women involved in sports. [3] [7] Moreover, women with patellofemoral pain may show increased Q-angle compared with women without patellofemoral pain.[ citation needed ]

Another cause of patellar symptoms is lateral patellar compression syndrome, which can be caused from lack of balance or inflammation in the joints. [8] The pathophysiology of the kneecap is complex, and deals with the osseous soft tissue or abnormalities within the patellofemoral groove. The patellar symptoms cause knee extensor dysplasia, and sensitive small variations affect the muscular mechanism that controls the joint movements. [9]

24% of people whose patellas have dislocated have relatives who have experienced patellar dislocations. [2]

Athletic population

Patellar dislocation occurs mainly in youths (under age 20) engaged in sports that may involve accidental rotation of the knee while in flexion, a movement clinically called valgus , which is the cause of some 93% of patellar dislocation cases. [3] It is more common in females than males and in young in-training military personnel who have a high incidence of patellar dislocation in relation to young athletes and the general population. [3] Direct trauma to the knee displacing the patella is rare. [3]

Displacement of the patella laterally out of its groove strains the medial stabilizing connective tissues, particularly the medial patellofemoral ligament (supporting 50–80% of the knee mechanisms in lateral patellar glide), which is torn usually at its femoral attachment. [3] Traumatic patellar dislocation may cause bleeding into the joint space, ligament and muscle attachment tearing, and fracture of the medial wing of the patella. [3] Fracture of the weight-bearing portion of the lateral femoral condyle occurs in 25% of traumatic patellar dislocations. [3] Surgical repair of the patellar stabilizing structures – the medial patellofemoral ligament and vastus medialis muscle – may be needed for athletes. [3]

Anatomical factors

People who have larger Q angles tend to be more prone to having knee injuries such as dislocations, due to the central line of pull found in the quadriceps muscles that run from the anterior superior iliac spine to the center of the patella. The range of a normal Q angle for men ranges from <15 degrees and for females <20 degrees, putting females at a higher risk for this injury. [10] An angle greater than 25 degrees between the patellar tendon and quadriceps muscle can predispose a person to patellar dislocation. [11]

In patella alta, the patella sits higher on the knee than normal. [11] Normal function of the VMO muscle (VMO) stabilizes the patella. Decreased VMO function results in instability of the patella. [2]

Forces

When there is too much tension on the patella, the ligaments will be susceptible to tearing due to shear force or torsion force, which then displaces the patella from its groove. [3] Patellar dislocation may also occur when the trochlear groove is shallow, a condition defined as trochlear dysplasia. [12]

Mechanism of injury

Anatomy of the Knee Knee diagram.svg
Anatomy of the Knee

Patellar dislocations occur by:

Anatomy of the knee

The patella is a triangular sesamoid bone that is embedded in tendon. It rests in the patellofemoral groove, an articular cartilage-lined hollow at the end of the thigh bone (femur) where the thigh bone meets the shin bone (tibia). Several ligaments and tendons hold the patella in place and allow it to move up and down the patellofemoral groove when the leg bends. The top of the patella attaches to the quadriceps muscle via the quadriceps tendon, [2] the middle to the vastus medialis obliquus and vastus lateralis muscles, and the bottom to the head of the tibia (tibial tuberosity) via the patellar tendon, which is a continuation of the quadriceps femoris tendon. [13] The medial patellofemoral ligament attaches horizontally in the inner knee to the adductor magnus tendon and is the structure most often damaged during a patellar dislocation. Finally, the lateral collateral ligament and the medial collateral ligament stabilize the patella on either side. [2] Any of these structures can sustain damage during a patellar dislocation.[ citation needed ]

Diagnosis

Patellar dislocation Patellaluxation ap 001.png
Patellar dislocation

To assess the knee, a clinician can perform the Patellar Aprehension Test by moving the patella back and forth while the people flexes the knee at approximately 30 degrees. [14]

The people can do the patella tracking assessment by making a single leg squat and standing, or by lying on his or her back with knee extended from flexed position. A patella that slips laterally on early flexion is called the J sign, and indicates imbalance between the VMO and lateral structures. [15]

On X-ray, with skyline projections, dislocations are readily diagnosed. In borderline cases of subluxation, the following measurements can be helpful:

  • A line connecting the most anterior points of the medial and lateral facets of the trochlea.
  • A tangent to the lateral facet of the patella.
With the knee in 20° flexed, this angle should normally open laterally. [16]

Prevention

The patella is a floating sesamoid bone held in place by the quadriceps muscle tendon and patellar tendon ligament. Exercises should strengthen quadriceps muscles such as rectus femoris, vastus intermedius, and vastus lateralis. However, tight and strong lateral quadriceps can be an underlying cause of patellar dislocation. If this is the case, it is advisable to strengthen the medial quadriceps, vastus medialis (VMO), and stretch the lateral muscles. [17] Exercises to strengthen quadriceps muscles include, but are not limited to, squats and lunges. Adding extra external support around the knee by using devices such as knee [orthotics] or athletic tape can help to prevent patellar dislocation and other knee-related injuries. [18] External supports, such as knee braces and athletic tape, work by providing movement in only the desired planes and help hinder movements that can cause abnormal movement and injuries. Women who wear high heels tend to develop short calf muscles and tendons. Exercises to stretch and strengthen calf muscles are recommended on a daily basis. [19]

Treatment

X-ray and MRI after luxation of the patella. There is a fragment and bone bruise at the medial surface of the patella and in the corresponding surface of the lateral condyle of the femur. The medial retinaculum of the patella is disrupted. Patella Luxation coronar3.png
X-ray and MRI after luxation of the patella. There is a fragment and bone bruise at the medial surface of the patella and in the corresponding surface of the lateral condyle of the femur. The medial retinaculum of the patella is disrupted.

Two types of treatment options are typically available:

Surgery may impede normal growth of structures in the knee, so doctors generally do not recommend knee operations for young people who are still growing. [20] [21] There are also risks of complications, such as an adverse reaction to anesthesia or an infection. [20] [21]

When designing a rehabilitation program, clinicians consider associated injuries such as chipped bones or soft tissue tears. Clinicians take into account the person's age, activity level, and time needed to return to work and/or athletics. Doctors generally only recommend surgery when other structures in the knee have sustained severe damage, or specifically when there is: [20]

Supplements like glucosamine and NSAIDs can be used to minimize bothersome symptoms. [14]

Rehabilitation

An effective rehabilitation program reduces the chances of re-injury and of other knee-related problems such as patellofemoral pain syndrome and osteoarthritis. Most patella dislocations are initially immobilized for the first 2–3 weeks to allow the stretched structures to heal. Rehabilitation focuses on maintaining strength and range of motion to reduce pain and maintain the health of the muscles and tissues around the knee joint. [14] The objective of any good rehabilitation program is to reduce pain, swelling and stiffness as well as increase range of motion. A common rehabilitation plan is to strengthen both the hip abductors, hip external rotators and the quadricep muscles. Commonly used exercises include isometric quadricep sets, side lying clamshells, leg dips with internal tibial rotation, etc. The idea is that because the medial side is most often stretched by the more common lateral dislocation, medial strengthening will add more stabilizing support. With progression more intense range of motion exercises are incorporated. [22]

Epidemiology

Rate in the United States are estimated 2.3 per 100,000 per year. [23] Rates for ages 10–17 were found to be about 29 per 100,000 persons per year, while the adult population average for this type of injury ranged between 5.8 and 7.0 per 100,000 persons per year. [24] The highest rates of patellar dislocation were found in the youngest age groups, while the rates declined with increasing ages. Females are more susceptible to patellar dislocation. Race is a significant factor for this injury, where Hispanics, African-Americans and Caucasians had slightly higher rates of patellar dislocation due to the types of athletic activity involved in: basketball (18.2%), soccer (6.9%), and football (6.9%), according to Brian Waterman. [23]

Lateral Patellar dislocation is common among the child population. Some studies suggest that the annual patellar dislocation rate in children is 43/100,000. [25] The treatment of the skeletally immature is controversial due to the fact that they are so young and are still growing. Surgery is recommended by some experts in order to repair the medial structures early, while others recommend treating it non operatively with physical therapy. If re-dislocation occurs then reconstruction of the medial patellofemoral ligament (MPFL) is the recommended surgical option. [26]

In animals, patellar luxation is a common condition in dogs, particularly small and miniature breeds. [27]

Related Research Articles

<span class="mw-page-title-main">Knee</span> Leg joint in primates

In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body. The knee is a modified hinge joint, which permits flexion and extension as well as slight internal and external rotation. The knee is vulnerable to injury and to the development of osteoarthritis.

<span class="mw-page-title-main">Patella</span> Kneecap, bone covering knee joint

The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mice, cats, birds and dogs, but not in whales, or most reptiles.

<span class="mw-page-title-main">Anterior cruciate ligament</span> Type of cruciate ligament in the human knee

The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments in the human knee. The two ligaments are also called "cruciform" ligaments, as they are arranged in a crossed formation. In the quadruped stifle joint, based on its anatomical position, it is also referred to as the cranial cruciate ligament. The term cruciate translates to cross. This name is fitting because the ACL crosses the posterior cruciate ligament to form an "X". It is composed of strong, fibrous material and assists in controlling excessive motion. This is done by limiting mobility of the joint. The anterior cruciate ligament is one of the four main ligaments of the knee, providing 85% of the restraining force to anterior tibial displacement at 30 and 90° of knee flexion. The ACL is the most injured ligament of the four located in the knee.

<span class="mw-page-title-main">Quadriceps</span> Group of human leg muscle

The quadriceps femoris muscle is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur. The name derives from Latin four-headed muscle of the femur.

<span class="mw-page-title-main">Luxating patella</span> Medical condition

A luxating patella, sometimes called a trick knee, is a condition in which the patella, or kneecap, dislocates or moves out of its normal location. It can be associated with damage to the anterior cruciate ligament.

<span class="mw-page-title-main">Anterior cruciate ligament reconstruction</span> Surgical process

Anterior cruciate ligament reconstruction is a surgical tissue graft replacement of the anterior cruciate ligament, located in the knee, to restore its function after an injury. The torn ligament can either be removed from the knee, or preserved before reconstruction through an arthroscopic procedure. ACL repair is also a surgical option. This involves repairing the ACL by re-attaching it, instead of performing a reconstruction. Theoretical advantages of repair include faster recovery and a lack of donor site morbidity, but randomised controlled trials and long-term data regarding re-rupture rates using contemporary surgical techniques are lacking.

<span class="mw-page-title-main">Vastus medialis</span> Extensor muscle located medially in the thigh that extends the knee.

The vastus medialis is an extensor muscle located medially in the thigh that extends the knee. The vastus medialis is part of the quadriceps muscle group.

The rectus femoris muscle is one of the four quadriceps muscles of the human body. The others are the vastus medialis, the vastus intermedius, and the vastus lateralis. All four parts of the quadriceps muscle attach to the patella by the quadriceps tendon.

The knee examination, in medicine and physiotherapy, is performed as part of a physical examination, or when a patient presents with knee pain or a history that suggests a pathology of the knee joint.

<span class="mw-page-title-main">Patellar tendon rupture</span> Medical condition

Patellar tendon rupture is a tear of the tendon that connects the knee cap (patella) to the tibia. Often there is sudden onset of pain and walking is difficult. In a complete rupture, the ability to extend that knee is decreased. A pop may be felt when it occurs.

<span class="mw-page-title-main">Patellar tendon</span> Tendon in the human knee

The patellar tendon is the distal portion of the common tendon of the quadriceps femoris, which is continued from the patella to the tibial tuberosity. It is also sometimes called the patellar ligament as it forms a bone to bone connection when the patella is fully ossified.

<span class="mw-page-title-main">Tuberosity of the tibia</span> Slight protrusion at the top front end

The tuberosity of the tibia or tibial tuberosity or tibial tubercle is an elevation on the proximal, anterior aspect of the tibia, just below where the anterior surfaces of the lateral and medial tibial condyles end.

<span class="mw-page-title-main">Unhappy triad</span> Medical condition of the knee

The unhappy triad, also known as a blown knee among other names, is an injury to the anterior cruciate ligament, medial collateral ligament, and meniscus. Analysis during the 1990s indicated that this 'classic' O'Donoghue triad is actually an unusual clinical entity among athletes with knee injuries. Some authors mistakenly believe that in this type of injury, "combined anterior cruciate and medial collateral ligament disruptions that were incurred during athletic endeavors" always present with concomitant medial meniscus injury. However, the 1990 analysis showed that lateral meniscus tears are more common than medial meniscus tears in conjunction with sprains of the ACL.

<span class="mw-page-title-main">Articular capsule of the knee joint</span>

The articular capsule of the knee joint is the wide and lax joint capsule of the knee. It is thin in front and at the side, and contains the patella, ligaments, menisci, and bursae of the knee. The capsule consists of an inner synovial membrane, and an outer fibrous membrane separated by fatty deposits anteriorly and posteriorly.

<span class="mw-page-title-main">Quadriceps tendon</span>

In human anatomy, the quadriceps tendon works with the quadriceps muscle to extend the leg. All four parts of the quadriceps muscle attach to the shin via the patella, where the quadriceps tendon becomes the patellar ligament. It attaches the quadriceps to the top of the patella, which in turn is connected to the shin from its bottom by the patellar ligament. A tendon connects muscle to bone, while a ligament connects bone to bone.

<span class="mw-page-title-main">Patellofemoral pain syndrome</span> Medical condition

Patellofemoral pain syndrome is knee pain as a result of problems between the kneecap and the femur. The pain is generally in the front of the knee and comes on gradually. Pain may worsen with sitting, excessive use, or climbing and descending stairs.

Patellar subluxation syndrome, is an injury that is concerned with the kneecap. Patellar subluxation is more common than patellar dislocation and is just as disabling.

The medial patellofemoral ligament is one of the several ligaments on the medial aspect of the knee. It originates on the superomedial aspect of the patella and inserts in the space between the adductor tubercle and the medial femoral epicondyle. Its main function is to prevent lateral displacement of the patella.

<span class="mw-page-title-main">Knee pain</span> Medical condition

Knee pain is pain in or around the knee.

<span class="mw-page-title-main">Medial knee injuries</span> Medical condition

Medial knee injuries are the most common type of knee injury. The medial ligament complex of the knee consists of:

References

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  17. ↑ Nomura E, Horiuchi Y, Kihara M (April 2000). "Medial patellofemoral ligament restraint in lateral patellar translation and reconstruction". The Knee. 7 (2): 121–127. doi:10.1016/s0968-0160(00)00038-7. PMID   10788776.
  18. ↑ Gerrard DF (May 1998). "External knee support in rugby union. Effectiveness of bracing and taping". Sports Medicine. 25 (5): 313–7. doi:10.2165/00007256-199825050-00002. PMID   9629609. S2CID   41629668.
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  27. ↑ Engdahl K, Bergström A, Höglund O, Hanson J (September 2023). "The epidemiology of patellar luxation in an insured Swedish dog population". Preventive Veterinary Medicine. 220: 106034. doi: 10.1016/j.prevetmed.2023.106034 . PMID   37801966.
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