Matthew B. Dobbs, Noppachart Limpaphayom, and J. Eric Gordon
DEFINITION
Congenital dislocation of the knee (CDK) is a rare deformity that presents at birth as recurvatum.
The incidence of CDK is estimated at 1 per 100,000 live births, which is approximately 1% of the incidence of congenital dislocation of the hip.7
It may be an isolated entity or occur with associated musculoskeletal anomalies such as dislocated hips, clubfoot, and congenital vertical talus. It can also occur with myelodysplasia, Larsen syndrome, and arthrogryposis.
It varies in severity and has been classified as simple hyperextension, subluxation, and anterior dislocation of the tibia on the femur (FIG 1).3
ANATOMY
The fundamental pathologic feature in CDK involves the quadriceps muscle. The amount of quadriceps muscle is small, and the muscle as well as the lateral retinaculum adheres to the femur.
The quadriceps femoris tendon is shortened and fibrosed, which is thought to be secondary to the dislocation rather than its cause.3
The patella is often laterally displaced.
There is hypoplasia of the suprapatellar pouch.
The hamstrings are often deficient, subluxed anteriorly, or both.
The anterior knee articular capsule is tight.
The menisci are usually present and normal.
The pathology in the cruciate ligaments is variable, from absence to elongated.5
PATHOGENESIS
The exact cause of CDK remains unknown.
A genetic etiology is supported by the presence of familial occurrence in some cases as well as the association of CDK with developmental hip dysplasia, idiopathic clubfoot, and congenital vertical talus, all three of which have a known or presumed genetic basis.1,11
FIG 1 • Congenital knee dislocation can vary from simple hyperextension (A) to subluxation (B) to complete anterior dislocation of the tibia on the femur (C).
Simple hyperextension of the knee in newborns may be caused by aberrations in intrauterine positions, such as frank breech presentation, which slowly stretches the hamstrings and posterior knee soft tissues.7 Chronic knee hyperextension results in anterior subluxation of the hamstrings, allowing them to function as knee extensors.
Severe CDK often occurs in association with disorders with muscle imbalance, such as myelodysplasia, arthrogryposis, Larsen syndrome, Ehlers-Danlos syndrome, Streeter syndrome, and oligohydramnios.3,11
NATURAL HISTORY
The natural history of CDK depends on the severity of the disorder on presentation. Simple hyperextension of the knee tends to resolve spontaneously or with splinting.2,6
In cases of subluxation and dislocation, spontaneous resolution is not common, and most patients require surgical correction.
Left untreated, these patients have great difficulty with ambulation owing to the inability to flex the knees. These patients often have associated neuromuscular or genetic syndromes.3
PATIENT HISTORY AND PHYSICAL FINDINGS
The physical findings of CDK are readily apparent at birth but of variable severity (FIG 2).
The knee is hyperextended, in severe cases to such a degree that the foot rests against the baby's face.
In cases of simple hyperextension, the knee can be passively brought into flexion.
In the more common scenario of subluxation, passive flexion is limited but improves with splinting, casting, or both.
FIG 2 • This infant has a unilateral knee dislocation. Note the deep skin creases across the front of the knee.
FIG 3 • A lateral radiograph of a newborn demonstrating complete dislocation of the tibia on the distal femur. The anterior aspect of the knee is on the right. Note the deep skin creases anteriorly.
In cases of dislocation, the knee cannot be easily passively flexed with simple manipulation. The patella is often laterally displaced and difficult to palpate. A deep crease may be present over the anterior aspect of the knee.
The more severe cases are more likely to have associated musculoskeletal anomalies.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Anteroposterior and lateral radiographs of the knee help to differentiate the mild hyperextension deformity from the more severe type of subluxation or fixed anterior dislocation of the tibia on the distal femur (FIG 3).
The ossification centers of the distal femur and proximal tibia are usually present in the full-term infant.
The patella is not yet ossified in the infant.
Ultrasound can also be used to make the diagnosis.
DIFFERENTIAL DIAGNOSIS
Simple hyperextension of the knee
NONOPERATIVE MANAGEMENT
Nonoperative treatment should be started as soon as possible.
Nonoperative treatment consists of serial manipulations and long-leg plaster castings.2,6,10
With the patient relaxed with a bottle of milk, gentle traction is applied to the tibia to stretch the contracted quadriceps muscle. After several minutes of stretching, a long-leg plaster cast is applied from the toes to the top of the thigh. The cast is applied in one section and is carefully molded to maintain the position achieved with stretching and to avoid skin sores.
The casts are changed on a weekly basis in the clinic. Once the tibia reaches the distal femur with traction, flexion of the knee is begun.
In cases of simple hyperextension, flexion of the knee can often be started quite early (FIG 4).
In cases of subluxation and complete dislocation of the knee, however, flexion of the knee often cannot be started for several weeks until the quadriceps muscle is adequately stretched.
It is very important to obtain a lateral radiograph of the knee once knee flexion reaches 45 degrees and again if 90 degrees of flexion is reached during serial casting. It is possible to create an iatrogenic physeal separation of the distal femur or to deform the proximal tibia plastically.
Closed treatment should be stopped if anatomic reduction of the tibia cannot be confirmed.
If 90 degrees of flexion is obtained and a normal restoration of the femoral–tibial articulation is demonstrated on a lateral radiograph, it is unlikely that any surgical intervention will be necessary.
Historically, nonoperative treatment has been successful in treating simple hyperextension of the knee and some cases of subluxation. Most patients with complete knee dislocation have an extensive surgical release operation after a failed attempt at casting.
SURGICAL MANAGEMENT
Preoperative Planning
If serial casting fails to obtain a reduction of the anteriorly dislocated tibia on the end of the femur, which is verified on a lateral radiograph of the knee, surgical management should be considered.
FIG 4 • Approximate amount of knee flexion achieved each week during serial castings.
Timing of the surgical correction depends on the particular technique that the surgeon chooses, but usually ranges from 1 month of age to 2 years.
Positioning
The patient is positioned supine on a radiolucent table. No tourniquet is used as this interferes with the location of the surgical incision.
The entire leg is prepared into the field from the hip to the tip of the toes to allow easy manipulation of the knee (FIG 5).
Approach
The approach depends on the surgeon's preference but varies from minimally invasive approaches to extensile approaches with quadriceps mechanism reconstruction.
FIG 5 • The entire leg is prepared into the field to allow easy manipulation of the knee.
TECHNIQUES
PERCUTANEOUS QUADRICEPS RECESSION
This procedure is ideally performed at 1 to 2 months of age and is described by Roy and coworkers.11
An assistant holds the affected leg and attempts to flex the knee.
A small stab incision is made one to two patellar lengths superior to the patella in the midline of the thigh, and the fascia overlying the rectus femoris is released (TECH FIG 1).
Medial and lateral stab incisions are then made at the superior border of the patella to release the medial and lateral quadriceps tendon and retinaculum.
After the release is performed, the knee is flexed to 90 degrees.
Sterile dressings are applied, followed by a long-leg plaster cast with the knee flexed at 90 degrees or greater.
The cast is worn for 4 to 6 weeks.
After cast removal the patient is placed in a Pavlik harness to maintain knee flexion for an additional 4 to 6 weeks.
TECH FIG 1 • Percutaneous quadriceps recession. A. The knee is held in maximum flexion. B. Medial and lateral stab incisions are made at the superior border of the patella to release the quadriceps and retinaculum. C. The knee is flexed to 90 degrees after release of the retinaculum is achieved.
MINI-OPEN QUADRICEPS TENOTOMY
This approach is ideally performed between 1 and 6 months of age and has been described by Dobbs and associates (TECH FIG 2).4
A 2-cm vertical midline incision is made just above the superior pole of the patella.
Dissection is carried down to the patella and the quadriceps tendon.
The quadriceps tendon is carefully isolated with blunt dissection using a hemostat.
The quadriceps tendon is transected completely about 1 cm proximal to its insertion on the superior pole of the patella.
The knee is then gently flexed until at least 90 degrees of flexion is obtained.
TECH FIG 2 • A. The solid purple lines outline the patella and the dotted line demonstrates the site of the surgical incision. B. Location of the skin incision. C. Location of the quadriceps tenotomy. D.Intraoperative photograph with solid purple lines outlining the patella. E. Surgical isolation of the quadriceps tendon before tenotomy. F–H. Knee flexion just before the quadriceps tenotomy (F) and after the tenotomy (G,H). I. Lateral radiograph demonstrating restoration of a normal relation of the tibia on the femur.
If 90 degrees of flexion cannot be obtained after the quadriceps tenotomy, the anterior knee capsule is released as well as the lateral retinaculum until 90 degrees of flexion is obtained.
An intraoperative lateral knee radiograph is obtained to ensure anatomic reduction of the tibia on the distal femur.
After wound closure, a sterile dressing is applied, followed by a long-leg plaster cast with the knee in 90 degrees of flexion.
EXTENSILE RECONSTRUCTION OF CONGENITAL KNEE DISLOCATION
This approach is usually performed between 6 months and 1 year of age.
A midline longitudinal incision or serpentine incision can be used. The midline incision extends from the tibial tubercle to the middle of the thigh; the serpentine incision extends from the tibial tubercle to the proximal thigh.3,7
The serpentine incision may facilitate wound closure and result in fewer wound-healing problems than the straight incision.
The patella, the quadriceps muscle and tendon, the patellar tendon, and the lateral retinaculum are all carefully exposed.
TECH FIG 3 • V-to-Y quadriceps advancement. A. The quadriceps tendon is exposed proximal to the patella, and most of the medial and lateral fibers are detached from the tendon. The medial and lateral retinaculum is divided to the collateral ligaments. The iliotibial band is divided if the tibia is in valgus and externally rotated. B. The posterior borders of the lateralis and the medialis are divided sharply and the flap of muscle created is dissected free of underlying attachments to the femur. This will permit the tibia and collateral ligaments to slide posteriorly and allow sufficient mobilization of the quadriceps. C.With the knee flexed at about 40 degrees, the medialis and lateralis are reattached to the quadriceps tendon, creating the V-to-Y advancement and repair. The retinaculum is not closed.
The quadriceps muscle is striking in that it is small, fibrosed, and often adherent to the distal femur.
In severe cases, the patella is subluxed laterally.
The quadriceps is lengthened using a V-to-Y advancement (TECH FIG 3).
If the tibia is in valgus and external rotation, the iliotibial band should be divided at this point.
The anterior knee joint capsule is released transversely to the collateral ligaments.
The quadriceps muscle and the lateral retinaculum must be dissected free from the distal femur. This usually allows the knee to be flexed to 90 degrees.
The hamstrings and the cruciate ligaments can be left alone as these structures do not prevent knee flexion in the vast majority of cases.
The quadriceps tendon is repaired with the knee in 30 to 40 degrees of flexion.1,3
A spica cast is used for immobilization with the knee in about 45 degrees of flexion to prevent recurrent subluxation.7
POSTOPERATIVE CARE
A lateral radiograph of the knee is essential to ensure anatomic reduction of the tibia on the distal femur.
Casting is required after each treatment method. The degree of knee flexion in the cast and the duration of casting vary with technique.
Percutaneous quadriceps resectio.
A long-leg plaster cast with the knee flexed at least 90 degrees is applied at the end of the procedure and worn for 4 to 6 weeks.
After cast removal, the patient is placed in a Pavlik harness to maintain knee flexion for an additional 4 to 6 weeks.
Mini-open quadriceps tenotom.
The initial long-leg plaster cast with the knee in 90 degrees of flexion is changed in the operating room at 3 weeks postoperatively to assess knee range of motion.
Another long-leg cast is applied with the knee in 70 degrees of flexion for 2 weeks. This cast is removed in the clinic and formal physical therapy is begun on an outpatient basis to maintain knee flexion and extension. Splints are also used for 4 to 6 weeks, alternating between a flexed and an extended position at the knee.
Extensile reconstruction: spica cast with the knee in about 45 degrees of flexion
Once casting is complete, close follow-up is mandatory to ensure maintenance of knee motion.
Splinting is also important after each treatment method to maintain maximal flexion and minimize loss of knee extension.
Physical therapy is also an essential part of postoperative rehabilitation and is done on an outpatient basis several times a week for up to 3 months.
OUTCOMES
Patients with a hyperextension deformity that requires only serial manipulation and castings do very well long term both clinically and radiographically.2,5,9,10
Roy and colleagues11 report good short-term results using the percutaneous quadriceps tenotomy, but there are no longterm data with this technique. This technique was successful only in patients without associated syndromes or neuromuscular deformities.
Dobbs and coworkers4 report good short-term results using the mini-open quadriceps tenotomy in patients with isolated CDK as well as in some children with associated genetic and neuromuscular conditions. No long-term follow-up is available for this technique.
Patients with severe dislocation who have undergone an extensive open procedure, but do not have any other associated musculoskeletal problem, generally do well long term if knee flexion is 80 degrees or greater.
Children with associated neuromuscular disorders or genetic syndromes do not do as well long term.
Children with bilateral deformities do not do as well as those with unilateral deformity.
Early correction has a more satisfactory result than late repair.4,7,11
COMPLICATIONS
Wound-healing problems have been reported with extensile approaches.
Loss of flexion initially gained at surgery can be a late complication.
Development of a flexion contracture can occur postoperatively and compromise long-term outcome.
Iatrogenic fractures of the distal femur, proximal tibia, or both can occur with casting and manipulation.
REFERENCES
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11. Roy DR, Crawford AH. Percutaneous quadriceps recession: a technique for management of congenital hyperextension deformities of the knee in the neonate. J Pediatr Orthop 1989;9:717–719.
12. Uhthoff HK, Ogata S. Early intrauterine presence of congenital dislocation of the knee. J Pediatr Orthop 1994;14:254–257.