Congenital Knee Dislocation Repair: An Intraoperative Masterclass in Pediatric Orthopaedic Surgery

Introduction and Epidemiology

Congenital dislocation of the knee is a rare and profound musculoskeletal deformity that presents immediately at birth, characterized by severe recurvatum and structural hyperextension of the tibiofemoral joint. The overall incidence of congenital dislocation of the knee is estimated at 1 per 100,000 live births, representing approximately 1% of the incidence of developmental dysplasia of the hip. Despite its rarity, the condition commands significant clinical attention due to its potential to cause severe, lifelong ambulatory dysfunction if left untreated.

Congenital dislocation of the knee may manifest as an isolated, idiopathic entity or occur in conjunction with a spectrum of associated musculoskeletal anomalies. The most frequently encountered concurrent conditions include developmental dysplasia of the hip, idiopathic clubfoot, and congenital vertical talus. Furthermore, severe and recalcitrant forms of congenital dislocation of the knee are heavily associated with complex syndromic and neuromuscular disorders. These include myelodysplasia, Larsen syndrome, arthrogryposis multiplex congenita, Ehlers-Danlos syndrome, Streeter dysplasia, and severe oligohydramnios.

The exact etiology of congenital dislocation of the knee remains multifactorial and is broadly divided into intrinsic genetic abnormalities and extrinsic mechanical factors. A genetic etiology is strongly supported by familial occurrences and its frequent association with other genetically linked conditions. Conversely, the mechanical theory posits that simple hyperextension in otherwise healthy newborns may result from aberrant intrauterine positioning, such as a frank breech presentation. This abnormal positioning applies chronic, progressive stretch to the posterior knee soft tissues and hamstrings, ultimately leading to structural recurvatum.

The severity of the deformity exists on a continuum and has been classically categorized into three distinct grades: simple hyperextension, subluxation, and complete anterior dislocation of the tibia on the femur.

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).

The natural history of the condition is highly dependent on its initial severity. Simple hyperextension often resolves spontaneously or responds rapidly to early splinting and serial casting. However, true subluxation and complete dislocation rarely resolve without intervention. Left untreated, the persistent anterior displacement of the tibia prevents knee flexion, rendering normal ambulation impossible and necessitating early, definitive surgical correction.

Surgical Anatomy and Biomechanics

A thorough understanding of the distorted anatomy and altered biomechanics in congenital dislocation of the knee is paramount for successful surgical reconstruction. The fundamental pathologic feature driving the deformity resides within the extensor mechanism, specifically the quadriceps femoris muscle complex.

In congenital dislocation of the knee, the absolute volume of the quadriceps muscle is markedly diminished. The muscle belly, along with the lateral retinaculum, is densely adherent to the underlying femoral diaphysis and metaphysis. The quadriceps femoris tendon is severely shortened and fibrosed. Current biomechanical consensus suggests that this fibrosis and contracture are secondary adaptations to the chronic intrauterine dislocation rather than the primary inciting cause, though they become the primary mechanical block to reduction postnatally.

FIG 4 • Intraoperative view demonstrating the severe fibrosis and shortening of the quadriceps tendon, which acts as a rigid tether preventing knee flexion.

Osseous and Articular Distortions

The patella is typically hypoplastic and laterally displaced, riding high on the distal femur due to the contracted extensor mechanism. The suprapatellar pouch is universally hypoplastic or entirely absent, obliterating the normal gliding mechanism of the distal quadriceps. The anterior knee articular capsule is severely contracted and thickened, forming a dense fibrous barrier that must be meticulously released during surgical intervention.

Ligamentous and Meniscal Pathology

The intra-articular structures exhibit variable degrees of pathology. The menisci are usually present and morphologically normal, though their anatomic relationship to the femoral condyles is distorted by the anterior tibial displacement. The cruciate ligaments exhibit significant variability; they may be entirely absent, severely attenuated, or elongated. The absence or insufficiency of the anterior cruciate ligament exacerbates the anterior translation of the tibia.

Biomechanical Alterations

Chronic knee hyperextension induces profound biomechanical shifts in the dynamic stabilizers of the knee. The hamstring tendons, normally the primary flexors of the knee, subluxate anteriorly past the mechanical axis of rotation of the tibiofemoral joint. Once positioned anterior to the coronal axis of the knee, the hamstrings undergo a paradoxical functional reversal, acting as knee extensors rather than flexors. This anterior subluxation creates a self-perpetuating mechanical block to reduction. Furthermore, the collateral ligaments are often displaced anteriorly, tightening as the knee is forced into flexion and creating a "cam effect" against the femoral condyles that resists closed reduction.

Indications and Contraindications

The decision-making process for the management of congenital dislocation of the knee relies on the severity of the deformity, the rigidity of the joint, and the presence of associated syndromic conditions. Early conservative management is the standard of care for mild cases, but operative intervention is strictly indicated when conservative measures fail or are deemed futile based on the initial presentation.

Table of Operative vs Non Operative Indications

Surgical intervention is typically pursued when serial casting fails to achieve at least 90 degrees of passive knee flexion. In syndromic cases, such as arthrogryposis multiplex congenita, the periarticular fibrosis is often so severe that conservative management is predictably unsuccessful, and early surgical planning is justified.

Pre Operative Planning and Patient Positioning

Meticulous preoperative planning begins with a comprehensive clinical and radiographic evaluation. The physical findings of congenital dislocation of the knee are readily apparent at birth. The knee is locked in severe hyperextension, and in the most extreme cases, the anterior aspect of the tibia rests against the anterior femur, allowing the infant's foot to rest against their face.

A hallmark clinical sign of congenital dislocation of the knee is the presence of deep transverse skin creases across the anterior aspect of the knee joint. These creases indicate chronic intrauterine hyperextension and highlight the redundancy of the anterior skin, which contrasts sharply with the tightly contracted posterior skin.

FIG 2 • This infant has a unilateral knee dislocation. Note, the deep skin creases across the front of the knee.

Radiographic Evaluation

Standard orthogonal radiographs are mandatory. A true lateral radiograph of the knee is the most critical imaging modality, as it definitively demonstrates the relationship between the proximal tibia and the distal femur. In a complete dislocation, the tibial metaphysis is positioned entirely anterior to the femoral condyles.

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.

When evaluating neonatal radiographs, the orthopedic surgeon must account for the lack of ossification in the distal femoral and proximal tibial epiphyses. The anatomic alignment must be extrapolated from the diaphyseal and metaphyseal axes. Ultrasonography or magnetic resonance imaging can occasionally be utilized to assess the unossified chondral anlage, though standard radiography is usually sufficient for surgical planning.

FIG 5 • Advanced imaging or careful evaluation of the metaphyseal axes is required to fully appreciate the extent of the anterior translation when the epiphyses are unossified.

Timing of Surgery and Patient Positioning

The optimal timing for surgical intervention is generally between 6 and 12 months of age. Intervening within this window allows the infant to grow sufficiently to tolerate general anesthesia and provides larger anatomic structures for surgical repair, while preventing irreversible deformation of the chondral surfaces that occurs with prolonged dislocation.

The patient is positioned supine on a radiolucent operating table to facilitate intraoperative fluoroscopy. A sterile pediatric pneumatic tourniquet is placed as high as possible on the proximal thigh. The entire affected lower extremity, including the ipsilateral hemipelvis, is prepped and draped freely to allow for dynamic assessment of knee range of motion and hip stability during the procedure.

Detailed Surgical Approach and Technique

The surgical correction of an irreducible congenital dislocation of the knee requires a comprehensive anterior release and lengthening of the extensor mechanism. The classic technique, heavily influenced by the work of Curtis and Fisher, involves an extensive V-Y quadricepsplasty combined with radical capsulotomy.

Surgical Approach and Incision

A generous anterior longitudinal midline incision is utilized. The incision extends from the middle third of the femoral diaphysis, directly over the midline of the quadriceps, crossing the patella, and terminating just distal to the tibial tubercle.

FIG 6 • The anterior longitudinal midline approach provides extensile exposure to the entire extensor mechanism and anterior joint capsule.

Full-thickness fasciocutaneous flaps are meticulously elevated medially and laterally to expose the entire extensor mechanism, the medial and lateral retinacula, and the anterior joint capsule. Extreme care must be taken during flap elevation to preserve the fragile subcutaneous vascular plexus, as the skin will be subjected to significant tension once the knee is acutely flexed.

Extensor Mechanism Dissection and Lengthening

Once exposed, the severe fibrosis and shortening of the quadriceps tendon become immediately apparent. The vastus medialis and vastus lateralis are identified and separated from the rectus femoris.

FIG 7 • Exposure of the fibrotic quadriceps mechanism. The muscle fibers are often pale and heavily interspersed with dense fibrous tissue.

An inverted V-shaped incision is designed for the quadricepsplasty. The apex of the "V" is placed proximally in the tendinous portion of the rectus femoris, and the limbs of the "V" extend distally and peripherally through the medial and lateral retinacula, terminating at the level of the joint line. The underlying vastus intermedius, which is often densely adherent to the anterior femur, must be sharply elevated and released from the periosteum.

FIG 8 • The inverted V-incision of the Curtis and Fisher quadricepsplasty, allowing for significant distal advancement of the extensor mechanism.

Capsulotomy and Intra Articular Release

Following the quadriceps tenotomy, the anterior joint capsule is exposed. The capsule is typically contracted and thick. A wide transverse anterior capsulotomy is performed just proximal to the meniscus, extending from the medial collateral ligament to the lateral collateral ligament.

FIG 9 • Extensive anterior capsulotomy is required to break the suction seal of the joint and allow the tibia to translate posteriorly.

The collateral ligaments must be carefully inspected. If they are displaced anteriorly, they act as a tether preventing flexion. In such cases, the anterior fibers of the collateral ligaments may require fractional lengthening or subperiosteal elevation from their femoral origins to allow them to slide posteriorly.

The hamstrings are evaluated next. If the biceps femoris, semimembranosus, and semitendinosus are subluxated anterior to the mechanical axis, they must be mobilized. The iliotibial band is also frequently contracted and may require a Z-lengthening or transverse release to eliminate its deforming lateral and anterior force vector.

Joint Reduction and Fixation

With the anterior structures released, gentle, sustained manual traction is applied to the tibia to distract the joint surfaces. The tibia is then translated posteriorly to achieve an anatomic reduction of the tibiofemoral joint. The knee is slowly and carefully flexed.

Forcible flexion must be strictly avoided. Excessive force can crush the unossified chondral anlage of the distal femur or cause an iatrogenic Salter-Harris fracture of the distal femoral or proximal tibial physis. If 90 degrees of flexion cannot be easily achieved, the surgeon must re-evaluate the soft tissues for residual tethers, paying close attention to the posterior capsule, which may paradoxically require release if it has adhered to the femoral condyles in the dislocated position.

Once a concentric reduction is achieved and the knee can be flexed to 90 degrees, the joint is stabilized. A smooth, stout Kirschner wire (K-wire) is driven percutaneously from the anterior aspect of the proximal tibia, across the joint space, and into the distal femur.

FIG 10 • Fluoroscopic or direct visualization is used to pass a smooth K-wire across the tibiofemoral joint, maintaining the reduction and 90 degrees of flexion.

Closure and Immobilization

With the knee held in 90 degrees of flexion, the extensor mechanism is repaired. The proximal apex of the distal quadriceps segment is sutured to the distal apices of the proximal segment, converting the inverted "V" into a "Y". This achieves substantial lengthening of the quadriceps tendon while restoring extensor continuity.

Clinical & Radiographic Imaging