Pediatric Fixed Knee Flexion Deformities Treatment & Management

Updated: Jul 09, 2019
  • Author: Peter M Stevens, MD; Chief Editor: Jeffrey D Thomson, MD  more...
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Approach Considerations

Indications for surgery

Children with teratologic fixed knee flexion deformity (FKFD) noted in the nursery are likely to undergo surgical treatment within the first 24 months of life. Depending on the need to correct hip and foot deformities, such treatment may be multilevel or simultaneous, or it may have to be staged.

Hamstring lengthening and posterior capsulotomy may constitute the initial treatment. [19, 20, 21, 22, 23]  As these children grow older and the deformity recurs, guided growth or supracondylar femoral osteotomy may be warranted. Patellar realignment may be necessary in some patients, and postoperative bracing and physical therapy may be indicated. The goal is to gain full extension and facilitate standing and walking.

Children with neurogenic FKFD will be considered together, with the acknowledgment that spasticity management for cerebral palsy and spinal cord detethering for spina bifida may play an important role.

For younger children, hamstring stretching, physical therapy, and bracing are useful temporizing measures. However, with growth, there may be inexorable progression of a crouch gait due to the insidious evolution of FKFD. When the fixed deformity surpasses 10º, most patients start to manifest symptoms such as fatigue, pain, or brace intolerance; these symptoms escalate when the deformity exceeds 20º. The energy costs of walking increase as endurance and velocity decrease. [15, 16]


The indications and techniques for supracondylar osteotomy of the femur have been well described in standard textbooks and journals. Opinions vary as to whether internal or external fixation is preferable. In addition to the known risks of fixation failure, overcorrection or undercorrection, fracture, neurovascular compromise, skin slough, and recurrent deformity are very common.

Frame distraction

There are specific situations in which the best option is gradual distraction and extension employing an external fixator. [24]  This may best serve those patients who have neglected or teratologic deformities, such as pterygium syndrome, or have reached skeletal maturity. Despite the touted advantages, it is a costly and slow process that usually requires a posterior release and that may not be well tolerated by the patient. Unfortunately, there is an acknowledged high rate of recurrent deformity despite postoperative bracing.

Guided growth

The distal femoral physis grows fairly rapidly, even in this population. Furthermore, skeletal maturity may be delayed, extending the window of opportunity for gradually straightening the knee by means of distal anterior femoral hemiepiphysiodesis. This may be safely undertaken even in relatively young children, without causing permanent growth arrest. [24, 25]  Staples were formerly preferred for this purpose; however, the rate of correction has been improved by using a pair eight-plates (Orthofix), one on each side of the patellofemoral sulcus. (See the image below.)

This ambulatory 15-year-old boy with arthrogryposi This ambulatory 15-year-old boy with arthrogryposis has never had an osteotomy; he was managed with stapling, followed by eight-plates, when he developed a recurrence. He has full extension on the right and 7º residual fixed knee flexion deformity on the left. The eight-plates are still in situ (on the left) pending further growth.

Contraindications for surgery

There are few contraindications for surgical correction of FKFD.

Contraindications for osteotomy include the following:

  • Nonambulatory status
  • Stiff or unstable knee
  • Severe osteopenia (fixation issues)
  • Flaccid paraplegia

Contraindications for guided growth include the following:

  • Closed physes
  • Stiff or unstable knee

Medical Therapy

Medical therapy for FKFD usually consists of onabotulinumtoxinA injections in the hamstrings or baclofen administered orally or through an intrathecal pump (for cerebral palsy). [26] This is only useful for the dynamic component of crouch gait; it may be an adjunct to osteotomy or guided growth. The patient is often working with a physical therapist on hamstring stretching, quadriceps strengthening, and gait training. This approach is suitable for younger patients, but after the age of 10 years, deformities are likely to progress despite concerted efforts to the contrary.


Surgical Therapy

Posterior capsulotomy/hamstring recession

This relatively invasive soft-tissue procedure poses some risks to the posterior neurovascular structures and requires immobilization with braces, casts, or frames. (See the image below.)

For flexion contracture, spasticity management (on For flexion contracture, spasticity management (onabotulinomtoxinA/phenol/baclofen) or hamstring recession may offer some improvement, but these measures cannot overcome fixed knee flexion deformity.


Supracondylar extension osteotomy of the femora has a long track record and is the default approach for many surgeons. Unfortunately, there are associated drawbacks, not the least of which is recurrence with growth, thus mitigating the temporary benefit of this maximally invasive treatment. (See the images below.) The varied techniques, tricks, results, and complications have been well described in standard textbooks and journals.

Starting at age 4 years, this patient subsequently Starting at age 4 years, this patient subsequently underwent bilateral extension osteotomies 4 times, with recurrence each time as expected. Perhaps this sequence could have been abbreviated with guided growth, which, even if repeated, requires no casts or delay in weight bearing.
Part 1 of 5. This 5-year-old boy presented with a Part 1 of 5. This 5-year-old boy presented with a congenital knee flexion deformity. His only prior surgery was a Symes disarticulation for fibular absence and a rigid teratologic foot deformity. He was ambulatory in a prosthesis.
Part 2 of 5. This patient underwent a supracondyla Part 2 of 5. This patient underwent a supracondylar extension osteotomy of the femur.
Part 3 of 5. Because of a relatively rapid recurre Part 3 of 5. Because of a relatively rapid recurrence of fixed knee flexion deformity, this patient underwent anterior stapling of the femur; unfortunately, the staples migrated, but the physis is still open.
Part 4 of 5. The staples in this patient were retr Part 4 of 5. The staples in this patient were retrieved and replaced with a pair of eight-plates.
Part 5 of 5. If we could turn back the clock, perh Part 5 of 5. If we could turn back the clock, perhaps guided growth would have been sufficient to correct the problem in this patient, without an osteotomy or cast. The effective gain in limb length would occur gradually, without risk to the neurovascular structures.

Frame distraction

With or without soft-tissue release, some authors favor frame distraction as a means of gradual correction of FKFD. However, the bilateral nature of these problems makes this method relatively expensive and unwieldy. Furthermore, even with protracted bracing, recurrence is relatively common.

This girl born with a teratologic knee flexion def This girl born with a teratologic knee flexion deformity and absent quadriceps had previous posterior capsulotomy, supracondylar osteotomy, and attempted stapling. Subsequently, she had a spatial frame applied to gradually extend the ankylosed knee; however, she fell and sustained a Salter I fracture of the proximal tibia.

Guided growth

Guided growth is a newer approach that consists of anterior hemiepiphysiodesis of the distal femora. [27] Staples were originally used, but it became apparent that some children were relatively small for the Blount staples. [25] These rigid devices would occasionally migrate or permit relatively slow correction.

Using a pair of eight-plates as an alternative has resolved the problem of hardware migration and enabled more rapid correction. The titanium plates, though intracapsular, are nonarticular, being placed medial and lateral to the patellofemoral sulcus. Thus, they are well tolerated, even by young children. (See the images below.)

Guided growth permits one to address the fixed kne Guided growth permits one to address the fixed knee flexion deformity at or close to the level of the CORA (center of rotational axis of deformity). This is efficient and prevents the need for translocation, such as is required in an osteotomy. The gradual correction poses no risk to the neurovascular structures.
With the C-arm in the lateral, horizontal position With the C-arm in the lateral, horizontal position, the physis is localized. A Keith needle is placed in the physis, and two 1.6-mm guide pins are inserted: one medial and one lateral to the sulcus. The cannulated 4.5-mm screws are then inserted. They need not be parallel, but they should not transgress the physis, joint, or posterior cortex.
For fixed knee flexion deformity, an eight-plate i For fixed knee flexion deformity, an eight-plate is placed on either side of the patellofemoral sulcus, through a small arthrotomy. Though intracapsular, the plates are nonarticular; synovitis has not been observed.
The efficacy of floor reaction braces is compromis The efficacy of floor reaction braces is compromised in the presence of fixed knee flexion deformity. However, they may be continued following guided growth, pending correction, whereupon bracing may be unnecessary, provided the quadriceps are sufficiently strong.

If one elects to employ guided growth, it is important to ascertain whether the distal femoral physes are open and whether there is, ideally, 12 months or more of predicted growth remaining. The decision to undertake concomitant multilevel reconstructive procedures, including hamstring recession for dynamic contracture, is left to the discretion of the surgeon.

Note, however, that as FKFD gradually corrects, there may be beneficial effects upon the hip, spine, and ankle. Therefore, it may be wise to await full knee extension and address residual deformities at the time of eight-plate removal.

The key aspects of the procedure may be summarized as follows:

  • Supine position with knee flexed on bolster
  • Tourniquet control
  • Image intensifier: parked in cross-table, horizontal position
  • Two incisions (3 cm long), medial and lateral to the patella
  • Open capsule and synovium
  • Keith or similar needle (sequentially) placed into the anteromedial and anterolateral physis
  • Application of an eight-plate (eg, Orthofix), usually 16 mm
  • Introduction of 1.6 guide pins, first epiphyseal and then metaphyseal - Pins need not be parallel but should avoid the physis and joint
  • Predrilling of cortex (to a depth of 5 mm)
  • Insertion of the 4.5-mm titanium, self-tapping, cannulated screws (24 or 32 mm in size)
  • Soft dressing

Postoperative Care

Typically, treatment is provided either on an outpatient basis or with an overnight stay. Immediate range of motion and weightbearing are encouraged. Bracing and physical therapy are resumed as indicated.

One study found that in children with cerebral palsy, the pain pump is effective in postoperative pain management after lower extremity orthopedic procedures. [28]



Complications of posterior capsulotomy include the following:

  • Neurovascular damage
  • Undercorrection or overcorrection (posterior cruciate ligament release)
  • Recurrent deformity

Complications of supracondylar osteotomy include the following:

  • Neurovascular damage
  • Loss of fixation
  • Undercorrection or overcorrection - 2º varus or valgus
  • Pathologic fracture
  • Recurrent deformity

Complications of frame distraction include the following:

  • Pin tract problems
  • Infection
  • Recurrent deformity

Complications of guided growth include the following:

  • Undercorrection, if not enough growth remains
  • Overcorrection, if the patient is lost to follow-up
  • Recurrent deformity
  • Premature growth arrest will not occur if the periosteum is protected

When compared to the other options, guided growth has far fewer risks and complications and is more cost-effective. The procedure is well tolerated, and the recovery is rapid. It may be repeated as necessary and is readily combined with other procedures as indicated.


Long-Term Monitoring

The patient should be seen at 3-month intervals to measure FKFD and assess gait. Functional limb length and stride length will improve as the knee straightens.

Remove plates if and when the knee is fully extended (avoid recurvatum). Reinsert plates as needed if FKFD recurs with growth.

Follow the patient until skeletal maturity isn reached.