Pediatric Fixed Knee Flexion Deformities Treatment & Management

Medical therapy for fixed knee flexion deformity (FKFD) usually consists of Botox injections in the hamstrings or baclofen administered orally or through an intrathecal pump (for cerebral palsy). 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 is suitable for younger patients, but after the age of 10 years, deformities are likely to progress despite concerted efforts to the contrary.

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.

Osteotomy

Supracondylar extension osteotomy of the femora has a long track record and is the default mode 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. The varied techniques, tricks, results, and complications have been well described in standard textbooks and journals.

Frame distraction

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

Guided growth

Guided growth is a new concept that consists of anterior hemiepiphysiodesis of the distal femora. Originally accomplished with staples, it became apparent that some children were relatively small for the Blount staples.^[20] These rigid devices would occasionally migrate or permit relatively slow correction. Using a pair of 8-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.

Guided growth

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 fixed knee flexion deformity (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 8-plate removal.

Guided growth

• 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
• Place Keith or similar needle (sequentially) into anteromedial and anterolateral physis
• Apply 8-plate (Orthofix): usually 16-mm size
• Introduce 1.6 guide pins: first the epiphyseal, then metaphyseal
• Pins need not be parallel but should avoid the physis and joint
• Predrill cortex (5-mm depth)
• Insert the 4.5-mm titanium, self-tapping, cannulated screws (24- or 32-mm size)
• Soft dressing

• Typically, either as outpatient or with an overnight stay
• Immediate range of motion and weight bearing are encouraged
• Resume bracing and physical therapy 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.^[23]

• At 3-month intervals, to measure fixed knee flexion deformity (FKFD) and assess gait
• Functional limb length and stride length will improve as the knee straightens
• Remove plates if/when knee is fully extended (avoid recurvatum)
• Reinsert plates as needed if FKFD recurs with growth
• Follow-up until skeletal maturity

Posterior capsulotomy

• Neurovascular damage
• Undercorrection or overcorrection (PCL release)
• Recurrent deformity

Supracondylar osteotomy

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

Frame distraction

• Pin tract problems
• Infection
• Recurrent deformity

Guided growth

• Undercorrection: if not enough growth remaining
• Overcorrection: if 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.

The natural history of fixed knee flexion deformity (FKFD) is insidious progression despite bracing, therapy, and even repeated surgical intervention. The goal of treatment is to maintain standing and, hopefully, walking ability while minimizing complications and encumbrance.

One must weigh the risk-to-benefit ratio of any invasive treatment, recognizing that it may need to be repeated. Like so many conditions, it is appealing to consider early intervention, before the onset of secondary problems such as patellar migration or fragmentation. With this in mind, repeated guided growth may be the pathway of least harm and maximum benefit.

In a clinical series of 18 patients with 29 cases of FKFD, the rate of correction was 1.74 º per month; the highest rate noted was nearly 4 º per month. Without the need for immobilization, these children have experienced rapid recovery with minimal setbacks from the surgery.

There may eventually be other methods of temporary physeal restraint. The allure of biodegradable implants or remote-control techniques by electronic or radiofrequency methodology will undoubtedly spur further research.