Pediatric Fixed Knee Flexion Deformities

Pediatric Fixed Knee Flexion Deformities

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Children with neuromuscular disorders often manifest fixed knee flexion deformity as a consequence of muscle weakness or imbalance. They tend to develop a crouch gait pattern that may prove refractory to physical therapy, bracing, or spasticity management (Botox/baclofen) [1] ; for those children, surgical management may be indicated.

In addition to hamstring recession for contracture, fixed deformities may require posterior capsulotomy or supracondylar osteotomy. Alternatively, or in addition to these procedures, some surgeons have resorted to external frame distraction. A more recently developed approach is to utilize guided growth of the anterior distal femur to achieve safe and gradual correction of the crouch pattern.

The image below depicts chronic fixed knee flexion deformity (FKFD).

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.

Normal knee anatomy is characterized by the following:

FKFD is characterized by the following:

Ipsilatera, regional deformity is characterized by the following:

Normal sagittal alignment includes the ability to lock the knee in full extension, stabilized posteriorly by the cruciate ligaments, posterior capsule, hamstrings, and gastrocnemius. This permits the child to bear full weight without pain, instability, or fatigue, because the ground reaction force is slightly anterior to the extended knee, allowing the child to lock the knee in extension during stance.

In cerebral palsy, spastic hip flexors and hamstrings combine to flex the knee, causing the ground reaction force to pass behind it and produce a flexion moment. With compromise of the hip extensors and quadriceps, gravity and fatigue force the child into a progressive crouch gait pattern. [3, 4, 5, 6] Knee pain is a frequent complaint, which may reflect fatigue of the quadriceps, tension failure of the patellar ligament or its bony attachments, or both. Ankle or hindfoot valgus will contribute to lever arm insufficiency and further decrease the extensor moment at the knee.

Children with spina bifida often have intrinsic weakness of the quadriceps, combined with sparing or (if tethered) spasticity of the hamstrings. This puts them at risk for the same problem of FKFD and progressive crouch gait. [6] Compounded by ankle valgus, and perhaps planovalgus of the foot, they too have lever arm dysfunction with loss of push-off strength.

Children with arthrogryposis, pterygium syndrome, and other teratologic conditions may manifest fixed knee flexion at birth, with or without congenital lateral dislocation of the patella. They often present unique challenges for the surgeon, and treatment must be individualized accordingly. The deformity may be oblique plane, including valgus or, less commonly, varus of the knee. Concurrent dislocation or stiffness of the hip and clubfoot or vertical talus may have to be addressed as well.

A number of relatively common conditions, especially cerebral palsy and spina bifida, may lead to progressive FKFD, despite appropriate physical therapy and bracing. Congenital FKFD, with or without fixed lateral dislocation of the patella, may be evident on perinatal ultrasonography.

Knee flexion contractures due to hamstring contractures or quadriceps weakness are prevalent in growing children with neuromuscular conditions, such as cerebral palsy, spina bifida, and arthrogryposis. A subset of these patients will develop FKFD; the frequency of FKFD is not known. This condition is a component of bilateral, multilevel deformities that may literally be the rate-limiting step with respect to functional ambulation.

The natural history of FKFD is one of insidious progression despite bracing, therapy, and even repeated surgical intervention. The goal of treatment is to maintain standing and, it is to be hoped, 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 1.74º per month; the highest rate noted was nearly 4º per month. Without the need for immobilization, these children have experienced rapid recovery with minimal setbacks from the surgical treatment.

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Peter M Stevens, MD Professor, Director of Pediatric Orthopedic Fellowship Program, Department of Orthopedics, University of Utah School of Medicine

Peter M Stevens, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Orthopaedic Surgeons, American Orthopaedic Association, Pediatric Orthopaedic Society of North America

Disclosure: Received royalty from Orthofix Inc for independent contractor; Received royalty from Orthopediatrics, Inc for independent contractor; Received honoraria from Orthopediatrics, Inc for speaking and teaching. for: Orthodox, Orthopediatrics.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Paul E Di Cesare, MD 

Paul E Di Cesare, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American College of Surgeons

Disclosure: Nothing to disclose.

Jeffrey D Thomson, MD Professor of Orthopedic Surgery, University of Connecticut School of Medicine; Director of Orthopedic Surgery, Connecticut Children’s Medical Center; Vice President of Medical Staff, Connecticut Children’s Medical Center

Jeffrey D Thomson, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, Pediatric Orthopaedic Society of North America, Scoliosis Research Society

Disclosure: Nothing to disclose.

Pediatric Fixed Knee Flexion Deformities

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