By Shalmali Pal
Knee pain is common in children with CP, but given the many health challenges facing this patient population, knee symptoms may not be given high priority. Proper diagnosis and treatment of knee pain, however, can be key to maximizing a childʼs mobility and quality of life.
Knee pain affects one in five ambulatory children with cerebral palsy (CP).1 But these patients have a range of health concerns—behavioral, cognitive, psychological, emotional, and biomechanical—and all require different levels of management. That’s why practitioners may not be aware of knee pain in children with CP unless they go looking for it.
“Clinicians are usually focusing on the bigger issues, so knee pain kind of falls down their checklist,” explained Frances Gavelli, PhD, lab chief of the National Institute of Biomedical Imaging and Bioengineering at the National Institutes of Health (NIH) in Bethesda, MD. “The child may not even mention it because what’s a little knee pain when they have more complex issues to deal with?”
Katharine Alter, MD, medical director of the NIH’s Gait Lab, agreed that if clinicians don’t ask about knee pain in this population, they won’t hear about it.
“A lot of practitioners don’t ask children with CP specifically about musculoskeletal pain, especially if they are under the age of twelve,” Alter said. “Of course, part of the problem is communication—how accurately can a three-year-old answer the question, ‘Are you having knee pain?’”
And yet, a recent study from the Children’s Orthopaedic Center in Los Angeles found a 21% prevalence of knee pain in ambulatory kids with CP. Susan Rethlefsen, PT, DPT, and colleagues retrospectively reviewed the records of 121 children with CP. Rethlefsen is the lead physical therapist (PT) at the center’s John C. Wilson Motion Analysis Lab.
The authors noted the following:
- The likelihood of knee pain was almost five times higher in girls than boys.
- The likelihood of knee pain increased with age by about 13% per year.
- The presence of malignant malalignment syndrome showed an association with knee pain severity, which trended toward statistical significance.
- The prevalence of knee pain was equal for Gross Motor Functional Classification System (GMFCS) levels I to III.
Finally, the group found that the eight children who walked with the greatest stance knee flexion (GMFCS level IV) did not report knee pain. The finding may seem counterintuitive because a more severe crouch is generally associated with patellofemoral pain (PFP). But the result did not come as a surprise to the authors.
In a joint email to LER, Rethlefsen, along with coauthor Robert Kay, MD, vice chief of the center, explained that the patients who walked with the greatest amount of knee flexion also walked the least.
“So it makes sense that they put less stress on their patellofemoral joint structures than their more ambulatory peers, and did not experience knee pain,” they wrote.
But that doesn’t mean clinicians can skip asking about knee pain in patients who are mainly sedentary, Rethlefsen and Kay pointed out.
“It is important that practitioners ask about leg and knee pain in children with CP,” they told LER. “Sometimes, the pain will be worsened by specific activities and/or positions, such as going up and down stairs, squatting, or sitting for prolonged times with flexed knees.”
Alter agreed that nonambulatory or less ambulatory patients can experience PFP just as often as ambulatory patients. She said that she’d like to see how the patients in the study by Rethlefsen’s group are doing in 10 years—for example, if a CP patient who continues to walk in crouch all day at school has a higher incidence of pain than those who do only household walking.
“There are a lot of different subpopulation studies within the larger population of children with CP that could…fine-tune our knowledge in regard to pain, crouch, and pain markers,” Alter wrote.
Rethlefsen said her group’s next step would be to investigate whether or not radiographic factors (such as patella alta, patellar pole abnormalities, and tibial tubercle abnormalities) are related to knee pain in children with CP.
In 2012, Gavelli, Alter, and colleagues conducted a case-controlled study in 20 CP patients, many of whom were in their teens, to quantify the role of patellofemoral kinematics in the development of anterior knee pain (AKP).2
Patients were assessed using a variety of physical tests and then underwent 3D magnetic resonance imaging (MRI), with images acquired during active leg extension and under volitional control. Kinematic markers associated with AKP included greater patellofemoral extension, valgus rotation, and superior and posterior patellar displacement relative to controls and to the subgroup of participants with CP and no AKP.
While Gavelli and Alter continue their research in this area, they suggest that practitioners be aware of those three markers when trying to get a handle on knee pain in younger CP patients sooner rather than later. That information can be incorporated into the physical exam and shared with the physical therapist, the physiatrist, the orthopedist, or the general pediatrician, Alter said.
The end game with identifying these markers is implementing early intervention, they explained. Regardless of the child’s level of ambulation, knee pain needs to be evaluated and managed to keep the patient as mobile as possible.
“The consequences of inactivity and/or a cessation of walking are a cascade that includes atrophy of muscles, deconditioning, increased weakness, joint problems, and loss of function in other areas. So whatever we can do to keep kids active, including walking, is great,” Alter wrote.
Tom Novacheck, MD, a pediatric orthopedic surgeon at Gillette Children’s Specialty Healthcare in St. Paul, MN, recommended a general gait analysis that includes the assessment of knee function as a reliable assessment tool that may be more accessible than MRI for most practitioners.
“You can get a measurement of the stresses on the knee joint, and that will tell you if the stresses are in the front or the inside or the outside of the knee,” explained Novacheck, who is also director of the James R. Gage Center for Gait and Motion Analysis at Gillette. “I find it more helpful than x-rays. X-rays may be abnormal, but that doesn’t necessarily tell you the cause of the pain. It’s actually more helpful to know where the stresses are, and I find that gait analysis is better for that.”
Malignant malalignment is often missed during a general physical exam, and requires computerized motion analysis to pinpoint, Rethlefsen and Kay explained, but there is a lower-tech screening option.
“An an easy way to screen for it is to place a mark on the patient’s patellas and video the patient walking from the front. If the knee points excessively in and the foot excessively out during stance phase, malignant malalignment is likely,” they wrote.
Gait analysis can also help determine if other biomechanical problems, particularly in the feet, play a role in CP-related knee pain. Novacheck pointed out that if flat foot (pes planus) is an issue for a patient, then patellofemoral pain may follow.
He added that gait analysis data can help practitioners with treatment decisions.
“Your diagnosis after the evaluation will help you decide what the goal is—is it pain management or improving gait? That determination may send your patient down different treatment pathways,” he said.
The treatment spectrum
Experts recommend mixing and matching from a spectrum of treatment options, starting with conservative modalities.
“For all treatment, there is a continuum where you may pick one or more treatments at different times, depending on the patient’s age and functional skills,” Alter explained.
For instance, spasticity is a major issue in the majority of patients with CP. As the leg muscles grow less and less elastic, increased pain and stiffness can lead to PFP. If an immediate goal is to diminish pain, then botulinum toxin injections are a good route. The pain reduction seen after toxin injections may be because of spasticity reduction or because of antinocioceptive effects that maintain or increase the patient’s mobility, Alter said.
Novacheck also recommended toxin injections for addressing high muscle tone and managing pain, as well as other tried-and-true methods such as ice and heat or anti-inflammatory medications.
Taping is another treatment option, the NIH specialists said, as it may reduce some of the abnormal movements of the patella during knee extension, thereby stopping it from subluxing up and over the lateral condyle (see “Patellofemoral taping: Pain relief mechanisms,” LER August 2010, page 25).
“Kids with CP tend to be hypomobile when it comes to the patella,” Gavelli explained. “There is such tension created by the spastic or shortened quadriceps that it has pulled the patella up too high and it’s like a bow string. So a small bit of extra force can offset the balance and cause dislocation. The constant wear and tear from the abnormal position of the patella and dislocation lead to joint problems and pain.”
Also on the treatment spectrum is physical therapy, which may include hip strengthening for reducing pain and increasing lower body strength or quadriceps and hamstring stretching to aid mobilization (see “Strength training improves function in children with CP,” LER: Pediatrics February 2014, page 15).
All of the experts agreed that physical therapy can work wonders for diminishing knee pain—but it also requires patient and caregiver commitment to be successful.
Alter stressed that physical therapy programs need to be based on the child’s level of engagement and, ideally, tailored to their interests. Possible barriers to physical therapy include language or communication issues, behavioral problems, or difficulty following directions.
As for knee braces and orthoses, the experts offered mixed opinions. As Novacheck pointed out earlier, orthoses may be an option if the patient has a foot health problem that is tied to the knee pain. A recent article in Current Opinion in Pediatrics recommended that orthoses be part of the treatment plan for CP-related foot deformities, noting that foot realignment may improve knee function during stance.3
Alter agreed that controlling distal biomechanical problems of the foot, ankle, or both may help the knee, but she cautioned that, when it comes to ankle-foot orthoses (AFOs), the style of the device is important.
“There are some braces that are designed to reduce crouch,” she explained. “But these may not be useful if the patient has a degree of knee flexion contracture.”
Many patients crouch through a combination of weakness and contracture, she said, and “in this subgroup of patients with crouch, these anti-crouch AFOs may not be tolerated or effective.” Alter said. She suggested that knee AFOs (KAFOs) may be useful in some patients with crouch because they can limit flexion, which in turn may alleviate knee pain.
But bracing is only valuable if the patient is compliant, and depending on the child’s age, that can be a major hurdle (see “Kids, clothes, and AFOs: Finding just the right fit,” LER: Pediatrics May 2014, page 9). Novacheck noted that it’s during adolescence, when growth spurts are occurring, that children with CP are most likely to complain about knee pain—but that is an age group that doesn’t smile on anything that makes them more different than their peers.
Finally, there is surgical intervention, which experts agree should be considered only when all other treatments have proven ineffective.
“The vast majority of these children do not require any surgery for their knee pain,” Rethlefsen and Kay stressed. “Surgery should only be considered if conservative measures have failed after a diligent nonoperative trial.”
Surgical options for addressing crouch or limited knee extension include quadriceps lengthening, patellar tendon advancement, surgery on the femur itself, or taking a wedge out of distal femur to improve the patellofemoral kinematics.
“I would say that, if the patient has a lot of bone and joint deformity—some of the common things are femoral anteversion, tibial torsion, knee contracture, foot deformity, patella alta, and patellar stress fractures—those are all things that don’t respond to conservative treatment,” Novacheck said. “Those require surgery.”
Shalmali Pal is a freelance writer based in Tucson, AZ.
- Rethlefsen SA, Nguyen DT, Wren TA, et al. Knee pain and patellofemoral symptoms in patients with cerebral palsy. J Pediatr Orthop 2014 Aug 28. [Epub ahead of print]
- Sheehan FT, Babushkina A, Alter KE. Kinematic determinants of anterior knee pain in cerebral palsy: a case-control study. Arch Phys Med Rehabil 2012;93(8):1431-1440.
- Kedem P, Scher DM. Foot deformities in children with cerebral palsy. Curr Opin Pediatr 2015;27(1):67-74.