cerebral palsy (CP): a motor disorder caused by a brain injury or brain development issues either before birth, at birth, or within the first few years of life. CP can be classified by the symptoms it causes (spastic, dyskinetic/athetoid, ataxic, or mixed), the number of body parts it affects (diplegic, triplegic, quadriplegic, or hemiplegic), and its severity (mild, moderate, or severe, or more specifically using the GMFCS scale, which ranks severity from I, mildest, to V, most severe). SDR was developed for people with spastic CP, but it may also benefit those with mixed CP if spasticity is their main issue. Most people who pursue SDR have spastic diplegia CP, which means that their spasticity is mainly in their legs. However, research has also shown that it can benefit those with quadriplegia (CP that affects the whole body), triplegic (CP that affects three limbs, typically both legs and one arm), and hemiplegia (CP that affects an arm and a leg on one side of the body).
contracture: permanent muscle tightness. Contractures can be caused by many factors, including long-term spasticity, growth spurts in people with CP, and gait patterns that don’t allow tendons and muscles to fully stretch. Contractures and can’t be addressed by stretching alone; the tendon needs to be surgically lengthened. (See also: percutaneous lengthening (PERCS).)
conus medullaris: the area at the end of the spinal cord where all the nerves meet. This is typically at the L1 level of the spine. Single-level SDR is performed at the conus medullaris.
diplegia: CP that mainly affects both legs. Many people with diplegia also have some upper-body involvement, but this isn’t always the case. Most SDR patients have diplegia. (See hemiplegia, triplegia, and quadriplegia for other types of CP.)
dystonia: muscle tone that goes back and forth between being normal and being too high. Sometimes, it might seem like the muscle is twitching, because a dystonic muscle contracts in a “random” way. These contractions can cause sudden, uncontrolled movements that can throw off a person’s balance. SDR does not address dystonia. Sometimes, dystonia is masked by spasticity and can become more obvious after SDR. However, many patients are wrongly diagnosed with dystonia because it can be difficult to tell it apart from spasticity.
hemiplegia: CP that affects only one arm and one leg on the same side of the body. Often, but not always, the arm is more severely affected than the leg. SDR patients with true hemiplegia have nerves cut on only one side of the body. (See diplegia, triplegia, and quadriplegia for other types of CP.)
hereditary spastic paraplegia (HSP): a genetic brain condition that can sometimes mimic spastic diplegia CP. HSP is often progressive, meaning that it gets worse over time. Some forms of HSP worsen quickly, and others worsen very slowly or not at all. Sometimes, HSP appears in early childhood and can be mistaken for CP. Other times, people don’t start experiencing symptoms until later in childhood, adolescence, or adulthood. Most forms of HSP are the pure form, which means that symptoms are mainly tightness and weakness in the lower body. If HSP involves other neurological symptoms, like cognitive issues or vision impairments, then it is called complex. SDR candidates with HSP typically have the pure form of the disorder.
multi-level SDR/multi-level laminectomy: a more invasive version of SDR. The surgeon removes many pieces of vertebrae from the back in order to access the spinal cord. The recovery process is longer for multilevel SDR, and studies have found that it can lead to a higher risk of back deformities like spinal curvature (scoliosis). (See also: single-level SDR.)
overflow: when a person tries to move one muscle group and another muscle group also activates. Everyone has overflow sometimes, even people without CP, but it is especially an issue for people with CP. Basically, the injured brain doesn’t send all of the right signals to turn ON muscles (excitatory inputs), but it also don’t send enough signals to turn OFF muscles (inhibitory inputs). As a result, sometimes muscles don’t activate enough and sometimes overflow happens, which is when they activate too much. SDR may help with this selective control issue, making it easier for people to isolate individual muscles, but it often continues to be an issue to some extent.
selective dorsal rhizotomy (SDR): currently the only treatment that can permanently reduce or eliminate spasticity. This surgery that involves cutting nerves in the spine that send too many signals to the lower body. Selective means only a fraction of the nerves are cut, typically the nerves that are overfiring the most. Dorsal means that only the dorsal (sensory) nerves are cut, which are the nerves that send information to the brain about the sensation and position of a muscle. (The ventral (motor) nerves are not cut during SDR. Ventral nerves send information from the brain to the muscles to tell the muscles to move.) Rhizotomy refers to any surgery that involves cutting nerves (or, more precisely, nerve branches) in the spinal cord.
single-level SDR/single-level laminectomy: a minimally invasive version of SDR. The surgeon removes a piece of bone from the spine, typically at the L1 level, which is slightly lower than the middle of the back. This is where a structure called the conus medullaris is. The conus medullaris is where all the nerves meet. As a result, the surgeon can test the nerves for multiple levels of the spinal cord without having to remove lots of bone to access each level of the spinal cord separately. This version of SDR is associated with a shorter recovery time and less risk of long-term spinal deformities, like scoliosis, which have been linked to multi-level SDR.
spasticity: an increase in muscle tightness that occurs especially when movements are fast. Spasticity happens when the injured brain is unable to send signals to turn off overfiring sensory nerves in the spinal cord. (See dystonia and overflow for other types of high muscle tone.)
tone: the amount of tension or contraction in a muscle. When someone has normal tone, it means that their muscles are contracted just a little bit—they aren’t hypotonic (too loose, which would make it harder for them to start a movement), but they aren’t hypertonic either (too tight). (See spasticity, dystonia, and overflow for specific descriptions of different types of tone, as well as the Science FAQ for more detail.)
triplegia: CP that significantly affects three limbs. People with triplegic CP are usually affected in both legs and in one arm. Oftentimes, this form of CP results from diplegia layered on top of hemiplegia, perhaps because of PVL (the brain injury that most often causes diplegia) layered on top of a stroke (the brain injury that most often causes hemiplegia). (See diplegia, hemiplegia, and quadriplegia for other types of CP.)
partial ventral rhizotomy (PVR): a surgery developed by Dr. Park in which a small percentage of ventral (motor) nerve rootlets are cut in order to stop the legs from crossing (i.e., scissoring) when a person takes steps. If Dr. Park determines that it is necessary, this surgery is done at the same time as SDR. If scissoring is mild, SDR alone may fix the issue completely. However, if too many motor signals are being sent to the adductor (inner thigh) muscles, removing spasticity may not be enough to stop the scissoring. By reducing some of the motor input to these muscles, this surgery aims to significantly reduce scissoring. Children who have PVR alongside SDR tend to have a bit of a longer recovery and more significant post-op motor weakness, but the success rate for Dr. Park’s PVR is pretty high. The goal of this procedure is to avoid needing adductor lengthening, because accidentally overlengthening the adductors can result in the legs being too far apart when somebody stands and walks. However, in some patients the PVR doesn’t fix the scissoring enough and they still need adductor lengthening.
percutaneous lengthening (PERCS): a minimally invasive tendon-lengthening surgery performed by Dr. Dobbs in St. Louis. This surgery typically involves making small cuts along the tendon like the slits in a feather. Traditional tendon lengthening procedures involve more cutting of the tendon and may result in more long-term weakness. Many people need PERCS after SDR to address tendon shortening.
periventricular leukomalacia (PVL): the brain injury most commonly associated with spastic diplegia. PVL is an injury to a boomerang-shaped area in the brain that sends signals to the legs. If the area of the injury widens by a few millimeters, PVL can also affect the upper body. This is a very common brain injury among premature babies because area around the ventricles of the brain is especially vulnerable to lack of blood flow or lack of oxygen. Sometimes, if it isn’t certain that somebody has spastic CP, the SDR surgeon will request an MRI scan to check for PVL. That’s because PVL is very highly linked to the presence of spasticity, so if a person has PVL, they’re more likely to be a candidate for SDR.
personal trainer: a person who works one-on-one with clients to help them work out and/or come up with an exercise plan. Personal trainers typically have some form of certification but are not physical therapists/physiotherapists because they do not have a degree in the field of physical therapy. Personal trainers’ services are not usually covered by insurance, but they can be very helpful for patients both pre- and post-SDR. Their routines are often quite intense, and many people with CP/HSP like working with them because they treat clients like athletes. Many people supplement their post-SDR rehab with a personal trainer. In later stages of rehab, some actually replace traditional therapy with personal training. Both trainers and therapists play an important role in SDR rehab, so speak with your care team to determine the best path forward for you.
physical therapist/physical therapy (PT): In American English, PT is a common abbreviation for physical therapist or physical therapy. UK English typically uses physiotherapist or physiotherapy.
quadriplegia: CP that significantly affects all four limbs. People with quadriplegic CP are usually affected in their whole body, so they may also have trouble with head control and significant core weakness as well. (See diplegia, hemiplegia, and triplegia for other types of CP.)
root/rootlet: the branch of a nerve. When we say that SDR involves cutting nerves, we actually mean that it involves cutting nerve rootlets. Nerves have branches (called roots), like the branches of a tree. The front branch is called the ventral/motor root, which receives motor information from the brain. The back branch is called the dorsal/sensory root, which sends sensory information to the brain. These roots then branch out into smaller branches called rootlets. During SDR, the sensory rootlets are separated from each other, individually tested, and cut.