Cervical Laminoplasty
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Table of Contents
Cervical spine laminoplasty is a treatment for multi-level cervical spondylotic myelopathy (CSM) without accompanying instability or cervical kyphosis. The goal is to decompress the spinal canal and relieve pressure on the spinal cord without destabilizing the spine.
CSM is caused by impingement of the spinal cord by degenerative bony and ligamentous structures that decrease the volume of the canal. Surgery reliably halts stepwise deterioration in neurologic function (e.g. loss of fine motor control, altered gait and balance).
CSM may be treated surgically through multiple approaches (anterior, posterior), with or without concomitant nerve root decompression, and with a variety of techniques (laminectomy, open-door laminoplasty, double-door laminoplasty).1 The video accompanying the article demonstrates a classic open-door cervical laminoplasty.
The patient with CSM may report neck pain and stiffness and very often headaches in the occipital region. Diffuse non-dermatomal patterns of numbness and paresthesias may be present. The patient may report weakness and have decreased manual dexterity manifested by dropping objects and having difficulty manipulating fine objects.
Gait disturbances are a strong indication for surgical intervention. The patient may report feeling unstable on feet and/or have weakness walking up and down stairs. Gait and balance can be evaluated by asking the patient to perform a heel to toe walk and a Romberg test. Urinary retention is a rare and late finding in CSM progression and hard to interpret due to the high prevalence of urinary dysfunction in an older population.
Weakness is often difficult to detect on physical exam. If present, lower extremity weakness is a very concerning finding. Proprioception dysfunction indicates dorsal column involvement and is also associated with a poor prognosis. Decreased pain or temperature sensation indicates involvement of the lateral spinothalamic tract. Decreased sensation to light touch is due to dysfunction of the ventral spinothalamic tracts.
Specific tests:
- The “finger escape” sign occurs when a patient holds fingers extended and adducted and their small finger spontaneously abducts due to weakness of the intrinsic muscles of the hand.
- The “grip and release” test is a fairly sensitive test for myelopathy affecting the intrinsic muscles of the hand. A patient without dysfunction should be able to make a fist and release it 20 times in 10 seconds.
- The inverted radial reflex is ipsilateral finger flexion when tapping the distal brachioradialis tendon.
- Hoffmann's test is performed by snapping the patient’s distal phalanx of their middle finger. Spontaneous flexion of other fingers is a positive sign.
- Sustained clonus (>3 beats) on reflex testing has a low sensitivity (about 13%) but close to 100% specificity for cervical myelopathy. However, spasticity and hyperreflexia may be absent when there is concomitant peripheral nerve disease (e.g. cervical or lumbar nerve root compression, spinal stenosis, diabetes).
- A positive Babinski test (great toe dorsiflexion) indicates damage to the corticospinal tract.
- A Romberg test is performed by having the patient stand with arms held forward and eyes closed. Loss of balance is consistent with posterior column dysfunction.
- The Lhermitte sign is present when extreme cervical flexion leads to electric shock-like sensations that radiate down the spine and into the extremities.
Several classification systems exist for CSM:
Nurick Classification- Grade 0 Root symptoms only or normal
- Grade 1 Signs of cord compression; normal gait
- Grade 2 Gait difficulties but fully employed
- Grade 3 Gait difficulties prevent employment, walks unassisted
- Grade 4 Unable to walk without assistance
- Grade 5 Wheelchair or bedbound
- Class I Pain, no neurologic deficit
- Class II Subjective weakness, hyperreflexia, dysesthesias
- Class IIIA Objective weakness, long tract signs, ambulatory
- Class IIIB Objective weakness, long tract signs, non-ambulatory
A point scoring system (17 total) based on function in the following categories:
- upper extremity motor function
- lower extremity motor function
- sensory function
- bladder function
Initial evaluation should include Cervical, AP, Lateral, Oblique, and Flexion/Extension views of the cervical spine. It is important to remember that radiographic findings do not always correlate with symptoms. 70% of patients >=70 years old will have radiographic evidence of degenerative changes. Findings to look for include degenerative changes of uncovertebral and facet joints, osteophyte formation, disc space narrowing, and a decreased sagittal diameter of the canal. The normal cord diameter is about 17mm and cord compression occurs with a diameter <13mm.
- Lateral view: the Torg-Pavlov ratio is the ratio of the canal to the vertebral body width on a lateral view. A normal ratio is 1.0 and a ratio <0.8 predisposes to stenosis and myelopathy, although this rule is not always valid in the case of large athletes.
- Oblique view: best to evaluate foraminal stenosis, which is often caused by uncovertebral joint arthrosis.
- Flexion and extension views: useful to evaluate angular or translational instability and to see evidence of compensatory subluxation above or below the stiff or spondylotic segment.
MRI is the study of choice to evaluate degree of spinal cord and nerve root compression. Myelomalacia shows up as bright signal on T2 weighted images.
Computed TomographyA CT without contrast can provide complementary information with an MRI and is more useful to evaluate OPLL and osteophytes. CT myelography is useful in patients that cannot have an MRI (pacemaker) or who have implants in the area of interest that would produce an artefact. Contrast is given via C1-C2 puncture and allowed to diffuse caudally, or given via a lumbar puncture and allowed to diffuse proximally by putting patient in the Trendelenburg position.
Representative images for this case:
Lateral C-spine 
Sagittal T2 C-spine 
Axial T2 C3C4 
Axial T2 C4C5 
Axial T2 C5C6 Nerve conduction studies have a high false negative rate but may be useful to distinguish peripheral from central process (ALS).CSM tends to be slowly progressive with intermittent periods of stability followed by deterioration, and it rarely improves with nonoperative modalities such as physical therapy.Aside from conservative therapy the main alternative to this procedure would be surgical laminectomy and fusion with instrumentation. Various other laminoplasty techniques have been described, including a double-door technique (Kurokawa’s method) and a Z-shaped laminoplasty which does not fully excise the laminae (Hattori’s method).The patient was symptomatic and had failed conservative therapy. The advantages of the open-door unilateral laminoplasty over standard laminectomy and fusion include a more minimally invasive approach, the avoidance of fusion and the possible resultant complications related to fusion, less blood loss and a faster, less painful recovery period.Some patients with CSM may be better candidates for a traditional laminectomy with fusion due to considerations of their anatomy, disease progression, degree of instability and size.
- High-speed burr
- Lamina retractor
- Escalate Laminoplasty plates, Stryker, Kalamazoo, MI
AP cervical spine 
Axial T2 C3C4 Cervical spondylotic myelopathy has a variety of clinical presentations, associated pathologies, and surgical treatments. Symptoms attributed directly to the spinal stenosis and myelopathy most often include some loss of fine motor control and altered balance and gait. They may include extremity spasticity and/or weakness and the loss of bowel and bladder function. Symptoms due to concomitant nerve root impingement include extremity pain or paresthesias in a dermatomal pattern, or weakness. Neck pain may also be caused by facet joint arthrosis.
Symptoms usually worsen in a stepwise fashion and are poorly controlled by nonoperative interventions such as soft cervical collars and epidural steroid injections. Cervical spinal canal stenosis is caused by degeneration in a number of structures about the spinal canal. These include: hypertrophic facet joints, thickened ligamentum flavum, ossified posterior longitudinal ligament, bulging intervertebral discs, and/or hypertrophic uncovertebral joints.
A variety of surgeries have been used to address CSM. These include multi-level anterior cervical discectomy and fusion (ACDF), anterior corpectomy and fusion, posterior laminectomy and fusion, and multiple posterior laminoplasty techniques.
The choice of approach, anterior or posterior, is determined by 1) the structures causing spinal cord impingement (as determined by MRI and clinical symptoms), 2) the number of levels of the spinal canal affected, 3) sagittal alignment, specifically the presence or absence of fixed kyphosis greater than 13 degrees, 4) the presence of instability (spondylolisthesis), and 5) surgeon experience.2
If a posterior approach is indicated and the spinal column is stable, laminoplasty is usually preferred. Multi-level partial laminectomy can lead to iatrogenic instability, with kyphosis and/or subluxation. Laminectomy and fusion with lateral mass plates can lead to hardware complications and adjacent segment degeneration.
Laminoplasty allows the surgeon to leave the posterior elements of the spine in place and not perform multi-level fusions. The two most commonly performed techniques of laminoplasty are the open-door and double-door (or “French-door”) techniques. Dr. Jenis demonstrates the open-door technique with this patient.
Outcome data for laminoplasty surgery is limited. Steinmetz et al showed recovery rate postoperatively to be between 50-70% with recovery stable through an average of 12 years.5
Wang et al reviewed 204 cases of open-door laminoplasty performed between 1986-2001. All patients presented with symptoms and magnetic resonance imaging (MRI) findings consistent with myelopathy secondary to multisegmental cervical stenosis with spondylosis and underwent decompression from C3 to C7.6 Improvement in myelopathy was assessed with the Nurick score. Average age was 63 years (range 36 to 92). Follow-up averaged 16 months. Postoperatively, Nurick scores improved by 1 point in 78 patients, 2 points in 37 patients, 3 points in 7 patients, and 4 points in 5 patients; 74 patients experienced no improvement, and 3 patients deteriorated by 1 point. In 2 patients there was radiographic progression of kyphosis, but in no case was subsequent fusion required. 6 patients without neck pain preoperatively developed new intractable neck pain after surgery.
The author has no financial relationship with the equipment companies mentioned in this article.
The patient undergoing the filmed procedure gave consent to being filmed for this video article and is aware that it may be published online.
Citations
- Mitsunaga LK, Klineberg EO, Gupta MC. Laminoplasty techniques for the treatment of multilevel cervical stenosis. Adv Orthop. 2012;2012:307916. doi:10.1155/2012/307916.
- Emery SE. Cervical spondylotic myelopathy: diagnosis and treatment. J Am Acad Orthop Surg. 2001;9(6):376-388. https://journals.lww.com/jaaos/Citation/2001/11000/Cervical_Spondylotic_Myelopathy__Diagnosis_and.3.aspx.
- Lehman RA Jr, Taylor BA, Rhee JM, Riew KD. Cervical laminaplasty. J Am Acad Orthop Surg. 2008;16(1):47-56. https://journals.lww.com/jaaos/Citation/2008/01000/Cervical_Laminaplasty.7.aspx.
- Steinmetz MP, Resnick DK. Cervical laminoplasty. Spine J. 2006;6(6)(suppl):S274-S281. doi:10.1016/j.spinee.2006.04.023.
- Ratliff JK, Cooper PR. Cervical laminoplasty: a critical review. J Neurosurg. 2003;98(3)(suppl):230-238. doi:10.3171/spi.2003.98.3.0230.
- Wang MY, Shah S, Green BA. Clinical outcomes following cervical laminoplasty for 204 patients with cervical spondylotic myelopathy. Surg Neurol. 2004;62(6):487-492. doi:10.1016/j.surneu.2004.02.040.
Cite this article
Louis Jenis, MD. Cervical laminoplasty. J Med Insight. 2014;2014(6). https://doi.org/10.24296/jomi/6Procedure Outline
Table of Contents
- General anesthesia is given in the operating room
- Patient is placed in the prone position
- Surgeons ensure that all bony prominences are padded
- If indicated, neuromonitoring is set up
- Patient is prepped and draped
- Landmarks (base of skull, spinous processes C2-C7) are identified by palpation and marked
- Midline skin incision is made
- Midline dissection is made through subcutaneous fat with electrocautery
- Ligamentum nuchae is identified and divided in the midline to bone
- Subperiosteal dissection of paraspinal musculature off of bilateral spinous processes, laminate, and lateral masses from C2-C7 using Bovie electrocautery
- X-ray confirmation of the appropriate levels of dissection using a Kocher clamp on a spinous process and dental probe in a facet joint
- Facet joint capsules are preserved as much as possible during dissection
- Left-sided bi-cortical osteotomies are made through the C2-C7 junctions of the laminate and lateral masses using a high-speed burr
- Underlying ligamentum flavum is palpated, but not violated at this point
- Bleeding by epidural vessels is tamponed with bone wax, FLOSEAL hemostatic matrix, and surgical sponges
- Right-sided uni-cortical osteotomies are made through the C2-C7 junctions of the laminate and lateral masses using a high-speed burr
- Cobb elevator, retractor, and fingers are used to open the left-sided osteotomy site through hinging on the right-sided uni-cortical osteotomy site
- Springiness/motion of the posterior elements is frequently checked, with further osteotomy of the hinge side as needed
- Partial release of the underlying ligamentum flavum with a curette is also performed as needed to further open the left-sided osteotomy location. The goal is an opening of 8mm
- Laminoplasty plates are inserted in the left-sided osteotomy location at C2-C6
- Through each plate, 1 screw is placed into the lamina and 2 screws into the lateral mass
- A starting awl is used to start each hole and screws are self-drilling and self-tapping. They are 6-8mm in length
- Inspect repair at each level
- Morselized bone graft from the removed spinous processes (below) is applied to the right-sided uni-cortical osteotomies to assist bony healing
- Spinous processes are partially removed from C2-C7 in order to facilitate a tension-free closure
- Interrupted sutures are used to close the paraspinal muscle fascia
- Running, subcuticular dermal closure with a Monocryl stitch
Transcription
INTRODUCTION
My name is Doctor Louis Jenis. I'm an orthopedic spine surgeon at the Boston Spine Group here at Newton-Wellesley Hospital. I'm going to describe a cervical laminaplasty in one of my patients. In general, the overview is that we bring the patient into the operating room, and after induction of general anesthesia, we place the Mayfield tongs onto the skull for prone positioning. After the patient is positioned, we then carefully perform an exposure of the posterior cervical spine and identify the appropriate levels for the laminaplasty to be performed. We create the laminaplasty defect and then hinge it open. The next step is to keep the hinge open by placing laminaplasty plates or instrumentation. The last part of the procedure is closure, and after the patient is returned to the supine position, the Mayfield tongs are removed and then - he is then excavated.
CHAPTER 1
So what we'll do is just mark out some landmarks here. This is the base of the skull. Midline. C2 spinous process should be right around here and C7 in this general area. So soon as - we'll just make an incision here.
Okay, so we'll - we'll start. So midline incision. So we just kind of slowly dissect down to the ligamentum nuchae, and the more midline we stay, the less bleeding will occur. C2 right here - and we'll just try to stay midline. The more midline you stay, the less muscle dissection there is. A little deeper. So we dissect right down to the tip of the spinous process. So after we get down to the midline, we'll start dissecting the paraspinal muscles off the spinous process and the lamina, and we try to stay subperiosteal as much as possible.
And then we start to come down on the lamina on each - at each level. C2 spinous process is right here. The - the muscle attachment, see, coming onto the C2 spinous process is very important to maintain, and if they are detached, at the closure we'll often try to reattach them for stability of the upper cervical spine. So we try to maintain them as much as possible. The other muscles are all stripped pretty easily though. So as we do the exposure, the sponges, which helps retract the muscle - and it also helps to control bleeding - and we will often just alternate side to side with the exposure until we get up to the junction of the lateral mass and lamina. So now we'll just dissect the other side. Okay? You see? I think that's too risky. You'll see that the tips of the spinous process are bifid. So you can see the spinous process here with both sides of it are almost bifid, which means when we're dissecting along the lamina, we often have to come around the spinous process to get to the lamina. And the Cobb retractor - the Cobb elevator allows us to pull the muscle away from the side.
Then we'll just take a localizing x-ray - just confirm the level of our dissection. Alright, two Kochers. So to mark the level, we'll put a Kocher clamp on the spinous process. Dental. The other way to mark the level, we could put something into the facet joint to mark, and we'll take a quick picture.
Okay, so C3 is right here. This is the lamina. This is the lateral mass on this side. So what we don't want to do is dissect too far onto the lateral mass capsule, which could potentially cause some instability postoperatively, so we try to stay a little bit superficial - preserve the facet joint capsule as much as possible. And the important landmark that we want to find is that junction of the lateral mass and lamina. That'll be the site of our laminaplasty - osteotomy will be right there. So that is as far as lateral as we typically need to get. Alright, so 3, 4, 5, 6, and 7 - great. So the first step of the procedure is the exposure. We have our levels marked. This is C3, C4, C5, C6, and C7. We can see the lamina and the lateral mass. The important anatomic landmark here is the junction of the lateral mass and lamina. Basically it's a small valley right here between the two. That's the site of the osteotomy. So we're going to hinge it open. The hinge on the right side will open it on the left side. So we're going to osteotomies the outer and inner cortex on this side, and on the right side, we'll just osteotomies the outer cortex and greenstick fracture the lamina open.
CHAPTER 2
So we'll start at each level, and then we'll go to the other side. 10-4. As we go through the outer cortex, we feel for the inner cortex, and the softness that we'll feel next will be the ligamentum flavum. Suction at 5. There we go. Good - that's nice and soft.
Okay. So typically, when do we do the osteotomy, the bleeding is going to occur from some epidural vessels. And sometimes we just take some bone wax, and we can use that to kind of tamponade the - the epidural. Give me some FloSeal. Let's actually use that in a sponge. Okay.
Let's - let's try working on your side now. So after the left side is osteotomized, now we'll make the hinge on the right side. Tell me when you're going.
Ready? On. Put that retractor back in.
So the next part of the procedure after we make the osteotomy on both sides is to start releasing the lamina and creating that greenstick fracture. Basically, what I like to do is put a Cobb in and in turn, very gently, you can start to see some give of the lamina. And we'll just kind of work each level as we go here, so we'll go to the next set. Ready? Go. Close up higher. And same thing - we just got to give it a little twist. Start releasing it. That's getting there - you can go just high. Tell me when. And it's been opened. I'm going to move this down a little bit. And it's going to open. Let's see - can you see there? Do want to move this down more or less? Could be my side to if you must. Just score it a little deeper in yours - then we'll go back to mine. There we go. Yeah, I think I can see my top end and my bottom end here.
CHAPTER 3
Small Cobb. So at this point the - the - the laminaplasty, the greenstick, has taken place. We are now ready to create that hinge, and what we're going to do is take this small instrument that's going to allow us to retract the lamina open. This is the time in the case that you just want to be patient and allow that lamina to just - to retract. The amount of retraction is variable. I tend to go for about 8 mm and that allows enough central canal decompression in for the spinal cord to migrate posteriorly. So what we'll do is just kind of grab the - grab the edge a little bit and just slowly start working that. Semos, if you could just reach around and hold that.
Two ways to do it. You could certainly use a retractor such as this. The other way is just with your thumb and pushing on the spinous process to create that - that gap. So the sucker is on the ligamentum flavum and right underneath that is the spinal cord. Here you can see the ligamentum flavum, and sometimes that ligamentum flavum will prevent the laminaplasty from opening, so we can release it with a curette that allows a little bit more play. There we go. I'll take the plate please. I could just suck that in one area right over there. So the laminaplasty plate - there's a lot of different types. This particular type that I use: the edge will sit over the lamina and the lateral edge on the lateral mass here. The width of this is 8 mm, which will allow us to do open up this defect by about 8 mm. Come off of that. Good. So we we retract and try to get the edge under the lamina. Think I'm stuck on the muscle here. Let that go down. Surgicel. Okay another plate. Try to come under. Okay, let that come down. So as the lamina is a - is released, the edge of the plate will sit right on the lateral mass, and that'll help maintain the opening here. It's not necessary to have instrumentation at every level. Go out there.
Go up to that four. Go up to this one over here when you're ready. Okay, can we have the screws now? So once the plates are in place, then we'll use a starting-all, and then we'll drill each one. Typically one screw into the - into the lamina and two screws into the lateral mass. Like that looks done. That's - no - it's kinda up too high, huh? Nice and easy. I think you got it, no? All. And then another screw. Bring your hand towards me a little Semos. All and an 8. Try to medialize a little - I'm not sure how much we are at the lateral edge here. Cobb. Cobb.
CHAPTER 4
So the instrumentation is in. We have a little bit better hemostasis on the epidurals, which we're going for a little bit.
At this point, what I like to do is resect the spinous process. Resecting the spinous process allows for closure of the fascial layers a little bit easier. Otherwise, they tend to be very prominent to the other side. So we'll - we'll take this bone off of several of these. So you... It's important when you take off the spinous processes at this point of the surgery not to twist and not to disrupt your instrumentation. We'll take each of the bifid at each level. We'll also use this bone to place along the hinge for extra healing of the - the hinge side, the greenstick side, of the laminaplasty.
CHAPTER 5
He's really harmless, but he's just painful. Are you going to put a gown over it? I am. It's going to go into this lightbox here. Is that what you're talking about? Yes so it's just hooking up to here.
DISCUSSION
So this patient has progressive neurological symptoms. He has the diagnosis of cervical spinal stenosis and is developing progressive numbness in his hands as well as weakness and clumsiness. So on this examination, he had a couple of findings that are very consistent with cervical spinal stenosis. One being hyperreflexia in both his upper and lower extremities and also pathological signs such as Hoffman signs.
So a Hoffman sign is when patients will have hyperreflexia in their upper extremities. And it is manifested by flicking of their middle finger, and you'll see concomitant flexion of their thumb at the same time. It's not fair to me a sign of upper motor neuron dysfunction. So the problem of Hoffman sign in particular is that it can be present in asymptomatic patients. So that's why it's very important to do a complete physical examination and correlate any examination findings with their MRI.
So the imaging work-up on this patient included plane X-rays and an MRI scan. The plane X-rays showed well-maintained lordosis of the cervical spine and no instability or significant degeneration on his flexion-extension views. The MRI was particularly impressive because of the multiple level spinal stenosis. There was also evidence of an intrinsic cord change behind the C4 vertebral body, which is called myelomalacia - a - again a very common sign we see with a spinal stenosis.
So the goal of a laminaplasty procedure is to decompress the spinal cord. In effect, we're trying to halt any further progression of neurological symptoms. So the reasonable outcome in the - in this situation is to halt any progression of numbness or weakness or lack of coordination. Typically, the - this type of procedure as well as a laminectomy infusion are very successful in doing that. There's very uncommon instances where patients will continue to have neurological decline, but the vast majority of them do experience some improvement. That improvement can take weeks to months at times, and some people will not peak in the neurological recovery up until a year after their surgery. So we follow these patients very closely. Decline after that period of time is very unusual unless there's an adjacent level problem that may be contributing to new onset of neurological symptoms.
So there are several surgical alternatives here, and we basically think about this as an anterior approach versus a posterior approach. So posterior cervical approaches are typically broken down into laminaplasty or a laminectomy or a laminectomy infusion. I think laminaplasty has some significant advantages though because effusion is not - is not performed. Theoretically at least, that patient is allowed to move a lot quicker, and they're not immobilized for a long period of time. And typically in the younger patients, we find that their range of motion is well preserved. Patients who have a laminectomy infusion well obviously we will lose some motion there, and I think this is a big advantage for a laminaplasty.
Certainly with a laminaplasty or a laminectomy infusion, there are some risks associated with them. One of the problems that we all see with laminectomy infusion is that the instrumentation certainly could loosen. If the fusion does take well, that does place the adjacent levels at risk for breaking down in the future also.
So cervical laminaplasty has been performed for the last several decades. It originated in the Far East, specifically in Japan. Patients there - a very high preponderance of what's called ossification of the posterior longitudinal ligament, or OPLL - basically spinal stenosis due to formation of bone. Cervical laminaplasty has gone through several iterations of techniques, and over the last decade or so, it's really been incorporated into a lot of United States spine surgeons' practices. It has significant advantages like, we said, of allowing early mobility, but there are some contraindications too that we should think about. And patients do need to have really good lumb - cervical lordosis - so maintain lordosis because that's how decompression is achieved, allowing the spinal cord to migrate posteriorly.
There are several types of laminaplasty procedures available to us today. Some are - really approach from the midline, and we'd call that a French door laminaplasty where the cut is raid - made right down the midline, and both hinges are then opened. The procedure that we're going to do today is called an open door. It's an asymmetric opening where one side is hinged open, and we keep the opening with instrumentation on that side. There's a lot of forms of instrumentation that have been used over the years, and sometimes we place just bone graft, suturing it in. And really the evolution has gone to very rigid laminaplasty plates, and that's what we're going to use with this patient.
So the real perils of this procedure - beyond positioning, beyond marking the levels - is to really be careful with placement of the trough. It has to be at the junction of the lateral mass and the lamina. If the trough is made a little bit too laterally into the lateral mass, you - more bone is removed, and it's very hard to open up the lamina. If the trough is made to mediately you're not going to get as much of a decompression. So really attention to landmarks and really looking for that junction where the lateral mass and lamina connect is really where you want to start the trough. So that junction where the lateral mass and lamina meet is the thinnest part of the cortical part of the bone, and that allows for much easier ability to open up the spinal canal.
So the patient needs to play a big role in the recovery in these procedures. Years ago, we used to immobilize them with a very rigid external collar. We thought that was the case because we wanted to get those hinges to heal, but we also found at that time that patients lost a lot of range of motion. So today, these - our patients are placed into a soft collar for comfort for - for a week or two, but then they're really encouraged to get moving. The advantage of instrumentation and the lateral mass plates is that we can start pushing them quicker. So we start an active range of motion pro - program with their neck and shoulders very quickly after surgery. So when they come back and see me after 4 weeks for their first visit, I want to hear that they're walking, they're carrying some light weights, and they're moving pretty well with their neck. Each patient is different in terms of getting back to their life. I would expect that at that first visit - at 4 weeks - most patients are pretty comfortable. We would likely place them into a gym at that time for some slight exercises with the typical recovery about three months, having them back to their life and doing most activities. We would probably restrict them from contact activities for some time until we're really assured of some adequate healing in their neck.