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Thread: Why Hooks are used at top of Fusions

  1. #1
    Join Date
    Oct 2014
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    Arizona
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    Why Hooks are used at top of Fusions

    I was curious as to why my surgeon chose to use hooks at the top of my fusion (T-6 & T-7) and leahdragonfly mentioned to me that Dr Hart told her it was to reduce the risk of proximal junction failure. I couldn't sleep last night, (weaning down the narcotics is messing with me), so I looked for the article in PubMed.

    Biomechanical Risk Factors for Proximal Junctional Kyphosis: A Detailed Numerical Analysis of Surgical Instrumentation Variables
    Spine Vol 39(8), 15 Apr 2014

    Since I can't post the whole article, I'll paste part of the discussion here, I hope that is acceptable. The study design used biomechanical analysis of proximal junctional kyphosis (PJK) through computer simulations and sensitivity analysis.

    "The comprehensive sensitivity analyses allowed the establishment of the correlations between the biomechanics of the PJSS and the instrumentation variables and thus the identification of potential biomechanical risk factors of PJK. The tested instrumentation variables had significant effects on the flexion loading on the PJSS and the PJ angle. Putting the results from this study in parallel with those reported in related studies helps to provide a more comprehensive assessment of PJK risk factors. This study showed that the dissection of posterior intervertebral elements was positively correlated to the mechanical stresses within the PJSS and the PJ angle, increasing the risk of PJK, which had previously been postulated in retrospective clinical studies and those based on cadaveric experiments.8,29 The simulated use of transverse process hooks instead of pedicle screws at UIV (upper instrumented vertebra) resulted in significantly lower PJ angle and flexion actions of the proximal moment and forces, which can be explained by the fact that the hook–vertebra connection is less rigid than the screw–vertebra connection. This finding was found to be consistent with clinical studies reporting that the change in junctional kyphosis was significantly greater with all pedicle screw constructs than that with hooks and hybrid constructs, suggesting that using hooks involved less supraadjacent facet capsule disruption than pedicle screws and provided a gradual stiffness transition to the proximal noninstrumented spinal segment until obtaining complete fusion. 5,6,10,30,31 The combination of posterior element disruption and increased construct rigidity is thus biomechanically confirmed to be an important factor involved in PJK. Simulations showed similar results to the finite-element analyses on the use of tapered rods at the proximal end with lower mechanical stresses within the PJSS and PJ angle.32 Although lower construct stiffness at the proximal end of the instrumentation may help reduce the risk of PJK, appropriate attention should be paid to the increased likelihood of pseudarthrosis because of the increased junctional micro motion magnitude under the same functional loading due to the reduced proximal construct stiffness. Our results also provided biomechanical support to the clinical belief that increasing the rod curvature with respect to the preoperative TK helps restore the TK, but could in the meantime lead to higher PJ angle, proximal flexion moment and forces, and cervical lordosis as a result of the postoperative adaptations of the patients such as the adaptation to have a forward field of vision.33–39 Therefore, the results of this study biomechanically support that the risk of PJK could be associated with the loss or changes of thoracic and thoracolumbar sagittal alignment. The deformity characteristics of the particular cases used in this study were found to have less significant effect than the independent variables as the general trends of all biomechanical indices were similar in all cases."

    As one of the variables in the model was flexion loading, I am going to make a better effort to not spend so much time looking down at my I Pad and use my desktop instead which keeps me in a better position with my head in a neutral position. Also, my computer chair IS the most comfortable chair in the house for me. It's made of a mesh fabric which is both very forgiving and also has a nice lumbar curve built in.
    Before 39* lumbar at age 18, progressed to 74* lumbar and 22* thoracic age 55
    ALIF Jan 13, 2015, PLIF Jan 15, 2015 with Dr William Stevens, Honor Health
    Fused T-7 to S-1 with pelvic fixation

    After 38* lumbar

    Xrays
    Before: http://www.scoliosis.org/forum/attac...7&d=1414268930

    After: http://www.scoliosis.org/forum/attac...6&d=1424894360

  2. #2
    Join Date
    Oct 2014
    Location
    Arizona
    Posts
    112
    Another article:

    Proximal Junctional Kyphosis and Failure After Spinal Deformity Surgery: A Systematic Review of the Literature as a Background to Classification Development
    Spine: Issue 39(25), Dec 1, 2014

    This article is a review of the literature and proposes a new classification scheme for for proximal junctional kyphosis and proximal junctional failure and indications for revision surgery for both.

    Some quotes below:

    "Most studies report PJK in approximately 20% to 40% of all patients who undergo spinal instrumentation and curvature correction for ASD (adult spinal deformity)."

    "The use of pedicle screws for long-segment instrumentation has been shown to be associated with higher rates of PJK. 22,30,31,48 Current concerns are that pedicle screws provide substantially rigid constructs and have higher chances of violating facets. 31 Therefore, hooks theoretically are advantageous in lessening the risk for PJK as they provide a more dynamic construct and are associated with lower incidence of facet violation (Figure 6A and B). 22,30,31 Hassanzadeh et al48 performed a comparative retrospective study of 47 adult patients who underwent instrumentation at 5 or more levels with either transverse process hooks or pedicle screws at the UIV. At 2-year follow-up, they found that significantly more patients in the pedicle screw group developed PJK (29.6% vs. 0.0%) and had significantly lower functional scores. Helgeson et al30 performed a multicenter retrospective study of 283 patients who underwent hook-only constructs, hybrid constructs (pedicle screws and hooks), pedicle screw-only constructs, and pedicle screws constructs with hooks only at the most cephalad level. The incidence of PJK was highest in the pedicle-only constructs and adjacent-level change in PJK at 2 years was significantly increased with pedicle-only constructs. Similarly, a study by Kim et al22 retrospectively compared 410 cases of posterior segmental spinal instrumentation and fusions and found that pedicle screw-only constructs had the highest rate of PJK (35.1%) compared with hook-only constructs (24.1%) and hybrid constructs (proximal hooks with distal pedicle screws) (29.1%). It seems that hooks are associated with lower rates of PJK, especially when utilized in the proximally instrumented vertebrae after long-segment instrumentation."

    They also looked at the use of cement to prevent PJK & PJF, but determined that bone density was a more important factor and cement was best used only for vertebra likely to fracture. Also cement had deleterious side effects by reducing nutrients to the vertebral disk and accelerating disk disease.
    Before 39* lumbar at age 18, progressed to 74* lumbar and 22* thoracic age 55
    ALIF Jan 13, 2015, PLIF Jan 15, 2015 with Dr William Stevens, Honor Health
    Fused T-7 to S-1 with pelvic fixation

    After 38* lumbar

    Xrays
    Before: http://www.scoliosis.org/forum/attac...7&d=1414268930

    After: http://www.scoliosis.org/forum/attac...6&d=1424894360

  3. #3
    Join Date
    May 2008
    Location
    reno,nevada
    Posts
    3,531
    Sagittal imbalance of our kyphotic and lordotic curves plays an important part on success rates. This was covered in a study Linda posted a few months back, its as if our scoliosis curves don’t really matter all that much. I had no problems at all in this area, my side view x-rays before my surgeries looked good and I was balanced front to back. I guess this might explain why no hooks were used on me, my surgeon didn’t foresee any future PJK problems in my case. Hard to say if he would have fused me lower in the upper thoracic areas what might have or could have happened.

    When surgeons analyze sagittal x-rays, the selection of levels and usage of screws and or hooks is more than likely one of their hardest decisions.

    They also do cadaver studies and I wonder how the bone changes after death? Is bone weaker or stronger?

    There are pros and cons to both screws and hooks.....

    Screws cost more, do most of their holding in the corticle layer or outer hard bone which is thin, and have the chance of breaching the spinal cord. They can also back out and are weaker than hooks. Screws also have to go through the pedicle which can be thin. Women and children have thin pedicles, especially up high in the thoracic. Screws can also back out, fall down, and end up in your socks. (Just kidding!)

    Hooks cost less but never usually break, can pop off and lose their grip, and patients seem to complain about feeling them....

    Kyphosis is worse than scoliosis. I don’t have any sagittal issues in my construct that really stand out but my C5-6, and C6-7 levels are herniated. These levels come in at 2nd place after the lower lumbar levels for herniation. Now imagine what that must be like for the kypho in the 100 degree or higher range? Neck herniation’s are extremely painful and produce incredible amounts of arm pain and finger numbness. Thank God for Medrol packs, and Diclofenac!

    Studies are very helpful. They provide a clue as to what works or not. As a patient, looking at studies has an affect on you. I also do look and read studies, and some of the numbers can be grim.... Its like race car drivers constantly looking at crash videos......Do they do this all the time? Probably not.

    Are all these studies done to drive us scoliosis geeks crazy? Probably so....(smiley face)

    Ed
    49 yr old male, now 58, the new 53...
    Pre surgery curves C12,T70,L70
    ALIF/PLIF T2-Pelvis 01/29/08, 01/31/08 7" pelvic anchors BMP
    Dr Brett Menmuir St Marys Hospital Reno,Nevada

    Bending and twisting pics after full fusion
    http://www.scoliosis.org/forum/showt...on.&highlight=

    My x-rays
    http://www.scoliosis.org/forum/attac...2&d=1228779214

    http://www.scoliosis.org/forum/attac...3&d=1228779258

  4. #4
    Join Date
    Oct 2014
    Location
    Arizona
    Posts
    112
    Well, in this era of 'evidence based medicine' being the great new thing, we will likely be seeing more of these kinds of studies than ever before. And insurance companies use these studies in deciding what they will and won't cover. Before my surgery, I found a document from one of the big insurance companies, and I couldn't believe how many studies they cited in their decision making process when certifying a scoli patient for surgery. We may think of insurance companies as being the bad guys, but they sort of have a role in preventing some of the surgery that is a really bad idea. And no, I don't work in insurance :-)

    Of course, you have to look critically at the methodology and take them for what they are worth. But it's good for patients that they are trying to answer important questions. To me right now, the greatest enigma is why do some patients fuse and others have problems. If only they knew more about how to crack this nut. This will give me something to look up tonight when I can't sleep. Since I work for a University, I have full text access to medical journals.

    I agree about the kyphosis being more problematic than plain scoli. I suspect that since I had lumbar kyphosis, that is why my correction is what it is. My surgeon told me his goal was BALANCE.

    The studies also point the way to the future. My 30 yo daughter is a scoli, never had any treatment (her decision, doctor wanted to brace her and she refused). So I'm looking out for her too.
    Before 39* lumbar at age 18, progressed to 74* lumbar and 22* thoracic age 55
    ALIF Jan 13, 2015, PLIF Jan 15, 2015 with Dr William Stevens, Honor Health
    Fused T-7 to S-1 with pelvic fixation

    After 38* lumbar

    Xrays
    Before: http://www.scoliosis.org/forum/attac...7&d=1414268930

    After: http://www.scoliosis.org/forum/attac...6&d=1424894360

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