Thomas Kishen

Restoration of compressive loading properties of lumbar discs with a nucleus implant-a finite element analysis study.

BACKGROUND CONTEXT Discectomy is a common procedure for treating sciatica. However, both the operation and preceding herniated disc alter the biomechanical properties of the spinal segment. The disc mechanics are also altered in patients with chronic contained herniation. The biomechanical properties of the disc can potentially be restored with an elastomeric nucleus replacement implanted via minimally invasive surgery. PURPOSE The purpose of this study was to determine whether the compressive characteristics of the intervertebral disc after a nucleotomy can be restored with an elastomeric nucleus replacement. STUDY DESIGN A finite element model of the L4-L5 intervertebral disc was created to investigate the effect of the implantation of an elastomeric nucleus replacement on the biomechanical properties of the disc under axial loading. METHOD A L4-L5 physiologic intervertebral disc model was constructed and then modified to contain a range by volume of nucleotomies and nucleus replacements. The material properties of the nucleus replacement were based on experimental data for an elastomeric implant. The compressive stiffness, radial annular bulge, and stress distribution of the nucleotomy and nucleus replacement models were investigated under displacement-controlled loading. RESULTS Removal of nucleus pulposus from the physiologic disc reduced the force necessary to compress the disc 2 mm by 50%, altered the von Mises stress distribution, and reduced the outward radial annular bulge. Replacing the natural nucleus pulposus of the physiologic disc with an artificial nucleus reduced the force required to compress the disc 2 mm by 10%, indicating a restoration of disc compressive stiffness. The von Mises stress distribution and annular bulge observed in the disc with an artificial nucleus were similar to that observed in the physiologic disc. CONCLUSION This study demonstrates that despite having different material properties, a nucleus replacement implant can restore the axial compressive mechanical properties of a disc after a discectomy. The implant carries compressive load and transfers the load into annular hoop stress.

Fusion Versus Disk Replacement for Degenerative Conditions of the Lumbar and Cervical Spine: Quid Est Testimonium?

This article compares the outcomes following spinal fusion and disk replacement for degenerative conditions of the lumbar and cervical spine. The short-term outcomes of lumbar and cervical total disk replacement are equivalent to that following spinal fusion. Long-term follow-up studies of total disk replacement are necessary to confirm its potential benefit in reducing or preventing adjacent level degeneration. Also discussed is the philosophy of the surgical management of degenerative conditions of the lumbar and cervical spine.

Hyaluronan : its potential application in intervertebral disc regeneration

Hyaluronan (HA) is a ubiquitous component of extracellular matrix in human tissues with diverse functions in skeletal biology. The biophysical properties of HA, such as high viscosity, elasticity and highly negative charge, make it useful in various therapeutic procedures. Although intra-articular administration of HA has been extensively used in the management of osteoarthritis (OA), there is a paucity of data on the clinical application of HA in intervertebral disc repair. This review discusses the biology and signaling mechanisms of HA, the patho- physiology of disc degeneration and summarises current evidence relating to the role of HA in cell phenotype maintenance, differentiation of chondrocytes, intervertebral disc cells and bone marrow stromal cells, and its application in tissue engineering. Based on recent advances in the clinical outcomes of OA treatment, HA has demonstrated potential as a bio-polymer filler, therapeutic agent and cell carrier in the management of intervertebral disc degeneration.

Veillonella spondylodiscitis in a healthy 76-year-old lady

PurposeTo report a case of Veillonella spondylodiscitis in a healthy 76-year-old lady.MethodsA previously healthy 76-year-old lady presented with worsening axial back pain at the thoracolumbar junction, fever and loss of weight. Examination revealed deep tenderness over the thoracolumbar junction with painful and restricted spinal movements. The lower limb motor power, sensation and reflexes were normal.ResultsRadiographs of the lumbosacral spine showed evidence of spinal instability with lateral translation and loss of disc space at L1–L2. MRI scans revealed fluid intensity within the L1–L2 disc with infective debris elevating the posterior longitudinal ligament and narrowing the spinal canal. Both tissue and blood cultures were positive for the anaerobic organism, Veillonella. A staged anterior-posterior spinal surgery followed by an extended course of antibiotics resulted in the clinical improvement and normalisation of blood parameters. A review of the literature on Veillonella infections is also presented.ConclusionThe aim of this report is to bring Veillonella spondylodiscitis to the attention of spinal surgeons and infectious disease specialists and discuss the management options.

Cranial subdural haematoma with concomitant spinal epidural and spinal subarachnoid haematomas : a case report

A 76-year-old man presented with a 4-day history of bilateral leg pain. Magnetic resonance imaging (MRI) of the lumbosacral spine revealed a spinal subarachnoid and spinal epidural haematomas. MRI of the brain revealed a chronic intracranial subdural haematoma with a midline shift. On further questioning, the patient reported a history of a fall 6 weeks earlier and had no evidence of coagulopathy. He underwent a burr-hole decompression of the intracranial subdural haematoma. At the one-year follow-up, the patient was symptom free with no leg pain or headache. The concomitant occurrence of an intracranial subdural haematoma with spinal epidural and spinal subarachnoid haematomas is rare. MRI of the brain and the entire spine is essential in the presence of a spontaneous spinal haematoma.

Primum non nocere and randomised placebo-controlled surgical trials: a dilemma?

In conducting a drug trial, a double-blinded randomised placebocontrolled design is considered the gold standard. Although the placebo control arm of a drug trial offers no therapeutic benefit, its inert and harmless nature does not usually raise significant ethical concerns. In surgery, however, there appears to be a different standard, where the use of a placebo is questioned. A placebo (sham) operation or surgery is a procedure performed on a control group participant to ensure that they experience the same incidental effects of the operation or procedure as do those participants on whom a true operation is performed. Placebo surgery, involves making at least a skin incision under some form of anaesthesia. Placebo controls are particularly useful for trials of devices or procedures with subjective (patient reported) endpoints as they neutralize the ancillary effects of a procedure, thereby improving the ability to differentiate between a placebo and procedural effect in an unbiased fashion. Patient blinding has been shown to be important in randomized trials, and such blinding can only be achieved in surgery by performing a placebo procedure. The ethical concerns related to sham surgery cover two areas: not providing effective treatment, and exposing the subject to potential risk. In effect, a reversal of the desired risk–benefit ratio. To rephrase the first concern: is it justifiable to subject a patient to a procedure that offers no therapeutic benefit and contradicts the ethics of clinical medicine and the physician’s duty of providing the best treatment to the patient? Miller and Brody argue against the notion of therapeutic beneficence by differentiating between the ethics of clinical medicine and the ethics of clinical research. In a clinical trial (research), the physician-investigator’s aim is to answer a research question rather than treat an individual patient, and to do this, the least biased study design should be used. The ethics of clinical research dictate that a placebo-controlled trial is justifiable as long as the patient is not being exploited, the risks are not excessive, and an informed consent is obtained after explaining the experimental nature of the trial to the patient. Ackerman states that although therapeutic beneficence should be the guiding philosophy when offering subjects’ participation in a clinical trial, it is not the absolute priority. Therapeutic misconception can occur when a subject transfers to the research setting, the presumption that exists in ordinary clinical treatment: i.e. that the physician will act only with the patient’s interests in mind. Hence, when obtaining informed consent, the patient must be made explicitly aware of the experimental nature of the trial and the possibility of not receiving any therapeutic benefit from the procedure. When a proven, effective treatment exists, it is logical (and is the usual practice when testing drugs) to provide that treatment in the control arm of a comparative study, thereby testing the new therapy against the current standard. The difficulty here is in defining a proven, effective treatment, as experience has taught us that many established treatments have been demonstrated to be ineffective, often after properly conducted trials have been performed. Examples of surgical procedures that have been shown to be ineffective in a placebo-controlled trial are: ligation of the internal mammary artery for angina; therapeutic arthroscopy for older patients with osteoarthritis of the knee; and intradiscal electrothermal annuloplasty (IDETA) for back pain. Particularly in surgery, many standard accepted treatments have not been subjected to a rigorous clinical trial and continue being performed as a matter of tradition. Tonsillectomy, grommets, radical mastectomy and splenectomy are examples of once common procedures that have significantly declined over time. Would they have declined sooner, or never gained popularity, if they had been subjected to properly conducted randomised trials? It has been argued that testing a new device or intervention against unproven but historic ‘standard treatment’ can be considered unethical. It can also be argued that the placebo effect of surgery is stronger than the placebo effect of medication, increasing the importance of placebo testing in surgery. Moreover, the World Medical Council has justified placebocontrolled trials even in the presence of proven effective treatment (i) when for compelling and scientifically sound methodological reasons its use is necessary to determine efficacy or safety, or (ii) where the investigation is for a minor condition and the patients who receive placebo will not be subject to any additional risk of serious or irreversible harm. The second concern, regarding the exposure to potential risk, seems to violate the dictum of primum non nocere. However, ethical considerations in research demand that we minimise harm, not eliminate it. Trial participants are often exposed to potential risks, and on the surface, surgery appears to be too risky. However, in sham surgery, the risk is usually limited to that of the incision and any associated anaesthetic (local, general or sedation). It can certainly be argued that the risks of a full surgical procedure are greater. The risk–benefit ratio of a placebo intervention should be compared to that of standard treatment options and should not be compared to non-treatment. Absence of excessive risk means that the risk–benefit ratio for placebo control subjects is only slightly less favorable than the risk–benefit ratio for subjects receiving active treatment. Accepted for publication 19 January 2009. No research grant or funding received. PERSPECTIVES

Multiple lumbar pedicle fractures in osteopetrosis: a case report.

Study Design. Single case report. Objective. To report the observation of multiple lumbar pedicle fractures in a patient with osteopetrosis. Summary of Background Data. Osteopetrosis is characterized by osteoclast dysfunction, impaired bone resorption, and poor bone remodeling. As a result, the bone is brittle but hard and is referred to as “marble bone disease.” Although long bone fractures are relatively common, fractures of the spine are rare. Spondylolysis has been reported in the cervical and lumbar spine, and pedicle fractures have been reported in the cervical spine. We report the case of a patient with autosomal dominant osteopetrosis with multiple lumbar pedicle fractures. To the best of our knowledge, there have been no previous reports of multiple lumbar pedicle fractures in osteopetrosis. Methods. A 73-year-old woman, with a known history of osteopetrosis, presented with acute nonradiating low back pain following a bout of coughing. The lower limb neurology and bladder and bowel function were normal. The imaging findings, clinical course, and treatment are discussed. Results. Initial computed tomography scans of the patient revealed the presence of multiple pedicle fractures with spondylolysis. The patient was advised bed rest for the first 3 days, and when the acute pain subsided, she was permitted to ambulate with a lumbosacral corset. The patient was asymptomatic for 8 months, when she was readmitted with another episode of acute low back pain. The CT scan revealed fresh fracture of the L4 pedicle, which was not seen on the previous scan. The pain settled down again with conservative measures. Conclusion. This case report discusses the rare occurrence of multiple lumbar pedicle fractures and pars interarticularis (spondylolysis) fractures in a patient with osteopetrosis.

Retroperitoneal lymphocele after lumbar total disc replacement: a case report and review of literature.

Background Retroperitoneal lymphoceles (RPLs) caused by injury to the lymphatics are commonly seen after pelvic lymphadenectomy, renal transplantation, and gynecologic tumor resection surgeries. Degenerative disc disease still remains the major cause of low-back pain. Anterior lumbar spinal procedures, such as anterior lumbar interbody fusion and anterior lumbar arthroplasty, have been increasingly performed for treatment of axial back pain. RPLs, as an approach-related complication, though infrequent, have been reported after anterior lumbar spinal surgery. We report a case of RPL after total disc replacement of the lumbar spine. To our knowledge, there has been no prior report of RPL after total disc replacement managed by percutaneous aspiration only. Methods A 49-year-old woman who underwent total disc replacement at the L4-5 level presented with a postoperative complication of RPL. The imaging findings, clinical course, and treatment are discussed, and a review of literature is presented. Results The patient presented with significant abdominal swelling and discomfort at 4 weeks after surgery without any signs or symptoms of infection. Investigations showed an RPL. She was treated by multiple aspirations under ultrasound guidance. At 12 months’ follow-up, the patient had no further abdominal symptoms and had gone back to her routine activities and work with significant improvement in back pain. Conclusions RPL is an uncommon complication after anterior lumbar surgery and can be managed effectively if detected and diagnosed early. Although repeated aspiration is associated with high recurrence and infection, it is a safe and minimally invasive procedure to manage RPL.

Post-traumatic thoracic scoliosis with rib head dislocation and intrusion into the spinal canal: a case report and review of literature.

The objective of the study was to report a rare occurrence of dislocation and intrusion of two rib heads into the spinal canal at the convex apex of a post-traumatic thoracic scoliosis in an adult in the absence of any neurological impairment. A 47-year-old male presented with a slowly progressive, post-traumatic thoracic scoliosis and a mild aching sensation over the posterior chest wall. The lower limb neurology and bowel and bladder function were normal. There was no clinical evidence of neurofibromatosis. CT scans showed that the 8th and 9th ribs on the convex apex of the scoliotic curve had intruded into the spinal canal and were lying adjacent to the dura and spinal cord. The MRI scan did not show any cord signal intensity changes. Although rib dislocation and intrusion into the spinal canal is uncommon, images should be carefully analysed to rule out this condition in sharp angular scoliotic curves.

Geometrical & Interfacial Modulation of a Biomimetic Spinal Implant

The nucleus of a spinal disc is seamlessly connective and protectively supportive of the joint within which it is enveloped. A range of nucleus prosthesis configurations have been proposed and applied with some success. Those that have demonstrated clinical efficacy have approximated physiological form and function using established biomaterials while preserving key anatomical structures. The minimally invasive biostable, biomimetic Columna Disc Device (CDD) partial spinal disc replacement has been developed to clinical trial stage. It mimics the geometry and response of the nucleus that it replaces. While the implant configuration and materials have been set, the geometry and interfacial properties of this prosthesis may be modulated to account for versatility in surgical deployment, implant stiffness, and subsequent long-term tissue remodelling response. FEA models were developed to study effects of implant jacket geometry and surface properties on implant deployment and biomechanics. Studded and dimpled textures provide a method for increasing surface area to diffuse jacket-filler interfacial stress and similar for the implant-tissue junction. Surface texture design elements observed in nature can protect against delamination and interlayer slippage. This is the case with adherent outer layers of human skin. A textured implant design is also proposed to guard against third body wear by housing debris remote of wear sites and by reducing sliding. The periodically varying strain fields provided by the textured jacket may also help mitigate for tears by diverting and arresting micro-fissures. Increasing friction at the implant-tissue interface to the point of tissue-attachment was shown to increase the stiffness of the implant in axial-loading. In contrast, increasing bulk surface area is expected to contribute to a decrease in implant stiffness. This is, however, dependent on the intimacy and properties of interfacing tissues.