3-D Printed Skull Model: Role in Identification of Site of Bone Defect in Cases with CSF Rhinorrhea.

Role of 3-D models in the identification of the site and extent of bone defects in the skull base for the treatment of CSF rhinorrhea is analyzed. Such models were used successfully in the management of two patients who failed previous attempts at basal reconstruction. The principal advantage of the models was in exact delineation of the size and site of bone defect and deciphering of its relationship with adjoining critical regions of the brain.

Post-Traumatic Central or Axial Atlantoaxial Dislocation Presenting with "Atypical" Symptoms-Analyzing the Role of Dynamic Imaging on the Basis of Experience with 14 Patients Treated by Atlantoaxial Fixation surgery.

BACKGROUND: This is a report of a series of 14 patients who presented with a range of "atypical" cranial, spinal, and systemic symptoms that started after they suffered a relatively severe injury to the head and/or neck several months or years before surgical treatment. The implications of diagnosing and treating central or axial atlantoaxial dislocation (CAAD) is discussed. Also, the role of dynamic rotatory and lateral head tilt imaging in the diagnosis and treatment is analyzed. METHODS: Of the 14 patients, 7 were men and 7 were women, with an age range of 21-64 years (average, 42 years). Due to the severity of the presenting neurological and non-neurological symptoms, all the patients had lost their occupation and were heavily dependent on painkillers and/or antidepressant drugs. In addition to other characteristic clinical and radiological evidence, CAAD was diagnosed made based on the facet alignments on lateral profile imaging in the neutral head position. Dynamic head flexion-extension, lateral head tilt, and neck rotation imaging findings confirmed and subclassified CAAD. All 14 patients underwent atlantoaxial fixation surgery. RESULT: A personalized self-assessment clinical scoring parameter and the World Health Organization Disability Assessment Schedule 2.0 was used to evaluate the outcome. One patient did not follow-up after surgery. At a minimum follow-up of 6 months after atlantoaxial fixation surgery, the remaining 13 patients experienced relief from all major symptoms. CONCLUSIONS: Diagnosing and treating CAAD can have major therapeutic implications for patients presenting with progressively worsening disabling clinical symptoms following relatively severe head and/or neck trauma.

Clinical analysis of surgical outcome of 89 patients having large cerebral arteriovenous malformations.

OBJECTIVE: The article analyzes the clinical features, morphological characteristics, surgical subtleties and long-term outcome of surgery in 89 cases of 'large' sized AVMs. MATERIALS AND METHODS: During the period 2004 to 2022, 89 cases of 'large' arteriovenous malformations were operated in the neurosurgery departments of the authors. Large AVMs were defined as those that were more than 4 cm on either lateral or antero-posterior view of digital subtraction angiogram. The factors that determined the extent of surgical difficulties included site and eloquence of the area, number of feeding vascular territories and draining veins, degree and rate of flow, presence of flow-related aneurysms, and the physical nature of the arteriovenous malformation. RESULTS: There were 59 males and 30 females and the average age was 32 years. Headache, giddiness and convulsions were the common presenting complaints. Six patients were unconscious after surgery. Of these, five patients died in the immediate post-operative period and one patient gradually recovered. Additionally, seven patients developed unilateral limb weakness that included hemiplegia (4 patients) and hemiparesis (3 patients) following surgery. Clinical follow-up ranged from 6 months to 18 years (average 43 months). All surviving patients are leading normal and essentially symptom free life and have recovered from their symptoms of headache, convulsions and giddiness. CONCLUSIONS: Large AVMs are amenable to 'curative' surgery with 'acceptable' results. The surgery can be challenging and appropriate case selection that is based on the surgeons experience is vital and decisive.

Anatomical analysis of white fiber tracts in SMA and its implications related to en-masse tumor resection technique.

OBJECTIVE: Anatomy and connections of the supplementary motor area (SMA) are studied essentially to analyze the SMA syndrome. Experience with surgical treatment of 19 tumors located in SMA is analyzed. MATERIAL AND METHODS: The cortical anatomy and subcortical connectivity of the SMA was studied on ten previously frozen and formalin fixed human cadaveric brain specimens. The white fiber dissection was performed using Klingler's method. Nineteen patients with low grade gliomas in the region of the SMA treated surgically were clinically analyzed. RESULTS: The white fiber connections of the SMA include short arcuate connections with the pre-central, middle and inferior frontal gyri, the medial part of the SLF, the cingulum, the frontal aslant tract (FAT), the claustro-cortical fibers, the fronto-striatal tract and the crossed frontal aslant tract. All tumors were operated using en-masse surgical technique described by us and its subsequent modifications that focused on attempts towards preservation of related critical fiber tracts namely FAT, cingulum and corpus callosum presumed to be responsible for postoperative SMA syndrome. Eight patients developed an SMA syndrome in the immediate post-operative period. Eleven patients did not develop any post-operative neurological deficits. In all these 11 patients it was apparent that the cingulum, FAT and the corpus callosal fibers were preserved during surgery by modifying the tumor resection technique. CONCLUSIONS: SMA syndrome is a frequent occurrence following surgery in patients with tumors in the region of the SMA complex. Surgical strategy that preserves the cingulum and the FAT can prevent the occurrence of the SMA syndrome.

Integration of Chronological Age Does Not Improve the Performance of a Mixed-Effect Model Using Comorbidity Burden and Frailty to Predict 90-Day Readmission After Surgery for Degenerative Scoliosis.

OBJECTIVE: We evaluated the contributions of chronological age, comorbidity burden, and/or frailty in predicting 90-day readmission in patients undergoing degenerative scoliosis surgery. METHODS: Patients were identified through the Healthcare Cost and Utilization Project Nationwide Readmissions Database. Frailty was assessed using the Johns Hopkins Adjusted Clinical Groups frailty-defining indicator. Comorbidity was assessed using the Elixhauser Comorbidity Index (ECI). Generalized linear mixed-effects models were created to predict readmission using age, frailty, and/or ECI. Area under the curve (AUC) was compared using DeLong's test. RESULTS: A total of 8104 patients were identified. Readmission rate was 9.8%, with infection representing the most common cause (3.5%). Our first model utilized chronological age, ECI, and/or frailty as primary predictors. The combination of ECI + frailty + age performed best, but the inclusion of chronological age did not significantly improve performance compared to ECI + frailty alone (AUC 0.603 vs. 0.599, P = 0.290). A second model using only chronological age and frailty as primary predictors performed better, however the inclusion of chronological age worsened performance when compared to frailty alone (AUC 0.747 vs. 0.743, P = 0.043). CONCLUSIONS: These data support frailty as a predictor of 90-day readmission within a nationally representative sample. Frailty alone performed better than combinations of ECI and age. Interestingly, the integration of chronological age did not dramatically improve the model's performance. Limitations include the use of a national registry and a single frailty index. This provides impetus to explore biological age, rather than chronological age, as a potential tool for surgical risk assessment.

Defining role of atlantoaxial and subaxial spinal instability in the pathogenesis of cervical spinal degeneration: Experience with "only-fixation" without any decompression as treatment in 374 cases over 10 years.

Aim: The authors analyze their published work and update their experience with 374 cases of cervical radiculopathy and/or myelopathy related to spinal degeneration that includes ossification of the posterior longitudinal ligament (OPLL). The role of atlantoaxial and subaxial spinal instability as the nodal point of pathogenesis and focused target of surgical treatment is analyzed. Materials and Methods: During the period from June 2012 to November 2022, 374 patients presented with acute or chronic symptoms related to radiculopathy and/or myelopathy that were attributed to degenerative cervical spondylotic changes or due to OPLL. There were 339 males and 35 females, and their ages ranged from 39 to 77 years (average 62 years). All patients were treated for subaxial spinal stabilization by Camille's transarticular technique with the aim of arthrodesis of the treated segments. Atlantoaxial stabilization was done in 128 cases by adopting direct atlantoaxial fixation in 55 cases or a modified technique of indirect atlantoaxial fixation in 73 patients. Decompression by laminectomy, laminoplasty, corpectomy, discoidectomy, osteophyte resection, or manipulation of OPLL was not done in any case. Standard monitoring parameters, video recordings, and patient self-assessment scores formed the basis of clinical evaluation. Results: During the follow-up period that ranged from 3 to 125 months (average: 59 months), all patients had clinical improvement. Of 130 patients who had clinical evidences of severe myelopathy and were either wheelchair or bed bound, 116 patients walked aided (23 patients), or unaided (93 patients) at the last follow-up. One patient in the series was operated on 24 months after the first surgery by anterior cervical route for "adjacent segment" disc herniation. No other patient in the entire series needed any kind of repeat or additional surgery for persistent, recurrent, increased, or additional related symptoms. None of the screws at any level backed out or broke. There were no implant-related infections. Spontaneous regression of the size of osteophytes was observed in 259 patients where a postoperative imaging was possible after at least 12 months of surgery. Conclusions: Our successful experience with only spinal fixation without any kind of "decompression" identifies the defining role of "instability" in the pathogenesis of spinal degeneration and its related symptoms. OPLL appears to be a secondary manifestation of chronic or longstanding spinal instability.

Unusual Extra-Axial and Extracranial Recurrence in an IDH Mutant Astrocytoma: A Case Report.

Isocitrate dehydrogenase mutant gliomas generally have a better prognosis than their wild-type counterpart. Recurrences are generally within the radiation field in the primary tumoral bed. Remote recurrence is uncommon and is usually intraparenchymal. Transformation to a higher grade has been observed with TP53 mutants. Presentation of glioma as an extra-axial lesion is extremely uncommon. No such cases of remote intracranial extra-axial recurrence have been reported in the literature. We describe the unique imaging findings in this case and attempt to formulate possible diagnoses. Intraoperative and pathological findings confirmed this unusual recurrence pattern.

Central Atlantoaxial Dislocation: Presenting Symptoms, Diagnostic Parameters, and Surgical Treatment from Reports on 15 Surgically Treated Patients.

AIM: This chapter reviews the clinical entity of central or axial atlantoaxial instability (CAAD). MATERIAL AND METHODS: From January 2018 to November 2020, 15 patients were identified as having CAAD, wherein there was no atlantoaxial instability when analyzed by conventional radiological parameters and wherein there was no evidence of neural or dural compression due to the odontoid process. The patients were identified as having atlantoaxial instability on the basis of the alignment of facets on lateral profile imaging and a range of telltale clinical and radiological indicators. The clinical statuses of the patients were recorded both before and after surgical treatment by using the specially designed Goel symptom severity index and visual analog scale (VAS) scores. All patients were treated via atlantoaxial fixation. RESULTS: There were six men and nine women ranging in age from 18 to 45 years (average: 37 years). The presenting clinical symptoms were relatively subtle and long-standing. Apart from symptoms that are generally related to neural compromise at the craniovertebral junction, a range of nonspecific cranial and spinal symptoms were prominent. The follow-up time after surgery ranged from 6 to 34 months. All patients showed early postoperative and sustained clinical recovery. CONCLUSIONS: The correct diagnosis and appropriate surgical treatment of CAAD can provide an opportunity for quick and lasting clinical recovery.

Sub-optimal maternal gestational gain is associated with shorter leukocyte telomere length at birth in a predominantly Latinx cohort of newborns.

OBJECTIVE: To assess in utero exposures associated with leukocyte telomere length (LTL) at birth and maternal LTL in a primarily Latinx birth cohort. STUDY DESIGN: Mothers and newborns were recruited postnatally before 24 h of life. Newborn LTL was collected via heelstick at birth and maternal LTL was collected postnatally. LTL was determined by quantitative PCR. Using a longitudinal design, we evaluated associations between neonatal and maternal LTL and appropriate maternal gestational gain as indicated by the American College of Obstetrics and Gynecology (ACOG). RESULT: Mean infant LTL was 2.02 ± 0.30 T/S (n = 386) and maternal LTL was 1.54 ± 0.26 T/S (n = 58). Independent risk factors for shorter LTL at birth included longer gestational duration (Coeff:-0.03, 95%CI: -0.05-0.01;p < 0.01) and maternal gestational weight gain below ACOG recommendations (Coeff:-0.10, 95%CI: -0.18 - -0.02; p = 0.01). CONCLUSION: Gestational weight gain below ACOG recommendations may adversely impact neonatal health in Latinx infants as indicated by shorter LTL at birth.

Unilateral facet fixation as a salvage procedure: Report of two cases with cervical primary bone tumors with extensive bone destruction.

We describe cases of two patients with primary cervical bone tumors that resulted in extensive destruction of bones of the region. In the first patient, the tumor and its growth resulted in the destruction of C3-C5 vertebral bodies and the unilateral destruction of facets and pedicles. In the second case, there was focal destruction of the body and odontoid process and unilateral pedicle and facet of C2. Tumor resection and spinal stabilization were the aims of the surgery. In both cases, unilateral fixation of facets was done. In the first patient, multi-segmental transarticular fixation by Camille's technique was done, and in the second patient, unilateral lateral mass plate and screw fixation was done by the Goel technique. Solid bone fusion of spinal segments was observed at more than a 2-year follow-up in both cases. Based on this experience, it appears that unilateral facetal fixation can provide firm stability and can be used when other more frequently and popularly used techniques are either not available or possible.

Central or axial atlantoaxial dislocation and craniovertebral junction alterations: a review of 393 patients treated over 12 years.

OBJECTIVE: The authors reviewed their scientific publications and updated their clinical material obtained over the last 12 years for cases of central or axial atlantoaxial dislocation (CAAD) identified in the presence of craniovertebral musculoskeletal and/or neural alteration(s). The management implications of diagnosing and treating CAAD are highlighted. METHODS: During a 12-year period, CAAD was diagnosed in 393 patients with craniovertebral junction-related musculoskeletal and neural alterations who underwent atlantoaxial fixation. No bone decompression was done. All CAAD-related craniovertebral junction structural changes were identified to have a naturally protective role. Hence, in this paper the term "craniovertebral alterations" is used for "craniovertebral junction anomalies" and the term "Chiari formation" is used instead of the commonly used term "Chiari malformation." RESULTS: The major radiological diagnosis was determined either singly or in cohort with one or more of other so-called pathological entities that included Chiari formation (367 cases), syringomyelia with Chiari (306 cases), idiopathic syringomyelia (12 cases), type B basilar invagination (147 cases), bifid arch of the atlas (9 cases), assimilation of the atlas (119 cases), C2-3 fusion (65 cases), Klippel-Feil alteration (4 cases), and dorsal kyphoscoliosis (15 cases). The follow-up period ranged from 6 to 155 months. Clinical improvement was observed in all patients. CONCLUSIONS: Understanding and treating CAAD may have significant implications in the surgical treatment of a number of clinical entities. The gratifying clinical outcomes obtained in patients after atlantoaxial fixation, without any type of decompression involving bone or soft-tissue resection, consolidate the concept that atlantoaxial instability has a defining role in the pathogenesis.

"Only fixation" in cases with failed decompression for lumbar canal stenosis - Analysis of outcome in 14 cases.

Aim: The rationale of "only fixation" of affected spinal segments without any form of bone or soft-tissue decompression in cases with failed decompressive laminectomy for lumbar canal stenosis is discussed on the basis of an experience with 14 cases. Materials and Methods: During the period between 2010 and 2022, 14 patients who symptomatically worsened or did not improve following a long-segment "wide" decompressive laminectomy for multisegmental lumbar canal stenosis were identified. All patients were treated by segmental spinal stabilization aimed at arthrodesis by facetal distraction by Goel's facetal spacers (6 cases) or Camille's transarticular facetal fixation (8 cases). No bone, soft tissue, or disc resection was done for spinal or neural canal "decompression." Oswestry Disability Index and Visual Analog Scale were used to clinically assess the patients before and after the surgery and at follow-up. In addition, video recordings of patient's self-assessment of clinical outcome were used to monitor the outcome. Results: During the average period of follow-up of 71 months (range 6 months to 16 years), all patients recovered in majority of their major symptoms, the recovery was observed in the immediate postoperative period. During the period of follow-up, none of the patients complained of recurrent symptoms or needed any additional surgery. There was firm stabilization and evidences of bone fusion of the treated spinal segments in all patients. There were no infections or implant failure. No patient worsened after treatment. Conclusions: Instability of the spinal segments is the primary issue in cases with lumbar canal stenosis and stabilization in the treatment.

Retro-Odontoid and Retro-C2 Body Pseudotumor, Pannus, and/or Cyst. A Study Based on Analysis of 63 Cases.

OBJECTIVE: The potential significance of relationship of atlantoaxial instability with retro-odontoid pseudotumor, pannus, and/or cyst (RPC) is analyzed. METHODS: We searched the database of patients with craniovertebral junction-related instability treated by atlantoaxial fixation from January 2000 to March 2020. We identified 63 patients in whom there was an RPC in the region posterior to the odontoid process or posterior to the posterior aspect of the C2 body. RESULTS: The RPC was solid in 10 patients, predominantly cystic in 39 patients, and had both solid and cystic components in 14 patients. The vertical dimension of the RPC varied from 4.5 to 10.5 mm (average, 7.9 mm) and the transverse dimension ranged from 2 to 5.2 mm (average, 3.4 mm). In 51 patients, the RPC was in the midline and in 9 patients, it was eccentric in location. In 38 patients, there was erosion of the C2 body adjoining the RPC. Analysis of investigations showed that in 100% of patients, the dome of the RPC was in line with the most susceptible point of potential bone compression of neural structures. The RPC was eccentric in location in 9 patients presenting with torticollis. RPC indicated the presence of atlantoaxial instability even when there were no other positive and validated radiologic indicators. After atlantoaxial stabilization, the RPC spontaneously regressed or disappeared. Direct resection of the RPC was neither performed nor was necessary in any case. CONCLUSIONS: RPCs are secondary consequences of atlantoaxial instability and need not be primarily addressed by surgical resection. Their location suggests that they might have a neural protective function.

Transarticular Fixation Following Mobilization of "High-Riding" Vertebral Artery.

BACKGROUND AND IMPORTANCE: The article identifies the feasibility of transarticular screw fixation after mobilizing the vertebral artery in cases where it is in a "high-riding" location. CLINICAL PRESENTATION: A 42-yr-old male patient had a 4-yr history of progressive quadriparesis. Investigations revealed severe basilar invagination. There was assimilation of atlas and C2-3 fusion. The vertebral artery was "high-riding" into the pedicle-facet of C2 vertebra on both sides. Vertebral artery loop was exposed and mobilized inferiorly on both sides after careful drilling of pedicular bone on the posterior aspect of the dome of the artery. C2 facetal bone on the anterior face of the vertebral artery dome was now available for screw insertion. The C1-2 facets and the articulation were directly in line, making transarticular screw fixation relatively straightforward. The wide bone space available permitted insertion of 2 screws in a transarticular fashion on both sides. The patient had satisfactory clinical improvement. Imaging after 22 mo showed bone fusion across the facets. CONCLUSION: Mobilization of the high-riding vertebral artery loop can help salvage the surgical procedure of lateral mass stabilization.

Adult idiopathic de novo lumbar scoliosis: Analysis of surgical treatment in 14 patients by "only fixation".

OBJECTIVE: The authors report their experience with 14 cases having adult idiopathic de novo lumbar scoliosis (AIDLS) and presenting with the predominant symptoms of claudication pain in the low back and legs. The patients were treated by only multisegmental stabilization, and the surgical procedure aimed for arthrodesis without any form of bone or soft-tissue decompression. The clinical outcome of this novel form of surgical treatment is presented. MATERIALS AND METHODS: During the period of June 2014 to June 2019, 14 patients having AIDLS (degenerative scoliosis) were surgically treated. Apart from clinical and radiological guides, instability was diagnosed on the basis of direct physical observation of the status of articulation and by manual manipulation of bones of the region. The Camille transarticular facet screw fixation technique provided a quick, safe, and strong segmental spinal fixation. An additional inter-screw metal link plate provided intersegmental stability at selected levels. The Oswestry Disability index and visual analog scale were used to assess the patients before and after surgery and at follow-up. In addition, a personalized Patient Satisfaction Score was used to assess the outcome of surgery. RESULTS: Clinical symptomatic recovery was observed in all patients in the immediate postoperative period. During the average follow-up period, 100% patients had varying degrees of symptomatic relief. CONCLUSIONS: Spinal instability is the nodal point of pathogenesis of spinal degeneration-related AIDLS. Only fixation of the involved spinal segments is necessary, and decompression by bone or soft-tissue resection is not necessary.

Chiari 1 Formation Redefined-Clinical and Radiographic Observations in 388 Surgically Treated Patients.

OBJECTIVE: The subject of Chiari formation is revisited and redefined. Results of surgical treatment of patients with Chiari formation by atlantoaxial fixation are presented. METHODS: Results were analyzed of 388 patients with Chiari formation surgically treated during 2010 to June 2019. RESULTS: Two hundred and sixty-six patients had syringomyelia. Two hundred and three patients had no craniovertebral bone abnormality and 74 patients had group A and 111 patients had group B basilar invagination. Twenty-nine patients had been earlier treated by foramen magnum decompression surgery with or without duroplasty. Clinical parameters, analysis of video recordings both before and after surgery, and patient self-assessment were included in the analysis of outcome. Immediate postoperative and sustained clinical improvement was observed in 385 patients (99.4%). CONCLUSIONS: Satisfactory clinical outcome in most patients after atlantoaxial fixation and without any manipulation of neural structures, dura, or bone in the region of foramen magnum consolidates the viewpoint that atlantoaxial instability is the nodal point of pathogenesis of Chiari 1 formation. The study suggests that Chiari 1 formation may be a secondary natural neural alteration in the face of atlantoaxial instability. The role of foramen magnum decompression surgery needs to be reassessed.

Familial Os Odontoideum.

BACKGROUND: To add to the confusion in the debate on pathogenesis of os-odontoideum, an additional report of its occurrence in two members of the same family is reported. CASE DESCRIPTION: This is a report of a rare coincidence wherein both father (51 years old) and daughter (25 years old) were diagnosed to have os odontoideum and presented with crippling neurologic deficits. CONCLUSIONS: Following atlantoaxial fixation, both recovered in their symptoms. Investigations revealed no genetic abnormality. Literature on the subject is briefly reviewed.

Cervical spondylosis in patients presenting with "severe" myelopathy: Analysis of treatment by multisegmental spinal fixation - A case series.

BACKGROUND: Surgical strategy of multisegmental spinal fixation that includes atlantoaxial joint for patients having cervical spondylosis-related symptoms of severe myelopathy is analyzed. OBJECTIVE: Surgical outcome of patients presenting with "severe" symptoms of cervical myelopathy having multisegmental degenerative cervical spondylosis and treated by multisegmental spinal fixation is analyzed. Atlantoaxial joint was included in the fixation construct in majority of patients. No bone, soft tissue, osteophyte, or disc resection for decompression was done. MATERIALS AND METHODS: Sixty-four patients having multisegmental cervical spondylosis who presented with symptoms of severe myelopathy were surgically treated during the period from March 2013 to December 2018. On the basis of the concept that instability is the primary cause of spinal degeneration, multisegmental spinal fixation was done in all patients. Atlantoaxial joint was included in the fixation construct in 48 patients. The levels of spinal fixation were determined on the basis of direct observation of facet joints and by manual manipulation and were guided by the presenting clinical features and radiological information. Clinical monitoring was done using Goel clinical grading, modified Japanese Orthopedic Association Score, and visual analog score parameters. Patient satisfaction index assessed the functional and symptomatic improvement. RESULTS: During the follow-up that ranged from 6 to 75 months, all patients improved in their clinical status. Fifty-five (85.9%) patients could walk independently or with mild support. CONCLUSIONS: Multisegmental spinal fixation that includes atlantoaxial joint in most patients forms a rational treatment strategy for patients of cervical spondylosis presenting with severe symptoms of myelopathy.

Transcranial Insertion of Atlas Facetal Screw for Atlantoaxial Fixation.

OBJECTIVE: We evaluated the technical feasibility and potential advantages of transcranial insertion of an atlas screw for atlantoaxial fixation. METHODS: From January 2016 to August 2018, the transcranial technique for atlas screw insertion was used in 6 patients. Conventional lateral mass atlantoaxial fixation was not possible because of the presence of a complex craniovertebral junctional abnormality and difficulty in direct exposure of the facet of the atlas. In all cases, severe basilar invagination and assimilation of the atlas was present. Of the 6 patients, 3 were male and 3 were female. The age range was 12-41 years (average, 23 years). The surgical technique involved a small suboccipital craniotomy in line with the facet of the axis. Extradural elevation of the cerebellum exposed the region of the occipital condyle and fused atlas. The screw was directed medially and inferiorly into the facet of the atlas. RESULTS: In all 6 patients, strong and successful atlantoaxial fixation was achieved. All patients showed clinical improvement after surgery. At an average follow-up period of 21 months, successful arthrodesis of atlantoaxial joint had been achieved in all 6 patients, with no complications. CONCLUSIONS: Transcranial insertion of atlas screw can be used as a salvage procedure when the conventional method of screw insertion is not possible because of technical difficulties.