Nabil A. Ebraheim

Radiographic and CT Evaluation of Tibiofibular Syndesmotic Diastasis: A Cadaver Study

Twelve cadaver lower limbs were used for radiographic and CT assessment of the tibiofibular syndesmosis. Plastic spacers were placed in the distal tibiofibular intervals of each specimen in successive 1-mm increments until diastasis could be appreciated on the plain radiographs. All 2- and 3-mm diastases could be noted and clearly identified on CT scans, while the 1-, 2-mm, and half of the 3-mm syndesmotic diastases could not be appreciated with routine radiographs. CT scanning is more sensitive than radiography for detecting the minor degrees of syndesmotic injuries. Therefore, a CT scan can be performed in cases of syndesmotic instability after ankle injuries and for preoperative or postoperative evaluation of the integrity of the distal tibiofibular syndesmosis in cases of doubtful condition of the syndesmosis.

Anatomic Considerations of Pedicle Screw Placement in the Thoracic Spine: Roy-camille Technique versus Open-lamina Technique

Study Design. In this cadaveric study, the outcomes of two techniques for pedicle screw placement in the thoracic spine were compared. Objectives. To assess the Roy‐Camille technique, and to determine whether pedicle screw placement, aided by partial laminectomy, could decrease the incidence of pedicle violations. Summary of Background Data. Pedicle screw fixation in the thoracic spine remains technically challenging. The Roy‐Camille method may be one of the leading techniques of thoracic pedicle screw placement. However, there are few studies evaluating this technique and determining methods to decrease the incidence of thoracic pedicle penetration with screw insertion. Methods. Ten cadaveric thoracic spines from T1 to T10 were used for pedicle screw placement. Two techniques of transpedicular screw placement were used, the Roy‐Camille technique (screw placed on the right side; used in 95 screw placements) and the open‐lamina technique screw placement with combined partial laminectomy (screw placed on the left side; used in 94 screw placements). After screw placement, all specimens were evaluated visually to determine violation of the pedicle. Results. The screw placement with the Roy‐Camille technique had a higher percentage of pedicle violation (54.7%) than did that with the open‐lamina technique (15.9%). No Grade III violation was seen in the screw placement with the open‐lamina technique. Conclusions. The Roy‐Camille technique was associated with a high incidence of pedicle violation, whereas screw placement with a partial laminectomy significantly reduced the incidence of pedicle violation. Pedicle screw fixation in the thoracic spine remains a technical challenge and should not be used routinely. Screw placement with the open‐lamina technique is recommended if pedicle screw fixation is strongly indicated in the thoracic spine.

Compartment syndrome in open tibial fractures.

A retrospective review of the cases of 180 patients who had 198 acute open fractures of the tibial shaft and were admitted to a multiple-trauma referral center over a three-year period revealed an incidence of accompanying compartment syndrome of 9.1 per cent (eighteen fractures in sixteen patients). Each of the eighteen compartment syndromes was documented by measurements of intracompartmental pressure that were obtained by the saline-injection technique, and all were treated by four-compartment fasciotomy. The incidence of compartment syndrome was found to be directly proportional to the degree of injury to soft tissue and bone; this complication occurred most often in association with a comminuted, grade-III open injury to a pedestrian. The physician must maintain a high index of suspicion to detect a compartment syndrome in the patient who has multiple trauma, as its clinical signs and symptoms may be masked by a closed injury of the head or the need for ventilatory support or prolonged anesthesia for other surgical procedures.

Anatomic consideration of C2 pedicle screw placement.

Study Design This anatomic study tested placement of C2 pedicle screws using cadaver specimens. Objectives To further assess the safety of transpedicular screw placement in the axis by comparing two surgical techniques. Summary of Background Data Transpedicular screw fixation of traumatic spondylolisthesis of the axis has been described in the literature. Recently, anatomic studies and clinical applications of transpedicular screw fixation for traumatic lesions of middle and lower cervical spine have been described. No previous study assessing the safety of C2 pedicle screw placement is available. Methods Sixteen embalmed cadaveric specimens were used for this study. In the first eight specimens (Method A), the point of entry for screw placement was chosen to be about 5 mm inferior to the superior border of C2 lamina and 7 mm lateral to the lateral border of the spinal canal. The screw direction was chosen to be about 30° medial to the sagittal plane and 20° cephalad to the transverse plane. A 3.5‐mm cortical screw of appropriate length, determined with depth gauge, was placed bilaterally into the C2 pedicle. In the next eight specimens (Method B), the direction of the drill bit was guided directly by the medial and superior aspect of the individual C2 pedicle. Gross dissection was done to view violation of dura, nerve roots, vertebral artery, and penetration of medial, lateral, superior, and inferior cortex of the C2 pedicle. Radiographs and computed tomography scans were obtained to evaluate screw placement in the C2 pedicle. Results In Method A, four screws had lateral violations into the vertebral artery. In Method B, only two cases of minimal penetration of pedicle cortex were found. No medial, superior, or inferior violation of the pedicle cortex was found in the present study. Conclusions The present anatomic study suggests that transpedicular screw fixation may be performed safely in the C2 pedicle by using the second technique. Using the first technique is not safe.

Anatomic relations of the thoracic pedicle to the adjacent neural structures.

Study Design. This study analyzed anatomic parameters between the thoracic pedicles and the spinal nerve roots. Objectives. To quantitatively determine the anatomic relations of the thoracic pedicle to the adjacent neural structures. Summary of Background Data. Pedicular screw placement carries with it potential hazard to the surrounding neural structures, especially in the thoracic spine. No studies exist regarding the anatomic relations of the thoracic pedicle to the adjacent nerve roots. Methods. Fifteen cadavers were obtained for study of the thoracic spine. All soft tissue was dissected off the thoracic spine. Laminectomy and total removal of the superior and inferior articular facets was then performed on C7‐T1 through T12‐L1 to expose the pedicles, nerve roots, and dura. Measurements were taken from the pedicle to the nerve root superiorly and inferiorly as well as between the pedicles. Also, the superoinferior diameter of the nerve root and the frontal angle of the nerve root were measured. Symmetrical structures were measured bilaterally. Results. The results showed that no epidural space could be found between the dural sac and the pedicle in all 15 cadavers. The average distances from the thoracic pedicle to the adjacent nerve roots superiorly or inferiorly at all levels ranged from 1.9 to 3.9 mm and from 1.7 to 2.8 mm, with a minimum of 1.3 mm, respectively. The interpedicular distance increased from T1 (13.8 mm) to T3, slightly decreased in T4‐T5, then gradually increased to T12 (16.6 mm). The superoinferior diameter of the nerve root increased consistently from 2.9 mm at T1 to 4.6 mm at T11. The frontal nerve root angle decreased consistently from T1 (120.1°) to T12 (57.1°), except at T4‐T5. Conclusions. This study suggested that more care be taken into consideration in placing a transpedicular screw in the transverse plane than in placing a screw in the sagittal plane in the thoracic spine.

Bone-graft harvesting from iliac and fibular donor sites: techniques and complications.

&NA; The ilium and the fibula are the most common sites for bone‐graft harvesting. The different methods for harvesting iliac bone graft include curettage, trapdoor or splitting techniques for cancellous bone, and the subcrestal‐window technique for bicortical graft. A tricortical graft from the anterior ilium should be taken at least 3 cm posterior to the anterior superior iliac spine (ASIS). Iliac donor‐site complications include pain, neurovascular injury, avulsion fractures of the ASIS, hematoma, infection, herniation of abdominal contents, gait disturbance, cosmetic deformity, violation of the sacroiliac joint, and ureteral injury. The neurovascular structures at risk for injury during iliac bone‐graft harvesting include the lateral femoral cutaneous, iliohypogastric, and ilioinguinal nerves anteriorly and the superior cluneal nerves and superior gluteal neurovascular bundle posteriorly. Violation of the sacroiliac joint can be avoided by limiting the harvested area to 4 cm from the posterior superior iliac spine (PSIS) and by not penetrating the inner cortex. The caudal limit for bone harvesting should be the inferior margin of the roughened area anterior to the PSIS on the outer table to keep from injuring the superior gluteal artery. Potential complications of fibular graft harvesting include neurovascular injury, compartment syndrome, extensor hallucis longus weakness, and ankle instability. The neurovascular structures at risk for injury during fibular bone‐graft harvesting include the peroneal nerves and their muscular branches in the proximal third of the fibular shaft and the peroneal vessels in the middle third.

Cervical Stabilization by Plate and Bone Fusion

Anterior stabilization with combined plate and bone fusion was performed after neural decompression on ten patients for spondylotlc cervical myelopathy, and for radiculopathy or trauma In three patients. Medial corpectomy was performed at one to four levels. Iliac crest or flbular bone grafts were secured by plates anchored to the graft and adjacent vertebral bodies. All patients were placed In Minerva braces postoperatively. There was successful fusion In all cases, and no graft dislodgement or kyphosis. Early Initiation of rehabilitation was achieved. Morbidity occurred In patients with severe spondylotic cervical myelopathy. This Included respiratory depression requiring relntubatlon In 2/13 procedures, dysphagia (2/13) from loosening of the screws or prominent hardware and graft, and screw loosening (2/13). Neurological Improvement was present In 85% (11/13) of patients. There was no deterioration of neurological function in any case. We conclude from this early follow-up that anterior bone fusion with supplemental plates provides effective stabilization for the unstable cervical spine. Greater morbidity risk exists in patients with severe spondylotic cervical myelopathy and spastic quadriparesis who required multilevel medial corpectomies and fusion.

Pathomechanism of ligamentum flavum hypertrophy: a multidisciplinary investigation based on clinical, biomechanical, histologic, and biologic assessments.

Study Design. A multidisciplinary study involving clinical, histologic, biomechanical, biologic, and immunohistologic approaches. Objective. To clarify the pathomechanism of hypertrophy of the ligamentum flavum. Summary of Background Data. The most common spinal disorder in elderly patients is lumbar spinal canal stenosis, causing low back and leg pain, and paresis. Canal narrowing, in part, results from hypertrophy of the ligamentum flavum. Although histologic and biologic literature on this topic is available, the pathomechanism of ligamentum flavum hypertrophy is still unknown. Methods. The thickness of 308 ligamenta flava at L2/3, L3/4, L4/5, and L5/S1 levels of 77 patients was measured using magnetic resonance imaging. The relationships between thickness, age, and level were evaluated. Histologic evaluation was performed on 20 ligamentum flavum samples, which were collected during surgery. Trichrome and Verhoeff-van Gieson elastic stains were performed for each ligamentum flavum to understand the degree of fibrosis and elastic fiber status, respectively. To understand the mechanical stresses in various layers of ligamentum flavum, a 3-dimensional finite element model was used. Von Mises stresses were computed, and values between dural and dorsal layers were compared. There were 10 ligamenta flava collected for biologic assessment. Using real-time reverse transcriptase polymerase chain reaction, transforming growth factor (TGF)-β messenger ribonucleic acid expression was quantitatively measured. The cellular location of TGF-β was also confirmed from 18 ligamenta flava using immunohistologic techniques. Results. The ligamentum flavum thickness increased with age, however, the increment at L4/5 and L3/4 levels was larger than at L2/3 and L5/S1 levels. Histology showed that as the ligamentum flavum thickness increased, fibrosis increased and elastic fibers decreased.This tendency was more predominant along the dorsal side. Von Misses stresses revealed that the dorsal fibers of ligamentum flavum were subjected to higher stress than the dural fibers. This was most remarkably observed at L4/5. The largest increase in ratio observed between the dorsal and dural layer was approximately 5-fold in flexion at L4/5 in flexion. Expression of TGF-β was observed in all ligamenta flava, however, the expression decreased as the ligamentum flavum thickness increased. Immunohistochemistry showed that TGF-β was released by the endothelial cells, not by fibroblasts. Conclusions. Fibrosis is the main cause of ligamentum flavum hypertrophy, and fibrosis is caused by the accumulation of mechanical stress with the aging process, especially along the dorsal aspect of the ligamentum flavum. TGF-β released by the endothelial cells may stimulate fibrosis, especially during the early phase of hypertrophy.

Biomechanical rationale for using polyetheretherketone (PEEK) spacers for lumbar interbody fusion-A finite element study.

Study Design. To determine the effect of cage/spacer stiffness on the stresses in the bone graft and cage subsidence. Objective. To investigate the effect of cage stiffness on the biomechanics of the fused segment in the lumbar region using finite element analysis. Summary of Background Data. There are a wide variety of cage/spacer designs available for lumbar interbody fusion surgery. These range from circular, tapered, rectangular with and without curvature, and were initially manufactured using titanium alloy. Recent advances in the medical implant industry have resulted in using medical grade polyetheretherketone (PEEK). The biomechanical advantages of using different cage material in terms of stability, subsidence, and stresses in bone graft are not fully understood. Methods. A previously validated 3-dimensional, nonlinear finite element model of an intact L3–L5 segment was modified to simulate posterior interbody fusion spacers made of PEEK (“E” = 3.6 GPa) and titanium (“E” = 110 GPa) at the L4/5 disc with posterior instrumentation. Bone graft (“E” = 12 GPa) packed between the spacers in the intervertebral space was also simulated. The posterior lumbar interbody fusion spacer with instrumentation and graft represent a simulation of the condition present immediately after surgery. Results. The peak centroidal Von Mises stresses in the graft bone increased by at least 9-fold with PEEK spacers as compared to titanium spacer. The peak centroidal Von Mises stresses in the endplates increased by at least 2.4-fold with titanium spacers over the PEEK spacers. These stresses were concentrated at places where the spacer interfaced with the endplate. The stiffness of the spacer did not affect the relative motion (stability) across the instrumented (L4/5) segment. Conclusions. Spacers less stiff than the graft will: (1) provide stability similar to titanium cages in the presence of posterior instrumentation, (2) reduce the stresses in endplates adjacent to the spacers, and (3) increase the load transfer through the graft, as evident from the increase in stresses in graft.

Fractures of the talus: experience of two level 1 trauma centers.

Fifty-eight patients with 60 talar fractures were retrospectively reviewed. There were 39 men and 19 women. The age average was 32 (range, 14–74). Eighty six percent of the patients had multiple injuries. The most common mechanism of injury was a motor vehicle accident. Twenty-seven (45%) of the fractures were neck, 22 (36.7%) process, and 11 (18.3%) body. Forty-eight fractures had operative treatment and 12 had non-operative management. The average follow-up period was 30 months (range, 24–65). Thirty-two fractures (53.3%) developed subtalar arthritis. Two patients had subsequent subtalar fusion. Fifteen fractures (25%) developed ankle arthritis. None of these patients required ankle fusion. Fractures of the body of the talus were associated with the highest incidence of degenerative joint disease of both the subtalar and ankle joints. Ten fractures (16.6%) developed avascular necrosis (AVN), only one of which had subsequent slight collapse. Avascular necrosis occurred mostly after Hawkins Type 3 and 2 fractures of the talar neck. Three rating scores were used in this series to assess the outcome: the American Orthopedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Score, Maryland Foot Score, and Hawkins Evaluation Criteria. The outcome was different with every rating system. However, the outcome with AOFAS Ankle-Hindfoot Score and Hawkins Evaluation Criteria were almost equivalent. Assessment with the three rating scores showed that the process fractures had the best results followed by the neck and then the body fractures.