Orthofix external fixation of distal radius fractures: complications associated with screw size

We did a retrospective analysis of 28 patients who were treated with the Orthofix external fixation system for complex fractures of the distal radius to study complications associated with screw size. The 14 patients in group 1 had a 4.5/3.5-mm tapered screw placed in the metacarpal bone; the 14 patients in group 2 had a 3.5/3.3-mm tapered screw placed in the metacarpal bone. Both groups had 4.5/3.5-mm tapered screws placed in the radius. Two patients in group 1 had metacarpal pin tract infections; no patients in group 2 had a distal pin tract infection. Two patients in group 1 had a fracture of the metacarpal; only one patient in group 2 had a fracture of the metacarpal. In both groups two patients had proximal pin tract infections at the radius screw fixation site. There was no screw breakage in either group. The unique design of the tapered Orthofix screw allows it to be removed almost painlessly in the clinic. At installation in the operating room, however, the surgeon must remember not to back the threaded pin out for fine adjustment of bony penetration. Any reverse excursion of the threaded shaft will loosen the tapered screw and cause early failure of the fixation. We no longer use the 4.5/3.5-mm screw when managing wrist fractures with the Orthofix external fixation system. It is now our policy to use the 3.5/3.3-mm screw for fixation of the Orthofix external frame to both the metacarpal bone and the radius.     

Microscrew and microplate systems for select osteotomies in orthognathic surgery

The use of the semirigid screw and plate systems is common place in orthognathic surgery by many oral and maxillofacial surgeons. The size of the screw and plate systems used is commonly designated as mini or osteotomy size. Screw diameter is generally 2.0 mm and plate thickness range is 0.8 mm to 1.2 mm. The systems available perform very well for the majority of osteotomies. There are circumstances when these mini systems are not appropriate. Recently developed microsystems have been applied by us in selected cases of orthognathic surgery. The smallest of the microsystem screws are 0.8 mm diameter and all are available in 2, 3, 4, 5, 6, 8 mm lengths. Some microplates are 0.3 mm thick and available in various shapes including a straight chain. The resultant profile thickness of screw plus plate system becomes 0.8 mm.     

Posterior C1-C2 transarticular screw fixation for atlantoaxial arthrodesis

OBJECTIVE: To assess the outcomes associated with C1-C2 transarticular screw fixation. METHODS: The clinical outcomes of 121 patients treated with posterior C1-C2 transarticular screws and wired posterior C1-C2 autologous bone struts were evaluated prospectively. Atlantoaxial instability was caused by rheumatoid arthritis in 48 patients, C1 or C2 fractures in 45, transverse ligament disruption in 11, os odontoideum in 9, tumors in 6, and infection in 2. RESULTS: Altogether, 226 screws were placed under lateral fluoroscopic guidance. Bilateral C1-C2 screws were placed in 105 patients; each of 16 patients had only one screw placed because of an anomalous vertebral artery (n = 13) or other pathological abnormality. Postoperatively, each patient underwent radiography and computed tomography to assess the position of the screw and healing. Most screws (221 screws, 98%) were positioned satisfactorily. Five screws were malpositioned (2%), but none were associated with clinical sequelae. Four malpositioned screws were reoperated on (one was repositioned, and three were removed). No patients had neurological complications, strokes, or transient ischemic attacks. Long-term follow-up (mean, 22 mo) of 114 patients demonstrated a 98% fusion rate. Two nonunions (2%) required occipitocervical fixation. In comparison, our C1-C2 fixations with wires and autograft (n = 74) had an 86% union rate. CONCLUSION: Rigidly fixating C1-C2 instability with transarticular screws was associated with a significantly higher fusion rate than that achieved using wired grafts alone. The risk of screw malpositioning and catastrophic vascular or neural injury is small and can be minimized by assessing the position of the foramen transversaria on preoperative computed tomographic scans and by using intraoperative fluoroscopy and frameless stereotaxy to guide the screw trajectory.     

Impact of chronic cough on quality of life

STUDY DESIGN: The biomechanical influence of in situ setting hydroxyapatite cement was examined for use in pedicle screw revision surgery. Pull-out testing of control and pedicle screws augmented with hydroxyapatite cement was performed in human cadaver vertebrae. OBJECTIVES: To determine the immediate effect of using hydroxyapatite cement to augment revision pedicle screws after failure of the primary pedicle screw fixation. SUMMARY OF BACKGROUND DATA: The potential problems associated with using polymethylmethacrylate to augment revision pedicular instrumentation have prompted the search for other solutions. The introduction of resorbable hydroxyapatite pastes may have provided new biocompatible solutions for pedicle screw revision. METHODS: Ten human cadaver vertebrae were instrumented with 6.0-mm pedicle screws in each pedicle. The screws were loaded to failure in axial tension (pull-out). The failed pedicles then were instrumented with 7.0-mm pedicle screws, either augmented with hydroxyapatite cement or nonaugmented, which also were loaded to failure. Finally, the nonaugmented 7.0-mm screw hole was reinstrumented with a hydroxyapatite cement-augmented, 7.0-mm pedicle screw and loaded to failure. RESULTS: The pull-out strength of the 7.0-mm, hydroxyapatite cement-augmented screws was 325% (P = 2.9 x 10(-5)) of that of the 6.0-mm control screws, whereas the strength of the 7.0-mm nonaugmented screws was only 73% (P = 2.0 x 10(-2)) of that of the 6.0-mm control screws. The 7.0-mm screws augmented with hydroxyapatite cement also were able to salvage 7.0-mm pull-out sites to 384% (P = 6.9E-5) of the pull-out strength of the 7.0-mm nonaugmented screws. CONCLUSIONS: Hydroxyapatite cement may be a mechanically viable alternative to polymethyl methacrylate for augmenting revision pedicular instrumentation and should be considered for future experimental, animal, and clinical testing.     

Treatment of tibial plateau fractures by limited internal fixation

Seventy-five adults who sustained 76 tibial plateau fractures were treated according to a prospective protocol using instability in extension as the principal indication for operative fixation. Patients showing instability underwent closed manipulative reduction under fluoroscopic guidance. If significant joint depression persisted after reduction, elevation of the fracture was performed either from below using bone punches through a cortical window or via limited arthrotomy. Iliac crest bone graft was used to buttress depressed fractures. Fixation was then secured using 7-mm cannulated screws with washers or buttress plates and screws. Postoperatively, 58 of 76 knees were managed in a hinged knee brace, allowing the patient early range of motion and protected weightbearing for 8 weeks. Patients who were found to have a stable knee were treated with Bledsoe braces according to the postoperative protocol. In the 75 patients, 18 of the 76 knees were unsuitable for percutaneous screw fixation because of fracture complexity requiring plates, severe open injuries, or inadequate reductions with limited fixation had been done. A minimum followup of 12 months was obtained in 55 patients (range, 12-59 months). All fractures had healed at the time of followup. Eighty-seven percent of the patients at followup had a successful outcome using Rasmussen's criteria. Fourteen of these patients had arthroscopic assisted reduction or evaluation. All seven patients who had poor outcomes had AO Type C3 fracture patterns. Severely depressed or comminuted fractures or fractures with significant metaphyseal diaphyseal extension may not be suitable for this technique and require the addition of an external fixation device or buttress plate to maintain the reduction and allow for early range of motion.     

Nitric oxide as a regulatory factor in sleep-wakefulness mechanisms

Most screws used in fracture fixation necessitate a separate step for tapping of the screw hole. Titanium screw systems have been developed in which the screws can be inserted directly after a drill hole is made. These self-tapping screws thereby eliminate an operative step. A retrospective study was conducted that evaluated all wrist and hand procedures performed between January 1992 and December 1994 by 1 surgeon using screw fixation. The results of 39 cases treated with standard tapped titanium screws were compared with 28 cases treated with self-tapping titanium screws. Nearly identical union and complication rates were obtained in each group. Comparable results can be obtained with self-tapping screw fixation, which limits the number of instruments needed, eliminates an operative step, and thereby may diminish operative risk and shorten operative time.     

Transcutaneous or transconjunctival peribulbar anesthesia?

The complications of 648 consecutively inserted Universal AO pedicle screws (140 in the thoracic spine and 508 in the lumbar spine) performed by one surgical team to treat 91 patients with spinal problems, were reviewed. The spinal pathology consisted of: scoliosis (34 patients), degenerative lower lumbar spinal disease (25 patients), neoplastic spinal disease (11 patients), thoracic kyphosis (8 patients), spinal fractures (7 patients), lumbo-sacral spondylolisthesis (3 patients), and osteomyelitis (3 patients). Intraoperative complications were: screw misplacement (n = 3), nerve root impingement (n = 1), cerebrospinal fluid leak (n = 2) and pedicle fracture (n = 2). Postoperative complications were; deep wound infection (n = 4), screw loosening (n = 2) and rod-screw disconnection (n = 1). The conclusion was that pedicle screw fixation has an acceptable complication rate and neurological injury during this procedure is unlikely.     

Clinical evaluation of the Alta hip bolt in peritrochanteric hip fractures

We reviewed the clinical and radiographic results of 58 patients with peritrochanteric fractures treated with the Alta hip bolt (a sliding compression device that inserts a dome plunger in the femoral head instead of a hip screw). This group was compared with a group of 53 patients treated with conventional hip screws. Three patients (5.2%) treated with the Alta hip bolt and three patients (5.7%) treated with conventional hip screw had failure of fixation. Failure of fixation consistently occurred in patients with unstable fracture patterns or significant osteopenia. There were no cases of bolt cut-out in stable intertrochanteric fractures. We conclude that the Alta hip bolt performs as well as sliding hip screws in peritrochanteric fractures, but the additional learning curve and increased cost do not justify its routine use at this point in time.     

Experimental analysis of functional stability of sagittal split ramus osteotomies secured by miniplates and position screws

PURPOSE: This study determined the relative functional stabilities of various miniplate systems and configurations used to stabilize sagittal split ramus osteotomies (SSROs) and compared them with conventional internal screw fixation. MATERIALS AND METHODS: The biomechanical model was a reproducible prototype of a mandible sagittal osteotomy with consistent material and geometric properties. After advancing the distal segment by 7 mm, each set of mandible analogs (1 set = 3 analogs) was fixed bilaterally by one of three miniplate systems applied in various configurations, and tested with and without a supplemental 2.4-mm bicortical screw applied in the retromolar region. Reduced analogs were placed in a straining frame, and simulated masticatory loads were applied alternatively to the mandibular first molars. Ensuing osteotomy site displacements were measured by transducers attached to a computer-based data acquisition program. A coordinate transformation procedure was used to convert the component displacements captured by the individual transducers into a common "instability factor" to reflect fixation stability for each construct and loading condition. Instability factors for the individual constructs were compared with each other and with those obtained from analogs reduced exclusively with 2.4-mm position screws. RESULTS: Osteotomies stabilized with a combination of miniplates and position screws were more stable than those stabilized exclusively with miniplates (P < .0001). Post-hoc comparisons of mean instability factors (Dunnet's method) showed the miniplate-position screw combinations to be more stable than the 2.4-mm position screw system used as standard (P < .05). Miniplate systems alone were the least stable of the test constructs, with differential rates of failure between the individual miniplate systems. CONCLUSIONS: Exclusive use of miniplate fixation may not provide the consistent stability necessary for early functional restoration after SSROs. The addition of a position screw in the retromolar region substantially enhances the fixation stability of miniplate systems. The use of miniplates with retromolar position screws offers both technical and stability advantages over conventional miniplate or internal screw fixation. The fixation stability of the miniplate-position screw combination is independent of the type of miniplate system used.     

Operative treatment of hip fractures in patients with renal failure

The conditions of a hip fracture and renal failure cause particularly high mortality. Eight patients (average age, 63 years) who had operative treatment for nine hip fractures were studied retrospectively. Three had intertrochanteric fractures fixed with sliding compression screws, and five had femoral neck fractures (bilateral in one patient): two nondisplaced femoral neck fractures were fixed with percutaneous screws, and four displaced femoral neck fractures were treated with arthroplasties in three and percutaneous screws in one. Operative treatment was done when the patient was in medically stable condition (average, 8 days). Full weightbearing was allowed on the injured limb after surgery. Early morbidity analysis showed no wound infections, thromboembolic events, or hemorrhagic complications. The first year mortality was three (38%). Late morbidity included one nonunion and one sliding screw penetration. Total mortality at 6 years was seven (88%) patients, with an average postoperative survival time of 28 months. Preoperative ambulation was preserved in five of seven (71%) patients. One the basis of this study, it appears that a team approach to operative management including nephrologist and surgeon helps to reduce short term complications and mortality and allows such patients to be mobilized and regain ambulation.     

An adult case of extra-hepatic portal obstruction with bleeding from esophageal varices

PURPOSE: This study examined the use of a locking reconstruction bone plate/screw system for use in mandibular surgery. PATIENTS AND METHODS: All patients treated with a locking reconstruction bone plate/screw system for fractures of the mandible or continuity defects in an 18-month period were prospectively studied. Ease of use of the locking plate/screw system, characteristics of the fractures/defects, and complications were tabulated. RESULTS: One hundred two locking bone plates were placed in 84 patients. Most patients (n=75) were treated for fractures of the mandible; there were eight continuity defects and one case of mandibular narrowing. There were no cases of malocclusion or difficulties encountered in using the plate/screw system. Loss of fixation was encountered in only one patient. CONCLUSIONS: The use of a locking plate/screw system was found to be simple, and it offers advantages over conventional bone plates by not requiring the plate to be compressed to the bone to provide stability.     

Small wire external fixation of high energy tibial plateau fractures

Open plate osteosynthesis for high energy tibial plateau fractures with dissociation between the metaphysis and diaphysis has been plagued with frequent soft tissue complications. The Harbor-University of California at Los Angeles Medical Center's experience with small wire external fixation supplemented by limited internal fixation is examined. This alternative method of adequate stable fixation offers the advantage of minimal soft tissue compromise. Twenty-four patients with Schatzker Type VI tibial fractures were treated with small wire external fixation. Supplementary limited internal fixation was used with percutaneous screws in 10 patients and with open reduction in one patient. Sixteen patients had isolated fractures, and eight others suffered multiple injuries. Minimum followup was 12 months. All fractures healed. Complications included one septic knee, two infections at screw sites, and one 10 degrees knee flexion contracture. One knee had Grade 3 radiographic arthrosis, five had Grade 2, 10 had Grade 1, and eight showed no arthrosis. The outcomes (Knee Society clinical rating system) of this study compare favorably with outcomes described in reports published previously for this type of fracture, despite inclusion of eight multiply injured patients. This technique preserves the goals of early range of motion and stable fixation for these devastating injuries, while decreasing the observed major wound complications and nonunion rates. However, longer followup may reveal higher arthrosis rates, specifically in those fractures that were not anatomically reduced.     

The reconstruction locked nail for complex fractures of the proximal femur

Thirty-seven patients with 37 proximal femoral fractures were treated with a reconstruction locked femoral nail. There were four ipsilateral intracapsular femoral neck and shaft fractures, two intertrochanteric fractures, 18 intertrochanteric fractures with diaphyseal extension, eight subtrochanteric fractures with involvement of the lesser trochanter, and five subtrochanteric fractures without involvement of the lesser trochanter. The overall union rate was 92%. Twenty-one complications developed in 13 patients (35%) which included three of the four femoral neck and shaft fractures, and six of 18 intertrochanteric fractures with diaphyseal extension. Of the five intertrochanteric fractures with diaphyseal extension in which anatomic reduction was not achieved, four developed a complication. Of the nine proximal screws in nine fractures, which were placed short (below the subchondral bone of the femoral head), six fractures developed a complication. The complications included three nonunions, one delayed union, two leg-length discrepancies of > 2.5 cm, two cases of varus deformity of > 10 degrees, two varus deformities < 10 degrees, four instances of revision surgery including one broken 13-mm nail, four proximal screws that backed out and required removal, two cases of pudendal nerve palsy, and one case of heterotopic ossification. Seven patients developed more than one complication. Eleven of the 13 patients with complications required a second surgery to treat the complication. We conclude that the reconstruction locked femoral nail is not a good choice for ipsilateral intracapsular neck and shaft fractures. Our recommendation is that anatomic reduction should be achieved for all cases using the reconstruction femoral nail, but it is absolutely required when treating the intertrochanteric fracture with diaphyseal extension. Reconstruction femoral nails have a high rate of complication due to the complex nature of the fractures as well as the device.     

Use of cervicothoracic junction pedicle screws for reconstruction of complex cervical spine pathology

STUDY DESIGN: A retrospective review of 21 patients in which cervical pedicle screw fixation was used at C7 with or without upper thoracic pedicle screw fixation. OBJECTIVE: To evaluate the use of pedicle screw placement in the lower cervical spine. SUMMARY OF BACKGROUND DATA: The use of posterior cervical spine fixation, including lateral mass fixation, has become increasingly popular in recent years. However, lateral mass fixation at C7 is often hindered by lack of substantial high quality bone. The end level of long cervical spine constructs is frequently C7 or T1. Dissatisfaction with lateral mass fixation at C7 and T1 led the authors to use lower cervical pedicle screw fixation for several cervical spine disorders. METHODS: Twenty-one patients who had undergone cervical pedicle screw fixation at C7 were reviewed retrospectively. There were 12 males and 9 females, with an average age of 52 years. All pedicle screws were placed, after direct palpation of the pedicle, with a right angle nerve hook after laminoforaminotomy at C7. RESULTS: There were no neurologic complications related to pedicle screw placement, and no patient was symptomatically worse after the operation. Six patients with root pathology improved. Of 14 patients with cervical myelopathy, 12 improved at least one Nurick grade, and 2 had no improvement. There were no failures of fixation or complications related to pedicle fixation at a minimum of 1 year follow-up. CONCLUSION: Pedicle screws in C7 placed with laminoforaminotomy and palpation technique appears to be safe and efficacious. Excellent fixation can be achieved.     

Osteosynthesis of the hand--indications, technique, results

Between January 1st 1992 and December 31st 1993 140 non-complex (i.e. nerve, vascular, tendon injuries) fractures of the peripheral hand skeleton were operated at the Policlinic of the Kantonsspital Basel. In a retrospective study we analyzed results, complications and absence from work. We treated 110 male and 30 female patients with a mean age of 47 years. 45 fractures were treated by plate fixation, 45 by screw fixation, 53 times we applied k-wires and once a mini-fix-ex (AO-Prototype). Plate and screw fixation were performed with AO-mini-implants. 90% of our patients had an uneventful postoperative course. In spite of functional after-treatment we noted in 8.6% of the patients a relevant loss of movement leading to operative tenolysis in 7 patients. Fractures at the level of PIP were most frequently associated with loss of movement. Absence from work was 59 days in average (1-206)! Conclusions: Peripheral osteosynthesis of the hand (non-complex) are effectively treated on an out-patient basis. In spite of functional after-treatment about 10% of patients have a relevant postoperative reduction in motility. Absence from work is relatively long after operative treatment of peripheral hand fractures.     

Stenting of "unprotected" left main coronary artery stenoses: early and late results

The effect of bone plug length and Kurosaka screw (DePuy, Warsaw, IN) diameter on graft holding strength of the bone-tendon-bone construct was determined. Random length porcine bone plugs were assigned to fixation with 7 or 9 mm Kurosaka screws. Peak load to failure was determined. There was a significant decrease in peak load to failure of the 5-mm long bone plugs compared with longer bone plugs. No difference was found between longer lengths of bone plug in either the 7- or 9-mm screw diameter groups. The 9-mm diameter screws significantly increased peak load to failure for both 1- and 2-cm bone plug lengths.     

A comparison of fixation screws for the scaphoid during application of cyclical bending loads

Matched pairs of scaphoids from cadavera were stressed with ramped intensity cyclical bending loads after osteotomy and fixation of one scaphoid with a Herbert screw and fixation of the other with an AO 3.5-millimeter cannulated screw, a Herbert-Whipple screw, an Acutrak cannulated screw, or a Universal Compression screw. The AO screw, Acutrak screw, and Herbert-Whipple screw demonstrated superior resistance to cyclical bending loads compared with the Herbert screw. The Universal Compression screw did not provide better fixation than the Herbert screw because of fractures that occurred at the time of insertion. The AO screw and the Herbert screw were then tested in a separate setup in which a segment of volar cortex had been removed in addition to the simple osteotomy. The loss of volar cortex greatly diminished the quality of the fixation provided by both of the screws during application of ramped intensity cyclical bending loads. CLINICAL RELEVANCE: A fixation device in the scaphoid must be able to withstand the stresses that are placed on the scaphoid as a result of its position spanning the proximal and distal carpal rows. Also, because of the prolonged time required for healing of fractures or non-unions of the scaphoid, the device must be able to withstand many such cycles of stress. The present study demonstrates that commonly used screws for fixation of the scaphoid vary significantly (p < 0.005) in their ability to resist cyclical bending loads.     

In vitro simulation. Early results of stereotaxy for pedicle screw placement

STUDY DESIGN: Frameless stereotaxy with doppler ultrasound and three dimensional computer model registration is assessed in vitro for pedicle screw placement. OBJECTIVE: To identify feasibility of pedicle screw navigation and placement using this technology. SUMMARY OF BACKGROUND DATA: Inaccurate pedicle screw placement can lead to neurovascular injury or suboptimal fixation. Present techniques in pedicle screw placement involve only confirmation of hole orientation. METHOD: Forty-four pedicle screws were placed in lumbosacral models and cadaver specimens. Accuracy was assessed with a computed tomography scan and vertebral cross sectioning. RESULTS: All screws were intrapedicular. Accuracy of anterior cortical fixation was 1.5 mm, with a range of 2.5 mm. CONCLUSION: In vitro frameless stereotaxy is accurate for pedicle screw placement. This technology adds a component of navigation to pedicle screw placement.     

Anatomic considerations of anterior transarticular screw fixation for atlantoaxial instability

STUDY DESIGN: Anatomic parameters of C1 and C2 were measured in 30 dried human cervical spines. Anterior transarticular C1-C2 screws were placed in 15 cadaveric spines. OBJECTIVE: To provide anatomic data for anterior transarticular atlantoaxial screw or C1-C2 screw and plate fixation. SUMMARY OF BACKGROUND DATA: A posterior approach to fixation in the atlantoaxial joint has been well described. Damage to the vertebral artery is documented as a rare complication of posterior atlantoaxial transarticular screw fixation. An anterior surgical approach to exposing the upper cervical spine for internal fixation and bone graft recently has been developed. No anatomic information regarding the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 is available in the literature. METHODS: Direct measurements using digital calipers and a goniometer were taken from 30 pairs of dried human C1 and C2 vertebrae. The anterior transarticular C1-C2 screw insertion point is at the junction of the lateral edge of the C2 vertebral body to 4 mm above the inferior edge of the C2 anterior arch. The parameters related to anterior transarticular atlantoaxial screw fixation or screw and plate fixation between the C1 lateral mass and the C2 vertebral body were measured. Fifteen embalmed cadavers were used for anterior C1-C2 transarticular screw placement. Longer screws (30-40 mm) were used to detect whether the screw tips violated the upper cervical canal or vertebral arteries. RESULTS: In the anterior transarticular atlantoaxial screw placement, lateral angulation of the screw placement relative to sagittal plane ranged from 4.8 +/- 1.8 degrees to 25.3 +/- 2.6 degrees. The posterior angulation of the screw placement relative to the coronal plane ranged from 12.8 +/- 3.1 degrees to 22.6 +/- 3.2 degrees. The length of the medial screw path ranged from 14.7 +/- 1.5 mm to 25.4 +/- 2.8 mm. In the anterior screw and plate fixation, the anteroposterior diameter of the inferior facet articular surface ranged from 16.2 +/- 1.6 mm to 17.1 +/- 1.8 mm. The anteroposterior diameter of the C2 vertebral body ranged from 9.3 +/- 1 mm to 16.2 +/- 1.8 mm. The anterior prevascular retropharyngeal approach appropriately exposed the atlantoaxial joint for anterior transarticular C1-C2 screw placement. No screws violated the vertebral artery and cervical canal. CONCLUSIONS: An anterior transarticular atlantoaxial screw 15-25 mm long can be inserted with a lateral angulation of 5-25 degrees relative to the sagittal plane and a posterior angulation of 10-25 degrees relative to the coronal plane. Additionally, in C1-C2 anterior plate fixation screws 15 mm long could be anchored in the inferior facet of the C1, and screws 9-15 mm long could be anchored in the C2 vertebral body.     

Quantitative anatomy of the occiput and the biomechanics of occipital screw fixation

STUDY DESIGN: The surgically relevant osseous anatomy of the human anatomy was carefully studied and described. The stability of cortical and cancellous screws placed in anatomic sites commonly used for internal fixation of the occiput was tested. OBJECTIVES: To define the bony anatomy of the occiput in quantitative terms and to measure the ability of cortical and cancellous screws inserted at sites commonly used for internal fixation. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, no previous studies described the gross anatomy of the occiput in specific relation to the internal venous structures in the cranium and to the biomechanical strength of screw fixation in different areas of the occiput. METHODS: Thirty-seven human occiputs were carefully measured using calipers. Thin sections from six such specimens were analyzed with specific attention to cortical thicknesses. Stability of screws placed in various locations in the occiput were tested in axial pullout. RESULTS: The thickness of the occiput varied from extremely thin to a 0.1-mm thickness in the region of the cerebellar fossa and increased to a maximum of 8.3 mm at the level of the superior nuchal line and at the transverse sulcus. Results of pullout testing showed that the cancellous screws were as strong as the cortical screws in this area. In areas of the occiput thicker than 7 mm, unicortical fixation was as strong as bicortical fixation. CONCLUSION: There is a wide variation in thickness of the bone of the occiput. The strength of screw fixation was proportional to the bone's thickness.