Joseph G. Craig

Complications in the Use of rhBMP-2 in PEEK Cages for Interbody Spinal Fusions

Study Design All patients of spinal interbody fusion using polyetheretherketone (PEEK) cages and recombinant human bone morphogenetic protein (rhBMP)-2 performed over a 16-month period were reviewed. Objective To determine the suitability of PEEK cages when used in conjunction with rhBMP-2 in interbody spinal fusion. Summary of Background Data Bone morphogenetic proteins are increasingly being used in spinal fusion to promote osteogenesis. PEEK is a semicrystalline aromatic polymer that is used as a structural spacer to maintain the disc and foraminal height. Their use has led to increased and predictable rates of fusion. However, not many reports of the adverse effects of their use are available. Methods Fifty-nine consecutive patients of interbody spinal fusion in the cervical or lumbar spine using a PEEK cage and rhBMP-2 were followed for an average of 26 months after surgery. A clinical examination and a record of Oswestry Disability Index, Visual Analog Scale for pain, and a pain diagram were performed preoperatively and at every follow-up visit. All patients had plain radiographs carried out to assess fusion. Ten patients of lumbar spine fusion were additionally evaluated with a computed tomography scan. Results All cases demonstrated an appreciable amount of new bone formation by 6 to 9 months in the cervical spine and by 9 to 12 months in the lumbar spine. End plate resorption was visible radiologically in all cervical spine fusions and majority of lumbar fusions. Cage migration was observed to occur maximally in patients with transforaminal lumbar interbody fusion and posterior lumbar interbody fusion. Disc space subsidence was seen in both cervical and lumbar arthrodesis with the latter showing a lesser incidence, but with a greater degree of collapse. Conclusions PEEK cages and rhBMP-2 when used in spinal fusion give consistently good fusion rates. However, the early role of BMP in the resorptive phase may cause loosening, cage migration, and subsidence.

INFECTION: ULTRASOUND-GUIDED PROCEDURES

The majority of fluid collections in the musculoskeletal system can be localized and aspirated under ultrasound guidance. Whether fluid is infected cannot be determined from ultrasound appearances and laboratory analysis is required. In complicated infection, particularly septic arthritis and osteomyelitis, combined use of MR imaging and aspiration under ultrasound is very useful.

Sonographic detection, evaluation and aspiration of infected acromioclavicular joints

Abstract Objective. To describe the sonographic findings of septic arthritis of the acromioclavicular joint. Design and patients. A retrospective study of five male patients was carried out. Four of the patients were referred because of signs and symptoms suggestive of glenohumeral joint septic arthritis, one for signs and symptoms suggestive of septic arthritis of the acromioclavicular joint. All the acromioclavicular joints were evaluated with ultrasound, aspirated and the aspirate cultured. Results. All patients had normal ultrasound findings of their glenohumeral joints and distended acromioclavicular joints as determined by ultrasound. Ultrasound examination elicited focal tenderness over the acromioclavicular joint. Aspirates of each acromioclavicular joint grew pyogenic organisms. Conclusion. Infection in the acromio-clavicular joint is uncommon, but is seen in increased frequency in immune-compromised patients and intravenous drug users. A normal glenohumeral joint on ultrasound in a patient suspected of having a septic shoulder should prompt careful review of the acromioclavicular joint. Aspiration of the acromioclavicular joint is easily performed under ultrasound guidance.

ULTRASOUND OF FRACTURE AND BONE HEALING

This article reviews the ultrasound appearance of common fractures that may mimic other pathologies. Recent works suggest a role for ultrasound in the assessment of callus formation in delayed union of fractures and following the Ilizarov reconstructive procedures.

Intraoperative monitoring with stimulus-evoked electromyography during placement of iliosacral screws : An initial clinical study

A consecutive series of twenty-seven patients who had thirty acute unstable (type-C) fractures of the pelvic ring was studied prospectively to evaluate the use of stimulus-evoked electromyography to decrease the risk of iatrogenic nerve-root injury during the insertion of iliosacral screws. A prerequisite for inclusion in the study was a normal neurological status preoperatively; somatosensory evoked potentials were monitored to further document the neurological status both before and after insertion of the screw or screws. A total of fifty-one iliosacral screws were inserted, and a current threshold of more than eight milliamperes was selected as the level that indicated that the drill-bit was a safe distance from the nerve root. Four of the fifty-one screws were redirected because of information obtained with stimulus-evoked electromyography. Postoperatively, all patients had a normal neurological status. Computerized tomography, although not accurate for detailed measurements, demonstrated that all of the screws were in a safe, intraosseous position. Monitoring with stimulus-evoked electromyography appears to provide reliable data and may decrease the risk of iatrogenic injury to the nerve roots during operations on the pelvic ring.

Longitudinal stress fracture: patterns of edema and the importance of the nutrient foramen.

Abstract Design and patients. We reviewed the MR appearances of six cases of longitudinal stress fracture of the lower extremity. Results. One fracture was in the femur and five were in the tibia. Four of the tibial fractures showed edema starting in the mid-tibia at the level of the nutrient foramen with the fracture on the anteromedial cortex. The other tibial fracture started at the nutrient foramen. Three fractures (two tibial and the femur fracture) showed eccentric marrow edema; all fractures showed either eccentric periosteal reaction or soft tissue edema. Conclusion. Primary diagnosis of longitudinal stress fracture is made by finding a vertical cleft on one or more axial images. Secondary signs of position of the nutrient foramen and patterns of edema may be useful.

Calcium sulfate used as bone graft substitute in acetabular fracture fixation.

The purpose of this study was to determine the natural history of calcium sulfate pellets implanted during acetabular fracture surgery. The study group consisted of patients sustaining an acetabular fracture with intraarticular comminution or marginal impaction or both in whom calcium sulfate pellets were implanted in lieu of autologous bone graft. Between 1997 and 1999, 32 fractures were treated. Followup adequate to delineate pellet outcome, including radiographs and computed tomography, was obtained in 31 patients. Evaluation of plain radiographs showed that the calcium sulfate pellets became undifferentiated from the surrounding bone at an average of 7 weeks postoperatively. In no case was a residual bony deficit seen. Computed tomography analysis showed that in 22 patients, the pellets essentially had been (> 90%) replaced by bone and in four patients, the majority (> 50%–90%) of the pellets had been replaced by bone. However, in five patients, less than 50% of the pellets had been replaced by bone, including one showing no bony replacement. The common finding in patients with an extensive residual deficit was direct communication of the pellets with the joint space shown on the postoperative computed tomography scan. Patients with the best results had complete containment of the pellets within bone. Therefore, it seems that implanted calcium sulfate pellets in contact with joint synovial fluid are at risk for resorption without significant bony response. If calcium sulfate pellets are to be implanted in a periarticular location, complete bony containment is desirable. Evaluation of the periacetabular bony response requires computed tomography scans, as plain radiographs are inadequate for this purpose.

Fractures of the greater trochanter: intertrochanteric extension shown by MR imaging.

Abstract Objective. To demonstrate the MR depiction of the intertrochanteric or femoral neck extension of fractures of the greater trochanter, when standard radiographs show only a fracture of the greater trochanter. Design and patients. A retrospective review was performed of the MR and radiographic findings in 13 consecutive patients (10 men, 3 women; ages 24–86 years) with radiographic evidence of fracture of the greater trochanter who were examined with MR imaging. Results. The MR study displayed the fracture of the greater trochanter in all cases. In all but three patients, MR examinations displayed an extension of the fracture into the intertrochanteric region, and in one, also an extension into the femoral neck, although the cortex at this level was not interrupted. Conclusion. When there is radiographic evidence of an isolated fracture of the greater trochanter, MR often shows an intertrochanteric or femoral neck extension of the fracture in both young and older adults. This finding may be a factor in determining the need for surgical intervention.

Musculoskeletal Ultrasound: Elbow Imaging and Procedures

Elbow injuries, both acute and chronic sports-related cases, have increased over the last decade. With one in every four members of a household participating in sports, both clinics and radiology departments are seeing more patients with elbow pain. High-resolution ultrasound is well suited for evaluating the elbow. Ultrasound is growing in popularity and fast becoming another modality that the radiologist can use to help diagnose elbow pathology. With advancing transducer technology and accessibility, ultrasound offers focused and real-time high-resolution imaging of tendons, ligaments, and nerve structures. Its advantages include the use of safe nonionizing radiation, accessibility, and cost effectiveness. Another unique advantage is its ability for dynamic assessment of tendon and ligament structures such as in cases of partial tears of the medial ulnar collateral ligament or ulnar nerve dislocation. It is also easy to assess the contralateral side as a control. Ultrasound is also useful in therapeutic guided injections for its multiplanar capability and clear visualization of major vessels and nerves. We discuss the unique application of ultrasound in evaluating common elbow pathology and in advanced ultrasound-guided treatments such as dextrose prolotherapy and platelet-rich plasma.

Intraoperative stimulus-evoked electromyographic monitoring for placement of iliosacral implants : An animal model

OBJECTIVE A canine model was designed to evaluate the feasibility of stimulus-evoked electromyographic (EMG) monitoring of the lumbosacral nerve roots during the insertion of iliosacral implants. STUDY DESIGN/METHODS Four 2.5-millimeter Kirschner wires (K-wires) were percutaneously inserted under general anesthesia into the S1 body of each of five dog hemipelves using C-arm fluoroscopy image-intensifier control in an actual attempt to compromise the S1 canal and the S1 nerve root. A searching current of twenty milliamperes was initially applied to the K-wire with monitoring electrodes placed in the gastrocnemius muscle. Current thresholds required to evoke an EMG response were recorded for each K-wire. Actual K-wire location was determined by anatomical dissection. RESULTS Evaluation of these twenty wires revealed that current threshold was directly related to the proximity of the K-wire to the nerve root, with a correlation coefficient of 0.94 (p < 0.001). CONCLUSIONS Stimulus-evoked EMG monitoring provided reliable data indicating the proximity of the iliosacral implants to the sacral nerve root. This method of intraoperative nerve monitoring could potentially decrease the risk of iatrogenic nerve root injury during pelvic ring surgery. Further study is warranted.