Biomechanical properties of the proximal femur determined in vitro by single-energy quantitative computed tomography.

To assess the use of quantitative computed tomography as an in vivo predictor of fracture in the osteoporotic hip, we examined the in vitro relationship between single-energy quantitative computed tomography data, calibrated for scanner drift, and the mechanical properties of trabecular bone from the proximal femur. For 49 samples, the apparent density and ultimate strength were measured and their functional relationship to the computed tomography data determined. Apparent density demonstrated a moderate linear correlation to the computed tomography numbers (R2 = 0.60), and the ultimate strength was related through a power law (R2 = 0.83). In addition, for 8 intact femora, average computed tomographic data from the sub-capital region were moderately correlated to the ultimate fracture load applied under controlled in vitro conditions (R2 = 0.64). The average fracture energy for these femora was 43 J, a value more than an order of magnitude less than the energy available in a fall from standing height, suggesting that fall mechanics are a more important determinant of fracture risk than has been previously thought. The relationship between the energy absorbed to failure and the computed tomography data was best described by a power law (R2 = 0.90). Based on these results, it appears that quantitative computed tomography provides a potentially useful approach for the direct estimate of that component of fracture risk that can be attributed to a reduction in bone strength.

Donor marrow-derived cells as immunogens and targets for the immune response to bone and skin allografts.

The relative importance of donor marrow-derived cells in the immunogenicity of bone and skin allografts was compared. Radiation chimeras were created to have marrow-derived cells (MDCs) of a different genotype from their nonmarrow-derived cells (NMDCs). Such animals were used as donors of bone or skin for recipients chosen so that either the MDCs or the NMDCs of the graft would be incompatible. Immunogenicity was determined by measuring the recipient antibody response. The effect of the immune response on the bone graft (rejection) was determined by impaired bone healing. When MDCs alone were H-2 disparate with the recipient, bone grafts were immunogenic, and the bone graft healing was impaired. In contrast, skin grafts in the same combinations were immunogenic but were not rejected if the differences were only expressed on the MDCs of the graft. The role of NMDCs in all of these experiments was more difficult to interpret, but the results suggested that NMDCs are relatively unimportant for healing of bone grafts, although critical for rejection of skin grafts. We conclude that, unlike the situation with skin grafts, the major inducers and targets of the immune response to bone allografts are marrow derived.

Orthotopic bone transplantation in mice. III. Methods of reducing the immune response and their effect on healing.

Various methods of reducing the immune response to allogeneic bone grafts, either by pretreating the graft or by immunosuppressing the recipient, were compared. Tibial grafts from B10.D2 mice, either untreated or pretreated in various ways, were transplanted into B10 recipients. The antibody response was followed and the extent of bone healing at 4 months was assessed. Pretreatment of the graft by X-irradiation, freezing, or by incubation in alloantisera (either anti-H-2 or anti-Ia) reduced or abolished the immunogenicity of the graft. Immunosuppression of the recipient with methotrexate or antilymphocyte serum (ALS) also greatly depressed the antibody response. But when healing was assessed, none of these treatments except ALS improved the delayed healing of the bone allografts. The reason for this failure was probably that X-irradiation, freezing, alloantiserum pretreatment, and methotrexate all interfered with bone healing directly, whereas ALS did not. We conclude that many methods will reduce the immune response to allogeneic bone, but that only ALS will improve the healing of the allogeneic bone. Furthermore, as a corollary to the observation that pretreatment with anti-Ia serum markedly reduced the immunogenicity of bone allografts, we conclude that much of the immunogenicity of bone allografts is attributable to a population of Ia-positive cells.

Esophagogastrectomy using the auto suture EEA surgical stapling instrument.

A stapling instrument, which creates end-to-end inverting anastomoses, is described for esophagogastrostomy. The inverted anastomosis is held together by a double staggered row of stainless-steel wire staples. Experience with 7 consecutive patients who underwent esophagogastrectomy for carcinoma of the distal esophagus or proximal stomach using this device is reported. Postoperative complications included atelectasis in 1 patient, cardiac failure in 1, and pneumonia in 1. A fibrotic stricture developed at the anastomotic site 5 months postoperatively in 1 patient. There were no anastomotic leaks. The stapled anastomosis takes 2 to 3 minutes to perform and seems to be at least comparable to handsewn anastomoses.

Posterior interbody arthrodesis with a fibular strut graft in spondylolisthesis.

We reviewed the results of posterior interbody arthrodesis of the fifth lumbar and first sacral vertebrae with the use of a fibular strut graft in nine patients who had had a grade-III, IV, or V spondylolisthesis. The average age of the patients at the time of the operation was twenty-seven years (range, seventeen to thirty-two years). The average duration of the symptoms preoperatively was three years (range, nine months to eleven years), and the average duration of follow-up was three years (range, two to five years). The most common preoperative symptom was back pain, which was rated an average of 8.3 points (7, 8, or 9 points) on a visual-analog scale of 1 to 10 points. The average angle of the slip was 45 degrees (range, 15 to 70 degrees). Four of the slips were grade III, four were grade IV, and one was grade V. Postoperatively, the average pain score was 1.4 points (1, 2, or 3 points). This improvement was significant (p < 0.05, Student t test). All nine patients had roentgenographic evidence of osseous fusion at the one-year follow-up examination. Complications included a dural tear in one patient, a superficial wound infection in two patients, temporary weakness of the evertors of the foot in six patients, and transient decreased sensation along the dorsum of the foot of the donor leg in two patients.

Spinal arachnoiditis.

A review of the literature points to the many causes of arachnoiditis and the failure of treatment to arrest or reverse its effects. The true incidence cannot be determined, although it is probably lower than might at first appear from the published articles. In the radiological literature the diagnosis seems to derive from an examination of the films alone, often without reference to the clinical findings or appearance at operation. While attempts at treatment are usually unsuccessful, some iatrogenic cases can be prevented by the avoidance of intrathecal steroid injections or unduly rough or repeated surgical exploration of the lumbar vertebral canal.

The AO spinal internal fixator.

The AO spinal internal fixation system uses 5.0 mm diameter transpedicular Schanz screws with 7.0 mm diameter fully threaded stainless steel rods. Originally developed for the treatment of thoracolumbar and lumbar spine fractures, it can be used for a variety of spinal disorders. A prospective study has been carried out, and the first 48 patients have been reviewed. The results for those patients with fractures are excellent. In burst fractures, it has been possible to decompress the canal and restore lordosis. In only half of the cases of spondylolisthesis has it been possible to improve the degree of slip. The fixator has provided rigid stabilization for a variety of other spinal problems.

Translaminar facet joint screw fixation for lumbar and lumbosacral fusion. A clinical and biomechanical study.

Various systems of supplementing bone grafts with internal fixation in the lumbosacral spine have been used in an effort to improve fusion rates. This study reports biomechanical data of cyclic loading cadaveric spines instrumented with translaminar facet screws as well as early clinical results on this technique. Static loading tests comparing uninstrumented and instrumented spinal motion units show that a ninefold increase in flexion load is necessary for constant displacement after facet screw fixation. Repetitive loading tests show only a small decrease in stiffness of instrumented segments even after 5,000 cycles. To date, 35 patients have undergone fusion by this technique as performed by one surgeon. After excluding Workers' Compensation cases and cases with less than 2 years follow-up, there were 18 cases available for review. Twelve of these 18 cases were two-level fusions. Ten patients underwent concomitant discectomy or nerve root decompression. There were no cases of iatrogenic neurologic injury or pseudoarthrosis. It is concluded that translaminar facet screws have a sound biomechanical basis and are a valuable addition to lumbar fusion procedures.

Indications for pedicle fixation. Results of NASS/SRS faculty questionnaire. North American Spine Society and Scoliosis Research Society.

STUDY DESIGN: The faculty of the North American Spine Society and Scoliosis Research Society pedicle fixation workshop were questioned about their use of pedicle screw implants for fixation of the spine. OBJECTIVES: This study ascertained which faculty members used pedicle implants given specific clinical scenarios and analyzed the data for trends and consensus. SUMMARY OF BACKGROUND DATA: For the past 4 years, the North American Spine Society in conjunction with the Scoliosis Research Society has sponsored a course on pedicle fixation of the spine. During these courses, techniques of pedicle fixation have been discussed. The indications, however, for pedicle fixation have remained controversial, even among the course faculty. METHODS: A questionnaire was developed with 20 clinical scenarios, and the faculty were asked whether they would use pedicle implants as part of their surgical treatment. RESULTS: Thirty-eight of 45 (84%) questionnaires have been received and analyzed. For most scenarios, there was statistically significant consensus among the faculty that they would use a pedicle implant. There was statistically significant consensus that the faculty would not use pedicle implants for thoracic fractures or adolescent idiopathic scoliosis. DISCUSSION: This study is useful in assessing pedicle implant usage in our community but should not be used as a guide for their indications and contraindications.

A comparative analysis of spondylolysis repair.

STUDY DESIGN: This retrospective study compared patient outcome after two surgical techniques for pars interarticularis repair: 1) buck screw fixation and 2) the modified Morscher-designed spondylolysis distraction hook. OBJECTIVES: To determine whether one technique was associated with higher radiographic, clinical, or implant failure. SUMMARY OF BACKGROUND DATA: Both techniques have been reported as giving good clinical results. METHODS: Twenty patients were included in this study. All patients had Type IIA spondylolytic defects with either a Grade 0 or Grade I spondylolisthesis. Nine patients were treated with the Morscher hook implant, and 11 patients were treated with the Buck technique. RESULTS: Radiographic follow-up of the Morscher implants demonstrated loosening in three and breakage in one. Radiographic analysis of the Buck technique demonstrated implant failure in one. Failure of healing occurred in four instances with the Morscher implant compared with two instances with the Buck technique. Clinical outcome was assessed using the modified Prolo score. The mean outcomes were 6.33 in the Morscher group and 6.09 in the Buck group. CONCLUSIONS: In these patients, the Morscher implant had a high failure rate. Furthermore, the clinical outcome in this group of patients was poor using either technique.

Screw fixation of odontoid fractures and nonunions.

Surgical treatment of odontoid fractures has usually been carried out by C1-2 arthrodesis rather than by fracture fixation. An alternative treatment of compression screw fixation was used to treat selected acute odontoid fractures and nonunions. Ten patients were operated on. A variety of lag-screw types were used to compress and secure the fracture. Screw placement was considered excellent in five cases; in four, the screw tip protruded through the posterosuperior cortex of the dens by 1-3 mm. One patient died as a result of multiple injuries 2 days after surgery. In all other cases, including four cases of odontoid pseudarthroses, the fractures achieved solid union. It was concluded that screw fixation can be used for the successful treatment of selected odontoid fractures and nonunions.

The value of facet joint blocks in patient selection for lumbar fusion.

The purpose of this study was to ascertain the correlation between diagnostic facet blocks and treatment outcome, both surgical and nonsurgical. One hundred twenty-six patients who had previously undergone diagnostic facet injections were reviewed. Eighty-two had subsequently undergone lumbar arthrodesis. The rest were treated with a variety of nonoperative modalities. Statistical analysis of accumulated data failed to show any significant correlation between the results of facet blocks and outcome of operative arthrodesis. In addition, statistical analysis failed to show any significant correlation between the facet block results and the outcome of nonoperative treatment. The authors concluded that lumbar facet joint injections cannot be used to determine appropriate patient treatment because they are not predictive of either surgical of nonsurgical success.

Intraosseous vertebral body pressures.

In an effort to determine the relationship between low-back pain and intraosseous hypertension, in vivo vertebral pressure measurements were performed on 19 patients. A cannulated screw was placed percutaneously into the middle of the vertebral body by a transpedicular route. Pressure measurements were recorded with the patient in various positions. Pressures were greatest in the sitting position, lowest in the prone position, and intermediate in the standing position. A correlation was found between intravertebral body pressure and patient position. Pressures were highest in the positions most commonly associated with low-back pain.

Classification of pseudarthroses of the lumbar spine.

Imaging studies and operative records of 55 patients who had undergone lumbar pseudarthrosis repair were studied, providing a total of 85 surgically documented pseudarthroses. Preoperative imaging studies were carefully analyzed for the anatomic characteristics of the involved levels and the morphology of the fusion mass. The pseudarthroses were found to fall into four distinct morphologic categories: atrophic, transverse, shingle, and complex. The atrophic pseudarthrosis type was noted to be strongly associated with the presence of intact facet joints or spinal hardware. This retrospective analysis indicates that stress shielding provided by intact facet joints or spinal implants may contribute to graft atrophy in certain patients. The classification scheme proposed may be useful in future analyses of different fusion techniques in determining the various causes of this surgical complication.

Marfan syndrome with back pain secondary to pedicular attenuation. A case report.

STUDY DESIGN: This is a report of a 31-year-old woman with Marfan syndrome with severe back pain secondary to pedicle fractures of the lumbar spine resulting from attenuation of the pedicles. OBJECTIVES: To report and discuss a case of Marfan syndrome. SUMMARY OF BACKGROUND DATA: The authors report the clinical course of a patient with Marfan syndrome and pedicle fractures secondary to thinning of the pedicles. METHODS: After initial diagnosis of Marfan syndrome was confirmed, radiologic techniques, including magnetic resonance imaging and bone scan, were used to evaluate any abnormalities of the lumbar spine. RESULTS: The patient was treated with pain medications and activity modification, which allowed for no marked improvement. CONCLUSIONS: Thinning and possible fracturing of the pedicles should be considered as an etiology of back pain in the patient with Marfan syndrome.

Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members.

A limited survey analysis of 617 surgical cases in which pedicle screw implants were used was undertaken to ascertain the incidence and variety of associated complications. The different implant systems used included variable spinal plating (n = 249), Edwards (n = 143), and AO fixateur interne (n = 101). The most common intraoperative problem was unrecognized screw misplacement (5.2%). Fracturing of the pedicle during screw insertion and iatrogenic cerebrospinal fluid leak occurred in 4.2% of cases. The postoperative deep infection rate was 4.2%. Transient neuropraxia occurred in 2.4% of cases, and permanent nerve root injury occurred in 2.3% of cases. Previously unreported injury to nerve roots occurred late in the postoperative course in three cases. Screw breakage occurred in 2.9% of cases. All other complications had an incidence of less than 2%. The authors conclude that pedicle screw placement may be associated with significant intraoperative and postoperative complications. This information is of value to surgeons using pedicle implant systems as well as to their patients. Repeat surgery is associated with greater numbers of complications.

Anterior cervical plate fixation with the titanium hollow screw plate system.

Although anterior cervical plates provide excellent fixation for the anterior column, the potential risk for injury to the spinal cord or soft tissues involved with their use has been the reason they have not gained universal acceptance. Morscher introduced a system that attempts to prevent the migration and loosening of screws by using a cross-split screw head that can be locked into the plate. The secondary advantage of this system is that it eliminates the requirement for posterior cortex purchase and thereby decreases the risk for spinal cord injury. This article reports the authors' experience using the Morscher titanium hollow screw cervical plate system. Forty-two patients in the series underwent anterior cervical arthrodesis for degenerative disease or trauma. The average number of levels fused were two. The fusion rate was 100%. Significant hardware loosening occurred in two patients. There was no iatrogenic injury to the spinal cord or esophagus. In conclusion, the titanium hollow screw cervical plate provides immediate stable fixation with minimal complications. Its use should be considered in the surgical treatment of patients requiring multilevel anterior cervical arthrodesis.

A histologic study of lumbar pseudarthrosis.

Biopsy specimens were obtained from 35 consecutive patients undergoing pseudarthrosis repair after failed posterior spinal fusions. Biopsy specimens were obtained when possible from the fusion mass, from areas of motion, and from the lumbar facet remnant where identifiable. Tissue found between adjacent bony segments was noted to contain predominantly fibrous tissue often accompanied by signs of local fibrocartilaginous metaplasia. In addition, small fragments of impacted bone, sometimes seen to be undergoing active resorption, also were noted frequently in these areas. The bone adjacent to the areas of motion was sclerotic and poorly organized, containing a mixture of woven and lamellar bone. Interestingly, multiple microtrabecular fracture with appositional new bone formation was a frequently seen feature. All facet joint biopsies were noted to have evidence of degenerative disease. Both cartilage fissuring and significant chondrocyte cloning were noted. Subchondral bony sclerosis was also a consistent feature.

Surgical anatomy of the sacrum. A guide for rational screw fixation.

Anterior sacral anatomy was studied to allow safe sacral screw placement. The study included 27 bony sacra. Intrapelvic dissections were performed. Cadaveric specimens were dissected and photographed. The position and angulation of the first sacral foramen was extremely variable. After the position of the L5 root, sacral roots, and iliac vessels, was considered, safe posterior sacral screw implantation could be assured through placement above the level of the first sacral foramen directed medially toward the promontory, parallel to the superior sacral end-plate. Complications of indiscriminate screw placement included L5-root damage, iliac vein penetration, and intractable perineal pain due to sacral root injury. Preoperative computed tomography with the scanner gantry tilted to parallel the superior sacral end-plate defined the great vessels, neural foramens, inclination of the superior sacral end-plate, and prominence of the posterior ileum. Surgical accuracy was evaluated after surgery with computed tomography.

In vivo diurnal variation in intervertebral disc volume and morphology.

STUDY DESIGN: Three-dimensional reconstructions of MRI scans measured volume, height, and diameter of intervertebral discs. These measurements were made in vivo. OBJECTIVES: This study documented diurnal change in lumbar disc volume and morphology. The authors studied the pattern of this change over the disc levels that were examined and documented individual differences. SUMMARY OF BACKGROUND DATA: There is a diurnal pattern of standing heights. The majority of this diurnal height change can be accounted for by height loss within the intervertebral disc, which bulges radially with loading. These studies have been performed in vivo. METHODS: Eight normal males were studied using two protocols. In one, the volunteers were in the supine position for 6 hours before MRI scanning. In the other, volunteers spent 4 hours standing and 3 hours sitting before MRI scanning. Three-dimensional MRI scanning was carried out on the L3-4, L4-5, and L5-S1 discs. RESULTS: Volume height and AP diameter of the lumbar intervertebral discs decreased significantly after the protocol of a day's activity. The mean decrease in disc volume at the L3-4 level after standing was 21.1%. At the L4-5 level, it decreased a mean of 18.7%, whereas at the L5-S1 level, there was a 21.6% mean decrease. CONCLUSIONS: The mean simulated diurnal volume decrease in the lower three lumbar discs is 16.2%. Most of the diurnal loss in disc height is due to volume loss. The effect of radial bulging is minimal.