Use of hydroxyapatite in spine surgery.

Hydroxyapatite- (HA-)based ceramics have been evaluated for a variety of applications in spinal surgery, utilizing in vivo animal models and human clinical series. In vivo animal studies have shown efficacy for these materials as a bone graft substitute in interbody fusions and as a bone graft extender or bioactive osteoinductive material carrier in posterolateral lumbar fusions. Clinically, HA ceramic has been shown to be effective as a bone graft extender in posterior spinal fusion surgery for childhood scoliosis, and as a structural bone graft substitute in anterior cervical spine fusions. As an osteoconductive material, it appears to function best as a bone graft extender or carrier for an osteoinductive bone growth factor rather than as a stand-alone bone graft substitute in nonstructural clinical applications. Injectable HA ceramics also hold promise as biocompatible and bioresorbable materials for use in spinal screw fixation strength augmentation and in minimally invasive vertebral body strength augmentation either following fracture or prophylactically in osteoporotic vertebrae.

Internal fixation of cervical trauma following corpectomy and reconstruction. The effects of posterior element injury.

Although biomechanical data indicates that anterior fixation alone in unstable cervical injuries may not provide adequate stability, reports of clinical series indicate general success with this method of treatment. The specific contribution of posterior column injury to overall stability following reconstruction has not been evaluated. This study examined the biomechanical stability of anterior and/or posterior plate fixation following anterior corpectomy and reconstruction for unstable cervical injuries with varying degrees of posterior element injury. The C4-C6 motion segments of ten fresh frozen bovine cervical spines were used. After mounting, nondestructive mechanical testing in axial compression, torsion, flexion, extension, and lateral bending was done as an intact control. A C5 corpectomy with reconstruction using a synthetic bone graft was performed and the posterior ligaments sectioned at the C5-C6 level. Each specimen was sequentially instrumented with anterior and posterior plating alone and in combination and each construct was mechanically retested. The specimens were then further destabilized by bilateral facetectomies at C5-C6 and again tested with the same instrumentation combinations. In comparison to the controls, the spines with a C5 corpectomy/bone graft and posterior ligament rupture with anterior plating demonstrated significantly increased stiffness in flexion, extension, and lateral bending; posterior plating increased stiffness in only flexion and lateral bending. In axial compression and torsion, anterior or posterior plating demonstrated stiffness similar to the controls. Further destabilization by facetectomy significantly decreased stiffness of the instrumented construct (less than control) in torsion with anterior or posterior plate fixation alone. Combined plating showed increased stability compared to controls in all loading conditions for both patterns of instability. Anterior plating alone was able to restore the stability of the cervical spines with posterior ligamentous injury after corpectomy, but it failed to do so with the addition of bilateral facetectomies. For the unstable cervical spine with significant bilateral loss of posterior bony contact, anterior or posterior plating alone may not provide sufficient stabilization in the absence of any additional external immobilization. Combined plating should be considered, which may obviate the need for external immobilization.

Use of the anterior interbody fresh-frozen femoral head allograft in circumferential lumbar fusions.

Many studies in the literature have documented the outcome of circumferential lumbar fusions. However, no study has specifically evaluated the performance of the anterior fresh-frozen femoral head allograft as a structural interbody graft material. All office and hospital records, including charts and radiographs, were reviewed to obtain pertinent clinical and radiographic information. The cases included 23 single-level fusions, 22 two-level fusions, and 5 fusions of three or more levels. In all, 88 fusion levels were analyzed radiographically. The mean follow-up time was 28 months (range, 24 to 36 months). All procedures were performed in a single stage. At the latest follow-up, clinical outcome was graded good to excellent in 39 (78%) cases, fair in 8 (16%) cases, and poor in 3 (6%) cases. The average time to anterior radiographic fusion was 6 months (range, 4 to 8 months). The overall fusion rate was 98%. The average preoperative anterior disk space height was 10 mm, 14 mm immediately after operation, and 13 mm at follow-up. The posterior disk space height averaged 5 mm before operation, 7 mm immediately after operation, and 6 mm at follow-up. The average segmental lordosis was 7 degrees before operation, 10 degrees immediately after operation, and 10 degrees at follow-up. Late postoperative disk space collapse of 3 mm or more was noted in 17% of the fused disk spaces examined. Seventy-eight percent of the disk spaces maintained a disk space height greater than that of their preoperative value at the latest follow-up. Segmental lordosis did not change significantly at follow-up. The occurrence of collapse did not correlate with the clinical result, smoking history, or surgical indication (p < 0.05). Perioperative complications included one pleural effusion, two urinary tract infections, and one deep wound infection. Late complications included five painful graft sites and two patients with pseudarthrosis. Fresh-frozen femoral head allograft fulfills its desired function as an anterior structural graft in combination with rigid posterior transpedicular fixation, maintaining the disk space height achieved at surgery while reliably allowing remodeling and incorporation into a solid anterior fusion.

The use of an injectable, biodegradable calcium phosphate bone substitute for the prophylactic augmentation of osteoporotic vertebrae and the management of vertebral compression fractures.

STUDY DESIGN: A biomechanical study comparing two materials for augmentation of osteoporotic vertebral bodies and vertebral bodies after compression fracture. OBJECTIVES: To compare an injected, biodegradable calcium phosphate bone substitute with injected polymethylmethacrylate bone cement for strengthening osteoporotic vertebral bodies and improving the integrity of vertebral compression fractures. SUMMARY OF BACKGROUND DATA: Injection of polymethylmethacrylate bone cement into fractured vertebral bodies has been used clinically. However, there is concern about thermal damage to the neural elements during polymerization of the polymethylmethacrylate bone cement as well as its negative effects on bone remodeling. Biodegradable calcium phosphate bone substitutes have been studied for enhancement of fixation in fractured vertebrae. METHODS: Forty fresh osteoporotic thoracolumbar vertebrae were used for two separate parts of this study: 1) injection into osteoporotic vertebrae: intact control (n = 8), calcium phosphate (n = 8), and polymethylmethacrylate bone cement (n = 8) groups. Each specimen then was loaded in anterior compression until failure; 2) injection into postfractured vertebrae: calcium phosphate (n = 8) and polymethylmethacrylate bone cement (n = 8) groups. Before and after injection, the specimens were radiographed in the lateral projection to determine changes in vertebral body height and then loaded to failure in anterior bending. RESULTS: For intact osteoporotic vertebrae, the average fracture strength was 527 +/- 43 N (stiffness, 84 +/- 11 N/mm), 1063 +/- 127 N (stiffness, 157 +/- 21 N/mm) for the group injected with calcium phosphate, and 1036 +/- 100 N (stiffness, 156 +/- 8 N/mm) for the group injected with polymethylmethacrylate bone cement. The fracture strength and stiffness in the calcium phosphate bone substitute group and those in the polymethylmethacrylate bone cement group were similar and significantly stronger than those in intact control group (P < 0.05). For the compression fracture study, anterior vertebral height was increased 58.5 +/- 4.6% in the group injected with calcium phosphate and 58.0 +/- 6.5% in the group injected with polymethylmethacrylate bone cement as compared with preinjection fracture heights. No significant difference between the two groups was found in anterior vertebral height, fracture strength, or stiffness. CONCLUSION: This study demonstrated that the injection of a biodegradable calcium phosphate bone substitute to strengthen osteoporotic vertebral bodies or improve vertebral compression fractures might provide an alternative to the use of polymethylmethacrylate bone cement.

The effect of locking fixation screws on the stability of anterior cervical plating.

STUDY DESIGN: Current anterior cervical plate systems were tested with locked and unlocked fixation screws and with unicortical and bicortical fixation screws to determine fixation rigidity and pull-off strengths. OBJECTIVES: To evaluate the effects of screw-plate locking and screw length on fixation strength and stability of anterior cervical plates. SUMMARY OF BACKGROUND DATA: New plate systems provide for rigid locking of the screw-plate interface, theoretically increasing construct rigidity, allowing unicortical fixation, and preventing screw back-out. There are few data on the effects of locking screws on the stability of anterior cervical plating. METHODS: Eighty fresh lamb vertebrae (C3-T1) were used. Test systems included: Cervical Spine Locking Plate (CSLP; Synthes, Paoli, PA, Orion plate (Sofamor-Danek, Memphis, TN), and Acroplate (AcroMed, Cleveland, OH). The CSLP and Orion plates were tested with fixation screws, locked and unlocked, and the AcroMed plate with unicortical and bicortical screw purchase. Biomechanical testing of the screw-plate constructs was performed to determine the initial bone-plate rigidity and pull-off strength. A 2.5-Nm cyclic bending moment was then applied to additional constructs for 10(5) cycles, and these constructs retested. RESULTS: Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading (P < 0.05). After cycling, the rigidity of all unlocked unicortical constructs decreased significantly (P < 0.05). There was no significant difference in pull-off strengths between the CSLP, the Orion, and the unicortical AcroMed plate. However, all had significantly less pull-off strength than the AcroMed plate with bicortical screws. A negative correlation was observed between initial pull-off strength and sagittal vertebral body diameter. CONCLUSIONS: Locking screws significantly increased the rigidity of the tested screw-plate systems initially and after cyclic loading. Because pull-off strength was affected by the vertebral body diameter, use of longer unicortical screws may be clinically beneficial in the patient with larger cervical vertebrae.

Optimal selection and preparation of fresh frozen corticocancellous allografts for cervical interbody spinal fusion.

STUDY DESIGN: Iliac crest corticocancellous allografts for anterior interbody fusion were harvested from six cadavers. The grafts were cut sequentially from left and right crests and randomly assigned to tricortical or bicortical preparations. Their compression strengths then were determined and compared by matched pair analysis. OBJECTIVES: To quantify the failure strength of the grafts from different iliac locations and determine the optimal type of preparation of the grafts for anterior interbody fusion. SUMMARY OF BACKGROUND DATA: Iliac crest corticocancellous autografts and allografts commonly are used for interbody cervical fusions. However, graft strengths for specific sites have not been determined fully. METHODS: Six paired, fresh frozen, iliac crests were sectioned using a customized miter box into multiple 1-cm-thick grafts 1.5 cm in depth to simulate cervical interbody grafts. The left and right sides of each pair were randomly assigned to tricortical and bicortical preparations. The samples were tested by applying a compressive load to failure using a specialized fixture to simulate vertebral body loading. RESULTS: The grafts closer to the anterosuperior iliac spine had significantly higher failure loads and failure strengths than those closer to the posterosuperior iliac spine. The strengths of the bicortical grafts were 72 +/- 14% of the strengths of the tricortical grafts (P < 0.001). CONCLUSIONS: Anterior iliac crest grafts were stronger in compression, even after removal of one cortical surface, than posterior iliac crest grafts.

Optimal selection and preparation of fresh frozen corticocancellous allografts for anterior interbody lumbar spinal fusion.

To determine the effect of graft preparation on graft strength, corticocancellous grafts suitable for anterior interbody fusion were obtained from six cadavers using five different donor bone sites with different graft sectioning orientations and locations. Graft compression strength was determined in simulated physiological loading. The distal tibia and femoral head lumbar interbody grafts are significantly stronger than grafts prepared from other corticocancellous donor sites. Graft fabrication by cutting perpendicular to the long axis and closer to the long bone ends results in increased graft strength.

An anatomic evaluation of L5 nerve stretch in spondylolisthesis reduction.

STUDY DESIGN: Lumbosacral spondylolisthesis was simulated using four embalmed human spines, and the path of the L5 nerve was studied. OBJECTIVES: To quantify the change in length of the L5 nerve root associated with reduction of spondylolisthesis, correction of slip angle, and changing disc height. SUMMARY OF BACKGROUND DATA: Stretch injury to the lumbar nerves remains a complication of spondylolisthesis reduction. To date, no anatomic studies have been performed to quantify this effect of reduction on the lumbar nerves. METHODS: The L5 vertebral body and the sacrum of four embalmed human spines were constrained in an adjustable jig, and the length of a simulated nerve was determined for various position variables--sagittal translation (0-100% slip), slip angle (-40 degrees to +20 degrees), and disc height (5 or 10 mm). Two standard points of reference were chosen to represent fixed points along the path of the L5 nerve. An inelastic cord was used to measure the path length between these points as L5 was reduced from 100% to 0% slip. Testing was performed using a 5-mm and a 10-mm disc height. The effect of varying slip angle alone was also studied. RESULTS: The effect of spondylolisthesis reduction and slip angle correction on nerve length varied depending on the location of L5 with respect to the sacrum. There was an increasing effect of partial reduction on nerve length as L5 approached full reduction. Initially, little strain was produced in the L5 nerve as L5 was reduced in higher grade slips. However, as L5 approached full reduction, the strain per increment of reduction increased rapidly. On average, the mean nerve strain was 4.0% for the first 50% of reduction and 10.0% for the second half of reduction. Increasing lordosis relaxed the nerve in high-grade slips and stretched the nerve in fully reduced slips. At 100% slip, the mean nerve excursion decreased 5.1 mm (nerve slackening) when L5 was rotated from +20 degrees to -40 degrees. At 0% slip, the mean nerve excursion increased 3.1 mm (nerve stretch). Increasing disc height directly stretched the L5 nerve. However, given a larger disc height, the strain on the nerve per increment of reduction was less than for the smaller height. CONCLUSION: The findings suggest that the risk of stretch injury to the L5 nerve with reduction of a high-grade spondylolisthesis is not linear; with 71% of the total L5 nerve strain occurring during the second half of reduction, partial reduction may be a significantly safer treatment approach for high-grade spondylolisthesis than complete reduction. Correction of lumbosacral kyphosis in high-grade spondylolisthesis may be protective of the L5 nerve.

Flexion failure of posterior cervical lateral mass screws. Influence of insertion technique and position.

STUDY DESIGN: The strength of posterior cervical lateral mass fixation was evaluated in a cadaver model for two techniques of screw insertion. OBJECTIVE: To compare the flexion failure strengths of posterior cervical plate fixation for two techniques of screw placement at the superior and inferior screw hole positions, and to evaluate the effect of bone mineral density on fixation strength. SUMMARY OF BACKGROUND DATA: Biomechanical analyses of various screw insertion techniques for posterior cervical lateral mass fixation have never evaluated the effect of screw position along the plate. METHODS: Individual C3-C6 segments of 24 human cadaveric cervical spines were used. The spinous process and lamina were removed to simulate a postlaminectomy situation. Vertebral body bone mineral density for each specimen was determined by dual-energy radiograph absorption scanning. In each lateral mass, a bicortical 3.5-mm screw was placed using either the Magerl or Roy-Camille insertion technique through an end hole of a titanium bone plate. For "superior" screws, the plate was directed caudally; for "inferior" screws, the plate was directed cranially. Screw violation of the surrounding facet joint was noted. An increasing flexion moment was applied by loading the plate 4 cm from the screw head at a rate of 10 cm/min using a servohydraulic testing machine until screw failure. RESULTS: For the superior screw hole position, the Magerl screw sustained a significantly higher average moment to failure (190.2 Ncm) than the Roy-Camille screw (138.7 Ncm; P < 0.05). For the inferior screw hole position, there was no significant difference in flexion failure strength between the two techniques (Magerl screws, 287.7 Ncm; Roy-Camille screws, 308.2 Ncm). For each insertion technique, inferior screws were nearly twice as strong as superior screws (P < 0.01). Violation of the inferior articular process occurred with 53% of Roy-Camille screws and with none of the Magerl screws. Lateral mass fracture on screw insertion occurred with 6% of the Roy-Camille screws and with 7% of the Magerl screws. Significant correlation between screw path length and load to failure was found only at the superior screw hole position. Correlation with vertebral body bone mineral density was significant at both positions. CONCLUSIONS: The Magerl technique has advantages over the Roy-Camille technique for placing the end screws when performing posterior cervical lateral mass plate fixation, providing greater strength superiorly and not violating unfused facet joints inferiorly. Evaluation of bone mineral density by dual-energy radiographic absorption scanning is predictive of failure strength for both test modes.

Determination of the mineral phases and structure of the bone-implant interface using Raman spectroscopy.

The bone-implant interface formed in a canine distal femur was examined by means of a Raman microprobe using an implant model designed to test calcium phosphate surface coatings. By using the 960 cm-1 band of calcium phosphate to characterize the interface and adjacent mineral, we obtained spatial and compositional information about the attachment of bone to the synthetic calcium phosphate coating on a titanium support. The interface between bone and the synthetic calcium phosphate is approximately 30-40 microns in width.

Cervical spine injuries in patients 65 and older.

STUDY DESIGN: This study was a retrospective data-base review of patients with cervical injuries admitted to a regional spinal cord injury center over a 9-year period. OBJECTIVES: Patients < 40 and > or = 65 were analyzed separately to determine differences in etiology, neurologic findings, mortality, and neurologic recovery. SUMMARY OF BACKGROUND DATA: Previous studies of cervical injuries in older patients have found a high percentage of falling as an etiology, a high incidence of injuries to C2, and a high mortality rate with spinal cord injury (SCI). METHODS: Three databases containing information on all SCI patients, SCI patients with 1-2 year follow-up, and neurogically intact spinal injury patients were reviewed retrospectively. RESULTS: A higher percentage of older patients had cervical injuries, and this group did not show the typical male predominance seen in young patients (4:1 vs. 1:1). Neurologic deficits were more common in the younger age group. In the older patients, falls were a much more common etiology, and upper cervical injuries, especially odontoid fractures, predominated. Cervical spondylosis and stenosis were more common in the older patients, and the mortality with associated SCI was 60 times higher than in younger patients. Younger patients more commonly had complete neurologic injuries, but had more early functional motor return in incomplete lesions. The older patients did show late functional return in incomplete deficits. CONCLUSIONS: Cervical spine injury commonly occurs with relatively minor trauma in patients > or = 65, with a mortality rate of approximately 26% with associated SCI. Return of functional motor recovery is delayed in older patients with incomplete deficits, but can be expected. C2 injuries, especially odontoid fractures, must be ruled out in older patients with neck pain after even a minor injury.

Hydroxyapatite enhancement of posterior spinal instrumentation fixation.

STUDY DESIGN: The ability of hydroxyapatite (HA) materials to enhance the fixation strength of posterior spinal instrumentation was examined in 19 adult mongrel dogs. METHODS: Sixteen dogs underwent bilateral placement of lumbar transpedicular screws from L1 to L6, sacral alar screws, and posterior iliac rods. The six transpedicular screw test groups included standard and plasma-sprayed HA-coated screws with the recommended insertion technique, standard and HA-coated screws with a poor initial fit insertion technique using an oversized pilot hole, and HA-grout augmentation of standard and HA-coated screws with a poor initial fit. The sacral alar screws and posterior iliac rods were either uncoated or HA-coated. Six dogs were killed immediately; ten dogs were killed at 6 weeks, and the fixation elements were mechanically tested or histologically examined. Three additional dogs and synthetic bone material were used for additional baseline mechanical testing. RESULTS: The strength of standard screws with recommended insertion did not change after 6 weeks in vivo. HA-coated screws were initially 13% less resistant to pull out than standard screws, but this difference was not significant at 6 weeks. Screws inserted with a poor initial fit technique were significantly weaker initially; at 6 weeks, pull-out strength was similar to the standard screws properly inserted. The HA-grout material significantly enhanced pull-out strength for both screw types at 6 weeks. Sacral alar screw pull-out strength was not significantly different between standard and HA-coated screws initially or at 6 weeks. HA-coated rods were initially twice as resistant to pull out than standard rods and became stronger after 6 weeks in vivo, whereas standard rods became significantly weaker. Histologically, the quantity and morphology of bone around all implants was similar, with HA-coated rods and screws demonstrating regions of direct attachment to bone. An osteoconductive response and new bone formation was observed within the HA-grout material. Scanning electron microscopic observation of mechanically tested implants revealed a shear failure of surrounding bone (and HA if present) at the screw outer thread margin or at the bone-metal or HA-metal interfaces for the posterior iliac rods. CONCLUSIONS: The strength of poorly inserted transpedicular screws was significantly enhanced in vivo by the resorbable HA-grout material. The lower strength of HA-coated screws was attributed to screw geometry changes resulting from the coating process, and modifications of screw coating are recommended.

Spinal instrumentation.

The past decade has seen a dramatic increase in the availability of spinal instrumentation devices, enabling surgeons to treat a variety of spinal disorders with improved results and lower morbidity. In each anatomic region new fixation systems exist. Improvement in fusion rates with supplemental plate fixation following anterior cervical diskectomies and reconstructions has been demonstrated; these devices can now be applied more safely than ever before. Posterior occipitocervical plating to the C-2 pedicle and C3-6 lateral masses can provide stable fixation despite incompetent posterior arch bony structures. Newer, more rigid anterior thoracolumbar instrumentation allows for correction of thoracolumbar and lumbar scoliosis along fewer levels and with better maintenance of lordosis and is also useful following anterior decompression for tumor and trauma. Segmental hook fixation of the posterior thoracolumbar spine has allowed for improved correction of deformity without increased morbidity or the need for postoperative bracing in many cases. Finally, the use of transpedicular screw fixation of the lumbosacral spine allows for excellent segmental fixation without intact posterior elements, including facet joints, and has significantly improved the fusion rate in lumbosacral fusions.

The perioperative course of combined anterior and posterior spinal fusion.

A retrospective study was undertaken to characterize and compare the perioperative course of 91 cases of one- and two-stage combined anterior and posterior spinal fusions over a 7-year period. The two patient populations were similar regarding preoperative characteristics and the number of levels fused. Significantly decreased operative and anesthesia time, operative blood loss, and postoperative hospital days were seen in the one-stage population compared to the two-stage cases (P < 0.05). For the spinal deformity subgroup, a longer chest-tube duration, decreased anesthesia time, and decreased postoperative hospital stay in the one-stage group were the only significant differences. Surgical treatment delays were noted in 8% of one-stage cases and in 23% of two-stage cases. Complications occurred in 53% of all cases, with a significantly higher major complication rate in patients with preoperative medical comorbidities who underwent two-stage combined fusion versus one-stage reconstruction. Higher complication rates were also associated with an age greater than 40 years, the presence of medical comorbidities, and cases treated with a thoracoabdominal anterior approach.

Evaluation of a low-temperature calcium phosphate particulate implant material: physical-chemical properties and in vivo bone response.

A study was conducted to evaluate the osteoconductive ability of a particulate, low-temperature hydroxylapatite (HA(LT)) material (OsteoGen; Impladent, Holliswood, NY). An implantable chamber model was used to determine the ability of this material to encourage bone ingrowth into channels lined with either rough-surfaced titanium or rough-surfaced plasma-sprayed hydroxylapatite. The HA(LT) material increased bone ingrowth into the titanium-lined channels comparable with that in plasma-sprayed hydroxylapatite-coated channels. It was incorporated into ingrowing bone without intervening soft tissue, with the bone bonding directly to the material surface in much the same fashion as it bonds at the plasma-sprayed hydroxylapatite surface. Mechanical testing of the ingrown bone showed no weakness because particles were incorporated. At 12 weeks, the particles began to show signs of dissolution. It was concluded that the HA(LT) material is a biocompatible, osteoconductive material that conducts bone ingrowth in much the same way as high-temperature particulate hydroxylapatite ceramics. This material has the additional desirable property of being slowly resorbable, a beneficial characteristic for many bone-filling applications.

The effect of low-level Nd:YAG laser energy on adult articular cartilage in vitro.

Reports of laser energy applied to soft tissues in vitro and in vivo suggest both stimulation and inhibition of specific metabolic processes, depending on the type of laser, the energy density (ED) used, the mode of delivery, and type of tissue studied. An earlier in vitro study of Nd:YAG laser irradiation of articular cartilage indicated stimulation of both matrix and DNA synthesis for 6 days following laser exposure. In vivo reports on the ability of Nd:YAG laser energy to stimulate the healing of partial-thickness cartilage defects are conflicting. In the present study, a noncontact continuous-wave Nd:YAG laser beam of varying EDs was applied to full-thickness adult articular cartilage explants maintained in organ culture; the metabolic processes of chondrocyte DNA synthesis and matrix synthesis were followed over 2 weeks. For both canine and bovine cartilage, low-levels of laser energy (ED 51-127 J/cm2) stimulated matrix synthesis at 6-7 days following laser exposure, with a concomitant decrease in baseline DNA synthesis. By 12-14 days, however, these dose-dependent effects were no longer seen, with no significant differences from control noted for any of the laser energies studied. Histologic analysis of the cartilage explants following laser exposure showed no significant differences in cell number or morphology between sample and control groups; however, a decrease in matrix proteoglycan staining was seen in the highest laser energy group at all time points. These findings indicate that exposure to low-level noncontact Nd:YAG laser energy promotes a significant stimulation of cartilage matrix synthesis. However, a single exposure may not be sufficient to promote a sustained upregulation of cartilage metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Lower limb-length discrepancy. An epidemiologic study.

Two retrospective epidemiologic studies have examined the incidence and prevalence of significant lower limb-length discrepancy and the number of surgical corrections by lengthening in 1987 in France. The incidence of apparatus prescriptions for asymmetry correction filled was 2.16 per 100,000 population. The prevalence of people using a corrective apparatus was one per 1000 population. The male-to-female ratio was 1.95:1. Because of biases in the study population, the actual incidence and prevalence of significant limb-length discrepancies is likely to be considerably higher. A questionnaire administered to surgeons of the French Orthopedic Society revealed that the majority of surgical lengthenings were performed by large orthopedic teams. In the 418 procedures reported, the tibia was lengthened more often than the femur (ratio 1.1:1). Gradual distraction techniques were used in 89.4% of cases, with the Ilizarov apparatus used in 57.4%, the Wagner apparatus in 20.6%, and the Orthofix fixator in 11.2%. Immediate distraction techniques were used in 7.9% of cases, 85% of which were done on the femur. Average total lengthening was 51 mm for tibia and femur. Average lengthening was greater for methods of gradual distraction (53.5 mm) than for immediate distraction (31.4 mm).

Molecular structure at the bone-implant interface: a vibrational spectroscopic characterization.

Test implant plates surgically retrieved from distal femurs of dogs were studied by Raman spectroscopy in order to characterize the bone-implant interface. The implant surface consisted of phosphate mineral, plasma sprayed on a titanium substrate. On the basis of its spectroscopic signature, the phosphate mineral of bone and the implant surface formed a mixed phase in the interface.

Fatigue failure of the sliding screw in hip fracture fixation: a report of three cases.

Hardware failure of the sliding screw system used in hip fracture fixation is rare. The fatigue failure of the sliding screw is always related clinically to nonunion or refracture along the path of the screw. In both situations, cyclic loading of the implant exceeds its endurance limit, and failure can ensue. Three cases of failure of the sliding screw are presented: a nonunion of a basicervical fracture, a nonunion secondary to stress fracture at the plate-barrel junction, and a refracture through the femoral neck after healing of an intertrochanteric fracture. A biomechanical analysis of the stresses on the sliding screw focuses on design features such as the internal threaded region used for the compression screw or the barrel length that creates increased stresses in the screw, thus lowering the number of cycles to failure. Based on this analysis, recommendations are made concerning implant design and surgical technique.