Outpatient Bryant's Overhead Traction Does Not Affect the Rate of Open Reduction or Avascular Necrosis in Developmental Dislocation of the Hip.

BACKGROUND: The efficacy of preliminary traction to increase the likelihood of closed reduction and/or decrease the incidence of avascular necrosis in the management of developmental dysplasia of the hip (DDH) is controversial. We sought to document compliance with and effectiveness of Bryant's outpatient traction in patients with idiopathic DDH. METHODS: Patients presenting between 6 and 24 months of age with idiopathic irreducible DDH were prospectively enrolled in the study. Prereduction outpatient traction was prescribed at participating surgeons' preference and parents' expressed willingness to comply with a traction protocol of at least 14 hours/day for 4 weeks. Traction hours were documented using a validated monitor; parents also reported average daily usage. Rate of successful closed reduction and evidence of capital epiphyseal growth disturbance 1 year' and 2 years' postreduction were documented. RESULTS: Ninety-six patients with 115 affected hips were enrolled. Reliable recorded traction hours were obtained in 31 patients with 36 affected hips. Defining compliance as 14 hours/day average use, 14 of 31 patients (45.2%) were compliant, 2 (6.5%) admitted noncompliance, while 15 (48.2%) claimed to be compliant, but were not. Overall, 68/115 hips (59.0%) were closed reduced. Age at treatment was the only demographic characteristic associated with an increased incidence of closed reduction (11.7 vs. 14.6 mo, P<0.01). Successful closed reduction was achieved in 10/16 hips (62.5%) of compliant patients, 12/20 (60.0%) of noncompliant patients, and 43/72 (59.7%) of no-traction patients. Irregular ossific nucleus development was noted 1-year postindex reduction in 5/16 (31.3%) of complaint-patient hips and 25/92 (27.2%) of noncomplaint and no-traction hips. Distorted proximal femoral epiphysis was noted at 2 years postreduction in 2/15 hips (13.3%) of compliant patients and 15/52 hips (28.8%) in noncompliant and no-traction patients. None of these differences was statistically significant. CONCLUSIONS: Parent-reported use of outpatient traction is unreliable. Four weeks of outpatient overhead Bryant's traction did not affect the rate of closed reduction or avascular necrosis in late-presenting DDH in this cohort. LEVEL OF EVIDENCE: Level II-prospective cohort.

Do We Really Need to Worry About Calcaneocuboid Subluxation During Lateral Column Lengthening for Planovalgus Foot Deformity?

BACKGROUND: Although lengthening of the lateral column through an osteotomy of the anterior calcaneus is an integral component of flatfoot reconstruction in younger patients with flexible planovalgus deformities, the procedure has been implicated in iatrogenic calcaneocuboid (CC) subluxation and subsequent degenerative changes at the CC articulation. The purpose of this study is to characterize alterations at the CC joint after lateral column lengthening (LCL) and determine if Steinmann pin stabilization of the CC joint before distraction maintains a normal relationship. METHODS: Seven matched pairs of fresh-frozen cadaveric feet underwent preprocedure plain radiography and cross-sectional computed tomography (CT) imaging. LCL by osteotomy through the anterior calcaneus was then performed. One foot of each matched pair had a single smooth Steinmann pin placed centrally across the CC joint before osteotomy distraction. Distraction across each osteotomy was then performed and maintained with a 12-mm porous titanium wedge. Repeat imaging was obtained and compared with preprocedure studies to quantify sagittal and rotational differences at the CC articulation. RESULTS: Following LCL, plain radiography demonstrated statistically significant increases in the percentage of the calcaneal articular surface dorsal to the superior aspect of the cuboid in both the pinned (8.2% vs. 17.6%, P=0.02) and unpinned (12.5% vs. 16.3%, P=0.04) specimens. No difference in the percentage of subluxation was found between the 2 groups after LCL. CT imaging demonstrated statistically significant increases in rotation between the calcaneus and cuboid after LCL in both the pinned (7.6±5.6 degrees, P=0.01) and unpinned (17±12.3 degrees, P=0.01) specimens. The degree of rotation was greater in unpinned specimens after LCL (P=0.043). CONCLUSIONS: Both sagittal and rotatory subluxation seem to occur at the CC joint after LCL regardless of pin stabilization. As a single pin would be expected to limit pure translation while having little effect on rotation, it is possible that the rotational changes identified on 3-dimensional imaging are interpreted as dorsal translation when viewed 2 dimensionally using plain radiography. Consideration should therefore be given to CC stabilization with 2 pins during LCL to prevent this rotatory subluxation. LEVEL OF EVIDENCE: Level V-cadaver study.

Effect of Lateral Column Lengthening on Subtalar Motion in a Cadaveric Model.

BACKGROUND: Although lengthening of the lateral column through a calcaneal neck osteotomy is an integral component of flatfoot reconstruction in younger patients with flexible planovalgus deformities, concern exists as to the effect of this intra-articular osteotomy on subtalar motion. The purpose of this study was to quantify the alterations in subtalar motion following lateral column lengthening (LCL). METHODS: The subtalar motion of 14 fresh-frozen cadaveric feet was assessed using a 3-dimensional motion capture system and materials testing system (MTS). Following potting of the tibia and calcaneus, optic markers were placed into the tibia, calcaneus, and talus. The MTS was used to apply a rotational force across the subtalar joint to a torque of 5 Nm. Abduction/adduction, supination/pronation, and plantarflexion/dorsiflexion about the talus were recorded. Specimens then underwent LCL via a calcaneal neck osteotomy, which was maintained with a 12-mm porous titanium wedge. Repeat subtalar motion analysis was performed and compared to pre-LCL motion using a paired t test. RESULTS: No statistically significant differences in subtalar abduction/adduction (10.9 vs 11.8 degrees, P = .48), supination/pronation (3.5 vs 2.7 degrees, P = .31), or plantarflexion/dorsiflexion (1.6 vs 1.0 degrees, P = .10) were identified following LCL. CONCLUSION: No significant changes in subtalar motion were observed following lateral column lengthening in this biomechanical cadaveric study. CLINICAL RELEVANCE: Although these findings do not obviate concerns of clinical subtalar stiffness following lateral column lengthening for planovalgus deformity correction, they suggest that diminished postoperative subtalar motion, when it occurs, may be due to soft tissue scarring rather than alterations of joint anatomy.

Can We Estimate the Amount of Malrotation in Supracondylar Humerus Fractures After CRPP?

BACKGROUND: Acceptable amounts of malrotation after CRPP for pediatric supracondylar humerus fracture (SCHFx) have yet to be defined. This is an attempt to correlate radiographic parameters of a malrotated SCHFx with degrees of rotational malalignment to assist intraoperative assessment of reduction. METHODS: 3D models of a left distal humerus were printed, simulating a transverse SCHFx with 5, 10, 15, 20, 25, and 30 degrees of malrotation. Four different scenarios were developed: (1) lateral cortical axis of rotation, (2) medial cortical axis of rotation, (3) centroid of the humerus longitudinal axis with the medial condyle rotated posteriorly, and (4) centroid of the humerus longitudinal axis with the medial condyle rotated anteriorly. Anteroposterior and lateral fluoroscopic views were taken with a consistent image profile. Five observers measured the amount of metaphyseal overhang on the lateral view and the width of the distal humerus just proximal to the fracture to establish amount of overhang as a percentage of distal humerus width. Regression analysis established "best fit" lines for the 4 scenarios. Ten observers used the observed characteristics of each type of malrotation and "best fit" lines to estimate axis and degrees of malrotation using the same fluoroscopy of the 24 models. RESULTS: The intraclass correlation coefficient of reliability for percentage of metaphyseal overhang ranged from 0.775 to 0.987. Observers correctly predicted axis of malrotation in 76% and correctly predicted amount of malrotation in 75% of models. CONCLUSIONS: Estimation of axis of malrotation and degrees of malrotation within 5 degrees in SCHFx can be predicted in 75% of our 3D printed models.

The point of epiphyseal penetration affects rotational stability of screw fixation in slipped capital femoral epiphysis: A biomechanical study.

The epiphyseal tubercle, a posterosuperior projection of the epiphysis into the metaphysis, serves as the axis of rotation in slipped capital femoral epiphysis (SCFE) and a source of physeal stability. We hypothesized that in a biomechanical model of single screw fixation of stable SCFE, a screw passing through the epiphyseal tubercle (the axis of rotation) would confer less rotational stability than a centrally placed screw. Three femurs were selected from a sample population of 8- to 15-year-old healthy hips to represent three stages of maturation: a "young" femur with a prominent epiphyseal tubercle and decreased epiphyseal cupping around the metaphysis, a "median" femur with a subsiding tubercle, and a "mature" femur with a subsided epiphyseal tubercle and increased peripheral epiphyseal cupping. Specimens were three-dimensional printed with one of two screw trajectories: passing centrally in the epiphysis or directly through the epiphyseal tubercle. Resistance to rotational displacement was measured through stiffness and maximum torque over 30° degrees of displacement. In the "young" model, epiphyseal tubercle screw position conferred less rotational stiffness and required less maximum torque during rotational displacement when compared to a centrally placed screw (P < .001). In the "median" and "mature" models where the tubercle has subsided and is replaced by peripheral epiphyseal cupping, screw position through the tubercle was associated with equal or greater rotational stiffness and maximum torque during displacement as a centrally placed screw.

Biomechanical Analysis of Retrograde Flexible Intramedullary Nail Constructs in a Simulated Pediatric Femur Fracture Model.

BACKGROUND: Various flexible intramedullary nail (FIMN) constructs for pediatric femur fractures are described; however, no biomechanical study has compared stability of medial-lateral entry versus all-lateral entry retrograde nailing. Our purpose is to compare the rotational and bending stiffness of 2 different FIMN constructs and 2 different materials in a simulated pediatric femur fracture model. METHODS: Eighty adolescent-sized composite femurs were used to simulate transverse (40 femurs) and oblique (40 femurs) mid-diaphyseal fractures. Retrograde FIMN of the femurs was performed using either 3.5 mm titanium (Ti) or 3.5 mm stainless-steel (SS) flexible nails in 2 configurations: 2 "C"-shaped nails (CC) placed through medial and lateral entry sites or 1 "C"-shaped nail and 1 "S"-shaped nail (CS) placed through a single lateral entry site. Models were first tested in 10 cycles of axial rotation to ±1 N m of torque at a rate of 0.5 degrees/s under 36 kg of compression. Axial compression was performed and bending stiffness defined as the force required to achieve 10 degrees varus at the fracture site. RESULTS: No differences were noted in rotational stiffness comparing Ti and SS nails regardless of nail configuration or fracture pattern. Comparable rotational stability was found for CC and CS configurations with SS implants for both fracture patterns. The CS construct (0.60 N m/degree) was stiffer in rotation than the CC construct (0.41 N m/degree) with Ti implants in the transverse fracture model (P<0.005). SS nails provided greater bending stiffness than Ti nails in both oblique and transverse fracture patterns, regardless of nail construct. The all-lateral entry (CS) construct demonstrated statistically significant greater bending stiffness regardless of implant material or fracture pattern (P<0.03). CONCLUSIONS: An all-lateral entry (CS) FIMN construct demonstrated greater bending stiffness in both fracture patterns and materials. Ti and SS implants have comparable rotational stiffness in all fracture patterns and materials; however, SS nails were superior at resisting bending forces in both fracture patterns. CS nail configuration and SS implants demonstrated superior bending stiffness and rotational stiffness when compared with the more commonly used CC construct and Ti implants. LEVEL OF EVIDENCE: NA (biomechanical study).

Retrograde Stainless Steel Flexible Nails Have Superior Resistance to Bending in Distal Third Femoral Shaft Fractures.

BACKGROUND: It has been shown that retrograde titanium flexible intramedullary nails (Ti FIN) provide superior resistance to bending compared to antegrade Ti FIN in distal femur fractures. The purpose of this study was to compare resistance to torsional and bending forces of stainless steel (SS) FIN, with or without a locking screw, and Ti FIN in distal third femoral shaft fractures. We hypothesize that locked retrograde SS FIN will demonstrate greater resistance to both bending and torsional forces. METHODS: Thirty adolescent synthetic femur models were used to simulate transverse distal femoral fractures at either 60 mm or 90 mm proximal to the distal femoral physis. The femurs were instrumented with antegrade Ti FIN, antegrade SS FIN, retrograde Ti FIN, retrograde SS FIN, or retrograde locked SS FIN. Three models for each construct at both osteotomy levels were tested. Models were analyzed to determine maximum resistance to bending and torsion. RESULTS: In fractures 60 mm from the physis, retrograde SS FIN demonstrated statistically superior resistance to bending when compared with both antegrade and retrograde Ti FIN (P=0.001 and 0.008, respectively) and antegrade SS FIN (P=0.0001). Locked SS constructs showed a trend towards greater resistance to bending forces when compared with unlocked constructs (P>0.05). No significant difference was seen in resistance to bending when fractures were 90 mm proximal to the distal femoral physis between the five groups. No significant differences were observed in resistance to torsion in either the proximal or distal fracture models, regardless of construct type. CONCLUSIONS: Retrograde SS FIN confer significantly greater resistance to bending forces for fractures 60 mm proximal to the distal femoral physis compared with Ti FIN or antegrade entry SS FIN. In fractures 90 mm from the physis, no differences were noted in our model. Our results support the use of retrograde SS nails in the pediatric patient with distal femoral shaft fractures. LEVEL OF EVIDENCE: Level II-comparative biomechanical study.

Biomechanical Considerations in Foot and Ankle Circular External Fixation: Maintenance of Wire Tension.

Initial tensioning of the forefoot wires to 130 kg followed by simultaneous tensioning of the calcaneal wires to 90 kg and using the rigid double-row foot plate closed anteriorly via threaded rods produce maximum preservation of the initial wire tension during foot circular external fixation.

Impact of tunnels and tenodesis screws on clavicle fracture: a biomechanical study of varying coracoclavicular ligament reconstruction techniques.

PURPOSE: The purpose of this study was to compare the load to fracture of distal clavicles with no tunnels, one tunnel, or 2 tunnels and to evaluate the effect of inserting tenodesis screws in the tunnels on load to fracture of the distal clavicle. METHODS: Fifty right sawbone clavicles were obtained and divided into 5 groups (n = 10): group 1, normal clavicle; group 2, one tunnel, no tenodesis screw; group 3, 2 tunnels, no tenodesis screws; group 4, one tunnel with tenodesis screw; and group 5, 2 tunnels with 2 tenodesis screws. Tunnels were created using a 5-mm-diameter reamer, and 5.5 × 10 mm polyethyl ethyl ketone tenodesis screws were used. A 4-point bending load was applied to the distal clavicles. Load to failure was noted for each specimen. RESULTS: Load to failure in clavicles without tunnels was significantly higher (1,157.18 ± 147.10 N) than in all other groups (P < .0005). No statistical differences were noted between groups 2, 3, 4, and 5. Load to failure was not statistically different in clavicles with one versus 2 tunnels. In addition, the use of tenodesis screws in the tunnels did not affect the load required to fracture. CONCLUSIONS: The use of tunnels in the clavicle for coracoclavicular (CC) ligament reconstruction significantly reduces the load required to fracture the distal clavicle. The addition of tenodesis screws does not appear to significantly increase the strength of the clavicle in this construct. CLINICAL RELEVANCE: CC ligament reconstruction techniques commonly use tunnels in the distal clavicle, which may render the clavicle more susceptible to fracture. This study helps quantify the effect of these tunnels on the strength of the distal clavicle.

Detecting a disruption of blood flow to the femoral head after ischemic injury using 4 different techniques: a preliminary study.

BACKGROUND: Disruption of blood flow to the femoral head can have a detrimental effect on the clinical outcome after a closed or open reduction for the treatment of developmental dysplasia of the hip and after a treatment of slipped capital femoral epiphysis. Availability of a clinically reliable and easy-to-use technique to monitor the blood flow before, during, and after a therapeutic intervention may allow early detection and more effective management of this complication. An experimental investigation was performed to evaluate 4 different sensors/techniques for their ability to detect an acute disruption of blood flow to the immature femoral head. METHODS: Under general anesthesia, the femoral heads of 10 immature pigs were exposed and total head ischemia was induced by ligating the femoral neck and transecting the ligamentum teres. Blood flow was assessed before and after the induction of ischemia using 1 of 4 techniques. The following sensors/techniques were evaluated: fiber optic pressure (FOP), piezoelectric pressure, partial pressure of oxygen, and laser Doppler flowmetry (LDF). The time taken to observe a 50% reduction of the preischemia level was determined and the sensor outputs were monitored until each reached a steady level. RESULTS: All techniques demonstrated a reduction in their respective measurements after a disruption of blood flow to the femoral head. However, the response time differed, even between the 2 pressure sensors (FOP and piezoelectric pressure at 3 and 15 min, respectively). The fastest response time for a 50% reduction was observed with the LDF (2 min) and the FOP (3 min) sensors. The partial pressure of oxygen was the slowest to change, taking over 30 minutes. Technique-dependent advantages and disadvantages were seen. The FOP sensor was fragile and susceptible to the positioning of the sensor tip. The LDF sensor was susceptible to motion artifact. CONCLUSIONS: The LDF and the FOP sensors demonstrated a rapid decline in their respective measurements after the induction of ischemia. CLINICAL RELEVANCE: These techniques may prove to be useful in the assessment of an acute disruption of the femoral head blood flow.

Novel dual-rod screw for thoracoscopic anterior instrumentation: biomechanical evaluation compared with single-rod and double-screw/double-rod anterior constructs.

STUDY DESIGN: A novel dual-rod screw was designed to provide a second-rod augmentation at the critical apical/middle segments of the single-rod thoracoscopic anterior construct. Biomechanical testing was performed on pig thoracic spines instrumented with 7-segment anterior scoliosis constructs. OBJECTIVES: To analyze the biomechanical performance of the new implant, and compare it to a single-rod and double-rod anterior constructs. SUMMARY OF BACKGROUND DATA: Using single-rod thoracoscopic anterior instrumentation for thoracic scoliosis, the complications of rod breakage at apex, high rate of nonunion, and resultant loss of coronal and sagittal correction has been reported. Inadequate construct stiffness because of a smaller diameter single rod has been implicated as the cause of these complications. METHODS: Twelve pig thoracic spines were instrumented over 7 segments with: (1) single-rod construct, (2) short second-rod augmentation at the apex of the single-rod construct, (3) long second-rod augmentation at middle segments of the single-rod construct, and (4) double-screw/double-rod anterior construct. The spines were tested in flexion-extension, left-right lateral bending, and torsion, using pure bending moments. Strain gauges attached to the primary single rod at the cephalad, middle, and caudal portions were used and the maximum tensile stress was recorded. RESULTS: In the single-rod construct, the middle portion stress was 39% to 51% greater than the stress in the cephalad and caudal portions in flexion-extension (P < 0.05), and the cephalad portion stress was 39% to 65% greater than the stress in the middle and caudal portions in right lateral bending and torsion (P < 0.05). When a second rod was added at the apical/middle portion, the middle portion stress decreased from 50% to 72% in flexion-extension and right lateral bending (P < 0.05). In addition, the second rod decreased the primary single-rod stress at the cephalad portion by 48% (left torsion) and the caudal portion by 50% (flexion). Double-screw/double-rod construct significantly increases the construct stiffness in comparison with the single-rod construct. However, it did not add any construct stiffness at the critical apical segments when compared to the constructs in which the second rod augmented the single-rod constructs. CONCLUSION: A novel dual-rod screw was designed to combine the standard single-rod construct with the addition of a second rod at the critical apical/middle segments and increase construct stiffness and stability. This implant may therefore prevent pseudarthrosis and rod breakage by enhancing construct stiffness.

A novel double-row rotator cuff repair exceeds strengths of conventional repairs.

Double-row rotator cuff repairs are becoming popular because of their ability to improve initial ultimate failure load for full-thickness rotator cuff tears, especially in middle-aged to elderly patients. We hypothesized a quasi-double-row repair using a combination of transosseous sutures, anchors, and double knots (TOAK technique) would exceed the clinically relevant 250-N load threshold and the initial mean ultimate failure loads of anchor-only and transosseous suture-only fixation. In simulated full-thickness supraspinatus tears in cadavers (mean age, 62 years; range, 50-77 years), failure loads of two repair techniques were compared with a TOAK repair using sutures and bioabsorbable anchors. Radiographic densitometry was conducted on all humeral heads. Testing was performed at 6 mm per minute in 18 bones in the following three groups (n = 6 per group): (1) transosseous suture-only with weave-type stitch and single-knot fixation; (2) anchor-only with horizontal mattress stitch and single-knot fixation; and (3) TOAK. The mean ultimate failure load was 238 N for the transosseous suture-only group and 215 N for the anchor-only group. Although the bones had lower density, TOAK specimens failed at 55% to 67% higher loads (mean, 404 N) than the other groups. These data support further evaluation of the TOAK technique for full-thickness supraspinatus tears in middle-aged to elderly patients.

New rod-plate anterior instrumentation for thoracolumbar/lumbar scoliosis: biomechanical evaluation compared with dual-rod and single-rod with structural interbody support.

STUDY DESIGN: A new rod-plate anterior implant was designed to provide plate fixation at the cephalad and caudal-end segments of a 5-level anterior spine construct. Biomechanical testing was performed on calf spines instrumented with 5-segment anterior scoliosis constructs. OBJECTIVES.: To analyze the initial and post-fatigue biomechanical performance of the new implant, and compare it to an anterior dual-rod construct and a single-rod construct with interbody cages. SUMMARY OF BACKGROUND DATA: Using single-rod anterior instrumentation for thoracolumbar and lumbar scoliosis, an unacceptable incidence of loss of correction, segmental kyphosis, and pseudarthrosis has been reported. Inadequate construct stiffness due to early postoperative bone-screw interface failure, especially at cephalad and caudal-end vertebrae, has been implicated as the cause of these complications. METHODS: Thirty calf spines were instrumented over 5 segments with: (1) single-rod augmented with rod-plate implants, (2) dual-rod construct, and (3) single-rod with titanium mesh cages. Stiffness in flexion-extension and lateral bending modes was determined initially and post-cyclical loading by measuring segmental range of motion (ROM). Post-fatigue screw pullout tests were also performed. RESULTS: In lateral bending, the caudal-end segmental ROM for rod-plate construct was 54% less than single-rod with cages construct (P < 0.05), with no difference between rod-plate and dual-rod constructs. In flexion-extension, the rod-plate construct showed 45% to 91% (initial test) and 84% to 90% (post-fatigue) less ROM than the single-rod with cages construct (P < 0.001). Again, there was no difference between rod-plate and dual-rod constructs at the cephalad and caudal-end segments. Post-fatigue screw pullout strengths of the rod-plate construct were significantly greater than those of the dual-rod and single-rod with cages constructs (P < 0.05). CONCLUSIONS: The rod-plate construct was significantly stiffer and provided greater stability of bone-screw interface than the single-rod with cages construct. It achieved similar stiffness and improved bone-screw interface stability compared to dual-rod construct.

Recombinant human bone morphogenetic protein-2 enhances anterior spinal fusion in a thoracoscopically instrumented animal model.

BACKGROUND: Thoracoscopically assisted anterior spinal arthrodesis and instrumentation is being used more widely to treat idiopathic scoliosis. However, harvesting autologous bone increases operative time and morbidity. The purpose of this study was to compare autologous iliac crest and rib graft with recombinant human bone morphogenetic protein-2 (rhBMP-2) in thoracoscopically assisted anterior spinal arthrodesis and instrumentation in an animal model. METHODS: Twenty-two pigs underwent thoracoscopically assisted anterior spinal arthrodesis. Each animal had five contiguous thoracic discectomies followed by anterior instrumentation. The animals were randomly assigned to five treatment groups. Group I consisted of control animals that received no graft material; group II, animals treated with autologous rib graft; group III, animals treated with autologous iliac crest graft; group IV, animals treated with an rhBMP-2-composite sponge (collagen-hydroxyapatite-tricalcium phosphate carrier); and group V, animals treated with a composite sponge carrier alone. The animals were killed four months after the procedure, and the spines were harvested. The fusion mass was assessed with use of axial and sagittal computed tomography scans. The spines were tested biomechanically with incremental loads applied in the frontal and axial planes to achieve bending moments of up to 6.0 N-m. Angular motion at each segment was recorded with use of a three-dimensional motion analysis system. Histomorphometric analysis of each undecalcified disc segment was also performed. RESULTS: The fusion grades, according to computed tomography analysis with use of a 4-point grading system in which scores of 3 and 4 indicated a solid fusion, were 0.6 point for group I, 2.1 points for group II, 2.3 points for group III, 3.8 points for group IV, and 0.4 point for group V. Group IV (the rhBMP-2-treated animals) had a higher grade than all of the other groups. Group II (rib graft) and group III (iliac crest) had similar grades, and both were greater than group I (the untreated controls) and group V (composite sponge alone) (p < 0.05). In axial rotation, lateral bending, and flexion-extension, the spines in group IV were stiffer than those in the four other groups (p < 0.05); the spines in groups II and III were similar, and the spines in both of those groups were stiffer than those in groups I and V (the control groups). Histologic analysis demonstrated that the total new-bone area, expressed as a percentage of the total disc space area, was 23.2% in group I, 37.1% in group II, 37.2% in group III, 48.5% in group IV, and 5.9% in group V. Group IV had significantly greater bone formation than all of the other groups (p < 0.001). The animals treated with rib graft (group II) and iliac crest (group III) had a similar amount of bone formation, and it was greater than that in both control groups (p < 0.001). CONCLUSIONS: The rhBMP-2 significantly increased the prevalence and quality of the spinal fusion after thoracoscopically assisted anterior arthrodesis and instrumentation in an animal model compared with that in the other treatment groups and in the controls.

Effect of displacement of ulna-shaft fractures on forearm rotation: a cadaveric model.

Nonoperative treatment of ulna-shaft fractures may result in healing with residual displacement. In the study reported here, we used a cadaveric model to try to determine whether displacement significantly reduces forearm supination and pronation. Transverse osteotomies were made one third, one half, and two thirds of the distance from the proximal end to the distal end of each of 7 fresh cadaveric forearms. Displacements of 50% and 100% were tested at each osteotomy site. Specimens were mounted on a material-testing machine, and forearm rotation was determined. Supination loss was less than 15 degrees for all directions of displacement at all osteotomy sites. Pronation loss was less than 10 degrees at the distal osteotomy site; at the middle osteotomy site, pronation loss was 19 degrees with 100% radial displacement (P < .05) and 20 degrees with 100% ulnar displacement (P< .05); and, at the proximal osteotomy site, pronation loss was 19 degrees with 50% radial displacement (P < .01), 41 degrees with 100% radial displacement (P < .0005), and 33 degrees with 100% ulnar displacement (P < .005). We conclude that large residual displacement in distal fractures and moderate residual displacement in midshaft fractures do not significantly compromise forearm rotation. Proximal displacement was less tolerated in this model and resulted in significantly reduced forearm rotation.

External fixation of the lumbar spine in a canine model.

OBJECTIVE: To compare the mechanical properties of two types of external skeletal fixation of the lumbar spine with polymethylmethacrylate (PMMA)/Steinmann pin fixation in a canine unstable spine model. STUDY DESIGN: Cadaver study. SAMPLE POPULATION: Lumbar spines of 17 mature large-breed dogs. METHODS: Spine stiffness (N-m/deg) in flexion, extension, and rotation under physiological loading conditions and spine strength (N-m) in flexion were determined. Spines were destabilized at L3-L4, instrumented and retested. Fixation techniques included four-pin PMMA (PMMA4), eight-pin PMMA (PMMA8), eight-pin biplanar type I external skeletal fixator (ESF) (SK), and eight-pin spinal arch ESF (ARCHES). RESULTS: All fixation groups were as stiff as intact spines in extension and rotation and were significantly stiffer in flexion. In flexion, both PMMA8 and ARCHES were significantly stiffer than SK, and PMMA8 was significantly stiffer than PMMA4. In rotation, PMMA8 and ARCHES were significantly stiffer than SK, and in flexion to failure, PMMA8 and ARCHES were significantly stiffer than PMMA4. CONCLUSIONS: External skeletal spinal fixation (ESSF) has mechanical properties comparable to more commonly used PMMA/pin internal fixation techniques. CLINICAL RELEVANCE: External fixation of the canine spine has several potential advantages over internal fixation including minimal dissection for pin placement, the ability to span affected vertebrae with placement of implants distant from the site of injury, postoperative adjustability, and complete removal of implants after healing. This study supports the biomechanical stability ESSF of the canine lumbar spine. Further studies are indicated to evaluate zones of consistently safe and secure placement of pins and clinical efficacy.