Significant Difference In Range Of Motion Research Articles

Oblique Lumbar Interbody Fixation

In vitro spine biomechanics. To determine the biomechanical properties of oblique lumbar interbody fixation (OLIF) in human cadaveric spines. OLIF has been used for stabilization of degenerative spondylolisthesis at the lumbosacral junction. Biomechanical properties and mode of failure of OLIF as a standalone device for motion segments without sagittal deformity has not yet been investigated. We hypothesize that the biomechanical properties of OLIF will be comparable with the contemporary standard of pedicle screw (PS) fixation. Randomly matched motion segments from L1 to L5 were allocated into 2 groups: (A) OLIF (group 1, n=5) or (B) PS (group 2, n=5). The intact and instrumented motion segments with and without anterior interbody graft were first tested under a combination of 200N axial compression and 5 Nm bending moments in flexion-extension and in lateral bending. Range of motion (ROM) and neutral zone were determined and compared between intact, OLIF and PS. A final load to failure test was carried out for each motion segment in either flexion or extension. OLIF resulted in reduction of flexion-extension ROM to 36%±14% of intact whereas PS resulted in reduction to 27%±22% of intact. The reduction of lateral bending ROM were 32%±13% and 32%±24% of intact with OLIF and PS. There were no significant difference in ROM between OLIF and PS (P=0.39). The mean failure loads with OLIF and PS in flexion were 1284 and 1158N, and in extension were 1879 and 1934N, respectively. Failure occurred at the ventral screw bone interface without pedicle fracture. These results indicate that stiffness and load to failure of the OLIF is comparable with PS fixation. OLIF failure occurred ventrally through the anterior cortical rim without concomitant pedicle fracture.

The importance of pronator quadratus repair in the treatment of distal radius fractures with volar plating

Open reduction internal fixation (ORIF) of distal radius fractures via a volar approach involves surgical release of the overlying pronator quadratus (PQ) muscle. Complete repair of the PQ, defined as full and stable replacement of the periphery of the PQ back to its original anatomic location, is not always possible upon conclusion of the operation. Postoperative consequences of incomplete PQ repair with regards to range of motion (ROM), grip strength, and complications are not well documented. It was hypothesized that the completeness of PQ repair would yield no significant difference in the postoperative ROM, grip strength, and incidence of complications. A retrospective review was performed of 110 repairs of distal radius fractures with ORIF via placement of a volar locking plate. The following clinical data were extracted: complete or incomplete PQ repair, patient age, gender, follow-up ROM/grip strength, and incidence of postoperative complications. No significant difference in ROM, grip strength, and postoperative complications was detected between the complete and incomplete PQ repair groups. Complications consisted of two incidences of malunion requiring revision surgery and one occurrence of complex regional pain syndrome. There were no tendon ruptures. No statistical difference in ROM/grip strength or incidence of postoperative complications was detected between the complete and incomplete PQ repair groups. Regardless of the level of injury sustained by the PQ, surgeons should make an effort to cover the distal aspect of the volar plate during closure following distal radius fracture ORIF. Coverage of the distal aspect of the plate with the PQ (at a minimum) provides adequate results in ROM and grip strength, as well as protection against flexor tendon injury. Therapeutic Level III: Retrospective Comparative Study.

Verification of pure moment testing in a multi–degree of freedom spine testing apparatus

BackgroundPure moment testing is a common method used in cadaveric spine testing. The fundamental basis for the widespread acceptance of applying a pure moment is uniform loading along the column of the spine. To our knowledge, this protocol has not been experimentally verified on a multi–degree of freedom testing apparatus. Given its ubiquitous use in spine biomechanics laboratories, confirmation of this comparative cadaveric test protocol is paramount. MethodsGroup A specimens (n = 13) were used to test the pure moment protocol, by use of 3 constructs that changed the number of involved vertebrae, orientation, and rigidity of the spine construct. Group B specimens (n = 6) were used to determine whether potting orientation, testing order, or degradation affected the range of motion (ROM) by use of 8 constructs. Each group was subjected to 3 cycles of flexion-extension, lateral bending, and axial torsion. The data from the third cycle were used to calculate the ROM for each method. ResultsGroup A testing resulted in significant differences in ROM across the 3 constructs for lateral bending and axial torsion (P < .02) and trended toward a difference for flexion-extension (P = .055). Group B testing showed an increase in ROM across 8 constructs (P < .04) but no significant difference due to the orientation change. ConclusionThe increased ROM across constructs observed in both groups indicates that the cause is likely the testing order or degradation of the specimens, with orientation having no observed effect. The data do not invalidate pure moment testing, and its use should persist.

Biomechanical stability of a bioabsorbable self-retaining polylactic acid/nano-sized &amp;beta;-tricalcium phosphate cervical spine interbody fusion device in single-level anterior cervical discectomy and fusion sheep models

PurposeThe aim of this study was to investigate the biomechanical stability provided by a novel, polylactic acid/nano-sized, β-tricalcium phosphate, bioabsorbable, self-retaining cervical fusion cage (BCFC).MethodsQuasistatic nonconstraining torques (maximum 1.5 NM) induced flexion, extension, lateral bending (±1.5 NM), and axial rotation (±1.5 NM) on 32 sheep cervical spines (C2–C5). The motion segment C3–C4 was first tested intact; the following groups were tested after complete discectomy: autologous tricortical iliac crest bone graft, Medtronic–Wego polyetheretherketone (PEEK) cage, Solis PEEK cage, and BCFC. The autologous bone graft group was tested with an anterior plate. The mean range of motion (ROM) was calculated from the load-displacement curves.ResultsBCFC significantly decreased ROM in lateral bending and axial rotation compared to other implants, and no significant difference in ROM between two types of PEEK cages and BCFC could be observed in flexion and extension. Anterior cervical plate (ACP) significantly decreased ROM in flexion and extension, but no significant difference in ROM between BCFC and bone graft plus ACP could be determined in lateral bending and axial rotation.ConclusionThe BCFC device showed better stability to autologous tricortical iliac crest bone graft and PEEK cages in single-level anterior cervical discectomy and fusion models and thus may be a potential alternative to the current PEEK cages.

Verification of Pure Moment Testing in a Multi-Degree of Freedom Spine Testing Apparatus

Background Pure moment testing is a common method used in cadaveric spine testing. The fundamental basis for the widespread acceptance of applying a pure moment is uniform loading along the column of the spine. To the author’s knowledge, this protocol has not been experimentally verified on a multi-degree-of-freedom testing apparatus. Due to its ubiquitous use in spine biomechanics laboratories, confirmation of this comparative cadaveric test protocol is paramount. Methods Group A specimens (n = 13) were used to test the pure moment protocol, using 3 constructs that changed the number of involved vertebrae, orientation and rigidity of the spine construct. Group B specimens (n = 6) were used to determine if potting orientation, testing order or degradation affected the range of motion (ROM) using 8 constructs. Each group was subjected to 3 cycles of flexion-extension, lateral bending and axial torsion. The data from the third cycle was used to calculate the ROM for each method. Results Group A testing resulted in significant differences in ROM across the 3 constructs for lateral bending and axial torsion ( P < 0.02), and trended towards a difference for flexion-extension ( P = 0.055). Group B testing showed an increase in ROM across 8 constructs ( P < 0.04), but no significant difference due to the orientation change. Conclusion The increased ROM across constructs observed in both groups indicates that the cause is likely due to the testing order or degradation of the specimens, with orientation having no observed effect. The data does not invalidate pure moment testing and its use should persist.

Comparison of the Minimally Invasive and Standard Medial Parapatellar Approaches for Total Knee Arthroplasty: Systematic Review and Meta-Analysis

This systematic literature review analysed the efficacy of minimally invasive subvastus (SV) and midvastus (MV) approaches, compared with the standard medial parapatellar (MP) approach, for total knee arthroplasty. Fixed- and random-effect meta-analyses were performed to pool the results of primary studies assessing the mean difference of each clinical outcome. Length of hospital stay was significantly different between the MP and SV approaches, but not between the MP and MV approaches. Blood loss was significantly higher following MP compared with SV. The number of days to perform a straight-leg raise was significantly longer following MP than either MV or SV. In the first 6 months postsurgery, MV was associated with a better range of motion (ROM) than MP. No significant difference in ROM between MP and SV was apparent at 1 year postsurgery. Quadriceps muscle strength recovered significantly more slowly following MP compared with SV. Future studies should assess the efficacy of the quadriceps-sparing approach and compare minimally invasive approaches, assessing intrinsic postoperative differences.

Children's rearfoot and midfoot motion while walking in school shoes

navicular, 1 st and 5 th metatarsal heads and hallux. Rearfoot motion was measured with a wand marker cluster through a window in the shoe. A standing reference trial was used to embed segment axes and thence to calculate motion of the distal segment relative to the proximal segment. Data were normalised to the stance phase which was sub-divided from the anterior/posterior force data as: contact period (initial contact - maximum negative force); midstance (maximum negative force zero) and propulsion (positive force - toe-off). Results Five boys and seven girls participated in the study (mean age 9 years, range 5-13 years). During the contact period shoes decreased midfoot range of motion (ROM) in the frontal plane from 3.4° to 1.7° (p=0.002) and in the transverse plane from 22.0° to 11.6° (p<0.001). No significant difference in ROM occurred during midstance at either the rearfoot or midfoot. During propulsion shoes reduced rearfoot ROM in the frontal plane from 12.0° to 9.6° (p=0.026) and midfoot ROM in the sagittal plan from 19.6° to 10.8° (p<0.001) and in the transverse plan from 10.1° to 4.3° (p<0.001). Conclusions Traditional school shoes restrict children’s foot motion during walking particularly at the midfoot during the contact period and propulsion phases of gait. The medium and long-term impacts of these changes are the focus of further research. The impact of school shoes on foot motion should be considered when assessing the paediatric patient and evaluating the effect of shoe or in-shoe interventions.

A novel crossed rod configuration incorporating translaminar screws for occipitocervical internal fixation: an in vitro biomechanical study

Background context Occipitocervical (OC) spinal instrumentation involving the axis (C2) entails the use of transarticular screws through C1–C2 or lateral mass screws at C1 and pedicle screws at C2 to achieve fusion. Because of the anatomical complexity, interpatient anomalous variation, and danger to the vertebral artery injury, there has been an increased interest in alternate sites for fixation. Recent studies have involved the placement of screws bilaterally into the C2 lamina. Several biomechanical studies have been carried out to evaluate the performance of C2 translaminar screws (TLSs). Purpose The aim of the study was to compare the biomechanics of an OC2 rigid construct using C2 pedicle screws and C2 TLSs. Also, this study included a new construct in which the OC2 fixation was carried out by connecting rods to the contralateral TLS. Study design Human cadaveric cervical spines were tested in an in vitro biomechanical flexibility experiment to investigate the biomechanical stability provided by a novel crossed rod (CR) configuration incorporating TLSs for OC2 internal fixation. Methods Seven fresh human cadaver occipitocervical spines (occipiut-C3) were tested by applying pure moments of ±1.5 Nm. After intact specimen testing, an occipital plate was implanted. Each specimen was then tested in the following modes: bilateral pedicle screws (BPSs) and rods at C2; TLSs at C2 with rods in parallel configuration (TLS+parallel rod); and TLSs at C2 with rods in crossed configuration (TLS+CR). OC2 range of motion (ROM) for each construct was obtained by applying pure moments in flexion-extension, lateral bending, and axial rotation. Results All three instrumented constructs significantly reduced ROM in all physiological planes when compared with the intact spine. The BPS construct similarly reduced ROM when compared with both the translaminar constructs. There was no significant difference in ROM between the translaminar constructs in all loading modes. Conclusions A cadaveric model was used to investigate the stability offered by a novel CR construct by using TLS fixation in an OC2 fusion construct. The results were compared with BPS fixation. All three constructs significantly decreased motion as compared with the intact state. There was no statistically significant difference in flexibility among any of the constructs. The novel CR construct provides as much stability as traditional constructs and may be a viable alternative for clinical use.

Spinal Kinematics and Facet Load Transmission After Total Disc Replacement

In vitro human cadaveric biomechanical study. The objectives were to determine the effect of total disc replacement (TDR) on kinematics, especially range of motion (ROM), helical axis of motion (HAM), and facet joint contact force. Ball-and-socket type artificial discs are designed to mimic normal motion, but the biomechanical effect on kinematics has not been thoroughly clarified. Fourteen human cadaveric L4-L5 units were tested before and after TDR. In 7 specimens, facet contact forces were directly measured with thin-film piezoresistive load transducers inserted in the facet joints. In the other 7 specimens, the facet joint capsules were kept intact. Moments (±7.5 Nm) were applied in flexion/extension, lateral bending, and axial rotation motion, with and without an axial compressive preload of 400 N. Three-dimensional motion was recorded, and each angular ROM and HAM were calculated. Without axial compressive preload, the TDR did not produce significant differences in ROMs in all cases. However, under compressive preload, the TDR produced significantly larger ROMs for flexion (4.0° and 8.7°) and lateral bending (2.4° and 5.6°) (intact state and TDR, respectively). The TDR did not alter the HAM significantly except the location in lateral bending without compressive preload and the orientation in flexion/extension against horizontal plane. The location of HAM was slightly shifted caudally by the compressive preload in intact and TDR states. Despite the increased ROMs, the facet contact forces were not significantly altered by the TDR either with or without compressive preload (26 N and 27 N in extension, 41 N and 41 N in lateral bending, 117 N and 126 N in axial rotation). TDR using a ball-and-socket type artificial disc significantly increased ROM under axial load and maintained the HAM with similar facet contact forces to the intact state.

Biomechanical Evaluation of a Posterolateral Lumbar Disc Arthroplasty Device

This in vitro analysis defines biomechanical properties of the Triumph Lumbar Disc (TLD) for posterolateral lumbar disc arthroplasty. To quantify segmental kinematics afforded by the TLD, determine whether intervertebral positional changes of the device affect spinal kinematics, and compare kinematics following TLD reconstruction with historical CHARITE data. As an alternative to arthrodesis, total disc arthroplasty serves to restore the biomechanical properties of the spine. However, there are kinematic and clinical concerns regarding posterior lumbar column destabilization and reconstruction using motion-preserving technology. Seven human lumbosacral spines were biomechanically evaluated under the following conditions: (1) Intact; (2) Unilateral facetectomy; (3) Facetectomy and discectomy; (4) TLD-posterior; (5) TLD-central; (6) TLD-anterior. Centers of intervertebral rotation (COR) and intradiscal pressures were compared at the operative/adjacent levels. In axial rotation, L4-L5 range of motion (ROM) increased to 110%+/-15.3% following unilateral facetectomy and 134.3%+/-26.9% following facet/discectomy. Implanting the TLD in 3 positions-posterior, central, and anterior-demonstrated no significant differences in ROM (P>0.05). Trends were similar in flexion/extension and lateral bending. The neutral zone increased under the facet/discectomy condition and TLD reconstructions compared to the intact condition (P<0.05). CORs were dispersed at the operative level following destabilization. TLD in posterior and central positions restored loci to near the intact condition, whereas the anterior position produced more diffuse CORs. Adjacent level intradiscal pressures decreased in flexion-extension following destabilization and reconstruction. Axial rotation ROM following TLD reconstruction (central position) was 131.5% of intact, compared to historical controls for the CHARITE device (162.0%). This indicates that lumbar disc arthroplasty performed using a posterolateral approach may offer biomechanical advantages over the anterior approach. Moreover, this approach may minimize surgical complications and allow simultaneous decompression of the neural elements. Intervertebral positional changes of the TLD were not shown to affect spinal kinematics.

Development and pilot testing of HEXORR: hand EXOskeleton rehabilitation robot.

BackgroundFollowing acute therapeutic interventions, the majority of stroke survivors are left with a poorly functioning hemiparetic hand. Rehabilitation robotics has shown promise in providing patients with intensive therapy leading to functional gains. Because of the hand's crucial role in performing activities of daily living, attention to hand therapy has recently increased.MethodsThis paper introduces a newly developed Hand Exoskeleton Rehabilitation Robot (HEXORR). This device has been designed to provide full range of motion (ROM) for all of the hand's digits. The thumb actuator allows for variable thumb plane of motion to incorporate different degrees of extension/flexion and abduction/adduction. Compensation algorithms have been developed to improve the exoskeleton's backdrivability by counteracting gravity, stiction and kinetic friction. We have also designed a force assistance mode that provides extension assistance based on each individual's needs. A pilot study was conducted on 9 unimpaired and 5 chronic stroke subjects to investigate the device's ability to allow physiologically accurate hand movements throughout the full ROM. The study also tested the efficacy of the force assistance mode with the goal of increasing stroke subjects' active ROM while still requiring active extension torque on the part of the subject.ResultsFor 12 of the hand digits'15 joints in neurologically normal subjects, there were no significant ROM differences (P > 0.05) between active movements performed inside and outside of HEXORR. Interjoint coordination was examined in the 1st and 3rd digits, and no differences were found between inside and outside of the device (P > 0.05). Stroke subjects were capable of performing free hand movements inside of the exoskeleton and the force assistance mode was successful in increasing active ROM by 43 ± 5% (P < 0.001) and 24 ± 6% (P = 0.041) for the fingers and thumb, respectively.ConclusionsOur pilot study shows that this device is capable of moving the hand's digits through nearly the entire ROM with physiologically accurate trajectories. Stroke subjects received the device intervention well and device impedance was minimized so that subjects could freely extend and flex their digits inside of HEXORR. Our active force-assisted condition was successful in increasing the subjects' ROM while promoting active participation.

Biomechanical Implications of Extending Occipitocervical Instrumentation to Include the Subaxial Spine

No clear biomechanical data exist regarding where to place the caudal end of a screw-rod occipitocervical instrumentation construct. This study examines whether range of motion (ROM) from the occiput to C2 is altered by subaxial extension of occipitocervical instrumentation constructs. Cadaver specimens underwent intact biomechanical testing followed by destabilization via an odontoid osteotomy. Subsequent biomechanical testing was performed of four occipitocervical constructs: occipital plate + C2 pars screws (construct 1), occipital plate + C2 pars screws + C4 lateral mass screws (construct 2), occipital plate + C1-C2 transarticular screws (construct 3), and occipital plate + C1-C2 transarticular screws + C4 lateral mass screws (construct 4). All constructs significantly reduced occiput-C2 ROM in all loading modes compared with the intact cervical spine, with one exception (construct 1, lateral bending). No significant ROM differences were noted when C4 lateral mass screws (construct 4) were added to construct 3. Addition of C4 lateral mass screws (construct 2) to construct 1 decreased the ROM in the flexion mode only. No significant ROM differences were seen between construct 2 and construct 3 in any loading mode. The addition of subaxial instrumentation to occipitocervical instrumentation constructs in this study decreased occiput-C2 ROM only when the construct was anchored by C2 pars screws and only in flexion. Screws that cross the C1 to C2 articulation provide stable fixation when combined with an occipital plate, and the addition of subaxial instrumentation to this construct for stabilizing the occipitocervical junction does not significantly decrease ROM.

Is the Extended Release of the Inferior Glenohumeral Ligament Necessary for Frozen Shoulder?

The aims of our study were to assess effects of the extent of capsular release and to define the benefit of additional release of the inferior glenohumeral ligament (IGHL) from inferior to posterior in frozen shoulder. Seventy-four consecutive patients with refractory frozen shoulder underwent arthroscopic capsular release and were divided into 2 groups randomly. The release of anterior capsular structures, including the anterior band of the IGHL, was performed in group 1. In group 2 the release extended inferiorly and posteriorly. Constant functional scores were used to assess the outcome. The range of motion (ROM) in various directions was also recorded preoperatively and postoperatively. Follow-up was obtained in 41 patients in group 1 and 29 patients in group 2, and it averaged 28 months. At the last follow-up, there was a significant improvement in Constant score (P < .01) postoperatively in all patients. There was a significant and rapid reduction in the visual analog scale score in both groups postoperatively. No statistical difference in the visual analog scale score was found between the 2 groups at the corresponding time points. Overall, patients had restored shoulder ROM at the last follow-up without difference between group 1 and group 2. Abduction, flexion, external rotation at 90 degrees of abduction, internal rotation at 0 degrees of abduction, and internal rotation at 90 degrees of abduction recovered more rapidly in group 2 within 3 months after surgery; however, there was no significant difference in ROM after 6 months. In this broad group of patients with recalcitrant adhesive capsulitis, the addition of the posterior capsular release did not improve patient function or ROM over anterior capsular release alone at 6 months. The extended release of the inferior and posterior IGHL would improve ROM more rapidly within the first 3 months postoperatively. Level I, therapeutic randomized controlled trial.

Biomechanic research on short-segment posterior pedicle screw fixation

Objective To compare the stability effect of the fixation segment using the new test system based robotics to simulate the complex human movement at natural state about the three-level fixa-tion by using four, five or six pedicle screws in treatment of thoracolumbar burst fractures. Methods Six human cadaveric spines were dissected from T_(11)-L_3. The inferior half part of L_1 vertebral bodies and L_1-L_2 dises were resected to mimie an unstable L_1 burst fracture with loss of anterior column support. Specimens were tested in accordance with the following order:intact, 4,5 and 6 pedicle screws fixation at the three-level fixation. The range of motion (ROM) of the fixation segment (T_(11)-L_3) was measured with the six-freedom degree robotics system controlled by mixed force and displacement during flexion, exten-sion, lateral bending and axial torsion, when the stiffness was calculated. One-way statistieal analysis was used for analyzing the collected data. Results With increased number of screws, the ROM of the fixa-tion segment (T_(11)-L_3) was gradually decreased and the stiffness gradually increased. The ROM under ax-ial rotation of six and five screws group became smaller than four screws group (P 0.05). There were no significant differences in ROM and stiffness under six different loading directions between six screws group and five screws group (P > 0.05). No statistical difference was observed for three fixation modes in aspects of ROMs and stiffness under flexion-extension or lateral ben-ding (P > 0.05). Conclusions Three-level fixation of burst fractures with five or six screws offers im-proved biomechanical stability compared with traditional four screws fixation. But the difference is insig-nificant between six and five screws fixations. Key words: Spinal fractures; Biomechanies; Internal fixators; Robotics

Biomechanical Study of Artificial Atlanto-Odontoid Joint

An in vitro biomechanical study. To determine the initial stability and function of a new artificial joint in a cadaveric cervical spine model by comparing it with a conventional method. Resection of the odontoid and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurologic complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion. There were 24 fresh human cadaveric cervical spines (C0-C3) randomly divided into 2 groups: group 1, resection of the odontoid with artificial atlanto-odontoid joint (AAOJ); and group 2, resection of the odontoid with Harms anterior atlantoaxial plate (Harms). For each specimen, the intact and resection of the odontoid underwent a flexibility test first, followed by the instrumented construct. Rotational angles of the C0-C3 segment were measured to study the immediate stability and function of resection of the odontoid and AAOJ, compared with the intact and resection of the odontoid and Harms. Compared with the intact state, resection of the odontoid and AAOJ resulted in a significant decrease in the range of motion (ROM) and neutral zone during flexion, extension, and lateral bending (P < 0.05); however, with regard to axial rotation, there was no significant difference in ROM (P > 0.05). Compared with resection of the odontoid and Harms, resection of the odontoid and AAOJ during flexion, extension, and lateral bending, there was no significant difference in ROM (P > 0.05). We have designed a new type of AAOJ for correcting atlantoaxial instability arising from C1 to C2 anterior decompression procedures. The unique aspect of this joint is that it restores, to a great extent, the C1-C2 axial rotation that is lost during current stabilization procedures.

Artificial atlanto-odontoid joint replacement through a transoral approach

Resection of the odontoid process and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurological complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion. However, this results in considerable loss of rotation function of the atlantoaxial complex. From the viewpoint of retaining the rotation function and providing stability, we designed an artificial atlanto-odontoid joint based on anatomical measurements of 50 pairs of dry atlantoaxial specimens by digital calipers and 10 fresh cadaveric specimens by microsurgical techniques. The metal-on-metal titanium alloy joint has an arc-shaped atlas component, and a hollow cylindrical bushing into which fits a rotation axle of an inverted v-shaped axis component and is implanted through a transoral approach. After the joint was implanted onto specimens with anterior decompression, biomechanical tests were performed to compare the stability parameters in the intact state, after decompression, after artificial joint replacement, and after fatigue test. Compared to the intact state, artificial joint replacement resulted in a significant decrease in the range of motion (ROM) and neutral zone (NZ) during flexion, extension, and lateral bending (P < 0.001); however, with regard to axial rotation, there was no significant difference in ROM (P = 0.405), a significant increase in NZ (P = 0.008), and a significant decrease in stiffness (P = 0.003). Compared to the decompressed state, artificial joint replacement resulted in a significantly decreased ROM (P B 0.021) and NZ (P B 0.002) and a significantly increased stiffness (P \ 0.001) in all directions. Following artificial joint replacement, there was no significant difference in ROM (P C 0.719), NZ (P C 0.580), and stiffness (P C 0.602) in all directions before and after the fatigue test. The artificial joint showed no signs of wear and tear after the fatigue test. This artificial atlanto-odontoid joint may be useful in cases of odontoid resection due to malunion or nonunion of odontoid fracture, atraumatic odontoid fracture, irreducible atlas dislocation, posterior atlantoaxial subluxation, or congenital skull base abnormalities.

In vitro biomechanical comparison of an anterior and anterolateral lumbar plate with posterior fixation following single-level anterior lumbar interbody fusion

Anterior lumbar interbody fusion (ALIF) is often supplemented with instrumentation to increase stability in the spine. If anterior plate fixation provided the same stability as posterior pedicle screw fixation (PSF), then a second approach and its associated morbidity could be avoided. Seven human cadaveric L4-5 spinal segments were tested under three conditions: ALIF with an anterior plate, ALIF with an anterolateral plate, and ALIF supplemented by PSF. Range of motion (ROM) was calculated for flexion/extension, lateral bending, and axial torsion and compared among the three configurations. There were no significant differences in ROM during flexion/extension, lateral bending, or axial torsion among any of the three instrumentation configurations. The addition of an anterior plate or posterior PS/rod instrumentation following ALIF provides substantially equivalent biomechanical stability. Additionally, the position of the plate system, either anterior or anterolateral, does not significantly affect the stability gained.

Kinematic Study of Back Movement in Clinically Sound Malinois Dogs with Consideration of the Effect of Radiographic Changes in the Lumbosacral Junction

To determine thoracolumbar spinal movement in dogs and the influence of subclinical radiographic changes involving the lumbosacral junction. Experimental study. Clinically sound Malinois dogs (n=22). Kinematic analysis of markers on the spinal processes of C7, T6, T13, L3, L7, and S3 was performed while dogs were walking on a treadmill. Range of motion (ROM) in the transverse and vertical direction and the time of occurrence (TOO) of the maximal marker position were calculated. ROM and TOO of angulations formed by the corresponding markers were calculated. Initial kinematic analysis was performed without knowledge of the radiographic changes, and then data were reanalyzed to determine whether vertebral changes influenced back motion. Based on the results of radiographic analysis of the lumbosacral junction, dogs were divided into 3 groups: 1=no radiographic changes; 2=shortened L7 vertebra; and 3=transitional vertebrae, spondylosis, subluxations, and spondylarthrosis of the lumbosacral junction. ROM and TOO were compared using ANOVA for repeated measures and a Bonferroni's post hoc test; P<.05 was considered significant. The highest transverse ROM was achieved by markers T6, T13, and L3, and in the vertical direction by S3; however, there were no significant differences in ROM in horizontal angulations. In the sagittal plane, T13-L3-L7 had a lower angulation than L3-L7-S3. In Group 3, transverse ROM for C7 was significantly higher than in Group 1; the horizontal angular maximum of T13-L3-L7 occurred significantly earlier. Significant kinematic changes were detected between clinically sound dogs with radiographic lumbosacral changes and dogs with no radiographic abnormalities. Kinematic data from clinically sound dogs can be used for comparison with data from dogs with gait disturbances associated with orthopedic or neurologic disease or changes associated with therapy.

Biomechanical Comparison of Instrumented and Uninstrumented Multilevel Cervical Discectomy Versus Corpectomy

In vitro flexibility test comparing biomechanics of cervical corpectomy versus discectomy with and without instrumentation. To evaluate whether the additional effort required to perform multilevel discectomies instead of corpectomies is worthwhile biomechanically. Both cervical corpectomy and discectomy have been shown to be effective clinically. No previous biomechanical comparison exists. Fourteen human cadaveric cervical spines were studied: 1) intact, 2) after discectomy and wedge grafting at C4-C5, C5-C6, and C6-C7 (Group 1) or corpectomy and strut grafting of C5 and C6 (Group 2), 3) after attaching a locking metal plate from C4-C7, and 4) after adding posterior locking lateral mass screw/rod instrumentation across C4-C7. Non-constraining, nondestructive torques induced flexion, extension, lateral bending, and axial rotation (maximum, 1.5 Nm) while angular motion was measured stereophotogrammetrically. Discectomy and grafting did not alter the range of motion (ROM) significantly from normal during any loading mode (P > 0.11). Corpectomy and grafting allowed a significantly greater range of motion than normal during flexion, lateral bending, and axial rotation (P < 0.05). Addition of an anterior plate reduced ROM to significantly less than normal during all loading modes in both groups (P < 0.005). Addition of posterior instrumentation further reduced ROM significantly in both groups (P < 0.01). There was no significant difference in ROM between corpectomy and discectomy groups in any loading mode whether uninstrumented (P > 0.18), anteriorly plated (P > 0.33), or anteriorly and posteriorly instrumented (P > 0.30). Less difference in stability was observed than was predicted between specimens receiving multilevel discectomy versus multilevel corpectomy, regardless of whether specimens were left unplated, plated anteriorly, or fixated with combined anterior/posterior instrumentation.

Effect of width of disk fenestration and a ventral slot on biomechanics of the canine C5-C6 vertebral motion unit

To investigate the effects of disk fenestration and ventral slot formation on vertebral motion unit (VMU) range of motion (ROM) and determine the effects of fenestration and ventral slot width on VMU ROM. C5-C6 VMUs from 10 skeletally mature canine cadavers. Specimens were assigned to 2 groups (5 specimens/group). Surgery was performed in which width of a fenestration and a ventral slot was 33% (group 1) or 50% (group 2) the width of the vertebral body. Flexion-extension, lateral bending, and axial torsion ROMs were measured during loading before surgery, after fenestration, and after ventral slot formation. Range of motion was compared within groups to determine effects of surgical procedure on stability and between groups to determine effects of width of fenestration and ventral slot on stability. For both groups, fenestration resulted in a significant increase in ROM during flexion-extension, compared with results for intact specimens. Ventral slot formation resulted in a significant increase in ROM during flexion-extension and lateral bending, compared with results for intact specimens. Ventral slot formation resulted in a significant increase in ROM only during flexion-extension, compared with results for fenestrated specimens. There were no significant differences in ROM of the intact, fenestrated, and ventral slot specimens between groups. Analysis of these results suggests that fenestration and ventral slot procedures each affect the biomechanics of the C5-C6 VMU. Width of a fenestration or ventral slot up to 50% of the width of C5-C6 may be clinically acceptable.