Cervical endplate bone density distribution measured by CT osteoabsorptiometry and direct comparison with mechanical properties of the endplate.

PURPOSE: Intervertebral device subsidence is one of the complications of anterior cervical discectomy and fusion. The biomechanical properties of vertebral bony endplate may be related to device subsidence. The aim of this study is to measure the cervical endplate bone density distribution using a novel 3D measurement method. METHODS: Eight human cadaver cervical spines were obtained and levels C3-C7 were dissected and CT scanned. Three-dimensional (3D) CT model was created with the same 3D coordinates of the original DICOM dataset. The regional strength and stiffness of the endplate were determined by indentation testing. The indentation points were recorded by a photograph and the location of the indentation points was projected to the 3D CT model. Three-dimensional coordinates of the indentation point was obtained in the 3D space determined by the DICOM dataset. The area underneath the indentation point was calculated by a trilinear interpolation method directly. Data in HU and correlations with the indentation strength and stiffness were analysed. RESULTS: A positive correlation was found between HU and strength (r = 0.52) and between HU and stiffness (r = 0.41). Overall, mechanical strength and stiffness and HU in the superior endplate of the caudal vertebra were lower than those in the inferior endplate of the cranial vertebra in the same intervertebral disc. CONCLUSIONS: The mechanical properties and the HU were found to be significantly correlated, which employed a novel 3D HU measurement method, thus demonstrating potential to predict cervical endplate failure risk in a clinical setting.

Three-dimensional computed tomographic evaluation of lateral lumbar interbody fusion: morphometric change of intervertebral structure.

PURPOSE: Two-dimensional (2D) analyses of intervertebral disc (IVD) height and foramen measurements following lateral lumbar interbody fusion (LLIF) have been reported. However, three-dimensional (3D) morphometric analysis of intervertebral structure using 3D computed tomography (3D CT) provides increased precision for measuring morphological changes. The purpose of this study was to evaluate 3D changes of lumbar IVD height and foramen diameter in degenerative lumbar disease patients following LLIF. METHODS: Subject-based 3D CT lumbar models were created for 26 patients before and following LLIF. IVD height (whole and five anatomical zones) and foramen diameter (minimum and maximum) were measured based on the model using custom software. The sagittal placement of cages (SPC) and cross-sectional area of the thecal sac (CSA) were measured. Changes in these parameters by LLIF were quantified and statistically analysed. RESULTS: Following LLIF, disc height increased by an average of 2.9 mm (P < 0.01). Post-operative measurements of both minimum and maximum diameters of the foramen were significantly increased by 1.0 mm and 1.9 mm, respectively (P < 0.01). Change in maximum foramen diameter was significantly correlated with change in disc height (P < 0.05). The SPC was significantly correlated with the changes in disc height and foraminal diameters (P < 0.05, respectively). No significant change between the change in disc height and CSA was found. CONCLUSION: This preliminary study quantifies disc height and foramen diameter changes in 3D following LLIF. The presented data provide baseline intervertebral changes for future comparisons with follow-up studies and clinical outcomes. LEVEL OF EVIDENCE I: Diagnostic: individual cross-sectional studies with the consistently applied reference standard and blinding.

Triazolecarbaldehyde Reagents for One-Step N-Terminal Protein Modification.

Site-specific modification of peptides and proteins is a key aspect of protein engineering. We developed a method for modification of the N terminus of proteins using 1H-1,2,3-triazole-4-carbaldehyde (TA4C) derivatives, which can be prepared in one step. The N-terminal specific labeling of bioactive peptides and proteins with the TA4C derivatives proceeds under mild reaction conditions in excellent conversion (angiotensin I: 92 %, ribonuclease A: 90 %). This method enables site-specific conjugation of various functional molecules such as fluorophores, biotin, and polyethylene glycol attached to the triazole ring to the N terminus. Furthermore, a functional molecule modified with a primary amine moiety can be directly converted into a TA4C derivative through a Dimroth rearrangement reaction with 1-(4-nitrophenyl)-1H-1,2,3-triazole-4-carbaldehyde. This method can be used to obtain N-terminal-modified proteins via only two steps: 1) convenient preparation of a TA4C derivative with a functional group and 2) modification of the N terminus of the protein with the TA4C derivative.

Segmental coupling effects during correction of three-dimensional lumbar deformity using lateral lumbar interbody fusion.

PURPOSE: Lateral lumbar interbody fusion (LLIF) has been performed to correct spinal deformity associated with lumbar degenerative disease. Although its usefulness has been studied, there are no reports of quantitative evaluation in three dimensions. Our purpose is to quantitate 3D deformity of the patients with lumbar degenerative disease and correction of the deformity by LLIF using patient-specific 3D CT models. METHODS: We measured the disc height and 3D alignment of the lumbar spine in 28 patients with degenerative disease undergoing LLIF using patient-specific 3D CT models created preoperatively and 3 months after surgery. The 3D alignment was calculated as wedge, lordosis and axial rotation angles at each motion segment. The disc height and the rotational angles were compared between before and after LLIF. RESULTS: A strong positive correlation was found between the wedge angle and the axial rotation angles (r = 0.718, P < 0.001) in the patients with lumbar degenerative disease preoperatively. The wedge and axial rotation angles decreased after surgery (P < 0.001 and P < 0.001, respectively). A positive correlation was found between the corrected wedge angle and the corrected axial rotation angle (r = 0.46, P < 0.001). CONCLUSION: The present study demonstrated positive correlations between the wedge deformity and the axial rotational deformity in the patients with lumbar degenerative disease. The axial rotational deformity was simultaneously corrected with LLIF only by leveling the intervertebral wedge deformity via cage insertion without additional correction procedure. These slides can be retrieved under Electronic Supplementary Material.

Lumbar facet joint subchondral bone density in low back pain and asymptomatic subjects.

OBJECTIVE: To report in vivo measurements of lumbar facet joint subchondral bone mineral density used in the description of facet joint loading patterns and to interrogate if low back pain is associated with changes in subchondral bone mineral density. MATERIALS AND METHODS: In vivo measurements of lumbar facet joint subchondral bone mineral density (L1/2 to L5/S1) in Hounsfield units were performed on 89 volunteers (56 controls and 33 with low back pain) by computed tomography osteoabsorptiometry at subchondral regions between 1.5 mm and 2.5 mm below the joint surface. The facet surface was divided into five topographic zones: cranial, lateral, caudal, medial, and central. RESULTS: We analyzed 1780 facet joint surfaces. Facets were denser (p < 0.0001) both in superior facets and in low back pain subjects (p < 0.0001). For the entire cohort, the facet center zone subchondral bone mineral density was higher (p < 0.0001) than that of the peripheral zones. The analyses indicate that subchondral bone mineral density is highest in patients with low back pain, the superior facets, and the center zone of the facets. CONCLUSIONS: Subchondral bone mineral density is thought to reflect cumulative, long-term distribution of stress acting on a joint. This work shows that higher subchondral bone mineral density values in the center zone indicate predominant stress transmission through the center of the facet joints. Finally, the greater subchondral bone mineral density in patients with low back pain may reflect both increased load bearing by the facets secondary to disc degeneration and misdistribution of loading within the joint.

Topographic Analysis of Lateral Versus Medial Femoral Condyle Donor Sites for Oblong Medial Femoral Condyle Lesions.

PURPOSE: To analyze the topographic matching of oblong osteochondral allografts to treat large oval medial femoral condyle (MFC) lesions using computer simulation models. The secondary objective was to determine whether lateral femoral condyle (LFC) grafts would have a similar surface matching when compared with MFC grafts in this setting. METHODS: Human femoral hemicondyles (10 MFCs, 7 LFCs) underwent 3-dimensional computed tomography. Models were created from computed tomography images and exported into point-cloud models. Donor-recipient matches with large condylar width mismatch were excluded. The remaining specimen were divided into 3 donor-recipient groups with 2 defect sizes (17 × 30 mm and 20 × 30 mm): 20 MFC donor (MFCd)-MFC recipient (MFCr), 27 ipsilateral LFC donor (LFCd)-MFCr, and 26 contralateral LFCd-MFCr. Grafts were optimally virtually aligned with the MFCr defect. Mismatch of the articular cartilage and subchondral bone surfaces between the graft and the defect and articular step-off were calculated. RESULTS: MFCd grafts resulted in articular cartilage surface mismatch and peripheral step of less than 0.5 mm for both defect sizes. The subchondral bone surface mismatch was significantly greater than the articular cartilage surface mismatch (P < .01) in both defect sizes). Conversely, the ipsilateral and contralateral LFCd grafts resulted in significantly greater articular cartilage surface mismatch and step-off for both defect sizes when compared to MFCd grafts (P < .01). CONCLUSIONS: Oblong MFC allografts provide acceptable topographic matching for large oval MFC lesions when condylar width differences are minimized. However, concern exists in using oblong LFC allografts for MFC defects, as this can result in increased peripheral step-off and surface mismatch. CLINICAL RELEVANCE: These data reinforce the ability to use oblong MFC osteochondral allograft for treating oval cartilage lesions of the MFC when condylar width is considered. Although other studies have demonstrated LFCs can be used to treat circular defects on the MFC, this may not be true for oblong grafts.

Computed Tomography-Based Three-Dimensional Analyses Show Similarities in Anterosuperior Acetabular Coverage Between Acetabular Dysplasia and Borderline Dysplasia.

PURPOSE: (1) To compare the acetabular coverage between dysplasia, borderline dysplasia, and control acetabulum in a quantitative 3-dimensional manner; and (2) to evaluate correlations between the radiologic parameters and the 3-dimensional zonal-acetabular coverage. METHODS: We reviewed contralateral hip computed tomography images of patients 16 to 60 years of age who underwent 1 of 3 types of surgeries: eccentric rotational acetabular osteotomy, curved intertrochanteric varus osteotomy, and total hip replacement with minimum 1-year follow-up from January 2013 to April 2018. A point-cloud model of the acetabulum created from computed tomography was divided into 6 zones. Three-dimensional acetabular coverage was measured radially at intervals of 1°. Mean radial acetabular coverage for each zone was named ZAC (zonal acetabular coverage) and was compared among the 3 subgroups (control: 25° ≤lateral center-edge angle [LCEA] <40°; borderline: 20° ≤LCEA <25°; and dysplasia: LCEA ≤20°) statistically. Further, the correlations between the ZAC in each zone and the LCEA were analyzed using Pearson's correlation coefficient. RESULTS: One-hundred fifteen hips were categorized as control (36 hips), borderline (32 hips), and dysplasia (47 hips). The mean anterocranial ZAC in the borderline (87.5 ± 5.7°) was smaller than that in the control (92.6 ± 5.9°, P = .005) but did not differ compared with the dysplasia (84.5 ± 7.6°, P = .131). In contrast, the anterocaudal (71.2 ± 5.0°), posterocranial (85.0 ± 6.4°), and posterocaudal (82.4 ± 4.5°) mean ZACs in the borderline were not different from those in the control (anterocaudal, 74.3 ± 4.6°, P = .090; posterocranial, 87.9 ± 4.3°, P = .082; posterocaudal, 85.1 ± 5.0°, P = .069) respectively. Although there was a very strong positive correlation with supra-anterior ZAC and LCEA (r = 0.750, P < .001), the correlation between the anterocranial ZAC and LCEA was relatively weak (r = 0.574, P < .001). CONCLUSIONS: The anterosuperior acetabular coverage in the borderline dysplastic acetabulum is more similar to the dysplastic acetabulum than to the normal acetabulum. CLINICAL RELEVANCE: This study emphasizes the importance of evaluating not only the lateral but also the anterior coverage in borderline dysplasia.

Dynamic Three-Dimensional Computed Tomography Mapping of Isometric Posterior Cruciate Ligament Attachment Sites on the Tibia and Femur: Single- Versus Double-Bundle Analysis.

PURPOSE: (1) To determine the area of posterior cruciate ligament (PCL) insertion sites on the lateral wall of the medial femoral condyle (LWMFC) that demonstrates the least amount of length change through full range of motion (ROM) and (2) to identify a range of flexion that would be favorable for graft tensioning for single-bundle (SB) and double-bundle (DB) PCL reconstruction. METHODS: Six fresh-frozen cadaveric knees were obtained. Three-dimensional computed tomography point-cloud models were obtained from 0° to 135°. A point grid was placed on the LWMFC and the tibial PCL facet. Intra-articular length was calculated for each point on the femur to the tibia at all flexion angles and grouped to represent areas for bone tunnels of SB and DB PCLR. Normalized length changes were evaluated. RESULTS: Femoral tunnel location and angle of graft fixation were significant contributors to mean, minimum, and maximum normalized length of the PCL (all p < .001). Tibial tunnel location was not significant in any case (all p < .22). A femoral tunnel in the location of the posteromedial bundle of the PCL resulted in the least length change at all tibial positions (maximum change 13%). Fixation of the anterolateral bundle in extension or at 30° flexion resulted in significant overconstraint of the PCL graft. The femoral tunnel location for a SB PCLR resulted in significant laxity at lower ranges of flexion. CONCLUSION: PCL length was significantly dependent on femoral tunnel position and angle of fixation, whereas tibial tunnel position did not significantly contribute to observed differences. All PCL grafts demonstrated anisometry, with the anterolateral bundle being more anisometric than the posteromedial bundle. For DB PCLR, the posteromedial bundle demonstrated the highest degree of isometry throughout ROM, although no area of the LWMFC was truly isometric. The anterolateral bundle should be fixed at 90° to avoid overconstraint, and SB PCLR demonstrated significant laxity at lower ranges of flexion. CLINICAL RELEVANCE: Surgeons can apply the results of this investigation to surgical planning in PCLR to optimize isometry, which may ultimately reduce graft strain and the risk of graft failure. Additionally, DB PCLR demonstrated superiority compared with SB PCLR regarding graft isometry, as significant laxity was encountered at lower ranges of flexion in SB PCLRs. Fixation of the ALB at 90° flexion should be performed to avoid overconstraint in knee extension.

Bony Ingrowth of Coil-Type Open-Architecture Anchors Compared With Screw-Type PEEK Anchors for the Medial Row in Rotator Cuff Repair: A Randomized Controlled Trial.

PURPOSE: To evaluate outcomes of screw-type and coil-type open-architecture suture anchors with respect to bony ingrowth, release of biological markers, and patient-reported outcome measures when used in rotator cuff repair (RCR). METHODS: Forty patients undergoing arthroscopic RCR for full-thickness rotator cuff tears were enrolled and prospectively randomized to receive a screw-type (19 patients) or coil-type (21 patients) suture anchor for the medial row during repair. All repairs used a transosseous-equivalent configuration with footprint anchors laterally. Marrow elements released during surgery were evaluated for 9 cytokine markers (insulin-like growth factor 1, fibroblast growth factor 2, bone morphogenetic proteins 7 and 2, platelet-derived growth factors AA and BB, epidermal growth factor, transforming growth factor beta1, and vascular endothelial growth factor). Postoperative computed tomography scans were performed at 6 months. Range of motion, strength, and validated patient-reported outcome measures (Simple Shoulder Test, Single Assessment Numeric Evaluation, visual analog scale, and American Shoulder and Elbow Surgeons scores) were gathered before the operation and at 6 months and 1 year postoperatively. RESULTS: Bone mineral density surrounding the coil-type anchor was significantly greater than that surrounding the screw-type anchor (P = .005). Bone mineral density values within the coil-type and screw-type anchors were comparable (P = .527); however, a larger amount of total bone mineral mass (in milligrams) was shown within the coil-type anchor owing to its larger volume (P < .01). Marrow elements released at the repair site were similar between groups (P > .05). Postoperatively, no statistically significant difference was found between groups for clinical outcome measures at 6 months or 1 year. Retear and complication rates were similar between groups (P > .05). CONCLUSIONS: Both the coil-type and screw-type anchors can be reliably used for RCR and produce similar clinical outcomes. The coil-type anchor resulted in superior bony growth surrounding the anchor and a larger total bone mineral mass within the anchor owing to its larger volume. LEVEL OF EVIDENCE: Level II, randomized prospective comparative study.

Site-Specific Modification of Proteins through N-Terminal Azide Labeling and a Chelation-Assisted CuAAC Reaction.

Site-specific modification of peptides and proteins is an important method for introducing an artificial function to the protein surface. Recently, we found that new bioconjugation reagents, 6-(azidomethyl)-2-pyridinecarbaldehyde (6AMPC) derivatives, allow specific N-terminal modification and enhance the reaction rate of the subsequent bioconjugation in a chelation-assisted CuAAC reaction. The N-terminal specific azide-labeling of bioactive peptides and proteins occurs under mild reaction conditions with 6AMPC derivatives (angiotensin I: 90%, ribonuclease A: 90%). Kinetic analysis of the CuAAC reaction with azide-labeled proteins reveals that the ligation is promoted in the presence of a copper-chelating pyridine moiety. Importantly, the introduction of an electron-donating methoxy group to the pyridine moiety further accelerates the CuAAC ligation. We demonstrate that this method enables site-specific conjugation of various functional molecules such as fluorophores, biotin, and polyethylene glycol.

Correction to: ISSLS PRIZE IN BASIC SCIENCE 2018: Growth differentiation factor-6 attenuated pro-inflammatory molecular changes in the rabbit anular-puncture model and degenerated disc-induced pain generation in the rat xenograft radiculopathy model.

The author "Ashish D. Diwan" receives educational consultant fees from Nuvasive Inc.

Surface Mapping of the Musculotendinous Attachments at the Pubic Symphysis in Cadaveric Specimens: Implications for the Treatment of Core Muscle Injury.

PURPOSE: To characterize the 3-dimensional muscular, musculotendinous, and neurovascular anatomy about the pubic symphysis relevant to core muscle injury (CMI). METHODS: Ten cadaveric hips were dissected to characterize the musculotendinous insertion of the rectus abdominis and inguinal ligament, origins of the adductor longus and adductor brevis, and the pubic cartilage plate. A 3-dimensional coordinate measuring system and data acquisition software were used to calculate structure cross-sectional area, and the landmark anatomical relationships to 1 another and relevant neurovascular structures. RESULTS: All specimens were male with an average age of 62 ± 2 years. The mean footprints of the rectus abdominis, inguinal ligament, adductor longus, and adductor brevis were 8.4 ± 3.1, 1.2 ± 0.5, 3.8 ± 1.6, and 2.9 ± 1.3 cm2, respectively. The mean pectineus and gracilis footprints were 6.3 ± 2.4 and 3.4 ± 0.9 cm2, respectively. The mean cross-sectional area of the cartilage plate was 24.8 ± 5.6 cm2. The adductor longus was an average 1.5 ± 0.25 cm from the adductor brevis and 0.69 ± 0.52 cm from the rectus abdominis. The genital branch of the genitofemoral nerve was an average of 4.3 cm (range, 2.8-6.4) lateral to the insertion of the inguinal ligament. The femoral vein and artery were 3.0 cm (range, 2.5-3.6) and 3.7 cm (range, 2.5-5.9) lateral to the inguinal ligament footprint. The obturator nerve was 2.5 cm (range, 1.6-3.4) lateral to the adductor longus. CONCLUSIONS: Familiarity with the anatomy of the pubic symphysis is essential for surgeons treating patients with CMI. We have shown that this relatively small area is the site of many muscular, musculotendinous, and neurovascular structures with various sized footprints and described the 3-dimensional anatomy of the anterior pubic symphysis. The origin of the adductor longus lies in close proximity to other structures, such as the adductor brevis, the insertion of the rectus abdominis, and the obturator nerve. These findings should be considered when operating in this region and treating patients with chronic groin pain. CLINICAL RELEVANCE: The anatomy of the pelvic region and pubic symphysis has not been well characterized. Intimate knowledge of relevant anatomy is essential to treating CMI, also known as athletic pubalgia or sports hernia.

Proximal fixation anterior to the lateral femoral epicondyle optimizes isometry in anterolateral ligament reconstruction.

PURPOSE: Concomitant anterolateral ligament (ALL) injury is often observed in patients with an anterior cruciate ligament injury leading some to recommend concurrent ALL reconstruction. In ligament reconstruction, it is imperative to restore desirable ligament length changes to prevent stress on the graft. The purpose of this investigation is to identify the optimal femoral and tibial locations for fixation in ALL reconstruction. METHODS: 3D computerized tomography (CT) knee models were obtained from six fresh-frozen, unpaired, cadaveric human knees at 0°, 10°, 20°, 30°, 40°, 90°, 110°, and 125°of knee flexion. Planar grids were projected onto the lateral knee. Isometry between each tibial and femoral grid point was calculated at each angle of flexion by the length change in reference to the length at 0° of knee flexion. The mean normalized length change over the range of motion was calculated for each combination of points at all angles of flexion were calculated. RESULTS: Fixation of the ALL to the lateral femoral epicondyle or 5 mm anterior to the epicondyle with tibial fixation on the posteroinferior aspect of the tibial condyle (14-21 mm posterior to Gerdy's tubercle and 13-20 mm below the joint line) provided the lowest average length change for all possible ALL tibial insertion points. Minimal length change for all femoral fixation locations occurred from 20° to 40° of flexion, which identifies the angle of flexion where graft tensioning should occur intraoperatively. CONCLUSION: With the use of 3D reconstructed models of knee-CT scans, we observed that there was no ALL fixation point that was truly isometric throughout range of motion. Fixation of the anterolateral ligament on the lateral femoral epicondyle or anterior to the lateral femoral epicondyle and on the inferoposterior aspect of the tibial condyle restores isometry. Additionally, minimal length change was observed between 20° and 40° of flexion, which is the most appropriate range of knee flexion to tension the graft. Reproducing isometry reduces stress on the graft, which minimizes the risk of graft failure.

ISSLS PRIZE IN BASIC SCIENCE 2018: Growth differentiation factor-6 attenuated pro-inflammatory molecular changes in the rabbit anular-puncture model and degenerated disc-induced pain generation in the rat xenograft radiculopathy model.

PURPOSE: To elucidate the effects of growth differentiation factor-6 (GDF6) on: (i) gene expression of inflammatory/pain-related molecules and structural integrity in the rabbit intervertebral disc (IVD) degeneration model, and (ii) sensory dysfunction and changes in pain-marker expression in dorsal nerve ganglia (DRGs) in the rat xenograft radiculopathy model. METHODS: Forty-six adolescent rabbits received anular-puncture in two non-consecutive lumbar IVDs. Four weeks later, phosphate-buffered saline (PBS) or GDF6 (1, 10 or 100 µg) was injected into the nucleus pulposus (NP) of punctured discs and followed for 4 weeks for gene expression analysis and 12 weeks for structural analyses. For pain assessment, eight rabbits were sacrificed at 4 weeks post-injection and NP tissues of injected discs were transplanted onto L5 DRGs of 16 nude rats to examine mechanical allodynia. The rat DRGs were analyzed immunohistochemically. RESULTS: In GDF6-treated rabbit NPs, gene expressions of interleukin-6, tumor necrosis factor-α, vascular endothelial growth factor, prostaglandin-endoperoxide synthase 2, and nerve growth factor were significantly lower than those in the PBS group. GDF6 injections resulted in partial restoration of disc height and improvement of MRI disc degeneration grades with statistical significance in rabbit structural analyses. Allodynia induced by xenograft transplantation of rabbit degenerated NPs onto rat DRGs was significantly reduced by GDF6 injection. Staining intensities for ionized calcium-binding adaptor molecule-1 and calcitonin gene-related peptide in rat DRGs of the GDF6 group were significantly lower than those of the PBS group. CONCLUSION: GDF6 injection may change the pathological status of degenerative discs and attenuate degenerated IVD-induced pain.

Dynamic 3-Dimensional Mapping of Isometric Anterior Cruciate Ligament Attachment Sites on the Tibia and Femur: Is Anatomic Also Isometric?

PURPOSE: The purpose of this study was to (1) map the length changes of the medial wall of the lateral femoral condyle (MWLFC) with respect to various points about the tibial anterior cruciate ligament (ACL) footprint to determine the area that demonstrates the least amount of length change through full range of motion and (2) to identify a range of flexion that would be favorable for graft tensioning. METHODS: Six fresh-frozen cadaveric knees were obtained from screened individuals with no prior history of arthritis, cancer, surgery, or any ligamentous knee injury. For each knee, 3-dimensional computed tomography point-cloud models were obtained in succession from 0° to 135°. A point grid was placed on the MWLFC and the tibia. Intra-articular length was calculated for each point on the femur to the tibia at all flexion angles and grouped to represent areas for bone tunnels. Normalized length changes were compared. RESULTS: Areas anterior/distal on the MWLFC increased with increasing flexion, and areas proximal/posterior decreased with increasing flexion. The area about the intersection of the lateral intercondylar ridge and the bifurcate ridge was most isometric throughout flexion as no significant change in ligament length was found throughout flexion. The normalized length changes from the central position of the tibia showed no significant difference compared with the anterior or posterior tibial position. CONCLUSIONS: No area of the MWLFC is truly isometric through flexion. Femoral tunnel placement slightly anterior to the center of the anteromedial and posterolateral bundles was most isometric. Minimal length change occurs between 10° and 40°, which reflects the range where graft tensioning was most often performed. The results of this study provide further support for an anatomic ACL reconstruction. CLINICAL RELEVANCE: The femoral tunnel location for ACL reconstruction with the least amount of length change through range of motion should encompass the direct fibers of the ACL.

Topographic Matching of Osteochondral Allograft Transplantation Using Lateral Femoral Condyle for the Treatment of Medial Femoral Condyle Lesions: A Computer-Simulated Model Study.

PURPOSE: The purpose of this study was to determine whether lateral femoral condyle (LFC) osteochondral allografts (OCAs) would have a similar articular cartilage contour and resulting subchondral bone contour when compared with medial femoral condyle (MFC) allografts for the treatment of MFC chondral defects. METHODS: In this controlled laboratory study, human femoral hemi-condyles (10 MFCs and 8 LFCs) were divided into 4 groups: MFC recipient, MFC donor, ipsilateral LFC donor, and contralateral LFC donor. Computed tomography (CT) images were obtained for each, and 3D CT models were created and exported into point-cloud models. Three circular defect and graft models were created on each condyle at 3 locations (0°, 45° posterior, and 90° posterior regions). The graft model in each donor group was virtually placed on the MFC recipient defect model. The least distances of the articular cartilage surface between the graft and the defect models and the resulting mean least distance of the subchondral bone surface were calculated. RESULTS: The mean least distance of the articular cartilage surface was less than 0.5 mm in all donor-recipients, and there was no significant difference among donor groups. Although the mean least distance of the subchondral bone surface was significantly greater than the articular cartilage surface in all donor groups (P < .001), there was no significant difference among donor groups. CONCLUSION: Ipsilateral and contralateral LFC grafts provided similar articular cartilage surface and resulting subchondral bone surface matching with that of MFC grafts, suggesting that LFCs could be a potential source of OCA for the treatment of MFC lesions. CLINICAL RELEVANCE: Ipsilateral and contralateral LFCs can be suitable donor sites for the treatment of MFC lesions with OCAs.

Which salvage fixation technique is best for the failed initial screw fixation at the cervicothoracic junction? A biomechanical comparison study.

PURPOSE: The pedicle screw construct is the most widely used technique for instrumentation at cervicothoracic junction (CTJ) because of its high biomechanical stability. However, we may need salvage fixation options for it as there might be a situation when pedicle screw is not available or it initially fails in order to obviate the need to instrument an additional motion segment. We aimed to evaluate the ability of using salvage screw fixations at CTJ (C7, T1, T2), when the initial fixation method fails. METHODS: Fifteen fresh-frozen cadaveric specimens (C7-T2) were tested for pull-out strength (POS, N) and insertion torque (IT, Nm) of three C7 fixation techniques (lateral mass, pedicle and laminar screw) and three upper thoracic spine instrumentation (pedicle screws with straight trajectory, anatomical trajectory pedicle screws and laminar screw). Data are shown as mean ± standard deviation (SD). RESULTS: C7 pedicle screws generated statistically greater IT and POS than other C7 fixation techniques (P < 0.05). Similar trends were observed with pedicle fixation as a salvage procedure (P < 0.05). Laminar screws yielded significantly higher POS values than lateral mass fixation when applied as a salvage C7 fixation (mean POS: lateral mass screw-299.4 ± 173.8 N, laminar screw-629.3 ± 216.1, P = 0.013). Significant relationship was established between IT and POS for all screws using Pearson correlation coefficient analysis (r = 0.624, P < 0.01). Pedicle screw with different trajectory (anatomical vs straightforward) did not show any significant difference in terms of POS as the initial and salvage fixation of upper thoracic spine. As a salvage fixation technique, there was no significant difference between laminar screw and a pedicle screw with different trajectory (P > 0.05). CONCLUSION: Laminar screws appear to provide stronger and more reproducible salvage fixation than lateral mass screws for C7 fixation, if pedicle screw should fail. If failure of initial pedicle screw is verified at the upper thoracic spine, both laminar screw and pedicle screw with different trajectory could be an option of salvage fixation. Our results suggest that pedicle screws and laminar screw similarly provide a strong fixation for salvage applications in the cervicothoracic junction.

Three-dimensional micro-computed tomography analysis for spinal instability after lumbar facetectomy in the rat.

PURPOSE: Intervertebral disc degeneration is thought to contribute to low back pain. However, the pathophysiological mechanisms remain controversial. In a previous study, we developed an animal model that showed delayed gait disturbance after lumbar facetectomy in the rat. We believe that this gait disturbance was caused by low back pain, although the mechanisms of this gait abnormality remain unknown. The purpose of this study was to evaluate structural changes of the lumbar spine after facetectomy in the rat utilizing three-dimensional micro-computed tomography (3DµCT) compared to histology. METHODS: Thirty male SD rats were divided into three groups. In the Sham group (n = 13), only exposure of bilateral facet joints at the L4-5 level was performed. In the Experimental group (n = 13), complete resection of bilateral L4-5 facet joints was achieved. Naïve rats (n = 4) were used for controls. At 7-week postoperative, 3DµCT and histological analyses were performed. RESULTS: On 3DµCT images, increased disc height and endplate irregularities at the L4-5 segment and decreased disc height at adjacent segments were observed in the Experimental group. Histological scores were also higher in the Experimental group than the Sham Group. CONCLUSIONS: Degenerative changes were observed at the facetectomy level. These may correspond with the previously reported delayed gait disturbance after facetectomy. This animal model may be useful to create mechanically induced disc degeneration without direct tissue damage to the disc.

Spatial geometric and magnetic resonance signal intensity changes with advancing stages of nucleus pulposus degeneration.

BACKGROUND: With advancing stages of degeneration, denaturation and degradation of proteoglycans in the nucleus pulposus (NP) lead to tissue dehydration and signal intensity loss on T2-weighted MR images. Pfirrmann grading is widely used for grading degeneration of intervertebral discs (IVDs). The criterion to differentiate IVDs of Pfirrmann Grade I from the other grades is NP homogeneity. Pfirrmann grading is qualitative and its assessment may be subjective. Therefore, assessment of quantitative objective measures correlating with early disc degeneration may complement the grading. This study aimed to evaluate the applicability of the distance between the center weighted by signal intensity (weighted center) and the geometric center as a parameter of NP homogeneity. Other phenomena related to advancing stages of degeneration were also investigated. METHODS: MR images of 65 asymptomatic volunteers with a total of 288 lumbar IVDs with clearly identifiable nucleus pulposus boundary (Pfirrmann Grade I, II and III) were included in this study. A custom-written program was developed to determine the IVD longitudinal axis, define the NP boundary, and to locate the coordinates of geometric and weighted NP centers on the mid-sagittal image of each studied IVD. The distances between the weighted and geometric centers on the longitudinal axis and the perpendicular axis of each IVD were calculated. RESULTS: The weighted center located posterior to the geometric center, which indicated the signal intensity was lower at the anterior portion of the NP, in 85.8% of studied IVDs. The distance between the weighted and geometric center on the longitudinal axis was significantly shorter in homogeneous (Pfirrmann Grade I) than in inhomogeneous (Grade II) IVDs. The distance on the perpendicular axis in Grade III IVDs was significantly larger than that in Grade I and Grade II IVDs. CONCLUSION: The relationship between the weighted and geometric centers can serve as an indicator for NP homogeneity. The distance between both centers through advancing stages of degeneration demonstrated decrease of signal intensity progressing along the longitudinal axis initially and then along the cranio-caudal direction at later stages. These findings could provide insights of initiation and subsequent progression of degenerative changes in IVDs.

Optimization of Anteromedial Portal Femoral Tunnel Drilling With Flexible and Straight Reamers in Anterior Cruciate Ligament Reconstruction: A Cadaveric 3-Dimensional Computed Tomography Analysis.

PURPOSE: To use 3-dimensional custom CAD technology to evaluate how knee flexion angle affects femoral tunnel length and distance to the posterior wall when using curved and straight guides for drilling through the anteromedial portal (AMP). METHODS: Six cadaveric knees were placed in an external fixator at various degrees of flexion (90°, 110°, 125°, and maximum 135° to 140°). Computed tomography scans were obtained at all flexion points for 3-dimensional point-cloud models. Using custom CAD software, surgical guides through the AMP were replicated along with virtual tunnels at each flexion angle. Distance from the posterior cortex and tunnel dimensions were collected after 8-mm and 10-mm tunnel creation. RESULTS: At 90° of flexion, the average tunnel length down the posterior aspect of 8-mm tunnel was 25.0 mm (95% confidence interval [CI] 16.2-33.8) and 12.0 mm (95% CI 7.3-16.7) for curved and straight guides, respectively; 31.0 mm (95% CI 26.8-35.2) and 28.6 mm (95% CI 24.8-32.4) at 110°; 33.8 mm (95% CI 30.1-37.5) and 31.1 mm (95% CI 26.8-35.4) at 125°; and 35.0 mm (95% CI 34.1-35.9) and 35.5 mm (95% CI 34.2-36.8) with maximal flexion. Values between curved and straight guides are significantly different (P < .001), with straight guides breaching the posterior wall at 90° and 110° of flexion in some specimens. The average distance to the posterior wall cortex was 0.9 mm (95% CI -1.5 to 3.3) and -0.6 mm (95% CI -2.3 to 1.1) for curved and straight guides, respectively, at 90° of flexion (P = .014); 2.3 mm (95% CI -0.2 to 4.8) and -0.1 mm (95% CI -2.4 to 2.2) at 110° (P = .001); 4.4 mm (95% CI 2.8-6.0) and 3.9 mm (95% CI 1.9-5.9) at 125° (P = .299); and 6.7 mm (95% CI 6.2-7.2) and 8.3 mm (95% CI 6.1-10.5) at maximal flexion (P = .184). Posterior wall blowout was noted when using 10-mm straight guides at both 90° (2 specimens) and 110° (3 specimens). Using 10-mm curved guides posterior blowout was noted in 1 specimen at 90°. Maximum footprint coverage occurred at 110° for straight guides and 90° for curved guides. CONCLUSIONS: When using the AMP, flexible guides and reamers result in a greater distance of the tunnel to the femoral cortex while preserving adequate tunnel length at lower knee flexion angles. To create long femoral tunnels without breaching the posterior cortex, the knee should be flexed to at least 110° for curved reamers and 125° for straight. CLINICAL RELEVANCE: Femoral tunnel drilling through the AMP using curved and straight reamers requires different degrees of knee flexion to achieve optimal tunnel dimensions.