Cranio-cervical connection is a well-established biomechanical concept. However, literature of this connection and its impact on cervical alignment is scarce. Chin incidence (CI) is defined as a complementary to the angle between chin tilt (CHT) and C2 slope (C2S) axes. This study aims to investigate the relationship between cervical sagittal alignment parameters and CI with its derivatives. A retrospective cross-sectional study carried out in a tertiary center. CT-neck radiographs of non-orthopedics patients were included. They had no history of spine related symptoms or fractures in cranium or pelvis. Images’ reports were reviewed to exclude those with tumors in the c-spine or anterior triangle of the neck. A total of 80 patients was included with 54% of them were males. The mean of age was 30.96± 6.03. Models of predictability for c2-c7 cobb's angle (CA) and C2-C7 sagittal vertical axis (SVA) using C2S, CHT, and CI were significant and consistent r20.585 (f(df3,76) =35.65, P ≤0.0001, r=0.764), r20.474 (f(df2,77) =32.98, P ≤0.0001, r=-0.550), respectively. In addition, several positive significant correlations were detected in our model in relation to sagittal alignment parameters. Nonetheless, models of predictability for CA and SVA in relation to neck tilt (NT), T1 slope (T1S) and thoracic inlet axis (TIA) were less consistent and had a significant marginally weaker attributable effect on CA, however, no significant effect was found on SVA r20.406 (f(df1,78) =53.39, P ≤0.0001, r=0.620), r20.070 (f(df3,76) =1.904, P 0.19), respectively. Also, this study shows that obesity and aging are linked to decreased CI which will result in increasing SVA and ultimately decreasing CA. CI model has a more valid attributable effect on the sagittal alignment in comparison to TIA model. Future investigations factoring this parameter might enlighten its linkage to many cervical spine diseases or post-op complications (i.e., trismus)

Cervical spine facet tropism (CFT) defined as the facets’ joints angles difference between right and left sides of more than 7 degrees. This study aims to investigate the relationship between cervical sagittal alignment parameters and cervical spine facets’ tropism. A retrospective cross-sectional study carried out in a tertiary center where cervical spine magnetic resonance imaging (MRI) radiographs of patients in orthopedics/spine clincs were included. They had no history of spine fractures. Images’ reports were reviewed to exclude those with tumors in the c-spine. A total of 96 patients was included with 63% of them were females. The mean of age was 45.53± 12.82. C2-C7 cobb's angle (CA) and C2-C7 sagittal vertical axis (SVA) means were −2.85±10.68 and 1.51± 0.79, respectively. Facet tropism was found in 98% of the sample in at least one level on either axial or sagittal plane. Axial C 2–3 CFT and sagittal C4-5 were correlated with CA (r=0.246, P 0.043, r= −278, P 0.022), respectively. In addition, C2-C7 sagittal vertical axis (SVA) was moderately correlated with axial c2-3 FT (r= −0.330, P 0.006) Also, several significant correlations were detected in our model Cervical vertebral slopes and CFT at the related level. Nonetheless, high BMI was associated with multi-level and multiplane CFT with higher odd's ratios at the lower levels. This study shows that CFT at higher levels is correlated with increasing CA and decreasing SVA and at lower levels with decreasing CA. Obesity is a risk factor for CFT

Background. Oblique implantable total disc replacements (TDR) have been developed in an attempt to partially resect the anterior longitudinal ligament (ALL), together with additional partial resection of lateral annulus fibres. To date, the literature has not addressed the impact of the TDR oblique implantation on the lumbar spine sagittal alignment. The hypothesis of this study was that TDR at the L4-L5 level does not change the sagittal alignment and the range of motion of the lumbar spine when the implant is placed in accurate position. Methods. Prospective single-center radiological investigation of L4/5 TDR inserted through an oblique approach for the treatment of disc disease. A series of 52 patients with a minimum of 2-year FU after oblique TDR at L4/L5 level was analysed for radiological changes in sagittal alignment and range of motion of the lumbar spine. The total sagittal lumbar lordosis (TSLL), the segmental sagittal lumbar lordosis (SSLL) of the operated level, and the range of motion of the TDR implant were determined in pre- and postoperative functional X-rays. The accuracy of the implant position was also evaluated. Results. A total of 52 patients (mean age, 42.7) were available. There were no revision surgeries for general and/or device-related complications. Only a 28.8% of cases (n=15) showed a satisfactory position. Off-center lateralised implants were the most common misplacements. Axial malrotated TDR accounted for the 28.1% of cases. From 3 to 24 months of FU, differences in range of motion were found in the total L1-S1 flexion, and in the mean range of motion of the implant both improving significantly. TDRs showing unsatisfactory implantation in the radiological studies (71.8%) demonstrated similar lumbar and segmental range of motion in comparison to properly implanted TDRs. Conclusions. Oblique implanted L4/L5 TDR significantly increases total lordosis while retaining segmental lordosis, independently of the accuracy of its intervertebral position. Oblique TDR maintains antero-posterior segmental and total balance in most cases. Further studies should evaluate whether this finding has any implication for the long-term outcome. Level of Evidence. Level III

Background. Using flexible tethering techniques, porcine models of scoliosis have been previously described. These scoliotic curves showed vertebral wedging but very limited axial rotation. In some of these techniques, a persistent scoliotic deformity was found after tether release. The possibility to create severe progressive true scoliosis in a big animal model would be very useful for research purposes, including corrective therapies. Methods. The experimental ethics committee of the main institution provide the approval to conduct the study. Experimental study using a growing porcine model. Unilateral spinal bent rigid tether anchored to two ipsilateral pedicle screws was used to induce scoliosis on eight pigs. Five spinal segments were left between the instrumented pedicles. The spinal tether was removed after 8 weeks. Ten weeks later the animals were sacrificed. Conventional radiographs and 3D CT-scans of the specimens were taken to evaluate changes in the coronal and sagittal alignment of the thoracic spine. Fine-cut CT-scans were used to evaluate vertebral and disc wedging and axial rotation. Results. After 8 weeks of rigid tethering, the mean Cobb angle of the curves was 24.3 ± 13.8 degrees. Once the interpedicular tether was removed, the scoliotic curves progressed in all animals until sacrifice. During these 10 weeks without spinal tethering the mean Cobb angle reached 50.1 ± 27.1 degrees. The sagittal alignment of the thoracic spine showed loss of physiologic kyphosis. Axial rotation ranges from 10 to 35 degrees. There was no auto-correction of the curve in any animal. A further pathologic analysis of the vertebral segments revealed that animals with greater progression had more damage of the neurocentral cartilages and epiphyseal plates at the sites of pedicle screw insertion. Interestingly, in these animals with more severe curves, compensatory curves were found proximal and distal to the tethered segments. Conclusions. Temporary interpedicular tethering at the thoracic spine induces severe scoliotic curves in pigs, with significant wedging and rotation of the vertebral bodies. As detailed by CT morphometric analysis, release of the spinal tether systematically results in progression of the deformity with development of compensatory curves outside the tethered segment. The clinical relevance of this work is that this tether release model will be very useful to evaluate both fusion and non-fusion corrective technologies in future research. Level of Evidence. Not apply for experimental studies

Background. Total Knee Replacement (TKR) is an effective treatment for knee arthritis. One long held principle of TKRs is positioning the components in alignment with the mechanical axis to restore the overall limb alignment to 180 ± 3 degrees. However, this view has been challenged recently. Given the high number of replacements performed, clarity on this integral aspect is necessary. Our objective was to investigate the association between malalignment and outcome (both PROMs and revision) following primary TKR. Metod. A systematic review of MEDLINE, CINHAL, and EMBASE was carried out to identify studies published from 2000 onwards. The study protocol including search strategy can be found on the PROSPERO database for systematic reviews. Results. From a total of 2107 citations, 18 studies, comprising of 2,214 patients, investigated the relationship between malalignment and PROMs. Overall 41 comparisons were made between a malalignment parameter and a PROM. Eleven comparisons (27%) demonstrated an association between malalignment and worse PROMs, with 30 comparisons (73%) demonstrating no association. Eight studies investigated the relationship between malalignment and revision. Four studies found an association between a measure of coronal alignment and revision rate, with four not demonstrating an association. Only one study examined axial and sagittal alignment and found an association with revision rates. Conclusion. When considering malalignment in an individual parameter, there is an inconsistent relationship with outcome. Malalignment may be related to worse outcome, but if that relationship exists it is weak and of dubious clinical significance. However, this evidence is subject to limitations mainly related to the methods of assessing alignment post operatively and by the possibility that the premise of traditional mechanical alignment is erroneous. Larger longitudinal studies with a standardised, timely, and robust method for assessing alignment outcomes are required. Level of evidence. 2a

It is known that excessive varus alignment of the femoral stem in total hip replacement (THR) creates a sub-optimal biomechanical environment which is associated with increased rates of revision surgery and component wear. Little is known regarding the effect of femoral stem alignment on patient functional outcome. Methods. Retrospective study of primary THR patients at the RNOH. Alignment of the femoral stem component in-situ was measured subjectively by a consultant musculoskeletal radiologist in both coronal and sagittal planes using post-operative anterior-posterior and lateral pelvic radiographs. Each THR was grouped into valgus, minor-valgus, neutral, minor-varus or varus coronal plane alignment and posterior, minor-posterior, neutral, minor-anterior or anterior sagittal plane alignment. Patient reported functional outcome was assessed by Oxford Hip Score (OHS) and WOMAC questionnaires. Data analysed using a linear regression model. Results. 90 THRs were studied in 87 patients (55 Female). Mean age at THR=62 (22-86). Mean follow-up=17 months (11-39 months). Median OHS=16, WOMAC=8. Coronal plane alignment of the femoral stem was not associated with any change in OHS (p>0.05) or WOMAC score (p>0.05). Sagittal plane alignment of the femoral stem was not associated with any change in OHS (p>0.05) or WOMAC score (p>0.05). Conclusion. Although it is known that alignment of the femoral stem on sagittal and coronal planes has a direct effect on survivorship of the prosthesis, our study does not demonstrate any relationship between femoral stem alignment and functional outcome in patients undergoing primary THR

Assessment of coronal knee laxity via manual stress testing is commonly performed during joint examination. While it is generally accepted that the knee should be flexed slightly to assess its collateral restraints, the importance of the exact degree of flexion at time of testing has not been documented. The aim of this study therefore was to assess the effect of differing degrees of knee flexion on the magnitude of coronal deflection observed during collateral stress testing. Using non-invasive infrared technology, the real-time coronal and sagittal mechanical femorotibial (MFT) angles of three asymptomatic volunteers were measured. A single examiner, blinded to the real-time display of coronal but not sagittal alignment, held the knee in maximum extension and performed manual varus and valgus stress manoeuvres to a perceived end-point. This sequence was repeated at 5° increments up to 30° of flexion. This provided unstressed, varus and valgus coronal alignment measurements as well as overall envelope of laxity (valgus angle – varus angle) which were subsequently regressed against knee flexion. Regression analysis indicated that all regression coefficients were significantly different to zero (p < 0.001). With increasing knee flexion, valgus MFT angles became more valgus and varus MFT angles became more. The overall laxity of the knee in the coronal plane increased approximately fourfold with 30° of knee flexion. The results demonstrated that small changes in knee flexion could result in significant changes in coronal knee laxity, an observation which has important clinical relevance and applications. For example the assessment of medial collateral ligament (MCL) injuries can be based on the perceived amount of joint opening with no reference made to knee flexion at time of assessment. Therefore, close attention should be paid to the flexion angle of the knee during stress testing in order to achieve a reliable and reproducible assessment

Summary Statement. We present a simple and useful geometrical equation system to carry out the pre-operative planning and intra-operative assessments for total knee arthroplasty. These methods are extremely helpful in severely deformed lower limbs. Introduction. Total knee arthroplasty is a highly successful surgery for most of the patients with knee osteoarthritis. With commercial instruments and jigs, most surgeons can correct the deformity and provided satisfactory results. However, in cases with severe extra-articular deformity, the instruments may mislead surgeons in making judgment of the true mechanical axis. We developed a geometrical equation system for pre-operative planning and intra-operative measurement to perform correct bony cuts and achieve good post-operative axis. Patients & Methods. From 2008 to 2012, twenty-four patients with severe extra-articular deformities of low limbs underwent total knee arthroplasties for osteoarthritis. The deformities included malunion of femoral or tibial shafts with angulation, non-union of femoral supracondylar fractures, failed high tibia osteotomies, severe bowing of femurs, and other post-traumatic sequelae. The intra-medullary or extra-medullary guide devices were not possible to provide correct axis in these cases. For pre-operative planning, we analyzed the deformities on triple-film scanography and standing anterior-posterior and lateral X-ray films. The angles needed to be corrected in coronal and sagittal planes were measured. A geometrical equation system was applied to calculate the thickness of the proximal tibia cut and distal femoral cut. If the flexion contracture was presented, the degree of necessary elevation of joint line was also calculated. Intra-operatively, the degree of rotation of anterior and posterior femoral cuts was assessed after proximal tibial and distal femoral cuts. The sizes of prosthesis were judged according to the balance between flexion and extension gaps. A 3-in-1 jig was used for chamfering of the femur. After fine-tuning of bony cuts and balancing of soft tissue, the prostheses were cemented. The conventional intra-medullary and extra-medullary guiding devices were not used during the whole procedure. Results. All of the patients achieved satisfactory results in the aspect of pain relief and functional outcomes. All patients had good post-operative axis in coronal plane (varus or valgus deformity < 3 degrees). Twenty-two patients (92%) achieved good sagittal alignments (deformity < 3 degrees). The results were compatible with those in the patient population without those severe deformities. There was no major complication among these patients. Discussion/Conclusion. In this series, we present a simple and useful geometrical equation system to carry out the pre-operative planning and intra-operative assessments for total knee arthroplasty. These methods are extremely helpful in severely deformed lower limbs. Optimal post-operative alignments were achieved in this series and no major complication was found

Summary. Computer assisted surgery (CAS) during total knee arthroplasty (TKA) is known to improve prosthetic alignment in coronal and sagittal plane. In this systematic review, no evidence is found that CAS also improves axial component orientation when used during TKA. Introduction. Primary total knee arthroplasty (TKA) is a safe and cost-effective treatment for end-stage knee osteoarthritis. Correct prosthesis alignment is essential, since malpositioning of the prosthesis leads to worse functional outcome and increased wear, which compromises survival of the prosthesis. Computer assisted surgery (CAS) has been developed to enhance prosthesis alignment during TKA. CAS significantly improves postoperative coronal and sagittal alignment compared to conventional TKA. However, the influence of CAS on rotational alignment is a matter of debate. Therefore purpose of this review is to assess published evidence on the influence of CAS during TKA on postoperative rotational alignment. Patients and Methods. This review was performed according to the PRISMA Statement. An electronic literature search was performed in Pubmed, Medline and Embase on studies published between 1991 and April 2013. Studies were included when rotational alignment following imageless CAS-TKA was compared to rotational alignment following conventional TKA. At least one of the following outcome measures had to be assessed: 1) rotational alignment of the femoral component, 2) rotational alignment of the tibial component, 3) tibiofemoral mismatch, 4) the amount of rotational outliers of the femoral component, 5) the amount of rotational outliers of the tibial component. Study selection was performed in two stages and data extraction and methodological quality assessment was conducted independently by two reviewers. Standardized mean difference (SMD) with 95% confidence interval (95% CI) was calculated for continuous variables. The SMDs were interpreted according to Cohen: an SMD of 0.2–0.4 was considered a small effect; 0.5–0.7 was considered moderate; and ≥ 0.8 was considered a large effect. For the comparison of the amount of outliers for femoral and tibial component rotation, the Odds ratio (OR) and 95% CI was calculated. The OR represents the odds of outliers occurring in the CAS group compared with the conventional group. An OR of < 1 favors the CAS group. The OR is considered statistically significant when the 95% CI does not include the value of 1. Results. Seventeen studies met the inclusion criteria. One study was considered of high, 15 studies of medium and one study of low methodological quality. SMD for rotation of the femoral component was −0.07 (−0.19–0.04). For rotation of the tibial component, the SMD was 0.11 (−0.01–0.24). Regarding tibiofemoral mismatch, the SMD was −0.27 (−0.57–0.02). For femoral outliers, the OR was 1.05 (0.78–1.43) and for tibial outliers the OR was 1.12 (0.86–1.47). Discussion / Conclusion. Results of this review show no evidence that CAS-TKA leads to better rotational alignment of the femoral or tibial component or tibiofemoral mismatch. Also no evidence was found that CAS results in a decrease of the amount of outliers regarding femoral or tibial component orientation. However, these conclusions have to be interpreted with caution. The number of included studies was low and strong heterogeneity existed between the studies. Of the 17 included studies, only one study was considered of high methodological quality. Moreover, different methods for assessing tibial component rotation have been used in the studies included

Summary Statement. A prospective randomised evaluation of primary TKA utilizing patient specific instruments demonstrated great accuracy of bone resection, improved sagittal alignment and the potential to improve functional outcomes and reduce operating room costs when compared to standard TKA instrumentation. Introduction. Patient specific instruments (PSI), an alternative to standard total knee arthroplasty (TKA) technology, have been proposed to improve the accuracy of TKA implant placement and post-operative limb alignment. Previous studies have shown mixed results regarding the effectiveness of PSI. The purposes of this study were (1) to evaluate the accuracy of the pre-operative predicted PSI plan compared to intra-operative TKA resection measurements, (2) to compare patient-reported outcome measures of PSI and standard TKA patients, and (3) to compare the incremental cost savings with PSI. Patients and Methods. This randomised, prospective pilot study of 19 patients undergoing primary TKA with a cruciate-retaining cemented prosthesis (NexGen, Zimmer Inc.) was conducted by a single high-volume arthroplasty surgeon (DCA). Patients were randomised to PSI or standard instrumentation. Patients randomised to the PSI cohort received a pre-operative knee MRI for PSI fabrication using Zimmer proprietary software. 10 standard TKA and 9 PSI TKA were completed. Pre-operative baseline SF-36 and WOMAC scores were collected. Operative data collected included operating room times, implant details, femoral (medial/lateral distal and posterior) and tibial (medial/lateral) cut thicknesses, and number of instrument trays used. Hospitalization data collected included length of stay, blood loss, drain output, and transfusion requirements. Follow-up occurred at 2 weeks, 6–8 weeks, 3 months, 6 months, and 1 year, with SF-36 and WOMAC scores collected at each time point. Routine radiographic analysis was carried out in both cohorts. Extensive financial data was collected including costs of operating room use and anesthesia, implants, and hospitalization. Statistical analyses included t-tests for continuous variables and chi-square tests for categorical variables. Results. All femoral and tibial implant sizes used during TKA matched the component sizes predicted by the PSI software. Flexion gap bone resection (posterior medial/lateral femoral cuts) was extremely accurate (<1 mm on average) when compared with PSI predictions. PSI proximal tibial bone resection was also extremely accurate and within 1 mm on average of predicted values. Sagittal plane tibial component posterior slope in PSI TKA was significantly more accurate (7.33 degrees) in comparison to standard instrumentation (4.20 degrees) (p<0.025). No significant differences in coronal mechanical limb alignment existed between the two cohorts (p>0.05). There were no differences in operating room times, length of stay, or transfusions between the two groups. PSI patients used 4 fewer instrument trays per case (p<0.0001). There were no significant differences in functional outcome scores between the two groups (p>0.05). Discussion/Conclusion. PSI TKA demonstrated outstanding accuracy in bone resection when compared with the custom operative plan. There was no difference in post-operative coronal limb alignment or individual component alignment between the two groups, but an improvement in tibial component alignment in the sagittal plane in the PSI cohort was statistically significant. The number of instrument trays in PSI TKA's were significantly less than standard TKA which led to less cost for instrument sterilization and assembly, and quicker room set-up. PSI instrumentation resulted in accurate bone resection and appropriate limb and component alignment after primary TKA in this prospective randomised evaluation

Objectives

Unicompartmental knee arthroplasty (UKA) is a demanding procedure, with tibial component subsidence or pain from high tibial strain being potential causes of revision. The optimal position in terms of load transfer has not been documented for lateral UKA. Our aim was to determine the effect of tibial component position on proximal tibial strain.