Muscle synergies for the control of single-limb stance with and without visual information in young individuals.

PURPOSE: Single-limb stance is a demanding postural task featuring a high number of daily living and sporting activities. Thus, it is widely used for training and rehabilitation, as well as for balance assessment. Muscle activations around single joints have been previously described, however, it is not known which are the muscle synergies used to control posture and how they change between conditions of normal and lack of visual information. METHODS: Twenty-two healthy young participants were asked to perform a 30 s single-limb stance task in open-eyes and closed-eyes condition while standing on a force platform with the dominant limb. Muscle synergies were extracted from the electromyographical recordings of 13 muscles of the lower limb, hip, and back. The optimal number of synergies, together with the average recruitment level and balance control strategies were analyzed and compared between the open- and the closed-eyes condition. RESULTS: Four major muscle synergies, two ankle-dominant synergies, one knee-dominant synergy, and one hip/back-dominant synergy were found. No differences between open- and closed-eyes conditions were found for the recruitment level, except for the hip/back synergy, which significantly decreased (p = 0.02) in the closed-eyes compared to the open-eyes condition. A significant increase (p = 0.03) of the ankle balance strategy was found in the closed-eyes compared to the open-eyes condition. CONCLUSION: In healthy young individuals, single-limb stance is featured by four major synergies, both in open- and closed-eyes condition. Future studies should investigate muscle synergies in participants with other age groups, as well as pathological conditions.

Migration of the femoral component and clinical outcomes after total knee replacement: a narrative review.

Loosening is considered as a main cause of implant failure in total knee replacement (TKR). Among the predictive signs of loosening, migration is the most investigated quantitative parameter. Several studies focused on the migration of the tibial component in TKR, while no reviews have been focused on the migration of the femoral component and its influence on patients' clinical outcomes. The aim of this narrative review was (1) to provide information about of the influence of migration in femoral component of TKR prostheses, (2) to assess how migration may affect patient clinical outcomes and (3) to present alternative solution to the standard cobalt-chrome prostheses. A database search was performed on PubMed Central® according to the PRISMA guidelines for studies about Cobalt-Chrome femoral component migration in people that underwent primary TKR published until May 2020. Overall, 18 articles matched the selection criteria and were included in the study. Few studies investigated the femoral component through the migration, and no clear migration causes emerged. The Roentgen Stereophotogrammetric Analysis has been mostly used to assess the migration for prognostic predictions. An annual migration of 0.10 mm seems compatible with good long-term performance and good clinical and functional outcomes. An alternative solution to cobalt-chrome prostheses is represented by femoral component in PEEK material, although no clinical evaluations have been carried out on humans yet. Further studies are needed to investigate the migration of the femoral component in relation to clinical outcomes and material used.

Two different posterior-stabilized mobile-bearing TKA designs: navigator evaluation of intraoperative kinematic differences.

PURPOSE: The purpose of this study was to compare two types of posterior-stabilized (PS) mobile-bearing (MB) total knee arthroplasties (TKAs). The hypothesis was that no major differences were going to be found among the two TKA designs. METHODS: Two cohorts of patients who were divided according to implant design (Cohort A, new design gradually reducing radius PS MB TKA; Cohort B, traditional dual-radius PS MB TKA) were analyzed by means of intraoperative navigation. All operations were guided by a non-image-based navigation system that recorded relative femoral and tibial positions in native and implanted knees during the following kinematic tests: passive range of motion (PROM), varus-valgus stress test at 0° and 30° (VV0, VV30) and anterior/posterior drawer test at 90° of flexion (AP90). RESULTS: There were no significative differences in kinematic tests between the two implants. Cohort A, however, showed a different post-implant trend for VV0 and VV30 that were lower than the pre-implant ones, as expected, while for Cohort B, the trend is opposite. However, the gradually reducing radius prosthesis (Cohort A) showed a trend of improving stability (29% compared to the preoperative status) in mid-flexion (VV30) which the traditional dual-radius design (Cohort B) would not. Moreover, we found no differences among postoperative results of the two TKA designs. CONCLUSION: Despite design variations, no difference has been found among the prostheses in terms of PROM, rotations and translations. Both design kinematics did not show paradoxical external rotations, but an increase in femoral translation in mid-flexion without affecting the functioning of the prosthesis. LEVEL OF EVIDENCE: II.

Instrumented platforms for balance and proprioceptive assessment in patients with total knee replacement: A systematic review and meta-analysis.

BACKGROUND: The functional outcome of total knee replacement (TKR) is usually satisfying. However, patients may show functional limitations for years after surgery, which have been ascribed to impairments in balance and proprioception, mainly during standing tasks. A number of instrumentations and parameters have been used, rising confusion for clinical decisions on the assessment of patients. RESEARCH QUESTION: Which are the most widespread and consistent procedures to assess balance and proprioception following TKR? METHODS: A literature review was conducted in Pubmed, PEDro, and Cochrane database. From a total sample of 112 articles, 23 original studies published between 2008 and 2019 met inclusion criteria. The primary outcomes selected were variables related to balance and proprioception assessment in static and dynamic tasks performed with instrumented platforms. Data from papers using the same instrumentation, on patients with unilateral TKA and at least 12 months postoperatively were synthesized quantitatively in a random effect meta-analysis. RESULTS: Fourteen articles were appropriate for the review. A large variability was found both in the instrumentation and the parameters used. The Neurocom Balance Master System™ was the most used instrument (four articles). On a total population of 186 patients with unilateral TKR 12 months postoperatively, a low degree of heterogeneity was found adopting the random effect in the four tasks explored (Firm and Foam Surface both with Eyes Open and Eyes Closed). SIGNIFICANCE: This review found a large variability in the instrumentation used to assess balance and proprioception in patients operated on TKR. The meta-analysis demonstrated that the Neurocom Balance Master System™ for static assessment of balance showed an acceptable consistency and can be considered as a reference for further studies. However, balance and proprioception impairments following TKR have not been widely quantified by means of instrumented platforms. Further research is needed to address this issue, and improve clinical practice.

Virtual simulation of an osseointegrated trans-humeral prosthesis: A falling scenario.

INTRODUCTION: Traditional prosthetic solutions expose the amputee to numerous problems that limit his ability to safely perform the normal activities of daily life. In order to eliminate the problems related to the use of the traditional prosthesis with socket, a new technique was developed for fixing the prosthesis to the amputees based on the principle of osseointegration. The aim of this paper is to study and analyze the stress distribution on the interface between a trans-humeral osseointegrated prosthetic implant and the residual bone, identifying the most stressed areas and thus foreseeing possible failure phenomena of the entire prosthetic system and, after, to compare the stress distribution on three different prosthetic designs that differ from each other for some geometric characteristics. MATERIALS AND METHODS: A healthy individual mimics two fall scenarios of which the trans-humeral amputees can most likely be victims: Static fall and Dynamic fall. A force platform (P-6000, BTS Bioengineering) is required for load data acquisition. The CAD model of the trans-humeral osseointegrated implant was created following the guidelines of the OPRA implant. The bone model was created starting from the CAT scan of a left humerus. The FEM simulation was conducted throught a linear analysis. RESULTS: Both during static fall and dynamic fall, similar trends have been observed for the reaction force Fz, the torque moment Tz, the bending moments Mx and My. From the analysis of the von Mises stress distribution it was found that the stress distribution is more homogeneous in the case where the thread of the fixture is made by a triangular profile with height of the thread equal to 0.5 mm. However, it can be seen that, when passing from a thread with height of 0.5 mm to a 1 mm, there is a slight decrease in the stress on the whole contact zone between the fixture and the humerus. The same improvement can also be seen in the case of trapezoidal threading. CONCLUSION: By modifying the height and/or by varying the thread profile, are obtained slightly better results with respect to the case with a 0.5 mm height triangular thread.

How cartilage status can be related to joint loads in anterior cruciate ligament reconstruction: a preliminary analysis including MRI t2 mapping and joint biomechanics.

The knee is the largest and most complex joint in the human body. Traumatic events, such as anterior cruciate ligament (ACL) tear, can lead to an alteration of joint tissues homeostasis. Literature reports an evident correlation between abnormal joint biomechanics and the status of articular tissues. These alterations, due to a sub-optimal ACL reconstruction, may result in an increasing risk of developing degenerative pathologies, such as osteoarthritis. Thus, the identification of the optimal surgical technique is a highly demanding issue in ACL reconstruction. The aim of this study was to analyze the correlation between joint cartilage conditions and knee biomechanics in ACL reconstructions, by integrating MRI T2 mapping investigations, radiostereophotogrammetry-based gait analysis and subject-specific musculoskeletal modelling.

Total knee replacement: intraoperative and postoperative kinematic assessment.

BACKGROUND AND AIM: The main goals of the total knee arthroplasty (TKA) is to reduce the perceived pain and  restore knee mobility and function in case of osteoarthritic knees joints. Literature shows how the three major causes of TKA failures are related to wear, loosening and instability and this is due to a problem of imbalance and malalignment. Intraoperative and postoperative kinematics analysis could be of benefit for improving surgery outcome. The aim of the present paper is to give an overview of the two set-up with the highest accuracy for intraoperative and postoperative TKA kinematics evaluation, currently in use at Istituto Ortopedico Rizzoli. Introperative and Postoperative Evaluation: For intraoperative evaluation it has been presented a navigation system with a specifically developed software, while for the postoperative it has been presented the roentgen stereophotogrammetric analysis (RSA). The navigation system consists in a laptop connected with an optoelectronic localizer (Polaris, Northern Digital Inc, Canada).  Two reference arrays with passive optical markers and a marked probe are used to localize the knee joint in the 3D space and track the joint kinematics. The RSA is a radiographic technique used in orthopaedic field for measuring micromotion at bone/prosthesis interface or for joint kinematics evaluation. The RSA uses two X-ray sources synchronized with two digital flat-panels. CONCLUSIONS: The present paper shows that using the navigation system allows the surgeon to easily perform kinematic and alignment evaluation during TKA surgery while the RSA allows a quantitative evaluation of the joint kinematics during the recovery time.

Kinematics of ACL and anterolateral ligament. Part I: Combined lesion.

PURPOSE: To quantify the influence of ALL lesions on static and dynamic laxity in ACL-deficient knee. METHODS: The study was performed in 10 fresh-frozen knees. The joints were analysed in the following conditions: intact, ACL resection and ACL + ALL resection. Testing parameters were defined as: anterior displacement at 30° and 90° of flexion (AP30, AP90) applying a manual-maximum load; internal rotation at 30° and 90° of flexion (INT30, INT90) applying a 5 N m torque and internal rotation and acceleration during manual pivot-shift (PS) test. Kinematics was acquired by a navigation system; a testing rig and a torquemeter were used to control the limb position and the applied torque. Paired Student's t test was conducted to assess statistical difference, and significance was set at P < 0.05. RESULTS: The ALL resection determined a significant increase in terms of internal rotation (INT30 P = 0.02, INT90 P = 0.03), while AP30 (P n.s) and AP90 (P n.s) were not affected. ALL resection produced a significant increase in terms of acceleration during PS test (P < 0.01), but no significant change in PS internal rotation was observed. CONCLUSION: The ALL plays a significant role in controlling static internal rotation and acceleration during PS test. On the other hand, ALL resection did not produce any significant change in terms of anterior displacement. A trend was seen for the internal rotation during the pivot-shift test to increase after ALL resection was higher when compared to the intact and isolated ACL lesion states; however, the differences were not significant. The results highlight the clinical relevance of this structure that should be assessed before an ACL reconstruction in order to avoid residual laxity.

Technical variables of ACL surgical reconstruction: effect on post-operative static laxity and clinical implication.

PURPOSE: The hypothesis was that an alteration of different surgical variables of ACL reconstruction would produce significant changes in post-operative static laxity of knee joint. METHODS: Joint laxity was acquired by a surgical navigation system for 17 patients just after graft fixation during single-bundle reconstruction with extra-articular lateral tenodesis. The analysed laxity parameters were: internal/external rotation at 30° (IE30) and 90° (IE90) of flexion, varus/valgus rotation at 0° (VV0) and 30° (VV30) of flexion and anterior/posterior displacement at 30° (AP30) and 90° (AP90) of flexion. As surgical variables, the angles between the tibial tunnel and the three planes were defined as well as the lengths of the tunnel and the relationship between native footprints and tunnels. The same analysis was performed for the femoral side. All surgical variables were combined in a multivariate analysis to assess for predictive factors between them and post-operative laxities values. To quantify the performance of each multivariate model, the correlation ratio (η 2) and the corresponding P value (*P < 0.050) have been evaluated. RESULTS: Multivariate analysis underlined statistically significant models for the estimation of: AP30 (η 2 = 0.987; P = 0.014), IE30 (η 2 = 0.995; P = 0.005), IE90 (η 2 = 0.568; P = 0.010), VV0 (η 2 = 0.932; P = 0.003). The parameters that greatly affected the identified models were the orientation of the tibial tunnel with respect to the three anatomical planes. The estimation of AP30, IE30 and IE90 got lower value as the orientation of the tibial tunnel with respect to transverse plane decreases. Considering the orientation to sagittal ([Formula: see text]) and coronal ([Formula: see text]) plane, we found that their reduction provoked a decrease in the estimation of AP30, IE30 and IE90 (except [Formula: see text] that did not appear in the estimation of AP30). The estimation of VV0 got an increase of [Formula: see text], and [Formula: see text] which led to a laxity reduction. CONCLUSION: The main finding of the present in vivo study was the possibility to determine significant effects on post-operative static laxity level of different surgical variables of ACL reconstruction. In particular, the present study defined the conditions that minimize the different aspects of post-operative laxity at time-zero after surgery.

Does meniscus removal affect ACL-deficient knee laxity? An in vivo study.

PURPOSE: The purpose of the present study was to determine, in vivo, the effect of different types of meniscectomy on an ACL-deficient knee. METHODS: Using a computer-assisted navigation system, 56 consecutive patients (45 men and 11 women) were subjected to a biomechanical testing with Lachman test (AP30), drawer test (AP90), internal/external rotation test, varus/valgus rotation test and pivot-shift test. The patients were divided into three groups according to the status of the medial meniscus. Group BH, 8 patients with bucket-handle tear of medial meniscus underwent a subtotal meniscectomy; Group PHB, 19 patients with posterior horn body of medial meniscus tear underwent a partial meniscectomy; and Group CG with isolated ACL rupture, as a control group, with 29 patients. RESULTS: A significant difference in anterior tibial translation was seen at 30 grades and in 90 grades between BH and PHB groups compared to the CG. In response to pivot-shift test, no significant differences in terms of AREA and POSTERIOR ACC were found among the three groups (n.s). Concerning the anterior displacement of the pivot shift a statistically significant differences among the three tested groups was found. CONCLUSION: The present study shows that meniscal defects significantly affect the kinematics of an ACL-deficient knee in terms of anterior tibial translation under static and dynamic testing.

DOES TOTAL KNEE REPLACEMENT MODIFY FLEXION AXIS OF THE KNEE ON FRONTAL AND AXIAL PLANE REGARDLESS FROM LIMB ALIGNMENT?

The optimal reference for rotational positioning of femoral component in total knee replacement (TKR) is debated. Navigation has been suggested for intra-op acquisition of patient’s specific kinematics and functional flexion axis (FFA). The main purpose of the present study is to prospectively investigate whether pre-operative FFA in patients with osteoarthritis (OA) and varus alignment changes after TKR and whether a correlation exists between post-op FFA and pre-op alignment. A navigated TKR was performed in 108 patients using a specific software to acquire passive joint kinematics before and after TKR. The knee was cycled through three passive range of motions (PROM), from 0° to 120°. FFA was computed using the mean helical axis algorithm. The angle between FFA and surgical TEA was determined on frontal (αf) and axial (αa) plane. The pre- and post-op hip-knee-ankle angle (HKA) was determined. Post-op FFA was different from pre-op FFA only on frontal plane. No significant difference was found on axial plane. No correlation was found between HKA-pre and αA-pre. A significant correlation was found between HKA-pre and αF–pre. The study concluded that TKR modifies FFA only on frontal plane. No difference was found on axial plane. Pre-op FFA is in a more varus position respect to TEA. The position of FFA on frontal plane is dependent on limb alignment. The present study has demonstrated TKR modifies the position of FFA only on frontal plane. The position of FFA on axial plane is not dependent on the amount of varus deformity and is not influenced by TKR. Level of evidence, IV, case series.

Return to sport after anterior cruciate ligament reconstruction in professional soccer players.

BACKGROUND: To investigate time to return to sport and rate of professional sport activity in a homogenous group of competitive soccer players 4 years after anterior cruciate ligament (ACL) reconstruction and rehabilitation. METHODS: Twenty-one male professional soccer players (mean age 22.9±5.4 years) underwent non-anatomical double-bundle autologous hamstring ACL reconstruction and followed the same rehabilitative protocol. Clinical evaluation was performed preoperatively and at 3, 6 and 12-month follow-up. Data regarding return to train and official match, sport activity, complications and revision surgeries were collected at 4-year follow-up. RESULTS: Laxity test (KT-2000) and total KOOS mean score resulted in a significant improvement from the preoperative status to the 12-month follow-up (p<0.0001). The KOOS mean value showed a significant progressive improvement from the preoperative status to 6-month follow-up (p=0.0010) as well, while values collected at 6 and 12-month follow-up were comparable (p=0.2349). Returned to official matches 186±53 days after surgery. After 12 months, 95% came back to the same activity level performed before injury. Four years after ACL reconstruction, 15 patients (71%) were still playing competitive soccer. One patient (5%) underwent ACL failure and subsequent revision. CONCLUSIONS: The ACL reconstruction with the presented technique followed by patient-tailored rehabilitation, allowed 95% and 62% professional male soccer players to return to the same sport activity 1 year and 4 years after surgery respectively. However, 71% were still able to play competitive soccer at final follow-up. Clinical scores were restored after 6 months. LEVEL OF EVIDENCE: IV, case series.

A simulation environment for estimation of the performance of RSA cages.

Roentgen stereophotogrammetric analysis (RSA) is an important technique for in vivo evaluation of joint kinematics and surgical outcome. However, its accuracy is highly affected by the experimental set-up. In this paper we present a new software environment for assessing the impact of calibration cage design on the accuracy of the reconstruction of 3D points, which can be easily used for preliminary evaluations also by non-expert users. The paper presents methods of the simulator and preliminary results in a clinical standard and custom environment. The software was realized using MATLAB and developed for the PC/Windows operating system. It is freeware under request to authors.

Precision assessment of model-based RSA for a total knee prosthesis in a biplanar set-up.

Model-based Roentgen Stereophotogrammetric Analysis (RSA) was recently developed for the measurement of prosthesis micromotion. Its main advantage is that markers do not need to be attached to the implants as traditional marker-based RSA requires. Model-based RSA has only been tested in uniplanar radiographic set-ups. A biplanar set-up would theoretically facilitate the pose estimation algorithm, since radiographic projections would show more different shape features of the implants than in uniplanar images. We tested the precision of model-based RSA and compared it with that of the traditional marker-based method in a biplanar set-up. Micromotions of both tibial and femoral components were measured with both the techniques from double examinations of patients participating in a clinical study. The results showed that in the biplanar set-up model-based RSA presents a homogeneous distribution of precision for all the translation directions, but an inhomogeneous error for rotations, especially internal-external rotation presented higher errors than rotations about the transverse and sagittal axes. Model-based RSA was less precise than the marker-based method, although the differences were not significant for the translations and rotations of the tibial component, with the exception of the internal-external rotations. For both prosthesis components the precisions of model-based RSA were below 0.2 mm for all the translations, and below 0.3 degrees for rotations about transverse and sagittal axes. These values are still acceptable for clinical studies aimed at evaluating total knee prosthesis micromotion. In a biplanar set-up model-based RSA is a valid alternative to traditional marker-based RSA where marking of the prosthesis is an enormous disadvantage.

Micromotion between the half bearings in the interax prosthesis: a roentgen stereophotogrammetric analysis.

We assessed the migration and movement between the half-bearings of the Interax prosthesis in 18 patients using roentgen stereophotogrammetric analysis (RSA). This study showed movements of the tibial component even in successful knee arthroplasty: 17 prostheses migrated only initially and remained stable after 1 year, whereas 1 prosthesis migrated consistently throughout 3-year follow-up. RSA revealed no or minimal displacement between the half-bearings until the 4-year follow-up, confirming that their fixation to the baseplate was adequate. In the case of loosening, a rotation about the longitudinal axis of 1.3 degrees and a medial-lateral translation of 0.5 mm was observed between the half-bearings. Cold flow was revealed by RSA in the posterior region of the medial half-bearing.

The mobility of the proximal tibio-fibular joint. A Roentgen Stereophotogrammetric Analysis on six cadaver specimens.

In six cadaver specimens the mobility of the proximal fibula in relation to the tibia was investigated during plantar/dorsiflexion of the ankle, using Roentgen Stereophotogrammetric Analysis (RSA). The role of the ankle joint, and of the calcaneofibular and talofibular ligaments was also evaluated. The greatest movements were observed along the mediolateral and anterior-posterior axes, resulting in an anterolateral displacement of the fibula head during dorsiflexion and in a postero-medial displacement during plantarflexion. This study demonstrated a limited mobility of the proximal tibiofibular joint. Moreover, the ligament cutting and the presence of constraints in the ankle region did not show any effect on the fibular movement.