Posterior Translation Research Articles

6DOF knee kinematic alterations due to increased load levels.

Whether load carriage leads to six-degrees-of-freedom (6DOF) knee kinematic alterations remains unclear. Exploring this mechanism may reveal meaningful knee kinematic information that can be used to improve load carriage conditions, the design of protective devices, and the knowledge of the effects of load carriage on knees. We recruited 44 subjects to explore kinematic alterations from an unloaded state to 60% bodyweight (BW) load carriage. A three-dimensional gait analysis system was used to collect the knee kinematic data. One-way repeated analysis of variance (ANOVA) was used to explore the effects of load levels on knee kinematics. The effects of increasing load levels on knee kinematics were smooth with decreased or increased trends. We found that knees significantly exhibited increased lateral tibial translation (up to 1.2 mm), knee flexion angle (up to 1.4°), internal tibial rotation (up to 1.3°), and tibial proximal translation (up to 1.0 mm) when they went from an unloaded state to 60%BW load carriage during the stance phase (p < 0.05). Significant small knee adduction/abduction angle and posterior tibial translation alterations (<1°/mm) were also identified (p < 0.05). Load carriage can cause significant 6DOF knee kinematic alterations. The results showed that knee kinematic environments are challenging during increased load. Our results contain kinematic information that could be helpful for knee-protection-related activities, such as target muscle training to reduce abnormal knee kinematics and knee brace design.

Knee Kinematic Patterns and Early Cartilage Lesion Characteristics in Patients with Anterior Cruciate Ligament Reconstruction.

Specific knee kinematic alterations have been theorized to correlate with the progression of cartilage degeneration, and therefore, post-traumatic osteoarthritis in patients with anterior cruciate ligament reconstruction (ACLR). However, how specific knee kinematic alterations contribute to knee joint cartilage degenerations remains to be unclear. To solve this problem, we hypothesized that there are specific cartilage-degenerating kinematic gait patterns that could be supported by the specific areas of cartilage lesions in ACLR knees. Thirty patients with unilateral ACLR knees and 30 healthy controls were recruited for the study. The kinematic differences between the ACLR knees and the healthy control knees during the stance phase were calculated to identify the kinematic patterns. Cartilage lesion distribution characteristics were acquired for patients with ACLR knees to validate the kinematic patterns using magnetic resonance images. Two kinematic patterns were modeled, i.e., sagittal (increased flexion angle and posterior tibial translation) and coronal (increased lateral tibial translation and abduction angle) kinematic patterns. For the sagittal pattern, the cartilage lesion distributions showed that there were more cartilage lesions (CLs) in the superoposterior regions than the posterior regions in the femoral condyles (p = 0.001), and more CLs in the posterior regions than the middle regions in the tibial plateau (p < 0.001). For the coronal pattern, the cartilage lesion distributions showed that there were more CLs in the lateral compartments near the tibial spine than the medial compartments near the tibial spine (tibial sides, p = 0.005 and femoral sides, p = 0.290). To conclude, the cartilage degeneration distribution evidence largely supports that the two kinematic patterns may contribute to cartilage degeneration in ACLR knees. These findings may provide a potential strategy of delaying early cartilage degeneration in ACLR knees by using motion (kinematic) pattern modification or training. However, investigations should be conducted on the actual effects of this potential strategy.

In vivo kinematic comparison of medial pivot total knee arthroplasty in weight-bearing and non-weight-bearing deep knee bending

BackgroundThis study aimed to determine the kinematics of medial pivot total knee arthroplasty by comparing weight-bearing and non-weight-bearing deep knee bending and to evaluate the effect of the weight-bearing state on the kinematics. MethodsThe kinematics of 19 knees were investigated under fluoroscopy during squatting (weight-bearing) and active-assisted knee bending (non-weight-bearing) using two- to three-dimensional registration technique. Accordingly, range of motion, anteroposterior translation for the medial and lateral low contact points, axial rotation of the femoral component relative to the tibial component and kinematic pathway were evaluated. FindingsThere was no difference in range of motion between the two states. The medial anteroposterior translation showed no significant movement with no anterior translation in both the weight-bearing and non-weight-bearing from 0° to 90° of flexion. Regarding the lateral anteroposterior translation, a posterior translation was observed during weight-bearing, whereas a slight anterior translation from 0° to 30° of flexion and subsequent posterior translation were found in the non-weight-bearing. Femoral external rotation was observed in the weight-bearing, whereas femoral internal rotation was seen from 0° to 30° of flexion and subsequent femoral external rotation was observed in the non-weight-bearing. The kinematic pathway showed medial pivot motion and subsequent bicondylar rollback in the weight-bearing, whereas only medial pivot motion was observed in the non-weight-bearing. InterpretationThe medial anteroposterior translation of the femur during deep knee bending showed no anterior motion in the two states. The lateral anteroposterior translation and femoral rotation were different in the mid-flexion range between the two states.

No Difference in Knee Kinematics Between Anterior Cruciate Ligament-First and Posterior Cruciate Ligament-First Fixation During Single-Stage Multiligament Knee Reconstruction: A Biomechanical Study.

Background:For combined reconstruction of both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), there is no consensus regarding which graft should be tensioned and fixed first.Purpose:The purpose of this study was to determine which sequence of graft tensioning and fixation better restores normal knee kinematics. The hypothesis was that ACL-first fixation would more closely restore normal knee kinematics, graft force, and the tibiofemoral orientation in the neutral (resting) position compared with PCL-first fixation.Study Design:Controlled laboratory study.Methods:A total of 15 unpaired human cadaveric knees were examined using a robotic testing system under the following 4 conditions: (1) 89.0-N anterior tibial load at different knee angles; (2) 89.0-N posterior tibial load at different knee angles; (3) combined rotational 7.0-N·m valgus and 5.0-N·m internal rotation load (simulated pivot shift) at 0°, 15°, and 30° of flexion; and (4) 5.0-N·m external rotation load at 0°, 15°, and 30° of flexion. The 4 evaluated knee states were (1) intact ACL and PCL (intact), (2) ACL and PCL deficient (deficient), (3) combined anatomic ACL-PCL reconstruction fixing the ACL first (ACL-first), and (4) combined anatomic ACL-PCL reconstruction fixing the PCL first (PCL-first). A 9.0 mm–diameter quadriceps tendon autograft was used for the ACL graft, tensioned with 40.0 N at 30° of flexion. A 9.5 mm–diameter hamstring tendon autograft (gracilis and semitendinosus, quadrupled loop, and augmented with an additional allograft strand if needed), tensioned with 40.0 N at 90° of flexion, was used for the PCL graft.Results:There were no statistically significant differences between ACL-first and PCL-first fixation regarding knee kinematics. ACL-first fixation restored anterior tibial translation to the intact state at all tested knee angles, while PCL-first fixation showed higher anterior tibial translation than the intact state at 90° of flexion (9.05 ± 3.05 and 5.87 ± 2.40 mm, respectively; P = .018). Neither sequence restored posterior tibial translation to the intact state at 30°, 60°, and 90° of flexion. At 15° of flexion, PCL-first fixation restored posterior tibial translation to the intact state, whereas ACL-first fixation did not.Conclusion:There were no differences in knee laxity between ACL-first and PCL-first fixation with the ACL graft fixed at 30° and the PCL graft fixed at 90°.Clinical Relevance:This study showed that there was no evidence to support the use of one tensioning sequence over the other in single-stage multiligament knee reconstruction.

Effect of the posterior sagging control device to the posterior tibial translation during posterior-stabilized total knee arthroplasty with modified gap technique.

In modern total knee arthroplasty (TKA), flexion and extension gaps between the femur and tibia are equilibrated before implanting the final components. Uncontrolled intraoperative posterior tibial translation (PTT) could cause an artifactual widening of the flexion gap, which could lead surgeons to alter the femoral component size. We designed an intraoperative posterior sagging control device to prevent intraoperative PTT. In this study, we investigated whether the use of this device could prevent artifactual widening of the flexion gap. Twenty-five patients, 21 women and four men, aged 74.2years, were enrolled in this prospective study. All patients underwent postero-stabilized TKA using a navigation system. Intraoperative PTT, flexion and extension gaps with or without using the posterior sagging control device were measured with navigation system. These measurements were compared with or without the posterior sagging control device and after the final implantation also. There were significant differences between the measurements performed with or without the posterior sagging control device when compared to the post-implantation measurements. The use of the device reduced the number of patients with a >3mm increase in flexion gap from 7 (28%) to 1 (4%). This study suggests that the posterior sagging control device prevents PTT and artificial flexion gap widening. This could prevent an unnecessary increase in component size.

ACLD patients exhibit additional knee kinematic asymmetries at the speed level of healthy subjects.

Anterior cruciate ligament deficiency (ACLD) patients tend to walk slowly but try to catch up with the speed level of healthy subjects daily. Exploring the effects of the walking speed level of healthy subjects on the ACLD patients’ knee kinematics is important to improving non-operative treatments and delaying the progression of posttraumatic knee osteoarthritis. This study aimed to explore whether healthy controls’ walking speed level leads to additional knee kinematic asymmetries in patients with ACLD. 27 ACLD patients and 29 healthy controls were recruited for the study. The ACLD patients walked at two levels of walking speed, including self-selected and healthy controls’ walking speed levels. A three-dimensional gait analysis system was used to collect their knee kinematic data. ACLD patients exhibited more kinematic asymmetries when walking at healthy controls’ walking speed level than at their self-selected speeds. The kinematic asymmetries included increased posterior tibial translation (4.6 mm) and anteroposterior tibial ROM (3.9 mm), abduction angle (1.5°), and distal tibial translation (3.2 mm) asymmetries (p < 0.05). Our findings are meaningful for developing non-operative treatment strategies for patients with ACLD. To get fewer knee kinematic asymmetries, self-selected walking speed could be suggested for patients with ACLD daily rather than the speed levels of healthy subjects.

46. Lower limb compensation in the setting of adult spinal deformity

<h3>BACKGROUND CONTEXT</h3> Numerous studies have reported the interplay between spinal deformity and pelvis compensatory mechanisms, but little data exist evaluating the contribution of lower extremity compensation (LE) to maintain upright posture. We hypothesis that hip, knee and ankle compensation is proportional to the severity of the spinal deformity and varies by demographics. <h3>PURPOSE</h3> Evaluate the association between spinal alignment and lower limbs compensation. <h3>STUDY DESIGN/SETTING</h3> Multicenter, prospective cohort. <h3>PATIENT SAMPLE</h3> This study included 288 patients treated for complex adult spinal deformity (ASD) with full body images available. <h3>OUTCOME MEASURES</h3> Pelvic retroversion (PT), hip extension (SFA), knee flexion (KA), ankle dorsiflexion (AA), pelvic translation (P.Shift) and patient reported outcomes (ODI, PROMIS and SRS-22). <h3>METHODS</h3> Surgical ASD patients were enrolled into a prospective study based on three criteria: deformity severity (PI-LL>25°, TPA>30°, SVA>15cm, TCobb>70° or TLCobb>50°), procedure complexity (>12 levels fused, 3CO or ACR) and/or age (>65 and >7 levels fused). Associations between lower extremity compensation (hip extension, knee flexion, and ankle dorsiflexion) and the magnitude of spinal deformity, patient demographics, patient frailty, and patient-reported outcomes (ODI, SRS, PROMIS-CAT) were assessed via regressions and partial correlations. <h3>RESULTS</h3> A total of 288/329 patients met inclusion criteria (60±15yo, 70.5% female), had moderate to severe spinal deformity (PI-LL:15±24, TPA:24±14, SVA:65±69mm, lumbar Cobb:34±24), and reported high pain (PROMIS pain interference; PI=62.7±7.8) and reduced physical function (PROMIS physical function; PF=35.6±7.6). Lower extremity compensation included pelvic retroversion (PT:24.1± 11.8), hip extension (SFA: 203±10.5), knee flexion (KA:5.5± 9.6), ankle dorsiflexion (AA: 5.3±4.5), and posterior pelvic translation (P.Shift: 30±51mm). Overall, lower extremity compensation increased with age (all p <0.001), BMI and frailty (all p <0.001, except SFA). For a similar PT, women had greater hip extension than men (SFA: 206 vs 200, p <0.001), with less KA (3.6 vs. 10.1, p <0.001), AA, and P.Shift. Lower extremity compensation increased with PI (r=0.2-0.45, p <0.001), TPA (r=0.5-0.9, p <0.001) and correlated with PROMS (ODI:0.26 - 0.37, PROMIS PF: -0.28 - -0.39, SRS Acti.: -0.20 - -0.33). When controlling for deformity severity and PI, most associations between lower limbs compensation and PROMS were lost. However, P.Shift and SFA remained weakly correlated with physical scores (ODI and PROMIS PF). <h3>CONCLUSIONS</h3> The recruitment of LE compensation is overall proportional to the severity of adult spinal deformity, with different patterns observed between men and women. Patients achieved similar PT by recruiting different patterns of LE compensation. Hip extension and posterior pelvic translation are independently associated with impairment in patient-reported outcomes. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

31. Quantifying the contribution of lower limb compensation to upright posture: what happens if ASD patients do not compensate?

<h3>BACKGROUND CONTEXT</h3> Adult spinal deformity (ASD) patients maintain upright posture by compensating through their spine, pelvis and lower extremities. Little data exist quantifying the contribution of lower extremity compensation through the hips, knees, and ankles to maintain upright posture. <h3>PURPOSE</h3> Evaluate the effect of the lower limb compensation by numerically unfolding patients. <h3>STUDY DESIGN/SETTING</h3> Multicenter, prospective cohort. <h3>PATIENT SAMPLE</h3> A total of 288 patients surgically treated for complex ASD with preoperative full body images. <h3>OUTCOME MEASURES</h3> Horizontal distance between vertebra centroid and ankle. <h3>METHODS</h3> Surgical ASD patients were enrolled into a prospective study based on three criteria deformity severity (PI-LL>25°, TPA>30°, SVA>15cm, TCobb>70° or TLCobb>50°), procedure complexity (>12 levels fused, 3CO or ACR) and/or age (>65 and >7 levels fused). Preop full-body images were evaluated and age and PI-adjusted normative values were used to model spine alignment based upon three configurations: COMP (all lower extremity compensatory mechanisms maintained), PARTIAL (removal of ankle dorsiflexion and knee flexion, maintained hip extension), UNCOMP (ankle, knee, and hip compensation eliminated by reset PT to the age and PI norms). The three configurations were compared, and COMP alignment was stratified by TPA percentiles to investigate the offsets from each vertebra to the ankle joint acting as a surrogate of the gravity line in free-standing position. <h3>RESULTS</h3> A total of 288 patients met inclusion criteria (60±15yo, 70.5% female, 27.4±5.9 BMI). COMP spine deformity magnitude included PI-LL 15±24, TPA 24±14, and SVA 65±69mm. As the model transitioned from COMP to UNCOMP alignment, the initial posterior translation of the pelvis decreased significantly to an anterior translation vs the ankle (P.Shift 30 to -7.6 mm). This was associated with a decrease in pelvic retroversion (PT 24.1 to 16.1), hip extension (SFA 203 to 200), knee flexion (KA 5.5 to -0.4), and ankle dorsiflexion (AA 5.3 to 3.7). As a result, the anterior malalignment of the trunk significantly increased SVA (65 to 120mm) and G-SVA (C7-Ankle from 36 to 127 mm), leading to a three-fold increase in bending moments sustained by the ankle joint. The stratification of the COMP position by TPA percentiles revealed that as the deformity increases, the vertebrae above T8 translate anteriorly, those below T10 move posteriorly, with the T8-T10 segment remaining ∼3cm posterior to the ankle joint independently of the deformity severity. <h3>CONCLUSIONS</h3> Removal of lower limbs' compensation revealed an unsustainable truncal malalignment with a three-fold increase of bending moments at the ankle joints. Combined, lower limb compensations permit "reducing" the SVA by two-fold and the C7-ankle SVA by three-fold. From a mechanical point of view, this compensation permits maintaining the trunk center of mass (T9) at a fixed offset of ∼3 cm from the ankle joint. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Kneeling Stress Radiography: A Forgotten Yet Dependable Tool for Postero-lateral Knee Instability.

Diagnosing postero-lateral knee instability is a challenge from both clinical and radiologic perspective and can lead to significant morbidity if left untreated. Delayed diagnosis leads to a more demanding surgery and prolonged rehabilitation for the patient. Kneeling stress radiograph is a lost art but remains invaluable in the assessment of postero-lateral knee instability. This prospective observational study is aimed at re-exploring the undeniable utility of this forgotten tool in early diagnosis of posterolateral knee instability and identifying the mean posterior tibial translation distance (PTTD) and also assessing side to side difference (SSD) between the injured and the contralateral normal knee. Total 27 patients were included in the study, with males being 4.4 times more commonly injured as compared to females. The most common mode of injury was motor vehicle accident (MVA). Out of 27 patients, 11 had isolated PCL (posterior cruciate ligament) injury while the rest had PLC (posterolateral corner) involvement. The mean SSD of PTTD was 8.79mm in patient with isolated PCL. This was increased by 1.65 times (14.52mm) in patients with co-existing PLC involvement. Stress radiography is an indelible tool and serves as an adjunct to MRI imaging. It is not a substitute for clinical assessment but assists in early diagnosis and management, facilitating surgical planning and furnishing objective evidence of PCL/PLC functionality which is not possible with any other imaging modality.

Determine the vertical ground reaction forces and knee mechanics with different gait inclinations in the sheep model.

Our current understanding of knee mechanics and anterior cruciate ligament (ACL) function is predominately based on data recorded during simulations of clinical examinations or the application of nonphysiologic loads and motions. These methodologies provide little information on knee and ACL mechanics during activities of daily living (ADLs). Additionally, researchers have not directly measured knee kinetics, knee contact pressures, and ACL forces, and it is unknown how these parameters change with different activities. This study quantified the effects of activity level on vertical ground reaction forces, knee kinematics, and joint and ligament forces during in vivo motions. Five female Suffolk sheep were walked twice weekly on a treadmill during level (0°), inclined (+6°), and declined (-6°) gait for 12 weeks. Electromagnetic (EM) trackers were surgically implanted onto the left distal femur and the left proximal tibia, and in vivo motions were recorded for all activities. Following sacrifice, the in vivo motions were applied to their respective knees using a serial robot with a multi-axis load cell. In vitro simulations were repeated to measure (a) total knee forces, (b) contact pressure maps, and (c) ACL-only forces. Declining the gait surface led to increased posterior translation during the swing phase and decreased flexion at hoof-strike, decreased medial contact pressure at push-off, decreased ACL force at hoof-strike and increased ACL force at push-off. This study established a system that can be used to examine knee mechanics and ACL forces during ADLs for different knee states to define design requirements for ACL reconstruction techniques.

Incidence of cervical kyphosis and cervical posterior translation in neck pain associated with radiological evidence of degenerative disc disease

BackgroundCervical kyphosis mechanically influences the intervertebral discs, which may lead to neck, shoulder, and scapular pain. ObjectivesTo investigate the incidence of cervical kyphosis and posterior displacement of cervical vertebrae (cervical posterior translation index) in patients with radiologically evident degenerative disc disease. DesignRetrospective-cohort study. MethodsNinety-five patients with radiologically evident degenerative disc disease were recruited at our clinic from 2015 to 2019. Radiography images were used to analyze the straight-line index in each patient in the upright posture. The straight-line index was calculated by drawing a reference line connecting the posterior inferior edges of C2 to C7 and normalizing the addition of the distances from the posterior inferior edges of C3, C4, C5, and C6 to the reference line, respectively. Straight-line index <0 was defined as cervical kyphosis and ≥0 as cervical lordosis, the cervical kyphosis. In cervical kyphosis group, the distance from the posterior inferior edges of C3, C4, C5, and C6 to the reference line was normalized by the reference line distance to determine posterior displacement. Multiple comparison tests aside from simple and multiple linear regression analysis were performed. ResultsThe incidence of cervical kyphosis in patients with radiologically evident degenerative disc disease was 60% (57/95 patients). Multiple comparison tests revealed that the cervical posterior translation indexes of C4 and C5 were significantly higher than those of C3, C4, and C6, in cervical kyphosis group. ConclusionsCervical kyphosis was present in 60% of patients with radiologically evident degenerative disc disease, with C5 showing the most posterior displacement.

In vivo knee kinematics of an innovative prosthesis design.

Up to 20% of patients after total knee arthroplasty (TKA) are not satisfied with the result. Several designs of new implants try to rebuild natural knee kinematics. We hypothesized that an innovative implant design leads to better results concerning femoral rollback compared to an established implant design. For this pilot study, 21 patients were examined during TKA, receiving either an innovative (ATTUNETM Knee System (DePuy Inc.), n = 10) or an established (PFCTM (DePuy Inc.), n = 11) knee system. All patients underwent computer navigation. Knee kinematics was assessed after implantation. Outcome measure was anterior–posterior translation between femur and tibia. We were able to demonstrate a significantly higher femoral rollback in the innovative implant group (p < 0.001). The mean rollback of the innovative system was 11.00 mm (95%-confidence interval [CI], 10.77–11.24), of the established system 8.12 mm (95%-CI, 7.84–8.42). This study revealed a significantly increased lateral as well as medial femoral rollback of knees with the innovative prosthesis design. Our intraoperative finding needs to be confirmed using fluoroscopic or radiographic three-dimensional matching under full-weight-bearing conditions after complete recovery from surgery.

Distinct Kinematic and Neuromuscular Activation Strategies During Quiet Stance and in Response to Postural Perturbations in Healthy Individuals Fitted With and Without a Lower-Limb Exoskeleton.

Many individuals with disabling conditions have difficulty with gait and balance control that may result in a fall. Exoskeletons are becoming an increasingly popular technology to aid in walking. Despite being a significant aid in increasing mobility, little attention has been paid to exoskeleton features to mitigate falls. To develop improved exoskeleton stability, quantitative information regarding how a user reacts to postural challenges while wearing the exoskeleton is needed. Assessing the unique responses of individuals to postural perturbations while wearing an exoskeleton provides critical information necessary to effectively accommodate a variety of individual response patterns. This report provides kinematic and neuromuscular data obtained from seven healthy, college-aged individuals during posterior support surface translations with and without wearing a lower limb exoskeleton. A 2-min, static baseline standing trial was also obtained. Outcome measures included a variety of 0 dimensional (OD) measures such as center of pressure (COP) RMS, peak amplitude, velocities, pathlength, and electromyographic (EMG) RMS, and peak amplitudes. These measures were obtained during epochs associated with the response to the perturbations: baseline, response, and recovery. T-tests were used to explore potential statistical differences between the exoskeleton and no exoskeleton conditions. Time series waveforms (1D) of the COP and EMG data were also analyzed. Statistical parametric mapping (SPM) was used to evaluate the 1D COP and EMG waveforms obtained during the epochs with and without wearing the exoskeleton. The results indicated that during quiet stance, COP velocity was increased while wearing the exoskeleton, but the magnitude of sway was unchanged. The OD COP measures revealed that wearing the exoskeleton significantly reduced the sway magnitude and velocity in response to the perturbations. There were no systematic effects of wearing the exoskeleton on EMG. SPM analysis revealed that there was a range of individual responses; both behaviorally (COP) and among neuromuscular activation patterns (EMG). Using both the OD and 1D measures provided a more comprehensive representation of how wearing the exoskeleton impacts the responses to posterior perturbations. This study supports a growing body of evidence that exoskeletons must be personalized to meet the specific capabilities and needs of each individual end-user.

Comparison of instantaneous knee kinematics during walking and running

BackgroundAccurate measurements of in-vivo knee joint kinematics are essential to elucidate healthy knee motion and the changes that accompany injury and repair. Although numerous experimental measurements have been reported, the accurate non-invasive analysis of in-vivo knee kinematics remains a challenge in biomechanics. Research questionThe study objective was to investigate in-vivo knee kinematics before, at, and after contact during walking and running using a combined high-speed dual fluoroscopic imaging system (DFIS) and magnetic resonance (MR) imaging technique. MethodsThree-dimensional (3D) knee models of ten participants were created using MR images. Knee kinematics during walking and running were determined using high-speed DFIS. The 3D knee models were then related to fluoroscopic images to obtain in-vivo six-degrees-of-freedom knee kinematics. ResultsBefore contact knee flexion, external femoral rotation, and proximal-distal distance were 11.9°, 3.4°, and 1.0 mm greater during running compared to walking, respectively. Similar differences were observed at initial contact (9.9°, 7.9°, and 0.9 mm, respectively) and after contact (6.4°, 2.2°, and 0.8 mm, respectively). Posterior femoral translation at initial contact was also increased during running compared to walking. SignificanceThis study demonstrated accurate instantaneous in-vivo knee kinematic characteristics that may further the understanding of the intrinsic biomechanics of the knee during gait.

Paper 05: The Role of the Long Head of the Biceps Tendon in Posterior Shoulder Stabilization during Forward Flexion

Objectives:The incidence of long head of the biceps tendon (LHBT) procedures is increasing, yet the role of the LHBT in glenohumeral stability is not fully understood. People lift most objects in the sagittal plane with forward flexion, which stresses the posterior aspect of the unconstrained glenohumeral joint. Determining the mechanism by which the shoulder maintains stability with functional motions is important to understanding the pathoanatomy of degenerative shoulders. We hypothesize that the LHBT resists posterior translation of the humeral head (HH) during forward flexion by tensioning the posterior capsuloligamentous complex.Methods:Ten fresh-frozen cadaveric shoulders were tested using an established shoulder simulator, which loads the rotator cuff, deltoid and LHB tendons through a system of pulleys and weights. A motion tracking system recorded glenohumeral translations with an accuracy of ±0.2mm. In each subject, the scapula was fixed and the humerus was tested in 6 positions: 30 and 60 degrees of glenohumeral forward flexion at i) maximum internal rotation (IR), ii) neutral rotation and iii) maximum external rotation (ER) (Figure 1). The deltoid was loaded with 100N, and the infraspinatus and subscapularis were loaded with 22N each. The difference in glenohumeral translation was calculated at each position comparing the LHBT loaded with 45N or unloaded.Results:When comparing the two states of LHBT loading vs unloading, unloading the LHBT led to an overall increase in posterior and superior translation of the humeral head (Figure 2) in all tested positions (neutral, maximum internal rotation, maximum external rotation in both 30 and 60 degrees of forward flexion). At 30 degrees of glenohumeral forward flexion, unloading the LHBT increased HH posterior translation by 2.46mm (±0.92mm) (p<0.001), 1.71mm (±1.02mm) (p<0.001) and 1.02mm (±0.88mm) (p=0.014) at maximum ER, neutral rotation, and maximum IR, respectively (Figure 3). At 60 degrees of glenohumeral forward flexion, unloading the LHBT increased HH posterior translation by 2.77mm (±1.16mm) (p<0.001), 2.43mm (±1.56mm) (p<0.001) and 1.66mm (±1.42mm) (p<0.001) at maximum ER, neutral rotation and maximum IR, respectively (Figure 4). Unloading the LHBT led to more posterior translation at 60 degrees of glenohumeral forward flexion compared to 30 degrees (p=0.013).Conclusions:LHBT loading resists posterior translation of the humeral head during forward flexion. This data supports the role of the LHBT as a posterior stabilizer of the shoulder, specifically when a person is carrying objects in front of them. Biceps tenotomy or tenodesis may contribute to microinstability of the glenohumeral joint and shift contact pressure posteriorly. Further work is needed to determine if unloading the LHBT, as is done with biceps tenotomy or tenodesis, may eventually contribute to the posterior glenoid wear seen with osteoarthritis.

Computational analysis of tibial slope adjustment with fixed-bearing medial unicompartmental knee arthroplasty in ACL- and PCL-deficient models.

AimsA functional anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) has been assumed to be required for patients undergoing unicompartmental knee arthroplasty (UKA). However, this assumption has not been thoroughly tested. Therefore, this study aimed to assess the biomechanical effects exerted by cruciate ligament-deficient knees with medial UKAs regarding different posterior tibial slopes.MethodsACL- or PCL-deficient models with posterior tibial slopes of 1°, 3°, 5°, 7°, and 9° were developed and compared to intact models. The kinematics and contact stresses on the tibiofemoral joint were evaluated under gait cycle loading conditions.ResultsAnterior translation increased in ACL-deficient UKA cases compared with intact models. In contrast, posterior translation increased in PCL-deficient UKA cases compared with intact models. As the posterior tibial slope increased, anterior translation of ACL-deficient UKA increased significantly in the stance phase, and posterior translation of PCL-deficient UKA increased significantly in the swing phase. Furthermore, as the posterior tibial slope increased, contact stress on the other compartment increased in cruciate ligament-deficient UKAs compared with intact UKAs.ConclusionFixed-bearing medial UKA is a viable treatment option for patients with cruciate ligament deficiency, providing a less invasive procedure and allowing patient-specific kinematics to adjust posterior tibial slope. Patient selection is important, and while AP kinematics can be compensated for by posterior tibial slope adjustment, rotational stability is a prerequisite for this approach. ACL- or PCL-deficient UKA that adjusts the posterior tibial slope might be an alternative treatment option for a skilled surgeon.Cite this article: Bone Joint Res 2022;11(7):494–502.

Poster 145: Posterior Glenoid Osteotomy with Capsulolabral Repair Restores Force in a Critical Bone Loss Biomechanical Model

Objectives:Bone loss in posterior shoulder instability is an increasingly recognized clinical phenomenon. There is no widespread consensus on the surgical treatment of posterior shoulder instability with critical posterior glenoid bone loss. Here, we study the effect of opening posterior wedge osteotomy on resistance force of soft tissue repair alone in the setting of 20% critical bone loss.Methods:Native glenoid retroversion was measured on 9 cadavers. The humerus was potted in 90 degrees of forward flexion and 30 degrees of internal rotation relative to the scapula and a posterior dislocation was performed in order to create a posterior capsulolabral injury model. The specimens were each taken through a fixed sequence of testing: (1) posteroinferior capsulolabral tear, (2) no glenoid bone loss with posteroinferior capsulolabral repair, (3) 20% posterior glenoid bone loss with posteroinferior capsulolabral repair, (4) and 20% glenoid bone loss with posterior glenoid opening wedge osteotomy and posteroinferior capsulolabral repair. The resultant peak forces with 1 centimeter of posterior translation were measured. A one-way repeated-measures analysis of variance (RM-ANOVA) was used to compare mean force values.Results:Following the initial dislocation event, all shoulder had a resultant posterior capsulolabral injury. Repairing the capsulolabral complex in the 20% posterior glenoid bone loss group did not result in a statistically significant increase in resistance force compared to the labral deficient group, p = 0.068. When 20% posterior bone loss was created, the posterior glenoid osteotomy with capsulolabral repair was significantly stronger than the posterior repair alone both with and without bone loss, p = 0.008 and p = 0.045, respectively.Conclusions:In the setting of critical posterior glenoid bone loss, an opening wedge posterior glenoid osteotomy with capsulolabral repair significantly improved resistance to posterior humeral translation compared to capsulolabral repair alone.

Poster 219: Posterior Sagittal Position of the Tibial Tubercle as Measured by the Sagittal Tibial Tubercle – Trochlear Groove Distance Correlates with an Increased Risk for Surgery in Patients with Patellofemoral Chondral Lesions

Objectives:The etiology of isolated patellofemoral (PF) cartilage defects without patellar instability is currently incompletely understood. The purpose of the present study was to evaluate the variation in knee sagittal alignment in patients with and without PF cartilage wear.Methods:This was a single-center, retrospective review of patients that underwent a cartilage restoration procedure for isolated PF cartilage wear from 2014-2020. Patients were matched in a 1:2:2 ratio for age, sex, and BMI to anterior knee pain diagnosis and meniscectomy procedure cohorts as controls. Exclusion criteria included knee flexion angle >10°, elevated Caton-Deschamps index (CDI>1.3), increased sulcus angle (>145°), increased patellar tilt (>5°), elevated coronal TT-TG (>15mm), varus/valgus malalignment (>5°), or ICRS patellofemoral cartilage defects of ≥3 in either control group. The sagittal TT-TG (sTT-TG) distance was measured on preoperative axial T2 magnetic resonance imaging (MRI) and was defined as the distance between a point at the nadir of the trochlear cartilage and the most anterior point of the tibial tubercle. Comparisons between the 3 groups were made using ANOVA testing with Bonferroni corrections. Reliability was assessed with the interclass correlation coefficient (ICC). Odds ratios were calculated based on a sTT-TG measurement threshold obtained from a receiver operative characteristic curve graph.Results:Two hundred and thirty-five patients (47 cartilage restoration, 94 anterior knee pain, 94 meniscectomy) were included. Mean age, BMI, and height were 33.8 +/- 8.7 and 26.7 +/- 5.7, 170.6 +/- 24.3 respectively, with 130 males (55%) and 105 females (45%). There were no significant differences between groups for age, BMI or sex(p>0.05). Mean sTT-TG was significantly more posterior in the cartilage restoration group compared to the meniscectomy group (-2.5 mm +/-5.9 vs 1.72 mm +/- 5.3, p<0.001). The anterior knee pain group sTT-TG was between the meniscectomy and cartilage restoration groups, but was not significantly different from either (p=0.067, p=0.13). Interrater reliability was excellent (ICC=0.927, p<0.001). Patients with a posterior translation of -2.15 or greater were 2.12 times more likely to undergo a cartilage restoration procedure (OR 2.12, 95% CI 1.1 to 4.1).Conclusions:Cartilage restoration procedure patients had a significantly more posterior tibial tubercle than partial meniscectomy controls. Anterior knee pain patient sagittal TT-TG was between both groups, but was not significantly different from either. Patients with sTT-TG of <-2.15 mm were 2.12 x more likely to have a cartilage restoration procedure.

The effects of initial graft tension on femorotibial relationship following anatomical rectangular tunnel anterior cruciate ligament reconstruction using bone–patellar tendon–bone graft

BackgroundThe purpose of this study was to elucidate the effects of the difference of initial graft tension on the femorotibial relationship on an axial plane and its chronological change following anatomical anterior cruciate ligament (ACL) reconstruction. MethodsA total of 63 patients who underwent anatomical ACL reconstruction were included in this study. The graft was fixed at full knee extension with manual maximum (higher graft tension; group H) and 80 N (lower graft tension; group L) pulls in 31 and 32 patients, respectively. The femorotibial positional relationship in axial computed tomography at 1 week and 1 year postoperatively were retrospectively evaluated. The side-to-side differences (SSDs) and the amount of changes of SSDs over 1 year were compared between groups. ResultsThe SSDs of the external rotational angle of the tibia in group H were significantly larger than those in group L at postoperative 1 week (2.7 ± 3.9° vs. 0.3 ± 3.3°; P < 0.01). The amount of internal rotational changes of SSDs of the internal–external rotational angles over 1 year in group H was significantly larger than that in group L (−3.6 ± 3.9° vs. − 0.3 ± 2.7°; P < 0.01). No significant differences were observed on the anterior–posterior translation distance and medial–lateral shift distance. ConclusionThe application of higher initial graft tension resulted in excessive external rotation of the tibia to the femur at 1 week postoperatively in anatomical ACL reconstruction, and the excessive early external tibial rotation had resolved over 1 year.

Posterior cruciate-retaining total knee arthroplasty exhibits small kinematic changes in the first postoperative year.

Fluoroscopic knee kinematics have historically been quantified at least 1year after total knee arthroplasty (TKA). The purpose of this study was to longitudinally assess knee kinematics at 6-12weeks, 6months, and 1year after TKA to determine if earlier evaluation may be justified. Twenty-one patients participated after undergoing TKA with a posterior cruciate ligament-retaining fixed-bearing prosthesis. Fluoroscopic examinations of lunge, kneel, and step-up activities were performed at 12 ± 4weeks (V1), 7 ± 2months (V2), and 13 ± 2months (V3) postoperatively. Images were analyzed using a three-dimensional to two-dimensional image registration technique. Maximum flexion poses for lunging and kneeling were compared between visits with repeated-measures statistical tests. For the step-up activity, mixed-effects linear models were constructed for condylar anteroposterior (AP) contact points and tibial internal rotation throughout flexion. Estimated marginal means of fitted values were plotted with 95% confidence intervals and used to compare mean kinematics between visits. There were no significant changes in maximum lunging flexion over time (p = 0.405), though significant increases in maximum kneeling flexion were observed between V1 (106 ± 8°) and V2 (110 ± 9°) (p = 0.006), and V1 and V3 (113 ± 9°) (p = 0.0003). While statistical differences were calculated for lunging medial condyle AP translation and kneeling tibial internal rotation, absolute differences in condylar AP contact locations were less than ~ 2mm between all visits during both movements. For the step-up activity, tibial internal rotation increased with flexion, and there were pair-wise significant differences at all flexion angles between V1-V2 (p < 0.001) and V1-V3 (p < 0.001). Anterior medial condylar translation was observed with flexion, with pair-wise significant differences present for V1-V3 (p = 0.005) and V2-V3 (p < 0.001). The lateral condyle exhibited initial posterior translation followed by anterior translation with increasing flexion, with pair-wise differences between all visits (p < 0.005 for all comparisons). Though statistical differences were observed between visits for all activities, variations in estimated mean condylar positions were within ~ 2mm from ~ 12weeks to 1year. Considering measurement error averages approximately 1mm for sagittal plane translations, these results indicate that knee kinematics during kneel, lunge, and step-up activities may be sustained from as early as 12weeks after TKA.