Higher Knee Flexion Angles Research Articles

Biomechanic Differences Between Anticipated and Unanticipated Volleyball Block Jump: Implications for Lower Limb Injury Risk

Volleyball is a high-intensity sport characterized by repetitive jumping, sudden directional changes, and overhead movements, all of which significantly increase the risk of injuries, particularly to the shoulders, knees, and ankles. Despite the frequency of injuries caused by actions like blocking and spiking, there has been limited research focused on the specific biomechanical risk factors unique to volleyball. This study aimed to investigate the lower limb biomechanics during block jumps in both the dominant and non-dominant directions, under both anticipated and unanticipated conditions, in fifteen elite male volleyball players. Kinematic and kinetic data from the ankle, knee, and hip joints were recorded. Our results revealed statistically significant differences between the dominant and non-dominant directions at the ankle, knee, and hip joints. The non-dominant direction exhibited a greater ankle dorsiflexion angle and velocity, as well as higher knee flexion angle, velocity, moment, power, and abduction moment, along with increased hip flexion angle and power. Additionally, unanticipated movements led to increases in vertical ground reaction force (vGRF), hip extension moment, and flexion power, while ankle dorsiflexion plantarflexion velocity and knee flexion power decreased. It appears that movements in the dominant direction were stiffer and less cushioned, potentially increasing the risk of injury. While the non-dominant direction provided better shock absorption, it also elevated the knee valgus moment, which could increase the load on the knee. Furthermore, in unanticipated situations, athletes with short reaction times, unable to quickly adjust their automated movement patterns, faced a higher risk of limb overuse, thereby increasing the likelihood of injury. In practice, coaches should consider differences in limb coordination and movement direction, incorporating unilateral preventive exercises to reduce the risk of injury.

Load-Dependent Characteristics of Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasty: A Biomechanical Study.

Increased load bearing across the patellofemoral and tibiofemoral articulations has been associated with total knee arthroplasty (TKA) complications. Therefore, the purpose of this study was to quantify the biomechanical characteristics of the patellofemoral and tibiofemoral joints and simulate varying weight-bearing demands after posterior cruciate ligament-retaining (CR) and posterior-stabilized (PS) TKAs. Eight fresh-frozen cadaveric knees (average age, 68.4 years; range, 40-86 years) were tested using a custom knee system with muscle-loading capabilities. The TKA knees were tested with a CR and then a PS TKA implant and were loaded at 6 different flexion angles from 15° to 90° with progressively increasing loads. The independent variables were the implant types (CR and PS TKA), progressively increased loading, and knee flexion angle (KFA). The dependent variables were the patellofemoral and tibiofemoral kinematics and contact characteristics. The results showed that at higher KFAs, the position of the femur translated significantly more posterior in CR implants than in PS implants (36.6 ± 5.2 mm and 32.5 ± 5.7 mm, respectively). The patellofemoral contact force and contact area were significantly greater in PS than in CR implants at higher KFAs and loads (102.4 ± 12.5 N and 88.1 ± 10.9 N, respectively). Lastly, the tibiofemoral contact force was significantly greater in the CR than the PS implant at flexion angles of 45°, 60°, 75°, and 90° KFA, the average at these flexion angles for all loads tested being 246.1 ± 42.1 N and 192.8 ± 54.8 N for CR and PS implants, respectively. In this biomechanical study, CR TKAs showed less patellofemoral contact force, but more tibiofemoral contact force than PS TKAs. For higher loads across the joint and at increased flexion angles, there was significantly more posterior femur translation in the CR design with a preserved posterior cruciate ligament and therefore significantly less patellofemoral contact area and force than in the PS design. The different effects of loading on implants are an important consideration for physicians as patients with higher load demands should consider the significantly greater patellofemoral contact force and area of the PS over the CR design.

No difference in stability among various knee flexion angles during fixation of anterolateral ligament reconstruction or lateral extra-articular tenodesis: A systematic review and meta-analysis of biomechanical studies.

The purpose of this study was to investigate the effect of anterolateral ligament reconstruction (ALLR) or lateral extra-articular tenodesis (LET) fixation at low versus high flexion angles during anterior cruciate ligament reconstruction (ACLR) on rotation or translational knee stability. The inclusion criteria for this study were (1) cadaveric study, (2) cadaveric specimens underwent ACLR, (3) cadaveric specimen underwent ALLR or LET and (4) specimen preparation technique described the knee flexion angle at the time of ALLR or LET tensioning and fixation. A priori, 'low flexion' was defined as 0-30° and 'high flexion' was defined as 60-90° at graft fixation. Main outcomes of interest included internal rotation and anterior translation. Data from 92 cadaveric knees (from 9 studies) were extracted and included in the meta-analysis. The mean pooled value for internal rotation was 10.1° (95% confidence interval [CI], 5.7-14.5°) for the low flexion group and 11.5° (95% CI, 7.4-15.7°) for the high flexion group (n.s.). The mean pooled value for anterior translation was 4.3 mm (95% CI, 0.5-8.1 mm) for the low flexion group and 3.0 mm (95% CI, 1.1-5.0 mm) for the high flexion group (n.s.). This meta-analysis of existing biomechanical research found that the rotational and translational stability of the knee were not significantly different between scenarios in which ALLR or LET fixation was performed at low knee flexion angles (0-30°) versus high knee flexion angles (60-90°). Level IV.

The Effects of Different Femoral Component Materials on Bone and Implant Response in Total Knee Arthroplasty: A Finite Element Analysis.

Due to the high stiffness of the biomaterials used in total knee arthroplasty, stress shielding can lead to decreased periprosthetic bone mineral density and bone resorption. As different materials and 3D-printed highly porous surfaces are available for knee femoral components from the industry nowadays, this study aimed to compare the effects of two same-design cruciate-retaining femoral components, made with CoCr and titanium alloy, respectively, on periprosthetic bone stresses through a finite element model of the implanted knee in order to evaluate the induced stress shielding. Moreover, the effect of the cementless highly porous surface of the titanium implant was analyzed in comparison to the cemented interface of the CoCr implant. The von Mises stresses were analyzed in different periprosthetic regions of interest of the femur with different configurations and knee flexion angles. The titanium component induced higher bone stresses in comparison with the CoCr component, mostly in the medial compartment at higher knee flexion angles; therefore, the CoCr component led to more stress shielding. The model was revealed to be effective in describing the effects of different femoral component materials on bone stress, highlighting how a cementless, highly porous titanium femoral component might lead to less stress shielding in comparison to a cemented CoCr implant with significant clinical relevance and reduced bone resorption after total knee arthroplasty.

Double-Bundle PCL Reconstruction in the Multiple-Ligament Injured Knee

Background: Multi-ligament knee injuries and knee dislocations are potentially devastating injuries that typically result in injury to both cruciate ligaments and variable injury to collateral ligament complexes. Indications: Surgical intervention typically leads to better patient outcomes than nonoperative management. We describe our preferred technique for bicruciate ligament reconstruction with a focus on double-bundle posterior cruciate ligament (PCL) reconstruction. Technique Description: A transtibial approach is used to drill the PCL tibial tunnel. A safety incision on the proximal medial tibia, which may incorporate the distal aspect of a medial-sided incision for medial collateral ligament (MCL) reconstruction, allows palpation of the PCL fovea for anatomic tunnel placement, protection of the posterior neurovascular structures, and egress of arthroscopic fluid during the case. This technique uses an inside-out approach for creation of the 2 femoral sockets to recreate the 2 PCL bundles. The grafts are passed in antegrade fashion, with passage and femoral fixation of the posteromedial (PM) bundle followed by the anterolateral (AL) bundle. After passage of the anterior cruciate ligament (ACL) graft and fixation on the femur in standard fashion, attention is turned to PCL tibia-sided fixation. We use a screw and spiked washer to fix the AL bundle at 90° of flexion with an anterior drawer maneuver. The PM bundle is then fixed with a polyetheretherketone (PEEK) interference screw in near full extension. Fixation of the ACL on the tibia in standard fashion completes the bicruciate ligament reconstruction. Results: In biomechanical cadaveric studies, double-bundle PCL reconstruction has been shown to more closely approximate native knee kinematics, with more restraint to posterior translation at all knee flexion angles and less internal rotation laxity at higher knee flexion angles. In clinical results, both single-bundle and double-bundle reconstructions improve knee stability and patient-reported outcomes. Double-bundle PCL reconstruction may provide improved objective posterior tibial stability and objective International Knee Documentation Committee (IKDC) scores. Discussion: Double-bundle PCL reconstruction can be performed efficiently with good outcomes and potentially less residual posterior translation or internal rotation laxity than single-bundle PCL reconstruction. Patient Consent Disclosure Statement: The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

A Biomechanical Comparison of 2 Over-the-Top Anterior Cruciate Ligament Reconstruction Techniques: A Cadaveric Study Using a Robotic Simulator.

For skeletally immature patients, over-the-top (OTT) anterior cruciate ligament (ACL) reconstruction (ACLR) is preferred. However, increased anterior laxity at deep knee flexion angles remains concerning. We modified the procedure to proximally shift the graft fixation site on the femur to prevent graft loosening at higher knee flexion angles and named it the supra-OTT procedure. To compare anterior laxity and in situ forces of the ACL graft between conventional OTT and supra-OTT ACLR in a cadaveric model. Controlled laboratory study. A total of 11 fresh-frozen cadaveric knee specimens underwent 4 robotic testing conditions: ACL intact, ACL resected, conventional OTT, and supra-OTT. For each condition, a 100-N load was applied at 0°, 15°, 30°, 60°, and 90° of knee flexion to simulate the Lachman test or anterior drawer test. In addition, a combined load of 5-N·m internal tibial torque and 10-N·m valgus torque was applied at 15° and 30° of knee flexion as a simulated pivot-shift test. Anterior tibial translation and in situ graft forces were recorded. The only difference between conventional OTT and supra-OTT ACLR was the graft fixation site on the femur. For conventional OTT ACLR, graft fixation was performed just on the proximal and lateral ends of the posterior condyle. For supra-OTT ACLR, the fixation point was around the proximal insertion of the lateral head of the gastrocnemius and the lateral edge of the posterior cortex, approximately 2 cm proximal to the conventional OTT position. On the simulated anterior drawer test at 60° and 90° of knee flexion, anterior tibial translation after supra-OTT ACLR was significantly smaller than after conventional OTT ACLR (P < .01). However, no significant differences were noted at other flexion angles or on the simulated pivot-shift test between the conventional OTT and supra-OTT procedures. Some overconstraint and higher graft forces were noted with both techniques, but the supra-OTT technique caused even more overconstraint at higher flexion angles. Supra-OTT ACLR showed better biomechanical performance to control anterior laxity than conventional OTT ACLR at higher knee flexion angles. The supra-OTT procedure may improve anterior stability at deep knee flexion angles.

Influence of posterior tibial slope on sagittal knee alignment with comparing contralateral knees of anterior cruciate ligament injured patients to healthy knees

Posterior tibial slope (PTS) has been known to contribute to anterior–posterior knee stability and play an essential biomechanical role in knee kinematics. This study aimed to investigate the effect of PTS on single-leg standing sagittal knee alignment of the intact knee. This study included 100 patients with unilateral ACL injury knee (ACL injury group, 53 patients) or with the normal knee (control group, 47 patients). The single-leg standing sagittal alignment of the unaffected knees of the ACL injury group and normal knees of the control group were assessed radiographically with the following parameters: knee extension angle (EXT), PTS, PTS to the horizontal line (PTS-H), femoral shaft anterior tilt to the vertical axis (FAT), and tibial shaft anterior tilt to the vertical axis (TAT). PTS was negatively correlated with EXT and positively correlated with TAT. EXT was significantly larger in the ACL injury group, whereas TAT was smaller in the ACL injury group. Patients with larger PTS tend to stand with a higher knee flexion angle by tilting the tibia anteriorly, possibly reducing tibial shear force. Patients with ACL injury tend to stand with larger EXT, i.e., there is less preventive alignment to minimize the tibial shear force.

Association between a Concomitant Anterolateral Ligament Tear and Pivot Shift Before and After Single-Bundle Anterior Cruciate Ligament Reconstruction: A Retrospective Cohort Study

BACKGROUND: Regardless of the type of intra-articular anterior cruciate ligament (ACL) reconstruction performed, a certain degree of rotatory instability is often seen after surgery. Recent studies suggest that the anterolateral ligament (ALL) plays a significant role in maintaining stability during internal rotation of the tibia at high knee flexion angles. Unrecognized damage to the ALL may potentially be associated with a positive pivot shift despite a surgically reconstructed ACL being done. AIM: The primary objective of this study was to determine whether a concomitant ALL tear is associated with a high-grade pivot shift before and after ACL reconstruction. METHODS: This study was a retrospective cohort study of patients that underwent single-bundle ACL reconstruction surgery in our institution from October 2014 to March 2017. One hundred and forty-four patients were included in this study. All data were extracted from the department of ACL registry. All knee MRIs were reviewed by the author and coauthor to determine the integrity of the ALL. Subjects were divided into two groups based on the grade of pivot shift before surgery. The prevalence of ALL tear based on MRI was further compared between high-grade and low-grade pivot-shift groups. RESULTS: Overall, the prevalence of a concomitant ALL tear was 70.83%. Comparing the prevalence of concomitant ALL tear between the high-grade pivot-shift group (73.11%) and low-grade pivot-shift group (60%), we had insufficient evidence to demonstrate an association between pre-surgery high-grade pivot shift and concomitant ALL tear. After surgery, none of the patients had a high-grade pivot shift or was positive for Lachman’s test. CONCLUSION: There is a high prevalence of concomitant ALL tear in patients with torn ACL. We have insufficient evidence to demonstrate an association between the presence of a torn ALL and high-grade pivot shift before and after single-bundle ACL reconstruction.

Knee flexor strength and symmetry vary by device, body position and angle of assessment following ACL reconstruction with hamstring grafts at long-term follow-up.

Persistent deficits in knee flexor strength following harvest of semitendinosus and gracilis for anterior cruciate ligament reconstruction are inconsistent in the literature. Variation in methodology, including measuring torque at higher knee flexion angles may partially explain these discrepant findings. The objective of this study was to determine whether positioning (seated vs supine), consideration of peak or joint-angle-specific torque or device (Isokinetic Dynamometer vs NordBord Hamstring Dynamometer) impact the magnitude of knee flexor strength differences between limbs. Participants (n = 31, 44.2 ± 10.7years,) who were at 14 ± 4.4years follow-up for unilateral ACL reconstruction with semitendinosus/gracilis grafts completed the ACL Quality of Life outcome and an assessment including isokinetic concentric knee extensor and flexor strength in seated and supine with peak torque and torque at 60° (T60) and 75° (T75) knee flexion measured, followed by an eccentric Nordic Hamstring Curl. Isokinetic concentric knee flexor torque was reduced in supine relative to seated, on the reconstructed limb against the unaffected, and at higher degrees of knee flexion relative to peak torque (T60 and T75 against peak torque). Limb symmetry varied by methodology (F(6,204) = 8.506, p = 0.001) with reduced symmetry in supine T75 against all measures (71.1 ± 16.5%, p < 0.05), supine T60 against seated peak torque (82.7 ± 14.2%, p < 0.05), and the NordBord was lower than seated peak torque that was not statistically significant (83.9 ± 12.8%, n.s.). Knee extensor peak (r2 = 0.167 (F(1,27) = 5.3, p = 0.03) and Nordic curl eccentric torque (r2 = 0.267, F(2,26) = 4.736, p = 0.02) were predictors of ACL-QoL score, although a combined model did not improve over Nordic torque alone. Limb symmetry cannot be assumed in clinical practice across differing assessment methods for knee flexor strength as deficits are greatest in the supine position with torque measured at 75° knee flexion. Isokinetic knee extensor and eccentric knee flexor torque during the Nordic hamstring curl were predictors of ACL-QoL scoring and should be considered alongside patient-reported outcomes for patients following ACL reconstruction with hamstring grafts. Level IV.

Biomechanical Effects of Combined Anterior Cruciate Ligament Reconstruction and Anterolateral Ligament Reconstruction: A Systematic Review and Meta-analysis.

Background:Combined anterior cruciate ligament (ACL) reconstruction (ACLR) and anterolateral ligament reconstruction (ALLR) are performed with the intention to restore native knee kinematics after ACL tears. There continue to be varying results as to the difference in kinematics between combined and isolated procedures, including anterior tibial translation (ATT) and internal tibial rotation (IR).Purpose:To perform a systematic review and meta-analysis to evaluate the kinematic changes of a combined ACLR/ALLR versus isolated ACLR and to assess the effects of different fixation techniques.Study Design:Systematic review.Methods:We conducted a systematic review and meta-analysis of 15 human cadaveric biomechanical studies evaluating combined ACLR/ALLR versus isolated ACLR and their effects on ATT and IR in 149 specimens. The primary outcomes were ATT and IR. Secondary outcomes included graft type and size as well as fixation methods such as type, angle, tension, and position of fixation. Meta-regression was used to examine the effect of various cofactors on the resulting measures.Results:Compared with isolated ACLR, combined ACLR/ALLR decreased ATT and IR by 0.01 mm (95% CI, –0.059 to 0.079 mm; P = .777) and 1.64° (95% CI, 1.30°-1.98°; P < .001), respectively. Regarding ACLR/ALLR, increasing the knee flexion angle and applied IR force led to a significant reduction in IR (P < .001 and P = .044, respectively). There was also a significant reduction in IR in combined procedures with semitendinosus ALL graft, higher flexion fixation angles, and tension but no change in IR with differing femoral fixation points (P < .001, P < .001, and P = .268, respectively). Multivariate meta-regression showed that the use of tibial-sided suture anchor fixation significantly reduced IR (P < .001).Conclusion:These results suggest that a combined ACLR/ALLR procedure significantly decreases IR compared with isolated ACLR, especially at higher knee flexion angles. Semitendinosus ALL graft, fixation at higher knee flexion, increased tensioning, and tibial-sided interference screw fixation in ALLR may help to further reduce IR.

Classification of Whole-Body Postural Discomfort Using Cluster Analysis.

The objectives of this study were to evaluate the effect of gender and postures of the neck, trunk, and knee on overall postural discomfort, and to classify combined postures into different postural discomfort groups. A total of 95 participants (42 males and 53 females) performed 45 different static postures, which were a combination of 3 neck angles, 5 trunk angles, and 3 knee angles, and rated the perceived postural discomfort. Non-hierarchical K-means cluster analysis was employed to classify the 45 different combined postures into several postural discomfort groups. Postural discomfort was significantly affected by gender and postures of the neck, trunk, and knee (p < 0.001). Three clusters (high, medium, and low discomfort) were identified and the postural discomfort was significantly different between clusters (p < 0.001). The high discomfort group consisted of mostly males with high knee and trunk flexion angles and a moderate neck flexion angle. The low discomfort group was female-dominant with low neck and trunk flexion angles and a moderate knee flexion angle. The different flexibility (stiffness) of the joint motions between genders may affect the gender difference in postural discomfort. The knee and trunk postures were critical to the postural balance, which may affect the perception of whole-body discomfort. This result will be useful for developing and improving postural observation tools.

Can knee flexion contracture affect cervical alignment and neck tension? A prospective self-controlled pilot study

BACKGROUND CONTEXTThe coordination of the alignment between the lower extremities and cervical spine helps to achieve balance and horizontal gaze during standing and walking. Malalignment in any segment can disturb the global balance, causing compensation in another segment. Knee flexion contracture (KFC) can cause spine inclination with increased C7 tilt or C7 SVA (sagittal vertical axis). Cervical alignment and the posterior muscles are essential for maintaining the horizontal gaze which is closely related to neck tension (NT). PURPOSEThis study aimed to determine whether KFC can affect cervical alignment and its potential effects on the posterior muscles and NT. DESIGNA prospective pilot study was carried out in preoperative (pre-op) and postoperative (post-op) phases. PATIENT SAMPLEThis study included 22 consecutive patients with KFC and 12 control subjects in our department who agreed to participate from between August 1, 2018 and February 28, 2019 in our department. OUTCOME MEASURESVisual analog scale (VAS) and neck disability index (NDI) were used. The sagittal alignment parameters and cervical range of motion (ROM) were measured on radiographic images, and included the C0–C2 lordosis (C0–2L), C2–C7 lordosis (C2–7L), C2 SVA, C7 SVA, T1 slope, thoracic kyphosis, lumbar lordosis (LL), pelvic tilt, sacral slope, and knee flexion angle (KA). Surface electromyography-based flexion-relaxation ratio (FRR) and ultrasound-based shear wave elastography (SWE) were performed. METHODSThe control group was matched for age, sex, and body mass index with the KFC group. Patients in the KFC group underwent arthroscopic surgery to correct knee alignment. Comparisons between pre-op and post-op phases were performed using paired sample t tests, comparisons between KFC and control groups were performed using independent samples t tests. The correlation analysis between the parameters was performed using Spearman analysis. Funding for this study was provided by the National Natural Science Foundation of China (60,000 USD), Beijing Municipal Administration of Hospitals Incubating Program (50,000 USD), and Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (20,000 USD). There were no conflicts of interest associated with this study. RESULTSThe average follow-up time for this pilot study was 11.4±1.5 days. Pre-op, the KFC group had higher KA, T1S, C7 SVA, C2 SVA, C0–2L, SWE, VAS, and NDI compared with the control group, but all of these parameters were decreased significantly post-op. The LL, FRR of splenius capitis (FRRsc), and ROM of the KFC group pre-op were lower than the control group, and all of these were increased significantly post-op. There were no differences in pelvic tilt, sacral slope, C2–7 L, or TK between the KFC and control groups, or in FRR of splenius capitis (FRRutr) between pre-op and post-op phases. KA had strong correlations with LL (r=−0.83), which correlated well with C7 SVA (r=−0.75). C7 SVA correlated strongly with C2 SVA (r=0.79), which also correlated strongly with C0–2 L (r=0.76). C0–2 L correlated well with FRRsc (r=−0.65) and SWEsc (r=0.72), and both of them correlated well with VAS (r=−0.54, r=0.71) and NDI (r=−0.57, r=0.76). ROM correlated well with FRRsc (r=0.71), SWEsc (r=−0.74), VAS (r=−0.66), and NDI (r=−0.66). CONCLUSIONSKFC may cause spine inclination and craniocervical malalignment, leading to NT and ROM reduction. The results of this pilot study may be helpful in guiding further studies concerning KFC and NT.

Comparison of lower extremity joint mechanics between healthy active young and middle age people in walking and running gait

Progression of age can influence gait characteristics. Previous research has investigated lower extremity joint mechanics between young and elderly people in locomotion, however little is known about whether differences exist between young and middle age people. Ten young healthy subjects (22.8 ± 5.3 years) and ten middle age healthy subjects (50.7 ± 6.0 years) engaged in treadmill walking (from 0.8 to 2.0 m/s) and running (from 1.8 to 3.8 m/s). The middle age group had higher ankle plantar flexor moment angular impulse (p = 0.002), total support moment impulse (p = 0.016), and hip stance positive work (p = 0.029) across walking speeds. Additionally, the middle age group had higher knee flexion angle at ground contact in walking (p = 0.005) and running (p = 0.037). These findings indicate that moderate age affects changes in ankle and hip kinetic characteristics in walking, and knee kinematic patterns in both walking and running.

Tibial Slope and Its Effect on Graft Force in Posterior Cruciate Ligament Reconstructions

Background: A flattened posterior tibial slope may cause excessive unwanted stress on the posterior cruciate ligament (PCL) reconstruction graft and place patients at risk for PCL reconstruction graft failure. To date, there is a paucity of biomechanical studies evaluating the effect of posterior tibial slope on the loading properties of single-bundle (SB) and double-bundle (DB) PCL grafts. Purpose/Hypothesis: The purpose of this study was to quantify the effect of sagittal plane tibial slope on PCL reconstruction graft force at varying slopes and knee flexion angles for SB and DB PCL reconstructions. The null hypothesis was that there would be no differences in SB or DB PCL graft forces with changes in posterior tibial slope or knee flexion angle. Study Design: Controlled laboratory study. Methods: Ten male fresh-frozen cadaveric knees had a proximal posterior tibial osteotomy performed and an external fixator placed for tibial slope adjustment. SB (anterolateral bundle [ALB] only) and DB PCL reconstruction procedures were performed and tested consecutively for each specimen. The ALB and posteromedial bundle graft forces were recorded before (unloaded force) and after (loaded force) compression with a 300-N axial load. Unloaded and loaded graft forces were tested at flexion angles of 45°, 60°, 75°, and 90°. Tibial slope was varied between −2° and 16° of posterior slope at 2° increments under these test conditions. Results: Modeling for unloaded testing revealed that tibial slope had an independently significant and linear decreasing effect on the force of all PCL grafts regardless of flexion angle (coefficient = −1.0, SE = 0.08, P < .001). Higher knee flexion angles were significantly associated with higher unloaded graft force for all PCL grafts (P < .001). After the graft was subjected to loading, tibial slope also had an independently significant and linear decreasing effect on the loaded force of all PCL grafts regardless of flexion angle (coefficient = −0.70, SE = 0.11, P < .001). The ALB graft of DB reconstructions had a significantly lower loaded graft force than the ALB graft of the SB PCL reconstruction (coefficient = 14.8, SE = 1.62, P < .001). The posteromedial bundle graft had a significantly lower loaded graft force than the ALB graft in both reconstruction states across all flexion angles (both P < .001). Higher knee flexion angles were also significantly associated with higher loaded graft force for all graft constructs (P < .001). Conclusion: PCL graft forces increased as tibial slope decreased (flattened) in the loaded and unloaded states. An increased posterior tibial slope was protective of PCL reconstruction grafts. The findings of this study support the effect of tibial slope on PCL grafts that has been noted clinically, and a flat tibial slope should be considered a factor when evaluating the cause of failed PCL reconstructions. Clinical Relevance: The authors validated that decreased tibial slope increased the loads on PCL reconstruction grafts. Patients with flat tibial slopes in chronic tears or revision PCL reconstruction cases should be evaluated closely for the possible need of a first-stage or concurrent slope-increasing tibial osteotomy.

How Accurately Can Soft Tissue Balance Be Determined in Total Knee Arthroplasty?

BackgroundSoft tissue balance is believed to be a major determinant of improved outcomes in total knee arthroplasty (TKA). We conducted this study to assess the accuracy of surgeon-defined assessment (SDA) of knee balance compared to pressure sensor data. We also assessed for any association between experience (learning curve) and accuracy of SDA. MethodsA total of 308 patients undergoing 322 mechanically aligned TKA were prospectively analyzed. Femoral and tibial trial implants were inserted before performing knee balancing. We compared the surgeon determination on knee balance at 10°, 45°, and 90° of flexion to sensor data at the same flexion angles. ResultsAccuracy of SDA was 63%, 57.5%, and 63.8% at 10°, 45°, and 90°, respectively, when compared to sensor data. SDA had an overall sensitivity of 81% and specificity of 37.7%. Capacity to determine an unbalanced knee worsened at higher knee flexion angles with SDA test specificity of 53.5%, 34.8%, and 24.8% at 10°, 45°, and 90°, respectively (P = .0004 at 10° vs 45°, P < .0001 at 10° vs 90°). Cohen’s kappa coefficient was 0.29 at 10° indicating fair agreement, and 0.14 and 0.12 at 45° and 90°, respectively, indicating poor agreement. The use of sensor had no time-based learning effect on capacity to determine knee balance. ConclusionSDA is a poor predictor of the true soft tissue balance when compared to sensor data, particularly in assessing whether a knee is unbalanced. In addition, increased use of sensors did not improve surgeon capacity to determine knee balance.

Effect of Meniscocapsular and Meniscotibial Lesions in ACL-Deficient and ACL-Reconstructed Knees: A Biomechanical Study

Background: Ramp lesions were initially defined as a tear of the peripheral attachment of the posterior horn of the medial meniscus at the meniscocapsular junction. The separate biomechanical roles of the meniscocapsular and meniscotibial attachments of the posterior medial meniscus have not been fully delineated. Purpose: To evaluate the biomechanical effects of meniscocapsular and meniscotibial lesions of the posterior medial meniscus in anterior cruciate ligament (ACL)–deficient and ACL-reconstructed knees and the effect of repair of ramp lesions. Study Design: Controlled laboratory study. Methods: Twelve matched pairs of human cadaveric knees were evaluated with a 6 degrees of freedom robotic system. All knees were subjected to an 88-N anterior tibial load, internal and external rotation torques of 5 N·m, and a simulated pivot-shift test of 10-N valgus force coupled with 5-N·m internal rotation. The paired knees were randomized to the cutting of either the meniscocapsular or the meniscotibial attachments after ACL reconstruction (ACLR). Eight comparisons of interest were chosen before data analysis was conducted. Data from the intact state were compared with data from the subsequent states. The following states were tested: intact (n = 24), ACL deficient (n = 24), ACL deficient with a meniscocapsular lesion (n = 12), ACL deficient with a meniscotibial lesion (n = 12), ACL deficient with both meniscocapsular and meniscotibial lesions (n = 24), ACLR with both meniscocapsular and meniscotibial lesions (n = 16), and ACLR with repair of both meniscocapsular and meniscotibial lesions (n = 16). All states were compared with the previous states. For the repair and reconstruction states, only the specimens that underwent repair were compared with their intact and sectioned states, thus excluding the specimens that did not undergo repair. Results: Cutting the meniscocapsular and meniscotibial attachments of the posterior horn of the medial meniscus significantly increased anterior tibial translation in ACL-deficient knees at 30° (P ≤ .020) and 90° (P < .005). Cutting both the meniscocapsular and meniscotibial attachments increased tibial internal (all P > .004) and external (all P < .001) rotation at all flexion angles in ACL-reconstructed knees. Reconstruction of the ACL in the presence of meniscocapsular and meniscotibial tears restored anterior tibial translation (P > .053) but did not restore internal rotation (P < .002), external rotation (P < .002), and the pivot shift (P < .05). To restore the pivot shift, an ACLR and a concurrent repair of the meniscocapsular and meniscotibial lesions were both necessary. Repairing the meniscocapsular and meniscotibial lesions after ACLR did not restore internal rotation and external rotation at angles >30°. Conclusion: Meniscocapsular and meniscotibial lesions of the posterior horn of the medial meniscus increased knee anterior tibial translation, internal and external rotation, and the pivot shift in ACL-deficient knees. The pivot shift was not restored with an isolated ACLR but was restored when performed concomitantly with a meniscocapsular and meniscotibial repair. However, the effect of this change was minimal; although statistical significance was found, the overall clinical significance remains unclear. The ramp lesion repair used in this study failed to restore internal rotation and external rotation at higher knee flexion angles. Further studies should examine improved meniscus repair techniques for root tears combined with ACLRs. Clinical Relevance: Meniscal ramp lesions should be repaired at the time of ACLR to avoid continued knee instability (anterior tibial translation) and to eliminate the pivot-shift phenomenon.

Multi-body optimization with subject-specific knee models: performance at high knee flexion angles

When estimating knee kinematics from skin markers and stereophotogrammetry, multi-body optimization (MBO) has provided promising results for reducing soft tissue artefacts (STA), but can still be improved. The goal of this study was to assess the performance of MBO with subject-specific knee models at high knee flexion angles (up to 110°) against knee joint kinematics measured by magnetic resonance imaging. Eight subjects were recruited. MBO with subject-specific knee models was more effective in compensating STA compared to no kinematic and spherical constraints, in particular for joint displacements. Moreover, it seems to be more reliable over large ranges of knee flexion angle. The ranges of root mean square errors for knee rotations/displacements were 3.0°–9.2°/1.3–3.5 mm for subject-specific knee models, 6.8°–8.7°/6.0–12.4 mm without kinematic constraint and 7.1°–9.8°/4.9–12.5 mm for spherical constraints.

Mediolateral force distribution at the knee joint shifts across activities and is driven by tibiofemoral alignment.

Tibiofemoral alignment is important to determine the rate of progression of osteoarthritis and implant survival after total knee arthroplasty (TKA). Normally, surgeons aim for neutral tibiofemoral alignment following TKA, but this has been questioned in recent years. The aim of this study was to evaluate whether varus or valgus alignment indeed leads to increased medial or lateral tibiofemoral forces during static and dynamic weight-bearing activities. Tibiofemoral contact forces and moments were measured in nine patients with instrumented knee implants. Medial force ratios were analysed during nine daily activities, including activities with single-limb support (e.g. walking) and double-limb support (e.g. knee bend). Hip-knee-ankle angles in the frontal plane were analysed using full-leg coronal radiographs. The medial force ratio strongly correlated with the tibiofemoral alignment in the static condition of one-legged stance (R² = 0.88) and dynamic single-limb loading (R² = 0.59) with varus malalignment leading to increased medial force ratios of up to 88%. In contrast, the correlation between leg alignment and magnitude of medial compartment force was much less pronounced. A lateral shift of force occurred during activities with double-limb support and higher knee flexion angles. The medial force ratio depends on both the tibiofemoral alignment and the nature of the activity involved. It cannot be generalised to a single value. Higher medial ratios during single-limb loading are associated with varus malalignment in TKA. The current trend towards a 'constitutional varus' after joint replacement, in terms of overall tibiofemoral alignment, should be considered carefully with respect to the increased medial force ratio. Cite this article: Bone Joint J 2017;99-B:779-87.

Effects of hip flexion angle on surface electromyographic activity of the biceps femoris and semitendinosus during isokinetic knee flexion.

Identifying combinations of the hip and knee joint angles which can selectively recruit specific hamstring muscles may be beneficial for injury prevention or rehabilitation. The purpose of this study was to examine the joint torque and electromyographic (EMG) activity of the semitendinosus (ST) and biceps femoris long head (BFlh). Twenty subjects performed maximum isokinetic concentric and eccentric knee flexor efforts at 60°·s-1, 120°·s-1 and 150°·s-1 from three different hip joint angles while surface EMG of ST and BFlh was recorded. Analysis of variance showed that there are no inter-muscular differences in EMG amplitude across testing conditions (p > .05). Peak EMG occurred near full knee extension for the BFLh and at a higher flexion angle for the ST while exercise from a prone position shifted the peak EMG towards higher knee flexion angle (p < 0.05). Maximal dynamic knee flexion exercises do not induce a higher EMG amplitude of BFlh or ST. Exercising from a higher hip flexion angle near full knee extension may selectively activate the BFlh. IIb.

The Effects of ACL Deficiency on the Meniscus and Articular Cartilage

Objectives:Through altered tibiofemoral kinematics, isolated tears of the anterior cruciate ligament (ACL) likely affect the meniscus and its ability to distribute joint forces. Changes in meniscal movement and deformation may result in altered cartilage contact location and volume, possibly leading to osteoarthritis. Little is known regarding the effects of acute ACL injury on meniscal translation and deformation as well as cartilage contact location and deformation. Using a newly developed, minimally invasive methodology, we investigated meniscal behavior and cartilage contact during dynamic knee flexion in ACL-intact and ACL-deficient states. We hypothesized that after ACL-transection, both the menisci and cartilage will show greater deformation and the menisci will translate more posteriorly.Methods:Five human cadaveric knees were tested with six 1.0 mm steel beads injected in both the medial and lateral meniscus and three into the femur and tibia. 3D bone models were created using CT scans and articular cartilage was mapped on MRIs to create rigid cartilage models. Dynamic stereo x-ray (DSX) images were obtained during dynamic knee flexion from 10-40 degrees with a 50 lb load before and after ACL transection (Figure 1). Meniscal deformation and movement were measured by change in arc length along the implanted bead locations and translation of the center of the created ellipse (Figure 1). Cartilage models were co-registered with DSX data to evaluate cartilage deformation, measured by depth of penetration and location of contact. ACL intact and ACL transected states were compared.Results:After ACL transection, the total arc length of the lateral meniscus decreased 2.7 mm in the mid portion and posterior horn while the change in arc length of the medial meniscus was minimal. The medial and lateral meniscus translated 0.9 mm (sd= 1.0 mm) and 1.6 mm (sd= 0.7 mm) more posteriorly. The cartilage penetration change was minimal in the medial and increased by 0.3 mm in the lateral compartment. Cartilage contact location moved posteriorly 1.7 mm and 2.7 mm in the medial and lateral meniscus, respectively (Figure 1).Conclusion:Following ACL-transection, both menisci and cartilage contact location translate more posteriorly, lateral compartment more than medial. Cartilage deformation increased in the lateral compartment as well. Circumferential meniscal deformation decreased in the lateral compartment along the mid portion and posterior horn. The authors hypothesize this may be due to meniscal complexity that is not completely understood. The posterior horn may be subjected to compressive forces or altered knee kinematics that have yet to be correlated. This model illustrates that dynamic evaluation of changes in the meniscus and cartilage is feasible and that ACL injury may lead to altered wear patterns. Further testing with higher knee flexion angles, higher loads, and other injury patterns will be performed. The authors thank and acknowledge the AOSSM for the Young Investigator Grant for the financial support of this study.