Knee extension moment arm variations relate to mechanical function in walking and running

The patellofemoral joint plays a crucial mechanical role during walking and running. It increases the knee extensor mechanism's moment arm and reduces the knee extension muscle forces required to generate the extension moment that supports body weight, prevents knee buckling and propels the centre of mass. However, the mechanical implications of moment arm variation caused by patellofemoral and tibiofemoral motion remain unclear. We used a data-driven musculoskeletal model with a 12-degree-of-freedom knee to simulate the knee extension moment arm during walking and running. Using a geometric method to calculate the moment arm, we found smaller moment arms during running than during walking in the swing phase. Overall, knee flexion causes differences between running and walking moment arms as increased flexion causes a posterior shift in the tibiofemoral rotation axis and patella articulation with the distal femur. Moment arms were also affected by knee motion direction and best predicted by separating by direction instead of across the entire gait cycle. Furthermore, we found high inter-subject variation in the moment arm that was largely explained by out-of-plane motion. Our results are consistent with the concept that shorter moment arms increase the effective mechanical advantage of the knee and may contribute to increased running velocity.

Knee joint loadings are related to tibial torsional alignments in people with radiographic medial knee osteoarthritis

Torsional malalignment was detected in subjects with medial knee osteoarthritis (KOA) but few studies have reported the effect of torsional deformity on knee joint loads during walking. Therefore, this study examined the relationships between lower limb torsional alignments and knee joint loads during gait in people with symptomatic medial KOA using cross-sectional study design. Lower limb alignments including tibial torsion, tibiofemoral rotation and varus/valgus alignments in standing were measured by EOS low-dose bi-planar x-ray system in 47 subjects with mild or moderate KOA. The external knee adduction moment (KAM), flexion moment (KFM) and the KAM index which was defined as (KAM/ (KAM+KFM)*100) during walking were analyzed using a motion analysis system so as to estimate the knee loads. Results revealed externaltibial torsion was positively associated with KAM in subjects with moderate KOA (r = 0.59, p = 0.02) but not in subjects with mild KOA. On the contrary, significant association was found between knee varus/valgus alignment and KAM in the mild KOA group (r = 0.58, p<0.001) and a sign of association in the moderate KOA group (r = 0.47, p = 0.08). We concluded tibial torsion and knee varus/valgus mal-alignments would be associated with joint loading in subjects with moderate medial KOA during walking. Radiographic severity might need to be considered when using gait modification as a rehabilitation strategy for this condition.

SPONTANEOUS CORRECTION OF EXTERNAL TIBIOFEMORAL ROTATION AND TIBIAL TUBEROSITY-TROCHLEAR GROOVE DISTANCE OCCURS AFTER MEDIAL PATELLOFEMORAL LIGAMENT RECONSTRUCTION IN FIXED OR OBLIGATORY DISLOCATORS

Background: Tibial tubercle to trochlear groove distance (TT-TG) and external tibiofemoral rotation (TFR) through the knee joint have been identified potential contributing factors to patellar instability. In patients with a fixed or obligatory lateral patella dislocation (FOD), the normal force vector of the extensor mechanism is altered, so instead of a direct axial pull to cause extension, it exerts a lateralizing and external rotatory force on the tibia via the tibial tubercle. Hypothesis/Purpose: The purpose of this study is to investigate postoperative changes in TT-TG and TFR after medial patellofemoral ligament reconstruction (MPFLR) in two clinical cohorts: standard traumatic patellar instability (SPI) patients and FOD patients. We hypothesized that by surgically relocating the patella in the trochlea, and re-establishing medial sided soft tissue tension, the increased medializing force vector on the patella may exert enough force to alter resting rotation of the tibia in relation to the femur in the FOD group. Methods: A retrospective study was performed from April 2009 to February 2019. FOD and SPI patients under 18 years with available magnetic resonance imaging (MRI) of the knee before and after MPFLR were eligible. All FOD patients in the time frame were analyzed and SPI patients were randomly selected. Exclusion criteria were outside institution MRI, concomitant alignment procedures done at the time of MPFLR, and prior MPFLR or tibial tubercle osteotomy. TT-TG and TFR (using the posterior femoral and tibial condylar lines) were measured blindly on initial axial MRI. Statistical analysis using a paired sample t-test was performed with significance set at p<0.05. Results: A total of 30 patients were included, 14 in the FOD group and 16 in the SPI group. The mean age at time of surgery was 13.9 years (range 10-17 years), 53% of the cohort was female, and the mean time from surgery to follow-up MRI was 2.0 years. Demographics by group are shown in Table 1. TT-TG and TFR were not significantly different preoperatively versus postoperatively in the SPI group (Table 2). In the FOD group, both TT-TG (17.7 vs 13.7, P=.019) and TFR (8.6 vs 3.1, P=.025) decreased significantly on postoperative MRI. Conclusion: The postoperative decrease in TT-TG and TFR in the FOD group suggests that MPFLR in fixed or obligatory dislocators can improve the external rotation deformity through the level of the joint, and thus may help normalize the forces acting through the extensor mechanism. Tables/ Figures [Table: see text][Table: see text]

Increased Tibiofemoral Rotation with Increasing Severity of Patellar Instability in the Pediatric Population

Objectives: Tibiofemoral rotation (TFR), specifically external tibial rotation, has been recently identified as a potential contributing factor to patellar instability. However, no previous studies have explored the clinical effects of differing degrees of TFR in relation to patellar instability. The purpose of this study is to investigate the relationship between severity of instability with degree of TFR. Our hypothesis is that fixed or obligatory dislocators (FOD) are more likely to have increased external TFR (tibial external rotation compared to femur) than standard patellar instability (SPI) patients requiring medial patellofemoral ligament (MPFL) reconstruction, who will have similar or slightly increased external TFR compared to normal controls. Methods: A retrospective study was performed with patients from 3 cohorts from April 2009 to February 2019: FOD, SPI, and controls with normal magnetic resonance imaging (MRI) of the knee. All FOD patients from the study time frame were analyzed, while controls and SPI patients were randomly selected. Patients were included for age under 18 years and diagnosis corresponding to one of the three cohorts, and excluded for outside institution MRI, and previous MPFL reconstruction or tibial tubercle osteotomy. TFR was measured on preoperative axial MRI using the posterior femoral and tibial condylar lines (Figure 1). Tibial tubercle to trochlear groove distance (TT-TG) was measured. Intraclass correlation coefficient (ICC) was calculated among 3 measurers. Statistical analysis using ANOVA and t-test was performed with significance set at α=0.05. Results: A total of 57 patients were included, 19 in each cohort. Average age was 13.2 years (range 10-17 years), with 31 females (54%). ICC for TT-TG and TFR were 0.90 and 0.72, respectively. TT-TG differed between the controls and SPI patients (both P<0.001), and controls and FOD patients (P<0.001), but not between SPI and FOD patients (P=0.12). TFR differed among the three groups: 8.4° (SD 16.7°) external TFR in FOD, 1.6° (SD 5.4°) external TFR in SPI, and 2.5° (SD 5.8°) internal TFR in controls (P=0.0089). FOD patients had significantly greater external tibial rotation than the SPI group (P=0.047). Conclusions: The degree of TFR is correlated with severity of patellar instability, with greater external tibial rotation seen in FOD than SPI patients, while TT-TG was not different. Further information on the relationship of TFR and patellar instability will not only improve understanding of pathogenesis and prognosis, but may also direct surgical treatment strategies in refractory or severe cases.

Mulligan Knee Taping Using Both Elastic and Rigid Tape Reduces Pain and Alters Lower Limb Biomechanics in Female Patients With Patellofemoral Pain

Background: Evidence supports the use of Mulligan knee taping in managing patellofemoral pain (PFP). However, no studies have compared the efficacy of rigid and elastic tape using this technique. Hypothesis: Mulligan knee taping applied with both rigid and elastic tape will produce similar reductions in knee pain, hip internal rotation, and knee flexion moments compared with no tape. Elastic tape will also be more comfortable than rigid tape. Study Design: Controlled laboratory study. Methods: A total of 19 female patients (mean age, 26.5 ± 4.5 years) with PFP performed a self-selected pain provocative task, single-leg squat (SLSq) task, and running task while wearing Mulligan knee taping applied with rigid tape, elastic tape at 100% tension, and no tape. Pain and taping comfort were recorded using 11-point numeric rating scales. An 18-camera motion capture system and in-ground force plates recorded 3-dimensional lower limb kinematics and kinetics for the SLSq and running tasks. Statistical analysis involved a series of repeated-measures analyses of variance. The Wilcoxon signed rank test was used for analyzing taping comfort. Results: Compared with no tape, both rigid and elastic tape significantly reduced pain during the pain provocative task (mean difference [MD], –0.97 [95% CI, –1.57 to –0.38] and –1.42 [95% CI, –2.20 to –0.64], respectively), SLSq (MD, –1.26 [95% CI, –2.23 to –0.30] and –1.13 [95% CI, –2.09 to –0.17], respectively), and running tasks (MD, –1.24 [95% CI, –2.11 to –0.37] and –1.16 [95% CI, –1.86 to –0.46], respectively). Elastic tape was significantly more comfortable than rigid tape generally ( P = .005) and during activity ( P = .022). Compared with no tape, both rigid and elastic tape produced increased knee internal rotation at initial contact during the running task (MD, 5.5° [95% CI, 3.6° to 7.4°] and 5.9° [95% CI, 3.9° to 7.9°], respectively) and at the commencement of knee flexion during the SLSq task (MD, 5.8° [95% CI, 4.5° to 7.0°] and 5.8° [95% CI, 4.1° to 7.4°], respectively), greater peak knee internal rotation during the running (MD, 1.8° [95% CI, 0.4° to 3.3°] and 2.2° [95% CI, 0.9° to 3.6°], respectively) and SLSq tasks (MD, 3.2° [95% CI, 2.1° to 4.3°] and 3.8° [95% CI, 2.3° to 5.2°], respectively), and decreased knee internal rotation range of motion during the running (MD, –3.6° [95% CI, –6.1° to –1.1°] and –3.7° [95% CI, –6.2° to –1.2°], respectively) and SLSq tasks (MD, –2.5° [95% CI, –3.9° to –1.2°] and –2.0° [95% CI, –3.2° to –0.9°], respectively). Conclusion: Mulligan knee taping with both rigid and elastic tape reduced pain across all 3 tasks and altered tibiofemoral rotation during the SLSq and running tasks. Clinical Relevance: Both taping methods reduced pain and altered lower limb biomechanics. Elastic tape may be chosen clinically for comfort reasons.

Tibiofemoral rotation alignment in the normal knee joints among Chinese adults: A CT analysis

Background: Consensus on tibial rotation in total knee arthroplasty (TKA) remains controversial. The present study aimed to investigate the closest anatomical reference to surgical epicondylar axis (SEA) among 10 tibial markers in Chinese adults.Methods: This study included examination of 122 normal lower extremities. Briefly, 10 axes were drawn on the axial sections: transverse axis of tibia (TAT), axis of medial edge of patellar tendon (MEPT), axis of medial 1⁄3 of patellar tendon attachment (M1/3), Akagi line, Insall line, axis of medial border of tibial tubercle (MBTT), and axis of anterior border of the tibia 1-4 (ATC1-4). The mean angles between TAT and SEA and that between other axes and the line perpendicular to SEA were measured. Pairwise differences among the 10 tibial axes were examined by applying one-way analysis of variance (ANOVA) and paired t-test.Results: In all the knees, the mean angles of M1/3, Akagi line, Insall line, MBTT, ATC1, ATC2, ATC3, and ATC4 axes were compared to the line perpendicular to the projected SEA and found to be 10.2 ± 5.1°, 1.4 ± 5.0°, 11.9 ± 5.4°, 3.6 ± 4.8°, 12.0 ± 6.9°, 7.2 ± 8.6°, 7.1 ± 10.4°, and 6.6 ± 13.5° external rotation, respectively, and the MEPT axis was 1.6 ± 4.5° internal rotation. The mean angle for TAT was 4.1 ± 5.3° external rotation. The M1⁄3 and Insall line were significantly more externally rotated than Akagi line, MEPT, MBTT, TAT, ATC2, ATC3, and ATC4 axes. No significant differences were noted between the TAT axis and the MBTT axis and among the ATC2, ATC3, and ATC4 axes.Conclusion: The Akagi line, MBTT, and TAT showed good consistency with SEA in the axial femorotibial alignment with knee in extension. The middle segment of the anterior tibial crest also demonstrated good alignment consistency with SEA for the axial femorotibial alignment. Hence, these markers can be used as reliable references for rotational alignment of the tibial component in TKA.