Joint-afferent-mediated muscle activations yield a near-maximum torque response of the quadriceps

The hamstring/quadriceps ratio is an indicator of function in ACL-deficient, but not in ACL-reconstructed knees

PURPOSE

The purpose of this study was to investigate the isokinetic, eccentric and isometric hamstring/quadriceps (HQ) ratios in patients before and after ACL reconstruction (ACLR) using bone-patellar tendon grafts and to establish the relationships between HQ ratio and knee function.

METHODS

Forty-four patients (mean age of 26.6 years) underwent isokinetic testing of quadriceps and hamstring muscles before and after ACLR and HQ ratios were calculated. Lysholm, IKDC and Cincinnati Scores were used to assess function. Isokinetic concentric and eccentric peak torque (Nm/kg) was measured at three different speeds: 60, 120, and 180°/s. Isometric strength was tested at 30° and 60° of knee flexion.

RESULTS

For the isometric tests, the HQ ratio between the involved and non-involved limb was not different for the ACLD knee (p = 0.28) at 30° knee flexion, but significant at the 60° flexion angle (p = 0.02) and for the ACLR knees at 30° and 60° (p = 0.02). For the isokinetic tests, the ratio between involved and non-involved limb was significant for ACL-deficient knees at both 60 (p = 0.039) and 120°/s (p = 0.05). There were significant differences between limbs for all speeds in ACLR knees (p = 0.0003-0.01). For the eccentric tests, the HQ ratio between the involved and non-involved limbs was not significant for both the ACLD (p = 0.19) and ACLR knees (p = 0.29) at the speed of 60°/s. At 120 and 180°/s, there were significant differences between limbs for both the ACLD (p = 0.02) and ACLR knees (p = 0.003). Linear regression did not reveal significant relationships between Cincinnati, Lysholm, and IKDC scores and HQ ratios in the ACLD (R² = 0.35, p = 0.58; R² = 0.34, p = 0.63; R² = 0.38, p = 0.49). In contrast, there were significant correlations between the Lysholm and IKDC scores and HQ ratios in the ACLR knees (R² = 0.84, p = 0.002; R² = 0.86, p = 0.001).

CONCLUSIONS

The findings of this study suggest that the HQ ratio in ACLD patients was not a predictor, but an indicator of patient-perceived knee function following ACLR.

LEVEL OF EVIDENCE

Level IV, case series.

A three-dimensional biomechanical evaluation of quadriceps and hamstrings function using electrical stimulation

Neurological disorders such as stroke impair locomotor control and result in abnormal 3-D gait kinematics. Establishment of effective rehabilitation strategies requires an understanding of how individual muscles contribute to pathological movement. Forward dynamic simulations account for complexities of interjoint coupling and can be used to predict dynamic muscle function. However to date, limited experimental validations of dynamic models have been performed. Our objective was to measure 3-D movement induced by the biceps femoris (BF), rectus femoris (RF), and vastus lateralis (VL) in limb configurations corresponding to the swing phase of gait, and to assess the biomechanical factors that affect dynamic function. Subjects were positioned in a robotic gait orthosis that included a compliant interface. Electrical stimulation was introduced into individual muscles while induced hip and knee joint movements were recorded. Measured hip to knee sagittal plane acceleration ratios were consistent with dynamic musculoskeletal model simulations. However RF and VL induced substantially larger frontal plane hip movements than model-based predictions. Sensitivity analyses on musculoskeletal model parameters revealed that muscle function depends primarily on moment arm assumptions. Though generic musculoskeletal models are suitable for predicting sagittal plane muscle function, improvements in moment arm accuracy are essential for investigation of 3-D pathological gait.

Determination of the abduction-adduction axis of rotation at the human knee: helical axis representation

This study used a finite helical axes representation to derive the axis of rotation of the human knee in the frontal plane for the neutral flexion/extension posture during resting and no load-bearing conditions. The three-dimensional finite helical axis pathway of the tibia relative to the femur was computed by passively adducting/abducting the lower limb via a servomotor system. Knee joint movements as a result of the positional perturbations were captured with an active marker kinematic tracking system. Contrary to traditional assumptions used in studies conducted under a similar experimental paradigm, our results indicated that the knee joint center, defined as the intercept point between the finite helical axis and the mid-coronal plane of the distal femur, was located within the femoral notch for a wide range of abduction and adduction angles (6 degrees abduction to 6 degrees adduction angles). Our data also indicated that at the neutral posture of the knee, the helical axes directions change as a function of the abduction/adduction perturbation angle. These findings are not only essential to error minimization during joint moment calculations, but can also facilitate new biomechanical interpretations of, for example, the functional role of the quadriceps and patellofemoral joint mechanics to overall knee stability in the medial-lateral direction.

The role of LPA1 in formation of synapses among cultured hippocampal neurons

We studied the lysophosphatidic acid receptor-1 (LPA1) gene, which we found to be expressed endogenously in cultured hippocampal neurons, and in vivo in young (1-week-old) rat brain slices. Overexpressed green fluorescent protein (GFP)-tagged, membrane-associated LPA1 accumulated in a punctate manner over the entire dendritic tree and caused an increase in dendritic spine density. About half of the dendritic spines in the LPA1-transfected neurons displayed distinct fluorescent puncta, and this subset of spines was also substantially larger than puncta-free, LPA1-transfected or control GFP spines. This phenotype could also be seen in cells transfected with a ligand-binding, defective mutant and is therefore not dependent on interaction with an ambient ligand. While spontaneous miniature excitatory synaptic currents were of the same amplitudes, they decayed slower in LPA1-transfected neurons compared with GFP controls. We propose that LPA1 may play a role in the formation and modulation of the dendritic spine synapse.