Purpose: While changes in muscle quality and quantity are common concerns as knee osteoarthritis (KOA) progresses, it is equally important to consider the central nervous system’s role in regulating muscle force output. This study aimed to elucidate the firing properties of motor units (MUs), muscle quantity, and muscle quality during submaximal isometric contractions in patients with early and severe KOA. Methods: This was a prospective study comparing 30 patients with KOA according to the Kellgren/Lawrence grading system divided into early and severe KOA groups. The participants performed ramp-up and sustained contractions at 10%, 30%, and 60% of their maximal voluntary contraction (MVC). High-density surface electromyography signals were recorded in the vastus medialis (VM) and vastus lateralis (VL) muscles on the affected side. Skeletal muscle quantity and quality were assessed using computed tomography based on cross-sectional area (CSA) and computed tomography attenuation value (CTV), respectively. Results: The CSA of the VM muscle was significantly smaller in the severe KOA group than in the early KOA group (p = 0.021). A total of 682 MUs were detected (early KOA, n = 348, severe KOA, n = 334). The ramp-down phase of the discharge rate (DR) of MUs recruited by the VL muscle in the severe KOA group was significantly lower than that in the early KOA group (p = 0.004). In addition, the knee extension torque of patients with early KOA was significantly correlated with the CSA of the VM muscle (r = 0.405) and the DR obtained at 30% MVC of the VM (r = 0.503) and VL (r = 0.610) muscle. Furthermore, the knee extension torque in patients with severe KOA was significantly correlated with the CTV of the VM (r = 0.677) and VL (r = 0.599) muscles. Conclusions: In patients with severe KOA, a small CSA of the VM is associated with a characteristic DR pattern depending on the contraction level. The VM and VL muscles fired without a hierarchical pattern in the early and severe KOA groups. These findings suggest that neuromuscular degeneration may occur not only in patients with severe KOA but also in patients with early KOA.

Background/Objectives: This single-center cohort study investigated preoperative risk factors such as physical function, quantity, and quality of the quadriceps femoris for physical activity (PA) 1 year after total knee arthroplasty (TKA). Methods: This study included 204 patients with knee osteoarthritis who underwent TKA; they were divided into increased and decreased PA groups. Items with significant differences between the two groups in non-operative-side quadriceps strength, knee injury and osteoarthritis outcome scores (KOOS), Sport/Rec scores, operative-side cross-sectional area (CSA) of the vastus medialis (VM), and operative-side computed tomography attenuation values (CTV) of the vastus lateralis (VL) were fitted in the multiple logistic regression analysis. The cutoff value of the preoperative CSA of the VM required for PA to exceed the required points at 1 year postoperatively was calculated using the receiver operating characteristic (ROC) curve. Results: Multivariate logistic regression analysis showed that the non-operative-side quadriceps strength KOOS sport/rec, operative-side CSA of VM, and operative-side CTV of the VL were significantly associated with increased PA after TKA. The ROC-calculated cutoff value was 10.2 cm². Conclusions: These results suggested that preoperative muscle quantity and quality, particularly in the VM, could play important roles in postoperative PA outcomes after TKA.

This prospective study aimed to investigate the relationship between preoperative psychological competitive ability and preoperative and 6 months postoperative subjective knee function in patients undergoing anterior cruciate ligament (ACL) reconstruction. Eighty-four patients who underwent ACL reconstruction and had a Tegner Activity Scale score of 6 or more were included in this study. Preoperatively, all patients were administered the Diagnostic Inventory of Psychological Competitive Ability for Athletes (DIPCA.3) for psychological competitive ability assessment and the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form for subjective knee function assessment. The IKDC subjective score was re-evaluated 6 months postoperatively. We evaluated the associations of volition for competition, mental stability and concentration, confidence, strategic ability, and cooperation (DIPCA.3 factors) with the IKDC subjective score preoperatively and 6 months postoperatively. Furthermore, patients were classified into two groups according to whether they could return to participate in the entire practice and compared the DIPCA.3 total score and IKDC subjective score. The DIPCA.3 confidence score negatively correlated with the preoperative IKDC subjective score (β = −0.34, p = 0.04). However, there was no association between the DIPCA.3 score for all variables and IKDC subjective score at 6 months after ACL reconstruction. Moreover, the DIPCA.3 total score was not related to return to participate in the entire practice 6 months after ACL reconstruction. Psychological competitive ability is not associated with a return to participate in the entire practice, and a low preoperative IKDC subjective score should not be viewed too negatively.

Background: Restoring knee extensor strength after anterior cruciate ligament (ACL) reconstruction using a quadriceps tendon (QT) autograft remains challenging. Whether altered quadriceps neuromuscular activity contributes to this weakness is unclear. Hypothesis: Quadriceps strength recovery after ACL reconstruction using QT would be impaired owing to altered quadriceps neuromuscular activity. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 31 patients (Tegner activity scale score ≥7) who had undergone ACL reconstruction 4 months earlier were enrolled into either the QT group (n = 15) or hamstring tendon (HT) group (n = 16). Knee extensor strength was assessed using maximum voluntary isometric and isokinetic (60 deg/s) force. Neuromuscular activity of the vastus lateralis (VL) and vastus medialis (VM) during isometric contraction was recorded with high-density surface electromyography to evaluate motor unit discharge rate (MU DR). A generalized linear mixed-effects model was used to test side (involved and uninvolved limbs) and task (25%, 50%, and 70% of isometric contraction) effects, and regression analysis was used to examine associations between side-to-side isometric strength and MU DR differences. Results: Baseline characteristics did not differ significantly between the QT (9 males, 6 females; mean age, 17.1 ± 3.9 years) and HT (10 males, 6 females; mean age, 18.2 ± 2.7 years) groups. The mean time from surgery to testing was also similar (QT group: 120.8 ± 8.0 days; HT group: 121.3 ± 7.2 days). The limb symmetry index for isometric strength showed no difference (QT group: 75.0% ± 19.6%; HT group: 78.2% ± 14.3%; P = .63). In contrast, isokinetic strength at 60 deg/s was significantly lower in the QT group (70.5% ± 13.2%) than in the HT group (83.9% ± 11.6%) ( P < .01). In the QT group, MU DR showed a side × task interaction, with higher discharge in the involved (11.7 ± 3.2 pluse per second [pps]) versus uninvolved (10.4 ± 1.9 pps) limbs during 70% isometric contraction in VM ( P < .01). Correlations were observed between isometric strength differences and MU DR in both VL ( r = 0.65; P = .01) and VM ( r = 0.67; P = .01). Conclusion: Neuromuscular changes were evident in the QT group, particularly in the VM, but not in the HT group. Notably, in the QT group, altered MU activity was correlated with muscle strength decline.