Hamstring antagonist torque generated in vivo following ACL rupture and ACL reconstruction

Hamstring Co-Contraction in the Early Stage of Rehabilitation After Anterior Cruciate Ligament Reconstruction: A Longitudinal Study

OBJECTIVE

Hamstring co-contraction may affect recovery from anterior cruciate ligament reconstruction. The aim of the study was to evaluate the changes in hamstring co-contraction during the early postoperative stages.

DESIGN

Twenty-five patients with anterior cruciate ligament reconstruction were followed up for 1-3 mos postoperatively, during which the Lysholm and International Knee Documentation Committee questionnaires were completed and surface electromyograms were assessed during terminal knee extension maximum voluntary contraction and step-up tests. The integrated electromyogram of the tested muscles and co-contraction ratio were analyzed.

RESULTS

Co-contraction ratio during terminal knee extension maximum voluntary contraction at 3 mos postoperatively was significantly less than that at 1 mo postoperatively (P < 0.0083), and it did not significantly differ from that of the uninvolved knee. In contrast, the co-contraction ratio during step-up was significantly higher at 2 and 3 mos postoperatively than that before surgery (P < 0.0167) and for the uninvolved knee (P < 0.05). Moreover, the postoperative hamstring co-contraction ratio in patients with a chronic injury was significantly higher during the step-up test than in patients with an early injury (P = 0.017).

CONCLUSIONS

Hamstring co-contraction ratio during terminal knee extension maximum voluntary contraction recovers during the early postoperative stages. However, hamstring co-contraction ratio during step-up, which may be related to knee joint proprioception, remains high, particularly for patients with a chronic injury.

CLINICAL TRIAL

ChiCTR-COC-17011167.

Quadriceps Strength and Endurance After Posterior Cruciate Ligament Tears Versus Matched Group With Anterior Cruciate Ligament Tears

PURPOSE

This study was designed to compare the preoperative strengths and endurances of the quadriceps and hamstring muscles in patients with anterior cruciate ligament (ACL) versus posterior cruciate ligament (PCL) tears.

METHODS

Quadriceps and hamstring muscle strength and endurance were compared between 20 prospectively enrolled patients with isolated PCL tears and a retrospective, matched control group of 20 patients with isolated ACL tears. The maximal torque (60°/s) and total work (180°/s) of the quadriceps and hamstring were evaluated with an isokinetic testing device.

RESULTS

Total work (1,094.4 ± 505.8 J v 797.5 ± 332.7 J, P = .035) and peak torque (129.9 ± 56.2 N ∙ m v 98.2 ± 37.4 N ∙ m, P = .046) of the quadriceps muscle on the involved side were higher in the PCL tear group than in the ACL tear group. However, there were no significant differences between the PCL tear group and ACL tear group in hamstring muscle strength (45.8 ± 42.3 N ∙ m and 46.0 ± 24.4 N ∙ m, respectively; P = .940) and endurance (429.3 ± 238.9 J and 382.4 ± 256.1 J, respectively; P = .574) on the involved side.

CONCLUSIONS

The strength and endurance of the quadriceps muscle of the injured limb were greater after PCL tears than after ACL tears. However, there were no significant between-group differences in hamstring muscle strength and endurance on the involved side.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Antagonist muscle moment is increased in ACL deficient subjects during maximal dynamic knee extension

INTRODUCTION

Coactivation of the hamstring muscles during dynamic knee extension may compensate for increased knee joint laxity in anterior cruciate ligament (ACL) deficient subjects. This study examined if antagonist muscle coactivation during maximal dynamic knee extension was elevated in subjects with anterior cruciate ligament (ACL) deficiency compared to age-matched healthy controls.

METHODS

Electromyography (EMG) and net knee joint moments were recorded during maximal concentric quadriceps and eccentric hamstring contractions, performed in an isokinetic dynamometer (ROM: 90-10°, angular speed: 30°/s). Hamstring antagonist EMG recorded during concentric quadriceps contraction was converted into antagonist moment based on the EMG-moment relationship observed during eccentric agonist contractions.

RESULTS

The magnitude of antagonist hamstring EMG was 65.5% higher in ACL deficient subjects compared to healthy controls (p<0.05). Likewise, antagonist hamstring moment expressed in percentage of the measured net extension moment was elevated in ACL deficient subjects (56 ± 8 to 30 ± 6%) compared to controls (36 ± 5 to 19 ± 2%) at 20-50° of knee flexion (0°=full extension) (p<0.05).

DISCUSSION

The results showed a marked increase in hamstring coactivation towards more extended joint positions. Notably, this progressive rise in coactivation was greater in ACL deficient subjects, which may reflect a compensatory strategy to provide stability to the knee joint in the anterior-posterior plane during isolated knee extension. The present study encourages further investigations of hamstring coactivation in ACL deficient subjects.

Effects of dimethylolpropionic acid modification on the characteristics of polyethylene terephthalate fibers

Polyethylene terephthalate (PET) fibers are widely used in the preparation of artificial ligaments. However, due to their lack of hydrophilicity, PET fibers have low biocompatibility, which usually results in the poor biological activity of the products. In the present study, in order to improve the hydrophilicity and biocompatibility of PET fibers, we modified their surface using dimethylolpropionic acid (DMPA). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), tensile testing and cell culture were employed to observe the effects of DMPA modification on the characteristics of the DMPA-PET fibers. In contrast to the original PET fibers, the surface of the DMPA-PET fibers became rough as demonstrated by SEM. The FTIR spectrum further confirmed that a number of hydrophilic groups were formed on the surface of DMPA-PET. However, there were no significant changes in crystallinity and tensile strength between the PET and the DMPA-PET fibers as revealed by DSC and XRD (P>0.05). Finally, the cell co-culture test revealed that the adhesion and proliferation of bone marrow‑derived stromal cells increased greatly on the DMPA-PET fibers compared to those on the original PET fibers (P<0.05). These results demonstrate that DMPA-PET fibers have significant potential as a material for the development of artificial ligaments.