Passive knee joint range of motion is unrelated to the mechanical properties of the patellar tendon

Passive torque influences the Hoffmann reflex pathway during the loading and unloading phases of plantar flexor muscles stretching

This study investigated the influence of passive tension on Hoffmann reflex during the loading (muscle stretched by passive joint movement) and unloading phase (joint returned to initial position) of muscle stretching. The maximal H‐reflex amplitude (H_max) was recorded in soleus in 19 young adults during the loading and unloading phases of a passive 30° dorsiflexion, from 90° ankle angle (reference position). H_max was evoked at similar angles (protocol‐1) or similar passive torque (PT; protocol‐2) during the loading and unloading phases, or during two loading phases separated by a 5‐min stretch hold at 30° ankle dorsiflexion relative to the reference position (protocol‐3). Homosynaptic depression (HD) was assessed with paired H reflexes (0.5‐s interstimulus interval) during the loading and unloading phases (protocol‐4; n=13). In protocol‐1, PT was lesser and H_max greater during the unloading than the loading phase (p < 0.001). In protocol‐2, no difference in H_max was observed between phases. In protocol‐3, PT was lesser and H_max greater during the second than the first loading phase (p < 0.001). Changes in PT during in these three protocols were associated with those in H_max (r² ≥ 0.97). In protocol‐4, HD increased and decreased during the loading and unloading phases, respectively (p < 0.001), without differing between phases. Additional experiments (n=12) showed a similar modulation of H_max in gastrocnemius medialis during loading and unloading phases, while muscle fascicle length did not differ between phases. This study indicates that the H‐reflex modulation during muscle stretching relies in part on mechanisms associated with the PT developed by the muscle‐tendon unit.

Patellar tendon length during knee flexion of meniscal-bearing and rotating total knee arthroplasty implants

PURPOSE

The length of the patellar tendon after total knee arthroplasty (TKA) has most commonly been compared with preoperative measurements. However, there are no reports that discuss changes in the length of the patellar tendon during knee flexion after TKA. The purpose of this study was to evaluate changes in the length of the patellar tendon during knee flexion and to clarify the impact of changes in patellar tendon strain on the length of the patellar tendon and post-operative range of motion (ROM) after TKA.

METHODS

Thirty-six patients undergoing sequential bilateral TKA for osteoarthritis were evaluated. Patients received a meniscal-bearing (MB) implant on one side and a rotating platform (RP) implant on the other and were followed for a median of 115 months (range 60-211 months). The lengths of the patellar tendon at maximum extension, 30°, 60°, 90° and maximum flexion were measured, and the post-operative ROM of both knees were assessed. The effects of implant design and the knee flexion angle on the length of the patellar tendon were analysed using a linear mixed-effects model. The relationship between patellar tendon strain and post-operative knee ROM was assessed using Pearson's correlation coefficients.

RESULTS

Post-operative clinical scores were similar for MB and RP implants. Neither the implant design nor the knee flexion angle significantly affected the length of the patellar tendon. The ROMs in the two designs at final follow-up were equivocal (114° in MB, 113° in RP). There was no correlation between patellar tendon strain and ROM in knees with either implant type.

CONCLUSIONS

Patellar tendon lengths after mobile-bearing TKA with implants that permitted different anteroposterior constraints were relatively constant at varying degrees of knee flexion. Differences in patellar tendon strain may not impact ROM. These results provide conclusive evidence that the quality of the patellar tendon may play a less important role in ROM after TKA.

LEVEL OF EVIDENCE

Therapeutic study, Level II.