Male and female gait compensations in a mouse model of medial meniscus destabilization

Abstract

Purpose: Destabilization of the medial meniscus (DMM) has become a common method for modeling the development of post-traumatic knee osteoarthritis in mice. Moreover, following a DMM surgery, male and female mice develop histologic signs of cartilage damage at different rates. Less is known about the development of disability in this model, as characterizations of the mouse gait pattern have been limited and primarily focused on spatiotemporal gait patterns. Recently, our group developed a highly sensitive gait analysis platform capable of detecting rodent spatiotemporal gait patterns in conjunction with ground reaction forces. Therefore, the aim of this study is to evaluate quadrupedal gait compensations and joint degeneration in male and female mice after DMM. Methods: For 20 C57/Bl6 mice, a medial para-patellar ligament incision was made on the right hind limb, and blunt dissection revealed the medial meniscotibial ligament. Sham animals (5 male, 5 female) were then closed. For DMM animals (5 male, 5 female), the meniscotibial ligament was transected and animals were closed. Ground reaction force data and spatiotemporal gait data were collected at 2, 4, 6, 9, and 12 weeks post-surgery. Animals were placed in a gait arena and allowed to freely explore. Ultra-high speed video (500fps) recorded sagittal and ventral views as the animal crossed the arena and walked over force panels. A linear regression was used to describe the expected gait for male or female sham animals at a given velocity and body weight. Residuals were calculated from this control line to determine the expected gait pattern at a given velocity and body weight. Groups were compared using a 2-way ANOVA with interaction (α = 0.05), while gait symmetries and imbalances were compared to expected values using Bonferroni-corrected student's t-tests. After 12 weeks, animals were euthanized, and knees were processed for histological grading. Results: Male DMM mice used higher hind limb duty factors in both limbs compared to sham animals (Fig 1A, left P = 0.001, right P = 0.037). Male DMM mice also used shorter stride lengths (P = 0.007). Both fore and hind limb peak vertical forces were lower in male DMM mice compared to sham mice (Fig 1C & 1E, fore left P = 0.001, fore right P = 0.029, hind left P = 0.010). Female DMM mice walked with lower hind limb duty factors compared to sham animals (Fig 1B, left P = 0.045, right P = 0.001), were temporally asymmetric in the hind limbs at week 12 (P = 0.005), and significantly loaded the right hind limb more than sham animals (Fig 1F, P = 0.039). Female DMM mice also took longer to load the right hind limb (P = 0.004). Histology confirmed no cartilage loss or osteophyte formation in sham animals. Male and female DMM animals presented similar cartilage matrix loss at the surface and at 50% lesion depths at 12 weeks. Additionally, total cartilage degeneration width was similar between genders (male = 69.81 ± 18.5%, female = 69.9 ± 28.9%). Conclusions: Male and female mice selected different gait compensations following meniscus destabilization. Male mice developed higher hind limb duty factors, indicating more time spent in stance on both limbs. Additionally, male DMM mice had shorter stride lengths and normal gait symmetries. Male DMM mice also had lower peak vertical forces on both hind limbs. Combined, these data indicate a bilateral shuffle-step compensation. Shuffle-stepping may protect the limb by reducing time where either leg must support load without contralateral support. Female DMM mice used lower hind limb duty factors in the right hind limb (injured). Additionally, female mice placed more load on the right hind limb, but also took longer to load the injured limb. Combined, these data may indicate a steppage gait compensation. It is not clear why male shuffle-step and female mice use a steppage-like compensation. These gender differences warrant further exploration, but may be important to how male and female animals respond to orthopaedic injuries. Finally, our histological data demonstrate the development of OA lesions in both male and female mice at 12 weeks. While prior reports have detailed more severe OA lesions in male mice relative to female mice, these histological investigations largely focused on post-operative timepoints of 8 weeks or less. Thus, it is plausible that the severity of OA in female mice had approached that of male mice by 12 weeks. Regardless, the two sexes developed different gait compensations in response to the injury, further highlighting sex differences in the progression of OA in mice.