Healing ligaments have shorter lifetime and greater strain rate during fatigue than creep at functional stresses

Does mechanical loading restore ligament biomechanics after injury? A systematic review of studies using animal models

BACKGROUND

Mechanical loading is purported to restore ligament biomechanics post-injury. But this is difficult to corroborate in clinical research when key ligament tissue properties (e.g. strength, stiffness), cannot be accurately measured. We reviewed experimental animal models, to evaluate if post-injury loading restores tissue biomechanics more favourably than immobilisation or unloading. Our second objective was to explore if outcomes are moderated by loading parameters (e.g. nature, magnitude, duration, frequency of loading).

METHODS

Electronic and supplemental searches were performed in April 2021 and updated in May 2023. We included controlled trials using injured animal ligament models, where at least one group was subjected to a mechanical loading intervention postinjury. There were no restrictions on the dose, time of initiation, intensity, or nature of the load. Animals with concomitant fractures or tendon injuries were excluded. Prespecified primary and secondary outcomes were force/stress at ligament failure, stiffness, laxity/deformation. The Systematic Review Center for Laboratory animal Experimentation tool was used to assess the risk of bias.

RESULTS

There were seven eligible studies; all had a high risk of bias. All studies used surgically induced injury to the medial collateral ligament of the rat or rabbit knee. Three studies recorded large effects in favour of ad libitum loading postinjury (vs. unloading), for force at failure and stiffness at 12-week follow up. However, loaded ligaments had greater laxity at initial recruitment (vs. unloaded) at 6 and 12 weeks postinjury. There were trends from two studies that adding structured exercise intervention (short bouts of daily swimming) to ad libitum activity further enhances ligament behaviour under high loads (force at failure, stiffness). Only one study compared different loading parameters (e.g. type, frequency); reporting that an increase in loading duration (from 5 to 15 min/day) had minimal effect on biomechanical outcomes.

CONCLUSION

There is preliminary evidence that post-injury loading results in stronger, stiffer ligament tissue, but has a negative effect on low load extensibility. Findings are preliminary due to high risk of bias in animal models, and the optimal loading dose for healing ligaments remains unclear.

The impaired healing hypothesis: a mechanism by which psychosocial stress and personal characteristics increase MSD risk?

While the effects of physical risk factors on MSD development have been a primary focus of musculoskeletal research, psychological stressors, and certain personal characteristics (e.g. ageing, sex, and obesity) are also associated with increased MSD risk. The psychological and personal characteristics listed above share a common characteristic: all are associated with disruption of the body's neuroendocrine and immune responses resulting in an impaired healing process. An impaired healing response may result in reduced fatigue life of musculoskeletal tissues due to a diminished ability to keep pace with accumulating damage (perhaps reparable under normal circumstances), and an increased vulnerability of damaged tissue to further trauma owing to the prolonged healing process. Research in engineered self-healing materials suggests that decreased healing kinetics in the presence of mechanical loading can substantially reduce the fatigue life of materials. A model of factors influencing damage accrual and healing will be presented. Practitioner summary: This article provides a potential reason why musculoskeletal disorder risk is affected by psychosocial stress, age, sex, and obesity. The reason is that these factors are all associated with a slower than normal healing response. This may lead to faster damage development in musculoskeletal tissues resulting in higher MSD risk.

Identifying Range-of-Motion Deficits and Talocrural Joint Laxity After an Acute Lateral Ankle Sprain

CONTEXT

Approximately 72% of patients with an ankle sprain report residual symptoms 6 to 18 months later. Although 44% of patients return to activity in less than 24 hours after experiencing a sprain, residual symptoms should be evaluated in the long term to determine if deficits exist. These residual symptoms may be due to the quality of ligament tissue and motion after injury.

OBJECTIVE

To compare mechanical laxity of the talocrural joint and dorsiflexion range of motion (DFROM) over time (24 to 72 hours, 2 to 4 weeks, and 6 months) after an acute lateral ankle sprain (LAS).

DESIGN

Cross-sectional study.

SETTING

Athletic training research laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 108 volunteers were recruited. Fifty-five participants had an acute LAS and 53 participants were control individuals without a history of LAS.

MAIN OUTCOME MEASURE(S)

Mechanical laxity (talofibular interval and anterior talofibular ligament length) was measured in inversion (INV) and via the anterior drawer test. The weight-bearing lunge test was conducted and DFROM was measured. The data were analyzed using repeated-measures analysis of variance, independent-samples t tests, and 1-way analysis of variance.

RESULTS

Of the 55 LASs, 21 (38%) were grade I, 27 (49%) were grade II, and 7 (13%) were grade III. Increases were noted in DFROM over time, between 24 and 72 hours, at 2 to 4 weeks, and at 6 months (P < .05). The DFROM was less in participants with grade III than grade I LASs (P = .004) at 24 to 72 hours; INV length was greater at 24 to 72 hours than at 2 to 4 weeks (P = .023) and at 6 months (P = .035) than at 24 to 72 hours. The anterior drawer length (P = .001) and INV talofibular interval (P = .004) were greater in the LAS group than in the control group at 6 months.

CONCLUSIONS

Differences in range of motion and laxity were evident among grades at various time points and may indicate different clinical responses after an LAS.

Long-term Effect of a Single Subcritical Knee Injury: Increasing the Risk of Anterior Cruciate Ligament Rupture and Osteoarthritis

BACKGROUND

Rupture of the anterior cruciate ligament (ACL) is a well-known risk factor for the development of posttraumatic osteoarthritis (PTOA), but patients with the "same injury" can have vastly different trajectories for the onset and progression of disease. Minor subcritical injuries preceding the critical injury event may drive this disparity through preexisting tissue pathologies and sensory changes.

PURPOSE

To investigate the role of subcritical injury on ACL rupture risk and PTOA through the evaluation of pain behaviors, joint mechanics, and tissue structural change in a mouse model of knee injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten-week-old male C57BL/6J mice were allocated to naïve control and subcritical knee injury groups. Injury was induced by a single mechanical compression to the right hindlimb, and mice were evaluated using joint histopathology, anteroposterior joint biomechanics, pain behaviors (mechanical allodynia and hindlimb weightbearing), and isolated ACL tensile testing to failure at 1, 2, 4, or 8 weeks after injury.

RESULTS

Subcritical knee injury produced focal osteochondral lesions in the patellofemoral and lateral tibiofemoral compartments with no resolution for the duration of the study (8 weeks). These lesions were characterized by focal loss of proteoglycan staining, cartilage structural change, chondrocyte pathology, microcracks, and osteocyte cell loss. Injury also resulted in the rapid onset of allodynia (at 1 week), which persisted over time and reduced ACL failure load (P = .006; mean ± SD, 7.91 ± 2.01 N vs 9.37 ± 1.01 N in naïve controls at 8 weeks after injury), accompanied by evidence of ACL remodeling at the femoral enthesis.

CONCLUSION

The present study in mice establishes a direct effect of a single subcritical knee injury on the development of specific joint tissue pathologies (osteochondral lesions and progressive weakening of the ACL) and allodynic sensitization. These findings demonstrate a predisposition for secondary critical injuries (eg, ACL rupture) and an increased risk of PTOA onset and progression (structurally and symptomatically).

CLINICAL RELEVANCE

Subcritical knee injuries are a common occurrence and, based on this study, can cause persistent sensory and structural change. These findings have important implications for the understanding of risk factors of ACL injury and subsequent PTOA, particularly with regard to prevention and management strategies following an often underreported event.

Fatigue damage of collagenous tissues: experiment, modeling and simulation studies

Mechanical fatigue damage is a critical issue for soft tissues and tissue-derived materials, particularly for musculoskeletal and cardiovascular applications; yet, our understanding of the fatigue damage process is incomplete. Soft tissue fatigue experiments are often difficult and time-consuming to perform, which has hindered progress in this area. However, the recent development of soft-tissue fatigue-damage constitutive models has enabled simulation-based fatigue analyses of tissues under various conditions. Computational simulations facilitate highly controlled and quantitative analyses to study the distinct effects of various loading conditions and design features on tissue durability; thus, they are advantageous over complex fatigue experiments. Although significant work to calibrate the constitutive models from fatigue experiments and to validate predictability remains, further development in these areas will add to our knowledge of soft-tissue fatigue damage and will facilitate the design of durable treatments and devices. In this review, the experimental, modeling, and simulation efforts to study collagenous tissue fatigue damage are summarized and critically assessed.

Proprioceptive Training and Injury Prevention in a Professional Men's Basketball Team: A Six-Year Prospective Study

Single limb stance instability is a risk factor for lower extremity injuries. Therefore, the development of proprioception may play an important role in injury prevention. This investigation considered a professional basketball team for 6 years, integrating systematic proprioceptive activity in the training routine. The purpose was to assess the effectiveness of proprioceptive training programs based on quantifiable instability, to reduce ankle sprains, knee sprains, and low back pain through developing refined and long-lasting proprioceptive control. Fifty-five subjects were studied. In the first biennium (2004-2006), the preventive program consisted of classic proprioceptive exercises. In the second biennium (2006-2008), the proprioceptive training became quantifiable and interactive by means of electronic proprioceptive stations. In the third biennium (2008-2010), the intensity and the training volume increased while the session duration became shorter. Analysis of variance was used to analyze the differences in proprioceptive control between groups, years, and bienniums. Injury rates and rate ratios of injury during practices and games were estimated. The results showed a statistically significant reduction in the occurrence of ankle sprains by 81% from the first to the third biennium (p < 0.001). Low back pain showed similar results with a reduction of 77.8% (p < 0.005). The reduction in knee sprains was 64.5% (not significant). Comparing the third biennium with the level of all new entry players, proprioceptive control improved significantly by 72.2% (p < 0.001). These findings indicate that improvements in proprioceptive control in single stance may be a key factor for an effective reduction in ankle sprains, knee sprains, and low back pain.

Time-dependent damage in predictions of fatigue behaviour of normal and healing ligaments

Ligaments are dense fibrous tissues that connect bones across a joint and are exposed daily to creep and fatigue loading. Ligaments are tensile load-bearing tissues; therefore, fatigue loading will have a component of time-dependent damage from the non-zero mean stress and cycle-dependent damage from the oscillating stress. If time-dependent damage is not sufficient to completely predict the fatigue response, then cycle-dependent damage could be an important contributor. Using data from normal ligaments (current study and Thornton et al., Clin. Biomech. 22:932-940, 2007a) and healing ligaments (Thornton and Bailey, J. Biomech. Eng. 135:091004-1-091004-6, 2013), creep data was used to predict the fatigue response considering time-dependent damage. Relationships between creep lifetime and test stress or initial strain were modelled using exponential or power-law regression. In order to predict fatigue lifetimes, constant rates of damage were assumed and time-varying stresses were introduced into the expressions for time-dependent damage from creep. Then, the predictions of fatigue lifetime were compared with curvefits to the fatigue data where exponential or power-law regressions were used to determine the relationship between fatigue lifetime and test stress or initial strain. The fatigue prediction based on time-dependent damage alone greatly overestimated fatigue lifetime suggesting that time-dependent damage alone cannot account for all of the damage accumulated during fatigue and that cycle-dependent damage has an important role. At lower stress and strain, time-dependent damage was a greater relative contributor for normal ligaments than healing ligaments; however, cycle-dependent damage was a greater relative contributor with incremental increases in stress or strain for normal ligaments than healing ligaments.