Mechanical Laxity Research Articles

Quantitative assessment of mechanical laxity in the functionally unstable ankle.

Delineating between functional and mechanical instability in those with chronic ankle dysfunction is a challenging task. Current methods of assessing ankle ligamentous laxity are subjective in nature and limit our ability to identify the site and extent of instability; therefore, a need exists for objective laxity measurements. The purpose of this study was to determine whether subjects with self-reported, functional ankle instability (FAI) demonstrated increased mechanical laxity when tested with instrumented arthrometry and stress radiography. Both ankles were tested in 51 subjects with self-reported unilateral FAI. An instrumented ankle arthrometer measured ankle-subtalar joint motion for total anteroposterior (AP) displacement (mm) during loading at 125 N and total inversion-eversion (I-E) rotation (degrees of ROM) during loading at 4 N x m. The Telos GA-II/E device provided either anterior or lateral stress (15 kp) while fluoroscopic radiographs were recorded for anterior displacement (mm) and talar tilt (degrees). The arthrometry measurements of anterior and total AP displacement and the radiographic measurements of anterior displacement were greater (P < 0.05) in the FAI ankles when compared with the uninjured ankles. There were no differences in total I-E rotation, inversion rotation, or talar tilt between ankles when analyzed with either measurement technique. The ability to objectively measure mechanical instability in the functionally unstable ankle is important to understanding the nature and cause of the instability. Ankle arthrometry and stress radiographic measurements are objective assessment tools for mechanical laxity. Despite finding greater laxity in the functionally unstable ankle, the clinical significance of the observed displacement remains unanswered. Further research is needed to determine the amount of laxity that constitutes mechanical instability and how this relates to FAI.

Quantitative measurement of ankle passive flexibility using an arthrometer on sprained ankles

Objective. The purpose of this study was to quantitatively examine the flexibility of sprained ankles using an arthrometer device and compare the differences in flexibility between ankles following the first sprains and ankles with repeated severe sprains and chronic symptoms. Design. A retrospective in vivo study was used. Background. Many in vitro studies have demonstrated a significant role of joint flexibility in determining mechanical laxity of human cadaveric ankles after sectioning of the lateral ligaments, but few in vivo studies have used the technique to provide objective measurement on the sprained ankles. Furthermore, there is a lack of extensive studies that compared the difference in the ankle flexibility between ankles following the first sprain and ankles with multiple repeated severe sprains and chronic symptoms. Methods. A total of 27 subjects with unilateral ankle sprains participated in this study. The subjects were divided into a first injury group (group A, n=12) and a chronic symptom group (group B, n=15) based on the history of their ankle injuries. The ankle flexibility in anterior drawer and inversion/eversion tests was measured in both ankles of the subjects using an arthrometer device, the ankle flexibility tester – a six-degree-of-freedom instrumented linkage used for measurements of applied forces/moments and resultant rotations and/or translations of the ankle joint complex. The difference in ankle flexibility between the injured ankle and the contralateral intact side was analyzed. Results. The flexibility in anterior drawer test of the injured ankles significantly increased compared to the intact ankles of the same individual in group B, but the same difference was not significant in group A. There were more subjects in group B (46.6%) than in group A (33.3%) who showed a sign of mechanical laxity in their injured ankles. Conclusions. The results indicated that the approach with measurement of ankle flexibility may be a potential tool used to detect the mechanical laxity in the sprained ankles. A tendency was found that patients with multiple ankle sprains and chronic symptoms had a higher occurrence rate of mechanical laxity. The result of the present study may also be interpreted that the ankles with mechanical laxity had higher risk of re-injury and leading to chronic symptoms. Relevance A non-invasive and objective measurement of ankle flexibility has potential to be developed into a diagnostic tool for the mechanical laxity of sprained ankles. The finding of this study may help clinicians in the plan of patient treatment.

The effects of ankle compliance and flexibility on ankle sprains.

The goal of this study was to examine the influence of changes in subtalar joint flexibility and compliance on ankle sprain occurrence. Muscle model driven simulations of 10 subjects performing the landing phase of a side-shuffle movement were performed. The passive flexibility or compliance of the subtalar joint was varied, and each subject-specific simulation was exposed to a set of perturbed floor conditions. Increases in flexibility and compliance both led to an increase in the occurrence of excessive supination, while changes in flexibility had a greater influence. Changes in flexibility or compliance caused only small changes in the occurrence of excessive supination torques. These results suggest that increased mechanical laxity does not directly cause an increase in sprain occurrence during side-shuffle movements.

Peak Passive Resistive Torque at Maximum Inversion Range of Motion in Subjects With Recurrent Ankle Inversion Sprains

Although a number of mechanical and neuromuscular processes have been identified, the primary mechanisms underlying residual functional instability of the ankle remain unclear. Understanding such mechanisms will help physical therapists identify where to focus treatment efforts, ultimately leading to more effective rehabilitation. In the present investigation, resistive torque at maximum ankle inversion was evaluated to determine if lateral ankle structures demonstrated mechanical laxity. Thirty subjects with a history of unilateral recurrent inversion sprains were tested bilaterally. A custom-made apparatus provided a stress to the lateral ankle in a method that was similar to the inversion stress test. Two measures of laxity were used: maximum passive inversion range of motion and peak passive resistive torque. Differences between the involved and uninvolved ankles were determined using analysis of covariance procedures. There were no significant differences between involved and uninvolved ankles for maximum inversion range of motion and for peak passive resistive torque. Post hoc testing confirmed adequate statistical power. The results support previous investigations, which suggest that functional instability can exist in the absence of mechanical lateral ankle laxity.

Mechanical Properties of the Urethra in Healthy and Stress Incontinent Females: Dynamic Measurements in the Resting Urethra

The relationship between pressure and cross-sectional area in the resting urethra during its inflation and deflation was examined in 30 healthy females and in 30 patients with genuine stress incontinence (GSI). Measurements were performed at the bladder neck, in the high-pressure zone and distally in the urethra.The mechanical properties of the urethra were found to vary significantly as a function of time after induction of a cross-sectional area (stress episode) in both groups of women. The pattern of response of the urethra showed significant differences between normals and GSI particularly during dynamic conditions. Our results indicate that mechanical laxity of the urethra at the bladder neck and midurethrally especially at dynamic events (stress episodes) is of pathophysiological importance in GSI. (J. Urol., 144: 1258–1262, 1990)