Summary

The role of the ACL as an anatomic structure for proprioception in joint motion is not completely understood. This study was able to show early changes in posture, reflected on an outcome level (e.g. weight balance distribution, stiffness) six weeks after ACL Surgery. In addition, an initial correlation with the somatosensoric system could be detected by posturography (Interactive Balance System).

Abstract

Introduction

The ACL plays a major role in the propioceptive loop of the knee joint. As a sensor unit it is responsible to feedback joint position and motion to central nervous system. Surgery of the ACL does not exclusively restore this function. Therefore, patients need a long time of rehabilitation and active training to accomplish sufficient joint propioception. Longitudinal pre- and post-operative evaluation of postural restoration in stability and their sub-systems are not completely investigated yet. A similar situation is postulated for the influence of a torn ACL to postural control and regulation acting like a „sensor defect and deficiency“.

Materials And Methods

77 patients with an ACL tear (30 female, 47 male, age: 31.3±11.3 years) were analysed during the entire process of rehabilitation (before surgery, 6, 12 and 24 weeks after ACL-Surgery) with the Interactive Balance System (IBS, neurodata, Wien, Austria). We here present the data of comparison from examination 1 (before surgery) to examination 2 (six weeks after surgery). The IBS consists of four independent force plates attached to the heels and forefeet in order to measure postural regulation (sampling rate: 32 Hz). Postural regulation was defined as stability indicator, weight distribution index, synchronization and sway intensities at different frequency ranges, determined by Fast Fourier Transformation (FFT) of the postural sway waves. The Fourier spectrum of postural sway is subdivided into four ranges of frequencies (F1: 0.03–0.1 Hz; F2-4: 0.1–0.5 Hz; F5-6: 0.5–1.0 Hz; F7-8: > 1.0 Hz). Postural subsystems were associated with these frequency bands (F1: optic and nigrostriatal system; F2-4: peripheral–vestibular system; F5-6: somatosensory system; F7-8: cerebellar system) based on numerous validity studies.

Results

After 6 weeks (Exam 1 to Exam 2), we observed significantly improvements in F5-6 (Eta²=0.147), postural stability (Eta²=0.120), weight distribution/postural stiffness (Eta²=0.163) and synchronization (Eta²=0.177). Based on a different analysis of patients with left- (n=35) and right-sided ACL injury (n=42), we calculated a significantly improvement in lateral direction. The patients were able to move their center of pressure in a more central position and avoided their protective posture (e.g., parameter left (%) right sided ACL injury: exam 1: 59.3 ± 10.5 vs. exam 2: 53.6 ± 4.11; Eta²=0.268). In contrast, the overload of forefeet (parameter: heel (%)) continued to increase in both populations (e.g., right sided ACL injury: exam 1: 45.1 ± 7.28 vs. exam 2: 42.0 ± 5.45; Eta²=0.176).

Conclusions

Our data highly demonstrate the negative consequences of an ACL-injury to postural stability and control to the patients, even after surgery and before intensive rehabilitation. The significant interaction of the anatomic pathology of the ACL-tear with the frequency range F5-6 (for somatosensoric system) underscores the validity of the IBS-system. Our results clearly show the massive influence of the injury and consecutive surgery of the ACL to the sensoric system. The IBS provides an assessment to depict postural rehabilitation after surgery sensitive, under low-risk and delivers valuable informations for physicians and therapists.