Towards an increased understanding of physiologic and pathologic multidirectional knee laxity measurements: a small step in the individualisation of care of anterior cruciate ligament injuries

ACL injuries are an increasing burden both for individuals, for who a return to preinjury quality of life as well as a limitation of long term consequences such as secondary injuries and osteoarthritis cannot yet be ensured, and for the society, which must cover the high direct and indirect costs of ACL injuries. The general purpose of this thesis was therefore to gain knowledge on ACL-injured patients and their knee laxity through the implementation of individualized patient and knee laxity profiles.
One third of ACL-injured patients are estimated to successfully compensate for their injury without surgery. However, current ACL registries rarely include nonoperatively treated patients thus delivering an incomplete picture of the ACL-injured population. Chapter 2 presents data from an intra-hospital registry and helped to identify 8 specific subtypes of ACL-injured patients according to gender, age, previous ACL injury and preinjury level of practice. The percentage of operated patients varied between these subtypes. The consideration of these patient profiles will help in the future for a better understanding of patients at risk for an ACL injury.
In the management of ACL-injured patients, knee laxity can play a role in prevention, diagnosis and follow-up. While anterior knee laxity is common, static rotational knee laxity has recently received an increased interest. Our understanding of the latter is however insufficient as it is much more complex than the former. For the present thesis, anterior knee laxity was evaluated with the GNRB® and rotational knee laxity with the Rotameter. These 2 devices displayed higher precision than previous arthrometers (Chapter 5). Arthrometers measuring rotational knee laxity display highly variable testing procedures (Chapter 3) which may have influenced the reproducibility of previous devices.
In Chapter 4 and 5, physiological knee laxity revealed to be complex. In healthy controls, anterior knee laxity was not influenced by individual characteristics such as gender, age, height or body mass. However, rotational knee laxity was greater in females compared to males and negatively influenced by body mass. The influence of individual characteristics as well as the high inter-subject variability observed in rotational knee laxity measurements prevented its direct comparison between groups of subjects. The influencing characteristics were thus considered in Chapter 5 to create individualized knee laxity scores. Then, as anterior and rotational knee laxity were poorly related to each other, both were combined to describe knee laxity profiles in healthy subjects. The diversity of identified profiles highlighted the complexity of multidirectional knee laxity. This finding also suggested the necessity to individualize knee laxity measurements in the care of knee injuries in the future. Knee laxity profiles of healthy controls were then compared to the healthy contralateral knee of ACL-injured patients in Chapter 6. The healthy contralateral knees of patients with a noncontact ACL injury displayed both increased internal rotation and anterior displacement compared to the healthy controls. This suggests that it may be relevant to identify an individual knee laxity profile for primary and secondary prevention programs of noncontact ACL injuries.
Finally, Chapter 7 focuses on knee laxity in the injured knees. The combination of anterior and rotational knee laxity measurements led to an excellent diagnostic power for ACL injury, provided that the slope of load-displacement curve was considered concomitantly with the final displacement. With this combination, a positive result was correct in all patients regardless of the subtype (complete, partial or healed) of the ACL tear and the associated injuries. Results in anterior knee laxity could partly distinguish between ACL subtypes of tear but requires further investigation.
Finally, Chapter 8 consists of a general discussion, which critically reviews the results from the current thesis and includes recommendations and future perspectives regarding the use of knee laxity measurements. Overall, the recent development of new arthrometers has offered the possibility to improve the understanding of physiological, pathological knee laxity before and after ACL reconstruction.