The Need for an Objective Measurement In Vivo of Rotational Stability of the ACL-Deficient Knee: How Can We Measure It?

Abstract

Rotational stability plays a key role in restoring normal function of the knee after anterior cruciate ligament (ACL) reconstruction [15]. Therefore, the accurate evaluation of rotational stability would be an important outcome indicator of ACL reconstruction. The only clinical test for examining rotational stability of the knee is the pivot-shift test [46]. Most surgeons now recognize the importance of the pivot-shift test. A positive pivot-shift test, regardless of the grade, is indicative of a functionally deficient ACL and remains the sine qua non indication for surgery [13]. Moreover, it is predictive of poor subjective and objective outcome, patient discomfort, disability, failure to return to previous level of sport, increased scintigraphic activity in the subchondral bone, and development of osteoarthritis of the knee at long term [20, 21, 24, 50]. Therefore, accurate assessment of the pivot-shift phenomenon is clinically mandatory. However, currently, the gold standard for evaluation of rotational knee stability after ACL tears in the office is based on patient history and subjective un-instrumented physical examination, the pivot-shift test, which is highly variable and dependent on examiner’s skill and experience and has both a low sensitivity and low interobserver reliability [32]. Moreover, the rotational load applied to the knee during the pivot-shift test is much lower than the load applied to the knee during sports activities. Furthermore, patient guarding can lead to false negatives. Moreover, clinical pivot-shift test cannot evaluate small rotational differences between the pathological/reconstructed and the healthy contralateral knee. Finally, the pivot-shift test is often only testable during examination under anesthesia. In our series, the sensitivity of the physical examination with the patient awake was 37.5 %, whereas the sensitivity of the physical examination with the patient under general anesthesia was 87.5 % [42]. Therefore, a negative clinical pivot-shift test does not necessarily involve a normal rotational stability. Currently, however, there is no simple, commercially available device to measure knee rotational stability in vivo.

Appendix: Relationship Between Obliquity of the Graft in the Coronal Plane and Rotational Stability After ACL Reconstruction

A correct femoral tunnel placement and graft obliquity in the sagittal plane are important for a successful ACL reconstruction; however, they are not enough. Graft orientation in the coronal plane has received less attention, and it is crucial in the clinical outcome after ACL reconstruction because there is a relationship between the obliquity of the graft in the coronal plane and rotational stability after ACL reconstruction without higher anterior tibial translation (Fig. 5.14).

Fig. 5.14

Correct femoral tunnel placement and graft obliquity in the sagittal plane in a patient with intact ACL graft and a positive pivot-shift test. However, the graft has a vertical graft orientation in the coronal plane

A vertical graft orientation in the coronal plane does not control tibial rotation and is associated with a non-satisfactory clinical result (Fig. 5.15). In this sense, Sanchis-Alfonso in a preliminary study comparing ACL reconstructions in the 11 or 1 o’clock position versus 10 or 2 o’clock position have found no differences in the pivot-shift test and Lachman test between both groups [41]. However, the subjective IKDC score regarding rotational stability was higher in the 10 or 2 o’clock position group [41]. The questions of the subjective IKDC related to the rotational stability are the following: what is the highest level of activity you can perform without significant giving way in your knee, and how does your knee affect your ability to jump and land on your affected limb. Moreover, a vertical graft could predispose it to early failure particularly with rotational stress the way it occurs in sports (Fig. 5.16).

Fig. 5.15

This is the case of a patient with a vertical graft orientation and non-satisfactory clinical result (positive pivot-shift). (a) Coronal MR image. Vertical graft orientation. (b) Axial MR image. High noon femoral tunnel ­placement. (c) Arthroscopic view. Previous femoral tunnel placement -arrow- (d) Arthroscopy view. We can see the obliquity of the new graft in the coronal plane

Fig. 5.16

This is the case of an elite international football player who was operated on twice. The graft failed at 6 months after the first operation after a banal noncontact mechanism after return to competitive sport. The question is, “what failed?” We believe that the key of the failure was a high-noon femoral tunnel placement. However, 8 years have passed since the second operation, and the patient is competing at a high level. What differences have we found regarding the first operation? A femoral tunnel at 10:30

Rue et al. [39] have shown that if we place the femoral tunnel at 10:30 or 1:30 position, we reconstruct portions of the anteromedial and posterolateral bundles of the ACL. It is possible to perform a femoral tunnel at the 10:30 position through a tibial tunnel angled 60° from the proximal tibial joint surface [39]. So, a single-bundle ACL transtibial reconstruction with a femoral tunnel placed in this position should provide rotational and anterior translation stability similar to that of double-bundle ACL reconstruction. But even in the best cases, single-bundle ACL reconstruction at 10:30 or 1:30 fails to restore normal kinetics and kinematics provided by the intact ACL at the pre-injury level, during high-demand activities such as jumping with pivoting. However, these patients are performing sports activities at a high level, which means that rotational stability given by the graft is enough to perform high-demand activities. However, the abnormal rotational motion after single-bundle ACL reconstruction may contribute to long-term osteoarthritis ­associated with ACL reconstruction.

The key question would be: How can we control the pivot shift? There are several options: additive lateral extra-articular tenodesis (see Chap. 13), reconsider primary repair of ACL tears in selected patients (see Chaps. 7, 8, and 18), and finally anatomic single-bundle or double-bundle ACL reconstruction (see Chaps. 19, 20, and 21). The final objective would be to improve knee kinematics in order to reduce the incidence of osteoarthritis.