Laxity measurement of internal knee rotation after primary anterior cruciate ligament rupture versus rerupture

Abstract

Purpose: The aim of the current study was to objectify the rotational laxity after primary anterior cruciate ligament (ACL) rupture and rerupture after ACL reconstruction by instrumented measurement. It was hypothesized that knees with recurrent instability feature a higher internal rotation laxity as compared to knees with a primary rupture of the native ACL.

Study design: Cross-sectional study, Level of evidence III.

Methods: In a clinical cross-sectional study successive patients with primary ACL rupture and rerupture after ACL reconstruction were evaluated clinically and by instrumented measurement of the rotational and antero-posterior laxity with a validated instrument and the KT1000^®, respectively. Clinical examination comprised IKDC 2000 forms, Lysholm Score, and Tegner Activity Scale. Power calculation and statistical analysis were performed (p value < 0.05).

Results: 24 patients with primary ACL rupture and 23 patients with ACL rerupture were included. There was no significant side-to-side difference in anterior translation. A side-to side difference of internal rotational laxity ≥ 10° was found significantly more frequent in reruptures (53.6%) compared to primary ruptures (19.4%; p < 0.001). A highly significant relationship between the extent of the pivot-shift phenomenon and side-to-side difference of internal rotation laxity could be demonstrated (p < 0.001). IKDC 2000 subjective revealed significantly better scores in patients with primary ACL tear compared to patients with ACL rerupture (56.4 ± 7.8 vs. 50.8 ± 6.2; p = 0.01). Patients with primary ACL tears scored significantly better on the Tegner Activity Scale (p = 0.02). No significant differences were seen in the Lysholm Score (p = 0.78).

Conclusion: Patients with ACL rerupture feature significantly higher internal rotation laxity of the knee compared to primary ACL rupture. The extend of rotational laxity can be quantified by instrumented measurements. This can be valuable data for the indication of an anterolateral ligament reconstruction in ACL revision surgery.

Keywords: ACL; ALL; Anterior cruciate ligament; Anterolateral ligament; Instrumented measurement; Rerupture; Rotational laxity.

Fig. 1

The rotational knee laxity was measured with a validated instrument (Laxitester^®). The femur was fixed at a knee flexion angle of 30° by medial and lateral counter-bearings at the femoral epicondyles. The foot was fixed in a precisely adjustable footplate. The ankle was locked by dorsiflexion using the trapezoidal shape of the talus. Rotation of the lower leg was performed by torque on the footplate. Under these conditions, the torque applied to the foot is transmitted to the lower leg (25)

Fig. 2

A significant side-to-side difference of internal rotation laxity was found with a mean of 8.7 ± 8.6° in patients with an ACL rerupture as compared to a mean of 3.6 ± 4.5° in patients with a primary ACL rupture (p = 0.014). IRO internal rotation, ERO external rotation

Fig. 3

A highly significant relationship between the extent of the pivot-shift phenomenon and side-to-side difference of internal rotation could be demonstrated (primary ACL tear r_s = 0.695; p (R²) < 0.001; ACL rerupture: r_s = 0.637; p (R²) < 0.001)

Fig. 4

Patients with a primary ACL tears scored significantly higher in the Tegner Activity Scale (p = 0.02) and the IKDC 2000 subjective questionnaire (p = 0.01) as compared to patients with an ACL rerupture. There was no significant difference in the Lysholm Score (p = 0.78)