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Laxity and compliance measurements after primary ACL reconstruction. A minimum 12 months follow-up cohort.
Author(s):
Pouderoux T. (France)
,
Pouderoux T. (France)
Affiliations:
Robert H.
,
Robert H.
Affiliations:
Pauvert A.
Pauvert A.
Affiliations:
ESSKA Academy. Pouderoux T. May 9, 2018; 209479; P06-714 Topic: Biomechanics
Mr. Thomas Pouderoux
Mr. Thomas Pouderoux
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Abstract
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Objectives: Laximetric measurement is widely used for diagnosis of acute anterior cruciate ligament rupture. But, following laximetry and compliance after surgery may be used to survey graft mechanical properties during the ligamentization process.
This study aimed to analyze the evolution of laxity and compliance of hamstring grafts after anterior cruciate ligament reconstruction (ACLR).

Methods: 47 patients (37 men, 10 women) with a mean age of 28.2 ± 9.6 years, operated for primary ACLR using hamstring tendons (short graft) associated or not with an extra-articular procedure, were enrolled between November 2013 and January 2016. Inclusion criteria were patients with a primary ACL rupture and sufficient follow-up (FU) Exclusion criteria were multi ligamentous injuries, re rupture or insufficient FU. The patients were evaluated with a robotic arthrometer before surgery, then at 15 days, 1, 3, 6, 9 months, 1 year postoperatively and at the last FU. The mean FU period was 14.6 ± 3.0 months.
The side-to-side differences in the anterior tibial translation (ΔL in mm) was measured at 30, and 60 N everytime, 90 N from 3 months and 134 N from 6 months. The scatter plot was modelized with a polynomial trend curve to obtain a coefficient of determination above 0.999. Graft compliance, capacity of the graft to stretch according to strength, was defined by the director coefficient of the tangent line at a given point of the force-deformation curve. Differential compliance (ΔC in µm/N) was calculated between operated and healthy knees.
The average values at each time were compared using a paired Student's t-test.

Results: Preoperatively, average ΔL and ΔC at 134 N were respectively 3.50 ± 1.32 mm and 16.40 µm/N. At the last FU, ΔL at 134 N was 1.44 ± 1.37 mm and ΔC 1.54 ± 6.74 µm/N with a significant difference (ΔL p<0.001 and ΔC p<0.001).
During the FU period, average ΔL and ΔC decreased significantly between preoperative and 1 month postoperative with every strength parameter (at 30N, ΔL: 0.84 mm, p<0.0001; ΔC: 25.94 µm/N, p<0.001). Between the periods of 1 month and 9 months postoperatively, ΔL increased significantly at 30 N (p=0.02) and 60 N (p<0.001). ΔC increased by 15.22 µm/N at 30 N (p=0.003) and 14.87 µm/N at 60N (p=0.001).
Between 9 months postoperatively and the last FU, there was no significant difference for ΔL and ΔC for every force range.

Conclusions: Our study reported a 3-stage evolution of graft laxity and compliance after ACLR. Between immediate postop and 1 month, we observed a good laxity and compliance restoration. There was a period of fragility between 1 and 9 months postoperatively followed by a stabilization of mechanical properties. These results are concordant with the biological description of the graft ligamentization process described by Amiel et al (J Orthop Res, 1984), Scranton et al (Arthroscopy, 1998) and Lane et al (Arthroscopy, 1993). This study sheds light on a normalization of laxity and compliance after 9 months postoperatively.

Keywords:
ACL reconstruction, laximetry, postoperative, robotic arthrometer
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