We monitored laximetry and compliance of hamstring short grafts for ACL reconstruction during the first post-operative year.
Laximetric measurement is widely used for diagnosis of acute anterior cruciate ligament rupture. But, monitoring 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).
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 (Delta L 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. Graft compliance was defined by the director coefficient of the tangent line at a given point of the force-deformation curve. Differential compliance (Delta C 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.
Preoperatively, average Delta L and Delta C at 134 N were respectively 3.50 ± 1.32 mm and 16.40 µm/N. At the last FU, Delta L at 134 N was 1.44 ± 1.37 mm and Delta C 1.54 ± 6.74 µm/N with a significant difference (Delta L p<0.001 and Delta C p<0.001).
During the FU period, average Delta L and Delta C decreased significantly between preoperative and 1 month postoperative with every strength parameter (at 30N, Delta L: 0.84, p<0.0001; Delta C: 25.94, p<0,001). Between the periods of 1 month and 9 months postoperatively, Delta L increased significantly at 30 N (p=0.02) and 60 N (p<0.001). Delta C 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 Delta L and Delta C for every force range.
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. The evolution was significative for low ranges of force, wich can be evaluated at each potoperative period. These results are concordant with the biological description of the graft ligamentization process. This study sheds light on a normalization of laxity and compliance after 9 months postoperatively.