Paper 84: Differences in Metrics of Knee Joint Loading Between Individuals Following a Primary Anterior Cruciate Ligament Repair (ACL-R) Surgery Versus Those Who Underwent a Standard ACL Reconstruction with a Patella Bone-Tendon-Bone Autograft (ACLR)
Authors: Singleton Steven , Hannon Joseph , Waller Alexandra , Garrison Craig , Scofield Harrison 
Published: July 2022

Objectives: Recent research suggests that the short- and long-term outcomes following Anterior Cruciate Ligament Reconstructions (ACLR) on knee joint health are worse than originally thought. The ACLR procedure may result in or expediate the arthritic process through a variety of factors including prolonged underloading of the knee joint following surgery. These recent findings have resulted in a renewed interest in the ACL repair (ACL-r) procedure as a potentially more joint “friendly” secondary to less surgical trauma with the preservation of the native ACL ligament. In several animal models and in human clinical data, ACL remnant preservation and ACL entire ligament repair/preservation has been shown to benefit lower extremity and knee biomechanics, proprioception, and short term clinical outcomes. However, there is limited data on the newer ACL-r techniques and their subsequent outcomes on knee joint loading. Therefore, the purpose of this study was to assess for differences in metrics of knee joint loading between individuals following a primary anterior cruciate ligament repair (ACL-r) surgery versus those who underwent a standard ACL reconstruction with a patella bone-tendon-bone autograft (ACLR). Methods: A total of 30 participants were enrolled into this study [ACL-r n: 15, age(yrs): 38.8±13.9, Ht(cm): 173.4±10.0, Wt(kg): 77.9±17.5; ACLR: n: 15, age(yrs): 25.60±1.7, Ht(cm): 173.5±10.3, Wt(kg): 75.4±15.6]. Participants in ACL-r group all sustained a proximal ACL disruption (Sherman Classification Type 1 or 2) that was amenable to repair and underwent primary ACL repair with suture fixation. ACL-r was performed under arthroscopic visualization with 2 or 3 standard portals in a technique similar to that described by van der list, MD (2017), but modified by the senior author to include only one 4.75mm swivelock (Arthrex) secured in the anterior aspect of the native footprint on the medial wall of the lateral femoral condyle. Participants in the ACLR group all underwent a primary ACLR with patella bone-tendon-bone autograft. The autograft bone blocks were crimped to 9mm and then two 10mm femoral and tibial tunnels created for the graft. An independent tunnel technique, utilizing the medial portal for creation of the femoral socket within the native ACL femoral attachment site, was performed in all ACLR patients. At 12 weeks following surgery participants in both groups completed the IKDC questionnaire and biomechanical testing with two AMTI force plates and a 10 camera Qualisys motion capture system. Peak knee extension moment (Nm/Ht*Wt) and total knee joint power (Watt/Ht*Wt) as a measure of eccentric loading (contraction) during the descent phase of a single-leg squat were calculated on the surgical limb and averaged across the middle three trials. Participants also completed quadriceps strength testing on both limbs (surgical and non-surgical) on an isokinetic dynamometer at 60 °/sec. The average peak torque of five repetitions were used to calculate a limb symmetry index (LSI) [Surgical/NonSurgical X100]. Independent t-tests were used to assess for differences between groups in three metrics. For descriptive purposes a separate independent t-test was used to assess for differences in age, height, mass, and IKDC scores. Statistical significance was set at P< 0.05 for all analyses. Results: There were no differences in height (p=0.996), mass(p=.678), or IKDC ( p=0.886) scores between the groups; however, there was a significant difference in age (p=0.009). The ACL-r had a significantly greater peak knee extension moment (ACL-r: -0.078±0.02; ACLR: -0.059±.02; p=0.014) and total knee joint power (ACL-r-0.03±0.01; ACLR: -0.02±0.01, p=0.016) than the ACLR group. The ACL-r also had a significantly great quadriceps LSI than the ACLR group (ACL-r: 65.09±20.4, ACLR: 49.2±11.4, p=0.014). Conclusions: The results of this study indicate that those individuals following ACL-r demonstrate increased knee joint loading during a single leg squat task compared to those who underwent ACLR. Decreases in knee extension moment have been reported across a variety of tasks and across a variety of time points following ACLR. Furthermore, decreased knee extension moments have been associated with movement profiles that have been linked to cartilage degeneration following ACLR. The improved knee extension moment in the ACL-r group at this early time may indicate a positive change in joint loading and potentially a decreased rate of cartilage degeneration. Knee joint total power accounts for both knee moment and angular velocity, indicating improved knee loading throughout the entire eccentric movement in the ACL-r group and further supports the notion of improved knee joint loading following ACL-r compared to ACLR. Decreased quadriceps muscle strength has been associated with changes in cartilage structure and it has been suggested that maximizing muscle strength in the first 6 months following surgery may promote improved cartilage healing, thus the increased quadriceps LSI in the ACL-r may be protective early in the recovery process.