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ACL Reconstruction using Hamstring Tendons

- Discussion:
    - anatomy of ACL;
    - ACL biomechanics;
    - graft tunnel sites / isometry:
    - hamstring ACL reconstruction is an alternative to bone patellar bone graft fixation
    - size and strength of graft:
            - double looped hamstring graft is more than twice as strong as normal ACL, as compared to bone patella bone (which is 1.3
                     times as strong);
            - this is true because more cicular shaped hamstring tendons have larger cross sectional area than a similarly sized BPB graft;
            - 8 mm double graft has a cross sectional of 50 sq mm vs a 10 mm BPB graft which has a cross sectional area of 35-40 sp mm; 
            - minimum acceptable graft size is about 7 mm (small grafts are associated with a higher failure rate); 
            - references:
                     - Hamstring autograft size can be predicted and is a potential risk factor for anterior cruciate ligament reconstruction failure. 
                     - Graft size not the only factor in determining better ACL reconstruction outcomes
                     - Impact of Hamstring Graft Diameter on Tendon Strength: A Biomechanical Study

    - preoperative considerations.
            - some surgeons elect to use hamstrings in patients who have had previous patellar tendon harvest or who have pre-existing
                       patellofemoral arthrosis;
            - in the uncommon case of concomitant ACL-PCL ruptures, often the bone patella bone graft is used for the PCL reconstruction,
                       and hamstrings are used for ACL reconstruction; 
            - main disadvantage of hamstrings is that the reconstruction is less stiff than BPB grafts, since a longer graft length (with
                       fixation outside of femoral and tibial tunnels) will undergo more strain; 
            - advantages:
                      - hamstring grafts allow more anatomic placement into the femoral foot print (as with the AM technique)
                      - there is the allowance for differential tensioning (posterior 2 halves can be fixed with a staple in 10 deg of flexion, and
                               the anterior two haves can be fixed with an interference screw in 40 deg flexion;

- PreOp Evaluation:  

- Surgical Technique:
    - positioning and setup:
    - hamstring harvest
            - references:
                  - A surgical technique using presoaked vancomycin hamstring grafts to decrease the risk of infection after anterior cruciate ligament reconstruction.
                  - The In Vitro Elution Characteristics of Vancomycin from Tendons
    - knee arthroscopy
    - notchplasty:
    - tibial tunnel:
           - consider undersizing reaming diameter and then using dilators at the distal aspect of the tunnel;
           - this will better accomodate the distal end of the graft which often is of larger diameter than the rest of the graft;
           - using this technique, allows the distal (wider diameter) end of the graft to act as a "stop" to proximal migration (in addition to 
                   interference screw);
    - femoral tunnel:
           - consider more posterior femoral tunnel with hamstring grafts noting their increased flexibility compared to BPB grafts;
           - by placing the knee in a partial figure 4 position, a transtibial technique can be performed which is essentially the equivalent of
                     the anteromedical technique;
    - graft fixation:
           - goal is to have 2 grafts tight in extension and two grafts tight in flexion;
           - identify the 2 posterior halves of  the graft, and place them under maximum tension with the knee in 10 deg flexion.
           - an 8 mm staple is straddled across these grafts about 1 cm distal to the tunnel, and impacted into place;
           - then the two anterior halves are placed under maximal tension, and the knee is placed in 45 deg flexion;
           - the interferences screw system is then applied;
           - after interference screw fixation of the tibial graft, there will often be a large residual portion of tendon graft which overhangs
                     from the tibial tunnel;
           - these overhanging graft ends may be sutured to the proximal tibial periosteum for additional fixation

- Post Op Care of ACL Reconstructions 

- References: 

The use of hamstring tendons for anterior cruciate ligament reconstruction. Technique and results.
Arthroscopically Assisted Reconstruction of the Anterior Cruciate Ligament. A prospective randomized analysis of three techniques
Clinical Outcome of Anterior Cruciate Ligament Reconstruction with Quadrupled Hamstring Tendon Graft and Bioabsorbable Interference Screw Fixation.
A Randomized Comparison of Patellar Tendon and Hamstring Tendon Anterior Cruciate Ligament Reconstruction.
Anterior Cruciate Ligament Reconstruction with a Four-Strand Hamstring Tendon Autograft.
Muscle and Tendon Morphology After Reconstruction of the Anterior Cruciate Ligament with Autologous Semitendinosus-Gracilis Graft.
Anterior Cruciate Ligament Reconstruction: Bone-Patellar Tendon-Bone Compared with Double Semitendinosus and Gracilis Tendon Grafts. A Prospective, Randomized Clinical Trial
Hamstring Tendon Versus Patellar Tendon Anterior Cruciate Ligament Reconstruction Using Biodegradable Interference Fit Fixation: a Prospective Matched-Group Analysis.