Background: Bone-patellar tendon-bone (BPTB) and a double-looped semitendinosus gracilis (hamstring group) graft are commonly used for ACL reconstruction. Short-term and mid-term studies show little to no significant difference between the two groups, and there are a few long term studies to compare results between the two grafts.

Purpose: To compare the results after using either BPTB grafts or hamstring grafts 18 years after ACL reconstruction.

Study design: Randomized controlled trial; Level of evidence II. Methods: 114 patients with ACL rupture between 2001 and 2004 were randomized to reconstruction with either BPTB graft or a hamstring graft. Patients were operated at four major hospitals. The 18-year follow-up evaluation included isokinetic testing of muscle strength, patient-reported outcome measures, clinical knee examination and an assessment of radiological osteoarthritis using the Kellgren-Lawrence classification.

Hypothesis:Hypothesis is that there will be no difference in the long-term outcome between the two groups, as well hypothesis of no difference in patients with prosthesis after ACL reconstruction, arthrosis difference in operated knees and the rate of graft failure between the two groups. Previous follow-up studies showed a significant difference in total flexion work between the two groups, so detecting a persistent difference between the groups will be point of interest.

Introduction Rupture of the anterior cruciate ligament (ACL) is a common soft-tissue knee injury, and has increased in number over the last twenty years. Reconstructing the ligament may be important for maintaining the stability and preventing further damaging of the knee. The two most commonly used grafts in reconstructions are the autologous patellar tendon grafts and hamstring tendon grafts There is yet to be a universally established agreement regarding which reconstruction method of an ACL is preferred. The method using the central third of the patellar tendon with proximal and distal bone blocks as the replacement has been used since the late 80s and is well documented with good results. When the technique using the hamstring tendon grafts was introduced, its popularity increased. Arguments favoring each of the methods depend on which variables one values the most. In some studies, the patellar tendon group reported problems regarding anterior knee pain and decreased sensitivity of the knee, whereas for the hamstring tendon group there was reported increased weakness of the hamstring muscles and knee laxity. However, the overall assessment and satisfaction in multiple short-term/semi-long studies have shown little to no difference .

The aim of this prospective randomized multicenter study is to compare the use of bone-patellar tendon-bone (BPTB) grafts and double-looped semitendinosus gracilis (DLSG) grafts for reconstruction of the anterior cruciate ligament, 17-20 years after the surgery. The null hypothesis is that there will be no significant differences at this long-term follow-up evaluation between the two methods.

Method and material of the first study- Drogset et al. recruited 115 patients with rupture of the anterior cruciate ligament in the period of 2001-2004, and randomized them to either reconstruction with bone-patellar tendon-bone (BPTB) grafts fixed with metal interference screw graft, or double-looped semitendinosus gracilis (DLSG) grafts fixed with Bone Mulch Screws and WasherLoc Screws. The surgeries were performed at four different hospitals.

After one and two years, the patients were examined by an independent observer, using a series of objective tests, as well as recording the patients' subjective opinion of their knee function. The subjective tests used were Tegner's activity score, Lysholm's functional score and Modified Cincinnati Score. The objective tests used were Lachmann's test, pivot shift and KT-1000, as well as Cybex and Biodex to measure muscle strength.

Method and material- The present study is a long-term follow-up of a prospective randomized multicenter study. The patient recorded outcome scores will be Tegner's activity score, Lysholms's functional score and the Knee injury Osteoarthritis Outcome Score (KOOS). The examinations include Lachmann's test, pivot shift and KT-1000. We also plan to include radiographs to evaluate the degree of arthrosis 17-20 years after the surgery, and Cybex or Biodex to examine the hamstring and quadriceps strength. The radiographic positioning will be knee AP weight-bearing standing bilateral and lateral view, as well as skyline projection. The Kellgren-Lawrence classification will be used to assess the degree of osteoarthritis.

Even though 115 patients were included in the original study, we will only attempt to contact 114 due to lost inclusion-papers between the 2-year and 7-year follow-up [8]. During the spring of 2022, the patients will receive an invite to participate in the follow-up study. Following this, patients will be contacted to uncover different circumstances that might exclude certain patients from the clinical assessment. This includes revision of the reconstruction in question, total knee replacement or total knee arthroplasty, and if the knee had been injured beforehand. The clinical examination will be carried out by both a medical student and an experienced orthopedic surgeon. Hopefully all the patients will be examined over the course of two days at each location, and if needed, the rest will be examined at a later date.

Hypothesis- Current hypothesis is that there will be no difference in the long-term outcome between the two groups. However, it will be interesting to see how many patients have received a prosthesis, and how many patients struggle with arthrosis. As the previous follow-up studies showed a significant difference in total flexion work between the two groups, we will be interested in detecting a persistent difference between the groups.

Another interesting aspect will be the rate of graft failure between the two groups.

Feasibility- The strength of the study is the randomization and the long follow-up period of 17-20 years. The possible limitations are the fact that there may be a problem recruiting enough patients to the follow-up, and that it might not be able to get x-rays of the patients at the different hospitals, as this is a matter of cost and availability. In addition, the different hospitals may not have a Biodex available.

Publicity plan- The goal for the paper is to be published in an international journal and probably be presented at conferences. For article, that hopefully will be published in journals, Marko Popovic will stand as first author, and Julie Holen and Julie Myhre as contributing authors. Jon Olav Drogset will be listed last, as the main supervisor.

Ethics- The REK-application was submitted on the 24th of December 2021. Application number: 391796. Additionally, the project will be reported to NSD when the REK-application is approved.

Inclusion Criteria:

• Primary reconstructions of isolated ACL-ruptures. Surgery at least 6 weeks after injury. Age 18-45 years.
• The patient must understand and accept the written consent. The written consent must be signed by the patient before surgery.
• Normal two-plane X-ray of the knee.

Exclusion Criteria:

->5mm + chronic MCL-injury in the same knee.

• Patient with major additional injury in the knee: combined instability, cartilage injuries Outerbridge grade 3-4 and at least 1cm in diameter on the femoral condyle and major meniscal lesions with meniscal repairs.
• Patients having problems following the protocol.
• The patient does not understand the written consent or will not sign it.
• Patients with a history of alcohol or drug abuse the last three years.
• The patient has received any investigational drugs within 30 days prior to admittance to this study.
• The patient has O.A., podagra, RA, Bechterew's disease or chondrocalcinosis.
• The patient has malalignment with more than 5 degrees valgus and no varus compared to a normal knee.
• The patient has patellofemoral instability.
• The patient is obese with BMI>30.
• The patient has a present or former serious illness that makes follow-up or rehabilitation of the patient difficult.
• Former major surgical procedures in the same knee, including prosthesis.
• Treated or untreated anterior cruciate ligament injury in the other knee.

Norwegian citizens. Patients from Trondelag county operated in Trondheim (StOlav Hospital), patients from Oslo operated at Lovisenberg Diaconal Hospital Oslo, patients from Hordaland operated at Haraldsplass Deaconess Hospital Bergen. Few patients from other counties who wanted operation at spesific hospital were also included if inclusion criteria were met.