This study is being done to test whether taking testosterone can prevent loss of muscle mass and strength due to anterior cruciate ligament (ACL) reconstructive surgery. Testosterone is the principal male sex hormone and an anabolic (muscle promoting) steroid. It is essential for the development of male reproductive tissues and promotes increased muscle, bone mass, and the growth of body hair.

The investigators hope to learn whether testosterone given before and after ACL reconstructive surgery will increase muscle mass and strength and potentially improve recovery time following surgery.

Overall Objective: The overall objective of this study is to determine if 8 weeks of testosterone first administered 2 weeks prior to surgery, can improve the outcome of anterior cruciate ligament (ACL) reconstruction.

Overall Hypothesis: Standard-of-care rehabilitation with the addition of testosterone administration will augment muscle mass, strength, and physical function following ACL reconstructive surgery compared to standard rehabilitation alone.

Significance: Muscle mass and strength are greatly reduced following ACL surgery. The investigators hypothesize that administration of testosterone will minimize these reductions or potentially increase muscle mass and strength. In doing so, testosterone may hasten a patient's return to physical activity. If testosterone improves recovery after ACL surgery, the same treatment may be used for other injuries that involve trauma and muscle atrophy. Furthermore, this study will examine the effect of trauma with or without testosterone on myogenic regulators in muscle tissue taken during ACL surgery-providing possible mechanistic insights for the clinical outcomes.

Inclusion Criteria:

• A complete ACL tear as visualized on MRI
• The ACL injury can be either "isolated" or combined with one or several of the following injuries visualized on MRI and/or arthroscopy:
• a meniscus tear that is either left untreated or treated with a partial resection
• a small, stable meniscus tear treated with fixation, but with the fixation not interfering with the rehabilitation protocol
• cartilage changes verified on MRI with an arthroscopically determined intact surface.
• A radiographic examination with normal joint status or combined with either one of the following findings:
• a small-avulsed fragment located laterally, usually described as a Segond fracture, JSN grade 1 or osteophytes grade 1 as determined by the OARSI atlas15

Exclusion Criteria:

• Previous major knee injury or knee surgery
• Associated posterior cruciate ligament (PCL) or medical collateral ligament (MCL) injury grade III
• Concomitant severe injury to contra-lateral knee
• Injury to the lateral/posterolateral ligament complex with significantly increased laxity
• Unstable longitudinal meniscus tear that requires repair and where the following postoperative treatment (we.e. bracing and limited range of motion) interferes with the rehabilitation protocol
• Bi-compartmental extensive meniscus resections
• Cartilage injury representing a full thickness loss down to bone
• Total rupture of MCL/LCL as visualized on MRI.
• History of deep vein thrombosis (DVT) or a disorder of the coagulative system
• Claustrophobia
• Prior or current use of anabolic steroids
• General systemic disease affecting physical function
• Chromosomal disorders
• Medications that interfere with testosterone production or function, including but not limited to 5α-reductase inhibitors
• Any other condition or treatment interfering with the completion of the trial

Trough the study completion (24-weeks).

All subjects were monitored/assessed for adverse events.