In 1979 sports medicine researchers from the Hospital for Special Surgery reported their primary ACL repair technique (Fig. 25.1 ) [32]. This technique was aggressively used and by 1982 these same authors reported an average of just over 2 year follow-up on 70 primary repair patients and concluded “that primary repairs of mid-substance tears are technically possible and recommended in an athlete” [33]. Further follow-up was humbling. When a group of 52 primary repair patients were reported at over six and a half years average follow-up, a 17% failure rate and 42% abnormal laxity rate were identified and it was declared “an unpredictable operative procedure” [10]. Many other sports medicine centers reported similar disappointing results of primary repair [7, 9, 10, 34]. Subsequently enthusiasm soared for reconstructive techniques.

A new era of i nterest in primary ACL repair has been stimulated by disappointing results of injury prevention programs [2, 3], concern for increasing rates of ACL injury in children [35], and long-term outcomes following typical ACL surgical reconstruction techniques [4]. A series of basic science publications led by Martha Murray have incrementally demonstrated the feasibility of primary ACL repair in a porcine model [36–42]. Similar promising results have been found using a goat model [43, 44], and in a dog model [45]. Some of the most compelling animal data involve the 1 year comparison of untreated, conventional reconstruction, and bio-enhanced ACL repairs regarding early arthritic changes (Fig. 25.2 ) [46–48]. Applications of these concepts to humans (i.e., translational research) are still pending [49, 50].