Working Diagnosis:
Chronic tear of the ACL with healing onto the PCL and an acute medial meniscus tear.

Treatment:
Patient declined operative treatment for his torn meniscus and abnormal ACL.

Outcome:
After declining surgery, the patient returned to play immediately and appeared in every game for the rest of the season with no further injury. At 3 years follow-up, he presented with no complaints of re-injury in his left knee.

Author's Comments:
The ACL remnant that heals onto the PCL has been noted to play a role in anterior knee constraint, proprioception, and biomechanics (1). However, it is unclear if this morphology provides sufficient stability for the football player requiring explosive movements and rapid change of direction. Reconstruction is indicated in the majority of high-demand sport athletes with ACL tears. Returning to play without a functional ACL can leave players vulnerable to repetitive instability episodes resulting in secondary injury to other structures in the knee such as the meniscus (2). However, players completely lacking an ACL have been able to sustain long NFL careers, most notably John Elway and Hines Ward (3).

Editor's Comments:
ACL tears occur from a variety of mechanisms but most commonly is the result of a low-energy, non-contact injury during sport. This often is a complete rupture with discontinuity of the ligament and retraction of the proximal and distal portions. Despite its rich blood supply the torn ACL has been shown to not heal well with speculation that this is due to its intra-articular environment not allowing for a bridge to form between the two ligament stumps. Gravity will occasionally cause the distal end to turn towards the nearby PCL and take advantage of its synovial blood supply. Despite this type of healing, as seen in this case, it is thought that while this ligament remnant remains viable its functionality is in question. For this reason, ACL reconstruction remains the gold standard treatment. Recently, remnant preservation techniques have been studied as a possible method to improve clinical outcomes. While several theoretical advantages are described the results remain controversial.

References:
1. Yanagisawa S, Kimura M, Hagiwara K, et al. The relationship between the clinical results and the remnant type following anterior cruciate ligament reconstruction using a hamstring tendon. J Orthop Surg (Hong Kong). 2019;27(2):2309499019837653.
2. Chahla J, Cinque ME, Godin JA, et al. Meniscectomy and Resultant Articular Cartilage Lesions of the Knee Among Prospective National Football League Players: An Imaging and Performance Analysis. Am J Sports Med. 2018;46(1):200-207.
3. Hauser, R.A., Steilen-Matias, D.R. and MMS, P., ACL reconstruction surgery alternatives and regenerative treatment options

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