Anterior Cruciate Ligament (ACL) Mucoid Degeneration

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Cruciate-ligaments.jpg
Anterior Cruciate Ligament, is an important structure of the knee joint. Anatomically, it is arranged in a crossed pattern with the Posterior Cruciate Ligament,forming an 'X', therefore, it is also known as cruciform ligament. This ligament conists of two fibers, mainly, the anterio-medial and postero-lateral fibers, respectively. The ligament is mainly responsible for restraning anterior translation of knee. Along with that, it also controls the internal rotation. Therefore, Anterior Cruciate Ligament tear is more susceptible during any injury to the knee.The cruciate ligament have mechanoreceptors, which are responsible to detect any change in position of the knee, direction, speed and tension.It is lined by the synovial fluid, which provides the nutrition and plays an integral part in healing.

What is Anterior Cruciate Ligament Mucoid Degeneration?

This is a rare pathological condition, in which, there is increased signal from within the ligament. Mucoid degeneration, is the irreversible degeneration of the tissue with the infiltration of mucin(glycosaminoglycans) within the fibers[1][2]. Multiple theories have been put forth that explains the pathological disorganisation in the collagen fibers of the Anterior Cruciate Ligament, such as synovial, traumatic, and degenerative,"Synovial” theory- states that there is accumulation of synovial fluid inside the substance of ACL in a herniated pouch of synovium."Traumatic” theory - post injury, ACL fibroblasts secrete glycosaminoglycans, the mucin substance within the ACL. Other theories include “Degenerative” theory- MD could occur due to ageing.[3] 

Clinical Findings

  • Painful terminal knee flexion[2][3]
  • Stiffness[2]
  • No instability[2][3]
  • No extension block[3]
  • Joint line tenderness[3]
  • Swelling[3]
  • Crepitation[3]
  • Posterior knee pain[3][4]
  • Difficulty in climbing stairs, cross-leg sitting, squatting[5]

Causes

  • Acute/Repeated Trauma[4][6]
  • Ageing
  • Primary condition- Osteoarthritis, degenerative menisci, meniscal tear[3], Menisectomy[4]

Complications

  • Impingement of the soft tissue in the vicinity[3]
  • Ganglionic cyst
  • Tendon tear/ Tendon rupture
Mucoid.jpg

Radiological Findings

MRI:

  • Characteristic:"celery stalk" appearance,[4] reflects ACL degeneration.
  • Ligaments and tendons are accumulated by mucoid change might display a thickened and/or hypertrophied appearance, with an increase in signal intensity.[3][4]
  • Narrowing of the intercondylar notch[5]
  • Sometimes, it is mislead as ACL tear on MRI findings, hence requires probing and histopathology for definitive diagnosis.[3][4]

Arthroscopy:

  • Arthroscopically ACL is intact but fibrillated, yellowish and hypertrophied, with interspersed yellowish mucinous material along the fibers, lack of synovial linning of the ACL[4]

Differential Diagnosis

Conditions that resembles the clinical findings are:

Treatment

Conservative

NSAIDS and Physiotherapy

Surgical

  1. Partial/Total ACL resection arthroscopically- There is marked improvement in the range and reduced posterior pain, but at the cost of increased post-operative knee laxity.[3][4][6]in some cases,and may lead to instability. The prognosis depends upon the age of the patient, and the associated injuries[2]
  2. Arthroscopic debridement[4]
  3. Notchplasty[3][6]

Postoperative Rehabilitation

  1. Wear knee brace[5]
  2. Intially, partial weightbearing is allowed.[5]
  3. ACL reconstructionprehabilitationrotocol is followed.[3][5]

References

  1. Palmer, W., Bancroft, L., Bonar, F. et al. Glossary of terms for musculoskeletal radiology. Skeletal Radiol 49, 1–33 (2020). https://doi.org/10.1007/s00256-020-03465-1
  2. 2.0 2.1 2.2 2.3 2.4 Khalid Ibn el Kadi et al. Mucoid degeneration of the anterior cruciate ligament: a case report. Pan African Medical Journal. 2013;15:59. [doi: 10.11604/pamj.2013.15.59.2534]
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 Pandey, Vivek et al. “Mucoid degeneration of the anterior cruciate ligament: Management and outcome.” Indian journal of orthopaedics vol. 48,2 (2014): 197-202. doi:10.4103/0019-5413.128765
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 Lintz F, Pujol N, Dejour D, Boisrenoult P, Beaufils P. Anterior cruciate ligament mucoid degeneration: selecting the best treatment option. Orthopaedics & Traumatology: Surgery & Research. 2010 Jun 1;96(4):400-6.
  5. 5.0 5.1 5.2 5.3 5.4 Loganathan D, Soma Sundar S, Sundar S, Sahanand S, Rajan DV. Mucoid degenerated anterior cruciate ligament (ACL) managed by arthroscopic ACL reconstruction: A case series. International Journal of Orthopaedics. 2018;4(4):875-80.
  6. 6.0 6.1 6.2 Lintz, Francois, et al. "Anterior Cruciate Ligament Mucoid Degeneration: a Review of the Literature and Management Guidelines." Knee Surgery, Sports Traumatology, Arthroscopy : Official Journal of the ESSKA, vol. 19, no. 8, 2011, pp. 1326-33.