The most important finding of the present study is that we have performed comprehensive immunohistochemical analysis of the LM. In every specimen rich arterial and vascular vessels along the entire LM are proven. Moreover, tiny nerves along the subsynovial layer in all samples of ligamentum mucosum are revealed. The fundament of the LM is composed of dense regular connective tissue, and the longitudinal bundles of collagen fibers constitute proof of this. Therefore, the arthroscopic ACL suturing technique using the LM lining can be a great addition to ACL reconstruction in certain cases. This type of surgery may therefore contribute to faster and more efficient rehabilitation of patients after ACL reconstruction.
The close relationship between the LM and the ACL is proven by Abreu et al.1. They have found retrospectively, using MRI, that abnormalities of IPFP, such as focal and diffuse edema, tears, scars and synovial proliferation, are more common in knees with torn ACLs than in knees with an intact ACLs. The potential value of another fat pad– PCL fat pad, is discussed by Malinowski et al.19, who based on their experience concluded that revascularization and synovialization may be useful while repairing torn ACL. The idea of using PCL fat pad seems very logical according to its perfect localization and therefore, an easy access. However, harvesting the PCL fat pad may weaken the blood supply to the PCL and additional parapatellar portal is needed. Therefore, we are proposing using LM as a donor of blood supply and the source of reinnervation.
Worth noting is that the synovial layer of the ACL plays important role in its survival rate after injury. Ateschrang et al.4 have proven, with high confidence interval (p = 0.0018), that the survival rate for one-part ACL tears is increased with patient whose synovial coverage of the ACL was intact. It may be explained by the fact that blood supply to the ACL is mostly provided by the vessels in the subsynovial layer derived from superficial branches of the middle genicular artery and small infrapatellar ramifications of the interior genicular arteries28,32. The most vulnerable part of the ACL is the anterior part of distal attachment as most of the vessels were seen to stop there, hence the vascularity there is poor28,30. According to our results LM seems to perfectly fit in the process of revascularization the torn or sutured ACL due to its rich vascular network and an easy access.
Not only the vascular profits may come from the LM. Due to the presence of nerves in the subsynovial layer along the ligament it may be possible to use them as a potential donor of neural tissue to ACL after injury. According to the newest studies approximately 200 000 ACL tears occur annually in the US, and 50% undergo reconstructive surgery in an attempt to restore stability27. However, it is a common problem that functional instability occurs due to both loss of the mechanical restraint to excessive motion and a lack of coordinated muscle activity8. The human ACL contains mechanoreceptors that detect changes in tension, acceleration, direction of movement, and the position of the knee joint5,16. Loss of this sensory feedback may impair neuromuscular function and contribute to functional instability after ACL injury34. Therefore it is vastly discussed in the world how to restore innervation of the injured ACL.
Last 20 years have shown increased interest in preserving ACL remnants during reconstruction as a potential source of mechanoreceptors that may lead to reinnervation and hence better clinical outcome. However, the scientists are dived into supporters and opponents of this idea. Lee et al.18 have observed mechanoreceptors in 33% of remnants, also Adachi et al.2 have revealed the correlation between the mechanoreceptors in remnants with better preoperative proprioceptive function. Based on these findings another authors have decided to try to prove the advantages of sparing the ACL remnants and they have obtained excellent results20,27. However, there are also studies that prove this idea to be wrong and that there are no evidence that significant mechanoreceptor reinnervation of ACL graft may occur in human26,34. Therefore instead of using ACL remnants we propose to use LM (especially if it is unharmed) as a donor of neural tissue and potential source of reinnervation.
Another interesting clinical issue regarding LM is its relationship with anterior knee pain, which is a common symptom, especially in adolescence, and often no specific cause is sought or identified9. It is often mentioned in the current literature that LM may be the cause of the anterior knee pain10. This condition may be caused by the inflammation of the LM and the IPFP that causes bulging on either side of the patellar tendon, with the synovial membrane being compressed against femoral condyles giving rise to effusions and pain12,31. Our findings may contribute with above mentioned studies as we have proven the presence of tiny nerves were confirmed along the subsynovial layer in all samples of ligamentum mucosum. Unfortunately, it was impossible to distinguish whether these nerve fibers are responsible for nociception and hence anterior knee pain, or they permit proprioceptive function, or they simply innervate the vascular network. Nevertheless, their presence should not go unnoticed as it may explain the anterior knee pain, especially when the rest of the knee joint structures are intact.
Unfortunately there are also limitations regarding our study, which is relatively low number of specimens and no follow up regarding the proposed procedure. However, it should be emphasized that this study is based on immunohistochemical analysis which is very time consuming and expensive so the clinical trials are generally low. We are aware that future studies are needed to support our hypothesis.