Date Published: May 21, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Brion Benninger, Taylor Delamarter.
Introduction. This study investigated the importance of the “oblique popliteal ligament” (OPL), and challenges its alleged ligament status. The currently named OPL is indigenous to the distal semimembranosus (SMT); therefore, by definition is not a ligament inserting from bone to bone. Clinically, a muscle-tendon unit is different then a ligament regarding proprioception and surgery. Methods. Literature search was conducted on texts, journals and websites regarding the formation of the OPL. Dissection of 70 knees included macro analysis, harvesting OPL, distal SMT and LCL samples and performing immunohistochemistry to 16 knees with antibody staining to the OPL, distal SMT and LCL. Results. All but one text claimed the OPL receives fibers from SMT. Macro dissection of 70 knees revealed the OPL forming from the distal SMT (100%). Microanalysis of OPL, distal SMT and LCL samples from 16 knees demonstrated expression of nervous tissue within selected samples. Discussion. No journals or texts have hypothesized that the OPL is a tendon. Clinically it is important we know the type of tissue for purposes of maximizing rehabilitation and surgical techniques. Conclusion. This study suggests the OPL be considered the oblique popliteal tendon as a result of the macro and micro evidence revealed.
The posterior aspect of the knee has been increasingly studied because of its clinical relevance. Surgeons, biomechanists, physical therapists, all health care providers dealing with the musculoskeletal system, and anatomists need to have a definitive and precise understanding of the structures of the posteromedial knee. A previous study conducted by the authors identified the clinical importance, morphology, and accurate terminology of the distal semimembranosus muscle tendon unit (SMTU) . This study also revealed that the currently named oblique popliteal ligament (OPL) was indigenous to the SMTU and, therefore, by definition is not a ligament inserting from bone to bone. This is clinically important because of the proprioception of a tendon versus a ligament, which may suggest a greater role by the distal semimembranosus tendon in posterior knee stability.
A literature search was conducted on anatomical and specialty texts, atlases, journals, and websites regarding the morphology of the distal semimembranosus muscle tendon unit and oblique popliteal ligament. Deep dissections were performed on 43 embalmed human cadavers (23 M and 20 F, age: 55–89, average: 79.6 yrs), 70 knees in total (39 Rt and 41 Lt), to reveal the SMTU and its final attachments. Exclusion criteria are amputation, knee replacement, or any gross damage to the knee joint. The most distal portion of the SMTU was reflected medial to lateral in order to analyze whether or not the alleged oblique popliteal ligament is a continuation of the distal SMTU, or if it was a structure attaching from bone to bone. The OPL’s distal (medial) and proximal (lateral) attachments were analyzed. Immunohistochemistry staining was performed on the SMTU, OPL, and LCL using the following protocols: PGP9.5 staining of human tendon/ligament sections with rabbit anti-PGP9.5 (Accurate Chemical)/goat anti-rabbit biotinylated (Vector), neuronal class III β-tubulin (NCT), and staining of human tendon/ligament sections with rabbit anti-NCT (Covance)/goat anti-rabbit biotinylated (Vector).
Literature search revealed that 11 of the 19 anatomical texts and atlases that consider or depict the OPL state that the distal semimembranosus tendon contributes fibers to the OPL [2–20]. A much higher percentage was found in orthopedic or radiologic specialty articles (11 of 12 stated that the distal semimembranosus tendon contributes fibers to the OPL) [21–32] (see Table 1). Deep dissections revealed that the alleged oblique popliteal ligament’s distal (medial) attachment originated from the SMTU in 100% of 70 knees. Its proximal (lateral) attachment was inserted into the joint capsule in 39/70, bone in 11/70, and both joint capsule and bone in 20/70 knees (see Figures 1(a), 1(b), 2, 3, and 4). Immunohistochemistry staining using rabbit anti-PGP9.5/goat anti-rabbit biotinylated revealed a positive stain for neuronal axons in both the SMT and the OPL and a negative stain in the LCL. Immunohistochemistry staining using neuronal class III β-tubulin (NCT) staining of human tendon/ligament sections with rabbit anti-NCT/goat anti-rabbit biotinylated revealed a positive stain for neuronal axons in each of three tissue types, OPL, SMT, and LCL (see Figures 5(a), 5(b), 5(c), 6(a), 6(b), 6(c) and 7).
Despite the fact that nearly 60 percent of anatomical texts and atlases as well as over 90 percent of specialty journal articles state that the distal semimembranosus tendon contributes fibers to the oblique popliteal ligament; none have hypothesized that this structure is itself a tendon [1–31]. A macroanalysis using deep dissection of the posterior knee revealed that the OPL’s distal (medial) attachment originated from the SMTU in 100% of the knees. This provided evidence in support of the author’s hypothesis; however, a microanalysis was also necessary to propitiate these findings. This study was the first to conduct a histological microanalysis of the OPL.
The macroanalysis of the OPL revealed unequivocally it is indigenous to the distal SMTU. The microanalysis using an immunohistochemistry stain with PGP9.5 revealed a positive result for neuronal axons within both the SMT and OPL. Further microanalysis using an immunohistochemistry stain with β-tubulin revealed a positive stain for neuronal axons in the SMT, OPL, and LCL. Though the latter result leads the authors to question the validity of differentiating tendon from ligament using this particular immunohistochemistry stain, the macroanalysis results are overwhelming, and the microanalysis reveals striking similarities in the histology of both the OPL and SMT. The authors strongly suggest that the oblique popliteal ligament be renamed the oblique popliteal tendon (O) due this macro- and microanalysis study. Clinically, this study improves terminology accuracy and medical international language, allowing for better understanding of successful rehabilitation methods and rationale for current and future surgical procedures.