- Email: [email protected]
An Anatomic Study of the Posterior Septum of the Knee
An Anatomic Study of the Posterior Septum of the Knee Leonardo Addêo Ramos, M.D., Ph.D., Diego Astur, M.D., João Victor Novaretti, B.S., Leandro Masini Ribeiro, B.S., Rogério Teixeira de Carvalho, M.D., Moisés Cohen, M.D., Ph.D., Sheila J. McNeill Ingham, M.D., M.S., and René Jorge Abdalla, M.D., Ph.D.
Purpose: To evaluate the posterior septum of the knee and determine the presence of a safe zone that could be removed, without significant damage to blood vessels and nerves. Methods: Nineteen fresh unpaired adult human cadaveric knees, with no macroscopic degenerative or traumatic changes, were used in this study. Microscopic evaluation was performed by analysis of H&E, CD-34, and S-100 staining. Results: The posterior septum of the knee is rich in type II and type IV mechanoreceptors and blood vessels. The superior half has a greater number of blood vessels (21.52 ⫾ 6.36 v 12.05 ⫾ 4.1, P ⬍ .001), higher-caliber vessels (2.2 ⫾ 0.89 m v 1.41 ⫾ 0.45 m, P ⬍ .006), and a greater number of mechanoreceptors per field (type II, 1.8 ⫾ 1.8 v 0.42 ⫾ 1, P ⫽ .04; type IV, 22.6 ⫾ 14 v 14.5 ⫾ 9.4, P ⫽ .04) than the inferior half of the septum. Conclusions: This study has shown that the posterior septum of the knee is highly vascularized and has a great number of type II and IV mechanoreceptors. The presence of these structures is significantly higher in the superior half of the septum. Clinical Relevance: If debridement of the posterior septum is necessary, it should be done at the inferior aspect so that a greater number of blood vessels and mechanoreceptors can be preserved.
T
he posterior septum of the knee divides this region into 2 compartments, medial and lateral,1,2 and is composed of connective tissue and fat cells. It lies between the knee’s synovial tissue1,3 and contains several neurovascular structures, 1 of which is the medial genicular artery that supplies the posterior cruciate ligament (PCL).4 A posterior approach to the knee has become more frequent, and examples of procedures performed are posterior synovectomy, removal of chondral lesions, posterior meniscus injury suture, and PCL reconstruction.1-3,5-7 The incidence of PCL injuries varies from 1% to 44%, and it is believed that in an athletic population,
From the Department of Orthopaedic Surgery, School of Medicine, Federal University of São Paulo, and Knee Institute, Hospital do Coração (S.J.M.I., R.J.A.), São Paulo, Brazil. Supported by a grant from PCE Brasil. The authors report no conflict of interest. Received February 10, 2011; accepted June 29, 2011. Address correspondence to René Jorge Abdalla, M.D., Ph.D., Rua Abilio Soares, 227, São Paulo, 04005-000, Brazil. E-mail: [email protected] © 2012 by the Arthroscopy Association of North America 0749-8063/11103/$36.00 doi:10.1016/j.arthro.2011.06.037
100
there is a higher incidence; this injury usually occurs together with other ligament injuries, and in this case, surgical treatment is warranted.8-12 The number of PCL injuries over the years has increased, and with better diagnostic tools and surgical techniques, the number of surgical treatments has also increased.13 With both the arthroscopic and open techniques, there is a need to explore the posterior septum of the knee.13,14 The aim of this study was to evaluate the posterior septum of the knee and determine the safe zone that could be removed, with minor damage to the blood vessels and nerves. We hypothesized that the posterior septum of the knee is important for PCL nutrition and innervation and, therefore, should not be removed unless deemed completely necessary.
METHODS Specimen Dissections Nineteen fresh unpaired adult human cadaveric knees, with no macroscopic degenerative or traumatic changes, were used in this study. The mean age of the donors at the time of death was 41.2 ⫾ 10.8 years
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 28, No 1 (January), 2012: pp 100-104
ANATOMY OF POSTERIOR SEPTUM OF KNEE (range, 34 to 55 years). The ethics committee of our university approved all procedures performed in this study. Preparation began with the removal of all extraarticular soft tissues, followed by careful dissection with a posterior approach, as described by Trickey.15 A 30-cm longitudinal S-shaped incision was made, from the lateral aspect of the thigh to the medial aspect of the medial head of the gastrocnemius muscle. The subcutaneous tissue was opened so that the medial sural cutaneous nerve and the small saphenous vein could be visualized and used as landmarks for the popliteus fossa. After this, the medial and lateral gastrocnemius heads were identified and detached from their femoral origins so that the posterior capsule of the knee could be viewed. A U-shaped posterior capsulotomy was performed, and the posterior capsule, as well as part of the tibial insertion site of the PCL and of the posterior septum, was removed (Fig 1). The posterior septum (Fig 2) was then divided, for comparison, into 2 parts, proximal and distal, because the middle genicular artery is superior and the PCL insertion site is inferior. The capsular side of the septum was measured and divided in 2. Histologic Evaluation The tissue was fixed in 10% formaldehyde overnight and posteriorly embedded in paraffin. All sections were cut at 4 m and stained with H&E. To determine the presence of blood vessels and mecha-
101
FIGURE 2. Posterior capsule and septum of knee showing entry of medial genicular artery in superior portion.
noreceptors, immunohistochemical staining with CD-34 (Dako North America, Carpinteria, CA) (1: 100) and S-100 (Dako North America) (1:17,000) was performed. The expressions of CD-34 and S-100, as well as the capillary density, were quantified by use of Northern Eclipse software (Empix Imaging, Mississauga, Ontario, Canada) by use of a previously described protocol.16 Vessels and mechanoreceptors were quantified by use of 15 random 200⫻ highpowered fields selected from each sample. Statistical Analysis Data are shown as mean ⫾ standard deviation. Differences in the quantity and size of the blood vessels and in the number of mechanoreceptors between the proximal and distal parts of the posterior septum were analyzed with the nonparametric Wilcoxon test and are the main outcomes evaluated. Statistical significance was assumed at P ⬍ .05. A post hoc power analysis was conducted. The statistical analysis was performed with the software package GraphPad Prism for Windows (GraphPad Software, San Diego, CA). RESULTS
FIGURE 1. Posterior aspect of knee. The gray arrow depicts the posterior septum together with the posterior capsule, the yellow markers show the medial and lateral meniscus, and the black arrow depicts the PCL.
The posterior septum is composed of adipose tissue surrounded by a synovial membrane that contains blood vessels and nerve endings. When the proximal and distal portions of the septum were compared, the
102
L. A. RAMOS ET AL. TABLE 1.
Blood Vessel Characteristics Proximal
No. of blood vessels Mean ⫾ SD Range Diameter (m) Mean ⫾ SD Range
Distal
21.52 ⫾ 6.36 12.05 ⫾ 4.1 15-37 4-19 2.2 ⫾ 0.89 1.1-4.4
1.41 ⫾ 0.45 0.7-2.1
P Value* ⬍.001 .006
*P value for difference between proximal and distal regions.
proximal portion had a higher concentration of blood vessels (P ⬍ .001) and these blood vessels had a greater caliber (P ⬍ .006) (Table 1). Mechanoreceptors were present in the posterior septum of the knee. The main mechanoreceptors found were type II (linked to proprioception) (Fig 3) and type IV (free neurologic endings) (Fig 4).17 Again, a greater concentration of mechanoreceptors was found in the proximal portion of the septum: 1.8 ⫾ 1.8 versus 0.42 ⫾ 1.0 type II mechanoreceptors per field (P ⫽ .04) and 22.6 ⫾ 14 versus 14.5 ⫾ 9.4 type IV mechanoreceptors per field (P ⫽ .04). A post hoc power analysis was performed, and with 19 specimens, a power of 87% was achieved.
FIGURE 4. Histologic evaluation of type IV mechanoreceptors with S-100 staining (original magnification ⫻400).
DISCUSSION
FIGURE 3. Histologic evaluation of type II mechanoreceptors with S-100 staining (original magnification ⫻400).
The posterior septum is present between the posterior capsule and the cruciate ligaments, and it is composed of connective tissue, fat, and a synovial membrane. This anatomic study has shown that the posterior septum of the knee is rich in mechanoreceptors and blood vessels, mainly in its superior portion. The posterior region of the knee, more specifically, the posterior septum, has been poorly studied and is, many times, injured during surgery. We believe that a greater knowledge of this tissue is needed so that a posterior approach to the knee can be made with minimal damage to important structures. The vascular supply of the intercondylar structures is provided by 3 main blood vessels, the medial genicular artery, the accessory medial genicular artery, and the inferior genicular artery.4 The blood vessels present in the posterior septum are branches of the medial genicular artery that, in itself, is a direct branch of the popliteus artery. The medial genicular artery supplies both cruciate ligaments and the medial femoral condyle4,18 and, like the popliteus artery, can be injured during posterior knee procedures, causing knee hemarthrosis.19,20 As this study has shown, the greater concentration of blood vessels in the superior
ANATOMY OF POSTERIOR SEPTUM OF KNEE portion of the septum leads us to conclude that if this superior portion is preserved during surgery, there will be a smaller chance of causing damage to the arteries and, thus, a smaller incidence of postoperative complications. Three nerves provide the knee’s innervation: the posterior articular nerve (which branches from the tibial nerve and supplies the posterior portion of the knee), the lateral articular nerve (which branches from the common fibular nerve), and the medial articular nerve (which branches from the saphenous nerve and supplies the medial structures of the knee, Hoffa fat pad, and patellar tendon). The posterior articular nerve enters the knee together with the medial genicular artery and divides itself into smaller branches to innervate the intercondylar synovial tissue and the posterior septum.21 Schultz et al22 were the first authors to show the presence of mechanoreceptors in the cruciate ligaments; these mechanoreceptors were found on the surface of the ligaments and were more prevalent near the femoral insertion site. Del Valle et al23 also showed the presence of mechanoreceptors in the PCL and suggested the importance of these structures in knee proprioception. In all portions of the septum, but mainly in the superior portion, a predominance of type II and type IV mechanoreceptors17 was found. Type IV mechanoreceptors are unspecialized, afferent, unmyelinated free nerve endings present in ligaments, synovial tissue, and the articular capsule.24 Type II mechanoreceptors, also known as Krause, Meissner, and Pacini receptors, respond to mechanical stimuli by firing action potentials and contribute to the joint’s proprioception.25 As is well-known, injury to the PCL causes a loss of proprioception,24 and preservation of mechanoreceptors may be important because they can contribute to joint stability. Johansson et al.26 have suggested that the cruciate ligament remnants should be preserved because this could contribute to postoperative stability as a result of mechanoreceptor preservation. So, the preservation of the superior part of the posterior septum might be important to maintain a greater number of mechanoreceptors and, consequently, improve proprioception.22,27 In light of the findings of this study, we believe that the posterior septum should be preserved.5,28 This study has limitations. First, a small sample size was used, and normal anatomic variation cannot be ruled out. Second, dissection was performed by human hands, and subjective decisions regarding the septum division could introduce an error. Third, although we believe the posterior septum should be
103
preserved based on the presence of mechanoreceptors, this is only an anatomic study, and more studies evaluating the influence of these mechanoreceptors on surgical outcomes are warranted. CONCLUSIONS This study has shown that the posterior septum of the knee is highly vascularized and has a great number of type II and type IV mechanoreceptors. The presence of these structures is significantly higher in the superior portion of the septum. Acknowledgment: The support of PCE Brasil is gratefully acknowledged.
REFERENCES 1. Ahn JH, Ha CW. Posterior trans-septal portal for arthroscopic surgery of the knee joint. Arthroscopy 2000;16:774-779. 2. Louisia S, Charrois O, Beaufils P. Posterior “back and forth” approach in arthroscopic surgery on the posterior knee compartments. Arthroscopy 2003;19:321-325. 3. Ahn JH, Lee YS, Lee DH, Ha HC. Intraarticular fibroma of the posterior compartment in the knee. A case report. Knee 2008; 15:155-158. 4. Scapinelli R. Vascular anatomy of the human cruciate ligaments and surrounding structures. Clin Anat 1997;10:151-162. 5. Ahn JH, Wang JH, Lee SH, Yoo JC, Jeon WJ. Increasing the distance between the posterior cruciate ligament and the popliteal neurovascular bundle by a limited posterior capsular release during arthroscopic transtibial posterior cruciate ligament reconstruction: A cadaveric angiographic study. Am J Sports Med 2007;35:787-792. 6. Lakdawala A, El-Zebdeh M, Ireland J. Excision of a ganglion cyst from within the posterior septum of the knee—An arthroscopic technique. Knee 2005;12:245-247. 7. Park SE, Stamos BD, DeFrate LE, Gill TJ, Li G. The effect of posterior knee capsulotomy on posterior tibial translation during posterior cruciate ligament tibial inlay reconstruction. Am J Sports Med 2004;32:1514-1519. 8. Fanelli GC. Posterior cruciate ligament injuries in trauma patients. Arthroscopy 1993;9:291-294. 9. Fanelli GC, Edson CJ. Posterior cruciate ligament injuries in trauma patients: Part II. Arthroscopy 1995;11:526-529. 10. Harner CD, Höher J. Evaluation and treatment of posterior cruciate ligament injuries. Am J Sports Med 1998;26:471482. 11. Lobenhoffer P, Lattermann C, Krettek C, Blauth M, Tscherne H. Rupture of the posterior cruciate ligament: Status of current treatment. Unfallchirurg 1996;99:382-399 (in German). 12. Shelbourne KD, Davis TJ, Patel DV. The natural history of acute, isolated, nonoperatively treated posterior cruciate ligament injuries. A prospective study. Am J Sports Med 1999;27: 276-283. 13. Bollen S. Epidemiology of knee injuries: Diagnosis and triage. Br J Sports Med 2000;34:227-228. 14. Chen CH, Chuang TY, Wang KC, Chen WJ, Shih CH. Arthroscopic posterior cruciate ligament reconstruction with hamstring tendon autograft: Results with a minimum 4-year follow-up. Knee Surg Sports Traumatol Arthrosc 2006;14:1045-1054.
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15. Trickey EL. Injuries to the posterior cruciate ligament: Diagnosis and treatment of early injuries and reconstruction of late instability. Clin Orthop Relat Res 1980:7681. 16. Pochini AD, Ejnisman B, Alves MT, et al. Overuse of training increases mechanoreceptors in supraspinatus tendon of rats SHR. J Orthop Res. 2 May, 2011. [Epub ahead of print.] 17. Freeman MA, Wyke B. The innervation of the knee joint. An anatomical and histological study in the cat. J Anat 1967;101: 505-532 (pt 3). 18. Reddy AS, Frederick RW. Evaluation of the intraosseous and extraosseous blood supply to the distal femoral condyles. Am J Sports Med 1998;26:415-419. 19. Armato DP, Czamecki D. Geniculate artery pseudoaneurysm: A rare complication of arthroscopic surgery. AJR Am J Roentgenol 1990;155:659. 20. Wu RW, Hsu CC, Wang CJ. Acute popliteal artery occlusion after arthroscopic posterior cruciate ligament reconstruction. Arthroscopy 2003;19:889-893. 21. Solomonow M, Krogsgaard M. Sensorimotor control of knee stability. A review. Scand J Med Sci Sports 2001;11:64-80. 22. Schultz RA, Miller DC, Kerr CS, Micheli L. Mechanoreceptors in human cruciate ligaments. A histological study. J Bone Joint Surg Am 1984;66:1072-1076.
23. Del Valle, Harwin SF, Maestro A, Murcia A, Vega JA. Immunohistochemical analysis of mechanoreceptors in the human posterior cruciate ligament: A demonstration of its proprioceptive role and clinical relevance. J Arthroplasty 1998;13:916-922. 24. Katonis P, Papoutsidakis A, Aligizakis A, Tzanakakis G, Kontakis GM, Papagelopoulos PJ. Mechanoreceptors of the posterior cruciate ligament. J Int Med Res 2008;36: 387-393. 25. Muaidi QI, Nicholson LL, Refshauge KM, Adams RD, Roe JP. Effect of anterior cruciate ligament injury and reconstruction on proprioceptive acuity of knee rotation in the transverse plane. Am J Sports Med 2009;37:1618-1626. 26. Johansson H, Sjölander P, Sojka P. A sensory role for the cruciate ligaments. Clin Orthop Relat Res 1991:161178. 27. Raunest J, Sager M, Bürgener E. Proprioceptive mechanisms in the cruciate ligaments: An electromyographic study on reflex activity in the thigh muscles. J Trauma 1996;41:488-493. 28. Ramos LA, de Carvalho RT, Cohen M, Abdalla RJ. Anatomic relation between the posterior cruciate ligament and the joint capsule. Arthroscopy 2008;24:1367-1372.
Purpose: To evaluate the posterior septum of the knee and determine the presence of a safe zone that could be removed, without significant damage to blood vessels and nerves. Methods: Nineteen fresh unpaired adult human cadaveric knees, with no macroscopic degenerative or traumatic changes, were used in this study. Microscopic evaluation was performed by analysis of H&E, CD-34, and S-100 staining. Results: The posterior septum of the knee is rich in type II and type IV mechanoreceptors and blood vessels. The superior half has a greater number of blood vessels (21.52 ⫾ 6.36 v 12.05 ⫾ 4.1, P ⬍ .001), higher-caliber vessels (2.2 ⫾ 0.89 m v 1.41 ⫾ 0.45 m, P ⬍ .006), and a greater number of mechanoreceptors per field (type II, 1.8 ⫾ 1.8 v 0.42 ⫾ 1, P ⫽ .04; type IV, 22.6 ⫾ 14 v 14.5 ⫾ 9.4, P ⫽ .04) than the inferior half of the septum. Conclusions: This study has shown that the posterior septum of the knee is highly vascularized and has a great number of type II and IV mechanoreceptors. The presence of these structures is significantly higher in the superior half of the septum. Clinical Relevance: If debridement of the posterior septum is necessary, it should be done at the inferior aspect so that a greater number of blood vessels and mechanoreceptors can be preserved.
T
he posterior septum of the knee divides this region into 2 compartments, medial and lateral,1,2 and is composed of connective tissue and fat cells. It lies between the knee’s synovial tissue1,3 and contains several neurovascular structures, 1 of which is the medial genicular artery that supplies the posterior cruciate ligament (PCL).4 A posterior approach to the knee has become more frequent, and examples of procedures performed are posterior synovectomy, removal of chondral lesions, posterior meniscus injury suture, and PCL reconstruction.1-3,5-7 The incidence of PCL injuries varies from 1% to 44%, and it is believed that in an athletic population,
From the Department of Orthopaedic Surgery, School of Medicine, Federal University of São Paulo, and Knee Institute, Hospital do Coração (S.J.M.I., R.J.A.), São Paulo, Brazil. Supported by a grant from PCE Brasil. The authors report no conflict of interest. Received February 10, 2011; accepted June 29, 2011. Address correspondence to René Jorge Abdalla, M.D., Ph.D., Rua Abilio Soares, 227, São Paulo, 04005-000, Brazil. E-mail: [email protected] © 2012 by the Arthroscopy Association of North America 0749-8063/11103/$36.00 doi:10.1016/j.arthro.2011.06.037
100
there is a higher incidence; this injury usually occurs together with other ligament injuries, and in this case, surgical treatment is warranted.8-12 The number of PCL injuries over the years has increased, and with better diagnostic tools and surgical techniques, the number of surgical treatments has also increased.13 With both the arthroscopic and open techniques, there is a need to explore the posterior septum of the knee.13,14 The aim of this study was to evaluate the posterior septum of the knee and determine the safe zone that could be removed, with minor damage to the blood vessels and nerves. We hypothesized that the posterior septum of the knee is important for PCL nutrition and innervation and, therefore, should not be removed unless deemed completely necessary.
METHODS Specimen Dissections Nineteen fresh unpaired adult human cadaveric knees, with no macroscopic degenerative or traumatic changes, were used in this study. The mean age of the donors at the time of death was 41.2 ⫾ 10.8 years
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 28, No 1 (January), 2012: pp 100-104
ANATOMY OF POSTERIOR SEPTUM OF KNEE (range, 34 to 55 years). The ethics committee of our university approved all procedures performed in this study. Preparation began with the removal of all extraarticular soft tissues, followed by careful dissection with a posterior approach, as described by Trickey.15 A 30-cm longitudinal S-shaped incision was made, from the lateral aspect of the thigh to the medial aspect of the medial head of the gastrocnemius muscle. The subcutaneous tissue was opened so that the medial sural cutaneous nerve and the small saphenous vein could be visualized and used as landmarks for the popliteus fossa. After this, the medial and lateral gastrocnemius heads were identified and detached from their femoral origins so that the posterior capsule of the knee could be viewed. A U-shaped posterior capsulotomy was performed, and the posterior capsule, as well as part of the tibial insertion site of the PCL and of the posterior septum, was removed (Fig 1). The posterior septum (Fig 2) was then divided, for comparison, into 2 parts, proximal and distal, because the middle genicular artery is superior and the PCL insertion site is inferior. The capsular side of the septum was measured and divided in 2. Histologic Evaluation The tissue was fixed in 10% formaldehyde overnight and posteriorly embedded in paraffin. All sections were cut at 4 m and stained with H&E. To determine the presence of blood vessels and mecha-
101
FIGURE 2. Posterior capsule and septum of knee showing entry of medial genicular artery in superior portion.
noreceptors, immunohistochemical staining with CD-34 (Dako North America, Carpinteria, CA) (1: 100) and S-100 (Dako North America) (1:17,000) was performed. The expressions of CD-34 and S-100, as well as the capillary density, were quantified by use of Northern Eclipse software (Empix Imaging, Mississauga, Ontario, Canada) by use of a previously described protocol.16 Vessels and mechanoreceptors were quantified by use of 15 random 200⫻ highpowered fields selected from each sample. Statistical Analysis Data are shown as mean ⫾ standard deviation. Differences in the quantity and size of the blood vessels and in the number of mechanoreceptors between the proximal and distal parts of the posterior septum were analyzed with the nonparametric Wilcoxon test and are the main outcomes evaluated. Statistical significance was assumed at P ⬍ .05. A post hoc power analysis was conducted. The statistical analysis was performed with the software package GraphPad Prism for Windows (GraphPad Software, San Diego, CA). RESULTS
FIGURE 1. Posterior aspect of knee. The gray arrow depicts the posterior septum together with the posterior capsule, the yellow markers show the medial and lateral meniscus, and the black arrow depicts the PCL.
The posterior septum is composed of adipose tissue surrounded by a synovial membrane that contains blood vessels and nerve endings. When the proximal and distal portions of the septum were compared, the
102
L. A. RAMOS ET AL. TABLE 1.
Blood Vessel Characteristics Proximal
No. of blood vessels Mean ⫾ SD Range Diameter (m) Mean ⫾ SD Range
Distal
21.52 ⫾ 6.36 12.05 ⫾ 4.1 15-37 4-19 2.2 ⫾ 0.89 1.1-4.4
1.41 ⫾ 0.45 0.7-2.1
P Value* ⬍.001 .006
*P value for difference between proximal and distal regions.
proximal portion had a higher concentration of blood vessels (P ⬍ .001) and these blood vessels had a greater caliber (P ⬍ .006) (Table 1). Mechanoreceptors were present in the posterior septum of the knee. The main mechanoreceptors found were type II (linked to proprioception) (Fig 3) and type IV (free neurologic endings) (Fig 4).17 Again, a greater concentration of mechanoreceptors was found in the proximal portion of the septum: 1.8 ⫾ 1.8 versus 0.42 ⫾ 1.0 type II mechanoreceptors per field (P ⫽ .04) and 22.6 ⫾ 14 versus 14.5 ⫾ 9.4 type IV mechanoreceptors per field (P ⫽ .04). A post hoc power analysis was performed, and with 19 specimens, a power of 87% was achieved.
FIGURE 4. Histologic evaluation of type IV mechanoreceptors with S-100 staining (original magnification ⫻400).
DISCUSSION
FIGURE 3. Histologic evaluation of type II mechanoreceptors with S-100 staining (original magnification ⫻400).
The posterior septum is present between the posterior capsule and the cruciate ligaments, and it is composed of connective tissue, fat, and a synovial membrane. This anatomic study has shown that the posterior septum of the knee is rich in mechanoreceptors and blood vessels, mainly in its superior portion. The posterior region of the knee, more specifically, the posterior septum, has been poorly studied and is, many times, injured during surgery. We believe that a greater knowledge of this tissue is needed so that a posterior approach to the knee can be made with minimal damage to important structures. The vascular supply of the intercondylar structures is provided by 3 main blood vessels, the medial genicular artery, the accessory medial genicular artery, and the inferior genicular artery.4 The blood vessels present in the posterior septum are branches of the medial genicular artery that, in itself, is a direct branch of the popliteus artery. The medial genicular artery supplies both cruciate ligaments and the medial femoral condyle4,18 and, like the popliteus artery, can be injured during posterior knee procedures, causing knee hemarthrosis.19,20 As this study has shown, the greater concentration of blood vessels in the superior
ANATOMY OF POSTERIOR SEPTUM OF KNEE portion of the septum leads us to conclude that if this superior portion is preserved during surgery, there will be a smaller chance of causing damage to the arteries and, thus, a smaller incidence of postoperative complications. Three nerves provide the knee’s innervation: the posterior articular nerve (which branches from the tibial nerve and supplies the posterior portion of the knee), the lateral articular nerve (which branches from the common fibular nerve), and the medial articular nerve (which branches from the saphenous nerve and supplies the medial structures of the knee, Hoffa fat pad, and patellar tendon). The posterior articular nerve enters the knee together with the medial genicular artery and divides itself into smaller branches to innervate the intercondylar synovial tissue and the posterior septum.21 Schultz et al22 were the first authors to show the presence of mechanoreceptors in the cruciate ligaments; these mechanoreceptors were found on the surface of the ligaments and were more prevalent near the femoral insertion site. Del Valle et al23 also showed the presence of mechanoreceptors in the PCL and suggested the importance of these structures in knee proprioception. In all portions of the septum, but mainly in the superior portion, a predominance of type II and type IV mechanoreceptors17 was found. Type IV mechanoreceptors are unspecialized, afferent, unmyelinated free nerve endings present in ligaments, synovial tissue, and the articular capsule.24 Type II mechanoreceptors, also known as Krause, Meissner, and Pacini receptors, respond to mechanical stimuli by firing action potentials and contribute to the joint’s proprioception.25 As is well-known, injury to the PCL causes a loss of proprioception,24 and preservation of mechanoreceptors may be important because they can contribute to joint stability. Johansson et al.26 have suggested that the cruciate ligament remnants should be preserved because this could contribute to postoperative stability as a result of mechanoreceptor preservation. So, the preservation of the superior part of the posterior septum might be important to maintain a greater number of mechanoreceptors and, consequently, improve proprioception.22,27 In light of the findings of this study, we believe that the posterior septum should be preserved.5,28 This study has limitations. First, a small sample size was used, and normal anatomic variation cannot be ruled out. Second, dissection was performed by human hands, and subjective decisions regarding the septum division could introduce an error. Third, although we believe the posterior septum should be
103
preserved based on the presence of mechanoreceptors, this is only an anatomic study, and more studies evaluating the influence of these mechanoreceptors on surgical outcomes are warranted. CONCLUSIONS This study has shown that the posterior septum of the knee is highly vascularized and has a great number of type II and type IV mechanoreceptors. The presence of these structures is significantly higher in the superior portion of the septum. Acknowledgment: The support of PCE Brasil is gratefully acknowledged.
REFERENCES 1. Ahn JH, Ha CW. Posterior trans-septal portal for arthroscopic surgery of the knee joint. Arthroscopy 2000;16:774-779. 2. Louisia S, Charrois O, Beaufils P. Posterior “back and forth” approach in arthroscopic surgery on the posterior knee compartments. Arthroscopy 2003;19:321-325. 3. Ahn JH, Lee YS, Lee DH, Ha HC. Intraarticular fibroma of the posterior compartment in the knee. A case report. Knee 2008; 15:155-158. 4. Scapinelli R. Vascular anatomy of the human cruciate ligaments and surrounding structures. Clin Anat 1997;10:151-162. 5. Ahn JH, Wang JH, Lee SH, Yoo JC, Jeon WJ. Increasing the distance between the posterior cruciate ligament and the popliteal neurovascular bundle by a limited posterior capsular release during arthroscopic transtibial posterior cruciate ligament reconstruction: A cadaveric angiographic study. Am J Sports Med 2007;35:787-792. 6. Lakdawala A, El-Zebdeh M, Ireland J. Excision of a ganglion cyst from within the posterior septum of the knee—An arthroscopic technique. Knee 2005;12:245-247. 7. Park SE, Stamos BD, DeFrate LE, Gill TJ, Li G. The effect of posterior knee capsulotomy on posterior tibial translation during posterior cruciate ligament tibial inlay reconstruction. Am J Sports Med 2004;32:1514-1519. 8. Fanelli GC. Posterior cruciate ligament injuries in trauma patients. Arthroscopy 1993;9:291-294. 9. Fanelli GC, Edson CJ. Posterior cruciate ligament injuries in trauma patients: Part II. Arthroscopy 1995;11:526-529. 10. Harner CD, Höher J. Evaluation and treatment of posterior cruciate ligament injuries. Am J Sports Med 1998;26:471482. 11. Lobenhoffer P, Lattermann C, Krettek C, Blauth M, Tscherne H. Rupture of the posterior cruciate ligament: Status of current treatment. Unfallchirurg 1996;99:382-399 (in German). 12. Shelbourne KD, Davis TJ, Patel DV. The natural history of acute, isolated, nonoperatively treated posterior cruciate ligament injuries. A prospective study. Am J Sports Med 1999;27: 276-283. 13. Bollen S. Epidemiology of knee injuries: Diagnosis and triage. Br J Sports Med 2000;34:227-228. 14. Chen CH, Chuang TY, Wang KC, Chen WJ, Shih CH. Arthroscopic posterior cruciate ligament reconstruction with hamstring tendon autograft: Results with a minimum 4-year follow-up. Knee Surg Sports Traumatol Arthrosc 2006;14:1045-1054.
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