Modern knee reconstructive surgery has evolved rapidly with the desire towards minimal invasive surgery and accelerated rehabilitation.
Patient with osteoarthritis 40% of people above the age of 70 have osteoarthritis of the knee but we are seeing increasing numbers of young patients present with osteoarthritis.
Ligament Applied Anatomy and Biomechanics
Medial Collateral Ligament
Ivar Palmer (Swedish Surgon) is one of the first to describe Tibial Collateral Ligament anatomy in detail in his book- On the Injuries to the Ligaments of the Knee Joint-1938. Warren and Marshall (1979) dissected 154 knees and described a three layered pattern to the medial structures. LaPrade (2007) has quantitatively described the attachment sites of the medial structures.
There are three bony prominences medially –
- Medial epicondyle- most anterior and distal osseous prominence over the medial aspect of the medial femoral condyle.
- Adductor tubercle- located 12.6 mm proximal and 8.3 mm posterior to the medial epicondyle along the medial supracondylar line.
- Gastrocnemius tubercle- slightly distal and posterior to the adductor tubercle and corresponded to the location of the attachment of the medial gastrocnemius tendon.
The superficial medial collateral ligament (sMCL) is the main medial ligament and has one femoral attachment and two tibial attachments.
Femoral attachment- oval in shape and located an average of 3.2 mm (range, 1.6 to 5.2 mm) proximal and 4.8 mm (range, 2.5 to 6.3 mm) posterior to the medial epicondyle.
Tibial attachment- main bony attachment is broad-based and located just anterior to the posteromedial crest of the tibia. The majority of the distal attachment is located within the pes anserine bursa.
The deep medial collateral ligament (dMCL) is a thickening of the medial joint capsule that is distinct anteriorly and blends with capsule posteriorly. The deep medial collateral ligament has distinct meniscofemoral and meniscotibial ligament components.
The posterior oblique ligament (POL) consisted of three fascial attachments that coursed off the distal aspect of the semimembranosus tendon at the knee and have been previously termed the superficial, central (tibial), and the capsular arms. POL anatomy and its function and technique of repair has been well described by Hughston (1973).
The superficial MCL and POL have comparable structural properties and load to failure. Amis has shown the maximum loads of the ligament bundles as follows: 534 N (sMCL), 194 N (dMCL), 425 N (PMC)
Role of medial structures in controlling laxity
- sMCL is the primary restraint to tibial valgus moments across the arc of knee flexion.
- sMCL is the primary restraint on the medial aspect of the knee to tibial external rotation and that the dMCL also provided some restraint when the knee was flexed beyond 30°.
- dMCL is a short ligament, so tibial rotations tighten it more rapidly than they do the longer sMCL fibers. This observation may explain why the dMCL is often damaged in association with the ACL in injuries with a tibial rotation mechanism.
- dMCL provides significant restraint to anterior drawer of the flexed and externally rotated tibia,(Basis of Slocum test).
- PMC is an important structure for controlling tibial posterior translation with the knee in extension (resisting 28-42% of posterior translation load).
Robert F. LaPrade, Anders Hauge Engebretsen, Thuan V. Ly, Steinar Johansen, Fred A. Wentorf and Lars Engebretsen. The Anatomy of the Medial Part of the Knee. J Bone Joint Surg Am. 2007;89:2000-2010
Warren LF, Marshall JL. The supporting structures and layers on the medial side of the knee: an anatomical analysis. J Bone Joint Surg Am. 1979 Jan;61(1):56-62.
Hughston JC. The importance of the posterior oblique ligament in repairs of acute tears of the medial ligaments in knees with and without an associated rupture of the anterior cruciate ligament. Results of long-term follow-up. J Bone Joint Surg Am. 1994 Sep;76(9):1328-44
Hughston JC, Eilers AF. The role of the posterior oblique ligament in repairs of acute medial (collateral) ligament tears of the knee. J Bone Joint Surg Am. 1973 Jul;55(5):923-40.
Robinson JR, Bull AM, Amis AA. Structural properties of the medial collateral ligament complex of the human knee. J Biomech. 2005 May;38(5):1067-74.
Robinson JR, Sanchez-Ballester J, Bull AM, Thomas Rde W, Amis AA. The posteromedial corner revisited. An anatomical description of the passive restraining structures of the medial aspect of the human knee. J Bone Joint Surg Br. 2004 Jul;86(5):674-81.
Robinson JR, Bull AM, Thomas RR, Amis AA. The role of the medial collateral ligament and posteromedial capsule in controlling knee laxity. Am J Sports Med. 2006 Nov;34(11):1815-23.
Anterior Cruciate Ligament
Anatomical descriptions of ACL can be found in Egyptian papyrus scrolls dating back to 3000 BC. Hippocrates (460-370BC) has described knee subluxation with ACL injury.
The knee originates from Femoral and Tibial mesenchyme by 4th week of gestation and the ACL starts forming by the 9th week.
Important Notch Anatomy
The intercondylar fossa has its maximum diameter in the posterior part and converges towards the anterior direction and is shaped like a Gothic arch. There are two important factors that affect risk of ACL rupture- Notch width and Notch roof angle. The width of the notch is smaller in women when compared to men thus explaining the higher risk of ACL rupture in women. The notch width index is the ratio of epicondylar width to notch width.
On conventional lateral knee radiographs the notch roof projects as a dense profile known as Blumensaat’s line. The average angle between the longitudinal axis of the femur and the notch roof (notch roof angle) is given as 37°, but varies between 23° and 60°. Smaller roof angle has higher ACL rupture risk.
ACL Bundles and Insertional Anatomy
The anterior cruciate ligament consists of primarily tension-carrying fibrous collagen. It also contains blood vessels, nerves and fibroblasts. The ACL is an intraarticular ligament but is enveloped by synovium. The length of the ACL fibers range from 22 mm to 41 mm with a mean of 32 mm. The PL bundle is shorter than the AM bundle. When this synovial sheath is torn during injury, blood dissipates within the joint and does not form a local fibrinous mesh at the site of injury. The dependence of ACL healing on an intact synovial lining has been demonstrated by the poor healing response in ACL transection studies performed in animals. Steadman has shown that surgical formation of a blood clot after proximal, partial ACL ruptures can lead to reattachment of the ACL at its origin (Healing response).
The ACL has two major functional bundles consisting of anteromedial and posterolateral bundles named for the orientation of their tibial attachments. Amis described three bundles- AM, intermediate and PL whilst other describe many fascicular subunits. Fibers of the anteromedial bundle originating in the most proximal part of the femoral insertion and inserting at the anteromedial tibial insertion. Fibers of the posterolateral bundle originate distally at the femur and insert on the posterolateral part of the tibial insertion.
The femoral ACL footprint lies on the lateral wall of the notch and spans a region on a clock face from 10:14 to 11:23. This localization of the footprint is based on a 3- to 9-o’clock axis placed on the posterior femoral condyles with the knee flexed 90 degrees. It has an average length of 18 mm, width of 10 mm, and a separation of up to 4 mm from the articular cartilage. “Resident’s ridge,” a term coined by William Clancy Jr., describes the raised bony landmark visualized just anterior to the femoral attachment of the ACL.
The tibial footprint of the ACL is about 18mm long and 10mm wide. The ACL does not attach to the tibial spines. The distance between the PCL notch and the posterior boundary of the ACL is between 6-10mm (Heming, Colombet). From the anterior border of the PCL the centre of the ACL footprint is 7-10mm but when referenced from the PCL notch the ACL centre is 15-19mm. The ACL inserts on the tibial plateau, medial to the insertion of the anterior horn of the lateral meniscus.
Function and Biomechanics
The ACL has proprioceptive and mechanical function. It is the primary restraint to anterior translation of the tibia.
The ultimate tensile load and stiffness of the human femur-ACL-tibia complex to be 2160 6 157 N and 242 6 28 N/mm. The forces on the ACL during normal walking is 303N or less. The highest loads and strains on the anterior cruciate ligament during daily function are quadriceps-powered extension of the knee, moving it from approximately 40 degrees of flexion to full extension (This explains why open kinetic chain exercises are avoided during early phases of rehabilitation)
The ACL carries load during entire range of motion. Transection of the anteromedial bundle increased anterior tibial translation at 60 degrees and 90 degrees of knee flexion. Isolated transection of the posterolateral bundle increased anterior tibial translation in response to 134-N anterior load at 30 degrees of knee flexion significantly and resulted in a significant increase in combined rotation at 0 degrees and 30 degrees (Amis, Zantop) The PL bundle is important in controlling not only anterior laxity toward knee extension but the rotational component of the pivot shift. Markolf has contradicted the role of the PL bundle in anterior laxity in extension more recently.
Anderson AF, Dome DC, Gautam S. Correlation of anthropometric measurements, strength, anterior cruciate ligament size, and intercondylar notch characteristics to sex differences in anterior cruciate ligament tears. Am J Sports Med. 2001;29:58-63.
LaPrade RF, Burnett QM. Femoral intercondylar notch stenosis and correlation to anterior cruciate ligament injuries: a prospective study. Am J Sports Med. 1994;22:198-202.
Shelbourne KD, Facibene WA, Hunt JJ. Radiographic and intraoperative intercondylar notch width measurements in men and women with unilateral and bilateral anterior cruciate ligament tears. Knee Surg Sports Traumatol Arthrosc. 1997;5:229-233.
Howell SM. Principles for placing the tibial tunnel and avoiding roof impingement during reconstruction of a torn anterior cruciate ligament. Knee Surg Sports Traumatol Arthrosc. 1998;6(Suppl 1): 49-55.
Steadman JR, Cameron-Donaldson ML, Briggs KK, Rodkey WG. A minimally invasive technique (“healing response”) to treat proximal ACL injuries in skeletally immature athletes. J Knee Surg. 2006 Jan;19(1):8-13.
Petersen W, Zantop T. Anatomy of the anterior cruciate ligament with regard to its two bundles. Clin Orthop Relat Res. 2007 Jan;454:35-47. Review
Colombet P, Robinson J, Christel P, et al. Morphology of anterior cruciate ligament attachments for anatomic reconstruction: a cadaveric dissection and radiographic study. Arthroscopy. 2006;22:984-992.
Heming JF, Rand J, Steiner ME. Anatomic limitations of transtibial drilling in ACL reconstruction. Am J Sports Med. 2007;35:1708-1715
Cooper DE, Small J, Urrea L. Factors affecting graft excursion patterns in anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 1998;6 Suppl 1:S20-S24.
Steiner ME, Murray MM, Rodeo SA. Strategies to improve anterior cruciate ligament healing and graft placement. Am J Sports Med. 2008 Jan;36(1):176-89. Review.
Hefzy MS, Grood ES, Noyes FR. Factors affecting the region of most isometric femoral attachments. Part II: the anterior cruciate ligament.Am J Sports Med. 1989;17:208-216.
Shelburne KB, Pandy MG, Anderson FC, Torry MR. Pattern of anterior cruciate ligament force in normal walking. J Biomech. 2004 Jun;37(6):797-805
Markolf KL, Park S, Jackson SR, McAllister DR. Contributions of the posterolateral bundle of the anterior cruciate ligament to anterior-posterior knee laxity and ligament forces. Arthroscopy. 2008 Jul;24(7):805-9
Zantop T, Herbort M, Raschke MJ, Fu FH, Petersen W. The role of the anteromedial and posterolateral bundles of the anterior cruciate ligament in anterior tibial translation and internal rotation. Am J Sports Med. 2007 Feb;35(2):223-7.
Amis AA, Dawkins GP. Functional anatomy of the anterior cruciate ligament. Fibre bundle actions related to ligament replacements and injuries. J Bone Joint Surg Br. 1991 Mar;73(2):260-7.
Woo SL-Y, Hollis JM, Adams DJ, et al: Tensile properties of the human femur-anterior cruciate ligament-tibia complex: The effects of specimen age and orientation. Am J Sports Med 1991:19: 217-225.