Description of the attachment geometry of the anteromedial and posterolateral bundles of the ACL from arthroscopic perspective for anatomical tunnel placement The anterior cruciate ligament -LRB- ACL -RRB- consists of an anteromedial bundle -LRB- AMB -RRB- and a posterolateral bundle -LRB- PLB -RRB- . A reconstruction restoring the functional two-bundled nature should be able to approximate normal ACL function better than the most commonly used single-bundle reconstructions . Accurate tunnel positioning is important , but difficult . The purpose of this study was to provide a geometric description of the centre of the attachments relative to arthroscopically visible landmarks . The AMB and PLB attachment sites in 35 dissected cadaver knees were measured with a 3D system , as were anatomical landmarks of femur and tibia . At the femur , the mean ACL centre is positioned 7.9 ± 1.4 mm -LRB- mean ± 1 SD -RRB- shallow , along the notch roof , from the most lateral over-the-top position at the posterior edge of the intercondylar notch and from that point 4.0 ± 1.3 mm from the notch roof , low on the surface of the lateral condyle wall . The mean AMB centre is at 7.2 ± 1.8 and 1.4 ± 1.7 mm , and the mean PLB centre at 8.8 ± 1.6 and 6.7 ± 2.0 mm . At the tibia , the mean ACL centre is positioned 5.1 ± 1.7 mm lateral of the medial tibial spine and from that point 9.8 ± 2.1 mm anterior . The mean AMB centre is at 3.0 ± 1.6 and 9.4 ± 2.2 mm , and the mean PLB centre at 7.2 ± 1.8 and 10.1 ± 2.1 mm . The ACL attachment geometry is well defined relative to arthroscopically visible landmarks with respect to the AMB and PLB . With simple guidelines for the surgeon , the attachments centres can be found during arthroscopic single-bundle or double-bundle reconstructions . Introduction The anterior cruciate ligament -LRB- ACL -RRB- consists of two functional bundles -LSB- 2 , 4 , 16 -RSB- . The anteromedial bundle -LRB- AMB -RRB- originates anteroproximal in the intercondylar notch , close to the over-the-top position at the posterior edge of the notch , from the deep high part of the femoral attachment area and inserts anteromedial on the anterior intercondylar area of the tibia . The posterolateral bundle -LRB- PLB -RRB- originates more posteriorly and distally in the notch , from the shallow low part of the femoral attachment area and inserts posterolateral on the anterior intercondylar area of the tibia . The ACL reconstruction aims at restoring normal knee function . Most ACL replacements are performed with the isometric single-bundle technique . Isometric positioning of a single-bundle graft results in replacement of the AMB only . Although tensioned over the complete range of motion , the fibres are mostly tight in flexion . The AMB is the major constraint for anterior tibial displacement of the flexed knee -LSB- 30 -RSB- , but can not restore normal knee laxity and kinematics near extension -LSB- 4 , 28 , 41 -RSB- . In an effort to improve knee mechanics , double-bundle anatomic ACL reconstructions are now developed with reconstruction of both AMB and PLB -LSB- 9 , 10 , 13 , 19 , 28 , 35 , 40 , 46 , 49 , 50 , 52 , 53 -RSB- . As presented in previous studies , a reconstructed PLB is able to restore stability in knee angles where an isometrically placed graft fails -LSB- 28 , 41 , 50 -RSB- . Additional restraint against anterior displacement in 15 ° of flexion -LSB- 48 -RSB- as well as prevention of the pivot shift is demonstrated -LSB- 28 , 50 -RSB- . Therefore , a reconstruction with two bundles should be able to approximate normal ACL function over the complete range of motion -LSB- 39 , 41 , 51 -RSB- . Tunnel positioning is an important factor for clinical success of ACL reconstructions . Incorrect tibial -LSB- 23 -RSB- and femoral -LSB- 29 , 55 -RSB- tunnel placements result in abnormal knee mechanics . Anatomical placement restores normal knee function better than isometric placement -LSB- 36 , 55 -RSB- . However , accurate tunnel placement seems difficult . Misplacement between 25 and 65 % of the tibial and femoral tunnels is reported -LSB- 8 , 27 , 47 -RSB- . Double-bundle ACL reconstructions require an anatomical placement of the bone tunnels . It is difficult to identify the ACL remnants in chronic ACL-injured knees . Therefore , detailed information about the approximate native position is essential to determine proper anatomic tunnel placement for the two bundles during arthroscopy -LSB- 17 -RSB- . The anatomical position has been the subject of many studies -LSB- 3 , 5 , 12 , 14 -- 16 , 20 , 26 , 33 , 34 , 37 , 38 , 44 -RSB- . Only a few recent studies have described the anatomic positions of the AM and PL bundles -LSB- 11 , 32 , 45 , 52 -RSB- . Due to the two-dimensional and limited view on the arthroscopic monitor , the landmarks and descriptions used in the above-mentioned studies seem not sufficient for correct positioning of the two separate bundles in all planes during arthroscopic surgery . This study is aimed at acquiring quantitative geometric data of the ACL attachments on tibia and femur , such that these data can be used in an arthroscopically guided procedure for reconstruction of the ACL . We hypothesized that reliable guidelines to find the centres of the AMB , PLB and ACL relative to arthroscopically visible landmarks can be established . For the purpose of an anatomically accurate reconstruction of the ACL , the variations should be equal to or less than reported in other studies . As regard to the dimensions of drilled tunnel holes , normally 10 up to 12 mm , 95 % -LRB- mean ± 2SD -RRB- of the attachment centres should be within this range . Therefore the a priori set assumption is that the maximally acceptable SD is 2.5 up to 3 mm . Methods Dissection Thirty-five intact human cadaveric knee joints of elderly donors preserved in formalin , without signs of gross bony deformity , previous fracture or degenerative disease and with intact knee ligaments were dissected . Because of local post-dissection handling procedures , no exact data on gender and age of the donors were available , but they were older than 60 years . The muscles and anterior capsule were removed . The ligaments were left intact in order to preserve controlled motion of the knee . The femur was fixated in a clamp , the tibia was moved , resulting in flexion and extension of the knee joint . During this repeated passive movement , the two functional components of the ACL were identified , based on a visually detectable difference in their tensioning patterns as described by Girgis et al. -LSB- 16 -RSB- . In 90 ° of flexion , an anterior load was manually applied . This caused tension in the fibres of the medial tibial attachment site , the AMB . The fibres of the PLB remained slack . This procedure enabled a separation of the two bundles at the tibial attachment from ventral . The femur was turned in the clamp to enable a posterior approach and the posterior cruciate ligament -LRB- PCL -RRB- was removed . In this position the initial division of the ACL at the tibial attachment was visible and used to extend the division towards the femoral origin . The tibia was moved towards extension . The PLB-fibres , inserting at the lateral femoral ACL attachment site , tightened , enabling to complete the separation as far as the femoral attachment . The outline contours of both AMB and PLB attachment areas were marked , with a waterproof felt pen . Anatomical position To quantify the position of the centres of the attachment sites relative to arthroscopically visible landmarks , three-dimensional -LRB- 3D -RRB- measurements were made with a 3Space Fastrak electromagnetic tracking system -LRB- Polhemus Navigation Sciences , Colchester , VT , USA -RRB- . The x , y and z co-ordinates of each measured point were recorded with an accuracy of 0.35 mm -LSB- 42 -RSB- . On the femur and tibia , the attachment sites of the AMB , PLB and the entire ACL were digitized by means of a collection of points placed at equal distances on the marked outlines . The 3D position of the centres of the ACL , AMB and PLB attachments were calculated by the geometric mean of all points on the outlines . The 3D distances between the centres of the two bundles were calculated . On both femur and tibia , an arthroscopically visible landmark was digitized that served as the origin of a local coordinate system . The absolute two-dimensional -LRB- 2D -RRB- positions of the centres relative to these landmarks were calculated . The position in the third dimension was determined by the surface geometry of the femoral condyle and the intercondylar tibial area , respectively . Absolute positions can depend on different knee sizes and the dimensions of the femoral notch and the intercondylar tibial area . To correct for this , the relative centre positions were also calculated . Additional reference points near the attachment area on femur and tibia were digitized . Between these points two reference lines were defined to create a 2D coordinate system . The distances defined the dimensions of the femoral notch and intercondylar tibial area . Absolute centre positions were transformed in positions relative to the reference lines -LRB- % -RRB- within femur and tibia . To detect whether the absolute position of the attachment centres was actually influenced by knee size , statistical analyses were performed . The relation between absolute position and knee size can be demonstrated with a correlation coefficient . The Pearson 's correlations between the distances of the absolute positions and the length of the reference lines , representing knee size , were calculated . Correlations with a Pearson 's correlation coefficient r > 0.6 and a significance level P < 0.05 , for a 95 % alpha level were considered relevant and confirmed the relation between knee size and absolute centre position . Femur In the anatomical nomenclature the femoral ACL attachment uses anterior/posterior and proximal/distal positions , relative to the extended knee -LSB- 17 -RSB- -LRB- Fig. 1a -RRB- . Since this study aimed at describing the positions of the AMB and PLB of the femoral attachment from an arthroscopic perspective , the arthroscopic nomenclature was used as recommended by the `` ESSKA Scientific Workshops '' in 1998 -LSB- 4 -RSB- . The definitions , shallow/deep and high/low , refer to the position along the wall and from the roof of the intercondylar notch in a 90 ° flexed knee -LRB- Fig. 1b -RRB- . Fig. 1The orientation in the femoral notch , used in this study , is based on the recommendations of the ESKKA 1998 -LSB- 4 -RSB- . The notch depth -LRB- ND -RRB- is directed from shallow to deep in anatomic distal -- proximal direction . The notch height -LRB- NH -RRB- is directed from low to high in anatomic dorsal -- ventral direction . The notch wall is located at the medial side of the lateral condyle . The notch roof is the connection between the two condyles The digitized points on the femur are represented in Fig. 2 . The main femoral landmark was derived from the over-the-top position , located at the posterior edge of the intercondylar notch . The most proximal high deep point -LRB- D -RRB- on the lateral condyle was found at the 10.30 o'clock position in the arc of the femoral notch , in a right knee -LRB- at 1.30 in a left knee -RRB- -LSB- 17 -RSB- -LRB- Fig. 2 -RRB- . The circumferences of the ACL attachments were digitized , as was the additional reference point , the most distal high shallow point -LRB- S -RRB- . This point is positioned on the distal cartilage edge of the lateral condyle in the anterior notch outlet -LRB- Fig. 2a -RRB- . The femoral coordinate system was defined with two reference lines -LRB- Fig. 3 -RRB- . The first-defined femoral reference line -LRB- from D to S -RRB- divided the notch roof from the notch wall and defined the length of the lateral notch depth -LRB- ND -RRB- . The lowest , dorsal point -LRB- L -RRB- on the posterior joint cartilage edge was found using a line parallel to the line DS . The second reference line -LRB- from L to H -RRB- was defined from point L perpendicular to crossing point H , high in the notch at the line DS . It indicated the magnitude of the notch height -LRB- NH -RRB- . After creating this coordinate system , the calculated attachment centres -LRB- C -RRB- of the ACL , AMB and PLB were projected on the line DS at point P . The absolute centre position -LRB- mm -RRB- was composed of the distance between the main femoral landmark , the high deep point D and the point P and the distance between the point P and the centre C . The relative -LRB- % -RRB- position was calculated by dividing the distance DP by DS -LRB- notch depth -RRB- and distance CP by LH -LRB- notch height -RRB- . Finally the individual results were displayed in a diagram to define the distribution of the centres relative to the means and the advised tunnel position . Fig. 2a Distal view at a left femur . The high shallow and high deep points of the cartilage border were determined by placing the stylus at the point of an imaginary rectangular corner , indicating the separation between wall and roof , this corresponds with the 1.30 o'clock position in a left knee -LRB- 10.30 o'clock in a right knee -RRB- . b View at the medial side of a left lateral femoral condyle . The points that were digitized : AMB -LRB- white rounds -RRB- and PLB -LRB- black rounds -RRB- attachments ; the cartilage border -LRB- grey asterisks -RRB- , with the most distal , high shallow point -LRB- black asterisk -RRB- and most proximal , high deep point -LRB- white asterisk -RRB- indicating the separation between the notch wall on the lateral condyle and the notch roofFig . 3A schematic arthroscopic femoral view through the anteromedial portal . The femoral coordinate system is indicated . The first reference line , from the high deep point -LRB- D -RRB- to the high shallow point -LRB- S -RRB- on the cartilage edge separated the notch wall on the lateral condyle from the notch roof and defined the notch depth -LRB- ND -RRB- . The second reference line , a perpendicular line , from the lowest point on the posterior cartilage edge -LRB- L -RRB- to the crossing point on the line DS -LRB- H -RRB- and defined the notch height -LRB- NH -RRB- . The calculated attachment centre of the ACL -LRB- C -RRB- was projected on line DS -LRB- P -RRB- . The absolute distances DP and CP were calculated , as were the distances relative to the reference lines -LRB- DP/DS and CP/LH -RRB- . This was also done for the AMB and PLB , for the sake of clearness , only the centre of the entire ACL is depicted Tibia The digitized points on the tibia are represented in Fig. 4 . The medial tibial spine -LRB- M -RRB- was determined as the main tibial landmark . The circumferences of the ACL attachments were digitized , as were the additional reference points . Those were , besides the lateral tibial spine -LRB- L -RRB- , the most anterior points on the margin of the articular surfaces of the medial tibial condyle -LRB- MA -RRB- and lateral tibial condyle -LRB- LA -RRB- . The tibial coordinate system was defined as follows -LRB- Fig. 5 -RRB- . The first tibial reference line -LRB- from M to L -RRB- was defined between the medial and the lateral tibial spine representing the interspinal distance -LRB- ID -RRB- . A line connecting the anterior points MA and LA indicated the anterior margin of the articular surface of the medial and lateral condyles of the tibia . The second reference line -LRB- from M to Q -RRB- connected the medial spine -LRB- M -RRB- perpendicular with the anterior margin at crossing point Q . The length of the second reference line represents the length of the anterior intercondylar area -LRB- AL -RRB- . After creating this coordinate system , the calculated attachment centres of the ACL , AMB and PLB were projected on the line ML at point P . The absolute centre position -LRB- mm -RRB- was composed of the distance between the major tibial landmark , the medial tibial spine M and the point P , and the distance between the point P and the centre C . The relative position -LRB- % -RRB- was calculated by dividing the distance MP by ML -LRB- interspinal distance -RRB- and distance CP by MQ -LRB- anterior length -RRB- . Finally the individual results were displayed in a diagram to define the distribution of the centres relative to the means and the advised tunnel position . Fig. 4Proximal view at the articular surfaces of the tibial condyles and the anterior intercondylar area . The points that were digitized : AMB -LRB- white rounds -RRB- and PLB -LRB- black rounds -RRB- attachments ; the lateral tibial spine -LRB- light grey oval -RRB- and medial tibial spine -LRB- dark grey oval -RRB- and the most anterior points on the margin of the articular surface of the medial and lateral tibial condyles -LRB- white asterisks -RRB- Fig. 5A schematic arthroscopic tibial view . The tibial coordinate system is indicated . The first reference line , from the medial spine -LRB- M -RRB- to the lateral spine -LRB- L -RRB- , defined the interspinal distance -LRB- ID -RRB- . The second reference line , from the medial spine -LRB- M -RRB- perpendicular to the crossing point -LRB- Q -RRB- at the anterior line between the most anterior points on the margin of the articular surface of the medial and lateral tibial condyles defined the anterior intercondylar length -LRB- AL -RRB- . The calculated attachment centre -LRB- C -RRB- was projected on line ML -LRB- P -RRB- . The absolute distances MP and CP were calculated , as were the distances relative to the reference lines -LRB- MP/ML and CP/MQ -RRB- . This was also done for the AMB and PLB , for the sake of clearness , only the centre of the entire ACL is depicted Surface To determine the surface dimensions of the bony attachment areas , a line was fitted through the digitized points on the outlines of both the AMB and PLB attachments on femur and on the tibia . The enclosed surface of all areas was calculated -LRB- in mm2 -RRB- , with the aid of a Delaunay triangulation based on the Qhull algorithm as provided by Matlab ® -LRB- version 7 The MathWorks , Inc , more details provided on http://www.mathworks.com -RRB- . The surface of the entire ACL attachment was calculated as the sum of AMB and PLB . Also the percentage of AMB and PLB surfaces was calculated relative to the ACL attachment surface . Statistical analyses to detect differences in size of the attachment surfaces were performed . Femoral AMB and femoral PLB , tibial AMB and tibial PLB and finally femoral ACL and tibial ACL were compared . A 2-tailed Student 's t test for paired data was used . Statistical significance was defined as P < 0.05 , for a 95 % alpha level . Results Femur The oval-shaped attachment of the anterior cruciate ligament was situated on the medial surface of the lateral femoral condyle . It was positioned deep in the notch , covering most of the proximal half of the wall . The fibres of the deep low border attached to the edge of the joint cartilage , following the contour of this edge posteriorly on the condyle . In only 4 of the 35 specimens , the attachment site was completely limited to the medial wall of the lateral condyle and had no footprint in the notch roof . In 31 femurs , a small part of the deep high AMB attachment extended into the intercondylar notch roof . The notch depth -LRB- DS = 31.8 ± 2.6 mm -RRB- was the largest distance of the femoral dimensions . On average it was 2 1/4 times the length of the notch height -LRB- LH = 14.3 ± 1.5 mm -RRB- . In shallow -- deep direction measured along the notch , relative to the notch depth , the centres of the two bundles were more close to each other , than in high -- low direction measured from the roof , relative to the notch height . The mean position of all AMB centres along the roofline of the notch was 7.2 mm shallow from the high deep corner at 1/4 of the ND-line -LRB- Table 1 ; Fig. 6 -RRB- . In 9 of the 35 femurs the centre of the AMB was not situated on the condyle wall , but above the transition line on the notch roof . Therefore , the average centre was high in the notch at 1/10 of the NH-line , 1.4 mm from the roof . The centre of the PLB was positioned slightly more shallow at less than 2 mm from the AMB -LRB- Table 1 ; Fig. 6 -RRB- . However , it was situated clearly lower , about 5 mm , on the femoral condyle wall , approximately halfway the notch height . The centre position of the entire ACL was in the middle between the AMB and the PLB at 1/4 of both reference lines . Approximately 96 % of the mean centres were inside a 12 mm drill hole , if positioned at the mean centre of the ACL attachment . The Pearson 's correlation coefficients between the absolute positions and the reference lines were smaller than 0.3 and not significant -LRB- P > 0.05 -RRB- . Table 1The positions of the ligament centres in the femoral notch Absolute distances -LRB- mm -RRB- mean -LRB- SD -RRB- Relative distances -LRB- % -RRB- mean -LRB- SD -RRB- DPCPDP/DSCP/LHAMB7 .2 -LRB- 1.8 -RRB- 1.4 -LRB- 1.7 -RRB- 23 -LRB- 6 -RRB- 10 -LRB- 12 -RRB- PLB8 .8 -LRB- 1.6 -RRB- 6.7 -LRB- 2.0 -RRB- 28 -LRB- 6 -RRB- 47 -LRB- 13 -RRB- ACL7 .9 -LRB- 1.4 -RRB- 4.0 -LRB- 1.3 -RRB- 25 -LRB- 5 -RRB- 28 -LRB- 9 -RRB- DP The absolute distance from the high deep point D until point P , the projection of the mean ligament centre at the DS-line , in the notch depth direction ; CP the absolute distance from the mean ligament centre until point P at the LH-line , in notch height direction ; DP/DS The relative position of the centre to the notch depth ; CP/LH The relative position of the centre to the notch heightFig . 6a A two-dimensional graph of the medial side of a right lateral femoral condyle with the individual centres , and the mean centres with the 95 % Confidence Interval of the AMB -LRB- red squares -RRB- , PLB -LRB- blue diamonds -RRB- and ACL -LRB- green dots -RRB- . The position of a 12 mm drill hole at the ACL centre is also displayed . b A schematic arthroscopic view through the anteromedial portal with the mean centres and the 95 % Confidence Interval areas of the AMB -LRB- red square with line -RRB- , PLB -LRB- blue diamond with line -RRB- and ACL -LRB- green dot with line -RRB- The mean centres of the AMB and PLB were situated 6.2 ± 1.2 mm from each other . The AMB attachment area , 45 % of the total ACL , was significantly -LRB- P = 0.005 -RRB- smaller than the PLB attachment area -LRB- Table 2 -RRB- . Table 2The surface dimensions of the ACL and the two bundles at femur and tibiaAbsolute surface area -LRB- mm -RRB- mean -LRB- SD -RRB- Relative surface to total ACL -LRB- % -RRB- mean -LRB- SD -RRB- ACLAMBPLBAMBPLBFemur184 -LRB- 52 -RRB- 81 -LRB- 27 -RRB- 103 -LRB- 39 -RRB- 45 -LRB- 11 -RRB- 55 -LRB- 11 -RRB- Tibia229 -LRB- 53 -RRB- 136 -LRB- 37 -RRB- 93 -LRB- 33 -RRB- 59 -LRB- 9 -RRB- 41 -LRB- 9 -RRB- Tibia The tibial attachment area of the ACL was situated between the medial and lateral tibial condyle covering the medial part of the anterior intercondylar area . It was stretched out from the region between the tibial spines to anterior with various extensions , more or less shaped as a footprint . The fibres of the AMB inserted medially along the cartilage edge of the articular surface of the medial tibial condyle . The PLB covered the lateral side of the attachment area and was bounded by the attachment of the anterior horn of the lateral meniscus . The interspinal distance -LRB- ML = 12.9 ± 1.6 mm -RRB- between the medial and the lateral spine was on the average half times the length of the anterior intercondylar area -LRB- MQ = 24.8 ± 2.7 mm -RRB- . The average centre of the AMB was situated closest to the medial spine , lateral at 1/4 of the ID . The PLB was 4 mm more lateral , approximately halfway between the medial and lateral spine -LRB- Table 3 ; Fig. 7 -RRB- . The ACL was in between at 2/5 of the ID . In anterior direction the AMB , ACL and PLB were close to each other , just over 1/3 of the anterior length . Approximately 94 % of the mean centres were inside a 10 mm drill hole , if positioned at the mean centre of the ACL attachment -LRB- Table 3 ; Fig. 7 -RRB- . The Pearson 's correlations coefficients between the absolute positions and the interspinal distance -LRB- reference line ML -RRB- were smaller than 0.3 and not significant -LRB- P > 0.05 -RRB- . The Pearson 's correlations coefficients between the absolute positions and the anterior length -LRB- reference line MQ -RRB- were significant -LRB- P < 0.05 -RRB- , however smaller than 0.6 . Table 3The positions of the ligament centres at the anterior intercondylar tibial areaAbsolute distances -LRB- mm -RRB- mean -LRB- SD -RRB- Relative distances -LRB- % -RRB- mean -LRB- SD -RRB- MPCPMP/MLCP/MQAMB3 .0 -LRB- 1.6 -RRB- 9.4 -LRB- 2.2 -RRB- 23 -LRB- 12 -RRB- 37 -LRB- 9 -RRB- PLB7 .2 -LRB- 1.8 -RRB- 10.1 -LRB- 2.1 -RRB- 55 -LRB- 13 -RRB- 38 -LRB- 9 -RRB- ACL5 .1 -LRB- 1.7 -RRB- 9.8 -LRB- 2.1 -RRB- 39 -LRB- 12 -RRB- 38 -LRB- 8 -RRB- MP The absolute distance from the medial spine -LRB- M -RRB- until the point P , the projection of the mean ligament centre at the line ML in lateral direction ; CP the absolute distance from the mean ligament centre until point P on the line ML , in anterior direction ; MP/ML The relative position of the centre to the interspinal distance ; CP/MQ The relative position of the centre to the anterior lengthFig . 7a A two-dimensional graph of a right anterior intercondylar tibial area with the individual centres , and the mean centres with the 95 % Confidence Interval of the AMB -LRB- red squares -RRB- , PLB -LRB- blue diamonds -RRB- and ACL -LRB- green dots -RRB- . The position of a 10 mm drill hole at the ACL centre is also displayed . b A schematic arthroscopic view with the mean centres and the 95 % Confidence Interval areas of the AMB -LRB- red square with line -RRB- , PLB -LRB- blue diamond with line -RRB- and ACL -LRB- green dot with line -RRB- The mean centres of the AMB and PLB were situated 4.5 ± 0.1 mm from each other . The tibial AMB attachment area of 59 % was significantly larger than the PLB attachment area -LRB- P < 0.001 -RRB- . The tibial attachment area of the ACL and of the AMB was significantly larger than on the femur -LRB- P < 0.001 -RRB- -LRB- Table 2 -RRB- . Discussion Incorrect tunnel placement , tibial -LSB- 22 , 25 -RSB- as well as femoral -LSB- 43 -RSB- , is seen as one of the most important causes of clinical failure in single-bundle ACL reconstructions -LSB- 1 -RSB- . In double-bundle ACL reconstruction , exact anatomic tunnel placement seems to be even more essential . Two bundles must be accurately placed relative to the surrounding structures and relative to each other . Although exact tunnel positioning is important , it seems difficult , even for experienced surgeons -LSB- 8 , 27 , 47 -RSB- . A clear description of the anatomic centres with guidelines to determine the correct tunnel position during arthroscopic procedures can improve the accuracy . The femoral positions of the two distinct bundles found in this study , the AMB deep high and the PLB shallow low in the notch , are broadly in line with literature -LSB- 11 , 20 , 32 , 45 , 52 -RSB- . Compared to others , the landmarks that are used in the present study are more easy to locate during arthroscopy . Harner et al. -LSB- 20 -RSB- quantified the cross-sectional shape and area of the femoral and tibial attachments of both components in 10 knees without describing the positions relative to landmarks . Yasuda et al. -LSB- 52 -RSB- limit their study to the femoral attachment , using five specimens . They describe the centre of the PLB 5 to 8 mm anterior to the edge of the joint cartilage , on the vertical line through the contact point between the femoral condyle and the tibial plateau in a 90 ° flexed knee . Because this point depends on the position of the knee , it can be difficult to locate accurately during an arthroscopic procedure . Colombet et al. -LSB- 11 -RSB- examined seven specimens , collecting especially data of the attachment dimensions . The femoral results presented by the studies of Mochizuki et al. -LSB- 32 -RSB- and Takahashi et al. -LSB- 45 -RSB- are more suitable for practical use during arthroscopy ; however , no exactly defined landmarks were used . The tibial results of Takahashi et al. -LSB- 45 -RSB- can not easily be transferred to the arthroscopic situation . Finally , above-mentioned studies did not present the centres of the ACL attachment . Tunnel positioning in the femoral notch is often determined by the ` clock ' method -LSB- 13 , 18 , 35 , 36 , 52 , 54 -RSB- . However , this only determines the high -- low position from the roof , in the transversal plane along the arc of the femoral notch -LSB- 17 , 54 -RSB- . The accuracy in the sagittal plane , deep -- shallow along the roof of the notch , seems to affect the functional outcome more -LSB- 17 , 21 , 29 , 55 , 56 -RSB- . This position is often determined with a femoral guide placed behind the posterior edge of the intercondylar notch , at the over-the-top position , not to be confused with the Resident 's ridge -LSB- 24 -RSB- . This seems sufficiently accurate for determining the AMB centre , when a guide with a 7 mm offset is placed in the 10.30 or 1.30 o'clock position . The 7 mm offset of the guide places the tunnel in the sagittal plane close to the AMB centre position , found in this study , i.e. 7.2 mm shallow along the roof . Although we did not translate the measured distance in a clock position , the 10.30 clock position seems close to the measured position in the transversal plane , 1.4 mm low from the roof on the condyle wall . This corresponds with the results of Mochizuki et al. -LSB- 32 -RSB- and Yasuda et al. -LSB- 52 -RSB- . However , the clock method is sensitive to subjective interpretation of positioning the face of the clock -LSB- 7 -RSB- . It is not sufficient to find the correct position for the PLB , especially in the sagittal plane . Therefore Colombet et al. -LSB- 11 -RSB- defined an extra guideline to position the PLB tunnel : 8 mm lower and ` shallower ' relative to the AMB centre , found with the clock method . The present study is more precise : 1.3 mm more shallow along the notch and 5.3 mm lower from the roof on the condyle wall , relative to the above-described position of the AMB centre . These positions can best be approached through an anteromedial arthroscopic portal -LSB- 6 -RSB- . Various methods can be used to determine the correct drill hole position at the tibia . Some authors prefer placement of the tibial tunnel based on avoiding graft impingement against the roof of the femoral notch with knee extension -LSB- 22 , 34 , 44 -RSB- . Others prefer guides that use the posterior cruciate ligament -LRB- PCL -RRB- attachment as reference point -LSB- 31 -RSB- . Based on these methods , positioning in anteroposterior direction , the sagittal plane , is defined . However , placement of the tunnel in mediolateral direction , the transversal plane , which is also important -LSB- 26 -RSB- , is not determined . Some studies describe the mediolateral position , relative to the width of the tibial plateau -LSB- 23 , 45 -RSB- . However , this guideline can not be used during an arthroscopic procedure . The results of this study can be used for arthroscopic positioning in both directions . The division of the AMB and PLB on the tibia in anteroposterior direction is similar to Harner et al. -LSB- 20 -RSB- , resulting in a medial AMB and lateral PLB . This deviates only marginally from other definitions , where the division is in an anteromedial and a posterolateral part -LSB- 3 , 16 , 38 -RSB- . The position of the centres in anteroposterior direction correspond with the results of Takahashi et al. -LSB- 45 -RSB- , who used similar reference points to define the anterior margin of the articular surface of the tibial condyles . The centres of the two bundles were more close to each other on the tibia , than on the femur . The size of the femoral ACL attachment 184 ± 52 mm2 was similar to the result of Odensten and Gillquist -LRB- 200 mm2 -RRB- -LSB- 38 -RSB- . Other studies found smaller attachment areas , 132 mm2 -LSB- 45 -RSB- and 113 mm2 -LSB- 20 -RSB- . This difference may be caused by a different measuring method , using the largest projection in a 2D image plane . Our study measured the actual three-dimensional attachment area . The partition of the femoral attachment area was nearly equal with 45 % , 55 % , respectively , for the AMB and PLB . This was comparable to Harner et al. -LSB- 20 -RSB- -LRB- AMB = 52 % , PLB = 48 % -RRB- and Takahashi et al. -LSB- 45 -RSB- -LRB- AMB = 50 % , PLB = 50 % -RRB- . The average tibial attachment area found in this study was larger than the femoral attachment . This is in line with the results of Girgis et al. -LSB- 16 -RSB- and Fuss et al. -LSB- 15 -RSB- . On the other hand , Takahashi et al. -LSB- 45 -RSB- found that the femoral attachment was larger than the tibial attachment -LRB- 132 vs 119 mm2 -RRB- . Harner et al. -LSB- 20 -RSB- and Odensten and Gillquist -LSB- 38 -RSB- found similar sizes for the tibial and femoral attachment areas . In our study the AMB occupied 59 % of the tibial attachment , nearly similar to the 57 % of Takahashi et al. -LSB- 45 -RSB- , slightly more than the 52 % Harner et al. -LSB- 20 -RSB- found . There was a large variation in knee sizes and dimensions of the reference lines . However , we did not find a correlation between the absolute distance of the attachment centres and the size of the reference lines , i.e. knee size . The absolute positions of the attachment centres were more or less similar for large and small knees . Therefore both absolute as well as relative data can be used as guidelines to find the anatomical positions . At the arthroscopic view , the absolute positions are more useful than the relative positions . As regards to the dimensions of drilled tunnel holes -LRB- 10 -- 12 mm -RRB- , the standard deviations of the attachment centres within 3 mm are acceptable . The femoral positions had less variations than the tibial positions . The positions for the entire ACL attachment had less variations than the attachment positions for the separate bundles . The results of this study seem to produce accurate guidelines to find the anatomic tunnel position during arthroscopic reconstruction . However , some limitations must be mentioned . The subdivision of the ACL in AMB and PLB is not based on anatomically distinct fibre bundles surrounded with fibrous issue -LSB- 5 , 15 , 33 , 38 -RSB- . Fibres of both bundles are twisted around each other -LSB- 33 -RSB- . Division of the ACL in separate bundles is not easy -LSB- 3 -RSB- . Therefore utmost care was taken to divide the two functional bundles according to a previously described method -LSB- 11 , 20 -RSB- . The method , based on observed tension variation during passive flexion -- extension movement was reported to be consistent -LSB- 32 -RSB- . This is expressed in the standard deviations -LRB- SD -RRB- of the mean attachment centres . The variation of the population is expressed by the SD of the ACL centre . The SD of the mean PLB and mean AMB centres show this variation combined with the division error . For the tibia the SDs of the PLB and AMB attachment centres are equal to that of the ACL . For the femur the SDs of the two bundle centres are slightly larger . However , these results do not point to large errors in the identification of the two bundles . The variations of attachment centre positions are actually rather small and similar to other studies -LSB- 11 , 45 -RSB- . The age of the cadaveric knee specimens was more than 60 years . However , only knees without severe arthritic signs were evaluated . It seems likely that the data can be transferred to the , mostly younger , population receiving an ACL reconstruction -LSB- 3 , 11 , 34 , 44 -RSB- . Perfusion fixation preserves the outer contours of shapes i.e. ligament bundles , so neither the identification nor the measurements of the various bundles can be assumed to have been hampered by the fixation . Conclusions This study was performed because no earlier study described the ACL , AMB and PLB attachment centres relative to arthroscopically visible landmarks . This resulted in quantitative data of the positions of the attachment centres of the ACL and its two bundles , relative to bony landmarks on femur and tibia , visible through an arthroscope . Using these results , the surgeon will be able to determine the anatomical position of the ACL and the two functional bundles during arthroscopy without additional images or fluoroscopic support . The results can be applied for anatomic single-bundle or anatomic double-bundle techniques .

O O O O O O O O O O O O O O O O O O O B I O B I I O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

anterior cruciate ligament
anteromedial bundle
posterolateral bundle
arthroscopic view
tunnel placement

anatomic acl reconstruction
double-bundle acl reconstruction
acl anatomy


Analysis of Oxford medial unicompartmental knee replacement using the minimally invasive technique in patients aged 60 and above : an independent prospective series We present the outcome of an independent prospective series of phase-3 Oxford medial mobile-bearing unicompartmental knee replacement surgery . Eight surgeons performed the 154 procedures in a community-based hospital between 1998 and 2003 for patients aged 60 and above . Seventeen knees were revised ; in 14 cases a total knee replacement was performed , in 3 cases a component of the unicompartmental knee prosthesis was revised , resulting in a survival rate of 89 % during these 2 -- 7 years follow-up interval . This study shows that mobile-bearing unicompartmental knee replacement using a minimally invasive technique is a demanding procedure . The study emphasises the importance of routine in surgical management and strict adherence to indications and operation technique used to reduce outcome failure . Introduction Modifications over the past 15 years have improved unicompartmental knee replacement surgery , as indicated in recent reports on the procedure -LSB- 1 -- 4 -RSB- . The designers -LSB- 5 -RSB- -LRB- the originators -RRB- of the Oxford unicompartmental knee prosthesis -LRB- Biomet , Warsaw , IN -RRB- reported in 1998 a 97.7 % cumulative survival rate of 10 years . An independent series with a 15-year survival analysis claimed a 94 % cumulative survival rate -LSB- 6 -RSB- . The outcome was dependent on proper patient selection , surgical techniques and implant design , -LSB- 4 , 7 -RSB- and the results have been attributed to improvements in these factors . The procedure is now performed through a short incision from the medial pole of the patella to the tibial tuberosity . Using this approach , there is little damage to the extensor mechanism , the patella is not dislocated , and the suprapatellar synovial pouch remains intact . As a result , patients recover more quickly . Patients achieve knee flexion , straight leg-raising , and independent stair-climbing three times faster than after total knee replacement -LRB- TKR -RRB- and twice faster than after open unicompartmental knee replacement surgery -LSB- 8 -RSB- . The minimally invasive procedure has been shown to be reliable and effective -LSB- 9 -RSB- . Because of the favourable published clinical results , surgeons at the Martini Hospital in Groningen , the Netherlands , began using the Oxford knee prosthesis in 1998 . The goal of this independent prospective study for patients 60 years of age and above was to compare and evaluate the clinical midterm results of the Oxford phase-3 unicompartmental knee replacement using the minimally invasive technique in a community hospital . Materials and methods Between December 1998 and 2003 , 154 successive Oxford unicompartmental knee replacements were performed in patients 60 years of age and above -LRB- Table 1 -RRB- . Of these , 132 patients underwent unilateral surgery , 10 patients underwent bilateral surgery on separate occasions , and 1 patient underwent concomitant bilateral surgery in the same OR session . There were 86 women ; the average patient 's age was 69.2 years -LRB- range 60 -- 93 years -RRB- . All patients gave informed consent before their inclusion in this prospective study . Five patients had secondary osteoarthritis because of previous trauma . The remaining patients had primary osteoarthritis . Table 1Oxford phase-3 unicompartmental knee replacementCriteriaResultsNumber of patients132Number of knees154Left/right knee -LRB- % -RRB- 53.8 / 46.2 Age -LRB- mean/range , in years -RRB- 69.2 -LRB- 60 -- 93 -RRB- Gender -LRB- M/W -RRB- 57 -LRB- 40 % -RRB- / 86 -LRB- 60 % -RRB- BMI30 .7 ± 4.9Follow-up range2 -- 7 years Standardised anteroposterior radiographs were obtained with the patient in a weight-bearing position -LRB- standing -RRB- , and lateral radiographs were obtained with the patient in a non-weight-bearing position -LRB- the patient lying horizontally -RRB- . The radiographs were examined for loosening or radiolucency around the femoral and tibial components , and the anatomical axis of the limb was measured . The imaging criterion for no increased risk for loosening of the bone was a < 2 mm thick radiolucent line -LSB- 10 -RSB- . The presence of osteoarthritic changes in the nonreplaced compartment was graded according to the Ahlback classification of osteoarthritis -LRB- Table 2 -RRB- -LSB- 11 -RSB- . These procedures were performed by eight senior staff surgeons over the study period . Mean preoperative range of motion was 122.9 ± 8.9 ° of flexion and − 0.7 ± 4.5 ° of extension . Table 2The Alhback radiological scoring system for estimating the severity of OAGrade 0 Normal Grade 1 Joint narrowing Grade 2 Joint obliteration Grade 3 Bone destruction < 5 mm Grade 4 Bone destruction > 5 mmGrade 5 Subluxation The results -LRB- preoperative , intraoperative , and follow-ups at 3 months , 6 months , and 1 year -RRB- were prospectively recorded with a historical record , procedure record , Knee Society score , SF-36 questionnaire -LRB- short form consisting of 36 questions -RRB- , and the Western Ontario McMaster -LRB- WOMAC -RRB- score . Knee Society score ratings of excellent -LRB- 90 -- 100 points -RRB- and good -LRB- 80 -- 89 points -RRB- indicated success . The preoperative scores of the patients are presented in Table 3 . Table 3Scoring results of the non-revised patientsScoringResultsKnee society scoreKnee score Preoperative39 .2 -LRB- SD 18.2 -RRB- Postoperative89 .4 -LRB- SD 14.0 -RRB- Function Preoperative55 .8 -LRB- SD 14.3 -RRB- Postoperative77 .1 -LRB- SD 24.7 -RRB- Total score Preoperative47 .6 -LRB- SD 12.3 -RRB- Postoperative83 .4 -LRB- SD 16.8 -RRB- WOMAC scorePain Preoperative50 .3 -LRB- SD 18.7 -RRB- Postoperative78 .6 -LRB- SD 21.5 -RRB- Stiffness Preoperative51 .2 -LRB- SD 22.6 -RRB- Postoperative71 .2 -LRB- SD 20.8 -RRB- Function Preoperative50 .6 -LRB- SD 20.7 -RRB- Postoperative76 .2 -LRB- SD 20.4 -RRB- SF-36 questionnaireFunction Preoperative35 .7 -LRB- SD 17.6 -RRB- Postoperative56 .1 -LRB- SD 24.5 -RRB- Physical Preoperative28 .2 -LRB- SD 37.2 -RRB- Postoperative57 .2 -LRB- SD 44.3 -RRB- Pain Preoperative32 .7 -LRB- SD 19.2 -RRB- Postoperative59 .8 -LRB- SD 26.5 -RRB- Health Preoperative63 .7 -LRB- SD 22.2 -RRB- Postoperative61 .4 -LRB- SD 21.7 -RRB- Social function Preoperative52 .6 -LRB- SD 17.1 -RRB- Postoperative64 .5 -LRB- SD 17.6 -RRB- Emotional Preoperative64 .5 -LRB- SD 44.6 -RRB- Postoperative70 .5 -LRB- SD 40.7 -RRB- Mental health Preoperative73 .7 -LRB- SD 17.9 -RRB- Postoperative75 .1 -LRB- SD 18.8 -RRB- SD standard deviation Preoperative weight-bearing radiographs showed that the knees had an average femorotibial alignment of 2.4 ° of valgus -LRB- range 8 ° -- 3 ° of varus -RRB- . Thirty-seven knees had grade-1 Ahlback osteoarthritis -LSB- 11 -RSB- in the lateral compartment on the preoperative radiographs , and one had grade-2 Ahlback osteoarthritis . The preoperative skyline view of the patellofemoral joint showed no bone loss with eburnation and longitudinal grooving in all the cases . All medial compartment arthroplasties were performed using the minimally invasive technique and under tourniquet control . The discharge criteria were control of immediate postoperative pain and the ability to flex the operated knee to a minimum of 90 ° with no lack of extension . All complications and revisions were reported , and a revision was defined as any surgical procedure resulting in removal or exchange of any of the prosthetic components . Results At the time of follow-up , two patients who had no known revisions were lost for the follow-up . The remaining 130 patients were available for follow-up . At the final follow-up , June 2006 , revision TKR was performed in 14 knees and a prosthetic component was exchanged in three knees . An overview of the revisions is given in Table 4 . Table 4Revisions of Oxford phase-3 knee replacement surgeryIncidenceRevision of a component of UKA3 Revision of the mobile bearing1 Revision of the femoral component and the bearing1 Revision of the tibial component and the bearing1Conversion to a TKR14Reason for revision to a TKA Inappropriate indication1 Misalignment and loosening5 Infection1 Progression of osteoarthritis in lateral compartment4 Persisting anteromedial pain > 1 year3 One bearing was replaced because of luxation after a hyperflexion trauma . A new bearing of the same size was inserted , and no recurrence of luxation was seen at follow-up . In another case of luxation of the bearing , the femoral component , and the bearing were changed 9 months after the primary surgery . The fixation of the femoral component in this case was insufficient . The multiple small drill holes were not made , and there was no cement in the large drill hole . With flexion , the loose femoral component moved distally , causing luxation of the bearing . The tibial component and bearing revision was performed seven months after the primary surgery because of misalignment of this tibial component . With flexion , there was impingement of the bearing with the tibial component , causing a clicking sensation and rotation of the bearing . In one case , there was grade-2 Ahlback osteoarthritis -LSB- 11 -RSB- in the lateral compartment on the preoperative radiograph . This patient had no relief of preoperative pain , and the knee underwent TKR 18 months after the primary surgery . In five cases loosening of the components occurred ; misalignment of the components is probably caused by impingement of the bearing . One patient had a deep Staphylococcus aureus infection , and a two-stage procedure was performed leading to a TKR . In four cases of revision , progression of osteoarthritis was seen in the lateral compartment with reported pain on the lateral side . These patients had a mean postoperative anatomical axis , femorotibial alignment of 18.6 ° . This overcorrection causes overloading of the lateral compartment with progression of arthritis in that compartment . Three patients with persisting anteromedial pain underwent revision . In two cases , no cause was found , and in both pain persisted after TKR . In the third case , the synovial biopsy showed synovitis villonodularis pigmentosa , and after the TKR this patient was pain-free . Except for the two patients with persisting anteromedial pain , all patients with a conversion to TKA were pain-free . No special augmentations or revision prosthetic components were necessary in these procedures ; there were no bone defects that required the use of particulate autograft or allograft , and primary cruciate-retaining TKA was used in the revisions . Postoperative complications occurred after the primary unicompartmental knee replacements . One patient had a traumatic medial tibia plateau fracture 4 weeks postoperatively , which was treated conservatively . Another patient developed hemarthrosis that required extended hospitalisation ; this was resolved with conservative treatment . There was one deep infection , and no deep venous thrombosis was reported . At the time of the most recent follow-up , average flexion was 125.8 ± 13.8 ° , with two patients achieving < 90 ° flexion . The average flexion deformity/extension was 0.3 ± 2.2 ° . The postoperative scores of those patients who did not undergo revision -LRB- 140 knees -RRB- at the latest follow-up are presented in Table 3 . The Knee Society score total was 83.4 . All three WOMAC scores improved . For the SF-36 , the function , physical , and pain scores showed an improvement in the outcome ; the other scores remained approximately the same . The final follow-up radiographs showed an average anatomical axis , femorotibial alignment of 8.8 ° of valgus -LRB- range 4 ° -- 22 ° of valgus -RRB- . The knees were corrected by an average of 6.4 ° -LRB- range 2 ° -- 14 ° -RRB- . This relative overcorrection gives increased stress on the lateral compartment . Signs of osteoarthritis progression in the uninvolved tibiofemoral compartment on the radiograph at the last follow-up were noted in 43 knees -LRB- grade-1 Ahlback osteoarthritis in 39 knees and grade-2 Ahlback osteoarthritis in four knees -RRB- . No grade-3 or -4 changes were noted . At final radiographic evaluation , no component showed evidence of loosening . No knees had > 2 mm of tibial cement-bone radiolucency . There were no radiolucent lines seen at the posterior aspect of the femoral components . Seventeen knees were revised , resulting in a survival rate of 89 % in these 2 -- 7 years of follow-up interval . Discussion The purpose of this prospective study was to evaluate midterm durability of Oxford unicompartmental knee replacement surgery for patients 60 years of age and older . We acknowledge that the present study has the limitations of a midterm follow-up . However , longer follow-up for this phase-III version with the minimally invasive technique is not possible , because the current version has been available only since 1998 -LSB- 7 -RSB- . Besides , most technical failures occur within the first 2 years -LSB- 12 -RSB- . In these 2 -- 7 years of follow-up interval , 11 % of unicompartmental knee arthroplasties in all patients needed revision -- a survival rate of 89 % . These results are considerably lower compared to the designer -LSB- 5 -RSB- series or the independent series -LSB- 6 -RSB- . The primary need for revision surgery could be attributed to indication and technical failures . Thirteen of the 17 revisions were probably related to human error , the remaining four are in one case a hyperflexion trauma and luxation of the bearing , one case with deep infection , and two cases with unexplained persisting anteromedial pain . Misalignment of the components was the primary cause of technical failure . With the minimally invasive technique , the visual field is restricted , making mobile-bearing unicompartmental knee replacement surgery a demanding procedure . Introduction of the minimally invasive option makes the terms surgical technique and pitfalls actual again . For the remaining 113 patients -LRB- 140 knees -RRB- who did not undergo revision , the Knee Society score , WOMAC and SF-36 questionnaires showed an improvement in the outcome . All three scores indicated less pain and improvement in function , as confirmed by an average clinical average flexion of 126 ° at the latest follow-up . The Knee Society score total of 83.4 indicates a successful outcome . Over the 7-year period of our study , eight senior surgeons performed the operation with an average of < 10 procedures a year per surgeon . All surgeons attended the instructional course organized by the designer group . There is no evidence for a learning curve in our study . The outcome should be attributed to the number of operations performed . As a result of the relatively low survival rate of this study , the number of senior surgeons performing the procedure in this hospital is now reduced to two . Conclusion Careful patient selection , surgeon experience , and proper instrumentation and surgical technique are important factors in mobile-bearing unicompartmental knee replacement surgery -LSB- 13 , 14 -RSB- . For unicompartmental replacement surgery , long-term results are related to the number performed by the unit -LSB- 14 -RSB- . The surgeon should be well versed in the routine , indications , and technique of this procedure to minimise failure rates .

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