Anterior cruciate ligament (ACL) tears are one of the most common sports-related injuries in a skeletally immature athlete, and the prevalence of ACL reconstruction in this population has increased over the past 2 decades1-4. Reconstruction in a skeletally immature patient carries the inherent risk of iatrogenic physeal damage and potential growth disturbance5; thus, ACL reconstruction was historically delayed until skeletal maturity in some patients6. However, recent studies have shown improved outcomes for patients undergoing reconstruction in the acute setting, as delayed treatment risks progressive chondral and meniscal damage7-9, chronic instability, and sports-related disability10.
Several reconstruction techniques for patients with open physes have been described, including combined intra-articular and extra-articular11, transphyseal12, partial transphyseal13-15, and all-epiphyseal16-18 methods19. All-epiphyseal and partial transphyseal techniques utilize an all-epiphyseal femoral tunnel placed within the native ACL footprint. While anatomic reconstruction and avoidance of physeal injury and growth disturbance are primary goals, surgeons must also be careful to avoid direct injury to other extra-articular structures including the lateral collateral ligament (LCL). Although LCL compromise has not been described in the orthopaedic literature, to our knowledge, it remains an ongoing clinical concern and may be underreported. A detailed 3-dimensional understanding of the anatomic relationship of the ACL and LCL of the knee may help to guide surgeons performing all-epiphyseal or partial transphyseal ACL reconstructions, and intraoperative radiography images may be used to quickly evaluate femoral drill-hole placement. The purposes of the present study were to evaluate the spatial relationship of the ACL and LCL femoral footprint origins in skeletally immature specimens, as viewed on lateral radiography, and to determine a safe method to avoid the LCL during all-epiphyseal femoral tunnel drilling.
Materials and Methods
Our institutional review board was consulted prior to the initiation of this study. As this study included access to cadaveric specimens without any patient identifiers or contact with the family, institutional review board approval was not deemed necessary20. The specimens were provided by an allograft harvesting facility (AlloSource), which had received family consent for the use of tissue for research purposes.
Dissection and Imaging
Fourteen skeletally immature knees from children who were between 7 and 11 years old at the time of death were examined by a group of 6 sports and/or pediatric fellowship-trained orthopaedic surgeons—all with prior pediatric cadaveric dissection experience—through gross dissection in 2 phases. In Phase 1, the superficial structures of the lateral aspect of the knee were dissected to identify and measure the femoral origin of the LCL. A metallic marker was placed in the middle of the LCL origin on the femur. A computed tomography (CT) scan using a GE LightSpeed 16-slice scanner with a 2-mm slice protocol was performed on each specimen with the metallic marker left in place.
In Phase 2, the knee specimens were disarticulated to better visualize the femoral footprint of the ACL. Commercially available metallic push pins were placed, marking the center of the ACL femoral footprint. A CT scan of each disarticulated femur was performed with the metallic marker still in place.
Between Phase 1 and Phase 2, 2 specimens were reserved for a subsequent project; thus, the LCL femoral origin was evaluated in 14 specimens and the ACL origin was evaluated in 12 specimens.
CT images were analyzed using OsiriX imaging software (version 6.5.2). In order to evaluate the ligament origin with respect to other anatomic landmarks, 3 sagittal plane CT images were superimposed to create a view analogous to an intraoperative C-arm image (Fig. 1). The 3 images selected from the CT scan sequence showed (1) the metallic marker placed in the femoral origin of the ligament, (2) the widest part of the lateral femoral condyle (LFC), and (3) the widest part of the femoral shaft. Digital markers were drawn overlying the metallic markers of the LCL and ACL. Separate superimposed image sequences for the LCL and ACL were created for each specimen.
The percent posterior-anterior (% P-A) measurements (Fig. 2) were made in the sagittal plane by measuring across the LFC, perpendicular to the posterior cortical reference line. First, the total depth of the ossified LFC (the distance from the most anterior margin of the condyle to the most posterior margin) was measured; articular and nonossified epiphyseal cartilage were excluded from our measurements (Fig. 2). The distance from the ligament origin (either ACL or LCL) to the most posterior aspect of the ossified LFC was then measured, divided by the total depth of the respective condyle, and multiplied by 100 to yield a % P-A. A measurement of 0% P-A would thus correspond to a ligament origin at the most posterior aspect of the condyle, while an origin measuring 100% P-A would be at the most anterior aspect of the femoral condyle.
The percent proximal-distal (% P-D) measurements (Fig. 3) were made in the sagittal plane by measuring across the ossified LFC, parallel to the posterior cortical reference line. The height of the condyle was measured from the most posterosuperior aspect of the physis to the most distal aspect of the ossified LFC (Fig. 3). The distance from the ligament origin to the most posterosuperior aspect of the physis was then measured, divided by the height of its respective condyle, and multiplied by 100 to yield a % P-D. A measurement of 0% P-D would correspond to the most proximal point at the distal femoral physis, while a measurement of 100% P-D would correspond to a point at the most distal aspect of the condyle.
The LFC ossified areas were calculated by multiplying the measured LFC depth by the corresponding LFC height.
Descriptive statistics, including median and interquartile range, were used to report these findings. Because of limited specimen availability, medians and interquartile ranges were used as they are less sensitive to outliers in small data sets than are means and standard deviations.
Femoral Origin of the LCL
The median distance from the most posterior aspect of the LFC to the midpoint of the LCL origin was 27% (27% P-A) of the total LFC depth, and the median of these distances was 1.3 cm (interquartile range, 1.1 to 1.5 cm). In 1 outlier, the distance from the posterior LFC to the LCL origin midpoint was only 0.4 cm (12% P-A), while the rest of these measured distances ranged from 22% to 33% P-A.
The median distance from the most proximal aspect of the posterior physis to the LCL origin midpoint was on average 37% P-D (0.9 cm), with an interquartile range of 33% to 44% P-D (0.7 to 1.1 cm).
Confidence intervals were calculated conservatively by treating P-A and P-D measurements as independent variables, yielding an elliptical 95% confidence interval (Fig. 4) centered at a point located at 27% P-A and 37% P-D, with vertices at 24% P-A and 37% P-D and at 30% P-A and 37% P-D, and co-vertices at 27% P-A and 41% P-D and at 27% P-A and 34% P-D.
The median width (diameter) of the LCL femoral origin was 0.4 cm (interquartile range, 0.38 to 0.50 cm).
There were no apparent relationships between the LCL footprint location and the size of the LFC ossified area. The LCL data are summarized in Table I.
Femoral Origin of ACL
The median distance from the most posterior aspect of the LFC to the midpoint of the ACL origin was 14% (14% P-A) of the total LFC depth, and the median of these distances was 0.7 cm (interquartile range, 0.5 to 0.8 cm). The interquartile range of the ACL origins was found to be 10% to 19% P-A.
The median distance from the most proximal aspect of the posterior physis to the ACL origin midpoint was 38% (38% P-D) of the total LFC height, with an interquartile range of 36% to 47% P-D. The median of these distances was 1.0 cm (interquartile range, 0.9 to 1.0 cm).
Confidence intervals were calculated by treating P-A and P-D measurements as independent of each other, yielding an elliptical 95% confidence interval centered at a point at 14% P-A and 39% P-D, with co-vertices at 12% P-A and 39% P-D and at 17% P-A and 39% P-D, and vertices at 14% P-A and 45% P-D and at 14% P-A and 34% P-D.
There were no apparent relationships between the ACL femoral footprint location and the size of the LFC ossified area. The ACL data are summarized in Table I.
The confidence intervals and distribution of individual ACL and LCL origins are summarized in Figure 4. In the lateral plane, the median ACL and LCL midpoints were separated by 0.61 cm on a median-sized knee.
This study demonstrated a consistent relationship between the LCL and ACL footprints when viewed on a simulated perfect lateral radiograph. The ACL origin within the intercondylar notch is 0.6 cm posterior and 0.1 cm distal to the LCL origin on the lateral femoral cortex. Both structures originate distal to the distal femoral physis and are posterior to the origin of the popliteus, which confirms the findings of other studies21-23. These landmarks may be helpful during surgery, as a lateral C-arm image may be obtained to confirm appropriate tunnel placement during all-epiphyseal ACL reconstruction or LCL repair or reconstruction. The median midpoints of the ACL and LCL femoral origins were 1.0 cm and 0.9 cm, respectively, distal to the physis.
These landmarks may also be used to avoid injury to other structures during all-epiphyseal drilling of the femur. Several structures are at risk, including the distal femoral physis, the articular cartilage, the origin of the popliteus, the anterolateral ligament, and the LCL. Clinically important injury to the distal femoral physis with subsequent growth disturbance is a potential complication of all-epiphyseal ACL reconstruction24. Although physeal injury has been a frequent topic of investigation, damage to other vital extra-articular structures, including the LCL, has not been studied, to our knowledge. This is of particular importance when using techniques that drill full-diameter tunnels across the entire lateral femoral condyle rather than partial tunnels or sockets that require only a pilot hole to breach the lateral femoral cortex. On the basis of the results of the current study, a tunnel as large as 8 mm, which starts posterior to the LCL origin on the lateral aspect of the femur and enters the joint at the ACL origin, can be placed without direct injury to the LCL. This drill orientation may avoid the LCL, but caution is necessary to avoid having the drill-hole exit too posteriorly, which may enter the articular cartilage region of the distal and/or posterior aspect of the lateral femoral condyle (e.g., “posterior wall blowout”). If the tunnel is started anterior to the LCL origin and perhaps too inferior to the LCL origin on the lateral femoral condyle, the popliteus tendon origin may be at risk. In order to minimize these risks, several steps may be taken. First, a drilling technique can be utilized that orients the tunnel from the center of the femoral ACL footprint directly lateral (e.g., perpendicular to the femoral axis and parallel to the posterior condylar axis) such that a guide pin appears as a dot on a perfect lateral fluoroscopic view of the knee. This would allow 6 mm of clearance to the origin of the LCL and would avoid posterior wall “blowout.” Second, in order to minimize lateral wall compromise, the surgeon could compress the hamstring graft in order to use the smallest possible tunnel25. Finally, using this drilling technique in conjunction with a partial-length tunnel and/or socket that does not fully traverse the lateral femoral condyle (e.g., suspensory fixation) would allow greater tolerance to slight variations in position while minimizing the risk of injury to the LCL femoral origin. This study information may also be valuable in rare cases of multiple ligament knee injury in a skeletally immature patient. In patients who require LCL reconstruction and/or repair, this information may guide placement of grafts, drill-holes, or soft-tissue repair devices.
This project is not without limitations. Access to pediatric cadaveric tissue is severely limited, and the sample size for this study is small. Larger sample sizes would strengthen the anatomic landmark recommendations. Larger sample sizes with a more diverse age range of pediatric and adolescent specimens would allow for a better understanding of how these anatomic landmarks and their relationships might change over time during skeletal development. However, the ages of the specimen donors in this study (7 to 11 years old) make our findings highly relevant for surgeons performing epiphysis-based reconstructions in the pediatric population. We also employed a simulated perfect lateral fluoroscopic view generated from CT scan images, and it remains to be studied whether small changes in rotation during fluoroscopic examination might change these reference points significantly, as has been shown in other knee reconstruction techniques such as medial patellofemoral ligament reconstruction26. However, using CT scans allowed us to obtain smaller slices (2 mm) than typically obtained by magnetic resonance imaging, which likely allowed for more accurate measurements that may not be obtainable using intraoperative lateral fluoroscopy. Future studies should attempt to verify these landmarks with different techniques, both cadaveric and, perhaps, with indirect imaging.
For skeletally immature patients with substantial growth remaining who require ligament reconstructions, these radiographic landmarks may guide precise surgical technique to improve anatomic placement of grafts and avoid secondary injury to other structures.
NOTE: AlloSource donated the cadaveric specimens and provided nonfinancial research support. The authors thank Tom Cycyota and Todd Huft (AlloSource) for their assistance, organization, and support of the dissections.
Investigation performed at St. Luke’s Sports Medicine, Boise, Idaho
Disclosure: The authors did not receive any external funding for this study. Specimens were provided by AlloSource. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had other relationships or activities that could be perceived to influence, or have the potential to influence, what was written in this work (http://links.lww.com/JBJS/A152).
1. Dodwell ER, Lamont LE, Green DW, Pan TJ, Marx RG, Lyman S. 20 years of pediatric anterior cruciate ligament reconstruction in New York State. Am J Sports Med. 2014 ;42(3):675–80. Epub 2014 Jan 29.
2. Swenson DM, Collins CL, Best TM, Flanigan DC, Fields SK, Comstock RD. Epidemiology of knee injuries among U.S. high school athletes, 2005/2006-2010/2011. Med Sci Sports Exerc. 2013 ;45(3):462–9.
3. Shea KG, Grimm NL, Ewing CK, Aoki SK. Youth sports anterior cruciate ligament and knee injury epidemiology: who is getting injured? In what sports? When? Clin Sports Med. 2011 ;30(4):691–706.
4. Shea KG, Pfeiffer R, Wang JH, Curtin M, Apel PJ. Anterior cruciate ligament injury in pediatric and adolescent soccer players: an analysis of insurance data. J Pediatr Orthop. 2004 ;24(6):623–8.
5. Yoo WJ, Kocher MS, Micheli LJ. Growth plate disturbance after transphyseal reconstruction of the anterior cruciate ligament in skeletally immature adolescent patients: an MR imaging study. J Pediatr Orthop. 2011 ;31(6):691–6.
6. Shifflett GD, Green DW, Widmann RF, Marx RG. Growth arrest following ACL reconstruction with hamstring autograft in skeletally immature patients: a review of 4 cases. J Pediatr Orthop. 2016 ;36(4):355–61.
7. Lawrence JT, Argawal N, Ganley TJ. Degeneration of the knee joint in skeletally immature patients with a diagnosis of an anterior cruciate ligament tear: is there harm in delay of treatment? Am J Sports Med. 2011 ;39(12):2582–7. Epub 2011 Sep 14.
8. Vavken P, Murray MM. Treating anterior cruciate ligament tears in skeletally immature patients. Arthroscopy. 2011 ;27(5):704–16.
9. Fabricant PD, Lakomkin N, Cruz AI, Spitzer E, Lawrence JTR, Marx RG. Early ACL reconstruction in children leads to less meniscal and articular cartilage damage when compared with conservative or delayed treatment. J ISAKOS. 2016;1(1):10–15.
10. Fabricant PD, Lakomkin N, Cruz AI, Spitzer E, Marx RG. ACL reconstruction in youth athletes results in an improved rate of return to athletic activity when compared with nonoperative treatment: a systematic review of the literature. J ISAKOS. 2016;1(2):62–9.
11. Kocher MS, Garg S, Micheli LJ. Physeal sparing reconstruction of the anterior cruciate ligament in skeletally immature prepubescent children and adolescents. J Bone Joint Surg Am. 2005 ;87(11):2371–9.
12. Calvo R, Figueroa D, Gili F, Vaisman A, Mocoçain P, Espinosa M, León A, Arellano S. Transphyseal anterior cruciate ligament reconstruction in patients with open physes: 10-year follow-up study. Am J Sports Med. 2015 ;43(2):289–94. Epub 2014 Nov 17.
13. Nawabi DH, Jones KJ, Lurie B, Potter HG, Green DW, Cordasco FA. All-inside, physeal-sparing anterior cruciate ligament reconstruction does not significantly compromise the physis in skeletally immature athletes: a postoperative physeal magnetic resonance imaging analysis. Am J Sports Med. 2014 ;42(12):2933–40. Epub 2014 Oct 16.
14. Andrews M, Noyes FR, Barber-Westin SD. Anterior cruciate ligament allograft reconstruction in the skeletally immature athlete. Am J Sports Med. 1994 ;22(1):48–54.
15. Lo IK, Kirkley A, Fowler PJ, Miniaci A. The outcome of operatively treated anterior cruciate ligament disruptions in the skeletally immature child. Arthroscopy. 1997 ;13(5):627–34.
16. Lawrence JT, Bowers AL, Belding J, Cody SR, Ganley TJ. All-epiphyseal anterior cruciate ligament reconstruction in skeletally immature patients. Clin Orthop Relat Res. 2010 ;468(7):1971–7. Epub 2010 Feb 20.
17. Anderson AF. Transepiphyseal replacement of the anterior cruciate ligament using quadruple hamstring grafts in skeletally immature patients. J Bone Joint Surg Am. 2004 ;86(Pt 2)(Suppl 1):201–9.
18. Guzzanti V, Falciglia F, Stanitski CL. Physeal-sparing intraarticular anterior cruciate ligament reconstruction in preadolescents. Am J Sports Med. 2003 ;31(6):949–53.
19. Fabricant PD, Jones KJ, Delos D, Cordasco FA, Marx RG, Pearle AD, Warren RF, Green DW. Reconstruction of the anterior cruciate ligament in the skeletally immature athlete: a review of current concepts: AAOS exhibit selection. J Bone Joint Surg Am. 2013 ;95(5):e28.
21. Behr CT, Potter HG, Paletta GA Jr. The relationship of the femoral origin of the anterior cruciate ligament and the distal femoral physeal plate in the skeletally immature knee. An anatomic study. Am J Sports Med. 2001 ;29(6):781–7.
22. Shea KG, Polousky JD, Jacobs JC Jr, Ganley TJ. Anatomical dissection and CT imaging of the posterior cruciate and lateral collateral ligaments in skeletally immature cadaver knees. J Bone Joint Surg Am. 2014 ;96(9):753–9.
23. Xerogeanes JW, Hammond KE, Todd DC. Anatomic landmarks utilized for physeal-sparing, anatomic anterior cruciate ligament reconstruction: an MRI-based study. J Bone Joint Surg Am. 2012 ;94(3):268–76.
24. Lawrence JTR, West RL, Garrett WE. Growth disturbance following ACL reconstruction with use of an epiphyseal femoral tunnel: a case report. J Bone Joint Surg Am. 2011 ;93(8):e39.
25. Cruz AI Jr, Fabricant PD, Seeley MA, Ganley TJ, Lawrence JT. Change in size of hamstring grafts during preparation for ACL reconstruction: effect of tension and circumferential compression on graft diameter. J Bone Joint Surg Am. 2016 ;98(6):484–9.
26. Ziegler CG, Fulkerson JP, Edgar C. Radiographic reference points are inaccurate with and without a true lateral radiograph: the importance of anatomy in medial patellofemoral ligament reconstruction. Am J Sports Med. 2016 ;44(1):133–42. Epub 2015 Nov 11.