ORIGINAL ARTICLE
The Relationship of the Femoral Physis and the Medial Patellofemoral Ligament in Children: A Cadaveric Study Kevin G. Shea, MD,* John D. Polousky, MD,w John C. Jacobs, Jr, BS,z Theodore J. Ganley, MD,y Stephen K. Aoki, MD,8 Nathan L. Grimm, BS,z and Shital N. Parikh, MDz
Background: Patellar dislocations are common in skeletally immature athletes, and the medial patellofemoral ligament (MPFL) is an important primary restraint to lateral patellar translation. The relationship between the MPFL femoral origin footprint and femoral physis is unclear. The purpose of this study was to evaluate the MPFL femoral origin footprint and its relationship to the femoral physis in skeletally immature anatomic specimens. Methods: Six skeletally immature cadaver knee specimens were examined through gross dissection (group A: 1, 11, and 11 mo; and group B: 8, 10, and 11 y). Metallic markers were placed at the center of the MPFL femoral origin footprint. Computed tomography scans for each specimen were analyzed. The MPFL footprint width, and the vertical distances from the center and proximal extent of the MPFL footprint to the medial aspect of the physis were measured. Results: The mean width of the MPFL femoral origin footprint was 0.70 cm (0.48 to 1.09 cm) and 1.12 cm (1.03 to 1.29 cm) for groups A and B, respectively. The mean distance from the center of the MPFL origin footprint to medial aspect of the distal femoral physis was 0.90 cm (0.52 to 1.30 cm) and 0.40 cm (0.00 to 0.86 cm) distal to the physis for groups A and B, respectively. The mean distance from the proximal extent of the MPFL origin footprint to the medial aspect of the femoral physis was 0.55 cm (0.28 to 1.03 cm) and 0.16 cm ( 0.34 to 0.64 cm) for groups A and B, respectively. Conclusions: All subjects were found to have a center of the MPFL origin footprint at or below the physis. The proximal From the *St. Luke’s Sports Medicine, St. Children’s Hospital, University of Utah Department of Orthopedics, Boise, ID; wRocky Mountain Youth Sports Medicine Institute, Rocky Mountain Hospital for Children, Denver, CO; zSchool of Medicine; 8Department of Orthopedics, University of Utah School of Medicine, Salt Lake City, UT; yChildren’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA; and zDivision of Orthopaedic Surgery, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH. There were no external sources of funding. However, the knee specimens used in this study are the property of an allograft facility (Allosource, Centennial, CO). This facility allowed us access to the specimens for our research/dissections, as well as use of their facilities to conduct our research. S.K.A. is an educational consultant for Pivot Medical and on the Surgical Advisory Board for Arthrocare. The remaining authors declare no conflicts of interest. Reprints: John C. Jacobs Jr, BS, School of Medicine, University of Utah, 30N. 1900 E., Salt Lake City, UT 84132. E-mail: jacobsjc013@ gmail.com. Copyright r 2014 by Lippincott Williams & Wilkins
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extent of the MPFL origin footprint was found to extend above the physis in the 2 older specimens. Clinical Relevance: The relationship of the MPFL origin footprint to the femoral physis in the skeletally immature is not well understood. These dissections may be useful to surgeons performing MPFL reconstructions in skeletally immature patients. Key Words: medial patellofemoral ligament, MPFL, physis, anatomy, pediatric, attachment, origin (J Pediatr Orthop 2014;34:808–813)
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reviously published literature has demonstrated that patella dislocations are relatively common in skeletally immature subjects.1–3 Fithian et al3 reported that females aged 10 to 17 years were at the greatest risk for patellar dislocation. The medial patellofemoral ligament (MPFL) plays an important role in patellar stability, and is one of the primary restraints to lateral patellar translation.4–9 The MPFL is commonly injured during patellar subluxation and dislocation, and surgical reconstruction of the MPFL has produced good outcomes in many series.10,11 Previous adult cadaveric dissections have identified the origin of the MPFL between the adductor tubercle and medial collateral ligament origin, and the insertion at the upper 2/3 of the medial border of the patella.4,6,9,12–14 Many surgical techniques utilize anchors and drill holes in the distal femur. In young patients, these surgical procedures carry the risk of physeal injury, as the MPFL origin is located close to the physis. In skeletally immature subjects, the location of the MPFL origin relative to the distal femoral physis remains controversial.15–17 Kepler et al15 reviewed magnetic resonance imaging (MRIs) of children and adolescents with acute patellar dislocation, and found the mean MPFL origin at 5 mm distal to the physis. The femoral MPFL attachment was found to be variable, with 86% attaching distal to, 7% were at, and 7% were above the physis or physeal scar. Shea and colleagues used the Schottle method18 to identify the origin of the MPFL on lateral radiographs of adolescents with open physis.17 The mean MPFL origin was found to be 2.7 and 4.6 mm proximal to the physis in females and males, respectively, with the origin attaching just proximal to the physis. Nelitz and colleagues used 2 previously described methods18,19 to identify the location of the MPFL origin on the lateral J Pediatr Orthop
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radiographs of children and adolescents with open physes and then cross-referenced them onto anteroposterior radiographs.16 They found the median origin of the MPFL to be 6.4 mm distal to the physis. Current literature used to describe the MPFL femoral origin in the skeletally immature is based off radiographic and MRI studies and varies in descriptive location relative to the physis. The purpose of this study was to identify the location of the origin of the MPFL and define the relationship between the distal femoral physis and the MPFL femoral origin footprint using pediatric cadaver dissections. A better understanding of the relationship of the MPFL and the distal femoral physis could improve current surgical techniques.
METHODS The institutional review board was consulted before performing this study. As these dissection studies were performed on cadaveric tissue, institutional review board review was unnecessary. The specimens were donated by an allograft harvest facility (Allosource, Centennial, CO). Six skeletally immature knee specimens from 5 human cadavers were examined through gross dissection (Table 1). These specimens were divided into 2 groups: group A: 1, 11, and 11 months; and group B: 8, 10, and 11 years. Metallic pins were placed to mark the femoral origin of the MPFL (Fig. 1). Computed tomography (CT) scans (GE Lightspeed 16 Slice Scanner) with 1-mm slices were obtained for each specimen and were analyzed using Osirix Imaging Software.20 In the sagittal view of the CT scan, the MPFL origin width was obtained by measuring the distance between the respective 2 metallic pins, using the Osirix Imaging Software (Fig. 2). The distances from the MPFL origin to the distal femoral physis were measured in the coronal view (Fig. 3). The vertical distance from the midpoint of the MPFL femoral origin to the midpoint of the medial aspect of the femoral physis (using a mean of the distance to the superior and inferior physeal boundaries, where appropriate) was measured (Fig. 3, point B). The distance to the medial aspect of the physis was referred to as “medial physis” in Table 2. The distance from the proximal extent of the MPFL origin to the medial aspect of the distal femoral physis was measured (Table 2). For this measurement, negative values indicate the proximal extent of the physis was found below the physis, whereas positive values indicate the proximal extent was found above the physis.
FIGURE 1. Right knee: image taken during dissection. The proximal and distal borders of the medial patellofemoral ligament femoral origin footprint are marked by a marking pen (white arrows) where the metallic pins were placed.
RESULTS The mean width of the MPFL footprint in the coronal plane at the femoral origin was 0.70 cm (0.48 to 1.09 cm) and 1.12 cm (1.03 to 1.29 cm) for groups A
TABLE 1. Specimen Demographics Specimen No. 1 2 3 4 5 6
r
Age
Sex
Knee Side
1 mo 11 mo 11 mo 8y 10 y 11 y
Female Male Male Male Female Male
Right Left Right Right Left Right
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FIGURE 2. Sagittal computed tomographic scan image of the 11-year-old specimen showing the origin footprint of the medial patellofemoral ligament (MPFL) at the proximal (white arrow) and distal (black arrow) points. In this specimen, the midpoint of the MPFL origin was located at the level of the medial aspect of the distal femoral physis. www.pedorthopaedics.com |
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whereas positive values indicate the proximal extent was found above the physis. The mean distance from the proximal extent of the MPFL footprint to the medial aspect of the distal femoral physis was 0.55 cm ( 0.28 to 1.03 cm) and 0.16 cm ( 0.34 to 0.64 cm) for groups A and B, respectively. The MPFL origin width was found to extend to or across the medial aspect of the physis in no group A specimens, and 2 group B specimens (Fig. 4).
DISCUSSION
FIGURE 3. Coronal computed tomographic scan image with measurements of the distance from the center of the medial patellofemoral ligament origin footprint (A) to: the proximal and distal borders of the medial aspect of the distal femoral physis (B).
and B, respectively (Table 2). For group A, the mean distance from the center of the MPFL footprint to the medial aspect of the distal femoral physis was 0.90 cm (0.52 to 1.30 cm) distal to the physis. For group B, the mean distance from the center of the MPFL footprint to the medial aspect of the distal femoral physis was 0.40 cm (0.00 to 0.86 cm) distal to the physis. Measurements were calculated from the center of the MPFL footprint to the most medial aspect of femoral physis. For all subjects under age 11, the center of the MPFL footprint was found to be below the most medial aspect of distal femoral physis. The center of the MPFL footprint of the 11-year-old specimen was at the level of the physis. For this measurement, negative values indicate the proximal extent of the physis was found below the physis,
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In skeletally immature patients, previous studies have reached different conclusions about the relationship between the distal femoral physis, and the femoral footprint of the MPFL. Some of the confusion in the literature may be related to the complex undulations of the distal femoral physis, which makes radiographic visualization of landmarks challenging.16 The dissections performed in this anatomic study demonstrated some variability in the relationship of the MPFL and the physis, but consistent findings were present in many of these specimens. Although the center of the MPFL origin footprint was below the medial distal femoral physis in 5 specimens, the overall coronal plane dimension of the MPFL footprint extended above the most medial aspect of the distal femoral physis in 2 specimens. Surgical treatment of recurrent patellar dislocations may include reconstruction of the MPFL.21,22 The use of consistent anatomic landmarks may help restore the natural function and kinematics of the MPFL.22–32 Placement of the MPFL origin on the femur includes the risk of physeal injury in children with a similar potential for growth disturbance as seen with anterior cruciate ligament reconstructions in this age group.33–36 Previous studies have used indirect methods to evaluate the location of the MPFL origin in relation to the distal femoral physis in children or adolescents with variable results.15–17 One study suggests that the midpoint of the MPFL origin is a few millimeters above the distal femoral physis,17 however, this study was limited in that it was an indirect study of the anatomy using the radiographic technique described by Schottle et al.18 This study was based upon a database of established skeletally immature radiographs, and was not based upon radiographic analysis of cadaveric knee specimens. A limitation of this previous study, highlighted by Nelitz et al,16 was that the MPFL origin location was only evaluated on lateral radiographs. Nelitz and colleagues evaluated the location of the midpoint of the MPFL origin on anteroposterior and lateral radiographs. In this work, Nelitz and colleagues concluded that the femoral origin midpoint of the MPFL was below the most medial aspect of the distal femoral physis. In the current study, the use of CT scan analysis allowed for more comprehensive evaluation of the MPFL origin footprint. The results of this study are supportive of the previous radiographic work of Nelitz and colleagues. In considering bone tunnels for graft fixation, this becomes even more important. We found the center r
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TABLE 2. Anatomic Measurements Specimen No.
Age
1 2 3 4 5 6
1 mo 11 mo 11 mo 8y 10 y 11 y
Femoral Origin Footprint Width (cm)
Center Origin Footprint to Medial Physis Distance (cm)
Center Origin Footprint Relation to Medial Physis*
Medial Physis to Proximal Extent of MPFL Origin Distance (cm)w
0.48 0.54 1.09 1.04 1.03 1.29
0.52 1.30 0.88 0.86 0.35 0.00
Below Below Below Below Below At
0.28 1.03 0.33 0.34 0.17 0.64
*Center MPFL origin footprint in relation to the medial aspect of the femoral physis: at, above, below the physis. wProximal extent of the origin footprint appears either above (positive value) or below (negative value) the medial physis. MPFL indicates medial patellofemoral ligament.
of the MPFL origin footprint of all specimens under age 11 to be distal to the medial aspect of the distal femoral physis, and the origin of the 11-year-old specimen to be at the level of the physis. Although the center of the MPFL origin footprint may be at or below the most medial aspect of the distal femoral physis, the proximal extension of the MPFL femoral footprint is above the medial physis to some degree in the 2 older specimens in this series. To avoid physeal injury in surgery, several options exist. In cases in which the native MPFL is of sufficient quality, repair and/or advancement of this structure may be performed. The MRI can usually locate the prominent area of injury to the patellar origin, mid-substance region, or femoral origin. Kepler et al15 analyzed MRIs of children with tears of the MPFL for tear location. They found tears at the patellar attachment in 61%, femoral attachment in 12%, and both patellar and femoral attachments in 12% of patients. The proximity of the MPFL to the femoral physis raises the question of physeal injury during MPFL femoral avulsion, but we have not observed this phenomenon in our practice.
FIGURE 4. Diagram illustrating the center and width of the medial patellofemoral ligament (MPFL) origin footprint in relation to the distal femoral physis. Each rectangle corresponds to the MPFL origin footprint of a specific specimen, with the center denoted by the horizontal white line. The vertical length of each rectangle corresponds to the origin footprint width. r
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In cases where the native tissue is not adequate for repair, surgical reconstruction avoiding the physis and perichondral ring may be an option. Bony tunnels may be placed in an anatomic or nonanatomic position depending upon its location with respect to the physis. The MPFL origin may also be fixed to the surrounding soft tissues rather than placing a femoral drill hole,37,38 although this position may place the MPFL origin above the native origin. At this stage, it is unclear if nonanatomic locations, which may have a lower risk of physeal injury, may provide adequate protection against future dislocation.39 To avoid physeal injury during anterior cruciate ligament reconstruction, nonanatomic techniques have been used with good clinical outcomes demonstrated with longer-term follow-up studies.40,41 There are several limitations to this study. The small number of specimens used in this study is problematic. This is due to the extreme difficulty in obtaining pediatric cadaver specimens for research purposes. Multiple allograft laboratories over a 3-year period were contacted in an attempt to locate specimens, and only 1 laboratory was able to provide a limited number of specimens. Dissection of the MPFL can be challenging in pediatric cadaveric specimens. Some specimens had a robust and distinct ligament, whereas some specimens had a less distinct structure. On the basis of previous published literature15–18 and the results of our study that shows close proximity of the physis to the MPFL attachment site, we recommend the following considerations when considering MPFL reconstructions in skeletally immature patients: (1) The medial aspect of the physis is more proximal than the central region of the physis. Review of lateral radiographs may show the most distal/central aspect of the femoral physis more clearly, as the more proximal/medial aspect of the distal femoral physis may not be well visualized on the lateral radiographs. This radiographic observation should be considered if the Schottle technique is utilized to identify the MPFL femoral location in skeletally immature patients.16,17 (2) The center of the MPFL femoral origin footprint may be below the medial aspect of the distal femoral physis in most patients, but the full proximal extent of the MPFL origin footprint may also extend proximally across the physis in some patients. www.pedorthopaedics.com |
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(3) In this small series, there appeared to be a trend that showed the femoral origin footprint of the MPFL was more proximal in older patients. Larger studies would help clarify this and other anatomic findings, but these specimens are exceptionally difficult to procure for study. (4) If drill holes are placed near the femoral physis for attachment of the MPFL origin, the use of small drill holes angled away from the physis, and drilling in a manner to limit the amount of heat generated near the physis, may lower the risk of physeal arrest.42 Placing a drill hole this close to the physis may increase the risk of physeal arrest or even physeal overgrowth, which may lead to angulation of the distal femur. In children with minimal growth remaining, this may not result in any significant impact on growth or distal femoral alignment. In a patient in which distal femoral valgus may be a contributing factor to patellofemoral instability, addressing the valgus alignment by delaying the medial physis growth is an example of “guided growth” that may be advantageous.43,44 In patients with significant growth remaining, a physeal injury in this area may be problematic due to a significant impact on overall length or angular alignment changes to the distal femur. Placement of a drill hole, especially near the peripheral aspect of the physis, carries a risk of physeal injury and secondary growth alteration.33,42,45 In some patients with significant growth remaining, procedures that do not use a femoral drill hole might be advantageous.38 These techniques may reduce the risk of deleterious growth alterations. We identified some variation in location of the origin of the MPFL, in relation to the femoral physis. The center of the MPFL origin footprint was below the distal femoral physis in 5 of 6 specimens, although the femoral footprint of the MPFL origin extended above the most medial aspect of the distal femoral physis in 2 of 6 cases. Different strategies may be employed to minimize the risk of physeal injury in younger patients who undergo surgical reconstruction of the MPFL. REFERENCES 1. Buchner M, Baudendistel B, Sabo D, et al. Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clin J Sport Med. 2005;15:62–66. 2. Nietosvaara Y, Aalto K, Kallio PE. Acute patellar dislocation in children: incidence and associated osteochondral fractures. J Pediatr Orthop. 1994;14:513–515. 3. Fithian DC, Paxton EW, Stone ML, et al. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med. 2004;32:1114–1121. [Research Support, Non-U.S. Gov’t]. 4. Burks RT, Desio SM, Bachus KN, et al. Biomechanical evaluation of lateral patellar dislocations. Am J Knee Surg. 1998;11:24–31. 5. Conlan T, Garth WP Jr, Lemons JE. Evaluation of the medial softtissue restraints of the extensor mechanism of the knee. J Bone Joint Surg Am. 1993;75:682–693. 6. Desio SM, Burks RT, Bachus KN. Soft tissue restraints to lateral patellar translation in the human knee. Am J Sports Med. 1998;26: 59–65. [Research Support, Non-U.S. Gov’t]. 7. Hautamaa PV, Fithian DC, Kaufman KR, et al. Medial soft tissue restraints in lateral patellar instability and repair. Clin Orthop Relat Res. 1998;349:174–182. 8. Reider B, Marshall JL, Warren RF. Clinical characteristics of patellar disorders in young athletes. Am J Sports Med. 1981;9:270–274.
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9. Smirk C, Morris H. The anatomy and reconstruction of the medial patellofemoral ligament. Knee. 2003;10:221–227. 10. Howells NR, Barnett AJ, Ahearn N, et al. Medial patellofemoral ligament reconstruction: a prospective outcome assessment of a large single centre series. J Bone Joint Surg Br. 2012;94:1202–1208. 11. Fisher B, Nyland J, Brand E, et al. Medial patellofemoral ligament reconstruction for recurrent patellar dislocation: a systematic review including rehabilitation and return-to-sports efficacy. Arthroscopy. 2010;26:1384–1394. [Review]. 12. Sallay PI, Poggi J, Speer KP, et al. Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med. 1996;24:52–60. 13. Baldwin JL. The anatomy of the medial patellofemoral ligament. Am J Sports Med. 2009;37:2355–2361. 14. LaPrade RF, Engebretsen AH, Ly TV, et al. The anatomy of the medial part of the knee. J Bone Joint Surg Am. 2007;89:2000–2010. 15. Kepler CK, Bogner EA, Hammoud S, et al. Zone of injury of the medial patellofemoral ligament after acute patellar dislocation in children and adolescents. Am J Sports Med. 2011;39:1444–1449. 16. Nelitz M, Dornacher D, Dreyhaupt J, et al. The relation of the distal femoral physis and the medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc. 2011;19:2067–2071. 17. Shea KG, Grimm NL, Belzer J, et al. The relation of the femoral physis and the medial patellofemoral ligament. Arthroscopy. 2010; 26:1083–1087. 18. Schottle PB, Schmeling A, Rosenstiel N, et al. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35:801–804. 19. Redfern J, Kamath G, Burks R. Anatomical confirmation of the use of radiographic landmarks in medial patellofemoral ligament reconstruction. Am J Sports Med. 2010;38:293–297. 20. Rosset A, Spadola L, Ratib O. OsiriX: an open-source software for navigating in multidimensional DICOM images. J Digit Imaging. 2004;17:205–216. 21. LeGrand AB, Greis PE, Dobbs RE, et al. MPFL reconstruction. Sports Med Arthrosc. 2007;15:72–77. 22. Drez D Jr, Edwards TB, Williams CS. Results of medial patellofemoral ligament reconstruction in the treatment of patellar dislocation. Arthroscopy. 2001;17:298–306. 23. Davis DK, Fithian DC. Techniques of medial retinacular repair and reconstruction. Clin Orthop Relat Res. 2002;402:38–52. 24. Ellera Gomes JL, Stigler Marczyk LR, Cesar de Cesar P, et al. Medial patellofemoral ligament reconstruction with semitendinosus autograft for chronic patellar instability: a follow-up study. Arthroscopy. 2004;20:147–151. 25. Feller JA, Feagin JA Jr, Garrett WE Jr. The medial patellofemoral ligament revisited: an anatomical study. Knee Surg Sports Traumatol Arthrosc. 1993;1:184–186. 26. Nomura E, Horiuchi Y, Kihara M. Medial patellofemoral ligament restraint in lateral patellar translation and reconstruction. Knee. 2000;7:121–127. 27. Nomura E, Inoue M. Surgical technique and rationale for medial patellofemoral ligament reconstruction for recurrent patellar dislocation. Arthroscopy. 2003;19:E47. 28. Sandmeier RH, Burks RT, Bachus KN, et al. The effect of reconstruction of the medial patellofemoral ligament on patellar tracking. Am J Sports Med. 2000;28:345–349. 29. Schoettle PB, Werner CM, Romero J. Reconstruction of the medial patellofemoral ligament for painful patellar subluxation in distal torsional malalignment: a case report. Arch Orthop Trauma Surg. 2005;125:644–648. 30. Steensen RN, Dopirak RM, McDonald WG III. The anatomy and isometry of the medial patellofemoral ligament: implications for reconstruction. Am J Sports Med. 2004;32:1509–1513. 31. Tuxoe JI, Teir M, Winge S, et al. The medial patellofemoral ligament: a dissection study. Knee Surg Sports Traumatol Arthrosc. 2002;10:138–140. 32. Warren LA, Marshall JL, Girgis F. The prime static stabilizer of the medical side of the knee. J Bone Joint Surg Am. 1974;56:665–674. 33. Shea KG, Grimm NL, Belzer JS. Volumetric injury of the distal femoral physis during double-bundle ACL reconstruction in r
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children: a three-dimensional study with use of magnetic resonance imaging. J Bone Joint Surg Am. 2011;93:1033–1038. Kocher MS, Saxon HS, Hovis WD, et al. Management and complications of anterior cruciate ligament injuries in skeletally immature patients: survey of the Herodicus Society and The ACL Study Group. J Pediatr Orthop. 2002;22:452–457. Koman JD, Sanders JO. Valgus deformity after reconstruction of the anterior cruciate ligament in a skeletally immature patient. A case report. J Bone Joint Surg Am. 1999;81:711–715. Lipscomb AB, Anderson AF. Tears of the anterior cruciate ligament in adolescents. J Bone Joint Surg Am. 1986;68:19–28. Baker RH, Carroll N, Dewar FP, et al. The semitendinosus tenodesis for recurrent dislocation of the patella. J Bone Joint Surg Br. 1972;54:103–109. Yercan HS, Erkan S, Okcu G, et al. A novel technique for reconstruction of the medial patellofemoral ligament in skeletally immature patients. Arch Orthop Trauma Surg. 2011;131: 1059–1065. Aoki SK, Grimm NL, Ewing KE, et al. Metaphyseal screw migration after medial patellofemoral ligament reconstruction in a
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skeletally immature patient: a case report. JBJS Case Connector. 2013;3:e28 1–e28 4. 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;87:2371–2379. Kocher MS, Garg S, Micheli LJ. Physeal sparing reconstruction of the anterior cruciate ligament in skeletally immature prepubescent children and adolescents. Surgical technique. J Bone Joint Surg Am. 2006;88(suppl 1 pt 2):283–293. Lawrence JT, 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:e39 (1-6). Stevens PM. Guided growth for angular correction: a preliminary series using a tension band plate. J Pediatr Orthop. 2007;27:253–259. Stevens PM, Klatt JB. Guided growth for pathological physes: radiographic improvement during realignment. J Pediatr Orthop. 2008;28:632–639. Ford LT, Key JA. A study of experimental trauma to the distal femoral epiphysis in rabbits. J Bone Joint Surg Am. 1956;38-A: 84–92.
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The Relationship of the Femoral Physis and the Medial Patellofemoral Ligament in Children: A Cadaveric Study Kevin G. Shea, MD,* John D. Polousky, MD,w John C. Jacobs, Jr, BS,z Theodore J. Ganley, MD,y Stephen K. Aoki, MD,8 Nathan L. Grimm, BS,z and Shital N. Parikh, MDz
Background: Patellar dislocations are common in skeletally immature athletes, and the medial patellofemoral ligament (MPFL) is an important primary restraint to lateral patellar translation. The relationship between the MPFL femoral origin footprint and femoral physis is unclear. The purpose of this study was to evaluate the MPFL femoral origin footprint and its relationship to the femoral physis in skeletally immature anatomic specimens. Methods: Six skeletally immature cadaver knee specimens were examined through gross dissection (group A: 1, 11, and 11 mo; and group B: 8, 10, and 11 y). Metallic markers were placed at the center of the MPFL femoral origin footprint. Computed tomography scans for each specimen were analyzed. The MPFL footprint width, and the vertical distances from the center and proximal extent of the MPFL footprint to the medial aspect of the physis were measured. Results: The mean width of the MPFL femoral origin footprint was 0.70 cm (0.48 to 1.09 cm) and 1.12 cm (1.03 to 1.29 cm) for groups A and B, respectively. The mean distance from the center of the MPFL origin footprint to medial aspect of the distal femoral physis was 0.90 cm (0.52 to 1.30 cm) and 0.40 cm (0.00 to 0.86 cm) distal to the physis for groups A and B, respectively. The mean distance from the proximal extent of the MPFL origin footprint to the medial aspect of the femoral physis was 0.55 cm (0.28 to 1.03 cm) and 0.16 cm ( 0.34 to 0.64 cm) for groups A and B, respectively. Conclusions: All subjects were found to have a center of the MPFL origin footprint at or below the physis. The proximal From the *St. Luke’s Sports Medicine, St. Children’s Hospital, University of Utah Department of Orthopedics, Boise, ID; wRocky Mountain Youth Sports Medicine Institute, Rocky Mountain Hospital for Children, Denver, CO; zSchool of Medicine; 8Department of Orthopedics, University of Utah School of Medicine, Salt Lake City, UT; yChildren’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA; and zDivision of Orthopaedic Surgery, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH. There were no external sources of funding. However, the knee specimens used in this study are the property of an allograft facility (Allosource, Centennial, CO). This facility allowed us access to the specimens for our research/dissections, as well as use of their facilities to conduct our research. S.K.A. is an educational consultant for Pivot Medical and on the Surgical Advisory Board for Arthrocare. The remaining authors declare no conflicts of interest. Reprints: John C. Jacobs Jr, BS, School of Medicine, University of Utah, 30N. 1900 E., Salt Lake City, UT 84132. E-mail: jacobsjc013@ gmail.com. Copyright r 2014 by Lippincott Williams & Wilkins
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extent of the MPFL origin footprint was found to extend above the physis in the 2 older specimens. Clinical Relevance: The relationship of the MPFL origin footprint to the femoral physis in the skeletally immature is not well understood. These dissections may be useful to surgeons performing MPFL reconstructions in skeletally immature patients. Key Words: medial patellofemoral ligament, MPFL, physis, anatomy, pediatric, attachment, origin (J Pediatr Orthop 2014;34:808–813)
P
reviously published literature has demonstrated that patella dislocations are relatively common in skeletally immature subjects.1–3 Fithian et al3 reported that females aged 10 to 17 years were at the greatest risk for patellar dislocation. The medial patellofemoral ligament (MPFL) plays an important role in patellar stability, and is one of the primary restraints to lateral patellar translation.4–9 The MPFL is commonly injured during patellar subluxation and dislocation, and surgical reconstruction of the MPFL has produced good outcomes in many series.10,11 Previous adult cadaveric dissections have identified the origin of the MPFL between the adductor tubercle and medial collateral ligament origin, and the insertion at the upper 2/3 of the medial border of the patella.4,6,9,12–14 Many surgical techniques utilize anchors and drill holes in the distal femur. In young patients, these surgical procedures carry the risk of physeal injury, as the MPFL origin is located close to the physis. In skeletally immature subjects, the location of the MPFL origin relative to the distal femoral physis remains controversial.15–17 Kepler et al15 reviewed magnetic resonance imaging (MRIs) of children and adolescents with acute patellar dislocation, and found the mean MPFL origin at 5 mm distal to the physis. The femoral MPFL attachment was found to be variable, with 86% attaching distal to, 7% were at, and 7% were above the physis or physeal scar. Shea and colleagues used the Schottle method18 to identify the origin of the MPFL on lateral radiographs of adolescents with open physis.17 The mean MPFL origin was found to be 2.7 and 4.6 mm proximal to the physis in females and males, respectively, with the origin attaching just proximal to the physis. Nelitz and colleagues used 2 previously described methods18,19 to identify the location of the MPFL origin on the lateral J Pediatr Orthop
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radiographs of children and adolescents with open physes and then cross-referenced them onto anteroposterior radiographs.16 They found the median origin of the MPFL to be 6.4 mm distal to the physis. Current literature used to describe the MPFL femoral origin in the skeletally immature is based off radiographic and MRI studies and varies in descriptive location relative to the physis. The purpose of this study was to identify the location of the origin of the MPFL and define the relationship between the distal femoral physis and the MPFL femoral origin footprint using pediatric cadaver dissections. A better understanding of the relationship of the MPFL and the distal femoral physis could improve current surgical techniques.
METHODS The institutional review board was consulted before performing this study. As these dissection studies were performed on cadaveric tissue, institutional review board review was unnecessary. The specimens were donated by an allograft harvest facility (Allosource, Centennial, CO). Six skeletally immature knee specimens from 5 human cadavers were examined through gross dissection (Table 1). These specimens were divided into 2 groups: group A: 1, 11, and 11 months; and group B: 8, 10, and 11 years. Metallic pins were placed to mark the femoral origin of the MPFL (Fig. 1). Computed tomography (CT) scans (GE Lightspeed 16 Slice Scanner) with 1-mm slices were obtained for each specimen and were analyzed using Osirix Imaging Software.20 In the sagittal view of the CT scan, the MPFL origin width was obtained by measuring the distance between the respective 2 metallic pins, using the Osirix Imaging Software (Fig. 2). The distances from the MPFL origin to the distal femoral physis were measured in the coronal view (Fig. 3). The vertical distance from the midpoint of the MPFL femoral origin to the midpoint of the medial aspect of the femoral physis (using a mean of the distance to the superior and inferior physeal boundaries, where appropriate) was measured (Fig. 3, point B). The distance to the medial aspect of the physis was referred to as “medial physis” in Table 2. The distance from the proximal extent of the MPFL origin to the medial aspect of the distal femoral physis was measured (Table 2). For this measurement, negative values indicate the proximal extent of the physis was found below the physis, whereas positive values indicate the proximal extent was found above the physis.
FIGURE 1. Right knee: image taken during dissection. The proximal and distal borders of the medial patellofemoral ligament femoral origin footprint are marked by a marking pen (white arrows) where the metallic pins were placed.
RESULTS The mean width of the MPFL footprint in the coronal plane at the femoral origin was 0.70 cm (0.48 to 1.09 cm) and 1.12 cm (1.03 to 1.29 cm) for groups A
TABLE 1. Specimen Demographics Specimen No. 1 2 3 4 5 6
r
Age
Sex
Knee Side
1 mo 11 mo 11 mo 8y 10 y 11 y
Female Male Male Male Female Male
Right Left Right Right Left Right
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FIGURE 2. Sagittal computed tomographic scan image of the 11-year-old specimen showing the origin footprint of the medial patellofemoral ligament (MPFL) at the proximal (white arrow) and distal (black arrow) points. In this specimen, the midpoint of the MPFL origin was located at the level of the medial aspect of the distal femoral physis. www.pedorthopaedics.com |
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whereas positive values indicate the proximal extent was found above the physis. The mean distance from the proximal extent of the MPFL footprint to the medial aspect of the distal femoral physis was 0.55 cm ( 0.28 to 1.03 cm) and 0.16 cm ( 0.34 to 0.64 cm) for groups A and B, respectively. The MPFL origin width was found to extend to or across the medial aspect of the physis in no group A specimens, and 2 group B specimens (Fig. 4).
DISCUSSION
FIGURE 3. Coronal computed tomographic scan image with measurements of the distance from the center of the medial patellofemoral ligament origin footprint (A) to: the proximal and distal borders of the medial aspect of the distal femoral physis (B).
and B, respectively (Table 2). For group A, the mean distance from the center of the MPFL footprint to the medial aspect of the distal femoral physis was 0.90 cm (0.52 to 1.30 cm) distal to the physis. For group B, the mean distance from the center of the MPFL footprint to the medial aspect of the distal femoral physis was 0.40 cm (0.00 to 0.86 cm) distal to the physis. Measurements were calculated from the center of the MPFL footprint to the most medial aspect of femoral physis. For all subjects under age 11, the center of the MPFL footprint was found to be below the most medial aspect of distal femoral physis. The center of the MPFL footprint of the 11-year-old specimen was at the level of the physis. For this measurement, negative values indicate the proximal extent of the physis was found below the physis,
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In skeletally immature patients, previous studies have reached different conclusions about the relationship between the distal femoral physis, and the femoral footprint of the MPFL. Some of the confusion in the literature may be related to the complex undulations of the distal femoral physis, which makes radiographic visualization of landmarks challenging.16 The dissections performed in this anatomic study demonstrated some variability in the relationship of the MPFL and the physis, but consistent findings were present in many of these specimens. Although the center of the MPFL origin footprint was below the medial distal femoral physis in 5 specimens, the overall coronal plane dimension of the MPFL footprint extended above the most medial aspect of the distal femoral physis in 2 specimens. Surgical treatment of recurrent patellar dislocations may include reconstruction of the MPFL.21,22 The use of consistent anatomic landmarks may help restore the natural function and kinematics of the MPFL.22–32 Placement of the MPFL origin on the femur includes the risk of physeal injury in children with a similar potential for growth disturbance as seen with anterior cruciate ligament reconstructions in this age group.33–36 Previous studies have used indirect methods to evaluate the location of the MPFL origin in relation to the distal femoral physis in children or adolescents with variable results.15–17 One study suggests that the midpoint of the MPFL origin is a few millimeters above the distal femoral physis,17 however, this study was limited in that it was an indirect study of the anatomy using the radiographic technique described by Schottle et al.18 This study was based upon a database of established skeletally immature radiographs, and was not based upon radiographic analysis of cadaveric knee specimens. A limitation of this previous study, highlighted by Nelitz et al,16 was that the MPFL origin location was only evaluated on lateral radiographs. Nelitz and colleagues evaluated the location of the midpoint of the MPFL origin on anteroposterior and lateral radiographs. In this work, Nelitz and colleagues concluded that the femoral origin midpoint of the MPFL was below the most medial aspect of the distal femoral physis. In the current study, the use of CT scan analysis allowed for more comprehensive evaluation of the MPFL origin footprint. The results of this study are supportive of the previous radiographic work of Nelitz and colleagues. In considering bone tunnels for graft fixation, this becomes even more important. We found the center r
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TABLE 2. Anatomic Measurements Specimen No.
Age
1 2 3 4 5 6
1 mo 11 mo 11 mo 8y 10 y 11 y
Femoral Origin Footprint Width (cm)
Center Origin Footprint to Medial Physis Distance (cm)
Center Origin Footprint Relation to Medial Physis*
Medial Physis to Proximal Extent of MPFL Origin Distance (cm)w
0.48 0.54 1.09 1.04 1.03 1.29
0.52 1.30 0.88 0.86 0.35 0.00
Below Below Below Below Below At
0.28 1.03 0.33 0.34 0.17 0.64
*Center MPFL origin footprint in relation to the medial aspect of the femoral physis: at, above, below the physis. wProximal extent of the origin footprint appears either above (positive value) or below (negative value) the medial physis. MPFL indicates medial patellofemoral ligament.
of the MPFL origin footprint of all specimens under age 11 to be distal to the medial aspect of the distal femoral physis, and the origin of the 11-year-old specimen to be at the level of the physis. Although the center of the MPFL origin footprint may be at or below the most medial aspect of the distal femoral physis, the proximal extension of the MPFL femoral footprint is above the medial physis to some degree in the 2 older specimens in this series. To avoid physeal injury in surgery, several options exist. In cases in which the native MPFL is of sufficient quality, repair and/or advancement of this structure may be performed. The MRI can usually locate the prominent area of injury to the patellar origin, mid-substance region, or femoral origin. Kepler et al15 analyzed MRIs of children with tears of the MPFL for tear location. They found tears at the patellar attachment in 61%, femoral attachment in 12%, and both patellar and femoral attachments in 12% of patients. The proximity of the MPFL to the femoral physis raises the question of physeal injury during MPFL femoral avulsion, but we have not observed this phenomenon in our practice.
FIGURE 4. Diagram illustrating the center and width of the medial patellofemoral ligament (MPFL) origin footprint in relation to the distal femoral physis. Each rectangle corresponds to the MPFL origin footprint of a specific specimen, with the center denoted by the horizontal white line. The vertical length of each rectangle corresponds to the origin footprint width. r
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In cases where the native tissue is not adequate for repair, surgical reconstruction avoiding the physis and perichondral ring may be an option. Bony tunnels may be placed in an anatomic or nonanatomic position depending upon its location with respect to the physis. The MPFL origin may also be fixed to the surrounding soft tissues rather than placing a femoral drill hole,37,38 although this position may place the MPFL origin above the native origin. At this stage, it is unclear if nonanatomic locations, which may have a lower risk of physeal injury, may provide adequate protection against future dislocation.39 To avoid physeal injury during anterior cruciate ligament reconstruction, nonanatomic techniques have been used with good clinical outcomes demonstrated with longer-term follow-up studies.40,41 There are several limitations to this study. The small number of specimens used in this study is problematic. This is due to the extreme difficulty in obtaining pediatric cadaver specimens for research purposes. Multiple allograft laboratories over a 3-year period were contacted in an attempt to locate specimens, and only 1 laboratory was able to provide a limited number of specimens. Dissection of the MPFL can be challenging in pediatric cadaveric specimens. Some specimens had a robust and distinct ligament, whereas some specimens had a less distinct structure. On the basis of previous published literature15–18 and the results of our study that shows close proximity of the physis to the MPFL attachment site, we recommend the following considerations when considering MPFL reconstructions in skeletally immature patients: (1) The medial aspect of the physis is more proximal than the central region of the physis. Review of lateral radiographs may show the most distal/central aspect of the femoral physis more clearly, as the more proximal/medial aspect of the distal femoral physis may not be well visualized on the lateral radiographs. This radiographic observation should be considered if the Schottle technique is utilized to identify the MPFL femoral location in skeletally immature patients.16,17 (2) The center of the MPFL femoral origin footprint may be below the medial aspect of the distal femoral physis in most patients, but the full proximal extent of the MPFL origin footprint may also extend proximally across the physis in some patients. www.pedorthopaedics.com |
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(3) In this small series, there appeared to be a trend that showed the femoral origin footprint of the MPFL was more proximal in older patients. Larger studies would help clarify this and other anatomic findings, but these specimens are exceptionally difficult to procure for study. (4) If drill holes are placed near the femoral physis for attachment of the MPFL origin, the use of small drill holes angled away from the physis, and drilling in a manner to limit the amount of heat generated near the physis, may lower the risk of physeal arrest.42 Placing a drill hole this close to the physis may increase the risk of physeal arrest or even physeal overgrowth, which may lead to angulation of the distal femur. In children with minimal growth remaining, this may not result in any significant impact on growth or distal femoral alignment. In a patient in which distal femoral valgus may be a contributing factor to patellofemoral instability, addressing the valgus alignment by delaying the medial physis growth is an example of “guided growth” that may be advantageous.43,44 In patients with significant growth remaining, a physeal injury in this area may be problematic due to a significant impact on overall length or angular alignment changes to the distal femur. Placement of a drill hole, especially near the peripheral aspect of the physis, carries a risk of physeal injury and secondary growth alteration.33,42,45 In some patients with significant growth remaining, procedures that do not use a femoral drill hole might be advantageous.38 These techniques may reduce the risk of deleterious growth alterations. We identified some variation in location of the origin of the MPFL, in relation to the femoral physis. The center of the MPFL origin footprint was below the distal femoral physis in 5 of 6 specimens, although the femoral footprint of the MPFL origin extended above the most medial aspect of the distal femoral physis in 2 of 6 cases. Different strategies may be employed to minimize the risk of physeal injury in younger patients who undergo surgical reconstruction of the MPFL. REFERENCES 1. Buchner M, Baudendistel B, Sabo D, et al. Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clin J Sport Med. 2005;15:62–66. 2. Nietosvaara Y, Aalto K, Kallio PE. Acute patellar dislocation in children: incidence and associated osteochondral fractures. J Pediatr Orthop. 1994;14:513–515. 3. Fithian DC, Paxton EW, Stone ML, et al. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med. 2004;32:1114–1121. [Research Support, Non-U.S. Gov’t]. 4. Burks RT, Desio SM, Bachus KN, et al. Biomechanical evaluation of lateral patellar dislocations. Am J Knee Surg. 1998;11:24–31. 5. Conlan T, Garth WP Jr, Lemons JE. Evaluation of the medial softtissue restraints of the extensor mechanism of the knee. J Bone Joint Surg Am. 1993;75:682–693. 6. Desio SM, Burks RT, Bachus KN. Soft tissue restraints to lateral patellar translation in the human knee. Am J Sports Med. 1998;26: 59–65. [Research Support, Non-U.S. Gov’t]. 7. Hautamaa PV, Fithian DC, Kaufman KR, et al. Medial soft tissue restraints in lateral patellar instability and repair. Clin Orthop Relat Res. 1998;349:174–182. 8. Reider B, Marshall JL, Warren RF. Clinical characteristics of patellar disorders in young athletes. Am J Sports Med. 1981;9:270–274.
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