ORIGINAL ARTICLE

The Patellar Insertion of 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, MD,z and Shital N. Parikh, MD#

Background: The purpose of this study was to evaluate the medial patellofemoral ligament (MPFL) patellar insertion in skeletally immature anatomic specimens. Methods: Nine pediatric cadaveric knee specimens were examined through gross dissection. Metallic markers were placed at the MPFL patellar insertion footprint. Computed tomographic scans for each specimen were analyzed. The MPFL insertion footprint width, patellar height, and patellar width were measured. The distance from the MPFL insertion footprint center to the midline of the patella was assessed. The proportion of the patella that the MPFL footprint inserted upon was calculated. Results: The mean width of the MPFL patellar insertion footprint was 12 mm (range, 8 to 18 mm). The mean patellar height was 31 mm (range, 20 to 48 mm). The mean patellar width was 27 mm (range, 21 to 39 mm). The center of the MPFL insertion footprint was found to be a mean 4.7 mm (range, 2 to 10.5 mm) above the midline of the patella, with insertion centers occurring both above and below the midline. The MPFL insertion footprint spanned a mean 41% (24% to 63%) of the longitudinal width of the patella. Conclusions: Most adult studies report the MPFL insertion on the upper 1/2 to 2/3 of the patella. This series of skeletally immature subjects demonstrated that the center of the MPFL insertion was above and below the midpoint of the patella. The MPFL insertions of some of the younger specimens did extend into the distal 1/3 of the patella. The insertion of the older specimens was found in the proximal 2/3 of the patella, a similar location to most previous adult anatomic studies. Clinical Relevance: This research suggests that the MPFL insertion on the patella may be at slightly different locations in some skeletally immature subjects compared with adults. The specimens dissected in the present study showed more variability From the *St. Luke’s Sports Medicine, St. Luke’s Children’s Hospital Boise, ID; wRocky Mountain Youth Sports Medicine Institute, Rocky Mountain Hospital for Children Denver, CO; zUniversity of Utah School of Medicine, Salt Lake City, UT; yChildren’s Hospital of Philadelphia, University of Pennsylvania School of Medicine Philadelphia, PA; 8Department of Orthopedics, University of Utah; zDepartment of Orthopaedic Surgery, Duke University Medical Center Durham, NC; and #Division of Orthopaedic Surgery, Cincinnati Children’s Hospital Medical Center Cincinnati, OH. None of the authors received financial support for this study. The authors declare no conflicts of interest. Reprints: John C. Jacobs, Jr, BS, University of Utah School of Medicine, 30 N. 1900 E., Salt Lake City, UT 84132. E-mail: jacobsjc013 @gmail.com. Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.

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than previously published reports, with some insertions extending into the distal 1/3 of the patella in the youngest subjects. These dissections may be useful to surgeons performing MPFL reconstructions in skeletally immature patients. Key Words: medial patellofemoral ligament, pediatric, knee, patella, dislocation (J Pediatr Orthop 2015;35:e31–e35)

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atella dislocations are relatively common in skeletally immature subjects.1–3 Nietosvaara et al2 reported an annual incidence of 43 per 100,000 in children under the age of 16 years. In an epidemiology study by Fithian et al,3 it was found that females aged 10 to 17 years had the highest risk for patellar dislocation.3 The medial patellofemoral ligament (MPFL) is the primary soft tissue stabilizer 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.10–12 In adult specimens, this ligament has an identified origin between the adductor tubercle and medial collateral ligament origin, and has been found to insert at the upper 2/3 of the medial border of the patella.4,6,9,13–18 The purpose of this study was to identify the location of the MPFL footprint insertion on the patella using pediatric cadaver dissections with computed tomographic (CT) scan correlation. A better understanding of the MPFL insertion site on the patella could improve current surgical technique for reconstruction in skeletally immature patients.

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 deemed unnecessary. Nine skeletally immature knee specimens were examined through gross dissection (Table 1). These specimens had an average age of 86.7 months, and consisted of the following age specimens: 2, 3, 3, 8, 8, 10, 10, 10, and 11 years. Metallic pins were placed to mark the patellar insertion of the MPFL (Fig. 1). CT scans (GE Lightspeed 16 Slice Scanner) with 1-mm slices were obtained for each www.pedorthopaedics.com |

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TABLE 1. Specimen Demographics Specimen No 1 2 3 4 5 6 7 8 9

Age (y)

Sex

Knee Side

2 3 3 8 8 10 10 10 11

Male Female Male Male Female Female Female Male Male

Right Right Left Right Right Right Left Right Right

specimen and were analyzed using Osirix Imaging Software.19 Because of the size of some of the younger specimens, in some knees, only 1 pin was placed to mark the MPFL insertion on the patella. These pins were inserted into the developing patella at the midpoint of the MPFL at the discretion of the dissecting surgeon. Therefore, the MPFL insertion footprint width (defined proximal to distal length of the MPFL insertion), patellar height, and patellar width measurements were obtained from measurements taken during the dissection, from dissection photos with rulers in the field (Fig. 2), or by measuring the distance between the respective 2 metallic pins in the coronal view of the CT scan, using the Osirix Imaging Software. These measurements were taken by 1 author (J.J.), and verified by the first author (K.S.). All meas-

FIGURE 2. Left knee of the 11-year-old specimen taken during dissection. The 4 poles of the patella are indicated as follows. D indicates distal; L, lateral; M, medial; P, proximal. The vastus medialis oblique is labeled “VMO.” Black asterisks outline the medial patellofemoral ligament.

urements of the patella included both the cartilaginous and osseous portions. The distance from the center of the MPFL insertion footprint to the midline of the patella was measured. The relation of the MPFL patellar insertion to the patellar height was determined (Fig. 3). For all measurements, negative values indicate the structure occurs below the midline of the patella, whereas positive values indicate the structure occurs above the midline.

RESULTS

FIGURE 1. Coronal computed tomographic scan image of the 11-year-old specimen showing the MPFL insertion footprint location on the patella. The 2 metallic pins that mark the proximal and distal extents of the MPFL footprint are indicated by 2 white arrows. Line A represents the measurement of the MPFL insertion footprint width. Line B represents the measurement of patellar height. Line C represents the measurement of patellar width. The measurements were taken using Osirix Imaging Software. MPFL indicates medial patellofemoral ligament.

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The mean width of the MPFL footprint at the patellar insertion was 12 mm (range, 8 to 18 mm) (Table 2). The mean patellar height was 31 mm (range, 20 to 48 mm). The mean patellar width was 27 mm (range, 21 to 39 mm). The center of the MPFL insertion footprint was found to be a mean 4.7 mm (range,  2 to 10.5 mm) above the midline of the patella. The MPFL insertion footprint spanned a mean 41% (24% to 63%) of the patella. The center of the MPFL insertion footprint was found to be below the midline of the patella in one specimen (aged 2 y) (Table 2). All other specimens had insertion midpoints located above the midline of the patella. The midpoint of every specimen was found to be within the upper 2/3 of the patella. However, the MPFL insertion was found to extend into the distal third of the patella in 2/9 specimens.

DISCUSSION MPFL anatomy and surgical techniques have received increased attention in recent years. Much of the MPFL literature has focused on adult populations, which may have different anatomy than the child or adolescent. Previous research on adult cadaveric specimens has Copyright

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Patellar Insertion of the MPFL in Children

FIGURE 3. Diagram illustrating the MPFL insertion footprint width and its insertion on the medial border of the patella. Each black rectangle corresponds to the vertical height of the patella. The included white rectangle represents the proportional MPFL insertion footprint and relative location on the patella. Each discrete rectangle set corresponds to the specimen number indicated. The percentage of patellar height that the MPFL attachment inserts upon is indicated inside each white rectangle. The 0-line of the x-axis represents the midline of the patella. MPFL indicates medial patellofemoral ligament.

identified the insertion of the MPFL to be on the upper 2/3 of the medial border of the patella. In the current study, pediatric cadaveric specimens were dissected, with CT scan correlation, and the center of the MPFL insertion was found to be slightly variable, with specimens having attachments above and below the midline of the patella. Most of the skeletally immature subjects in this series demonstrated that the patellar attachment of the MPFL is

in a similar location to that seen in adults, although some of the younger specimens demonstrated an MPFL insertion that extended more distally on the patella. Many studies have reported the insertion of the MPFL footprint to be on the upper 2/3 to upper 1/2 of the medial border of the patella.14,20–24 Baldwin14 dissected 50 cadaveric knees with a mean age of 71 years. They reported an attachment on the upper 2/3 of the patella and a mean MPFL insertion footprint width of 28.2 mm (range, 18 to 40 mm). Studies by Tuxoe et al24 and Balcarek et al21 confirm this insertion location on the upper 2/3 of the patella. Philippot et al23 dissected 23 cadaveric knees with a mean age of 75 years. They found the insertion to be on the upper half of the patella, with a mean insertion width of 24.2 mm (range, 17 to 32 mm). Kang et al22 confirmed this insertion location. Conversely, Arago et al20 dissected 15 cadaveric knees and found the location of the MPFL insertion on the patella to be variable. In the 15 specimens with an identifiable MPFL, they found that 2 had insertions along the upper 1/3 of the patella, 1 on the middle 1/3, 6 on the upper 2/3, 2 on the lower 2/3, and 4 on the entire length of the patella. Kang et al22 dissected 12 adult cadaveric knees and found that the MPFL patellar insertion inserted upon approximately 50% of the total height of the patella. In the present study, the MPFL insertion footprint on the patella was also found to be somewhat variable. Of the 9 total knees, 1 specimen was found to have a midpoint of the patellar insertion footprint occurring below the midline of the patella (aged 2 y). The remaining specimens had MPFL patellar insertion midpoints occurring above the midline of the patella. The width of the insertion footprint was found to extend both above and below the patellar midline in various specimens, with insertion spanning 24% to 63% of the medial longitudinal aspect patella. The mean insertion width of the specimens analyzed in this study was found to be smaller than those reported in the literature. This discrepancy could be due to the young age of the specimens analyzed, compared with predominantly adult specimens analyzed by others. Between the ages of 4 and 8, the ossification center of the patella emerges.25 Ossification of the patella is complete between 16 and 17 years of age, and proceeds

TABLE 2. Anatomic Measurements Specimen No 1 2 3 4 5 6 7 8 9

Age (y)

Patellar Insertion Width (mm)

2 3 3 8 8 10 10 10 11

17 9 18 8 11 10 10 15 10 12

Mean

Patellar Height Patellar Width Center MPFL Insertion to Patellar (mm) (mm) Midline (mm) 27 27 32 33 37 28 20 48 24 31

22 22 31 31 31 26 21 39 24 27

MPFL Insertion: % of Patellar Height 63 33 56 24 30 36 50 31 42 41

2 4 1 5.5 10 5 4 10.5 4 5

MPFL indicates medial patellofemoral ligament.

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proximally to distally.26 Therefore, the younger specimens’ patellar insertion of the MPFL may not represent the final insertion location. Although in the present study no clear trend could be identified in correlation with progressing age, 1 specimen did have an MPFL insertion center that occurred below the midpoint of the patella. In addition, 2 of the younger specimens also had a portion whose MPFL insertion footprint that extended into the distal third of the patella. Further research should be performed to further clarify the location of the MPFL insertion on the patella and how this changes with age. Several studies have reported that the MPFL is injured in most patellar dislocations.27–29 Recent studies have shown good outcomes in patellar instability patients treated with an MPFL reconstruction. Howells et al10 prospectively assessed 193 MPFL reconstructions for recurrent patellar dislocation, traumatic dislocation, and instability. A statistically significant improvement in outcomes was found, and no recurrent patellar dislocation after reconstruction was reported, with a mean follow-up of 16 months. Nelitz et al12 found that 21 skeletally immature patients who underwent anatomic MPFL reconstruction for patellofemoral instability had a significant improvement in knee function scores, with a mean of 2.8 years follow-up after surgery. Reconstruction techniques currently provide good outcomes for adults and children alike; however, better outcomes may be achieved with techniques developed from additional information of knee ligament anatomy in the skeletally immature.30,31 As patella dislocations occur at the highest rate in these skeletally immature populations, future research with larger sample sizes could further clarify the anatomy of the MPFL insertion on the patella. Anatomic research on the ligaments about the knee in skeletally immature subjects is important, as several studies have demonstrated that significant physeal injury can occur after ligament reconstruction, leading to growth disturbance.32–34 Surgical techniques that avoid physeal injury are advantageous, especially in younger patients with significant growth remaining. Because of the severe limitations on access to pediatric cadavers, computer modeling techniques may be advantageous.31,35 Limited anatomic research on pediatric knee anatomy is available for anterior cruciate ligament, posterior cruciate ligament, and lateral collateral ligament.36–38 Fortunately, the risk of significant physeal injury for ligament reconstruction of the patellar attachment of the MPFL is very low, but the risks of physeal injury on the MPFL femoral origin may be more significant.18 Future research could include comparing the MPFL insertion locations identified in the present study on MRI. This comparison could be important, as visualization of the MPFL insertion on MRI is challenging due to the small dimensions of the MPFL and slice thickness of MRI. This study has several limitations. The small number of specimens restricts the conclusions about the location of the MPFL insertion, and a larger number of specimens would make this information more generalizable. Locating pediatric specimens for knee dissection is exceptionally

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difficult, and this research group was only able to locate a very small number after contacting multiple cadaveric harvest facilities. Several surgeons participated in the dissections, and the use of 1 surgeon might have reduced some of the variability in the findings. However, despite the dissections being conducted by different surgeons, the entire group of surgeons reviewed the anatomic findings before placing the markers for later CT and ruler measurement. Three of the 9 specimens were 3 years old or below. The MPFL patellar insertions had more variability in this age group, with 1 specimen having a central insertion site located below the patellar midline. Although interesting, the current clinical application of the specimens 3 years old and below is not known as traumatic patellar dislocations are not well described in this particular age group.

CONCLUSIONS Previous research has identified an MPFL insertion footprint on the proximal 1/2 to 2/3 of the medial border of the patella. Many of the specimens dissected in the present study did identify the MPFL inserting on the upper 2/3 of the patella. However, 2 specimens under 4 years of age did have MPFL insertion footprints that extended into the distal 1/3 of the patella. The results of this study do identify a possibly different location of the MPFL insertion in very young subjects compared with older children and adults. This information may be of value to surgeons that care for skeletally immature patients with patellar instability. ACKNOWLEDGMENTS The authors thank Allosource (Centennial, CO) for the donation of the cadaveric specimens and nonfinancial research support. The authors also thank Tom Cycyota and Todd Huft (Allosource) for their assistance, organization, and support of the dissections. 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. 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. 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. 9. Smirk C, Morris H. The anatomy and reconstruction of the medial patellofemoral ligament. Knee. 2003;10:221–227.

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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. 12. Nelitz M, Dreyhaupt J, Reichel H, et al. Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: surgical technique and clinical outcome. Am J Sports Med. 2013;41:58–63. 13. 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. 14. Baldwin JL. The anatomy of the medial patellofemoral ligament. Am J Sports Med. 2009;37:2355–2361. 15. 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. 16. 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. 17. Ladd PE, Laor T, Emery KH, et al. Medial collateral ligament of the knee on magnetic resonance imaging: does the site of the femoral origin change at different patient ages in children and young adults? J Pediatr Orthop. 2010;30:224–230. 18. Shea KG, Grimm NL, Belzer J, et al. The relation of the femoral physis and the medial patellofemoral ligament. Arthroscopy. 2010;26:1083–1087. 19. Rosset A, Spadola L, Ratib O. OsiriX: an open-source software for navigating in multidimensional DICOM images. J Digit Imaging. 2004;17:205–216. 20. Aragao JA, Reis FP, de Vasconcelos DP, et al. Metric measurements and attachment levels of the medial patellofemoral ligament: an anatomical study in cadavers. Clinics. 2008;63:541–544. 21. Balcarek P, Ammon J, Frosch S, et al. Magnetic resonance imaging characteristics of the medial patellofemoral ligament lesion in acute lateral patellar dislocations considering trochlear dysplasia, patella alta, and tibial tuberosity-trochlear groove distance. Arthroscopy. 2010;26:926–935. 22. Kang HJ, Wang F, Chen BC, et al. Functional bundles of the medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc. 2010;16:1511–1516. 23. Philippot R, Chouteau J, Wegrzyn J, et al. Medial patellofemoral ligament anatomy: implications for its surgical reconstruction. Knee Surg Sports Traumatol Arthrosc. 2009;17:475–479. 24. Tuxoe JI, Teir M, Winge S, et al. The medial patellofemoral ligament: a dissection study. Knee Surg Sports Traumatol Arthrosc. 2002;10:138–140.

Copyright

r

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Patellar Insertion of the MPFL in Children

25. Ogden JA. Radiology of postnatal skeletal development. X. Patella and tibial tuberosity. Skeletal Radiol. 1984;11:246–257. 26. Jozwiak M, Pietrzak S. Evaluation of patella position based on radiologic and ultrasonographic examination: comparison of the diagnostic value. J Pediatr Orthop. 1998;18:679–682. 27. Elias DA, White LM, Fithian DC. Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology. 2002;225:736–743. 28. Sanders TG, Morrison WB, Singleton BA, et al. Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr. 2001;25:957–962. 29. Spritzer CE, Courneya DL, Burk DL Jr, et al. Medial retinacular complex injury in acute patellar dislocation: MR findings and surgical implications. AJR Am J Roentgenol. 1997;168:117–122. 30. 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. 31. Shea KG, Belzer J, Apel PJ, et al. Volumetric injury of the physis during single-bundle anterior cruciate ligament reconstruction in children: a 3-dimensional study using magnetic resonance imaging. Arthroscopy. 2009;25:1415–1422. 32. 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. 33. 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. 34. Rozbruch SR, Fryman C, Schachter LF, et al. Growth arrest of the tibia after anterior cruciate ligament reconstruction: lengthening and deformity correction with the Taylor Spatial Frame. Am J Sports Med. 2013;41:1636–1641. 35. Shea KG, Grimm NL, Belzer JS. Volumetric injury of the distal femoral physis during double-bundle ACL reconstruction in children: a three-dimensional study with use of magnetic resonance imaging. J Bone Joint Surg Am. 2011;93:1033–1038. 36. 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;29:781–787. 37. Kocher MS, Hovis WD, Curtin MJ, et al. Anterior cruciate ligament reconstruction in skeletally immature knees: an anatomical study. Am J Orthop (Belle Mead NJ). 2005;34:285–290. 38. Shea KG, Polousky JD, Jacobs JJC, et al. Anatomical dissection and CT imaging of the posterior cruciate and lateral collateral ligaments in skeletally immature cadaver knees. J Bone Joint Surg. 2014;96:753–759.

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The patellar insertion of the medial patellofemoral ligament in children: a cadaveric study.

The purpose of this study was to evaluate the medial patellofemoral ligament (MPFL) patellar insertion in skeletally immature anatomic specimens...
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