Clinical Imaging xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Clinical Imaging journal homepage: http://www.clinicalimaging.org
MRI evaluation and complications of medial patellofemoral ligament reconstruction Maha Torabi ⁎, Sean Wo, Dharmesh Vyas, Joanna Costello UPMC Department of Radiology, 200 Lothrop St., Pittsburgh, PA 15213
a r t i c l e
i n f o
Article history: Received 26 March 2014 Received in revised form 2 July 2014 Accepted 10 July 2014 Available online xxxx Keywords: Knee MRI Medial patellofemoral ligament reconstruction Recurrent patellar dislocation MPFL reconstruction Complication
a b s t r a c t Medial patellofemoral ligament (MPFL) reconstruction is a relatively new surgical technique for the treatment of recurrent patellar instability and dislocation. Radiologic findings following MPFL reconstruction are not well described in the existing literature. Here, we review the anatomy and biomechanics of the MPFL, review imaging findings following double-bundle MPFL reconstruction, and show examples of complications arising from reconstruction. © 2014 Elsevier Inc. All rights reserved.
1. Introduction Lateral patellar dislocation is a disabling condition that often results in medial patellofemoral ligament (MPFL) laxity, tear, or dysfunction. Recurrent patellar dislocation occurs in up to 44% of conservatively treated patients. Surgery may be required if conservative treatment fails. The ultimate goal is to restore stability and correct maltracking in order to preserve patellofemoral articular cartilage. Although numerous surgeries have been described for this condition, the concept of MPFL reconstruction is relatively new, and to our knowledge, the imaging findings following MPFL reconstruction have not yet been well described in the radiology literature. In this article, we review the anatomy and biomechanics of the MPFL, describe the double-bundle technique for MPFL reconstruction, and show examples of MPFL reconstruction and postoperative complications.
2. MPFL anatomy 2.1. Femoral insertion The MPFL is located in layer 2 of the medial aspect of the knee, between the crural fascia (layer 1) and the capsule of the knee joint (layer 3) [1–3]. The exact origin from the medial femoral epicondyle
⁎ Corresponding author. Wake Forest School of Medicine, One Medical Center Boulevard, Winston-Salem, NC 27157. E-mail address: [email protected] (M. Torabi).
remains controversial [2–7]. Studies suggest that it originates just proximal to the femoral attachment of the superficial medial collateral ligament and distal to the attachment of adductor magnus (Fig. 1). A study by Schottle et al. [6] has been used by orthopedic surgeons to identify a radiographic landmark for the anatomical femoral origin of the MPFL as shown in Fig. 2. The circle represents the mean site of femoral origin of the MPFL as documented in eight cadavers in this study and is outlined by: ‐ Line 1: posterior femoral cortex ‐ Line 2: perpendicular to line 1, intersecting the contact point of the medial condyle and the posterior cortex ‐ Line 3: perpendicular to line 1, intersecting the most posterior point of the Blumensaat line. Based on our experience, the adductor magnus attachment as seen on sagittal and axial magnetic resonance images can be used as reference landmark for evaluation of femoral tunnel location. The femoral tunnel should be slightly distal and anterior (within 5 mm) to the adductor tubercle [3]. 2.2. Patellar insertion The MPFL fans out towards its insertion upon the superior medial border of patella, with the patellar insertion being slightly wider than the femoral origin [5,8]. Two functional bundles of the MPFL functional have been described [8]: ‐ The inferior-straight bundle, which is the main static soft tissue restraint, attaching to the midaspect of the medial border of the patella.
http://dx.doi.org/10.1016/j.clinimag.2014.07.007 0899-7071/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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patellar suture anchor for the inferior bundle to be straight, and the patellar insertion of the superior-oblique bundle should be 10–12 mm proximal to the patellar insertion of the inferior-straight bundle. 3. Biomechanics The MPFL has been shown to be the most important ligamentous stabilizer preventing lateral dislocation, particularly in the first 30° of knee flexion, where the patella is most vulnerable due to lesser osseous engagement by the trochlea [7,9,10]. The MPFL is nonisometric and becomes tight in extension and lax in flexion (Fig. 3) [3,9,11]. In contrast to the MPFL, the lateral retinaculum is lax in extension and tightens in flexion [12,13]. 4. Patellofemoral instability treatment options [14–17]:
Fig. 1. MPFL anatomy. Femoral origin is just proximal to the femoral attachment of the superficial medial collateral ligament (MCL) and distal to the attachment of adductor magnus tendon (AMT).
‐ The superior-oblique bundle, which is associated with the vastus medialis oblique muscle and serves as the main dynamic soft tissue restraint. The patellar insertion of the superior-oblique bundle is 10– 12 mm proximal to the patellar insertion of the inferior-straight bundle. Knowledge of this anatomy can be used in the radiographic evaluation of the femoral and patellar fixation sites of the reconstructed MPFL intraoperatively and postoperatively. On the lateral extended radiograph of the knee, the femoral tunnel should be at the same level as the distal
• • • • • •
Nonoperative MPFL reconstruction Distal tibial tuberosity transfer Medial tibial tuberosity transfer Lateral retinacular release More extensive osteotomies including trochleoplasty, supracondylar femoral osteotomy, derotation femoral osteotomy, etc. Using a simplified approach, excluding more extensive osteotomies, the patients can be placed into four categories [18]: 1. Normal patellar height, normal tibial tuberosity trochlear groove (TTTG) distance: MPFL reconstruction. 2. Patella alta, normal TTTG distance: MPFL reconstruction and distal tibial tuberosity transfer. 3. Patella alta, increased TTTG distance: medial and distal tibial tuberosity transfer±MPFL reconstruction. 4. Normal patellar height, increased TTTG distance: medial tibial tuberosity transfer±lateral retinacular release.
5. MPFL reconstruction Various techniques and approaches have been described, including primary repair with or without augmentation, and reconstruction using autogenous tendon, allografts, and synthetic graft materials. MPFL reconstruction techniques include single- and double-bundle methods [19–22]. Graft choices include semitendinosus, gracilis, quadriceps tendon, and even synthetic grafts [23–26]. At our institution, double-bundle technique is commonly performed using either allograft or autograft. No clear data have been presented demonstrating the superiority of one surgical technique over another [27]. With both single- and double-bundle techniques, the surgery ideally will restore patellar position and stability. The goal is anatomic reconstruction to optimize patellofemoral stability throughout the range of motion, particularly in the first 30° of knee flexion where the patella is most vulnerable to dislocation. 6. Importance of femoral tunnel position
Fig. 2. Radiographic landmark (circle) for anatomical femoral origin of MPFL as suggested by Schottle (1: posterior femoral cortex, 2: perpendicular to line 1, intersecting the contact point of medial condyle and the posterior cortex, 3: perpendicular to line 1, intersecting the most posterior point of the Blumensaat line).
Placing the femoral tunnel too proximally on the medial epicondyle will result in a reconstructed MPFL that is lax in extension and tight in flexion; this may cause loss of knee flexion and excessive pressure resulting in chondral loss on the medial patellar facet [2,28,29] (Fig. 4). Conversely, placing the femoral origin MPFL reconstruction too distally on the medial epicondyle will result in an overly tight MPFL in extension and a lax ligament in flexion. This may result in an extensor lag, as the tension in the reconstructed ligament may be greater than in the patellar tendon when the quadriceps muscles are maximally contracted (Fig. 5).
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 3. MPFL biomechanics: The MPFL is nonisometric and becomes tight in extension (a) and lax in flexion (b).
Fig. 4. Proximal placement of femoral tunnel on the medial epicondyle, with graft being lax in extension (a) and tight in flexion (b). This may cause loss of knee flexion and excessive pressure resulting in chondral loss on the medial patellar facet.
Fig. 5. Distal placement of femoral tunnel on the medial epicondyle, with graft being overly tight in extension (a) and lax in flexion (b). This may result in an extensor lag.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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ative fluoroscopy as described by Schottle et al. (Fig. 6). While several techniques exist for graft fixation, surgeons at our institution prefer to fix the graft on the patella using two bioabsorbable suture anchors placed in the superior one half of the patella. On the femoral side, the graft is fixed with an interference screw within a bony tunnel (Figs. 7, 8). Final tensioning and fixation are done with the knee at 30° of flexion. The goal is to achieve lateral glides symmetric to the contralateral/unaffected side. Care is taken to not overconstrain the patella. 8. Complications of MPFL reconstruction
Fig. 6. Intraoperative fluoroscopy to establish the position of the femoral tunnel as recommended by Schottle.
7. Surgical technique for double-bundle MPFL reconstruction Incisions are made over the medial edge of the patella and the medial femoral epicondyle. Surgical exposure is done to tunnel between fascial layers 2 and 3 of the medial knee. The MPFL graft (either autograft or allograft) is passed between these layers and secured on the patella and femur for ligament reconstruction. The tunnel position is verified on a perfect lateral X-ray using intraoper-
Fig. 7. Double-bundle anatomic MPFL reconstruction with interference screw used for fixation of the femoral side and suture anchors for the patellar side.
A meta-analysis review of literature [20] has shown a relatively high rate of success with a total of 164 complications in 629 knees (26.1%). Given the numerous surgical techniques for MPFL reconstruction, with variability of graft choice, patellar fixation, femoral fixation, graft tensioning, and angle of knee flexion at the time of fixation, there is a paucity of information regarding the relative advantages, disadvantages, success rates, and complication rates of one versus another surgical approach. Further high-level studies reviewing the differing techniques and analyzing the relative longterm clinical benefits and complications are needed to better understand the overall efficacy of MPFL reconstruction. It is important to define failure versus success based on clinical, imaging, and patientreported outcome parameters. A normal graft on magnetic resonance imaging (MRI) should demonstrate low signal intensity on T1- and T2-weighted images and appear continuous, taut, anatomically oriented, and anchored, without associated imaging stigmata of hardware- or wound-related complications. The patellar anchors should be within 1 cm of each other with the more inferior one at the equator of patella such that the inferior bundle of graft has a relatively horizontal or true axial orientation. The femoral tunnel should be just distal to the attachment of the adductor magnus. The most common complications include: • Nonanatomic MPFL reconstruction (Figs. 9–11): The femoral and patellar fixation points of the graft are not anatomic, therefore altering the biomechanics of the graft. In addition, an overly constrained graft with resultant increased patellofemoral contact pressures may lead to accelerated degeneration of the patellofemoral articular cartilage, while undertensioning may lead to recurrent patellofemoral instability. • Patellar stress fracture (Fig. 12): Larger drill holes and holes that go into the center of the patella may act as stress risers and increase risk for postoperative patellar fracture. • Recurrent dislocation and instability (Figs. 13, 14): In postoperative clinical examinations, the patient may show apprehension, patellar hypermobility, or subluxation/dislocation. • Hardware failure or symptomatic hardware (Figs. 15, 16): Hardware failure can occur at either femoral or patellar attachment. Symptomatic hardware has been reported only at the femoral attachment. Hardware prominence usually becomes apparent once the postoperative soft tissue swelling resolves. • Patellofemoral chondrosis: The ultimate goal of MPFL reconstruction is to preserve patellofemoral articular cartilage. High-grade patellofemoral chondrosis on the other hand is a contraindication for MPFL reconstruction. Nonanatomic orientation of the graft and/or an overly tensioned graft may accelerate patellofemoral chondral degeneration. • Limited range of motion with extensor lag or limited flexion: This complication usually results from nonanatomic MPFL reconstruction or overly constrained graft and may require subsequent manipulation under anesthesia. • Wound complications and pain: These include subcutaneous hematoma, wound infections, wound dehiscence, and postoperative neuroma related to graft harvest. Significant postoperative pain may be due to symptomatic hardware, patellofemoral chondrosis, or persistent knee pain.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 8. A 23-year-old athletic trainer with recurrent patellofemoral instability. Lateral (a) and frontal (b) views of the knee after MPFL reconstruction show anatomic location of femoral tunnel (arrows) and patellar anchors (arrowheads). In this patient with patella alta and increased TTTG distance, tibial tubercle osteotomy for distalization and medialization was performed as well.
9. Conclusion As MPFL reconstruction is becoming a recommended procedure in some instances of recurrent patellar instability, the musculoskeletal radiologist should become familiar with optimal sites for graft anchoring and be aware of the imaging appearance of potential postreconstruction complications. Although some studies favor double-bundle MPFL reconstruction over single-bundle technique, long-term prospective outcome results are lacking. On radiographs, the method suggested by Schottle (Fig. 6) can be used to evaluate the position of the femoral tunnel. The patellar anchors should be within 1 cm of each other with the more inferior one at the equator of patella. The inferior bundle of graft should have a relatively horizontal course. On MRI, attachment of the adductor magnus can be used as reference point for the evaluation of femoral tunnel position.
References [1] 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. [2] Steensen RN, Dopirak RM, McDonald WG. The anatomy and isometry of the medial patellofemoral ligament: implications for reconstruction. Am J Sports Med 2004;32:1509–13. [3] Smirk C, Morris H. The anatomy and reconstruction of the medial patellofemoral ligament. Knee 2003;10:221–7. [4] Wijdicks CA, Griffith CJ, LaPrade RF, Johansen S, Sunderland A, Arendt EA, Engebretsen L. Radiographic identification of the primary medial knee structures. J Bone Joint Surg Am 2009;91:521–9. [5] Amis AA, Firer P, Mountney J, Senavongse W, Thomas NP. Anatomy and biomechanics of the medial patellofemoral ligament. Knee 2003;10:215–20 [Erratum in Knee 2004;11:73]. [6] Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med 2007;35:801–4. [7] Feller JA, Feagin JA, Garrett WE. The medial patellofemoral ligament revisited: an anatomical study. Knee Surg Sports Traumatol Arthrosc 1993;1:184–6. [8] Kang HJ, Wang F, Chen BC, Su YL, Zhang ZC, Yan CB. Functional bundles of the medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc 2010;18:1511–6. [9] Conlan T, Garth WP, Lemons JE. Evaluation of the medial soft-tissue restraints of the extensor mechanism of the knee. J Bone Joint Surg Am 1993;75:682–93.
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Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 9. A 16-year-old female with nonanatomic single-bundle MPFL reconstruction. Lateral (a) and frontal (b) radiographs show single patellar tunnel with anterior nonanatomic location of femoral tunnel (arrows). Axial proton density with fat saturation image (c) shows single-bundle MPFL graft fixed with single patellar and femoral interference screws. Note excessively anterior position of femoral tunnel.
Fig. 10. A 28-year-old research scholar with recurrent patellofemoral instability, patella alta, and trochlear groove–tibial tuberosity distance measuring 21 mm. Lateral (a) and frontal (b) views of the knee after MPFL reconstruction show anatomic location of patellar anchors (arrowheads). The femoral tunnel has been placed slightly too proximal (arrows). In this patient, due to patella alta and increased TTTG, a tibial tubercle osteotomy with distalization and medialization was performed as well.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 11. A 24-year-old female with nonanatomic MPFL reconstruction. Frontal (a) and lateral (b) plain film radiographs show distal and anterior location of femoral tunnel (arrowheads). The patellar suture anchors are proximal, resulting in oblique orientation of both graft bundles.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 12. An 18-year-old female with anatomic double-bundle MPFL reconstruction. Lateral (a) and frontal (b) radiographs show anatomic location of femoral tunnel (arrows) and patellar anchors (arrowheads). Note relative horizontal orientation of the inferior straight bundle. Two months later, the patient developed sudden pain and swelling when walking down steps not wearing her brace. Lateral radiograph (c), sagittal proton density (d), and coronal T1-weighted (e) images show acute transverse fracture of patella through stress riser at the distal anchor tract. Larger drill holes and holes that go into the center of the patella might act as stress risers and increase risk for postoperative patellar fracture. Sagittal proton density images (f, g) show anatomic location of femoral tunnel (arrowhead) just distal and anterior to adductor magnus insertion (arrow). Note intact low-signal-intensity MPFL graft fibers near the femoral tunnel.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 13. A 19-year-old female with recurrent dislocation 1 year after MPFL reconstruction. Axial (a) and sagittal (b) proton density fat-saturated images show large effusion. Discontinuity of the graft at its femoral attachment (arrow) is evident with effects of a recent patellar dislocation. Clinically, the graft was insufficient, and the patient was scheduled for revision.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 14. A 14-year-old male with recurrent instability and chronic patellar avulsion of MPFL. Patient continued to have persistent maltracking after MPFL reconstruction. Axial preoperative plain film radiograph (a) shows chronic patellar avulsion of MPFL (arrow) with small fracture fragments and heterotopic ossification. Postoperative axial spoiled gradient recalled echo sequence (b) through patellofemoral joint shows the more distal patellar anchor located in small medial fracture fragment (arrow). Coronal proton density (c) image shows patellar suture anchors (arrows) located in the small, incompletely united medial fracture fragment. Coronal and axial T2 fat-saturated (d, e) images show fluid equivalent signal between small bone fragments in which patellar anchors reside, and patella indicating incomplete healing of avulsion fragments and thus insufficient graft fixation on patellar side.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 15. An 18-year-old male 9 months post MPFL reconstruction with recurrent instability after an episode of dislocation. Axial T2 fat-saturated image (a) shows graft failure at the patellar attachment with back out of patellar anchors and posteromedial graft retraction (arrow). Femoral anchor position is relatively anterior. Coronal T1 and T2 fat-saturated images (b, c) show backed out patellar anchors (arrows) with posteromedially retracted patellar end of the graft at the level of the skin marker indicating the patient’s site of maximal pain.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 16. A 17-year-old male with symptomatic hardware and loosening 3 months after MPFL reconstruction. Frontal plain film radiograph (a) postoperatively shows minimally proud femoral interference screw (arrow). Three months later, radiograph (b), coronal proton density (c), and axial T2 fat-saturated (d) images show interference screw to be partially backed out of the femoral tunnel with adjacent inflammation (arrows). Sagittal proton density image (e) shows femoral tunnel located anatomically, just inferior to adductor magnus insertion (arrow).
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
Contents lists available at ScienceDirect
Clinical Imaging journal homepage: http://www.clinicalimaging.org
MRI evaluation and complications of medial patellofemoral ligament reconstruction Maha Torabi ⁎, Sean Wo, Dharmesh Vyas, Joanna Costello UPMC Department of Radiology, 200 Lothrop St., Pittsburgh, PA 15213
a r t i c l e
i n f o
Article history: Received 26 March 2014 Received in revised form 2 July 2014 Accepted 10 July 2014 Available online xxxx Keywords: Knee MRI Medial patellofemoral ligament reconstruction Recurrent patellar dislocation MPFL reconstruction Complication
a b s t r a c t Medial patellofemoral ligament (MPFL) reconstruction is a relatively new surgical technique for the treatment of recurrent patellar instability and dislocation. Radiologic findings following MPFL reconstruction are not well described in the existing literature. Here, we review the anatomy and biomechanics of the MPFL, review imaging findings following double-bundle MPFL reconstruction, and show examples of complications arising from reconstruction. © 2014 Elsevier Inc. All rights reserved.
1. Introduction Lateral patellar dislocation is a disabling condition that often results in medial patellofemoral ligament (MPFL) laxity, tear, or dysfunction. Recurrent patellar dislocation occurs in up to 44% of conservatively treated patients. Surgery may be required if conservative treatment fails. The ultimate goal is to restore stability and correct maltracking in order to preserve patellofemoral articular cartilage. Although numerous surgeries have been described for this condition, the concept of MPFL reconstruction is relatively new, and to our knowledge, the imaging findings following MPFL reconstruction have not yet been well described in the radiology literature. In this article, we review the anatomy and biomechanics of the MPFL, describe the double-bundle technique for MPFL reconstruction, and show examples of MPFL reconstruction and postoperative complications.
2. MPFL anatomy 2.1. Femoral insertion The MPFL is located in layer 2 of the medial aspect of the knee, between the crural fascia (layer 1) and the capsule of the knee joint (layer 3) [1–3]. The exact origin from the medial femoral epicondyle
⁎ Corresponding author. Wake Forest School of Medicine, One Medical Center Boulevard, Winston-Salem, NC 27157. E-mail address: [email protected] (M. Torabi).
remains controversial [2–7]. Studies suggest that it originates just proximal to the femoral attachment of the superficial medial collateral ligament and distal to the attachment of adductor magnus (Fig. 1). A study by Schottle et al. [6] has been used by orthopedic surgeons to identify a radiographic landmark for the anatomical femoral origin of the MPFL as shown in Fig. 2. The circle represents the mean site of femoral origin of the MPFL as documented in eight cadavers in this study and is outlined by: ‐ Line 1: posterior femoral cortex ‐ Line 2: perpendicular to line 1, intersecting the contact point of the medial condyle and the posterior cortex ‐ Line 3: perpendicular to line 1, intersecting the most posterior point of the Blumensaat line. Based on our experience, the adductor magnus attachment as seen on sagittal and axial magnetic resonance images can be used as reference landmark for evaluation of femoral tunnel location. The femoral tunnel should be slightly distal and anterior (within 5 mm) to the adductor tubercle [3]. 2.2. Patellar insertion The MPFL fans out towards its insertion upon the superior medial border of patella, with the patellar insertion being slightly wider than the femoral origin [5,8]. Two functional bundles of the MPFL functional have been described [8]: ‐ The inferior-straight bundle, which is the main static soft tissue restraint, attaching to the midaspect of the medial border of the patella.
http://dx.doi.org/10.1016/j.clinimag.2014.07.007 0899-7071/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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patellar suture anchor for the inferior bundle to be straight, and the patellar insertion of the superior-oblique bundle should be 10–12 mm proximal to the patellar insertion of the inferior-straight bundle. 3. Biomechanics The MPFL has been shown to be the most important ligamentous stabilizer preventing lateral dislocation, particularly in the first 30° of knee flexion, where the patella is most vulnerable due to lesser osseous engagement by the trochlea [7,9,10]. The MPFL is nonisometric and becomes tight in extension and lax in flexion (Fig. 3) [3,9,11]. In contrast to the MPFL, the lateral retinaculum is lax in extension and tightens in flexion [12,13]. 4. Patellofemoral instability treatment options [14–17]:
Fig. 1. MPFL anatomy. Femoral origin is just proximal to the femoral attachment of the superficial medial collateral ligament (MCL) and distal to the attachment of adductor magnus tendon (AMT).
‐ The superior-oblique bundle, which is associated with the vastus medialis oblique muscle and serves as the main dynamic soft tissue restraint. The patellar insertion of the superior-oblique bundle is 10– 12 mm proximal to the patellar insertion of the inferior-straight bundle. Knowledge of this anatomy can be used in the radiographic evaluation of the femoral and patellar fixation sites of the reconstructed MPFL intraoperatively and postoperatively. On the lateral extended radiograph of the knee, the femoral tunnel should be at the same level as the distal
• • • • • •
Nonoperative MPFL reconstruction Distal tibial tuberosity transfer Medial tibial tuberosity transfer Lateral retinacular release More extensive osteotomies including trochleoplasty, supracondylar femoral osteotomy, derotation femoral osteotomy, etc. Using a simplified approach, excluding more extensive osteotomies, the patients can be placed into four categories [18]: 1. Normal patellar height, normal tibial tuberosity trochlear groove (TTTG) distance: MPFL reconstruction. 2. Patella alta, normal TTTG distance: MPFL reconstruction and distal tibial tuberosity transfer. 3. Patella alta, increased TTTG distance: medial and distal tibial tuberosity transfer±MPFL reconstruction. 4. Normal patellar height, increased TTTG distance: medial tibial tuberosity transfer±lateral retinacular release.
5. MPFL reconstruction Various techniques and approaches have been described, including primary repair with or without augmentation, and reconstruction using autogenous tendon, allografts, and synthetic graft materials. MPFL reconstruction techniques include single- and double-bundle methods [19–22]. Graft choices include semitendinosus, gracilis, quadriceps tendon, and even synthetic grafts [23–26]. At our institution, double-bundle technique is commonly performed using either allograft or autograft. No clear data have been presented demonstrating the superiority of one surgical technique over another [27]. With both single- and double-bundle techniques, the surgery ideally will restore patellar position and stability. The goal is anatomic reconstruction to optimize patellofemoral stability throughout the range of motion, particularly in the first 30° of knee flexion where the patella is most vulnerable to dislocation. 6. Importance of femoral tunnel position
Fig. 2. Radiographic landmark (circle) for anatomical femoral origin of MPFL as suggested by Schottle (1: posterior femoral cortex, 2: perpendicular to line 1, intersecting the contact point of medial condyle and the posterior cortex, 3: perpendicular to line 1, intersecting the most posterior point of the Blumensaat line).
Placing the femoral tunnel too proximally on the medial epicondyle will result in a reconstructed MPFL that is lax in extension and tight in flexion; this may cause loss of knee flexion and excessive pressure resulting in chondral loss on the medial patellar facet [2,28,29] (Fig. 4). Conversely, placing the femoral origin MPFL reconstruction too distally on the medial epicondyle will result in an overly tight MPFL in extension and a lax ligament in flexion. This may result in an extensor lag, as the tension in the reconstructed ligament may be greater than in the patellar tendon when the quadriceps muscles are maximally contracted (Fig. 5).
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 3. MPFL biomechanics: The MPFL is nonisometric and becomes tight in extension (a) and lax in flexion (b).
Fig. 4. Proximal placement of femoral tunnel on the medial epicondyle, with graft being lax in extension (a) and tight in flexion (b). This may cause loss of knee flexion and excessive pressure resulting in chondral loss on the medial patellar facet.
Fig. 5. Distal placement of femoral tunnel on the medial epicondyle, with graft being overly tight in extension (a) and lax in flexion (b). This may result in an extensor lag.
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ative fluoroscopy as described by Schottle et al. (Fig. 6). While several techniques exist for graft fixation, surgeons at our institution prefer to fix the graft on the patella using two bioabsorbable suture anchors placed in the superior one half of the patella. On the femoral side, the graft is fixed with an interference screw within a bony tunnel (Figs. 7, 8). Final tensioning and fixation are done with the knee at 30° of flexion. The goal is to achieve lateral glides symmetric to the contralateral/unaffected side. Care is taken to not overconstrain the patella. 8. Complications of MPFL reconstruction
Fig. 6. Intraoperative fluoroscopy to establish the position of the femoral tunnel as recommended by Schottle.
7. Surgical technique for double-bundle MPFL reconstruction Incisions are made over the medial edge of the patella and the medial femoral epicondyle. Surgical exposure is done to tunnel between fascial layers 2 and 3 of the medial knee. The MPFL graft (either autograft or allograft) is passed between these layers and secured on the patella and femur for ligament reconstruction. The tunnel position is verified on a perfect lateral X-ray using intraoper-
Fig. 7. Double-bundle anatomic MPFL reconstruction with interference screw used for fixation of the femoral side and suture anchors for the patellar side.
A meta-analysis review of literature [20] has shown a relatively high rate of success with a total of 164 complications in 629 knees (26.1%). Given the numerous surgical techniques for MPFL reconstruction, with variability of graft choice, patellar fixation, femoral fixation, graft tensioning, and angle of knee flexion at the time of fixation, there is a paucity of information regarding the relative advantages, disadvantages, success rates, and complication rates of one versus another surgical approach. Further high-level studies reviewing the differing techniques and analyzing the relative longterm clinical benefits and complications are needed to better understand the overall efficacy of MPFL reconstruction. It is important to define failure versus success based on clinical, imaging, and patientreported outcome parameters. A normal graft on magnetic resonance imaging (MRI) should demonstrate low signal intensity on T1- and T2-weighted images and appear continuous, taut, anatomically oriented, and anchored, without associated imaging stigmata of hardware- or wound-related complications. The patellar anchors should be within 1 cm of each other with the more inferior one at the equator of patella such that the inferior bundle of graft has a relatively horizontal or true axial orientation. The femoral tunnel should be just distal to the attachment of the adductor magnus. The most common complications include: • Nonanatomic MPFL reconstruction (Figs. 9–11): The femoral and patellar fixation points of the graft are not anatomic, therefore altering the biomechanics of the graft. In addition, an overly constrained graft with resultant increased patellofemoral contact pressures may lead to accelerated degeneration of the patellofemoral articular cartilage, while undertensioning may lead to recurrent patellofemoral instability. • Patellar stress fracture (Fig. 12): Larger drill holes and holes that go into the center of the patella may act as stress risers and increase risk for postoperative patellar fracture. • Recurrent dislocation and instability (Figs. 13, 14): In postoperative clinical examinations, the patient may show apprehension, patellar hypermobility, or subluxation/dislocation. • Hardware failure or symptomatic hardware (Figs. 15, 16): Hardware failure can occur at either femoral or patellar attachment. Symptomatic hardware has been reported only at the femoral attachment. Hardware prominence usually becomes apparent once the postoperative soft tissue swelling resolves. • Patellofemoral chondrosis: The ultimate goal of MPFL reconstruction is to preserve patellofemoral articular cartilage. High-grade patellofemoral chondrosis on the other hand is a contraindication for MPFL reconstruction. Nonanatomic orientation of the graft and/or an overly tensioned graft may accelerate patellofemoral chondral degeneration. • Limited range of motion with extensor lag or limited flexion: This complication usually results from nonanatomic MPFL reconstruction or overly constrained graft and may require subsequent manipulation under anesthesia. • Wound complications and pain: These include subcutaneous hematoma, wound infections, wound dehiscence, and postoperative neuroma related to graft harvest. Significant postoperative pain may be due to symptomatic hardware, patellofemoral chondrosis, or persistent knee pain.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 8. A 23-year-old athletic trainer with recurrent patellofemoral instability. Lateral (a) and frontal (b) views of the knee after MPFL reconstruction show anatomic location of femoral tunnel (arrows) and patellar anchors (arrowheads). In this patient with patella alta and increased TTTG distance, tibial tubercle osteotomy for distalization and medialization was performed as well.
9. Conclusion As MPFL reconstruction is becoming a recommended procedure in some instances of recurrent patellar instability, the musculoskeletal radiologist should become familiar with optimal sites for graft anchoring and be aware of the imaging appearance of potential postreconstruction complications. Although some studies favor double-bundle MPFL reconstruction over single-bundle technique, long-term prospective outcome results are lacking. On radiographs, the method suggested by Schottle (Fig. 6) can be used to evaluate the position of the femoral tunnel. The patellar anchors should be within 1 cm of each other with the more inferior one at the equator of patella. The inferior bundle of graft should have a relatively horizontal course. On MRI, attachment of the adductor magnus can be used as reference point for the evaluation of femoral tunnel position.
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[10] Hautamaa PV, Fithian DC, Kaufman KR, Daniel DM, Pohlmeyer AM. Medial soft tissue restraints in lateral patellar instability and repair. Clin Orthop Relat Res 1998;349:174–82. [11] Thaunat M, Erasmus PJ. The favourable anisometry: an original concept for medial patellofemoral ligament reconstruction. Knee 2007;14:424–8. [12] Luo ZP, Sakai N, Rand JA, An KN. Tensile stress of the lateral patellofemoral ligament during knee motion. Am J Knee Surg 1997;10:139–44. [13] Ishibashi Y, Okamura Y, Otsuka H, Tsuda E, Toh S. Lateral patellar retinaculum tension in patellar instability. Clin Orthop Relat Res 2002;397:362–9. [14] Cash JD, Hughston JC. Treatment of acute patellar dislocation. Am J Sports Med 1988;16:244–9. [15] Cofield RH, Bryan RS. Acute dislocation of the patella: results of conservative treatment. J Trauma 1977;17:526–31. [16] Hawkins RJ, Bell RH, Anisette G. Acute patellar dislocations: the natural history. Am J Sports Med 1986;14:117–20. [17] Mäenpää H, Lehto MU. Patellar dislocation: the long-term results of nonoperative management in 100 patients. Am J Sports Med 1997;25:213–7. [18] Colvin AC, West RV. Current concepts review: patellar instability. J Bone Joint Surg Am 2008;90:2751–62. [19] Schöttle PB, Hensler D, Imhoff AB. Anatomical double-bundle MPFL reconstruction with an aperture fixation. Knee Surg Sports Traumatol Arthrosc 2010;18:147–51. [20] Shah JN, Howard JS, Flanigan DC, Brophy RH, Carey JL, Lattermann C. A systematic review of complications and failures associated with medial patellofemoral ligament reconstruction for recurrent patellar dislocation. Am J Sports Med 2012;40:1916–23. [21] Kang H, Cao J, Yu D, Zheng Z, Wang F. Comparison of 2 different techniques for anatomic reconstruction of the medial patellofemoral ligament: a prospective randomized study. Am J Sports Med 2013;41:1013–21. [22] Wang CH, Ma LF, Zhou JW, Ji G, Wang HY, Wang F, Wang J. Double-bundle anatomical versus single-bundle isometric medial patellofemoral ligament reconstruction for patellar dislocation. Int Orthop 2013;37:617–24. [23] Schock EJ, Burks RT. Medial patellofemoral ligament reconstruction using a hamstring graft. Oper Tech Sports Med 2001;9:169–75. [24] Burks RT, Luker MG. Medial patellofemoral ligament reconstruction. Tech Orthop 1997;12:185–91. [25] Chassaing V, Tremoulet J. Medial patellofemoral ligament reconstruction with gracilis autograft for patellar instability. Rev Chir Orthop Reparatrice Appar Mot 2005;9194:335–40. [26] Nomura E, Inoue M, Suqiura H. Ultrastructural study of the extra-articular LeedsKeio ligament prosthesis. J Clin Pathol 2005;58:665–6. [27] LeGrand AB, Greis PE, Dobbs RE, Burks RT. MPFL reconstruction. Sports Med Arthrosc 2007;15(2):72–7. [28] Elias JJ, Cosqarea AJ. Technical errors during medial patellofemoral ligament reconstruction could overload medial patellofemoral cartilage: a computational analysis. Am J Sports Med 2006;34:1478–85. [29] Stephen JM, Kaider D, Lumpaopong P, Deehan DJ, Amis AA. The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction. Am J Sports Med 2014;42:364–72.
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Fig. 9. A 16-year-old female with nonanatomic single-bundle MPFL reconstruction. Lateral (a) and frontal (b) radiographs show single patellar tunnel with anterior nonanatomic location of femoral tunnel (arrows). Axial proton density with fat saturation image (c) shows single-bundle MPFL graft fixed with single patellar and femoral interference screws. Note excessively anterior position of femoral tunnel.
Fig. 10. A 28-year-old research scholar with recurrent patellofemoral instability, patella alta, and trochlear groove–tibial tuberosity distance measuring 21 mm. Lateral (a) and frontal (b) views of the knee after MPFL reconstruction show anatomic location of patellar anchors (arrowheads). The femoral tunnel has been placed slightly too proximal (arrows). In this patient, due to patella alta and increased TTTG, a tibial tubercle osteotomy with distalization and medialization was performed as well.
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
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Fig. 11. A 24-year-old female with nonanatomic MPFL reconstruction. Frontal (a) and lateral (b) plain film radiographs show distal and anterior location of femoral tunnel (arrowheads). The patellar suture anchors are proximal, resulting in oblique orientation of both graft bundles.
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Fig. 12. An 18-year-old female with anatomic double-bundle MPFL reconstruction. Lateral (a) and frontal (b) radiographs show anatomic location of femoral tunnel (arrows) and patellar anchors (arrowheads). Note relative horizontal orientation of the inferior straight bundle. Two months later, the patient developed sudden pain and swelling when walking down steps not wearing her brace. Lateral radiograph (c), sagittal proton density (d), and coronal T1-weighted (e) images show acute transverse fracture of patella through stress riser at the distal anchor tract. Larger drill holes and holes that go into the center of the patella might act as stress risers and increase risk for postoperative patellar fracture. Sagittal proton density images (f, g) show anatomic location of femoral tunnel (arrowhead) just distal and anterior to adductor magnus insertion (arrow). Note intact low-signal-intensity MPFL graft fibers near the femoral tunnel.
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Fig. 13. A 19-year-old female with recurrent dislocation 1 year after MPFL reconstruction. Axial (a) and sagittal (b) proton density fat-saturated images show large effusion. Discontinuity of the graft at its femoral attachment (arrow) is evident with effects of a recent patellar dislocation. Clinically, the graft was insufficient, and the patient was scheduled for revision.
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Fig. 14. A 14-year-old male with recurrent instability and chronic patellar avulsion of MPFL. Patient continued to have persistent maltracking after MPFL reconstruction. Axial preoperative plain film radiograph (a) shows chronic patellar avulsion of MPFL (arrow) with small fracture fragments and heterotopic ossification. Postoperative axial spoiled gradient recalled echo sequence (b) through patellofemoral joint shows the more distal patellar anchor located in small medial fracture fragment (arrow). Coronal proton density (c) image shows patellar suture anchors (arrows) located in the small, incompletely united medial fracture fragment. Coronal and axial T2 fat-saturated (d, e) images show fluid equivalent signal between small bone fragments in which patellar anchors reside, and patella indicating incomplete healing of avulsion fragments and thus insufficient graft fixation on patellar side.
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Fig. 15. An 18-year-old male 9 months post MPFL reconstruction with recurrent instability after an episode of dislocation. Axial T2 fat-saturated image (a) shows graft failure at the patellar attachment with back out of patellar anchors and posteromedial graft retraction (arrow). Femoral anchor position is relatively anterior. Coronal T1 and T2 fat-saturated images (b, c) show backed out patellar anchors (arrows) with posteromedially retracted patellar end of the graft at the level of the skin marker indicating the patient’s site of maximal pain.
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Fig. 16. A 17-year-old male with symptomatic hardware and loosening 3 months after MPFL reconstruction. Frontal plain film radiograph (a) postoperatively shows minimally proud femoral interference screw (arrow). Three months later, radiograph (b), coronal proton density (c), and axial T2 fat-saturated (d) images show interference screw to be partially backed out of the femoral tunnel with adjacent inflammation (arrows). Sagittal proton density image (e) shows femoral tunnel located anatomically, just inferior to adductor magnus insertion (arrow).
Please cite this article as: Torabi M, et al, MRI evaluation and complications of medial patellofemoral ligament reconstruction, Clin Imaging (2014), http://dx.doi.org/10.1016/j.clinimag.2014.07.007
