Knee Surg Sports Traumatol Arthrosc (2014) 22:2414–2418 DOI 10.1007/s00167-014-3174-3
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Medial patellofemoral ligament avulsion injury at the patella: classification and clinical outcome Petri J. Sillanpää · Essi Salonen · Harri Pihlajamäki · Heikki M. Mäenpää
Received: 26 November 2013 / Accepted: 7 July 2014 / Published online: 25 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose To define medial patellofemoral ligament (MPFL) injury characteristics at the patellar attachment and clinical outcome in patients with primary traumatic patellar dislocation and MPFL avulsion injury at the patella. Methods Magnetic resonance imaging (MRI) was used to assess patients with primary (first-time) patellar dislocation and MPFL injury at the medial margin of the patella. Fiftysix patients with patellar attachment MPFL injury were enrolled in the study. Thirteen patients underwent surgical fixation of the avulsed MPFL and patellar medial margin osteochondral fracture, and the remaining patellar MPFL injures were treated nonoperatively. Forty-four patients were evaluated clinically at median four (range 1–10) years after patellar dislocation. The follow-up included evaluation of recurrent patellar instability, subjective symptoms, and functional limitations. Results Three types of patellar MPFL injuries were found; type P0 with ligamentous disruption at the patellar attachment, type P1 with bony avulsion fracture from the medial margin of the patella, and type P2 with bony avulsion involving articular cartilage from the medial facet of the patella. Of the patellar MPFL avulsion injuries that underwent initial surgical fixation, two patients (2/13) reported an unstable patella at follow-up. Fifty-five per cent (17/31) of patellar MPFL avulsion injuries that were treated nonoperatively had recurrent patellar instability (n.s.). The P. J. Sillanpää (*) · E. Salonen · H. M. Mäenpää Department of Orthopaedic Surgery and Trauma, Tampere University Hospital, Teiskontie 35, 33521 Tampere, Finland e-mail: [email protected] H. Pihlajamäki Department of Orthopaedic Surgery, Seinajoki Central Hospital, Seinajoki, Finland
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median Kujala score was 90 for patellar avulsion with surgical fixation and 86 for patellar avulsion without surgical fixation (n.s.). Conclusion Patellar attachment MPFL injury showed three different patterns, classified as types P0, P1, and P2. MRI can be used to assess the injury pattern. Patellar MPFL avulsion injuries do not benefit from acute surgical repair compared with nonsurgical treatment. Type P2 patellar MPFL avulsion includes an osteochondral fracture that may require surgical fixation. Level of evidence Prognostic study, Level III. Keywords Medial patellofemoral ligament · Medial patellofemoral ligament reconstruction · Patella · Dislocation · Magnetic resonance imaging
Introduction Medial patellofemoral ligament (MPFL) acts as the major ligamentous restraint against lateral patellar dislocation [1, 2, 4, 6, 10, 19]. MPFL is frequently injured in acute patellar dislocation, and primary (first-time) traumatic patellar dislocation results in total or partial MPFL disruption [7, 13, 19]. MPFL injury can be diagnosed using magnetic resonance imaging (MRI) [7]. MPFL injuries have been classified into three categories based on location: at the level of the MPFL patellar insertion, at the midsubstance, and at the femoral origin of the MPFL [7, 16, 18]. The proportion of MPFL patellar attachment injury of all MPFL injuries has varied between 13 and 76 % [7, 9, 11, 20, 26, 27]. MPFL patellar attachment injury can have various characteristics seen in MRI, including bony fragments from medial patellar margo or soft tissue disruptions of MPFL fibres near the patellar attachment. A patellar
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attachment MPFL injury may include an osteochondral avulsion fracture of the medial patellar margin, although rarely described in the literature [25]. The precise injury characteristics and clinical outcome for patellar MPFL avulsion fracture have not been described in the literature, to our knowledge. The aim of the present study was to define MPFL patellar attachment injury characteristics and the clinical outcome in patients with MPFL patellar insertion avulsion treated either surgically or conservatively. It was hypothesised that a patellar MPFL avulsion with an osteochondral fracture leads to subsequent patellar instability if the avulsion fracture is not initially fixated. The main outcome measure was subsequent patellar redislocation, and secondary measures were functional outcome (subluxations, pain).
Materials and methods The main inclusion criterion for the present study was primary traumatic patellar dislocation with patellar attachment MPFL injury as determined by MRI (within 21 days from the injury). The MRIs from a prospectively collected primary traumatic patellar dislocation cohort in the study hospital were reviewed to identify patients with MPFL injury at the patellar attachment. To define the MPFL injury location, the MRIs were independently reviewed by two musculoskeletal radiologists not involved in the treatment and blinded to the original interpretation of the images. The radiologists were also blinded to each other’s interpretations and, in case of discrepancy, the images were reviewed to reach consensus. A 1.5-Tesla MRI Siemens Magnetom Avanto scanner was used (Erlangen, Germany). The MRI sequences were coronal and axial T2-weighted and proton density-weighted in combination with fat saturation, and sagittal T2-weighted and proton density-weighted. Slice thickness was 3 mm, with a 0.5- or 1.0-mm intersection gap. Characterisation of the MPFL injury and study participants The MPFL injury location was assessed on both coronal and sagittal images, and first categorised based on the three locations described by Elias et al. [7]: MPFL injury at the level of patellar attachment, at the midsubstance (and medial retinaculum), and at the femoral origin. Midsubstance and femoral MPFL injuries were excluded from the study. We defined patellar MPFL avulsion injury as an osteochondral fracture involving variable-sized fragments displaced from the medial patellar margin (MPFL patellar insertion; Fig. 1) and the ligamentous fibres of the medial conjoined fascial tissue (including the MPFL) had to be continuously attached to the fragment(s) (Fig. 2). Patients
Fig. 1 Medial patellofemoral ligament (MPFL) injury with osteochondral avulsion fracture. A transverse T2-FSE MR image of the knee obtained at the level of the MPFL patellar insertion shows complete avulsion of the medial patellofemoral ligament from its patellar insertion, with articular surface involvement (arrow)
Fig. 2 Medial patellofemoral ligament (MPFL) injury with small avulsion fracture. A transverse T2-FSE MR image of the knee obtained at the level of the MPFL patellar insertion shows complete avulsion of the medial patellofemoral ligament from its patellar insertion arrow
with patellar MPFL avulsion with combined femoral or midsubstance MPFL disruption were excluded from the study. MRI was also used to exclude additional injuries in the knee and to assess patellofemoral joint anatomy, including trochlear dysplasia [5, 22]. As the purpose of this study was to investigate the clinical outcome of patients with patellar MPFL avulsion injury, we excluded patients who underwent any additional
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surgical procedures (MPFL reconstruction) other than avulsion fragment fixation, as described later. The medical records were carefully reviewed to confirm the primary nature of the patellar dislocation. An orthopaedic surgeon performed a patient interview and clinical examination within 21 days from the injury to all study participants. Excluded was anyone with prior patellar instability or additional knee injuries. After careful review of MRIs and the medical records, 56 patients were enrolled. Twelve patients (two patients from the surgical group and ten patients from the nonoperative group) were lost to follow-up (could not be reached or refused to participate).
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Statistical methods The Kruskal–Wallis test was used to test differences in the nonparametric ordinal data, and the independent samples t test was used for continuous, normally distributed data in the tests between the injury locations. Differences in the two-way tables were determined with the Pearson chi-square test or Fisher exact test when appropriate. Significance was set at P ≤ 0.05. SPSS 19.0 statistical package was used for statistical calculations.
Results Surgical technique Patient characteristics In 13 patients, who had a significant (>10 mm) articular cartilage involvement (Fragment Fixation group), initial surgical fixation of the avulsed patellar medial margin osteochondral fracture was performed. Under the subcutaneous fatty tissue, the conjoined fascial layer and the MPFL near the medial patella were identified. Reduction of the avulsion fracture was performed with internal fixation with number one polydioxanone suture through bone tunnels (first six cases) or with 3.5-mm suture anchor (Twin-Fix, Smith and Nephew, Andover, MA; latter seven cases). If patellar articular cartilage surface was significantly involved, the articulating osteochondral fragment was fixated with bioabsorbable pins (SmartNail, ConMed Linvatec, Largo, FL, or ActivaPin, Bioretec, Tampere, Finland). The remaining 31 patients (No Fragment Fixation group) with patellar avulsion fracture without significant articular cartilage involvement underwent nonsurgical treatment. The rehabilitation protocol was identical for all of the patients. Immediate straight-leg standing exercises were allowed, but weight bearing with a flexed knee was restricted and crutches were used for 4 weeks. The rehabilitation period included muscle strengthening with combined open and closed chain exercises supervised by a physiotherapist and full activity was allowed at 3 months. Follow‑up protocol Follow-up included assessment of patellar redislocation and functional outcomes. Kujala score [12], a 100-mm visual analogue scale, and Tegner scale [23] were used. An independent physician not involved with the surgery or conservative treatment clinically evaluated patients. Patients were asked whether they had regained their preinjury level of activity by follow-up. Institutional Review Board (IRB) approval was obtained from the study hospital (IRB#R9N071), and written consent was obtained from all patients enrolled in the follow-up study.
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The majority of the patients were men (44/56) with a median age of 23 years (range 15–31 years) at the time of injury. All of the patients were skeletally mature and injury mechanism was sports related. Of the 56 subjects, 44 participated in the median 4-year follow-up (range 1–10 years). Radiographic characteristics Three patterns of patellar attachment MPFL injuries were found (Fig. 3). Two of the types included osteochondral avulsion fractures, classified as type P2: articular cartilage involvement (medial patellar facet articular surface; Fig. 3) and type P1: without articular cartilage involvement (only bone from medial patellar margo; Fig. 3). The third type of patellar MPFL injury was classified as type P0 and was previously described as patellar insertion MPFL disruption without bony involvement [7]. Trochlear shape was classified as grade A dysplasia in 25/44 patients, grade B dysplasia in 7/44 patients, and normal in 12 patients. Nearly even distribution was seen in patients with grade of trochlear dysplasia regarding the MPFL P1 [14 (32 %) grade A, 5 (11 %) grade B] and P2 [11 (25 %) grade A, 2 (5 %) grade B] injury types. Follow-up radiographs of patients in No Fragment Fixation group frequently (in 24/31 patients) showed medial patellar ossicles. Six patients in the No Fragment Fixation group underwent subsequent arthroscopic removal of loose body fragment(s) (symptomatic during follow-up period). Ossicles were rare (in 2/13 patients) in Fragment Fixation group. Clinical outcome Among patients in Fragment Fixation group, two of the 13 reported recurrent patellar dislocation. Among patients in No Fragment Fixation group, recurrent patellar dislocation occurred in 17 of 31 cases (n.s.).
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Fig. 3 Three types of patellar MPFL injuries; a type P0 with ligamentous disruption at the patellar attachment, b type P1 with bony avulsion fracture from the medial margin of the patella, and c type P2 with bony avulsion involving articular cartilage from the medial facet of the patella
Preinjury activity level was regained in 71 % of Fragment Fixation group and in 55 % of No Fragment Fixation group (n.s.). The median Kujala score was 90 for patients in Fragment Fixation group and 86 for patients in No Fragment Fixation group, respectively (n.s.). The median follow-up Tegner activity scores were 6 for patients in Fragment Fixation group (range 4–7), and 5 for patients in No Fragment Fixation group (range 4–7) (n.s.).
Discussion The most important finding of the present study was that patellar MPFL avulsion in primary traumatic patellar dislocation does not benefit from acute surgical repair compared to nonsurgical treatment. There were no statistically significant differences in the redislocation rate or subjective scores between the surgical and nonsurgical study groups. Patellar insertion MPFL injuries can be classified into three categories: type P0 with ligamentous disruption, type P1 with bony avulsion fragment, and type P2 with bony avulsion involving articular cartilage surface from the medial facet of the patella. Patellar MPFL avulsion injury is associated with a relatively high rate of subsequent patellar dislocation. Patellar MPFL avulsion injury comprised two different types of osteochondral avulsion fractures: those with articular cartilage involvement (medial patellar facet articular surface) and those without articular cartilage involvement (only bone from medial patellar margin). In chronic instability cases, medial patellar ossicles can occasionally be observed as a sign of previous patellar MPFL avulsion fracture. Based on previous studies, between 40 and 90 % of MPFL disruptions are located in the femoral attachment [9, 20], whereas some studies have reported figures up to 50 to 60 % at the patellar insertion [7, 11, 26, 27]. The MPFL
midsubstance region seems to be less frequently affected [10, 20]. Although more than one MPFL injury location can sometimes be seen in MRI, total disruption is usually at one of the locations described above. Previous randomised studies of primary patellar dislocations concluded that surgery was not systemically superior to nonsurgical treatment if all the patients with different types of MPFL injuries were treated similarly [15, 17, 19]. Although, a recent prospective randomised study in which nonsurgical treatment was compared to surgical reinsertion in either femoral or patellar attachment, surgery resulted in better stability than nonoperative treatment [3]. Due to the significance, 44 to 70 % redislocation rate after primary dislocation reported in the literature, some cases might benefit from initial surgery, and surgery should definitely be considered for patients with a high risk of failure after nonsurgical treatment. Based on a previous study, ruptures at the MPFL midsubstance or patellar insertion regions without an osteochondral avulsion fragment are generally not related to significant subsequent patellar instability [20]. We therefore may suggest that a rupture of the MPFL at its midsubstance or near the patellar attachment should be treated nonsurgically. Patients with significant patellar MPFL avulsion fracture and femoral attachment MPFL disruption may be at greater risk [20]. This study was limited by its retrospective nature. In addition, surgical fixation was performed in the first six patients using sutures and in latter seven cases by suture anchors. The Fragment Fixation group included patients with significant articular cartilage involvement, whereas the No Fragment Fixation group consisted of patients without significant cartilage lesions. Therefore, patients in the Fragment Fixation group can be considered as having had more severe injury as those in No Fragment Fixation group. If the fracture involved large fragments acting as loose bodies and produced symptoms, subsequent arthroscopic removal of the
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fragment(s) was performed (in six patients). The follow-up was most likely too short to evaluate differences in development of osteoarthritic characteristics of the patellofemoral joint between the study groups. In addition to MPFL injury location, various factors may affect the clinical outcome of primary patellar dislocation. The well-known anatomical factors, such as trochlear dysplasia, and patella alta [5, 8, 10, 24] can predispose a patient to recurrent patellar instability, regardless of MPFL injury location. Most likely, the more dysplastic the trochlear shape, the more devastating an injury to the MPFL is to patellar stability. In this study, trochlear dysplasia was frequently seen, but similarly in patients with different types of patellar attachment MPFL injuries. Based on the results from this study, MPFL patellar attachment avulsion injury in young adult population with high level of physical activity results recurrent dislocation in up to half of the cases, indicating same rate that in the previous patellar dislocation study populations [14, 15, 17, 21].
Conclusion In patients with primary patellar dislocation, patellar attachment MPFL injury showed three different patterns, classified as types P0, P1, and P2. MRI is recommended to assess the injury pattern. Patellar attachment MPFL avulsion injury did not benefit from initial surgical repair. Surgery can be considered for P2 cases with significant articular surface involvement, with the aim to restore cartilage integrity.
References 1. Avikainen VJ, Nikku RK, Seppänen-Lehmonen TK (1993) Adductor magnus tenodesis for patellar dislocation. Technique and preliminary results. Clin Orthop Relat Res 297:12–16 2. Burks RT, Desio SM, Bachus KN, Tyson L, Springer K (1998) Biomechanical evaluation of lateral patellar dislocations. Am J Knee Surg 11(1):24–31 3. Camanho GL, Viegas Ade C, Bitar AC, Demange MK, Hernandez AJ (2009) Conservative versus surgical treatment for repair of the medial patellofemoral ligament in acute dislocations of the patella. Arthroscopy 25(6):620–625 4. Conlan T, Garth WP Jr, Lemons JE (1993) Evaluation of the medial soft-tissue restraints of the extensor mechanism of the knee. J Bone Joint Surg Am 75(5):682–693 5. Dejour H, Walch G, Nove-Josserand L, Guier C (1994) Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 2(1):19–26 6. Desio SM, Burks RT, Bachus KN (1998) Soft tissue restraints to lateral patellar translation in the human knee. Am J Sports Med 26(1):59–65 7. Elias DA, White LM, Fithian DC (2002) Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology 225(3):736–743
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Knee Surg Sports Traumatol Arthrosc (2014) 22:2414–2418 8. Fucentese SF, von Roll A, Koch PP, Epari DR, Fuchs B, Schottle PB (2006) The patella morphology in trochlear dysplasia—a comparative MRI study. Knee 13:145–150 9. Guerrero P, Li X, Patel K, Brown M, Busconi B (2009) Medial patellofemoral ligament injury patterns and associated pathology in lateral patella dislocation: an MRI study. Sports Med Arthrosc Rehabil Ther Technol 1:17 10. Hensler D, Sillanpää PJ, Schoettle PB (2014) Medial patellofemoral ligament: anatomy, injury and treatment in the adolescent knee. Curr Opin Pediatr. doi:10.1097/MOP.0000000000000055 11. Kepler CK, Bogner EA, Hammoud S, Malcolmson G, Potter HG, Green DW (2011) Zone of injury of the medial patellofemoral ligament after acute patellar dislocation in children and adolescents. Am J Sports Med 39:1444–1449 12. Kujala UM, Jaakkola LH, Koskinen SK, Taimela S, Hurme M, Nelimarkka O (1993) Scoring of patellofemoral disorders. Arthroscopy 9(2):159–163 13. LaPrade RF, Engebretsen AH, Ly TV, Johansen S, Wentorf FA, Engebretsen L (2007) The anatomy of the medial part of the knee. J Bone Joint Surg Am 89(9):2000–2010 14. Matic GT, Magnussen RA, Kolovich GP, Flanigan DC (2014) Return to activity after medial patellofemoral ligament repair or reconstruction. Arthroscop. doi:10.1016/j.arthro.2014.02.044 15. Nikku R, Nietosvaara Y, Aalto K, Kallio PE (2005) Opera tive treatment of primary patellar dislocation does not improve medium-term outcome: a 7-year follow-up report and risk analysis of 127 randomized patients. Acta Orthop 76(5):699–704 16. Nomura E (1999) Classification of lesions of the medial patello-femoral ligament in patellar dislocation. Int Orthop 23(5):260–263 17. Palmu S, Kallio PE, Donell ST, Helenius I, Nietosvaara Y (2008) Acute patellar dislocation in children and adolescents: a randomized clinical trial. J Bone Joint Surg Am 90(3):463–470 18. Sillanpaa PJ, Maenpaa H, Mattila VM, Visuri T, Pihlajamaki H (2008) Arthroscopic surgery for primary traumatic patellar dislocation: a prospective, nonrandomized study comparing patients treated with and without acute arthroscopic stabilization with a median 7-year follow-up. Am J Sports Med 36(12):2301–2319 19. Sillanpaa PJ, Mattila VM, Maenpaa H, Kiuru M, Visuri T, Pihlajamaki H (2009) Treatment with and without initial stabilizing surgery for primary traumatic patellar dislocation. A prospective randomized study. J Bone Joint Surg Am 91(2):263–273 20. Sillanpaa PJ, Peltola E, Mattila VM, Kiuru M, Visuri T, Pihlajamaki H (2009) Femoral avulsion of the medial patellofemoral ligament after primary traumatic patellar dislocation predicts subsequent instability in men: a mean 7-year nonoperative follow- up study. Am J Sports Med 37(8):1513–1521 21. Stefancin JJ, Parker RD (2007) First-time traumatic patellar dislocation: a systematic review. Clin Orthop Relat Res 455:93–101 22. Tecklenburg K, Dejour D, Hoser C, Fink C (2006) Bony and cartilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc 14:235–240 23. Tegner Y, Lysholm J (1985) Rating systems in the evaluation of knee ligament injuries. Clin Orthop Relat Res 198:43–49 24. Teitge RA (2008) Patellofemoral syndrome a paradigm for current surgical strategies. Orthop Clin North Am 39(3):287–311 25. Vainionpää S, Laasonen E, Silvennoinen T, Vasenius J, Rokkanen P (1990) Acute dislocation of the patella. A prospective review of operative treatment. J Bone Joint Surg Br 72(3):366–369 26. Weber-Spickschen TS, Spang J, Kohn L, Imhoff AB, Schottle PB (2011) The relationship between trochlear dysplasia and medial patellofemoral ligament rupture location after patellar dislocation: an MRI evaluation. Knee 18(3):185–188 27. Zaidi A, Babyn P, Astori I, White L, Doria A, Cole W (2006) MRI of traumatic patellar dislocation in children. Pediatr Radiol 36(11):1163–1170
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Medial patellofemoral ligament avulsion injury at the patella: classification and clinical outcome Petri J. Sillanpää · Essi Salonen · Harri Pihlajamäki · Heikki M. Mäenpää
Received: 26 November 2013 / Accepted: 7 July 2014 / Published online: 25 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose To define medial patellofemoral ligament (MPFL) injury characteristics at the patellar attachment and clinical outcome in patients with primary traumatic patellar dislocation and MPFL avulsion injury at the patella. Methods Magnetic resonance imaging (MRI) was used to assess patients with primary (first-time) patellar dislocation and MPFL injury at the medial margin of the patella. Fiftysix patients with patellar attachment MPFL injury were enrolled in the study. Thirteen patients underwent surgical fixation of the avulsed MPFL and patellar medial margin osteochondral fracture, and the remaining patellar MPFL injures were treated nonoperatively. Forty-four patients were evaluated clinically at median four (range 1–10) years after patellar dislocation. The follow-up included evaluation of recurrent patellar instability, subjective symptoms, and functional limitations. Results Three types of patellar MPFL injuries were found; type P0 with ligamentous disruption at the patellar attachment, type P1 with bony avulsion fracture from the medial margin of the patella, and type P2 with bony avulsion involving articular cartilage from the medial facet of the patella. Of the patellar MPFL avulsion injuries that underwent initial surgical fixation, two patients (2/13) reported an unstable patella at follow-up. Fifty-five per cent (17/31) of patellar MPFL avulsion injuries that were treated nonoperatively had recurrent patellar instability (n.s.). The P. J. Sillanpää (*) · E. Salonen · H. M. Mäenpää Department of Orthopaedic Surgery and Trauma, Tampere University Hospital, Teiskontie 35, 33521 Tampere, Finland e-mail: [email protected] H. Pihlajamäki Department of Orthopaedic Surgery, Seinajoki Central Hospital, Seinajoki, Finland
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median Kujala score was 90 for patellar avulsion with surgical fixation and 86 for patellar avulsion without surgical fixation (n.s.). Conclusion Patellar attachment MPFL injury showed three different patterns, classified as types P0, P1, and P2. MRI can be used to assess the injury pattern. Patellar MPFL avulsion injuries do not benefit from acute surgical repair compared with nonsurgical treatment. Type P2 patellar MPFL avulsion includes an osteochondral fracture that may require surgical fixation. Level of evidence Prognostic study, Level III. Keywords Medial patellofemoral ligament · Medial patellofemoral ligament reconstruction · Patella · Dislocation · Magnetic resonance imaging
Introduction Medial patellofemoral ligament (MPFL) acts as the major ligamentous restraint against lateral patellar dislocation [1, 2, 4, 6, 10, 19]. MPFL is frequently injured in acute patellar dislocation, and primary (first-time) traumatic patellar dislocation results in total or partial MPFL disruption [7, 13, 19]. MPFL injury can be diagnosed using magnetic resonance imaging (MRI) [7]. MPFL injuries have been classified into three categories based on location: at the level of the MPFL patellar insertion, at the midsubstance, and at the femoral origin of the MPFL [7, 16, 18]. The proportion of MPFL patellar attachment injury of all MPFL injuries has varied between 13 and 76 % [7, 9, 11, 20, 26, 27]. MPFL patellar attachment injury can have various characteristics seen in MRI, including bony fragments from medial patellar margo or soft tissue disruptions of MPFL fibres near the patellar attachment. A patellar
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attachment MPFL injury may include an osteochondral avulsion fracture of the medial patellar margin, although rarely described in the literature [25]. The precise injury characteristics and clinical outcome for patellar MPFL avulsion fracture have not been described in the literature, to our knowledge. The aim of the present study was to define MPFL patellar attachment injury characteristics and the clinical outcome in patients with MPFL patellar insertion avulsion treated either surgically or conservatively. It was hypothesised that a patellar MPFL avulsion with an osteochondral fracture leads to subsequent patellar instability if the avulsion fracture is not initially fixated. The main outcome measure was subsequent patellar redislocation, and secondary measures were functional outcome (subluxations, pain).
Materials and methods The main inclusion criterion for the present study was primary traumatic patellar dislocation with patellar attachment MPFL injury as determined by MRI (within 21 days from the injury). The MRIs from a prospectively collected primary traumatic patellar dislocation cohort in the study hospital were reviewed to identify patients with MPFL injury at the patellar attachment. To define the MPFL injury location, the MRIs were independently reviewed by two musculoskeletal radiologists not involved in the treatment and blinded to the original interpretation of the images. The radiologists were also blinded to each other’s interpretations and, in case of discrepancy, the images were reviewed to reach consensus. A 1.5-Tesla MRI Siemens Magnetom Avanto scanner was used (Erlangen, Germany). The MRI sequences were coronal and axial T2-weighted and proton density-weighted in combination with fat saturation, and sagittal T2-weighted and proton density-weighted. Slice thickness was 3 mm, with a 0.5- or 1.0-mm intersection gap. Characterisation of the MPFL injury and study participants The MPFL injury location was assessed on both coronal and sagittal images, and first categorised based on the three locations described by Elias et al. [7]: MPFL injury at the level of patellar attachment, at the midsubstance (and medial retinaculum), and at the femoral origin. Midsubstance and femoral MPFL injuries were excluded from the study. We defined patellar MPFL avulsion injury as an osteochondral fracture involving variable-sized fragments displaced from the medial patellar margin (MPFL patellar insertion; Fig. 1) and the ligamentous fibres of the medial conjoined fascial tissue (including the MPFL) had to be continuously attached to the fragment(s) (Fig. 2). Patients
Fig. 1 Medial patellofemoral ligament (MPFL) injury with osteochondral avulsion fracture. A transverse T2-FSE MR image of the knee obtained at the level of the MPFL patellar insertion shows complete avulsion of the medial patellofemoral ligament from its patellar insertion, with articular surface involvement (arrow)
Fig. 2 Medial patellofemoral ligament (MPFL) injury with small avulsion fracture. A transverse T2-FSE MR image of the knee obtained at the level of the MPFL patellar insertion shows complete avulsion of the medial patellofemoral ligament from its patellar insertion arrow
with patellar MPFL avulsion with combined femoral or midsubstance MPFL disruption were excluded from the study. MRI was also used to exclude additional injuries in the knee and to assess patellofemoral joint anatomy, including trochlear dysplasia [5, 22]. As the purpose of this study was to investigate the clinical outcome of patients with patellar MPFL avulsion injury, we excluded patients who underwent any additional
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surgical procedures (MPFL reconstruction) other than avulsion fragment fixation, as described later. The medical records were carefully reviewed to confirm the primary nature of the patellar dislocation. An orthopaedic surgeon performed a patient interview and clinical examination within 21 days from the injury to all study participants. Excluded was anyone with prior patellar instability or additional knee injuries. After careful review of MRIs and the medical records, 56 patients were enrolled. Twelve patients (two patients from the surgical group and ten patients from the nonoperative group) were lost to follow-up (could not be reached or refused to participate).
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Statistical methods The Kruskal–Wallis test was used to test differences in the nonparametric ordinal data, and the independent samples t test was used for continuous, normally distributed data in the tests between the injury locations. Differences in the two-way tables were determined with the Pearson chi-square test or Fisher exact test when appropriate. Significance was set at P ≤ 0.05. SPSS 19.0 statistical package was used for statistical calculations.
Results Surgical technique Patient characteristics In 13 patients, who had a significant (>10 mm) articular cartilage involvement (Fragment Fixation group), initial surgical fixation of the avulsed patellar medial margin osteochondral fracture was performed. Under the subcutaneous fatty tissue, the conjoined fascial layer and the MPFL near the medial patella were identified. Reduction of the avulsion fracture was performed with internal fixation with number one polydioxanone suture through bone tunnels (first six cases) or with 3.5-mm suture anchor (Twin-Fix, Smith and Nephew, Andover, MA; latter seven cases). If patellar articular cartilage surface was significantly involved, the articulating osteochondral fragment was fixated with bioabsorbable pins (SmartNail, ConMed Linvatec, Largo, FL, or ActivaPin, Bioretec, Tampere, Finland). The remaining 31 patients (No Fragment Fixation group) with patellar avulsion fracture without significant articular cartilage involvement underwent nonsurgical treatment. The rehabilitation protocol was identical for all of the patients. Immediate straight-leg standing exercises were allowed, but weight bearing with a flexed knee was restricted and crutches were used for 4 weeks. The rehabilitation period included muscle strengthening with combined open and closed chain exercises supervised by a physiotherapist and full activity was allowed at 3 months. Follow‑up protocol Follow-up included assessment of patellar redislocation and functional outcomes. Kujala score [12], a 100-mm visual analogue scale, and Tegner scale [23] were used. An independent physician not involved with the surgery or conservative treatment clinically evaluated patients. Patients were asked whether they had regained their preinjury level of activity by follow-up. Institutional Review Board (IRB) approval was obtained from the study hospital (IRB#R9N071), and written consent was obtained from all patients enrolled in the follow-up study.
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The majority of the patients were men (44/56) with a median age of 23 years (range 15–31 years) at the time of injury. All of the patients were skeletally mature and injury mechanism was sports related. Of the 56 subjects, 44 participated in the median 4-year follow-up (range 1–10 years). Radiographic characteristics Three patterns of patellar attachment MPFL injuries were found (Fig. 3). Two of the types included osteochondral avulsion fractures, classified as type P2: articular cartilage involvement (medial patellar facet articular surface; Fig. 3) and type P1: without articular cartilage involvement (only bone from medial patellar margo; Fig. 3). The third type of patellar MPFL injury was classified as type P0 and was previously described as patellar insertion MPFL disruption without bony involvement [7]. Trochlear shape was classified as grade A dysplasia in 25/44 patients, grade B dysplasia in 7/44 patients, and normal in 12 patients. Nearly even distribution was seen in patients with grade of trochlear dysplasia regarding the MPFL P1 [14 (32 %) grade A, 5 (11 %) grade B] and P2 [11 (25 %) grade A, 2 (5 %) grade B] injury types. Follow-up radiographs of patients in No Fragment Fixation group frequently (in 24/31 patients) showed medial patellar ossicles. Six patients in the No Fragment Fixation group underwent subsequent arthroscopic removal of loose body fragment(s) (symptomatic during follow-up period). Ossicles were rare (in 2/13 patients) in Fragment Fixation group. Clinical outcome Among patients in Fragment Fixation group, two of the 13 reported recurrent patellar dislocation. Among patients in No Fragment Fixation group, recurrent patellar dislocation occurred in 17 of 31 cases (n.s.).
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Fig. 3 Three types of patellar MPFL injuries; a type P0 with ligamentous disruption at the patellar attachment, b type P1 with bony avulsion fracture from the medial margin of the patella, and c type P2 with bony avulsion involving articular cartilage from the medial facet of the patella
Preinjury activity level was regained in 71 % of Fragment Fixation group and in 55 % of No Fragment Fixation group (n.s.). The median Kujala score was 90 for patients in Fragment Fixation group and 86 for patients in No Fragment Fixation group, respectively (n.s.). The median follow-up Tegner activity scores were 6 for patients in Fragment Fixation group (range 4–7), and 5 for patients in No Fragment Fixation group (range 4–7) (n.s.).
Discussion The most important finding of the present study was that patellar MPFL avulsion in primary traumatic patellar dislocation does not benefit from acute surgical repair compared to nonsurgical treatment. There were no statistically significant differences in the redislocation rate or subjective scores between the surgical and nonsurgical study groups. Patellar insertion MPFL injuries can be classified into three categories: type P0 with ligamentous disruption, type P1 with bony avulsion fragment, and type P2 with bony avulsion involving articular cartilage surface from the medial facet of the patella. Patellar MPFL avulsion injury is associated with a relatively high rate of subsequent patellar dislocation. Patellar MPFL avulsion injury comprised two different types of osteochondral avulsion fractures: those with articular cartilage involvement (medial patellar facet articular surface) and those without articular cartilage involvement (only bone from medial patellar margin). In chronic instability cases, medial patellar ossicles can occasionally be observed as a sign of previous patellar MPFL avulsion fracture. Based on previous studies, between 40 and 90 % of MPFL disruptions are located in the femoral attachment [9, 20], whereas some studies have reported figures up to 50 to 60 % at the patellar insertion [7, 11, 26, 27]. The MPFL
midsubstance region seems to be less frequently affected [10, 20]. Although more than one MPFL injury location can sometimes be seen in MRI, total disruption is usually at one of the locations described above. Previous randomised studies of primary patellar dislocations concluded that surgery was not systemically superior to nonsurgical treatment if all the patients with different types of MPFL injuries were treated similarly [15, 17, 19]. Although, a recent prospective randomised study in which nonsurgical treatment was compared to surgical reinsertion in either femoral or patellar attachment, surgery resulted in better stability than nonoperative treatment [3]. Due to the significance, 44 to 70 % redislocation rate after primary dislocation reported in the literature, some cases might benefit from initial surgery, and surgery should definitely be considered for patients with a high risk of failure after nonsurgical treatment. Based on a previous study, ruptures at the MPFL midsubstance or patellar insertion regions without an osteochondral avulsion fragment are generally not related to significant subsequent patellar instability [20]. We therefore may suggest that a rupture of the MPFL at its midsubstance or near the patellar attachment should be treated nonsurgically. Patients with significant patellar MPFL avulsion fracture and femoral attachment MPFL disruption may be at greater risk [20]. This study was limited by its retrospective nature. In addition, surgical fixation was performed in the first six patients using sutures and in latter seven cases by suture anchors. The Fragment Fixation group included patients with significant articular cartilage involvement, whereas the No Fragment Fixation group consisted of patients without significant cartilage lesions. Therefore, patients in the Fragment Fixation group can be considered as having had more severe injury as those in No Fragment Fixation group. If the fracture involved large fragments acting as loose bodies and produced symptoms, subsequent arthroscopic removal of the
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fragment(s) was performed (in six patients). The follow-up was most likely too short to evaluate differences in development of osteoarthritic characteristics of the patellofemoral joint between the study groups. In addition to MPFL injury location, various factors may affect the clinical outcome of primary patellar dislocation. The well-known anatomical factors, such as trochlear dysplasia, and patella alta [5, 8, 10, 24] can predispose a patient to recurrent patellar instability, regardless of MPFL injury location. Most likely, the more dysplastic the trochlear shape, the more devastating an injury to the MPFL is to patellar stability. In this study, trochlear dysplasia was frequently seen, but similarly in patients with different types of patellar attachment MPFL injuries. Based on the results from this study, MPFL patellar attachment avulsion injury in young adult population with high level of physical activity results recurrent dislocation in up to half of the cases, indicating same rate that in the previous patellar dislocation study populations [14, 15, 17, 21].
Conclusion In patients with primary patellar dislocation, patellar attachment MPFL injury showed three different patterns, classified as types P0, P1, and P2. MRI is recommended to assess the injury pattern. Patellar attachment MPFL avulsion injury did not benefit from initial surgical repair. Surgery can be considered for P2 cases with significant articular surface involvement, with the aim to restore cartilage integrity.
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