Factors Influencing Graft Function following MPFL Reconstruction: A Dynamic Simulation Study

2020 ◽  
Author(s):  
Miho J. Tanaka ◽  
Andrew J. Cosgarea ◽  
Jared M. Forman ◽  
John J. Elias
Keyword(s):  
Dynamic Simulation ◽  
Knee Flexion ◽  
Patellar Instability ◽  
Graft Function ◽  
Lateral Position ◽  
Tibial Tuberosity ◽  
Mpfl Reconstruction ◽  
Patellar Tracking ◽  
Graft Tension ◽  
Patellar Maltracking

AbstractMedial patellofemoral ligament (MPFL) reconstruction is currently the primary surgical procedure for treating recurrent lateral patellar instability. The understanding of graft function has largely been based on studies performed with normal knees. The current study was performed to characterize graft function following MPFL reconstruction, focusing on the influence of pathologic anatomy on graft tension, variations with knee flexion, and the influence on patellar tracking. Knee squatting was simulated with 15 multibody dynamic simulation models representing knees being treated for recurrent lateral patellar instability. Squatting was simulated in a preoperative condition and following MPFL reconstruction with a hamstrings tendon graft set to allow 0.5 quadrants of lateral patellar translation with the knee at 30 degrees of flexion. Linear regressions were performed to relate maximum tension in the graft to parameters of knee anatomy. Repeated measures comparisons evaluated variations in patellar tracking at 5-degree increments of knee flexion. Maximum graft tension was significantly correlated with a parameter characterizing lateral position of the tibial tuberosity (maximum lateral tibial tuberosity to posterior cruciate ligament attachment distance, r 2 = 0.73, p < 0.001). No significant correlations were identified for parameters related to trochlear dysplasia (lateral trochlear inclination) or patella alta (Caton–Deschamps index and patellotrochlear index). Graft tension peaked at low flexion angles and was minimal by 30 degrees of flexion. MPFL reconstruction decreased lateral patellar shift (bisect offset index) compared with preoperative tracking at all flexion angles from 0 to 50 degrees of flexion, except 45 degrees. At 0 degrees, the average bisect offset index decreased from 0.81 for the preoperative condition to 0.71. The results indicate that tension within an MPFL graft increases with the lateral position of the tibial tuberosity. The graft tension peaks at low flexion angles and decreases lateral patellar maltracking. The factors that influence graft function following MPFL reconstruction need to be understood to limit patellar maltracking without overloading the graft or over constraining the patella.

Clinical Comparison of Medial Patellofemoral Ligament Reconstruction With or Without Tibial Tuberosity Transfer for Recurrent Patellar Instability

2021 ◽  
pp. 036354652110377
Author(s):  
Jong-Min Kim ◽  
Jae-Ang Sim ◽  
HongYeol Yang ◽  
Young-Mo Kim ◽  
Joon-Ho Wang ◽  
...  
Keyword(s):  
Clinical Outcomes ◽  
Patellar Instability ◽  
Medial Patellofemoral Ligament ◽  
Tibial Tuberosity ◽  
Mpfl Reconstruction ◽  
Trochlear Groove ◽  
Functional Failure ◽  
Radiological Parameters ◽  
Recurrent Patellar Instability

Background: No clear guidelines or widespread consensus has defined a threshold value of tibial tuberosity–trochlear groove (TT-TG) distance for choosing the appropriate surgical procedures when additional tibial tuberosity osteotomy (TTO) should be added to augment medial patellofemoral ligament (MPFL) reconstruction for recurrent patellar instability. Purpose: To compare the clinical outcomes between MPFL reconstruction and MPFL reconstruction with TTO for patients who have patellar instability with a TT-TG distance of 15 to 25 mm. Study Design: Cohort study; Level of evidence, 3. Methods: We retrospectively analyzed 81 patients who underwent surgical treatment using either MPFL reconstruction or MPFL reconstruction with TTO for recurrent patellar instability with a TT-TG distance of 15 to 25 mm; the mean follow-up was 25.2 months (range, 12.0-53.0 months). The patients were divided into 2 groups: isolated MPFL reconstruction (iMPFL group; n = 36) performed by 2 surgeons and MPFL reconstruction with TTO (TTO group; n = 45) performed by another 2 surgeons. Clinical outcomes were assessed using the Kujala score, Knee injury and Osteoarthritis Outcome Score, and Tegner activity score. Radiological parameters, including patellar height, TT-TG distance, patellar tilt, and congruence angle were compared between the 2 groups. Functional failure based on clinical apprehension sign, repeat subluxation or dislocation, and subjective instability and complications was assessed at the final follow-up. We also compared clinical outcomes based on subgroups of preoperative TT-TG distance (15 mm ≤ TT-TG ≤ 20 mm vs 20 mm < TT-TG ≤ 25 mm). Results: All of the clinical outcome parameters significantly improved in both groups at the final follow-up ( P < .001), with no significant differences between groups. The radiological parameters also showed no significant differences between the 2 groups. The incidence of functional failure was similar between the 2 groups (3 failures in the TTO group and 2 failures in the iMPFL group; P = .42). In the TTO group, 1 patient experienced a repeat dislocation postoperatively and 2 patients had subjective instability; in the iMPFL group, 2 patients had subjective instability. The prevalence of complications did not differ between the 2 groups ( P = .410). In the subgroup analysis based on TT-TG distance, we did not note any differences in clinical outcomes between iMPFL and TTO groups in subgroups of 15 mm ≤ TT-TG ≤ 20 mm and 20 mm < TT-TG ≤ 25 mm. Conclusion: MPFL reconstruction with and without TTO provided similar, satisfactory clinical outcomes and low redislocation rates for patients who had patellar instability with a TT-TG distance of 15 to 25 mm, without statistical difference. Thus, our findings suggest that iMPFL reconstruction is a safe and reliable treatment for patients with recurrent patellar dislocation with a TT-TG distance of 15 to 25 mm, without the disadvantages derived from TTO.

scholarly journals The Reversed Dynamic Patellar Apprehension Test (ReDPAT) mimics anatomical complexity in lateral patellar instability

2019 ◽  
Vol 7 (6_suppl4) ◽  
pp. 2325967119S0022
Author(s):  
Felix Zimmermann ◽  
Peter Balcarek
Keyword(s):  
Risk Factors ◽  
Knee Joint ◽  
Knee Flexion ◽  
Patellar Instability ◽  
Trochlear Dysplasia ◽  
Valgus Deformity ◽  
Tibial Tuberosity ◽  
Flexion Angle ◽  
Knee Flexion Angle ◽  
Joint Flexion

Aims and Objectives: To develop a dynamic physical examination test that functionally simulates actual patellar instability events and that mimics the range of patellar stabilizer insufficiency in an individual patient. Materials and Methods: Seventy-four consecutive patients (male/female 33/41; mean age 22±7 years) with recurrent lateral patellar instability and thirty controls (male/female 16/14; mean age 31±14 years) were prospectively evaluated using the reversed dynamic patellar apprehension test (ReDPAT). The examination starts with the knee flexed at 120°. The knee is then extended while the patella is translated laterally. The maneuver is stopped at first onset of a subjective apprehensive reaction, and the ReDPAT result is considered positive according to this knee joint flexion angle. Anatomical predisposition was assessed according to Dejour’s classification of trochlear dysplasia, tibial tuberosity-trochlear groove distance, tibial tuberosity-posterior cruciate ligament distance, patellar height, and varus/valgus malalignment. Results: The study group had an average of 3.4 ± 1.0 (1-6) anatomical risk factors for lateral patellar dislocation. Severe trochlear dysplasia (84%) and patella alta (49%) were the most common. Test sensitivity, specificity, and accuracy reached 97.3%, 90%, and 95.2%, respectively, and test-retest reliability was good (Pearson’s r 0.84; p<0.0001). The ReDPAT results became positive at a mean knee flexion angle of 58°±17° (20°-90°). Knee flexion angle correlated significantly with the severity of trochlear dysplasia (p=0.018), valgus deformity (p=0.011), and the total number of anatomical risk factors (p=0.02). Conclusion: This study introduced the reversed dynamic patellar apprehension test as a reliable clinical examination tool in the assessment of lateral patellar instability. The results of this study indicate that the degree of knee joint flexion at which the provocative sense of apprehension becomes positive correlates with severity of trochlear dysplasia, valgus deformity and the total number of anatomical risk factors for patellar instability.

scholarly journals MPFL GRAFT TENSIONING TO TREAT PATELLAR INSTABILITY RELATED TO PATELLA ALTA: DYNAMIC SIMULATION

2020 ◽  
Vol 8 (4_suppl3) ◽  
pp. 2325967120S0015
Author(s):  
Travis Jones ◽  
Kerwyn C. Jones ◽  
John J. Elias
Keyword(s):  
Dynamic Simulation ◽  
Patellar Instability ◽  
Simulation Models ◽  
Knee Function ◽  
Patella Alta ◽  
Mpfl Reconstruction ◽  
Maximum Pressure ◽  
Lateral Translation ◽  
Lateral Subluxation ◽  
Mri Scans

Background: Medial patellofemoral ligament (MPFL) reconstruction is a popular treatment for lateral patellar instability. For knees with patella alta, however, tibial tuberosity distalization is the most common approach due to concerns about graft tensioning. A MPFL graft is tensioned intra-operatively to prevent lateral subluxation without over-constraining the patella by allowing some translation. Purpose: To analyze the effects of MPFL reconstruction on lateral tracking and cartilage pressure for knees with patella alta using dynamic simulation of knee function. Methods: Knee function was simulated with 8 multibody dynamic simulation models (RecurDyn) constructed from 3.0 T MRI scans of subjects being treated for recurrent patellar instability. The models were validated in previous studies and included ligaments, tendons, and retinacular structures represented by tension-only springs (Fig1). Four models displayed patella alta; the remaining 4 models were made to reflect patella alta by lengthening the springs. Forces were applied to simulate a dual limb squat from 0º to 90º. Motion was simulated in a pre-operative condition and for three MPFL graft tensioning techniques (1.0, 0.5, and 0 patellar quadrants of lateral translation). The maximum bisect offset index during flexion was used as a measure of patellar instability and the maximum pressures applied to patellar cartilage (lateral, medial) as measures of the risk of overloading cartilage. Statistics were used to compare the parameters with significance set at p < 0.05. Post- and pre-operative maximum bisect offset index were also correlated. Results: MPFL reconstruction with 0.5 and 0 quadrants of allowed lateral translation significantly decreased the maximum bisect offset index compared to the pre-operative condition, but not for 1.0 quadrants (Table 1). MPFL reconstruction did not significantly influence the maximum pressure applied to medial or lateral cartilage. The maximum post-operative bisect offset index was significantly correlated with the pre-operative bisect offset index for 1.0 and 0.5 quadrants of lateral translation allowed (r2 = 0.80, 0.65, and 0.48 for grafts allowing 1, 0.5 and 0 quadrants of translation, respectively). Conclusion: For knees with patella alta, the influence of MPFL reconstruction on patellar tracking varied with the allowed patellar translation during graft tensioning. None of the graft tensioning conditions significantly decreased the maximum lateral pressure or increased the medial cartilage pressure. Significance: The graft tensioning process for MPFL reconstruction typically allows some lateral patellar translation to avoid overconstraining the knee. For knees with patella alta, reducing the allowed lateral translation seems to limit maltracking without overconstraining the knee. [Table: see text][Figure: see text]

scholarly journals MPFL reconstruction and tibial tuberosity transposition in patients with patellar instability: May it troubleshots also trochlear dysplasia?

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
A. Castelli ◽  
E. Jannelli ◽  
E. Ferranti Calderoni ◽  
G. Galanzino ◽  
A. Ivone ◽  
...  
Keyword(s):  
Patellar Instability ◽  
Trochlear Dysplasia ◽  
Functional Results ◽  
Activity Level ◽  
Tibial Tuberosity ◽  
Mpfl Reconstruction ◽  
Trochlear Groove ◽  
Patellar Tilt ◽  
Sulcus Angle

Abstract Purpose This study aimed to highlight short- and medium-term outcomes of combined medial patello-femoral ligament (MPFL) reconstruction and anterior tibial tuberosity (ATT) transposition surgery in patients with recurrent patellar instability and different degrees of trochlear dysplasia. Methods Between January 2014 and May 2019, 25 patients with patellar instability underwent a surgical procedure combining the lowering/transposition of the ATT and the MPFL reconstruction. Each patient were preoperative assessed by Kujala score, International Knee Documentation Committee (IKDC), Tegner activity level scale. The assessment of instability predisposing factors was carried out with patellar height, tibial tuberosity-trochlear groove (TT-TG) distance, trochlear dysplasia, sulcus angle, patellar tilt and MPFL injuries. Functional outcomes were evaluated with Kujala, IKDC and Tegner scores at 3, 6 and 12 months after surgery. Results The average age of the patients was 20 years (range 13–43 years). Pre- operative Caton–Deschamps index was pathological in 10 (40%). Sulcus angle was elevated in 13 patients (52%) and TT-TG distance was irregular in 17 patients (68%). Trochlear dysplasia was present in 13 patients (9 type A, 3 type B, 1 type C according to Dejour’s Classification). No re-dislocation occurred during the follow-up. There was a significant increase in the Kujala, IKDC and Lysholm scores after 3, 6 and 12 months, and the results were compared for the different follow-up times and patient’s trochlear dysplasia degree. Conclusion This prospective observational longitudinal study identified good clinical outcomes in patients who underwent MPFL reconstruction and ATT transposition for patellar instability. Finally, the different risk factors for patellar instability examined, particularly the presence of trochlear dysplasia, did not significantly influence the final functional results, which range from good to excellent without re-dislocation episodes.

Patellar instability can be classified into four types based on patellar movement with knee flexion: a three-dimensional computer model analysis

2018 ◽  
Vol 3 (6) ◽  
pp. 328-335 ◽  
Author(s):  
Yuzo Yamada ◽  
Yukiyoshi Toritsuka ◽  
Shuji Horibe ◽  
Norimasa Nakamura ◽  
Kazuomi Sugamoto ◽  
...  
Keyword(s):  
Healthy Volunteers ◽  
Computer Model ◽  
Knee Flexion ◽  
Patellar Instability ◽  
Three Dimensional ◽  
Computer Models ◽  
Patellar Tracking ◽  
Movement Direction ◽  
Lateral Deviation ◽  
A Value

ObjectivePatellar instability (PI) represents various underlying pathologies, including patellar malalignment. Continuous patellar alignment develops to patellar tracking and is regarded as the end product of combined predisposing factors. We quantitatively investigated the inhomogeneity of patellar tracking in PI.MethodsSixty knees of 56 patients with PI and 15 knees of 10 healthy volunteers (HVs) were studied. Three-dimensional (3D) computer models were created based on MRIs at 10° intervals over 0°–50° of flexion, and patellar tracking was quantitatively analysed using patellar 3D shift. Classification was performed according to the maximum 3D shift (max-shift), indicating the extent of lateral deviation, and the change of 3D shift from 0° to 50° (change0–50), indicating movement direction. First, the cut-off value (COV) of the max-shift was defined based on the data from HVs. When a value was greater than the COV, it was defined as a major subluxation, and when the value was smaller it was defined as a minor subluxation. Next, the two COVs of change0–50 were similarly defined. When a value was greater than the upper COV, it was defined as a major-lateral type, laterally moving the patella with flexion, and when smaller than the lower COV it was defined as a major-medial type, medially moving the patella with flexion. When a value fell between the two COVs, it was defined as a major-straight type.ResultsFifty-three patellae (88%) with values larger than the COV of the max-shift (mean +1 SD of HV) were defined as major subluxations and seven (12%) showing smaller values as minor subluxations. Among the major subluxations, 25 (42%) showing a smaller value than the lower COV of change0–50 (mean –2 SD of HV) were defined as major-medial type, while 7 (12%) showing a larger value than the upper COV of change0–50 (mean +2 SD) were defined as major-lateral type. Twenty-one (35%) were defined as major-straight type. No further analysis was performed on the seven minor subluxations (the minor type).ConclusionPI was quantitatively classified into four types according to the extent of lateral deviation and the movement direction of the patellae with flexion, showing inhomogeneity of patellar tracking.

scholarly journals Accuracy and Reliability of The Visual Assessment of Patellar Tracking

2019 ◽  
Vol 7 (3_suppl2) ◽  
pp. 2325967119S0019
Author(s):  
Matthew Best ◽  
Miho Jean Tanaka ◽  
Shadpour Demehri ◽  
Andrew J. Cosgarea
Keyword(s):  
Quantitative Analysis ◽  
Qualitative Analysis ◽  
Patellar Instability ◽  
Visual Assessment ◽  
Patellar Tracking ◽  
4D Ct ◽  
Lateral Translation ◽  
Patellar Maltracking ◽  
Radiographic Measurements ◽  
Grade 3

Objectives: Clinicians treating patients with patellar instability describe abnormal tracking as a “J sign” when the patella exhibits excessive lateral displacement as the knee is actively extended. The purpose of this study is to determine the accuracy and reliability of the visual assessment of patellar tracking among patellofemoral experts when compared to objective radiographic measurements. Methods: Active knee extension was video recorded and a dynamic CT scan (4D CT) was obtained in study patients being evaluated for patellar instability. Patellar bisect offset (BO) was measured directly from the 4D CT at 10-degree increments from 0-50 degrees of flexion. The greatest BO value was used to determine quadrants of lateral translation. Practicing orthopedic surgeons from the International Patellofemoral Study Group (IPSG) were asked to view videos and determine the presence or absence of maltracking (2 or more quadrants of lateral translation) in 10 single-knee videos (qualitative analysis). Participants were then asked to grade patella tracking in 20 different single-knee videos (quantitative analysis). J-sign grade was defined as follows: grade 0 - less than 1 patellar quadrant of lateral translation; grade 1 - at least 1 but less than 2 quadrants; grade 2 - at least 2 but less than 3 quadrants; grade 3 - 3 or more quadrants lateral translation. Results: Thirty-two practicing orthopedic surgeon IPSG members completed the survey. In the qualitative analysis, the videos were correctly identified as demonstrating patellar maltracking 68% of the time (free marginal kappa= 0.44). In the quantitative analysis, 53% of survey participants identified grade 3 J sign correctly, 51% correctly identified grade 2, 48% correctly identified grade 1, and 68% correctly identified grade 0 (free marginal kappa= 0.42). Conclusion: This is the first study to compare visual assessment of patellar tracking with objective BO measurements from 4D CT. Using visual assessment alone, patellofemoral experts were able to correctly identify the presence of patellar maltracking in only two-thirds of the videos and were able to correctly grade patellar maltracking in only half. There is inadequate interobserver agreement (free marginal kappa<0.70) to support the use visual assessment alone in determining the presence or degree of patellar maltracking, reinforcing the importance of objective radiographic measurements.

scholarly journals Clinical results after distal femoral osteotomies in patients with patellar maltracking

2017 ◽  
Vol 5 (4_suppl4) ◽  
pp. 2325967117S0014
Author(s):  
Jannik Frings ◽  
Tobias C. Drenck ◽  
Ralph Akoto ◽  
Arno Schmeling ◽  
Karl-Heinz Frosch
Keyword(s):  
Patellar Instability ◽  
Clinical Results ◽  
Individual Therapy ◽  
Mpfl Reconstruction ◽  
Lateral Release ◽  
Tibial Tubercle ◽  
Therapy Algorithm ◽  
Patellar Maltracking ◽  
Leg Axis ◽  
Torsional Osteotomy

Aims and Objectives: Few clinical trials analyze the results after distal femoral osteotomies (torsional and axial adjustment) for patellar maltracking with or without patellar instability. The purpose of the presented study is to capture the clinical results as well as the reluxation rate after torsional osteotomy or axial adjustment (Types 3d, 3e and 5 according to Frosch et al.). Materials and Methods: Between 2010 and 2015 294 cases of patellar instability and/or maltracking were treated in our hospital, 277 surgically. All patients were classified according to Frosch et al. and treated by the corresponding algorithm. 49 patients received a distal femoral osteotomy. Torsional angle and leg axis were radiologically measured in all patients. We used the common scoring systems and determined the redislocation rate. Results: Type 3e and 5 27 cases (18 patients, average 22y) torsional osteotomies were performed. 21 of 27 cases were classified as type 3e (7%), 6 as type 5 (2%). 22 other cases (19 patients) with an average age of 27 years (14-46 years) were classified as type 3d (7,5% of all cases). 17 axial adjustments were performed, 4 isolated MPFL reconstructions and 1 osteotomy of the tibial tubercle. Average femoral antetorsion was 38,6° (±9,3°), die tibial torsion was 35,1° (±11,7°). The average deviation of the leg axis in the frontal plane was 5° (±2,4°) varus (n=9) and 2,8° (±2,9°) valgus (n=14). The mean TT-TG distance was 19,9 mm (±4,9 mm). Torsional osteotomy was combined with MPFL-reconstruction (n=19), tibial tubercle transfer (Ø12,6 mm, n=13) or axial correction (Ø4° varus, Ø6° valgus, n=13), 5 double osteotomies. Torsion was corrected by 13° femoral and 11° tibial on average. After 19 months VAS was 1.2, Kujala 78.8, a Lysholm 79.1, Tegner 4. Only one patient experienced a subluxation after a fall. No redislocation. 3d 7,5% (n=22) showed a mean axial deviation of 6,5° (±2,2°) valgus. Average TT-TG distance was 18,3 mm (±5,8 mm). We performed 15 closed-wedge varus distal femoral osteotomies (Ø6,8°±2,3°), combined with an Elmslie-Trillat (n=14) or Fulkerson procedure (n=1), MPFL reconstruction (n=15) or lateral release (n=1). 4 isolated MPFL reconstructions. One case of a pathological lateral slope with patellar instability was treated by double osteotomy (8° femoral to varus, 4° tibial to valgus). One tibial varisation (5,5°) with MPFL reconstruction and Elmslie-Trillat procedure. Tibial tubercle was medialized by 11 mm ±6,7 mm on average. 22 MPFL reconstructions were done. After average 33 months VAS was 2.3, Kujala 72, Lysholm 79, Tegner 4. No redislocation. Conclusion: Torsional and axis correcting osteotomies are suitable techniques to treat patellar instability or maltracking. Clinically the patients’ benefit is substantial. Consideration of additional procedures is crucial to success, a thorough analysis of all causal pathologies is mandatory. The results approve our individual therapy algorithm in the treatment of patellar instability and maltracking caused by torsional deformities or axis deviations.

scholarly journals Why do MPFL reconstructions fail today?

2020 ◽  
Vol 8 (5_suppl4) ◽  
pp. 2325967120S0029
Author(s):  
Felix Zimmermann ◽  
Peter Balcarek
Keyword(s):  
Risk Factors ◽  
Revision Surgery ◽  
Patellar Instability ◽  
Trochlear Dysplasia ◽  
Valgus Deformity ◽  
Patellar Height ◽  
Tibial Tuberosity ◽  
Mpfl Reconstruction ◽  
Trochlear Groove ◽  
Type B

Aims and Objectives: The medial patellofemoral ligament (MPFL) is the most important passive stabilizer of the patella. In recurrent lateral patellar dislocations reconstruction of the MPFL with an autologous tendon transplant is a frequently performed surgical procedure that shows a low redislocation rate between 1%-7%. However, a complication rate of up to 26% and a reoperation rate of 4% has also been observed. The question, therefore, arises which parameter determines MPFL reconstruction failure. Thus, the purpose of this study was to identify reasons for MPFL reconstruction failure with regard to patients’ complaints leading to reoperation. Materials and Methods: Between July 2015 and May 2019 28 patients (M/F 9/19; mean age 27 ± 8 years) with postoperative complaints after MPFL reconstructive surgery had to undergo revision surgery. Preoperative failure analysis included clinical examination (ROM, ReDPAT, J-sign, and Patella-Glide Test) and radiological imaging with regard to anatomical risk factors of patellar instability and MPFL tunnel positioning. Anatomical predisposition was assessed according to Dejour’s classification of trochlear dysplasia, tibial tuberosity-trochlear groove distance, tibial tuberosity-posterior cruciate ligament distance, patellar height, varus/valgus malalignment and torsional profile. Results: Three major reasons for revision surgery were identified: (1) patellar redislocation, (2) limited range of motion (ROM), and (3) anterior knee pain (AKP). Sixteen of the 28 patients (57%) suffered from recurrent patellar dislocation. Severe trochlear dysplasia (type B/D according to Dejour) (44%), valgus deformity (19%), increased patellar height (19%), and misplaced femoral drill channels (31%) could be identified as risk factors for redislocation. An increased TT-TG (>20mm) or TT-PCL (>24mm) distance could not be observed in any patient in this group. Limited ROM with an average maximum flexion ability of about 92 ± 26° was observed in 10 of the 28 patients (36%), of which 9 patients additionally complained of AKP. Misplaced femoral drill channels (80%), severe trochlear dysplasia (type B/D according to Dejour) (20%) and postoperative decreased patellar height (20%) could be identified as risk factors for postoperative limited ROM. Other reasons for postoperative AKP were increased femoral antetorsion (n=1) and retropatellar cartilage damage (n=2) without any loss of ROM. Conclusion: Recurrent dislocation of the patella, limited ROM and AKP were identified as most common complications after MPFL reconstruction leading to revision surgery. Failures are mainly due to neglected bony risk factors of patellar instability (trochlear dysplasia, patella alta and valgus deformity) and to misplaced femoral drill channels. Appropriate patient selection and an accurate surgical technique appear mandatory for a good clinical outcome when patellar instability is treated solely with an MPFL reconstruction.

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