The role of the medial ligamentous structures on patellar tracking during knee flexion

Patellar Dislocations and Reduction Procedure

Acute patellar dislocations are a common injury occurring in adolescents involved in sports and dancing activities. This injury usually occurs when the knee is in full extension and sustains a valgus stress on the knee. The medial patellofemoral ligament is the medial restraint that assists in stabilizing the patella from lateral dislocations. The patella usually dislocates laterally and is usually not difficult to reduce after patient evaluation and prereduction radiographs. After postreduction radiographs confirm proper position of the patella postreduction and the absence of fractures, the patient is usually treated conservatively with initial immobilization, orthopedic referral, and physical therapy.

Reconstruction of the medial patellofemoral ligament by means of the anatomical double-bundle technique using metal anchors

Objective

To evaluate double-bundle reconstruction of the medial patellofemoral ligament (MPFL) using a graft from the semitendinosus tendon and fixation with metal anchors over the medium term.

Methods

This was a prospective cross-sectional study. After approval from the research ethics committee, 31 patients with patellofemoral instability who underwent MPFL reconstruction by means of the anatomical double-bundle technique, with fixation using metal anchors, were analyzed between May 2010 and January 2015. To evaluate the effectiveness of the MPFL reconstruction surgery, the Kujala scale and the Tegner–Lysholm score were assessed before the procedure and one year afterwards, along with clinical data such as pain levels, range of motion and J sign. The data were tabulated in the Excel^® software and were analyzed using the SPSS Statistics^® software, version 21. The statistical analysis was performed using the Wilcoxon T test and the McNemar test.

Results

The mean preoperative score from the Kujala test was 45.64 ± 1.24 and the postoperative score was 94.03 ± 0.79 (p < 0.001). The preoperative Tegner–Lysholm score was 40.51 ± 1.61 and the postoperative score was 91.64 ± 0.79 (p < 0.001). The preoperative range of motion was 125.96 ± 2.11 and the postoperative range was 138.38 ± 1.49 (p < 0.05).

Conclusion

MPFL reconstruction by means of the anatomical double-bundle technique is easily reproducible, without episodes of recurrence, with satisfactory results regarding restoration of stability and function of the patellofemoral joint.

Combined Reconstruction of the Medial Patellofemoral Ligament With Quadricipital Tendon and the Medial Patellotibial Ligament With Patellar Tendon

Although the medial patellotibial ligament (MPTL) has been neglected regarding its function in patellar stability, recently, its importance in terminal extension and during flexion has been recognized. Indications for reconstruction of the medial patellofemoral ligament combined with the MPTL are extension subluxation, flexion instability, children with anatomic risk factors for patellar instability, and knee hyperextension associated with generalized laxity. We describe a combined reconstruction of the medial patellofemoral ligament with quadricipital tendon and reconstruction of the MPTL with patellar tendon autografts.

Reconstruction of medial patellofemoral ligament using quadriceps tendon combined with reconstruction of medial patellotibial ligament using patellar tendon: initial experience

OBJECTIVE

To describe a surgical technique for anatomical reconstruction of the medial patellofemoral ligament using the quadriceps tendon, combined with reconstruction of the medial patellotibial ligament using the patellar tendon; and to present the initial results from a case series.

METHOD

The proposed technique was used on a series of cases of patients with diagnoses of patellofemoral instability and indications for surgical treatment, who were attended by the Knee Group of HC-IOT, University of São Paulo. The following were evaluated before and after the operation: range of motion (ROM), apprehension test, lateral translation test, patellar inclination test, inverted J sign, subluxation upon extension, pain from compression of the patella and pain from contraction of the quadriceps. After the operation, the patients were asked whether any new episode of dislocation had occurred, what their degree of satisfaction with the surgery was (on a scale from 0 to 10) and whether they would be prepared to go through this operation again.

RESULTS

Seven knees were operated, in seven patients, with a mean follow-up of 5.46 months (±2.07). Four patients who presented apprehension before the operation did not show this after the operation. The lateral translation test became normal for all the patients, while the patellar inclination test remained positive for two patients. The patients with an inverted J sign continued to be positive for this sign. Five patients were positive for subluxation upon extension before the operation, but all patients were negative for this after the operation. None of the patients presented any new episode of dislocation of the patella. All of them stated that they were satisfied: five gave a satisfaction score of 9 and two, a score of 10. All of them said that they would undergo the operation again. Only one patient presented a postoperative complication: dehiscence of the wound.

CONCLUSION

Reconstruction of the medial patellofemoral ligament using the quadriceps tendon, combined with reconstruction of the medial patellotibial ligament using the patellar tendon, was technically safe and presented good objective and subjective clinical results in this case series with a short follow-up.

Recovery of gait pattern after medial patellofemoral ligament reconstruction for objective patellar instability

Gait pattern alterations were previously reported in association with objective patellar instability (OPI). Gait pattern comparison between a series of patients having undergone medial patellofemoral ligament (MPFL) reconstruction and a sample of control subjects. Thirty patients at 6 months postoperatively after MPFL reconstruction and thirty control subjects were enrolled in the study for a clinical and biomechanical assessment including gait analysis at three selected walking rates using the GAITRite(®) system. The mean raw IKDC score was 73 (± 19), and the mean Kujala knee function was 84 (± 17.5). The study of gait did not demonstrate any significant difference between the two groups at a normal and fast walking rate. At a 10 km/h running speed, the single-support phase was significantly shortened by a mean 2.33% (p < 0.05), the swing phase by a mean 2.64% (p < 0.05) and the double-support phase by a mean 3.49% (p < 0.05) on the operated side. MPFL reconstruction reported good midterm functional and clinical results in the management of OPI. At 6 months postoperatively, the patient gait pattern was similar to that observed in healthy subjects at a normal and fast walking speed. However, our study revealed persistent gait abnormalities at a 10 km/h running speed. These gait alterations seemed to be related to the ligament reconstruction in itself due to the higher strain applied on the reconstructed MPFL during running cycle (10 km/h). Level of evidence IV.

Radiographic Reference Points Are Inaccurate With and Without a True Lateral Radiograph: The Importance of Anatomy in Medial Patellofemoral Ligament Reconstruction

BACKGROUND

Studies have reported methods for radiographically delineating medial patellofemoral ligament (MPFL) femoral tunnel position on a true lateral knee radiograph. However, obtaining a true lateral fluoroscopic radiograph intraoperatively can be challenging, rendering radiographic methods for tunnel positioning potentially inaccurate.

PURPOSE

To quantify the magnitude of MPFL femoral tunnel malposition that occurs on true lateral and aberrant lateral knee radiographs when using a previously reported radiographic technique for MPFL femoral tunnel localization.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Ten fresh-frozen cadaveric knees were dissected to expose the MPFL femoral insertion and surrounding medial knee anatomy. True lateral and aberrant lateral knee radiographs at 2.5°, 5°, and 10° off-axis were obtained with a standard mini C-arm in 4 orientations: anterior to posterior, posterior to anterior, caudal, and cephalad. A previously reported radiographic method for MPFL femoral localization was performed on all radiographs and compared in reference to the anatomic MPFL attachment center.

RESULTS

The radiographic point, as previously described, was a mean distance of 4.1 mm from the anatomic MPFL attachment on a true lateral knee radiograph. The distance between the anatomic MPFL attachment center and the radiographic point significantly increased on aberrant lateral knee radiographs with as little as 5° of rotational error in 3 of 4 orientations of rotation when a standard mini C-arm was used. This corresponded to a malposition of 7.5, 9.2, and 8.1 mm on 5°-aberrant radiographs in the anterior-posterior, posterior-anterior, and cephalad orientations, respectively (P < .005). In the same 3 orientations of rotation, MPFL tunnel malposition on the femur exceeded 5 mm on 2.5° aberrant radiographs.

CONCLUSION

The commonly utilized radiographic point, as previously described for MPFL femoral tunnel placement, results in inaccurate tunnel localization on a true lateral radiograph, and this inaccuracy is perpetuated with aberrant radiography. Aberrant lateral knee imaging of as little as 5° off-axis from true lateral has a significant effect on placement of a commonly used radiographic point relative to the anatomic MPFL femoral attachment center and results in nonanatomic MPFL tunnel placement.

CLINICAL RELEVANCE

This study demonstrates that radiographic localization of the MPFL femoral tunnel results in inaccurate tunnel placement on a true lateral radiograph, particularly when there is deviation from a true lateral fluoroscopic image, which can be difficult to obtain intraoperatively. Assessing anatomy directly intraoperatively, rather than relying solely on radiographs, may help avoid MPFL tunnel malposition.

Injury patterns of medial patellofemoral ligament and correlation analysis with articular cartilage lesions of the lateral femoral condyle after acute lateral patellar dislocation in adults: An MRI evaluation

OBJECTIVES

The purpose of this study was to investigate the injury characteristics of medial patellofemoral ligament (MPFL), and to analyse the correlations between the injury patterns of MPFL and articular cartilage lesions of the lateral femoral condyle in adults with acute lateral patellar dislocation (LPD).

METHODS

Magnetic resonance (MR) images were prospectively obtained in 121 consecutive adults with acute LPD. Images were acquired using standardised protocols and these were independently evaluated by two radiologists.

RESULTS

Forty-eight cases of partial MPFL tear and 71 cases of complete MPFL tear were identified. Injuries occurred at an isolated femoral attachment (FEM) in 48 cases, an isolated patellar insertion (PAT) in 36 cases and an isolated mid-substance (MID) in five cases. More than one site of injury to the MPFL (COM) was identified in 30 cases. The prevalence rate of chondral and osteochondral lesions of the lateral femoral condyle were 4.2% (2/48) and 6.3% (3/48) in the FEM subgroup, 19.4% (7/36) and 22.2% (8/36) in the PAT subgroup and 6.7% (2/30) and 13.3% (4/30) in the COM subgroup, respectively. The PAT subgroup showed significantly higher prevalence rate of chondral and osteochondral lesions in the lateral femoral condyle when compared with the FEM subgroup. The prevalence rate of chondral and osteochondral lesions of the lateral femoral condyle were 8.5% (6/71) and 19.7% (14/71) in the complete MPFL tear subgroup and 10.4% (5/48) and 4.2% (2/58) in the partial MPFL tear subgroup, respectively. The subgroup of the complete MPFL tear showed significantly higher prevalence rate of osteochondral lesions in the lateral femoral condyle when compared with the subgroup of the partial MPFL tear.

CONCLUSIONS

Firstly, the MPFL is most easily injured at the FEM, and secondly at the PAT in adults after acute LPD. The complete MPFL tear is more often concomitant with osteochondral lesions of the lateral femoral condyle than the partial MPFL tear. The isolated patellar-sided MPFL tear is more easily concomitant with chondral lesions and osteochondral lesions of the lateral femoral condyle than the isolated femoral-sided MPFL tear.

Patellofemoral Pressure Changes After Static and Dynamic Medial Patellofemoral Ligament Reconstructions

BACKGROUND

Reconstructing the medial patellofemoral ligament (MPFL) has become a key procedure for stabilizing the patella. Different techniques to reconstruct the MPFL have been described: static techniques in which the graft is fixed rigidly to the bone or dynamic techniques with soft tissue fixation. Static MPFL reconstruction is most commonly used. However, dynamic reconstruction deforms more easily and presumably functions more like the native MPFL.

PURPOSE/HYPOTHESIS

The aim of the study was to evaluate the effect of the different MPFL fixation techniques on patellofemoral pressures compared with the native situation. The hypothesis was that dynamic reconstruction would result in patellofemoral pressures closer to those generated in an intact knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven fresh-frozen knee specimens were tested in an in vitro knee joint loading apparatus. Tekscan pressure-sensitive films fixed to the retropatellar cartilage measured mean patellofemoral and peak pressures, contact area, and location of the center of force (COF) at fixed flexion angles from 0° to 110°. Four different conditions were tested: intact, dynamic, partial dynamic, and static MPFL reconstruction. Data were analyzed using linear mixed models.

RESULTS

Static MPFL reconstruction resulted in higher peak and mean pressures from 60° to 110° of flexion (P < .001). There were no differences in pressure between the 2 different dynamic reconstructions and the intact situation (P > .05). The COF in the static reconstruction group moved more medially on the patella from 50° to 110° of flexion compared with the other conditions. The contact area showed no significant differences between the test conditions.

CONCLUSION

After static MPFL reconstruction, the patellofemoral pressures in flexion angles from 60° to 110° were 3 to 5 times higher than those in the intact situation. The pressures after dynamic MPFL reconstruction were similar as compared with those in the intact situation, and therefore, dynamic MPFL reconstruction could be a safer option than static reconstruction for stabilizing the patella.

CLINICAL RELEVANCE

This study showed that static MPFL reconstruction results in higher patellofemoral pressures and thus enhances the chance of osteoarthritis in the long term, while dynamic reconstruction results in more normal pressures.

The ability of medial patellofemoral ligament reconstruction to correct patellar kinematics and contact mechanics in the presence of a lateralized tibial tubercle

BACKGROUND

Tibial tubercle (TT) transfer and medial patellofemoral ligament (MPFL) reconstruction are used after patellar dislocations. However, there is no objective evidence to guide surgical decision making, such as the ability of MPFL reconstruction to restore normal behavior in the presence of a lateralized TT.

HYPOTHESIS

MPFL reconstruction will only restore joint contact mechanics and patellar kinematics for TT-trochlear groove (TG) distances up to an identifiable limit.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees (mean TT-TG distance, 10.4 mm) were placed on a testing rig. Individual quadriceps heads and the iliotibial band were loaded with 205 N in physiological directions using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film and an optical tracking system. The MPFL attachments were marked. TT osteotomy was performed, and a metal T-plate was fixed to the anterior tibia with holes at 5-mm intervals for TT fixation. The anatomic TT position was restored after plate insertion. The TT was lateralized in 5-mm intervals up to 15 mm, with pressure and tracking measurements recorded. The MPFL was transected and all measurements repeated before and after MPFL reconstruction using a double-stranded gracilis tendon graft. Data were analyzed using repeated-measures ANOVA, Bonferroni post hoc analysis, and paired t tests.

RESULTS

MPFL transection significantly elevated lateral patellar tilt and translation and reduced mean medial contact pressures during early knee flexion. These effects increased significantly with TT lateralization. MPFL reconstruction restored patellar translation and mean medial contact pressures to the intact state when the TT was in anatomic or 5-mm lateralized positions. However, these were not restored when the TT was lateralized by 10 mm or 15 mm. Patellar tilt was restored after 5-mm TT lateralization but not after 10-mm or 15-mm lateralization.

CONCLUSION

Considering the mean TT-TG distance in this study (10.4 mm), findings suggest that in patients with TT-TG distances up to 15 mm, patellofemoral kinematics and contact mechanics can be restored with MPFL reconstruction. However, for TT-TG distances greater than 15 mm, more aggressive surgery such as TT transfer may be indicated.

CLINICAL RELEVANCE

This provides guidance to surgeons as to the threshold at which MPFL reconstruction may satisfactorily restore patellofemoral mechanics, beyond which more invasive surgery such as TT transfer may be indicated.

Anatomy of the Medial Patello-Femoral Ligament: a systematic review of the last 20 years literature

BACKGROUND

Although many studies have investigated the anatomy of the Medial Patello-Femoral Ligament (MPFL), some studies have even questioned its existence. In the last 20 years, there is a renewed interest on the role of the MPFL in patello-femoral instability. As a result, several studies have been published that describe the anatomy, function and possible surgical reconstruction of the MPFL. Despite the large amount of literature produced, there is still a lack of consensus on what is its real anatomy as there are currently no systematic reviews on this topic.

PURPOSES

Thus, the aim of this review is to systematically report the results in literature regarding in anatomical papers, the existence, size, insertion sites and relationships of this ligament with the other medial structures of the knee.

METHODS

We have systematically analyzed anatomical studies currently available in literature between 1980 and December 2012. The search was carried out on Medline, Embase, Cochrane Library and Google Scholar. We checked reference lists of articles, reviews and textbooks identified by the search strategy for other possible relevant studies.

RESULTS

The outcomes examined are the presence of the ligament, its size (length, width, thickness), and its patellar and femoral insertions. A total of 312 cadaveric knees were included in the 17 studies; the MPFL was identified in 99% of cases (309).

CONCLUSIONS

The consensus is that the MPFL is almost always present in the dissected knees. The size and insertions of the ligament demonstrate great variation between cadavers.

LEVEL OF EVIDENCE

Systematic review of anatomical study, Level 1.

Length change behavior of virtual medial patellofemoral ligament fibers during in vivo knee flexion

BACKGROUND

In vivo length change behavior of native medial patellofemoral ligament (MPFL) fibers throughout the range of knee motion has not been reported in vivo.

PURPOSE

To measure the length changes of various fibers of the MPFL and to determine their length change patterns during in vivo passive knee flexion.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The right knees of 11 living subjects were scanned with a high-resolution computed tomography scanner at 0°, 30°, 60°, 90°, and 120° of knee flexion, and 3-dimensional (3D) models were constructed using customized software. Five patellar points were determined: 20% (point 20), 30% (point 30), 40% (point 40), 50% (point 50), and 60% (point 60) from the superior pole of the patella. The Schöttle femoral point (point F) was marked on a translucent 3D model of a true lateral view. Five virtual fibers connecting these points on the 3D knee model were created, and the lengths of various fibers were digitally measured.

RESULTS

The average length changes were 9.1±2.5 mm in F20, 9.1±2.5 mm in F30, 8.1±2.6 mm in F40, 6.9±2.4 mm in F50, and 6.9±1.7 mm in F60. There were significant differences in length changes of these 5 fibers (P<.001). The lengths of 2 superior fibers (F20 and F30) increased as the knee flexed from 0° to 30° and decreased as the knee flexed over 30°. The lengths of a middle fiber (F40) and an inferior fiber (F50) increased from 0° to 30°, reached a plateau from 30° to 60°, and then decreased from 60° to 120°. F60 showed an increase from 0° to 30°, and then a plateau pattern from 30° to 90°, followed by a decrease during further flexion.

CONCLUSION

Superior fibers exhibited their maximum lengths at low flexion angles, and inferior fibers exhibited their maximum lengths at midflexion angles. The MPFL is a complex of functionally various fibers with some taut and others slack over the whole range of knee motion.

CLINICAL RELEVANCE

The results for lengths and length change patterns of various MPFL fibers are expected to serve as a theoretical background for anatomic double-bundle MPFL reconstruction.

Morphology of the femoral insertion site of the medial patellofemoral ligament

PURPOSE

The purpose of this study was to identify the femoral insertion of the medial patellofemoral ligament (MPFL) and related osseous landmarks.

METHODS

A total of 31 unpaired human cadaveric knees were studied. The MPFL was identified, and the site of its femoral insertion was marked. Three-dimensional images were created, and the location and morphology of the femoral insertion of the MPFL and related osseous structures were analyzed.

RESULTS

The MPFL was identified in all knees. The femoral insertion of the MPFL was elliptical in shape, and the mean surface area was 56.5 ± 16.9 mm(2). The characteristic features of the femoral insertion of the MPFL could not be identified, but the adductor tubercle was clearly identified in all knees. The centre of the femoral insertion of the MPFL was 10.6 ± 2.5 mm distal to the apex of the adductor tubercle on the long axis of the femur, and the position of the insertion site was consistent in all knees.

CONCLUSION

The adductor tubercle was clearly identified as an osseous landmark. The femoral insertion of the MPFL was approximately 10 mm distal to the adductor tubercle. These findings may improve understanding of the anatomy of the femoral insertion of the MPFL and may assist surgeons in performing anatomical reconstruction.

Injury patterns of medial patellofemoral ligament and correlation analysis with articular cartilage lesions of the lateral femoral condyle after acute lateral patellar dislocation in children and adolescents: An MRI evaluation

OBJECTIVES

The purpose of this study was to investigate the injury characteristics of medial patellofemoral ligament (MPFL), and to analyse the correlations between the injury patterns of MPFL and articular cartilage lesions of the lateral femoral condyle in children and adolescents with acute lateral patellar dislocation (LPD).

METHODS

Magnetic resonance (MR) images were prospectively obtained in 127 consecutive children and adolescents with acute LPD. Images were acquired using standardised protocols and these were independently evaluated by two radiologists.

RESULTS

Fifty-four cases of partial MPFL tear and 69 cases of complete MPFL tear were identified. Injuries occurred at an isolated patellar insertion (PAT) in 47 cases, an isolated femoral attachment (FEM) in 41 cases and an isolated mid-substance (MID) in four cases. More than one site of injury to the MPFL (COM) was identified in 31 cases. The prevalence rate of chondral and osteochondral lesions of the lateral femoral condyle were 23.4% (11/47) and 29.8% (14/47) in the PAT subgroup, 7.3% (3/41) and 9.8% (4/41) in the FEM subgroup and 25.8% (8/31) and 32.3% (10/31) in the COM subgroup, respectively. The PAT and COM subgroups showed significantly higher prevalence rate of chondral and osteochondral lesions in the lateral femoral condyle when compared with the FEM subgroup. The prevalence rate of chondral and osteochondral lesions of the lateral femoral condyle were 17.4% (12/69) and 30.4% (21/69) in the complete MPFL tear subgroup and 20.4% (11/54) and 13% (7/54) in the partial MPFL tear subgroup, respectively. The subgroup of the complete MPFL tear showed significantly higher prevalence rate of osteochondral lesions in the lateral femoral condyle when compared with the subgroup of the partial MPFL tear.

CONCLUSIONS

Firstly, the MPFL is most easily injured at the PAT, and secondly at the FEM in children and adolescents after acute LPD. The complete MPFL tear is more often concomitant with osteochondral lesions of the lateral femoral condyle than the partial MPFL tear. The isolated patellar-sided MPFL tear and the combined MPFL tear are more easily concomitant with chondral lesions and osteochondral lesions of the lateral femoral condyle than the isolated femoral-sided MPFL tear.

Medial patellofemoral ligament reconstruction: clinical and radiographic results in a series of 90 cases

INTRODUCTION

Among the numerous techniques available, medial patellofemoral ligament (MPFL) reconstruction is increasingly used for the surgical treatment of objective patellar instability. The main objective of the present study was to assess efficacy in preventing recurrence of patellar dislocation and in correcting radiographic patellar tilt. The study hypothesis was that MPFL reconstruction, isolated or with associated bone surgery, by restoring "favorable" graft anisometry, provides a good trade-off between patellar stability and absence of postoperative stiffness.

MATERIALS AND METHODS

Eighty-seven patients (90 reconstructions) presenting with objective patellar instability were prospectively included. The standardized procedure comprised MPFL reconstruction using the gracilis tendon. Femoral fixation used an interference screw in a blind tunnel between the adductor magnus tubercle and the medial epicondyle; patellar fixation used 2 anchors. Complementary distal bone graft was associated in 21 patients due to a preoperative tibial tubercle-trochlear groove (TT-TG) distance exceeding 20mm or to patella alta. Functional IKDC and Kujala scores and radiographic measurement of patellar tilt and femoral tunnel position were assessed preoperatively and at end of follow-up.

RESULTS

Mean follow-up was 24.3months (range, 6-49months). Three patients showed recurrence of patellar dislocation. Mean Kujala score rose from 53.88 preoperatively to 86.24 postoperatively, and mean real IKDC score from 45.15 to 73.92 (P<0.001). Patellar tilt decreased significantly between pre- and postoperative X-ray (P<0.001).

DISCUSSION

MPFL gracilis reconstruction provides good clinical results and good radiologic correction of patellar tilt, making it a technique of choice in the treatment of objective patellar instability.

LEVEL OF EVIDENCE

Level IV. Retrospective case series study.

A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty

Musculoskeletal (MS) models should be able to integrate patient-specific MS architecture and undergo thorough validation prior to their introduction into clinical practice. We present a methodology to develop subject-specific models able to simultaneously predict muscle, ligament, and knee joint contact forces along with secondary knee kinematics. The MS architecture of a generic cadaver-based model was scaled using an advanced morphing technique to the subject-specific morphology of a patient implanted with an instrumented total knee arthroplasty (TKA) available in the fifth “grand challenge competition to predict in vivo knee loads” dataset. We implemented two separate knee models, one employing traditional hinge constraints, which was solved using an inverse dynamics technique, and another one using an 11-degree-of-freedom (DOF) representation of the tibiofemoral (TF) and patellofemoral (PF) joints, which was solved using a combined inverse dynamic and quasi-static analysis, called force-dependent kinematics (FDK). TF joint forces for one gait and one right-turn trial and secondary knee kinematics for one unloaded leg-swing trial were predicted and evaluated using experimental data available in the grand challenge dataset. Total compressive TF contact forces were predicted by both hinge and FDK knee models with a root-mean-square error (RMSE) and a coefficient of determination (R2) smaller than 0.3 body weight (BW) and equal to 0.9 in the gait trial simulation and smaller than 0.4 BW and larger than 0.8 in the right-turn trial simulation, respectively. Total, medial, and lateral TF joint contact force predictions were highly similar, regardless of the type of knee model used. Medial (respectively lateral) TF forces were over- (respectively, under-) predicted with a magnitude error of M < 0.2 (respectively > −0.4) in the gait trial, and under- (respectively, over-) predicted with a magnitude error of M > −0.4 (respectively < 0.3) in the right-turn trial. Secondary knee kinematics from the unloaded leg-swing trial were overall better approximated using the FDK model (average Sprague and Geers' combined error C = 0.06) than when using a hinged knee model (C = 0.34). The proposed modeling approach allows detailed subject-specific scaling and personalization and does not contain any nonphysiological parameters. This modeling framework has potential applications in aiding the clinical decision-making in orthopedics procedures and as a tool for virtual implant design.

Shape and size of the medial patellofemoral ligament for the best surgical reconstruction: a human cadaveric study

PURPOSE

The aim of this study was to investigate the shape and the attachments of the medial patellofemoral ligament (MPFL) in cadaver specimens to determine an anatomical basis for the best MPFL reconstruction.

METHODS

Twenty fresh-frozen knees were used. Dissection protocol implied performing dissections from within the knee joint. We investigated the shape and the attachments between the MPFL and the quadriceps tendon, the patellar and femur insertions, and all the other relationships with the medial soft tissues of the knee.

RESULTS

The distal fibers of MPFL were interdigitated with the deep layer of the medial retinaculum. All isolated ligament had a sail-like shape with the patellar side bigger than the femoral side. The femoral insertion, distinct both from medial epicondyle and adductor tubercle, was located at 9.5 mm (range 4-22) distal and anterior respect to adductor tubercle and proximal and posterior to epicondyle. The medial third of the thickness of patella was involved in the insertion. The proximal third of the patella is always involved in the MPFL attachment; in 45% of the cases, it was extended to the medial third and in one case, an extension at the distal third was found. Additionally in 35% (7 cases), it extended to the quadriceps tendon and it were inconstantly attached at the vastus medialis obliques (VMO) tendon and at the vastus intermedius (VI) tendon in an aponeurotic structure.

CONCLUSIONS

The MPFL is a distinct structure that goes from patella to femur with a sail-like shape; its patellar insertion, that mostly occur via an aponeurosis tissue with VMO and VI, is at the proximal third of the patella but it may extend in some cases to the medial third patella or to the quadriceps tendon, or very rarely to the distal third of the patella. In the femoral side, the MPFL is inserted in its own site, in most cases distinct both from epicondyle and adductor tubercle, located on average at a 9.5 mm distance distally and anteriorly in respect to the adductor tubercle. Its lower margin was difficult to define. Given the importance of this structure, it must be reconstructed as anatomically as possible in its insertion and in its shape. Many attempts have been made to make functional reconstructions with less than excellent results.

Medial patellotibial ligament (MPTL) reconstruction for patellar instability

PURPOSE

To evaluate mid-term clinical and radiographic outcomes after an original medial patellotibial ligament reconstruction in patients with patellar dislocation.

METHODS

Twenty-nine knees (27 patients, 8 males and 19 females) treated for patellar dislocation with medialization of the patellar tendon medial third combined with medial and lateral release were evaluated clinically and radiographically at a mean follow-up of 6.1±2.5 years. Trochleoplasty was performed in case of severe flat trochlea (6 knees, 21%). Aetiology of patellofemoral instability was traumatic in 6 (21%) and atraumatic in 23 (79%) knees. The mean age at first dislocation was 19.2±10.1 years. WOMAC, subjective and objective IKDC, Kujala, VAS for pain, Tegner activity and EQ-5D scores were used. Anteroposterior, lateral and 30° axial views were performed for radiographic monitoring.

RESULTS

There was a significant improvement of all clinical scores and significant reduction in knee pain. Twenty-four knees (83%) were normal or nearly normal by objective IKDC score at final follow-up. Radiographs showed a higher incidence of patella alta and flat trochlea in the atraumatic group. Severe signs of patellar osteoarthritis were found in 1 knee (3%). A higher body mass index (BMI) was correlated with worse pre-operative scores. Four knees (14%) were considered failures (2 further dislocations, 2 revision surgeries). The overall survival rate at 6 years was 0.811.

CONCLUSIONS

The presented techniques produced good clinical and radiographic results at mean 6.1 years follow-up, with 14 % failures. Signs of patellofemoral dysplasia were found in patients with atraumatic patellar dislocation. BMI was related to worse pre-operative clinical status.

LEVEL OF EVIDENCE

Retrospective study, Level IV.

Medial patellofemoral ligament reconstruction for patellar maltracking following total knee arthroplasty is effective

PURPOSE

Maltracking of the patella after total knee arthroplasty (TKA) remains a well-recognized problem. The medial patellofemoral ligament (MPFL) has shown to be important for patellar stabilization and reconstructions of the MPFL have already shown excellent functional outcomes for patellar instability of the native knee. Nevertheless, there is only limited literature on using an MPFL reconstruction for correction of patellar maltracking after TKA. In this retrospective study, a consecutive case series was evaluated.

METHODS

Between 2007 and 2010, nine patients (nine knees) with anterior knee pain and symptomatic (sub)luxations of the patella after primary or revision TKA were treated by reconstruction of the MPFL in combination with a lateral release. In two cases, an additional tibial tuberosity transfer was performed, due to insufficient per-operative correction. Pre-operative work-up included a CT scan to rule out component malrotation and disorders in limb alignment. Pre- and post-operative patellar displacement and lateral patellar tilt were measured on axial radiographs. Clinical outcome was evaluated using the visual analogue scale (VAS) satisfaction, VAS pain, dislocation rate and Bartlett patella score.

RESULTS

Median patellar displacement improved from 29 mm (0-44) to 0 mm (0-9) post-operatively. Median lateral patellar tilt was 45° (23-62) pre-operative and changed to a median 15° (-3 to 21) post-operative. Median VAS satisfaction was 8 (5-9) and only one patient reported a subluxing feeling afterwards. The Bartlett patella score displayed a diverse picture.

CONCLUSIONS

Patellar maltracking after primary or revision TKA without malrotation can effectively be treated by MPFL reconstruction in combination with a lateral release. Only in limited cases, an additional tibial tuberosity transfer is needed.

LEVEL OF EVIDENCE

IV.

Is tibial tuberosity-trochlear groove distance an appropriate measure for the identification of knees with patellar instability?

PURPOSE

Tibial tuberosity-trochlear groove distance (TT-TG) has been regarded as a useful tool for establishing therapeutic choices for patellar instability. Recently, it has been shown that TT-TG negatively correlated with the quadriceps angle, suggesting that if used individually, neither provide a valid measure of instability. This study aimed to compare TT-TG distance between both knees in patients with unilateral instability to assess whether this measurement is a decisive element in the management decisions for patellar instability.

METHODS

Sixty-two patients (18 male and 44 female), reporting to a specialist patella clinic for recurrent unilateral patellar instability, were included in the study. Patients underwent bilateral long leg computed tomography scan to determine TT-TG distance in both knees. Tibial TT-TG in symptomatic and asymptomatic knees in the same individual was compared statistically.

RESULTS

Mean TT-TG distance in the symptomatic knee was 16.9 (±4.9) mm, compared to 15.6 (±5.6) mm in the asymptomatic knee. Tibial TT-TG was not significantly different between stable and unstable knees (n.s.).

CONCLUSIONS

The lack of difference in TT-TG distance between stable and unstable knees suggests that TT-TG distance alone may not be a decisive element in establishing therapeutic choices for patellar instability. It should, therefore, be interpreted with caution during clinical evaluations.

LEVEL OF EVIDENCE

II.

Tibial Tuberosity Osteotomy: Indications, Techniques, and Outcomes

Tibial tuberosity osteotomy (TTO) is a well-described treatment option for a broad range of patellofemoral joint disorders, including patellofemoral instability, patellar and trochlear focal chondral lesions, and patellofemoral arthritis. The purpose of this article is to review the evolution of the TTO procedure, from the original Hauser procedure to the current anteromedialization procedure, as well as discuss the pertinent anatomy and radiographs that accompany this procedure. The article highlights the surgical techniques for some of the more commonly performed TTO procedures and discusses the outcomes of the various TTO techniques. Complications, as well as clinical pearls to avoid these complications, are also included.

Vastus medialis obliquus muscle morphology in primary and recurrent lateral patellar instability

The morphology of the vastus medialis obliquus (VMO) muscle in the anatomical setting of an unstable patella has not been described. Therefore, the purpose of this study was to investigate the morphological parameters of the VMO muscle that delineate its importance in the maintenance of patellofemoral joint stability. Eighty-two consecutive subjects were prospectively enrolled in this study. The groups were composed of thirty patients with an acute primary patellar dislocation, thirty patients with recurrent patellar dislocation, and twenty-two controls. Groups were adjusted according to sex, age, body mass index, and physical activity. Magnetic resonance imaging was used to measure the VMO cross-sectional area, muscle-fiber angulation, and the craniocaudal extent of the muscle in relation to the patella. No significant difference was found with respect to all measured VMO parameters between primary dislocation, recurrent dislocation, and control subjects with a trend noted for only the VMO cross-sectional area and the VMO muscle-fiber angulation. This finding is notable in that atrophy of the VMO has often been suggested to play an important role in the pathophysiology of an unstable patellofemoral joint.

Non-anatomical capsular closure of a standard parapatellar knee arthrotomy leads to patellar maltracking and decreased range of motion: a cadaver study

PURPOSE

A parapatellar approach disrupts the medial soft tissue stabilizers of the patella. We hypothesized that soft tissue realignment during arthrotomy closure of native cadaveric knees influences patellar kinematics leading to decreased range of motion.

METHODS

Parapatellar arthrotomy was performed in seven native human cadaveric knees that did not contain arthroplasty components. Capsular closure was performed with figure-of-eight sutures in five different positions for each specimen. The capsule was closed anatomically, and then shifted 1.5 or 3 cm distal, or 1.5 or 3 cm proximal relative to surgical markings of the patellar poles. In each closure position, real-time patellar kinematics and range of motion were recorded using a navigation system with patellar tracking function.

RESULTS

Maximum knee flexion was significantly reduced with closure shifted 3 cm proximal (133° ± 8.2°, p < 0.001) or distal (139° ± 6.4°, p < 0.05) compared to anatomical closure (147° ± 4.1°). All closure positions significantly influenced patellar rotation at 45°, 90°, and 120° of flexion (p < 0.001). Closure 1.5 or 3 cm distal increased lateral patellar shift relative to the mechanical axis (p < 0.01). Patellar tilt was significantly decreased at 90° and 120° by closure 3 cm distal (p < 0.01) and at 120° when closed 1.5 cm distal (p < 0.05).

CONCLUSIONS

Imprecise arthrotomy closure significantly impacted patellar kinematics and passive range of motion. Therefore, every effort should be made to provide anatomical closure of the extensor mechanism to preserve native patellar movement kinematics.

LEVEL OF EVIDENCE

V.

Femoral tunnel enlargement after medial patellofemoral ligament reconstruction: prevalence, risk factors, and clinical effect

BACKGROUND

In recent years, significantly more attention has been focused on the role of the medial patellofemoral ligament (MPFL) in patellar stability, and MPFL reconstruction has become a mainstay of surgical treatment of episodic patellar dislocations. Although previously described in detail after reconstruction of the anterior cruciate ligament, tunnel enlargement has not been investigated after MPFL reconstruction.

HYPOTHESES

(1) Femoral tunnel enlargement occurs after MPFL reconstruction. (2) Patella alta, trochlear dysplasia, and tunnel malposition are risk factors for tunnel enlargement. (3) The presence of tunnel enlargement is not associated with recurrent dislocations or poorer patient-reported outcome scores after MPFL reconstruction.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Fifty-five of 59 knees treated for episodic patellar dislocations with MPFL reconstruction between 2005 and 2010 were evaluated at 1 year postoperatively for the presence of tunnel enlargement on lateral radiographs. Tunnel enlargement was defined as a tunnel area greater than 2 times that of the original tunnel. Knees with tunnel enlargement at 1 year were compared with those without tunnel enlargement. Patients were assessed for recurrent subluxations or dislocations at a mean of 3 years postoperatively, and patient-reported outcome scores were assessed in a subset of patients at a mean of 3.7 years postoperatively.

RESULTS

Tunnel enlargement was noted in 23 knees (41.8%). No differences in patient age or body mass index were noted between the 2 groups. The mean patellar height was significantly higher in the enlarged tunnel group (P = .03). A higher prevalence of trochlear dysplasia or tunnel malposition was not demonstrated in the enlarged tunnel group. Patient-reported outcome scores and the risk of recurrent patellar instability were equal in the 2 groups.

CONCLUSION

Femoral tunnel enlargement after MPFL reconstruction is common, with patients with patella alta at an increased risk. The influence of tunnel malposition and trochlear dysplasia on this condition requires further research. Recurrent instability and patient-reported outcome scores are not affected by tunnel enlargement.

Sectioning the medial patellofemoral ligament alters patellofemoral joint kinematics and contact mechanics

Medial patellofemoral ligament (MPFL) disruption may alter patellofemoral joint (PFJ) kinematics and contact mechanics, potentially causing pain and joint degeneration. In this controlled laboratory study, we investigated the hypothesis that MPFL transection would change patellar tracking and PFJ contact pressures and increase the distance between the attachment points of the MPFL. Eight fresh frozen dissected cadaveric knees were mounted in a rig with the quadriceps and ITB loaded to 205 N. An optical tracking system measured joint kinematics, and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Length patterns of the distance between the femoral and patellar attachments of the MPFL were measured using a suture led to a linear displacement transducer. Measurements were repeated with the MPFL intact and following MPFL transection. A significant increase in the distance between the patellar and femoral MPFL attachment points was noted following transection (p < 0.05). MPFL transection resulted in significantly increased lateral translation and lateral tilt of the patella in early flexion (p < 0.05). Peak and mean medial PFJ contact pressures were significantly reduced and peak lateral contact pressures significantly elevated in early knee flexion following MPFL transection (p < 0.05). MPFL transection resulted in significant alterations to PFJ tracking and contact pressures, which may affect articular cartilage health.

The influence of medial patellofemoral ligament on patellofemoral joint kinematics and patellar stability

PURPOSE

Retinacular restraints have a critical role in patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is probably the main stabilizer against lateral displacement; few studies are focused on MPFL role on patellofemoral kinematics and patellar stability. The main goal of this in vitro study was to analyse the influence of the MPFL on the kinematics of the patellofemoral joint and patellar stability.

METHODS

Using a non-image-based navigation system, kinematics and anatomical data of six fresh-frozen specimens were collected. A passive flexion-extension from 0° to 90° and static acquisitions at 0°, 30°, 60° and 90°, with and without 25 N of lateral load, were performed with intact and resected MPFL with a 60 N axial force applied to the isolated quadriceps tendon. Patellar tilt and shift were analysed.

RESULTS

The MPFL intact state showed a shift in medial direction during the first degrees of knee flexion-that disappeared in MPFL resected condition-followed by a lateral shift, similar to that of MPFL resected condition. Tilt analysis showed that patella rotated laterally until 85° of knee flexion for intact MPFL condition and until 70° for resected MPFL condition and after rotated medially. Static tests showed that patellar stability was significantly affected by MPFL resected condition in particular at 30° and 60°.

CONCLUSIONS

The MPFL has an aponeurotic nature. It works as a restraint during motion, with an active role under high stress on lateral side, but with a small contribution during neutral knee flexion. Its biomechanical behaviour under loading conditions should be kept into account when performing surgical reconstruction of this ligamentous structure.

Evaluation of patellofemoral joint in ADVANCE Medial-pivot total knee arthroplasty

PURPOSE

ADVANCE Medial Pivot (MP) (Wright Medical) total knee arthroplasty (TKA) was established to replicate normal tibio-femoral knee joint kinematics, however, its influence on the patello-femoral (PF) joint is unclear. The purpose in this study was to assess the PF joint conditions in Advance MP TKA, via radiography and three-dimensional image-matching software.

METHODS

Ten subjects with osteoarthritis were treated with the ADVANCE MP TKA. Pre-operatively and one month after surgery, skyline views at 30, 60, and 90° of flexion were taken, and patella shift and tilt were measured. With 2D-3D registration techniques using software, implant orientations were matched with the pre-operative CT and changes in the anterior part of the femoral prosthesis, condylar twist angle (CTA) for femoral rotation, and tibial rotation were evaluated. The relationships between morphological and rotational changes were evaluated.

RESULTS

There were significant differences in patella tilt at 60° and patella shift at all angles between pre- and post-operation (p < 0.05). No correlation was found between morphological changes in the anterior femur with patella tilt and shift. A positive correlation between postoperative CTA and patella shift at 90° was found (p < 0.05); however, no correlation was found between rotational alignment of the tibial component and patella tilt and shift.

CONCLUSIONS

ADVANCE MP TKA changed patello-femoral joint kinematics, compared to that found before surgery. The kinematic features were mainly due to the design concepts for tibio-femoral joint motion, indicating the difficulty to reproduce normal patello-femoral joint kinematics after TKA.

Non-surgical treatment for acute patellar dislocation with special emphasis on the MPFL injury patterns

PURPOSE

The objective of present study was to propose a new classification for acute MPFL injury, which can help choose optimal treatment method for certain injury type.

METHODS

Eighty-five patients with acute patellar dislocation treated non-surgically were retrospectively reviewed. They were assigned into two groups according to the newly introduced classification scheme, which classified MPFL injury into three types: injury in overlap region, injury in non-overlap region and combined injury of both regions. For study purpose, patients with combined injury were not included. Of 85 patients, 33 were in the overlap-region group (Group 1) and 52 in the non-overlap-region group (Group 2). Clinical patellar instability rate and patellofemoral score were measured and recorded at 2-year follow-up.

RESULTS

The patellar instability rate was 15.2 % in Group 1 and 38.5 % in Group 2, with statistically significant difference between the two groups (P = 0.022). The mean visual analogue scale for Group 1 and Group 2 was 15.6 points and 28.3 points, respectively (P = 0.026). The mean Kujala score was 91.1 points and 82.6 points (P = 0.009), with a good or excellent subjective result recorded for 27 of 33 patients (81.8 %) in Group 1 compared with 30 of 52 patients (57.7 %) in Group 2 (P = 0.021).

CONCLUSIONS

Non-surgical treatment achieves better clinical outcomes with respect to a lower patellar instability rate and better subjective function for the overlap-region injury of MPFL than for the non-overlap-region injury, and can be considered as treatment of choice for overlap-region injury of MPFL. The optimal choice for the non-overlap-region injury still requires further researches.

LEVEL OF EVIDENCE

Therapeutic, Level IV.

Anatomic study of the attachment of the medial patellofemoral ligament and its characteristic relationships to the vastus intermedius

PURPOSE

The aim of this study was to investigate the attachment of the medial patellofemoral ligament (MPFL) using cadaver specimens and establish an anatomic basis for optimal MPFL reconstruction to achieve better patella stability.

METHODS

Sixteen knees of eight cadavers were used in this study. The relationship of the MPFL with quadriceps muscles was investigated from outside after removal of the distal part of the vastus medialis and the rectus femoris and then evaluated from intra-articular side after release of lateral margin of the vastus lateralis muscle, patella and patella tendon.

RESULTS

The proximal fibres of MPFL were mainly attached to the vastus intermedius tendon, without tight adhesion to the vastus medialis. The distal fibres of MPFL were interdigitated with the deep layer of the medial retinaculum that was attached to the medial margin of the patella tendon.

CONCLUSION

These findings imply that MPFL, which was directly attached to the vastus intermedius and patella and indirectly continued to the patella tendon, could keep pulling them medially as one unit and consequently make the patella move smoothly on the trochlea during whole movement of the knee. Clinically, dysfunction of both proximal and distal MPFL fibres should be considered in the diagnosis and treatment of patella instability after traumatic patella dislocation. MPFL reconstruction with both fibres has a possibility to lead ideal function of MPFL and better instability of the patella.

A detailed and validated three dimensional dynamic model of the patellofemoral joint

A detailed 3D anatomical model of the patellofemoral joint was developed to study the tracking, force, contact and stability characteristics of the joint. The quadriceps was considered to include six components represented by 15 force vectors. The patellar tendon was modeled using four bundles of viscoelastic tensile elements. Each of the lateral and medial retinaculum was modeled by a three-bundle nonlinear spring. The femur and patella were considered as rigid bodies with their articular cartilage layers represented by an isotropic viscoelastic material. The geometrical and tracking data needed for model simulation, as well as validation of its results, were obtained from an in vivo experiment, involving MR imaging of a normal knee while performing isometric leg press against a constant 140 N force. The model was formulated within the framework of a rigid body spring model and solved using forth-order Runge-Kutta, for knee flexion angles between zero and 50 degrees. Results indicated a good agreement between the model predictions for patellar tracking and the experimental results with RMS deviations of about 2 mm for translations (less than 0.7 mm for patellar mediolateral shift), and 4 degrees for rotations (less than 3 degrees for patellar tilt). The contact pattern predicted by the model was also consistent with the results of the experiment and the literature. The joint contact force increased linearly with progressive knee flexion from 80 N to 210 N. The medial retinaculum experienced a peak force of 18 N at full extension that decreased with knee flexion and disappeared entirely at 20 degrees flexion. Analysis of the patellar time response to the quadriceps contraction suggested that the muscle activation most affected the patellar shift and tilt. These results are consistent with the recent observations in the literature concerning the significance of retinaculum and quadriceps in the patellar stability.