The medial patellofemoral ligament: location of femoral attachment and length change patterns resulting from anatomic and nonanatomic attachments

Relationship between bony tunnel and knee function in patients after patellar dislocation triple surgeries-a CT-based study

We aimed to assess the CT-based bony tunnel valuations and their correlation with knee function after patellar dislocation triple surgeries. A retrospective study was performed on 66 patients (70 knees) who underwent patellar dislocation triple surgeries. The surgery was MPFL reconstruction primarily, combined with lateral retinaculum release and tibial tubercle osteotomy. CT examinations were performed to determine the femoral tunnel position, along with the patellar and femoral tunnel width 3 days and more than 1 year after operation for follow-up. Functional evaluation based on Kujala and Lysholm scores was also implemented. We compared tunnel width of the first and last examinations and correlated femoral tunnel position of the last examination with knee function. At the last follow-up, femoral tunnel position in the anterior-posterior direction was moderately correlated with knee function. Femoral tunnel position in the proximal-distal direction was not associated with postoperative knee function. Patellar and femoral tunnel width increased significantly at the last follow-up. However, no significant functional difference was found between patients with and without femoral tunnel enlargement. Our results suggested that the tunnel malposition in anterior-posterior position based on CT was related to impaired knee function during the follow-ups.

Current Concepts in the Management of Patellar Instability

Patellar instability is a common presenting clinical entity in the field of orthopedics. This not only can occur from baseline morphologic variability within the patellofemoral articulation and alignment, but also from traumatic injury. While conservative management is many times employed early in the treatment course, symptomatic patellar instability can persist. This article reviews the available indexed published literature regarding patellar instability. Given the debilitating nature of this condition and the long term sequelae that can evolve from its lack of adequate recognition and treatment, this article details the most current methods in the evaluation of this entity as well as reviews the most up-to-date surgical treatment regimens that are available to address this condition.

Reconstruction of the Medial Patellofemoral Ligament Using a Synthetic Graft With Arthroscopic Control of Patellofemoral Congruence

PURPOSE

To compare the results of reconstruction of the medial patellofemoral ligament (MPFL) using a synthetic graft (Poly-Tape) between knee joints in which the patella was reduced to the strict center and those in which it was slightly lateral to the center of the trochlea to determine whether patellar position within this range affects the results.

METHODS

Forty-six knee joints in 46 patients were examined retrospectively with a minimum follow-up of 2 years. The position of the patellar central ridge in the trochlea on arthroscopy immediately after reconstruction of the MPFL was measured. The joints were classified into group 1 (6 male and 12 female patients), in which the patella was reduced to the strict center of the trochlea, and group 2 (10 male and 18 female patients), in which the patella was reduced slightly lateral to the center. The mean age was 20.7 years in group 1 and 20.3 years in group 2. Knee joints were assessed using the Kujala score and the International Knee Documentation Committee (IKDC) subjective evaluation score.

RESULTS

The mean Kujala and IKDC scores improved significantly in both groups after surgery (both P < .001). There was no significant difference between the groups for any assessment before surgery or in the Kujala score after surgery (P = .075). However, the IKDC score after surgery was significantly better in group 2 (91.3 ± 9.1) than in group 1 (82.8 ± 13.1) (P = .012).

CONCLUSIONS

When recurrent dislocation of the patella was treated with MPFL reconstruction using a synthetic graft, subjective evaluations were better in knee joints in which the patella was repositioned slightly lateral to the center of the trochlea than in those in which the patella was reduced to the strict center, although there was no significant difference in knee function between them.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Evaluation of the isometry of different points of the patella and femur for medial patellofemoral ligament reconstruction

BACKGROUND

The location of patellar and femoral fixation of the graft in medial patellofemoral ligament reconstructions has been widely discussed. This study aimed to assess the distances between different patellar and femoral fixation points to identify the least anisometric pairs of points.

METHODS

Ten cadaver knees were attached to an apparatus that simulated an active range of motion of 120°, with three metallic markers fixed onto the medial side of the patella, and seven markings onto the medial epicondyle. The examined points included the proximal patella pole (1), the patellar center (3), the midpoint between points 1 and 3 (2), a point directly on the epicondyle (6), points 5mm anterior (5) and posterior (7) to the epicondyle, points 5mm anterior to point 5 (4) and 5mm posterior to point 7 (8), and points 5mm proximal (9) and distal (10) to the epicondyle. The distances between patella and femur points were measured by a photogrammetry system at 15° intervals.

FINDINGS

The pair of points that exhibited the lowest average variability in distance, and hence was the most isometric, was the patella center combined with the anterior to the medial femoral epicondyle. The pairs of points that exhibited the highest average variability in distance, and hence were the least isometric, were the ones located distal or posterior to the medial femoral epicondyle, with less influence by the patellar location.

INTERPRETATION

Surgeons should avoid positioning the graft distally or posterior to the epicondyle due to the increase in anisometry.

Dynamic Simulation of the Effects of Graft Fixation Errors During Medial Patellofemoral Ligament Reconstruction

Background:

Medial patellofemoral ligament (MPFL) reconstruction is performed to prevent recurrent instability, but errors in femoral fixation can elevate graft tension.

Hypothesis:

Errors related to femoral fixation will overconstrain the patella and increase medial patellofemoral pressures.

Study Design:

Controlled laboratory study.

Methods:

Five knees with patellar instability were represented with computational models. Kinematics during knee extension were characterized from computational reconstruction of motion performed within a dynamic computed tomography (CT) scanner. Multibody dynamic simulation of knee extension, with discrete element analysis used to quantify contact pressures, was performed for the preoperative condition and after MPFL reconstruction. A standard femoral attachment and graft resting length were set for each knee. The resting length was decreased by 2 mm, and the femoral attachment was shifted 5 mm posteriorly. The simulated errors were also combined. Root-mean-square errors were quantified for the comparison of preoperative patellar lateral shift and tilt between computationally reconstructed motion and dynamic simulation. Simulation output was compared between the preoperative and MPFL reconstruction conditions with repeated-measures Friedman tests and Dunnett comparisons against a control, which was the standard MPFL condition, with statistical significance set at P < .05.

Results:

Root-mean-square errors for simulated patellar tilt and shift were 5.8° and 3.3 mm, respectively. Patellar lateral tracking for the preoperative condition was significantly larger near full extension compared with the standard MPFL reconstruction (mean differences of 8 mm and 13° for shift and tilt, respectively, at 0°), and lateral tracking was significantly smaller for a posterior femoral attachment (mean differences of 3 mm and 4° for shift and tilt, respectively, at 0°). The maximum medial pressure was also larger for the short graft with a posterior femoral attachment than for standard MPFL reconstruction, with a significant increase in the mean value of 1.6 MPa at 30°.

Conclusion:

MPFL reconstruction reduces lateral tracking, but nonanatomic femoral fixation and overtensioning the graft overcorrect patellar tracking and increase pressure applied to medial patellar cartilage.

Clinical Relevance:

Errors in femoral fixation and graft tensioning can lead to postoperative loss of flexion and overloading of medial cartilage.

Does radiographic location ensure precise anatomic location of the femoral fixation site in medial patellofemoral ligament surgery?

PURPOSE

To correlate the location of the medial patellofemoral ligament femoral fixation site in knees suffering a chronic lateral patellar instability, by using radiographic references and by using the most important anatomic reference point (i.e. the adductor tubercle) identified by means of 3-dimensional (3D) surface reconstructions by computed tomography (CT) imaging.

METHODS

Thirty consecutive knee 3D-CT examinations at 0º of knee extension were obtained from patients (20 females, 10 males; median age of 23.5 years; range, 14-48 years) treated for chronic lateral patellar instability with at least two documented patellar dislocations. For each knee, three virtual 7-mm-diameter femoral tunnels were created. One of the tunnels used an anatomic fixation landmark (anatomic fixation), while the other two used established radiologic methods. We calculated the percentage of the anatomic tunnel covered by the tunnel created according to the method described by Schoettle, and the percentage of the anatomic tunnel covered by the tunnel created according to the method described by Stephen. These percentages were compared using paired Student's t test.

RESULTS

The percentage of anatomic tunnel area covered by the femoral tunnel created using Schoettle's method was 36.7 ± 25.2 %. When using Stephen's method, the percentage of overlap with the anatomic femoral tunnel was 25.5 ± 21.5 %. There were no significant differences between the two radiographic methods (n.s.).

CONCLUSION

None of the standard radiographic methods allowed a precise anatomic femoral placement. Conventional radiographic identification of the femoral graft placement site is only an approximation and should not be the sole basis for femoral attachment location.

LEVEL OF EVIDENCE

IV.

Reconstruction of the Medial Patellofemoral Ligament With Arthroscopic Control of Patellofemoral Congruence Using Electrical Stimulation of the Quadriceps

Reconstruction of the medial patellofemoral ligament (MPFL) for recurrent patellar dislocation provides significant improvements in knee function. However, various complications have been reported, with most attributed to incorrect positioning of anchoring sites for the reconstructed MPFL and inappropriate graft tension. Patellofemoral congruence at 30° of flexion on arthroscopy was therefore controlled using devices able to modify the length of the reconstructed MPFL. This was done under circumstances of external rotation of the knee joint and electrical stimulation of the quadriceps with the purpose of maintaining the patella in a lateral shift. Advantages of this technique include completely controllable correction on arthroscopy under the worst patellofemoral congruence induced by external rotation of the knee joint and electrical stimulation of the quadriceps at 30° of flexion of the knee joint; in other words, voluntary determination of lateral shift during arthroscopy.

Femoral insertion site in medial patellofemoral ligament reconstruction

BACKGROUND

The optimal femoral insertion point in MPFL (medial patellofemoral ligament)-reconstruction still remains ambiguous. Three-dimensional knee simulations based on computerized tomography (CT) images acquired under physiological loading conditions give further insights to predict the optimal femoral insertion site of the MPFL. The hypothesis of the present study is that the optimal insertion point is not as reliable as thought and is dependent on subject-specific anatomical factors.

METHODS

High-resolution 3D images of the knee were acquired in ten weight-bearing knees of healthy subjects in five flexion angles (0 to 120°). The distance between different femoral insertion points and two defined patellar points was computed in each position to quantify length of respective bundles and isometry of the femoral insertion site.

RESULTS

The median length of both bundles was maximal in full extension (proximal bundle: 62.2mm and distal bundle: 59.9mm). The shortest ligament length was obtained in the flexion position 90° for bundle I (57.3mm) and 30° for bundle II (85.3mm). The calculated most isometric femoral attachment point showed a non-uniform distribution pattern related to anatomic landmarks. The radiographic landmark showed the worst isometric score value compared to virtually defined spots by surgeons and the computed most isometric point.

CONCLUSIONS

This study provides results on the MPFL path length under physiological loading conditions using high-resolution bone geometry. The most important finding of this study was that the computed, best isometric femoral insertion point showed a variable anatomical distribution. This suggests that the optimal position for femoral MPFL-graft fixation is patient specific.

The Efficacy of Medial Patellofemoral Ligament Reconstruction Combined with Tibial Tuberosity Transfer in the Treatment of Patellofemoral Instability

A systematic review of the literature was undertaken to evaluate the efficacy of medial patellofemoral ligament (MPFL) reconstruction combined with tibial tuberosity transfer (TTT) in the treatment of patellofemoral instability. Using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, a systematic search was carried out to identify and review the published literature pertinent to MFPL reconstruction combined with TTT. Relevant studies were critically appraised with narrative data synthesis. Studies that met the eligibility criteria were suitable for appraisal and consisted of case series and therapeutic series (levels IV & III). All studies had inherent variations in outcomes reporting and limited follow-up. Combined treatment offers restoration of normal anatomy, thus adding clinical value to the currently recommended anatomic approach to MPFL reconstruction. Nevertheless, the current body of evidence does not determine the threshold at which patellofemoral axis requires the need for adjunctive distal realignment as opposed to MPFL reconstruction alone. This review highlighted numerous recurring limitations in the conduct and presentation of the studies, which inadvertently mitigated the interpretation of their results. Future priority should be awarded to larger randomised controlled trials utilising validated patient reported outcome measures.

Effect of Medial Patellofemoral Ligament Reconstruction Method on Patellofemoral Contact Pressures and Kinematics

BACKGROUND

There remains a lack of evidence regarding the optimal method when reconstructing the medial patellofemoral ligament (MPFL) and whether some graft constructs can be more forgiving to surgical errors, such as overtensioning or tunnel malpositioning, than others.

HYPOTHESIS

The null hypothesis was that there would not be a significant difference between reconstruction methods (eg, graft type and fixation) in the adverse biomechanical effects (eg, patellar maltracking or elevated articular contact pressure) resulting from surgical errors such as tunnel malpositioning or graft overtensioning.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine fresh-frozen cadaveric knees were placed on a customized testing rig, where the femur was fixed but the tibia could be moved freely from 0° to 90° of flexion. Individual quadriceps heads and the iliotibial tract were separated and loaded to 205 N of tension 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 inserted between the patella and trochlea, in conjunction with an optical tracking system. The MPFL was transected and then reconstructed in a randomized order using a (1) double-strand gracilis tendon, (2) quadriceps tendon, and (3) tensor fasciae latae allograft. Pressure maps and tracking measurements were recorded for each reconstruction method in 2 N and 10 N of tension and with the graft positioned in the anatomic, proximal, and distal femoral tunnel positions. Statistical analysis was undertaken using repeated-measures analyses of variance, Bonferroni post hoc analyses, and paired t tests.

RESULTS

Anatomically placed grafts during MPFL reconstruction tensioned to 2 N resulted in the restoration of intact medial joint contact pressures and patellar tracking for all 3 graft types investigated (P > .050). However, femoral tunnels positioned proximal or distal to the anatomic origin resulted in significant increases in the mean medial joint contact pressure, medial patellar tilt, and medial patellar translation during knee flexion or extension, respectively (P < .050), regardless of graft type, as did tensioning to 10 N.

CONCLUSION

The importance of the surgical technique, specifically correct femoral tunnel positioning and graft tensioning, in restoring normal patellofemoral joint (PFJ) kinematics and articular cartilage contact stresses is evident, and the type of MPFL graft appeared less important.

CLINICAL RELEVANCE

The correct femoral tunnel position and graft tension for restoring normal PFJ kinematics and articular cartilage contact stresses appear to be more important than graft selection during MPFL reconstruction. These findings emphasize the importance of the surgical technique when undertaking this procedure.

An Algorithmic Approach to the Management of Recurrent Lateral Patellar Dislocation

High-level evidence supports nonoperative treatment for first-time lateral acute patellar dislocations. Surgical intervention is often indicated for recurrent dislocations. Recurrent instability is often multifactorial and can be the result of a combination of coronal limb malalignment, patella alta, malrotation secondary to internal femoral or external tibial torsion, a dysplastic trochlea, or disrupted and weakened medial soft tissue, including the medial patellofemoral ligament (MPFL) and the vastus medialis obliquus. MPFL reconstruction requires precise graft placement for restoration of anatomy and minimal graft tension. MPFL reconstruction is safe to perform in skeletally immature patients and in revision surgical settings. Distal realignment procedures should be implemented in recurrent instability associated with patella alta, increased tibial tubercle-trochlear groove distances, and lateral and distal patellar chondrosis. Groove-deepening trochleoplasty for Dejour type-B and type-D dysplasia or a lateral elevation or proximal recession trochleoplasty for Dejour type-C dysplasia may be a component of the treatment algorithm; however, clinical outcome data are lacking. In addition, trochleoplasty is technically challenging and has a risk of substantial complications.

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.

The triangle zone as a femoral attachment location in medial patellofemoral ligament reconstruction: An in vivo three-dimensional analysis using an open MRI scanner

BACKGROUND

The exact isometric points for medial patellofemoral ligament (MPFL) fixation during MPFL reconstruction remain a matter of debate.

PURPOSE

The aim of this study was to characterize the functional length changes of various patellar and femoral fixation sites using in vivo three-dimensional (3D) movement patterns and to determine the ideal fixation sites at which the graft remains largely isometric.

METHODS

Twelve right knees of healthy volunteers were examined at early flexion angles (0°, 10°, 20°, 30°, 40°, 50°, and 60°) with a horizontal-type open magnetic resonance scanner, and 3D models were reconstructed using the marching cubes algorithm. Six points on the femoral condyle and three points on the medial aspect of the patella were simulated. The matching points represented the MPFL, which crossed the bony obstacle. The MPFL length changes were analyzed at various flexion degrees.

RESULTS

The lengths from the dome of Blumensaat's line (G), the point 10mm inferior to the adductor tubercle (H), to the midpoint between the adductor tubercle and the medial epicondyle (I) were more isometric than other points. The lengths between the dome of Blumensaat's line and the superior pole of the patella changes significantly between 20° and 60° of flexion (p=0.040).

CONCLUSIONS

The femoral fixation site may be more accurately located during MPFL reconstruction at the G, H, and I points to restore the native biomechanical function of the MPFL. The dome of Blumensaat's line should be avoided during MPFL reconstruction with the superficial quad technique.

CLINICAL RELEVANCE

A triangular region composed of the dome of Blumensaat's line, 10mm inferior to the adductor tubercle, and the midpoint between the adductor tubercle and medial epicondyle is recommended as the femoral fixation site.

Clinical-radiographic correlation of the femoral insertion point of the graft in reconstruction of the medial patellofemoral ligament

OBJECTIVE

To analyze the radiographic positioning of the femoral tunnel and correlate this with the postoperative clinical results among patients undergoing reconstruction of the medial patellofemoral ligament (MPFL) alone.

METHOD

This was a retrospective study in which 30 knees of 26 patients with recurrent dislocation of the patella that underwent MPFL reconstruction were evaluated. The femoral insertion point of the graft and the postoperative clinical condition were analyzed and correlated using the Kujala and Lysholm scales.

RESULTS

22 knees presented a femoral tunnel in the anatomical area (group A) and 8 outside of this location (group B). In group A, the mean score on the Kujala scale was 89.68 points and on the Lysholm scale was 92.45 points. In group B, the mean score on the Kujala scale was 84.75 points and on the Lysholm scale was 92 points. The difference between the means was not significant on either of the two scales.

CONCLUSION

Correlation with the clinical results did not show any difference in relation to the positioning of the femoral insertion of the graft.

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.

Medial Patellofemoral Ligament Reconstruction: A Comprehensive Review

It has been suggested that in the majority of patellar dislocation cases, the medial patellofemoral ligament (MPFL) is disrupted with a high recurrence rate especially in female patients. Although MPFL tear is not the primary cause of instability, MPFL reconstruction is effective for stabilizing the knee and may alone prevent lateral patellar dislocation. There is limited but growing evidence that MPFL reconstruction for patellofemoral instability leads to excellent functional outcomes. Growing awareness of the biomechanical contribution of the MPFL has led to an upsurge in the publication of techniques and trials dealing with reconstructive techniques, warranting a review that includes the most recent evidence. The aim of this article was to review and summarize the recent literatures concerning MPFL reconstruction and provide a comprehensive review of previous studies ranging from basic science to current surgical techniques and results.

Simulation of varying femoral attachment sites of medial patellofemoral ligament using a musculoskeletal multi-body model

The medial patellofemoral ligament (MPFL) is a key structure in the treatment of habitual and traumatic patellofemoral instability. However, there exists little knowledge about its behaviour during deep knee flexion after femoral refixation. Since improper femoral attachment sites may lead to unnatural length change patterns in the ligament and consequently to osteoarthritis due to pathological femoro-patellar contact pressure, the understanding of the patella kinematics and MPFL behaviour is crucial.

The purpose of this numerical study was to compute the six-degree-of-freedom motion pattern of the human patella during deep knee flexion for systematic analysis of varying landmarks for the femoral attachment in medial patellofemoral ligament reconstruction surgery by means of multibody simulation.

Therefore, based on a previously presented musculoskeletal model [1] the dynamic pathways of the patella were computed. Then, the spatial motion was approximated by rheonomic polynomials and exploited for systematic evaluation of the MPFL length change patterns. Hence, 16 femoral attachment points at a radius of 5 mm and 10 mm around the radiographic centre point [2] were defined and the absolute length changes were recorded during deep knee flexion to 120 degree.

This approach allows for a systematic evaluation of numerous MPFL attachment sites while exploiting the physiological patella kinematics. The patella kinematics including shift, flexion, tilt and rotation as well as the MPFL length change patterns were consistent to in vitro and in vivo data in the literature [3–7] and therefore indicate validity of the numerical approach. The parameter study on the femoral attachment site should enable to determine the most isometric point and non-isometric variations corresponding to patellofemoral instability, arthritis or high graft load.

Accuracy of femoral tunnel placement in medial patellofemoral ligament reconstruction: the effect of a nearly true-lateral fluoroscopic view

BACKGROUND

Reconstruction of the medial patellofemoral ligament (MPFL) is an established operative procedure for patients with recurrent episodes of lateral patellar instability. However, recent articles have reported remarkable complication rates, with nonanatomic femoral tunnel positioning in up to 64% of patients.

PURPOSE

To evaluate the sensitivity of femoral tunnel placement using lateral fluoroscopic guidance to minor degrees of deviation from the true-lateral view using established radiographic landmarks.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six human cadaveric femora were used for this study. A 6-mm radiopaque eyelet was used to mark the native femoral insertion of the MPFL according to previously described radiographic landmarks. Radiographic landmarks were also applied with the femur positioned in 2.5° and 5° of internal and external rotation, respectively, and with the femur in 2.5° and 5° of hip abduction and adduction, respectively. The distance between the center of the 6-mm eyelet to the center of the native femoral MPFL insertion, as established in the true-lateral view, was measured and determined as the degree of shift in each position.

RESULTS

Hip adduction, abduction, and internal and external rotations of 2.5° resulted in a shift from the native femoral MPFL insertion point to a more distal (adduction), proximal (abduction), anterior (internal rotation), and posterior location (external rotation) of 2.7 ± 0.7, 2.0 ± 0.7, 2.7 ± 1.1, and 3.0 ± 1.3 mm, respectively (all P < .05). Malpositioning increased to a distance of 5.0 ± 0.7 mm distally, 3.6 ± 1.0 mm proximally, 5.2 ± 0.8 mm anteriorly, and 6.2 ± 0.6 mm posteriorly to the native insertion point when the attachment was marked with 5° of divergence from the true-lateral view (all P < .05).

CONCLUSION

The results of this study indicate the high sensitivity of femoral tunnel placement using lateral fluoroscopic guidance to minor degrees of deviation from the true-lateral view.

CLINICAL RELEVANCE

The study highlights the importance of an exact lateral view when fluoroscopic guidance is used for femoral tunnel positioning in the daily practice of MPFL reconstruction, and a possible explanation for the high incidence of nonanatomic tunnel placement is suggested.

Reconstruction of the medial patellofemoral ligament in cases of acute traumatic dislocation of the patella: current perspectives and trends in Brazil

OBJECTIVE

To evaluate the approaches and procedures used by knee surgeons in Brazil for treating medial patellofemoral lesions (MPFL) of the knee in cases of acute traumatic dislocation of the patella.

MATERIALS AND METHODS

A questionnaire comprising 15 closed questions on topics relating to treating MPFL of the knee following acute dislocation of the patella was used. It was applied to Brazilian knee surgeons during the three days of the 44th Brazilian Congress of Orthopedics and Traumatology, in 2012.

RESULTS

106 knee surgeons completely filled out the questionnaire and formed part of the sample analyzed. Most of them were from the southeastern region of Brazil. The majority (57%) reported that they perform fewer than five MPFL reconstruction procedures per year. Indication of non-surgical treatment after a first episode of acute dislocation of the patella was preferred and done by 93.4% of the sample. Only 9.1% of the participants reported that they had never observed postoperative complications. Intraoperative radioscopy was used routinely by 48%. The professionals who did not use this tool to determine the point of ligament fixation in the femur did not have a statistically greater number of postoperative complications than those who used it (p > 0.05).

CONCLUSIONS

There are clear evolutionary trends in treatments and rehabilitation for acute dislocation of the patella due to MPFL, in Brazil. However, further prospective controlled studies are needed in order to evaluate the clinical and scientific benefit of these trends.

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.

Length change patterns in the lateral extra-articular structures of the knee and related reconstructions

BACKGROUND

Lateral extra-articular soft tissue reconstructions in the knee may be used as a combined procedure in revision anterior cruciate ligament surgery as well as in primary treatment for patients who demonstrate excessive anterolateral rotatory instability. Only a few studies examining length change patterns and isometry in lateral extra-articular reconstructions have been published.

PURPOSE

To determine a recommended femoral insertion area and graft path for lateral extra-articular reconstructions by measuring length change patterns through a range of knee flexion angles of several combinations of tibial and femoral insertion points on the lateral side of the knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees were freed of skin and subcutaneous fat. The knee was then mounted in a kinematics rig that loaded the quadriceps muscles and simulated open-chain knee flexion. The length changes of several combinations of tibiofemoral points were measured at knee flexion angles between 0° and 90° by use of linear variable displacement transducers. The changes in length relative to the 0° measurement were recorded.

RESULTS

The anterior fiber region of the iliotibial tract displayed a significantly different (P < .001) length change pattern compared with the posterior fiber region. The reconstructions that had a femoral insertion site located proximal to the lateral epicondyle and with the grafts passed deep to the lateral collateral ligament displayed similar length change patterns to each other, with small length increases during knee extension. These reconstructions also showed a significantly lower total strain range compared with the reconstruction located anterior to the epicondyle (P < .001).

CONCLUSION

These findings show that the selection of graft attachment points and graft course affects length change pattern during knee flexion. A graft attached proximal to the lateral femoral epicondyle and running deep to the lateral collateral ligament will provide desirable graft behavior, such that it will not suffer excessive tightening or slackening during knee motion.

CLINICAL RELEVANCE

These results provide a surgical rationale for lateral extra-articular soft tissue reconstruction in terms of femoral graft fixation site and graft route.

Troubleshooting the Femoral Attachment During Medial Patellofemoral Ligament Reconstruction: Location, Location, Location

The medial patellofemoral ligament (MPFL) has been recognized as an important soft tissue restraint in preventing lateral patellar translation. As many patients with acute or chronic patellar instability will have a deficient MPFL, reconstruction of this ligament is becoming more common. Appropriately, significant research has been undertaken regarding graft biomechanics and techniques, as intraoperative errors in graft placement often result in poor patient outcomes. Although the research has not answered all of the dilemmas encountered during reconstruction, publications consistently emphasize the importance of re-establishing an anatomic femoral attachment. The purpose of this study was to briefly review the current literature on MPFL reconstruction. Graft selection and patellar graft attachment and fixation are discussed, but the main focus is the femoral attachment as this is where most errors are seen and, unfortunately, where getting it right appears to matter the most. Using a sawbones knee model, the concepts of an MPFL graft that is “high and tight” or “low and loose” are presented, with the goal of providing physicians with intraoperative tools to adjust an incorrectly placed femoral MPFL attachment. This model is also used to justify the recommendation of graft fixation in 30° to 45° of knee flexion.

MPFL reconstruction: technique and results

Patellar instability is a common problem, and medial patellofemoral ligament (MPFL) injury is inherent with traumatic patellar dislocations. Initial nonoperative management is focused on reconditioning and strengthening the dynamic stabilizers of the patella. For those patients who progress to recurrent instability, further investigation into the predisposing factors is required. MPFL reconstruction is indicated in patients with recurrent instability and insufficient medial restraint due to MPFL injury. A technique of MPFL reconstruction is outlined. This procedure may also be performed in combination with other realignment procedures.

Kinematic behaviour and soft tissue management in guided motion total knee replacement

PURPOSE

Dissatisfaction after total knee arthroplasty (TKA) may be caused by abnormal knee kinematics, and there is concern that 'guided motion' TKAs, designed to replicate normal knee kinematics, cause anterolateral knee pain due to stretching of soft tissues. It was hypothesised that excessive tibial internal rotation and femoral rollback during flexion were to blame.

METHODS

Eighteen fresh-frozen specimens were used in two studies. The first study used a knee extension rig and transducers to measure ligament length changes during flexion. The second study used a knee flexion rig and optical trackers to measure tibiofemoral kinematics. Both experiments used the intact knee and were repeated with three TKAs: two guided motion (Journey and Journey II) and a conventional Genesis II PS TKA.

RESULTS

TKA did not cause significant elongation of any of the ligaments examined. The medial patellofemoral ligament and the medial collateral ligament tended to be slacker post-TKA, and all three TKAs caused some tightening of the superficial iliotibial band, but these changes were not significant. Normal knee kinematics was not restored by any of the devices. The screw-home mechanism was absent in all three TKAs; anterior laxity was increased in all three devices up to 90° flexion, but tibial internal rotation was not increased. The conventional TKA allowed significantly greater anterior laxity than normal, while the Journey I caused greater tibial anterior translation in flexion.

CONCLUSIONS

The hypothesis that over-internal rotation and rollback in the original guided motion knee caused excessive tightening in the soft tissues around the knee was supported; the updated design reduced that tendency. If similar changes occur during real-life activities, these results imply a potential reduction in the incidence of anterolateral knee pain clinically in patients with a guided motion TKA.

Simulation of the optimal femoral insertion site in medial patellofemoral ligament reconstruction

PURPOSE

To develop and validate a new simulation system to predict the optimal femoral insertion site of the medial patellofemoral ligament (MPFL) using preprogrammed conditions of graft length change.

METHODS

A computed tomography scan was performed for constructing bone surface models of the patella and the femur. Lateral radiographs of the knee and axial radiographs of the patellofemoral joint at knee flexion were used for constructing a three-dimensional patellofemoral joint model by 3D-2D image matching at each knee flexion angle. To determine the optimal femoral insertion site, the following three conditions were devised: (1) MPFL behaves isometric from 0° to 60°, (2) MPFL is most taut at full extension, and (3) MPFL is slack at more than 60° of knee flexion. Every condition was applied to the femoral bone surface model, and the area that fulfilled all three conditions was defined as the optimal femoral insertion site of MPFL. Twenty knees of ten healthy volunteers were assessed to verify the simulation. Comparison between simulated optimal femoral insertion and anatomical insertion was done.

RESULTS

The mean simulated optimal femoral insertion was close to the anatomical insertion site. There were no significant differences in the proximal-distal position and anterior-posterior position between the simulated insertion and the anatomical insertion sites.

CONCLUSION

The system can be useful for predicting the optimal femoral insertion site as a part of a preoperative plan for MPFL reconstruction, and it may help surgeons to determine the optimal femoral insertion site during MPFL reconstruction.

Patellar thickness and lateral retinacular release affects patellofemoral kinematics in total knee arthroplasty

PURPOSE

To study the effect of increasing patellar thickness (overstuffing) on patellofemoral kinematics in total knee arthroplasty and whether subsequent lateral retinacular release would restore the change in kinematics.

METHODS

The quadriceps of eight fresh-frozen knees were loaded on a custom-made jig. Kinematic data were recorded using an optical tracking device for the native knee, following total knee arthroplasty (TKA), then with patellar thicknesses from -2 to +4 mm, during knee extension motion. Staged lateral retinacular releases were performed to examine the restoration of normal patellar kinematics.

RESULTS

Compared to the native knee, TKA led to significant changes in patellofemoral kinematics, with significant increases in lateral shift, tilt and rotation. When patellar composite thickness was increased, the patella tilted further laterally. Lateral release partly corrected this lateral tilt but caused abnormal tibial external rotation. With complete release of the lateral retinaculum and capsule, the patella with an increased thickness of 4 mm remained more laterally tilted compared to the TKA with normal patellar thickness between 45° and 55° knee flexion and from 75° onwards. This was on average by 2.4° ± 2.9° (p < 0.05) and 2.°9 ± 3.0° (p < 0.01), respectively. Before the release, for those flexion ranges, the patella was tilted laterally by 4.7° ± 3.2° and 5.4° ± 2.7° more than in the TKA with matched patellar thickness.

CONCLUSION

Patellar thickness affects patellofemoral kinematics after TKA. Although lateral tilt was partly corrected by lateral retinacular release, this affected the tibiofemoral kinematics.

LEVEL OF EVIDENCE

IV.

The anterolateral ligament

There have been differing descriptions of the anterolateral structures of the knee, and not all have been named or described clearly. The aim of this study was to provide a clear anatomical interpretation of these structures. We dissected 40 fresh-frozen cadaveric knees to view the relevant anatomy and identified a consistent structure in 33 knees (83%); we termed this the anterolateral ligament of the knee. This structure passes antero-distally from an attachment proximal and posterior to the lateral femoral epicondyle to the margin of the lateral tibial plateau, approximately midway between Gerdy’s tubercle and the head of the fibula. The ligament is superficial to the lateral (fibular) collateral ligament proximally, from which it is distinct, and separate from the capsule of the knee. In the eight knees in which it was measured, we observed that the ligament was isometric from 0° to 60° of flexion of the knee, then slackened when the knee flexed further to 90° and was lengthened by imposing tibial internal rotation.

Cite this article: Bone Joint J 2014;96-B:325–31.

Guidelines for medial patellofemoral ligament reconstruction in chronic lateral patellar instability

The standard surgical approach for chronic lateral patellar instability with at least two documented patellar dislocations is to stabilize the patella by using an anatomic medial patellofemoral ligament reconstruction with a mini-open technique and a graft that is stronger than the native ligament to compensate for the uncorrected predisposing factors underlying patellar instability. Even though medial patellofemoral ligament reconstruction has evolved notably during the past two decades, many aspects of the surgical technique need to be refined, and more information is needed toward this end. Adequate positioning of the graft on the femur, as well as inducing the appropriate degree of tension, are critical steps for the overall outcome of medial patellofemoral ligament reconstruction. Moreover, it is necessary in some cases to pair medial patellofemoral ligament reconstruction with other surgical procedures to address additional patellar instability risk factors, such as trochlear dysplasia, malalignment, and patella alta.

The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction

BACKGROUND

An incorrect femoral tunnel position or inappropriate graft tensioning during medial patellofemoral ligament (MPFL) reconstruction may cause altered patellofemoral joint kinematics and contact mechanics, potentially resulting in pain and joint degeneration.

HYPOTHESIS

Nonanatomic positioning of the tunnel or graft overtensioning during MPFL reconstruction will have an adverse effect on patellar tracking and patellofemoral joint contact mechanics.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees were placed on a customized testing rig, with the femur fixed and the tibia mobile through 90° of flexion. Individual heads of the quadriceps muscle and the iliotibial band were separated and loaded with 205 N in anatomic directions using a system of cables and weights. Patellofemoral contact pressures and patellar tracking were measured through the flexion range at 10° intervals using Tekscan pressure-sensitive film inserted between the patella and trochlea and an optical tracking system. The MPFL was transected and then reconstructed using a double-strand gracilis tendon graft. Pressures and kinematics were recorded for reconstructions with the graft positioned in anatomic, proximal, and distal tunnel positions. Measurements were then repeated with an anatomic tunnel and graft tension of 2 N, 10 N, and 30 N, fixed at 3 different flexion angles of 0°, 30°, and 60°. Statistical analysis was undertaken using repeated-measures analysis of variance, Bonferroni post hoc analysis, and paired t tests.

RESULTS

For a graft tensioned to 2 N, anatomically positioned MPFL reconstruction restored intact medial and lateral joint contact pressures and patellar tracking (P > .05), but femoral tunnels positioned proximal or distal to the anatomic origin resulted in significant increases in peak and mean medial pressures and medial patellar tilt during knee flexion or extension, respectively (P < .05). Grafts tensioned with 10 N or 30 N also caused significant increases in medial pressure and tilt. Graft fixation at 30° or 60° restored all measures to intact values (P > .05), but fixation at 0° caused significant increases (P < .05) in medial joint contact pressures compared with intact knees.

CONCLUSION

Anatomically positioned reconstruction with 2-N tension fixed at 30° or 60° of knee flexion restored joint contact pressures and tracking. However, graft overtensioning or femoral tunnels positioned too proximal or distal caused significantly elevated medial joint contact pressures and increased medial patellar tilting. The importance of a correct femoral tunnel position and graft tensioning in restoring normal patellofemoral joint kinematics and articular cartilage contact stresses is therefore evident.

CLINICAL RELEVANCE

A malpositioned femoral tunnel or overtensioned graft during MPFL reconstruction resulted in increased medial contact pressures and patellar tilting. This may lead to adverse outcomes such as early degenerative joint changes or pain if occurring in a clinical population.

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.

Are the tubular grafts in the femoral tunnel in an anatomical or isometric position in the reconstruction of medial patellofemoral ligament?

PURPOSE

The purpose of this study was to evaluate the biomechanical results from the in vitro reconstruction of medial patellofemoral ligament (MPFL) using a navigation-assisted technique on a cadaveric model and its effects on patellar stability and kinematics. The authors investigated the hypothesis that patellar kinematics after reconstruction with a tubular graft are not optimal when compared with the original fan-shaped MPFL.

METHODS

In six fresh-frozen cadaveric knees, lateral loads (25 N) were applied on the patella at 0°, 30°, 60° and 90° of knee flexion in three different MPFL states: intact, cut and reconstructed. The arrangement allowed positional measurements of patellar motion to be tracked in six degrees of freedom. Medial to lateral patellar translation and patellar tilt were recorded. The kinematics after a technique of MPFL reconstruction, performed with a gracilis tendon in a blind femoral tunnel guided by navigation, were compared against kinematics recorded in the MPFL intact state. A temporary fixation of adequate tension to engage the lateral patellar facet in extension was applied to the MPFL and, after graft cycling, the final fixation was done at 70° knee flexion with an interference screw.

RESULTS

There was a comparable medial to lateral patellar translation and tilting of the patella in the MPFL-intact and the MPFL-reconstructed state. Static patellar translation in the MPFL-reconstructed state, with and without the application of load, was comparable to patellar translation in the MPFL-intact state. The dynamic patellofemoral shift kinematics recorded an under-constraint in early flexion and over-constraint in late flexion, while an opposite effect was recorded in patellar tilt. However, these differences were not statistically significant.

CONCLUSION

The study confirmed the major role of the MPFL in case of medial loading between 0° and 60°, by focusing on the importance of kinematically identifying the proper femoral point for fixation. While the study demonstrates the importance of kinematic determination of the proper femoral point of fixation, as the anatomical insertion remains difficult to identify. Even in dissected cadavers, the authors recorded a slightly anterior placement than native MPFL. After reconstruction, patellar stability in terms of lateral translation and tilt was similar to the intact MPFL, but patellar kinematics were not optimal with the use of a smaller and tubular graft than the native wider and fan-shaped MPFL.