Medial Patellofemoral Ligament Reconstruction: Impact of Knee Flexion Angle During Graft Fixation on Dynamic Patellofemoral Contact Pressure-A Biomechanical Study

Biomechanical Properties and Kinematics of Medial Patellofemoral Ligament Reconstruction: A Systematic Review

Background

While the biomechanical properties of the native medial patellofemoral ligament (MPFL) have been well studied, there is no comprehensive summary of the biomechanics of MPFL reconstruction (MPFLR). An accurate understanding of the kinematic properties and functional behavior of current techniques used in MPFLR is imperative to restoring native biomechanics and improving outcomes.

Purpose

To provide a comprehensive review of the biomechanical effects of variations in MPFLR, specifically to determine the effect of graft choice and reconstruction technique.

Study Design

Systematic review.

Methods

A systematic review was performed in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. A total of 32 studies met inclusion criteria: (1) using ≥8 human cadaveric specimens, (2) reporting on a component of MPFLR, and (3) having multiple comparison groups.

Results

Gracilis, semitendinosus, and quadriceps grafts demonstrated an ultimate load to failure (N) of 206.2, 102.8, and 190.0 to 205.0 and stiffness (N/mm) of 20.4, 8.5, and 21.4 to 33.6, respectively. Single-bundle and double-bundle techniques produced an ultimate load to failure (N) of 171 and 213 and stiffness (N/mm) of 13.9 and 17.1, respectively. Anchors placed centrally and superomedially in the patella produced the smallest degree of length changes throughout range of motion in contrast to anchors placed more proximally. Sutures, suture anchors, and transosseous tunnels all produced similar ultimate load to failure, stiffness, and elongation data. Femoral tunnel malpositioning resulted in significant increases in contact pressures, patellar translation, tilt, and graft tightening or loosening. Low tension grafts (2 N) most closely restored the patellofemoral contact pressures, translation, and tilt. Graft fixation angles variably and inconsistently altered contact pressures, and patellar translation and tilt.

Conclusion

Data demonstrated that placement of the MPFLR femoral tunnel at the Schöttle point is critical to success. Femoral tunnel diameter should be ≥2 mm greater than graft diameter to limit graft advancement and overtensioning. Graft fixation, regardless of graft choice or fixation angle, is optimally performed under minimal tension with patellar fixation at the medial and superomedial patella. However, lower fixation angles may reduce graft strain, and higher fixation angles may exacerbate anisometry and length changes if femoral tunnel placement is nonanatomic.

Medial Patellofemoral Complex Reconstruction (Combined Reconstruction of Medial Patellofemoral Ligament and Medial Quadriceps Tendon-Femoral Ligament) With Semitendinosus Autograft Resulted in Similar Clinical and Radiographic Outcomes to Medial Patellofemoral Ligament Reconstruction in Treating Recurrent Patellar Dislocation

PURPOSE

To compare clinical and radiographic outcomes of medial patellofemoral ligament reconstruction (MPFL-R) and medial patellofemoral complex reconstruction (MPFC-R) for recurrent patellar dislocation. Outcome measures were compared based on the Insall-Salvati index.

METHODS

Patients who were diagnosed with recurrent patellar dislocation and underwent either MPFL-R or MPFC-R (combined reconstruction of MPFL and medial quadriceps tendon-femoral ligament) were retrospectively analyzed. Group allocation was based on surgical procedure and patient characteristics were collected. Clinical assessments included patient-reported outcome measures (PROMs) and return-to-sports rates. Minimal clinically important difference analysis was performed. A subgroup analysis of PROMs was carried out between patients with an Insall-Salvati index ≤1.2 versus >1.2. The patellar tilt angle, lateral patellar displacement, and bisect offset ratio were measured pre- and postsurgery. Functional failures and complications were assessed.

RESULTS

Overall, 70 patients (72 knees) in the MPFL-R group and 58 patients (61 knees) in the MPFC-R group were included. Patient characteristics were comparable between the groups. At a minimum follow-up of 24 (mean, 50.6 ± 22.1) months, all PROMs were substantially improved (P < .001), without significant intergroup differences. The percentages of patients reaching the minimal clinically important difference were similar after MPFL-R and MPFC-R: 98.6% versus 93.4% (International Knee Documentation Committee), 97.2% versus 98.4% (Lysholm), 98.6% versus 100% (Kujala), and 77.8% versus 72.1% (Tegner). The subgroup analysis based on patellar height and the return-to-sport rates also suggested comparable results. Radiographic evaluation demonstrated significantly smaller lateral patellar displacements (P = .004) and bisect offset ratios (P < .001) but similar patellar tilt angles after MPFC-R. Four (5.6%) patients receiving MPFL-R and 2 (3.3%) patients receiving MPFC-R reported recurrence of functional instability, without statistically significant difference.

CONCLUSIONS

MPFC-R resulted in similar overall clinical and radiographic outcomes to MPFL-R in treating recurrent patellar dislocation. MPFC-R might not provide additional benefits for patients with an Insall-Salvati index >1.2.

LEVEL OF EVIDENCE

Level IV, therapeutic, retrospective cohort study.

Lateral Retinacular Release During Medial Unicompartmental Knee Arthroplasty in the Presence of Patello-Femoral Joint Arthritis Relieves Patello-Femoral Joint Pressure and Improves Associated Symptoms

BACKGROUND

This study evaluated the effects of concomitant lateral patellar retinacular release (LPRR) during medial unicompartmental knee arthroplasty (UKA).

METHODS

We retrospectively analyzed 100 patients who had patello-femoral joint (PFJ) arthritis who underwent medial UKA with (n = 50) and without (n = 50) LPRR who had ≥2 years follow-up. Radiological parameters associated with lateral retinacular tightness, including patellar tilt angle (PTA), lateral patello-femoral angle (LPFA), and congruence angle, were measured. Functional evaluation was performed using the Knee Society Pain Score, Knee Society Function Score (KSFS), Kujala Score, and the Western Ontario McMaster Universities Osteoarthritis Index score. Intraoperative patello-femoral pressure evaluation was performed on 10 knees to evaluate the pressure changes before and after LPRR. Mann-Whitney U-tests were used for statistical analyses.

RESULTS

Demographic data did not differ between the LPRR(+) and LPRR(-) groups. A decrease in PTA and an increase in LPFA were observed in the LPRR(+) group compared to those in the LPRR(-) group (PTA; -0.54 versus -1.74, P = .002, LPFA; 0.51 versus 2.01, P = .010). The LPRR(+) group showed significantly better KSFS and Kujala scores than the LPRR(-) group (KSFS: 90 versus 80, P = .017; Kujala score: 86 versus 79, P = .009). Intraoperative patello-femoral pressure analysis showed a 22.6% reduction in the PFJ contact pressure and an 18.7% reduction in PFJ peak pressure after LPRR. (P = .0015, P < .0001, respectively) CONCLUSION: A LPRR during UKA may be a simple and useful adjunct procedure to relieve PFJ symptoms with concomitant PFJOA.

Editorial Commentary: From Lateral Release and Medial Plication to Complex Medial Patellofemoral Ligament Reconstruction Techniques: Medial Quadriceps Tendon Femoral Ligament Reconstruction Is the Most Anatomic Repair

Patella instability and dislocation are common in younger patients, and 1 in 5 patients are at risk of recurrent dislocations. Conservative treatment should be considered for first dislocations unless other concomitant injuries are present. Historically, lateral patella release and medial plication techniques were used for repair but have been superseded by medial patellofemoral ligament reconstruction. Overconstraint is a potential problem and often related to nonanatomic femoral tunnel position and graft tension, which could result in increased patellar contact pressures and graft failure. The medial quadriceps tendon-femoral ligament reconstruction technique (MQTFL) avoids patellar tunnels without the risk of patella fracture. When comparing medial patellofemoral ligament, MQTFL, and the combination of both techniques in a cadaver model, MQTFL resulted in less constraint with no differences for patellar contact pressures. Medial quadriceps tendon femoral ligament reconstruction is the most anatomic repair.

Medial patellofemoral ligament reconstruction using nonresorbable sutures yields comparable outcomes to reconstruction with a pedicled quadriceps tendon autograft when performed in addition to bony risk factor correction

PURPOSE

To evaluate the results for reconstruction of the medial patellofemoral ligament using synthetic nonresorbable sutures (S-MPFL-R) in comparison to MPFL-R using quadriceps tendon autograft (QT-MPFL-R) in patients undergoing simultaneous correction of anatomic risk factors for lateral patellar instability (LPI) at a minimum of 2 years of follow-up.

METHODS

Between November 2018 and June 2019, 19 patients (male/female 8/11; mean age 26 ± 7 years) underwent S-MPFL-R (FiberTape^®) in combination with the correction of predisposing risk factors for LPI. The control group of 38 patients (male/female 16/22, mean age 26 ± 6 years) who underwent QT-MPFL-R was matched 1:2 by sex, age, anatomic risk factors, and concomitant surgical correction of bony risk factors. The Banff Patella Instability Instrument 2.0 (BPII 2.0) and a numerical analog scale (NAS 0-10) for patellofemoral pain and subjective knee joint function were used to assess patients' reported quality of life before and after surgery.

RESULTS

The BPII 2.0 score increased from 35.0 ± 21.7 points to 79.7 ± 13.3 points (p < 0.0001) in the S-MPRL-R group and from 44.3 ± 19.6 points to 80.9 ± 15 points (p < 0.0001) in the QT-MPFL-R group from preoperatively to postoperatively, respectively, without any significant difference between the groups. In the S-MPFL-R group and QT-MPFL-R group, 95% (18/19) and 92% (35/38) of patients, respectively, crossed the minimally clinically important difference reported for the BPII 2.0. NAS values for pain and subjective knee joint function improved significantly in both groups (p < 0.0001, p < 0.0001) without any significant difference between the groups at the final follow-up.

CONCLUSIONS

This study demonstrates that nonresorbable sutures can serve as a viable option for MPFL-R, yielding comparable outcomes compared to quadriceps tendon autograft reconstruction when performed concomitantly with the correction of anatomic risk factors for LPI. This option reduces the need for autologous tendon harvesting or the use of allografts for MPFL-R.

LEVEL OF EVIDENCE

Level III.

Medial patellofemoral ligament reconstruction using a digital tensiometer to determine graft tension: Surgical technique and mid-term follow-up

PURPOSE

The optimal method for achieving proper graft tension during patellofemoral ligament reconstruction is a topic of debate. In the past, a digital tensiometer was used to simulate the knee structure, and a tension of approximately 2N was identified as suitable for restoring the patellofemoral track. However, it is unclear whether this tension level is sufficient during the actual surgery. The objective of this study was to verify the efficacy of graft tension using a digital tensiometer for medial patellofemoral ligament (MPFL) reconstruction and to conduct a mid-term follow-up.

METHODS

The study enrolled 39 patients who had experienced recurrent patellar dislocation. Preoperative computed tomography scans and X-rays confirmed patellar instability, patellar tilt angle patellar congruence angle and the history of dislocation and patellar apprehension test. Knee function was evaluated using preoperative and postoperative Lysholm and Kujala scores.

RESULTS

The study included 39 knees, comprising 22 females and 17 males, with an average age of 21.10 ± 7.26. The patients were followed up for at least 24 months through telephone or face-to-face questionnaires. All patients had a preoperative history of ≥2 patellar dislocations, none of which were surgically treated. During surgery, all patients underwent isolated MPFL reconstruction and lateral retinacula release. The mean Kujala and Lysholm scores were 91.28 ± 4.90 and 90.67 ± 5.15, respectively. The mean PTA and PCA were 11.5 ± 2.63 and 2.38 ± 3.58, respectively. The study found that a tension of approximately 27.39 ± 5.57N (14.3-33.5N) was required to restore the patellofemoral track in patients with recurrent patellar dislocation. No patients required reoperation during the follow-up period. Overall, 36 out of 39 patients (92.31%) reported no pain when completing daily activities at the last follow-up.

CONCLUSION

In conclusion, a tension level of approximately 27.39 ± 5.57N is necessary to restore normal patellofemoral relationships during clinical practice, which indicates that using a tension of 2N is too low. The use of a tensiometer during patellofemoral ligament reconstruction is a more accurate and reliable surgical procedure for treating recurrent patellar dislocation.

Accuracy of femoral tunnel positioning in medial patellofemoral ligament reconstruction: anatomic insertion leads to better clinical outcome

PURPOSE

The medial patello-femoral ligament (MPFL) is considered the primary restraint against patellar dislocation and its reconstruction is indicated in recurrent patellar instability. An anatomical positioning of MPFL femoral insertion is recommended to achieve satisfactory clinical outcomes and prevent osteoarthritis (OA) due to an altered kinematics. The purpose of the study was first to assess the relationship between correct femoral tunnel position and better clinical outcomes and lower patellofemoral osteoarthritis rate. Second, correlation of outcomes with factors potentially affecting the results, such as the type of graft, patellar height and trochlear dysplasia.

METHODS

Fifty-three patients (58 knees) who underwent MPFL reconstruction between 2009 and 2018 by a senior knee surgeon were retrospectively evaluated. Knee radiographs were performed before surgery, 12 months later and at last follow-up to assess trochlear dysplasia, patellar height and patellofemoral OA. The tibial tuberosity-trochlear groove (TT-TG) value was measured on a CT scan. The accuracy of graft positioning was evaluated on sagittal radiographs according to Schöttle et al. Subjective outcomes were collected before surgery, at 12 months and at last follow-up using several validated scores.

RESULTS

Forty-six patients (51 knees) with a mean age of 24.1 ± 7.4 years were included in the study. Mean follow-up was 8.9 ± 2.1 years. A significant improvement in all clinical scores was observed at 12 months and final follow-up. Anatomic Insertion (AI) of reconstructed MPFL was considered optimal in 33 (64.7%) and sub-optimal in 18 (35.3%) patients. Sub-optimal AI resulted in lower Kujala, IKCD and higher VAS score (p < 0.01); moreover, for every 1 mm distance in any direction from the ideal insertion, a decrease of 0.8 [95% CI (-1.4; -0.2)] in Kujala score and 0.8 [95% CI (-1.3; -0.3)] in IKDC was observed. At final follow-up, 8 patients presented patellofemoral OA Iwano grade 3 (15.7%): although that incidence did not correlate to graft positioning, the use the artificial ligament in all these cases appeared to be significant.

CONCLUSION

The present study confirms the importance of an optimal anatomic femoral insertion in MPFL reconstruction, reporting a significant positive correlation between graft positioning and clinical outcome. No significant correlations were found between anatomic insertion and patello-femoral OA development.

LEVEL OF EVIDENCE

IV.

Plantaris tendon is valuable graft for the medial patellofemoral ligament reconstruction: A biomechanical study

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction is a standard treatment option for selected patients with patellar instability. Although frequently performed, the optimal graft source for the procedure has not yet been established. This study aimed to determine whether a two-strand plantaris tendon construct possesses the biomechanical properties needed to act as an MPFL reconstruction graft.

METHODS

Thirty paired plantaris and gracilis tendons were harvested from 15 cadavers, mean age at death of 42.7 years. All specimens were frozen and maintained at -20 °C until biomechanical testing. Prior to mechanical testing, specimens were thawed at room temperature. The two-strand plantaris tendon and two-strand gracilis tendon constructs were created and secured in a uniaxial tensile testing machine in a triangular-shaped mode. Biomechanical properties for tensile testing to failure were determined using validated method. Results obtained were compared with the previously published data on native MPFL biomechanical properties.

RESULTS

The mean maximal force was 220.3 ± 108.1 N and 448.1 ± 117 N for the two-strand plantaris tendon construct and two-strand gracilis tendon construct, respectively. Significant differences were observed between all biomechanical properties of two-strand plantaris tendon and two-strand gracilis tendon constructs. The mean maximal force of a two-strand plantaris tendon construct and a two-strand gracilis tendon construct were greater than the mean maximal force of the native MPFL reported in all previous studies.

CONCLUSIONS

This study suggests that, due to its biomechanical properties, the two-strand plantaris tendon graft is suitable as a graft for MPFL reconstruction.

Dynamic versus static medial patellofemoral ligament reconstruction technique in the treatment of recurrent patellar dislocation: a randomized clinical trial protocol

BACKGROUND

The redislocation rate of conservatively treated patella instability is high. One of the leading surgical strategies is medial patellofemoral ligament reconstruction. Over-tensioning is one of the most challenging complications in static medial patellofemoral ligament reconstruction as the graft used for reconstruction is isometric and the anatomical MPFL is a mostly dynamic structure. As an alternative to established static reconstruction techniques, dynamic graft techniques have been introduced for stabilizing the patella with the aim of providing a more physiological reconstruction of the medial patellofemoral ligament. To date, data on clinical outcomes are scarce and on biomechanical outcomes of the dynamic MPFL reconstruction are lacking. Here, we present the protocol of a randomized clinical trial for comparing clinical and biomechanical outcomes of dynamic versus static medial patellofemoral ligament reconstruction.

METHODS

This study is a prospective, single blinded, randomized, multicenter, multimodal (clinical and biomechanical) clinical trial. Patients with recurrent patella dislocation requiring isolated MPFL reconstruction will be recruited and randomized to the dynamic or static reconstruction technique. Participants will be followed up for 2 years with a total of five follow-ups. Preoperative magnetic resonance imaging, upright radiographs, surgical reports and patient records will be evaluated, and clinical and functional outcomes will be measured. Patient-reported knee function and anterior knee pain as assessed with the Kujala score will serve as primary outcome. For biomechanical outcome, pre- and postoperative evaluations will be performed to assess isokinetic muscle strength, gait asymmetry, joint kinematics and kinetics, and timing of muscle activity.

DISCUSSION

The results of the study will clarify whether the reported surgery success for patella stabilization via dynamic MPFL reconstruction is due to muscle contraction or to the passive tenodesis effect combined with clinical outcome measures. With this study, we will provide much needed information on knee biomechanics after dynamic versus static MPFL reconstruction to provide evidence to support orthopedic surgeons in evidence-based decision-making in their quest for surgical techniques most favorable for their patients. Trial registration The study protocol was registered at clinicaltrials.gov (NCT04849130). Registered 19 April 2021, https://clinicaltrials.gov/ct2/show/NCT04849130 .

[Three-dimensional finite element study on combined proximal and distal knee extension rearrangement for recurrent patellar dislocation]

OBJECTIVE

To establish a three-dimensional finite element analysis model of the knee joint in fresh frozen cadavers, to verify the validity of the model and to simulate the stress distribution characteristics of the patellofemoral joint after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation.

METHODS

One male and one female fresh frozen cadavers (4 knees in total), using voluntary body donations, were used to measure the maximum pressure on the patellofemoral articular surface at each passive flexion angle (0°, 30°, 60°, 90°, 120°) of the normal knee joint and the model after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation with tibial tuberosity-trochlear groove distance (TT-TG) value >2.00 cm using pressure-sensitive paper, respectively. Then, the 2 freshly frozen cadavers were used to construct three-dimensional finite element models of normal knee joints and postoperative knee joints, and the maximum pressure on the patellofemoral articular surface was measured at various passive flexion angles. The maximum pressure was compared with the measurement results of the pressure-sensitive paper to verify the validity of the three-dimensional finite element model. In addition, the maximum pressure on the patellofemoral joint surface measured by three-dimensional finite element was compared between the normal knee joint and the postoperative knee joint at various passive flexion angles, so as to obtain an effective three-dimensional finite element model for the simulation study of the stress distribution characteristics of the patellofemoral joint after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation.

RESULTS

The maximum pressure on the patellofemoral joint surface measured by pressure-sensitive paper and three-dimensional finite element measurements were similar at all passive flexion angles in the normal knee joint, with a difference of -0.08-0.06 MPa; the maximum pressure on the patellofemoral joint surface measured by pressure-sensitive paper and three-dimensional finite element measurements were also similar at all passive flexion angles in the knee after combined proximal and distal knee extension rearrangement surgery, with a difference of -0.04-0.09 MPa. The maximum pressure on the patellofemoral joint surface measured by three-dimensional finite elements were also similar between the normal knee joint and the knee joint after combined proximal and distal knee extension rearrangement surgery at all passive flexion angles, with a difference of -0.50--0.03 MPa.

CONCLUSION

The three-dimensional finite element model of the normal knee joint and the knee joint after combined proximal and distal knee extension rearrangement surgery can accurately and effectively quantify the change in the maximum pressure on the patellofemoral joint surface; for recurrent patellar dislocations with TT-TG value>2.00 cm, the combined proximal and distal knee extension rearrangement surgery can achieve a maximum pressure of the patellofemoral joint surface similar to that of the normal knee joint.

Lateral Release With Tibial Tuberosity Transfer Alters Patellofemoral Biomechanics Promoting Multidirectional Patellar Instability

PURPOSE

The purpose of this study was to develop and validate a finite element (FE) model of the patellofemoral (PF) joint to characterize patellofemoral instability, and to highlight the effect of lateral retinacular release in combination with tibial tuberosity transfer with respect to contact pressures (CP), contact area (CA), and kinematics during knee flexion.

METHODS

A comprehensive, dynamic FE model of the knee joint was developed and validated through parametric comparison of PF kinematics, CP, and CA between FE simulations and in vitro, cadaveric experiments. Using this FE model, we characterized the effect of patellar instability, lateral retinacular release (LR), and tibial tuberosity transfer (TTT) in the setting of medial patellofemoral ligament injury during knee flexion.

RESULTS

There was a high level of agreement in CP, CA, lateral patellar displacement, anterior patellar displacement, and superior patellar displacement between the FE model and the in vitro data (P values 0.19, 0.16, 0.81, 0.10, and 0.36, respectively). Instability conditions demonstrated the greatest CP compared to all of the other conditions. During all degrees of flexion, TTT and concomitant lateral release (TTT + LR) decreased CP significantly. TTT alone shows a consistently lower CA compared to nonrelease conditions with subsequent lateral release further decreasing CA.

CONCLUSIONS

The results of this study demonstrate that the FE model described reliably simulates PF kinematics and CP within 1 SD in uncomplicated cadaveric specimens. The FE model is able to show that tibial tubercle transfer in combination with lateral retinacular release markedly decreases patellofemoral CP and CA and increases lateral patellar displacement that may decrease bony stabilization of the patella within the trochlear groove and promote lateral patellar instability.

CLINICAL RELEVANCE

The goal of surgical correction for patellar instability focuses on reestablishing normal PF kinematics. By developing an FE model that can demonstrate patient PF kinematics and the results of different surgical approaches, surgeons may tailor their treatment to the best possible outcome. Of the surgical approaches that have been described, the biomechanical effects of the combination of TTT with lateral retinacular release have not been studied. Thus, the FE analysis will help shed light on the effect of the combination of TTT with lateral retinacular release on PF kinematics.

Arthroscopic Patellofemoral Measurements Can Reliably Assess Patellar Instability

PURPOSE

To arthroscopically describe patellar position based on lateralization, tilt, and engagement, and compare measurements in normal, medial patellofemoral complex-(MPFC) deficient, and MPFC-reconstructed knees.

METHODS

In 10 cadaveric knees, arthroscopic patellar position was assessed by performing digital measurements on arthroscopic images obtained through a standard anterolateral portal. Lateralization was measured as millimeters overhang of the patella past the lateral edge of the lateral femoral condyle, viewing from the lateral gutter. Patellar tilt was calculated as the difference in medial and lateral distances from the patella to the trochlea, viewing from the sunrise view. Patellotrochlear distance was measured as the anteroposterior distance between the central trochlear groove and patella on the sunrise view. Measurements were obtained at 10° intervals of knee flexion from 0° to 90°, in intact knees (group 1), after arthroscopically transecting the MPFC fibers (group 2), and after MPFC reconstruction (group 3). Optimal cutoff values were identified to distinguish between intact versus MPFC-deficient states.

RESULTS

When compared to group 1, group 2 demonstrated increased patellar lateralization by 22.5% at 0°-40° knee flexion (P = .006), which corrected to baseline in group 3 (P = .006). Patellar tilt measurements demonstrated no differences between groups. Patellotrochlear distance increased by 21.0% after MPFC transection (P = .031) at 0°-40° knee flexion, with correction to baseline after MPFC reconstruction (P = .031). More than 7 mm of lateral overhang at 20°-30° flexion and >6 mm of patellotrochlear distance at 10°-20° flexion were found to indicate MPFC deficiency.

CONCLUSIONS

Utilizing standardized arthroscopic views, we identified significant increases in patellar lateralization and patellotrochlear distance in early knee flexion angles after MPFC transection, and these changes normalized after MPFC reconstruction.

CLINICAL RELEVANCE

Arthroscopic assessments of patellar position may be useful in evaluating patellofemoral stability during patellar stabilization surgery.

Effect of Lateral Retinacular Release on Medial Patellofemoral Ligament Reconstruction

Background:

When performing a medial patellofemoral ligament (MPFL) reconstruction, surgeons may place the MPFL graft under higher than anatomic tension to minimize the chance of recurrent instability.

Purpose:

To investigate whether a lateral retinacular release (LRR) significantly decreases patellofemoral contact pressures after an overtensioned (OT) MPFL reconstruction.

Study Design:

Controlled laboratory study.

Methods:

Mean and peak pressure across the patellofemoral joint at 30°, 45°, and 60° of flexion was assessed in 14 cadaveric knee specimens with intact MPFL, transected MPFL, reconstructed MPFL with graft OT, and OT MPFL with LRR. The Wilcoxon signed rank test was used to determine differences across states, with W and C values calculated when possible.

Results:

Mean pressure decreased significantly after MPFL transection compared with intact at 30° (456.9 ± 116.8 vs 410.9 ± 109.4 N, P = .006, W < 7) and 45° (404.9 ± 91.7 vs 369.4 ± 85.3 N, P = .005, W < 5) and increased significantly from intact to OT graft at 30° (456.9 ± 116.8 vs 563.0 ± 11.2 N, P = .003, W < 7), 45° (404.9 ± 91.7 vs 481.4 ± 14.8 N, P = .005, W < 5), and 60° (272.9 ± 139.0 vs 367.0 ± 53.7 N, P = .007, W < 3). Peak pressure increased significantly between intact and OT graft at 30° (1364.0 ± 478.2 vs 2094.4 ± 619.8 N, P = .002, W < 9), 45° (1224.7 ± 491.5 vs 1676.7 ± 779.1 N, P = .005, W < 5), and 60° (1117.7 ± 566.8 vs 1604.2 ± 772.9 N, W < 3). In knees with significantly increased mean pressure after overtensioning, mean pressure increased by 23.3% (11/14 knees) at 30°, 18.3% (10/14 knees) at 45°, and 35.0% (10/14 knees) at 60°. Peak pressure increased significantly by 35.3% (30°), 25.2% (45°), and 29.3% (60°). A significant decrease in mean pressure, toward but not to baseline, was observed between the OT and LRR states at 30° (563.0 ± 11.2 vs 501.5 ± 9.3 N, W < 7) and 60° (367.0 ± 53.7 vs 302.0 ± 13.8 N, W < 5) and a decrease in peak pressure at 30° (2094.4 ± 619.8 vs 1886.5 ± 655.3 N; W < 9).

Conclusion:

LRR led to a statistically significant decrease in pressure across the patellofemoral joint in knees that demonstrated increased contact pressures after an OT MPFL graft.

Clinical Relevance:

LRR after an MPFL reconstruction in which the MPFL graft has been OT may help reduce patellofemoral contact pressures at the time of surgery.

Lateral Translation of the Patella in MPFC Reconstruction: A Biomechanical Study of Three Approaches

The purpose of this study was to investigate whether differences exist in preventing lateral patellar translation between three distinct medial patellofemoral complex (MPFC) reconstruction procedures at varying knee flexion angles. Six cadaveric knee specimens were dissected, potted, and placed in a customized jig for testing. Lateral patellar displacement was measured at intervals between 0 and 90 degrees of knee flexion using a tensile testing machine with a 20 N lateral force applied to the patella. Each specimen was tested with the MPFC intact, sectioned, and after each of the three reconstruction techniques: MPFL, hybrid, and medial quadriceps-tendon femoral (MQTFL) reconstructions. There was significantly increased lateral patellar displacement following MPFC sectioning when compared with the intact state in early degrees of flexion (10-30 degrees) (p < 0.05). All three reconstruction groups restored patella stability and reduced lateral patellar displacement following sectioning from 0 to 30 degrees of flexion (p < 0.05). When compared with the intact group, all three reconstruction groups demonstrated reduced patella translation at full knee extension, while the MPFL and hybrid reconstruction groups additionally demonstrated significant reduction in patella translation at 10 degrees of flexion (p < 0.05). No significant differences were observed between the three reconstruction groups. This biomechanical study demonstrates the efficacy of three MPFC reconstruction techniques in patella stabilization following sectioning. Our results suggest that MPFL reconstruction may provide the most robust patella stabilization, whereas MQTFL reconstruction may be the most forgiving construct. This study suggests that MQTFL and hybrid reconstructions provide adequate resistance to lateral translation and may be used as an alternative to MPFL reconstruction.

Femoral interference screw insertion significantly increases graft tension in medial patellofemoral ligament reconstruction

PURPOSE

This study aimed to quantify the effect of interference screw insertion on MPFL graft tension when securing the femoral attachment after patellar fixation. It was hypothesized that interference screw insertion significantly increases graft tension.

METHODS

Ten fresh frozen human cadaveric femurs were utilized to compare graft tension at three different preloading conditions (2 N, 5 N, 10 N) using a tensile testing machine (Admet Inc., Norwood, MA). Each preloading condition was analyzed with varying graft sizes (5-8 mm), tunnel diameters (7-9 mm), and interference screw sizes (7-9 mm). Non-parametric statistical analysis was utilized to compare testing conditions among each other.

RESULTS

Graft tension significantly increased after interference screw insertion by 100% to 552%, with 2 N preload showing the greatest increase (p < 0.001). Grafts with a larger diameter (7-8 mm) had a significantly greater increase in tension than smaller grafts (5-6 mm), regardless of preloading conditions (p < 0.001). Interference screw size had no influence on graft tension (n.s.). A graft-tunnel interference (tunnel diameter-graft diameter) fit of 0 mm and 1 mm significantly increased graft tension for each preloading condition when compared to a slightly looser fit of ≥ 2 mm (p < 0.05).

CONCLUSION

Femoral interference screw insertion significantly increases graft tension in MPFL reconstruction even in low preloading conditions, with graft size and graft-tunnel interference fit having a considerably effect on graft tension. Surgeons should be aware of the inadvertent increases in graft tension even in low preloading conditions to mitigate the risk of graft overtensioning.

Elongation and orientation pattern of the medial patellofemoral ligament during lunging

Unfavorable clinical outcomes after medial patellofemoral ligament (MPFL) reconstruction, such as early osteoarthritis of the patellofemoral joint, were considered to be associate with tunnel malpositioning. Length change studies have found that small changes in the femoral position can cause great changes in elongation trends. Further studying the MPFL kinematics may help us to understand the consequences of tunnel malpositioning and optimize the reconstruction techniques. Fifteen healthy subjects were studied with a combined computed tomography and biplane fluoroscopic imaging technique during a lunge motion. Five femoral and three patellar attachments were used to simulate different MPFL bundles. Kinematics of MPFL was defined as elongation and orientation changes (i.e., deviation angle and elevation angle). The mean deviation angle was 28.7° (95% confidence interval, 28.0°-29.4°) at full extension and remained nearly unchanged up to 60° of flexion, and increased to 56.5° (54.1°-58.9°) at 110°. The elevation angle decreased linearly from 12.6° (9.3°-15.9°) at full extension to -86.2° (-92.7-79.7°) at 110° of flexion. The MPFL was most stretched anteriorly and laterally relative to femur from full extension to 30° of flexion and remained near isometric beyond 30°. The current study found that proximal and anterior femoral attachments caused excessive lateral stretching of the MPFL at deeper flexion angles. Such abnormal MPFL kinematics may subsequently cause overconstraint and increased cartilage pressures of the medial patellofemoral joint.

Single-Incision, Single Patellar Tunnel For Double-Bundle Medial Patellofemoral Ligament Reconstruction: A Technical Note

The medial patellofemoral ligament (MPFL) is the main medial stabilizer of the patella, while reconstruction of the ligament is a common surgery performed by orthopedic surgeons. Although several surgical methods have been described regarding MPFL reconstruction, the common goals of these surgeries are to imitate the anatomic features of the native MPFL. In the single-incision and single patellar tunnel and double-bundle MPFL reconstruction technique, we will present the anatomical footprint of the MPFL located in the medial aspect of the patella, which is filled with the graft. In this technique, graft fixation is performed in the femoral tunnel using only one bioabsorbable screw without the need for fixation in the patella.

Patellar Fixation With Suspensory Fixation Device in Single-Tunnel Medial Patellofemoral Ligament Reconstruction

The medial patellofemoral ligament (MPFL) is the primary soft-tissue stabilizer of the patellofemoral joint. Among the patellofemoral instability surgery options, MPFL reconstruction is the most preferred soft-tissue procedure. There is no gold-standard surgical treatment method in MPFL reconstruction, and many surgical methods have been described. We describe our surgical technique for MPFL reconstruction wherein the semitendinosus autograft is fixed to a single tunnel opened in the patella with a suspensory fixation device and only a single interference screw on the femoral side.

Studies of the criteria for determining optimal location of medial patellofemoral ligament attachment sites

Identifying appropriate attachment sites is important in the planning of medial patellofemoral ligament (MPFL) reconstruction. Two criteria are advanced to describe normal MPFL function, namely isometric criterion and desired pattern criterion. Subsequently, computational methods have applied these criteria to determine optimal attachment sites. So far, there is no study that compares the outcomes of these two criteria. For five subjects' 3D models of the patella and femur, three patellar sites and many femoral sites were identified as pairs of candidate attachment sites. For each patellar site, the criteria were applied to identify the matching femoral sites that satisfy them. The matching femoral site with the smallest length change was identified as the optimal femoral site. The desired pattern criterion finds fewer matching sites compared to the isometric criterion. In contrast, the isometric criterion can always find matching sites. The optimal femoral sites obtained vary significantly across different subjects. For most subjects, the optimal sites obtained using the isometric criterion are closer to known anatomical sites than those obtained using the desired pattern criterion. This study reaffirms that MPFL reconstruction is subject specific. The isometric criterion may be more reliable than the desired pattern criterion for determining optimal attachment sites. Graphical Abstract. Highlight of the paper. The location of the patella site significantly affects the location of the optimal femoral site. The isometric criterion option 1, with length at 0° regarded as MPFL's natural length, may be more reliable than other criteria or options for the planning of MPFL surgery because the optimal sites that it finds are closest to known anatomical sites.ᅟ.

Medial Patellofemoral Ligament Reconstruction in Traumatic Patellar Dislocation without Patellar Fixation

Acute traumatic patellar dislocation is a common injury, and spontaneous reduction may occur at the time of injury or may be reduced at the field of the accident by someone. It may be associated with osteochondral fractures and rupture of medial patellar stabilizers leading to recurrent patellar instability. The aim of this prospective study was to evaluate the outcomes of medial patellofemoral (PF) ligament (MPFL) reconstruction in recurrent traumatic patellar dislocation. Forty-five patients presented with PF instability as a result of traumatic rupture MPFL with normal patellar tracking underwent MPFL reconstruction without patellar fixation hardware through two parallel transpatellar tunnels and one screw in femoral tunnel. All patients were evaluated clinically preoperatively and at a minimum follow-up of 24 months, and International Knee Documentation Committee (IKDC) and Kujala scores were used to assess the clinical results. All patients were available for evaluation at a minimum of 24 months (up to 36 months). The mean age of these patients at the time of surgery was 22.82 years (range: 18-34 years). All patients gave history of trauma of their knees. Mean IKDC scale showed significant improvement as it rose from 47.17 preoperatively to 77.94 postoperatively, and mean Kujala score rose from 53.88 preoperatively to 86.24 postoperatively (p < 0.001). No recurrence of dislocation was recorded. Only three patients had mild atrophy of thigh and one patient had some difficulty in jumping. Reconstruction of MPFL by this method provides good clinical result in the treatment of PF instability by using autologous graft (semitendinosus and gracilis). Less hardware were used with less complications.

Patellofemoral Contact Pressure for Medial Patellofemoral Ligament Reconstruction Using Suture Tape Varies With the Knee Flexion Angle: A Biomechanical Evaluation

PURPOSE

The purpose of this study was to evaluate the effect of the knee flexion angle during graft fixation on patellofemoral (PF) contact pressure in medial patellofemoral ligament (MPFL) reconstruction using polyester suture tape and knotless anchors.

METHODS

Nine human knees (mean age 74.9 ± 14.1 years) were used in this study. Polyester suture tape was fixed at the medial edge of the patella with two 3.5-mm knotless anchors, and then to the femur with a 4.75-mm knotless anchor at 4 different knee flexion angles (0°, 30°, 60°, and 90°). A pressure sensor was used to measure the maximum contact pressure (MCP) of the medial and lateral PF joints in the intact knee and in postreconstruction knees at each knee flexion angle (0°, 30°, 60°, and 90°). Each MCP was normalized to that of the intact knee. A statistical comparison was made between MCP in the intact and reconstructed knees.

RESULTS

The normalized MCP of the medial PF joint fixed at either 0° or 30° significantly increased at 60° of knee flexion (P = .036 and .042, respectively) and at 90° of knee flexion (P = .002 and .001, respectively). Conversely, the normalized MCP fixed at 60° and 90° remained at the same level as the intact knees at all angles of knee flexion. The normalized MCP of the lateral PF joint showed no significant difference at any fixation angle compared with intact knees.

CONCLUSION

To avoid excessive PF joint contact pressure after MPFL reconstruction, it may be best to fix polyester suture tape between 60° and 90° of knee flexion.

CLINICAL RELEVANCE

Fixation of the polyester suture tape with a knotless anchor for MPFL reconstruction should be at 60° to 90° of knee flexion to most closely restore PF joint contact pressures to that of the intact knee.

Selective bundle tensioning in double-bundle MPFL reconstruction to improve restoration of dynamic patellofemoral contact pressure

PURPOSE

To evaluate the optimal graft tension angles in a medial patellofemoral ligament (MPFL) reconstruction with selective bundle tensioning in order to restore patellofemoral contact pressure distributions closest to the native state.

METHODS

Twelve human cadaveric knee specimens were mounted with the femur on a custom-made fixation device allowing free range of motion in the knee joint for testing. Using a sensitive pressure film (Tekscan) patellofemoral contact pressure was measured in 15° intervals during a dynamic flexion movement from 0°-90° in the native state, in cut MPFL and after MPFL-reconstruction with a gracilis tendon. The graft was separated in two bundles and was fixed independently on the patella using two knotless anchors. Two groups were made with either the proximal or distal bundle fixed at the femur at a knee flexion angle of 30° and the corresponding other bundle subsequently fixed at the femur at 15°, 45°, 60°, 75° and 90° of knee flexion using extra-cortical fixation and controlled tension of 2N in both groups. The sequence of the flexion angles at the graft fixation was alternated. Pressure measurements were repeated after every fixation of the graft.

RESULTS

Cutting the MPFL resulted in significantly reduced patellofemoral contact pressure at all flexion angles. After MPFL reconstruction the patellofemoral contact pressure remained significantly reduced during dynamic knee flexion in all tested double-bundle combinations (p < 0.05) except for fixation of the proximal bundle in 30° and the distal bundle in 75°. Selective evaluation of lateral patellofemoral contact pressure, however, showed significant reduction in all tested double-bundle combinations (p < 0.05) from 15° to 90°. Evaluation of isolated medial patellofemoral pressure changes showed no significant difference in all tested combinations compared to the intact knee. Furthermore, evaluation of the isolated proximal and distal patellofemoral contact pressure also revealed a significantly reduced contact pressure in all tested double-bundle combinations (p < 0.05) except for fixation of the proximal bundle in 30° and the distal bundle in 75°.

CONCLUSION

According to this study, selective bundle tensioning in anatomic MPFL-reconstruction should be considered as an easy and more anatomic alternative to current popular techniques to restore patella kinematics and give clear recommendation about knee flexion angle and tension during fixation. Although tensioning two bundles separately may further improve clinical results. If performed, fixation of the graft is recommended under low tension (2N) with the proximal bundle at 30° and the distal bundle at 75° of knee flexion.

Extensive Lateral Release and Medial Patellofemoral Ligament Reconstruction in 25 Years of Chronic Fixed Lateral Patellar Dislocation: A 5-Year Follow-Up Case Report

Lateral dislocation of the patella is not uncommon and may impede daily activities as this causes compressive dysfunction and instabilities. Most cases of patellar lateral dislocation are due to damage to the medial patellofemoral ligament (MPFL), either rupture of detachment of the patella or femoral attachment. MPFL reconstruction alone was considered adequate for the treatment of this condition. We present a case of a 49-year-old male with chronic posttraumatic lateral patellar dislocation of the right knee of 25 years, which we treated with extensive lateral release and right medial patellofemoral ligament reconstruction with 5-year follow-up data.

Evaluation of Patellar Contact Pressure Changes after Static versus Dynamic Medial Patellofemoral Ligament Reconstructions Using a Finite Element Model

OBJECTIVES

To evaluate the effect of various medial patellofemoral ligament (MPFL) fixation techniques on patellar pressure compared with the native knee.

METHODS

A finite element model of the patellofemoral joint consisting of approximately 30,700 nodes and 22,200 elements was created from computed tomography scans of 24 knees with chronic lateral patellar instability. Patellar contact pressures and maximum MPFL graft stress at five positions of flexion (0°, 30°, 60°, 90°, and 120°) were analyzed in three types of MPFL reconstruction (MPFLr): (1) static/anatomic, (2) dynamic, using the adductor magnus tendon (AMT) as the femoral fixation, and (3) dynamic, using the quadriceps tendon as the attachment (medial quadriceps tendon-femoral ligament (MQTFL) reconstruction).

RESULTS

In the static/anatomic technique, the patellar contact pressures at 0° and 30° were greater than in the native knee. As in a native knee, the contact pressures at 60°, 90°, and 120° were very low. The maximum MPFL graft stress at 0° and 30° was greater than in a native knee. However, the MPFL graft was loose at 60°, 90°, and 120°, meaning it had no tension. In the dynamic MPFLr using the AMT as a pulley, the patellar contact pressures were like those of a native knee throughout the entire range of motion. However, the maximum stress of the MPFL graft at 0° was less than that of a native ligament. Yet, the maximum MPFL graft stress was greater at 30° than in a native ligament. After 30° of flexion, the MPFL graft loosened, similarly to a native knee. In the dynamic MQTFL reconstruction, the maximum patellar contact pressure was slightly greater than in a normal knee. The maximum stress of the MPFL graft was much greater at 0° and 30° than that of a native MPFL. After 30° of flexion, the MQPFL graft loosened just as in the native knee.

CONCLUSIONS

The patellar contact pressures after the dynamic MPFLr were like those of the native knee, whereas a static reconstruction resulted in greater pressures, potentially increasing the risk of patellofemoral osteoarthritis in the long term. Therefore, the dynamic MPFLr might be a safer option than a static reconstruction from a biomechanical perspective.

Knee Flexion Angle During Graft Fixation for Medial Patellofemoral Ligament Reconstruction: A Systematic Review of Outcomes and Complications

PURPOSE

To determine the effect of knee flexion angle during graft fixation on outcomes and complications following medial patellofemoral ligament (MPFL) reconstruction.

METHODS

Three databases (PubMed, EMBASE, and MEDLINE) were searched from database inception to January 2018. After screening based on inclusion and exclusion criteria, patient demographics, fixation technique, graft selection, outcomes, and complications were extracted from the included studies. The studies were grouped based on flexion angle used during graft fixation: low (0°-30°) and high (45°-90°) flexion angle group. Methodological Index for Non-Randomized Studies criteria were used to assess the quality of each included study. Descriptive statistics are presented.

RESULTS

Seventeen studies (of 3,399) were included and were either cohort (n = 1) or case series (n = 17) study designs. A total of 556 patients with a mean age of 23.6 years (range, 10-60 years) underwent MPFL reconstructions, with 458 patients in the 0° to 30° fixation group and 98 in the 45° to 90° fixation group. The mean Kujala score improved from 45 to 72.9 (365 patients) preoperatively to 83 to 94.5 (460 patients) postoperatively for the 0° to 30° fixation group and from 53.3 to 72 preoperatively to 92.2 to 95.2 postoperatively for the 45° to 90° fixation group (98 patients).

CONCLUSIONS

The knee flexion angle during MPFL graft fixation ranges from 20° to 90°. Graft fixation at low and high knee flexion angles during MPFL reconstruction showed excellent patient-reported outcomes and low patellar redislocation rates overall, with no clear differences between the 2 groups based on the currently available data.

LEVEL OF EVIDENCE

Level IV, systematic review of Level III-IV studies.

Editorial Commentary: The "F" in MPFL (Medial Patellofemoral Ligament) Reconstruction-How Should We Fix It and Does It Matter?

Our understanding of the medial patellofemoral complex anatomy has evolved significantly over the past several decades, and this has informed our current surgical approach to management of lateral patellar instability. Medial patellofemoral ligament reconstruction remains the gold standard for decreasing the risk of secondary patellar dislocation and returning patients to active physical function. However, concerns about isometry, overconstraint, secondary arthrosis, and surgical-site morbidity remain with femoral socket fixation, particularly when patella alta, rotational malalignment, or hypermobility is present. Medial patellofemoral ligament reconstruction with soft-tissue fixation, on either the patellar or femoral side, may mitigate some of these risks by offering a more dynamic checkrein to lateral translation. However, longer-term studies are required to determine comparative efficacy with varying surgical techniques, and the ideal graft tension and degree of knee flexion during fixation have not yet been determined.

Proximal medial patellar restraints and their surgical reconstruction

Reconstruction of the medial patellofemoral ligament (MPFL) has been increasing as a surgical solution for treatment of recurrent lateral patellofemoral dislocation. Recent attention has been given to fibers extending from the femur to the quadriceps tendon, proximal to the MPFL, termed the medial quadriceps tendon-femoral ligament. This article briefly reviews the proximal medial patellar restraints and surgical procedures for their reconstruction.

Avoiding Complications with MPFL Reconstruction

PURPOSE OF REVIEW

To discuss the potentially significant complications associated with medial patellofemoral ligament (MPFL) reconstruction. Additionally, to review the most current and relevant literature with an emphasis on avoiding these potential complications.

RECENT FINDINGS

Multiple cadaveric studies have characterized the anatomy of the MPFL and the related morphologic abnormalities that contribute to recurrent lateral patellar instability. Such abnormalities include patella alta, excessive tibial tubercle to trochlear grove (TT-TG) distance, trochlear dysplasia, and malalignment. Recent studies have evaluated the clinical outcomes associated with the treatment of concomitant pathology in combination with MPFL reconstruction, which is critical in avoiding recurrent instability and complications. Although there remains a lack of consensus regarding various critical aspects of MPFL reconstruction, certain concepts remain imperative. Our preferred methods and rationales for surgical techniques are described. These include appropriate work up, a combination of procedures to address abnormal morphology, anatomical femoral insertion, safe and secure patellar fixation, appropriate graft length fixation, and thoughtful knee flexion during fixation.

Surgical Technique: Anatomic Medial Patellofemoral Ligament Retensioning Repair

The medial patellofemoral ligament (MPFL) and the MPFL/vastus medialis obliquus complex are essential for patellar stability. Insufficiency of the MPFL can lead to altered biomechanics and patellofemoral joint contact pressure, high recurrence rate, osteochondral lesions, compromised knee function, and patellofemoral osteoarthritis. Most frequently surgical reconstruction of the MPFL is performed to address patellar instability; however, open physis and donor site morbidity can be a concern. This Technical Note presents a surgical technique to identify the insufficient MPFL and describes in detail an anatomical retensioning repair of the MPFL to restore patellar stability.

Editorial Commentary: Knee Medial Patellofemoral Ligament Reconstruction Does Not Always Result in the "Bee's Knees"

Reconstruction of the medial patellofemoral ligament has gained in popularity as a surgical technique to reconcile recurrent lateral patellar instability. This technique has shown success in a variety of settings including with concomitant osseous abnormalities. Despite the general good to excellent results with medial patellofemoral ligament reconstruction, a number of technical errors are still commonly made and may result in decreased range of motion, pain, chondrosis, and arthrofibrosis. In a recent study, the importance of knee flexion angle during final fixation of the graft is emphasized. Even with appropriate tunnel placement, and minimal tension on the graft, graft fixation performed at less than or greater than 60° of knee flexion results in medial patellar overload with risk of the aforementioned complications.