The Medial Patellofemoral Ligament Is a Dynamic and Anisometric Structure: An In Vivo Study on Length Changes and Isometry

MPFL reconstruction with proximal rather than distal femoral tunnel position leads to less favorable short-term results

BACKGROUND

This study aimed to compare the clinical and radiological outcomes of medial patellofemoral ligament (MPFL) reconstruction (MPFLR) between anatomic femoral tunnel positions: proximal (near adductor tubercle [AT]) and distal (near medial epicondyle [ME]).

HYPOTHESIS

MPFLR with the proximal femoral tunnel position has worse clinical and radiological outcomes than those with the distal femoral tunnel position.

PATIENTS AND METHODS

Fifty-five patients who underwent isolated MPFLR with proximal or distal femoral tunnels with at least 2 years of follow-up were retrospectively analyzed. Based on postoperative CT images, 28 patients were classified as group AT and the remaining 27 patients were classified as group ME. The International Knee Documentation Committee, Lysholm, Tegner, Kujala scores, and complications were evaluated. Radiologically, the Caton-Deschamps Index (CDI), patellar tilt angle, patellofemoral osteoarthritis (PFOA), patellofemoral cartilage status by the International Cartilage Repair Society (ICRS) grade, bone contusion, and MPFL graft signal intensity were evaluated.

RESULTS

All clinical scores significantly improved in both groups (p<0.01). No statistically significant difference was noted between the two groups in regards to their preoperative demographic data, postoperative clinical scores, complications, or radiological findings (CDI, patellar tilt angle, PFOA, bone contusion, and graft signal intensity). The group AT had worse cartilage status on the medial facet of the patella (p=0.02). The ICRS grade for the medial facet of the patella statistically progressed in group AT compared to group ME (p=0.04) as well.

DISCUSSION

Both groups showed significantly improved clinical outcomes. However, for the medial facet of the patella, MPFLR with the proximal femoral tunnel position had worse cartilage status and ICRS grade progression than those with the distal femoral tunnel position.

LEVEL OF EVIDENCE

III; retrospective comparative study.

Implications for Femoral Tunnel Placement in Medial Patellofemoral Ligament Reconstruction Considering the Sagittal Trochlear Groove Curvature in Severe Trochlear Dysplasia Before and After Deepening Trochleoplasty

BACKGROUND

Medial patellofemoral ligament reconstruction (MPFL-R) aims to restore proper ligament function with minimal changes in length during range of motion, yet the ideal area for femoral fixation of the graft remains controversial.

PURPOSE

To determine the region where the isometric circular path of a simulated MPFL graft (best-fit circle) follows the sagittal radius curvature of the trochlea in normal (nontrochlear dysplastic) knees and to evaluate the best-fit circle coverage of different femoral fixation points in knees with severe trochlear dysplasia (TD) and after deepening trochleoplasty.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve patients (4 male, 8 female; mean age, 24 ± 8 years) who underwent surgical treatment for recurrent lateral patellar instability due to severe TD were prospectively enrolled in this study. Four previously defined reference points for the femoral MPFL-R (Schöttle, Fujino, Stephen, and Oka) were identified, and the best-fit circle was drawn along the sagittal trochlear groove curvature. The divergence between each best-fit circle and the trochlear groove was calculated, with negative values indicating relative slackening and positive values indicating relative tightening of the simulated MPFL graft. Measurements were made on true-lateral fluoroscopic images before and after deepening trochleoplasty and compared with those of a sex-matched control group.

RESULTS

The best-fit circle of the Schöttle point followed the sagittal curvature of the trochlea most closely in both the control and trochlear dysplastic knees, followed by the Fujino, Stephen, and Oka points. As the radius of the trochlear groove curvature increased, the divergence of all best-fit circles to the trochlear groove became negative (all P < .05). This effect was most pronounced at the Stephen and Oka points, followed by the Fujino and Schöttle points (all P < .05). After deepening trochleoplasty, the divergence of the Schöttle point changed toward positive values (11.6% at 40°; P < .001). Concurrently, the best-fit circle divergence of all other reference points improved toward baseline (all P < .05).

CONCLUSION

The isometric circle of the Schöttle point provides the best congruence with the sagittal trochlear groove curvature in both the normal trochlea and the dysplastic trochlea. After trochleoplasty, the best-fit circles of more distal femoral fixation points resulted in better congruence with the deepened trochlear groove, whereas the best-fit circle of Schöttle indicated graft tension during flexion.

CLINICAL RELEVANCE

According to the present study, different femoral fixation points should be considered depending on whether the TD is corrected.

Anatomic double-bundle transtibial anterior cruciate ligament reconstruction restores graft length changes but leads to larger graft bending angles

PURPOSE

The purpose of this study was to evaluate the femoral tunnel position using a modified anatomic transtibial (TT) double-bundle anterior cruciate ligament reconstruction (DBACLR) and to investigate the knee kinematics, graft length and graft bending angle following DBACLR.

METHODS

Ten patients who underwent DBACLR using the modified TT technique were included in the study. All patients performed a single-legged lunge under a dual fluoroscopic imaging system to assess the 6 degrees of freedom tibiofemoral kinematics. Femoral tunnel position was evaluated via postoperative three-dimensional (3D) computed tomography. The area centroids of anteromedial (AM) and posterolateral (PL) bundles were determined on 3D knee models. The lengths of AM and PL bundles, as well as graft bending angle at the femoral tunnel aperture, were measured by created virtual fibres.

RESULTS

The reconstructed knee rotated more externally compared with the contralateral knee between 0° and 60° (p ≤ 0.049). There is no significant difference in the length change of AM bundle (n.s.) and PL bundle (n.s.) between the two sides from 0° to 120° during the lunge motion. The maximum graft bending angle at the femoral tunnel aperture occurred at 0° of knee flexion, with the AM graft bending angle was 72.6° ± 9.0° and the PL graft bending angle was 90.3° ± 9.7°.

CONCLUSION

The modified TT technique used in this study could achieve anatomical ACL reconstruction, restoring graft length change patterns compared to contralateral knees. However, residual rotational instability of the reconstructed knee was observed after DBACLR, despite achieving anatomic tunnel placement. Therefore, double-bundle reconstruction may not sufficiently address the persistent rotational instability of the knee. Additionally, larger graft bending angles at the femoral tunnel aperture were found with the modified TT technique. Therefore, further improvement to the TT technique should focus on reducing the graft's curvature while maintaining the anatomical properties of the knee joint. The findings of this study highlight the need for improved surgical techniques to address residual rotational instability and optimise graft curvature. These improvements are crucial for enhancing patient outcomes and long-term joint function following ACL reconstruction.

LEVELS OF EVIDENCE

Level II.

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.

Quadriceps muscle contraction causes medial patellofemoral ligament elongation by intermeshed fibers of vastus medialis oblique muscle

The first aim of this study was to compare the medial patellofemoral length between contracted and relaxed quadriceps muscle and second to assess the importance of the intermeshed vastus medialis oblique fibers. After a priori power analysis (α = 0.05, power [1-β] = 0.95), 35 healthy males aged 18-30 were prospectively examined with a 3.0-T magnetic resonance imaging (MRI) scanner in 10-15° of knee flexion. Two axial MRI sequences (25 s each) were made with relaxed and contracted quadriceps. Two blinded, independent raters measured twice medial patellofemoral ligament length (curved line) and attachment-to-attachment length (straight line). Mean medial patellofemoral ligament length and attachment-to-attachment length with relaxed quadriceps was: 65.5 mm (SD = 3.7), 59.7 mm (SD = 3.6), and after contraction, it increased to 68.7 mm (SD = 5.3), 61.2 mm (SD = 4.7); p < 0.01 and <0.001, respectively. Intraclass correlation coefficients for intra- and inter-rater reliabilities ranged from 0.55 (moderate) to 0.97 (excellent). Mean medial patellofemoral ligament length elongation after quadriceps contraction was significantly greater (3.2 mm, SD = 3.9) than mean attachment-to-attachment length elongation (1.6 mm, SD = 2.8); p < 0.001. Contraction of quadriceps muscle causes elongation of the medial patellofemoral ligament to the extent greater than the elongation of distance between its attachments. This confirms that medial patellofemoral ligament elongation after quadriceps contraction results not only from movement of its patellar attachment but also directly from intermeshed vastus medialis oblique fibers pulling medial patellofemoral ligament in a different direction creating a bow-like construct in agreement with the "pull-and-guide mechanism" proposed in the literature.

Anatomic femoral tunnel position in medial patellofemoral ligament reconstruction: anterior versus posterior

BACKGROUND

This study aimed to compare the clinical and radiological outcomes of medial patellofemoral ligament reconstruction (MPFLR) between anatomic femoral tunnel positions at anterior and posterior footprints.

METHODS

Fifty-seven patients who underwent MPFLR for patellofemoral instability with anterior or posterior femoral tunnels between 2014 and 2021 with at least 2 years of follow-up were retrospectively analyzed. Based on postoperative images, the femoral tunnel positions anterior to the line connecting the adductor tubercle and medial epicondyle were assigned to the anterior group, group A, and those posterior to the line to the posterior group, group P. Thirty-two patients were included in group A (mean age, 22.4 ± 8.8 years), and another 25 patients were included in group P (mean age, 21.1 ± 6.1 years). The International Knee Documentation Committee (IKDC) subjective score, Lysholm score, Tegner activity score, Kujala score, and complications were evaluated. Radiologically, the Caton-Deschamps index (CDI), patellar tilt angle, and patellofemoral osteoarthritis (PFOA) using the Kellgren-Lawrence (KL) scale were evaluated. The patellofemoral cartilage status according to the International Cartilage Repair Society (ICRS) grade, bone contusion, femoral tunnel enlargement, and MPFL graft signal intensity were also evaluated.

RESULTS

All clinical scores significantly improved in both groups (p < 0.01). No differences were noted between the two groups in terms of their preoperative demographic data, postoperative clinical scores (IKDC, Lysholm, Tegner, and Kujala), complications, or radiological findings (CDI, patellar tilt angle, PFOA, bone contusion, femoral tunnel enlargement, and graft signal intensity). The ICRS grade for the medial facet of the patella progressed in group A (30%, p = 0.02) but not in group P (18%, p = n.s.). Additionally, no significant differences were observed in the other compartments of the patellofemoral joint.

CONCLUSIONS

The clinical outcomes were significantly improved in both groups; however, MPFLR with anterior femoral tunnel position had worse cartilage status on the medial facet of the patella than the posterior femoral tunnel position.

LEVEL OF EVIDENCE

Level III.

Length Changes of the Medial Patellofemoral Ligament During In Vivo Knee Motion: An Evaluation Using Dynamic Computed Tomography

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction is associated with high complication rates because of graft overloading from incorrect graft positioning. To improve clinical outcomes, it is crucial to gain a better understanding of MPFL elongation patterns.

PURPOSE

To assess MPFL length changes in healthy knees from 0° to 90° of dynamic flexion and their relationship with anatomic parameters of the patellofemoral joint.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Dynamic computed tomography scans of an active flexion-extension-flexion movement in 115 knees from 63 healthy participants were evaluated to construct knee joint models. Using these models, the MPFL length was measured as the shortest wrapping path from the Schöttle point on the femur to 3 insertion points on the superomedial border of the patella (proximal, central, and distal). MPFL length changes (%) relative to the length in full extension were calculated, and their correlations with the tibial tuberosity-trochlear groove distance, Caton-Deschamps index, and lateral trochlear inclination were analyzed.

RESULTS

The proximal fiber was the longest in full extension and progressively decreased to a median length of -6.0% at 90° of flexion. The central fiber exhibited the most isometric pattern during knee flexion, showing a median maximal decrease of 2.8% relative to the full extension length and no evident elongation. The distal fiber first slightly decreased in length but increased at deeper flexion angles. The median overall length changes were 4.6, 4.7, and 5.7 mm for the proximal, central, and distal patellar insertion, respectively. These values were either not or very weakly correlated with the tibial tuberosity-trochlear groove distance, Caton-Deschamps index, and lateral trochlear inclination when the anatomic parameters were within the healthy range.

CONCLUSION

The median MPFL length changed by approximately 5 mm between 0° and 90° of flexion. Proximally, the length continuously decreased, indicating slackening behavior. Distally, the length increased at deeper flexion angles, indicating tightening behavior.

CLINICAL RELEVANCE

In MPFL reconstruction techniques utilizing the Schöttle point to establish the femoral insertion, one should avoid distal patellar insertion, as it causes elongation of the ligament, which may increase the risk for complications due to overloading.

Stiffness and Instability After MPFL Reconstruction Using a Fluoroscopic Versus Open Technique to Localize the Femoral Attachment Site: A Systematic Review and Meta-analysis

Background

Open and fluoroscopic techniques have been described for localization of the femoral attachment site in medial patellofemoral ligament (MPFL) reconstruction. No study to date has evaluated if one technique is superior to another in terms of complications.

Purpose

To review the literature comparing clinical outcomes of MPFL reconstruction using the fluoroscopic versus open technique to localize the site of femoral graft placement.

Study Design

Systematic review; Level of evidence, 4.

Methods

A systematic literature review was performed via PubMed, Embase, and CINAHL to identify articles published between the inception of these databases and March 1, 2022, in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. This search yielded 4183 publications for initial review. Studies with at least a 2-year follow-up and complete reporting of patient-reported outcomes, range of motion, recurrent instability, and/or complications (ie, stiffness, infection, persistent pain) were included. We excluded studies of patients with collagen disorders; revision surgeries; surgeries with concomitant procedures; synthetic MPFL reconstruction; MPFL repairs; combined open and radiographic technique; and case series that included <10 patients. A proportional meta-analysis was performed by calculating the pooled estimate of incidence with 95% CIs using a fixed-effects model with double arcsine transformation (Freeman-Tukey) for each type of surgical technique (fluoroscopic or open).

Results

A total of 29 studies met our inclusion criteria, of which 15 studies (566 patients) used the open technique and 14 studies (620 patients) used fluoroscopy. There were no significant differences between the open and fluoroscopic techniques in the incidence of postoperative apprehension (P = .4826), postoperative subjective instability (P = .1095), postoperative objective instability (P = .5583), reoperations (P = .7981), recurrent dislocation (P = .6690), or arthrofibrosis (P = .8118).

Conclusion

Both open and radiographic localization of the femoral graft position in MPFL reconstruction offer similar outcomes and rates of complications.

Combined Medial Patellofemoral Ligament, Medial Quadriceps Tendon-Femoral Ligament, and Medial Patellotibial Ligament Reconstruction for Patellar Instability: A Technical Note

Lateral patellar dislocations often occur in a young, athletic population of recurrent dislocators with generalized laxity and an interest in returning to an active lifestyle. A recent appreciation for the distal patellotibial complex has directed surgeons toward attempting to re-create the native anatomy and knee biomechanics during medial patellar reconstructive procedures. By reconstructing the medial patellotibial ligament (MPTL) in addition to the medial patella-femoral ligament (MPFL) and medial quadriceps tendon-femoral ligament (MQTFL), the current article describes a potentially more stable construct that can be utilized in patients with subluxation with the knee in full extension, patellar instability with the knee in deep flexion, genu recurvatum, and generalized hyperlaxity. Additionally, the current technique utilizes a tibialis anterior allograft. The purpose of this Technical Note is to describe, in detail, the current authors' technique for a combined MPFL, MQTFL, and MPTL reconstruction.

Loaded open-kinetic-chain exercises stretch the anterior cruciate ligament more than closed-kinetic-chain exercises: In-vivo assessment of anterior cruciate ligament length change

BACKGROUND

Usage of open-kinetic-chain (OKC) or closed-kinetic-chain (CKC) exercises during rehabilitation planning after anterior cruciate ligament (ACL) reconstruction has been debated for decades. However, the ACL elongation pattern during different rehabilitation exercises at different loadings remains unclear.

OBJECTIVES

This study aimed to determine the effects of OKC and CKC exercises on the length of ACL anteromedial bundle (AMB) and posterolateral bundle (PLB) to provide biomechanical support for making rehabilitation schedules.

DESIGN

Laboratory Descriptive Study.

METHOD

Eighteen healthy volunteers were asked to perform two OKC motions, including non-weight-bearing and 10 kg loaded seated knee extension (OKC-0, OKC-10), as well as two CKC motions, including box squat (BS) and deep single-legged lunge (Lunge). Techniques of 2D-to-3D image registration and 3D ligament simulation were used to quantify length changes of ACL.

RESULTS

The motion which led to the least and most ACL elongation were OKC-0 and OKC-10, respectively. The AMB and PLB were significantly longer in OKC-10 than those in OKC-0 during 0-60° and 0-55° of knee flexion (p < 0.01). Compared with reference length, the AMB and PLB were stretched during 0-30° and 0-10° respectively during OKC-10. During CKC exercises, the AMB and PLB were also stretched from 0 to 25°and 0-5°, respectively. Additionally, no significant difference was found in the length change of ACL bundles between BS and lunge.

CONCLUSIONS

OKC-0 may be safe for the rehabilitation program after ACL reconstruction, and loaded exercises shall be applied when restricted with >30° in early-stage rehabilitation.

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 .

Influence of the Fluoroscopy Setting towards the Patient When Identifying the MPFL Insertion Point

(1) The malposition of the femoral tunnel in medial patellofemoral ligament (MPFL) reconstruction can lead to length changes in the MPFL graft, and an increase in medial peak pressure in the patellofemoral joint. It is the cause of 36% of all MPFL revisions. According to Schöttle et al., the creation of the drill canal should be performed in a strictly lateral radiograph. In this study, it was hypothesized that positioning the image receptor to the knee during intraoperative fluoroscopy would lead to a relevant mispositioning of the femoral tunnel, despite an always adjusted true-lateral view. (2) A total of 10 distal femurs were created from 10 knee CT scans using a 3D printer. First, true-lateral fluoroscopies were taken from lateral to medial at a 25 cm (LM25) distance from the image receptor, then from medial to lateral at a 5 cm (ML5) distance. Using the method from Schöttle, the femoral origin of the MPFL was determined when the femur was positioned distally, proximally, superiorly, and inferiorly to the image receptor. (3) The comparison of the selected MPFL insertion points according to Schöttle et al. revealed that the initial determination of the point in the ML5 view resulted in a distal and posterior shift of the point by 5.3 mm ± 1.2 mm when the point was checked in the LM25 view. In the opposite case, when the MPFL insertion was initially determined in the LM25 view and then redetermined in the ML5 view, there was a shift of 4.8 mm ± 2.2 mm anteriorly and proximally. The further positioning of the femur (distal, proximal, superior, and inferior) showed no relevant influence. (4) For fluoroscopic identification of the femoral MPFL, according to Schöttle et al., attention should be paid to the position of the fluoroscopy in addition to a true-lateral view.

Medial Patellofemoral Ligament Reconstruction Using Adductor-Transfer and Adductor-Sling at Nonanatomic Femoral Attachment Sites Leads to Unfavorable Graft-Length Change Patterns: A Descriptive Biomechanical Study

PURPOSE

To compare the graft length change patterns in nonanatomic adductor-transfer (AT) and adductor-sling (AS) medial patellofemoral ligament (MPFL) reconstruction with those in anatomic MPFL reconstruction (MPFLR) and to investigate the favorable isometric ranges (FIRs) of knee flexion.

METHODS

Eight small fresh-frozen cadaveric knees were mounted in a knee-customized jig with tensioned muscles to measure graft length changes from two patellar points to four femoral attachments using a linear variable displacement transducer. Femoral attachments were at the MPFL footprint center (MPFL-C) in anatomic MPFLR, adductor magnus (AM) footprint center (AM-C) in AT, and at 5-mm (AM-5) or 10-mm (AM-10) points proximal to AM-C in AS. The FIRs of these femoral attachments were determined after zeroing the graft length changes at different initial fixation angles.

RESULTS

Anatomic MPFL-C resulted in almost isometric graft length changes from 0° to 90°. At AM-C, the graft length changes displayed an increase from 0° to 45° and significantly greater length changes than those at MPFL-C from 60° to 90°. The graft length changes at both AM-5 and at AM-10 continuously increased with knee flexion angles and presented significantly larger graft length changes than those at MPFL-C and at AM-C from 30° to 90° and 60° to 90°, respectively. After zeroing graft length changes at different fixation angles, the FIRs of the MPFL-C covered all knee flexion angles, regardless of the patellar attachments and initial fixation angles. Moreover, with the smaller FIRs of AM-C observed at any fixation angle when compared with MPFL-C, fixing the graft at 0° to 30° in AT allowed the FIRs to cover the whole functional flexion range. However, the significantly larger graft length changes of both AM-5 and AM-10 resulted in extremely limited FIRs at any fixation angle.

CONCLUSION

Anatomic MPFL-C resulted in a favorable graft length change range (less than 2 mm) at 0° to 90° of knee flexion, which was close to the isometric graft behavior. However, nonanatomic attachments of AM-C in AT, and both AM-5 and AM-10 in AS caused significant anisometric graft length change patterns and limited FIRs. Moreover, AT had a smaller range of graft length change but wider FIRs compared to AS, indicating superior graft behavior for MPFLR.

CLINICAL RELEVANCE

Anatomic MPFLR is preferable for the treatment of in skeletally immature patients, followed in preference by nonanatomic AT. Nonanatomic AS should be performed cautiously.

Editorial Commentary: The Medial Patellofemoral Ligament Is Not Isometric and Anatomic Reconstruction Is Important, But Just a Small Piece of the Patellar Instability Puzzle

Medial patellofemoral ligament (MPFL) reconstruction has proven to be a reliable procedure to reduce patellar instability events in patients with recurrent patellar instability. As our reconstruction techniques have evolved to address pathology in a diverse patient population, there continues to be an obsessive focus on the precise anatomy of the MPFL origin on the medial knee, due in large part to concerns that improper femoral tunnel position may result in excessive graft anisometry and failure. However, recurrent patellar instability involves many complexities and should not be simply reduced to a single point on the medial knee.

Are Patellofemoral Ligaments and Retinacula Distinct Structures of the Knee Joint? An Anatomic, Histological and Magnetic Resonance Imaging Study

There is disagreement regarding the description of the patellofemoral ligaments (PFLs), considered by some authors as capsular thickening and by others as independent ligaments. It was hypothesised that the PFLs and retinacula are structures with different histological features. The aim of this study was to describe the stabilising structures of the patella in detail and to determine if the PFLs and retinacula are different and separable structures from a macroscopic, microscopic and imaging viewpoint. An anatomical study was performed on eight knees from five cadavers (mean age, 56.2 years; range, 35–63 years), and a histological study was conducted on specimens from nine patients having a mean age of 65 years (range 35–84 years) who had undergone surgical knee procedures. The imaging study was based on 100 MRIs (96 patients). The mean age was 46 years (range 16–88), and the study analysed the capsular-ligamentous structures. In the medial compartment, the layers and structures were as follows: superficial layer, medial retinaculum; intermediate layer, Medial Collateral Ligament (MCL), Posterior Oblique Ligament (POL) and Medial Patellofemoral Ligament (MPFL); deep layer, deep part of the MCL and joint capsule. In the lateral compartment, the layers and structures were the following: superficial layer, lateral retinaculum; intermediate layer, Lateral Collateral Ligament (LCL) and Lateral Patellofemoral Ligament (LPFL); deep layer, joint capsule. All of the knees examined presented a clearly distinguishable MPFL and LPFL separable from the capsular layer. Histological study: there was a higher density of nerve fibres in retinacula compared to ligaments (p = 0.0034) and a higher content of elastic fibres in retinacula (p < 0.0005). In imaging, there was no difference between medial and lateral retinaculum thickness (p > 0.05). In conclusion, both the lateral and medial compartment can be described using the three-layer scheme. PFLs and retinacula are separate structures both macroscopically and according to imaging analysis. The retinacula respond to their specific function with a higher nerve fibre content and higher number of elastic fibres compared to the ligaments.

Medial patellofemoral ligament reconstruction: A review

INTRODUCTION

Reconstruction of the medial patellofemoral ligament (MPFL) is an effective surgical method for the treatment of lateral patellar instability. At present, there is not much controversies regarding the femoral attachment, however, the controversies regarding patellar attachment versus attachment, number of graft strands, tension, isometry and so on. The following electronic databases will be searched: PubMed, the Cochrane Library, Embase, Web of Science, Medline. We will consider articles published between database initiation and March 2021. MPFL in the subject heading will be included in the study. Language is limited to English. Research selection, data extraction, and research quality assessment were independently completed by 2 researchers.

CONCLUSIONS

MPFL reconstruction is a reliable technique for the treatment of patellofemoral instability. The Schöttle point is still the mainstream method for locating the femoral attachment, the patellar attachment for single-bundle is located at the junction of the proximal one third and the distal two third of the longitudinal axis of the patella. For double-bundles, one is located in the proximal one third of the medial patellar edge and another is in the center of the patellar edge. Meanwhile, the adjustment of graft tension during operation is very important.

The novel dynamic MPFL-reconstruction technique: cheaper and better?

PURPOSE

Reconstruction of the medial patellofemoral ligament (MPFL) is an established procedure to restore patellar stability. Aim of this study is to evaluate the results of a dynamic MPFL reconstruction technique in a large university hospital setting.

METHODS

Two hundred and thirteen consecutive patients with 221 knees were surgically treated for recurrent lateral patellar dislocation. All patients obtained dynamic reconstruction of the MPFL with detachment of the gracilis tendon at the pes anserinus while maintaining the proximal origin at the gracilis muscle. Patellar fixation was performed by oblique transpatellar tunnel transfer. Follow-up data including Kujala and BANFF score, pain level as well as recurrent patella instability were collected at a minimum follow-up of 2 years.

RESULTS

Follow-up could be obtained from 158 patients (71%). The mean follow-up time was 5.4 years. Mean pain level was 1.9 ± 2.0 on the VAS. Mean Kujala score was 78.4 ± 15.5. Mean BANFF score was 62.4 ± 22.3. MPFL-reconstructions that were performed by surgeons with a routine of more than ten procedures had a significantly shorter surgical time 52.3 ± 17.6 min. Male patients yielded higher satisfaction rates and better clinical scores compared to females. Complications occurred in 27.2% of procedures, 20.9% requiring revision surgery of which were 9.5% related to recurrent patellar instability. 78% of all patients indicated they would undergo the procedure again.

CONCLUSION

Dynamic MPFL reconstruction presents a reproducible procedure with increased complication rates, inferior to the results of static reconstruction described in the literature. Despite, it appears to be an efficient procedure to restore patellar stability in a large university hospital setting, without the necessity for intraoperative fluoroscopy.

TRIAL REGISTRATION

The study was registered in ClinicalTrials.gov with the registration number NCT04438109 on June 18th 2020.

In Vivo Knee Kinematics in Patients With Arthrofibrosis After Anterior Cruciate Ligament Reconstruction

Context: Arthrofibrosis after anterior cruciate ligament (ACL) reconstruction can be detrimental to the knee joint function and patient outcomes. However, the effects of arthrofibrosis on the in vivo tibiofemoral and patellofemoral joint kinematics after ACL reconstruction remain unclear. Objective: The objective of this study was to quantify the in vivo knee kinematics during a dynamic lunge task in the knee with arthrofibrosis after ACL reconstruction. Methods: Eleven patients with arthrofibrosis in one knee after ACL reconstruction participated in this study. Computed tomography and dual fluoroscopic imaging were used to evaluate in vivo kinematics of affected and contralateral knees during a lunge task. Differences in 6 degrees of freedom tibiofemoral kinematics and patellar tracking between limbs were assessed via repeated-measures analysis of variance. Results: Internal tibial rotation (5.2° vs 7.5°, respectively; P < .001) and inferior patellar shift (24.6 mm vs 28.9 mm, respectively; P < .001) were significantly lower in the arthrofibrotic knee compared with the contralateral knee from 15° to 75° of knee flexion. The patella in the arthrofibrotic knee significantly less flexed by 9.1° (P = .009) throughout the measured ROM and less laterally tilted by 3° (P = .017) compared with the contralateral knee from 30° to 75° of knee flexion. Conclusions: A significant superior shift and medial tilt of the patella were found in the affected knee compared with those in the contralateral knee during the dynamic lunge. Decreased internal tibial rotation and patellar flexion were found in knees with arthrofibrosis following ACL reconstruction; whether these kinematic changes are caused by arthrofibrosis need further investigation.

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.

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

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

A computed tomography cadaveric study of the radiological anatomy of the patella: the size of the patella correlates with bone bridge between tunnels and R angles are introduced for safe tunnel drilling during MPFL reconstruction

PURPOSE

To measure the safe range of angles during tunnel drilling and map ideal patella tunnel placement with the use of preoperative computed tomography (CT) scan and compare results after medial patellofemoral ligament (MPFL) reconstruction using a hardware-free patellar fixation technique with two semi-patellar tunnels between a) a free-hand technique, and b) its modification with the use of an anterior cruciate ligament (ACL) tibia aiming device.

METHODS

CT scan was performed on 30 fresh-frozen cadaveric knees a) prior to any intervention and b) after MPFL reconstruction. For MPFL reconstruction, specimens were randomly allocated to 1) Group A, which consisted of knees operated with free-hand, hardware-free patellar fixation technique with two semi-patellar tunnels and 2) Group B, which consisted of knees operated on with a technique modification with the ACL tibia device.

PATELLAR MEASUREMENTS

L1 was the maximal patellar length. L2 was the minimum possible distance of placement for the upper tunnel from the proximal pole of the patella. The maximum bone bridge between tunnels was calculated as half of L1 minus the L2 distance (L1/2-L2). We also measured R1 and R2 angles at the proximal and distal tunnel that represent safe angles at the entry point during tunnel drilling (without breaching the anterior cortex or articular cartilage).

RESULTS

Preoperatively, mean L1 was 3.45 cm (range 3.05-4.52). Mean L2 was 0.62 cm (range 0.49-0.89). The mean maximum possible bone bridge between tunnels (L1/2-L2) was 1.1 cm (range 0.77-1.58). R1 was 6.05⁰ (range 4.78-7.44), R2 was 6.64⁰ (range 4.57-9.03), and their difference reached statistical significance (p = 0.03). Postoperatively, in group A, in 4 out of 15 patellas, multiple attempts were made during tunnel drilling in order to avoid anterior cortex or cartilage breaching. In group B, all tunnels were correctly drilled with the first attempt. Bone bridge between tunnels was significantly shorter postoperatively (0.93 cm, p < 0.01).

CONCLUSION

Small-size patellae correlate with short maximum bone bridge between tunnels, which makes anatomic, double-bundle, hardware-free patella fixation, with two semi-patellar tunnels MPFL reconstruction challenging. Furthermore, R angles create a narrow window to avoid intraoperative breaching, rendering the use of the ACL tibia device an extremely useful instrument.

LEVEL OF EVIDENCE

II.

Medial Patellofemoral Reconstruction Using Quadriceps Tendon Autograft, Tibial Tubercle Osteotomy, and Sulcus-Deepening Trochleoplasty for Patellar Instability

Recurrent patellar dislocations have been correlated with an elevated risk of further patellar dislocations, often requiring surgical treatment. Risk factors include medial patellofemoral ligament (MPFL) tears, patella alta, trochlear dysplasia, and an increased tibial tubercle-trochlear groove distance. Surgical management must be based on a patient's unique joint pathoanatomy and may require MPFL reconstruction with tibial tubercle osteotomy or trochleoplasty either alone or in combination. This article discusses our preferred technique for surgical treatment of recurrent patellar instability with MPFL reconstruction using a quadriceps tendon autograft, an open trochleoplasty, and a tibial tubercle osteotomy for patients with patella alta, trochlear dysplasia, and an increased tibial tubercle-trochlear groove distance.

The quadriceps insertion of the medial patellofemoral complex demonstrates the greatest anisometry through flexion

PURPOSE

A comprehensive understanding of the biomechanical properties of the medial patellofemoral complex (MPFC) is necessary when performing an MPFC reconstruction. How components of the MPFC change over the course of flexion can influence the surgeon's choice of location for graft fixation along the extensor mechanism. The purpose of this study was to (1) determine native MPFC length changes throughout a 90° arc using an anatomically based attachment and using Schöttle's point, and (2) compare native MPFC length changes with different MPFC attachment sites along the extensor mechanism.

METHODS

Eight fresh-frozen (n = 8), cadaveric knees were dissected of all soft tissue structures except the MPFC. The distance between the femoral footprint (identified through anatomical landmarks and Schottle's point) and the MPFC was calculated at four attachment sites along the extensor mechanism [midpoint of the patella [MP], the center of the osseous footprint of the MPFC (FC), the superomedial corner of the patella at the quadriceps insertion (SM), and the proximal extent of the MPFC along the quadriceps tendon (QT)] at 0°, 20°, 40°, 60°, and 90° of flexion.

RESULTS

Length changes were investigated between the MPFL femoral attachment site and the radiographic surrogate of the MPFL attachment site, Schottle's Point (SP). Paired t tests at each of the four components showed no differences in length change from 0° to 90° when comparing SP to the anatomic MPFC insertion. MPFL length changes from 0° to 90° were greatest at the QT point (13.9 ± 3.0 mm) and smallest at the MP point (2.7 ± 4.4 mm). The FC and SM points had a length change of 6.6 ± 4.2 and 9.0 ± 3.8, respectively. Finally, when examining how the length of the MPFC components changed through flexion, the greatest differences were seen at QT where all comparisons were significant (p < 0.01) except when comparing 0° vs 20° (n.s.).

CONCLUSION

The MPFC demonstrates the most significant length changes between 0° and 20° of flexion, while more isometric behavior was seen during 20°-90°. The attachment points along the extensor mechanism demonstrate different length behaviors, where the more proximal components of the MPFC display greater anisometry through the arc of motion. When performing a proximal MPFC reconstruction, surgeons should expect increased length changes compared to reconstructions utilizing distal attachment sites.

[Research progress in femoral tunnel positioning points of medial patellofemoral ligament reconstruction]

Objective

To review the research progress of location methods and the best femoral insertion position of medial patellofemoral ligament (MPFL) reconstruction of femoral tunnel, and provide reference for surgical treatment.

Methods

The literature about femoral insertion position of the MPFL reconstruction in recent years was extensively reviewed, and the anatomical and biomechanical characteristics of MPFL, as well as the advantages and disadvantages of femoral tunnel positioning methods were summarized.

Results

The accurate establishment of the femoral anatomical tunnel is crucial to the success of MPFL reconstruction. At present, there are mainly two kinds of methods for femoral insertion: radiographic landmark positioning method and anatomical landmark positioning method. Radiographic landmark positioning method has such advantages as small incision and simple operation, but it can not be accurately positioned for patients with severe femoral trochlear dysplasia. It is suggested to combine with the anatomical landmark positioning method. These methods have their own advantages and disadvantages, and there is no unified positioning standard. In recent years, the use of three-dimensional design software can accurately assist in the MPFL reconstruction, which has become a new trend.

Conclusion

Femoral tunnel positioning of the MPFL reconstruction is very important. The current positioning methods have their own advantages and disadvantages. Personalized positioning is a new trend and has not been widely used in clinic, its effectiveness needs further research and clinical practice and verification.

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.

Dual fluoroscopic imaging and CT-based finite element modelling to estimate forces and stresses of grafts in anatomical single-bundle ACL reconstruction with different femoral tunnels

PURPOSE

Little is known about the in vivo forces and stresses on grafts used in anterior cruciate ligament (ACL) reconstruction. The aims of this study were to evaluate and compare the forces and stresses on grafts used in anatomical single-bundle ACL reconstruction at different locations of the femoral footprint (anterior vs middle vs posterior; high vs middle vs low) during a lunge motion.

METHODS

Establish subject-specific finite element models with different graft's tunnel loci to represent the primary ACL reconstructions. A displacement controlled finite element method was used to simulate lunge motions (full extension to ~ 100° of flexion) with six-degree-of-freedom knee kinematics data obtained from the validated dual fluoroscopic imaging techniques. The reaction force of the femur and maximal principal stresses of the grafts were subsequently calculated during knee flexion.

RESULTS

Increased and decreased graft forces were observed when the grafts were located higher and lower on the femoral footprint, respectively; anterior and posterior graft placement did not significantly affect the graft force. Lower and posterior graft placement resulted in less stress on the graft at higher degrees of flexion; there were no significant differences in stress when the grafts were placed from 0° to 30° of flexion on the femoral footprint.

CONCLUSION

The proposed method is able to simulate knee joint motion based on in vivo kinematics. The results demonstrate that posterior to the centre of the femoral footprint is the strategic location for graft placement, and this placement results in anatomical graft behaviour with a low stress state.

Comparison of Ligament Isometry and Patellofemoral Contact Pressures for Medial Patellofemoral Ligament Reconstruction Techniques in Skeletally Immature Patients

BACKGROUND

Adult medial patellofemoral ligament (MPFL) reconstruction techniques are not appropriate for the skeletally immature patient given the proximity of the distal femoral physis. Biomechanical consequences of reconstructions aimed at avoiding the physis have not been adequately studied.

PURPOSE

To quantify the biomechanical effects of MPFL reconstruction techniques intended for skeletally immature patients.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four MPFL reconstruction techniques were evaluated using a computationally augmented cadaveric model: (1) Schoettle point: adult-type reconstruction; (2) epiphyseal: socket distal to the femoral physis; (3) adductor sling: graft wrapped around the adductor tendon; (4) adductor transfer: adductor tendon transferred to patella. A custom testing frame was used to cycle 8 knees for each technique from 10° to 110° of flexion. Patellofemoral kinematics were recorded using a motion camera system, contact stresses were recorded using Tekscan pressure sensors, and MPFL length was computed using an inverse kinematics computational model. Change in MPFL length, patellar facet forces, and patellar kinematics were compared using generalized estimating equation modeling.

RESULTS

Schoettle point reconstruction was the most isometric, demonstrating isometry from 10° to 100°. The epiphyseal technique was isometric until 60°, after which the graft loosened with increasing flexion. The adductor sling and adductor transfer techniques were significantly more anisometric from 40° to 110°. Both grafts tightened with knee flexion and resulted in significantly more lateral patellar tilt versus the intact state in early flexion and significantly higher contact forces on the medial facet versus the epiphyseal technique in late flexion.

CONCLUSION

In this cadaveric simulation, the epiphyseal technique allowed for a more isometric ligament until midflexion, when the patella engaged within the trochlear groove. The adductor sling and adductor transfer grafts became tighter in flexion, resulting in potential loss of motion, pain, graft stretching, and failure. Marginal between-condition differences in patellofemoral contact mechanics and patellar kinematics were observed in late flexion.

CLINICAL RELEVANCE

In the skeletally immature patient, using an epiphyseal type MPFL reconstruction with the femoral attachment site distal to the physis results in a more isometric graft compared with techniques with attachment sites proximal to the physis.

Femoral Origin Anatomy of the Medial Patellofemoral Complex: Implications for Reconstruction

PURPOSE

To report the shape and orientation of the medial patellofemoral complex (MPFC) footprint on the medial femur and describe the difference between the proximal (medial quadriceps tendon femoral ligament, MQTFL) and distal (medial patellofemoral ligament, MPFL) fibers.

METHODS

In 20 cadaveric knees, the MPFC footprint on the medial femur was exposed. Images of the medial femur were analyzed using ImageJ software. The length and width of the MPFC footprint were described to the nearest 0.1 mm; the angle of its long axis was described relative to the axis of the femoral shaft (0.1°). The footprint's most proximal and distal margins were described in relation to the adductor tubercle and medial epicondyle. The differences between each were compared using paired t tests.

RESULTS

17 knees from 10 cadavers were included in this study. The MPFC footprint had a length of 11.7 ± 1.8 mm and a width of 1.7 ± 0.4 mm. The long axis of the footprint was at an angle 14.6° ± 16.6° anterior to the axis of the femoral shaft. The most proximal (MQTFL) fibers originated 7.4 ± 3.8 mm anterior and 1.8 ± 4.7 mm distal to the adductor tubercle and 4.1 ± 2.9 mm posterior and 8.4 ± 5.6 mm proximal to the medial epicondyle. The most distal (MPFL) fibers originated 4.9 ± 4.2 mm anterior and 12.7 ± 4.3 mm distal to the adductor tubercle, as well as 7.1 ± 2.4 mm posterior and 0.5 ± 5.6 mm distal to the medial epicondyle. The distal margin of the femoral MPFC footprint was 10.9 ± 1.7 mm distal (p < .001) and 2.6 ± 3.2 mm more posterior (p = .005) than the proximal margin.

CONCLUSIONS

The femoral footprint of the MPFC has a length almost 7 times greater than its width, with the distal margin being 10.9 mm distal and 2.6 mm posterior to the proximal margin.

CLINICAL RELEVANCE

This differential anatomy within the femoral origin suggests that MPFL and MQTFL reconstruction may require separate positions of femoral fixation to recreate the anatomy of these fibers.

Techniques for In Vivo Measurement of Ligament and Tendon Strain: A Review

The critical clinical and scientific insights achieved through knowledge of in vivo musculoskeletal soft tissue strains has motivated the development of relevant measurement techniques. This review provides a comprehensive summary of the key findings, limitations, and clinical impacts of these techniques to quantify musculoskeletal soft tissue strains during dynamic movements. Current technologies generally leverage three techniques to quantify in vivo strain patterns, including implantable strain sensors, virtual fibre elongation, and ultrasound. (1) Implantable strain sensors enable direct measurements of tissue strains with high accuracy and minimal artefact, but are highly invasive and current designs are not clinically viable. (2) The virtual fibre elongation method tracks the relative displacement of tissue attachments to measure strains in both deep and superficial tissues. However, the associated imaging techniques often require exposure to radiation, limit the activities that can be performed, and only quantify bone-to-bone tissue strains. (3) Ultrasound methods enable safe and non-invasive imaging of soft tissue deformation. However, ultrasound can only image superficial tissues, and measurements are confounded by out-of-plane tissue motion. Finally, all in vivo strain measurement methods are limited in their ability to establish the slack length of musculoskeletal soft tissue structures. Despite the many challenges and limitations of these measurement techniques, knowledge of in vivo soft tissue strain has led to improved clinical treatments for many musculoskeletal pathologies including anterior cruciate ligament reconstruction, Achilles tendon repair, and total knee replacement. This review provides a comprehensive understanding of these measurement techniques and identifies the key features of in vivo strain measurement that can facilitate innovative personalized sports medicine treatment.

Adverse effects of total hip arthroplasty on the hip abductor and adductor muscle lengths and moment arms during gait

Background

Precise evaluation of the hip abductor and adductor muscles function in total hip arthroplasty (THA) patients during gait could help prevent postoperative complications and optimize the rehabilitation training program. The purpose of this study was to elucidate the effects of THA on the hip abductor and adductor muscle lengths and moment arms of in vivo patients during gait.

Methods

Ten unilateral THA patients received CT scans and dual fluoroscopic imaging for the hip kinematics during gait. The hip abductor and adductor muscle insertions were digitized on the 3D hip model for the determination of their dynamic lines of action and moment arms. Changes in the hip abductor and adductor muscle lengths and moment arms of THA patients between the implanted and non-implanted sides were quantified during gait.

Results

The adductor longus, adductor brevis, and pectineus of the implanted hips had significantly (P < 0.05) less elongation than that of the non-implanted side during the stance phase. The gluteus medius, gluteus minimus, and piriformis moment arms of the implanted side were significantly shorter. The piriformis muscle moment arm was significantly larger. In the double support phase, the adductor magnus and adductor longus moment arms of the implanted sides were significantly decreased.

Conclusions

Results suggested that the adverse effects of THA on hip stability. Development of a rehabilitation program considering the effects of THA is essential. Accurate surgical techniques may reduce the impact of THA on the peripheral muscles.