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

Abstract

Background: Medial patellofemoral ligament (MPFL) reconstruction is associated with a high rate of complications, including recurrent instability and persistent knee pain. Technical errors are among the primary causes of these complications. Understanding the effect of adjusting patellofemoral attachments on length change patterns may help surgeons to optimize graft placement during MPFL reconstruction and to reduce graft failure rates. Purpose: To determine the in vivo length changes of the MPFL during dynamic, weightbearing motion and to map the isometry of the 3-dimensional wrapping paths from various attachments on the medial femoral epicondyle to the patella. Study Design: Descriptive laboratory study. Methods: Fifteen healthy participants were studied with a combined computed tomography and biplane fluoroscopic imaging technique during a lunge motion (full extension to ~110° of flexion). On the medial femoral epicondyle, 185 attachments were projected, including the anatomic MPFL footprint, which was divided into 5 attachments (central, proximal, distal, posterior, and anterior). The patellar MPFL area was divided into 3 possible attachments (proximal, central, and distal). The length changes of the shortest 3-dimensional wrapping paths of the various patellofemoral combinations were subsequently measured and mapped. Results: For the 3 patellar attachments, the most isometric attachment, with an approximate 4% length change, was located posterior and proximal to the anatomic femoral MPFL attachment, close to the adductor tubercle. Attachments proximal and anterior to the isometric area resulted in increasing lengths with increasing knee flexion, whereas distal and posterior attachments caused decreasing lengths with increasing knee flexion. The anatomic MPFL was tightest in extension, decreased in length until approximately 30° of flexion, and then stayed near isometric for the remainder of the motion. Changing both the femoral and patellar attachments significantly affected the length changes of the anatomic MPFL ( P < .001 for both). Conclusion: The most isometric location for MPFL reconstruction was posterior and proximal to the anatomic femoral MPFL attachment. The anatomic MPFL is a dynamic, anisometric structure that was tight in extension and early flexion and near isometric beyond 30° of flexion. Clinical Relevance: Proximal and anterior MPFL tunnel positioning should be avoided, and the importance of anatomic MPFL reconstruction is underscored with the results found in this study.

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

“…17 The in vitro studies that measured the path length between femoral and patellar attachment points for a graft showed a wide variety of results, including a decrease in graft length with flexion, 27 isometric function over the flexion range, [23][24][25][26] and an increase in graft length with flexion. 28 Previous studies that measured the path length with computational models reconstructed from imaging data of subjects indicated that graft length decreases with flexion, 29 decreases in early flexion followed by an increase, 30 and increases in early flexion followed by a decrease 31 Differences with respect to the previously published data are likely related to the experimental approach. The previous studies did not directly measure tension within the graft or consider the intraoperative graft tensioning protocol included in the current study.…”

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

“…181 This approach also revealed that reconstructing the medial patellofemoral ligament (MPFL) to a location posterior and proximal to its anatomic femoral attachment results in the most isometric graft behaviour during lunging. 90 Similarly, at the shoulder, virtual fibre elongation techniques have allowed an insight into otherwise difficult to access dynamic musculoskeletal interactions. Maximal external rotation at 90°abduction significantly elongates the anterior bundle of the inferior glenohumeral ligaments while only slightly elongating the posterior bundle.…”

“…Significant uncertainty in reported ligament lengths originates from both the identification of the tissue attachment footprints and virtual fibre insertion sites within the footprint. 90 The determination of ligament insertion sites on MR images can show large variations especially in some ligaments like the sMCL, which has large attachment areas (nearly 400 mm 2 on its tibial proximal attachment). 98 However, for other ligaments such as the ACL, footprints can be accurately identified from MRI images.…”

“…Therefore, movements such as single legged lunge are often studied as the knee remains within the FOV. 90,173 To track walking or running gait activities, the subject has to walk on a treadmill with only portions of the gait cycle such as stance phase being imaged. 108,181 Future Work…”

Adverse Effects of Total Hip Arthroplasty on The Hip Abductor and Adductor Muscle Lengths and Moment Arms During Gait

“…The dual uoroscopic imaging system (DFIS)-based tracking technique has been extensively applied to capture the motion of in vivo lower limb joints during gait and allowed accurate quanti cation of 3D joint kinematics [9][10][11]. Recently, some researchers have used the DFIS for the measurement of soft tissue length changes during motion [12,13]. However, it has not been used to quantify the effects of THA on the hip muscle lengths and moment arms.…”