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

Vasileios Raoulis,Michael Hantes,Aristeidis Zibis,Apostolos Fyllos,Ioannis Tsifountoudis,Michael-Alexander Malahias,Apostolos Karantanas

doi:10.1186/s40634-021-00348-9

Abstract

PurposeTo 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.MethodsCT 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 measurementsL1 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).ResultsPreoperatively, 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).ConclusionSmall-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 evidenceII

Highlights

Medial patellofemoral ligament (MPFL) anatomy and biomechanical properties have been extensively studied in the last twenty years in order to improve surgical reconstruction technique and clinical results [10, 12,13,14,15, 17, 20].Kang et al introduced the concept of the two functional bundles of MPFL [10]
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
Small-size patellae correlate with short maximum bone bridge between tunnels, which makes ana‐ tomic, double-bundle, hardware-free patella fixation, with two semi-patellar tunnels MPFL reconstruction challenging

Summary

Introduction

Medial patellofemoral ligament (MPFL) anatomy and biomechanical properties have been extensively studied in the last twenty years in order to improve surgical reconstruction technique and clinical results [10, 12,13,14,15, 17, 20].Kang et al introduced the concept of the two functional bundles of MPFL [10]. Medial patellofemoral ligament (MPFL) anatomy and biomechanical properties have been extensively studied in the last twenty years in order to improve surgical reconstruction technique and clinical results [10, 12,13,14,15, 17, 20]. The doublebundle technique has an angular synergy effect that simulates the broad footprint of the MPFL upon the patella, enabling a greater capacity to resist patellar dislocation at the early knee flexion angles [41]. The doublebundle MPFL reconstruction remains popular due to better clinical results and its low rates of failure and complications compared with single-bundle reconstruction [33, 39]

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