Abstract
Objectives:
Patients with recurrent patellofemoral instability are indicated for medial patellofemoral ligament (MPFL) reconstruction. Multiple different patellar graft fixation methods exist in MPFL reconstruction surgery, namely bone tunnels, interference screws, and suture anchors. Meta analysis has shown suture patellar fixation to have superior patient reported outcomes with no statistical difference in failure rates when compared to transpatellar tunnel fixation clinically. Amongst suture anchor designs, all-soft-suture anchors occupy a smaller volume than solid suture anchors, requiring a smaller diameter tunnel during placement and thus theoretically can reduce the risk of patella fracture and articular surface violation. However, there is concern that all-soft-suture anchors may be biomechanically inferior to their hard-bodied anchor counterparts. Additionally, there is a paucity of research comparing different anchor designs (knotted vs knotless) amongst hard-bodied anchors in the setting of MPFL reconstruction. The purpose of this study is to perform a biomechanical comparison of newer generation soft-bodied anchors and hard-bodied suture anchors with different fixation methods when performing an osseous-based MPFL reconstruction in a cadaveric model.
Methods:
Fourteen patellae were randomized into three groups: PEEK hard-body knotless (HB-knotless), PEEK hard-body knotted (HB-knotted), and soft-body knotless (SB-knotless) anchors placed at the anatomic MPFL insertions in the direct medial position and at the superomedial aspect of each patella. Prior to anchor placement, bone density at the sites of anatomic MPFL insertions was measured on standard radiographs. After anchor placement, patellae were potted, and anchors were tested in a materials test system in a cyclic regimen (10-30 N, 100 cycles) immediately followed by load-to-failure (6mm/sec). All testing was performed in line with the anchor alignment (Figure 1). Outcome measures included maximum load and cyclic creep, defined as the difference in segment length from the peak load of the first cycle to the peak load of the 100th cycle of testing. One-way ANOVA and Fisher exact tests were used to evaluate outcomes between groups. Statistical significance was set at p < 0.05.
Results:
Analysis included 6 SB-knotless, 14 HB-knotted, and 8 HB-knotless anchors. The groups were equivalent in age (range 30 years – 70 years; p = 0.657) and bone density (p = 0.134) in a 4:3 male-to- female ratio.
There was no significant difference in cyclic creep detected between SB-knotless (3.00 ± 0.79 mm), HB- knotless (2.80 ± 0.42 mm), and HB-knotted (3.25mm ± 0.70 mm) groups (p = 0.301).
HB-knotted exhibited a lower maximum load (111.30 ± 43.71 N) than HB-knotless (180.01 ± 58.87 N) (p = 0.017), but no significant difference to SB-knotless (149.34 ± 61.38 N) (p = 0.310) (Figure 2). HB- knotless and SB-knotless did not have a significant difference in maximum load (p = 0.529).
When evaluating the influence of patellar anchor site on performance, there was no significant difference in cyclic creep or maximum load between direct medial and superomedial anchor positioning in SB-Knotless (p = 0.800, p = 0.800), HB-Knotted (p = 0.719, p = 0.219), or HB-Knotless (p = 0.886, p = 0.057) groups, respectively.
There were 6 SB-knotless, 12 HB-knotted, and 7 HB-knotless anchors that failed by anchor pull-out, with 2 HB-knotted and 1 HB-knotless which failed either by the suture breaking within the anchor or the knot failing (Figure 3). This difference between failure mechanisms was not significant.
Conclusions:
Hard-body knotless anchors provide superior load to failure than traditional hardbody knotted anchors. Additionally, all-soft-suture anchors performed as well as their counterparts in both load to failure and resistance to cyclic creep. This work suggests surgeons should be comfortable using either hard-body or all-soft-suture anchors when performing osseous-based MPFL reconstructions and may consider opting for a knotless mechanism when utilizing a PEEK hard-bodied anchor for this purpose. A clinical study should take place next to validate these cadaveric findings.
