Anisometry and malpositioned tunnels can present clinically as a loss of flexion or tightness or as recurrent instability. While direct palpation of anatomic structures is beneficial and worthwhile in understanding the native anatomy in reconstructing the MPFL at its origin, sometimes body habitus or revision surgery with scar makes this challenging and difficult to do. Schottle’s point, Fig. 9.2, helps to alleviate some of this variability by providing a radiographic reference of the anatomic origin of the native MPFL using intraoperative C-arm imaging [14].
Malposition of the femoral attachment can have devastating consequences to the postoperative range of motion. A systematic review has shown that 3.4% of patients developed postoperative loss of knee flexion, which ultimately resulted in an overall 1.4% procedural complication rate of manipulation under anesthesia (MUA) for loss of flexion [5]. Meaning, for those patients who developed postoperative arthro- fibrosis or stiffness, 40% ultimately required a MUA. Mulliez et al. also reported postoperative stiffness rates of 1.5% resulting from MPFL reconstructive with con- comitant TTO [6].
Shah et al. reported that 32% of all reported complications were associated with recurrent apprehension [5]. There were 3.7% clinical failures with frank repeat sub- luxation/dislocation events reported across 11 studies [5]. 8.3% of their study population continued to report subjective apprehension on postoperative examination
Take-Home Points
1. Patella fracture is the most common and severe complication associated with MPFL reconstruction
2. Avoid large or transverse patellar tunnels
3. Use short blind-ended patellar tunnels with interference screws or suture anchors or consider short, oblique tunnels less than 4.5 mm with looped graft placement
without documented re-dislocation [5]. Ultimately, reoperation rates for recurrent instability by subluxation or dislocation were 0.9% [5]. Schiphouwer et al. stated across a series of patients 5.2% had objective recurrence of instability and a signifi- cantly higher recurrence rate of patellar instability in skeletally immature vs mature patients, 33.3% vs 3.8%, respectively, but there was no difference between the iso- lated MPFL reconstruction vs combined procedure results [4]. Lower re-dislocation rates have also been reported at 0.8%, with similar surgical techniques reported as a soft tissue proximal stabilization procedure by MPFL reconstruction combined with a TTO distally [6]. The heterogeneity across the literature once again makes compari- sons difficult; yet, these values are within reasonably reported data for MPFL recon- struction failure rates for recurrent instability.
This systematic study also reported that suture techniques compared to tunnel technique demonstrated an increased rate of recurrent subluxation/dislocation at 4.8% and hypermobility/apprehension at 24%, versus 3.3% and 8.6%, respectively [5]. While clear comparisons cannot be gleamed from this information given the differences of techniques, concomitant procedures recorded, and lack of overall sample sizes reported, it does raise the question as to bone tunnels providing better inherent stability with or without fixation. This could be attributed to the soft tissue graft-suture fixation construct failing or stretching out. Biomechanical studies have shown lower implant load to failure rates, which could contribute to these higher rates of symptomatic apprehension and dislocation seen clinically [10, 11].
Fig. 9.2 Appropriate lateral radiograph with tunnel placed at Schottle’s point
How to Avoid It
Limiting the complication of tunnel malposition (with resultant anisometry/loss of flexion or recurrent instability) is vital. Patellar graft placement has been shown to be less critical in determining graft isometry as long as the graft is fixed in the upper medial one-third to one-half of the patella. The crucial part of the procedure is the correct placement of the femoral tunnel for the insertion of the MPFL reconstruc- tion. A key part of this is obtaining a perfect lateral intraoperative C-arm image of the knee. Significant deviation from Schottle’s point, as described in the previous chapter’s surgical techniques, can result in either recurrent instability from early graft loosening or may have untoward effects of increasing patellar contract pres- sures and resultant loss of range of motion secondary to graft malposition and tight- ness. Correctly placed, there will not be any significant graft lengthening throughout range of motion (Fig. 9.3). Intraoperatively this can be assessed after the guide pin is drilled in the femur and the graft wrapped around the beath pin and the knee taken through its arc of motion. Assessing for graft length displacement will help determine its isometry and the relative positioning of the femoral tunnel.
Troubleshooting graft position intraoperatively can be aided by remembering two catchphrases that describe graft behavior as the knee is flexed: “high and tight”
or “low and loose.” If the graft is placed 1 cm too proximal, it will be loose in exten- sion and the patella will be unstable. The converse will be true as the knee is flexed, where it will be tight, resulting in loss of terminal flexion, graft rupture, or patella chondrosis (Fig. 9.4). This proximal femoral placement would result in a graft that tightens with flexion and result in a “high and tight” pattern. If instead the graft is secured 1 cm distal to the anatomic origin, it will be too tight in extension and will be loose in flexion, unable to control the patella, which may result in recurrent instability (Fig. 9.5). Hence a “low and loose” picture would be seen intraopera- tively as the knee is flexed through a range of motion [15]. Having correctly placed the femoral bone tunnel will help to ensure that the graft length and isometry are appropriate and limit the risk of continued patellar instability or excessive com- pressive forces. The position of the knee when the graft is fixed and the “tension”
placed also play a role, and these will be discussed in the next section.
Take-Home Points
1. The true anatomic insertion of the graft on the femur needs to be deter- mined and confirmed as the knee is fully ranged (check graft length change throughout arc of knee motion to ensure proper positioning of the femoral tunnel). Fluoroscopy should be used to help confirm or localize the femo- ral insertion point.
2. Perfect lateral every time.
3. Schottle’s point is key.