Our group found 25 articles reporting MPFL reconstruction for patellar instability. Only 2 studies were classified as Level II evidence; none were Level I. This indicates a paucity of high-level evidence to evaluate the success and failure of MPFL reconstructions. Given that MPFL reconstructions have become a popular surgical procedure, this is somewhat concerning as this study found that the overall complication rate is not trivial. With an overall cumulative complication rate of 26.1%, caution is indicated when this procedure is performed. Major complications included patellar fracture, post-operative instability, flexion loss, and pain. Many patients returned to the operative suite for manipulations to address decreased range of motion and removal of symptomatic hardware.
A large proportion of the complications were recurrent apprehension (52/164 = ~32% of all complications). It is unclear whether patients with recurrent instability had a failure due to graft loosening, rupture, or failure to recognize additional risk factors for recurrent patella instability. It is possible that the rate of recurrent apprehension and subluxation may be due to other unrecognized and uncorrected risk factors for patellofemoral instability such as an increased tibial tubercle-trochlear groove measurement, patella alta, or higher grade trochlea dysplasia. This underlines the importance of recognizing additional risk factors in patients with recurrent patella subluxations and dislocations. We suggest that authors should be held to report on the perceived reasons for failure as the various reported techniques each have numerous and unique reasons for potential failure of the graft.
The MPFL graft fixation methods vary within the literature but can generically be categorized as suture or tunnel techniques. provides descriptive data regarding the complication rate observed among both tunnel and suture techniques. A trend of more overall complications was observed utilizing the tunnel techniques (29.8%) compared to suture techniques (21.6%). However, the suture techniques demonstrated a higher rate of recurrent dislocation/subluxation (4.8%) and apprehension/hypermobility (24.0%) than the tunnel technique (3.3% and 8.6%, respectively). While this information raises questions regarding complication risk associated with each procedure, clear comparisons between the procedures cannot be made because of the relatively small sample sizes available, the variety of concomitant procedures performed with MPFL reconstruction, a lack of uniform reporting of complications, and variations in length of follow-up.
Arguably the most severe complication reported was a post-operative patella fracture. Four patella fractures were reported, all in patients who underwent MPFL reconstructions using single or double transverse bone tunnels (n = 429). The range of bone tunnels created in these 4 patients ranges from 3.2-mm to 4.5-mm. One patient sustained a transverse patella fracture after a fall. His/Her fixation called for a transverse 3.2 mm patellar tunnel with a polyester graft that was fixed to the lateral patella using a knot. Two patients had a 4.5-mm patellar tunnel that exited the anterior patella. The authors used a semitendinosus autograft with the free end passed through the tunnel, folded over, and sutured into place. A fourth patient developed a post-operative patella fracture when rising from a chair. The surgeons looped a gracilis graft through two 4.5-mm transverse patella tunnels separated by 10 to 15 mm. No patella fractures were reported in studies using a docking technique, anchors or a soft tissue attachment on the patella (n = 125). Even though the incidence of patella fracture is certainly not high enough to draw statistically relevant conclusions, it behooves the surgeon to consider using a technique that does not carry the inherent risk of fracture. In this context, a docking anchor based or suture fixation could be safer to use.
Another frequently reported complication after MPFL reconstruction is the loss of knee flexion. This was reported in 22 patients (13.4% of all complications), out of which half required post-operative manipulation under anesthesia. The MPFL is a non-isometric ligament which acts primarily as a restraint. The concept of “tensioning” of the MPFL at any reported flexion angle therefore may be a conceptual problem. In its native state the MPFL is not under tension; it only comes under tension when a laterally displacing force acts on the patella. Therefore, “tensioning” the MPFL graft may in fact restrict range of motion. In addition, it may be important to clearly determine the femoral point of fixation intraoperatively according to easily identifiable landmarks. In many patients, it is very hard to clearly palpate the adductor tubercle. A reliable method described by Schottle et al.34
used radiographic landmarks that can easily be found under fluoroscopy. Schottle et al.'s point is 1-mm anterior to the posterior cortex extension line, 2.5-mm distal to the posterior origin of the medial femoral condyle, and proximal to the posterior point of the Blumensaat line on the lateral radiograph.34
However, a recent study showed potential anisometry of the MPFL graft related to the degree of patella alta. Tateishi et al.34
had 10 patients with average patellar height ratio of 1.4 +/− 0.2 whose graft length increased 3 to 5.5-mm with knee range of motion. The femoral fixation was near but not exactly at Schottle et al.'s specifications.39
For this group, the femoral tunnel averaged −1.2 +/− 5.6-mm relative to the posterior cortex, 4.9 +/− 2.1-mm distal to the posterior origin of the medial femoral condyle, and 3.1 +/− 1.5-mm proximal to the Blumensaat line.
Fixation at various flexion angles has been recommended. The angle of knee flexion at the time of graft placement may play a role in postoperative patellar stability. provides descriptive data for the influence of knee flexion angle on complication rate. A trend of those undergoing fixation at less than 60° knee flexion (32.6%, n = 230 knees) and experiencing a higher overall complication rate than those undergoing fixation at 60° or greater knee flexion (23.8%, n=319 knees) was observed. Similarly, a lower rate of recurrent subluxation/dislocation (1.6% vs. 6.1%) and continued apprehension/hypermobility (9.1% vs. 9.6%) was observed among those undergoing fixation at 60° or greater compared to those undergoing fixation at less than 60°. However, caution is urged in interpreting these values as they are only descriptive in nature and previously discussed limitations prevent direct statistical comparison. At full extension the medial retinaculum and MFPL is most taught and resists patellar subluxation.2
The patella subluxes most easily at 20° of flexion.35
As knee flexion increases, the medial retinaculum slackens and the femoral trochlea limits medial and lateral displacement of the patella. Previous work also reports that maximal graft length occurs at 60° flexion.37
Some authors advocate graft fixation at increased knee flexion angles to prevent over tightening of the graft1
while others call for fixation at decreased knee flexion because the maximal effect of the MPFL occurs from 0 to 20 degrees.32
This area requires further comparative investigations before conclusions can be drawn.
This study revealed that a significant number of patients had to return to the operating room for additional surgical procedures. The highest number of secondary surgeries was reported for manipulations under anesthesia (1.4%), for loss of knee motion, and for removal of symptomatic hardware (1.1%). We addressed the concerns regarding the loss of range of motion in the above paragraph. One should also be aware of the fact that any hardware at the edge of the patella or the medial side of the knee may become prominent once the surgical swelling has resolved. Patients may tolerate hardware in these areas less well than in other areas of the knee (e.g., proximal tibia after anterior cruciate ligament reconstructions) thus requesting hardware removal. A total of 19 patients across 5 studies complained of painful hardware.6, 8, 16,26, 38
Of these 5 studies, 133 patients underwent MPFL reconstruction with metallic implants. In one study some patients in the cohort did not have implanted hardware and were excluded from the previous total.38
Twelve patients experienced symptomatic staples, 3 had painful lag screws, and 3 had symptomatic interference screws. All of these implants were located on the femoral side. One patient had symptomatic hardware related to TTT.
The ability to draw conclusions from this review is greatly limited because of a lack of uniform reporting of methodology across the included studies. Significant variability was observed in the complication rate reported in individual studies with complications rates ranging from 0% to 85.2%.26
Similarly, the large standard deviations for the mean rates of recurrent subluxation/dislocation and continued hypermobility/apprehension suggest that complication rates were highly variable between the included studies and not normally distributed. This variability is likely not the result of tremendous variations in the overall clinical outcome between studies, but rather is a function of the variation in study methodology for the reporting of complications and length of follow-up.
In conclusion, reconstruction of the MPFL overall is a popular procedure that can yield successful outcomes in many patients. However, despite its popularity, it is a procedure that can be associated with significant intra and post-operative complications that should be considered prior to choosing a technique. Also, there is a paucity of high-level studies evaluating MPFL reconstruction techniques, thus limiting our ability to judge the true outcome of this procedure with regards to complication rate. Further high-level studies with uniform reporting of methodology and clinical outcomes including complications are needed to detect the overall outcome, risks and benefits of this procedure. In particular, it will be necessary to better define clinical failure versus success based upon clinical, radiographic and patient reported outcomes parameters.