Failed Medial Patellofemoral Ligament Reconstruction: Causes and Treatment
Laurie A. Hiemstra
Lateral patellofemoral instability is challenging to manage because of its multifactorial etiology, as well as the fact that predisposing pathoanatomic features vary from individual to individual.
Medial patellofemoral ligament (MPFL) reconstruction (MPFLR) is widely recognized as a safe and reliable means of reestablishing lateral stability in patients with recurrent lateral patellofemoral instability and minimal predisposing anatomic risk factors.
For patients with significant predisposing risky pathoanatomy, concurrent procedures such as a tibial tubercle osteotomy, lateral release or lengthening, derotation osteotomy, or trochleoplasty may be performed in addition to the MPFL reccontruction.6 There is a lack of explicit evidence regarding the thresholds for including any of these additional procedures.
MPFLR with or without concomitant procedures has been shown to effectively and consistently improve function and quality of life outcomes.3,5,7,8,9,10,11
Despite these excellent results, there have been several reports on complications and failures following MPFLR.10,12,13,14,15,16,17,18 Although a few large case series have been published, the information on surgical failure rates has largely been described in systematic reviews. These reviews report a surgical failure rate ranging from 1% to 5%.3,5,10,19,20
FAILURE OF MPFLR
Failure of a surgical procedure can be defined in many ways. For patients with patellofemoral instability, surgical failure has been variously described in the literature as redislocation of the patella, subluxation of the patella, residual or recurrent apprehension, pain, and poor quality of life.
Although all these factors can influence the outcomes of MPFLR, for the purposes of this discussion, failure will be defined as ongoing lateral patellofemoral instability including redislocation or resubluxation of the patella.
What Leads to Failure?
From a biomechanical perspective, failure occurs when more strain goes through the reconstructed ligament than it can withstand, and the graft stretches or tears.
Increased graft strain can result from a purely traumatic force in an otherwise normal knee joint. This excessive strain can also occur in the presence of pathoanatomic features that increase the lateral force on the patella, as well as on the reconstructed MPFL graft.
The force required to tear the graft will be lower when the anatomy and biomechanics of the knee joint are suboptimal.
Tissue quality and extensibility of the reconstructed graft may contribute to failure in patients with generalized joint hypermobility.
Poor neuromuscular control can contribute to failure by increasing forces through the MPFL graft.
What Does the Literature Tell Us About the Causes of Failure?
Information on the failure rate of MPFLR has largely been derived from case series and has subsequently been reported in several systematic reviews.3,5,10,19,20,21 The current reported failure rate for MPFLR ranges from 1% to 5%. This failure rate is based on the recent literature, with short- to medium-term follow-up,
reporting on a pooled group of over 600 patients with the authors noting that the incidence of failure increases with time from surgery.3,22
Several descriptive case series have examined the potential causes of MPFL graft failure.
Nelitz et al reported on 19 patients with clinical concerns following MPFLR, of which 6 were recurrent instability.23 All six failures had high-grade trochlear dysplasia, and in five of these cases, the dysplasia was addressed at the time of revision MPFLR with a concurrent trochleoplasty.
Parikh et al reported on complications after MPFLR in a cohort of 179 knees, and assessed 8 failure cases.13 These authors identified that in seven of the eight failures, there was malpositioning of the femoral tunnel.
Chatterton et al reported on 23 cases of failed MPFLR and assessed that a nonanatomic femoral tunnel was present in two-thirds of the cohort.24 There was no significant difference reported in the incidence of trochlear dysplasia in the failure cases compared to successful MPFLRs in this study.
Unfortunately, all of these studies include a low number of failure cases, making it difficult to accurately determine the causes responsible for failure. In addition, the rates and range of risky pathoanatomy in the failure cohorts were not specifically reported, or compared to a similar group of intact MPFLRs.
A recent study that was not included in these systematic reviews reported a failure rate of 5.1% in a large cohort of 256 patients following isolated MPFLR.25 The demographic risk factors of the successful MPFLR and graft failure groups were compared and demonstrated that the failed cases had a statistically significantly younger age at the time of surgery. This may be reflective of a higher risk of recurrence with presentation at a younger age, a finding consistent with previous research.26 There was no statistically significant difference between the groups for sex, body mass index, or age at the time of the first dislocation. The pathoanatomic risk factors were also compared, and there was no statistically significant difference in trochlear dysplasia, generalized joint hypermobility, patellar alta, or tibial tubercle-trochlear groove (TT-TG) distance between the failed cases and successful stabilizations. None of the failures were secondary to technical causes or incorrect femoral tunnel position. Interestingly, this study did demonstrate that the patients who failed had statistically significantly lower postoperative quality of life scores before the failure occurred compared with the successful stabilization cases.
Although demographic risk factors such as bilaterality, age, and sex26,27,28,29 and pathoanatomic risk factors such as trochlear dysplasia, increased TT-TG, and patella alta27,30,31,32,33 have been associated with the risk of recurrence after a first-time dislocation, the relationship of these risk factors to failure has yet to be determined.
Potentially, this is the result of the multifactorial nature of patellofemoral instability. Each patient is unique, and factors that may influence one patient outcome may not affect another.
CAUSES OF FAILURE OF MPFLR
Femoral Tunnel Malposition
Several papers have reported that up to 50% of MPFLR failures are the result of technical error.12,13,14,15
Biomechanical studies have demonstrated that femoral tunnel position has a significant effect on the forces in the MPFL graft as well as on the patellofemoral joint.15,34
A number of case series have also reported femoral tunnel malposition as the cause of MPFLR failure13,24,35,36 (Figure 38.1).
In contrast to these findings, other studies have not been able to demonstrate a relationship between femoral tunnel position and graft failure or disease-specific quality of life outcomes.1,37
One reason for this finding could be the challenge of using radiographic landmarks as the reference standard for optimal femoral tunnel position. Some recent literature has called into question the correlation between radiographic assessment of tunnel position and the true anatomic insertion point of the MPFL.38,39
Type of fixation has been identified as a contributing factor to failure of MPFLR.
Lind et al described a nonanatomic, soft-tissue fixation technique using a free gracilis autograft looped around the adductor tendon insertion in children compared to a femoral tunnel insertion in a large adult cohort.40 The failure rate in children was 25% compared to 2.8% in adults. These authors concluded that the technique using soft-tissue graft fixation yielded inferior results with higher failure rates.
Parikh et al also examined complications following a soft-tissue fixation MPFLR technique in children and assessed an increased failure rate when soft-tissue fixation was employed (personal communication).13
Patellar fracture is a known complication of MPFLR.16,41 Because of this, surgical techniques have been employed to avoid large tunnels in the patella as well as through-patellar tunnels.
Location of the patellar fixation may also play a role in the risk of patellar fracture. Placing drill holes in the center of the anterior posterior thickness of the patella and avoiding subchondral bone perforation will decrease the risk of patellar fracture.
The incidence of patellar fractures appears to be decreasing, likely because of increased attention to the location of the patellar fixation and the emergence of newer surgical techniques that avoid through-bone tunnels.
Management of patellar fracture following MPFL surgery is further discussed in Chapter 40.
Uncorrected pathoanatomy such as trochlear dysplasia, patella alta, abnormal TT-TG, rotational abnormalities, valgus alignment, and patellar tilt may all contribute to increased forces in the MPFL graft and can ultimately contribute to failure.
If these pathoanatomic features are significant and remain uncorrected, the patellar stabilization surgery may be relying on a soft-tissue procedure to address a bony problem.
Physical examination should include assessment of the trochlear shape with medial and lateral translation of the patella.
The J-sign can provide some insight into the severity of the dysplasia and its effect on patellar tracking.
True lateral radiographs as well as axial imaging (either magnetic resonance imaging [MRI] or computed tomography [CT]) are required to fully assess trochlear dysplasia.42 The lateral radiographs allow for a simple assessment of the trochlear bump, whereas the axial imaging provides a more thorough assessment of the relationship of the dysplastic trochlea to the patella (Figure 38.2).
Trochlear dysplasia has been identified as the most significant pathoanatomic risk factor in patellar instability and, potentially, also for failure of MPFLR.
One large case series assessed the significant pathoanatomic factors that contributed to MPFLR failure and demonstrated that high-grade trochlear dysplasia was evident in 64.5% of the MPFLR surgical graft failure patients compared to 48.4% of the patients in the entire data set. In two-thirds of these patients, a trochleoplasty was performed during the revision MPFLR surgery to improve patellofemoral mechanics and optimize the biomechanical forces on the graft.
These data are in keeping with other recent studies that have demonstrated that clinical outcome is affected by high-grade trochlear dysplasia43 and that
the treatment of high-grade trochlear dysplasia, with trochleoplasty, can decrease the failure rate and improve clinical outcome.44
In patients with a failed MPFLR and high-grade trochlear dysplasia, consideration should be given to correcting the dysplasia with a trochleoplasty. Sulcus deepening trochleoplasty should be considered for all failures with Dejour types B and D trochlear dysplasia and a significant trochlear bump (Figure 38.2). For the rare Dejour type C dysplasia, an Albee-type trochleoplasty can be considered.
Patella alta is best assessed with lateral radiographs. A number of reliable ratios have been used, including the Caton-Deschamps, Blackburne-Peel, and Insall-Salvati.
Plain radiographs allow for an assessment of the bony relationship between the height of the patella and the tibia; however, it does not take into consideration the cartilaginous trochlear morphology.
Biedert et al described the patellotrochlear index that assesses the relationship of the patella to the articular surface of the trochlea.
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