Complications of Medial Patellofemoral Ligament Reconstruction

Peters T. Otlans

Beth E. Shubin Stein

Jacqueline M. Brady

INTRODUCTION

Medial patellofemoral ligament (MPFL) reconstruction is commonly used to treat patellofemoral instability by restoration of the checkrein to lateral patellar translation.
A free tendon graft is secured to the patella and femur, or, alternatively, a portion of a tendon already secured to one of these locations (for instance, the quadriceps or adductor tendon) is rotated to a new attachment site.
Unlike with a more robust ligament such as the anterior cruciate ligament, virtually any graft chosen to reconstruct the MPFL improves the biomechanical strength of the original ligament, so grafts are chosen according to their respective risks and benefits and overall surgeon experience and preference.¹ See Table 37.1 for a list of graft choices and an overview of their benefits and risks.
MPFL reconstruction is often combined with distal bony realignment or other soft-tissue procedures, such as lateral retinacular release or lengthening. Each procedure has its own complication profile. Overall, outcomes are favorable and complications are acceptably low, but they do occur and, in many instances, they can be avoided. In this chapter, we focus on reported complications associated with MPFL reconstruction.

OVERALL COMPLICATION RATE

True complication rates after MPFL reconstruction surgery are difficult to ascertain because many series do not focus on complications and many series include patients who underwent multiple procedures to treat patellofemoral instability.
Reported rates range from 0%, in a 51-patient case series,² to 26.1% in a systematic review focused on complication rates.³ The true complication rate is likely in between those rates. In a 179-knee, single-institution series, Parikh et al reported a complication rate of 16.2% in young patients.⁴
Because MPFL reconstruction surgery becomes more widespread and techniques are improved over time, there has been a demonstrable decrease in complication rates. Stupay et al’s systematic review showed that older studies (1992-2011) had a complication rate of around 18% compared to 9% complication rate for newer studies.⁵
Technical considerations can greatly decrease the risk of complications because up to half of complications may be because of error in technique.⁴ Other identified risk factors, however, are inherent to the treatment population. In one study, female patients were at 5.45 times the risk of complications as compared to males (P < 0.05), and patients undergoing bilateral reconstruction were 1.81 times more likely to have a complication (P = 0.11).⁴ Schiphouwer et al, reviewing isolated and combined procedure MPFL reconstruction, reported that patients who had complications were on average 2.4 years younger than those who did not.⁶

COMMON COMPLICATIONS

Patellar Fracture

Patellar fracture is a serious complication of MPFL reconstruction; Chapter 40 includes a comprehensive review of risk factors and types of patellar fractures after MPFL reconstruction, as well as strategies for avoiding them.

Recurrent Instability

Recurrent dislocation after MPFL reconstruction is an unusual event and is often associated with a fall or direct traumatic blow to the knee, such as a sports injury or motor vehicle collision.⁷,⁸ Atraumatic recurrence is commonly related to untreated or unrecognized anatomic risk factors.

TABLE 37.1 Graft Options for Medial Patellofemoral Ligament Reconstruction

Graft	Pros	Cons
Hamstring: semitendinosus or gracilis	Familiar to most orthopedic surgeons Predictable length	Requires additional incision Potential injury to saphenous nerve
Hamstring tendon through posteromedial approach	Predictable length Cosmetic incision Safe for saphenous nerve	Unfamiliar to most orthopedic surgeons Potential for vascular injury
Quadriceps tendon	No requirement for additional patellar fixation	Anisometry of graft owing to superior location relative to patella Disruption of extensor mechanism: theoretical potential for additional quadriceps atrophy
Adductor tendon	No requirement for additional femoral fixation	Anisometry of graft owing to posterior/superior location relative to Schöettle’s point Danger to neurovascular bundle with harvest
Allograft	No donor site morbidity	Slower incorporation than autograft Cost
Artificial ligament	No donor site morbidity	Limited outcomes data in medial patellofemoral ligament reconstruction High rate of failure across all historical uses

Reports in the literature related to the rates of recurrent dislocation range from 0% to 13.3%.⁹ Systematic reviews have revealed that true rate is low. Shah et al performed a systematic review of MPFL reconstruction outcomes studies and found an overall rate of recurrent instability of 3.7%, with 2% requiring a return to the operating room.³ Schneider et al reported a 1.2% risk of recurrent instability.¹⁰ There may be some risk factors for recurrent dislocation because Schiphouwer et al found that patients with open physes were more likely to have recurrent dislocation that those without.⁶ And although the vast majority of these cases involve recurrent lateral instability, Schiphouwer et al reported a case of medial dislocation in the setting of MPFL reconstruction combined with lateral retinacular release.⁶

TABLE 37.2 Anatomic Risk Factors for Patellar Instability

Anatomic Factor	Manifestation on Examination/Imaging
Trochlear dysplasia	Shallow, flat, or convex femoral trochlear groove; supratrochlear spur; and/or large trochlear “boss”
Genu valgum	Valgus standing alignment, genu valgum on bilateral full-length (hip to ankle) weight-bearing radiograph
Lateralized tibial tubercle	Increased Q-angle, high tibial tubercle-trochlear groove distance or tibial tuberosity-posterior cruciate ligament distance
Patella alta	Patellar height indices on lateral radiograph
Tight lateral retinaculum	Lateral patellar tilt
Ligamentous laxity	High score on Beighton criteria, particularly knee hyperextension
Rotational malalignment	Increased femoral anteversion, increased external tibial torsion Computed tomography/magnetic resonance imaging rotational profile

Frustratingly, even in cases that demonstrate no frank dislocation, subluxation and/or apprehension can persist. Shah et al reported apprehension, patellar hypermobility, or a sensation of instability in 8.2% patients at final follow-up.³ Schneider et al reported a 3.6% rate of apprehension following MPFL reconstruction.¹⁰ Fortunately, as techniques have improved, the rates of what Stupay et al termed “functional failures,” including apprehension, subluxation, and dislocation, have decreased from 9.55% to 4.77% in newer studies.⁵
Two types of errors can lead to recurrence: inappropriate surgical indications and errors in surgical technique.

Table 37.2 lists the anatomic risk factors for recurrent patellar instability. Unrecognized dysplasia or malalignment in the coronal, sagittal, or axial (rotational)
planes can lead to inadequacy of the MPFL reconstruction (Figure 37.1).

Figure 37.1 Atraumatic failure of medial patellofemoral ligament (MPFL) reconstruction over a period of time caused by underlying high-grade trochlear dysplasia. The MPFL graft is intact but stretched, leading to recurrent patellar dislocation. The femoral tunnel position was appropriate. Courtesy: Shital N. Parikh, MD.

Errors in surgical technique can lead to an ineffective graft, most notably fixation of the graft with inadequate restraint to lateral patellar translation. Most authors recommend fixation of the MPFL graft to allow one to two quadrants of medial and lateral patellar translation. Controversy exists regarding the position of graft fixation, with some surgeons preferring a position of early flexion (30°), and others preferring 60° of flexion. Shah et al reported a trend toward higher rates of postoperative apprehension and subjective hypermobility when the graft is fixed at less than 60° of knee flexion.³
Tunnel or socket position is a key player in MPFL graft effectiveness. As the fulcrum of motion, the femoral fixation plays the most significant role in graft isometry.¹¹ Schöettle et al described radiographic criteria for placement of the femoral fixation point.¹² The most common malposition of the femoral tunnel is anterior placement (Figure 37.2). Parikh et al noted that seven of eight patients with recurrent instability had femoral tunnel malpositioning. Four had tunnels placed too anteriorly, whereas one each had a tunnel too anterior and proximal, too distal and proximal, and too distal.⁴
Assessment of femoral tunnel on lateral radiographs or fluoroscopy is very sensitive to the position of femoral condyles. Perfect posterior and distal overlap of medial and lateral femoral condyles is required in order to avoid errors in femoral tunnel position assessment (Figure 37.3).
In the presence of distal femoral shaft bow or dysplasia, there might be difficulty in localization of femoral tunnel position (Figure 37.4). Isometric assessment or open identification of landmark structures (adductor tendon, adductor tubercle, and saddle between adductor tubercle and medial epicondyle) can help with accurate placement of femoral tunnel.

Figure 37.2 The femoral tunnel (arrow) is malpositioned anteriorly, and the patient required revision surgery. Courtesy: Shital N. Parikh, MD.
Evaluation of graft isometry is helpful before definitive fixation, as well, particularly in the case of malalignment such as a high tibial tubercle-trochlear groove distance or patella alta.¹³
Another technical error can involve patellar fixation of the MPFL graft. The location of patellar fixation can be particularly relevant to graft failure if breech occurs during fixation. Figure 37.5 demonstrates a patient who underwent MPFL reconstruction using a template that spaces the anchor fixation points at a standard distance. Unfortunately, the proximal anchor was too close to the superior patellar pole, causing cortical breech and rendering the proximal limb of the graft incompetent, resulting in recurrent dislocation when the appropriate stress was applied.
Catastrophic failure of MPFL graft could occur in case of graft pull-out or cut-out from the tunnel (Figure 37.6).

Stiffness

Postoperative stiffness is a known complication that may be multifactorial.

The degree and direction of loss of motion can vary. In a series of 15 patients by Drez et al, 4 patients lost flexion compared to the contralateral knee, but none more than 10°.¹⁴ Shah et al reported on 22 of 629 patients (3.5%) who suffered from residual flexion loss, and 9 underwent manipulation under anesthesia.³ Parikh et al reported a 4.5% rate of flexion loss requiring manipulation though there were no extension deficits noted.⁴

Figure 37.3 Radiographic identification of femoral tunnel has some limitations. Black line represents the posterior cortex of distal femur. A, Intraoperative fluoroscopic view shows adequate position of femoral tunnel when both femoral condyles overlap perfectly. On cursory evaluation of postoperative radiographs (B, C), both lateral views appear to be similar. These radiographs show the effect of mild rotation on assessment of femoral tunnel. B, Mild external rotation of knee gives the effect of anterior malposition of femoral tunnel. C, Mild internal rotation of knee gives the effect of posterior placement of femoral tunnel. Black arrows mark the lateral femoral condyle. Courtesy: Shital N. Parikh, MD.

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