1 Introduction

Patients presenting with patellar instability may have multiple factors contributing to their pathology.¹ Stability in the patellofemoral joint depends on bony structures, such as lower limb alignment and trochlear shape, as well as soft tissue structures, especially the medial patellofemoral ligament (MPFL).² During initial knee flexion (<30°), the major restraints to lateral translation and dislocation, are soft tissue; however, after 30° the bony structures are the primary determinants for patellar stability as the patella reduces within the trochlear groove.³ Instances where this paradigm may be altered is for those patients with patella alta, whereby the patella may not reduce into the trochlear groove until a high flexion angle, potentially predisposing patients to instability.⁴

The medial patellofemoral ligament (MPFL) is the primary soft tissue restraint against lateral translation of the patella within the patellofemoral joint during early to mid-knee flexion.^5–9 During primary dislocation, commonly the result of a rotational injury during early knee flexion or stance, the MPFL may be injured as it undergoes failure from excessive lateral translation of the patella.^8,9 This injury is considered the “essential” lesion of patellar dislocation, similar to the Bankart lesion in anterior glenohumeral instability.^8,9 MPFL reconstruction is designed to stabilize the patella, restore proper kinematics and reconstitute physiologic load transmissions across the patellofemoral joint.¹⁰ MPFL reconstruction in patients with otherwise normal joint morphology and lower limb alignment is an effective surgical procedure with favorable outcomes for patients presenting with recurrent patellar dislocations.^11,12

Patients with patellar malalignment (increased Q angle, increased tibial tubercle to trochlear groove distance (TT-TG), excessive knee valgus, or the combination of these factors with femoral anteversion and pronated midfoot) may report perennial patellar instability and experience frequent low-energy patellar dislocations. In patients who elect conservative treatment, recurrence is noted to be between 15% and 44%.^13,14 Surgical stabilization for these patients has traditionally centered around tibial tubercle transfer to correct the underlying biomechanics at the patellofemoral joint.¹ Tibial tubercle transfer (TTT) is a realignment procedure designed to reduce contact forces across the patellofemoral joint and medialize the extensor mechanism.¹⁵ Specifically, TTT is used to correct excessive (>20 mm) TT-TG distance, thereby increasing the stability of the patellofemoral joint.¹⁶ Additionally, medialization (and obligate anteriorization) may be accompanied by distal advancement of the tubercle to correct patella alta in cases where this is thought to be an underlying reason for instability.

For patients presenting with both a ruptured MPFL and patellar malalignment, restoring physiologic load transmission across the patellofemoral joint while optimizing stability is a challenge for the treating sports medicine physician. A combined MPFL reconstruction and TTT surgery can be performed to address the soft tissue insufficiency and the underlying skeletal abnormality. While anatomically this approach makes sense, there has been considerable apprehension on the side of orthopedic surgeons in performing the combined surgery with the thought process that this might represent “too much surgery” as well as promote post-operative stiffness and arthrofibrosis. Therefore, the primary objective of this retrospective study is to compare patient outcomes following a combined approach (MPFL reconstruction and TTT) to outcomes reported in the literature by patients who required either only an isolated TTT procedure to treat pathologic lateral patellar instability or isolated MPFL reconstruction to treat patellar dislocation due to MPFL insufficiency. Our hypothesis is that a combined approach is a safe and effective treatment for malalignment and recurrent patellar instability with insufficiency of the MPFL with results that are comparable to both procedures performed in isolation.

2 Materials and methods

Between December 2008 and December 2010, 31 patients (34 knees) underwent simultaneous MPFL reconstruction and TTT surgery to treat recurrent patellofemoral instability. Twenty-three patients (25 knees), [74%] met our inclusion criteria and were included in this analysis. Prior to surgery, all patients noted feeling subjective patellofemoral instability and had documented episodes of dislocation (>2). Insufficiency of the MPFL was documented at 0–30° along with increased lateral patella translation and apprehension through early knee flexion. Additionally, Q-angles for all patients were recorded pre-operatively and at the time of surgery due to the absence of sensitive MRI measurements. In order to confirm physical exam findings, magnetic resonance imaging (MRI) was obtained in all patients where insufficiency of the MPFL was confirmed, as was an elevated TT-TG (tibial tubercle – trochlear groove) distance on axial cuts (>20 mm). Patients were excluded from our study if they were under the age of 18 at the time of their final follow-up, had a congenital skeletal abnormality, required additional ligamentous procedures in addition to the index surgery, or had inadequate follow-up.

IRB approval was obtained for this study. All patients were treated by one of two fellowship trained sports medicine physicians. Patients were evaluated for recurrence of instability and complications, and were assessed using the Kujala and Lysholm outcome scores. Final scores were tallied by a single researcher and patients were included if they had achieved a minimum follow-up interval of 2 years.

3 Results

During the time period studied, 23 patients (25 knees) met our inclusion criteria for combined treatment and are included in this analysis (Table 1).

The average Q-Angle prior to surgery was 21.2° (range: 15° to 25°). The average age of patients, at final follow-up, in this series was 25 years old (range 18–41) and the average follow-up time was 44 (range 28–92) months. There were 12 left knees and 13 right knees, 1 male and 22 females. At final follow-up, the average Kujala score was 81.56 ± 14.7, while the average Lysholm score was 76.72 ± 18.9. One patient (4.3%) sustained a recurrence of instability (Table 2).

Additional procedures were performed in ten patients and included: lateral meniscectomy, loose body removal, and arthroscopic chondroplasty of the patella or trochlea. Three patients (13%) experienced a total of 3 complications: wound complications requiring repeat surgery (2) and stiffness requiring manipulation under anesthesia (1). There were no infections in this series. Six patients underwent subsequent surgical procedures to the affected knee for removal of symptomatic hardware. Additionally, one patient required open reduction and internal fixation surgery one-year post-operatively for a separate mid tibial stress fracture that became complete. This surgery was felt to be unrelated to the index procedure as the fracture was well distal to the previous osteotomy site of the tubercle.

4 Discussion

The medial patellofemoral ligament (MPFL) is the primary soft tissue restraint to lateral translation of the patella.^5–9 During primary dislocation, the MPFL is damaged and studies have shown that the ligament heals poorly and with attenuation.^8,9 Reconstruction of the MPFL is an effective surgical technique that is designed to stabilize the patella, restore proper kinematics and reconstitute load transmissions throughout the patellofemoral joint.¹⁰ In addition to the soft tissue insufficiencies, there are four anatomic factors (trochlear dysplasia, patella alta, patellar tilt, and an excessive tibial tubercle-trochlear groove distance) that have been identified that increase the risk for patellar dislocation.¹⁶ One of these risks is patellar malalignment, measured by calculating the Q-angle or perhaps more importantly, the TT-TG distance.¹⁶ Trochlear dysplasia has been noted to be present in 85%–96% of patients with recurrent patellar instability.^19–21 In patients with patellar instability and patellar malalignment, a TTT is frequently performed to reduce contact forces across the patellofemoral joint and to medialize the extensor mechanism, reducing strain on the ligament reconstruction.¹⁵

The primary objective of this retrospective study was to compare patient outcomes following a combined approach (MPFL reconstruction and TTT) to outcomes reported by patients who required either only an isolated TTT procedure or isolated MPFL reconstruction. Our hypothesis was that a combined approach is a safe and effective treatment for malalignment and recurrent patellar instability with insufficiency of the MPFL. Our analysis indicates that, in patients with a ruptured MPFL and patellar malalignment, MPFL reconstruction combined with TTT has a high rate of success, with similar complication rates to a singular approach to treatment. Of particular note is that only one patient in our cohort required a manipulation under anesthesia. Certainly there is concern that the multiple procedure knee is at risk for capsular scarring and adhesions; however, this was not seen in our study. This may have been due to the hypermobile nature of these patients in general. Also, restoring the patellofemoral joint to a relative “normal” state does not predispose one to arthrofibrosis and the reconstruction is performed in an extra-capsular manner. Future studies can help to clarify this point by obtaining Beighton hypermobility scores on all study patients going forward.

In our patient population the recurrence of dislocation/subluxation rate was 4.3% (or 1 patient). We believe that this rate is very favorable considering that patients in our practice who receive combined surgery are deemed our highest risk patients for recurrent subluxation as they demonstrate both skeletal malalignment (TT-TG> 20 mm) in addition to rupture of the MPFL. Kujala and Lysholm outcome scores were obtained in order to directly compare to prior studies reporting on the patient populations studied. A study of 193 patients (211 knees) who underwent MPFL reconstruction reported an average post-op Kujala score of 81.69.¹⁰ Another study of 12 patients (15 knees) who underwent MPFL reconstruction reported an average post-op Kujala score of 91.9.²² Other studies looking at MPFL reconstruction have reported average Kujala outcome scores of 85.7, 84.0, and 95.2.^18,23,24 The average Kujala score observed in our combined groups was 81.6 which is comparable to these other studies reporting on isolated MPFL reconstruction.

A case series investigating outcomes following combined Fulkerson osteotomy and lateral release procedure in 34 athletes (41 procedures) reporting patellofemoral instability from 1999 to 2004 represents the largest case series of realignment osteotomies to date in athletes.¹⁷ The average reported Lysholm score of these patients was 91.8 at an average of 46 months post-op.¹⁷ The average Lysholm score observed in our combined group was 76.7, which is lower than this study reporting on TTT alone. The complication rate reported in this study of 5.8% was lower than that of our cohort (14%).¹⁷ The higher outcome scores (91.8 v. 76.7) and lower complication rate reported in these patients may be partially attributable to differences in patient population, as our investigation was not focused solely on athletes.

Currently, there is considerable debate regarding the efficacy of concomitant MPFL reconstruction and tibial tubercle transfer. Schottle et al., in a study population of 12 patients (15 knees), did not observe an effect from additional TTT performed in 8 patients who had a pre-operative TT-TG of greater than 15 mm.²⁴ Further, Watanabe et al. concluded in a series of 40 patients (42 knees) that patients receiving isolated MPFL reconstruction achieved similar or better outcomes than combined MPFL reconstruction with TTT. Eight patients received the combined procedure simultaneously while five patients underwent a staged procedure with TTT followed by MPFL reconstruction due to patients presenting with continued persistent instability. The other 29 patients in their cohort underwent isolated MPFL reconstruction.²⁵ However, it is important to note that patients in their patient population presented with average Q-angles close to 13° in both groups.²⁵ In our study the average Q-angle was 21.2° (range 15–25).

Several additional studies have suggested that MPFL reconstruction alone is sufficient in most cases with objective patellofemoral instability criteria.^26–31 Nonetheless, it is important to note that numerous studies, including a few reporting that MPFL reconstruction alone is sufficient in cases with objective patellofemoral instability, advocated performing a TTT in patients with high TT-TG distance (20 mm or greater).^27,32,33

Additionally, prior literature has reported mixed results regarding the effect that increased TT-TG distance has on MPFL reconstruction. Several studies have reported no significant differences with favorable clinical outcomes, between patients with increased TT-TG distance and patients without increased TT-TG distances undergoing isolated MPFL reconstruction.^34–36 On the other hand, Joanna et al. reported TTT is appropriate for patients with TT-TG distance of 20 mm or greater.³⁶ Additionally, numerous studies have suggested that, in patients with a Q-angle greater than 20°, anteromedial TTT may be a good solution; however, in patients presenting with a straight knee this would be overtreatment.^15,34,35,37

The patients in our cohort were unique as they presented with patellar instability as well as malalignment of their knees as indicated by recurrent instability (documented episodes of dislocation (>2)), increased Q-angle (average: 21.2°) and a TT-TG of 20 mm or greater on the axial cuts of MRI. Therefore, MPFL reconstruction and TTT were performed concomitantly to address the soft tissue insufficiency and the underlying skeletal abnormality. In patients presenting to our practice with recurrent patellar instability without malalignment (increased TT-TG), the standard of care is to perform an isolated MPFL reconstruction.

Further, a trochleoplasty procedure was not performed as an additional procedure as this technique has not yet gained widespread acceptance in the United States. Trochleoplasty is not employed as standard of care in our practice due to the risk of patellofemoral joint degeneration.²⁷ Recurrent dislocation is uncommon with trochleoplasty; however, persistent pain is common and articular cartilage damage is a concern.²⁷³ Systematic literature reviews have analyzed publications reporting on radiographic and clinical outcomes after corrective trochleoplasty. These reviews cautioned the use of trochleoplasty and concluded this procedure should be reserved for cases of extreme dysplasia where other treatment options cannot provide patellofemoral stability.^27,38 Additionally, prospective studies are necessary to determine the long-term efficacy of trochleoplasty.³⁸

There are several limitations to our study. The retrospective nature of the study design and lack of preoperative outcome scores makes it difficult to draw conclusions regarding the effects of treatment. Our ultimate goal was to establish the safety and efficacy of this procedure relative an acceptable standard of care and we feel that this study establishes this safety profile and efficacy. Additionally, multiple surgeons performed the procedures on this cohort; however, this bias was limited by communication amongst our group to standardize the technique for the patients in this cohort. Use of the Q-angle as a reliable predictor of patellar tracking and kinematics has been questioned in prior studies; however, prior studies have utilized this method to determine inclusion criteria for tubercle transfer.¹⁷ Further we did not have reliable axial imaging from every patient on the same MRI to reliably report TT-TG distance in our patient population. An additional limitation of this analysis is the inability to control for chondral pathology. This may have been reflective in our outcome scores, particularly when comparing our patients to those that have been previously published in the literature. Outcome scores are not just dependent upon stability of the patellofemoral joint, but on pain and function as well. While many of our patients achieved excellent functional outcomes and minimal recurrent instability, occasional discomfort and mild restrictions may have led to poorer outcomes than those that are seen in more athletic populations. Many of our patients also had chondroplasty procedures to treat articular cartilage defects. With the limited numbers of patients that undergo this surgery, even for a large referral practice, minimizing this bias is a significant challenge.

We feel that patients necessitating a combined approach to stabilization represent patients at the highest risk for recurrent instability, similar to those patients with shoulder instability and osseous defects of the humeral head and glenoid. For this reason, the recurrence rates exhibited in our study demonstrate an excellent result with regard to overall stability and function of the most “at-risk” joint. In this vain, comparing the combined approach patients to isolated procedures, may not be a direct apples to apples comparison, and the lower Lysholm and Kujala scores (when compared to historical controls from the literature) may be a mere representation of this phenomenon. Further prospective, and perhaps randomized comparative studies may be necessary to truly demonstrate equivalent outcomes.

5 Conclusion

MPFL reconstruction combined with TTT has a high rate of success for patients presenting with patellar instability due to combined MPFL rupture and patellar malalignment. The risk of recurrence in the current series was low (4.3%), and the risk of complications is equivalent to other outcomes previously reported in the literature. Therefore, we conclude that for patients presenting with a ruptured MPFL and malalignment with a heightened Q angle, combined MPFL reconstruction and TTT is a safe technique that provides patients with improved patellofemoral stability, and achieves similar outcomes to patients receiving isolated reconstruction. We anticipate that longer-term studies performed on this patient population will demonstrate sustained improvement over time. However, this study does raise the question of whether a combined approach (MPFL with TTT) offers any clear advantage over distal realignment alone in patients with patellofemoral instability and an elevated Q angle.