Clinical outcomes of a minimally invasive isolated medial patellofemoral ligament (MPFL) reconstruction technique without considering bone anatomical factors in patients with patellar instability

doi:10.21203/rs.3.rs-4820705/v1

Objective: The aim of this study was to demonstrate the clinical results of a minimally invasive anatomic reconstruction technique for isolated MPFL in cases of recurrent patellar instability, without consideration of Patella alta, TT-TG distance, and trochlear dysplasia.

Methods: Retrospective analysis was conducted on prospectively collected data from patients who underwent minimally invasive isolated MPFL reconstructive surgery at Norinco General Hospital between 2014 and 2019. Preoperative evaluation included assessment of the J-sign, trochlear dysplasia according to Dejour classification, patellar height using the Caton-Deschamps index (CDI), and tibial tubercle–trochlear groove (TT-TG) distance. Postoperatively, Kujala score, International Knee Documentation Committee (IKDC) score, and Tegner score were assessed. Complications such as re-dislocation of the patella, patellar fracture, hematoma formation, and knee stiffness were recorded as failure if they severely affected knee function after MPFL reconstruction.

Results: A total of 106 patients (Average age, 21.5 ±5.9 years; 68% females; mean follow-up, 7.2±1.6 years) were included. 28 individuals (26%) presented with a preoperative positive J-sign, trochlear dysplasia was observed in 102 cases (A,48%; B,22%; C,18%; D,8%). The mean CDI value was 1.18±0.16 (range,0.9-1.5); average TT-TG distance, 21.0±3.8 mm (range,10-26 mm). The final follow-up mean Kujala score was 83.2 ± 14.6 (range 40-100); mean IKDC score, 77.8 ± 12.6 (range 24 - 93); mean Tegner score, 4.0 ± 1.8 (range 1-9). Postoperative patellar instability and re-dislocation were observed in 5 patients (5%). Knee pain emerged as the most prevalent postoperative complication (17%). Joint release surgery was required for two patients experiencing postoperative knee stiffness. The Kujala score of 70 patients was ≥80, and the clinical excellent rate reached 66%. Patients with positive J-sign and severe trochlear dysplasia before surgery are more likely to have unsatisfactory results（Kujala score＜80）, and both have significant differences. However, the two anatomical factors, CDI and TT-TG value, had no statistical significance on the satisfied and unsatisfied results of Kujala scores.

Conclusion: The reconstruction of the isolated medial patellofemoral ligament has shown positive clinical results in treating patellar instability. Especially for young female patients, a minimally invasive MPFL reconstruction technique with minimal scarring leads to increased patient satisfaction. However, in cases where preoperative assessment shows a positive J-Sign and severe trochlear dysplasia, it may be necessary to consider incorporating bony procedures such as tibial tubercle osteotomy or trochleoplasty.

Health sciences/Health care/Therapeutics/Surgery

Health sciences/Health care/Therapeutics/Surgery/Reconstruction

isolated medial patellofemoral ligament reconstruction

patellar instability

MPFL

patella alta

J-sign

tibial tubercle–trochlear groove (TT TG) distance

trochlear dysplasia

The incidence of patellar instability is quite common in young individuals, often leading to restrictions in sports involvement, interference with daily activities, and the potential for long-term disability and early joint degeneration (1). Patellar instability is a multifaceted problem, with key contributing factors including a weakened or torn medial patellofemoral ligament (MPFL) (2), patella alta (3), increased distance between the tibial tubercle and trochlear groove (TT-TG) (4), and trochlear dysplasia (4, 5). The MPFL acts as the primary medial stabilizer for the patella during 0 to 30 degrees of knee flexion(6)and is found to be compromised in up to 96% of patients with patellar instability (7). Therefore, reconstruction of the MPFL is widely acknowledged as an essential aspect of current treatment strategies for addressing patellar instability.

MPFL reconstruction often involves concurrent osseous procedures, such as distalization, medialization, and anteromedialization of the tibial tuberosity or trochleoplasty in cases with patella alta and an increased TT-TG distance or high-grade trochlear dysplasia (8). While these procedures effectively treat patellar instability, they also result in longer operative time, surgical trauma, extensive scarring, higher risk of complications, and longer recovery time (4, 10). As a result, ongoing research is being conducted to explore the potential benefits of a minimally invasive isolated MPFL reconstruction technique for patients with patellar instability regardless of Patella alta, increased TT-TG distance, and trochlear dysplasia.

This retrospective study included 106 patients with patellar instability who received isolated MPFL reconstructive surgery at Norinco General Hospital(NGH) between 2014 and 2019. Ethics approval for this study was obtained from the ethics committee of NGH༈NO. 202406021137000318810༉. All procedures were conducted following the appropriate guidelines and regulations. Prior consent was obtained from all participants and/or their authorized representatives.

Patient Selection

The inclusion criteria encompassed patients who had experienced recurrent patellar dislocation or multiple subluxation events ( ≧ 2). Patients with a history of knee surgery, severe cartilage defect (Outerbridge grade IV; in patella or femoral condyles) combined with meniscus tears and other ligament injuries, as well as those with a follow-up date of less than 5 years, were excluded. The surgeries were performed by two senior surgeons (Yongqiang Zhang and Zhao Zhang).

Surgical Procedure

The surgical procedures were carried out by two experienced surgeons using the same method. The patient was positioned supine with a tourniquet applied to the thigh, and a diagnostic arthroscopy was performed. A 1.5cm incision was made on the lateral side of the ankle to expose and harvest the peroneus longus tendon. An autogenous tendon graft was then prepared. A 1 cm incision was made over the junction of the middle and proximal one third of the patella, and a 3.2mm guide pin was drilled from the medial edge of the patella to its anterior surface at an equivalent level. A 4.5mm tunnel was created following the guide pin. The graft tendon was threaded through the patellar tunnel and pulled back over the front surface of the patella. Both ends of the graft were passed between the deep fascia and knee joint capsule, exiting through a 1.5 cm incision over the medial epicondyle. The two ends of the graft were anchored in a 6mm tunnel approximately 2.5cm long at the schottle point, identified with fluoroscopy and guided by a transfemoral pin (11). The tension of the graft was adjusted by cyclically moving the knee from full extension to full flexion. Subsequently, an interference screw (Smith-Nephew) measuring 2.5mm in length and 6mm in diameter was used to securely fixate the graft within the tunnel at a knee flexion angle of 30 degrees. Refer to Fig. 1 for a visual representation of this surgical procedure.

Postoperative rehabilitation

The postoperative rehabilitation protocol involves immediate weightbearing with a knee brace and full range of motion exercises. After 6 weeks, the brace is removed and patients gradually resume daily activities. Return to sports typically takes 3 months.

Clinical and Radiographic Evaluation

Knee function was assessed by the Kujala score, recorded the International Knee Documentation Committee (IKDC) score (12), and evaluated sporting activity level with the Tegner score (13). To examine the impact of anatomic factors on patient function following isolated MPFL reconstruction, we categorized Kujala scores as either satisfactory or unsatisfactory, using a total score threshold of 80 for satisfaction. This specific cutoff point has been previously established for the Kujala score (14). Physical examinations were conducted both before surgery and during the final follow-up (15). We documented all complications. Failure was defined as re-dislocation of the patella and complications that significantly affected knee function after MPFL reconstruction, such as patellar fracture, hematoma formation, and knee stiffness.

Preoperative imaging data of all patients were collected and analyzed. Dejour classification(16)(grade A, B, C or D) of femoral trochlea was performed by preoperative lateral radiographs and axial CT scans. TT-TG values were measured and recorded by axial CT scan following the method outlined by Schottle et al (11). The index CDI (17), which reflects the height of patella, was also measured. All the radiographic assessments were measured by 2 senior authors (Bo Wang and Yong Shen)

Statistical Analysis

The statistical analysis was conducted using IBM SPSS Statistics 27. Descriptive data analysis was performed to examine the characteristics of the criteria used in this study. Quantitative data were analyzed by calculating various statistics, such as the number of observed values, mean and standard deviation (SD), as well as minimum and maximum values. Qualitative data were evaluated by determining the number of observed values and the percentage of patients per category. To compare associations with satisfactory and unsatisfactory Kujala scores, categorical and continuous data were assessed using a Fisher exact test and Mann-Whitney U test respectively. Statistical significance was defined as p<0.05.

The research group included 106 patients who had undergone minimally invasive isolated MPFL reconstruction for unilateral patellar instability. The average age at the time of surgery was 21.5 ± 5.9 years (range, 13-40 years), with females making up 68% of the patient population. The mean follow-up duration was 7.2 ± 1.6 years (range, 5-9.6 years). Among these patients, 28 individuals (26%) had a preoperative positive J-sign, while trochlear dysplasia was observed in 102 cases (96%), categorized as A in 48%, B in 22%, C in18%, and D in8%. The mean CDI value was calculated to be 1.18 ± 0.16 (range,0.9-1.5), and the average TT-TG distance measured 21.0 ± 3 .8 mm (range,10-26 mm). Detailed descriptive analyses of the entire cohort are summarized in Table1.

Table 2 provides a summary of the clinical outcomes for patients. The average Kujala score at final follow-up was 83.2 ± 14.6 (range 40-100), the average IKDC score was 77.8 ± 12.6 (range 24 - 93), and the average Tegner score was 4.0 ±1 .8 (range l-9). Five patients (5%) experienced postoperative patellar instability and re-dislocation, while knee pain was the most common complication after surgery, occurring in 17% of patients. Two patients required joint release surgery due to postoperative knee stiffness, and one patient underwent patellar fracture reduction and MPFL revision one year after isolated MPFL reconstruction following a fall injury.

The effect of anatomic factors on postoperative function is shown in table 3. The Kujala score of 70 patients was ≥80, and the clinical excellent rate reached 66%. By comparing the influence of all anatomical factors on the result of Kujala scores (Table 3), it is found that patients with positive J-sign and severe trochlear dysplasia before surgery are more likely to have unsatisfactory results（Kujala score＜80）, and both have significant differences. However, the two anatomical factors, CDI and TT-TG value, had no statistical significance on the satisfied and unsatisfied results of Kujala scores.

This study focused on conducting minimally invasive isolated MPFL reconstruction for treating recurrent patellar instability, with an average follow-up period of 7.2 years. Favorable clinical outcomes were achieved irrespective of bone anatomical factors such as TT-TG value, patellar height, and trochlear dysplasia. It is noteworthy that this research has identified two predictive factors for failure: severe trochlear dysplasia (18) (Dejour type B and D), as well as a preoperative positive J-sign. Currently, there is a lack of literature or consensus to guide the identification of patients with recurrent patellar instability who may require an additional bony procedure alongside MPFL reconstruction. In contrast, MPFL reconstruction is considered a necessary surgical procedure for the treatment of recurrent patellar instability (19). Surgical interventions aimed at correcting anatomical factors contributing to patellar instability, such as tibial tubercle osteotomy, trochleoplasty, and femur rotary osteotomy, are associated with increased trauma, prolonged patient recovery time, and larger scars on the affected knee. These factors can potentially impact surgical outcomes and patient satisfaction rates(20). However, the isolated procedure of MPFL anatomic reconstruction is characterized by shorter duration, reduced invasiveness, minimal scarring (Fig. 2), and higher acceptance among surgeons and patients, particularly for young female with patellar instability. Therefore, in cases where additional bone surgery is not required, performing MPFL reconstruction alone can yield favorable surgical outcomes, presenting an ideal scenario.

In this research, patients with a positive J sign and severe trochlear dysplasia showed decreased clinical scores after undergoing isolated MPFL reconstruction. Severe type trochlear dysplasia can lead to abnormal patellar tracking, especially when a positive J-sign is detected during clinical examination. The J-sign refers to the lateral subluxation of the patella that occurs in terminal knee extension due to an atypical path followed by the patella within the first 30° of flexion (21). A significant correlation was observed between the presence of severe trochlear dysplasia (type B and D) and the occurrence of a positive J-sign (21). Severe dysplasia of the trochlea may be the underlying anatomical reason for a positive J-sign. In a group of individuals who have experienced recurrent patellar instability, Dejour et al (15) found that 96% of patients had trochlear dysplasia. Our data shows a similar percentage of cases. Some research suggests that performing isolated MPFL reconstruction can be effective and should be considered for patients, even in cases of severe trochlear dysplasia (22, 23). However, other studies (24, 25) have indicated that trochlear dysplasia is associated with poorer outcomes and higher rates of failure. Kita et al (26) reported the findings of a study on 42 cases of isolated MPFL reconstructions conducted for recurrent patellar instability, with an average follow-up period of 3.2 years. After the surgery, two patients encountered a subsequent dislocation event. The researchers identified severe trochlear dysplasia as the primary factor linked to recurring patellar instability following isolated MPFL reconstruction. Therefore, it may be necessary to consider additional trochnoplasty in order to achieve optimal outcomes in patients with this specific profile.

Our research showed that the TT-TG distance, patellar height, and trochlear mild dysplasia (Dejour type A and B) did not have a significant impact on the clinical outcomes of isolated MPFL reconstruction for recurrent patellar instability. These findings are consistent with the results presented by Erickson BJ (18) and Pappa N(27). The results of a follow-up study lasting at least 10 years indicate that isolated MPFL reconstruction is an effective long-term treatment option for recurrent patellofemoral instability with low recurrence rates when patients meet specific criteria, including CDI < 1.4 and a TT-TG distance less than 20mm (28). In our retrospective study, the average CDI value among all patients included in the analysis was 1.2, while the mean TT-TG distance measured 21mm. The values exhibit a modest range, potentially attributed to our early patient selected criteria for isolated MPFL reconstruction. In the treatment algorithm for lateral patellar instability, it is suggested to consider distalization of the tibial tubercle for cases with patella alta and a CDI ≥ 1.2, while medialization of the tibial tubercle is recommended for cases with a TT-TG distance ≥ 20 mm. As a result, patients with severe anatomical abnormalities and patellar instability may have been implicitly excluded from the inclusion criteria of these two studies. The variations in inclusion criteria for isolated MPFL reconstruction in patients with patellar instability could potentially contribute to differing findings observed across multiple studies.

Shatrov J et al. (28) also found that over 10 years after isolated MPFL reconstruction, radiographic evidence of patellofemoral arthritis was observed in one-third of patients. This observation may provide a potential explanation for the presence of anterior knee pain in certain individuals within our study cohort.

Currently, there are multiple surgical options for MPFL reconstruction. Research has shown that using suture anchors for patellar fixation is preferred over patellar tunnels due to the increased risk of patellar fracture associated with the latter option (20). A recent study suggests that utilizing small and oblique tunnels is a safe method for patellar fixation in MPFL reconstruction. Choosing small, oblique tunnels instead of two suture anchors can result in cost savings without significantly raising the risk of fractures or complications (29). The patellar tunnel in all of our patients was a 4.5mm oblique tunnel. Notably, only one out of 106 patients experienced a patellar fracture at the bone tunnel due to fall trauma, resulting in an incidence rate of merely 0.9%. Consequently, we maintain our confidence in the efficacy and suitability of patellar tunnel. Interference screw fixation was chosen for femoral graft fixation, as it is a widely utilized method of fixation. While other methods such as suture anchors exist, a systematic review comparing isolated MPFL reconstructive femoral graft anchoring versus interference screw fixation have reported similar clinical scores and rates of apprehension test, persistent joint instability, re-dislocations, and revisions(30). The femoral anatomic insertion of MPFL was determined using intraoperative fluoroscopy (11), Subsequently, a minimal 1.5cm incision on the medial condyle of the femur suffices to accomplish graft fixation during the surgical procedure. The hamstring autograft is the most frequently utilized graft for MPFL reconstruction. However, considering the aesthetic impact of the knee incision scar in the donor area, we opted for harvesting the anterior half of the peroneus longus tendon, requiring only a 1.5cm surgical incision at the lateral ankle to obtain the graft. Furthermore, the visibility of the scar from the incision made on the lateral ankle is minimal. Undoubtedly, it is crucial to minimize skin scarring around the knee joint for aesthetically conscious young female patients.

In our clinical practice, bony procedures for primary patellar stabilization surgery, such as tibial tubercle osteotomy and trochleoplasty, are selectively performed in patients with identified risk factors for failure, including a positive J-sign and severe trochlear dysplasia.

The study had some limitations. Firstly, the retrospective nature of the study limited our findings. The average CDI value was 1.2 and the mean TT-TG distance was 21mm among all included patients, suggesting no significant anatomical abnormalities in individuals with patellar instability. Secondly, only 70% of the patients contacted for the final follow-up underwent clinical examination; the remaining participants completed all knee function assessments via telephone. Thirdly, it was not possible to establish a control group for comparison due to the absence of a definitive gold standard treatment for patellar instability.

Isolated MPFL reconstruction has demonstrated favorable clinical outcomes in the management of patellar instability. Particularly for younger female patients, a minimally invasive MPFL reconstruction technique with minimal scarring is associated with heightened patient satisfaction. However, in cases where preoperative assessment reveals positive J-Sign and severe trochlear dysplasia, consideration should be given to incorporating bony procedures such as tibial tubercle osteotomy or trochleoplasty.

The authors declare that they have no competing interests.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Author Contribution

Yongqiang Zhang, Zhanhai Yin and Zhao Zhang were involved in the study design and contributed to data collection, analysis, interpretation of results, and writing of the manuscript; Meng Wu, Yadong Zhou, Bo Wang and Yong Shen contributed to data collection, analysis, and manuscript writing; Yalong Yang, Yang Li ,Junliang Liu and Na Hu participated in the study design and contributed to interpretation of results and manuscript writing. All authors have reviewed and approved the final version of the manuscript, and agree with the authorship order.

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Table 1. Patient characteristics before surgery (N = 106)

Variable

N (%)

Mean±SD

Minimum

Maximum

Gender

Male

Female

Age (Year)

BMI (kg/m2)

Side

Right

Left

Year’s follow-up

J-sign

Positive

Negative

Trochlear dysplasia

Normal

Type A

Type B

Type C

Type D

CDI

＜1.2

≥1.2

TT-TG distance (mm)

＜20

≥20

34 (32%)

72 (68%)

59 (55%)

47 (45%)

28 (26%)

78 (74%)

4 (4%)

51 (48%)

23 (22%)

19 (18%)

9 (8%)

67（63%）

39（37%）

50（47%）

56（53%）

21.5 ±5.9

22.5±4.4

7.2±1.6

1.18±0.16

21.0±3.8

13

15.8

5

0.9

10

40

38.6

9.6

1.5

26

BMI = body mass index

CDI =Caton-Deschamps index

TT-TG= tibial tubercle–trochlear groove

Trochlear dysplasia grades according to Dejour classification

Table 2. Clinical outcomes at last follow-up (N=106)

N (%)

Mean±SD

Minimum

Maximum

Kujala score

IKDC score

Tegner score

Patellar re-dislocation or instability

Complications

knee pain

knee stiffness

patella fracture

hematoma

Knee Arthrosis Infection

5 (5%)

21 (20%)

18 (17%)

2 (2%)

1 (1%)

0

83.2±14.6

77.8±12.6

4.0±1.8

40

24

1

100

93

9

Table 3. The effect of anatomic factors on postoperative function (N=106)

Anatomic factors

Kujala ≥80

N=70

Kujala ＜80

N=36

P value

J-sign (Pre-operation)

Positive（28）

Negative（78）

Trochlear dysplasia

Normal（4）

Mild type (70)

Severe type (32)

CDI

TT-TG distance (mm)

13

57

4

50

16

1.16±0.16

19.0±4.7

15

21

0

20

16

1.21±0.17

20.5±3.4

0.019^*

0.039^*

0.138

0.113

CDI =Caton-Deschamps index

TT-TG= tibial tubercle–trochlear groove

Trochlear dysplasia grades according to Dejour classification

Trochlear dysplasia mild type=Dejour A and C; Trochlear dysplasia severe type=Dejour B and D

“*” P <0.05 = significance

No competing interests reported.

Clinical outcomes of a minimally invasive isolated medial patellofemoral ligament (MPFL) reconstruction technique without considering bone anatomical factors in patients with patellar instability

Status:

Version 1

Abstract

Figures

Introduction

Materials and Methods

Patient Selection

Surgical Procedure

Postoperative rehabilitation

Clinical and Radiographic Evaluation

Statistical Analysis

Results

Discussions

Conclusion

Statements and Declarations

References

Tables

Additional Declarations

Status:

Version 1