
==== Front
BMC Musculoskelet Disord
BMC Musculoskelet Disord
BMC Musculoskeletal Disorders
1471-2474
BioMed Central London

39143601
7722
10.1186/s12891-024-07722-5
Research
Results of medial patellofemoral ligament reconstruction with and without tibial tubercle osteotomy in patellar instability: a systematic review and single-arm meta-analysis
Su Peng 12
Yao Dongying 3
Zhang Lu 4
Li Gang sdszylg@163.com

5
1 grid.464402.0 0000 0000 9459 9325 Shandong University of Traditional Chinese Medicine, Jinan, Shandong China
2 grid.410638.8 0000 0000 8910 6733 Department of Hand and Foot Surgery, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong China
3 https://ror.org/011ashp19 grid.13291.38 0000 0001 0807 1581 Department of Orthopedic Surgery, West China Hospital, Sichuan University, Chengdu, Sichuan China
4 grid.443420.5 0000 0000 9755 8940 School of Finance, Department of Economics and Management, Qilu University of Technology (Shandong Academy of Sciences), Jinan, Shandong China
5 https://ror.org/052q26725 grid.479672.9 Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan, Shandong China
14 8 2024
14 8 2024
2024
25 64229 8 2023
21 7 2024
© The Author(s) 2024, corrected publication 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Purpose

To confirm which method provides lower rate of recurrent instability and superior clinical outcomes.

Method

We searched PubMed, Embase and Web of Science for the trials involving one intervention or both for patellar instability: medial patellofemoral ligament reconstruction (MPFLR) with and without tibial tubercle osteotomy (TTO). The postoperative Kujala score, Lysholm score, Tegner scores and the rate of recurrent instability (dislocation or subluxation) were analyzed as the primary clinical outcome parameters in a random or fixed effects meta-analysis.

Results

In total, 43 articles met inclusion criteria after full-text review. A total of 2046 patients were analyzed. The overall mean age was 20.3 years (range, 9.5–60.0 years), with a mean follow-up time of 3.2 years (range, 1–8 years). The mean Kujala scores in MPFLR and MPFLR + TTO were 89.04 and 84.44, respectively. There was significant difference in Kujala scores between MPFLR and MPFLR + TTO (MD = 4.60, 95%CI: 1.07–8.13; P = 0.01). The mean Lysholm scores in MPFLR and MPFLR + TTO were 90.59 and 88.14, respectively. There was no significant difference in Lysholm scores between MPFLR and MPFLR + TTO (MD = 2.45, 95%CI: -3.20-8.10; P = 0.40). The mean Tegner scores in MPFLR and MPFLR + TTO were 5.30 and 4.88, respectively. There was no significant difference in Tegner scores between MPFLR and MPFLR + TTO (MD = 0.42, 95%CI: -0.39-1.23; P = 0.31). At final follow-up, the rates of recurrent instability in MPFLR and MPFLR + TTO were 3% and 4%, respectively. There was no significant difference in the rates between MPFLR and MPFLR + TTO (OR = 0.99, 95%CI: 0.96–1.02; P = 0.4848).

Conclusion

MPFLR and MPFLR + TTO are effective and reliable treatments in the setting of patellofemoral instability. MPFLR seems to show a better performance in functional outcomes than MPFLR + TTO. Moreover, their rates of recurrent instability are very low, and no significant difference exists.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-024-07722-5.

Keywords

Medial patellofemoral ligament reconstruction
Tibial tubercle osteotomy
Kujala score
Lysholm score
Tegner score
Recurrent instability
issue-copyright-statement© BioMed Central Ltd., part of Springer Nature 2024
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pmcIntroduction

Recurrent patellar dislocation is a frequently encountered disease, which occurs in adolescents and young adults with a morbidity rate of 29 per 100,000 [1]. Many factors can lead to recurrent patellar dislocation, and surgical methods ranging from soft tissue surgery (medial patellofemoral ligament reconstruction, MPFLR) to bony correction (medial or distal tubercle transfer) are usually selected for treatment. When the knee flexes from zero to 30°, the medial patellofemoral ligament (MPFL) is the most important structure to limit patellar lateral dislocations [2–6]. It has been proved that MPFL injury is available during all lateral patellar dislocations [7]. Therefore, MPFLR has become popular to address patellofemoral instability. Many studies also have reported satisfactory clinical outcomes and low rate of recurrent instability after MPFLR [8–10]. However, the causes leading to patellar instability is multi-dimensional, [8, 9] and it might be necessary to bring MPFLR and tibial tubercle osteotomy (TTO) together. Although several studies described the outcome of isolated MPFLR, which method provides lower complication rates and superior clinical outcomes is still in controversy. In addition, It is difficult to carry out a case control study for the study of surgical methods. For the treatment of patellar dislocation, the current research is mainly single arm clinical research without control group. For solving the problem, single arm meta analysis was invented recently.

The purpose of this study was to confirm which method provides lower rate of recurrent instability and superior clinical outcomes. The hypothesis of this systematic review and meta-analysis was that MPFLR with TTO provides lower rate of recurrent instability and superior clinical outcomes than isolated MPFLR in patients with lateral patellar Instability.

Methods

A comprehensive review of the literature was performed according to the preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed, web of science and Embase were searched using the following keywords: MPFLR or medial patellofemoral ligament or medial quadriceps tendon femoral ligament or MQTFL. We selected articles published from 1990 to 2023. The details were shown in Fig. 1.

Fig. 1 The flow chart of literature search

Two independent reviewers separately conducted the search. Given the linguistic capabilities of authors, all publications in English were reviewed. According to the Oxford Centre of Evidence Based Medicine, Level I to IV articles were considered. The same investigators screened.

the articles for inclusion. The criteria for inclusion were shown in Table 1.

Table 1 Inclusion and exclusion criteria. Abbreviation: MPFLR, medial patellofemoral ligament reconstruction; TTO: tibial tubercle osteotomy

Inclusion criteria	Exclusion criteria	
Studies including patients treated with MPFLR or MPFLR combined with TTT for patellar instability	Studies including patients treated with Trochlea plasty	
Studies reporting preoperative constitutions and post-operative clinical outcomes or re-dislocation after operative treatment for patellar instability	Studies including patients treated with other surgery treatments for patellar instability	
Human studies	Studies that did not report both preoperative constitutions and post-operative clinical outcomes or re-dislocation after operative treatment for patellar

instability

	
Level I–IV evidence	Non-human studies	
	Level V evidence, review articles, technical notes, current concept articles, experimental, laboratory studies, case reports	

The postoperative Kujala score, Lysholm score, Tegner score and postoperative recurrent instability rate were analyzed as the primary clinical outcome parameters in a random or fixed effects meta-analysis.

Data extraction

Data extraction was performed by two independent reviewers (A, B), and any differences were reconciled by mutual agreement. All investigators extracted the following data independently: demographic, type of surgery, graft type, indication of osteotomy, outcome measures, recurrent instability rate (dislocation or subluxation), follow-up time and Level of evidence. The details of the studies included in this research were shown in Table 2.

Table 2 The details of the studies included in this research. Abbreviation: MPFLR, medial patellofemoral ligament reconstruction; TTO, tibial tubercle osteotomy; CDI, Caton-Deschamps Index; TT-TG, tibial tubercle-trochlear groove

Author	Surgery included	Number of patients	Graft type	Indications of osteotomy	Outcome	Level of evidence	Follow-up time	
MPFL	MPFL + TTO	
MIKASHIMA	MPFL	24	——	autogenous semitendinosus tendon	——	Kujala、Recurrent instability	IV	3 years	
Ambrozic	MPFL	29	——	autogenous gracilis tendon	——	Kujala、Tegner	IV	4 years	
Bitar	MPFL	21	——	autogenous patellar ligament	——	Kujala、Recurrent instability	I	2 years	
Blanke	MPFL	52	——	autogenous gracilis tendon	——	Lysholm、Tegner、Recurrent instability	IV	2 years	
Deie	MPFL	29	——	autogenous semitendinosus tendon	——	Kujala、Recurrent instability	IV	3 years	
Drez	MPFL	19	——	autogenous semitendinosus and gracilis tendon	——	Kujala、Tegner	IV	2 years	
Erickson	MPFL	90	——	autogenous or allogenous semitendinosus tendon	——	Kujala、Recurrent instability	IV	2 years	
Goyal	MPFL	32	——	autogenous quadriceps tendon.	——	Kujala、Recurrent instability	IV	3 years	
Hopper	MPFL	68	——	autogenous hamstring tendon.	——	Recurrent instability	IV	3 years	
Kang	MPFL	40	——	autogenous semitendinosus tendon	——	Kujala、Lysholm、Recurrent instability	II	2 years	
Kang	MPFL	42	——	autogenous semitendinosus tendon	——	Kujala、Lysholm、Recurrent instability	II	2 years	
Kita(2012)	MPFL	24	——	autogenous semitendinosus tendon	——	Kujala、Recurrent instability	IV	2 years	
Kita(2015)	MPFL	42	——	autogenous semitendinosus tendon	——	Kujala、Recurrent instability	III	3 years	
Liu	MPFL	121	——	autogenous or allogenous hamsting tendon	——	Recurrent instability	IV	2 years	
Ma	MPFL	32	——	autogenous semitendinosus tendon	——	Kujala、Tegner、Recurrent instability	II	3 years	
Matsushita	MPFL	34	——	autogenous semitendinosus tendon	——	Kujala、Lysholm、Recurrent instability	III	3 years	
Matthews	MPFL	21	——	autogenous semitendinosus and gracilis tendon	——	Kujala、Tegner、Recurrent instability	IV	3 years	
Nelitz(2013)	MPFL	21	——	autogenous gracilis tendon	——	Kujala、Tegner、Recurrent instability	IV	3 years	
Nelitz(2018)	MPFL	25	——	autogenous quadriceps tendon	——	Kujala、Tegner、Recurrent instability	III	3 years	
Nomura	MPFL	12	——	autogenous semitendinosus tendon	——	Kujala、Tegner、Recurrent instability	IV	4 years	
Panni	MPFL	48	——	autogenous semitendinosus tendon	——	Kujala、Lysholm、Recurrent instability	IV	3 years	
Pesenti	MPFL	25	——	autogenous semitendinosus and gracilis tendon	——	Kujala、Recurrent instability	IV	3 years	
Sappey-Marinier	MPFL	211	——	autogenous hamstring tendon	——	Recurrent instability	IV	6 years	
Sillanpaa	MPFL	18	——	autogenous adductor magnus tendon	——	Kujala、Recurrent instability	III	8 years	
Valkering	MPFL	31	——	autogenous gracilis tendon	——	Kujala、Recurrent instability	IV	3 years	
von Engelhardt	MPFL	30	——	autogenous gracilis tendon	——	Kujala、Lysholm、Recurrent instability	IV	2 years	
Wagner	MPFL	50	——	autogenous gracilis tendon	——	Kujala、Recurrent instability	IV	1 year	
WitoNski	MPFL	10	——	autogenous patellar ligament	——	Kujala、Recurrent instability	IV	2 years	
Mellecker	MPFL + TTO	——	26	allogenous hamstring tendon	TT-TG: 12–24 mm	Recurrent instability	IV	4 years	
Ahmad	MPFL + TTO	——	15	autogenous gracilis tendon	TT-TG>18 mm; CDI>1.2	Kujala、Recurrent instability	IV	3 years	
Allen	MPFL + TTO	——	28	autogenous semitendinosus, gracilis and quadriceps tendon, allogenous gracilis tendon	TT-TG>20 mm; CDI>1.2	Kujala、Tegner、Recurrent instability	IV	4 years	
Chen	MPFL + TTO	——	25	autogenous semitendinosus tendon	TT-TG>20 mm	Kujala、Lysholm、Recurrent instability	III	3 years	
Cossey	MPFL + TTO	——	19	autogenous medial retinaculum	No mentioned	Lysholm、Tegner、Recurrent instability	IV	2 years	
Damasena	MPFL + TTO	——	17	autogenous semitendinosus tendon	TT-TG: 15 ± 3.5 mm	Recurrent instability	I	5 years	
Franciozi(2017)	MPFL + TTO	——	48	autogenous semitendinosus tendon	TT-TG>17 mm	Recurrent instability	III	4 years	
Frings	MPFL + TTO	——	72	autogenous semitendinosus and gracilis tendon	TT-TG>16 mm	Kujala、Lysholm、Tegner、Recurrent

instability

	IV	2 years	
Jos	MPFL + TTO	——	21	autogenous hamstring tendon	TT-TG>15 mm; CDI>

1.4

	Kujala、Lysholm、Recurrent instability	IV	3 years	
Song	MPFL + TTO	——	11	autogenous semitendinosus tendon	TT-TG>15 mm	Recurrent instability	IV	3 years	
Franciozi(2019)	MPFL、MPFL + TTO	24	18	autogenous semitendinosus tendon	TT-TG: 17–20 mm; CDI>

1.2

	Kujala、Lysholm、Tegner、Recurrent instability	II	3 years	
Mulliez	MPFL、MPFL + TTO	91	38	autogenous gracilis tendon	TT-TG>20 mm	Kujala、Recurrent instability	I	1 year	
Neri	MPFL、MPFL + TTO	84	42	autogenous gracilis tendon	TT-TG>20 mm; CDI>

1.4

	Recurrent instability	IV	6 years	
Schottle	MPFL、MPFL + TTO	7	8	autogenous semitendinosus tendon	TT-TG>15 mm	Kujala、Recurrent instability	IV	4 years	
Tscholl	MPFL、MPFL + TTO	72	43	autogenous gracilis tendon	TT-TG>15 mm; CDI>

1.2

	Kujala、Tegner、Recurrent instability	IV	5 years	
WATANABE	MPFL、MPFL + TTO	29	13	autogenous hamstring tendon	No mentioned	Lysholm	IV	4 years	

Quality assessment

To assess the quality of the studies, we used the Coleman Methodology Score (CMS), [10] which assesses methodology using 10 criteria, giving a total score ranging between 0 and 100 points. A score of 100 indicates that the study largely avoids chance, various biases, and confounding factors. The final score can be defined as excellent (85 to 100 points), good (70 to 84 points), fair (50 to 69 points), or poor (<50 points). The Subsections that make up the CMS are based on the Subsections of the CONSORT statement (for randomized controlled trials) and are modified to allow for other trial designs. Each study has been scored by two reviewers (A, B) independently and in duplicate for each of the criteria adopted to give a total CMS between 0 and 100. Each author performed this procedure twice.

Statistical analysis

Continuous variables were reported by mean and standard deviation (SD). Non-continuous data such as the rate of recurrent instability were reported by frequencies and proportions. The post-operative Kujala scores, Lysholm scores and Tegner scores were used to calculate the mean differences and 95%CI. The post-operative rates of recurrent instability were used to calculate RR and 95%CI. For continuous data (Kujala scores, Lysholm scores and Tegner scores), mean and SD were estimated by the method by Hozo et al. [11] when median and range were reported.

The meta-analysis was implemented by Stata (Stata version 15.0). The software code for calculating was shown in Appendix. Heterogeneity was assessed by the I2 index. Thresholds were ‘‘low’’ for I2 values between 25% and 49%, ‘‘moderate’’ for I2 values between 50% and 74%, and ‘‘high’’ for I2 values above 75%. A fixed-effects model was applied for outcome data with low heterogeneity, whereas a random-effects model was used for outcome data. Z test [12] was used to compare the functional outcomes and the rate of recurrent instability between patients who underwent MPFLR, and those who underwent MPFLR + TTO. The details of Z test were shown in Supplemental Data File.

An Egger test were used to evaluate publication bias. And influence analysis was used to evaluate the effect of each study included on the whole effect. A significance threshold of a 0.05 was used for all statistical tests.

Results

The literature search identified 311 articles, of which 43 were found to be eligible for inclusion in the present systematic review and meta-analysis. The flow chart of literature search was shown in Fig. 1.

A total of 1952 patients were included, with an overall mean age of 20.3 years. The mean follow-up was 3.2 years. The following studies were included: Level I-3 [13–15], Level II-3 [16–18], Level III-6 [19–24] and Level IV-31 [25–39]. There was considerable risk of bias in most of the included studies. The majority of the studies were analyses of single-arm studies or comparative studies without randomization. This situation, however, is representative of the studied field. The details were shown in Supplemental Data File.

The MPFLR group comprised of 1508 patients. The MPFLR was usually performed using gracilis tendon or semitendinosus tendon as autograft or allograft. The MPFLR + TTO comprised of 444 patients. A tibial tuberosity distalization or a medialization of the tibial tuberosity was usually performed on patients.

Kujala score

At final follow-up, the mean Kujala scores in MPFLR and MPFLR + TTO were 89.04 and 84.44, respectively. There was significant difference in Kujala scores between MPFLR and MPFLR + TTO (MD = 4.60, 95%CI: 1.07–8.13; P = 0.01). The Heterogeneity I2 for MPFLR and MPFLR + TTO were 0.945 and 0.918. The details were shown in Tables 2 and 3. The forest plot of the combined effect value for Kujala scores was shown in Supplemental Data File. The Egger test showed a relatively low level of publication bias in studies included in our analysis. Influence analysis showed that 3 studies had an obvious effect on the whole effect size. The details were shown in Supplemental Data File.

Lysholm score

The mean Lysholm scores in MPFLR and MPFLR + TTO were 90.59 and 88.14, respectively. There was no significant difference in Lysholm scores between MPFLR and MPFLR + TTO (MD = 2.45, 95%CI: -3.20-8.10; P = 0.40). The Heterogeneity I2 for MPFLR and MPFLR + TTO was 0.856 and 0.975. The details were shown in Tables 2 and 3. The forest plot of the combined effect value for Lysholm scores was shown in Appendix 2. The Egger test showed a relatively low level of publication bias in studies included in our analysis. Influence analysis showed that 2 studies had an obvious effect on the whole effect size. The details were shown in Supplemental Data File.

Tegner score

The mean Tegner scores in MPFLR and MPFLR + TTO were 5.30 and 4.88, respectively. There was no significant difference in Tegner scores between MPFLR and MPFLR + TTO (MD = 0.42, 95%CI: -0.39-1.23; P = 0.31). The Heterogeneity I2 for MPFLR and MPFLR + TTO was 0.722 and 0.944. The details were shown in Tables 2 and 3. The forest plot of the combined effect value for Tegner scores was shown in Supplemental Data File. The Egger test showed a relatively low level of publication bias in studies included in our analysis. Influence analysis showed that one study had an obvious effect on the whole effect size. The details were shown in Supplemental Data File.

The functional outcomes after operation in MPFLR group and MPFLR + TTO group were very good. The Kujala scores indicated that the functional outcome in MPFLR group seemed to be better than those in MPFLR + TTO.

Recurrent instability rate

At final follow-up, the rates of recurrent instability in MPFLR and MPFLR + TTO were 3% and 4%, respectively. There was no significant difference in the rates between MPFLR and MPFLR + TTO (OR = 0.99, 95%CI: 0.96–1.02; P = 0.4848). The details were shown in Tables 3 and 4.

Table 3 Summary of combined effect value for MPFLR and MPFLR + TTO. Abbreviation: MPFLR, medial patellofemoral ligament reconstruction; TTO, tibial tubercle osteotomy; OR, odd ratio; MD, mean difference

Outcome	Subgroup	Number of studies included	Heterogeneity test ( I2 )	OR/MD ( 95%CI )	
Kujala	MPFLR	29	0.945	89.04 (87.39, 90.70)	
MPFLR + TTO	9	0.918	84.44 (81.05, 87.82)	
Lysholm	MPFLR	8	0.856	90.59 (88.27, 92.91)	
MPFLR + TTO	6	0.975	88.14 (82.98, 93.29)	
Tegner	MPFLR	9	0.722	5.30 (4.97, 5.64)	
MPFLR + TTO	5	0.944	4.88 (4.14, 5.61)	
Recurrent instability	MPFLR	15	0.333	0.03 (0.02, 0.05)	
MPFLR + TTO	6	0	0.04 (0.01, 0.06)	

Table 4 Comparison results of the combined effect value between MPFLR and MPFLR + TTO. Abbreviation: MPFLR, medial patellofemoral ligament reconstruction; TTO, tibial tubercle osteotomy; OR, odd ratio; MD, mean differ

Outcome	Comparison	OR/MD ( 95%CI )	Z value	P value	
Kujala	MPFLR vs. MPFLR + TTO	4.60 (1.07, 8.13)	2.55	0.01	
Lysholm	2.45 (-3.20, 8.10)	0.85	0.40	
Tegner	0.42 (-0.39, 1.23)	1.02	0.31	
Recurrent instability	0.99 (0.96 1.02)	0.69	0.48	

The forest plot of the combined effect value for recurrent instability rates was shown in Appendix 2. The Heterogeneity I2 for MPFLR and MPFLR + TTO was 0.333 and 0. The Egger test showed a relatively low level of publication bias in studies included in our analysis. Influence analysis showed that no study had an obvious effect on the whole effect size. This indicated MPFLR and MPFLR + TTO could maintain the joint stability well. The details were shown in Supplemental Data File.

Quality assessment

The mean value of the CMS score was 62 points, with a range from 42 to 84, showing that the mean quality of included study was fair. Significant difference was not found between the mean CMS value calculated by the two examiners.

Discussion

The most important findings of this study were: there was no significant difference in the rates of recurrent instability between MPFLR and MPFLR + TTO; The functional outcome in MPFLR group seemed to be better than those in MPFLR + TTO.

So far, only one meta-analysis [40] compared MPFLR with MPFLR + TTO in returning to sport using observative data, which indicated that returning to sport did not differ significantly in patients undergoing MPFLR versus MPFLR + TTO, and the most common complication was recurrent instability. What is more, two systematic reviews described MPFLR and MPFLR + TTO using observative data without calculating statistical difference, which were not convincing. One review [41] indicated that the outcomes of MPFL reconstruction with or without TTO treating recurrent or habitual patella dislocation with increased TT-TG distance appeared to be similar. The other review [42] indicated that the outcomes and risk profiles of MPFLR + TTO are similar to those of isolated MPFLR. The number of patients included in the above studies was small, and the largest was 930, while the number of patients included in this study was 2036, which was more convincing.

Furthermore, A recent randomized controlled trial of TTO + MPFLR versus TTO alone [14] indicated that there was no significant decrease in CDI of MPFLR, which means that MPFLR has little impact on CDI; There was significant decrease in CDI of MPFLR + TTO, which meant that MPFLR + TTO had great impact on CDI. CDI improvement from baseline, favoring MPFLR + TTO over MPFL, could be related to the improved patellofemoral tracking achieved by the biomechanical advantages added by TTO. However, the change in CDI did not seem to significantly increase stability. In this study, there was no significant difference in the rates of recurrent instability between MPFLR and MPFLR + TTO.

Except for recurrent instability, another potential complication after MPFLR should be carefully monitored and reported to patients, which are joint stiffness. The causes are multifactorial and will need to be analyzed carefully. Stiffness may be related to the soft tissue irritation due to the hardware and femoral tunnel mal-positioning. Some authors suggested that femoral mal-positioning led to over-constraint of the patella [43]. Because anterior and proximal mal-positioning were related with reduced flexion (≤ 120°), a significant correlation was observed between mal-positioning and a stiffness level of flexion (P<0.01). The majority of complication in MPFLR + TTO is fixation screws revision. The additional TTO supposedly increases the chances for tibial fracture and reoperation due to symptomatic hardware removal [44]. It is absolutely necessary to fully penetrate them into the bone and cover them by the medial retinaculum to avoid soft tissue irritation. Besides CDI and TT-TG, many studies have been conducted on patellar tilt. Damasena et al. demonstrated that isolated MPFLR could reduce patellar tilt [14]. Thomas Neri et al. confirmed these results, reporting a significant correlation between patellar tilt correction and functional score improvement [45]. The studies above indicated that MPFLR + TTO could improve the mal-tracking of patella. However, not all levels of mal-tracking seemed to contribute to recurrent instability. The relationship between the level of mal-tracking and recurrent instability needs to be explored by further study.

By this study, we can learn that MPFLR or MPFLR combined with TTO is an effective and reliable treatment in the setting of patellofemoral instability. Surgeons can counsel their patients that they can expect a ideal outcome after MPFLR alone or with TTO.

Limitations of this study were also determined by the quality of included studies which are not randomized trials but comparative or observative trials. This study was limited by the considerable heterogeneity, variety of techniques, variety of selection criterions for surgery (TT-TG distances, patella alta, and trochlear dysplasia) among the included studies. In clinical practice, considering that tibial tuberosity osteotomy is more beneficial for restoring patellar stress balance, surgeons tend to perform tibial tuberosity osteotomy for patients with TT-TG greater than 20 mm. At present, the follow-up time of the studies included in this research institute is still relatively short, and longer follow-up studies are needed to clarify the long-term effects of the two treatment methods. Even when acknowledging these limitations, this was the first study that allows a quantitative comparison between MPFLR and MPFLR + TTO procedures in functional outcomes and recurrent instability for patients with patellar instability, and Z test was used to calculate the statistical significance for the effect size between MPFLR and MPFLR + TTO. It is proposed that in future well-designed randomized studies with a precise pro-operative analysis and the adoption of new instability-related outcome measures were used for detecting the differences between MPFLR and MPFLR + TTO.

Conclusion

MPFLR seems to show a better performance in functional outcomes than MPFLR + TTO. Moreover, their rates of recurrent instability are very low, and no significant difference exists.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary Material 1: Appendix 1 The forest plot of the combined effect value for Kujala, Lysholm, Tegner scores and recurrent instability rates. Appendix 2 The Egger test for publication bias and the influence analysis for detecting the effect of each study on the whole effect value. Appendix 3 The formula of Z test and program code for single-arm continuous variables and binary variables

Acknowledgements

Not applicable.

Author contributions

G. L designed the study, P.S and L.Z wrote the main manuscript text and D.Y prepared the tables and figures. All authors reviewed the manuscript.

Funding

There was no funding for this study.

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Declarations

Ethical approval

Not applicable.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

The original version of this article was revised: the authors added the missing note for the co-first authors ‘†Peng Su and Dongying Yao are the co-first authors’.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Peng Su and Dongying Yao are the co-first authors.

Change history

9/13/2024

A Correction to this paper has been published: 10.1186/s12891-024-07847-7
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