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Table of Contents
Year : 2020  |  Volume : 22  |  Issue : 1  |  Page : 1-6

Factors affecting outcomes of injection laryngoplasty: A systematic review

1 Department of ENT, Al-Jaber Oto-Rhino-Laryngology and Ophthalmology Hospital, Ahsa, MOH, Saudi Arabia
2 Department of Family Medicine, King Fahad Hospital, Ahsa, MOH, Saudi Arabia

Date of Submission04-Nov-2019
Date of Decision19-Nov-2019
Date of Acceptance15-Dec-2019
Date of Web Publication01-Jun-2020

Correspondence Address:
Dr. Isra Ali Al-Jazeeri
Department of ENT, Al-Jaber Oto-Rhino-Laryngology and Ophthalmology Hospital, MOH
Saudi Arabia
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/SJOH.SJOH_17_19

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Vocal cord palsy is a common reason for visiting an otolaryngologist. In cases of unilateral involvement, patients primarily present with recurrent choking and aspiration, breathy voice, and inability to perform the Valsalva maneuver. Injection laryngoplasty (IL) is one of the least invasive and promising lines of treatment for unilateral vocal cord palsy (UVCP). The present study identified the existing evidence on factors that may affect the voice and swallowing outcomes of IL in adult patients with UVCP. This review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and PRISMA checklist. The U.S. National Library of Medicine (PubMed) database was searched for studies on UVCP managed with IL. Sixteen articles investigated six distinct factors that affected the outcomes of IL. These six factors include early intervention, the approach used for injection, the degree of the posterior glottic gap, the number of irregular peaks, previous radiation therapy history, and the material used for injection.: This review is the first study to investigate all of the possible factors that affect IL. This review found six distinct factors that affected the outcomes of IL. Each of the retrieved studies investigated a different factor without considering the confounding effect of the other factors. This review guides future research for the development of a much more structured protocol to elucidate the weight of each factor in affecting outcomes.

Keywords: Injection laryngoplasty, unilateral vocal cord palsy, vocal cord paralysis

How to cite this article:
Al-Jazeeri IA, Al-Jazeeri HA. Factors affecting outcomes of injection laryngoplasty: A systematic review. Saudi J Otorhinolaryngol Head Neck Surg 2020;22:1-6

How to cite this URL:
Al-Jazeeri IA, Al-Jazeeri HA. Factors affecting outcomes of injection laryngoplasty: A systematic review. Saudi J Otorhinolaryngol Head Neck Surg [serial online] 2020 [cited 2023 Mar 27];22:1-6. Available from: https://www.sjohns.org/text.asp?2020/22/1/1/285552

  Introduction Top

Most otolaryngologists encounter patients with unilateral vocal cord palsy (UVCP) on a regular basis in the clinic. Unilateral vocal cord paralysis is a clinical finding that may be caused by various pathological conditions that affect the vagus nerve or the recurrent laryngeal nerve throughout their course from the medulla to the neck and mediastinum. Patients with UVCP typically present with hoarseness of voice or aspiration.

When conservative measures are not sufficient to control the patient's symptoms, surgical interventions may be used. There are four main techniques to surgically manage UVCP, including injection laryngoplasty (IL), medialization thyroplasty (MT), arytenoid adduction, and laryngeal reinnervation. There is no evidence to suggest the superiority of any of these interventions over others with regard to voice and swallowing outcomes.[1] The ability to perform IL in the office setting makes IL a preferable intervention. IL is a time- and cost-saving technique that is simpler and requires a shorter learning curve compared to the other interventions.

Knowledge of which patients will most likely benefit from IL remains challenging. The prediction of the outcome helps the early detection of patients who are least likely to benefit from IL, and earlier use of other methods is encouraged in these cases. Another benefit of having knowledge of the factors that favor a better outcome is being able to determine more optimal conditions when choosing IL to obtain the greatest benefit of this intervention. The other goal of this review is to detect the potential favoring factors that require further studies to guide future research.

  Methods Top

This review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and PRISMA checklist.[2]

The U.S. National Library of Medicine (PubMed) database was searched. The search was performed on articles published from January 1, 1990, to January 1, 2019. The following search terms were included: “ unilateral,” “vocal cord,” “ vocal fold” “paralysis,” “ dysfunction,” “immobility,” “injection,” and “laryngoplasty.”

Selection criteria

Two reviewers (J.I. and J.H.) independently screened the abstracts for inclusion and exclusion criteria. The inter-reviewer agreement was assessed using Cohen's Kappa score, and any discrepancies were resolved through consensus.

Inclusion criteria

  1. The study design was a controlled trial or observational study, including a case series
  2. The articles were published from January 1, 1990, to January 1, 2019 1
  3. Adult patients aged ≥18 years were studied
  4. Both genders were included
  5. Studies that included patients diagnosed with UVCP
  6. Studies that included patients treated with IL
  7. Studies that included voice or swallowing outcomes
  8. Studies that included a control group defined as patients with UVCP who underwent other surgical interventions or who were managed with conservative management
  9. The outcome included at least 1 month of follow-up
  10. Studies published in English.

Exclusion criteria

  1. Studies that included patients with bilateral vocal cord palsy
  2. Studies that included associated pathologies of the vocal cords other than immobility
  3. Studies that only included children
  4. Studies that lacked voice or swallowing outcomes
  5. Studies that reported outcomes for the presence of an affecting factor without a comparison group
  6. Animal and cadaver studies
  7. Duplicate studies and studies that used the same data set
  8. Review articles
  9. Case reports
  10. The full article was not available.

Assessment of quality and risk of bias

The quality of the included studies was evaluated using the Newcastle–Ottawa Scale (NCO) for observational studies.[3] The risk of bias for clinical trials was evaluated using the standard criteria outlined by the Cochrane Collaboration.[4]

Statistical analysis of data was performed using IBM SPSS Statistics version 22 (IBM Corp., Armonk, NY). and Review Manager (RevMan) software version 5.3 (Nordic Cochrane Centre, Cochrane Collaboration, 2011, Copenhagen, Denmark). Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014. The significance value was set at P < 0.05.

  Results Top

A total of 1627 articles were retrieved using the search strategy. After screening the abstracts, 96 articles were chosen for full-text assessment. Sixteen articles met all of the inclusion and exclusion criteria. Cohen's kappa for the inter-reviewer agreement was 0.95.

Six main factors affected the outcomes of IL, including early intervention, the approach used for injection, degree of the posterior glottic gap, number of irregular peaks, previous radiation therapy history, and the material used for injection [Figure 1].
Figure 1: Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart

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The outcome measures found may be described as primary and secondary. Primary voice outcome was described using subjective measures (voice handicap index [VHI], voice-related quality of life, and the laryngeal stroboscopic finding) and objective measures (acoustics, including jitter, shimmer, and noise-to-harmonic ratio and aerodynamics, including mean phonation time). Secondary voice outcomes were the need for additional intervention, including a second injection or framework surgery. The primary swallowing outcome included the subjective ability to tolerate an oral diet and the objective flexible endoscopic evaluation of swallowing. The secondary swallowing outcome was the same as the secondary voice outcome and was described as a need for additional intervention.

  Discussion Top


Five main approaches were described: direct laryngoscopic approach, transoral and transcutaneous approaches, transthyrohyoid, transcricothyroid, or transcartilaginous.

All of the approaches may be performed under local anesthesia in awake patients as office-based procedures, except the direct laryngoscopic approach, which is performed under general anesthesia. Although the laryngoscopic approach provides far better visualization and control, it produces comparable results to the office-based procedures described by Bovs et al.[5] and Mathison et al.[6] This comparability makes the office-based approaches a more reasonable choice when possible because of time and cost-effectiveness.

Woo et al.[7] studied the differences between the thyrohyoid and cricothyroid approaches and found that both techniques significantly improved subjective and objective voice outcomes, with comparable VHI. The thyrohyoid approach produced better voice outcomes, especially in stroboscopic findings. This difference is likely due to the better visualization and precision of the thyrohyoid approach.[7]

Chun et al.[8] proposed the introduction of the needle using a contralateral paramedian approach to improve the visualization of the computed tomography approach.

Clary et al.[9] recently suggested the use of an introducer needle through the thyroid notch and the advancing of a spinal needle through this route. This proposed approach will likely provide better precision by allowing flexibility to the movement. The introducer needle may move laterally or medially, and the spinal needle may move in an anterior to posterior direction. This study describes 21 patients who underwent IL using this technique.[9]

Early intervention

Conventionally, physicians used a period of conservative management for UVCP from 9 months to 1 year to allow for spontaneous recovery.[10] The recent trend is toward the early intervention. Most of the studies defined early intervention as < 6 months and suggested that early IL was more beneficial than late IL in preventing the need for ML.

[Table 1] summarizes the articles that study the effect of early intervention on the outcome of the IL. All of these articles suggest better outcomes when IL is performed earlier, except for Fang et al.[13] who did not find any difference between early and late IL. Pei et al.[14] has supported this conclusion with a very high level of evidence in a randomized controlled trial. [Figure 2]. Four studies were appropriate for a meta-analysis, with a similar outcome measurement of the need for ML. Vila et al.[19] performed a systematic review and meta-analysis on the same studies. They used the I [2] statistic to evaluate heterogeneity, which was moderate. No evidence of publication bias was found using the forest plot. They found that patients who did not receive early IL were four times more likely to need a permanent ML. Vila et al.[19] concluded that, with Grade C evidence, early IL was recommended within 6 months of diagnosis for adults with UVCP.
Table 1: Summery of the articles that study the effect of early intervention on injection laryngoplasty outcome

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Figure 2: Pei et al. risk of bias assessment

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Posterior glottic gap

Aspiration and dysphonia are the two main complaints in patients with UVCP. The posterior glottic gap affects swallowing more than the anterior part of the glottic gap. The voice is affected more with the anterior glottic gap over the vibrating part.

Mor et al.[18] found that aspiration was highly predictive of the ultimate need for an MT. However, poor voice quality was not correlated to the need for MT.[18]

This result is logical because IL will not address the posterior part of the glottic opening between the arytenoids, which is more anatomically important for the occurrence of aspiration.

Fang et al.[13] studied the effect of the posterior glottic gap in predicting the success of IL using the need for permanent framework surgery. They examined a prospective cohort of 42 cases. The glottic gap was described as normalized glottal gap area (NGGA) using image processing computer software (Image J 1.44p National Institutes of Health, Bethesda, Md) and the method proposed by Omori et al.[20] Multivariate logistic regression analysis revealed that the NGGA was the only statistically significant (P = 0.010) predictor of permanent framework surgery when early IL (within 6 months) was used.[13]

Choi et al.[21] found that the posterior glottic gap was one of only two factors that increased the odds of improvement. This study included 59 patients. The glottic gap was determined using stroboscopic imaging and manual measurement of the distance between the medial sides of the vocal process divided by the width to the midpoint of the membranous vocal fold on the normal side. The glottic gap was defined as small when it was less than half of the normal vocal fold width.[21]

Number of irregular peaks

The number of irregular peaks is a new voice quality indicator that was introduced by Tsou et al.[22] in 2016 as a predictor for IL failure. Failure was defined as the recurrence of nonrecoverable hoarseness and the need for revision IL or ML 6 months after the initial IL. A significant difference (P< 0.05) in the grade, roughness, breathiness, asthenia, strain (GRBAS), aerodynamics, and acoustic was found between the preinjection and postinjection measures. The NCO score for this study was 8/8. However, the study population was very small (n = 9 for success and n = 8 for failure groups), and hence, it is insufficient to draw a conclusion. Other studies to confirm the reliability and validity of this proposed indicator are required.

Radiation versus no radiation

Two studies that compared the effect of previous radiation therapy on the success of IL were found [Table 2]. Both studies found decreased success in cases where the patient had received radiotherapy to the neck.
Table 2: Summery of the articles studying the effect of radiation on injection laryngoplasty outcome

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Both articles found a relationship between the history of radiation and poor outcome. Chang et al.[23] used a small sample size (n = 9) and concluded that the outcome was poorer in irradiated patients despite its efficacy when the outcome was defined as the interval until an additional intervention was needed.

Mor et al.[18] chose the need for framework surgery as the outcome for the success of IL. This outcome measure may cause selection bias because MT is generally avoided in cases of the previous radiation due to higher rates of complications.[24],[25] Despite this selection bias, there were more irradiated patients who needed MT than nonirradiated patients. This result means that the difference in outcome may be even larger than reported.

Material used

A variety of injectable materials were effective and used for IL, including calcium hydroxyapatite,[7],[26],[27] hyaluronic acid,[14],[28],[29],[30] autologous fat,[31],[32],[33] collagen-based products,[30],[34] polyacrylamide hydrogel,[35] autologous fascia,[36],[37],[38] and polydimethylsiloxane.[39],[40]

Despite the presence of numerous materials that exhibit different properties, the choice of material for IL is one of the poorly studied factors. There is no evidence to support the superiority of any of these materials.


The observational nature of the studies included in this review is one of the largest and unavoidable inherent limitations. It leads to selection bias and confounding effect, and it prevents strong conclusions of causal relationships.

The diverse nature of outcome measures and the fact that every author used a different set of outcome measures made it difficult to compare some of the studies. Whether the objective measures represent subjective improvement by the patients is not well known.

One of the major questionable outcomes is the need for additional therapeutic measures, including MT. None of the studies that included this outcome mentioned the possible bias of patient refusal. As IL may be performed in multiple sessions over a long period of time and produce unsatisfactory results, it is rational for patients to cope with their condition and refuse to undergo yet another presumably unsuccessful intervention.

The present review noted that most of the included studies did not document the ease of the procedure or patient acceptance. There was also limited mention of the complications encountered.

  Conclusion and Implications for Practice and Research Top

The present review identified six factors that affected voice outcomes in an adult patient undergoing IL.

  • There is sufficient evidence that early IL (earlier than 6 months) decreases the need for MT
  • There is fair evidence suggesting that more posterior glottic gaps reduce the likelihood of success and increase the need for subsequent surgical framework surgery
  • There is no sufficient evidence to support that the number of irregular peaks, a previous history of radiation, the approach used, or the choice of injectable material affects the results of IL.

The present exploratory review identified the shortcomings in the understanding of IL and identified factors that affect its outcome. These results provide numerous opportunities for future research, which should be performed considering the items included within the limitations section of this review.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2]

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