Assessing the Outcomes Associated with Accessory Navicular Bone Surgery—a Systematic Review

Abstract

Purpose of Review

The purpose of this review is to evaluate the existing literature in order to compare the clinical outcomes and complications associated with the kidner procedure and simple excision procedure. Furthermore, this review will help determine if one procedure is advantageous over the other in treating accessory navicular among patients.

Recent Findings

Previous research on this topic has seen a low success rate in treating patients with symptomatic accessory navicular using conservative treatment options such as shoe-wear modification, braces, and/or nonsteroidal anti-inflammatory. Surgical treatment such as simple excision and kidner procedure has shown to have minor complications including scarring and wound irritation with a generally high satisfaction rate from patients. However, cases where patients that had planovalgus or hindfoot valgus accompanying the accessory navicular were required to undergo revision surgery to treat the recurrent pain following the kidner procedure. Similarly, patients that underwent simple excision procedure with having flat foot were unable to complete the heel test postoperatively despite not reporting feelings of pain.

Summary

Both simple excision and the Kidner procedure appear to be efficacious procedures with low complication profiles and high rates of patient satisfaction. Moreover, it has appeared that the female demographic is more likely to present symptomatic accessory navicular and undergo surgical treatment. To further explore the ideal indication for each, more prospective comparative studies are needed as well as radiological assessments pre- and post-operatively to evaluate anatomical changes in the posterior tibialis tendon area between both procedures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12178-022-09772-5.

Introduction

The accessory navicular bone is a supernumerary bone in the foot, first discovered by Bahuin in 1605 [1, 2]. The accessory navicular bone is described to be an anatomical variant present in 4 to 21% of the human population and can be further classified into three subtypes [2]. Type I is a small round ossicle that is embedded within the posterior tibial tendon [3]. Type II is a triangular-shaped ossicle connected to the navicular tuberosity by a synchondrosis [3]. Type III is an enlarged medial horn of the navicular which is referred to as a cornuate navicular [3]. This accessory bone can be asymptomatic for certain individuals, yet it has the potential to become symptomatic in others. Some of the conservative treatments available for symptomatic accessory navicular includes nonsteroidal anti-inflammatory medication, shoe-wear modification, braces, custom orthotics, and steroid injections [1]. Initial treatment for the accessory navicular consists of the aforementioned nonoperative therapy. In recalcitrant cases failing conservative management, surgery can then be considered [1]. Surgeons may perform a simple excision of the accessory navicular or perform a Kidner procedure, which consists of excising the accessory navicular with an additional step of relocating the posterior tibialis tendon to the undersurface of the navicular bone [4, 5]. Although the Kidner and simple excision surgical procedures are commonly used as surgical methods to treat symptomatic accessory naviculars, there are currently no systematic reviews that outline and collate the associated complications from past literature. This systematic review aims to compile clinical outcomes and notable complications that arise from both the Kidner procedure and simple excision surgical techniques. The primary hypothesis was that the postoperative outcomes would be similar between the two surgical procedures. The secondary hypothesis was that the complication rates would be relatively low in both procedures.

Material and Methods

Search Strategy

Search terms were first compiled in accordance to the topic of this review which were constructed to be comprehensive and inclusive of the surgical topics and key terms associated with symptomatic accessory navicular and are reported in Supplemental Table 1. The search was conducted on Ovid EMBASE and MEDLINE (including Epub Ahead of Print). The purpose, research question, and eligibility criteria for the search were determined a priori. The eligibility criteria of the review are presented in Table 1. The search terms were linked with appropriate truncations and proximity operators to generalize the search results Supplemental Table 1. Search results included literature on the topic from data inception to January 2021 and the results were approved by the senior author. Key articles identified prior to the search were also identified within the search results. A gray literature search was conducted using the POSNA (Paediatric Orthopedic Society of North America) search engine.

Table 1.

Eligibility criteria

Inclusion criteria	Exclusion criteria
Kidner Procedure for Type 1/2/3 Accessory Navicular Bone	Surgical procedures that utilize hardware
Excision of Type 1/2/3 Accessory Navicular Bone	Arthrodesis of Type 2/3 Accessory Navicular Bone
Concomitant with pes planus (flat foot)	Non-surgical treatment
Clinical Outcomes reported	Review articles, technical papers
	Any concomitant issues other than pes planus (flat foot)

Study Screening

The systematic screening approach was completed in accordance with the PRISMA (Preferred Reporting Items for Systematic Review and Meta-analyses) criteria from title to full text screening. Title to full text screening was completed by two reviewers in duplicates using Rayyan [6]. Screening was completed in accordance with the eligibility criteria. Any conflicts in decision at the title and abstract screening were automatically included to the full-text screening stage. Conflict raised in the full-text screening was resolved with input from a senior author.

Quality Assessment

Included articles of this review underwent a quality assessment using the Methodological Index for Non-Randomized Studies (MINORS) that contain 12 items of assessments [7]. The first 8 items are directed for non-comparative studies and the total 12 items were assessed for comparative studies. Each item of assessment is scored using a 3-point scale of 0-2. The maximum score for non-comparative and comparative studies are 16 and 24, respectively. Scoring of the literature was done in duplicates and conflicts in scoring was resolved through discussion amongst the reviewers and the senior author. As there is no established MINORS score categorization, the scores were categorized a priori. For non-comparative studies, a score of 0–5 was considered poor quality, a score of 6–10 was considered fair quality, and a score of 11–16 was considered excellent quality. For comparative studies, a score of 0–12 was considered poor quality, a score of 13–18 was considered fair quality, and a score of 19–24 was considered excellent quality.

Data Abstraction and Statistical Analysis

Data abstraction was completed independently and collected using the collaborative features on Google Documents. Data points were randomly verified by the second reviewer and any conflicts in regards to the data or decision were discussed in collaboration with the reviewers and senior researcher. Inter-reviewer agreement was calculated at each stage of screening and during quality assessment, and reported with a Kappa (k) statistic. Agreement was categorized a priori as follows: ⩽0.20: poor, 0.21–0.40: fair, 0.41–0.60: moderate, 0.61–0.80: substantial, and 0.81–0.99: excellent [8].

Results

Study Characteristics

Throughout each screening stage; title/abstract, full-text and MINORS, there was substantial agreement amongst reviewers with kappa scores of .802, .775, and 0.852, respectively. Of the 316 papers identified from our search strategy, 14 of the studies met the inclusion criteria (Fig. 1). One additional paper was identified manually and was included for this review [9••]. Of these 15 papers, there were 8 retrospective cohort studies, 2 prospective cohort studies, and 5 case series/reports (Tables 2 and 3).

Fig. 1.

Prisma flow diagram

Table 2.

Study characteristics kidner group

Author	Title	Study Design	Study Location	Mean Age (Years)	Mean Follow-up (Years)
Zeng G. et al.,	Comparison of outcomes of arthrodesis and reconstruction (advancement), posterior tibial tendon with excision of accessory tarsal navicular bone (Kidner procedure) in type 2 accessory navicular	Retrospective cohort	China	16.6	Not Reported
Ray S.; Goldberg V.M.;	Surgical treatment of the accessory navicular	Case series	USA	17.3	4.5
Pretell-Mazzini, Juan et al.,	Surgical treatment of symptomatic accessory navicular in children and adolescents.	Case series	USA	13.2	Not Reported
Prichasuk S.; Sinphurmsukskul O.;	Kidner procedure for symptomatic accessory navicular and its relation to pes planus	Case series	USA	23.3	3.2
Dawson et al.,	Modified kidner procedure utilizing a Mitek bone anchor	Retrospective	USA	38.4	1.1
Cha et al.,	Simple excision vs the Kidner procedure for type 2 accessory navicular associated with flatfoot in pediatric population	Prospective	South Korea	12.6	3.2
Macnicol, M.F, Voutsinas, S	Surgical treatment of the symptomatic accessory navicular	Retrospective	USA	Not Reported	10
Choi et al.,	Revision Surgery for Recurrent Pain after Excision of the Accessory Navicular and Relocation of the Tibilais posterior Tendon	Retrospective cohort	Korea	27.5	12

Table 3.

Study characteristics simple excision group

Author	Title	Study Design	Study Location	Mean Age (Years)	Mean Follow Up (Years)
Pretell-Mazzini, Juan et al.,	Surgical treatment of symptomatic accessory navicular in children and adolescents.	Case series	USA	13.2	Not Reported
Jasiewicz B. et al.,	Results of simple excision technique in the surgical treatment of symptomatic accessory navicular bones	Retrospective cohort	USA	14.1	5.6
Kopp F.J.; Marcus R.E.;	Clinical Outcome of Surgical Treatment of the Symptomatic Accessory Navicular	Retrospective cohort	USA	28.2	8.61
Kiter E. et al.,	Evaluation of simple excision in the treatment of symptomatic accessory navicular associated with flat feet	Retrospective cohort	USA	28	3
Smith, Teresa Riemer	Management of dancers with symptomatic accessory navicular: 2 case reports.	Case Report	USA	11	0.2
Micheli et al.,	Treatment of painful accessory navicular: a modification to simple excision	Prospective	USA	13.5	7.2
Cha et al.,	Simple excision vs the Kidner procedure for type 2 accessory navicular associated with flatfoot in pediatric population	Prospective	South Korea	11.3	3.21
Macnicol, M.F, Voutsinas, S	Surgical treatment of the symptomatic accessory navicular	Retrospective	USA	Not Reported	12
Bennett et al.,	Surgical Treatment of Symptomatic Accessory Tarsal Navicular	Retrospective	USA	12.6	10.2
Boni Rietveld et al.,	Surgical Treatment of the Accessory Navicular (Os Tibiale Externum) in Dancers: A Retrospective Case Series	Case Series	Netherlands	17.2	4.7

Quality Assessment

The mean MINORS score for these studies is a 9.07, indicating poor quality.

Patient Demographics

This review analyzed a total of 280 patients, of whom 58% (n=164) had undergone the simple excision procedure and 41% (n= 116) had undergone the Kidner procedure. Furthermore, there were 2 studies that reported their sample size in feet rather than number of participants [10, 11]. Amongst these studies, 14 feet were operated on using the simple excision procedure and 18 feets were operated on using the Kidner procedure. Of the studies that reported age, the mean age for the simple excision and Kidner procedure was 16.06 ± 7.12 years (n= 143) and 18.92 ± 5.92 years (n= 84), respectively. Sex was documented amongst 264 patients in which the simple excision procedure group contained 34% male patients (56/164), and the Kidner procedure group contained 35% male patients (35/100) (Table 4).

Table 4.

Patient demographics

	Simple excision procedure	Kidner procedure
Sample Size	164	116
Sample Size in feeta	14	18
Mean age SD (years)	16.06 ± 7.12 (of n=143 reporting)	18.92 ± 5.92 (of n=84 reporting)
Male Participants	56/164 (34.14%)	35/100 (35%)
Type I AN	0 (of n= 47 reporting)	0 (of n=63 reporting)
Type II AN	47 (of n= 47 reporting)	63 (of n=63 reporting)
Type III AN	0 (of n= 47 reporting)	0 (of n=63 reporting)
Type I AN in feeta	9 (of n= 85 reporting)	3 (of n=57 reporting)
Type II AN in feet	60 (of n= 85 reporting)	52 (of n=57 reporting)
Type III AN in feeta	16 (of n= 85 reporting)	2 (of n=57 reporting)

^aRow is dedicated for studies that reported population in terms of feet rather than number of participants

Nine out of 15 papers included in this study reported the specific type of accessory navicular that was operated on in their respective procedures [5, 12–16]. Five out of the nine studies reported their accessory navicular classifications by the number of patients rather than individual feet; with 47 and 63 patients having type II accessory navicular for the simple excision and Kidner procedure groups, respectively [5, 12–16]. The remaining four papers reported the type of accessory navicular that was operated on by individual feet. Of the accessory naviculars operated on in the simple excision group (n=85 feet), 10% were type I, 70% type II, and 19% type III [4, 17, 18]. Of the accessory naviculars operated on in the Kidner procedure group (n= 57 feet), 5% were type I, 91% were type II, and 4% type III (Table 4) [17, 18].

Clinical Outcomes

Clinical outcomes were organized in three categories according to pain levels and the ability to conduct activities post operatively. Patients that reported no pain, were able to return to daily activities without difficulties, and no footwear problems were ranked as excellent. Patients that reported mild levels of pain, no restriction of activity, and/or plus and minus and footwear modification were ranked as moderate. Patients that reported moderate levels of pain with restriction in activity and/or plus and minus and footwear modification were ranked as poor.

Individuals that underwent the Kidner procedure ranked their postoperative outcomes on a rating of excellent, moderate or poor. It should be noted that certain papers only reported postoperative outcomes per foot rather than per patient; these were appropriately separated from the data pool. The Kidner procedure postoperative outcomes were reported as 58% excellent, 27% moderate, and 13% poor (Table 5). Of the papers that reported Kidner procedure outcomes per foot they were reported as 46% excellent, 46% moderate, and 8% poor (Table 5). Of the five papers that reported their mean follow up with Kidner procedure patients it was reported as 3.35 years (SD=4.4) [5, 10, 11, 15, 18].

Table 5.

Clinical outcomes

	Excellent %	Moderate %	Poor %
Kidner Patients n= 101	58.42	27.72	13.86
Kidner Feet n= 37a	45.95	45.95	8.11
Simple Excision Patients n= 136	80.15	17.65	2.21
Simple Excision Feet n= 41a	92.68	4.88	2.44

^aRow is dedicated for studies that reported outcomes in terms of feet rather than patients

Individuals undergoing the simple excision procedure ranked their postoperative outcomes on a rating of excellent, moderate or poor. It should be noted that certain papers only reported postoperative outcomes per foot rather than per patient; these were appropriately separated from the data pool. The simple excision postoperative outcomes were reported as 80% excellent, 18% moderate, and 2% poor (Table 5). Of the papers that reported simple excision outcomes per foot they were reported as 93% excellent, 5% moderate, and 2% poor (Table 5). Of the nine papers that reported their mean follow up with simple excision procedure patients it was reported as 5.91 years (SD=3.68) [4, 13–16, 18–21].

Simple Excision Complications

The paper by Kiter et al. shows the importance of clinical evaluation of the posterior tibialis tendon to assess the success of the procedure which was seen in the group of patients that had flat foot and accessory navicular. 5/7 of patients who reported excellent (no pain, no restriction of activity) and 3/5 patients that reported good (minor shoewear modification had difficulty performing the single heal test pre- and post-operatively [14]. On the basis of these results, the authors concluded that the simple excision procedure may not be appropriate for patients with flat foot and accessory navicular syndrome [14].

Ten patients that underwent the simple excision procedure experienced residual enlargement in the region of the resected accessory tarsal navicular. It should be noted that this complication was isolated to a single study and was not observed in any other studies (Table 6) [21]. Additionally, five other individuals reported complications with scarring post-operatively. Two patients reported sensitive scars, two patients reported painful scars, and one patient developed a keloid scar.

Table 6.

Complications

Complication	Kidner	Simple excision
Wound Infection	1	0
Sensitive Scars	0	2
Painful Scar	0	2
Keloid Scar	0	1
Tibial Tendonitis	2	1
Residual Enlargementa	0	10
Recurrent Painb	9	0

^aIsolated to a single study (Bennet et al.,)

^bIsolated to a single study (Choi et al.,)

Kidner Procedure Complications

Choi and Lee completed a review of clinical outcomes for 9 patients that had undergone revision surgery after experiencing persistent pain after kidner procedure. For the revision surgery, physicians either performed tibialis posterior (TP) advancement (4 cases), TP Lengthening (4 cases), or Flexor digitorum longus (FDL) (1 case) [9••]. After the revision surgery, all patients were able to now perform the heel test, and improvement in all patients in the AOFAS score, VAS, radiographics parameters [9••]. Furthermore, all the patients in this study had either planovalgus or hindfoot valgus which lead the authors to suspect that both planovalgus and hindfoot valgus deformities are associated with recurrent pain after kidner procedure as it can induce tension on the TP tendon leading to pain and atrophy of the tendon [9••].

Other complications associated with the kidner procedure were tibial tendonitis amongst two patients and a superficial wound infection acquired by one patient.

Overall, surgical reoperation rates were low amongst both Kidner and simple excision procedure groups with thirteen and two patients requiring a second surgery, respectively.

Radiological Assessment

Plain radiographs are the first modality used in assessment of accessory navicular foot pain. Standard anteroposterior, lateral and 45 eversion oblique views are used to determine the type of the accessory navicular and the presence of synchondrosis [1]. Bone scintigraphy is not the best modality for diagnosing a symptomatic accessory navicular as it has 100% sensitivity and 50% specificity. The clinical presentation and physical examination can confirm symptomatic accessory navicular [16]. MRI and ultrasound has a role for assessment of tibialis posterior dysfunction [1].

Gang Zeng et al. did a study comparing the pre- and post- operative radiological indices between kidner procedure group and arthrodesis procedure group. The indices included the calcaneal pitch angle, the talocalcaneal coverage angel and the lateral talo-first metatarsal angle [12]. They concluded that calcaneal pitch angle increased postoperatively in both groups [12]. The talocalcaneal coverage angle and the lateral talo-first metatarsal angle showed no significant changes after surgery and there is no significant difference in postoperative radiological indices between kidner procedure and arthrodesis procedure [12].

The paper by Cha et al. provided a detailed radiological assessment pre- and postoperatively between patients that underwent either the simple excision or kidner procedure. In their assessment they had found the calcaneal pitch angle to improve in both procedures, while no significant changes were seen when measuring the talo-first metatarsal and talocalcaneal angles [15]. Moreover, in the final follow-up, there were no significant changes in the talo–first metatarsal angle, talocalcaneal angle, or calcaneal pitch angle between the two procedures [15].

Discussion

The results of this systematic review demonstrate that both the Kidner and simple excision procedures for treatment of the symptomatic accessory navicular yield low complication rates. Both the primary and secondary hypotheses were confirmed, as both procedures yielded similar high rates of patient satisfaction alongside low complication rates. Included sample sizes were relatively low and the majority of studies being retrospective cohort studies.

Although the findings of this systematic review purport the relative safety and efficacy of surgical excision of the accessory navicular, it is important to note that all included studies managed patients conservatively prior to surgical excision. Shoewear and activity modification to offload the medial foot, as well as non-steroidal anti-inflammatories, are considered first-line [22•]. However, a 2019 study by Wynn et al. that examined 169 patients with symptomatic accessory naviculae found that only 28% experienced complete pain relief following an average of 8 months of nonoperative treatment. 30% of the patient sample in that study progressed to surgical intervention, failing conservative management [22•].

Our review also confirms the epidemiologic findings of Knapik et al. and other authors; that females have a propensity to undergo surgical management of the accessory navicular and are also more likely to present with symptomatic accessory naviculae [23••]. In our review, females comprised 65% of excision patients and 73% of Kidner patients.

Complications reported by the included studies were mild, ranging from superficial infection to scarring and wound irritation, with an incidence of complications collectively at 18/250 (7.2%) excluding a single study reporting residual enlargement [21]. We did note that complications related to scarring were all reported in the simple excision group, whereas infection complications were reported secondary to the Kidner procedure. We speculate this may be related to longer surgical time required for the Kidner procedure, although this is not reported and there is insufficient data to make this conclusion.

The reoperation rate for both procedures was relatively low with thirteen reoperations from the Kidner group and two from the Simple excision groups. Three of the reoperations in the Kidner group and one reoperation from the Simple Excision group did not report what the reoperation was for [17]. A patient that required reoperation from the Kidner group developed mid foot pain in their daily activities following the initial surgery. Radiographs of the patient revealed that the suture anchor screw used for the relocation of the posterior tibialis tendon penetrated the navicular joint surface, resulting in the need for talonavicular fusion surgery 15 months later [12]. A patient from the simple excision group underwent reoperation due to the development of medial midfoot pain a few months after the initial surgery. Radiographs of the patient revealed an osseous spur under the navicular bone. The origin of the spur was unknown and was excised from the patient 1 year after the initial surgery [13]. Nine patients underwent reoperation from the Kidner group due to recurrent pain and were treated with MDCO and LCL procedures [9••].

The distribution of Types 1/2/3 naviculars appeared to be even between both the Kidner and simple excision procedures and we did not note any trend or justification for choice in procedure based on the type of accessory navicular.

Limitations of this study include small sample size, inconsistent reporting of outcomes and dissimilar patient reported outcome scores, as well as relatively low-quality studies. Furthermore, the studies included in this review were inconsistent in the method they reported outcomes, as certain papers reported per patient and others per foot. The included papers were mostly retrospective or case series studies, with only two of the included studies being prospective in nature. However, this paper is the first systematic review of outcomes and complications for surgical management of the accessory navicular to date, with follow-up for the Kidner procedure over 3 years, and for simple excision, over 5 years. This paper highlights a relatively low complication rate and profile yet does draw attention to a dearth of high quality prospective evidence to assist clinicians in determining the ideal procedure for patients failing. It should also be noted that papers that reported complications that were associated with the surgery did not report detailed explanations of the origin of complication nor treatment of the complications. Moreover, it is encouraged that future studies conduct radiological assessment using an MRI or ultrasound pre- and post-operatively to highlight anatomical changes in the posterior tibialis tendon area. These images can assist clinicians to assess the level of dysfunction in the posterior tibialis tendon and make decisions accordingly in regards to treatment.

Conclusion

Ultimately, in the case of failure of conservative management, both simple excision and the Kidner procedure appear to be efficacious procedures with low complication profiles. To further explore the ideal indication for each, more prospective comparative studies are needed. Furthermore, it would be beneficial to delve into the postoperative treatments that arose from the surgical procedures.

Declarations

Conflict of Interest

The authors have no financial or proprietary interest in any material discussed in this article.