Introduction

Foot surgery has greatly developed over the past two decades. Continuous effort in understanding the anatomy and biomechanics of foot with technological advancement and growing social needs has facilitated newer innovations. Digital deformities are the commonest forefoot presentation to the foot and ankle clinic [1]. Among the common digital deformities, Hallux Valgus (HV) has long been an area of interest to the foot and ankle surgeons. The complex multifactorial nature and biomechanical dysfunction have resulted in numerous surgical correction techniques [2-4].

Minimal invasive HV surgery is one of the greatest advances in operating field of orthopedic. Advantages like short operating time, quicker recovery, reduced hospital stay and fewer complications compare to traditional open surgeries contributed to diversity. Invention of new techniques and modification of existing techniques have changed the operating principle of HV surgery. Despite all of the available minimal invasive techniques on correction of HV, scientific validation of the safety and efficacy of these techniques is still inconclusive. Previously published systematic reviews by Maffulli et al. [5], Roukis [1] National Institute for Clinical Excellence (NICE) guidelines and Trnka [1,5- 7] have well identified the limitations of the available evidence to determine clear recommendations for MIS in HV correction [1,5- 7]. The renewed interest in the recent past has seen emerging trends of newer techniques such as the Minimally Invasive Chevron and Akin (MICA) and Endolog that aim to improve clinical outcomes [8,9]. However, the topic remains highly controversial due to limited evidence.

This systematic review aims to establish the efficacy and safety of minimally invasive surgery for HV correction and to provide patients and medics with evidence in determining their choice of surgery. Furthermore, if the procedure is safe and efficacious, does it offer cost effective management.

Materials and Methods

A systematic search of the following databases CINAHL, Embase, Medline, Science Direct and Cochrane Central Regristry of Controlled Trials from inception of database till 28th February 2014 was conducted. Combinations of words used to locate appropriate studies were Percutaneous, Minimally invasive, HV, Bunion, SERI (simple effective, rapid, inexpensive), Riverdin, Riverdin-isham Osteotomy, Endolog system, less invasive, minimal incision and MICA. Full text English articles were obtained based on search strategy and keywords. Only articles found in peer-reviewed journals are considered. Each article is reviewed and information gathered regarding study details including name and type of the study, number of patients involved, year of publication and procedure or technique used. Selected articles show minimal invasive Hallux Valgus surgery with clinical or radiological assessment score to determine the efficacy of the procedure. Safety of the procedure was based on specific complications analysis reported by individual publications. Conference abstracts were not included due to limitation to appraise study methodology.

Quality assessment of the included studies was done by two independent assessors using the modified Coleman Methodology Scale (CMS) which are based on the subsections of the Consolidated Standards of Reporting Trials (CONSORT) statement [5,10]. The obtained values were based on the average obtained from both the assessors. The reporting of this systematic review was also done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [11]. The authors used Review manager (Version 5.1) to evaluate the magnitude of intervention assessed if pooling of data was possible. However, based on the evidence level of the available literature and between study heterogeneity, narrative synthesis of the study findings were undertaken.

Results

Electronic searches of the database resulted in retrieval of 71 relevant articles and a further 33 articles were identified from the review of the references. Only 27 articles were selected based on this review’s inclusion and exclusion criteria. These articles included a total of 1485 patients with 1952 various techniques of MIHVS.

The evidence reviewed included 24 retrospective case series with level IV evidence, 3 retrospective comparative studies with level III evidence and 1 prospective comparative study with level II evidence. Various techniques of MIS were used and summarized in (Table 1).

CMS assesses the methodology of the study by using 10 criteria with a total score of 0 to 100. Chance, various biases and confounding factors are absent if the study has a total score of 100. Average CMS values for all of the 27 articles agreed by two assessors were calculated and shown in (Table 2). Highest score was 60 and lowest was 31. Most of the studies had methodological drawbacks such as poor study sample and short follow up time with average score of 40.6.13 studies used the American Orthopedic Foot and Ankle Society (AOFAS) score to assess the clinical outcome. AOFAS score ranges from 0 to 100 with high scores indicate better outcome clinically. Average preoperative scores were 48.5 and average postoperative scores were 87.5. Radiological measurements of hallux valgus angle (HVA) preoperative and postoperative are 31.7 and 14.2. Intermetatarsal angle (IMA) showed preoperative average value of 13.9 and postoperative average value of 7.7. List of complications associated with minimally invasive hallux valgus surgery are summarized in (Table 3).

Discussion

The increasing trend towards MIHVS aims to reduce surgical complications, reduce operative times and provide patients with quicker recovery time [1,36,37,38]. However, the technical maturity and advancement achieved are not proportionate to the quality of available publications. The present systematic review reinforces the issue that most of the available evidence is observational in nature which consists of case series. Only one prospective and 3 retrospective comparative case control studies were available in this systematic review [4,14,24,29].

The lack of homogeneity among studies reviewed is the major limiting factor towards generalizing the available evidence. The broad term of HV surgery consists of a wide variety of procedures including percutaneous distal metatarsal osteotomy with percutaneous lateral release and proximal phalanx osteotomy, percutaneous distal metatarsal osteotomy without soft tissue procedure, minimally invasive distal metatarsal osteotomy, modified minimal incision distal metatarsal osteotomy, minimal incision distal oblique osteotomy using the Endolog system, percutaneous double metatarsal osteotomy,percutaneous distal soft tissue release with Akin procedure and the arthroscopic assisted HV correction [8,9,20,24,26,28,31]. No techniques have shown superiority to others due to lack of randomized control trials and insufficient comparative case control studies.

Metatarsal osteotomy plays an important role in determining the outcome of the procedure. Most authors practicing the MIHVS correction have always used the conventional distal linear metatarsal osteotomy and frequently associated with postoperative complications like nonunion, delayed union and loss of correction. However, Sun et al. operated on 150 feet using oblique technique for metatarsal osteotomy and there was no reported nonunion, delayed union, avascular necrosis, infection and recurrence. Oblique osteotomy which provides a larger surface area for bony contact and union may have resulted in lesser incidence of postoperative nonunion [32].

Stabilization techniques in HV surgery differ and need to be highlighted due to its importance [39,40]. Bosch started with the use of a single extra articular Kirschner-wire (K-wire) as a stabilization technique of the osteotomy site [13]. Several other authors have used a similar pattern of stabilization using a single k-wire [4,25,26] while others have modified the available techniques to use two k-wires to provide greater stability [24]. Sun et al. and Martinez et al. [28,32] have described sole use of postoperative bandaging without hardware placement for stabilization of metatarsal osteotomy [28,32]. Newer innovations led to the emergence of Endolog system and percutaneous screws for stabilization [9,20].

The varying use of intraoperative fluoroscopy is another technical aspect that differs among the studies reviewed. Several studies have advocated the use of fluoroscopy as part of MIHVS [15,19,26,33]. However, some studies have excluded the use of intraoperative fluoroscopy aimed at reducing intraoperative radiation exposure [4,24,32]. Several experienced authors have stressed the importance of radiological control to avoid complications arising from decreased visualization of the surgical field and improve the accuracy of positioning the surgical instrumentation [41]. Although fluoroscopy provides reassurance towards the correction achieved, but efficacy and cost effectiveness of this procedure may be affected significantly due to its influence on increasing operative time, radiation exposure and manpower requirements.

The feasibility of applying a surgical treatment modality to the general population very much relies on patient selection. This review highlights an important setback to the current available evidence in deciding the efficacy and reproducibility of this procedure. Most studies have correctly excluded patients with inflammatory arthritis, adjacent joint degeneration, peripheral vascular disease and systematic conditions such as diabetes mellitus [4,24,29]. However several studies lacked appropriate exclusion of patients and have a potential to influence interpretation of the available evidence. The studies that have included patients with underlying systemic comorbidities have failed to relate their association with complications reported [31]. HV in rheumatoid arthritis is a complex interaction of both soft tissue and osseous elements [42]. When procedure like minimally invasive distal metatarsal osteotomy (MIDMO) is used to correct this complex HV deformity purely relying on bony component, neglecting the soft tissue correction may lead to recurrence of the deformity. This once again reinforces that patient selection within the studies reviewed may have potential of skewing the available evidence due to poorly specified exclusion criteria.

The outcome measures used are of fundamental importance when evaluating the success of surgical procedure. In HV surgery the post-surgical assessment is commonly based on clinical and radiological assessment. AOFAS score is the commonest clinical outcome that has been utilized in the current review. Unfortunately, the AOFAS score has not been validated [43,44,45,46]. It is known to be a surgeon designed outcome scale, lacks quality of life assessment and patient based outcome assessment [47].

Soo Hoo et al. [43] evaluated the validity of the AOFAS clinical rating system in 2003. Pearson correlation coefficient for patients with forefoot disorders ranged from -0.05 -0.25 when AOFAS score is compared to Medical Outcome Study Short Form-36(SF-36) that has been well validated. The relatively low correlation reflects poor validity and reliability of AOFAS to assess functional outcome in forefoot disorders. The current review deals with majority of case series that have used retrospective collection of preoperative data that may have potential to overestimate the improvement achieved using the AOFAS scale [48]. Maffulli et al. [24] in 2009 was the only study in our review that had utilized the validated Foot and Ankle Outcome Score (FAOS) [24]. The FAOS and MOFQ have been validated and are a reliable patient orientated assessment although their usage remains limited in our review [49,50]. The dependence on a non- validated scale to define the efficacy of a procedure reflects the poor reliability of the available evidence.

The outcome analysis that relates radiological assessment needs to be reviewed with caution. This review includes HVA and IMA but excludes DMMA due to its poor inter and intraobserver reliability [51,52,53]. Radiological outcome may not be a true reflection of the clinical outcome. Angthong et al. [12] reviewed 36 feet with predominant moderate HV treated with DLMO at mean follow up of 10 months in 2013 [12]. The mean AOFAS scores improved from 70.2 ± 11.3 to 95 ± 6.4. At final follow up, they observed nine feet (25%) with recurrence of deformity (HVA>15°, significant sagittal malunion in twenty-four feet (66.7%) and significant sesamoid lateralization observed (p<0.05). These radiological abnormalities did not correlate with reported clinical outcomes including the postoperative AOFAS score (p>0.05). It is therefore important to bear in mind that radiological assessment may not represent the measure of clinical and functional efficacy.

The review of complications encountered following MIHVS revealed contrasting reports. While some authors [4,9] have revealed no major complications with the procedure, others [19] have described significant complications that include recurrence of deformity in 18.8%, stiffness of first MTPJ in 8.8%, hallux varus in 9.4%. Dorsal malunions in 15.6% and infection rates ranging from 3.5-8.9%. Comparative case control studies using MIS revealed equal or less complication rates in comparison to conventional open techniques such as scarf osteotomy, Ludloff and Chevron osteotomy. Maffulli et al. [24] in 2009 reported higher rates of intraoperative fractures (8.3%) and hardware intolerance (13.9%) with conventional scarf osteotomy as compared to the MIDMO technique [24]. Gianini et al. [4] in 2013 compared the scarf technique with SERI technique in 20 patients with bilateral HV [4]. Each patient was subjected to a separate procedure on either foot. They reported higher incidence of hardware intolerance (10%) in patients with scarf osteotomy. One possible explanation to this is the low rates experienced using the minimally invasive technique is that the reporting done by the centers with extensive experience and expertise dealing with MIHVS.

Conclusion

MIHVS have several advantages such as shorter operating time, quicker recovery and return to work or sports, reduced hospital stay and fewer complications compare to open surgery. But, the MIHVS studies available at present differ in terms of procedure, patient selection, techniques, instrumentation and rehabilitation protocol, use of fluoroscopy and outcome measure. These factors may have a significant influence on study outcomes and limit the generalizability of this procedure. Future research involving MIHVS should include adequately sized randomized control trials, standardization of treatment protocols, use of validated tools for measurement of clinical outcome and future reporting by non-specialized centers to accept overwhelming evidence and theoretical advantage of MIHVS compare to open surgeries.

Acknowledgement

A special thanks to Professor Nicola Maffulli and Professor Hans-Joerg Trnka for their support, guidance and encouragement.

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  Table 1: Details of the studies included.

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  Table 2: Clinical and radiological outcome measure from available studies.

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  Table 3: Complications seen in minimally invasive hallux valgus surgery.