Subtalar Implant for Foot Deformity

Number: 0669

Table Of Contents

Policy
Applicable CPT / HCPCS / ICD-10 Codes
Background
References

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Policy

Scope of Policy

This Clinical Policy Bulletin addresses subtalar implant for foot deformity.

1. Experimental and Investigational

   Aetna considers subtalar implants experimental and investigational because the effectiveness has not been established for the following:

   1. For treatment of any of the following indications (not an all-inclusive list):
      
      
      1. Subtalar instability
      2. Talipes equinovarus deformity (club foot)
      3. Foot drop (dangle foot)
      4. Flatfoot deformity including congenital and adult-onset (acquired) flatfoot deformity (e.g., pes planus, pes planovalgus, pes valgus) and posterior tibial tendon dysfunction); or
      5. any other conditions;
         
         
   2. Use of any of the following subtalar implants (not an all-inclusive list):
      
      
      1. Angled Subtalar Implant (ASI)
      2. Arthrex Prostop and Arthrex Prostop Plus Subtalar Arthroeresis Implant
      3. Bioarch Subtalar Arthroereisis Implant
      4. bioBLOCK Resorbable Subtalar Implant
      5. BioPro Horizon Subtalar Implant
      6. Conical Subtalar Implant (CSI)
      7. Disco Subtalar Implant
      8. Extraosseous Talotarsal Stabilization (EOTTS)
      9. Futura Angled Subtalar Implant
      10. Futura Conical Subtalar Implant
      11. HyProCure Sinus Tarsi Implant
      12. IFS Subtalar Implant
      13. Instratek Sub‐Talar Lok Arthroereisis Implant System
      14. Kalix II
      15. Lundeen Subtalar Implant
      16. Maxwell-Brancheau arthroereisis (MBA) Implant
      17. MBA Resorb Implant
      18. MetaSurg BioArch Subtalar Implant System
      19. Nexa Orthopedics Subtalar Peg
      20. Normed Vario Subtalar Screw
      21. OsteoMed Talar-Fit Subtalar Implant System
      22. OsteoSpring FootJack Subtalar Implant System
      23. Smith Subtalar Arthroereisis Implant
      24. Solana Surgical Gaitway Implant
      25. STA-Peg
      26. SubFix Arthroereisis Implant
      27. Subtalar Maxwell-Brancheau Arthroereisis (MBA) Implant System
      28. Sub-Talar Lok Arthroereisis Subtalar Implant System
      29. Talus of Vilex (TOV) Subtalar Implant
      30. Trilliant Twist Subtalar Implant.

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Table:

CPT Codes / HCPCS Codes / ICD-10 Codes

Code	Code Description
Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":
There is no specific CPT code for subtalar implants:
CPT codes not covered for indications listed in the CPB:
0335T	Extra-osseous subtalar joint implant for talotarsal stabilization
0510T - 0511T	Removal and removal/reinsertion of sinus tarsi implant
Other CPT codes related to the CPB:
28735	Arthrodesis, midtarsal or tarsometatarsal, multiple or transverse; with osteotomy (e.g., flatfoot correction)
29907	Arthroscopy, subtalar joint, surgical; with subtalar arthrodesis
HCPCS codes not covered for indications listed in the CPB:
S2117	Arthroereisis, subtalar
ICD-10 codes not covered for indications listed in the CPB (not all-inclusive):
E64.3	Sequela of rickets
M21.071 - M21.079 M21.371 - M21.379 M21.6x1 - M21.6x9	Other acquired deformities of ankle and foot [foot drop]
M21.40 - M21.42	Flat foot [pes planus] (acquired)
M21.541 - M21.549	Acquired clubfoot
M24.871 - M24.876 M25.271 - M25.279 M25.371 - M25.376	Other joint derangement/instability not elsewhere classified involving ankle and foot [subtalar instability]
Q66.0	Congenital talipes equinovarus
Q66.50 - Q66.52	Congenital pes planus
Q66.6	Other congenital valgus deformities of feet
Q66.80 - Q66.89	Other congenital deformities of feet

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Background

Flatfoot (hyperpronation and flattening-out of the longitudinal arch); also known as pes planus or pes planovalgus) is a common deformity among children and adults.  Another cause of flatfoot can be attributed to posterior tibial tendon dysfunction.  Conservative treatments to relieve pain from the foot and leg associated with flatfoot include orthotics, stretching exercises, and medication (e.g., non-steroidal anti-inflammatory drugs).  Corticosteroid injections continue to be controversial.  These methods may fail to provide relief and do not provide any correction at the point of contact.  Various surgical techniques of subtalar joint arthroereisis have been used in the treatment of patients who have failed conservative approaches.  Some surgeons use bone blocks and bond grafts placed into the sinus tarsi to limit excessive subtalar joint pronation.  Others advocate the use of endoprosthetic devices. 

Arthroereisis is the limitation of exogenous joint motion without complete arthrodesis. Subtalar arthroereisis is a surgical procedure that involves placing an implant that has the appearance of a threaded cylinder into the sinus tarsi between the talus and calcaneus (heel) to stabilize the foot. It may be performed on both children and adults for congenital and adult onset flatfoot (eg, pes planus, pes planovalgus and pes valgus) deformities.

Examples of U.S. Food and Drug Administration (FDA) cleared implants utilized during subtalar arthroereisis include, but may not be limited to: Arthrex ProStop Plus Arthroereisis subtalar implant; HyProCure subtalar implant system; OsteoMed Subtalar implant; Solana Surgical Gaitway implant; subtalar arthroeresis peg; Silastic silicone sphere; SubFix arthroereisis implant; Sub Talar Lok implant; Subtalar Maxwell-Brancheau Arthroereisis (MBA) system; and Trilliant Surgical subtalar implant

The Subtalar MBA implant (KMI - Kinetikos Medical Incorporated, San Diego, CA) was cleared by the U.S. Food and Drug Administration (FDA) via a 510(k) premarket notification in 1996.  It is an "internal orthotic" designed for correction of pediatric pes valgus and adult posterior tibial dysfunction deformity.  There are 5 different MBA implant sizes: 6, 8, 9, 10, and 12 mm in diameter.  The implant is a soft-threaded titanium device that is inserted into the sinus tars.  It aims to restore the arch by blocking the anterior and inferior displacement of the talus and by preventing the foot from pronating; thus allowing normal subtalar joint motion.  Tissue grows normally around the implant and aids in holding it in place.  In adults, ancillary procedures may be performed simultaneously (e.g., an Achilles tendon lengthening if an equines deformity is present).  The patient can ambulate the day after surgery in a Cam Walker for approximately 3 weeks.  Thereafter, regular shoes can be worn with an ankle brace for an additional 2 to 3 weeks.

Husain and Fallat (2002) performed biomechanical analysis of MBA implants in fresh-frozen cadaver limbs to quantitate the effects on subtalar joint motion restriction and radiographic angles.  This study did not contain any clinical data on the value of MBA implants.

Well-designed studies are needed to ascertain the effectiveness and durability of the Subtalar MBA implant for the treatment of pathologic flatfoot.

Needleman (2006) ascertained the functional outcomes as well as radiographical results of adult patients who had an operation for flexible flatfeet without any hind-foot osteotomies or fusions.  A total of 28 feet in 23 patients with problems caused by their flexible flatfoot deformities had reconstructive foot and ankle surgery that included a subtalar arthroereisis with the MBA sinus tarsi implant.  The American Orthopedic Foot and Ankle Society (AOFAS) Hind-foot Scale and a patient assessment questionnaire were obtained from all patients before surgery and at final follow-up.  Pre-operative and post-operative standing radiographs were analyzed to determine radiographical correction of the deformities.  The average follow-up was 44 months.  The MBA implant was surgically removed in 11 of 28 feet (39 %) because of sinus tarsi pain.  The average pre-operative AOFAS score was 52 and had improved to 87 (p < 0.00001) at final follow-up.  The average response to 4 of 5 questions in the patient assessment had significantly improved (p < 0.05).  On a 10-point scale, average patient satisfaction was 8.3 points; 78 % said that they would have the surgery again.  Correction after surgery was significant (p < 0.0001) in each of the 3 radiographical parameters evaluated for 'correction with MBA' and "final correction".  With the numbers available, no significant differences could be detected after the MBA was removed.  Complications included sinus tarsi pain in 46 % (13) of the 28 feet in this study; after implant removal, 73 % (8) of 11 feet had less discomfort than before surgery with AOFAS scores 80 or better.  The author concluded that reconstructive foot and ankle surgery that included a subtalar arthroereisis with the MBA sinus tarsi implant resulted in favorable clinical outcomes and patient satisfaction in 78 % (18) of 23 patients.  In spite of the high incidence of temporary sinus tarsi pain until the implant was removed, this operative approach compares favorably with other operations for flexible flatfoot deformities in adults.  The major drawbacks of this study were its small sample size as well as the multiple etiologies of the flexible flatfoot deformity (13 feet had congenital etiologies and 15 feet had acquired etiologies).  Other pitfalls of this study included the 42 % occurrence of sinus tarsi discomfort and the associated 8 post-operative months of pain until the implant was removed.

In a review on acquired adult flatfoot deformity (AAFD), Pinney and Lin (2006) described the key elements of AAFD and outlined therapeutic options based on the peer-reviewed literature.  The authors stated that the limited research on subtalar arthroereisis (the use of a sinus tarsi plug or implant to restrict eversion of the subtalar joint) in adult patients with AAFD means that there is insufficient evidence to make a recommendation for or against this treatment option.

The Interventional Procedures Advisory Committee of the National Institute for Clinical Excellence (NICE, 2008) examined sinus tarsi implant insertion for mobile flatfoot.  Provisional recommendations from the Committee stated "[c]urrent evidence on the safety and efficacy of sinus tarsi implant for mobile flatfoot is inadequate in quality and quantity".  Furthermore, a review of the published literature on this procedure that was commissioned by NICE (2008) identified 8 case series and 4 case reports (643 feet) of sinus tarsi implant insertion for mobile flatfoot; no prospective comparative data were found.  The published literature focused mainly on the pediatric population.  Only 1 case series (n = 23) was reported in adults.  The provisional review found that the procedures described in the studies varied significantly, particularly in relation to the design, size and instrumentation/insertion of the implant(s).  The Committee recommended that this procedure should only be used with special arrangements for clinical governance, consent and audit or research.  Formal guidance on this procedure (NICE, 2009) concluded: "Current evidence on the safety and efficacy of sinus tarsi implant insertion for mobile flatfoot is inadequate in quality and quantity.  Therefore this procedure should only be used with special arrangements for clinical governance, consent and audit or research."

In a retrospective study, Scharer et al (2010) evaluated the outcome of pediatric patients who have undergone MBA subtalar implants for the treatment of painful pediatric flatfoot deformities.  A total of 39 patients (68 feet) were evaluated clinically and radiographically.  The mean age of the patients was 12 years (range of 6 to16 years).  The mean period of follow-up was 24 months (range of 6 to 61 months).  Statistical evaluation was performed on all radiographical measurements.  Additional surgical procedures (gastrocnemius recession, Achilles tendon lengthening, Kidner posterior tibial tendon advancement) were performed in 22 of 68 feet.  There were 10 (15 %) complications, which consisted of 10 re-operations in 10 feet.  Implants were exchanged in 9 feet because of implant migration, under-correction, and over-correction.  There was 1 re-operation (in 1 foot) for implant removal because of persistent sinus tarsi pain.  Radiographical evaluation demonstrated an improvement of all parameters determined.  The parameters that were evaluated include talo-navicular joint coverage, as well as lateral and anterior-posterior talo-calcaneal angles.  There were significant changes noted in pre- and post-operative measurements (p < 0.001).  The authors concluded that the MBA implant is effective for the correction of painful, flexible flatfoot deformity in children in short-term follow-up.  However, this is a multi-planar deformity, and additional procedures may be needed in addition to the MBA.

Yu et al (2011) reviewed the application progress of subtalar arthroereisis for the correction of pediatric flatfoot in children and analyzed the problems at present as well as to predict the trend of development in the field.  Domestic and abroad literature concerning the methods of subtalar arthroereisis applied in pediatric flatfoot in recent years was reviewed extensively and thoroughly analyzed.  Subtalar arthroereisis has proved to yield good results for correction of the flatfoot in children.  In addition to the advantages of subtalar arthroereisis for pediatric flatfoot treatment (simple procedure, mature technology, and less complications), it allows further surgery if needed.  The authors concluded that subtalar arthroereisis is a simple and effective way to treat flatfoot in children, however, its biomechanics mechanism and managements to complication need to be explored further.

Metcalfe et al (2011) noted that pediatric flexible flatfoot is a common deformity for which a small, but significant number undergo corrective surgery.  Arthroereisis is a technique for treating flexible flatfoot by means of inserting a prosthesis into the sinus tarsi.  The procedure divides opinion in respect of both its effectiveness and safety.  A database search up until 2010 was used to find articles regarding arthroereisis in pediatric patients.  These researchers summarized the findings of this study.  A total of 76 studies were identified; 8 of the 9 radiographical parameters reported show significant improvement following arthroereisis reflecting both increased static arch height and joint congruency.  Calcaneal inclination angle demonstrated the least change with only small increases following arthroereisis.  Arthroereisis remains associated with a number of complications including sinus tarsi pain, device extrusion, and under-correction.  Complication rates range between 4.8 % and 18.6 % with unplanned removal rates between 7.1 % and 19.3 % across all device types.  The authors concluded that current evidence is limited to consecutive case series or ad hoc case reports.  Limited evidence exists to suggest that devices may have a more complex mode of action than simple motion blocking or axis altering effects.  The interplay between osseous alignment and dynamic stability within the foot may contribute to the effectiveness of this procedure.  They stated that although literature suggests patient satisfaction rates of between 79 % to 100 %, qualitative outcome data based on disease specific, validated outcome tools may improve current evidence and permit comparison of future study data.

Shah and colleagues (2015) noted that subtalar arthroereisis (SA) has been a procedure used for the correction of painful flexible flatfoot deformity in adults and children. Clinical studies of patients who had a SA are sparse and with mixed results and variable indications. These researchers determined the current practice among orthopedic foot and ankle specialists regarding SA. Web-based questionnaires were e-mailed to members of the AOFAS. Requested information included demographics and practice patterns in regard to performing SA surgery. A total of 572 respondents completed the survey (32 % response rate). A total of 273 respondents (48 %) have performed SA. Of this group, 187 respondents (69 %) still perform this procedure (33 % of total respondents currently perform SA). Of the respondents, 401 (70 %) practice in the United States, 40 % have performed SA, and 60 % of those still perform this procedure. Of non-US respondents, 66 % have performed SA, and 80 % of those still perform it. The most common US indications are painful congenital flatfoot, posterior tibial tendon dysfunction, and flatfoot associated with accessory navicular. The authors concluded that many doctors have performed SA, and a significant number no longer perform this procedure for various reasons. A greater percentage of non-US practitioners have performed and continue to perform SA than their counterparts in the US. There is a common list of surgical indications. Most doctors who still perform this procedure have removed the implants, commonly for pain.

Gross and colleagues (2015) noted that as the number of total ankle replacements (TARs) performed has risen, so has the need for revision. These investigators performed a systematic review of clinical outcomes following a salvage ankle arthrodesis from a failed TAR to identify patient- and technique-specific prognostic factors and determined the clinical outcomes and complications following an ankle arthrodesis for a failed TAR. They searched PubMed, Medline, EMBASE, and the Cochrane Central Register of Controlled Trials for studies that analyzed ankle fusion after failed TAR with a minimum follow-up of 1 year. These investigators included 16 studies (193 patients). The majority of patients (41 %) underwent the index TAR for rheumatoid arthritis. The majority of these revision surgeries were secondary to component loosening, frequently of the talar component (38 %). In the cases that were revised to an ankle arthrodesis, 81 % fused after their first arthrodesis procedure. The intercalary bone graft group and the blade plate group had the highest rate of fusion after the first attempt at fusion at 100 %, whereas the tibiotalocalcaneal fusion with cage group had the lowest fusion rate at 50 %. The overall complication rate was 18.2 %, whereas the overall nonunion rate was 10.6 %. The authors concluded that a salvage ankle arthrodesis for a failed TAR resulted in favorable clinical end-points and overall satisfaction at short-term follow-up if the patients achieve fusion. The bone graft fusion and blade plate group resulted in the highest first-attempt fusion rate, with a low complication rate. Moreover, they stated that future studies should include prospective, comparative control or surgical groups and use standardized outcome measurements that will make direct comparisons easier.

Saxena and colleagues (2016) noted that the implant used for subtalar joint arthroereisis (STA) often needs to be removed because of sinus tarsi pain.  They reported that endoscopic gastrocnemius recession did not exert any influence on the rate of implant removal (p = 0.19).  After STA for adult acquired flatfoot deformity, 22 % of the implants were removed.  No significant difference was found in the incidence of removal according to patient age or endoscopic gastrocnemius recession.  However, a significant difference was found for implant size, with 11-mm implants explanted most frequently.

Chen et al (2022) noted that the HyProCure procedure is a new surgery for SA; however, very few available studies reported the therapeutic effects of the HyProCure procedure, especially in pediatric flexible flatfoot.  In a retrospective, cohort study, these investigators examined the clinical and radiological outcomes of the HyProCure procedure for pediatric flexible flatfoot and analyzed the risk factors for therapeutic outcomes and sinus tarsi pain.  This trial included 69 pediatric flexible flatfoot patients (107 feet) who underwent the HyProCure procedure between July 2015 and September 2020.  All patients underwent the HyProCure procedure with or without gastrocnemius recession.  The Maryland foot score (MFS), VAS, radiographic data, and complications were assessed at a minimum 1-year follow-up and statistically analyzed.  The mean follow-up was 35.9 months (range of 13 to 73 months).  At the last follow-up, VAS (0.64 ± 1.16) was significantly lower than the pre-operative VAS (4.06 ± 1.43) (p < 0.001); MFS (90.39 ± 12.10) was significantly higher than the pre-operative MFS (71.36 ± 10.25) (p < 0.001).  The AP talar-2nd metatarsal angle (T2MT angle) significantly decreased from 17.0 ± 5.4° pre-operatively to 11.4 ± 5.2° at the last follow-up (p < 0.001).  The lateral talar-1st metatarsal angle (Meary's angle) significantly decreased from 13.8 ± 6.4° pre-operatively to 6.3 ± 5.0° at the last follow-up (p < 0.001).  The calcaneal declination angle (Pitch angle) significantly increased from 13.5 ± 4.9° pre-operatively to 14.8 ± 4.4° at the last follow-up (p < 0.001).  Logistic regression analysis indicated that patients with a longer distance from the tail end of the implant exceeding the longitudinal talar bisection line had 275.8 % greater odds of MFS less than 90.  Yet, no risk factors were found in connection with sinus tarsi pain.  The authors concluded that the HyProCure procedure for pediatric flexible flatfoot achieved satisfactory curative effects with a low complication rate; implant depth was associated with unsatisfactory post-operative outcome. 

The authors stated that his study had several drawbacks.  First, recall bias was unavoidable because of the retrospective design.  Second, the relatively small sample size (n = 69 subjects) could not provide more reliable results, especially regarding the occurrence of complications.  Third, there was a shortage of short-term follow-up; thus, long-term results, essential for teenagers, still need to be examined.

Flexible Flat-Foot Deformity / Acquired Flat-Foot Deformity

Caravaggi and colleagues (2018) stated that flexible flatfoot (FFF) is a common alteration of the foot diagnosed in the pediatric population causing pain and decreased quality of life (QOL).  Surgical treatment via arthroereisis of the subtalar joint can be recommended when non-invasive options do not result in sufficient pain relief.  While clinical outcome of subtalar joint arthroereisis (SJA) is generally positive, no functional evaluation has thus far been reported following surgery.  In a prospective study, these investigators evaluated the effects of 2 arthroereisis implants for the correction of bilateral FFF on foot and lower limb biomechanics during gait.  This trial entailed a total of 13 children affected by bilateral symptomatic FFF.  Patients underwent bilateral SJA during the same surgery using 2 types of poly-L-lactide bioabsorbable implants: an expanding endo-orthotic implant, and a calcaneo-stop screw.  Radiological parameters and gait analysis were performed pre-operatively and at 1 year follow-up and compared to those from an age-matched normal-arched control population.  Lower limb and multi-segment foot kinematic analysis, along with electromyography (EMG) of the main ankle flexor/extensor muscles, were performed during level walking at comfortable speed.  Paired non-parametric Wilcoxon signed-rank test was used to assess differences in radiological and kinematic parameters between pre-op and post-op assessments.  All radiological parameters, and frontal-plane orientation of the rear-foot in double-leg standing were improved at 1-year follow-up in both implant groups (e.g., calcaneo-stop: pre-op = 15 ± 7 degrees; post-op = 6 ± 9 degrees; p < 0.01).  The endo-orthotic implant group showed significantly lower pronation/supination at the ankle and mid-tarsal joint.  Activation of the tibialis anterior muscle was more physiological after surgery in both groups.  The authors concluded that according to the present analysis, both implants appeared effective in restoring physiological alignment of the rear-foot, however the endo-orthotic implant appeared more effective in restoring a more correct frontal-plane mobility of foot joints.  This was a small study (n = 15) with short-term follow-up (1 year).  These preliminary findings need to be validated by well-designed studies with larger sample size and long-term follow-up.

Walley and associates (2019) examined the radiographic and clinical outcomes and complications following the use of a SJA implant as an adjunct for correction acquired flatfoot deformity secondary to posterior tibial tendon dysfunction (PTTD).  These researchers carried out a retrospective case-control study querying all patients undergoing surgical flatfoot correction between January 1, 2010 and January 1, 2015.  The experimental group included patients undergoing arthroereisis augmentation at the time of flatfoot correction.  Patients undergoing the same flatfoot correction without the use of an arthroereisis implant were used as controls.  Radiographic measurements were evaluated pre-operatively and at final radiographic follow-up and included talo-navicular (TN) coverage angle, and lateral talar-1st metatarsal angle (T1MA).  Patient-reported outcomes were assessed using pre-operative visual analog scale (VAS) pain scores and post-operative Short Form-36 (SF-36), VAS, and satisfaction at final orthopedic follow-up.  A total of 15 patients underwent flatfoot correction and were augmented with an arthroereisis implant and were matched with 30 controls.  Post-operative, mid-term T1MA and regional analysis was found to be improved in the experimental group versus control.  Patients undergoing adjunct subtalar arthroereisis demonstrated an increased likelihood of achieving radiographically normal TN coverage of less than 7° compared with the control group at follow-up.  The authors concluded that the adjunct use of an arthroereisis implant resulted in improved and maintained radiographic and clinical measurements in patients undergoing stage II flatfoot.  They stated that these findings suggested utility of a subtalar arthroereisis implant as an adjunct to flatfoot correction with little additional risk of harm to the patient.  Levels of Evidence = III.

Junxian and associates (2020) compared radiological and functional outcomes of patients with symptomatic AFFD secondary to stage 2B PTTD treated with either a SA implant or a lateral column lengthening (LCL) procedure.  These researchers examined if the subtalar arthroereisis (SA) procedure is an acceptable surgical adjunct in the treatment armamentarium.  A total of 21 patients (22 feet) were evaluated; 12 consecutive patients (n = 12) underwent a SA procedure while 9 patients (n = 10) underwent a LCL procedure.  Functional outcomes were evaluated using the AOFAS mid-foot score, SF-36 VAS, pre-operatively and at 6 and 12 months post-operatively.  A total of 10 radiological parameters were analyzed; all complications were tabulated.  Significant improvements in functional outcomes were noted in both groups of patients.  Radiographically, some loss of correction was noted in the SA group and no loss of correction in the LCL group, respectively.  In the SA group, 6 patients complained of sinus tarsi pain in the post-operative period and 4 required removal of implants.  No implants were removed in the LCL group.  The authors concluded that the findings of this study suggested that SA implantation may be a reasonable procedure to utilize in the treatment of AAFD, albeit with a relatively high implant-removal rate.

Bernasconi and colleagues (2020) noted that the role of SA for treating FFF in children is controversial.  These investigators hypothesized that SA provided significant radiographic correction of low longitudinal arch and fore-foot abduction in pediatric FFF; and that mid-term clinical outcomes were satisfactory and comparable to a normal population.  They carried out a retrospective, comparative study of pediatric patients with symptomatic FFF who underwent SA between 2012 and 2015.  Multiple measurements on pre-operative and latest follow-up radiographs were recorded by 2 observers and compared to evaluate for correction of the FFF.  Intra- and inter-observer reliability was also assessed.  Ankle and hind-foot range of motion (ROM), AOFAS hind-foot score and VAS-FA score were compared with controls without foot symptoms or deformity.  From 70 consecutive feet, 62 (31 patients) treated at 10.5 years of age were identified and compared to 48 controls (24 patients).  Mean follow-up was 62 months.  Intra- and inter-observer reliability was excellent for all angles (range of 0.81 to 0.97).  Radiographic measurements demonstrated significant improvement after surgery (p < 0.001); however, significance was not reached in TN coverage angle (p = 0.49) and calcaneo-5th metatarsal angle (p = 0.53) on dorso-plantar view.  At latest follow-up, patients had less hind-foot inversion than controls (15.1° versus 19.3°, p = 0.03), lower AOFAS scores (94.1 versus 99.6 points, p = 0.01), due to pain (p = 0.01) and alignment (p = 0.006) sub-scores.  Using the VAS-FA score, patients were found to demonstrate higher pain at rest (p range of 0.02 to 0.03) and during activity (p = 0.009), and felt limited when standing on 1 leg (p range of 0.01 to 0.03) and running (p = 0.04).  No loss of correction was found after removal of the implant.  The authors concluded that the findings of this study showed that SA corrected the low longitudinal arch in symptomatic pediatric FFF, but did not correct fore-foot abduction in relation to the hind-foot.  Mid-term assessment revealed SA provided satisfactory ankle and hind-foot ROM, pain and function levels, but limitations were witnessed compared to unaffected individuals.  These researchers stated that this aspect should be considered when counselling patients and their parents or care-givers to allow for realistic expectations.  Level of Evidence = III.

Vogt and colleagues (2021) stated that STA is a minimally invasive and reversible surgery to correct symptomatic FFF in children.  Various techniques have been described either applying expandable sinus tarsi implants or lateral calcaneus stop screws.  Studies comparing the outcome of STA with different devices are rare.  In a retrospective, single-center, cohort study, these researchers analyzed the results of STA using 3 different implants.  A total of 113 STAs were performed in 73 consecutive patients (28 females).  Mean age at surgery was 10.8 years (range of 5 to 16).  Mean follow-up was 29.0 months (range of 1 to 111).  In 21 feet the non-absorbable Kalix endorthesis and in 56 feet the absorbable Giannini endorthesis were applied.  Subtalar extra-articular screw arthroereises (SESA) was performed in 36 feet.  Clinical, radiographic and pedobarographic parameters were analyzed.  No intra-operative complications were observed.  All 3 procedures achieved comparable improvements of the clinical, radiographic and pedobarographic parameters.  The mean foot function index (FFI) improved from 36.4 (range of 12 to 63) to 22.8 (range of 2 to 55).  The mean pre-operative calcaneal inclination angle and the lateral talo-calcaneal angle improved from 9.5° (range of 0 to 22) and 42.3° (range of 21 to 62) to 12.8° (range of 0 to 26) and 37.6° (range of 15 to 56), respectively.  Pedobarographically determined values of the arch index, the medial mid-foot contact area and the medial fore-foot peak pressure decreased . In contrast to SESA (1/36, 3 %), a higher incidence of implant-related complications was observed using Kalix (6/21, 29 %) and Giannini (10/56, 8 %) sinus tarsi implants.  Peroneal muscle contractures only occurred in the SESA group (4/36, 11 %).  Premature removal due to treatment-related complications was needed in 6/21 Kalix implants (29 %), 4/56 Giannini implants (7 %) and 4/36 SESA implants (11 %).  Implant choice for treatment of painful FFF in children with STA appeared to play a subordinate role.  Clinical, radiographic and pedobarographic outcomes were comparable between the applied implants.  Surgeons and patients should be aware of the different spectrum of implant-related complications.  Treatment can be reliably monitored by radiation-free pedobarography providing dynamic information about the deformity.

The authors stated that this study had several drawbacks as a consequence of its retrospective character and is biased by different cohort sizes, availability of the implants and uneven distribution of the etiologies. Patients were only included until 2013 since due to logistic reason pedobarographic analysis was inconsistently available after 2013. STA implants were used consecutively due to their availability and not during the same period. Time related parameters such as the surgeon’s expertise, evolution of implants and improved outcome measures with time might limit comparability of the studied cohorts. The statistical findings of this study should carefully be interpreted. We encourage readers to focus more on the clinical, radiographic and pedobarographic outcomes, rather than statistical comparisons and p-values. The fact that some patients were treated bilaterally and others unilaterally can limit comparability. Some statistical findings might not be applicable to every patient group. Most patients were immature at the time of implant removal or last follow-up and the study lacks long-term observation after treatment focusing on maintenance of the correction and occurrence of recurrent deformity. Furthermore, this study does not provide a control group to compare the outcome with the natural development of pediatric foot shape over time. Prospective randomized trials are needed to compare the benefits and disadvantages of the available implants with a long-term follow-up.

In a retrospective study, Wang et al (2022) reported the mid-term outcomes of STA using Talar-Fit implant for the treatment of flexible flatfoot patients; compared clinical and radiographic outcomes between arthroereisis with and without adjunctive operative procedures to examine the effects of adjuncts on the outcomes; and analyzed the risk factors associated with sinus tarsi pain, which is the most common post-operative complication of arthroereisis.  A total of 31 flexible flatfoot children and adolescents (46 feet) treated with STA using Talar-Fit implant from June 2014 to May 2019 were analyzed.  The feet were divided into 4 treatment groups: arthroereisis alone, arthroereisis with gastrocnemius recession, arthroereisis with Kidner procedure, and arthroereisis with gastrocnemius recession and Kidner procedure.  Clinical function was evaluated based on the AOFAS ankle and hind-foot score.  The following angles were measured for radiographic evaluation: talar-first metatarsal angle, calcaneal pitch angle, and talar declination angle on the lateral view; and talar-first metatarsal angle, talocalcaneal angle, and antero-posterior (AP) talonavicular coverage angle on the AP view.  The paired Student's t-test was used to compare the pre- and post-operative angular measurements and AOFAS scores.  The Wilcoxon rank-sum test was performed to determine the outcome differences among the 4 treatment groups.  Multi-variate logistic regression analysis was used to analyze risk factors for sinus tarsi pain; a “p” value of < 0.05 was considered statistically significant.  The mean follow-up of the feet was 32.8 months (range of 10 to 71 months).  The mean AOFAS score significantly improved from 55.5 ± 14.5 pre-operatively to 86.3 ± 9.9 (p < 0.001).  Comparison of radiographic outcomes showed that the lateral talar-first metatarsal angle decreased by a mean of 19.1° ± 11.9° (p < 0.001), the calcaneal pitch angle increased by a mean of 5.4° ± 3.4° (p < 0.001), the talar declination angle decreased by a mean of 14.8° ± 9.9° (p < 0.001), the AP talar-first metatarsal angle decreased by a mean of 15.6° ± 10.3° (p < 0.001), the AP talocalcaneal angle decreased by a mean of 7.2° ± 8.3° (p = 0.001), and the AP talonavicular coverage angle decreased by a mean of 20.4° ± 9.0° (p < 0.001).  There were no statistically significant differences with regard to AOFAS score and all angle measurements on both the AP and lateral views among the 4 treatment groups.  There was 1 dislocation case caused by a fall 6 weeks after surgery, which was treated non-operatively.  The incidence of sinus tarsi pain was 13 % and logistic regression analysis indicated that patients with a longer distance from the tail end of the implant to the lateral calcaneal wall had 38.8 % greater odds of developing sinus tarsi pain.  The authors concluded that the findings of this study indicated that the mid‐term clinical and radiographic results were satisfactory in patients who underwent STA using Talar‐Fit implant, alone or in combination with other adjuncts, for the treatment of flexible flatfoot.  These researchers noted that implant position was associated with post-operative sinus tarsi pain; and further prospective RCTs are needed to confirm these findings.

The authors stated that this study had several drawbacks, and its results should be understood with these drawbacks in mind.  First, it was retrospective and may be biased, such as selection bias as well as information bias.  Second, the evaluation of STA could have been compared with patients treated with non-operative methods and this trial lacked a control group.  Third, although the overall sample size was not small, these researchers only had a small number of feet in each treatment group, which may have affected the reliability of these findings.  Fourth, aside from the factors in their logistic regression model, there may be other significative factors such as the shape and material type of the implant; therefore, these findings may have changed if these factors were considered.

Smolle et al (2022) stated that although pediatric FFF is a common condition, only a minority of patients become symptomatic.  Long-term outcomes of surgically treated pediatric patients with symptomatic FFF are largely unknown.  In a systematic review, these researchers analyzed studies that provided outcomes at a mean follow-up of at least 4 years after the procedure in these patients.  PubMed search was carried out involving original articles published up to July 2021 on outcome in children aged 6 to 14 with surgically treated FFF and mean (or minimum) follow-up of at least 4 years. Radiographic and clinical outcomes were analyzed.  Of initially 541 entries, 10 could be included in the systematic review (all level IV), involving 846 pediatric patients with 1,536 symptomatic FFF.  Pooled mean radiological (n = 8) and clinical follow-up (n = 10) was 5.3 (range of 0.5 to 15) and 7.0 (range of 4.1 to 15) years, respectively.  Surgical procedures included arthroereisis (n = 8), lateral column lengthening (n = 1), and Horseman procedure (n = 1).  Overall relative frequency of implant-associated complications and wound-healing problems was 3.2 % and 1.3 %, as well as 2.8 % and 1.6 % following subtalar arthroereisis only.  From pre-operative to latest radiological assessment following subtalar arthroereisis (including 3 studies with radiological follow-up of less than 48 months), pooled median decrease in TN coverage angle (TNCA; -9.2°), AP talocalcaneal angle (A-TCA; -6.5°), lateral talocalcaneal angle (L-TCA; -3.5°), talar declination angle (TDA; -14°), Moreau Costa Bertani angle (MCB; -13°), and talo-firstmetatarsal angle (L-T1MA; -10°) was observed, as was an increase in calcaneal pitch (4.5°).  The authors concluded that in children with symptomatic FFF refractory to conservative treatment, surgical therapy was associated with a manageable complication profile, and eventually resulted in satisfactory long-term clinical as well as radiological outcome.  These researchers stated that although a clear correlation between clinical and radiological outcomes following surgery for pediatric flexible FFF is yet to be clarified, the current pooled results point towards concordant overall improvement in radiological and clinical parameters by surgical therapy.  Moreover, these researchers stated that the evidence of studies included herein was low, few provided patient-reported outcome measures, and long-term results on definite bony corrections are still missing.  These investigators stated that larger studies in symptomatic pediatric FFF are needed, ideally comparing different therapeutic approaches.

The authors stated that this study had several drawbacks.  First, all studies meeting the defined inclusion criteria were based on level IV retrospective cohorts with a mean Newcastle Ottawa Scale (NOS) of 4.9 points.  These data must be interpreted bearing a potential selection bias in mind.  Second, 3 different surgical procedures were included in this systematic review, with 8 of 10 studies reporting on outcomes following subtalar arthroereisis. Therefore, pooled results were given both for all studies combined as well as for those on STA only, to enable a better interpretation of the data depending on the surgical procedure performed.  Third, information on clinical and radiological parameters was inconsistently reported by individual studies, complicating a comprehensive data analysis.  Related to this, there was a considerable diversity of participants included, as was similarly the definition of indication for surgical correction of the FFF.  Consequently, more homogeneous patient cohorts should be strived for in the future, allowing for distinct conclusions to be drawn.

In a retrospective, cohort study, Bernasconi et al (2022) examined if STA as adjunct procedure would improve radiographic correction of stage IIb AAFD); and evaluated the STA-related complication rate.  These researchers carried out a retrospective analysis of 22 feet (21 patients) diagnosed with stage IIb AAFD treated by medializing calcaneal osteotomy (MCO), flexor digitorum longus (FDL) transfer, spring ligament (SL) repair with or without Cotton osteotomy and with or without STA in a single center.  A total of 7 measurements were recorded on pre- and post-operative (minimum of 24 weeks) radiographs by 2 observers and repeated twice by 1 observer.  Inter- and intra-observer reliabilities were assessed.  The association of demographic (gender, side, age, body mass index [BMI]) and surgical variables (Cotton, STA) with radiographic change was tested with univariate analysis followed by a multi-variable regression model.  Excellent inter- and intra-observer reliabilities were demonstrated for all measurements (intra-class correlation coefficient [ICC], range of 0.75 to 0.99).  Gender, side, Cotton osteotomy, and STA were included in the multi-variable analysis.  Regression showed that STA was the only predictor of change in TNCA (R2 = 0.31; p = 0.03) and in calcaneo-fifth metatarsal angle (CFMA) (R2 = 0.40; p = 0.02) on dorsoplantar view.  STA was associated to a greater change in TNCA by 10.1° and in CFMA by 5°; 4 patients out of 12 STA complained of sinus tarsi pain after STA, and removal of the implant resolved symptoms in 3 of them.  The authors concluded that in this series, STA as an adjunct procedure to MCO, FDL transfer, SL repair in the treatment of stage IIb AAFD led to improvement in correction of forefoot abduction; and STA-related complication and removal rates were 33 %.  Moreover, these investigators encouraged further comparative and ideally randomized studies with larger cohorts with the aim of confirming these findings.  Levels of Evidence = IV.

In a retrospective study, Bistolfi et al (2022) examined the clinical-functional and radiographic results in pediatric patients with painful and disabling FFF refractory to conservative treatment who underwent percutaneous subtalar arthroereisis with a MBA implant.  Patients aged 8 to 14 years with a minimum follow-up of 24 months were included.  A pre- and post-operative radiographic evaluation was performed analyzing Meary's angle, internal Moreau-Costa-Bartani´s angle, Talar declination angle, Calcaneal Pitch, Kite's angle, Talar-1st metatarsal angle, and Talonavicular coverage angle.  In those patients with more than 5 years of follow-up, the development of subtalar osteoarthritis (OA) was examined.  A clinical-functional evaluation was performed using the AOFAS ankle-hindfoot rating scale.  Pre- and post-operative pain was evaluated using the VAS.  Post-operative complications were described.  A total of 14 patients (19 feet) met the inclusion criteria . The mean age at surgery was 12 years with a mean follow-up of 68.26 months.  All radiographic angles improved significantly.  No signs of subtalar OA were identified.  The mean pre- and post-operative pain according to VAS was 7.05 and 0.77, respectively.  The mean pre- and post-operative AOFAS was 75.42 and 97.05, respectively.  One female patient had persistent pain in both feet (VAS = 4).  However, she was able to do sports and activities of daily living (ADL) without restrictions.  None of the implants needed to be removed due to intolerance or pain.  The authors concluded that subtalar arthroereisis appeared to be effective to improve the clinical-functional and radiographic parameters in moderate pediatric FFF.  Level of Evidence = IV.

Shi et al (2023) stated that accessory navicular is accompanied by the deformity of valgus flexible flatfoot.  The surgical treatment includes reconstruction of insertion of posterior tibial tendon following resection of the accessory navicular.  However, this treatment could not correct completely the deformity of valgus flexible flatfoot.  In a retrospective study, these researchers examined the effectiveness of subtalar arthroereisis combined with medial soft tissue reconstruction in treating 8- to 14-year-old flexible flatfoot patients with accessory navicular.  Clinical data of 35 pediatric flatfoot patients (with 50 feet) with accessory navicular who underwent subtalar arthroereisis and medial soft tissue reconstruction between April 2013 and September 2018 were analyzed.  Antero-posterior, lateral, and hind-foot alignment radiological images were measured in the weight-bearing position, and VAS, AOFAS ankle-hindfoot scale, and satisfaction degree were evaluated.  Furthermore, surgical complications were recorded.  The average follow-up time of the patients was 30 ± 9.3 months.  None of the patients presented wound complications, and no implant loosening was detected.  The AOFAS and VAS scores improved significantly (p < 0.001).  Radiological parameters, such as the talar 1st metatarsal angle and talonavicular coverage angle on antero-posterior foot view, Meary's angle and calcaneal pitch angle on the lateral view, and calcaneus valgus angle on hind-foot alignment view improved significantly (p < 0.001).  Post-operative complications were observed in 3 patients.  The authors concluded that subtalar arthroereisis combined with medial soft tissue reconstruction significantly alleviated pain and improved the functions in pediatric and adolescent flexible flatfoot patients with accessory navicular; also, the radiological manifestations and functions improved.

The authors stated that this study had several drawbacks.  This was a retrospective study, and patients were followed-up for a short period (30 months); therefore, there is no study on whether the removal of implants will affect the effectiveness; these researchers stated that data from longer follow-up are needed.

Posterior Tibial Tendon Dysfunction

Wong and colleagues (2017) noted that SJA has been introduced to control the hyper-pronation in cases of flatfoot.  These researchers evaluated the biomechanical consequence of SJA to restore the internal stress and load transfer to the intact state from the attenuated biomechanical condition induced by PTTD.  A 3-D finite element model of the foot and ankle complex was constructed based on clinical images of a healthy female (age of 28 years, height of 165 cm, body mass of 54 kg).  The boundary and loading condition during walking was acquired from the gait experiment of the model subject.  Five sets of simulations (conditions) were completed: intact condition, mild PTTD, severe PTTD, mild PTTD with SJA, severe PTTD with SJA. The maximum von Mises stress of the metatarsal shafts and the load transfer along the mid-foot during stance were analyzed.  Generally, SJA deteriorated the joint force of the medial cuneo-navicular and calcaneo-cuboid joints during late stance, while that of the metatarso-cuneiform joints during early stance were over-corrected.  Only the calcaneo-cuboid joint force at 45 % stance demonstrated a trend of improvement.  Besides, SJA exaggerated the increased stress of the metatarsals compared to the PTTD conditions, except that of the 1st metatarsal.  The authors concluded that the findings of this study did not support the hypothesis that SJA could restore the internal load transfer and mid-foot stress; SJA could not compensate the salvage of mid-foot stability attributed by PTTD and could be biomechanically insufficient to restore the biomechanical environment.  They stated that additional procedures such as orthotic intervention may be necessary.

Acquired Neuropathic Pes Planus

Martucci and colleagues (2019) noted that ulcerations under the medial column in patients with acquired neuropathic pes planus may be intractable to conservative techniques such as regular debridement, off-loading, bracing, and accommodative shoes.  When surgery becomes necessary for these patients, the foot and ankle surgeon has the option of exostectomy, medial column beaming, medial column fusion, and external fixation, among others.  In the case of a flexible mid-foot collapse, the option of arthroereisis for indirect medial column support may be warranted.  In this preliminary report, these investigators described a technique of Achilles tendon lengthening, SA implantation, and advanced cellular tissue product application in an attempt at wound coverage and prevention of recurrence.  A total of 3 patients presenting with intractable medial column ulcerations of approximately 1-year duration underwent this procedure, and within 7 weeks (range of 5 to 7), all medial column ulcerations healed.  These patients remained healed at last follow-up (average of 29 months; range of 8 to 44).  The authors concluded that the findings of this preliminary report provided evidence for a minimally invasive procedure aimed at off-loading, healing, and preventing recurrence of medial column ulcerations in patients with flexible neuropathic pes planus.  Level of Evidence = IV.

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References