Journal of Foot and Ankle Surgery (Asia-Pacific)
Volume 10 | Issue 2 | Year 2023

Subtalar Arthroereisis as a Surgical Option in the Reconstruction of Progressive Collapsing Foot Deformity: A Prospective 3-year Follow-up Study on Patient Satisfaction and Causes for Implant Removal in 40 Cases treated with the HyProCure Implant

Martin Ålundhttps://orcid.org/0000-0002-2285-6462

Department of Orthopaedic Surgery, Sahlgrenska University Hospital, Gothenburg, Västra Götaland County, Sweden

Corresponding Author: Martin Ålund, Department of Orthopaedic Surgery, Sahlgrenska University Hospital, Gothenburg, Västra Götaland County, Sweden, Phone: +46(0)709520407, e-mail: martin.alund@vgregion.se

Received on: 08 February 2023; Accepted on: 25 March 2023; Published on: 11 April 2023


Background and purpose: Subtalar arthroereisis in the surgical treatment of Progressive Collapsing Foot Deformity is associated with high implant removal rates. This study reports the mid-term incidence and causes for implant removal, patient-reported outcomes, and radiographical results.

Patients and methods: Prospectively collected data from 40 cases in 37 patients were analyzed. Subtalar arthroereisis was performed with a HyProCure-I implant as a single procedure in 19 cases and as an adjuvant procedure in 21 cases. In all cases, a Self-reported Foot and Ankle Score (SEFAS) was completed preoperatively. At the final follow-up, SEFAS was available in 32 cases. Standard weightbearing lateral and anteroposterior (AP) radiographs were obtained preoperatively in all cases and at final follow-up in 29 cases.

Results: The implant was removed in four single procedure cases and four combined procedure cases (20%). Causes for pain leading to implant removal are discussed. Patient satisfaction in the remaining 32 cases was similar in both groups. Mean SEFAS improvement was 14.5 points [95% confidence interval (CI), 10.6–18.5] in the single procedure group and 17.2 points (95% CI, 12.0–22.3) in the combined procedure group. Similar radiographical improvements were noted in the two groups.

Interpretation: Subtalar arthroereisis with a HyProCure-I implant, performed as either a single or a combined procedure, may yield good subjective results and radiographical improvement with high patient satisfaction rates. The 20% mid-term implant removal rate is still relatively high, and careful patient selection is needed for either procedure.

How to cite this article: Ålund M. Subtalar Arthroereisis as a Surgical Option in the Reconstruction of Progressive Collapsing Foot Deformity: A Prospective 3-year Follow-up Study on Patient Satisfaction and Causes for Implant Removal in 40 Cases Treated with the HyProCure Implant. J Foot Ankle Surg (Asia-Pacific) 2023;10(2):92-101.

Source of support: Nil

Conflict of interest: None

Keywords: Adult Flatfoot, HyProCure, Progressive collapsing foot deformity, Subtalar arthroereisis.


A multifactorial etiology of adult flatfoot deformity is commonly recognized. Recently, an expert consensus group has suggested the term Progressive Collapsing Foot Deformity, addressing the fact that the deformity may result from a number of morphological mid- and hindfoot changes that do not always begin in adulthood.1 Being a three-plane deformity, the flatfoot can be described as a rotational deformity of the foot around the talus, described as peritalar subluxation.2,3,4

One surgical option in order to balance the hindfoot is to stabilize the talus on the calcaneus by means of a subtalar arthroereisis (Greek—arthro = joint, ereisis = rais up/prop up). An implant is placed into the sinus tarsi/tarsal canal with the hindfoot in a reduced position. The principle of all sinus tarsi implants is to block hyperpronation without restricting natural pronation. Arthroereisis may be performed either as a single procedure or as an adjunctive procedure in conjunction with other soft tissue and bony procedures. The indication is the same as for a medial displacement calcaneal osteotomy. The advantage of arthroereisis is that it is easy to perform with less immobilization required and fewer potential complications. The main disadvantage is implant intolerance. Although good results have been achieved, the incidence of implant removal is reported to be high, ranging from 5 to 40%.5,6 Sinus tarsi pain is the most common reason.7 Risk factors for implant removal have been studied with contradicting results. Implant size has been found to be both correlated,7 and uncorrelated to the incidence of implant removal.8 Other factors, such as age and body mass index, have not been found to have any significant impact on implant removal rates. The aim of this study was to evaluate the incidence and causes for implant removal, as well as patient-reported outcomes and radiographical changes in a consecutive series of patients undergoing flatfoot reconstruction with a minimum 3-year follow-up.



In the period from March 2016 to March 2018, the author performed subtalar athroereisis using the first-generation HyProCure® implant (Gramedica, Macomb, Michigan, United States of America) in a consecutive series of 37 symptomatic adult patients. All had failed conservative treatment with shoe modifications and physiotherapy, resulting in the need for surgery involving hindfoot balancing. Inclusion criteria were a diagnosed flexible flatfoot and a given consent to arthroereisis, either as a single procedure or as part of a composite procedure. Patients were informed about possible complications in terms of pain and subsequent implant removal. The exclusion criterion was missing consent. In the study period, there were no exclusions. One patient with a talocalcaneal coalition with an otherwise flexible foot was included (case 23). Bilateral surgery was performed on three patients, resulting in a total of 40 cases. All cases were prospectively followed for a minimum of 3 years. The spectrum of patients comprised young athletic individuals as well as nonathletic middle-aged and older individuals. Ethical approval was not required for this study. It started as a pilot study, and the entire work has been conducted in the context of a routine clinical and radiographical follow-up.

Patient-reported Outcome

For functional and subjective assessment of patient outcome, the SEFAS was used. It is a specific foot and ankle patient-reported outcome measurement that has been validated for different foot and ankle disorders.9,10 The maximum achievable score is 48, representing normal foot function. The lowest score of 0 represents severe disability.


Weightbearing AP and lateral radiographs were obtained preoperatively and at the final follow-up. Meary’s angle and the talar coverage angle were recorded on the AP view. On the lateral view, the distance from the plantar cortex of the medial cuneiform to the floor was recorded. The author performed all measurements twice, blinded to the previous result with a minimum 2-week interval. In case of diverging results the mean difference was recorded.

Surgical Indication and Technique

Athroereisis was performed as a single procedure in patients who; (1) were able to perform repeated single heel rise and (2) were capable of fully realigning the medial arch in an upright standing position without elevation of the first metatarsal Fig. 1A (i–ii). An additional open wedge osteotomy of the first metatarsal, a Cotton osteotomy or a naviculocuneiform arthrodesis, was performed in patients who were able to realign the medial arch, but with a considerable elevation of the first metatarsal Figs 1B (i–ii) and 1C (i–ii). Patients who were unable to perform a single heel rise, along with incomplete or absent active realignment of the medial arch, were treated with an arthroereisis in conjunction with reinforcement and augmentation of the medial soft tissues and naviculocuneiform arthrodesis. Regardless of any other concomitant procedure, a gastrocnemius release (Strayer procedure) was performed in patients with a positive Silverskiöld test. For insertion of the HyProCure® implant, a lateral 3 cm incision is made along the skin tension lines over the sinus tarsi. After blunt dissection of the subcutaneous tissue, taking care not to injure any anastomosing branch of the sural nerve, the underlying fascia is cut along its fibers. Going bluntly through the sinus tarsi fat pad, the interosseus talocalcaneal ligament is cut using a pair of Stevens-type scissors (Gramedica, Macomb, Michigan, United States of America). A guide pin is inserted across the tarsal canal, the tip being palpable on the medial side. The HyProCure® implant has a conical head and a cylindrical shaft designed for being seated in the canal, making it a medially anchored device (Fig. 2). Trial implants are inserted over the pin, and peritalar subluxation is evaluated in a sequenced manner by visual inspection when a cephalad-directed force is applied on the plantar aspect of the fifth metatarsal head. While performing this maneuver, not more than 4 degrees of forefoot valgus should be tolerated. Proper seating of the implant is confirmed with intraoperative fluoroscopy. The leading edge of the base of the implant should not extrude the lateral margin of the overlying talar neck (Figs 3A to C).

Figs 1A to C: Active realignment of the medial arch: relaxed stance and neutral stance showing significant elevation of the first metatarsal

Fig. 2: First generation HyProCure® implant used in this series

Figs 3A to C: (A) peritalar subluxation evaluated by visual inspection of the foot during forced manual eversion; (B) Maximum 4° of forefoot valgus is desired for optimal implant size; (C) Proper seating of the implant is confirmed with intraoperative radiographic evaluation

Statistical Methods

Continuous variables are described with mean, standard deviation (SD), median, range, and 95% CI for mean. For the comparison of continuous variables over time, a linear non-parametric permutation test for paired observations was used. All tests were two-tailed and conducted at the 5% significance level. All analyses were performed with (Statistical Analysis Software) SAS version 9.4, SAS Institute, Cary, North Carolina, United States of America.


A total of 40 procedures were performed on 37 patients, of whom 10 were male with a mean age of 51.5 years, and 27 were female with a mean age of 44 years (Table 1). The average follow-up time was 46 (range 35–60) months. A single procedure was performed in 19 cases (five males and 14 females), and a combined procedure in another 21 cases (five males and 16 females). Preoperative SEFAS forms were completed in all cases. Postoperative SEFAS forms were completed at the final follow-up in 32 cases (15 single and 17 combined procedures). In the remaining eight cases, the implant had been removed prior to the final follow-up. The average time between implantation and removal was 20 (range 2–54) months.

Table 1: The dataset
Case Sex Age Side Op Adjuvant diagnosis (note) TMT1 MT1 Cotton NC1 NC1/2 TN PMGR Strayer Tib ext Spring FDL Other Patient satisfaction Likelihood
1 F 50 R Comb RA 1 Very satisfied Very likely
2 F 46 L Comb (Right side = case 17) 1 1 1 Very satisfied Very likely
3 M 39 L Single Plantar heel pain Neither nor Likely
4 M 29 L Comb 1 Very satisfied Very likely
5 F 50 L Single (Right side = case 6) Plate removed* Satisfied Very likely
6 F 50 R Single (left side = case 5) Satisfied Very likely
7 M 53 R Single Very satisfied Very likely
8 F 19 R Comb 1 Very unsatisfied Likely
9 M 66 L Comb HV 1 Very satisfied Very likely
10 F 51 R Comb Rec prev surg 1 Removed
11 F 36 L Comb 1 Removed
12 F 27 R Single Removed
13 F 55 L Comb Ankle OA 1 Removed
14 F 46 R Single HV + Tailors bunion Removed
15 F 38 R Single HV (Left side = case 24) Satisfied Very likely
16 M 54 R Single Satisfied Very likely
17 F 47 R Comb HV (Left side = case 2) 1 Very satisfied Very likely
18 F 45 L Comb HV + Med Sesam Sesamoidectomy Neither nor Very likely
19 F 70 R Comb HV 1 Very satisfied Very likely
20 F 66 R Single Satisfied Likely
21 F 31 R Comb Os tibiale externum 1 1 Very satisfied Very likely
22 M 76 L Single PB dislocation Retinaculoplasty Neither nor Very likely
23 F 30 R Comb Talocalcaneal coalition Coalition resected Satisfied Likely
24 F 39 L Single (right side = case 15) Very satisfied Very likely
25 F 67 R Comb 1 1 1 TP/FDL tenodesis Satisfied Very likely
26 F 14 L Single Very satisfied Likely
27 F 53 L Single Very satisfied Very likely
28 M 59 L Comb 1 1 Satisfied Very likely
29 F 23 L Comb Os tibiale externum 1 1 Kidner procedure Removed
30 F 57 R Single Neither nor Not likely
31 M 30 L Single Removed
32 F 52 R Single Very satisfied Very likely
33 F 23 L Single Very satisfied Very likely
34 F 42 L Single Very satisfied Very likely
35 F 26 L Single Removed
36 F 58 R Comb 1 1 1 Neither nor Likely
37 F 55 R Comb Rec prev surg 1 1 Very unsatis-fied Not likely
38 F 56 L Comb RA 1 Satisfied Very likely
39 M 45 R Comb 1 Very satisfied Very likely
40 M 64 R Comb 1 Very satisfied Very likely

Patient data, coexisting diagnoses, procedures and patient satisfaction; comb, combined procedure; single, single procedure; TMT1, TMT1 fusion; MT1, first metatarsal open wedge osteotomy; Cotton = Cotton osteotomy; NC1, naviculocuneiform 1 fusion; NC1/2, naviculocuneiform 1 + 2 fusion; TN, talonavicular fusion; PMGR, proximal medial gastrocnemius release; Strayer, Strayer procedure; Tib ext, os tibiale externum excision; spring, spring ligament repair; FDL, FDL transfer; RA, rheumatoid arthritis; HV, hallux valgus; rec prev surg, recurrent flatfoot after previous surgery; OA, osteoarthritis; med sesam, medial sesamoiditis; PB dislocation, peroneus brevis tendon dislocation; *previous ankle fracture

Patient Satisfaction

No difference was found between the single and combined procedure groups regarding patient satisfaction. All eight patients who had had the implant removed were unsatisfied with the procedure (Table 2). SEFAS score for the whole group of patients improved significantly with a mean change of +15.9 (SD 8.7, p < 0.001). For the single and combined procedure groups, SEFAS score improvement was +14.5 (SD 7.1, p < 0.0001) and +17.2 (SD 10.0, p < 0.0001), respectively (Tables 3A and 3B). In two of the three patients with bilateral procedures, SEFAS score improvement was similar for both sides, the difference being 1 point between the left and right foot (cases 5 + 6 and 15 + 24). One patient had similar postoperative SEFAS scores on both sides, although the improvement was twice as large on one side with a very low preoperative SEFAS score (cases 2 + 17).

Table 2: Patient satisfaction
Single procedure (n = 15 cases)
 Pleased or very pleased 12
 Original pain in the foot is gone 8
 Likely or very likely to recommend procedure 14
Combined procedure (n = 17 cases)
 Pleased or very pleased 14
 Original pain in the foot is gone 11
 Likely or very likely to recommend procedure 16
Implant removed (n = 8 cases)
 Unpleased or very unpleased 8
 Original pain in the foot is gone 0
 Likely or very likely to recommend procedure 0
Table 3A: Functional and radiographical results for single procedures
Variable Preoperative Final follow-up Change p-value
SEFAS 20.9 (8.1) 34.7 (10.3) 14.5 (7.1) <0.0001
23 (4; 34) 38 (11; 45) 13 (3; 26)
(17.0; 24.8) (29.0; 40.3) (10.6; 18.5)
(n = 19) (n = 15) (n = 15)
Meary’s angle 21.0 (7.9) 11.6 (8.3) −9.3 (5.7) 0.0002
17.4 (8.7; 35.4) 10.5 (0.5; 29) −9.6 (−20; −1.4)
(16.2; 25.7) (6.6; 16.6) (−12.8; −5.9)
(n = 13) (n = 13) (n = 13)
Talar coverage angle 21.8 (11.8) 14.3 (11.7) −7.5 (4.2) 0.0002
17.2 (7.1; 45.9) 11.4 (0.4; 42.6) −6.7 (−14.4; −1.6)
(14.7; 28.9) (7.3; 21.4) (−10; −5)
(n = 13) (n = 13) (n = 13)
Cun1-floor distance 17.9 (4.2) 24.1 (5.6) 6.2 (4.6) 0.0012
18.5 (8.2; 24.3) 24.1 (15.7; 33.1) 6.6 (−2.8; 13.6)
(15.4; 20.4) (20.7; 27.5) (3.4; 8.9)
(n = 13) (n = 13) (n = 13)

SEFAS, Meary’s angle in the frontal plane (degrees), talar coverage angle (degrees), cuneiform 1 to floor distance (mm), mean (± SD)/median (min; max)/(95% CI for mean)

Table 3B: Functional and radiographical results for combined procedures
Variable Preoperative Final follow-up Change p-value
SEFAS 16.9 (8.6) 35.6 (11.1) 17.2 (10.0) <0.0001
17.0 (4; 30) 39 (7; 47) 18 (−2; 39)
(12.9; 20.8) (29.9; 41.3) (12.0; 22.3)
(n = 21) (n = 17) (n = 17)
Meary’s angle 22.0 (12.3) 16.8 (10.0) −5.2 (9.0) 0.036
22 (2.2; 44.4) 16.4 (1.9; 35.7) −7.5 (−15.6; 19.1)
(15.4; 28.5) (11.4; 22.1) (−10.0; −0.5)
(n = 16) (n = 16) (n = 16)
Talar coverage angle 25.2 (8.6) 17.0 (9.6) −8.3 (7.5) 0.0005
23.1 (8.1; 42.2) 16.7 (0; 33.5) −6.4 (−22.1; 1.6)
(20.6; 29.8) (11.9; 22.1) (−12.3; −4.3)
(n = 16) (n = 16) (n = 16)
Cun1-floor distance 17.9 (6.6) 26.8 (6.0) 8.9 (6.5) 0.0002
17 (8.4; 29.9) 26.7 (11.4; 35) 8.7 (−1.0; 19.3)
(14.3; 21.4) (23.6; 29.9) (5.4; 12.4)
(n = 16) (n = 16) (n = 16)

SEFAS, Meary’s angle in the frontal plane (degrees), talar coverage angle (degrees), cuneiform 1 to floor distance (mm), mean (± SD)/median (min; max)/(95% CI for mean)

Functional Results Single Procedure Group (n = 15 Cases)

Regarding longer walks and activities, 11 patients (11 cases = 73.3%) reported they had no pain or discomfort. Two patients (cases 22 and 30) had the same limitations as before surgery, with case 22 eventually being scheduled for a talonavicular arthrodesis. One patient (case 3) had persistent limitations that were not related to the sinus tarsi implant. These three patients were neither pleased nor unpleased with the procedure. One patient with some postoperative discomfort was still pleased with the procedure (case 5).

Functional Results Combined Procedure Group (n = 17 Cases)

Regarding longer walks and activities, 11 patients (12 cases = 70.6%) reported they had no pain or discomfort. One patient (case 39) returned to work teaching tennis 16 months after surgery. One patient (case 40) managed to achieve a top 5 Ironman ranking 17 months after surgery. The bilaterally operated patient (cases 2 + 17) reported the same degree of satisfaction for both sides. Another three patients (three cases = 17.6%) reported mild pain or discomfort with little impact on daily activities. Two patients (two cases = 11.8%) had persistent limitations that were not related to the sinus tarsi implant.

Radiographical Results

Weightbearing radiographs showed in all cases one or more signs of flatfoot deformity preoperatively—a break in Meary’s line, an increased talar coverage angle, and/or a decreased medial cuneiform to floor distance. Non-weightbearing radiographs showed, in all cases, a proper position of the implant postoperatively (Figs 4A and B). At the final follow-up, weightbearing radiographs were collected in 29 cases. Three cases were not available for radiographical follow-up examination (cases 4, 26, and 30). Meary’s angle in the frontal plane, talar coverage angle, and Cuneiform 1 floor distance for the whole group of patients improved significantly with a mean change of −7.1° (SD 7.8, p < 0.001), –7.9° (SD 6.1, p < 0.001) and +7.7 mm (SD 5.8, p < 0.001) respectively. For the single procedure group, the mean changes were −9.3 (SD 5.7, p = 0.0002), −7.5 (SD 4.2, p = 0.0002), and +6.2 (SD 4.6, p = 0.0012), respectively. For the combined procedure group, the mean changes were −5.2 (SD 9.0, p = 0.036), −8.3 (SD 7.5, p = 0.0005), and +8.9 (SD 6.5, p = 0.0002), respectively (Tables 3A and 3B).No associations between implant removal and implant size or between implant removal and preoperative values for Meary’s angle, talar coverage angle, and Cuneiform 1 floor distance were found (Table 4).

Table 4: Implant size and preoperative radiographical measurements in cases with and without removed implant
Variable Total (N = 40) Implant not removed (n = 32) Implant removed (n = 8) p-value Difference between groups Mean (95% CI)
Implant size 5.8 (0.7) 5.8 (0.7) 5.6 (1.1) 0.8 0.2 (−0.4; 0.8)
6 (5; 8) 6 (5; 7) 5 (5; 8)
Meary’s angle 21.5 (10.0) 21.0 (10.1) 23.4 (9.7) 0.6 −2.4 (−10.2; 5.9)
20.6 (2.2; 44.4) 18.8 (2.2; 44.4) 22.6 (10.9; 37.7)
Talar coverage angle 23.3 (9.3) 23.2 (9.9) 23.8 (6.9) 0.9 −0.6 (−7.8; 7.2)
22.2 (7.1; 45.9) 22.2 (7.1; 45.9) 23.6 (12.1; 35.4)
Cun1-floor distance 18.4 (5.6) 18.1 (5.4) 19.7 (6.8) 0.5 −1.6 (−6.2; 3.1)
18.4 (8.2; 29.9) 18 (8.2; 29.9) 21.2 (9.6; 29.5)

Mean (±SD); median (min; max); and mean difference (95% CI for mean)

Figs 4A and B: Postoperative radiographs showing implant in proper position; (A) Single procedure and (B) Combined procedure

Reoperations (n = 40 Cases)

A total of 10 patients underwent further surgery related to the HyProCure implant (Table 5). Two patients were reoperated because of pain and recurrent deformity (cases 10 and 38). In both cases, the position of the implant had changed. Case 10 had gross overweight. Although a Cotton osteotomy had been performed, stabilization of the medial column was insufficient, resulting in an insufficient realignment of the foot. Repositioning of the implant, along with a change to a smaller size, a medial displacement calcaneal osteotomy, and a fusion of the 1st and 2nd naviculocuneiform joints, was performed 25 months after the index operation. Another 6 months later, at a total of 54 months, the HyProCure implant was removed because of pain. Case 38 had both overweight and rheumatoid arthritis. An adjunctive proximal medial gastrocnemius release had been performed but no medial column procedure. A repositioning of the implant, a Cotton osteotomy, along with an open tendo Achilles lengthening, and a medial soft tissue reconstruction were performed 10 months after the index operation. Seven patients were reoperated because of pain alone (cases 11, 12, 14, 26, 29, 31, and 35). These patients all had a desired implant position, determined on postoperative and follow-up radiographs, as well as an appropriate foot alignment. In case 11, the implant was changed to a smaller size after 1 month and removed a month later. A new implant of the same size was reinserted along with a fusion of the talonavicular joint 18 months after implant removal. Case 12 had the implant removed 12 months after the index operation. A medial displacement calcaneal osteotomy along with an advancement of the posterior tibial (PT) tendon (Kidner procedure) was performed 8 months later. Case 14 had no further surgery after implant removal, which was done along with bunion surgery 31.5 months after the index operation. Case 26 had the implant changed to a larger size after 3 weeks. Case 29 had the implant removed after 23 months. A fusion of the talonavicular joint was performed 33 months after implant removal. Another 13 months later, an additional calcaneocuboid arthrodesis along with an arthrodesis of the 1st and 2nd naviculocuneiform joints was performed. Case 31 had the implant removed after 7 months. A medial displacement calcaneal osteotomy along with Cotton osteotomy, shortening of the PT tendon, and flexor digitorum longus (FDL) transfer was performed 13 months later. Case 35 had the implant removed after 19 months and is scheduled for a medial displacement calcaneal osteotomy, a gastrocnemius release, and a Cotton osteotomy. The reoperation has been delayed because of the COVID-19 pandemic. One patient (case 13) had the implant removed because of overcorrection. This patient had both flatfoot and asymmetrical arthritis in the ankle joint. After the initial procedure, pain in the ankle joint increased along with a varus tilt of the foot, making implant removal and, subsequently, a total ankle replacement necessary 12 months after the index operation. In total, eight implants were removed (20%) during the follow-up time, with a mean of 20 (2–54) months between the index operation and removal.Two patients were reoperated for reasons not related to the HyProCure implant. One patient (case 3) with flatfoot and recurrent severe plantar heel pain had good realignment of the foot and was initially pain-free. However, heel pain returned, and the patient requested further surgery with a plantar fasciotomy. The surgery did not make the patient pain-free. In case 37, hardware from the Lisfranc joint was removed.

Table 5: Reoperations listed for all cases
Case Size No. Cause Smaller Larger Repositioned Removed New implant MDCO Cotton NC fusion TN fusion TAL FDL transfer
1 5
2 7
3 S6
4 6
5 S6
6 S6
7 S6
8 5
9 6
10 6 2 Pain and recurrence 1 1 1 1 1
11 8 4 Pain 1 1 1 1
12 S6 1 Pain 1 1 1
13 5 1 Overcorrection 1
14 S5 1 Pain 1
15 S6
16 S7
17 6
18 5
19 5
20 S6
21 6
22 S7
23 6
24 S6
25 5
26 S5 1 Pain 1
27 S7
28 5
29 5 1 Pain 1 1
30 S5
31 S5 2 Pain 1 1 1 1
32 S6
33 S6
34 S5
35 S5 1 Pain 1
36 5
37 6
38 6 1 Pain and recurrence 1 1 1
39 6
40 S5

Size, implant size (S + size = single procedure); no, total number of reoperations (some of which include more than one procedure); cause, reoperation cause; smaller, change to smaller size; larger, change to larger size; MDCO, medial displacement calcaneal osteotomy; Cotton, Cotton osteotomy; NC fusion, naviculocuneiform 1/2 fusion; TN fusion, talonavicular fusion; TAL, tendo Achilles lengthening; FDL transfer, flexor digitorum longus transfer


Along with the concept of soft tissues put under constant stress, there is evidence that they might not always have to be repaired. For instance, the PT tendon in the early stages of Progressive Collapsing Foot Deformity can recover when the foot is balanced.11,12 This is the primary rationale for balancing the foot by means of either a subtalar arthroereisis or a medial displacement calcaneal osteotomy without reconstruction of the soft tissues. A subtalar arthroereisis provides a three-plane correction of the deformity but is generally not considered to be a standalone procedure.5,6 In this series, a single procedure arthroereisis was performed in patients with functionally intact soft tissues, that is, patients that actively were able to perform a realignment of the medial arch without elevating the first ray. If any elevation of the first ray is left untreated, inferior results after a single procedure arthroereisis would be expected. It is important to note that a sinus tarsi implant alone has a limited capacity to stabilize the medial column.13 Probably due to careful patient selection, our results did, in fact, show that single-procedure patients had subjective and functional results comparable to those who had arthroereisis combined with other surgical procedures. Overall, patient satisfaction being similar in both groups, our results support the use of a single procedure arthroereisis in selected cases. However, errors can still be made when patients are selected. In this series, case 22 most likely had a single procedure performed on the wrong indication and was eventually scheduled for a talonavicular arthrodesis. Mercun et al.14 found inferior results in their combined procedure group as compared with their single procedure group. However, in their study, procedures performed along with the arthroereisis were classified as combined procedures, even if they were not related to the flatfoot deformity. It was speculated that subclinical cartilage degeneration might be present in cases requiring combined surgery and that non-related pathologies might influence results negatively in the combined procedure group. In this study, all procedures classified as combined procedures had a relation to a flatfoot deformity. Our results are in accordance with Needleman,5 who reported a 78% satisfaction rate in a series of 23 adult flatfoot patients undergoing combined procedures, including a subtalar arthroereisis with a sinus tarsi implant.

Patient Satisfaction and Implant Removal

In this series, eight patients had pain related to the HyProCure® implant, all of which were reoperated with implant removal. With appropriate implant position and maintained foot realignment, technical failure could be one reason. For instance, the implant may be too small or too large. A small implant can allow for painful subtalar instability. Noticeably, five of the eight removed implants were size 5, which is the smallest available implant. In one case, the implant was changed from size 5 to 6, making the patient pain-free (case 26). A large implant, on the other hand, may impinge on the walls of the tarsal canal. All patients experiencing discomfort had pain when their hindfoot was passively forced into inversion but not when forced into eversion. Since the sinus tarsi open laterally when the hindfoot is inverted, the pain was probably not caused by lateral impingement. A possible impingement would more likely be at the cylindrical medial portion of the implant. In order to achieve proper denervation of the sinus tarsi, Viladot et al. recommend cauterization of the sinus tarsi walls before implant insertion.15 In this series, no attempt to denervate the sinus tarsi was made. Instead, attention was focused on careful sizing and proper placement of the implant. Nevertheless, the sizing and positioning of the implant is a subjective assessment made by the surgeon. For the individual surgeon, there is a learning curve. Although not as good compared with the 6% removal rate reported by Graham et al.,16 our current 20% removal rate is equal or better compared with other reports.5-7,15,17,18

Interosseus Ligament and Implant Dislocation

The interosseus talocalcaneal ligament is considered to be an important hindfoot stabilizer.19 The HyProCure implant, in contrast to other commonly used sinus tarsi implants, is seated fully into the tarsal canal. Therefore, the interosseus ligament is cut prior to insertion. Importantly, however, the ligament remnants are left in place, forming fibrous scar tissue around the implant. Other implants are placed, as the name implies, in the sinus tarsi, without intruding into the canal. In these cases, the interosseus talocalcaneal ligament is left intact. With a central placement in the canal, a predictive stabilizing effect on the subtalar joint as well as a low implant dislocation rate, is expected. In this series, two implants were dislocated. After repositioning, there was no recurrent dislocation.

Radiographical Changes

Radiographical results matched poorly with subjective and functional results in both the single and combined procedure group. These findings correspond to the findings of Myerson et al.20-22 In their study on medial calcaneal displacement osteotomy and transfer of the FDL tendon; the authors noted a similar lack of correlation between radiographical parameters and subjective outcome. Compared with the single procedure group, a better improvement of radiographical parameters could have been expected in the combined procedure group. However, only a marginal difference was noted. A possible reason could be a type II error.

What to do after Implant Removal

When postoperative radiographs after the index operation shows undercorrection, there is an increased risk for implant removal.8 It follows that the need for further surgery increases in these cases. Logically, if an arthroereisis procedure has failed to stabilize the subtalar joint complex for whatever reason, a subtalar arthrodesis could be the next step. However, just as in the case of an arthroereisis, it is not a standalone procedure as long as there is any residual forefoot varus.20,21 Even a subtalar arthrodesis must be followed by a medial column procedure that corrects the midfoot. In order to spare the subtalar joint, a failed subtalar arthroereisis is more likely to be followed by a medial calcaneal displacement osteotomy, the indication for these two procedures being the same. If needed, it should be combined with a medial column procedure for the same reason as for a subtalar arthrodesis.Generally, pain-free patients with recurrent deformities after the removal of a sinus tarsi implant are likely to postpone any further surgery until the foot becomes painful. It is assumed that the soft tissues have a potential for regeneration if the sinus tarsi implant has been in place for at least 1 year. A reoperation may therefore be postponed in the same way an ankle replacement or fusion is postponed after a supramalleolar osteotomy. In this series, three of eight patients have been reoperated due to recurrent deformity. One patient is still scheduled for further surgery (stand February 2023).The strength of this study is the single surgeon prospective study design with a minimum 3-year follow-up. A limitation is the relatively small number of patients. A multicenter prospective follow-up study with a larger number of patients is pending. In order to further evaluate the role of arthroereisis in the adult patient, a randomized study, as well as a randomization between arthroereisis and medial displacement calcaneal osteotomy, is warranted.In conclusion, subtalar arthroereisis seems to be effective in the treatment of Progressive Collapsing Foot Deformity, both as a standalone and an adjunctive procedure. In either case, careful patient selection is needed. When performed in a nonobese patient with a functionally intact PT tendon and a stable medial column, a standalone subtalar arthroereisis may achieve good subjective and functional results from a mid-term perspective. In all other cases, the implant alone will most likely not do the job in terms of maintaining hind- and midfoot balance. If medial column instability is not taken care of, the demands on the sinus tarsi implant will simply be too great. Consequently, the implant fails to keep the arch up, and adjunctive procedures must be performed. More studies need to be conducted in order to further outline the proper technique and correct sizing of the implant. Both are critical for the maintenance of the correction initially achieved and for long-term patient tolerance.


Martin Ålund https://orcid.org/0000-0002-2285-6462


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