Modified Posterior 2-Portal Technique of Arthroscopic Subtalar Joint Arthrodesis: Improved Pain and Functional Outcome at Mean 15 Months Follow-up—A Case Series

Abstract

Introduction

Posterior arthroscopic subtalar joint arthrodesis (PASTA) via a posterior 2-portal technique has been described. We modified the surgical technique of creating the portals in the plane of the posterior facet (under fluoroscopy guidance) to enhance the ease of access to the joint, easier and complete removal of articular cartilage along with maintaining the heel height.

Methods

Patients of post-traumatic subtalar joint arthritis, treated by PASTA during 2016 till 2019 were included in the study. Exclusion criteria: significant height collapse of calcaneum, lateral blow out or heel widening. The confirmation of subtalar joint as the source of pain was done by injection of local anaesthetic inside the joint under the image intensifier, bringing immediate pain relief. The primary outcome variables assessed were the pain and functional scores, assessed using visual analogue scale and AOFAS (American Orthopaedic Foot and Ankle Society) score, respectively.

Results

The total of 16 patients (7 males, 9 females) was included. The average age was 40.68 years (23–58 years). The underlying pathology in all patients was post-traumatic subtalar arthritis secondary to calcaneus fracture malunion in 8 patients (50%), talus fracture malunion in 4 (25%) and ligament injury in 2 patients (12.5%). No bone grafting was done. The mean duration of follow-up was 15.6 months (9–24 months). There was a statistically significant improvement (p < 0.001) in mean VAS score at follow up (2; range 0–4) as compared to the mean preoperative score (7; range 6–9). The AOFAS score also improved significantly (p < 0.001) at the follow up (mean 79; range 68–89) as compared to the preoperative score (mean 18; range 10–25).

Conclusion

The posterior arthroscopic fusion of subtalar joint gives good results in terms of pain relief and functional scores when done for carefully selected patients of subtalar joint arthritis. Our slight modification of the original technique improves the ease of removing cartilage from subtalar joint with minimal height loss; thus, precluding any need for bone graft. It also makes the instrument movement easier inside the joint.

Introduction

Ankle and subtalar joint (STJ) arthroscopy technique was described by Dijk et al. [1] using the 2-posterior portal technique in prone position. Arthroscopic subtalar joint arthrodesis (ASTA) has been described in the previous studies, with different approached. Tasto et al. [2] performed the ASTA using the anterolateral and posterolateral portals in the lateral decubitus position, fusing both the facets of subtalar joint. Carro et al.[3], on the other hand, described the technique of prone posterior subtalar arthrodesis, fusing only the posterior facet.

Posterior arthroscopic subtalar joint arthrodesis (PASTA) via two/three portal technique, has been described previously by few studies. All the previous reports performed fusion for subtalar joint arthritis due to multiple causes, e.g. post-traumatic, adult acquired flat foot, tarsal coalition, inflammatory arthritis, etc. We present here a mid-term follow-up outcome of arthroscopic subtalar joint arthrodesis in 16 cases of post-traumatic subtalar joint arthritis. We did a few modifications to the posterior two-portal surgical technique for ease of access and complete removal of cartilage from the subtalar joint, simultaneously maintaining the heel height. The aim of the study was to assess the outcome of posterior arthroscopic subtalar arthrodesis in post-traumatic arthritis using the above-mentioned modification in surgical technique. This would be the first study to report results only on post-traumatic subtalar joint arthritis treated with PASTA.

Materials and Methods

Methodology

This is a prospective case series. All the patients presenting to our outpatient clinic from 2016 to 2019with complaints of hind-foot pain due to post-traumatic subtalar joint arthritis were included in the study. The exclusion criteria were significant height collapse of calcaneum (managed with open arthrodesis with iliac crest bone grafting), lateral blow out or heel widening, inflammatory arthritis, etc. Clinical examination and radiographs of the foot were examined; patients with arthritis in any other joint in the foot or having multiple sources of foot pain were excluded. All those included in the study underwent modified PASTA (Posterior Arthroscopic Subtalar arthrodesis) by a single surgeon as mentioned in surgical technique below. Informed consent was obtained from all the patients.

The confirmation of subtalar joint as the source of pain was done by injection of local anaesthetic inside the joint under the image intensifier, bringing immediate pain relief. The primary outcome variables assessed were the pain and functional scores. The pain was assessed using VAS (visual analogue scale) score. The functional scoring was done by AOFAS (American Orthopaedics Foot and Ankle Society). A score of 90–100 was taken as excellent, 75- 89 as good, 50–74 as fair and less than 50 as poor. Both scores were measured preoperatively and at the last follow-up. The radiological union was assessed on the antero-posterior and lateral radiographs of foot on serial follow-up.

The data were analyzed using SPSS v.21. Correlation between various parameters has been calculated using Pearson's Correlation Coefficient. Continuous data between cases and controls was compared using independent sample t test. A p value of less than 0.05 was considered as statistically significant.

Surgical Technique

The patient was positioned in prone position after general anaesthesia with foot hanging down from the table end. Thigh tourniquet was applied. Preoperative single antibiotic injection of third-generation cephalosporin was given. A calcaneal Denham’s pin was inserted to provide for intraoperative traction and control of varus/valgus position during fixation. Image intensifier was positioned to view the lateral radiograph of the subtalar joint. A spinal needle 18G was placed on the skin laterally over the subtalar joint such that it laid along the posterior facet in the radiograph and the path was marked (Fig. 1). The site of posterolateral portal was marked where the needle touched the lateral border of Achilles tendon (Fig. 2). After incising the skin, subcutaneous tissues were dissected to enable the straight artery forceps to reach the subtalar joint. The direction of artery forceps was kept towards the web space between first and second metatarsals and directed in line with the mark of needle. The aim was to reach the posterior aspect of subtalar joint, which can be checked with radiograph. Subsequently cannula sheath and 4 mm 30° arthroscope was passed through the portal. We have used 4 mm arthroscope here as we did not encounter any problems while manoeuvring it in the subtalar space. In the previous descriptions of the STJ scopy, few authors have also used the 4 mm scope for fusion [1, 4, 5]. The posteromedial portal was also made at the same level of the lateral portal, just medial to the Achilles tendon. The method of making and advancing instruments through this portal was the same as described by Dijk et al. [1]. The whole working area remained lateral to the Flexor Hallucis Longus (FHL) tendon to avoid injury to the blood vessels. Posterior subtalar capsule is thin and can be removed easily with arthroscopic punch. Sometime posterior talus osteophytes are present which can hinder the view and instrument movement. They can be easily burred out. We recommend here to move the calcaneum via the pin and do ankle movements to correctly identify the subtalar space. This is important in cases where large posterior osteophytes hinder correct identification of the talus.

Fig. 1.

Intraoperative positioning of the spinal needle in the plane of subtalar joint posterior facet, on lateral view

Fig. 2.

Marking the portal sites at the lateral border of tendo-achilles where the needle touches

After the joint was opened by shaving the posterior capsule, preparation of the joint space for arthrodesis can be started. The arthroscope was moved to the posteromedial portal and a small chisel [6–8 mm] was inserted with edge vertical, through the posterolateral portal. After reaching the joint margin, the chisel was rotated 90 degree to make the edge horizontal, thus easily entering into the joint (Fig. 3). Cartilage from the articular surfaces can be easily removed without damaging much subchondral bone, as the chisel is oriented parallel to the joint due to conscious positioning of the portals under fluoroscopy to facilitate that. This reduced the amount of gap created after joint preparation as less bone is removed; hence the heel height loss is negligible.

Fig. 3.

Arthroscopic view of the chisel after introduction through the portal and rotated 90 degrees to make it parallel to the articular surface

Compression across the joint was achieved via two partially threaded cannulated screws inserted from the non-weight bearing surfaces of the calcaneum (Fig. 4). The opposition of raw surfaces has to be achieved for good fusion and should be checked fluoroscopically and arthroscopically. Although inserting the guidewire and screws, slight calcaneum valgus was maintained via calcaneal pin. The follow-up showed good union (Fig. 4).

Fig. 4.

The comparison of the preoperative radiograph of a patient with calcanuem fracture through posterior facet (left) and the final follow-up image (right), good fusion with symptom improvement

Post-operatively patients were mobilized non-weight bearing and given a below-knee slab for 6 weeks. Gradual ankle movements were started at 6 weeks after slab removal. Progressive weight bearing as tolerated was started after 6 weeks. Aspirin 75 mg was given for prophylactic anticoagulation for 6 weeks.

Results

A total of 16 subjects [7 males, 9 females] were operated. The average age was 40.68 ± 9.14 years (23 – 58 years). The underlying pathology in all patients was post-traumatic subtalar arthritis secondary to calcaneus fracture malunion in 8 patients (50%), talus fracture malunion in 4 (25%) and ligament injury in 2 patients (12.5%). In two patients we did not find any significant underlying cause of osteoarthritis after trauma. The two patients with ligament injury had given history of twisting injury to foot due to road traffic accident with swelling in the region of lateral talo-calcaneal ligament and were managed outside our hospital before presenting to us. Although on examination they did not have any excess laxity in medial or lateral ligaments. Hence, the post-operative protocol was kept the same for them. The malunion cases did not require any corrective surgery. The chief complaint was pain while walking with mean duration of symptoms before surgery of 15.25 ± 15.65 months (range 4–60).

The mean duration of follow-up was 15.56 ± 5.12 months (9–24 months). Bony union was achieved in all the patients at an average of 3.71 ± 0.79 months (2.5–5 months) after surgery. There was a statistically significant improvement (p < 0.001) in mean VAS score at follow-up (2.06 ± 1.48; range 0–4) when compared with the mean preoperative score (7.43 ± 1.03; range 6–9). Three (18.75%) patients had a residual moderate pain (VAS > 3). The AOFAS score also improved significantly (p < 0.001) at the follow-up (mean 78.93 ± 7.57; range 68–89) when compared with the preoperative score (mean 18 ± 5.7; range 10–25) (Table 1). Five (31.25%) patients achieved fair functional status while 11 (68.75%) patients achieved good functional status, none had poor or excellent functional outcome. Two patients had wound healing complications at the screw insertion site, it was managed successfully by giving antibiotics for 2 weeks. No other major complication was encountered.

Table 1.

The master chart of the demographic and follow-up data of the patients

	Patient age (years)	Sex	Duration of complaints	Pre-existing cause	Follow up (months)	VAS score		AOFAS ankle hindfoot score	Time to union
						Preop	Post-op
1	35	M	8 months	Talus fracture malunion	9	7	2	77	4
2	47	M	1 year	Ligament injury around ankle due to road accident	9	8	4	73	3.5
3	58	F	5 years	Ligament injury around ankle due to ankle twisting	10	6	1	87	3
4	50	F	9 months	Osteoarthritis	12	9	4	68	2.5
5	23	M	1 year	Calcaneum fracture malunion	12	8	3	75	3
6	29	F	10 months	Calcaneum fracture malunion	13	7	1	83	3
7	45	F	1 year	Calcaneum fracture malunion	14	9	2	81	4
8	37	M	4 year	Talus fracture malunion	14	6	2	76	4
9	45	F	6 months	Osteoarthritis	15	8	4	68	4.5
10	35	M	1 year	Calcaneum fracture malunion	15	8	3	73	5
11	28	F	7 months	Talus fracture malunion	16	7	4	71	4
12	47	F	1 year	Calcaneum fracture malunion	18	7	2	77	3.5
13	45	F	1.5 year	Calcaneum fracture malunion	20	9	0	89	3.5
14	39	M	4 months	Talus fracture malunion	24	7	1	87	2.5
15	41	F	6 months	Calcaneum fracture malunion	24	7	0	89	4.5
16	47	M	8 months	Calcaneum fracture malunion	24	6	0	89	5

The VAS scores at the follow-up showed a negative correlation with the follow-up duration of patients (spearman r = − 0.401; p = 0.053). The AOFAS score, on the other hand, showed a positive correlation (spearman r = 0.455; p = 0.077) with the same. Both associations were statistically non-significant. None of the patient needed revision surgery, and were able to walk comfortably.

Discussion

In the year 2000, Van Dijk et.al [1] published the technique for endoscopic evaluation of posterior ankle pathologies via posterior portals. Tasto et al. [2] in 2003 described the arthroscopic technique for subtalar arthrodesis in lateral decubitus position vial the anterolateral and accessory portals. Carro et al. [3] in 2007 published the technique in 4 patients operated for subtalar arthrodesis via the posterior two-portal approach in prone position. Lee et al. [6], observed that anterior arthroscopic subtalar arthrodesis (AASTA) needed removal of interosseous ligaments and their neurovascular structures in order to fuse fully the subtalar joints, but this may lead to AVN of talus and nerve dysfunction. PASTA has been tried by many authors with either 2 or 3 portals. PASTA offers several advantages over AASTA through lateral and anterior portals, such as preservation of blood supply, faster recovery, less pain, preservation of foot proprioception and fewer complications as noted by Oliva et al. [7], although is more demanding technically. In the current study, we were able to achieve union in all the patients. This is coherent with the results reported by the previous studies on PASTA technique by Carro et al. [3], Albert et al. [4] and Vila Rico et al. [8]. Amendola et al. [9] and Oliva et al. [7] reported one case each of non-union after surgery. These results indicate towards excellent outcome of the PASTA surgery in STJ arthritis cases. Coulomb et al. [10] reported 72.7% CT fusion rate at 12 months follow-up after PASTA, the functional and satisfaction scores were independent of the whether the STJ fusion was complete/partial. We followed the methodology of Rungprai et al. [11] of defining the clinical union which included the absence of pain on walking with no STJ movement or crepitus on examination.

In our study, we have included only post-traumatic STJ arthritis cases, due to calcaneus fracture, talus fracture or ligament injury. Previous studies of arthroscopic posterior STJ fusion had variable underlying diagnoses ranging including trauma/fracture, tarsal coalition, inflammatory arthritis, adult acquired flat foot and subtalar joint primary osteoarthritis [2–4, 7, 9, 11, 12]. The posterior facet of the STJ has been a common site of pathology in STJ arthritis secondary to various etiologies [3, 4, 9, 11, 12], hence the use of posterior portals provides an anatomical advantage during the surgery. This study is the second largest case series focusing only on post-traumatic STJ arthritis outcome following PASTA. Only two studies have been published previously reporting similar pathology. The first was by El Shazly et al. [13] (2009), reporting outcome in 10 patients of post-calcaneal fracture STJ arthritis. The second study was by Vila-Rico et al. [12] (2018) reporting outcome in 37 patients of post-calcaneal fracture STJ arthritis.

The subtalar joint is a small volume joint with limited space. This space is further reduced due to the arthritic changes, posterior osteophyte formation and erosion which can significantly limit the movement of the instruments. We modified the surgical technique to orient the arthroscope and other instruments (as described in our technique above) in the plane of the posterior facet joint. This eased the view and movement inside the subtalar joint. Another advantage of staying in the plane of joint is that while using the chisel, articular cartilage can be removed in a thin file leaving flat subchondral bone behind. This helps in good apposition and compression of the surfaces. As the cartilage is removed with precision with minimal bone erosion, subsequent talocalcaneal height loss is negligible. As mentioned above, we achieved good fusion result in all the cases operated with this technique. Prone position offers several advantages, such as safe access to posteromedial corner and allows shape of subtalar joint to be better understood, better placement of screws from calcaneum to talar neck and ease of fluoroscopic imaging in screw placement. The study by Sitler et al. [14], broke the common myth of ease of neurovascular damage with posterior portals due to its close proximity to neurovascular bundles. They showed that there is sufficient space between PM portal and PTA (9.6 mm), tibial nerve (6.4 mm), medial calcaneal nerve (17.1 mm). As observed by Carro et al. [3], postero-medial corner assessment with lateral port is sometimes difficult, which could lead to residual bone and cartilage, which in turn can interfere with arthrodesis. Also, working in direct axis of the joint provides better control of arthrodesis position, more thorough preparation of fusion site, minimal bone loss and less chances of valgus-varus malunion.

In our study, all the patients achieved bony union with the average of 3.7 months for fusion with no major complications. El Shazly et al. [13] reported 11.44 week fusion time, while Vila-Rico et al. [12] reported 12.5 weeks to union. Although Scanton [15] advocated requirement of bone graft to avoid non-union, Dahm et al. [16], and Tasto et al. [2], showed that even without bone graft, union can be achieved in every case. Rungprai et al. [11] performed posterior 3-portal arthroscopic subtalar fusion in 69 patients with use of demineralized bone matrix or platelet concentrate in most cases, reported 94.2% union rate. In the present study it was observed that bone graft is not required for achieving union, though it can be used to hasten union. The structural bone graft can also be used to restore the heel height in cases where there is significant erosion and collapse. To avoid this bias, we excluded all such cases from this study; they were managed with open arthrodesis and bone grafting.

In our study, there was significant improvement in VAS (2.06 ± 1.48) & AOFAS score (78.93 ± 7.57) at final follow up of 15.56 ± 5.12 months (p < 0.001). Vila-Rico et al. [12] have also reported the significant improvement in AOFAS score (76.0 ± 8.0) at final follow up of 57.5 months (p < 0.001). Similarly, El Shazly et al. [13] have also reported significant improvement in the AOFAS score (74) (p < 0.05) and pain and walking distance (p < 0.05) at 2-year follow-up. The scoring data from this study indicate towards the improvement in functional scores as the follow-up duration increases in the subjects. The follow-up duration of patients showed a negative correlation with VAS scores at the follow-up (Spearman r = – 0.401; p = 0.053) and, positive correlation with the AOFAS score (spearman r = 0.455; p = 0.077). Although both associations were statistically non-significant, it indicates a trend towards a better patient satisfaction with increment of duration after the surgery. Such a correlation has not been performed by any earlier study to perform any comparison.

Open arthrodesis has been used traditionally and is still being used at many centres. Quayle et al. [17] showed a significantly decreased union rate after open arthrodesis (83%) when compared to arthroscopic subtalar arthrodesis (98%). In addition, complication rates were higher in open technique, although when non-union was excluded, complication rates were similar. In a systematic review, Mok et al. [18] showed that when compared with open surgery, arthroscopic arthrodesis had a greater fusion rate, lower projected blood loss, shorter tourniquet time, and shorter hospital stay.

Another arthroscopic posterior subtalar arthrodesis technique that has been recently popularized among foot and ankle surgeons as anterolateral arthroscopic posterior subtalar arthrodesis (ALAPSTA) is worth mentioning. Lintz et al. [19] in their cadaveric study demonstrated no nerve damage in 30 feet. Carranza-Bencano et al. [20] reproduced same results in 77 feet being followed for an average of 50 months showed 92% union rates. We did not compare this technique with the one we described, but do report no such complication with excellent union rates.

The strength of the study includes a fair number of sample size and reproducibility of good-fair results with modification of PASTA performed. The limitations of the study include dependence on radiographs for purpose of defining union, shorter duration of follow-up and use of invalidated foot scoring systems (AOFAS) for functional assessment. PASTA is a safe and effective surgical option for STJ arthritis and future studies need to focus on the outcomes based on the aetiology of STJ arthritis. The requirement of the bone grafting during STJ fusion is also an area which need more research and randomized trials. We need more randomized trials comparing the posterior and lateral approach to STJ fusion via arthroscopy.

Conclusion

The PASTA gives good results in terms of pain relief and functional scores when done for carefully selected patients of subtalar joint arthritis. Portal formation under image intensifier guidance for localizing the plane of the posterior facet increases the ease of removing cartilage from subtalar joint with minimal height loss; thus, precluding any need for bone graft to maintain heel height. It also makes the instrument movement easier inside the joint.

Funding

The authors did not receive support from any organization for the submitted work.

Declarations

Conflict of interest

The authors have no conflicts of interest to declare that are relevant to the content of this article.

Ethical approval

Institutional Ethical Committee (IEC) of All India Institute of Medical Sciences (AIIMS), Jodhpur, Rajasthan, India. Reg. No: AIIMS/IEC/2020–21/3052.

Study design

Prospective case series.