Safety and Clinical Ecacy of Double Posterolateral Coaxial Portals for Endoscopic Management of Posterior Ankle Impingement Syndrome

Double Posterolateral Coaxial Portals has been designed by us for Endoscopic Management of Posterior Ankle Impingement. This study’s purpose was analyzed the safety and clinical ecacy of this new designed portals. Six fresh foot samples were randomly selected. The distances of two posterolateral portals to sural nerve in the neutral, dorsiexion and plantar exion positions were measured to evaluate the safety. The clinical ecacy of the operative approach for endoscopic management of posterior ankle impingement syndrome was prospectively analyzed, and its effectiveness and complications were evaluated. In 6 samples, the mean distances of the rst and second portals to sural nerve were 2.26 ± 0.22 cm and 1.59 ± 0.12 cm in the neutral position,2.21 ± 0.21 cm and 1.55 ± 0.12 cm in the dorsiexion 30°position, and 2.46 ± 0.29 cm and 1.73 ± 0.19 cm in the plantar exion 30°position; thus, two portals had a big safety distance to sural nerve. Totally 38 patients received the endoscopic treatment of posterior ankle impingement syndrome with double posterolateral coaxial portals from January 2012 to December 2017. Such operative approach provided a full eld of subtalar joint and posterior ankle during operation. The mean follow-up time was 28.2 (range, 24–72) months, the satisfaction rate was 94.7%; none of patients experienced complications; VAS score was decreased to 0.50 at the last visit from 5.82 before operation(P < .001), while AOFAS score was increased to 92.34 from 71.68, and the differences were both statistically signicant (P < .001); the excellent/good rate was 97.3(cid:0). In treating posterior ankle impingement syndrome, double posterolateral coaxial portals have such advantages of good safety, miniature nerve injury, a good eld of posterior ankle and subtalar joint, good clinical ecacy, and few thus they operative


Background
Posterior ankle impingement syndrome is de ned as posterior ankle pain caused by repeated excessive plantar exion or sudden acute plantar exion of ankle, and it is mostly seen in ballet dancers, soccer and volleyball players. 1 The abnormal factors for impingement include soft tissue and bone abnormalities. 2 There are two types of treatment for posterior ankle impingement syndrome: conservative treatment and operative treatment. Conservative treatment includes taking a good rest, ice compress, oral administration of non-steroidal anti-in ammatory drugs (NSAIDs) and intra-articular injection of hyaluronate sodium. 3 Operative treatment includes open surgery and arthroscopic surgery. Open surgery has some shortcomings, e.g., exposure di culty, big trauma, and easy injury to blood vessels and nerves. 4 Therefore, endoscopic surgery becomes a fashion and trend, and the reasonable selection of portals is important for operative operation and e cacy. The current arthroscopic portals include: 1) bilateral paratendinal portal, with such disadvantages as a demand for changing the body position during operation if requiring the treatment of anterior ankle lesions and a observation blind area of posterior ankle 5 ; 2) lateral portal, with a defect of easy injury to sural nerve; 3) medial portal, with a defect of easy injury to tarsal tunnel 6 ; 4) anterior portal, with some defects, e.g., operation di culty, requiring full traction, and failure to observe subtalar joint synchronously 7 ; 5) bilateral coaxial portal, with a defect of easy injury to tarsal tunnel. 8 An operative approach is urgently needed which causes little injury to nerves and blood vessels, provides a good intraoperative eld, and can manage anterior and posterior lesions. Therefore, we designed double posterolateral coaxial portals based on the considerations of avoiding peroneus longus tendon, peroneus brevis tendon and lateral collateral ligament, fully protecting sural nerve, full exposure and a clear eld of posterior subtalar joint and posterior ankle articular cavity. In this study, we validated the safety of the designed portals using foot samples, and then by prospective investigation. In this study, we intend to verify the safety of this approach through foot specimen study. On this basis, we will further analyze the clinical e cacy of this approach in the treatment of posterior malleolus impingement syndrome through a prospective study.
Materials And Methods

Anatomic measurement
Six fresh frozen cadaver samples were selected, there were 4 males and 2 females. The rst and second portals were established according to the operative operation methods and steps. Then, the trocar was dwelled in the joint, and two Kirschner wires were inserted along the direction of trocar and xed, the diameters of the trocar and Kirschner wires is 1.5mm and 1.0mm. After the withdrawal of trocar, the samples were dissected to expose sural nerve. The distances of two Kirschner wires to sural nerve were measured with the precision of 0.01cm in the dorsi exion 30°, neutral and plantar exion 30° position of ankle, respectively (Fig. 1).

Study objects
Before operation, all patients received X-ray, CT and MRI examinations and completed AOFAS scoring, VAS scoring and routine admission assessment.The inclusion criteria were as follows: 1) severe posterior ankle impingement syndrome, i.e., posterior ankle pain, aggravated at plantar exion, in uencing the daily life; 2) failure of conservative treatment for ≥ 6 months, including drugs, local block, and physical rehabilitation. The exclusion criteria were described below: 1) severe medical diseases and 2) serious infection.
From January 2012 to December 2017, totally 38 patients with posterior ankle impingement syndrome received endoscopic management by double posterolateral coaxial portals after a failure of conservative treatment. The preoperative course of disease was 32 (range, 6-360) months, and the average age of patients was 36.4 (range, 18-62) years.

Ethical approval
This experiment is to study the "Safety and Clinical E cacy of Double Posterolateral Coaxial Portals for Endoscopic Management of Posterior Ankle Impingement Syndrome". The study was permitted by the Ethics Committee of the Southwest Hospital A liated with the Third Military Medical University after enough discussion. The private disease information and imaging information of clinical patients, and the measurement of relevant foot specimen data have passed the informed consent of patients and their families. The experimental research team will strictly follow the principles of Helsinki Declaration and the international code of ethics for biomedical research involving human beings jointly formulated by the World Health Organization and the Council of international medical science organizations to ensure that the medical records (research medical records / X-ray imaging pictures, etc.) of the subjects will be completely preserved, and any public report on the research results will disclose the individual identity of the patients. We will make every effort to protect the privacy of the subjects' personal medical data, disease information, life information and genetic information within the scope permitted by law.

Operative methods
After satisfactory anesthetization, the patients were kept in a side-lying position, and then the routine disinfection and draping were nished. The rst portal was established using the tourniquet with an in ation pressure of 270mmHg, and the speci c procedures were as follows: a 3-4mm skin incision was made at the inferior border of apex capitis bulae anterior to calcaneus bular ligament (Fig. 2), and then the tissues were bluntly dissected with artery forceps avoiding the injury to tendons and cutaneous nerve; the blunt tip was attened against the bular border and then slid forward or backward and broken through the articular capsule after exploring calcaneo bular ligament; posterior ankle and posterior subtalar joint were explored by 30° arthroscopy. The second portal was established under arthroscope, and the procedures were below: a parallel line to planta pedis was marked at lateral ankle, and then a 3-4mm skin incision was made at 5-10mm beside lateral achilles tendon on the intersection of the parallel line and lateral achilles tendon and dilated with artery forceps; thereafter, the blunt tip was punctured vertically in the skin, and the trocar was inserted to establish the second portal. Two portals could be alternatively used as observation and operation portals. The lesion tissues were removed with planer, grinding drill, at-nose pliers and blue pliers, a negative pressure drainage tube was dwelled in the wound after hemostasis by plasma radio-frequency ablation or the complete removal of lesions was con rmed by C-arm X-ray system for bony impingement, and then the wound was sutured layer by layer.

Preoperative and postoperative function follow-up
At 3month and the last visit after operation, the function assessment and satisfaction evaluation were performed using VAS pain scoring and AOFAS hindfoot function scoring. The ankle-hindfoot function scoring results were assessed as below: 90-100 scores, excellent; 72-89 scores, good; 41-71 scores, medium; 1-40 scores, poor. The excellent and good results were satisfactory, while the medium and poor results were unsatisfactory. At 1d after operation, the complete removal of bony impingement was con rmed by X-ray examination; the postoperative complications were observed.

Statistical analysis
The measurement data were presented as . SPSS13.0 statistical software was used. The AOFAS score and VAS score before and after operation were analyzed by pair-wise t test. P<.05 suggested that a difference was statistically signi cant.

Safety analysis
Two portals both had a safety distance to sural nerve and thus exhibited a low risk of injury to sural nerve in the neutral, dorsi exion 30°and plantar exion 30° positions for 6 samples. Generally, we think that the safe distance between the approach and the nerve is 5mm. In our tests, the maximum minimum and mean distances of two portals to sural nerve are More than 1.0cm in the neutral, dorsi exion 30°and plantar exion 30°positions. therefore, the Two portals are a big safety distance to sural nerve (Table1). a A is minimum distances of two portals to sural nerve, B is maximum distances of two portals to sural nerve, C is mean distances of two portals to sural nerve, the unit of the distances is cm.

Effectiveness analysis
During operation, the whole eld of posterior ankle was clearly observed, including medial exor hallucis longus tendon and posterior talar bursa; when the ankle was under dorsi exion, posterior talar apex was fully observed. With these portals, the whole eld of posterior subtalar joint was obtained, and the arthroscopic lens and operating devices could be deepened to medial subtalar joint for observation and operation (Fig. 3).
since January 2012, 38 patients were effectively followed up, including 22 males and 16 females, 20 cases of right ankle and 18 cases of left ankle. the average age of patients was 36.4 (range, 18-62) years. The mean follow-up time was 28.2 (range, 24-72) months. Thirty-six patients achieved satisfactory e cacy, with a satisfaction rate of 94.7%; two patient experienced residual walking pain postoperatively for traumatic subtalar arthritis, thus the e cacy was just acceptable. After operation, X-ray examination showed that all bony impingements were completely removed (Fig. 4).
VSA score was decreased to 0.51±0.44 after operation from 5.68±1.61 before operation, AOFAS score was increased to 92.34±5.30 from 71.68±6.10, and the differences were both statistically signi cant (P<.05). The excellent/good rate was 97.3 . None of the 38 patients developed complications.

Discussion
Posterior ankle impingement syndrome is a common clinical disease, which is caused by repeated subclinical trauma due to overuse. 9 Impingement pain localized at the posterolateral aspect of the ankle behind the peroneal tendon is the main symptom. 10  Nonoperative measures may yield good results in some patients without osseous pathology, but if there is a symptomatic osseous impingement, operative intervention has to be required in most cases. Traditional operative treatment through an open approach may achieve good clinical outcomes. Coetzee et al followed the clinical outcomes of the open approach for posterior impingement in 37 dancers and athletes for 46.1 months. They reported an initial slow return to full activity with 46% good to excellent results at 3 months that improved to 96% at 1 year. a low complication rate with 3 transient sural nerve injuries and 1 case of complex regional pain syndrome was reported in their study 12 . More recently posterior ankle arthroscopy has been employed. Comparing with traditional open operation, Endoscopic management has the advantages of less trauma, faster recovery, and lower morbidity, and provides good/excellent results at 2-5 years follow-up in 80% of patients. 4 Therefore, endoscopic surgery becomes a fashion and trend, but the correct selection of operative approaches plays a key role in clearly exposing posterior ankle, effectively protecting nerves and blood vessels, and reducing complications 13 . As the blood vessels and nerves in medial ankle have a complex structure, posteromedial ankle portal for arthroscopy will greatly injure medial blood vessels and nerves when being established medially. 6 Bilateral coaxial portal supports the entry into the articular cavity in back of Tibialis posterior muscle tendon 8 , but only provides a limited space for operative operation due to the obstruction of the above tendon yet which reduces the risk of vascular and nerve injury. Medial portal designed by Sim 14 and Allegra 15 offers a certain safe space, but enables the limited observation of subtalar joint. Double paratendinal portals designed by Van Dijk are a classic approach for posterior ankle arthroscopy, and its safety has been investigated in many studies. 16 Therefore, this operative approach is recognized by numerous investigators and widely applied in endoscopic posterior ankle surgery, but it only supports the limited observartion of posterior subtalar joint. Due to the anatomic obstrucation of calcaneus and talus, such double portals only enable the observation of partial posterior subtalar joint, require a change of body position during operation to manage anterior ankle lesions, and have an observation blind area of posterior ankle 5 . Based on the disadvantages of the above portals, we designed double posterolateral coaxial portals with the considerations of minature injury to nervers and blood vessles, a good intraoperative eld, managing anteiror and posterior ankle lesions, avoiding peroneus longus tendon, peroneus brevis tendon and lateral collateral ligament, fully protecting sural nerve, full exposure and a clear eld of posterior subtalar joint and posterior ankle articular cavity. Sitler et al 17 evaluated the safety of paratendinal portal for posterior ankle arthroscopy against small saphenous vein and proved that this portal had a certain safety distance to small saphenous vein. Therefore, we only measured the distances of double posterolateral coaxial portals to sural nerve to evaluate the safety against nerves; as shown by measurement, there was a certain safety distance between these portals and sural nerve. Our portals pass through upper edge of peroneus longus tendon, and the tendon can prevent sural nerve and small saphenous vein from the injury by operative operations as natural marker, thus these portals exhibit good safety against lateral blood vessles and nerves; besides, they provide a big space for safe operation because of no direct contact with lateral and medial ankle nerves and vascular bundles, and enable the effective observation of exor pollicis longus muscle tendon as a warning marker of operation under endoscope to prevent the injury caused by the deep entry of operative instruments. We proved in the clinical application that none of patients using our designed portals experienced medial vascular and nerve injury. However, the arthroscopic group returned to activity almost 6 weeks earlier than the open group (6 vs 11.9 weeks). 18 The similar results were found in study by Noguchi et al, who reported on the arthroscopic excision of an os trigonum in 12 soccer players. The average return to sports was 5.9 weeks with a 8.3% (one of 12) incidence of complications. They concluded arthroscopic treatment of posterior ankle impingement syndrome was recommended for athletes who wish to return to play earlier . 19 Nickisch et al compared favorably to the Abramowitz et al, who reported a 20% (8 out of 41 cases) sural nerve neuropraxia incidence in the open treatment of posterior ankle impingement. 20 Ribbans et al compared open and arthroscopic debridement. In their review paper, the incidences of nerve injury and wound complication in open cases were 4.2% and 2.8% compared to 3.7% and 0.96% in arthroscopic cases respectively. 13 Nickisch et al detailed the postoperative complications of posterior ankle and hindfoot arthroscopy in a retrospective study of 189 subjects. A total of 16 cases of complications were observed (7 cases of nerve, 2 cases of infection, 4 cases of Achilles tendon tightness, 1 case of portal cyst, 2 cases of complex regional pain syndrome). Five of the 7 patients (3.7% of the nerve injury rate) were completely resolved. The results showed posterior ankle and hindfoot arthroscopy was a safe procedure to diagnose and treat many intra-articular and extra-articular ankle disorders, which was consistent with our study. However, within their cohort of 189 subjects, 46 and 20 cases of subtalar and ankle arthritis, respectively, were treated. This is atypical in comparison to most other studies reporting outcomes and complications of operative treatment of PAIS. 21 As proven by clinical e cacy, the improvement of symptoms was satisfactory during the follow-up of 38 patients with posterior ankle impingement syndrome who received endoscopic treatment by double posterolateral coaxial portals, but there was no case of injury to nerves, blood vessels and peroneus longus tendon, peroneus brevis tendon.
In summary, in treating posterior ankle impingement syndrome, double posterolateral coaxial portals have such advantages of good safety, miniature nerve injury, a good eld of posterior ankle and subtalar joint, good clinical e cacy, and few complications, thus they are an operative approach which is reliable, effective, safe and worthy of being popularized.