- Email: [email protected]
Arthroscopic Excision of a Symptomatic Os Trigonum
Arthroscopic Excision of a Symptomatic Os Trigonum William M. Weiss, M.D., F.R.C.S.C., Eric J. Sanders, B.S., John M. Crates, M.D., and F. Alan Barber, M.D.
Purpose: To report the clinical outcomes of arthroscopic excision for a symptomatic os trigonum initially viewing through the posteromedial ankle portal with the motorized instrument in the posterolateral portal. Methods: A retrospective review of a consecutive series of patients with symptomatic os trigonum failing nonoperative management and treated with arthroscopic excision was performed. Demographic data, clinical data, American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot scores, and Single Assessment Numeric Evaluation scores were obtained. Any complications and the time required to return to sports or full activities were recorded. Results: Twenty-four patients with an arthroscopic excision of a symptomatic os trigonum were included. There were 13 male and 11 female patients. The average age was 36.7 17 years. Twenty-one isolated os trigonum excisions and 3 excisions combined with other procedures were studied. At a mean follow-up of 26 months (range, 24 to 31 months), average preoperative AOFAS scores significantly improved from 55.3 to 92.3 postoperatively (P < .0001). The preoperative AOFAS function component improved from 17.1 to 33.8 (P < .0001). The mean postoperative Single Assessment Numeric Evaluation score was 90. Patients reported full activity at an average of 1.5 months with no limitations at an average of 7.8 months after surgery. The only complication was a posterior tibial nerve calcaneal branch neurapraxia. Conclusions: Arthroscopic excision in the prone position without traction of a symptomatic os trigonum viewing initially through the posteromedial portal with a high-speed burr in the posterolateral portal resulted in significantly improved AOFAS scores with a single transient neurapraxia in 24 patients. Patients returned to their normal daily activities without limitations at an average of 1.5 months. Level of Evidence: Level IV, therapeutic case series.
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osterior ankle pain is often caused by impingement between the posterior tibia and calcaneus. Softtissue compression may also occur between an os trigonum and the talus.1,2 The os trigonum is an accessory bone resulting from the nonunion of the lateral tubercle of the posterior process of the talus, and represents an anatomic variant that is not symptomatic under normal circumstances (Fig 1A). This nonunited portion of the talus forms from a secondary ossification center, lateral to the groove for the tendon of the flexor hallucis longus (FHL). Due to their anatomic proximity, os trigonum impingement is often associated with FHL pathology.2-5 From Plano Orthopedics Sports Medicine and Spine Center, Plano, Texas, U.S.A. Presented at the 2014 Arthroscopy Association of North America 33rd Annual Meeting, May 2, 2014, Hollywood, Florida. The authors report the following potential conflict of interest or source of funding: J.M.C. receives support from Arthrex. F.A.B. receives support from DePuy Mitek, Linvatec, and Arthrex. Received July 2, 2014; accepted April 10, 2015. Address correspondence to F. Alan Barber, M.D., Plano Orthopedics Sports Medicine and Spine Center, 5228 W Plano Pkwy, Plano, TX 75093, U.S.A. Ó 2015 The Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved. 0749-8063/14553/$36.00 http://dx.doi.org/10.1016/j.arthro.2015.04.086
The literature reports the prevalence of an os trigonum to vary.5,6 It has been estimated to be present in 7% to 14% of adults and occur bilaterally in 1.4%.7 The initial treatment of os trigonum impingement is nonoperative and includes activity modification, physical therapy, nonsteroidal anti-inflammatory drugs, and steroid injections. Failure of nonoperative management may necessitate the surgical excision of a symptomatic os trigonum. Open excision using a posterolateral approach, while successful,2,8 requires immobilization and a lengthy recovery.9 Reported operative complication rates range from 10% to 24%2,8,10 and include infection, neurovascular injuries (commonly involving the sural nerve), hematoma, adhesions, peroneal tendonitis, and regional sympathetic dystrophy.1,2,8,10,11 Outpatient arthroscopic excision is less invasive, providing improved visualization with less morbidity.3,12-15 Concerns exist about the proximity of the posteromedial portal to the posterior tibial nerve and artery. However, peritendinous portals placed adjacent to the Achilles tendon in the prone patient are safe.4,12,16-20 The purpose of the study was to report the clinical outcomes of arthroscopic excision for a symptomatic os trigonum initially viewing through the posteromedial ankle
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W. M. WEISS ET AL. Fig 1. (A) Preoperative lateral weight-bearing radiograph in 25 of external rotation of a patient with a symptomatic os trigonum (arrow). (B) Immediate postoperative lateral weight-bearing radiograph of the same patient in 25 of external rotation after arthroscopic excision of the os trigonum (prior location identified by arrow). Ó 2015 F. Alan Barber. All Rights Reserved.
portal with the motorized instrument in the posterolateral portal. Our hypothesis was that this approach would be both safe and effective and would provide comparable outcomes, a comparable complication rate, and a comparable recovery to other arthroscopic techniques.
Methods A retrospective review from the senior author’s (J.M.C.) database was performed evaluating a consecutive series of patients presenting with a symptomatic os trigonum starting in April 2012. Inclusion criteria consisted of patients with a symptomatic os trigonum verified by examination, imaging, and diagnostic injection who failed nonoperative management. Exclusion criteria included the absence of an os trigonum, the presence of Outerbridge grade 3 or 4 osteoarthritic changes in the ankle, and those patients unwilling to undergo surgical treatment. Patients failing nonoperative treatment subsequently underwent arthroscopic surgical excision. No information regarding the preoperative time frame was collected. All procedures were performed by the senior author. Using a computer search program, the database was purged of patient-identifying health data and patient names were replaced by a code. Demographic data (age, sex, affected side) and clinical data including the mechanism of injury or the pattern of symptom onset, activity status, American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot scores,21 and Single Assessment Numeric Evaluation (SANE) scores were extracted, merged, and reported as a whole, blinding the data related to any specific patient. The AOFAS hindfoot score was documented preoperatively and postoperatively for all patients. This score consists of 3 components that are combined to give a maximum possible score of 100 points: pain (50 points), function (40 points), and alignment (10 points). In addition, the AOFAS hindfoot score “function” component was evaluated separately. Postoperative evaluation also included physical examination, radiographs, and the time to return to full activity (work or sport). The
SANE score was obtained at final follow-up. It provides a subjective numeric quantification of overall ankle function ranging from 0 to 100, with 100 being normal. Diagnosis of a symptomatic os trigonum was made based on a combination of history, physical examination, and radiographs. Posterior ankle pain with activities requiring plantar flexion and a mechanism of ankle acute or chronic injury including plantar flexion or the demonstration of subsequent ankle instability were consistently reported. The diagnosis of a symptomatic os trigonum was based on several factors including the presence of tenderness at the posterior ankle joint and pain with passive hyperplantar flexion. A positive hyper-plantar flexion test (posterior ankle pain with passive quick and repetitive hyper-plantar flexion while the patient was sitting with the knee flexed to 90 ) was also present.22 A positive response to a diagnostic injection of local anesthetic (elimination of the pain) was also required. Tenosynovitis of the FHL was ruled out by confirming the absence of tenderness or crepitus posterior to the medial malleolus at the level of the ankle joint during repetitive active plantar flexion and dorsiflexion of the great toe. Preoperative radiographs of the foot and ankle (anteroposterior, lateral in 25 of external rotation, and oblique) were obtained for all ankles to visualize the area posterior to the ankle joint, confirm the presence of an os trigonum, and rule out other pathology (Fig 1A). Postoperative radiographs (Fig 1B) were obtained to confirm complete excision of the os trigonum. After confirmation of a symptomatic os trigonum, all patients underwent nonoperative management consisting of anti-inflammatory medication, corticosteroid injections, physical therapy, and activity modification. Those who failed to improve were considered candidates for surgical excision. Surgical Technique All patients were treated with an initial tibiotalar and then subtalar arthroscopy followed by excision of the os trigonum and any hypertrophic or inflammatory tissue in the area of impingement. In addition, any possible
SYMPTOMATIC OS TRIGONUM
Fig 2. Arthroscopic view with the arthroscope inserted through the posteromedial portal of a left ankle looking toward the posterolateral corner of the subtalar joint. The talus is superior and the calcaneus is inferior. Ó 2015 F. Alan Barber. All Rights Reserved.
causes of posterior ankle pain were debrided as part of the technique. All procedures were performed under general anesthesia by a fellowship-trained foot and ankle orthopaedic surgeon (J.M.C.). Patients were positioned prone on the operating table with the foot extending unsupported beyond the end of the operating room table. A tourniquet is placed on the operative extremity but not inflated, and the limb is prepared and draped in the standard fashion. Ringer lactate solution is used for irrigation with the level of flow determined by gravity. No distraction device is used to prevent unnecessary tension on the neurovascular structures. No intraoperative fluoroscopy is used. A straight line drawn with a skin marker between the inferior poles of the medial and lateral malleoli serves as a portal placement guide. The medial and lateral edges of the Achilles tendon are identified at this level.23 The posteromedial portal is placed just medial to the Achilles tendon 10 mm superior to the tip of the medial malleolus. A superficial incision is created in the skin alone followed by blunt dissection through the subcutaneous tissues using a mosquito clamp in the direction of the posterolateral corner of the subtalar joint (nick and spread technique). The 2.7-mm 30 arthroscope sleeve with a blunt trocar is then introduced through the posteromedial portal into the posterolateral corner of the subtalar joint (away from medial neurovascular structures) and the trocar removed and the camera
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inserted (Fig 2). All portals are made using the same technique. The posterolateral portal is placed immediately lateral to the Achilles tendon and 10 mm superior to the tip of the lateral malleolus. No joint insufflation is performed. Care is taken to protect the sural nerve by inserting the instruments in the direction of the posterolateral corner of the subtalar joint under arthroscopic visualization from the posteromedial portal. The blunt trocar is inserted in this posterolateral portal and positioned so that it is clearly visualized with the camera. The trocar is then replaced with a 4.5-mm motorized shaver (Fig 3). The debridement is initially intra-articular (tibiotalar and subtalar) and then moves into the adjacent tissue. We believe that this is safer because starting in the intra-articular area allows for better orientation and starts in a safer position. Bursts of suction are used in the resection for improved safety and to avoid collapsing the space. Placing the camera in the posteromedial portal protects the medial neurovascular structures and allows clear visualization of the posterolateral subtalar joint. The open end of the resector in the posterolateral portal should face the camera lens. This allows a cautious debridement of the fat and scar tissue of the posterolateral subtalar joint. Afterward, a progressive debridement of this tissue moving from lateral to medial reveals the os trigonum. The os is then probed to assess stability.
Fig 3. Arthroscopic view with the motorized shaver inserted through the posteromedial portal (viewing from the posterolateral portal) into the subtalar joint (left ankle). Ó 2015 F. Alan Barber. All Rights Reserved.
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the surrounding tissues from multiple passes associated with extracting fragments of the os trigonum piecemeal with rongeurs or clamps. As with the shaver blade, the burr is positioned with the open end facing the camera to protect the medial structures. Suction is only used when the burr is stopped to minimize the risk of “pulling” neurovascular structures into the burr with the suction. After complete os trigonum removal, the ankle is placed through a full range of motion while visualizing the posterior structures to ensure no further impingement exists (Fig 6). The FHL is visualized along its course distally into its tunnel ensuring no impingement or restriction. A final arthroscopic examination of the tibiotalar and subtalar joints is performed. The operative wounds are closed using subcutaneous biodegradable sutures and compressive absorptive dressings applied. No immobilization is applied, and the patient is permitted to bear weight as tolerated immediately postoperatively. Fig 4. The arthroscope is inserted through the posteromedial portal and the shaver through the posterolateral portal to continue the debridement and define clearly the os trigonum (left ankle). Ó 2015 F. Alan Barber. All Rights Reserved.
Once the resection reaches the mid-sagittal plane, the camera is transferred into the posterolateral portal and the motorized shaver placed in the posteromedial portal. After triangulating again, the shaver blade is angulated toward the posterolateral corner. An unobstructed view of the subtalar joint from the posterolateral portal is required. With the open end of the shaver blade again facing the camera (laterally) to protect the medial neurovascular structures, the remainder of the os trigonum is demarcated and debrided of soft tissue and any ligamentous attachments (Fig 4). Specifically, the posterior talofibular ligament, FHL retinaculum, and posterior talocalcaneal ligaments are removed to allow unimpeded access. Superior-medially, the FHL is identified before it enters the fibro-osseous tunnel distally. This is an important safety landmark. After the FHL is identified, any attachments to the os trigonum or its surrounding tissue are debrided while carefully keeping the open end of the shaver blade facing the camera. The FHL is routinely assessed and, if necessary, is debrided and decompressed. The remainder of the posterior ankle is also assessed, and any potential causes of posterior ankle impingement syndrome are examined and debrided or decompressed as needed. After the os trigonum is completely cleared of soft tissue and clearly defined, a 3.5-mm hooded highspeed ball burr (Linvatec, Largo FL) is inserted through the posteromedial portal and used to resect the os trigonum completely (Fig 5). The bevel of the burr is always pointed away from the FHL and neurovascular bundle. The use of this small ball burr avoids trauma to
Statistical Methods The results were calculated as the mean and standard deviation of quantitative variables. Changes from baseline for the AOFAS scores were analyzed with use of paired t tests. A P value of < .05 was considered to be significant.
Results Twenty-four patients with a symptomatic os trigonum were included in this study. There were 13 male
Fig 5. The burr is inserted through the posterolateral portal (viewing left ankle from posteromedial portal) and used to morselize the os trigonum. The burr faces the arthroscope. Ó 2015 F. Alan Barber. All Rights Reserved.
SYMPTOMATIC OS TRIGONUM
Fig 6. Completed resection of os trigonum (left ankle viewed from posterolateral portal). Ó 2015 F. Alan Barber. All Rights Reserved.
and 11 female patients. The right ankle was involved in 9 and the left in 15. The average age was 36.7 17 years (range, 15 to 82 years). There were 4 patients in whom symptom onset was associated with injury or trauma, and 20 described a gradual onset. Of the 24 procedures, 5 were isolated excisions of the os trigonum and 19 were associated with other procedures. These included tenolysis of the FHL in 14, 2 of which were also associated with the debridement of an exostosis and 1 that was not; 1 distal tarsal tunnel release including Baxter’s nerve and the lateral plantar nerve; and 3 debridements and drillings of osteochondral lesions of the talus. At a mean follow-up of 26 months (range, 24 to 31 months), the average preoperative AOFAS score of 55.3 21 (range, 31 to 90) significantly improved to 92.3 7.5 (range, 80 to 100) (P < .0001). The preoperative function component of the AOFAS score (maximum of 40) was 17.1 8.49 (range, 0 to 30) and increased postoperatively to 33.8 6.5 (range, 20 to 40) (P < .0001). The mean postoperative SANE score was 90 12 (range, 70 to 100). Patients reported a return to full activity at an average of 1.5 0.3 months after surgery and no residual limitations at all at an average of 7.8 5.4 months. A single complication (neurapraxia of the calcaneal branch of the posterior tibial nerve near the tarsal tunnel) was observed.
Discussion Arthroscopic excision of a symptomatic os trigonum in the prone position without traction, viewing first through the posteromedial portal and then through the
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posterolateral portal and using a high-speed burr in the posterolateral portal and then the medial portal, is both safe and effective. This technique provides comparable outcomes to other approaches, as well as a low complication rate, and resulted in significantly improved AOFAS scores. Arthroscopic excision of a symptomatic os trigonum is an established technique. Various approaches have been described, all of which result in good postoperative AOFAS scores and a consistent return to full activity. While these techniques describe the use of posterolateral and anterolateral portals,16 they present a challenge because instruments must be placed through the subtalar joint.9,12 Variations of the procedure have been described. These include the use of a posterolateral portal coupled with either an accessory or stacked posterolateral portal. Use of these stacked portals creates a problem of instrument crowding. A transeAchilles tendon portal with a standard posterolateral portal has also been described but carries the risk of damage to the Achilles tendon. The most common approach was originally described by van Dijk12 and uses a posterolateral and posteromedial portal.23 Our technique also employs posterolateral and posteromedial portals with the patient in the prone position. However, it differs in the order and manner in which these portals are used and the technique by which the os trigonum is removed. Distraction, which is often used for ankle arthroscopy3 and is a source of tissue trauma, carries the risk of neurovascular injury and was not used in this technique. In van Dijk’s technique,12 the arthroscope is placed first in the posterolateral portal in line with the first interdigital web space. Next, the shaver blade is inserted through the posteromedial portal at 90 to the camera shaft, and contact is maintained while the shaver blade is advanced into view. With the shaver blade’s opening facing the arthroscope, fat and scar tissue are debrided progressively from lateral to medial, gradually revealing the posterior ankle structures. In our technique, the arthroscope is initially inserted through the posteromedial portal directed toward the posterolateral corner of the subtalar joint and away from the medial neurovascular structures. The shaver blade is inserted through the posterolateral portal. In this configuration, the arthroscope is medial to the resector and protects the medial neurovascular structures. Once the soft-tissue resection reaches the midsagittal plane and the anatomy is better defined, the arthroscope and resector are switched. At that point, with the medially located motorized shaver’s opening always in view of the laterally placed arthroscope, debridement can continue safely to fully reveal the os trigonum. In our opinion, the advantages of this approach are the improved protection of the medial
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neurovascular structures provided by inserting the instruments toward the posterolateral corner of the subtalar joint and the placement of the arthroscope between them and the shaver. This occurs at the beginning of the procedure when visualization is most challenging. We believe that instead of starting with the arthroscope in the posterolateral portal and the shaver in the posteromedial portal, the subtalar joint can be entered with less risk to the neurovascular structures because the arthroscope serves to protect them. As the debridement progresses, the os exposure is developed, and once the debridement extends to the midline and a clear view is established, the shaver can be safely transferred to the posterolateral portal. In other techniques, the os trigonum is typically removed as a large fragment or several smaller fragments using a grasper often repeatedly inserted through an arthroscopic portal. Often, the assistance of a periosteal elevator or osteotome is required. A larger os trigonum is usually broken into smaller pieces prior to removal.24,25 Our technique avoids this repeated tissue trauma, and we believe that this minimizes postoperative scarring and stiffness by the use of a small high-speed burr. Others have also reported the use of a burr.26 The primary benefit of an arthroscopic approach is the decreased morbidity compared with open procedures. The open excision of an os trigonum results in a slower recovery, increased scar formation, and longer healing times compared with arthroscopic approaches. This delays the return to full activity, which can average between 3 and 6 months.1,2,8,10 In the present investigation, patients reported an average return to full activity at 6 weeks after surgery. While much of the reported data are based on case reports and small series,12 the results after arthroscopic excision of a symptomatic os trigonum have been good. Scholten et al.9 reported 42 os trigonum excisions (from a series of 55 patients) using a posterior arthroscopic approach. They demonstrated improvement of the AOFAS scores from 75 preoperatively to 90 postoperatively an average of 36 months after surgery. The complication rate for posterior ankle arthroscopy ranges from 2.3% to 9%25 and was 3.8% in a recent meta-analysis.15 Neurologic complications account for almost half of those observed. The primary safety concern is the medial neurovascular bundle and its relation to the posteromedial portal and FHL tendon. The sural nerve and its proximity to the posterolateral portal are also an issue. Neurovascular complications are more commonly found with the use of distraction or a tourniquet, and therefore these are not employed in this approach. Only one temporary neurologic injury was observed in this study group. A symptomatic and inflamed os trigonum lateral to the FHL tendon is often associated with tendinopathy.
The symptomatic os trigonum is reported to be associated in 60% to 85% of the cases with FHL pathology.2-5 This frequency underscores the need for a careful inspection of the entire FHL length including following the FHL into the fibrous-osseous tunnel distally in the inferomedial quadrant. In this series FHL pathology requiring tenolysis and debridement was present in 14 of 24 cases (58%). Limitations This was a retrospective review of patient data with no control group and with limited long-term follow-up. While we believe a symptomatic os trigonum is underreported, it is certainly uncommonly diagnosed. This is particularly true of the isolated lesion. Consequently, heterogeneous pathology was included. The additional pathology can impact subjective scores and obscure the impact of an os trigonum excision. The only clinical outcome score used was the AOFAS hindfoot score. This has not been validated for the measurement of os trigonum symptoms and is not ideal for use in a young active population. Nonetheless, using the AOFAS hindfoot score allows a direct comparison between this technique and others. No information regarding the length of preoperative symptoms was collected or evaluated. Performing arthroscopy in the prone position limits the extent to which the anterior ankle and subtalar joints can be surgically examined. If anterior access is required, the patient must be turned to the supine position. The lack of traction will limit the ability to address the anterior ankle and subtalar joints.
Conclusions Arthroscopic excision in the prone position without traction of a symptomatic os trigonum viewing initially through the posteromedial portal with a high-speed burr in the posterolateral portal resulted in significantly improved AOFAS scores with a single transient neurapraxia in 24 patients. Patients returned to their normal daily activities without limitations at an average of 1.5 months.
References 1. Hedrick MR, McBryde AM. Posterior ankle impingement. Foot Ankle Int 1994;15:2-8. 2. Hamilton WG, Geppert MJ, Thompson FM. Pain in the posterior aspect of the ankle in dancers. Differential diagnosis and operative treatment. J Bone Joint Surg Am 1996;78:1491-1500. 3. Smyth NA, Zwiers R, Wiegerinck JI, et al. Posterior hindfoot arthroscopy: A review. Am J Sports Med 2014;42: 225-234. 4. van Dijk C. Hind-foot endoscopy for posterior ankle pain. Instr Course Lect 2006;55:545-554. 5. Bizarro AH. On sesamoid and supernumerary bones of the limbs. J Anat 1921;55:256-268 (pt 4).
SYMPTOMATIC OS TRIGONUM 6. Burman MS, Lapidus PW. The functional disturbances caused by the inconstant bones and sesamoids of the foot. Arch Surg 1931;22:936-975. 7. Lawson JP. Symptomatic radiographic variants in extremities. Radiology 1985;157:625-631. 8. Abramowitz Y, Wollstein R, Barzilay Y, et al. Outcome of resection of a symptomatic os trigonum. J Bone Joint Surg Am 2003;85:1051-1057. 9. Scholten PE, Sierevelt IN, van Dijk CN. Hindfoot endoscopy for posterior ankle impingement. J Bone Joint Surg Am 2008;90:2665-2672. 10. Marotta JJ, Micheli LJ. Os trigonum impingement in dancers. Am J Sports Med 1992;20:533-536. 11. Marumoto JM, Ferkel RD. Arthroscopic excision of the os trigonum: A new technique with preliminary clinical results. Foot Ankle Int 1997;18:777-784. 12. van Dijk C. Hindfoot endoscopy. Sports Med Arthrosc Rev 2000;8:365-371. 13. Lijoi F, Lughi M, Baccarani G. Posterior arthroscopic approach to the ankle: An anatomic study. Arthroscopy 2003;19:62-67. 14. Jerosch J, Fadel M. Endoscopic resection of a symptomatic os trigonum. Knee Surg Sports Traumatol Arthrosc 2006;14: 1188-1193. 15. Donnenwerth MP, Roukis TS. The incidence of complications after posterior hindfoot endoscopy. Arthroscopy 2013;29:2049-2054. 16. Williams MM, Ferkel RD. Subtalar arthroscopy: Indications, technique, and results. Arthroscopy 1998;14:373-381.
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17. Sitler DF, Amendola A, Bailey CS, Thain LM, Spouge A. Posterior ankle arthroscopy: An anatomic study. J Bone Joint Surg Am 2002;84:763-769. 18. Voto SJ, Ewing JW, Fleissner PR Jr, Alfonso M, Kufel M. Ankle arthroscopy: Neurovascular and arthroscopic anatomy of standard and trans-Achilles tendon portal placement. Arthroscopy 1989;5:41-46. 19. Frey C, Gasser S, Feder K. Arthroscopy of the subtalar joint. Foot Ankle Int 1994;15:424-428. 20. Feiwell LA, Frey C. Anatomic study of arthroscopic portal sites of the ankle. Foot Ankle 1993;14:142-147. 21. Kitaoka HB, Alexander IJ, Adelaar RS, et al. Clinical rating systems for the ankle-hindfoot, midfoot, hallux, and lesser toes. Foot Ankle Int 1994;15:349-353. 22. van Dijk CN, Stibbe AB, Marti RK. Posterior impingement. In: Nyska M, Mann G, eds. The unstable ankle. Champaign, IL: Human Kinetics, 2002;139-148. 23. van Dijk CN, de Leeuw PA, Scholten PE. Hindfoot endoscopy for posterior ankle impingement. Surgical technique. J Bone Joint Surg Am 2009;91:287-298. 24. Horibe S, Kita K, Natsu-ume T, et al. A novel technique of arthroscopic excision of a symptomatic os trigonum. Arthroscopy 2008;24:121.e1-121.e4. 25. Ahn JH, Kim YC, Kim HY. Arthroscopic versus posterior endoscopic excision of a symptomatic os trigonum: A retrospective cohort study. Am J Sports Med 2013;41:1082-1089. 26. Willits K, Sonneveld H, Amendola A, et al. Outcome of posterior ankle arthroscopy for hindfoot impingement. Arthroscopy 2008;24:196-202.
Purpose: To report the clinical outcomes of arthroscopic excision for a symptomatic os trigonum initially viewing through the posteromedial ankle portal with the motorized instrument in the posterolateral portal. Methods: A retrospective review of a consecutive series of patients with symptomatic os trigonum failing nonoperative management and treated with arthroscopic excision was performed. Demographic data, clinical data, American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot scores, and Single Assessment Numeric Evaluation scores were obtained. Any complications and the time required to return to sports or full activities were recorded. Results: Twenty-four patients with an arthroscopic excision of a symptomatic os trigonum were included. There were 13 male and 11 female patients. The average age was 36.7 17 years. Twenty-one isolated os trigonum excisions and 3 excisions combined with other procedures were studied. At a mean follow-up of 26 months (range, 24 to 31 months), average preoperative AOFAS scores significantly improved from 55.3 to 92.3 postoperatively (P < .0001). The preoperative AOFAS function component improved from 17.1 to 33.8 (P < .0001). The mean postoperative Single Assessment Numeric Evaluation score was 90. Patients reported full activity at an average of 1.5 months with no limitations at an average of 7.8 months after surgery. The only complication was a posterior tibial nerve calcaneal branch neurapraxia. Conclusions: Arthroscopic excision in the prone position without traction of a symptomatic os trigonum viewing initially through the posteromedial portal with a high-speed burr in the posterolateral portal resulted in significantly improved AOFAS scores with a single transient neurapraxia in 24 patients. Patients returned to their normal daily activities without limitations at an average of 1.5 months. Level of Evidence: Level IV, therapeutic case series.
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osterior ankle pain is often caused by impingement between the posterior tibia and calcaneus. Softtissue compression may also occur between an os trigonum and the talus.1,2 The os trigonum is an accessory bone resulting from the nonunion of the lateral tubercle of the posterior process of the talus, and represents an anatomic variant that is not symptomatic under normal circumstances (Fig 1A). This nonunited portion of the talus forms from a secondary ossification center, lateral to the groove for the tendon of the flexor hallucis longus (FHL). Due to their anatomic proximity, os trigonum impingement is often associated with FHL pathology.2-5 From Plano Orthopedics Sports Medicine and Spine Center, Plano, Texas, U.S.A. Presented at the 2014 Arthroscopy Association of North America 33rd Annual Meeting, May 2, 2014, Hollywood, Florida. The authors report the following potential conflict of interest or source of funding: J.M.C. receives support from Arthrex. F.A.B. receives support from DePuy Mitek, Linvatec, and Arthrex. Received July 2, 2014; accepted April 10, 2015. Address correspondence to F. Alan Barber, M.D., Plano Orthopedics Sports Medicine and Spine Center, 5228 W Plano Pkwy, Plano, TX 75093, U.S.A. Ó 2015 The Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved. 0749-8063/14553/$36.00 http://dx.doi.org/10.1016/j.arthro.2015.04.086
The literature reports the prevalence of an os trigonum to vary.5,6 It has been estimated to be present in 7% to 14% of adults and occur bilaterally in 1.4%.7 The initial treatment of os trigonum impingement is nonoperative and includes activity modification, physical therapy, nonsteroidal anti-inflammatory drugs, and steroid injections. Failure of nonoperative management may necessitate the surgical excision of a symptomatic os trigonum. Open excision using a posterolateral approach, while successful,2,8 requires immobilization and a lengthy recovery.9 Reported operative complication rates range from 10% to 24%2,8,10 and include infection, neurovascular injuries (commonly involving the sural nerve), hematoma, adhesions, peroneal tendonitis, and regional sympathetic dystrophy.1,2,8,10,11 Outpatient arthroscopic excision is less invasive, providing improved visualization with less morbidity.3,12-15 Concerns exist about the proximity of the posteromedial portal to the posterior tibial nerve and artery. However, peritendinous portals placed adjacent to the Achilles tendon in the prone patient are safe.4,12,16-20 The purpose of the study was to report the clinical outcomes of arthroscopic excision for a symptomatic os trigonum initially viewing through the posteromedial ankle
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W. M. WEISS ET AL. Fig 1. (A) Preoperative lateral weight-bearing radiograph in 25 of external rotation of a patient with a symptomatic os trigonum (arrow). (B) Immediate postoperative lateral weight-bearing radiograph of the same patient in 25 of external rotation after arthroscopic excision of the os trigonum (prior location identified by arrow). Ó 2015 F. Alan Barber. All Rights Reserved.
portal with the motorized instrument in the posterolateral portal. Our hypothesis was that this approach would be both safe and effective and would provide comparable outcomes, a comparable complication rate, and a comparable recovery to other arthroscopic techniques.
Methods A retrospective review from the senior author’s (J.M.C.) database was performed evaluating a consecutive series of patients presenting with a symptomatic os trigonum starting in April 2012. Inclusion criteria consisted of patients with a symptomatic os trigonum verified by examination, imaging, and diagnostic injection who failed nonoperative management. Exclusion criteria included the absence of an os trigonum, the presence of Outerbridge grade 3 or 4 osteoarthritic changes in the ankle, and those patients unwilling to undergo surgical treatment. Patients failing nonoperative treatment subsequently underwent arthroscopic surgical excision. No information regarding the preoperative time frame was collected. All procedures were performed by the senior author. Using a computer search program, the database was purged of patient-identifying health data and patient names were replaced by a code. Demographic data (age, sex, affected side) and clinical data including the mechanism of injury or the pattern of symptom onset, activity status, American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot scores,21 and Single Assessment Numeric Evaluation (SANE) scores were extracted, merged, and reported as a whole, blinding the data related to any specific patient. The AOFAS hindfoot score was documented preoperatively and postoperatively for all patients. This score consists of 3 components that are combined to give a maximum possible score of 100 points: pain (50 points), function (40 points), and alignment (10 points). In addition, the AOFAS hindfoot score “function” component was evaluated separately. Postoperative evaluation also included physical examination, radiographs, and the time to return to full activity (work or sport). The
SANE score was obtained at final follow-up. It provides a subjective numeric quantification of overall ankle function ranging from 0 to 100, with 100 being normal. Diagnosis of a symptomatic os trigonum was made based on a combination of history, physical examination, and radiographs. Posterior ankle pain with activities requiring plantar flexion and a mechanism of ankle acute or chronic injury including plantar flexion or the demonstration of subsequent ankle instability were consistently reported. The diagnosis of a symptomatic os trigonum was based on several factors including the presence of tenderness at the posterior ankle joint and pain with passive hyperplantar flexion. A positive hyper-plantar flexion test (posterior ankle pain with passive quick and repetitive hyper-plantar flexion while the patient was sitting with the knee flexed to 90 ) was also present.22 A positive response to a diagnostic injection of local anesthetic (elimination of the pain) was also required. Tenosynovitis of the FHL was ruled out by confirming the absence of tenderness or crepitus posterior to the medial malleolus at the level of the ankle joint during repetitive active plantar flexion and dorsiflexion of the great toe. Preoperative radiographs of the foot and ankle (anteroposterior, lateral in 25 of external rotation, and oblique) were obtained for all ankles to visualize the area posterior to the ankle joint, confirm the presence of an os trigonum, and rule out other pathology (Fig 1A). Postoperative radiographs (Fig 1B) were obtained to confirm complete excision of the os trigonum. After confirmation of a symptomatic os trigonum, all patients underwent nonoperative management consisting of anti-inflammatory medication, corticosteroid injections, physical therapy, and activity modification. Those who failed to improve were considered candidates for surgical excision. Surgical Technique All patients were treated with an initial tibiotalar and then subtalar arthroscopy followed by excision of the os trigonum and any hypertrophic or inflammatory tissue in the area of impingement. In addition, any possible
SYMPTOMATIC OS TRIGONUM
Fig 2. Arthroscopic view with the arthroscope inserted through the posteromedial portal of a left ankle looking toward the posterolateral corner of the subtalar joint. The talus is superior and the calcaneus is inferior. Ó 2015 F. Alan Barber. All Rights Reserved.
causes of posterior ankle pain were debrided as part of the technique. All procedures were performed under general anesthesia by a fellowship-trained foot and ankle orthopaedic surgeon (J.M.C.). Patients were positioned prone on the operating table with the foot extending unsupported beyond the end of the operating room table. A tourniquet is placed on the operative extremity but not inflated, and the limb is prepared and draped in the standard fashion. Ringer lactate solution is used for irrigation with the level of flow determined by gravity. No distraction device is used to prevent unnecessary tension on the neurovascular structures. No intraoperative fluoroscopy is used. A straight line drawn with a skin marker between the inferior poles of the medial and lateral malleoli serves as a portal placement guide. The medial and lateral edges of the Achilles tendon are identified at this level.23 The posteromedial portal is placed just medial to the Achilles tendon 10 mm superior to the tip of the medial malleolus. A superficial incision is created in the skin alone followed by blunt dissection through the subcutaneous tissues using a mosquito clamp in the direction of the posterolateral corner of the subtalar joint (nick and spread technique). The 2.7-mm 30 arthroscope sleeve with a blunt trocar is then introduced through the posteromedial portal into the posterolateral corner of the subtalar joint (away from medial neurovascular structures) and the trocar removed and the camera
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inserted (Fig 2). All portals are made using the same technique. The posterolateral portal is placed immediately lateral to the Achilles tendon and 10 mm superior to the tip of the lateral malleolus. No joint insufflation is performed. Care is taken to protect the sural nerve by inserting the instruments in the direction of the posterolateral corner of the subtalar joint under arthroscopic visualization from the posteromedial portal. The blunt trocar is inserted in this posterolateral portal and positioned so that it is clearly visualized with the camera. The trocar is then replaced with a 4.5-mm motorized shaver (Fig 3). The debridement is initially intra-articular (tibiotalar and subtalar) and then moves into the adjacent tissue. We believe that this is safer because starting in the intra-articular area allows for better orientation and starts in a safer position. Bursts of suction are used in the resection for improved safety and to avoid collapsing the space. Placing the camera in the posteromedial portal protects the medial neurovascular structures and allows clear visualization of the posterolateral subtalar joint. The open end of the resector in the posterolateral portal should face the camera lens. This allows a cautious debridement of the fat and scar tissue of the posterolateral subtalar joint. Afterward, a progressive debridement of this tissue moving from lateral to medial reveals the os trigonum. The os is then probed to assess stability.
Fig 3. Arthroscopic view with the motorized shaver inserted through the posteromedial portal (viewing from the posterolateral portal) into the subtalar joint (left ankle). Ó 2015 F. Alan Barber. All Rights Reserved.
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the surrounding tissues from multiple passes associated with extracting fragments of the os trigonum piecemeal with rongeurs or clamps. As with the shaver blade, the burr is positioned with the open end facing the camera to protect the medial structures. Suction is only used when the burr is stopped to minimize the risk of “pulling” neurovascular structures into the burr with the suction. After complete os trigonum removal, the ankle is placed through a full range of motion while visualizing the posterior structures to ensure no further impingement exists (Fig 6). The FHL is visualized along its course distally into its tunnel ensuring no impingement or restriction. A final arthroscopic examination of the tibiotalar and subtalar joints is performed. The operative wounds are closed using subcutaneous biodegradable sutures and compressive absorptive dressings applied. No immobilization is applied, and the patient is permitted to bear weight as tolerated immediately postoperatively. Fig 4. The arthroscope is inserted through the posteromedial portal and the shaver through the posterolateral portal to continue the debridement and define clearly the os trigonum (left ankle). Ó 2015 F. Alan Barber. All Rights Reserved.
Once the resection reaches the mid-sagittal plane, the camera is transferred into the posterolateral portal and the motorized shaver placed in the posteromedial portal. After triangulating again, the shaver blade is angulated toward the posterolateral corner. An unobstructed view of the subtalar joint from the posterolateral portal is required. With the open end of the shaver blade again facing the camera (laterally) to protect the medial neurovascular structures, the remainder of the os trigonum is demarcated and debrided of soft tissue and any ligamentous attachments (Fig 4). Specifically, the posterior talofibular ligament, FHL retinaculum, and posterior talocalcaneal ligaments are removed to allow unimpeded access. Superior-medially, the FHL is identified before it enters the fibro-osseous tunnel distally. This is an important safety landmark. After the FHL is identified, any attachments to the os trigonum or its surrounding tissue are debrided while carefully keeping the open end of the shaver blade facing the camera. The FHL is routinely assessed and, if necessary, is debrided and decompressed. The remainder of the posterior ankle is also assessed, and any potential causes of posterior ankle impingement syndrome are examined and debrided or decompressed as needed. After the os trigonum is completely cleared of soft tissue and clearly defined, a 3.5-mm hooded highspeed ball burr (Linvatec, Largo FL) is inserted through the posteromedial portal and used to resect the os trigonum completely (Fig 5). The bevel of the burr is always pointed away from the FHL and neurovascular bundle. The use of this small ball burr avoids trauma to
Statistical Methods The results were calculated as the mean and standard deviation of quantitative variables. Changes from baseline for the AOFAS scores were analyzed with use of paired t tests. A P value of < .05 was considered to be significant.
Results Twenty-four patients with a symptomatic os trigonum were included in this study. There were 13 male
Fig 5. The burr is inserted through the posterolateral portal (viewing left ankle from posteromedial portal) and used to morselize the os trigonum. The burr faces the arthroscope. Ó 2015 F. Alan Barber. All Rights Reserved.
SYMPTOMATIC OS TRIGONUM
Fig 6. Completed resection of os trigonum (left ankle viewed from posterolateral portal). Ó 2015 F. Alan Barber. All Rights Reserved.
and 11 female patients. The right ankle was involved in 9 and the left in 15. The average age was 36.7 17 years (range, 15 to 82 years). There were 4 patients in whom symptom onset was associated with injury or trauma, and 20 described a gradual onset. Of the 24 procedures, 5 were isolated excisions of the os trigonum and 19 were associated with other procedures. These included tenolysis of the FHL in 14, 2 of which were also associated with the debridement of an exostosis and 1 that was not; 1 distal tarsal tunnel release including Baxter’s nerve and the lateral plantar nerve; and 3 debridements and drillings of osteochondral lesions of the talus. At a mean follow-up of 26 months (range, 24 to 31 months), the average preoperative AOFAS score of 55.3 21 (range, 31 to 90) significantly improved to 92.3 7.5 (range, 80 to 100) (P < .0001). The preoperative function component of the AOFAS score (maximum of 40) was 17.1 8.49 (range, 0 to 30) and increased postoperatively to 33.8 6.5 (range, 20 to 40) (P < .0001). The mean postoperative SANE score was 90 12 (range, 70 to 100). Patients reported a return to full activity at an average of 1.5 0.3 months after surgery and no residual limitations at all at an average of 7.8 5.4 months. A single complication (neurapraxia of the calcaneal branch of the posterior tibial nerve near the tarsal tunnel) was observed.
Discussion Arthroscopic excision of a symptomatic os trigonum in the prone position without traction, viewing first through the posteromedial portal and then through the
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posterolateral portal and using a high-speed burr in the posterolateral portal and then the medial portal, is both safe and effective. This technique provides comparable outcomes to other approaches, as well as a low complication rate, and resulted in significantly improved AOFAS scores. Arthroscopic excision of a symptomatic os trigonum is an established technique. Various approaches have been described, all of which result in good postoperative AOFAS scores and a consistent return to full activity. While these techniques describe the use of posterolateral and anterolateral portals,16 they present a challenge because instruments must be placed through the subtalar joint.9,12 Variations of the procedure have been described. These include the use of a posterolateral portal coupled with either an accessory or stacked posterolateral portal. Use of these stacked portals creates a problem of instrument crowding. A transeAchilles tendon portal with a standard posterolateral portal has also been described but carries the risk of damage to the Achilles tendon. The most common approach was originally described by van Dijk12 and uses a posterolateral and posteromedial portal.23 Our technique also employs posterolateral and posteromedial portals with the patient in the prone position. However, it differs in the order and manner in which these portals are used and the technique by which the os trigonum is removed. Distraction, which is often used for ankle arthroscopy3 and is a source of tissue trauma, carries the risk of neurovascular injury and was not used in this technique. In van Dijk’s technique,12 the arthroscope is placed first in the posterolateral portal in line with the first interdigital web space. Next, the shaver blade is inserted through the posteromedial portal at 90 to the camera shaft, and contact is maintained while the shaver blade is advanced into view. With the shaver blade’s opening facing the arthroscope, fat and scar tissue are debrided progressively from lateral to medial, gradually revealing the posterior ankle structures. In our technique, the arthroscope is initially inserted through the posteromedial portal directed toward the posterolateral corner of the subtalar joint and away from the medial neurovascular structures. The shaver blade is inserted through the posterolateral portal. In this configuration, the arthroscope is medial to the resector and protects the medial neurovascular structures. Once the soft-tissue resection reaches the midsagittal plane and the anatomy is better defined, the arthroscope and resector are switched. At that point, with the medially located motorized shaver’s opening always in view of the laterally placed arthroscope, debridement can continue safely to fully reveal the os trigonum. In our opinion, the advantages of this approach are the improved protection of the medial
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neurovascular structures provided by inserting the instruments toward the posterolateral corner of the subtalar joint and the placement of the arthroscope between them and the shaver. This occurs at the beginning of the procedure when visualization is most challenging. We believe that instead of starting with the arthroscope in the posterolateral portal and the shaver in the posteromedial portal, the subtalar joint can be entered with less risk to the neurovascular structures because the arthroscope serves to protect them. As the debridement progresses, the os exposure is developed, and once the debridement extends to the midline and a clear view is established, the shaver can be safely transferred to the posterolateral portal. In other techniques, the os trigonum is typically removed as a large fragment or several smaller fragments using a grasper often repeatedly inserted through an arthroscopic portal. Often, the assistance of a periosteal elevator or osteotome is required. A larger os trigonum is usually broken into smaller pieces prior to removal.24,25 Our technique avoids this repeated tissue trauma, and we believe that this minimizes postoperative scarring and stiffness by the use of a small high-speed burr. Others have also reported the use of a burr.26 The primary benefit of an arthroscopic approach is the decreased morbidity compared with open procedures. The open excision of an os trigonum results in a slower recovery, increased scar formation, and longer healing times compared with arthroscopic approaches. This delays the return to full activity, which can average between 3 and 6 months.1,2,8,10 In the present investigation, patients reported an average return to full activity at 6 weeks after surgery. While much of the reported data are based on case reports and small series,12 the results after arthroscopic excision of a symptomatic os trigonum have been good. Scholten et al.9 reported 42 os trigonum excisions (from a series of 55 patients) using a posterior arthroscopic approach. They demonstrated improvement of the AOFAS scores from 75 preoperatively to 90 postoperatively an average of 36 months after surgery. The complication rate for posterior ankle arthroscopy ranges from 2.3% to 9%25 and was 3.8% in a recent meta-analysis.15 Neurologic complications account for almost half of those observed. The primary safety concern is the medial neurovascular bundle and its relation to the posteromedial portal and FHL tendon. The sural nerve and its proximity to the posterolateral portal are also an issue. Neurovascular complications are more commonly found with the use of distraction or a tourniquet, and therefore these are not employed in this approach. Only one temporary neurologic injury was observed in this study group. A symptomatic and inflamed os trigonum lateral to the FHL tendon is often associated with tendinopathy.
The symptomatic os trigonum is reported to be associated in 60% to 85% of the cases with FHL pathology.2-5 This frequency underscores the need for a careful inspection of the entire FHL length including following the FHL into the fibrous-osseous tunnel distally in the inferomedial quadrant. In this series FHL pathology requiring tenolysis and debridement was present in 14 of 24 cases (58%). Limitations This was a retrospective review of patient data with no control group and with limited long-term follow-up. While we believe a symptomatic os trigonum is underreported, it is certainly uncommonly diagnosed. This is particularly true of the isolated lesion. Consequently, heterogeneous pathology was included. The additional pathology can impact subjective scores and obscure the impact of an os trigonum excision. The only clinical outcome score used was the AOFAS hindfoot score. This has not been validated for the measurement of os trigonum symptoms and is not ideal for use in a young active population. Nonetheless, using the AOFAS hindfoot score allows a direct comparison between this technique and others. No information regarding the length of preoperative symptoms was collected or evaluated. Performing arthroscopy in the prone position limits the extent to which the anterior ankle and subtalar joints can be surgically examined. If anterior access is required, the patient must be turned to the supine position. The lack of traction will limit the ability to address the anterior ankle and subtalar joints.
Conclusions Arthroscopic excision in the prone position without traction of a symptomatic os trigonum viewing initially through the posteromedial portal with a high-speed burr in the posterolateral portal resulted in significantly improved AOFAS scores with a single transient neurapraxia in 24 patients. Patients returned to their normal daily activities without limitations at an average of 1.5 months.
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