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Dislocation of Os Trigonum Presenting as a Loose Body in the Ankle
Dislocation of Os Trigonum Presenting as a Loose Body in the Ankle Baris Kocaoglu, MD,1 Umut Akgun, MD,2 Rustu Nuran, MD,3 and Mustafa Karahan, MD4 Dislocation of the os trigonum presenting as a loose body is a rare clinical entity. In this report, we describe the case of a 34-year-old male who presented with symptoms of acute left ankle pain that was aggravated by motion and weight bearing. He also displayed lateral collateral ligamentous laxity, without the presence of an effusion. Radiographic inspection revealed a 10 ⫻ 15-mm loose body within the ankle joint cavity. Arthroscopic intervention showed the loose body to be round and smooth, and it could not be deformed with the tip of a probe, although it could be displaced up to 5 mm with ankle manipulation, in particular with inversion stress of the ankle. The loose body was removed with an arthroscopic forceps. Based on its location within the ankle, and the lack of any articular cartilage on the removed joint fragment, we determined the loose body to represent a dislocated os trigonum. The rarity of this case presentation makes one consider the association of symptomatic os trigonum with ankle instability. Level of Clinical Evidence: 4 ( The Journal of Foot & Ankle Surgery 48(2):215–219, 2009) Key Words: ankle arthroscopy, instability, loose body, os trigonum
Isuchndividuals who perform plantarflexion-type activities, as ballet, may acquire a posterior ankle and subtalar joint impingement syndrome (1, 2). This condition typically results from impaction of a large trigonal process or os trigonum between the posterior margin of the distal tibia and the calcaneus on plantarflexion, and is also known as os trigonum syndrome. Os trigonum syndrome is usually diagnosed clinically when there is pain in the anterior aspect of the retrocalcaneal space, supported by radiological findings indicative of a large trigonal process or os trigonum. Loose bodies within the ankle may be either chondral or osteochondral, and may arise from defects in the talus or tibia, talotibial osteophytes, as well as synovial chondromatosis (2, 3). The presence of a completely separated and displaced loose body in the posterior aspect of the ankle joint, suggestive of a displaced os trigonum, is not a common clinical finding. Address correspondence to: Baris Kocaoglu, MD, Department of Orthopeadic Surgery and Traumatology, Acibadem Hospital, Tekin sok:8, Kadikoy, 34718 Istanbul/Turkey. E-mail: [email protected] 1 Staff physician, Acibadem Kadikoy Hospital, Department of Orthopaedic Surgery, Istanbul, Turkey. 2 Staff physician, Acibadem Kozyatagi Hospital, Department of Orthopaedic Surgery, Istanbul, Turkey. 3 Staff physician, Mardin Government Hospital, Department of Orthopaedic Surgery, Istanbul, Turkey. 4 Professor of Orthopedics, Marmara University, School of Medicine, Department of Orthopedics, Istanbul, Turkey. Financial Disclosure: None reported. Conflict of Interest: None reported. Copyright © 2009 by the American College of Foot and Ankle Surgeons 1067-2516/09/4802-0019$36.00/0 doi:10.1053/j.jfas.2008.10.005
Dislocation of the os trigonum presenting as a loose body in the ankle is a clinical entity that, to our knowledge, has not been previously described in the biomedical literature. In this report, we describe the case of a patient who presented with a loose osseous body in the posterior aspect of the ankle that, after surgical inspection and consideration of possible etiologies, was felt to be a displaced os trigonum. Case Report A 34-year-old male amateur athlete presented to the authors’ clinic with a complaint of 3 months’ duration of excruciating left ankle pain that was sudden in onset, associated with a feeling of something catching inside his ankle, and aggravated by standing and walking. He also related an approximately 10-year history of chronic left lateral ankle instability associated with recurrent ankle sprains. He described the pain as being localized to the posterior aspect of the ankle, and further localized slightly more lateral than medial. Over the month preceding presentation to our clinic, the pain had become noticeable even with non–weightbearing passive motion. He denied any recent ankle sprains or twisting injuries. The Achilles tendon was neither painful nor swollen. Physical examination of the patient’s left ankle and foot revealed no evidence of an effusion, acute cutaneous compromise, or focal tenderness to palpation and manipulation of the ankle ligaments, sinus tarsi, midtarsal joints, body of the calcaneus, plantar heel, or Achilles tendon. The left ankle was markedly unstable in response to inversion stress and anterior drawer maneuvers, with subluxation of the VOLUME 48, NUMBER 2, MARCH/APRIL 2009
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FIGURE 1 (A) Anteroposterior standard radiographic view of the left ankle with the loose ossicle visualized laterally, near the fibula. (B) Stress inversion view showing the ossicle more clearly as the space between the talus and the tibia is widened.
talus in relation to the tibia. With the exception of vague, deep pain at the posterior aspect of the subtalar and ankle joints, as well as the lateral collateral ligament instability, the physical examination was largely inconclusive. Radiographic inspection, however, clearly showed a loose, osseous body measuring approximately 10 ⫻ 15 mm in size, visualized on the anteroposterior (AP) and varus stress AP plain films (Figure 1, A and B). Although difficult to clearly outline, the loose body was also evident on the lateral plain film radiograph (Figure 2). Close inspection of the standard radiograph of the ankle failed to reveal any evidence of an osteochondral defect involving the talus, tibia, or the fibular articulating surfaces. Furthermore, there was no evidence of multiple radiopaque bodies suggestive of synovial chondromatosis. Magnetic resonance image (MRI) scans of the left ankle revealed a solitary, loose, round osseous body that measured 10 ⫻ 15 mm, located immediately anterior to the posterior talofibular ligament, and situated between the talus and the tibia (Figure 3). In both T1-weighted and T2weighted images, there was no evidence of a cartilage defect localized to the distal tibial-bearing surface, the dome of the talus, or the fibula. Moreover, there was a slight indentation in the body of the talus consistent with the usual origin of 216
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the posterolateral trigonal process, or the attachment of the os trigonum, with no sign of either an intact trigonal process or os trigonum. Based on the clinical and diagnostic imaging findings, diagnoses of suspected displaced os trigonum and chronic lateral ankle instability were made. After discussion of the suspected diagnoses, prognosis, and treatment options, surgical stabilization of the ankle and arthroscopic inspection and removal of the loose body were recommended. After considering the options, the patient consented only to removal of the loose body, with the understanding that regular use of an ankle brace would thereafter be indicated and recommended. After making the usual preparations, including administration of prophylactic antibiotics (cefazolin, 1 gram, intravenous, 30 minutes prior to commencement of the operation) and low-dose heparin (5000 units subcutaneous 60 minutes preoperative), left ankle arthroscopy was undertaken with the patient initially placed in a supine position, under general anesthesia, and with a tourniquet placed around his upper thigh. Once anesthetized, and the skin surgically prepped, the left hip was flexed and abducted and put in a lithotomy support, while the right lower extremity was slightly flexed at the knee and allowed to rest on
FIGURE 2 Standard lateral radiographic view of the left ankle showing the loose ossicle situated between the talus and the tibia, in the posterior aspect of the joint. Note, too, the concavity at the posterior aspect of the talar body, distal to the loose body, where the trigonal process, or os trigonum, would usually be attached.
FIGURE 3 Lateral magnetic resonance image showing a solitary, loose, round osseous body measuring 10 ⫻ 15 mm, located immediately anterior to the posterior talofibular ligament, situated between the talus and the tibia.
the table. After placement of a central anterior incision, situated between the tibialis anterior and extensor hallucis longus tendons, the left ankle joint was inflated with physiologic saline, and the capsule was distended bluntly to avoid damage to the neurovascular structures. A standard 4-mm 30° arthroscope was introduced into the ankle joint through the anterior portal and, without the use of a specific traction device other than the hanging position of the foot
FIGURE 4 Arthroscopic view showing the loose body (LB) situated between the talus (TA), posterior talofibular ligament (PTFL), and fibula (F) prior to extraction.
and occasional application of manual traction to the heel, a 2-mm hook was inserted into the joint through an additional anteromedial portal. Thereafter, a systematic arthroscopic examination was used to visualize the intra-articular structures, wherein a 10-point examination was used to inspect the anterior component of the articular cavity, and a 5-point examination was used to inspect the central and posterior components of the ankle (1). As soon as the arthroscope entered the space between the talus and tibia, a 10 ⫻ 15-mm, smooth, oblong, loose body was identified (Figure 4). The loose body was firm, and could not be deformed with the tip of the probe; and despite being loose enough to move approximately 5 mm upon ankle dorsiflexion, plantarflexion, and valgus stress, soft tissue adhesions prevented extraction of the loose body until a thin arthroscopic punch was used to section the attachments on the distal and posterior aspect of the ossicle. Thereafter, an arthroscopic forceps was used to grasp the loose body, and to extract it from the joint. After wound closure, a sterile bandage without a cast was used, and the patient was allowed to resume full weight bearing on the second postoperative day. Prior to that time, crutches were used and the patient instructed to avoid placing weight on the operated left lower extremity. Pathological inspection of the removed loose body revealed the specimen to be composed of bone covered with cartilage (Figure 5). Supervised physiotherapy (PT) was initiated after the first postoperative week, and carried out for 6 weeks, and included ankle range of motion exercises, strengthening of the muscles of the anterior compartment of the leg, the peroneal musculature, and the calf musculature. These exercises were performed every day for 2 weeks and then twice daily for an additional 4 weeks. Sports activity was allowed at 3 months following the operation. Overall, VOLUME 48, NUMBER 2, MARCH/APRIL 2009
217
FIGURE 5 Pathological inspection of the removed loose body revealed the specimen to be composed of bone covered with cartilage (hematoxylin and eosin, original magnification ⫻100).
the patient progressed unremarkably, and after 24 months of follow-up the patient had a pain-free ankle with persistent lateral collateral ligament instability on physical examination. He was also able to play tennis without any discomfort, with the use of a lace-up ankle brace. Discussion The os trigonum forms from a secondary center of ossification located at the posterolateral aspect of the body of the talus, just lateral to the groove for the flexor hallucis longus (FHL) (1, 2). The prevalence of this ossicle ranges from 1.7% to 7.7%, and is present unilaterally twice as often as bilaterally (2, 3). If not present as a separate ossicle, the trigonal process usually extends a short distance in the posterolateral direction from the talar body, forming the lateral margin of the groove for FHL. Development of the os trigonum is generally considered to be congenital, although it may be acquired secondary to traumatic disruption of the trigonal process. When present as a separate ossicle, the os trigonum usually appears by 8 to 10 years of age in girls and 11 to 13 years of age in boys, and fusion with the main body of the talus occurs at approximately 1 year following its appearance (2, 3). Persistence of the separation between the os trigonum and the body of the talus may occur in response to repetitive microtrauma (4). In most cases, an os trigonum remains asymptomatic until some sort of injury leads to disruption of either the trigonal process or the ossicle itself (5). It can also become symptomatic in young athletes who actively plantarflex their ankle, and is particularly prevalent in ballet dancers, gymnasts, ice skaters, and, to a lesser degree, soccer players (6, 7). 218
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Loose bodies may be either chondral or osteochondral and may arise from defects in the talus or tibia, osteophytes, or degenerative joint disease (3). A trauma, minor or major, to the ankle joint may result in a chondral or osteochondral lesion and then lead to a loose body floating within the joint. Loose bodies can also be seen with osteophytes and synovial chondromatosis. Such lesions can cause locking or catching with attempted ankle motion, and are usually associated with ankle pain and swelling, and MRI scans often reveal a joint effusion. The physical examination may not be very specific with vague areas of tenderness, loss of motion, and catching. Osseous loose bodies are easily seen on plain radiographs, but chondral loose bodies may not be visible on routine studies. Computerized tomography (CT) scans, alone or in conjunction with a contrast arthrogram or MRI scans, will usually reveal even the smallest loose body within the joint. Ideally, the treatment of a loose body within the ankle should focus on extraction of the lesion, improvement in range of motion, and diminished pain, and aiding in the determination of the cause of the lesion. Since the os trigonum is an accessory ossicle, extracting the loose body serves as the foundation for the surgical treatment of this lesion, and usually results in complete resolution of symptoms. In cases where concomitant ankle ligamentous instability exists, both nonsurgical and surgical therapies may be indicated. Staples (8) reported that 42% of patients with grade III lateral ankle sprains treated nonoperatively remained symptomatic at follow-up, although severe disability was uncommon. Other authors have documented a 20% to 40% incidence of residual functional instability after nonoperative treatment of grade III lateral ligament injuries (9, 10). Functional instability and loss of normal ankle kinematics as a complication of ankle sprains may lead to chronic, recurrent injury and early degenerative changes (11). Talar displacement of greater than 1 mm reduces the ankle’s weight-bearing surface by 42.3%, thus creating asymmetric load bearing of the articular surface (12). Understanding these relationships makes clear the likelihood that degenerative changes with in the ankle could develop in response to even small amounts of articular displacement or abnormal shearing forces secondary to collateral ligament instability. Based on our understanding of the patient’s history and clinical examination, as well as inspection of his standard foot radiographs, stress ankle radiographs, and T1-weighted and T-2 weighted MRI scans, as well as the intraoperative and histopathological appearance of the ossicle, it is our opinion that the boney specimen represented a displaced os trigonum. In support of this conclusion, the patient described in this report related an approximately 10-year history of lateral ankle ligamentous instability, without distinct or focal pain at the posterior aspect of the talus. Until approximately 3 months before his presentation to our clinic, his only symptomatology had been frequent lateral
ankle sprains and associated lateral ligamentous pain. Close inspection of the lateral ankle radiograph (Figure 2) showed what could reasonably be considered to be a talar body concavity consistent with the original articulation with an os trigonum, suggesting that the loose ossicle was the dislocated os trigonum. Furthermore, the MRI (Figure 3) reinforced this suspicion by failing to reveal any evidence of an osteochondral lesion involving the talar dome, tibia, or fibula, and there were no magnetic resonance (MR) changes suggestive of a fracture or synovial proliferation. Still further, based on the radiographic and MRI findings, as well as the patient’s history, it was extremely unlikely that a 10 ⫻ 15-mm, loose osseous lesion situated near the posterior aspect of the dome of the talus, between the talus and tibia, could have originated in any fashion other than as a displaced os trigonum. Finally, according to the histology report describing the excised lesion, the specimen displayed an old ossification center and was composed of both cartilage and bone, and this was consistent with a displaced os trigonum. There are only anecdotal referrals based on personal experience (5). Although it is very difficult to make a solid conclusion, we believe that the displacement of the os trigonum is the result of the patient’s ankle instability. In conclusion, loose bodies in the ankle may arise from defects in the talus or tibia, periarticular osteophytes, or cartilage forming synovial pathologies. Functional instability and the loss of normal ankle kinematics may create asymmetrical load bearing on the articular surfaces, and may cause intra-articular displacement of the os trigonum. Presentation of a patient with ankle pain and a suspected displaced os trigonum is a rare clinical entity that, to our knowledge, has never before been described in the biomedical literature. In addition to its uniqueness, the current case raises the question of whether or not there is a relationship between the presence of a symptomatic os trigonum and
chronic lateral collateral ankle ligament instability. Based on our experience with the patient described in this report, we recommend that dislocation of the os trigonum be included in the differential diagnosis of a painful loose body localized to the posterior aspect of the ankle. References 1. Horibe S, Kita K, Natsu-ume T, Hamada M, Mae T, Shino K. A novel technique of arthroscopic excision of a symptomatic os trigonum. Arthroscopy 241:121–124, 2008. 2. Berkowitz MJ, Kim DH. Process and tubercle fractures of the hindfoot. J Am Acad Orthop Surg 138:492–502, 2005. 3. Milgram JW. The classification of loose bodies in human joints. Clin Orthop 124:282–291, 1977. 4. Bosien WR, Staples OS, Russell SW. Residual instability following acute ankle sprains. J Bone Joint Surg 37A:1237–1247, 1955. 5. Renstrom PAFH, Kannus P. Injuries of the foot and ankle In: Orthopedic Sports Medicine, pp 1748 –1749, edited by JC De Lee, D Drez, W. B. Saunders Company, Philadelphia, 1994. 6. Bureau NJ, Cardinal E, Hobden R, Aubin B. Posterior ankle impingement syndrome: MR imaging findings in seven patients. Radiology 215:497–503, 2000. 7. Wredmark T, Carlstedt CA, Bauer H, Saartok T. Os trigonum syndrome: a clinical entity in ballet dancers. Foot Ankle 11:404 – 406, 1991. 8. Staples OS. Rupture of the fibular collateral ligaments of the ankle. J Bone Joint Surg 57A:101–107, 1975. 9. Choi WJ, Lee JW, Han SH, Kim BS, Lee SK. Chronic lateral ankle instability: the effect of intra-articular lesions on clinical outcome. Am J Sports Med 2008 36(11):2167–72, 2008. [Epub ahead of print 2008 Jul 31]. 10. Cass JR, Morrey BF, Katoh Y, Chao EYS. Ankle instability: comparison of primary repair and delayed reconstruction after long-term follow-up study. Clin Orthop 198:110 –117, 1985. 11. Harrington KD. Degenerative arthritis of the ankle secondary to long standing lateral ligament instability. J Bone Joint Surg 61A:354 –361, 1979. 12. Johnson EE, Markolf K. The contribution of the anterior talofibular ligament to ankle laxity. J Bone Joint Surg 65A:81– 88, 1983.
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Isuchndividuals who perform plantarflexion-type activities, as ballet, may acquire a posterior ankle and subtalar joint impingement syndrome (1, 2). This condition typically results from impaction of a large trigonal process or os trigonum between the posterior margin of the distal tibia and the calcaneus on plantarflexion, and is also known as os trigonum syndrome. Os trigonum syndrome is usually diagnosed clinically when there is pain in the anterior aspect of the retrocalcaneal space, supported by radiological findings indicative of a large trigonal process or os trigonum. Loose bodies within the ankle may be either chondral or osteochondral, and may arise from defects in the talus or tibia, talotibial osteophytes, as well as synovial chondromatosis (2, 3). The presence of a completely separated and displaced loose body in the posterior aspect of the ankle joint, suggestive of a displaced os trigonum, is not a common clinical finding. Address correspondence to: Baris Kocaoglu, MD, Department of Orthopeadic Surgery and Traumatology, Acibadem Hospital, Tekin sok:8, Kadikoy, 34718 Istanbul/Turkey. E-mail: [email protected] 1 Staff physician, Acibadem Kadikoy Hospital, Department of Orthopaedic Surgery, Istanbul, Turkey. 2 Staff physician, Acibadem Kozyatagi Hospital, Department of Orthopaedic Surgery, Istanbul, Turkey. 3 Staff physician, Mardin Government Hospital, Department of Orthopaedic Surgery, Istanbul, Turkey. 4 Professor of Orthopedics, Marmara University, School of Medicine, Department of Orthopedics, Istanbul, Turkey. Financial Disclosure: None reported. Conflict of Interest: None reported. Copyright © 2009 by the American College of Foot and Ankle Surgeons 1067-2516/09/4802-0019$36.00/0 doi:10.1053/j.jfas.2008.10.005
Dislocation of the os trigonum presenting as a loose body in the ankle is a clinical entity that, to our knowledge, has not been previously described in the biomedical literature. In this report, we describe the case of a patient who presented with a loose osseous body in the posterior aspect of the ankle that, after surgical inspection and consideration of possible etiologies, was felt to be a displaced os trigonum. Case Report A 34-year-old male amateur athlete presented to the authors’ clinic with a complaint of 3 months’ duration of excruciating left ankle pain that was sudden in onset, associated with a feeling of something catching inside his ankle, and aggravated by standing and walking. He also related an approximately 10-year history of chronic left lateral ankle instability associated with recurrent ankle sprains. He described the pain as being localized to the posterior aspect of the ankle, and further localized slightly more lateral than medial. Over the month preceding presentation to our clinic, the pain had become noticeable even with non–weightbearing passive motion. He denied any recent ankle sprains or twisting injuries. The Achilles tendon was neither painful nor swollen. Physical examination of the patient’s left ankle and foot revealed no evidence of an effusion, acute cutaneous compromise, or focal tenderness to palpation and manipulation of the ankle ligaments, sinus tarsi, midtarsal joints, body of the calcaneus, plantar heel, or Achilles tendon. The left ankle was markedly unstable in response to inversion stress and anterior drawer maneuvers, with subluxation of the VOLUME 48, NUMBER 2, MARCH/APRIL 2009
215
FIGURE 1 (A) Anteroposterior standard radiographic view of the left ankle with the loose ossicle visualized laterally, near the fibula. (B) Stress inversion view showing the ossicle more clearly as the space between the talus and the tibia is widened.
talus in relation to the tibia. With the exception of vague, deep pain at the posterior aspect of the subtalar and ankle joints, as well as the lateral collateral ligament instability, the physical examination was largely inconclusive. Radiographic inspection, however, clearly showed a loose, osseous body measuring approximately 10 ⫻ 15 mm in size, visualized on the anteroposterior (AP) and varus stress AP plain films (Figure 1, A and B). Although difficult to clearly outline, the loose body was also evident on the lateral plain film radiograph (Figure 2). Close inspection of the standard radiograph of the ankle failed to reveal any evidence of an osteochondral defect involving the talus, tibia, or the fibular articulating surfaces. Furthermore, there was no evidence of multiple radiopaque bodies suggestive of synovial chondromatosis. Magnetic resonance image (MRI) scans of the left ankle revealed a solitary, loose, round osseous body that measured 10 ⫻ 15 mm, located immediately anterior to the posterior talofibular ligament, and situated between the talus and the tibia (Figure 3). In both T1-weighted and T2weighted images, there was no evidence of a cartilage defect localized to the distal tibial-bearing surface, the dome of the talus, or the fibula. Moreover, there was a slight indentation in the body of the talus consistent with the usual origin of 216
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the posterolateral trigonal process, or the attachment of the os trigonum, with no sign of either an intact trigonal process or os trigonum. Based on the clinical and diagnostic imaging findings, diagnoses of suspected displaced os trigonum and chronic lateral ankle instability were made. After discussion of the suspected diagnoses, prognosis, and treatment options, surgical stabilization of the ankle and arthroscopic inspection and removal of the loose body were recommended. After considering the options, the patient consented only to removal of the loose body, with the understanding that regular use of an ankle brace would thereafter be indicated and recommended. After making the usual preparations, including administration of prophylactic antibiotics (cefazolin, 1 gram, intravenous, 30 minutes prior to commencement of the operation) and low-dose heparin (5000 units subcutaneous 60 minutes preoperative), left ankle arthroscopy was undertaken with the patient initially placed in a supine position, under general anesthesia, and with a tourniquet placed around his upper thigh. Once anesthetized, and the skin surgically prepped, the left hip was flexed and abducted and put in a lithotomy support, while the right lower extremity was slightly flexed at the knee and allowed to rest on
FIGURE 2 Standard lateral radiographic view of the left ankle showing the loose ossicle situated between the talus and the tibia, in the posterior aspect of the joint. Note, too, the concavity at the posterior aspect of the talar body, distal to the loose body, where the trigonal process, or os trigonum, would usually be attached.
FIGURE 3 Lateral magnetic resonance image showing a solitary, loose, round osseous body measuring 10 ⫻ 15 mm, located immediately anterior to the posterior talofibular ligament, situated between the talus and the tibia.
the table. After placement of a central anterior incision, situated between the tibialis anterior and extensor hallucis longus tendons, the left ankle joint was inflated with physiologic saline, and the capsule was distended bluntly to avoid damage to the neurovascular structures. A standard 4-mm 30° arthroscope was introduced into the ankle joint through the anterior portal and, without the use of a specific traction device other than the hanging position of the foot
FIGURE 4 Arthroscopic view showing the loose body (LB) situated between the talus (TA), posterior talofibular ligament (PTFL), and fibula (F) prior to extraction.
and occasional application of manual traction to the heel, a 2-mm hook was inserted into the joint through an additional anteromedial portal. Thereafter, a systematic arthroscopic examination was used to visualize the intra-articular structures, wherein a 10-point examination was used to inspect the anterior component of the articular cavity, and a 5-point examination was used to inspect the central and posterior components of the ankle (1). As soon as the arthroscope entered the space between the talus and tibia, a 10 ⫻ 15-mm, smooth, oblong, loose body was identified (Figure 4). The loose body was firm, and could not be deformed with the tip of the probe; and despite being loose enough to move approximately 5 mm upon ankle dorsiflexion, plantarflexion, and valgus stress, soft tissue adhesions prevented extraction of the loose body until a thin arthroscopic punch was used to section the attachments on the distal and posterior aspect of the ossicle. Thereafter, an arthroscopic forceps was used to grasp the loose body, and to extract it from the joint. After wound closure, a sterile bandage without a cast was used, and the patient was allowed to resume full weight bearing on the second postoperative day. Prior to that time, crutches were used and the patient instructed to avoid placing weight on the operated left lower extremity. Pathological inspection of the removed loose body revealed the specimen to be composed of bone covered with cartilage (Figure 5). Supervised physiotherapy (PT) was initiated after the first postoperative week, and carried out for 6 weeks, and included ankle range of motion exercises, strengthening of the muscles of the anterior compartment of the leg, the peroneal musculature, and the calf musculature. These exercises were performed every day for 2 weeks and then twice daily for an additional 4 weeks. Sports activity was allowed at 3 months following the operation. Overall, VOLUME 48, NUMBER 2, MARCH/APRIL 2009
217
FIGURE 5 Pathological inspection of the removed loose body revealed the specimen to be composed of bone covered with cartilage (hematoxylin and eosin, original magnification ⫻100).
the patient progressed unremarkably, and after 24 months of follow-up the patient had a pain-free ankle with persistent lateral collateral ligament instability on physical examination. He was also able to play tennis without any discomfort, with the use of a lace-up ankle brace. Discussion The os trigonum forms from a secondary center of ossification located at the posterolateral aspect of the body of the talus, just lateral to the groove for the flexor hallucis longus (FHL) (1, 2). The prevalence of this ossicle ranges from 1.7% to 7.7%, and is present unilaterally twice as often as bilaterally (2, 3). If not present as a separate ossicle, the trigonal process usually extends a short distance in the posterolateral direction from the talar body, forming the lateral margin of the groove for FHL. Development of the os trigonum is generally considered to be congenital, although it may be acquired secondary to traumatic disruption of the trigonal process. When present as a separate ossicle, the os trigonum usually appears by 8 to 10 years of age in girls and 11 to 13 years of age in boys, and fusion with the main body of the talus occurs at approximately 1 year following its appearance (2, 3). Persistence of the separation between the os trigonum and the body of the talus may occur in response to repetitive microtrauma (4). In most cases, an os trigonum remains asymptomatic until some sort of injury leads to disruption of either the trigonal process or the ossicle itself (5). It can also become symptomatic in young athletes who actively plantarflex their ankle, and is particularly prevalent in ballet dancers, gymnasts, ice skaters, and, to a lesser degree, soccer players (6, 7). 218
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Loose bodies may be either chondral or osteochondral and may arise from defects in the talus or tibia, osteophytes, or degenerative joint disease (3). A trauma, minor or major, to the ankle joint may result in a chondral or osteochondral lesion and then lead to a loose body floating within the joint. Loose bodies can also be seen with osteophytes and synovial chondromatosis. Such lesions can cause locking or catching with attempted ankle motion, and are usually associated with ankle pain and swelling, and MRI scans often reveal a joint effusion. The physical examination may not be very specific with vague areas of tenderness, loss of motion, and catching. Osseous loose bodies are easily seen on plain radiographs, but chondral loose bodies may not be visible on routine studies. Computerized tomography (CT) scans, alone or in conjunction with a contrast arthrogram or MRI scans, will usually reveal even the smallest loose body within the joint. Ideally, the treatment of a loose body within the ankle should focus on extraction of the lesion, improvement in range of motion, and diminished pain, and aiding in the determination of the cause of the lesion. Since the os trigonum is an accessory ossicle, extracting the loose body serves as the foundation for the surgical treatment of this lesion, and usually results in complete resolution of symptoms. In cases where concomitant ankle ligamentous instability exists, both nonsurgical and surgical therapies may be indicated. Staples (8) reported that 42% of patients with grade III lateral ankle sprains treated nonoperatively remained symptomatic at follow-up, although severe disability was uncommon. Other authors have documented a 20% to 40% incidence of residual functional instability after nonoperative treatment of grade III lateral ligament injuries (9, 10). Functional instability and loss of normal ankle kinematics as a complication of ankle sprains may lead to chronic, recurrent injury and early degenerative changes (11). Talar displacement of greater than 1 mm reduces the ankle’s weight-bearing surface by 42.3%, thus creating asymmetric load bearing of the articular surface (12). Understanding these relationships makes clear the likelihood that degenerative changes with in the ankle could develop in response to even small amounts of articular displacement or abnormal shearing forces secondary to collateral ligament instability. Based on our understanding of the patient’s history and clinical examination, as well as inspection of his standard foot radiographs, stress ankle radiographs, and T1-weighted and T-2 weighted MRI scans, as well as the intraoperative and histopathological appearance of the ossicle, it is our opinion that the boney specimen represented a displaced os trigonum. In support of this conclusion, the patient described in this report related an approximately 10-year history of lateral ankle ligamentous instability, without distinct or focal pain at the posterior aspect of the talus. Until approximately 3 months before his presentation to our clinic, his only symptomatology had been frequent lateral
ankle sprains and associated lateral ligamentous pain. Close inspection of the lateral ankle radiograph (Figure 2) showed what could reasonably be considered to be a talar body concavity consistent with the original articulation with an os trigonum, suggesting that the loose ossicle was the dislocated os trigonum. Furthermore, the MRI (Figure 3) reinforced this suspicion by failing to reveal any evidence of an osteochondral lesion involving the talar dome, tibia, or fibula, and there were no magnetic resonance (MR) changes suggestive of a fracture or synovial proliferation. Still further, based on the radiographic and MRI findings, as well as the patient’s history, it was extremely unlikely that a 10 ⫻ 15-mm, loose osseous lesion situated near the posterior aspect of the dome of the talus, between the talus and tibia, could have originated in any fashion other than as a displaced os trigonum. Finally, according to the histology report describing the excised lesion, the specimen displayed an old ossification center and was composed of both cartilage and bone, and this was consistent with a displaced os trigonum. There are only anecdotal referrals based on personal experience (5). Although it is very difficult to make a solid conclusion, we believe that the displacement of the os trigonum is the result of the patient’s ankle instability. In conclusion, loose bodies in the ankle may arise from defects in the talus or tibia, periarticular osteophytes, or cartilage forming synovial pathologies. Functional instability and the loss of normal ankle kinematics may create asymmetrical load bearing on the articular surfaces, and may cause intra-articular displacement of the os trigonum. Presentation of a patient with ankle pain and a suspected displaced os trigonum is a rare clinical entity that, to our knowledge, has never before been described in the biomedical literature. In addition to its uniqueness, the current case raises the question of whether or not there is a relationship between the presence of a symptomatic os trigonum and
chronic lateral collateral ankle ligament instability. Based on our experience with the patient described in this report, we recommend that dislocation of the os trigonum be included in the differential diagnosis of a painful loose body localized to the posterior aspect of the ankle. References 1. Horibe S, Kita K, Natsu-ume T, Hamada M, Mae T, Shino K. A novel technique of arthroscopic excision of a symptomatic os trigonum. Arthroscopy 241:121–124, 2008. 2. Berkowitz MJ, Kim DH. Process and tubercle fractures of the hindfoot. J Am Acad Orthop Surg 138:492–502, 2005. 3. Milgram JW. The classification of loose bodies in human joints. Clin Orthop 124:282–291, 1977. 4. Bosien WR, Staples OS, Russell SW. Residual instability following acute ankle sprains. J Bone Joint Surg 37A:1237–1247, 1955. 5. Renstrom PAFH, Kannus P. Injuries of the foot and ankle In: Orthopedic Sports Medicine, pp 1748 –1749, edited by JC De Lee, D Drez, W. B. Saunders Company, Philadelphia, 1994. 6. Bureau NJ, Cardinal E, Hobden R, Aubin B. Posterior ankle impingement syndrome: MR imaging findings in seven patients. Radiology 215:497–503, 2000. 7. Wredmark T, Carlstedt CA, Bauer H, Saartok T. Os trigonum syndrome: a clinical entity in ballet dancers. Foot Ankle 11:404 – 406, 1991. 8. Staples OS. Rupture of the fibular collateral ligaments of the ankle. J Bone Joint Surg 57A:101–107, 1975. 9. Choi WJ, Lee JW, Han SH, Kim BS, Lee SK. Chronic lateral ankle instability: the effect of intra-articular lesions on clinical outcome. Am J Sports Med 2008 36(11):2167–72, 2008. [Epub ahead of print 2008 Jul 31]. 10. Cass JR, Morrey BF, Katoh Y, Chao EYS. Ankle instability: comparison of primary repair and delayed reconstruction after long-term follow-up study. Clin Orthop 198:110 –117, 1985. 11. Harrington KD. Degenerative arthritis of the ankle secondary to long standing lateral ligament instability. J Bone Joint Surg 61A:354 –361, 1979. 12. Johnson EE, Markolf K. The contribution of the anterior talofibular ligament to ankle laxity. J Bone Joint Surg 65A:81– 88, 1983.
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