Ankle injuries are an extremely common problem seen by the general practitioner and the physiotherapist. Ankle injuries account for approximately 12% of all injuries seen in emergency departments. Sprains alone account for about 15% of all sports injuries ( Rubin and Sallis 1996 ). In 1986 McBryde found that ankle problems comprised of 13.2% of injuries sustained in 1000 consecutively treated runners. Of the impingement type ankle problems in these runners, posterior ankle impingement was diagnosed in 18% ( Hendrick and McBryde 1994 ).
Posterior ankle impingement is defined as “impingement occurring at the anatomical interval between the posterior tibial articular surface and the calcaneus” ( Hedrick and McBryde 1994). It can be an acute or chronic injury or both, with an acute episode followed by repeated microtrauma.
The posterior process of the talus extends both posteriorly and medially from the talus and has two projections designated as the medial and lateral tubercules. Between these tubercles is a groove containing the flexor hallucis longus tendon. The medial tubercule, which is shorter and wider than the lateral, serves as a site for the attachment of the posterior tibiotalar ligament, which is part of the deltoid ligament. The portion of the talus lateral to the groove, the lateral tubercule may present as a process, either short or long. If it is long it can be termed a Stieda’s Process ( Brodsky and Khalil 1986 ) or a Trigonal Process (Marumoto and Ferkel 1997 ).
Instead of a process there may be an ossicle of bone attached to the talus by a fibrous tissue, and this is known as an Os Trigonum. The posterior talofibular ligament and the posterior talocalcaneal ligament combine to form a bifurcated ligament that stem upward to the groove between the two processes.
The os trigonum develops as a secondary centre of ossification and appears in males between the age of 11-13 and in females between the ages of 8-10 years (Hendrick and McBryde 1994 ). This usually fuses within one year of its appearance. The moment it ossifies with the talus, it ceases being an os trigonum. Different literature give varying population incidence, but it seems to be reported between 7-13%. This is for the presence of a unilateral os trigonum, the likelihood of having it bilateral is about half again ie 3-7%. The majority of the population that do have one ( or two ) remain asymptomatic.
It is purely anatomical semantics whether the individual has an os trigonum or a trigonal process, the symptoms and mechanism of pain are the same. That is, there is impingement of the posterior talus or its process on the posterior articular margin of the tibia in the plantar flexed position. The pathomechanics that give rise to these symptoms occur in three ways;
1/ The os trigonum or trigonal process may impede full plantar flexion by acting as a bony block. The bone tissue itself may be injured “like a nut in a nutcracker” or the adjacent soft tissues may be impinged.
2/ A previously intact trigonal process or a cartilaginous syncchondrosis may be fractured from the compressive forces as described above.
3/ The posterior talofibular ligament and posterior talocalcaneal ligaments have been shown to distract a fractured trigonal process in cadavers, giving rise to possibility of an avulsion injury also ( Marumoto and Ferkel 1997 ).
A prominence of the posterior process of the os calcis can also contribute to the impingement ( Hendrick and McBryde 1994 ).
As suggested, there are a percentage of the population that have this condition that remain asymptomatic. Those that do develop symptoms are usually athletes such as ballet dancers from plantar flexion stress in the ‘en point’ position, soccer players that plantar flex while kicking and downhill runners. In fact, any running based sport that involves forced plantar flexion may be implicated. This would include the Surf Lifesaving beach sprint athlete, who runs predominantly on his or her toes and given the lack of resistance from the soft sand results in a very plantar flexed running position. This plantar flexion can be emphasised in the uneven soft sand.
The forceful and/or repetitive plantar flexion performed by the athletes predisposes the posteriolateral aspect of the talus to impinge between the calcaneus and the posterior aspect of the tibial plafond ( Brown et al 1995 ). The onset of symptoms may either be gradual with increased activity, or following an acute injury such as an ankle sprain.
Diagnosis of posterior impingement is based on history, physical examination, clinical judgement and x-rays. The patient will often describe the pain and tenderness in the posterior lateral aspect of the ankle, with localised tenderness on palpation directly posterior to the lateral malleolus. Stiffness is also reported. The patients pain is reproduced with end of range plantar flexion and a sudden end point to motion is often encountered. Paulos et al found a reduced plantar flexion of 25 degrees in patients with a fractured os trigonum.
There may be mild to moderate swelling depending on the acute or chronic stage of the injury occupying the space anterior to the Archilles tendon, and because of the close anatomical proximity of the flexor hallucis longus tendon, there may be some pain with resisted flexion of the big toe.
X-rays are best taken in a lateral view with flexion and extension, thus demonstrating the impinged element. The ossicle is seen entrapped between the posterior lip of the tibia and the dorsum of the calcaneus. Because much of the os trigonum is cartilaginous, it frequently occupies a larger area than is first appreciated on plain x-rays (Marotta and Micheli 1992 ). The os trigonum is usually triangular, but may appear round or oval. It is usually solitary and less than 1 cm in size, but may be bipartite or even multipartite ( Karasick and Schweitzer 1996 ). The margins of the ossicle may be smooth or serrated, indicating a more recent fracture. With continued impingement, there may be hypertrophy of the ossicle or lateral tubercle.
A CT scan with coronal views can be utilised to identify the size and shape of the impinged element. Bone scans often show an increase in uptake in this region of traumatised tissue ( Marotta and Micheli 1992 ). Some authors believe the os trigonum is palpable at the posteriolateral joint line.
Sagittal CT reconstruction shows large os trigonum ( O )
Confirmation of the diagnosis can be made by injecting the area with a local anaesthetic, which will relieve the pain, but not alter the end of range movement or end feel.
This condition is often misdiagnosed as tendonitis. The differential diagnoses include; flexor hallucis longus tendonitis, peroneal and Archilles tendonitis, retrocalcaneal bursitis, capsulitis, ankle joint arthritis or an acute fracture of the talar tuberosities.
Index of suspicion should be high when symptoms are reproduced with passive plantar flexion and or tenderness on palpation in the posterior aspect of the subtalar joint between the Archilles tendon and the lateral malleolus ( Brown et al, 1995 ) .
The subject of this case study is an eighteen year old female beach sprinter whom while training with the Auckland Representative Surf Lifesaving Team underwent a forced plantar flexion injury. This athlete competes at a district level and at the time of injury was the current Auckland Beach Sprint and Flags titleholder in the U/19 division as well as the National Titleholder in the Beach Flags. Both of these events involve sprinting short distances over soft sand.
The training session in which the injury occurred, the athlete was well warmed up and was doing sprint starts in the soft sand at Mairangi Bay. She had dug herself starting blocks in the sand, as one does in a race, ran out and back in a shuttle run type manner, and ran over her blocks on the way back. The athletes right foot landed deeply in the starting blocks, which is basically a specifically dug hole in the sand. As she landed in the hole, her foot was in a near end range plantar flexed and inverted position. She and other athletes around her heard an audible “crack”. There was immediate pain and tears!
Ice was applied immediately and her coach took her to an Accident and Emergency Clinic within the hour. The athlete hopped into the clinic, unable to weight bear. She was assessed by the general practitioner who felt sure it was an inversion sprain, and prescribed NSAID’s, rest, ice, compression and referred her to physiotherapy.
The physiotherapy findings included;
- limping gait
- moderate swelling over the lateral malleolus
- reduced inversion and plantar flexion by half
- tenderness on palpation over the anterior and lateral aspects of the lateral ligament of the right ankle and the distal half of the peroneals
At this stage the goal of treatment was to be able to compete in the National Interdistrict competition in 4 days time!
Treatment over that 4 day period included;
- ice, compression bandage
- ultrasound, pulsed 0.8 w/cm2 for 5 mins
- gentle soft tissue massage and frictions to the distal half of the peroneals, and the anterior and lateral aspects of the lateral ligament
- instruction and advice regarding normal heel toe gait
- resisted walking
During the two day competition the ankle was heavily strapped and frequently iced. There is no doubt the athlete was in discomfort and didn’t compete to her usual form.
Following this weekend of competition on assessment Monday morning the ankle was back to its original state, including reduced range of motion, moderate swelling and very tender to palpate. There was now a ten day period until the National Surf Lifesaving Championships to rehabilitate the athlete.
Over the ten day period the athlete had seven physiotherapy treatments. Initially the treatments involved modalities and techniques as employed immediately after the initial injury, and then progressed to include wobble board work and a graduated return to sprint training, initially on the track at lower intensities, then on the track at increased intensities, then hard sand and finally starts on soft sand.
The rehabilitation progressed very well, to reach the point that the athlete was running pain free on soft sand at full pace prior to travelling to the Nationals.
To compete the ankle was again heavily strapped, and ice was employed between races and at the end of each of the 3 days of competition. The first two days went well, and the athlete defended her National title in the beach flags event. However, following this she was in agony, and was mentally exhausted with the pain. Her beach sprint semi final was not long after, and she ran very poorly obviously lacking confidence in her ankle.
The six week period post Nationals the athlete rested and the acuteness of the injury subsided. However, she was not painfree and was aware of pain in the posteriorlateral aspect of the right ankle, particularly in work shoes with a high heel. The athlete attempted training again, starting her winter preparation. She was unable to run due to posteriolateral ankle pain.
The athlete returned to physiotherapy. This examination revealed the following;
- normal gait with walking
- mild swelling in the T.A. region
- full range inversion, eversion
- discomfort end of range dorsiflexion
- severe reproduction of patients pain with end of range plantar flexion, heel thrust manoeuvre.
- tightness and tenderness in soleus and medial gastrocnemius
- tenderness in the posteriolateral aspect of the ankle, just lateral to the T.A. Less tenderness in the lateral ligaments
Thinking along the lines of a posterior capsulitis the physiotherapeutic management included;
- frictions to the posteriolat aspect of the ankle
- ultrasound, pulsed at 1.0 w/cm2 for 4 mins
- soft tissue massage to the soleus and medial gastrocnemius
- acupuncture on one occasion
After three treatments at this stage and no improvement the physiotherapist returned the athlete to her G.P. with a letter suggesting an orthopaedic assessment may be warranted. The G.P. was in agreance and the athlete saw an orthopaedic surgeon on May 4th 1998, ten weeks after the initial injury and seven weeks following Nationals.
The orthopaedic examination revealed;
- slightly limped gait
- small amount of ankle swelling
- good active and passive dorsiflexion
- pain in posteriolateral aspect of ankle with plantar flexion
- tenderness in the posteriolateral ankle region
- pain on eversion with associated peroneal tendon discomfort
His comments suggested the athlete had an injury to the posterior talar process that would benefit from some debridement. He was also concerned there may be some peroneal tendonitis, and wanted a bone scan prior to the surgery.
The bone scan came back all clear, ruling out peroneal tendonitis and the surgery was approved by ACC.
As the athlete had complained of developing anterior pain prior to the surgery the surgical procedures included;
1/ Arthroscopy of the anterior of the left ankle. This revealed the ankle surfaces looked good, there was just a small amount of contusion to the anterior aspect of the anterior tibial plafond. This was debrided back with a shaver.
There was also an area of synovitis and inflammation at the ankle synndesmosis between the fibula and the tibia. This was also debrided with the shaver.
2/ A lateral incision was made just beside the Achilles tendon and dissection continued through the capsule to the posterior process of the talus. An osteome was used to remove the posterior talar process and ‘spur’. The FHL tendon was seen to be intact.
The athlete was in a below knee boot and the wounds had been dressed. She was to stay on crutches till the follow visit two weeks post op.
At the two week review the orthopaedic surgeon commented that her wounds looked good, and he removed the sutures. The ankle had very little swelling at this stage. She was encouraged to wean herself off the crutches over the coming two weeks and to increase her activities as symptoms allowed. The surgeon suggested to start with some cycling and then progress to running approximately 8 weeks post op.
The athlete returned to physiotherapy 4 weeks post op. At this stage assessment revealed;
- walking painfree
- continued to have tight and tender soleus and gastrocnemius
- tenderness around scar and deep to it
- numbness lateral to scar behind lateral malleolus
- good 1 leg balance
The physiotherapy management at this stage included;
- soft tissue massage to soleus and gastrocnemius
- gentle friction massage around scar
- soleus and gastrocnemius stretches
The activity progression was as follows;
4 weeks post op – walking in the home unassisted
5 weeks post op - increased walking around the streets, up to 1 hour
6 weeks post op - returned to the track, walking drills and jogging
weight training within painfree range
7 weeks post op - running drills but nil bounding
interval running, again within painfree range
After this seventh week, the athlete was aware of some discomfort in the early stages of her training session, and did have some pain in posteriolateral aspect of ankle at end of range plantar flexion. She was advised to back off the training a little over the next 4-5 days and let it settle right down again. It was found that following soft tissue massage of the lateral soleus the pain at end of range plantar flexion diminished.
At this stage she was only having physiotherapy once a week, but there were very good lines of communication between the physiotherapist, the athlete and the coach. The athlete was instructed to warm up well and do numerous soleus stretches, as well as get her mother to do some massage to the soleus at home.
It would seem that this athlete had a lengthened talar process that was causing some impingement in the posterior aspect of the ankle. It came about because of an initial forced plantar flexion injury, and then subsequent trauma due to continued competition. There was no fracture as such, it just became symptomatic because of the nature of the injury and the continued activity. Neither in the x-ray report nor the surgical report was there ever any mention of an os trigonum, however there was reference to a ‘spur’.
It is important to note that not only did the bony ossicle disrupt the normal function of this ankle, but so to the inflammation of the soft tissues within the region, namely the capsule and synovium. Repetitive impingement of the soft tissues in this interval can result in hypertrophic capsulitis ( Hendrick and McBryde 1994 ) and associated flexor hallucis longus tenosynovitis ( Karasick and Schweitzer 1996 ).
The anterior pain which developed as the injury became more chronic was most likely due to the continued inflammation in the ankle joint, resulting in synovial thickening. During surgery it was noted that there was some inflammation in the ligamentous tissue between the tibia and fibula. With this debrided, the athlete had no complaints of anterior pain post surgery.
There was also an inversion sprain, but this did settle down following the rest from training after nationals.
Rosenmuller is credited with first describing the os trigonum in 1804 ( Marumoto and Ferkel 1997 ). Sheppard, an early English anatomist, in 1882, felt this bony curiosity was due to a fracture and became known as the “Sheppards Fracture”. After the invention of radiograph, case reports of posterior ankle impingement were described by Meisenbach in 1927, Milch in 1941, McDougall in 1955 and Lapidus in 1972 ( Hendrick and McBryde 1994 ).
McDougall in 1955 proposed three different mechanisms for the presence of an os trigonum;
1/ failure of fusion of the secondary ossification center
2/ repeated microtrauma, with impingement resulting in a fracture of the posterior process
3/ sudden, severe trauma to the plantar flexed ankle, causing an acute fracture of the posterior process of the talus.
The operative treatment of posterior ankle impingement was not well described until 1982 when Howse described the posterior block of the ankle joint, which he treated surgically in dances at the royal ballet school in London. In the same year Ihle and Cochran reported on the operative excision of a fractured os trigonum in a professional basketball player. A year later, in 1983, Quirk described the lateral approach used in the surgical excision of the os trigonum.
When an os trigonum or trigonal process is clinically diagnosed as a source of posteriorlateral pain, conservative treatment has been recommended, however it efficacy has not been well documented in the literature. Only two reports mention the success rate of conservatively treating patients. Because patients who are successfully treated non-operatively by primary physicians are not referred, it is therefore difficult to derive actual success rate for conservative treatment ( Marumot and Ferkel 199 ).
When the symptoms of either an os trigonum or a trigonum remain persistent despite conservative measures, operative excision has been reported to yield good results.
In an experiment by Marotta and Micheli in 1992 sixteen patients had their os trigonums surgically removed. The patients pre-operative symptoms included localised posterior pain, decreased range of motion, weakness and swelling. All patients had failed with conservative methods such as modified activity, NSAID’s, massage, ice, ultrasound and rehabilitation exercises. Three to five days following their surgery the subjects began formalised physiotherapy for progressive weight bearing and increased range of motion. All of these subjects returned to full participation in their chosen activity ( dancing ) without restriction. The average time to full participation was three months post surgery. The authors stressed the importance of early return to weight bearing and activity.
Within the literature there is a question more recently, not whether surgery is a good option, but rather whether open surgery or arthroscopic surgery is preferential. This discussion seems to be in the early stages.
Brown et al, 1995 proposed four mechanisms of injury that result in posterior ankle impingement;
1/ forced plantar flexion and resultant posterior lateral impingement
2/ direct trauma to area
3/ Excessive dorsiflexion, thus increasing the tension of the posterior ligament and avulsing the os trigonum
4/ detachment of the os trigonum by repeated minor injury ( thought to be most common )
Hendrick and McBryde suggest that the mechanism of injury is due to a plantar flexion injury and can involve any anatomical structure in the posterior ankle interval. They suggest it can be visualised simplistically as a “nut in a nutcracker”.
It would seem the subject of this case study was reasonably typical in the description of posterior ankle impingement. She sustained a forced plantar flexion injury at end range and then had subsequent micro trauma. Conservative measures of rest, NSAID’s, massage and exercise was unsuccessful in treating her symptoms. She had classic symptoms of pain elicited with passive end of range plantar flexion and tenderness in the posteriorlateral aspect of the ankle, between the T.A. and the lateral malleolus.
The surgical intervention revealed a lengthened posterior talar process and the excision of this relieved the patient of the symptoms. Her rehabilitation was rapid and at the time of this paper being written, at 7 weeks post op, the return to activities of sprinting are going well.
As reported in the literature, a number of these patients do experience some discomfort in the posterior aspect of the ankle after surgery, but never intense enough to alter their athletic participation.
Injuries to the ankle are among the most common is orthopaedics. Although the majority of ankle sprains respond to conservative treatment, there is a small group that will remain symptomatic ( Veazey et al 1992 )
In summary, it would seem that posterior ankle impingement is becoming more frequently recognised in certain athletes, in particular dancers, and is being caused predominantly by the presence of either an os trigonum or a trigonum. The conservative treatment is often unsuccessful, but the surgical excision of the bony prominence has proven to safe and lead to immediate relief, and a short rehabilitation period of approximately 2 – 3 months to return to high performance activities.
I would like to thank the surgeons at Unisportsmed, Auckland for their assistance, as well as Dr. J Gorden for her review and comments.
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Hedrick, M. and McBryde, M. Posterior Ankle Impingement. Foot and Ankle, Vol. 15, No.1, January, 1994.
Marotta, J. and Micheli, L. Os trigonum impingement in dancers. The American Journal of Sports Medicine, Vol. 20, No.5, 1992.
Marumoto, J. and Ferkel, R. Arthroscopic Excision of the Os Trigonum: A New Technique with Preliminary Clinical Results. Foot and Ankle International, Vol 18, No.12, December, 1997.
Rubin, A. and Sallis, R. Evaluation and Diagnosis of Ankle Injuries. American Family Physician, Vol. 54, No. 5, October, 1996.
Karasick, D. and Schweitzer, M. The Os Trigonum Syndrome: Imaging Features. American Journal of Radiology Vol 166: 125-129, 1996.
Veazey, B. et al. Excision of Ununited Fractures of the Posterior Process of the Talus: A Treatment for Chronic Posterior Ankle Pain. Foot and Ankle, Vol. 13, No.8, October, 1992.
Wredmark, T. et al. Os Trigonum Syndrome: Aclinical Entity in Ballet Dancers. Foot and Ankle, Vol.11, No.6, June, 1991.
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Katrina is a NZ trained physio holding a Masters degree. She is one of the few qualified Manipulative Physiotherapists on the beautiful Sunshine Coast in Australia.
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