Clinical diagnosis
Case 183
【Progress】
She was under conservative treatment, being given arch support for heel pain
【Discussion】
There are six types of synovial joints: pivot, hinge, condyloid, saddle, plane, and ball-and socket-joints. Hip joint is a ball and socket type, knee joint is a hinge type and ankle (tibia-tarsal) joint is a plane (gliding) type (1). In a plane type, although various motions seem to be possible, the actual motion is small and tightly constrained by surrounding ligament, tendon and neighboring bones. Synovial joint plane is smaller in tibia-tarsal joint than in hip or knee joints, the weight burden is greater in tibia-tarsal joint than in hip or knee joints. However, the incidence of osteochondrosis in ankle joint is less than in hip joint and knee joint. This is probably because the motion of ankle joint is simple and limited, inducing less damaged to ankle joint than to knee or hip joint (1). It is reported that ankle osteoarthrosis is relatively rare and occurs of injury such as malleolar fracture or tibial fracture rather than aging or weight bearing (2, 3).
Articular joint contains synovial fluid which is produced by synovial cells. Osteoarthritis relates with injury, infection, aging and weight burden (3, 4). Osteochondrosis is caused by volume-loss of cartilage in articular joint. It induces production of lubricating synovial fluid to lessen friction, inducing swollen and painful joint. Bursa which originally exists near articular joint to lessen friction to ligament or muscle tendon, responds to cartilage loss producing lubricating fluid, causing bursitis.
Joint capsule composes of synovial layer and fibrous layer. Excessive synovial fluids expand and form a synovial cyst which has synovial cells lining. Meanwhile, ganglion has fibrous capsule without synovial cells lining. Ganglion cyst might be formed when excessive fluid enters crevice or perforate to the space outside articular joint. Synovial cyst communicates with articular joint but bursitis and ganglion do not (5). On MRI, cystic formation near articular joint is commonly shown in articular joint but sometimes difficult to differentiate ganglion cyst from bursitis (6).
Further, cartilage loss induces stress to ligament surrounding articular joint, causing injury to ligament or muscle tendon. Furthermore, it induces proliferation of osteophyte, sub-cartilage ossification, bone edema, bone necrosis and bone cyst.
Trigonal bone is situated behind talus and connects to talus by a fibrous band. Trigonal bone is believed to be a remnant (of lateral tubercle) of talus which failed to fuse during adolescence. It is estimated to be present in 7 to 10 % of adults and bilateral os trigonum is seen in 2%, indicative of hemi-lateral os trigonum being more often (7). Plantarflexion induces os trigonum caught in between tibia and calcaneus and impinges these bones. Repeated plantarflexion like ballet dancer or soccer player causes os trigonum syndrome. Os trigonum syndrome mimic Achilles tendon injury, ankle sprain and talus fracture. There exits musculus flexor hallucis longes between lateral tubercle and medial tubercle. This muscle usually damages with os trigonum syndrome. When os trigonum does not exist, it can cause injury of lateral (trigonum) tubercle of talus which is termed as posterior impingement syndrome.
In our case, she had normal trigonal bone but bone marrow edema and necrosis were found at both of tibia and talus indicative of chronic osteoarthritis of ankle joint. Further bursitis and/or ganglion was also found surrounding musculus flexor hallucis longes.
【Summary】
We present a sixty nine-year-old female for painful left ankle joint, especially at medial posterior area of left ankle joint, where it was swollen sized pachinko ball and as hard as bone protrusion. Ankle MRI showed normal os trigonum but chronic arthritis with bursitis surrounding musculus flexor hallucis longes. It is borne in mind that ankle joint is a plane (gliding) joint and ankle osteoarthritis arises following malleolar fracture or tibial fracture rather than aging. Osteoarthritis begins from cartilage volume loss, articular fluid increases to lessen friction and induces formation of osteophyte, subchondral ossification, bone edema, necrosis and cyst. Further it induces synovial cyst, ganglion cyst and bursitis. Further, it causes injury of ligament and tendon. Repeated plantarflexion causes os trigonum syndrome or posterior impingement syndrome in case of presence of os trigonum. Musculus flexor hallucis longes runs between lateral tubercle and medial tubercle of talus.
【References】
1.Synovial joint From Wikipedia, the free encyclopedia
2.Coester LM, et al. Long-term results following ankle arthrodesis for post-traumatic arthritis. J Bone Joint Surg Am. 2001;83:219–228.
3.Aurich M, et al. Differential matrix degradation and turnover in early cartilage lesions of human knee and ankle joints. Arthritis Rheum. 2005;52:112–119.
4.Valderrabano, V, et al. Etiology of Ankle Osteoarthritis. lin Orthop Relat Res. 2009 Jul; 467(7): 1800–1806.
5.Neto, N, et al. Spectrum of MRI features of ganglion and synovial cysts. Insights Imaging. 2016 Apr; 7(2): 179–186.
6.Perdikakis E, et al. MRI characteristics of cysts and “cyst-like” lesions in and around the knee: what the radiologist needs to know. Insights Imaging. 2013 Jun; 4(3): 257–272.
7.Knapik D, et al. Incidence and Fusion of Os Trigonum in a Healthy Pediatric Population Journal of Pediatric Orthopaedics. 39(9):e718–e721, 2019
2020.3.11