CLINICAL IMAGING 1993;17:137-141 137

OSSICLES ANTERIOR TO THE PROXIMAL TIBIA

RONALD A. BLOOM, JOHN GOMORI, AND CHARLES MILGROM

Ossicles anterior to the anterior tibia are most usually seen in relation to the tibia1 tuberosity. While these are usually taken to represent sequelae of previous Osgood-Schlatter disease, they may, on occasion, rep- resent normal variants in ossification ofthe tuberosity. Ossicles superior to the tuberosity may have similar origins. Representative examples are presented, as is a very large ossicle separated from the anterior tibia by a prolongation of the knee joint space. Theories of causation of such ossicles are discussed.

KEY WORDS: Bones; Tibia; Bone anomaly; Trauma; M.R.I.

INTRODUCTION

Ossicles anterior to the proximal tibia are uncommon. They are most often related to the tibia1 tuberosity and may be single or multiple. While in many instances a previous history of Osgood-Schlatter disease can be obtained, such ossicles may be an incidental finding. These latter small bones may be normal variants in ap- pearance of the tuberosity, but some believe that they are sequelae of previous trauma occurring before os- sification of the apophysis (l-4). Ossicles found supe- rior to the tuberosity have been described as a normal variant or as a posttraumatic sequel of Osgood-Schlatter disease (4, 5).

In the present report, a discussion of the appear- ances and theories of causation of these ossicles is presented. In addition, we present a full description

Frum the Departments of Radiology (R.A.B., J.G.) and Orthopaedic Surgery (CM.), Hadassah University Hospital, Jerusalem, Israel.

Address reprint requests to: Dr. R.A. Bloom, Department of Radi- ology, Hadassah University Hospital, Ein Kerem, Jerusalem, Israel.

Received April 1992; accepted August 1992. 0 1993 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0899-7071/93/$6.00

of a very large ossicle seen anterior to the proximal tibia and separated from it by a prolongation of the knee joint space. We can find no previous description of such a bone in the literature.

CASE REPORTS

Case 1 A young man was referred with acute knee pain after a work accident. No previous history of Osgood- Schlatter disease or knee trauma was obtained. A plain radiograph of the knee demonstrated a small ossicle anterior to the tibia1 tuberosity (Figure 1). No tender- ness in this region was found.

Case 2

A 1%year-old man was referred for magnetic resonance imaging (MRI) with the suspicion of a torn medial meniscus of the right knee. On plain radiographs two ossicles were seen anterior to the proximal tibia. The larger measured 2 cm in diameter and was situated su- perior to the tibia1 tuberosity. A smaller ossicle.;was seen anterior to the tuberosity (Figure 2). On MFU, the larger ossicle was seen to be situated in the deep por- tion of the distal patella tendon, indenting the joint capsule (Figure 3).

Case 3

A X&year-old man presented to Hadassah University Hospital with a history of minor knee trauma a month previously and subsequent pain over the lateral side of the knee joint. On physical examination the find- ings were suggestive of a tear of the lateral meniscus. No previous history of trauma to the knee or operative procedure was obtained and no scar in relation to the knee was seen. Radiographs of the knee demonstrated a large bone, somewhat resembling the patella, in the

138 BLOOM ET AL. CLINICAL WAGING VOL. 17, NO. 2

FIGURE 1. Corticated unfused portion oft (arrow) (case 1).

.ibial apophysis FIGURE 3. h4Rl showing the large ossicle situated within the patella tendon, and indenting the knee joint space.

FIGURE 2. Lateral view of knee 1 sicle anterior to the tibia1 tuberosi perior to the tuberosity (case 2).

demonstrating a small OS- ty, and a large ossicle su-

FIGURE 4. Lateral radiograph of the knee demonstrating the large bone situated at the antero-superior aspect of the tibia (case 3).

position of the tibia1 tubercle (Figure 4). MRl demon- strated the bone to be separated from the tibia by fluid. There was an attachment of the bone to the tibia by a ligament with the same characteristics as the patella ligament (Figure 5). Knee artbrography was performed. No evidence of a meniscal tear was seen. The extra bone was separated from the tibia by a projection of the knee

APRIL-JUNE 1993 ANTERIOR TIBIAL OSSICLES 139

FIGURE 5. Sagittal MRI of the knee obtained with a some- what m-weighted partial flip-angle gradient echo image. TR = 240 msec, TE = 19 msec, flip angle = 15. The menisci appear dark, while the chondroid cartilage and joint fluid appear white. The tibia1 patella is surrounded posteriorly and antero-superiorly with joint fluid. It is connected by the patellar ligament to the patella superiorly and to the tibia inferiorly.

joint space. A lucent stripe between the bone and the joint space was interpreted to be articular cartilage (Fig- ure 6). The bone moved in relation to the tibia but to a lesser degree than the patella in relation to the fe- mur. This extra bone was not tender, and the patient admitted to no previous knee symptoms.

DISCUSSION

The tibia1 tuberosity arises from an apophysis which begins to ossify at the ages of 8 to 10 years, the process beginning earlier in girls than in boys. In the first stage, a small tongue of ossification projects inferiorly from the antero-inferior edge of the proximal tibia1 epiphy- sis. Between the ages of 10 to 12 years the tongue of ossification extends distally and the beak so formed varies very considerably in appearance. One or more separate centers of ossification in the distal portion of the apophysis may arise. Between the ages of 12 to 14 years the centers of ossification fuse and the proximal tibia1 epiphysis and the tibia1 apophysis become con- tinuous. Between the ages of 14 to 16 years the line of separation between the combined epiphysis and apophysis, and the diaphysis, is slowly obliterated and they fuse into a solid whole (2).

Occasionally, a separate, ununited ossification cen- ter for the tibia1 tubercle may be seen. This center may

FIGURE 6. Lateral view of arthrogram. Air and contrast (closed arrowhead) are seen between the tibia1 patella and the tibia.

be well corticated around the whole of its circumfer- ence (Figure 1) or the inferior margin may appear un- corticated (l-3). This unfused ossicle is often taken to indicate a sequel of Osgood-Schlatter disease or other trauma (2, 3). It is nevertheless a fact that such ossi- cles are seen incidentally with no previous history of pain or trauma at this site. These ossicles may well be normal variations in appearance of the tuberosity and not necessarily indicative of previous Osgood-Schlatter disease which is primarily a clinical diagnosis. It is generally believed to represent traumatic avulsion of the ossification center of the tubercle and is charac- terised by pain and tenderness to palpation over the tubercle. Radiographically, one may see obliteration of the soft tissue planes around the patella tendon resulting from edema and fragmentation of the ossifi- cation center of the apophysis.

The condition has been ascribed in the past to avas- cular necrosis of the apophysis (2). This view has been rendered unlikely by the studies of Ehrenborg and Lagergren (6) and Ogden and Southwick (7), which have shown an excellent blood supply to the tuberosity and consider that the appro’priate preconditions do not seem to exist in this particular cartilaginous epiphy- sis to allow an avascular basis for Osgood-Schlatter disease.

The late manifestations of Osgood-Schlatter disease

140 BLOOM ET AL. CLINICAL IMAGING VOL. 17, NO. 2

have been described (4). Small, irregular bony frag- ments are seen representing corticated remnants of the avulsed apophysis. The ossicles seen in subjects with no previous history of Osgood-Schlatter disease are, in our experience, invariably smooth and either rounded or ovoid, as in our case 1 (Figure l), and we have seen numerous such ossicles that have always been asymptomatic. A study by Woolfrey and Chan- dler (4) tends to confirm this impression. In their popu- lation, 26 of 290 patients with painful knees had changes in the tibia1 tuberosity. A parallel study of 470 patients referred for radiographs of regions other than the knee was made. Each of these patients had postero- anterior and lateral radiographs of both knees. Eleven of these patients had changes in the tibia1 tuberosities that corresponded to those found in the patients with painful knees. None of these patients had symptoms referable to the tuberosity in question.

Ossicles superior to the tuberosity, but still anterior to the proximal tibia arerarer than those in direct rela- tionship to the tuberosity, and such ossicles are poorly recognized in the literature.“Keats illustrates two ex- amples of small ossicles in this position, which he describes asossicles or sesamoid bones in the patellar tendon and regards as normal variants (1). Woolfrey and Chandler consider such ossicles to be posttraumatic in origin. However, they report five cases where they removed small ossicles imbedded in the posterior as- pect of the patella tendon anterior and superior to the tibia1 tuberosity. In each case the tuberosity itself ap- ‘peared normal with the patellar tendon inserted in its normal position on the tuberosity. Histological exami- nation of the removed ossicles revealed viable cancel- lous bone surrounded by cartilage, with no evidence of necrosis or inflammation (4).

Mital et al. (5) removed 15 ossicles at the proximal aspect of the tubercle. All ossicles were attached to the distal part of the undersurface of the ligament patellae and were separated from the tubercle by a bursa or scar tissue. They considered these ossicles to be posttrau- matic and termed the condition “the so-called un- resolved Osgood Schlatter’s lesion.” No report of ossi- cles superior to the tubercle was made, and all illustrated ossicles appeared small. Bilateral fractures through giant patellar tendon ossicles have been reported, the ossicles being ascribed to previous Osgood-Schlatter disease (8). From the illustration, they appear to be approximately the same size as the larger ossicle in our case 2. The giant ossicle in our case is seen superior to the tuberosity (Figure 2), and on the MRI study is demonstrated to be applied to, or situated within the posterior aspect of the patella ten- don, indenting the joint capsule [Figure 31. No previ-

ous history of Osgood-Schlatter disease or other knee lesion was obtained.

In our case 3 the remarkable size of the anterior tibia1 bone appears to be unique (Figure 4). Arthrography demonstrated this bone to be separated from the tibia by a prolongation of the knee joint articular space (Fig- ure 6)) and in the MRI study a tendon united the lower pole of this bone to the tibia (Figure 5). The origin of this large bone is obscure, and no traumatic history was obtained. The appearance of the bone is not dis- similar to the patella, being of approximately the same size, and being separated from the tibia by a prolonga- tion of the knee joint. We have been tempted to call this bone a tibia1 patella, but as the other knee appeared radiographically normal, and no similar bone has been described in the literature, it is highly unlikely to be of developmental origin.

In spite of the lack of a history of trauma, it appears most likely that the origin of this bone was, in fact, trau- matic. The trauma could have been perinatal or in early childhood, and thus not recalled by the patient. The fracture type would be presumably a Watson-Jones Type 3 fracture of the tibia1 tubercle, which is analo- gous to a Salter-Harris Type 3 epiphyseal plate injury. In the case of the tibia1 tubercle, the fracture line passes upwards and backwards into the joint with resultant displacement of the proximal base of the distal tibia1 epiphysis. A review by Henard and Bobo of avulsion fractures of the tibia1 tubercle prior to epiphyseal clo- sure revealed only 76 such injuries reported in the liter- ature between 1935-1982 (9). These occurred between the ages of 11 to 17 years, overwhelmingly in boys. Type 3 fractures were most often seen in older adolescents from 15 to 17 years of age, while the less severe Type 1 and 2 fractures were mostly seen between 12 to 14 years of age (9).

All the fractures were treated by open reduction and internal fixation, or by closed reduction and plaster immobilization. No case of nonunion was reported. In our case, no skin scar was seen, and it is, in any case, inconceivable that the patient had experienced such a severe injury in adolescence and had forgotten it.

No such fracture has been reported in infancy, but it is not impossible that lack of immobilization lead- ing to nonunion could occur. As the fracture line in- volves the joint space, a prolongation of the knee joint synovial space between the fragments could follow. The shallow defect seen in the adjacent tibia in Figure 4 tends to confirm this presumption. While a nontrau- matic developmental split of the tibia cannot be ex- cluded, it seems a less likely option.

In summary, small and large ossicles anterior to the upper tibia can be found. While many are a sequel of

APRIL-JUNE 1993 ANTERIOR TIBIAL OSSICLES 141

trauma, usually of the Osgood-Schlatter type, in many cases no previous symptomatology can be elicitated. A developmental origin to many of these latter cases can be assumed.

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