Over the years, ankle-foot orthoses and fracture bracing have been used for the orthotic management of below-knee fractures and ankle fractures. Fractures of the talar dome, also referred to as osteochondritis dis-secans, are extremely uncommon, i.e., about 0.9% of all fractures, and have generally been treated without an orthosis.1 A more precise definition of osteochondritis dissecans, also called a transchondral fracture, was given by Berndt and Harty, as "a fracture of the articular surface produced by a force transmitted from the articular surface of a contiguous bone across the joint surface, through the articular cartilag'e and into the subchondral bone trabeculae of the fractured bone."2 The severity of fractures of the transchondral surface is categorized as follows:
Compression of a small area bone
A partial tear
A complete fracture or detachment of bone
A complete detachment and displacement of a fragment of bone3
As with other fractures, the transchondral surface can heal if the fracture is reduced and immobilized. However, it must also be noted that due to the poor vascular supply of the talar surface, early and continued weight- bearing may shear off any ingrowing capillaries or break off any remaining attachment point, therefore changing the condition from a Class I or 11 to a Class III or IV.4 Canale and Belding suggest non-operative treatment for Class I and 11 fractures by placing the extremity in a cast or a fairly standard PTB orthosis.5 However, more severe cases such as Grades III and IV, especially lateral lesions, require surgery followed by 8 to 12 weeks on a short leg non-weight-bearing cast.6
Two patients were presented with Grade IV lateral talar dome fractures where surgery was performed. Due to the patients' job requirements or inability to comply with non-weight-bearing, an orthosis was requested to allow the patients to ambulate without the use of crutches and a cast.
Patient #1, A.M., a 31 year old white female and registered nurse, felt that she would be unable to function adequately at her job and financially unable to remain away from work for eight to 12 weeks.
Patient #2, F.F., is a 27 year old white male. It was felt that his compliance to physician orders with regard to non-weight-bearing was unlikely. A prescription was written for a weight-bearing orthosis, in this case, a PTB weight-bearing orthosis, as he (as in case #1) had already rejected ischial weight-bearing designs.
A search of the literature revealed that at least 70% of the body weight is borne by a PTB orthosis when a fixed ankle joint is used and the heel clearance is increased by approximately one inch. However, weight-bearing drops off to approximately 60% during pushoff.7
Weight-bearing percentage during push-off can be increased by adding a rocker sole to the orthosis.8 It was also noted that at heel strike, weight-bearing probably was not better than 70% for a true PTB orthosis.9 It was felt that a higher weight loading could be achieved in this orthosis by using model modification methods similar to those used for the UCLA total surface bearing below-knee prosthesis by lining the weight-bearing surfaces with firm PE-LITE$reg; , and by adding a patten bottom, i.e., a weight-bearing pad or sole, to the design. The patten bottom shape and the ultimate design of the orthosis in the foot area differed between the two patients based upon: (1) compliance level; (2) acceptance and adaptability to the brace; (3) the patient's weight; and (4) whether the patient had a tendency to plantar flex at mid- stance even though the whole foot may be suspended off the ground.
Both patients were measured and cast as for a standard PTB orthosis. After the casts were modified, a 1/4" PE-LITE$reg; (firm) liner was formed over the positive models. Polypropylene (3/16") posterior and anterior shells were vacuum formed over the liners (except as noted below). Double metal uprights with double action ankle joints were contoured to fit the posterior shell. The pat-ten bottoms were constructed by gluing two pieces of 10 oz. russet leather together with spring steel shanks sandwiched between the two layers. Double action stirrups were contoured and riveted to the leather/steel pads. Crepe was subsequently glued to the leather/ stirrup components. The sides were shaped and sanded to flare slightly in the M/L axis and to form a rocker sole in the A/P axis. The trim lines and patten bottom shape varied slightly between the two patients based on the above mentioned criteria. Patient A.M. was able to relax the foot past mid-stance and did not plantar flex while suspended in the orthosis. The design incorporated a small rectangular, rocker-soled, single steel shank patten bottom (Figure 1) . There was no foot section to the anterior opening PTB weight-bearing orthosis (the plastic shell did not extend distal of about mid-calf). Therefore, the patient was totally suspended with no weight on the talus during any phase of the gait cycle.
Patient F.F., due to possible non-compliance and his inability to plantar flex past mid-stance even when suspended in the orthosis, was provided with a different design. A patten bottom that approximated the sole pattern of a shoe from mid-tarsal to heel was fabricated, and the bottom of the patient's foot was suspended 1 1/2" proximal to the patten bottom. The patten was given a rocker contour and reinforced with two steel shanks rather than one. A foot section was also included in the posterior shell of the
PTB weight-bearing component with some modifications. The foot weight-bearing area was double lined with 1/4" PE-LITE$reg; and 1/ 4" Aliplast and the polypropylene of the posterior shell from just distal of the malleoli to approximately 1/2" proximal to the metatarsal heads was cut out (Figure 2) . Therefore, as the patient's volume changed and the leg tended to drop down into the orthosis, there would still be no weight-bearing on the talar dome. With the double durometer foam on the forefoot and with the foot section weakened by the amount of material removed, the orthosis would also flex in this area, therefore avoiding undue loading of the foot as the patient plantar flexed past mid-stance. A forefoot strap was added to maintain foot contact with the orthosis as the patient ambulated. Sole buildup to the shoes of the non-affected side was required to prevent leg length discrepancies and pelvic obliquity.
Patient A.M. returned to work two weeks post-surgery wearing the described orthosis. She readily adapted to the orthosis, and by changing and adding layers of stockinette material to adjust the fit, she wore the orthosis 14 to 16 hours per day with no ill effects. She continued wearing the orthosis for 10 weeks without the use of crutches. At that time, orthotic use was discontinued and therapy was started to increase range of motion. One year post-surgery and graft, there are no residual problems, the patient has full range of motion, and x-rays of the talar surface are normal.
Patient F.F. had undergone similar surgery previously, but due to suspected noncompliance regarding non-weight-bearing, a closer follow-up was required. Due to the patient's obesity and dramatic initial volume changes (two weeks post-surgery), the orthotic shell was refit by adding padding in weight-bearing areas. The patient was told about volume changes and how to adjust fit with layers of socks. He wore the orthosis for 18 weeks and was compliant with regard to wearing the brace, as evidenced by the pat-ten bottom, which required resoling due to wear generated by 12 to 15 hours use per day. X-ray examination at the end of the wearing period indicated healing of the talar surface, albeit slow. The patient again did not require use of crutches while wearing the orthosis.
Osteochondritis dissecans of the talar dome, though an infrequent condition, does appear to be manageable post-surgically with a modified PTB orthosis with patten bottom. Proper prosthetic measuring, casting, and fitting techniques must be followed to ensure as much total surface bearing as possible in the proximal third of the AFO and pre-tibial shell. The patient must be compliant in terms of monitoring the condition of the skin and maintaining hygienic conditions inside the orthosis and must be able to understand the requirement to adjust layers of socks and stockinette for proper fit. Follow-up should be monitored closely for the first two weeks and twice a month after this initial break-in period.
George Madden, C.P.O.(A), CP(C), M.A., is Director, Prosthetic/Orthotic Department, Alberta Childrens Hospital, Calgary, Alberta.