ORIGNAL ARTICLE

COMMUNICATIONS PRESENTED AT ISCHIA (Dec. 90)

RADIOLOGIC CLASSIFICATION OF AVASCULAR NECROSIS OF THE FEMORAL HEAD IN RELATION TO NATURAL HISTORY

Ohzono K, Saito M and Takaoka K

Department of Orthopaedic Surgery, Osaka University Medical School

Ohzono K, Saito M, Takaoka K: Radiologic Classification of Avascular Necrosis of The Femoral Head in Relation to Natural History. Arco News Letter, 3:n°2, 105-107, 1991.

Understanding the natural history of avascular necrosis of the femoral head (ANFH) is quite important for predicting fate of ANFH, choosing therapeutic procedure and evaluating results of various therapies in patients with this disease. However few researches has conducted a comprehensive study dealing with the subject. We surveyed the natural history of ANFH in relation to the new radiological classification.

MATERIALS

Of the patients with ANFH who were treated at our Hip Clinic since 1964, those who had been under close observation without surgical treatment more than two years were selected for this study. When massive collapse of the femoral head or destruction of the hip joint occurred within two years of follow-up, this case was also included in this study. The total number of the patients was 87 (115 hip joints), 54 males and 33 females. Patient’s age at entry to the study ranged from 18 to 70 years (mean : 40.8 years). There were 49 cases of steroid-induced ANFH, 21 of ANFH associated with alcoholic abuse and 17 of idiopathic nature. The period from the onset of symptoms to initial diagnosis at our hospital ranged from 1 month to 8 years (mean : 8 months).

METHODS

The affected femoral head was classified into four stages, from the preradiological stage (stage I) to that of osteoarthritic change (stage IV) according to Ficat (1980). Based on localization and extent of the necrotic lesion in the femoral head and a flatness of the weight bearing surface, the affected femoral heads were classified into six types; 1-A, 1-B, 1-C, 2, 3-A and 3-B (Fig. 1). Type 1 necrotic lesions were further divided into three subtypes according to its territory occupying the weight bearing division of the femoral head. Type 2 was characterized with early manifestation of the surface flatness and lack of demarcation line surrounding the necrotic lesion. Type 3 cystic lesions were also divided into two subtypes, whether located in the weight-bearing area (type3-B) or not (type 3-A). For each subject, disease progress was checked by a periodic radiologic examination at least six months interval. The average duration of follow-up was 5 years and 3 months (maximum : 18 years).

RESULTS

Of the 115 hip joints, 5 were classified as type 1-A, 16 as type 1-B, 68 as type 1-C, 4 as type 2, 17 as type 3-A and 5 as type 3-B. There was no significant difference in the incidence of type 1-C and type 2 between steroid-induced ANFH and that not associated with steroid. The incidence of type 1-A, 1-B, 3-A and 3-B was much higher in patients with steroid-induced ANFH, because they tended to be under close medical observation for their underlying disease.

Twenty-two joints of type 1-A or 3-A had so-called minimal necrotic lesions. All of these joints were at stage II at the entry to follow-up study. At the final examination, 20 hip joints (91% of these hip joints) were still at stage II, and only 2 joints (9%) had collapsed and advanced to stage III. Even in these 2 joints, severity and extent of collapse were minimum and no further collapse progressed thereafter.

All the 16 hip joints of type 1-B were at stage II at the entry to follow-up study. At the final examination, 13 hip joints (81%) were still at stage II, while 3 hip joints (19%) presented with collapse of the femoral head and one had advanced to stage IV.

Type 1-C was seen most frequently. Of the 68 hip joints of type 1-C, 32 were at stage II and 36 at stage Ill at the entry to follow-up study. Of the 32 type 1-C hip joints which were at stage II at the initial examination, 28 hip joints (88%) advanced to stage III during follow-up. Total incidence of collapse in type 1-C femoral heads, including 32 hips of stage II and 36 hips of stage III at the entry to the follow-up study, reached 94%. In the cases which developed collapse of the femoral head during follow-up, the interval from the entry to follow-up to collapse of the femoral head was usually less than 3 years. Within six years after the entry to follow-up, 69% of this group developed osteoarthritic change and advanced to stage IV.

Only 4 hip joints were classified into type 2. In these cases, the demarcation line surrounding the necrotic lesion was poorly demonstrated, although bone scan and other findings led to diagnosis of ANFH. Three months to one year after the start of follow-up, the weight-bearing surface of the femoral head developed flattening and collapse was noted, followed by massive collapse and destruction of the joint. All 5 hip joints classified as type 3-B developed femoral head collapse in 3 to 16 months (mean : 11 months) after the entry to follow-up study.

The relationship between each disease type and incidence of collapse of the femoral head was summarized in table 1.

Table I

DISCUSSION

If the roentgenographic characteristics of ANFH teach us a potential hazard to joint destruction, this enables us to set up more effective measures to prevent the disaster. Bearing this in mind, the criteria for typing of ANFH was firstly proposed by the Japanes Investigation Committee (Ono 1987) and then the authors conducted this study, which disclosed a close relationship between types of ANFH and progress of this disease. While transient pain remission is often seen even at stage III ANFH, once the femoral head has collapsed, osteoarthric change is likely to occur eventually, accompanied by worsening of pain. The type of ANFH as depicted in this study will be highly appreciated for decision making regarding choice of treatment of the disease and evaluating the treatment results.

ARCO news, 1991, 3 :2