Classifications of necrosis of the humeral head 14

14.1 Classification of osteonecrosis of bone according to Cruess [25]

Since the diagnosis of osteonecrosis is made on radiologic and clinical grounds, it must be emphasized that the insult that leads to either radiographic changes or symptoms must have occurred at least months earlier. There have been various attempts at staging the development of the lesion to aid in understanding the process and to apply appropriate therapy. The most widely recognized system of staging is that of Marcus et al. [83], but it has as a defect the fact that there is no prediagnostic stage. For this reason, a modification of the staging system first pro- posed by Arlet and Ficat [4] appears to be the most worthwhile. The modification is proposed because there are therapeutic implications to Stage 5, the phase at which acetabular changes are visible (Fig. 61).

Classifications of necrosis of the humeral head 14

Fig. 61. Classification of osteo- necrosis of bone modified for the humeral head according to Nov-Josseand and Basso [105a] based on Cruess [25]

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Stage 1: this is the preradiologic stage and is characterized by a total absence of radiologic features. Some patients will complain of a stiff, painful hip and there is occasionally even limitation of motion. Scin- timetry may show either absence of uptake in areas of the femoral head or (and this is much more likely) increased uptake in the femo- ral head as a whole. Such an increase indicates that the area of osteo- necrosis has already provoked a reparative response.

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Stage 2: this stage is characterized by radiologic evidence of repair in the presence of a femoral head with a well-preserved shape. A variety of radiologic changes are reported. Ficat and Arlet describe three forms (A) diffuse osteoporosis, (B) a sclerotic form, and (C) a mixed osteoporotic/sclerotic form. A fourth form may be recognized as a localized subchondral osteolytic lesion. It is reasonable to as- sume that the sclerotic changes represent a later stage in the develop- ment-beyond that of either osteolysis or osteoporosis ±during which time the body has laid down appositional new bone as part of the re- pair process. However, with a preserved femoral head shape, this form is still classed in Stage 2.

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Stage 3: this stage is characterized by the classical radiographic fea- ture of osteonecrosis, the so called ªcrescent signº. The stage repre- sents collapse of the subchondral bone with the area of collapse be- ginning characteristically in the anterolateral area of the femoral head, best seen on a lateral view or on tomograms. Changes vary from slight flattening to extensive collapse. This is a frequent obser- vation in symptomatic patients. The relationship of the radiologic changes, symptom change, and clinical pathology would all favour the development of a subchondral fracture.

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Stage 4: there is extensive collapse of subchondral bone and severe deformity of the head due to flattening superiorly. This stage corre- lated with the operative findings of a separated, sometimes free, os- teocartilagenous flap lying on depressed subchondral bone. Ob- viously, not all lesions may reach Stage 4.

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Stage 5: the difference between Stages 4 and 5 rests in the appearance of the acetabulum. This is normal in Stage 4, but shows pathologic changes in Stage 5. The reason for adding this stage relates to the ra- tionale for therapy. As long as acetabular cartilage remains relatively normal, hemiarthroplasty is a reasonable therapeutic choice.

166 14 Classifications of necrosis of the humeral head

14.2 Classification of avascular necrosis

of the humeral head according to Neer [102]

The pathologic changes that occur in the humeral head are similar to those occurring in the femoral head as described by Ficat and Arlet [147] and Springfield and Enneking [148] but with some differences.

The differences are best explained by describing the point of maximum joint reaction force and the anatomical contour of the glenoid compared to that of the acetabulum. The glenoid is flat, and the point of maxi- mum pressure on the head seems to occur when the arm has been raised about 908. At this point the scapula has rotated 308, so that the area of the head that is placed under maximum pressure is that contact- ing the glenoid when the humerus has been elevated 608. This area of contact is the site where the humeral head consistently collapses in avascular necrosis and where maximum wear and sclerosis occur in os- teoarthritis.

Avascular changes with collapse of the articular surfaces in the el- bows of two paraplegic patients, as mentioned above, confirm the im- portance of pressure and load in the configuration of avascular necrosis of the humeral head. In their discussions of the aetiology of avascular necrosis, both Cruess [149] and Springfield and Enneking [148] pointed out that the alterations in the femoral head did not match the anatomi- cal configuration of the blood vessels in the femoral head nor the ran- dom site of infarction that might occur if the infarcts were due to ªslud- gingº. Since the location of the crescent sign and the later collapse at the head correspond to the point of maximum joint reaction force on the humeral head, Neer [102] believes the consistent location of the wedge-shaped area of infarction is largely due to pressure.

To assist in describing the indications and treatment of this condi- tion, Neer has adapted the excellent classifications of Ficat and Ennek- ing to the shoulder. As illustrated in Fig. 62.

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Stage I. Stage I disease shows only subtle changes that are not always

definitely diagnostic. Recent developments with magnetic resonance

imaging (MRI) are helpful. The head retains its normal shape. There

may be slight mottling of the trabecular pattern or an area of sub-

chondral decalcification. There may be no pain, but some patients do

have pain. Patients with infarctional diseases (Gaucher's disease and

sickle cell disease) have more very early pain. Unfortunately, at this time there is no infallible way to document the diagnosis.

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Stage II. Stage II disease has an articular surface that is grossly round when inspected at surgery, and although the articular cartilage can be intended on pressure in an area where it has lost the support of the subchondral bone, it returns to its normal shape. This is the area where a ªmeniscus signº can be seen. Tomograms and MRI are especially helpful in evaluating the extent of head involvement. Pain is usually present and may be severe. The severe pain probably corre- sponds to minute fractures and the sudden slight collapse of sub- chondral bone.

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Stage III. Stage III disease is characterized by an area of wrinkled and loose articular cartilage. This corresponds to the wedge-shaped area of fracturing and collapse of subchondral bone. Eventually the edge of this detached cartilage may become torn, forming a flap.

With each episode of collapse of the subchondral bone, the pain is intensified. Eventually the X-ray film shows a ªstep-offº phenome- non, and the diagnosis is quite obvious. The articular surface of the glenoid remains intact.

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Stage IV. Stage IV disease shows involvement of the articular surface of the glenoid due to the incongruity of the humeral head. As sec- ondary arthritic changes occur, a ring of marginal excrescences de- velops around the head, particularly inferiorly, and the articular sur- face of the glenoid becomes warn unevenly, as in osteoarthritis. Be- cause of the way the arms are used in everyday activities, the in con- gruous head presses more intensely on the posterior part of the gle-

Fig. 62. Classification of avascular necrosis of the humeral head according to Neer [102]

noid, leading to uneven wear and eventually to a posterior subluxa- tion. With the posterior subluxation, the posterior glenoid becomes rounded off and sclerotic, and an indentation develops in the head because of contact against the posterior edge of the glenoid. By this time, osteochondral bodies and a general synovitis of the joint are present.

14.3 Classification of the extend

of osteonecrosis of the humeral head according to Hattrup and Cofield [56]

The authors assessed the extent of osteonecrosis of the humeral head ra- diologically. The extent of involvement was classified from the maxi- mum involvement shown on any single view. Four groups were defined:

those with less than one quarter of the humeral head involved, those

with involvement between one quarter and one half of the diameter of

the humeral head, those with involvement between one half and three

quarters of the humeral head, and those with more than three quarters

of the diameters of the humeral head involved.