In Stage I, hips with little or no pain (40–44 points) showed mean radiographic progression of the necrotic lesion by 7.6 points on a scale of 21, whereas hips with mild to severe pain (0–39 points) progressed 6.6 points. In Stage II, patients with hips with little or no pain progressed 9.2 points and those with mild to severe pain progressed 11.0 points.
In Stages I and II, hips which did not require THR had a mean gain of 24 points in their Harris hip score between the preoperative and final postoperative evaluations, whereas hips that required THR lost a mean of 31 points. Hips which initially had little or no pain lost a mean of 22 points, whereas hips that initially had mild to severe pain gained a mean of 6 points. This implies that patients with relatively asymptomatic hips actually had a worse clinical outcome than patients with painful hips, however this observation can be misleading. Because the Harris hip score is weighted heavily toward pain (44 of 100 points),5 patients with asymptomatic hips with a high initial score could gain few if any points if they did well clinically, yet could lose a significant number of points if the necrosis progressed. Conversely, patients with painful hips with a low initial score could lose few points if they had additional deterioration, yet could increase their pain score considerably if they had clinical improvement. Therefore the change in the Harris hip score is not a valid method to compare improvement or deterioration specifically between painful hips and hips which were asymptomatic or minimally symptomatic.
It generally is accepted that most hips clinically diagnosed with ON will progress to collapse if untreated.1,2,11,13,17–19 Although there are differing opinions as to which surgical procedure is best, many agree that some form of early surgical intervention before femoral head collapse generally will yield better results than symptomatic treatment.2,11,15–19 Many surgeons, however, are reluctant to surgically treat hips which are asymptomatic or have minimal symptoms.4,18,19 This is based in part on the assumption that the prognosis for these patients, without treatment, is better than for patients with hip pain. However, this has not been documented. Sporadic reports have appeared in the literature, but most are retrospective studies involving small numbers of patients and their conclusions differ substantially.3,4,6,8–10,20,21
Our study was done to determine the relationship between pain and outcome in hips with ON. It was prospective and included 328 hips, 201 of which were Stages I or II, which were evaluated clinically and radiographically. All hips had core decompression and grafting done by one surgeon, following a standard regimen. It did not include hips which had primary THRs, nor did we include untreated hips in this study because of the documented history of progression without treatment. Such cases have been described in the literature cited. The overall outcome for hips treated by core decompression, with or without supplemental bone grafting, has been shown to be better than for hips treated nonoperatively at our institution15,17 and by other investigators.1,2,11,13,18,19
The literature reflects differing opinions regarding the relationship between pain and outcome in patients with ON. In 1980 Lee et al10 reported on 11 untreated, asymptomatic hips with ON. All eventually showed radiographic progression. In 1993 Bradway and Morrey3 described 15 asymptomatic and radiographically normal hips in patients with contralateral ON. They found that all of these hips eventually collapsed at a mean of 23 months. However, they did not discuss their criteria for excluding numerous patients from this study. Takatori et al21 evaluated 32 radiographically normal, asymptomatic hips in 25 patients treated nonoperatively. The diagnosis of ON was made using MRI. They found no evidence of femoral head collapse in 15 cases with small lesions. However, 14 of 17 hips (82%) with moderate to large lesions collapsed in a mean of 15 months. Therefore they found a clear correlation between outcome and lesion size but no correlation with pain. Koo et al8 observed 15 patients with asymptomatic ON, treated nonoperatively. Eleven (73%) had femoral head collapse. Jergesen and Khan6 reported that of 75 patients with nontraumatic ON 46 (61%) initially had pain in only one hip. Twenty-two of the asymptomatic hips had radiographic evidence of ON. Three of these had core decompressions, whereas 19 were untreated. Fourteen of these 19 untreated hips (74%) eventually became painful. Davidson et al4 observed 133 patients with known, symptomatic ON in one hip in which the opposite hip was asymptomatic. Of 77 asymptomatic hips with no radiographic or MRI evidence of ON, only six (7.8%) later had ON develop. Fifty-six asymptomatic hips did have ON diagnosed initially by plain radiographs or MRI. Forty one (73%) of these progressed and became symptomatic at an average of 24 months from the initial observation: two of seven (29%) with Stage I lesions, 34 of 43 (79%) with Stage II lesions, and five of six (83%) with Stage III lesions. Davidson et al4 concluded that more than 79% of patients who present with asymptomatic Stages II and III ON will progress to symptomatic disease and might be candidates for early surgical intervention, although this was not their standard practice at the time.
Not all authors share these opinions. Kopecky et al9 identified 25 hips with asymptomatic ON, diagnosed by MRI, in 104 renal transplant recipients. Pain and radiographic changes developed in seven hips (28%) and one hip became symptomatic despite a normal radiograph. In seven hips the MRI showed a decrease in lesion size and in six of these the appearance of the hips on MRI scans eventually became normal. Sugioka et al20 observed that in some conservatively treated hips with asymptomatic ON, they were unable to detect progression, and that occasionally in hips with small lesions the necrotic area decreased. Specific numbers were not cited in their study. Mulliken et al12 diagnosed ON in 15 hips (10 patients) of 132 renal transplant recipients evaluated by MRI. Eleven hips were preradiographic and asymptomatic. Only one of these eventually progressed. Four hips were symptomatic and radiographically positive for ON, and an additional seven patients with previously diagnosed ON were excluded from the study.
Therefore in five of the studies which specifically evaluated asymptomatic hips with osteonecrosis,3,4,6,8,10 73–100% progressed without treatment. Takatori et al21 found, as did we, that small lesions had a better prognosis than moderate to large lesions. No collapse was seen in 15 hips with small lesions, whereas 14 of 17 with moderate to large lesions (82%) collapsed. In three studies9,12,20 progression was noted in only 9–28% of hips.
These findings compare closely with the work of previous investigators who have reported overall progression in 70–80% of untreated hips with clinically established ON, many of which were painful.1,2,11,13,17–19 This stands in contrast to the 37% prevalence of THRs for hips treated surgically in the current study and by other investigators.2,11,15,17–19 Although the overall prevalence of progression without specific treatment is higher than after surgical treatment, in neither group was there evidence that asymptomatic or minimally symptomatic hips had a better prognosis than hips with pain, if lesion size and stage were considered.
In the current study we found that hips with femoral head collapse were more painful and had a worse prognosis than hips without collapse. Before collapse, outcome was correlated with lesion size, thereby confirming previous observations.7,14,16,17,19 No correlation was found between lesion size and pain, nor was there a correlation between pain and outcome as determined by radiographic progression and the need for THR. Despite the beneficial effects of core decompression, numerous relatively asymptomatic hips deteriorated.
Our observations, although limited to hips which had core decompression and grafting, support previous reports which found that pain did not predict the outcome of untreated hips with ON, seen before femoral head collapse. These conclusions also might be applicable to hips which have forms of prophylactic treatment other than core decompression. Asymptomatic or minimally symptomatic hips do not have a better prognosis than hips with significant pain if stage and lesion size are accounted for. Although many factors must be considered in determining the optimum treatment of patients with ON, early prophylactic surgery should not be withheld solely because of the absence or paucity of pain.
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© 2004 Lippincott Williams & Wilkins, Inc.
21. Takatori Y, Kokubo T, Ninomiya S, et al. Avascular necrosis of the femoral head: Natural history and magnetic resonance imaging. J Bone Joint Surg