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© 1996 The Journal of Bone and Joint Surgery, Inc. Bilateral Primary Cystic Arthrosis of the Acetabulum. A Case Report*  , BALTIMORE, MARYLANDInvestigation performed at the University of Maryland, Baltimore
There is considerable controversy about whether cystic arthrosis is a primary or secondary phenomenon in the development of degenerative joint disease of the hip1,2,4,5,8,10,13,15,18. Proponents of the bone-contusion theory have suggested that a localized area of subchondral necrosis of bone resulting from repetitive microtrauma leads to cystic degeneration, leaving the articular cartilage intact1,2,4,8,13,18. Proponents of the synovial intrusion theory believe that traumatic defects in the articular cartilage allow intrusion of synovial fluid through subchondral microfractures, resulting in cystic degeneration5,10,15. Both groups of proponents agree that, in the later stages of degenerative osteoarthrosis of the hip, subchondral fractures, cystic collapse of the acetabulum, and diffuse degenerative changes predominate on both sides of the joint. Both groups also agree that it should be possible to slow the progression of the disease by timely and appropriate operative intervention. Often, by the time patients who have pain in the hip secondary to degenerative joint disease are seen, there are characteristic roentgenographic changes, such as decreased joint space, increased subchondral sclerosis, subchondral cysts, and osteophytosis; thus, it is impossible to determine whether the cystic changes were the precursor of the late changes. This report illustrates the evolution of degenerative joint disease of the hip. The sequence of changes supports the theory that cystic arthrosis is a primary phenomenon that may precede and hasten the onset of osteoarthrosis in some patients.
A thirty-three-year-old man was involved in a motor-vehicle accident in July 1988; his automobile was struck from behind by a vehicle traveling at approximately sixty-four kilometers (forty miles) per hour. The patient had pain in the lumbosacral region and left hip, although there were no osseous injuries. Before the accident, he had had no symptoms related to the hip but he had a history of recurrent ganglia in the right wrist. The initial roentgenograms showed a two-centimeter supra-acetabular cyst on the left side. The right acetabulum appeared normal (Fig. 1).
Over the following three years, the pain in the left hip worsened with the activities of daily living. The patient also noted the insidious onset of pain in the right hip, although the pain in the back resolved fully. He continued to work as a carpenter but became increasingly uncomfortable when climbing a ladder or when working on an uneven surface (such as a roof). In August 1991, roentgenograms revealed slight enlargement of the left supra-acetabular cyst and numerous smaller cysts that had developed in the left and right supra-acetabular regions. There was no narrowing of the joint space and no alteration in the structure or density of either femoral head. Computerized tomography and magnetic resonance images showed no evidence of subchondral disruption, synovial hypertrophy, capsular thickening, or a soft-tissue mass. The magnetic resonance images confirmed the cystic nature of the acetabular radiolucent areas and revealed incomplete septation and fluid in the spaces (Fig. 2).
The patient had to stop working because of the constant pain and stiffness in the left hip. Roentgenograms showed progression of the cystic changes, and in November 1991 an open transiliac biopsy of the supra-acetabular region was done on the left side to rule out a neoplasm. The largest cyst was filled with serous fluid that was not viscous and with sparse tan hemorrhagic tissue. There was no evidence of a well defined cyst wall or communication with the joint space. Histopathological evaluation of the contents of the cyst revealed benign fibroproliferative tissue and chronic inflammatory cells. Bacterial and fungal cultures showed no growth. The patient was discharged to his home on the third postoperative day with instructions for partial weight-bearing on the left lower extremity for six weeks and a home program of physical therapy to maintain the range of motion of the hip and the strength of the abductor muscles. Roentgenograms made in January 1992 showed further enlargement of the cysts in both hips (Fig. 3) and, for the first time, narrowing of the joint space and early marginal osteophytes were seen in the left hip. The patient continued to have severe pain in the left hip that prevented him from returning to work. Multiple trials of non-steroidal anti-inflammatory drugs had failed. He was offered the options of either an arthrodesis or a total arthroplasty of the hip and, after lengthy discussions of the changes in lifestyle as well as the advantages and disadvantages involved with each procedure, he chose the latter. He was fully aware of the restrictions after hip replacement, as well as the possibility of revision, but his primary goal was to return to full employment with less pain. He adamantly refused arthrodesis of the hip.
On January 23, 1992, a left total hip arthroplasty was done with the use of a porous-coated component and no cement. At the time of the operation, several one to two-millimeter defects were seen in the weight-bearing articular surface of the acetabulum. Each defect appeared to be filled with mucoid tissue. The defects were explored and each was found to communicate with a large loculated cystic cavity in the ilium. A small amount of mucoid tissue within the large cavity was easily evacuated. The findings on pathological evaluation of the contents were consistent with the previous results. The large cystic cavity was curetted through the smaller defects. The rest of the subchondral bone was left undisturbed, as was the surrounding cartilage. The acetabulum then was reamed, and there was no evidence of unroofing of the cysts; good bleeding bone was present. The cysts were packed with an autogenous graft from the femoral head and the cup was press-fit. Three screws were placed to secure the cup further. The rest of the procedure was that of a standard hip replacement. Although there were few symptoms associated with the right hip, the cysts were increasing in size. The patient chose to have a concurrent transiliac ablation of the cysts with bone-grafting, with the hope of altering the course of what appeared to be a process similar to that in the left hip. The cysts contained a small amount of gelatinous straw-colored fluid with tan soft tissue that was centrally located within the cavity. No lining of the cyst wall was evident, and there was no obvious communication with the joint. Iodinated contrast material was injected into the cavity, and intraoperative roentgenograms showed no intra-articular communication. The cyst cavity was curetted and was filled with fresh-frozen irradiated cancellous allograft. Histopathological analysis revealed fibrocartilaginous and osseous tissue with foci of necrosis and mild chronic inflammation. There was no growth on bacterial and fungal cultures of material obtained at the time of the operation. The postoperative course was uncomplicated, and the patient returned home on the ninth postoperative day. On the first postoperative day, he was allowed to sit in a chair and an exercise program was started to regain motion of the hip. He was instructed to use a four-point gait with crutches to limit weight-bearing bilaterally for six weeks. At twenty-three months, the patient had complete resolution of the preoperative pain in the left hip, a slight left abductor lurch, and mild incisional pain in the left hip. The right hip had been painless since the fifth week. Roentgenograms made at twenty-three months showed good placement of the components and partial consolidation and sclerosis of both supra-acetabular regions (Fig. 4). The patient returned to his former work as a carpenter and did not need analgesics.
The differential diagnosis of supra-acetabular cysts includes neoplasms (giant-cell tumor, pigmented villonodular synovitis, and metastatic lesions), intraosseous ganglia, fibrous dysplasia, and degenerative cysts3,9,11,17. Isolated cysts in this region, with no other evidence of osteoarthrosis, have been reported previously by many investigators2,6,8,12,14,18. Most affected patients have been less than fifty years old and have had disabling pain in the hip with no other evidence of osteoarthrosis2,7,8,17,18. Most reports have described a progressive course leading to severe degenerative disease, sometimes involving both hips, if treatment is not given2,8,10. Eggers et al., Jacobs, and Marottoli and Didier all reported good results after ablation of the cysts and bone-grafting. In a report on four patients, Pauwels showed that acetabular cysts can resolve spontaneously after femoral osteotomy. Our findings support the belief that primary cystic arthrosis may be distinct from the typical osteoarthrosis of the hip that is seen in elderly patients. The sequence of events in our patient showed the gradual development of degenerative joint disease after cystic changes in the acetabulum. The initial roentgenograms showed no narrowing of the joint space or abnormality of the femoral head. Magnetic resonance images confirmed the cystic nature of the acetabular radiolucent areas and demonstrated no other abnormality of the joint. There was no evidence of communication between the cysts and the joint space early in the course of the disease, but an obvious communication developed later. These changes are consistent with the theory of primary cystic arthrosis1,2,4,8,13,18. Histopathological analysis of the contents of the cysts excluded the presence of a neoplastic lesion. Despite the gelatinous nature of the fluid in the cysts in the right acetabulum, the presence of an inflammatory component makes intraosseous ganglia an unlikely possibility3,17. Despite the current advances in total hip arthroplasty, many prosthetic implants fail within twenty years, and this process is accelerated in young active patients16. The ideal goal is to eliminate the need for arthroplasty or to defer it until the sixth or seventh decade, when the rate of revision is substantially lower. If patients who have primary cystic arthrosis are identified at an early stage, curettage of the cysts or osteotomy of the femur may halt or slow the progression of the disease2,8,12,14. Recognition of the characteristic features on plain roentgenograms and magnetic resonance images is essential if the disease is to be treated in the early stages.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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