Bilateral, uncemented hip replacements were performed on a 45-year-old woman with autosomal dominant osteopetrosis. The hips showed degenerative changes and protrusio acetabuli. Difficulties were encountered especially during preparation of the femoral canal. At ten-year follow-up she has an excellent clinical and radiological result with no sign of osteolysis. Uncemented hip replacement, while technically demanding, can be successful in the intermediate term for patients with this condition.
Osteopetrosis or Marble Bone disease is an uncommon condition. The sex-linked recessive form is associated with childhood problems and early death. However, the autosomal dominant form is compatible with a normal life span, and as many as 40% of patients may remain asymptomatic.1,2 Bollerslev and Mosekilde1 described two forms of autosomal dominant osteopetrosis (ADO). In Type 1, there is increased thickness of the cranial vault, diffuse osteosclerosis of the lumbar spine and pelvis and symmetrical, long-bone involvement. Type 1 shows more basal skull involvement, a 'rugger jersey' spine and 'endobones' within the pelvis. Type 2 patients are more prone to fractures which are difficult to treat.
Degenerative changes may occur in the hip and knee after the fifth decade, sometimes in the presence of deformity, especially coxa vara,3,4 and sometimes without.5-10 There have been several early reports of hip arthroplasty for this condition, hut we believe that this is the first report of an uncemented total hip arthroplasty (THA) in osteopetrosis.
In 1992, a 45-year-old female laundry worker presented with a seven-year history of low hack and bilateral hip pain with stiffness. She had severe pain at rest and at night, a walking duration of 10 minutes without aids and was unable to put on shoes or socks. She had 80 of hip flexion on both sides with no rotation, adduction or abduction. Her Harris Hip score (HHS) was 39 (pain 10, function 21).
Radiographs showed bilateral protrusio acctabuli and degenerative changes of the hips (Fig. 1). The long bones were uniformly dense with very narrow medullary canals. The lumbar vertebrae were also dense with degenerative changes present. The radiograph of the skull showed thickening of the cranial vault. These changes were consistent with ADO Type 1.
She underwent bilateral, staged THA three months apart. The femoral neck was very hard to cut and the cut surface showed no obvious medullary canal. A 52 mm CLS Expansion cup (Center-pulse Orthopedics, Munsinger, Switzerland) was inserted into the acetabulum after routine power reaming. Drills were used to create a medullary canal breaking two drill bits in the process. The femur was then sequentially reamed with power reamers and hand-held conical reamers to allow the insertion of a 14 mm Wagner cone prosthesis (Centerpulse Orthopedics) which has a rough-blasted, titanium, conical stem with fins. There were no post-operative complications.
Histopathological examination of the femoral head revealed a thickened cortex and variably thickened bony trabeculae. In some areas, the trabeculae were markedly widened with both a woven and lamellar pattern, and islands of pale staining, alcianbluc positive, myxoid material (Fig. 2) which may represent the remnant cartilaginous bridges which are typical of osteopetrosis. Delicately vascularised adipose tissue replaced haemopoietic marrow. Osteoclasts were seen in neither histological nor electronmicrographic sections. These histological features indicate abnormal hone remodelling and, when taken in conjunction with the clinical and radiological findings, are consistent with ADO Type 1 as described by Bollerslev and Mosekilde.1 The articular surface was eburnated and any remaining articular cartilage was fibrillated, as is seen in osteoarthritis.
At two-year follow-up, tomography (Fig. 3) suggested hone ongrowth with trabecular lines seen running from the threads of the cup. The HHS was 93 (pain 40, function 44). At the latest follow-up (ten years), she continues to have a good result with an HHS of 91 (pain40, function 42), an Oxford-12 item hip score of 25, and a WOMAC score of 60 (pain 12, motion 5, function 43). Her short-form (SF)-12 physical score is 41.41 and her mental score is 42.20. She has residual discomfort from her lumbar spine hut is satisfied with the results of her hip arthroplasties. The latest radiograph (Fig. 4) shows apparently solid fixation of the components with no osteolysis. There has been minimal remodelling of the canal created distal to the femoral stem.
The gene disorders in osteopetrosis result in decreased osteoclastic resorption of hone. Where present, osteoclasts lack the usual ruffled horder that is important in hone resorption. The abnormal osteoclastic function results in very hard hone with thickened trabeculae. Coxa vara is a well-recognised complication of osteopctrosis with most cases developing during childhood,2,10 sometimes after fracture of the femoral neck or suhtrothanteric region.'
Degenerative changes often occur after the age of 40(5-10) in the absence of deformity. Articular cartilage is not affected by the disorder, and it has therefore been suggested that the degeneration occurs because of the hard unyielding subchondral bonc.6,8 Protrusio has not been reported previously. We speculate that it may have occurred because the acetabular bone was relatively less hard than the femoral head.
There are several case reports of hip and knee arthroplasty with follow-up ranging from six months to six years.3-10 Technical difficulty has been experienced especially on the femoral side. Drills and high-speed burrs, guided by fluoroscopy, have been used to help create a medullary canal. Previously, cemented components have been used. Matsuno and Katayama4 used a press-fit acetahuIar component with screw fixation, since it would be difficult to obtain good quality hone-cement interface, hut considered that to use a cementless femoral component risked fracturing the shaft. We found that the use of the Expansion cup allowed more controlled insertion and may reduce the risk of acetabular fracture. The shape and small size of the Wagner cone prosthesis allowed power reaming of the femur and avoided downsizing the component to allow a cement mantle. Poor cement-hone penetration would he expected to occur in the dense sclerotic hone.
Fracture healing occurs slowly in osteopetrosis and slow bony ongrowth to the titanium prosthesis would he expected, which appears to have occurred in our case. Serial radiographs over a period of 10 years show no progressive osteolysis despite a high level of activity. There has been minimal remodelling of the femur where the medullary canal was reamed out. The osteoclast has a central role in osteolysis due to paniculate debris and patients with osteopetrosis may have an inhibited process of osteolysis.
In summary, we believe that this is the first reported case of fully cementless THA in osteopetrosis. At intermediate follow-up often years, the clinical and radiological results are good. Protrusio acetabuli has not previously been described in this condition.
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.
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D. P. Gwynne Jones, B. F. Hodgson, N. A. Hung
From the Dunedin Hospital, Dunedin, New Zealand
* D. P. Gwynne Jones, FRACS, Senior Lecturer and Consultant Orthopaedic Surgeon
* B. F. Hodgson, FRACS, Consultant Orthopaedic Surgeon
* N. A. Hung, FRCPA, Consultant Pathologist Department of Orthopaedic Surgery, Dunedin Hospital, Great King Street, Dunedin, New Zealand.
Correspondence should be sent to Mr D. P. Gwynne Jones.
©2004 British Editorial Society of Bone and Joint Surgery
doi:10.1302/0301-620X. 86B2. 14354 $2.00
J Bone Joint Surg [Br] 2004;86-B:276-8.
Received 26 March 2003;
Accepted after revision 26 June 2003
Copyright British Editorial Society of Bone & Joint Surgery Mar 2004
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