Isolated acetabular osteoporosis in TOH in pregnancy: a case report.

Abstract: Transient osteoporosis of the hip (TOH) is a rare, self-limiting syndrome characterized by hip pain in the 2nd or 3rd trimester of pregnancy. Conventional radiography shows demineralization of the femoral head. Diagnosis is confirmed by MRI scan. Over the course of a few months, the radiological abnormalities and the pain disappear spontaneously with complete resolution. We report the case of a patient with isolated acetabular involvement during pregnancy, confirmed by MRI scan, who obtained spontaneous remission of her symptoms.

Key Words: transient osteoporosis of hip, acetabular osteoporosis, osteoporosis in pregnancy

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Transient osteoporosis of the hip (TOH) in the last trimester of pregnancy was first reported in 1959 by Curtis and Kincaid. (1) The syndrome is self-limiting and normally resolution occurs within 6 months to a year. (2) The etiology of this disease is still unknown, but various theories regarding the pathophysiology have been postulated. (3) To make a diagnosis of TOH, other causes of hip pain must be excluded. These include avascular necrosis of the femoral head, septic arthritis of the hip, osteomyelitis, stress fractures, or a metastatic lesion in the femoral head. (4) An MRI scan showing an abnormally high signal intensity of the affected bone in T2-weighted images, predominantly in the femoral head, is the best diagnostic modality for confirmation of TOH. (5,6) Occasionally, the area involved includes the femoral neck and trochanters, and even extends to the acetabulum and the iliac wing. (3) We report the case of a patient who had spontaneous recovery following primarily acetabular osteoporosis during pregnancy.

Case Report

In February 2002, a 27-year-old woman of 37 weeks' gestation was admitted with a history of gradually progressive left lower limb pain, especially in the knee, for a period of one month. This was her first pregnancy. She was apyrexial with restricted rotation and flexion of her left hip. A complete blood count, uric acid level, and LFTs were within normal limits. X-rays performed following delivery of a healthy baby were normal. She was unable to weight bear due to pain. Subsequently, MRI scans (Fig. 1) of her pelvis showed bone marrow edema involving the left acetabulum associated with thickening of the overlying cortex in the course of the pectineal line (T1-weighted images). A bone scan excluded bony metastasis. She was treated with protected weight-bearing and anti-inflammatory drugs and recovered within 3 months of conservative treatment. Repeat MRI (Fig. 2) scan of the pelvis at 6 months showed complete resolution of her acetabular osteoporosis. She continued to walk comfortably without recurrence of pain.

Discussion

This syndrome was given the name of transient osteoporosis of the hip by Hunder and Kelly in 1967. (7) One-third of these patients are pregnant women in their last trimester. Although the hip is the most affected joint (76%), other joints may be involved. (3) The onset of pain can be gradual or acute and is severe enough to incapacitate the patient, as evidenced by our patient. The left hip is commonly involved. (8) Clinical examination is usually normal except for restricted abduction and rotation of the involved hip. Laboratory investigations are usually within normal limits. Conventional x-rays are important for diagnosis, but these are contraindicated in the last trimester of pregnancy. The first x-ray abnormalities (demineralization of the femoral head without narrowing of the joint) are present 3 to 6 weeks following the onset of symptoms. (3)

[FIGURE 1 OMITTED]

MRI scans are the mainstay of the diagnosis. Edema and fat necrosis in the acetabular region results in a reduced T1 signal, whereas T2 signals are increased due to osteopenia. If the femoral head is involved, it is important to differentiate it from avascular necrosis of the femoral head. (9) An adequate follow up with repeat MRI scans are required to completely exclude avascular necrosis, but in cases with a primarily acetabular involvement, avascular necrosis could be excluded earlier.

Several predisposing factors have been described, such as a negative calcium balance, increased activity of the adrenal cortex and an increased demand for protein and minerals. (10) At least two prospective trials have demonstrated marked evidence of bone loss in the initial 6 months during lactation, and recovery from lactation during the ensuing two-year period. (11) Pregnancy may unmask patients with low bone mass. (12)

Primary acetabular involvement of the weight-bearing zone probably reflects upon the abnormal bone metabolism during pregnancy. The absence of femoral head involvement made us rethink our diagnosis, as a literature search did not reveal a single case of isolated acetabular involvement in this condition. Disappearance of the osteoporosis in the subsequent scans made us conclude the diagnosis retrospectively.

[FIGURE 2 OMITTED]

Postpartum, the patient should be thoroughly investigated for generalized osteopenia, advised about adequate calcium intake and followed to determine serial bone density measurement. (13) Patients with TOH should be treated with care since they are prone to develop fractures, if allowed to bear weight. Stress fractures of the osteopenic femoral neck have been reported in TOH of pregnancy. (14)

Conclusion

In our view, primary acetabular osteoporosis of TOH in pregnancy runs a more benign course than the TOH with femoral head involvement. Diagnosis must be made after excluding more sinister pathologies involving the hip. All patients should have a bone scan and MRI scans performed as soon as possible. Treatment for these patients includes non-weight bearing for 6 weeks and the institution of NSAIDs with calcium supplementation.

References

1. Curtiss PH, Kincaid WE. Transitory demineralization of the hip in pregnancy. A report of three cases. J Bone Joint Surg Am 1959;41A:1327-1333.

2. Samdani A, Lachmann E, Nagler W. Transient osteoporosis of the hip during pregnancy. Am J Phys Med Rehabil 1998;77:153-156.

3. Bijl M, van Leeuwen, MA, van Rijswijl MH. Transient osteoporosis of the hip: presentation of atypical cases and a review of literature. Clin Exp Rheumatol 1999;17:601-604.

4. Axt-Fliedner R, Schneider G, Seil R, et al. Transient bilateral osteoporosis of the hip in pregnancy. Gynecol Obstet Invest 2002;51:138-140.

5. Daniel WW, Colleen Sanders P, Alarcon GS. The early diagnosis of transient osteoporosis by magnetic resonance imaging. A case report. J Bone Joint Surg Am 1992;74A:1262-1264.

6. Urbanski SR, de Lange EE, Eschenroeder HC Jr. MRI of transient osteoporosis of the hip. A case report. J Bone Joint Surg Am 1991;73:451-455.

7. Hunder GG, Kelly PJ. Transient osteoporosis of the hip: A clinical syndrome? [abstract] Arthritis Rheum 1967;10:285.

8. Rosen RA. Transitory demineralization of the femoral head. Radiology 1970;94:509-512.

9. Guerra J, Steinberg M. Distinguishing transient osteoporosis from avascular necrosis of the hip. J Bone Joint Surg Am 1995;77:616-624.

10. Schapira D. Transient osteoporosis of the hip. Semin Arthritis Rheum 1968;22:787-792.

11. Showers MF, Carton G, Shapiro B, et al. Changes in bone density with lactation. J Am Med Asso 1993;269:3130-3135.

12. Eisman J. Relevance of pregnancy and lactation to osteoporosis? Lancet 1998;352:504-505.

13. Sweeny AT, Blake MA, Holick MF. Transient osteoporosis of pregnancy. A case report. J Clin Densitom. 2000 Fall;3:291-297.

14. Brodell JD, Burns JE Jr., Heiple KG. Transient osteoporosis of the hip of pregnancy. Two cases complicated by pathological fracture. J Bone Joint Surg Am 1989;71:1251-1257.

I have enjoyed greatly the second blooming ... suddenly you find--at the
age of 50, say--that a whole new life has opened before you.
--Agatha Christie

U. K. Debnath, FRCS, R. Kishore, MRCS, and R. J. Black, FRCS

From SpR Trauma & Orthopaedics, All Wales Higher Training Programme, Cardiff, Wales; the Department of Radiology, Dafen, Llanelli, Wales; and West Wales General Hospital, Carmarthen, Wales.

Reprint requests to Mr. UK Debnath, SpR Trauma & Orthopaedics, All Wales Higher Training Programme, 23, Barons Court Road, Cardiff, CF23 9DF. Email: [e-mail]

Accepted November 12, 2004.

RELATED ARTICLE: Key Points

* TOH in pregancy usually affects the femoral head.

* Isolated acetabular involvement is rare and is a self limiting disease.

* Early MRI scans are the mainstay of diagnosis.

* Treatment includes non-weight bearing for six weeks along with calcium supplementation and NSAIDs.