AVN of the Femoral Head

Jeff Easom, D.O.

Garden City Hospital

Introduction

Debilitating disease that usually leads to hip joint destruction

30 to 50 year old age group (avg. 33) Ten to twenty thousand new patients annually 5 to 12% of THA annually secondary to AVN BL in 50 to 80 of pts

Etiology

Healthy cancellous bone replaced by dead trabecular bone.

Bone and marrow death can result from vascular interruption by various means and may extend to subchondral plate

Anterolateral femur predominantly affected

Presumed mechanism of mechanical failure due to accumulated stress fractures of unrepaired necrotic trabeculae

“Crescent sign” - Earliest sign of mechanical failure

No collateral vasculature in areas of subchondral bone

Clinical Conditions Assoc. with AVN

Corticosteroids(SLE, RA, renal transplant, asthma) ETOH, Sickle Cell, Gaucher, coagulation

deficiencies, myeloproliferative disorders, trauma, Caisson disease, radiation

ETOH and corticosteroids account for approx 90% of AVN (non-traumatic)-Mont et al, JBJS, Vol 77A, No. 3, March 1995

Increased risk in individuals who drink as little as 400ml/week (JBJS, Vol 77A, No. 3, March 1995

Pathogenesis

Multiple theories Thromboemboli, nitrogen bubbles, abnormally

shaped RBC’s, ^bone marrow pressure, radiation damage, altered lipid metabolism, vasoactive factor release as Gaucher disease

AVN is multifactorial in origin with a final common pathway

Pathology

Subchondral infarcted bone>inneffective healing response>resorption of dead bone>replacement with fibrous and granulation tissue>thick trabeculae formation>cartilage collapse

Clinical Features

Severe pain over anterior hip and groin (deep or throbbing pain)

Pain worsened with WB and motion (esp. forced internal rotation)

Acute or insiduous onset Night pain Positive Trendelenburg sign

Diagnosis

AP/frog-leg lateral radiographs Bone scan/bone bx- not standard diagnostic test MRI - aids in determining extent. Earliest finding

is a single density line on T1-weighted images, double-line sign on T2-weighted images

Diagnosis does not depend on a single finding, but based on the entire clinical picture, hx, and PE.

HIGH index of suspicion

Staging

Ficat and Arlet - Based on standard radiographs Steinberg - Expanded Ficat and Arlet to include

extent of femoral head involvement Marcus Japanese Investigation Committee - Modified Ficat

and Arlet to include location of lesion

Ficat and Arlet

Steinberg

Mild - <15% of femoral head involved

Moderate – 15 to 30%

Severe - >30%

Marcus

ARCO(Association Research Circulation Osseous) - proposed new classification to include prior 3 classification systems. Not universally accepted or finalized yet.(JBJS,Vol 77-A, No. 3, March 1995)

Expanded Ficat and Arlet to incorporate concept of location of lesion on radiograph.

Type-A-medial, Type-B-central, and Type C-lateral

Stage II

Stage III

Crescent sign – Early collapse of femoral head

Stage IV

MRI

Natural History

Remains uncertain Studies have shown that > 85% rate of collapse

within 2 years when stages I and II symptomatic hips were left untreated

Overall, when the diagnosis is made, the condition will progress

Non-Operative Treatment

Observation Protected Weight-Bearing 21 studies/819 hips - 182(22%) with satisfactory

clinical result with avg. f/u of 34 months. (Mont et al JBJS, Vol 77-A, No. 3, March 1995

Pharmacological Tx - Limited use and studies uncontrolled

Preliminary investigation of vasoactive and lipid-lowering agents are ongoing at several centers

Electrical stimulation - Remains experimental. Mixed outcomes with published articles

Operative Treatment

Core Decompression (with/without electrical stimulation). Stages I and II

Osteotomy(Varus, Flexion, Rotational). Stages III and IV

Non-Vascularized Bone-Grafting Vascularized Grafts Bipolar hemiarthroplasty, TARA, THA

Core Decompression

Stage I and II - no subchondral fracture or collapse

Mont et al, CORR, No. 324, March 1996

42 studies/2025 hips tx with core decompression(1206 hips) and non-operative management(819). Satisfactory results (63.5%/24 studies) of core decompression. 63% showed no evidence of radiograph disease prog.

22.7% success/21 studies of non-operative group

84% femoral head survival with Stage I, 65% with Stage II, and 47% with Stage III in the core decompression group

35% hip survival rates for Stage I, 31% for Stage II, and 13% for Stage III in non-operative treatment group

Stulberg et al, CORR, No. 268, July 1991

Prospective study over 4 year period 55 hips/36 patients 29 core decompression/26 non-operative Avg. age 38 Avg. f/u 27 months

Result

Success based on HHS. Stage I - 70% (7/10 operative hips) and 20%(1/5) in non-operative hips. Stage II - 71% (5/7) and 0/7 of non-operative. Stage III - 73% (8/11) operative and 1/10 non-operative

Results of success based on HHS and not on radiographic criteria

Core and Bone Grafting - Vascularized Fibular Graft

Attempts to enhance revascularization and arrest progression of necrosis

60 to 90% success rate Stage II, III, IV, V - Urbaniak

Urbaniak et al, JBJS, Vol 77-A, No. 5, May 1995

Free vascularized fibular grafting in symptomatic AVN - prospective

103 hips/89 pts followed (median f/u 7 years Followed yearly with regard to HHS, radiographic

progression, and conversion to THA

Results Probability of conversion to THA within 5 years

was 11%(Stage II), 23%(Stage III), 43% (Stage IV), 32% (Stage V)

HHS - Improvement from 56 to 80 (Stage II), 52 to 85 (Stage III), 41 to 76 (stage IV), and 36 to 75 (Stage V).

Radiographic progression occurred in 7/19 stage II, 21/22 stage III, 31/40 stage IV, and 16/22 stage V

Osteotomy

Predicated on concept of realignment with relief of lesion from weightbearing zone (delivered from weight bearing or contained within acetabulum)

Varus, flexion, valgus-flexion, and rotational osteotomies

With lesions of a total of 200 degrees, osteotomy is not recommended

All usually require an extended period of limited weight bearing of up to a year

Sugioka et al - Transtrochanteric rotational osteotomy. Technically demanding and results have not been duplicated

Various osteotomies exist with outcomes being widely varied

Difficulty with osteotomy is the increased difficulty in obtaining a satisfactory result if a THA is necessary

93/105 THA’s after osteotomy had intraoperative difficulties(screw removal and femoral reaming)

Ideal candidate is stage III with a small lesion and no ongoing cause of AVN

Additional Treatment Alternatives

Bipolar hemiarthroplasty - not recommended now TARA - Older design prosthesis yielded poor

results, while newer prosthetic design may yield better outcomes

Arthrodesis- Not widely advocated

Hungerford et al, JBJS, Vol 80-A, No. 11, November 1998

33 hips/25 pts Ficat Stage III and early Stage IV-( collapse

without involvement of acetabulum) TARA (Depuy) Mean f/u – 10.5 years Mean age – 41 y.o. Femoral head resurfacing only

Results

30 hips/91% survived at least 5 years Mean f/u 10.5 yrs – Overall, 20 hips(61%) had

good or excellent results based on HHS;13(39%) had fair or poor result and required THA

Mean interval b/w TARA and THA – 60 months

HHS – Mean improvement from 38 points (range of 29 to 61 points) preoperatively to 91 points(range of 80 to 100.

Conclusion

After determination of whether or not collapse has occurred, one must consider the extent of the lesion, which has been found to be important prognostically(lesions involving < 15% of femoral head fare better with all treatment method than moderate or severe lesions

Medial (type-A) lesions have been found to have a much better prognosis than central (type-B), or lateral (type-C).

Overall, patients with multisystem disease or post transplantation state should have THA as a definitive procedure rather than preservation procedures

Conservative tx – 20% survival rate at 3 to 5 years for Stage I and II AVN

Core decompression – 70 to 80% survival rate in Stage I and II AVN at 3 to 5 years

Vascularized fibular grafting – Clinical success approx 70 – 80% in Stage III, IV, and V AVN

Osteotomy – 50 to 70% success rate at 5 years in Stage III AVN

THA – Higher rate of failure than for OA, but clinically better than alternatives for advanced disease

TARA – Best study represents 61% clinical success at 10.5 years