Protrusio acetabuli (Otopelve)

Protrusão acetabular (Otopelve)

Protrusio acetabuli (Otopelve)

Protrusão acetabular (Otopelve)

Alceu Gomes Chueire^I; Wilson Abou Rejaili^II; Antonio Fernando dos Santos^III

^IPhD-Professor and Departament Head

^IIDoctor Orthopaedics and Master

^IIIProfessor

^{Address for correspondence}

SUMMARY

Protrusio acetabuli is a disease characterized by a deformity of the medial wall of the acetabulum with a progressive migration of the femoral head into the pelvic cavity, resulting in some mechanical disorders, pain and limited limb hip movement. It was first described by Otto in 1824 as an intrapelvic protusion of the femoral head. It is considered multifactorial, and it is suggested that there is a heredity background to this disease. It is classified as primary (75,3%) or secundary (24,7%) according to aetiology; mild, moderate and severe radiologically.

This review aims to present some treatment techniques using arthroplasties which are several and little explored. As in the literature, the choice was bone graft since there is no migration of the cemented acetabulum and no necessity of a titanium cup of great diameter.

Key words: Protrusio acetabuli; arthroplasties; hip; bone graft

RESUMO

A protrusão acetabular é caracterizada por deformidade da parede medial do acetábulo com migração progressiva da cabeça femoral para o interior da pelve, causando distúrbios mecânicos, dor e importante limitação funcional da articulação do quadril. Descrita inicialmente por Otto em 1824, como uma deformidade da pelve, caracterizada pela maior profundidade da cavidade cotilóide, devido a seu afundamento. Considerada multifatorial, acredita-se haver uma tendência familiar. Quanto à etiologia é classificada em primária (75,3%) ou secundária (24,7%) e, de acordo com parâmetros radiológicos em leve, moderada e grave.

O objetivo desta revisão é apresentar as técnicas de tratamento com artroplastias que são múltiplas e pouco exploradas. Em nossos pacientes, como a maioria dos autores da literatura, a protrusão da parede medial do acetábulo foi tratada com enxerto ósseo, superando e evitando a migração do componente acetabular cimentado e não havendo a necessidade de uso das conchas de titânio de grande diâmetro.

Descritores: Protrusão Acetabular; artroplastias; quadril; enxerto ósseo

INTRODUCTION

Protrusio acetabuli was initially described by Otto in 1824, in cadaver studies as a deformity of the medial wall of the acetabulum with a consequent migration of the femoral head into the pelvis⁽¹²⁾.

The first case reported in English literature was described by White in 1883. Scherlin in 1910 was the first to perform radiographic diagnosis¹².

Primary or essential protrusion of acetabulum is a pelvian deformity characterized by increased depth of cotiloid cavity with depression⁽¹⁾.

The aim of this paper is to review the literature in regard of surgical treatment of protrusio acetabuli with arthroplasties, since this procedure is not specifically explored nowadays; it is polemical and there is no standardization for this treatment.

INCIDENCE AND EPIDEMIOLOGY

It is more frequent in female (10:1), and bilateral; is very common in advanced rheumatoid arthritis patients⁽¹⁾.

In Sotelo-Garza and Charnley⁽²⁵⁾ studies, the incidence of primary protrusio acetabuli was of 75.3% and as secondary causes, rheumatoid arthritis was evident, with 18.7%.

It is believed to have a familial trend as suggested by Donald MacDonald⁽¹⁶⁾, Simmons⁽²⁴⁾ et al., Hooper⁽¹²⁾ et al., Friedenberg⁽⁶⁾ who reported changes in acetabular cartilage ossification leading to protrusion.

ETIOLOGY AND CLASSIFICATION

It is considered as multifactorial and can be classified into two basic types⁽²⁶⁾.

Primary: also called idiopathic, affects young patients nevertheless is generally diagnosed at adult age. Its etiology in childhood is attributed to changes in triradiated cartilage ossification. It can also come from osteoconditis, asthenia, congenital deep acetabulum and rheumatic diseases. The expression otopelvis is used only in primary acetabular protrusion. McCollum⁽¹⁸⁾ et al. report that protrusion is progressive and only stops when the great trochanter touches acetabular border.

Secondary: the protrusion is due to a pre-existing disease, which weakens medial acetabular wall, such as rheumatoid arthritis, ankylosing spondilitis, osteoarthritis, chronic renal osteodistrophy, rachitism, osteoporosis, Paget's disease, neoplasias, surgery sequelae, traumas and infections, and even Marfan's syndrome⁽⁵⁾.

DIAGNOSIS

Primary form, or essential protrusion is generally bilateral and there are difficulties in its diagnosis due to symptoms are minimal or absent. Frequently the diagnosis is incidental in radiographs taken for other reasons or for discrete limitation of hip movements. Thus, protrusio acetabuli diagnosis is made by classic radiograph (pelvis in AP).

Several methods were proposed to rate protrusio acetabuli, all of them based on radiographic studies. Some of these, the simplest, are adequate for identifying protrusion, but not to grade it as: tear drop signal (changed as in Figure 1), Wiberg's angle (increased in Figure 2) and changes in the Shenton's arch or line (broken — Figure 3). The most accepted and diffused is the one by Ranawat (Figure 4).

Other rating with good parameters is based on the Kohler's line (Figure 5). It is an ilial-ischiatic line, measuring the distance from it to the medial wall of the acetabulum; several authors use it^{(2,11,14,15,19)}. With this method we can assess the variant distance in males (> 3 mm) and females (³ 6 mm)^(2,11).

Turibio and Ramos⁽²⁶⁾ synthesized a rating based on the distance of the medial wall of the acetabulum to Kohler's line (Table 1).

Sotelo-Garza and Charnley⁽²⁵⁾ propose a more elastic rating based on the distance measured by their method (Figure 6).

Degree I — 1-5 mm (Light Protrusion)

Degree II — 6-15 mm (Mild Protrusion)

Degree III — more than 15 mm (Severe Protrusion)

They stress that 44.5% were Degree I, 46% were Degree II and only 9.5% were Degree III.

TREATMENT DISCUSSION

Even though it is difficult to discuss the subject given there were few reports in the last years, the treatment of choice of protrusio acetabuli was surgical, as recommended in the literature ^{(4,10,13, 17,23,26)}. This procedure is per-formed when there is important movement limitation together with intense pain, aiming to relieve pain, strengthen the medial wall, restore the rotation center and to preserve the range of movement.

Turibio and Ramos⁽²⁶⁾ report that in early phases corrective valgizing osteotomy of the proximal femur would have place for reducing the degree of protrusion.

Most of the authors use a lateral approach, and large trochanter osteotomy to make easier the view and procedure ^(3,20,21,25). It was used chopped impacted femoral head graft, cementing the acetabular piece, delaying load up to total graft integration. This was considered effective by the authors when radiographic aspect of the graft was homogenous and similar to the density of pelvian bone without evidence of radiotransparence suggesting non-integration (Figure 7).

The most important complication post total hip replacement found by the authors was blind migration of the polyethylene acetabular component due to weakness of the medial wall, and this a medialization of the acetabular component leading to an alteration in the rotational center of the hip, reducing the life of the acetabular component⁽²⁰⁾. Hastings⁽⁹⁾ et al. suggest always using titanium cups for closing the defect and so, improving the rotational center. However there is a consensus in the use of grafting from the femoral head improving the rotational center and, thus, avoiding further migration of the acetabular component^(20,21,25).

The largest series are in the studies by Ranawat⁽²¹⁾ and Sotelo-Garza and Charnley⁽²⁵⁾. Among them there is a consensus of using femoral head grafting only in defects larger than 5 mm, without need of using artificial large diameter cups.

In these studies^(21,25), the use of bone cement for closing bony defects resulted in further acetabular component migration, thus being not indicated as a substitute for acetabular defect correction.

Sharp et al.⁽²³⁾ recommend acetabular prosthesis with a ring reinforcement that did not prove effective in long term. Ranawat⁽²¹⁾ used solid bone graft, removed from the femoral head, but abandoned this technique. There is currently a group following Execter's⁽⁸⁾ prosthesis principles, who recommends a reinforcement of the bottom of the acetabulum with chopped (not crushed) grafts smaller than 3 mm⁽²²⁾, as initially done and with good results.

Trabalho recebido em 17/05/2002. Aprovado em 26/07/2002

Work performed at Departamento de Ortopedia e Traumatologia da FAMERP/

FUNFARME - São José do Rio Preto - SP

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Publication Dates

• Publication in this collection
  25 Feb 2003
• Date of issue
  Dec 2002

History

• Accepted
  26 May 2002
• Received
  17 May 2002