Osteoarthritis of the Hip Joint 



K. LiTTi.i; and L. H. Pimm 



The Nuffield Orthopaedic Centre, Oxford, and 



The Atomic Energy Research Estahlishincnt, Harwell 



With the increasing longevity of the population as 

 a whole the degenerative wear and tear changes 

 which occur in the joints are becoming one of the 

 greatest problems facing modern orthopaedics. 

 These changes, which we term "Osteoarthritis'", 

 aflfect principally the main weight-bearing joints, 

 and thus the head of the femur in the hip joint is 

 most often involved. The gross and microscopic 

 changes of the established condition have been 

 studied for many years, but little is known of the 

 pathology underlying the origin of the lesion. 



In an attempt to elucidate the problem a con- 

 siderable amount of work has been carried out at the 

 Nuffield Orthopaedic Centre, Oxford, and studies 

 of the histological changes and vascular patterns 

 have been published by Trueta, Harrison and 

 Schajowicz (3, 9). One of their fundamental discov- 

 eries was that the initial lesion is in the hyaline 

 articular cartilage covering the head of the femur 

 and in the «o«-pressure area, contrary to what might 

 be expected. 



The light microscope shows disruption of the 

 superficial layer of cartilage, followed by the appear- 

 ance of collagen bundles, lissuration and an altera- 

 tion in staining properties, leading ultimately to 

 ulceration and destruction of the cartilage and its 

 replacement by fibrocartilage. The bony changes 

 occur later and are secondary. 



This study and the work carried out in Sweden 

 by Ingelmark and Saaf (5), Tngelmark (4), Ekholm 

 (1) and Ekholm and Norbiick (2) suggests that 

 mechanical forces are concerned with the nutrition 

 of the cartilage from vessels lying immediately 

 below it in the bone and probably also from the 

 synovial fluid as there are never any vessels in hya- 

 line cartilage itself. It seems possible that there is 

 some intermittent pumping action as the pressure 

 on the segments of cartilage varies, the cartilage 

 itself behaving something like a sponge. Muller as 

 long ago as 1929 suspected something like this and 

 in support of the hypothesis Matthews (6) has shown 

 that the weight bearing areas do comprise the 

 thickest cartilage with the highest mucopolysaccha- 

 ride content: whereas the non-pressure areas suffer 

 nutritional deficiency changes first. 



Electron microscopy has made it possible to see 

 that the collagen fibrils are closely surrounded by the 

 polysaccharide containing matrix which appears to 

 be of a gelatinous or spongy nature. Four distinct 

 sizes of collagen fibrils have been noted, and in the 

 normal articular cartilage these fibrils are present in 

 a three dimensional network with no preferred orien- 

 tation and surrounded by the ground substance. 



In the h\aline cartilage from the arthritic joint 

 two differences are apparent. Firstly the collagen has 

 a very definite orientation (figure I). Secondly the 

 electron microscope shows a decreased proportion 

 of ground substance, so that the material in the 

 section has a rather more open appearance (figure 

 2). This is in agreement with the chemical analyses 

 performed by Matthews (7), in which it was found 

 that the total quantity of polysaccharide was de- 

 creased considerably in arthritic cartilage. 



Although the onset of orientation changes can be 

 seen easily in sections viewed in the electron micro- 

 scope, the area of specimen examined, and indeed 

 the whole specimen, is so small, being only about ^ 

 mm across, that finding the direction of this orienta- 

 tion is difficult. Information on this point can be 

 gained by using x-ray diffraction in conjunction with 

 electron microscopy. A survey of the changes in 

 orientation produced both by normal ageing and by 

 the onset of osteoarthritic changes has therefore 

 been carried out using x-ray diffraction. 



Fig. 1. Hyaline cartilage from an osleoarilinlic hip joml 

 showing the definite orientation of the fibrils. Magnification 

 13,000. 



Fig. 2. Hyaline cartilage from an osteoarthritic hip joint 

 showing the open appearance of the ground substance 

 typical in this condition. Magnification 26,000. 



