Bone formers: osteophyte and enthesophyte formation are positively associated

Abstract

Objective: To test the hypothesis that enthesophyte formation and osteophyte growth are positively associated and to look for associations between bone formation at different sites on the skeleton so that a simple measure of bone formation could be derived.

Methods: Visual examination of 337 adult skeletons. All common sites of either enthesophyte or osteophyte formation were inspected by a single observer who graded bone formation at these sites on a 0-3 scale. The total score for each feature was divided by the number of sites examined to derive an enthesophyte and an osteophyte score. Cronbach's alpha and principal components analysis were used to identify groupings.

Results: Enthesophyte formation was associated with gender (M > F) and age. There was a positive correlation between enthesophytes and osteophytes (r = 0.65, 95% confidence interval, 0.58 to 0.71) which remained after correction for age and gender. Principal components analysis indicated four different groupings of enthesophyte formation. By choosing one site from each group a simple index of total skeletal bone formation could be derived.

Conclusions: Osteophytes and enthesophytes are associated, such that a proportion of the population can be classified as "bone formers". Enthesophyte groupings provide some clues to aetiopathogenesis. Bone formation should be investigated as a possible determinant of the heterogeneity of outcome and of treatment responses in common musculoskeletal disorders.

Figure 1

(A) Knees showing marked osteophytes grade III and enthesophytes at the tibial tubercle grade II. (B) Grade III osteophyte around the carpo-metacarpal joint of the thumb. (C) Calcaneum with grade II enthesophyte and patellae with grade III enthesophyte. (D) Radius with grade II enthesophyte at occipital protuberance and grade I osteophyte at radioulnar articulation. Ulna humeral joint has grade II osteophyte. (E) Hip joint showing greater trochanter of femur with grade II enthesophyte and lesser trochanter with grade I enthesophyte. The iliac crest also has enthesophytes, grade I, and the ischial tuberosity enthesophytes grade II.

Figure 2

Histogram of the frequencies of skeletons in each category of osteophyte score. Each category has a range of 0.2 units. A positive skew is clearly evident

Figure 3

Histogram of the frequencies of skeletons in each category of enthesophyte score. Each category has a range of 0.2 units. A positive skew is clearly evident.

Figure 4

The loadings from each of the ligament insertion sites for the second and third principal components. This plot has been used to informally identify four groups of sites.

Figure 5

Characteristics of different "bone former" definitions—agreement with occurrence of DISH and prevalence.