Differences in hip bone mineral density may explain the hip fracture pattern in osteoarthritic hips

Figures & data

Figure 1. Zero rotation position (A) and 10–15° external rotation position (B) in bilateral femoral DXA scans. In the latter, the external rotation shows the prominence of the lesser trochanter.

Table 1. Characteristics of patients. Values are mean (SD)

	OAH	Rotation group
No. of patients	40	21
Age, years	55 (8.8)	64 (12)
Sex (M/F)	20/20	5/16
Weight, kg	80 (13)	72 (14)
Length, cm	172 (8.8)	167 (9.9)
BMI	27 (3.2)	22 (3.4)
Z-FN (n = 37)	0.77 (1.2)	0.05 (1.0)
Z-TR (n = 37)	–0.25 (1.2)	–0.4 (1.0)
Z-TH (n = 37)	0.12 (1.1)	–0.3 (0.9)
Z-Total Body	0.71 (1.1)	not measured

Table 2. Bone mineral density of the proximal femurs and heels, and Z-scores. Values are mean (SD)

	n	OAH limb	Control limb	Δ (%) ^a	p-value ^b
BMD-FN	37	1.05 (0.14)	1.01 (0.13)	4.1%	<0.001
BMD-TR	37	0.82 (0.14)	0.89 (0.13)	–8.3%	<0.001
BMD-TH	37	1.01 (0.14)	1.06 (0.14)	–4.6%	<0.001
BMD-Heel	38	0.54 (0.08)	0.55 (0.09)	–1.7%	0.3
Z-FN	37	0.8 (1.2)	0.4 (1.0)	n.a.	n.a.
Z-TR	37	–0.2 (1.2)	0.4 (1.2)	n.a.	n.a.
Z-TH	37	0.1 (1.1)	0.5 (1.1)	n.a.	n.a.

^a Percentage difference OAH–Control

^b Paired t-test

BMD in g/cm²

Z-scores: sex- and age-matched reference values adjusted for weight

n.a.: not applicable.

Table 3. Bone mineral content and projected bone area at the proximal femur. Values are mean (SD)

Part ^a	OAH limb	Control limb	Δ (%) ^b	p-value ^c
BMC-FN (g)	6.2 (1.4)	5.3 (0.9)	18%	<0.001
BMC-TR (g)	10.9 (3.4)	13.3 (3.7)	–18%	<0.001
BMC-TH (g)	36 (7.4)	37.9 (7.1)	–4.5%	<0.05
Area-FN (cm^2)	5.9 (0.8)	5.2 (0.6)	13%	<0.001
Area-TR (cm^2)	13.2 (2.9)	14.9 (2.8)	–11%	<0.001
Area-TH (cm^2)	36 (4.3)	36 (4.0)	–0.1%	0.9

^a FN: femoral neck; TR: trochanteric region; TH: total hip.

^b Percentage difference OAH–Control

^c Paired t-test; n = 36

Table 4. Body composition of the lower limb measured with DXA for 38 patients with unilateral osteoarthritis of the hip. Values are mean (SD)

Lower limb ^a	OAH limb	Control limb	Δ(%) ^b	p-value ^c
BMC ^d	0.57 (0.11)	0.60 (0.10)	–4.8%	<0.001
FM ^d	4.16 (1.68)	4.23 (1.75)	–1.7%	0.06
LTM ^d	7.87 (1.76)	7.96 (2.06)	–1.1%	0.7
TLLM ^d	12.60 (2.05)	12.79 (2.49)	–1.5%	0.5
BMC% ^e	4.5%	4.9%	–6.8%	0.2
FM% ^e	32.8%	33.3%	–1.5%	0.7
LTM% ^e	62.7%	61.8%	1.4%	0.5

^a FM – fat mass; LTM – lean tissue mass; TLLM – total lower limb mass

^b Percentage difference OAH–Control

^c Paired t-test

^d Expressed as 10³ g

^e Expressed as a percentage of total lower limb mass

Table 5. The effect of rotation of the proximal femur on BMD of the hip (rotation group, 21 patients, 42 hips). Values are mean (SD) in g/cm²

Part ^a	Zero	External	Δ(%) ^b	p-value ^c
FN	0.87 (0.13)	0.87 (0.13)	0.3%	0.7
TR	0.72 (0.12)	0.74 (0.12)	–2.4%	<0.001
TH	0.88 (0.13)	0.88 (0.13)	–0.5%	0.3

^a FN: femoral neck; TR: trochanteric region; TH: total hip.

^b Percentage difference Zero–External

^c Paired t-test