Estimated Prevalence of PTOA
Thousand two hundred ninety (1290) patients attending the orthopedics service were diagnosed with a hip or knee joint disease and data on medical records. Sixty-eight patients were excluded for osteonecrosis or a previous fracture without OA evidence. In total, 842 patients had the following diagnosis: 641 patients (76%) with primary -OA, 104 patients with PTOA (12.4%), 72 with Rheumatoid arthritis (8.6%), and 25 patients (3%) with OA secondary to other joint abnormalities (hip dysplasia or dislocation, Leg Perthes, Femoroacetabular Impingement and epiphysiolistesis of proximal femoral). Among all patients with OA, PTOA represents 13.5% of the cases (See Figure 1).
Fractures were the most common injury for patients with PTOA; knee fractures in 30% of the knee-PTOA and femoral fractures (principally acetabular) in 26% of hip-PTOA cases (Figure 2). Meniscal injuries and tears represented 23% of cases. Other types of injuries attributed to PTOA were ligament injuries (11%), hip dislocation (4%), and patellar dislocation (1%). Finally, in a group of former recreational soccer players (n=6), there were no records of the injury and the subject did not recall the mechanism or diagnosis (Unknown mechanism, 6%). There were differences in the principal injuries associated with PTOA by gender; knee fractures were more common in males and hip fractures in females (Figure 2, 31% and 37.5%, respectively).
Patients with PTOA and primary OA experienced a similar level of pain and disability (Mean Maximum Pain reported= 7.3 for OA and 6.9 for PTOA, P-adj= 0.29 and P-adj=0.92 for walking disability). Within the patients with PTOA, there were significant differences in the degree of pain according to the various injuries related to PTOA (Figure 3, Adjusted-P=0.036). Patients with PTOA due to meniscal injuries had the highest pain score (Figure 3, 8.3/10). In patients with PTOA due to past hip fractures, 45% had difficulty or were unable to walk, having two times higher odds for disability than patients with primary OA with only 32% (OR=1.99, CI:0.93-4.26). Former recreational soccer players with an unknown injury mechanism had less pain and disability than other injury groups or primary OA cases (Figure 3).
Comparison between PTOA and Primary -OA cases
Most cases of primary osteoarthritis occurred in women (65%), and most cases of PTOA were in men (61%) (Table 1, P<0.001). PTOA cases were 7,5 years younger than patients with primary osteoarthritis (Table 1, P<0.001). Most patients with PTOA sustained an injury during adolescence or young adulthood, starting with symptoms (pain) 6,5 years earlier than primary OA patients (47.8 (±1.2) and 54.3 (±0.48), respectively, P<0.001). Knee was the most affected joint in PTOA and OA cases (73% and 70% respectively). Alcohol consumption was more frequent in PTOA than in primary OA cases (Table 1, P=0.01). However, after gender, age, and BMI adjustment was no significant (Table 1, P-Unadjusted P=0.01 and P after adjustment=0.89, respectively). Diabetes was less frequent in PTOA than in primary OA cases even after adjustment for age, sex, and BMI (Table 1, OR=0.56. 95%CI: 0.31-0.99). There were more subjects with hypertension and hypothyroidism (HPT) in the group with primary OA than PTOA (Table 1, unadjusted P<0.05). Differences were not significant after adjustment (Table 1, P=0.83 for hypothyroidism and P= 0.37 for hypertension). Desk jobs were the past more frequent occupations for patients with PTOA than primary OA (34% vs 17%, Table 1, OR=2.01, 95%CI=1.24-3.27). Patients with PTOA had higher odds of OP fractures than patients with primary OA, even after excluding the initial PTOA-related fracture (Table 1, OR= 2.0, CI=1.06-3.78). Patients with PTOA had 2.9 higher odds of having Psychosis (from bipolar disorder or schizophrenia), borderline significant (Table 1, OR=2.90, CI=-0.91-9.18). Painkillers were less used in the group with PTOA than primary-OA (OR=0.56, 95%CI: 0.40-1.0, Table 1, P=0.05). All other factors were similar between PTOA and primary OA after adjusting for age, sex, and BMI (Table 1).
Table 1. Descriptive statistics of the studied population
Characteristics
|
Univariate analyses
|
|
OA
(n= 641)
|
PTOA (n=104)
|
P-value
|
OR
|
95% CI
|
P-Value
|
Age: Mean (SD)
|
67.2 (0.44)
|
59.7 (1.02)
|
<0.001
|
|
|
|
AGE CATEGORIES
< 60 years
|
138 (215)
|
51 (49%)
|
<0.001
|
6.28
|
3.46 – 11.4
|
<0.001
|
Sex Male
|
226 (35)
|
64 (61)
|
<0.001
|
2.94
|
1.92 – 4.50
|
<0.001
|
BMI (kg/m²)
|
30.3 (0.23)
|
29.3 (0.57)
|
0.096
|
|
|
|
Obesity (BMI >30)
|
30.2 (47.1)
|
42 (40.4)
|
0.202
|
0.80
|
0.51 – 1.25
|
0.32
|
Adjusted analyses
|
Occupation: Desk jobs
|
109 (17)
|
35 (34)
|
<0.001
|
2.01
|
1.24 – 3.27
|
0.005
|
Knee joint
|
459 (72)
|
73 (70)
|
0.60
|
0.60
|
0.38 – 0.93
|
0.02
|
Hip Joint
|
182 (28)
|
31 (30)
|
Hypertension
|
442 (69)
|
58 (57%)
|
0.013
|
0.95
|
0.58 – 1.54
|
0.83
|
Hypercholesterolemia
|
233 (37)
|
29 (30)
|
0.15
|
0.86
|
0.53 – 1.40
|
0.54
|
Diabetes Mellitus
|
183 (29)
|
17 (16)
|
0.009
|
0.56
|
0.31 – 0.99
|
0.05
|
Osteoporosis*
|
179 (28)
|
69 (66)
|
<0.001
|
2.00
|
1.06 – 3.78
|
0.03
|
Smoking**
|
183 (29)
|
37 (36)
|
0.15
|
0.91
|
0.57 – 1.76
|
0.69
|
Alcohol use**
|
111 (17)
|
29 (28)
|
0.01
|
0.96
|
0.56 – 1.65
|
0.89
|
Mental Comorbidities
|
75 (12)
|
13 (13)
|
0.82
|
1,28
|
0.65 – 2.51
|
0.47
|
Psychosis
|
11 (2)
|
5 (5)
|
0.03
|
2.90
|
0.91 – 9.18
|
0.07
|
Analgesics use
|
474 (74)
|
66 (64)
|
0.026
|
0.63
|
0.40 – 1.00
|
0.05
|
Walking Disability (Bin)
|
500 (78)
|
71 (68)
|
0.03
|
0.76
|
0.47 – 1.22
|
0.25
|
Stairs difficulty (Bin)
|
562 (88)
|
84 (81)
|
0.05
|
1.06
|
1.02 – 1.11
|
0.28
|
Hypothyroidism
|
83 (13)
|
6 (6)
|
0.036
|
0.66
|
0.27-1.66
|
0.37
|
Anemia
|
19 (3)
|
2 (2)
|
0.57
|
0.66
|
0.18-2.8
|
0.66
|
Pulmonary dis.
|
51 (8)
|
5 (5)
|
0.33
|
0.62
|
0.24-1.60
|
0.33
|
Cardiovascular dis.
|
79 (12)
|
10 (10)
|
0.43
|
1.00
|
0.47 – 2.17
|
0.99
|
Univariate analysis: the values are means or numbers and standard error (SD) or percentages for categorical variables in parentheses. (BMI) = Body mass index (weight in kilograms / (height in meters²). Adjusted analyses: the values presented are Odd Ratios (OR) with a 95% confidence interval (CI). Reference = primary OA cases. Exclusion of fracture associated with PTOA. ** past and current versus never used. Bold and italics for significant P values. *** Psychosis includes bipolar disorder and schizophrenia cases.